lithium-ion secondary batteries

Abstract

Provided is a lithium-ion secondary battery with a large capacity and excellent charge-discharge cycle characteristics. A lithium-ion secondary battery comprises a positive electrode, the positive electrode comprising a positive electrode active material, the positive electrode active material comprising lithium cobalt oxide, the lithium cobalt oxide comprising magnesium, aluminum, and nickel, the positive electrode active material having an O3-type crystalline structure in a discharged state, and, when the positive electrode is analyzed by powder X-ray diffraction in a charged state, the crystalline structure of the positive electrode active material belongs to the space group R-3m, wherein the coordinates of cobalt and oxygen are represented by (0,0,0.5) and (0,0,x), respectively, where 0.20≤x≤0.25.

Description

[0001] This application is a divisional application of the Chinese patent application entitled “Positive Electrode Active Material and Method for Manufacturing Positive Electrode Active Material” with national application number 201980004083.2 after the PCT international application with international application number PCT / IB2019 / 056304 and international application date July 24, 2019 entered the Chinese stage. Technical Field

[0002] One embodiment of the present invention relates to an article, method, or manufacturing method. In addition, one embodiment of the present invention relates to a process, machine, product, or composition of matter. One embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a storage device, a lighting device, or an electronic device and a method for manufacturing the same. In particular, it relates to a positive electrode active material that can be used in a secondary battery, a secondary battery, and an electronic device having a secondary battery.

[0003] Note that in this specification, the term "electrical storage device" refers to any element or device that has an electrical storage function. For example, electrical storage devices include lithium-ion secondary batteries (also called secondary batteries), lithium-ion capacitors, and electric double-layer capacitors.

[0004] Note that in this specification, electronic equipment refers to any device having a power storage device. Examples of electronic equipment include electro-optical devices and information terminal devices having a power storage device. Background Art

[0005] In recent years, research and development of various energy storage devices, including lithium-ion secondary batteries, lithium-ion capacitors, and air batteries, has become increasingly intense. In particular, with the development of the semiconductor industry for portable information devices such as mobile phones, smartphones, tablets, and notebook personal computers, portable music players, digital cameras, medical equipment, and next-generation clean energy vehicles (such as hybrid electric vehicles (HEVs), electric vehicles (EVs), and plug-in hybrid electric vehicles (PHEVs)), the demand for high-output, high-energy-density lithium-ion secondary batteries has increased dramatically. As a rechargeable energy source, they have become essential in the modern information society.

[0006] Characteristics currently required of lithium-ion secondary batteries include higher energy density, improved cycle characteristics, and improved safety and long-term reliability in various operating environments.

[0007] Therefore, the improvement of the positive electrode active material for the purpose of improving the cycle characteristics of lithium ion secondary batteries and increasing the capacity is studied (Patent Document 1 and Patent Document 2). In addition, research on the crystalline structure of the positive electrode active material has been carried out (Non-Patent Document 1 to Non-Patent Document 3).

[0008] X-ray diffraction (XRD) is one of the methods for analyzing the crystal structure of a positive electrode active material. XRD data can be analyzed by using the Inorganic Crystal Structure Database (ICSD) introduced in Non-Patent Document 5.

[0009] Patent Document 3 discloses the Jahn-Teller effect in nickel-based layered oxides.

[0010] [Prior technical literature]

[0011] [Patent Document]

[0012] [Patent Document 1] Japanese Patent Application Publication No. 2002-216760

[0013] [Patent Document 2] Japanese Patent Application Publication No. 2006-261132

[0014] [Patent Document 3] Japanese Patent Application Publication No. 2017-188466

[0015] [Non-patent literature]

[0016] [Non-patent document 1] Toyoki Okumura et al, "Correlation of lithium iondistribution and X-ray absorption near-edge structure in O3-and O2-lithiumcobalt oxides from first-principle calculation", Journal of MaterialsChemistry, 2012, 22, p.17340-17348

[0017] [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

[0018] [Non-patent document 3] Zhaohui Chen et al., “Staging Phase Transitions in LixCoO2”, Journal of The Electrochemical Society, 2002, 149(12)A1604-A1609

[0019] [Non-patent document 4] WE Counts et al, Journal of the American Ceramic Society, (1953) 36[1]12-17. Fig.01471

[0020] [Non-patent document 5] Belsky, A. et al., "New developments in the InorganicCrystal Structure Database (ICSD): accessibility in support of materials research and design", Acta Cryst., (2002), B58, 364-369. Summary of the Invention

[0021] Technical problem to be solved by the invention

[0022] One of the purposes of one embodiment of the present invention is to provide a positive electrode active material for a lithium ion secondary battery having a large capacity and excellent charge and discharge cycle characteristics, and a method for producing the same. Alternatively, one of the purposes of one embodiment of the present invention is to provide a method for producing a positive electrode active material with high productivity. Alternatively, one of the purposes of one embodiment of the present invention is to provide a positive electrode active material that, when contained in a lithium ion secondary battery, suppresses the capacity drop caused by charge and discharge cycles. Alternatively, one of the purposes of one embodiment of the present invention is to provide a large-capacity secondary battery. Alternatively, one of the purposes of one embodiment of the present invention is to provide a secondary battery having good charge and discharge characteristics. Alternatively, one of the purposes of one embodiment of the present invention is to provide a positive electrode active material that can suppress the dissolution of transition metals such as cobalt even when a high voltage charging state is maintained for a long time. Alternatively, one of the purposes of one embodiment of the present invention is to provide a secondary battery with high safety or reliability.

[0023] Another object of one embodiment of the present invention is to provide a novel substance, active material particles, a power storage device, or a method for producing the same.

[0024] Note that the inclusion of these objectives does not preclude the existence of other objectives. One embodiment of the present invention does not necessarily achieve all of the above objectives. Furthermore, objectives other than the above objectives may be extracted from the description, drawings, and claims.

[0025] Means of solving technical problems

[0026] One embodiment of the present invention is a positive electrode active material comprising lithium, cobalt, magnesium, oxygen, and fluorine, wherein when a pattern obtained by powder X-ray diffraction using CuKα1 radiation is subjected to Rietveld analysis, a crystalline structure having a space group R-3m is observed, which is greater than 2.814×10 -10 m and less than 2.817×10 -10 m, and the c-axis lattice constant is greater than 14.05×10 -10 m and less than 14.07×10 -10 When m is subjected to X-ray photoelectron spectroscopy analysis, the relative value of the magnesium concentration when the cobalt concentration is 1 is 1.6 or more and 6.0 or less.

[0027] In addition, one embodiment of the present invention is a positive electrode active material containing lithium, cobalt, magnesium, oxygen and fluorine. In a lithium ion secondary battery in which the positive electrode active material is used for the positive electrode and lithium metal is used for the negative electrode, constant current charging is first performed under a 25°C environment until the battery voltage becomes 4.7V, and then constant voltage charging is performed until the current value becomes 0.01C. Then, when the positive electrode is subjected to powder X-ray diffraction analysis using CuKα1 rays, a first diffraction peak with 2θ of greater than 19.10° and less than 19.50° and a second diffraction peak with 2θ of greater than 45.50° and less than 45.60° are observed.

[0028] In addition, in any of the above structures, in a lithium ion secondary battery in which the positive electrode active material is used for the positive electrode and lithium metal is used for the negative electrode, constant current charging is first performed under a 25°C environment until the battery voltage becomes 4.7V, and then constant voltage charging is performed until the current value becomes 0.01C. Then, when powder X-ray diffraction analysis is performed on the positive electrode using CuKα1 rays, a first diffraction peak with 2θ being greater than 19.10° and less than 19.50° and a second diffraction peak with 2θ being greater than 45.50° and less than 45.60° are observed.

[0029] Furthermore, in any of the above structures, when X-ray photoelectron spectroscopy is performed, the relative value of the magnesium concentration when the cobalt concentration is 1 is preferably 1.6 or more and 6.0 or less.

[0030] In any of the above structures, nickel, aluminum, and phosphorus are preferably contained.

[0031] In addition, one embodiment of the present invention is a method for manufacturing a positive electrode active material, which includes a first step of mixing a lithium source, a fluorine source and a magnesium source to form a first mixture, a second step of mixing a composite oxide containing lithium, cobalt and oxygen and the first mixture to form a second mixture, a third step of heating the second mixture to form a third mixture, a fourth step of mixing the third mixture and an aluminum source to form a fourth mixture, and a fifth step of heating the fourth mixture to form a fifth mixture, wherein the number of aluminum atoms contained in the aluminum source in the fourth step is greater than 0.001 times and less than 0.02 times the number of cobalt atoms contained in the third mixture.

[0032] Furthermore, in the above structure, the number of magnesium atoms contained in the magnesium source in the first step is 0.005 times or more and 0.05 times or less the number of cobalt atoms contained in the composite oxide in the second step.

[0033] Effects of the Invention

[0034] According to one embodiment of the present invention, a positive electrode active material for a lithium ion secondary battery having a large capacity and excellent charge and discharge cycle characteristics and a method for manufacturing the same can be provided. In addition, according to one embodiment of the present invention, a method for manufacturing a highly productive positive electrode active material can be provided. In addition, according to one embodiment of the present invention, a positive electrode active material that suppresses the reduction in capacity during the charge and discharge cycle by being used in a lithium ion secondary battery can be provided. In addition, according to one embodiment of the present invention, a large-capacity secondary battery can be provided. In addition, according to one embodiment of the present invention, a secondary battery with excellent charge and discharge characteristics can be provided. In addition, according to one embodiment of the present invention, a positive electrode active material that suppresses the dissolution of transition metals such as cobalt even when a high-voltage charging state is maintained for a long time can be provided. In addition, according to one embodiment of the present invention, a secondary battery with high safety or reliability can be provided. According to one embodiment of the present invention, a novel substance, active material particles, storage device or a method for manufacturing them can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] [ Figure 1 ] Figure 1 This is a diagram illustrating the charge depth and crystal structure of the positive electrode active material.

[0036] [ Figure 2 ] Figure 2 This is a diagram illustrating the charge depth and crystal structure of the positive electrode active material.

[0037] [ Figure 3 ] Figure 3 This is an XRD pattern calculated from the crystal structure.

[0038] [Figure 4] Figure 4A is the lattice constant calculated from XRD. Figure 4Bis the lattice constant calculated from XRD. Figure 4C is the lattice constant calculated from XRD.

[0039] [Figure 5] Figure 5A is the lattice constant calculated from XRD. Figure 5B is the lattice constant calculated from XRD. Figure 5C is the lattice constant calculated from XRD.

[0040] [ Figure 6 ] Figure 6 This is a diagram illustrating an example of a method for producing a positive electrode active material according to one embodiment of the present invention.

[0041] [ Figure 7 ] Figure 7 This is a diagram illustrating an example of a method for producing a positive electrode active material according to one embodiment of the present invention.

[0042] [ Figure 8 ] Figure 8 This is a diagram illustrating an example of a method for producing a positive electrode active material according to one embodiment of the present invention.

[0043] [ Figure 9 ] Figure 9 This is a diagram illustrating an example of a method for producing a positive electrode active material according to one embodiment of the present invention.

[0044] [Figure 10] Figure 10A This is a cross-sectional view of an active material layer when a graphene compound is used as a conductive additive. Figure 10B This is a cross-sectional view of an active material layer when a graphene compound is used as a conductive additive.

[0045] [Figure 11] Figure 11A This is a diagram explaining a method of charging a secondary battery. Figure 11B This is a diagram explaining a method of charging a secondary battery. Figure 11C This is a diagram explaining a method of charging a secondary battery.

[0046] [Figure 12] Figure 12A This is a diagram explaining a method of charging a secondary battery. Figure 12B This is a diagram explaining a method of charging a secondary battery. Figure 12C This is a diagram explaining a method of charging a secondary battery.

[0047] [Figure 13] Figure 13A This is a diagram explaining a method of charging a secondary battery. Figure 13B This is a diagram illustrating a method of discharging a secondary battery.

[0048] [Figure 14] Figure 14A It is a diagram illustrating a coin-type secondary battery. Figure 14B It is a diagram illustrating a coin-type secondary battery. Figure 14C This is a diagram illustrating the current and electrons during charging.

[0049] [Figure 15] Figure 15A It is a diagram illustrating a cylindrical secondary battery. Figure 15B It is a diagram illustrating a cylindrical secondary battery. Figure 15C It is a diagram illustrating a plurality of cylindrical secondary batteries. Figure 15D It is a diagram illustrating a plurality of cylindrical secondary batteries.

[0050] [Figure 16] Figure 16A It is a diagram illustrating an example of a battery pack. Figure 16B This is a diagram illustrating an example of a battery pack.

[0051] [Figure 17] Figure 17A1 It is a diagram illustrating an example of a secondary battery. Figure 17A2 It is a diagram illustrating an example of a secondary battery. Figure 17B1 It is a diagram illustrating an example of a secondary battery. Figure 17B2 It is a diagram illustrating an example of a secondary battery.

[0052] [Figure 18] Figure 18A It is a diagram illustrating an example of a secondary battery. Figure 18B It is a diagram illustrating an example of a secondary battery.

[0053] [ Figure 19 ] Figure 19 It is a diagram illustrating an example of a secondary battery.

[0054] [Figure 20] Figure 20A It is a diagram illustrating a laminated secondary battery. Figure 20B It is a diagram illustrating a laminated secondary battery. Figure 20C It is a diagram illustrating a laminated secondary battery.

[0055] [Figure 21] Figure 21A It is a diagram illustrating a laminated secondary battery. Figure 21B It is a diagram illustrating a laminated secondary battery.

[0056] [ Figure 22 ] Figure 22 It is a diagram showing the appearance of a secondary battery.

[0057] [ Figure 23 ] Figure 23 It is a diagram showing the appearance of a secondary battery.

[0058] [Figure 24] Figure 24A It is a diagram for explaining a method for manufacturing a secondary battery. Figure 24B It is a diagram for explaining a method for manufacturing a secondary battery. Figure 24C It is a diagram for explaining a method for manufacturing a secondary battery.

[0059] [Figure 25] Figure 25A A diagram illustrating a flexible secondary battery. Figure 25B1 A diagram illustrating a flexible secondary battery. Figure 25B2 A diagram illustrating a flexible secondary battery. Figure 25C A diagram illustrating a flexible secondary battery. Figure 25D A diagram illustrating a flexible secondary battery.

[0060] [Figure 26] Figure 26A A diagram illustrating a flexible secondary battery. Figure 26B A diagram illustrating a flexible secondary battery.

[0061] [Figure 27] Figure 27A It is a diagram illustrating an example of an electronic device. Figure 27B It is a diagram illustrating an example of an electronic device. Figure 27C It is a diagram illustrating an example of an electronic device. Figure 27D It is a diagram illustrating an example of an electronic device. Figure 27E It is a diagram illustrating an example of an electronic device. Figure 27F It is a diagram illustrating an example of an electronic device. Figure 27G It is a diagram illustrating an example of an electronic device. Figure 27H It is a diagram illustrating an example of an electronic device.

[0062] [Figure 28] Figure 28A It is a diagram illustrating an example of an electronic device. Figure 28B It is a diagram illustrating an example of an electronic device. Figure 28C It is a diagram illustrating an example of an electronic device.

[0063] [ Figure 29 ] Figure 29 It is a diagram illustrating an example of an electronic device.

[0064] [Figure 30] Figure 30A This is a diagram illustrating an example of a vehicle. Figure 30B This is a diagram illustrating an example of a vehicle. Figure 30C This is a diagram illustrating an example of a vehicle.

[0065] [Figure 31] Figure 31A It is a graph showing the continuous charge resistance of the secondary battery. Figure 31B It is a graph showing the continuous charge resistance of the secondary battery.

[0066] [Figure 32] Figure 32A It is a graph showing the continuous charge resistance of the secondary battery. Figure 32B It is a graph showing the continuous charge resistance of the secondary battery.

[0067] [Figure 33] Figure 33A It is a graph showing the cycle characteristics of the secondary battery. Figure 33B It is a graph showing the cycle characteristics of the secondary battery.

[0068] [Figure 34] Figure 34A It is a graph showing the XRD evaluation results of the positive electrode. Figure 34B It is a graph showing the XRD evaluation results of the positive electrode.

[0069] [Figure 35] Figure 35A It is a graph showing the XRD evaluation results of the positive electrode. Figure 35B It is a graph showing the XRD evaluation results of the positive electrode.

[0070] [Figure 36] Figure 36A It is a graph showing the continuous charge resistance of the secondary battery. Figure 36B It is a graph showing the continuous charge resistance of the secondary battery.

[0071] [ Figure 37 ] Figure 37 It is a graph showing the cycle characteristics of the secondary battery.

[0072] [Figure 38] Figure 38A It is a graph showing the charge and discharge curve of the secondary battery. Figure 38B It is a graph showing the charge and discharge curve of the secondary battery. Figure 38C It is a graph showing the charge and discharge curve of the secondary battery.

[0073] [Figure 39] Figure 39A It is a diagram showing the results of TEM observation of the positive electrode active material. Figure 39B It is a diagram showing the EDX analysis results of the positive electrode active material.

[0074] [Figure 40] Figure 40A It is a graph showing the XRD evaluation results of the positive electrode. Figure 40B It is a graph showing the XRD evaluation results of the positive electrode.

[0075] Modes for Carrying Out the Invention

[0076] The following describes embodiments of the present invention in detail with reference to the accompanying drawings. Note that the present invention is not limited to the following description, and those skilled in the art will readily appreciate that its methods and details can be modified in various forms. Furthermore, the present invention should not be construed as being limited solely to the following embodiments.

[0077] In this specification, etc., crystallization planes and orientations are represented by Miller indices. In crystallography, numbers are marked with superscripts to represent crystallization planes and orientations. However, in this specification, etc., due to the symbol limitations in patent applications, - (minus sign) is sometimes placed before numbers to represent crystallization planes and orientations, instead of marking numbers with superscripts. In addition, "[]" represents the individual orientations of the orientation within the crystal, "<>" represents the collective orientations of all equivalent crystal directions, "()" represents the individual faces of the crystallization plane, and "{}" represents the collective faces with equivalent symmetry.

[0078] In this specification and the like, segregation refers to a phenomenon in which a certain element (for example, B) is spatially non-uniformly distributed in a solid containing a plurality of elements (for example, A, B, and C).

[0079] In this specification, the surface portion of a particle of an active material or the like refers to the region from the surface to about 10 nm. Furthermore, the surface formed by a crack or fissure may also be referred to as the surface. The region deeper than the surface portion is referred to as the interior.

[0080] In this specification, etc., the layered rock-salt-type crystalline structure of a composite oxide containing lithium and a transition metal refers to a crystalline structure having a rock-salt-type ionic arrangement with alternating cations and anions, with the transition metal and lithium arranged regularly to form a two-dimensional plane, allowing lithium to diffuse two-dimensionally. Furthermore, defects such as vacant cations or anions may also be included. Strictly speaking, a layered rock-salt-type crystalline structure may also refer to a structure in which the lattice of the rock-salt-type crystal is deformed.

[0081] In addition, in this specification, etc., the rock salt type crystal structure refers to a structure in which cations and anions are arranged alternately. In addition, vacancies of cations or anions may also be included.

[0082] In this specification, etc., the pseudo-spinel crystal structure of a composite oxide containing lithium and a transition metal refers to the space group R-3m, that is, although it is not a spinel crystal structure, ions of cobalt, magnesium, etc. occupy oxygen 6-coordination positions, and the arrangement of the cations has a symmetry similar to that of the spinel structure. In addition, in some cases, a pseudo-spinel crystal structure exists in which a light element such as lithium occupies oxygen 4-coordination positions. In this case, the arrangement of the ions also has a symmetry similar to that of the spinel structure.

[0083] In addition, although the pseudo-spinel crystal structure contains Li irregularly between layers, it can also have a crystal structure similar to the CdCl2 type crystal structure. This crystal structure similar to the CdCl2 type is similar to the crystal structure of lithium nickelate charged to a depth of charge of 0.94 (Li 0.06 However, pure lithium cobaltate or layered rock salt-type positive electrode active materials containing a large amount of cobalt generally do not have such a crystal structure.

[0084] The anions of layered rock salt type crystals and rock salt type crystals form cubic closest packing structures (face-centered cubic lattice structures) respectively. It can be inferred that the anions in the pseudo-spinel type crystals also have cubic closest packing structures. When these crystals are in contact, there is a crystallization plane with the same orientation of the cubic closest packing structure formed by the anions. The space group of layered rock salt type crystals and pseudo-spinel type crystals is R-3m, which is different from the space group Fm-3m (general rock salt type crystal space group) and Fd-3m (rock salt type crystal space group with the simplest symmetry) of rock salt type crystals. Therefore, the Miller index of the crystallization plane that meets the above conditions of layered rock salt type crystals and pseudo-spinel type crystals is different from that of the rock salt type crystals. In this manual, sometimes in layered rock salt type crystals, pseudo-spinel type crystal structures and rock salt type crystals, the orientation consistency of the cubic closest packing structure formed by the anions refers to that the crystal orientation is roughly consistent.

[0085] The crystalline orientations of the two regions can be judged to be roughly consistent based on TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high angle annular dark field-scanning transmission electron microscope) images, ABF-STEM (annular bright field scanning transmission electron microscope) images, etc. In addition, X-ray diffraction (XRD), electron diffraction, neutron diffraction, etc. can be used as a basis for judgment. In TEM images, etc., the arrangement of cations and anions is observed as repetitions of bright lines and dark lines. When the orientation of the cubic closest packing structure in layered rock salt type crystals and rock salt type crystals is aligned, it can be observed that the angle formed by the repetition of bright lines and dark lines is less than 5 degrees, more preferably less than 2.5 degrees. Note that in TEM images, etc., light elements such as oxygen and fluorine cannot sometimes be clearly observed. In this case, the consistency of the orientation can be judged based on the arrangement of the metal elements.

[0086] In this specification, the theoretical capacity of a positive electrode active material refers to the amount of charge that can be stored when all the lithium that can be intercalated and deintercalated in the positive electrode active material is released. For example, the theoretical capacity of LiCoO2 is 274 mAh / g, the theoretical capacity of LiNiO2 is 274 mAh / g, and the theoretical capacity of LiMn2O4 is 148 mAh / g.

[0087] In this specification and other documents, the depth of charge when all the lithium that can be absorbed and desorbed is absorbed is represented as 0, and the depth of charge when all the lithium that can be absorbed and desorbed in the positive electrode active material is desorbed is represented as 1.

[0088] In this specification, etc., charging refers to the movement of lithium ions from the positive electrode to the negative electrode within the battery and the movement of electrons from the negative electrode to the positive electrode in the external circuit. Charging of the positive electrode active material refers to the release of lithium ions. In addition, positive electrode active materials with a depth of charge of 0.7 or more and 0.9 or less are sometimes referred to as high-voltage charged positive electrode active materials.

[0089] Similarly, discharge refers to the movement of lithium ions from the negative electrode to the positive electrode within the battery and the movement of electrons from the positive electrode to the negative electrode in the external circuit. Discharge of the positive electrode active material refers to the insertion of lithium ions. Furthermore, positive electrode active material with a depth of charge of 0.06 or less, or positive electrode active material that has been discharged from a high-voltage charged state to a capacity exceeding 90% of its charge capacity, is considered fully discharged.

[0090] In this specification, a non-equilibrium phase transition refers to a phenomenon that causes a nonlinear change in a physical quantity. For example, a non-equilibrium phase transition can occur near the peak of a dQ / dV curve, obtained by differentiating capacitance (Q) and voltage (V), causing a significant change in the crystal structure.

[0091] (Implementation Method 1)

[0092] In this embodiment, a positive electrode active material according to one embodiment of the present invention is described.

[0093] [Structure of positive electrode active material]

[0094] Materials with a layered rock salt-type crystalline structure, such as lithium cobalt oxide (LiCoO2), have a high discharge capacity and are considered to be excellent positive electrode active materials for secondary batteries. Examples of materials with a layered rock salt-type crystalline structure include composite oxides represented by LiMO2. Examples of element M include one or more selected from Co and Ni. Furthermore, examples of element M include one or more selected from Al and Mn, in addition to one or more selected from Co and Ni.

