JP2001338680A - Secondary electric power source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary electric power source with high reliability at charge and discharge cycle, which has high withstand voltage, high capacity, high energy density, preventing the deterioration of a negative pole material accompanied by repeated charge and discharge. SOLUTION: The secondary electric power source comprises a positive pole including activated carbon, a negative pole including carbon material capable of occluding and releasing lithium ion, and an organic electrolyte including lithium ion. The organic electrolyte includes at least one kind of cyclic carboxylester compound shown by the formula (A), (where; R1 and R2 represent H, F, CH3, or CF3, and they can be either same with or different from each other).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary power supply having a high withstand voltage, a large capacity, and a high rapid charge / discharge cycle reliability.

[0002]

2. Description of the Related Art Polarizable electrodes mainly composed of activated carbon are used for both positive and negative electrodes of conventional electric double layer capacitors. The withstand voltage of the electric double layer capacitor is 1.2 V when an aqueous electrolyte is used, and 2.5 to 3.3 V when an organic electrolyte is used. Since the energy of the electric double layer capacitor is proportional to the square of the withstand voltage, the organic electrolyte having a higher withstand voltage has higher energy than the aqueous electrolyte. However, even an electric double layer capacitor using an organic electrolyte has an energy density of 1/10 or less of a secondary battery such as a lead storage battery, and further improvement in energy density is required. Increasing the voltage is most effective for improving the energy density of the electric double layer capacitor. However, increasing the voltage causes decomposition of the electrolytic solution and greatly affects the life. In addition, the positive electrode is activated carbon, the negative electrode is mainly composed of a carbon material capable of absorbing and desorbing lithium ions such as a graphite-based carbon material, and a secondary power supply using an organic electrolytic solution containing lithium ions as an electrolytic solution includes a positive electrode, The negative electrode can have a higher voltage than a conventional electric double layer capacitor that mainly uses activated carbon.However, at the time of charge and discharge, an electrochemical reaction such as occlusion and desorption of lithium ions into carbon occurs at the negative electrode. In some cases, deterioration of the negative electrode material was observed.

[0003]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems in the prior art, and has a high withstand voltage, a high capacity, a high energy density, and suppresses deterioration of the negative electrode material due to repetition of charge and discharge. An object is to provide a secondary power supply with high cycle reliability.

[0004]

Means for Solving the Problems The present invention provides the following (1)-
The object is solved by adopting the configuration of (4). (1) In a secondary power supply including a positive electrode containing activated carbon, a negative electrode containing a carbon material capable of absorbing and desorbing lithium ions, and an organic electrolyte containing lithium ions, the organic electrolyte has a formula (A) ( Wherein R ¹ and R ² are H, F, CH ₃
Or at least one of CF ₃ , which may be the same or different).

Embedded image (2) The secondary power source according to (1), wherein the proportion of the cyclic carbonate compound represented by the formula (A) contained in the organic electrolyte is 0.5 to 10% by mass. (3) The secondary power source according to (1) or (2), wherein the carbon material is a carbon material having a [002] plane spacing of 0.334 to 0.410 nm by X-ray diffraction. (4) The secondary power supply according to any one of (1) to (3), wherein the positive electrode contains a lithium-containing transition metal oxide in addition to activated carbon.

[0005] In the present specification, a positive electrode containing a positive electrode containing activated carbon and a current collector are joined together to form a positive electrode. Similarly, a negative electrode body is formed by joining and integrating a negative electrode mainly composed of a carbon material capable of absorbing and desorbing lithium ions with a current collector. Further, both the secondary battery and the electric double layer capacitor are one kind of secondary power supply. In this specification, however, the specific configuration of the secondary battery includes activated carbon in the positive electrode and carbon capable of absorbing and desorbing lithium ions in the negative electrode. The secondary power supply is simply called a secondary power supply. In a lithium ion secondary battery, the positive electrode is an electrode mainly composed of a transition metal oxide containing lithium, and the negative electrode is an electrode mainly composed of a carbon material capable of absorbing and desorbing lithium ions. Lithium ions are desorbed from the transition metal oxide and stored in a carbon material capable of occluding and desorbing lithium ions of the negative electrode, lithium ions are desorbed from the negative electrode by discharge, and lithium ions are stored in the positive electrode.
Therefore, lithium ions in the electrolyte do not essentially participate in charging and discharging of the battery.

