Niobium pentoxide

Example 1

Electrolytic zirconium powder as the source material was mixed with niobium powder and niobium pentoxide powder, proceeding from the required content of niobium and oxygen in the alloy. The powder mixture was used for pressing briquettes having an inner hole into which a recycled metal bar made of zirconium-niobium alloy was placed. The electrode made in this way was tied round with bars of zirconium iodide and twice melted. The obtained alloy ingot contained, in percent by weight: niobium—0.9, oxygen—0.053, unavoidable impurities, zirconium—the rest.

Example 2

This example illustrates a laboratory scale embodiment of a preferred process of the present invention for making niobium pentoxide precursor and a niobium pentoxide (Nb₂O₅) product of the present invention.

Reactor bath double boilers (filled with DI water) were set to 98° C. Stock solution of niobium oxyfluoride (concentration of 210 g niobium pentoxide/liter) was preheated to about 76° C. The niobium solution was added to the first reactor at an average rate of 13.1 ml/minute. Stock solution of 5N (7.8 wt. %) ammonia was also added to reactor one at an average rate of 98.2 ml/minute. These reactants were then agitated with a resultant average temperature and pH of 61° C. and 9.14, respectively.

The resulting suspension flowed into the second reactor where an additional 5.6 ml/minute of niobium oxyfluoride solution was added with agitation. The resultant average temperature and pH of reactor two were 73° C. and 8.28, respectively. The resulting suspension flowed into the third reactor for further mixing. The reaction was run for 315 minutes, prior to collection of samples, for a total of approximately eleven residence times, average residence time being 27 minutes.

Two liters of suspension were collected and filtered. The filtered cake was washed and re-slurried with two liters of 5N (7.8 wt. %) ammonia solution at about 85° C. The resulting slurry was then filtered. The wash and filtration were repeated four additional times. The resulting retained cake was dried for sixteen hours at 85° C. The dried cake was then calcined at 900° C. for four hours. The uncalcined cake weighed 223.5 g (44.3% moisture) and contained 460 ppm fluoride. The calcined cake weighed 85.8 g, containing 180 ppm fluoride and 73.5% of the material was larger than 96 microns in size.

The process conditions utilized and results obtained are also set forth in Table 1 below.

Example 1

A first transparent material layer, a metal layer, and a second transparent material layer were sequentially formed on a transparent substrate by using a thin film forming apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2014-34701 shown in FIG. 2. A COP film of 50 μm thickness was used as the transparent substrate.

The thin film forming apparatus can simultaneously laminate thin films of a plurality of materials in sequence, and in the present example, targets of niobium oxide, silver, and a composite oxide of zinc-tin are arranged in this order from the side closer to the film unwinding side. Each target is connected to an individual power source and can cause discharge by applying arbitrarily controllable power. Further, each target is housed in an independent container, and the partition wall separating the targets has only a small gap near the can roll, so that a substantially different gas atmosphere can be realized.

A film was formed by a sputtering method by evacuating the entire vacuum chamber of the thin film forming apparatus to 1×10⁻³ Pa or less, introducing argon gas into the first cathode part provided with niobium oxide in the vacuum chamber while adjusting the flow rate to be 150 sccm by a mass flow controller, and then applying power to the niobium oxide target to cause discharge. At this time, in order to suppress the light absorption of niobium oxide due to oxygen shortage, 6 sccm of oxygen was added to form a transparent oxide layer. The running speed of the film was 3 m/min. After measuring a relation between the electric power and the film thickness, the electric power was previously adjusted based on the measurement so that niobium oxide with a thickness of 46 nm could be formed at a running speed of 3 m/min.

After niobium oxide was formed at the first cathode part, a silver thin film was formed at the second cathode part. Specifically, a film was formed by a sputtering method by introducing argon gas into the second cathode part in the vacuum chamber while adjusting the flow rate to be 450 sccm by a mass flow controller, and then applying power to the silver target to cause discharge. Although two adjacent cathodes are used in this example, it is not necessary to use two adjacent cathodes. Depending on the configuration of the apparatus, the entire cathode chamber may be used as a partition wall instead of using one cathode chamber. After measuring a relation between the electric power and the film thickness, the electric power was previously adjusted based on the measurement so that silver film with a thickness of 9 nm could be formed at a running speed of 3 m/min.

After a silver thin film was formed at the second cathode part, a zinc-tin composite oxide was formed at the third cathode part. Specifically, a film was formed by a sputtering method by introducing argon gas into the third cathode part of the vacuum chamber while adjusting the flow rate to be 150 sccm by a mass flow controller, and then applying power to the zinc-tin composite oxide target to cause discharge. At this time, a small amount of oxygen was introduced separately from argon gas while adjusting the amount of oxygen by a mass flow controller so as not to cause poor conductivity due to insufficient oxygen or excessive oxygen to obtain an excellent transparent conductive oxide. Although two adjacent cathodes are used in this example, it is not necessary to use two adjacent cathodes. Depending on the configuration of the apparatus, one entire cathode chamber may be used as a partition wall instead of using individual cathode chambers. After measuring a relation between the electric power and the film thickness, the electric power was previously adjusted based on the measurement so that zinc-tin composite oxide with a thickness of 50 nm could be formed at a running speed of 3 m/min.

All the film thicknesses were calculated in advance by computer simulation and designed to have the highest transmittance.

After forming the three layers, a sample was prepared by continuously winding the film having the configure shown in FIG. 1, introducing air into the entire apparatus, and then taking out the sample.

A sample was prepared under the same conditions as in Example 1 except that zinc oxide was used as the first transparent material, the film thickness of which was adjusted to 64 nm, the silver film thickness was adjusted to 7 nm, and the zinc-tin composite oxide film thickness was adjusted to 46 nm.

Comparative Example 1 uses zinc oxide as the first transparent material layer. As shown in Table 1, in the sample of Comparative Example 1, the total light transmittance is greatly deteriorated in comparison with Example 3 having the same silver film thickness, and the light absorption is also increased, indicating that using zinc oxide as the first transparent material layer will increase the absorption.

Example 2

A sample was prepared under the same conditions as in Example 1 except that the niobium oxide film thickness was adjusted to 49 nm, the silver film thickness was adjusted to 8 nm, and the zinc-tin composite oxide film thickness was adjusted to 52 nm.

A sample was prepared under the same conditions as in Example 1 except that zinc-tin composite oxide was used as the first transparent material, the film thickness of which was adjusted to 77 nm, the silver film thickness was adjusted to 7 nm, and niobium oxide was used as the second transparent material, the film thickness of which was adjusted to 35 nm.

In Comparative Example 2, contrary to the structure shown in Examples 1 to 6, zinc-tin composite oxide was used for the first transparent material layer and niobium oxide was used for the second transparent material layer. As shown in Table 1, the sample of Comparative Example 2 has a lower total light transmittance and an increased light absorption as compared with Example 3 having the same silver film thickness. This implies that the mechanism causing the absorption at the interface between the first transparent material layer and the metal layer (silver) and the mechanism causing the absorption at the interface between the metal layer (silver) and the second transparent material layer are different.

Example 3

A sample was prepared under the same conditions as in Example 1 except that the niobium oxide film thickness was adjusted to 52 nm, the silver film thickness was adjusted to 7 nm, and the zinc-tin composite oxide film thickness was adjusted to 53 nm.

A sample was prepared under the same conditions as in Example 1 except that the niobium oxide film thickness was adjusted to 55 nm, the silver film thickness was adjusted to 6 nm, and the zinc-tin composite oxide film thickness was adjusted to 54 nm.

