Lithium ion secondary battery

Abstract

To provide a secondary battery and a positive electrode active material, in which the energy density per unit weight and volume is improved.SOLUTION: A secondary battery includes a positive electrode, and the positive electrode has lithium cobaltate. The lithium cobaltate has, in a convex part, one or two or more selected from at least Hf, V, Nb, Ce, and Sm. The convex part may further have Mg, F, Ni, or Al as an additive element. The secondary battery is manufactured through a process of manufacturing a mixed liquid by mixing lithium cobaltate with metal alkoxide having one or two or more selected from Hf, V, Nb, Ce, and Sm. By such a positive electrode active material, the secondary battery with high charging voltage can be achieved.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a secondary battery, a vehicle equipped with a secondary battery, a method for manufacturing a secondary battery, and the like. [Background technology]

[0002] Research and development of secondary batteries is actively underway because they can be made larger in capacity and smaller in size. Among secondary batteries, those with lithium ions as the carrier ion are called lithium-ion secondary batteries. To improve the energy density per weight and volume of lithium-ion secondary batteries, it is essential to improve the performance of the positive electrode active material.

[0003] Lithium cobalt oxide is known as a material used as a positive electrode active material. Aiming to improve the performance of secondary batteries, research and development is being conducted into adding elements other than the main components to lithium cobalt oxide. Patent Document 1 discloses a positive electrode active material in which magnesium and fluorine are added as elements other than the main components to lithium cobalt oxide, and a method for producing the same.

[0004] In order to improve the cycle characteristics and capacity of lithium ion secondary batteries, improvements in the positive electrode active material have been investigated (for example, Patent Document 2, Non-Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-195581 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-163356 [Non-patent literature]

[0006] [Non-Patent Document 1] Suppression of Cobalt Dissolution from the LiCoO2 Cathodes with Various Metal-Oxide Coatings,Yong Jeong Kim et.,al.,Journal of The Electrochemical Society,150(12)A1723-A1725(2003) Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 1, the crystalline structure of a positive electrode active material is evaluated using an XRD pattern. However, Patent Document 1 states that the target crystalline structure could not be obtained from the XRD pattern of a positive electrode active material charged at 4.7 V or higher, and therefore the upper limit of the charging voltage in the cycle test is set at 4.6 V.

[0008] In view of the above-mentioned Patent Document 1, an object of the present invention is to provide a positive electrode active material that can withstand a high charging voltage, or a secondary battery having the positive electrode active material, and a vehicle equipped with the secondary battery.

[0009] The description of the above problems does not preclude the existence of other problems. For example, problems related to safety may exist. Note that one embodiment of the present invention does not necessarily solve all of these problems. Note that problems other than these can be extracted from the description of the specification, drawings, and claims of this application. [Means for solving the problem]

[0010] One aspect of the present invention is a secondary battery including a positive electrode, the positive electrode containing lithium cobalt oxide, the lithium cobalt oxide containing one or more elements selected from at least Hf, V, Nb, Zr, Ce, and Sm in convex portions.

[0011] One aspect of the present invention is a secondary battery including a positive electrode, the positive electrode containing lithium cobalt oxide, the lithium cobalt oxide containing one or more elements selected from at least Hf, V, Nb, Zr, Ce, and Sm in convex portions, the convex portions further containing Mg.

[0012] One aspect of the present invention is a secondary battery including a positive electrode, the positive electrode containing lithium cobalt oxide, the lithium cobalt oxide containing one or more elements selected from at least Hf, V, Nb, Zr, Ce, and Sm in convex portions, the convex portions further containing Mg and F.

[0013] One aspect of the present invention is a secondary battery including a positive electrode, the positive electrode containing lithium cobalt oxide, the lithium cobalt oxide containing one or more elements selected from at least Hf, V, Nb, Zr, Ce, and Sm in convex portions, the convex portions further containing Mg, F, and Ni.

[0014] One aspect of the present invention is a secondary battery including a positive electrode, the positive electrode containing lithium cobalt oxide, the lithium cobalt oxide containing protruding portions that contain one or more elements selected from at least Hf, V, Nb, Zr, Ce, and Sm, the protruding portions further containing Mg and F, and Al at the boundaries between the protruding portions and the interior of the lithium cobalt oxide.

[0015] In any one of the aspects of the present invention, it is preferable that one or more elements selected from Hf, V, Nb, Zr, Ce and Sm are unevenly distributed in the convex portions.

[0016] The secondary battery according to one embodiment of the present invention is preferably mounted on a vehicle.

[0017] One aspect of the present invention is a method for producing a secondary battery, comprising the steps of: mixing lithium cobalt oxide with a metal alkoxide containing one or more elements selected from Hf, V, Nb, Zr, Ce, and Sm to prepare a mixed solution; stirring the mixed solution to prepare a mixture; and heating the mixture.

[0018] One aspect of the present invention is a method for producing a secondary battery, comprising: a step of mixing lithium cobalt oxide and a magnesium source to prepare a first mixture; a first heating step of heating the first mixture; a step of mixing the heated first mixture with a metal alkoxide containing one or more elements selected from Hf, V, Nb, Zr, Ce, and Sm to prepare a mixed solution; a step of stirring the mixed solution to prepare a second mixture; and a second heating step of heating the second mixture.

[0019] One aspect of the present invention is a method for producing a secondary battery, comprising: a step of mixing lithium cobalt oxide, a magnesium source, and a fluorine source to prepare a first mixture; a first heating step of heating the first mixture; a step of mixing the heated first mixture with a metal alkoxide containing one or more elements selected from Hf, V, Nb, Zr, Ce, and Sm to prepare a mixed solution; a step of stirring the mixed solution to prepare a second mixture; and a second heating step of heating the second mixture.

[0020] In any one of the aspects of the present invention, the second heating step is preferably carried out for a shorter time than the first heating step.

[0021] In any one of the aspects of the present invention, the second heating step is preferably carried out at a temperature lower than that of the first heating step. [Effects of the Invention]

[0022] According to one embodiment of the present invention, it is possible to provide a positive electrode active material having high energy density per weight and per volume, or a secondary battery including the positive electrode active material, and a vehicle including the secondary battery. [Brief explanation of the drawings]

[0023] [Figure 1] 1A and 1B are diagrams showing cross sections of a positive electrode active material. [Figure 2] 2A and 2B are diagrams showing cross sections of the positive electrode active material. [Figure 3]FIG. 3 is a diagram illustrating the crystal structure of the positive electrode active material. [Figure 4] FIG. 4 shows the XRD pattern calculated from the crystal structure. [Figure 5] FIG. 5 is a diagram illustrating the crystal structure of a positive electrode active material of a comparative example. [Figure 6] FIG. 6 shows the XRD pattern calculated from the crystal structure. [Figure 7] 7A to 7C are diagrams showing cross sections of the positive electrode. [Figure 8] 8A and 8B are diagrams showing the appearance of a laminated secondary battery. [Figure 9] 9A to 9C are diagrams showing the steps of manufacturing a laminated secondary battery. [Figure 10] 10A and 10B are diagrams showing the steps of producing a positive electrode. [Figure 11] 11A and 11B are diagrams showing the appearance and cross section of a coin-type secondary battery. [Figure 12] 12A to 12D are diagrams showing the external appearance and cross section of the secondary battery. [Figure 13] 13A to 13C are diagrams showing the external appearance and cross section of the secondary battery. [Figure 14] 14A to 14C are diagrams showing the external appearance and cross section of the secondary battery. [Figure 15] 15A to 15C are diagrams showing the external appearance of the secondary battery and the system. [Figure 16] 16A to 16D are diagrams showing a vehicle or the like equipped with a secondary battery. [Figure 17] 17A and 17B are diagrams showing a house or the like equipped with a secondary battery. [Figure 18] 18A to 18D are diagrams showing electronic devices and the like equipped with secondary batteries. [Figure 19] 19A and 19B are SEM images of Sample 1. [Figure 20] 20A and 20B are SEM images of Sample 2. [Figure 21] 21A and 21B are SEM images of Sample 3. [Figure 22] 22A and 22B1 to 22B6 show the results of EDX area analysis of Sample 3. [Figure 23] FIG. 23 shows the results of EDX analysis of Sample 3. [Figure 24] 24A to 24C show the EDX point analysis results of Sample 3. [Figure 25] 25A and 25B are graphs showing the cycle characteristics of half cells having Samples 1 to 3. [Figure 26] 26A and 26B are graphs showing the cycle characteristics of half cells having Samples 1 to 3. [Figure 27] 27A and 27B are graphs showing the cycle characteristics of half cells having Samples 1 to 3. [Figure 28] 28A and 28B are graphs showing the cycle characteristics of half cells having Samples 1 to 3. [Figure 29] 29A and 29B are graphs showing the cycling characteristics of half cells containing Samples 4a to 4c. [Figure 30] 30A and 30B are graphs showing the cycle characteristics of half cells having Samples 4a to 4c. [Figure 31] 31A and 31B are graphs showing the cycle characteristics of half cells having Samples 4a to 4c. [Figure 32] 32A and 32B are graphs showing the cycling characteristics of half cells having Samples 4a to 4c. [Figure 33] 33A and 33B are SEM images of Sample 5. [Figure 34] 34A and 34B are SEM images of Sample 6. [Figure 35] 35A, 35B1, 35B2, 35B3, and 35B4 are SEM images of Sample 5. [Figure 36] 36A, 36B1, 36B2, and 36B3 are SEM images of Sample 6. [Figure 37] 37A and 37B are graphs showing the cycle characteristics of half cells containing Sample 5 and Sample 6. [Figure 38] 38A and 38B are graphs showing the cycle characteristics of half cells containing Sample 5 and Sample 6. [Figure 39] 39A and 39B show the results of EDX area analysis of Sample 5. [Figure 40] 40A and 40B show the results of EDX area analysis of Sample 6. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be readily understood by those skilled in the art that various modifications can be made to the embodiments and details. Furthermore, the present invention should not be interpreted as being limited to the description of the embodiments shown below.

[0025] (Embodiment 1) In this embodiment, a positive electrode active material of one embodiment of the present invention will be described with reference to FIGS.

[0026] 1A shows a positive electrode active material 100. Although the positive electrode active material 100 is sometimes called a positive electrode active material particle due to its shape, it can take various shapes other than particulate. The positive electrode active material 100 may be a primary particle having multiple crystallites, or a secondary particle formed by aggregation of primary particles.

[0027] The positive electrode active material 100 has first particles 101, and the particle size of the first particles 101 is preferably 1 μm or more and 50 μm or less, and more preferably 5 μm or more and 20 μm or less.

[0028] The particle size can be measured, for example, by laser diffraction particle size distribution measurement, and can be expressed as D50. D50 is the particle size when the cumulative particle amount curve of the particle size distribution measurement results indicates 50% of the cumulative amount, i.e., the median diameter. Measurement of particle size is not limited to laser diffraction particle size distribution measurement. For example, when the particle size is below the lower limit of measurement by laser diffraction particle size distribution measurement, the cross-sectional diameter of the particle cross section may be measured by analysis using an SEM (scanning electron microscope) or TEM (transmission electron microscope). When the cross-sectional shape of a particle is not circular, for example, the particle size can be measured by measuring the area of ​​the particle cross section using image processing, and the particle size can be calculated as the diameter of a circle having that area.

[0029] The particle size of the first particle 101 may be measured by cross-sectional diameter, or may be a median diameter (D50).

[0030] In the case of a ternary composite oxide such as Ni-Mn-Co, the particle size can be considered assuming that the first particle 101 is a secondary particle. A secondary particle is a particle formed by agglomeration of multiple primary particles and isolated from other secondary particles. In other words, a secondary particle is an agglomerate, and the original particle of the agglomerate is called a primary particle.

[0031] FIG. 1A shows an example of a positive electrode active material 100 having protrusions on its surface. The protrusions can be said to be particles fixed or attached to the surface of the first particles 101, and may therefore also be called second particles. A fixed state means that the protrusions do not fall off the surface of the first particles 101 even when ultrasonic dispersion is performed. The number, shape, and size of the protrusions vary, and FIG. 1A shows protrusions 102, 103, and 104. The protrusions are regions where the additive element is unevenly distributed.

[0032] The term "uneven distribution" refers to the concentration of a certain element being higher in one region than in another. In other words, the term "uneven distribution of an additive element" refers to the state in which the additive element is present unevenly or unevenly, and may refer to the state in which the concentration in one region is higher than the concentration in another region. Uneven distribution may also be expressed as segregation or precipitation. As a result of the precipitation of an element, convex portions containing the element may be formed on the surface of the first particle 101, and in this case, the element may be unevenly distributed in the convex portions.

[0033] The protrusions 102 to 104 are located on the surface of the first particle 101, and may be observed as semicircular like the protrusion 104 in a cross section of the first particle 101. In the cross section, the length of the base of the protrusion is 20 nm or more and 1 μm or less, and the height of the protrusion is 10 nm or more and 200 nm or less. In a STEM image, the first particle 101 and the protrusions 102 to 104 can be distinguished based on the difference in contrast. A STEM image is an image obtained by a scanning transmission electron microscope (STEM), and the image can be obtained by detecting electrons that have transmitted through an observation sample.

[0034] FIG. 1B shows a positive electrode active material 100 showing grain boundaries 105 located between crystallites. The configuration in FIG. 1B is the same as that in FIG. 1A except for the grain boundaries 105. The grain boundaries 105 are often not linear because they are formed during the crystal growth of the crystallites, but they may be linear. When the positive electrode active material 100 is a secondary particle, the grain boundaries 105 may be considered to be interfaces between primary particles. The interfaces between primary particles are also often not linear, but they may be linear.

[0035] 2A corresponds to a cross section of FIG. 1A. From FIG. 2A, surface layer portion 106 of positive electrode active material 100 can be seen. Surface layer portion 106 is located near the surface of positive electrode active material 100. Surface layer portion 106 is a region that exists within 50 nm, more preferably within 35 nm, even more preferably within 20 nm, and most preferably within 10 nm from the surface of positive electrode active material 100 toward the inside in a cross section.

[0036] 2B corresponds to a cross section of FIG. 1B. From FIG. 2B, surface layer portion 106 of positive electrode active material 100 having grain boundaries 105 can be seen. The other configurations are the same as those in FIG. 2A. Grain boundaries 105 and / or surface layer portion 106 are regions where the additive element is unevenly distributed.

[0037] "Maldistribution" refers to the state in which the concentration of a certain element is higher in one region than in another. In other words, "maldistribution of an added element" refers to the state in which the added element is present unevenly or unevenly, and can refer to the state in which the concentration in one region is higher than the concentration in another region. Maldistribution can also be written as segregation or precipitation.

[0038] A material capable of inserting and extracting carrier ions can be used as the positive electrode active material 100. The carrier ions can be lithium ions, alkali metals (e.g., sodium or potassium), or alkaline earth metals (e.g., calcium, strontium, barium, beryllium, or magnesium).

[0039] Materials capable of intercalating and deintercalating lithium ions include lithium composite oxides with olivine-type, layered rock-salt-type, or spinel-type crystal structures. For example, a lithium composite oxide with an olivine-type crystal structure is represented by LiMPO4 (where M = Fe, Mn, Ni, or Co). Because of their excellent thermal stability, Fe and Mn are expected to be next-generation cathode materials. For example, a lithium composite oxide with a layered rock-salt-type crystal structure is represented by LiMO2 (where M = Fe, Mn, Ni, or Co). When M is Co, it is represented by LiCoO2, which is sometimes referred to as LCO or lithium cobalt oxide. LiCoO2, LCO, or lithium cobalt oxide essentially does not contain manganese. "Substantially free of manganese" refers to a manganese content of 600 ppm or less, preferably 100 ppm or less, by weight, when analyzed using glow discharge mass spectrometry (GD-MS).

[0040] In a lithium composite oxide having a layered rock salt crystal structure, it may contain a plurality of Fe, Mn, Ni, and Co. Those having Ni, Mn, and Co are LiNi x Co y Mn z There are NiCoMn-based (also referred to as NCM, lithium nickel-cobalt-manganese oxide) represented by O2 (x > 0, y > 0, 0.8 < x + y + z < 1.2), etc. Specifically, in the above, it is preferable to satisfy 0.1x < y < 8x and 0.1x < z < 8x. As an example, x, y, and z preferably satisfy x:y:z = 1:1:1 and values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 5:2:3 and values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 8:1:1 and values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 6:2:2 and values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 1:4:1 and values in the vicinity thereof.

[0041] In addition to this, oxides such as V2O5 and Nb2O5 are being studied as cathode active material materials. For example, lithium composite oxides having a spinel crystal structure include lithium manganese spinel (LiMn2O4), etc.

[0042] The lithium composite oxide may contain at least one or two or more elements selected from nickel, chromium, aluminum, iron, magnesium, molybdenum, zinc, zirconium, indium, gallium, copper, titanium, niobium, silicon, fluorine, phosphorus, etc. The said element is preferably an element other than the cathode active material material (main component), and is referred to as an additive element (additive element X).

[0043] The cathode active material of the present invention is a lithium composite oxide having an additive element (additive element Y) different from the above-described additive element X. The additive element Y is a Group 4 element or a Group 5 element, and it is preferable to have Hf, V, Nb, or Hf and Zr. Also, the additive element Y is a lanthanoid element, and it is preferable to have Ce or Sm.

[0044] In the positive electrode active material, the additive element X and the additive element Y (collectively referred to as additive elements) are present in concentrations lower than the above-mentioned positive electrode active material (main component), and therefore are sometimes called impurity elements.

[0045] The additive element is preferably distributed unevenly near the surface of the positive electrode active material, rather than inside the positive electrode active material, including the protrusions formed on the surface of the lithium composite oxide and the surface layer of the lithium composite oxide.

[0046] To reiterate, uneven distribution refers to the concentration of a certain element being higher in one region than in another. In other words, uneven distribution of an additive element refers to the state in which the additive element is present unevenly or unevenly, and may refer to the state in which the concentration in one region is higher than the concentration in another region. Uneven distribution may also be expressed as segregation or precipitation. As a result of the precipitation of an element, convex portions containing the additive element may be formed on the surface of the first particle 101, and in this case, the additive element may be unevenly distributed in the convex portions.

[0047] The Nb concentration in the positive electrode active material determined by EDX analysis is preferably 1.0 atomic % (hereinafter referred to as at %) to 6.0 at %, more preferably 1.5 at % to 4.7 at %.

[0048] The Ce concentration on the surface of the positive electrode active material determined by EDX analysis is preferably from the lower detection limit to 4.0 at %, more preferably from the lower detection limit to 3.3 at %.

[0049] The Sm concentration in the vicinity of the surface of the positive electrode active material determined by EDX analysis is preferably from the lower detection limit to 36.0 at %, more preferably from the lower detection limit to 35.1 at %.

[0050] Some additive elements do not contribute to the capacity of the positive electrode active material, and it is considered preferable for such additive elements to be unevenly distributed near the surface of the positive electrode active material.

[0051] Furthermore, when the additive element is present in a higher concentration near the surface than inside the positive electrode active material, the positive electrode active material is less likely to deteriorate even at high charging voltages. If the additive element is unevenly distributed near the surface, which is more susceptible to structural changes due to insertion and desorption of carrier ions, the positive electrode active material is less likely to deteriorate, which is preferable.

[0052] In the lithium composite oxide shown in FIGS. 1A and 1B, the additive element is present at a higher concentration in the protrusions 102 to 104 than in the interior. That is, the lithium composite oxide shown in FIGS. 1A and 1B has protrusions on the surface, and is a positive electrode active material having an additive element (Hf, V, Nb, or Hf and Zr) on the protrusions, or a positive electrode active material having an additive element (Ce or Sm) on the protrusions. The protrusions may be regions where the additive element (Hf, V, Nb, or Hf and Zr) is unevenly distributed, or regions where the additive element (Ce or Sm) is unevenly distributed. Such lithium composite oxides are less likely to deteriorate even at high charging voltages, and therefore can increase the charging voltage of secondary batteries.

[0053] 1B, there is a grain boundary 105, and the additive element (Hf, V, Nb or Hf and Zr) or the additive element (Ce or Sm) may be unevenly distributed at the grain boundary 105. The region where the additive element (Hf, V, Nb or Hf and Zr) is unevenly distributed, or the region where the additive element (Ce or Sm) is unevenly distributed may be the grain boundary. Such a lithium composite oxide is less likely to deteriorate even at a high charging voltage, and therefore the charging voltage of the secondary battery can be increased.

