JP2005310747A - Binder for forming nonaqueous electrochemical element electrode, electrode mix, electrode structure, and electrochemical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a binder for forming a nonaqueous electrochemical element electrode giving an electrode having stability to a nonaqueous electrolyte and good adhesiveness to a collector base body and giving electrode mix slurry having good application processing suitabilty for forming the electrode. <P>SOLUTION: A vinylidene fluoride homopolymer A having an inherent viscosity of 0.5-1.5 dl/g and a vinylidene fluoride polymer B having an inherent viscosity 1.4 or more times higher than that of the polymer A are mixed so that a ratio of the polymer A to the total quantity of the polymers A and B becomes 60-98 wt.%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a vinylidene fluoride polymer binder for forming a non-aqueous battery electrode suitable for forming an electrode that is stable with respect to a non-aqueous electrolyte and has good adhesion to a current collecting substrate, and the binder. The present invention relates to an electrode mixture, an electrode structure, and a non-aqueous electrochemical element formed using the same.

  Vinylidene fluoride polymers are used as binders for electrode active materials in non-aqueous electrochemical devices such as non-aqueous batteries and electric double layer capacitors, but conventional vinylidene fluoride polymers are bound to active materials. Due to the relatively weak adhesion and adhesion to the current collector, phenomena such as falling off of the active material and peeling of the mixture layer from the current collector were observed during use. For this reason, the decrease in the discharge capacity may become large during long-term use of the battery, which is a practical problem.

  In order to solve this problem, it has an adhesive functional group such as a silane-modified vinylidene fluoride polymer (Patent Document 1) and a vinylidene fluoride polymer containing a carboxyl group or a carbonate group (Patent Document 2). Vinylidene fluoride polymers have been proposed, but none of them is yet satisfactory in terms of material stability and productivity, and on the other hand, the initial swelling degree with respect to the electrolytic solution is increased as compared with conventional vinylidene fluoride polymers. The fault was also recognized.

In contrast, the molecular weight (weight average molecular weight is about 400,000 or less or inherent viscosity is 1.5 dl / g or less) of a conventional vinylidene fluoride polymer (weight average molecular weight is 600,000 or more, or inherent). By using ultra-high molecular weight vinylidene fluoride polymer (viscosity exceeding 2.0 dl / g), it is possible to improve the holding power of the powder electrode material while maintaining good swelling resistance against non-aqueous electrolyte Has also been proposed (Patent Document 3). However, such an ultra-high molecular weight vinylidene fluoride polymer has a remarkably high viscosity of an electrode mixture obtained by dispersing a binder solution formed by dissolving in an organic solvent and a powder electrode material such as an electrode active material. If it is not in a heated state, there is a problem in processing characteristics that it may be impossible to apply and form electrodes.
JP-A-6-93025 Japanese Patent Laid-Open No. 6-172452 Japanese Patent Laid-Open No. 9-289023 Japanese Patent Laid-Open No. 9-320607

  Therefore, the main object of the present invention is to provide a non-aqueous electrochemical device electrode that is stable with respect to the non-aqueous electrolyte, has good adhesion to the current collecting substrate, and further satisfies the processing characteristics at the time of electrode formation. It is an object to provide a vinylidene fluoride polymer binder suitable for the formation of.

  Another object of the present invention is to provide an electrode mixture, an electrode structure, and a non-aqueous electrochemical device having good characteristics using the binder.

  The binder for forming a non-aqueous electrochemical element electrode of the present invention has been developed to achieve the above-mentioned object, and a vinylidene fluoride homopolymer having an inherent viscosity of 0.5 to 1.5 dl / g ( A) and a vinylidene fluoride polymer (B) having an inherent viscosity of 1.4 times or more that of the polymer (A), the polymer (A) with respect to the total amount of the polymers (A) and (B) ) Is in the range of 60 to 98% by weight.

  The binder for forming a non-aqueous electrochemical device electrode of the present invention is mainly composed of a medium to high molecular weight vinylidene fluoride homopolymer (A) represented by an inherent viscosity of 0.5 to 1.5 dl / g. It is composed of a relatively small amount of ultra-high molecular weight vinylidene fluoride polymer (B) as a component, and has both stability to a non-aqueous electrolyte, good adhesion to a current collecting substrate, and good workability during electrode formation. It is a feature. The reason why the binder for forming a non-aqueous electrochemical element electrode of the present invention shows excellent harmony of properties due to the combination of the two polymers (A) and (B) is not necessarily clear, but is estimated as follows. Yes.

