Lithium ion secondary battery

Abstract

To provide a positive electrode active material in which the decrease in discharge capacity during charge / discharge cycles is suppressed, and a secondary battery using the same.SOLUTION: A positive electrode active material exhibits minimal change in a crystal structure between the discharged state and the high-voltage charged state, e.g., minimal shift in the CoO2 layer. For example, this positive electrode active material has a layered rock-salt crystal structure in the space group R-3m in the discharged state, and a crystal structure belonging to the space group P2 / m in the charged state, and x in LixCoO2 is greater than 0.1 and less than or equal to 0.24. When analyzed by powder X-ray diffraction, the diffraction pattern exhibits peaks at least at 2θ=19.47±0.10° and 2θ=45.62±0.05°.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] One aspect of the present invention relates to an article, a method, or a manufacturing method. , machine, manufacture, or composition of matter One embodiment of the present invention is a power storage device including a secondary battery, a semiconductor device, a display device, a light-emitting device, a lighting device, a The present invention relates to a device, an electronic device, or a method for manufacturing the same.

[0002] In this specification, the term "electronic device" refers to any device having a power storage device. Electro-optical devices having a power storage device, and information terminal devices having a power storage device are all electronic devices. [Background technology]

[0003] In recent years, lithium-ion secondary batteries, lithium-ion capacitors, air batteries, all-solid-state batteries, etc. In particular, the development of various types of energy storage devices is being actively pursued. Demand for rechargeable batteries has rapidly expanded along with the development of the semiconductor industry, and It has become an indispensable source of information in today's information society.

[0004] In particular, secondary batteries for mobile electronic devices have a large discharge capacity per weight, and There is a high demand for secondary batteries with excellent recycling characteristics. There have been many efforts to improve positive electrode active materials (for example, Patent Documents 1 to 3). In addition, research on the crystal structure of positive electrode active materials is also being conducted (Non-Patent Documents 1 to 3 ).

[0005] X-ray diffraction (XRD) is one of the methods used to analyze the crystalline structure of positive electrode active materials. ICSD (Inorganic Crystal Sulfide) introduced in Non-Patent Document 4 XRD data is analyzed using the Structure Database. For the Rietveld analysis, for example, the analysis program RIETAN-F P (Non-Patent Document 5) can be used. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-179758 [Patent Document 2] WO2020 / 026078 Brochure [Patent Document 3] Japanese Patent Publication No. 2020-140954 [Non-patent literature]

[0007] [Non-Patent Document 1] Toyoki Okumura et al, “Correlation of lithium ion distribution and X-ray absorption near-edge structure in O3-and O2-lithium cobalt oxides from first-principle calculation”, Journal of Materials Chemistry, 2012, 22, p.17340-17348 [Non-patent document 2] Motohashi, T. et al, “Electronic phase diagram of the layered cobalt oxide system LixCoO2 (0.0≦x≦1.0)”, Physical Review B, 80(16);165114 [Non-patent document 3] Zhaohui Chen et al, “Staging Phase Transitions in LixCoO2”, Journal of The Electrochemical Society, 2002, 149(12) A1604-A1609 [Non-patent document 4] Belsky, A. et al., “New developments in the Inorganic Crystal Structure Database (ICSD): accessibility in support of materials research and design”, Acta Cryst., (2002) B58 364-369. [Non-Patent Document 5] F.Izumi and K.Momma,Solid State Phenom.,130,15-20(2007) [Non-patent document 6] Rasband, WS, ImageJ, US National Institutes of Health, Bethesda, Maryland, USA, http: / / rsb.info.nih.gov / ij / , 1997-2012. [Non-Patent Document 7] Schneider, CA, Rasband, WS, Eliceiri, KW ``NIH Image to ImageJ: 25 years of image analysis''. Nature Methods 9, 671-675, 2012. [Non-patent document 8] Abramoff, MD, Magelhaes, PJ, Ram, SJ ``Image Processing with ImageJ''. Biophotonics International, volume 11, issue 7, pp. 36-42, 2004. Summary of the Invention [Problem to be solved by the invention]

[0008] Lithium-ion secondary batteries have many advantages, such as discharge capacity, cycle characteristics, reliability, safety, and cost. There is still room for improvement in many areas.

[0009] Therefore, the positive electrode active material used in this battery also has the potential to improve discharge capacity and cycle life when used in a secondary battery. There is a demand for materials that can improve issues such as drive characteristics, reliability, safety, and cost.

[0010] One embodiment of the present invention can be used in a lithium ion secondary battery, and One of the objectives of the present invention is to provide a positive electrode active material or composite oxide in which the decrease in discharge capacity is suppressed. Alternatively, a positive electrode active material or composite oxide whose crystalline structure is resistant to collapse even after repeated charge and discharge Another object of the present invention is to provide a positive electrode active material or composite acid having a large discharge capacity. Another object of the present invention is to provide a safe and highly reliable secondary battery. One of the goals is to

[0011] Another embodiment of the present invention is a positive electrode active material, a composite oxide, a power storage device, or a manufacturing method thereof. One of our goals is to provide

[0012] The description of these problems does not preclude the existence of other problems. It is not necessary for one embodiment to solve all of these problems. It is possible to extract other problems from the claims. [Means for solving the problem]

[0013] In order to solve the above problem, one aspect of the present invention is to charge a battery at a high voltage and x CoO2 To provide a positive electrode active material or composite oxide in which the change in crystal structure is small even when x in the Let's say.

[0014] Alternatively, in one aspect of the present invention, the charging voltage is 4.6 V or more and 4.8 V or less, or Li x CoO In 2, x is greater than 0.1 and less than 0.24, typically between 0.15 and 0.17. Even when the CoO2 layer is displaced, the crystal structure is different from the H1-3 type crystal structure and the displacement of the CoO2 layer is suppressed. The present invention provides a positive electrode active material.

[0015] More specifically, one aspect of the present invention is to provide a layered rock salt crystal of the space group R-3m when in a discharged state. It has a crystal structure and Li x When x in CoO2 is greater than 0.1 and less than 0.24, Space group P2 / m, lattice constant a=4.88±0.01Å, b=2.82±0.01Å, c= Crystals with 4.84±0.01Å, α=90°, β=109.58±0.01°, γ=90° It is a positive electrode active material having the structure.

[0016] Also, in the above, Li x x in CoO2 is greater than 0.1 and less than 0.24 in charge state The crystal structure is such that the coordinates of cobalt and oxygen in the unit cell are Co1(0.5,0 ,0.5), Co2(0,0.5,0.5), O1(0.232,0,0.645), O 2(0.781, 0.5, 0.679), is preferable.

[0017] Another aspect of the present invention is that, in a discharged state, the crystal structure has a layered rock salt structure of the space group R-3m. Li x When x in CoO2 is greater than 0.1 and less than 0.24, powder X When analyzed by X-ray diffraction, the diffraction pattern showed at least 2θ of 19.37° to 19.57°. and a positive electrode active material having a peak at 45.57° or more and 45.67° or less.

[0018] Another aspect of the present invention is that, in a discharged state, the crystal structure has a layered rock salt structure of the space group R-3m. Li x When x in CoO2 is greater than 0.1 and less than 0.24, powder X When analyzed by X-ray diffraction, the diffraction pattern showed that 2θ was at least 19.13° or more and less than 19.37°. 19.37° to 19.57°, 45.37° to 45.57°, and 4 This is a positive electrode active material having peaks at angles of 5.57° or more and 45.67° or less.

[0019] Another embodiment of the present invention is a positive electrode active material containing lithium cobalt oxide, When a battery is fabricated using the active material as the positive electrode and lithium metal as the negative electrode, the battery can be used for 4.7 hours. After CCCV charging multiple times at voltages above 100V, the positive electrode of the battery was charged with CuK in an argon atmosphere. When analyzed by powder X-ray diffraction using α1 radiation, the XRD pattern must be at least 2θ=19.4 7±0.10° and 2θ=45.62±0.05°. It's quality.

[0020] Another embodiment of the present invention is a positive electrode active material containing lithium cobalt oxide, The material is used as the positive electrode, lithium metal is used as the negative electrode, and 1 mol / L of lithium hexafluorophosphate is used. and ethylene carbonate (EC) and diethyl carbonate (DEC) in the ratio EC:DEC= The electrolyte used was a mixture containing 2 wt% vinylene carbonate (VC) at a volume ratio of 3:7. When the battery was manufactured, the battery was placed in a 45°C environment and the current value was 1 After charging at a constant current of 0 mA / g, the positive electrode was powdered using CuKα1 radiation in an argon atmosphere. When analyzed by X-ray diffraction, the XRD pattern showed at least 2θ=19.47±0.10°, and a diffraction peak at 2θ=45.62±0.05°.

[0021] Another embodiment of the present invention is a positive electrode active material containing lithium cobalt oxide, The material was analyzed by Raman spectroscopy using a laser wavelength of 532 nm and an output of 2.5 mW. For the integrated intensity, 580cm -1 ~600cm -1 I2, 665cm -1 ~68 5cm -1 When I3 is taken as I3, the value of I3 / I2 is 1% or more and 10% or less. is.

[0022] In the above, the transition metal M contained in the positive electrode active material is 90 atomic % or more of cobalt. It is preferable that

[0023] In the above, the H1-3 type and O1 type crystal structures account for 50% or less of the positive electrode active material. It is preferable.

[0024] In the above, the positive electrode active material has magnesium, nickel, and aluminum as a surface layer. It is preferable that the ion exchange resin is contained in the part.

[0025] In the above, the positive electrode active material is found to be The peaks of magnesium and nickel concentrations are more positive than the peak of aluminum concentration. It is preferable that the electrode be located on the surface side of the electrode active material. [Effects of the Invention]

[0026] According to one embodiment of the present invention, the present invention can be used in a lithium-ion secondary battery, and the charge-discharge cycle It is possible to provide a positive electrode active material or composite oxide in which the decrease in discharge capacity is suppressed. Alternatively, a positive electrode active material or composite oxide whose crystal structure is resistant to breakdown even after repeated charge and discharge is used. Alternatively, a positive electrode active material or a composite oxide having a large discharge capacity can be provided. Alternatively, a secondary battery with high safety and reliability can be provided.

[0027] According to one embodiment of the present invention, a positive electrode active material, a composite oxide, a power storage device, or a manufacturing method thereof It can provide a law.

[0028] The description of these effects does not preclude the existence of other effects. An embodiment does not necessarily have to have all of these effects. The above will be made clear from the description, drawings, claims, etc. It is possible to extract other effects from the descriptions in the aspects and claims. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1(A) is a cross-sectional view of the positive electrode active material, and FIG. 1(B1) and FIG. 1(B2) are part of the cross-sectional view of the positive electrode active material. [Figure 2] Figure 2 shows an example of a TEM image in which the crystal orientation is roughly consistent. [Figure 3] Figure 3(A) is an example of a STEM image in which the crystal orientations are roughly consistent. Figure 3(B) is an FFT pattern of the rock-salt-type crystal RS region, and Figure 3(C) is an FFT pattern of the layered rock-salt-type crystal LRS region. [Figure 4] FIG. 4 is a diagram illustrating the crystal structure of the positive electrode active material. [Figure 5] FIG. 5 is a diagram illustrating the crystal structure of a conventional positive electrode active material. [Figure 6]Figures 6(A1) and 6(A2) are partial cross-sectional views of the positive electrode active material, and Figures 6(B1) to 6(C) show the results of calculations of the crystal planes and magnesium distribution of lithium cobalt oxide. [Figure 7] 7(A) and 7(B) are cross-sectional views of the positive electrode active material, and FIG. 7(C1) and FIG. 7(C2) are partial cross-sectional views of the positive electrode active material. [Figure 8] FIG. 8 shows an XRD pattern calculated from the crystal structure. [Figure 9] FIG. 9 shows the XRD pattern calculated from the crystal structure. [Figure 10] 10(A) and 10(B) are diagrams showing XRD patterns calculated from the crystal structure. [Figure 11] 11(A) to 11(C) show the lattice constants calculated from XRD. [Figure 12] 12(A) to 12(C) show the lattice constants calculated from XRD. [Figure 13] FIG. 13 is a cross-sectional view of the positive electrode active material. [Figure 14] FIG. 14 is a cross-sectional view of the positive electrode active material. [Figure 15] 15A to 15C are diagrams illustrating a method for manufacturing a positive electrode active material. [Figure 16] FIG. 16 is a diagram illustrating a method for producing a positive electrode active material. [Figure 17] 17A to 17C are diagrams illustrating a method for manufacturing a positive electrode active material. [Figure 18] 18(A) and 18(B) are cross-sectional views of an active material layer in the case where graphene or a graphene compound is used as the conductive material. [Figure 19] 19(A) and 19(B) are diagrams illustrating an example of a secondary battery. [Figure 20] 20A to 20C are diagrams illustrating examples of secondary batteries. [Figure 21] 21(A) and 21(B) are diagrams illustrating an example of a secondary battery. [Figure 22]22(A) and 22(B) are diagrams illustrating a coin-type secondary battery, and Fig. 22(C) is a diagram illustrating charging and discharging of a secondary battery. [Figure 23] 23(A) to 23(D) are diagrams illustrating a cylindrical secondary battery. [Figure 24] 24A and 24B are diagrams illustrating examples of a power storage device. [Figure 25] 25A to 25D illustrate examples of a power storage device. [Figure 26] 26(A) and 26(B) are diagrams illustrating an example of a secondary battery. [Figure 27] FIG. 27 is a diagram illustrating an example of a secondary battery. [Figure 28] 28(A) to 28(C) are diagrams illustrating a laminated secondary battery. [Figure 29] 29(A) and 29(B) are diagrams illustrating a laminated secondary battery. [Figure 30] FIG. 30 is a diagram showing the appearance of a secondary battery. [Figure 31] FIG. 31 is a diagram showing the appearance of a secondary battery. [Figure 32] 32A to 32C are diagrams illustrating a method for manufacturing a secondary battery. [Figure 33] 33A to 33H are diagrams illustrating examples of electronic devices. [Figure 34] 34A to 34C are diagrams illustrating examples of electronic devices. [Figure 35] FIG. 35 is a diagram illustrating an example of an electronic device. [Figure 36] 36A to 36D are diagrams illustrating examples of electronic devices. [Figure 37] 37A to 37C are diagrams showing examples of electronic devices. [Figure 38] 38(A) to 38(C) are diagrams illustrating an example of a vehicle. [Figure 39]39(A) to 39(F) are SEM images of the surface of the positive electrode active material. [Figure 40] 40(A) to 40(H) are SEM images of the surface of the positive electrode active material. [Figure 41] 41(A) and 41(B) are HAADF-STEM images of the positive electrode active material. [Figure 42] 42(A) and 42(B) are HAADF-STEM images of the positive electrode active material. [Figure 43] 43(A) and 43(B) are HAADF-STEM images of the positive electrode active material. [Figure 44] Figure 44(A) and Figure 44(B) are electron microbeam diffraction patterns. [Figure 45] Figure 45(A) and Figure 45(B) are electron microbeam diffraction patterns. [Figure 46] Figure 46(A) and Figure 46(B) are electron microbeam diffraction patterns. [Figure 47] Figure 47(A) is an HAADF-STEM image of the positive electrode active material, Figure 47(B) is a cobalt mapping image, Figure 47(C) is an oxygen mapping image, Figure 47(D) is a magnesium mapping image, Figure 47(E) is an aluminum mapping image, and Figure 47(F) is a silicon mapping image. [Figure 48] FIG. 48(A) is a diagram showing the scanning method for STEM-EDX line analysis, and FIG. 48(B) is a profile of the STEM-EDX line analysis. [Figure 49] FIG. 49 is an enlarged view of a part of FIG. 48(B). [Figure 50] Figure 50(A) and Figure 50(B) are HAADF-STEM images of the positive electrode active material. [Figure 51] Figure 51(A) and Figure 51(B) are electron microbeam diffraction patterns. [Figure 52] Figure 52(A) and Figure 52(B) are electron microbeam diffraction patterns. [Figure 53] Figure 53(A) and Figure 53(B) are electron microbeam diffraction patterns. [Figure 54]Figure 54(A) is an HAADF-STEM image of the positive electrode active material, Figure 54(B) is a silicon mapping image, Figure 54(C) is an oxygen mapping image, Figure 54(D) is a magnesium mapping image, Figure 54(E) is an aluminum mapping image, and Figure 54(F) is a nickel mapping image. [Figure 55] FIG. 55(A) is a diagram showing the scanning method for STEM-EDX line analysis, and FIG. 55(B) is a profile of the STEM-EDX line analysis. [Figure 56] FIG. 56 is an enlarged view of a part of FIG. 55(B). [Figure 57] Figure 57(A) and Figure 57(B) are HAADF-STEM images of the positive electrode active material. [Figure 58] 58(A) and 58(B) show the measurement results of the particle size distribution of the positive electrode active material. [Figure 59] 59(A) to 59(C) are SEM images of the surface of the positive electrode active material. [Figure 60] 60(A) to 60(C) are graphs showing the distribution of grayscale values ​​of positive electrode active materials. [Figure 61] 61(A) to 61(C) are luminance histograms of the positive electrode active material. [Figure 62] 62(A) to 62(D) are graphs showing the cycle characteristics of the secondary battery. [Figure 63] 63(A) to 63(D) are graphs showing the cycle characteristics of the secondary battery. [Figure 64] 64(A) to 64(D) are graphs showing the cycle characteristics of the secondary battery. [Figure 65] 65(A) to 65(D) are graphs showing the cycle characteristics of the secondary battery. [Figure 66] 66(A) and 66(B) are graphs showing the cycle characteristics of the secondary battery. [Figure 67] Figure 67(A) is a photograph of the pellet, and Figure 67(B) and Figure 67(C) are SEM images of the surface of the positive electrode active material. [Figure 68]FIG. 68(A) is a surface SEM image of the positive electrode active material, and FIG. 68(B) is a cross-sectional STEM image of the positive electrode active material. [Figure 69] Figures 69(A1) and 69(B1) are cross-sectional HAADF-STEM images of the positive electrode active material, and Figures 69(A2) to 69(A4) and Figures 69(B2) to 69(B4) are EDX mapping images. [Figure 70] FIG. 70 shows the dQ / dV vs. V curve of a secondary battery. [Figure 71] FIG. 71 shows the dQ / dV vs. V curve of a secondary battery. [Figure 72] FIG. 72 shows the dQ / dV vs. V curve of a secondary battery. [Figure 73] FIG. 73 shows the dQ / dV vs. V curve of a secondary battery. [Figure 74] Figure 74 shows the XRD pattern of the positive electrode. [Figure 75] 75(A) and 75(B) are enlarged XRD patterns of a part of FIG. 74. [Figure 76] Figure 76 shows the XRD pattern of the positive electrode. [Figure 77] 77(A) and 77(B) are enlarged XRD patterns of a part of FIG. [Figure 78] Figure 78 shows the XRD pattern of the positive electrode. [Figure 79] 79(A) and 79(B) are enlarged XRD patterns of a part of FIG. 78. [Figure 80] Figure 80 shows the XRD pattern of the positive electrode. [Figure 81] 81(A) and 81(B) are enlarged XRD patterns of a part of FIG. [Figure 82] Figure 82 shows the XRD pattern of the positive electrode. [Figure 83] 83(A) and 83(B) are enlarged XRD patterns of a part of FIG. [Figure 84] Figure 84 shows the XRD pattern of the positive electrode. [Figure 85]85(A) and 85(B) are enlarged XRD patterns of a part of FIG. [Figure 86] Figure 86 shows the XRD pattern of the positive electrode. [Figure 87] 87(A) and 87(B) are enlarged XRD patterns of a part of FIG. [Figure 88] Figure 88 shows the XRD pattern of the positive electrode. [Figure 89] 89(A) and 89(B) are enlarged XRD patterns of a part of FIG. 88. [Figure 90] Figure 90 shows the XRD pattern of the positive electrode. [Figure 91] 91(A) and 91(B) are enlarged XRD patterns of a part of FIG. [Figure 92] FIG. 92 is a diagram relating to powder resistivity measurement. [Figure 93] FIG. 93 is a graph showing the discharge curve measured by the current rest method. [Figure 94] FIG. 94 shows a method for analyzing current resting method measurements. [Figure 95] 95(A) and 95(B) are diagrams showing the analysis results of the current rest method measurement. [Figure 96] FIG. 96 shows the analysis results of the current rest method measurement. [Figure 97] Figures 97(A) and 97(B) show the Raman spectra of the positive electrode active material. [Figure 98] FIG. 98(A) is the Raman spectrum of the positive electrode active material, and FIG. 98(B) is the Raman spectrum of the positive electrode. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The present invention should not be construed as being limited to the following embodiments. The mode of carrying out the invention can be changed within the scope of the present invention.

[0031] In this specification, the space group is represented by the international notation (or Hermann-Mauguin notation) S The crystal plane and the crystal structure are expressed using Miller indices. The individual faces that indicate crystal faces are written in parentheses. Space groups, crystal faces, and In crystallography, the notation of the crystal direction is given by adding a superscript bar to the number, but in this specification, there is no restriction on the format. For the sake of convenience, instead of putting a bar above the number, put a minus sign (-) before the number. Also, individual directions that indicate directions within a crystal are shown in [ ], and a collective direction that indicates all equivalent directions is shown in [ ]. The composite orientation is indicated by < >, the individual faces representing the crystal faces are indicated by ( ), and the collective faces with equivalent symmetry are indicated by { The trigonal crystal, which is expressed in the space group R-3m, is easy to understand the structure. Therefore, it is generally expressed as a hexagonal complex hexagonal lattice, and the Miller indices are not only (hkl) but also Sometimes we use (hkil), where i is -(h+k).

[0032] In this specification, particles are not limited to those having a spherical shape (a circular cross section). , the cross-sectional shape of individual particles is elliptical, rectangular, trapezoidal, triangular, square with rounded corners, asymmetric Furthermore, each particle may have an irregular shape.

[0033] The theoretical capacity of the positive electrode active material is the capacity when all of the intercalable lithium contained in the positive electrode active material is deintercalated. For example, the theoretical capacity of LiCoO2 is 274mAh / g, The theoretical capacity of NiO2 is 274mAh / g, and that of LiMn2O4 is 148mAh / g is.

[0034] The amount of lithium remaining in the positive electrode active material that can be inserted or removed is determined by the x , for example, Lix In the case of the positive electrode active material in a secondary battery, x = (theoretical volume For example, when LiCoO2 is used as the positive electrode active material, the theoretical capacity can be calculated as follows: When a secondary battery is charged at 219.2mAh / g, Li 0.2 CoO2 or x=0. 2. Li x A small value of x in CoO2 is, for example, 0.1 <x≦0. It means 24.

[0035] Before being used in the positive electrode, properly synthesized lithium cobalt oxide approximately satisfies the stoichiometric ratio. In this case, the cobalt contained in the secondary battery after discharge is LiCoO2 and x=1. Lithium oxide is also LiCoO2, so x = 1. For example, when the current is less than 100mAh and the voltage is less than 3.0V or 2.5V This refers to

[0036] Li x The charge and / or discharge capacity used to calculate x in CoO2 is the short circuit and It is preferable to measure under conditions where there is little or no influence from decomposition of the electrolyte, etc. Data on secondary batteries that have experienced a sudden change in capacity, which may be due to a short circuit, should not be used to calculate x. Not possible.

[0037] The space group of the crystal structure is identified by XRD, electron diffraction, neutron diffraction, etc. Therefore, in this specification and the like, "belonging to a certain space group," "belonging to a certain space group," or Being in a certain space group can be rephrased as being identified with a certain space group.

[0038] If the anions have a structure like ABCABC, where three layers are stacked with each other, Therefore, the anions do not need to be in a strictly cubic lattice. At the same time, since real crystals always have defects, analytical results do not necessarily match the theory. For example, electron diffraction patterns or FFT (Fast Fourier Transform) patterns such as TEM images In this case, the spot may appear at a position slightly different from the theoretical position. If the orientation with respect to the position is less than 5 degrees or less than 2.5 degrees, it is said to have a cubic close-packed structure. good.

[0039] Homogeneity means that in a solid consisting of multiple elements (e.g., A, B, C), a certain element (e.g., For example, A) is a phenomenon in which a certain area is distributed with similar characteristics. The concentration of the elements must be substantially the same. For example, the difference in the concentration of elements between specific regions is 10%. The specific region may be, for example, a surface layer, a surface, a convex portion, a concave portion, or an interior portion. Examples include:

[0040] In addition, the positive electrode active material to which the additive element is added is called a composite oxide, a positive electrode material, a positive electrode material for secondary batteries, etc. In this specification and the like, the positive electrode active material of one embodiment of the present invention may be referred to as a positive electrode material. In this specification and the like, the positive electrode active material according to one embodiment of the present invention preferably includes a compound. The substance preferably has a composition. The electrode active material preferably has a composite.

[0041] In addition, when describing the characteristics of individual particles of the positive electrode active material in the following embodiments, etc., However, not all particles need to have this characteristic. For example, if three or more particles are randomly selected, Of the particles of the positive electrode active material, 50% or more, preferably 70% or more, more preferably 90% or more If the above has the characteristics, the properties of the positive electrode active material and the secondary battery having the same can be sufficiently improved. It can be said that this has the effect of raising

[0042] As the charging voltage of the secondary battery increases, the voltage of the positive electrode generally increases. The positive electrode active material has a stable crystal structure even at high voltages. The stable crystalline structure of the material prevents the decrease in charge / discharge capacity due to repeated charging / discharging. It is possible.

[0043] In addition, a short circuit in the secondary battery may cause malfunctions in the charging and / or discharging operations of the secondary battery. This not only causes a malfunction but also may lead to heat generation and fire. In order to achieve this, it is preferable that the short circuit current be suppressed even at a high charging voltage. In the positive electrode active material of this embodiment, short-circuit current is suppressed even at a high charging voltage. A secondary battery that combines high discharge capacity with safety can be obtained.

[0044] Unless otherwise specified, the materials contained in the secondary battery (positive electrode active material, negative electrode active material, electrolyte, The description of the state of the secondary battery (separator, etc.) before deterioration will be given. The decrease in discharge capacity due to aging and burn-in treatment is not considered degradation. For example, lithium ion secondary cells and lithium ion secondary batteries (hereinafter referred to as lithium-ion secondary battery) has a discharge capacity of 97% or more of its rated capacity. In this case, it can be said that the battery is in a state before deterioration. Secondary batteries comply with JIS C 8711:2019. Other lithium-ion In the case of secondary batteries, in addition to the above JIS standards, other JIS and IE standards for electric vehicle propulsion and industrial use are also applicable. Complies with C standards, etc.

[0045] In this specification, the state of the materials of a secondary battery before deterioration is referred to as an initial product, or This is called the initial state, and the state after deterioration (a secondary battery with a discharge capacity of less than 97% of its rated capacity) (condition in case) as a used item or in a used state, or as a used item or in a used state It may be referred to as.

[0046] (Embodiment 1) In this embodiment, a positive electrode active material 100 of one embodiment of the present invention will be described with reference to FIGS. I will explain.

[0047] FIG. 1A is a cross-sectional view of a positive electrode active material 100 according to one embodiment of the present invention. Enlarged views of the area around AB are shown in Figure 1(B1) and Figure 1(B2).

[0048] As shown in FIGS. 1(A) to 1(B2), the positive electrode active material 100 includes a surface layer 100a and In these figures, the boundary between the surface layer 100a and the interior 100b is indicated by a dashed line. In addition, part of the grain boundary 101 is shown by a dashed line in FIG. 1(A).

[0049] In this specification, the surface layer 100a of the positive electrode active material 100 refers to, for example, the area extending from the surface to the inside. Within 50 nm from the surface to the interior, more preferably within 35 nm from the surface to the interior, Preferably, the thickness is within 20 nm from the surface toward the inside, and most preferably, the thickness is within 20 nm from the surface toward the inside. The term "almost perpendicular" refers to the area within 10 nm perpendicular to the surface. The surface is also considered to be the surface if it is cracked or / and if it is cracked. The surface layer 100a is synonymous with the near surface, near-surface region, or shell.

[0050] The region deeper than the surface layer 100a of the positive electrode active material is referred to as the inner portion 100b. is synonymous with inner region or core.

[0051] The surface of the positive electrode active material 100 is a composite oxide including the surface layer 100a and the inner portion 100b. Therefore, the positive electrode active material 100 is aluminum oxide (AlO 3) and other metal oxides that do not have lithium sites that can contribute to charging and discharging. This does not include carbonates, hydroxyl groups, etc. that are chemically adsorbed after the preparation of the positive electrode active material. The attached metal oxide is, for example, a metal oxide whose crystal structure does not match that of the internal 100b. say.

[0052] The electrolyte, organic solvent, binder, conductive material, or any of these attached to the positive electrode active material 100 It also does not include compounds derived from

[0053] The positive electrode active material 100 is a compound containing a transition metal and oxygen that can insert and extract lithium. Therefore, transition metals M (e.g., Co, Ni, Mn, The interface between the area where Fe and oxygen are present and the area where they are not present is the surface of the positive electrode active material. The surface caused by slips, cracks and / or fractures is also called the surface of the positive electrode active material. When the positive electrode active material is subjected to analysis, a protective film may be attached to the surface. The protective film is not included in the active material. It can be a single layer film of carbon, metal, oxide, resin, etc. Multilayer films may be used.

[0054] Therefore, the surface of the positive electrode active material in STEM-EDX ray analysis etc. is the surface where the transition metal M is , the average value of the internal detection amount M AVE and the mean background value M BG 50% of the sum of The point where oxygen is detected is the average value of the amount of oxygen detected inside. AVE and the mean background O BG The point where the sum of the transition metal M and oxygen is 50% of the internal and background If the 50% point of the sum of the fields is different, the metal oxides and carbonates containing oxygen that adhere to the surface Therefore, the average amount of the detected amount of the transition metal M inside the AVE And, back Ground average value M BG The point at which 50% of the sum of the transition metal M In the case of a positive electrode active material having a plurality of elements, the element M having the largest count number in the inner portion 100b is A VE and M BG The surface can be found using

[0055] The average value of the background of the transition metal M BG For example, the detected amount of transition metal M Avoid the area where the increase begins and calculate the average value over the outer range of 2 nm or more, preferably 3 nm or more. In addition, the average value of the internal detection amount M AVE is the transition metal M and oxygen The area where the transition metal M begins to increase is the area where the transition metal M is saturated and stable. 0 nm or more, preferably more than 50 nm, and 2 nm or more, preferably 3 nm or more The average oxygen background value O BG and oxygen The average amount of detected AVE can also be found in the same way.

