JP7224850B2 - Positive electrode or separator for power storage device containing output improving agent for power storage device, and power storage device containing them - Google Patents

Description

TECHNICAL FIELD The present invention relates to an output improver for use in electrical storage devices such as lithium ion batteries, lithium ion capacitors and electric double layer capacitors.

Electricity storage devices such as lithium-ion batteries, lithium-ion capacitors, and electric double-layer capacitors are required to shorten the charging time, improve the power assist rate when starting, and improve the energy regeneration efficiency as automobiles become more electrified. . For that purpose, it is necessary to improve the rate property of the electric storage device, that is, the input/output characteristics. Conventionally, as a method for improving the rate property, it has been common to increase the amount of the conductive additive added to the electrode to increase the electron conductivity. However, when a large amount of conductive aid is added, there is a problem that the amount of active material occupying the positive and negative electrodes decreases, resulting in a decrease in capacity. In addition, acetylene black and ketjen black, which are commonly used as conductive aids, are bulky, and if added in large amounts, problems such as an increase in the viscosity of the electrode paint and a decrease in electrode density occur. Furthermore, there is an additive amount at which the improvement of electrical conductivity by adding a conductive aid reaches a ceiling, and addition beyond that amount is useless.

Therefore, a method has been proposed in which the conductivity aid is improved and the rate property is improved with a small addition amount. For example, Patent Document 1 discloses a lithium ion secondary battery in which a positive electrode plate, a positive electrode layer, an electrolyte layer, a negative electrode layer, and a negative electrode plate are arranged in this order, wherein the positive electrode layer includes a positive electrode active material and A lithium ion secondary battery is described that includes a conductive material and a binder, wherein the conductive material is a carbon nanotube. It is said that a lithium ion secondary battery with excellent cycle characteristics and rate characteristics can be obtained by using carbon nanotubes as a conductive material. Further, in Patent Document 2, fibrous carbon and carbon black are connected, the average diameter of the fibrous carbon is 100 nm or less, the content of the fibrous carbon is 1 to 50% by mass, and , an ash content defined by JIS K 1469 of 1.0% by mass or less, and a specific surface area defined by JIS K 6217-2 of 85 to 115 m ² /g or more. It is According to this document, a carbon black composite in which fibrous carbon such as a carbon nanotube and carbon black are linked is excellent in the ability to impart conductivity, and can be suitably used for electrodes for batteries and the like.

However, all of the above-mentioned methods are intended to improve the conductive aid for the purpose of improving the electronic conductivity, and there is a limit to improving the rate property, and improvement has been desired.

JP-A-2003-77476 Japanese Patent No. 5518317

The present invention has been made to solve the above problems, and Li _x TiO ₄ (3 An object of the present invention is to provide an output improver for an electricity storage device comprising lithium titanate represented by .8≦x≦4.2).

The above problem is solved by providing an output improver for an electricity storage device comprising lithium titanate represented by Li _x TiO ₄ (3.8≦x≦4.2).

At this time, it is preferable that the lithium titanate has a specific surface area of 0.5 to 50 m ² /g. A positive electrode or separator for an electric storage device containing the output improving agent for an electric storage device made of lithium titanate is a preferred embodiment, and an electric storage device containing the positive electrode for an electric storage device or a separator is also a preferred embodiment.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an output improver for an electricity storage device comprising lithium titanate represented by Li _x TiO ₄ (3.8≦x≦4.2). The output improver for an electricity storage device comprising the lithium titanate obtained in this manner can suppress the generation of gas, and can be suitably used as an electricity storage device having excellent rate characteristics and cycle characteristics.

It is a schematic diagram which shows the structure of the produced electrical storage device.

The power storage device output improver of the present invention comprises lithium titanate represented by Li _x TiO ₄ (3.8≦x≦4.2). As a result of intensive studies by the present inventors, it was found that gas generation can be suppressed by including the lithium titanate output improving agent for an electricity storage device in the positive electrode or separator, and the rate performance of the electricity storage device can be improved. The inventors have found that the cycle characteristics can be improved. Since it is common technical knowledge that the input/output characteristics of a power storage device deteriorate if an additive that is not conductive and does not contribute to power storage is added to the positive electrode, etc. of the power storage device, this finding overturns conventional common technical knowledge. be.