In Comparative Example 3, the structure was the same as in Examples 1 to 6, and the thickness of the metal layer (silver) was changed to be 6 nm. As shown in Table 1, in the sample of Comparative Example 3, reducing the thickness of the metal layer (silver) degraded the effect of the present disclosure since the continuity of the silver thin film could not be maintained, resulting in formation of an island-like structure in the film, so that the surface resistance rapidly increased and the amount of light absorption significantly increased.

Example 4

A sample was prepared under the same conditions as in Example 1 except that the niobium oxide film thickness was adjusted to 43 nm, the silver film thickness was adjusted to 10 nm, and the zinc-tin composite oxide film thickness was adjusted to 49 nm.

A sample was prepared under the same conditions as in Example 1 except that the niobium oxide film thickness was adjusted to 55 nm, the silver film thickness was adjusted to 7 nm, and niobium oxide was used as the second transparent material, the film thickness of which was adjusted to 42 nm.

In Comparative Example 4, both the first transparent material and the second transparent material were composed of niobium oxide. As shown in Table 1, in the sample of Comparative Example 4, the total light transmittance is degraded in comparison with Example 3 having the same silver film thickness, indicating that using a material containing zinc as the second transparent material will suppress light absorption. In addition, the surface resistance of the niobium oxide also increased because of its low conductivity.

Example 5

A sample was prepared under the same conditions as in Example 1 except that the niobium oxide film thickness was adjusted to 40 nm, the silver film thickness was adjusted to 11 nm, and the zinc-tin composite oxide film thickness was adjusted to 47 nm.

A sample was prepared under the same conditions as in Example 1 except that zinc oxide was used as the first transparent material, the film thickness of which was adjusted to 64 nm, the silver film thickness was adjusted to 7 nm, and zinc oxide was used as the second transparent material, the film thickness of which was adjusted to 46 nm.

Example 6

A sample was prepared under the same conditions as in Example 1 except that the niobium oxide film thickness was adjusted to 38 nm, the silver film thickness was adjusted to 12 nm, and the zinc-tin composite oxide film thickness was adjusted to 46 nm.

A sample was prepared under the same conditions as in Example 1 except that zinc oxide was used as the first transparent material, the film thickness of which was adjusted to 66 nm, the silver film thickness was adjusted to 7 nm, and indium-zinc composite oxide was used as the second transparent material, the film thickness of which was adjusted to 44 nm.

Example 7

A sample was prepared under the same conditions as in Example 1 except that titanium oxide was used as the first transparent material, the film thickness of which was adjusted to 39 nm, the silver film thickness was adjusted to 10 nm, and the zinc-tin composite oxide film thickness was adjusted to 52 nm.

A sample was prepared under the same conditions as in Example 1 except that zinc oxide was used as the first transparent material, the film thickness of which was adjusted to 58 nm, the silver film thickness was adjusted to 7 nm, and aluminum-zinc composite oxide was used as the second transparent material, the film thickness of which was adjusted to 51 nm.

Example 8

A sample was prepared under the same conditions as in Example 1 except that zirconium oxide was used as the first transparent material, the film thickness of which was adjusted to 71 nm, the silver film thickness was adjusted to 7 nm, and the zinc-tin composite oxide film thickness was adjusted to 42 nm.

A sample was prepared under the same conditions as in Example 1 except that zinc oxide was used as the first transparent material, the film thickness of which was adjusted to 74 nm, the silver film thickness was adjusted to 8 nm, and titanium oxide was used as the second transparent material, the film thickness of which was adjusted to 31 nm.

Evaluation Results

Each sample was cut to an arbitrary size and then measured and evaluated. The surface resistance was measured in accordance with “JIS K-7194” by using “Loresta GP (registered trademark) (available from Dia Instruments)”.

The total light transmittance was measured in accordance with “JIS K-7105” by using “NDH 5000 (available from Nippon Denshoku Industries)”.

The transmittance and reflectance at an incidence angle of 5° were measured by using a spectroscope “U-4100 (available from Hitachi High Technologies)”, and the light absorption amount for each value at a wavelength of 550 nm was defined by the following equation (1).
Light Absorption (%)=100(%)−(Transmittance (%)+Reflectance (%))  (1)

In other words, the light which are neither reflected nor transmitted was regarded as being converted into (absorbed as) heat in the thin film and the substrate. In practice, although light absorption may appear to increase because of the substantial reduction in transmittance and reflectance due to scattering or the like, since the substrate used in the present disclosure is extremely small in absorption and has a smooth surface, the light absorption obtained by the above formula (1) can be substantially regarded as the absorption by the laminated films.

In the present disclosure, it is preferable that the surface resistance should be as low as possible and the total light transmittance should be as high as possible. Generally-used ITO (Indium Tin composite Oxide) films usually have a total light transmittance of around 88% at a surface resistance of 100 Ω/square, though this depends on the film thickness of ITO. Therefore, in order to prove the superiority of the present disclosure, the resistance value is preferably 20 Ω/square or less and the total light transmittance is preferably 90% or more.

Example 9

A sample was prepared under the same conditions as in Example 1 except that hafnium oxide was used as the first transparent material, the film thickness of which was adjusted to 62 nm, the silver film thickness was adjusted to 7 nm, and the zinc-tin composite oxide film thickness was adjusted to 47 nm.

Example 10

A sample was prepared under the same conditions as in Example 1 except that tantalum pentoxide was used as the first transparent material, the film thickness of which was adjusted to 58 nm, the silver film thickness was adjusted to 7 nm, and the zinc-tin composite oxide film thickness was adjusted to 50 nm.

Example 11

A sample was prepared under the same conditions as in Example 1 except that tungsten oxide was used as the first transparent material, the film thickness of which was adjusted to 63 nm, the silver film thickness was adjusted to 7 nm, and the zinc-tin composite oxide film thickness was adjusted to 47 nm.

Example 12

A sample was prepared under the same conditions as in Example 1 except that molybdenum oxide was used as the first transparent material, the film thickness of which was adjusted to 65 nm, the silver film thickness was adjusted to 7 nm, and the zinc-tin composite oxide film thickness was adjusted to 48 nm.

Example 13

A sample was prepared under the same conditions as in Example 1 except that the niobium oxide film thickness was adjusted to 51 nm, the silver film thickness was adjusted to 7 nm, and zinc oxide was used as the second transparent material, the film thickness of which was adjusted to 53 nm.

Example 14

A sample was prepared under the same conditions as in Example 1 except that the niobium oxide film thickness was adjusted to 53 nm, the silver film thickness was adjusted to 7 nm, and indium-zinc composite oxide was used as the second transparent material, the film thickness of which was adjusted to 51 nm.

Example 15

A sample was prepared under the same conditions as in Example 1 except that the niobium oxide film thickness was adjusted to 47 nm, the silver film thickness was adjusted to 7 nm, and aluminum-zinc composite oxide was used as the second transparent material, the film thickness of which was adjusted to 58 nm.