[0056] In addition, the surface of the positive electrode active material 100 in a cross-sectional STEM (scanning transmission electron microscope) image, etc. The boundary between the region where an image originating from the crystalline structure of the positive electrode active material is observed and the region where it is not observed. Therefore, among the metal elements that make up the positive electrode active material, the element with a larger atomic number than lithium The outermost region where atomic columns originating from the child nuclei can be confirmed. The intersection of the tangent line drawn to the brightness profile from the surface to the bulk and the depth axis Surfaces in STEM images, etc. may be evaluated in conjunction with higher spatial resolution analysis.

[0057] In addition, the spatial resolution of STEM-EDX is about 1 nm. The maximum value of the film may deviate by about 1 nm. Even if there is a maximum value for the profile of added elements such as magnesium, the difference between the maximum value and the surface is 1 nm. If it is less than this, it can be considered an error.

[0058] In addition, peaks in STEM-EDX ray analysis refer to the detected intensity in each element profile. The maximum value of the characteristic X-rays for each element is used for STEM-EDX ray analysis. The noise in the measurement is less than the spatial resolution (R), for example, the half-width measurement value is less than R / 2. Possible reasons include:

[0059] The influence of noise can be reduced by scanning the same area multiple times under the same conditions. For example, The integrated value measured by 6 scans can be used as the profile of each element. The number of scans is The number of measurements is not limited to six, and more measurements can be performed, and the average can be used as the profile for each element.

[0060] The STEM-EDX analysis can be carried out, for example, as follows. A protective film is deposited on the surface of the substrate. For example, an ion sputtering device (Hitachi High-Tech MC1000 ) carbon can be deposited.

[0061] Next, the positive electrode active material is sliced ​​into thin slices to prepare a STEM cross-section sample. Thinning can be done using a Hitachi High-Tech XVision 200TBS. The pick-up is performed using an MPS (micro-probing system), and the finishing conditions are can be set to, for example, an acceleration voltage of 10 kV.

[0062] STEM-EDX analysis is performed using a STEM device (Hitachi High-Tech HD-2700). The EDX detector is an EDAX Octane T Ultra W (two-pole). During EDX analysis, the emission current of the STEM device is 6 μA. Set the voltage to 10μA or less, and measure the depth and roughness of the thinned sample. The magnification is, for example, about 150,000 times. The conditions for EDX analysis are: drift correction Positive and negative, line width 42 nm, pitch 0.2 nm, number of frames 6 or more.

[0063] The grain boundary 101 is, for example, a portion where particles of the positive electrode active material 100 adhere to each other. The area where the crystal orientation changes within the positive electrode active material 100, i.e., the bright and dark lines in the STEM image, etc. Areas where the repetition of is discontinuous, areas containing many crystal defects, and areas where the crystal structure is disordered Crystal defects are observed using cross-sectional TEM (transmission electron microscope) and cross-sectional STEM images. Possible defects, i.e., structures in which other atoms have entered between the lattices, cavities, etc. The grain boundary 101 can be considered as one of the planar defects. This refers to the region within 10 nm of the

[0064] <Contained elements> The positive electrode active material 100 contains lithium, cobalt, oxygen, and an additive element. The positive electrode active material 100 is lithium cobalt oxide (LiCoO2) with added elements. However, the positive electrode active material 100 of one embodiment of the present invention may have a crystal structure described later. Therefore, the composition of lithium cobalt oxide is strictly Li:Co:O=1:1:2. However, it is not limited to the above.

[0065] The positive electrode active material of a lithium-ion secondary battery maintains charge neutrality even when lithium ions are inserted and removed. In order to maintain the positive electrode active material, it is necessary to have a transition metal that can be oxidized and reduced. It is preferable that the substrate 100 mainly uses cobalt as the transition metal responsible for the oxidation-reduction reaction. In addition to ballast, at least one or two selected from nickel and manganese may be used. Among the transition metals contained in the positive electrode active material 100, cobalt accounts for 75 atomic % or more, preferably When the content is 90 atomic % or more, more preferably 95 atomic % or more, synthesis is relatively easy and it is possible to obtain the desired product. It is preferable because it has many advantages such as being easy to handle and having excellent cycle characteristics.

[0066] Cobalt is contained in the transition metals of the positive electrode active material 100 at 75 atomic % or more, preferably at 90 atomic % or more. % or more, more preferably 95 atomic % or more, lithium nickel oxide (LiNiO 2) and other composite oxides in which nickel accounts for the majority of the transition metal, Li x CoO When x in 2 is small, the stability is better. This is because cobalt is more stable than nickel. This is thought to be because the influence of distortion due to the Van der Teller effect is small. The strength of the Jahn-Teller effect varies depending on the number of electrons in the d orbital of the transition metal. Octahedrally coordinated, low-spin nickel(III), such as lithium nickelate, accounts for the majority of transition metals. The layered rock salt type composite oxides, such as those mentioned above, are significantly affected by the Jahn-Teller effect, and The octahedral oxygen layers are prone to distortion, so the crystal structure In addition, nickel ions are larger than cobalt ions, The size of the lithium ion is close to that of the transition metal, as in lithium nickel oxide. In the layered rock salt type composite oxides that make up the majority of the group, nickel and lithium cation mixtures are However, there is a problem in that it is prone to signaling.

[0067] The additive elements contained in the positive electrode active material 100 include magnesium, fluorine, nickel, and aluminum. Aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, One or more elements selected from zinc, silicon, sulfur, phosphorus, boron, bromine, and beryllium The sum of the transition metals among the additive elements is preferably less than 25 atomic %. It is preferably less than 10 atomic %, and more preferably less than 5 atomic %.

[0068] That is, the positive electrode active material 100 is lithium cobalt oxide to which magnesium and fluorine are added. Lithium cobalt oxide doped with magnesium, fluorine and titanium, magnesium , fluorine and aluminum doped lithium cobalt oxide, magnesium, fluorine and and nickel-doped lithium cobalt oxide, magnesium, fluorine, nickel and Lithium cobalt oxide doped with aluminum, etc.

[0069] The additive element is preferably dissolved in the positive electrode active material 100. For example, ST When EM-EDX line analysis was performed, the depth at which the amount of added elements detected increased with the transition metal A position deeper than the depth at which the amount of detected group M increases, i.e., the inside of the positive electrode active material 100 Preferably, it is located to the side.

[0070] In this specification, the amount of a certain element detected in the line analysis of STEM-EDX is The depth at which the value increases is the measurement value that can be determined not to be noise in terms of intensity and spatial resolution. This refers to the depth at which the above-mentioned values ​​can be obtained continuously.

[0071] These additive elements further stabilize the crystal structure of the positive electrode active material 100, as will be described later. In this specification and the like, the term "additive element" has the same meaning as "a mixture" or "a part of a raw material."

[0072] The added elements do not necessarily include magnesium, fluorine, nickel, aluminum, or titanium. Zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, It may be free of sulfur, phosphorus, boron, bromine, or beryllium.

[0073] For example, if the positive electrode active material 100 does not substantially contain manganese, it is relatively easy to synthesize. The advantages mentioned above, such as ease of handling and excellent cycle characteristics, are further enhanced. The weight of manganese contained in the electrode active material 100 is, for example, 600 ppm or less, more preferably It is preferably 100 ppm or less.

[0074] <Crystal structure> <Li x When x in CoO2 is 1≫ The positive electrode active material 100 according to one embodiment of the present invention is in a discharged state, i.e., Li xWhen x=1 in CoO2 In this case, it is preferable that the layered rock salt type crystal structure belongs to the space group R-3m. The salt-type composite oxide has a high discharge capacity and has two-dimensional lithium ion diffusion paths. It is suitable for the insertion / extraction reaction of ammonium ions and is an excellent positive electrode active material for secondary batteries. In particular, the inner portion 100b, which occupies most of the volume of the positive electrode active material 100, has a layered rock salt type crystal structure. FIG. 4 shows a layered rock salt type crystal structure labeled R-3m O3.

[0075] On the other hand, the surface layer 100a of the positive electrode active material 100 according to one embodiment of the present invention is Even if lithium is removed from 100, the layer structure consisting of the octahedron of cobalt and oxygen in the inner 100b remains. It is preferable that the surface layer 100a has a function of reinforcing the structure so that it does not break. It is preferable that the positive electrode active material 100 functions as a barrier film for the positive electrode active material 100. It is preferable that the surface layer 100a reinforces the positive electrode active material 100. The positive electrode active material 100 is a cathode active material having a surface layer 100a and an inner portion 100b thereof, which includes oxygen desorption. Suppressing structural changes and / or preventing the electrolyte from being oxidized and decomposed on the surface of the positive electrode active material 100 This refers to preventing the spread of infection.

[0076] Therefore, it is preferable that the surface layer 100a has a different crystal structure from that of the inner layer 100b. Moreover, the surface layer 100a has a composition and crystal structure that is more stable at room temperature (25° C.) than the inner layer 100b. For example, the surface layer 100 of the positive electrode active material 100 according to one embodiment of the present invention may have the following structure: Preferably, at least a part of the surface layer 100 has a rock salt type crystal structure. It is preferable that a has both a layered rock salt type and a rock salt type crystal structure. It is preferable that the surface layer 100a has characteristics of both the layered rock salt type and the rock salt type crystal structure. It's nice.

[0077] The surface layer 100a is the region where lithium ions are first desorbed during charging, and the inner layer 100b The surface layer 100a is a region where the lithium concentration is likely to be lower than that of the positive electrode active material. The atoms on the surface of a particle with a quality of 100 can be said to be in a state where some of the bonds are broken. The portion 100a is likely to become unstable, and is a region where the crystal structure is likely to start to deteriorate. If the surface layer 100a can be sufficiently stabilized, Li x Even when x in CoO2 is small, For example, even if x is 0.24 or less, the layer structure consisting of the inner 100b cobalt and oxygen octahedrons is broken. Furthermore, the inner 100b cobalt and oxygen octahedron structure The misalignment of the layers can be suppressed.

[0078] In order to give the surface layer 100a a stable composition and crystal structure, the surface layer 100a contains an additive element. It is preferable that the surface layer portion 100 has the additive element, and it is more preferable that the surface layer portion 100 has a plurality of additive elements. It is preferable that the concentration of one or more selected from the additive elements in the inner portion 100a is higher than that in the inner portion 100b. In addition, one or more additive elements selected from the additive elements contained in the positive electrode active material 100 have a concentration gradient. In addition, the distribution of the positive electrode active material 100 varies depending on the added element. For example, the depth from the surface of the concentration peak varies depending on the added element. It is more preferable that the concentration peak is in the surface layer portion 100a or in the region 5 from the surface. This refers to the maximum concentration at or below 0 nm.

[0079] For example, some of the additive elements, such as magnesium, fluorine, nickel, titanium, silicon, and phosphorus, Boron, calcium, etc., are distributed from the inside 100b to the outside as shown by the gradation in Figure 1(B1). It is preferable that the concentration gradient increases toward the surface. The additive element will be referred to as additive element X.

[0080] Other added elements, such as aluminum and manganese, are indicated by the density of the hatching in Figure 1(B2). As shown in Fig. 1, there is a concentration gradient and the concentration peak is located in a region deeper than the added element X. The concentration peak may be present in the surface layer 100a or may be present in a region deeper than the surface layer 100a. For example, a peak may be present in the region of 5 nm to 30 nm from the surface to the inside. It is preferable that the additive element having such a concentration gradient is referred to as additive element Y. do.

[0081] 〔magnesium〕 For example, magnesium, one of the additive elements X, is divalent, and magnesium ions are It is more stable at the lithium site than at the cobalt site in the salt-type crystal structure. Therefore, magnesium can easily enter the lithium site. When present at an appropriate concentration, it is easier to maintain the layered rock salt crystal structure. This is because the magnesium present in the umsite acts as a pillar supporting the CoO2 layers. It is speculated that the presence of magnesium x For example, if x in CoO2 is 0. In a state of 24 or less, the desorption of oxygen around magnesium can be suppressed. The presence of magnesium is expected to increase the density of the positive electrode active material 100. If the magnesium concentration in the surface layer 100a is high, the electrolytic solution may decompose and react with hydrofluoric acid. It is also expected to improve corrosion resistance.

[0082] At an appropriate concentration, magnesium has a negative effect on the insertion and extraction of lithium during charging and discharging. However, if there is an excess of magnesium, the lithium This may have a negative effect on insertion and desorption, and may also reduce the effect on stabilizing the crystal structure. This is because magnesium may occupy the cobalt site in addition to the lithium site. In addition, it is thought that the Unnecessary magnesium compounds (oxides and fluorides, etc.) do not displace and remain on the surface of the positive electrode active material. The magnesium concentration in the positive electrode active material may segregate and become a resistance component in the secondary battery. As the temperature rises, the discharge capacity of the positive electrode active material may decrease. This is thought to be because too much magnesium enters the battery, reducing the amount of lithium that contributes to charging and discharging. .

[0083] Therefore, it is preferable that the amount of magnesium contained in the entire positive electrode active material 100 is appropriate. For example, the number of magnesium atoms is between 0.002 and 0.06 times the number of cobalt atoms. A value of 0.005 to 0.03 times is preferable, and a value of about 0.01 times is even more preferable. The amount of magnesium contained in the entire positive electrode active material 100 is preferably, for example, G The values ​​were obtained by performing elemental analysis of the entire positive electrode active material 100 using D-MS, ICP-MS, etc. It may be based on the value of the blend of raw materials in the process of producing the positive electrode active material 100. It is also possible.

[0084] 〔nickel〕 In addition, nickel, one of the added elements X, is located either at the cobalt site or the lithium site. When present at the cobalt site, it has a lower redox potential than cobalt. This leads to an increase in discharge capacity, which is preferable.

[0085] When nickel is present at the lithium site, a layered structure consisting of cobalt and oxygen octahedra is formed. The structural deviation can be suppressed. Also, the change in volume caused by charging and discharging is suppressed. This is because the nickel present in the lithium site also It is thought that this is because they function as pillars supporting each other. This is preferable because it is expected that the crystal structure will be more stable in the above charged state.

[0086] In addition, the distance between the cations and anions in nickel oxide (NiO) is smaller than that in MgO and CoO. The distance between the cations and anions of LiCoO2 is closer to the average distance, and the orientation of LiCoO2 is Easy to match.

[0087] The ionization tendency is smallest in the order of magnesium, aluminum, cobalt, and nickel. Therefore, it is thought that nickel is less likely to dissolve into the electrolyte than the other elements mentioned above during charging. Therefore, it is considered that the effect of stabilizing the crystalline structure of the surface layer in the charged state is high.

[0088] Furthermore, nickel is Ni 2+ , Ni 3+ , Ni 4+ Of which Ni 2+ is the most stable, Nickel has a higher trivalent ionization energy than cobalt. It is known that nickel alone does not have a spinel-type crystal structure. It is believed to have the effect of suppressing the phase change from a layered rock salt type to a spinel type crystal structure.

[0089] On the other hand, excessive nickel increases the influence of strain due to the Jahn-Teller effect, which is not desirable. Also, excessive nickel may adversely affect lithium insertion and extraction. .

[0090] Therefore, it is preferable that the amount of nickel contained in the entire positive electrode active material 100 is appropriate. For example, the number of nickel atoms in the positive electrode active material 100 is more than 0% of the number of cobalt atoms. 7.5% or less is preferable, 0.05% to 4% is preferable, and 0.1% to 2% is preferable. It is preferable that the content of the saturation agent is 0.2% or more and 1% or less, and more preferable that the content of the saturation agent is more than 0% and 4% or less. Alternatively, it is preferably more than 0% and not more than 2%. Alternatively, it is preferably 0.05% or more and not more than 7.5%. Alternatively, 0.05% or more and 2% or less is preferable. Alternatively, 0.1% or more and 7.5% or less is preferable. It is preferable that the nickel content is 0.1% or more and 4% or less. It may also be a value obtained by performing elemental analysis of the entire positive electrode active material using D-MS, ICP-MS, or the like. Alternatively, it may be based on the values ​​of the blending of raw materials in the process of producing the positive electrode active material.

[0091] 〔aluminum〕 Aluminum, one of the added elements Y, acts as a cobalt salt in the layered rock salt crystal structure. Aluminum is a trivalent element and its valence does not change during charging and discharging. Therefore, the lithium around the aluminum is difficult to move. Lithium acts as a pillar, suppressing changes in the crystal structure. The Al-O bond has the effect of suppressing the dissolution of Co and improving the durability of continuous charging. Since it is stronger than the -O bond, it can suppress the detachment of oxygen from the surrounding aluminum. These effects improve the thermal stability. This improves safety when the positive electrode active material 100 is used in a secondary battery. This makes it possible to obtain a positive electrode active material 100 whose crystal structure is resistant to collapse even when turned over.

[0092] On the other hand, excessive aluminum may adversely affect the insertion and extraction of lithium. do.

[0093] Therefore, it is preferable that the total amount of aluminum contained in the positive electrode active material 100 is appropriate. For example, the number of aluminum atoms in the entire positive electrode active material 100 is 1 / 1 the number of cobalt atoms. 0.05% or more and 4% or less is preferable, 0.1% or more and 2% or less is preferable, 0.3% or more More preferably, it is 1.5% or less. Alternatively, it is 0.05% or more and 2% or less. Alternatively, it is 0.1 % or more and 4% or less. The amount contained in the entire positive electrode active material 100 is, for example, The values ​​are obtained by performing elemental analysis on the entire positive electrode active material 100 using GD-MS, ICP-MS, etc. Alternatively, it may be based on the value of the blending of raw materials in the process of producing the positive electrode active material 100. .

[0094] [Fluorine] Fluorine, which is one of the additive elements X, is a monovalent anion, and in the surface layer portion 100a When part of the oxygen is replaced by fluorine, the lithium desorption energy decreases. The redox potential of the cobalt ion accompanying lithium desorption differs depending on whether or not fluorine is present. In other words, when there is no fluorine, the cobalt ions change from trivalent to tetravalent as lithium is released. On the other hand, when fluorine is present, the cobalt ion changes to a tetravalent state upon lithium elimination. The redox potential of the cobalt ion changes from trivalent to trivalent. When part of the oxygen in the surface layer 100a of the active material 100 is substituted with fluorine, the fluorine This means that the desorption and insertion of nearby lithium ions can occur smoothly. When the active material 100 is used in a secondary battery, it is possible to improve the charge / discharge characteristics, large current characteristics, etc. Furthermore, the presence of fluorine in the surface layer portion 100a, which has the surface that is in contact with the electrolyte, This effectively improves the corrosion resistance against hydrofluoric acid. However, the melting points of fluorides, including lithium fluoride, are higher than those of other additive element sources. If low, it acts as a fluxing agent to lower the melting point of other added element sources It is possible.

[0095] In addition, it is known that the oxide of titanium, which is one of the added elements X, has superhydrophilicity. Therefore, by using the positive electrode active material 100 having titanium oxide in the surface layer portion 100a, the polarity When used in a secondary battery, the positive electrode active material 1 00 and the highly polar electrolyte, which may improve the contact at the interface and suppress the increase in internal resistance. There is a possibility.

[0096] Furthermore, when phosphorus, which is one of the additive elements X, is contained in the surface layer portion 100a, Li x x in CoO2 When the voltage is kept small, it is possible to prevent short circuits, which is preferable. For example, it is preferable that it exists in the surface layer portion 100a as a compound containing phosphorus and oxygen.

[0097] When the positive electrode active material 100 contains phosphorus, the phosphorus is generated by decomposition of the electrolyte or electrolyte. This is preferable because hydrogen fluoride reacts with phosphorus, potentially reducing the hydrogen fluoride concentration in the electrolyte. stomach.

[0098] If the electrolyte contains LiPF6, there is a risk of hydrogen fluoride being generated by hydrolysis. In addition, polyvinylidene fluoride (PVDF) and alkaline electrolytes, which are used as components of the positive electrode, There is also a risk of hydrogen fluoride being generated by the reaction with hydrogen fluoride. The hydrogen fluoride concentration in the electrolyte decreases. This may prevent corrosion of the current collector and / or peeling of the coating 104. In addition, it may be possible to suppress the decrease in adhesiveness due to gelation and / or insolubilization of PVDF. be.

[0099] When the positive electrode active material 100 contains phosphorus together with magnesium, Li x x in CoO2 is small This is preferable because the stability in the cold state is extremely high. The number of phosphorus atoms is preferably 1% to 20% of the number of cobalt atoms, and more preferably 2% to 10%. More preferably, it is 3% or more and 8% or less, and even more preferably, it is 1% or more and 10% or less. Preferably, the range is 1% or more and 8% or less, or preferably, 2% or more and 20% or less. Alternatively, 2% or more and 8% or less is preferable. Alternatively, 3% or more and 20% or less is preferable. Alternatively, 3% In addition, the number of magnesium atoms is preferably 0.1 times the number of cobalt atoms. % or more and 10% or less is preferable, 0.5% or more and 5% or less is more preferable, and 0.7% or more and 4% or less is more preferable. More preferably, it is 0.1% or more and 5% or less. Or, it is 0.1% or more and 4% or less. Preferably, 0.5% or more and 10% or less is preferable. Or, 0.5% or more and 4% or less is preferable. Or, 0.7% to 10% or less is preferable. Or, 0.7% to 5% or less is preferable. The concentrations of phosphorus and magnesium shown here are preferably determined by, for example, GC-MS, ICP- The value may be a value obtained by performing elemental analysis of the entire positive electrode active material 100 using MS or the like, or may be a value obtained by performing elemental analysis of the positive electrode active material 100 using MS or the like. It may be based on the value of the raw material composition in the process of making the substance 100 .

[0100] In addition, when the positive electrode active material 100 has cracks, the positive electrode active material having the cracks on the surface The buried portion 102, for example, contains phosphorus, more specifically, a compound containing phosphorus and oxygen. The presence of these metals can inhibit the progression of cracks.

[0101] [Synergistic effect of multiple elements] Furthermore, when the surface layer 100a contains both magnesium and nickel, divalent magnesium It is possible that divalent nickel can exist more stably near Li. x C Even when x in oO2 is small, the elution of magnesium can be suppressed. This may contribute to the stabilization of 0a.

[0102] For the same reason, in the manufacturing process, when adding additive elements to lithium cobalt oxide, It is preferable that the nesium is added in a step before the nickel. Nickel is preferably added in the same process. Magnesium has a large ionic radius, Regardless of the process used to add it, it tends to remain on the surface of the lithium cobalt oxide. In the absence of magnesium, it can diffuse widely inside the lithium cobalt oxide. Therefore, when nickel is added before magnesium, the nickel is embedded in the lithium cobalt oxide. There is a concern that it will diffuse and not remain in the desired amount on the surface.

[0103] In addition, if additive elements with different distributions, such as additive element X and additive element Y, are combined, a wider range of For example, the positive electrode active material 100 contains a part of the additive element X. It contains magnesium and nickel, which are the elements of the alloy, and aluminum, which is one of the additive elements Y. This stabilizes the crystal structure in a wider area than when only one of the added elements X and Y is present. In this way, when the positive electrode active material 100 contains both the additive element X and the additive element Y, The surface stabilization is sufficiently achieved by the addition of elements X such as magnesium and nickel. However, the additive element Y such as aluminum is not essential for the surface. Rather, aluminum is needed for the deeper It is preferable that the thickness is widely distributed in the region, for example, 1 nm to 25 nm in the depth direction from the surface. It is preferable that aluminum is detected continuously in the region of 0 nm to 10 nm from the surface. 0 nm or less, preferably in the region of 0.5 nm to 50 nm from the surface. It is preferable to use a crystalline structure having a larger area since the crystalline structure can be stabilized in a wider area.

[0104] When multiple additive elements are present as described above, the effects of each additive element are synergistically enhanced. Magnesium, nickel and aluminum in particular can contribute to further stabilization of 00a. When the crystalline structure has the above formula, it is highly effective in providing a stable composition and crystal structure, and is therefore preferred.

[0105] However, if the surface layer 100a is occupied only by a compound of the added element and oxygen, lithium intercalation will be difficult. For example, if the surface layer 100a is made of MgO or Mg O and NiO(II) solid solution structure, and / or MgO and CoO(II) solid solution structure Therefore, the surface layer 100a should be made of at least cobalt. In the discharged state, it also contains lithium, and it is necessary to have a path for lithium insertion and desorption. There is a need.

[0106] In order to ensure sufficient paths for lithium insertion and desorption, the surface layer 100a is made of magnesium. For example, the number of magnesium atoms (Mg) is higher than the number of cobalt atoms (Mg). The ratio of the number of atoms of Mg to Co is preferably 0.62 or less. The surface layer 100a preferably has a higher concentration of cobalt than nickel. It is preferable that the concentration of cobalt is higher than that of fluorine. A high concentration of cobalt is preferred.

[0107] Furthermore, if there is too much nickel, there is a risk of inhibiting the diffusion of lithium. It is preferable that the concentration of magnesium is higher than that of nickel. For example, The number is preferably 1 / 6 or less of the number of magnesium atoms.

[0108] Some of the added elements, especially magnesium, nickel and aluminum, also contribute to the formation of the inner 100 Although it is preferable that the concentration of the surface layer 100a is higher than that of the inner layer 100b, the inner layer 100b is also randomly It is preferable that magnesium and aluminum are present in the inner portion 100b in a dilute state. When present at an appropriate concentration at the lithium site, it maintains the layered rock-salt crystal structure as described above. In addition, nickel exists in the interior 100b at an appropriate concentration. In this case, the deviation of the layer structure consisting of octahedra of cobalt and oxygen can be suppressed in the same manner as above. When magnesium and nickel are contained together, the elution of magnesium is suppressed in the same manner as above. A synergistic effect can be expected.

[0109] Furthermore, due to the concentration gradient of the added element as described above, the It is preferable that the crystal structure changes continuously. It is preferable that the crystal orientations are roughly the same.

[0110] For example, from the inside 100b of the layered halite type, the halite type, or both the halite type and the layered halite type It is preferable that the crystal structure continuously changes toward the surface and the surface layer 100a having the characteristics. Alternatively, the surface layer 100a may be of a rock salt type, or may have characteristics of both the rock salt type and the layered rock salt type. It is preferable that the orientation of the inner portion 100b of the layered rock salt mold is approximately the same.

[0111] In this specification and the like, a composite oxide containing lithium and a transition metal such as cobalt The layered rock salt type crystal structure of the material, which belongs to the space group R-3m, is composed of cations and anions. The transition metals and lithium are regularly arranged in a two-dimensional structure. This refers to a crystal structure that allows two-dimensional diffusion of lithium due to the formation of a plane. The layered rock salt crystal structure may have defects such as ions or anions missing. In other words, the lattice of the rock salt crystal may have a distorted structure.

[0112] The rock salt crystal structure is a cubic crystal structure including the space group Fm-3m. It refers to a structure in which cations and anions are arranged alternately. There may be a defect.

[0113] The crystal structure of both the layered rock salt type and the rock salt type is also confirmed by electron diffraction, TEM, and This can be determined by using a cross-sectional STEM image, etc.

[0114] The rock salt type has no distinction in the cation sites, but the layered rock salt type has a distinction in the cation sites of the crystal structure. There are two types, one dominated by lithium and the other by transition metals. The layered structure in which two-dimensional planes of ions and two-dimensional planes of anions are alternately arranged is called rock salt type and layered rock salt. The bright spots in the electron diffraction pattern correspond to the crystal planes that form this two-dimensional plane. Among them, when the central spot (transparent spot) is set as the origin 000, the point closest to the central spot is The bright spots are, for example, the (111) plane in the ideal rock salt type, and the bright spots are, for example, the (0 03) plane. For example, the electron diffraction patterns of rock-salt MgO and layered rock-salt LiCoO2 When comparing the distance between the bright spots on the (003) surface of LiCoO2, the distance between the bright spots on the (111) surface of MgO is The distance between the bright spots is about half of the distance between the bright spots. In the case of the two phases of rock salt MgO and layered rock salt LiCoO2, the electron diffraction pattern shows a strong There are plane orientations in which bright spots and weak spots are alternately arranged. Bright spots common to the salt type have a strong brightness, while bright spots that occur only in the layered rock salt type have a weak brightness.

[0115] In addition, when the layered rock-salt crystal structure was observed from a direction perpendicular to the c-axis in cross-sectional STEM images, When the quartz crystal is formed, layers with strong brightness and layers with weak brightness are observed alternately. This characteristic is not observed because there is no distinction between the cation sites. In the case of a crystal structure that has both characteristics, when observed from a specific crystal orientation, cross-sectional STEM images, etc. In the case of the IR spectrum, layers observed with high brightness and layers observed with low brightness are observed alternately, and then A metal with an atomic number greater than that of lithium exists in a portion of the luminous layer, i.e., the lithium layer.

[0116] Layered rock salt crystals and the anions of rock salt crystals are in a cubic close-packed structure (face-centered cubic lattice structure) ) The O3' type and monoclinic O1(15) crystals described later also have anions in a cubic close-packed arrangement. Therefore, when layered rock salt crystals come into contact with each other, anions There are crystal planes where the orientation of the cubic close-packed structure composed of

[0117] Alternatively, it can be explained as follows: The {111} plane of the cubic crystal structure The anions have a triangular lattice. The layered rock salt type has a space group of R-3m and a rhombohedral structure. However, to make it easier to understand the structure, it is generally expressed as a complex hexagonal lattice, and the layered rock salt type (00 The triangular lattice of the cubic {111} plane is similar to that of the layered rock salt type (000 1) The atomic arrangement is the same as that of a hexagonal lattice. The compatibility of the two lattices is called the cubic maxima. This means that the orientation of the close-packed structure is aligned.

