LITHIUM ION CAPACITOR POSITIVE ELECTRODE

Abstract

There is demand for a lithium ion capacitor positive electrode that can improve the battery characteristics (and, in particular, the rate characteristics) of a lithium ion capacitor. This lithium ion capacitor positive electrode is characterized by containing, in a positive electrode active material, at least one titanate selected from among Li.sub.2TiO.sub.3, Li.sub.4Ti.sub.5O.sub.12, Na.sub.2TiO.sub.3, and K.sub.2Ti.sub.2O.sub.5.

Claims

1. A lithium ion capacitor positive electrode comprising, in a positive electrode active material, at least one titanate selected from Li.sub.2TiO.sub.3, Li.sub.4Ti.sub.5O.sub.12, Na.sub.2TiO.sub.3, and K.sub.2Ti.sub.2O.sub.5.

2. The lithium ion capacitor positive electrode according to claim 1, wherein a content of the titanate is 0.5 to 50 wt % relative to the positive electrode active material.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0036] FIG. 1 schematically illustrates a structure of a lithium ion capacitor (lithium ion capacitors in Examples 1 to 11 and Comparative Examples 1, 3, and 4) produced using Li.sub.4Ti.sub.5O.sub.12 as a negative electrode active material.

[0037] FIG. 2 schematically illustrates a structure of a lithium ion capacitor (lithium ion capacitors in Examples 12 and 13 and Comparative Example 2) produced using graphite as a negative electrode active material.

DESCRIPTION OF EMBODIMENTS

Examples

[0038] Next, the lithium ion capacitor positive electrode according to the present invention will be described in detail based on Examples and Comparative Examples. The present invention is not limited to Examples below.

Example 1

(Production of Positive Electrode)

[0039] First, 300 g of an anatase titanium oxide (AMT-100 manufactured by TAYCA Corporation) and 266 g of lithium hydroxide (manufactured by FMC) were mixed with each other in a wet process. Then, the resulting mixture was fired in the air at 750 C. for 2 hours to obtain a 213-type lithium titanate (Li.sub.2TiO.sub.3).

[0040] Subsequently, 4.60 g of activated carbon (AP-20-0001 manufactured by AT Electrode Co., Ltd.) serving as a positive electrode active material, 0.54 g of acetylene black (DENKA BLACK manufactured by Denka Company Limited) serving as a conductive aid, and 0.025 g of the Li.sub.2TiO.sub.3 serving as an additive were added to 12.47 g of a 1.4 wt % aqueous solution of carboxymethyl cellulose (manufactured by DKS Co., Ltd.) serving as a thickener and dispersed using a dispersing machine. Furthermore, 1.37 g of styrene-butadiene rubber (manufactured by JSR Corporation) serving as a binding agent was added thereto and mixed using a dispersing machine. The resulting mixture (coating material) was applied onto an etched aluminum foil (manufactured by JAPAN CAPACITOR INDUSTRIAL Co., Ltd.) serving as a current collector and dried to produce a lithium ion capacitor positive electrode in Example 1 that contained Li.sub.2TiO.sub.3. The content of Li.sub.2TiO.sub.3 relative to the positive electrode active material (activated carbon) was 0.5 wt %.

(Production of Negative Electrode)

[0041] First, 520 g of an orthotitanic acid (manufactured by TAYCA Corporation) and 218 g of lithium hydroxide monohydrate (manufactured by FMC) were mixed with each other in a wet process. Then, the resulting mixture was fired in the air at 650 C. for 2 hours to obtain fine particles of Li.sub.4Ti.sub.5O.sub.12 having a specific surface area of 70 m.sup.2/g.

[0042] Subsequently, 4.62 g of the Li.sub.4Ti.sub.5O.sub.12 serving as a negative electrode active material and 0.54 g of acetylene black (DENKA BLACK manufactured by Denka Company Limited) serving as a conductive aid were added to 12.47 g of a 1.4 wt % aqueous solution of carboxymethyl cellulose (manufactured by DKS Co., Ltd.) serving as a thickener and dispersed using a dispersing machine. Furthermore, 1.37 g of styrene-butadiene rubber (manufactured by JSR Corporation) serving as a binding agent was added thereto and mixed using a dispersing machine. The resulting mixture (coating material) was applied onto an etched aluminum foil (manufactured by JAPAN CAPACITOR INDUSTRIAL Co., Ltd.) serving as a current collector and dried to obtain a negative electrode. The specific surface area of the Li.sub.4Ti.sub.5O.sub.12 used was 70 m.sup.2/g.