[0054] Furthermore, it is believed that the formation of protrusions on the positive electrode active material reduces the amount of cobalt and other elements eluted into the electrolyte. Reducing the contact area with the electrolyte suppresses decomposition of the electrolyte and reduces the reduction of the positive electrode active material. As a result, the positive electrode active material is less susceptible to degradation even at high charging voltages, allowing for increased charging voltages for secondary batteries. Therefore, it is desirable for the positive electrode active material to have multiple protrusions.

[0055] 2A and 2B show a lithium composite oxide without protrusions. Even in a lithium composite oxide without protrusions, the additive element is unevenly distributed in the surface layer 106, where it is present at a higher concentration than in the interior of the positive electrode active material 100. That is, the lithium composite oxide shown in FIGS. 2A and 2B is a positive electrode active material having an additive element (Hf, V, Nb, or Hf and Zr) or an additive element (Ce or Sm) in the surface layer 106. Such a lithium composite oxide is thought to be less susceptible to deterioration even at high charging voltages, and can increase the charging voltage of secondary batteries.

[0056] 2B shows grain boundaries 105, which may contain an additive element (Hf, V, Nb, or Hf and Zr), or an additive element (Ce or Sm). A region where the additive element (Hf, V, Nb, or Hf and Zr) is unevenly distributed, or a region where the additive element (Ce or Sm) is unevenly distributed, may be the grain boundary. Such lithium composite oxides are thought to be less susceptible to deterioration even at high charging voltages, and can increase the charging voltage of secondary batteries.

[0057] In addition to the additive element Y, the bumps 102 to 104 and / or the surface layer 106 may contain at least one of Mg and F as additive element X. By including one or more of Mg and F, the positive electrode active material becomes less susceptible to deterioration even at a high charging voltage, and the charging voltage of the secondary battery can be increased.

[0058] The protrusions 102 to 104 and / or the surface layer 106 may contain at least one of Ni and Al as an additional element X in addition to the additional element Y. The presence of one or more of Ni and Al makes the positive electrode active material less susceptible to deterioration even at high charging voltages, thereby increasing the charging voltage of the secondary battery.

[0059] The protrusions 102 to 104 and / or the surface layer 106 may contain at least Zr as an additional element X in addition to the additional element Y. Zr makes the positive electrode active material less susceptible to deterioration even at high charging voltages, and can increase the charging voltage of the secondary battery.

[0060] The protrusions 102 to 104 and / or the surface layer 106 may contain one or more additive elements X selected from Mg, F, Al, and Ni in addition to the additive element Y. The one or more additive elements selected from Mg, F, Al, and Ni provide a positive electrode active material that is less likely to deteriorate even at high charging voltages, and the charging voltage of the secondary battery can be increased.

[0061] In addition to the additive element, one or more elements selected from Mg, F, Al, Ni, and Zr contained in lithium composite oxide may be present in the bumps 102 and 104 and / or the surface layer 106. The one or more elements selected from Mg, F, Al, Ni, and Zr provide a positive electrode active material that is less likely to deteriorate even at high charging voltages, and the charging voltage of the secondary battery can be increased.

[0062] <Crystal structure> The crystal structure of a positive electrode active material of one embodiment of the present invention will be described with reference to Figures 3 to 6. In Figures 3 to 6, lithium cobalt oxide is used as the positive electrode active material.

[0063] <Conventional positive electrode active materials> First, Figure 5 shows lithium cobalt oxide without added Mg (referred to as conventional lithium cobalt oxide). It is known that the crystal structure of conventional lithium cobalt oxide changes depending on the charge depth, that is, the occupancy rate of lithium in lithium cobalt oxide. The occupancy rate of lithium in lithium cobalt oxide is Li x It can be expressed by the value of x in CoO2.

[0064] As shown in Figure 5, Li x Conventional lithium cobalt oxide, where CoO2 x = 1 (discharged state), has a region with a crystal structure of space group R-3m, where lithium occupies octahedral sites and there are three CoO2 layers in the unit cell. For this reason, this crystal structure is sometimes called an O3-type crystal structure. Note that a CoO2 layer is an octahedral structure in which cobalt is six-coordinated with oxygen, and the layers are connected in a plane with edge sharing.

[0065] Also Li x When x = 0 in CoO2, conventional lithium cobalt oxide has a crystal structure of space group P-3m1, with one CoO2 layer in the unit cell. Therefore, this crystal structure is sometimes called the O1-type crystal structure or trigonal O1-type crystal structure.

[0066] Also, for example, Li x When x = 0.12 for CoO2, conventional lithium cobalt oxide has a crystal structure of the space group R-3m. This structure can be described as a structure in which a CoO2 structure such as P-3m1(O1) and a LiCoO2 structure such as R-3m(O3) are alternately stacked. Therefore, this crystal structure is sometimes referred to as the H1-3 crystal structure. Note that because actual lithium insertion and extraction can be uneven, the H1-3 crystal structure is experimentally observed from x = 0.25. In fact, the H1-3 crystal structure has twice the number of cobalt atoms per unit cell compared to other structures. However, in Figure 5 and elsewhere in this specification, the c-axis of the H1-3 crystal structure is shown as half the unit cell to facilitate comparison with other crystal structures.

[0067] As an example, the coordinates of the cobalt and oxygen atoms in the unit cell of the H1-3 crystal structure can be expressed as Co(0, 0, 0.42150±0.00016), O1(0, 0, 0.27671±0.00045), and O2(0, 0, 0.11535±0.00045). O1 and O2 are oxygen atoms. Thus, the H1-3 crystal structure is expressed by a unit cell using one cobalt atom and two oxygen atoms.

[0068] On the other hand, the O3'-type crystal structure of one embodiment of the present invention, which will be described later, is represented by a unit cell using one cobalt and one oxygen. This indicates that the symmetry between cobalt and oxygen differs between the O3'-type crystal structure and the H1-3-type structure, and that the O3'-type crystal structure varies less from the O3 structure than the H1-3-type structure.

[0069] High voltage charging that reaches 4.6V or more based on the redox potential of lithium metal, or Li x When conventional lithium cobalt oxide is repeatedly charged and discharged so that the x of CoO becomes less than 0.24, the crystal structure changes repeatedly (i.e., a non-equilibrium phase change) between the H1-3 type crystal structure and the R-3m(O3) structure in the discharged state.

[0070] As shown by the dotted lines and arrows in the H1-3 type crystal structure in Figure 5, the CoO2 layer in the H1-3 type crystal structure is significantly deviated from R-3m(O3), and these two crystal structures show a large deviation of the CoO2 layer. Such dynamic structural changes can adversely affect the stability of the crystal structure.

[0071] Furthermore, the difference in volume is large: when compared per the same number of cobalt atoms, the difference in volume between the H1-3 crystal structure and the O3 crystal structure in the discharged state is more than 3.0%.

[0072] In addition, Li x A structure with continuous CoO2 layers, such as P-3m1(O1) where x=0, is unstable.

[0073] Thus, the crystal structure of conventional lithium cobalt oxide is Li x When CoO2 is repeatedly charged and discharged to a value below x = 0.24, the crystal structure begins to break down. This break in the crystal structure causes a deterioration in cycle characteristics. The break in the crystal structure also reduces the number of sites where lithium can exist stably, making it difficult for lithium to be inserted and extracted.

[0074] <Positive Electrode Active Material of One Embodiment of the Present Invention> A case where lithium cobalt oxide is used as the positive electrode active material 100 of one embodiment of the present invention and the lithium cobalt oxide contains an additive element will be described. x CoO2 x=1 and Li x The crystal structure of CoO2 when x = 0.2 is shown. The added element is preferably Mg. Although the added Mg is thought to substitute for the lithium site, Mg is omitted in Figure 3.

[0075] Li in Figure 3 x The crystal structure of CoO2 when x=1 (discharged state) is R-3m(O3), the same as in FIG. 5. On the other hand, the positive electrode active material 100 according to one embodiment of the present invention, when fully charged (for example, Li x When x = 0.2 for CoO2, the crystal has a structure different from the H1-3 type crystal structure. This structure belongs to the space group R-3m, and ions such as cobalt occupy the oxygen hexa-coordinated positions. Furthermore, the symmetry of the CoO2 layer in this structure is the same as that of the O3 type. Therefore, this structure is referred to as the O3' type crystal structure in this specification.

[0076] In addition, in the O3' type crystal structure in Figure 3, Li x Considering the x value of CoO2, lithium is assumed to exist at all lithium sites with a probability of 1 / 5 (this is referred to as a Li occupancy of 20%). However, the positive electrode active material 100 of one embodiment of the present invention is not limited to this, and lithium may exist unevenly at some of the lithium sites. For example, Li belonging to the space group P2 / m 0.5 As with CoO2, lithium may be present at some of the ordered lithium sites. The distribution of lithium can be analyzed, for example, by neutron diffraction.

[0077] In the positive electrode active material 100 according to one embodiment of the present invention, as shown by the dotted line in the O3'-type crystal structure in FIG. 3, there is almost no displacement of the CoO2 layer. x It can be seen that the change in the crystal structure of CoO when X2 is about x=0.2 is more suppressed than in conventional lithium cobalt oxide.

[0078] For example, lithium cobalt oxide to which Mg is added can be used as the positive electrode active material 100 of one embodiment of the present invention. x In the case of repeated charge and discharge in which x of CoO2 becomes about 0.2, the displacement of the CoO2 layer can be reduced. xWhen x of CoO2 is about 0.2, the change in the crystal structure and the difference in volume per the same number of cobalt atoms are small. Furthermore, the positive electrode active material 100 of one embodiment of the present invention can be said to have a highly stable crystal structure.

[0079] More specifically, there is a region in which the cathode active material 100 of one embodiment of the present invention can have the O3'-type crystal structure at a voltage of, for example, 4.65 V or more and 4.7 V or less relative to the potential of lithium metal. Furthermore, even when the charge voltage is lower, for example, 4.5 V or more and less than 4.6 V relative to the potential of lithium metal, the cathode active material 100 of one embodiment of the present invention may be able to have the O3'-type crystal structure.

[0080] 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" or "being a certain space group" can be rephrased as "identified with a certain space group."

[0081] In the O3'-type crystal structure, the coordinates of the cobalt and oxygen atoms in the unit cell can be expressed in the range of Co(0,0,0.5), O(0,0,x), 0.20≦x≦0.25. Regarding the lattice constants of the unit cell, the a-axis is preferably 2.797≦a≦2.837 (Å), more preferably 2.807≦a≦2.827 (Å), typically a=2.817 (Å). The c-axis is preferably 13.681≦c≦13.881 (Å), more preferably 13.751≦c≦13.811 (Å), typically c=13.781 (Å).

[0082] Such a positive electrode active material according to one embodiment of the present invention can achieve excellent cycle characteristics. Furthermore, the positive electrode active material according to one embodiment of the present invention can have a stable crystal structure. Therefore, the positive electrode active material according to one embodiment of the present invention may be less susceptible to short circuits. In such cases, safety is further improved, which is preferable.

[0083] <XRD> Figures 4 and 6 show the ideal powder XRD patterns calculated from the O3'-type crystal structure and H1-3-type crystal structure models using CuKα1 radiation. x CoO2 x=1, LiCoO2(O3) and Li x The ideal XRD pattern calculated from the crystal structure of CoO2(O1) with x = 0 for CoO2 is also shown. The patterns for LiCoO2(O3) and CoO2(O1) were created using Reflex Powder Diffraction, a module of Materials Studio (BIOVIA), from crystal structure information obtained from the ICSD (Inorganic Crystal Structure Database). The 2θ range was 15° to 75°, with a step size of 0.01 and a wavelength of λ1 = 1.540562 × 10 -10 No settings were made for m and λ2, and the monochromator was set to single. The XRD pattern of the O3'-type crystal structure was fitted using TOPAS ver.3 (crystal structure analysis software manufactured by Bruker) based on the O3'-type crystal structure shown in Figure 3, and an XRD pattern was created in the same way as the others.

[0084] As shown in Figure 4, in the O3'-type crystal structure, diffraction peaks appear at 2θ = 19.30 ± 0.20° (19.10° to 19.50°) and 2θ = 45.55 ± 0.10° (45.45° to 45.65°). More specifically, diffraction peaks appear at 2θ = 19.30 ± 0.10° (19.20° to 19.40°) and 2θ = 45.55 ± 0.05° (45.50° to 45.60°). However, as shown in Figure 6, no diffraction peaks appear at these positions in the H1-3-type crystal structure and CoO2(P-3m1, O1). Therefore, Li x The appearance of diffraction peaks at 2θ=19.30±0.20° and 2θ=45.55±0.10° when x of CoO2 is 0.2 or less can be said to be a characteristic of the positive electrode active material 100 of one embodiment of the present invention.

[0085] This is Li x The crystal structure of CoO X2 x=1 and Lix It can also be said that the diffraction peak positions are close to each other in the crystal structure where x in CoO2 is 0.2 or less. More specifically, the difference in the diffraction peak positions of two or more, preferably three or more, of the main diffraction peaks of both materials is 2θ=0.7° or less, more preferably 2θ=0.5° or less.

[0086] The positive electrode active material 100 according to one embodiment of the present invention is Li x When x in CoO2 is 0.2 or less, not all of the material may have the O3'-type crystal structure. The positive electrode active material 100 of one embodiment of the present invention may contain other crystal structures, or may be partially amorphous. However, when Rietveld analysis is performed, the O3'-type crystal structure is preferably 50% or more, more preferably 60% or more, and even more preferably 66% or more. If the O3'-type crystal structure is 50% or more, more preferably 60% or more, and even more preferably 66% or more, the positive electrode active material will have sufficiently excellent cycle characteristics. The O3'-type crystal structure may be present in the surface layer or protrusions of the positive electrode active material.

[0087] Furthermore, when Rietveld analysis is performed after 100 or more charge / discharge cycle tests, the O3' type crystal structure is preferably 35% or more, more preferably 40% or more, and even more preferably 43% or more.

[0088] Furthermore, the sharpness of diffraction peaks in an XRD pattern indicates the degree of crystallinity. Therefore, it is preferable that each diffraction peak after charging is sharp, i.e., has a narrow half-width. The half-width varies depending on the XRD measurement conditions and / or the value of 2θ, even for diffraction peaks arising from the same crystalline phase. Under the measurement conditions described above, for diffraction peaks observed between 2θ = 43° and 46°, the half-width is preferably 0.2° or less, more preferably 0.15° or less, and even more preferably 0.12° or less. Note that not all diffraction peaks necessarily meet this requirement. If some diffraction peaks meet this requirement, it can be said that the crystallinity of that crystalline phase is high. This contributes to the stabilization of the crystalline structure after charging.

[0089] Such a positive electrode active material according to one embodiment of the present invention can achieve excellent cycle characteristics. x CoO2 can have a stable crystal structure when x is 0.2 or less. x When the x of CoO2 is kept at 0.2 or less, short circuits may be less likely to occur. In such cases, safety is further improved, which is preferable.

[0090] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0091] (Embodiment 2) In this embodiment, the positive electrode will be described with reference to FIG.

[0092] [Positive electrode] FIG. 7A shows an example of a cross-sectional view of a positive electrode 503. The positive electrode has a positive electrode active material layer 571 on a positive electrode current collector 550. The positive electrode active material layer 571 includes a positive electrode active material 561, a positive electrode active material 562, a binder (binding agent) 555, a conductive additive 553, and an electrolyte 556. The positive electrode active material 561 has a larger particle size than the positive electrode active material 562. One or two selected from the positive electrode active material 561 and the positive electrode active material 562 may be those described in the first embodiment. In FIG. 7A, the positive electrode active material 561 has the convex portions described in the first embodiment. The conductive additive 553 is a particulate conductive additive.

[0093] 7A , regions that are not filled with positive electrode active material 561, positive electrode active material 562, conductive additive 553, etc. are hollow, and some regions are impregnated with electrolyte 556. Positive electrode active material 561, etc. have gaps that allow electrolyte 556 to easily penetrate, and these gaps become voids.

[0094] In Figure 7A, the positive electrode active material 561 is shown as particulate, and also as having a shape with protrusions on the surface, but is not limited to being particulate. As shown in Figure 7B, the cross-sectional shape of the positive electrode active material 561 may be elliptical, rectangular, trapezoidal, conical, square with rounded corners, or asymmetrical. Note that the particulate positive electrode active material may be deformed into a shape such as that shown in Figure 7B by pressing during the positive electrode fabrication process.

[0095] In FIG. 7B, the binder 555 is omitted and only the conductive additive 554 is shown. The positive electrode 503 shown in FIG. 7B has at least two conductive additives. The conductive additive 554 is different in shape from the conductive additive 553, and the conductive additive 554 is a sheet-like conductive additive. The sheet-like conductive additive may appear linear in a cross section, but has a shape that extends three-dimensionally. The use of a sheet-like conductive additive can improve the dispersibility of the particulate conductive additive.

[0096] 7B, regions that are not filled with positive electrode active material 561, positive electrode active material 562, conductive additive 553, conductive additive 554, etc. are hollow, and some regions are impregnated with electrolyte 556. Positive electrode active material 561, etc. have gaps that allow electrolyte 556 to easily penetrate, and these gaps become voids.

[0097] 7C illustrates an example of a positive electrode in which binder 555 is omitted and conductive additive 558 is used instead of conductive additive 554 in FIG. 7B. Conductive additive 558 differs in at least its shape from conductive additives 553 and 554, and conductive additive 558 is a fibrous conductive additive. Use of a fibrous conductive additive can improve the dispersibility of the particulate conductive additive.

[0098] 7C , regions that are not filled with positive electrode active material 561, positive electrode active material 562, conductive additive 553, and conductive additive 558 are hollow, and some regions are impregnated with electrolyte 556. Positive electrode active material 561 and the like have gaps that allow electrolyte 556 to easily penetrate, and these gaps become voids.

[0099] 7A to 7C, the positive electrode active material 561 and the like may undergo volume changes during charge and discharge, but by disposing a fluorine-containing electrolyte 556 such as a fluorinated carbonate between the multiple positive electrode active materials 561, the material becomes slippery even when volume changes during charge and discharge, and cracks are suppressed, thereby improving cycle characteristics. It is important that a fluorine-containing organic compound exists between the multiple active materials that make up the positive electrode.

[0100] Specific materials and the like used are shown in FIGS. 7A to 7C.

[0101] [Cathode active material] The positive electrode active material layer 571 has a positive electrode active material 561 or a positive electrode active material 562, and is filled with at least the positive electrode active material 561. In the positive electrode active material layer 571, it is preferable that the filling density of the positive electrode active material 561 is high. Therefore, the positive electrode active material 562 having a different particle size may be added. The different particle sizes refer to different median diameters (D50).

[0102] For example, the particle size of the positive electrode active material 562 is smaller than that of the positive electrode active material 561, which means that the median diameter (D50) is smaller. The median diameter (D50) of the positive electrode active material 562 is preferably 1 / 6 to 1 / 10 of the median diameter (D50) of the positive electrode active material 561. Mixing positive electrode active materials with different particle sizes leads to an improvement in the packing density of the positive electrode active material in the positive electrode active material layer 571.

[0103] Although the above description has been given using the median diameter (D50), the particle size obtained by measuring the cross-sectional diameter may also be used.

[0104] The gaps in the positive electrode active material during packing can be reduced according to the size of the protrusions of the positive electrode active material 561 with a large particle size. Therefore, the packing density can be increased even without the positive electrode active material 562. When the positive electrode active material 562 is not used, the manufacturing process can be reduced, leading to further cost reduction.

[0105] Although not shown in FIGS. 7A to 7C, the positive electrode active material 562 may also have a protrusion.

[0106] In positive electrode active material 561 and / or positive electrode active material 562, the additive element is present near the surface. That is, the concentration of the additive element near the surface of positive electrode active material 561 and / or positive electrode active material 562 is preferably higher than the concentration of the additive element inside. Because the additive element is unevenly distributed on the surface, the additive element is absent or present in small amounts in the bulk of positive electrode active material 561 and / or positive electrode active material 562. Even if the additive element does not contribute to the capacity value, it is believed that the capacity value of positive electrode active material 561 and / or positive electrode active material 562 is not reduced if the additive element is absent or present in small amounts in the bulk. Furthermore, to prevent structural degradation, it is sufficient for the additive element to be present at least near the surface, resulting in a positive electrode active material that is less susceptible to degradation even at high charging voltages.

