JP5670759B2 - Binder for electrode mixture and electrode sheet comprising aromatic polyamide - Google Patents

Description

  The present invention relates to an electrode sheet used in an electrochemical device such as a lithium ion secondary battery, an electric double layer capacitor, or a lithium ion capacitor, and a binder used at the time of electrode preparation.

  As symbolized by recent advances in electronic devices such as portable communication devices and high-speed information processing devices, there are remarkable things in reducing the size and weight of electronic devices and improving their performance. In particular, there are great expectations for high-performance batteries and capacitors that can withstand long-term use with a small size, light weight, high capacity, wide application, and rapid development of components. In order to meet this demand, there is an increasing need for technology and quality development for binders for binding electrode active materials in battery and capacitor electrode sheets.

General properties required for the binder include (1) binding property of the active material, (2) adhesion to the current collector, (3) electrochemical stability, and (4) stability to the electrolyte. be able to.
Conventionally, as a binder material, polyvinylidene fluoride (PVdF) is widely used as a solvent-based binder, and styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), and the like are widely used as an aqueous binder.

  Although these materials have good physical properties as binders, PVdF and PTFE binders have adhesive strength with current collectors in applications that require long-term reliability, such as in-vehicle lithium ion (LIB) batteries. Is not necessarily sufficient. On the other hand, the SBR binder does not have sufficient oxidation resistance and cannot be used as a positive electrode for LIB.

  As other binder materials, various polymers have been studied, and electrode sheets using aromatic polyamides have been proposed so far. For example, Patent Document 1 (WO 2007/12517) and Patent Document 2 (Japanese Patent Laid-Open No. 2008-159810) show a method for producing an electrode sheet using a slurry containing meta-aramid and a solvent. Specific examples of meta-aramid include polymetaphenylene isophthalamide and copolymers thereof, but attention has not been paid to improving the storage stability of the binder, that is, workability.

Moreover, since the aramid polymer has high heat resistance and can be dried at high temperature, the moisture content of the aramid polymer solution has not been considered.
In Patent Document 3 (WO2008 / 13247), Patent Document 4 (Japanese Patent Laid-Open No. 2007-158163), and Patent Document 5 (Japanese Patent Laid-Open No. 2010-93027), a mechanical shearing force is applied to randomly form “aramid fibrids”. The electrode sheet to which the active material (carbon-based material) is bound is shown by the entanglement of the material called ”, but these are not binders using organic solvents, but aramid fibrids dispersed in water. Is.

  Patent Document 6 (WO2009 / 51263) shows nanofibers and fiber structures made of aramid containing a third component, and the molecular chain structure when the content of the third component is 1 to 10 mol%. However, it is described that gelation does not occur because the crystallinity is disturbed and the crystallinity is lowered and it exists stably without adding an alkali metal salt. However, Patent Document 6 is a technique related to a fiber structure and a method for producing the same, and has not been studied in detail as a binder for an electrode mixture that particularly needs to be considered up to the influence on electrical characteristics. Appropriate copolymer composition, viscosity, and production method for binders have not been clarified.

Moreover, the stability of the solution required for this technique is the stability until it is subjected to the spinning process, and the longer-term solution stability as required for the binder for electrode mixture has not been considered.
In recent years, alloy-based negative electrodes such as Si-based and Su-based materials have attracted attention as LIB negative-electrode materials. However, these alloy-based negative electrodes have a large theoretical capacity compared to carbon-based negative electrodes that are generally used at present, and are expected as next-generation negative electrode materials, but the volume expansion during charging and discharging is very large. There is a problem that electrode destruction occurs when the charge and discharge cycle is repeated.

  Patent Document 7 (Japanese Patent Application Laid-Open No. 2009-152037) describes at least one element selected from the group consisting of a negative electrode active material that is an element that can be alloyed with lithium or a compound containing the element, and polyimide, polyamideimide, and polyamide. Lithium ion secondary batteries containing the above-mentioned binders are shown, but specific examples of aliphatic polyamides and semi-aromatic polyamides have been made, but details of the structure and the like of fully aromatic polyamides, that is, aramids, are shown. No description is given, and only specific examples relating to polyimide are disclosed.

