JP6438249B2 - Electrode material, electrode layer using the same, battery, and electrochromic device - Google Patents

Description

Embodiments to be described later relate to an electrode material exhibiting band conduction characteristics, an electrode layer using the same, a battery, and an electrochromic device.

Various materials such as metal oxide and carbon are used for the electrode material. International Publication No. 2013/146194 (Patent Document 1) discloses a battery electrode material using tungsten oxide powder.
As shown in Patent Document 1, a metal oxide powder such as a tungsten oxide powder is subjected to a sublimation process such as plasma treatment to produce a tungsten oxide powder (WO ₃ ). In Patent Document 1, heat treatment is performed in an oxidizing atmosphere in order to prepare the crystal structure of the obtained tungsten oxide powder. By performing such heat treatment, a tungsten oxide powder having a stabilized crystal structure is obtained.
Thus, the metal oxide powder used for the electrode material has stabilized the crystal structure by performing heat treatment in an oxidizing atmosphere. Storage characteristics are improved by stabilizing the crystal structure.
On the other hand, when a tungsten oxide powder that has been heat-treated in an oxidizing atmosphere as in Patent Document 1 is used as an electrode material, no further improvement in power storage characteristics was observed.

International Publication No. 2013/146194

As a result of investigating the cause of no improvement in the storage characteristics, it was found that the resistivity of the metal oxide powder increases as the crystal structure stabilizes. The metal oxide powder having increased resistivity decreases the ease of electricity flow. It has been found that when the ease of electricity flow is reduced, the characteristics as an electrode material are not further improved.
There are roughly two types of conduction mechanisms showing the ease of electricity flow in electrode materials: band conduction and hopping conduction. Conventional metal oxide powders have band conduction because they stabilize the crystal structure. On the other hand, when the crystal structure is stabilized, the crystal has no defects. When the defect disappears, the resistivity increases. Even if the electrode material having a high resistivity has band conduction, the characteristics as the electrode material are insufficient. When the cause was investigated, it was found that the activation energy of band conduction was insufficient.

The problem to be solved by the present invention is to provide an electrode material having an average particle size of 50 μm or less and an activation energy E _α of band conduction of 0.20 eV or more. By controlling the activation energy of band conduction, electrons can be transferred efficiently. For this reason, when it uses for the electrode layer using the electrode material concerning embodiment, a battery, and the material for electrochromic elements, the outstanding effect can be acquired.

A mathematical expression showing the resistivity of mixed band conduction and hopping conduction. The graph which illustrates the relationship between the measurement temperature and resistivity of the tungsten oxide powder concerning Examples 1-3 and Comparative Examples 1-2. The graph which illustrates the relationship between the heat processing temperature in nitrogen atmosphere of the tungsten oxide powder concerning Examples 1-3 and Comparative Examples 1-2, and carrier density. Drawing which illustrates electrode material. The figure which shows the structure of the sample for measuring the relationship between measurement temperature and resistivity. The figure for showing the composition of the capacitor concerning an embodiment. The figure which shows the charging / discharging characteristic of the electrode layer using the tantalum oxide powder (electrode material) of Example 1 and Comparative Example 1. The figure which shows the voltammogram of the electrode layer using the tantalum oxide powder (electrode material) of Example 1 and Comparative Example 1. The figure which shows the equivalent circuit for measuring an impedance by alternating current impedance method. The figure which shows the Cole-Cole plot of the tantalum oxide powder (electrode material) of Example 1 and Comparative Example 1.

The electrode material according to the embodiment is characterized in that the average particle size is 50 μm or less and the activation energy E _α of band conduction is 0.20 eV or more.
When the average particle size exceeds 50 μm, the surface area per unit decreases. When the surface area is reduced, the electron transfer efficiency is lowered. Therefore, the average particle diameter of the electrode material is preferably 50 μm or less, and more preferably 10 μm or less.
Then, it is effective activation energy E _alpha band conduction is equal to or greater than 0.20 eV.
In addition, FIG. 1 shows a mathematical expression showing a resistivity in which band conduction and hopping conduction are mixed. In the formula, ρ is resistivity, q is elementary charge (elementary ch)
large), N is the number of sites (number of sites), and μ is the carrier mobility (
mobility of carriers), k is the Boltzmann constant, T is the measurement temperature (unit Kelvin), E _a is the activation energy due to band conduction, and ε is the activation energy due to hopping conduction. Further, μ _b is carrier mobility due to band conduction, and μ _h is carrier mobility due to hopping conduction.
Further, the activation energy E _α being 0.20 eV or more indicates that the band conduction characteristic is strong. In other words, it shows a state having almost no hopping conduction characteristics.
Band conduction refers to a state where electrons (or holes) are electrically conducted in a relatively wide range (wide band region) in a semiconductor (or ionic crystal) or the like. Electrons (or holes) are generated when the semiconductor (or ionic crystal) deviates from the stoichiometric composition.

