Secondary battery

Abstract

To provide a novel secondary battery, and provide a secondary battery in which precipitation of lithium in a form of dendrite in a negative electrode at charging can be suppressed.SOLUTION: A secondary battery includes a negative electrode and a separator. The negative electrode includes a negative electrode active material and a cover layer that covers at least a part of the negative electrode active material. The cover layer includes a region in contact with the separator. The cover layer includes a material containing titanium. As the material containing titanium, for example, metal titanium can be used.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] One embodiment of the present invention relates to a secondary battery and a manufacturing method thereof.

[0002] One aspect 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 aspect 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, a vehicle, or a manufacturing method thereof.

[0003] In this specification, the term "electronic device" refers to any device having a power storage device, and an electro-optical device having a power storage device, an information terminal device having a power storage device, and the like are all classified as electronic devices.

[0004] In this specification, the term "power storage device" refers to elements and devices in general that have a power storage function, and includes, for example, power storage devices such as lithium ion secondary batteries (also called secondary batteries), lithium ion capacitors, and electric double layer capacitors. [Background technology]

[0005] In recent years, various types of power storage devices, such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries, have been actively developed. In particular, the demand for high-output, high-energy-density lithium-ion secondary batteries has rapidly expanded in conjunction with the development of the semiconductor industry, for example, in portable information terminals such as mobile phones, smartphones, and notebook computers, portable music players, digital cameras, medical equipment, and next-generation clean energy automobiles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs), and has become indispensable in the modern information society as a repeatedly rechargeable energy source.

[0006] A lithium ion secondary battery has at least a positive electrode, a negative electrode, and an electrolyte. When charging a lithium ion secondary battery, lithium ions are released from the positive electrode and lithium ions are inserted into the negative electrode. When discharging a lithium ion secondary battery, lithium ions are released from the negative electrode and lithium ions are inserted into the positive electrode. The positive electrode and negative electrode each have an active material (positive electrode active material, negative electrode active material). An active material is a material involved in the insertion and removal of ions (lithium ions) that act as carriers.

[0007] As the negative electrode active material, metallic lithium, graphite, silicon, etc. have preferable characteristics because of low oxidation-reduction potential and high specific capacity per unit volume and unit weight. However, when metallic lithium is used as the negative electrode active material, lithium may be precipitated in a dendritic (whisker-like) form on the metallic lithium during charging, and this dendritic precipitation may penetrate the separator and short-circuit with the positive electrode, causing the lithium-ion secondary battery to catch fire. The lithium precipitated in a dendritic form is also metallic lithium. Even when graphite, silicon, etc. are used as the negative electrode active material, lithium may be precipitated in a dendritic form on the negative electrode active material when charging at a low temperature or charging with an excessive charging current. Problems caused by lithium precipitated in a dendritic form include not only short-circuiting inside the secondary battery, but also separation of the lithium precipitated in a dendritic form at the base (the region close to the negative electrode current collector) during discharge and separation from the negative electrode (also called dead lithium formation). In this case, lithium that can be exchanged between the positive and negative electrodes of the secondary battery is lost, resulting in a decrease in discharge capacity.

[0008] For this reason, research is being conducted to suppress the precipitation of lithium in the form of dendrites (Patent Document 1).

[0009] Research into secondary batteries has also been conducted into the use of carbon nanotubes (CNTs) in secondary batteries (Patent Document 2). [Prior art documents] [Patent documents]

[0010] [Patent Document 1] WO2015 / 145288 [Patent Document 2] Patent Publication No. 2020-35956 Summary of the Invention [Problem to be solved by the invention]

[0011] An object of one embodiment of the present invention is to suppress dendritic precipitation of lithium in a negative electrode during charging. Another object is to provide a lithium ion secondary battery having good cycle characteristics. Another object is to provide a secondary battery having a large capacity per unit mass or unit volume. Another object of one embodiment of the present invention is to provide a novel negative electrode, a novel secondary battery, a novel power storage device, a novel method for manufacturing a negative electrode, a novel method for manufacturing a secondary battery, or a novel method for manufacturing a power storage device.

[0012] 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 have to solve all of these problems. Note that problems other than these will become apparent from the description of the specification, drawings, claims, etc., and it is possible to extract problems other than these from the description of the specification, drawings, claims, etc. [Means for solving the problem]

[0013] One embodiment of the present invention is a secondary battery having a negative electrode and a separator, in which the negative electrode has a negative electrode active material and a coating layer that covers at least a part of the negative electrode active material, and the coating layer has a region in contact with the separator.

[0014] Alternatively, one embodiment of the present invention is a secondary battery having a negative electrode and a separator, in which the negative electrode has a negative electrode active material and a coating layer covering at least a part of the negative electrode active material, the coating layer has a region in contact with the separator, and the coating layer has a material containing titanium.

[0015] Another embodiment of the present invention is a secondary battery having a negative electrode and a separator, in which the negative electrode has a negative electrode active material and a coating layer covering at least a part of the negative electrode active material, the coating layer has a region in contact with the separator, and the coating layer has metallic titanium.

[0016] Another embodiment of the present invention is a secondary battery having a negative electrode and a separator, in which the negative electrode has a negative electrode active material and a coating layer covering at least a part of the negative electrode active material, the coating layer has a region in contact with the separator, and the coating layer contains titanium oxide.

[0017] In addition, in any one of the secondary batteries described above, the negative electrode active material preferably contains metallic lithium.

[0018] Alternatively, in any one of the secondary batteries described above, the negative electrode active material preferably contains silicon.

[0019] Alternatively, one embodiment of the present invention is a secondary battery having a negative electrode, the negative electrode including a negative electrode current collector, a negative electrode active material layer on the negative electrode current collector, and a coating layer on the negative electrode active material layer, the negative electrode active material layer including metallic lithium, and the coating layer including metallic titanium.

[0020] One embodiment of the present invention is a secondary battery having a negative electrode, the negative electrode including a negative electrode current collector, a negative electrode active material layer on the negative electrode current collector, and a coating layer on the negative electrode active material layer, the negative electrode active material layer including silicon, and the coating layer including metallic titanium.

[0021] In addition, in any one of the secondary batteries described above, the coating layer has a thickness of 1 nm or more and 50 nm or less. Effect of the Invention

[0022] According to one embodiment of the present invention, it is possible to suppress the precipitation of lithium in a dendrite shape in a negative electrode during charging. In addition, it is possible to provide a lithium ion secondary battery having good cycle characteristics. In addition, it is possible to provide a secondary battery having a large capacity per unit mass and volume. Alternatively, one embodiment of the present invention can provide a novel negative electrode, a novel secondary battery, a novel power storage device, a novel method for manufacturing a negative electrode, a novel method for manufacturing a secondary battery, or a novel method for manufacturing a power storage device.

[0023] 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 effects other than these from the description in the specification, drawings, claims, etc. [Brief description of the drawings]

[0024] [Figure 1] 1(A) and 1(B) are schematic cross-sectional views of a secondary battery. [Diagram 2] 2A to 2D are schematic cross-sectional views of the negative electrode. [Diagram 3] 3(A) to 3(C) are schematic cross-sectional views of the negative electrode and the separator. [Figure 4] 4(A) and 4(B) are schematic cross-sectional views of the negative electrode. [Diagram 5] FIG. 5(A) is a schematic cross-sectional view of a positive electrode, and FIG. 5(B) and FIG. 5(C) are schematic cross-sectional views of a secondary battery. [Figure 6] FIG. 6 is a diagram showing the external appearance of a secondary battery. [Figure 7] 7A to 7C are diagrams illustrating a method for manufacturing a secondary battery. [Figure 8] 8A to 8H are diagrams illustrating examples of electronic devices. [Figure 9]9A to 9D are diagrams illustrating examples of electronic devices. [Figure 10] 10A to 10C are diagrams illustrating examples of electronic devices. [Figure 11] 11(A) to 11(C) are diagrams illustrating an example of a vehicle. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, the 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 easily understood by those skilled in the art that the form and details of the present invention can be modified in various ways. Furthermore, the present invention is not to be interpreted as being limited to the description of the embodiments shown below.

[0026] In addition, in each drawing described in this specification, the size and thickness of each component such as the positive electrode, the negative electrode, the active material layer, the separator, the exterior body, etc. may be exaggerated for clarity of explanation. Therefore, each component is not necessarily limited to its size, and the relative sizes between each component are not necessarily limited.

[0027] In addition, in this specification, ordinal numbers such as first, second, third, etc. are used for convenience and do not indicate the order of steps, hierarchical relationships, etc. Therefore, for example, "first" can be appropriately replaced with "second" or "third" to explain. In addition, the ordinal numbers described in this specification and the like may not match the ordinal numbers used to specify one embodiment of the present invention.

[0028] In the configuration of one embodiment of the present invention described in this specification, the same reference numerals are used in different drawings for the same parts or parts having similar functions, and repeated explanations are omitted. In addition, when referring to parts having similar functions, the same hatch pattern may be used and no particular reference numeral may be used.

[0029] Furthermore, the contents described in the description of the embodiment of the present invention can be used in appropriate combination.

[0030] (Embodiment 1) In this embodiment, a structure example of a secondary battery of one embodiment of the present invention will be described with reference to FIGS.

[0031] <Secondary battery> Fig. 1(A) is a schematic diagram illustrating a part of a cross section of a secondary battery 10 according to one embodiment of the present invention. Fig. 1(B) is an enlarged view illustrating a configuration example of a region A surrounded by a dashed line in Fig. 1(A). Fig. 5(B) and Fig. 5(C) are enlarged views illustrating a configuration example of a region B surrounded by a dashed line in Fig. 1(A).

