JP2007087714A - Energy storage device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an energy storage device having high capacity and high reliability. <P>SOLUTION: The energy storage device is comprised of a positive electrode mainly comprising activated carbon, a negative electrode mainly comprising a carbonaceous material capable of absorbing and releasing lithium ions and previously absorbed with lithium ions, and an electrolyte, and the electrolyte contains an organic compound having a π-bond. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a high-capacity and reliable energy storage device.

  Energy storage devices are roughly divided into two types: secondary batteries and electric double layer capacitors. In particular, an electric double layer capacitor that can be charged and discharged with a large current is promising for applications such as a power source for electric vehicles, a backup power source for momentary power interruption, and an uninterruptible power source. Since this electric double layer capacitor consists of a polarizable electrode mainly composed of activated carbon having a non-Faraday reaction mechanism in both positive and negative electrodes, it is faster to charge and discharge than a lithium secondary battery having an electrode having a Faraday reaction mechanism. And has the advantages of high cycle characteristics and high durability during voltage application. On the other hand, since the electrodes of the electric double layer capacitor are made of activated carbon for both positive and negative electrodes, the energy density is lower than that of the lithium secondary battery, and the withstand voltage is low.

The withstand voltage of the electric double layer capacitor is 1.2 V because it is determined by the decomposition voltage of water in the case of having an aqueous electrolyte, and is about 2.5 to 3.3 V even in the case of having an organic electrolyte. The cell capacity C _t of the electric double layer capacitor is _expressed by 1 / C _t = 1 / C _a + 1 / C _c (C _a : negative electrode capacity, C _c : positive electrode capacity), and when both positive and negative electrodes are mainly activated carbon, The capacities of the positive electrode and the negative electrode are substantially equal (C _a = C _c = C), the cell capacity is C _t = C / 2, and the cell energy E is E = 1 / 2C _t V ² = ¼ CV ² (V: Voltage). An electric double layer capacitor having an organic electrolytic solution having a higher withstand voltage than an aqueous electrolytic solution has higher energy. However, even an electric double layer capacitor having an organic electrolyte has an energy density that does not reach that of a secondary battery.

Instead, Patent Document 1 discloses a carbon material exhibiting a Faraday-like reaction mechanism in which an electrode mainly composed of activated carbon is used as a positive electrode and a [002] plane interval by X-ray diffraction is 0.338 to 0.356 nm. A secondary power supply with an upper limit of 3.0 V has been proposed in which an electrode previously occluded with lithium ions is used as a negative electrode. Since the secondary power source proposed in Patent Document 1 has a negative electrode capacity sufficiently larger than the positive electrode capacity, the cell capacity of this capacitor is 1 / C _t = 1 / C _a + 1 / C _c ≈1 / C _c , and C _c When C = C, the cell energy E becomes E = 1 / 2C _t V ² = 1 / 2CV ² , and the cell energy can be improved twice as compared with the electric double layer capacitor.

Patent Document 2 proposes a battery using, as a negative electrode, a carbon material in which lithium ions are occluded in advance by a chemical method or an electrochemical method in a carbon material that can occlude and desorb lithium ions. The capacitance Q of the cell is Q = C _t V, and the capacitance of the cell can be increased by increasing the withstand voltage V. Patent Document 3 proposes a secondary power supply with an upper limit voltage of 4.0 V, having a negative electrode that supports a carbon material capable of inserting and extracting lithium ions on a porous current collector that does not form an alloy with lithium.

  In order to further increase the cell energy while enabling rapid charge / discharge, further increase in capacity is required, and a withstand voltage of 4.0 V or more is required. The energy storage device is mainly used as a power storage device, and it is necessary to always store power. Therefore, it is necessary to continue to apply a voltage of 4.0 V or more, there is a possibility of decomposition of the electrolytic solution, gas generation associated therewith, and safety is also required at the same time.

JP-A 64-14882 Japanese Patent Laid-Open No. 8-1007048 JP-A-9-55342

  It is an object of the present invention to provide a high capacity and reliable energy storage device.

