JP2001110403A - Electrode for electrochemical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for an electrochemical device, and especially to provide a lithium ion secondary battery which does not use liquid electrolyte. SOLUTION: An ion conductive high molecular solid electrolyte using high molecular compound with ether coupling, an electrode activating substance, and an electroconductive agent are filled so that a hole ratio in an electrode should be not more than 20% for reducing the hole ratio, therefore, an electrochemical device which does not contain liquid and has superior properties, where movements of ions should not be hindered in an interface of the electrode and the electrolyte as well as in the electrode can be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an electrode using a solid ion-conductive polymer solid electrolyte, and particularly to a battery,
The present invention relates to an electrode material suitable as a material for an electrochemical device such as a capacitor, a photoelectric conversion element, and a sensor.

[0002]

2. Description of the Related Art
Electrode materials that make up electrochemical devices such as batteries, capacitors, photoelectric conversion elements, and sensors use liquid organic compounds as an ion-conducting medium, which may cause damage to equipment or fire due to liquid leakage. However, there have been pointed out problems such as the thinning of the battery using the same and the limitation in the degree of freedom of the shape.

In order to improve the characteristics of the interface between the ion diffusion in the electrode and the solid polymer electrolyte, a method of impregnating a solid ionic conductive substance with a polar solvent (Japanese Patent Laid-Open No. 5-9481).
No. 9) and a method using a gel polymer containing a polar solvent (Japanese Patent Application Laid-Open No. 9-129218), etc., all of which use a liquid organic compound as a medium. In order to produce an all-solid-state lithium battery with higher safety, it is necessary to eliminate a liquid ionic conductor from the battery configuration, and a battery using no liquid at all is desired.

[0004]

According to the present invention, the porosity of the electrode is reduced, and the ionic conductive polymer solid electrolyte having an ether bond as the electrode material is used to obtain excellent solid-state battery performance. We have developed an electrode that works.

The electrode according to the present invention is characterized in that the porosity in the total volume of the electrode filled with a solid ionic conductive material comprising a polymer material having an ether bond is 20% or less. It is a device electrode. The electrode of the present invention has an ion-conductive polymer solid electrolyte filled in the electrode so that the porosity in the entire volume is 20% or less, preferably 15% or less. To the positive electrode and / or
Alternatively, a battery used as the negative electrode, in particular, a solid lithium secondary battery is also provided. In an electrode having a porosity exceeding 20%, the movement of ions in the electrode does not sufficiently occur, the interface resistance with the solid polymer electrolyte increases, and the performance as a battery decreases.
In addition, the energy density per capacity becomes low, which is not preferable.

[0006] An electrode is prepared by using an ionic conductive polymer compound alone or a mixture with a non-ionic conductive polymer compound such as polyvinylidene fluoride (hereinafter referred to as PVDF) which functions as a binder, as an electrode active material, a conductive agent, A method of mixing and molding with an electrolyte salt compound or the like, or an electrode active material,
After molding with a conductive agent and a binder such as PVDF, there is a method of filling with an ionic conductive polymer solid electrolyte (an electrolyte salt compound dissolved in an ionic conductive polymer compound). A solvent may be used for mixing the electrode materials. When mixing using a solvent, a uniform layer can be obtained by uniformly applying the mixture on a current collector (usually using a metal foil) and removing the solvent. A solvent such as water or an organic solvent may be used for mixing them. When an organic solvent is used as a solvent, various polar solvents such as tetrahydrofuran, acetone, acetonitrile, dimethylformamide, dimethylsulfoxide, dioxane, methyl ethyl ketone, methyl isobutyl ketone, and toluene are used alone or in combination. In the case of mixing without using a solvent, a uniform layer can be obtained by dissolving this mixture in a solvent, applying the mixture on a current collector and removing the solvent. If the layer does not contain an ion-conductive polymer solid electrolyte,
After the layer is impregnated with the ion-conductive polymer solid electrolyte dissolved in the solvent, the solvent is removed or the layer is filled with the molten ion-conductive polymer solid electrolyte. The electrodes are formed by compression molding the layers so that the porosity of the electrode layers other than the current collector is 20% or less. Compression molding, roll press,
A parallel plate press or the like is used. At this time, heating may be performed. The electrodes prepared by these methods can take a large current value and have little deterioration even when charged and discharged.

