Patent ID: 12256503

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail below with reference to drawings. However, the present invention is not limited to the description below, and it is easily understood by those skilled in the art that modes and details disclosed herein can be modified in various ways. Further, the present invention is not construed as being limited to description of the embodiments.

Embodiment 1

In this embodiment, an example of an electronic device in which an arm-worn secondary battery is provided with a display portion is described.FIG.1Ais a cross-sectional view of the electronic device, andFIG.1Bis a perspective view of the electronic device.

As illustrated inFIG.1A, an electronic device100includes a flexible secondary battery103over a curved surface of a support structure body101and a display portion102over the secondary battery103.

The support structure body101is in the form of a bracelet obtained by curving a band-like structure body. At least part of the support structure body101has flexibility and can be moved in the direction of arrows105; thus, the electronic device can be put around a wrist. An end portion of the support structure body101illustrated inFIG.1Ais bendable, and a middle portion apart from the end portion hardly changes its shape. Therefore, the middle portion of the support structure body101maintains a curvature with which the secondary battery and the display portion are attached and fixed in fabrication; thus, the secondary battery103and the display portion102overlapping with the middle portion are hardly damaged even when the electronic device is repeatedly put on and taken off from an arm.

In the case where an active-matrix display device is provided as the display portion, the active-matrix display device includes at least a layer including transistors. The reliability of the layer including transistors is not easily decreased when the layer is only attached to and fixed to the curved surface of the support structure body101. However, the reliability might be decreased when the layer including transistors is repeatedly bent in such a manner that the layer including transistors is curved toward one side into a concave shape, returned to a flat shape, and then curved toward the other side into a convex shape. Also in this regard, since the middle portion of the support structure body101illustrated inFIG.1Ahardly changes its shape, when the layer including transistors is fixed to the curved surface of the support structure body101, the layer is curved toward only one side even if it is bent. In other words, the support structure body101functions as a protective member which prevents the display portion102and the secondary battery103from being curved excessively or from being twisted and deformed significantly.

As a material of the support structure body101, a metal, a resin, a natural material, or the like can be used. The support structure body101preferably has a small thickness so as to be lightweight. A metal is preferably used as a material of the support structure body101because a metal has high impact resistance and high heat conductivity. A resin is preferably used as a material of the support structure body101because the resin can achieve a reduction in weight and does not cause metal allergy.

The shape of the electronic device illustrated inFIG.1Bis an example, and a belt or a clasp for fixing to a wrist may be provided. Alternatively, the electronic device may be in the form of a ring or a cylinder tube so as to surround a wrist.

Although the example of the electronic device to be worn on an arm such as a wrist (a lower arm including a wrist) or an upper arm is described, the position is not particularly limited, and the electronic device may be worn on any part of a human body such as a waist or an ankle. In the case where the electronic device is worn on an ankle, the electronic device may be manufactured to have a shape different from that illustrated inFIGS.1A and1Band have a size to fit an ankle shape. In the case where the electronic device is worn on a waist, the electronic device may be manufactured in a size to be wrapped around a waist like a belt.

An example of a method for manufacturing the electronic device100is described below.

First, the support structure body101is prepared. A stainless steel material whose region with a large radius of curvature in a cross-section does not change its shape and whose end portion is bendable is used for the support structure body101. The stainless steel material serves as a protective material which prevents the display portion102and the secondary battery103from being curved excessively or from being twisted and deformed significantly. The stainless steel material only allows a change into a certain shape, i.e., bending in one direction, in putting the electronic device on an arm, which improves the reliability.

Next, the secondary battery103to be attached to the region with a large radius of curvature of the support structure body101is prepared.

The secondary battery103is not particularly limited as long as it is a lithium-ion secondary battery and is flexible. The flexible secondary battery includes a thin flexible film as an exterior body and can change its shape along a curved surface portion of the region with a large radius of curvature of the support structure body101.

In this embodiment, an example in which a laminated secondary battery is used as the flexible secondary battery is described.FIG.2Aillustrates a top view of the laminated secondary battery.FIG.2Bis a schematic cross-sectional view taken along a dashed-dotted line A-B inFIG.2A.

A secondary battery used is fabricated in such a manner that a sheet-like positive electrode203, a separator207, and a sheet-like negative electrode206are stacked, the other region is filled with an electrolytic solution210, and these components are enclosed by an exterior body made of one or two films. Note that the positive electrode203includes a positive electrode current collector201and a positive electrode active material layer202. The negative electrode206includes a negative electrode current collector204and a negative electrode active material layer205.