As is clear from the comparison between the examples and comparative examples described later, in the comparative examples in which conductive acetylene black, ketjen black, or the like was added to the positive electrode as an output improver, a comparison was made in which no output improver was added. Compared with Example 1, the cell resistance was lowered and the rate property was slightly improved, but it was confirmed that the cycle characteristics were lowered and the volume change of the electricity storage device was increased. This is because industrially obtained carbonaceous materials have active sites (for example, carboxyl groups) on their surfaces, which induces gas generation. Therefore, addition of a large amount is not preferable from the viewpoint of gas generation. On the other hand, in the comparative example in which TiO ₂ and Al ₂ O ₃ having no conductivity were added to the positive electrode and the separator as output improvers, the cell resistance increased compared to Comparative Example 1 in which no output improver was added. It was confirmed that the rate property was significantly lowered, the cycle characteristics were also lowered, and the volume change of the electricity storage device was increased. On the other hand, by adding lithium titanate represented by Li _x TiO ₄ (3.8 ≤ x ≤ 4.2) which does not have conductivity to the positive electrode or separator as an output improving agent, the capacity and capacity retention rate It was found that the rate and cycle characteristics of the battery were greatly improved, the volume change of the electricity storage device was small, and the generation of gas could be suppressed.

As described above, when non-conductive materials such as TiO ₂ and Al ₂ O ₃ are added to the positive electrode and the separator as output improvers, the cell resistance increases, the rate performance greatly decreases, and the cycle characteristics deteriorate. decrease, and the volume change of the electricity storage device becomes large. On the other hand, when acetylene black or the like is added for the purpose of imparting conductivity, the rate performance is slightly improved, but the cycle characteristics are degraded and the volume change of the electricity storage device is increased. From the viewpoint of improving the rate property, it has been a conventional technical common sense that there is no choice but to add a conductive substance such as acetylene black. In the present invention, although the lithium titanate itself does not have conductivity, the lithium titanate is contained in the positive electrode or the separator as an output improving agent, thereby decreasing the cell resistance contrary to common technical knowledge and enabling the storage of electricity. It is possible to greatly improve the rate performance of the device.

The lithium titanate used in the present invention preferably has a specific surface area of 0.5 to 50 m ² /g. ^If the specific surface ^area is less than 0.5 m ² /g, the effect of improving the rate property may not be sufficiently obtained. , 3 m ² /g or more. ^{On the} other hand, if the specific surface area exceeds 50 m ² /g, handling such as an increase in viscosity or gelation of the paint may become difficult. is more preferred, and 25 m ² /g or less is particularly preferred.

In the lithium titanate used in the present invention, D50 in particle size distribution is preferably 0.5 to 20 μm. If the D50 is less than 0.5 μm, handling such as an increase in viscosity or gelation of the paint may become difficult. is particularly preferred. On the other hand, if the D50 exceeds 20 μm, irregularities may occur on the surfaces of the electrodes and the separator, which may induce short circuits. In particular, when it is applied to the separator, the thickness of the separator increases, and there is a possibility that the rate property may deteriorate. D50 is more preferably 10 μm or less, even more preferably 7 μm or less. D50 means the median diameter obtained by measuring the particle size distribution using a laser diffraction particle size distribution analyzer (Microtrac MT-3000, manufactured by Nikkiso Co., Ltd.).

Further, in the lithium titanate used in the present invention, D100 in particle size distribution is preferably 1 to 50 μm. If D100 is less than 1 μm, handling such as increase in viscosity or gelation of the paint may become difficult. . On the other hand, if the D100 exceeds 50 μm, irregularities may occur on the surfaces of the electrodes and the separator, which may induce short circuits. In particular, when it is applied to the separator, the thickness of the separator increases, and there is a possibility that the rate property may deteriorate. D100 is more preferably 40 μm or less, still more preferably 30 μm or less, particularly preferably 25 μm or less, and most preferably 18 μm or less. D100 means the maximum diameter obtained by measuring the particle size distribution using a laser diffraction particle size distribution analyzer (Microtrac MT-3000 manufactured by Nikkiso Co., Ltd.).