The porosity of the electrode is calculated as porosity (%) = (1− (measured density / theoretical density)) × 100, but the metal foil functioning as a current collector is not included in the calculation. The theoretical density of the electrode is calculated from the mixture ratio and density of the elements to be mixed, and the measured density is calculated from the volume and weight of the electrode.

In the production of an electrode, an electrode active material, a conductive agent,
The compounding ratio of the ionic conductive polymer compound, the electrolyte salt compound and the non-ionic conductive polymer compound is such that the total of the electrode active material and the conductive agent is 50 to 95% of the total weight, the ionic conductive polymer compound, the electrolyte salt compound and It is desirable that the total amount of the nonionic conductive polymer compound is 5 to 50% of the total weight. When the weight ratio of the total of the electrode active material and the conductive agent is lower than 50%, the capacity of the electrode is undesirably small. On the other hand, if the weight ratio between the electrode active material and the conductive agent exceeds 95%, the ionic conductivity of the electrode deteriorates, which is not preferable. The weight ratio of the electrode active material to the conductive agent is preferably 40:60 to 90:10, and the weight ratio of the nonionic conductive polymer compound to the ionic conductive polymer compound is 0: 100.
To 60:40 is preferred.

The ion-conductive polymer compound of the present invention is a polymer compound having an ether bond, and a polyether compound such as ethylene oxide is suitable for facilitating the transfer of ions.

In particular, regarding the operating characteristics in a low temperature state,
Polyether compounds having an ethylene oxide unit in the main chain and side chain show very excellent performance. This is because a polymer compound having an ether bond in the main chain and the side chain has a low glass transition temperature and a high ionic conductivity even at a low temperature.

The polyether compound having an ethylene oxide unit in the main chain and the side chain is represented by the following formula (1):

[0012]

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[Wherein R ¹ , R ² and R ³ represent a hydrogen atom or -C
H ₂ O (CH ₂ CH ₂ O) _n R, where n and R may be different between R ¹ , R ² and R ³ . However, all of R ¹ , R ² and R ³ are not hydrogen atoms at the same time. R is carbon number 1-12
And n is 1-12. 5 to 95 mol% of a repeating unit derived from a monomer represented by the formula:
Formula (2) as a component

[0014]

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95 to 5 mol% of a repeating unit derived from a monomer represented by the following formula (C): a repeating unit derived from a monomer having one epoxy group and at least one reactive functional group as component (C). It is a polyether multi-component copolymer comprising the components (A), (B) and (C) having a content of about 15 mol%.

The ionic conductivity at 25 ° C. of a polymer compound having an ether bond containing an electrolyte salt compound is 1 × 10 ⁻⁵ S / cm.
Above, preferably 3 × 10 ⁻⁵ S / cm or more are suitable. When the ionic conductivity is less than 1 × 10 ⁻⁵ S / cm, the movement of ions in the electrode does not sufficiently occur, and the performance of the battery is significantly reduced.