The positive electrode current collector201and the negative electrode current collector204can each be formed using a highly conductive material which is not alloyed with a carrier ion of lithium or the like, such as a metal typified by stainless steel, gold, platinum, zinc, iron, nickel, copper, aluminum, titanium, or tantalum or an alloy thereof. Alternatively, an aluminum alloy to which an element which improves heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, is added can be used. Still alternatively, a metal element which forms silicide by reacting with silicon can be used. Examples of the metal element which forms silicide by reacting with silicon include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, and the like. The positive electrode current collector201and the negative electrode current collector204can each have a foil-like shape, a plate-like shape (sheet-like shape), a net-like shape, a cylindrical shape, a coil shape, a punching-metal shape, an expanded-metal shape, or the like as appropriate. The positive electrode current collector201and the negative electrode current collector204each preferably have a thickness greater than or equal to 10 μm and less than or equal to 30 μm.

For the positive electrode active material layer202, a material into and from which lithium ions can be inserted and extracted can be used. For example, a lithium-containing material with an olivine crystal structure, a layered rock-salt crystal structure, and a spinel crystal structure can be used. As the positive electrode active material, a compound such as LiFeO2, LiCoO2, LiNiO2, LiMn2O4, V2O5, Cr2O5, and MnO2can be used.

Typical examples of the lithium-containing material with an olivine crystal structure (represented by a general formula, LiMPO4(M is one or more of Fe(II), Mn(II), Co(II), and Ni(II)), are LiFePO4, LiNiPO4, LiCoPO4, LiMnPO4, LiFeaNibPO4, LiFeaCobPO4, LiFeaMnbPO4, LiNiaCobPO4, LiNiaMnbPO4(a+b≤1, 0<a<1, and 0<b<1), LiFecNidCoePO4, LiFecNidMnePO4, LiNicCodMnePO4(c+d+e≤1, 0<c<1, 0<d<1, and 0<e<1), and LiFefNigCohMniPO4(f+g+h+i≤1, 0<f<1, 0<g<1, 0<h<1, and 0<i<1).

LiFePO4is particularly preferable because it properly has properties necessary for the positive electrode active material, such as safety, stability, high capacity density, high potential, and the existence of lithium ions which can be extracted in initial oxidation (charging).

Examples of the lithium-containing material with a layered rock-salt crystal structure include lithium cobalt oxide (LiCoO2); LiNiO2; LiMnO2; Li2MnO3; an NiCo-based lithium-containing material (a general formula thereof is LiNixCo1-xO2(0<x<1)) such as or LiNi0.8Co0.2O2; an NiMn-based lithium-containing material (a general formula thereof is LiNixMn1-xO2(0<x<1)) such as LiNi0.5Mn0.5O2; and an NiMnCo-based lithium-containing material (also referred to as NMC, and a general formula thereof is LiNixMn1-xCo1-x-yO2(x>0, y>0, x+y<1)) such as LiNi1/3Mn1/3Co1/3O2. Moreover, the examples further include Li(Ni0.8Co0.15Al0.05)O2and Li2MnO3-LiMO2(M═Co, Ni, or Mn).

Examples of the lithium-containing material with a spinel crystal structure include LiMn2O4, Li1+xMn2-xO4, Li(MnAl)2O4, and LiMn1.5Ni0.5O4.

It is preferable to add a small amount of lithium nickel oxide (LiNiO2or LiNi1-xMO2(M═Co or Al, for example)) to a lithium-containing material with a spinel crystal structure which contains manganese such as LiMn2O4because advantages such as minimization of the elution of manganese and the decomposition of an electrolytic solution can be obtained.

Alternatively, a lithium-containing material represented by a general formula, Li(2-j)MSiO4(M is one or more of Fe(II), Mn(II), Co(II), and Ni(II), 0≤j≤2), can be used as the positive electrode active material. Typical examples of Li(2-j)MSiO4(general formula) include lithium compounds such as Li(2-j)FeSiO4, Li(2-j)NiSiO4, Li(2-j)CoSiO4, Li(2-j)MnSiO4, Li(2-j)FekNilSiO4, Li(2-j)FekColSiO4, Li(2-j)FekMnlSiO4, Li(2-j)NikCoiSiO4, Li(2-j)NikMnlSiO4(k+l≤1, 0<k<1, and 0<l<1), Li(2-j)FemNinCoqSiO4, Li(2-j)FemNinMnqSiO4, Li(2-j)NimConMnqSiO4(m+n+q≤1, 0<m<1, 0<n<1, and 0<q<1), and Li(2-j)FerNisCotMnuSiO4(r+s+t+u≤1, 0<r<1, 0<s<1, 0<t<1, and 0<u<1).

Still alternatively, a NASICON compound represented by a general formula, AxM2(XO4)3(A═Li, Na, or Mg, M═Fe, Mn, Ti, V, Nb, or Al, and X═S, P, Mo, W, As, or Si), can be used as the positive electrode active material. Examples of the NASICON compound include Fe2(MnO4)3, Fe2(SO4)3, and Li3Fe2(PO4)3. Still further alternatively, a compound represented by a general formula, Li2MPO4F, Li2MP2O7, or Li5MO4(M═Fe or Mn), a perovskite fluoride such as NaF3or FeF3, a metal chalcogenide (a sulfide, a selenide, or a telluride) such as TiS2or MoS2, a lithium-containing material with an inverse spinel crystal structure such as LiMVO4, a vanadium oxide-based (e.g., V2O5, V6O13, or LiV3O8), a manganese oxide-based, or an organic sulfur-based material can be used as the positive electrode active material, for example.

