JP3168592B2 - Solid electrode composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid electrode composition,
In particular, the present invention relates to a solid electrode composition for an electrochemical element such as a lithium secondary battery using a solid or solid lithium ion conductive electrolyte.

[0002]

2. Description of the Related Art Electrochemical devices such as lightweight, high-energy density batteries, large-area electrochromic devices, and biochemical sensors using microelectrodes can be expected.
Conductive polymer electrodes are being actively studied. Since polyacetylene is unstable and impractical as an electrode, other π-electron conjugated conductive polymers have been studied, and relatively stable polymers such as polyaniline, polypyrrole, polyacene, and polythiophene have been developed. The lithium secondary batteries used have been developed. These polymer electrodes are formed in a film form exclusively by an electrolytic polymerization method, and are used in a lithium secondary battery in combination with a liquid electrolyte in which a lithium salt is dissolved in an aprotic organic solvent.

[0003]

When a liquid electrolyte is used, the electrolyte can enter the inside of the electropolymerized film, and therefore the battery reaction can be performed well without increasing the polarization. When configuring a solid state lithium secondary battery using a solid electrolyte,
An electrolyte material having a good affinity for the electrode material has not been obtained, the contact between the electrolyte and the electrode has been insufficient, the polarization has increased, and it has been difficult to extract a large output current from the battery. That is, a good electron-ion network is not necessarily formed in the solid electrode composition, and the solid-state electrode composition has a disadvantage of increasing polarization.

An object of the present invention is to solve the above-mentioned drawbacks and to provide a solid electrode composition for a lithium secondary battery capable of extracting a large current even in a solid or solid state.

[0005]

Means for Solving the Problems To solve this problem, a solid electrode composition of the present invention comprises a π-electron conjugated conductive polymer powder, a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate. And a lithium salt, and at least one of propylene carbonate and eletine carbonate.

[0006]

According to this structure, the solid electrode composition of the present invention is characterized in that a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate is dissolved in at least one of propylene carbonate and eletine carbonate in which a lithium salt is dissolved. A gel-like solid electrolyte is formed.
This solid electrolyte has a high affinity for the conductive polymer powder. The conductive polymer powder is uniformly dispersed in the solid electrode composition to form a low-polarization electrode / electrolyte interface. Furthermore, the solid electrolyte acts as a binder for the conductive polymer powder, and gives the solid electrode composition good mechanical strength and workability.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A solid electrode composition according to one embodiment of the present invention will be described below with reference to the drawings.

As the π-electron conjugated conductive polymer powder,
0 to ± 1.0 volt for Ag / AgCl electrode of polyaniline, polypyrrole, polythiophene, polyacene, etc.
And a conductive polymer powder which causes a highly reversible oxidation-reduction reaction is effectively used. It may be obtained by any of electrolytic polymerization and chemical polymerization. Those having an average particle diameter of 0.1 to 10 microns and an electric conductivity of 10 ^-1 s / cm are preferably used. You may mix a conductive material as needed. As the conductive material in this case, a carbon material is preferably used. Natural graphite, artificial graphite, amorphous carbon, fibrous,
Any of powder, petroleum pitch, and coal coke can be used. The particle or fiber size is 0.01 to 10 microns in diameter or fiber diameter and several microns in fiber length.
It is preferably from m to several mm.

A copolymer of acrylonitrile and methyl acrylate or methyl methacrylate can be obtained by polymerizing an acrylonitrile monomer with methyl acrylate or methyl methacrylate by a usual polymerization method. Those having a molecular weight of 30,000 to 100,000 are preferably used. Acrylonitrile (hereinafter referred to as AN)
And a copolymerization ratio (AN / MA) of methyl acrylate or methyl methacrylate (hereinafter referred to as MA) is 50: 1.
About 2: 1 (molar ratio) is preferred.

As the lithium salt, lithium iodide, lithium perchlorate, lithium trifluorosulfonate, lithium borofluoride and the like are used.