International Publication No. 2007/12517 JP 2008-159810 A International Publication No. 2008/13247 Pamphlet JP 2007-158163 A JP 2010-93027 A International Publication No. 2009/512263 Pamphlet JP 2009-152037 A

  The present invention solves the above-mentioned problems of the prior art and has basic characteristics for battery use such as binding properties, adhesiveness, electrochemical stability, and resistance to electrolytes, and has excellent handling properties. It is providing the binder used at the time of electrode sheet preparation. In particular, it is intended to provide a binder that can produce an electrode having excellent characteristics when used in producing an alloy-based negative electrode.

  As a result of intensive studies to solve the above problems, the present inventors have used an aromatic polyamide copolymer having a specific structure, and devised a method for preparing the polymer solution, so that foreign matter, insoluble matter, and moisture It has been found that by using a small amount of binder, it is possible to produce an electrode that contributes to process stability at the time of producing an electrode and has excellent characteristics, and the present invention has been completed. In particular, when the binder of the present invention is used during the preparation of an alloy-based negative electrode, there is an optimal polymer structure that retains the flexibility required for the electrode sheet while having rigidity that suppresses expansion of the active material. The present inventors have found that an electrode having excellent cycle characteristics can be produced.

That is, according to the present invention, (1) a binder for an electrode mixture containing an aromatic polyamide and an amine solvent, wherein the gel fraction in the binder is 1% or less , and the aromatic polyamide is In the aromatic polyamide skeleton containing the repeating structural unit represented by the formula (1), an aromatic diamine component or an aromatic dicarboxylic acid halide component different from the main structural unit of the repeating structure is used as the third component of the aromatic polyamide. A binder for an electrode mixture, which is an aromatic polyamide copolymerized so as to be 1 to 6.5 mol% based on the total amount of repeating structural units ;
-(NH-Ar1-NH-CO-Ar1-CO)-(1)
Here, Ar1 represents a divalent aromatic group.
(2) An electrode sheet comprising an electrode mixture binder of (1), an electrode active material and a conductive agent, a lithium ion secondary battery using the electrode sheet of (3) (2), (4) (2) An electric double layer capacitor using the electrode sheet described above and a lithium ion capacitor using the electrode sheet described in (5) (2) are provided.

  Since the binder of the present invention comprises an aromatic polyamide polymer having a specific structure, it has excellent solution stability and excellent process stability in the electrode slurry preparation step and the electrode slurry application step. In particular, by reducing the gel fraction and moisture content in the solution, battery characteristics can be improved as compared with conventional aromatic polyamide binders. In addition, when the specific third component is copolymerized, since the copolymerization is performed in an optimum range for suppressing the expansion of the alloy-based negative electrode, the cycle characteristics of the alloy-based negative electrode can be improved.

Hereinafter, embodiments of the present invention will be described in detail.
In the present invention, the polymer used for the binder is excellent in heat resistance, flame retardancy, chemical resistance and insulation, and one or two or more divalent aromatic groups are directly linked by an amide bond. It is an aromatic polyamide containing a repeating unit represented by the following formula (1) as a main constituent unit.
-(NH-Ar1-NH-CO-Ar1-CO)-(1)

  Here, Ar1 is a divalent aromatic group. The aromatic group of formula (1) may be one in which two aromatic rings are bonded with oxygen, sulfur or an alkylene group. In addition, these divalent aromatic groups may include a lower alkyl group such as a methyl group or an ethyl group, a halogen group such as a methoxy group, or a chloro group. Furthermore, these amide bonds are not limited and may be either a para type or a meta type, but a meta type is preferred.

  The polymer used for the binder of the present invention is a copolymer of an aromatic diamine component or an aromatic dicarboxylic acid halide component different from the main structural unit of the repeating structure with respect to the total amount of the repeating structural unit of the aromatic polyamide as the third component. It is preferable to be an aromatic polyamide. The content of the third component is 1 to 10 mol%, and preferably 1 to 6.5 mol%.