The positive electrode active material layer202may further include a binder for increasing adhesion of active materials, a conductive additive for increasing the conductivity of the positive electrode active material layer202, and the like in addition to the above-described positive electrode active materials.

A material with which lithium can be dissolved and precipitated or a material into and from which lithium ions can be inserted and extracted can be used for the negative electrode active material layer205; for example, a lithium metal, a carbon-based material, or an alloy-based material can be used.

The lithium metal is preferable because of its low redox potential (3.045 V lower than that of a standard hydrogen electrode) and high specific capacity per unit weight and per unit volume (3860 mAh/g and 2062 mAh/cm3).

Examples of the carbon-based material include graphite, graphitizing carbon (soft carbon), non-graphitizing carbon (hard carbon), a carbon nanotube, graphene, carbon black, and the like.

Examples of the graphite include artificial graphite such as meso-carbon microbeads (MCMB), coke-based artificial graphite, or pitch-based artificial graphite and natural graphite such as spherical natural graphite.

Graphite has a low potential substantially equal to that of a lithium metal (0.1 V to 0.3 V vs. Li/Li+) when lithium ions are intercalated into the graphite (while a lithium-graphite intercalation compound is formed). For this reason, a lithium-ion secondary battery can have a high operating voltage. In addition, graphite is preferable because of its advantages such as relatively high capacity per unit volume, small volume expansion, low cost, and safety greater than that of a lithium metal.

For the negative electrode active material, an alloy-based material which enables charge-discharge reactions by an alloying reaction and a dealloying reaction with lithium can be used. In the case where carrier ions are lithium ions, a material containing at least one of Mg, Ca, Al, Si, Ge, Sn, Pb, Sb, Bi, Ag, Au, Zn, Cd, In, Ga, and the like can be used as an alloy-based material, for example. Such elements have higher capacity than carbon. In particular, silicon has a significantly high theoretical capacity of 4200 mAh/g. For this reason, silicon is preferably used for the negative electrode active material. Examples of the alloy-based material using such elements include SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, SbSn, and the like. Note that SiO refers to the powder of a silicon oxide including a silicon-rich portion and can also be referred to as SiOy(2>y>0). Examples of SiO include a material containing one or more of Si2O3, Si3O4, and Si2O and a mixture of Si powder and silicon dioxide (SiO2). Furthermore, SiO may contain another element (e.g., carbon, nitrogen, iron, aluminum, copper, titanium, calcium, and manganese). In other words, SiO refers to a colored material containing two or more of single crystal silicon, amorphous silicon, polycrystal silicon, Si2O3, Si3O4, Si2O, and SiO2. Thus, SiO can be distinguished from SiO, (x is 2 or more), which is clear and colorless or white. Note that in the case where a secondary battery is fabricated using SiO as a material thereof and the SiO is oxidized because of repeated charge and discharge cycles, SiO is changed into SiO2in some cases.

Alternatively, for the negative electrode active material, an oxide such as titanium dioxide (TiO2), lithium titanium oxide (Li4Ti5O12), lithium-graphite intercalation compound (LixC6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), or molybdenum oxide (MoO2) can be used.

Still alternatively, for the negative electrode active material, Li3-xMxN (M═Co, Ni, or Cu) with a Li3N structure, which is a nitride containing lithium and a transition metal, can be used. For example, Li2.6Co0.4N3is preferable because of high charge and discharge capacity (900 mAh/g and 1890 mAh/cm3).

A nitride containing lithium and a transition metal is preferably used, in which case lithium ions are contained in the negative electrode active material and thus the negative electrode active material can be used in combination with a material for a positive electrode active material which does not contain lithium ions, such as V2O5or Cr3O8. In the case of using a material containing lithium ions as a positive electrode active material, the nitride containing lithium and a transition metal can be used for the negative electrode active material by extracting the lithium ions contained in the positive electrode active material in advance.

Alternatively, a material which causes a conversion reaction can be used for the negative electrode active material; for example, a transition metal oxide which does not cause an alloy reaction with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may be used. Other examples of the material which causes a conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, sulfides such as CoS0.89, NiS, and CuS, nitrides such as Zn3N2, Cu3N, and Ge3N4, phosphides such as NiP2, FeP2, and CoP3, and fluorides such as FeF3and BiF3. Note that any of the fluorides can be used as a positive electrode active material because of its high potential.

The negative electrode active material layer205may further include a binder for increasing adhesion of active materials, a conductive additive for increasing the conductivity of the negative electrode active material layer205, and the like in addition to the above-described negative electrode active materials.