EXAMPLE 1

• • Step 1, deionized water that was 1.75 times the loose packing volume of all raw materials for a bottom coating layer was provided.
  • Step 2, the deionized water was added to 25 g of sodium silicate, and they were stirred to be uniform, obtaining a mixture I.
  • Step 3, 2 g of lanthanum oxide, 2 g of niobium pentoxide, 15 g of aluminum oxide, 9 g of bismuth oxide, 2 g of boron oxide, 2 g of zinc oxide, 2 g of silicon oxide, 7 g of titanium dioxide, and 3 g of titanium nitride, each of which had a particle size of 1-10 μm respectively, were mixed and ball milled in a high-energy ball mill for 4-6 h, obtaining a further refined powder mixture II.
  • Step 4, 12 g of graphite fluoride with a thickness of 1-10 μm and a particle size of 1-30 μm, and 4 g of nano silicon carbide whisker with a length of 10-60 μm were added to the powder mixture II obtained in step 3, and they were stirred in a mixer for 0.5-1 h at a stirring rate of 50-150 rpm, obtaining a mixture III.
  • Step 5, the mixture I obtained in step 2 was added to the mixture III obtained in step 4, and they were stirred in a mixer for 0.5-1 h at a stirring rate of 50-150 rpm, obtaining a bottom coating.
  • Step 6, deionized water that was 1.75 times the loose packing volume of all raw materials for a surface coating layer was provided.
  • Step 7, the deionized water was added to 25 g of the sodium silicate, and they were stirred to be uniform, obtaining a mixture IV.
  • Step 8, 2 g of lanthanum oxide, 2 g of niobium pentoxide, 7 g of chromium oxide, 7 g of aluminum oxide, 9 g of bismuth oxide, 2 g of boron oxide, 2 g of zinc oxide, 2 g of silicon oxide, 3 g of titanium nitride, 7 g of silicon carbide, 4 g of nano silicon carbide whisker, and 4 g of cobalt green, each of which had a particle size of 1-10 μm respectively, were mixed and ball milled in a high-energy ball mill for 4-6 h, obtaining a further refined powder mixture V.
  • Step 9, 12 g of graphite fluoride with a thickness of 1-10 μm and a particle size of 1-30 μm, and 4 g of nano silicon carbide whisker with a length of 10-60 μm were added to the powder mixture V obtained in step 8, and they were stirred in a mixer for 0.5-1 h at a stirring rate of 50-150 rpm, obtaining a mixture VI.
  • Step 10, the mixture IV obtained in step 7 was added to the mixture VI obtained in step 9, and they were stirred in a mixer for 0.5-1 h at a stirring rate of 50-150 rpm, obtaining a surface coating.
  • Step 11, the environment was inspected, and a temperature of 25° C. and a relative humidity of 60% were maintained in the construction environment, and the temperature of a substrate was ensured to be at least 3° C. higher than the dew point temperature.
  • Step 12, a surface of the substrate was pretreated by using a sandblasting technology until a cleanliness of Sa3.0 level and a roughness of 25-75 μm were reached.
  • Step 13, the coating was stirred again at 50-150 rpm for 0.5-1 h before spraying. The bottom coating was sprayed onto the surface of the substrate by using an air atomization spray gun, and dried. The thickness of the bottom coating layer was measured, and controlled to be 50-100 μm. When the thickness of the bottom coating layer was qualified, the surface coating was sprayed onto the bottom coating layer, and dried. The overall thickness of the ceramic coating was measured, and controlled to be 200-300 μm. When the overall thickness was qualified, the substrate sample with the two-layer-compounded coating was heated to 400° C. and maintained at the temperature for 30 min, obtaining the anti-corrosion and anti-coking ceramic coating with easy state identification.

The cross-sectional structure of the ceramic coating obtained in Example 1 is shown in FIG. 1. As can be seen from FIG. 1, the bottom coating layer is well combined with the substrate; the bottom coating layer is well combined with the surface coating layer with no obvious gap; the internal structure of the ceramic coating is dense with no visible pores. In the present disclosure, the powder of raw materials is refined by using a high-energy ball mill, such that a micro-nano-scale rough structure with low surface energy is formed on the surface of the prepared ceramic coating, as shown in FIG. 2. Table 1 shows test results of key use parameters such as bonding strength and thermal shock performance of the ceramic coating. The results show that the ceramic coating exhibits a bonding strength of about 38 MPa, and could withstand at least 80-time thermal shock test, indicating that the ceramic coating exhibits excellent reliability in use. FIGS. 3A-3B shows an operating state of a water wall in a combustion region of a boiler of a power station in Hami, China before renovation by using the ceramic coating according to the present disclosure. As shown in FIGS. 3A-3B, the surface of the water wall is seriously coked and there is high-temperature corrosion (FIG. 3A shows the coking situation, and FIG. 3B shows the surface corrosion after coke cleaning). FIG. 4 shows a state of the water wall in this area after operation of 14,000 h, the water wall being renovated by using the ceramic coating according to the present disclosure. As shown in FIG. 4, there is no coking and slagging on the surface of the water wall, and the high-temperature corrosion is completely alleviated.

FIG. 5 shows an inspection situation of a water wall of a boiler of a power station in Changji, China after operation of 8,000 h, the water wall being renovated by using the ceramic coating according to the present disclosure. As shown in FIG. 5, the current operating state of the ceramic coating can be directly judged by visual inspection (a green area represents that the current surface coating layer is in good condition; a white area represents a loss of the surface coating layer, and a further surface coating needs to be re-sprayed onto the white bottom coating layer).

The foregoing description is only preferred implementations of the present disclosure. It should be noted that a person of ordinary skill in the art can also make several improvements and modifications without departing from the principle of the present disclosure. These improvements and modifications should also fall within the scope of the present disclosure.

Example 1

First, FIG. 12A illustrates a structure body 191 used for fabrication of a power storage device. FIG. 12B is an enlarged view of a region 60 illustrated in FIG. 12A.

The structure body 191 has a depression 192. The surface of the depression 192 is preferably polished to a mirror-smooth state to have improved planarity. The depression 192 is provided with an uneven structure 192a.

The depths, widths, and interval length of depressions of the uneven structure 192a can be determined in accordance with the heights, widths, and interval length of projections of the uneven structure to be formed on a member with rubber elasticity. Note that the depths, widths, and interval lengths of all the depressions can be either equal to or different from each other. For example, in the case where the battery unit 120 has both a portion resistant to bending stress and a portion susceptible to bending damage, the sizes and interval lengths of depressions are varied between the portions so that the portion susceptible to bending damage is prevented from being bent so much and the portion resistant to bending stress can be bent with an acute angle.

Note that the uneven structure 192a is not limited to the structure with a plurality of depressions. The uneven structure 192a may include a plurality of projections. In that case, the member with rubber elasticity can be provided with a plurality of depressions corresponding to the plurality of projections.

For example, a metallic mold can be used as the structure body 191. A material used for the structure body 191 is not limited to metal. For example, a material such as glass, ceramic, an organic resin, or wood may be used for the structure body 191.

In fabricating a power storage device, two structure bodies 191 are made to overlap with each other such that the depressions 192 face each other as illustrated in FIG. 12C. Next, the battery unit 120 is disposed in a space surrounded by the two depressions 192.

Although two structure bodies 191 are used in FIG. 12C, one embodiment of the present invention is not limited to this example. Two structure bodies with different shapes may be used. The depressions 192 of the two structure bodies can have either the same shape or different shapes, for example. Furthermore, the uneven structures 192a of the two structure bodies can have either the same shape or different shapes. Note that the use of a structure body provided with the uneven structure 192a on the depression 192 and a structure body with the flat depression 192 enables formation of the uneven structure on only one surface of the power storage device. Thus, for example, the power storage device 100 in FIG. 1A and the like can be fabricated.