  The present invention relates to an energy storage device including a positive electrode mainly composed of activated carbon, a negative electrode mainly composed of a material in which lithium ions are previously occluded in a carbonaceous material capable of absorbing and desorbing lithium ions, and an electrolytic solution. It contains an organic compound having a π bond.

  According to the present invention, the electrolytic solution contains the organic compound having the π bond that oxidizes at the positive electrode potential, thereby forming a stable film on the positive electrode surface, and applying a voltage of 4.0 V or more for a long time. The decomposition reaction of the electrolyte solution on the surface of the positive electrode active material can be suppressed.

  In the present invention, one or more organic compounds having a π bond are added to the electrolytic solution, and specific examples thereof are as follows.

  (1) An organic compound having a π bond contained in the non-aqueous electrolyte is represented by (Formula 1).

At least one of R _{1 to} R ₄ includes a substituent that satisfies the following conditions: an alkyl group (including a double bond or a cyclized group), a phenyl group, or an alkoxy group (including a double bond). A phenoxy group, a carbonyl group or a halogen group.

  (2) The organic compound having a π bond contained in the non-aqueous electrolyte is represented by (Formula 2).

At least one of R _{1 to} R ₆ includes a substituent that satisfies the following conditions: an alkyl group (including a double bond or a cyclized group), a phenyl group, or an alkoxy group (including a double bond). A phenoxy group, a carbonyl group or a halogen group.

  (3) An organic compound having a π bond contained in the non-aqueous electrolyte is represented by (Formula 3).

R _{1 to} R ₅ may include a substituent that satisfies the following conditions: an alkyl group (including a double bond or a cyclized group), a phenyl group, an alkoxy group (including a double bond) A phenoxy group, a carbonyl group or a halogen group.

  (4) An organic compound having a π bond contained in the non-aqueous electrolyte is represented by (Formula 4).

n = 0 to 6 and R _{1 to} R ₁₀ may include a substituent that satisfies the following conditions: an alkyl group (including a double bond or a cyclized group), a phenyl group, an alkoxy group A group (including a double bond or a cyclized group), a phenoxy group, a carbonyl group or a halogen group.

  (5) An organic compound having a π bond contained in the non-aqueous electrolyte is represented by (Formula 5).

R _{1 to} R ₁₀ may include a substituent that satisfies the following conditions: an alkyl group (including a double bond or a cyclized group), a phenyl group, an alkoxy group (including a double bond) A phenoxy group, a carbonyl group or a halogen group.

  (6) The organic compound having a π bond contained in the nonaqueous electrolytic solution is represented by (Formula 6).

R _{1 to} R ₁₄ may include a substituent that satisfies the following conditions: an alkyl group (including a double bond or a cyclized group), a phenyl group, an alkoxy group (including a double bond) A phenoxy group, a carbonyl group or a halogen group.

  (7) An organic compound having a π bond contained in the non-aqueous electrolyte is represented by (Formula 7).

R _{1 to} R ₄ may include a substituent that satisfies the following conditions: an alkyl group (including a double bond or a cyclized group), a phenyl group, an alkoxy group (including a double bond) A phenoxy group, a carbonyl group or a halogen group.

  (8) An organic compound having a π bond contained in the non-aqueous electrolyte is represented by (Formula 8).

R _{1 to} R ₅ may include a substituent that satisfies the following conditions: an alkyl group (including a double bond or a cyclized group), a phenyl group, an alkoxy group (including a double bond) A phenoxy group, a carbonyl group or a halogen group.

  (9) The organic compound having a π bond contained in the nonaqueous electrolytic solution is represented by (Formula 9).

R _{1 to} R ₄ may include a substituent that satisfies the following conditions: an alkyl group (including a double bond or a cyclized group), a phenyl group, an alkoxy group (including a double bond) A phenoxy group, a carbonyl group or a halogen group.

