Lithium-ion battery

Abstract

The purpose of the present invention is to provide a lithium-ion battery having a large discharge capacity and good rate characteristics. This lithium-ion battery has a positive electrode, a negative electrode, and a first electrolyte. The positive electrode has a positive electrode active material. The positive electrode active material has an olivine-type crystal structure, and has lithium, manganese, iron, zinc, phosphorus, and oxygen, where the atomic ratio of manganese to the sum of manganese, iron, and zinc contained in the positive electrode active material (Mn / (Mn + Fe + Zn)) exceeds 0.5, and the atomic ratio of zinc in the sum of manganese, iron, and zinc contained in the positive electrode active material (Zn / (Mn + Fe + Zn)) is 0.01 or more and less than 0.05.

Description

Lithium-ion battery

[0001] One embodiment of the present invention relates to an article, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, a manufacture, or a composition of matter. One embodiment of the present invention relates to a power storage device including a secondary battery, a semiconductor device, a display device, a light-emitting device, a lighting device, an electronic device, or a manufacturing method thereof. Another embodiment of the present invention relates to an article that can be used as a secondary battery and an active material therein, or a manufacturing method thereof.

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

[0003] In recent years, various types of power storage devices, such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries, have been actively developed. In particular, demand for high-power, high-energy-density lithium-ion secondary batteries has rapidly expanded in conjunction with the development of portable information terminals, such as mobile phones, smartphones, and notebook computers, portable music players, digital cameras, medical devices, next-generation clean-energy automobiles, such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs), and the semiconductor industry, making them indispensable to modern society as a rechargeable energy source.

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

[0005] A. Yamada, S. C. Chung and K. Hinokuma, “Optimized LiFePO▲4▼ for Lithium Battery Cathodes”, J. Electrochem. Soc. , 148, A224-229 (2001).

[0006] JP 2011-222494 A

[0007] However, LiFePO ４ Compared with the positive electrode active materials of other lithium ion batteries in practical use, the energy density per weight of the positive electrode active material is low at 578 Wh / kg.

[0008] LiMnPO ４ is LiFePO ４ It is expected that the energy density can be further increased because it exhibits a higher redox potential than LiMnPO. ４ and LiFePO ４ A solid solution of LiMn ｘ Fe １−ｘ P.O. ４ (0<x<1) (e.g., LiMn ０．５ Fe ０．５ P.O. ４ Materials such as these are also being considered (Patent Document 1).

[0009] However, LiMnPO ４ and LiMn ｘ Fe １−ｘ P.O. ４ (0<x<1) is LiFePO ４ However, lithium-ion batteries have the drawback of lower electrical conductivity than conventional batteries and a small solid-state lithium ion diffusion coefficient. As a result, their charge / discharge capacity may be lower than theoretically expected. Furthermore, there is a problem of reduced charge / discharge capacity at high rates or low temperatures (e.g., below 0°C). For example, when used in an EV, if the discharge capacity at high rates is insufficient, the vehicle may not be able to accelerate sufficiently. Furthermore, if the charge / discharge capacity at low temperatures compared to room temperature is extremely low, the EV may become unusable due to a drop in the outside temperature.

[0010] Furthermore, at high temperatures (for example, 45° C. or higher and 60° C. or lower), the plateau resulting from the oxidation-reduction of manganese is no longer maintained as the charge-discharge cycle progresses, resulting in a problem of a decrease in energy density.

[0011] In view of the above, an object of one embodiment of the present invention is to provide a cathode active material or composite oxide having high energy density, or a secondary battery using the same. Another object is to provide a cathode active material or composite oxide having a large discharge capacity, or a secondary battery using the same. Another object is to provide a cathode active material or composite oxide having a high oxidation-reduction potential (also referred to as a voltage plateau) that maintains a high oxidation-reduction potential even after charge-discharge cycles, or a secondary battery using the same. Another object is to provide a cathode active material or composite oxide in which a decrease in charge-discharge capacity at low temperatures is suppressed, or a secondary battery using the same. Another object is to provide a cathode active material or composite oxide in which a decrease in capacity during high-rate charge-discharge is suppressed, or a secondary battery using the same. Another object is to provide a cathode active material or composite oxide in which a decrease in energy density at high temperatures is suppressed, or a secondary battery using the same. Another object is to provide a secondary battery that exhibits good electrical characteristics over a wide temperature range. Another object is to provide a secondary battery that is safe or highly reliable.

[0012] Another object of one embodiment of the present invention is to provide a novel positive electrode active material, a composite oxide, a power storage device, or a manufacturing method thereof.

[0013] Note that the description of these problems does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily solve all of these problems. Note that problems other than these can be extracted from the description in the specification, drawings, and claims.

[0014] In order to solve the above problem, in one aspect of the present invention, LiMn ｘ Fe １−ｘ P.O. ４A small amount of an additive element is dissolved in (0<x<1). The additive element is preferably an element that can only become a divalent cation. For example, one or more elements selected from zinc and magnesium can be used, with zinc being particularly preferred.

[0015] One embodiment of the present invention is a lithium-ion battery including a positive electrode, a negative electrode, and a first electrolyte solution. The positive electrode includes a positive electrode active material having an olivine crystal structure and including lithium, manganese, iron, zinc, phosphorus, and oxygen. The atomic ratio of manganese to the sum of manganese, iron, and zinc contained in the positive electrode active material (Mn / (Mn+Fe+Zn)) is greater than 0.5, and the atomic ratio of zinc to the sum of manganese, iron, and zinc contained in the positive electrode active material (Zn / (Mn+Fe+Zn)) is equal to or greater than 0.01 and less than 0.05.

[0016] In the above, the atomic ratio of manganese to the sum of manganese, iron, and zinc contained in the positive electrode active material (Mn / (Mn+Fe+Zn)) is more preferably 0.7 or less.

[0017] In addition, in the above, the olivine type crystal structure belongs to the space group Pnma (No. 62), and the positive electrode CuKα １ When a Rietveld analysis is performed on a powder X-ray diffraction pattern using X-rays, it is preferable that the lattice constant of the a-axis of the olivine-type crystal structure is 10.3889 Å or more and 10.3997 Å or less, the lattice constant of the b-axis is 6.0550 Å or more and 6.0616 Å or less, and the lattice constant of the c-axis is 4.7210 Å or more.

[0018] In the above, the olivine type crystal structure preferably has a crystallite size LVol-IB of 50 nm or more and less than 90 nm.

[0019] In addition, in the above, a half cell having a positive electrode and a second electrolyte solution of ethylene carbonate, diethyl carbonate, and vinylene carbonate preferably has a discharge capacity of 149 mAh / g or more per weight of positive electrode active material when subjected to a charge-discharge test, in which a measurement environment is 25°C, CCCV charging with a charge current of 34 mA / g, a charge voltage of 4.5 V, and a cut-off current of 3.4 mA / g is performed, and CC discharging with a discharge current of 34 mA / g and a cut-off voltage of 2.5 V is performed in this order.

[0020] In addition, in the above-mentioned half cell having a positive electrode and a second electrolytic solution containing ethylene carbonate, diethyl carbonate, and vinylene carbonate, it is preferable that the ratio of the discharge capacity in a 0.2 C discharge test to the discharge capacity in a 5 C discharge test is 88% or more. The 0.2C charge-discharge test was conducted in a measurement environment of 25°C, and involved sequentially conducting CCCV charging with a charge current of 34 mA / g, a charge voltage of 4.5 V, and a cut-off current of 3.4 mA / g per weight of positive electrode active material, and CC discharging with a discharge current of 34 mA / g and a cut-off voltage of 2.5 V. The 5C discharge test was conducted in a measurement environment of 25°C, and involved sequentially conducting CCCV charging with a charge current of 34 mA / g, a charge voltage of 4.5 V, and a cut-off current of 3.4 mA / g per weight of positive electrode active material, and CC discharging with a discharge current of 850 mA / g and a cut-off voltage of 2.5 V.

[0021] Furthermore, in the above, when a charge-discharge cycle test is performed on a half cell having a positive electrode and a second electrolytic solution of ethylene carbonate, diethyl carbonate, and vinylene carbonate at a measurement environment of 60°C, it is preferable that the difference in discharge capacity between Peak (1), the position where the peak of the discharge dV / dQ curve appears in the first cycle, and Peak (100), the position where the peak of the discharge dV / dQ curve appears in the 100th cycle, in the range of 25 mAh / g or more and 125 mAh / g or less, Peak (1) - Peak (100) is 12 mAh / g or less.

[0022] Furthermore, in the above, when a charge-discharge cycle test is performed on a half cell having a positive electrode and a second electrolytic solution of ethylene carbonate, diethyl carbonate, and vinylene carbonate at a measurement environment of 25°C, it is preferable that the difference in discharge capacity between Peak (1), the position where the peak of the discharge dV / dQ curve appears in the first cycle, and Peak (100), the position where the peak of the discharge dV / dQ curve appears in the 100th cycle, in the range of 25 mAh / g or more and 125 mAh / g or less, Peak (1) - Peak (100) is 8 mAh / g or less.

[0023] According to one embodiment of the present invention, a cathode active material or composite oxide having a high energy density, or a secondary battery using the same, can be provided. Alternatively, a cathode active material or composite oxide having a large discharge capacity, or a secondary battery using the same, can be provided. Alternatively, a cathode active material or composite oxide having a high voltage plateau that is maintained even after charge-discharge cycles, or a secondary battery using the same, can be provided. Alternatively, a cathode active material or composite oxide in which a decrease in charge-discharge capacity at low temperatures is suppressed, or a secondary battery using the same, can be provided. Alternatively, a cathode active material or composite oxide in which a decrease in capacity during high-rate charge-discharge is suppressed, or a secondary battery using the same, can be provided. Alternatively, a cathode active material or composite oxide in which a decrease in energy density at high temperatures is suppressed, or a secondary battery using the same, can be provided. Alternatively, a secondary battery exhibiting good electrical characteristics over a wide temperature range can be provided. Alternatively, a secondary battery with high safety or reliability can be provided.

[0024] According to one embodiment of the present invention, a novel positive electrode active material, a composite oxide, a power storage device, or a manufacturing method thereof can be provided.

[0025] Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of these effects. Note that effects other than these will become apparent from the description in the specification, drawings, claims, etc., and it is possible to extract other effects from the description in the specification, drawings, claims, etc.

[0026] 1A, 1B, 1C, and 1D are diagrams illustrating a cathode active material according to one embodiment of the present invention. FIG. 2 is a diagram illustrating an example of a method for manufacturing a cathode active material according to one embodiment of the present invention. FIGS. 3A, 3B, and 3C are diagrams illustrating a lithium-ion battery according to one embodiment of the present invention. FIGS. 4A, 4B, and 4C are diagrams illustrating an electric vehicle according to one embodiment of the present invention. FIGS. 5A, 5B, 5C, 5D, and 5E are diagrams illustrating a vehicle or the like according to one embodiment of the present invention. FIGS. 6A, 6B, 6C, and 6D are diagrams illustrating an electronic device or the like according to one embodiment of the present invention. FIG. 7 is an XRD pattern of a cathode active material according to an example. FIGS. 8A, 8B, and 8C are graphs illustrating lattice constants and zinc concentrations. FIG. 9 is a graph illustrating a LiMn ｘ Fe １−ｘ P.O. ４ 10A and 10B are diagrams illustrating a unit cell (0<x<1). FIGS. 10A and 10B are rate characteristics of a half cell according to an example. FIG. 11 is charge / discharge cycle characteristics of a half cell according to an example. FIGS. 12A and 12B are charge / discharge cycle characteristics of a half cell according to an example. FIGS. 13A, 13B, and 13C are charge / discharge curves of a half cell according to an example. FIGS. 14A, 14B, and 14C are dVdQ curves of a half cell according to an example. FIGS. 15A, 15B, and 15C are dVdQ curves of a half cell according to an example. FIGS. 16A, 16B, and 16C are graphs showing the rate of change of lattice constant and zinc concentration according to an example. FIG. 17 is a graph showing the rate of change of the product of lattice constants and magnesium concentration according to an example.

[0027] Hereinafter, examples of embodiments of the present invention will be described with reference to the drawings, etc. However, the present invention should not be construed as being limited to the following examples. The embodiments of the present invention can be modified within the scope of the spirit of the present invention.

[0028] In addition, in the drawings, the size, layer thickness, or area may be exaggerated for clarity, and therefore are not necessarily limited to the scale.

[0029] Furthermore, ordinal numbers such as "first" and "second" used in this specification are used to avoid confusion between components, and do not indicate any order or ranking, such as the order of processes or stacking. Even if a term is not used in this specification, an ordinal number may be used in the claims to avoid confusion between components. Even if a term is used in this specification, a different ordinal number may be used in the claims. Even if a term is used in this specification, the ordinal number may be omitted in the claims.

[0030] In this specification, space groups are expressed using short notation in international notation (or Hermann-Mauguin notation). In addition, space group numbers may be added. Crystal planes and crystal directions are expressed using Miller indices. In crystallography, space groups, crystal planes, and crystal directions are expressed by adding a superscript bar to the numbers. However, due to formatting constraints, in this specification, instead of adding a bar above the numbers, a minus sign (-) may be added before the numbers. Individual orientations indicating directions within a crystal are expressed using [ ], collective orientations indicating all equivalent directions are expressed using < >, individual planes indicating crystal planes are expressed using ( ), and collective planes with equivalent symmetry are expressed using {}. Even with the same space group number, the notation of space groups may differ depending on the orientation of the crystal axes. For example, Pnma(a, b, c), Pmnb(a, b, -c), Pbnm(c, a, b), Pcmn(-c, b, a), Pmcn(b, c, a) and Pnam(a, -c, b), which belong to space group number 62, have different crystal axis settings, but all represent the same unit cell.