Part of the battery unit 120 may be exposed to the outside of the space surrounded by the two depressions 192. FIG. 12D illustrates an example where electrode leads 123 (a positive electrode lead and a negative electrode lead) of the battery unit 120 are exposed to the outside of the space surrounded by the two depressions 192. Furthermore, part of an exterior body and the like may be exposed. Furthermore, the whole battery unit 120 may be located inside the space surrounded by the two depressions 192. For example, the whole light-emitting unit is disposed inside the space surrounded by the two depressions 192, whereby the light-emitting device 150 (see FIG. 9A and the like) can be fabricated.

Next, the space surrounded by the two depressions 192 is filled with a liquid filler 195. As the filler 195, for example, a high molecular material can be used. The filler 195 may exhibit a light transmitting property after being cured. As the filler 195, a single-component-type material that does not need a curing agent or a two-component-type material that is cured by mixing a main agent and a curing agent can be used, for example. Alternatively, a material that is cured by heating, irradiation with light such as ultraviolet light can be used. The filler 195 may include a desiccant that inhibits passage of moisture.

In this embodiment, a two-component-type material that becomes light-transmitting silicone rubber after being cured is used as the filler 195.

The filler 195 is cured so as to reflect the shape of the two depressions 192, whereby the member 109 with rubber elasticity can be formed. After the formation of the member 109 with rubber elasticity, the two structure bodies 191 are separated. Note that it is preferable to apply a remover onto surfaces of the depressions 192 before the space is filled with the filler 195, in which case the member 109 with rubber elasticity can be separated easily from the structure bodies 191.

FIG. 32A illustrates a battery unit 500. Although FIG. 32A illustrates a mode of a thin storage battery as an example of the battery unit 500, one embodiment of the present invention is not limited to this example. For example, a storage battery using a wound body or a cylindrical or coin-type storage battery can be used in the power storage device of one embodiment of the present invention.

As illustrated in FIG. 32A, the battery unit 500 includes a positive electrode 503, a negative electrode 506, a separator 507, and an exterior body 509. The battery unit 500 may include a positive electrode lead 510 and a negative electrode lead 511.

FIGS. 33A and 33B each illustrate an example of a cross-sectional view along dashed-dotted line A1-A2 in FIG. 32A. FIGS. 33A and 33B each illustrate a cross-sectional structure of the battery unit 500 that is formed using a pair of the positive electrode 503 and the negative electrode 506.

As illustrated in FIGS. 33A and 33B, the battery unit 500 includes the positive electrode 503, the negative electrode 506, the separator 507, an electrolytic solution 508, and the exterior bodies 509. The separator 507 is interposed between the positive electrode 503 and the negative electrode 506. A space surrounded by the exterior bodies 509 is filled with the electrolytic solution 508.

The positive electrode 503 includes a positive electrode active material layer 502 and a positive electrode current collector 501. The negative electrode 506 includes a negative electrode active material layer 505 and a negative electrode current collector 504. The active material layer can be formed on one or both surfaces of the current collector. The separator 507 is positioned between the positive electrode current collector 501 and the negative electrode current collector 504.

The battery unit includes one or more positive electrodes and one or more negative electrodes. For example, the battery unit can have a layered structure including a plurality of positive electrodes and a plurality of negative electrodes.

FIG. 34A illustrates another example of a cross-sectional view along dashed-dotted line A1-A2 in FIG. 32A. FIG. 34B is a cross-sectional view along dashed-dotted line B1-B2 in FIG. 32A.

FIGS. 34A and 34B each illustrate a cross-sectional structure of the battery unit 500 that is formed using a plurality of pairs of the positive and negative electrodes 503 and 506. There is no limitation on the number of electrode layers of the battery unit 500. In the case of using a large number of electrode layers, the power storage device can have high capacity. In contrast, in the case of using a small number of electrode layers, the power storage device can have a small thickness and high flexibility.

The examples in FIGS. 34A and 34B each include two positive electrodes 503 in each of which the positive electrode active material layer 502 is provided on one surface of the positive electrode current collector 501; two positive electrodes 503 in each of which the positive electrode active material layers 502 are provided on both surfaces of the positive electrode current collector 501; and three negative electrodes 506 in each of which the negative electrode active material layers 505 are provided on both surfaces of the negative electrode current collector 504. In other words, the battery unit 500 includes six positive electrode active material layers 502 and six negative electrode active material layers 505. Note that although the separator 507 has a bag-like shape in the examples illustrated in FIGS. 34A and 34B, the present invention is not limited to this example and the separator 507 may have a strip shape or a bellows shape.

FIG. 32B illustrates the appearance of the positive electrode 503. The positive electrode 503 includes the positive electrode current collector 501 and the positive electrode active material layer 502.

FIG. 32C illustrates the appearance of the negative electrode 506. The negative electrode 506 includes the negative electrode current collector 504 and the negative electrode active material layer 505.

The positive electrode 503 and the negative electrode 506 preferably include tab regions so that a plurality of stacked positive electrodes can be electrically connected to each other and a plurality of stacked negative electrodes can be electrically connected to each other. Furthermore, an electrode lead is preferably electrically connected to the tab region.

As illustrated in FIG. 32B, the positive electrode 503 preferably includes the tab region 281. The positive electrode lead 510 is preferably welded to part of the tab region 281. The tab region 281 preferably includes a region where the positive electrode current collector 501 is exposed. When the positive electrode lead 510 is welded to the region where the positive electrode current collector 501 is exposed, contact resistance can be further reduced. Although FIG. 32B illustrates the example where the positive electrode current collector 501 is exposed in the entire tab region 281, the tab region 281 may partly include the positive electrode active material layer 502.

As illustrated in FIG. 32C, the negative electrode 506 preferably includes the tab region 282. The negative electrode lead electrode 511 is preferably welded to part of the tab region 282. The tab region 282 preferably includes a region where the negative electrode current collector 504 is exposed. When the negative electrode lead electrode 511 is welded to the region where the negative electrode current collector 504 is exposed, contact resistance can be further reduced. Although FIG. 32C illustrates the example where the negative electrode current collector 504 is exposed in the entire tab region 282, the tab region 282 may partly include the negative electrode active material layer 505.

Although FIG. 32A illustrates the example where the ends of the positive electrode 503 and the negative electrode 506 are substantially aligned with each other, part of the positive electrode 503 may extend beyond the end of the negative electrode 506.

In the battery unit 500, the area of a region where the negative electrode 506 does not overlap with the positive electrode 503 is preferably as small as possible.

In the example illustrated in FIG. 33A, the end of the negative electrode 506 is located inward from the end of the positive electrode 503. With this structure, the entire negative electrode 506 can overlap with the positive electrode 503 or the area of the region where the negative electrode 506 does not overlap with the positive electrode 503 can be small.

The areas of the positive electrode 503 and the negative electrode 506 in the battery unit 500 are preferably substantially equal. For example, the areas of the positive electrode 503 and the negative electrode 506 that face each other with the separator 507 therebetween are preferably substantially equal. For example, the areas of the positive electrode active material layer 502 and the negative electrode active material layer 505 that face each other with the separator 507 therebetween are preferably substantially equal.