[0107] [Binder] The binder 555 is provided to prevent the positive electrode active material 561 etc. or the conductive additive 553 etc. from peeling off from the positive electrode current collector 550. The binder 555 also plays a role in binding the positive electrode active material 561 etc. and the conductive additive 553 etc. Therefore, the binder 555 is positioned so as to be in contact with the positive electrode current collector 550, positioned between the positive electrode active material 561 etc. and the conductive additive 553 etc., or positioned so as to be entangled with the conductive additive 553 etc.

[0108] The binder 555 contains a resin, which is a polymer material. If a large amount of binder is contained, the proportion of the positive electrode active material 561, etc. in the positive electrode active material layer 571 may decrease. A decrease in the proportion of the positive electrode active material 561, etc. leads to a decrease in the discharge capacity of the secondary battery, so the amount of binder 555 mixed is minimized. Since the positive electrode active material 561, etc. of the present invention has protrusions on the surface, it easily binds to the binder 555, and the amount of binder 555 mixed can be reduced.

[0109] The above-described conductive additive 553 can be replaced with conductive additive 554 and conductive additive 558 depending on the configuration of positive electrode 503. Furthermore, the above-described positive electrode active material 561 can be replaced with positive electrode active material 562 depending on the configuration of positive electrode 503.

[0110] [Conductive additive] The conductive additives 553, 554, and 558 are composed of materials having lower resistance than the positive electrode active material 561 and the like. The positive electrode active material 561 is a composite oxide and therefore may have high resistance. This makes it difficult to collect current from the positive electrode active material 561 and the like to the positive electrode current collector 550. Therefore, the conductive additives 553, 554, and 558 function to assist the current path between the positive electrode active material 561 and the like and the positive electrode current collector 550, the current path between multiple positive electrode active materials 561 and the like, and the current path between multiple positive electrode active materials and the positive electrode current collector 550. To fulfill these functions, the conductive additives 553, 554, and 558 are some that are positioned so as to be in contact with the positive electrode current collector 550, and some that are positioned in the gaps between the positive electrode active material 561 and the like.

[0111] The conductive additive is also called a conductivity imparting agent or a conductive material due to its role, and is made of a carbon material or a metal material. Carbon black (furnace black, acetylene black, graphite, etc.) is an example of a carbon material used for the conductive additive 553. Carbon black has a smaller particle size than the positive electrode active material 561, and since the positive electrode active material 561 of the present invention has protrusions on its surface, the carbon black is likely to be located near the protrusions. Multilayer graphene is an example of a sheet-like carbon material used for the conductive additive 554. Carbon nanotubes (CNTs) and VGCF (registered trademark) are examples of fibrous carbon materials used for the conductive additive 558.

[0112] The particulate conductive additive 553 can penetrate into the gaps between multiple positive electrode active materials and is prone to agglomeration. Therefore, the particulate conductive additive 553 can assist the conductive path between nearby positive electrode active materials (between adjacent positive electrode active materials). The sheet-like conductive additive 554 or the fibrous conductive additive 558 has a folded region, but has a shape with longer sides than the positive electrode active material 561. Therefore, the sheet-like conductive additive 554 or the fibrous conductive additive 558 can assist the conductive path between adjacent positive electrode active materials as well as between positive electrode active materials arranged at a distance.

[0113] The conductive assistant may be a mixture of particulate and sheet-like conductive assistants, such as conductive assistant 553 and conductive assistant 554. Alternatively, the conductive assistant may be a mixture of particulate and fibrous conductive assistants, such as conductive assistant 553 and conductive assistant 558. Alternatively, the conductive assistant may be a mixture of sheet and fibrous conductive assistants, such as conductive assistant 554 and conductive assistant 558.

[0114] When graphene is used as a sheet-like conductive additive and is mixed with carbon black as a particulate conductive additive, the weight of the carbon black in the slurry is preferably 1.5 to 20 times, and more preferably 2 to 9.5 times, the weight of the graphene.

[0115] Furthermore, when the mixture ratio of graphene and carbon black is within the above range, the dispersion stability of the carbon black is excellent during slurry preparation, and the carbon black is easily dispersed without aggregation. Furthermore, when the mixture ratio of graphene and carbon black is within the above range, the electrode density can be increased compared to when only carbon black is used as the conductive additive. Increasing the electrode density can increase the capacity per volume. Specifically, the density of the positive electrode active material layer, calculated by dividing the weight of the positive electrode active material layer (positive electrode, conductive additive, and binder) excluding the current collector by the volume, can be increased to more than 3.5 g / cm3. Furthermore, when the positive electrode active material of the present invention is used as the positive electrode active material 561 and the mixture ratio of graphene and carbon black is within the above range, the secondary battery has a higher capacity. A synergistic effect can be expected between the mixture of graphene and carbon black as the conductive additive and the presence of protrusions on the surface of the positive electrode active material, which is preferable.

[0116] In addition, when a positive electrode using only graphene as a conductive additive is compared with a positive electrode using a mixture of graphene and carbon black, the positive electrode in which the mixture ratio of graphene and carbon black is within the above range can accommodate rapid charging. Furthermore, when the positive electrode active material of the present invention is used in a secondary battery, a high capacity can be achieved. The ability of the secondary battery to accommodate rapid charging can be expected to have a synergistic effect in vehicles.

[0117] The secondary batteries installed in vehicles are, for example, laminated secondary batteries. To increase capacity, the number of laminated secondary batteries is increased, a so-called assembled battery structure, is used to extend the vehicle's mileage. However, the laminated batteries increase the vehicle's weight, which increases the energy required to move the vehicle. However, if a high-density secondary battery like the present invention can be used, there is no need to increase the number of laminated secondary batteries, making it possible to extend the vehicle's mileage with almost no change in the vehicle's total weight.

[0118] Furthermore, when the capacity of a secondary battery mounted on a vehicle increases, a high level of power is required for charging, and charging can be completed in a short time. Furthermore, when the capacity of a secondary battery mounted on a vehicle increases, rapid charging becomes possible in what is called regenerative charging, in which temporary power is generated when the vehicle brakes are applied and the generated power is charged, which is preferable.

[0119] One embodiment of the present invention is also effective in a portable information terminal, because a secondary battery can be miniaturized and have a high capacity. Furthermore, one embodiment of the present invention enables rapid charging of the portable information terminal.

[0120] [Electrolytes] The electrolyte 556 can be liquid, solid, or semi-solid. Liquid electrolytes are sometimes called electrolyte solutions. In addition to organic solvents, ionic liquids can also be used as electrolyte solutions. Ionic liquids are flame-retardant, which can improve the safety of secondary batteries.

[0121] Electrolyte 556 is filled in positive electrode active material layer 571, and in the case of an electrolyte solution, it is present so as to soak into the gaps in positive electrode active material 561. Positive electrode active material 561 can be described as being impregnated with the electrolyte solution. Furthermore, if there are no gaps in positive electrode active material 561, electrolyte 556 may not soak in easily.

[0122] The volume of the positive electrode active material 561 may change during charging and discharging of the secondary battery, and it is preferable to have fluorine such as fluorinated carbonate as the electrolyte 556 in the gaps between the positive electrode active materials 561. Even if the volume changes during charging and discharging, the positive electrode active materials 561 may become more slippery against each other.

[0123] Furthermore, although cracks may occur in the positive electrode active material 561 due to volume changes during charge and discharge, the occurrence of such cracks may be suppressed if the electrolyte 556 contains fluorine, such as fluorinated carbonate ester. Suppressing the occurrence of cracks improves the cycle characteristics of the secondary battery.

[0124] By using an electrolyte 556 having a wide operating temperature range, it is possible to provide a secondary battery that can be used at temperatures lower than room temperature and at temperatures higher than room temperature.

[0125] [Current collector] The positive electrode current collector 550 can be a metal foil containing aluminum, titanium, copper, nickel, or the like. A slurry containing a positive electrode active material layer 571 is applied to the metal foil and dried to complete the positive electrode 503. A carbon material may be coated on the metal foil. A structure coated with a carbon material is sometimes referred to as a carbon-coated structure.

[0126] The slurry to be applied onto the positive electrode current collector 550 contains at least a positive electrode active material 561, a binder 555, and a solvent, and preferably further contains a conductive additive 553 and the like. The slurry is sometimes called an electrode slurry or an active material slurry, and is sometimes called a positive electrode slurry when forming a positive electrode active material layer, and sometimes called a negative electrode slurry when forming a negative electrode active material layer.

[0127] A secondary battery can be fabricated using any one of the positive electrodes shown in Figures 7A to 7C. A separator is placed on the positive electrode, and the laminate, in which the negative electrode is placed on the separator, is placed in a container (such as an outer casing or a metal can) and filled with an electrolyte. Figure 8 illustrates a laminated secondary battery.

[0128] [Laminated secondary battery] 8A and 8B show examples of the external appearance of a laminated secondary battery 500. The laminated secondary battery 500 has a positive electrode 503, a negative electrode 506, a separator 507, an exterior body 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511. FIG. 8A shows an example in which the positive electrode lead electrode 510 and the negative electrode lead electrode 511 are arranged on the same side of the exterior body 509. FIG. 8B shows an example in which the positive electrode lead electrode 510 and the negative electrode lead electrode 511 are arranged on opposite sides of the exterior body 509. The area of ​​the exterior body 509 in which each lead electrode is arranged is also referred to as a tab region. The area and shape of the tab region are not limited to those shown in FIGS. 8A and 8B.

[0129] [Negative electrode] The negative electrode 506 includes a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer may also include a conductive additive and a binder.

[0130] [Negative electrode active material] The negative electrode active material may be, for example, an alloy-based material or a carbon-based material. The negative electrode active material used in the secondary battery of one embodiment of the present invention preferably contains fluorine as a halogen. Fluorine has a high electronegativity, and the presence of fluorine in the surface layer of the negative electrode active material may have the effect of facilitating the desorption of a solvated solvent from the surface of the negative electrode active material.

[0131] As the negative electrode active material, an element capable of undergoing a charge-discharge reaction by alloying and dealloying reaction with lithium carrier ions can be used. For example, a material containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used. These elements have a larger capacity than carbon, and silicon in particular has a high theoretical capacity of 4200 mAh / g. For this reason, it is preferable to use silicon as the negative electrode active material. Alternatively, a compound containing these elements may be used. For example, SiO (silicon monoxide, SiO X where x is preferably 0.2 or more and 1.5 or less), Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, SbSn, etc. Here, elements that can undergo charge-discharge reactions through alloying and dealloying reactions with lithium, and compounds containing such elements, are sometimes referred to as alloy-based materials.

[0132] Silicon nanoparticles can be used as the silicon-containing negative electrode active material. The median diameter (D50) of the silicon nanoparticles is 5 nm or more and less than 1 μm, preferably 10 nm or more and 300 nm or less, and more preferably 10 nm or more and 100 nm or less. The silicon nanoparticles may be crystalline. Furthermore, the silicon nanoparticles may have a crystalline region and an amorphous region.

[0133] Although the above description has been given using the median diameter (D50), the particle size obtained by measuring the cross-sectional diameter may also be used.

[0134] The silicon-containing negative electrode active material may be in the form of silicon monoxide particles containing one or more silicon crystal grains. The silicon monoxide may be amorphous. The silicon monoxide particles may be carbon-coated. The carbon-coated particles may be mixed with graphite to form the negative electrode active material.

[0135] Examples of carbon-based materials that can be used include graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, and carbon black. It is preferable to incorporate fluorine into these carbon-based materials. A carbon-based material containing fluorine can also be called a particulate or fibrous fluorinated carbon material. When measuring a carbon-based material by X-ray photoelectron spectroscopy, the fluorine concentration is preferably 1 at% or more relative to the total concentration of fluorine, oxygen, lithium, and carbon.

[0136] Furthermore, although negative electrode active materials may undergo volume changes during charge and discharge, disposing an organic compound containing fluorine, such as a fluorinated carbonate, between the negative electrode active materials makes them slippery even when volume changes occur during charge and discharge, suppressing cracks and improving cycle characteristics. It is important that an organic compound containing fluorine exists between multiple negative electrode active materials.

[0137] 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 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.

[0138] When lithium ions are inserted into graphite (when lithium-graphite intercalation compounds are formed), graphite exhibits a low potential similar to that of metallic lithium (0.05V to 0.3V vs. Li / Li + ) This allows lithium-ion secondary batteries to exhibit high operating voltages. Furthermore, graphite is preferred because it has advantages such as a relatively high capacity per unit volume, a relatively small volume expansion, low cost, and higher safety compared to lithium metal.

[0139] In addition, titanium dioxide (TiO2), lithium titanium oxide (Li4Ti5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), molybdenum oxide (MoO2), and other oxides can be used.

[0140] In addition, the negative electrode active material is a composite nitride of lithium and transition metals, Li3N-type. 3-x M x N (M=Co, Ni, Cu) can be used. For example, Li 2.6 Co 0.4 N3 has a large charge / discharge capacity (900mAh / g, 1890mAh / cm 3 ) and is preferred.

[0141] When a composite nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, and therefore it can be preferably combined with a material that does not contain lithium ions, such as V2O5 or Cr3O8, as the positive electrode active material. Even when a material containing lithium ions is used as the positive electrode active material, the composite nitride of lithium and a transition metal can be used as the negative electrode active material by first desorbing the lithium ions contained in the positive electrode active material.

[0142] Materials that undergo a conversion reaction can also be used as the negative electrode active material. For example, transition metal oxides that do not form alloys with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), can be used as the negative electrode active material. The conversion reaction can also occur in oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, and CoS 0.89 It also occurs with sulfides such as NiS and CuS, nitrides such as Zn3N2, Cu3N and Ge3N4, phosphides such as NiP2, FeP2 and CoP3, and fluorides such as FeF3 and BiF3.

[0143] [Fluorine-modified conductive additive] The conductive additive in the negative electrode 506 is preferably modified with fluorine. For example, the conductive additive may be a material obtained by modifying the conductive additive with fluorine.

[0144] The fluorine modification of the conductive additive can be carried out, for example, by treatment with a fluorine-containing gas, heat treatment, plasma treatment in a fluorine-containing gas atmosphere, etc. Examples of the fluorine-containing gas that can be used include fluorine gas and lower fluorine hydrocarbon gases such as fluoromethane (CF4).

[0145] For example, the conductive additive may be immersed in a solution containing hydrofluoric acid, tetrafluoroboric acid, hexafluorophosphoric acid, or the like, or a solution containing a fluorine-containing ether compound, to modify the conductive additive with fluorine.

[0146] By modifying the conductive additive with fluorine, the structure of the conductive additive is stabilized, and it is expected that side reactions will be suppressed during the charge and discharge process of the secondary battery. The suppression of side reactions can improve charge and discharge efficiency. It can also suppress the decrease in capacity due to repeated charge and discharge. Therefore, by using a fluorine-modified conductive additive, a secondary battery with excellent battery characteristics can be realized.

[0147] By stabilizing the structure of the conductive agent, the conductive properties are stabilized, and high output characteristics may be achieved.

[0148] [Negative electrode current collector] The negative electrode current collector may be made of the same material as the positive electrode current collector, but it is preferable that the negative electrode current collector be made of a material that does not alloy with carrier ions such as lithium.

[0149] [Separator] Separator 507 is disposed between positive electrode 503 and negative electrode 506. Separator 507 may be formed from, for example, cellulose-containing fibers such as paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, or polyurethane. The separator is preferably processed into a bag shape and disposed so as to enclose either the positive electrode or the negative electrode.

[0150] Separator 507 may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine-based material, a polyamide material, or a mixture of these. Examples of ceramic materials that can be used include aluminum oxide particles and silicon oxide particles. Examples of fluorine-based materials that can be used include PVDF and polytetrafluoroethylene. Examples of polyamide materials that can be used include nylon and aramid (meta-aramid, para-aramid).

[0151] Coating with ceramic materials improves oxidation resistance, suppressing separator degradation during high-voltage charging and discharging and improving the reliability of secondary batteries. Coating with fluorine-based materials also improves adhesion between the separator and electrodes, improving output characteristics. Coating with polyamide materials, especially aramid, improves heat resistance, improving the safety of secondary batteries.

[0152] For example, both sides of a polypropylene film may be coated with a mixed material of aluminum oxide and aramid, or the surface of the polypropylene film that comes into contact with the positive electrode may be coated with a mixed material of aluminum oxide and aramid, and the surface that comes into contact with the negative electrode may be coated with a fluorine-based material.

[0153] When a separator with a multilayer structure is used, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, and therefore the capacity per volume of the secondary battery can be increased.

[0154] [Electrolytes] The electrolyte can be selected from the same electrolytes as those described with reference to FIGS. 7A to 7C.

[0155] [Method for manufacturing laminated secondary batteries] An example of a method for manufacturing the laminate type secondary battery shown in FIG. 8A will be described with reference to FIGS. 9A to 9C.

[0156] First, a positive electrode 503 and a negative electrode 506 are prepared. The positive electrode 503 has a tab 501 and a positive electrode active material layer 502. The negative electrode 506 has a tab 504 and a negative electrode active material layer 505.

[0157] The negative electrode 506, separator 507, and positive electrode 503 are stacked in this order. Figure 9B shows the stacked negative electrode 506, separator 507, and positive electrode 503. The separator 507 is larger than the negative electrode 506 and positive electrode 503 and has a longer side. This is to prevent short-circuiting between the positive electrode 503 and the negative electrode 506. Figure 9B shows an example using five pairs of negative electrodes and four pairs of positive electrodes. This can also be called a laminate consisting of a negative electrode, a separator, and a positive electrode. Next, the tab regions of the positive electrodes 503 are joined together, and a positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For example, ultrasonic welding or the like may be used for joining. Similarly, the tab regions of the negative electrodes 506 are joined together, and a negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0158] Next, the laminate of negative electrode 506 , separator 507 and positive electrode 503 is placed on exterior body 509 .

[0159] Next, as shown in FIG. 9C, the exterior body 509 is folded at the portion indicated by the dashed line. Thereafter, the outer periphery of the exterior body 509 is joined. For joining, for example, thermocompression bonding or the like may be used. At this time, an area (hereinafter referred to as an inlet) that is not joined is provided on a part (or one side) of the exterior body 509 so that an electrolyte can be introduced later. For the exterior body 509, it is preferable to use a film that has excellent water barrier properties and gas barrier properties. Furthermore, the exterior body 509 can be made to have a laminated structure, and by using a metal foil (for example, aluminum foil) as one of the intermediate layers, high water barrier properties and gas barrier properties can be achieved.

[0160] Next, an electrolyte (not shown) is introduced into the inside of the exterior body 509 through an inlet provided in the exterior body 509. The introduction of the electrolyte is preferably carried out under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is joined. In this manner, the laminate-type secondary battery 500 can be produced.

[0161] By using the positive electrode active material 100 of the present invention for the positive electrode 503, a secondary battery having a high capacity, a high charge / discharge capacity, and excellent cycle characteristics can be obtained.

[0162] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0163] (Embodiment 3) In this embodiment, a method for manufacturing a positive electrode active material of one embodiment of the present invention will be described with reference to FIGS.

[0164] As shown in FIG. 10A, in one embodiment of the cathode active material of the present invention, a lithium composite oxide (LiMO2) containing a transition metal M is prepared (Step S15). At least two additive elements are added to LiMO2, and the addition process is repeated at least twice. In FIG. 10A, an additive element (X) is added to LiMO2 (Step S21), and then an additive element (Y) is added to LiMO2 (Step S51). The additive element (Y) is a Group 4 element, a Group 5 element, or a lanthanoid element. The Group 4 element, the Group 5 element, or the lanthanoid element includes one or more elements selected from Hf, V, Nb, Ce, Sm, Hf, and Zr. Through these steps, a cathode active material 100 is obtained (Step S66) as shown in FIG. 10A.

[0165] Each step shown in Figure 10A includes one or more steps selected from the steps of preparing a material source (sometimes referred to as a starting material, precursor, or precursor), mixing the materials, obtaining a mixture, heating, and classifying. The steps are described in detail using Figure 10B.

[0166] <Step S11> 10B, at least a lithium source (Li source) and a transition metal source (M source) are prepared. The lithium source (Li source) and the transition metal source (M source) are the main components of the positive electrode active material, and the Li source and the M source are also called starting materials, precursors, or precursors.

[0167] It is preferable to use a transition metal that can form a layered rock-salt type composite oxide belonging to the space group R-3m together with lithium. A composite oxide containing lithium is sometimes referred to as a lithium composite oxide. The transition metal can be one or more selected from manganese, cobalt, nickel, etc. Furthermore, aluminum, etc. may be added to the starting material.