[0031] In this specification and the like, when simply referring to a positive electrode active material, there are cases where the description refers to multiple positive electrode active material particles and cases where the description refers to a single positive electrode active material particle, depending on the analytical method, etc. For example, in the case of descriptions relating to scanning transmission electron microscope-energy dispersive X-ray spectroscopy (STEM-EDX) line analysis, STEM-electron energy loss spectroscopy (STEM-EELS), and electron diffraction, the description refers to a single positive electrode active material particle unless otherwise specified. On the other hand, in the case of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), various mass analyses, etc., the description refers to multiple positive electrode active material particles unless otherwise specified.

[0032] In this specification and the like, the term "particle" is not limited to referring only to spherical particles (having a circular cross-sectional shape), but may also refer to cross-sectional shapes of individual particles such as ellipsoids, rectangles, trapezoids, triangles, squares with rounded corners, asymmetric shapes, etc. Furthermore, individual particles may have irregular shapes. Furthermore, when simply referring to particles, this term includes primary particles and secondary particles.

[0033] Furthermore, when describing the characteristics of particles of a positive electrode active material, it is not necessary for all particles to have the characteristics. For example, if 50% or more, preferably 70% or more, and more preferably 90% or more of three or more randomly selected particles of a positive electrode active material have the preferred characteristics described below, it can be said that the positive electrode active material and the secondary battery having the same are sufficiently effective in improving their properties.

[0034] The distribution of a certain element refers to a region in which the element is continuously detected within a range that is not a noise by a certain continuous analytical method. A region in which the element is continuously detected within a range that is not a noise can also be referred to as a region in which the element is always detected when the analysis is performed multiple times.

[0035] The space group of a crystal structure is identified by XRD, electron diffraction, neutron diffraction, etc. Therefore, in this specification and the like, "belonging to a certain space group," "belonging to a certain space group," or "being a certain space group" can be rephrased as "identified with a certain space group."

[0036] Unless otherwise specified, the materials (positive electrode active material, negative electrode active material, electrolyte, separator, etc.) contained in the secondary battery are described in their pre-degradation state. A decrease in discharge capacity due to aging treatment during secondary battery manufacturing is not considered to be degradation. For example, a lithium-ion secondary cell or lithium-ion secondary battery pack (hereinafter referred to as a lithium-ion secondary battery) can be said to be in its pre-degradation state if it has a discharge capacity of 97% or more of its rated capacity. For lithium-ion secondary batteries for portable devices, the rated capacity conforms to JIS C 8711:2019. For other lithium-ion secondary batteries, the rated capacity conforms to not only the above JIS standard but also various JIS and IEC standards for electric vehicle propulsion, industrial use, etc.

[0037] Embodiment 1 In this embodiment, features of a positive electrode active material 100 of one embodiment of the present invention will be described with reference to FIGS. 1A to 1D. FIG.

[0038] The positive electrode active material 100 contains lithium, manganese, iron, an additive element, phosphorus, and oxygen. As the additive element, it is preferable to use an element that does not take a valence other than a divalent cation when solid-dissolved in the positive electrode active material 100. For example, one or more selected from zinc and magnesium can be used, with zinc being particularly preferable. In other words, only zinc, only magnesium, or both zinc and magnesium may be used as the additive element. The positive electrode active material 100 may also be LiMn ｘ Fe １−ｘ P.O. ４ It has an olivine type crystal structure represented by (0<x<1).

[0039] LiMn ｘ Fe １−ｘ P.O. ４The olivine-type crystal structure represented by (0<x<1) is an orthorhombic crystal (also called an orthorhombic crystal) and belongs to the space group Pnma (No. 62). Oxygen has a hexagonal close-packed structure, with lithium, manganese, iron, and magnesium existing in octahedral sites, and phosphorus existing in tetrahedral sites. Although oxygen has a hexagonal close-packed structure, it has distortion compared to an ideal hexagonal close-packed structure. It may also have defects such as cation or anion deficiencies. The composition of the positive electrode active material 100 is not strictly limited to Li:(Mn+Fe+additive element):P:O=1:1:1:4 (atomic ratio).

[0040] The atomic ratio of manganese to the sum of manganese, iron, and additional elements contained in the positive electrode active material 100 (Mn / (Mn + Fe + additional elements)) is preferably greater than 0.5, and more preferably 0.55 or greater. The higher the atomic ratio of manganese to the sum of manganese, iron, and additional elements contained in the positive electrode active material 100, the higher the energy density of the secondary battery. On the other hand, if the atomic ratio of manganese to the sum of manganese, iron, and additional elements becomes too high, there is a concern that the electrical conductivity will decrease and the lithium ion diffusion coefficient will become smaller. Therefore, it may be preferable that (Mn / (Mn + Fe + additional elements)) is less than 0.8 or 0.7 or less.

[0041] If the amount of additive element contained in the positive electrode active material 100 is too small, the decrease in charge / discharge capacity at high rates or low temperatures (for example, 0°C or lower) may not be sufficiently suppressed. In this specification, a high rate refers to a current per weight of positive electrode active material of 2C (340mA / g) or more when 1C = 170mA / g, typically 5C (850mA / g). A low rate refers to a current per weight of positive electrode active material of less than 2C (340mA / g) when 1C = 170mA / g, typically 0.2C (34mA / g). A low temperature refers to a temperature below 0°C, typically -20°C or higher and 0°C or lower.

[0042] Furthermore, if the amount of added element is too small, the oxidation-reduction of manganese (Mn ２＋ / Mn ３＋In this specification, high temperature refers to 45°C or higher, or 45°C to 90°C, typically 60°C. The plateau refers to the region where the voltage remains constant relative to the change in charge / discharge capacity. ２＋ / Mn ３＋ The plateau due to the charge transfer is influenced by the internal resistance of the battery, but is typically between 4.0 V and 4.2 V (vs. Li / Li ＋ ) appears in the oxidation-reduction of iron (Fe ２＋ / Fe ３＋ ) is typically about 3.5 V (vs Li / Li ＋ ) appears.

[0043] However, elements that do not take a valence other than divalent cations do not contribute to charge / discharge capacity because their valence does not change. Therefore, if the amount of added element is too large, the charge / discharge capacity decreases regardless of the rate and temperature. Therefore, the atomic ratio of the added element to the sum of manganese, iron, and added element (added element / (Mn + Fe + added element)) is preferably greater than 0.01 and less than 0.1, more preferably greater than 0.01 and less than 0.05. The atomic ratio of the added element to the sum of manganese, iron, and added element can also be 0.015 or more and 0.025 or less. Similarly, when zinc is used as the added element, the atomic ratio of zinc to the sum of manganese, iron, and zinc (Zn / (Mn + Fe + Zn)) is preferably greater than 0.01 and less than 0.1, more preferably greater than 0.01 and less than 0.05. The atomic ratio of zinc to the sum of manganese, iron, and zinc can also be 0.015 or more and 0.025 or less. When the additive elements are contained within the above ranges, the positive electrode active material can have good rate characteristics and low-temperature characteristics.

[0044] The additive element is preferably present in the positive electrode active material 100 as a solid solution. The lattice constant of the olivine-type crystal structure changes depending on the proportion of the additive element in solid solution. When the additive element is solid-solved within the above range, the lattice constant becomes slightly shorter than that of an olivine-type crystal structure in which the additive element is not solid-solved. The olivine-type crystal structure of the positive electrode active material 100 using zinc as the additive element belongs to the space group Pnma (No. 62), and when a Rietveld analysis is performed on a pattern obtained by diffraction, the lattice constant of the a-axis is preferably 10.3700 Å or more and 10.3997 Å or less, more preferably 10.3889 Å or more and 10.3997 Å or less, and most preferably 10.3970 Å or more and 10.3997 Å or less. The lattice constant of the b-axis is preferably 6.0440 Å to 6.0616 Å, more preferably 6.0550 Å to 6.0616 Å, and most preferably 6.0600 Å to 6.0616 Å. The lattice constant of the c-axis is preferably 4.7180 Å to 4.7220 Å, more preferably 4.7210 Å to 4.7220 Å, and most preferably 4.7218 Å to 4.7220 Å.

[0045] The lattice constant being in the above range is one factor indicating that zinc is dissolved in a solid solution at a preferable ratio. ｘ Fe １−ｘ P.O. ４ It is preferable that the metal is solid-dissolved in the Mn and Fe sites (0<x<1), but it may be solid-dissolved in the Li site.

[0046] LiMn ｘ Fe １−ｘ P.O. ４ Manganese and iron in (0<x<1) are Mn ２＋ and Fe ２＋ When lithium is released, Mn ｘ Fe １−ｘ P.O. ４ (0<x<1), and in this case, manganese and iron are Mn ３＋ and Fe ３＋The lithium intercalation / deintercalation reaction of olivine-type positive electrode active materials is known to be a two-phase reaction, and it is believed that the phase boundary moves rapidly, causing the entire crystal to undergo a phase change. At this phase boundary, strain occurs due to the volume difference between the crystal structure in the lithium-intercalated and lithium-deintercalated states. Therefore, the greater the volume difference before and after lithium intercalation / deintercalation, the greater the energy required for strain propagation, i.e., the higher the activation barrier at the phase boundary, which leads to a deterioration in rate performance and low-temperature characteristics.

[0047] This volume difference is due to the lithium-inserted Mn ２＋ and Fe ２＋ Therefore, Mn in the lithium-extracted state ３＋ and Fe ３＋ This is caused by the smaller ionic radius of LiMn. In addition to the change in ionic radius, the strain due to the Jahn-Teller effect of manganese is also thought to be a factor. ｘ Fe １−ｘ P.O. ４ (0<x<1) has Fe and Mn in an octahedral configuration and high spin, and Fe ２＋ (3d ６ ), Fe ３＋ (3d ５ ) and Mn ２＋ (3d ５ ) have a weak or no Jahn-Teller effect. ３＋ (3d ４ ) has a strong Jahn-Teller effect, and the octahedron is greatly distorted. Therefore, the deformation of the octahedron in the change from divalent to trivalent manganese is greater than that of iron. Therefore, LiFePO ４ LiMnPO having manganese ４ and LiMn ｘ Fe １−ｘ P.O. ４ In the case of (0<x<1), the difference in volume before and after lithium intercalation and deintercalation is large, and the activation barrier at the phase boundary is likely to become a problem.

[0048] Therefore, it is preferable to dissolve an additive element in the Mn and Fe sites so as to suppress the volume difference before and after lithium insertion and desorption. ２＋ (high spin) and Fe２＋ (High spin) is smaller than Mn ３＋ (high spin) and Fe ３＋ (High spin) is preferably larger than that of Mn ２＋ (high spin) and Fe ２＋ (high spin), it is preferable that the additive element is also a divalent cation when solid-dissolved.

[0049] Zinc and magnesium satisfy all of these characteristics, and furthermore, since they are not transition metals, they do not exhibit the Jahn-Teller effect.

[0050] Zinc and magnesium do not contribute to charge compensation during charge and discharge. This is because zinc and magnesium can stably exist in oxidation states of 0 or 2, and charge compensation associated with the insertion and desorption of lithium, a monovalent cation, requires a change in valence of 1, for example, a change between divalent and trivalent. Therefore, it may be difficult for lithium to be inserted or removed from the surrounding zinc and magnesium. However, if the surrounding manganese is oxidized to a tetravalent state, lithium may be inserted or removed, which may have less adverse effects on the lithium diffusion pathway.

[0051] As described above, it is preferable to use an element that does not take on any valence other than divalent cations when solid-dissolved in the positive electrode active material 100 as the additive element. However, elements that take on other valences may also be used. For example, in addition to at least one of zinc and magnesium, an element that becomes a trivalent cation, such as aluminum, may also be used as the additive element. Trivalent cations, such as aluminum, tend to be present in the surface layer of the positive electrode active material 100, and can suppress side reactions between the positive electrode active material 100 and the electrolyte. A synergistic effect can be expected by using both an element that tends to be present in the surface layer and an element that does not take on any valence other than divalent cations solid-dissolved in the interior as the additive element.

[0052] <<Shape>> As shown in Fig. 1A , the positive electrode active material 100 is preferably a secondary particle having a plurality of primary particles 101. In this specification and the like, the term "secondary particle" refers to a plurality of primary particles that are aggregated, adhered, and / or sintered.

[0053] Furthermore, the primary particles 101 of the positive electrode active material 100 are preferably single crystals. For example, when the grain boundaries of the primary particles observable with a scanning electron microscope (SEM) coincide with the areas of the mapping of the crystal orientation captured by electron backscatter diffraction (EBSD), it can be determined that the primary particles 101 are single crystals.

[0054] Furthermore, the positive electrode active material 100 is preferably coated with carbon, and it is more preferable that each of the primary particles 101 is coated with carbon. By being coated with carbon, the conductivity of the positive electrode active material 100 can be increased, and the resistance of the secondary battery can be suppressed.

[0055] Although Fig. 1A shows an example in which the primary particles 101 are spherical or elongated spheroids, one embodiment of the present invention is not limited thereto. For example, as shown in Fig. 1B, the positive electrode active material 100 may have distorted spherical primary particles 101a. As shown in Fig. 1C, the positive electrode active material 100 may have flat plate-like or approximately plate-like primary particles 101b. As shown in Fig. 1D, the positive electrode active material 100 may have needle-like primary particles 101c.

[0056] Furthermore, the positive electrode active material 100 preferably has a small crystallite size to reduce the diffusion resistance of lithium. For example, the olivine-type crystal structure of the positive electrode active material 100 preferably has a crystallite size of 50 nm to 90 nm when a Rietveld analysis is performed on a pattern obtained by a diffraction method.

[0057] <<Rate Characteristics>> As a result of the rate characteristics of the positive electrode active material 100 being improved by the above-described additive elements, the difference between the battery characteristics at a low rate (typically 0.2 C, 34 mA / g) and the battery characteristics at a high rate (typically 5 C, 850 mA / g) of a secondary battery including the positive electrode active material 100 is small. However, the range in which the positive electrode active material 100 with improved rate characteristics exhibits its effect is not necessarily limited to 5 C; for example, the battery characteristics are expected to be good even when charging and discharging at a current greater than 0.2 C and less than 5 C, or at a current greater than 5 C.

