lithium-ion secondary batteries

Abstract

One embodiment of the present invention provides a lithium-ion secondary battery having no active material provided on the negative electrode. One embodiment of the present invention includes: a positive electrode; a negative electrode; an electrolyte; and a separator between the positive electrode and the negative electrode, wherein the negative electrode includes a negative electrode current collector, the negative electrode current collector includes a region in direct contact with at least one of the electrolyte and the separator, the electrolyte contains fluorine, and has the function of causing precipitates containing lithium to precipitate on the surface of the negative electrode current collector during charging. Furthermore, a spacer may be included between the separator and the negative electrode. The electrolyte may also include an organic compound containing fluorine. By supplying fluorine from the electrolyte to the lithium precipitated on the surface of the negative electrode, the precipitation of lithium in the form of dendrites (whiskers) in subsequent precipitation can be suppressed.

Description

[0001] This application is a divisional application of the following invention patent application:

[0002] Invention name: Lithium-ion secondary battery; Application date: March 12, 2015; Application number: 201580016096.3. Technical Field

[0003] One embodiment of the present invention relates to a lithium ion secondary battery and a method for manufacturing the same.

[0004] Note that one embodiment of the present invention is not limited to the above-mentioned technical field. The technical field of one embodiment of the invention disclosed in this specification and the like relates to an object, method, or manufacturing method. Alternatively, one embodiment of the present invention relates to a process, machine, product, or composition of matter. Therefore, specifically, as examples of the technical field of one embodiment of the present invention disclosed in this specification, semiconductor devices, display devices, light-emitting devices, power storage devices, storage devices, driving methods of these devices, or manufacturing methods of these devices can be cited. Background Art

[0005] Examples of the secondary battery include nickel-hydrogen batteries, lead secondary batteries, and lithium-ion secondary batteries.

[0006] These secondary batteries are used as power sources for portable information terminals such as mobile phones, etc. Among them, lithium-ion secondary batteries are particularly popular because they can achieve high capacity and miniaturization, and therefore their development is becoming increasingly intense.

[0007] Lithium-ion secondary batteries consist of multiple components, including electrode collectors, active material, electrolyte, separators, and lead electrodes in the outer packaging. Manufacturing is a multi-step process. Given their wide range of applications, low-cost manufacturing is crucial. The fewer components, manufacturing steps, and time required, the lower the cost.

[0008] Generally, the negative electrode of a lithium-ion secondary battery is manufactured by coating an active material composed of a carbon material onto a negative electrode current collector. The active material is a substance that acts as a carrier for the insertion and removal of ions (lithium ions). The active material layer, created by coating the current collector with the active material, may also contain a conductive additive, a binder, and other ingredients in addition to the active material.

[0009] Because of its low redox potential and high specific capacity per unit volume / weight, metallic lithium has preferred characteristics as a material suitable for the negative electrode. However, in secondary batteries, lithium in the electrolyte sometimes precipitates on lithium metal in the form of dendrites (whiskers) during charging and passes through the separator, causing a short circuit. In addition, the following problem also occurs: during discharge, the roots of the dendrites (whiskers) dissolve into the electrolyte to generate separated lithium, thereby reducing the cycle characteristics. Therefore, in practical lithium-ion secondary batteries, an active material composed of a carbon material is coated on the collector to provide an active material layer, and the absorption and release reaction of lithium ions is used as the negative electrode reaction (non-patent document 1).

[0010] However, when manufacturing the active material layer, a variety of equipment is required as an apparatus, such as a kneading device for manufacturing the slurry, a coating machine for applying the slurry, a dryer for drying the slurry, etc. In addition, each process using such an apparatus takes time. Furthermore, components such as active materials, conductive additives, and adhesives require costs. In addition, in an electrode using an active material layer, the cell potential is reduced by a potential equivalent to the reaction potential of the active material in the secondary battery, so the energy density is reduced. On the other hand, if it is possible to adopt a method of directly depositing lithium onto the current collector, the potential of the negative electrode will be the lowest among all systems inside the secondary battery, thereby making it possible to manufacture a secondary battery with the highest energy density.

[0011] [Patent Document]

[0012] [Patent Document 1] Japanese Patent Application Publication No. 4-328277

[0013] [Patent Document 2] Japanese Patent Application Publication No. 2007-106634

[0014] [Non-patent literature]

[0015] [Non-Patent Document 1] Zenpachi Kokumi, “Lithium Secondary Batteries,” 1st edition, Ohmsha Co., Ltd., March 20, 2008, pp. 104 Summary of the Invention

[0016] One of the purposes of one embodiment of the present invention is to manufacture a negative electrode without using an active material composed of a carbon-based material. One of the purposes of one embodiment of the present invention is to provide a lithium-ion secondary battery without incurring time and money costs associated with the formation of a negative electrode active material layer. One of the purposes of one embodiment of the present invention is to reduce the dendritic (whisker-like) lithium that is formed by precipitating onto the surface of metallic lithium in the negative electrode during charging. One of the purposes of one embodiment of the present invention is to provide a lithium-ion secondary battery with good cycle characteristics. One of the purposes of one embodiment of the present invention is to provide a secondary battery with a large capacity per unit mass and volume. One of the purposes of one embodiment of the present invention is to provide a novel secondary battery, a novel power storage device, a novel method for manufacturing a secondary battery, or a novel method for manufacturing a power storage device.

[0017] Note that the inclusion of these objectives does not preclude the existence of other objectives. Furthermore, one embodiment of the present invention does not necessarily achieve all of the aforementioned objectives. Furthermore, objectives other than the aforementioned may be readily apparent from, and may be inferred from, the description, drawings, claims, and the like.

[0018] One embodiment of the present invention is a lithium-ion secondary battery comprising: a positive electrode; a negative electrode; an electrolyte; and a separator between the positive electrode and the negative electrode, wherein the negative electrode includes a negative electrode collector, the negative electrode collector includes a region in direct contact with at least one of the electrolyte and the separator, the electrolyte contains fluorine, and is capable of causing a precipitate containing lithium to precipitate onto the surface of the negative electrode collector during charging.

[0019] Another embodiment of the present invention is a lithium-ion secondary battery comprising: a positive electrode; a negative electrode; an electrolyte; a separator between the positive electrode and the negative electrode; and a spacer between the separator and the negative electrode, wherein the negative electrode comprises a negative electrode collector, the negative electrode collector is in direct contact with the spacer, the electrolyte contains fluorine, and is capable of causing precipitates containing lithium to precipitate into the region between the separator and the negative electrode collector.

[0020] Another embodiment of the present invention is a lithium-ion secondary battery, comprising: a positive electrode; a negative electrode; an electrolyte; a separator between the positive electrode and the negative electrode; and a thin sheet-like spacer between the separator and the negative electrode, wherein the porosity of the thin sheet-like spacer is higher than that of the separator, the negative electrode includes a negative electrode collector, the negative electrode collector is in direct contact with the spacer, the electrolyte contains fluorine, and can cause precipitates containing lithium to precipitate into the area between the separator and the negative electrode collector.

[0021] Another embodiment of the present invention is a lithium-ion secondary battery comprising: a positive electrode; a negative electrode; an electrolyte; a separator between the positive electrode and the negative electrode; and a spacer between the separator and the negative electrode, wherein the negative electrode comprises a negative electrode collector, the negative electrode collector is in direct contact with the spacer, the electrolyte contains fluorine, the positive electrode, the negative electrode, the separator and the spacer are flexible, and can allow precipitates containing lithium to precipitate into the area between the separator and the negative electrode collector.

[0022] In one embodiment of the present invention, the organic compound or inorganic base in the electrolyte may contain fluorine, and the organic compound or inorganic base accounts for more than 2wt% of the weight of the electrolyte. In one embodiment of the present invention, the organic compound may be fluoroethylene carbonate. In one embodiment of the present invention, the inorganic base may be lithium tetrafluoroborate or lithium hexafluorophosphate. In one embodiment of the present invention, the negative electrode may not include an active material layer. In one embodiment of the present invention, the negative electrode collector may have copper. In one embodiment of the present invention, the precipitate having lithium may be lithium fluoride.

[0023] For example, when lithium is directly deposited onto a negative electrode current collector formed of copper without using an active material layer composed of a carbon material, it is ideal to form a film of lithium on the current collector, and to grow the film of lithium as the battery is charged. However, when lithium is deposited onto the negative electrode current collector, dendritic (whisker-like) lithium is produced, which becomes a problem. Therefore, the conditions for preventing whiskers from forming during charging were studied, and it was found that fluorine on the surface of the current collector inhibits the formation of whiskers.

[0024] In other words, it has been confirmed that when an alkali containing fluorine in addition to lithium, such as lithium tetrafluoroborate or lithium hexafluorophosphate, is used as an alkali containing lithium in the electrolyte of a secondary battery, the formation of dendritic (whisker-like) lithium on the surface of the negative electrode collector can be suppressed. In addition, the cycle characteristics of the secondary battery are improved, and the battery capacity per unit weight and volume is also increased.

