JPH05325631A - Solid electrolyte - Google Patents

Abstract

PURPOSE:To provide a solid electrolyte with high ionic conductivity from which substantial driving force can be obtained. CONSTITUTION:This is a solid electrolyte 1 formed between a pair of electrodes 2, 3, wherein the solid electrolyte has a difference in the percentage content of a lone electron pair (x) in a molecule from a negative electrode 2 side to a positive electrode 3 side and is constituted by laminating a substrate polymer P into three layers or more so as to sequentially increase the percentage content of a lone electron pair and then doping an ion carrier therein. Thereby, the gradient of concentration of alkali metal ions is formed within a solid electrolyte, so that the dissolution of negative electrode alkali metal is accelerated to provide a large driving force whereby a solid electrolyte having high ion conductivity may be obtained. Also, a solid electrolyte with the desired ionic conductivity may be easily obtained by changing the percentage content of the lone electron pair within the substrate polymer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolyte, and more particularly to a solid electrolyte having high ionic conductivity and suitable as a material for various electrochemical devices.

[0002]

2. Description of the Related Art As a solid electrolyte, a polymer solid electrolyte is known to exhibit extremely high ionic conductivity even at room temperature, and is regarded as a promising material for various electrochemical devices including batteries operating at room temperature. ing. However, the ion conduction mechanism of the conventional solid electrolyte is mainly ion hopping to the free volume generated by the segmental motion of the polymer serving as the substrate. However, in this mechanism, since there is essentially no driving force, even if the substrate polymer is chemically modified by molecular design, it is the conductivity of the solution-based electrolyte.
It is difficult to exceed ^-2 S / cm. Further, even when utilizing the concept of tunnel or canal (layered) ion paths proposed for the inorganic solid electrolyte, there is no essential driving force, and there is a limit to achieving high conductivity.

[0003]

In order to improve the ionic conductivity of the solid electrolyte, it is necessary to retain the alkali metal ion in the solid electrolyte, and therefore, the anion-cation between the doped alkali metal salt is retained. The ionic bond must be broken. To break this bond,
A solid electrolyte is formed by using a substance having a coordination ability for an alkali metal ion, generally a polymer having a lone electron pair in the molecular chain as a substrate polymer.

However, even if the solid electrolyte is formed by a single layer of the substrate polymer having the lone electron pairs, the lone electron pairs are scattered in the solid electrolyte, and the essential driving force cannot be obtained, and the ions of the solid electrolyte are not obtained. It was difficult to improve the conductivity.

An object of the present invention is to solve the above problems and to provide a polymer solid electrolyte having an essential driving force and high ionic conductivity.

[0006]

Means for Solving the Problems The present inventor has focused on the structure of the above-mentioned solid electrolyte and has achieved the above-mentioned object by providing a structure in which a matrix polymer constituting the solid electrolyte has a concentration gradient of lone electron pairs. The inventors have found that they can do so and have completed the present invention. That is, the polymer solid electrolyte of the present invention is a solid electrolyte formed between a pair of electrodes, the solid electrolyte is different in the lone electron pair content in the molecule from the negative electrode side to the positive electrode side, and, It is formed by laminating a substrate polymer in three or more layers so that the content of lone electron pairs is sequentially increased, and is doped with ion carriers.

[0007]

According to the above construction, the substrate polymer having a concentration gradient of the lone electron pair content forms a solid electrolyte, so that the concentration gradient of the ion carriers is formed by doping this with an ion carrier. Therefore, when this is used in an alkaline battery, a concentration gradient of alkali metal ions is formed in the solid electrolyte, the dissolution of the alkali metal in the negative electrode is promoted, and a large driving force is obtained. Further, by varying the lone electron pair content in the substrate polymer, the concentration gradient of alkali metal ions in the solid electrolyte can be changed, so that the ionic conductivity of the solid electrolyte can be easily adjusted.

The present invention will be described below in more detail with reference to the drawings. FIG. 1 is a schematic diagram showing the constitution of the solid electrolyte of the present invention, in which 1 is a solid electrolyte, and three or more layers of substrates having different contents of lone electron pairs x in the molecule between the negative electrode 2 and the positive electrode 3. It is composed of polymer layers P _{1 to} P _n (n ≧ 3).