[0095] The magnitude of the Jahn-Teller effect of transition metal oxides is believed to vary depending on the number of electrons in the d orbital of the transition metal.

[0096] Nickel-containing compounds can sometimes be prone to distortion due to the Jan-Teller effect. Consequently, when LiNiO2 is charged and discharged at high voltages, there is a concern that this distortion may cause the crystal structure to collapse. LiCoO2 is preferred because it has less negative effects from the Jan-Teller effect and sometimes offers superior charge and discharge resistance at high voltages.

[0097] The following reference Figure 1 and Figure 2 The positive electrode active material is described. Figure 1 and Figure 2 In the description, the case of using cobalt as the transition metal contained in the positive electrode active material is described.

[0098] <Positive Electrode Active Material 1>

[0099] Figure 1 The positive electrode active material 100C shown is lithium cobalt oxide (LiCoO2) to which halogen and magnesium are not added in the manufacturing method described later. Figure 1 As described in Non-Patent Documents 1 and 2, the crystal structure of lithium cobalt oxide changes depending on the depth of charge.

[0100] like Figure 1 As shown, lithium cobalt oxide with a depth of charge of 0 (discharged state) includes a region having a crystalline structure of space group R-3m, including three CoO2 layers in the unit cell. Therefore, this crystalline structure is sometimes referred to as an O3-type crystalline structure. Note that a CoO2 layer refers to a structure in which an octahedral structure formed by cobalt and six coordinated oxygen atoms maintains a state of edge sharing on a single plane.

[0101] When the depth of charge is 1, it has a crystal structure of space group P-3m1, and the unit cell includes one CoO2 layer. Therefore, this crystal structure is sometimes called an O1-type crystal structure.

[0102] When the depth of charge is about 0.88, lithium cobalt oxide has a crystalline structure of space group R-3m. It can also be said that this structure is a structure in which CoO2 structures such as P-3m1(O1) and LiCoO2 structures such as R-3m(O3) are alternately stacked. Therefore, this crystalline structure is sometimes called H1-3 type crystalline structure. In fact, the number of cobalt atoms in the unit cell of H1-3 type crystalline structure is twice that of other structures. However, in Figure 1 In this specification, the c-axis in the H1-3 type crystal structure is represented as 1 / 2 of the unit cell for easy comparison with other structures.

[0103] As an example of an H1-3 type crystalline structure, as disclosed in non-patent document 3, the coordinates of cobalt and oxygen in a unit cell can be represented by Co(O, O, 0.42150±0.00016), O1(O, O, 0.27671±0.00045), O2(O, O, 0.11535±0.00045). O1 and O2 are both oxygen atoms. In this way, the H1-3 type crystalline structure is represented by a unit cell using one cobalt and two oxygens. On the other hand, as described below, it is preferred to represent a pseudo-spinel type crystalline structure of one embodiment of the present invention by a unit cell using one cobalt and one oxygen. This indicates that the difference between the pseudo-spinel type crystalline structure and the H1-3 type crystalline structure lies in the symmetry of cobalt and oxygen, and the pseudo-spinel type crystalline structure has a smaller change from the O3 structure than the H1-3 type crystalline structure. For example, any unit cell may be selected under the condition that the GOF (goodness of fitness) value in performing Rietveld analysis on the XRD pattern is as small as possible so as to more appropriately represent the crystal structure of the positive electrode active material.

[0104] When high voltage charging with a charging voltage of 4.6 V or more relative to the redox potential of lithium metal or deep charging and discharging with a charging depth of 0.8 or more is repeatedly performed, the crystal structure of lithium cobalt oxide repeatedly changes between the H1-3 type crystal structure and the R-3m (O3) crystal structure in the discharged state (i.e., non-equilibrium phase transition).

[0105] However, the deviation between the two crystalline structures of CoO2 layers is large. Figure 1 As shown by the dotted line and arrows, in the H1-3 crystal structure, the CoO2 layer deviates significantly from the R-3m (O3). This dynamic structural change can have a negative impact on the stability of the crystal structure.

[0106] Furthermore, the volume difference is also significant. When compared per the same number of cobalt atoms, the volume difference between the H1-3 type crystal structure and the O3 type crystal structure in the discharged state is 3.0% or more.

[0107] In addition to the above, the structure of the H1-3 type crystal structure having a continuous CoO2 layer such as P-3m1(O1) is likely to be unstable.

[0108] Therefore, repeated high-voltage charge and discharge cycles cause the crystal structure of lithium cobalt oxide to collapse. This crystal structure collapse leads to a deterioration in cycle characteristics. This is because the collapse of the crystal structure reduces the number of sites where lithium can stably exist, making it difficult for lithium to be inserted and removed.

[0109] <Positive electrode active material 2>

[0110] "internal"

[0111] The positive electrode active material of one embodiment of the present invention can reduce the deviation of the CoO2 layer even when repeatedly charged and discharged at a high voltage. Furthermore, the volume change can be reduced. Therefore, the positive electrode active material of one embodiment of the present invention can achieve excellent cycle characteristics. In addition, the positive electrode active material of one embodiment of the present invention can also have a stable crystalline structure in a high-voltage charging state. As a result, sometimes the positive electrode active material of one embodiment of the present invention is not prone to short circuit when maintaining a high-voltage charging state. In this case, the stability is further improved, so it is preferred.

[0112] The positive electrode active material of one embodiment of the present invention has a small change in crystal structure between a fully discharged state and a high voltage charged state, and a small volume difference per the same number of transition metal atoms when compared.

[0113] Figure 2 Figure 1 shows the crystal structure of positive electrode active material 100A before and after charge and discharge. Positive electrode active material 100A is a composite oxide containing lithium, cobalt, and oxygen. It preferably contains magnesium in addition to the above elements. Furthermore, it preferably contains a halogen such as fluorine or chlorine.

[0114] Figure 2 The crystal structure of the charge depth 0 (discharge state) is Figure 1 The same R-3m (O3). However, the positive electrode active material 100A has a crystalline structure different from the H1-3 type crystalline structure when it has a fully charged depth of charge. This crystalline structure is a space group R-3m, not a spinel type crystalline structure, but ions of cobalt, magnesium, etc. occupy oxygen 6 coordination positions, and the arrangement of cations has a symmetry similar to that of the spinel type. Therefore, in this specification, the above-mentioned crystalline structure is referred to as a pseudo-spinel type crystalline structure. In addition, in order to illustrate the symmetry of the cobalt atom and the symmetry of the oxygen atom, in Figure 2 Although lithium is omitted from the diagram of the pseudo-spinel crystal structure, lithium is actually present between the CoO2 layers, for example, at a concentration of 20 atomic % or less relative to cobalt. Furthermore, in both the O3-type crystal structure and the pseudo-spinel crystal structure, a small amount of magnesium is preferably present between the CoO2 layers, i.e., in the lithium position. Furthermore, a small amount of halogen, such as fluorine, is preferably present irregularly in the oxygen position.

[0115] In addition, in the pseudo-spinel crystal structure, a light element such as lithium may occupy a four-coordinate position with oxygen. In this case, the arrangement of the ions also has a symmetry similar to that of the spinel structure.

[0116] In addition, the pseudo-spinel crystal structure may have a crystal structure similar to the CdCl2 type crystal structure, although it contains Li irregularly between the layers. This crystal structure similar to the CdCl2 type is similar to the crystal structure of lithium nickelate charged to a depth of charge of 0.94 (Li 0.06However, pure lithium cobaltate or layered rock salt-type positive electrode active materials containing a large amount of cobalt generally do not have such a crystal structure.

[0117] The anions of layered rock salt type crystals and rock salt type crystals form cubic closest packing structures (face-centered cubic lattice structures) respectively. It can be inferred that the anions in the pseudo-spinel type crystals also have cubic closest packing structures. When these crystals are in contact, there is a crystallization plane with the same orientation of the cubic closest packing structure formed by the anions. The space group of layered rock salt type crystals and pseudo-spinel type crystals is R-3m, which is different from the space group Fm-3m (general rock salt type crystal space group) and Fd-3m (rock salt type crystal space group with the simplest symmetry) of rock salt type crystals. Therefore, the Miller index of the crystallization plane that meets the above conditions of layered rock salt type crystals and pseudo-spinel type crystals is different from that of the rock salt type crystals. In this manual, sometimes in layered rock salt type crystals, pseudo-spinel type crystal structures and rock salt type crystals, the orientation consistency of the cubic closest packing structure formed by the anions refers to that the crystal orientation is roughly consistent.

[0118] In the positive electrode active material 100A, the change in the crystal structure when a large amount of lithium is released during high voltage charging is suppressed compared to the positive electrode active material 100C. Figure 2 As shown by the middle dotted line, there is almost no deviation of the CoO2 layer in the above crystal structure.

[0119] More specifically, the positive electrode active material 100A has structural stability even at high charging voltages. For example, even at a charging voltage where the positive electrode active material 100C becomes an H1-3 type crystalline structure, such as a voltage of approximately 4.6V relative to the potential of lithium metal, the positive electrode active material 100A includes a region where the charging voltage can maintain the R-3m(O3) crystalline structure. Furthermore, in regions with even higher charging voltages, such as a voltage of approximately 4.65V to 4.7V relative to the potential of lithium metal, the positive electrode active material 100A also includes a region where the pseudo-spinel crystalline structure can be maintained. H1-3 type crystals are only observed when the charging voltage is further increased. For example, when graphite is used as the negative electrode active material of a secondary battery, even at a secondary battery voltage of 4.3V or higher and 4.5V or lower, the positive electrode active material 100A includes a region where the charging voltage can maintain the R-3m(O3) crystalline structure. Furthermore, in regions with even higher charging voltages, such as a voltage of 4.35V or higher and 4.55V or lower relative to the potential of lithium metal, the positive electrode active material 100A includes a region where the pseudo-spinel crystalline structure can be maintained.

[0120] Therefore, even if charge and discharge are repeated at a high voltage, the crystal structure of the positive electrode active material 100A is unlikely to collapse.

[0121] The coordinates of cobalt and oxygen in the unit cell of the pseudo-spinel crystal structure can be represented by Co (0, 0, 0.5) and O (0, 0, x) (0.20≤x≤0.25), respectively.

[0122] Magnesium, which is irregularly present in small amounts between CoO2 layers (i.e., at lithium locations), has the effect of suppressing the deviation of the CoO2 layers. Therefore, when magnesium is present between CoO2 layers, a pseudo-spinel crystal structure is easily obtained. Therefore, it is preferable that magnesium is distributed throughout the particles of the positive electrode active material 100A. In addition, in order to distribute magnesium throughout the particles, it is preferable to perform a heat treatment during the manufacturing process of the positive electrode active material 100A.

[0123] However, if the heat treatment temperature is too high, cation mixing may occur, increasing the likelihood that magnesium will invade the cobalt site. Magnesium's presence at the cobalt site will not maintain the R-3m effect. Furthermore, if the heat treatment temperature is too high, there is concern that adverse effects such as cobalt reduction to divalent ions and lithium evaporation may occur.

[0124] Therefore, it is preferable to add a halogen compound such as a fluorine compound to the lithium cobalt oxide before the heat treatment to distribute the magnesium throughout the particles. Adding the halogen compound lowers the melting point of the lithium cobalt oxide. This lowering of the melting point facilitates the distribution of magnesium throughout the particles at temperatures where cation mixing is less likely to occur. The presence of the fluorine compound can be expected to improve corrosion resistance to hydrofluoric acid generated by decomposition of the electrolyte.

[0125] Note that when the magnesium concentration is higher than the desired value, the effect of stabilizing the crystal structure sometimes becomes smaller. This is because magnesium not only enters the lithium position but also the cobalt position. The number of magnesium atoms contained in the positive electrode active material of one embodiment of the present invention is preferably greater than 0.001 times and less than 0.1 times the number of cobalt atoms, more preferably greater than 0.01 times and less than 0.04 times, and further preferably about 0.02 times. The magnesium concentration shown here can be, for example, a value obtained by elemental analysis of the entire particle of the positive electrode active material using ICP-MS or the like, or a value obtained by mixing raw materials in the manufacturing process of the positive electrode active material.

[0126] For example, it is preferred to add one or more metals selected from nickel, aluminum, manganese, titanium, vanadium and chromium as a metal other than cobalt (hereinafter referred to as metal Z) to lithium cobaltate, and it is particularly preferred to add one or more of nickel and aluminum. Manganese, titanium, vanadium and chromium are sometimes stable and easy to become tetravalent, and sometimes very helpful for structural stabilization. By adding metal Z, the crystalline structure of the positive electrode active material of one embodiment of the present invention can be made more stable, for example, in a high-voltage charging state. Here, it is preferred to add metal Z to the positive electrode active material of one embodiment of the present invention in a concentration that does not greatly change the crystallinity of lithium cobaltate. For example, the amount of metal Z added is preferably such that the above-mentioned Jan-Taylor effect or the like is not caused.

[0127] An increase in the magnesium concentration of the positive electrode active material of one embodiment of the present invention sometimes reduces the capacity of the positive electrode active material. This is mainly because, for example, magnesium enters the lithium position, reducing the amount of lithium that contributes to charging and discharging. In addition, excess magnesium sometimes produces magnesium compounds that do not contribute to charging and discharging. The positive electrode active material of one embodiment of the present invention contains nickel as metal Z in addition to magnesium, which sometimes increases the capacity per unit weight and volume. In addition, the positive electrode active material of one embodiment of the present invention contains aluminum as metal Z in addition to magnesium, which sometimes increases the capacity per unit weight and volume. In addition, the positive electrode active material of one embodiment of the present invention contains nickel and aluminum as metal Z in addition to magnesium, which sometimes increases the capacity per unit weight and volume.

[0128] The concentrations of elements such as magnesium and metal Z contained in the positive electrode active material of one embodiment of the present invention are shown below in terms of the number of atoms.

[0129] The number of nickel atoms contained in the positive electrode active material of one embodiment of the present invention is preferably 7.5% or less of the number of cobalt atoms, more preferably 0.05% or more and 4% or less, and even more preferably 0.1% or more and 2% or less. The nickel concentration shown here can be, for example, a value obtained by elemental analysis of the entire positive electrode active material particle using ICP-MS or the like, or a value obtained based on the raw material mixing during the production process of the positive electrode active material.

[0130] The number of aluminum atoms contained in the positive electrode active material of one embodiment of the present invention is preferably 0.05% to 4% of the number of cobalt atoms, and more preferably 0.1% to 2%. The aluminum concentration shown here can be, for example, a value obtained by elemental analysis of the entire positive electrode active material particle using ICP-MS or the like, or a value obtained based on the raw material mixing during the production process of the positive electrode active material.

[0131] The positive electrode active material of one embodiment of the present invention preferably contains element X, and phosphorus is preferably used as element X. Furthermore, the positive electrode active material of one embodiment of the present invention more preferably contains a compound containing phosphorus and oxygen.

[0132] The positive electrode active material of one embodiment of the present invention contains a compound containing the element X, and thus short circuiting may be less likely to occur even when a high voltage charging state is maintained.

[0133] When the positive electrode active material of one embodiment of the present invention contains phosphorus as the element X, hydrogen fluoride generated by decomposition of the electrolyte may react with phosphorus to reduce the concentration of hydrogen fluoride in the electrolyte.

[0134] When the electrolyte contains LiPF6, hydrogen fluoride may be generated by hydrolysis. Furthermore, hydrogen fluoride may also be generated by the reaction of PVDF, a component of the positive electrode, with a base. Reducing the concentration of hydrogen fluoride in the electrolyte can sometimes suppress current collector corrosion and membrane peeling. Furthermore, it can sometimes prevent a decrease in adhesion due to gelation or insolubility of PVDF.

[0135] When the positive electrode active material of one embodiment of the present invention contains magnesium in addition to element X, its stability in a high-voltage charging state is extremely high. When element X is phosphorus, the number of phosphorus atoms is preferably 1% or more and 20% or less of the number of cobalt atoms, more preferably 2% or more and 10% or less, and even more preferably 3% or more and 8% or less. Furthermore, the number of magnesium atoms is preferably 0.1% or more and 10% or less of the number of cobalt atoms, more preferably 0.5% or more and 5% or less, and even more preferably 0.7% or more and 4% or less. The phosphorus and magnesium concentrations shown here can be values ​​obtained by elemental analysis of the entire positive electrode active material particles using ICP-MS or the like, or values ​​obtained based on the mixing of raw materials during the production process of the positive electrode active material.

[0136] When the positive electrode active material contains cracks, phosphorus, more specifically, a compound containing phosphorus and oxygen, may be present inside the material, thereby suppressing the expansion of the cracks.

[0137] Surface

[0138] Magnesium is preferably distributed throughout the particles of the positive electrode active material 100A. However, the magnesium concentration in the surface of the particles is preferably higher than the average of the entire particles. For example, the magnesium concentration in the surface of the particles measured by XPS or the like is preferably higher than the average magnesium concentration of the entire particles measured by ICP-MS or the like.

[0139] Furthermore, when the positive electrode active material 100A contains an element other than cobalt, for example, one or more metals selected from nickel, aluminum, manganese, iron, and chromium, the concentration of the metal in the particle surface is higher than the average concentration of the entire particle. For example, the concentration of the element other than cobalt in the particle surface measured by XPS or the like is preferably higher than the average concentration of the element in the entire particle as measured by ICP-MS or the like.

[0140] The particle surface is full of crystal defects, and because lithium is extracted from the surface during charging, the lithium concentration at the surface is lower than that within the particle. Consequently, the particle surface becomes unstable, and the crystal structure is easily disrupted. A high magnesium concentration in the surface layer can more effectively suppress changes in the crystal structure. Furthermore, a high magnesium concentration in the surface layer can be expected to improve corrosion resistance to hydrofluoric acid generated by electrolyte decomposition.

[0141] The concentration of halogens such as fluorine in the surface of the positive electrode active material 100A is preferably higher than the average concentration of the entire particle. The presence of halogens in the surface of the region in contact with the electrolyte effectively improves the corrosion resistance to hydrofluoric acid.

[0142] Thus, it is preferred that the surface portion of the positive electrode active material 100A has a higher concentration of magnesium and fluorine than the interior, and has a composition different from that of the interior. A crystalline structure that is stable at room temperature is preferably used as this composition. Thus, the surface portion may also have a crystalline structure different from that of the interior. For example, at least a portion of the surface portion of the positive electrode active material 100A may have a rock salt-type crystalline structure. Note that when the surface portion has a crystalline structure different from that of the interior, the orientation of the crystals in the surface portion and the interior is preferably substantially identical.

[0143] However, if the surface layer consists solely of MgO or a solid solution of MgO and CoO(II), lithium insertion and removal are difficult. Therefore, the surface layer must contain at least cobalt and also contain lithium during discharge to provide pathways for lithium insertion and removal. Furthermore, the cobalt concentration is preferably higher than the magnesium concentration.

[0144] Furthermore, the element X is preferably located near the surface of the particles of the positive electrode active material 100A. For example, the positive electrode active material 100A may be covered with a film containing the element X.

[0145] Crystal Boundary

[0146] The magnesium or halogen contained in the positive electrode active material 100A may be present randomly and in small amounts inside, but it is more preferable that a part of them be segregated at the grain boundaries.

[0147] In other words, the magnesium concentration in the grain boundaries and their vicinity of the positive electrode active material 100A is preferably higher than that in other internal regions. Furthermore, the halogen concentration in the grain boundaries and their vicinity is preferably higher than that in other internal regions.

[0148] Like particle surfaces, grain boundaries are also surface defects. As a result, they are prone to instability and the crystal structure is prone to change. Therefore, when the magnesium concentration is high at the grain boundaries and near them, changes in the crystal structure can be more effectively suppressed.

[0149] Furthermore, when the magnesium and halogen concentrations are high at and near the grain boundaries, even if cracks form along the grain boundaries of the positive electrode active material 100A particles, the magnesium and halogen concentrations are high near the surface where the cracks form. Therefore, the corrosion resistance of the positive electrode active material to hydrofluoric acid can be improved even after the cracks form.

[0150] Note that in this specification and the like, the vicinity of a grain boundary refers to a region ranging from the grain boundary to approximately 10 nm.

[0151] Particle Size

[0152] If the particle size of the positive electrode active material 100A is too large, problems such as difficulty in lithium diffusion and excessively rough surface of the active material layer when applied to the current collector may occur. On the other hand, if the particle size of the positive electrode active material 100A is too small, problems such as difficulty in supporting the active material layer when applied to the current collector and excessive reaction with the electrolyte may occur. Therefore, the average particle size (D50: median diameter) is preferably 1 μm to 100 μm, more preferably 2 μm to 40 μm, and even more preferably 5 μm to 30 μm.

[0153] Analytical Methods

[0154] To determine whether a particular positive electrode active material is the positive electrode active material 100A according to one embodiment of the present invention that exhibits a pseudospinel crystal structure when charged at a high voltage, the positive electrode charged at a high voltage can be analyzed using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), or other methods. XRD is particularly preferred due to its advantages: it can analyze the symmetry of transition metals such as cobalt in the positive electrode active material at high resolution; it can compare the degree of crystallinity and the orientation of the crystals; it can analyze the periodic distortion of the lattice and the grain size; and it can achieve sufficient accuracy even when directly measuring the positive electrode obtained by disassembling a secondary battery.

[0155] As described above, the positive electrode active material 100A of one embodiment of the present invention is characterized by little change in crystal structure between the high-voltage charge state and the discharge state. Materials in which the crystal structure that changes significantly between high-voltage charge and discharge accounts for 50 wt% or more are not preferred because they cannot withstand high-voltage charge and discharge. Note that sometimes the desired crystal structure cannot be achieved simply by adding impurity elements. For example, a positive electrode active material of lithium cobalt oxide containing magnesium and fluorine sometimes has a pseudo-spinel crystal structure of 60 wt% or more, and sometimes has an H1-3 type crystal structure of 50 wt% or more, when charged at a high voltage. In addition, when a specified voltage is used, the pseudo-spinel crystal structure becomes almost 100 wt%, and when the specified voltage is further increased, the H1-3 type crystal structure sometimes occurs. Therefore, when determining whether it is the positive electrode active material 100A of one embodiment of the present invention, it is necessary to analyze the crystal structure by XRD or the like.

[0156] However, the crystal structure of positive electrode active materials in high-voltage charging or discharging states may change when exposed to air. For example, the pseudo-spinel crystal structure may change to an H1-3 type crystal structure. Therefore, all samples are preferably handled in an inert atmosphere such as argon.

[0157] Charging Methods

[0158] For high voltage charging to determine whether a composite oxide is the positive electrode active material 100A of one embodiment of the present invention, for example, a coin battery (CR2032 type, 20 mm in diameter, 3.2 mm in height) using lithium as a counter electrode can be prepared and charged.

[0159] More specifically, as the positive electrode, a slurry obtained by mixing a positive electrode active material, a conductive additive, and a binder and applying it to a positive electrode current collector of aluminum foil can be used.

[0160] Lithium metal can be used as the counter electrode. Note that the potential of a secondary battery using a material other than lithium metal as the counter electrode is different from the potential of the positive electrode. Unless otherwise specified, the voltage and potential in this specification refer to the potential of the positive electrode.

[0161] The electrolyte contained in the electrolytic solution was 1 mol / L lithium hexafluorophosphate (LiPF6). The electrolyte solution was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 3:7 and 2 wt% vinylene carbonate (VC).

[0162] Polypropylene with a thickness of 25 μm can be used as the separator.

[0163] The positive electrode can and the negative electrode can may be formed of stainless steel (SUS).

[0164] The coin cell manufactured under the above conditions is charged at a constant current of 4.6V and 0.5C, and then the constant voltage charge is continued until the current value reaches 0.01C. Here, 1C is set to 137mA / g. The temperature is set to 25°C. After charging as described above, the coin cell is disassembled in an argon atmosphere glove box to remove the positive electrode, thereby obtaining a positive electrode active material charged at a high voltage. In order to prevent reaction with external components when performing various analyses later, it is preferably sealed under an argon atmosphere. For example, XRD can be performed under the condition of being sealed in a sealed container in an argon atmosphere.

