JP3022317B2 - Polymer solid electrolyte - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid polymer electrolyte, and more particularly to a solid polymer electrolyte suitable as a material for electrochemical devices such as batteries, capacitors and sensors.

[0002]

2. Description of the Related Art
Electrolytes for electrochemical devices such as batteries, capacitors, and sensors are used in the form of solutions or pastes because of their ionic conductivity. It requires a separator impregnated with, so that problems have been pointed out, such as limitations on ultra-miniaturization and thinning of devices.
On the other hand, solid electrolytes such as inorganic crystalline substances, inorganic glasses, and organic polymer substances have been proposed. Organic polymer-based materials are generally excellent in processability and moldability, and the resulting solid electrolyte has flexibility and bendability, and its progress has been made in terms of increasing the degree of freedom in the design of applied devices. Expected. However, at present, it is inferior to other materials in terms of ion conductivity.

For example, Japanese Patent Application Laid-Open No. 2-235957, which includes the present applicant, has proposed an attempt to apply a specific alkali metal salt to a mixture of an epichlorohydrin rubber and a low molecular weight polyethylene glycol derivative to apply it to a solid polymer electrolyte. However, a practically sufficient conductivity value has not been obtained. Also, JP-A-3-47833 and JP-A-4-47.
No. 68064, having an average molecular weight of 1,000 to 20,000.
Although the polymer solid electrolyte obtained by crosslinking the polymer compound of No. 00 shows relatively good ionic conductivity in a practical temperature range, it is still required to have improved ionic conductivity.

The applicant's JP-A-63-154736 and JP-A-63-241026, and furthermore, European Patent Publication No. 43
The polyether copolymer having an oligooxyethylene side chain described in No. 4011 suggests application to a polymer solid electrolyte or an antistatic material for plastics, but a specific copolymer having a specific side chain length and a specific copolymer composition is suggested. There is no description or suggestion that it has specific superior properties as an ion-conductive solid electrolyte.

[0005]

Means for Solving the Problems The present inventors have developed a polyer copolymer having a specific composition ratio, in which an ethylene oxide is combined as a copolymer component with an oligoethylene glycol glycidyl ether having a specific side chain length, to obtain a soluble electrolyte. It has been found that by adding a salt compound, a solid electrolyte having significantly increased ionic conductivity can be obtained as compared with a combination of other epoxides, for example, propylene oxide or epichlorohydrin.
That is, in the present invention, the main chain structure has a structural unit of the following formula (1) of 5 to 30 mol% and a structural unit of the formula (2) of 95 to 70 mol%
(1) a solid random copolymer comprising:
The degree of polymerization n of the oxyethylene unit in the side chain portion of the formula is from 1 to 1.
2. Polyether having an oligooxyethylene side chain having a number average molecular weight of 100,000 to 2,000,000, a glass transition point measured by a differential scanning calorimeter (DSC) of -60 ° C or less, and a heat of fusion of 70 J / g or less. A solid polymer electrolyte comprising a polymer and an electrolyte salt compound soluble in the copolymer, and a battery using the same.

[0006]

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[0007]

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The method for producing the polyether copolymer having an oligooxyethylene side chain (hereinafter abbreviated as polyether copolymer) used in the present invention is described in
No. 154736. That is, using a catalyst system mainly composed of organic aluminum, a catalyst system mainly composed of organic zinc, a catalyst system composed of an organic tin-phosphate ester condensate, or the like as a ring-opening polymerization catalyst, the above formula (1) and (2) It is obtained by reacting each monomer corresponding to the formula in the presence or absence of a solvent at a reaction temperature of 10 to 80 ° C. with stirring.

The polyether copolymer used in the present invention has a molar ratio of the structural units (1) and (2) of the formula (1) of 5 to 30 mol%, preferably 10 to 30 mol% and (2). ) Those of the formula 95-70 mol%, preferably 90-70 mol% are suitable. When the molar ratio of the formula (2) exceeds 95 mol%, the glass transition point is increased and crystallization of the structural unit of the formula (2) is caused, and the glass transition point is -60 ° C. or less and the heat of fusion is 70 J.
/ G or less cannot be maintained, and as a result, the ionic conductivity of the solid electrolyte is significantly deteriorated. It is generally known that the ionic conductivity is improved by lowering the crystallinity of polyethylene oxide, but the effect of improving the ionic conductivity was found to be significantly large in the case of the polyether copolymer of the present invention. . On the other hand, when the molar ratio of the formula (2) is less than 70 mol%, the softening temperature of the copolymer decreases, and it becomes difficult to obtain a solid electrolyte at room temperature (for example, 20 ° C.). The above glass transition point and heat of fusion are measured by a differential scanning calorimeter (DSC). In the present invention, the glass transition point of the polyether copolymer is -60 ° C.
Or less, preferably -65 ° C or less, and the heat of fusion is 70 J / g.
Below, preferably 50 J / g or less are suitable for use. When the glass transition point and the heat of fusion exceed the above values, the ion conductivity is reduced.