[0025] Furthermore, it has been confirmed that adding a fluorine-containing organic compound, such as fluoroethylene carbonate, to the electrolyte as an additive further improves cycle characteristics and further increases the battery capacity per unit weight and volume. Furthermore, even if a fluorine-containing base is not used as the electrolyte, the presence of a fluorine-containing organic compound as an additive in the electrolyte supplies fluorine to the negative electrode surface, thereby improving cycle characteristics.

[0026] In addition, when a spacer is included between the separator and the negative electrode current collector, an area where lithium can be precipitated can be ensured between the separator and the negative electrode current collector. Although lithium can be precipitated onto the surface of the negative electrode current collector even without a spacer, the area where lithium can be precipitated can be further increased by providing a spacer. In addition, in order to ensure that this area is larger, the volume occupied by the spacer is preferably small. For example, when a spacer is formed into a thin sheet, the porosity is preferably high. By adopting a spacer with a high porosity, the weight of the lithium-ion secondary battery can be further reduced.

[0027] On the other hand, because the spacer does not need to support the structure of the lithium-ion secondary battery, a flexible spacer can be used instead of a spacer with a fixed shape. It is also possible to apply a flexible spacer to a flexible lithium-ion secondary battery, so that the spacer can also deform according to the deformation of the lithium-ion secondary battery.

[0028] Since the negative electrode is used for the lithium ion secondary battery without providing an active material layer, the secondary battery can be manufactured while suppressing the equipment cost, time cost, and money cost required for the step of forming the active material layer.

[0029] According to one embodiment of the present invention, a negative electrode can be manufactured without using an active material composed of a carbon-based material. According to one embodiment of the present invention, a lithium-ion secondary battery can be provided without incurring time and money costs associated with the formation of a negative electrode active material layer. According to one embodiment of the present invention, dendritic (whisker-like) lithium formed on the surface of metallic lithium in the negative electrode during charging can be reduced. According to one embodiment of the present invention, a lithium-ion secondary battery with good cycle characteristics can be provided. According to one embodiment of the present invention, a secondary battery with a large capacity per unit mass and volume can be provided. According to one embodiment of the present invention, a novel secondary battery, a novel power storage device, a novel method for manufacturing a secondary battery, or a novel method for manufacturing a power storage device can be provided.

[0030] Note that the description of these effects does not preclude the existence of other effects. Furthermore, one embodiment of the present invention does not necessarily have all of the effects described above. Furthermore, effects other than the above may be readily apparent from, and can be extracted from, the description of the specification, drawings, claims, and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A and Figure 1 B is a diagram showing a secondary battery according to one embodiment of the present invention;

[0032] Figure 2 : is a graph showing the results of XPS analysis of the negative electrode surface of a secondary battery according to one embodiment of the present invention;

[0033] Figure 3 A and Figure 3 B is a diagram showing a SEM observation image of the negative electrode surface of the secondary battery according to one embodiment of the present invention;

[0034] Figure 4 is a graph showing charge and discharge curves of a secondary battery according to one embodiment of the present invention;

[0035] Figure 5 is a graph showing charge and discharge curves of a secondary battery according to one embodiment of the present invention;

[0036] Figure 6 is a graph showing cycle characteristics of a secondary battery according to one embodiment of the present invention;

[0037] Figure 7 A to Figure 7 D is a graph illustrating the radius of curvature;

[0038] Figure 8 A to Figure 8 C is a diagram illustrating the radius of curvature;

[0039] Figure 9 A to Figure 9 D is a diagram showing an electronic device including a secondary battery according to one embodiment of the present invention;

[0040] Figure 10 A to Figure 10 C is a diagram showing an electronic device including a secondary battery according to one embodiment of the present invention;

[0041] Figure 11 is a side view of an electronic device including a secondary battery according to one embodiment of the present invention;

[0042] Figure 12 A and Figure 12 B is a diagram showing an SEM observation image of the negative electrode surface of the secondary battery;

[0043] Figure 13 1 is a diagram illustrating a secondary battery according to one embodiment of the present invention. DETAILED DESCRIPTION

[0044] The following describes embodiments of the present invention in detail with reference to the accompanying drawings. However, the present invention is not limited to the following description. Those skilled in the art will readily appreciate that the embodiments and details of the present invention can be modified in various forms. Furthermore, the present invention should not be construed as being limited solely to the embodiments described below.

[0045] In addition, in the drawings described in this specification, the dimensions of the positive electrode, negative electrode, active material layer, separator, outer packaging, and other components, such as size and thickness, are sometimes exaggerated for clarity. Therefore, the dimensions of each component are not limited to their own size, nor are the relative sizes of the components limited to each other.

[0046] Note that in this specification, etc., ordinal numbers such as first, second, and third are used for convenience and do not indicate the order of steps or upper and lower positional relationships. In addition, in this specification, etc., these ordinal numbers do not indicate proper names for designating the matters of the invention.

[0047] In the configuration of one embodiment of the present invention described in this specification, the same reference numerals are used in common across different drawings to denote the same components or components having the same function, and their repeated descriptions are omitted. Furthermore, components having the same function may be represented by the same hatching without being specifically labeled.

[0048] Furthermore, the contents described in the embodiments for implementing the present invention can be combined as appropriate.

[0049] Implementation Method 1

[0050] Next, use Figure 1 A and Figure 1 B describes a method for manufacturing the lithium-ion secondary battery 110 according to one embodiment of the present invention. Figure 1 B is a cross-sectional view of the lithium-ion secondary battery 110 . Figure 1 B is a schematic cross-sectional view of a stacked structure of a positive electrode current collector 101a, a positive electrode active material layer 101b, a separator 104, and a negative electrode current collector 102, which are then sealed together with an electrolyte 105 using an outer packaging body 106. Note that a stacked structure can also be used as a secondary battery. The positive electrode 101 includes the positive electrode collector 101a and the positive electrode active material layer 101b, while the negative electrode does not include a negative electrode active material layer. Therefore, the negative electrode collector 102 is the main component of the negative electrode. The negative electrode collector 102 sometimes directly contacts the separator 104. In this case, the negative electrode collector 102 directly contacts the electrolyte 105 present in the pores of the separator 104. On the other hand, when the separator 104 is not in contact with the negative electrode collector 102, the electrolyte 105 contacts the negative electrode collector 102 over the entire area of ​​at least one surface of the negative electrode collector 102.

[0051] The negative electrode does not include an active material layer, and the negative electrode current collector 102 is a main component of the negative electrode.

[0052] The negative electrode current collector 102 can be made of a metal such as stainless steel, gold, platinum, zinc, iron, copper, aluminum, titanium, or tantalum, or alloys thereof that have high conductivity and do not alloy with carrier ions such as lithium. Furthermore, an aluminum alloy to which heat-resistant elements such as silicon, titanium, neodymium, scandium, or molybdenum are added can be used. Alternatively, the negative electrode current collector 102 can be made of a metal element that reacts with silicon to form a silicide. Examples of metal elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel.

[0053] Lithium metal is preferred due to its low redox potential and high specific capacity per unit volume / weight. However, its reactivity in the atmosphere poses safety concerns. Therefore, it is preferable not to use lithium metal as the negative electrode current collector. Even if lithium metal precipitates onto the current collector during secondary battery charging, this problem does not occur because the secondary battery is sealed.

[0054] The negative electrode current collector 102 includes at least an area that can be in direct contact with the electrolyte 105 or the separator, and this area is not covered by the active material layer. As a result, lithium is deposited in this area of ​​the negative electrode current collector 102 due to the reaction generated by charging. However, as charging progresses, the lithium in the electrolyte is deposited in the form of dendrites (whiskers) on this lithium. As charging progresses further, the dendritic (whisker-like) lithium grows and sometimes passes through the separator to cause a short circuit. In addition, the following problem also occurs: during discharge, the roots of the dendrites (whiskers) dissolve into the electrolyte to generate separated lithium. The capacity is reduced due to the lithium disappearing in the electrolyte without going through the battery reaction, thereby reducing the cycle characteristics.

[0055] This problem can also be avoided by providing an active material layer composed of, for example, a carbon material on the negative electrode current collector. However, when manufacturing the active material layer, a variety of equipment is required as an apparatus, such as a kneading device for making a slurry, a coating machine for applying the slurry, a dryer for drying the slurry, etc. In addition, each process using such an apparatus takes time. Furthermore, components such as active materials, conductive additives, and adhesives require costs. In a secondary battery according to one embodiment of the present invention, since the active material layer is not provided on the negative electrode current collector, a part of the manufacturing equipment of the secondary battery can be omitted, thereby reducing the manufacturing cost.

[0056] Furthermore, when using electrodes with active material layers, the cell potential in the secondary battery decreases by an amount equivalent to the reaction potential of the active material, thereby reducing energy density. On the other hand, because lithium is deposited directly onto the current collector in a secondary battery according to one embodiment of the present invention, the negative electrode has the lowest potential of all systems within the secondary battery, enabling the manufacture of a secondary battery with the highest energy density.

[0057] Through the above steps, the negative electrode of the lithium ion secondary battery can be manufactured.

[0058] The positive electrode 101 will be described.