[0058] For example, in a secondary battery having the positive electrode active material 100, the difference between the discharge capacity in a 0.2 C discharge test and the discharge capacity in a 5 C discharge test, when measured at 25° C., is preferably 18 mAh / g or less. Alternatively, the ratio of the discharge capacities is preferably 88% or more.

[0059] At this time, the lithium salt and the electrolyte solution may contain, for example, 1 mol / dm ３ LiPF ６ A battery containing 2% by weight of vinylene carbonate (VC) in a volume ratio of 3:7 (ethylene carbonate (EC):diethyl carbonate (DEC)) can be used. The rate characteristic test can be performed by charging using constant current / constant voltage (CCCV) (charging current: 34 mA / g, charging voltage: 4.5 V, cut-off current: 3.4 mA / g) and discharging using CC (cut-off voltage: 2.5 V, arbitrary discharge current), with a 10-minute pause between charging and discharging. The arbitrary discharge current can be in the following order: 34mA / g (0.2C), 34mA / g (0.2C), 34mA / g (0.2C), 85mA / g (0.5C), 170mA / g (1C), 340mA / g (2C), 510mA / g (3C), 680mA / g (4C), 850mA / g (5C), 34mA / g (0.2C).

[0060] <Low-Temperature Characteristics> As a result of the above-described additive elements improving the low-temperature characteristics of the positive electrode active material 100, the difference between the battery characteristics at 25° C. and those at low temperatures becomes smaller in a secondary battery including the positive electrode active material 100. However, the range in which the positive electrode active material 100, in which the deterioration of battery characteristics at low temperatures is suppressed, exhibits its effects is not necessarily limited to a temperature range of −20° C. or higher and 0° C. or lower; for example, the battery characteristics such as charge / discharge capacity and rate characteristics are expected to be good even at temperatures of 0° C. or higher and lower than 25° C.

[0061] For example, it is preferable that a secondary battery having the positive electrode active material 100 has a ratio of 30% or more of the discharge capacity at the 20th cycle when the charge-discharge cycle test is performed in a measurement environment of −20° C. to the discharge capacity at the 20th cycle when the charge-discharge cycle test is performed in a measurement environment of 25° C. In this case, the charge-discharge cycle test at −20° C. is performed by performing two charge-discharge cycles at 25° C. as an aging treatment, and then changing the measurement environment to −20° C., and the number of cycles is counted including the two cycles of the aging treatment.

[0062] At this time, the lithium salt and the electrolyte solution may contain, for example, 1 mol / dm ３ LiPF ６ A 3:7 volume ratio of ethylene carbonate (EC):diethyl carbonate (DEC) with 2% by weight of vinylene carbonate (VC) can be used. The charge-discharge cycle test can be performed by charging at constant current / constant voltage (CCCV) (4.5 V, 85 mA / g, cut-off current 8.5 mA / g) and discharging at constant current (CC) (85 mA / g, cut-off voltage 2.5 V), with a 10-minute pause between charge and discharge.

[0063] <High-Temperature Characteristics> Furthermore, the added element improves the charge-discharge characteristics of the positive electrode active material 100, and the volume difference before and after lithium insertion / extraction is suppressed. Therefore, a secondary battery having the positive electrode active material 100 can be prevented from undergoing oxidation-reduction of manganese (Mn ２＋ / Mn ３＋ This is particularly effective in charge-discharge cycle tests at high temperatures.

[0064] Manganese oxidation-reduction (Mn ２＋ / Mn ３＋ When the plateau resulting from the manganese oxidation-reduction (Mn ２＋ / Mn ３＋When the plateau due to the reduction of the capacity of the battery is reduced, the peaks appearing in the range of 25 mAh / g to 125 mAh / g tend to appear on the lower capacity side, resulting in a decrease in the energy density. ２＋ / Mn ３＋ The dV / dQ curve is not related to the plateau resulting from the

[0065] Here, when a charge-discharge cycle test is performed at a measurement environment of 60°C, the position where the peak of the discharge dV / dQ curve for the first cycle appears in the range of 25 mAh / g to 125 mAh / g of the discharge dV / dQ curve is defined as Peak (1). Similarly, the position where the peak of the discharge dV / dQ curve for the 100th cycle appears is defined as Peak (100). In a secondary battery having positive electrode active material 100, the difference in discharge capacity between Peak (1) and Peak (100), Peak (1) - Peak (100), is preferably 12 mAh / g or less.

[0066] Similarly, when a charge-discharge cycle test is carried out in a measurement environment of 25° C., a secondary battery having the positive electrode active material 100 preferably has a Peak(1)-Peak(100) of 8 mAh / g or less.

[0067] At this time, the lithium salt and the electrolyte solution may contain, for example, 1 mol / dm ３ LiPF ６ A 3:7 volume ratio of ethylene carbonate (EC):diethyl carbonate (DEC) with 2% by weight of vinylene carbonate (VC) can be used. The charge-discharge cycle test can be performed by CCCV charging (4.5 V, 85 mA / g, end current 8.5 mA / g) and CC discharging (85 mA / g, end voltage 2.5 V), with a 10-minute pause between charge and discharge.

[0068] In this specification, the number of cycles does not strictly indicate the number of charge / discharge cycles since the secondary battery was manufactured. As long as the secondary battery is in a state before deterioration, counting the number of cycles can be started at any time. Therefore, for example, after an aging treatment involving several charge / discharge cycles, a charge / discharge cycle test under the above conditions can be started, and the first charge / discharge cycle test under the above conditions can be counted as the first cycle.

[0069] <Charge / Discharge Curve and dV / dQ Curve> As described above, the positive electrode active material 100 of one embodiment of the present invention may be characterized by a change in charge / discharge voltage. The change in voltage can be read from a Q-dQ / dV charge curve and a Q-dQ / dV discharge curve, which are obtained by differentiating (dV / dQ) the voltage (V) of the charge / discharge curve with respect to the capacity (Q). The redox potential differs before and after the peaks in these dQ / dV curves. It is believed that a change in the type of transition metal that is oxidized and reduced with the insertion / extraction of lithium ions and / or a change in the level of the crystalline phase occurs before and after the peaks.

[0070] In practice, due to the limited resolution of measurement devices, approximate calculations using numerical differentiation are used to obtain dV / dQ curves. The dV / dQ curve requires data on the voltage and current during charging and discharging. While the method and device for acquiring these measurement data are not particularly limited, for example, a setting can be made such that during charging, only voltage increases from the previously recorded value are recorded, and during discharging, only voltage decreases from the previously recorded value are recorded. This data acquisition method allows for the use of measurement data acquired during CC (constant current) charging and CC discharging, and also reduces noise, allowing for appropriate approximate calculations using numerical differentiation. The value obtained by integrating the current value and time during charging is the charge capacity, and the equivalent value during discharging is the discharge capacity.

[0071] In the approximation calculation, n consecutive points of measurement data are used to find the ratio of the average voltage value to the amount of change, and this sequence of points is used as approximate data, where n is the number of times averaging is performed.

[0072] The larger the number of averaging processes, the more noise caused by the resolution of the measuring device can be reduced, which is particularly effective when the charge / discharge rate is low. On the other hand, if the number is too large, disadvantages may arise, such as the numerical derivative value being unable to represent the ratio of local fluctuations and the average voltage value becoming unrelated to reality. Therefore, it is preferable that the number of averaging processes is 1 or more and 32 or less. Unless otherwise specified in this specification, the number of averaging processes is 8.

[0073] Note that peaks in the dV / dQ curve can also occur due to changes in other elements of the secondary battery, such as structural changes in the negative electrode and decomposition of the electrolyte. Therefore, it is preferable to know in advance the voltage at which the structural change in the negative electrode and / or decomposition of the electrolyte begins. Furthermore, it is more preferable to perform dV / dQ analysis of the positive electrode active material 100 using a half cell with metallic lithium as the counter electrode.

[0074] <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, inductively coupled plasma mass spectrometry (ICP-MS), etc. Furthermore, if necessary, evaluation can also be performed by combining multiple quantitative and semi-quantitative analyses, such as ICP-MS, X-ray fluorescence analysis, GD-MS (glow discharge mass spectrometry), EDX (energy dispersive X-ray spectroscopy), and EPMA (electron probe microanalyzer), in addition to ICP-MS.

[0075] <Crystallite Size Determined by Diffraction Method> As described above, the olivine-type crystal structure of the positive electrode active material 100 preferably has a crystallite size of 50 nm or more and 90 nm or less when a Rietveld analysis is performed on a pattern obtained by a diffraction method. １ X-ray diffraction by MoKα １ X-ray diffraction using X-rays, synchrotron X-ray diffraction, neutron diffraction, etc. are preferred because of their high accuracy. Furthermore, the measurement object may be a powder of the positive electrode active material, or a positive electrode or secondary battery having the positive electrode active material.

[0076] However, in the state of a positive electrode or secondary battery, the positive electrode active material may be oriented due to the effects of pressure and other factors during the manufacturing process. Strong orientation can make it difficult to accurately calculate the crystallite size. Therefore, it is more preferable to obtain the sample by removing the positive electrode active material layer from the positive electrode, removing some of the binder and other materials in the positive electrode active material layer using a solvent, etc., and then filling the sample into a sample holder. Another method is to apply grease to a silicon non-reflective plate and then attach the powder sample to it.

[0077] The crystallite size can be calculated using, for example, a Bruker D8 ADVANCE, with CuKα as the X-ray source, 2θ of 15° to 120°, increment of 0.005, 1 sec / step, and a LYNXEYE XE-T detector, using a diffraction pattern acquired with the literature value of lithium iron phosphate, ICSD Coll. Code. 193640. Analysis can be performed using DIFFRAC. TOPAS ver. 6 as the crystal structure analysis software, and can be set, for example, as follows: Emission Profile: CuKa5. lam Background: Chebychev polynomial, 5th Instrument Primary radius: 280mm Secondary radius: 280mm Linear PSD 2Th angular range: 2.9 FDS angle: 0.3 Full Axial Convolution Filament length: 12mm Sample length: 15mm Receiving Slit length: 12mm Primary Sollers: 2.5 Secondary Sollers: 2.5 Corrections Specimen displacement: Refine LP Factor: 0

[0078] It is preferable to use the value of LVol-IB, which is the crystallite size corrected by the integral width standard calculated by the above method, as the crystallite size. Note that if the calculated preferred orientation is less than 0.8, the orientation of the sample may be too strong and it may not be suitable for determining the crystallite size.

[0079] <Lattice Constant> The lattice constant of the olivine-type crystal structure of the positive electrode active material 100 can be determined by Rietveld analysis of a pattern obtained by a diffraction method. The Rietveld analysis can be performed by a method similar to the calculation of the crystallite size described above.

[0080] This embodiment mode can be combined with the contents of other embodiment modes as appropriate.

[0081] Embodiment 2 In this embodiment, an example of a method for manufacturing a positive electrode active material of one embodiment of the present invention will be described with reference to FIGS.

[0082] <Step S11> First, in step S11 shown in Fig. 2, an additive element source, a lithium source, a manganese source, an iron source, and a phosphate source are prepared. It is also preferable to prepare a grinding medium and a solvent for mixing.

[0083] When zinc is used as an additive element, examples of the zinc source include zinc oxide, zinc hydroxide, zinc carbonate, and zinc phosphate (Zn ３ (P.O. ４ ) ２ ・4H ２ O), zinc acetate (Zn(CH ３ COO) ２ , Zn(CH ３ COO) ２ ・2H ２ O), zinc oxalate (ZnC ２ O ４ ・2H ２ O), zinc nitrate (Zn(NO ３ ) ２ ・6H ２ O), zinc compounds such as zinc chloride, zinc sulfate, and zinc fluoride can be used.

[0084] When magnesium is used as an additive element, examples of the magnesium source include magnesium oxide, magnesium hydroxide, magnesium carbonate, and magnesium phosphate (Mg(H ２ P.O. ４ ) ２ ・4H ２ O, MgHPO ４ ・3H ２ O, Mg ３ (P.O.４ ) ２ ・8H ２ O), magnesium acetate (Mg(CH ３ COO) ２ , (CH ３ COO) ２ Mg 4H ２ O), magnesium oxalate (MgC ２ O ４ ・2H ２ O), magnesium nitrate (Mg(NO ３ ) ２ ・6H ２ O), magnesium chloride (MgCl ２ ・6H ２ O), magnesium sulfate (MgSO ４ , MgSO ４ ・7H ２ O), magnesium fluoride (MgF ２ ) and other magnesium compounds can be used.

[0085] Examples of the lithium source include lithium carbonate, lithium hydroxide, lithium oxide, and lithium phosphate (Li ３ P.O. ４ ), lithium acetate (CH ３ CO ２ Li, Li(CH ３ COO) 2H ２ O), lithium oxalate (Li ２ C ２ O ４ ), lithium nitrate (LiNO ３ ), lithium chloride (LiCl), lithium sulfate (Li ２ SO ４ ), lithium compounds such as lithium fluoride (LiF) can be used.

[0086] Examples of manganese sources include manganese carbonate and manganese oxide (MnO, Mn ３ O ４ , Mn ２ O ３ , MnO ２ , MnO ３ etc.), manganese hydroxide, manganese phosphate (MnPO ４ ), manganese acetate (Mn(OCOCH ３ ) ２, (CH ３ COO) ３ Mn 2H ２ O, (CH ３ COO) ２ Mn 4H ２ O), manganese oxalate (MnC ２ O ４ ・2H ２ O), manganese nitrate (Mn(NO ３ ) ２ , Mn(NO ３ ) ２ ・4H ２ O, Mn(NO ３ ) ２ ・6H ２ O), manganese chloride (MnCl ２ ・4H ２ O), manganese sulfate (MnSO ４ , MnSO ４ ・H ２ O, MnSO ４ ・4H ２ O, MnSO ４ ・5H ２ O, MnSO ４ ・7H ２ O,) Manganese fluoride (MnF ２ , MnF ３ ) and other manganese compounds can be used.