  Two or more organic compounds having a π bond can be used in combination. In addition, the organic compound having a π bond can be contained in the electrolyte solution in the range of 0.1 to 5.0% by weight. If the content is too large, the conductivity of the electrolyte solution is lowered and cell characteristics are reduced. With regard to a compound having a low polymerization potential, there is a possibility that a conductive polymer is generated by polymerization and an internal short circuit is caused between the positive and negative electrodes. If the content is too small, the action becomes small and the effect is lost. Therefore, a content of 1.0 to 2.0% by weight is preferable.

  There are a physical method, a chemical method, and an electrochemical method as a precharge method for preliminarily storing lithium ions in the graphite-based carbon material of the negative electrode. There are roughly two electrochemical methods. There are a method of controlling by an electric current and a method of spontaneously by a short circuit between positive and negative electrodes. Since the former requires control, charging takes time, so the latter method is preferable. In particular, charging using an electromotive force due to short circuit is an equilibrium reaction, and when the short circuit is performed with an excess amount of lithium than the lithium storage amount of the negative electrode active material, the reaction proceeds faster and the amount of lithium storage increases, so the charging time In order to shorten the length, it is preferable to increase the amount of lithium metal.

As a method of preliminarily inserting lithium ions into the graphite-based carbon material of the negative electrode by a short circuit, there is a method of monitoring the value of the flowing current and calculating the charge capacity and ending with the specified capacity or ending with the charge time. Although there is a method of monitoring the potential difference, the negative electrode potential during short-circuiting is almost 0 V (Li / Li ⁺ ), so that determination is extremely difficult. The determination can be made from the OCV in the open circuit state after the end of the short circuit, but it takes time and effort to stop the short circuit once and stabilize the OCV as the determination reference. If it is the same cell configuration, it is possible to control the lithium storage amount by time, and by creating a calibration curve of the relationship between short circuit time and capacity, the lithium storage amount can be controlled by charging time, It is most preferable to control the amount of occlusion of thium ions in the negative electrode graphite carbon material by this method.

  FIG. 1 is a cross-sectional view of a cell for a float charging test of an energy storage device according to the present invention, wherein 1 is a press cell made of SUS, 2 is a polyethylene separator having a thickness of 40 μm, and 3 and 4 are collections of positive electrodes. It is an electric body. 3 is a rolled 20 μm thick aluminum foil, 4 is an electrolytically etched 20 μm thick aluminum foil, 5 activated carbon mixture is applied onto 4 and pressed, and 5 activated carbon mixture is placed on top. Applied and pressed are bound. 6 and 7 are 20 μm-thick copper foils rolled with a negative electrode current collector, and 8 is applied with a graphite mixture and pressed, and 5 and 8 are 2 separators. Are arranged facing each other. In addition, a lithium metal foil having a thickness of 1 mm is arranged in the back direction through two separators. The electrolyte solution is infiltrated into all the separators 2.

  [Comparative Example 1] A mixture of 80% by weight of petroleum coke activated carbon powder activated by a steam activation treatment method, 10% by weight of carbon black and 10% by weight of polyvinylidene fluoride and kneaded by adding N-methylpyrrolidone. , Applied to an etched aluminum foil having a width of 5 cm, a length of 15 cm, and a thickness of 20 μm, dried at 120 ° C. for 3 hours as an electrode sheet, and punched into a size of 15Φ as a positive electrode .

  A mixture of 98% by weight of amorphous graphite, 1% by weight of a crosslinked styrene-butadiene copolymer, and 1% by weight of carboxymethylcellulose, kneaded, applied to a rolled copper foil having a width of 13 cm, a length of 15 cm, and a thickness of 20 μm. And what was dried at 120 degreeC for 3 hours was used as the electrode sheet, and what punched this sheet | seat to the magnitude | size of 15 (PHI) was used as the negative electrode.

A solution in which 1.5 mol / L LiPF ₆ was dissolved in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a ratio of 1: 3 was used as an electrolytic solution.

  A separator made of a polyethylene sheet having a thickness of 40 μm and a porosity of 45% was used.