[0165] XRD

[0166] Figure 3 The ideal powder XRD pattern represented by the CuKα1 line calculated from the model of the pseudo-spinel crystal structure and the H1-3 type crystal structure is shown. In addition, for comparison, the ideal XRD pattern calculated from the crystal structure of LiCoO2(O3) with a charge depth of 0 and CoO2(O1) with a charge depth of 1 is also shown. The patterns of LiCoO2(O3) and CoO2(O1) are calculated using the Reflex PowderDiffraction, one of the modules of Materials Studio (BIOVIA), using the crystal structure information obtained from ICSD (Inorganic Crystal Structure Database: Inorganic Crystal Structure Database) (see non-patent document 5). The range of 2θ is set to 15° to 75°, Step size = 0.01, and wavelength λ1 = 1.540562×10 -10 m, λ2 were not set, and Monochromator was set to single. The pattern of the H1-3 type crystal structure was prepared in the same manner as the crystal structure information described in Non-Patent Document 3. The pattern of the pseudo-spinel crystal structure was prepared by the following method: the crystal structure was inferred from the XRD pattern of the positive electrode active material of one embodiment of the present invention and fitted using TOPAS ver.3 (crystal structure analysis software manufactured by Bruker), and the XRD pattern was prepared in the same manner as other structures.

[0167] like Figure 3 As shown, in the pseudo-spinel crystal structure, the diffraction peak at 2θ is 19.30±0.20°

[0168] (above 19.10° and below 19.50°) and 2θ appears at 45.55±0.10° (above 45.45° and below 45.65°). More specifically, sharp diffraction peaks appear at 2θ of 19.30±0.10° (above 19.20° and below 19.40°) and 2θ of 45.55±0.05° (above 45.50° and below 45.60°). However, the H1-3 type crystal structure and CoO2 (P-3m1, O1) do not appear at the above positions. Therefore, it can be said that the appearance of peaks at 2θ of 19.30±0.20° and 2θ of 45.55±0.10° in a state of high voltage charging is a characteristic of the positive electrode active material 100A of one embodiment of the present invention.

[0169] It can be said that the positions of the diffraction peaks observed by XRD between the crystalline structure with a charge depth of zero and the crystalline structure during high voltage charging are close. More specifically, it can be said that the positional difference between two or more, preferably three or more, of the main diffraction peaks of the two is 2θ = 0.7 or less, and more preferably 2θ = 0.5 or less.

[0170] Note that the positive electrode active material 100A of one embodiment of the present invention has a pseudo-spinel crystal structure when charged at a high voltage, but it is not necessary for all particles to have a pseudo-spinel crystal structure. It can have other crystal structures, and a part can also be amorphous. Note that when the XRD pattern is subjected to Rietveld analysis, the pseudo-spinel crystal structure is preferably 50 wt% or more, more preferably 60 wt% or more, and further preferably 66 wt% or more. When the pseudo-spinel crystal structure is 50 wt% or more, more preferably 60 wt% or more, and further preferably 66 wt% or more, a positive electrode active material with sufficiently excellent cycle characteristics can be achieved.

[0171] Furthermore, the pseudo-spinel crystal structure as determined by Rietveld analysis after 100 or more charge and discharge cycles from the start of measurement is preferably 35 wt % or more, more preferably 40 wt % or more, and even more preferably 43 wt % or more.

[0172] In addition, the grain size of the pseudo-spinel crystal structure possessed by the particles of the positive active material is only reduced to about 1 / 10 of that of LiCoO2 (O3) in the discharged state. Therefore, even under the same XRD measurement conditions as the positive electrode before charge and discharge, a clear peak of the pseudo-spinel crystal structure can be confirmed after high-voltage charging. On the other hand, even if a part of the pure LiCoO2 can have a structure similar to the pseudo-spinel crystal structure, the grain size will become smaller and its peak will become wider and smaller. The grain size can be obtained from the half-width value of the XRD peak.

[0173] As described above, the positive electrode active material of one embodiment of the present invention is preferably not susceptible to the Jahn-Teller effect. The positive electrode active material of one embodiment of the present invention preferably has a layered rock salt-type crystal structure and primarily contains cobalt as a transition metal. Furthermore, the positive electrode active material of one embodiment of the present invention may contain the aforementioned metal Z other than cobalt, within a range where the Jahn-Teller effect is minimal.

[0174] By performing XRD analysis, the range of the lattice constant in the positive electrode active material where the influence of the Jahn-Teller effect is small was examined.

[0175] Figure 4A and Figure 4B The results of estimating the a-axis and c-axis lattice constants by XRD are shown when the positive electrode active material according to one embodiment of the present invention has a layered rock salt type crystal structure and contains cobalt and nickel. Figure 4A The results for the a-axis are shown, while Figure 4B The results of the c-axis are shown. Figure 4A and Figure 4B The XRD results for the lattice constants shown are for the positive electrode active material powder after synthesis and before assembly into the positive electrode. The nickel concentration on the horizontal axis represents the nickel concentration when the sum of the number of cobalt and nickel atoms is taken as 100%. The positive electrode active material is produced through steps S21 to S25, described later, with a cobalt source and a nickel source used in step S21. The nickel concentration represents the nickel concentration in step S21 when the sum of the number of cobalt and nickel atoms is taken as 100%.

[0176] Figure 5A and Figure 5B The results of estimating the a-axis and c-axis lattice constants by XRD are shown when the positive electrode active material according to one embodiment of the present invention has a layered rock salt type crystal structure and contains cobalt and manganese. Figure 5A The results for the a-axis are shown, while Figure 5B The results of the c-axis are shown. Figure 5A and Figure 5B The XRD results for the lattice constants shown are for the powdered positive electrode active material after synthesis and before assembly into the positive electrode. The manganese concentration on the horizontal axis represents the manganese concentration when the sum of the number of cobalt and manganese atoms is taken as 100%. The positive electrode active material is produced through steps S21 to S25, described later, with a cobalt source and a manganese source used in step S21. The manganese concentration represents the manganese concentration in step S21 when the sum of the number of cobalt and manganese atoms is taken as 100%.

[0177] Figure 4C The results showing the lattice constants are shown in Figure 4A and Figure 4B The value obtained by dividing the a-axis lattice constant of the positive electrode active material by the c-axis lattice constant (a-axis / c-axis). Figure 5C The results showing the lattice constants are shown in Figure 5A and Figure 5B The value of the a-axis lattice constant of the positive electrode active material divided by the c-axis lattice constant (a-axis / c-axis).

[0178] Depend on Figure 4C It can be seen that at nickel concentrations of 5% and 7.5%, the a-axis / c-axis ratio changes significantly, and the a-axis tilt increases. This tilt is likely due to the Jan-Teller tilt. When the nickel concentration is lower than 7.5%, an excellent positive electrode active material with a small Jan-Teller tilt can be obtained.

[0179] Then, by Figure 5A It is known that when the manganese concentration is 5% or higher, the lattice constant changes in a different way and no longer follows Vegard's law. Therefore, when the manganese concentration is 5% or higher, the crystal structure changes. Therefore, the manganese concentration is preferably 4% or lower, for example.

[0180] Furthermore, the above-mentioned nickel concentration and manganese concentration ranges do not necessarily apply to the particle surface portion. In other words, the nickel concentration and manganese concentration in the particle surface portion may be higher than the above-mentioned concentrations.

[0181] In summary, when examining the preferred range of the lattice constant, it can be seen that in the positive electrode active material of one embodiment of the present invention, the lattice constant of the a-axis in the layered rock salt type crystal structure contained in the particles of the positive electrode active material in the non-charged or discharged state, which can be inferred from the XRD pattern, is preferably greater than 2.814×10 -10 m and less than 2.817×10 -10 m, and the lattice constant of the c-axis is preferably greater than 14.05×10 -10 m and less than 14.07×10 -10 The state without charge and discharge may refer to, for example, the state of powder before the positive electrode of the secondary battery is produced.

[0182] Alternatively, the value of the a-axis lattice constant divided by the c-axis lattice constant (a-axis / c-axis) in the layered rock salt type crystal structure contained in the positive electrode active material particles in the non-charged or discharged state is preferably greater than 0.20000 and less than 0.20049.

[0183] Alternatively, in a layered rock salt type crystalline structure contained in particles of the positive electrode active material in a state without charge and discharge or in a discharged state, when XRD analysis is performed, a first peak with 2θ of 18.50° or more and 19.30° or less is sometimes observed, and a second peak with 2θ of 38.00° or more and 38.80° or less is observed.

[0184] XPS

[0185] X-ray photoelectron spectroscopy (XPS) can analyze from the surface to a depth of approximately 2 to 8 nm (typically around 5 nm), allowing quantitative analysis of the concentration of each element in approximately half the surface area. Furthermore, by performing narrow scan analysis, the bonding state of the elements can be analyzed. XPS measurement accuracy is generally around ±1 atomic%, and although it varies depending on the element, the detection limit is around 1 atomic%.

[0186] When performing XPS analysis of the positive electrode active material 100A, the relative value of the magnesium concentration when the cobalt concentration is 1 is preferably 1.6 or more and 6.0 or less, and more preferably 1.8 or more and less than 4.0. In addition, the relative value of the halogen concentration such as fluorine is preferably 0.2 or more and 6.0 or less, and more preferably 1.2 or more and 4.0 or less.

[0187] When performing XPS analysis, monochromated aluminum is used as an X-ray source, and the extraction angle is, for example, 45°.

[0188] Furthermore, when analyzing the positive electrode active material 100A using XPS, it is preferred that the peak value of the bonding energy between fluorine and other elements be greater than 682 eV and less than 685 eV, more preferably around 684.3 eV. This value differs from the bonding energy of lithium fluoride, which is 685 eV, and the bonding energy of magnesium fluoride, which is 686 eV. In other words, when the positive electrode active material 100A contains fluorine, bonding other than lithium fluoride and magnesium fluoride is preferred.

[0189] Furthermore, when performing XPS analysis on the positive electrode active material 100A, it is preferred that the peak value of the bonding energy between magnesium and other elements be 1302 eV or higher and less than 1304 eV, more preferably around 1303 eV. This value differs from the bonding energy of magnesium fluoride, which is 1305 eV, and is close to the bonding energy of magnesium oxide. In other words, when the positive electrode active material 100A contains magnesium, bonding other than magnesium fluoride is preferred.

[0190] EDX

[0191] In EDX measurement, the method of performing two-dimensional evaluation within a region while scanning the region is sometimes referred to as EDX surface analysis. Furthermore, the method of extracting data from linear regions from EDX surface analysis to evaluate the atomic concentration distribution within positive electrode active material particles is sometimes referred to as line analysis.

[0192] EDX surface analysis (e.g., elemental mapping) can quantitatively analyze the concentrations of magnesium and fluorine in the interior, surface layer, and near the grain boundaries. Furthermore, EDX ray analysis can analyze the peak concentrations of magnesium and fluorine.

[0193] When performing EDX analysis on the positive electrode active material 100A, the magnesium concentration peak in the surface layer preferably appears in a range of 3 nm from the surface of the positive electrode active material 100A to the center, more preferably appears in a range of 1 nm in depth, and even more preferably appears in a range of 0.5 nm in depth.

[0194] Furthermore, the fluorine distribution of the positive electrode active material 100A preferably overlaps with the magnesium distribution. Therefore, when performing EDX analysis, the fluorine concentration peak in the surface layer preferably appears in the range from the surface of the positive electrode active material 100A to a depth of 3 nm toward the center, more preferably to a depth of 1 nm, and even more preferably to a depth of 0.5 nm.

[0195] dQ / dVvsV Curve

[0196] Furthermore, the positive electrode active material of one embodiment of the present invention exhibits a characteristic voltage change near the end of discharge when discharged at a low rate, for example, 0.2C or less, after being charged at a high voltage. This voltage change is clearly observed when at least one peak in the dQ / dV vs. V curve calculated from the discharge curve lies within the range of 3.5V to 3.9V.

[0197] [Method 1 for producing positive electrode active material]

[0198] Next, refer to Figure 6 and Figure 7 An example of a method for producing a positive electrode active material according to one embodiment of the present invention will be described. Figure 8 and Figure 9 Another example of a more specific production method will be described.

[0199] <Step S11>

[0200] like Figure 6 As shown in step S11, first, a halogen source such as a fluorine source or a chlorine source and a magnesium source are prepared as materials for the mixture 902. In addition, a lithium source is preferably also prepared.

[0201] As a fluorine source, for example, lithium fluoride, magnesium fluoride, etc. can be used. Among them, lithium fluoride has a relatively low melting point of 848°C and is easy to melt in the annealing process described later, so it is preferred. As a chlorine source, for example, lithium chloride, magnesium chloride, etc. can be used. As a magnesium source, for example, magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, etc. can be used. As a lithium source, for example, lithium fluoride and lithium carbonate can be used. In other words, lithium fluoride can be used as both a lithium source and a fluorine source. In addition, magnesium fluoride can be used as both a fluorine source and a magnesium source.

[0202] In this embodiment, lithium fluoride LiF is prepared as a fluorine source and a lithium source, and magnesium fluoride MgF2 (as a Figure 6 Specific examples Figure 8 Step S11). When lithium fluoride LiF and magnesium fluoride MgF2 are mixed at a molar ratio of LiF:MgF2=65:35, it is most effective in lowering the melting point (non-patent document 4). When there is more lithium fluoride, there is too much lithium and the cycle characteristics may be deteriorated. For this reason, the molar ratio of lithium fluoride LiF and magnesium fluoride MgF2 is preferably LiF:MgF2=x:1 (0≤x≤1.9), more preferably LiF:MgF2=x:1 (0.1≤x≤0.5), and further preferably LiF:MgF2=x:1 (near x=0.33). In addition, in this specification, etc., near refers to a value greater than 0.9 times and less than 1.1 times its value.

[0203] In addition, when the subsequent mixing and pulverizing steps are performed by a wet method, a solvent is prepared. As the solvent, ketones such as acetone, alcohols such as ethanol and isopropyl alcohol, ether, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. can be used. It is preferred to use an aprotic solvent that is not easy to react with lithium. In this embodiment, acetone (see Figure 8 Step S11).

[0204] <Step S12>

[0205] Next, the materials of the mixture 902 are mixed and crushed ( Figure 6 and Figure 8 Mixing can be performed dry or wet, with wet methods being preferred because they can pulverize the materials into smaller pieces. Mixing can be performed using, for example, a ball mill or sand mill. When using a ball mill, zirconium balls are preferably used as the medium. The mixing and pulverization steps are preferably performed thoroughly to micronize the mixture 902.

[0206] <Step S13, Step S14>

[0207] The mixed and crushed materials are recovered ( Figure 6 and Figure 8 Step S13) to obtain a mixture 902 ( Figure 6 and Figure 8 Step S14).

[0208] For example, the D50 of the mixture 902 is preferably 600 nm or more and 20 μm or less, and more preferably 1 μm or more and 10 μm or less. By using the thus micronized mixture 902, when mixed with a composite oxide containing lithium, a transition metal, and oxygen in a subsequent step, the mixture 902 is more easily uniformly attached to the surface of the composite oxide particles. When the mixture 902 is uniformly attached to the surface of the composite oxide particles, it is preferable because halogen and magnesium can be contained in the surface of the composite oxide particles after heating. When regions that do not contain halogen and magnesium are present in the surface, the aforementioned pseudo-spinel crystal structure is less likely to form in a charged state.

[0209] Then, through steps S21 to S25 , a composite oxide containing lithium, transition metal and oxygen is obtained.

[0210] <Step S21>

[0211] First, if Figure 6 As shown in step S21, a lithium source and a transition metal source are prepared as materials of a composite oxide containing lithium, a transition metal, and oxygen.

[0212] As the lithium source, for example, lithium carbonate, lithium fluoride, or the like can be used.

[0213] As the transition metal, for example, at least one of cobalt, manganese, and nickel can be used.

[0214] When using a positive electrode active material having a layered rock salt crystal structure, the material ratio can be a mixed ratio of cobalt, manganese, and nickel that can have a layered rock salt crystal structure. In addition, aluminum can be added to the transition metal within a range that can have a layered rock salt crystal structure.

[0215] As the transition metal source, oxides and hydroxides of the above-mentioned transition metals can be used. As the cobalt source, for example, cobalt oxide and cobalt hydroxide can be used. As the manganese source, manganese oxide and manganese hydroxide can be used. As the nickel source, nickel oxide and nickel hydroxide can be used. As the aluminum source, aluminum oxide and aluminum hydroxide can be used.

[0216] <Step S22>

[0217] Next, the lithium source and transition metal source ( Figure 6 Mixing can be performed by a dry method or a wet method. For example, a ball mill, a sand mill, or the like can be used for mixing. When a ball mill is used, zirconium balls are preferably used as the medium.

[0218] <Step S23>

[0219] Next, the mixed materials are heated. To distinguish this from the subsequent heating process, this process is sometimes referred to as roasting or first heating. Heating is preferably performed at a temperature of 800°C or higher and lower than 1100°C, more preferably 900°C or higher and lower than 1000°C, and even more preferably around 950°C. Excessively low temperatures may result in decomposition and insufficient melting of the starting materials. Excessively high temperatures may lead to over-reduction of the transition metal, resulting in defects such as cobalt becoming divalent due to evaporation of lithium.

[0220] The heating time is preferably 2 hours or more and 20 hours or less. Calcination is preferably carried out in an atmosphere with little moisture, such as dry air (for example, a dew point of -50°C or less, preferably -100°C or less). For example, it is preferred to heat at 1000°C for 10 hours, with a heating rate of 200°C / h and a dry atmosphere flow rate of 10 L / min. The heated material can then be cooled to room temperature. For example, the cooling time from the specified temperature to room temperature is preferably 10 hours or more and 50 hours or less.

[0221] However, the cooling in step S23 does not necessarily have to be performed to room temperature. As long as the subsequent steps S24, S25, and S31 to S34 can be performed, cooling to a temperature higher than room temperature is not a problem.

[0222] The metal contained in the positive electrode active material can be introduced in the above-mentioned steps S22 and S23, and a part of the metal can be introduced in the steps S41 to S46 described later. More specifically, metal M1 (M1 is one or more selected from cobalt, manganese, nickel and aluminum) is introduced in steps S22 and S23, and metal M2 (M2 is, for example, one or more selected from manganese, nickel and aluminum) is introduced in steps S41 to S46. In this way, by introducing metal M1 and metal M2 in different processes, the profile of each metal in the depth direction can sometimes be changed. For example, the concentration of metal M2 in the surface portion can be made higher than the concentration of metal M2 in the interior of the particle. In addition, taking the number of atoms of metal M1 as a standard, the atomic number ratio of metal M2 in the surface portion relative to the standard is higher than the atomic number ratio of metal M2 in the interior.

[0223] In the positive electrode active material of one embodiment of the present invention, it is preferred to select cobalt as the metal M1 and nickel and aluminum as the metal M2.

[0224] <Step S24, Step S25>

[0225] Recycling the above-mentioned roasted materials ( Figure 6 In step S24), a composite oxide ( Figure 6Specifically, lithium cobaltate, lithium manganate, lithium nickelate, lithium cobaltate in which a portion of cobalt is replaced by manganese, or nickel-manganese-lithium cobaltate is obtained.

[0226] In addition, in step S25, a pre-synthesized composite oxide containing lithium, transition metal and oxygen (see Figure 8 ). In this case, steps S21 to S24 may be omitted.

[0227] When using a pre-synthesized composite oxide containing lithium, a transition metal, and oxygen, it is preferred to use a composite oxide with few impurities. In this specification, etc., as a composite oxide containing lithium, a transition metal, and oxygen and a positive electrode active material, lithium, cobalt, nickel, manganese, aluminum, and oxygen are considered as their main components, and elements other than the above main components are considered as impurities. For example, when analyzed by glow discharge mass spectrometry, the total impurity concentration is preferably 10,000 ppm wt or less, more preferably 5000 ppm wt or less. In particular, the total impurity concentration of transition metals such as titanium and arsenic is preferably 3000 ppm wt or less, more preferably 1500 ppm wt or less.

[0228] For example, lithium cobalt oxide particles (trade name: CELLSEED C-10N) manufactured by Nippon Chemical Industry Co., Ltd. can be used as presynthesized lithium cobalt oxide. The average particle size (D50) of this lithium cobalt oxide is approximately 12 μm. In impurity analysis using glow discharge mass spectrometry (GD-MS), the magnesium concentration and fluorine concentration are 50 ppm wt or less, the calcium concentration, aluminum concentration, and silicon concentration are 100 ppm wt or less, the nickel concentration is 150 ppm wt or less, the sulfur concentration is 500 ppm wt or less, the arsenic concentration is 1100 ppm wt or less, and the concentration of elements other than lithium, cobalt, and oxygen is 150 ppm wt or less.

[0229] Alternatively, lithium cobalt oxide particles (trade name: CELLSEED C-5H) manufactured by Nippon Chemical Industry Co., Ltd. can be used. The average particle size (D50) of this lithium cobalt oxide is approximately 6.5 μm, and the concentration of elements other than lithium, cobalt, and oxygen, as determined by GD-MS impurity analysis, is approximately the same as or lower than that of C-10N.

[0230] In this embodiment, cobalt is used as the transition metal, and pre-synthesized lithium cobalt oxide particles (CELLSEED C-10N manufactured by Nippon Chemical Industry Co., Ltd.) are used. Figure 8 ).

[0231] The composite oxide containing lithium, a transition metal, and oxygen in step S25 preferably has a layered rock salt-type crystal structure with few defects and deformation. For this reason, it is preferable to use a composite oxide with few impurities. If the composite oxide containing lithium, a transition metal, and oxygen contains a large amount of impurities, the crystal structure is likely to have a large number of defects or deformation.

[0232] Here, the positive electrode active material 100C may contain cracks. Cracks may occur, for example, during any one or more of steps S21 to S25. For example, cracks may occur during the calcination in step S23. The number of cracks may vary depending on conditions such as the calcination temperature and the rate of temperature increase or decrease. Furthermore, cracks may occur, for example, during steps such as mixing and pulverization.

[0233] <Step S31>

[0234] Next, the mixture 902 and a composite oxide containing lithium, a transition metal, and oxygen ( Figure 6 8 ) The number of transition metal atoms TM in the composite oxide containing lithium, transition metal and oxygen and the magnesium Mg in the mixture 902 Mix1 The atomic ratio of TM:Mg is preferably Mix1 =1:y (0.005≤y≤0.05), more preferably TM:Mg Mix1 =1:y(0.007≤y≤0.04), more preferably TM:Mg Mix1 =1:about 0.02.

[0235] To avoid damaging the composite oxide particles, the mixing in step S31 is preferably performed under milder conditions than the mixing in step S12. For example, it is preferably performed at a lower rotational speed or for a shorter time than the mixing in step S12. Furthermore, the dry method provides milder conditions than the wet method. Mixing can be performed using, for example, a ball mill or sand mill. When using a ball mill, zirconium balls are preferably used as the mixing medium.

[0236] <Step S32, Step S33>

[0237] Recycling of the above mixed materials ( Figure 6 and Figure 8 Step S32) to obtain a mixture 903 ( Figure 6 and Figure 8 Step S33).

[0238] Note that while this embodiment describes a method of adding a mixture of lithium fluoride and magnesium fluoride to lithium cobalt oxide, which has few impurities, one embodiment of the present invention is not limited thereto. Instead of using the mixture 903 in step S33, a mixture obtained by adding a magnesium source and a fluorine source to the starting material of lithium cobalt oxide and then calcining the mixture may be used. In this case, the process of steps S11 to S14 and steps S21 to S25 need not be separated, resulting in a simpler process and higher productivity.

[0239] Alternatively, lithium cobalt oxide to which magnesium and fluorine have been added in advance may be used. Using lithium cobalt oxide to which magnesium and fluorine have been added can omit the steps up to step S32, thereby simplifying the process.

[0240] Furthermore, a magnesium source and a fluorine source may be added to lithium cobaltate to which magnesium and fluorine have been added in advance.

[0241] <Step S34>

[0242] Next, the mixture 903 is heated. To distinguish it from the previous heating step, this step is sometimes referred to as annealing or second heating.

[0243] Annealing is preferably performed at an appropriate temperature and time. The appropriate temperature and time vary depending on the size and composition of the particles of the composite oxide containing lithium, transition metal, and oxygen in step S25. In the case of small particles, it is sometimes preferable to perform annealing at a lower temperature or for a shorter time than in the case of large particles.

