Secondary battery

Abstract

To provide a secondary battery excellent in impact resistance, and a manufacturing method thereof.SOLUTION: A positive electrode, a negative electrode, and an exterior body that accommodates the positive electrode and the negative electrode, wherein the positive electrode and the exterior body, and the negative electrode and the exterior body are connected to each other at at least two locations on one side of the exterior body, the value of the interfacial resistance is 2.0 * 10-3 Ω·cm2 or less, the value of the interfacial resistance being obtained by performing inverse problem analysis using measured potentials obtained by measuring the surfaces of the negative electrode active material layers with a plurality of measuring probes and calculated potentials calculated by a model of electrodes composed of the current collector layers, the active material layers, and the interfacial resistance layers.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] One embodiment of the present invention relates to an object, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, a manufacture, or a composition of matter. One embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, an electronic device, or a manufacturing method thereof.

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

[0003] In this specification, the term "power storage device" refers to elements and devices in general that have a power storage function, including, for example, power storage devices such as lithium ion batteries (also called secondary batteries), lithium ion capacitors, and electric double layer capacitors. [Background technology]

[0004] Development of various secondary battery energy storage devices, such as lithium-ion batteries, lithium-ion capacitors, and air batteries, is currently underway. Lithium-ion batteries, which offer high power output and high energy density, are used in a variety of applications, including mobile phones, smartphones, tablets, and laptop computers, as well as portable music players, digital cameras, medical devices, clean-energy vehicles (e.g., hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs)), agricultural machinery, mopeds (including electrically assisted bicycles), motorcycles, electric wheelchairs, electric carts, ships, submarines, aircraft, rockets, satellites, space probes, planetary probes, and spacecraft. Demand for lithium-ion batteries has expanded rapidly alongside the development of the semiconductor industry, making them an essential rechargeable energy source for today's information-driven society.

[0005] Wearable devices have been actively developed in recent years. Because wearable devices are worn, they are preferably curved to fit the curves of the body or to bend in accordance with body movements. Therefore, it is desirable for secondary batteries installed in wearable devices to be flexible, just like displays and other housings.

[0006] Furthermore, even in devices other than wearable devices, it is preferable for secondary batteries to be flexible, since being able to deform the secondary battery when it is installed can increase the efficiency of utilization of the internal space of the device.

[0007] As examples of flexible secondary batteries, Patent Documents 1 and 2 disclose electrochemical devices (e.g., secondary batteries, capacitors, etc.) that are covered with a metal laminate and have a structure that allows them to be easily curved and maintained in a curved state.

[0008] There is also an increasing demand for electronic devices that can withstand harsh environments, specifically low temperatures (e.g., -50°C) or high temperatures (e.g., 100°C), and are intended for use over a wide range of operating temperatures. Examples include observation equipment around the Antarctic or Arctic, seismometers installed around the craters of active volcanoes, satellites orbiting the Earth, and probes intended for use in investigating other planets.

[0009] It is also desirable for the seismometer or probe to be highly resistant to shocks, such as those caused by being dropped. It would be convenient if the seismometer could be dropped from an unmanned aircraft and installed near a crater where it would be dangerous for humans to carry the measuring device. There are also plans to drop a penetrator from a satellite orbiting the planet to install a seismometer from the planet's surface to its interior. A penetrator is an exploration probe equipped with a dual-axis seismometer.

[0010] Conventionally, 18650 type cylindrical batteries have been used as the power source for such electronic devices. Conventionally, primary batteries have been used for one-time use, and are disposable after a short period of use and function as a power source.

[0011] However, when considering long-term measurements or weight restrictions during transportation, it is desirable to use secondary batteries that can be charged using solar cells. It is also desirable to be able to collect the measuring equipment after installation and reuse it.

[0012] The present applicant has disclosed in Patent Documents 3 and 4 a strong secondary battery that can bend even when an external force is applied thereto.

[0013] An electrode used in a secondary battery is composed of a metal foil (also called a current collector) and an active material layer formed by applying an active material to one or both sides of the metal foil. Patent Documents 5 and 6 disclose a method for determining the quality of the adhesion between the metal foil and the active material layer, in which the resistance at the interface between the metal foil and the active material layer is measured and the quality of the adhesion between the metal foil and the active material layer is determined from the measured value. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Patent Publication No. 2004-241250 [Patent Document 2] Patent Publication No. 2018-6336 [Patent Document 3] Patent Publication No. 2015-233004 [Patent Document 4] Patent Publication No. 2016-139609 [Patent Document 5] Patent Publication No. 2015-206754 [Patent Document 6] Patent Publication No. 2016-027311 Summary of the Invention [Problem to be solved by the invention]

[0015] One type of astronomical observation device is a rocket-shaped probe called a penetrator, which performs autonomous observations. The secondary batteries installed in penetrators are required to have high impact resistance. While it is possible to enclose the secondary batteries with thick metal plates to provide impact resistance, this would significantly increase the total weight of the penetrator.

[0016] Conventional 18650-type cylindrical lithium-ion batteries are constructed by filling a cylindrical can with electrolyte and connecting the wound body inside the can to external terminals. Because a large amount of electrolyte is required to fill the can, there is a risk that the wound body may shift position due to impact. Temperature changes also pose a risk of the electrolyte expanding or gasifying. Therefore, secondary batteries using conventional cylindrical cans are vulnerable to drop impacts and are at risk of leakage.

[0017] Furthermore, because all-solid-state batteries are at least partially made of ceramics, they are brittle when subjected to impact, and if they crack, they lose conductivity and may become unusable.

[0018] Therefore, a laminated battery that uses a lightweight laminate film as an exterior body, rather than a cylindrical or coin-shaped battery, is preferable as a secondary battery with high impact resistance. However, even in a laminated battery, depending on the battery structure, problems such as electrodes being displaced inside the battery when subjected to a strong impact, poor adhesion between the metal foil and the active material layer, causing the active material layer to peel off from the current collector in the electrode inside the battery, and gaps between electrodes being partially widened inside the battery may occur.

[0019] In view of the above problems, an object of one embodiment of the present invention is to provide a secondary battery having high impact resistance.

[0020] Another object of one embodiment of the present invention is to provide a secondary battery with a novel structure. Specifically, an object of one embodiment of the present invention is to provide a secondary battery with a novel flexible structure. Another object of one embodiment of the present invention is to provide a novel power storage device, an electronic device equipped with the novel secondary battery, or the like.

[0021] Note that the description of these problems does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily need to solve all of these problems. Note that problems other than these will become apparent from the description in the specification, drawings, claims, etc., and it is possible to extract other problems from the description in the specification, drawings, claims, etc. [Means for solving the problem]

[0022] To solve the above problems, a secondary battery according to one embodiment of the present invention has a structure in which a positive electrode and an outer casing are connected at two locations, and a negative electrode and an outer casing are connected at two locations. The secondary battery according to one embodiment of the present invention also has an electrode in which the current collector and the active material layer have high adhesion. Regarding the adhesion between the current collector and the active material layer, the resistance (interface resistance) at the interface between the current collector and the active material layer can be used as an index of adhesion. For example, in a negative electrode, if the value of the interface resistance between the negative electrode current collector and the negative electrode active material layer is 3.0×10 -3 Ω cm 2 If it is less than or equal to 2.0×10, it is preferably -3 Ω cm 2 The case where the thickness is less than or equal to the above is preferable because the negative electrode current collector and the negative electrode active material layer have good adhesion to each other.

[0023] One embodiment of the present invention is a secondary battery including a negative electrode and an exterior body that houses the negative electrode, the negative electrode and the exterior body being connected to each other at at least two locations on one side of the exterior body, and the negative electrode including a negative electrode current collector, a coating layer on the negative electrode current collector, and a negative electrode active material layer on the coating layer.

[0024] Alternatively, one embodiment of the present invention is a secondary battery including a positive electrode, a negative electrode, and an exterior body that houses the positive electrode and the negative electrode, wherein the positive electrode and the exterior body are connected to each other at at least two points on one side of the exterior body, and the negative electrode and the exterior body are connected to each other at at least two points on one side of the exterior body, and the negative electrode includes a negative electrode current collector, a coating layer on the negative electrode current collector, and a negative electrode active material layer on the coating layer.

[0025] In the above, the value of the interface resistance between the negative electrode current collector and the negative electrode active material layer is 2.0 × 10 -3 Ω cm 2 The value of the interfacial resistance is obtained by performing an inverse problem analysis using a measured potential obtained by measuring the surface of the negative electrode active material layer with a plurality of measurement probes and a calculated potential calculated by an electrode model composed of a current collector layer, an active material layer, and an interfacial resistance layer.

[0026] The coating layer preferably contains carbon nanotubes and carbon black. [Effects of the Invention]

[0027] According to one embodiment of the present invention, a secondary battery having high impact resistance can be provided.

[0028] According to one embodiment of the present invention, a secondary battery with a novel structure can be provided. More specifically, a secondary battery with a novel flexible structure can be provided. According to one embodiment of the present invention, a novel power storage device, an electronic device including the novel secondary battery, or the like can be provided.

[0029] Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of these effects. Note that effects other than these will become apparent from the description in the specification, drawings, claims, etc., and it is possible to extract other effects from the description in the specification, drawings, claims, etc. [Brief explanation of the drawings]

[0030] [Figure 1] 1A and 1B are perspective views illustrating an example of the configuration of a secondary battery. [Figure 2] FIG. 2A is a top view illustrating an example of the configuration of a secondary battery, and FIG. 2B is a cross-sectional view illustrating an example of the configuration of a secondary battery. [Figure 3] 3A to 3C are cross-sectional views illustrating examples of the configuration of a secondary battery. [Figure 4] 4A to 4C are top views illustrating examples of the configuration of a secondary battery. [Figure 5] FIG. 5A is a top view illustrating a configuration example of a positive electrode, and FIGS. 5B and 5C are cross-sectional views illustrating the configuration example of a positive electrode. [Figure 6] FIG. 6A is a top view illustrating a structural example of a negative electrode, and FIGS. 6B and 6C are cross-sectional views illustrating the structural example of a negative electrode. [Figure 7] FIG. 7 is a diagram showing an example of a production flow of the coating layer. [Figure 8] FIG. 8 is a diagram showing an example of a manufacturing flow of a secondary battery. [Figure 9] Figures 9(A1) and 9(A2) are oblique views of the positive electrode, Figure 9(A3) is a cross-sectional view of the positive electrode, Figures 9(B1) and 9(B2) are oblique views of the pre-doping electrode, and Figure 9(B3) is a cross-sectional view of the pre-doping electrode. [Figure 10] FIG. 10(A1) is a perspective view of the positive electrode, FIG. 10(A2) is a perspective view of the pre-doping electrode, FIG. 10(A3) is a perspective view of the negative electrode, and FIG. 10(B) is a perspective view of the laminate and the exterior body. [Figure 11] FIG. 11(A) is a side view of the liquid injection process, FIG. 11(B) is a top view of the secondary battery cell, and FIG. 11(C) is a cross-sectional view of the secondary battery cell. [Figure 12] FIG. 12(A) is a side view showing the exterior body when it is being cut, and FIG. 12(B) is a side view immediately after the pre-doping electrode has been pulled out. [Figure 13] FIG. 13(A) is a perspective view of the secondary battery, and FIG. 13(B) is a cross-sectional view of the secondary battery. [Figure 14] 14A to 14C are diagrams illustrating a method for manufacturing a secondary battery. [Figure 15] 15(A) and 15(B) are diagrams illustrating examples of connections between a secondary battery and an electronic device. [Figure 16] 16(A) to 16(C) are diagrams for explaining connection examples when a secondary battery is mounted on a penetrator. [Figure 17] 17(A) and 17(B) are cross-sectional views illustrating the positive electrode active material. [Figure 18] 18A to 18F are cross-sectional views illustrating the positive electrode active material. [Figure 19] FIG. 19 is a diagram illustrating the crystal structure of the positive electrode active material. [Figure 20] FIG. 20 is a diagram illustrating the crystal structure of a conventional positive electrode active material. [Figure 21] FIG. 21 shows the XRD pattern calculated from the crystal structure. [Figure 22] FIG. 22 shows the XRD pattern calculated from the crystal structure. [Figure 23] FIG. 23 is a diagram illustrating an example of the configuration of a current collector. [Figure 24] FIG. 24 is a diagram illustrating a method for producing a negative electrode active material layer. [Figure 25] FIG. 25 is a diagram illustrating a method for producing a negative electrode active material layer. [Figure 26] FIG. 26 is a diagram illustrating a film processing method. [Figure 27] 27(A) to 27(E) are diagrams for explaining a film processing method. [Figure 28] 28(A) and 28(B) are diagrams illustrating a method for processing a film. [Figure 29] 29A to 29D are diagrams illustrating a method for manufacturing a positive electrode active material. [Figure 30]Figure 30(A) is a schematic cross-sectional view of the heating furnace, Figure 30(B) is a top view of the lid, and Figure 30(C) is a schematic cross-sectional view explaining the height of the container, lid, and object to be heated. [Figure 31] Figure 31(A) is a diagram illustrating an example of a manufacturing apparatus, and Figure 31(B) is a diagram illustrating the arrangement of rollers. [Figure 32] FIG. 32 is a diagram illustrating an example of a manufacturing apparatus. [Figure 33] FIG. 33 is a diagram illustrating a method for manufacturing a positive electrode active material. [Figure 34] 34A to 34C are diagrams illustrating a method for manufacturing a positive electrode active material. [Figure 35] FIG. 35 is a phase diagram showing the relationship between the composition of lithium fluoride and magnesium fluoride and the temperature. [Figure 36] FIG. 36 is a diagram illustrating the results of the DSC analysis. [Figure 37] 37(A) to 37(H) are diagrams illustrating an example of an electronic device. [Figure 38] 38A to 38D are diagrams illustrating examples of electronic devices. [Figure 39] 39A to 39C are diagrams illustrating an example of an electronic device. [Figure 40] 40(A) to 40(C) are diagrams illustrating an example of a vehicle. [Figure 41] 41(A) to 41(D) are diagrams illustrating an example of space equipment. [Figure 42] FIG. 42 is a diagram showing the interface resistance of the example. [Figure 43] FIG. 43 is a diagram showing the charge-discharge cycle characteristics of the example. DETAILED DESCRIPTION OF THE INVENTION

[0031] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be readily understood by those skilled in the art that various modifications can be made to the embodiments and details. Furthermore, the present invention should not be interpreted as being limited to the description of the embodiments shown below.

[0032] For ease of understanding, the position, size, range, etc. of each component shown in the drawings etc. may not represent the actual position, size, range, etc. Therefore, the disclosed invention is not necessarily limited to the position, size, range, etc. disclosed in the drawings etc.

[0033] In addition, in the drawings illustrating the present invention, some components (e.g., the ratio of the size and thickness of the electrodes) may be exaggerated to facilitate understanding, and some components may be omitted to avoid cluttering the drawings.

[0034] Ordinal numbers such as "first," "second," and "third" are used to avoid confusion of components.

[0035] In this specification, "parallel" refers to a state in which two straight lines are arranged at an angle of -10° or more and 10° or less. Therefore, it also includes a state in which the angle is -5° or more and 5° or less. Furthermore, "substantially parallel" or "roughly parallel" refers to a state in which two straight lines are arranged at an angle of -30° or more and 30° or less.

[0036] In this specification, "perpendicular" refers to a state in which two straight lines are arranged at an angle of 80° or more and 100° or less. Therefore, this also includes cases in which the angle is 85° or more and 95° or less. Furthermore, "substantially perpendicular" or "roughly perpendicular" refers to a state in which two straight lines are arranged at an angle of 60° or more and 120° or less.

[0037] (Embodiment 1) In this embodiment, with reference to FIGS. 1 to 6C, a structural example of a flexible secondary battery (also referred to as a flexible battery, a bendable battery, a curved battery, or a bendable battery) according to one embodiment of the present invention, which has high impact resistance, will be described.

[0038] [Secondary battery] 1A to 6C are schematic diagrams of a secondary battery 10 of one embodiment of the present invention. Fig. 1A is a perspective view of the secondary battery 10. Fig. 1B is a perspective view showing the internal structure of the secondary battery 10 in a dashed line portion A in Fig. 1A.

[0039] 1(A) is a schematic diagram of a flexible secondary battery 10, showing the secondary battery 10 curved in one direction. The secondary battery 10 has a first positive electrode lead 23A, a second positive electrode lead 23B, a first negative electrode lead 33A, and a second negative electrode lead 33B extending from the inside to the outside of a space (also referred to as the internal space of the secondary battery 10) enclosed by an exterior body 50 and a sealing portion 52 formed by bonding the exterior bodies 50 together.

[0040] The first positive electrode lead 23A, the second positive electrode lead 23B, the first negative electrode lead 33A, and the second negative electrode lead 33B are connected to a sealing portion 52 on a first side of the exterior body 50.

[0041] The exterior body 50 has a second side opposite the first side. The secondary battery 10 has a fixing portion 55 that clamps the exterior body 50 from the exterior side of the secondary battery 10 in an area including the second side. Note that the fixing portion 55 preferably fixes the exterior body 50 so as to eliminate the internal space of the secondary battery 10 that overlaps with the fixing portion 55. Fixing the exterior body 50 in this manner by the fixing portion can reduce the excess internal space of the secondary battery 10.

[0042] Fig. 1(B) is a perspective view showing the internal structure of the secondary battery 10 at dashed line portion A in Fig. 1(A). In Fig. 1(B), the exterior body 50 and the like are omitted. Fig. 2(A) is a top view of the secondary battery 10, and Fig. 2(B) is a cross-sectional view showing the cut surface between dashed and dotted lines X1-X2 in Fig. 2(A).

[0043] 1(B), 2(A), and 2(B), a secondary battery 10 has a positive electrode 11, a negative electrode 12, and a separator (not shown) in an internal space. The positive electrode 11 and the negative electrode 12 are stacked with the separator interposed therebetween, and the stacked positive electrode 11, negative electrode 12, and separator are called a laminate 60.

[0044] 1(B) and 2(A), the laminate 60 has, in the internal space of the secondary battery 10, a first protrusion 11A and a second protrusion 11B formed by protruding portions of the positive electrode 11, and a third protrusion 11C and a fourth protrusion 11D formed by protruding portions of the negative electrode 12. The first protrusion 11A, the second protrusion 11B, the third protrusion 11C, and the fourth protrusion 11D protrude from the laminate 60 toward the first side. Preferably, the first protrusion 11A, the second protrusion 11B, the third protrusion 11C, and the fourth protrusion 11D are arranged so as not to overlap with each other.

[0045] 1(B) and 2(A), the positive electrode 11 is connected to the first positive electrode lead 23A at the first protrusion 11A and to the second positive electrode lead 23B at the second protrusion 11B. The negative electrode 12 is connected to the first negative electrode lead 33A at the third protrusion 11C and to the second negative electrode lead 33B at the fourth protrusion 11D. In other words, the positive electrode 11 is connected to the sealing portion 52 of the exterior body 50 via the first positive electrode lead 23A at the first protrusion 11A and to the sealing portion 52 of the exterior body 50 via the second positive electrode lead 23B at the second protrusion 11B. Similarly, the negative electrode 12 is connected to the sealing portion 52 of the exterior body 50 via the first negative electrode lead 33A at the third protrusion 11C, and is connected to the sealing portion 52 of the exterior body 50 via the second negative electrode lead 33B at the fourth protrusion 11D. A sealant 56 may be provided at the connection between the lead and the sealing portion 52. In this case, the lead and the sealing portion 52 are connected via the sealant 56.

[0046] In other words, the positive electrode 11 is connected to the exterior body 50 at two points on the first side via the first positive electrode lead 23A and the second positive electrode lead 23B. Similarly, the negative electrode 12 is connected to the exterior body 50 at two points on the first side via the first negative electrode lead 33A and the second negative electrode lead 33B.

[0047] 2(A) and 2(B), the fixing portion 55 fixes the exterior body 50 in a region including the second side opposite the first side. At this time, the fixing portion 55 is preferably provided so as not to overlap with the laminate 60. In other words, the fixing portion 55 preferably does not fix the laminate 60. In other words, the fixing portion 55 preferably does not fix the positive electrode 11, the negative electrode 12, or the separator 13.

[0048] 3(A) to 3(C) will be used to describe the effect of providing a fixing portion 55 as a configuration of the secondary battery 10. Fig. 3(A) is a schematic cross-sectional view showing an enlarged view of the dashed line portion B in Fig. 2(B). Figs. 3(B) and 3(C) are schematic cross-sectional views of a case where the fixing portion 55 is not provided at the dashed line portion B.

[0049] As shown in FIG. 3(B), when the fixing portion 55 is not provided, a space C is formed at the position indicated by the dashed line. Because the exterior body 50 of one embodiment of the present invention is made of a flexible material, this space C may deform into a shape like the space C' shown in FIG. 3(C) when the secondary battery is subjected to an external force such as a large impact. When a space like the space C' is formed inside the secondary battery, as shown in FIG. 3(C), a part of the electrode (positive electrode or negative electrode) inside the secondary battery may deform so as to separate from the laminate 60, which may inhibit the electrochemical reaction (also referred to as the battery reaction) inside the secondary battery.

[0050] On the other hand, as shown in FIG. 3(A), the secondary battery 10 of one embodiment of the present invention has the fixing portion 55 as described above, and therefore has little excess space such as the space C shown in FIG. 3(B). Therefore, even if the secondary battery 10 is subjected to an external force such as a large impact, deformation of the internal space of the secondary battery 10 is suppressed. Therefore, deformation of a part of the electrode (positive electrode or negative electrode) so as to separate from the stack 60 can be suppressed. As a result, even if the secondary battery 10 of one embodiment of the present invention is subjected to an external force such as a large impact, inhibition of the battery reaction can be suppressed. In other words, the secondary battery 10 of one embodiment of the present invention can have high impact resistance due to the fixing portion 55.

[0051] Using Figures 4(A) and 4(B), the effects of connecting the positive electrode 11 and the outer casing 50 at two points and connecting the negative electrode 12 and the outer casing 50 at two points as described above in the configuration of the secondary battery 10 will be explained.

[0052] FIG. 4(A) is a schematic top view partially illustrating the internal structure of a secondary battery in which an electrode (negative electrode 12a) and an outer casing 50 are connected at one location. The double-headed arrow in FIG. 4(A) indicates the direction in which the electrode position changes when the secondary battery is subjected to an impact. In such a case, the electrode position may change in a direction rotating around the point where the electrode and the outer casing are connected. If the electrode position changes as shown in FIG. 4(A), there is a risk of a malfunction in which the positive electrode and the negative electrode do not face each other. There is also a risk of a malfunction in which the positive electrode and the negative electrode come into direct contact with each other, causing an internal short circuit in the secondary battery.

[0053] On the other hand, as shown in FIG. 4B , the secondary battery 10 of one embodiment of the present invention has a structure in which the electrode (negative electrode 12) and the exterior body 50 are connected at two locations, as described above. Therefore, the position of the electrode can be prevented from shifting in the direction indicated by the double-headed arrow in FIG. 4B . As a result, the secondary battery 10 of one embodiment of the present invention can prevent inhibition of the battery reaction even when subjected to an external force such as a large impact. That is, the secondary battery 10 of one embodiment of the present invention has a structure in which the electrode and the exterior body are connected at two locations, thereby achieving high impact resistance. The positive and negative electrodes are preferably connected in the following order on one side of the exterior body, from one end to the other, as shown in FIG. 2A : the first positive electrode lead 23A, the first negative electrode lead 33A, the second positive electrode lead 23B, and the second negative electrode lead 33B. In other words, the two positions where the positive electrode and the negative electrode are connected are preferably not adjacent positions but are positioned apart, which makes it possible to achieve high impact resistance.

[0054] Furthermore, it is preferable that one side of the exterior body to which the electrodes are fixed be arranged parallel to the direction in which a large impact is applied. In other words, it is preferable that the protrusions to which the positive electrode lead and the negative electrode lead are connected be arranged perpendicular to the direction in which a large impact is applied. By arranging the secondary battery 10 in this manner, even when subjected to an external force such as a large impact, changes in the positions of the positive and negative electrodes are suppressed, and the laminate 60 is less likely to be distorted.

[0055] Furthermore, to configure the secondary battery 10 with high impact resistance, the laminate 60 may be fixed using adhesive tape 61, as shown in Fig. 4(C). In this case, it is preferable that the adhesive tape 61 is not provided in the laminate 60 at a position close to the second side of the exterior body 50, as shown in Fig. 4(C).

[0056] <Electrode> The secondary battery 10 has a positive electrode 11 and a negative electrode 12 as electrodes. FIGS. 5(A) to 5(C) are diagrams illustrating the positive electrode 11, and FIGS. 6(A) to 6(C) are diagrams illustrating the negative electrode 12. FIG. 5(A) is a top view of the positive electrode 11, and FIGS. 5(B) and 5(C) are cross-sectional views taken along dashed line P1-P2 in FIG. 5(A). FIG. 6(A) is a top view of the negative electrode 12, and FIGS. 6(B) and 6(C) are cross-sectional views taken along dashed line P3-P4 in FIG. 6(A).

[0057] As shown in FIG. 5(A), the positive electrode 11 has a positive electrode current collector 21 and a positive electrode active material layer 22. In the positive electrode 11, the positive electrode active material layer 22 may be provided directly on the positive electrode current collector 21 as shown in FIG. 5(B). Alternatively, as shown in FIG. 5(C), an intermediate layer 24 may be provided between the positive electrode current collector 21 and the positive electrode active material layer 22. The intermediate layer 24 may also be referred to as an undercoat layer, anchor coat layer, or coat layer. The intermediate layer 24 contains a conductive material and / or a binder. Providing an appropriate intermediate layer 24 is preferable because it improves the adhesion and electronic conductivity between the positive electrode current collector 21 and the positive electrode active material layer 22.

[0058] As shown in FIG. 6(A), the negative electrode 12 has a negative electrode current collector 31 and a negative electrode active material layer 32. In the negative electrode 12, the negative electrode active material layer 32 may be provided directly on the negative electrode current collector 31 as shown in FIG. 6(B). Alternatively, as shown in FIG. 6(C), an intermediate layer 34 may be provided between the negative electrode current collector 31 and the negative electrode active material layer 32. The intermediate layer 34 may also be referred to as an undercoat layer, anchor coat layer, or coat layer. The intermediate layer 34 includes a conductive material and a binder. Providing an appropriate intermediate layer 34 is preferable because it improves the adhesion and electronic conductivity between the negative electrode current collector 31 and the negative electrode active material layer 32.

[0059] <Method for producing the coating layer> An example of a method for producing the coating layers (intermediate layer 24, intermediate layer 34) will be described with reference to FIG.

[0060] In step S1 of FIG. 7, a conductive material, a binder, a thickener, and a solvent are prepared.

[0061] As the conductive material, for example, one or more of the following can be used: carbon black such as acetylene black (AB) and furnace black; graphite such as artificial graphite and natural graphite; carbon fiber such as carbon nanofiber and carbon nanotube (CNT); graphene; and graphene compounds.

[0062] As the binder, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, etc. Also, as the binder, fluororubber can be used.

[0063] Furthermore, it is preferable to use materials such as polystyrene, polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate (PMMA)), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose as the binder.

[0064] It may also be preferable to use a thickener in addition to the binder. For example, it is preferable to use a water-soluble polymer as the thickener. For example, polysaccharides can be used as the water-soluble polymer. For example, cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, or starch can be used as the polysaccharide. If a thickener is not required, no thickener is prepared in step S1.

[0065] Next, as shown in step S2 of FIG. 7, the materials prepared in step S1 are mixed. A rotation-revolution type agitator can be used for mixing. The mixing method is not limited to the above method, and any known mixing method can be used as appropriate. Furthermore, ultrasonic treatment can be performed to improve the dispersibility of the conductive material during mixing. The ultrasonic treatment can be performed at a frequency of 25 kHz or more and 40 kHz or less.

[0066] By carrying out the above-mentioned mixing, the mixture of step S3 in Fig. 7 is obtained. The mixture of step S3 is also called a slurry.

[0067] Next, as shown in step S4 of FIG. 7, a metal foil is prepared. The type of metal foil is appropriately selected depending on whether the current collector with a coating layer prepared in this preparation flow is to be used for a positive electrode or a negative electrode. For example, when preparing a current collector with a coating layer to be used for a positive electrode, aluminum foil may be prepared in step S4. Alternatively, when preparing a current collector with a coating layer to be used for a negative electrode, copper foil may be prepared in step S4. Details of current collectors that can be used for positive and negative electrodes will be described later.

[0068] Next, as shown in step S5 of Fig. 7, the mixture (slurry) from step S3 is applied to the metal foil prepared in step S4. For application, a slot die method, a gravure method, a blade method, or a combination thereof can be used. Alternatively, a continuous coater or the like can be used for application.

[0069] Next, drying is performed to remove the solvent from the coated mixture as shown in step S6 of Fig. 7. The drying method is not particularly limited, and can be performed by methods such as ventilation drying and reduced pressure (vacuum) drying.