The solid electrolyte composition of this embodiment is manufactured as follows. First, a lithium salt is heated and dissolved in a solvent mainly composed of at least one of propylene carbonate and ethylene carbonate to obtain a solution of the lithium salt. Next, a powder of a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate is added to this solution, and the mixture is heated at 150 ° C. to 180 ° C. to dissolve the powder to obtain a uniform transparent solution. Acrylonitrile is added and the solution is diluted 2-3 times by weight. The diluted solution and the conductive polymer powder are mixed, and the resulting slurry is cast on a glass plate. After drying at room temperature, the solid electrolyte composition is obtained by vacuum heating and drying at 60 ° C. under a reduced pressure of 1 Torr. If necessary, LiI in the _{slurry, Li 3 N-LiI-B} 2
Lithium ion conductive powders such as O ₃ , LiI.H ₂ O, and Li-β-Al ₂ O ₃ may be added.

Example 1 3.58 g of lithium trifluorosulfonate, 10.47 g of propylene carbonate,
7.86 g of ethylene carbonate was mixed and heated to 120 ° C. to obtain a homogeneous solution. Acrylonitrile having a molecular weight of 60,000 and a methyl acrylate copolymer (AN / M) were added to this solution.
A = 10/1, molar ratio) 3 g of powder were mixed and sealed 1
Heat to 150 ° C. in a 00 ml Erlenmeyer flask. The copolymer was completely dissolved to obtain a transparent liquid. 30 g of acrylonitrile was added to this liquid to obtain a diluted solution. 10 g of dilute solution and polyaniline powder having an average particle size of 3 microns 1.
And 0 g to obtain an electrode paste. The polyaniline powder used was prepared in a sulfuric acid acidic aqueous solution of 1M (M = mol / dm ³ ) and 5M Na ₂ SO ₄ having a pH of 1.0 and a saturated calomel reference electrode in a concentration of 1.2 to 1%. .5vo
It was obtained by performing constant potential electrolysis with lt. The conductivity of the sulfuric acid-doped polyaniline thus obtained was measured at a density of 1.6 g / cm.
It is about 2S at room temperature when measured by pressure molding into the pellet of ^3.
/ cm. After applying the electrode paste on a smooth glass plate using a doctor blade, the electrode paste is dried for 1 hour in a dry argon gas stream at 40 ° C., and further vacuum-dried at 60 ° C. for 5 hours to obtain a size of 40 × 80 mm and a thickness of 150 μm. The solid electrode composition A in the form of a sheet was obtained.

Example 2 Polyaniline powder having an average particle size of 1.5 μm was synthesized by a chemical polymerization method using aniline in an acidic aqueous solution and cupric borofluoride as an oxidizing agent.
_{g, LiI-Li 3 N-} B 2 O 3 ( molar ratio 1: 1: 1) to obtain a mixed powder by mixing powder 1.0g in a mortar. AN / M
A diluted solution was obtained in the same manner as in Example 1 except that a copolymer having an A molar ratio of 20/1 and a molecular weight of 55,000 was used.
An electrode slurry was obtained by mixing 10 g of the diluted solution with the mixed powder, cast into a glass Petri dish having a diameter of 90 mm as in Example 1, and then dried to form a flexible sheet-like solid electrode having a thickness of about 180 μm. Composition B was obtained.

Comparative Example 1 A polymer electrolyte solution was prepared by dissolving 5 g of linear polyethylene oxide having a molecular weight of 4.5 million and 2.36 g of lithium trifluorosulfonate in 350 ml of acetonitrile and diluting with acetonitrile. To 200 ml of this solution was added 1.0 g of the polyaniline powder obtained in the same manner as in Example 1, and the mixture was uniformly dispersed with a homogenizer.
and concentrated to 1. The concentrated solution was cast on a glass Petri dish having a diameter of 90 mm, and then dried to obtain a solid electrode composition C having a thickness of about 145 μm.

Comparative Example 2 A solid electrode composition D having a thickness of about 150 μm was prepared in the same manner as in Example 1 except that polyacrylonitrile having a molecular weight of 55,000 was used instead of acrylonitrile and methyl acrylate copolymer. I got

(Evaluation of Battery Characteristics) In FIG.
2, and the solid electrode compositions obtained in Comparative Examples 1 and 2 were punched into a disk having a diameter of 22 mm, and the punched electrode disk 1
Was placed in a case 2 made of stainless steel having an inner diameter of 22 mm so as to be in contact with the bottom surface of the case to form a positive electrode module. On the other hand, the opening of the case 2 in which the concave portion is in contact with the lithium metal disk 3 having a thickness of 0.3 mm and a diameter of 17 mm is sealed with a sealing ring 4 made of polypropylene.
Solid electrolyte 6 before heating diluted to 0 ° C. to give fluidity
To form a negative electrode module. A battery for evaluating electrode characteristics was assembled by closing the opening of the positive electrode module with the negative electrode module so that the solid electrolyte 6 was in contact with the electrode disk 1. Note that the solid electrolyte of Example 1 was used as the solid electrolyte 6 of the battery of the comparative example. All evaluations are 20
C. was performed.