The structure of the aromatic diamine component or aromatic dicarboxylic acid halide component as the third component is the following formula (2), (3), or formula (4), (5), respectively.
H ₂ N—Ar ₂ —NH 2 (2)
H ₂ N—Ar ₂ —Y—Ar ₂ —NH ₂ (3)
XOC-Ar3-COX (4)
XOC-Ar3-Y-Ar3-COX (5)
Here, Ar2: a divalent aromatic group different from Ar1, Ar3: a divalent aromatic group different from Ar1, Y: an oxygen atom, a sulfur atom, an alkylene group, etc., X: a halogen atom.

  When the content of the third component is 1 to 10 mol%, the molecular chain structure is disturbed, the crystallinity is lowered, and it is easy to exist stably without adding an alkali metal salt, so that gelation hardly occurs. That is, the binder of the present invention may not contain an alkali metal salt and / or an alkaline earth metal salt.

  Further, when the aromatic polyamide containing the repeating unit represented by the formula (1) as a main structural unit is a meta-type aramid, the aromatic diamine component of the formula (2) or (3), which is a copolymer component, or the formula ( 4) The aromatic dicarboxylic acid halide component of (5) preferably has a linking group at the para position. In general, by introducing a copolymer component having a linking group at the para position, the meta-aramid has a rigid structure. By using a rigid structure, especially when used in the production of electrodes with large expansion, such as an alloy-based negative electrode of a lithium ion secondary battery, it is possible to suppress the expansion of the electrode that causes a decrease in cycle characteristics, This leads to improved characteristics. However, if the amount of the copolymer component having a bonding group at the para-position is too large, the rigidity is excessively increased, and therefore, when dissolved in a solvent, the viscosity range that is easy to handle as an electrode mixture binder is exceeded. Moreover, since it becomes an electrode with a low flexibility at the time of electrode sheet preparation, when an electrode sheet is wound, a crack may arise. In addition, since the binding property of the active material and the adhesiveness with the current collector are reduced, there is a possibility that the device characteristics are deteriorated, particularly, the characteristics are deteriorated during long-term use. Therefore, when the copolymer component having a bonding group at the para position is introduced, the content is preferably 1 to 6.5 mol%.

In this case, the copolymer component having a bonding group at the para position is preferably diteroid terephthalate or paraphenylenediamine.
The polymer polymerization method is not particularly limited, but a solution polymerization method and an interfacial polymerization method described in JP-B-35-14399, US Pat. No. 3,360,595, JP-B-47-10863, and the like may be used.

  Specific examples of the aromatic diamines represented by the formulas (2) and (3) to be copolymerized as the third component include, for example, p-phenylenediamine, chlorophenylenediamine, methylphenylenediamine, acetylphenylenediamine, and aminoanisidine. Benzidine, bis (aminophenyl) ether, bis (aminophenyl) sulfone, diaminobenzanilide, diaminoazobenzene and the like. Specific examples of the aromatic dicarboxylic acid dichloride represented by the formulas (4) and (5) include, for example, terephthalic acid chloride, 1,4-naphthalenedicarboxylic acid chloride, 2,6-naphthalenedicarboxylic acid chloride, 4,4 Examples include '-biphenyldicarboxylic acid chloride, 5-chloroisophthalic acid chloride, 5-methoxyisophthalic acid chloride, bis (chlorocarbonylphenyl) ether, and the like.

  The intrinsic viscosity of the aromatic polyamide copolymer contained in the binder obtained by the present invention is preferably in the range of 0.5 to 4.0 dl / g, more preferably 1.0 to 2.0. . An intrinsic viscosity of less than 0.5 dl / g is not preferable because the viscosity when mixed with an electrode active material to form a slurry is too low. On the other hand, when the intrinsic viscosity is larger than 4.0 dl / g, the degree of polymerization is too high, so that the solvent solubility is deteriorated, and the viscosity in the case of a slurry is high and the coating property is deteriorated.

  Examples of amine solvents include N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and the like. N-methyl-2-pyrrolidone, N, N -Dimethylacetamide or a mixture thereof is preferred.