[0070] Through the above steps, a current collector with a coating layer can be obtained as shown in step S7 of Fig. 7. In addition to the coating method described above, the coating layer may also be formed by spraying the mixture of step S3.

[0071] 5(A) and 5(C), the current collector with a coating layer used for the positive electrode has a configuration including a positive electrode current collector 21 and an intermediate layer 24. When a positive electrode active material layer 22 is provided on the positive electrode current collector 21, the adhesion between the positive electrode current collector 21 and the positive electrode active material layer 22 can be increased when the intermediate layer 24 is present compared to when the intermediate layer 24 is not present.

[0072] 6(A) and 6(C), the current collector with a coating layer used for the negative electrode has a configuration including a negative electrode current collector 31 and an intermediate layer 34. When a negative electrode active material layer 32 is provided on the negative electrode current collector 31, the adhesion between the negative electrode current collector 31 and the negative electrode active material layer 32 can be increased when the intermediate layer 34 is present compared to when the intermediate layer 34 is not present.

[0073] The adhesion at the interface between the current collector and the active material layer can be evaluated using an electrode resistance measuring device that employs the techniques described in, for example, Patent Document 5 and Patent Document 6. This evaluation method can calculate the interfacial resistance between the current collector and the active material layer, and it can be determined that the lower the interfacial resistance between the current collector and the active material layer, the higher the adhesion.

[0074] <Electrode resistance measurement> As the electrode resistance measuring device, an "Electrode Resistance Measuring Instrument XF057" or "Electrode Resistance Measuring System RM2610" manufactured by Hioki E.E. Corporation can be used, but the device is not limited to these as long as it is capable of performing similar measurements and analyses.

[0075] The electrode resistance can be measured, for example, using the following equipment and conditions. Measuring device: Hioki E.E. Corporation electrode resistance measuring instrument XF057 Measurement probe: 46 pins Measurement current: 1mA Voltage range: 0.5V Measurement speed: Normal

[0076] In the above-mentioned electrode resistance measurement, when a current is passed between two of the multiple measurement probes in contact with the surface of the active material layer of the electrode sample, a potential distribution is generated on the surface of the electrode sample due to the current distribution. This surface potential distribution is obtained by measuring the potential at multiple points using multiple measurement probes other than the above-mentioned two measurement probes, and the actual potential is obtained from various directions by changing the combination of the two measurement probes through which the current is passed.

[0077] An inverse problem analysis is performed using the actual potential measured in this way and a calculated potential calculated using an electrode model consisting of a current collector layer, an active material layer, and an interfacial resistance layer. In the electrode model, the thickness of the current collector, the thickness of the active material layer, and the volume resistivity of the current collector are assumed to be known values, but the volume resistivity and interfacial resistance of the active material layer are assumed to be unknown values.

[0078] Specifically, the analysis method involves performing an inverse problem analysis in which unknown values ​​of the volume resistivity and interfacial resistance of the active material layer are appropriately changed to obtain a calculated potential, and the difference between the calculated potential and the measured potential is reduced. In this way, the volume resistivity and interfacial resistance of the active material layer of the electrode sample can be calculated.

[0079] As described above, the value of the interface resistance can be obtained by performing an inverse problem analysis using the measured potential obtained by measuring the surface of the active material layer of the electrode sample using multiple measurement probes and the calculated potential calculated by an electrode model consisting of a collector layer, an active material layer, and an interface resistance layer.

[0080] The value of the interface resistance obtained by such measurements and analysis is 3.0 × 10 -3 Ω cm 2 Preferably, it is 2.0 x 10 or less. -3 Ω cm 2 An electrode having such an interface resistance value can be said to have good adhesion between the current collector and the active material layer and high electronic conductivity, and is suitable as an electrode for use in a secondary battery having high impact resistance.

[0081] A method for manufacturing the above-described secondary battery 10 will be described with reference to FIGS. 8 to 14C. FIGS. 8 to 14C illustrate a method for manufacturing a secondary battery having a pre-doped negative electrode as an example of a method for manufacturing a secondary battery. However, the secondary battery 10 of one embodiment of the present invention may use a negative electrode that is not pre-doped. Note that in this specification and the like, pre-doping refers to a process performed so that carrier ions (e.g., lithium ions or sodium ions) remain in the negative electrode of the secondary battery even when the secondary battery is in a discharged state.

[0082] <How to make a battery> A method for manufacturing the secondary battery 10 of one embodiment of the present invention using the above-described pre-doped negative electrode 12 will be described with reference to FIGS.

[0083] FIG. 8 is a flow chart showing an example of a method for producing the secondary battery 10.

[0084] First, prepare a positive electrode 11 having a first protrusion and a second protrusion, a negative electrode 12 having a third protrusion and a fourth protrusion, and a pre-doping electrode 45. In this embodiment, an example of a secondary battery 10 is shown in which a single-sided coated positive electrode or negative electrode is used and a set of the positive electrode 11 and the negative electrode 12 is enclosed in an outer casing 50, but this is not particularly limited, and a process can be used in which a double-sided coated positive electrode or negative electrode is used and a plurality of sets are enclosed in a single outer casing.

[0085] The positive electrode 11 and the pre-doping electrode 45 can be formed by coating a positive electrode active material layer 22 on one side of a current collector. Here, the first protrusion and the second protrusion are provided on the positive electrode current collector 21 as shown in FIG. 9(A1). It is preferable that the first protrusion and the second protrusion of the positive electrode 11 do not have the positive electrode active material layer 22. As shown in FIG. 8, the pre-doping electrode 45 can be formed in step S21, and the positive electrode 11 can be formed separately in step S31. However, if the same material and size are used, the positive electrode 11 and the pre-doping electrode 45 can be fabricated in the same process. The current collectors used for the positive electrode 11 and the pre-doping electrode 45 can be made of highly conductive materials such as metals such as stainless steel, gold, platinum, aluminum, and titanium, and alloys thereof. Furthermore, when a current collector is used for the positive electrode 11, it is preferable that the current collector does not dissolve at the potential of the positive electrode 11. Aluminum alloys containing elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, and molybdenum, can also be used. The current collector can be in any suitable shape, such as foil, plate (sheet), mesh, punched metal, or expanded metal. The current collector used has a thickness of 5 μm to 30 μm.

[0086] The positive electrode active material layer 22 may be made of a positive electrode active material, a conductive material, and a binder, which will be described later.

[0087] An example of the positive electrode active material layer 22 will be described. For example, the film thickness of the positive electrode active material layer 22 is determined by the viscosity or components of the slurry to be applied onto the positive electrode current collector 21 or the film-forming conditions of the application device. When preparing the slurry, a positive electrode active material, a binder, a solvent, and a conductive material are mixed. Polyvinylidene fluoride (PVDF) is used as the binder, N-methyl-2-pyrrolidone (NMP) is used as the solvent, and acetylene black is used as the conductive material. The film thickness of the positive electrode active material layer 22 also varies depending on the heating conditions or pressing conditions after application.

[0088] Then, a first film 13a is provided to wrap the positive electrode 11. The first film 13a is processed into a bag shape and fixed with tape or the like. This stage is shown in FIGS. 9(A2) and 9(A3). FIG. 9(A3) is a cross-sectional view of the positive electrode taken along the chain line X1-X2 in FIG. 9(A2). In FIGS. 9(A1) and 9(A2), a positive electrode active material layer is formed on the lower surface of the positive electrode current collector 21, and therefore is not shown.

[0089] 9(A1) and 9(A2) show perspective views of the positive electrode current collector 21 and the separator 13. A single first film 13a that will become the separator 13 is folded, and the end of the first film 13a is fixed as an adhesive region 51a, with the tab region of the positive electrode current collector 21 protruding from the first film 13a, resulting in the state shown in FIG. 9(A2). The separator 13 refers to the region sandwiched between the positive electrode and the negative electrode, and is part of the first film. While FIG. 9(A2) shows an example in which the separator 13 is fixed as an adhesive region 51a on two sides, it may also be fixed by providing adhesive regions on four sides.

[0090] Each current collector is provided with a protruding portion (also called a protruding region, tab portion, or tab region) for connection to a lead, and the positive electrode active material layer 22 or the like is not formed in that region, leaving the conductive surface exposed.

[0091] The pre-doping electrode 45 is also wrapped in a second film 47a in the same manner as the positive electrode 11. FIGS. 9(B1) and 9(B2) show perspective views of the pre-doping electrode 45 and the second film 47a. As shown in FIG. 9(B1), the pre-doping electrode 45 is formed by folding a single second film 47a, fixing the end of the second film 47a as an adhesive region 51b, and causing the tab region of the pre-doping electrode 45 to protrude from the second film 47a, as shown in FIG. 9(B2). The cross-sectional view taken along the chain line X3-X4 in FIG. 9(B2) corresponds to FIG. 9(B3). For the subsequent extraction process, the second film 47a may have a larger area than the first film 13a of the positive electrode, providing a gripping margin. Since the pre-doping electrode 45 is an electrode that is removed during the production of the secondary battery 10, it may have one protrusion, but in order to make it easier to remove the pre-doping electrode 45, it is preferable that it have two protrusions, as shown in Figures 9(B1) and 9(B2).

[0092] Furthermore, it is preferable that the negative electrode current collector 31 used in the negative electrode 12 is not alloyed with carrier ions such as lithium. Specifically, copper or a copper alloy is used as the material for the negative electrode current collector 31. Furthermore, as shown in step S11, the negative electrode active material layer 32 is formed by coating one side of the negative electrode current collector 31. Here, the third protrusion and the fourth protrusion are provided on the negative electrode current collector 31 as shown in FIG. 10(A3). Note that, in the negative electrode 12, it is preferable that the third protrusion and the fourth protrusion do not have the negative electrode active material layer 32. Then, as shown in FIG. 10(A3), the negative electrode leads 33 (negative electrode lead 33A and negative electrode lead 33B) are ultrasonically bonded to the protrusions of the negative electrode current collector 31 on which the negative electrode active material layer 32 is not formed.

[0093] The negative electrode active material is a mixture of carbon particles and silicon-based materials. Silicon has a theoretical capacity of 4200 mAh / g, more than 10 times that of graphite (372 mAh / g). However, a negative electrode made solely of silicon suffers from rapid cycle degradation due to expansion and contraction during charging and discharging. To improve cycle degradation, it is preferable to use nanosilicon, which is made by miniaturizing silicon particles.

[0094] A polymer compound having a carboxy group is used as the binder for the negative electrode 12. Specifically, a polymer having polyacrylic acid is used as the binder.

[0095] As the carbon particles, graphite, carbon having a layer structure like graphite, amorphous carbon, and hard carbon are used. The carbon particles used in this specification specifically refer to graphite particles, which are abundant in nature and therefore inexpensive, making them preferable as a negative electrode active material.

[0096] In the above configuration, the silicon particles refer to silicon powder used as a negative electrode active material for lithium-ion secondary batteries, and have an average particle diameter of approximately 100 nm, which are sometimes called nanosilicon particles. The silicon particles used are preferably prepared by pulverizing silicon raw materials to adjust the particle diameter to a uniform size. The silicon particles may contain at least one of silicon, silicon oxide, and silicon alloy.

[0097] A conductive material may also be added when forming the negative electrode active material layer 32. Acetylene black (also called AB) is a typical carbon material used as a conductive material. Acetylene black is a bulky particle with an average particle diameter of several tens to several hundreds of nanometers, making it difficult to bring it into surface contact with other materials, and point contact is more likely. Therefore, when an active material is mixed with acetylene black, the contact resistance between the active material and acetylene black increases. Using a large amount of acetylene black to reduce the contact resistance reduces the ratio of active material to the entire electrode, resulting in a decrease in the discharge capacity of the secondary battery. Carbon fiber may also be used as a conductive material.

[0098] Acetylene black is a material that tends to aggregate, so it is preferable to mix it so that it is uniformly dispersed. The weight ratio of acetylene black is less than or equal to the weight ratio of silicon particles. Of course, it is possible to prepare a negative electrode without adding the conductive material (acetylene black).

[0099] Through the above steps, the positive electrode 11 wrapped in the first film 13a, the pre-doping electrode 45 wrapped in the second film 47a, and the negative electrode 12 can be prepared.

[0100] Next, in step S100, the positive electrode 11 wrapped in the first film 13a, the pre-doping electrode 45 wrapped in the second film 47a, and the negative electrode 12 are stacked and aligned, and then fixed with adhesive tape to form a laminate. The positive electrode lead 23 (positive electrode lead 23A and positive electrode lead 23B) is bonded to the tab region of the positive electrode 11, the negative electrode lead 33 (negative electrode lead 33A and negative electrode lead 33B) is bonded to the tab region of the negative electrode 12, and the pre-doping lead 48 is bonded to the tab region of the pre-doping electrode by ultrasonic bonding. Next, the periphery of the above-mentioned laminate is thermocompressed using a heat bar sealer so as to sandwich it between laminate films that will become the exterior body.

[0101] Note that Figure 10(A1) shows an oblique view before connecting the positive electrode lead 23 (positive electrode lead 23A and positive electrode lead 23B), Figure 10(A2) shows an oblique view before connecting the pre-doping leads 48 (48A and 48B), and Figure 10(A3) shows an oblique view before connecting the negative electrode lead 33 (negative electrode lead 33A and negative electrode lead 33B), and they are aligned so that the dashed lines in the figures overlap.

[0102] 10(B) shows a perspective view of one laminate film 50a that will become the exterior body 50 before folding. The negative electrode has a larger area than the positive electrode, and they are stacked with their centers aligned, and their edges are not perfectly aligned but are nearly aligned. As shown in FIG. 10(B), the edges of the positive electrode 11, the pre-doping electrode 45, and the negative electrode 12 are stacked so that they are nearly aligned, while the edge of the second film 47a is designed to have a larger area than the first film 13a so that it can be used as a gripping area.

[0103] When the periphery is thermocompression-bonded using a heat bar sealer, the thermocompression is performed leaving one side for later filling with the electrolyte. For example, as shown in FIG. 10(B), the above-mentioned laminated body is placed in a predetermined position inside a laminate film 50a folded in half. Thereafter, as shown in FIG. 11(A), thermocompression is performed in the first compression region 52a (step S101). After thermocompression-bonding, the laminate film 50a becomes a bag-shaped exterior body 50, and the positive electrode 11, the pre-doping electrode 45, and the negative electrode 12 are placed inside, aligned, and sealed with the bag-shaped exterior body 50. This state is also called three-sided sealing.

[0104] Then, the bag-shaped exterior body 50 is fixed with the portion containing the electrolyte solution 40 facing up, and the electrolyte solution 40 is poured into the exterior body 50 (step S102) in an argon gas atmosphere. It is preferable to dry the exterior body 50 and the laminated body contained therein before the pouring process. For example, the drying conditions may be a drying process at 80°C for 10 hours in a reduced pressure environment. The drying conditions are not limited to those described above, as long as the moisture adsorbed in the exterior body and the laminated body can be removed.

[0105] 11(A) shows a side view of the injection process of the electrolyte solution 40. The exterior body 50 is fixed in place by the first pressure-bonding region 52a. The portion of the laminate film folded to form one side does not need to be pressure-bonded, but is pressure-bonded in this embodiment. The first pressure-bonding region 52a, which overlaps with the folded portion of the laminate film, functions as a guide for aligning the exterior body and the laminate, thereby preventing misalignment of the overlapping electrodes.

[0106] After the injection of the electrolyte solution 40 is completed, the device is subjected to reduced pressure sealing (step S103).

[0107] The reduced pressure sealing is a sealing process performed in a reduced pressure environment, and the reduced pressure environment is preferably 50,000 Pa or less, and more preferably 40,000 Pa or less, 30,000 Pa or less, 20,000 Pa or less, 10,000 Pa or less, 5,000 Pa or less, or 1,000 Pa or less. Depending on the type of electrolyte 40 used, excessive pressure reduction may cause volatilization, so the reduced pressure value is adjusted depending on the electrolyte 40 used.

[0108] After the injection of the electrolytic solution 40, an impregnation treatment may be performed to facilitate impregnation of the electrolytic solution 40 into the pores of the positive electrode active material layer 22, the negative electrode active material layer 32, and the separator 13. As the impregnation treatment, a decompression treatment (also referred to as a vacuuming treatment) is preferably performed, and the decompression treatment and the pressure recovery treatment may be performed multiple times.

[0109] The environmental pressure during the decompression treatment is preferably about -60 kPa as a gauge pressure (40,000 Pa as an absolute pressure). The exterior body can be sealed at the same environmental pressure as the decompression treatment described above, or at an environmental pressure different from that used for the decompression treatment.

[0110] During the reduced pressure sealing shown in step S103, a second thermocompression bonding is performed, and second compression bonding region 52e is provided to close the opening of bag-shaped exterior body 50. Thereafter, excess laminate film is cut off.

[0111] A secondary battery cell having a pre-doping electrode is fabricated through the above steps, and Fig. 11(B) shows a top view of the secondary battery cell. Fig. 11(C) shows a cross-sectional view taken along the chain line X5-X6 in Fig. 11(B).

[0112] As shown in FIG. 11(C), an electrolyte solution 40 is sealed inside an exterior package 50, and a laminate is arranged inside the exterior package 50. The laminate arranged inside the exterior package 50 has the negative electrode 12, the pre-doping electrode 45, and the positive electrode 11 laminated in this order. The positive electrode 11 has a positive electrode active material layer 22 formed on a positive electrode current collector 21, and is wrapped in a separator 13 which is a first film 13a. The pre-doping electrode 45 has a pre-doping active material layer 46 formed on the pre-doping electrode 45, and is wrapped in a separator 47 which is a second film 47a. The negative electrode 12 has a negative electrode active material layer 32 formed on a negative electrode current collector 31.

[0113] Then, in step S104, a charging process for pre-doping is performed. In the charging process for pre-doping, charging is performed so that the battery capacity is 10% to 40%, preferably 30%. The pre-doping capacity is calculated in advance based on an estimated value (design capacity) of the capacity of the battery to be finally manufactured, and the charging amount can be determined, and is calculated taking into consideration the material and weight of the positive electrode active material layer 22 and the configuration of the negative electrode. In this embodiment, the configuration of the negative electrode 12 is a mixture of graphite and nanosilicon at a rate less than that of graphite, specifically, the weight ratio of graphite:nanosilicon:AB:polyacrylic acid = 72:8:6:14, and the optimal value of the pre-doping capacity is 30% of the capacity of the battery to be finally manufactured.

[0114] The final battery is generally subjected to initial charge and discharge (also referred to as aging or conditioning) before normal use. In a battery according to one embodiment of the present invention that has undergone initial charge and discharge, the capacity remaining in the negative electrode in a discharged state (also referred to as remaining capacity) is preferably 1% to 30%, more preferably 5% to 15%, and even more preferably 7% to 10%.

[0115] During the charging process for pre-doping, an external power source and a pre-doping lead 48 (48A or 48B) are connected, and an external power source and a negative electrode lead 33 (negative electrode lead 33A or negative electrode lead 33B) are connected and energized. The charging process for pre-doping may be performed so that a target remaining capacity is reached in one charging process, but is not limited to this. As the charging process for pre-doping, after charging to a capacity exceeding the target remaining capacity, a discharging process may be performed so that the target remaining capacity is reached. Moreover, the charging process for pre-doping may be performed after repeating charging and discharging one or more times.

[0116] After the charging process for pre-doping is completed, the pre-doping electrode 45 is no longer needed, so a process of cutting a part of the exterior body 50 to remove it (step S105) is performed. When cutting, a part of the pre-doping leads 48 (48A and 48B) is also cut. Note that FIG. 12(A) shows a side view of the exterior body when cutting, and the pre-doping leads 48 (48A and 48B) are fixed in a position where they are facing upward to prevent leakage of the internal electrolyte. The dashed line 49 in FIG. 12(A) is the cut line, as shown.

[0117] Then, in an argon gas atmosphere, a process of pulling out the pre-doping electrode 45 and the separator 47 (step S106) is performed. Figure 12 (B) shows a side view immediately after the pre-doping electrode 45 is pulled out, illustrating the state in which the pre-doping electrode 45 and the separator 47 are pulled out together with the partially cut pre-doping leads 48 (48A and 48B). It is important to use insulating tweezers to quickly or smoothly pull out the separator 47 and the pre-doping electrode 45 so that the positions of the positive electrode and the negative electrode do not shift.

[0118] Then, a third thermocompression bonding (third compression bonding region 52b) is performed under reduced pressure to close the opening, and reduced pressure sealing is performed in step S107. Note that an electrolyte can be added before the third thermocompression bonding. The added electrolyte may have the same composition as the initially injected electrolyte, or may have a different composition. For example, the added electrolyte may contain an electrolyte with a different additive from the initially injected electrolyte. Note that the additive contained in the added electrolyte preferably contains an additive that acts on the positive electrode side.

[0119] In this manner, the secondary battery 10 according to one embodiment of the present invention using the pre-doped negative electrode 12 can be fabricated.

[0120] In addition, when removing the pre-doping electrode 45, instead of overlapping the positive electrode 11 and the pre-doping electrode 45, which are of the same size, by shifting the positions of the positive electrode 11 and the pre-doping electrode 45 by about 3 mm, the separator 47 also protrudes by 3 mm, so that this portion can be grasped and smoothly removed. Also, even when fixing the positive electrode 11 and the separator 13 with tape to prevent misalignment, by shifting them by 3 mm, the overlapping portion between the adhesive tape and the separator 47 is reduced, allowing for smooth removal. When accurately aligning multiple metal foils, it is preferable to use a guide or jig for alignment.

[0121] The fabricated secondary battery 10 is preferably subjected to initial charge and discharge (also called aging treatment). As the aging treatment, for example, the following methods described as Aging 1 to Aging 4 may be used. Note that the aging treatment method is not limited to the following methods, and other methods may also be used.

[0122] Next, after maintaining the battery at an ambient temperature of 25°C for 24 hours, aging processes (aging 1 and 2) are performed in step S108. The conditions for the first aging process (aging 1) are 0.01C (when 1C is 200mA / g) constant current (CC) charging, stopping at 15mAh / g. The second aging process (aging 2) is 0.1C CC charging, stopping at 105mAh / g.

[0123] After the high temperature is maintained, a degassing process (step S109) is performed. The high temperature is maintained at 60°C for 24 hours. The degassing process is performed to release gas that is generated during charge and discharge.

[0124] A portion of the exterior body (including the second crimped region 52e) is cut to provide an opening, gas is released, and then the opening is resealed (step S110). The side to be cut is the portion that was subjected to the third thermocompression bonding. Under reduced pressure, a fourth thermocompression bonding is performed to close the opening that was released in the fourth crimped region 52c. The reduced pressure is then returned to atmospheric pressure.

[0125] Then, in step S111, aging processes (aging 3 and 4) are performed. The third aging (aging 3) involves an ambient temperature of 25°C, conditions of 0.1C, constant current / constant voltage (CC / CV) upper limit voltage of 4.5V, cutoff at 0.01C, followed by discharge at an ambient temperature of 25°C, conditions of 0.2C, CC, and cutoff at a lower limit voltage of 2.5V. A rest period may be provided between the discharge and the next charge.

[0126] For the fourth aging (aging 4), the battery was discharged at an ambient temperature of 25°C, with conditions of 0.2C, a CC / CV upper limit voltage of 4.5V, and cut off at 0.02C, followed by discharging at an ambient temperature of 25°C, and cut off at conditions of 0.2C, CC, and a lower limit voltage of 2.75V.

[0127] Here, we will explain the rates at which a storage device is charged and discharged. For example, when a secondary battery with a capacity of X [Ah] is charged at a constant current, a charge rate of 1C is a current value I [A] at which charging is completed in exactly one hour, and a charge rate of 0.2C is I / 5 [A] (i.e., a current value at which charging is completed in exactly five hours). Similarly, a discharge rate of 1C is a current value I [A] at which discharging is completed in exactly one hour, and a discharge rate of 0.2C is I / 5 [A] (i.e., a current value at which discharging is completed in exactly five hours).

[0128] The above steps produce the secondary battery 10a before providing the fixing portion 55. Fig. 13(A) shows an external view of the produced secondary battery 10a, and Fig. 13(B) shows a cross section taken along the chain line A1-A2 in Fig. 13(A).

[0129] The secondary battery 10a shown in FIGS. 13(A) and 13(B) has an exterior body 50 sealed with a first crimping region 52a, a third crimping region 52b, and a fourth crimping region 52c, which surround a sealed region 53.

[0130] Next, a process of providing the fixing portion 55 on the secondary battery 10a will be described with reference to FIGS. 14(A) to 14(C). FIG. 14(A) is a schematic diagram illustrating a cross section of the secondary battery 10a taken along the dashed line B1-B2 in FIG. 13(A). When the secondary battery 10 according to one embodiment of the present invention is used as a curved secondary battery, the secondary battery 10a is curved before the fixing portion 55 is provided, as shown in FIG. 14(B). Then, as shown in FIG. 14(C), the fixing portion 55 is provided in a region including the second side of the exterior body 50. At this time, the exterior body 50 is sandwiched and deformed from the outside of the secondary battery 10a so as to compress the excess space, and the fixing portion 55 is fixed so as to maintain the deformed shape (step S112). The fixing portion 55 may have a shape that sandwiches the exterior body 50 by combining two rectangular parallelepiped-shaped components, as shown in FIGS. 1(A), 14(C), and the like. The two components may be fixed together using screws, adhesive, joints, sawtooth fixing portions, etc. Plastic, metal, etc. may be used as the material for fixing portion 55. Note that the shape, structure, and material of fixing portion 55 are not limited to the above examples, as long as fixing portion 55 can hold exterior body 50 as described in this specification.

[0131] Through the above steps, the secondary battery 10 of one embodiment of the present invention can be manufactured.

[0132] Note that the secondary battery 10 of one embodiment of the present invention may have a positive electrode lead 23 in which the first positive electrode lead 23A and the second positive electrode lead 23B are integrated outside the sealing portion 52 of the secondary battery 10, as shown in FIG. 15(A), or may have a negative electrode lead 33 in which the first negative electrode lead 33A and the second negative electrode lead 33B are integrated.

[0133] Furthermore, the secondary battery 10 of one embodiment of the present invention may be connected to a circuit board 70 as shown in FIG. 15(B). FIG. 15(B) illustrates an example in which a first positive electrode lead 23A, a second positive electrode lead 23B, a first negative electrode lead 33A, and a second negative electrode lead 33B are each connected to the circuit board 70. The circuit board 70 may have, for example, a positive electrode potential wiring connected to the first positive electrode lead 23A and the second positive electrode lead 23B, and a negative electrode potential wiring connected to the first negative electrode lead 33A and the second negative electrode lead 33B. Such a configuration can be fabricated by using a laminated printed circuit board as the circuit board 70. Furthermore, as shown in FIG. 15(B), a positive electrode potential wire 71A and a negative electrode potential wire 71B may be configured to extend from the inside to the outside of the circuit board 70. Furthermore, the secondary battery 10 can be discharged to a battery device or the like that incorporates the secondary battery 10, and the secondary battery 10 can be charged, through the positive electrode potential wire 71A and the negative electrode potential wire 71B.

[0134] 16(A) to 16(C) show an example of a penetrator 1000 equipped with the secondary battery 10 of one embodiment of the present invention, as an example of a battery device equipped with the secondary battery 10. Fig. 16(A) is a perspective view of the penetrator 1000, and Fig. 16(B) is a cross-sectional schematic diagram illustrating the arrangement of the secondary battery 10 inside the penetrator 1000.

[0135] As shown in Figure 16(A), the secondary battery 10 is connected to a main unit 1010 inside the penetrator 1000. The main unit 1010 includes a calculation unit, a memory unit, a communication unit, a sensor unit, etc., and can be driven by power supplied from the secondary battery 10. Although not shown, the penetrator 1000 may also include power generation means such as a solar cell device or a temperature difference power generation device.

[0136] 16(A) and 16(B), the secondary battery 10 of one embodiment of the present invention is flexible and can therefore be installed in a curved state inside the penetrator 1000. When installing the secondary battery 10 in such a shape, the secondary battery 10 may be curved to fit the internal shape of the penetrator 1000, and then fixed with a fixing portion 55 as shown in FIG. 16(B). The fixing portion 55 may also be configured to be connected to the inside of the penetrator 1000.

[0137] The secondary battery 10 according to one embodiment of the present invention is not limited to the configuration described above, and may have a configuration in which two secondary batteries 10 are sandwiched and fixed by one fixing portion 55, as shown in Fig. 16(C), for example. Also, Fig. 16(A) shows an example in which the secondary battery 10 is mounted on the cylindrical portion at the rear of the penetrator 1000, but the secondary battery 10 may also be mounted on the conical portion at the tip of the penetrator 1000.

[0138] 16(A) to 16(C), electronic devices such as the penetrators described in Fig. 16(A) to 16(C) may be used in outer space, on celestial bodies other than the Earth, in cold regions on the Earth, etc. Therefore, it is preferable to use a positive electrode active material that can withstand high voltage and obtain a high charge capacity during charging in a low-temperature environment as a positive electrode active material for a lithium-ion battery that has excellent charge and discharge characteristics even in a low-temperature environment.