For example, as illustrated in FIGS. 34A and 34B, the area of the positive electrode 503 on the separator 507 side is preferably substantially equal to the area of the negative electrode 506 on the separator 507 side. When the area of a surface of the positive electrode 503 on the negative electrode 506 side is substantially equal to the area of a surface of the negative electrode 506 on the positive electrode 503 side, the region where the negative electrode 506 does not overlap with the positive electrode 503 can be small (does not exist, ideally), whereby the battery unit 500 can have reduced irreversible capacity. Alternatively, as illustrated in FIGS. 34A and 34B, the area of the surface of the positive electrode active material layer 502 on the separator 507 side is preferably substantially equal to the area of the surface of the negative electrode active material layer 505 on the separator 507 side.

As illustrated in FIGS. 34A and 34B, the end of the positive electrode 503 and the end of the negative electrode 506 are preferably substantially aligned with each other. Ends of the positive electrode active material layer 502 and the negative electrode active material layer 505 are preferably substantially aligned with each other.

In the example illustrated in FIG. 33B, the end of the positive electrode 503 is located inward from the end of the negative electrode 506. With this structure, the entire positive electrode 503 can overlap with the negative electrode 506 or the area of the region where the positive electrode 503 does not overlap with the negative electrode 506 can be small. In the case where the end of the negative electrode 506 is located inward from the end of the positive electrode 503, a current sometimes concentrates at the end portion of the negative electrode 506. For example, concentration of a current in part of the negative electrode 506 results in deposition of lithium on the negative electrode 506 in some cases. By reducing the area of the region where the positive electrode 503 does not overlap with the negative electrode 506, concentration of a current in part of the negative electrode 506 can be inhibited. As a result, for example, deposition of lithium on the negative electrode 506 can be inhibited, which is preferable.

As illustrated in FIG. 32A, the positive electrode lead 510 is preferably electrically connected to the positive electrode 503. Similarly, the negative electrode lead 511 is preferably electrically connected to the negative electrode 506. The positive electrode lead 510 and the negative electrode lead 511 are exposed to the outside of the exterior body 509 so as to serve as terminals for electrical contact with an external portion.

The positive electrode current collector 501 and the negative electrode current collector 504 can double as terminals for electrical contact with an external portion. In that case, the positive electrode current collector 501 and the negative electrode current collector 504 may be arranged such that part of the positive electrode current collector 501 and part of the negative electrode current collector 504 are exposed to the outside of the exterior body 509 without using electrode leads.

Although the positive electrode lead 510 and the negative electrode lead 511 are provided on the same side of the battery unit 500 in FIG. 32A, the positive electrode lead 510 and the negative electrode lead 511 may be provided on different sides of the battery unit 500 as illustrated in FIG. 35. The electrode leads of the battery unit of one embodiment of the present invention can be freely positioned as described above; therefore, the degree of freedom in design is high. Accordingly, a product including the battery unit of one embodiment of the present invention can have a high degree of freedom in design. Furthermore, a yield of products each including the battery unit of one embodiment of the present invention can be increased.

The components of the battery unit will be described in detail below.

<<Current Collector>>

There is no particular limitation on the current collector as long as it has high conductivity without causing a significant chemical change in a power storage device. For example, the positive electrode current collector and the negative electrode current collector can each be formed using a metal such as stainless steel, gold, platinum, zinc, iron, nickel, copper, aluminum, titanium, tantalum, or manganese, an alloy thereof, sintered carbon, or the like. Alternatively, copper or stainless steel that is coated with carbon, nickel, titanium, or the like may be used. Alternatively, the current collectors can each be formed using an aluminum alloy to which an element that improves heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, is added. Still alternatively, a metal element that forms silicide by reacting with silicon can be used to form the current collectors. Examples of the metal element that forms silicide by reacting with silicon include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel.

An irreversible reaction with an electrolytic solution is sometimes caused on a surface of the current collector. Thus, the current collector preferably has low reactivity with an electrolytic solution. Stainless steel or the like is preferably used for the current collector, in which case reactivity with an electrolytic solution can be lowered in some cases, for example.

The positive electrode current collector and the negative electrode current collector can each have any of various shapes including 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, a porous shape, and a shape of non-woven fabric as appropriate. The positive electrode current collector and the negative electrode current collector may each be formed to have micro irregularities on the surface thereof in order to enhance adhesion to the active material layer. The positive electrode current collector and the negative electrode current collector each preferably have a thickness of 5 μm to 30 μm inclusive.

An undercoat layer may be provided over part of a surface of the current collector. The undercoat layer is a coating layer provided to reduce contact resistance between the current collector and the active material layer or to improve adhesion between the current collector and the active material layer. Note that the undercoat layer is not necessarily formed over the entire surface of the current collector and may be partly formed to have an island-like shape. In addition, the undercoat layer may serve as an active material to have capacity. For the undercoat layer, a carbon material can be used, for example. Examples of the carbon material include carbon black such as acetylene black, a carbon nanotube, and graphite. Examples of the undercoat layer include a metal layer, a layer containing carbon and high molecular compounds, and a layer containing metal and high molecular compounds.

<<Active Material Layer>>

The active material layer includes the active material. An active material refers only to a material that is involved in insertion and extraction of ions that are carriers. In this specification and the like, a material that is actually an “active material” and the material including a conductive additive, a binder, and the like are collectively referred to as an active material layer.

The positive electrode active material layer includes one or more kinds of positive electrode active materials. The negative electrode active material layer includes one or more kinds of negative electrode active materials.

The positive electrode active material and the negative electrode active material have a central role in battery reactions of a power storage device, and receive and release carrier ions. To increase the lifetime of the power storage device, the active materials preferably have a little capacity involved in irreversible battery reactions, and have high charge and discharge efficiency.

For the positive electrode active material, a material into and from which carrier ions such as lithium ions can be inserted and extracted can be used. Examples of a positive electrode active material include materials having an olivine crystal structure, a layered rock-salt crystal structure, a spinel crystal structure, and a NASICON crystal structure.

As the positive electrode active material, a compound such as LiFeO₂, LiCoO₂, LiNiO₂, or LiMn₂O₄, V₂O₅, Cr₂O₅, or MnO₂ can be used.

As an example of a material having an olivine crystal structure, lithium-containing complex phosphate (LiMPO₄ (general formula) (M is one or more of Fe(II), Mn(II), Co(II), and Ni(II))) can be given. Typical examples of LiMPO₄ are compounds such as LiFePO₄, LiNiPO₄, LiCoPO₄, LiMnPO₄, LiFe_aNi_bPO₄, LiFe_aCo_bPO₄, LiFe_aMn_bPO₄, LiNi_aCo_bPO₄, LiNi_aMn_bPO₄ (a+b≤1, 0<a<1, and 0<b<1), LiFe_cNi_dCo_ePO₄, LiFe_cNi_dMn_ePO₄, LiNi_cCo_dMn_ePO₄ (c+d+e≤1, 0<c<1, 0<d<1, and 0<e<1), and LiFe_fNi_gCo_hMn_iPO₄ (f+g+h+i≤1, 0<f<1, 0<g<1, 0<h<1, and 0<i<1).

For example, lithium iron phosphate (LiFePO₄) is 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).

The use of LiFePO₄ for the positive electrode active material allows fabrication of a highly safe power storage device that is stable against an external load such as overcharging. Such a power storage device is particularly suitable for, for example, a mobile device, a wearable device, and the like.