On the other hand, in the secondary power supply according to the present invention, the positive electrode is an electrode containing activated carbon used in an electric double layer capacitor, and the negative electrode is a carbon material capable of inserting and extracting lithium ions used in a lithium ion secondary battery. It is a hybrid type of electrode containing electrodes. Anions in the electrolyte are adsorbed on the activated carbon of the positive electrode by charging, and lithium ions in the electrolyte are occluded in a carbon material capable of occluding and desorbing lithium ions of the negative electrode. Then, lithium ions are desorbed from the negative electrode by discharge, and anions are desorbed from the positive electrode. That is, in the secondary power supply of the present invention, the solute of the electrolytic solution is essentially involved in charging and discharging, and the charging and discharging mechanism at the positive electrode differs from that of the lithium ion secondary battery. And, unlike a lithium ion secondary battery, lithium ions do not occlude and desorb in the positive electrode active material itself, and there is no deterioration of the positive electrode due to occlusion and desorption of lithium ions. Deterioration due to charge / discharge cycles is small and long-term reliability is excellent. In the present specification, the term "adsorption" refers to the adsorption of ions to activated carbon by the formation of an electric double layer during charging, and the term "occlusion" refers to a reaction involving charge transfer. In addition, detachment of ions from activated carbon during discharge is called desorption, and that accompanied by charge transfer is called desorption.

The inventors of the present invention have studied various means for suppressing capacity deterioration during charge / discharge cycles, and have found that a specific method having a structure similar to ethylene carbonate or propylene carbonate used as a solvent in an organic electrolyte is used. It has been found that capacity deterioration can be suppressed by adding a compound. That is, the secondary power supply according to the present invention is a secondary power supply having a positive electrode including activated carbon, a negative electrode including a carbon material capable of absorbing and desorbing lithium ions, and an organic electrolyte including lithium ions, The organic electrolytic solution contains at least one kind of the cyclic carbonate compound represented by the formula (A).

When the compound represented by the formula (A) is added to the organic electrolyte, the charge / discharge cycle characteristics can be improved. Further, even in rapid charge / discharge with a charge / discharge current density of 10 mA / cm ² or more, a decrease in capacity can be reduced. In the case of the conventional organic electrolyte containing no additive, the capacity was significantly deteriorated in the charge / discharge cycle. One of the causes is considered that a film formed on the negative electrode carbon during charging is not stable. In other words, when a film such as a passive film is formed on the surface of the carbon material during charging, lithium ions are occluded in the carbon material. Is used to compensate for it, and it is considered that the capacity is deteriorated as a result. Therefore, it is presumed that the effect of the addition of the compound represented by the formula (A) is because the film formed on the negative electrode carbon during charging can be stabilized.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The organic electrolyte constituting the secondary power supply according to the present invention contains a supporting electrolyte (lithium salt) and a cyclic carbonate compound represented by the above formula (A) in a solvent. Examples of the solvent for the organic electrolyte include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, sulfolane, dimethoxyethane, and the like.These may be used alone or as a mixed solvent of two or more kinds. it can. The supporting electrolyte contained in the organic electrolyte has a cation of lithium ion and an anion of PF ₆ ⁻ , BF ₄ ⁻ , ClO ₄ ⁻ , N (SO ₂ C
F ₃ ) ₂ ⁻ , CF ₃ SO ₃ ⁻ , C (SO ₂ C
One or more members selected from the group consisting of F ₃ ) ₃ ⁻ , AsF ₆ ⁻ and SbF ₆ ⁻ are preferred. The concentration of the supporting electrolyte (lithium salt) in the electrolyte is preferably 0.5 to 2 mol / l because of its high electric conductivity.