On the other hand, hopping conduction refers to a state in which electrons are almost localized in a semiconductor (or ionic crystal) or the like, and electrical conduction is carried out by jumping (hopping) between them one after another. In hopping conduction, the mean free process of electrons is about the distance between atoms (in the case of impurity conduction, the distance between impurity atoms), and the electrical conductivity is much smaller than that of free electrons, and free electrons with a long mean free process. Shows a contrasting behavior. The hopping process is aided by thermal vibrations of the atoms. "Electrons are almost in a localized state"
Indicates a state where electrons existing in the conduction band (conduction band) are present near the energy minimum point of the conduction band. Since hopping conduction needs to be controlled so that “electrons are almost in a localized state”, manufacturing management becomes complicated.

The electrode material preferably has a resistivity at 1000 Ωcm or less at room temperature (25 ° C.) and exhibits band conduction characteristics. The electrode material has a resistivity of 10 Ωcm at room temperature (25 ° C.)
Is preferably 1000 Ωcm or less. The resistivity at room temperature (25 ° C) is 100
By setting it to 0 Ωcm or less, the delivery of electrons can be improved. Further, the resistivity is preferably 0.95 or less when the resistivity in a state without defects is 1. In addition, you may use a theoretical value as a state without a defect.
Band conduction properties are caused by the electrode material deviating from stoichiometric composition. Due to this deviation from the stoichiometric composition, the resistivity of the metal oxide powder decreases. On the other hand, normal temperature (25 ℃)
If the resistivity at 10 is lower than 10 Ωcm, the deviation from the stoichiometric composition becomes too large, and the charge / discharge efficiency may not be improved. On the other hand, if the resistivity exceeds 1000 Ωcm, the resistivity is high, so that the delivery of electrons decreases. For this reason, the resistivity at room temperature (25 ° C.) is preferably more than 10 Ωcm and 1000 Ωcm or less.

Moreover, it is preferable to have a defect due to oxygen deficiency or impurity doping. By providing the defect, a deviation from the stoichiometric composition can be caused. By this deviation from the stoichiometric composition can be increased activation energy E _alpha band conduction.
For example, in the case of tungsten trioxide, stoichiometry becomes WO _3. When a deviation from the stoichiometric composition occurs, WO _3−x and 0 <x.
Moreover, it is preferable that oxygen deficiency is 1 * 10 < ¹⁷ > cm <^-3> or less. Oxygen deficiency is the amount of oxygen atoms missing from the crystal lattice. By forming oxygen vacancies, a path for electrons can be created.

The carrier density is preferably 1 × 10 ¹⁷ cm ⁻³ or less. If the carrier density is 1 × 10 ¹⁷ cm ⁻³ or less, the resistivity is easily lowered. Moreover, it is preferable that the minimum of a carrier density is 1 * 10 < ¹⁴ > cm < ^-3 > or more. Carrier density is 1 × 10 ¹⁴ cm ⁻³
As described above, the storage capacity can be increased. Carriers are electrons and holes. The carrier density indicates the abundance of electrons or holes (holes) serving as carriers. In the p-type semiconductor, the carrier is a hole, and in the n-type semiconductor, the carrier is an electron. The carrier density is obtained by the product of the density of states and the Fermi Dirac distribution function.
In addition, the carrier density is 1 × 10 ¹⁴ cm ⁻³ or more and 1 × 1 after having band conduction characteristics.
By setting it to 0 ¹⁷ cm ⁻³ or less, it is possible to increase the accumulation amount and emission amount of electrons (or ions).
Further, by controlling the carrier density, it is possible to easily impart band conduction characteristics. In band conduction, electrons in the conduction band that is a band region contribute to electrical conduction. On the other hand, the electrons below the band region do not contribute to electrical conduction. A region where electrons exist below the band region is called an impurity region. By controlling the carrier density, an increase in Fermi level can be suppressed. If the increase of the Fermi level can be suppressed, band conduction characteristics can be imparted because electric conduction is possible with electrons in the band region. In other words, it can have band conduction characteristics until the Fermi level rises and reaches the impurity region.
As described above, a method of heat treatment in a non-oxidizing atmosphere is effective for controlling oxygen vacancies and carrier density, as will be described later.

Moreover, it is preferable to show band conduction in the range of −23 ° C. to 127 ° C. -23 ° C (25
0K) is 1000 / T = 4.0. At 127 ° C (400K), 1000 / T = 2
. 5. As will be described later, the electrode material according to the embodiment is suitable for an electrode layer, a battery, and an electrochromic element material. These materials are mainly used at room temperature (25 ° C.). For this reason, it is preferable to show band conduction near room temperature. Also, the temperature may rise during use. Therefore, it is preferable that band conduction is exhibited at 127 ° C. (400K) or lower, and further 60 ° C. (333K) or lower.