[0118] However, the space group of the layered rock salt crystal and O3' type crystal is R-3m, and the space group of the rock salt type crystal is Since the space group is different from Fm-3m (the space group of general rock salt crystals), the above conditions are met. The Miller indices of the crystal planes are different between the layered rock salt crystal and the O3' crystal, and the rock salt crystal. In the specification, the layered rock salt type crystal, the O3' type and the rock salt type crystal are composed of anions. When the orientation of the cubic close-packed structure is aligned, the crystal orientation is said to be roughly the same. In addition, they have a three-dimensional structural similarity, with the crystal orientation roughly matching. The same crystallographic orientation is called topotaxy.

[0119] The crystal orientation of the two regions roughly coincides with that of the other regions. Electron Microscope, Transmission Electron Microscope) image, STEM (Scann Transmission Electron Microscope, Scanning Transmission HAADF-STEM (High-angle Annular D Dark Field Scanning TEM, High Angle Scattering Annular Dark Field Scanning Transmission Electron Microscope Mirror) image, ABF-STEM (Annular Bright-Field Scanni) ng Transmission Electron Microscope, Circular Vision FFT of scanning transmission electron microscope (STEM) images, electron beam diffraction patterns, TEM images, STEM images, etc. This can be determined from the pattern, etc. XRD (X-ray Diffraction, X-ray diffraction, electron diffraction, neutron diffraction, etc. can also be used as materials for judgment.

[0120] Figure 2 shows a TEM image in which the orientation of the layered rock salt crystal LRS and the rock salt crystal RS roughly coincides. Examples are shown below. For TEM images, STEM images, HAADF-STEM images, ABF-STEM images, etc. An image reflecting the crystal structure is obtained.

[0121] For example, in high-resolution TEM images, contrast originating from crystal planes can be observed. By the diffraction and interference of the electron beam, for example, the electron beam is perpendicular to the c-axis of the layered rock salt type composite hexagonal lattice. When incident light is incident, a bright band (bright strip) originating from the (0003) plane appears. This is because the bright spots are observed in the TEM image as a repetition of dark bands (dark strips). Repeated lines and dark lines are observed, and light lines (for example, L shown in Figure 2) RS and L LRS ) corner If the difference is 5 degrees or less, or 2.5 degrees or less, the crystal faces are roughly coincident, i.e., the crystal faces are Similarly, if the angle between the dark lines is less than 5 degrees, it can be judged that the orientation of the crystals is roughly the same. Even if the difference is less than 2.5 degrees, it can be determined that the crystal orientation is roughly the same. can.

[0122] In addition, the contrast in the HAADF-STEM image is proportional to the atomic number. For example, the layered rocksalt type nuclei belonging to the space group R-3m are observed as brighter elements. In the case of lithium baltate, cobalt (atomic number 27) has the highest atomic number, so The electron beam is strongly scattered at the cobalt atom positions, and the arrangement of the cobalt atoms appears as a bright line or a highly luminous line. It is observed as an arrangement of dots. Therefore, lithium cobalt oxide has a layered rock salt type crystal structure. When observed perpendicular to the c-axis, the arrangement of cobalt atoms perpendicular to the c-axis appears as a bright line or a strong luminance line. The arrangement of lithium and oxygen atoms is observed as a dark line or a low brightness area. The lithium cobalt oxide is doped with fluorine (atomic number 9) and The same is true when magnesium (atomic number 12) is present.

[0123] Therefore, in the HAADF-STEM image, bright and dark lines appear in two regions with different crystal structures. If the repetition of the above is observed and the angle between the bright lines is less than 5 degrees or less than 2.5 degrees, It can be determined that the arrangement of the molecules is roughly the same, that is, the orientation of the crystals is roughly the same. Similarly, if the angle between the dark lines is less than 5 degrees or less than 2.5 degrees, the crystal It can be determined that the orientations are roughly the same.

[0124] In ABF-STEM, elements with smaller atomic numbers are observed brighter. Similar to HAADF-STEM, the contrast obtained is dependent on the HAADF. The crystal orientation can be determined in the same way as with F-STEM images.

[0125] Figure 3(A) shows the STE in which the orientation of the layered rock salt crystal LRS and the rock salt crystal RS are roughly the same. An example of an M image is shown in Fig. 3(B). The FFT pattern of the rock salt type crystal RS region is shown in Fig. 3(C). The FFT pattern of the crystal LRS region is shown in Figure 3(C). The composition, JCPDS card number, and the calculated d value and angle are shown in The measured values ​​are shown on the right. The spot marked with O is the zeroth diffraction order.

[0126] The spot marked A in Figure 3(B) is due to the 11-1 reflection of the cubic crystal. The spot marked A in (C) is derived from the 0003 reflection of the layered rock salt type. From Fig. 3(B) and Fig. 3(C), the orientation of the 11-1 reflection of the cubic crystal and the 0003 reflection of the layered rock salt type are In other words, the line passing through AO in Figure 3(B) and It can be seen that the line passing through AO in FIG. 3(C) is roughly parallel to the line passing through AO. "Approximately parallel" means that the angle is 5 degrees or less, or 2.5 degrees or less.

[0127] Thus, the FFT pattern and electron diffraction pattern show that layered rock salt crystals and rock salt crystals are When the crystal orientations are roughly the same, the layered rock salt type has a <0003> orientation and the rock salt type has a <11-1> orientation. In this case, these reciprocal lattice points are spot-shaped. It is preferable that the reciprocal lattice points are not continuous with each other. The fact that the reciprocal lattice points are not continuous with each other means that the crystallinity is high.

[0128] As mentioned above, the 11-1 reflection of the cubic crystal and the 0003 reflection of the layered rock salt crystal are When and are roughly the same, depending on the incident direction of the electron beam, the layered rock salt type 0003 reflection A spot that is not due to the layered rocksalt type 0003 reflection is observed in the reciprocal lattice space, which is different from the orientation of the For example, the spot marked B in Figure 3(C) is a layered rock salt type 1014 This is due to the reciprocal lattice point (Fig. 3( C) is at an angle of 52° or more and 56° or less from the direction of A) (i.e., ∠AOB is 52° and d is between 0.19 nm and 0.21 nm. This index is just an example, and does not necessarily have to match. For example, , and reciprocal lattice points equivalent to 0003 and 1014 may also be used.

[0129] Similarly, the 11-1 reflection of the cubic crystal is observed in a different reciprocal lattice space from the 11-1 reflection of the cubic crystal. Spots not originating from the -1 reflection may be observed. For example, the spot marked with B in Figure 3(B) The spot is due to the 200 reflection of the cubic crystal. The angle is between 54° and 56° from the direction of the previous reflection (A in Figure 3(B)) (i.e., Diffraction spots may be observed where the angle AOB is between 54° and 56°. This index is just an example and does not necessarily have to match. For example, 11-1 and 200 equivalent reciprocal lattice points may also be used.

[0130] In addition, layered rock salt type positive electrode active materials such as lithium cobalt oxide have a (0003) plane. and its equivalent planes, as well as the (10-14) plane and its equivalent planes, appear as crystal planes. Therefore, it is important to carefully observe the shape of the positive electrode active material using an SEM or other device. In order to make it easier to observe the (0003) plane, for example, in a TEM, the electron beam is focused on [12- 10] It is possible to thin the observation sample using FIB etc. so that the incident light is When you want to judge the coincidence of the orientation of the layered rock salt type, the (0003) plane is easy to observe. It is preferable to thin the film.

[0131] <Li x CoO2 with small x≫ The positive electrode active material 100 according to one embodiment of the present invention has the above-described distribution of the additive elements in a discharged state. and / or due to the crystal structure, Li x When x in CoO2 is small The crystal structure of the positive electrode active material is different from that of conventional positive electrode active materials. <x≦0 This refers to .24.

[0132] Using Figs. 4 to 8, Li x Regarding the change in the crystal structure with the change in x in CoO2, The description will be made while comparing a conventional positive electrode active material with the positive electrode active material 100 of one embodiment of the present invention.

[0133] The change in the crystal structure of the conventional positive electrode active material is shown in Figure 5. The conventional positive electrode active material shown in Figure 5 has The lithium cobalt oxide (LiCoO2) does not contain any additive elements. The change in the crystal structure of lithium cobalt oxide that has not been reported is described in Non-Patent Documents 1 to 3. are.

[0134] Figure 5 shows R-3m O3 and Li x Lithium cobalt oxide with x=1 in CoO2 has This crystal structure shows that lithium occupies octahedral sites. There are three CoO2 layers in the unit cell. The CoO2 layer is an octahedral structure in which cobalt is coordinated with six oxygen atoms. This is called the structure in which the cobalt and oxygen atoms are connected in a plane with the edges shared. It can also be called the layer made up of the body.

[0135] In addition, in conventional lithium cobalt oxide, the symmetry of lithium increases when x is about 0.5, It is known that it has a crystal structure that belongs to the monoclinic space group P2 / m. There is one CoO2 layer in the unit cell. Therefore, it is called O1 type or monoclinic O1 type. There may be cases where this happens.

[0136] When x = 0, the positive electrode active material has a crystal structure of the trigonal space group P-3m1, There is one CoO2 layer in the beam unit cell. Therefore, this crystal structure is called O1 type or It is sometimes called trigonal O1 type. Also, when the trigonal crystal is converted into a composite hexagonal lattice, it becomes a hexagonal O1 type. It is sometimes called.

[0137] In addition, when x is about 0.12, conventional lithium cobalt oxide has a crystal structure in the space group R-3m. This structure is different from the trigonal O1 type CoO2 structure and the R-3m O3 type This crystal structure can be said to be a structure in which the LiCoO2 structure and the LiCoO2 structure are alternately stacked. This is sometimes called the H1-3 type crystal structure. The lithium concentration is not uniform throughout the crystal, and the x The H1-3 type crystal structure is observed from about =0.25. has twice the number of cobalt atoms per unit cell as the other structures. In this specification, the c-axis of the H1-3 type crystal structure is used to facilitate comparison with other crystal structures. is shown as a diagram of half a unit cell.

[0138] As an example, the H1-3 type crystal structure has a unit cell as described in Non-Patent Document 3. The coordinates of cobalt and oxygen in 1(0,0,0.27671±0.00045), O2(0,0,0.11535±0. 00045), where O1 and O2 are oxygen atoms. The unit cell that should be used to represent the crystal structure of a material can be determined by, for example, XRD patterns. In this case, the GOF (Goodness of Fit) can be determined by Rietveld analysis. The unit cell with the smallest value of (s of fit) should be adopted.

[0139] Li x When charging and discharging are repeated so that x in CoO2 becomes 0.24 or less, The lithium cobalt oxide has a H1-3 type crystal structure, a discharged R-3m O3 structure, and The crystal structure changes (i.e., non-equilibrium phase changes) occur repeatedly between the two phases.

[0140] However, these two crystal structures have a large misalignment of the CoO2 layers. As shown by the arrows and the CoO2 layer in the H1-3 crystal structure, the R-3m O This dynamic structural change is detrimental to the stability of the crystal structure. It can have an impact.

[0141] Furthermore, the difference in volume between these two crystal structures is large. In this case, the difference in volume between the H1-3 type crystal structure and the R-3m O3 type crystal structure in the discharged state is 3. It exceeds 5%, typically 3.9% or more.

[0142] In addition, the H1-3 type crystal structure has a structure in which the CoO2 layers are continuous, as in the trigonal O1 type. The structure is likely to be unstable.

[0143] Therefore, if charge and discharge are repeated so that x becomes 0.24 or less, the conventional lithium cobalt oxide The crystal structure of the battery will collapse. This collapse of the crystal structure will cause a deterioration in cycle characteristics. In the case of lithium ions, the crystal structure is broken, and the number of sites where lithium ions can exist stably decreases. This is because it becomes difficult for the ammonium to be inserted and removed.

[0144] On the other hand, in the positive electrode active material 100 of one embodiment of the present invention shown in FIG. x x in CoO2 is 1 The change in the crystal structure during discharge and when x is 0.24 or less is greater than that of conventional positive electrode active materials. More specifically, the CoO2 layer in the state where x is 1 and the state where x is 0.24 or less The deviation of the volume per cobalt atom can be reduced. Therefore, in the positive electrode active material 100 of one embodiment of the present invention, when x is 0.2 Even after repeated charge and discharge cycles that drop below 4, the crystal structure remains stable and provides excellent cycle characteristics. In addition, the positive electrode active material 100 according to one embodiment of the present invention can be realized by Li x In CoO2 When x is 0.24 or less, the material can have a more stable crystal structure than conventional positive electrode active materials. Therefore, the positive electrode active material 100 according to one embodiment of the present invention is Li x x in CoO2 is 0.24 or less In such a case, the safety of the secondary battery is improved. This is preferable as it improves safety.

[0145] Li x When x in CoO2 is 1, approximately 0.2, or approximately 0.15, the positive electrode active material 100 The crystal structure of the inner portion 100b of the positive electrode active material 100 is shown in FIG. This accounts for the majority of the CoO2 layer and contributes greatly to charging and discharging. Change is the most problematic part.

[0146] When x=1, the positive electrode active material 100 is the same as conventional lithium cobalt oxide, R-3m O3. It has a crystalline structure.

[0147] However, the positive electrode active material 100 is a material that has a H1-3 type crystal structure, unlike conventional lithium cobalt oxide. When x is 0.24 or less, for example, about 0.2 or 0.15, a different structure It has a crystal structure.

[0148] When x=approximately 0.2, the positive electrode active material 100 according to one embodiment of the present invention is a trigonal space group R- It has a crystal structure attributed to 3m, which means that the symmetry of the CoO2 layer is the same as that of O3. Therefore, this crystal structure is called the O3' type crystal structure. This crystal structure is shown below.

[0149] The O3' type crystal structure has the coordinates of cobalt and oxygen in the unit cell as Co(0,0 ,0.5), O(0,0,x), and can be shown to be in the range 0.20≦x≦0.25. The lattice constant of the unit cell is preferably 2.797≦a≦2.837 (Å) for the a-axis. 2.807≦a≦2.827(Å) is more preferable, and typically a=2.817(Å). The c-axis is preferably 13.681 ≦ c ≦ 13.881 (Å), and 13.751 ≦ c ≦ 1 3.811 (Å) is more preferable, and typically c=13.781 (Å).

[0150] Furthermore, when x=approximately 0.15, the positive electrode active material 100 according to one embodiment of the present invention has a monoclinic space It has a crystal structure that belongs to the group P2 / m, which means that there is one CoO2 layer in the unit cell. At this time, the amount of lithium present in the positive electrode active material 100 is about 15 atomic % of the discharged state. Therefore, this crystal structure is called the monoclinic O1(15) type crystal structure. This crystal structure is designated as P2 / m monoclinic O1(15).

[0151] The monoclinic O1(15) crystal structure has the coordinates of cobalt and oxygen in the unit cell as follows: Co1(0.5,0,0.5), Co2(0,0.5,0.5), O1(X O1 ,0,Z O1 ), 0.23≦X O1 ≦0.24, 0.61≦Z O1 ≦0.65, O2(X O2 ,0.5,Z O2 ), 0.75≦X O2 ≦0.78, 0.68≦Z O2 ≦0.71, can be shown within the range The lattice constant of the unit cell is a = 4.880 ± 0.05 Å, b = 2.817 ± 0.05 Å, c = 4.839 ± 0.05 Å, α=90°, β=109.6±0.1°, γ=90°.

[0152] This crystal structure also shows lattice constants in the space group R-3m if some error is allowed. In this case, the coordinates of cobalt and oxygen in the unit cell are Co(0,0,0.5), O(0,0,Z O ), 0.21≦Z O ≦0.23. The lattice constant of the unit cell is a = 2.817 ± 0.02 Å, c=13.68±0.1 Å.

[0153] Both the O3' and monoclinic O1(15) crystal structures contain cobalt, nickel, magnesium, Ions such as nesium occupy the hexa-coordinated oxygen positions. Light elements may occupy the oxygen tetracoordinate positions.

[0154] As shown by the dotted line in Figure 4, the R-3m O3 in the discharge state, O3' and monoclinic O1( 15) type crystal structure, there is almost no deviation of the CoO2 layer.

[0155] In addition, the R-3m O3 in the discharged state and the O3'-type crystal structure have the same number of cobalt atoms. The difference in product is not more than 2.5%, more particularly not more than 2.2%, typically not more than 1.8%.

[0156] Also, R-3m O3 in the discharge state and the same number of cobalt atoms with the monoclinic O1(15) type crystal structure The volume difference per unit is 3.3% or less, more specifically 3.0% or less, typically 2.5%. be.

[0157] Table 1 shows the discharged R-3m O3, O3', monoclinic O1(15), H1-3 type and The difference in volume per cobalt atom between the trigonal O1 and the trigonal O1 crystal structures used in the calculations in Table 1 is shown. The lattice constants of the R-3m O3 and trigonal O1 structures in the discharged state are given in the literature. (ICSD coll.code.172909 and 88721). For details of 1-3, see Non-Patent Document 3. O3', monoclinic O1(15) This can be calculated from the experimental values ​​of XRD.

[0158] [Table 1]

[0159] As described above, in the positive electrode active material 100 according to one embodiment of the present invention, Li x When x in CoO2 is small, In other words, the change in the crystal structure when a large amount of lithium is released is more pronounced than in conventional positive electrode active materials. The change in volume is also suppressed when compared per the same number of cobalt atoms. Therefore, the positive electrode active material 100 is repeatedly charged and discharged so that x becomes 0.24 or less. Therefore, the positive electrode active material 100 is resistant to breakdown in the charge-discharge cycle. The decrease in capacitance is suppressed. In addition, more lithium is stably used than with conventional positive electrode active materials. Therefore, the positive electrode active material 100 has a large discharge capacity per weight and per volume. Therefore, by using the positive electrode active material 100, it is possible to obtain high discharge capacity per weight and per volume. It is possible to create a secondary battery.

[0160] The positive electrode active material 100 is Li x When x in CoO2 is 0.15 or more and 0.24 or less, O It has been confirmed that the compound may have a 3'-type crystal structure, and x is greater than 0.24 and less than 0.27. It is estimated that the crystal structure is O3' type even under low temperature. x x in CoO2 is 0. When x is greater than 1 and less than 0.2, typically when x is 0.15 or more and less than 0.17, monoclinic O1(1 It has been confirmed that there are cases where the crystal structure is of type 5). x C It is affected not only by x in O2 but also by the number of charge / discharge cycles, charge / discharge current, temperature, electrolyte, etc. Therefore, the range of x is not necessarily limited to the above range.

[0161] Therefore, the positive electrode active material 100 is Li x When x in CoO2 is greater than 0.1 and less than 0.24 It may have only the O3' type, or only the monoclinic O1(15) type, or both. Alternatively, all of the particles in the interior 100b of the positive electrode active material 100 may have a crystal structure of O3 The crystal structure does not have to be monoclinic O1(15) type and / or monoclinic O1(15) type. The amorphous material may be partially amorphous or may be partially amorphous.

[0162] Also Li x To make the x in CoO2 small, it is generally necessary to charge at a high charging voltage. Therefore, Li x CoO2 with a small x was charged at a high charging voltage. For example, when the potential of lithium metal is 4.6V or higher When CC / CV charging is performed at a voltage of 25°C, the conventional positive electrode active material forms an H1-3 type crystal. Therefore, the charging voltage is high, above 4.6V, based on the potential of lithium metal. In this specification, unless otherwise specified, the charging voltage is expressed relative to the potential of lithium metal.

[0163] Therefore, the positive electrode active material 100 according to one embodiment of the present invention can be used at a high charging voltage, for example, at 25°C. Even when charged at a voltage of 4.6 V or higher, the crystal structure with the symmetry of R-3m O3 can be maintained. In other words, it is preferable to use a higher charging voltage, for example, at 25°C. When charged at a voltage between 4.65V and 4.7V, the O3'-type crystal structure can be formed. In other words, it is preferable to use a higher charging voltage, for example, at 25°C. When charged at a voltage above 4.7 V but below 4.8 V, the monoclinic O1(15) type crystal structure is formed. This can be rephrased as being preferable because it is possible to obtain it.

[0164] Even with 100% positive electrode active material, when the charging voltage was further increased, H1-3 type crystals were finally observed. As mentioned above, the crystal structure may change depending on the number of charge / discharge cycles, charge / discharge current, temperature, and voltage. If the charging voltage is lower, for example, at 25°C, the battery may be affected by electrolytes, etc. Even if the voltage is 4.5 V or more and less than 4.6 V, the positive electrode active material 100 according to one embodiment of the present invention has the O3'-type crystal structure. Similarly, when charging at a voltage between 4.65V and 4.7V at 25°C, When charged, it may take on a monoclinic O1(15) type crystal structure.

[0165] In addition, when graphite is used as the negative electrode active material in a secondary battery, the amount of graphite is more than that described above. The voltage of the secondary battery drops by the amount of the potential. The potential of graphite is based on the potential of lithium metal. Therefore, the negative electrode active material of a secondary battery using graphite is about 0.05V to 0.2V. In this case, the same crystal structure is obtained at a voltage obtained by subtracting the potential of graphite from the above voltage.

[0166] In addition, in O3' and monoclinic O1(15) in Figure 4, lithium occupies all lithium sites equally. However, this is not limited to the case where the lithium atoms are present at a certain lithium site. For example, the monoclinic O1(Li 0.5 CoO2) The distribution of lithium can be determined by, for example, neutron diffraction analysis. can be done.

[0167] The O3' and monoclinic O1(15) crystal structures have random lithium atoms between the layers. However, it can be said that the crystal structure is similar to that of CdCl2. The crystal structure similar to CdCl2 type is Lithium nickel oxide 0.06 Charged up to NiO2 The crystal structure is similar to that of pure lithium cobalt oxide or lithium cobalt-rich lithium cobalt oxide. It is known that layered rock salt type positive electrode active materials do not usually have a CdCl2 type crystal structure. .

[0168] The concentration gradient of the additive element is the same at multiple locations on the surface layer 100a of the positive electrode active material 100. In other words, the reinforcement due to the added elements is preferably in the surface layer portion 100a. Even if a part of the surface layer portion 100a is reinforced, the part without reinforcement is preferably uniform. If there is a portion of the positive electrode active material 100 where stress is present, stress may be concentrated in the portion where there is no stress. When the particles are concentrated, defects such as cracks occur, causing the positive electrode active material to break and the discharge capacity to decrease. There is a risk of it leading down.

[0169] However, it is not always necessary that the additive element is the same throughout the entire surface layer portion 100a of the positive electrode active material 100. The CD area in FIG. 1(A) is enlarged as shown in FIG. 6(A). 1) and 6(A2). An example of the distribution of the added element X near the CD in FIG. 1(A) is shown in FIG. An example of the distribution of the added element Y near the CD is shown in FIG. 6(A1) and FIG. 6(A2).

[0170] Here, the CD region has a layered rock-salt type crystal structure of R-3m, and the surface has a (001) orientation. The distribution of the added elements on the (001) oriented surface is different from that on the other surfaces. For example, the (001) oriented surface and its surface layer 100a may be formed by adding the additive element X and and the additive element Y, the distribution of one or more concentration peaks is other than the (001) orientation. It may be limited to a shallow portion from the surface compared to the surface. Or, it may be (001) oriented. The surface and its surface layer 100a have the added element X and the added element B in comparison with the surface other than the (001) oriented surface. The concentration of one or more selected from the additive elements Y may be low. The surface and its surface layer 100a are formed by adding one or more additional elements selected from the group consisting of additional elements X and additional elements Y. The upper concentration may be below the lower limit of detection.

[0171] In the layered rock-salt crystal structure of R-3m, cations are arranged parallel to the (001) plane. This is a structure in which CoO2 layers and lithium layers are alternately stacked parallel to the (001) plane. Therefore, the diffusion path of lithium ions is parallel to the (001) plane. do.

[0172] Since the CoO2 layer is relatively stable, the surface of the positive electrode active material 100 has a (001) orientation. The (001) plane is the main diffusion path for lithium ions during charging and discharging. Not yet.

[0173] On the other hand, the diffusion paths of lithium ions are exposed on surfaces other than the (001) orientation. Therefore, the surface and the surface layer portion 100a other than the (001) orientation maintain the diffusion path of lithium ions. This is an important region for the purpose of preventing the desorption of lithium ions, and is also an important region for preventing the desorption of lithium ions. Therefore, the surface and the surface layer portion 100a other than the (001) orientation are reinforced. This is extremely important for maintaining the crystal structure of the entire positive electrode active material 100 .

[0174] Therefore, in the positive electrode active material 100 according to another embodiment of the present invention, the surface and and the distribution of the additive elements in the surface layer 100a is as shown in FIG. 1(B1) or FIG. 1(B2). It is important that the distribution is uniform. It is preferable that the (001) orientation is detected on the outer surface and its surface layer 100a. As described above, the concentration of the additive element in the surface and its surface layer 100a may be low. Or it may not be necessary.

[0175] For example, the distribution of magnesium in the (001) oriented surface and its surface layer 100a The half width is preferably 10 nm or more and 200 nm or less, and more preferably 50 nm or more and 15 It is more preferable that the thickness is 0 nm or less, and even more preferable that the thickness is 80 nm or more and 120 nm or less. Furthermore, the surface that is not (001) oriented and the distribution of magnesium in the surface layer 100a The half width is preferably more than 200 nm and not more than 500 nm, and More preferably, it is greater than 230 nm and less than 270 nm. It is even more preferable that

[0176] The distribution of nickel in the surface and the surface layer 100a that is not (001) oriented is The half-width is preferably 30 nm or more and 150 nm or less, and more preferably 50 nm or more and 130 nm or less. It is more preferable that the thickness is 70 nm or more and 110 nm or less, and it is even more preferable that the thickness is 70 nm or more and 110 nm or less. .

[0177] As will be explained in a later embodiment, after producing high-purity LiCoO2, the additive elements are added later. The manufacturing method of mixing and heating the materials mainly allows the added elements to spread through the diffusion path of lithium ions. Therefore, the distribution of the additive elements in the surface other than the (001) orientation and in the surface layer 100a thereof is preferably controlled. It is easy to set it to a desired range.

[0178] Using Figures 6(B1) to 6(C), after producing high-purity LiCoO2, The results of calculations on the distribution of added elements when elements are mixed and heated will be explained below.

[0179] FIG. 6(B1) shows the calculation results for the (104) oriented surface and its surface layer 100a. This is the result of a classical molecular dynamics calculation. LiF and MgF2 were placed at the top of the system as a magnesium source, a lithium source, and a fluorine source. The ensemble was NVT, and the density of the initial structure was 1.8 g / cm 3 , the temperature of the system is 2000K The elapsed time is 100 psec, and the potential is optimized for the LCO crystal structure. is a mixture with UFF, the number of atoms in the system is about 10,000, and the charge of the system is neutral. , Co atoms and Mg atoms are selectively shown.

[0180] Figure 6(B2) was calculated similarly up to 200 psec, and Figure 6(B3) was calculated up to 1200 psec. This is the result.

[0181] From the above calculations, it is inferred that magnesium diffuses through the following process. (1) Lithium is released from LCO by heat. (2) Magnesium is released into the lithium layer of LCO. (3) Lithium from LiF enters the lithium layer of LCO, (1 ) to supplement the lost lithium.

[0182] After 100 psec, magnesium atoms are diffusing into the LCO. The magnesium atoms diffuse along the arrangement of cobalt atoms, and In Figure 6(B3) after 200 psec, the magnesium atoms prepared at the top of the system are almost All of this is incorporated into the LCO.

[0183] FIG. 6(C) shows the results of calculations similar to those in FIG. 6(B1) except that the orientation was (001). In Figure 6(C), it can be seen that the magnesium atoms remain on the surface of the LCO. Figure 6(C) shows the calculation results after 100 psec has elapsed. For example, since the LCO is heated for more than two hours, magnesium atoms are embedded inside the LCO. It is thought to spread slowly.

[0184] After producing high-purity LiCoO2 in this way, additive elements are mixed and heated. By this method, the surface other than the (001) orientation and its surface layer portion 100a The additive elements can be distributed in a preferred manner.

[0185] In the manufacturing method involving initial heating, which will be described later, the lithium in the surface layer portion 100a is removed by the initial heating. is expected to be released from LiCoO2, and furthermore, magnesium and other This makes it easier to distribute the added elements in high concentration in the surface layer.

[0186] In addition, it is preferable that the surface of the positive electrode active material 100 is smooth and has few irregularities, but this is not necessarily the case. However, it is not necessary that the entire surface of the positive electrode active material 100 is made of the layered rock salt type R-3m. The complex oxides with a crystalline structure have a plane parallel to the (001) plane, for example, a plane where lithium is arranged. For example, as shown in Figure 7(A), where the (001) plane exists, slip is likely to occur. In this case, the (001) plane is formed as shown by the arrow in Figure 7(B) by a process such as pressing. Slip may occur parallel to the surface, causing deformation.

[0187] In this case, the surface newly formed as a result of the slip and the surface layer 100a thereof contain the additive. In some cases, the element is not present or its concentration is below the detection limit. This is an example of the surface and its surface layer 100a newly formed as a result of the chipping. The results are shown in Figures 7(C1) and 7(C2). Unlike FIGS. 1(B1) and 1(B2), the additional element X and the additional element Y are not distributed.

[0188] However, slip tends to occur parallel to the (001) plane, so the newly formed surface and its The surface layer portion 100a tends to have a (001) orientation. In this case, the diffusion path of lithium ions is exposed. Since it is relatively stable and does not emit any added elements, the concentration is below the detection limit. There are almost no problems.

[0189] As mentioned above, the composition is LiCoO2 and the crystal structure is R-3m, which is a layered rock salt type. In the oxide, the cobalt atoms are aligned parallel to the (001) plane. In the M image, the cobalt in LiCoO2, which has the largest atomic number, has the highest brightness. Therefore, in the HAADF-STEM image, the arrangement of bright atoms is the arrangement of cobalt atoms. This repeating pattern of high brightness is synonymous with crystalline or lattice fringes.

[0190] <Grain boundary> The additive elements contained in the positive electrode active material 100 of one embodiment of the present invention may be distributed as described above. It is more preferable that at least a part of the particles be unevenly distributed at the grain boundaries 101 and their vicinity.