As an electrolyte in the electrolytic solution210, a material which contains lithium ions serving as carrier ions is used. Typical examples of the electrolyte are lithium salts such as LiPF6, LiClO4, Li(FSO2)2N, LiAsF6, LiBF4, LiCF3SO3, Li(CF3SO2)2N, and Li(C2F5SO2)2N. One of these electrolytes may be used alone, or two or more of them may be used in an appropriate combination and in an appropriate ratio. In order to stabilize a reaction product, a small amount (1 wt %) of vinylene carbonate (VC) may be added to the electrolytic solution so that the decomposition amount of the electrolytic solution is further reduced.

As a solvent of the electrolytic solution210, a material in which carrier ions can transfer is used. As the solvent of the electrolytic solution, an aprotic organic solvent is preferably used. Typical examples of aprotic organic solvents include ethylene carbonate (EC), propylene carbonate, dimethyl carbonate, diethyl carbonate (DEC), γ-butyrolactone, acetonitrile, dimethoxyethane, tetrahydrofuran, and the like, and one or more of these materials can be used. When a gelled high-molecular material is used as the solvent of the electrolytic solution, safety against liquid leakage and the like is improved. Furthermore, the secondary battery can be thinner and more lightweight. Typical examples of gelled high-molecular materials include a silicone gel, an acrylic gel, an acrylonitrile gel, polyethylene oxide, polypropylene oxide, a fluorine-based polymer, and the like. Alternatively, the use of one or more of ionic liquids (room temperature molten salts) which have features of non-flammability and non-volatility as a solvent of the electrolytic solution can prevent the secondary battery from exploding or catching fire even when the secondary battery internally shorts out or the internal temperature increases owing to overcharging and others.

As the separator207, an insulator such as cellulose (paper), polyethylene with pores, and polypropylene with pores can be used.

FIG.2Billustrates an example in which the number of electrode layers is two (two layers of the positive electrode203and the negative electrode206). In order that the area (size) of the secondary battery is decreased without change in capacity of the secondary battery, the secondary battery can be downsized by increasing the number of electrode layers to more than two. However, if the number of electrode layers exceeds 40, the secondary battery has a large thickness and might lose its flexibility. Therefore, the number of electrode layers is set to 40 or less, preferably 20 or less. In the case of double-sided coating by which both sides of the positive electrode current collector are coated with the positive electrode active material layer202, or in the case of double-sided coating by which both sides of the negative electrode current collector204are coated with the negative electrode active material layer205, the number of electrode layers can be decreased to 10 or less without change in capacity of the secondary battery.

The stacked layer including the sheet-like positive electrode203, the separator207, and the sheet-like negative electrode206is sealed by heat sealing.

In the secondary battery, a thin flexible film (such as a laminate film) is used as an exterior body. The laminate film refers to a stacked film of a base film and an adhesive synthetic resin film, or a stacked film of two or more kinds of films. For the base film, polyester such as PET or PBT, polyamide such as nylon 6 or nylon 66, an inorganic film formed by evaporation, or paper may be used. For the adhesive synthetic resin film, polyolefin such as PE or PP, an acrylic-based synthetic resin, an epoxy-based synthetic resin, or the like may be used. An object is laminated with the laminate film by thermocompression bonding using a laminating apparatus. Note that an anchor coat agent is preferably applied as pretreatment for the laminating step so that the adhesion between the laminate film and the object can be increased. As the anchor coat agent, an isocyanate-based material or the like may be used.

In this specification, heat sealing refers to sealing by thermocompression bonding, and means that an adhesive layer partly covering the base film or an outermost or innermost layer with a low melting point in the laminate film is melted by heat and attached by pressure.

The positive electrode current collector201and the negative electrode current collector204also serve as terminals for electrical contact with the outside. For this reason, the positive electrode current collector201and the negative electrode current collector204are provided so that part of the positive electrode current collector201and part of the negative electrode current collector204are exposed outside a film208and an exterior body209as illustrated inFIG.2A. In the case where a larger number of electrode layers are stacked, a plurality of positive electrode current collectors201are electrically connected by ultrasonic welding, and a plurality of negative electrode current collectors204are electrically connected by ultrasonic welding. Note that inFIG.2B, part of the negative electrode current collector204extends to the outside beyond the exterior body209.

The laminated secondary battery obtained as described above is first attached to the region with a large radius of curvature of the support structure body101and then to the other region. By first attaching the secondary battery to the region with a large radius of curvature, damage to the secondary battery can be reduced during attachment to the support structure body101.

AlthoughFIG.2Aillustrates the example of sealing with the film208and the exterior body209, the present invention is not particularly limited to this example, and a single film folded in half may be used as an exterior body. An example different from that inFIGS.2A and2Bis illustrated inFIGS.10A to10FA film11is folded in half so that two end portions overlap, and is sealed on three sides with an adhesive layer. A manufacturing method in this example is described below with reference toFIGS.10A to10F.