Examples of a material with a layered rock-salt crystal structure include lithium cobalt oxide (LiCoO₂), LiNiO₂, LiMnO₂, Li₂MnO₃, a NiCo-containing material (general formula: LiNi_xCo_1-xO₂ (0<x<1)) such as LiNi_0.8Co_0.2O₂, a NiMn-containing material (general formula: LiNi_xMn_1-xO₂ (0<x<1)) such as LiNi_0.5Mn_0.5O₂, a NiMnCo-containing material (also referred to as NMC) (general formula: LiNi_xMn_yCo_1-x-yO₂ (x>0, y>0, x+y<1)) such as LiNi_1/3Mn_1/3Co_1/3O₂. Moreover, Li(Ni_0.8Co_0.15Al_0.05)O₂, Li₂MnO₃—LiMO₂ (M=Co, Ni, or Mn), and the like can be given as the examples.

In particular, LiCoO₂ is preferable because it has advantages such as high capacity, higher stability in the air than that of LiNiO₂, and higher thermal stability than that of LiNiO₂.

Examples of a material with a spinel crystal structure include LiMn₂O₄, Li_1+xMn_2−xO₄ (0<x<2), LiMn_2−xAl_xO₄ (0<x<2), and LiMn_1.5Ni_0.5O₄.

It is preferred that a small amount of lithium nickel oxide (LiNiO₂ or LiNi_1−xMxO₂ (0<x<1, M=Co, Al, or the like)) be added to a material with a spinel crystal structure that contains manganese, such as LiMn₂O₄, in which case advantages such as inhibition of the dissolution of manganese and the decomposition of an electrolytic solution can be obtained.

Alternatively, a lithium-containing complex silicate expressed by Li_(2−j)MSiO₄ (general formula) (M is one or more of Fe(II), Mn(II), Co(II), or Ni(II); 0≤j≤2) may be used as the positive electrode active material. Typical examples of the general formula Li_(2−j)MSiO₄ are compounds such as Li_(2−j)FeSiO₄, Li_(2−j)NiSiO₄, Li_(2−j)CoSiO₄, Li_(2−j)MnSiO₄, Li_(2−j)Fe_kNi_lSiO₄, Li_(2−j)Fe_kCo_lSiO₄, Li_(2−j)Fe_kMn_lSiO₄, Li_(2−j)Ni_kCo_lSiO₄, Li_(2−j)Ni_kMn_lSiO₄ (k+l≤1, 0<k<1, and 0<l<1), Li_(2−j)Fe_mNi_nCo_qSiO₄, Li_(2−j)Fe_mNi_nMn_qSiO₄, Li_(2−j)Ni_mCo_nMn_qSiO₄ (m+n+q≤1, 0<m<1, 0<n<1, and 0<q<1), and Li_(2−j)Fe_rNi_sCo_tMn_uSiO₄ (r+s+t+u≤1, 0<r<1, 0<s<1, 0<t<1, and 0<u<1).

Still alternatively, a NASICON compound expressed by A_xM₂(XO₄)₃ (general formula) (A=Li, Na, or Mg, M=Fe, Mn, Ti, V, Nb, or Al, X=S, P, Mo, W, As, or Si) can be used for the positive electrode active material. Examples of the NASICON compound are Fe₂(MnO₄)₃, Fe₂(SO₄)₃, and Li₃Fe₂(PO₄)₃.

Further alternatively, for example, a compound expressed by Li₂MPO₄F, Li₂MP₂O₇, or Li₅MO₄ (general formula) (M=Fe or Mn), a perovskite fluoride such as FeF₃, a metal chalcogenide (a sulfide, a selenide, or a telluride) such as TiS₂ and MoS₂, a lithium-containing material with an inverse spinel structure such as LiMVO₄ (M=Mn, Co, or Ni), a vanadium oxide (V₂O₅, V₆O₁₃, LiV₃O₈, or the like), a manganese oxide, or an organic sulfur compound can be used as the positive electrode active material.

Further alternatively, any of the aforementioned materials may be combined to be used as the positive electrode active material. For example, a solid solution obtained by combining two or more of the above materials can be used as the positive electrode active material. For example, a solid solution of LiCo_1/3Mn_1/3Ni_1/3O₂ and Li₂MnO₃ can be used as the positive electrode active material.

In the case where carrier ions are alkali metal ions other than lithium ions, or alkaline-earth metal ions, a compound containing carriers such as an alkali metal (e.g., sodium and potassium) or an alkaline-earth metal (e.g., calcium, strontium, barium, beryllium, and magnesium) instead of lithium of the lithium compound, the lithium-containing complex phosphate, or the lithium-containing complex silicate may be used as the positive electrode active material.

The average diameter of primary particles of the positive electrode active material is preferably, for example, greater than or equal to 5 nm and less than or equal to 100 μm.

For example, lithium-containing complex phosphate having an olivine crystal structure used for the positive electrode active material has a one-dimensional lithium diffusion path, so that lithium diffusion is slow. Thus, in the case of using lithium-containing complex phosphate having an olivine crystal structure, the average diameter of particles of the positive electrode active material is, for example, preferably greater than or equal to 5 nm and less than or equal to 1 μm so that the charge and discharge rate is increased. The specific surface area of the positive electrode active material is, for example, preferably greater than or equal to 10 m²/g and less than or equal to 50 m²/g.

An active material having an olivine crystal structure is much less likely to be changed in the crystal structure by charging and discharging and has a more stable crystal structure than, for example, an active material having a layered rock-salt crystal structure. Thus, a positive electrode active material having an olivine crystal structure is stable against operation such as overcharging. The use of such a positive electrode active material allows fabrication of a highly safe power storage device.

As the negative electrode active material, for example, a carbon-based material, an alloy-based material, or the like can be used.

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. In addition, examples of the shape of the graphite include a flaky shape and a spherical shape.

Graphite has a low potential substantially equal to that of a lithium metal (higher than or equal to 0.1 V and lower than or equal 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 preferred 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 example, in the case where carrier ions are lithium ions, a material including at least one of Mg, Ca, Ga, Si, Al, Ge, Sn, Pb, As, Sb, Bi, Ag, Au, Zn, Cd, Hg, In, and the like can be used as the alloy-based material. Such elements have a higher capacity than carbon. In particular, silicon has a high theoretical capacity of 4200 mAh/g, and therefore, the capacity of the power storage device can be increased. Examples of an alloy-based material (compound-based material) using such elements include Mg₂Si, Mg₂Ge, Mg₂Sn, SnS₂, V₂Sn₃, FeSn₂, CoSn₂, Ni₃Sn₂, Cu₆Sn₅, Ag₃Sn, Ag₃Sb, Ni₂MnSb, CeSb₃, LaSn₃, La₃Co₂Sn₇, CoSb₃, InSb, and SbSn.

Alternatively, for the negative electrode active material, an oxide such as SiO, SnO, SnO₂, titanium dioxide (TiO₂), lithium titanium oxide (Li₄Ti₅O₁₂), lithium-graphite intercalation compound (Li_xC₆), niobium pentoxide (Nb₂O₅), tungsten oxide (WO₂), or molybdenum oxide (MoO₂) can be used. Here, SiO is a compound containing silicon and oxygen. When the atomic ratio of silicon to oxygen is represented by α:β, α preferably has an approximate value of β. Here, when α has an approximate value of β, an absolute value of the difference between α and β is preferably less than or equal to 20% of a value of β, more preferably less than or equal to 10% of a value of β.

Still alternatively, for the negative electrode active material, Li_3−xM_xN (M=Co, Ni, or Cu) with a Li₃N structure, which is a nitride containing lithium and a transition metal, can be used. For example, Li_2.6Co_0.4N₃ is preferable because of high charge and discharge capacity (900 mAh/g and 1890 mAh/cm³).