The substrate polymer layer P is formed by increasing the content of the lone electron pair x from the negative electrode 2 side to the positive electrode 3 side, and the substrate polymer layer P ₁ in contact with the negative electrode 2 has the lone electron pair x in the polymer. The substrate polymer layer P _n which does not contain or contains the least amount of other substrate polymer layers and which is in contact with the positive electrode 3 is formed so as to contain most lone electron pairs x in the polymer. It

In the present invention, a known polymer having a lone electron pair in the molecule can be used as the substrate polymer. For example, specifically, a unit (1) having a lone electron pair represented by the following chemical formula, A polymer in which any one of (2), (3) or (4) is introduced into the molecule can be preferably used.

[0011]

[Chemical 1]

However, m is a positive integer, n is 0 or a positive integer and is not particularly limited, but usually m = 1 to 15
0, n = 0 to 9 is used, and preferably m = 40 to 7
0, n = 2-5.

[0013]

[Chemical 2]

However, m and n represent positive integers, and although not particularly limited, m = 1 to 650 and n = 1 to 20 are usually used, and preferably m = 400 to 500 and n = 2 to 5.
Is.

[0015]

[Chemical 3]

However, m and n represent positive integers and are not particularly limited, but usually m = 1 to 500, n = 1 to 100.
0 is used, preferably m = 120 to 150, n = 5
~ 8.

[0017]

[Chemical 4]

However, m is a positive integer, n is 0 or a positive integer and is not particularly limited, but usually m = 1 to 15
0, n = 0 to 20 are used, and preferably m = 70 to 1
10, n = 3 to 11.

The above-mentioned unit is introduced into the polymer by a known polymerization means such as graft copolymerization,
It is made by block copolymerization, living polymerization and the like. The lone electron pair content in the polymer molecular chain is adjusted by varying the compounding amount of the monomer having the above unit during polymer polymerization.

The above-mentioned three or more substrate polymer layers P are formed by dipping a solution of the above polymer in an organic solvent by a dip coating method, a casting method, a Langmuir-Blodgett method, etc. A method of forming a film on the surface, drying each time the film is formed, removing the solvent and forming the next film, or laminating a plurality of layers, followed by drying,
It is made by a method of removing the solvent. Further, in the present invention, at least 3 in the order of the lone electron pair content in the substrate polymer.
It is laminated in layers, preferably 5 layers or more, more preferably 10 layers or more.

The film thickness of each of the above substrate polymers is from 1 to
The thickness of the solid electrolyte layer is 150 μm, preferably 5 to 80 μm, and more preferably 10 to 50 μm.
A thickness of 30 to 1000 μm, preferably 40 to 300 μm, and more preferably 50 to 150 μm is suitable. If the thickness of this matrix polymer layer is less than 1 μm,
It becomes difficult to process a homogenous sheet, and 150 μm
If the thickness is thicker, the conductivity is lowered, which is not preferable. Further, if the thickness of the solid electrolyte layer is less than 30 μm, the mechanical strength is inferior, which makes it extremely weak against deformation and distortion, which causes a problem in practicality. Even with the driving force due to the gradient, the ionic conductivity is inferior to the conventional one, which is not preferable.

In the present invention, in order to make the solid electrolyte as a whole integral, it is desirable that the above-mentioned substrate polymers are the same or polymers having a structure as similar as possible are used. However, it is also possible to form a solid electrolyte by combining two or more substrate polymers having different structures.

The solid electrolyte of the present invention contains LiClO ₄ , Li
I, LiBF ₄ , LiCF ₃ SO ₃ , LiAsF _{6 and the} like are used after being doped with ion carriers by a known method of immersion treatment in an organic solvent solution of an alkali metal salt. When the ion carrier is doped, the ion carrier comes to exist in the solid electrolyte with a concentration gradient. Therefore, this solid electrolyte is
In the initial state, a concentration gradient also occurs in the alkali metal ion concentration in the solid electrolyte, and the alkali metal of the negative electrode is easily dissolved in the solid electrolyte, which serves as a driving force to increase the ionic conductivity.

As a result, when the ionic conductivity of the solid electrolyte was measured by an AC impedance analyzer, it was 10 ^-3 S
Since it exhibits a high ionic conductivity on the order of / cm, this solid electrolyte is useful as a material for various electrochemical devices such as batteries, sensors, displays and capacitors.