(Production of Lithium Ion Capacitor)

[0043] The positive electrode and negative electrode produced by the above methods were arranged (stacked) with a separator (manufactured by NIPPON KODOSHI Corporation) disposed therebetween as illustrated in FIG. 1. Subsequently, a 1 M LiBF.sub.4/PC (manufactured by KISHIDA CHEMICAL Co., Ltd.) serving as an electrolyte was injected and then sealed to produce a lithium ion capacitor including the lithium ion capacitor positive electrode in Example 1. The electric capacity of the lithium ion capacitor was 600 Ah.

Example 2

[0044] A lithium ion capacitor positive electrode in Example 2 was produced in the same manner as in Example 1, except that the content of Li.sub.2TiO.sub.3 relative to the positive electrode active material (activated carbon) was changed to 1 wt %. A lithium ion capacitor was produced using the lithium ion capacitor positive electrode.

Example 3

[0045] A lithium ion capacitor positive electrode in Example 3 was produced in the same manner as in Example 1, except that the content of Li.sub.2TiO.sub.3 relative to the positive electrode active material (activated carbon) was changed to 10 wt %. A lithium ion capacitor was produced using the lithium ion capacitor positive electrode.

Example 4

[0046] A lithium ion capacitor positive electrode in Example 4 was produced in the same manner as in Example 1, except that the content of Li.sub.2TiO.sub.3 relative to the positive electrode active material (activated carbon) was changed to 20 wt %. A lithium ion capacitor was produced using the lithium ion capacitor positive electrode.

Example 5

[0047] A lithium ion capacitor positive electrode in Example 5 was produced in the same manner as in Example 1, except that the content of Li.sub.2TiO.sub.3 relative to the positive electrode active material (activated carbon) was changed to 30 wt %. A lithium ion capacitor was produced using the lithium ion capacitor positive electrode.

Example 6

[0048] A lithium ion capacitor positive electrode in Example 6 was produced in the same manner as in Example 1, except that the content of Li.sub.2TiO.sub.3 relative to the positive electrode active material (activated carbon) was changed to 50 wt %. A lithium ion capacitor was produced using the lithium ion capacitor positive electrode.

Example 7

[0049] First, 520 g of an orthotitanic acid (manufactured by TAYCA Corporation) and 218 g of lithium hydroxide monohydrate (manufactured by FMC) were mixed with each other in a wet process. Then, the resulting mixture was fired in the air at 700 C. for 2 hours to obtain fine particles of Li.sub.4Ti.sub.5O.sub.12 having a specific surface area of 50 m.sup.2/g.

[0050] Subsequently, a lithium ion capacitor positive electrode in Example 7 was produced in the same manner as in Example 4. On the other hand, the negative electrode active material was changed to the Li.sub.4Ti.sub.5O.sub.12 having a specific surface area of 50 m.sup.2/g. A lithium ion capacitor was produced using the lithium ion capacitor positive electrode and the negative electrode.

Example 8

[0051] First, 520 g of an orthotitanic acid (manufactured by TAYCA Corporation) and 218 g of lithium hydroxide monohydrate (manufactured by FMC) were mixed with each other in a wet process. Then, the resulting mixture was fired in the air at 550 C. for 2 hours to obtain fine particles of Li.sub.4Ti.sub.5O.sub.12 having a specific surface area of 100 m.sup.2/g.

[0052] Subsequently, a lithium ion capacitor positive electrode in Example 8 was produced in the same manner as in Example 4. On the other hand, the negative electrode active material was changed to the Li.sub.4Ti.sub.5O.sub.12 having a specific surface area of 100 m.sup.2/g. A lithium ion capacitor was produced using the lithium ion capacitor positive electrode and the negative electrode.