[0087] The iron source may be, for example, iron carbonate (FeCO ３ ), iron oxide (FeO, Fe ３ O ４ , Fe ２ O ３ ), iron hydroxide, iron phosphate (FePO ４ ・2H ２ O, FePO ４ ・5H ２ O), iron acetate (Fe(CH ３ CO ２ ) ２ ), iron oxalate (Fe(C ２ O ４ ) 2H ２ O, Fe ２ (C ２ O ４ ) ３ ・6H ２ O), iron nitrate (Fe(NO ３ )３ ・9H ２ O, Fe(NO ３ ) ３ ・6H ２ O), iron chloride (FeCl ２ , FeCl ２ ・4H ２ O, FeCl ３ , FeCl ３ ・6H ２ O), iron sulfate (FeSO ４ , FeSO ４ ・H ２ O, FeSO ４ ・4H ２ O, FeSO ４ ・5H ２ O, FeSO ４ ・7H ２ O), iron fluoride (FeF ２ , FeF ２ ・4H ２ O, FeF ３ , FeF ３ ・3H ２ Iron compounds such as CrO can be used.

[0088] The phosphate source may be, for example, ammonium dihydrogen phosphate (NH ４ H ２ P.O. ４ ), diammonium hydrogen phosphate ((NH ４ ) ２ HPO ４ ), lithium dihydrogen phosphate (LiH ２ P.O. ４ ) and other phosphate compounds can be used.

[0089] The additive element source, lithium source, manganese source, iron source, and phosphate source do not necessarily have to be separate sources, and a compound serving multiple purposes may be used. For example, using lithium hydroxide containing magnesium or lithium carbonate containing magnesium can serve as both a magnesium source and a lithium source, and the cost of lithium purification can be reduced. Furthermore, using lithium dihydrogen phosphate can serve as both a lithium source and a phosphate source.

[0090] In this embodiment, zinc oxide is used as the zinc source, lithium carbonate as the lithium source, manganese carbonate as the manganese source, iron (II) oxalate dihydrate as the iron source, and ammonium dihydrogen phosphate as the phosphate source, and the resulting mixture is Li:Mn:Fe:Mg:PO ４ The components are weighed so that the molar ratio becomes 1:0.59:0.4:0.01:1.

[0091] In addition to the above, if a planetary mill such as a ball mill is used for mixing, grinding media must be prepared. Zirconia balls, for example, can be used as the grinding media. Furthermore, if wet mixing is used, a solvent must be prepared. Dehydrated acetone, for example, can be used as the solvent.

[0092] <Step S12> Next, in step S12, the zinc source, lithium source, manganese source, iron source, and phosphate source are mixed. Mixing can be performed wet using, for example, a ball mill. In this embodiment, zirconia balls with a diameter of 3 mm are used as the grinding medium, and dehydrated acetone is used as the solvent. Mixing is performed for 2 hours at 300 rpm while cooling using a planetary rotation ball mill.

[0093] <Step S13> Next, in step S13, if wet mixing was used, the solvent is dried, and if grinding media were used, the grinding media are removed by sieving to obtain a mixture. To distinguish this from other steps, this may be referred to as the first mixture. In this embodiment, the mixture is dried using a ventilated drying oven, and then sieved with a 300 μm mesh to recover the mixture.

[0094] <Step S14> Next, in step S14, the first mixture is heated. The heating temperature is preferably 250°C or higher and 450°C or lower, more preferably 300°C or higher and 400°C or lower, and most preferably around 350°C. The heating time is preferably 1 hour or higher and 60 hours or lower, more preferably 2 hours or higher and 20 hours or lower, and most preferably around 10 hours. If the heating temperature is too low and / or the heating time is too short, the reaction may not terminate, for example, the evaporation of the hydrate and / or carbon dioxide gas may not be completed. On the other hand, if the heating temperature is too high and / or the heating time is too long, the fuel cost for heating may increase, and productivity may decrease.

[0095] During heating, an inert or reducing atmosphere, such as a nitrogen or argon atmosphere, may be used. The reaction chamber may be evacuated and then purged with an inert atmosphere to prevent the atmosphere from entering or leaving the reaction chamber, or a constant flow of the atmosphere may be maintained.

[0096] The heating furnace may be, for example, a muffle furnace, a roller hearth kiln, or a rotary kiln. The container for accommodating the object to be heated may be an aluminum oxide crucible or an aluminum oxide setter (also called a sheath). It is preferable to cover the crucible or setter before heating, as this prevents the material from volatilizing. Mullite-cordierite may also be used as the material for the crucible and setter.

[0097] In this embodiment, the first mixture is placed in a crucible made of aluminum oxide with a purity of 99.9%, and the crucible is covered with a lid. The crucible is heated in a muffle furnace in a nitrogen flow atmosphere at 350° C. for 10 hours.

[0098] <Steps S15 and S16> Next, in step S15, the heated material is sieved. In this embodiment, the material is sieved through a sieve with openings of 300 μm. Through these steps, a composite oxide is obtained (step S16).

[0099] <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.

[0100] Examples of carbon sources that can be used include compounds containing carbon, such as sugars including glucose and sucrose, polysaccharides including starch and cellulose, and synthetic resins including polyvinyl alcohol (PVA) and polyacrylic acid. Also usable are carbon blacks including acetylene black, graphene, graphene oxide, and graphite. A combination of these may also be used.

[0101] For details about the grinding medium and the solvent, please refer to the description of step S11.

[0102] <Step S18> Next, in step S18, the composite oxide obtained in step S16 is mixed with a carbon source. Mixing can be performed wet using, for example, a ball mill. In this embodiment, zirconia balls with a diameter of 3 mm are used as the grinding medium, and dehydrated acetone is used as the solvent. Mixing is performed for 2 hours at 300 rpm while cooling using a planetary rotation ball mill.

[0103] <Step S19> Next, in step S19, if wet mixing was performed, the solvent is dried, and if grinding media were used, the grinding media are removed by sieving to obtain a mixture. To distinguish this from other steps, this may be referred to as the second mixture. For details on drying and sieving, please refer to the description of step S13.

[0104] <Step S20> Next, in step S20, the second mixture is heated. The heating temperature is preferably 500°C or higher and 900°C or lower, more preferably 600°C or higher and 700°C or lower, and most preferably around 650°C. The heating time is preferably 1 hour or higher and 60 hours or lower, more preferably 2 hours or higher and 20 hours or lower, and most preferably around 10 hours. If the heating temperature is too low and / or the heating time is too short, there is a risk that an olivine-type crystal structure will not be formed or that the carbon source will not be sufficiently carbonized. On the other hand, if the heating temperature is too high and / or the heating time is too long, there is a risk that sintering will proceed, secondary particles will become too large, productivity will decrease, etc.

[0105] For the atmosphere, heating furnace, and container during heating, the description of step S14 can be referred to.

[0106] In this embodiment, the second mixture is placed in a crucible made of aluminum oxide with a purity of 99.9%, and the crucible is covered with a lid. The second mixture is heated in a muffle furnace in a nitrogen flow atmosphere at 650° C. for 10 hours.

[0107] <Steps S21 and S22> Next, in step S21, the heated material is sieved. In this embodiment, the heated material is sieved through a sieve with openings of 53 μm. Through these steps, positive electrode active material 100 is obtained (step S22).

[0108] The positive electrode active material 100 can be produced through the above steps.

[0109] 2 illustrates an example in which a positive electrode active material is produced by a solid-phase method, but this is not a limitation of the present invention. The positive electrode active material can be produced by a method other than the solid-phase method, such as a hydrothermal method, a coprecipitation method, a sol-gel method, or a spray-drying method. Furthermore, the positive electrode active material can be produced by a combination of a plurality of methods selected from these methods.

[0110] This embodiment mode can be combined with the contents of other embodiment modes as appropriate.

[0111] Embodiment 3 In this embodiment, a structure of a lithium ion battery will be described.

[0112] [Positive Electrode] The positive electrode includes a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer includes a positive electrode active material and may further include at least one of a conductive additive and a binder. The positive electrode active material may be any of those described in the above embodiment.

[0113] <Positive Electrode Active Material> As the positive electrode active material, a mixture of the positive electrode active material 100 described in the above embodiment and another positive electrode active material may be used.

[0114] Other examples of the positive electrode active material include composite oxides having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure. For example, LiFePO ４ , LiFeO ２ , LiCoO ２ , LiNiO ２ , LiMnO ２ , LiNi ａ Mn ｂ Co ｃ O ２ (a+b+c=1), LiMn ２ O ４ , V ２ O ５ , Cr２ O ５ , MnO ２ The following compounds are exemplified:

[0115] Other positive electrode active materials include LiMn ２ O ４ Lithium-containing materials having a spinel-type crystal structure containing manganese, such as lithium nickel oxide (LiNiO ２ or LiNi １−ｘ M ｘ O ２ It is preferable to mix (0<x<1) (M=Co, Al, etc.) This configuration can improve the characteristics of the secondary battery.

[0116] <Conductive additive> The conductive additive is also called a conductivity imparting agent or conductive material, and a carbon material can be used. By attaching the conductive additive between multiple active materials, the multiple active materials are electrically connected to each other, thereby increasing the conductivity. In this specification, the term "attachment" does not only refer to physical adhesion between the active material and the conductive additive, but also includes cases where a covalent bond is formed, bonding due to van der Waals forces, where the conductive additive covers part of the surface of the active material, where the conductive additive is embedded in the surface irregularities of the active material, and where the active material is electrically connected even when not in contact with each other.

[0117] Specific examples of carbon materials that can be used as the conductive additive include carbon black (furnace black, acetylene black, graphite, etc.), graphene, multi-graphene, graphene oxide, and / or reduced graphene oxide.

[0118] Furthermore, the use of a mixture of graphene and acetylene black is preferable because it allows for rapid charging, which is particularly effective when used in automotive lithium-ion batteries.

[0119] <Binder> Examples of the binder that can be used include rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene-propylene-diene copolymer. Fluorine rubber can also be used.

[0120] Furthermore, it is preferable to use, for example, a water-soluble polymer as the binder. Examples of the water-soluble polymer that can be used include polysaccharides. Examples of the polysaccharide that can be used include one or more of cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, and starch. It is even more preferable to use these water-soluble polymers in combination with the above-mentioned rubber material.

[0121] Alternatively, it is preferable to use, as the binder, materials such as polystyrene, polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose.

[0122] Additionally, graphene, multigraphene, graphene oxide, and / or reduced graphene oxide can function not only as a conductive additive but also as a binder.

[0123] The binder may be used in combination with two or more of the above.

[0124] <Positive Electrode Current Collector> The current collector can be made of a highly conductive material, such as a metal such as stainless steel, gold, platinum, aluminum, or titanium, or an alloy thereof. It is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. Aluminum alloys containing elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, can also be used. The current collector may also be made of a metal element that reacts with silicon to form a silicide. Examples of metal elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collector can be in the form of a foil, plate, sheet, mesh, punched metal, expanded metal, or the like. It is preferable to use a current collector with a thickness of 5 μm to 30 μm.

[0125] [Negative Electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer has a negative electrode active material, and may further have a conductive additive and a binder.

[0126] <Negative Electrode Active Material> As the negative electrode active material, for example, an alloy material and / or a carbon material can be used.

[0127] The carbon material used for the negative electrode active material may be one or more selected from graphite, easily graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon fiber (carbon nanotube), graphene, graphene compounds, carbon black, and the like.

[0128] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape and is therefore preferred. Furthermore, it is relatively easy to reduce the surface area of ​​MCMB, and this may be preferred. Examples of natural graphite include flake graphite and spherical natural graphite.

[0129] When lithium ions are inserted into graphite (when a lithium-graphite intercalation compound is formed), graphite exhibits a potential as low as that of metallic lithium (0.05 V to 0.3 V vs. Li / Li ＋ This allows lithium-ion batteries using graphite to exhibit high operating voltages. Graphite is also preferred because it has advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and greater safety compared to lithium metal.

[0130] The negative electrode active material may be an element capable of undergoing a charge-discharge reaction through alloying and dealloying reactions with lithium. For example, one or more materials selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. may be used. These elements have a larger capacity than carbon, and silicon, in particular, has a high theoretical capacity of 4200 mAh / g. Compounds containing these elements may also be used. For example, SiO, Mg ２ Si, Mg ２ Ge, SnO, SnO ２ , Mg ２ Sn, SnS ２ , V ２ Sn ３ , FeSn ２ , CoSn ２ , Ni ３ Sn ２ , Cu ６ Sn ５ , Ag ３ Sn, Ag ３ Sb, Ni ２ MnSb, CeSb ３ , LaSn ３ , La ３ Co ２ Sn ７ , CoSb ３ , InSb, SbSn, etc. Here, elements capable of undergoing charge-discharge reactions by alloying / dealloying reactions with lithium, and compounds containing such elements, are sometimes referred to as alloy-based materials. Compared to graphite, alloy-based materials such as silicon may be more suppressed in decreasing charge-discharge capacity at low temperatures, and are therefore preferred as negative electrode active materials for low-temperature secondary batteries.

[0131] In this specification, "SiO" refers to, for example, silicon monoxide. ｘ Here, x preferably has a value of 1 or close to 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

[0132] Furthermore, a material used in forming the graphene compound may be mixed with the graphene compound and used in the active material layer. For example, particles used as a catalyst in forming the graphene compound may be mixed with the graphene compound. Examples of catalysts used in forming the graphene compound include silicon oxide (SiO ２ , SiO ｘ (x<2)), aluminum oxide, iron, nickel, ruthenium, iridium, platinum, copper, germanium, etc. The particles preferably have a D50 of 1 μm or less, more preferably 100 nm or less.