[Example 1]
The same as Comparative Example 1 except that 1% by weight of cyclohexylbenzene was added to the electrolytic solution in Comparative Example 1.

[Example 2]
The same as Comparative Example 1 except that 1% by weight of 4-methylanisole was added to the electrolytic solution in Comparative Example 1.

[Example 3]
The same as Comparative Example 1 except that 1% by weight of biphenyl was added to the electrolytic solution in Comparative Example 1.

[Example 4]
The same as Comparative Example 1 except that 1% by weight of o-terphenyl was added to the electrolytic solution in Comparative Example 1.

[Example 5]
The same as Comparative Example 1 except that 1% by weight of 3-chlorothiophene was added to the electrolytic solution in Comparative Example 1.

[Example 6]
The same as Comparative Example 1 except that 1% by weight of N-methylpyrrole was added to the electrolytic solution in Comparative Example 1.

[Example 7]
The same as Comparative Example 1 except that 1% by weight of furan was added to the electrolyte in Comparative Example 1.

In order to stabilize the capacity in the cells of Comparative Example 1 and Examples 1 to 7, a charge / discharge cycle in which Li / Li ⁺ is charged from 2 V to 4.2 V at 4 C rate and then discharged to 2 V at 4 C rate. Table 1 shows the results obtained by performing 4 cycles and setting the discharge capacity after 4 cycles as the initial capacity.

Next, the cells of Comparative Example 1 and Examples 1 to 7 were charged from 2V to 4.2V with Li / Li ⁺ at a 4C rate, and then CV charged for 24 hours under a voltage application condition of 4.2V. Table 1 shows the results of performing 20 charge / discharge cycles to discharge to 2 V, setting the discharge capacity after 20 cycles (about 500 hours) as the post-test capacity, and the capacity maintenance ratio of the post-test capacity relative to the initial capacity as the maintenance ratio. Show.

  As shown in Table 1, the capacity retention rate of the cells of Examples 1 to 7 was improved in the discharge capacity after 20 cycles as compared with the cell of Comparative Example 1 which did not contain an organic compound having a π bond in the electrolyte. ing. From this, it was confirmed that by containing an organic compound having a π bond that oxidizes at the positive electrode potential in the electrolytic solution, it can withstand 4.2 V for a long time and the capacity reduction rate is reduced.

  INDUSTRIAL APPLICABILITY The present invention can be applied to an energy storage device that can provide high-capacity energy when supplying power during a momentary power failure or the like.

Sectional drawing of the cell for the float charge test of the energy storage device by this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Press cell, 2 ... Separator, 3 ... Positive electrode collector foil, 4 ... Positive electrode collector, 5 ... Positive electrode activated carbon mixture, 6 ... Negative electrode collector foil, 7 ... Negative electrode collector, 8 ... Negative electrode carbonaceous material Mixture, 9 ... lithium metal foil.

Claims (15)

  A positive electrode mainly composed of activated carbon; a negative electrode mainly composed of a material in which lithium ions are previously occluded in a carbonaceous material capable of occluding and desorbing lithium ions; and a non-aqueous electrolyte solution, the non-aqueous electrolyte solution having a π bond An energy storage device comprising an organic compound. The energy storage device according to claim 1, wherein the organic compound having a π bond contained in the non-aqueous electrolyte is represented by (Formula 1).

At least one of R _{1 to} R ₄ includes a substituent that satisfies the following conditions: an alkyl group (including a double bond or a cyclized group), a phenyl group, or an alkoxy group (including a double bond). A phenoxy group, a carbonyl group or a halogen group. The energy storage device according to claim 1, wherein the organic compound having a π bond contained in the non-aqueous electrolyte is represented by (Formula 2).

At least one of R _{1 to} R ₆ includes a substituent that satisfies the following conditions: an alkyl group (including a double bond or a cyclized group), a phenyl group, or an alkoxy group (including a double bond). A phenoxy group, a carbonyl group or a halogen group. The energy storage device according to claim 1, wherein the organic compound having a π bond contained in the non-aqueous electrolyte is represented by (Formula 3).