The method for producing the lithium titanate used in the present invention is not particularly limited, and a step of mixing a titanium source and a lithium source as raw materials (hereinafter sometimes abbreviated as "mixing step") is performed, Then, a step of firing at 500 to 1000° C. (hereinafter sometimes abbreviated as “firing step”) can be carried out to produce the desired product. The titanium source is not particularly limited, and hydrous titanium oxide such as orthotitanic acid or metatitanic acid may be used, or anatase-type or rutile-type titanium oxide may be used. Among them, orthotitanic acid can be preferably used. Orthotitanic acid can be suitably produced from titanyl sulfate or the like. As the orthotitanic acid, one prepared to contain less than 5% by weight of sulfate group (SO ₃ ) is preferably used, more preferably used to contain less than 3% by weight, and less than 1% by weight. is most preferably used. Moreover, the lithium source is not particularly limited, and lithium hydroxide, lithium carbonate, lithium nitrate, or the like can be used. Among them, at least one selected from lithium hydroxide and lithium carbonate is preferable, and lithium hydroxide is more preferable.

In the mixing step, the titanium source and the lithium source may be mixed by a dry method or may be mixed by a wet method, but mixing by a wet method is preferable. Among them, a preferred embodiment is a wet method in which the lithium source is mixed with the slurry containing the titanium source. In the mixing step, the titanium source and the lithium source are suitably mixed so that the Li/Ti (molar ratio) is 3.8 to 4.2, and the Li/Ti (molar ratio) is 4.0. is more preferable. The Li/Ti (molar ratio) calculated from the composition formula of Li ₄ TiO ₄ is 4.0. In the case of 3.8 to 4.2, it is acceptable as a range that does not adversely affect the function of the power storage device output improver. That is, the power storage device output improver of the present invention, which is obtained so that the Li/Ti (molar ratio) is 3.8 to 4.2, is Li _x TiO ₄ (3.8≦x≦4.2) When x is 3.8≦x≦4.2, it is allowed as a range that does not adversely affect the function of the power storage device output improver. Among them, lithium titanate represented by Li ₄ TiO ₄ in which x is 4.0 is preferable.

After performing the mixing step, a step of drying to obtain the dried lithium titanate precursor (hereinafter sometimes abbreviated as a “drying step”) is performed, then a carbon source is mixed, and the firing is performed. It is a preferred embodiment to carry out the process. By performing the step of obtaining the dried lithium titanate precursor, the reactivity between the titanium source and the lithium source can be improved, and the lithium titanate of high purity can be obtained. The drying temperature is not particularly limited, and is preferably 80 to 220°C, more preferably 90 to 200°C. Although the drying method is not particularly limited, a method of spray drying is preferably employed. Then, a carbon source is mixed, and the carbon source is carbonized in the firing step, thereby preventing sintering of the lithium titanate. As a result, the lithium titanate having the suitable particle size distribution can be obtained. Polyvinyl alcohol, sucrose, coal tar pitch, and the like can be used as the carbon source, but it is preferable to use polyvinyl alcohol because a small amount thereof can prevent sintering of the lithium titanate.

In a preferred embodiment, after performing the drying step, a step of firing at 500 to 1000° C. in a non-oxidizing atmosphere is performed. The atmosphere is not particularly limited as long as it is non-oxidizing. For example, nitrogen or argon is preferably used. If the firing is performed in an oxidizing atmosphere, the carbonization does not occur, so the lithium titanate is significantly sintered and the lithium titanate having the suitable particle size distribution cannot be obtained. If the firing temperature is less than 500°C, the high-purity lithium titanate may not be obtained. is particularly preferred. On the other hand, if the firing temperature exceeds 1000°C, the lithium titanate having the suitable particle size distribution may not be obtained, and the firing temperature is more preferably 980°C or lower. In a preferred embodiment, after the sintering step, the sintered body is once cooled and additionally sintered at 500 to 800° C. in an oxidizing atmosphere. The reason for firing in an oxidizing atmosphere is to burn off and remove carbonaceous matter. If the carbonaceous matter is not removed, it is not preferable because it induces gas generation. If the additional firing temperature is lower than 500°C, the carbonaceous matter may not be removed, so the temperature is more preferably 550°C or higher. On the other hand, if the additional firing exceeds 800°C, the lithium titanate may be significantly sintered and the lithium titanate having the preferred particle size distribution may not be obtained.