[0032] 1(A), the secondary battery 10 has a positive electrode 20, a negative electrode 30, a separator 40, and an exterior body 50. In the secondary battery 10, the positive electrode 20, the negative electrode 30, and the separator 40 are located inside the secondary battery 10 covered with the exterior body 50. The positive electrode 20 and the negative electrode 30 have an overlapping region with the separator 40 interposed therebetween. Although not shown, the secondary battery 10 has an electrolyte inside the secondary battery 10 covered with the exterior body 50.

[0033] <Negative electrode> A negative electrode 30 of one embodiment of the present invention will be described with reference to Fig. 1B. In Fig. 1B, the negative electrode 30 includes a coating layer 33 and a negative electrode active material 34. The separator 40 has voids, and the voids contain an electrolyte. The electrolyte contains lithium ions.

[0034] The negative electrode active material 34 has a coating layer 33 on its surface, and the coating layer 33 has a region in contact with the separator 40 .

[0035] [Coating layer] The coating layer 33 has a function of allowing lithium ions contained in the electrolyte to permeate, and during charging of the secondary battery 10, as shown by arrow D1 in Fig. 1(B), lithium ions move from the electrolyte contained in the voids of the separator 40 through the coating layer 33 to the negative electrode active material 34. During discharging of the secondary battery 10, lithium ions move from the negative electrode active material 34 through the coating layer 33 to the electrolyte contained in the voids of the separator 40, as shown by arrow D2 in Fig. 1(B).

[0036] [charging] In this way, when the secondary battery 10 is charged, the negative electrode active material 34 can insert lithium through the coating layer 33. In this configuration, it is believed that the flow of lithium can be dispersed by moving through the coating layer 33. As a result, it is possible to suppress localized deposition of lithium on the surface of the negative electrode active material 34. In addition, it is believed that localized deposition of lithium on the negative electrode is the cause of lithium precipitation in a dendritic form. In other words, the secondary battery 10 of one embodiment of the present invention can suppress dendritic deposition of lithium by having the coating layer 33 on the surface of the negative electrode active material 34.

[0037] As described above, the electrolyte contains lithium ions. The lithium ions in the electrolyte are said to be in a state of being solvated by the solvent molecules contained in the electrolyte. Here, the lithium ions may exist individually or in groups of multiple ions. Here, the group of multiple lithium ions is called a lithium cluster.

[0038] When the lithium clusters are present, there is a possibility that lithium may be promoted to be precipitated in a dendrite shape when lithium is locally precipitated in the negative electrode. Here, in the case where the coating layer 33 is provided on the surface of the negative electrode active material 34 as in one embodiment of the present invention, the negative electrode active material 34 can insert or remove lithium ions through the coating layer 33. At this time, since the lithium clusters cannot permeate the coating layer 33 in the state of lithium clusters, it is considered that the lithium clusters are dispersed when permeating the coating layer 33, and each moves independently to the negative electrode active material 34. In other words, it is considered that the secondary battery 10 of one embodiment of the present invention can suppress lithium from being precipitated in a dendrite shape even when lithium clusters are present in the electrolyte by having the coating layer 33 on the surface of the negative electrode active material 34.

[0039] [Discharge] Furthermore, during discharge of the secondary battery 10, the negative electrode active material 34 can release lithium through the coating layer 33. In such a configuration, it is believed that the movement of lithium through the coating layer 33 can disperse the flow of the lithium.

[0040] Here, it is known that negative electrode active materials such as silicon and tin that form alloys with lithium undergo large volume changes during charging and discharging. Therefore, when lithium is released from the negative electrode active material during discharging, lithium is released from the surface side of the negative electrode active material, so that the volume of the negative electrode active material shrinks from the surface side, and the negative electrode active material may crack.

[0041] On the other hand, in the secondary battery 10 according to one embodiment of the present invention, lithium desorbed from the negative electrode active material 34 is not desorbed directly into the electrolyte, but is desorbed into the electrolyte through the coating layer 33. Therefore, by having the coating layer 33, lithium desorbed from the negative electrode active material 34 may be dispersed. In addition, the coating layer 33 may have a function of maintaining the shape of the negative electrode active material 34. In other words, by having the coating layer 33 on the surface of the negative electrode active material 34, the secondary battery 10 according to one embodiment of the present invention may be able to suppress cracking of the negative electrode active material 34.

[0042] As described above, in the secondary battery 10 according to one embodiment of the present invention, the negative electrode active material 34 has the coating layer 33. The coating layer 33 is preferably provided on the entire surface of the negative electrode active material 34, but is not necessarily provided on the entire surface of the negative electrode active material 34. It is preferable that the coating layer 33 is provided on at least a part of the negative electrode active material 34. For example, the coating layer 33 is preferably provided on 50% or more of the surface of the negative electrode active material 34, more preferably on 60% or more, more preferably on 70% or more, more preferably on 80% or more, more preferably on 90% or more, and more preferably on 95% or more. Thus, the coating layer 33 may be provided so as to cover the entire surface of the negative electrode active material 34, or may be provided in an island shape on the surface of the negative electrode active material 34. The coating layer 33 may have a region where the surface of the negative electrode active material 34 and the electrolyte 45 are in contact with each other.

[0043] A conductor (also called a conductive material) or a semiconductor material can be used for the coating layer 33. For example, a material containing titanium can be used for the coating layer 33. The material containing titanium refers to titanium and titanium compounds. An example of a titanium compound is titanium oxide. Note that titanium, which is a metal, may be explicitly called metallic titanium. For example, in metallic titanium, lithium can pass through the crystal grain boundaries of metallic titanium.

[0044] The presence or absence of metallic titanium can be analyzed by, for example, XPS (X-ray photoelectron spectroscopy), and if metallic titanium is present, an energy peak can be confirmed in the vicinity of 454 eV.

[0045] Alternatively, for example, a material containing ruthenium can be used as the coating layer 33. The material containing ruthenium refers to ruthenium and ruthenium compounds. An example of the ruthenium compound is ruthenium oxide.

[0046] The thickness of the coating layer 33 can be 1 nm or more and 10 μm or less, preferably 1 nm or more and 1 μm or less, more preferably 1 nm or more and 100 nm or less, more preferably 1 nm or more and 50 nm or less, more preferably 1 nm or more and 40 nm or less, more preferably 1 nm or more and 30 nm or less, more preferably 1 nm or more and 20 nm or less, more preferably 1 nm or more and 10 nm or less, more preferably 1 nm or more and 5 nm or less, and more preferably 1 nm or more and 2 nm or less. By setting the thickness of the coating layer 33 in the above range, lithium can be suitably inserted and desorbed from the negative electrode active material 34.

[0047] A structural example of a negative electrode 30 having a coating layer 33 according to one embodiment of the present invention will be described with reference to FIGS.

[0048] [Negative electrode configuration example 1] As an example of the configuration of the negative electrode 30, FIG. 2(A) shows a schematic cross-sectional view of a negative electrode 30A.

[0049] The negative electrode 30A has a negative electrode active material layer 32 and a coating layer 33. In the negative electrode 30A, the coating layer 33 is provided on the negative electrode active material layer 32. In the secondary battery 10, the coating layer 33 of the negative electrode 30A is located on the separator 40 side.

[0050] The negative electrode active material layer 32 has a film-like (also referred to as a sheet-like, layer-like, foil-like, etc.) negative electrode active material 34 or a particulate negative electrode active material 34. In the configuration of the negative electrode 30A, when the negative electrode active material layer 32 is a film-like negative electrode active material 34, the negative electrode active material layer 32 is the same as the negative electrode active material 34, and the negative electrode active material layer 32 can be called the negative electrode active material 34. In addition, in the configuration of the negative electrode 30A, when the negative electrode active material layer 32 has particulate negative electrode active material 34, the negative electrode active material layer 32 has a plurality of particulate negative electrode active materials 34, and can be called a composite layer, a coated electrode layer, etc.

[0051] The coating layer 33 may be made of the above-mentioned titanium-containing material, and is preferably made of metallic titanium. The negative electrode active material 34 may be made of, for example, metallic lithium, a carbon material, or an alloy-based material. Details of metallic lithium, a carbon material, or an alloy-based material that may be used as the negative electrode active material 34 will be described later in [Negative electrode active material].

[0052] As a configuration example of the negative electrode 30A, for example, a film of metallic lithium can be used as the negative electrode active material 34, and for example, metallic titanium can be used as the coating layer 33. In this case, the metallic lithium can also be called a negative electrode active material layer 32.

[0053] Here, for example, a metallic lithium foil can be used as the negative electrode active material 34, and a metallic titanium film can be formed on the metallic lithium foil as the coating layer 33. The metallic titanium film can be formed by a film formation method such as a sputtering method, a CVD (Chemical Vapor Deposition) method, a vacuum deposition method, an EB (Electron Beam) deposition method, or an ALD (Atomic Layer Deposition) method (thermal ALD, plasma ALD).

[0054] When forming a film of metallic titanium by a sputtering method, it is preferable to use film formation conditions that allow columnar crystals to form in the formed film.

[0055] Alternatively, for example, a titanium foil may be used as the titanium metal, and a lithium metal film may be formed on the titanium foil. The lithium metal film may be formed by a film forming method such as a vacuum deposition method or an EB deposition method.