  That is, since the electrode binder of the present invention has a medium to high molecular weight vinylidene fluoride homopolymer (A) as a main component, as in the case where the ultra high molecular weight vinylidene fluoride polymer (B) is a main component, The binder solution obtained by dissolving in an organic solvent and the electrode mixture obtained by further dispersing the powder electrode material do not significantly increase the viscosity, and the electrode processing characteristics by coating are maintained well. And it is thought that the favorable stability with respect to a non-aqueous electrolyte exists in the favorable crystallinity of the vinylidene fluoride homopolymer (A) which mainly occupies a main component. The electrode binder of the present invention is not only a case where the ultrahigh molecular weight vinylidene fluoride polymer (B) is a copolymer having a functional group (Examples 4 to 8 described later), but also a vinylidene fluoride homopolymer. In some cases (Examples 1 to 3 below), good adhesion to the current collecting substrate is exhibited. This is greater than the increase in adhesion seen when increasing the inherent viscosity using only the vinylidene fluoride homopolymer (ie, the mixed binder of the present invention is based on the inherent viscosity of the homopolymer). Rather than estimated, it shows a greater adhesion to the current collector substrate at the same inherent viscosity, in other words, an improvement in adhesion is obtained without causing a significant increase in binder solution viscosity. In the development of the invention of the above-mentioned Patent Document 3, an increase in adhesive force was observed with an increase in inherent viscosity. This was mainly obtained as an improvement in the holding power of the powder electrode material with an increase in molecular weight. Thus, the improvement in adhesion to the current collector substrate was not so much. On the other hand, the mixed binder of the present invention exhibits a relatively large adhesive force to the current collecting substrate as compared with its inherent viscosity between the crystalline parts formed by the main component vinylidene fluoride homopolymer. This is presumably because the ultrahigh molecular weight vinylidene fluoride polymer (B) is unevenly distributed in the amorphous part. Thus, the high crystallinity of the medium to high molecular weight vinylidene fluoride homopolymer (A) contributes to the functional manifestation of the electrode binder of the present invention, and is obtained by suspension polymerization in an aqueous medium. Are preferably used.

  In addition, the inventors have already prepared a binder composition comprising a combination of a high to ultrahigh molecular weight vinylidene fluoride polymer having an inherent viscosity of 1.2 dl / g or more and a vinylidene fluoride polymer having an adhesive functional group. Although it has already been proposed (Patent Document 4), since it is not composed mainly of a crystalline, medium to high molecular weight vinylidene fluoride polymer, the viscosity of the electrode mixture slurry is increased, and the coating processability is always satisfactory. It wasn't possible.

  The main component of the binder for forming a non-aqueous electrochemical device electrode of the present invention is a vinylidene fluoride homopolymer (A), and its inherent viscosity (in this document, 4 g of resin is added to 1 liter of N, N- Logarithmic viscosity at 30 ° C. of a solution dissolved in dimethylformamide) is 0.5 to 1.5 dl / g, preferably 0.8 to 1.3 dl / g, particularly preferably 1.0 to 1.3 dl / g. Use what is. If it is less than 0.5 dl / g, since the viscosity of the electrode mixture slurry is low, the coating processability is inferior and it is difficult to maintain the adhesiveness. Moreover, when it exceeds 1.5 dl / g, the viscosity of an electrode mixture slurry will become high too much and productivity will be inferior. As described above, those formed by suspension polymerization in an aqueous medium and having high crystallinity are preferred.

  The vinylidene fluoride polymer (B) that forms the binder for forming a non-aqueous electrochemical device electrode of the present invention together with the above-mentioned vinylidene fluoride homopolymer (A) is a vinylidene fluoride homopolymer or copolymer as described above. Any of polymers may be used. The vinylidene fluoride copolymer includes vinylidene fluoride and other monomers copolymerizable therewith, such as hydrocarbon monomers such as ethylene and propylene, or vinyl fluoride / trifluoroethylene, trifluoro Copolymers with fluorinated monomers other than vinylidene fluoride such as chloroethylene, tetrafluoroethylene, hexafluoropropylene, fluoroalkyl vinyl ether, etc. are included, but in the case of copolymers, vinylidene fluoride units are 90 mol% As mentioned above, it is preferable to maintain in the range of 95 mol% or more.