[0244] For example, when the average particle size (D50) of the particles in step S25 is about 12 μm, the annealing temperature is preferably 600° C. to 950° C. The annealing time is preferably 3 hours or more, more preferably 10 hours or more, and even more preferably 60 hours or more.

[0245] When the average particle size (D50) of the particles in step S25 is about 5 μm, the annealing temperature is preferably, for example, 600° C. to 950° C. The annealing time is preferably, for example, 1 hour to 10 hours, more preferably about 2 hours.

[0246] The temperature drop time after annealing is preferably, for example, 10 hours to 50 hours.

[0247] It is believed that when mixture 903 is annealed, the material with a low melting point (e.g., lithium fluoride, melting point 848°C) in mixture 902 melts first and is distributed in the surface layer of the composite oxide particles. Subsequently, it is speculated that the presence of this melted material lowers the melting point of other materials, causing them to melt. For example, it is believed that magnesium fluoride (melting point 1263°C) melts and is distributed in the surface layer of the composite oxide particles.

[0248] Then, it is considered that the elements contained in the mixture 902 distributed in the surface layer portion form a solid solution in the composite oxide containing lithium, transition metal, and oxygen.

[0249] The elements contained in the mixture 902 diffuse faster in the surface portion and near the grain boundaries than in the interior of the composite oxide particles. Therefore, the concentrations of magnesium and halogen in the surface portion and near the grain boundaries are higher than those in the interior of the composite oxide particles. As will be described later, a higher magnesium concentration in the surface portion and near the grain boundaries effectively suppresses changes in the crystal structure.

[0250] <Step S35, Step S36>

[0251] Recycling the above annealed material ( Figure 6 and Figure 8 Step S35) to obtain positive electrode active material 100A_1 ( Figure 6 and Figure 8 Step S36).

[0252] [Method 2 for producing positive electrode active material]

[0253] The positive electrode active material 100A_1 obtained in step S36 may be subjected to another treatment. Here, a treatment is performed to add metal Z. Performing this treatment after step S25 can sometimes increase the concentration of metal Z in the surface layer of the positive electrode active material particles compared to the concentration of metal Z in the particles, which is preferable.

[0254] For example, in step S31 , a material containing metal Z may be mixed with the mixture 902 or the like to perform a process for adding metal Z. In this case, the number of steps can be reduced to simplify the process, which is preferable.

[0255] Alternatively, as described below, a process of adding metal Z may be performed after steps S31 to S35. In this case, for example, formation of a compound between magnesium and metal Z may be suppressed.

[0256] Through steps S41 to S53 described below, metal Z is added to the positive electrode active material of one embodiment of the present invention. Metal Z can be added by, for example, a liquid phase method such as a sol-gel method, a solid phase method, a sputtering method, a vapor deposition method, a CVD (chemical vapor deposition) method, a PLD (pulsed laser deposition) method, or the like. For example, the metal M2 addition process described below can be employed.

[0257] <Step S41>

[0258] like Figure 7As shown, first, in step S41, a metal source is prepared. In addition, when a sol-gel method is used, a solvent for the sol-gel method is prepared. As the metal source, metal alkoxides, metal hydroxides, metal oxides, etc. can be used. When metal Z is aluminum, for example, the concentration of aluminum contained in the metal source when the number of cobalt atoms contained in lithium cobaltate is 1 is 0.001 times or more and 0.02 times or less. When metal Z is nickel, for example, the concentration of nickel contained in the metal source when the number of cobalt atoms contained in lithium cobaltate is 1 is 0.001 times or more and 0.02 times or less. When metal Z is aluminum and nickel, for example, the concentration of aluminum contained in the metal source when the number of cobalt atoms contained in lithium cobaltate is 1 is 0.001 times or more and 0.02 times or less, and the concentration of nickel contained in the metal source is 0.001 times or more and 0.02 times or less.

[0259] Here, as an example, a sol-gel method is shown in which aluminum isopropoxide is used as a metal source and isopropanol is used as a solvent ( Figure 9 Step S41).

[0260] <Step S42>

[0261] Next, aluminum alkoxide is dissolved in alcohol and lithium cobalt oxide particles ( Figure 7 and Figure 9 Step S42).

[0262] The amount of metal alkoxide required varies depending on the particle size of the lithium cobalt oxide. For example, when aluminum isopropoxide is used and the particle size (D50) of the lithium cobalt oxide is approximately 20 μm, the concentration of aluminum in the aluminum isopropoxide is preferably 0.001 to 0.02 times the concentration of aluminum in the lithium cobalt oxide, based on the number of cobalt atoms in the lithium cobalt oxide being 1.

[0263] Next, the mixture of the alcohol solution of the metal alkoxide and the lithium cobalt oxide is stirred in an atmosphere containing water vapor. For example, a magnetic stirrer can be used for stirring. The stirring time is sufficient for the water in the atmosphere to undergo hydrolysis and polycondensation reactions with the metal alkoxide. For example, stirring can be performed at 25°C for 4 hours at a humidity of 90% RH (Relative Humidity). Alternatively, stirring can be performed in an atmosphere where the humidity and temperature are not controlled, such as in the atmospheric atmosphere of a ventilated room. In this case, the stirring time is preferably longer, for example, stirring at room temperature for more than 12 hours.

[0264] By reacting water vapor in the atmosphere with the metal alkoxide, the sol-gel reaction can proceed more slowly than when adding liquid water. Furthermore, by reacting the metal alkoxide with water at room temperature, for example, compared to heating at a temperature exceeding the boiling point of the solvent alcohol, the sol-gel reaction can proceed more slowly. By allowing the sol-gel reaction to proceed slowly, a high-quality coating layer with uniform thickness can be formed.

[0265] <Steps S43 and S44>

[0266] The precipitate is recovered from the mixed solution after the above treatment ( Figure 7 and Figure 9 The metal alkoxide is dissolved in the solvent of the precipitate. The metal alkoxide is then dried and solidified using ... recovered by filtration, centrifugation, or drying and solidification. The precipitate can be washed with the same alcohol as the solvent used to dissolve the metal alkoxide. Furthermore, when drying and solidification is performed by evaporation, the solvent and precipitate can be separated in this step without separation. For example, the precipitate can be recovered in the drying step of the next step (step S44).

[0267] Then, the recovered residue was dried to obtain a mixture 904 ( Figure 7 and Figure 9 Step S44). For example, vacuum drying or ventilation drying is performed at 80°C for 1 hour or more and 4 hours or less.

[0268] <Step S45>

[0269] Next, the obtained mixture 904 ( Figure 7 and Figure 9 Step S45).

[0270] As for the roasting time, the holding time within the specified temperature range is preferably 1 hour or more and 50 hours or less, more preferably 2 hours or more and 20 hours or less. When the roasting time is too short, the crystallinity of the compound containing metal Z formed on the surface portion is sometimes low, the diffusion of metal Z is insufficient, or organic matter remains on the surface. However, when the heating time is too long, there is a concern that the concentration of metal Z in the surface portion and near the grain boundary will decrease due to excessive diffusion. Productivity is also reduced.

[0271] The predetermined temperature is preferably 500° C. to 1200° C., more preferably 700° C. to 920° C., and even more preferably 800° C. to 900° C. If the predetermined temperature is too low, the crystallinity of the compound containing metal Z formed in the surface layer may be low, diffusion of metal Z may be insufficient, or organic matter may remain on the surface.

[0272] Calcination is also preferably performed in an atmosphere containing oxygen. When the oxygen partial pressure is low, the calcination temperature needs to be reduced as much as possible to avoid reduction of Co.

[0273] In this embodiment, heating is performed under the following conditions: a predetermined temperature of 850° C.; a holding time of 2 hours; a heating rate of 200° C. / h; and an oxygen flow rate of 10 L / min.

[0274] By setting the cooling time after calcination to be long, it is easy to stabilize the crystal structure, so it is preferred. For example, the cooling time from the specified temperature to room temperature is preferably more than 10 hours and less than 50 hours. Here, the calcination temperature of step S45 is preferably lower than the calcination temperature of step S34.

[0275] <Step S46 and Step S47>

[0276] Then, the cooled particles are recovered ( Figure 7 and Figure 9 Step S46). In addition, the particles are preferably screened. Through the above steps, the positive electrode active material 100A_2 ( Figure 7 and Figure 9 Step S47).

[0277] Furthermore, after step S47, the processes from step S41 to step S46 may be repeated. The number of repetitions may be once or twice or more.

[0278] Furthermore, the types of metal sources used in multiple treatments may be the same or different. When different metal sources are used, for example, an aluminum source may be used in the first treatment and a nickel source may be used in the second treatment.

[0279] <Step S51>

[0280] Next, a compound containing element X is prepared as the first raw material 901 ( Figure 7 and Figure 9 Step S51).

[0281] In step S51, the first raw material 901 may be pulverized. The pulverization may be performed using, for example, a ball mill or a sand mill. The powder obtained after the pulverization may be classified using a sieve.

[0282] The first raw material 901 is a compound containing element X, and phosphorus can be used as element X. In addition, the first raw material 901 is preferably a compound containing a bond between element X and oxygen.

[0283] As the first raw material 901, for example, a phosphate compound can be used. The phosphate compound can contain element D. Element D is one or more elements selected from lithium, sodium, potassium, magnesium, zinc, cobalt, iron, manganese, and aluminum. In addition to element D, the phosphate compound can also contain hydrogen. Alternatively, an ammonium salt containing ammonium phosphate and element D can be used.

[0284] Examples of the phosphoric acid compound include lithium phosphate, sodium phosphate, potassium phosphate, magnesium phosphate, zinc phosphate, aluminum phosphate, ammonium phosphate, lithium dihydrogen phosphate, magnesium monohydrogen phosphate, and lithium cobalt phosphate. As the positive electrode active material, lithium phosphate and magnesium phosphate are particularly preferably used.

[0285] In this embodiment, lithium phosphate is used as the first raw material 901 ( Figure 7 and Figure 9 Step S51).

[0286] <Step S52>

[0287] Next, the first raw material 901 obtained in step S51 and the positive electrode active material 100A_2 obtained in step S47 are mixed. Figure 7 and Figure 9 In step S52, preferably 0.01 mol to 0.1 mol, more preferably 0.02 mol to 0.08 mol, of the first raw material 901 is mixed with 1 mol of the positive electrode active material 100A_2 obtained in step S47. Mixing can be performed using, for example, a ball mill or a sand mill. The powder obtained after mixing can be classified using a sieve.

[0288] <Step S53>

[0289] Then, the mixed materials are heated ( Figure 7 and Figure 9 (Step S53). This step may not be performed during the production of the positive electrode active material. If heating is performed, it is preferably performed at a temperature of 300°C or higher and lower than 1200°C, more preferably 550°C or higher and lower than 950°C, and even more preferably around 750°C. Excessively low temperatures may result in decomposition of the starting materials and inadequate melting. Excessively high temperatures may lead to excessive reduction of the transition metal, resulting in defects due to lithium evaporation, etc.

[0290] Heating may generate a reaction product between the positive electrode active material 100A_2 and the first raw material 901 .

[0291] The heating time is preferably 2 hours or more and 60 hours or less. Calcination is preferably carried out in an atmosphere with little moisture, such as dry air (for example, a dew point of -50°C or less, preferably -100°C or less). For example, it is preferred to heat at 1000°C for 10 hours, with a heating rate of 200°C / h and a dry atmosphere flow rate of 10 L / min. The heated material can then be cooled to room temperature. For example, the cooling time from the specified temperature to room temperature is preferably 10 hours or more and 50 hours or less.

[0292] However, the cooling in step S53 does not necessarily have to be performed to room temperature. As long as the subsequent step S54 can be performed, the cooling may be performed to a temperature higher than room temperature.

[0293] <Step S54>

[0294] Recover the above calcined material ( Figure 7 and Figure 9 In step S54), a positive electrode active material 100A_3 containing element D is obtained.

[0295] The positive electrode active material 100A_1, the positive electrode active material 100A_2 and the positive electrode active material 100A_3 can refer to Figure 2 etc., and the like, for the description related to the positive electrode active material 100A.

[0296] (Implementation Method 2)

[0297] This embodiment describes examples of materials that can be used in a secondary battery including the positive electrode active material 100 described in the above embodiment. This embodiment describes a secondary battery in which a positive electrode, a negative electrode, and an electrolyte solution are surrounded by an outer casing.

[0298] [positive electrode]

[0299] The positive electrode includes a positive electrode active material layer and a positive electrode current collector.

[0300] <Positive Electrode Active Material Layer>

[0301] The positive electrode active material layer contains at least a positive electrode active material. In addition to the positive electrode active material, the positive electrode active material layer may also contain other substances such as a coating on the surface of the active material, a conductive additive, or a binder.

[0302] As the positive electrode active material, the positive electrode active material 100 described in the above embodiment can be used. By using the positive electrode active material 100 described in the above embodiment, a secondary battery having high capacity and excellent cycle characteristics can be realized.

[0303] As the conductive additive, carbon materials, metal materials, or conductive ceramic materials can be used. In addition, fibrous materials can also be used as the conductive additive. The proportion of the conductive additive in the total active material layer is preferably from 1 wt% to 10 wt%, more preferably from 1 wt% to 5 wt%.

[0304] By using a conductive additive, a conductive network can be formed in the active material layer. By using a conductive additive, a conductive path between the positive electrode active materials can be maintained. By adding a conductive additive to the active material layer, an active material layer with high electrical conductivity can be achieved.

[0305] As the conductive auxiliary agent, for example, natural graphite, artificial graphite such as mesophase carbon microbeads, carbon fibers, etc. can be used. As carbon fibers, for example, carbon fibers such as mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers can be used. As carbon fibers, carbon nanofibers or carbon nanotubes can be used. For example, carbon nanotubes can be produced by vapor phase growth methods, etc. As the conductive auxiliary agent, for example, carbon materials such as carbon black (acetylene black (AB), etc.), graphite (graphite) particles, graphene, or fullerene can be used. In addition, for example, metal powders or metal fibers of copper, nickel, aluminum, silver, gold, etc., conductive ceramic materials, etc. can be used.

[0306] Furthermore, a graphene compound may also be used as a conductive auxiliary agent.

[0307] Graphene compounds sometimes have excellent electrical properties such as high conductivity and excellent physical properties such as high flexibility and high mechanical strength. In addition, graphene compounds have a planar shape. Graphene compounds can form surface contacts with low contact resistance. Graphene compounds sometimes have very high conductivity even if they are thin, so a conductive path can be formed efficiently in a small amount in the active material layer. Therefore, by using a graphene compound as a conductive auxiliary agent, the contact area between the active material and the conductive auxiliary agent can be increased, so it is preferred. Preferably, by using a spray drying device, a graphene compound used as a conductive auxiliary agent for a coating can be formed in a manner that covers the entire surface of the active material. In addition, resistance can be reduced, so it is preferred. Here, it is particularly preferred to use, for example, graphene, multilayer graphene or RGO as the graphene compound. Here, RGO refers to a compound obtained by reducing graphene oxide (graphene oxide: GO), for example.

[0308] When using an active material with a small particle size, for example, an active material with a particle size of less than 1 μm, the specific surface area of ​​the active material is large, so more conductive paths connecting the active materials are required. Therefore, the amount of conductive additive tends to increase, and there is a trend that the content of active material decreases relatively. When the content of active material decreases, the capacity of the secondary battery also decreases. In this case, as a conductive additive, since it is not necessary to reduce the content of active material, it is particularly preferred to use a graphene compound that can efficiently form a conductive path even in a small amount.

[0309] Hereinafter, an example of a cross-sectional structure of an active material layer 200 containing a graphene compound as a conductive auxiliary agent will be described as an example.

[0310] Figure 10AThis is a longitudinal cross-sectional view of an active material layer 200. The active material layer 200 includes a granular positive electrode active material 100, a graphene compound 201 serving as a conductive additive, and a binder (not shown). Here, as the graphene compound 201, for example, graphene or multilayer graphene can be used. Furthermore, the graphene compound 201 preferably has a sheet shape. The graphene compound 201 can be formed into a sheet by partially overlapping multiple multilayer graphenes or (and) multiple single-layer graphenes.

[0311] In the longitudinal cross section of the active material layer 200, as shown in FIG. Figure 10B As shown in FIG, the flake-shaped graphene compound 201 is dispersed almost uniformly inside the active material layer 200. Figure 10B In the figure, although the graphene compound 201 is schematically represented by a bold line, in reality, the graphene compound 201 is a thin film having a thickness of a single or multiple carbon molecules. Since the multiple graphene compounds 201 are formed so as to partially cover the multiple positive electrode active material particles 100 or adhere to the surfaces of the multiple positive electrode active material particles 100, they are in surface contact with each other.

[0312] Here, by combining multiple graphene compounds with each other, a meshed graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net) can be formed. When the graphene net covers the active material, the graphene net can be used as an adhesive to combine the compounds with each other. Therefore, the amount of adhesive can be reduced or no adhesive is used, thereby increasing the proportion of active material in the electrode volume or electrode weight. In other words, the capacity of the secondary battery can be increased.

[0313] Here, it is preferred to use graphene oxide as the graphene compound 201, mix this graphene oxide with an active material to form a layer to become the active material layer 200, and then reduce it. By using graphene oxide with extremely high dispersibility in a polar solvent to form the graphene compound 201, the graphene compound 201 can be dispersed approximately uniformly in the active material layer 200. By volatilizing and removing the solvent from the dispersion medium containing the uniformly dispersed graphene oxide and reducing the graphene oxide, the graphene compounds 201 remaining in the active material layer 200 partially overlap and are dispersed in a manner that forms surface contact, thereby forming a three-dimensional conductive path. Furthermore, the reduction of the graphene oxide can also be performed, for example, by heat treatment or the use of a reducing agent.

[0314] Therefore, unlike granular conductive additives such as acetylene black, which form point contact with the active material, the graphene compound 201 can form surface contact with low contact resistance. Therefore, the conductivity between the granular positive electrode active material 100 and the graphene compound 201 can be improved with a smaller amount of graphene compound 201 than with typical conductive additives. Consequently, the proportion of the positive electrode active material 100 in the active material layer 200 can be increased. Consequently, the discharge capacity of the secondary battery can be increased.

[0315] Furthermore, by using a spray drying device in advance, the graphene compound serving as a conductive auxiliary agent for the coating can be formed so as to cover the entire surface of the active material, and the graphene compound can form a conductive path between the active materials.

[0316] Preferred adhesives include rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-isoprene-styrene rubber, butadiene rubber, and ethylene-propylene-diene copolymer. Fluororubber can also be used as the adhesive.

[0317] In addition, as the binder, for example, a water-soluble polymer is preferably used. As the water-soluble polymer, for example, polysaccharides can be used. As the polysaccharide, cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, starch, etc. can be used. More preferably, these water-soluble polymers are used in combination with the above-mentioned rubber material.

[0318] Alternatively, as the adhesive, it is preferred to use materials such as polystyrene, polymethyl acrylate, polymethyl methacrylate (PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene monomer polymer, polyvinyl acetate, and nitrocellulose.

[0319] As the binder, a plurality of the above-mentioned materials may be used in combination.

[0320] For example, it is also possible to combine materials with other materials that have a particularly high viscosity adjustment function and use them. For example, although rubber materials etc. have high cohesive force and high elasticity, it is sometimes difficult to adjust the viscosity when mixed in a solvent. In such a case, for example, it is preferably mixed with a material that has a particularly high viscosity adjustment function. As a material that has a particularly high viscosity adjustment function, for example, a water-soluble polymer can be used. In addition, as a particularly good water-soluble polymer with a viscosity adjustment function, the above-mentioned polysaccharides can be used, for example, cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose and diacetyl cellulose, regenerated cellulose, and starch can be used.

[0321] Note that cellulose derivatives such as carboxymethyl cellulose, when converted to salts such as sodium or ammonium carboxymethyl cellulose, have increased solubility, making them more effective as viscosity modifiers. This increased solubility improves the dispersibility of the active material and other components when forming the electrode slurry. In this specification, cellulose and cellulose derivatives used as electrode binders include their salts.

[0322] By dissolving a water-soluble polymer in water to stabilize its viscosity, the active material and other materials used as a binder, such as styrene-butadiene rubber, can be stably dispersed in the aqueous solution. Because water-soluble polymers contain functional groups, they are expected to readily and stably adhere to the surface of the active material. Cellulose derivatives such as carboxymethyl cellulose often have functional groups such as hydroxyl and carboxyl groups. Because of these functional groups, the polymers are expected to interact with each other and extensively cover the surface of the active material.

[0323] When the binder forms a film covering or contacting the active material surface, it is also expected to function as a passivation film, thereby inhibiting electrolyte decomposition. A passivation film is a film with no or very low conductivity. For example, when formed on the active material surface, it can inhibit electrolyte decomposition at the battery reaction potential. More preferably, the passivation film can transport lithium ions while suppressing conductivity.

[0324] <Positive Electrode Current Collector>

[0325] As the positive electrode current collector, materials with high conductivity such as stainless steel, gold, platinum, aluminum, titanium and alloys thereof can be used. In addition, the material used for the positive electrode current collector is preferably not dissolved by the potential of the positive electrode. In addition, aluminum alloys to which elements such as silicon, titanium, neodymium, scandium, and molybdenum that improve heat resistance are added can also be used. In addition, metal elements that react with silicon to form silicides can also be used. As metal elements that react with silicon to form silicides, there are zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, etc. The current collector can appropriately have shapes such as foil, plate (sheet), mesh, punched metal mesh, and drawn metal mesh. The thickness of the current collector is preferably not less than 5 μm and not more than 30 μm.

[0326] [negative electrode]

[0327] The negative electrode includes a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer may also contain a conductive additive and a binder.

[0328] <Negative Electrode Active Material>

[0329] As the negative electrode active material, for example, an alloy material or a carbon material can be used.

[0330] As the negative electrode active material, an element capable of undergoing charge-discharge reactions through alloying / de-alloying reactions with lithium can be used. For example, a material containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium can be used. These elements have a greater capacity than carbon, with silicon, in particular, having a theoretical capacity of 4200 mAh / g. Therefore, silicon is preferably used for the negative electrode active material. In addition, compounds containing these elements can also be used. Examples include SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, and SbSn. Elements that can undergo charge and discharge reactions through alloying / de-alloying reactions with lithium, and compounds containing these elements are sometimes referred to as alloying materials.

[0331] In this specification, SiO refers to silicon monoxide, for example. Alternatively, SiO can also be expressed as SiO x Here, x preferably represents a value close to 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

[0332] As the carbon-based material, graphite, easily graphitizable carbon (soft carbon), hardly graphitizable carbon (hard carbon), carbon nanotubes, graphene, carbon black, and the like can be used.

[0333] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB sometimes has a spherical shape, so it is preferred. MCMB is also relatively easy to reduce its surface area, so it is sometimes preferred. Examples of natural graphite include flake graphite and spheroidized natural graphite.

[0334] When lithium ions are intercalated in graphite (when lithium-graphite intercalation compounds are generated), graphite exhibits a potential as low as that of lithium metal (0.05 V to 0.3 V vs. Li / Li). + This allows lithium-ion secondary batteries to exhibit high operating voltages. Graphite also has the following advantages: high capacity per unit volume; relatively low volume expansion; low cost; and greater safety compared to lithium metal, making it a preferred material.

[0335] In addition, as the negative electrode active material, oxides such as titanium dioxide (TiO2), lithium titanium oxide (Li4Ti5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), molybdenum oxide (MoO2), etc.

[0336] In addition, as the negative electrode active material, LiN-type ... 3-x M x N (M = Co, Ni, Cu). For example, Li 2.6 Co 0.4 N3 shows a larger charge and discharge capacity (900 mAh / g, 1890 mAh / cm 3 ), so it is preferred.

[0337] When a nitride containing lithium and a transition metal is used as the negative electrode active material, lithium ions are contained in the negative electrode active material. Therefore, this negative electrode active material can be combined with a material that does not contain lithium ions, such as V2O5 or Cr3O8, used as the positive electrode active material, which is preferred. Note that when a material containing lithium ions is used as the positive electrode active material, by preliminarily removing the lithium ions contained in the positive electrode active material, a nitride containing lithium and a transition metal can also be used as the negative electrode active material.