[0059] The positive electrode 101 includes at least a positive electrode current collector 101 a and a positive electrode active material layer 101 b .

[0060] As the positive electrode active material, a material capable of intercalating and deintercalating carrier ions such as lithium ions can be used, and examples thereof include lithium-containing materials having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure.

[0061] Typical examples of lithium-containing materials with olivine structure (general formula LiMPO4 (M is Fe(II), Mn(II), Co(II) or Ni(II))) include LiFePO4, LiNiPO4, LiCoPO4, LiMnPO4, LiFe a Ni b PO4、LiFe a Co b PO4、LiFe a Mn b PO4、LiNi a Co b PO4、LiNi a Mn b PO4 (a+b is less than 1, 0<a<1, 0<b<1), LiFe c Ni d Co e PO4、LiFe c Ni d Mn e PO4、LiNi c Co d Mn e PO4 (c+d+e is less than 1, 0<c<1, 0<d<1, 0<e<1), LiFe f Ni g Co h Mn i PO4 (f+g+h+i is less than 1, 0<f<1, 0<g<1, 0<h<1, 0<i<1), etc.

[0062] In particular, lithium iron phosphate (LiFePO 4 ) is preferred because it uniformly satisfies the conditions required of a positive electrode active material, such as safety, stability, high capacity density, high generation potential, and the presence of lithium that can be extracted during initial oxidation (charging).

[0063] Examples of lithium-containing materials having a layered rock salt crystal structure include lithium cobalt oxide (LiCoO2); LiNiO2; LiMnO2; Li2MnO3; LiNi 0.8 Co 0.2 O2 and other NiCo types (general formula LiNi x Co 1-x O2(0<x<1));LiNi 0.5 Mn 0.5 O2 and other NiMn types (general formula LiNi x Mn 1-x O2(0<x<1)); and LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2 and other NiMnCo (also known as NMC. The general formula is LiNi x Mn y Co 1-x-y O2 (x>0, y>0, x+y<1)). In addition, Li(Ni 0.8 Co 0.15 Al 0.05 )O2, Li2MnO3-LiMO2 (M is Co, Ni, Mn), etc.

[0064] In particular, LiCoO 2 is preferred because of its advantages such as high capacity, stability in the atmosphere compared to LiNiO 2 , and thermal stability compared to LiNiO 2 .

[0065] Examples of lithium-containing materials having a spinel crystal structure include LiMn2O4, Li 1+x Mn 2-x O4、Li(MnAl)2O4、LiMn 1.5 Ni 0.5 O4, etc.

[0066] When a lithium-containing material compound containing manganese such as LiMn2O4 and having a spinel crystal structure is mixed with a small amount of lithium nickelate (LiNiO2 or LiNi 1-x MO2 (M = Co, Al, etc.) is preferred because it has advantages such as suppressing the dissolution of manganese and the decomposition of the electrolyte.

[0067] Alternatively, as the positive electrode active material, a material having the general formula Li (2-j) A composite oxide represented by MSiO4 (M is Fe(II), Mn(II), Co(II) or Ni(II), and j is 0 or more and 2 or less). (2-j) Typical examples of MSiO4 include Li (2-j) FeSiO4、Li (2-j) NiSiO4、Li(2-j) CoSiO4、Li (2-j) MnSiO4、Li (2-j) Fe k Ni l SiO4、Li (2-j) Fe k Co l SiO4、Li (2-j) Fe k Mn l SiO4、Li (2-j) Ni k Co l SiO4、Li (2-j) Ni k Mn l SiO4 (k+l is less than 1, 0<k<1, 0<l<1), Li (2-j) Fe m Ni n Co q SiO4、Li (2-j) Fe m Ni n Mn q SiO4、Li (2-j) Ni m Co n Mn q SiO4 (m+n+q is 1 or less, 0<m<1, 0<n<1, 0<q<1), Li (2-j) Fe r Ni s Co t Mn u SiO4 (r+s+t+u is less than 1, 0<r<1, 0<s<1, 0<t<1, 0<u<1), etc.

[0068] In addition, as the positive electrode active material, the following formula A can be used: x A sodium superion conductor (nasicon) type compound represented by M2(XO4)3 (A is Li, Na or Mg, M is Fe, Mn, Ti, V, Nb or Al, and X is S, P, Mo, W, As or Si). Examples of sodium superion conductor type compounds include Fe2(MnO4)3, Fe2(SO4)3, and Li3Fe2(PO4)3. In addition, as positive electrode active materials, the following can be used: compounds represented by the general formula Li2MPO4F, Li2MP2O7, and Li5MO4 (M is Fe or Mn); perovskite fluorides such as NaFeF3; metal chalcogenides (sulfides, selenides, and tellurides) such as TiS2 and MoS2; lithium-containing materials having an inverse spinel crystal structure such as LiMVO4; vanadium oxides (V2O5, V6O 13, LiV3O8, etc.); manganese oxides; and organic sulfur materials.

[0069] When the carrier ions are alkali metal ions, alkaline earth metal ions, beryllium ions or magnesium ions other than lithium ions, alkali metals (e.g., sodium, potassium, etc.), alkaline earth metals (e.g., calcium, strontium, barium, etc.), beryllium or magnesium may be used as the positive electrode active material instead of the lithium in the above compounds or oxides. For example, NaFeO2 or Na 2 / 3 [Fe 1 / 2 Mn 1 / 2 ]O2 and other sodium-containing layered oxides are used as positive electrode active materials.

[0070] As the positive electrode active material, a material formed by combining multiple of the above materials can also be used. For example, a solid solution formed by combining multiple of the above materials can be used as the positive electrode active material. For example, LiCo 1 / 3 Mn 1 / 3 Ni 1 / 3 The solid solution of O2 and Li2MnO3 serves as the positive electrode active material.

[0071] As the positive electrode active material, particles having an average primary particle diameter of 50 nm or more and 100 μm or less are preferably used.

[0072] As the conductive additive for the electrode, acetylene black (AB), graphite (graphite) particles, carbon nanotubes, graphene, fullerene, etc. can be used.

[0073] The conductive additive forms an electron conduction network within the electrode. The conductive additive maintains the conductive path between the positive electrode active materials. By adding the conductive additive to the positive electrode active material layer, a positive electrode active material layer 101b with high electron conductivity can be achieved.

[0074] In addition, as a binder, in addition to typical polyvinylidene fluoride (PVDF), polyimide, polytetrafluoroethylene, polyvinyl chloride, EPDM polymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluororubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, etc. can also be used.

[0075] The content of the binder in the total amount of the positive electrode active material layer 101b is preferably from 1 wt% to 10 wt%, more preferably from 2 wt% to 8 wt%, and even more preferably from 3 wt% to 5 wt%. The content of the conductive additive in the total amount of the positive electrode active material layer 101b is preferably from 1 wt% to 10 wt%, more preferably from 1 wt% to 5 wt%.

[0076] When forming the positive electrode active material layer 101b by coating, the positive electrode active material, binder, conductive additive, and dispersion medium are mixed to prepare an electrode slurry, which is then applied to the positive electrode current collector 101a and dried. In this embodiment, a metal material containing aluminum as its main component is used for the positive electrode current collector 101a.

[0077] As the positive electrode current collector 101a, materials having high conductivity and not alloying with carrier ions such as lithium, such as stainless steel, gold, platinum, aluminum, titanium, and alloys thereof, can be used. In addition, aluminum alloys to which elements such as silicon, titanium, neodymium, scandium, and molybdenum that improve heat resistance are added can also be used. In addition, metal elements that react with silicon to form silicides can also be used. Metal elements that react with silicon to form silicides include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The positive electrode current collector can be appropriately in the form of foil, plate (sheet), mesh, punched metal mesh, drawn metal mesh, and the like.

[0078] Through the above steps, the positive electrode of the lithium ion secondary battery can be manufactured.

[0079] The separator 104 will be described.

[0080] The separator 104 may be made of paper, nonwoven fabric, glass fiber, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic resin, polyolefin, or polyurethane. Note that the separator 104 must be made of a material that is insoluble in the electrolyte solution described below.

[0081] More specifically, as the material of the insulator 104, for example, one or a combination of two or more selected from fluorinated polymers, polyethers such as polyethylene oxide and polypropylene oxide, polyolefins such as polyethylene and polypropylene, polyacrylonitrile, polyvinylidene chloride, polymethyl methacrylate, polymethyl acrylate, polyvinyl alcohol, polymethacrylonitrile, polyvinyl acetate, polyvinyl pyrrolidone, polyethyleneimine, polybutadiene, polystyrene, polyisoprene, and polyurethane polymers and derivatives of the above substances; cellulose; paper; non-woven fabrics; and glass fibers.

[0082] Separator 104 must have insulating properties to prevent contact between the two electrodes, the ability to retain the electrolyte, and ion conductivity. Methods for manufacturing membranes used as separators include stretching methods. For example, there is the stretching pore method, in which a molten polymer material is spread and heat is dissipated, and the resulting membrane is stretched in biaxial directions parallel to the membrane to form pores.