[0191] In this specification, uneven distribution means that the concentration of an element in a certain region is different from that in other regions. Segregation, precipitation, unevenness, bias, or the mixture of high concentration and low concentration areas. It is synonymous with "ru."

[0192] For example, the magnesium concentration at and near the grain boundary 101 of the positive electrode active material 100 is It is preferable that the grain boundary 101 and its vicinity are higher than the other regions of the portion 100b. The fluorine concentration is also preferably higher than that in other regions of the interior 100b. The nickel concentration in and around the inner portion 100b is also preferably higher than in other regions of the inner portion 100b. The aluminum concentration at and near the grain boundary 101 is also higher than other regions of the interior 100b. preferable.

[0193] The grain boundary 101 is one of the planar defects. Therefore, it is easily unstable like the grain surface. Therefore, the concentration of the added element at the grain boundary 101 and its vicinity If the value is high, the change in the crystal structure can be more effectively suppressed.

[0194] In addition, when the magnesium concentration and fluorine concentration at and near the grain boundary 101 are high, When cracks occur along the grain boundaries 101 of the positive electrode active material 100 according to one embodiment of the present invention, However, magnesium and fluorine concentrations become higher near the surface where cracks occur. Therefore, it is possible to improve the corrosion resistance of the positive electrode active material against hydrofluoric acid even after cracks have occurred. can be done.

[0195] <Particle size> If the particle size of the positive electrode active material 100 according to one embodiment of the present invention is too large, it becomes difficult for lithium to diffuse. When the active material layer is applied to the current collector, the surface of the active material layer becomes too rough. If the particle size is too small, it will be difficult to support the active material layer when applying it to the current collector, and excessive reaction with the electrolyte will occur. Therefore, the median diameter (D50) is 1 μm or more and 100 μm or less. Preferably, the thickness is 2 μm or less and 40 μm or less, more preferably, 5 μm or more and 30 μm or less. It is more preferable that the thickness is 1 μm or less and 40 μm or less. Preferably, the thickness is 30 μm or less, or 2 μm or more and 100 μm or less, or 2 μm Preferably, the thickness is 5 μm or more and 30 μm or less, or 5 μm or more and 100 μm or less. Preferably, the thickness is 40 μm or more and 40 μm or less.

[0196] <Analysis method> A certain positive electrode active material is Li x When x in CoO2 is small, O3' type and / or monoclinic Whether the positive electrode active material 100 of one embodiment of the present invention has an O1(15) type crystal structure or not can be determined by Li x Positive electrodes with positive electrode active materials with small x in CoO2 were analyzed by XRD, electron diffraction, and neutron This can be determined by analyzing using X-ray diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. I can say no.

[0197] In particular, XRD can analyze the symmetry of transition metals such as cobalt contained in the positive electrode active material with high resolution. It is possible to compare the crystallinity and orientation of the crystals, and to measure the periodic distortion of the lattice and the crystallite size. The size of the cathode obtained by disassembling the secondary battery can be analyzed with sufficient accuracy. Among XRD methods, powder XRD is preferred in that the volume of the positive electrode active material 100 Diffraction peaks reflecting the crystalline structure of the interior 100b of the positive electrode active material 100, which accounts for the majority of the can be.

[0198] When analyzing crystallite size using powder XRD, the influence of orientation due to pressure, etc. is excluded from the measurement. For example, a secondary battery is disassembled, and the positive electrode active material is extracted from the positive electrode. It is preferable to measure the powder sample.

[0199] As described above, the positive electrode active material 100 according to one embodiment of the present invention is Li x x in CoO2 It is characterized by the fact that there is little change in the crystal structure when the ratio is 1 and when it is 0.24 or less. When charged, the crystal structure changes significantly. Materials with a crystal structure of 50% or more are suitable for high voltage charging. This is not desirable because it cannot withstand charging and discharging.

[0200] In addition, the addition of an additional element alone does not result in the formation of an O3' or monoclinic O1(15) type crystal structure. It should be noted that there are cases where this is not possible. For example, Lithium baltate or lithium cobaltate with magnesium and aluminum Although they have in common the point that, depending on the concentration and distribution of the added elements, x x in CoO2 is 0.24 or less and the O3' and / or monoclinic O1(15) crystal structures are 60% or more In some cases, the H1-3 type crystal structure accounts for 50% or more.

[0201] In addition, even in the positive electrode active material 100 of one embodiment of the present invention, when x is too small, such as 0.1 or less, Under conditions where the charge voltage exceeds 4.9 V, the crystal structure becomes H1-3 type or trigonal O1 type. Therefore, when determining whether or not the positive electrode active material 100 is one aspect of the present invention, To determine this, we need to analyze the crystal structure using XRD and other methods, and also the charge capacity or charge voltage. Information such as the above is required.

[0202] However, when the positive electrode active material has a small x value, the crystal structure may change when it comes into contact with the air. For example, the crystal structure of the O3' type and monoclinic O1(15) type has been converted to the H1-3 type crystal structure. Therefore, all samples used for crystal structure analysis were stored in an argon atmosphere. It is preferable to handle the material in an inert atmosphere such as air.

[0203] In addition, it is possible to determine whether the distribution of the additive elements contained in a certain positive electrode active material is in the state described above. For example, XPS, energy dispersive X-ray spectroscopy (EDX) ersive X-ray spectroscopy), EPMA (electron probe microanalysis) This can be determined by analyzing the data using methods such as FTIR analysis.

[0204] The crystal structure of the surface layer 100 a, the grain boundary 101 , etc. is similar to the electron structure of the cross section of the positive electrode active material 100 . It can be analyzed by X-ray diffraction or the like.

[0205] ≪Charging method≫ In order to determine whether a certain composite oxide is the positive electrode active material 100 of one embodiment of the present invention, Charging is done using a coin cell (CR2032 type, 20mm diameter, 3. 2mm) can be created and charged.

[0206] More specifically, the positive electrode is formed by mixing a positive electrode active material, a conductive material, and a binder in a slurry. Alternatively, a positive electrode current collector made of aluminum foil may be coated with the conductive material.

[0207] Lithium metal can be used for the counter electrode. When the secondary battery is in a charged state, the potential of the secondary battery is different from the potential of the positive electrode. is the potential of the positive electrode unless otherwise specified.

[0208] The electrolyte contained 1 mol / L of lithium hexafluorophosphate (LiPF6). The electrolyte used was ethylene carbonate (EC) and diethyl carbonate (DEC). EC:DEC = 3:7 (volume ratio), vinylene carbonate (VC) was mixed at 2 wt%. The above can be used.

[0209] The separator can be a 25 μm thick porous polypropylene film.

[0210] The positive and negative electrode cans can be made of stainless steel (SUS). Cut.

[0211] The coin cell made under the above conditions was then charged to any voltage (e.g., 4.5V, 4.55V, 4. Charge at any voltage (6V, 4.65V, 4.7V, 4.75V or 4.8V). There is no particular restriction on the charging method as long as it can be charged over a period of 10 minutes. For example, charging with CCCV In this case, the current for CC charging can be 20mA / g or more and 100mA / g or less. CV charging can be completed at 2mA / g or more and 10mA / g or less. To observe the phase change, it is desirable to charge with such a small current value. After charging in this way, the coin cell was placed in an argon atmosphere. By disassembling the battery in an atmospheric glove box and removing the positive electrode, the positive electrode active material of any desired charging capacity can be obtained. When various analyses are carried out after this, the sample is kept in an argon atmosphere to prevent reactions with external components. For example, XRD is preferably sealed in a sealed container with an argon atmosphere. After the charging is completed, it is preferable to quickly remove the positive electrode and subject it to analysis. Specifically, it is preferable to do so within one hour after charging is complete, and more preferably within 30 minutes.

[0212] In addition, when analyzing the crystal structure in the charged state after multiple charge / discharge cycles, the multiple charge / discharge conditions The charging conditions may differ from those stated above. For example, charging can be performed at any voltage (e.g., 4.6V , 4.65V, 4.7V, 4.75V or 4.8V), current value 20mA / g or more Charge at a constant current of 0.00 mA / g or less, and then charge at a current of 2 mA / g or more and 10 mA / g or less. Charge at a constant voltage until the battery reaches a certain level, then discharge at a constant current of 2.5V, 20mA / g or more and 100mA / g or less. It can be electricity.

[0213] Furthermore, when analyzing the crystal structure in the discharged state after multiple charge / discharge cycles, for example, at 2.5V The discharge current can be constant at a current value of 20 mA / g or more and 100 mA / g or less.

[0214] <XRD> The apparatus and conditions for XRD measurement are not particularly limited. For example, the apparatus and conditions are as follows: It can be measured in terms of: XRD equipment: Bruker AXS, D8 ADVANCE X-ray source:CuKα1 ray Output: 40kV, 40mA Divergence angle: Div.Slit, 0.5° Detector: LynxEye Scan method: 2θ / θ continuous scan Measurement range (2θ): 15° to 90° Step width (2θ): 0.01° setting Counting time: 1 second / step Sample stage rotation: 15 rpm

[0215] If the sample is a powder, place it in a glass sample holder or grease it. It can be set up by sprinkling the sample on a coated silicone anti-reflective plate. When the measurement sample is a positive electrode, attach the positive electrode to the substrate with double-sided tape and can be set to match the measurement surface required by the device.

[0216] The crystal structure of the O3' type, the monoclinic O1(15) type, and the H1-3 type crystal structure The ideal powder XRD patterns using CuKα1 radiation calculated from the model are shown in Figures 8, 9, and 10. 10(A) and 10(B). For comparison, Li x Li in CoO2 with x=1 CoO2O3 and the ideal XRD pattern calculated from the trigonal O1 crystal structure with x = 0 Figure 10(A) and Figure 10(B) show the O3' type crystal structure, monoclinic O1(15) The XRD patterns of the H1-3 type crystal structure and the H1-3 type crystal structure are shown together in Figure 10(A). 10(B) is the region where the 2θ range is 18° or more and 21° or less, and FIG. 10(C) is the region where the 2θ range is 42° or more and 4 The area below 6° is enlarged. The pattern 2(O1) is ICSD (Inorganic Crystal Structure Mat was created from the crystal structure information obtained from the Crystal Database (see Non-Patent Document 4). Reflex, one of the modules of serials Studio (BIOVIA) Powder Diffraction was used. The 2θ range was from 15° to 7°. 5°, Step size = 0.01, wavelength λ1 = 1.540562 × 10 -10 m , λ2 was not set, and Monochromator was set to single. H1-3 type crystal The structure pattern was similarly created from the crystal structure information described in Non-Patent Document 3. The pattern of the monoclinic O1(15) type crystal structure is the XRD pattern of the positive electrode active material of one embodiment of the present invention. The crystal structure was estimated from the turn and analyzed using TOPAS ver.3 (Bruker Crystal Structure Analysis). The XRD patterns were generated similarly to the others by fitting using the software.

[0217] As shown in Figure 8, Figure 10(A) and Figure 10(B), in the O3' type crystal structure, 2θ = 19.25 ± 0.12° (between 19.13° and 19.37°), and 2θ = 45. A diffraction peak appears at 47±0.10° (45.37° or more and less than 45.57°).

[0218] In addition, in the monoclinic O1(15) crystal structure, 2θ=19.47±0.10° (19.3 7° or more and 19.57° or less), and 2θ=45.62±0.05° (45.57° or more) Diffraction peaks appear at angles below 45.67°.

[0219] However, as shown in Figure 9, Figure 10(A) and Figure 10(B), the H1-3 type crystal structure and In the case of Li and trigonal O1, no peaks appear at these positions. x x in CoO2 When the angle is small, the angle is 19.13° or more but less than 19.37° and / or 19.37° or more but less than 19. 0.57° or less, and 45.37° or more but less than 45.57° and / or 45.57° or more The appearance of a peak at or below 45.67° is a characteristic of the positive electrode active material 100 according to one embodiment of the present invention. This can be said to be a sign.

[0220] This is because the positions where XRD diffraction peaks appear are the same for the crystal structures of x=1 and x≦0.24. More specifically, the main phases of the crystal structure for x=1 and x≦0.24 are For the peaks that appear at 2θ between 42° and 46°, the difference in 2θ is 0 It can be said that the angle is less than 0.7°, and more preferably less than 0.5°.

[0221] The positive electrode active material 100 according to one embodiment of the present invention is Li x When x in CoO2 is small, O3' The crystal structure is monoclinic O1(15) type and / or monoclinic O1(15) type, but all of the particles are O3' type. and / or monoclinic O1(15) type crystal structure. However, the XRD pattern may be Rietve When the lattice analysis was performed, the crystal structure of O3' and / or monoclinic O1(15) was % or more, more preferably 60% or more, and more preferably 66% or more. It is more preferred that the O3' type and / or monoclinic O1(15) type crystal structure is 50 % or more, more preferably 60% or more, and even more preferably 66% or more, it is sufficient for cycling. It is possible to obtain a positive electrode active material having excellent dielectric properties.

[0222] In addition, even after more than 100 charge / discharge cycles from the start of measurement, Rietveld analysis was performed. When the O3' and / or monoclinic O1(15) crystal structure is more than 35% It is preferable that the ratio is 40% or more, more preferable that the ratio is 43% or more. stomach.

[0223] Similarly, when Rietveld analysis was performed, the H1-3 and O1 crystal structures were found to be 50 % or less is preferable.

[0224] In addition, the sharpness of the diffraction peaks in the XRD pattern indicates high crystallinity. Each of the subsequent diffraction peaks is preferably sharp, i.e., the half-value width, for example, the full width at half maximum, is preferably narrow. The width of the peaks varies depending on the XRD measurement conditions and the 2θ value, even for peaks arising from the same crystalline phase. Under the above measurement conditions, the peak observed at 2θ=43° or more and 46° or less In this case, the full width at half maximum is preferably 0.2° or less, more preferably 0.15° or less, and more preferably 0. It is more preferable that the angle is 12° or less. However, not all peaks necessarily meet this requirement. If some of the peaks satisfy this requirement, it can be said that the crystallinity of the crystalline phase is high. Such high crystallinity contributes to the stabilization of the crystal structure after sufficient charging.

[0225] In addition, the positive electrode active material 100 has a crystal structure of O3' type and monoclinic O1(15). The particle size decreases to only about 1 / 20 of that of LiCoO2(O3) in the discharged state. Therefore, even if the XRD measurement conditions were the same as those for the positive electrode before and after charging and discharging, the Li x x in CoO2 is small When the crystal structure is not clearly defined, peaks of the O3' type and / or monoclinic O1(15) crystal structure can be confirmed. On the other hand, in conventional LiCoO2, some of the structures are O3' and / or monoclinic O1(15). Even if a structure similar to a crystalline structure is obtained, the crystallite size becomes small and the peak becomes broad. The crystallite size can be determined from the half-width of the XRD peak.

[0226] In the positive electrode active material 100 according to one embodiment of the present invention, as described above, the influence of the Jahn-Teller effect As long as the influence of the Jahn-Teller effect is small, the Other additive elements may include transition metals such as nickel and manganese.

[0227] XRD analysis of the positive electrode active material suggests that the Jahn-Teller effect is small. The range of the nickel and manganese ratios and lattice parameters to be used is considered.

[0228] FIG. 11 shows a positive electrode active material 100 of one embodiment of the present invention having a layered rock salt crystal structure and containing cobalt. The lattice constants of the a-axis and c-axis were calculated using XRD for the case of the alloy containing titanium and nickel. The results are shown in Fig. 11(A) for the a-axis and Fig. 11(B) for the c-axis. The XRD pattern used in the calculation was the powder after synthesis of the positive electrode active material, and The nickel concentration on the horizontal axis is calculated by dividing the sum of the number of cobalt and nickel atoms by 100. The positive electrode active material does not use an aluminum source, but the nickel concentration is shown in Figure 1. It was prepared according to the method of preparation of 15.

[0229] FIG. 12 shows a positive electrode active material 100 of one embodiment of the present invention having a layered rock salt crystal structure. In the case of Fe and Mn, the lattice parameters of the a-axis and c-axis were estimated using XRD. The results are shown in Fig. 12(A) for the a-axis and Fig. 12(B) for the c-axis. The lattice constant shown in 2 is the powder after synthesis of the positive electrode active material, and was measured before being incorporated into the positive electrode. The manganese concentration on the horizontal axis is the ratio of the number of cobalt and manganese atoms. The manganese concentration is shown when the total is taken as 100%. The fabrication method was the same as that shown in Figure 15, except that a fluorine source was used and no aluminum source was used. Ta.

[0230] FIG. 11(C) shows the results of the lattice constants of the positive electrode active material shown in FIG. 11(A) and FIG. 11(B). For a material, the value obtained by dividing the a-axis lattice constant by the c-axis lattice constant (a-axis / c-axis) is shown. 2(C) shows the lattice constants of the positive electrode active materials shown in Figures 12(A) and 12(B). The values ​​obtained by dividing the lattice constant of the a-axis by the lattice constant of the c-axis (a-axis / c-axis) are shown.

[0231] From Figure 11(C), it can be seen that the a-axis / c-axis changes significantly when the nickel concentration is 5% and 7.5%. At a nickel concentration of 7.5%, the distortion of the a-axis is large. This may be due to the Jahn-Teller distortion of nickel. It is suggested that an excellent cathode active material with small Jahn-Teller distortion can be obtained in this case. .

[0232] Next, from Figure 12(A), when the manganese concentration is 5% or more, the behavior of the change in lattice constant This suggests that the manganese concentration is different and does not follow Vegard's law. Therefore, the preferred manganese concentration is, for example, 4% or less. I wish.

[0233] The above-mentioned ranges of nickel concentration and manganese concentration are not necessarily set in the surface layer portion 100a. That is, in the surface layer 100a, even if the concentration is higher than the above, good.

[0234] From the above, the preferable range of the lattice constant was considered, and it was found that the positive electrode of one embodiment of the present invention In the active material, the state without charge and discharge or discharged state that can be estimated from the XRD pattern In the layered rock salt type crystal structure of the positive electrode active material 100 in an electrically charged state, the lattice constant of the a-axis is 2 .814×10-10 m, 2.817×10 -10 smaller than m and the grid of the c axis The child constant is 14.05 x 10 -10 m, 14.07 × 10 -10 be smaller than m It has been found that this is preferable. The state in which no charge and discharge is performed is, for example, when preparing a positive electrode for a secondary battery. It may be in a powder state before being mixed.

[0235] Alternatively, the layered structure of the positive electrode active material 100 in a state where no charge / discharge is performed or in a discharged state may be In a rock-salt crystal structure, the lattice constant of the a-axis divided by the lattice constant of the c-axis (a-axis / c-axis) is preferably greater than 0.20000 and less than 0.20049.

[0236] Alternatively, the layered structure of the positive electrode active material 100 in a state where no charge / discharge is performed or in a discharged state may be In the rock salt crystal structure, when XRD analysis was performed, 2θ was 18.50° or more and 19.30° or less. The first peak is observed at 2θ of 38.00° or less and the second peak is observed at 2θ of 38.80° or less. A peak may be observed.

[0237] XPS In X-ray photoelectron spectroscopy (XPS), in the case of inorganic oxides, monochromatic aluminum is used as the X-ray source. When Kα rays are used, the area from the surface to a depth of about 2 to 8 nm (usually 5 nm or less) Since the analysis is possible, the amount of each element can be measured in an area approximately half the depth of the surface layer 100a. The concentration can be quantitatively analyzed. In addition, narrow scan analysis can be used to analyze the bonding state of elements. The quantitative accuracy of XPS is usually about ±1 atomic percent, and the The limit is about 1 atomic %, depending on the element.

[0238] The positive electrode active material 100 according to one embodiment of the present invention has a concentration of one or more selected from the group consisting of additive elements. It is preferable that the temperature is higher in the surface layer 100a than in the interior 100b. The concentration of one or more of the additive elements in the positive electrode active material is higher than the average of the entire positive electrode active material. Therefore, for example, the surface layer measured by XPS, etc. The concentration of one or more additive elements selected from the part 100a is measured by ICP-MS (inductively coupled plasma mass spectrometry). The positive electrode activity measured by Glow Discharge Mass Spectrometry (GD-MS) or GD-MS (Glow Discharge Mass Spectrometry) It can be said that the concentration of the added element is preferably higher than the average concentration of the added element in the entire substance 100. For example, the magnesium concentration of at least a part of the surface layer 100a measured by XPS or the like is preferably higher than the magnesium concentration in the entire positive electrode active material 100. The nickel concentration in at least a part of the positive electrode active material 100 is higher than the nickel concentration in the whole positive electrode active material 100. It is also preferable that the aluminum concentration in at least a part of the surface layer portion 100a is It is preferable that the aluminum concentration in the surface layer 100 is higher than that in the entire positive electrode active material 100. The fluorine concentration of at least a part of a is higher than the fluorine concentration of the whole positive electrode active material 100. It is preferable that:

[0239] The surface and surface layer 100a of the positive electrode active material 100 according to one embodiment of the present invention are Carbonates, hydroxyl groups, etc. chemically adsorbed after the preparation of 100 are not included. This does not include the electrolyte, binder, conductive material, or compounds derived from these materials attached to the surface of 100. Therefore, when quantifying the elements contained in the positive electrode active material, it is necessary to use a surface analysis method such as XPS. Even after corrections to exclude carbon, hydrogen, excess oxygen, excess fluorine, etc. that can be detected by area analysis, For example, XPS can analyze and separate the types of bonds, and binder-derived A correction to exclude the C—F bond may be made.

[0240] Furthermore, before being subjected to various analyses, the electrolyte, binder, and conductive material adhering to the surface of the positive electrode active material were removed. In order to remove compounds derived from these, samples of the positive electrode active material and the positive electrode active material layer are In this case, lithium may be dissolved in the solvent used for washing. However, even in this case, the added elements are difficult to dissolve, so the atomic ratio of the added elements It does not have any impact on the

[0241] The concentration of the added element may also be compared in terms of its ratio to cobalt. This allows comparison by reducing the influence of carbonates and other substances that are chemically adsorbed after the positive electrode active material is produced. For example, the ratio of the number of magnesium atoms to the number of cobalt atoms, Mg / C, determined by XPS analysis, is On the other hand, the Mg / Co is preferably 0.001 or more and 0.06 or less.

[0242] Similarly, the positive electrode active material 100 has a surface layer to ensure sufficient paths for lithium insertion and desorption. In the portion 100a, it is preferable that the concentrations of lithium and cobalt are higher than those of the additional elements. This is one or more selected from the additive elements contained in the surface layer portion 100a measured by XPS or the like. The concentrations of lithium and cobalt in the surface layer portion 100a are higher than the concentrations of each of the two or more additional elements. For example, it is preferable that the surface layer portion 100a measured by XPS or the like The magnesium concentration of the surface layer portion 100a measured by XPS or the like is higher than that of at least a part of the surface layer portion 100a. It is preferred that at least some of the cobalt be present in a high concentration. In addition, it is preferable that the concentration of cobalt is higher than that of nickel. Similarly, it is preferable that the lithium concentration is higher than the nickel concentration. It is also preferable that the concentration of cobalt is higher than that of aluminum. It is preferable that the concentration of lithium is higher than that of fluorine. Similarly, a higher concentration of lithium than fluorine is preferred.

[0243] Furthermore, the additive element Y, such as aluminum, is present in deep regions, for example, It is more preferable that the particle size is widely distributed in the range of 5 nm to 50 nm. Analysis of the entire positive electrode active material 100 using S, GD-MS, etc. revealed that aluminum and other Although the added element Y is detected, if its concentration is below the detection limit in XPS, etc., preferable.

[0244] Furthermore, when the positive electrode active material 100 according to one embodiment of the present invention was subjected to XPS analysis, the cobalt The number of magnesium atoms is preferably 0.4 to 1.2 times the number of atoms of the alloy, and is preferably 0.6 It is more preferable that the number of nickel atoms is 5 times or more and 1.0 times or less. The ratio is preferably 0.15 or less, and more preferably 0.03 to 0.13. The number of aluminum atoms is preferably 0.12 times or less than the number of barium atoms, and 0.09 times or less. The number of fluorine atoms is preferably 0.3 times or more compared to the number of cobalt atoms. The range is preferably 0.9 times or less, and more preferably 0.1 times or more and 1.1 times or less. This means that these additive elements are attached to a narrow area on the surface of the positive electrode active material 100. It shows that the positive electrode active material 100 is not only dispersed but is widely distributed in a preferred concentration in the surface layer 100a of the positive electrode active material 100. It can be said that.

[0245] When performing XPS analysis, for example, monochromated aluminum Kα rays are used as the X-ray source. The take-off angle can be set to, for example, 45°. For example, the following equipment and conditions can be used: It can be measured by Measurement equipment: PHI Quantera II X-ray source: Monochromatic Al Kα (1486.6eV) Detection area: 100 μmφ Detection depth: Approximately 4 to 5 nm (take-off angle 45°) Measurement spectrum: Wide scan, narrow scan for each detected element

[0246] Furthermore, when the positive electrode active material 100 according to one embodiment of the present invention was analyzed by XPS, fluorine and other elements were The peak showing the bond energy of the element is preferably 682 eV or more and less than 685 eV. It is more preferable that the bond energy of lithium fluoride is about 684.3 eV. 685 eV, the binding energy of magnesium fluoride, and 686 eV In other words, the positive electrode active material 100 according to one embodiment of the present invention contains fluorine. If present, it is preferably a bond other than lithium fluoride and magnesium fluoride.

[0247] Furthermore, when the positive electrode active material 100 according to one embodiment of the present invention was analyzed by XPS, magnesium The peak showing the binding energy between uranium and other elements is between 1302 eV and 1304 eV. It is preferable that the energy is about 1303 eV, and more preferably about 1303 eV. This is a different value from the 1305 eV binding energy of magnesium oxide. In other words, the positive electrode active material 100 according to one embodiment of the present invention is When the compound has a magnesium fluoride bond, it is preferably a bond other than magnesium fluoride.

[0248] EDX One or more additive elements contained in the positive electrode active material 100 have a concentration gradient. In addition, the positive electrode active material 100 has a concentration peak from the surface thereof due to the addition of an element. It is more preferable that the depths are different. The concentration gradient of the added element can be obtained by, for example, FIB (Fo The cross section of the positive electrode active material 100 is exposed by a cusped ion beam or the like, and the cross section is Energy Dispersive X-ray Spectroscopy (EDX) Analysis using methods such as Electron Probe Microanalysis (EPMA) and Ray Spectroscopy (AY Spectroscopy). It can be evaluated by doing so.

[0249] Among EDX measurements, the measurement is performed while scanning the area, and the area is evaluated two-dimensionally. This is called DX area analysis. It is also possible to measure the atomic concentration by scanning linearly. Evaluating the distribution of the data is called line analysis. Furthermore, data on linear regions can be extracted from the EDX area analysis. The measurement of an area without scanning is sometimes called line analysis. This is called point analysis.

[0250] By EDX area analysis (for example, element mapping), it was found that the surface layer 100a of the positive electrode active material 100 The concentration of the added element in the interior 100b and in the vicinity of the grain boundary 101 is quantitatively analyzed. In addition, EDX analysis can be used to analyze the concentration distribution and maximum value of added elements. In addition, analysis of thin-sectioned samples, such as STEM-EDX, allows for the observation of the depth direction. The depth from the surface to the center of the positive electrode active material in a specific region is not affected by the distribution of This is more preferable because it allows for analysis of the density distribution in the direction.

[0251] Therefore, the positive electrode active material 100 according to one embodiment of the present invention was subjected to EDX area analysis or EDX point analysis. When the concentration of each additional element in the surface layer portion 100a, particularly the additional element X, is It is preferable that it is higher than

[0252] For example, EDX area analysis of the positive electrode active material 100 containing magnesium as an added element Alternatively, when EDX point analysis is performed, the magnesium concentration in the surface layer 100a is higher than that in the interior 100b. It is preferable that the concentration of magnesium is higher than that of magnesium. The peak of the magnesium concentration at point a is at a depth of 3n from the surface of the positive electrode active material 100 toward the center. Preferably, the pores are present at a depth of up to 1000 nm, more preferably at a depth of up to 1000 nm, and It is more preferable that the magnesium concentration is present up to 0.5 nm. It is preferable that the peak is attenuated to 60% or less at a depth of 1 nm from the top. It is preferable that the peak value is attenuated to 30% or less at a point 2 nm deep from the tip. The peak of concentration refers to the maximum value of the concentration.

[0253] In addition, in the positive electrode active material 100 containing magnesium and fluorine as additive elements, fluorine It is preferable that the distribution of fluorine overlaps with the distribution of magnesium. The difference in the depth direction between the peaks of the magnesium concentration is preferably within 10 nm, and 3 nm. It is more preferable that the thickness is within 1 nm, and even more preferable that the thickness is within 1 nm.

[0254] In addition, when EDX analysis was performed, the peak of the fluorine concentration in the surface layer 100a was It is preferable that the surface of the 00 is located at a depth of 3 nm from the surface to the center, and the depth of 1 nm is It is more preferable that the surface is already present, and it is even more preferable that the surface is present to a depth of 0.5 nm. The fluorine concentration peak is located slightly closer to the surface than the magnesium concentration peak. For example, the peak of the fluorine concentration is It is more preferable that the thickness is 0.5 nm or more on the surface side from the peak of the concentration of the silicon, and 1.5 nm or more on the surface side. It is more preferable that the surface side be the surface side.

[0255] In the positive electrode active material 100 containing nickel as an additive element, the nickel in the surface layer portion 100a The peak of the concentration of ions is present within a depth of 3 nm from the surface of the positive electrode active material 100 toward the center. It is preferable that the thickness of the pores is within 1 nm, and more preferable that the thickness of the pores is within 0.5 nm. It is more preferable that the positive electrode active material containing magnesium and nickel is present in the positive electrode active material. In 100, the distribution of nickel preferably overlaps with the distribution of magnesium. For example, the difference in depth between the nickel concentration peak and the magnesium concentration peak is within 10 nm. It is preferable that the thickness is within 3 nm, and it is even more preferable that the thickness is within 1 nm. .