[0168] As the Li source in step S11, one or more selected from lithium carbonate, lithium fluoride, and the like can be used.

[0169] The M source in step S11 can be one or more selected from transition metal oxides, transition metal hydroxides, etc. Cobalt sources can be one or more selected from cobalt oxide, cobalt hydroxide, etc. Manganese sources can be one or more selected from manganese oxide, manganese hydroxide, etc. Nickel sources can be one or more selected from nickel oxide, nickel hydroxide, etc.

[0170] When aluminum is used as the starting material, the aluminum source can be one or more selected from aluminum oxide, aluminum hydroxide, aluminum-containing alkoxides, and the like.

[0171] <Step S12> Step S12 in Fig. 10B includes mixing the Li source, M source, and the like. Mixing can be performed using one or more methods selected from dry and wet methods. Depending on the mixing conditions, the mixture may be pulverized.

[0172] When the mixing process is performed by a wet method, a solvent is prepared. Examples of solvents that can be used include alcohols such as acetone, ethanol, and isopropanol, ethers such as diethyl ether, dioxane, acetonitrile, and N-methyl-2-pyrrolidone (NMP). Dehydrated or super-dehydrated solvents can be used, such as dehydrated acetone or super-dehydrated acetone. For example, dehydrated acetone refers to acetone with a water content of 50 ppm or less, preferably 20 ppm or less. A solvent with a water content of 10 ppm or less is called super-dehydrated acetone. It is more preferable to use an aprotic solvent, which is less likely to react with the lithium compound in the mixture. In a wet mixing process, the mixture is often pulverized.

[0173] A ball mill, a bead mill, etc. can be used as a tool for mixing. When using a ball mill, it is preferable to use zirconia balls. The rotation speed in step S12 is preferably 300 rpm or more and 500 rpm or less.

[0174] Furthermore, although this step may be merely mixing, it is preferable to crush the starting materials using the above-mentioned tools to make the resulting mixture finer.

[0175] The mixture obtained in step S12 preferably has a median diameter (D50) of 0.1 μm or more, for example, 0.1 μm to 100 μm, more preferably 1 μm to 50 μm, and even more preferably 1 μm to 15 μm.

[0176] Although the above description has been given using the median diameter (D50), the particle size obtained by measuring the cross-sectional diameter may also be used.

[0177] <Step S14> Step S14 in FIG. 10B involves heating the mixture (sometimes referred to as the mixed material) obtained in step S12. This step may be referred to as the first heating step, with an ordinal number added, to distinguish it from subsequent heating steps. Alternatively, this step may be referred to as firing. The first heating step may be performed continuously or batchwise.

[0178] The atmosphere for the first heating is preferably an atmosphere with little water, such as dry air (for example, a dew point of -50°C or less, more preferably -100°C or less). To obtain a dry atmosphere, dry oxygen or the like may be supplied. The flow rate of dry oxygen or the like is preferably 5 L / min or more and 35 L / min or less.

[0179] The temperature range of the first heating is preferably 800°C or higher and lower than 1100°C, more preferably 900°C or higher and lower than 1100°C, and even more preferably 950°C or higher and lower than 1100°C.

[0180] If the temperature of the first heating is lower than the lower limit of 800°C, the decomposition and melting of the Li source and the M source may be insufficient. If the temperature of the first heating is higher than the upper limit of 1100°C, defects may occur due to factors such as lithium evaporation or sublimation. Alternatively, if cobalt is used as the transition metal, if the temperature is higher than 1100°C, defects may occur in which cobalt becomes divalent. Therefore, considering the use of cobalt, the temperature of the first heating is preferably 900°C or higher and 1000°C or lower, and more preferably 950°C or higher and 1000°C or lower.

[0181] The first heating time is preferably 1 hour to 100 hours, and more preferably 2 hours to 20 hours. The temperature increase rate can be 150°C / h to 250°C / h. The temperature can be decreased by either forced cooling or natural cooling, provided that the mixture can be cooled to room temperature (e.g., 25°C).

[0182] However, if there are no problems in the subsequent steps from step S42 onwards, it is possible to proceed to step S42 even if the temperature in step S14 is higher than room temperature. In other words, cooling to room temperature is not essential in step S14.

[0183] In the first heating, it is advisable to place a lid on the container containing the mixture in step S12. By placing a lid on the container, the reaction atmosphere can be controlled. Alternatively, the lid may be placed on the container while controlling the reaction atmosphere in the heat treatment furnace. Methods for controlling the reaction atmosphere in the heat treatment furnace include purging, which prevents gas from entering or leaving the reaction atmosphere in the heat treatment furnace, and flow, which allows gas from the reaction atmosphere to enter or leave the heat treatment furnace. Examples of heat treatment furnaces include muffle furnaces.

[0184] <Step S15> Step S15 in Fig. 10A includes recovering the material obtained by the first heating to obtain a lithium composite oxide (LiMO2) containing a transition metal M. In this manner, LiMO2 can be prepared. The median diameter (D50) of LiMO2 is preferably 1 µm or more and 100 µm or less, more preferably 1 µm or more and 50 µm or less, and even more preferably 1 µm or more and 15 µm or less.

[0185] Although the above description has been given using the median diameter (D50), the particle size obtained by measuring the cross-sectional diameter may also be used.

[0186] Furthermore, LiMO2 that has been synthesized in advance may be used in step S15, in which case steps S11 to S14 can be omitted.

[0187] When M is cobalt as pre-synthesized LiMO2, lithium cobalt oxide manufactured by Nippon Chemical Industry Co., Ltd. can be used.

[0188] <Step S21> Step S21 includes preparing an additive element source (X source) for the lithium composite oxide (LiMO2). The additive element X can be one or more selected from nickel, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. In this embodiment, a fluorine source and a magnesium source are used as the X source. A lithium source may also be prepared simultaneously with the X source.

[0189] The additional element X may be added in two or more steps. When added in two or more steps, the additional element X may be distinguished by adding an ordinal number such as additional element X1, additional element X2, etc., and the starting materials may be distinguished by adding the same ordinal number such as the X1 source, X2 source, etc.

[0190] The fluorine source may be a chlorine source or the like, or a halogen source including a fluorine source and a chlorine source may be used. In addition, a lithium source may also be prepared. The fluorine source and the magnesium source are starting materials.

[0191] Examples of fluorine sources that can be used include lithium fluoride (LiF), magnesium fluoride (MgF2), aluminum fluoride (AlF3), titanium fluoride (TiF4), cobalt fluoride (CoF2, CoF3), nickel fluoride (NiF2), zirconium fluoride (ZrF4), vanadium fluoride (VF5), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF2), calcium fluoride (CaF2), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF2), cerium fluoride (CeF2), lanthanum fluoride (LaF3), and sodium aluminum hexafluoride (Na3AlF6). The fluorine source is not limited to a solid, and may be, for example, fluorine (F2), carbon fluoride, sulfur fluoride, or oxygen fluoride (OF2, O2F2, O3F2, O4F2, O2F), which may be mixed into the atmosphere during the heating step described below. A mixture of multiple fluorine sources may also be used. Among these, lithium fluoride is preferred because it has a relatively low melting point of 848°C and is easily melted during the heating step described below. A fluorine source containing Li may also be called a Li source.

[0192] As the chlorine source, for example, lithium chloride, magnesium chloride, etc. can be used.

[0193] As the magnesium source, for example, magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, etc. can be used.

[0194] Examples of lithium sources that can be used include lithium fluoride and lithium carbonate. That is, lithium fluoride can be used as both a lithium source and a fluorine source. Magnesium fluoride can be used as both a fluorine source and a magnesium source.

[0195] Consider the case where lithium fluoride (LiF) is prepared as the fluorine source and magnesium fluoride (MgF2) is prepared as the fluorine source and magnesium source. When lithium fluoride (LiF) and magnesium fluoride (MgF2) are mixed in a molar ratio of approximately LiF:MgF2 = 65:35, the effect of lowering the melting point of the mixture containing the fluorine source and magnesium is maximized. On the other hand, if the amount of lithium fluoride is too high, there is a concern that the lithium will be excessive, resulting in deterioration of cycle characteristics. Therefore, the molar ratio of lithium fluoride (LiF) to magnesium fluoride (MgF2) is preferably LiF:MgF2 = x:1 (0≦x≦1.9), more preferably LiF:MgF2 = x:1 (0.1≦x≦0.5), and even more preferably LiF:MgF2 = x:1 (x = 0.33 or thereabouts). In this specification, "nearby" refers to a value greater than 0.9 times but less than 1.1 times the value.

[0196] When LiMO2 is lithium cobalt oxide, magnesium is more likely to substitute for the lithium site than for the cobalt site, given the ionic radius. Furthermore, lithium cobalt oxide and magnesium oxide are more stable when separated than when dissolved, and therefore do not actively dissolve. However, by performing appropriate heating, such as in step S44, magnesium oxide can dissolve in the surface layer, convex portions, or defects such as grain boundaries, cracks, or voids of the lithium cobalt oxide. When lithium cobalt oxide is desorbed during charging and discharging, the interlayer distance between the CoO2 layers may shorten or the CoO2 layers may shift. However, when magnesium substitutes for the lithium site, the interlayer distance between the CoO2 layers can be maintained even when lithium is desorbed, thereby suppressing changes in the crystal structure. Since crystal structure collapse begins at the surface layer, convex portions, or defects such as grain boundaries, cracks, or voids of the lithium cobalt oxide, it is preferable for magnesium to be concentrated in the surface layer or convex portions. This lithium cobalt oxide serves as a positive electrode active material whose crystal structure is resistant to collapse even during repeated high-voltage charging and discharging.

[0197] When LiMO2 is lithium cobalt oxide, fluorine can function as a fluxing agent to melt magnesium. It is also possible that fluorine substitutes for the oxygen position of lithium cobalt oxide. Therefore, fluorine may exist throughout the lithium cobalt oxide. The presence of such fluorine lowers the Li desorption energy of lithium cobalt oxide, facilitating Li insertion and desorption. It is also expected to have HF resistance.

[0198] <Step S22> Step S22 in Fig. 10B includes mixing the starting materials. Mixing can be performed using one or more methods selected from dry and wet methods. Depending on the mixing conditions, the mixture may be pulverized.

[0199] In step S22, a wet method is preferable since it allows for strong mixing. In a wet mixing step, the mixture is often pulverized.

[0200] When the mixing step is performed in a wet manner, a solvent is prepared. As the solvent, the solvent shown in step S12 can be used.

[0201] The mixing tool can be one or more selected from a ball mill, a bead mill, etc. When using a ball mill, it is preferable to use zirconia balls as the grinding tool. The rotation speed in step S22 is preferably 300 rpm or more and 500 rpm or less.

[0202] Furthermore, although this step may be merely mixing, it is preferable to crush the starting materials using the above-mentioned tools or the like to make the resulting mixture finer.

[0203] The mixture may be further sieved. The mixture preferably has a uniform median diameter (D50) of 0.01 μm or more and 10 μm or less, more preferably 0.1 μm or more and 1 μm or less.

[0204] Although the above description has been given using the median diameter (D50), the particle size obtained by measuring the cross-sectional diameter may also be used.

[0205] <Step S23> Step S23 in FIG. 10B includes a process of recovering the materials mixed as described above to obtain a mixture 902.

[0206] It is preferable that the mixture 902 has the above-mentioned median diameter (D50). The mixture 902 having such a median diameter is likely to be uniformly attached to the surface of LiMO2 when mixed with LiMO2 in step S15. If the mixture 902 is uniformly attached to the surface of LiMO2 in step S15, the mixture 902 is likely to be distributed in the surface layer of LiMO2 after heating in step S44, etc.

[0207] Although the above description has been given using the median diameter (D50), the particle size obtained by measuring the cross-sectional diameter may also be used.

[0208] <Step S42> Step S42 in Fig. 10B includes mixing the LiMO2 of step S15 with the mixture 902. Mixing can be performed using one or more methods selected from a dry method and a wet method. In step S42, the dry method is more preferable than the wet method because it is less likely to destroy particles.

[0209] When the grinding and mixing steps are performed wet, a solvent is prepared. The solvent shown in step S12 can be used as the solvent.

[0210] In this step, the mixture may be simply mixed, but may also be pulverized using a ball mill, bead mill, etc. When a ball mill is used, it is preferable to use zirconia balls, for example.

[0211] In this step, the starting materials may be simply mixed, but it is preferable to crush the starting materials using the above-mentioned tools or the like in order to reduce the particle size of the resulting lithium composite oxide.

[0212] The mixture may be further sieved. It is preferable that the mixture has a uniform median diameter (D50) of 10 μm or more and 15 μm or less.

[0213] Although the above description has been given using the median diameter (D50), the particle size obtained by measuring the cross-sectional diameter may also be used.

[0214] The mixing conditions in step S42 are preferably milder than the mixing conditions in step S12 and step S22 to avoid damaging the LiMO particles. For example, milder conditions can be achieved by using a lower rotation speed or a shorter time. The rotation speed in step S42 is preferably 100 rpm or more and 300 rpm or less.

[0215] In step S42, the ratio of the number of transition metal M atoms in LiMO2 to the number of magnesium Mg atoms in the mixture 902 is preferably M:Mg=100:y (0.1≦y≦6), and more preferably M:Mg=100:y (0.3≦y≦3).

[0216] Furthermore, aluminum and / or nickel may be further mixed in the mixing in step S42. The aluminum source and nickel source may be referred to as X2 source.

[0217] Let's consider the case where the lithium composite oxide is lithium cobalt oxide. The Al of the X2 source is trivalent and has a strong bond with oxygen, suppressing oxygen desorption. Furthermore, it is difficult for the lithium around the Al to move during charge and discharge. Therefore, when Al enters the cobalt site, it is possible to suppress changes in the crystal structure. When Al enters the cobalt site in the surface layer, the area around the Al functions as a pillar, suppressing changes in the crystal structure. This makes it possible to create a positive electrode active material whose crystal structure is resistant to collapse even when repeatedly charged and discharged at high voltages.

[0218] Let us consider the case where the lithium composite oxide is lithium cobalt oxide. Ni, the X2 source, can be substituted at both the cobalt site and the lithium site. Substitution at the cobalt site lowers the redox potential, leading to increased capacity. Furthermore, substitution at the lithium site reduces the lattice constant deviation, suppressing changes in the crystal structure. This allows for a positive electrode active material whose crystal structure is resistant to collapse even after repeated charging and discharging at high voltages.

[0219] It is preferable that Al and Ni are present in the surface layer of the positive electrode active material. More preferably, Ni is present in a position similar to that of Mg, and Al is present more inward than Mg. In consideration of the preferable positions of Al and Ni, it is preferable to add at least Al in a step separate from that of Mg.

[0220] As the Ni source, one or more selected from nickel oxide, nickel hydroxide, nickel alkoxide, and the like can be used.

[0221] As the Al source, one or more selected from aluminum oxide, aluminum hydroxide, aluminum alkoxide, and the like can be used.

[0222] <Step S43> Step S43 in FIG. 10A includes a process of recovering the mixed materials to obtain a mixture 903.

[0223] Although the procedure for obtaining the mixture 903 has been described as adding the mixture 902 of LiF and MgF2 to LiMO2, the procedure is not limited to this. The mixture 903 can be obtained by adding a Mg source, an F source, etc. to the Li source and the M source in step S11. Alternatively, the Mg source and the F source may be added to the LiMO2 in step S14 and the mixing in step S42 may be performed without going through the mixing in step S22. In these cases, several steps can be omitted, making the process simple and highly productive.

[0224] Alternatively, lithium cobalt oxide to which magnesium and fluorine have been added in advance may be used as the mixture 903. If lithium cobalt oxide to which magnesium and fluorine have been added is used, the steps up to step S42 can be omitted, which is simpler.

[0225] A mixture 903 may be obtained by further adding a magnesium source and a fluorine source to lithium cobalt oxide to which magnesium and fluorine have been added in advance, according to step S21 or the like.

[0226] Thus, various methods for obtaining the mixture 903 are conceivable.

[0227] <Step S44> Step S44 in Fig. 10A includes heating the mixture 903 obtained in step S43. This step may be referred to as the second heating, with an ordinal number added to distinguish it from the first heating. This step may also be referred to as annealing. The second heating is performed using a continuous or batch process, etc.

[0228] In step S44, a crucible can be used, but it is preferable to use a flat container called a sheath or setter (also simply referred to as a container) that has a larger capacity than a crucible, with mass synthesis in mind. This is preferable for mass synthesis, as it makes it easier to adjust the conditions, such as the elements added to the mixture 903. The container is preferably made of one or more raw materials selected from alumina, mullite, magnesia, and zirconia.

[0229] The atmosphere for the second heating is preferably an oxygen-containing atmosphere or so-called dry air. Dry air is the gas remaining after removing water vapor from air. Specifically, dry air refers to compressed air with a dew point lower than -10°C. That is, the atmosphere for the second heating is preferably an oxygen-containing atmosphere with little water (for example, a dew point lower than -50°C, more preferably a dew point lower than -80°C).

[0230] To control the atmosphere of the second heating, there are two methods: a purge method, which prevents gas from entering or leaving the reaction atmosphere in the heat treatment furnace, and a flow method, which allows gas from the reaction atmosphere to enter or leave the heat treatment furnace.

[0231] During the second heating, compounds lighter than oxygen, such as LiF, may volatilize or sublime due to heating. This may result in a decrease in the concentration of one or more elements selected from the Li concentration and the F concentration in mixture 903. Therefore, when heating mixture 903, it is preferable to control at least the fluorine concentration or the partial pressure of fluoride in the atmosphere inside the container within an appropriate range. For example, one method for preventing the volatilization or sublimation of LiF is to place a lid on the container or the like that stores mixture 903.

[0232] The second heating is preferably heating that has an adhesion suppression effect so as to prevent adhesion between particles of mixture 903. Examples of heating that has an adhesion suppression effect include heating while stirring mixture 903, heating while vibrating a container containing mixture 903, and the like.

[0233] The temperature range of the second heating must be equal to or higher than the temperature at which the reaction between LiMO2 and mixture 902 proceeds. The temperature at which the reaction proceeds may be any temperature at which interdiffusion occurs between LiMO2 and the elements contained in mixture 902. Therefore, the temperature of the second heating may be, for example, 500°C or higher and 950°C or lower.

[0234] It is considered preferable that the lower limit of the temperature of the second heating be equal to or higher than the temperature at which at least a portion of the mixture 903 melts, as this facilitates the reaction. Therefore, the temperature of the second heating is preferably equal to or higher than the eutectic point of the additive elements of the mixture 902. When the mixture 902 contains LiF and MgF2 as additive elements, the eutectic point of LiF and MgF2 is around 742°C, so it is preferable to set the second heating temperature to 742°C or higher.

[0235] Furthermore, in the mixture 903 in which the molar ratio of LiCoO2:LiF:MgF2 was 100:0.33:1, an endothermic peak was observed around 830°C in differential scanning calorimetry (DSC measurement). Therefore, it is considered that a lower limit of the temperature for the second heating is more preferably 830°C or higher.

[0236] The higher the heating temperature, the easier the reaction will proceed, and the shorter the heating time will be. A shorter heating time is preferable as it increases productivity.

[0237] The upper limit of the temperature for the second heating must be below the decomposition temperature of LiMO2 (1130°C for LiCoO2). At temperatures near the decomposition temperature, there is concern that LiMO2 may decompose, albeit in trace amounts. Therefore, the upper limit of the temperature for the second heating is preferably 1130°C or lower, more preferably 1000°C or lower, even more preferably 950°C or lower, and even more preferably 900°C or lower. The temperature for the second heating is preferably a temperature that does not destroy LiMO2 in step S14, and the temperature for the second heating is lower than the temperature for the first heating.

[0238] Therefore, the temperature range for the second heating is preferably 500°C to 1130°C, more preferably 500°C to 1000°C, even more preferably 500°C to 950°C, and even more preferably 500°C to 900°C. Also, the temperature range is preferably 742°C to 1130°C, more preferably 742°C to 1000°C, even more preferably 742°C to 950°C, and even more preferably 742°C to 900°C. Also, the temperature range is preferably 830°C to 1130°C, more preferably 830°C to 1000°C, even more preferably 830°C to 950°C, and even more preferably 830°C to 900°C.

[0239] Furthermore, when the mixture 903 is heated, it is preferable to control the partial pressure of fluorine or fluoride in the atmosphere within an appropriate range.