FIG. 2 shows a graph illustrating the relationship between the measurement temperature and resistivity of the tungsten oxide powder.
In FIG. 2, the horizontal axis is 1000 / T, and T is the measured temperature (unit Kelvin: K). Further, the vertical axis represents resistivity, and the unit is Ωcm. FIG. 2 shows Examples 1 to 3 and Comparative Examples 1 and 2 described later. Comparative Example 1 was not subjected to heat treatment in nitrogen, and Examples 1 to 3 and Comparative Example 2 were subjected to the heat treatment conditions in nitrogen shown in Table 1.

In FIG. 2, in Examples 1 to 3, the resistivity increases as 1000 / T increases from 2.5 to 4.0. That is, Examples 1 to 3 are graphs that rise to the right. This indicates that the resistivity increases as the measurement temperature decreases. In band conduction, electrons (or holes) move through a wide band. Band conduction characteristics are highly temperature dependent. Therefore, in Examples 1 to 3, the resistivity decreases continuously as the measurement temperature increases (1000 / T value decreases). In other words, if the resistivity has temperature dependence, it can be said that it has band conduction characteristics.
On the other hand, in Comparative Example 2, the resistivity hardly changed in the region of 2.5 to 4.0. If it has a hopping conduction characteristic, it shows a characteristic with substantially no change in resistivity. For this reason, it can be said that when the resistivity does not depend on temperature, it has hopping conduction characteristics.

In addition, when a graph in which the horizontal axis is 1000 / T value (where T is the measured temperature (unit: Kelvin)) and the resistivity (Ωcm) is plotted on the vertical axis, 1000 / T is a resistance of 2.5. When the rate is R1, and the resistivity when R is 1000 / T is 4.0, the slope of the straight line from R1 to R2 is obtained. The slopes of the graphs of Examples 1 to 3 are larger than the slope of the graph of Comparative Example 1. The fact that the slope of the graph is large indicates that the activation energy Eα of band conduction is large.
When the slope of the straight line drawn from R1 to R2 is small (substantially horizontal) as in Comparative Example 2, it means that the temperature dependence of the resistivity is small. When the temperature dependency is small, the hopping conduction characteristic is enhanced. For this reason, there is a possibility that the effect of efficiently accumulating and releasing electrons (or ions) due to the band conduction characteristics may be insufficient.

The electrode material according to the embodiment is not particularly limited as long as the electrode material has band conduction characteristics. As the electrode material, metal compound powder or carbon powder is preferable.
These materials are easy to control the activation energy using the amount of defects.
The metal compound is preferably at least one selected from tungsten oxide, molybdenum oxide, titanium oxide, lithium tungstate, lithium molybdate, lithium titanate, and molybdenum sulfide. These materials tend to be semiconductors. By becoming a semiconductor, it becomes easy to impart band conduction characteristics.

Specific examples of these metal compounds include the following.
(1) Tungsten oxide: WO _3-x , 0 ≦ x ≦ 1.
(2) Molybdenum oxide: MoO _3-x , 0 ≦ x ≦ 1.
(3) Titanium oxide: TiO _2-x , 0 ≦ x ≦ 1.
(4) Mo _x W _y O _z , 0 <x ≦ 1, 0 <y ≦ 1, and x + y = 1, 2 ≦ z ≦ 3.
(5) When W _x Ti _y O _z , 0 <x ≦ 1, 0 <y ≦ 1, and x + y = 1, 2 ≦ z ≦ 3.
(6) Mo _x Ti _y O _z , 0 <x ≦ 1, 0 <y ≦ 1, and x + y = 1, 2 ≦ z ≦ 3.
(7) Mo _x W _y O _z Ti _α , 0 <x ≦ 1, 0 <y ≦ 1, 0 <α ≦ 1, and x + y + α = 1, 2 ≦ z ≦ 3.
(8) Lithium tungstate: Li _x W _y O _3-z , 0 <x ≦ 1, 0 <y ≦ 1, 0 ≦ z
≦ 1.
(9) Lithium molybdate: Li _x Mo _y O _3-z , 0 <x ≦ 1, 0 <y ≦ 1, 0 ≦ z
≦ 1.
(10) Lithium titanate: Li _x Ti _y O _3-z , 0 <x ≦ 1, 0 <y ≦ 1, 0 ≦ z ≦
1.
(11) Molybdenum sulfide: MoS _2-x , 0 <x ≦ 1.
As described above, since the metal oxide and the metal composite oxide have oxygen as a constituent element, oxygen vacancies are easily formed. As a result, it is easy to impart band conduction characteristics. X, y, z
When α exceeds the above range, it becomes chemically unstable and the capacity for storing electrons decreases. Band conduction characteristics can be imparted by either oxygen deficiency or impurity doping.