[0083] Next, as a method for placing separator 104 in the secondary battery, a method of inserting the separator between the positive electrode and the negative electrode can be used. Alternatively, a method of placing separator 104 in one of the positive and negative electrodes and then combining it with the other can be used. The positive electrode, negative electrode, and separator can be housed in an outer packaging, and the outer packaging can be filled with an electrolyte to form a secondary battery.

[0084] Furthermore, by forming separator 104 into a thin sheet or strip large enough to cover both sides of the positive electrode or negative electrode, and forming the electrode wrapped in separator 104, the electrode can be protected from mechanical damage during secondary battery manufacturing, making electrode handling easier. The separator-wrapped electrode and another electrode can be housed in an outer package, which is then filled with an electrolyte to form a secondary battery.

[0085] Moreover, the separator 104 may also be a plurality of layers. The separator 104 can be formed using the above method, but the range of the size or thickness of the pores in the membrane is limited due to the mechanical strength of the constituent materials and the membrane. The first separator and the second separator can be manufactured using a stretching method, and these separators can be used in secondary batteries. As the material constituting the first separator and the second separator, one or more materials selected from the above materials or materials other than the above materials can be used. According to the formation conditions and stretching conditions of the membrane, the size of the pores in the membrane, the proportion of the volume occupied by the pores (also called porosity), the thickness of the membrane and other characteristics can be determined. By using the first separator and the second separator having different characteristics from each other, a variety of properties of the separator of the secondary battery can be selected compared to the case of using only one membrane.

[0086] Furthermore, the secondary battery can also be flexible. When a flexible secondary battery is subjected to deformation stress, the stress can be relieved by sliding between the first and second separators at the interface between the first and second separators. Therefore, the structure using two separators is suitable for the separator structure of a flexible secondary battery.

[0087] In a lithium-ion secondary battery in which the active material layer is not provided on the negative electrode, the active material layer is not included between the separator and the negative electrode collector. Therefore, sometimes the following electrolyte fills the space between the separator and the negative electrode collector, and at least a portion of the negative electrode collector is in direct contact with the separator. In addition, if there is no spacer for maintaining the distance between the separator and the negative electrode collector, at least a portion of the negative electrode collector is sometimes in direct contact with the separator. In this case, since the separator has an opening, the electrolyte present in the opening is in direct contact with the negative electrode collector without passing through the active material layer. In addition, when the negative electrode collector and the separator are intended to be separated from each other, a spacer may be provided between the negative electrode collector and the separator.

[0088] The spacer will be described.

[0089] In a lithium-ion secondary battery according to one embodiment of the present invention, a spacer may be provided between the negative electrode current collector and the separator. When a spacer is provided between the separator and the negative electrode current collector, an area where lithium can be deposited can be ensured between the separator and the negative electrode current collector. Although lithium can be deposited on the surface of the negative electrode current collector even without a spacer, the area where lithium can be deposited can be made larger by providing a spacer. In addition, although lithium can be deposited into the voids in the separator even without a spacer, the use of a spacer can prevent the lithium deposited in the separator from causing a short circuit between the positive and negative electrodes.

[0090] Figure 13 A cross-sectional view of a lithium ion secondary battery according to one embodiment of the present invention is shown, in which a spacer 108 is provided between a separator 104 and a negative electrode current collector 106 .

[0091] In addition, in order to ensure that this area is large, the volume of the spacer occupied by the space between the separator and the negative electrode collector is preferably small. For example, when a thin sheet-shaped spacer is used, its porosity is preferably high, and preferably higher than the porosity of the separator. By using a spacer with a high porosity, not only can the area where lithium can be precipitated be large, but the weight of the spacer can also be reduced, thereby preventing the weight of the lithium-ion secondary battery from increasing.

[0092] Furthermore, because the spacer does not need to support the structure of the lithium-ion secondary battery, it does not require a rigid, fixed-shape spacer; instead, a flexible spacer can be used. Furthermore, a flexible spacer can be used in a flexible lithium-ion secondary battery. Since the spacer deforms as the lithium-ion secondary battery deforms, the spacer does not damage the separator or the negative electrode current collector, and the spacer itself is not damaged. Note that a spacer with high rigidity is acceptable.

[0093] Furthermore, when a spacer is placed between the separator and the negative electrode current collector, the separator and the negative electrode current collector can partially contact each other, without completely separating them. Of course, the separator and the negative electrode current collector do not need to be in direct contact. Simply ensure that the area where lithium can precipitate is larger than when no spacer is included.

[0094] In addition to the aforementioned thin sheet shape, spacers can also be spherical or cylindrical. Thin sheet-shaped spacers can be sandwiched between the separator and the negative electrode current collector, while spherical or cylindrical spacers can be dispersed over the separator or negative electrode current collector. Furthermore, by forming a film on the separator or negative electrode current collector and patterning the film, spacers of a specific shape can be placed at specific locations.

[0095] As materials for the spacers, similar to those used for the separators, paper, nonwoven fabrics, glass fibers, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol-based fibers), polyester, acrylic resin, polyolefin, and polyurethane can be used. In addition, as a type of nylon (polyamide), aramid can be particularly used. Note that the material should be selected to be insoluble in the electrolyte solution described below.

[0096] The electrolyte solution 105 will be described.

[0097] In lithium-ion secondary batteries, the electrolyte refers to the liquid electrolyte that serves as a path for lithium ions, facilitating charge transfer between the positive and negative electrodes. Note that aqueous electrolytes cannot be used because they undergo electrolysis due to lithium. Therefore, organic solvents containing lithium-containing bases are used as electrolytes.

[0098] The electrolyte solution 105 that can be used in the lithium ion secondary battery is preferably a non-aqueous solution (solvent) containing an electrolyte (solute).

[0099] An aprotic organic solvent is preferably used as the solvent for the electrolyte 105. For example, one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chlorophenyl carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc. can be used in any combination and ratio.

[0100] Furthermore, when a gelled polymer material is used as the solvent for the electrolyte 105, safety, including leakage resistance, is improved. Furthermore, the lithium-ion secondary battery can be made thinner and lighter. Typical examples of gelled polymer materials include silicone glue, acrylic resin glue, acrylonitrile glue, polyethylene oxide, polypropylene oxide, and fluorine-based polymers.

[0101] Furthermore, by using one or more flame-retardant and low-evaporation ionic liquids (also known as room-temperature molten salts) as the solvent for the electrolyte 105, even if the internal temperature of the lithium-ion secondary battery rises due to an internal short circuit, overcharge, etc., the lithium-ion secondary battery can be prevented from rupturing or catching fire. This can improve the safety of the lithium-ion secondary battery.

[0102] In addition, as an electrolyte dissolved in the above-mentioned solvent, an inorganic base containing fluorine can be used in any combination and ratio, such as one or more lithium salts such as LiPF6, LiAsF6, LiBF4, LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2.

[0103] For example, when an electrolyte having lithium tetrafluoroborate (LiBF4) or lithium hexafluorophosphate (LiPF6) is used for a secondary battery using a negative electrode current collector including a region in which no active material is formed, it can be confirmed that lithium is precipitated onto the negative electrode current collector at the initial stage of charging, and then lithium and fluorine are bonded to form lithium fluoride. In addition, it can also be confirmed that the generation of dendrites (whiskers) of the precipitated lithium can be reduced. In addition, in a secondary battery in which no active material is provided at the negative electrode, the initial charge capacity when an inorganic base having fluorine is used for the electrolyte is larger than when an inorganic base having fluorine is not used for the electrolyte.

[0104] In this way, in a secondary battery without an active material layer at the negative electrode, the use of an inorganic base containing fluorine in the electrolyte can suppress the formation of dendritic (whisker-like) lithium on the negative electrode surface, suppressing the generation of lithium that does not contribute to the battery reaction, while maintaining the discharge capacity and thereby increasing the discharge capacity. Thus, in a secondary battery without an active material layer at the negative electrode, the use of an inorganic base containing fluorine in the electrolyte can achieve the novel and significant effects of the inorganic base containing fluorine.

[0105] By providing the electrolyte with fluorine, fluorine can be provided to the lithium deposited on the surface of the current collector. In addition, an organic compound containing fluorine can be added to the electrolyte as an additive, thereby inhibiting the formation of dendritic (whisker-like) lithium on the surface of the negative electrode, inhibiting the production of lithium that does not contribute to the battery reaction, and maintaining the discharge capacity, thereby increasing the discharge capacity.

[0106] An example of an additive added to the electrolyte is a fluorine-containing ethylene carbonate, such as fluoroethylene carbonate (4-fluoro-1,3-dioxolane-2-one: FEC). When this additive is added to the electrolyte, it has been confirmed that the cycle characteristics are improved depending on the amount added. Thus, in a secondary battery without an active material layer at the negative electrode, by adding a fluorine-containing organic compound to the electrolyte, a novel and significant effect can be achieved.

[0107] Note that although the carrier ions described above are lithium ions, carrier ions other than lithium ions may also be used. When the carrier ions are alkali metal ions, alkaline earth metal ions, beryllium ions, or magnesium ions other than lithium ions, alkali metals (e.g., sodium, potassium, etc.), alkaline earth metals (e.g., calcium, strontium, barium, etc.), beryllium, or magnesium may be used as electrolytes instead of the lithium in the lithium salts described above.