Example 9

[0053] First, 300 g of an anatase titanium oxide (AMT-100 manufactured by TAYCA Corporation) and 128 g of lithium hydroxide (manufactured by FMC) were mixed with each other in a wet process. Then, the resulting mixture was fired in the air at 825 C. for 2 hours to obtain a 4512-type lithium titanate (Li.sub.4Ti.sub.5O.sub.12).

[0054] Subsequently, a lithium ion capacitor positive electrode in Example 9 was produced in the same manner as in Example 4, except that the Li.sub.4Ti.sub.5O.sub.12 was used instead of the Li.sub.2TiO.sub.3. A lithium ion capacitor was produced using the lithium ion capacitor positive electrode.

Example 10

[0055] First, 300 g of an anatase titanium oxide (AMT-100 manufactured by TAYCA Corporation) and 399 g of sodium hydroxide (manufactured by Sigma-Aldrich) were mixed with each other in a wet process. Then, the resulting mixture was fired in the air at 750 C. for 2 hours to obtain a 213-type sodium titanate (Na.sub.2TiO.sub.3).

[0056] Subsequently, a lithium ion capacitor positive electrode in Example 10 was produced in the same manner as in Example 4, except that the Na.sub.2TiO.sub.3 was used instead of the Li.sub.2TiO.sub.3. A lithium ion capacitor was produced using the lithium ion capacitor positive electrode.

Example 11

[0057] First, 300 g of an anatase titanium oxide (AMT-100 manufactured by TAYCA Corporation) and 249 g of potassium hydroxide (manufactured by Sigma-Aldrich) were mixed with each other in a wet process. Then, the resulting mixture was fired in the air at 750 C. for 2 hours to obtain a 225-type potassium titanate (K.sub.2Ti.sub.2O.sub.5).

[0058] Subsequently, a lithium ion capacitor positive electrode in Example 11 was produced in the same manner as in Example 4, except that the K.sub.2Ti.sub.2O.sub.5 was used instead of the Li.sub.2TiO.sub.3. A lithium ion capacitor was produced using the lithium ion capacitor positive electrode.

Example 12

(Production of Positive Electrode)

[0059] A lithium ion capacitor positive electrode in Example 12 was produced in the same manner as in Example 1, except that the content of Li.sub.2TiO.sub.3 relative to the positive electrode active material (activated carbon) was changed to 10 wt %.

(Production of Negative Electrode)

[0060] To 12.47 g of a 1.4 wt % aqueous solution of carboxymethyl cellulose (manufactured by DKS Co., Ltd.) serving as a thickener, 4.62 g of natural graphite (manufactured by Nippon Graphite Industries Co., Ltd.) serving as a negative electrode active material and 0.54 g of acetylene black (DENKA BLACK manufactured by Denka Company Limited) serving as a conductive aid were added, and dispersed using a dispersing machine. Furthermore, 1.37 g of styrene-butadiene rubber (manufactured by JSR Corporation) serving as a binding agent was added thereto and mixed using a dispersing machine. The resulting mixture (coating material) was applied onto a copper foil (manufactured by Fukuda Metal Foil & Powder Co., Ltd.) serving as a current collector and dried to obtain a negative electrode. The specific surface area of the natural graphite used was 4 m.sup.2/g.

(Production of Lithium Ion Capacitor)

[0061] The positive electrode and negative electrode produced by the above methods and 1.5 mg of a Li metal piece (manufactured by Honjo Metal Co., Ltd.) were arranged (stacked) with a separator (manufactured by NIPPON KODOSHI Corporation) disposed between the positive electrode and the negative electrode as illustrated in FIG. 2. Subsequently, a 1 M LiPF.sub.6/EC:DEC=1:2 (manufactured by KISHIDA CHEMICAL Co., Ltd.) serving as an electrolyte was injected, then sealed, and left to stand for 10 days to produce a lithium ion capacitor including the lithium ion capacitor positive electrode in Example 12. The electric capacity of the lithium ion capacitor was 600 Ah.

Example 13

[0062] A lithium ion capacitor positive electrode in Example 13 was produced in the same manner as in Example 12, except that the content of Li.sub.2TiO.sub.3 relative to the positive electrode active material (activated carbon) was changed to 20 wt %. A lithium ion capacitor was produced using the lithium ion capacitor positive electrode.