If the metal oxide has a stoichiometric composition, the resistivity at room temperature (25 ° C.) is 1000 Ωc.
The value exceeds m. The metal oxide powder according to the embodiment preferably has a resistivity (25 ° C.) of more than 10 Ωcm and 1000 Ωcm or less. Control of resistivity leads to control of the amount of defects. As a result, the activation energy Eα of band conduction can be increased. Thereby, delivery of electrons (or ions) can be performed efficiently. For this reason, the capacitor using the metal oxide powder according to the embodiment for the electrode layer has improved charge / discharge efficiency.
When charge / discharge efficiency is high, loss can be reduced when discharging charged electricity. Therefore, it is effective for devices that perform charging and discharging.

The metal oxide powder according to the embodiment preferably has an average particle size of 50 μm or less, more preferably 10 μm or less. The average particle diameter is the average particle diameter of the primary particle diameter. When the average particle size is larger than 50 μm, the usability is deteriorated when used as an electrode layer or an electrochromic material. If the particle size is too large, it becomes difficult to uniformly impart band conduction characteristics to a large number of powders.

Since the electrode material as described above has band conduction characteristics, it is possible to efficiently accumulate or emit electrons. Therefore, the ratio of the accumulated amount of electrons (or ions) to the emitted amount (=
(Release amount / accumulation amount) can be increased. In addition, since the transfer of electrons (or ions) can be performed efficiently, the storage and discharge can be speeded up. Therefore, it is effective to use for products that exchange electrons. Examples of such a product include any one of an electrode layer, a battery, and an electrochromic element material.

In addition, when used as an electrode material, the ratio of the accumulated amount of electrons (or ions) to the emitted amount can be increased, so that the charge / discharge efficiency is improved. The battery using the electrode material according to the embodiment can increase the charge / discharge efficiency. As for the battery, a secondary battery, a capacitor, a capacitor and the like can be given. Moreover, it is preferable to use the electrode layer which made the electrode material layered as a negative electrode. The negative electrode is particularly suitable because it delivers and receives electrons. Moreover, it is preferable to use for a capacitor in order to make use of the charge / discharge characteristics. The capacitor using the electrode material of the embodiment is
The power density can be 500 W / kg or more, further 1500 W / kg or more.
In addition, Li ions contained in the electrolytic solution can be efficiently delivered. Moreover, even if it is a capacitor with high power density, a capacitor with high charge / discharge efficiency can be achieved.

It is also effective to use it as a material for electrochromic elements. An electrochromic device material is a material in which a reversible change in optical properties is observed when an electric charge is applied. For this reason, it is used for display devices (electrochromic elements) such as electronic books and displays. Since the ratio between the amount of accumulated electrons and the amount of emitted electrons is increased, the reversible change in optical properties can be accelerated.

Next, the manufacturing method of the electrode material concerning embodiment is demonstrated. The electrode material according to the embodiment is not particularly limited as long as the average particle size is 50 μm or less and the activation energy E _α of band conduction is 0.20 eV or more. Can be mentioned.
First, a raw material powder for an electrode material is prepared. As the raw material powder, a metal compound powder is prepared when the electrode material is a metal compound, and a carbon powder is prepared when the electrode material is carbon. For metal compound powder,
A metal oxide powder (including a metal composite oxide) or a metal sulfide powder is prepared. Regarding the metal oxide powder, the metal oxide powder or metal composite oxide powder shown in the above (1) to (10) is preferable. The metal sulfide is preferably molybdenum sulfide powder.
The electrode material powder preferably has an average particle size of 50 μm or less, and more preferably an average particle size of 10 μm or less.
More preferably, the average particle size is 5 μm or less. The smaller the average particle size, the easier it is to give defects.
Further, the surface area per unit volume can be increased when the average particle size is smaller. By increasing the surface area, the region for transferring electrons (or ions) increases, so that the storage capacity can be improved.

Moreover, the method of utilizing a sublimation process is mentioned as a method of manufacturing powder with a small particle size.
The sublimation process is preferably any one of plasma treatment, arc discharge treatment, laser treatment, and electron beam treatment. As the plasma treatment, inductively coupled plasma treatment is preferable. Inductively coupled plasma treatment uses a plasma flame to reduce the average particle size to 50 μm or less.
Furthermore, it is easy to obtain a metal compound powder of 10 μm or less. Moreover, when producing metal oxide powder (including metal composite oxide), the sublimation process is performed in an oxygen-containing atmosphere. Moreover, when producing metal sulfide powder, the sublimation process shall be performed in a sulfur-containing atmosphere.
Further, the metal oxide powder obtained after the sublimation process may be heat-treated in an oxygen-containing atmosphere. The oxygen-containing atmosphere includes air. Moreover, you may heat-process in sulfur containing atmosphere with respect to the metal sulfide powder obtained after the sublimation process. By performing heat treatment in an oxygen-containing atmosphere or a sulfur-containing atmosphere after the sublimation step, a metal compound powder having no defect can be produced. By performing such a process, it becomes easy to control the amount of defects in the process of providing defects.
Moreover, although demonstrated here as the heat processing process after a sublimation process, you may carry out with respect to the metal compound powder manufactured with manufacturing methods other than a sublimation process.