[0338] In addition, materials that induce conversion reactions can also be used as negative electrode active materials. For example, transition metal oxides that do not form alloys with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), can be used as negative electrode active materials. Other materials that induce conversion reactions include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, CoS 0.89 , NiS, CuS and other sulfides, Zn3N2, Cu3N, Ge3N4 and other nitrides, NiP2, FeP2, CoP3 and other phosphides, FeF3, BiF3 and other fluorides.

[0339] As the conductive additive and binder that may be contained in the negative electrode active material layer, the same materials as those that may be contained in the positive electrode active material layer can be used.

[0340] <Negative Electrode Current Collector>

[0341] As the negative electrode current collector, the same materials as those for the positive electrode current collector can be used. In addition, as the negative electrode current collector, it is preferable to use a material that does not alloy with carrier ions such as lithium.

[0342] [Electrolyte]

[0343] The electrolyte comprises a solvent and an electrolyte. As the solvent of the electrolyte, an aprotic organic solvent is preferably used, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, vinyl chloride carbonate, vinylene carbonate, γ-butyrolactone, 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, ethylene glycol dimethyl ether (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme (methyl diglyme), acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc. can be used, or two or more of the above can be used in any combination and ratio.

[0344] In addition, by using one or more ionic liquids (room temperature molten salts) with flame retardancy and difficulty in volatility as the solvent of the electrolyte, even if the internal temperature is raised due to the internal short circuit, overcharge, etc. of the secondary battery, the rupture or ignition of the secondary battery can be prevented. The ionic liquid is made up of a cation and anion, including an organic cation and anion. As the organic cation for the electrolyte, the aromatic cations such as aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations and quaternary phosphonium cations or imidazolium cations and pyridinium cations can be enumerated. In addition, as the anion for the electrolyte, monovalent amide anions, monovalent methylate anions, fluorosulfonic acid anions, perfluoroalkyl sulfonic acid anions, tetrafluoroborate anions, perfluoroalkyl borate anions, hexafluorophosphate anions or perfluoroalkyl phosphate anions can be enumerated.

[0345] In addition, as the electrolyte dissolved in the above solvent, for example, LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl 10 、Li2B 12 Cl 12 , one of the lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, or two or more of the above can be used in any combination and ratio.

[0346] As the electrolyte for secondary batteries, it is preferred to use a highly purified electrolyte with a low content of granular dust or elements other than the constituent elements of the electrolyte (hereinafter referred to as "impurities"). Specifically, the ratio of impurities to the weight of the electrolyte is 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0347] In addition, additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxaloyl borate) (LiBOB), or dinitrile compounds such as succinonitrile and adiponitrile may be added to the electrolyte. The concentration of the added material can be set to, for example, 0.1 wt% or more and 5 wt% or less of the total solvent.

[0348] Alternatively, a polymer gel electrolyte in which a polymer is swollen with an electrolyte solution may be used.

[0349] Furthermore, the use of a polymer gel electrolyte improves safety against leakage and enables thinner and lighter secondary devices.

[0350] As the gelled polymer, silicone gel, acrylic acid gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, fluorine polymer gel, etc. can be used.

[0351] As the polymer, for example, a polymer having a polyoxyalkylene structure such as polyethylene oxide (PEO), PVDF and polyacrylonitrile, and copolymers thereof can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. In addition, the formed polymer can also have a porous shape.

[0352] Alternatively, solid electrolytes made of inorganic materials such as sulfides or oxides, or polymer materials such as PEO (polyethylene oxide), can be used instead of electrolytes. Using a solid electrolyte eliminates the need for separators or spacers. Furthermore, since the entire battery can be solidified, there's no risk of leakage, significantly improving safety.

[0353] [Isolated Body]

[0354] The secondary battery preferably includes a separator. Examples of the separator include paper, nonwoven fabric, glass fiber, ceramic, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic resin, polyolefin, and polyurethane. The separator is preferably formed into a bag-like shape and positioned so as to surround either the positive electrode or the negative electrode.

[0355] The separator can have a multilayer structure. For example, a thin film of an organic material such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture thereof. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aromatic polyamides (meta-aramid and para-aramid).

[0356] Applying ceramic materials can improve oxidation resistance, thereby suppressing separator degradation during high-voltage charge and discharge, thereby improving the reliability of the secondary battery. Applying fluorine-based materials facilitates close contact between the separator and the electrode, thereby improving output characteristics. Applying polyamide materials (particularly aromatic polyamide) can improve heat resistance, thereby enhancing the safety of the secondary battery.

[0357] For example, a mixture of aluminum oxide and aramid can be coated on both sides of a polypropylene film. Alternatively, the surface of the polypropylene film that contacts the positive electrode can be coated with a mixture of aluminum oxide and aramid, while the surface that contacts the negative electrode can be coated with a fluorine-based material.

[0358] By adopting a multi-layered separator, the safety of the secondary battery can be ensured even if the total thickness of the separator is small, and thus the capacity per unit volume of the secondary battery can be increased.

[0359] [Outer packaging]

[0360] The outer packaging of the secondary battery can be made of, for example, metal materials such as aluminum, or resin materials. Alternatively, a film-like outer packaging can be used. For example, a three-layer structure can be used: a film made of polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, for example, is provided on top of a film made of a material such as aluminum, stainless steel, copper, or nickel, and an insulating synthetic resin film such as a polyamide resin or polyester resin is further provided on top of the metal film to form the outer surface of the outer packaging.

[0361] [Charge and discharge method]

[0362] The charging and discharging of the secondary battery can be performed, for example, as follows.

[0363] CC Charging

[0364] First, CC charging will be described as one of the charging methods. CC charging is a charging method in which a constant current flows through the secondary battery throughout the entire charging period and charging is stopped when the voltage of the secondary battery reaches a predetermined voltage. Figure 11A As shown in the figure, the secondary battery is assumed to be an equivalent circuit of internal resistance R and secondary battery capacity C. In this case, the secondary battery voltage V B is the voltage V applied to the internal resistor R R and the voltage V applied to the secondary battery capacity C C The sum of .

[0365] During CC charging, if Figure 11A As shown, the switch is turned on and a constant current I flows through the secondary battery. During this period, since the current I is constant, the voltage V applied to the internal resistor R is R According to V R =R×I is constant according to Ohm's law. On the other hand, the voltage V applied to the secondary battery capacity C is C As time goes by, the secondary battery voltage V B Rising over time.

[0366] And, when the secondary battery voltage V B When the voltage reaches the specified value, for example, 4.3V, charging is stopped. Figure 11B As shown, the switch is closed and the current I = 0. Therefore, the voltage V applied to the internal resistor R RTherefore, the secondary battery voltage V B decline.

[0367] Figure 11C The secondary battery voltage V during CC charging and after CC charging is stopped is shown. B With the charging current example. Figure 11C It can be seen that the secondary battery voltage V B It decreases slightly after stopping CC charging.

[0368] CCCV Charging

[0369] Next, a different charging method, CCCV charging, is described. CCCV charging involves first performing CC charging to a specified voltage, and then performing CV (constant voltage) charging until the current decreases, specifically until the final current value is reached.

[0370] During CC charging, if Figure 12A As shown, the constant current switch is turned on and the constant voltage switch is turned off, so a constant current I flows through the secondary battery. During this period, since the current I is constant, the voltage V applied to the internal resistor R is R According to V R =R×I is constant according to Ohm's law. On the other hand, the voltage V applied to the secondary battery capacity C is C As time goes by, the secondary battery voltage V B Rising over time.

[0371] And, when the secondary battery voltage V B When the voltage reaches a specified value, for example, 4.3V, the battery switches from CC charging to CV charging. Figure 12B As shown, the constant current switch is turned on and the constant voltage switch is turned off, so the secondary battery voltage V B On the other hand, the voltage V applied to the secondary battery capacity C is constant. C As time goes by, it increases. Because V B =V R +V C , so the voltage V applied to the internal resistor R R As the voltage V applied to the internal resistor R R becomes smaller, and the current I flowing through the secondary battery changes according to V R =R×I and becomes smaller according to Ohm's law.

[0372] Then, when the current I flowing through the secondary battery reaches a predetermined current, for example, a current corresponding to 0.01C, charging is stopped. Figure 12C As shown, all switches are closed, and the current I = 0. Therefore, the voltage V applied to the internal resistor R R However, the voltage V applied to the internal resistor R is sufficiently reduced by CV charging. R , so even if the voltage of the internal resistor R no longer drops, the secondary battery voltage V B It hardly drops.

[0373] Figure 13A The secondary battery voltage V during CCCV charging and after CCCV charging is stopped is shown. B With the charging current example. Figure 13A It can be seen that the secondary battery voltage V B Even after CCCV charging is stopped, the voltage hardly decreases.

[0374] CC Charging

[0375] Next, CC discharge, one of the discharge methods, is described. CC discharge is a method in which a constant current is discharged from a secondary battery throughout the discharge period, and the secondary battery voltage V B A discharge method that stops discharging when the voltage reaches a specified value, such as 2.5V.

[0376] Figure 13B The secondary battery voltage V during CC discharge is shown B With the discharge current example. Figure 13B It can be seen that the secondary battery voltage V B Decreases as discharge progresses.

[0377] Here, we will explain the discharge rate and charge rate. The discharge rate refers to the ratio of the current during discharge to the battery capacity and is expressed in units of C. For a battery with a rated capacity of X (Ah), the current equivalent to 1C is X (A). When discharging with a current of 2X (A), it can be said to be discharged at 2C, and when discharging with a current of X / 5 (A), it can be said to be discharged at 0.2C. The same applies to the charge rate: when charging with a current of 2X (A), it can be said to be charged at 2C, and when charging with a current of X / 5 (A), it can be said to be charged at 0.2C.

[0378] (Implementation 3)

[0379] In this embodiment, an example of the shape of a secondary battery including the positive electrode active material 100 described in the above embodiment will be described. Materials used for the secondary battery described in this embodiment can refer to the description of the above embodiment.

[0380] [Coin-type secondary battery]

[0381] First, an example of a coin-type secondary battery will be described. Figure 14A This is the appearance of a coin-type (single-layer flat) secondary battery. Figure 14B is its cross-sectional view.

[0382] In a coin-type secondary battery 300, a positive electrode can 301, which also serves as a positive terminal, and a negative electrode can 302, which also serves as a negative terminal, are insulated and sealed by a gasket 303 made of polypropylene or the like. A positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact therewith. A negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact therewith.

[0383] The active material layer included in each of the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 may be formed on only one surface of the positive electrode and the negative electrode.

[0384] For the positive electrode can 301 and the negative electrode can 302, metals such as nickel, aluminum, and titanium, alloys thereof, or alloys of these with other metals (e.g., stainless steel) that are resistant to corrosion by the electrolyte can be used. Furthermore, to prevent corrosion from the electrolyte, the positive electrode can 301 and the negative electrode can 302 are preferably covered with nickel, aluminum, or the like. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307.

[0385] By impregnating the negative electrode 307, the positive electrode 304 and the separator 310 in an electrolyte, such as Figure 14B As shown, the positive electrode can 301 is placed at the bottom, and the positive electrode 304, separator 310, negative electrode 307 and negative electrode can 302 are stacked in this order. The positive electrode can 301 and negative electrode can 302 are press-fitted with a gasket 303 interposed therebetween to manufacture the coin-type secondary battery 300.

[0386] By using the positive electrode active material described in the above embodiment for the positive electrode 304 , a coin-type secondary battery 300 having a high capacity and excellent cycle characteristics can be realized.

[0387] Here, refer to Figure 14CDescribes how current flows when a secondary battery is charged. When a secondary battery using lithium is regarded as a closed circuit, the direction of lithium ion migration is the same as the direction of current flow. Note that in a secondary battery using lithium, since the anode and cathode, oxidation reaction and reduction reaction are swapped according to charging or discharging, the electrode with a high reaction potential is called the positive electrode, and the electrode with a low reaction potential is called the negative electrode. Therefore, in this specification, the positive electrode is called the "positive electrode" or "+ electrode", and the negative electrode is called the "negative electrode" or "- electrode" even when charging, discharging, supplying reverse pulse current, and supplying charging current. If the terms anode and cathode related to oxidation reaction and reduction reaction are used, the anode and cathode are opposite during charging and discharging, which may cause confusion. Therefore, in this specification, the terms anode and cathode are not used. When the terms anode and cathode are used, it is clearly indicated whether it is charging or discharging, and whether it corresponds to the positive electrode (+ electrode) or the negative electrode (- electrode).

[0388] Figure 14C The two terminals shown are connected to a charger to charge the secondary battery 300. As the charging of the secondary battery 300 progresses, the potential difference between the electrodes increases.

[0389] [Cylindrical secondary battery]

[0390] Next, refer to 15A to 15D An example of a cylindrical secondary battery will be described. Figure 15A An external view of a cylindrical secondary battery 600 is shown. Figure 15B is a schematic cross-sectional view of a cylindrical secondary battery 600. Figure 15B As shown, a cylindrical secondary battery 600 has a positive electrode cover (battery cover) 601 on the top and a battery can (exterior can) 602 on the side and bottom. The positive electrode cover and battery can (exterior can) 602 are insulated by a gasket (insulating gasket) 610.

[0391] A battery element is provided inside the hollow cylindrical battery can 602, in which a strip-shaped positive electrode 604 and a strip-shaped negative electrode 606 are wound with a separator 605. Although not shown in the figure, the battery element is wound around a center pin. One end of the battery can 602 is closed and the other end is open. As the battery can 602, metals such as nickel, aluminum, titanium, etc. that are resistant to corrosion by the electrolyte, their alloys, or alloys of them with other metals (such as stainless steel, etc.) can be used. In addition, in order to prevent corrosion caused by the electrolyte, the battery can 602 is preferably covered with nickel or aluminum. Inside the battery can 602, the battery element formed by winding the positive electrode, the negative electrode and the separator is sandwiched by a pair of opposing insulating plates 608 and 609. In addition, a non-aqueous electrolyte (not shown) is injected into the interior of the battery can 602 where the battery element is provided. As the non-aqueous electrolyte, the same electrolyte as that of a coin-type secondary battery can be used.

[0392] Because the positive and negative electrodes used in cylindrical storage batteries are wound, the active material is preferably formed on both surfaces of the current collector. The positive electrode 604 is connected to the positive terminal (positive electrode current collecting lead) 603, while the negative electrode 606 is connected to the negative terminal (negative electrode current collecting lead) 607. Both the positive terminal 603 and the negative terminal 607 can be made of metal materials such as aluminum. The positive terminal 603 is resistance-welded to the safety valve mechanism 612, while the negative terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 612 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. When the internal pressure of the battery rises above a specified threshold, the safety valve mechanism 612 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604. The PTC element 611 is a thermally sensitive resistor whose resistance increases with temperature. This increase in resistance limits the current flow to prevent abnormal heating. As the PTC element, barium titanate (BaTiO 3 )-based semiconductor ceramics or the like can be used.

[0393] In addition, if Figure 15C As shown, multiple secondary batteries 600 can be sandwiched between conductive plates 613 and 614 to form a module 615. Multiple secondary batteries 600 can be connected in parallel, in series, or in parallel and then in series. By forming a module 615 including multiple secondary batteries 600, a larger amount of power can be extracted.

[0394] Figure 15D FIG is a top view of the module 615. For the sake of clarity, the conductive plate 613 is represented by a dotted line. Figure 15DAs shown, module 615 may include wires 616 that electrically connect the plurality of secondary batteries 600. A conductive plate may be provided on the wires 616 so as to overlap the wires 616. Furthermore, temperature control devices 617 may be provided between the plurality of secondary batteries 600. Temperature control devices 617 can be used to cool the secondary batteries 600 when they are overheated, and to heat the secondary batteries 600 when they are overcooled. This reduces the impact of external temperature on the performance of module 615. The heat medium included in temperature control devices 617 is preferably insulating and non-flammable.

[0395] By using the positive electrode active material described in the above embodiment for the positive electrode 604 , a cylindrical secondary battery 600 having a high capacity and excellent cycle characteristics can be realized.

[0396] [Structural Example of Secondary Battery]

[0397] Reference 16A to 20C Another structural example of the secondary battery will be described.

[0398] Figure 16A and Figure 16B 9 is an external view of a battery pack. The battery pack includes a circuit board 900 and a secondary battery 913. A label 910 is attached to the secondary battery 913. Figure 16B As shown, the secondary battery 913 includes a terminal 951 and a terminal 952 .

[0399] Circuit board 900 includes circuit 912. Terminal 911 is connected to terminal 951, terminal 952, antenna 914, and circuit 912 via circuit board 900. Alternatively, multiple terminals 911 may be provided, each used as a control signal input terminal, a power supply terminal, and the like.

[0400] Circuit 912 may also be provided on the back side of circuit board 900. Furthermore, the shape of antenna 914 is not limited to a coil shape and may also be a linear or plate shape. Furthermore, other antennas may be used, such as a planar antenna, an aperture antenna, a traveling wave antenna, an EH antenna, a magnetic field antenna, or a dielectric antenna.

[0401] Alternatively, antenna 914 can be a flat conductor. This flat conductor can also serve as one of the electric field coupling conductors. In other words, antenna 914 can be used as one of the two conductors in a capacitor. This allows for the exchange of power using not only electromagnetic and magnetic fields but also electric fields.

[0402] The battery pack includes a layer 916 between the antenna 914 and the secondary battery 913. The layer 916 has a function of, for example, shielding an electromagnetic field from the secondary battery 913. As the layer 916, for example, a magnetic material can be used.

[0403] The structure of the secondary battery is not limited to Figure 16A and Figure 16B The structure shown.

[0404] For example, Figure 17A1 and Figure 17A2 As shown, it can also be Figure 16A and Figure 16B The secondary battery 913 shown has antennas provided on a pair of opposing surfaces. Figure 17A1 is an external view showing one side of the pair of surfaces, Figure 17A2 is an external view showing the other surface side of the pair of surfaces. Figure 16A and Figure 16B The same parts as those of the secondary battery shown can be appropriately used Figure 16A and Figure 16B Description of the secondary battery shown.

[0405] like Figure 17A1 As shown, an antenna 914 is provided on one of a pair of surfaces of a secondary battery 913 with a layer 916 interposed therebetween. Figure 17A2 As shown, an antenna 918 is provided on the other of the pair of surfaces of the secondary battery 913 via a layer 917. The layer 917 has a function of shielding the electromagnetic field from the secondary battery 913. As the layer 917, for example, a magnetic material can be used.

[0406] By adopting the above structure, the size of both antenna 914 and antenna 918 can be increased. Antenna 918 has the function of, for example, communicating data with an external device. Antenna 918 can be, for example, an antenna having a shape that can be used with antenna 914. Communication between the secondary battery and other devices using antenna 918 can be achieved using a communication method such as NFC (Near Field Communication) that can be used between secondary batteries and other devices.

[0407] Or, as Figure 17B1 As shown, it can also be Figure 16A and Figure 16B The secondary battery 913 shown is provided with a display device 920. The display device 920 is electrically connected to the terminal 911. In addition, the label 910 may not be attached to the portion where the display device 920 is provided. Figure 16A and Figure 16B The same parts as those of the secondary battery shown can be appropriately used Figure 16A and Figure 16B Description of the secondary battery shown.

[0408] The display device 920 may display, for example, an image indicating whether charging is in progress or an image indicating the amount of stored electricity. For example, electronic paper, a liquid crystal display, or an electroluminescent (EL) display may be used as the display device 920. For example, the use of electronic paper can reduce power consumption of the display device 920.

[0409] Or, as Figure 17B2 As shown, it can also be Figure 16A and Figure 16B The secondary battery 913 shown in FIG. 1 is provided with a sensor 921. The sensor 921 is electrically connected to the terminal 911 via the terminal 922. Figure 16A and Figure 16B The same parts as those of the secondary battery shown can be appropriately used Figure 16A and Figure 16B Description of the secondary battery shown.

[0410] Sensor 921 may have the function of measuring, for example, displacement, position, velocity, acceleration, angular velocity, rotational speed, distance, light, liquid, magnetism, temperature, chemical substances, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, slope, vibration, odor, or infrared light. By providing sensor 921, for example, data indicating the environment in which the secondary battery is installed (such as temperature) can be detected and stored in the memory of circuit 912.

[0411] Furthermore, refer to Figure 18A and Figure 18B as well as Figure 19 An example of the structure of the secondary battery 913 will be described.

[0412] Figure 18A The secondary battery 913 shown includes a wound body 950 provided with terminals 951 and 952 inside a housing 930. The wound body 950 is immersed in an electrolyte inside the housing 930. The terminal 952 is in contact with the housing 930, while the terminal 951 is not in contact with the housing 930 due to an insulating material. Figure 18A Frame 930 is shown separated in the figure, but in reality, wound body 950 is covered by frame 930, and terminals 951 and 952 extend outside frame 930. Frame 930 can be made of a metal material (eg, aluminum) or a resin material.

[0413] In addition, if Figure 18B As shown, multiple materials can also be used to form Figure 18A For example, in the Figure 18BIn the secondary battery 913 shown, a frame 930 a and a frame 930 b are bonded together, and a wound body 950 is provided in a region surrounded by the frame 930 a and the frame 930 b .

[0414] An insulating material such as an organic resin can be used for the housing 930a. In particular, using an organic resin or other material for the antenna surface can suppress electric field shielding caused by the secondary battery 913. Furthermore, if the electric field shielding caused by the housing 930a is low, an antenna such as the antenna 914 or the antenna 918 can be provided inside the housing 930a. For example, a metal material can be used for the housing 930b.

[0415] Furthermore, Figure 19 The structure of a wound body 950 is shown. The wound body 950 includes a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is formed by stacking the negative electrode 931 and the positive electrode 932 with the separator 933 interposed therebetween to form a laminated sheet, and then winding the laminated sheet. Alternatively, multiple layers of negative electrodes 931, positive electrodes 932, and separators 933 may be stacked.

[0416] The negative electrode 931 is connected to the terminal 951 or the terminal 952. Figure 16A and Figure 16B The positive electrode 932 is connected to the terminal 911 shown in FIG. Figure 16A and Figure 16B Terminal 911 is shown connected.

[0417] By using the positive electrode active material described in the above embodiment for the positive electrode 932 , a secondary battery 913 having a high capacity and excellent cycle characteristics can be realized.

[0418] [Laminated secondary battery]

[0419] Next, refer to Figures 20A to 26B An example of a laminated secondary battery will be described. When a flexible laminated secondary battery is mounted on an electronic device at least partially flexible, the secondary battery can be bent along with the deformation of the electronic device.

[0420] Reference 20A to 20C The laminated secondary battery 980 is described. The laminated secondary battery 980 includes Figure 20A The wound body 993 shown. The wound body 993 includes a negative electrode 994, a positive electrode 995 and a separator 996. Figure 19 Similar to the previously described wound body 950 , the wound body 993 is formed by overlapping a negative electrode 994 and a positive electrode 995 with a separator 996 interposed therebetween to form a laminated sheet, and then winding the laminated sheet.

[0421] The number of stacked layers consisting of the negative electrode 994, the positive electrode 995, and the separator 996 can be appropriately designed according to the required capacity and device volume. The negative electrode 994 is connected to the negative electrode current collector (not shown) via one of the lead electrode 997 and the lead electrode 998, and the positive electrode 995 is connected to the positive electrode current collector (not shown) via the other of the lead electrode 997 and the lead electrode 998.

[0422] like Figure 20B As shown, the wound body 993 is accommodated in a space formed by laminating a film 981 to be an outer packaging body and a film 982 having a recess by heat pressing or the like, thereby manufacturing Figure 20C Secondary battery 980 shown. A wound body 993 includes lead electrodes 997 and 998, and a space formed by a film 981 and a film 982 having recesses is impregnated with an electrolyte.

[0423] The film 981 and the film with the recess 982 are made of, for example, a metal material such as aluminum or a resin material. When a resin material is used as the material of the film 981 and the film with the recess 982, the film 981 and the film with the recess 982 can be deformed when a force is applied from the outside, thereby manufacturing a flexible storage battery.

[0424] In addition, Figure 20B and Figure 20C Although an example using two films is shown in FIG, one film may be bent to form a space, and the wound body 993 may be accommodated in the space.