R _{1 to} R ₅ may include a substituent that satisfies the following conditions: an alkyl group (including a double bond or a cyclized group), a phenyl group, an alkoxy group (including a double bond) A phenoxy group, a carbonyl group or a halogen group. The energy storage device according to claim 1, wherein the organic compound having a π bond contained in the non-aqueous electrolyte is represented by (Formula 4).

n = 0 to 6 and R _{1 to} R ₁₀ may include a substituent that satisfies the following conditions: an alkyl group (including a double bond or a cyclized group), a phenyl group, an alkoxy group A group (including a double bond or a cyclized group), a phenoxy group, a carbonyl group or a halogen group. The energy storage device according to claim 1, wherein the organic compound having a π bond contained in the non-aqueous electrolyte is represented by (Formula 5).

R _{1 to} R ₁₀ may include a substituent that satisfies the following conditions: an alkyl group (including a double bond or a cyclized group), a phenyl group, an alkoxy group (including a double bond) A phenoxy group, a carbonyl group or a halogen group. The energy storage device according to claim 1, wherein the organic compound having a π bond contained in the non-aqueous electrolyte is represented by (Formula 6).

R _{1 to} R ₁₄ may include a substituent that satisfies the following conditions: an alkyl group (including a double bond or a cyclized group), a phenyl group, an alkoxy group (including a double bond) A phenoxy group, a carbonyl group or a halogen group. The energy storage device according to claim 1, wherein the organic compound having a π bond contained in the nonaqueous electrolytic solution is represented by (Formula 7).

R _{1 to} R ₄ may include a substituent that satisfies the following conditions: an alkyl group (including a double bond or a cyclized group), a phenyl group, an alkoxy group (including a double bond) A phenoxy group, a carbonyl group or a halogen group. The energy storage device according to claim 1, wherein the organic compound having a π bond contained in the non-aqueous electrolyte is represented by (Formula 8).

R _{1 to} R ₅ may include a substituent that satisfies the following conditions: an alkyl group (including a double bond or a cyclized group), a phenyl group, an alkoxy group (including a double bond) A phenoxy group, a carbonyl group or a halogen group. The energy storage device according to claim 1, wherein the organic compound having a π bond contained in the non-aqueous electrolyte is represented by (formula 9).

R _{1 to} R ₄ may include a substituent that satisfies the following conditions: an alkyl group (including a double bond or a cyclized group), a phenyl group, an alkoxy group (including a double bond) A phenoxy group, a carbonyl group or a halogen group.   The energy storage device containing 2 or more types as which the organic compound which has the said (pi) bond is chosen from the group which consists of the organic compound in any one of Claims 2-10. The solute of the non-aqueous electrolyte is LiPF ₆ , LiBF ₄ , LiClO ₄ , LiCF ₃ CO ₂ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiCF ₃ SO ₃ , LiC (SO ₂ CF _{3) 3,} LiAsF ₆ and LiSbF include one or more selected from the group consisting of _6, the energy storage device according to any one of claims 1 to 11 solute concentration is 0.4~2.0mol / L .   The solvent of the non-aqueous electrolyte is ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, tetrahydrofuran, 1,2-dioxane, 1,3-dioxane, 1,4- The energy storage device according to any one of claims 1 to 12, which is a mixed solvent containing at least one selected from the group consisting of dioxane, 1,3-dioxolane and γ-butyrolactone.   The energy storage device according to any one of claims 1 to 13, wherein the positive electrode contains one or more selected from activated carbon and vapor grown carbon.   Carbonaceous material for negative electrode is natural graphite, artificial graphite, graphitized mesocarbon spherule, graphite whisker, graphitized carbon fiber, vapor-grown carbon, petroleum coke, coal coke and pitch coke, graphitizable chemical conversion carbon material, full The energy storage device according to any one of claims 1 to 14, which is at least one material selected from a fired product of a furyl alcohol resin, a fired product of a novolac resin, and a fired product of a phenol resin.

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