  The vinylidene fluoride polymer (B) includes 0.1 to 3 parts by weight of a carboxyl group, an epoxy group, and a hydroxyl group with respect to 100 parts by weight of the monomer constituting the vinylidene fluoride homopolymer or copolymer. A vinylidene fluoride polymer modified by copolymerizing a monomer having at least one adhesive functional group selected from a carbonyl group and a copolymerizable with vinylidene fluoride, and introducing these adhesive functional groups It is also preferable to use (B). Examples of the monomer having a carboxyl group include unsaturated monobasic acids such as acrylic acid and crotonic acid, unsaturated dibasic acids such as maleic acid and citraconic acid, and monoalkyl esters thereof. Examples of the monomer having an epoxy group include allyl glycidyl ether, methallyl glycidyl ether, crotonic acid glycidyl ester, and allylic acetic acid glycidyl ester. Examples of the monomer having a hydroxyl group include hydroxyethyl acrylate and hydroxypropyl acrylate; and examples of the monomer having a carbonyl group include ethylene carbonate. Since these monomers having an adhesive functional group are a small amount of 0.1 to 3 parts by weight with respect to 100 parts by weight of the vinylidene fluoride polymer forming monomer having no adhesive functional group, vinylidene fluoride polymer formation It can be formed by suspension polymerization in an aqueous medium with monomers.

  According to the present invention, the vinylidene fluoride polymer (B) preferably having an adhesive functional group described above is 1.4 times or more, preferably 1.6 times the inherent viscosity of the vinylidene fluoride homopolymer (A). Those having an inherent viscosity of twice or more, more preferably 2.0 times or more are used. If this ratio is less than 1.4 times, the effect of using the ultrahigh molecular weight vinylidene fluoride polymer (B) in addition to the vinylidene fluoride homopolymer (A) becomes poor. When this ratio exceeds 20, dissolution in a solvent becomes difficult, preferably 15 or less, more preferably 10 or less.

  The vinylidene fluoride polymer (B) is used in an amount range of 2 to 40% by weight, preferably 5 to 30% by weight, based on the total amount with the vinylidene fluoride homopolymer (A). If it is less than 2% by weight, the combined effect of the ultra-high molecular weight vinylidene fluoride polymer (B) is poor, and if it exceeds 40% by weight, the crystalline medium to high molecular weight vinylidene fluoride homopolymer (A) is mainly used. The effect of the electrode binder of the present invention as a component cannot be obtained.

  The vinylidene fluoride polymers (A) and (B) described above can be produced by methods such as suspension polymerization, emulsion polymerization, solution polymerization, etc., but from the viewpoint of ease of post-treatment, etc. Aqueous suspension polymerization and emulsion polymerization are preferable, and as described above, aqueous suspension polymerization is particularly preferable. This is especially true for the production of the crystalline vinylidene fluoride homopolymer (A).

  In suspension polymerization using water as a dispersion medium, a suspending agent such as methyl cellulose, methoxylated methyl cellulose, propoxylated methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, polyvinyl alcohol, polyethylene oxide, and gelatin is added to 0.005 with respect to water. It is used by adding in the range of -1.0% by weight, preferably 0.01-0.4% by weight.

  As polymerization initiators, diisopropyl peroxydicarbonate, dinormalpropyl peroxydicarbonate, dinormalheptafluoropropyl peroxydicarbonate, isobutyryl peroxide, di (chlorofluoroacyl) peroxide, di (perfluoroacyl) Peroxide and the like can be used. The amount used is 0.1 to 5% by weight, preferably 0.5 to 2% by weight, based on the total amount of monomers.

  Chain transfer agents such as ethyl acetate, methyl acetate, acetone, ethanol, n-propanol, acetaldehyde, propyl aldehyde, ethyl propionate, and carbon tetrachloride can be added to adjust the degree of polymerization of the resulting polymer. is there. The amount used is usually 0.1 to 5% by weight, preferably 0.5 to 3% by weight, based on the total amount of monomers.