  The polymer solution is not particularly limited, and an amide solvent solution containing an aromatic polyamide copolymer obtained by the above solution polymerization or interfacial polymerization may be used. It is also possible to use a product obtained by isolating and dissolving it in an amide solvent.

  As described above, by selecting a specific aromatic polyamide copolymer, it becomes easy to exist stably without adding an alkali metal salt, so that gelation hardly occurs. However, when no alkali metal salt and / or alkaline earth metal salt is contained, gelation hardly occurs at first glance, but fine gel-like lumps are easily generated. This is particularly noticeable when N-methyl-2-pyrrolidone, which is used as a solvent in the electrode slurry process, is selected as the solvent.

  In order to affect device characteristics when used as a binder when a minute gel-like lump exists, the binder of the present invention is characterized in that the gel fraction in the solution is reduced to 1% or less. And

  The method for lowering the gel fraction in the binder is not particularly limited, but when the polymer once isolated is dissolved in a solvent, (a) the polymer is pulverized in advance to form a fine powder, which is insoluble. (B) When adding powder to solvent, use powder and amine solvent with low water content to reduce insoluble content, (c) Filter solution with mesh The method of removing an insoluble content etc. is mentioned by this.

  Further, by controlling the moisture content of the binder within a specific range, the solution stability can be further increased, and the process stability can be improved. The method for reducing the amount of water in the binder is not particularly limited, but when producing a binder using an amine solvent solution containing an aromatic polyamide copolymer, a dehydrating agent is added to the solution, or nitrogen gas is added. A method of reducing the moisture content by blowing in may be used. In addition, when producing a binder by isolating the polymer from a polymerization solution and dissolving it in an amine solvent, a method of using a polymer that has been sufficiently dried to reduce the moisture content, an amine solvent having a low moisture content is used. Methods and the like.

  When the amine solvent is used by the method as described above, the water content is preferably 2% or less, more preferably 1% or less, and further preferably 0.5% or less. When the water content of the amine solvent exceeds 2%, it is not preferable because it causes generation of a minute gel content.

  As described above, when using a binder in which the gel fraction or the moisture content of the solvent to be used is controlled within a specific range, the dispersion uniformity of the slurry is increased, and the uneven distribution of the electrode material in the electrode sheet is suppressed. A device having excellent characteristics can be manufactured.

  The solution viscosity of the binder of the present invention is preferably 2500 mPa · s or less, and more preferably 2100 mPa · s or less. When the solution viscosity exceeds 2500 mPa · s, the viscosity after slurry adjustment is also increased, and coating is difficult.

  In addition to the aromatic polyamide copolymer binder of the present invention, other binders may be used in combination. Other binders include aromatic polymers such as polyimide, polyamideimide, semi-aromatic polyamide, wholly aromatic polyamide; fluorine-containing polymers such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), fluororubber, Modified products thereof; polymers having rubbery elasticity such as styrene butadiene rubber (SBR), ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, butadiene rubber, polybutadiene, polyethylene oxide, and modified products thereof; polyamide, Thermoplastic polymers such as polyvinyl chloride, polyvinyl pyrrolidone, polyethylene, and polypropylene, and their modified products; acrylic polymers such as acrylic acid, methacrylic acid, acrylic ester, and methacrylic ester; And the like; starch, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, regenerated cellulose, diacetylcellulose and other polysaccharides and their modified products; and one or more of these can be used. .

The electrode active material used in the present invention is not particularly limited as long as it functions as a battery or capacitor electrode.
Specifically, in the case of a lithium ion secondary battery, as a positive electrode, for example, lithium metal oxide such as lithium cobaltate, lithium chromate, lithium vanadate, lithium chromate, lithium nickelate, lithium manganate And, as the negative electrode, for example, natural graphite, artificial graphite, resin charcoal, carbide of natural products, carbonaceous materials such as petroleum coke, coal coke, pitch coke, mesocarbon microbeads,
Metal lithium, a compound containing an element that can be alloyed with Li, or the like can be used.