[0240] In the above-described fabrication method, for example, LiF, which is a fluorine source, functions as a flux, which allows the temperature of the second heating step to be lower than the decomposition temperature of LiMO, for example, to between 742°C and 950°C, and distributes one or more additive elements selected from magnesium and fluorine near the surface, thereby producing a positive electrode active material with excellent characteristics.

[0241] The second heating is preferably performed for an appropriate time. The appropriate second heating time varies depending on conditions such as the second heating temperature, the size and composition of the LiMO particles in step S14, etc. If the particles are small, a lower temperature or a shorter time may be more preferable than if the particles are large.

[0242] For example, if the median particle diameter (D50) of the particles in step S14 is 12 μm, the second heating temperature is preferably, for example, 600° C. or more and 950° C. or less. The second heating time is, for example, preferably 3 hours or more, more preferably 10 hours or more, and even more preferably 60 hours or more.

[0243] On the other hand, when the median diameter (D50) of the particles in step S14 is 5 μm, the second heating temperature is preferably, for example, 600° C. to 950° C. The second heating time is preferably, for example, 1 hour to 10 hours, more preferably about 2 hours.

[0244] Although the above description has been given using the median diameter (D50), the particle size obtained by measuring the cross-sectional diameter may also be used.

[0245] The temperature-lowering time after the second heating is preferably, for example, 10 hours or more and 50 hours or less.

[0246] The second heating can be performed using a rotary kiln. Rotary kilns can heat the mixture while stirring, whether they are continuous or batchwise, and are therefore preferred as a heating method that can suppress adhesion. Continuous kilns are particularly preferred because of their high productivity. Batch kilns are preferred because they allow for easy atmosphere control.

[0247] The second heating may be performed by a roller hearth kiln. The roller hearth kiln preferably vibrates a container containing the mixture 903 during heating. The roller hearth kiln is a continuous type, which is preferable because it has good productivity.

[0248] After the second heating, the additional element X may be unevenly distributed in the surface layer portion of the positive electrode active material. That is, the additional element X may be located in the surface layer portion of the positive electrode active material.

[0249] Furthermore, after the second heating, the additional element X may be unevenly distributed in the protruding portions of the positive electrode active material. That is, the additional element X may be located in the protruding portions of the positive electrode active material.

[0250] Of the additive elements X, aluminum may be unevenly distributed at the boundary between the protrusions and the surface layer.

[0251] Fluorine, one of the additive elements X, may be present throughout the positive electrode active material without being unevenly distributed.

[0252] <Step S51> Step S51 in Fig. 10B includes preparing an additive element source (Y source). In this embodiment, the Y source is one or more elements selected from Group 4 or Group 5 elements, particularly Hf, V, and Nb. Alternatively, the additive element may be one or more elements selected from lanthanoid elements, particularly Ce and Sm. Zr may be added simultaneously with one or more elements selected from Hf, V, and Nb.

[0253] An X source may be added in step S51.

[0254] A metal alkoxide can be used as the Y source. For example, a metal alkoxide containing Hf, V, Nb, Ce, or Sm is prepared. When adding Zr, a metal alkoxide containing Zr is also prepared. In this case, it is preferable to simultaneously add an X source that can be prepared as a metal alkoxide. For example, starting materials such as aluminum and / or nickel can be prepared as a metal alkoxide.

[0255] <Steps S52 and S53> Step S52 in FIG. 10B includes a mixing step of dissolving metal alkoxide in alcohol, and a mixed solution 904 is obtained in step S53.

[0256] The amount of metal alkoxide required varies depending on the particle size of the mixture 903, but for example, when triisopropoxycerium(III) is used and the particle size (D50) of the lithium cobalt oxide is about 20 μm, it is preferable to add it so that the number of cobalt atoms in the lithium cobalt oxide is 1 and the concentration of Ce in the triisopropoxycerium(III) is 0.001 to 0.02 times.

[0257] <Step S62> 10B includes a mixing process of stirring, in an atmosphere containing water vapor, a mixture of mixed solution 904 and particles of mixture 903 that has been subjected to the second heating. Note that the second heating can also serve as the third heating shown in the next step S63.

[0258] Stirring can be performed, for example, with a magnetic stirrer. The stirring time may be long enough to cause hydrolysis and polycondensation reactions between the water and metal alkoxide in the atmosphere, and may be, for example, 4 hours at 25°C and 90% RH (relative humidity). Stirring may also be performed in an atmosphere without humidity or temperature control, for example, in the air atmosphere in a draft chamber. In such cases, it is preferable to use a longer stirring time, for example, 12 hours or more at room temperature.

[0259] By gradually incorporating water vapor from the atmosphere and gradually volatilizing the alcohol, the water and metal alkoxide react, allowing the sol-gel reaction to proceed more gently. Furthermore, by reacting the metal alkoxide with water at room temperature, the sol-gel reaction can proceed more gently than when, for example, heating is performed at a temperature above the boiling point of the solvent alcohol.

[0260] Alternatively, water may be added actively. If a gentle reaction is desired, the reaction time may be controlled by gradually adding water diluted with alcohol, reducing the amount of alcohol, adding a stabilizer, or the like.

[0261] It is preferable to proceed with the sol-gel reaction gently, as this facilitates the formation of a coating film containing at least the additive element Y. However, the resulting coating film is not necessarily uniform and may be dotted.

[0262] <Step S63> Step S63 in FIG. 10B includes a process of obtaining a mixture 905. First, a precipitate is recovered from the mixture that has been processed in step S62. Recovery methods that can be used include filtration, centrifugation, and evaporation to dryness. The precipitate can be washed with the same alcohol as the solvent in which the metal alkoxide was dissolved. When evaporation to dryness is used, it is not necessary to separate the solvent and the precipitate in this step; the precipitate can be recovered, for example, in a drying process.

[0263] The collected residue can be dried to obtain mixture 905. The drying step can be performed, for example, at 80° C. for 1 hour to 4 hours under vacuum or ventilation.

[0264] Instead of the sol-gel method, a coating film containing the additive element Y may be formed on the mixture 903 by sputtering or vapor deposition.

[0265] <Step S64> Step S64 in Fig. 10B includes heating the resulting mixture. Step S63 is the heating step following step S44, and is designated the third heating step by adding an ordinal number. The third heating step can use the conditions described for the first or second heating step.

[0266] In order to prevent the Y source from diffusing into the positive electrode active material, the third heating is preferably performed for a shorter time than the second heating, and at a lower temperature than the second heating.

[0267] After the third heating, the additional element X may be unevenly distributed in the surface layer portion of the positive electrode active material. That is, the additional element X may be located in the surface layer portion of the positive electrode active material.

[0268] Furthermore, after the third heating, the additional element X may be unevenly distributed in the protruding portions of the positive electrode active material. That is, the additional element X may be located in the protruding portions of the positive electrode active material.

[0269] Of the additive elements X, aluminum may be unevenly distributed at the boundary between the protrusions and the surface layer.

[0270] Fluorine, one of the additive elements X, may be present throughout the positive electrode active material without being unevenly distributed.

[0271] After the third heating, the additional element Y may be unevenly distributed in the surface layer portion of the positive electrode active material. That is, the additional element Y can be located in the surface layer portion of the positive electrode active material.

[0272] Furthermore, after the third heating, the additional element Y may be unevenly distributed in the protruding portions of the positive electrode active material. That is, the additional element Y can be located in the protruding portions of the positive electrode active material.

[0273] <Step S66> 10B includes a step of collecting the particles. Furthermore, the particles are preferably sieved. In this manner, the positive electrode active material 100 of one embodiment of the present invention can be produced.

[0274] The heating described above has been described as the first to third heatings, but the number of heatings may be N (N>3). The conditions (temperature or time) may be changed for each heating. Furthermore, for one or more selected from the first to third heatings, the step including heating and cooling may be repeated M (M>2) times. The step including heating and cooling may include a step of recovering the mixture.

[0275] In the lithium composite oxide, the contained elements such as the transition metal M and / or the additional element are unevenly distributed in the protrusions and / or the surface layer. Furthermore, the transition metal M and / or the additional element have a concentration gradient. For example, at the boundary between the protrusions and / or the surface layer and the interior, the transition metal M and / or the additional element have a concentration gradient.

[0276] The positive electrode active material of the present invention may have an O3'-type crystal structure, which is resistant to collapse even when repeatedly charged and discharged at high voltages. The O3'-type crystal structure is formed, for example, in lithium cobalt oxide, when magnesium is present between the CoO2 layers, i.e., at the lithium site. The presence of magnesium between the CoO2 layers tends to result in a stable crystal structure. To cause magnesium to exist between the CoO2 layers, an Mg source or the like may be prepared in step S21, rather than step S11, and a mixture 902 may be formed in step S23. This mixture may then be mixed with LiMO2 in step S14 and heated in step S44 or step S64.

[0277] If the heating temperature in step S44 and / or step S64 is too high, cation mixing occurs, increasing the possibility that magnesium will enter the cobalt site. Magnesium present in the cobalt site is ineffective in maintaining the crystal structure when repeatedly charged and discharged at high voltages. Furthermore, if the heating temperature is too high, there is concern that adverse effects such as cobalt being reduced to a divalent state and lithium being evaporated or sublimated may occur. Therefore, at least the second heating in step S44 and the third heating in step S64 should be performed under the conditions described above.

[0278] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0279] (Fourth embodiment) In this embodiment mode, examples of a plurality of shapes of secondary batteries each having a positive electrode or a negative electrode manufactured by the manufacturing method described in the previous embodiment will be described.

[0280] [Coin-type secondary battery] An example of a coin-type secondary battery will be described below: Fig. 11A is an external view of a coin-type (single-layer flat) secondary battery, and Fig. 11B is a cross-sectional view thereof.

[0281] In a coin-type secondary battery 300, a positive electrode can 301, which also serves as a positive electrode terminal, and a negative electrode can 302, which also serves as a negative electrode terminal, are insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided so as to be in contact with the positive electrode current collector 305. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided so as to be in contact with the negative electrode current collector 308.

[0282] In addition, in the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300, the active material layer may be formed only on one side of the current collector.

[0283] Metals such as nickel, aluminum, and titanium that are corrosion-resistant to the electrolyte, or alloys of these metals or alloys of these metals with other metals (such as stainless steel), can be used for the positive electrode can 301 and the negative electrode can 302. To prevent corrosion by the electrolyte, it is preferable to coat the positive electrode can 301 and the negative electrode can 302 with nickel, aluminum, or the like. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307.

[0284] These negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte, and as shown in FIG. 11B, the positive electrode can 301 is placed downward, and the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are stacked in this order, and the positive electrode can 301 and the negative electrode can 302 are crimped together via a gasket 303, to produce a coin-type secondary battery 300.

[0285] The positive electrode active material of one embodiment of the present invention is used for the positive electrode 304 in a secondary battery, whereby the coin-type secondary battery 300 has high capacity, high charge / discharge capacity, and excellent cycle characteristics. Note that the separator 310 may not be necessary in the coin-type secondary battery.

[0286] [Cylindrical secondary battery] An example of a cylindrical secondary battery will be described with reference to Fig. 12A. As shown in Fig. 12A, a cylindrical secondary battery 616 has a positive electrode cap (battery lid) 601 on the top surface and a battery can (external can) 602 on the side and bottom surfaces. The battery can (external can) 602 is formed from a metal material and has excellent water barrier properties and gas barrier properties. The positive electrode cap 601 and the battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0287] 12B is a schematic diagram showing the cross section of a cylindrical secondary battery. The cylindrical secondary battery shown in FIG. 12B has a positive electrode cap (battery lid) 601 on the top surface and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap 601 and the battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0288] A battery element is provided inside a hollow cylindrical battery can 602, in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 sandwiched between them. Although not shown, the battery element is wound around a center pin. One end of the battery can 602 is closed and the other end is open. The battery can 602 can be made of a metal, such as nickel, aluminum, or titanium, or an alloy of these or an alloy of these with another metal (e.g., stainless steel), which is corrosion-resistant to electrolytes. To prevent corrosion by the electrolyte, the battery can 602 is preferably coated with nickel, aluminum, or the like. Inside the battery can 602, the wound battery element, in which the positive electrode, negative electrode, and separator are wound, is sandwiched between a pair of opposing insulating plates 608 and 609. An electrolyte (not shown) is injected into the battery can 602, in which the battery element is provided. The electrolyte can be the same as that used in coin-type secondary batteries.

[0289] Since the positive and negative electrodes used in a cylindrical storage battery are wound up, it is preferable to form active materials on both sides of the current collector.

[0290] By using the positive electrode active material of the present invention, a cylindrical secondary battery 616 having a high capacity, a high charge / discharge capacity, and excellent cycle characteristics can be obtained.

[0291] A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be made of a metal material such as aluminum. The positive electrode terminal 603 is resistance-welded to a safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 613 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the increase in internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 is a thermosensitive resistor whose resistance increases with an increase in temperature. This increase in resistance limits the amount of current and prevents abnormal heat generation. The PTC element can be made of a barium titanate (BaTiO3)-based semiconductor ceramic or the like.

[0292] 12C shows an example of a power storage system 615. The power storage system 615 has a plurality of secondary batteries 616. The positive electrodes of the respective secondary batteries are in contact with and electrically connected to conductors 624 separated by insulators 625. The conductors 624 are electrically connected to a control circuit 620 via wiring 623. The negative electrodes of the respective secondary batteries are electrically connected to the control circuit 620 via wiring 626. A charge / discharge control circuit that performs charging / discharging and the like and a protection circuit that prevents overcharging or overdischarging can be applied as the control circuit 620.

[0293] 12D shows an example of a power storage system 615. The power storage system 615 has a plurality of secondary batteries 616, which are sandwiched between a conductive plate 628 and a conductive plate 614. The plurality of secondary batteries 616 are electrically connected to the conductive plate 628 and the conductive plate 614 by wiring 627. The plurality of secondary batteries 616 may be connected in parallel, in series, or in parallel and then further connected in series. By configuring the power storage system 615 to have a plurality of secondary batteries 616, it is possible to extract a large amount of power.

[0294] A plurality of secondary batteries 616 may be connected in parallel and then further connected in series.

[0295] A temperature control device may be provided between the multiple secondary batteries 616. When the secondary batteries 616 are overheated, they can be cooled by the temperature control device, and when the secondary batteries 616 are too cold, they can be heated by the temperature control device. This makes the performance of the power storage system 615 less susceptible to the outside temperature.

[0296] 12D, power storage system 615 is electrically connected to control circuit 620 via wiring 621 and wiring 622. Wiring 621 is electrically connected to the positive electrodes of multiple secondary batteries 616 via conductive plate 628, and wiring 622 is electrically connected to the negative electrodes of multiple secondary batteries 616 via conductive plate 614.

[0297] [Other examples of secondary battery structures] An example of the structure of the secondary battery will be described with reference to FIGS.

[0298] A secondary battery 913 shown in Fig. 13A has a wound body 950 provided with terminals 951 and 952 inside a housing 930. The wound body 950 is immersed in an electrolyte inside the housing 930. The terminal 952 contacts the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. Note that in Fig. 13A, for convenience, the housing 930 is shown separated, but in reality, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (for example, aluminum) or a resin material.

[0299] 13B, the housing 930 shown in Fig. 13A may be formed from a plurality of materials. For example, the secondary battery 913 shown in Fig. 13B has housings 930a and 930b bonded together, and a wound body 950 is provided in the area surrounded by housings 930a and 930b.

[0300] The housing 930a can be made of an insulating material such as organic resin. In particular, by using a material such as organic resin on the surface on which the antenna is formed, it is possible to prevent the secondary battery 913 from blocking the electric field. Note that if the electric field blocking by the housing 930a is small, the antenna may be provided inside the housing 930a. The housing 930b can be made of, for example, a metal material.

[0301] 13C shows the structure of wound body 950. Winding body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. Winding body 950 is a wound body in which negative electrode 931 and positive electrode 932 are stacked on top of each other with separator 933 sandwiched therebetween, and the stacked sheet is wound. Note that multiple stacks of negative electrode 931, positive electrode 932, and separator 933 may be stacked.

[0302] Alternatively, a secondary battery 913 may be provided having a wound body 950a as shown in Fig. 14. The wound body 950a shown in Fig. 14A has a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 has a negative electrode active material layer 931a. The positive electrode 932 has a positive electrode active material layer 932a.

[0303] By using the positive electrode active material of the present invention for the positive electrode 932, the secondary battery 913 can have a high capacity, a high charge / discharge capacity, and excellent cycle characteristics.

[0304] The separator 933 has a width greater than that of the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap with the negative electrode active material layer 931a and the positive electrode active material layer 932a. From the standpoint of safety, it is preferable that the width of the negative electrode active material layer 931a be greater than that of the positive electrode active material layer 932a. A wound body 950a having such a shape is preferable due to its high safety and productivity.

[0305] 14A and 14B, negative electrode 931 is electrically connected to terminal 951. Terminal 951 is electrically connected to terminal 911a. Positive electrode 932 is electrically connected to terminal 952. Terminal 952 is electrically connected to terminal 911b.

[0306] 14C, wound body 950a and the electrolyte are covered with casing 930 to form secondary battery 913. It is preferable to provide casing 930 with a safety valve, an overcurrent protection element, etc. The safety valve is a valve that opens when the pressure inside casing 930 reaches a predetermined level to prevent the battery from exploding.

[0307] As shown in Fig. 14B, the secondary battery 913 may have multiple wound bodies 950a. Using multiple wound bodies 950a can result in a secondary battery 913 with a larger charge / discharge capacity. For other elements of the secondary battery 913 shown in Figs. 14A and 14B, the descriptions of the secondary battery 913 shown in Figs. 13A to 13C can be referred to.

[0308] (Embodiment 5) In this embodiment, an example of application to an electric vehicle (EV) will be shown with reference to FIG.

[0309] The electric vehicle is equipped with first batteries 1301a and 1301b as main driving secondary batteries, and a second battery 1311 that supplies power to an inverter 1312 that starts a motor 1304. The second battery 1311 is also called a cranking battery (also called a starter battery). The second battery 1311 only needs to have high output, and does not need to have a large capacity, and the capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0310] The internal structure of the first battery 1301a may be a wound type or a layered type.

[0311] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more may be connected in parallel. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack having multiple secondary batteries, it is possible to extract large amounts of power. The multiple secondary batteries may be connected in parallel, in series, or in series after being connected in parallel. A plurality of secondary batteries is also called a battery pack.

[0312] In addition, in order to cut off power from a plurality of secondary batteries in a vehicle, a service plug or circuit breaker that can cut off high voltage without using tools is provided in the first battery 1301a.

[0313] The power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V in-vehicle components (such as an electric power steering 1307, a heater 1308, and a defogger 1309) via a DC-DC circuit 1306. When a rear motor 1317 is provided for the rear wheels, the first battery 1301a is also used to rotate the rear motor 1317.

[0314] Furthermore, the second battery 1311 supplies power via the DC-DC circuit 1310 to 14V in-vehicle components (audio 1313, power windows 1314, lamps 1315, etc.).

[0315] The first battery 1301a will be described with reference to FIG. 15A.

[0316] FIG. 15A shows an example in which nine prismatic secondary batteries 1300 are used as one battery pack 1415. Furthermore, nine prismatic secondary batteries 1300 are connected in series, with one electrode fixed by fixing portion 1413 made of an insulator and the other electrode fixed by fixing portion 1414 made of an insulator. While this embodiment shows an example in which the batteries are fixed by fixing portions 1413 and 1414, the prismatic secondary batteries 1300 may also be housed in a battery housing box (also called a casing). Because it is expected that the vehicle will be subjected to external vibrations or shaking (such as from the road surface), it is preferable to fix multiple secondary batteries by fixing portions 1413 and 1414 or a battery housing box. Furthermore, one electrode is electrically connected to control circuit unit 1320 by wiring 1421. Furthermore, the other electrode is electrically connected to control circuit unit 1320 by wiring 1422.

[0317] A memory circuit including a transistor using an oxide semiconductor may be used for the control circuit unit 1320. A charge control circuit or a battery control system having 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.

[0318] The control circuit 1320 detects the terminal voltage of the secondary battery and manages the charge / discharge state of the secondary battery. For example, to prevent overcharging, it can turn off both the output transistor and the cutoff switch of the charging circuit almost simultaneously.

[0319] FIG. 15B shows an example of a block diagram of the battery pack 1415 shown in FIG. 15A.