Next, a step of providing defects in the raw material powder of the electrode material is performed. The step of providing defects is preferably a step of imparting defects by oxygen deficiency or impurity doping.
In order to provide oxygen vacancies, it is effective to perform heat treatment in a non-oxidizing atmosphere. Examples of the non-oxidizing atmosphere include an inert atmosphere such as nitrogen and argon, and a reducing atmosphere such as hydrogen. Among these, heat treatment in a nitrogen atmosphere is preferable. Nitrogen gas has a cost advantage because it is less expensive than argon gas or hydrogen gas.

Moreover, it is preferable that the heat processing temperature in non-oxidizing atmosphere is the range of 200 degreeC or more and less than 530 degreeC. If the heat treatment temperature is less than 200 ° C., the amount of oxygen vacancies tends to decrease, so that the band conduction characteristics cannot be obtained sufficiently. On the other hand, if heat treatment is performed at a high temperature of 530 ° C. or higher, the amount of oxygen defects becomes too large, and the activation energy E _α of band conduction may be warped and become small. Therefore, the heat treatment temperature is 200 ° C. or higher and lower than 530 ° C., and further 280 ° C. or higher and 510 ° C.
The following is preferred. The heat treatment time is preferably 1 minute or longer. The upper limit of the heat treatment time is 6
0 minutes or less is preferable. When heat treatment is performed for longer than 60 minutes, oxygen defects increase too much and the amount of oxygen in the metal oxide powder decreases too much. If oxygen is reduced too much from the metal oxide powder, it becomes chemically unstable and the capacity for storing electrons decreases. Moreover, since long-time heat treatment is accompanied by grain growth, the average particle size may exceed 10 μm. The heat treatment time is preferably 1 to 60 minutes, more preferably 3 to 20 minutes.

A reducing atmosphere such as a hydrogen atmosphere may be used as the non-oxidizing atmosphere. Also,
In addition to this, there is a method of forming defects by impurity doping.

(Example)
(Examples 1-3, Comparative Examples 1-2)
A tungsten oxide powder of 1.5 μm was prepared as a raw material powder. This raw material powder is sprayed onto an inductively coupled plasma flame using air as a carrier gas so as to have an average flow rate of 1.5 m / s, and a tungsten oxide (WO ₃ ) powder is obtained by a sublimation process in which an oxidation reaction is performed while sublimating the raw material powder. It was. The average particle diameter of the obtained tungsten oxide (WO3) powder was 8.2 nm (0.008
μm).
Thereafter, heat treatment was performed in air at 450 ° C. for 50 hours to produce monoclinic WO 3 powder. The average particle size of the obtained WO ₃ powder was 25 nm. The WO ₃ powder obtained by this step was designated as Comparative Example 1. The WO _{3 of} Comparative Example 1 was heat treated in nitrogen under the conditions shown in Table 2. Through this process, tungsten oxide powders according to Examples 1 to 3 and Comparative Example 2 were prepared.

The composition and average particle diameter of the obtained tungsten oxide powder were measured. The composition (oxygen defect) analysis of the tungsten oxide powder was performed by chemical analysis to determine the amount of KMnO ₄ required to oxidize all W (W ⁴⁺ , W ⁵⁺ ) ions with a KMnO ₄ solution to W ^6+. It was done by doing.
By this analysis, it was replaced with WO _3-x to obtain the x value. This x value was defined as the amount of oxygen defects. The particle size was converted from the BET specific surface area measurement. In addition, the activation energy E _α (
eV) was measured. The activation energy _E α was determined by the Arrhenius plot.
The results are shown in Table 3.

As can be seen, the tungsten oxide powder according to the embodiment the activation energy E _alpha band conduction is equal to or greater than 0.20 eV.
For the tungsten oxide powders according to Examples 1 to 3 and Comparative Examples 1 and 2, the relationship between temperature and resistivity was measured. The result is shown in FIG.
In FIG. 2, the horizontal axis is 1000 / T, T is the measured temperature (unit Kelvin), and the vertical axis is the resistivity (unit Ω).
cm). The resistivity was measured when the measurement temperature was changed. FIG. 5 shows the structure of a measurement sample for measuring the relationship between measurement temperature and resistivity.
In FIG. 5, 2 is a measurement sample, 3 is an n-Si substrate, 4 is a SiO ₂ layer, 5 is an electrode layer made of tungsten oxide powder of an example (or comparative example), and 6 is a metal electrode. The SiO ₂ layer 4 has a thickness of 400 nm, the electrode layer 5 made of tungsten oxide powder has a thickness of 100 nm, and the metal electrode layers 6 (6a, 6b, 6c, 6d) have a thickness of 50 nm (diameter 200 μm).
m).