[0256] In addition, when the positive electrode active material 100 contains aluminum as an added element, EDX analysis is performed. When the aluminum concentration peak is higher in the surface layer 100a than in the magnesium and nickel Alternatively, it is preferable that the peak of the fluorine concentration is close to the surface. The gap exists at a depth of 0.5 nm to 50 nm from the surface toward the center of the positive electrode active material 100. It is preferable that the pores are present at a depth of 5 nm or more and 50 nm or less.

[0257] In addition, when EDX analysis, area analysis, or point analysis was performed on the positive electrode active material 100, The ratio of the number of magnesium Mg to cobalt Co atoms at the peak of sodium concentration (Mg / Co ) is preferably 0.05 or more and 0.6 or less, and more preferably 0.1 or more and 0.4 or less. The ratio of the number of aluminum Al to cobalt Co atoms at the peak of the aluminum concentration (Al / Co ) is preferably 0.05 or more and 0.6 or less, and more preferably 0.1 or more and 0.45 or less. The ratio of the number of atoms of nickel Ni to cobalt Co (Ni / Co) at the peak of the nickel concentration is 0. The peak of the fluorine concentration is preferably from 0.01 to 0.1, and more preferably from 0.01 to 0.1. The ratio of the number of atoms of fluorine F to cobalt Co (F / Co) in the compound is preferably 0 or more and 1.6 or less. It is preferable that the ratio is 0.1 or more and 1.4 or less.

[0258] The surface of the positive electrode active material 100 in the EDX analysis results is estimated as follows: The elements that are uniformly present in the interior 100b of the positive electrode active material 100, for example, For example, for oxygen or cobalt, the point where the detected amount of the internal 100b is 1 / 2 is taken as the surface. do.

[0259] Since the positive electrode active material 100 is a composite oxide, the surface can be estimated using the detected amount of oxygen. Specifically, first, the oxygen concentration is measured from the region where the amount of detected oxygen in the interior 100b is stable. Average degree O ave At this time, chemical adsorption occurs in an area that can be clearly determined to be outside the surface. or oxygen O that may be due to background bg If detected, the measured value O bg The average oxygen concentration is calculated by subtracting ave This average value O ave 1 of The value of / 2, that is, 1 / 2O ave The measurement point showing the closest measured value to the surface of the positive electrode active material It can be estimated that:

[0260] The surface can also be estimated in the same way as above using the amount of cobalt detected. It can also be estimated in the same way by summing the detected amounts of several transition metals. The amount of detected transition metals is less susceptible to chemical adsorption, making it suitable for estimating the surface.

[0261] When the positive electrode active material 100 is subjected to a line analysis or a surface analysis, the positive electrode active material 100 is The ratio of the number of atoms of the additive element A to the number of atoms of cobalt Co (A / Co) is 0.020 or more and 0.50 or less. It is more preferable that the value is 0.025 or more and 0.30 or less. It is even more preferable that the value is 0.030 or more. Preferably, it is between 0.20 and 0.30. Or, it is between 0.020 and 0.30. Or, it is 0. Preferably, it is 0.020 or more and 0.20 or less. Or, it is 0.025 or more and 0.50 or less. Preferably, the ratio is 0.025 or more and 0.20 or less, or 0.030 or more and 0.50 or less. Alternatively, it is preferable that the ratio is 0.030 or more and 0.30 or less.

[0262] For example, when the additive element is magnesium, the positive electrode active material 100 is subjected to line analysis or area analysis. When the crystal grains were grown, the ratio of the number of magnesium and cobalt atoms in the vicinity of the grain boundary (Mg / Co) is preferably 0.020 or more and 0.50 or less, and more preferably 0.025 or more and 0.30 or less. It is preferably 0.030 or more and 0.20 or less. Preferably, it is between 0.30 and 0.30. Or, it is between 0.020 and 0.20. Or, it is 0. Preferably, it is 0.025 or more and 0.50 or less. Or, it is 0.025 or more and 0.20 or less. or preferably 0.030 or more and 0.50 or less, or preferably 0.030 or more and 0.30 or less. In addition, the positive electrode active material 100 is preferably in the above range at a plurality of locations, for example, at three or more locations. The additive element does not adhere to a narrow area on the surface of the positive electrode active material 100, but adheres to the entire surface of the positive electrode active material 100. This indicates that the surface layer 100a of 00 is widely distributed at a preferred concentration.

[0263] EPMA EPMA (Electron Probe Microanalysis) can also quantify elements. The distribution can be analyzed.

[0264] When a cross section of the positive electrode active material 100 according to one embodiment of the present invention was analyzed by EPMA, EDX Similar to the analysis results of (1), one or more selected additive elements have a concentration gradient. In addition, the depth from the surface of the concentration peak varies depending on the added element. The preferred range of the concentration peak of each added element is the same as that in the case of EDX.

[0265] However, EPMA analyzes the area from the surface to a depth of about 1 μm. The quantitative values ​​of the positive electrode active material 10 may differ from the measurement results obtained using other analytical methods. When the surface of the sample was analyzed by EPMA, the concentrations of the additive elements present in the surface layer 100a were as follows: May be lower than the XPS results.

[0266] <Charging curve and dQ / dV vs V curve> The positive electrode active material 100 according to one embodiment of the present invention exhibits a characteristic voltage change during charging. The change in voltage can be calculated by differentiating the capacity (Q) of the charging curve with the voltage (V) (dQ / dV). For example, dQ / dV can be read from the dQ / dV vs V curve obtained by Before and after the peak in the vsV curve, a non-equilibrium phase change occurs, and the crystal structure changes significantly. In this specification, a non-equilibrium phase change refers to a non-linear change in a physical quantity. This term refers to the phenomenon that causes transformation.

[0267] The positive electrode active material 100 according to one embodiment of the present invention exhibits a dQ / dV vs. V curve of 4.55 V. The peak near 4.55 V is due to the O3 type crystal structure. This reflects the change in voltage when the phase changes from the O3' type crystal structure to the O3' type crystal structure. A broad peak requires more time to extract lithium than a sharp peak. This means that there is little change in energy, which means there is little change in the crystal structure. The smaller the change, the less the influence of the displacement of the CoO2 layer and the change in volume is, which is preferable.

[0268] More specifically, in the dQ / dV vs V curve of the charging curve, When the maximum value that appears below is the first peak, the full width at half maximum of the first peak is 0.10 V or more. In this specification, the half width of the first peak is The full range of values ​​is determined by setting the minimum value of the dQ / dV value that appears between 4.3V and 4.5V as the first minimum value. When the voltage is 4.6V or more and 4.8V or less, the average value HWHM1 of the first peak and the first minimum value is The first peak and the second maximum when the minimum value of the dQ / dV values ​​shown below is the second minimum value. The difference between the average value HWHM2 and the smallest value is

[0269] When acquiring the dQ / dV vs V curve, the charge is constant at 10 mA / g up to, for example, 4.9 V. When obtaining the dQ / dV of the initial charge, the 2 Discharge the battery to 2.5V at a current between 0mA / g and 100mA / g, then start charging. It is preferable that:

[0270] The data acquisition interval during charging can be set to, for example, 1 second intervals or when there is a 1mV voltage fluctuation. The voltage and current when the current is accumulated over time can be set to be acquired. The value is the charging capacity.

[0271] The difference between the nth and n+1th data of the charge capacity data is the nth change in capacity dQ. Similarly, the difference between the nth and n+1th data of the voltage data is used as the voltage change. Let n be the nth value of the transformation dV.

[0272] However, when using the above data, the influence of minute noise is large, so the voltage and charging capacity The dQ / dV value may be calculated from the moving average of a certain number of intervals. For example, it can be set to 500.

[0273] Specifically, calculate the average value of dQ from the nth to the n+500th, and similarly calculate the nth of dV. Calculate the average value from the th to n+500th. dQ(average of 500) / dV(500 The dQ / dV value can be calculated by dividing the horizontal axis of the dQ / dV vs V graph by the average of the number of Similarly, the moving average value of 500 sections can be used for voltage. If you use a moving average with 500 intervals, the data will be from the 501st data from the end to the last data. It is preferable not to use data in the dQ / dV vs V graph because it is subject to large noise influences. stomach.

[0274] In addition, when analyzing the dQ / dV vs V curve after multiple charge / discharge cycles, The charging conditions may differ from those stated above. For example, charging may be performed at any voltage (e.g., 4.6 V, 4.65V, 4.7V, 4.75V or 4.8V), 20mA / g or more 100mA Charge at a constant current of 2mA / g or less, and then charge at a constant current until the current value becomes 2mA / g or more and 10mA / g or less. Charge at a voltage of 2.5V, and discharge at a constant current of 20mA / g or more and 100mA / g or less. It is possible.

[0275] At around 4.55V, the phase changes from O3 type crystal structure to O3' type crystal structure. In this case, the O3 type crystal structure is Li x The x in CoO2 is about 0.3. It has the same symmetry as the O3 type crystal structure with x=1 described above, but the distance between the CoO2 layers is slightly different. In this specification and the like, when distinguishing between O3 type crystal structures having different values ​​of x, x=1 The O3 type crystal structure of O3 (2θ = 18.85) is O3, and the O3 type crystal structure of about x = 0.3 is O3 (2θ=18.57). This is because 2θ is around 19° in XRD measurement. This is because the position of the peak that appears in the graph corresponds to the CoO2 interlayer distance.

[0276] <Discharge curve and dQ / dV vs V curve> Furthermore, the positive electrode active material 100 according to one embodiment of the present invention can be charged at a high voltage, for example, at 40 mA. When discharging at a low current of 1 / g or less, a characteristic voltage change may occur near the end of discharge. This change appears around 3.9V in the dQ / dV vs V curve obtained from the discharge curve. There is at least one peak in the range of up to 3.5V that is lower than the peak that appears. This can be clearly confirmed by

[0277] ESR The positive electrode active material 100 of one embodiment of the present invention contains cobalt and nickel and It is preferable to have magnesium. 3+ Ni 3+ is replaced by Also, some Li + Mg 2+ It is preferred that Li be substituted. + Mg 2+ is replaced by In accordance with this, the Ni 3+ is reduced to Ni 2+ In addition, some L i + Mg 2+ is replaced by Mg 2+ Nearby Co 3+ is reduced to Co 2+ to In addition, some Co 3+ Mg 2+ is replaced by Mg 2+ Nearby Co 3+ is oxidized to Co 4+ This may occur.

[0278] Therefore, the positive electrode active material 100 is Ni 2+ , Ni 3+ , Co 2+ and Co 4+ Either It is preferable that the positive electrode active material has one or more Ni. 2+ , N i 3+ , Co 2+ and Co 4+ The spin density due to one or more of the following is 2.0×10 17 spins / g or more 1.0×10 21It is preferable that the value is less than spins / g. By providing the positive electrode active material 100 with the above spin density, the crystal structure is stable, especially in the charged state. However, if the magnesium concentration is too high, 2+ , Ni 3+ , Co 2 + and Co 4+ The spin density may be reduced due to one or more of the above.

[0279] The spin density in the positive electrode active material can be measured by, for example, electron spin resonance (ESR) method. It can be analyzed using techniques such as spin resonance.

[0280] <Surface roughness and specific surface area> The positive electrode active material 100 of one embodiment of the present invention preferably has a smooth surface with few irregularities. The smooth surface and minimal irregularities are due to the full effect of the flux, which will be described later. This shows that the surface of the element source and the lithium cobalt oxide are melted. This is one factor that indicates that the distribution of added elements is good.

[0281] The surface is smooth and has few irregularities, as can be seen, for example, in the cross-sectional SEM image of the positive electrode active material 100 or can be determined from a cross-sectional TEM image, the specific surface area of ​​the positive electrode active material 100, and the like.

[0282] For example, as shown below, the surface smoothness is calculated numerically from a cross-sectional SEM image of 100 positive electrode active materials. It can be made into

[0283] First, the cathode active material 100 is processed by FIB or the like to expose a cross section. It is preferable to cover the positive electrode active material 100 with a protective agent or the like. The SEM image of the interface is taken. The SEM image is then processed using image processing software. After applying Gaussian blur (σ=2), the image is binarized. Then, the boundary is extracted using image processing software. Furthermore, an automatic selection tool or the like is used to select the interface line between the protective film or the like and the positive electrode active material 100. The data is extracted into a spreadsheet or similar software. A regression curve (quadratic) is created using the functions of the spreadsheet or similar software. The parameter for calculating roughness is calculated from the data after the slope correction. The root mean square surface roughness (RMS) is calculated by calculating the difference. The active material has a surface roughness of at least 400 nm around the periphery of the particle.

[0284] On the particle surfaces of the positive electrode active material 100 of this embodiment, the root mean square, which is an index of roughness, Root mean square (RMS) surface roughness is less than 3 nm, preferably less than 1 nm, and more preferably less than 0 A root mean square surface roughness (RMS) of less than 0.5 nm is preferred.

[0285] There are no particular restrictions on the image processing software used for noise processing, boundary extraction, etc. For example, "ImageJ" described in Non-Patent Documents 6 to 8 can be used. There is no particular limitation on spreadsheet software, but for example, Microsoft fice Excel can be used.

[0286] For example, the actual specific surface area S measured by the gas adsorption method using the constant volume method R And ideal Specific surface area S i The surface smoothness of the positive electrode active material 100 can also be quantified from the ratio of Cut.

[0287] Ideal specific surface area S iis that all particles have the same diameter as D50 and the same weight. The shape is calculated assuming an ideal sphere.

[0288] The median diameter D50 can be measured using a particle size distribution analyzer that uses the laser diffraction and scattering method. The specific surface area can be measured using a specific surface area measuring device that uses a gas adsorption method based on a constant volume method, for example. It can be measured by

[0289] The positive electrode active material 100 according to one embodiment of the present invention has an ideal specific surface area calculated from the median diameter D50. Product S i and the actual specific surface area S R The ratio S R / S i is preferably 2.1 or less.

[0290] Alternatively, the surface roughness can be determined from a cross-sectional SEM image of the positive electrode active material 100 by the following method. Softness can be quantified.

[0291] First, a surface SEM image of the positive electrode active material 100 is obtained. The observation surface is preferably perpendicular to the electron beam. When comparing samples, the measurement conditions and observation area should be the same.

[0292] Next, the above SEM image is processed using image processing software (e.g., "ImageJ"), for example. The image converted to 8 bits (called a grayscale image) is obtained. A grayscale image contains luminance (brightness information). For example, an 8-bit grayscale image contains The brightness can be expressed in 2 to the power of 8 = 256 levels. The dark areas have a lower number of levels, and the bright areas have a The number of gradations is higher in the darker areas. The brightness change can be quantified in relation to the number of gradations. This numerical value is called a grayscale value. By obtaining the grayscale value, the unevenness of the positive electrode active material can be determined. can be evaluated numerically.

[0293] Furthermore, it is possible to express the brightness change of the target area as a histogram. It is a three-dimensional representation of the gradation distribution in the target area, and is also called a brightness histogram. By obtaining a stogram, the unevenness of the positive electrode active material can be visually evaluated in an easy-to-understand manner. It becomes possible.

[0294] The positive electrode active material 100 according to one embodiment of the present invention has a difference between the maximum and minimum values ​​of the gray scale. is preferably 120 or less, more preferably 115 or less, and is more preferably 70 or more and It is more preferable that the standard deviation of the gray scale values ​​is 11 or less. It is preferable that the number of saturates is 8 or less, more preferable that the number of saturates is 4 or more and 8 or less. Preferred.

[0295] ≪Current pause method≫ Additives such as magnesium contained in the surface layer of the positive electrode active material 100 of one embodiment of the present invention The distribution of elements may change slightly during repeated charging and discharging. The fabric becomes better and the resistance to electronic conduction may decrease. During this period, the electrical resistance, that is, the fast-response resistance component R( 0.1s) may decrease.

[0296] For example, if we compare the nth (n is a natural number greater than 1) charge with the n+1th charge, The resistance component R(0.1s) with a fast response measured by the current rest method is n+ The capacity may be lower in the first discharge. The capacity may be high. When n is 1, that is, when comparing the first charge and the second charge, The increase in second charge capacity is especially likely to occur with positive electrode active materials that do not contain additive elements. Therefore, n is preferably, for example, 2 or more and 10 or less. This is not limited to this. The charge / discharge capacity is approximately the same as the rated capacity, for example, 97% or more of the rated capacity. When the amount of charge is large, it can be said that the charge / discharge cycle is in its early stage.

[0297] <Raman spectroscopy> As described above, the positive electrode active material 100 according to one embodiment of the present invention has at least the surface layer 100a. It is preferable that a part of the positive electrode active material 100 has a rock salt type crystal structure. When the positive electrode containing this was analyzed by Raman spectroscopy, the rock salt type was identified along with the layered rock salt crystal structure. It is preferable to observe the cubic crystal structure including the STEM image described later. In the electron diffraction pattern, lithium atoms are frequently observed at the lithium position in the depth direction during observation. Without the substitutional cobalt and the cobalt present at the oxygen tetracoordinate site, the STEM image and On the other hand, they cannot be detected as bright spots in Raman spectroscopy. Since this method captures the vibrational modes of bonds such as Co-O, the relevant Co-O bond Even if the amount of is small, the wave number peak of the corresponding vibration mode can sometimes be observed. Furthermore, Raman spectroscopy can measure the surface area of ​​a few μm 2 It is possible to measure a depth of about 1 μm. Therefore, it is possible to capture with high sensitivity the state that exists only on the particle surface.

[0298] For example, when the laser wavelength is 532 nm, the layered rock salt LiCoO2 has a wavelength of 470 cm - 1up to 490 cm -1 , 580 cm -1 up to 600 cm -1 has a peak (vibration mode: E g , A 1g is observed. On the other hand, cubic CoO x (0 < x < 1) (rock salt type Co 1-y O (0 < y < 1) or spinel type Co3O4), a peak at 665 cm -1 up to 685 cm -1 has a peak (vibration mode: A 1g ) is observed.

[0299] Therefore, when the integrated intensity of each peak is taken as I1 for 470 cm -1 up to 490 cm -1 , I2 for 580 c m -1 up to 600 cm -1 , and I3 for 665 cm -1 up to 685 cm -1 , it is preferable that the value of I3 / I2 is 1% or more and 10% or less, and more preferably 3% or more and 9% or less. , If a cubic crystal structure including a rock salt type is observed within the above range, it can be said that the surface layer portion 100a of the positive electrode active material 100 has a rock salt type crystal structure within a preferable range.

[0300] ≪Ultra - micro electron beam diffraction pattern≫ Similar to Raman spectroscopy, it is preferable that the characteristics of the rock salt type crystal structure are also observed in the ultra - micro electron beam diffraction pattern together with the crystal structure of the layered rock salt. However, in the STEM image and the ultra - micro electron beam diffraction pattern, taking into account the above - mentioned difference in sensitivity, the characteristics of the rock salt type crystal structure do not become too strong in the surface layer portion 100a, especially the outermost surface (

[0301] for example, a depth of 1 nm from the surface). It is preferable that the outermost surface is covered with a rock salt type crystal structure. The presence of an additive element such as magnesium in the lithium layer ensures a diffusion path for lithium. This is because the crystal structure can be more effectively stabilized and the crystal structure can be more easily stabilized.

[0302] Therefore, for example, the ultrafine electron diffraction pattern of the area below 1 nm from the surface and the area below 3 When the ultrafine electron diffraction pattern of the region from 1000 nm to 1500 nm is obtained, It is preferable that the difference in lattice constant calculated from the above is small.

[0303] For example, there are two types of measurement points: one is a measurement point that is 1 nm or less deep from the surface, and the other is a measurement point that is 3 nm to 10 nm deep. The difference in lattice constant calculated from a fixed point is preferably 0.1 Å or less for the a axis, and c It is preferable that the a-axis is 1.0 Å or less. It is also preferable that the a-axis is 0.05 Å or less. It is more preferable that the c-axis is 0.6 Å or less, and it is even more preferable that the a-axis is 0.0 It is more preferably 4 Å or less, and even more preferably 0.3 Å or less for the c-axis.

[0304] <Additional Features> The positive electrode active material 100 may have recesses, cracks, dents, V-shaped cross sections, etc. These are defects, and repeated charging and discharging causes cobalt to leach out of them, causing the crystal structure to collapse. However, there is a risk that cracks may occur in the positive electrode active material 100, oxygen may be released, etc. As shown in FIG. 1(A), the presence of the buried portion 102 suppresses the elution of cobalt. Therefore, the positive electrode active material 100 has excellent reliability and cycle characteristics. It is possible.

[0305] As described above, if the additive element contained in the positive electrode active material 100 is in excess, lithium intercalation and Furthermore, when the positive electrode active material 100 is used in a secondary battery, the internal On the other hand, if the surface layer 100 is insufficient, it may cause an increase in the resistance of the surface layer 100 and a decrease in the charge / discharge capacity. If the crystal structure is not distributed throughout the entire crystal, the effect of suppressing deterioration of the crystal structure may be insufficient. The additive element must be at an appropriate concentration in the positive electrode active material 100, but this concentration can be easily adjusted. isn't it.

[0306] Therefore, if the positive electrode active material 100 has a region where the additive element is unevenly distributed, excessive additive element A part of the atoms of the element is removed from the interior 100b of the positive electrode active material 100, and the atoms of the element are properly removed from the interior 100b. This allows for an appropriate concentration of added elements, which reduces the increase in internal resistance when used as a secondary battery. Therefore, it is possible to suppress a decrease in charge / discharge capacity, etc. It is possible to suppress an increase in the internal resistance of the secondary battery. This is particularly true in the case of large current charging and discharging, for example, charging and discharging at 400 mA / g or more. This is a desirable characteristic.

[0307] In addition, in the positive electrode active material 100 having a region where the additive element is unevenly distributed, Therefore, the margin in production is wide. This is desirable.

[0308] A coating may be attached to at least a portion of the surface of the positive electrode active material 100. 3 shows an example of a positive electrode active material 100 to which a coating portion 104 is attached.

[0309] The coating portion 104 is formed by the accumulation of decomposition products of the electrolyte and the organic electrolyte solution during charging and discharging, for example. It is preferable that the material is Li x x in CoO2 is 0.24 or less When repeated charging is performed, the surface of the positive electrode active material 100 has a coating portion derived from the electrolyte solution, It is expected that the charge-discharge cycle characteristics will improve. This is because the impedance of the positive electrode active material surface The reason is to suppress the increase in the temperature or to suppress the elution of cobalt. Preferably, the electrolyte contains, for example, carbon, oxygen, and fluorine. When using SUN (suberonitrile), it is possible to obtain a high-quality coating. Therefore, it is preferable to use a material containing one or more of boron, nitrogen, sulfur, and fluorine. The coating portion 104 may be a high-quality coating portion, which is preferable. It is not necessary to cover the entire surface of the positive electrode active material 100. For example, 50% or more of the surface of the positive electrode active material 100 may be covered. It is sufficient if the surface is covered by 70% or more, and more preferably by 90% or more. It's nice.

[0310] In addition, the positive electrode active material is charged at 4.5V or higher, or at high temperatures, such as 45°C. Charging and discharging in the above environment causes progressive defects that progress from the surface to the interior. Pitting corrosion (Pi) is a phenomenon in which defects in the positive electrode active material progress and form holes. The holes caused by this phenomenon are called "tting corrosion" and are In books, it is also called the pit.

[0311] FIG. 14 shows a cross-sectional view of a positive electrode active material 51 having pits. The crystal plane 55 is also shown. Since FIG. 14 is a cross-sectional view, the pits 54 and 58 are not shown. However, these openings are not circular but have a groove-like shape with depth. As shown in the pits 54 and 58, unlike the recessed portion 52, the lithium ions It tends to occur parallel to the arrangement.

[0312] The surface layer of the positive electrode active material 51 where the additive element is present is indicated by 53 and 56. The surface layer where this occurred had less added elements than 53 and 56 or the concentration was below the detection limit. It is expected that the function of the barrier film is reduced. It is thought that the crystal structure of the layered rock salt will be disrupted and a different crystal structure will be formed. When the pits break down, they inhibit the diffusion and release of lithium ions, which are carrier ions. This is thought to be a factor in the deterioration of cycle characteristics.

[0313] The source of the pits may be point defects. Point defects in the positive electrode active material may develop as a result of repeated charging and discharging. It changes when exposed to the surrounding electrolyte, and is corroded chemically or electrochemically by the surrounding electrolyte. It is thought that the pits are caused by deterioration of the material. This deterioration occurs uniformly on the surface of the positive electrode active material. It does not occur in a large area, but rather in a concentrated localized area.

[0314] Furthermore, as shown by the crack 57 in FIG. 14, the positive electrode active material expands and contracts due to charging and discharging. This may cause defects such as cracks (also called fissures). Cracks and pits are different. Immediately after the production of the positive electrode active material, cracks may be present but pits may not. Pits do not exist. For example, pits may occur under high voltage conditions (4.5V or higher) or high temperatures (45°C or higher). By charging and discharging, several layers of cobalt and oxygen are removed, creating holes, and the cobalt dissolves. Cracks can be thought of as new cracks that occur when physical pressure is applied. The cracks are caused by the uneven surface or the grain boundary 101. Cracks may also occur due to expansion and contraction of the material. In some cases, pits may occur from cavities inside the positive electrode active material.

[0315] This embodiment can be used in combination with other embodiments.

[0316] (Embodiment 2) In this embodiment, an example of a method for producing a positive electrode active material 100, which is one embodiment of the present invention, will be described. We will explain about this.

[0317] The distribution, composition, and / or crystal structure of the additive elements as described in the previous embodiment may be In order to prepare a positive electrode active material 100 that satisfies the above requirements, the method of adding the additive element is important. It is also important that 100b has good crystallinity.

[0318] Therefore, in the process of producing the positive electrode active material 100, lithium cobalt oxide is first synthesized, and then It is preferable to mix the post-addition element source and then perform heat treatment.

[0319] A cobalt source, a lithium source, and an additive element source are mixed at the same time to form a cobalt containing additive element. In the method of synthesizing lithium oxide, it is difficult to increase the concentration of the added element in the surface layer portion 100a. In addition, after synthesizing lithium cobalt oxide, the additive element source must be mixed without heating. The added element does not dissolve in the lithium cobalt oxide but simply adheres to it. Without this process, it is difficult to distribute the added elements well. It is preferable to synthesize the aluminum, mix it with the additive element source, and then perform a heat treatment. The heat treatment after mixing the sources is sometimes called annealing.

[0320] However, if the annealing temperature is too high, cation mixing occurs, and the added elements and For example, magnesium is more likely to enter the cobalt site. Magnesium is Li x When x in CoO2 is small, the layered rocksalt type crystal structure of R-3m is obtained. Furthermore, if the heat treatment temperature is too high, cobalt will be reduced to a divalent state. There are also concerns about adverse effects such as lithium evaporating.

[0321] Therefore, it is preferable to mix a material that functions as a flux together with the source of the additive element. If the melting point is lower than that of lithium fluoride, it can be said to be a material that functions as a flux. Fluorine compounds such as thium are preferred. The addition of a flux provides a source of the additive element and The melting point of lithium cobalt oxide is lowered. This lowering of the melting point causes cation mixing. This makes it easier to achieve a good distribution of the additive elements at a temperature where the temperature is not easily affected.

[0322] [Initial heating] Furthermore, if heating is performed after synthesizing lithium cobalt oxide and before mixing the additive elements, This heating is sometimes called initial heating.

[0323] By the initial heating, lithium is desorbed from a part of the surface layer 100a of the lithium cobalt oxide. This results in a better distribution of the added elements.

[0324] More specifically, the initial heating causes the distribution to differ depending on the added elements through the following mechanism: First, lithium is released from a part of the surface layer portion 100a due to the initial heating. Next, the lithium cobalt oxide having the lithium-deficient surface layer 100a is mixed with nickel. The additive element sources, including the zinc source, aluminum source, and magnesium source, are mixed and heated. Of the added elements, magnesium is a divalent typical element, and nickel is a transition metal but is divalent. Therefore, Mg is easily ionized in a part of the surface layer 100a. 2+ and Ni 2+ And, Co reduced by deficiency of lithium 2+ A rock salt phase is formed having the following structure: This phase is formed in a part of the surface layer 100a, so it is difficult to see it in an electron microscope image such as a STEM. In some cases, it may not be clearly visible in the electron diffraction pattern.

[0325] Among the additive elements, nickel is used when the surface layer 100a is a layered rock salt type lithium cobalt oxide. However, if a part of the surface layer 100a is of the rock salt type, Therefore, by performing initial heating, nickel and other metals tend to remain in the layer 100a. This makes it possible for the divalent additive element to remain in the surface layer portion 100a. The result is particularly noticeable on the surface other than the (001) orientation of the positive electrode active material 100 and on the surface layer 100a thereof. It's big.

[0326] In addition, in these rock salt structures, the bond distance between the metal Me and oxygen (Me-O distance) is longer than that in the layered rock salt structure. tend to be longer than usual.

[0327] For example, rock salt Ni 0.5 Mg 0.5 The Me-O distance in O is 2.09 Å, and the rocksalt M The Me-O distance in gO is 2.11 Å. Even if a spinel-type phase is formed, the Me-O distance of the spinel-type NiAl2O4 is 2.012. The Me-O distance in spinel-type MgAl2O4 is 2.02 Å. The distance is more than 2 Å. Note that 1 Å = 10 -10 m.

[0328] On the other hand, in the layered rock salt structure, the bond distance between metals other than lithium and oxygen is shorter than the above. For example, the Al-O distance in layered rocksalt LiAlO2 is 1.905 Å (the Li-O distance is 2.1 1Å). The Co-O distance in layered rocksalt LiCoO2 is 1.9224Å (L The iO distance is 2.0916 Å.

[0329] Shannon's ionic radius (Shannon et al., Acta A 32 (1976) 751.), the ionic radius of hexacoordinated aluminum is 0.535 Å. The ionic radius of hexacoordinated oxygen is 1.4 Å, and the sum of these is 1.935 Å.

[0330] From the above, aluminum is cheaper in the non-lithium sites of the layered rocksalt structure than the rocksalt structure. Therefore, aluminum is considered to be present in the rock salt type even in the surface layer portion 100a. Deeper regions with layered salt phases and / or inner layers than regions closer to the surface with layered salt phases It is easy to distribute in part 100b.