First, the film11is folded in half as illustrated inFIG.10A. In addition, a positive electrode current collector12, a separator13, and a negative electrode current collector14which are components of a secondary battery and stacked as illustrated inFIG.10Bare prepared. Furthermore, two lead electrodes16with sealing layers15illustrated inFIG.10Care prepared. The lead electrodes16are each also referred to as a lead terminal and provided in order to lead a positive electrode or a negative electrode of a secondary battery to the outside of an exterior film. Then, one of the lead electrodes is electrically connected to a protruding portion of the positive electrode current collector12by ultrasonic welding or the like. Aluminum is used as a material of the lead electrode connected to the protruding portion of the positive electrode current collector12. The other lead electrode is electrically connected to a protruding portion of the negative electrode current collector14by ultrasonic welding or the like. Nickel-plated copper is used as a material of the lead electrode connected to the protruding portion of the negative electrode current collector14. Then, two sides of the film11are sealed by thermocompression bonding, and one side is left open for introduction of an electrolytic solution. In thermocompression bonding, the sealing layers15provided over the lead electrodes are also melted, thereby fixing the lead electrodes and the film11to each other. After that, in a reduced-pressure atmosphere or an inert atmosphere, a desired amount of electrolytic solution is introduced to the inside of the film11in the form of a bag. Lastly, the side of the film which has not been subjected to thermocompression bonding and is left open is sealed by thermocompression bonding. In this manner, a secondary battery40illustrated inFIG.10Dcan be manufactured. An edge region indicated by a dotted line inFIG.10Dis a thermocompression-bonded region17. An example of a cross-section taken along a dashed-dotted line A-B inFIG.10Dis illustrated inFIG.10E. As illustrated inFIG.10E, the positive electrode current collector12, a positive electrode active material layer18, the separator13, a negative electrode active material layer19, and the negative electrode current collector14are stacked in this order and placed inside the folded film11, an end portion is sealed with an adhesive layer30, and the other space is provided with an electrolytic solution20.

Here, a current flow in charging a secondary battery will be described with reference toFIG.10F. When a secondary battery using lithium is regarded as a closed circuit, lithium ions transfer and a current flows in the same direction. Note that in the secondary battery using lithium, an anode and a cathode change places in charge and discharge, and an oxidation reaction and a reduction reaction occur on the corresponding sides; hence, an electrode with a high redox potential is called a positive electrode and an electrode with a low redox potential is called a negative electrode. For this reason, in this specification, the positive electrode is referred to as a “positive electrode” and the negative electrode is referred to as a “negative electrode” in all the cases where charge is performed, discharge is performed, a reverse pulse current is supplied, and a charging current is supplied. The use of the terms “anode” and “cathode” related to an oxidation reaction and a reduction reaction might cause confusion because the anode and the cathode change places at the time of charging and discharging. Thus, the terms “anode” and “cathode” are not used in this specification. If the term “anode” or “cathode” is used, it should be mentioned that the anode or the cathode is which of the one at the time of charging or the one at the time of discharging and corresponds to which of a positive electrode or a negative electrode.

Two terminals inFIG.10Fare connected to a charger, and the secondary battery40is charged. As the charge of the secondary battery40proceeds, a potential difference between electrodes increases. The positive direction inFIG.10Fis the direction in which a current flows from one terminal outside the secondary battery40to the positive electrode current collector12, flows from the positive electrode current collector12to the negative electrode current collector14in the secondary battery40, and flows from the negative electrode current collector14to the other terminal outside the secondary battery40. In other words, a current flows in the direction of a flow of a charging current.

Next, a display module to be attached to the secondary battery103is prepared. The display module refers to a display panel provided with at least an FPC. The display module includes the display portion102, an FPC104, and a driver circuit and preferably further includes a converter for power feeding from the secondary battery103.

In the display module, the display portion102is flexible and a display element is provided over a flexible film. The secondary battery103and the display portion102are preferably disposed so as to partly overlap with each other. When the secondary battery103and the display portion102are disposed so as to partly or entirely overlap with each other, the electrical path, i.e., the length of a wiring, from the secondary battery103to the display portion can be shortened, whereby power consumption can be reduced.

Examples of methods for manufacturing the display element over the flexible film include a method in which the display element is directly formed over the flexible film, a method in which a layer including the display element is formed over a rigid substrate such as a glass substrate, the substrate is removed by etching, polishing, or the like, and then the layer including the display element and the flexible film are attached to each other, a method in which a separation layer is provided over a rigid substrate such as a glass substrate, a layer including the display element is formed thereover, the rigid substrate and the layer including the display element are separated from each other using the separation layer, and then the layer including the display element and the flexible film are attached to each other, and the like.

In this embodiment, a manufacturing method which allows heat treatment to be performed at 400° C. or higher and which can improve the reliability of the display element, i.e., a technique in which a separation layer is provided over a rigid substrate such as a glass substrate as disclosed in Japanese Published Patent Application No. 2003-174153, is used so that the display portion102can be an active-matrix display device capable of displaying high-resolution images.