Comparative Example 1

[0063] A lithium ion capacitor positive electrode in Comparative Example 1 was produced in the same manner as in Example 1, except that the Li.sub.2TiO.sub.3 was not added to the positive electrode. A lithium ion capacitor was produced using the lithium ion capacitor positive electrode.

Comparative Example 2

[0064] A lithium ion capacitor positive electrode in Comparative Example 2 was produced in the same manner as in Example 12, except that the Li.sub.2TiO.sub.3 was not added to the positive electrode. A lithium ion capacitor was produced using the lithium ion capacitor positive electrode.

Comparative Example 3

[0065] A lithium ion capacitor positive electrode in Comparative Example 3 was produced in the same manner as in Example 4, except that TiO.sub.2 (JA-1 manufactured by TAYCA Corporation) was used instead of the Li.sub.2TiO.sub.3. A lithium ion capacitor was produced using the lithium ion capacitor positive electrode. Note that TiO.sub.2 does not have electrical conductivity like Li.sub.2TiO.sub.3, for example.

Comparative Example 4

[0066] A lithium ion capacitor positive electrode in Comparative Example 4 was produced in the same manner as in Example 4, except that Al.sub.2O.sub.3 (manufactured by Sigma-Aldrich) was used instead of the Li.sub.2TiO.sub.3. A lithium ion capacitor was produced using the lithium ion capacitor positive electrode. Note that Al.sub.2O.sub.3 does not have electrical conductivity like Li.sub.2TiO.sub.3, for example.

[0067] Next, the battery characteristics (rate characteristics) and the effect of suppressing generation of gas were evaluated for each of the produced lithium ion capacitors.

(Evaluation of Rate Characteristics (Rapid Charge/Discharge Characteristics))

[0068] Each of the produced lithium ion capacitors was charged and discharged at charge/discharge rates of 1 C and 300 C at 25 C. in the voltage range of 1.5 to 2.8 V. Then, the rate characteristics (rapid charge/discharge characteristics) were evaluated on the basis of calculation formula below.

Discharge capacity at 300 C/Discharge capacity at 1 C100=Rate characteristics (%)

(Measurement of Amount of Gas Generated)

[0069] First, the initial volume of each of the produced lithium ion capacitors in Examples 1 to 13 and Comparative Examples 1 to 4 was measured on the basis of the Archimedes' principle. Specifically, each lithium ion capacitor was sunk in a water tank filled with water at 25 C., and the initial volume of each lithium ion capacitor was calculated from the weight change.

[0070] Subsequently, three cycles of charge and discharge were performed on each lithium ion capacitor at a charge/discharge rate of 0.5 C at 60 C. in the voltage range of 1.5 to 2.9 V. Then, the volume of each lithium ion capacitor after charge and discharge was calculated by the same method as above. The volume change of each lithium ion capacitor before and after charge and discharge was determined from the difference from the initial volume to measure the amount of gas generated from each lithium ion capacitor. The percentage of the volume change of each lithium ion capacitor was also determined from calculation formula below.

Percentage of volume change (%)=Volume change (ml)/Initial volume (ml)100

[0071] Table 1 illustrates the results. The results show that the lithium ion capacitors including the lithium ion capacitor positive electrodes in Examples had better rate characteristics (rapid charge/discharge characteristics) than the lithium ion capacitors including the lithium ion capacitor positive electrodes in Comparative Examples.

[0072] The results also show that, in addition to the rate characteristics, the lithium ion capacitors including the lithium ion capacitor positive electrodes in Examples had higher electric capacity than the lithium ion capacitors including the lithium ion capacitor positive electrodes in Comparative Examples. Herein, since Li.sub.2TiO.sub.3, Li.sub.4Ti.sub.5O.sub.12, Na.sub.2TiO.sub.3, and K.sub.2Ti.sub.2O.sub.5 themselves do not contribute to charge and discharge, this finding also overturns the common general technical knowledge in the related art.

[0073] The results also show that the lithium ion capacitors including the lithium ion capacitor positive electrodes in Examples had a smaller amount (absolute quantity) of gas generated and a smaller percentage of volume change (more specifically, a percentage of volume change of 5% or less) than the lithium ion capacitors including the lithium ion capacitor positive electrodes in Comparative Examples.