[0425] By using the positive electrode active material described in the above embodiment for the positive electrode 995 , a secondary battery 980 having a high capacity and excellent cycle characteristics can be realized.

[0426] Although Figure 20B and Figure 20C In the example of a secondary battery 980 including a wound body in a space formed by a film serving as an outer package, it is also possible to adopt a secondary battery 980 having a wound body. Figure 21A and Figure 21B As shown, the secondary battery includes a plurality of rectangular positive electrodes, separators, and negative electrodes in a space formed by a film serving as an outer casing.

[0427] Figure 21AThe illustrated laminated secondary battery 500 includes a positive electrode 503 including a positive electrode current collector 501 and a positive electrode active material layer 502; a negative electrode 506 including a negative electrode current collector 504 and a negative electrode active material layer 505; a separator 507; an electrolyte 508; and an outer casing 509. Separator 507 is provided between positive electrode 503 and negative electrode 506, which are disposed within outer casing 509. Furthermore, outer casing 509 is filled with electrolyte 508. The electrolyte described in Embodiment 2 can be used as electrolyte 508.

[0428] exist Figure 21A In the illustrated laminated secondary battery 500, the positive electrode current collector 501 and the negative electrode current collector 504 also serve as terminals for electrical contact with the outside. Therefore, portions of the positive electrode current collector 501 and the negative electrode current collector 504 may be exposed outside the outer casing 509. Alternatively, a lead electrode may be ultrasonically welded to the positive electrode current collector 501 or the negative electrode current collector 504 using a lead electrode to expose the lead electrode outside the outer casing 509, while preventing the positive electrode current collector 501 and the negative electrode current collector 504 from being exposed outside the outer casing 509.

[0429] In the laminated secondary battery 500, as the outer packaging body 509, for example, a laminate film with the following three-layer structure can be used: a highly flexible metal film of aluminum, stainless steel, copper, nickel, etc. is arranged on a film composed of materials such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc., and an insulating synthetic resin film of polyamide resin, polyester resin, etc. is arranged on the metal film as the outer surface of the outer packaging body.

[0430] also, Figure 21B An example of a cross-sectional structure of a laminated secondary battery 500 is shown. For simplicity, Figure 21A An example including two current collectors is shown, but in practice Figure 21B As shown the battery comprises a plurality of electrode layers.

[0431] Figure 21B An example of the secondary battery 500 includes 16 electrode layers. In addition, even if the secondary battery 500 includes 16 electrode layers, it has flexibility. Figure 21B The structure shown has 8 layers of negative electrode current collector 504 and 8 layers of positive electrode current collector 501, totaling 16 layers. Figure 21B A cross-section of the negative electrode extraction portion is shown, showing ultrasonic welding of eight layers of negative electrode current collector 504. Of course, the number of electrode layers is not limited to 16 and can be more or less. A larger number of electrode layers can produce a secondary battery with a higher capacity. Furthermore, a smaller number of electrode layers can produce a thinner and more flexible secondary battery.

[0432] Here, Figure 22 and Figure 23 An example of an external view of a laminated secondary battery 500 is shown. Figure 23 The battery includes: a positive electrode 503; a negative electrode 506; a separator 507; an outer package 509; a positive electrode lead electrode 510; and a negative electrode lead electrode 511.

[0433] Figure 24A The following diagram shows the appearance of the positive electrode 503 and the negative electrode 506. The positive electrode 503 includes a positive electrode current collector 501, and a positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. In addition, the positive electrode 503 has an area where a portion of the positive electrode current collector 501 is exposed (hereinafter referred to as the tab region). The negative electrode 506 has a negative electrode current collector 504, and a negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. In addition, the negative electrode 506 has an area where a portion of the negative electrode current collector 504 is exposed, namely, the tab region. The area or shape of the tab region of the positive electrode and the negative electrode is not limited to Figure 24A Example shown.

[0434] [Method for manufacturing laminated secondary battery]

[0435] Here, refer to Figure 24B and Figure 24C Right Figure 22 An example of a method for manufacturing a laminated secondary battery will be described, with its appearance shown in FIG.

[0436] First, the negative electrode 506 , the separator 507 , and the positive electrode 503 are stacked. Figure 24B The stacked negative electrode 506, separator 507, and positive electrode 503 are shown. Here, an example using five negative electrode sets and four positive electrode sets is shown. Next, the tab regions of the positive electrodes 503 are bonded together, and the positive electrode lead electrode 510 is bonded to the outermost tab region of the positive electrode. This bonding can be achieved by, for example, ultrasonic welding. Similarly, the tab regions of the negative electrode 506 are bonded together, and the negative electrode lead electrode 511 is bonded to the outermost tab region of the negative electrode.

[0437] Next, the negative electrode 506 , the separator 507 , and the positive electrode 503 are placed on the outer package 509 .

[0438] Below, as Figure 24C As shown, the outer packaging body 509 is folded along the portion indicated by the dotted line. Then, the outer periphery of the outer packaging body 509 is bonded. For example, heat compression bonding can be used as the bonding method. At this time, an area (hereinafter referred to as an inlet) that is not bonded to a portion (or one edge) of the outer packaging body 509 is provided for subsequent injection of the electrolyte 508.

[0439] Next, an electrolyte 508 (not shown) is introduced into the outer packaging 509 from an inlet provided in the outer packaging 509. The electrolyte 508 is preferably introduced under a reduced pressure atmosphere or an inert gas atmosphere. Finally, the inlet is joined. In this manner, the laminated secondary battery 500 is manufactured.

[0440] By using the positive electrode active material described in the above embodiment for the positive electrode 503 , a secondary battery 500 having a high capacity and excellent cycle characteristics can be realized.

[0441] [Flexible secondary battery]

[0442] Next, refer to Figure 25A 、 Figure 25B1 and Figure 25B2 、 Figure 25C and Figure 25D as well as Figure 26A and Figure 26B An example of a flexible secondary battery will be described.

[0443] Figure 25A A schematic top view of a flexible secondary battery 250 is shown. Figure 25B1 、 Figure 25B2 25C are respectively along Figure 25A Schematic cross-sectional views taken along lines C1-C2, C3-C4, and A1-A2 in FIG. Secondary battery 250 includes an outer packaging body 251, a positive electrode 211a, and a negative electrode 211b housed within outer packaging body 251. A lead 212a electrically connected to positive electrode 211a and a lead 212b electrically connected to negative electrode 211b extend outside outer packaging body 251. Furthermore, an electrolyte (not shown) is sealed within the area surrounded by outer packaging body 251, in addition to positive electrode 211a and negative electrode 211b.

[0444] Reference Figure 26A and Figure 26B The positive electrode 211 a and the negative electrode 211 b included in the secondary battery 250 will be described. Figure 26A It is a perspective view illustrating the stacking order of the positive electrode 211 a , the negative electrode 211 b , and the separator 214 . Figure 26B It is a perspective view showing the lead wires 212a and 212b in addition to the positive electrode 211a and the negative electrode 211b.

[0445] like Figure 26AAs shown, secondary battery 250 includes multiple rectangular positive electrodes 211a, multiple rectangular negative electrodes 211b, and multiple separators 214. Positive electrodes 211a and negative electrodes 211b each include a protruding tab portion and a portion outside the tab. A positive electrode active material layer is formed on the portion outside the tab on one side of the positive electrode 211a, while a negative electrode active material layer is formed on the portion outside the tab on one side of the negative electrode 211b.

[0446] The positive electrode 211 a and the negative electrode 211 b are stacked such that the surfaces of the positive electrode 211 a not having the positive electrode active material layer formed thereon are in contact with each other and the surfaces of the negative electrode 211 b not having the negative electrode active material layer formed thereon are in contact with each other.

[0447] In addition, a separator 214 is provided between the surface of the positive electrode 211a on which the positive electrode active material layer is formed and the surface of the negative electrode 211b on which the negative electrode active material layer is formed. Figure 26A The separator 214 is shown by a dotted line.

[0448] like Figure 26B As shown, a plurality of positive electrodes 211a and a lead wire 212a are electrically connected in a joint 215a. In addition, a plurality of negative electrodes 211b and a lead wire 212b are electrically connected in a joint 215b.

[0449] Next, refer to Figure 25B1 、 Figure 25B2 、 Figure 25C 、 Figure 25D The outer package body 251 will be described.

[0450] The outer packaging body 251 is in the form of a thin film and is folded in half to sandwich the positive electrode 211a and the negative electrode 211b. The outer packaging body 251 includes a folded portion 261, a pair of sealing portions 262, and a sealing portion 263. The pair of sealing portions 262 are provided to sandwich the positive electrode 211a and the negative electrode 211b and can also be referred to as side seals. Furthermore, the sealing portion 263 includes a portion that overlaps with the lead wires 212a and 212b and can also be referred to as a top seal.

[0451] The outer package 251 preferably has a corrugated shape with ridge lines 271 and valley lines 272 alternately arranged in the portion overlapping the positive electrode 211a and the negative electrode 211b. The sealing portions 262 and 263 of the outer package 251 are preferably flat.

[0452] Figure 25B1 This is a cross section cut at the portion overlapping with the ridge line 271. Figure 25B2 This is a cross section cut at a portion overlapping with the valley bottom line 272 . Figure 25B1 、 Figure 25B2 Both correspond to cross sections of the secondary battery 250 and the positive electrode 211 a and the negative electrode 211 b in the width direction.

[0453] Here, the distance La is the distance between the ends of the positive electrode 211a and the negative electrode 211b in the width direction, that is, the ends of the positive electrode 211a and the negative electrode 211b and the sealing portion 262. When the secondary battery 250 is deformed, such as by bending, as described later, the positive electrode 211a and the negative electrode 211b deform in a staggered manner in the longitudinal direction. At this time, if the distance La is too short, the outer packaging 251 may rub against the positive electrode 211a and the negative electrode 211b strongly, causing damage to the outer packaging 251. In particular, when the metal film of the outer packaging 251 is exposed, the metal film may be corroded by the electrolyte. Therefore, it is preferable to set the distance La to be as long as possible. On the other hand, if the distance La is too long, the volume of the secondary battery 250 will increase.

[0454] Furthermore, it is preferable that the distance La between the positive electrode 211 a and the negative electrode 211 b and the sealing portion 262 be longer as the total thickness of the stacked positive electrode 211 a and the negative electrode 211 b increases.

[0455] More specifically, when the total thickness of the stacked positive electrode 211a, negative electrode 211b, and separator 214 (not shown) is thickness t, distance La is 0.8 to 3.0 times, preferably 0.9 to 2.5 times, and more preferably 1.0 to 2.0 times, the thickness t. By setting distance La within this range, a compact battery with high reliability against bending can be achieved.

[0456] Furthermore, when the distance between the pair of sealing portions 262 is the distance Lb, it is preferable that the distance Lb is sufficiently greater than the width of the positive electrode 211a and the negative electrode 211b (here, the width Wb of the negative electrode 211b). Thus, when the secondary battery 250 is deformed, such as by repeated bending, even if the positive electrode 211a and the negative electrode 211b come into contact with the outer packaging 251, portions of the positive electrode 211a and the negative electrode 211b can be offset in the width direction, effectively preventing friction between the positive electrode 211a and the negative electrode 211b and the outer packaging 251.

[0457] For example, the difference between the distance Lb between the pair of sealing portions 262 and the width Wb of the negative electrode 211b is 1.6 to 6.0 times, preferably 1.8 to 5.0 times, and more preferably 2.0 to 4.0 times the thickness t of the positive and negative electrodes 211a and 211b.

[0458] In other words, the distance Lb, the width Wb, and the thickness t preferably satisfy the following equation 1.

[0459] [Formula 1]

[0460]

[0461] Here, a is 0.8 or more and 3.0 or less, preferably 0.9 or more and 2.5 or less, and more preferably 1.0 or more and 2.0 or less.

[0462] also, Figure 25C 212a, which is a cross section including the wire 212a, and corresponds to a cross section in the length direction of the secondary battery 250, the positive electrode 211a, and the negative electrode 211b. Figure 25C As shown, the folded portion 261 preferably includes a space 273 between the ends of the positive electrode 211 a and the negative electrode 211 b in the longitudinal direction and the outer package 251 .

[0463] Figure 25D A schematic cross-sectional view of the battery 250 when it is bent is shown. Figure 25D Equivalent to following Figure 25A The section of the truncation line B1-B2 in .

[0464] When the secondary battery 250 is bent, a portion of the outer packaging 251 located outside the bend deforms to extend, while another portion of the outer packaging 251 located inside the bend deforms to contract. More specifically, the portion of the outer packaging 251 located outside the bend deforms in a manner that produces a small wave amplitude and a large wave period. On the other hand, the portion of the outer packaging 251 located inside the bend deforms in a manner that produces a large wave amplitude and a small wave period. Deforming the outer packaging 251 in this manner can alleviate the stress applied to the outer packaging 251 due to the bend, thereby omitting the need for the material constituting the outer packaging 251 to be stretchable. As a result, the secondary battery 250 can be bent with minimal force without damaging the outer packaging 251.

[0465] In addition, if Figure 25D As shown, when the secondary battery 250 is bent, the positive electrode 211a and the negative electrode 211b are offset relative to each other. At this time, because the ends of the multiple stacked positive electrodes 211a and negative electrodes 211b on the side of the sealing portion 263 are fixed by the fixing member 217, they are offset in such a way that the closer they are to the folded portion 261, the greater the offset. This can alleviate the stress applied to the positive electrode 211a and the negative electrode 211b, and the positive electrode 211a and the negative electrode 211b themselves do not necessarily need to be flexible. As a result, the secondary battery 250 can be bent without damaging the positive electrode 211a and the negative electrode 211b.

[0466] Furthermore, since the space 273 is provided between the positive electrode 211 a and the negative electrode 211 b and the outer casing 251 , the positive electrode 211 a and the negative electrode 211 b located inside can be relatively offset so as not to contact the outer casing 251 during bending.

[0467] Figure 25A 、 Figure 25B1 and Figure 25B2 、 Figure 25C and Figure 25D as well as Figure 26A and Figure 26B The illustrated secondary battery 250 is a battery that is less susceptible to damage to the outer casing, the positive electrode 211a, and the negative electrode 211b, even when repeatedly bent and stretched, and its battery characteristics are less likely to deteriorate. By using the positive electrode active material described in the above embodiment for the positive electrode 211a included in the secondary battery 250, a battery with high capacity and excellent cycle characteristics can be achieved.

[0468] (Implementation 4)

[0469] In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is incorporated into an electronic device will be described.

[0470] first, Figures 27A to 27G An example of incorporating the flexible secondary battery described in part of Embodiment 3 into an electronic device is shown. Examples of electronic devices to which the flexible secondary battery can be applied include televisions (also referred to as televisions or television receivers), displays for computers, digital cameras, digital video cameras, digital photo frames, mobile phones (also referred to as mobile phones or mobile phone devices), portable game consoles, portable information terminals, audio reproduction devices, and large-scale game consoles such as pinball machines.

[0471] Furthermore, the flexible secondary battery can be assembled along the curved surfaces of the inner or outer walls of houses and buildings, or the interior or exterior of automobiles.

[0472] Figure 27A An example of a mobile phone is shown. Mobile phone 7400 includes a display portion 7402 incorporated into a housing 7401, operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. Mobile phone 7400 also includes a secondary battery 7407. Using a secondary battery according to one embodiment of the present invention as secondary battery 7407 allows for a lightweight mobile phone with a long service life.

[0473] Figure 27BThe figure shows a state where the mobile phone 7400 is bent. When the mobile phone 7400 is deformed and bent as a whole due to an external force, the secondary battery 7407 disposed therein is also bent. FIG27C shows the state of the secondary battery 7407 when bent. The secondary battery 7407 is a thin storage battery. The secondary battery 7407 is fixed in the bent state. The secondary battery 7407 has a lead electrode electrically connected to the current collector. For example, the current collector is copper foil, and a portion of it is alloyed with gallium to improve the adhesion with the active material layer in contact with the current collector, thereby improving the reliability of the secondary battery 7407 when bent.

[0474] Figure 27D An example of a wristband display device is shown. A portable display device 7100 includes a housing 7101, a display portion 7102, operation buttons 7103, and a secondary battery 7104. Figure 27E A bent secondary battery 7104 is shown. When the bent secondary battery 7104 is put on the user's arm, the frame of the secondary battery 7104 is deformed, so that the curvature of a part or all of the secondary battery 7104 changes. The value of the degree of curvature of any point of the curve expressed by the value of the equivalent circle radius is the curvature radius, and the reciprocal of the curvature radius is called the curvature. Specifically, a part or all of the main surface of the frame or the secondary battery 7104 is deformed in a range where the curvature radius is greater than or equal to 40 mm and less than or equal to 150 mm. As long as the curvature radius in the main surface of the secondary battery 7104 is within the range of greater than or equal to 40 mm and less than or equal to 150 mm, high reliability can be maintained. By using a secondary battery of one embodiment of the present invention as the above-mentioned secondary battery 7104, a portable display device that is lightweight and has a long service life can be provided.

[0475] Figure 27F A portable information terminal 7200 is an example of a wristwatch-type portable information terminal. The portable information terminal 7200 includes a housing 7201, a display portion 7202, a strap 7203, a buckle 7204, operation buttons 7205, input / output terminals 7206, and the like.

[0476] The portable information terminal 7200 can execute various application programs such as mobile phone use, e-mail, article reading and writing, music playback, Internet communication, and computer games.

[0477] The display portion 7202 has a curved display surface, capable of displaying along the curved display surface. Furthermore, the display portion 7202 includes a touch sensor, which allows operation by touching the screen with a finger or a stylus. For example, an application can be launched by touching an icon 7207 displayed on the display portion 7202.

[0478] In addition to time setting, operation button 7205 may have various functions such as power on / off, wireless communication on / off, silent mode on / off, power saving mode on / off, etc. For example, the function of operation button 7205 can be freely set by utilizing the operating system incorporated in portable information terminal 7200.

[0479] Furthermore, the portable information terminal 7200 can perform standardized short-range wireless communication. For example, by communicating with a headset capable of wireless communication, a hands-free call can be made.

[0480] Furthermore, the portable information terminal 7200 includes an input / output terminal 7206, which allows data to be directly transmitted to or received from another information terminal via a connector. Furthermore, charging can be performed via the input / output terminal 7206. Furthermore, charging can also be performed using wireless power supply, without using the input / output terminal 7206.

[0481] The display unit 7202 of the portable information terminal 7200 includes a secondary battery of one embodiment of the present invention. By using a secondary battery of one embodiment of the present invention, a lightweight portable information terminal with a long service life can be provided. For example, a bent state can be Figure 27E The secondary battery 7104 shown is incorporated into the housing 7201 , or the secondary battery 7104 is incorporated into the strap 7203 in a bendable state.

[0482] The portable information terminal 7200 preferably includes a sensor. Examples of the sensor preferably include a fingerprint sensor, a pulse sensor, a body temperature sensor, and other human body sensors, a touch sensor, a pressure sensor, and an acceleration sensor.

[0483] Figure 27G An example of an armband-type display device is shown. A display device 7300 includes a display portion 7304 and a secondary battery according to one embodiment of the present invention. The display device 7300 may include a touch sensor in the display portion 7304 and be used as a portable information terminal.

[0484] The display surface of the display portion 7304 is curved and can display along the curved display surface. In addition, the display device 7300 can change the display state by utilizing standardized short-range wireless communication or the like.

[0485] The display device 7300 has input / output terminals, and can directly transmit and receive data to and from other information terminals via a connector. Furthermore, the input / output terminals can be used for charging. Furthermore, charging can also be performed using wireless power supply, rather than using the input / output terminals.

[0486] By using the secondary battery of one embodiment of the present invention as the secondary battery included in the display device 7300 , a lightweight and long-life display device can be provided.

[0487] In addition, refer to Figure 27H 、 Figures 28A to 28C and Figure 29 An example in which the secondary battery having excellent cycle characteristics described in the above embodiment is incorporated into an electronic device will be described.

[0488] By using a secondary battery according to one embodiment of the present invention as a secondary battery for household electronic devices, it is possible to provide lightweight and long-life products. For example, household electronic devices include electric toothbrushes, electric shavers, and electric beauty devices. The secondary batteries in these products are expected to be small, lightweight, and have a large capacity, and to be easy for users to hold in a rod-like shape.

[0489] Figure 27H This is a perspective view of a device called a liquid-containing smoking device (electronic cigarette). Figure 27H In the embodiment, electronic cigarette 7500 includes: an atomizer 7501 including a heating element; a secondary battery 7504 for powering the atomizer; and a cartridge 7502 including a liquid supply container and sensors. To enhance safety, a protection circuit to prevent overcharging and over-discharging of secondary battery 7504 may also be electrically connected to secondary battery 7504. Figure 27H The secondary battery 7504 shown includes external terminals for connecting to a charger. When handling, the secondary battery 7504 is positioned at the top, preferably with a short overall length and light weight. Because the secondary battery of one embodiment of the present invention has a high capacity and excellent cycle characteristics, a compact and lightweight electronic cigarette 7500 can be provided that can be used for extended periods of time.

[0490] then, Figure 28A and Figure 28B An example of a tablet terminal that can be folded in half is shown. Figure 28A and Figure 28B The illustrated tablet terminal 9600 includes a housing 9630a, a housing 9630b, a movable portion 9640 connecting the housings 9630a and 9630b, a display portion 9631 including a display portion 9631a and a display portion 9631b, switches 9625 to 9627, a fastener 9629, and an operation switch 9628. By using a flexible panel for the display portion 9631, a tablet terminal with a larger display portion can be realized. Figure 28A The tablet terminal 9600 is shown in an open state. Figure 28B The tablet terminal 9600 is shown in a closed state.

[0491] The tablet terminal 9600 includes a power storage body 9635 inside a housing 9630a and a housing 9630b. The power storage body 9635 is provided in the housing 9630a and the housing 9630b through a movable portion 9640.

[0492] The display portion 9631 can be used entirely or partially as a touch panel area, and data can be input by touching images, characters, input boxes, and the like including icons displayed on the area. For example, a keyboard can be displayed entirely on the display portion 9631a on the housing 9630a side, while information such as characters and images can be displayed on the display portion 9631b on the housing 9630b side.

[0493] The display portion 9631a on the housing 9630b side can be used to display a keyboard, and the display portion 9631b on the housing 9630a side can be used to display information such as text and images. Alternatively, a keyboard display switching button on the touch panel can be displayed on the display portion 9631, and the keyboard can be displayed on the display portion 9631 by touching the display portion 9631 with a finger or a stylus pen.

[0494] Furthermore, touch input can be performed simultaneously on the touch panel area of ​​the display portion 9631a on the housing 9630a side and the touch panel area of ​​the display portion 9631b on the housing 9630b side.

[0495] In addition to being used as an interface for operating the tablet terminal 9600, switches 9625 through 9627 can also be used as an interface for switching various functions. For example, at least one of switches 9625 through 9627 can be used as a switch for turning the tablet terminal 9600 on and off. Furthermore, at least one of switches 9625 through 9627 can have a function for switching the display orientation, such as between portrait and landscape, or for switching between black and white and color. Furthermore, at least one of switches 9625 through 9627 can have a function for adjusting the brightness of the display portion 9631. Furthermore, the brightness of the display portion 9631 can be optimized based on the amount of external light detected by a light sensor built into the tablet terminal 9600 during use. Note that in addition to the light sensor, the tablet terminal may also include other detection devices, such as sensors for detecting tilt, such as a gyroscope and an accelerometer.

[0496] also, Figure 28AWhile the display portion 9631a on the housing 9630a side and the display portion 9631b on the housing 9630b side have substantially the same display area, there is no particular limitation on the display areas of the display portions 9631a and 9631b. The size of one may be different from the other, and the display quality may also be different. For example, one of the display portions 9631a and 9631b may display a higher-definition image than the other.

[0497] Figure 28B The tablet terminal 9600 is folded in half and includes a housing 9630, a solar cell 9633, and a charge and discharge control circuit 9634 including a DC-DC converter 9636. A secondary battery according to one embodiment of the present invention is used as the power storage body 9635.