[0139] Furthermore, it is preferable that the electrolyte of a lithium ion battery that has excellent charge and discharge characteristics even in a low-temperature environment uses a material that has excellent lithium ion conductivity even when charging and / or discharging (charging and discharging) in a low-temperature environment (e.g., 0°C, preferably −20°C, more preferably −30°C, more preferably −40°C).

[0140] A preferred positive electrode, negative electrode, and electrolyte for a lithium ion battery having excellent charge and discharge characteristics even in a low-temperature environment will be described in detail below.

[0141] [Positive electrode] The positive electrode includes a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, and may further include at least one of a conductive material and a binder.

[0142] <Cathode active material> The positive electrode active material has the function of absorbing and releasing lithium ions during charge and discharge. The positive electrode active material used in one embodiment of the present invention can be a material that exhibits minimal deterioration (or minimal increase in resistance) during charge and / or discharge (hereinafter also referred to as "charge and discharge") in a low-temperature environment, even at high charge voltages (unless otherwise specified, this refers to a voltage value based on lithium metal; hereinafter, also referred to as "high charge voltage"). Specifically, it is preferable to use a positive electrode active material (composite oxide) obtained by the preparation method described in embodiment 1 and having a particle size (strictly speaking, a median diameter (D50)) of 12 μm or less (preferably 10.5 μm or less, more preferably 8 μm or less). Of course, a positive electrode active material having a particle size greater than 12 μm and equal to or less than 20 μm may also be used. This positive electrode active material is a material containing the additive element A described in embodiment 1. In this embodiment, the additive element A will be divided into additive elements X, Y, and Z, and detailed description will be given. In other words, the positive electrode active material described in this embodiment contains one or more of the additional element X, the additional element Y, and the additional element Z. The additional element X, the additional element Y, and the additional element Z will be described in detail in <Containing Elements>. The additional element X described in this embodiment corresponds to the additional element A1 described in Embodiment 1. The additional element Y and the additional element Z described in this embodiment correspond to the additional element A2 described in Embodiment 1.

[0143] Particle size can be measured using a particle size distribution analyzer that uses a laser diffraction / scattering method. The median diameter (D50) is the particle diameter at which the cumulative volume in the cumulative curve of the particle size distribution measurement results accounts for 50%. Particle size measurement is not limited to laser diffraction particle size distribution measurement; the long diameter of the particle cross section can also be measured by analysis using a scanning electron microscope (hereinafter referred to as SEM) or a transmission electron microscope (hereinafter referred to as TEM). For example, a method for measuring the median diameter (D50) using analysis using SEM or TEM can involve measuring 20 or more particles, creating a cumulative curve, and determining the particle diameter at which the cumulative volume accounts for 50% as the median diameter (D50).

[0144] As an evaluation of low-temperature characteristics, it is preferable that the discharge capacity value in a low-temperature environment is 50% or more (preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, and most preferably 90% or more) of the discharge capacity value at 20° C. Note that the above values ​​should be obtained assuming that the measurement conditions other than the environmental temperature are the same.

[0145] Alternatively, even at high charging voltages, by using a material that is less prone to deterioration during charging and discharging (or a material that is less prone to increase in resistance) as the positive electrode active material, it is possible to obtain a large discharge capacity even at low temperature environments.

[0146] More specifically, the discharge capacity when charging and discharging at -40°C is preferably 60% or more, more preferably 65% ​​or more, more preferably 70% or more, and even more preferably 75% or more, of the discharge capacity when charging and discharging at 25°C. Note that although -40°C is used, this temperature may be any low temperature, and may be interpreted as other low temperatures such as -20°C or -30°C. For example, the discharge condition may be discharge at a current rate of 0.1C (where 1C = 200mA / g (per weight of positive electrode active material)). In the evaluation of low-temperature characteristics as described above, evaluation may be performed at a low rate as long as the measurement conditions other than the ambient temperature are consistent.

[0147] As another evaluation of low-temperature characteristics, the discharge energy density value in a low-temperature environment should be 50% or more (preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, and most preferably 90% or more) of the discharge energy density value at 25°C.

[0148] As used herein, the term "ambient temperature" refers to the temperature of a lithium-ion battery. When measuring battery characteristics using a thermostatic chamber, the ambient temperature can be considered to be the temperature set in the chamber. Therefore, after placing the battery to be measured (e.g., a test battery or half-cell) in the thermostatic chamber, it is recommended to wait a sufficient amount of time (e.g., one hour or more) until the test cell reaches the same temperature as the thermostatic chamber before starting the measurement, but this method is not necessarily limited to this.

[0149] A positive electrode active material 100 according to one embodiment of the present invention will be described with reference to FIGS. 17A to 18F. The positive electrode active material 100 exhibits little deterioration due to repeated charging and discharging at a high voltage relative to lithium metal, and therefore can provide sufficient battery characteristics even in a low-temperature environment. In this embodiment, the high voltage is 4.6 V, preferably 4.65 V, and more preferably 4.7 V relative to lithium metal.

[0150] 17(A) and 17(B) are cross-sectional views of a positive electrode active material 100 according to one embodiment of the present invention. Enlarged views of the vicinity of AB in FIG. 17(B) are shown in FIGS. 18(A) to 18(C). Enlarged views of the vicinity of CD in FIG. 17(B) are shown in FIGS. 18(D) to 18(F).

[0151] 17(A), the positive electrode active material 100 has a surface layer portion 100a and an interior portion 100b. In these figures, the boundary between the surface layer portion 100a and the interior portion 100b is indicated by a dashed line, but the boundary is not clearly defined.

[0152] The surface layer 100a of the positive electrode active material 100 refers to, for example, a region extending from the surface toward the interior within 50 nm, more preferably within 35 nm, even more preferably within 20 nm, and most preferably within 10 nm, perpendicular or approximately perpendicular from the surface toward the interior. A narrow region extending from the surface toward the interior, specifically within 20 nm, is called a shell. Note that "approximately perpendicular" includes perpendicular, specifically, an angle between 80° and 100°. Surfaces resulting from cracks and / or fissures may also be referred to as the surface. The surface layer 100a is synonymous with the near-surface or near-surface region.

[0153] The region of the positive electrode active material deeper than the surface layer 100a is referred to as the inner portion 100b, which is synonymous with the inner region or core.

[0154] Furthermore, when positive electrode active material 100 has a layered rock salt crystal structure of space group R-3m, surface layer portion 100a has edge region 100a1 and basal region 100a2, as shown in FIG. 17(B).

[0155] In Figures 17(A) and 17(B), the straight line labeled (00l) represents the (00l) plane. The basal region 100a2 has a particle surface (called the basal plane) that is parallel or approximately parallel to the (00l) plane. The particle surface other than the basal plane is called the edge plane, and the region having the edge plane is called the edge region 100a1. When lithium cobalt oxide is used in the positive electrode active material 100, lithium ions can be inserted and removed at the edge plane.

[0156] The surface of the positive electrode active material 100 refers to the surface of the composite oxide including the surface layer 100a and the interior 100b. Therefore, the positive electrode active material 100 does not include metal oxides such as aluminum oxide (Al2O3) that do not have lithium sites that can contribute to charge and discharge, carbonates that are chemically adsorbed after the preparation of the positive electrode active material, hydroxyl groups, etc. The attached metal oxide refers to, for example, a metal oxide whose crystal orientation does not match that of the interior 100b.

[0157] The fact that the crystal orientations of the two regions roughly coincide can be determined from TEM (Transmission Electron Microscope) images, STEM (Scanning Transmission Electron Microscope) images, HAADF-STEM (High-Angle Annular Dark Field Scanning TEM) images, ABF-STEM (Annular Bright-Field Scanning Transmission Electron Microscope) images, electron diffraction patterns, etc. It can also be determined from FFT patterns of TEM images and STEM images, etc. XRD (X-ray Diffraction), neutron diffraction, etc. can also be used as materials for determination.

[0158] The positive electrode active material does not include the electrolyte solution, decomposition products of the electrolyte, organic solvent, binder, conductive material, or compounds derived therefrom that are attached to the positive electrode active material 100. In other words, the attached electrolyte solution, decomposition products of the electrolyte, organic solvent, binder, conductive material, or compounds derived therefrom are removed from the surface of the positive electrode active material.

[0159] Since the positive electrode active material 100 is a compound containing a transition metal and oxygen capable of lithium insertion / extraction, the interface between the region where the transition metal M (e.g., Co, Ni, Mn, Fe, etc.) that is oxidized and reduced upon lithium insertion / extraction and the region where oxygen is present and the region where oxygen is not present may be the surface of the positive electrode active material. Therefore, surfaces resulting from slippage, cracks, and / or fissures are also included in the surface of the positive electrode active material. When the positive electrode active material is subjected to analysis, a protective film may be applied to the surface, but the protective film is not included in the positive electrode active material. The protective film may be a single-layer or multi-layer film of carbon, metal, oxide, resin, etc.

[0160] <Contained elements> The positive electrode active material 100 contains lithium, cobalt, oxygen, and an additive element. Alternatively, the positive electrode active material 100 can contain lithium cobalt oxide (LiCoO) to which the additive element has been added. However, the positive electrode active material 100 of one embodiment of the present invention may have any of the crystal structures described below. Therefore, the composition of the lithium cobalt oxide is not strictly limited to Li:Co:O=1:1:2.

[0161] The additive elements contained in the positive electrode active material 100 are preferably one or more selected from magnesium, fluorine, nickel, aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, barium, bromine, and beryllium.

[0162] The additive element is preferably present in the form of a solid solution in the positive electrode active material 100. The additive element further stabilizes the crystal structure of the positive electrode active material 100, as will be described later.

[0163] For example, if the cathode active material 100 is substantially free of manganese, the advantages of relatively easy synthesis and handling, and excellent cycle characteristics, as described above, will be enhanced. The weight of manganese contained in the cathode active material 100 is preferably, for example, 600 ppm or less, more preferably 100 ppm or less.

[0164] The surface layer 100a, especially the edge region having the edge surface, is the region from which lithium ions are first desorbed during charging, and is the region where the lithium concentration is likely to be lower than that of the interior 100b. In addition, in the surface layer 100a from which lithium ions are desorbed, especially in the edge region, some of the bonds of the atoms on the surface of the particles of the positive electrode active material 100 are broken. Therefore, the surface layer 100a is likely to become unstable, and is the region where deterioration of the crystal structure is likely to begin. On the other hand, if the surface layer 100a, especially the edge region, can be made sufficiently stable, Li xEven when x in CoO2 is small, for example, 0.24 or less, the layered structure of the inner portion 100b made of cobalt and oxygen octahedra can be made less likely to break. Furthermore, if the surface layer portion 100a, especially the edge region, can be made sufficiently stable, it is possible to suppress displacement of the layer made of cobalt and oxygen octahedra in the inner portion 100b.

[0165] To provide the surface layer 100a with a stable composition and crystal structure, the surface layer 100a preferably contains the above-mentioned additive elements, and more preferably contains a plurality of additive elements. Furthermore, the surface layer 100a preferably has a higher concentration of one or more selected from the additive elements than the interior 100b. Furthermore, the edge region 100a1 preferably has a higher concentration of one or more selected from the additive elements than the basal region 100a2.

[0166] The distribution of the added elements will be described. Figures 18(A) to 18(C) are enlarged views of the vicinity of AB in Figure 17(B) and are views illustrating the edge region 100a1 of the positive electrode active material 100. Figures 18(D) to 18(F) are enlarged views of the vicinity of CD in Figure 17(B) and are views illustrating the basal region 100a2 of the positive electrode active material 100.

[0167] For example, some of the additive elements, such as magnesium, fluorine, and titanium, preferably have a concentration gradient that increases from the interior 100b toward the surface. In Figures 18(A) and 18(D), the concentration gradient is expressed using the density of the hatching. An additive element having such a concentration gradient will be referred to as additive element X. However, the concentration of magnesium, fluorine, titanium, etc. may be higher in the edge region 100a1 than in the basal region 100a2.

[0168] Another additive element, such as aluminum, preferably has a concentration gradient and a concentration peak in a region deeper than the additive element X shown in Figures 18(B) and 18(E). In Figures 18(B) and 18(E), the concentration gradient and peak region are expressed using hatch darkness. The concentration peak may be present in the surface layer portion 100a or may be deeper than the surface layer portion 100a. For example, it is preferable that the peak be present in a region of 5 nm to 30 nm from the surface toward the interior. An additive element having such a concentration gradient will be referred to as additive element Y. However, the concentration of aluminum, etc., may be higher in the edge region 100a1 than in the basal region 100a2.

[0169] Another additive element, such as nickel, may be clearly present in the edge region 100a1 but substantially absent in the basal region 100a2, as indicated by the presence or absence of hatching and the density of the hatching in FIGS. 18(C) and 18(F). The concentration of nickel or the like may be higher in the edge region 100a1 than in the basal region 100a2. Note that "clearly present" here refers to a case where a characteristic X-ray energy spectrum of the element is detected in a cross-sectional STEM-EDX analysis of the positive electrode active material 100. An additive element having such a distribution is referred to as additive element Z.

[0170] "Substantially free" refers to a case where the characteristic X-ray energy spectrum of the element is not detected in a cross-sectional STEM-EDX analysis of the positive electrode active material 100. This also refers to the element being below the lower limit of detection in a STEM-EDX analysis. In this case, it also refers to the element being below the lower limit of detection in a STEM-EDX analysis.

[0171] For example, magnesium, which is one of the additive elements X, is divalent, and magnesium is more stable at the lithium site than at the cobalt site in the layered rock salt crystal structure, so it is easy to enter the lithium site. The presence of magnesium at an appropriate concentration at the lithium site in the surface layer 100a makes it easier to maintain the layered rock salt crystal structure. This is presumably because the magnesium present at the lithium site functions as a pillar supporting the CoO2 layers. In addition, the presence of magnesium makes it easier to maintain the Li x When x in CoO2 is, for example, 0.24 or less, the desorption of oxygen from around magnesium can be suppressed.

[0172] At an appropriate concentration, magnesium does not adversely affect the intercalation and deintercalation of lithium during charging and discharging, providing the above benefits. However, excessive magnesium may adversely affect the intercalation and deintercalation of lithium. Furthermore, it may have a reduced effect on stabilizing the crystal structure. This is thought to be due to magnesium occupying the cobalt site in addition to the lithium site. In addition, excess magnesium compounds (e.g., oxides or fluorides) that do not substitute for either the lithium or cobalt site may segregate on the surface of the positive electrode active material and become a resistive component in lithium-ion batteries. Furthermore, as the magnesium concentration in the positive electrode active material increases, the discharge capacity of the positive electrode active material may decrease. This is thought to be due to excessive magnesium occupancy at the lithium site, reducing the amount of lithium contributing to charging and discharging.

[0173] Therefore, it is preferable that the amount of magnesium contained in the entire positive electrode active material 100 is appropriate. For example, the number of magnesium atoms is preferably 0.001 to 0.1 times the number of cobalt atoms, more preferably more than 0.01 to less than 0.04 times, and even more preferably about 0.02 times. The amount of magnesium contained in the entire positive electrode active material 100 referred to here may be a value obtained by performing elemental analysis of the entire positive electrode active material 100 using, for example, GD-MS, ICP-MS, or the like, or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material 100.

[0174] Furthermore, aluminum, one of the additive elements Y, can exist at the cobalt site in the layered rock-salt crystal structure. Because aluminum is a trivalent typical element and its valence remains constant, lithium around the aluminum is less likely to move during charging and discharging. Therefore, the aluminum and its surrounding lithium function as pillars, potentially suppressing changes in the crystal structure. Aluminum also inhibits the elution of surrounding cobalt, improving continuous charging durability. Furthermore, because the Al-O bond is stronger than the Co-O bond, it can inhibit the desorption of oxygen around the aluminum. These effects improve thermal stability. Therefore, the presence of aluminum as an additive element can improve safety when used in lithium-ion batteries. Furthermore, it can produce a positive electrode active material 100 whose crystal structure is less likely to collapse even with repeated charging and discharging. However, excessive aluminum may adversely affect lithium insertion and extraction.

[0175] Therefore, it is preferable that the total amount of aluminum contained in the positive electrode active material 100 is appropriate. For example, the number of aluminum atoms contained in the total amount of aluminum contained in the positive electrode active material 100 is preferably 0.05% to 4% of the number of cobalt atoms, preferably 0.1% to 2% and more preferably 0.3% to 1.5%. Alternatively, 0.05% to 2% is preferable. Alternatively, 0.1% to 4% is preferable. The amount contained in the total amount of aluminum contained in the positive electrode active material 100 referred to here may be, for example, a value obtained by performing elemental analysis of the total amount of aluminum contained in the positive electrode active material 100 using GD-MS, ICP-MS, or the like, or may be based on the value of the composition of raw materials used in the production process of the positive electrode active material 100.

[0176] Nickel, which is one of the additive elements Z, can exist on either the cobalt site or the lithium site. When nickel exists on the cobalt site, its redox potential is lower than that of cobalt, which leads to an increase in discharge capacity, which is preferable.

[0177] Furthermore, when nickel is present at the lithium site, it can suppress the shift in the layered structure consisting of octahedra of cobalt and oxygen. It also suppresses the volume change during charging and discharging. It also increases the elastic modulus, meaning the battery becomes harder. This is presumably because the nickel present at the lithium site also functions as a pillar supporting the CoO2 layers. Therefore, it is expected that the crystal structure will be more stable, especially at high temperatures, such as 45°C or higher, during charging.

[0178] On the other hand, excessive nickel is undesirable because it increases the influence of strain due to the Jahn-Teller effect, and excessive nickel may also adversely affect lithium insertion and extraction.

[0179] Therefore, it is preferable that the total amount of nickel in the positive electrode active material 100 is appropriate. For example, the number of nickel atoms in the positive electrode active material 100 is preferably greater than 0% and less than 7.5% of the total number of cobalt atoms, preferably 0.05% to 4%, preferably 0.1% to 2%, and more preferably 0.2% to 1%. Alternatively, it is preferably greater than 0% and less than 4%. Alternatively, it is preferably greater than 0% and less than 2%. Alternatively, it is preferably 0.05% to 7.5%. Alternatively, it is preferably 0.05% to 2%. Alternatively, it is preferably 0.1% to 7.5%. Alternatively, it is preferably 0.1% to 4%. The amount of nickel indicated here may be, for example, a value obtained by performing elemental analysis of the entire positive electrode active material using GD-MS, ICP-MS, or the like, or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material.

[0180] Furthermore, fluorine, one of the additive elements X, is a monovalent anion. When some of the oxygen atoms in the surface layer 100a are replaced by fluorine, the lithium desorption energy decreases. This is because the valence of the cobalt ion changes with lithium desorption (from trivalent to tetravalent in the absence of fluorine, and from divalent to trivalent in the presence of fluorine), resulting in different redox potentials. Therefore, when some of the oxygen atoms in the surface layer 100a of the positive electrode active material 100 are replaced by fluorine, the desorption and insertion of lithium ions near the fluorine atoms can occur more smoothly. This improves charge / discharge characteristics, rate characteristics, low-temperature characteristics, and other properties when used in lithium-ion batteries. Furthermore, the presence of fluorine in the surface layer 100a, which has a surface that contacts the electrolyte, effectively improves corrosion resistance against hydrofluoric acid. As will be described in a later embodiment, when the melting point of a fluoride, such as lithium fluoride, is lower than that of other additive element sources, it can function as a flux (also known as a fluxing agent) to lower the melting point of the other additive element sources.

[0181] Furthermore, titanium oxide, which is one of the additive elements X, is known to have superhydrophilic properties. Therefore, by providing the cathode active material 100 with titanium oxide in the surface layer portion 100a, it is possible that the cathode active material 100 may have good wettability with highly polar solvents. When used in a secondary battery, this may improve the contact at the interface between the cathode active material 100 and a highly polar electrolyte, thereby suppressing an increase in internal resistance.

[0182] Furthermore, when the surface layer 100a shown in FIG. 18(A) has magnesium and the surface layer 100a shown in FIG. 18(C) has nickel, that is, when both magnesium and nickel are present, there is a possibility that divalent nickel can exist more stably near the divalent magnesium. x Even when x in CoO2 is small, the elution of magnesium can be suppressed, which can contribute to the stabilization of the surface layer portion 100a.

[0183] 18(C) and 18(F), the additive element Z is preferably contained in a large amount in the edge region 100a1 (also referred to as being contained preferentially or selectively), which is preferable because it improves the stability of the crystal structure of the edge region 100a1, where lithium ions enter and exit the positive electrode active material 100 during charging and discharging of the lithium ion battery. Furthermore, when the additive element Z has the above-described distribution, for example, when the positive electrode active material 100 is lithium cobalt oxide, it is preferable because it can minimize the effects of adding the additive element Z, such as a decrease in discharge voltage or a decrease in discharge capacity.

[0184] As described above, when multiple additive elements are present, the effects of each additive element are synergistic, which can contribute to further stabilization of the surface layer portion 100a. In particular, the presence of magnesium, nickel, and aluminum is highly effective in achieving a stable composition and crystal structure, and is therefore preferable. In particular, it is preferable that the surface layer portion 100a of the positive electrode active material 100 has a region where aluminum is distributed more inward than magnesium. Furthermore, in addition to the region where magnesium and aluminum are distributed, it is most preferable that the surface layer portion 100a of the positive electrode active material 100 has a region where the nickel distribution and the magnesium distribution overlap in the edge region 100a1.

[0185] <Crystal structure> One aspect of the present invention is to provide a lithium ion battery with improved battery characteristics in a low-temperature environment, but the XRD measurements and other measurements used to identify the crystal structure and other properties were performed at room temperature.

[0186] <Li x When x in CoO2 is 1> The positive electrode active material 100 according to one embodiment of the present invention is in a discharged state, i.e., Li xWhen x = 1 in CoO2, it preferably has a layered rock-salt type crystal structure belonging to the space group R-3m. Layered rock-salt type composite oxides have high discharge capacity, have two-dimensional lithium ion diffusion paths, and are suitable for lithium ion insertion / extraction reactions, making them excellent as positive electrode active materials for lithium ion batteries. Therefore, it is preferable that the inner part 100b, which occupies the majority of the volume of the positive electrode active material 100, has a layered rock-salt type crystal structure.

[0187] On the other hand, the surface layer portion 100a of the cathode active material 100 according to one embodiment of the present invention preferably has a function of reinforcing the inner portion 100b so that the layered structure of octahedra of cobalt and oxygen in the inner portion 100b is not destroyed even when lithium is released from the cathode active material 100 upon charging. Alternatively, the surface layer portion 100a preferably functions as a barrier film for the cathode active material 100. Alternatively, the surface layer portion 100a, which is the outer periphery of the cathode active material 100, preferably reinforces the cathode active material 100. Here, "reinforcement" refers to suppressing structural changes in the surface layer portion 100a and inner portion 100b of the cathode active material 100, such as oxygen release, and / or suppressing oxidative decomposition of the electrolyte on the surface of the cathode active material 100.

[0188] To provide a reinforcing function, the surface layer portion 100a may have a different crystal structure from the interior portion 100b. For example, the surface layer portion 100a preferably has a composition and crystal structure that are more stable at room temperature (25°C) than the interior portion 100b. For example, at least a portion of the surface layer portion 100a of the positive electrode active material 100 of one embodiment of the present invention may have a rock salt crystal structure. Alternatively, the surface layer portion 100a may have both a layered rock salt crystal structure and a rock salt crystal structure. Alternatively, the surface layer portion 100a may have characteristics of both a layered rock salt crystal structure and a rock salt crystal structure.

[0189] Furthermore, the fact that it has both the characteristics of the layered rock salt type and the rock salt type crystal structure can be determined by electron diffraction, TEM images, cross-sectional STEM images, etc.

[0190] Furthermore, it is preferable that some of the added elements, especially magnesium, have a higher concentration in the surface layer 100a than in the interior 100b, and that they exist randomly and dilutely in the interior 100b. Furthermore, when aluminum is present at an appropriate concentration at the lithium sites in the interior 100b, it has the effect of making it easier to maintain the layered rock-salt crystal structure, as described above. Furthermore, when nickel is present at an appropriate concentration in the interior 100b, it can suppress the deviation of the layered structure consisting of octahedra of cobalt and oxygen, as described above. Furthermore, when magnesium and nickel are present together, divalent magnesium may be able to exist more stably near divalent nickel, which is expected to have a synergistic effect of suppressing magnesium elution.

[0191] Furthermore, due to the magnesium concentration gradient described above, it is preferable that the crystal structure changes continuously from the interior 100b toward the surface, or that the crystal orientation of the surface layer 100a and the interior 100b roughly coincide.

[0192] In this specification, the layered rock-salt crystal structure belonging to the space group R-3m, which is possessed by a composite oxide containing lithium and a transition metal such as cobalt, refers to a crystal structure having a rock-salt ion arrangement in which cations and anions are alternately arranged, and in which the transition metal and lithium are regularly arranged to form a two-dimensional plane, allowing two-dimensional diffusion of lithium. Defects such as vacancies of cations or anions may also be present. Furthermore, strictly speaking, the layered rock-salt crystal structure may have a distorted lattice structure, and the orientation of the crystals may be roughly the same.

[0193] The rock salt crystal structure is a cubic crystal structure, such as a crystal structure belonging to the space group Fm-3m, in which cations and anions are arranged alternately. Note that cation or anion defects are also acceptable.

[0194] The rock salt crystal structure does not distinguish between cation sites, but the layered rock salt crystal structure has two types of cation sites in the crystal structure, one of which is mostly occupied by lithium and the other by the transition metal M. The layered structure, in which two-dimensional planes of cations and two-dimensional planes of anions are alternately arranged, is the same for both the rock salt and layered rock salt structures.

[0195] The layered rock salt crystal structure and the anions in the rock salt crystal structure form a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that the anions in the O3' crystal, which will be described later, also form a cubic close-packed structure. Therefore, when the layered rock salt crystal structure and the rock salt crystal structure come into contact, there are crystal faces where the cubic close-packed structure formed by the anions is oriented in the same direction.

[0196] Alternatively, it can be explained as follows: Anions on the {111} plane of the cubic crystal structure have a triangular lattice. Layered rocksalt has a space group of R-3m and a rhombohedral structure, but to make the structure easier to understand, it is generally expressed as a compound hexagonal lattice, and the (0001) plane of the layered rocksalt has a hexagonal lattice. The triangular lattice on the cubic {111} plane has the same atomic arrangement as the hexagonal lattice on the (0001) plane of the layered rocksalt. The compatibility of the two lattices can be said to be the alignment of the cubic close-packed structure.

[0197] However, the space group of the layered rock salt crystal structure and the O3'-type crystal structure described below is R-3m, which is different from the space group Fm-3m of the rock salt crystal structure (the space group of a general rock salt crystal), and therefore the Miller indices of the crystal planes that satisfy the above conditions are different for the layered rock salt crystal structure, the O3'-type crystal structure, and the rock salt crystal structure. In this specification, when the orientations of the cubic close-packed structures formed by anions are aligned in the layered rock salt crystal structure, the O3'-type crystal structure, and the rock salt crystal structure, it may be said that the crystal orientations are approximately the same.

[0198] <Li x When x in CoO2 is small> The cathode active material 100 according to one embodiment of the present invention has the above-described magnesium distribution and / or crystalline structure, and therefore, xThe crystal structure in the state where x in CoO2 is small is different from that of conventional positive electrode active materials. <x≦0.24をいうこととする。

[0199] 19 to 22, Li x The change in the crystal structure accompanying the change in x in CoO2 will be described by comparing a conventional positive electrode active material with the positive electrode active material 100 according to one embodiment of the present invention.

[0200] The change in the crystal structure of a conventional positive electrode active material is shown in Figure 20. The conventional positive electrode active material shown in Figure 20 is lithium cobalt oxide (LiCoO2) that does not contain magnesium.

[0201] Figure 20 shows R-3m O3 and Li x This shows the crystal structure of lithium cobalt oxide with x=1 in CoO2. In this crystal structure, lithium occupies the octahedral site, and there are three CoO2 layers in the unit cell. For this reason, this crystal structure is sometimes called an O3-type crystal structure. Note that a CoO2 layer is an octahedral structure in which cobalt is coordinated with six oxygen atoms, and these structures are connected in a plane with edge sharing. This is sometimes called a layer consisting of octahedra of cobalt and oxygen.

[0202] Conventional lithium cobalt oxide is known to have a crystal structure that belongs to the monoclinic space group P2 / m when the symmetry of lithium increases when x is around 0.5. This structure has one CoO2 layer in the unit cell. For this reason, it is sometimes called the O1 type or monoclinic O1 type.

[0203] When x = 0, the positive electrode active material has a trigonal space group P-3m1 crystal structure, with one CoO2 layer in each unit cell. This crystal structure is sometimes called the O1 type or trigonal O1 type. The trigonal structure may also be converted to a composite hexagonal lattice, which is sometimes called the hexagonal O1 type.