[0108] As the electrolyte for secondary batteries, it is preferred to use a highly purified electrolyte that contains a low content of granular dust or elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities"). Specifically, the mass ratio of impurities in the electrolyte is preferably set to 1% or less, more preferably 0.1% or less, and even more preferably 0.01% or less. In addition, additives such as vinylene carbonate may be added to the electrolyte.

[0109] Next, the outer packaging 106 will be described. For example, a three-layer film structure can be used as the outer packaging 106: a highly flexible metal film made of a material such as aluminum, stainless steel, copper, or nickel is placed on an inner surface made of polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide resin or polyester resin is placed on the outer surface of the outer packaging. This three-layer structure blocks the permeation of electrolyte and gas while ensuring insulation and electrolyte resistance. A sealed structure can be formed by folding the outer packaging inward and overlapping it, or by overlapping the two outer packagings with their inner surfaces facing each other and heating them, causing the material inside to dissolve and weld the two outer packagings together.

[0110] When the portion of the outer packaging body that is sealed by welding or other means is considered the sealed portion, when the outer packaging body is folded inward and overlapped, the sealed portion is formed in the portion other than the folded portion, for example, a first region of the outer packaging body that is welded and a second region that overlaps the first region. When two outer packaging bodies are overlapped, the sealed portion is formed along the entire periphery by methods such as heat welding.

[0111] By selecting flexible materials from the materials of the various components described in this embodiment, a flexible lithium-ion secondary battery can be manufactured. In recent years, research and development of deformable devices has intensified. Secondary batteries used in such devices are in demand for flexibility.

[0112] When a secondary battery having electrodes and an electrolyte solution 1805 sandwiched between two films as an outer package is bent, the curvature radius 1802 of the film 1801 on the side closer to the center of curvature 1800 of the secondary battery is smaller than the curvature radius 1804 of the film 1803 on the side farther from the center of curvature 1800 ( Figure 7A). When the secondary battery is bent to have an arc-shaped cross section, a compressive stress is applied to the surface of the film near the center of curvature 1800, and a tensile stress is applied to the surface of the film far from the center of curvature 1800 ( Figure 7 B).

[0113] When a flexible lithium-ion secondary battery is deformed, the outer packaging is subjected to significant stress. However, by forming a pattern of concave and convex portions on the outer packaging surface, even if compressive or tensile stress is applied due to deformation of the secondary battery, the effects of deformation can be suppressed. Therefore, the secondary battery can deform within a radius of curvature of 30 mm, preferably 10 mm, on the outer packaging near the center of curvature.

[0114] Reference Figure 8 A to Figure 8 C indicates the radius of curvature of the surface. Figure 8 In A, on a plane 1701 that cuts off the curved surface 1700 , a portion of a curve 1702 of the curved surface is approximated to an arc, the radius of the circle is taken as the radius of curvature 1703 , and the center of the circle is taken as the center of curvature 1704 . Figure 8 B shows a top view of the curved surface 1700 . Figure 8 C shows a cross-sectional view of curved surface 1700 cut along plane 1701. When a curved surface is cut along a plane, the radius of curvature of the curve of the curved surface varies depending on the plane used for cutting. The radius of curvature of the curve of the cross-sectional shape of the curved surface when the curved surface is cut along the plane with the smallest radius of curvature is defined as the radius of curvature of the surface.

[0115] In addition, the cross-sectional shape of the secondary battery is not limited to a simple arc shape, and a portion thereof may have an arc shape, for example, Figure 7 The shape shown in C, the wavy ( Figure 7 D), S-shaped, etc. When the curved surface of the secondary battery has a shape having multiple centers of curvature, the secondary battery can be deformed within the following range: in the curved surface with the smallest curvature radius among the curvature radii of each of the multiple centers of curvature, the curvature radius of one of the two outer packaging bodies closest to the center of curvature is 30 mm, preferably 10 mm.

[0116] Although this embodiment illustrates application to a lithium-ion secondary battery as an example, one embodiment of the present invention is not limited thereto. It can also be applied to various secondary batteries, such as lead secondary batteries, lithium-ion polymer secondary batteries, nickel-metal hydride secondary batteries, nickel-cadmium secondary batteries, nickel-iron secondary batteries, nickel-zinc secondary batteries, silver-zinc oxide secondary batteries, solid-state batteries, and air batteries. Furthermore, it can also be applied to various power storage devices, such as primary batteries, capacitors, and lithium-ion capacitors.

[0117] This embodiment mode can be implemented in combination with other embodiment modes and examples as appropriate.

[0118] Implementation Method 2

[0119] In this embodiment, the Figure 9 A to Figure 9 D. An example of an electronic device including the secondary battery described in the above embodiment will be described.

[0120] Examples of electronic devices to which the secondary battery is applicable include digital cameras, digital video cameras, digital photo frames, mobile phones (also referred to as mobile phones or mobile phone devices), portable game consoles, portable information terminals, and audio playback devices. Figure 9 A to Figure 9 D shows specific examples of these electronic devices.

[0121] Figure 9 A shows an example of a mobile phone. Mobile phone 800 includes a display portion 802 incorporated into a housing 801, operation buttons 803, a speaker 805, a microphone 806, and the like. Furthermore, a secondary battery 804, which is one embodiment of the present invention, is used within mobile phone 800 to reduce the weight of the mobile phone.

[0122] Figure 9 The mobile phone 800 shown in A can input data by touching the display portion 802 with a finger or the like. In addition, operations such as making a call or creating an e-mail can be performed by touching the display portion 802 with a finger or the like.

[0123] The display unit 802 has three main screen modes: a display mode that primarily displays images, an input mode that primarily inputs text and other data, and a display+input mode that combines both display and input modes.

[0124] For example, when making a phone call or composing an e-mail, the display unit 802 is set to a text input mode mainly for text input, and the text displayed on the screen can be input.

[0125] Furthermore, by providing a detection device having sensors for detecting inclination such as a gyro sensor and an acceleration sensor within the mobile phone 800, the orientation (portrait or landscape) of the mobile phone 800 can be determined, and the screen display of the display unit 802 can be automatically switched.

[0126] The screen mode is switched by touching the display portion 802 or operating the operation button 803 of the housing 801. Alternatively, the screen mode can be switched according to the type of image displayed on the display portion 802. For example, when the image signal displayed on the display portion is moving image data, the screen mode is switched to the display mode, and when the image signal displayed on the display portion is text data, the screen mode is switched to the input mode.

[0127] Furthermore, when it is detected by detecting a signal detected by the optical sensor of the display portion 802 in the input mode that there has been no touch operation input to the display portion 802 for a certain period of time, control may be performed to switch the screen mode from the input mode to the display mode.

[0128] The display unit 802 can also be used as an image sensor. For example, by touching the display unit 802 with a palm or finger, palm prints or fingerprints can be captured, enabling personal identification. Furthermore, by using a backlight or a sensor light source that emits near-infrared light in the display unit, finger veins or palm veins can be captured.

[0129] Figure 9 B shows a state where the mobile phone 800 is bent. When the mobile phone 800 is deformed by an external force and bent as a whole, the secondary battery 804 provided therein is also bent. Figure 9 C shows the state of the bent secondary battery 804 at this time. The secondary battery 804 is a laminated secondary battery.

[0130] Figure 9 D shows an example of an armband-type display device. Armband-type display device 7200 includes a housing 7201 and a display portion 7202. Although not shown, armband-type display device 7200 includes a flexible secondary battery, and the shape of the flexible secondary battery changes as the shape of armband-type display device 7200 changes.

[0131] In addition, the structure described in this embodiment mode can be used in combination with the structure described in other embodiment modes as appropriate.

[0132] Implementation 3

[0133] In this embodiment, an example of an electronic device equipped with the lithium ion secondary battery obtained in Embodiment 1 is described. Figure 10 A is a photograph of the appearance of an electronic device equipped with the lithium ion secondary battery obtained in Embodiment 1. Figure 10 B is a photo of the electronic device taken from the side. Figure 10 C is a photo of the electronic device taken from the back. Figure 11 It is a schematic diagram of the structure of the electronic device when viewed from the side.

[0134] Figure 10 A to Figure 10 C and Figure 11 The electronic device shown is a display device that can be worn on the wrist and can display images or information. Because the lithium-ion secondary battery is flexible, the electronic device can be shaped to fit the wrist. The electronic device has an excellent design and can be used as a decorative item.

[0135] Figure 10 A to Figure 10 C and Figure 11 The electronic device shown includes a support structure 1001, a secondary battery 1002, a control substrate 1004, a display module 1011, a protective member 1013, and a case 1012. Specifically, the secondary battery 1002 is disposed on the support structure 1001, the control substrate 1004 is disposed on the secondary battery 1002, the protective member 1013 is disposed on the control substrate 1004, and the display module 1011 and the case 1012 are disposed on the protective member 1013. In addition, the electronic device includes a wireless charging antenna 1005, which is capable of wireless charging according to the Qi standard. Furthermore, the electronic device has a communication device 1007 for wirelessly transmitting displayed data to an external device.