By using the lithium titanate obtained as described above as the output improving agent for an electricity storage device of the present invention, gas generation can be suppressed, and excellent rate performance and cycle characteristics can be obtained. Among them, a positive electrode for an electric storage device or a separator containing the output improving agent for an electric storage device of the present invention is a preferred embodiment, and an electric storage device containing the positive electrode for an electric storage device or a separator is a more preferred embodiment. The electricity storage device is not particularly limited, and is preferably at least one electricity storage device selected from the group consisting of lithium ion batteries, lithium ion capacitors and electric double layer capacitors, more preferably lithium ion capacitors.

In the positive electrode for an electric storage device containing the output improving agent for an electric storage device of the present invention, it is preferable that the output improving agent is contained in an amount of 0.5 to 50% by weight based on the total amount of the positive electrode. If the content of the output improver is less than 0.5% by weight, an electricity storage device with excellent rate characteristics and cycle characteristics may not be obtained, and the content is more preferably 3% by weight or more, and 6% by weight or more. more preferably, 10% by weight or more is particularly preferable, and 12% by weight or more is most preferable. On the other hand, if the content of the output improver exceeds 50% by weight, the positive electrode becomes too thick, and the rate performance may deteriorate. is more preferable, and 25% by weight or less is particularly preferable.

As described above, in the present invention, a preferred embodiment is a power storage device separator containing the output improving agent. When it is used for a separator, it is preferable to apply the output improving agent to the separator, and from this point of view, a power storage device separator to which the output improving agent is applied is a more preferred embodiment. In the power storage device separator containing the power storage device output improving agent of the present invention, it is preferable that the output power improving agent is applied in an amount of 1 to 50 g/m ² . If ^the coating amount is less than 1 g/m ^{2 ,} an electricity storage device with excellent rate properties and cycle characteristics may not be obtained. is more preferred, 10 g/m ² or more is particularly preferred, and 12 g/m ² or more is most preferred. On the other hand ^, when the application amount of the output improver exceeds 50 g/m ² , the separator becomes too thick and the rate property may deteriorate ^. It is more preferably 25 g/m 2 or less, particularly preferably 25 g/m ² or less.

As described above, the positive electrode or separator for an electricity storage device containing the output improving agent for an electricity storage device of the present invention can suppress the generation of gas, and exhibits excellent effects in rate characteristics and cycle characteristics. Therefore, an electricity storage device including the positive electrode for an electricity storage device or a separator is a more preferred embodiment. The electricity storage device is not particularly limited, and is preferably at least one electricity storage device selected from the group consisting of lithium ion batteries, lithium ion capacitors and electric double layer capacitors, more preferably lithium ion capacitors.

EXAMPLES The present invention will be described in more detail below using Examples, but the present invention is not limited to these Examples.

[Production of Li ₄ TiO ₄ ]
(Creation example 1)
After dissolving 400 g of titanyl sulfate (TM Crystal, manufactured by Tayca Co., Ltd.) in 1000 g of pure water, 24% aqueous ammonia was added dropwise to adjust the pH to 7.5 to crystallize orthotitanic acid. Next, the orthotitanic acid was filtered and washed with water until the sulfate group (SO ₃ ) was less than 1 wt%, and the resulting orthotitanic acid cake was suspended in water to prepare 2320 g of a 5 wt% suspension. To this, 168 g of lithium hydroxide (manufactured by FMC) was added and wet-mixed. At this time, Li/Ti (molar ratio) was 4.0. Then, the particle size distribution was adjusted by spray drying using a spray dryer (spray pressure 0.7 MPa, air volume 3 m ³ /min, temperature 180 ° C.), D50: 1 μm, D100: 10 μm Li ₄ TiO ₄ precursor dried product got 100 g of the obtained dried precursor and 100 g of polyvinyl alcohol (manufactured by Nippon Acetate & Poval Co., Ltd., molecular weight: 5000) were dry-mixed and then calcined in nitrogen at 950° C. for 2 hours. Furthermore, after cooling to 100° C. or less, additional firing was performed at 550° C. in the air for 2 hours to prepare Li ₄ TiO ₄ of Production Example 1.