[0498] Furthermore, as described above, tablet terminal 9600 can be folded in half. Therefore, when not in use, housing 9630a and housing 9630b can be folded so that they overlap. Folding housing 9630a and housing 9630b protects the display portion 9631, thereby improving the durability of tablet terminal 9600. Furthermore, since the power storage element 9635 of the secondary battery using one embodiment of the present invention has a high capacity and excellent cycle characteristics, tablet terminal 9600 can be provided that can be used for a long period of time.

[0499] also, Figure 28A and Figure 28B The tablet terminal 9600 shown can also have the following functions: displaying various information (static images, dynamic images, text images, etc.); displaying the calendar, date or time, etc. on the display unit; performing touch input operations or touch input for editing the information displayed on the display unit; controlling processing through various software (programs), etc.

[0500] The solar cell 9633 mounted on the surface of the tablet terminal 9600 can supply power to the touch panel, display unit, image signal processing unit, and the like. Note that the solar cell 9633 can be provided on one or both surfaces of the housing 9630, enabling efficient charging of the power storage unit 9635. Using a lithium-ion battery as the power storage unit 9635 offers advantages such as enabling miniaturization.

[0501] In addition, refer to Figure 28C The block diagram shown is Figure 28B The structure and operation of the charge and discharge control circuit 9634 shown in FIG. Figure 28CThe solar cell 9633, the power storage body 9635, the DCDC converter 9636, the converter 9637, the switches SW1 to SW3, and the display portion 9631 are shown. The power storage body 9635, the DCDC converter 9636, the converter 9637, the switches SW1 to SW3 correspond to Figure 28B The charge and discharge control circuit 9634 is shown.

[0502] First, an example of operation when the solar cell 9633 generates electricity using external light will be described. The DC-DC converter 9636 steps up or down the voltage of the electricity generated by the solar cell to a voltage sufficient to charge the power storage device 9635. Furthermore, when the display portion 9631 is operated using the power from the solar cell 9633, the switch SW1 is turned on, and the converter 9637 steps up or down the voltage to the voltage required by the display portion 9631. Alternatively, when the display portion 9631 is not displaying, the switch SW1 can be turned off and the switch SW2 can be turned on to charge the power storage device 9635.

[0503] Note that although the solar cell 9633 is shown as an example of a power generation unit, the present invention is not limited to this. Other power generation units such as a piezoelectric element or a thermoelectric conversion element (Peltier element) may be used to charge the power storage body 9635. For example, a contactless power transmission module that can transmit and receive power wirelessly (contactlessly) for charging may be used, or other charging methods may be combined for charging.

[0504] Figure 29 Examples of other electronic devices are shown. Figure 29 In the embodiment of the present invention, the display device 8000 is an example of an electronic device using a secondary battery 8004 according to one embodiment of the present invention. Specifically, the display device 8000 corresponds to a display device for receiving television broadcasts, and includes a housing 8001, a display unit 8002, a speaker unit 8003, and a secondary battery 8004. The secondary battery 8004 according to one embodiment of the present invention is disposed inside the housing 8001. The display device 8000 can receive power from a commercial power source and can also use the power stored in the secondary battery 8004. Therefore, even when power cannot be supplied from a commercial power source due to a power outage, the display device 8000 can be used by using the secondary battery 8004 according to one embodiment of the present invention as an uninterruptible power supply.

[0505] As the display portion 8002, a semiconductor display device such as a liquid crystal display device, a light-emitting device having a light-emitting element such as an organic EL element in each pixel, an electrophoretic display device, a DMD (digital micromirror device), a PDP (plasma display panel), and an FED (field emission display) can be used.

[0506] Furthermore, the display device includes not only display devices for television broadcast reception but also all display devices for displaying information, such as display devices for personal computers and display devices for displaying advertisements.

[0507] exist Figure 29 In the embodiment of the present invention, the mounting type lighting device 8100 is an example of an electronic device using a secondary battery 8103 according to one embodiment of the present invention. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, and a secondary battery 8103. Figure 29 The example in FIG. 8 illustrates a case where the secondary battery 8103 is installed inside a ceiling 8104 in which a housing 8101 and a light source 8102 are mounted. However, the secondary battery 8103 may also be installed inside the housing 8101. The lighting device 8100 can receive power from a commercial power source and use the power stored in the secondary battery 8103. Therefore, even when power cannot be supplied from a commercial power source due to a power outage or the like, the lighting device 8100 can be used by using the secondary battery 8103 according to one embodiment of the present invention as an uninterruptible power supply.

[0508] In addition, although Figure 29 The example shows a mounted lighting device 8100 installed on the ceiling 8104, but the secondary battery according to one embodiment of the present invention can be used in a mounted lighting device installed outside the ceiling 8104, such as a side wall 8105, a floor 8106 or a window 8107, and can also be used in a desktop lighting device, etc.

[0509] Alternatively, an artificial light source that artificially generates light using electricity may be used as the light source 8102. Specifically, examples of the artificial light source include incandescent bulbs, discharge lamps such as fluorescent lamps, and light-emitting elements such as LEDs and organic EL elements.

[0510] exist Figure 29 In the embodiment of the present invention, an air conditioner having an indoor unit 8200 and an outdoor unit 8204 is an example of an electronic device using a secondary battery 8203 according to one embodiment of the present invention. Specifically, the indoor unit 8200 includes a housing 8201, an air outlet 8202, and a secondary battery 8203. Figure 29 , the secondary battery 8203 is shown as being installed in the indoor unit 8200. However, the secondary battery 8203 may also be installed in the outdoor unit 8204. Alternatively, the secondary battery 8203 may be installed in both the indoor unit 8200 and the outdoor unit 8204. The air conditioner can receive power from a commercial power source or use the power stored in the secondary battery 8203. In particular, when the secondary battery 8203 is installed in both the indoor unit 8200 and the outdoor unit 8204, the air conditioner can be used even when power cannot be supplied from the commercial power source due to a power outage or the like, by using the secondary battery 8203 according to one embodiment of the present invention as an uninterruptible power supply.

[0511] In addition, although Figure 29 In the embodiment, a split-type air conditioner composed of an indoor unit and an outdoor unit is exemplified. However, the secondary battery according to one embodiment of the present invention may also be used in an integrated air conditioner having the functions of an indoor unit and an outdoor unit in one housing.

[0512] exist Figure 29 In the embodiment, the electric refrigerator-freezer 8300 is an example of an electronic device using a secondary battery 8304 according to one embodiment of the present invention. Specifically, the electric refrigerator-freezer 8300 includes a housing 8301, a refrigerator door 8302, a freezer door 8303, and a secondary battery 8304. Figure 29 In the embodiment, secondary battery 8304 is provided inside housing 8301. Electric refrigerator-freezer 8300 can receive power from a commercial power source or use the power stored in secondary battery 8304. Therefore, even when power cannot be supplied from a commercial power source due to a power outage or the like, electric refrigerator-freezer 8300 can be used by using secondary battery 8304 according to one embodiment of the present invention as an uninterruptible power supply.

[0513] Among these electronic devices, high-frequency heating devices such as microwave ovens and rice cookers require high amounts of power for short periods of time. Therefore, by using a power storage device according to one embodiment of the present invention as an auxiliary power source to supplement power that cannot be fully supplied by the commercial power supply, it is possible to prevent the main switch of the commercial power supply from tripping when the electronic devices are in use.

[0514] Furthermore, during periods when electronic devices are not in use, particularly during periods when the ratio of the actual amount of power used to the total amount of power available from the commercial power supply (referred to as the power usage rate) is low, power is stored in the secondary battery. This can suppress increases in the power usage rate during periods other than these periods. For example, in the case of an electric refrigerator-freezer 8300, power is stored in the secondary battery 8304 at night when the temperature is low and the refrigerator door 8302 or freezer door 8303 is not opened or closed. Furthermore, during the day when the temperature is high and the refrigerator door 8302 or freezer door 8303 is opened or closed, the secondary battery 8304 is used as an auxiliary power source, thereby suppressing the power usage rate during the day.

[0515] By adopting a method of the present invention, the cycle characteristics of the secondary battery can be improved and the reliability can be improved. In addition, by adopting a method of the present invention, a high-capacity secondary battery can be realized and the characteristics of the secondary battery can be improved, and the secondary battery itself can be miniaturized and lightweight. Therefore, by installing the secondary battery of one method of the present invention in the electronic device described in this embodiment, a longer service life and lighter electronic device can be provided. This embodiment can be implemented in combination with other embodiments as appropriate.

[0516] (Implementation 5)

[0517] In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted on a vehicle is described.

[0518] When secondary batteries are installed in vehicles, a new generation of clean energy vehicles such as hybrid electric vehicles (HEV), electric vehicles (EV), or plug-in hybrid electric vehicles (PHEV) can be realized.

[0519] exist Figures 30A to 30C In the embodiment, a vehicle using the secondary battery of one embodiment of the present invention is exemplified. Figure 30A The car 8400 shown is an electric car that uses an electric motor as a power source for traveling. Alternatively, the car 8400 is a hybrid car that can appropriately use an electric motor or an engine as a power source for traveling. By using a secondary battery of one embodiment of the present invention, a vehicle with a long driving distance can be realized. In addition, the car 8400 is equipped with a secondary battery. As a secondary battery, Figure 15C 15D is arranged in the floor portion of the vehicle. In addition, multiple Figure 18A and Figure 18B The battery pack composed of the secondary batteries shown is installed in the floor of the vehicle. The secondary batteries not only drive the electric motor 8406 but also supply power to lighting devices such as the headlights 8401 and interior lights (not shown).

[0520] Furthermore, the secondary battery can supply electric power to a display device such as a speedometer and a tachometer included in the automobile 8400. Furthermore, the secondary battery can supply electric power to a semiconductor device such as a navigation system included in the automobile 8400.

[0521] exist Figure 30B In the illustrated automobile 8500 , a secondary battery included in the automobile 8500 can be charged by receiving electric power from an external charging device using a plug-in method or a contactless power supply method. Figure 30B The figure shows a situation where a secondary battery 8024 installed in a car 8500 is charged from a ground-mounted charging device 8021 via a cable 8022. When charging, the charging method or connector specifications, etc. can be appropriately performed in accordance with the provisions of CHAdeMO (registered trademark) or the Combined Charging System. As the charging device 8021, a charging station installed in a commercial facility or a home power supply can also be used. For example, by supplying power from the outside using plug-in technology, the secondary battery 8024 installed in the car 8500 can be charged. Charging can be performed by converting AC power into DC power using a conversion device such as an AC / DC converter.

[0522] Although not shown, it is also possible to install a power receiving device in the vehicle and charge it through contactless power supply from an above-ground power transmission device. When using a contactless power supply method, by integrating the power transmission device into the road or an exterior wall, charging can be performed not only while the vehicle is parked but also while it is in motion. Furthermore, this contactless power supply method can be used to send and receive power between vehicles. Furthermore, solar cells can be installed on the exterior of the vehicle to charge the secondary battery while the vehicle is parked or in motion. This contactless power supply can be achieved using electromagnetic induction or magnetic field resonance.

[0523] Figure 30C This is an example of a two-wheeled vehicle using the secondary battery of one embodiment of the present invention. Figure 30C The scooter 8600 shown includes a secondary battery 8602, a rearview mirror 8601, and a turn signal light 8603. The secondary battery 8602 can supply power to the turn signal light 8603.

[0524] In addition, Figure 30C In the illustrated scooter 8600, a secondary battery 8602 can be stored in an under-seat storage box 8604. Even though the under-seat storage box 8604 is small, the secondary battery 8602 can be stored in the under-seat storage box 8604. The secondary battery 8602 is detachable, so when charging, the secondary battery 8602 can be brought indoors, charged, and then stored before driving.

[0525] By adopting one embodiment of the present invention, the cycle characteristics and capacity of the secondary battery can be improved. As a result, the secondary battery itself can be made small and lightweight. In addition, if the secondary battery itself can be made small and lightweight, it will help to achieve the lightweight of the vehicle, thereby extending the driving distance. In addition, the secondary battery installed in the vehicle can be used as a power supply source outside the vehicle. In this case, for example, the use of commercial power sources can be avoided during peak power demand periods. If the use of commercial power sources can be avoided during peak power demand periods, it will help to save energy and reduce carbon dioxide emissions. In addition, if the cycle characteristics are excellent, the secondary battery can be used for a long period of time, thereby reducing the use of rare metals such as cobalt.

[0526] This embodiment mode can be implemented in combination with other embodiment modes as appropriate.

[0527] [Example 1]

[0528] In this example, a positive electrode active material containing magnesium, fluorine, and phosphorus was manufactured, and a secondary battery having a positive electrode using the positive electrode active material was manufactured to evaluate the continuous charge resistance and cycle characteristics of the secondary battery.

[0529] <Manufacturing of Positive Electrode Active Material>

[0530] Reference Figure 8 and Figure 9 Note that steps S42 to S47 are not performed.

[0531] First, a mixture 902 containing magnesium and fluorine is prepared ( Figure 8 (See steps S11 to S14 shown in the figure). LiF and MgF2 were weighed at a molar ratio of LiF:MgF2 = 1:3, and acetone was added as a solvent. Mixing and pulverization were performed using a wet process. Mixing and pulverization were performed using a ball mill using zirconium balls at 150 rpm for 1 hour. The recovered materials were then collected to obtain mixture 902.

[0532] Next, a positive electrode active material containing cobalt is prepared (step S25). Here, CELLSEED C-10N manufactured by Nippon Chemical Industry Co., Ltd. is used as pre-synthesized lithium cobalt oxide. CELLSEED C-10N is a lithium cobalt oxide with a D50 of approximately 12 μm and low impurities.

[0533] Next, the mixture 902 and lithium cobalt oxide are mixed (step S31). The conditions for the atomic weight of magnesium contained in the mixture 902 are set relative to the atomic weight of cobalt contained in the lithium cobalt oxide. Weighing is performed when the conditions are approximately 0.5%, 1.0%, 2.0%, 3.0%, and 6.0%. The atomic weight of magnesium in each prepared positive electrode active material is shown in Tables 1 and 2 described below. Mixing is performed by a dry method. Mixing is performed at 150 rpm for 1 hour using a ball mill using zirconium balls.

[0534] Next, the processed materials are recovered to obtain a mixture 903 (steps S32 and S33).

[0535] Next, the mixture 903 is placed in an alumina crucible and annealed at 850°C for 60 hours in an oxygen atmosphere muffle furnace (step S34). The alumina crucible is covered during annealing. The oxygen flow rate is set to 10 L / min. The temperature is raised at 200°C / hr and the temperature is lowered for more than 10 hours. The material after heat treatment is recovered (step S35) and screened to obtain the positive electrode active material ( Figure 8 The positive electrode active material 100A_1 shown in FIG3 is prepared (step S36). Hereinafter, the positive electrode active materials 100A_1 having magnesium concentrations of 0.5%, 1.0%, 2.0%, 3.0%, and 6.0% are referred to as Sample 11, Sample 12, Sample 13, Sample 14, and Sample 15, respectively. In the positive electrode production described later, both the positive electrode active material 100A_1 obtained in this step and the positive electrode active material obtained by performing steps S51 to S54 described later after this step are used.

[0536] Then, no Figure 9 The metal addition process from step S42 to step S47 proceeds to step S51.

[0537] Next, lithium phosphate is prepared (step S51). Then, lithium phosphate and positive electrode active material 100A_1 are mixed (step S52). 0.06 mol of lithium phosphate is mixed with respect to 1 mol of positive electrode active material 100A_1. Mixing is performed at 150 rpm for 1 hour using a ball mill using zirconium balls. After mixing, the mixture is screened with a sieve with a mesh size of 300 μmφ. Then, the obtained mixture is placed in an alumina crucible, covered with a lid, and annealed at 750°C for 20 hours in an oxygen atmosphere (step S53). Then, the powder is recovered by screening with a sieve with a mesh size of 53 μmφ (step S54). Through the above process, a positive electrode active material to which a phosphorus-containing compound is added and the conditions for the amount of magnesium added are set respectively is obtained (hereinafter, the positive electrode active materials with magnesium concentrations of 0.5%, 1.0%, 2.0%, 3.0% and 6.0% are referred to as sample 21, sample 22, sample 23, sample 24 and sample 25, respectively).

[0538] <Manufacturing of Secondary Batteries>

[0539] Each positive electrode was manufactured using the positive electrode active materials obtained above. Each positive electrode was formed by mixing the positive electrode active material, AB, and PVDF in a weight ratio of 95:3:2. This slurry was then applied to the current collector. NMP was used as the solvent for the slurry.

[0540] After applying the slurry to the current collector, the solvent is evaporated. Then, the positive electrode of the secondary battery is pressurized at 210 kN / m and then at 1467 kN / m. After the above steps, the positive electrode is obtained. The positive electrode loading is about 20 mg / cm 2 .

[0541] A coin-type secondary battery of the CR2032 type (20 mm in diameter and 3.2 mm in height) was produced using the formed positive electrode.

[0542] Lithium metal was used as the counter electrode.

[0543] The electrolyte contained 1 mol / L of lithium hexafluorophosphate (LiPF6). A mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 3:7 was used. Furthermore, for the secondary batteries evaluated for cycling performance, 2 wt% of vinylene carbonate (VC) was added to the electrolyte.

[0544] Polypropylene with a thickness of 25 μm was used as the separator.

[0545] The positive electrode can and the negative electrode can are formed of stainless steel (SUS).

[0546] <Continuous charging resistance>

[0547] Next, the secondary batteries using each of the positive electrode active materials were tested for their continuous charge resistance. First, a cycle test of CCCV charge (0.05C, 4.5V or 4.6V, end current 0.005C) and CC discharge (0.05C, 2.5V) was repeated twice at 25°C.

[0548] Next, perform CCCV charging (0.05C) at 60°C. Set the upper voltage limit to 4.55V or 4.65V, and continue testing until the secondary battery voltage drops below the value obtained by subtracting 0.01V from the upper voltage limit (for example, a value below 4.54V when the upper voltage limit is 4.55V). If the secondary battery voltage drops below the upper voltage limit, short circuits and other phenomena may occur. 1C is set to 200mA / g.

[0549] The test time of each secondary battery is shown in Tables 1 and 2. Table 1 shows the results using the positive electrode active material obtained in step S36, and Table 2 shows the results using the positive electrode active material formed in steps S51 to S54, that is, the positive electrode active material to which the phosphorus compound was added.

[0550] [Table 1]

[0551]

[0552] [Table 2]

[0553]

[0554] Figure 31A and Figure 31B The time-current characteristics when the charging voltage is 4.55 V and the time-current characteristics when the charging voltage is 4.65 V are shown respectively as the results of using the positive electrode active material obtained in step S36 .

[0555] Figure 32A and Figure 32B The time-current characteristics at a charging voltage of 4.55 V and the time-current characteristics at a charging voltage of 4.65 V are shown respectively when the positive electrode active material formed through steps S51 to S54 , that is, the positive electrode active material to which the phosphorus compound is added, is used.

[0556] This shows that the addition of the phosphorus compound lengthens the time until the voltage drop occurs, thereby improving the continuous charge resistance. Furthermore, when the magnesium addition amount is 2%, the continuous charge resistance is significantly improved.

[0557] <Cycling Characteristics>

[0558] Next, cycle tests were performed on each secondary battery using each of the resulting positive electrode active materials. First, a CCCV charge (0.05C, 4.6V, end current 0.005C) and CC discharge (0.05C, 2.5V) cycle was performed twice at 25°C. Then, a CCCV charge (0.2C, 4.6V, end current 0.02C) and CC discharge (0.2C, 2.5V) cycle was repeated at 25°C.

[0559] exist Figure 33A and Figure 33B , the horizontal axis represents cycles, and the vertical axis represents discharge capacity. Figure 33A This is the result of using the positive electrode active material obtained in step S36. Figure 33B This is the result of using the positive electrode active material formed through steps S51 to S54, that is, the positive electrode active material to which the phosphorus compound is added.

[0560] Looking at the rate of capacity reduction relative to the number of cycles, no significant differences were observed depending on the magnesium concentration. On the other hand, the higher the magnesium concentration, the more significant the decrease in initial capacity. This is because the proportion of phosphorus compounds in the active material weight increases, while the proportion of cobalt decreases relatively, reducing the proportion of substances contributing to the charge and discharge reactions.

[0561] [Example 2]

[0562] In this embodiment, a positive electrode active material containing magnesium, fluorine, cobalt and metals other than cobalt is manufactured, and a secondary battery using a positive electrode of the positive electrode active material is manufactured to evaluate the XRD of the positive electrode after charging of the secondary battery, the continuous charging resistance of the secondary battery and the cycle characteristics of the secondary battery.

[0563] <Manufacturing of Positive Electrode Active Material>

[0564] Reference Figure 8 and Figure 9 Samples 30 to 35 as positive electrode active materials were manufactured using the following process. Note that steps S51 to S54 were not performed.

[0565] First, a mixture 902 containing magnesium and fluorine was prepared as samples 30 to 35 (steps S11 to S14). LiF and MgF₂ were weighed at a molar ratio of LiF:MgF₂ = 1:3, and acetone was added as a solvent. The mixture was then wet-mixed and ground. Mixing and grinding were performed using a ball mill using zirconium balls at 150 rpm for one hour. The recovered materials were then collected to obtain mixture 902.

[0566] Next, CELLSEED C-10N manufactured by Nippon Chemical Industry Co., Ltd., which is a positive electrode active material containing cobalt, was prepared as samples 30 to 35 (step S25 ).

[0567] Next, mixture 902 and lithium cobalt oxide were mixed as samples 30 to 35 (step S31). The mixture 902 was weighed so that the atomic weight of magnesium relative to the atomic weight of cobalt in the lithium cobalt oxide was 2.0%. Mixing was performed using a dry process. Mixing was performed at 150 rpm for 1 hour using a ball mill using zirconium balls.

[0568] Next, the processed materials are recovered as samples 30 to 35 to obtain a mixture 903 (steps S32 and S33).

[0569] Next, as samples 30 to 35, mixture 903 was placed in an alumina crucible and annealed in an oxygen atmosphere muffle furnace at 850°C for 60 hours (step S34). The alumina crucible was covered during annealing. The oxygen flow rate was set to 10 L / min. The temperature was increased at 200°C / hr, and the temperature was decreased over 10 hours. The heat-treated material was recovered and screened (step S35) to obtain positive electrode active material 100A_1 (step S36).

[0570] Next, samples 31 to 35 were processed through steps S41 to S46. Note that the metal source addition process of steps S41 to S46 was not performed for sample 30. First, the positive electrode active material 100A_1 and the metal source were mixed in step S41 for samples 31 to 35. Furthermore, a solvent was added as needed.

[0571] Addition of Aluminum

[0572] As samples 31 and 32, a covering layer containing aluminum was formed on the positive electrode active material 100A_1 using a sol-gel method. Aluminum isopropylate was used as a raw material and 2-isopropyl alcohol was used as a solvent. Sample 31 was processed under the condition that the atomic weight of aluminum was 0.1% relative to the total atomic weight of cobalt and aluminum, while sample 32 was processed under the condition that the atomic weight of aluminum was 0.5% relative to the total atomic weight of cobalt and aluminum. Then, the obtained mixture was placed in an alumina crucible, covered with a lid, and annealed at 850°C for 2 hours in an oxygen atmosphere (step S45). Then, the powder was recovered by screening with a sieve with a mesh of 53μmφ (step S46), and samples 31 and 32 as positive electrode active materials were obtained.

[0573] Nickel Addition

[0574] As samples 33 and 34, nickel hydroxide as a metal source and positive electrode active material 100A_1 were mixed. Sample 33 was mixed under the condition that the atomic weight of nickel was 0.1% relative to the total atomic weight of cobalt and nickel, while sample 34 was mixed under the condition that the atomic weight of nickel was 0.5% relative to the total atomic weight of cobalt and nickel. Mixing was carried out at 150 rpm for 1 hour using a ball mill using zirconium balls. After mixing, the mixture was screened with a sieve with a mesh of 300 μmφ. Then, the obtained mixture was placed in an alumina crucible, covered with a lid, and annealed at 850°C for 2 hours in an oxygen atmosphere (step S45). Then, the powder was recovered by screening with a sieve with a mesh of 53 μmφ (step S46), and samples 33 and 34 as positive electrode active materials were obtained.