In the measurement of the resistivity, the applied voltage and current to the metal electrode 6a are V ₁ and I ₁ . Metal electrode 6b
Is a measurement terminal, a detection voltage is V ₂ , and a detection current is I ₂ . The metal electrode 6c is also a measurement terminal, the detection voltage is V ₃ , and the detection current is I ₃ . Further, the applied voltage and current to the metal electrode 6d are V ₄ and I ₄ . A voltage V ₁ and a current I ₁ are applied between the metal electrodes 6a and 6d. The resistance difference ((V ₂ −V ₃ ) / I ₁ (unit ohm Ω)) with respect to the voltage difference (V ₂ −V ₃ (unit volt V)) between the metal electrodes 6 b and 6 c as the measurement terminals was examined. This resistance difference ((V ₂ −V ₃ ) / I
₁ ) was used as the electrode layer 5 made of tungsten oxide powder. In measurement, the voltage V1 is set to -15.
Performed at ~ 15V.

As can be seen from FIG. 2, the tungsten oxide powders according to Examples 1 to 3 show temperature dependency of the resistivity in a region where 1000 / T is 2.5 to 4.0. As a result, it can be seen that the tungsten oxide powders according to Examples 1 to 3 mainly have band conduction characteristics.
On the other hand, the tungsten oxide powder according to Comparative Example 1 is a graph that rises to the right.
For this reason, although band conduction is shown, the resistivity is high. In Comparative Example 2, the resistivity is hardly changed. For this reason, it turns out that the comparative example 2 is mainly hopping conduction.

FIG. 3 shows carrier densities of tungsten oxide powders according to Examples 1 to 3 and Comparative Example 2 (
cm ⁻³ ) was measured. The carrier density was measured by the product of the state density and the Fermi Dirac distribution function. The tungsten oxide powder according to the example has a carrier density of 1 × 10 ¹⁴ c.
It was found to be m ⁻³ or more and 1 × 10 ¹⁷ cm ⁻³ or less. On the other hand, the tungsten oxide powder according to Comparative Example 2 had a carrier density of 1 × 10 ²¹ cm ⁻³ or more.

(Example 4)
A 2.0 μm tungsten oxide powder was prepared as a raw material powder. This raw material powder is sprayed onto an inductively coupled plasma flame using air as a carrier gas so as to have an average flow rate of 1.2 m / s, and a tungsten oxide (WO ₃ ) powder is obtained by a sublimation process in which an oxidation reaction is performed while sublimating the raw material powder. It was. The average particle diameter of the obtained tungsten oxide (WO ₃ ) powder was 12.1 nm (0.00
12 μm). Thereafter, heat treatment is performed in the atmosphere at 450 ° C. for 50 hours to obtain monoclinic WO ₃
A powder was prepared. The average particle size of the obtained WO ₃ powder was 27 nm.
The WO3 powder obtained in this step was heat-treated at 400 ° C. in a nitrogen atmosphere.
The heat treatment time was 0 minutes, 30 seconds, 1 minute, 3 minutes, 5 minutes, 8 minutes, 10 minutes, 20 minutes, and 30 minutes.
The tungsten oxide powder after the heat treatment had an average particle size of 5 μm or less.
When the resistivity at 1000 / T was confirmed for each sample, 20 minutes or more 20
Those heat-treated for less than a minute were found to exhibit band conduction characteristics.
In addition, the resistivity (25 ° C.) of 1 to 20 minutes was over 10 Ωcm and 1000 Ωcm or less. The carrier density (cm ⁻³ ) was also measured. The results are shown in Table 4.

As can be seen from the table, the resistivity and carrier density can be controlled by controlling the heat treatment time. In addition, when the heat treatment is performed for a long time, the amount of defects increases and the activation energy E of band conduction
It was found that _α was warped and decreased.

(Examples 1A to 3A, Comparative Example 1A)
Capacitors were fabricated using the tungsten oxide powders according to Examples 1 to 3 and Comparative Example 1. The configuration of the capacitor is shown in FIG. In FIG. 6, 20 is a capacitor, 21 is a negative electrode layer, 22 is a negative electrode layer, 23 is a separator layer, 24 is a positive electrode layer, and 25 is a positive electrode layer.
The negative electrode layer 21 and the positive electrode layer 25 are 15 μm thick aluminum foil.
Next, a tungsten oxide powder according to Example or Comparative Example, acetylene black as a conductive auxiliary agent, and PVDF as a binder were mixed to prepare a paste. The paste was applied on the negative electrode layer 21 and dried to prepare a negative electrode layer 22. Next, as a positive electrode material, L
Using iCoO ₂ powder, a paste was prepared in the same manner as the above negative electrode, applied onto the positive electrode layer 25 and dried, and then the positive electrode layer 24 was prepared. The negative electrode layer 22 and the positive electrode layer 24 have an electrode area of 2c.
He was m ^2.