(Measurement method of sulfate group)
After drying the orthotitanic acid at 120° C. for 12 hours in vacuum, it was pulverized and pressure-molded to prepare a measurement sample. Using a fluorescent X-ray spectrometer (manufactured by Rigaku, Super mini), the sulfate group (SO ₃ ) was quantified by the FP method.

(Method for measuring specific surface area)
The specific surface area of Li ₄ TiO ₄ was measured by the BET one-point method using a nitrogen adsorption measuring device (Macsorb HM model-1208 manufactured by Mountec Co., Ltd.). In addition, the pretreatment was performed at 150° C. in vacuum. Table 1 shows the results.

(Method for measuring particle size distribution)
The particle size distribution of Li ₄ TiO ₄ was measured using a particle size distribution analyzer (Microtrac MT-3000 manufactured by Nikkiso Co., Ltd.). At this time, the medium was water, and ultrasonic dispersion was not performed. Table 1 shows the results.

(Production example 2)
98 g of anatase type titanium oxide (AMT-100, manufactured by Tayca Corporation) as a titanium source and 168 g of lithium hydroxide (manufactured by FMC) as a lithium source were wet mixed. At this time, the medium was water, the Li/Ti (molar ratio) was 4.0, and the average dispersed particle size of the anatase type titanium oxide was 0.5 μm. Then, the particle size distribution was adjusted by spray drying using a spray dryer (spray pressure 0.7 MPa, air volume 3 m ³ /min, temperature 180 ° C.), D50: 4 μm, D100: 15 μm Li ₄ TiO ₄ precursor dried product got 100 g of the obtained dried precursor and 100 g of polyvinyl alcohol (manufactured by Nippon Acetate & Poval Co., Ltd., molecular weight: 5000) were dry-mixed and then calcined in nitrogen at 950° C. for 2 hours. Furthermore, after cooling to 100° C. or less, additional firing was performed at 550° C. in the air for 2 hours to prepare Li ₄ TiO ₄ of Production Example 2. The specific surface area and particle size distribution of the obtained Li ₄ TiO ₄ were measured in the same manner as in Preparation Example 1. Table 1 shows the results.

(Production example 3)
Li ₄ TiO ₄ precursor having D50: 8 μm and D100: 20 μm in the same manner as in Preparation Example 2 except that spray drying was performed at a spray pressure of 0.5 MPa, an air volume of 2.5 m ³ /min, and a temperature of 180° C. A dry product was obtained. Further, Li ₄ TiO ₄ of Production Example 3 was produced in the same manner as in Production Example 2, except that additional firing was performed at 725° C. for 2 hours in the air. The specific surface area and particle size distribution of the obtained Li ₄ TiO ₄ were measured in the same manner as in Preparation Example 1. Table 1 shows the results.

(Production example 4)
Li _3.8 TiO ₄ of Production Example 4 was produced in the same manner as in Production Example 1, except that the amount of lithium hydroxide added was 160 g. The specific surface area and particle size distribution of the obtained Li _3.8 TiO ₄ were measured in the same manner as in Preparation Example 1. Table 1 shows the results.

(Production example 5)
Li _4.2 TiO ₄ of Production Example 4 was produced in the same manner as in Production Example 1, except that the amount of lithium hydroxide added was 176 g. The specific surface area and particle size distribution of the obtained Li _4.2 TiO ₄ were measured in the same manner as in Preparation Example 1. Table 1 shows the results.

Example 1
(Preparation of negative electrode)
Spinel-type lithium titanate (BP-263, manufactured by Tayca Corporation) as a negative electrode active material, acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., Denka black powder) as a conductive agent, and polyvinylidene fluoride (manufactured by Kureha Corporation) as a binder. , KF polymer) were mixed at a ratio of 80:10:10, and N-methyl-2-pyrrolidone was used as a dispersion medium to prepare an electrode mixture slurry. This electrode mixture slurry was coated on an etched aluminum foil (20CB, manufactured by Nippon Electric Capacitor Industry Co., Ltd.) as a current collector, dried, and roll-pressed to prepare a negative electrode having a thickness of 35 μm.