  The total charge of the monomers is 1: 1 to 1:10, preferably 1: 2 to 1: 5, in a weight ratio of the total amount of monomer to water, and the polymerization is performed at a temperature of 10 to 50 ° C. Perform for ~ 100 hours.

  In the binder of the present invention, the ratio of the polymer (A) to the total amount of the vinylidene fluoride polymer (A) and the vinylidene fluoride polymer (B) is preferably 60 to 98% by weight, preferably It is obtained by mixing so that it may become 70 to 95 weight%. If it is less than 60% by weight, it is difficult to obtain the above-described effect of the present invention that makes use of its crystallinity as a main component. When it is used in excess of 98% by weight, it is difficult to obtain an effect of improving the adhesive force by the combined use of the ultrahigh molecular weight vinylidene fluoride polymer (B).

  The binder of the present invention is a powder mixture of the vinylidene fluoride polymer (A) and the vinylidene fluoride polymer (B), mixed with a powder electrode material described later, and collected by melt molding or powder molding. It is also possible to use the electrode mixture layer on the electric substrate. However, more preferably, by utilizing the low viscosity suitability and film-forming properties when dissolved in the organic solvent, the binder solution is formed by dissolving in the organic solvent, and the electrode mixture slurry is further dispersed by dispersing the powder electrode material. It is preferable that the binder effect is generated with a smaller amount of use with respect to the powder electrode material by preventing the increase of the internal resistance of the electrode mixture layer. When dissolving the vinylidene fluoride polymer in the organic solvent, after adding the ultra-high molecular weight vinylidene fluoride polymer (B) first, and confirming that it was substantially dissolved (that is, substantially dissolved), It is desirable to add and dissolve the medium to high molecular weight vinylidene fluoride polymer (A). By selecting such an order, a solution in which the polymer (A) and the polymer (B) are intertwined more uniformly can be obtained. As a result, when used as an electrode binder, the adhesive force to the current collecting substrate is improved. By adopting the above order, this is because the polymer (A) and the polymer (B) in the binder composition simply start to crystallize earlier than if they existed without affecting each other separately. This is probably because the uneven distribution structure in which the polymer (A) is conveniently arranged around the combined body (B) is possible.

  The organic solvent used for dissolving the vinylidene fluoride polymers (A) and (B) to obtain the binder solution of the present invention is preferably polar, for example, N-methyl-2-pyrrolidone. , N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoamide, dioxane, tetrahydrofuran, tetramethylurea, triethylphosphate, trimethylphosphate, and the like. Among the above polar organic solvents, nitrogen-containing organic solvents such as N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide and the like having a high dissolving power are more preferably used. These organic solvents can be used not only alone but also as a mixed solvent in which two or more kinds are mixed.

  In obtaining the binder solution of the present invention, the total amount of the vinylidene fluoride polymers (A) and (B) per 100 parts by weight of these organic solvents is 0.1 to 20 parts by weight, more preferably 0. It is preferable to dissolve at a ratio of 5 to 15 parts by weight, particularly 1 to 10 parts by weight. If it is less than 0.1 part by weight, the proportion of the polymer in the solution is too small, and the effect as a binder for binding the powder electrode materials to each other cannot be obtained. On the other hand, when the amount exceeds 20 parts by weight, since the ultrahigh molecular weight vinylidene fluoride polymer (B) is contained, the viscosity of the solution itself becomes excessively high and adjustment of the electrode mixture may be difficult.

  The electrode mixture of the present invention can be applied to any of a positive electrode mixture, a negative electrode mixture of a non-aqueous battery, and an electrode mixture for forming a polarizable electrode of an electric double layer capacitor.

  To the vinylidene fluoride polymer binder solution of the present invention obtained as described above, a powder electrode material (a nonaqueous battery electrode active material or a powder carbon material for forming a polarizable electrode of an electric double layer capacitor, and if necessary) Electrode mixture slurry can be obtained by dispersing and mixing conductive auxiliary agents and other auxiliary agents added accordingly.