The ratio of the compound represented by the formula (A) to be added to the organic electrolyte is such that the concentration of the compound represented by the formula (A) in the electrolyte is 0.5 to 10% by mass. Is preferred. If the concentration is less than 0.5% by mass, the effect is small,
On the other hand, if it exceeds 10% by mass, the amount of the compound to be added increases, which increases the cost and makes the compound impractical.

Occludes lithium ions used for the negative electrode,
As a desorbable carbon material, the [002] plane obtained by the X-ray diffraction method has a plane spacing of 0.334 to 0.410 n.
m, natural graphite, artificial graphite, hard carbon, oil or coal pitch, heat-treated coke, and the like. These include graphite with improved crystallinity, amorphous carbon, carbon to which boron is added, and the like, and any of them can be preferably used. The negative electrode body is manufactured by, for example, adding a binder (binder) such as polyvinylidene fluoride, polyamide imide, or polyimide and a solvent to these carbon materials to form a paste, applying the paste on a current collector, and drying the paste. It can be carried out.

Activated carbon is used for the positive electrode. The activated carbon preferably has a specific surface area of 300 to 3000 m ² / g. The raw material and activation conditions of the activated carbon are not limited. For example, the raw material includes bean, phenol resin, petroleum coke and the like, and the activation method includes a steam activation method and a molten alkali activation method. In order to reduce the resistance of the electrode, it is also preferable to include a conductive material such as conductive carbon black or graphite in the electrode. In this case, the conductive material should be 0.1 to 20% by mass in the positive electrode. Is preferred.

Further, in the secondary power supply according to the present invention,
Activated carbon may contain lithium-containing transition metal oxides.
No. In this case, the reaction that occurs at the negative electrode during charging is
Of lithium ions and lithium ions desorbed from the positive electrode
It is occlusion. Lithium-containing transition metal oxide in this case
Is the active lithium ion that accompanies the charge / discharge cycle.
Work to compensate for the decrease in energy consumption. Lithium contained in positive electrode
V, Fe, Co, Mn, N
One or more transitions selected from the group consisting of i, W, and Zn
A composite oxide of a metal and lithium is preferred. Especially preferred
Is selected from the group consisting of Co, Mn and Ni.
Complex oxide of at least one species and lithium, and further Li
_xCo_yNi _(1-y)O_TwoOr Li_zMn_TwoO_Four(However
0 <x <2, 0 ≦ y ≦ 1, 0 <z <2)
No. The content of the lithium-containing transition metal oxide in the positive electrode is 1
-30% by mass, more preferably 5-20% by mass
%. If less than 1% by mass, lithium ion
And the effect is small, and more than 30% by mass.
The amount of activated carbon in the positive electrode is relatively small,
It is preferable because the capacity decrease in the charge / discharge cycle increases.
Not good.

As a method for producing a positive electrode body, for example, an activated carbon powder is mixed with a lithium-containing transition metal oxide powder and / or a conductive agent such as carbon black as necessary, and a binder such as polytetrafluoroethylene is mixed and kneaded. Thereafter, there is a method in which the positive electrode is formed into a sheet shape and the positive electrode is fixed to a current collector using a conductive adhesive. In addition, activated carbon powder, and if necessary, lithium-containing transition metal oxide powder and / or a conductive agent are dispersed in a varnish in which polyvinylidene fluoride, polyamide imide, polyimide, etc. are dissolved as a binder, and this liquid is collected by a doctor blade method or the like. It may be obtained by coating on an electric body and drying. The amount of the binder contained in the positive electrode is preferably 1 to 20% by mass in view of the balance between the strength of the positive electrode body and characteristics such as capacity.