TABLE-US-00001 TABLE 1 Content of Rate Percentage titanate Type of characteristics Electric Initial Volume of volume relative negative Specific surface (rapid charge/ capacity of volume of change of change of to positive electrode area of negative discharge lithium ion lithium ion lithium ion lithium ion Type of electrode active active electrode active characteristics, capacitor capacitor capacitor capacitor titanate material (wt %) material material (m.sup.2/g) %) (Ah) (ml) (ml) (%) Example 1 Li.sub.2TiO.sub.3 0.5 Li.sub.4Ti.sub.5O.sub.12 70 40 600 2.23 0.10 4.5 Example 2 Li.sub.2TiO.sub.3 1 Li.sub.4Ti.sub.5O.sub.12 70 42 613 2.24 0.06 2.7 Example 3 Li.sub.2TiO.sub.3 10 Li.sub.4Ti.sub.5O.sub.12 70 56 748 2.32 0.02 0.9 Example 4 Li.sub.2TiO.sub.3 20 Li.sub.4Ti.sub.5O.sub.12 70 61 893 2.34 0.01 0.4 Example 5 Li.sub.2TiO.sub.3 30 Li.sub.4Ti.sub.5O.sub.12 70 66 1042 2.32 0.03 1.3 Example 6 Li.sub.2TiO.sub.3 50 Li.sub.4Ti.sub.5O.sub.12 70 71 1349 2.32 0.09 3.9 Example 7 Li.sub.2TiO.sub.3 20 Li.sub.4Ti.sub.5O.sub.12 50 50 881 2.36 0.01 0.2 Example 8 Li.sub.2TiO.sub.3 20 Li.sub.4Ti.sub.5O.sub.12 100 78 903 2.37 0.04 1.7 Example 9 Li.sub.4Ti.sub.5O.sub.12 20 Li.sub.4Ti.sub.5O.sub.12 70 65 814 2.34 0.03 1.3 Example 10 Na.sub.2TiO.sub.3 20 Li.sub.4Ti.sub.5O.sub.12 70 69 641 2.35 0.01 0.2 Example 11 K.sub.2Ti.sub.2O.sub.5 20 Li.sub.4Ti.sub.5O.sub.12 70 69 706 2.35 0.01 0.4 Example 12 Li.sub.2TiO.sub.3 10 graphite 4 70 1420 2.37 0.09 3.8 Example 13 Li.sub.2TiO.sub.3 20 graphite 4 76 1700 2.39 0.05 2.1 Comparative Blank 0 Li.sub.4Ti.sub.5O.sub.12 70 30 586 2.22 0.15 6.7 Example 1 Comparative Blank 0 graphite 4 53 593 2.38 0.20 8.4 Example 2 Comparative TiO.sub.2 20 Li.sub.4Ti.sub.5O.sub.12 70 12 485 2.31 0.15 6.5 Example 3 Comparative Al.sub.2O.sub.3 20 Li.sub.4Ti.sub.5O.sub.12 70 15 477 2.32 0.15 6.5 Example 4

[0074] It has been found from the above results that, according to the lithium ion capacitor positive electrode of the present invention, when the positive electrode of a lithium ion capacitor contains a particular titanate as an additive, the rate characteristics of the lithium ion capacitor can be improved despite the fact that the titanate itself has no electrical conductivity.

[0075] It has also been found that, in the lithium ion capacitor positive electrode according to the present invention, the generation of various gases such as carbonic acid gas, hydrogen gas, and fluorine gas during operation or due to time-varying changes can be suppressed while the rate characteristics are improved.

INDUSTRIAL APPLICABILITY

[0076] The lithium ion capacitor positive electrode according to the present invention is applicable to lithium ion capacitors.

REFERENCE SIGNS LIST

[0077] 1 lithium ion capacitor [0078] 2 positive electrode (containing at least one titanate selected from Li.sub.2TiO.sub.3, Li.sub.4Ti.sub.5O.sub.12, Na.sub.2TiO.sub.3, and K.sub.2Ti.sub.2O.sub.5) [0079] 3 separator [0080] 4 negative electrode [0081] 5 tab lead [0082] 6 case [0083] 7 Li metal piece