[0133] Alternatively, silicon particles covered with a graphene compound may be used as the negative electrode active material. In this case, it is more preferable that there is a space between the graphene compound and the silicon particles that can buffer structural changes.

[0134] Titanium dioxide (TiO ２ ), lithium titanium oxide (Li ４ Ti ５ O １２ ), lithium-graphite intercalation compound (Li ｘ C ６ ), niobium pentoxide (Nb ２ O ５ ), tungsten dioxide (WO ２ ), molybdenum dioxide (MoO ２ ) and the like can be used.

[0135] In addition, as the negative electrode active material, a nitride of lithium and a transition metal, Li ３ Li with N-type structure ３−ｘ M ｘ N (M=Co, Ni, Cu) can be used. For example, Li ２．６Co ０．４ N has a large discharge capacity (900 mAh / g, 1890 mAh / cm ３ ) and is preferred.

[0136] When a nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, so V, which does not contain lithium ions, is used as the positive electrode active material. ２ O ５ , Cr ３ O ８ It is preferable that the material can be combined with a material such as the above. Even when a material containing lithium ions is used as the positive electrode active material, it is possible to use a nitride of lithium and a transition metal as the negative electrode active material by first desorbing the lithium ions contained in the positive electrode active material.

[0137] Furthermore, a material that undergoes a conversion reaction can also be used as the negative electrode active material. For example, a transition metal oxide that does not form an alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), or iron oxide (FeO), can be used as the negative electrode active material. Further examples of materials that undergo a conversion reaction include Fe ２ O ３ ,CuO,Cu ２ O, RuO ２ , Cr ２ O ３ oxides such as CoS ０．８９ , sulfides such as NiS and CuS, Zn ３ N ２ , Cu ３ N, Ge ３ N ４ Nitrides such as NiP ２ , FeP ２ , CoP ３ Phosphides such as FeF ３ , BiF ３ Fluorides such as:

[0138] In addition, a combination of the above-mentioned negative electrode active materials may be used; for example, a negative electrode active material obtained by mixing graphite and silicon particles may be used. Silicon particles are silicon powder used as a material for the negative electrode active material of lithium-ion secondary batteries. Silicon particles refer to silicon powder having an average particle size distribution, i.e., an average particle size of approximately 100 nm, and are sometimes referred to as nanosilicon particles. The silicon particles used are preferably prepared by pulverizing silicon raw materials to a uniform particle size. Silicon particles may include at least one of silicon, silicon oxide, and silicon alloy. While laser diffraction particle size distribution measurement is typically used to measure particle size, the measurement is not limited to laser diffraction particle size distribution measurement. The major axis of the particle cross section may also be measured by analysis using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0139] Furthermore, as the conductive additive and binder that can be contained in the negative electrode active material layer, the same materials as the conductive additive and binder that can be contained in the positive electrode active material layer can be used.

[0140] <Negative electrode current collector> The negative electrode current collector may be made of the same material as the positive electrode current collector, or may be made of copper, etc. It is preferable that the negative electrode current collector be made of a material that does not alloy with carrier ions such as lithium.

[0141] [Electrolyte Solution] The electrolyte solution contains an organic solvent, but the organic solvent of the electrolyte according to one embodiment of the present invention is not limited to being liquid at 25°C, and may be solid at 25°C or semi-solid at room temperature. The organic solvent of the electrolyte according to one embodiment of the present invention is preferably liquid over a wide temperature range, including temperatures from below freezing to high temperatures, but is not limited thereto. The organic solvent may be liquid, solid, or semi-solid over a wide temperature range, including temperatures from below freezing to high temperatures.

[0142] The organic solvent is preferably an aprotic organic solvent, and examples thereof include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), 1,3-propane sultone (PS), fluoroethylene carbonate (FEC), methyl 3,3,3-trifluoropropionate (MTFP), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, and sultones, and any combination and ratio of two or more of these may be used.

[0143] Because PS has HOMO and LUMO levels equivalent to those of EC and DEC, it is resistant to oxidation and reduction even at high cutoff voltages, and when decomposed on the surface of the positive electrode active material, it tends to form polymers. Therefore, it has the advantage of being less likely to gasify into small molecular weight decomposition products. Therefore, the electrolyte preferably contains 0.1 wt% to 10 wt%, more preferably 0.25 wt% to 7.5 wt% of PS.

[0144] FEC is a cyclic carbonate with a high dielectric constant, and when used in an organic solvent, it promotes the dissociation of lithium salts. On the other hand, FEC has electron-withdrawing substituents, making it easier to desolvate with lithium ions than EC. Specifically, the solvation energy of lithium ions in FEC is lower than that of EC without electron-withdrawing substituents. Therefore, FEC easily releases lithium ions from the surfaces of the positive and negative electrode active materials, thereby reducing the internal resistance of the secondary battery. Furthermore, FEC has a deep highest occupied molecular orbital (HOMO) level, making it less susceptible to oxidation and improving oxidation resistance. On the other hand, there are concerns about the high viscosity of FEC. Therefore, it is recommended to use a mixed organic solvent containing MTFP in addition to FEC alone in the electrolyte. MTFP is a type of chain carbonate, and can reduce the viscosity of the electrolyte solution or maintain the viscosity at room temperature (typically 25°C) even at low temperatures (typically 0°C). Furthermore, although MTFP has a lower solvation energy than methyl propionate (abbreviated as "MP"), which does not have an electron-withdrawing substituent, it may form a solvation with lithium ions when used in an electrolyte solution. When a mixed organic solvent containing both FEC and MTFP is used, when the volume ratio is FEC:MTFP=1:y, y is preferably 2 or more and 20 or less, more preferably 4 or more and 9 or less.

[0145] The organic solvent described above is free from granular dust or molecules other than the constituent molecules of the organic solvent (hereinafter simply referred to as "impurities"), and oxygen (O ２ ), water (H ２ 0) or water. ) content is preferably low and highly purified. Furthermore, it is preferable that reaction by-products during synthesis are suppressed through appropriate purification. Specifically, the impurities in the electrolyte are 100 ppm or less, preferably 50 ppm or less, and more preferably less than 10 ppm. The concentration of water among the impurities can be detected by Karl Fischer titration.

[0146] Furthermore, it is preferable that the above-mentioned organic solvent has almost no peaks due to impurities that can be confirmed by NMR measurement or the like. "Almost no peaks can be confirmed" means that the ratio of the integrated area of ​​the peak due to the impurity to the integrated area of ​​the peak due to the main component (simply referred to as "integral ratio") is 0.005 or less, preferably 0.002 or less. The device used for NMR measurement is not particularly limited, but for example, Bruker's "AVANCE III 400" can be used. Furthermore, among the five peaks of acetonitrile derived from acetonitrile-d3 used as a solvent in 1H-NMR measurement, the central peak can be located at 1.94 ppm.

[0147] For example, in the case of MTFP, it is known that when 1H-NMR is measured using acetonitrile-d3 solvent, four peaks appear at δ between 3.29 ppm and 3.43 ppm. However, if other peaks appear in this vicinity, for example, if a peak appears at δ between 3.24 ppm and 3.29 ppm, the peak is considered to be derived from impurities. Therefore, if the ratio (integral ratio) of the peak area between 3.24 ppm and 3.29 ppm to the peak area between 3.29 ppm and 3.43 ppm is 0.005 or less, preferably 0.002 or less, it can be said that peaks due to impurities are almost impossible to confirm.

[0148] Furthermore, by using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as the solvent for the electrolyte, it is possible to prevent the electricity storage device from exploding or catching fire even if the internal temperature rises due to an internal short circuit or overcharging of the electricity storage device. The ionic liquid is composed of a cation and an anion, and includes an organic cation and an anion. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.

[0149] The electrolyte to be dissolved in the solvent is, for example, LiPF ６ , LiClO ４ , LiAsF ６ , LiBF ４ , LiAlCl ４ , LiSCN, LiBr, LiI, Li ２ SO ４ , Li ２ B １０ Cl １０ , Li ２ B １２ Cl １２ , LiCF ３ SO ３ , LiC ４ F ９ SO ３ , LiC(CF ３ SO ２ ) ３ , LiC(C ２ F ５ SO ２ ) ３ , LiN(CF ３ SO ２ ) ２ , LiN(C ４ F ９ SO ２ ) (CF ３SO ２ ), LiN(C ２ F ５ SO ２ ) ２ , lithium bis(oxalato)borate (Li(C) ２ O ４ ) ２ , LiBOB), or two or more of these can be used in any combination and ratio.

[0150] The electrolyte solution may also contain an additive. The additive can suppress reactive decomposition of the electrolyte solution that may occur on the positive electrode surface or the negative electrode surface when the secondary battery is operated at high voltage and / or high temperature. Examples of additives that can be used include propane sultone (PS), vinylene carbonate (VC), tert-butylbenzene (TBB), lithium bis(oxalate)borate (LiBOB), 1,3,6-hexanetricarbonitrile, ethyl 2-methylbutyrate, ethyl 2-methylvalerate, and propyl 2-methylbutyrate. PS is particularly preferred because it improves cycle characteristics as an additive.

[0151] The additive may be one or more dinitrile compounds, such as succinonitrile, glutaronitrile, adiponitrile (ADN), or ethylene glycol bis(propionitrile) ether (EGBE).

[0152] Fluorobenzene may also be added to the organic solvent. The concentration of the additive is, for example, 0.1 wt% to 5 wt% of the total electrolyte solution. PS or EGBE are preferred because they form a good coating on the positive electrode during charge and discharge, improving cycle characteristics. Fluorobenzene (FB) is preferred because it improves the wettability of the organic solvent to the positive and negative electrodes. Dinitrile compounds are preferred because their nitrile groups orient to the positive and negative electrodes, inhibiting oxidative decomposition of the organic solvent and improving voltage resistance. Furthermore, dinitrile compounds are preferred because they can prevent copper dissolution during overdischarge when a copper-containing current collector is used on the negative electrode. Considering the use of secondary batteries at high voltages, adding a nitrile compound is preferred.

[0153] The electrolyte used in the electricity storage device is preferably a highly purified electrolyte with a low content of granular waste or elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities"). Specifically, the weight ratio of impurities to the electrolyte is preferably 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0154] Instead of the electrolytic solution, a polymer gel electrolyte in which a polymer is swollen with the electrolytic solution may be used.

[0155] The use of a polymer gel electrolyte improves safety against leakage, etc. It also enables the secondary battery to be made thinner and lighter.

[0156] Examples of polymers that can be gelled include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, and fluorine-based polymer gel. For example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing these can be used. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The polymer formed may also have a porous shape.

[0157] In addition, the electrolyte can be a solid electrolyte containing an inorganic material such as a sulfide or oxide, or a polymer material such as a polyethylene oxide (PEO)-based solid electrolyte. When a solid electrolyte is used, the installation of a separator or spacer is unnecessary. Furthermore, since the entire battery can be solidified, the risk of leakage is eliminated, dramatically improving safety.

[0158] [Separator] When an electrolyte solution and a polymer gel electrolyte are used, a separator is disposed between the positive electrode and the negative electrode. Examples of separators that can be used include cellulose-containing fibers such as paper, nonwoven fabrics, glass fibers, ceramics, and synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol-based fibers), polypropylene (referred to as PP), polyimide (referred to as PI), polyester, acrylic, polyolefin, and polyurethane. The porosity of the separator can be 35% to 90%, preferably 60% to 85%. Separators using polypropylene can have a porosity of 35% to 45%. Separators using polyimide can have a porosity of 75% to 85%. The separator thickness is preferably 10 μm to 80 μm, more preferably 20 μm to 60 μm. A separator using polyimide can have a high porosity, and therefore can be made thick (typically, the thickness is 50 μm or more and 60 μm or less) without increasing the lithium ion transport resistance, which is preferable because it improves the safety of the lithium ion battery.

[0159] The separator is preferably processed into a bag shape and disposed so as to encase either the positive electrode or the negative electrode.

[0160] The separator may have a multilayer structure. For example, an organic film such as polypropylene or polyethylene may be coated with a ceramic material, a fluorine-based material, a polyamide material, or a mixture of these. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine-based materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aramid (meta-aramid, para-aramid).

[0161] By using a multilayer separator, the safety of the lithium-ion battery can be maintained even if the overall thickness of the separator is thin, and therefore the capacity per volume of the lithium-ion battery can be increased.

[0162] [Exterior Body] The exterior body of a lithium-ion battery can be made of a metal material such as aluminum or a resin material. Alternatively, a film-like exterior body can be used. Examples of the film include a three-layer structure film in which a thin, flexible metal film such as aluminum, stainless steel, copper, or nickel is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide resin or polyester resin is further provided on the thin metal film as the outer surface of the exterior body.

[0163] This embodiment can be used in combination with other embodiments.

[0164] Embodiment 4 In this embodiment, an example of a lithium ion battery will be described with reference to FIGS. 3A to 3C.

[0165] Fig. 3A is a diagram illustrating a wound body 950a of a lithium ion battery 913, Fig. 3B is an exploded perspective view of the lithium ion battery 913, and Fig. 3C is an external view of the lithium ion battery 913. The lithium ion battery 913 has a positive electrode 932 having the positive electrode active material described in the previous embodiment, a negative electrode 931, an electrolyte layer, and a separator 933, and the negative electrode 931 has a negative electrode active material layer 931a. The positive electrode 932 has a positive electrode active material layer 932a. These are wound as shown in Fig. 3A.

[0166] The separator 933 has a width wider than the negative electrode active material layer 931 a and the positive electrode active material layer 932 a, and is wound so as to overlap the negative electrode active material layer 931 a and the positive electrode active material layer 932 a. From the standpoint of safety, it is preferable that the negative electrode active material layer 931 a be wider than the positive electrode active material layer 932 a. A wound body 950 a having such a shape is preferable due to its high safety and productivity.