The mixing ratio (mass ratio) of the tungsten oxide powder and acetylene black was tungsten oxide powder: acetylene black = 100: 10. The total weight of the negative electrode material obtained by adding the tungsten oxide powder and acetylene black was adjusted to 10 mg / cm ^2, and the film thickness after drying was 20 μm and the porosity was 50%. In addition, the basis weight of the positive electrode material was set to an amount having a sufficient margin with respect to the electric capacity of the negative electrode material.
Further, a polyethylene porous film (film thickness 20 μm) was used as the separator layer 23. These laminates of electrodes and separator layers were assembled in an aluminum cell, impregnated with an electrolytic solution, defoamed and sealed to produce a capacitor. The electrolyte is LiPF as an electrolyte in EC / DEC solution.
A solution in which ₆ was dissolved was used. EC is Ethylene Carbonate, D
EC is an abbreviation for Diethyl Carbonate.
Using the capacitor, charge / discharge characteristics were examined. First, in order to measure the electric capacity, a charge / discharge test was performed in a voltage range of 1.0 V to 2.0 V using a charge / discharge device. Charging was first performed in the constant current mode, and when 2.0V was reached, the mode shifted to the 2.0V constant voltage mode, and charging was continued until the amount of current decreased to a constant value. After charging, the battery was discharged at a constant current, and the capacitance of the capacitor was determined from the capacitance at the time of discharge. As the value of the electric capacity, the electric capacity (mAh / g) per 1 g of the negative electrode material was obtained as the initial electric capacity.
Next, the internal resistance was measured by the direct current method. Discharge current at a constant current of 1 mA / cm ²
The internal resistance (Ω · cm ² ) was determined from the relationship between the discharge start voltage and the load current amount, under the condition of changing at two levels of 5 mA / cm ² .

Furthermore, in order to investigate the charge / discharge cycle characteristics of the capacitor, the charge / discharge test similar to the method for measuring the capacitance was repeated 1000 times to evaluate the capacity retention rate. The capacity after 1000 cycles was compared with the initial capacity, and the capacity retention rate after the cycle test was determined. The capacity retention rate after the cycle test is (electric capacity after cycle test / initial electric capacity) × 100 (
%).
Table 5 shows the initial electric capacity, the capacity retention rate after the cycle test, and the internal resistance value.

Moreover, the power density of the capacitor concerning Example 1A-3A and Comparative Example 1A was calculated | required.
The power density (W / kg) was determined by a formula of 0.25 × (V2 ² −V1 ² ) / R / cell weight. V2 is the discharge start voltage, V1 is the discharge end voltage, and R is the cell resistance (cell electrode area 2903).
cm ² ) and the cell weight was 120 g. The results are shown in Table 6.

As can be seen from the table, the capacitor according to the example has a high power density and can be charged and discharged at high speed.

Next, charge / discharge efficiency was determined using the capacitors of Examples 1A to 3A and Comparative Example 1A.
The charge / discharge efficiency is obtained by performing charging and discharging at a constant current, changing the discharge conditions without changing the charging conditions, and determining the ratio of the storage capacity (mAh) during charging to the storage capacity (mAh) during discharging. Calculated. Rate (C) is based on the amount of electricity that reaches the theoretical capacity in one hour. It shows that it can charge / discharge early, so that an electrical capacitance ratio is large. The results are shown in Table 7.

A comparison of rate characteristics between Example 1A and Comparative Example 1A is shown in FIG. In FIG. 7, the horizontal axis indicates the rate (C), and the vertical axis indicates the capacitance ratio. As can be seen from FIG. 7, the capacitor according to Example 1A has a high capacitance ratio. This indicates that the amount of electricity stored is made the amount of electricity to be discharged. This tungsten oxide powder according to Example (electrode material) is because the activation energy E _alpha has a band conduction properties than 0.20 eV.
Next, the voltammogram (voltamm) of the capacitor according to Example 1A and Comparative Example 1A.
ogram). The results are shown in FIG. The voltammogram shows the potential applied on the horizontal axis and the response current value on the vertical axis. When the potential is swept in the negative direction, a reduction wave (upper side) is generated. Further, when the potential is swept in the positive direction, an oxidation wave (lower side) is generated. The voltammogram measures the response current of a redox reaction involving electron transfer. When the potential is swept in the positive direction, the charging current flows, and when the potential is swept in the negative direction, the discharging current flows, and the intercalation is most activated at the peak voltage value. The closer the peak value (potential difference) of this charge and discharge is, the higher the reversibility of the reaction and the faster charge / discharge is possible. As can be seen from FIG. 8, it can be seen that, compared to the comparative example, the example has a narrower potential difference between peaks and can be charged and discharged at high speed.