Si, Ge, and Sn are preferable as an element that can be alloyed with Li, and the compound may have two or more of these elements. Specifically, Si, Ge, or Sn (a simple substance of these elements); Ge or Sn-containing alloys (intermetallic compounds such as Cu6Sn5, Sb3Co, SbNiMn, Sn7Ni3, Mg2Sn); Si, Ge, or Sn oxides; These may be used, and these may be used alone or in combination of two or more. In addition, when using the oxide of Si, Ge, or Sn, the surface may be coat | covered with carbon.

  In the case of capacitors, the activated carbon, foamed carbon, carbon nanotube, polyacene, nanogate carbon, etc. used for the electrical double layer capacitor that stores electricity by utilizing the electrical double layer discovered by Helmholtz in 1879 Examples thereof include carbon-based materials; metal oxides that can also utilize pseudocapacitance accompanied by a redox reaction; conductive polymers; organic radicals and the like.

  The conductive agent used in the present invention is not particularly limited as long as it has a function of improving the electrical conductivity of the electrode sheet. For example, carbon black such as acetylene black and ketjen black, artificial graphite, and easy graphite At least one material selected from the group consisting of carbonized carbon and non-graphitizable carbon, a fibrous or coiled carbon material, and a fibrous or coiled metal can be suitably used.

  Moreover, the binder of the present invention can be mixed with the above active material, conductive auxiliary, and, if necessary, a solvent to prepare a slurry. The solvent at that time is not particularly limited, and examples thereof include amine solvents and water. The amine solvent contained in the binder of the present invention is preferred.

  In the present invention, the amount of binder used during slurry preparation is not particularly limited, but the binder is based on the total amount of solids contained in the binder and the powder electrode material (active material, conductive additive). It is preferable that the solid content is usually in the range of 1 to 20 wt%, particularly in the range of 2 to 15 wt%. When the usage-amount of a binder increases too much exceeding the said range, generally a binder will cover a powder electrode material and the function of a device will fall.

The prepared slurry is applied to one or both sides of a current collector using a slurry coating device such as a doctor knife, and passed through a continuous drying furnace or dried in a stationary drying furnace, for example, to thereby form an electrode sheet Can be produced.
The current collector used here is not particularly limited as long as it is made of a conductive material and is stable with respect to the electrode, the solvent and the electrolytic solution. Specifically, for example, an aluminum thin plate, a platinum thin plate, and the like. A thin metal plate such as a copper thin plate can be used.

At this time, the shape of the aromatic polyamide copolymer is preferably changed to constitute the electrode sheet by drying at a temperature equal to or higher than the glass transition temperature of the aromatic polyamide copolymer contained in the binder of the present invention. That is, when the aromatic polyamide copolymer contracts by heating at a temperature equal to or higher than the glass transition temperature, the contact area between the electrode materials increases while the electrode active materials are firmly bound to each other. Therefore, high conductivity of the electrode sheet is achieved, and the resistance value decreases. Furthermore, since the aromatic polyamide copolymer heated at a temperature equal to or higher than the glass transition temperature has a high adhesive force, the adhesion with the current collector is also improved, and a long-term reliable electrode can do.
The electrode sheet can be further improved in sheet density and mechanical strength by, for example, pressing at a high pressure between a pair of flat plates or between metal rolls.

Hereinafter, the present invention will be described in more detail with reference to examples. The evaluation methods used in the examples are as follows.

(1) Intrinsic viscosity (IV)
Dissolve the polymer in NMP at 100 mg / 20 mL and use an Ostwald viscometer 30
Measured at ° C.

(2) Moisture content evaluation The solution immediately after melt | dissolving a polymer in the solvent was sampled, and it measured with the Karl Fischer method using the microinstrument measuring device (CA-21 type | mold) by Dia Instruments Co., Ltd.