When a nitride containing lithium and a transition metal is used, 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 that does not contain lithium ions, such as V₂O₅ or 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 that causes a conversion reaction can be used for the negative electrode active material; for example, a transition metal oxide that 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 CoS_0.89, NiS, and CuS, nitrides such as Zn₃N₂, Cu₃N, and Ge₃N₄, phosphides such as NiP₂, FeP₂, and CoP₃, and fluorides such as FeF₃ and BiF₃.

The average diameter of primary particles of the negative electrode active material is preferably, for example, greater than or equal to 5 nm and less than or equal to 100 μm.

The positive electrode active material layer and the negative electrode active material layer may each include a conductive additive.

Examples of the conductive additive include a carbon material, a metal material, and a conductive ceramic material. Alternatively, a fiber material may be used as the conductive additive. The content of the conductive additive in the active material layer is preferably greater than or equal to 1 wt % and less than or equal to 10 wt %, more preferably greater than or equal to 1 wt % and less than or equal to 5 wt %.

A network for electric conduction can be formed in the electrode by the conductive additive. The conductive additive also allows maintaining of a path for electric conduction between the negative electrode active material particles. The addition of the conductive additive to the active material layer increases the electric conductivity of the active material layer.

Examples of the conductive additive include natural graphite, artificial graphite such as mesocarbon microbeads, and carbon fiber. Examples of carbon fiber include mesophase pitch-based carbon fiber, isotropic pitch-based carbon fiber, carbon nanofiber, and carbon nanotube. Carbon nanotube can be formed by, for example, a vapor deposition method. Other examples of the conductive additive include carbon materials such as carbon black (e.g., acetylene black (AB)), graphite (black lead) particles, graphene, and fullerene. Alternatively, metal powder or metal fibers of copper, nickel, aluminum, silver, gold, or the like, a conductive ceramic material, or the like can be used.

Flaky graphene has an excellent electrical characteristic of high conductivity and excellent physical properties of high flexibility and high mechanical strength. Thus, the use of graphene as the conductive additive can increase electrical conductivity between the active materials or between the active material and the current collector.

Note that graphene in this specification includes single-layer graphene and multilayer graphene including two to hundred layers. Single-layer graphene refers to a one-atom-thick sheet of carbon molecules having π bonds. Graphene oxide refers to a compound formed by oxidation of such graphene.

Graphene is capable of making low-resistance surface contact and has extremely high conductivity even with a small thickness. Therefore, even a small amount of graphene can efficiently form a conductive path in an active material layer.

In the case where an active material with a small average particle diameter (e.g., 1 μm or less) is used, the specific surface area of the active material is large and thus more conductive paths for the active material particles are needed. In such a case, it is particularly preferred that graphene with extremely high conductivity that can efficiently form a conductive path even in a small amount is used.

The positive electrode active material layer and the negative electrode active material layer may each include a binder.

In this specification, the binder has a function of binding or bonding the active materials and/or a function of binding or bonding the active material layer and the current collector. The binder is sometimes changed in state during fabrication of an electrode or a battery. For example, the binder can be at least one of a liquid, a solid, and a gel. The binder is sometimes changed from a monomer to a polymer during fabrication of an electrode or a battery.

As the binder, for example, a water-soluble high molecular compound can be used. As the water-soluble high molecular compound, a polysaccharide or the like can be used. As the polysaccharide, a cellulose derivative such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, or regenerated cellulose, starch, or the like can be used.

As the binder, a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, fluororubber, or ethylene-propylene-diene copolymer can be used. Any of these rubber materials may be used in combination with the aforementioned water-soluble high molecular compound. Since these rubber materials have rubber elasticity and easily expand and contract, it is possible to obtain a highly reliable electrode that is resistant to stress due to expansion and contraction of an active material by charging and discharging, bending of the electrode, or the like. On the other hand, the rubber materials have a hydrophobic group and thus are unlikely to be soluble in water in some cases. In such a case, particles are dispersed in an aqueous solution without being dissolved in water, so that increasing the viscosity of a composition containing a solvent used for the formation of the active material layer 102 (also referred to as an electrode binder composition) up to the viscosity suitable for application might be difficult. A water-soluble high molecular compound having excellent viscosity modifying properties, such as a polysaccharide, can moderately increase the viscosity of the solution and can be uniformly dispersed together with a rubber material. Thus, a favorable electrode with high uniformity (e.g., an electrode with uniform electrode thickness or electrode resistance) can be obtained.

Alternatively, as the binder, a material such as PVdF, polystyrene, poly(methyl acrylate), poly(methyl methacrylate) (PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, isobutylene, polyethylene terephthalate, nylon, polyacrylonitrile (PAN), polyvinyl chloride, ethylene-propylene-diene polymer, polyvinyl acetate, polymethyl methacrylate, or nitrocellulose can be used.

Two or more of the above materials may be used in combination for the binder.

The content of the binder in the active material layer is preferably greater than or equal to 1 wt % and less than or equal to 10 wt %, more preferably greater than or equal to 2 wt % and less than or equal to 8 wt %, and still more preferably greater than or equal to 3 wt % and less than or equal to 5 wt %.

<<Electrolytic Solution>>

As a solvent of the electrolytic solution 508, an aprotic organic solvent is preferably used. For example, one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate (VC), 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, and sultone can be used, or two or more of these solvents can be used in an appropriate combination in an appropriate ratio.

Alternatively, the use of one or more kinds 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 a power storage device from exploding or catching fire even when a power storage device internally shorts out or the internal temperature increases owing to overcharging or the like. An ionic liquid contains a cation and an anion. The ionic liquid of one embodiment of the present invention contains an organic cation and an anion. Examples of the organic cation used for the electrolytic solution include aliphatic onium cations such as a quaternary ammonium cation, a tertiary sulfonium cation, and a quaternary phosphonium cation, and aromatic cations such as an imidazolium cation and a pyridinium cation. Examples of the anion used for the electrolytic solution include a monovalent amide-based anion, a monovalent methide-based anion, a fluorosulfonate anion, a perfluoroalkylsulfonate anion, a tetrafluoroborate anion, a perfluoroalkylborate anion, a hexafluorophosphate anion, and a perfluoroalkylphosphate anion.

In the case of using lithium ions as carriers, as an electrolyte dissolved in the above-described solvent, one of lithium salts such as LiPF₆, LiClO₄, LiAsF₆, LiBF₄, LiAlCl₄, LiSCN, LiBr, LiI, Li₂SO₄, Li₂B₁₀Cl₁₀, Li₂B₁₂Cl₁₂, LiCF₃SO₃, LiC₄F₉SO₃, LiC(CF₃SO₂)₃, LiC(C₂F₅SO₂)₃, LiN(CF₃SO₂)₂, LiN(C₄F₉SO₂) (CF₃SO₂), and LiN(C₂F₅SO₂)₂ can be used, or two or more of these lithium salts can be used in an appropriate combination in an appropriate ratio.

The electrolytic solution used for a power storage device is preferably highly purified and contains a small amount of dust particles and elements other than the constituent elements of the electrolytic solution (hereinafter, also simply referred to as impurities). Specifically, the weight ratio of impurities to the electrolytic solution is less than or equal to 1%, preferably less than or equal to 0.1%, and more preferably less than or equal to 0.01%.

Furthermore, an additive agent such as vinylene carbonate (VC), propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), or LiBOB may be added to the electrolytic solution. The concentration of such an additive agent in the whole solvent is, for example, higher than or equal to 0.1 wt % and lower than or equal to 5 wt %.