[0204] Furthermore, conventional lithium cobalt oxide (LiCOO) with x = 0.12 or so has a crystal structure of the space group R-3m. This structure can be thought of as a structure in which a trigonal O1-type CoO2 structure and an R-3m O3-type LiCoO2 structure are alternately stacked. For this reason, this crystal structure is sometimes referred to as the H1-3-type crystal structure. In reality, the H1-3-type crystal structure has twice the number of cobalt atoms per unit cell compared to other structures. However, in Figure 20 and other parts of this specification, the c-axis of the H1-3-type crystal structure is shown as half the unit cell to facilitate comparison with other crystal structures.

[0205] As an example of an H1-3 type crystal structure, the coordinates of cobalt and oxygen in the unit cell can be expressed as Co(0, 0, 0.42150±0.00016), O1(0, 0, 0.27671±0.00045), and O2(0, 0, 0.11535±0.00045). O1 and O2 are oxygen atoms. The unit cell that should be used to represent the crystal structure of the positive electrode active material can be determined, for example, by Rietveld analysis of the XRD pattern. In this case, it is best to use the unit cell that results in a small GOF (goodness of fit) value, specifically one that is close to 1.

[0206] Li x When conventional lithium cobalt oxide is repeatedly charged and discharged so that x in CoO2 becomes 0.24 or less, the crystal structure changes repeatedly (i.e., a non-equilibrium phase change) between the H1-3 type crystal structure and the R-3m O3 structure in the discharged state.

[0207] However, these two crystal structures have a large misalignment of the CoO2 layers. As shown by the dotted lines and arrows in Figure 20, in the H1-3 crystal structure, the CoO2 layers are significantly misaligned from those in the R-3m O3 discharged state. Such dynamic structural changes can adversely affect the stability of the crystal structure.

[0208] Furthermore, the difference in volume between these two crystal structures is large: when compared per the same number of cobalt atoms, the difference in volume between the H1-3 crystal structure and the discharged R-3m O3 crystal structure exceeds 3.5%, typically 3.9% or more.

[0209] In addition, the H1-3 type crystal structure, which has continuous CoO2 layers like the trigonal O1 type, is likely to be unstable.

[0210] Therefore, when charging and discharging are repeated so that x is 0.24 or less, the crystal structure of conventional lithium cobalt oxide collapses. This collapse of the crystal structure causes a deterioration in cycle characteristics. This is because the collapse of the crystal structure reduces the number of sites where lithium can exist stably and makes it difficult for lithium to be inserted and extracted.

[0211] On the other hand, in the positive electrode active material 100 according to one embodiment of the present invention shown in FIG. x The change in the crystal structure between the discharge state where x in CoO2 is 1 and the state where x is 0.24 or less, specifically, x is 0.2 (this state may be referred to as a 20% Li existence probability), is smaller than that of conventional positive electrode active materials. More specifically, the deviation of the CoO2 layer between the state where x is 1 and the state where x is 0.24 or less can be reduced. Furthermore, the change in volume compared per cobalt atom can be reduced. Therefore, the positive electrode active material 100 of one embodiment of the present invention is less likely to collapse in crystal structure even when repeatedly charged and discharged so that x is 0.24 or less, and excellent cycle characteristics can be achieved. Furthermore, the positive electrode active material 100 of one embodiment of the present invention has a low Li content. x When x in CoO2 is 0.24 or less, the positive electrode active material 100 can have a more stable crystal structure than conventional positive electrode active materials. x When x in CoO2 is kept at 0.24 or less, short circuits are less likely to occur, which is preferable as it further improves the safety of the lithium-ion battery.

[0212] Li x19 shows the crystal structure of the interior 100b of the positive electrode active material 100 when x in CoO2 is approximately 1 and 0.2. The interior 100b occupies the majority of the volume of the positive electrode active material 100 and is the part that contributes greatly to charge and discharge, so it can be said that the displacement of the CoO2 layer and changes in volume are the most problematic part.

[0213] When x=1, the positive electrode active material 100 has the same crystal structure of R-3m O3 as conventional lithium cobalt oxide.

[0214] However, the positive electrode active material 100 has a crystal structure different from that of conventional lithium cobalt oxide when x is 0.24 or less, for example, about 0.2 or 0.12, which results in an H1-3 type crystal structure.

[0215] When x=0.2 or so, the cathode active material 100 of one embodiment of the present invention has a crystal structure belonging to the trigonal space group R-3m. This has the same symmetry as the CoO2 layer of O3. Therefore, this crystal structure is referred to as an O3'-type crystal structure. Furthermore, when x=0.2 or so, the cathode active material 100 of one embodiment of the present invention does not have a spinel structure, but the XRD pattern may show a pattern similar to a spinel structure, and this crystal structure is sometimes referred to as a pseudo-spinel structure. This crystal structure is shown in Figure 19, labeled R-3m O3'.

[0216] The O3' type crystal structure can be expressed by the coordinates of cobalt and oxygen in the unit cell being Co(0,0,0.5), O(0,0,x), with the range of 0.20≦x≦0.25. The lattice constant of the unit cell is 2.797≦a≦2.837(×10 -1 nm), and 2.807≦a≦2.827(×10 -1 nm) is more preferable, and typically a=2.817(×10 -1 nm). The c-axis is 13.681≦c≦13.881(×10 -1 nm), 13.751≦c≦13.811 is more preferable, and typically c=13.781(×10 -1 nm).

[0217] In the O3' crystal structure, ions of cobalt, magnesium, etc. occupy six oxygen coordination positions, while light elements such as lithium may occupy four oxygen coordination positions.

[0218] As shown by the dotted line in FIG. 19, there is almost no deviation in the CoO2 layer between the R-3m(O3) in the discharged state and the O3'-type crystal structure.

[0219] The difference in volume per the same number of cobalt atoms between R-3m(O3) in a discharged state and the O3'-type crystal structure is 2.5% or less, more specifically 2.2% or less, and typically 1.8%.

[0220] In this way, in the positive electrode active material 100 according to one embodiment of the present invention, Li x When x in CoO2 is small, i.e., when a large amount of lithium is released, the change in crystal structure is suppressed compared to conventional cathode active materials. Furthermore, the change in volume per the same number of cobalt atoms is also suppressed. Therefore, cathode active material 100 is resistant to crystal structure collapse even when repeatedly charged and discharged so that x is 0.24 or less. Therefore, cathode active material 100 suppresses the decrease in charge / discharge capacity during charge / discharge cycles. Furthermore, because it can stably utilize more lithium than conventional cathode active materials, cathode active material 100 has a large discharge capacity per weight and per volume. Therefore, by using cathode active material 100, lithium-ion batteries with high discharge capacity per weight and per volume can be fabricated.

[0221] The positive electrode active material 100 is Li x It has been confirmed that when x in CoO2 is between 0.15 and 0.24, it may have an O3' type crystal structure, and it is also estimated that when x is between 0.24 and 0.27, it also has an O3' type crystal structure. However, the crystal structure is Li x Since it is affected not only by x in CoO2 but also by the number of charge / discharge cycles, charge / discharge current, temperature, electrolyte, etc., it is not necessarily limited to the above range of x.

[0222] Therefore, the positive electrode active material 100 is Li xWhen x in CoO2 is more than 0.1 and not more than 0.24, the entire interior 100b of the positive electrode active material 100 does not have to have an O3'-type crystal structure, but may contain other crystal structures, or may be partially amorphous.

[0223] Also Li x To make the x in CoO2 small, it is generally necessary to charge at a high charging voltage. x A state in which x in CoO2 is small can be rephrased as a state in which the material is charged at a high charging voltage.

[0224] In other words, the positive electrode active material 100 of one embodiment of the present invention is preferable because it can maintain a crystal structure with R-3m O3 symmetry even when charged at a high charging voltage, for example, a voltage of 4.6 V or higher at 25° C. In other words, it is preferable because it can adopt an O3′-type crystal structure when charged at a higher charging voltage, for example, a voltage of 4.65 V or higher and 4.7 V or lower at 25° C.

[0225] In some cases, the H1-3 crystal structure is finally observed when the charge voltage is further increased, even in the positive electrode active material 100. Furthermore, as described above, the crystal structure is affected by the number of charge / discharge cycles, the charge / discharge current, the electrolyte, and the like. Therefore, even when the charge voltage is lower, for example, even when the charge voltage is 4.5 V or higher but lower than 4.6 V at 25° C., the positive electrode active material 100 of one embodiment of the present invention may be able to adopt the O3′ crystal structure.

[0226] In addition, when graphite is used as the negative electrode active material in a lithium-ion battery, the voltage of the lithium-ion battery is lower than the above by the potential of the graphite. The potential of graphite is approximately 0.05 V to 0.2 V relative to the potential of lithium metal. Therefore, a lithium-ion battery using graphite as the negative electrode active material has a similar crystal structure at a voltage obtained by subtracting the potential of graphite from the voltage when lithium metal is used as the negative electrode active material.

[0227] In addition, in O3' of FIG. 19, lithium is shown to exist at all lithium sites with equal probability, but this is not limited to this. It may exist unevenly at some lithium sites, for example, in the monoclinic O1 (Li 0.5 The lithium distribution can be analyzed by neutron diffraction, for example.

[0228] To achieve the O3'-type crystal structure, it is preferable that the magnesium concentration gradient be similar across multiple locations in the surface layer 100a of the positive electrode active material 100. In other words, it is preferable that the magnesium-derived reinforcement be uniformly present across the surface layer 100a. Even if a portion of the surface layer 100a is reinforced, if there are areas without reinforcement, stress may be concentrated in those areas. If stress is concentrated in a portion of the positive electrode active material 100, defects such as cracks may occur, which may lead to breakage of the positive electrode active material and a decrease in discharge capacity. However, it is not necessary for magnesium to have a similar concentration gradient across the entire surface layer 100a of the positive electrode active material 100.

[0229] In the layered rock-salt crystal structure of R-3m, cations are arranged parallel to the (001) plane. This can be said to be a structure in which CoO2 layers and lithium layers are alternately stacked parallel to the (001) plane. Therefore, the diffusion path of lithium ions also exists parallel to the (001) plane. Again, the (001) plane is called the basal plane, and planes other than the (001) plane that expose the diffusion path of lithium ions are called edge planes.

[0230] Since the CoO2 layer is relatively stable, it is more stable for the surface of the positive electrode active material 100 to have a (001) orientation. The main diffusion path of lithium ions during charge and discharge is not exposed on the (001) plane.

[0231] On the other hand, the diffusion paths of lithium ions are exposed on surfaces other than the (001) plane. Therefore, the surfaces other than the (001) plane and the surface layer portion 100a having such surfaces are important regions for maintaining the diffusion paths of lithium ions, but at the same time, they are the regions from which lithium ions are first desorbed and are therefore prone to instability. Therefore, reinforcing the surfaces other than the (001) plane and the surface layer portion 100a having such surfaces is extremely important for maintaining the crystal structure of the entire positive electrode active material 100.

[0232] <Analysis method> A certain positive electrode active material is Li x When x in CoO2 is small, whether the positive electrode active material 100 of one embodiment of the present invention has an O3'-type crystal structure or not can be determined by Li x This can be determined by analyzing a positive electrode having a positive electrode active material with a small x in CoO2 using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. Among XRD methods, powder XRD is preferred because it can provide diffraction peaks that reflect the crystalline structure of the interior 100b of the positive electrode active material 100, which occupies most of the volume of the positive electrode active material 100.

[0233] Furthermore, even in the case of the cathode active material 100 of one embodiment of the present invention, an H1-3 type or trigonal O1 type crystal structure may be formed if x is too small, such as 0.1 or less, or under conditions where the charge voltage exceeds 4.9 V. Therefore, to determine whether or not the cathode active material 100 of one embodiment of the present invention is a cathode active material, analysis of the crystal structure using XRD or other methods, as well as information such as the charge capacity or the charge voltage, is required.

[0234] Furthermore, when positive electrode active materials with a small x are exposed to air, their crystal structure may change. For example, they may change from an O3'-type crystal structure to an H1-3-type crystal structure. Therefore, it is recommended that all samples used for crystal structure analysis be handled in an inert atmosphere such as an argon atmosphere.

[0235] Furthermore, whether or not the distribution of the additive elements contained in the positive electrode active material is in the state described above can be determined by analysis using, for example, XPS, energy dispersive X-ray spectroscopy (EDX), electron probe microanalysis (EPMA), or the like.

[0236] Furthermore, the crystal structure of the surface layer 100a, the grain boundaries, etc. can be analyzed by electron beam diffraction of a cross section of the positive electrode active material 100, etc.

[0237] ≪Charging method≫ To determine whether a composite oxide is the positive electrode active material 100 of one embodiment of the present invention, a coin cell (CR2032 type, 20 mm in diameter and 3.2 mm in height) can be fabricated using the composite oxide as a positive electrode and lithium metal as a counter electrode, and then charged. The coin cell includes an electrolyte, a separator, a positive electrode can, and a negative electrode can.

[0238] More specifically, the positive electrode may be prepared by coating a positive electrode current collector made of aluminum foil with a slurry containing a positive electrode active material, a conductive material, and a binder.

[0239] The counter electrode can be made of lithium metal.

[0240] The lithium salt used is 1 mol / L lithium hexafluorophosphate (LiPF6), and the electrolyte is a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7, with vinylene carbonate (VC) added as an additive at 2 wt% of the mixed solvent.

[0241] The separator can be a 25 μm thick porous polypropylene film.

[0242] The positive electrode can and the negative electrode can may be made of stainless steel (SUS).

[0243] The coin cell prepared under the above conditions is charged at a desired voltage (e.g., 4.5 V, 4.55 V, 4.6 V, 4.65 V, 4.7 V, 4.75 V, or 4.8 V). The charging method is not particularly limited as long as the desired voltage is charged for a sufficient period of time. For example, when charging using CCCV, the CC charging current can be set to 20 mA / g or more and 100 mA / g or less per weight of positive electrode active material. CV charging can be terminated at 2 mA / g or more and 10 mA / g or less per weight of positive electrode active material. Charging at such a low current value is desirable to observe the phase change of the positive electrode active material. The temperature is set to 25°C. After charging in this manner, the coin cell is disassembled in a glove box under an argon atmosphere and the positive electrode is removed to obtain a positive electrode active material with the desired charge capacity. When various analyses are performed after this, it is preferable to seal the cell in an argon atmosphere to prevent reactions with external components. For example, XRD can be performed by sealing the cell in a sealed container under an argon atmosphere. It is also preferable to remove the positive electrode promptly after charging is complete and subject it to analysis. Specifically, it is preferable to do so within one hour after the completion of charging, and more preferably within 30 minutes.

[0244] When analyzing the crystal structure in the charged state after multiple charge / discharge cycles, the conditions for the multiple charge / discharge cycles may be different from the above-mentioned conditions. For example, charging may be performed by constant current charging up to a given voltage (e.g., 4.6 V, 4.65 V, 4.7 V, 4.75 V, or 4.8 V) at a current value of 20 mA / g or more and 100 mA / g or less per weight of the positive electrode active material, followed by constant voltage charging until the current value becomes 2 mA / g or more and 10 mA / g or less per weight of the positive electrode active material, and discharging by constant current discharging at 2.5 V at a current value of 20 mA / g or more and 100 mA / g or less.

[0245] Furthermore, when analyzing the crystal structure in the discharged state after multiple charge / discharge cycles, constant current discharge can be performed at, for example, 2.5 V, with a current value of 20 mA / g or more and 100 mA / g or less per weight of the positive electrode active material.

[0246] <xrd> The XRD measurement apparatus and conditions are not particularly limited as long as they are properly adjusted and calibrated. For example, the measurement can be performed using the following apparatus and conditions. XRD equipment: Bruker AXS, D8 ADVANCE X-ray: Cu Kα2 Output: 40kV, 40mA Divergence angle: Div.Slit, 0.5° Detector: LynxEye Scan method: 2θ / θ continuous scan Measurement range (2θ): 15° to 90° Step width (2θ): 0.01° setting Counting time: 1 second / step Sample stage rotation: 15 rpm The standard sample used for adjustment and calibration may be, for example, a standard aluminum oxide sintered plate SRM 1976 from NIST (National Institute of Standards and Technology).

[0247] If the measurement sample is a powder, it can be set by placing it on a glass sample holder, or by sprinkling the sample on a greased silicone anti-reflective plate, etc. If the measurement sample is a positive electrode, the positive electrode can be attached to the substrate with double-sided tape, and the positive electrode active material layer can be set to match the measurement surface required by the device.

[0248] To monochromatize the characteristic X-rays, a filter can be used, or after obtaining the XRD pattern, XRD data analysis software can be used. For example, DIFFRAC.EVA (XRD data analysis software manufactured by Bruker) can be used to remove the peak due to CuKα2 radiation and extract only the peak due to CuKα1 radiation. The same software can also be used to remove background noise.

[0249] In this specification, data processing when referring to the 2θ value of a diffraction peak will be described. First, a calculation model is fitted to the XRD pattern using crystal structure analysis software to obtain a calculated pattern. In the calculated pattern, the 2θ value at which the peak top of the diffraction peak appears is referred to as the 2θ value of the diffraction peak. The crystal structure analysis software used for fitting is not particularly limited, but for example, TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker) can be used.

[0250] The ideal powder XRD patterns calculated from the O3'-type crystal structure and the H1-3-type crystal structure model using CuKα1 radiation are shown in Figures 21 and 22. For comparison, Li x The ideal XRD patterns calculated from the crystal structure of LiCoO2O3 with x = 1 in CoO2 and trigonal O1 with x = 0 are also shown. The patterns for LiCoO2(O3) and CoO2(O1) were created using Reflex Powder Diffraction, a module of Materials Studio (BIOVIA), based on crystal structure information obtained from the ICSD (Inorganic Crystal Structure Database). The 2θ range was 15° to 75°, with a step size of 0.01 and a wavelength of λ1 = 1.540562 × 10 -10 m and λ2 were not set, and the monochromator was set to single. The XRD pattern of the H1-3 type crystal structure was created in the same manner as above, based on the information on the H1-3 type crystal structure shown in Figure 22. The XRD pattern of the O3' type crystal structure was estimated from the XRD pattern of the positive electrode active material of one embodiment of the present invention, and fitting was performed using TOPAS ver.3 (crystal structure analysis software manufactured by Bruker), and an XRD pattern was created in the same manner as the others.

[0251] As shown in FIG. 21, in the O3' type crystal structure, diffraction peaks appear at 2θ=19.25±0.12° (19.13° or more and 19.37° or less) and 2θ=45.47±0.10° (45.37° or more and 45.57° or less).

[0252] However, as shown in Figure 22, no peaks appear at these positions in the H1-3 type crystal structure and trigonal O1. x The appearance of diffraction peaks at 2θ=19.25±0.12° (19.13° or more and 19.37° or less) and 2θ=45.47±0.10° (45.37° or more and 45.57° or less) when x in CoO2 is small can be said to be a characteristic of the positive electrode active material 100 of one embodiment of the present invention.

[0253] This can also be said to be because the positions at which XRD diffraction peaks appear are close between the crystal structures with x = 1 and x ≦ 0.24. More specifically, for the main diffraction peaks of the crystal structures with x = 1 and x ≦ 0.24 that appear at 2θ angles of 42° to 46°, the difference in 2θ is 0.7° or less, more preferably 0.5° or less.

[0254] The positive electrode active material 100 according to one embodiment of the present invention is Li x When x in CoO2 is small, the material has an O3'-type crystal structure, but it does not have to be entirely O3'-type. It may contain other crystal structures, or it may be partially amorphous. However, when Rietveld analysis is performed on the XRD pattern, the O3'-type crystal structure is preferably 50% or more, more preferably 60% or more, and even more preferably 66% or more. If the O3'-type crystal structure is 50% or more, more preferably 60% or more, and even more preferably 66% or more, it can be a positive electrode active material with sufficiently excellent cycle characteristics.

[0255] Furthermore, the sharpness of diffraction peaks in an XRD pattern indicates the degree of crystallinity. Therefore, it is preferable that each diffraction peak after charging is sharp, i.e., has a narrow half-width. The half-width varies depending on the XRD measurement conditions or the value of 2θ, even for peaks arising from the same crystalline phase. Under the measurement conditions described above, for peaks observed between 2θ = 43° and 46°, the half-width is preferably 0.2° or less, more preferably 0.15° or less, and even more preferably 0.12° or less. A narrow half-width and high crystallinity contribute to the stabilization of the crystal structure after charging. On the other hand, with conventional LiCoO2, even if a portion of the peak can adopt a structure similar to the O3'-type crystal structure, the crystallite size becomes small, resulting in broad and small peaks.

[0256] <xps> In the case of inorganic oxides, X-ray photoelectron spectroscopy (XPS) can analyze a region from the surface to a depth of approximately 2 to 8 nm (usually 5 nm or less) by using monochromatic aluminum Kα X-rays. This allows quantitative analysis of the concentration of each element in a region approximately half the depth of the surface layer 100a. Furthermore, narrow scan analysis can be used to analyze the bonding state of elements. The quantitative accuracy of XPS is often approximately ±1 atomic %, and the lower detection limit is approximately 1 atomic %, depending on the element.

[0257] The concentration of the added element may also be compared in terms of its ratio to cobalt. Using the ratio to cobalt is preferable because it allows comparisons to be made while reducing the influence of carbonates and other substances chemisorbed after the preparation of the positive electrode active material. For example, the ratio of the number of magnesium atoms to cobalt atoms (Mg / Co) determined by XPS analysis is preferably 0.400 or more, more preferably 0.500 or more, more preferably 0.600 or more, more preferably 0.700 or more, more preferably 0.800 or more, more preferably 0.900 or more, and more preferably 1.000 or more. Furthermore, Mg / Co is preferably 2.000 or less, more preferably 1.500 or less, more preferably 1.400 or less, more preferably 1.300 or less, or even more preferably 1.200 or less.

[0258] Furthermore, the ratio of the number of nickel and cobalt atoms, Ni / Co, as determined by XPS analysis, is preferably 0.05 or more, more preferably 0.06 or more, more preferably 0.07 or more, more preferably 0.08 or more, and even more preferably 0.09 or more. Furthermore, Ni / Co is preferably 0.200 or less, preferably 0.150 or less, preferably 0.140 or less, preferably 0.130 or less, preferably 0.120 or less, or preferably 0.110 or less.

[0259] Furthermore, the ratio of the number of fluorine atoms to the number of cobalt atoms, F / Co, as determined by XPS analysis, is preferably 0.100 or more, more preferably 0.200 or more, more preferably 0.300 or more, more preferably 0.400 or more, more preferably 0.500 or more, more preferably 0.600 or more, and more preferably 0.700 or more. Furthermore, F / Co is preferably 1.500 or less, preferably 1.200 or less, preferably 1.100 or less, preferably 1.000 or less, and preferably 0.900 or less.

[0260] The above range indicates that these additive elements are not attached to a narrow area on the surface of the positive electrode active material 100, but are widely distributed at preferred concentrations in the surface layer portion 100a of the positive electrode active material 100. In other words, as a result of the XPS analysis of the positive electrode active material 100, the above range indicates that the crystalline structure is less likely to collapse even when charging and discharging are repeated so that x is 0.24 or less, and excellent cycle characteristics can be achieved.

[0261] Furthermore, when the positive electrode active material 100 according to one embodiment of the present invention is analyzed by XPS, the peak representing the bond energy between fluorine and other elements is preferably equal to or greater than 682 eV and less than 685 eV, and more preferably about 684.3 eV, which is different from both the bond energy of lithium fluoride (685 eV) and the bond energy of magnesium fluoride (686 eV).

[0262] Furthermore, when the positive electrode active material 100 according to one embodiment of the present invention is analyzed by XPS, the peak showing the bond energy between magnesium and other elements is preferably equal to or greater than 1302 eV and less than 1304 eV, and more preferably about 1303 eV, which is different from the bond energy of magnesium fluoride, 1305 eV, and is close to the bond energy of magnesium oxide.

[0263] <edx> It is preferable that one or more selected from the additive elements contained in the positive electrode active material 100 have a concentration gradient. It is more preferable that the depth from the surface of the concentration peak varies depending on the additive element in the positive electrode active material 100. The concentration gradient of the additive element can be evaluated, for example, by exposing a cross section of the positive electrode active material 100 using a focused ion beam (FIB) or the like and analyzing the cross section using energy dispersive X-ray spectroscopy (EDX), electron probe microanalysis (EPMA), or the like.

[0264] Among EDX measurements, EDX area analysis is performed by scanning an area and evaluating the area in two dimensions. Linear analysis is performed by scanning a line to evaluate the distribution of atomic concentrations within the positive electrode active material. Linear analysis is also sometimes used to extract data from a linear area of ​​EDX area analysis. Point analysis is performed by measuring an area without scanning.

[0265] EDX area analysis (e.g., element mapping) can quantitatively analyze the concentration of the additive element in the surface layer 100a, the interior 100b, and near the grain boundaries of the positive electrode active material 100. Furthermore, EDX line analysis can analyze the concentration distribution and maximum value of the additive element. Furthermore, analysis after thinning the sample using FIB or the like is more suitable because it can analyze the concentration distribution in the depth direction from the surface to the center of the positive electrode active material in a specific region without being affected by the distribution in the depth direction.

[0266] Therefore, when EDX area analysis or EDX point analysis is performed on positive electrode active material 100 of one embodiment of the present invention, it can be confirmed that the concentration of each additional element, particularly additional element X, in surface layer portion 100a is higher than that in interior portion 100b.

[0267] In STEM-EDX ray analysis, the graph of the detected amount of characteristic X-rays of the element does not change sharply in principle or due to measurement errors, and it may be difficult to precisely determine the surface. Therefore, when referring to the depth direction in STEM-EDX ray analysis, the detected amount of characteristic X-rays of the transition metal M is the average value M of the detected amount of characteristic X-rays of the internal transition metal M. AVE and the average amount of the characteristic X-rays of the transition metal M in the background, M BG The point where the detected amount of oxygen characteristic X-rays is 50% of the sum of the two, or the detected amount of oxygen characteristic X-rays is the average value O AVE and the average amount of background oxygen characteristic X-rays detected, O BG The reference point on the surface is the point where the detected amount of the characteristic X-rays of the transition metal M is 50% of the sum of the average value of the detected amount of the characteristic X-rays of the transition metal M inside and the average value of the detected amount of the characteristic X-rays of the transition metal M in the background. If the point where the detected amount of the characteristic X-rays of oxygen is 50% of the sum of the average value of the detected amount of the characteristic X-rays of oxygen inside and the average value of the detected amount of the characteristic X-rays of oxygen in the background is different from the point where the detected amount of the characteristic X-rays of oxygen is 50% of the sum of the average value of the detected amount of the characteristic X-rays of oxygen inside and the average value of the detected amount of the characteristic X-rays of oxygen in the background, this is considered to be due to the influence of metal oxides, carbonates, etc. containing oxygen attached to the surface. AVE and the average amount of the characteristic X-rays of the transition metal M in the background, M BG The point where the sum of the transition metals M and M is 50% can be used as the surface position of the positive electrode active material. In the case of a positive electrode active material containing multiple transition metals M, the M of the element with the largest amount of characteristic X-rays detected inside can be used as the surface position of the positive electrode active material. AVE and M BG The reference point can be determined using the following formula:

[0268] The average value of the background of the transition metal M BG can be obtained by averaging the area of ​​2 nm or more, preferably 3 nm or more, of the outermost part of the positive electrode active material, avoiding the area where the detected amount of the transition metal M starts to increase. AVE The average value of the oxygen background O can be determined by averaging a range of 2 nm or more, preferably 3 nm or more, at a depth of 30 nm or more, preferably more than 50 nm, from the region where the counts of the transition metal M and oxygen are saturated and stable, for example, the region where the detected amount of the transition metal M begins to increase. BG and the average value of the internal detected amount of oxygen, O AVE can also be found in the same way.

[0269] The surface of the positive electrode active material 100 in a cross-sectional STEM (scanning transmission electron microscope) image or the like is the boundary between an area where an image derived from the crystalline structure of the positive electrode active material is observed and an area where it is not observed, and is the outermost area where atomic columns derived from the atomic nuclei of metal elements having atomic numbers larger than that of lithium among the metal elements constituting the positive electrode active material are observed. The surface in a STEM image or the like may be determined in conjunction with an analysis with higher spatial resolution.

[0270] In STEM-EDX analysis, a peak refers to a convex maximum value that appears in a graph of the characteristic X-ray intensity for each element, or the maximum value of the characteristic X-ray for each element. Note that noise in STEM-EDX analysis can be measured values ​​with a half-width less than the spatial resolution (R), for example, R / 2 or less.