[0056] Alternatively, as another example of the configuration of the negative electrode 30A, for example, metallic lithium may be used as the negative electrode active material 34, and for example, titanium oxide may be used as the coating layer 33.

[0057] Here, for example, a metallic lithium foil can be used as the metallic lithium, and a titanium oxide film can be formed on the metallic lithium foil. The titanium oxide film can be formed by a film formation method such as a sputtering method, a CVD method, a vacuum deposition method, an EB deposition method, or an ALD method.

[0058] The configuration example of the negative electrode 30A is not limited to the above example, and one or more materials selected from the negative electrode active material materials shown in [Negative electrode active material] described later can be used as the negative electrode active material 34, and one or more materials selected from the materials that can be used for the coating layer 33 described above can be used.

[0059] [Negative electrode configuration example 2] As an example of the configuration of the negative electrode 30, a schematic cross-sectional view of a negative electrode 30B is shown in FIG.

[0060] The negative electrode 30B has a negative electrode current collector 31, a negative electrode active material layer 32, and a coating layer 33. In the negative electrode 30B, the negative electrode active material layer 32 is provided on the negative electrode current collector 31, and the coating layer 33 is provided on the negative electrode active material layer 32. In the secondary battery 10, the coating layer 33 of the negative electrode 30B is located on the separator 40 side.

[0061] As in the description of the negative electrode 30A, the negative electrode active material layer 32 has the negative electrode active material 34 in the form of a film or particulates.

[0062] The materials usable for the negative electrode active material 34 and the materials usable for the coating layer 33 can be the materials described for the negative electrode 30A. In addition, the materials usable for the negative electrode current collector 31, such as titanium foil, copper foil, and stainless steel foil, can be the materials described in [Negative electrode current collector] described later.

[0063] As a configuration example of the negative electrode 30B, for example, a copper foil can be used as the negative electrode current collector 31, for example, a film-like metallic lithium can be used as the negative electrode active material 34, and for example, metallic titanium can be used as the coating layer 33. In this case, the metallic lithium can also be called the negative electrode active material layer 32.

[0064] Here, for example, a film of metallic lithium may be formed on a copper foil, and a film of metallic titanium may be formed on the metallic lithium. The film-forming methods for metallic lithium and metallic titanium may be the same as those described for negative electrode 30A.

[0065] Alternatively, as another configuration example of the negative electrode 30B, for example, a copper foil can be used as the negative electrode current collector 31, for example, a film-like silicon can be used as the negative electrode active material 34, and for example, metallic titanium can be used as the coating layer 33. Note that the silicon in this case can also be called the negative electrode active material layer 32.

[0066] Here, for example, a silicon film can be formed on a copper foil, and a metallic titanium film can be formed on the silicon. The silicon film can be formed by a film formation method such as a sputtering method, a CVD method, a vacuum deposition method, or an EB deposition method. The metallic titanium film can be formed by the film formation method described for the negative electrode 30A.

[0067] The configuration example of the negative electrode 30B is not limited to the above example, and it is possible to use an appropriate combination of the negative electrode current collector 31 selected from the materials described in [Negative electrode current collector] described later, the negative electrode active material 34 selected from the negative electrode active material materials shown in [Negative electrode active material] described later, and the above-mentioned coating layer 33.

[0068] [Negative electrode configuration example 3] As an example of the configuration of the negative electrode 30, a schematic cross-sectional view of a negative electrode 30C is shown in FIG.

[0069] Negative electrode 30C has an underlayer 37 on negative electrode current collector 31, a negative electrode active material layer 32 on underlayer 37, and a coating layer 33 on negative electrode active material layer 32. In secondary battery 10, coating layer 33 of negative electrode 30C is located on the separator 40 side.

[0070] As in the description of the negative electrode 30A, the negative electrode active material layer 32 has the negative electrode active material 34 in the form of a film or particulates.

[0071] The materials usable for the negative electrode active material 34 and the materials usable for the coating layer 33 can be the materials described for the negative electrode 30A. The materials usable for the negative electrode current collector 31 can be the materials described for the negative electrode 30B.

[0072] As an example of the configuration of the negative electrode 30C, for example, a titanium foil can be used as the negative electrode current collector 31, metallic titanium can be used as the underlayer 37, metallic lithium can be used in the form of a film as the negative electrode active material 34, and metallic titanium can be used as the coating layer 33. In this case, the metallic lithium can also be called the negative electrode active material layer 32.

[0073] Here, for example, a film of metallic lithium can be formed on a titanium foil, and a film of metallic titanium can be formed on the metallic lithium. The film formation method described for the negative electrode 30A can be used to form the metallic lithium and metallic titanium films.

[0074] As in the above example, when forming a film of metallic lithium, if metallic titanium is formed as underlayer 37, it is expected that the flatness of the metallic lithium will be improved.

[0075] The configuration example of the negative electrode 30C is not limited to the above example. For the negative electrode current collector 31, one selected from the materials described in [Negative electrode current collector] described later can be used, for the negative electrode active material 34, one or more materials selected from the negative electrode active material materials shown in [Negative electrode active material] described later can be used, and one or more materials selected from the materials that can be used for the coating layer 33 described above can be used.

[0076] [Negative electrode configuration example 4] As an example of the configuration of the negative electrode 30, a schematic cross-sectional view of a negative electrode 30D is shown in FIG.

[0077] The negative electrode 30D has a catalyst layer 38 on the negative electrode current collector 31, a negative electrode active material layer 32 on the catalyst layer 38, and a coating layer 33 on the negative electrode active material layer 32. In the secondary battery 10, the coating layer 33 of the negative electrode 30D is located on the separator 40 side.

[0078] The negative electrode active material layer 32 of the negative electrode 30D has a film-like negative electrode active material 34, and the negative electrode active material 34 has a carbon material such as CNT (Carbon nanotube) or graphite.

[0079] The catalyst layer 38 refers to a layer having a material that promotes the formation of CNTs when CNTs are formed using a CVD method. Iron chloride (FeCl2) can be used as the catalyst layer 38. The materials that can be used for the coating layer 33 are the same as those described for the negative electrode 30A. The materials that can be used for the negative electrode current collector 31 are the same as those described for the negative electrode 30B.

[0080] As an example of the configuration of the negative electrode 30C, for example, titanium foil can be used as the negative electrode current collector 31, powdered iron chloride (FeCl2) can be used as the catalyst layer 38, film-like CNT can be used as the negative electrode active material 34, and metallic titanium can be used as the coating layer 33. Note that the CNT in this case can also be called the negative electrode active material layer 32.

[0081] Here, for example, powdered iron chloride (FeCl2) is dispersed on a titanium foil, and then CNTs are formed by a CVD method, and a titanium metal film is formed on the CNTs. The titanium metal film can be formed by the film formation method described for the negative electrode 30A. The CNT film can be formed, for example, by using a CVD device in an environment of 500 Pa to 2000 Pa and 800°C to 900°C using acetylene gas.

[0082] As in the above example, when forming a CNT film, by providing the catalyst layer 38 on the negative electrode current collector 31, it becomes possible to form the CNTs well. Furthermore, by forming the CNTs under the above conditions, it is possible to align the growth direction of the CNTs substantially perpendicular to the upper surface of the negative electrode current collector 31. Note that substantially perpendicular specifically means that the angle with the surface is 80° or more and 100° or less.

[0083] The configuration example of the negative electrode 30D is not limited to the above example, and one selected from the materials described in [Negative electrode current collector] described later can be used as the negative electrode current collector 31, and one or more materials selected from the materials that can be used for the coating layer 33 described above can be used.

[0084] [Negative electrode configuration example 5] As an example of the configuration of the negative electrode 30, a schematic cross-sectional view of a negative electrode 30E and a separator 40 is shown in FIG.

[0085] The negative electrode 30E has a negative electrode current collector 31 and a negative electrode active material layer 32. In the secondary battery 10, the negative electrode active material layer 32 of the negative electrode 30E is located on the separator 40 side.

[0086] 2(A) to 2(D), an example has been shown in which the coating layer 33 is provided at a position in contact with the separator 40, but the position at which the coating layer 33 is provided is not limited to the above example. For example, when the negative electrode active material layer 32 has particulate negative electrode active material 34, it is preferable to provide the coating layer 33 on the surface of the particulate negative electrode active material 34.

[0087] 3(B) and 3(C) show examples in which a coating layer 33 is provided on the surface of the negative electrode active material 34 of the negative electrode active material layer 32. Each of Fig. 3(B) and Fig. 3(C) is an enlarged view for explaining a configuration example of a region C surrounded by a dashed line in Fig. 3(A).

[0088] FIG. 3B is a diagram showing an example in which a coating layer 33 is provided in the process of producing the negative electrode 30. As shown in FIG.

[0089] 3(A) and 3(B), the negative electrode 30E has a negative electrode active material layer 32 on a negative electrode current collector 31, and the negative electrode active material layer 32 has a negative electrode active material 34, a coating layer 33, and a conductive material 36. An electrolyte 45 may be contained in the voids of the negative electrode active material layer 32.

[0090] 3(B) can be produced by applying a slurry containing the negative electrode active material 34 (a solution in which the negative electrode active material 34, a conductive material 36, and a dispersion medium are mixed) onto the negative electrode current collector 31, drying the slurry, and then providing the coating layer 33. Although not shown, a binder may be included to fix the negative electrode active material layers 32 together and to fix the negative electrode active material 34 to the negative electrode current collector 31.