Alternatively, a polymer gelled electrolyte obtained in such a manner that a polymer is swelled with an electrolytic solution may be used.

Examples of a host polymer include a polymer having a polyalkylene oxide structure, such as polyethylene oxide (PEO); PVdF; polyacrylonitrile; and a copolymer containing any of them. For example, PVdF-HFP, which is a copolymer of PVdF and hexafluoropropylene (HFP) can be used. The formed polymer may be porous.

An electrolytic solution may be gelated by adding a polymerization initiator and a cross-linking agent to the electrolytic solution. For example, the ionic liquid itself may be polymerized in such a manner that a polymerizable functional group is introduced into a cation or an anion of the ionic liquid and polymerization thereof is caused with the polymerization initiator. Then, the polymerized ionic liquid may be gelated with a cross-linking agent.

In combination with the electrolytic solution, a solid electrolyte including an inorganic material such as a sulfide-based inorganic material and an oxide-based inorganic material, or a solid electrolyte including a macromolecular material such as a polyethylene oxide (PEO)-based macromolecular material may alternatively be used. For example, the solid electrolyte may be formed over a surface of the active material layer. In the case of using the solid electrolyte and the electrolytic solution in combination, at least one of a separator and a spacer does not need to be provided in some cases.

When a macromolecular material that undergoes gelation is used as the solvent for the electrolytic solution, safety against liquid leakage and the like is improved. Furthermore, the power storage device can be thinner and more lightweight. For example, a polyethylene oxide-based polymer, a polyacrylonitrile-based polymer, a polyvinylidene fluoride-based polymer, a polyacrylate based polymer, and a polymethacrylate-based polymer can be used. A polymer which can gelate the electrolytic solution at normal temperature (e.g., 25° C.) is preferably used. Alternatively, a silicone gel may be used. In this specification and the like, the term polyvinylidene fluoride-based polymer, for example, refers to a polymer including polyvinylidene fluoride (PVdF), and includes a poly(vinylidene fluoride-hexafluoropropylene) copolymer and the like.

The above polymer can be qualitatively analyzed using a Fourier transform infrared (FT-IR) spectrometer or the like. For example, the polyvinylidene fluoride-based polymer has an absorption peak showing a C—F bond in a spectrum obtained with the FT-IR spectrometer. Furthermore, the polyacrylonitrile-based polymer has an absorption peak showing a C≡N bond in a spectrum obtained with the FT-IR spectrometer.

<<Separator>>

As the separator 507, paper, nonwoven fabric, a glass fiber, ceramics, a synthetic fiber such as nylon (polyamide), vinylon (a polyvinyl alcohol based fiber), polyester, acrylic, polyolefin, or polyurethane, or the like can be used. The separator 507 may have a single-layer structure or a layered structure.

More specifically, as a material for the separator 507, any of a fluorine-based polymer, polyethers such as polyethylene oxide and polypropylene oxide, polyolefin such as polyethylene and polypropylene, polyacrylonitrile, polyvinylidene chloride, polymethyl methacrylate, polymethylacrylate, polyvinyl alcohol, polymethacrylonitrile, polyvinyl acetate, polyvinylpyrrolidone, polyethyleneimine, polybutadiene, polystyrene, polyisoprene, and polyurethane, derivatives thereof, cellulose, paper, nonwoven fabric, and fiberglass can be used either alone or in combination.

<<Exterior Body>>

It is preferred that the surface of the exterior body 509 that is in contact with the electrolytic solution 508, i.e., the inner surface of the exterior body 509, does not react with the electrolytic solution 508 significantly. When moisture enters the battery unit 500 from the outside, a reaction between a component of the electrolytic solution 508 or the like and water might occur. Thus, the exterior body 509 preferably has low moisture permeability.

As the exterior body 509, a film having a three-layer structure can be used, for example. In the three-layer structure, a highly flexible metal thin film of aluminum, stainless steel, copper, nickel, or the like is provided over a film formed using polyethylene, polypropylene, polycarbonate, ionomer, polyamide, or the like, and an insulating synthetic resin film of a polyamide-based resin, a polyester-based resin, or the like is provided as the outer surface of the exterior body over the metal thin film can be used. With such a three-layer structure, the passage of an electrolytic solution and a gas can be blocked and an insulating property and resistance to the electrolytic solution can be provided. The exterior body is folded inside in two, or two exterior bodies are stacked with the inner surfaces facing each other, in which case application of heat melts the materials on the overlapping inner surfaces to cause fusion bonding between the two exterior bodies. In this manner, a sealing structure can be formed.

The battery unit 500 can be flexible by using the exterior body 509 with flexibility. When the battery unit has flexibility, it can be used in a power storage device or an electronic device at least part of which is flexible, and the battery unit 500 can be bent as the power storage device or electronic device is bent.

FIG. 48A is a top view illustrating a light-emitting panel. FIG. 48B is a cross-sectional view along dashed-dotted line P1-Q1 in FIG. 48A. FIG. 48C is a cross-sectional view along dashed-dotted line P2-Q2 in FIG. 48A. FIG. 48D is a cross-sectional view along dashed-dotted line P3-Q3 in FIG. 48A.

The light-emitting panel illustrated in FIGS. 48A to 48D includes a substrate 901, an insulating layer 903, an auxiliary electrode 921 (also referred to as an auxiliary wiring), a light-emitting element 930, an insulating layer 925, an adhesive layer 927, a conductive layer 911, a conductive layer 912, a drying agent 913, and a substrate 991.

The light-emitting element 930 is an organic EL element having a bottom-emission structure; specifically, a lower electrode 931 transmitting visible light is provided over the substrate 901, an EL layer 933 is provided over the lower electrode 931, and an upper electrode 935 reflecting visible light is provided over the EL layer 933.

In the light-emitting panel illustrated in FIGS. 48A to 48D, the light-emitting element 930 is provided over the substrate 901 with the insulating layer 903 provided therebetween. The auxiliary electrode 921 provided over the insulating layer 903 is electrically connected to the lower electrode 931. The conductive layer 911 provided over the insulating layer 903 is electrically connected to the lower electrode 931. As illustrated in FIGS. 48A and 48C, part of the conductive layer 911 is exposed and functions as a terminal. The conductive layer 912 provided over the insulating layer 903 is electrically connected to the upper electrode 935. As illustrated in FIGS. 48A and 48D, part of the conductive layer 912 is exposed and functions as a terminal. The end portion of the lower electrode 931 is covered with the insulating layer 925. The insulating layer 925 is provided to cover the auxiliary electrode 921 with the lower electrode 931 provided therebetween.

The light-emitting element 930 is sealed with the substrate 901, the substrate 991, and the adhesive layer 927. A method for sealing the light-emitting panel is not limited, and either solid sealing or hollow sealing can be employed. For example, a glass material such as a glass frit, or a resin material such as a two-component-mixture-type resin which is curable at room temperature, a light curable resin, or a thermosetting resin can be used for the adhesive layer 927. The sealed space 929 may be filled with an inert gas such as nitrogen or argon, or a resin that can be used for the adhesive layer. Furthermore, a drying agent may be contained in the resin.

The drying agent 913 is provided in contact with the substrate 991. Since the light-emitting panel illustrated in FIGS. 48A to 48D has a bottom-emission structure, the drying agent 913 can be provided in the space 929 without reducing light extraction efficiency. With the drying agent 913, the lifetime of the light-emitting element 930 can be increased, which is preferable.