The technique disclosed in Japanese Published Patent Application No. 2003-174153 enables transistors including polysilicon in active layers or transistors including oxide semiconductor layers to be provided over a flexible substrate or film. These transistors are used as switching elements, and electroluminescent (EL) elements are provided.

In a common structure of the EL element, a layer including a light-emitting organic compound or inorganic compound (hereinafter referred to as a light-emitting layer) is provided between a pair of electrodes, and when a voltage is applied to the element, electrons and holes are each injected and transported from the pair of electrodes to the light-emitting layer. When those carriers (electrons and holes) recombine, an excited state of the light-emitting organic compound or inorganic compound is formed, and when the light-emitting organic compound or inorganic compound returns to a ground state, light is emitted.

Further, kinds of excited state that can be formed by an organic compound are a singlet excited state and a triplet excited state. Light emission in the case of a singlet excited state is referred to as fluorescence, and light emission in the case of a triplet excited state is referred to as phosphorescence.

Such a light-emitting element is usually formed of thin films which have an approximate thickness of submicrons to several microns. Therefore, they can be manufactured to be thin and light, which is a large advantage. Further, such light-emitting elements also have an advantage in that the period of time from when the carriers are injected until light is emitted is microseconds at the most, so they have a very high response speed. Moreover, because sufficient light emission can be obtained with a direct current voltage of approximately several to several tens of volts, power consumption is also relatively low.

EL elements have a wider viewing angle than that of liquid crystal elements and are preferable as display elements in the display portion102when a display region has a curved surface. In addition, EL elements are preferable as display elements in the display portion102in that unlike liquid crystal elements, EL elements do not require a backlight, which makes it possible to reduce power consumption, the number of components, and the total thickness.

Note that methods for manufacturing display elements over a flexible film are not limited to the method mentioned above (Japanese Published Patent Application No. 2003-174153). Methods and materials for manufacturing EL elements may be known methods and materials and are therefore not described here.

The display device used as the display portion102may only be capable of simply displaying single-color images or displaying numbers. Therefore, a passive-matrix display device may be used, in which case a display element may be manufactured over a flexible film using a method other than the technique disclosed in Japanese Published Patent Application No. 2003-174153.

The display module obtained by the above method is attached to the secondary battery103, and the secondary battery103and the display portion102are electrically connected to each other, whereby the electronic device100illustrated inFIG.1Bis completed. Furthermore, a metal cover, a plastic cover, or a rubber cover may be provided over a portion other than the display portion102to improve the appearance of the electronic device100.

In the case where the electronic device100is provided with the display portion, the screen size is not particularly limited as long as the display portion is of such a size that it can be disposed over the support structure body. For example, in the case where the electronic device is worn on an arm, the maximum screen size is the product of an arm girth of 23 cm and a wrist-to-elbow length because the girth of an adult arm near a wrist is 18 cm±5 cm. The wrist-to-elbow length of an adult is shorter than or equal to a feet (30.48 cm); thus, the maximum screen size of the display portion that can be disposed over the support structure body in the form of a cylinder tube in the electronic device100that is worn on an arm is 23 cm×30.48 cm. Note that the screen size here does not refer to the size in a curved state but refers to the size in a flat state. A plurality of display portions may be provided in one electronic device; for example, a second display portion smaller than a first display portion may be included in an electronic device. The dimension of the support structure body101is set larger than the screen size of the display portion. In the case of using EL elements, when the display portion is of such a screen size that it can be disposed over the support structure body, the sum of the weights of the display panel and the FPC can be more than or equal to 1 g and less than 10 g.

The thickness of the thinnest portion of the electronic device provided with the display portion (the thickness of the support structure body101, the display portion102, and the secondary battery103overlapping with each other) can be less than or equal to 5 mm. The thickness of the thickest portion of the electronic device, which is a portion where the display panel and the FPC are connected to each other, can be less than 1 cm.

The total weight of the electronic device100can be less than 100 g.

The electronic device100can be put on an arm because part of the support structure body can be moved in the direction of the arrows105illustrated inFIG.1A. The electronic device100has a total weight less than 100 g, preferably less than or equal to 50 g and a small maximum thickness less than or equal to 1 cm; thus, a lightweight electronic device can be provided.

The electronic device100has a plurality of curved surfaces with different radii of curvature in a cross-section as illustrated inFIG.7A.FIG.7Aillustrates a center700of curvature and a center701of curvature.

Description is given of the radius of curvature of a surface with reference toFIGS.9A to9C. InFIG.9A, on a plane1701along which a curved surface1700is cut, part of a curve1702is approximate to an arc of a circle, and the radius of the circle is referred to as a radius1703of curvature and the center of the circle is referred to as a center1704of curvature.FIG.9Bis a top view of the curved surface1700.FIG.9Cis a cross-sectional view of the curved surface1700taken along the plane1701. When a curved surface is cut along a plane, the radius of curvature of a curve depends on along which plane the curved surface is cut. Here, the radius of curvature of a curved surface is defined as the radius of curvature of a curve on a plane along which the curved surface is cut such that the curve has the smallest radius of curvature.