[0167] 3B, the negative electrode 931 is electrically connected to a terminal 951. The terminal 951 is electrically connected to a terminal 911a. The positive electrode 932 is electrically connected to a terminal 952. The terminal 952 is electrically connected to a terminal 911b.

[0168] 3C , wound body 950 a is covered with housing 930 to form lithium ion battery 913. Housing 930 is preferably provided with a safety valve, an overcurrent protection element, etc. The safety valve is a valve that opens when the inside of housing 930 reaches a predetermined internal pressure to prevent the battery from exploding.

[0169] 3B, the lithium ion battery 913 may have a plurality of wound bodies 950a. By using a plurality of wound bodies 950a, the lithium ion battery 913 can have a larger charge / discharge capacity.

[0170] By using the positive electrode active material of the present invention in the lithium ion battery 913 having a wound body, a secondary battery having high energy density and good electrical characteristics over a wide temperature range can be obtained.

[0171] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0172] Embodiment 5 In this embodiment, an example of application to an electric vehicle (EV) will be described with reference to FIGS. 4A to 4C.

[0173] 4A , the electric vehicle is equipped with first batteries 1301 a and 1301 b as main driving lithium ion batteries, and a second battery 1311 that supplies power to an inverter 1312 that starts a motor 1304. By using the positive electrode active material of the present invention for the first batteries 1301 a and 1301 b, a secondary battery that has high energy density and exhibits good electrical characteristics over a wide temperature range can be obtained.

[0174] The second battery 1311 is also called a cranking battery (also called a starter battery). The second battery 1311 only needs to have high output, and does not need to have a large capacity, and the capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0175] The internal structure of the first battery 1301a may be a wound type or a stacked type. The first battery 1301a may be a lithium-ion battery including the positive electrode active material of one embodiment of the present invention. By using the lithium-ion battery including the positive electrode active material of one embodiment of the present invention for the first battery 1301a, an electric vehicle with a long driving range and usable in a wide range of ambient temperatures can be obtained.

[0176] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more batteries may be connected in parallel. Furthermore, if the first battery 1301a can store sufficient power, the first battery 1301b may be omitted. By configuring a battery pack having multiple lithium ion batteries, it is possible to extract large amounts of power. The multiple lithium ion batteries may be connected in parallel, in series, or in series after being connected in parallel. A plurality of lithium ion batteries is also called a battery pack.

[0177] In addition, in an in-vehicle lithium-ion battery, in order to cut off power from multiple lithium-ion batteries, a service plug or circuit breaker that can cut off high voltage without using tools is provided in the first battery 1301a.

[0178] The power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V in-vehicle components (such as an electric power steering 1307, a heater 1308, and a defogger 1309) via a DCDC circuit 1306. When a rear motor 1317 is provided for the rear wheels, the first battery 1301a is also used to rotate the rear motor 1317.

[0179] In addition, the second battery 1311 supplies power to 14V in-vehicle components (audio 1313, power windows 1314, lamps 1315, etc.) via the DCDC circuit 1310.

[0180] The first battery 1301a will be described with reference to FIG. 4B.

[0181] FIG. 4B shows an example in which nine prismatic lithium-ion batteries 1300 are combined into one battery pack 1415. Furthermore, nine prismatic lithium-ion batteries 1300 are connected in series, with one electrode fixed by a fixing portion 1413 made of an insulator and the other electrode fixed by a fixing portion 1414 made of an insulator. While this embodiment shows an example in which the batteries are fixed by the fixing portions 1413 and 1414, they may also be housed in a battery housing box (also referred to as a casing). Because it is expected that a vehicle will be subjected to external vibrations or shaking (e.g., from the road surface), it is preferable to fix multiple lithium-ion batteries using the fixing portions 1413 and 1414 and the battery housing box. Furthermore, one electrode is electrically connected to the control circuit unit 1320 by wiring 1421. The other electrode is electrically connected to the control circuit unit 1320 by wiring 1422.

[0182] A memory circuit including a transistor using an oxide semiconductor may be used for the control circuit portion 1320. A charge control circuit or a battery control system including a memory circuit including a transistor using an oxide semiconductor may be referred to as a battery operating system (BTOS) or a battery oxide semiconductor (BTOS).

[0183] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, a metal oxide such as In-M-Zn oxide (wherein element M is one or more selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, and magnesium) may be used as the oxide. In particular, the In-M-Zn oxide that can be used as the oxide is preferably a C-Axis Aligned Crystal Oxide Semiconductor (CAAC-OS) or a Cloud-Aligned Composite Oxide Semiconductor (CAC-OS). Alternatively, an In oxide, an In—Ga oxide, or an In—Zn oxide may be used as the oxide.

[0184] Furthermore, since the control circuit unit 1320 can be used in low-temperature environments, it is preferable to use a transistor using an oxide semiconductor. To simplify the process, the control circuit unit 1320 may be formed using a unipolar transistor. A transistor using an oxide semiconductor for the semiconductor layer has a wider operating ambient temperature range than single-crystal Si, from −40° C. to 150° C., and its characteristics change less when the lithium-ion battery is heated than single-crystal Si. The off-current of a transistor using an oxide semiconductor is below the lower limit of measurement regardless of temperature, even at 150° C., whereas the off-current characteristics of a single-crystal Si transistor are highly temperature-dependent. For example, at 150° C., the off-current of a single-crystal Si transistor increases, and the current on / off ratio does not become sufficiently large. The control circuit unit 1320 can improve safety.

[0185] The control circuit unit 1320, which uses a memory circuit including transistors using oxide semiconductors, can also function as an automatic control device for lithium-ion batteries to address 10 causes of instability, such as micro-short circuits. The functions for addressing the 10 causes of instability include overcharging prevention, overcurrent prevention, overheating control during charging, cell balancing in the battery pack, over-discharging prevention, a fuel gauge, automatic control of charging voltage and current according to temperature, control of charging current according to the degree of degradation, detection of abnormal behavior of micro-short circuits, and prediction of abnormalities related to micro-short circuits. The control circuit unit 1320 has at least one of these functions. Furthermore, the automatic control device for lithium-ion batteries can be miniaturized.

[0186] Micro-short circuits are tiny short circuits that occur inside lithium-ion batteries. One of the causes of micro-short circuits is said to be local current concentration in parts of the positive electrode and negative electrode due to uneven distribution of the positive electrode active material caused by multiple charge and discharge cycles, or the generation of by-products due to side reactions, which causes micro-short circuits.

[0187] In addition to detecting micro-short circuits, the control circuit 1320 can also be said to detect the terminal voltage of the lithium-ion battery and manage the charge / discharge state of the lithium-ion battery. For example, to prevent overcharging, it can turn off both the output transistor and the cutoff switch of the charging circuit almost simultaneously.

[0188] FIG. 4C shows an example of a block diagram of the battery pack 1415 shown in FIG. 4B.

[0189] The control circuit 1320 includes a switch unit 1324 including at least a switch for preventing overcharging and a switch for preventing overdischarging, a control circuit 1322 for controlling the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit 1320 sets upper and lower voltage limits for the lithium-ion battery used and limits the upper limit of the external current and the upper limit of the output current. The range between the lower and upper voltage limits for the lithium-ion battery is within the recommended voltage range. If the voltage falls outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent overcharging and overdischarging. For example, if the control circuit 1322 detects a voltage that could cause overcharging, it turns off the switch unit 1324 to cut off the current. Furthermore, a PTC element may be provided in the charge / discharge path to provide a function for cutting off the current in response to an increase in temperature. The control circuit section 1320 also has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0190] The switch unit 1324 can be configured by combining an n-channel transistor and a p-channel transistor. The switch unit 1324 is not limited to a switch having a Si transistor using single crystal silicon, and may be, for example, Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), GaO ｘThe switch portion 1324 may be formed using a power transistor having gallium oxide (x is a real number greater than 0). Furthermore, a memory element using an OS transistor can be freely arranged by stacking it on a circuit using a Si transistor, and thus integration can be easily achieved. By stacking the control circuit portion 1320 using an OS transistor on the switch portion 1324 and integrating them, it is possible to form it into a single chip, thereby enabling miniaturization.

[0191] The first batteries 1301a and 1301b mainly supply power to on-board equipment in the 42V system (high voltage system), while the second battery 1311 supplies power to on-board equipment in the 14V system (low voltage system). Lead-acid batteries are often used as the second battery 1311 due to their cost advantages. Using a lithium-ion battery as the second battery 1311 has the advantage of being maintenance-free, but after prolonged use, e.g., three years or more, there is a risk of abnormalities occurring that cannot be detected at the time of manufacture. In particular, if the second battery 1311 that starts the inverter becomes inoperable, even if the first batteries 1301a and 1301b have remaining capacity, the second battery 1311 is charged to maintain a full charge state by supplying power from the first battery to the second battery.

[0192] In this embodiment, an example in which lithium ion batteries are used for both the first battery 1301 a and the second battery 1311 is shown, but a lead-acid battery, an all-solid-state battery, or an electric double layer capacitor may be used for the second battery 1311. By using the positive electrode active material of the present invention in the above-described lithium ion battery, a secondary battery having high energy density and excellent electrical characteristics over a wide temperature range can be obtained.

[0193] Furthermore, regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305, and is then charged into the second battery 1311 from the motor controller 1303 and the battery controller 1302 via the control circuit unit 1321. Alternatively, the first battery 1301a is charged from the battery controller 1302 via the control circuit unit 1320. Alternatively, the first battery 1301b is charged from the battery controller 1302 via the control circuit unit 1320. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b be capable of rapid charging.

[0194] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set charging conditions in accordance with the charging characteristics of the lithium ion batteries used, and can perform rapid charging.

[0195] Although not shown, when an external charger is connected, the charger's outlet or the charger's connection cable is electrically connected to the battery controller 1302. Power supplied from the external charger is charged to the first batteries 1301a, 1301b via the battery controller 1302. Some chargers are provided with a control circuit, and although the functions of the battery controller 1302 may not be used, it is preferable to charge the first batteries 1301a, 1301b via the control circuit unit 1320 to prevent overcharging. The control circuit unit 1320 may also be provided in the connection cable or the charger's connection cable. The control circuit unit 1320 is sometimes called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) provided in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU includes a microcomputer. The ECU uses a CPU or a GPU.

[0196] External chargers installed at charging stations and the like come in a variety of types, including 100V outlets, 200V outlets, and three-phase 200V and 50kW outlets. Charging can also be performed by receiving power from external charging equipment using a wireless power supply system or the like.

[0197] Next, an example in which a lithium-ion battery according to one embodiment of the present invention is mounted on a vehicle, typically a transportation vehicle, will be described.

[0198] Furthermore, installing lithium-ion batteries in vehicles will enable next-generation clean energy automobiles such as hybrid vehicles (HVs), electric vehicles (EVs), plug-in hybrid vehicles (PHVs), etc. Lithium-ion batteries can also be installed in transportation vehicles such as agricultural machinery, mopeds including electrically assisted bicycles, motorcycles, electric wheelchairs, electric carts, small or large ships, submarines, aircraft such as fixed-wing aircraft and rotary-wing aircraft, rockets, artificial satellites, space probes, planetary probes, and spacecraft.

[0199] 5A to 5E show examples of vehicles and the like using the lithium-ion battery of one embodiment of the present invention.

[0200] 5A illustrates an example of an electric bicycle using the lithium-ion battery of one embodiment of the present invention. The lithium-ion battery of one embodiment of the present invention can be applied to an electric bicycle 8700 illustrated in FIG. 5A. The lithium-ion battery of one embodiment of the present invention may include a protection circuit.

[0201] The electric bicycle 8700 includes a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists a rider. The power storage device 8702 can be detached from the main body of the electric bicycle 8700 and can be carried around. The power storage device 8702 includes a plurality of lithium-ion batteries of one embodiment of the present invention, and the remaining battery charge and the like can be displayed on a display unit. By using the positive electrode active material of the present invention for the lithium-ion battery, a secondary battery with high energy density and favorable electrical characteristics over a wide temperature range can be obtained.

[0202] FIG. 5B illustrates an example of a motorcycle using a lithium-ion battery of one embodiment of the present invention. A scooter 8600 illustrated in FIG. 5B includes a power storage device 8602, a side mirror 8601, and a turn signal light 8603. The scooter 8600 can store the power storage device 8602 in an under-seat storage compartment 8604. The power storage device 8602 can supply electricity to the turn signal light 8603. When the scooter has a motor, the power storage device 8602 can also supply electricity to the motor. By using the positive electrode active material of the present invention for the lithium-ion battery included in the power storage device 8602, a secondary battery with high energy density and favorable electrical characteristics over a wide temperature range can be obtained.

[0203] The automobile 2001 shown in FIG. 5C is an electric automobile that uses an electric motor as a power source for traveling. Alternatively, it is a hybrid automobile that can appropriately select and use an electric motor or an engine as a power source for traveling. When a lithium-ion battery is mounted on a vehicle, an example of the lithium-ion battery shown in the above embodiment is installed in one or more locations. By using the positive electrode active material of the present invention in the lithium-ion battery mounted on the vehicle, a secondary battery that has a high energy density and exhibits good electrical characteristics over a wide temperature range can be obtained.

[0204] 5C includes a battery pack 2200, which includes a battery module to which a plurality of lithium-ion batteries are connected. The battery pack 2200 further preferably includes a charge control device electrically connected to the battery module.

[0205] Furthermore, the automobile 2001 can charge its lithium-ion battery by receiving power supply from an external charging facility using a plug-in system, a contactless power supply system, or the like. The charging method and connector standards may be appropriately determined using a predetermined system such as CHAdeMO (registered trademark) or Combo. The external charging facility may be a charging station installed in a commercial facility, a household power source, or the like. For example, plug-in technology can be used to charge the power storage device installed in the automobile 2001 using an external power supply. Charging can be performed by converting AC power to DC power via a conversion device such as an AC-DC converter.