[0136] The secondary battery 1002 obtained in one embodiment of the present invention includes a thin and flexible film as an outer packaging body, so that the secondary battery 1002 can be attached to the support structure 1001 having a curved surface, and the secondary battery 1002 can be deformed along the curved surface portion of the support structure 1001 in an area with a large curvature radius.

[0137] like Figure 10 B and Figure 10 As shown in C, when a light-transmitting plastic substrate is used as the supporting structure 1001 of the electronic device, the secondary battery 1002 can be seen from the back side of the electronic device, and the embossed film surface of the secondary battery 1002 can be observed.

[0138] Furthermore, support structure 1001 is flexible. Therefore, support structure 1001 can be easily bent. Support structure 1001 can also be made of materials other than plastic. Support structure 1001 is shaped like a bracelet, a band-like structure that is bent. Furthermore, at least a portion of support structure 1001 is flexible, allowing support structure 1001 to be deformed and worn on the wrist.

[0139] Protective member 1013 protects the internal structures of the electronic device, particularly control substrate 1004, from unexpected external impacts. Protective member 1013 deforms as part of the electronic device, and therefore can be made of the same material as support structure 1001. Note that protective member 1013 can also be made of a different material than support structure 1001.

[0140] The cover 1012 is a light-shielding film with an adhesive applied to one surface. It surrounds the entire electronic device, integrating the various components, and has an opening in the display portion 1015. Because of its light-shielding properties, the cover 1012 can conceal the internal components, enhancing the design of the electronic device. Note that the electronic device can also be designed so that the internal components are visible from the outside, and in such a design, the cover 1012 does not need to have light-shielding properties. Furthermore, when the protective member 1013 has light-shielding properties, the cover 1012 does not need to have light-shielding properties.

[0141] The control substrate 1004 has a slit for bending and is also equipped with a Bluetooth (registered trademark, equivalent to IEEE802.15.1) standard communication device 1007, a microcontroller, a storage device, an FPGA, a D / A converter, a charging control IC, a level shifter, etc. In addition, the control substrate 1004 is connected to the display module 1011 having a display portion 1015 via an input / output connector 1014. In addition, the control substrate 1004 is connected to the antenna 1005 via a wiring 1008 and is connected to the secondary battery 1002 via a wiring 1003 and a connecting portion 1010. The power supply control circuit 1006 controls the charging and discharging of the secondary battery 1002.

[0142] The display module 1011 refers to a display panel to which at least the FPC 1009 is mounted. Figure 11 The electronic device shown preferably includes a display portion 1015 , an FPC 1009 , and a driver circuit, and further includes a converter for supplying power from a secondary battery 1002 .

[0143] In the display module 1011, the display portion 1015 is flexible and includes a display element on a flexible film. Furthermore, the secondary battery 1002 and the display portion are preferably arranged in a partially overlapping manner. By partially or fully overlapping the secondary battery 1002 and the display portion, the power path from the secondary battery 1002 to the display portion 1015 is shortened, that is, the wiring distance is shortened, thereby reducing power consumption. Furthermore, by placing the display module between the protective member 1013 and the case 1011, the display module 1011 can be protected from unexpected deformation, such as wrinkles and twisting, thereby extending the lifespan of the electronic device as a product.

[0144] As methods for manufacturing display elements on flexible films, there are the following methods: a method of directly manufacturing a display element on a flexible film; a method of forming a layer including a display element on a rigid substrate such as a glass substrate, removing the substrate by etching or polishing, and then bonding the layer including the display element to a flexible film; a method of providing a peeling layer on a rigid substrate such as a glass substrate, forming a layer including a display element thereon, then separating the rigid substrate from the layer including the display element by using the peeling layer, and bonding the layer including the display element to a flexible film; etc.

[0145] Furthermore, a touch panel may be provided in the display portion 1015 , and data input and operation of the electronic device can be performed using the touch panel.

[0146] In addition, the structure and the like described in this embodiment can be used in combination with the structure and the like described in other embodiment modes as appropriate.

[0147] In addition, the content described in a certain embodiment (or part thereof) can be applied to, combined with or replaced with other content described in that embodiment (or part thereof) and / or content described in one or more other embodiments (or part thereof).

[0148] Furthermore, the contents described in the embodiments refer to the contents explained using various drawings in each embodiment or the contents described using the texts described in the specification.

[0149] In addition, more drawings can be formed by combining a drawing described in a certain embodiment (or a part thereof) with other parts of the drawing, other drawings described in the embodiment (or a part thereof) and / or drawings described in one or more other embodiments (or a part thereof).

[0150] Furthermore, matters not specified in the drawings or text of this specification may constitute an embodiment of the invention other than that specified. Furthermore, when a numerical range, such as an upper limit and a lower limit, is specified for a certain value, by arbitrarily narrowing the range or excluding a portion of the range, an embodiment of the invention that excludes that portion of the range may be specified. Thus, for example, it may be possible to specify that prior art is not within the technical scope of an embodiment of the present invention.

[0151] Furthermore, in this specification, etc., when a drawing or article describing a particular embodiment shows at least one specific example, a person skilled in the art can readily understand that a broader concept can be derived from that specific example. Therefore, when a drawing or article describing a particular embodiment shows at least one specific example, the broader concept of that specific example is also one embodiment of the disclosed invention and can constitute one embodiment of the invention. Furthermore, it can be said that one embodiment of the invention is clear.

[0152] Furthermore, in this specification and other documents, at least the content shown in the drawings (or a portion thereof) is one embodiment of the disclosed invention and can constitute one embodiment of the invention. Therefore, even if a certain content is not described in the text, if it is shown in the drawings, it can be said that it is one embodiment of the disclosed invention and can constitute one embodiment of the invention. Similarly, a drawing with a portion removed is also one embodiment of the disclosed invention and can constitute one embodiment of the invention. Furthermore, it can be said that one embodiment of the invention is clear.

[0153] Example 1

[0154] In this example, the results of SEM observation of lithium deposited on the surface of the negative electrode current collector during charge of a lithium ion secondary battery having no active material provided on the negative electrode, which is one embodiment of the present invention, will be described.

[0155] [Manufacturing of positive and negative electrodes]

[0156] First, the negative electrode is described. In the negative electrode, a rolled copper foil current collector (18 μm) is used as the current collector.

[0157] In addition, in the secondary battery of one embodiment of the present invention, an active material layer is not formed on the current collector. Therefore, there is no need for the apparatus required for the process of setting the active material on the negative electrode current collector, that is, a kneading device for making a slurry, a coating machine for applying the slurry, a dryer for drying the slurry, etc. As a result, the time required for each process when using these apparatuses can be omitted. Furthermore, the cost of components such as active materials, conductive additives, and adhesives is not required. Furthermore, there is no need to consider the yield rate of the process of setting the active material on the negative electrode current collector, thereby improving the yield rate of the overall manufacturing process of the secondary battery.

[0158] Next, the manufacturing process of the positive electrode is described. In the positive electrode, LiFePO4 is used as the active material, graphene oxide (GO) is used as the conductive additive, and PVDF is used as the binder. LiFePO4, GO, and PVDF are mixed in a ratio of 94.4:0.6:5 ​​(weight %), and N-methyl-2-pyrrolidone (NMP) is used as the solvent to form the electrode slurry.

[0159] The prepared slurry was then applied to an aluminum current collector (20 μm) with a pre-formed underlayer and then dried. A continuous coater was used, with a slot die coating method and a metering pump supply method at a coating speed of 1.0 m / min. Drying was performed at 80°C under atmospheric pressure until the NMP completely evaporated. Chemical reduction of the graphene oxide was then performed.

[0160] Chemical reduction conditions involved reducing graphene oxide by reacting in a solvent containing a reducing agent. The reduction treatment was performed at 60°C for 4.5 hours. Ascorbic acid was used as the reducing agent. Ethanol was used as the solvent, and the reducing agent concentration was 13.5 g / L. The product was then washed with ethanol and dried at 70°C for 10 hours. Drying was performed under vacuum.

[0161] Next, the positive electrode active material layer was formed by pressing and compacting the resultant by a roll pressing method.

[0162] [Manufacturing of Secondary Batteries]

[0163] Next, a secondary battery was manufactured using the manufactured positive and negative electrodes. For characteristic evaluation, a coin-shaped secondary battery of type CR2032 (20 mm in diameter and 3.2 mm in height) was used. As a separator, a 25 μm thick polypropylene was laminated on the positive electrode side, and a cellulose fiber was laminated on the negative electrode side. The area of ​​the positive and negative electrodes was 1.13 cm 2 The positive electrode can and the negative electrode can are made of stainless steel (SUS).

[0164] Three electrolyte solutions were prepared: electrolyte A, electrolyte B, and comparative electrolyte A. A 1:1 volume ratio of EC (ethylene carbonate) and DEC (diethyl carbonate) was used as the solvent for each electrolyte solution. Lithium hexafluorophosphate (LiPF6) was dissolved in the mixed solvent at a concentration of approximately 1 mol / L to prepare electrolyte A, and secondary battery A was manufactured using electrolyte A. Separately, lithium tetrafluoroborate (LiBF4) was dissolved in the mixed solvent at a concentration of approximately 1 mol / L to prepare electrolyte B, and secondary battery B was manufactured using electrolyte B.