(3) Evaluation of gel fraction After preparing the binder, it was filtered through a 100 mesh SUS wire mesh (aperture 0.15 mm), the filtered wire mesh was dried at 280 ° C. × 2 hr, and the weight was measured. The weight of insoluble matter was calculated.
Gel fraction (% by weight) = solid content remaining on the mesh / total solid content in the binder

(4) Solution stability After leaving the binder to stand at 25 ° C. and 60% RH for 7 days, it was ◯ when it was completely transparent without white turbidity by visual observation, and △ when it was slightly cloudy. The one with white turbidity was marked with x.
(Production of electrode sheet and cell)
Cell 1 production:
A paste slurry was prepared by adding LiNi _1/3 Mn _1/3 Co _1/3 O 2 (average particle size 6 μm) as a positive electrode active material, graphite as a conductive agent, and PVdF / NMP solution binder as a binder and mixing. At this time, in the solid content excluding the solvent, the ratio of the positive electrode active material was 89 wt%, the ratio of the conductive agent was 6 wt%, and the polymer solid content in the binder was 5 wt%.
This slurry was applied to an aluminum foil (thickness: 15 μm) serving as a positive electrode current collector, dried, and then compression molded with a roller press to form a positive electrode. The electrode density was 3.0 g / cm ³ .
Further, graphite (average particle size 20 μm) was used as the negative electrode active material, and the binders described in the examples and comparative examples were used as binders to prepare a paste slurry. At this time, the proportion of the negative electrode active material in the solid content excluding the solvent was 90% by weight, and the polymer solid content in the binder was 10% by weight.
This slurry was applied to an electrolytic copper foil (thickness: 10 μm) serving as a negative electrode current collector, and after drying, compression molding was performed with a roller press to form a negative electrode. The electrode density was 1.6 g / cm ³ .
Next, the positive electrode and the negative electrode formed as described above are punched into a predetermined size (about 30 mm × about 60 mm), laminated via a separator (polypropylene microporous membrane, manufactured by Celgard), the tab is adhered, and the exterior is attached. To give a laminate. This laminate was dried under reduced pressure at 80 ° C. for 8 hours. An electrolyte solution in which LiPF ₆ was added at a concentration of 1 mol / L to a mixed solvent of 30% by weight of propylene carbonate and 70% by weight of ethyl methyl carbonate was injected into this laminate. Thereafter, the liquid inlet of the exterior material was sealed to produce a single-layer laminate cell. The work after electrode drying was performed in a dry box having a dew point of −50 ° C. or lower.
Cell 2 production:
Similarly to the cell 1, a positive electrode was formed.
Mixing using SiO-carbon-coated particles (SiO: carbon = 85: 15 (mass ratio)) and graphite as an anode active material and graphite, ketjen black as a conductive additive, and the binder described in the examples as a binder. Thus, a paste-like slurry was produced. At this time, in the solid content excluding the solvent, the ratio of the alloy-based negative electrode active material is 60% by weight, the ratio of graphite is 30% by weight, the ratio of the conductive auxiliary agent is 2% by weight, and the solid content of the polymer in the binder is 8%. It was made to become the ratio of weight%.
This slurry was applied to an electrolytic copper foil (thickness: 10 μm) serving as a negative electrode current collector, and after drying, compression molding was performed with a roller press to form a negative electrode.
Subsequently, using these positive electrode and negative electrode, a single-layer laminate cell was produced in the same manner as in the cell 1.

(5) Electrode sheet evaluation About the electrode sheet produced for the negative electrode of the cell 1, the tape peeling test and the electrode bending test were done. In the tape peeling test, when the tape was applied to the surface of the electrode sheet and peeled off, the active material layer was hardly attached to the tape, and the foil was not visible. The case was Δ, and the case where the active material layer adhered to the entire tape was marked X. In the electrode bending test, the electrode sheet was bent at 180 ° C., and the case where powder did not fall off was indicated as “◯”, the case where part of the powder was dropped was indicated as “Δ”, and the case where powder was completely removed was indicated as “X”.

(6) Battery characteristic evaluation About the single-layer laminated cell produced as mentioned above, it charged on 20 degreeC on the conditions of the charging voltage 4.2V and the charging time 1.5 hours, and discharged after that. This cycle was repeated to determine the 200th charge capacity retention rate with respect to the initial charge capacity.
In the case of the cell 1, the case where the capacity retention rate was 85% or more was evaluated as “◯”, the case where it was less than 85% and 80% or more as Δ, and the case where it was less than 80% as “X”.
In the case of the cell 2, the case where the capacity retention rate was 70% or more was evaluated as ◯, and the case where it was less than 70% was evaluated as ×.