In the present invention, the degree of polymerization n of the oxyethylene unit in the side chain of formula (1) of the polyether copolymer is preferably from 1 to 12, and if it exceeds 12, the ionic conductivity of the obtained solid electrolyte becomes poor. It is not preferable because it decreases. The molecular weight of the polyether copolymer is preferably from 100,000 to 200, in order to obtain processability, moldability, mechanical strength and flexibility.
Ten thousand, preferably 200,000 to 1.5 million are suitable. When the number average molecular weight is less than 100,000, the obtained electrolyte becomes liquid, causing liquid leakage, which is not practically preferable.
If the number exceeds 10,000, problems arise in workability and formability.

The electrolyte salt compound used in the present invention may be any as long as it is soluble in the polyether copolymer of the present invention. In the present invention, the following compounds are preferably used. That is, metal cations, ammonium ions, amidinium ions, and cations selected from guanidinium ions, chloride ions, bromine ions, iodine ions, perchlorate ions, thiocyanate ions, tetrafluoroborate ions, Nitrate ion, As
F ₆ ⁻ , PF ₆ ⁻ , stearyl sulfonate ion, octyl sulfonate ion, dodecylbenzene sulfonate ion, naphthalene sulfonate ion, dodecyl naphthalene sulfonate ion, 7,7,8,8-tetracyano-
p-quinodimethane ion, R ₁ SO ₃ ⁻ , (R ₁ S
O ₂ ) (R ₂ SO ₂ ) N ⁻ , (R ₁ SO ₂ ) (R ₂ SO
₂ ) (R ₃ SO ₂ ) C ⁻ and (R ₁ SO ₂ ) (R ₂ S
O ₂₎ YC ^- compound comprising the selected anions from the like. Here, R ₁ , R ₂ , R ₃ and Y are electron-withdrawing groups. Preferably, R ₁ , R ₂ , and R ₃ are each independently a perfluoroalkyl group or a perfluoroaryl group having 1 to 6 carbon atoms, and Y is a nitro group, a nitroso group, a carbonyl group, a carboxyl group or Cyano group
It is. R ₁ , R ₂ and R ₃ are each the same,
It may be different. A transition metal cation can be used as the metal cation. Preferably Mn, Fe,
A cation of a metal selected from Co, Ni, Cu, Zn and Ag metals is used. Li, Na, K, Rb,
Preferable results can be obtained by using a cation of a metal selected from Cs, Mg, Ca and Ba metals. It is free to use two or more of the aforementioned compounds as electrolyte salt compounds.

In the present invention, the amount of the soluble electrolyte salt compound used is based on the total number of moles of ethylene oxide units including the main chain and the side chains of the polyether copolymer, based on the number of moles of the soluble electrolyte salt compound / the number of ethylene oxide units. Is 0.0001 to 5, preferably 0.001 to 5.
A range of 0.5 is preferred. If this value exceeds 5, processability, moldability, mechanical strength and flexibility of the obtained solid electrolyte are reduced, and ion conductivity is also reduced.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for producing a solid polymer electrolyte according to the present invention is not particularly limited, but usually the respective components are mixed mechanically or dissolved in a solvent and mixed, and then the solvent is removed. It is manufactured by such a method. Various kneaders, open rolls,
An extruder or the like can be used arbitrarily. When produced using a solvent, various polar solvents, for example, tetrahydrofuran, acetone, acetonitrile, dimethylformamide, dimethyl sulfoxide, dioxane, methyl ethyl ketone,
Methyl isobutyl ketone or the like is used alone or as a mixture. The concentration of the solution is not particularly limited, but is 1 to 50% by weight.
Is preferred. Further, the solid electrolyte may be cross-linked if necessary. As crosslinking agents for crosslinking the copolymer, 2-4-tolylene diisocyanate, 2-6-tolylene diisocyanate, 4-4-diphenylmethane diisocyanate,
An isocyanate compound such as hexamethylene diisocyanate can be exemplified.