[0025]

EXAMPLES Hereinafter, the present invention will be described more specifically by showing examples. Needless to say, the present invention is not limited to this. Example 1 FIG. 1 is a schematic diagram of a solid electrolyte showing an example of the present invention. In the figure, reference numeral 1 is a solid electrolyte, and five substrate polymer layers P _{1 to} P having different contents of lone electron pairs x.
_n (n = 5). These matrix polymer layers were formed as follows.

(Preparation of Polymer) Five types of block copolymers of polystyrene-12-crown-4 substituted polyethylene, in which n = 0-4 of the unit (1) having a lone electron pair represented by the following chemical formula, are prepared: After synthesis by living polymerization method, 10% by weight each with dimethylacetamide
Prepared into a solution.

[0027]

[Chemical 5]

(Preparation of Solid Electrolyte 1) The above polymer solutions were spin-coated on a glass plate in the order of n = 0, and the thickness of ether oxygen was 1 in this order.
A polymer layer of 00 μm was sequentially laminated. At this time, in order to avoid mixing of the respective layers, after forming the polymer layer, 80 ° C / 2
The solvent was sufficiently removed under the condition of 2 mmHg, and then the following polymer layer was laminated by a method of forming a film. After forming the polymer layer consisting of the above 5 layers, this is further heated at 80 ° C./22 mmHg
When dried under reduced pressure and immersed in water under the conditions described above, the laminated polymer layer started to peel from the glass plate and completely peeled after 10 minutes. This polymer layer was taken out and dried under reduced pressure again.

Then, the above polymer layer was added at 50 ° C. and a concentration of
After immersing in an ethanol solution of 0 wt% LiClO ₄ for 8 hours, this was taken out and dried in a vacuum dryer for 8 hours in an atmosphere of 1 Torr and 70 ° C. to remove the solvent and the like, and a lithium ion-doped solid electrolyte. 1 was produced. When the ionic conductivity of this solid electrolyte 1 was measured with an AC impedance analyzer (manufactured by Solartron), 1.3 ×
The ionic conductivity was 10 ⁻³ S / cm.

On the other hand, as a comparative example, each of the above five independent films of n = 0 to 4 was prepared in the same manner as described above, and the ionic conductivity was measured.
It was on the order of ^-5 S / cm.

[0031]

[Table 1]

Example 2 (Preparation of Polymer) A saturated solution of 5 kinds of polythioethers in dimethylsulfoxide having n = 2 to 6 of the unit (2) having a lone electron pair represented by the following chemical formula was prepared.

[0033]

[Chemical 6]

(Preparation of Solid Electrolyte 1) The above solution was deposited on a quartz glass plate in order from n = 2 by a casting method to form a film 5
A polymer layer of layers was formed. In addition, for each layer film formation, 6
The solvent was sufficiently removed under the condition of 5 ° C./5 mmHg and drying was performed. The obtained polymer layer was treated in the same manner as in Example 1 to prepare a lithium ion-doped solid electrolyte 1. When the ionic conductivity of this solid electrolyte 1 was measured by an AC impedance analyzer, it was 1.1 × 10 ⁻³ S
The ionic conductivity was / cm.

For comparison, a solid electrolyte was prepared from a polythioether monolayer film with n = 2, and its ionic conductivity was measured to be 3.5 × 10 ^-5 S / cm.

Example 3 A polyethylene derivative having oxymethylene in 10 kinds of side chains with n = 0 to 9 of a unit (3) having a lone electron pair represented by the following chemical formula was synthesized, respectively. Ten polymer layers were formed by the same method. The obtained polymer layer was treated in the same manner as in Example 1 to prepare a lithium ion-doped solid electrolyte 1. When the ionic conductivity of this solid electrolyte 1 was measured with an AC impedance analyzer, the ionic conductivity was 2.3 × 10 ⁻³ S / cm.