In the present invention, the following electrolyte salts
Compounds are preferably used. That is, metal cations,
Ammonium ion, amidinium ion, and guanidinium
Cations selected from umium ions, chlorine ions, and bromine
Ion, iodine ion, perchlorate ion, thiocyanate
Ion, tetrafluoroborate ion, nitrate ion,
AsF₆ ^-, PF₆ ^-, Stearyl sulfonate ion, octyl
Sulfonate ion, dodecylbenzene sulfonate ion
, Naphthalenesulfonic acid ion, dodecylnaphthalene
Sulfonate ion, 7,7,8,8-tetracyano-p-quinodime
Tanion, X₁SO_Three ^-, [(X₁SO_Two) (X_TwoSO_Two) N]^-, [(X₁SO_Two) (X
_TwoSO_Two) (X_ThreeSO_Two) C]^-, And [(X₁SO_Two) (X_TwoSO_Two) YC] ^- Choose from
And a compound comprising an anion. However,
X₁, X_Two, X_ThreeAnd Y are electron-withdrawing groups. Preferably
X₁, X_Two, And X_ThreeAre each independently a group of 1 to 6 carbon atoms.
-Fluoroalkyl group or perfluoroaryl group
Y is nitro, nitroso, carbonyl, carbo
Xyl group or cyano group. X₁, X_TwoAnd X_ThreeAre the same
Or may be different. As metal cation
Can use a cation of a transition metal. Preferably
Of metals selected from Mn, Fe, Co, Ni, Cu, Zn and Ag metals
Cations are used. Also, Li, Na, K, Rb, Cs, Mg, C
It is also preferable to use a cation of a metal selected from a and Ba metals.
Good results are obtained. As described above as an electrolyte salt compound
It is free to use two or more compounds in combination.

In the present invention, the amount of the electrolyte salt compound used is such that the value of the number of moles of the electrolyte salt compound / the total number of moles of oxyethylene units is 0.0001 to 5, preferably 0.001 to 0.5. If this value exceeds 5, processability, moldability, mechanical strength and flexibility of the obtained electrode are reduced, and ion conductivity is also reduced.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for producing an electrode of the present invention is not particularly limited, but after mechanically mixing the respective components, forming them into a layer on a current collector, and then adjusting the porosity by compression or the like. Manufactured. As a means for mechanically mixing, a kneading machine such as a mixing roll such as a two roll or a three roll, a dispersion stirrer such as a disperser and a homogenizer, and a dispersion mixer such as a ball mill and a planetary mill can be arbitrarily used.

The electrode according to the present invention is characterized in that the porosity in the electrode is not more than 20%, the active material, the conductive agent and the ionic conductive polymer compound are densely packed, and the resistance is low. And the point of ion migration is excellent. By lowering the porosity, the transfer of ions at the electrode / electrolyte interface and within the electrode is not hindered without using a liquid ionic conductor, creating an excellent liquid-free electrochemical device. It is possible.

For example, a battery using the electrode of the present invention can be manufactured. In this case, the active material of the positive electrode includes lithium-manganese composite oxide, lithium cobaltate, vanadium pentoxide, polyacetylene, polypyrene, polyaniline, polyphenylene, polyphenylene sulfide, polyphenylene oxide, polypyrrole, polyfuran, and polyazulene. Examples of the conductive agent include graphite and carbon black. Examples of the nonionic conductive binder polymer include polytetrafluoroethylene, ethylene tetrafluoride / propylene hexafluoride copolymer, ethylene tetrafluoride / ethylene copolymer, polyvinylidene fluoride, polyvinylidene fluoride copolymer, and polyolefin. There are various fluoropolymers such as vinyl chloride, SBR rubber, and polyolefins. Examples of the negative electrode material include an intercalation compound in which lithium is occluded between graphite or carbon layers, lithium metal, lithium-lead alloy, lithium-aluminum alloy, lithium-tin alloy, lithium-silicon alloy, and the like. When an interlayer compound is used for the negative electrode, a graphite material, easily graphitizable carbon, non-graphitizable carbon, low-temperature fired carbon, or the like can be used as the negative electrode active material.

[0022]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples. Example 1 A method for producing an ion-conductive polymer solid electrolyte.

[0023]

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50 g of a polyether copolymer (glycidyl ether compound represented by formula (3): ethylene oxide: allyl glycidyl ether = 16: 83: 1 mol%, weight average molecular weight (Mw) = 800,000) in acetonitrile, Lithium borofluoride 7 g, azobisisobutyronitrile 0.2 as a crosslinking agent
g, bismaleimide (1.2 g) was mixed as a cross-linking aid, then cast on a PET film, and after removing the solvent, cross-linking was performed for 3 hours while drying at 100 ° C. under reduced pressure to obtain a 50 μm polymer solid electrolyte film. I got The ionic conductivity of this film showed a value of 4 × 10 ⁻⁵ cm / S at 25 ° C.