Further, the impedance characteristics of the capacitors according to Example 1A and Comparative Example 1A were examined. The impedance characteristics were measured by the AC impedance method using the equivalent circuit shown in FIG. The result is shown as a Cole-Cole plot in FIG. The horizontal axis in FIG. 10 is the real component of impedance, and the vertical axis is the imaginary component of impedance. The AC impedance method can measure the charge transfer resistance at the interface between the electrode and the electrolyte.
As can be seen from FIG. 10, the size of the semicircle of the graph is larger in Comparative Example 1A than in Example 1A. The size of this semicircle indicates the charge transfer resistance at the interface between the electrode layer and the electrolyte. Example 1A is a small semicircle. Therefore, Example 1A means that the charge transfer resistance is small. Thus, it can be seen that the electrode layer using the electrode material in which the oxygen deficiency is controlled and the band conduction characteristics are controlled, and the battery has a high capacity and can be charged and discharged at high speed.

(Examples 5-6, Comparative Example 3)
A molybdenum oxide (MoO ₃ ) powder having an average particle diameter of 1 μm was prepared. The molybdenum oxide powder was heat-treated in the atmosphere for 60 minutes.
Next, heat treatment was performed in a nitrogen atmosphere under the conditions shown in Table 8.

The composition and average particle diameter of the obtained molybdenum oxide powder were measured. In addition, activation energy E _α (eV) of band conduction, oxygen deficiency, and carrier density were measured. The results are shown in Table 9.

The relationship between temperature and resistivity of the molybdenum oxide powders according to Examples 5 to 6 and Comparative Example 3 was measured in the same manner as in Example 1. As a result, as with the tungsten oxide powder (FIG. 2), 100
It had band conduction characteristics when 0 / T was in the range of 2.5 to 4.0.

(Examples 5A to 6A, Comparative Example 3A)
A capacitor was prepared in the same manner as in Example 1 except that the electrode material was changed to Examples 5 to 6 and Comparative Example 3. In the same manner as in Example 1A, the initial electric capacity, the capacity retention rate after the cycle test, and the internal resistance value were determined. The results are shown in Table 10.

Using the capacitors of Examples 5A to 6A and Comparative Example 3A, charge / discharge efficiency was determined in the same manner as in Example 1A. The results are shown in Table 11.

As can be seen from the table, the capacitor according to the example had excellent electrical characteristics. Thus, it can be seen that the characteristics of the battery (capacitor) are improved by using the electrode material having the band conduction characteristics by controlling the activation energy _Eα and the carrier density.

As mentioned above, although several embodiment of this invention was illustrated, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and without departing from the spirit of the invention,
Various omissions, replacements, changes, etc. can be made. These embodiments and their variations are
The invention is included in the scope and gist of the invention, and is included in the invention described in the claims and the equivalent scope thereof. Further, the above-described embodiments can be implemented in combination with each other.

DESCRIPTION OF SYMBOLS 1 ... Metal oxide powder 2 ... Sample for measurement 3 ... n-Si layer 4 ... SiO ₂ layer 5 ... Electrode layer 6 made of tungsten oxide powder of Example (or Comparative Example) ... Metal electrode 20 ... Capacitor 21 ... Negative electrode side Electrode layer 22 ... Negative electrode layer 23 ... Separator layer 24 ... Positive electrode layer 25 ... Positive electrode layer electrode layer

Claims (9)

Tungsten oxide or oxide having an average particle size of 50 μm or less, a band conduction activation energy E _α of 0.20 eV or more , and a resistivity at room temperature (25 ° C.) of more than 10 Ωcm to 1000 Ωcm, oxygen deficiency or impurity deficiency An electrode material characterized by being molybdenum . The electrode material according to claim 1, which exhibits band conduction characteristics . 3. The electrode material according to claim 1, wherein the carrier density is 1 × 10 ¹⁷ cm ⁻³ or less. Electrode material according to any one of claims 1 to 3, characterized in that the carrier density is than 1 × 10 ¹⁴ cm ^-3. The electrode material according to any one of claims 1 to 4, wherein an average particle diameter is 10 µm or less. An electrode layer comprising the electrode material according to any one of claims 1 to 5 in an amount of 50 wt% to 100 wt%. A battery comprising the electrode layer according to claim 6 . A battery comprising the electrode layer according to claim 6 as a negative electrode. An electrochromic device comprising the electrode material according to any one of claims 1 to 5 .

Images