As an active material for a lithium ion secondary battery, in the case of a positive electrode, the general formula LiMY ₂ (M is at least one of transition metals such as Co, Ni, Fe, Mn, Cr, V, etc .: Y is O, S, etc. Composite metal chalcogen compounds represented by the above-mentioned chalcogen elements, in particular, composite metal oxides including LiNi _x Co _1-x O ₂ (0 ≦ x ≦ 1) and spinel structures such as LiMn ₂ O ₄ Things are preferred. In the case of the negative electrode, in addition to powdered carbonaceous materials such as graphite, activated carbon, or a baked carbonized material such as phenol resin or pitch, metal oxide-based GeO, GeO ₂ , SnO, SnO ₂ , PbO, PbO ₂ Or composite metal oxides thereof (for example, those disclosed in JP-A-7-249409) are used.

As a powder carbon material for forming an electrode mixture for forming a polarizable electrode of an electric double layer capacitor, a specific surface area of 500 to 3000 m ² / g can be suitably used. As a specific example, Examples include coconut-based activated carbon, phenol-based activated carbon, petroleum coke-based / pitch-based activated carbon, polyvinylidene chloride-based activated carbon, and polyacene.

A conductive auxiliary agent is added as necessary for the purpose of improving the conductivity of the electrode mixture layer when an active material having a low electron conductivity such as LiCoO ₂ is used in the battery or in an electric double layer capacitor. Thus, carbonaceous material such as carbon black, graphite fine powder or fiber, metal fine powder such as nickel or aluminum, or fiber is used.

  The electrode mixture of the present invention comprises 100 parts by weight of a powder electrode material and 0.1 to 50 parts by weight, particularly 1 to 20 parts by weight of vinylidene fluoride polymer (A) and ( It is preferably formed by mixing with a binder solution containing B).

  The electrode mixture slurry formed as described above, for example, as shown in a cross-sectional view in FIG. 1, consists of a metal foil or a metal net of iron, stainless steel, steel, copper, aluminum, nickel, titanium, etc. The thickness is 5 to 100 μm, and in the case of a small scale, for example, it is applied to at least one side, preferably both sides, of the current collector 11 such as 5 to 20 μm, and dried at 50 to 170 ° C. In this case, the non-aqueous battery electrode 10 is formed by forming the electrode mixture layers 12a and 12b having a thickness of 10 to 1000 μm.

  FIG. 2 is a partially exploded perspective view of a lithium secondary battery as an example of the non-aqueous electrochemical element of the present invention including the electrode formed as described above.

  In other words, this secondary battery basically has a spiral structure in which a separator 3 made of a microporous film of a polymer material such as polypropylene or polyethylene impregnated with an electrolyte is disposed between a positive electrode 1 and a negative electrode 2. The electric power generating element wound around is housed in a bottomed metal casing 5 forming the negative electrode terminal 5a. In this secondary battery, the negative electrode is further electrically connected to the negative electrode terminal, the gasket 6 and the safety valve 7 are arranged at the top, and then the top portion constituting the positive electrode terminal 8a electrically connected to the positive electrode 1 at the convex portion. The plate 8 is disposed, and the top rim 5b of the casing 5 is caulked to form a sealed structure. The positive electrode 1 and / or the negative electrode 2 show the structure of the electrode structure 10 shown, for example in FIG.

  As the nonaqueous electrolytic solution impregnated in the separator 3, for example, an electrolyte such as a lithium salt dissolved in a nonaqueous solvent (organic solvent) can be used.

Here, examples of the electrolyte include LiPF ₆ , LiAsF ₆ , LiClO ₄ , LiBF ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiCl, and LiBr. Moreover, as an organic solvent of the electrolyte, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, methyl propionate, ethyl propionate , And mixed solvents thereof are used, but are not necessarily limited thereto.

  In addition, although the example of the cylindrical battery was shown in the above, it is also possible to comprise the non-aqueous battery of the present invention as a coin type, a square type or a paper type battery.