In the case of curving the electronic device100which has a lower arm contact surface (exposed back surface) of the exterior body on the inner side and a film surface (exposed front surface) of the display panel on the outer side, a radius1802of curvature of an exterior body1801(exposed back surface) on the side closer to a center1800of curvature of the secondary battery and in contact with a support structure body1805is smaller than a radius1804of curvature of a film1803on the side farther from the center1800of curvature (FIG.8A). When the electronic device100is curved and has an arc-shaped cross section, compressive stress is applied to the exposed back surface of the exterior body on the side closer to the center1800of curvature, and tensile stress is applied to the exposed surface of the film on the side farther from the center1800of curvature (FIG.8B). The electronic device100can change its shape such that the exterior body1801on the side closer to the center of curvature has a curvature radius greater than or equal to 10 mm, preferably greater than or equal to 30 mm.

Note that the cross-sectional shape of the electronic device100is not limited to a simple arc shape, and the cross-section of a portion in contact with a wrist can have an arc shape; for example, a shape illustrated inFIG.8Cor the like can be used. When the curved surface of the secondary battery has a shape with a plurality of centers of curvature, the electronic device100can change its shape such that a curved surface with the smallest radius of curvature among radii of curvature with respect to the plurality of centers of curvature, which is a surface of the exterior body1801on the side closer to the center of curvature, has a curvature radius greater than or equal to 10 mm, preferably greater than or equal to 30 mm.

FIG.7Billustrates a bottom view of the electronic device100which is seen from the exposed back surface side of the support structure body.FIG.7Cillustrates a side view of the electronic device100.

Embodiment 2

In this embodiment, an example of a method for charging a secondary battery using an antenna is described.

Since an electronic device is to be in contact with part of a human body, it is preferable for safety that input and output terminals for charging or discharging a secondary battery be not exposed. In the case where the input and output terminals are exposed, the input and output terminals might short-circuit by water such as rain, or the input and output terminals might be in contact with a human body and cause an electric shock. The use of an antenna enables a structure in which the input and output terminals are not exposed on a surface of the electronic device.

Note that this embodiment is the same as Embodiment 1 except that an antenna and an RF power feed converter are provided; therefore, the other components are not described in detail here.

In accordance with Embodiment 1, a flexible secondary battery is fixed to a support structure body, and a display module is attached to the secondary battery. An RF power feed converter and an antenna which are electrically connected to the secondary battery are provided. The RF power feed converter is fixed so as to overlap with part of a display portion.

The RF power feed converter and the antenna weigh less than or equal to 10 g, and the total weight does not significantly differ from that in Embodiment 1.

FIG.3illustrates a schematic diagram of an electronic device300including an antenna (not illustrated) and a charger301. When the electronic device300is disposed over the charger301, electric power can be supplied from an antenna of the charger301to the electronic device300to charge a secondary battery of the electronic device300.

Information such as the remaining amount or time to full charge can be displayed on a display portion of the electronic device300.

This embodiment can be freely combined with Embodiment 1.

Embodiment 3

In this embodiment, an example of a structure for preventing the formation of wrinkles or the leakage of an electrolytic solution which might occur when a secondary battery is curved is described with reference toFIGS.4A and4B.

In Embodiment 1, the secondary battery is sealed with the laminate film, and the periphery is fixed in one portion (in the cross-sectional view). Thus, if the sealing is broken at any place when the secondary battery is bent repeatedly or subjected to impact, the electrolytic solution leaks from the inside. In the case where the laminate film is fixed in one portion, bending stress due to repeated bending of or impact on the secondary battery is concentrated in that portion, whereby the sealing cannot be maintained.

In view of this, in this embodiment, two films are fixed in two portions as illustrated inFIG.4A.FIG.4Aillustrates a schematic cross-sectional view of a secondary battery400whose positive and negative electrodes are sealed with two films. By fixing in two portions, bending stress is relaxed and the sealing can be maintained.

A structural example different from that in Embodiment 1 is illustrated inFIG.4B.

FIG.4Billustrates an example in which a display portion402is provided on the front surface side of a support structure body401and the secondary battery400is disposed on the back surface side.

InFIG.4B, the support structure body401is provided with an opening, and an FPC403extending from the display portion402and an FPC404extending from the secondary battery are electrically connected to each other through the opening.

In this embodiment, the size of the opening provided in the support structure body401is not particularly limited, and as long as a certain degree of mechanical strength can be secured, the area of the opening may be larger than that of the display portion402, and the display portion may be set in the opening. In that case, the secondary battery400and the display portion402may be in contact with each other. As the size of the opening increases, the weight of the support structure body decreases. Thus, the total weight can be decreased.