[0331] In addition, the initial heating is expected to have the effect of increasing the crystallinity of the layered rock salt type crystal structure in the inner 100b. I can wait.

[0332] Therefore, especially Li x When x in CoO2 is, for example, between 0.15 and 0.17, To prepare a positive electrode active material 100 having a clinic O1(15) type crystal structure, this initial heating is It is preferable to do so.

[0333] However, initial heating is not necessarily required. By controlling the atmosphere, temperature, time, etc., x When x in CoO2 is small, O When it is possible to prepare a positive electrode active material 100 having a 3' type and / or a monoclinic O1(15) type There is.

[0334] <<Method 1 for preparing positive electrode active material>> Regarding the manufacturing method 1 of the positive electrode active material 100 through annealing and initial heating, FIG. 15(A) 15(C) will be used to explain.

[0335] <Step S11> In step S11 shown in FIG. 15(A), the starting materials, lithium and transition metal materials, As the above, a lithium source (Li source) and a cobalt source (Co source) are prepared.

[0336] As the lithium source, it is preferable to use a compound containing lithium, for example, lithium carbonate. Lithium, lithium hydroxide, lithium nitrate, lithium fluoride, etc. can be used. The ammonium source preferably has a high purity, for example, a material with a purity of 99.99% or higher.

[0337] As the cobalt source, it is preferable to use a compound containing cobalt, for example, cobalt oxide. Cobalt hydroxide, cobalt hydroxide, etc. can be used.

[0338] The cobalt source preferably has a high purity, for example, a purity of 3N (99.9%) or more, is 4N (99.99%) or more, more preferably 4N5 (99.995%) or more, and even more preferably Preferably, materials with a purity of 5N (99.999%) or higher should be used. This allows the impurities in the positive electrode active material to be controlled. As a result, the capacity of the secondary battery is increased. And / or the reliability of the secondary battery is improved.

[0339] In addition, it is preferable that the cobalt source has high crystallinity, for example, single crystal grains. The crystallinity of the lead source was evaluated using TEM (transmission electron microscope) images and STEM (scanning transmission electron microscope) images. High-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image, AB Evaluation by F-STEM (annular bright-field scanning transmission electron microscope) images, or X-ray diffraction (XR D), electron diffraction, neutron diffraction, etc. The method can be applied to evaluate the crystallinity of not only cobalt sources but also other sources.

[0340] <Step S12> Next, in step S12 shown in FIG. 15(A), the lithium source and the cobalt source are crushed and The mixture is then ground and mixed to form a blend. The grinding and mixing can be done in a dry or wet manner. The wet method is preferable because it allows for smaller crushing. When using the wet method, a solvent must be prepared. The solvents used are ketones such as acetone, alcohols such as ethanol and isopropanol. ether, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. Use an aprotic solvent that does not react easily with lithium. In this embodiment, it is more preferable to use dehydrated acetone with a purity of 99.5% or more. Dehydrated acetone with a purity of 99.5% or more, with a water content of 10 ppm or less It is preferable to mix the lithium source and the cobalt source in the above mixture, and then grind and mix the mixture. By using dehydrated acetone of a high purity, it is possible to reduce impurities that may be present.

[0341] A ball mill, a bead mill, or the like can be used as a means for pulverizing and mixing. When using a mill, aluminum oxide balls or zirconium oxide balls are used as the milling media. Zirconium oxide balls are preferable because they emit less impurities. Also, when using a ball mill or bead mill, contamination from the media may occur. To suppress this, it is advisable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less. In this embodiment, the peripheral speed is 838 mm / s (rotation speed 400 rpm, diameter of the ball mill 40 mm ) will be implemented.

[0342] <Step S13> Next, in step S13 shown in FIG. 15(A), the mixed material is heated. It is preferable to carry out the treatment at 800°C or higher and 1100°C or lower, and more preferably at 900°C or higher and 1000°C or lower. If the temperature is too low, the lithium source and On the other hand, if the temperature is too high, the lithium and cobalt sources may not be decomposed and melted sufficiently. This is caused by lithium evaporation from the lithium source and / or excessive reduction of cobalt. For example, cobalt may change from trivalent to divalent, resulting in oxygen vacancies. This may induce:

[0343] If the heating time is too short, lithium cobalt oxide will not be synthesized, but if it is too long, productivity will decrease. For example, the heating time should be between 1 hour and 100 hours, and between 2 hours and 20 hours. It is more preferable that:

[0344] The temperature rise rate depends on the heating temperature reached, but it should be between 80℃ / h and 250℃ / h. For example, if you are heating at 1000°C for 10 hours, the temperature rise rate should be 200°C / h. .

[0345] Heating is preferably carried out in an atmosphere with little water, such as dry air, for example, at a dew point of -50°C. More preferably, the atmosphere has a dew point of -80°C or less. Heating is carried out in an atmosphere at -93°C. Also, impurities that may be mixed into the material are suppressed. In order to achieve this, the impurity concentrations of CH4, CO, CO2, and H2 in the heated atmosphere must be: It is recommended that each be kept below 5 ppb (parts per billion).

[0346] The heating atmosphere is preferably an oxygen-containing atmosphere. For example, dry air is continuously introduced into the reaction chamber. In this case, the flow rate of dry air is preferably 10 L / min. The method in which oxygen is continuously introduced into the reaction chamber and flows through the reaction chamber is called flow.

[0347] When the heating atmosphere is an atmosphere containing oxygen, a method without flow may be used. For example, the reaction chamber is depressurized and then filled with oxygen (or purged), and the oxygen is then pumped into the reaction chamber. For example, the pressure in the reaction chamber can be reduced to -970 hPa. Then fill with oxygen up to 50 hPa.

[0348] After heating, the product can be cooled naturally, but the time required to cool from the specified temperature to room temperature must be 10 hours or more. However, it is not necessary to cool it down to room temperature, and the next step It is sufficient that the temperature is cooled to a temperature acceptable to the boiler.

[0349] Heating in this step may be carried out using a rotary kiln or a roller hearth kiln. Heating in a rotary kiln is done while stirring, whether it is a continuous or batch type. Can be heated.

[0350] The crucible used for heating is preferably an aluminum oxide crucible. The crucible is made of a material that does not easily release impurities. In this embodiment, the purity is 99.9%. % aluminum oxide crucible is used. It is preferable to heat the crucible with a lid on. This can prevent the ingredients from evaporating.

[0351] It is also preferable to use a second-hand crucible rather than a new one. In this context, a new crucible is one that contains materials containing lithium, transition metals M, and / or additive elements. Used crucibles are those that have been heated twice or less. The material containing the transition metal M and / or the additive element is heated three or more times. This means that when a new crucible is used, lithium fluoride and other This is because some of the material may be absorbed, diffused, migrated and / or adhere to the sheath. When a part of the material is lost due to these reasons, the distribution of elements in the surface layer of the positive electrode active material becomes undesirable. This raises concerns that the temperature may not fall within the desired range. However, this risk is less with used crucibles.

[0352] After heating, the mixture may be crushed and sieved as necessary. When recovering the material, it may be transferred from the crucible to a mortar and then recovered. It is preferable to use an aluminum oxide mortar. Aluminum oxide mortars emit impurities. Specifically, the purity is 90% or more, preferably 99% or more. An aluminum oxide mortar is used. In the heating process described below except for step S13, Even in this case, the same heating conditions as in step S13 can be applied.

[0353] <Step S14> By the above process, lithium cobalt oxide (Li) is obtained as shown in step S14 of FIG. iCoO2) can be synthesized.

[0354] Steps S11 to S14 show an example of producing a composite oxide by a solid phase method. However, the composite oxide may be prepared by a coprecipitation method or a hydrothermal method.

[0355] <Step S15> Next, in step S15 shown in FIG. 15(A), the lithium cobalt oxide is heated. Since this is the first heating for lithium phosphate, the heating in step S15 is called initial heating. Or, since it is heated before step S20 described below, it is not necessary to preheat or This is sometimes called pre-processing.

[0356] As described above, the initial heating causes lithium to be removed from a part of the surface layer 100a of the lithium cobalt oxide. In addition, the effect of increasing the crystallinity of the inner portion 100b can be expected. The lithium and / or cobalt sources prepared in the 11th experiment contain impurities. The reduction of impurities from the lithium cobalt oxide completed in step S14 can be achieved by This is possible with initial heating.

[0357] Furthermore, initial heating has the effect of smoothing the surface of the lithium cobalt oxide. A smooth surface means that there are few irregularities, the composite oxide is rounded overall, and the corners are It refers to a rounded appearance. Furthermore, a state in which there is little foreign matter adhering to the surface is called smooth. Foreign matter is thought to be a cause of unevenness, and it is preferable that it does not adhere to the surface.

[0358] For this initial heating, it is not necessary to prepare a lithium compound source. Alternatively, no material that functions as a flux may be provided.

[0359] If the heating time in this process is too short, sufficient effect will not be obtained, but if it is too long, productivity will decrease. For example, the heating conditions can be selected from those described in step S13. In addition to the heating conditions, the heating temperature in this step is set to the following in order to maintain the crystal structure of the composite oxide: The temperature in this step is preferably lower than that in step S13. To maintain the structure, the time should be shorter than that of step S13. For example, the time should be 700°C or more. It is advisable to heat the material at a temperature of 000°C or less for 2 to 20 hours.

[0360] The effect of increasing the crystallinity of the inner portion 100b is, for example, the effect of increasing the crystallinity of the outer portion 100b formed in step S13. This is the effect of reducing distortion, displacement, etc., which are caused by differential shrinkage, etc., which lithium phosphate has.

[0361] The lithium cobalt oxide is heated in step S13 to form a layer on the surface of the lithium cobalt oxide. Temperature differences may occur inside the container. Temperature differences may cause differential shrinkage. It is thought that the difference in fluidity between the surface and the interior due to the difference in temperature causes the difference in shrinkage. The associated energy gives the lithium cobalt oxide a difference in internal stress. The difference is also called strain, and the energy is sometimes called strain energy. In other words, the strain energy is removed by the initial heating in step S15. It is thought that the initial heating causes homogenization. When the strain energy is homogenized, the cobalt oxide The distortion of the lithium is reduced, and the surface of the lithium cobalt oxide may become smoother. It is possible that the surface is improved. In other words, after step S15, the cobalt It is thought that this will alleviate the difference in shrinkage that occurs in the lithium nitrate, making the surface of the composite oxide smooth. do.

[0362] The difference in shrinkage also causes microscopic deviations in the lithium cobalt oxide, such as deviations in crystal structure. In order to reduce the deviation, it is advisable to carry out this step. It is possible to equalize the deviation of the composite oxide. The surface of the oxide may become smooth. This is also called grain alignment. Then, after step S15, the deviation of the crystals and the like generated in the composite oxide is alleviated, and the composite oxide It is thought that the surface of

[0363] When lithium cobalt oxide, which has a smooth surface, is used as the positive electrode active material, it can be used as a secondary battery. Deterioration during discharge is reduced, and cracking of the positive electrode active material can be prevented.

[0364] In addition, lithium cobalt oxide synthesized in advance may be used in step S14. In this case, steps S11 to S13 can be omitted. By performing step S15 on the lithium cobalt oxide thus formed, the surface becomes smooth. Therefore, lithium cobalt oxide can be obtained.

[0365] <Step S20> Next, as shown in step S20, the additive element A is added to the lithium cobalt oxide that has undergone the initial heating. When the additive element A is added to the lithium cobalt oxide after the initial heating, the additive element A is Therefore, the additive element A is added after the initial heating. The step of adding the additional element A is preferably performed in the order of (B) and (C) of FIG. ) will be used to explain.

[0366] <Step S21> In step S21 shown in FIG. 15(B), a source of an additional element A to be added to lithium cobalt oxide is A lithium source may be prepared together with the additive element A source.

[0367] The additive element A may be any of the additive elements described in the previous embodiment, for example, additive element X and The additive element Y can be used. Specifically, magnesium, fluorine, nickel, aluminum Aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc One or more elements selected from lead, silicon, sulfur, phosphorus and boron can be used. Also, one or two elements selected from bromine and beryllium can be used.

[0368] When magnesium is selected as the additive element, the additive element source can be called a magnesium source. The magnesium source may be magnesium fluoride, magnesium oxide, magnesium hydroxide, or the like. The magnesium source may be, for example, magnesium carbonate or magnesium carbonate. A plurality of may be used.

[0369] When fluorine is selected as the additive element, the source of the additive element can be called a fluorine source. The source of the element is, for example, lithium fluoride (LiF), magnesium fluoride (MgF2), Aluminum fluoride (AlF3), titanium fluoride (TiF4), cobalt fluoride (CoF2 , CoF3), Nickel Fluoride (NiF2), Zirconium Fluoride (ZrF4), Fluoride Vanadium (VF5), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, fluorine Zinc fluoride (ZnF2), calcium fluoride (CaF2), sodium fluoride (NaF), Potassium fluoride (KF), barium fluoride (BaF2), cerium fluoride (CeF3, Ce F4), lanthanum fluoride (LaF3), or sodium aluminum hexafluoride (Na3A Among them, lithium fluoride has a relatively high melting point of 848°C. This is preferable because it has a low viscosity and is easily melted in the heating step described below.

[0370] Magnesium fluoride can be used as both a fluorine source and a magnesium source. Lithium fluoride can also be used as a lithium source. Another potential source of lithium is lithium carbonate.

[0371] The fluorine source may also be a gas, such as fluorine (F2), fluorocarbons, sulfur fluorides, or fluorides. Using oxygen (OF2, O2F2, O3F2, O4F2, O5F2, O6F2, O2F), etc. The fluorine source may be mixed in the atmosphere during the heating step described below. It may be used.

[0372] In this embodiment, lithium fluoride (LiF) is prepared as a fluorine source. Prepare magnesium fluoride (MgF2) as a magnesium source. When magnesium fluoride is mixed at a molar ratio of LiF:MgF2=65:35, the melting point On the other hand, if the amount of lithium fluoride is too high, the lithium will be excessive. There is a concern that the cycle characteristics will deteriorate over time. The molar ratio of LiF to MgF is preferably LiF:MgF2=x:1 (0≦x≦1.9), and More preferably, LiF:MgF2=x:1 (0.1≦x≦0.5), and LiF:MgF2=x :1 (x=near 0.33) is more preferable. The value shall be greater than 0.9 times and less than 1.1 times.

[0373] <Step S22> Next, in step S22 shown in FIG. 15(B), the magnesium source and the fluorine source are crushed and This step is carried out under the conditions selected from the grinding and mixing conditions described in step S12. It is possible.

[0374] <Step S23> Next, in step S23 shown in FIG. 15(B), the crushed and mixed materials are collected. In this way, the additive element A source (A source) can be obtained. has multiple starting materials and can be called a mixture.

[0375] The particle size of the above mixture is such that D50 (median diameter) is 600 nm or more and 10 μm or less. The thickness is preferably 1 μm or more and more preferably 5 μm or less. Even when various materials are used, the D50 (median diameter) is 600 nm or more and 10 μm or less. It is preferable that the thickness is 1 μm or less and more preferable that the thickness is 1 μm or more and 5 μm or less.

[0376] Such a finely powdered mixture (including cases where only one type of added element is added) can be used in subsequent processes. When mixed with lithium cobalt oxide, the mixture is evenly distributed on the surface of the lithium cobalt oxide particles. When the mixture is evenly adhered to the surface of the lithium cobalt oxide particles, This is preferred because it is easy to distribute or diffuse the additive elements uniformly in the surface layer 100a of the composite oxide after heating. I wish.

[0377] <Step S21> A process different from that shown in FIG. 15(B) will be described with reference to FIG. 15(C). In step S21 shown in FIG. 1, four kinds of additive element sources to be added to lithium cobalt oxide are prepared. That is, Fig. 15(C) differs from Fig. 15(B) in the type of additive element source. The lithium source may be prepared by

[0378] The four additive element sources are magnesium source (Mg source), fluorine source (F source), and nickel source. A magnesium source and a fluorine source are prepared. The nickel source can be selected from the compounds described in FIG. 15(B). As the aluminum source, nickel oxide, nickel hydroxide, etc. can be used. Aluminum chloride, aluminum hydroxide, etc. can be used.

[0379] <Steps S22 and S23> Steps S22 and S23 shown in FIG. 15(C) are the same as those described in FIG. 15(B). Same as Tep.

[0380] <Step S31> Next, in step S31 shown in FIG. 15(A), lithium cobalt oxide and a source of the additive element A are mixed. The number of cobalt atoms in lithium cobalt oxide is Co, and the number of added elements is A source. The ratio of the number of magnesium atoms in Co to Mg is Co:Mg=100:y (0.1≦y≦6 ), and more preferably M:Mg=100:y (0.3≦y≦3). I wish.

[0381] The mixing in step S31 is carried out in a manner that prevents the shape of the lithium cobalt oxide particles from being destroyed. It is preferable to use milder conditions than those in step S12. For example, It is preferable to use conditions with a lower rotation speed or shorter time than mixing. It can be said that the dry method has milder conditions. For mixing, for example, a ball mill, a bead mill, etc. When a ball mill is used, for example, zirconium oxide can be used as the media. It is preferable to use a mullet ball.

[0382] In this embodiment, a ball mill using zirconium oxide balls with a diameter of 1 mm is used. The mixture shall be mixed dry at 0 rpm for 1 hour. This should be done in a dry room at a temperature below 10°C.

[0383] <Step S32> Next, in step S32 of FIG. 15(A), the mixed materials are collected and the mixture is 903 is obtained. Upon recovery, the product may be crushed and then sieved, if necessary.

[0384] In addition, in Fig. 15(A) to Fig. 15(C), the additive element is added only after the initial heating. However, the present invention is not limited to the above method. The timing can be varied depending on the element. It may be possible.

[0385] For example, in step S11, that is, in the stage of the starting material of the composite oxide, the additive element is added to lithium. In step S13, the cobalt source containing the additive element is added. In this case, lithium phosphate can be obtained by steps S11 to S14. There is no need to separate the steps S21 to S23. It can be said to be an expensive method.

[0386] Alternatively, lithium cobalt oxide containing some of the additive elements may be used. For example, if lithium cobalt oxide doped with magnesium and fluorine is used, step S11 Some of the steps S14 to S20 can be omitted. Therefore, it can be said that this is a highly productive method.

[0387] In addition, for lithium cobalt oxide to which magnesium and fluorine have been added in advance, After the heating in step S15, the magnesium source and the fluorine source are added in step S20. Alternatively, a magnesium source, a fluorine source, a nickel source, and an aluminum source may be added.

[0388] <Step S33> Next, in step S33 shown in FIG. 15(A), the mixture 903 is heated. The heating conditions can be selected from those explained in 13. The heating time is preferably 2 hours or more. I wish.

[0389] Here, a supplementary note about the heating temperature is provided. The lower limit of the heating temperature in step S33 is the temperature at which lithium cobaltate is heated. The temperature must be higher than the temperature at which the reaction between the lithium and the added element source proceeds. The temperature may be any temperature at which mutual diffusion of elements contained in the lithium barium oxide and the additive element source occurs. The melting point T m 0.757 times (Tanman temperature T d ) and solid-state diffusion occurs. Therefore, the heating temperature in step S33 should be 650° C. or higher.

[0390] Of course, the temperature is higher than the melting point of one or more of the materials contained in the mixture 903. For example, the reaction proceeds more easily when LiF and MgF2 are used as the additive element source. In this case, the eutectic point of LiF and MgF2 is around 742°C, so the heating temperature in step S33 is The lower limit is preferably 742°C or higher.

[0391] In addition, the molar ratio of LiCoO2:LiF:MgF2 was 100:0.33:1. The mixture 903 obtained by mixing the above was found to have a temperature of 830°C in differential scanning calorimetry (DSC measurement). Therefore, the lower limit of the heating temperature is preferably 830°C or higher. .

[0392] A higher heating temperature is preferable because the reaction proceeds more easily, the heating time is shorter, and productivity is higher.

[0393] The upper limit of the heating temperature is below the decomposition temperature of lithium cobalt oxide (1130°C). At temperatures around , there is concern that lithium cobalt oxide may decompose, albeit in a small amount. It is more preferable that the temperature is 1000°C or less, and even more preferable that the temperature is 950°C or less, and it is more preferable that the temperature is 900°C or less. It is more preferable that the ratio is less than or equal to:

[0394] Considering these, the heating temperature in step S33 is set to 650°C or higher. 0°C or less is preferable, 650°C or more and 1000°C or less is more preferable, 650°C or more and 950°C or less is more preferable. ° C. or less, and more preferably 650° C. or more and 900° C. or less. Preferably, the temperature is 742°C or higher and 1000°C or lower. More preferably, the temperature is 742°C or higher and 900°C or lower. , 800°C or higher and 1100°C or lower, 830°C or higher and 1130°C or lower are preferred, and 830°C or higher 1000°C or less is more preferable, 830°C or more and 950°C or less is even more preferable, 830°C or more and 950°C or less is even more preferable. The heating temperature in step S33 is preferably 900° C. or more. It would be better if it was higher than the S13.

[0395] Furthermore, when the mixture 903 is heated, the partial pressure of fluorine or fluoride resulting from the fluorine source, etc. It is preferable to control the temperature within an appropriate range.

[0396] In the manufacturing method described in this embodiment, some materials, for example, LiF, which is a fluorine source, are melted. This function may reduce the heating temperature to the decomposition temperature of lithium cobalt oxide. For example, the temperature can be lowered to between 742°C and 950°C, and the surface layer can be made of magnesium or other materials. By distributing the additive elements, a positive electrode active material with good characteristics can be produced.

[0397] However, since LiF has a lower specific gravity in gaseous state than oxygen, LiF volatilizes when heated. If it volatilizes, the LiF in the mixture 903 will decrease. Therefore, it is necessary to heat the LiF while suppressing its volatilization. Even if LiF is not used as a fluorine source, the Li and fluorine on the LiCoO2 surface The fluorine source F may react to produce LiF, which may then volatilize. Even if a fluoride with a high evaporation point is used, it is still necessary to suppress evaporation.

[0398] Therefore, the mixture 903 is heated in an atmosphere containing LiF, that is, the L It is preferable to heat the mixture 903 under a high partial pressure of iF. The volatilization of LiF in the mixture 903 can be suppressed.

[0399] The heating in this step is preferably carried out so that the particles of the mixture 903 do not stick together. When the particles of the mixture 903 adhere to each other during heating, the contact area with the oxygen in the atmosphere decreases, and By blocking the route for the diffusion of additional elements (e.g. fluorine), the additional elements (e.g. This may result in poor distribution of minerals (e.g. magnesium and fluorine).

[0400] In addition, if the added element (e.g., fluorine) is uniformly distributed in the surface layer, the surface will be smooth and have few irregularities. It is believed that a positive electrode active material can be obtained. , in order to maintain or further smooth the surface, the mixture 903 It is better if the particles do not stick together.

[0401] In addition, when heating using a rotary kiln, the flow rate of the atmosphere containing oxygen in the kiln For example, the flow rate of the oxygen-containing atmosphere is reduced, and the initial After the oxygen atmosphere is introduced into the kiln, the atmosphere is purged and no air flow is performed. Flowing oxygen may evaporate the fluorine source, which may cause the surface to become smooth. It is not desirable to maintain it.

[0402] When heating by a roller hearth kiln, for example, a container containing the mixture 903 is covered. By disposing the above, the mixture 903 can be heated in an atmosphere containing LiF.

[0403] Regarding the heating time, the heating time depends on the heating temperature, the amount of lithium cobalt oxide in step S14, and the amount of the oxidized lithium cobalt oxide in step S14. The amount of lithium cobalt oxide varies depending on the size of the lithium cobaltate and other conditions such as its composition. A lower temperature or shorter time may be more preferable than a larger one.

[0404] In step S14 of FIG. 15(A), the median diameter (D50) of the lithium cobalt oxide is 12 In the case of a thickness of about μm, the heating temperature is preferably, for example, 650° C. or more and 950° C. or less. For example, 3 hours or more and 60 hours or less is preferable, and 10 hours or more and 30 hours or less is more preferable. The temperature-lowering time after heating is, for example, 10 hours to 50 hours. It is preferable to set it to 0.5 or less.

[0405] On the other hand, in step S14, the median diameter (D50) of the lithium cobalt oxide is about 5 μm. In this case, the heating temperature is preferably, for example, 650°C or more and 950°C or less. The heating time is, for example, 1 hour. The temperature-reducing time after heating is preferably 10 hours or more and 5 hours or less, and more preferably about 5 hours. For example, it is preferable to set the time to 10 hours or more and 50 hours or less.

[0406] <Step S34> Next, in step S34 shown in FIG. 15(A), the heated material is collected and, if necessary, The particles are then crushed to obtain the positive electrode active material 100. At this time, the collected particles are further sieved. By the above steps, the positive electrode active material 100 according to one embodiment of the present invention can be produced. The positive electrode active material of one embodiment of the present invention has a smooth surface.

[0407] <<Method 2 for preparing positive electrode active material>> Next, a positive electrode active material according to another embodiment of the present invention, which is different from the positive electrode active material manufacturing method 1, The second method for preparing the positive electrode active material will be described with reference to FIGS. 16 to 17(C). Method 2 differs from Method 1 mainly in the number of times the additive elements are added and the mixing method. For details, please refer to the description of Preparation Method 1.

[0408] In FIG. 16, steps S11 to S15 are performed in the same manner as in FIG. 15(A), and the initial processing is A heated lithium cobalt oxide is prepared.

[0409] <Step S20a> Next, as shown in step S20a, the additive element A is added to the lithium cobalt oxide that has undergone the initial heating. It is preferable to add 1.

[0410] <Step S21> In step S21 shown in FIG. 17(A), a first additive element source is prepared. The element source is selected from the additive elements A described in step S21 shown in FIG. 15(B). For example, the additive element A1 can be magnesium, fluorine, or potassium. One or more of the following can be preferably used: In A), a magnesium source (Mg source) and a fluorine source (F source) are used as the first additive element source. Examples of use are given below.

[0411] Steps S21 to S23 shown in FIG. 17A are the same as those shown in FIG. 15B. This can be done under the same conditions as steps S21 to S23. The additive element source (A1 source) can be obtained in step S23.

[0412] 16. Steps S31 to S33 shown in FIG. 16 are the same as steps S31 to S33 shown in FIG. 15(A). This can be done in the same steps as steps S31 to S33.

[0413] <Step S34a> Next, in step S33, the heated material is recovered and a lithium cobalt oxide having the additive element A1 is formed. This is also called the second composite oxide to distinguish it from the composite oxide in step S14. .

[0414] <Step S40> In step S40 shown in Fig. 16, the additive element A2 is added. The explanation will also refer to (C).

[0415] <Step S41> In step S41 shown in FIG. 17(B), a second additive element source is prepared. The element source is selected from the additive elements A described in step S21 shown in FIG. 15(B). For example, the additive element A2 can be nickel, titanium, boron, di Preferably, one or more selected from the group consisting of zinc and aluminum are used. In FIG. 17(B), a nickel source (Ni source) and an aluminum source are used as the second additive element source. An example will be given in which an aluminum source (Al source) is used.

[0416] Steps S41 to S43 shown in FIG. 17B are the same as those shown in FIG. 15B. This can be done under the same conditions as steps S21 to S23. The source of the additional element (A2 source) can be obtained in step S43.

[0417] FIG. 17(C) shows a modified example of the steps described with reference to FIG. 17(B). In step S41 shown in FIG. 17(C), a nickel source (Ni source) and an aluminum source (Al In step S42a, each of the powders is crushed independently. In step 3, a plurality of second additive element sources (A2 sources) are prepared. The difference between this example and the example shown in FIG. 17(B) is that the additive elements are separately crushed in step S42a. do.

[0418] <Steps S51 to S53> Next, steps S51 to S53 shown in FIG. 16 are the same as steps shown in FIG. 15(A). The heating step can be carried out under the same conditions as steps S31 to S34. The conditions for step S53 are a lower temperature and a shorter time than those for step S33. In step S54, the positive electrode active material 100 according to one embodiment of the present invention can be produced. The positive electrode active material according to one embodiment of the present invention has a smooth surface.

[0419] As shown in FIGS. 16 and 17, in the manufacturing method 2, the additive element to the lithium cobalt oxide is The additional element A1 and the additional element A2 are introduced separately. The depth profile of the element can be changed. For example, the additive element A1 can be made The concentration of the added element A2 is higher in the inner layer than in the surface layer. It is also possible to profile the concentration so that it is high at 1000 kJ / cm2.

[0420] After the initial heating described in this embodiment, a positive electrode active material with a smooth surface can be obtained. do.

[0421] The initial heating shown in this embodiment is performed on lithium cobalt oxide. The heating temperature is lower than that for obtaining lithium cobalt oxide, and The heating time is preferably shorter than that required to obtain the desired result. The step of adding the hydroxybenzoate is preferably carried out after the initial heating. The step of adding the hydroxybenzoate can be divided into two or more steps. This process is preferable because it maintains the smooth surface obtained by the initial heating. I wish.

[0422] This embodiment can be used in combination with other embodiments.

[0423] (Embodiment 3) In this embodiment, an example of a secondary battery according to an aspect of the present invention will be described using FIGS. 18 to 21. will be described.

[0424] <Example of the configuration of a secondary battery 1> Hereinafter, a secondary battery in which a positive electrode, a negative electrode, and an electrolytic solution are wrapped in an exterior body will be described as an example. will be described.

[0425] [Positive electrode] The positive electrode has a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer has a positive electrode active material, and may have a conductive material (synonymous with a conductive auxiliary agent) and a binder. As the positive electrode active material, a positive electrode active material produced using the production method described in the previous embodiment is used. will be used.

[0426] Also, the positive electrode active material described in the previous embodiment and another positive electrode active material may be mixed and used. .

[0427] Examples of other positive electrode active materials include composite oxides having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure. For example, compounds such as LiFePO4, LiFeO2, LiNiO2, LiMn2O4, V2O5, Cr2O5, and MnO2 can be mentioned. can be mentioned.