[0165] Furthermore, lithium perchlorate (LiClO 4 ) was dissolved in a mixed solvent at a concentration of approximately 1 mol / L to prepare a comparative electrolyte solution A, and a comparative secondary battery A was manufactured using the comparative electrolyte solution A.

[0166] Next, each of the three manufactured thin secondary batteries was charged and discharged. During charging and discharging, constant current charging and discharging was performed at a current of 1.7 mA. The upper limit voltage for charging and discharging was 4 V, and the lower limit voltage was 2 V. Furthermore, charging and discharging were performed at a temperature of 25°C.

[0167] [SEM observation]

[0168] During the initial charge, the battery was stopped when the upper voltage limit of 4V was reached. The battery was disassembled, and the negative electrode, which still had lithium deposits, was removed and cleaned. Dimethyl carbonate was used as the cleaning liquid. The surface of the negative electrode was observed using a scanning electron microscope (SEM). Figure 3 A and Figure 3 B and Figure 12 A shows the results of SEM observation.

[0169] Figure 3 A is a SEM observation image of the negative electrode taken out from a secondary battery (secondary battery A) having lithium hexafluorophosphate (LiPF6) as an alkali in the electrolyte solution. Figure 3 B is a SEM observation image of a negative electrode taken out from a secondary battery (secondary battery B) having lithium tetrafluoroborate (LiBF 4 ) as an alkali in an electrolyte solution. Figure 12 A is a SEM observation image of a negative electrode taken out from a secondary battery (comparative secondary battery A) having lithium perchlorate (LiClO 4 ) as an alkali in an electrolyte solution.

[0170] like Figure 3 As shown in A, whisker-like lithium was observed on the current collector taken out from the secondary battery A. On the other hand, as shown in Figure 3 As shown in B, less dendritic (whisker-like) lithium was observed on the current collector taken out from secondary battery B than on the current collector taken out from secondary battery A. Figure 12 As shown in Figure A, the most common type of lithium deposited was in the form of dendrites (whiskers) on the current collector extracted from comparative secondary battery A. The SEM observation results confirm that the generation of lithium dendrites (whiskers) 200 can be reduced in the negative electrode of a secondary battery using an inorganic base containing fluorine as the electrolyte.

[0171] The relationship between the electrolyte and the deposition of dendritic (whisker-like) lithium will be described later.

[0172] Example 2

[0173] In this example, the results of XPS analysis of lithium deposited on the surface of the negative electrode current collector during charge in a lithium ion secondary battery having no active material provided on the negative electrode, which is one embodiment of the present invention, will be described.

[0174] The secondary battery manufactured in this example will be described. The manufacturing conditions for the positive and negative electrodes are the same as those described in Example 1, so their description will be omitted. The manufacturing conditions for the secondary battery, other than the electrolyte manufacturing conditions, are also the same as those described in Example 1, so their description will be omitted.

[0175] [Manufacturing of Secondary Batteries]

[0176] The electrolyte used for the secondary battery manufactured in this embodiment is described. As the electrolyte, two electrolytes, electrolyte C and electrolyte D, were used. A mixed solvent obtained by mixing EC and DEC at a volume ratio of 3:7 was used as a solvent, and lithium hexafluorophosphate (LiPF6) was dissolved in the mixed solvent at a concentration of 1 mol / L to manufacture electrolyte C. Secondary battery C was manufactured using electrolyte C. Furthermore, a mixed solvent obtained by mixing EC and DEC at a volume ratio of 1:1 was used as a solvent, and lithium tetrafluoroborate (LiBF4) was dissolved in the mixed solvent at a concentration of approximately 1 mol / L to manufacture electrolyte D. Secondary battery D was manufactured using electrolyte D.

[0177] Next, each of the two manufactured thin secondary batteries was charged and discharged. During charging and discharging, constant current charging and discharging was performed at a current of 1.7 mA. The upper limit voltage for charging and discharging was 4 V, and the lower limit voltage was 2 V. Furthermore, charging and discharging were performed at a temperature of 25°C.

[0178] [XPS analysis]

[0179] During the initial charge, the battery was stopped when the upper voltage reached 4 V. The battery was disassembled, and the negative electrode, where lithium was deposited, was removed and cleaned using dimethyl carbonate as the cleaning solution. Figure 2 The results of analyzing the surface of the negative electrode using X-ray photoelectron spectroscopy (XPS) are shown.

[0180] Figure 2 It is an XPS spectrum of the area where the peak originating from lithium fluoride appears. The peak originating from lithium fluoride is clearly observed on the surface of the negative electrode taken out from the secondary battery D. In addition, on the surface of the negative electrode taken out from the secondary battery C, a peak originating from lithium fluoride is also observed, although smaller. Through this analysis, it is confirmed that the surface of the lithium precipitated on the negative electrode surface contains lithium fluoride in both batteries. In addition, the amount of lithium fluoride in the negative electrode of the secondary battery D using lithium tetrafluoroborate (LiBF4) is more than that in the negative electrode of the secondary battery C using lithium hexafluorophosphate (LiPF6).

[0181] The relationship between the electrolyte and lithium fluoride deposited on the surface of the negative electrode will be described later.

[0182] Example 3

[0183] In this example, the charge and discharge characteristics of a lithium ion secondary battery having no active material provided in the negative electrode, which is one embodiment of the present invention, will be described.

[0184] The secondary battery manufactured in this example will be described. Since the negative electrode conditions are the same as those described in Example 1, their description will be omitted. Since the secondary battery manufacturing conditions other than the electrolyte manufacturing conditions are also the same as those described in Example 1, their description will be partially omitted.

[0185] [Manufacturing of positive electrode]

[0186] First, LiFePO 4 , acetylene black (hereinafter referred to as AB), and PVDF were mixed at a ratio of 90:5:5 (weight %), and NMP was used as a solvent to prepare a positive electrode slurry.

[0187] The prepared slurry was then applied to an aluminum current collector (20 μm) with a pre-formed underlayer, and then dried at 80°C under atmospheric pressure until the NMP completely evaporated. The positive electrode active material layer was then pressed and densified using a roll press.

[0188] Next, the values ​​used for calculating the positive electrode capacity are described. When calculating the positive electrode capacity, 170 mAh / g is used as the capacity of LiFePO 4 .

[0189] [Manufacturing of Secondary Batteries]

[0190] The electrolyte used in the secondary battery manufactured in this embodiment is described. Two electrolytes, electrolyte E and electrolyte F, were used. A mixed solvent obtained by mixing EC and DEC at a volume ratio of 1:1 was used as a solvent, and lithium hexafluorophosphate (LiPF6) was dissolved in the mixed solvent at a concentration of 1 mol / L to manufacture electrolyte E. Secondary battery E was manufactured using electrolyte E. Electrolyte F was manufactured by dissolving lithium tetrafluoroborate (LiBF4) in the mixed solvent at a concentration of 1 mol / L using electrolyte F as a solvent. Secondary battery F was manufactured using electrolyte F.

[0191] [Charge and discharge characteristics]

[0192] Next, the manufactured secondary battery was charged and discharged. During charging and discharging, constant current charging and discharging was performed at a current of 1.7 mA. The upper limit voltage of charging and discharging was 4 V, and the lower limit voltage was 2 V. Furthermore, charging and discharging were repeated at a temperature of 25°C. Figure 4 The initial charge and discharge characteristics are shown.

[0193] like Figure 4As shown, it can be confirmed that the initial discharge capacity of the secondary battery F using lithium tetrafluoroborate (LiBF4) as the electrolyte is higher than that of the secondary battery E using lithium hexafluorophosphate (LiPF6) as the electrolyte.

[0194] In lithium-ion secondary batteries with an active material provided at the negative electrode, lithium tetrafluoroborate (LiBF4) has lower chemical stability and is easily decomposed compared to lithium hexafluorophosphate (LiPF6), and has a lower discharge capacity when used in an electrolyte. Figure 4 The results shown are contrary to this. Compared with the secondary battery E using lithium hexafluorophosphate (LiPF6) as the electrolyte, the discharge capacity of the secondary battery F using lithium tetrafluoroborate (LiBF4) as the electrolyte is higher.

[0195] The results shown in Examples 1 to 3 are summarized. That is, when a portion of lithium tetrafluoroborate (LiBF4) in the electrolyte decomposes, the lithium precipitated on the surface of the negative electrode current collector is provided with fluorine to form lithium fluoride. The lithium fluoride formed on the surface of the negative electrode inhibits the formation of dendritic (whisker-like) lithium during the subsequent charging of the secondary battery. As a result, the generation of lithium that does not contribute to the battery reaction due to the dissolution of the roots of the whiskers during discharge is suppressed, and the discharge capacity does not disappear but can be maintained, so that its discharge capacity is larger than that of a secondary battery using lithium hexafluorophosphate (LiPF6).