Example 2 80 g of lithium cobaltate, 10 g of graphite, polyether copolymer (glycidyl ether compound represented by formula (2): ethylene oxide = 30: 70 mol%, Mw = 1100,000) 10
g and lithium borofluoride (1.3 g) were mixed with a mixing roll, and this mixture was dispersed in acetonitrile (100 g). The dispersion of this mixture was uniformly applied on an Al foil, and allowed to stand at room temperature for 30 minutes to evaporate acetonitrile.
Dry in oven at 30 ° C. for 30 minutes. After drying, a roll press was performed to obtain a positive electrode. The obtained electrode has a thickness of 52 μm,
Specific gravity was 2.96 g / cm ³ (porosity 12.3%), and resistance value was 12 Ω / cm ² . As the resistance value, a DC resistance value in a state where the produced electrode was sandwiched between SUS electrodes and a pressure of 2 kg was applied was adopted. The obtained electrode and the electrolyte membrane prepared in Example 1 were dried under reduced pressure at 110 ° C. for 48 hours, and a battery was prepared using metal Li as a counter electrode, and a charge / discharge test was performed. Initial discharge capacity of 13 per weight of positive electrode active material
The discharge capacity at the time of 0 mAh / g and the 10th time was 125 mAh / g.

Example 3 Polyether copolymer (glycidyl ether compound represented by formula (2): ethylene oxide = 30: 70 mol%, Mw = 11
(0000,000) 15 g and 3.2 g of lithium borofluoride are dissolved in 150 g of acetonitrile, 60 g of lithium manganate and 25 g of graphite are added to the solution, and the mixture is stirred with a disper.
The dispersion of this mixture is uniformly applied on an Al foil, and
Let stand for a minute to evaporate the acetonitrile and further dry in an oven at 100 ° C. for 30 minutes. After drying, a parallel plate press is performed to obtain a positive electrode. The resulting electrode is 47 μm thick,
Specific gravity was 2.00 g / cm ³ (porosity: 18.9%), and DC resistance was 9 Ω / cm ² . Using the obtained electrode, a battery was prepared in the same manner as in Example 2, and a charge / discharge test was performed. The initial discharge capacity was 100 mAh / g and the 10th discharge capacity was 96 mAh /
g.

Example 4 5 g of PVDF, 7 g of a polyether copolymer (glycidyl ether compound represented by the formula (2): ethylene oxide = 30: 70 mol%, Mw = 1100,000) and 0.9 g of lithium borofluoride were converted to N-methyl. Dissolved in 150 g of pyrrolidone, lithium manganate 70
g, 10 g of graphite and 8 g of carbon black are added to the solution and dispersed with a disper. Disperse this mixture in Al
Apply evenly on foil and dry in oven at 100 ° C for 2 hours. After drying, roll pressing is performed to obtain a positive electrode. The obtained electrode had a thickness of 49 μm and a specific gravity of 2.85 g / cm ³ (porosity of 4.0
%), And the direct current resistance was 3Ω / cm ² . Using the obtained electrode, a battery was prepared in the same manner as in Example 2, and a charge / discharge test was performed. The initial discharge capacity is 98mAh /
g, the 10th discharge capacity was 95 mAh / g.