[Example 1]
The aromatic polyamide copolymer of the present invention was produced as follows by an interfacial polymerization method according to the method described in Japanese Patent Publication No. 47-10863.
25.13 g (99 mol%) of isophthalic acid dichloride and 0.25 g (1 mol%) of terephthalic acid dichloride (TPC) were dissolved in 125 ml of tetrahydrofuran having a water content of 2 mg / 100 ml and cooled to −25 ° C. While stirring this, 13.52 g (100 mol%) of metaphenylenediamine was added over about 15 minutes as a trickle of a solution obtained by dissolving 125 ml of the above tetrahydrofuran to prepare a white emulsion (A). Separately, 13.25 g of anhydrous sodium carbonate was dissolved in 250 ml of water at room temperature, and this was cooled to 5 ° C. with stirring to precipitate sodium carbonate hydrate crystals to prepare a dispersion (B). The emulsion (A) and dispersion (B) were mixed vigorously. After further mixing for 2 minutes, 200 ml of water was added for dilution, and the resulting polymer was precipitated as a white powder. Filtration, washing with water and drying were carried out from the polymerization completed system to obtain the desired polymer. The intrinsic viscosity (IV) measured for the obtained polymer was 3.3. Here, the TPC corresponds to the third component.
The obtained polymer was dissolved in NMP so that it might become 10 wt%. The moisture content in the NMP used at this time was 90 ppm. The polymer solution immediately after dissolution was sampled to evaluate the moisture content.
This NMP solution was filtered with a mesh filter made of SUS to obtain a binder. This binder was subjected to gel fraction evaluation and solution stability evaluation.

[Comparative Example 1]
A binder was prepared in the same manner as in Example 1 except that the NMP solution after dissolution was not filtered with a filter.

[ Comparative Example 2 ]
A binder was prepared in the same manner as in Example 1 except that NMP having a moisture content of 1250 ppm was used.

[Examples 2 to 4, Comparative Examples 3 to 5 ]
According to the same production method as in Example 1, the same operation as in Example 1 was performed except that the addition ratio of the third component was changed as shown in Table 1.

[Examples 5 to 6 ]
The same operation as in Example 1 was performed except that a polymer produced so that paraphenylenediamine (PPD) had the addition ratio shown in Table 1 was used as the third component.

[Examples 7 to 9 ]
A binder was produced in the same manner as in Example 1 except that the polymer produced in Example 3 was dissolved in NMP so as to be 8 wt%, 13 wt%, and 14 wt%, respectively.

[Example 10 ]
A binder was prepared in the same manner as in Example 1 except that the polymer produced in Example 2 was dissolved in DMAc.

[ Comparative Example 6 ]
A binder was prepared by performing the same operation as in Example 1 except that a polymer to which the third component was not added was used.

[Comparative Example 7 ]
Except for using a polymer to which the third component was not added, the same operation as in Comparative Example 1 was performed to prepare a binder.

[ Comparative Example 8 ]
A binder was prepared by adding 5 wt% of CaCl ₂ to the binder of Comparative Example 6 .

[Reference example]
When the cells 1 and 2 were prepared, an electrode sheet evaluation and a battery characteristic evaluation were performed using a PVdF / NMP solution binder (polymer concentration 12 wt%) as a negative electrode binder.
Table 1 shows the results of viscosity measurement, moisture content evaluation, gel fraction evaluation, solution stability evaluation, binding property evaluation, and battery characteristics (cycle characteristics) evaluation for each binder.

From Table 1, it can be seen that the binders of the examples, in particular, polymers having a specific content of the third component and having a gel fraction and a water content of a specific content or less have high solution stability. This contributes to process stability at the time of electrode manufacture. Further, when the electrode sheet is produced, an electrode having high active material binding properties and excellent flexibility can be produced.
Moreover, the cell using the electrode produced using the binder of an Example is excellent in a battery characteristic. It turns out that it is excellent also in the cycling characteristics at the time of especially alloy type negative electrode use.