In the secondary power supply according to the present invention, as a material of the separator separating the positive electrode body and the negative electrode body, polyethylene, polypropylene, rayon, polybutylene phthalate, polyphenylene sulfide, and the like, which are insoluble in an organic electrolyte and have strength, can be used. It is. As the form, a porous film, a non-woven fabric, or the like is preferably used. Polyethylene, polypropylene and rayon are advantageous in terms of cost, while those made of polybutylene phthalate and polyphenylene sulfide are advantageous in terms of heat resistance.

[0016]

Next, the present invention will be described in more detail with reference to Examples (Examples 1 to 6) and Comparative Examples (Example 7), but the present invention is not limited thereto. In addition, Examples 1 to
The dew point was -60 ° C for all cell fabrication and measurements in 7
Performed in the following argon glove box. The cell used was a coin cell having a diameter of 10.8 mm and a height of 1.7 mm. All of the fabricated cells have higher voltages (conventional positive electrode,
Activated carbon electric double layer capacitor for both negative electrode is 2.5 ~
3.3 V), and both the positive electrode and the negative electrode had a higher energy density than the activated carbon electric double layer capacitor. [002] by X-ray diffraction
The measurement of the surface spacing was performed by RINT10 manufactured by Rigaku Corporation.
00 was used.

Example 1 70% by mass of activated carbon having a specific surface area of 2000 m ² / g, 20% by mass of conductive carbon black, and 10% by mass of polytetrafluoroethylene as a binder were obtained by using a phenol resin as a raw material by a steam activation method. Ethanol was added to the mixture consisting of mass%, kneaded and rolled, and then vacuum dried at 200 ° C. for 2 hours to obtain an electrode sheet. This sheet was adhered to a coin cell cap using a conductive adhesive having polyamideimide as a binder, and heat-treated under reduced pressure at 300 ° C. for 2 hours to obtain a positive electrode body. Further, a heat treatment was performed at 800 ° C. using a phenol resin as a raw material.
A 73 nm carbon material (hard carbon) and a vapor grown carbon (VGCF) treated at 2800 ° C. as a conductive agent were mixed with polyvinylidene fluoride (PVD) as a binder component.
F) was dispersed in N-methyl-2-pyrrolidone in which F was dissolved, applied to a copper current collector, dried, and welded to a coin cell case to obtain a negative electrode body. The mass composition ratio of the electrode is carbon material: V
GCF: PVDF = 7: 1: 2.

The positive electrode body and the negative electrode body obtained in this manner are opposed to each other with a polypropylene separator interposed therebetween, and 1.0 mol / l of LiBF ₄ and the compound represented by the formula (B) are reacted with each other. 1.0% by mass of ethyl methyl carbonate and ethylene carbonate (volume ratio 1:
A coin cell was prepared using 1) as an electrolytic solution. The initial capacity of this secondary power supply was measured in a range from 4.2 V to 2.75 V, and thereafter, at a charge / discharge current of 10 mA / cm ² ,
The charge and discharge cycle was performed 1,000 times in an atmosphere of 25 ° C. in the range of 4.2 V to 2.75 V, the capacity was measured, and the rate of change in capacity from the initial stage was calculated. Table 1 shows the results.

Embedded image

[Example 2] The same positive electrode, negative electrode and separator as in Example 1 were used. 1.0 mol / liter L
A coin cell was prepared using ethyl methyl carbonate and ethylene carbonate (volume ratio 1: 1) each containing iBF ₄ and the compound represented by the formula (C) in an amount of 1.0% by mass. This secondary power supply was evaluated in the same manner as in Example 1. Table 1 shows the results.

Embedded image

Example 3 The same positive electrode, negative electrode and separator as in Example 1 were used. 1.0 mol / liter L
A coin cell was prepared using, as electrolytes, ethyl methyl carbonate and ethylene carbonate (volume ratio 1: 1) containing iBF ₄ and the compound represented by the formula (D) at 1.0% by mass. This secondary power supply was evaluated in the same manner as in Example 1. Table 1 shows the results.