[0271] For example, when EDX area analysis or EDX point analysis is performed on a cathode active material 100 containing magnesium as an additive element, the magnesium concentration in the surface layer 100a is preferably higher than the magnesium concentration in the interior 100b. Furthermore, when EDX line analysis is performed, the magnesium concentration peak in the surface layer 100a is preferably present at a depth of 3 nm from the surface toward the center of the cathode active material 100, more preferably at a depth of 1 nm, and even more preferably at a depth of 0.5 nm. Alternatively, it is preferably within ±1 nm from the surface. Furthermore, the magnesium concentration preferably decays to 60% or less of the peak at a depth of 1 nm from the peak. Furthermore, it preferably decays to 30% or less of the peak at a depth of 2 nm from the peak. Here, the "peak concentration" refers to the maximum concentration. Due to the influence of spatial resolution in EDX line analysis, the position where the magnesium concentration peak exists may take a negative value as a depth from the surface toward the interior.

[0272] In the positive electrode active material 100 containing magnesium and fluorine as additive elements, the fluorine distribution preferably overlaps with the magnesium distribution. For example, the difference in depth between the peak of the fluorine concentration and the peak of the magnesium concentration is preferably within 10 nm, more preferably within 3 nm, and even more preferably within 1 nm.

[0273] Furthermore, when EDX analysis is performed, the fluorine concentration peak of the surface layer portion 100a is preferably present at a depth of 3 nm from the surface toward the center of the positive electrode active material 100, more preferably at a depth of 1 nm, and even more preferably at a depth of 0.5 nm. Alternatively, it is preferable that the fluorine concentration peak be present within ±1 nm from the surface. Furthermore, it is more preferable that the magnesium concentration peak be present slightly inward from the fluorine concentration peak, as this increases resistance to hydrofluoric acid. For example, it is more preferable that the magnesium concentration peak be present at a depth of 0.5 nm or more inward from the fluorine concentration peak, and even more preferable that the magnesium concentration peak be present at a depth of 1.5 nm or more inward from the fluorine concentration peak.

[0274] In a positive electrode active material 100 containing nickel as an additive element, the nickel concentration peak in the surface layer 100a preferably exists within a depth of 3 nm from the surface toward the center of the positive electrode active material 100, more preferably within a depth of 1 nm, and even more preferably within a depth of 0.5 nm. Alternatively, it is preferable that the nickel concentration peak be within ±1 nm from the surface. In a positive electrode active material 100 containing magnesium and nickel, the nickel distribution preferably overlaps with the magnesium distribution. For example, the difference in depth between the nickel concentration peak and the magnesium concentration peak is preferably within 10 nm, more preferably within 3 nm, and even more preferably within 1 nm.

[0275] Furthermore, when the positive electrode active material 100 contains aluminum as an additive element, it is preferable that the magnesium, nickel, or fluorine concentration peak be closer to the surface than the aluminum concentration peak in the surface layer portion 100 a when EDX analysis is performed. For example, the aluminum concentration peak is preferably present at a depth of 0.5 nm to 50 nm, more preferably 3 nm to 30 nm, from the surface to the center of the positive electrode active material 100.

[0276] Furthermore, when EDX line analysis, area analysis, or point analysis is performed on the positive electrode active material 100, the ratio of the number of atoms of magnesium (Mg) to cobalt (Co) (Mg / Co) at the peak of the magnesium concentration is preferably 0.05 to 0.6, more preferably 0.1 to 0.4. The ratio of the number of atoms of aluminum (Al) to cobalt (Co) (Al / Co) at the peak of the aluminum concentration is preferably 0.01 to 0.6, more preferably 0.05 to 0.45. The ratio of the number of atoms of nickel (Ni) to cobalt (Co) (Ni / Co) at the peak of the nickel concentration is preferably 0 to 0.2, more preferably 0.01 to 0.1, more preferably 0.05 to 0.1. The ratio of the number of atoms of fluorine (F) to cobalt (Co) (F / Co) at the peak of the fluorine concentration is preferably 0 to 1.6, more preferably 0.1 to 1.4.

[0277] <Cleaning> Various analyses have been described, but before subjecting the samples to analysis, such as the positive electrode active material and the positive electrode active material layer, may be washed to remove the electrolyte, binder, conductive material, or compounds derived from these adhering to the surface of the positive electrode active material. In this case, lithium may dissolve in the solvent used for washing, but even in this case, the added element is unlikely to dissolve, and therefore the atomic ratio of the added element is not affected.

[0278] <Positive electrode current collector> A metal foil can be used as the positive electrode current collector. The positive electrode can be formed by applying a slurry onto the metal foil and drying it. Note that pressing may be performed after drying. The positive electrode is formed by forming an active material layer on the positive electrode current collector 21.

[0279] The current collector can be made of a highly conductive material, such as a metal such as stainless steel, gold, platinum, aluminum, or titanium, or an alloy thereof. The material used for the positive electrode current collector is preferably one that does not dissolve at the potential of the positive electrode. Aluminum alloys containing elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, can also be used. The current collector can be in any suitable shape, such as a foil, plate, sheet, mesh, punched metal, or expanded metal. The current collector should preferably have a thickness of 5 μm or more and 30 μm or less.

[0280] As shown in FIG. 23, a laminated current collector 17 having a structure in which metal layers 16 are formed on both sides of an organic material film 15 can be used as the current collector. The organic material film 15 can be made of an organic material film such as polypropylene, polyethylene, nylon, or polyethylene terephthalate. The metal layer 16 can be made of a highly conductive material such as stainless steel, gold, platinum, aluminum, titanium, or an alloy thereof. The laminated current collector 17 can be fabricated by bonding an organic material film to a metal foil (metal layer 16). In this case, an adhesive layer is provided between the organic material film and the metal layer. Alternatively, the laminated current collector 17 can be fabricated by forming the metal layers 16 on both sides of the organic material film 15 by a sputtering method, a vapor deposition method, or the like. When the laminated current collector 17 is used as a positive electrode current collector 21, it is preferable to use aluminum as the metal layer 16. Another example of the laminated current collector configuration is one in which a graphene layer is used instead of the metal layer.

[0281] <Positive electrode binder> The binder that can be used in the positive electrode will be described.

[0282] As the binder, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, etc. Also, as the binder, fluororubber can be used.

[0283] Furthermore, it is preferable to use materials such as polystyrene, polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate (PMMA)), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose as the binder.

[0284] It may be preferable to use a thickener in addition to the binder. For example, a water-soluble polymer is preferably used as the thickener. For example, a polysaccharide can be used as the water-soluble polymer. For example, a cellulose derivative such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, or regenerated cellulose, or starch can be used as the polysaccharide.

[0285] When the binder covers the surface of the active material, or when the binder in contact with the surface forms a film, it can serve as a passive film and is expected to have the effect of suppressing decomposition of the electrolyte. Here, the "passive film" refers to a film with no electrical conductivity or a film with extremely low electrical conductivity. For example, when a passive film is formed on the surface of the active material, it can suppress decomposition of the electrolyte at the battery reaction potential. Furthermore, it is more desirable that the passive film suppresses electrical conductivity while still allowing lithium ions to conduct.

[0286] <Conductive material> The conductive material that can be used for the positive electrode and the negative electrode is also called a conductivity imparting agent or conductive material, and is preferably a carbon material. By attaching the conductive material between multiple active materials, the multiple active materials are electrically connected to each other, thereby increasing the conductivity. Note that the term "attachment" does not only refer to physical adhesion between the active material and the conductive material, but also includes cases where a covalent bond is formed, bonding due to van der Waals forces, where the conductive material covers a part of the surface of the active material, where the conductive material is embedded in the surface irregularities of the active material, and where the active material is electrically connected even when not in contact with each other.

[0287] As the conductive material, for example, one or more of carbon black such as acetylene black (AB) and furnace black, graphite such as artificial graphite and natural graphite, carbon fiber such as carbon nanofiber and carbon nanotube, graphene, and graphene compounds can be used.

[0288] Acetylene black is difficult to bring into surface contact with other active materials, and tends to result in point contact. Therefore, when an active material is mixed with acetylene black, it is possible to use a large amount of acetylene black to reduce contact resistance, but this reduces the proportion of active material, resulting in a decrease in the discharge capacity of the secondary battery. In addition, acetylene black is a material that tends to aggregate, so it is preferable to form a slurry using a dispersant or the like to ensure uniform dispersion.

[0289] In view of these considerations, it is preferable to set the weight ratio of acetylene black in the negative electrode to be equal to or less than the weight ratio of silicon particles used in the negative electrode active material. In other words, by satisfying this weight ratio, acetylene black can be mixed to exhibit high dispersibility without reducing the proportion of silicon particles. This can increase the discharge capacity of the secondary battery.

[0290] Examples of the carbon fiber that can be used include mesophase pitch-based carbon fiber and isotropic pitch-based carbon fiber. Carbon nanofibers or carbon nanotubes can also be used as the carbon fiber. Carbon nanotubes can be produced by vapor phase growth, for example. VGCF (registered trademark) can also be used as the carbon fiber.

[0291] The above-mentioned graphene includes graphene, multilayer graphene, multigraphene, etc. Furthermore, the above-mentioned graphene compounds include graphene oxide, multilayer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multi-graphene oxide, graphene quantum dots, etc. Graphene refers to a substance containing carbon, having a shape such as a plate or sheet, and having a two-dimensional structure formed by six-membered carbon rings. The two-dimensional structure formed by six-membered carbon rings may also be called a carbon sheet. Furthermore, graphene is preferably rigid and has a curved shape. Graphene compounds may have holes in the carbon rings, may have more than six rings, and may also have functional groups. Furthermore, because graphene compounds are soft, they may be rolled up into, for example, carbon nanofibers.

[0292] Since graphene or a graphene compound can be in surface contact with an active material, a smaller amount of graphene or a graphene compound is required than a conventional conductive material. This allows the proportion of the active material in the active material layer to be increased, thereby increasing the discharge capacity of the secondary battery.

[0293] Although carbon fibers are in surface contact with active materials, their long axis is longer than their short axis, allowing for an appropriate electrical path between active materials that are spaced apart. This allows for a smaller amount of carbon fiber than a typical conductive material. This allows for a larger proportion of active material in the active material layer, thereby increasing the discharge capacity of the secondary battery.

[0294] <Electrolyte> One form of electrolyte solution is an electrolyte solution having a solvent and an electrolyte dissolved in the solvent. The solvent is preferably an aprotic solvent, such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, or sultone, or two or more of these can be used in any combination and ratio. When two or more solvents are used, they are sometimes referred to as mixed solvents.

[0295] As another example of an electrolyte solution, one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) can be used as the solvent. In this case, even if the internal temperature of the power storage device rises due to an internal short circuit or overcharging, the power storage device can be prevented from exploding or catching fire. The ionic liquid is composed of cations and anions, including organic cations and anions. Examples of organic cations used in the electrolyte solution include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte solution include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.

[0296] Examples of the electrolyte (also called lithium salt) dissolved in the solvent include LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, and Li2B 10 Cl 10 , Li2B 12 Cl 12 Lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(FSO2)2(LiFSI), LiN(CF3SO2)2(LiTFSI), LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, and lithium bis(oxalato)borate (Li(C2O4)2, LiBOB) can be used alone or in any combination and ratio of two or more of these.

[0297] An additive may be mixed into the mixed solvent containing the lithium salt. Examples of the additive include vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalato)borate (LiBOB), LiFSI, LiTFSI, and dinitrile compounds such as succinonitrile and adiponitrile. The concentration of the additive may be, for example, 0.1 wt% to 5 wt% of the mixed solvent containing the lithium salt.

[0298] <Electrolyte example 1> The mixed solvent used in one embodiment of the present invention can be a material that has excellent lithium ion conductivity even during charging and / or discharging (charging and discharging) in a low-temperature environment.

[0299] An example of the electrolyte solution will be described below. The electrolyte solution described in this embodiment is a mixed solvent in which a lithium salt is dissolved, and the mixed solvent is liquid at room temperature. The mixed solvent is not limited to being liquid at room temperature, and a solid electrolyte that becomes solid at room temperature can also be used. Alternatively, a semi-solid electrolyte that contains both liquid and solid at room temperature can also be used. The semi-solid electrolyte includes a gel-like electrolyte.

[0300] The mixed solvent of the electrolyte solution according to one embodiment of the present invention may contain two or more selected from fluorinated cyclic carbonates (also referred to as fluorinated cyclic carbonates) and fluorinated chain carbonates (also referred to as fluorinated chain carbonates).

[0301] Examples of fluorinated cyclic carbonates that can be used include fluoroethylene carbonate (fluoroethylene carbonate, FEC, F1EC), difluoroethylene carbonate (DFEC, F2EC), trifluoroethylene carbonate (F3EC), and tetrafluoroethylene carbonate (F4EC). DFEC has isomers such as cis-4,5 and trans-4,5. Since all of these fluorinated cyclic carbonates have electron-withdrawing substituents, they are believed to have low solvation energies for lithium ions.

[0302] The following structural formula (H10) is the structural formula of FEC, in which the electron-withdrawing substituent is an F group.

[0303] [ka]

[0304] Methyl 3,3,3-trifluoropropionate is an example of a fluorinated chain carbonate. The following structural formula (H22) is the structural formula of methyl 3,3,3-trifluoropropionate. The abbreviation for methyl 3,3,3-trifluoropropionate is "MTFP." In MTFP, the electron-withdrawing substituent is a CF3 group.

[0305] [ka]

[0306] As a fluorinated chain carbonate, there is trifluoromethyl 3,3,3-trifluoropropionate. The following structural formula (H23) is the structural formula of trifluoromethyl 3,3,3-trifluoropropionate. The electron-withdrawing substituent is the CF3 group.

[0307] [Chemical formula]

[0308] As a fluorinated chain carbonate, there is trifluoromethyl propionate. The following structural formula (H24) is the structural formula of trifluoromethyl propionate. The electron-withdrawing substituent is the CF3 group.

[0309] [Chemical formula]

[0310] As a fluorinated chain carbonate, there is methyl 2,2-difluoropropionate. The following structural formula (H25) is the structural formula of methyl 2,2-difluoropropionate. The electron-withdrawing substituent is the CF2 group.

[0311] [Chemical formula]

[0312] <FEC and MTFP> The mixed solvent described in this embodiment may preferably contain FEC and MTFP. The reason will be explained.

[0313] FEC is a cyclic carbonate with a high dielectric constant. When used in an organic solvent, it promotes the dissociation of lithium salts. However, because FEC contains electron-withdrawing substituents, it desolvates with lithium ions more readily than ethylene carbonate (EC). Specifically, the solvation energy of lithium ions in FEC is lower than that of EC without electron-withdrawing substituents. This facilitates the release of lithium ions from the surfaces of the positive and negative electrode active materials, thereby reducing the internal resistance of secondary batteries. Furthermore, FEC has a deep highest occupied molecular orbital (HOMO) level, making it less susceptible to oxidation and improving oxidation resistance. However, FEC's high viscosity is a concern. Therefore, it is recommended to use an organic solvent mixture containing MTFP in addition to FEC in the electrolyte. MTFP is a chain carbonate that can reduce the viscosity of the electrolyte or maintain its viscosity at room temperature (typically 25°C) even at low temperatures (typically 0°C). Furthermore, although MTFP has a lower solvation energy than methyl propionate (abbreviated as "MP"), which does not have electron-withdrawing substituents, it may still form solvates with lithium ions when used in an electrolyte solution.

[0314] The organic solvents described above are preferably highly purified, with a low content of particulate waste or molecules other than the constituent molecules of the organic solvent (hereinafter simply referred to as "impurities," including oxygen (O), water (HO), or moisture). Furthermore, it is preferable that the reaction by-products produced during synthesis are suppressed through appropriate purification. Specifically, the impurities in the electrolyte are 100 ppm or less, preferably 50 ppm or less, and more preferably less than 10 ppm. The concentration of moisture among the impurities can be detected by Karl Fischer titration.

[0315] Furthermore, it is preferable that the above-mentioned organic solvents have almost no peaks due to impurities that can be detected by NMR measurement or the like. "Almost no peaks can be detected" means that the ratio of the integrated area of ​​the peak due to the impurity to the integrated area of ​​the peak due to the main component (simply referred to as "integral ratio") is 0.005 or less, preferably 0.002 or less. The device used for NMR measurement is not particularly limited, but for example, Bruker's "AVANCE III 400" can be used. Furthermore, in 1H-NMR measurement, the central peak of the five peaks derived from acetonitrile-d3 used as the solvent can be located at 1.94 ppm.

[0316] For example, in the case of MTFP, it is known that when 1H-NMR is measured using acetonitrile-d3 solvent, four peaks appear at δ between 3.29 ppm and 3.43 ppm. However, if other peaks appear in this vicinity, for example, if a peak appears at δ between 3.24 ppm and 3.29 ppm, the peak is considered to be derived from impurities. Therefore, if the ratio (integral ratio) of the peak area between 3.24 ppm and 3.29 ppm to the peak area between 3.29 ppm and 3.43 ppm is 0.005 or less, preferably 0.002 or less, it can be said that peaks due to impurities are almost impossible to detect.

[0317] The measured values ​​of the HOMO level, solvation energy, and melting point are summarized in the table below.

[0318] [Table 1]

[0319] FEC and MTFP having such physical properties can be mixed and used in a volume ratio of x:100-x (where 5≦x≦30, preferably 10≦x≦20), where the total content of these two mixed solvents is 100 vol%. That is, the mixed solvent should contain more MTFP than FEC. Note that the above volume ratio may be the volume ratio measured before mixing the mixed solvent, and the ambient temperature when mixing the mixed solvent may be room temperature (typically 25°C). A mixed solvent containing FEC and MTFP is preferable because it exhibits a viscosity that allows operation as a lithium-ion battery and maintains an appropriate viscosity even in a low-temperature environment.

[0320] Because typical solvents used in lithium ion batteries freeze at around −20° C., it is difficult to fabricate a lithium ion battery that can be charged and discharged at −30° C., preferably −40° C. However, the mixed solvent described as an example in this embodiment allows the freezing point to be −30° C. or lower, preferably −40° C. or lower, thereby realizing a lithium ion battery that can be charged and discharged even in low-temperature environments. As a result, a lithium ion battery that can be charged and discharged over a wide temperature range, including at least low-temperature environments, can be realized.

[0321] Although FEC has been used as a representative example above, all of the organic compounds described as fluorinated cyclic carbonates have the following characteristics: they have the effect of promoting the dissociation of lithium salts, they have small solvation energies so that the bonds between lithium ions and solvents are easily broken, and they have high viscosities, making them difficult to use below freezing when used alone.

[0322] Although MTFP has been described above as a representative example, any of the organic compounds described as fluorinated chain carbonates can be said to have the effect of reducing or maintaining the viscosity of the electrolyte solution of one embodiment of the present invention. Therefore, if the mixed solvent of one embodiment of the present invention contains a fluorinated cyclic carbonate and a fluorinated chain carbonate, it is possible to provide a lithium ion battery that can be charged and discharged in a low-temperature environment.

[0323] <Electrolyte example 2> As a mixed solvent for an electrolytic solution, which is another aspect of the present invention, it contains ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). When the total content of the ethylene carbonate, the ethyl methyl carbonate, and the dimethyl carbonate is 100 vol%, a mixed solvent having a volume ratio of the ethylene carbonate, the ethyl methyl carbonate, and the dimethyl carbonate of x:y:100 - x - y (where 5 ≤ x ≤ 35 and 0 < y < 65) can be used. More specifically, a mixed solvent containing EC, EMC, and DMC in a volume ratio of EC:EMC:DMC = 30:35:35 can be used. Note that the above volume ratio may be the volume ratio before mixing the mixed solvent, and the outside air temperature when mixing the mixed solvent may be room temperature (typically, 25°C).

[0324] EC is a cyclic carbonate and has a high relative dielectric constant, so it has the effect of promoting the dissociation of lithium salts. On the other hand, EC has a high viscosity and a high freezing point (melting point) of 38°C. Therefore, when using EC alone as a solvent, it is difficult to use in a low-temperature environment. Thus, the solvent specifically described as one aspect of the present invention contains not only EC alone but also further contains EMC and DMC. EMC is a chain carbonate and has the effect of lowering the viscosity of the electrolytic solution, and its freezing point is -54°C. Also, DMC is also a chain carbonate and has the effect of lowering the viscosity of the electrolytic solution, and its freezing point is -43°C. An electrolytic solution prepared using a mixed solvent obtained by mixing EC, EMC, and DMC having such physical properties so that the total content of these three mixed solvents is 100 vol% and the volume ratio is x:y:100 - x - y (where 5 ≤ x ≤ 35 and 0 < y < 65) has the characteristic that its freezing point is -40°C or lower.

[0325] A typical electrolyte used in lithium ion batteries solidifies at about −20° C., making it difficult to fabricate a battery that can be charged and discharged at −40° C. The electrolyte described as an example in this embodiment has a freezing point of −40° C. or lower, making it possible to realize a lithium ion battery that can be charged and discharged even in a low-temperature environment of −40° C.

[0326] The lithium salt to be dissolved in the solvent may be, for example, LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, or Li2B 10 Cl 10 , Li2B 12 Cl 12 Lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, and lithium bis(oxalato)borate (LiBOB) can be used, or any combination and ratio of two or more of these can be used. The lithium salt dissolved in the solvent is preferably 0.5 mol / L to 1.5 mol / L, preferably 0.7 mol / L to 1.3 mol / L, and more preferably 0.8 mol / L to 1.2 mol / L, relative to the volume of the solvent. A specific example of use is LiPF6, which is preferably 0.5 mol / L to 1.5 mol / L, preferably 0.7 mol / L to 1.3 mol / L, and more preferably 0.8 mol / L to 1.2 mol / L, relative to the volume of the solvent.

[0327] Furthermore, the mixed solvent is preferably highly purified, with a low content of granular dust or elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities"). Specifically, the weight ratio of impurities to the electrolyte is preferably 1% or less, more preferably 0.1% or less, and even more preferably 0.01% or less.

[0328] Furthermore, for the purpose of improving safety, etc., a coating (solid electrolyte interphase film) may be formed at the interface between the electrode (active material layer) and the electrolyte solution. Additives such as vinylene carbonate (VC), propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate)borate (LiBOB), or dinitrile compounds such as succinonitrile or adiponitrile may be added to the electrolyte solution. The concentration of the additive may be, for example, 0.1 wt% to 5 wt% relative to the solvent.

[0329] In the electrolyte solution example 2, the lithium salt may be the same as that described in the electrolyte solution example 1. The additive may also be the same as that described in the electrolyte solution example 1.

[0330] As described above, examples of the electrolyte solution that can be used in the lithium-ion battery of one embodiment of the present invention have been described, but the electrolyte solution that can be used in the lithium-ion battery of one embodiment of the present invention is not limited to this example. Other materials can also be used as long as they have excellent lithium-ion conductivity even during charge and discharge in a low-temperature environment.

[0331] [Negative electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector, and the negative electrode active material layer has a negative electrode active material.

[0332] <Negative electrode binder> A polymer having a carboxy group is preferably used as the binder for the negative electrode, which is one embodiment of the present invention. A carboxy group can be said to have two basic oxygen atoms, one acidic hydrogen atom, and one electrophilic carbon atom. Furthermore, a carboxy group can be said to have a polar group, containing a hydroxyl group (OH) and a carbonyl group (C=O). When a binder contains a polar group such as a carboxy group, it is expected to interact with lithium ions, which are carrier ions. For example, by attracting lithium ions, it may assist in the insertion of lithium ions into the negative electrode active material. Carboxy groups can be identified using FT-IR or other methods.

[0333] Examples of polymers with carboxyl groups include polyglutamic acid (sometimes written as PGA), polyacrylic acid (sometimes written as PAA), and alginic acid (sometimes written as polysaccharide). Polyamino acids may also be used as polymers with carboxyl groups, and specifically, polyornithine and polysarcosine may be used as binders. Furthermore, polyaspartic acid may also be used as a binder for polymers with ketone groups. Furthermore, binary copolymers (copolymers) may also be used as polymers with ketone groups, and copolymers of acrylic acid and maleic acid, or copolymers of acrylic acid and sulfonic acid may also be used as binders. Using these as binders for the negative electrode also has the effect of reducing the amount of binder mixed in the negative electrode.

[0334] Among the above polymers, polyglutamic acid or polyacrylic acid is particularly preferable as a binder for use in a negative electrode. The structural formula of polyglutamic acid is shown below.

[0335] [ka]

[0336] As is clear from the structural formula, polyglutamic acid contains nitrogen in addition to carboxyl groups, and since the nitrogen has an unshared electron pair, it is expected to interact with lithium ions, which are carrier ions. For example, the unshared electron pair may attract lithium ions and assist their insertion into the negative electrode active material.

[0337] Furthermore, as is clear from the structural formula, polyglutamic acid has a carbonyl group, C=O, in addition to the carbonyl group. If the binder has a polar group such as a carbonyl group, it is expected to interact with lithium ions, which are carrier ions, and may, for example, assist the insertion and desorption of lithium ions in the negative electrode active material.

[0338] Either linear γ-polyglutamic acid or cross-linked γ-polyglutamic acid may be used as the binder. These are collectively referred to as a structure mainly composed of γ-polyglutamic acid. Cross-linked γ-polyglutamic acid is more suitable for binders because it has a network structure. Furthermore, the molecular weight of the polyglutamic acid should be 1 million or more, preferably 3 million or more, and more preferably 10 million to 50 million.

[0339] Depending on the method for preparing polyglutamic acid, it can be said to have a structure mainly composed of γ-glutamic acid containing other elements (e.g., Ca, Al, Na, Mg, Fe, Si, S). That is, polyglutamic acid may be neutralized with alkali metal ions, such as lithium ions or sodium ions.

[0340] Such polyglutamic acid is hydrophilic, so deionized water can be used as a solvent, which is suitable for forming a slurry.

[0341] The structural formula of polyacrylic acid is shown below.

[0342] [ka]

[0343] As is clear from the structural formula, polyacrylic acid has a carboxy group.

[0344] A material obtained by cross-linking polyacrylic acid may also be used. This is preferable because it can form a cross-linked structure, i.e., a network structure, which may enhance the function as a binder.

[0345] <Negative electrode active material> A negative electrode according to one embodiment of the present invention includes both carbon particles and silicon particles as negative electrode active materials. Examples of the carbon particles include graphite, carbon having a layer structure similar to graphite, amorphous carbon, and hard carbon. Specifically, graphite particles are preferably used as the carbon particles used in this specification.

[0346] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape and is preferred. Furthermore, it is relatively easy to reduce the surface area of ​​MCMB, and this may be preferred. Examples of natural graphite include flake graphite and spherical natural graphite.

[0347] The graphite particles according to one embodiment of the present invention preferably have an average particle size of 1 μm or more, preferably 5 μm or more, preferably 10 μm or more, and more preferably 20 μm or more. The graphite particles may be mixed with silicon particles before use in the negative electrode.

[0348] The average particle size of the graphite particles can be measured by a particle size distribution analyzer using a laser diffraction / scattering method, etc. In this specification and the like, the average particle size of the graphite particles can be determined as the median diameter (D50).

[0349] The specific surface area of ​​graphite particles is 0.5m 2 / g or more 3m 2 / g or less is preferable. The specific surface area can be measured by the BET method. The specific surface area by the BET method is a value measured by the nitrogen gas adsorption BET single-point method, and can be measured using an automatic specific surface area / pore distribution measuring device, Tristar II 3020 (manufactured by Shimadzu Corporation).

[0350] Silicon particles with an average particle diameter of 100 nm or thereabouts are preferably used, and these are sometimes called nanosilicon particles. Silicon has a capacity of 4200 mAh / g by weight, which is more than 10 times the capacity of graphite (372 mAh / g per active material weight). However, silicon has the problem of rapid cycle degradation due to expansion and contraction during charge and discharge. Therefore, to improve cycle degradation, nanosilicon particles, in which silicon is refined to the above average particle diameter, are suitable.

[0351] The average particle size of silicon particles can be measured by a particle size distribution analyzer using a laser diffraction / scattering method, etc. In this specification, etc., the average particle size of silicon particles can be determined as the median diameter (D50).

[0352] The silicon particles are preferably prepared by crushing silicon raw materials and adjusting them to a uniform particle size. Through this adjustment, silicon particles with an average particle size of less than 1 μm can be obtained. Note that if the average particle size is large, the negative electrode active material layer may become thick, so it is preferable that the average particle size is less than 1 μm. The silicon particles may be made of any silicon-based material, and specifically, may contain at least one of silicon, silicon oxide, and silicon alloy.

[0353] The specific surface area of ​​silicon particles is 10m 2 / g or more 35m 2 / g or less, preferably 10m 2 / g or more 15m 2 / g or less is preferable. The specific surface area can be measured by the BET method. The specific surface area by the BET method is a value measured by the nitrogen gas adsorption BET single-point method, and can be measured using an automatic specific surface area / pore distribution measuring device, Tristar II 3020 (manufactured by Shimadzu Corporation).