Regarding the battery assembled in this manner,
Cyclic voltammograms were measured between 1.5-4.0V. The voltage sweep speed was 10 mV / sec. FIG. 2 shows cyclic voltammograms of the batteries A and B of Examples 1 and 2, and the batteries C and D of Comparative Examples 1 and 2. In addition, the open circuit voltage and internal resistance after assembly of each battery,
The polarization values at a battery voltage of 3.5 V when charged at a constant voltage of 4.0 V for 17 hours and then discharged at a constant current of 500 μA are summarized in (Table 1).

[0018]

[Table 1]

The internal resistance is an AC impedance value at an open circuit voltage obtained using an AC signal of 10 mV and 10 KHz. When the discharge voltage reaches 3.5 V, the polarization value
The temporary discharge was stopped to open the circuit, and the battery was allowed to stand until the battery voltage became constant. The difference was obtained as the difference between the battery voltage 0.1 sec after the discharge was stopped and the battery voltage one hour after the discharge. Note that for the battery C of the comparative example, the current value was too large at 500 μA and the polarization value could not be measured.
It was measured at 50 μA.

As shown in Table 1, the battery A of the embodiment
In B and B, the polarization value is extremely small as compared with the battery C of the comparative example. As is clear from FIG. 2, in the batteries A and B of Examples 1 and 2, a large oxidizing current (charging current) exceeding 1 mA was obtained when the voltage was around 3.6 V, and around 2.8 V when the voltage was around 3.6 V. Also, a large reduction current (discharge current) exceeding 1 mA is obtained. On the other hand, in the battery C of Comparative Example 1, only a small oxidation current of about 20 μA was obtained at around 3.6 V, and only a reduction current of 20 μA was obtained at around 2.8 V. In the battery D of Comparative Example 2, only a redox current of 0.3 mA was obtained at around 3.6 V and 2.8 V.

[0021]

As is apparent from the above description of the examples, according to the solid electrode composition of the present invention, π-electron conjugated conductive polymer powder, acrylonitrile and methyl acrylate or methyl methacrylate are used. By combining a copolymer of a copolymer and lithium, a lithium salt, and a solid electrolyte mainly composed of at least one of propylene carbonate and ethylene carbonate, a solid electrode composition having small polarization can be obtained. By using this electrode in combination with, for example, a negative electrode mainly composed of metallic lithium and a lithium ion conductive solid or solid electrolyte, it is possible to constitute a solid state high energy density lithium secondary battery in which a large current charge / discharge can be expected. it can.

In the examples, only the polyaniline powder was shown as the π-electron conjugated conductive polymer powder. Needless to say, the same effect can be obtained with powder.

Although only the battery is shown as an example,
In addition to batteries, an electrochromic device having a high coloring / fading speed by using the solid electrode composition of the present invention as a counter electrode,
A biochemical sensor such as a glucose sensor having a fast response speed can be obtained, and an electrochemical analog memory having a fast writing / reading speed can be configured.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a configuration of a battery used for evaluating characteristics of a solid electrode composition according to one embodiment of the present invention.

FIG. 2 is a graph showing current-voltage characteristics of the battery.

[Explanation of symbols]

 Reference Signs List 1 electrode disk (solid electrolyte composition) 3 metal lithium disk 6 solid electrolyte

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Teruju Kamihara 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. In-company (56) References JP-A-2-297867 (JP, A) JP-A-1-311561 (JP, A) JP-A-63-135453 (JP, A) JP-A-62-119860 (JP, A) JP-A-61-133582 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/02-4/04 H01B 1/06 H01M 4/60 H01M 4/62 H01M 10 / 40 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. A solid electrode composition comprising a π-electron conjugated conductive polymer powder, a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate, a lithium salt, and at least one of propylene carbonate and ethylene carbonate. object.