Embedded image

Example 4 The same positive electrode, negative electrode and separator as in Example 1 were used. 1.0 mol / liter L
A coin cell was manufactured using ethyl methyl carbonate and ethylene carbonate (volume ratio 1: 1) containing iBF ₄ and the compound represented by the formula (E) in an amount of 1.0% by mass. This secondary power supply was evaluated in the same manner as in Example 1. Table 1 shows the results.

Embedded image

Example 5 The same positive electrode body and separator as in Example 1 were used. Mesocarbon microbeads heat-treated at 2800 ° C (available from Osaka Gas Co., Ltd.
A negative electrode body was produced in the same manner as in Example 1 using trade name: MCMB6-28). 1.0 mol / L LiBF
_A coin cell was prepared using ethyl methyl carbonate and ethylene carbonate (volume ratio 1: 1) containing 1.0 and 4% by mass of the compound represented by Formula ₄ and the compound represented by the formula (B) as electrolytes. This secondary power supply was evaluated in the same manner as in Example 1. Table 1 shows the results
Shown in

Example 6 70% by mass of activated carbon, 20% by mass
Of a conductive carbon black and 10% by weight of polytetrafluoroethylene, instead of 63% by weight of the same activated carbon, 7% by weight of LiCoO ₂ , 20% by weight
A coin cell was produced in the same manner as in Example 1, except that a mixture containing conductive carbon black of the formula (1) and 10% by mass of polytetrafluoroethylene was used. This secondary power supply was evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 7 A coin cell was prepared in the same manner as in Example 1, except that the compound represented by the formula (B) was not added to the electrolytic solution. This secondary power supply was evaluated in the same manner as in Example 1. Table 1 shows the results.

[0025]

[Table 1]

From Table 1, it can be seen that the secondary power source containing the cyclic carbonate compound in the organic electrolyte according to the present invention (Examples 1 to 6) is the same as the secondary power source according to the present invention except that the organic carbonate does not contain the cyclic carbonate compound. While having the same initial capacity as the secondary power supply (Example 7) having the same configuration as the secondary power supply, the capacity change rate after 1000 cycles due to charging and discharging at a high voltage up to 4.2 V is significantly smaller. It can be seen that the secondary power supply has a high withstand voltage, a large capacity and a high reliability of rapid charge / discharge cycles.

[0027]

According to the present invention, by including a cyclic carbonate compound having a specific structure in an organic electrolytic solution, a secondary voltage having a high withstand voltage, a large capacity and a high charge-discharge cycle reliability can be improved. Power can be provided.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Car Isamu 1150 Hazawa-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture Asahi Glass Co., Ltd. F-term (reference) 5H029 AJ03 AJ05 AK03 AK08 AK18 AL06 AM03 AM05 AM07 DJ08 DJ16 DJ17 EJ12 HJ01 HJ13 5H050 AA07 AA08 BA17 CA08 CA16 CA29 CB07 EA10 EA24 FA19 HA01 HA13

Claims (4)

[Claims] 1. A secondary power supply comprising a positive electrode containing activated carbon, a negative electrode containing a carbon material capable of inserting and extracting lithium ions, and an organic electrolytic solution containing lithium ions, wherein the organic electrolytic solution has the formula (A) Wherein R ¹ and R ² are H,
F, CH _3, or CF ₃ , which may be the same or different). Embedded image 2. The organic electrolytic solution according to claim 1, wherein the proportion of the cyclic carbonate compound represented by the formula (A) is 0.5 to 10%.
2. The secondary power supply according to claim 1, wherein the secondary power supply is mass%. 3. 3. The method according to claim 1, wherein the carbon material is [00] by X-ray diffraction.
2] The secondary power supply according to claim 1 or 2, wherein the surface spacing is 0.334 to 0.410 nm. 4. The secondary power supply according to claim 1, wherein the positive electrode contains a transition metal oxide containing lithium in addition to activated carbon.