Example 5 5 g of PVDF, 80 g of lithium cobaltate, 5 g of graphite, 5 g of carbon black and 50 g of N-methylpyrrolidone were kneaded using a mixing roll, and the mixture paste was mixed with N-methylpyrrolidone at 30,000 cps. Dilute to viscosity. This diluted mixture dispersion was uniformly applied on an Al foil, and 100
Dry in oven at 2 ° C for 2 hours. Dissolve 5 g of a polyether copolymer (glycidyl ether compound represented by the formula (2): ethylene oxide: allyl glycidyl ether = 29: 70: 1 mol%, Mw = 1.15 million) and 0.7 g of lithium perchlorate in 70 g of acetonitrile A dried solution is made and impregnated into this mixture layer on the dried Al foil. The acetonitrile of the impregnated solution is slowly removed at room temperature and then dried in an oven at 100 ° C. for 30 minutes. After drying, roll pressing is performed to obtain a positive electrode. The resulting electrode is 47 μm thick, specific gravity 3.44 g
/ cm ³ (porosity 4.3%) and DC resistance 6 Ω / cm ² . Using the obtained electrode, a battery was prepared in the same manner as in Example 2, and a charge / discharge test was performed. The initial discharge capacity was 133 mAh / g and the 10th discharge capacity was 122 mAh / g per weight of the positive electrode active material.

Example 6 Polyether copolymer (glycidyl ether compound represented by formula (2): ethylene oxide = 30: 70 mol%, Mw = 11
100,000) 10 g and lithium perchlorate 1.3 g in acetonitrile
Dissolve it in 100 g, add 90 g of non-graphitizable carbon to the solution, and stir with a disper. The mixture dispersion was evenly applied on a Cu foil and allowed to stand at room temperature for 30 minutes to evaporate acetonitrile,
Further, it is dried in an oven at 100 ° C. for 30 minutes. After drying,
A parallel plate press is performed to obtain a negative electrode. The obtained electrode had a thickness of 57 μm and a specific gravity of 1.58 g / cm ³ (a porosity of 2.9%). Using the obtained electrode, a battery was prepared in the same manner as in Example 2, and a charge / discharge test was performed. The initial discharge capacity was 310 mAh / g and the tenth discharge capacity was 303 mAh / g per weight of the negative electrode active material.

Comparative Example 1 The same mixture as in Example 2 was prepared, coated on Al, dried, and a positive electrode was obtained without pressing. The obtained electrode had a thickness of 93 μm, a specific gravity of 1.68 g / cm ³ (porosity of 50.2%), and a DC resistance of 36 Ω / cm ² . A battery was prepared in the same manner as in Example 2 except that this electrode was used, and a charge / discharge test was performed.
The initial discharge capacity per weight of the positive electrode active material was 84 mAh / g, and the discharge capacity at the 10th cycle was 7 mAh / g.

[0031]

The electrode shown in the present invention is an electrode active material,
By densely filling the conductive agent and the ionic conductive polymer compound, low resistance and excellent ion transfer are obtained. By lowering the porosity, the transfer of ions at the electrode / electrolyte interface and within the electrode is not hindered without using a liquid ionic conductor, creating an excellent liquid-free electrochemical device. It is possible.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takaaki Sakai 1-10-8 Edobori, Nishi-ku, Osaka-shi, Osaka Daiso Corporation F-term (reference) 4J002 CH021 DD046 DD086 DE196 DF036 DG036 DH006 DK006 ET006 EV216 EV236 EV256 EV266 FD116 GQ02 HA05 5H014 AA01 BB08 EE01 HH02 HH04 HH08 5H029 AJ12 AK02 AK03 AK05 AK16 AL07 AL08 AL12 AM16 DJ09 EJ12 HJ09 HJ14 HJ20

Claims (4)

[Claims] 1. An electrode for an electrochemical device, wherein a porosity in an entire volume of an electrode filled with a solid ionic conductive substance comprising a polymer substance having an ether bond is 20% or less. 2. The electrode for an electrochemical device according to claim 1, wherein the polymer substance having an ether bond is a polymer substance having an ether bond in a main chain and a side chain. 3. The polymer material according to claim 2, wherein the polymer material has an ionic conductivity of 1 × 10 ⁻⁵ S / cm or more at 25 ° C. by adding an electrolyte salt compound. Electrodes for electrochemical devices. 4. A solid lithium secondary battery using the electrode according to claim 1 as a positive electrode and / or a negative electrode.