[0575] Addition of aluminum and nickel

[0576] As sample 35, nickel hydroxide as a metal source and positive electrode active material 100A_1 are mixed using a ball mill, and then a covering layer containing aluminum is formed using a sol-gel method. Aluminum isopropylate is used as a metal source and 2-isopropyl alcohol is used as a solvent. Mixing is performed under the condition that the atomic weight of nickel and aluminum is 0.5% relative to the sum of the atomic weights of cobalt, nickel and aluminum. Then, the obtained mixture is placed in an alumina crucible, covered with a lid, and annealed at 850°C for 2 hours in an oxygen atmosphere (step S45). Then, the powder is recovered by screening with a sieve with a mesh size of 53μmφ (step S46), and sample 35 as a positive electrode active material is obtained.

[0577] <Manufacturing of Secondary Batteries>

[0578] Each positive electrode was manufactured using Samples 30 to 35 obtained above as the positive electrode active material. Each positive electrode was formed by mixing the positive electrode active material, AB, and PVDF in a weight ratio of 95:3:2, and applying the resulting slurry to the current collector. NMP was used as the solvent for the slurry.

[0579] After applying the slurry to the current collector, the solvent was evaporated. Then, the pressure was applied at 210 kN / m and then at 1467 kN / m. After the above steps, the positive electrode was obtained. The positive electrode loading capacity was about 20 mg / cm 2 .

[0580] A coin-type secondary battery of the CR2032 type (20 mm in diameter and 3.2 mm in height) was produced using the formed positive electrode.

[0581] Lithium metal was used as the counter electrode.

[0582] The electrolyte contained 1 mol / L of lithium hexafluorophosphate (LiPF6). A mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 3:7 was used. Furthermore, for the secondary batteries evaluated for cycling performance, 2 wt% of vinylene carbonate (VC) was added to the electrolyte.

[0583] Polypropylene with a thickness of 25 μm was used as the separator.

[0584] The positive electrode can and the negative electrode can are formed of stainless steel (SUS).

[0585] <XRD of positive electrode>

[0586] First, XRD analysis of the positive electrode was performed before charge and discharge. Figure 34A and Figure 34BThe XRD of the positive electrode before charge and discharge is shown. Peaks are significantly observed at 2θ of 18.89° and 2θ of 38.85°. Figure 34A and Figure 34B In FIG, the horizontal axis shows 2θ, and the vertical axis shows intensity.

[0587] <XRD of the positive electrode after charging>

[0588] Next, each secondary battery was subjected to CCCV charging at one of the conditions selected from 4.55V, 4.6V, 4.65V and 4.7V. Specifically, constant current charging was performed at 0.2C at 25°C until each voltage was reached, and then constant voltage charging was performed until the current value became 0.02C. Note that 1C is set to 191mA / g here. Next, the charged secondary battery was disassembled in an argon atmosphere glove box and the positive electrode was taken out, and the electrolyte was washed with DMC (dimethyl carbonate). Then, it was sealed in an argon atmosphere and XRD analysis was performed.

[0589] Figure 35A and Figure 35B The XRD patterns of sample 35 corresponding to various charging voltage conditions are shown. Figure 35A and Figure 35B In FIG, the horizontal axis represents 2θ, and the vertical axis represents intensity.

[0590] Figure 35A The peaks observed in the range of 2θ of 18° to 20° are shown. The peak observed under the condition of a charging voltage of 4.55V is considered to be caused by the O3 type crystal structure. As the charging voltage increases, the peak position drifts to the high angle side. Under the condition of a charging voltage of 4.65V, not only a peak near 18.9° but also a peak near 19.2° is observed, which means a two-phase mixed state of two crystal structures having an O3 type crystal structure and a pseudo-spinel type crystal structure. The peak near 19.3° observed under the condition of a charging voltage of 4.7V is considered to be caused by the pseudo-spinel type crystal structure.

[0591] Figure 35B Peaks are observed in the range of 2θ from 40° to 50°. As the charge voltage increases, a minute peak at approximately 43.9°, attributed to the H1-3 type crystal structure, is observed at a charge voltage as high as 4.7 V.

[0592] In summary, the positive electrode active material of one embodiment of the present invention produces a region where the O3 type crystal structure changes to a pseudo-spinel type crystal structure when the charging voltage is as high as 4.65V. In addition, when the charging voltage is as high as 4.7V, although there is partially an H1-3 type crystal structure, it mainly has a pseudo-spinel type crystal structure. It can be seen that the positive electrode active material of one embodiment of the present invention also has high stability at high charging voltage.

[0593] <Continuous charging resistance>

[0594] Next, the secondary batteries were tested for their continuous charge resistance. First, at 25°C, secondary batteries using samples 30 to 35 as the positive electrode active material were subjected to two cycles of CCCV charge (0.05C, 4.5V or 4.6V, end current 0.005C) and CC discharge (0.05C, 2.5V).

[0595] Next, perform CCCV charging (0.05C) at 60°C. Set the upper voltage limit to 4.55V or 4.65V, and continue testing until the secondary battery voltage drops below the value obtained by subtracting 0.01V from the upper voltage limit (for example, a value below 4.54V when the upper voltage limit is 4.55V). If the secondary battery voltage drops below the upper voltage limit, short circuits and other phenomena may occur. 1C is set to 200mA / g.

[0596] Table 3 shows the test time of each secondary battery. Note that two secondary batteries were manufactured under each condition. Table 3 shows the average value of the two results.

[0597] [Table 3]

[0598]

[0599] Figure 36A and Figure 36B The results of using Sample 30, Sample 32, Sample 34, and Sample 35 are shown respectively as the time-current characteristics when the charging voltage is 4.55 V and the time-current characteristics when the charging voltage is 4.65 V.

[0600] This shows that the addition of aluminum prolongs the time until the voltage drop occurs, improving the continuous charge resistance. Furthermore, the addition of nickel and aluminum significantly improves the continuous charge resistance compared to the case where only nickel is added.

[0601] <Cycling Characteristics>

[0602] Next, cycle tests were performed on secondary batteries using Samples 30, 32, 34, and 35. First, a CCCV charge (0.05C, 4.6V, end current 0.005C) and CC discharge (0.05C, 2.5V) cycle test was performed twice at 25°C. Then, a CCCV charge (0.2C, 4.6V, end current 0.02C) and CC discharge (0.2C, 2.5V) cycle test was repeated at 25°C.

[0603] Figure 37The results of the cycle characteristics are shown. Figure 37 , the horizontal axis represents cycles, and the vertical axis represents discharge capacity. Figure 38A The initial charge and discharge curve of sample 32 is shown. Figure 38B The initial charge and discharge curve of sample 34 is shown. Figure 38C The initial charge-discharge curve for Sample 35 is shown. The addition of nickel improves the initial capacity (Sample 34). Furthermore, the addition of nickel and aluminum suppresses capacity loss with cycling, with even better results achieved under the conditions in which nickel and aluminum are added (Sample 35).

[0604] [Example 3]

[0605] In this example, the positive electrode was evaluated by direct current resistance measurement.

[0606] <Manufacturing of Secondary Batteries>

[0607] Each positive electrode was manufactured using Sample 11 described in Example 1 as the positive electrode active material. Each positive electrode was formed by mixing the positive electrode active material, carbon black, and PVDF in a weight ratio of 90:5:5. This slurry was then applied to the current collector. NMP was used as the solvent for the slurry.

[0608] After applying the slurry to the current collector, the solvent was evaporated. Then, the pressure was applied at 210 kN / m and then at 1467 kN / m. After the above steps, the positive electrode was obtained. The positive electrode loading capacity was about 20 mg / cm 2 .

[0609] A coin-type secondary battery of the CR2032 type (20 mm in diameter and 3.2 mm in height) was produced using the formed positive electrode.

[0610] Lithium metal was used as the counter electrode.

[0611] The electrolyte contained 1 mol / L of lithium hexafluorophosphate (LiPF6). A mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 3:7 was used. Furthermore, for the secondary batteries evaluated for cycling performance, 2 wt% of vinylene carbonate (VC) was added to the electrolyte.

[0612] Polypropylene with a thickness of 25 μm was used as the separator.

[0613] The positive electrode can and the negative electrode can are formed of stainless steel (SUS).

[0614] <Charge and discharge cycle test>

[0615] The DC resistance was measured before the charge-discharge cycle test and after 50 charge-discharge cycle tests. The charge-discharge cycle test can refer to the conditions shown in Example 1.

[0616] <DC Resistance Measurement>

[0617] Next, the DC resistance was measured using the fabricated secondary battery. The measuring device used was the HJ1001SM8A type electrochemical measurement system manufactured by Hokuto Denko Corporation, Japan.

[0618] First, CCCV charging was performed until 4.5 V in an environment of 25 °C and then stopped for 20 minutes. Next, CC discharge was performed until 3.0 V and then stopped for 20 minutes. DC resistance measurements were carried out by setting SOC conditions based on the measured discharge capacity.

[0619] First, CCCV charging was performed until 4.5 V in an environment of 25 °C. Next, discharge was carried out, and DC resistance measurements were respectively performed in three states where the SOC was 70%, 20%, and 10%.

[0620] At each SOC, after the discharge capacity reached the specified SOC, current was allowed to flow for a certain period of time, and the DC resistance was obtained. Table 4 shows the obtained DC resistance.

[0621] [Table 4]

[0622]

[0623] It can be seen from this that the smaller the SOC, the larger the DC resistance. It can also be seen that after the cycle test, the DC resistance increased to about 1.3 to 1.4 times.

[0624] [Example 4]

[0625] In this example, cross-sectional TEM-EDX analysis was performed on the particles contained in the positive electrode active material of one mode of the present invention.

[0626] Each sample was processed into a thin slice using FIB (Focused Ion Beam System: focused ion beam processing observation device), and then the TEM image was observed. Figure 39A The cross-sectional TEM image of Sample 35 fabricated in Example 2 is shown.

[0627] <TEM-EDX Analysis>

[0628] For the part surrounded by the dotted line in Figure 39A TEM-EDX analysis was performed. Linear analysis was carried out from the particle surface to the inside. The line was substantially perpendicular to the surface. Figure 39BThe following table shows the results of EDX analysis. These results show that the concentration of aluminum is relatively high near the surface, while the concentration of cobalt is relatively low. Furthermore, the concentration of magnesium also increases near the surface. This indicates that aluminum, magnesium, and other elements contribute to structural stabilization on the surface of the particles contained in the positive electrode active material.

[0629] [Example 5]

[0630] In this example, a secondary battery including a positive electrode using the positive electrode active material according to one embodiment of the present invention was manufactured, and the XRD of the positive electrode of the secondary battery after charging was analyzed.

[0631] Positive electrodes were fabricated using Sample 30 and Sample 35 formed in Example 2, and secondary batteries were fabricated using the positive electrodes. The manufacturing method described in Example 2 was used to fabricate the positive electrodes and the secondary batteries.

[0632] <XRD of the positive electrode after charging>

[0633] Next, each secondary battery was subjected to CCCV charging under either 4.6V or 4.65V. Specifically, constant current charging was performed at 0.2C at 45°C until each voltage was reached, and then constant voltage charging was performed until the current value became 0.02C. Note that 1C is set to 191mA / g here. Next, the charged secondary battery was disassembled in an argon atmosphere glove box and the positive electrode was taken out, and the electrolyte was washed with dimethyl carbonate (DMC). Then, it was sealed in an argon atmosphere and XRD analysis was performed.

[0634] Figure 40A and Figure 40B The XRD results are shown. At high charge voltages, Sample 30 shows not only a peak indicating an H1-3 type crystalline structure, but also prominent peaks near 20.9° and 36.8°. The peaks near 20.9° and 36.8° are due to CoO2, which causes lithium to escape, leading to an unstable state where the crystalline structure collapses. In contrast, Sample 35 shows a pseudo-spinel crystalline structure, which is also stable at high charge voltages.

[0635] [Explanation of symbols]

[0636] 100: Positive electrode active material, 100A: Positive electrode active material, 100A_1: Positive electrode active material, 100A_2: Positive electrode active material, 100A_3: Positive electrode active material, 100C: Positive electrode active material, 200: Active material layer, 201: Graphene compound, 211a: Positive electrode, 211b: Negative electrode, 212a: Lead wire, 212b: Lead wire, 214: Separator, 215a: Joint, 215b: Joint, 217: Fixing member, 250: Secondary battery, 251: Outer package, 261: Folding member Stacked part, 262: Sealing part, 263: Sealing part, 271: Ridge line, 272: Valley bottom line, 273: Space, 300: Secondary battery, 301: Positive electrode can, 302: Negative electrode can, 303: Gasket, 304: Positive electrode, 305: Positive electrode collector, 306: Positive electrode active material layer, 307: Negative electrode, 308: Negative electrode collector, 309: Negative electrode active material layer, 310: Separator, 500: Secondary battery, 501: Positive electrode collector, 502: Positive electrode active material layer, 503: Positive electrode, 504: Negative electrode collector, 505: Negative electrode active material layer, 506: Negative electrode, 507: Separator, 508: Electrolyte, 509: Outer packaging, 510: Positive electrode lead electrode, 511: Negative electrode lead electrode, 600: Secondary battery, 601: Positive electrode cap, 602: Battery can, 603: Positive terminal, 604: Positive electrode, 605: Separator, 606: Negative electrode, 607: Negative terminal, 608: Insulating plate, 609: Insulating plate, 611: PTC element, 612: Safety valve mechanism, 613: Conductive plate, 614: Conductive plate, 615: Module, 616: Lead wire, 617: Temperature control device, 900: Circuit board, 901: Raw material, 902: Mixture, 903: Mixture, 904: Mixture, 910: Label, 911: Terminal, 912: Circuit, 913: Secondary Battery, 914: Antenna, 916: Layer, 917: Layer, 918: Antenna, 920: Display, 921: Sensor, 922: Terminal, 930: Frame, 930a: Frame, 930b: Frame, 931: Negative Electrode, 932: Positive Electrode, 933: Separator, 950: Winding, 951: Terminal, 952: Terminal, 980: Secondary Battery, 981: Film, 982: Film, 993: Winding, 994: Negative Electrode, 995: Positive Electrode, 996: Separator, 997: Lead Electrode, 998: Lead Electrode, 7100: Portable Display, 7101: Frame, 7102: Display, 7103: Operation Button,7104: Secondary battery, 7200: Portable information terminal, 7201: Housing, 7202: Display unit, 7203: Strap, 7204: Buckle, 7205: Operation button, 7206: Input / output terminal, 7207: Icon, 7300: Display device, 7304: Display unit, 7400: Mobile phone, 7401: Housing, 7402: Display unit, 7403: Operation button, 7404: External connection port, 7405: Speaker, 7406: Microphone, 7407: Secondary battery, 7500: Electronic cigarette, 7501: Atomizer, 7502: Cigarette cartridge, 7504: Secondary battery, 8000: Display device, 8001: Housing, 8002: Display unit, 8003: Speaker unit, 8004: Secondary battery, 8021: Charging device, 8022: Cable, 8024: Secondary battery, 8100: Lighting device, 8101: Frame, 8102: Light source, 8103: Secondary battery, 8104: Ceiling, 8105: Side wall, 8106: Floor, 8107: Window, 8200: Indoor unit, 8201: Frame, 8202: Air outlet, 8203: Secondary battery, 8204: Outdoor Unit, 8300: Electric Refrigerator / Freezer, 8301: Frame, 8302: Refrigerator Door, 8303: Freezer Door, 8304: Secondary Battery, 8400: Automobile, 8401: Headlamp, 8406: Electric Motor, 8500: Automobile, 8600: Scooter, 8601: Rearview Mirror, 8602: Secondary Battery, 8603: Turn Signal, 8604: Underseat Storage Box, 9600: Tablet Computer , 9625: Switch, 9627: Switch, 9628: Operation switch, 9629: Fastener, 9630: Frame, 9630a: Frame, 9630b: Frame, 9631: Display unit, 9631a: Display unit, 9631b: Display unit, 9633: Solar cell, 9634: Charge and discharge control circuit, 9635: Storage body, 9636: DCDC converter, 9637: Converter, 9640: Movable unit.

Claims

1. A lithium ion secondary battery comprising a positive electrode containing a positive electrode active material, in, The positive electrode active material comprises lithium cobaltate, and the lithium cobaltate comprises magnesium, aluminum and nickel. The positive electrode active material has an O3 type crystal structure in the discharge state, When the positive electrode is analyzed by powder X-ray diffraction using CuKα1 radiation in a charged state, the XRD pattern of the positive electrode active material has a first diffraction peak at 19.30±0.20° and a second diffraction peak at 45.55±0.10°.

2. A lithium ion secondary battery comprising a positive electrode containing a positive electrode active material, in, The positive electrode active material comprises lithium cobaltate, and the lithium cobaltate comprises magnesium, aluminum and nickel. The positive electrode active material has an O3 type crystal structure and a charge depth of less than 0.

06. Moreover, when the positive electrode is analyzed by powder X-ray diffraction, the crystalline structure of the positive electrode active material with a charge depth of greater than 0.7 and less than 0.9 belongs to the space group R-3m, wherein the coordinates of cobalt and oxygen are represented by (0, 0, 0.5) and (0, 0, x), respectively, where 0.20≤x≤0.

25.

3. A lithium ion secondary battery comprising a positive electrode containing a positive electrode active material, in, The positive electrode active material comprises lithium cobaltate, and the lithium cobaltate comprises magnesium, aluminum and nickel. When the sum of the number of nickel atoms and the number of cobalt atoms in the positive electrode active material is 100%, the number of nickel atoms is less than 7.5%, The magnesium concentration in the surface layer of the positive electrode active material is higher than the magnesium concentration in the interior of the positive electrode active material. The positive electrode active material has an O3 type crystal structure and a charge depth of less than 0.

06. Moreover, when the positive electrode is analyzed by powder X-ray diffraction, the crystalline structure of the positive electrode active material with a charge depth of greater than 0.7 and less than 0.9 belongs to the space group R-3m, wherein the coordinates of cobalt and oxygen are represented by (0, 0, 0.5) and (0, 0, x), respectively, where 0.20≤x≤0.

25.

4. A lithium ion secondary battery comprising a positive electrode containing a positive electrode active material, in, The positive electrode active material comprises lithium cobaltate, and the lithium cobaltate comprises magnesium, aluminum and nickel. The number of nickel atoms in the positive electrode active material is not less than 0.05% and not more than 4% of the number of cobalt atoms. The magnesium concentration in the surface layer of the positive electrode active material is higher than the magnesium concentration in the interior of the positive electrode active material. The positive electrode active material has an O3 type crystal structure and a charge depth of less than 0.

06. Moreover, when the positive electrode is analyzed by powder X-ray diffraction, the crystalline structure of the positive electrode active material with a charge depth of greater than 0.7 and less than 0.9 belongs to the space group R-3m, wherein the coordinates of cobalt and oxygen are represented by (0, 0, 0.5) and (0, 0, x), respectively, where 0.20≤x≤0.

25.

5. A lithium ion secondary battery comprising a positive electrode containing a positive electrode active material, in, The positive electrode active material comprises lithium cobaltate, and the lithium cobaltate comprises magnesium, aluminum and nickel. The positive electrode active material has an O3 type crystal structure and a charge depth of less than 0.

06. Moreover, when the positive electrode is analyzed by powder X-ray diffraction using CuKα1 rays, the XRD pattern of the positive electrode active material having a charge depth of 0.7 to 0.9 has a first diffraction peak at 19.30±0.20° 2θ and a second diffraction peak at 45.55±0.10° 2θ.

6. A lithium ion secondary battery comprising a positive electrode containing a positive electrode active material, in, The positive electrode active material comprises lithium cobaltate, and the lithium cobaltate comprises magnesium, aluminum and nickel. The magnesium concentration in the surface layer of the positive electrode active material is higher than the magnesium concentration in the interior of the positive electrode active material. The positive electrode active material has an O3 type crystal structure and a charge depth of less than 0.

06. Moreover, when the positive electrode is analyzed by powder X-ray diffraction using CuKα1 rays, the XRD pattern of the positive electrode active material having a charge depth of 0.7 to 0.9 has a first diffraction peak at 19.30±0.20° 2θ and a second diffraction peak at 45.55±0.10° 2θ.

7. A lithium ion secondary battery comprising a positive electrode containing a positive electrode active material, in, The positive electrode active material comprises lithium cobaltate, and the lithium cobaltate comprises magnesium, aluminum and nickel. The number of nickel atoms in the positive electrode active material is not less than 0.05% and not more than 4% of the number of cobalt atoms. The magnesium concentration in the surface layer of the positive electrode active material is higher than the magnesium concentration in the interior of the positive electrode active material. The positive electrode active material has an O3 type crystal structure and a charge depth of less than 0.

06. Moreover, when the positive electrode is analyzed by powder X-ray diffraction using CuKα1 rays, the XRD pattern of the positive electrode active material having a charge depth of 0.7 to 0.9 has a first diffraction peak at 19.30±0.20° 2θ and a second diffraction peak at 45.55±0.10° 2θ.

8. A lithium ion secondary battery comprising a positive electrode containing a positive electrode active material, in, The positive electrode active material comprises lithium cobaltate, and the lithium cobaltate comprises magnesium, aluminum and nickel. Moreover, when the positive electrode is analyzed by powder X-ray diffraction, the crystalline structure of the positive electrode active material in a battery including the positive electrode and a lithium counter electrode charged at 4.7V belongs to the space group R-3m, wherein the coordinates of cobalt and oxygen are represented by (0,0,0.5) and (0,0,x), respectively, where 0.20≤x≤0.

25.

9. A lithium ion secondary battery comprising a positive electrode containing a positive electrode active material, in, The positive electrode active material comprises lithium cobaltate, and the lithium cobaltate comprises magnesium, aluminum and nickel. Furthermore, when the positive electrode is analyzed by powder X-ray diffraction using CuKα1 rays, the XRD pattern of the positive electrode active material in a state where a battery including the positive electrode and a lithium counter electrode is charged at 4.7 V has a first diffraction peak at 2θ of 19.30±0.20° and a second diffraction peak at 2θ of 45.55±0.10°.

10. The lithium ion secondary battery according to any one of claims 2 to 7, in, When all the lithium that can be inserted and removed is inserted, the depth of charge is 0. Furthermore, when all the lithium that can be inserted and removed in the positive electrode active material is removed, the depth of charge is 1.

11. The lithium ion secondary battery according to any one of claims 2 to 4, in, When the XRD pattern of the positive electrode active material having a depth of charge of 0.7 or more and 0.9 or less is subjected to Rietveld analysis, the pseudo-spinel crystal structure accounts for 60 wt % or more.

12. The lithium ion secondary battery according to any one of claims 5 to 7, in, When the XRD pattern of the positive electrode active material having a depth of charge of 0.7 or more and 0.9 or less is subjected to Rietveld analysis, the pseudo-spinel crystal structure accounts for 60 wt % or more.

13. The lithium ion secondary battery according to claim 8, in, When a Rietveld analysis is performed on an XRD pattern of the positive electrode active material in a state where a battery including the positive electrode and a lithium counter electrode is charged at 4.7 V, a pseudo-spinel crystal structure accounts for 60 wt % or more.

14. The lithium ion secondary battery according to claim 9, in, When a Rietveld analysis is performed on an XRD pattern of the positive electrode active material in a state where a battery including the positive electrode and a lithium counter electrode is charged at 4.7 V, a pseudo-spinel crystal structure accounts for 60 wt % or more.

15. The lithium ion secondary battery according to any one of claims 1, 2, 5, 8 and 9, in, The surface layer of the positive electrode active material contains fluorine.

16. The lithium ion secondary battery according to any one of claims 3, 4, 6 and 7, in, The surface layer of the positive electrode active material contains fluorine.

17. The lithium ion secondary battery according to any one of claims 1, 2, 5, 8 and 9, in, The surface layer portion of the positive electrode active material is a region extending from the surface of the positive electrode active material to 10 nm.

18. The lithium ion secondary battery according to any one of claims 3, 4, 6 and 7, in, The surface layer portion of the positive electrode active material is a region extending from the surface of the positive electrode active material to 10 nm.

19. The lithium ion secondary battery according to any one of claims 1 to 9, in, The positive electrode includes a conductive additive, and Furthermore, the conductive additive includes carbon nanotubes.

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