[0354] In one embodiment of the present invention, when the negative electrode active material contains both graphite particles and silicon particles, a lithium ion battery with a high discharge capacity can be realized. Furthermore, since the average particle diameter of the graphite particles is different from that of the silicon particles, when a mixture of these particles is used in the negative electrode, the amount of the negative electrode active material supported can be increased. Furthermore, in this specification, the amount supported refers to the weight of the negative electrode active material per unit surface area of ​​the negative electrode current collector. The amount of the negative electrode active material supported can be determined according to the capacity of the positive electrode. A small amount of support can improve the output characteristics of the lithium ion battery, but a small amount will result in a small discharge capacity. Therefore, the amount of the negative electrode active material supported is set to 1.5 mg / cm. 2 The above is preferable.

[0355] In one embodiment of the present invention, the weight ratio of graphite particles in the negative electrode active material layer is preferably greater than the weight ratio of silicon particles, for example, the weight ratio of graphite particles is preferably 5 to 15 times the weight ratio of silicon particles. In other words, the weight ratio of silicon to the total weight of the powder materials constituting the negative electrode active material is preferably 7.5 wt% to 37.5 wt%.

[0356] Furthermore, a conductive material may be added when forming the negative electrode active material layer.

[0357] In a lithium-ion battery, a negative electrode active material layer can be formed on one or both sides of a negative electrode current collector. The negative electrode active material layer is completed by applying a slurry onto the negative electrode current collector and then drying it.

[0358] In this specification, the weight ratio of each raw material may be regarded as the blending ratio of each raw material when preparing the slurry. That is, the weight ratio of the negative electrode active material is the blending ratio (wt%) of the negative electrode active material to the total weight of the negative electrode active material and binder in the slurry, or to the total weight of the negative electrode active material, binder, and conductive material. The weight ratio and blending ratio can be understood by replacing the negative electrode active material with the binder.

[0359] The weight ratio of the binder is preferably smaller than the weight ratio of the graphite particles, and in order to exert the effect as a binder, the weight ratio of the binder is preferably greater than 5 wt %.

[0360] <Negative electrode current collector> The negative electrode current collector can be made of the same material as the positive electrode current collector, as well as copper, etc. However, metals that alloy with lithium ions, such as aluminum, cannot be used for the negative electrode current collector.

[0361] Similarly to the positive electrode current collector, the laminated current collector can be used as the negative electrode current collector 31. When the laminated current collector 17 is used as the negative electrode current collector 31, it is preferable to use copper for the metal layer 16.

[0362] <Method for producing negative electrode active material layer> Here, a method for producing a negative electrode active material layer will be described. The negative electrode slurry according to one embodiment of the present invention may be prepared by mixing graphite particles, silicon particles, and a binder having a carboxy group, followed by adding a solvent and mixing. In the slurry according to one embodiment of the present invention, the graphite particles, silicon particles, and a binder having a carboxy group can be mixed simultaneously, which is preferable because it can shorten the process. Furthermore, when preparing the slurry, the graphite particles, silicon particles, a binder having a carboxy group, and a solvent can also be mixed simultaneously. Furthermore, when preparing the slurry, a conductive material can also be mixed simultaneously. The conductive material may be any of the above-mentioned conductive materials, and acetylene black, for example, may be used.

[0363] An example of a flow for producing a negative electrode active material layer is shown in FIG.

[0364] First, there are prepared graphite particles 400, silicon particles 401, binder 402, and conductive material 403. As the binder, a polymer having a carboxy group is used.

[0365] <Step S60> The above-mentioned raw materials are each weighed, and the first mixing is performed in step S60 of Figure 24. Specifically, the weight ratio of silicon particles 401 to the total weight of the powders mixed in the first mixing ranges from 7.5 wt% to 37.5 wt%, and the weight ratio of binder 402 to the total weight ranges from 10 wt% to 50 wt%. Furthermore, the weight ratio of conductive material 403 to the total weight ranges from 0 wt% to 20 wt%. Note that acetylene black is preferably used as conductive material 403 to satisfy the above weight ratios.

[0366] For example, silicon particles 401, graphite particles 400, binder 402, and conductive material 403 are weighed out so that their weight ratio is 3:5:1:1. Alternatively, without using a conductive material, silicon particles 401, graphite particles 400, and binder 402 are weighed out so that their weight ratio is 3:5:1. Alternatively, graphite particles 400, silicon particles 401, and binder 402 may be weighed out so that their weight ratio is 9:1:1.

[0367] <Mixing of mixture 404 and solvent 405> In one embodiment of the present invention, in step S60, all the raw materials are powders, so they are mixed before adding the solvent to obtain a mixture 404. Mixing the powders together allows for a uniform mixture. After that, a solvent 405 is preferably added. Deionized water is preferably used as the solvent 405.

[0368] <Step S61> After the solvent 405 is added, a second mixing is performed in step S61 of Fig. 24 to prepare a slurry 406. The second mixing is sometimes called a slurry preparation.

[0369] The slurry 406 is a liquid material used to form an active material layer on a current collector, and contains at least an active material, a binder, and a solvent, and may further contain a conductive material. The slurry is sometimes called an electrode slurry or an active material slurry.

[0370] Then, in step S62 of FIG. 24, the slurry 406 is applied onto the negative electrode current collector 407. The negative electrode current collector 407 is preferably the current collector with the coating layer described with reference to FIGS. 6 and 7. Thereafter, in step S63 of FIG. 24, the negative electrode current collector 407 is dried. The drying conditions may include preliminary drying and main drying. That is, two drying steps are performed, with the first drying step being under milder conditions. For example, the slurry 406 may be dried in a dryer at a temperature of 40° C. to 60° C. for 10 minutes to 1 hour, which may be referred to as preliminary drying. Next, as main drying, the slurry 406 may be dried in a dryer at a temperature of 60° C. to 90° C. for 30 minutes to 1.5 hours. Pressing may be performed simultaneously with drying.

[0371] After drying, a pressing process is performed as step S64 in FIG. 24. A roll press can be used for the pressing process, but the upper and lower rollers can be set to temperatures of 100°C to 150°C. In other words, heating can be performed simultaneously with the pressing process. The linear pressure during pressing should be 0.3 MPa to 1 MPa. Of course, the lithium-ion battery can be operated even if the pressing process is omitted.

[0372] Through the above steps, a negative electrode 408 having a negative electrode active material layer over a negative electrode current collector 407 can be manufactured.

[0373] A lithium ion battery using the negative electrode 408 thus obtained has a large discharge capacity and exhibits excellent cycle characteristics.

[0374] It is advisable to prevent the silicon particles from being oxidized. For example, when preparing a slurry, it is preferable to carry out a mixing process so that the silicon particles are not oxidized.

[0375] The above-described method for producing a negative electrode active material layer has been described with reference to a case where the negative electrode active material contains both graphite particles and silicon particles. Fig. 25 shows a method for producing a negative electrode active material layer using graphite particles as the negative electrode active material.

[0376] The method for producing a negative electrode active material layer shown in Fig. 25 differs from the method described in Fig. 24 in that graphite particles, a binder, a thickener, a conductive material, and a solvent are prepared as materials. Also, Fig. 25 shows step S160, which is different from step S60, as a process corresponding to step S60 in Fig. 24. In the mixing in step S160, the ratio of graphite particles:binder:thickener:conductive material can be, for example, 96:2:1:1 by weight, but is not limited to this ratio and may be changed as appropriate.

[0377] Note that steps S161, S162, and S163 in FIG. 25 can be processed in the same manner as steps S62, S63, and S64 in FIG. 24, respectively.

[0378] In this manner, a negative electrode active material layer using graphite particles as the negative electrode active material can be produced.

[0379] [Separator] A separator is placed between the positive electrode and the negative electrode. The separator can be made of, for example, cellulose-containing fibers such as paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, or polyurethane. The separator is preferably processed into a bag shape and placed so as to encase either the positive electrode or the negative electrode.

[0380] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene may be coated with a ceramic material, a fluorine-based material, a polyamide material, or a mixture of these. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine-based materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aramid (meta-aramid, para-aramid).

[0381] Coating with ceramic materials improves oxidation resistance, suppressing separator degradation during high-voltage charging and improving the reliability of secondary batteries. Coating with fluorine-based materials also improves adhesion between the separator and electrodes, improving output characteristics. Coating with polyamide materials, especially aramid, improves heat resistance, improving the safety of secondary batteries.

[0382] For example, both sides of a polypropylene film may be coated with a mixed material of aluminum oxide and aramid, or the surface of the polypropylene film that contacts the positive electrode may be coated with a mixed material of aluminum oxide and aramid, and the surface that contacts the negative electrode may be coated with a fluorine-based material.

[0383] When a separator with a multilayer structure is used, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, and therefore the capacity per volume of the secondary battery can be increased.

[0384] [Exterior body] The battery's exterior can be made of a metal material such as aluminum, stainless steel, or titanium, or a resin material. A film-like exterior can also be used. Examples of films include a three-layer structure in which a flexible metal thin film or metal foil such as aluminum, stainless steel, titanium, copper, or nickel is provided on a membrane made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide resin or polyester resin is further provided on the metal thin film as the exterior surface of the exterior. Such a multilayer structure film can be called a laminate film. In this case, the laminate film may be referred to as an aluminum (aluminum) laminate film, stainless steel laminate film, titanium laminate film, copper laminate film, nickel laminate film, or the like, using the name of the material of the metal layer.

[0385] The material or thickness of the metal layer of the laminate film may affect the flexibility of the battery. For example, an aluminum laminate film having a polypropylene layer, an aluminum layer, and nylon is preferably used as an exterior body for a battery with excellent flexibility (flexibility). Here, the thickness of the aluminum layer is preferably 50 μm or less, more preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less. If the aluminum layer is thinner than 10 μm, there is a concern that pinholes in the aluminum layer may reduce the gas barrier properties, so the thickness of the aluminum layer is preferably 10 μm or more.

[0386] Alternatively, a graphene sheet may be used as the laminate film instead of the metal layer. The graphene sheet may be a multilayer graphene sheet having a thickness of 100 nm to 30 μm, preferably 200 nm to 20 μm. The graphene sheet is flexible, has an interlayer distance of 0.34 nm, and has gas barrier properties, making it suitable for use as an exterior body for a secondary battery.

[0387] [Processing method for film with concave and convex parts] Next, a method for processing a film that can be used for the exterior body will be described. As the film, the above-mentioned laminate film can be used.

[0388] For example, a laminate film can be used as the laminate film. For example, a laminate film having a heat seal layer on one or both surfaces of a metal film can be used as the laminate film. For the adhesive layer, a heat-sealable resin film containing polypropylene, polyethylene, or the like can be used. In this embodiment, an aluminum laminate film is used which has a nylon resin on the surface of an aluminum foil and an acid-resistant polypropylene film and a polypropylene film laminate on the back surface of the aluminum foil.

[0389] The film is then embossed, resulting in a film with a concave-convex pattern. The film has a plurality of concave-convex portions, giving it a visible wavy pattern.

[0390] Embossing, which is a type of press working, will be explained below.

[0391] Figure 26 is a cross-sectional view showing an example of embossing. Embossing is a type of press processing, and refers to a process in which an embossing roll with an uneven surface is pressed against a film to form unevenness in the film that corresponds to the unevenness of the embossing roll. An embossing roll is a roll with a pattern engraved on its surface.

[0392] 26 shows an example of embossing on both sides of a film, and a method of forming a film with convex portions having peaks on one side.

[0393] 26 shows a state in which a film 90 is sandwiched between an embossing roll 95 in contact with one side of the film and an embossing roll 96 in contact with the other side, and the film 90 is being fed in a film traveling direction 91. A pattern is formed on the film surface by pressure or heat. Alternatively, a pattern may be formed on the film surface by both pressure and heat.

[0394] As the embossing roll, a metal roll, a ceramic roll, a plastic roll, a rubber roll, an organic resin roll, a wooden roll, or the like can be used as appropriate.

[0395] In Figure 26, embossing is performed using an embossing roll 96, which is a male-pattern embossing roll, and a female-pattern embossing roll 95. The male-pattern embossing roll 96 has multiple convex portions 96a. These convex portions correspond to the convex portions to be formed on the film to be processed. The female-pattern embossing roll 95 has multiple convex portions 95a. Adjacent convex portions 95a form recesses that fit into the convex portions to be formed on the film by the convex portions 96a provided on the male-pattern embossing roll 96.

[0396] By successively performing embossing to raise a portion of the film 90 and blank pressing to depress a portion of the film 90, it is possible to continuously form convex portions and flat portions. As a result, a pattern can be formed on the film 90.

[0397] Next, a film having a plurality of convex portions with shapes different from those shown in Fig. 26 will be described with reference to Fig. 27(A) to Fig. 27(E). By changing the convex shapes of the embossing roll 95 and the embossing roll 96 shown in Fig. 26 to shapes different from those shown in Fig. 26, it is possible to perform embossing processing with various cross-sectional shapes shown in Fig. 27(A) to Fig. 27(E).

[0398] Fig. 27(A) is a cross-sectional schematic diagram of an embossment having a wavy shape, and Fig. 27(B) to Fig. 27(E) are modifications of Fig. 27(A). Fig. 27(B) and Fig. 27(C) are diagrams showing an example in which the wavy shape is formed in a staircase pattern, Fig. 27(D) is a diagram showing an example in which the wavy shape is formed in a rectangular pattern, and Fig. 27(E) is a diagram showing an example in which the wavy shape is formed with acute-angled valley shapes and trapezoidal peak shapes.

[0399] 28(A) and 28(B) are bird's-eye views showing the finished shape when the embossing process shown in FIGS. 26 to 27(E) is performed twice by changing the direction of the film 90. Specifically, the film 90 is embossed in a first direction, and then embossed in a second direction rotated 90 degrees from the first direction, thereby obtaining a film 81 (81a, 81b) having the embossed shape (which can be called a cross-wave shape) shown in FIGS. 28(A) and 28(B). Note that the film 81a having the cross-wave shape shown in FIG. 28(A) shows the outer shape used when fabricating a secondary battery from a single film 81a, and can be folded in half along the dashed line for use. In addition, film 81b having a cross-wave shape and film 81c that has not been embossed as shown in Figure 28(B) show the external shapes used when making a secondary battery using two films (film 81b, film 81c), and film 81b and film 81c can be used by stacking them.

[0400] As described above, by performing processing using an embossing roll, it is possible to miniaturize the device. Furthermore, since processing can be performed without cutting the film, it is excellent in mass productivity. Note that processing is not limited to using an embossing roll, and for example, the film may be processed by pressing a pair of embossing plates with uneven surfaces against the film. In this case, one of the embossing plates may be flat, and processing may be performed in multiple steps.

[0401] In the above-described configuration example of the secondary battery, an example is shown in which the exterior body on one side of the secondary battery has an embossed shape and the exterior body on the other side does not have an embossed shape. However, the configuration of a secondary battery of one embodiment of the present invention is not limited to this. For example, the exterior body on one side of the secondary battery and the exterior body on the other side may have the same embossed shape. Furthermore, the exterior body on one side of the secondary battery and the exterior body on the other side may have different embossed shapes.

[0402] The content of this embodiment can be freely combined with the content of other embodiment modes.

[0403] (Embodiment 2) 29 to 34C, a method for manufacturing a positive electrode active material applicable to a lithium-ion battery having excellent charge-discharge characteristics even in a low-temperature environment will be described. Features of the positive electrode active material applicable to a lithium-ion battery will be described in Embodiment 2.

[0404] <Example 1 of a method for producing a positive electrode active material> An example of a method for manufacturing a positive electrode active material that can be used as one embodiment of the present invention (Example 1 of a method for manufacturing a positive electrode active material) will be described with reference to FIGS.

[0405] First, in step S10, lithium cobalt oxide is prepared as a starting material. The starting lithium cobalt oxide may have a particle size (strictly speaking, a median diameter (D50)) of 10 μm or less (preferably 8 μm or less). The lithium cobalt oxide having a median diameter (D50) of 10 μm or less may be a known or commonly used (in short, commercially available) lithium cobalt oxide, or may be prepared through steps S11 to S14 shown in FIG. 29(B). A representative example of commercially available lithium cobalt oxide having a median diameter (D50) of 10 μm or less is lithium cobalt oxide (product name: CellSeed C-5H) manufactured by Nippon Chemical Industry Co., Ltd. CellSeed C-5H has a median diameter (D50) of approximately 7 μm. A method for preparing lithium cobalt oxide having a median diameter (D50) of 10 μm or less through steps S11 to S14 is described below.

[0406] <Step S11> In step S11 shown in FIG. 29(B), a lithium source (Li source) and a cobalt source (Co source) are prepared as starting materials for lithium and transition metal, respectively.

[0407] As the lithium source, it is preferable to use a compound containing lithium, such as lithium carbonate, lithium hydroxide, lithium nitrate, or lithium fluoride. It is preferable that the lithium source has high purity, and for example, it is recommended to use a material with a purity of 99.99% or higher.

[0408] As the cobalt source, a compound containing cobalt is preferably used, such as tricobalt tetroxide or cobalt hydroxide. The cobalt source preferably has a high purity, for example, a material with a purity of 3N (99.9%) or higher, preferably 4N (99.99%) or higher, more preferably 4N (99.995%) or higher, and even more preferably 5N (99.999%) or higher. By using a high-purity material, impurities in the positive electrode active material can be controlled. As a result, the capacity of the secondary battery is increased, and the reliability of the secondary battery is improved.

[0409] <Step S12> Next, in step S12 shown in FIG. 29(B), the lithium source and the cobalt source are pulverized and mixed to prepare a mixed material. The pulverization and mixing can be performed in a dry or wet manner. Wet pulverization and mixing allows for smaller pulverization, which is preferable for obtaining lithium cobalt oxide with a median diameter (D50) of 10 μm or less as a starting material. When using the wet method, a solvent is prepared. Examples of solvents that can be used include ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, and N-methyl-2-pyrrolidone (NMP). However, it is preferable to use an aprotic solvent that does not react easily with lithium. In this embodiment, dehydrated acetone with a purity of 99.5% or higher is used. It is preferable to mix the lithium source and the transition metal source in dehydrated acetone with a purity of 99.5% or higher, with a water content of 10 ppm or less, and then pulverize and mix them. Using dehydrated acetone with the above purity reduces the amount of impurities that may be present.

[0410] <Step S13> Next, in step S13 shown in Figure 29(B), the mixed material is heated. The heating temperature is preferably 800°C or higher and 1100°C or lower, more preferably 900°C or higher and 1000°C or lower, and even more preferably about 950°C or lower (1000°C or lower). If the temperature is too low, the decomposition and melting of the lithium source and transition metal source may be insufficient. On the other hand, if the temperature is too high, lithium may evaporate from the lithium source and / or cobalt may be excessively reduced, which may result in defects.

[0411] If the heating time is too short, lithium cobalt oxide will not be synthesized, but if it is too long, productivity will decrease. Therefore, the heating time should be from 1 hour to 100 hours, preferably from 2 hours to 20 hours, and more preferably from 2 hours to 10 hours.

[0412] The temperature rise rate depends on the heating temperature reached, but should be between 80°C / h and 250°C / h. For example, if heating at 1000°C for 10 hours, the temperature rise rate should be 200°C / h.

[0413] Heating is preferably carried out in an atmosphere with little moisture, such as dry air, for example, an atmosphere with a dew point of -50°C or less, more preferably an atmosphere with a dew point of -80°C or less. In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. In addition, to suppress impurities that may be mixed into the material, it is preferable that the impurity concentrations of CH4, CO, CO2, and H2 in the heating atmosphere be each 5 ppb (parts per billion) or less.

[0414] The heating atmosphere is preferably an atmosphere containing oxygen. For example, dry air can be continuously introduced into the reaction chamber. In this case, the flow rate of the dry air is preferably 10 L / min. The method in which oxygen is continuously introduced into the reaction chamber and flows through the reaction chamber is called flow.

[0415] When the heating atmosphere is an atmosphere containing oxygen, a method that does not allow oxygen to flow may be used. For example, the reaction chamber may be depressurized and then filled with oxygen to prevent the oxygen from entering or leaving the reaction chamber, a method called purging. For example, the reaction chamber may be depressurized to -970 hPa (differential pressure gauge) and then filled with oxygen to 50 hPa.

[0416] After heating, the material can be cooled naturally, but it is preferable that the time required to cool the material from the specified temperature to room temperature is between 10 and 50 hours. However, cooling to room temperature is not always necessary, as long as the material is cooled to a temperature acceptable for the next step.

[0417] The heating in this step may be carried out using a rotary kiln or a roller hearth kiln. Heating in a rotary kiln can be carried out while stirring, whether in a continuous or batch system.

[0418] The container for holding the object to be heated during heating is preferably an aluminum oxide crucible or an aluminum oxide setter (also called a sheath). An aluminum oxide crucible is a material that is almost free of impurities. In this embodiment, a setter made of aluminum oxide with a purity of 99.9% is used. It is preferable to place a lid on the crucible or setter before heating, as this prevents the material from volatilizing.

[0419] After the heating is completed, the mixture may be crushed and sieved as necessary.

[0420] <Step S14> Through the above steps, lithium cobalt oxide (LiCoO) can be synthesized as shown in step S14 in FIG. 29(B). The lithium cobalt oxide (LiCoO) shown in step S14 is an oxide containing multiple metal elements in its structure, and can therefore be called a composite oxide. In this specification and the like, the term "composite oxide" refers to an oxide containing multiple metal elements in its structure. Note that after step S13, a crushing step and a classification step may be performed to adjust the particle size distribution, and then the lithium cobalt oxide (LiCoO) shown in step S14 may be obtained.

[0421] Although the composite oxide is produced by the solid phase method in steps S11 to S14, the composite oxide may also be produced by a coprecipitation method or a hydrothermal method.

[0422] Through steps S11 to S14, lithium cobalt oxide can be obtained as a starting material for obtaining a positive electrode active material applicable to lithium ion batteries having excellent charge / discharge characteristics even in low-temperature environments. Specifically, lithium cobalt oxide having a median diameter (D50) of 10 μm or less can be obtained as the starting material.

[0423] <Step S15> Next, in step S15 shown in Fig. 29(A), the starting material lithium cobalt oxide is heated. The heating in step S15 is sometimes referred to as initial heating in this specification, etc., because it is the first heating of the lithium cobalt oxide. Alternatively, because it is heating before step S31 described below, it is sometimes referred to as preheating or pretreatment.

[0424] The initial heating causes lithium compounds and other substances unintentionally remaining on the surface of the lithium cobalt oxide to be desorbed. It is also expected to have the effect of enhancing the internal crystallinity. Although the lithium source and / or cobalt source prepared in step S11 and other steps may contain impurities, the initial heating can reduce the amount of impurities in the lithium cobalt oxide starting material. The effect of enhancing the internal crystallinity is, for example, the effect of alleviating distortion, misalignment, and the like, which are caused by differences in shrinkage and the like, of the lithium cobalt oxide prepared in step S14.

[0425] Furthermore, initial heating has the effect of smoothing the surface of the lithium cobalt oxide. Initial heating also has the effect of mitigating cracks, crystal defects, and the like that the lithium cobalt oxide has. In this specification and elsewhere, a "smooth" surface refers to a surface with few irregularities, a rounded overall surface, and rounded corners. Alternatively, a state in which there is little foreign matter attached to the surface is also referred to as "smooth." Foreign matter is considered to be a cause of irregularities, so it is preferable not to allow it to adhere to the surface.

[0426] In this initial heating, it is not necessary to separately prepare a material that functions as a lithium source, an additive element source, or a flux.

[0427] If the heating time in this step is too short, sufficient effects will not be obtained, but if it is too long, productivity will decrease. An appropriate heating time range can be selected, for example, from the heating conditions described in step S13. The heating temperature in step S15 should be lower than the temperature in step S13 in order to maintain the crystalline structure of the complex oxide. Furthermore, the heating time in step S15 is preferably shorter than the time in step S13 in order to maintain the crystalline structure of the complex oxide. For example, heating is preferably performed at a temperature of 700°C to 1000°C (more preferably, 800°C to 900°C) for 1 hour to 20 hours (more preferably, 1 hour to 5 hours).

[0428] The heating in step S13 can cause a temperature difference between the surface and interior of the lithium cobalt oxide. This temperature difference can induce a shrinkage difference. It is thought that the temperature difference causes a difference in fluidity between the surface and interior, resulting in a shrinkage difference. The energy associated with the shrinkage difference causes a difference in internal stress in the lithium cobalt oxide. This difference in internal stress is also called strain, and this energy is sometimes called strain energy. The internal stress is removed by the initial heating in step S15; in other words, the strain energy is homogenized by the initial heating in step S15. When the strain energy is homogenized, the strain in the lithium cobalt oxide is relaxed. This smooths the surface of the lithium cobalt oxide. Alternatively, it can be said that the surface is improved. In other words, by going through step S15, the shrinkage difference that occurred in the lithium cobalt oxide is alleviated, resulting in a smooth surface for the composite oxide.

[0429] Furthermore, the difference in shrinkage may cause microscopic misalignment, such as crystal misalignment, in the lithium cobalt oxide. To reduce this misalignment, it is preferable to perform step S15. By performing step S15, it is possible to equalize the misalignment of the composite oxide (alleviate the misalignment of crystals, etc., that has occurred in the composite oxide, or align the crystal grains). As a result, the surface of the composite oxide becomes smooth.

[0430] As described above, in step S10, pre-synthesized lithium cobalt oxide having a median diameter (D50) of 12 μm or less, preferably 10 μm or less, and more preferably 8 μm or less may be used. In this case, steps S11 to S13 can be omitted. It is useful to perform step S15 on pre-synthesized lithium cobalt oxide, and this is a preferred step because it allows lithium cobalt oxide with a smooth surface to be obtained.

[0431] Note that step S15 is not an essential configuration in one aspect of the present invention, and therefore an aspect in which step S15 is omitted is also included in one aspect of the present invention.

[0432] The positive electrode active material of one embodiment of the present invention preferably contains an additional element A. A method for adding the additional element A will be described in the following steps.

[0433] <Step S20> Next, details of step S20 of preparing the additional element A as the A source will be described with reference to FIGS. 29(C) and 29(D).

[0434] <Step S21> Step S20 shown in Figure 29(C) includes steps S21 to S23. In step S21, an additive element A is prepared. Specific examples of the additive element A include one or more selected from magnesium, fluorine, nickel, aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, barium, bromine, and beryllium. Figure 29(C) illustrates a case where a magnesium source (Mg source) and a fluorine source (F source) are prepared. In step S21, a lithium source may be separately prepared in addition to the additive element A.

[0435] When magnesium is selected as the additional element A, the source of the additional element A can be called a magnesium source. As the magnesium source, magnesium fluoride (MgF), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)), magnesium carbonate (MgCO), etc. can be used. Multiple magnesium sources may be used.

[0436] When fluorine is selected as the additive element A, the source of the additive element A can be called a fluorine source. Examples of the fluorine source that can be used include lithium fluoride (LiF), magnesium fluoride (MgF), aluminum fluoride (AlF), titanium fluoride (TiF), cobalt fluoride (CoF, CoF), nickel fluoride (NiF), zirconium fluoride (ZrF), vanadium fluoride (VF), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF), calcium fluoride (CaF), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF), cerium fluoride (CeF, CeF), lanthanum fluoride (LaF), and sodium aluminum hexafluoride (NaAlF). Among these, lithium fluoride is preferred because it has a relatively low melting point of 848°C and is easily melted in the heating step described below.

[0437] Magnesium fluoride can be used as both a fluorine source and a magnesium source. Lithium fluoride can also be used as a lithium source. Other lithium sources that can be used in step S21 include lithium carbonate.

[0438] The fluorine source may be a gas, such as fluorine (F), carbon fluoride, sulfur fluoride, or oxygen fluoride (OF, OF, OF, OF, OF, OF, OF), which may be mixed into the atmosphere during the heating step described below. Multiple fluorine sources may be used.

[0439] In this embodiment, lithium fluoride (LiF) is prepared as the fluorine source, and magnesium fluoride (MgF2) is prepared as both the fluorine source and the magnesium source. Furthermore, if the melting point of a fluorine compound (sometimes called a fluoride) such as lithium fluoride is lower than that of the other additive element source, the fluorine compound can function as a fluxing agent (also called a fluxing agent) to lower the melting point of the other additive element source. When the fluorine compound contains LiF and MgF2, the eutectic point P of LiF and MgF2 is approximately 742°C (T1) as shown in Figure 35. Therefore, when a fluoride mixture containing LiF and MgF2 is used as the additive element source, it is preferable to set the heating temperature to 742°C or higher in the heating step after mixing the additive element.

[0440] Here, differential scanning calorimetry (DSC) measurements of the mixed fluoride and mixture will be explained with reference to FIG. 36. The curve labeled "mixed fluoride" in FIG. 36 is the result of DSC measurement of a mixture of LiF and MgF2. The mixed fluoride was prepared by mixing LiF:MgF2 = 1:3 (molar ratio). The curve labeled "mixture" in FIG. 36 is the result of DSC measurement of a mixture prepared by mixing lithium cobalt oxide, LiF, and MgF2. The mixture was prepared by mixing LiCoO2:LiF:MgF2 = 100:0.33:1 (molar ratio).