[0206] Furthermore, although not shown, a power receiving device can be mounted on a vehicle and power can be supplied contactlessly from a ground-based power transmitting device to charge the vehicle. In the case of this contactless power supply method, by incorporating a power transmitting device into a road or an exterior wall, charging can be performed not only while the vehicle is stopped but also while the vehicle is moving. This contactless power supply method can also be used to transmit and receive power between two vehicles. Furthermore, solar cells can be installed on the exterior of the vehicle to charge the lithium-ion battery while the vehicle is stopped and while moving. For such contactless power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0207] FIG. 5D shows, as an example, a large transport vehicle 2003 having an electrically controlled motor. The battery module of the transport vehicle 2003 can have a maximum voltage of 600 V, for example, by connecting in series one hundred or more lithium-ion batteries with a nominal voltage of 3.0 V to 5.0 V. The battery module of the transport vehicle 2003 has the same functions as the battery pack 1415 shown in FIG. 4B except for the number of cells connected in series or the number of cells constituting the battery module, and therefore a description thereof will be omitted. By using the positive electrode active material of the present invention in the lithium-ion batteries of the module, a secondary battery having a high energy density and good electrical characteristics over a wide temperature range can be obtained.

[0208] 5E shows, as an example, an aircraft 2004 having an engine that burns fuel. The aircraft 2004 has wheels for takeoff and landing, and can therefore be considered a part of a transportation vehicle. The aircraft 2004 has a battery pack 2203 including a battery module formed by connecting multiple lithium-ion batteries and including the battery module and a charge control device.

[0209] The battery module of the aircraft 2004 is, for example, eight 4 V lithium ion batteries connected in series, with a maximum voltage of 32 V. Other than the number of lithium ion batteries constituting the battery module of the battery pack 2203, the battery module has the same functions as those shown in Fig. 5C, and therefore a description thereof will be omitted.

[0210] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0211] (Embodiment 6) In this embodiment, an example of mounting a lithium-ion battery according to one embodiment of the present invention in an electronic device will be described. Examples of electronic devices mounting a lithium-ion battery include television sets (also referred to as televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also referred to as mobile phones or mobile phone devices), portable game consoles, personal digital assistants, sound players, and large game consoles such as pachinko machines. Examples of personal digital assistants include notebook personal computers, tablet devices, e-book readers, and mobile phones.

[0212] 6A shows an example of a mobile phone. The mobile phone 2100 includes a display portion 2102 built into a housing 2101, operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. The mobile phone 2100 also includes a lithium ion battery 2107. By using the positive electrode active material of the present invention in the lithium ion battery, a secondary battery having high energy density and excellent electrical characteristics over a wide temperature range can be obtained.

[0213] The mobile phone 2100 can execute various applications such as mobile phone calls, e-mail, document browsing and creation, music playback, internet communication, and computer games.

[0214] The operation button 2103 can be provided with various functions such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, power saving mode activation / deactivation, etc. For example, the functions of the operation button 2103 can be freely set by an operating system incorporated in the mobile phone 2100.

[0215] The mobile phone 2100 is also capable of performing standardized short-range wireless communication, and can also make hands-free calls by communicating with a wirelessly enabled headset, for example.

[0216] The mobile phone 2100 also includes an external connection port 2104, which allows direct data exchange with other information terminals via a connector. Charging can also be performed via the external connection port 2104. Note that charging may be performed by wireless power supply without using the external connection port 2104.

[0217] The mobile phone 2100 preferably has a sensor, such as a fingerprint sensor, a pulse sensor, a body temperature sensor, a touch sensor, a pressure sensor, an acceleration sensor, or the like.

[0218] 6B shows an unmanned aerial vehicle 2300 having a plurality of rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 includes a lithium-ion battery 2301 according to one embodiment of the present invention, a camera 2303, and an antenna (not shown). The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. By using the positive electrode active material of the present invention in a lithium-ion battery, a secondary battery having high energy density and favorable electrical characteristics over a wide temperature range can be obtained.

[0219] Fig. 6C shows an example of a robot. The robot 6400 shown in Fig. 6C includes a lithium ion battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a movement mechanism 6408, a computing device, etc.

[0220] The microphone 6402 has a function of detecting the user's speaking voice, environmental sounds, etc. The speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.

[0221] The display unit 6405 has a function of displaying various information. The robot 6400 can display information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a detachable information terminal, which can be installed in a fixed position on the robot 6400 to enable charging and data transfer.

[0222] The upper camera 6403 and the lower camera 6406 have the function of capturing images of the surroundings of the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0223] The robot 6400 includes a lithium-ion battery 6409 according to one embodiment of the present invention and a semiconductor device or an electronic component in its internal region. By using the positive electrode active material of the present invention for the lithium-ion battery, the secondary battery can have high energy density and good electrical characteristics over a wide temperature range.

[0224] 6D shows an example of a cleaning robot. The cleaning robot 6300 includes a display unit 6302 arranged on the top surface of a housing 6301, a plurality of cameras 6303 arranged on the side surfaces, a brush 6304, an operation button 6305, a lithium-ion battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust from a suction port arranged on the bottom surface.

[0225] For example, the cleaning robot 6300 can analyze an image captured by the camera 6303 and determine whether or not there is an obstacle such as a wall, furniture, or a step. Furthermore, when an object that may become entangled in the brush 6304, such as a wire, is detected through image analysis, the cleaning robot 6300 can stop the rotation of the brush 6304. The cleaning robot 6300 includes a lithium-ion battery 6306 according to one embodiment of the present invention and a semiconductor device or electronic component in its internal region. By using the positive electrode active material of the present invention in the lithium-ion battery, a secondary battery with high energy density and favorable electrical characteristics over a wide temperature range can be obtained.

[0226] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0227] In this example, LiMn ｘ Fe １−ｘ P.O. ４ A positive electrode active material was prepared by dissolving zinc as an additive element in (0<x<1), and its characteristics were evaluated.

[0228] <Preparation of Positive Electrode Active Material> Preparation of the positive electrode active material in this example will be described with reference to the preparation method shown in FIG.

[0229] ZnO as a zinc source (Zn source), Li as a lithium source (Li source) ２ CO ３ , MnCO as a manganese source (Mn source) ３ , FeC as an iron source (Fe source) ２ O ４ ・2H ２ O, NH as a phosphate source ４ H ２ P.O. ４The composition is LiMn ０．５９ Fe ０．４ Zn ０．０１ P.O. ４ Zirconia balls with a diameter of 3 mm were used as the grinding medium, and dehydrated acetone was used as the solvent.

[0230] These were mixed for 2 hours at 300 rpm using a planetary ball mill while cooling. After drying in a ventilation drying oven, the first mixture was passed through a sieve with 300 μm openings to recover the first mixture.

[0231] The first mixture was placed in a crucible made of aluminum oxide with a purity of 99.9%, and the crucible was covered with a lid and heated in a muffle furnace in a nitrogen flow atmosphere at 350°C for 10 hours. The heated mixture was passed through a sieve with 300 µm openings to obtain a composite oxide.

[0232] Glucose was used as a carbon source (C source), and the composite oxide and the C source were weighed out so that the weight ratio of composite oxide:C source was 10:1. Zirconia balls with a diameter of 3 mm were used as a grinding medium, and dehydrated acetone was used as a solvent.

[0233] These were mixed using a planetary ball mill at 300 rpm for 2 hours, dried in a ventilation drying oven, and then passed through a sieve with 300 μm openings to recover the second mixture.

[0234] The second mixture was placed in a 99.9% pure aluminum oxide crucible, and the lid was placed on the crucible. The crucible was heated in a muffle furnace at 650°C for 10 hours in a nitrogen flow atmosphere. The heated mixture was sieved through a 53 μm mesh sieve to obtain a positive electrode active material. The carbon-coated positive electrode active material prepared in the above process was then sieved into a C / LiMn ０．５９ Fe ０．４ Zn ０．０１ P.O. ４ Or, it will be called Zn 1%.

[0235] A comparative example containing no Zn and a positive electrode active material containing 10% Zn were prepared in the same manner as above except for the amounts of the zinc source and manganese source. The compositions are shown in Table 1.

[0236]

[0237] <XRD> XRD measurements were performed on the three samples prepared above, and Rietveld analysis was performed. The XRD device and measurement conditions were as described in the first embodiment. The XRD device was installed at room temperature (according to JIS Z 8703). Figure 7 shows the XRD patterns of the three samples. The horizontal axis shows 2θ (°), and the vertical axis shows intensity (arbitrary unit (a.u.)). No particular heterophase was observed. These patterns were analyzed using LiFePO ４ (ICSD coll.code.193640) The results of the refined Rietveld analysis assuming a single phase are shown in Table 2.

[0238]

[0239] 8A to 8C are graphs showing the relationship between the zinc concentration of each sample and the change in the lattice constant of the unit cell obtained from the above analysis. Fig. 8A is a graph of the a-axis lattice constant (Lattice constant a) and zinc concentration, Fig. 8B is a graph of the b-axis lattice constant (Lattice constant b) and zinc concentration, and Fig. 8C is a graph of the c-axis lattice constant (Lattice constant c) and zinc concentration. Fig. 9 shows the relationship between the zinc concentration of each sample and the change in the lattice constant of the unit cell obtained from the above analysis. ４ As shown in Figure 9, the lithium diffusion path exists in the b-axis direction.

[0240] As shown in Figures 8A to 8C, increasing the zinc concentration resulted in smaller lattice constants and smaller unit cells. The a-axis and b-axis contracted significantly. Furthermore, the contraction of all lattice constants was linear and followed Vegard's law. This suggests that zinc is dissolved in an olivine-type crystal structure. For the 1% Zn sample, the a-axis lattice constant was 10.3700 Å to 10.3997 Å, specifically 10.3889 Å to 10.3997 Å, and more specifically 10.3970 Å to 10.3997 Å. The b-axis lattice constant was 6.0440 Å to 6.0616 Å, specifically 6.0550 Å to 6.0616 Å, and more specifically 6.0600 Å to 6.0616 Å. The c-axis lattice constant was 4.7180 Å or more, specifically 4.7210 Å or more, and more specifically 4.7218 Å or more.

[0241] Furthermore, as shown in Table 2, the crystallite size LVol-IB of the sample containing 1% Zn was 50 nm or more and less than 90 nm, specifically 71.2 nm.

[0242] <Charge-Discharge Characteristics> Coin cells (CR2032 type, diameter 20 mm, height 3.2 mm) (hereinafter also referred to as half cells) using the three samples of positive electrode active material prepared above and lithium metal as the negative electrode were prepared, and their characteristics were evaluated.

[0243] Polypropylene was used for the separator. The electrolyte solution and the electrolyte were 1 mol / dm ３ LiPF ６ The mixture used was EC:DEC=3:7 (volume ratio) to which 2 wt % of VC was added.

[0244] Acetylene black was used as the conductive additive, and PVDF was used as the binder. The positive electrode active material, acetylene black, the binder, and NMP as the solvent were mixed to prepare a slurry. The weight ratio of the positive electrode active material, conductive additive, and PVDF was 90:5:5.

[0245] A carbon-coated aluminum foil was used as a positive electrode current collector, and the slurry was applied to the positive electrode current collector. The amount of the positive electrode active material supported was 5 mg / cm. ２ After drying, the sheet was pressed at 210 kN / m and 120°C.

[0246] The rate characteristic test was performed by charging using CCCV (constant current constant voltage) (charging current 34 mA / g, charging voltage 4.5 V, end current 3.4 mA / g), discharging using CC (end voltage 2.5 V, arbitrary discharge current), and resting for 10 minutes after charging and discharging. The arbitrary discharge current was 34 mA / g (0.2 C), 34 mA / g (0.2 C), 34 mA / g (0.2 C), 85 mA / g (0.5 C), 170 mA / g (1 C), 340 mA / g (2 C), 510 mA / g (3 C), 680 mA / g (4 C), 850 mA / g (5 C), and 34 mA / g (0.2 C). The measurement environment was 25 ° C. n = 2.

[0247] The results of the rate characteristic test are shown in Figure 10A. The horizontal axis of the graph shows the charge rate / discharge rate, and the vertical axis shows the discharge capacity per weight of the positive electrode active material after the carbon coating process. Figure 10B shows the discharge capacity ratio, normalized to the discharge capacity at the third 0.2C charge / discharge cycle as 1. As shown in Figures 10A and 10B, the cell containing 1% Zn positive electrode active material suppressed the decrease in discharge capacity at high rates, and the ratio of the discharge capacity at the 0.2C discharge test to the discharge capacity at the 5C discharge test was 88% or more. More specifically, the ratio of the discharge capacity at the 0.2C discharge test to the discharge capacity at the 5C discharge test was 87.3% and 85.4% in the comparative example, while it was 88.7% and 88.3% in the 1% Zn cell. The difference in discharge capacity was 18.9 mAh / g and 21.6 mAh / g in the comparative example, while it was 16.9 mAh / g and 17.6 mAh / g in the Zn 1% case.

[0248] Furthermore, the cells containing 1% Zn as a positive electrode active material had a large discharge capacity, and the discharge capacity per weight of the positive electrode active material in a 0.2 C discharge test was 149 mAh / g or more in all cases.

[0249] The charge-discharge cycle test consisted of CCCV charging (4.5 V, 85 mA / g, final current 8.5 mA / g) and CC discharging (85 mA / g, final voltage 2.5 V), with a 10-minute pause between charging and discharging. The measurement environment was 25°C, 60°C, or -20°C.