[0037]

[Chemical 7]

Example 4 A polymer having a 12-azacrown-4-thioether derivative in five side chains with n = 2 to 6 of a unit (4) having a lone electron pair represented by the following chemical formula was synthesized. did. These polymers were sequentially deposited in the same manner as in Example 2 to prepare 5 polymer layers. The obtained polymer layer was treated in the same manner as in Example 1 to prepare a lithium ion-doped solid electrolyte 1. When the ionic conductivity of this solid electrolyte 1 was measured with an AC impedance analyzer, the ionic conductivity was 8.5 × 10 ⁻⁴ S / cm.

[0039]

[Chemical 8]

Example 5 A dimethyl sulfoxide solution of a 12-azacrown-4-thioether derivative when n = 6 in the above Example 4, a polythioether dimethyl sulfoxide solution of n = 2 in Example 2, and an n in Example 3 = 3 in the dimethylformamide solution of a polyethylene derivative having an oxymethylene unit in the side chain of Example 2 in this order.
Three polymer layers were prepared in the same manner as in. The obtained polymer layer was treated in the same manner as in Example 1 to prepare a lithium ion-doped solid electrolyte 1. When the ionic conductivity of this solid electrolyte 1 was measured with an AC impedance analyzer, the ionic conductivity was 8.7 × 10 ⁻⁴ S / cm.

Example 6 Polystyrene-1 when n = 0 in the above Example 1
A solution of a block copolymer of 2-crown-4 substituted polyethylene in dimethylacetamide, n = 3 in Example 2.
Of the polythioether dimethyl sulfoxide solution of Example 3 and a dimethyl sulfoxide solution of a polymer having a 12-azacrown-4-thioether derivative in the side chain of n = 6 in Example 4 in the same manner as in Example 2
A polymer layer of layers was made. The obtained polymer layer was treated in the same manner as in Example 1 to prepare a lithium ion-doped solid electrolyte 1. When the ionic conductivity of this solid electrolyte 1 was measured by an AC impedance analyzer, the ionic conductivity was 1.0 × 10 ⁻³ S / cm.

(Application Example) Using the solid electrolyte obtained in Example 1, a lithium battery having the structure shown in FIG. 2 was assembled. In the figure, D is a lithium battery, which is composed of a solid electrolyte 1 composed of _five polymer layers P _{1 to} P ₅ , a negative electrode 2 and a positive electrode 3. A lithium anode 2 is attached to the polymer layer P ₁ of the solid electrolyte 1, and a cathode 3 made of manganese dioxide, acetylene black and polytetrafluoroethylene is attached to the polymer layer P ₅ . Further, a stainless steel can 7 was attached to the positive electrode 3 via a current collector 5a, and a stainless steel cap 6 was attached to the negative electrode 2 via a current collector 5b to obtain a test lithium battery D.

When the electromotive force of this lithium battery D was measured by the two-end method, it was 3.5V. Further, the lithium battery was charged and discharged repeatedly at a current of 0.5 mA / cm, with an upper limit voltage of 3.5 V and a lower limit voltage of 2 V. The discharge capacity at the 10th cycle was 12.0 mAh. Further, the charging and discharging were repeated and the discharge capacity at the 100th time was measured.

[0044]

As described in detail above, according to the solid electrolyte of the present invention, a concentration gradient of alkali metal ions is formed in the solid electrolyte, the dissolution of the alkali metal in the negative electrode is promoted, and a large driving force is obtained. As a result, a solid electrolyte having high ionic conductivity can be obtained. Further, since the ionic conductivity of the solid electrolyte can be easily adjusted by changing the concentration gradient of the alkali metal ions, a solid electrolyte having a desired ionic conductivity can be easily obtained. Therefore, by using the solid electrolyte of the present invention, a battery having high electromotive force and excellent cycle characteristics can be manufactured.

[Brief description of drawings]

FIG. 1 is a schematic view of a solid electrolyte showing an example of the present invention.

FIG. 2 is a schematic diagram of a lithium battery showing an application example of the present invention.

[Explanation of symbols]

1 solid electrolyte P ₁ , P _n polymer layer 2 negative electrode 3 positive electrode x lone electron pair

Claims (1)

[Claims] 1. A solid electrolyte formed between a pair of electrodes, wherein the solid electrolyte has a different lone electron pair content in the molecular chain from the negative electrode side to the positive electrode side, and has a lone electron pair content. A solid electrolyte formed by laminating a substrate polymer in three or more layers so as to sequentially increase the number of ions, and doping this with ion carriers.