  According to the present invention, since the process stability at the time of electrode production is improved and an electrode having excellent battery characteristics can be produced, an electrochemical device that requires large capacity, high output, or low profile is required. It is extremely useful for this. In particular, when the binder of the present invention is used when preparing an alloy-based negative electrode, an electrode having excellent cycle characteristics can be prepared.

Claims (20)

A binder for an electrode mixture containing an aromatic polyamide and an amine solvent, wherein the gel fraction in the binder is 1% or less , and the aromatic polyamide is a repeating structural unit represented by the following formula (1) In the aromatic polyamide skeleton containing, an aromatic diamine component or an aromatic dicarboxylic acid halide component different from the main structural unit of the repeating structure is used as the third component in an amount of 1 to 6 based on the total amount of the repeating structural unit of the aromatic polyamide. A binder for electrode mixture, which is an aromatic polyamide copolymerized so as to be 5 mol% .
-(NH-Ar1-NH-CO-Ar1-CO)-(1)
Here, Ar1 represents a divalent aromatic group. Alkali metal salts and / or claim 1, wherein the electrode mixture for a binder that does not contain alkaline earth metal salts. The binder for electrode mixture according to claim 1 or 2 , wherein the moisture content is 2% or less. The binder for an electrode mixture according to any one of claims 1, 2, and 3 , wherein the solution viscosity is 2500 mPa · s or less. The binder for electrode mixtures of any one of Claims 1-4 which does not contain an alkali metal salt and / or an alkaline-earth metal salt. The binder for an electrode mixture according to any one of claims 1 to 5 , wherein the moisture content is 2% or less. The binder for electrode mixture of any one of Claims 1-6 whose solution viscosity is 2500 mPa * s or less. Aromatic diamine as a third component constituting the aromatic polyamide has the formula (2), (3), or an aromatic dicarboxylic acid halide to be the third component is of the formula (4), according to claim 1 which is (5) The binder for electrode mixtures of any one of -7.
_{H 2 N-Ar2-NH 2} ··· (2)
H ₂ N—Ar ₂ —Y—Ar ₂ —NH ₂ (3)
XOC-Ar3-COX (4)
XOC-Ar3-Y-Ar3-COX (5)
Here, Ar2: a divalent aromatic group different from Ar1, Ar3: a divalent aromatic group different from Ar1, Y: an oxygen atom, a sulfur atom, an alkylene group, etc., X: a halogen atom. The binder for an electrode mixture according to any one of claims 1 to 8 , wherein the repeating structural unit of the aromatic polyamide is metaphenylene isophthalamide. The binder for an electrode mixture according to any one of claims 1 to 9 , wherein the third component constituting the aromatic polyamide is terephthalic acid dichloride or paraphenylenediamine. The binder for an electrode mixture according to any one of claims 1 to 10 , wherein the solvent is N-methyl-2-pyrrolidone, N, N-dimethylacetamide, or a mixture thereof. An electrode sheet comprising the binder for an electrode mixture according to any one of claims 1 to 11 , an electrode active material, and a conductive agent. Wherein electrode mixture for a binder according to any one of claims 1 to 11, is mixed with the electrode active material to prepare a slurry, coating the slurry on the current collector, can be obtained by drying An electrode sheet. The electrode sheet according to claim 13 , wherein the drying is performed at a temperature equal to or higher than the glass transition temperature of the aromatic polyamide. The electrode sheet according to claim 12, 13 or 14 , wherein the electrode active material is a negative electrode active material which is an element capable of being alloyed with Li or a compound having the element. The electrode sheet according to claim 15 , wherein the negative electrode active material is a compound containing Si, Ge, or Sn as a constituent element. The lithium ion secondary battery using the electrode sheet of any one of Claims 12-16 . The electric double layer capacitor using the electrode sheet of any one of Claims 12-16 . The lithium ion capacitor using the electrode sheet of any one of Claims 12-16 .   The method for producing a binder for an electrode mixture according to claim 1, wherein a solution containing an aromatic polyamide and an amine solvent is filtered through a mesh.