[0441] As shown in Fig. 36, an endothermic peak is observed around 735°C for the mixed fluoride. Also, an endothermic peak is observed around 830°C for the mixture. Therefore, the heating temperature after mixing the additive element (such as step S33 described later) is preferably 742°C or higher, more preferably 830°C or higher. Alternatively, it may be 800°C (T2 in Fig. 35) or higher, which is between these temperatures.

[0442] Furthermore, when lithium fluoride and magnesium fluoride are mixed at a molar ratio of approximately LiF:MgF2 = 65:35, the melting point lowering effect is maximized. Furthermore, if the proportion of lithium fluoride is too high, there is a concern that the lithium will become excessive, resulting in deterioration of cycle characteristics. Therefore, the molar ratio of lithium fluoride to magnesium fluoride is preferably LiF:MgF2 = x:1 (0 ≦ x ≦ 1.9), more preferably LiF:MgF2 = x:1 (0.1 ≦ x ≦ 0.5), and even more preferably LiF:MgF2 = x:1 (x = 0.33 or thereabouts). In this specification, unless otherwise specified, "near a certain value" refers to a value greater than 0.9 times and less than 1.1 times that value.

[0443] <Step S22> 29(C), the magnesium source and the fluorine source are pulverized and mixed. This step can be performed under pulverization and mixing conditions selected from those described in step S12.

[0444] <Step S23> 29(C), the pulverized and mixed materials are collected to obtain a source of the additional element A (A source). Note that the source of the additional element A shown in step S23 contains a plurality of starting materials and can also be called a mixture.

[0445] The particle size of the mixture is preferably a median diameter (D50) of 100 nm to 10 μm, more preferably 300 nm to 5 μm. Even when a single material is used as the source of the additive element A, the median diameter (D50) is preferably 100 nm to 10 μm, more preferably 300 nm to 5 μm.

[0446] When the mixture (including the case where only one kind of additive element is contained) pulverized in step S22 is mixed with lithium cobalt oxide in a later step, the mixture can be easily adhered uniformly to the surface of the lithium cobalt oxide. If the mixture is evenly adhered to the surface of the lithium cobalt oxide, the additive element can be easily distributed or diffused uniformly in the surface layer portion 100a of the composite oxide after heating, which is preferable.

[0447] <Step S21> A process different from that shown in Figure 29(C) will be described with reference to Figure 29(D). Step S20 shown in Figure 29(D) includes steps S21 to S23.

[0448] In step S21 shown in Fig. 29(D), four types of additive element A sources to be added to lithium cobalt oxide are prepared. That is, Fig. 29(D) differs from Fig. 29(C) in the types of additive element A sources. In addition to the additive element A sources, a lithium source may be separately prepared.

[0449] As sources of the four additive elements A, a magnesium source (Mg source), a fluorine source (F source), a nickel source (Ni source), and an aluminum source (Al source) are prepared. The magnesium source and the fluorine source can be selected from the compounds described in FIG. 29(C). Nickel oxide, nickel hydroxide, etc. can be used as the nickel source. Aluminum oxide, aluminum hydroxide, etc. can be used as the aluminum source.

[0450] <Step S22> and <Step S23> Next, steps S22 and S23 shown in FIG. 29(D) are the same as steps S22 and S23 described with reference to FIG. 29(C).

[0451] <Step S31> Next, in step S31 shown in FIG. 29(A), the lithium cobalt oxide that has undergone step S15 (initial heating) is mixed with an additive element A source (Mg source). Here, the ratio of the number of cobalt atoms Co in the lithium cobalt oxide that has undergone step S15 to the number of magnesium atoms Mg in the additive element A is preferably Co:Mg=100:y (0.1≦y≦6), and more preferably Co:Mg=100:y (0.3≦y≦3). Note that adding the additive element A to the lithium cobalt oxide that has undergone initial heating allows the additive element A to be added evenly. For this reason, it is preferable to add the additive element A after the initial heating (step S15), rather than adding the additive element A and then performing the initial heating (step S15).

[0452] Furthermore, when nickel is selected as the additional element A, it is preferable to perform the mixing in step S31 so that the number of nickel atoms in the nickel source is 0.05% or more and 4% or less of the number of cobalt atoms in the lithium cobalt oxide that has undergone step S15. Furthermore, when aluminum is selected as the additional element A, it is preferable to perform the mixing in step S31 so that the number of aluminum atoms in the aluminum source is 0.05% or more and 4% or less of the number of cobalt atoms in the lithium cobalt oxide that has undergone step S15.

[0453] The mixing in step S31 is preferably performed under milder conditions than the pulverization and mixing in step S12 so as not to destroy the shape of the lithium cobalt oxide. For example, the rotation speed is preferably lower or the time is preferably shorter than in step S12. Dry mixing is also preferred. For example, a particle compounding device, a ball mill, a bead mill, etc. can be used for mixing.

[0454] Known particle compositing devices include Mechanofusion (registered trademark) and Nobilta (registered trademark) manufactured by Hosokawa Micron Corporation. Mechanofusion has a fixed blade inside a cylindrical container, and the rotation of the cylindrical container applies mechanical energy to the powder, thereby enabling mixing. Nobilta has a rotating blade inside a cylindrical container, and the rotation of the blade applies mechanical energy to the powder, thereby enabling mixing. In this embodiment, mixing is performed using Nobilta at 3000 rpm for 10 minutes.

[0455] <Step S32> Next, in step S32 of Fig. 29(A), the mixed materials are collected to obtain a mixture 903. When collecting the materials, they may be crushed and then sieved, if necessary.

[0456] <Step S33> Next, in step S33 shown in FIG. 29(A), the mixture 903 is heated. The heating temperature in step S33 is preferably 800°C or higher and 1100°C or lower, more preferably 800°C or higher and 950°C or lower, and even more preferably 850°C or higher and 900°C or lower. The heating time in step S33 may be 1 hour or higher and 100 hours or lower, and preferably 1 hour or higher and 10 hours or lower. The lower limit of the heating temperature in step S33 must be a temperature at which the reaction between the lithium cobalt oxide and the additive element A source proceeds. The temperature at which the reaction proceeds may be a temperature at which interdiffusion of elements contained in the lithium cobalt oxide and the additive element A source occurs, and may be lower than the melting temperature of these materials. For example, taking an oxide as an example, the melting temperature T m 0.757 times (Tanman temperature T d ), solid-phase diffusion occurs, so the heating temperature in step S33 should be 500° C. or higher.

[0457] The reaction proceeds more easily when the temperature is equal to or higher than the melting point of one or more materials contained in the mixture 903. For example, when LiF and MgF2 are contained as the source of the additional element A, the eutectic point of LiF and MgF2 is around 742°C as described above, so the lower limit of the heating temperature in step S33 is preferably set to 742°C or higher.

[0458] Furthermore, as described above, the mixture 903 obtained by mixing LiCoO2:LiF:MgF2=100:0.33:1 (molar ratio) exhibits an endothermic peak at around 830°C in differential scanning calorimetry (DSC measurement). Therefore, the lower limit of the heating temperature is more preferably 830°C or higher.

[0459] A higher heating temperature is preferable because the reaction proceeds more easily, the heating time is shorter, and productivity is higher.

[0460] The upper limit of the heating temperature is set to be lower than the decomposition temperature (1130°C) of lithium cobalt oxide. At temperatures close to the decomposition temperature, there is a concern that lithium cobalt oxide may decompose, albeit only slightly. Therefore, the upper limit of the heating temperature is preferably 1000°C or lower, more preferably 950°C or lower, and even more preferably 900°C or lower.

[0461] Furthermore, when the mixture 903 is heated, it is preferable to control the partial pressure of fluorine or fluoride resulting from the fluorine source or the like within an appropriate range.

[0462] In the fabrication method described in this embodiment, some materials, such as LiF, which is a fluorine source, may function as a flux. This function allows the heating temperature to be lowered below the decomposition temperature of lithium cobalt oxide, for example, to 742°C or higher and 950°C or lower, and allows magnesium and other additive elements to be distributed in the surface layer, thereby producing a positive electrode active material with excellent characteristics.

[0463] However, since LiF has a lower specific gravity in a gaseous state than oxygen, heating may cause LiF to volatilize or sublime, and if it volatilizes, the amount of LiF in the mixture 903 will decrease. In this case, its function as a flux will be weakened. Therefore, it is preferable to heat the mixture while suppressing the volatilization or sublimation of LiF.

[0464] Therefore, it is preferable to heat the mixture 903 in an atmosphere containing LiF, that is, to heat the mixture 903 in a state where the partial pressure of LiF is high in the heating furnace. By heating in this manner, it is possible to suppress the volatilization or sublimation of LiF in the mixture 903.

[0465] Furthermore, the heating in this step is preferably performed so as not to cause the particles of mixture 903 to stick together. If the particles of mixture 903 stick together during heating, the contact area with oxygen in the atmosphere will decrease, and the route along which the added element (for example, fluorine) diffuses will be blocked, which may result in a poor distribution of the added element (for example, magnesium and fluorine) in the surface layer portion.

[0466] Furthermore, when the additive element (e.g., fluorine) is uniformly distributed in the surface layer portion, a smooth cathode active material with few irregularities can be obtained. Therefore, in this process, in order to maintain or further smooth the surface by heating in step S15, it is preferable that the particles of mixture 903 do not stick to each other.

[0467] An example in which step S33 is performed in a heating furnace is shown in FIG.

[0468] The heating furnace 220 shown in FIG. 30(A) has a heating furnace space 202, a hot plate 204, a pressure gauge 221, a heater unit 206, and a heat insulator 208. A container 216 and a lid 218 are shown as setters for accommodating the object to be heated. It is preferable to heat the container 216 with the lid 218 attached. FIG. 30(B) shows a top view of the lid 218, and FIG. 30(C) shows a cross-sectional schematic diagram of the container 216 and the lid 218. Simply placing the lid 218 on the container 216 creates a sealed space, but because it is not completely sealed, the inside of the container does not become abnormally high pressure, ensuring safety. Because a source of additive element A (typically fluoride) is added to the container 216 in advance, the inside of the space 219 defined by the container 216 and the lid 218 can be made into an atmosphere containing fluoride. During heating, by keeping the concentration of gasified fluoride in the space 219 constant or preventing it from decreasing by covering the space 219, it is possible to contain additive element A, such as fluorine and magnesium, near the particle surfaces of the mixture 903. Because the volume of the space 219 is smaller than the space 202 inside the heating furnace, a small amount of fluoride volatilizes, creating an atmosphere containing fluoride. In other words, the atmosphere of the reaction system can be made to contain fluoride without significantly reducing the amount of fluoride contained in the mixture 903. Furthermore, by using the lid 218, the mixture 903 can be heated in an atmosphere containing fluoride simply and inexpensively.

[0469] Furthermore, before heating in the heating furnace space 202, a step of creating an oxygen-containing atmosphere in the heating furnace space 202 and a step of placing the container 216 containing the mixture 903 in the heating furnace space 202 are performed. By performing these steps in this order, the mixture 903 can be heated in an atmosphere containing oxygen and fluoride. For example, heating can be performed while a gas is flowing (flow). The gas can be introduced from the bottom of the heating furnace space 202 and exhausted to the top. Also, during heating, the heating furnace space 202 can be sealed to form a closed space to prevent the gas from being transported to the outside (purging).

[0470] There are no particular limitations on the method for creating an oxygen-containing atmosphere in the heating furnace space 202, but examples include a method of evacuating the heating furnace space 202 and then introducing an oxygen-containing gas such as oxygen gas or dry air, or a method of infusing an oxygen-containing gas such as oxygen gas or dry air for a certain period of time. Among these, it is preferable to evacuate the heating furnace space 202 and then introduce oxygen gas (oxygen substitution). Note that the air in the heating furnace space 202 may be considered to be an oxygen-containing atmosphere.

[0471] Furthermore, a source of the additive element A (typically a fluoride) that has been impregnated into the inner walls of the container 216 and the lid 218 can be re-emitted by heating and attached to the mixture 903 .

[0472] There is no particular limitation on the process for heating the heating furnace 220. Heating may be performed using a heating mechanism provided in the heating furnace 220.

[0473] The conditions for placing the mixture 903 in the container 216 will be described with reference to FIG. 30(C). As shown in FIG. 30(C), the mixture 903 is preferably placed so that the top surface of the mixture 903 is flat relative to the bottom surface of the container 216, in other words, so that the height H of the top surface of the mixture 903 is uniform. The height H of the top surface of the mixture 903 is preferably 4.0 mm or less, and more preferably 2.0 mm or less. By setting the height H of the top surface of the mixture 903 within the above conditions, oxygen in the atmosphere can reach the mixture 903 near the bottom surface of the container 216. On the other hand, if the height H of the top surface of the mixture 903 is greater than 4.0 mm, the amount of oxygen reaching the mixture 903 near the bottom surface of the container 216 will be insufficient, resulting in poor battery performance when the cathode active material subjected to this process is used in a battery. Furthermore, if the height H of the top surface of the mixture 903 is too low, the amount of mixture 903 that can be placed in the container 216 will be reduced, resulting in poor productivity. Therefore, the height H of the upper surface of the mixture 903 is preferably 0.5 mm or more, or 1.0 mm or more. To summarize the above, the height H of the upper surface of the mixture 903 is preferably 0.5 mm or more and 4.0 mm or less, and more preferably 1.0 mm or more and 2.0 mm or less.

[0474] The heating in step S33 is preferably performed while controlling the pressure inside the furnace with a pressure gauge 221. The inside of the furnace is preferably kept at atmospheric pressure or under pressure. For example, it is believed that the surface of lithium cobalt oxide is more likely to melt when exposed to a pressurized state. Therefore, the surface of lithium cobalt oxide heated together with LiF and MgF2 can be melted by applying pressure.

[0475] Furthermore, when heating the mixture 903, it is preferable to control the partial pressure of fluorine or fluorine compounds resulting from the fluorine source or the like within an appropriate range. The partial pressure can also be controlled by heating the container used in this step with a lid on. As mentioned above, the lid can prevent the material from volatilizing or sublimating.

[0476] In the manufacturing method described in this embodiment, a material for the source of the additive element A (typically a fluoride), for example, LiF as a fluorine source, may function as a flux. This function allows the heating temperature to be lowered below the decomposition temperature of lithium cobalt oxide, for example, to 742°C or higher and 950°C or lower, and allows the additive elements such as magnesium to be distributed in the surface layer, thereby enabling the manufacturing of a positive electrode active material with good characteristics.

[0477] However, because LiF has a lower specific gravity in a gaseous state than oxygen, there is a possibility that LiF will volatilize or sublime when heated. If it volatilizes, the amount of LiF in the mixture 903 will decrease. This will weaken its function as a flux. Therefore, it is necessary to heat the mixture while suppressing the volatilization of LiF. Even if LiF is not used as a fluorine source, Li on the surface of the lithium cobalt oxide may react with F in the fluorine source, producing LiF, which may then volatilize. Therefore, even if a fluorine compound with a higher melting point than LiF is used, it is still necessary to suppress the volatilization.

[0478] Therefore, it is preferable to heat the mixture 903 in an atmosphere containing LiF, that is, to heat the mixture 903 in a state where the partial pressure of LiF is high in the heating furnace. By heating in this manner, it is possible to suppress the volatilization of LiF in the mixture 903. To suppress the volatilization of LiF, it is also preferable to place a lid on the setter container. Because the setter container and the lid are exposed to high temperatures, if they are made of materials with different thermal expansion coefficients, there is a risk that the gap between the setter container and the lid will become large. Therefore, it is preferable that the setter container and the lid are made of the same material.

[0479] <Roller hearth kiln> The manufacturing apparatus according to one embodiment of the present invention may be a roller hearth kiln that continuously processes materials contained in containers. Figure 31(A) is a cross-sectional schematic diagram of a roller hearth kiln 150. Figure 31(B) is a diagram illustrating rollers 152 of the roller hearth kiln.

[0480] The roller hearth kiln 150 has a kiln body 151, a plurality of rollers 152, heating means 153a and 153b, atmosphere control means 154, and adhesion suppression means 155a, 155b, and 155c. The roller hearth kiln 150 also preferably has one or more baffle plates 157 and measuring devices 120a and 120b. Figure 31(A) shows an example having three baffle plates 157 (shown as baffle plate 157a, baffle plate 157b, and baffle plate 157c).

[0481] The kiln body 151 is tunnel-shaped. A plurality of rollers 152 have the function of transporting a container 160 containing an object to be heated 161. The container 160 is transported by the plurality of rollers 152 through the tunnel-shaped kiln body 151 to the outside. Note that the description of the container 216 and mixture 903 described in Figure 30(C) can be referenced for the container 160 and the object to be heated 161. In other words, the height of the top surface of the object to be heated 161 contained in the container 160 relative to the bottom surface of the container 160 is preferably 0.5 mm or more and 4.0 mm or less, and more preferably 1.0 mm or more and 2.0 mm or less.

[0482] The kiln body 151 has an upstream portion and a downstream portion along the conveying direction of the multiple rollers 152. The kiln body 151 has a heating means 153a in the upstream portion and a heating means 153b in the downstream portion. A shield plate 157b may be provided between the upstream portion and the downstream portion. By providing the shield plate 157b, the atmosphere in the upstream portion and the downstream portion can be controlled separately. Furthermore, the shield plate 157b may be provided near the entrance of the kiln body 151, and the shield plate 157c may be provided near the exit. By providing these, it becomes easier to control the atmosphere inside the kiln body 151.

[0483] The adhesion suppression means 155 of the roller hearth kiln 150 is, for example, a means for vibrating the container 160. For example, as shown in FIG. 31(A), the adhesion suppression means 155 may be a rod-shaped or plate-shaped device provided between the rollers 152, as in the three adhesion suppression means 155 (shown as adhesion suppression means 155a, adhesion suppression means 155b, and adhesion suppression means 155c). The adhesion suppression means 155a, adhesion suppression means 155b, and adhesion suppression means 155c may be fixed, or may move to vibrate the container 160. Although FIG. 31(A) illustrates a configuration in which three adhesion suppression means 155 are provided, this is not a limitation of one embodiment of the present invention. One, two, or four or more adhesion suppression means 155 may be provided.

[0484] The sticking prevention means of the roller hearth kiln 150 may be a plurality of rollers 152 with different inclinations, as shown in FIG. 31(B).

[0485] 31(A) can be referred to for the heating means 153a and 153b, the atmosphere control means 154, etc. Also, for the measuring device 120a and the measuring device 120b, the description of FIG.

[0486] The roller hearth kiln 150 is preferable because it has high productivity since it continuously processes the materials to be treated.

[0487] <Cooling section of roller hearth kiln> The roller hearth kiln may be provided with a cooling section.

[0488] The roller hearth kiln 150b shown in Figure 32 is an example that, in addition to the configuration of the roller hearth kiln 150 shown in Figure 31(A), has a temperature rising zone 121, a first cooling zone 124, and a second cooling zone 125. The area located upstream and heated by heating means 153a is referred to as the first holding zone 122, and the area located downstream and heated by heating means 153b is referred to as the second holding zone 123.

[0489] Atmosphere control means 154 preferably has a function of controlling the atmosphere in each of five zones (heating zone 121, first holding zone 122, second holding zone 123, first cooling zone 124, and second cooling zone 125). For example, gas is introduced from atmosphere control means 154 into each of the five zones. The gases introduced from atmosphere control means 154 into each of the five zones may differ in type, temperature, flow rate, etc.

[0490] 32 shows an example in which five zones are separated by shield plates 157, but a configuration in which no shield plate is provided between adjacent zones may also be used. For example, a configuration in which no shield plate is provided between temperature increasing zone 121 and first holding zone 122 may also be used. Furthermore, for example, a configuration in which no shield plate is provided between the first cooling zone and second cooling zone may also be used.

[0491] The temperature increasing zone 121 has a heating means 153j. Here, it is preferable that the temperature of the heating means 153j varies depending on the region. For example, it is preferable that the temperature gradually increases from the upstream side to the downstream side. Specifically, for example, the heating means 153j may have a plurality of blocks, each block provided with a heater, and the heater temperature may increase sequentially from the upstream block to the downstream side.

[0492] The first cooling zone 124 has a heating means 153k. Here, the temperature of the heating means 153k may vary depending on the region. For example, the temperature may gradually decrease from the upstream side to the downstream side. Specifically, for example, the heating means 153j may have a plurality of blocks, each block provided with a heater, and the heater temperature may decrease from the upstream block to the downstream side.

[0493] The second cooling zone 125 is, for example, a region at room temperature. By performing cooling at room temperature, the temperature drop rate can be increased.

[0494] Cooling may be performed using cooling water in the first cooling zone 124 and the second cooling zone 125. By using cooling water, the temperature drop rate can be increased.

[0495] In addition, in one embodiment of the roller hearth kiln of the present invention, either the first cooling zone 124 or the second cooling zone 125 may be omitted.

[0496] For example, the first cooling zone 124 may not be provided, and the second holding zone 123 may be connected to the second cooling zone, and cooling may be performed at room temperature immediately after the temperature holding step, thereby increasing the temperature drop rate.

[0497] For example, a silicon carbide heater, a carbon heater, a metal heater, a molybdenum disilicide heater, or the like can be used as the heating means 153j and the heating means 153k.

[0498] <Step S34> Next, in step S34 shown in FIG. 29(A), the heated material is recovered and crushed as necessary to obtain a positive electrode active material 100. At this time, it is preferable to further sieve the recovered positive electrode active material 100. Through the above steps, a positive electrode active material 100 (composite oxide) having a median diameter (D50) of 12 μm or less (preferably 10.5 μm or less, more preferably 8 μm or less) can be produced. The positive electrode active material 100 contains an additive element A.

[0499] <Example 2 of a method for producing a positive electrode active material> 33 and 34(C), another example of a method for producing a positive electrode active material that can be used as one embodiment of the present invention (Example 2 of Method for Producing a Positive Electrode Active Material) will be described. Example 2 of Method for Producing a Positive Electrode Active Material differs from Example 1 of Method for Producing a Positive Electrode Active Material described above in the number of times the additive elements are added and the mixing method, but the rest of the description in Example 1 of Method for Producing a Positive Electrode Active Material can be applied.

[0500] 33, steps S10 and S15 are performed in the same manner as in Fig. 29(A) to prepare lithium cobalt oxide that has undergone initial heating. Note that step S15 is not an essential configuration in one aspect of the present invention, and therefore an aspect in which step S15 is omitted is also included in one aspect of the present invention.

[0501] <Step S20a> Next, as shown in step S20a, a first additive element A1 source (A1 source) is prepared. Details of step S20a will be described with reference to FIG.

[0502] <Step S21> In step S21 shown in Fig. 34(A), a first additive element A1 source (A1 source) is prepared. The A1 source can be selected from the additive elements A described in step S21 shown in Fig. 29(C). For example, the additive element A1 can be one or more selected from magnesium, fluorine, and calcium. Fig. 34(A) illustrates the case where a magnesium source (Mg source) and a fluorine source (F source) are used as the additive element A1.

[0503] Steps S21 to S23 shown in Fig. 34(A) can be performed under the same conditions as steps S21 to S23 shown in Fig. 29(C). As a result, an additional element A1 source (A1 source) can be obtained in step S23.

[0504] Steps S31 to S33 shown in FIG. 33 can be performed under the same conditions as steps S31 to S33 shown in FIG. 29(A).

[0505] <Step S34a> Next, in step S33, the heated material is recovered to obtain lithium cobalt oxide containing the additional element A1. Here, this is also referred to as the second composite oxide to distinguish it from the lithium cobalt oxide (first composite oxide) that has been subjected to step S15.

[0506] <Step S40> In step S40 shown in Fig. 33, a source of the second additional element A2 (A2 source) is prepared. Step S40 will be described with reference to Fig. 34(B) and Fig. 34(C).

[0507] <Step S41> In step S40 shown in FIG. 34(B), a second additive element A2 source (A2 source) is prepared. The A2 source can be selected from the additive elements A described in step S20 shown in FIG. 29(C). For example, the additive element A2 can be one or more selected from nickel, titanium, boron, zirconium, and aluminum. FIG. 34(B) illustrates an example in which a nickel source and an aluminum source are used as the additive element A2.

[0508] Steps S41 to S43 shown in Fig. 34(B) can be performed under the same conditions as steps S21 to S23 shown in Fig. 29(C). As a result, a source of the additional element A2 (A2 source) can be obtained in step S43.

[0509] Steps S41 to S43 shown in Figure 34(C) are a modification of Figure 34(B). In step S41 shown in Figure 34(C), a nickel source (Ni source) and an aluminum source (Al source) are prepared, and in step S42a, they are each independently pulverized. As a result, in step S43, a plurality of second additional element A2 sources (A2 sources) are prepared. Thus, step S40 in Figure 34(C) differs from step S40 in Figure 34(B) in that the additional element sources are independently pulverized in step S42a.

[0510] <Steps S51 to S53> Next, steps S51 to S53 shown in Fig. 33 can be performed under the same conditions as steps S31 to S34 shown in Fig. 29(A). The conditions for step S53, which is related to the heating step, are preferably the same as or lower than the heating temperature of step S33 shown in Fig. 33. The heating time is preferably shorter than that of step S33. Specifically, the heating temperature is preferably 800°C or higher and 950°C or lower, more preferably 820°C or higher and 870°C or lower, and even more preferably 850°C ± 10°C. The heating time is preferably 0.5 hours or higher and 8 hours or lower, and more preferably 1 hour or higher and 5 hours or lower.

[0511] When nickel is selected as the additional element A2, it is preferable to perform the mixing in step S51 so that the number of nickel atoms in the nickel source is 0.05% to 4% of the number of cobalt atoms in the lithium cobalt oxide that has undergone step S15. When aluminum is selected as the additional element A2, it is preferable to perform the mixing in step S51 so that the number of aluminum atoms in the aluminum source is 0.05% to 4% of the number of cobalt atoms in the lithium cobalt oxide that has undergone step S15.

[0512] <Step S54> Next, in step S54 shown in FIG. 33, the heated material is recovered and crushed as necessary to obtain a positive electrode active material 100. Through the above steps, a positive electrode active material 100 (composite oxide) having a median diameter (D50) of 12 μm or less (preferably 10.5 μm or less, more preferably 8 μm or less) can be produced. Alternatively, a positive electrode active material 100 applicable to lithium-ion batteries having excellent charge / discharge characteristics even in low-temperature environments can be produced. The positive electrode active material 100 contains the additive element A1 and the additive element A2.

[0513] In the above-described example 2 of the manufacturing method, as shown in Fig. 33 to Fig. 34(C), the additive element into lithium cobalt oxide is introduced separately as a first additive element A1 and a second additive element A2. By introducing them separately, the distribution of each additive element in the depth direction can be changed.

[0514] The content of this embodiment can be freely combined with the content of other embodiment modes.

[0515] (Embodiment 3) In this embodiment, examples of mounting a secondary battery which is one embodiment of the present invention in an electronic device will be described with reference to FIGS.

[0516] 37A to 37G show examples in which the secondary battery having the positive electrode active material described in the above embodiment is mounted in an electronic device. Examples of electronic devices to which the secondary battery is applied include television devices (also referred to as televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also referred to as mobile phones or mobile phone devices), portable game machines, personal digital assistants, sound reproducing devices, and large game machines such as pachinko machines.

[0517] Furthermore, a secondary battery having a flexible shape can be incorporated along the curved surfaces of the inner or outer walls of houses, buildings, etc., or the interior or exterior of automobiles.

[0518] 37A shows an example of a mobile phone. The mobile phone 7400 includes a display portion 7402 built into a housing 7401, operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. Note that the mobile phone 7400 includes a secondary battery 7407. By using the secondary battery of one embodiment of the present invention as the secondary battery 7407, a lightweight mobile phone with a long life can be provided.

[0519] Figure 37(B) shows the mobile phone 7400 in a bent state. When the mobile phone 7400 is deformed by an external force and bent as a whole, the secondary battery 7407 provided inside is also bent. Figure 37(C) shows the state of the bent secondary battery 7407 at that time. The secondary battery 7407 is a thin storage battery. The secondary battery 7407 is fixed in a bent state. The secondary battery 7407 has leads electrically connected to a current collector.

[0520] FIG. 37D shows an example of a bangle-type display device. The portable display device 7100 includes a housing 7101, a display portion 7102, operation buttons 7103, and a secondary battery 7104. FIG. 37E shows a bent secondary battery 7104. When the secondary battery 7104 is worn on a user's arm in a bent state, the housing deforms, causing a change in the curvature of part or the entire secondary battery 7104. Note that the degree of curvature at any point on the curve, expressed as the radius of the corresponding circle, is called the radius of curvature, and the reciprocal of the radius of curvature is called the curvature. Specifically, part or the entire main surface of the housing or the secondary battery 7104 changes when the radius of curvature is 40 mm to 150 mm. High reliability can be maintained when the radius of curvature of the main surface of the secondary battery 7104 is 40 mm to 150 mm. By using the secondary battery of one embodiment of the present invention as the secondary battery 7104, a lightweight and long-life portable display device can be provided.