[0320] The control circuit unit 1320 includes a switch unit 1324 including at least a switch for preventing overcharging and a switch for preventing overdischarging, a control circuit 1322 for controlling the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 sets upper and lower voltage limits for the secondary battery used and limits the upper limit of the current input and the upper limit of the output current to the external device. The range between the lower and upper voltage limits of the secondary battery is within the recommended voltage range. If the secondary battery voltage falls outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit unit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent overcharging and / or overdischarging. For example, if the control circuit 1322 detects a voltage that could cause overcharging, it turns off the switch unit 1324 to cut off the current. A PTC element may also be provided in the charge / discharge path to cut off the current in response to a rise in temperature. The control circuit section 1320 also has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0321] The switch unit 1324 can be configured by combining n-channel transistors and p-channel transistors. The switch unit 1324 is not limited to a switch having a Si transistor using single crystal silicon. For example, the switch unit 1324 may be formed of a power transistor having Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), or GaOx (gallium oxide; x is a real number greater than 0). Furthermore, memory elements using OS transistors can be freely arranged by stacking them on circuits using Si transistors, etc., making integration easy. Furthermore, OS transistors can be fabricated using the same manufacturing equipment as Si transistors, allowing for low-cost fabrication. Specifically, a control circuit unit 1320 using OS transistors can be stacked on the switch unit 1324 and integrated into a single chip. The control circuit unit 1320 occupies a smaller volume, enabling miniaturization.

[0322] 15C, first batteries 1301a and 1301b mainly supply power to 42V (high voltage) in-vehicle devices, and second battery 1311 supplies power to 14V (low voltage) in-vehicle devices. A lead-acid battery is often used as second battery 1311 because of its cost advantage.

[0323] In this embodiment, an example is shown in which lithium ion secondary batteries are used as both the first battery 1301a and the second battery 1311. The second battery 1311 may be a lead storage battery, an all-solid-state battery, or an electric double layer capacitor.

[0324] Furthermore, regenerated 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 regenerated energy, it is desirable that the first batteries 1301a and 1301b be capable of being rapidly charged.

[0325] The battery controller 1302 can set the charging voltage, charging current, etc. of the first batteries 1301a and 1301b. The battery controller 1302 can set charging conditions in accordance with the charging characteristics of the secondary battery used, and can perform rapid charging.

[0326] Although not shown, when an external charger is connected, the charger's outlet or the charger's connection cable is electrically connected to the battery controller 1302. The power supplied from the external charger is charged to the first batteries 1301a, 1301b via the battery controller 1302. Some chargers are provided with a control circuit, and although the function of the battery controller 1302 may not be used, it is preferable to charge the first batteries 1301a, 1301b via a control circuit unit 1320 to prevent overcharging. In some cases, the connection cable or the charger's connection cable is provided with a control circuit. The control circuit unit 1320 is also called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) provided in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU includes a microcomputer. The ECU uses a CPU or a FIGPU.

[0327] Next, an example in which a secondary battery according to one embodiment of the present invention is mounted on a vehicle, typically a transportation vehicle, will be described.

[0328] Furthermore, by installing a secondary battery according to one embodiment of the present invention in a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs) can be realized. Furthermore, a secondary battery according to one embodiment of the present invention 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, astronauts, and spacecraft. The secondary battery according to one embodiment of the present invention can be a high-capacity secondary battery. Therefore, the secondary battery according to one embodiment of the present invention is suitable for miniaturization and weight reduction and can be suitably used in transportation vehicles.

[0329] 16A to 16D illustrate examples of transportation vehicles using a secondary battery according to one embodiment of the present invention. The automobile 2001 shown in FIG. 16A 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. The automobile 2001 shown in FIG. 16A includes a battery pack 2200, which includes a secondary battery module to which multiple secondary batteries are connected. It is preferable that the automobile further includes a charge control device electrically connected to the secondary battery module.

[0330] Furthermore, automobile 2001 can charge its secondary battery by receiving power supply from an external charging facility using a plug-in system, a contactless power supply system, or the like. Charging can be performed using a predetermined charging method or connector standard, such as CHAdeMO (registered trademark) or Combo, as appropriate. The charging facility may be a charging station installed in a commercial facility or a household power source. For example, plug-in technology can be used to charge the secondary battery installed in automobile 2001 using an external power supply. Charging can be performed by converting AC power to DC power via a conversion device such as an AC-DC converter.

[0331] Although not shown, a power receiving device can be mounted on a vehicle and power can be supplied contactlessly from a ground-based power transmitting device for charging. In the case of this contactless power supply method, by incorporating a power transmitting device into the road or an exterior wall, charging can be performed not only while the vehicle is stopped but also while the vehicle is moving. This contactless power supply method can also be used to transmit and receive power between two vehicles. Furthermore, a solar cell can be installed on the exterior of the vehicle, and the secondary battery can be charged while the vehicle is stopped or moving. For such contactless power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0332] 16B shows a large transport vehicle 2002 having an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 is, for example, a four-cell unit of secondary batteries of 3.5V to 4.7V, with 48 cells connected in series for a maximum voltage of 170V. Apart from the number of secondary batteries constituting the secondary battery module of the battery pack 2201, the transport vehicle 2002 has the same functions as those shown in FIG. 16A, and therefore a description thereof will be omitted.

[0333] FIG. 16C shows, as an example, a large transport vehicle 2003 having an electrically controlled motor. The secondary battery module of the transport vehicle 2003 has, for example, a maximum voltage of 600 V, with more than 100 secondary batteries connected in series with a voltage of 3.5 V to 4.7 V. Therefore, a secondary battery with little variation in characteristics is required. By using a secondary battery that uses the positive electrode active material of the present invention in the positive electrode, a secondary battery with stable battery characteristics can be manufactured, and from the standpoint of yield, mass production at low cost is possible. Furthermore, except for the number of secondary batteries constituting the secondary battery module of the battery pack 2202, the same functions as those of FIG. 16A are provided, and therefore a description thereof will be omitted.

[0334] As an example, Fig. 16D shows an aircraft 2004 having a fuel-burning engine. The aircraft 2004 shown in Fig. 16D has wheels for takeoff and landing, and can therefore be considered part of a transportation vehicle. It has a battery pack 2203 including a secondary battery module formed by connecting multiple secondary batteries and a charge control device.

[0335] The secondary battery module of the aircraft 2004 has, for example, eight 4 V secondary batteries connected in series for a maximum voltage of 32 V. Other than the number of secondary batteries constituting the secondary battery module of the battery pack 2203, it has the same functions as those in FIG. 16A, and therefore a description thereof will be omitted.

[0336] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0337] (Embodiment 6) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted in a building will be described with reference to FIGS. 17A and 17B.

[0338] 17A includes a power storage device 2612 including a secondary battery of one embodiment of the present invention, and a solar panel 2610. The power storage device 2612 is electrically connected to the solar panel 2610 through a wiring 2611 or the like. The power storage device 2612 may be electrically connected to a ground-mounted charging device 2604. The power storage device 2612 can be charged with power obtained by the solar panel 2610. The power stored in the power storage device 2612 can be charged to a secondary battery included in a vehicle 2603 via the charging device 2604. The power storage device 2612 is preferably installed in an underfloor space. By installing the power storage device 2612 in the underfloor space, the space above the floor can be effectively utilized. Alternatively, the power storage device 2612 may be installed on the floor.

[0339] The power stored in the power storage device 2612 can also be supplied to other electronic devices in the house. Therefore, even when power cannot be supplied from a commercial power source due to a power outage or the like, the power storage device 2612 of one embodiment of the present invention can be used as an uninterruptible power supply, enabling the use of electronic devices.

[0340] 17B illustrates an example of a power storage device according to one embodiment of the present invention. As illustrated in FIG. 17B, a power storage device 791 according to one embodiment of the present invention is installed in an underfloor space 796 of a building 799.

[0341] A control device 790 is installed in the power storage device 791, and the control device 790 is electrically connected to a distribution board 703, a power storage controller 705 (also called a control device), a display 706, and a router 709 by wiring.

[0342] Electric power is sent from commercial power source 701 to distribution board 703 via service line attachment section 710. Electric power is also sent to distribution board 703 from power storage device 791 and commercial power source 701, and distribution board 703 supplies the sent electric power to general load 707 and power storage load 708 via an outlet (not shown).

[0343] The general load 707 is, for example, an electrical appliance such as a television or a personal computer, and the power storage load 708 is, for example, an electrical appliance such as a microwave oven, a refrigerator, or an air conditioner.

[0344] The power storage controller 705 has a measurement unit 711, a prediction unit 712, and a planning unit 713. The measurement unit 711 has a function of measuring the amount of power consumed by the general load 707 and the power storage load 708 during one day (for example, from midnight to midnight). The measurement unit 711 may also have a function of measuring the amount of power of the power storage device 791 and the amount of power supplied from the commercial power source 701. The prediction unit 712 has a function of predicting the amount of power demand to be consumed by the general load 707 and the power storage load 708 during the next day, based on the amount of power consumed by the general load 707 and the power storage load 708 during the previous day. The planning unit 713 has a function of creating a plan for charging and discharging the power storage device 791, based on the amount of power demand predicted by the prediction unit 712.

[0345] The amount of power consumed by the general load 707 and the power storage load 708 measured by the measurement unit 711 can be confirmed on the display 706. It can also be confirmed on an electrical device such as a television or a personal computer via the router 709. It can also be confirmed on a mobile electronic device such as a smartphone or a tablet via the router 709. The amount of power demand for each time period (or each hour) predicted by the prediction unit 712 can also be confirmed on the display 706, the electrical device, and the mobile electronic device.

[0346] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0347] (Embodiment 7) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted in an electronic device will be described. Examples of electronic devices that mount a secondary 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 terminals, e-book readers, and mobile phones.

[0348] 18A shows an example of a mobile phone. Mobile phone 2100 includes a display unit 2102 built into housing 2101, as well as operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. Note that mobile phone 2100 also includes secondary battery 2107. By including secondary battery 2107 using the positive electrode active material of the present invention in the positive electrode, high capacity can be achieved, and a configuration that can accommodate space savings associated with miniaturization of the housing can be realized.

[0349] 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.

[0350] The operation button 2103 can be provided with various functions, such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, power saving mode activation / deactivation, etc. For example, the functions of the operation button 2103 can be freely set by an operating system built into the mobile phone 2100.

[0351] 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.

[0352] The mobile phone 2100 also has 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. Charging may also be performed by wireless power supply without using the external connection port 2104.

[0353] 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, or an acceleration sensor.

[0354] FIG. 18B shows an unmanned aerial vehicle 2300 having multiple rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 includes a secondary battery 2301 according to one embodiment of the present invention, a camera 2303, and an antenna (not shown). The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. A secondary battery using the positive electrode active material of the present invention for its positive electrode has a high energy density and is highly safe, allowing for safe use over a long period of time. Therefore, the secondary battery is suitable as a secondary battery to be installed in the unmanned aerial vehicle 2300.

[0355] Fig. 18C shows an example of a robot. A robot 6400 shown in Fig. 18C includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a movement mechanism 6408, a computing device, etc.

[0356] 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.

[0357] 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.

[0358] 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.

[0359] The robot 6400 includes a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or an electronic component in its internal region. A secondary battery using the positive electrode active material of the present invention for its positive electrode has high energy density and high safety, and therefore can be used safely for a long period of time. Therefore, the secondary battery 6409 is suitable for use in the robot 6400.

[0360] 18D shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 arranged on the top surface of a housing 6301, multiple cameras 6303 arranged on the side, a brush 6304, an operation button 6305, a secondary battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust from a suction port arranged on the bottom surface.

[0361] 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 is detected through image analysis, the cleaning robot 6300 can stop the rotation of the brush 6304. The cleaning robot 6300 includes a secondary battery 6306 of one embodiment of the present invention and a semiconductor device or an electronic component in its internal region. A secondary battery using the positive electrode active material of the present invention for its positive electrode has high energy density and high safety, and therefore can be used safely for a long period of time. Therefore, the secondary battery 6306 is suitable for use in the cleaning robot 6300.

[0362] This embodiment mode can be implemented in appropriate combination with other embodiment modes. [Example]

[0363] In this example, we prepared Sample 1, which added a Hf source as the Y source, an additive element source for lithium cobalt oxide; Sample 2, which added a V source; Sample 3, which added a Nb source; and Samples 4a to 4c, which added Hf and Zr sources in different amounts. Furthermore, each sample contained a Mg source and a F source as the X source 1, and a Ni source and an Al source as the X source. The sample conditions are shown in the table below.

[0364] [Table 1]

[0365] The manufacturing process for each sample will be described below.

[0366] <Sample 1> 10B, the fabrication process of Sample 1 will be described. In Sample 1, lithium cobalt oxide (product name: CellSeed C-10N) manufactured by Nippon Chemical Industry Co., Ltd. was used as the lithium composite oxide, and the lithium cobalt oxide was produced in Step S15. CellSeed C-10N has a median diameter (D50) of 10 μm or more and 15 μm or less. Elemental analysis by GD-MS revealed that the magnesium and fluorine concentrations were 50 ppm wt or less, the calcium, aluminum, and silicon concentrations were 100 ppm wt or less, the nickel concentration was 150 ppm wt or less, the sulfur concentration was 500 ppm wt or less, the arsenic concentration was 1100 ppm wt or less, and the concentrations of other elements other than lithium, cobalt, and oxygen were 150 ppm wt or less.

[0367] Alternatively, lithium cobalt oxide particles (product name: CellSeed C-5H) manufactured by Nippon Chemical Industry Co., Ltd. may be used as the lithium cobalt oxide in step S15. CellSeed C-5H is a lithium cobalt oxide having a median diameter (D50) of 5 μm or more and 10 μm or less, and in elemental analysis by GD-MS, the concentrations of elements other than lithium, cobalt, and oxygen are similar to or lower than those of C-10N.

[0368] As described above, since Cell Seed C-10N was used, steps S11 to S14 in FIG. 10B were omitted.

[0369] Next, the process of step S21 in Fig. 10B was carried out. Since the additive element X was added in two separate batches, an X1 source was first prepared. As the X1 source for Sample 1, MgF2 was prepared as the Mg source, and LiF was prepared as the F source. Then, LiF was weighed out so that it was 0.33 mol% relative to the lithium cobalt oxide, and MgF2 was 0.1 mol% relative to the lithium cobalt oxide.

[0370] Next, according to the process of step S22 in FIG. 10B, LiF and MgF2 were mixed using a wet method. The solvent was ultra-dehydrated acetone, and the mixture was mixed using a ball mill at a rotation speed of 400 rpm for 12 hours. Under these conditions, the mixture was simultaneously mixed and pulverized. After mixing, the mixture was passed through a sieve with 300 μm openings, and mixture 902 was obtained in step S23.

[0371] Next, the X2 source was prepared. Ni and Al sources were prepared as the X2 source. Ni(OH)2 was prepared as the Ni source, and Al(OH)3 was prepared as the Al source. They were weighed out so that Ni(OH)2 and Al(OH)3 were each 0.5 mol% relative to the lithium cobalt oxide. Ni(OH)2 and Al(OH)3 were each pulverized using a ball mill at a rotation speed of 400 rpm for 12 hours, and then sieved with a 300 μm mesh to prepare the X2 source.

[0372] In step S42 of FIG. 10B, the X1 source and X2 source were added to the lithium cobalt oxide from step S14 and mixed by a dry method, with a rotation speed of 150 rpm and a mixing time of 1 hour. In step S42, the rotation speed was slower than in step S22 and the rotation time was shorter than in step S22. Since the purpose of step S42 was mixing, a dry method was used, unlike step S22. If step S42 were mixed under the same conditions as step S22, the lithium cobalt oxide would break down into powder, which would likely result in poor cycle performance. Finally, the mixture was sieved with a 300 μm mesh to obtain mixture 903.

[0373] In step S44 of FIG. 10B, the mixture 903 was heated.

[0374] Step S44 is the heating step following step S14, and is sometimes called the second heating step with an ordinal number attached, but in sample 1, step S14 is omitted.

[0375] In step S44, the mixture 903 was put into an alumina container, covered with a lid, placed in a muffle furnace which is a heat treatment furnace, heated at 850 °C for 60 hours, and then sieved through a sieve with a mesh size of 53 μm. The muffle furnace was in an oxygen atmosphere, and oxygen was flowed into the muffle furnace at a flow rate of 10 L / min. Flowing oxygen is called oxygen flow.

[0376] Next, a Hf source was prepared as the Y source in step S51 of FIG. 10B. Note that hafnium ethoxide was prepared as the Hf source, and hafnium ethoxide was weighed so as to be 0.25 mol% with respect to lithium cobaltate. 2-propanol was also prepared as the alcohol. Since there was only one Y source, steps S52 and S53 were omitted.

[0377] The heated mixture 903 and the Y source were mixed to form a mixed solution, and in step S62 of FIG. 10B, they were mixed at a rotation speed of 300 rpm at room temperature. In order to promote hydrolysis, the bottle containing the mixed solution 904 was not covered with a lid. The sol-gel reaction such as hydrolysis is preferable for forming a coating film containing Hf.

[0378] In step S63 of FIG. 10B, the precipitate was recovered after the treatment in step S62, and a mixture 905 was obtained. Then, in step S64, heating was performed, and then it was sieved through a sieve with a mesh size of <53 μm>. Step S64 is the next heating after step S44 and is sometimes called the third heating. In step S64, the mixture 905 was put into an alumina container, covered with a lid, placed in a muffle furnace, and heated at 850 °C for 2 hours. The muffle furnace was in an oxygen atmosphere, and oxygen was flowed into the furnace at a flow rate of 10 L / min. The heating time in step S64 was shorter than that in step S44. In order to suppress the diffusion of the Y source into the interior of the positive electrode active material, the heating conditions in step S64 may be such that the heating temperature is lower or the heating time is shorter than those in step S44.

[0379] In this way, the positive electrode active material 100 was obtained as shown in step S66 of FIG. 10B.

[0380] <SEM Observation> Sample 1 was observed using an SEM, model S4800, manufactured by Hitachi High-Tech Corporation. The accelerating voltage was 5 kV. SEM images of the positive electrode active material of Sample 1 are shown in Figures 19A and 19B. Although Sample 1 was produced under the same conditions, the external appearance of the lithium cobalt oxide differs between Figures 19A and 19B. In both Figures 19A and 19B, protrusions can be seen on the surface of the lithium cobalt oxide. This indicates that Sample 1 is lithium cobalt oxide with protrusions on its surface.

[0381] 19A and 19B, multiple protrusions are observed. The multiple protrusions are confirmed to be at least first protrusions having a first size and second protrusions smaller than the first size, and the number of second protrusions is greater than the number of first protrusions. Furthermore, as can be seen from FIGS. 19A and 19B, no cracks were observed in Sample 1.

[0382] The convex portions of Sample 1 contain at least Hf. Hf may be unevenly distributed in the convex portions due to the third heating in step S64. The elements present in the convex portions may be one or more selected from Mg, F, Ni, and Al, in addition to Hf.

[0383] Sample 1 may have magnesium at the lithium site, and may have an O3'-type crystal structure upon charging.

[0384] <Sample 2> Next, Sample 2 will be described, which was produced using a V source as a Y source in addition to an Mg source, an F source, an Ni source, and an Al source as sources of additional elements to lithium cobalt oxide.

[0385] In the manufacturing process of Sample 2, the processes different from those of Sample 1 are Step S44 and Step S51. Step S44 is the condition regarding the second heating, and in Sample 2, it was set to 900°C for 20 hours. Further, in Sample 2, Ni(OH)2 was added as the X2 source after Step S44. Furthermore, in Sample 2, aluminum isopropoxide was prepared as the Al source, and it was weighed so that the amount of aluminum isopropoxide relative to lithium cobaltate would be 0.5 mol%. In Sample 2, vanadium (V) oxide triisopropoxide was prepared as the V source in Step S51, and it was weighed so that the amount of vanadium (V) oxide triisopropoxide relative to lithium cobaltate would be 0.25 mol%. In Sample 2, aluminum isopropoxide and vanadium (V) oxide triisopropoxide in Step S51 were mixed according to Step S52 to obtain the mixed solution 904 in Step S53. The mixing of metal alkoxides may follow Step S52. Then, lithium cobaltate to which the Ni source was added was mixed with the mixed solution 904.

[0386] The heating condition in Step S64 was to lower the heating temperature or shorten the heating time compared to Step S44 in order to suppress the diffusion of the Y source into the interior of the positive electrode active material.