[0428] In addition, as another positive electrode active material, a lithium-containing material having a spinel-type crystal structure containing manganese such as LiMn2O4 is preferably mixed with lithium nickelate (LiNiO2 or LiNi 1-x M x O2 (0 <x <1) (M = Co, Al, etc.)). With this configuration This makes it possible to improve the characteristics of the secondary battery.

[0429] In addition, other positive electrode active materials include those with the composition formula Li a Mn b M c O d Lithium can be expressed as A lithium-manganese composite oxide can be used. Here, the element M is any element other than lithium and manganese. It is preferable to use a metal element selected from the outside, silicon, or phosphorus, and nickel is the preferred It is more preferable to measure the entire particle of the lithium manganese composite oxide. , 0 <a / (b+c)<2、かつc>0 during discharge, and 0.26≦(b+c) / d<0. It is preferable that the metal and silicon content of the entire lithium manganese composite oxide particle is 5. The composition of carbon, phosphorus, etc. is measured using, for example, an ICP-MS (inductively coupled plasma mass spectrometer). The oxygen composition of the entire lithium manganese composite oxide particle can be determined by, for example, For example, it can be measured using EDX (energy dispersive X-ray analysis). Combined with CP-MS analysis, fusion gas analysis and XAFS (X-ray absorption fine structure) analysis are used to evaluate the valence of The lithium manganese composite oxide is at least Both refer to oxides containing lithium and manganese, and chromium, cobalt, aluminum, nickel Kel, iron, magnesium, molybdenum, zinc, indium, gallium, copper, titanium, containing one or more elements selected from the group consisting of boron, silicon, and phosphorus. That's fine.

[0430] As an example, graphene or a graphene compound is used as a conductive material in the active material layer 200. An example of a cross-sectional configuration when using the above will be described.

[0431] ​ FIG. 18(A) shows a vertical cross-sectional view of the active material layer 200. The active material layer 200 is made of granular positive electrode active material. The material 100, graphene or a graphene compound 201 as a conductive material, and a binder ( (not shown).

[0432] In this specification and the like, the graphene compound 201 refers to multi-layer graphene, multi-graphene , graphene oxide, multilayer graphene oxide, multi-graphene oxide, reduced graphene oxide Graphene, reduced multi-layer graphene oxide, reduced multi-graphene oxide, graphene amount Graphene compounds include carbon nanotubes and nanotubes that have a shape such as a flat plate or a sheet. and has a two-dimensional structure formed by a six-membered carbon ring. The two-dimensional structure is sometimes called a carbon sheet. Graphene compounds may have functional groups. In addition, the graphene compound preferably has a curved shape. The object may be rolled up into a shape similar to carbon nanofiber.

[0433] In this specification and the like, graphene oxide is a material that contains carbon and oxygen and has a sheet-like shape. , those having functional groups, particularly epoxy groups, carboxy groups or hydroxy groups.

[0434] In this specification and the like, reduced graphene oxide refers to a sheet-like graphene oxide having carbon and oxygen. It has a two-dimensional structure formed by a six-membered carbon ring. Although a single sheet of graphene works, multiple sheets can also be stacked. Phen has a carbon concentration greater than 80 atomic % and an oxygen concentration of 2 atomic %. It is preferable that the carbon concentration is 15 atomic % or more. By adjusting the oxygen concentration, even a small amount can function as a highly conductive material. In addition, reduced graphene oxide exhibits a decrease in the intensity of the G and D bands in the Raman spectrum. The ratio G / D is preferably 1 or more. The reduced oxidation graph having such an intensity ratio is Even a small amount of ethylene can function as a highly conductive material.

[0435] Graphene compounds have excellent electrical properties, such as high conductivity, as well as high flexibility and In some cases, the graphene has excellent physical properties, such as high mechanical strength. The graphene compound has a sheet-like shape. The graphene compound may have a curved surface. It allows for surface contact with low contact resistance. In addition, even if it is thin, it can have very high conductivity. Therefore, a conductive path can be efficiently formed in the active material layer with a small amount of graphene. By using a compound as a conductive material, the contact area between the active material and the conductive material can be increased. It is desirable that the graphene compound covers 80% or more of the area of ​​the active material. It is preferable that the laphene compound is attached to at least a part of the active material particles. It is preferable that the graphene compound overlaps at least a portion of the active material particles. It is preferable that the shape of the graphene compound coincides with at least a part of the shape of the active material particles. The shape of the active material particles may be, for example, the unevenness of a single active material particle or the unevenness of a plurality of active material particles. The graphene compound is a material that is formed by the active material particles. It is preferable that the graphene compound has a hole. .

[0436] When using active material particles with a small particle size, for example, active material particles with a particle size of 1 μm or less, The specific surface area of ​​the particles is large, and more conductive paths are required to connect the active material particles together. In such cases, graphene compounds that can efficiently form conductive paths even in small amounts are used. It is preferable to use

[0437] Because of the above-mentioned properties, secondary batteries that require rapid charging and rapid discharging are It is particularly effective to use graphene compounds as conductive materials. Secondary batteries for vehicles and drones require rapid charging and discharging characteristics. In addition, there are cases where rapid charging characteristics are required for mobile electronic devices. Discharge refers to, for example, charging at 200mA / g, 400mA / g, or 1000mA / g or more. This refers to electricity and discharge.

[0438] In the vertical cross section of the active material layer 200, as shown in FIG. 18(B), In the portion, the sheet-like graphene or graphene compound 201 is dispersed almost uniformly. In FIG. 18(B), graphene or a graphene compound 201 is schematically represented by a thick line. Although it is called a graphene nanoparticle, it is actually a thin film with a thickness of a single layer or multiple layers of carbon molecules. The graphene or graphene compound 201 is disposed so as to partially cover the plurality of granular positive electrode active material particles 100. Alternatively, since the positive electrode active material 100 is formed so as to be attached to the surface of a plurality of granular positive electrode active materials 100, They are in face-to-face contact with each other.

[0439] Here, a plurality of graphenes or graphene compounds are bonded to each other to form a network structure. The graphene compound sheet (hereinafter referred to as the graphene compound net or graphene net) When the active material is covered with a graphene net, The binder can also function as a binder that binds the active materials together. The amount of electrode can be reduced or eliminated, so the electrode volume and The ratio of the active material to the weight can be improved. can be increased.

[0440] Here, graphene oxide is used as the graphene or graphene compound 201, and an active material It is preferable to mix the active material with the material to form a layer that will become the active material layer 200, and then reduce the layer. The active material layer preferably contains reduced graphene oxide. Graphene oxide, which has extremely high dispersibility in polar solvents, was used to form phene compound 201. By this, graphene or graphene compound 201 is formed inside active material layer 200. The graphene oxide particles can be dispersed uniformly in a dispersion medium containing the uniformly dispersed graphene oxide particles. The solvent is removed by evaporation from the active material layer 200, and the graphene oxide is reduced. The graphene or graphene compound 201 is divided into two layers, each of which is partially overlapped and comes into surface contact with the other. By dispersing the graphene oxide, a three-dimensional conductive path can be formed. The reduction may be carried out, for example, by heat treatment or by using a reducing agent.

[0441] Therefore, unlike granular conductive materials such as acetylene black, which come into point contact with the active material, graphene Since the graphene or graphene compound 201 enables surface contact with low contact resistance, A granular positive electrode active material 100 and graphene or graphene compound in a smaller amount than normal conductive materials. Therefore, the electrical conductivity between the active material layer 201 and the positive electrode active material 100 can be improved. 200, which increases the discharge capacity of the secondary battery. It can be done.

[0442] In addition, by using a spray dryer, the entire surface of the active material is covered with a conductive material in advance. A graphene compound is formed as a coating, and the active material is further bonded to the graphene compound. A conductive path can also be formed.

[0443] In addition, the graphene compound is mixed with the materials used to form the graphene compound. It may be used in the active material layer 200. For example, it may be used as a catalyst when forming a graphene compound. The particles may be mixed with the graphene compound. Examples of catalysts include silicon oxide (SiO2, SiO x (x<2)), aluminum oxide Particles containing aluminum, iron, nickel, ruthenium, iridium, platinum, copper, germanium, etc. The particles preferably have a median diameter (D50) of 1 μm or less, and It is more preferable that the thickness is 0 nm or less.

[0444] [Binder] Examples of binders include styrene-butadiene rubber (SBR) and styrene-isopropyl Ethylene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene- It is preferable to use a rubber material such as a propylene-diene copolymer. For this purpose, fluororubber can be used.

[0445] As the binder, it is preferable to use, for example, a water-soluble polymer. As the molecule, for example, polysaccharides can be used. cellulose (CMC), methylcellulose, ethylcellulose, hydroxypropyl Cellulose, cellulose derivatives such as diacetyl cellulose and regenerated cellulose, starch, etc. In addition, these water-soluble polymers can be used in combination with the above-mentioned rubber material. It is more preferable to use it in combination with

[0446] Alternatively, the binder may be polystyrene, polymethyl acrylate, or polymethacrylic acid. Methyl (Polymethyl methacrylate, PMMA), Sodium polyacrylate, Polyvinyl Polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, Polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene Polyethylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride Polyvinyl chloride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer It is preferable to use materials such as polyvinyl acetate and nitrocellulose.

[0447] The binder may be used in combination with two or more of the above.

[0448] For example, a material having a particularly excellent viscosity adjusting effect may be used in combination with other materials. For example, rubber materials have excellent adhesive strength and / or elasticity, but when mixed with a solvent, they tend to become sticky. In such cases, it may be difficult to adjust the viscosity. As a material having a particularly excellent viscosity adjusting effect, for example, a water-soluble polymer Furthermore, the aforementioned polysaccharides are water-soluble polymers that are particularly effective in adjusting viscosity. carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose cellulose, hydroxypropyl cellulose, diacetyl cellulose, regenerated cellulose, etc. Cellulose derivatives, starch, etc. can be used.

[0449] The cellulose derivatives such as carboxymethyl cellulose are, for example, The solubility of cellulose is improved by converting it into salts such as sodium salts and ammonium salts. The increased solubility of the compound makes it easier for it to exert its effect as a viscosity adjuster. When preparing a slurry, it is also possible to improve the dispersibility of the active material and other components. In the specification, cellulose and cellulose derivatives used as binders for electrodes The term "compounds" also includes salts thereof.

[0450] The water-soluble polymer stabilizes the viscosity by dissolving in water, and also Other materials that are combined as a catalyst, such as styrene butadiene rubber, are stable in aqueous solution. In addition, since it has functional groups, it can be easily and stably adsorbed onto the surface of the active material. In addition, cellulose derivatives such as carboxymethyl cellulose are expected to be Many of the materials have functional groups such as hydroxyl groups and carboxyl groups. Therefore, it is expected that the polymers will interact with each other and cover the surface of the active material widely.

[0451] When the binder that covers or contacts the surface of the active material forms a film, it is called a passive film. It is expected that the passive film will also act as a barrier to prevent the decomposition of the electrolyte. A film with no electrical conductivity or extremely low electrical conductivity, for example, on the surface of an active material When a passive film is formed, it is possible to suppress the decomposition of the electrolyte at the battery reaction potential. In addition, the passive film suppresses electrical conductivity and does not allow lithium ions to be conducted. It is even more desirable to

[0452] [Current collector] The current collector may be made of metals such as stainless steel, gold, platinum, aluminum, titanium, or any of these. The material used for the positive electrode current collector is a highly conductive material, such as an alloy of It is preferable that the material does not dissolve at the potential of the positive electrode. It uses aluminum alloys containing elements such as sulphur and molybdenum that improve heat resistance. It can also be formed from a metal element that reacts with silicon to form silicide. Metal elements that react with silicon to form silicide include zirconium, titanium, and Niobium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, Cobalt, nickel, etc. Current collectors are available in foil, plate, sheet, mesh, and punched metal. The current collector may be in the form of a metal foil, an expanded metal, or the like. It is recommended to use a thickness of 30 μm or more.

[0453] [Negative electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector. and a binder.

[0454] [Negative electrode active material] As the negative electrode active material, for example, an alloy-based material and / or a carbon-based material can be used. Cut.

[0455] As a negative electrode active material, it can carry out charge-discharge reactions by alloying and dealloying reactions with lithium. Any element can be used, such as silicon, tin, gallium, aluminum, Select from germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. Materials containing one or more of these elements may be used. The charge / discharge capacity is large, and silicon in particular has a high theoretical capacity of 4200mAh / g. It is preferable to use silicon as the negative electrode active material. For example, SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn , SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag 3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, SbSn, etc. Here, alloying and dealloying reactions with lithium The elements capable of undergoing charge / discharge reactions and compounds containing such elements are used as alloy materials. It is sometimes called.

[0456] In this specification, SiO refers to, for example, silicon monoxide. Alternatively, SiO refers to Si O x Here, it is preferable that x has a value close to 1. For example, x can be expressed as It is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less. Preferably, it is 0.3 or more and 1.5 or less.

[0457] Carbon materials include graphite, easily graphitizable carbon (soft carbon), and non-graphitizable carbon (hard carbon). carbon nanotubes, graphene, carbon black, etc. stomach.

[0458] Examples of graphite include artificial graphite and natural graphite. Examples include carbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Here, as the artificial graphite, spherical graphite having a spherical shape can be used. For example, the MCMB may have a spherical shape, which is preferable. It is relatively easy to reduce the particle size, which is sometimes preferable. Examples include flake graphite and spherical natural graphite.

[0459] When lithium ions are inserted into graphite (the formation of lithium-graphite intercalation compounds), ) shows a low potential similar to that of lithium metal (0.05V to 0.3V vs.Li / Li + This allows lithium-ion secondary batteries to exhibit high operating voltages. Furthermore, graphite has a relatively high charge / discharge capacity per unit volume, a relatively small volume expansion, It is preferable because it has advantages such as being inexpensive and being safer than metallic lithium.

[0460] In addition, titanium dioxide (TiO2) and lithium titanium oxide (Li4 Ti5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5 ), tungsten oxide (WO2), molybdenum oxide (MoO2), etc. can be done.

[0461] In addition, the negative electrode active material is a composite nitride of lithium and transition metals, which has a Li3N structure. つLi 3-x M x N (M=Co, Ni, Cu) can be used. For example, Li 2. 6Co 0.4 N3 has a large charge / discharge capacity (900mAh / g, 1890mAh / cm 3 )of This is preferable.

[0462] When a composite nitride of lithium and transition metals is used, lithium ions are included in the negative electrode active material, As a positive electrode active material, materials that do not contain lithium ions, such as V2O5 and Cr3O8, are used. In addition, when a material containing lithium ions is used as the positive electrode active material, However, by first removing the lithium ions contained in the positive electrode active material, As the lithium-transition metal nitride, a complex nitride of lithium and a transition metal can be used.

[0463] In addition, a material that undergoes a conversion reaction can also be used as the negative electrode active material. For example, lithium oxides such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO) A transition metal oxide that does not form an alloy with aluminum may be used as the negative electrode active material. Further materials that produce this include Fe2O3, CuO, Cu2O, RuO2, and Cr2O3 oxides such as CoS 0.89 , NiS, CuS and other sulfides, Zn3N2, Cu3N, Ge Nitrides such as 3N4, phosphides such as NiP2, FeP2, CoP3, FeF3, BiF3, etc. This also occurs with fluoride.

[0464] The conductive material and binder that can be contained in the negative electrode active material layer are the same as those that can be contained in the positive electrode active material layer. The same materials as the conductive material and binder that can be used can be used.

[0465] [Negative electrode current collector] The negative electrode current collector can be made of the same material as the positive electrode current collector. It is preferable to use a material that does not alloy with carrier ions such as lithium.

[0466] [Electrolyte] The electrolytic solution contains a solvent and an electrolyte. The solvent for the electrolytic solution is preferably an aprotic organic solvent. Preferably, for example, ethylene carbonate (EC), propylene carbonate (PC), Ethylene carbonate, chloroethylene carbonate, vinylene carbonate, gamma-butyro Lactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfone oxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran One of tetrahydrofuran, sulfolane, sultone, etc., or two or more of these can be used in combinations and ratios of:

[0467] In addition, a flame-retardant and non-volatile ionic liquid (room-temperature molten salt) is used as the solvent for the electrolyte. By using one or more, the internal temperature of the secondary battery will rise due to an internal short circuit or overcharging. Even if the battery is damaged, it can prevent the secondary battery from exploding and / or catching fire. It consists of thiones and anions, and contains organic cations and anions. As cations, quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations Aliphatic onium cations such as nium cations, imidazolium cations and pyridinium cations Examples of anions used in electrolytes include aromatic cations such as ammonium cations. Monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluorinated anions fluoroalkylsulfonic acid anion, tetrafluoroborate anion, perfluoroalkyl alkylborate anion, hexafluorophosphate anion, or perfluoroanion alkyl phosphate anions and the like.

[0468] The electrolyte to be dissolved in the solvent is, for example, LiPF6, LiClO4, L iAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO 4. Li2B 10 Cl 10 , Li2B 12 Cl 12 , LiCF3SO3, LiC4F9S O3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2 )2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, etc. One or more of these titanium salts may be used in any combination and ratio. This can be done.

[0469] The electrolyte used in secondary batteries is made of granular waste or elements other than the constituent elements of the electrolyte (hereinafter referred to as simple It is preferable to use a highly purified electrolyte solution with a low content of impurities. Specifically, the weight ratio of impurities to the electrolyte is 1% or less, preferably 0.1% or less. More preferably, it is set to 0.01% or less.

[0470] In addition, the electrolyte contains vinylene carbonate, propane sultone (PS), and tert-butyl Benzene (TBB), Fluoroethylene carbonate (FEC), Lithium bis(oxa) Lithium borate (LiBOB), as well as dinitriles such as succinonitrile and adiponitrile The concentration of the additives may be, for example, The content should be between 0.1wt% and 5wt%. VC or LiBOB has a good coating. This is particularly preferable because it is easy to form.

[0471] Alternatively, a polymer gel electrolyte may be used in which a polymer is swollen with an electrolytic solution.

[0472] The use of polymer gel electrolyte increases safety against leakage etc. The pond can be made thinner and lighter.

[0473] Gelled polymers include silicone gel, acrylic gel, and acrylonitrile gel. , polyethylene oxide gel, polypropylene oxide gel, fluorine-based polymer A gel or the like can be used.

[0474] Examples of polymers include polyalkylene oxides such as polyethylene oxide (PEO). Polymers with side structures, PVDF, polyacrylonitrile, etc., and their For example, a copolymer containing PVDF and hexafluoropropylene (H PVDF-HFP, a copolymer of PVDF and PVDF, can be used. The mer may have a porous shape.

[0475] Alternatively, instead of an electrolytic solution, a solid electrolyte containing an inorganic material such as a sulfide or oxide may be used. Use of a solid electrolyte containing a polymer material such as PEO (polyethylene oxide) When using a solid electrolyte, the installation of a separator and / or spacer is not necessary. In addition, the entire battery can be solidified, eliminating the risk of leakage and dramatically improving safety. improves to.

[0476] [Separator] The secondary battery preferably has a separator. Examples of the separator include: Paper, nonwoven fabric, glass fiber, ceramics, or nylon (polyamide), vinylon (polyamide) vinyl alcohol fiber), polyester, acrylic, polyolefin, polyurethane The separator can be made of synthetic fibers or the like. It is preferable to process the electrode into a shape and place it so as to wrap either the positive electrode or the negative electrode.

[0477] The separator may have a multi-layer structure. For example, the separator may be made of an organic material such as polypropylene or polyethylene. The material film is made of ceramic material, fluorine material, polyamide material, or a combination of these. The ceramic material can be, for example, aluminum oxide. Examples of the fluorine-based material include aluminum particles, silicon oxide particles, etc. For example, PVDF, polytetrafluoroethylene, etc. can be used. For example, nylon, aramid (meta-aramid, para-aramid), etc. can be done.

[0478] Coating with ceramic materials improves oxidation resistance, making it possible to use separators during high-voltage charging and discharging. This suppresses the deterioration of the battery and improves the reliability of the secondary battery. Coating the separator and electrodes makes them adhere more easily, improving output characteristics. Coating polyamide materials, especially aramid, improves heat resistance, making it suitable for secondary batteries. Safety can be improved.

[0479] For example, a mixture of aluminum oxide and aramid is coated on both sides of a polypropylene film. Alternatively, aluminum oxide may be applied to the surface of the polypropylene film that comes into contact with the positive electrode. The surface that comes into contact with the negative electrode may be coated with a mixed material of rubber and aramid, and a fluorine-based material may be coated on the surface that comes into contact with the negative electrode. .

[0480] By using a multilayer separator, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin. Since the above condition can be maintained, the discharge capacity per volume of the secondary battery can be increased.

[0481] [Exterior body] The exterior of the secondary battery may be made of a metal material such as aluminum and / or Resin materials can be used. Also, a film-like exterior body can be used. Examples of materials include polyethylene, polypropylene, polycarbonate, and ionomer. A film made of a material such as polyamide is coated with a material such as aluminum, stainless steel, copper, or nickel. A thin metal film with excellent flexibility is provided, and a polyamide resin is further provided on the thin metal film as the outer surface of the exterior body. Use a three-layer film with an insulating synthetic resin film such as oil or polyester resin. can be done.

[0482] <Configuration example 2 of secondary battery> As an example of the configuration of a secondary battery, the configuration of a secondary battery using a solid electrolyte layer is described below. explain.

[0483] As shown in FIG. 19A, a secondary battery 400 according to one embodiment of the present invention includes a positive electrode 410, a solid-state battery 412, a It has an electrolyte layer 420 and a negative electrode 430 .

[0484] The positive electrode 410 includes a positive electrode current collector 413 and a positive electrode active material layer 414. 4 has a positive electrode active material 411 and a solid electrolyte 421. The positive electrode active material 411 has the same structure as in the previous embodiment. The positive electrode active material layer 4 is made of the positive electrode active material prepared by the method described in the embodiment. 14 may include a conductive material and a binder.

[0485] The solid electrolyte layer 420 includes a solid electrolyte 421. The solid electrolyte layer 420 includes a positive electrode 410. and the negative electrode 430, and does not have either the positive electrode active material 411 or the negative electrode active material 431. This is a challenging area.

[0486] The negative electrode 430 includes a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 has a negative electrode active material 431 and a solid electrolyte 421. In addition, when metallic lithium is used for the negative electrode 430, As shown in FIG. 19(B), the negative electrode 430 does not have a solid electrolyte 421. The use of metallic lithium in the negative electrode 430 improves the energy density of the secondary battery 400. This is preferable.

[0487] The solid electrolyte 421 of the solid electrolyte layer 420 may be, for example, a sulfide-based solid electrolyte, An oxide-based solid electrolyte, a halide-based solid electrolyte, or the like can be used.

[0488] Sulfide-based solid electrolytes include thiolithium-based (Li 10 GeP2S 12 , Li 3.25 G e 0.25 P 0.75 S4, etc.), sulfide glass (70Li2S・30P2S5, 30Li 2S·26B2S3·44LiI, 63Li2S·36SiS2·1Li3PO4, 57 Li2S・38SiS2・5Li4SiO4, 50Li2S・50GeS2, etc.), sulfides Glass-ceramic (Li7P3S 11 , Li3.25 P 0.95 S4, etc.) are included. Solid electrolytes based on ZnO have high conductivity, can be synthesized at low temperatures, and are relatively soft. Because it is soft, it has the advantage of easily maintaining conductive paths even after charging and discharging.

[0489] Oxide-based solid electrolytes include materials with a perovskite crystal structure (La 2 / 3-x L i 3x TiO3, etc.), materials with NASICON-type crystal structure (Li 1-x Al x Ti2 -x (PO4)3, etc.), materials with garnet-type crystal structure (Li7La3Zr2O 12 etc.), materials with LISICON-type crystal structure (Li 14 ZnGeO 16 etc.), LLZ O(Li7La3Zr2O 12 ), oxide glass (Li3PO4-Li4SiO4, 50 Li4SiO4·50Li3BO3, etc.), oxide crystallized glass (Li 1.07 Al 0.6 9Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, etc.) Oxide-based solid electrolytes have the advantage of being stable in the atmosphere.

[0490] Halide solid electrolytes include LiAlCl4, Li3InBr6, LiF, and LiC These halide-based solid electrolytes are also used in polar Composite materials containing aluminum oxide and / or porous silica filled into the pores are also available. It can be used as a solid electrolyte.

[0491] Also, different solid electrolytes may be mixed and used.

[0492] Among them, Li 1+x Al x Ti 2-x (PO4)3 (0 < x < 1) (hereinafter referred to as LATP) contains elements that the positive electrode active material used in the secondary battery 400 of one aspect of the present invention may have, such as aluminum and titanium, so an improvement in cycle characteristics is expected to have a synergistic effect and is preferable. Also, an improvement in productivity due to reduction of processes can be expected . In the present specification and the like, the NASICON-type crystal structure is a compound represented by M2(XO4)3 (M: transition metal, X: S, P, As, Mo, W, etc.), and refers to a structure in which MO6 octahedrons and X O4 tetrahedrons share vertices and are three-dimensionally arranged.

[0493] 〔Shape of the exterior body and the secondary battery〕 For the exterior body of the secondary battery 400 of one aspect of the present invention, those of various materials and shapes can be used , but it is preferable to have a function of pressing the positive electrode, the solid electrolyte layer, and the negative electrode .

[0494] For example, FIG. 20 is an example of a cell for evaluating the materials of an all-solid-state battery.

[0495] FIG. 20(A) is a schematic cross-sectional view of the evaluation cell. The evaluation cell has a lower member 761, an upper member 762, and a fixing screw or wing nut 764 for fixing them, and fixes the evaluation material by pressing the electrode plate 753 by rotating the pressing screw 7 63. An insulator 766 is provided between the lower member 761 and the upper member 762 made of a stainless material. Also, an O-ring 765 for sealing is provided between the upper member 762 and the pressing screw 763. Also, an O-ring for sealing is provided between the upper member 762 and the pressing screw 763. There is a 765-seater.

[0496] The evaluation material is placed on an electrode plate 751, surrounded by an insulating tube 752, and It is pressed by the electrode plate 753. The perspective view is shown in Figure 20(B).

[0497] As an example of the evaluation material, a stack of a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c was used. The cross-sectional view is shown in FIG. 20(C). The same symbols are used for the same parts throughout the specification.

[0498] The electrode plate 751 and the lower member 761 electrically connected to the positive electrode 750a are The electrode plate electrically connected to the negative electrode 750c corresponds to the electrode terminal. The electrode plate 753 and the upper member 762 can be said to correspond to the negative electrode terminal. While applying pressure to the evaluation material through the electrode 751 and the electrode plate 753, It is possible to measure things like:

[0499] In addition, a package with excellent airtightness is used for the exterior body of the secondary battery according to one embodiment of the present invention. For example, it is preferable to use a ceramic package and / or a resin package. In addition, when sealing the exterior body, the outside air is blocked and the inside of the body is sealed in a sealed atmosphere, for example. It is preferable to carry out this in a glove box.

[0500] FIG. 21(A) shows a secondary battery of one embodiment of the present invention having an exterior body and a shape different from those in FIG. 20. The secondary battery in FIG. 21(A) has external electrodes 771 and 772 and a plurality of panels. It is sealed in an exterior body having a packaging member.

[0501] An example of a cross section taken along the dashed line in FIG. 21(A) is shown in FIG. 21(B). The laminate having the solid electrolyte layer 750b and the negative electrode 750c is a flat plate having an electrode layer 773a. The package member 770a, the frame-shaped package member 770b, and the electrode layer on the flat plate The package member 770c is provided with the semiconductor device 773b, and the semiconductor device 773b is enclosed and sealed. The package members 770a, 770b, and 770c are made of an insulating material, for example, a resin material and and / or ceramics may be used.

[0502] The external electrode 771 is electrically connected to the positive electrode 750a via the electrode layer 773a. The external electrode 772 also functions as an electrode. It is electrically connected to the negative terminal.

[0503] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0504] (Fourth embodiment) In this embodiment, an example of the shape of the secondary battery having the positive electrode described in the previous embodiment will be described. The materials used in the secondary battery described in this embodiment are the same as those described in the previous embodiment. This can be taken into consideration.

[0505] <Coin-type secondary battery> First, an example of a coin-type secondary battery will be described. 22(A) is an external view of a coin-type secondary battery, and FIG. 22(B) is a cross-sectional view thereof. In this specification, the coin battery is a button-type battery. Includes batteries.

[0506] The coin-type secondary battery 300 has a positive electrode can 301 that also serves as a positive electrode terminal and a negative electrode can 302 that also serves as a negative electrode terminal. The can 302 is insulated and sealed with a gasket 303 made of polypropylene or the like. The positive electrode 304 is composed of a positive electrode current collector 305 and a positive electrode active material layer 30 provided 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 current collector 308 which is set in contact with the negative electrode current collector 308. The negative electrode active material layer 309 is formed by the bonding.

[0507] The positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 are active The material layer only needs to be formed on one side.

[0508] The positive electrode can 301 and the negative electrode can 302 are made of nickel and aluminum, which are corrosion-resistant to the electrolyte. Metals such as aluminum and titanium, or their alloys and / or alloys of these with other metals (e.g. For example, stainless steel can be used. In addition, nickel is used to prevent corrosion by the electrolyte. It is preferable that the cathode can 301 is coated with aluminum or the like. The negative electrode can 302 is electrically connected to the negative electrode 307 .

[0509] The negative electrode 307, the positive electrode 304, and the separator 310 are impregnated with an electrolyte, and the negative electrode 307, the positive electrode 304, and the separator 310 are then placed in a sealed container. As shown in Fig. 1B, the positive electrode can 301 is placed downward, and the positive electrode 304, separator 310, and negative electrode 307 are placed in the same container. The positive electrode can 301 and the negative electrode can 302 are stacked in this order, and the positive electrode can 301 and the negative electrode can 302 are secured together with a gasket 303. The coin-type secondary battery 300 is manufactured by crimping the battery.

[0510] By using the positive electrode active material described in the above embodiment for the positive electrode 304, a high discharge capacity can be obtained. The coin-type secondary battery 300 can have excellent cycle characteristics.