This embodiment can be freely combined with Embodiment 1.

Example 1

FIG.5is a photograph of an electronic device which is manufactured in accordance with Embodiment 1 and is worn on an arm with an image displayed on a display portion.

The electronic device shown inFIG.5is 77 mm long, 60 mm wide, and 57 mm high, and the dimension is determined by a stainless steel support structure body. A display panel has an external size of 51.5 mm×92.15 mm, and the display region has a size of 42.12 mm×74.88 mm. The electronic device has a total weight of 40 g to 50 g, and the sum of the weights of the display panel and an FPC can be approximately 2 g. Note that the term “FPC” in this specification refers to a flexible printed wiring board, in which a plurality of metal foil (e.g., Cu, Ni, or Au) patterns are formed over a base member of a polyimide resin, an epoxy resin, or the like. An anisotropic conductive film (ACF) used for compression bonding is formed along a side of an end of the FPC so as to cross end portions of the plurality of arranged metal foil patterns. An external connection terminal of the display panel and the FPC are electrically connected to each other by compression bonding using the ACF provided over the FPC.

As a secondary battery, a laminated secondary battery is used, and as a positive electrode active material, lithium iron phosphate (LiFePO4) is used. Lithium iron phosphate can improve the safety of the secondary battery.

FIG.6is a schematic cross-sectional view of the secondary battery. In this secondary battery, sheet-like positive electrode current collectors601, sheet-like positive electrode active material layers602, separators607, negative electrode current collectors604, and negative electrode active material layers605are stacked, the other region is filled with an electrolytic solution610, and these components are enclosed by a film608and an exterior body609made of a film with a depressed portion.

As illustrated inFIG.6, the number of electrode layers is 16. The structure shown inFIG.6includes eight layers of negative current collectors604and eight layers of positive electrode current collectors601, i.e., 16 layers in total. Note that in a cross-section of a negative electrode extraction portion illustrated inFIG.6, the eight layers of negative electrode current collectors604are bonded by ultrasonic welding.

The thickness of the thinnest portion of the electronic device provided with the display portion (the thickness of the support structure body, the display portion, and the secondary battery overlapping with each other) is 3.2 mm. The thickness of the thickest portion of the electronic device, which is a portion where the display panel and the FPC are connected (a region where an external connection terminal is provided), is 6 mm. Note that an IC chip, a passive electronic component, or the like may be directly attached to the FPC. However, in that case, the IC chip or the like is not regarded as part of the FPC. In the case where a passive electronic component such as an L, C, or R component, a driver circuit IC chip, a CPU, a memory, or the like is directly attached to the FPC, that portion may be the thickest portion of the electronic device.

In this example, lithium iron phosphate is used as the positive electrode active material. By appropriately changing, for example, the positive electrode active material or the negative electrode active material so as to increase the volume energy density of the secondary battery, further reductions in size and weight can be achieved. For example, when lithium cobalt oxide (LiCoO2) is used as the positive electrode active material, the volume energy density is increased. Thus, when a secondary battery having the same capacity as that of this example is fabricated using lithium cobalt oxide, the secondary battery can be thinner and lighter.

Electric power for displaying the image shown inFIG.5is supplied only from the secondary battery overlapping with the display portion.

As a matter of course, the image displayed on the display portion inFIG.5is not processed and is the one actually displayed in full color. The resolution of the display portion inFIG.5is 326 ppi. Each pixel includes three transistors, and an oxide semiconductor (InGaO3(ZnO)m) is used in the transistors. Connection terminals for charging and for video signal inputting are provided in an end portion of the support structure body and are connected to an external charging device or an external driving device when the electronic device is not in use by a user, i.e., at the time of charging or video signal inputting. When the electronic device is in use by a user, i.e., worn on an arm with an image displayed, a cord such as a wiring is not connected to an external driving device.

The electronic device shown inFIG.5has a total weight of 50 g or less and is light when worn on an arm. In addition, the electronic device presents an appearance with an attractive design and can thus be used as an accessory.

EXPLANATION OF REFERENCE

100: electronic device,101: support structure body,102: display portion,103: secondary battery,104: FPC,105: arrow,201: positive electrode current collector,202: positive electrode active material layer,203: positive electrode,204: negative electrode current collector,205: negative electrode active material layer,206: negative electrode,207: separator,208: film,209: exterior body,210: electrolytic solution,300: electronic device,301: charger,400: secondary battery,401: support structure body,402: display portion,403: FPC,404: FPC,601: positive electrode current collector,602: positive electrode active material layer,604: negative electrode current collector,605: negative electrode active material layer,607: separator,608: film,609: exterior body, and610: electrolytic solution.

This application is based on Japanese Patent Application serial no. 2013-147187 filed with Japan Patent Office on Jul. 16, 2013, the entire contents of which are hereby incorporated by reference.