[0091] If the CVD method, sputtering method, or vapor deposition method is used as the film formation method for the coating layer 33 in this configuration example, it is difficult to form the coating layer 33 on the negative electrode active material 34 in a portion far from the inner surface of the negative electrode active material layer 32. Therefore, in this configuration example, it is preferable to form the coating layer 33 by the ALD method or a sol-gel method using a liquid such as titanium alkoxide. By forming the coating layer 33 by the ALD method, the sol-gel method, or the like, it is possible to provide the coating layer 33 on the entire surface of the particles of the negative electrode active material 34 contained in the negative electrode active material layer 32.

[0092] When the coating layer 33 is a conductor such as metallic titanium, the negative electrode active material layer 32 may not have a material that assists conductivity (also referred to as a conductive assistant), such as the conductive material 36. On the other hand, when the coating layer 33 is a semiconductor having a lower conductivity than a conductor, such as titanium oxide, the negative electrode active material layer 32 preferably has the conductive material 36. As the conductive material 36 that the negative electrode active material layer 32 can have, one or more materials selected from the materials described in [Conductive material] described later can be used.

[0093] When the coating layer 33 is a semiconductor having a lower conductivity than a conductor, such as titanium oxide, the conductivity of the coating layer 33 can be increased by reducing the coating layer 33. For example, when titanium oxide is used as the coating layer 33, the titanium oxide can be reduced using hydrogen, sodium borohydride, or the like as a reducing agent. As a result, the conductivity of the coating layer can be improved.

[0094] Next, a configuration example of a negative electrode 30E different from that shown in Fig. 3(B) will be described with reference to Fig. 3(C). Fig. 3(C) is a diagram showing an example in which a coating layer 33 is provided in the process of producing a negative electrode active material .

[0095] 3(A) and 3(C), the negative electrode 30E has a negative electrode active material layer 32 on a negative electrode current collector 31, and the negative electrode active material layer 32 has a negative electrode active material 34, a coating layer 33, a binder 35, and a conductive material 36. An electrolyte 45 may be contained in the voids of the negative electrode active material layer 32.

[0096] The configuration example shown in FIG. 3(C) can be produced by performing a process of providing a coating layer 33 on the negative electrode active material 34, and then coating a slurry containing the negative electrode active material 34 (a solution in which the negative electrode active material 34, a dispersion medium, a binder 35, and a conductive material 36 are mixed) on the negative electrode current collector 31 and drying the slurry.

[0097] The coating layer 33 can be formed on the negative electrode active material 34 by the ALD method, a sol-gel method using a liquid such as titanium alkoxide, or a barrel sputtering method (a type of sputtering method in which a film is formed while particulate powder is stirred), or the like.

[0098] 2(A) to 3(C) used in the description of the above-mentioned negative electrode configuration examples 1 to 5 are illustrated as uniformly covering the surface of the film-like negative electrode active material 34 or the surface of the particulate negative electrode active material 34 without any gaps, but the coating layer 33 may have cracks CR, cavities CA, gaps GA where the coating layer 33 is not provided, etc., as shown in Fig. 4(A). For example, in the gaps GA shown in Fig. 4(A), the negative electrode active material 34 may come into contact with the electrolyte.

[0099] 2(A) to 3(C) used in the description of the above-mentioned negative electrode configuration examples 1 to 5 clearly show the boundary between the surface of the film-like negative electrode active material 34 or the surface of the particulate negative electrode active material 34 and the coating layer 33, but as shown in Fig. 4(B), an interface layer 39 may be provided between the negative electrode active material 34 and the coating layer 33. The interface layer 39 may be a region in which at least a part of the elements contained in the negative electrode active material 34 and the elements contained in the coating layer 33 are mixed.

[0100] The negative electrodes 30 (negative electrodes 30B to 30E) shown in FIGS. 2E to 3C used in the description of the negative electrode configuration example 2 to the negative electrode configuration example 5 above are examples in which the negative electrode active material layer 32 and the coating layer 33 are provided on one surface of the negative electrode current collector 31. However, the negative electrode of one embodiment of the present invention is not limited to such a single-sided negative electrode, and may be a double-sided negative electrode (negative electrode 30F) as shown in FIG. 4C. The negative electrode 30F shown in FIG. 4C is a configuration example of a double-sided negative electrode, and shows a case in which the negative electrode 30B shown in FIG. 2B is made into a double-sided negative electrode. The negative electrode 30F has the negative electrode active material layers 32 on one surface and the other surface of the negative electrode current collector 31, respectively, and has the coating layer 33 on each of the negative electrode active material layers 32. As in the examples shown in FIGS. 2B and 4C, the negative electrodes 30C to 30E may also be configured as double-sided negative electrodes.

[0101] [Example of providing a coating layer on a separator] In the above-mentioned negative electrode configuration example 1 to negative electrode configuration example 5, examples in which the coating layer 33 is provided on the negative electrode 30 are described. As one embodiment of the present invention, a secondary battery 10 may be provided that has a separator 40 having a coating layer 33 and a negative electrode that does not have the coating layer 33. In this case, the separator 40 may have the coating layer 33 on at least one surface of the separator 40, and the surface having the coating layer 33 may be provided so as to face the negative electrode side that does not have the coating layer. The material that can be used for the coating layer 33 and the method for forming the coating layer 33 may be any of the methods described above.

[0102] [Binder] As the binder, it is preferable to use one or more of the following rubber materials: styrene-butadiene rubber, styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, butyl rubber, ethylene-propylene rubber, fluororubber, silicone rubber, and urethane rubber. The above-mentioned rubber materials can be dispersed in a dispersion medium and used. As the dispersion medium, for example, one or more of the following can be used: water, N-methylpyrrolidone (NMP), methanol, ethanol, acetone, tetrahydrofuran (THF), dimethylformamide (DMF), and dimethylsulfoxide (DMSO).

[0103] Also, for example, a water-soluble polymer can be used as the binder. 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.

[0104] Alternatively, the binder may be made of 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.

[0105] The binder may be used in combination of two or more of the above.

[0106] For example, a material having a particularly excellent viscosity adjusting effect may be used in combination with another material. For example, while rubber materials and the like have excellent adhesive strength and elasticity, it may be difficult to adjust the viscosity when mixed with a solvent. In such a case, it is preferable to mix the material with a material having a particularly excellent viscosity adjusting effect. For example, a water-soluble polymer may be used as a material having a particularly excellent viscosity adjusting effect. In addition, as a water-soluble polymer having a particularly excellent viscosity adjusting effect, the above-mentioned polysaccharides, for example, carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, and diacetylcellulose, cellulose derivatives such as regenerated cellulose, or starch may be used.

[0107] In addition, the solubility of cellulose derivatives such as carboxymethylcellulose is increased by converting them into salts such as sodium salt or ammonium salt of carboxymethylcellulose, and they are more likely to exhibit their effect as viscosity adjusters. The increased solubility can also increase the dispersibility with the active material or other components when preparing a slurry for an electrode. In this specification, the cellulose and cellulose derivatives used as the binder for an electrode include their salts.

[0108] Water-soluble polymers stabilize the viscosity by dissolving in water, and can stably disperse the active material and other materials combined as a binder, such as styrene-butadiene rubber, in the aqueous solution. In addition, since they have functional groups, they are expected to be easily and stably adsorbed onto the surface of the active material. In addition, many cellulose derivatives, such as carboxymethyl cellulose, have functional groups such as hydroxyl groups or carboxyl groups, and since they have functional groups, the polymers interact with each other and are expected to widely cover the surface of the active material.

[0109] When the binder covers the active material surface or contacts the surface to form a film, it is expected to act as a passive film and suppress the decomposition of the electrolyte. Here, the "passive film" refers to a film with no electronic conductivity or a film with extremely low electronic conductivity. For example, when a passive film is formed on the surface of the active material, it can suppress the decomposition of the electrolyte at the battery reaction potential. It is more preferable that the passive film suppresses the electronic conductivity and can conduct lithium ions.

[0110] [Negative electrode active material] As the negative electrode active material, for example, metallic lithium, a carbon material, an alloy material, or the like can be used.

[0111] When metallic lithium is used as the negative electrode active material, metallic lithium on a foil can be used. Alternatively, metallic lithium can be vapor-deposited on a substrate such as a current collector.

[0112] Examples of carbon materials that can be used include graphite (natural graphite, artificial graphite), graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon fiber (carbon nanotube), graphene, and carbon black.

[0113] 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, as the artificial graphite, spherical graphite having a spherical shape can be used. For example, MCMB may have a spherical shape, which is preferable. In addition, it is relatively easy to reduce the surface area of ​​MCMB, which may be preferable. Examples of natural graphite include flake graphite and spheroidized natural graphite.

[0114] When lithium ions are inserted into graphite (when lithium-graphite intercalation compounds are formed), graphite exhibits a low potential similar to that of metallic lithium (0.05 V to 0.5 V vs. Li / Li +) This allows lithium-ion batteries using graphite to exhibit high operating voltages. Furthermore, graphite is preferred because it has the advantages of being relatively high capacity per unit volume, relatively small volume expansion, inexpensive, and safer than metallic lithium.

[0115] The non-graphitizable carbon can be obtained by calcining, for example, a synthetic resin such as a phenolic resin, or an organic matter derived from a plant. The non-graphitizable carbon contained in the negative electrode active material of the lithium ion battery according to one embodiment of the present invention has a (002) plane spacing measured by X-ray diffraction (XRD) of preferably 0.34 nm or more and 0.50 nm or less, more preferably 0.35 nm or more and 0.42 nm or less.