[0250] The results of the charge-discharge cycle test conducted at 25°C are shown in Figure 11. The horizontal axis represents the number of cycles, and the vertical axis represents the discharge capacity per weight of the positive electrode active material after the carbon coating process. The cell with 1% Zn positive electrode active material had a higher discharge capacity than the comparative example, demonstrating favorable charge-discharge cycle characteristics. Furthermore, the cell with 1% Zn positive electrode active material showed less decrease in discharge capacity from the first to the 20th cycle than the comparative example. Specifically, the difference between the first discharge capacity and the 20th cycle discharge capacity of the comparative example was 6 mAh / g and 5.6 mAh / g, respectively, while the difference for the 1% Zn positive electrode active material was 4.3 mAh / g and 4 mAh / g.

[0251] The charge-discharge cycle test in a -20°C measurement environment was performed by performing two charge-discharge cycles at 25°C as an aging treatment, followed by changing the measurement environment to -20°C. The results of the charge-discharge cycle test in a -20°C measurement environment are shown in Figures 12A and 12B. The horizontal axis shows the number of cycles, and the vertical axis shows the discharge capacity per weight of the positive electrode active material after the carbon coating process. Figure 12A shows the discharge capacity after two charge-discharge cycles at 25°C as an aging treatment, and Figure 12B shows the discharge capacity after the measurement environment was changed to -20°C. Although the ranges on the vertical axis are different, the same cells are indicated by a common marker. Figure 12B shows the number of cycles including the two aging cycles. Even at -20°C, the Zn 1% battery had a higher discharge capacity than the comparative example.

[0252] Manganese oxidation-reduction at 60°C (Mn ２＋ / Mn ３＋ To compare the plateaus resulting from the carbon coating process, the charge-discharge curves for the first and 100th cycles of a half-cell containing a comparative example cathode active material are shown in Figure 13A, Figure 13B, and Figure 13C, respectively. The vertical axis shows voltage, and the horizontal axis shows charge-discharge capacity per weight of the cathode active material after the carbon coating process. In both cases, the first cycle is shown by a solid line, and the 100th cycle is shown by a dotted line. For clarity of the graph, n = 1.

[0253] As shown in FIGS. 13A to 13C, in the comparative example, the plateau due to the oxidation-reduction of manganese decreased after the charge-discharge cycle, but this was suppressed in the case of 1% Zn and was hardly observed in the case of 10% Zn.

[0254] 14A to 15C show the charge / discharge dV / dQ curves for the first and 100th cycles of the discharge curves at 60°C and 25°C. For clarity of the graphs, n = 1. Fig. 14A shows the charge / discharge dV / dQ curve for the comparative example at 60°C, Fig. 14B shows the charge / discharge dV / dQ curve for 1% Zn at 60°C, Fig. 14C shows the charge / discharge dV / dQ curve for 10% Zn at 60°C, Fig. 15A shows the charge / discharge dV / dQ curve for the comparative example at 25°C, Fig. 15B shows the charge / discharge dV / dQ curve for 1% Zn at 25°C, and Fig. 15C shows the charge / discharge dV / dQ curve for 10% Zn at 25°C. The peaks (Peak_charge) in the range of 25 mAh / g or more and 125 mAh / g or less on the charge dV / dQ curve are indicated by crosses, and the peaks (Peak_discharge) in the range of 25 mAh / g or more and 125 mAh / g or less on the discharge dV / dQ curve are indicated by black squares.

[0255] To quantify the decrease in the plateau due to manganese oxidation-reduction, discharge dV / dQ curves were calculated for the first, tenth, and hundredth cycles of the discharge curves at 60°C and 25°C. The discharge dV / dQ curves were obtained using the method described in embodiment 1, and the number of averaging treatments was eight. Table 3 shows the values ​​at which peaks appear in the discharge dV / dQ curve range of 25 mAh / g to 125 mAh / g. The peak in the discharge dV / dQ curve range of 25 mAh / g to 125 mAh / g indicates the timing of the transition from the plateau due to manganese oxidation-reduction to the plateau due to iron oxidation-reduction. The higher the capacity at which this peak appears, the more the plateau due to manganese oxidation-reduction is maintained.

[0256] Table 3 also shows the difference Peak(1) - Peak(100) between the position where the peak of the discharge dV / dQ curve in the first cycle appears, Peak(1), and the position where the peak of the discharge dV / dQ curve in the 100th cycle appears, Peak(1) - Peak(100).

[0257]

[0258] As shown in Table 3 and Figures 14A to 15C, in the half-cells in which the plateau due to the manganese oxidation-reduction was reduced, the peak position of the discharge dV / dQ curve in the range of 25 mAh / g to 125 mAh / g shifted significantly toward lower capacities as the charge-discharge cycles progressed. Conversely, in the half-cells in which the plateau due to the manganese oxidation-reduction was suppressed, the shift in the peak position was small. This is presumably because the zinc suppressed the volume difference before and after lithium insertion / extraction.

[0259] More specifically, at 1% Zn, where the plateau decrease was suppressed, Peak(1)-Peak(100) was 12 mAh / g or less when measured at 60°C, and Peak(1)-Peak(100) was 8 mAh / g or less when measured at 25°C.

[0260] In this example, in order to evaluate the crystal structure of the positive electrode active material prepared in Example 1, XRD measurement was performed on the electrode sample after charging or discharging, and the obtained diffraction pattern was analyzed.

[0261] <Preparation of Positive Electrode Active Material> Positive electrode active materials for the comparative example and Zn 1% were prepared in the same manner as in Example 1, and half cells were prepared using these materials.

[0262] <Aging Treatment> The fabricated half cell was subjected to two charge / discharge cycles as an aging treatment under the following conditions: Charge: CCCV 17 mA / g, upper limit voltage 4.5 V, cut-off current 1.7 mA / g, 10-minute rest Discharge: CC 17 mA / g, cut-off voltage 2.5 V, 10-minute rest The waiting time from setting in the charge / discharge tester to the start of charge / discharge was 6 hours. In the present examples, the measurement environment was 25°C unless otherwise specified.

[0263] <Post-Discharge XRD> The half-cell in a discharged state after the aging treatment was disassembled in a glove box under an argon atmosphere, and the positive electrode was removed, flattened, and placed in an airtight cell. Unless otherwise specified, ceramic tweezers were used to handle the positive electrode after disassembly. The airtight cell was set in the XRD device so that the positive electrode matched the measurement surface required by the device, and XRD measurement was performed under the same conditions as in Example 1 except for the sample setting. This was designated as post-discharge XRD. n = 2.

[0264] <XRD after charging> Another half-cell that had undergone the above-mentioned aging treatment was charged under the following conditions: Charging: CCCV 17 mA / g, upper limit voltage 4.5 V, end current 1.7 mA / g, rest 10 minutes

[0265] The charge capacity of each half-cell at this time is shown in Table 4. n=2.

[0266]

[0267] The half-cell that had undergone the above charging was disassembled in a glove box under an argon atmosphere, and the positive electrode was removed, flattened, and placed in an airtight cell. Care was taken to avoid short circuits and shocks. The airtight cell was also handled without shocks. The positive electrode was set in an XRD device so that the positive electrode matched the required measurement surface of the device, and XRD measurements were performed in the same manner as the XRD after discharge. This was designated as the XRD after charging. n = 2.

[0268] The XRD device, measurement and analysis conditions for the post-discharge XRD and post-charge XRD were as follows: XRD device: Bruker D8 ADVANCE X-ray source: Cu Output: 40 kV, 40 mA Detector: LYNXEYE XE-T Scanning method: 2θ / θ continuous scan Measurement range (2θ): 15° to 75° increment: 0.01° Counting time: 1 sec / step Sample stage rotation: 15 rpm Sample setting: Measurement was performed by placing the electrode after charging or discharging in an airtight cell. 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

[0269] The acquired diffraction patterns were subjected to Rietveld analysis using DIFFRAC. TOPAS ver. 6 to determine the lattice constant. The analysis conditions were as follows. <Post-Discharge XRD> As literature values, ICSD Coll. Code 72545 was used for lithium iron phosphate and ICSD Coll. Code 18839 was used for aluminum. Lattice constants were determined by fitting to two phases of lithium iron phosphate and aluminum. <Post-Discharge XRD> As literature values, ICSD Coll. Code 92199 was used for iron phosphate and ICSD Coll. Code 18839 was used for aluminum. Lattice constants were determined by fitting to two phases of iron phosphate and aluminum.

[0270] Figures 16A to 16C show the rate of change of the a-axis lattice constant, b-axis lattice constant length, and c-axis lattice constant of the comparative example after discharge, calculated as above, when they are set to 100%. Figure 16A is a graph with the a-axis lattice constant change rate of the comparative example and 1% Zn as the vertical axis. Figure 16B is a graph with the b-axis lattice constant change rate of the comparative example and 1% Zn as the vertical axis. Figure 16C is a graph with the c-axis lattice constant change rate of the comparative example and 1% Zn as the vertical axis. All are average values ​​for n = 2.

[0271] 17 shows a graph with the vertical axis representing the rate of change in the product of the b-axis lattice constant and the c-axis lattice constant for the comparative example and 1% Zn, calculated from the values ​​in FIGS. 16B and 16C. The comparative example after discharge was set to 100%.

[0272] 16A to 17, the change in the lattice constants of the a-axis and b-axis after discharge and charge was reduced by the presence of zinc. The change in the product of the lattice constants of the b-axis and c-axis, i.e., the area change rate of the plane perpendicular to the a-axis, after discharge and charge was also reduced by the presence of zinc.

[0273] From the above, it has been shown that by dissolving zinc as an additive element, the lattice mismatch of the crystal structure of the positive electrode active material 100 before and after charge and discharge, particularly in the plane perpendicular to the a-axis, is suppressed. [Explanation of symbols] 100 Positive electrode active material 101: Primary particle 101a: Primary particle 101b: Primary particle 101c: Primary particle

Claims

A lithium ion battery having a positive electrode, a negative electrode, and a first electrolyte solution, the positive electrode has a positive electrode active material, the positive electrode active material has an olivine-type crystal structure and contains lithium, manganese, iron, zinc, phosphorus, and oxygen; the ratio of the number of atoms of manganese to the sum of manganese, iron, and zinc contained in the positive electrode active material (Mn / (Mn+Fe+Zn)) exceeds 0.5; a ratio of the number of atoms of zinc to the sum of manganese, iron, and zinc contained in the positive electrode active material (Zn / (Mn+Fe+Zn)) of 0.01 or more and less than 0.05; 　 In claim 1, a ratio of the number of atoms of manganese to the sum of manganese, iron, and zinc contained in the positive electrode active material (Mn / (Mn+Fe+Zn)) of 0.7 or less; 　 In claim 2, The olivine-type crystal structure belongs to the space group Pnma (No. 62), CuKα of the positive electrode １ When Rietveld analysis was performed on the powder X-ray diffraction pattern using the The olivine-type crystal structure, The lattice constant of the a-axis is 10.3889 Å or more and 10.3997 Å or less, The lattice constant of the b axis is 6.0550 Å or more and 6.0616 Å or less, A lithium-ion battery having a c-axis lattice constant of 4.7210 Å or greater. 　 In claim 3, The lithium ion battery, wherein the olivine-type crystal structure has a crystallite size L Vol -IB of 50 nm or more and less than 90 nm. 　 In any one of claims 1 to 4, For a half cell having the positive electrode and a second electrolyte solution of ethylene carbonate, diethyl carbonate, and vinylene carbonate, When a charge / discharge test is performed, the discharge capacity per weight of the positive electrode active material is 149 mAh / g or more, The charge / discharge test was performed in a measurement environment of 25°C. CCCV charging with a charging current of 34 mA / g, a charging voltage of 4.5 V, and a cut-off current of 3.4 mA / g; A lithium-ion battery is sequentially discharged by CC discharge with a discharge current of 34 mA / g and an end voltage of 2.5 V. 　 In any one of claims 1 to 4, For a half cell having the positive electrode and a second electrolyte solution of ethylene carbonate, diethyl carbonate, and vinylene carbonate, The ratio of the discharge capacity in a 0.2 C discharge test to the discharge capacity in a 5 C discharge test is 88% or more, The 0.2C charge / discharge test was performed in a measurement environment of 25°C. CCCV charging with a charging current of 34 mA / g, a charging voltage of 4.5 V, and a cut-off current of 3.4 mA / g per weight of the positive electrode active material; CC discharge with a discharge current of 34 mA / g and a cut-off voltage of 2.5 V. The 5C discharge test was performed in a measurement environment of 25°C. CCCV charging with a charging current of 34 mA / g, a charging voltage of 4.5 V, and a cut-off current of 3.4 mA / g per weight of the positive electrode active material; A lithium-ion battery in which a discharge current of 850 mA / g and a CC discharge with an end voltage of 2.5 V are sequentially performed. 　 In any one of claims 1 to 4, For a half cell having the positive electrode and a second electrolyte solution of ethylene carbonate, diethyl carbonate, and vinylene carbonate, When the charge / discharge cycle test was performed in a measurement environment of 60 ° C, In the range of 25 mAh / g or more and 125 mAh / g or less of the discharge dV / dQ curve, A lithium ion battery in which the difference in discharge capacity between Peak(1), the position where the peak of the discharge dV / dQ curve at the first cycle appears, and Peak(100), the position where the peak of the discharge dV / dQ curve at the 100th cycle appears, namely, Peak(1) - Peak(100) is 12 mAh / g or less. 　 In any one of claims 1 to 4, For a half cell having the positive electrode and a second electrolyte solution of ethylene carbonate, diethyl carbonate, and vinylene carbonate, When the charge / discharge cycle test was performed in a measurement environment of 25°C, In the range of 25 mAh / g or more and 125 mAh / g or less of the discharge dV / dQ curve, A lithium ion battery in which the difference in discharge capacity between Peak(1), the position where the peak of the discharge dV / dQ curve at the first cycle appears, and Peak(100), the position where the peak of the discharge dV / dQ curve at the 100th cycle appears, namely, Peak(1) - Peak(100), is 8 mAh / g or less.

Images