(Preparation of positive electrode)
Activated carbon (YP-50F, manufactured by Kuraray Co., Ltd.) as a positive electrode active material, Li ₄ TiO ₄ of Preparation Example 1 as an output improver, acetylene black (Denka Black powder, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive aid, and polyfluoride as a binder. Vinylidene chloride (KF Polymer manufactured by Kureha Co., Ltd.) was used, these were mixed at a ratio of 76:1:9:14, and N-methyl-2-pyrrolidone was used as a dispersion medium to prepare an electrode mixture slurry. bottom. This electrode mixture slurry was coated on an etched aluminum foil (20CB, manufactured by Nippon Denki Kogyo Co., Ltd.) as a current collector, dried, and roll-pressed to prepare a positive electrode having a thickness of 80 μm.

(Production of power storage device)
When the positive electrode and the negative electrode prepared as described above were punched into 3.0 cm×4.0 cm (12.0 cm ² ) and 3.3 cm×4.3 cm (14.2 cm ² ) pieces, respectively, the capacity of the positive electrode was The capacity of the negative electrode was 1.40 mAh, the capacity of the negative electrode was 4.20 mAh, and the capacity ratio of the positive and negative electrodes was 3.00. The above positive electrode and negative electrode were opposed to each other with a cellulose separator interposed therebetween, and 1.0 M LiBF ₄ /PC was injected as an electrolytic solution, followed by lamination sealing to produce an electricity storage device.

(Capacitance measurement at 1C)
A 3-cycle charge/discharge test was performed at a charge/discharge rate of 1C and a voltage range of 1.5 to 2.8V using the electricity storage device produced above. At this time, the obtained discharge capacity at the third cycle was taken as the capacity (mAh) at 1C. The measurement was performed using a charge/discharge test device (HJ0610SD8Y manufactured by Hokuto Denko Co., Ltd.). Table 3 shows the results.

(Measurement of cell resistance)
Then, the cell resistance was measured using a resistance meter (manufactured by Hioki Electric Co., Ltd., RM3542A). Table 3 shows the results.

(Rating evaluation)
(Measurement of capacity and capacity retention rate at 300C)
Using the electricity storage device produced above, a 1-cycle charge/discharge test was performed at a charge/discharge rate of 300 C and a voltage range of 1.5 to 2.8 V, and the obtained discharge capacity was taken as the capacity at 300 C (mAh). Furthermore, the capacity retention rate (%) at 300C was calculated by the following formula. The measurement was performed using a charge/discharge test device (HJ0610SD8Y manufactured by Hokuto Denko Co., Ltd.). Table 3 shows the results.
Capacity at 300C (mAh)/Capacity at 1C (mAh) x 100 = Capacity retention rate at 300C (%)

(Cycle characteristics evaluation)
(Measurement of capacity and capacity retention rate after 100 cycles)
Then, after performing a 100 cycle charge/discharge test at a charge/discharge rate of 100C and a voltage range of 1.5 to 2.8V, one cycle charge/discharge was performed at a charge/discharge rate of 1C and a voltage range of 1.5 to 2.8V. A test was conducted, and the obtained discharge capacity was taken as the capacity (mAh) after 100 cycles. Furthermore, using the capacity (mAh) at 1C measured above, the capacity retention rate (%) after 100 cycles was calculated by the following formula. The measurement was performed using a charge/discharge test device (HJ0610SD8Y manufactured by Hokuto Denko Co., Ltd.).
Capacity after 100 cycles (mAh)/Capacity at 1C (mAh) x 100 = Capacity retention rate after 100 cycles (%)

(Measurement of gas generation amount)
The amount of gas generated was measured by measuring the volume change of the electricity storage device before and after the cycle characteristic evaluation based on Archimedes' principle. Specifically, the electricity storage device was submerged in a water tank filled with water at 25° C., and the change in volume of the electricity storage device was obtained from the change in weight at that time to measure the amount of gas generated.