[0116] In addition, the negative electrode active material can use an element capable of performing a charge / discharge reaction by alloying / dealloying reaction with lithium. For example, a material containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used. Such elements have a larger capacity than carbon, and are preferably used as the negative electrode active material. Compounds containing these elements may also be used. For example, SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, SbSn, etc. Here, elements capable of carrying out charge / discharge reactions through alloying / dealloying reactions with lithium, and compounds containing such elements, are sometimes referred to as alloying materials.

[0117] In this specification, "SiO" refers to, for example, silicon monoxide. Alternatively, SiO may be SiO x Here, x preferably has a value of 1 or close to 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less. In addition, not only compounds in which silicon and oxygen exist in a uniform composition, but also mixtures of silicon and silicon dioxide are sometimes called SiO.

[0118] Although one type of negative electrode active material from among the above-listed negative electrode active materials can be used, a combination of multiple types can also be used, for example, a combination of a carbon material and silicon, or a combination of a carbon material and SiO.

[0119] [Negative electrode current collector] As the current collector used for the negative electrode, a material having high electrical conductivity, such as metals such as stainless steel, gold, platinum, copper, titanium, and alloys thereof, can be used. In addition, it is preferable that the material used for the negative electrode current collector does not form an alloy with Li at the potential of the negative electrode. The current collector can be appropriately used in a shape such as a foil, a plate, a sheet, a mesh, a punched metal, or an expanded metal. It is preferable to use a current collector having a thickness of 5 μm or more and 30 μm or less. As described above, when a layer having Ti on a lithium foil is used as the negative electrode, the lithium foil can also function as the negative electrode current collector, so that the negative electrode current collector does not need to be provided. Alternatively, even when the coating layer 33 functions as the negative electrode current collector, the negative electrode current collector does not need to be provided.

[0120] [Conductive material] The conductive material is also called a conductive agent or conductive assistant, and is made of a carbon material. By attaching the conductive material between a plurality of active materials, the active materials are electrically connected to each other, and the conductivity is increased. Note that the term "attachment" does not only refer to the physical adhesion between the active material and the conductive material, but also includes the case where a covalent bond is formed, the case where the conductive material is bonded by van der Waals forces, the case where the conductive material covers a part of the surface of the active material, the case where the conductive material is embedded in the surface irregularities of the active material, and the case where the two materials are electrically connected even if they are not in contact with each other.

[0121] The active material layers, such as the positive electrode active material layer and the negative electrode active material layer, preferably contain a conductive material.

[0122] As the conductive material, for example, one or more of carbon blacks such as acetylene black and furnace black, graphites such as artificial graphite and natural graphite, carbon fibers such as carbon nanofibers and carbon nanotubes, and graphene compounds can be used.

[0123] As the carbon fiber, for example, mesophase pitch carbon fiber, isotropic pitch carbon fiber, etc. can be used. In addition, as the carbon fiber, carbon nanofiber or carbon nanotube can be used. Carbon nanotube can be produced by, for example, vapor phase growth method.

[0124] In the present specification and the like, the graphene compound includes graphene, multi-layer graphene, multi-graphene, graphene oxide, multi-layer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multi-layer graphene oxide, reduced multi-graphene oxide, graphene quantum dots, and the like. The graphene compound has carbon, has a shape such as a plate shape or a sheet shape, and has a two-dimensional structure formed by six-membered carbon rings. The two-dimensional structure formed by six-membered carbon rings may be called a carbon sheet. The graphene compound may have a functional group. In addition, the graphene compound preferably has a curved shape. In addition, the graphene compound may be rolled up like a carbon nanofiber.

[0125] The active material layer may also contain, as a conductive material, metal powder or metal fiber of copper, nickel, aluminum, silver, gold, or the like, a conductive ceramic material, or the like.

[0126] The content of the conductive material relative to the total amount of the active material layer is preferably 1 wt % or more and 10 wt % or less, and more preferably 1 wt % or more and 5 wt % or less.

[0127] Unlike granular conductive materials such as carbon black, which are in point contact with the active material, the graphene compound allows for surface contact with low contact resistance, and therefore can improve the electrical conductivity between the granular active material and the graphene compound with a smaller amount than that of a normal conductive material. This allows the ratio of the active material in the active material layer to be increased, thereby increasing the discharge capacity of the battery.

[0128] Particulate carbon-containing compounds such as carbon black and graphite, or fibrous carbon-containing compounds such as carbon nanotubes, tend to enter microspaces. Microspaces refer to, for example, regions between a plurality of active materials. By using a combination of a carbon-containing compound that tends to enter microspaces and a sheet-like carbon-containing compound such as graphene that can impart conductivity across a plurality of particles, the density of the electrode can be increased and an excellent conductive path can be formed. The battery obtained by the manufacturing method of one embodiment of the present invention has a high capacity density and can be stable, and is effective as an in-vehicle battery.

[0129] <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. The conductive material and the binder may be the same as those described in the negative electrode.

[0130] The positive electrode can be formed by applying the slurry onto a current collector and drying it. After drying, the slurry may be pressed. The positive electrode is formed by forming an active material layer on a current collector.

[0131] The slurry is a material liquid used to form an active material layer on a current collector, and contains an active material, a binder, and a solvent, and preferably further contains a conductive material. The slurry is also called an electrode slurry or an active material slurry, and when a positive electrode active material layer is formed, it is also called a positive electrode slurry.

[0132] As shown in FIG. 5(A), a positive electrode 20 has a positive electrode active material layer 22 on a positive electrode current collector .

[0133] The positive electrode 20 may have a coating layer like the coating layer 33 described for the negative electrode 30, and in this case, the positive electrode active material 24 has the coating layer 23. As the material that can be used for the coating layer 23, those described in <Negative electrode> can be used.

[0134] 5(B) and 5(C) show examples of providing a coating layer 23 on the surface of the positive electrode active material 24. Fig. 5(B) and Fig. 5(C) are enlarged views for explaining configuration examples of the region B surrounded by the dashed line in Fig. 1(A).

[0135] FIG. 5(B) is a diagram showing an example in which a coating layer 23 is provided in the process of producing the positive electrode 20. As shown in FIG.

[0136] 5(A) and 5(B), a positive electrode 20 has a positive electrode active material layer 22 on a positive electrode current collector 21, and the positive electrode active material layer 22 has a positive electrode active material 24 and a coating layer 23. An electrolyte 45 may be contained in the voids of the positive electrode active material layer 22.

[0137] 5(B) can be produced by applying a slurry (a solution in which the positive electrode active material 24 and a dispersion medium are mixed) containing the positive electrode active material 24 onto the positive electrode current collector 21, drying it, and then providing the coating layer 23. Although not shown, a binder may be included to fix the positive electrode active material layers 22 together and to fix the positive electrode active material 24 and the positive electrode current collector 21 together.

[0138] If a CVD method, a sputtering method, or a vapor deposition method is used as a method for forming the coating layer 23 in this configuration example, it is difficult to form the coating layer 23 on the positive electrode active material 24 in a portion far from the inner surface of the positive electrode active material layer 22. Therefore, in this configuration example, it is preferable to form the coating layer 23 by an ALD method or a sol-gel method using a liquid such as titanium alkoxide. By forming the coating layer 23 by an ALD method, a sol-gel method, or the like, it is possible to provide the coating layer 23 on the entire surface of the particles of the positive electrode active material 24 contained in the positive electrode active material layer 22.

[0139] When the coating layer 23 is a conductor such as metallic titanium, the positive electrode active material layer 22 does not need to contain a material that assists conductivity, such as a conductive material, as shown in Fig. 5(B). On the other hand, when the coating layer 23 is a semiconductor having a lower conductivity than a conductor, such as titanium oxide, the positive electrode active material layer 22 preferably contains a conductive material.

[0140] When the coating layer 23 is a semiconductor having a lower conductivity than a conductor, such as titanium oxide, it is preferable to increase the conductivity of the coating layer 23 by performing a reduction treatment on the coating layer 23. For example, when titanium oxide is used as the coating layer 23, the titanium oxide can be reduced using hydrogen, sodium borohydride, or the like as a reducing agent. As a result, the conductivity of the coating layer can be improved.

[0141] Next, a configuration example of the positive electrode 20 different from that shown in Fig. 5(B) will be described with reference to Fig. 5(C). Fig. 5(C) is a diagram showing an example in which a coating layer 23 is provided in the process of producing a positive electrode active material 24.

[0142] 5(A) and 5(C), the positive electrode 20 has a positive electrode active material layer 22 on a positive electrode current collector 21, and the positive electrode active material layer 22 has a positive electrode active material 24, a coating layer 23, a binder 25, and a conductive material 26. An electrolyte 45 may be present in the voids of the positive electrode active material layer 22. As the conductive material 26 that can be contained in the positive electrode active material layer 22, one or more materials selected from the materials described in the above-mentioned [Conductive material] can be used.

[0143] The configuration example shown in FIG. 5(C) can be produced by performing a process of providing a coating layer 23 on a positive electrode active material 24, and then applying a slurry containing the positive electrode active material 24 (a solution in which the positive electrode active material 24, a dispersion medium, a binder 25, and a conductive material 26 are mixed) onto a positive electrode current collector 21 and drying the slurry.

[0144] The coating layer 23 can be formed on the positive electrode active material 24 by an ALD method, a sol-gel method using a liquid such as titanium alkoxide, a barrel sputtering method, or the like.

[0145] [Cathode active material] As the positive electrode active material, at least one of a composite oxide having a layered rock-salt structure, a composite oxide having an olivine structure, and a composite oxide having a spinel structure can be used.