When the polymer solid electrolyte described in the present invention is used, a large area thin film solid electrolyte having flexibility, which is an advantage of a polymer, can be easily obtained. For example, a battery using the polymer electrolyte shown in the present invention can be manufactured.
In this case, examples of the cathode material include lithium-manganese composite oxide, lithium cobalt oxide, vanadium pentoxide, polyacene, polypyrene, polyaniline, polyphenylene, polyphenylene sulfide, polyphenylene oxide, polypyrrole, polyfuran, and polyazulene. Examples of the negative electrode material include an interlayer compound in which lithium is occluded between layers of graphite or carbon, lithium metal, lithium-lead alloy, and the like. Example 8 shows an example of the battery. In addition, utilization of a cation such as an alkali metal ion, a Cu ion, a Ca ion, and a Mg ion as a diaphragm of an ion electrode using high electric conductivity can be considered.

[0015]

【Example】

Examples 1 to 4 Comparative Examples 1 to 5 1 g of the polyether copolymer shown in Tables 1 and 2 (Comparative Example 3 was polyethylene oxide) was added to tetrahydrofuran 20
Then, a solution of lithium perchlorate in tetrahydrofuran was mixed so that the number of moles of the soluble electrolyte salt compound / the total number of moles of ethylene oxide units was 0.005.
This mixture was cast on a polytetrafluoroethylene mold and dried sufficiently to obtain a film. The results of Examples and Comparative Examples are summarized in Tables 1 and 2, respectively. In Tables 1 and 2, the glass transition point and the heat of fusion were measured using a differential scanning calorimeter DSC8230B manufactured by Rigaku Denki Co., Ltd., in a nitrogen atmosphere, in a temperature range of -100 to 80 ° C, and at a heating rate of 10 ° C.
/ Min. The conductivity σ was measured by the complex impedance method using platinum as an electrode, an alternating current method at a voltage of 0.5 V and a frequency range of 5 Hz to 1 MHz.

Example 5 1 g of a polyether copolymer having 5 mol% of the structural unit of the formula (1) and 95 mol% of the structural unit of the formula (2) was dissolved in 20 ml of acetonitrile, and lithium bistrifluoromethanesulfonylimide ( A solution of LiTFSI in acetonitrile was mixed so that the number of moles of LiTFSI / the total number of moles of ethylene oxide units was 0.005. This mixture was cast on a polytetrafluoroethylene mold and dried sufficiently to obtain a film. The characteristics of the film were measured in the same manner as in Examples 1 to 4. 3
The conductivity of the solid electrolyte at 0 ° C. is 4.0 × 10 ⁻⁴ S /
cm.

EXAMPLE 6 1 g of a polyether copolymer having 12 mol% of the structural unit of the formula (1) and 88 mol% of the structural unit of the formula (2) was dissolved in 20 ml of acetonitrile, and the number of moles of LiTFSI / ethylene oxide unit was obtained. L such that the total number of moles of
A solution of iTFSI in acetonitrile was mixed. This mixture was cast on a polytetrafluoroethylene mold and dried sufficiently to obtain a film. The characteristics of the film were measured in the same manner as in Examples 1 to 4.

Example 7 A film was obtained in the same manner as in Example 6, except that the mole number of LiTFSI / the total mole number of ethylene oxide units was 0.05. The characteristics of the film were measured in the same manner as in Examples 1 to 4. It is clear that the electrolyte of the present invention has particularly excellent ionic conductivity in comparison with Comparative Examples.

Example 8 A secondary battery was constructed using the solid polymer electrolyte obtained in Example 3 as an electrolyte, a lithium metal foil as a negative electrode, and lithium cobalt oxide (LiCoO ₂ ) as a positive electrode.
The size of the polymer solid electrolyte is 10 mm × 10 mm × 1 mm. The size of the lithium foil is 10 mm X 10 mm X 0.1 mm. Lithium cobaltate was prepared by mixing predetermined amounts of lithium carbonate and cobalt carbonate powder and then firing at 900 ° C. for 5 hours. Next, this was pulverized and further added with an appropriate amount of acetylene black, and then press-molded to 10 mm × 10 mm × ² mm at a pressure of 300 Kgw / cm ² to obtain a positive electrode of a battery. The polymer solid electrolyte obtained in Example 3 was sandwiched between a lithium metal foil and a lithium cobaltate plate, and the charge / discharge characteristics of the battery were examined while applying a pressure of 10 Kgw / cm ² so that the interface was in close contact. The discharge current at an initial terminal voltage of 3.2 V is 0.4
mA / cm ² , and could be charged at 0.3 mA / cm ² . Since the battery of this embodiment can be easily manufactured to be thin, it is lightweight and has a large capacity.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

The polymer solid electrolyte of the present invention is excellent in workability, moldability, mechanical strength, flexibility and the like, and its ionic conductivity is remarkably improved. Therefore, application to electronic devices such as solid-state batteries, large-capacity capacitors, and display devices such as electrochromic displays is expected.