Examples 2-4
(Preparation of positive electrode)
In Example 1, the compounding ratio of activated carbon (positive electrode active material): Li ₄ TiO ₄ (output improver): acetylene black (conductive assistant): polyvinylidene fluoride (binder) was 72:5:9:14, respectively. , 67:10:9:14 and 57:20:9:14, positive electrodes of Examples 2 to 4 were produced in the same manner as in Example 1. At this time, compared with Example 1, the capacity of the positive electrode was maintained at 1.40 mAh by increasing the added amount of the active carbon as the amount decreased. The film thicknesses in Examples 2 to 4 after roll pressing were 83 μm, 85 μm and 88 μm, respectively. Using the produced positive electrodes of Examples 2 to 4, electricity storage devices were produced in the same manner as in Example 1 and evaluated. Results are shown in Tables 2 and 3.

Examples 5-9
(Production of separator)
After kneading 8.6 g of Li ₄ TiO ₄ of Preparation Example 1 and 4.5 g of polyvinylidene fluoride, the mixture was diluted with 16.9 g of N-methyl-2-pyrrolidone to prepare a separator paint. Next, a wire bar was used to apply the prepared paint to a cellulose separator, thereby producing a separator for an electricity storage device. Five types (levels) of the paint were prepared so that the coating amounts of Li ₄ TiO ₄ were 5, 10, 15, 20 and 25 g/m ² , respectively, and each was applied to a cellulose separator. Using the produced separators of Examples 5 to 9, electricity storage devices were produced in the same manner as in Example 1 and evaluated. Results are shown in Tables 2 and 3.

Examples 10-12
(Production of separator)
Energy storage device separators of Examples 10 to 12 were produced in the same manner as in Examples 5 to 9, except that Li ₄ TiO ₄ of Production Example 2 was used. Three types (levels) of 15, 20, and 25 g/m ² were prepared with respect to the application amount. Using the produced separators of Examples 10 to 12, electricity storage devices were produced in the same manner as in Example 1 and evaluated. Results are shown in Tables 2 and 3.

Examples 13-15
(Production of separator)
Energy storage device separators of Examples 13 to 15 were produced in the same manner as in Examples 5 to 9, except that Li ₄ TiO ₄ of Production Example 3 was used. Three types (levels) of 15, 20, and 25 g/m ² were prepared with respect to the coating amount. Using the produced separators of Examples 13 to 15, electricity storage devices were produced in the same manner as in Example 1 and evaluated. Results are shown in Tables 2 and 3.

Example 16
(Production of separator)
A power storage device separator of Example 16 was produced in the same manner as in Examples 5 to 9, except that Li _3.8 TiO ₄ of Production Example 4 was used. As for the applied amount, a sample with a coating amount of 20 g/m ² was produced. Using the produced separator of Example 16, an electricity storage device was produced in the same manner as in Example 1 and evaluated. Results are shown in Tables 2 and 3.

Example 17
(Production of separator)
A power storage device separator of Example 17 was produced in the same manner as in Examples 5 to 9, except that Li _4.2 TiO ₄ of Production Example 5 was used. As for the applied amount, a sample with a coating amount of 20 g/m ² was produced. Using the produced separator of Example 17, an electricity storage device was produced in the same manner as in Example 1 and evaluated. Results are shown in Tables 2 and 3.

Comparative example 1
(Preparation of positive electrode)
Activated carbon (YP-50F, manufactured by Kuraray Co., Ltd.) as a positive electrode active material, acetylene black (Denka black powder, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive agent, and polyvinylidene fluoride (KF Polymer, manufactured by Kureha Co., Ltd.) as a binder. , and these were mixed at a ratio of 77:9:14, and N-methyl-2-pyrrolidone was used as a dispersion medium to prepare an electrode mixture slurry. This electrode mixture slurry was coated on an etched aluminum foil (20CB, manufactured by Nippon Denki Kogyo Co., Ltd.) as a current collector, dried, and roll-pressed to prepare a positive electrode having a thickness of 78 μm. Using the produced positive electrode of Comparative Example 1, an electricity storage device was produced in the same manner as in Example 1 and evaluated. Results are shown in Tables 2 and 3.