[0146] As the composite oxide having a layered rock salt structure, any one or more of lithium cobalt oxide, lithium nickel-cobalt-manganese oxide, lithium nickel-cobalt-aluminate, and lithium nickel-manganese-aluminate can be used. The composition formula can be expressed as LiM1O2 (M1 is one or more selected from nickel, cobalt, manganese, and aluminum), but the coefficients of the composition formula are not limited to integers.

[0147] As the lithium cobalt oxide, for example, lithium cobalt oxide to which magnesium and fluorine are added can be used. Alternatively, lithium cobalt oxide to which magnesium, fluorine, aluminum, and nickel are added can be used. Alternatively, lithium cobalt oxide to which magnesium, fluorine, aluminum, nickel, and titanium are added can be used.

[0148] As the lithium nickel-cobalt-manganese oxide, for example, lithium nickel-cobalt-manganese oxide having a ratio of nickel:cobalt:manganese=1:1:1, nickel:cobalt:manganese=6:2:2, nickel:cobalt:manganese=8:1:1, nickel:cobalt:manganese=9:0.5:0.5, etc. can be used. In addition, as the lithium nickel-cobalt-manganese oxide, it is preferable to use lithium nickel-cobalt-manganese oxide to which one or more of aluminum, calcium, barium, strontium, and gallium have been added.

[0149] The composite oxide having an olivine structure may be any one or more of lithium iron phosphate, lithium manganese phosphate, lithium cobalt phosphate, and lithium iron manganese phosphate. The composition formula can be LiM2PO4 (where M2 is one or more selected from iron, manganese, and cobalt), but the coefficients of the composition formula are not limited to integers.

[0150] Alternatively, it can be used as a composite oxide having a spinel structure, such as LiMn2O4.

[0151] [Positive electrode current collector] As the positive electrode current collector, a material having high electrical conductivity, such as metals such as stainless steel, gold, platinum, aluminum, and titanium, and alloys thereof, can be used. In addition, it is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. In addition, an aluminum alloy to which an element that improves heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, is added, can be used. The current collector can be appropriately used in a shape such as a foil, plate, sheet, net, punched metal, or expanded metal. It is preferable to use a current collector having a thickness of 5 μm or more and 30 μm or less.

[0152] <Electrolyte> As one form of the electrolyte, an electrolyte solution having a solvent and an electrolyte dissolved in the solvent can be used. The electrolyte solution has a solvent and a lithium salt. As the solvent of the electrolyte solution, an aprotic organic solvent is preferable, and for example, one of 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, sultone, etc., or two or more of these can be used in any combination and ratio.

[0153] When the electrolyte contains ethylene carbonate (EC) and diethyl carbonate (DEC), the volume ratio of ethylene carbonate and diethyl carbonate can be x:100-x (where 20≦x≦40) when the total content of ethylene carbonate and diethyl carbonate is 100 vol%. More specifically, a mixed organic solvent containing EC and DEC in a volume ratio of EC:DEC=30:70 can be used.

[0154] When using, as the electrolytic solution, a composition containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), when the total content of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate is 100 vol%, a composition in which the volume ratio of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate is x:y:100-x-y (where 5≦x≦35 and 0<y<65) can be used. More specifically, a mixed organic solvent containing EC, EMC, and DMC at a volume ratio of EC:EMC:DMC = 30:35:35 can be used.

[0155] Furthermore, as the electrolytic solution, a mixed organic solvent containing a cyclic fluorinated carbonate (which may also be referred to as a fluorinated cyclic carbonate) or a chain fluorinated carbonate (which may also be referred to as a fluorinated chain carbonate) can be used. Preferably, the above mixed organic solvent contains both a cyclic fluorinated carbonate and a chain fluorinated carbonate. Both the cyclic fluorinated carbonate and the chain fluorinated carbonate have an electron-withdrawing substituent, which is preferable as it reduces the solvation energy of lithium ions. Therefore, both the cyclic fluorinated carbonate and the chain fluorinated carbonate are suitable for the electrolytic solution, and such a mixed organic solvent is suitable.

[0156] As the cyclic fluorinated carbonate, for example, fluoroethylene carbonate (fluoromethylenecarbonate, FEC, F1EC), difluoroethylene carbonate (DFEC, F2EC), trifluoroethylene carbonate (F3EC), or tetrafluoroethylene carbonate (F4EC) can be used. Note that DFEC has isomers such as cis-4,5 and trans-4,5. Since any of these cyclic fluorinated carbonates has an electron-withdrawing substituent, it is considered that the solvation energy of lithium ions is low. In FEC, the electron-withdrawing substituent is the F group.

[0157] Methyl 3,3,3-trifluoropropionate is an example of a fluorinated chain carbonate. The abbreviation for methyl 3,3,3-trifluoropropionate is "MTFP." In MTFP, the electron-withdrawing substituent is the CF3 group.

[0158] FEC is one of the cyclic carbonates and has a high relative dielectric constant, so when used in an organic solvent, it has the effect of promoting the dissociation of lithium salts. Furthermore, since FEC has a substituent that exhibits electron-withdrawing properties, it is easy to bind with lithium ions by Coulomb force or the like. Specifically, since the solvation energy of lithium ions in FEC is smaller than that of ethylene carbonate (EC), which does not have a substituent that exhibits electron-withdrawing properties, it can be said that FEC is easy to form solvation with lithium ions. Furthermore, FEC is thought to have a deep highest occupied molecular orbital (HOMO) level, and if the HOMO level is deep, it is difficult to oxidize and the oxidation resistance is improved. On the other hand, there is a concern that FEC has a high viscosity. Therefore, it is recommended to use a mixed organic solvent containing not only FEC but also MTFP in the electrolyte. MTFP is one of the chain carbonates, and it is possible to have the effect of lowering the viscosity of the electrolyte or maintaining the viscosity at room temperature (typically 25°C) even at low temperatures (typically 0°C). Furthermore, since MTFP has a smaller solvation energy than methyl propionate (abbreviated as "MP"), which does not have an electron-withdrawing substituent, it may form a solvate with lithium ions when used in an electrolyte.

[0159] The total content of the mixed organic solvent containing FEC and MTFP having such physical properties is taken as 100 vol%, and the volume ratio is preferably x:100-x (where 5≦x≦30, preferably 10≦x≦20). In other words, the mixed organic solvent is preferably mixed so that MTFP is more than FEC. The negative electrode of one embodiment of the present invention has a coating layer on the surface of the negative electrode active material. When metallic titanium is used for the coating layer, a passive coating can be formed on the metallic titanium surface even when fluorine ions are generated in the electrolyte solution containing the above-mentioned FEC or MTFP. Therefore, the negative electrode of one embodiment of the present invention can be suitably combined with an electrolyte solution containing a mixed organic solvent containing FEC and MTFP.

[0160] In addition, by using one or more ionic liquids (room-temperature molten salts) that are flame-retardant and non-volatile as a solvent for the electrolyte, even if the internal temperature of the secondary battery rises due to an internal short circuit or overcharging, etc., the secondary battery can be prevented from exploding and / or catching fire. The ionic liquid is composed of a cation and an anion, and includes an organic cation and an anion. Examples of the organic cation used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of the anion used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.

[0161] [Lithium salt] Examples of the lithium salt (also called electrolyte) dissolved in the above-mentioned solvent include LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl 10 , Li2B 12 Cl 12Lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, etc. can be used alone or in any combination and ratio of two or more of these. The lithium salt should be 0.5 mol / L or more and 3.0 mol / L or less relative to the solvent. The use of fluorides such as LiPF6 and LiBF4 improves the safety of lithium-ion secondary batteries.

[0162] The above-mentioned electrolyte is preferably a highly purified electrolyte with a low content of granular waste or elements other than the constituent elements of the electrolyte (hereinafter, simply referred to as "impurities"). Specifically, the weight ratio of impurities to the electrolyte is 1 wt% or less, preferably 0.1 wt% or less, and more preferably 0.01 wt% or less.

[0163] [Additives] The electrolyte may contain an additive. The additive can suppress the reactive decomposition of the electrolyte that may occur on the positive electrode surface or the negative electrode surface when the secondary battery is operated at high voltage and / or high temperature. For example, vinylene carbonate (VC), propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), and lithium bis(oxalate)borate (LiBOB) can be used as the additive. LiBOB is particularly preferred because it is easy to form a good coating. VC or FEC is preferred because it can form a good coating on the negative electrode during aging or charging in the early stages of use of the secondary battery, thereby improving the cycle characteristics.

[0164] As the additive, any one or more of dinitrile compounds can be used. Specific examples of the dinitrile compound include succinonitrile, glutaronitrile, adiponitrile (ADN), and ethylene glycol bis(propionitrile) ether (EGBE).

[0165] Further, fluorobenzene may be added to the organic solvent. The concentration of the additive may be, for example, 0.1 wt% or more and 5 wt% or less with respect to the entire electrolyte. PS or EGBE is preferable because it can form a good coating on the positive electrode during charging and discharging, thereby improving cycle characteristics. FB is preferable because it improves the wettability of the organic solvent to the positive electrode and the negative electrode. Dinitrile compounds are preferable because the nitrile groups are oriented to the positive electrode and the negative electrode, inhibiting the oxidative decomposition of the organic solvent, thereby improving the high voltage resistance. Furthermore, dinitrile compounds are preferable because they can prevent the dissolution of copper during overdischarge when a current collector having copper is used for the negative electrode. Considering the use of secondary batteries at high voltages, it is preferable to add a nitrile compound.