[0387] In this way, the positive electrode active material 100 was obtained as shown in Step S66 of FIGURE 10.

[0388] <SEM Observation> SEM observation of Sample 2 was performed. The SEM used for the observation was the SEM, S4800 manufactured by Hitachi High-Tech Corporation. The acceleration voltage was set to 5 kV. The SEM images of the positive electrode active material of Sample 2 are shown in FIGS. 20A and 20B. While Samples 2 were prepared under the same conditions, in FIGS. 20A and 20B, the external shapes of lithium cobaltate are different. Grain boundaries were confirmed in FIGS. 20A and 20B. In common to FIGS. 20A and 20B, convex portions can be confirmed on the surface of lithium cobaltate. Therefore, it can be understood that Sample 2 is lithium cobaltate having convex portions on the surface.

[0389] In FIGS. 20A and 20B, a plurality of convex portions are confirmed. Comparing with FIGS. 19A and 19B which are SEM images of the positive electrode active material of Sample 1, the number of convex portions in Sample 2 was small. Also, as can be seen from FIGS. 20A and 20B, cracks were not confirmed in Sample 2.

[0390] The convex portion of Sample 2 has at least V. V may be unevenly distributed in the convex portion by the third heating in Step S64. As elements present in the convex portion, one or more selected from Mg, F, Ni, and Al in addition to V are conceivable.

[0391] There may be magnesium in the lithium site of Sample 2, and it may have an O3' type crystal structure during charging.

[0392] <Sample 3> In the manufacturing process of Sample 3, the processes different from the manufacturing process of Sample 2 are Step S44 and Step S51. Step S44 is the condition regarding the second heating, which was set to 850°C for 60 hours. In Sample 3, pentaisobutoxyniobium was prepared as the Nb source in Step S51, and it was weighed so that pentaisobutoxyniobium was 0.25 mol% with respect to lithium cobaltate. Then, aluminum isopropoxide and pentaisobutoxyniobium were mixed according to Step S52, and the mixed solution 904 in Step S53 was obtained.

[0393] The heating condition in Step S64 was to lower the heating temperature or shorten the heating time from Step S44 in order to suppress the diffusion of the Y source into the interior of the positive electrode active material.

[0394] In this way, the positive electrode active material 100 was obtained as shown in Step S66 of FIG. 10.

[0395] <SEM Observation> SEM observation of Sample 3 was carried out. The SEM used was the SEM, S4800 manufactured by Hitachi High-Tech Corporation. The acceleration voltage was set at 5 kV. The SEM images of the positive electrode active material of Sample 3 are shown in FIGS. 21A and 21B. Although Samples 3 were fabricated under the same conditions, the appearance shapes of lithium cobaltate are different in FIGS. 21A and 21B. Grain boundaries were confirmed in FIG. 21A. In common with FIGS. 21A and 21B, convex portions can be confirmed on the surface of lithium cobaltate. Therefore, it can be understood that Sample 3 is lithium cobaltate having convex portions on the surface.

[0396] In FIGS. 21A and 21B, a plurality of convex portions are confirmed. When compared with FIGS. 19A and 19B which are the SEM images of the positive electrode active material of Sample 1, the number of convex portions in Sample 3 was small. Also, as can be seen from FIGS. A and 21B, cracks were not confirmed in Sample 3.

[0397] The convex portions of Sample 3 have at least Nb. Nb may be unevenly distributed in the convex portions by the third heating in Step S64. As elements present in the convex portions, one or more selected from Mg, F, Ni, and Al in addition to Nb are conceivable.

[0398] There is a possibility that magnesium exists in the lithium site in Sample 3 and it may have an O3' type crystal structure.

[0399] <STEM analysis, EDX analysis> FIG. 22A shows a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of a cross section of Sample 3. The HAADF-STEM image was taken under the following conditions. Sample pretreatment: Thinning by FIB method (μ-sampling method) Transmission electron microscope: JEM-ARM200F manufactured by JEOL Ltd. Observation conditions Acceleration voltage: 200 kV Magnification accuracy: ±3%

[0400] 22A, a convex portion 50 can be seen in the center of the image, and based on the difference in contrast, the convex portion 50 can be distinguished from a surface layer 51. Above the convex portion 50, a resin layer, a carbon coating layer, and a Pt layer are attached for observation purposes.

[0401] The protrusions 50 and the surface layer 51 are located near the surface of the lithium cobalt oxide. The inside of the lithium cobalt oxide particle is the interior 52. The boundary between the interior 52 and the protrusions 50 is included in the surface layer 51. The presence of additive elements can be examined by distinguishing between the protrusions 50, the surface layer 51, and the interior 52.

[0402] 22B1 to 22B6 show element mapping images obtained by area analysis of EDX for Sample 3. In the element mapping images, values ​​below the detection limit are shown in black, and the higher the count, the higher the brightness.

[0403] FIG. 22B1 is a mapping image of cobalt, FIG. 22B2 is a mapping image of niobium, FIG. 22B3 is a mapping image of aluminum, FIG. 22B4 is a mapping image of nickel, FIG. 22B5 is a mapping image of fluorine, and FIG. 22B6 is a mapping image of magnesium.

[0404] 22A and 22B1 show that cobalt is present throughout the positive electrode active material. Cobalt is present in the interior 52 and the protrusions 50. Furthermore, when the protrusions 50 and the interior 52 are compared, it is seen that more cobalt is present in the interior 52.

[0405] 22A and 22B2, it can be seen that niobium is present in the protrusions 50. Niobium was hardly detected in the interior 52. In other words, it can be seen that more niobium is present in the protrusions 50 than in the interior 52. This state is sometimes described as niobium being unevenly distributed in the protrusions 50.

[0406] 22A and 22B3, aluminum can be seen in the protrusions 50 and the interior 52, but it is found to be present in large amounts in the surface layer 51, including the boundary between the protrusions 50 and the interior 52. This state may be described as aluminum being unevenly distributed in the surface layer 51, particularly at the boundary. The state of aluminum may be similar even when the added element Y is other than Nb.

[0407] 22A and 22B4, it can be seen that nickel is distributed more in the protrusions 50 than in the interior 52. This state is sometimes described as nickel being unevenly distributed in the protrusions 50. The state of nickel may be similar even when the additional element Y is other than Nb.

[0408] 22A and 22B5 show that fluorine is present throughout the positive electrode active material. The state of fluorine may be similar even when the additive element Y is other than Nb.

[0409] 22A and 22B6, it can be seen that magnesium is present in the protrusions 50. Magnesium was barely detectable in the interior 52. In other words, it can be seen that magnesium is more distributed in the protrusions 50 than in the interior 52. This state is sometimes described as magnesium being unevenly distributed in the protrusions 50. The state of magnesium may be similar even when the added element Y is other than Nb.

[0410] Figure 23 shows the results of EDX analysis through the center line 55 of the protrusions of Sample 3. As with Figure 22A and Figures 22B1 to 22B6, it can be seen that niobium, nickel, magnesium, etc. are present in the protrusions, that cobalt, etc. is present in large amounts inside, and that fluorine, etc. is present in the protrusions and inside. It can be seen that there is less niobium in the protrusions than nickel and magnesium. It can also be seen that cobalt is present in the protrusions.

[0411] Figure 24A shows the results of EDX point analysis of the convex portions of sample 3. In Figure 24A, the position of the point analysis target is circled and marked with point 1. Point 1 is located at the bottom end of the convex portion. In Figure 24B, the position of the point analysis target is circled and marked with point 2. Point 2 is located at the center of the convex portion. In Figure 24C, the position of the point analysis target is circled and marked with point 3. Point 3 is located inside. The results of EDX point analysis for points 1 to 3 are shown in the table below. The detection limit is approximately 1 atomic %. Also, some elements below the detection limit are not shown, so the total does not reach 100%.

[0412] [Table 2]

[0413] EDX point analysis etc. revealed that Nb, Ni and Mg were present in the convex parts etc.

[0414] Considering the results of Figures 24A to 24C, it is clear that there is more niobium in the protruding parts than in the interior. This is a similar trend to the results shown in Figure 22B2. From Figures 24A, 24B, and Table 2, it is believed that the niobium concentration in the protruding parts is at least 1.5 at% or more and 4.7 at% or less. Furthermore, from Figure 24C and Table 2, it is clear that the niobium concentration in the interior is 0.6 at%, below the lower detection limit, and is lower than in the protruding parts.

[0415] Considering the results of Figures 24A to 24C, there is more magnesium in the convex parts than in the interior. This is a similar trend to the results shown in Figure 22B6. ​​From Figures 24A, 24B, and Table 2, it is believed that the magnesium concentration in the convex parts is at least 10.3 at% or more and 10.7 at% or less. Furthermore, from Figure 24C and Table 2, it is clear that the magnesium concentration in the interior is 0.2 at%, below the detection limit, and is lower than in the convex parts.

[0416] Considering the results of Figures 24A to 24C, there is more nickel in the protruding parts than in the interior. This is a similar trend to the results shown in Figure 22B4. From Figures 24A, 24B, and Table 2, it is believed that the nickel concentration in the protruding parts is at least 4.1 at% or more and 5.7 at% or less. Furthermore, from Figure 24C and Table 2, it is clear that the nickel concentration in the interior is 0.3 at%, below the detection limit, and is lower than in the protruding parts.

[0417] The aluminum concentration was below the detection limit.

[0418] <Sample 4> The manufacturing process of Sample 4 differs from that of Sample 3 in step S51. Regarding step S51, tetraisopropoxy zirconium and tetraisopropoxy hafnium were prepared for Sample 4, and Samples 4a, 4b, and 4c were prepared with different concentrations of Zr and Hf relative to lithium cobalt oxide. Aluminum isopropoxide, tetraisopropoxy zirconium, and tetraisopropoxy hafnium were mixed according to step S52, and a mixed solution 904 was obtained in step S53.

[0419] For Sample 4a, the tetraisopropoxy zirconium and tetraisopropoxy hafnium were 0.25 mol% and 0.25 mol%, respectively, relative to the lithium cobalt oxide. For Sample 4b, the tetraisopropoxy zirconium and tetraisopropoxy hafnium were 0.05 mol% and 0.05 mol%, respectively, relative to the lithium cobalt oxide. For Sample 4b, the tetraisopropoxy zirconium and tetraisopropoxy hafnium were 0.25 mol% and 0.05 mol%, respectively, relative to the lithium cobalt oxide.

[0420] In this way, the positive electrode active material 100 was obtained as shown in step S66 of FIG.

[0421] Samples 4a to 4c may have magnesium at the lithium site and may have an O3' type crystal structure.

[0422] <Cycle test> Half-cell type coin cells were fabricated using Samples 1 to 3 and Samples 4a to 4c, and a cycle test was carried out.

[0423] First, Samples 1 to 3 and Samples 4a to 4c were prepared as the positive electrode active material, acetylene black (AB) was prepared as the conductive additive, and polyvinylidene fluoride (PVDF) was prepared as the binder. These were mixed in a weight ratio of positive electrode active material:AB:PVDF=95:3:2 to prepare a slurry, which was then applied to an aluminum current collector. NMP was used as the solvent for the slurry.

[0424] After the slurry was applied to the current collector, the solvent was evaporated. The pressing conditions were 210 kN / m and then 1467 kN / m. A positive electrode was obtained through these steps. The amount of active material carried on the positive electrode was approximately 7 mg / cm. 2 and the electrode density is approximately 4 g / cm 3 It was.

[0425] The positive electrode and a lithium metal counter electrode were used to assemble a half cell, and the characteristics of each coin cell type battery (sometimes referred to as a test battery) were measured.

[0426] The electrolyte for the test battery was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7, with 2 wt% vinylene carbonate (VC) added as an additive, and the electrolyte contained 1 mol / L lithium hexafluorophosphate (LiPF6). The separator for the test battery was made of polypropylene with a thickness of 25 μm.

[0427] First, let's explain the discharge rate and charge rate, which are cycle test conditions. The discharge rate is the relative ratio of the current during discharge to the battery capacity, and is expressed in units of C. For a battery with a rated capacity of X (Ah), the current equivalent to 1C is X (A). When discharging at a current of 2X (A), it is said to have been discharged at 2C, and when discharging at a current of X / 5 (A), it is said to have been discharged at 0.2C. The same applies to the charge rate; when charging at a current of 2X (A), it is said to have been charged at 2C, and when charging at a current of X / 5 (A), it is said to have been charged at 0.2C.

[0428] In measuring the charge and discharge cycles during a cycle test, the battery voltage and current flowing through the battery are preferably measured using the four-terminal method. During charging, electrons flow from the positive electrode terminal through the charge / discharge meter to the negative electrode terminal, resulting in a charging current flowing from the negative electrode terminal through the charge / discharge meter to the positive electrode terminal. During discharging, electrons flow from the negative electrode terminal through the charge / discharge meter to the positive electrode terminal, resulting in a discharging current flowing from the positive electrode terminal through the charge / discharge meter to the negative electrode terminal. The charging and discharging currents are measured using an ammeter in the charge / discharge meter. The integrated amounts of electricity flowing during one charging cycle and one discharging cycle are the charge capacity and discharge capacity, respectively. For example, the integrated amount of electricity flowing during the first discharging cycle can be referred to as the first-cycle discharge capacity, and the integrated amount of electricity flowing during the 50th discharging cycle can be referred to as the 50th-cycle discharge capacity.

[0429] Furthermore, the battery characteristics obtained from the results of cycle tests are sometimes referred to as cycle characteristics, and cycle characteristics include discharge capacity, charge / discharge curve, discharge capacity retention, and the like.

[0430] The cycle characteristics of Samples 1 to 3 are shown in FIGS.

[0431] In Figure 25A, both the charge rate and discharge rate were 0.5 C (1 C = 200 mA / g), and measurements were taken at a charge voltage of 4.65 V and a temperature of 25°C. Charging was completed when the current reached 0.05 C. Discharging was completed when the voltage reached 2.5 V. A rest period was provided between the end of charging and the start of discharging, and between the end of discharging and the start of charging. Each rest period was 10 minutes.

[0432] This figure shows the discharge capacity (mAh / g) versus the number of cycles in this cycle test. The vertical axis of Figure 25A shows the discharge capacity (mAh / g), and the horizontal axis shows the number of cycles. Note that the charge voltage is higher than 4.6 V.

[0433] Fig. 25B shows the discharge capacity retention rate obtained from Fig. 25A, where the maximum discharge capacity is set to 100%. In Fig. 25B, the vertical axis represents the discharge capacity retention rate (%), and the horizontal axis represents the number of cycles (times).

[0434] In FIGS. 25A and 25B, the results of Sample 1 are shown by a solid line, the results of Sample 2 are shown by a dashed line, and the results of Sample 3 are shown by a dashed-dotted line.

[0435] 25B, when measured at a temperature of 25° C., the discharge capacity retention rate is maintained at 80% or more and 95% or less for both Sample 1 and Sample 2. Sample 1 more preferably maintains the rate at 90% or more and 95% or less.

[0436] This example shows that the positive electrode active material of one embodiment of the present invention has a high charge voltage and a high capacity and excellent cycle characteristics.

[0437] Figure 26A shows measurements taken at a charge and discharge rate of 0.5C (1C = 200mA / g), a charge voltage of 4.65V, and a temperature of 45°C. Charging was completed when the current reached 0.05C. Discharging was completed when the voltage reached 2.5V. A rest period was provided between the end of charging and the start of discharging, and between the end of discharging and the start of charging. Each rest period was 10 minutes.

[0438] This figure shows the discharge capacity (mAh / g) versus the number of cycles in this cycle test. The vertical axis of Figure 26A shows the discharge capacity (mAh / g), and the horizontal axis shows the number of cycles. Note that the charging voltage was higher than 4.6 V and the temperature was 45°C, which is higher than 25°C.

[0439] Fig. 26B shows the discharge capacity retention rate obtained from Fig. 26A, where the maximum discharge capacity is set to 100%. In Fig. 26B, the vertical axis represents the discharge capacity retention rate (%), and the horizontal axis represents the number of cycles (times).

[0440] In FIGS. 26A and 26B, the results of Sample 1 are shown by a solid line, the results of Sample 2 are shown by a dashed line, and the results of Sample 3 are shown by a dashed-dotted line.

[0441] As shown in FIG. 26B, when measured at a temperature of 45° C., the discharge capacity retention ratios of both Sample 1 and Sample 2 are maintained at 40% or more and 60% or less.

[0442] This example shows that the positive electrode active material of one embodiment of the present invention has a high charge voltage. This example also shows that the positive electrode active material of one embodiment of the present invention has a high capacity and excellent cycle characteristics. This example also shows that the positive electrode active material of one embodiment of the present invention has excellent high-temperature characteristics.

[0443] 25A and 26A, it can be seen that the cycle characteristics measured at a temperature of 45° C. for both Sample 1 and Sample 2 have a higher discharge capacity than the cycle characteristics measured at a temperature of 25° C. Comparing FIG. 25B and FIG. 26B, it can be seen that the discharge capacity retention rate measured at a temperature of 25° C. is also higher than that measured at a temperature of 45° C.

[0444] Figure 27A was measured at a charge and discharge rate of 0.5C (1C = 200mA / g), a charge voltage of 4.7V, and a temperature of 25°C. Charging was completed when the current reached 0.05C. Discharging was completed when the voltage reached 2.5V. A rest period was provided between the end of charging and the start of discharging, and between the end of discharging and the start of charging. The rest period was 10 minutes.

[0445] This figure shows the discharge capacity (mAh / g) versus the number of cycles in this cycle test. The vertical axis of Figure 27A shows the discharge capacity (mAh / g), and the horizontal axis shows the number of cycles. Note that the charge voltage is higher than 4.6 V.

[0446] Fig. 27B shows the discharge capacity retention rate obtained from Fig. 27A, with the maximum discharge capacity taken as 100%. The vertical axis represents the discharge capacity retention rate (%), and the horizontal axis represents the number of cycles (times).

[0447] In FIGS. 27A and 27B, the results of Sample 1 are shown by a solid line, the results of Sample 2 are shown by a dashed line, and the results of Sample 3 are shown by a dashed-dotted line.

[0448] 27B, when measured at a temperature of 25° C., the discharge capacity retention rate is maintained at 65% or more and 80% or less for both Sample 1 and Sample 2. Sample 1 more preferably maintains the rate at 70% or more and 85% or less.

[0449] This example shows that the positive electrode active material of one embodiment of the present invention has a high charge voltage and a high capacity and excellent cycle characteristics.

[0450] Figure 28A shows measurements taken at a charge and discharge rate of 0.5C (1C = 200mA / g), a charge voltage of 4.7V, and a temperature of 45°C. Charging was completed when the current reached 0.05C. Discharging was completed when the voltage reached 2.5V. A rest period was provided between the end of charging and the start of discharging, and between the end of discharging and the start of charging. Each rest period was 10 minutes.

[0451] This figure shows the discharge capacity (mAh / g) versus the number of cycles in this cycle test. The vertical axis of Figure 28A shows the discharge capacity (mAh / g), and the horizontal axis shows the number of cycles. Note that the charge voltage is higher than 4.6 V.

[0452] Fig. 28B shows the discharge capacity retention rate determined from Fig. 28A, with the maximum discharge capacity taken as 100%. The vertical axis represents the discharge capacity retention rate (%), and the horizontal axis represents the number of cycles (times), as in Fig. 28A.

[0453] In FIGS. 28A and 28B, the results of Sample 1 are shown by a solid line, the results of Sample 2 are shown by a dashed line, and the results of Sample 3 are shown by a dashed-dotted line.

[0454] As shown in FIG. 28B, when measured at a temperature of 45° C., the discharge capacity retention ratios of both Sample 1 and Sample 2 are maintained at 35% or more and 65% or less.

[0455] This example shows that the positive electrode active material of one embodiment of the present invention has a high charge voltage. This example also shows that the positive electrode active material of one embodiment of the present invention has a high capacity and excellent cycle characteristics. This example also shows that the positive electrode active material of one embodiment of the present invention has excellent high-temperature characteristics.

[0456] 27A and 28A, it can be seen that the cycle characteristics measured at a temperature of 45° C. are higher in discharge capacity than the cycle characteristics measured at a temperature of 25° C. for both Sample 1 and Sample 2. Comparing FIG. 27B and FIG. 28B, it can be seen that the discharge capacity retention rate measured at a temperature of 25° C. is higher than that measured at a temperature of 45° C.