[0196] Note that in the secondary battery using lithium hexafluorophosphate (LiPF 6 ), the formation of lithium fluoride on the surface was confirmed from the XPS results, and thus it was confirmed that the effect of the formation of lithium fluoride was obtained, although in a small amount.

[0197] Thus, by using an inorganic base containing fluorine in the electrolyte, the formation of dendritic (whisker-like) lithium can be suppressed, the generation of lithium that does not contribute to the battery reaction can be suppressed, and the discharge capacity can be maintained, thereby increasing the discharge capacity of the secondary battery.

[0198] Example 4

[0199] In this example, a lithium ion secondary battery having a negative electrode and no active material provided thereon, in which fluorine-containing ethylene carbonate is added as an additive to an electrolyte, will be described as one embodiment of the present invention.

[0200] The secondary battery manufactured in this example is described below. The negative electrode conditions are the same as those described in Example 1, so their description is omitted. The positive electrode conditions are the same as those described in Example 3, so their description is omitted. The secondary battery manufacturing conditions, other than the electrolyte manufacturing conditions, are also the same as those described in Example 1, so their description is partially omitted.

[0201] [Manufacturing of Secondary Batteries]

[0202] The electrolyte G used in the secondary battery manufactured in this example is described below. First, lithium tetrafluoroborate (LiBF4) was dissolved in PC (propylene carbonate) at a concentration of 1 mol / L. Fluoroethylene carbonate (FEC) was added as an additive to the resulting solution under four different conditions to produce electrolytes G-1 to G-4.

[0203] Specifically, electrolyte G-2 was prepared by adding FEC at 2 wt% of the solution weight. Electrolyte G-3 was prepared by adding FEC at 20 wt% of the solution weight. Electrolyte G-4 was prepared by adding FEC at 50 wt% of the solution weight. Electrolyte G-1 was a solution without FEC.

[0204] Secondary batteries G-1 to G-4 were manufactured using the electrolytic solutions G-1 to G-4.

[0205] [Charge and discharge characteristics]

[0206] Next, the manufactured secondary battery was charged and discharged. During charging and discharging, constant current charging and discharging was performed at a current of 1.7 mA. The upper limit voltage of charging and discharging was 4 V, and the lower limit voltage was 2 V. Furthermore, charging and discharging were repeated at a temperature of 25°C. Figure 5 The initial charge and discharge characteristics are shown. Figure 6 The cycle characteristics are shown.

[0207] like Figure 5 As shown, adding FEC to the electrolyte of a secondary battery significantly improves discharge capacity. The effect of FEC is already evident at 2 wt% and becomes even more pronounced at 20 wt%. While the effect tends to saturate at 50 wt%, it is confirmed that discharge capacity increases with increasing FEC addition.

[0208] This is because: on the surface of the negative electrode collector, FEC supplies fluorine to the lithium deposited by charging, forming lithium fluoride on the surface of the deposited lithium. This lithium fluoride prevents lithium from being deposited in the form of dendrites (whiskers) when lithium is deposited by subsequent charging, and reduces the lithium that disappears without contributing to the battery reaction, thereby suppressing the reduction in discharge capacity.

[0209] Depend on Figure 6 The cycle characteristics shown here can be confirmed to be improved according to the amount of FEC added. This is because the addition of FEC reduces the amount of lithium that disappears without contributing to the battery reaction, thereby maintaining the discharge capacity.

[0210] [SEM observation]

[0211] A secondary battery was manufactured under the same conditions as secondary battery G-3. During the initial charge, the battery was stopped when the voltage reached the upper limit of 4V. The battery was disassembled, and the negative electrode, which had lithium deposited, was removed and cleaned. Dimethyl carbonate was used as the cleaning liquid. The surface of the negative electrode was observed using a scanning electron microscope (SEM). Figure 12 B shows the results of SEM observation. Figure 12 No dendritic (whisker-like) lithium was observed deposited on the current collector taken out of secondary battery G-3 in B. Fluorine is supplied to the lithium on the negative electrode surface not only from lithium tetrafluoroborate (LiBF4) in the electrolyte but also from FEC, forming lithium fluoride, thereby suppressing the formation of dendritic (whisker-like) lithium.

[0212] The above examples confirm that by supplying fluorine from the electrolyte to the negative electrode surface, it is possible to suppress the deposition of lithium in the form of dendrites (whiskers) on the negative electrode surface during charging, thereby enabling the manufacture of a lithium-ion secondary battery without using a negative electrode active material. Fluorine can be included in the base of the electrolyte or as an additive in the electrolyte.

[0213] Description of Reference Numerals

[0214] 101: Positive electrode; 101a: Positive electrode current collector; 101b: Positive electrode active material layer; 102: Negative electrode current collector; 104: Separator; 105: Electrolyte; 106: Outer packaging; 108: Spacer; 110: Lithium-ion secondary battery; 115: Lead electrode; 116: Sealing portion; 200: Dendrite (whisker); 800: Mobile phone; 801: Frame; 802: Display; 803: Operation button; 804: Secondary battery; 805: Speaker; 806: Microphone; 1001: Support structure; 1002: Secondary battery; 1003: Wiring; 1004: Control substrate; 1005: Antenna; 1006: Power supply control circuit; 1007: Communication device; 1008: Wiring; 1 009: FPC; 1010: Connecting part; 1011: Display module; 1012: Cover; 1013: Protective component; 1014: Input / output connector; 1015: Display part; 1700: Curved surface; 1701: Plane; 1702: Curve of curved surface; 1703: Radius of curvature; 1704: Center of curvature; 1800: Center of curvature; 1801: Thin film; 1802: Radius of curvature; 1803: Thin film; 1804: Radius of curvature; 1805: Electrode and electrolyte, etc.; 7100: Portable display device; 7101: Frame; 7102: Display part; 7103: Operation button; 7104: Secondary battery; 7200: Armband-type display device; 7201: Frame; 7202: Display part.

Claims

1. A secondary battery comprising: positive electrode; a negative electrode including a negative electrode current collector; a separator between the positive electrode and the negative electrode; a sheet-like spacer between the negative electrode and the separator; as well as electrolyte, including fluorine, Wherein, the sheet-like spacer comprises any one of paper, non-woven fabric, glass fiber and synthetic fiber, wherein the negative electrode current collector is in direct contact with the thin sheet spacer, wherein the negative electrode current collector is configured to cause a precipitate containing lithium to precipitate on the surface of the negative electrode current collector during charging, and The surface of the negative electrode current collector faces the thin-sheet separator.

2. The secondary battery according to claim 1, wherein The separator is in direct contact with the sheet-like spacer.

3. A secondary battery comprising: positive electrode; a negative electrode including a negative electrode current collector; a separator between the positive electrode and the negative electrode; a spacer between the negative electrode and the separator; as well as electrolyte, including fluorine, wherein the spacer has a spherical or cylindrical shape, Wherein, the spacer comprises any one of paper, non-woven fabric, glass fiber and synthetic fiber, wherein the negative electrode current collector is in direct contact with the spacer, wherein the negative electrode current collector is configured to cause a precipitate containing lithium to precipitate on the surface of the negative electrode current collector during charging, and The surface of the negative electrode current collector faces the separator.

4. The secondary battery according to claim 3, wherein The insulator is in direct contact with the spacer.

5. The secondary battery according to claim 1 or 3, wherein The negative electrode current collector is in contact with the electrolyte.

6. The secondary battery according to claim 1 or 3, wherein The negative electrode current collector includes a region in direct contact with the separator.

7. The secondary battery according to claim 1 or 3, in, The electrolyte includes lithium tetrafluoroborate or lithium hexafluorophosphate.

8. The secondary battery according to claim 1 or 3, in, The electrolyte further includes an organic compound containing fluorine, and The organic compound accounts for more than 2 wt% of the weight of the electrolyte.

9. The secondary battery according to claim 8, wherein The organic compound is fluoroethylene carbonate.

10. The secondary battery according to claim 1 or 3, wherein The negative electrode current collector includes stainless steel, gold, platinum, zinc, iron, copper, aluminum or titanium.

11. A secondary battery comprising: positive electrode; a negative electrode including a negative electrode current collector; a separator between the positive electrode and the negative electrode; and An electrolyte containing fluorine, Wherein, the negative electrode current collector comprises stainless steel, gold, platinum, zinc, iron, copper, aluminum or titanium, wherein the negative electrode contains a compound containing lithium and fluorine during charging, wherein the compound is in contact with the negative electrode current collector, wherein the negative electrode current collector includes a region in direct contact with the separator, and The negative electrode current collector is configured so that a precipitate containing lithium is deposited on a surface of the negative electrode current collector during charge.

12. The secondary battery according to claim 11, in, The electrolyte includes lithium tetrafluoroborate or lithium hexafluorophosphate.

13. The secondary battery according to claim 11, in, The electrolyte further includes an organic compound containing fluorine, and The organic compound accounts for more than 2 wt% of the weight of the electrolyte.

14. The secondary battery according to claim 13, wherein The organic compound is fluoroethylene carbonate.

15. The secondary battery according to claim 11, further comprising: a spacer between the negative electrode and the separator, Wherein, the negative electrode current collector is in direct contact with the separator.

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