[0166] [Gel electrolyte] As the gel electrolyte, a polymer gel in which a polymer is swollen with an electrolytic solution may be used. By using a polymer gel electrolyte, a semi-solid electrolyte layer can be provided, and safety against leakage and the like can be improved. In addition, it is possible to make the secondary battery thinner and lighter.

[0167] Examples of the polymer that can be gelled include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, and fluorine-based polymer gel.

[0168] Examples of the polymer that can be used include polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing these. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The polymer that is formed may have a porous shape.

[0169] [Solid electrolyte] Instead of the electrolyte, a solid electrolyte containing an inorganic material such as a sulfide or oxide, or a solid electrolyte containing a polymer material such as a PEO (polyethylene oxide) can be used. When a solid electrolyte is used, the installation of a separator and / or spacer becomes unnecessary. In addition, since the entire battery can be solidified, there is no risk of leakage, and safety is dramatically improved.

[0170] <separator> The secondary battery preferably has a separator. The separator may be made of, for example, paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyolefin, or polyurethane. The separator is preferably processed into an envelope shape and disposed so as to encase either the positive electrode or the negative electrode.

[0171] The separator may have a multi-layer structure. For example, an organic material film such as polypropylene or polyethylene may be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture of these. As the ceramic material, for example, aluminum oxide particles or silicon oxide particles may be used. As the fluorine material, for example, PVDF or polytetrafluoroethylene may be used. As the polyamide material, for example, nylon or aramid (meta-aramid or para-aramid) may be used.

[0172] Coating with ceramic materials improves oxidation resistance, suppressing the deterioration of the separator during high-voltage charging and improving the reliability of the secondary battery. Coating with fluorine-based materials also improves adhesion between the separator and electrodes, improving output characteristics. Coating with polyamide-based materials, especially aramid, improves heat resistance, improving the safety of the secondary battery.

[0173] For example, both sides of a polypropylene film may be coated with a mixture of aluminum oxide and aramid.Alternatively, the surface of the polypropylene film that contacts the positive electrode may be coated with a mixture of aluminum oxide and aramid, and the surface that contacts the negative electrode may be coated with a fluorine-based material.

[0174] By using a separator with a multi-layer structure, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, and therefore the discharge capacity per volume of the secondary battery can be increased.

[0175] <Exterior body> The exterior body of the battery can be made of a metal material such as aluminum, stainless steel, or titanium, or a resin material. A film-shaped exterior body can also be used. As the film, a three-layer structure film can be used in which one side of a metal thin film or metal foil having excellent flexibility such as aluminum, stainless steel, titanium, copper, or nickel has a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and the other side has an insulating synthetic resin film such as a polyamide resin or polyester resin. Such a multilayer structure film can be called a laminate film. In this case, the laminate film may be called an aluminum (aluminum) laminate film, a stainless steel laminate film, a titanium laminate film, a copper laminate film, a nickel laminate film, or the like, using the material name of the metal layer of the laminate film.

[0176] <Laminated secondary battery and its manufacturing method> An example of an external view of a laminated secondary battery 500 is shown in Fig. 6 and Fig. 7. Fig. 6 and Fig. 7 have a positive electrode 503, a negative electrode 506, a separator 507, an exterior body 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511. If the laminated secondary battery has a flexible structure and is mounted in an electronic device having at least a part having flexibility, the secondary battery can also be bent in accordance with the deformation of the electronic device. An example of a method for manufacturing the laminated secondary battery will be described with reference to Figs. 7(A) to 7(C).

[0177] First, the negative electrode 506, the separator 507, and the positive electrode 503 are laminated. FIG. 7(B) shows the laminated negative electrode 506, the separator 507, and the positive electrode 503. Here, an example is shown in which five pairs of negative electrodes and four pairs of positive electrodes are used. Next, the tab regions of the positive electrodes 503 are bonded to each other, and the positive electrode lead electrode 510 is bonded to the tab region of the outermost positive electrode. For example, ultrasonic welding or the like may be used for the bonding. Similarly, the tab regions of the negative electrodes 506 are bonded to each other, and the negative electrode lead electrode 511 is bonded to the tab region of the outermost negative electrode. FIG. 1(A) shows a battery configuration in which the negative electrode, the positive electrode, and the separator are each one sheet, but as shown in FIG. 7(B), multiple negative electrodes, positive electrodes, and separators can be used.

[0178] Next, the negative electrode 506 , the separator 507 and the positive electrode 503 are placed on the exterior body 509 .

[0179] Next, as shown in Fig. 7(C), exterior body 509 is folded at the portion indicated by the dashed line. After that, the outer periphery of exterior body 509 is joined. For the joining, for example, thermocompression bonding or the like may be used. At this time, a region (hereinafter referred to as an inlet) that is not joined is provided in a part (or one side) of exterior body 509 so that an electrolyte can be introduced later.

[0180] Next, an electrolyte (not shown) is introduced into the inside of the exterior body 509 through an inlet provided in the exterior body 509. The introduction of the electrolyte is preferably performed under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is joined. In this manner, the laminate type secondary battery 500 can be produced.

[0181] By using the positive electrode active material described in the above embodiment for the positive electrode 503, the secondary battery 500 can have a high discharge capacity and excellent cycle characteristics.

[0182] This embodiment mode can be used in appropriate combination with other embodiment modes.

[0183] (Embodiment 2) In this embodiment, an example in which a secondary battery which is one embodiment of the present invention is mounted on an electronic device will be described with reference to FIGS.

[0184] 8A to 8G show examples of electronic devices to which the secondary battery having the positive electrode active material described in the above embodiment is mounted. Examples of electronic devices to which the secondary battery is applied include television devices (also called televisions or television receivers), monitors for computers, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game machines, personal digital assistants, audio playback devices, and large game machines such as pachinko machines.

[0185] Furthermore, a secondary battery having a flexible shape can be incorporated along the curved surfaces of the inner or outer walls of a house or building, or the interior or exterior of an automobile.

[0186] 8A 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.

[0187] FIG. 8(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. FIG. 8(C) shows the bent state of the 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 a lead electrode electrically connected to a current collector.

[0188] FIG. 8D shows an example of a bangle-type display device. The portable display device 7100 includes a housing 7101, a display unit 7102, an operation button 7103, and a secondary battery 7104. FIG. 8E shows a bent state of the secondary battery 7104. When the secondary battery 7104 is worn on a user's arm in a bent state, the housing is deformed, and the curvature of the secondary battery 7104 changes in part or in whole. Note that the degree of bending at any point of the curve expressed by the value of 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, the housing or the main surface of the secondary battery 7104 changes in part or in whole when the radius of curvature is in the range of 40 mm to 150 mm. High reliability can be maintained if the radius of curvature of the main surface of the secondary battery 7104 is in the range of 40 mm to 150 mm. By using the secondary battery of one embodiment of the present invention as the secondary battery 7104, a lightweight portable display device with a long life can be provided.

[0189] 8F shows an example of a wristwatch-type portable information terminal. A 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.

[0190] The portable information terminal 7200 can execute various applications such as mobile telephone, e-mail, document browsing and creation, music playback, Internet communication, and computer games.

[0191] The display surface of the display portion 7202 is curved, and 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, a stylus, or the like. For example, an application can be started by touching an icon 7207 displayed on the display portion 7202.

[0192] The operation button 7205 can have various functions, such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / cancellation, power saving mode activation / cancellation, etc. For example, the function of the operation button 7205 can be freely set by an operating system built into the mobile information terminal 7200.

[0193] The mobile information terminal 7200 can also perform short-distance wireless communication according to a communication standard. For example, the mobile information terminal 7200 can communicate with a wireless headset to enable hands-free calling.

[0194] 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 by wireless power supply without using the input / output terminal 7206.

[0195] A display portion 7202 of a 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 portable information terminal that is lightweight and has a long life can be provided. For example, the secondary battery 7104 shown in FIG. 8E can be incorporated in a curved state inside a housing 7201 or in a bendable state inside a band 7203.

[0196] The portable information terminal 7200 preferably has a sensor. For example, it is preferable that a fingerprint sensor, a pulse sensor, a human body sensor such as a body temperature sensor, a touch sensor, a pressure sensor, an acceleration sensor, or the like is mounted as the sensor.

[0197] 8G illustrates an example of an armband-type display device. The display device 7300 includes a display portion 7304 and a secondary battery of one embodiment of the present invention. The display device 7300 can also include a touch sensor in the display portion 7304 and can function as a portable information terminal.

[0198] The display surface of the display portion 7304 is curved, and display can be performed along the curved display surface. In addition, the display device 7300 can change the display state by short-range wireless communication according to a communication standard.

[0199] The display device 7300 also includes an input / output terminal, and can directly exchange data with other information terminals via a connector. Charging can also be performed via the input / output terminal. Note that charging may be performed by wireless power supply without using the input / output terminal.

[0200] By using the secondary battery of one embodiment of the present invention as a secondary battery included in the display device 7300, a lightweight display device with a long lifetime can be provided.

[0201] Further, an example in which the secondary battery having good cycle characteristics described in the above embodiment is mounted on an electronic device will be described with reference to FIGS.

[0202] By using the 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 the secondary battery of these products, a stick-shaped secondary battery that is small, lightweight, and has a large discharge capacity is desired in consideration of ease of holding by users.