──────────────────────────────────────────────────続 き Continued from the front page (72) Inventor Masayoshi Watanabe 30-3-Oimatsu-cho, Nishi-ku, Yokohama-shi, Kanagawa Prefecture ▲ Yoshi ▼ Eiichi Sawa (56) References JP-A-63-154736 (JP, A) JP-A-61-83249 (JP, A) JP-A-3-200864 (JP, A) JP-A-3-200865 (JP, A) JP-A-6-76829 (JP, A) JP-A-5-304051 (JP, A) JP-A-5-202281 (JP, A) (58) Fields investigated (Int. Cl. ⁷⁾ , DB name) C08L 71/00-71/14 H01M 6 / 18,10 / 40 H01G 9/00-9/02

Claims (10)

(57) [Claims] The main chain structure is represented by the following structural unit (1):
A solid random copolymer comprising 30 mol% and 95 to 70 mol% of the structural unit of the formula (2), wherein the degree of polymerization n of the oxyethylene unit in the side chain portion of the formula (1) is 1 to 12, Number average molecular weight 100,000-2,000,000, differential scanning calorimeter (DS
It comprises a polyether copolymer having an oligooxyethylene side chain having a glass transition point of −60 ° C. or lower and a heat of fusion of 70 J / g or lower as measured in C), and an electrolyte salt compound soluble in the copolymer. Characterized polymer solid electrolyte. Embedded image Embedded image 2. The polymer solid electrolyte according to claim 1, wherein a polyether copolymer comprising 10 to 30 mol% of the structural unit of the formula (1) and 90 to 70 mol% of the structural unit of the formula (2) is used. 3. The polymer solid electrolyte according to claim 1, wherein a polyether copolymer having a glass transition point of −65 ° C. or less and a heat of fusion of 50 J / g or less is used. 4. An electrolyte salt compound comprising a cation selected from a metal cation, an ammonium ion, an amidinium ion, and a guanidinium ion, a chloride ion, a bromine ion, an iodine ion, a perchlorate ion, and a thiocyanate ion. , Tetrafluoroborate ion, nitrate ion, As
F ₆ ⁻ , PF ₆ ⁻ , stearyl sulfonate ion, octyl sulfonate ion, dodecylbenzene sulfonate ion, naphthalene sulfonate ion, dodecyl naphthalene sulfonate ion, 7,7,8,8-tetracyano-p-quinodimethane Ions, R ₁ SO ₃ ⁻ , (R ₁ SO ₂ ) (R ₂ S
^{_{O 2) N -, (R}} 1 SO 2) (R 2 SO 2) (R 3 SO
₂₎ C ^-, and _{(R 1 SO 2) (R} 2 SO 2) YC - a compound consisting of a selected anionic from which claim 1
4. The polymer solid electrolyte according to any one of 3. Where R ₁ ,
R ₂ , R ₃ and Y are electron withdrawing groups. 5. R ₁ , R ₂ , and R ₃ are each independently a perfluoroalkyl group or a perfluoroaryl group having 1 to 6 carbon atoms, and Y is a nitro group, a nitroso group, a carbonyl group, The polymer solid electrolyte according to claim 4, which is a carboxyl group or a cyano group . 6. The method according to claim 1, wherein the metal cation is Li, Na, K, Rb,
The polymer solid electrolyte according to claim 4, which is a cation of a metal selected from Cs, Mg, Ca, and Ba metals. 7. The solid polymer electrolyte according to claim 4, wherein the metal cation is a cation of a transition metal. 8. The method according to claim 1, wherein the metal cation is Mn, Fe, Co, N
The polymer solid electrolyte according to claim 4, which is a cation of a metal selected from i, Cu, Zn, and Ag metals. 9. The method according to claim 1, wherein the compounding ratio of the electrolyte salt compound and the polyether copolymer is such that the value of the number of moles of the electrolyte salt compound / the total number of moles of ethylene oxide units is 0.0001 to 5. The solid polymer electrolyte according to the above. 10. A battery using the polymer solid electrolyte according to claim 1.