[0521] 37F shows an example of a wristwatch-type portable information terminal 7200. The portable information terminal 7200 includes a housing 7201, a display portion 7202, a band 7203, a buckle 7204, operation buttons 7205, an input / output terminal 7206, and the like.

[0522] The portable information terminal 7200 can execute various applications such as mobile phone calls, e-mail, document browsing and creation, music playback, internet communication, and computer games.

[0523] The display surface of the display portion 7202 is curved, and a display can be performed along the curved display surface. The display portion 7202 is also provided with a touch sensor, and can be operated by touching the screen with a finger or a stylus. For example, an application can be started by touching an icon 7207 displayed on the display portion 7202.

[0524] The operation button 7205 can be provided with various functions, such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, power saving mode activation / deactivation, etc. For example, the functions of the operation button 7205 can be freely set by an operating system incorporated in the mobile information terminal 7200.

[0525] The mobile information terminal 7200 is also capable of performing standardized short-range wireless communication. For example, hands-free conversation is also possible by communicating with a wirelessly enabled headset.

[0526] The portable information terminal 7200 also includes an input / output terminal 7206, and can directly exchange data with another information terminal via a connector. Charging can also be performed via the input / output terminal 7206. Note that charging may be performed wirelessly without using the input / output terminal 7206.

[0527] The display portion 7202 of the portable information terminal 7200 includes the secondary battery of one embodiment of the present invention. By using the secondary battery of one embodiment of the present invention, a lightweight portable information terminal with a long life can be provided. For example, the secondary battery 7104 shown in FIG. 37E can be incorporated into the housing 7201 in a curved state or into the band 7203 in a bendable state.

[0528] The portable information terminal 7200 preferably has a sensor, such as a fingerprint sensor, a pulse sensor, a body temperature sensor, a touch sensor, a pressure sensor, an acceleration sensor, or the like.

[0529] 37G shows an example of an armband-type display device. The display device 7300 includes a display portion 7304 and the secondary battery of one embodiment of the present invention. The display device 7300 can also be provided with a touch sensor in the display portion 7304 and can function as a portable information terminal.

[0530] The display surface of the display portion 7304 is curved, and display can be performed along the curved display surface. The display state of the display device 7300 can be changed by short-range wireless communication according to a communication standard.

[0531] The display device 7300 also includes an input / output terminal, allowing direct data exchange with other information terminals via a connector. Charging can also be performed via the input / output terminal. Note that charging may be performed wirelessly without using the input / output terminal.

[0532] By using the secondary battery of one embodiment of the present invention as the secondary battery included in the display device 7300, a lightweight display device with a long lifetime can be provided.

[0533] An example in which the secondary battery with good cycle characteristics described in the above embodiment is mounted on an electronic device will be described with reference to FIGS.

[0534] By using a secondary battery of one embodiment of the present invention as a secondary battery in daily electronic devices, products that are lightweight and have a long life can be provided. For example, daily electronic devices include electric toothbrushes, electric shavers, and electric beauty devices. For secondary batteries in these products, a stick-shaped secondary battery that is easy for users to hold, small, lightweight, and has a large discharge capacity is desired.

[0535] FIG. 37(H) is a perspective view of a device also known as a tobacco-containing smoking device (electronic cigarette). In FIG. 37(H), the electronic cigarette 7500 includes an atomizer 7501 including a heating element, a secondary battery 7504 that supplies power to the atomizer, and a cartridge 7502 that includes a liquid supply bottle, a sensor, and the like. To enhance safety, a protection circuit that prevents overcharging and / or over-discharging of the secondary battery 7504 may be electrically connected to the secondary battery 7504. The secondary battery 7504 shown in FIG. 37(H) has external terminals so that it can be connected to a charging device. Because the secondary battery 7504 is the tip portion when held, it is desirable that the total length be short and the weight be light. The secondary battery of one embodiment of the present invention has a high discharge capacity and favorable cycle characteristics, and thus a small and lightweight electronic cigarette 7500 that can be used for a long period of time can be provided.

[0536] Figure 38(A) shows an example of a wearable device. Wearable devices use secondary batteries as a power source. Furthermore, when used at home or outdoors, there is a demand for wearable devices that can be charged wirelessly as well as via wired charging, with an exposed connector, in order to improve splash-proof, water-resistant, or dust-proof performance.

[0537] For example, the secondary battery of one embodiment of the present invention can be mounted on an eyeglasses-type device 4000 as shown in FIG. 38A. The eyeglasses-type device 4000 includes a frame 4000a and a display portion 4000b. Mounting the secondary battery on temple portions of the curved frame 4000a makes it possible to provide the eyeglasses-type device 4000 with a lightweight design, a good weight balance, and a long continuous use time. By including the secondary battery of one embodiment of the present invention, a configuration that can accommodate space saving due to a miniaturized housing can be realized.

[0538] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a headset device 4001. The headset device 4001 includes at least a microphone unit 4001a, a flexible pipe 4001b, and an earphone unit 4001c. The secondary battery can be provided in the flexible pipe 4001b and / or the earphone unit 4001c. By providing the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving due to a smaller housing can be realized.

[0539] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a device 4002 that can be directly attached to the body. A secondary battery 4002b can be provided in a thin housing 4002a of the device 4002. By providing the secondary battery according to one embodiment of the present invention, a space-saving configuration can be realized that accompanies a miniaturized housing.

[0540] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a device 4003 that can be attached to clothing. A secondary battery 4003b can be provided in a thin housing 4003a of the device 4003. By providing the secondary battery according to one embodiment of the present invention, a space-saving configuration can be realized that accompanies a miniaturized housing.

[0541] Furthermore, the secondary battery of one embodiment of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 includes a belt portion 4006a and a wireless power receiving portion 4006b, and the secondary battery can be mounted inside the belt portion 4006a. By including the secondary battery of one embodiment of the present invention, a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0542] Furthermore, the secondary battery of one embodiment of the present invention can be mounted on the wristwatch device 4005. The wristwatch device 4005 has a display portion 4005a and a belt portion 4005b, and the secondary battery can be provided on the display portion 4005a or the belt portion 4005b. By providing the secondary battery of one embodiment of the present invention, a space-saving configuration can be realized that accompanies a miniaturized housing.

[0543] The display unit 4005a can display not only the time but also various other information such as incoming emails and phone calls.

[0544] Furthermore, since the wristwatch type device 4005 is a wearable device that is worn directly on the wrist, it may be equipped with sensors that measure the user's pulse, blood pressure, etc. Data on the user's exercise amount and health can be accumulated to manage the user's health.

[0545] FIG. 38(B) shows a perspective view of the wristwatch type device 4005 removed from the wrist.

[0546] 38C shows a side view of the display portion 4005a. FIG. 38C shows a state in which a secondary battery 913 is built inside the display portion 4005a. The secondary battery 913 is the secondary battery described in Embodiment 3. The secondary battery 913 is provided at a position overlapping with the display portion 4005a, and is small and lightweight.

[0547] 38(D) shows a perspective view of the electronic device 2240. The electronic device 2240 is a so-called goggle-type head-mounted display (HMD), and can be worn on the head.

[0548] The electronic device 2240 can be used as an electronic device for XR (Cross Reality), such as AR (Augmented Reality), VR (Virtual Reality), MR (Mixed Reality), etc. A user wearing the electronic device 2240 can view 3D images using parallax, with different images on the left and right.

[0549] The electronic device 2240 has a housing 2215 and a band 2242. The band 2242 has a function of fixing the housing 2215 to the head. The band 2242 can also include a battery 2210 inside.

[0550] When the battery 2210 is provided, it is preferably provided in a position where the weight of the battery 2210 can be used as a counterweight against the housing 2215, for example, in a position on the back of the head side as shown in FIG. 38(D). The battery 2210 is preferably curved to fit the shape of the band 2242. For example, when the length of the band 2242 is adjusted to fit the shape of the wearer's head when wearing the electronic device 2240, the secondary battery 10 of one embodiment of the present invention, which can be deformed in accordance with the deformation of the band 2242, is preferably used as the battery 2210.

[0551] Camera 2241R and camera 2241L are provided on the surface of housing 2215. By displaying images captured by camera 2241R and camera 2241L in real time, the user can grasp the external situation even while wearing electronic device 2240. In addition, a video see-through function can be realized. By using two or more cameras, a three-dimensional image can be created using parallax.

[0552] Lens 2212R functioning as an eyepiece for the right eye and lens 2212L functioning as an eyepiece for the left eye are provided in the portion located in front of the user's eyes on the user side of housing 2215. Also provided inside housing 2215 are display device 2211R for displaying an image for the right eye and display device 2211L for displaying an image for the left eye.

[0553] An input terminal and an output terminal may be provided on the surface of the housing 2215. A cable for supplying a video signal from a video output device or the like, or power for charging the battery 2210, can be connected to the input terminal. The output terminal functions as, for example, an audio output terminal, and earphones, headphones, or the like can be connected. Note that if the configuration is such that audio data can be output via wireless communication, or if audio is output from an external video output device, the audio output terminal need not be provided.

[0554] The housing 2215 may also include a wireless communication module, a storage module, and the like. The wireless communication module performs wireless communication, and the content to be viewed can be downloaded and stored in the storage module. This allows the user to view the downloaded content offline whenever they like.

[0555] Furthermore, the electronic device 2240 may be provided with an infrared camera, a LiDAR (Light Detection and Ranging) sensor, and the like in addition to the camera 2241R and the camera 2241L.

[0556] 39A shows an example of a cleaning robot. The cleaning robot 6300 includes a display unit 6302 arranged on the top surface of a housing 6301, a plurality of cameras 6303 arranged on the side surfaces, a brush 6304, an operation button 6305, a secondary battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust from a suction port arranged on the bottom surface.

[0557] For example, the cleaning robot 6300 can analyze an image captured by the camera 6303 to determine whether or not there is an obstacle such as a wall, furniture, or a step. Furthermore, when an object that may become entangled in the brush 6304, such as a wire, is detected by image analysis, the cleaning robot 6300 can stop rotation of the brush 6304. The cleaning robot 6300 includes a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or electronic component therein. By using the secondary battery 6306 according to one embodiment of the present invention in the cleaning robot 6300, the cleaning robot 6300 can be a highly reliable electronic device with a long operating time.

[0558] Fig. 39(B) shows an example of a robot. The robot 6400 shown in Fig. 39(B) includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a moving mechanism 6408, a transmitting / receiving device, a computing device, etc.

[0559] The microphone 6402 has a function of detecting the user's speaking voice, environmental sounds, etc. The speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.

[0560] The display unit 6405 has a function of displaying various information. The robot 6400 can display information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a detachable information terminal, which can be installed in a fixed position on the robot 6400 to enable charging and data transfer.

[0561] The upper camera 6403 and the lower camera 6406 have the function of capturing images of the surroundings of the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0562] The robot 6400 includes a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or an electronic component inside the robot 6400. By using the secondary battery according to one embodiment of the present invention in the robot 6400, the robot 6400 can be a highly reliable electronic device with a long operating time.

[0563] Fig. 39(C) shows an example of an aircraft. An aircraft 6500 shown in Fig. 39(C) has a propeller 6501, a camera 6502, a secondary battery 6503, and the like, and has a function of autonomous flight.

[0564] For example, image data captured by the camera 6502 is stored in the electronic component 6504. The electronic component 6504 can analyze the image data and detect the presence or absence of an obstacle when moving. Furthermore, the electronic component 6504 can estimate the remaining battery charge from a change in the storage capacity of the secondary battery 6503. The flying object 6500 includes the secondary battery 6503 according to one embodiment of the present invention therein. By using the secondary battery according to one embodiment of the present invention in the flying object 6500, the flying object 6500 can be an electronic device with a long operating time and high reliability.

[0565] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0566] (Fourth embodiment) In this embodiment, an example is shown in which a secondary battery including the positive electrode active material of one embodiment of the present invention is mounted on a vehicle.

[0567] By installing secondary batteries in vehicles, next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs) can be realized.

[0568] 40A and 40B illustrate an example of a vehicle using a secondary battery according to one embodiment of the present invention. An automobile 8400 shown in FIG. 40A is an electric automobile using an electric motor as a power source for traveling. Alternatively, it is a hybrid automobile that can appropriately select and use an electric motor or an engine as a power source for traveling. By using one embodiment of the present invention, a vehicle with a long cruising distance can be realized. The automobile 8400 also includes a secondary battery. For example, secondary battery modules can be arranged on the floor of the interior of the automobile. The secondary battery not only drives the electric motor 8406 but also supplies power to light-emitting devices such as a headlight 8401 and a room light (not shown).

[0569] The secondary battery can also supply power to display devices such as a speedometer and a tachometer included in the automobile 8400. The secondary battery can also supply power to semiconductor devices such as a navigation system included in the automobile 8400.

[0570] The automobile 8500 shown in FIG. 40(B) can charge its secondary battery by receiving power from an external charging facility using a plug-in system and / or a wireless power supply system. FIG. 40(B) shows a state in which a ground-mounted charging device 8021 charges a secondary battery 8024 mounted on the automobile 8500 via a cable 8022. The charging method and connector specifications may be determined appropriately using a predetermined system such as CHAdeMO (registered trademark) or Combo. The charging device 8021 may be a charging station installed in a commercial facility or a household power source. For example, plug-in technology can be used to charge the secondary battery 8024 mounted on the automobile 8500 using external power supply. Charging can be performed by converting AC power to DC power using a conversion device such as an AC-DC converter.

[0571] Furthermore, although not shown, a power receiving device can be mounted on a vehicle and can be charged by receiving power contactlessly from a ground-based power transmitting device. In the case of this contactless power supply method, by incorporating a power transmitting device into the road and / or exterior wall, charging can be performed not only while the vehicle is stopped but also while it is moving. This contactless power supply method can also be used to transmit and receive power between vehicles. Furthermore, a solar cell can be provided on the exterior of the vehicle, and a secondary battery can be charged while the vehicle is stopped and / or moving. For such contactless power supply, an electromagnetic induction method and / or a magnetic field resonance method can be used.

[0572] 40C shows an example of a two-wheeled vehicle using the secondary battery of one embodiment of the present invention. A scooter 8600 shown in FIG. 40C includes a secondary battery 8602, a side mirror 8601, and a turn signal light 8603. The secondary battery 8602 can supply electricity to the turn signal light 8603.

[0573] 40(C) can store a secondary battery 8602 in under-seat storage 8604. Even if under-seat storage 8604 is small, secondary battery 8602 can be stored in under-seat storage 8604. Secondary battery 8602 is removable, and when charging, secondary battery 8602 can be carried indoors, charged, and stored before riding.

[0574] According to one aspect of the present invention, the cycle characteristics of the secondary battery are improved, and the discharge capacity of the secondary battery can be increased. Therefore, the secondary battery itself can be made smaller and lighter. If the secondary battery itself can be made smaller and lighter, it will contribute to reducing the weight of the vehicle, thereby improving the cruising range. Furthermore, the secondary battery installed in the vehicle can also be used as a power supply source for purposes other than the vehicle. In this case, for example, it is possible to avoid using a commercial power source during peak power demand. Avoiding the use of a commercial power source during peak power demand can contribute to energy conservation and reduction of carbon dioxide emissions. Furthermore, if the cycle characteristics are good, the secondary battery can be used for a long period of time, and the amount of rare metals used, such as cobalt, can be reduced.

[0575] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0576] (Embodiment 5) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted on space equipment will be described.

[0577] 41A shows an artificial satellite 6800 as an example of space equipment. The artificial satellite 6800 includes a body 6801, a solar panel 6802, an antenna 6803, and a secondary battery 6805. The solar panel may be called a solar cell module.

[0578] When sunlight is irradiated onto the solar panel 6802, the power required for the operation of the satellite 6800 is generated. However, for example, when sunlight is not irradiated onto the solar panel or when the amount of sunlight irradiating the solar panel is small, the generated power is small. Therefore, the power required for the operation of the satellite 6800 may not be generated. To operate the satellite 6800 even under conditions where the generated power is small, it is preferable to provide a secondary battery 6805 in the satellite 6800. By using the positive electrode active material of the present invention for the secondary battery, the secondary battery can have a high discharge capacity and excellent cycle characteristics.

[0579] The satellite 6800 can generate a signal. The signal is transmitted via an antenna 6803, and can be received by, for example, a receiver on the ground or another satellite. By receiving the signal transmitted by the satellite 6800, for example, the position of the receiver that received the signal can be measured. As described above, the satellite 6800 can constitute, for example, a satellite positioning system.

[0580] Alternatively, the artificial satellite 6800 may be configured to include a sensor. For example, by including a visible light sensor, the artificial satellite 6800 may have the function of detecting sunlight reflected from an object on the ground. Alternatively, by including a thermal infrared sensor, the artificial satellite 6800 may have the function of detecting thermal infrared rays emitted from the earth's surface. As described above, the artificial satellite 6800 may function as, for example, an earth observation satellite.

[0581] FIG. 41(B) shows a probe 6900 having a solar sail (also called a sun sail) as an example of space equipment. The probe 6900 has a body 6901, a solar sail 6902, and a secondary battery 6905. By using the positive electrode active material of the present invention for the secondary battery, it is possible to obtain a secondary battery with high discharge capacity and excellent cycle characteristics. When photons emitted from the sun hit the surface of the solar sail 6902, momentum is transferred to the solar sail 6902. Therefore, the surface of the solar sail 6902 preferably has a thin film with high reflectivity and preferably faces the sun.

[0582] The solar sail 6902 may also be designed to be folded up small until it leaves the atmosphere, and then unfold into a large sheet once outside the Earth's atmosphere (outer space) as shown in Figure 41(B).

[0583] FIG. 41(C) shows a spacecraft 6910 as an example of space equipment. The spacecraft 6910 includes a body 6911, a solar panel 6912, and a secondary battery 6913. By using the positive electrode active material of the present invention for the secondary battery, the secondary battery can have a high discharge capacity and excellent cycle characteristics. The body 6911 can have, for example, a pressurized compartment and a non-pressurized compartment. The pressurized compartment may be designed to accommodate a crew member. Electric power generated by sunlight irradiating the solar panel 6912 can be charged into the secondary battery 6913.

[0584] 41(D) shows a rover 6920 as an example of space equipment. The rover 6920 includes a body 6921 and a secondary battery 6923. By using the positive electrode active material of the present invention for the secondary battery, the secondary battery can have a high discharge capacity and excellent cycle characteristics. The rover 6920 may include a solar panel 6922.

[0585] The rover 6920 may be designed to accommodate a crew member. The secondary battery 6923 may be charged with electricity generated by sunlight irradiating the solar panel 6912, or may be charged with electricity generated by other power sources, such as a fuel cell, a radioisotope thermoelectric converter, or the like.

[0586] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate. [Example]

[0587] In this example, a negative electrode according to one embodiment of the present invention was fabricated and its characteristics were investigated.

[0588] <Preparation of current collector with coating layer> The current collector with the coating layer used in this example will be described with reference to the manufacturing method shown in FIG.

[0589] According to step S1 of FIG. 7, a conductive material, a binder, a thickener, and a solvent were prepared.

[0590] In this example, CNT (manufactured by GELON, model number: CNT-1015 multi-wall type) and acetylene black (manufactured by Denka Co., Ltd., model number: Li-100) were prepared as the conductive material. In addition, SBR (SBR 50% aqueous dispersion, manufactured by JSR Corporation, model number: TRD2001) was prepared as the binder, CMC (manufactured by Kishida Chemical Co., Ltd., model number: 020-14515) was prepared as the thickener, and water (deionized water) was prepared as the solvent.

[0591] Next, according to step S2 in Figure 7, the prepared CNT, AB, SBR, CMC, and water were mixed. The mixing ratio by weight was CNT:AB:SBR:CMC:water = 0.06g:0.24g:0.20g:0.20g:5.0g. In this way, a slurry for the coating layer was prepared. Note that the above SBR (0.20g) was mixed with 0.40g of a 50% aqueous dispersion of SBR.

[0592] According to FIG. 7, copper foil was prepared as a negative electrode current collector, and the above slurry was applied to the copper foil according to step S5.

[0593] The slurry was dried according to step S6 in Fig. 7 to obtain a current collector with a coating layer. For pre-drying, the copper foil coated with the slurry was fixed to a hot plate heated to 50°C and left for 15 minutes. Then, for main drying, the copper foil coated with the slurry was left for 45 minutes in a forced air dryer at 80°C. In this way, a current collector with a coating layer was produced.

[0594] <Preparation of negative electrode> Next, the negative electrode used in this example will be described with reference to the fabrication method shown in Fig. 25. The negative electrode current collector used was the current collector with the coating layer fabricated above.

[0595] Graphite particles (manufactured by Eitan Co., Ltd., pulverized MCMB carbon-coated, model number: PWSHC) were prepared according to Fig. 25. In addition, SBR (SBR 50% aqueous dispersion, manufactured by JSR Corporation, model number: TRD2001) was prepared as a binder, CMC (manufactured by Kishida Chemical, model number: 020-14515) was prepared as a thickener, carbon fiber (manufactured by Resonac Co., Ltd., model number: VGCF-H (registered trademark)) was prepared as a conductive material, and water (deionized water) was prepared as a solvent.

[0596] According to step S160 of FIG. 25, graphite particles:SBR:CMC:carbon fiber:water=4.8 g:0.1 g:0.05 g:0.05 g:2.9 g (weight ratio) were mixed to prepare a negative electrode slurry.

[0597] According to FIG. 25, the above-described current collector with the coating layer was prepared as a negative electrode current collector.

[0598] According to step S161 of FIG. 25, the negative electrode slurry was applied onto the current collector with the coating layer.

[0599] The negative electrode slurry was dried according to step S162 of FIG. 25 to obtain a negative electrode. The copper foil coated with the slurry was fixed to a hot plate heated to 50°C for 30 minutes as a preliminary drying step. The copper foil coated with the slurry was then dried in a forced air dryer at 80°C for 45 minutes as a final drying step. After drying, the negative electrode was pressed (step S163). The pressing was performed under a pressure of 84 kN / m.

[0600] In this way, negative electrode sample 1 was produced. Furthermore, as a comparative example, negative electrode sample 2 was produced in the same manner as negative electrode sample 1, except that copper foil without a coating layer was used as the negative electrode current collector. The amount of negative electrode active material carried in negative electrode sample 1 and negative electrode sample 2 was approximately 12 mg / cm. 2 It was.

[0601] <Winding test> To measure the strength of negative electrode sample 1 and negative electrode sample 2, a winding test was carried out.

[0602] For the winding test, several cylindrical measuring jigs with different diameters were prepared, and negative electrode sample 1 or negative electrode sample 2 was wound around the jigs. The winding test was performed starting with the jig with the largest diameter, and then gradually changing to jigs with smaller diameters to evaluate whether cracks had occurred in the active material layer. The jigs used for the test had diameters of 30 mm, 20 mm, 9.9 mm, 8.9 mm, 7.9 mm, 6.9 mm, 5.9 mm, 4.9 mm, 4.1 mm, and 3.1 mm. For the winding test, two test pieces were prepared for each of negative electrode sample 1 and negative electrode sample 2, and the winding test was performed. The results of the winding test are shown in Table 2.

[0603] [Table 2]

[0604] In Table 2, the results of the winding test are listed as "no change," "microcracks," or "cracks." "No change" indicates that no cracks were observed in the negative electrode active material layer during the winding test. "Microcracks" indicates that one or two thin cracks were observed on the surface of the negative electrode active material layer. "Cracks" indicates that multiple clear cracks were observed in the negative electrode active material layer. "Skip" indicates that the test was not performed.

[0605] As shown in Table 2, it was confirmed that negative electrode sample 1 having a coating layer according to one embodiment of the present invention had higher adhesion between the negative electrode current collector and the negative electrode active material layer than negative electrode sample 2 having no coating layer.

[0606] <Electrode resistance measurement> Next, to evaluate the adhesion at the interface between the current collector and the active material layer, the electrode resistance of negative electrode sample 1 and negative electrode sample 2 was measured. As described in embodiment 1, this evaluation method allows the interfacial resistance between the current collector and the active material layer to be calculated, and it can be determined that the lower the interfacial resistance between the current collector and the active material layer, the higher the adhesion.

[0607] The electrode resistance was measured using the following equipment and conditions. Measuring device: Hioki E.E. Corporation electrode resistance measuring instrument XF057 Measurement probe: 46 pins Measurement current: 1mA Voltage range: 0.5V Measurement speed: Normal

[0608] In addition, the volume resistivity of the current collector (copper foil) of negative electrode sample 1 and negative electrode sample 2 was 1.7 × 10 -6 The capacitance was set to Ω·cm, and the thickness of the negative electrode active material layer of negative electrode sample 1 was set to 92.3 μm, and the thickness of the negative electrode active material layer of negative electrode sample 2 was set to 87.3 μm. The thicknesses of the negative electrode active material layers were measured using a micrometer.

[0609] The electrode resistance was measured at five different locations on each of negative electrode sample 1 and negative electrode sample 2. The results of the electrode resistance measurements are shown in FIG.

[0610] As shown in FIG. 42, the negative electrode sample 1 had a 2.0×10 -3 Ω cm 2 On the other hand, for negative electrode sample 2, the value was 3.0 × 10 or less at all five measurement points. -3 Ω cm 2 That is, it was found that negative electrode sample 1, which used a current collector with a coating layer, had a lower interfacial resistance value at all five measurement points than negative electrode sample 2, which used a current collector without a coating layer. This result confirmed that negative electrode sample 1, which has a coating layer according to one embodiment of the present invention, has higher adhesion and electronic conductivity between the negative electrode current collector and the negative electrode active material layer than negative electrode sample 2, which does not have a coating layer.

[0611] <Coin cell fabrication> A coin cell (also called a half cell) using lithium metal as the counter electrode was fabricated using the negative electrode sample 1 and negative electrode sample 2 fabricated above. In the half cell, the negative electrode sample 1 and negative electrode sample 2 functioned as the positive electrode.

[0612] Coin cells were fabricated using negative electrode sample 1, negative electrode sample 2, lithium metal foil, a separator, an electrolyte, a coin cell positive electrode can, and a coin cell negative electrode can. The size of the half cell was 2032 type (diameter 20 mm, thickness 3.2 mm). Negative electrode sample 1 and negative electrode sample 2 were each circular with a diameter of 12 mm.

[0613] The electrolyte used was a solution in which 1 mol / L of lithium hexafluorophosphate (LiPF6) was dissolved in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of EC:DEC = 3:7.

[0614] As the separator, a glass fiber filter paper (manufactured by Whatman) having a thickness of 260 μm was used.

[0615] Coin cells were fabricated in this manner. The coin cell fabricated using negative electrode sample 1 was referred to as cell 1, and the coin cell fabricated using negative electrode sample 2 was referred to as cell 2.

[0616] <Charge / discharge cycle test> A charge-discharge cycle test was carried out using the cells 1 and 2 prepared above.

[0617] The coin cell was discharged at a current of 0.5 C until the battery voltage reached 0.01 V, followed by constant voltage charging at 0.01 V until the current fell below 0.05 C (constant current-constant voltage discharge). The coin cell was charged at a constant current of 0.5 C until the battery voltage reached 1.0 V (constant current charging). The ambient temperature for charging and discharging was 25°C, and the above discharge and charge cycle was repeated 50 times. In this example, 1 C was defined as 372 mA / g of negative electrode active material weight.

[0618] The results of the charge-discharge cycle test are shown in Figure 43. In Figure 43, the horizontal axis represents the number of repeated charge-discharge cycles (number of cycles), and the vertical axis represents the charge capacity (mAh / g) obtained by dividing the discharge capacity (mAh) of the cell by the weight (g) of the negative electrode active material contained in negative electrode sample 1 or negative electrode sample 2.

[0619] As shown in Figure 43, negative electrode sample 1 having a coating layer according to one embodiment of the present invention had superior charge-discharge cycle characteristics compared to negative elec...

Claims

1. a negative electrode and an exterior body that houses the negative electrode, The negative electrode and the outer casing are connected at least at two points on one side of the outer casing, The negative electrode includes a negative electrode current collector, a coating layer on the negative electrode current collector, and a negative electrode active material layer on the coating layer. Secondary battery.

2. a positive electrode, a negative electrode, and an exterior body that houses the positive electrode and the negative electrode; The positive electrode and the outer casing are connected at least at two points on one side of the outer casing, The negative electrode and the outer casing are connected to each other at at least two points on the one side, The negative electrode includes a negative electrode current collector, a coating layer on the negative electrode current collector, and a negative electrode active material layer on the coating layer. Secondary battery.

3. In claim 1 or claim 2, The value of the interface resistance between the negative electrode current collector and the negative electrode active material layer is 2.0 × 10 －３ Ω cm ２ Below is the Secondary battery.

4. In claim 3, the value of the interface resistance is obtained by performing an inverse problem analysis using a measured potential obtained by measuring the surface of the negative electrode active material layer with a plurality of measurement probes and a calculated potential calculated by an electrode model including a current collector layer, an active material layer, and an interface resistance layer; Secondary battery.

5. In claim 1 or claim 2, the coating layer contains carbon nanotubes and carbon black; Secondary battery.

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