[0203] FIG. 8(H) is a perspective view of a device also called a tobacco-receiving smoking device (electronic cigarette). In FIG. 8(H), the electronic cigarette 7500 is composed of an atomizer 7501 including a heating element, a secondary battery 7504 that supplies power to the atomizer, and a cartridge 7502 including a liquid supply bottle, a sensor, and the like. To enhance safety, a protection circuit that prevents overcharging and / or overdischarging of the secondary battery 7504 may be electrically connected to the secondary battery 7504. The secondary battery 7504 shown in FIG. 8(H) has an external terminal so that it can be connected to a charging device. Since the secondary battery 7504 is the tip part when held, it is desirable that the total length is short and the weight is light. Since the secondary battery of one embodiment of the present invention has a high discharge capacity and good cycle characteristics, a small and lightweight electronic cigarette 7500 that can be used for a long period of time can be provided.

[0204] Fig. 9(A) shows an example of a wearable device. Wearable devices use secondary batteries as a power source. In addition, when a user uses the device in daily life or outdoors, there is a demand for wearable devices that can be charged wirelessly as well as by wires with exposed connectors in order to improve splash-proof, water-resistant, or dust-proof performance.

[0205] For example, the secondary battery according to one embodiment of the present invention can be mounted on a glasses-type device 4000 as shown in FIG. 9A. The glasses-type device 4000 includes a frame 4000a and a display unit 4000b. By mounting a secondary battery on the temples of the curved frame 4000a, the glasses-type device 4000 can be lightweight, well-balanced in weight, and has a long continuous use time. By including the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving associated with a smaller housing can be realized.

[0206] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on the headset type device 4001. The headset type device 4001 has 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 associated with a miniaturized housing can be realized.

[0207] 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 configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0208] 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 configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0209] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on the belt type device 4006. The belt type device 4006 has a belt portion 4006a and a wireless power receiving portion 4006b, and a secondary battery can be mounted inside the belt portion 4006a. By providing the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving associated with miniaturization of the housing can be realized.

[0210] Furthermore, the secondary battery according to 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 according to one embodiment of the present invention, a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0211] The display unit 4005a can display not only the time, but also various other information such as incoming e-mails and phone calls.

[0212] In addition, since the wristwatch type device 4005 is a wearable device that is directly wrapped around the arm, it may be equipped with sensors that measure the user's pulse, blood pressure, etc. Data on the user's amount of exercise and health can be accumulated to manage the user's health.

[0213] FIG. 9(B) shows a perspective view of the wristwatch type device 4005 removed from the wrist.

[0214] 9C is a side view. FIG 9C shows a state in which a secondary battery 913 is built in. The secondary battery 913 is the secondary battery described in Embodiment 2. The secondary battery 913 is provided at a position overlapping with the display portion 4005a, and is small and lightweight.

[0215] 9D shows an example of a wireless earphone. Here, the wireless earphone is illustrated having a pair of main bodies 4100a and 4100b, but the pair is not necessarily required.

[0216] The main bodies 4100a and 4100b each have a driver unit 4101, an antenna 4102, and a secondary battery 4103. They may also have a display unit 4104. They also preferably have a substrate on which a circuit such as a wireless IC is mounted, a charging terminal, and the like. They may also have a microphone.

[0217] The case 4110 has a secondary battery 4111. It is preferable that the case 4110 also has a board on which circuits such as a wireless IC and a charge control IC are mounted, and a charging terminal. It may also have a display unit, buttons, and the like.

[0218] The main units 4100a and 4100b can wirelessly communicate with other electronic devices such as smartphones. This allows the main units 4100a and 4100b to play back audio data sent from other electronic devices. If the main units 4100a and 4100b have a microphone, the audio captured by the microphone can be sent to the other electronic device, and the audio data processed by the electronic device can be sent back to the main units 4100a and 4100b for playback. This allows the main units 4100a and 4100b to be used as a translator, for example.

[0219] In addition, a secondary battery 4103 included in a main body 4100a can be charged from a secondary battery 4111 included in a case 4110. As the secondary battery 4111 and the secondary battery 4103, a coin-type secondary battery, a cylindrical secondary battery, or the like described in the above embodiments can be used.

[0220] 10A shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 arranged on the top surface of a housing 6301, a plurality of cameras 6303 arranged on the side surface, 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.

[0221] For example, the cleaning robot 6300 can analyze an image captured by the camera 6303 and determine the presence or absence of an obstacle such as a wall, furniture, or a step. When an object that may become entangled in the brush 6304, such as a wire, is detected by image analysis, the rotation of the brush 6304 can be stopped. 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 an electronic device with long operating time and high reliability.

[0222] Fig. 10B shows an example of a robot. The robot 6400 shown in Fig. 10B 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 computing device, and the like.

[0223] The microphone 6402 has a function of detecting the user's 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.

[0224] 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 removable information terminal, and by installing it in a fixed position on the robot 6400, charging and data transfer are possible.

[0225] The upper camera 6403 and the lower camera 6406 have a function of capturing images of the surroundings of the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of an obstacle in the moving direction when the robot 6400 moves forward using the moving 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.

[0226] 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.

[0227] Fig. 10C shows an example of an aircraft. An aircraft 6500 shown in Fig. 10C includes a propeller 6501, a camera 6502, a secondary battery 6503, and the like, and has a function of flying autonomously.

[0228] 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. The electronic component 6504 can estimate the remaining battery charge from a change in the power storage capacity of the secondary battery 6503. The flying object 6500 includes therein the secondary battery 6503 according to one embodiment of the present invention. 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.

[0229] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0230] (Embodiment 3) In this embodiment, an example is described in which a secondary battery including the positive electrode active material of one embodiment of the present invention is mounted on a vehicle.

[0231] 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.

[0232] FIG. 11 illustrates an example of a vehicle using a secondary battery according to one embodiment of the present invention. An automobile 8400 illustrated in FIG. 11A is an electric automobile using an electric motor as a power source for running. Alternatively, it is a hybrid automobile that can use an electric motor and an engine as a power source for running. By using one embodiment of the present invention, a vehicle with a long cruising distance can be realized. In addition, the automobile 8400 has a secondary battery. For example, secondary battery modules can be arranged on the floor of the vehicle. The secondary battery can not only drive the electric motor 8406 but also supply power to light-emitting devices such as a headlight 8401 and a room light (not shown).

[0233] 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.

[0234] The automobile 8500 shown in FIG. 11(B) can charge the secondary battery of the automobile 8500 by receiving power supply from an external charging facility by a plug-in method and / or a non-contact power supply method. FIG. 11(B) shows a state in which a secondary battery 8024 mounted on the automobile 8500 is being charged from a ground-mounted charging device 8021 via a cable 8022. When charging, the charging method and connector standards may be appropriately performed by a predetermined method such as CHAdeMO (registered trademark) or combo. The charging device 8021 may be a charging station installed in a commercial facility or a home power source. For example, the secondary battery 8024 mounted on the automobile 8500 can be charged by an external power supply using plug-in technology. Charging can be performed by converting AC power to DC power via a conversion device such as an ACDC converter.

[0235] Although not shown, a power receiving device may be mounted on a vehicle, and charging may be performed by supplying power contactlessly from a ground power transmitting device. In the case of this contactless power supply method, by incorporating a power transmitting device in the road and / or an exterior wall, charging may be performed not only while the vehicle is stopped but also while it is moving. This contactless power supply method may also be used to transmit and receive power between vehicles. Furthermore, a solar cell may be provided on the exterior of the vehicle, and a secondary battery may 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 may be used.

[0236] 11C is an example of a two-wheeled vehicle using the secondary battery of one embodiment of the present invention. A scooter 8600 shown in FIG. 11C 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.

[0237] 11(C) is capable of storing a secondary battery 8602 in the under-seat storage 8604. Even if the under-seat storage 8604 is small, the secondary battery 8602 can be stored in the under-seat storage 8604. The secondary battery 8602 is removable, and when charging, the secondary battery 8602 can be carried indoors, charged, and stored before riding.

[0238] 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 small and lightweight. If the secondary battery itself can be made small and lightweight, it contributes to reducing the weight of the vehicle, and the cruising distance can be improved. In addition, the secondary battery mounted on the vehicle can be used as a power supply source other than the vehicle. In this case, for example, it is possible to avoid using a commercial power source during peak power demand. If it is possible to avoid using a commercial power source during peak power demand, it is possible to contribute to energy conservation and reduction of carbon dioxide emissions. In addition, 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, including cobalt, can be reduced.

[0239] This embodiment mode can be implemented in appropriate combination with other embodiment modes. [Explanation of symbols]

[0240] 10 Secondary battery 20 positive electrode 21 Positive electrode current collector 22 Cathode active material layer 23 Covering layer 24 Cathode active material 25 Binder 26 Conductive materials 30 negative electrode 31 Negative electrode current collector 32 Negative electrode active material layer 33 Covering layer 34 Negative electrode active material 35 Binder 36 Conductive materials 37 Base layer 38 Catalyst layer 39 Interface layer 40 Separator 45 Electrolytes 50 Exterior body

Claims

1. A secondary battery having a negative electrode and a separator, The negative electrode comprises a negative electrode active material and a coating layer covering at least a portion of the negative electrode active material. The coating layer has a region that is in contact with the separator, The coating layer has metallic titanium, The aforementioned titanium metal has a function that allows lithium to pass through the grain boundaries of the crystal. The negative electrode active material is silicon, in a secondary battery.

2. In the secondary battery according to Claim 1, A secondary battery in which the thickness of the coating layer is 1 nm or more and 50 nm or less.

Images