[0457] The cycle characteristics of Samples 4a to 4c are shown in Figures 29 to 32. In Figures 29 to 32, the results for Sample 4a are shown by a solid line, the results for Sample 4b are shown by a dashed line, and the results for Sample 4c are shown by a dashed line. To facilitate comparison of the cycle test conditions, Figures 29 to 32 were set to the same conditions as those shown in Figures 25 to 28, respectively.

[0458] 29A and 29B show the results when the test conditions were a temperature of 25°C and a charging voltage of 4.65V. It can be seen from FIGS. 29A and 29B that Samples 4a to 4c, which contained both Hf and Zr, were positive electrode active materials with superior cycle characteristics compared to Sample 1, which contained only Hf. The characteristics of Sample 4a were particularly favorable.

[0459] 30A and 30B show the results when the test conditions were a temperature of 45°C and a charging voltage of 4.65V. It can be seen from FIGS. 30A and 30B that Samples 4a to 4c, which contain both Hf and Zr, have better cycle characteristics than Sample 1, which contains only Hf. The characteristics of Sample 4c were particularly favorable.

[0460] 31A and 31B show the results when the test conditions were a temperature of 25°C and a charging voltage of 4.7V. It can be seen from FIGS. 31A and 31B that Samples 4a to 4c, which contained both Hf and Zr, were positive electrode active materials with superior cycle characteristics compared to Sample 1, which contained only Hf. The characteristics of Sample 4a were particularly favorable.

[0461] 32A and 32B show the results when the test conditions were a temperature of 45°C and a charging voltage of 4.7V. It can be seen from FIGS. 32A and 32B that Samples 4a to 4c, which contained both Hf and Zr, had better cycle characteristics than Sample 1, which contained only Hf. The characteristics of Samples 4b and 4c were particularly favorable.

[0462] This example shows the cycle characteristics of half cells with a charge voltage of 4.65 V or 4.7 V. This example demonstrates that the positive electrode active material of one embodiment of the present invention can achieve an upper limit of the charge voltage in a cycle test of 4.6 V or higher, thereby providing a secondary battery with a high charge voltage. This example also demonstrates that the positive electrode active material of one embodiment of the present invention has high capacity and excellent cycle characteristics. Furthermore, this example demonstrates that the positive electrode active material of one embodiment of the present invention has excellent high-temperature characteristics.

[0463] In this specification, unless otherwise specified, the voltage is stated for a lithium counter electrode. Even with the same positive electrode, the voltage varies depending on the material used for the negative electrode. For example, when the positive electrode of the present invention is used and graphite is used for the negative electrode, the charging voltage is approximately 0.1 V lower than when a lithium counter electrode is used. [Example]

[0464] In this example, Sample 5 was prepared by adding a Ce source as the Y source, which is an additive element source for lithium cobalt oxide, and Sample 6 was prepared by adding a Sm source. Furthermore, each sample contained an Mg source and an F source as the X source 1, and a Ni source and an Al source as the X source. The sample conditions are shown in the table below.

[0465] [Table 3]

[0466] The manufacturing process for each sample will be described below.

[0467] <Sample 5> In the manufacturing process of Sample 5, the process different from that of Sample 4 is Step S51. In Sample 5, a Ce source was prepared as the Y source. Triisopropoxycerium(III) was prepared as the Ce source, and triisopropoxycerium(III) was weighed so as to be 0.25 mol% with respect to lithium cobaltate. 2-Propanol was prepared as the alcohol. Aluminum isopropoxide and triisopropoxycerium(III) were mixed according to Step S52 to obtain the mixed solution 904 of Step S53.

[0468] In this way, a positive electrode active material 100 was obtained as shown in Step S66 of FIG. 10.

[0469] <SEM Observation> SEM observation of Sample 5 was performed. For EDX measurement, SEM, SU8030 manufactured by Hitachi High-Technologies Corporation was used. The acceleration voltage was set to 5 kV. SEM images of the positive electrode active material of Sample 5 are shown in FIGS. 33A and 33B. Although it is Sample 5 manufactured under the same conditions, in FIGS. 33A and 33B, the external shapes of lithium cobaltate are different. Also, in FIG. 33B, grain boundaries can be confirmed. Common to FIGS. 33A and 33B, convex portions can be confirmed on the surface of lithium cobaltate. Therefore, it can be understood that Sample 5 is lithium cobaltate having convex portions on the surface.

[0470] In FIGS. 33A and 33B, a plurality of convex portions are confirmed. As the plurality of convex portions, at least a first convex portion having a first size and a second convex portion smaller than the first size can be confirmed, and more of the second convex portions can be confirmed than the first convex portion. Also, as can be seen from FIGS. 33A and 33B, no cracks were confirmed in Sample 5.

[0471] The convex portions of Sample 5 contain at least Ce. Ce may be unevenly distributed in the convex portions by the third heating in Step S64. As the elements present in the convex portions, one or more selected from Mg, F, Ni, and Al in addition to Ce are conceivable.

[0472] Sample 5 may have magnesium in the lithium site and may have an O3’ type crystal structure.

[0473] <Sample 6> In the manufacturing process of Sample 6, the process different from that of Sample 5 is Step S51. In Step S51, samarium(III) triisopropoxide was prepared for Sample 6.

[0474] In this way, lithium cobaltate was obtained as the positive electrode active material 100 as shown in Step S66 of FIG. 10.

[0475] <SEM Observation> SEM observation of Sample 6 was performed. The SEM used for the observation was the SEM, S4800 manufactured by Hitachi High-Technologies Corporation. The acceleration voltage was 5 kV. The SEM images of the positive electrode active material of Sample 6 are shown in FIGS. 34A and 34B. Although it is Sample 6 manufactured under the same conditions, in FIGS. 34A and 34B, the external shapes of lithium cobaltate are different. Grain boundaries could not be confirmed in FIGS. 34A and 34B. In common with FIGS. 34A and 34B, convex portions can be confirmed on the surface of lithium cobaltate. Therefore, it can be understood that Sample 6 is lithium cobaltate having convex portions on the surface.

[0476] In FIGS. 34A and 34B, a plurality of convex portions are confirmed. When compared with FIGS. 33A and 33B which are SEM images of the positive electrode active material of Sample 5, in Sample 6, the number of convex portions was small and the size of the convex portions was large. Also, small convex portions (the second convex portion of Sample 5) such as those of Sample 5 were not confirmed in Sample 6. Also, as can be seen from FIGS. 34A and 34B, cracks were not confirmed in Sample 6.

[0477] The convex portions of Sample 6 have at least Sm. Sm may be unevenly distributed in the convex portions by the third heating in Step S64. As elements present in the convex portions, one or more selected from Mg, F, Ni, and Al in addition to Sm are conceivable.

[0478] Sample 6 may have magnesium present in the lithium sites and may have an O3’ type crystal structure.

[0479] <SEM-EDX analysis> Analysis of Sample 5 was performed by SEM-EDX. For the EDX measurement, an apparatus was used in which an EDX unit EX-350X-MaX80 manufactured by Horiba, Ltd. was installed in a SEM, SU8030 manufactured by Hitachi High-Tech Corporation. The acceleration voltage during the EDX measurement was set to 15 kV. Fig. 35A shows a SEM image of Sample 5 which is the object of the EDX measurement.

[0480] Figs. 35B-1 to 35B-4 respectively show element mapping images using EDX surface analysis. In the element mapping images, when it is below the detection limit, it is shown in black, and it is displayed with higher brightness as the count increases.

[0481] Fig. 35B-1 is a mapping image of cobalt, Fig. 35B-2 is a mapping image of cerium, Fig. 35B-3 is a mapping image of aluminum, and Fig. 35B-4 is a mapping image of magnesium.

[0482] From Fig. 35A and Fig. 35B-1, it can be seen that cobalt is present throughout the surface of the positive electrode active material.

[0483] From Fig. 35A and Fig. 35B-2, it can be seen that cerium is present in a smaller amount than cobalt. ]]

[0484] From Fig. 35A and Fig. 35B-3, it can be seen that aluminum is present throughout the surface of the positive electrode active material.

[0485] From Fig. 35A and Fig. 35B-4, it can be seen that magnesium is present throughout the surface of the positive electrode active material.

[0486] In Figure 35A, spectra 1 to 12 are attached to the positive electrode active material, which are the measurement regions of the EDX point analysis. From Figure 35A, it can be seen that some of the measurement regions overlap with the convex portions. The EDX point analysis results for each point are shown in the table below. The detection limit is approximately 1 atomic %. Also, because some elements below the detection limit are not shown, the total does not reach 100%.

[0487] [Table 4]

[0488] Considering the results of Figure 35A, Figures 35B1 to 35B4, and Table 4, it is clear that cerium is present at least on the surface. It is possible that cerium is present in lesser amounts than cobalt, aluminum, and magnesium. Sample 5 is considered to be an active material in which cerium is present on the surface and the EDX analysis shows that the cerium concentration is at least above the lower detection limit and below 3.3 at%. From Figures 35A to 35B2 and Table 4, the range of cerium concentration on the convex surface can be determined.

[0489] The surface aluminum concentration was at the lower limit of detection.

[0490] 35A to 35B4 and Table 4, it is clear that magnesium is present at least on the surface. Sample 5 is considered to be an active material in which magnesium is present on the surface and the EDX analysis shows that the magnesium concentration is at least above the lower detection limit and below 1.7 at%. From FIGS. 35A to 35B4 and Table 4, the range of magnesium concentration on the convex surface can be determined.

[0491] Sample 6 was analyzed by SEM-EDX in the same manner as Sample 5. Figure 36A shows an SEM image of Sample 6, which was the subject of EDX measurement.

[0492] 36B1 to 36B3 show elemental mapping images obtained by EDX area analysis. In the elemental mapping images, values ​​below the detection limit are displayed in black, and the higher the count, the higher the brightness.

[0493] FIG. 36B1 is a mapping image of cobalt, FIG. 36B2 is a mapping image of samarium, and FIG. 36B3 is a mapping image of aluminum.

[0494] It can be seen from FIG. 36A and FIG. 36B1 that cobalt is present over the entire surface of the positive electrode active material.

[0495] From Figures 36A and 36B2, samarium is present in trace amounts compared to cobalt.

[0496] It can be seen from FIG. 36A and FIG. 36B3 that aluminum is present over the entire surface of the positive electrode active material.

[0497] In Figure 36A, spectra 1 to 7 are attached to the positive electrode active material, and these represent the measurement regions of the EDX point analysis. Figure 36A shows that some of the measurement regions overlap with the convex portions. The concentrations of Sm and other elements determined from the EDX point analysis at each point are shown in the table below. The detection limit is approximately 1 atomic %. Also, because some elements below the detection limit are not shown, the total does not reach 100%.

[0498] [Table 5]

[0499] Considering the results of Figure 36A and Figures 36B1 to 36B3, it is clear that samarium is present at least on the surface. Samarium may be present in smaller amounts than cobalt and aluminum. Based on Table 5, the concentration of samarium on the surface is considered to be at least above the detection limit and below 35.1 at%.

[0500] The surface aluminum concentration was below the detection limit.

[0501] The surface magnesium concentration was below the detection limit.

[0502] <Cycle test> A half-cell type coin cell was fabricated using Sample 5 and Sample 6, and a cycle test was carried out. The half-cell type coin cell was fabricated in the same manner as in Example 1.

[0503] The cycle characteristics for Samples 5 and 6 are shown in FIGS.

[0504] Figure 37A shows measurements taken at a charge and discharge rate of 0.5C (1C = 200mA / g), a charge voltage of 4.65V, and a temperature of 25°C. Charging was completed when the current reached 0.05C. Discharging was completed when the voltage reached 2.5V. A rest period was provided between the end of charging and the start of discharging, and between the end of discharging and the start of charging. Each rest period was 10 minutes.

[0505] This figure shows the discharge capacity (mAh / g) versus the number of cycles in this cycle test. The vertical axis of Figure 37A shows the discharge capacity (mAh / g), and the horizontal axis shows the number of cycles. Note that the charge voltage is higher than 4.6 V.

[0506] Fig. 37B shows the discharge capacity retention rate obtained from Fig. 37A, where the maximum discharge capacity is set to 100%. In Fig. 37B, the vertical axis represents the discharge capacity retention rate (%), and the horizontal axis represents the number of cycles (times).

[0507] In Figures 37A and 37B, the results for Sample 5 are shown by a solid line, and the results for Sample 6 are shown by a dashed line.

[0508] 37B, when measured at a temperature of 25° C., the discharge capacity retention ratio was 80% or more and 95% or less for both Sample 5 and Sample 6. Sample 5 was more preferable, with a discharge capacity retention ratio of 90% or more and 95% or less.

[0509] This example shows that the positive electrode active material of one embodiment of the present invention has a high charge voltage and a high capacity and excellent cycle characteristics.

[0510] Figure 38A shows measurements taken at a charge and discharge rate of 0.5C (1C = 200mA / g), a charge voltage of 4.65V, and a temperature of 45°C. Charging was completed when the current reached 0.05C. Discharging was completed when the voltage reached 2.5V. A rest period was provided between the end of charging and the start of discharging, and between the end of discharging and the start of charging. Each rest period was 10 minutes.

[0511] This graph shows the discharge capacity (mAh / g) versus the number of cycles in this cycle test. The vertical axis of Figure 38A shows the discharge capacity (mAh / g), and the horizontal axis shows the number of cycles. Note that the charging voltage was higher than 4.6 V and the temperature was 45°C, which is higher than 25°C.

[0512] Fig. 38B shows the discharge capacity retention rate obtained from Fig. 38A, where the maximum discharge capacity is set to 100%. In Fig. 38B, the vertical axis represents the discharge capacity retention rate (%), and the horizontal axis represents the number of cycles (times).

[0513] In Figures 38A and 38B, the results for Sample 5 are shown by a solid line, and the results for Sample 6 are shown by a dashed line.

[0514] As shown in FIG. 38B, when measured at a temperature of 45° C., the discharge capacity retention rates of both Sample 5 and Sample 6 were 60% or more and 80% or less.

[0515] This example shows that the positive electrode active material of one embodiment of the present invention has a high charge voltage. This example also shows that the positive electrode active material of one embodiment of the present invention has a high capacity and excellent cycle characteristics. This example also shows that the positive electrode active material of one embodiment of the present invention has excellent high-temperature characteristics.

[0516] 37A and 38A, it can be seen that for both Sample 5 and Sample 6, the cycle characteristics measured at a temperature of 25° C. have a higher discharge capacity than those measured at a temperature of 45° C. Comparing FIG. 37B and FIG. 38B, it can be seen that the discharge capacity retention ratio measured at a temperature of 25° C. is also higher than that measured at a temperature of 45° C.

[0517] Figure 39A was measured at a charge and discharge rate of 0.5C (1C = 200mA / g), a charge voltage of 4.7V, and a temperature of 25°C. Charging was completed when the current reached 0.05C. Discharging was completed when the voltage reached 2.5V. A rest period was provided between the end of charging and the start of discharging, and between the end of discharging and the start of charging. The rest period was 10 minutes.

[0518] This figure shows the discharge capacity (mAh / g) versus the number of cycles in this cycle test. The vertical axis of Figure 39A shows the discharge capacity (mAh / g), and the horizontal axis shows the number of cycles. Note that the charge voltage is higher than 4.6 V.

[0519] Fig. 39B shows the discharge capacity retention rate obtained from Fig. 39A, where the maximum discharge capacity is set to 100%. In Fig. 39B, the vertical axis represents the discharge capacity retention rate (%), and the horizontal axis represents the number of cycles (times).

[0520] In Figures 39A and 39B, the results for Sample 5 are shown by a solid line, and the results for Sample 6 are shown by a dashed line.

[0521] 39B, when measured at a temperature of 25° C., the discharge capacity retention rate was 75% or more and 90% or less for both Sample 5 and Sample 6. Sample 6 was more preferable, being 85% or more and 90% or less.

[0522] This example shows that the positive electrode active material of one embodiment of the present invention has a high charge voltage and a high capacity and excellent cycle characteristics.

[0523] Figure 40A was measured at a charge and discharge rate of 0.5C (1C = 200mA / g), a charge voltage of 4.7V, and a temperature of 45°C. Charging was completed when the current reached 0.05C. Discharging was completed when the voltage reached 2.5V. A rest period was provided between the end of charging and the start of discharging, and between the end of discharging and the start of charging. The rest period was 10 minutes.

[0524] This figure shows the discharge capacity (mAh / g) versus the number of cycles in this cycle test. The vertical axis of Figure 40A shows the discharge capacity (mAh / g), and the horizontal axis shows the number of cycles. Note that the charge voltage is higher than 4.6 V.

[0525] Fig. 40B shows the discharge capacity retention rate obtained from Fig. 40A, where the maximum discharge capacity is set to 100%. In Fig. 40B, the vertical axis represents the discharge capacity retention rate (%), and the horizontal axis represents the number of cycles (times).

[0526] In Figures 40A and 40B, the results for Sample 5 are shown by a solid line, and the results for Sample 6 are shown by a dashed line.

[0527] As shown in FIG. 40B, when measured at a temperature of 45° C., the discharge capacity retention ratios of both Sample 5 and Sample 6 were 40% or more and 55% or less.

[0528] This example shows that the positive electrode active material of one embodiment of the present invention has a high charge voltage. This example also shows that the positive electrode active material of one embodiment of the present invention has a high capacity and excellent cycle characteristics. This example also shows that the positive electrode active material of one embodiment of the present invention has excellent high-temperature characteristics.

[0529] 39A and 40A, it can be seen that the discharge capacity of both Sample 5 and Sample 6 measured at 25° C. is higher than that measured at 45° C. Comparing FIG. 39B and FIG. 40B, it can be seen that the discharge capacity retention rate measured at 25° C. is also higher than that measured at 45° C.

[0530] In this example, cycle characteristics using half cells with charge voltages of 4.65 V or 4.7 V were shown. According to this example, the positive electrode active material of one embodiment of the present invention can achieve an upper limit of charge voltage of 4.6 V or higher in a cycle test, thereby providing a secondary battery with a high charge voltage. This example also demonstrates that the positive electrode active material of one embodiment of the present invention has high capacity and excellent cycle characteristics. Furthermore, this example demonstrates that the positive electrode active material of one embodiment of the present invention has excellent high-temperature characteristics.

[0531] In this specification, unless otherwise specified, the voltage is stated for a lithium counter electrode. Even with the same positive electrode, the voltage varies depending on the material used for the negative electrode. For example, when the positive electrode of the present invention is used and graphite is used for the negative electrode, the voltage is about 0.1 V lower than when a lithium counter electrode is used. [Explanation of symbols]

[0532] 100: positive electrode active material, 101: first particle, 102: protrusion, 103: protrusion, 104: protrusion, 105: grain boundary, 106: surface layer

Claims

1. A negative electrode and a positive electrode are provided, the positive electrode has a plurality of positive electrode active material particles, the positive electrode active material particles contain lithium cobalt oxide, the positive electrode active material particles contain impurity elements, the impurity element includes at least one or more selected from Hf, V, Nb, Zr, Ce, and Sm; The lithium ion secondary battery, wherein the concentration of the additive element is higher in the protrusions of the positive electrode active material particles than in the interior of the positive electrode active material particles.

2. A negative electrode and a positive electrode are provided, the positive electrode has a plurality of positive electrode active material particles, the positive electrode active material particles contain lithium cobalt oxide, the positive electrode active material particles contain a first impurity element and a second impurity element, the first additional element includes at least one or more selected from Hf, V, Nb, Zr, Ce, and Sm, and the second impurity element includes Mg; a concentration of the first additional element is higher in the protrusions of the positive electrode active material particles than in the interior of the positive electrode active material particles; a concentration of the second impurity element being higher in a surface layer portion of the positive electrode active material particle than in an interior portion of the positive electrode active material particle;

3. A negative electrode and a positive electrode are provided, the positive electrode has a plurality of positive electrode active material particles, the positive electrode active material particles contain lithium cobalt oxide, the positive electrode active material particles contain a first impurity element and a second impurity element, the first additive element includes at least one or more selected from Hf, V, Nb, Zr, Ce, and Sm, and the second impurity element includes Mg and F; a concentration of the first additional element is higher in the protrusions of the positive electrode active material particles than in the interior of the positive electrode active material particles; a concentration of the second impurity element being higher in a surface layer portion of the positive electrode active material particle than in an interior portion of the positive electrode active material particle;

4. In any one of claims 1 to 3, the negative electrode has a negative electrode active material, The negative electrode active material comprises graphite and silicon.

Images