[0511] Here, the flow of current during charging of the secondary battery will be explained using FIG. When a secondary battery is considered as a closed circuit, the movement of lithium ions and the flow of current go in the same direction. In secondary batteries that use lithium, the anode and cathode are connected by charging and discharging. The cathode and the oxidation reaction are reversed, and the reaction potential is The electrode with a higher reaction potential is called the positive electrode, and the electrode with a lower reaction potential is called the negative electrode. In this case, even during charging, discharging, or when a reverse pulse current is applied, Even when a charging current is flowing, the positive electrode is called the "positive electrode" or "+ electrode (plus electrode)" and the negative electrode is called the "+ electrode (plus The electrode is called the "negative electrode" or "-electrode (minus electrode)." Oxidation and reduction reactions The terms anode and cathode, which are related to the When the current is applied, the anode is turned on and off, which can cause confusion. The terms cathode and cathode are not used in this specification. When using the terms anode and cathode, it is important to remember that they are used during charging and discharging. Also, indicate whether it corresponds to the positive (plus) or negative (minus) pole. It will be decided.

[0512] A charger is connected to the two terminals shown in FIG. 22(C), and the secondary battery 300 is charged. As the charging of the secondary battery 300 progresses, the potential difference between the electrodes increases.

[0513] <Cylindrical secondary battery> Next, an example of a cylindrical secondary battery will be described with reference to FIG. 23. Cylindrical secondary battery 60 FIG. 23(A) shows an external view of the cylindrical secondary battery 600. FIG. 23(B) shows a cross section of the cylindrical secondary battery 600. As shown in FIG. 23(B), the cylindrical secondary battery 600 has a It has a positive electrode cap (battery lid) 601 and a battery can (external can) 602 on the side and bottom. The positive electrode cap 601 and the battery can (external can) 602 are connected by a gasket (insulating It is insulated by 610.

[0514] Inside the hollow cylindrical battery can 602, a strip-shaped positive electrode 604 and a negative electrode 606 are placed with a separator. The battery element is wound with the battery 605 sandwiched between them. The battery can 602 is closed at one end and open at the other. The battery can 602 is made of nickel, aluminum, or titanium, which is resistant to corrosion by the electrolyte. or alloys thereof and / or alloys thereof with other metals (e.g., stainless steel, In addition, nickel and It is preferable to coat the battery can 602 with aluminum or the like. In the battery element, a positive electrode, a negative electrode, and a separator are wound together, and a pair of opposing insulating plates are The battery element is sandwiched between 608 and 609. The inside of the battery can 602 in which the battery element is provided is A non-aqueous electrolyte (not shown) is injected into the battery. The non-aqueous electrolyte is the same as that of a coin-type secondary battery. can be used.

[0515] The positive and negative electrodes used in cylindrical storage batteries are wound, so active material is formed on both sides of the current collector. A positive electrode terminal (positive electrode current collecting lead) 603 is connected to the positive electrode 604, and a negative A negative electrode terminal (negative electrode current collecting lead) 607 is connected to the positive electrode 603. The positive electrode terminal 607 can be made of a metal material such as aluminum. 603 is resistance-welded to the safety valve mechanism 612, and the negative terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 612 is a PTC (Positive Temperature Coefficient) element. The positive electrode cap 601 is electrically connected to the positive electrode cap 601 via a positive electrode coefficient 611. The safety valve mechanism 612 releases the positive electrode cap 601 when the internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 cuts off the electrical connection between the positive electrode 604 and the positive electrode 604. It is a thermal resistor whose resistance increases when the temperature rises, and the increase in resistance limits the amount of current. It prevents abnormal heat generation. The PTC element is made of barium titanate (BaTiO3) Semiconductor ceramics and the like can be used.

[0516] 23(C), a plurality of secondary batteries 600 are mounted on a conductive plate 613 and a conductive plate 61 4 to form a module 615. The plurality of secondary batteries 600 may be connected in parallel. They may be connected in series, or may be connected in parallel and then in series. By configuring a module 615 having a plurality of secondary batteries 600, , a large amount of power can be extracted.

[0517] FIG. 23(D) is a top view of module 615. For clarity, conductive plate 613 As shown in FIG. 23(D), the module 615 is made up of a plurality of secondary batteries 600. The conductive plate may be placed on the conductive wire 616. In addition, even if a temperature control device 617 is provided between the plurality of secondary batteries 600, When the secondary battery 600 is overheated, the temperature control device 617 cools it down. If 600 is too cold, it can be heated by the temperature control device 617. Therefore, the performance of the module 615 is less affected by the outside temperature. The heat transfer medium is preferably insulating and non-flammable.

[0518] By using the positive electrode active material described in the above embodiment for the positive electrode 604, a high discharge capacity can be obtained. The cylindrical secondary battery 600 can be made to have excellent cycle characteristics.

[0519] <Structural example of a power storage device including a secondary battery> Another structural example of a power storage device including a secondary battery will be described with reference to FIGS.

[0520] 24(A) and 24(B) are diagrams showing the external appearance of the battery pack. The battery 913 includes a secondary battery 913 and a circuit board 900. The secondary battery 913 is connected to an antenna 914 via a label 910. Furthermore, as shown in FIG. 24(B), the secondary battery 913 has a terminal 951 and , and terminal 952. The circuit board 900 is fixed with a seal 915. There are.

[0521] The circuit board 900 has a terminal 911 and a circuit 912. The terminal 911 is connected to the terminal 95. 1, terminal 952, antenna 914, and circuit 912. Each of the plurality of terminals 911 may be used as a control signal input terminal, a power supply terminal, etc. stomach.

[0522] The circuit 912 may be provided on the back surface of the circuit board 900. The shape of the antenna is not limited to a coil, but may be, for example, a wire or a plate. Antennas such as face antennas, traveling wave antennas, EH antennas, magnetic field antennas, and dielectric antennas Alternatively, the antenna 914 may be a flat conductor. The body can function as one of the conductors for electric field coupling. The antenna 914 may function as one of the two conductors. Power can be exchanged not only using electromagnetic fields and magnetic fields, but also using electric fields.

[0523] The battery pack has a layer 916 between the antenna 914 and the secondary battery 913. Layer 916 has a function of shielding an electromagnetic field generated by, for example, a secondary battery 913. For example, a magnetic material can be used as 6.

[0524] The structure of the battery pack is not limited to that shown in FIG.

[0525] For example, as shown in FIGS. 25(A) and 25(B), In the secondary battery 913 shown in FIG. 1, an antenna may be provided on each of a pair of opposing surfaces. FIG. 25(A) is an external view showing one of the pair of surfaces, and FIG. 25(B) is an external view showing the pair of surfaces. 24(A) and 24(B) are external views showing the other side of the secondary battery. For the same parts as those described above, the description of the secondary battery shown in FIGS. 24(A) and 24(B) is used as appropriate. can.

[0526] As shown in FIG. 25(A), a layer 916 is sandwiched between one of the two surfaces of a secondary battery 913. 25(B), a retainer 914 is provided on the other of the pair of surfaces of the secondary battery 913. An antenna 918 is provided across the layer 917. The layer 917 is, for example, a secondary battery 913. The layer 917 has a function of shielding the electromagnetic field. It is possible.

[0527] By adopting the above structure, the size of both the antenna 914 and the antenna 918 can be increased. The antenna 918 can perform data communication with an external device, for example. The antenna 918 has a function of being able to receive the signal. A method for communication between a secondary battery and other devices via an antenna 918 can be applied. The method is to use NFC (near field communication) between secondary batteries and other devices. It is possible to apply a response method that can be used.

[0528] Alternatively, as shown in FIG. 25(C), the secondary battery 91 shown in FIG. 24(A) and FIG. 24(B) A display device 920 may be provided on the terminal 911. The display device 920 is electrically connected to the terminal 911. It is not necessary to provide the label 910 in the area where the display device 920 is provided. The same parts as those of the secondary battery shown in FIGS. 24(A) and 24(B) are shown in FIGS. The description of the secondary battery shown in FIG. 24(B) can be used as appropriate.

[0529] The display device 920 displays, for example, an image indicating whether charging is in progress or not, an image indicating the amount of stored power, etc. The display device 920 may be, for example, an electronic paper, a liquid crystal display, an electronic For example, an electroluminescence (EL) display device can be used. By using the polarizer, the power consumption of the display device 920 can be reduced.

[0530] Alternatively, as shown in FIG. 25(D), the secondary battery 91 shown in FIG. 24(A) and FIG. 24(B) A sensor 921 may be provided on the terminal 911 via a terminal 922. It should be noted that the same parts as those of the secondary battery shown in Fig. 24(A) and Fig. 24(B) are For this purpose, the description of the secondary battery shown in FIGS. 24(A) and 24(B) can be used as appropriate.

[0531] The sensor 921 may be, for example, a sensor for measuring displacement, position, velocity, acceleration, angular velocity, number of rotations, distance, Light, liquid, magnetism, temperature, chemical substances, sound, time, hardness, electric field, current, voltage, power, radiation, It is sufficient if it has the function of measuring flow rate, humidity, gradient, vibration, odor, or infrared. By providing the sensor 921, for example, data indicating the environment in which the secondary battery is placed can be obtained. It is also possible to detect data (such as temperature) and store it in memory within the circuit 912.

[0532] Furthermore, an example of the structure of the secondary battery 913 will be described with reference to FIGS.

[0533] The secondary battery 913 shown in FIG. 26(A) has a terminal 951 and a terminal 952 inside a housing 930. The winding body 950 is impregnated with an electrolyte inside the housing 930. The terminal 952 is in contact with the housing 930, and the terminal 951 is in contact with the housing 930 by using an insulating material or the like. It is not in contact with the housing 930. For convenience, in FIG. 26(A), the housing 930 is shown separated. However, in reality, the winding body 950 is covered by the housing 930, and the terminals 951 and 952 are 52 extends outside the housing 930. The housing 930 is made of a metal material (e.g., aluminum). For example, a material such as aluminum or a resin material can be used.

[0534] As shown in FIG. 26(B), the housing 930 shown in FIG. 26(A) can be made of a plurality of materials. For example, the secondary battery 913 shown in FIG. 26(B) may be formed by a housing 930a and a housing The area surrounded by the housing 930a and the housing 930b is where the wound body is placed. 950 is provided.

[0535] The housing 930a can be made of an insulating material such as organic resin. By using a material such as organic resin on the surface on which the capacitor is formed, the electric field generated by the secondary battery 913 If the shielding of the electric field by the housing 930a is small, the housing 930a An antenna such as antenna 914 may be provided inside the housing 930b. A metallic material can be used.

[0536] Furthermore, the structure of the wound body 950 is shown in Fig. 27. The wound body 950 includes a negative electrode 931, The wound body 950 has a positive electrode 932 and a separator 933. The wound body 950 has the separator 933 sandwiched therebetween. Then, the negative electrode 931 and the positive electrode 932 are stacked one on top of the other, and the laminated sheet is wound. The negative electrode 931, the positive electrode 932, and the separator 933 may be further laminated. Multiple layers may be stacked.

[0537] The negative electrode 931 is connected to the terminal 911 shown in FIG. 24 via one of the terminals 951 and 952. The positive electrode 932 is connected to the terminal 951 shown in FIG. Connected to 11.

[0538] When the positive electrode 932 is formed using the positive electrode active material described in the above embodiment, the discharge capacity is high. The secondary battery 913 can have excellent cycle characteristics.

[0539] <Laminated secondary battery> Next, an example of a laminated secondary battery will be described with reference to FIGS. 28 to 32(A). If the laminated secondary battery is made flexible, the flexible portion can be If the secondary battery is mounted in at least some of the electronic equipment, it will bend in accordance with the deformation of the electronic equipment. It is also possible to do so.

[0540] A laminated secondary battery 980 will be described with reference to FIG. The secondary battery 980 has a wound body 993 shown in FIG. 4, a positive electrode 995, and a separator 996. The wound body 993 is the same as that described in FIG. Similar to the wound body 950, a negative electrode 994 and a positive electrode 995 are stacked with a separator 996 sandwiched therebetween. The laminated sheet is then wound up.

[0541] The number of layers of the negative electrode 994, the positive electrode 995, and the separator 996 may be as many as necessary. The negative electrode 994 may be appropriately designed according to the charge / discharge capacity and the volume of the element. and a lead electrode 998, and the positive electrode 995 is connected to a negative electrode current collector (not shown). Connected to a positive electrode current collector (not shown) via the other of the lead electrode 997 and the lead electrode 998 will be done.

[0542] As shown in FIG. 28(B), a film 981 that serves as an exterior body and a film 982 having a recess are The above-mentioned wound body 993 is housed in a space formed by bonding the above-mentioned wound body 993 and the above-mentioned wound body 82 together by thermocompression bonding or the like. By doing so, a secondary battery 980 can be fabricated as shown in FIG. 93 has a lead electrode 997 and a lead electrode 998, and a film 981 and a recessed portion. The inside of the film 982 is impregnated with an electrolyte.

[0543] The film 981 and the film 982 having the recesses are made of a metal material such as aluminum. The film 981 and the recessed portion may be made of a metal and / or a resin material. If a resin material is used as the material for Film 982, Film 9 will bend when external force is applied. 81 and the film 982 having the recesses can be deformed to form a flexible storage battery. It can be made.

[0544] In addition, although Fig. 28(B) and Fig. 28(C) show examples using two films, A space is formed by folding one film, and the above-mentioned wound body 9 is inserted into the space. 93 may also be accommodated.

[0545] By using the positive electrode active material described in the previous embodiment for the positive electrode 995, the discharge capacity is high. The secondary battery 980 can have excellent cycle characteristics.

[0546] In addition, in FIG. 28, a secondary battery having a wound body in a space formed by a film that serves as an exterior body is shown. For example, as shown in Figure 29, the shape of the outer film is It can also be used as a secondary battery having a plurality of rectangular positive electrodes, separators, and negative electrodes in the space formed. good.

[0547] The laminated secondary battery 500 shown in FIG. 29(A) includes a positive electrode current collector 501 and a positive electrode active material. A positive electrode 503 having a material layer 502 and a negative electrode current collector 504 and a negative electrode active material layer 505 are provided. The battery includes a negative electrode 506, a separator 507, an electrolyte 508, and an exterior body 509. A separator 507 is provided between a positive electrode 503 and a negative electrode 506 provided in a housing 509. The exterior body 509 is filled with an electrolyte 508. The electrolyte 508 contains The electrolyte solution shown in Embodiment 3 can be used.

[0548] In the laminated secondary battery 500 shown in FIG. 29(A), a positive electrode current collector 501 and The negative electrode current collector 504 also serves as a terminal for electrical contact with the outside. A part of the electrode current collector 501 and the negative electrode current collector 504 is exposed to the outside from the outer casing 509. In addition, the positive electrode current collector 501 and the negative electrode current collector 504 may be disposed in the outer casing 509. The lead electrode is connected to the positive electrode current collector 501 or the negative electrode current collector 502 by using the lead electrode. The lead electrode may be exposed to the outside by ultrasonic bonding to the electrode current collector 504 .

[0549] In the laminated secondary battery 500, the exterior body 509 is made of, for example, polyethylene, polypropylene, or the like. On a membrane made of a material such as polypropylene, polycarbonate, ionomer, or polyamide, A thin metal film with excellent flexibility, such as aluminum, stainless steel, copper, or nickel, is applied. On the metal thin film, an insulating composite such as polyamide resin or polyester resin is used as the outer surface of the exterior body. A laminate film having a three-layer structure provided with a resin film can be used.

[0550] An example of the cross-sectional structure of a laminated secondary battery 500 is shown in FIG. For simplicity, (A) shows an example of a structure with two current collectors, but in reality, as shown in Figure 29(B ) it is composed of multiple electrode layers.

[0551] In FIG. 29(B), as an example, the number of electrode layers is set to 16. In FIG. 29(B), the negative electrode current collector 504 is made up of eight layers. 29(B) shows a structure of 16 layers in total, with 8 layers of the positive electrode current collector 501. The cross section of the extraction part is shown, and eight layers of negative electrode current collector 504 are ultrasonically bonded. Of course, the number of electrode layers is not limited to 16, and may be more or less. In this case, a secondary battery having a larger discharge capacity can be obtained. If no such electrode is present, the secondary battery can be made thinner and more flexible.

[0552] An example of an external view of a laminated secondary battery 500 is shown in FIGS. 30 and 31. 30 and 31 show a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead The positive electrode 510 and the negative electrode 511 are provided.

[0553] FIG. 32(A) shows an external view of the positive electrode 503 and the negative electrode 506. The positive electrode 503 is connected to the positive electrode current collector 5 01, and the positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. The electrode 503 has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as a tab region). The electrode 506 has a negative electrode current collector 504, and the negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. The negative electrode 506 is formed in a region where the negative electrode current collector 504 is partially exposed, i.e., a tab. The area and shape of the tab regions of the positive electrode and negative electrode are as shown in FIG. Examples are not limited to:

[0554] <Method for manufacturing laminated secondary batteries> Here, an example of a method for manufacturing a laminated secondary battery, the external view of which is shown in FIG. 30, will be described with reference to FIG. 2(B) and (C) will be used to explain.

[0555] First, the negative electrode 506, the separator 507, and the positive electrode 503 are stacked. The negative electrode 506, separator 507, and positive electrode 503 are shown. Next, the bonding of the tab regions of the positive electrode 503 and the bonding of the tabs of the positive electrode on the outermost surface are shown. The positive electrode lead electrode 510 is bonded to the bonding region. For example, ultrasonic welding or the like is used for bonding. Similarly, the tab regions of the negative electrodes 506 are bonded to each other, and the negative electrode is bonded to the tab region of the negative electrode on the outermost surface. The lead electrode 511 is bonded.

[0556] Next, the negative electrode 506 , the separator 507 and the positive electrode 503 are placed on the exterior body 509 .

[0557] Next, as shown in Figure 32(C), the exterior body 509 is folded at the portion indicated by the broken line. After that, the outer periphery of the exterior body 509 is bonded. For example, thermocompression bonding may be used for bonding. At this time, a part (or one side) of the outer casing 509 is provided so that the electrolyte 508 can be poured therein later. A region (hereinafter referred to as an inlet) that is not joined to the substrate is provided.

[0558] Next, electrolyte 508 (not shown) is introduced into the exterior body 509 through an inlet provided in the exterior body. The electrolyte solution 508 is introduced into the inside of the electrode 509 under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is bonded. A secondary battery 500 of this type can be fabricated.

[0559] By using the positive electrode active material described in the above embodiment for the positive electrode 503, the discharge capacity can be increased. The secondary battery 500 can have excellent cycle characteristics.

[0560] In all-solid-state batteries, a certain pressure is applied in the stacking direction of the stacked positive and negative electrodes. Therefore, the contact state of the internal interfaces can be maintained in a good condition. By applying a certain pressure to the This can improve the reliability of the all-solid-state battery.

[0561] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0562] (Embodiment 5) 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. Reveal.

[0563] First, the bendable secondary battery described in the previous embodiment is mounted on an electronic device. Examples are shown in Figures 33(A) to 33(G). As a child device, for example, a television device (also called a television or television receiver) , computer monitors, digital cameras, digital video cameras, digital photo frame, mobile phone (also called mobile phone, mobile phone device), portable game machine, portable information Examples include information terminals, audio playback devices, and large game machines such as pachinko machines.

[0564] In addition, the flexible secondary battery can be mounted on the inner or outer wall of a house, building, etc., or on an automobile. It can also be incorporated into curved surfaces of the interior or exterior of a vehicle.

[0565] FIG. 33A shows an example of a mobile phone. The mobile phone 7400 has a housing 740 1, in addition to a display unit 7402, operation buttons 7403, an external connection port 7404, The mobile phone 7400 is equipped with a speaker 7405, a microphone 7406, and the like. The secondary battery 7407 is a secondary battery of one embodiment of the present invention. This allows us to provide lightweight, long-lasting mobile phones.

[0566] FIG. 33(B) shows the mobile phone 7400 in a bent state. When the entire 00 is deformed by an external force and curved, the secondary battery installed inside The secondary battery 7407 is also bent. At this time, the state of the bent secondary battery 7407 is as shown in FIG. The secondary battery 7407 is a thin storage battery. The secondary battery 7407 is bent. The secondary battery 7407 is fixed in a state where the lead electrode is electrically connected to the current collector. For example, the current collector is made of copper foil, and some of it is alloyed with gallium to form a contact with the current collector. This improves adhesion with the active material layer, making the secondary battery 7407 highly reliable when bent. It is composed of:

[0567] FIG. 33(D) shows an example of a bangle-type display device. The portable display device 7100 is , a housing 7101, a display unit 7102, operation buttons 7103, and a secondary battery 7104. FIG. 33(E) shows the bent state of the secondary battery 7104. When the device is bent and worn on the user's arm, the housing may deform and damage part of the secondary battery 7104 or The total curvature changes. The degree of curvature at any point on the curve is expressed as the radius of the corresponding circle. The value expressed as the radius of curvature is called the radius of curvature, and the reciprocal of the radius of curvature is called the curvature. A part of the main surface of the housing or secondary battery 7104 within the range of 40 mm to 150 mm in diameter The radius of curvature of the main surface of the secondary battery 7104 is 40 mm or more. If the thickness is within the range of 0 mm or less, high reliability can be maintained. By using the secondary battery of one embodiment of the present invention, a lightweight and long-life portable display device can be provided.

[0568] FIG. 33(F) shows an example of a wristwatch-type portable information terminal. Portable information terminal 7200 The watch includes a housing 7201, a display unit 7202, a band 7203, a buckle 7204, and an operation button 7 205, an input / output terminal 7206, etc.

[0569] The portable information terminal 7200 is capable of performing functions such as mobile phone calls, e-mails, document browsing and creation, music playback, internet connection, and so on. It can run various applications such as internet communication and computer games. Cut.

[0570] The display surface of the display unit 7202 is curved, and the display is performed along the curved display surface. The display portion 7202 is provided with a touch sensor, and can be operated by a finger, a stylus, or the like. For example, the icon displayed on the display unit 7202 can be used to operate the device. You can launch the application by touching button 7207.

[0571] The operation button 7205 is used to set the time, turn the power on and off, and turn wireless communication on and off. It has various functions such as auto-start, silent mode activation and deactivation, power saving mode activation and deactivation, etc. For example, an operating system built into the mobile information terminal 7200 can be The system also allows the functions of the operation buttons 7205 to be freely set.

[0572] In addition, the mobile information terminal 7200 is capable of performing standardized short-range wireless communication. For example, by communicating with a wireless headset, hands-free You can also make calls.

[0573] The portable information terminal 7200 also has an input / output terminal 7206, and a connector for connecting to other information terminals. Data can be exchanged directly via the input / output terminal 7206. The charging operation can be performed by wireless power supply without going through the input / output terminal 7206. It is also possible.

[0574] The display portion 7202 of the portable information terminal 7200 includes the secondary battery of one embodiment of the present invention. By using the secondary battery of one embodiment of the present invention, a lightweight and long-life portable information terminal can be provided. For example, the secondary battery 7104 shown in FIG. 33(E) is curved and inserted into the housing 7201. The flexible support 7204 may be incorporated into the band 7203 in a flexible state or may be incorporated into the band 7203 in a flexible state.

[0575] The mobile information terminal 7200 preferably has a sensor. For example, a fingerprint sensor may be used as the sensor. Sensors, pulse sensors, body temperature sensors, touch sensors, pressure sensors, acceleration sensors It is preferable that a sensor, etc. be installed.

[0576] FIG. 33G shows an example of a wristband-type display device. The display device 7300 has a display unit The display device 7300 includes a secondary battery 7304 according to one embodiment of the present invention. The display portion 7304 may be provided with a touch sensor, and may function as a portable information terminal. It is also possible to do so.

[0577] The display surface of the display unit 7304 is curved, and images are displayed along the curved display surface. The display device 7300 can also communicate with the display device 7300 by short-distance wireless communication according to a communication standard. You can change the situation.

[0578] The display device 7300 is also provided with an input / output terminal, and can be directly connected to other information terminals via a connector. It is also possible to charge the device via the input / output terminals. The charging operation may be performed by wireless power supply without using the input / output terminals.

[0579] When the secondary battery of one embodiment of the present invention is used as the secondary battery included in the display device 7300, A lightweight, long-life display device can be provided.

[0580] In addition, an example in which the secondary battery with good cycle characteristics shown in the above embodiment is mounted on an electronic device will be described. This will be explained using Figures 33(H), 34 and 35.

[0581] By using the secondary battery of one embodiment of the present invention as a secondary battery in everyday electronic devices, it is possible to achieve lighter weight and a longer life. For example, we can provide daily electronic products such as electric toothbrushes, electric shavers, Examples include electric beauty devices, and the secondary batteries for these products are designed to be easy for users to hold. Therefore, a secondary battery with a stick shape, small size, light weight, and large discharge capacity is desired. are.

[0582] FIG. 33(H) is a perspective view of a device also called a tobacco-containing smoking device (electronic cigarette). In FIG. 33(H), an electronic cigarette 7500 includes an atomizer 7501 including a heating element and an atomizer 7502. It includes a secondary battery 7504 that supplies power to the tomizer, a liquid supply bottle, a sensor, etc. It consists of a cartridge 7502. To enhance safety, the secondary battery 7504 is not overcharged. A protection circuit may be electrically connected to the secondary battery 7504 to prevent overcharge and / or overdischarge. The secondary battery 7504 shown in FIG. 33(H) has an external terminal so that it ca...

Claims

1. A lithium ion secondary battery having a positive electrode having a positive electrode active material containing lithium, cobalt, and oxygen, When the positive electrode was measured by Raman spectroscopy at a laser wavelength of 532 nm, －１ From 600cm －１ The integrated intensity of the peak at I2, 665 cm －１ From 685 cm －１ where I3 is the integrated intensity of the peak of the lithium ion secondary battery, and the value of I3 / I2 is 1% or more and 10% or less.

2. The positive electrode active material further contains magnesium, When the positive electrode active material is analyzed by XPS, the number of magnesium atoms relative to the number of cobalt atoms is 0.65 to 1.0 times. The lithium ion secondary battery according to claim 1 .

3. When the positive electrode active material is analyzed by XPS, the number of magnesium atoms relative to the number of cobalt atoms is 0.76 to 0.95 times. The lithium ion secondary battery according to claim 2 .

4. The positive electrode active material further contains fluorine, When the positive electrode active material is analyzed by XPS, the number of fluorine atoms relative to the number of cobalt atoms is 0.53 to 0.61 times. The lithium ion secondary battery according to claim 1 .

5. The positive electrode active material further contains aluminum, When the positive electrode active material was analyzed by XPS, the number of aluminum atoms relative to the number of cobalt atoms was 0.12 or less. The lithium ion secondary battery according to claim 1 .

6. The positive electrode active material further contains magnesium, When the particles of the positive electrode active material are thinned by an FIB method and a cross section of the thinned particle is subjected to line analysis by STEM-EDX, the ratio of the number of magnesium atoms to the number of cobalt atoms (Mg / Co) at a magnesium peak is 0.05 or more and 0.6 or less. The lithium ion secondary battery according to claim 1 .

7. When the particles of the positive electrode active material are thinned by an FIB method and a cross section of the thinned particle is subjected to line analysis by STEM-EDX, the ratio of the number of magnesium atoms to the number of cobalt atoms (Mg / Co) at a magnesium peak is 0.05 or more and 0.6 or less. The lithium ion secondary battery according to claim 2 or 3.

8. The positive electrode active material further contains aluminum, When the particles of the positive electrode active material are thinned by an FIB method and a cross section of the thinned particle is subjected to line analysis by STEM-EDX, the ratio of the number of aluminum atoms to the number of cobalt atoms (Al / Co) at an aluminum peak is 0.05 or more and 0.6 or less. The lithium ion secondary battery according to any one of claims 1 to 3 and claim 6.

9. When the particles of the positive electrode active material are thinned by an FIB method and a cross section of the thinned particle is subjected to line analysis by STEM-EDX, the ratio of the number of aluminum atoms to the number of cobalt atoms (Al / Co) at an aluminum peak is 0.05 or more and 0.6 or less. The lithium ion secondary battery according to claim 5 .

10. When the positive electrode active material is subjected to elemental analysis by ICP-MS, the number of magnesium atoms is 0.002 to 0.06 times the number of cobalt atoms. The lithium ion secondary battery according to claim 2, claim 3, or claim 6.

11. When the positive electrode active material is subjected to elemental analysis by ICP-MS, the number of magnesium atoms is 0.002 to 0.06 times the number of cobalt atoms. The lithium ion secondary battery according to claim 7.

12. When the positive electrode active material is subjected to elemental analysis by ICP-MS, the number of aluminum atoms is 0.05% or more and 4% or less of the number of cobalt atoms. The lithium ion secondary battery according to claim 5 .

13. When the positive electrode active material is subjected to elemental analysis by ICP-MS, the number of aluminum atoms is 0.05% or more and 4% or less of the number of cobalt atoms. The lithium ion secondary battery according to claim 8.

14. The positive electrode is A half cell was prepared under the following preparation conditions, and the charge curve was obtained by charging the half cell to 4.9 V at a measurement temperature of 25° C. with a current amount per weight of the positive electrode active material of 10 mA / g. In the dQ / dV vs. V curve, When a peak appearing between 4.5 V and 4.6 V is defined as a first peak, the full width at half maximum of the first peak is 0.10 V or more, The full width at half maximum of the first peak is the average value of the maximum value and the first minimum value of the first peak when the minimum value of the dQ / dV value appearing between 4.3 V and 4.5 V is defined as the first minimum value. １ and the minimum value of the dQ / dV value appearing between 4.6 V and 4.8 V is defined as the second minimum value, and HWHM is the average value of the maximum value of the first peak and the second minimum value. ２ The difference between the voltage at and The lithium ion secondary battery according to claim 1 . Fabrication conditions: A coin-shaped half cell was fabricated using the above-described positive electrode, lithium metal for the negative electrode, a mixture of ethylene carbonate and diethyl carbonate to which vinylene carbonate was added as the electrolyte, lithium hexafluorophosphate for the electrolyte, and polypropylene for the separator.

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