Comparative example 2
(Preparation of positive electrode)
Activated carbon (Kuraray YP-50F) as a positive electrode active material, acetylene black (Denka Black powder, manufactured by Denki Kagaku Kogyo Co., Ltd.) as an output improver, acetylene black (Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive aid powder), using polyvinylidene fluoride (manufactured by Kureha Co., Ltd., KF Polymer) as a binder, mixing these at a ratio of 72:5:9:14, and using N-methyl-2-pyrrolidone as a dispersion medium. , an electrode mixture slurry was prepared. This electrode mixture slurry was coated on an etched aluminum foil (20CB, manufactured by Nippon Electric Power Co., Ltd.) as a current collector, dried, and roll-pressed to prepare a positive electrode having a thickness of 83 μm. Using the produced positive electrode of Comparative Example 2, an electricity storage device was produced in the same manner as in Example 1 and evaluated. Results are shown in Tables 2 and 3.

Comparative Examples 3 and 4
(Preparation of positive electrode)
In Comparative Example 2, the compounding ratios of activated carbon (positive electrode active material):acetylene black (output improver):acetylene black (conductive aid):polyvinylidene fluoride (binder) were 67:10:9:14 and 57, respectively. Positive electrodes of Comparative Examples 3 and 4 were prepared in the same manner as in Comparative Example 2, except that the ratio was 20:9:14. At this time, compared with Comparative Example 2, the capacity of the positive electrode was maintained at 1.40 mAh by increasing the amount of applied activated carbon to compensate for the reduced amount of activated carbon. The film thicknesses in Comparative Examples 3 and 4 after roll pressing were 85 μm and 88 μm, respectively. Using the produced positive electrodes of Comparative Examples 3 and 4, electricity storage devices were produced in the same manner as in Example 1 and evaluated. Results are shown in Tables 2 and 3.

Comparative Examples 5, 6 and 8
(Preparation of positive electrode)
In Comparative Example 3, the acetylene black used as the output improver was Ketjenblack (manufactured by Kao Corporation), TiO ₂ (manufactured by Tayka Co., Ltd., JA-1), Al ₂ O ₃ (manufactured by Sumitomo Chemical, AKP -3000), positive electrodes of Comparative Examples 5, 6 and 8 were produced in the same manner as in Comparative Example 3. Note that TiO ₂ and Al ₂ O ₃ do not have conductivity like Li ₄ TiO ₄ . Using the produced positive electrodes of Comparative Examples 5, 6 and 8, electricity storage devices were produced in the same manner as in Example 1 and evaluated. Results are shown in Tables 2 and 3.

Comparative Examples 7 and 9
(Production of separator)
In Example 7, Li ₄ TiO ₄ used as an output improver was TiO ₂ (manufactured by Tayca Co., Ltd., JA-1) and Al ₂ O ₃ (manufactured by Sumitomo Chemical, AKP-3000). Electrical storage device separators of Comparative Examples 7 and 9 were produced in the same manner as in Example 7. Note that TiO ₂ and Al ₂ O ₃ do not have conductivity like Li ₄ TiO ₄ . Using the produced separators of Comparative Examples 7 and 9, electricity storage devices were produced in the same manner as in Example 1 and evaluated. Results are shown in Tables 2 and 3.

REFERENCE SIGNS LIST 1 power storage device 2 positive electrode 3 separator 4 negative electrode 5 tab lead 6 case

Claims (5)

An output improver for an electricity storage device comprising a lithium titanate represented by Li _x TiO ₄ (3.8≦x≦4.2) (excluding those in which the surface of the lithium-nickel composite oxide is modified by firing) ) for a power storage device . 2. A positive electrode for an electricity storage device containing the output improving agent for an electricity storage device according to claim 1, wherein the lithium titanate has a specific surface area of 0.5 to 50 m ² /g. An output improver for an electricity storage device comprising a lithium titanate represented by Li _x TiO ₄ (3.8≦x≦4.2) (excluding those in which the surface of the lithium-nickel composite oxide is modified by firing) ) for a power storage device . The power storage device separator containing the power storage device output improving agent according to claim 3 , wherein the lithium titanate has a specific surface area of 0.5 to 50 m ² /g. An electric storage device comprising the positive electrode for an electric storage device according to claim 1 or 2 or the separator for an electric storage device according to claim 3 or 4 .

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