An example of the electric double layer capacitor is the one shown in FIG. That is, FIG. 3 is a cross-sectional view of an example of a single cell electric double layer capacitor. In this electric double layer capacitor, a separator 23 is sandwiched between two polarizable electrodes 21 and 22, and these are further sandwiched between a stainless steel cap 24 and a stainless steel can 25 containing an electrolyte solution 26 through a packing 27. Is enclosed. As a result, the electrolyte solution 26 is impregnated in the separator 23 and disposed between the pair of polarizable electrodes 21 and 22. Propylene carbonate is generally used as the solvent for the electrolytic solution, and quaternary phosphonium salts and quaternary ammonium salts are generally used as the electrolyte. For example, a propylene carbonate solution of (C ₂ H ₅ ) ₄ NBF _{4 or} the like. The organic electrolyte solution can be used. The concentration of the electrolyte in the electrolytic solution can be appropriately selected within the range of 5 to 95% by weight.

  Hereinafter, the present invention will be described more specifically with reference tests, examples and comparative examples.

<Polymers (A) and (B)>
The following polymers (1) to (11) having different inherent viscosities (hereinafter abbreviated as “η _inh ”) were prepared as vinylidene fluoride homopolymer (A) or ultrahigh molecular weight vinylidene fluoride polymer (B). .

(Polymers (1) to (3) and (9))
As the polymers (1), (2), (3) and (9), “KF # 850” which is a homopolymer of vinylidene fluoride manufactured by Kureha Chemical Industry Co., Ltd. (η _inh = 0.85 dl / g) , “KF # 1100” (η _inh = 1.1 dl / g), “KF # 1300” (η _inh = 1.3 dl / g) and “KF # 1000” (η _inh = 1.0 dl / g), respectively used.

(Polymer (4)): η _inh = 1.9 dl / g
An autoclave having an internal volume of 2 liters was charged with 1075 g of ion-exchanged water, 0.4 g of methylcellulose, 420 g of vinylidene fluoride and 3.8 g of diisopropyl peroxydicarbonate (IPP), and suspension polymerization was carried out at 25 ° C. After the polymerization was completed, the polymer slurry was dehydrated, washed with water, dehydrated, and dried at 80 ° C. for 20 hours to obtain a polymer powder. Η _inh of the obtained vinylidene fluoride polymer was 1.9 dl / g.

(Polymer (5)): η _inh = 3.1 dl / g
Polymerization was conducted in the same manner as in Polymer Example (4) except that the amount of diisopropyl peroxydicarbonate (IPP) was changed to 1.9 g. After dehydration, washing and dehydration, the polymer powder was dried at 80 ° C. for 20 hours. Obtained. Η _inh of the obtained vinylidene fluoride polymer was 3.1.

(Polymer (6)): η _inh = 7.8 dl / g
Polymerization was carried out in the same manner as in Polymer Example (4) except that the amount of diisopropyl peroxydicarbonate (IPP) charged was 0.3 g, dehydrated, washed with water, dehydrated and dried at 80 ° C. for 20 hours to obtain a polymer powder. Obtained. Η _inh of the obtained vinylidene fluoride polymer was 7.8 dl / g.

(Polymer (7)): P (VDF / HEP / MMM) copolymer; η _inh = 3.1 dl / g
An autoclave with an internal volume of 2 liters was charged with 1040 g of ion exchange water, 0.8 g of methyl cellulose, 388 g of vinylidene fluoride, 12 g of propylene hexafluoride, 0.9 g of diisopropyl peroxydicarbonate (IPP), and 1.2 g of maleic acid monomethyl ester, Suspension polymerization was performed at 29 ° C. for 42 hours. After the polymerization was completed, the polymer slurry was dehydrated, washed with water and then dried at 80 ° C. for 20 hours to obtain a polymer powder. Η _inh of the obtained vinylidene fluoride polymer was 3.1 dl / g, and the carbonyl group content was 0.4 × 10 ⁻⁴ mol / g.

(Polymer (8)): P (VDF / MMM) copolymer; η _inh = 1.7 dl / g
An autoclave with an internal volume of 2 liters was charged with 1040 g of ion exchange water, 0.8 g of methyl cellulose, 396 g of vinylidene fluoride, 3.0 g of diisopropyl peroxydicarbonate (IPP), and 4.0 g of maleic acid monomethyl ester, and suspended at 28 ° C. for 45 hours. Turbid polymerization was performed. After the polymerization was completed, the polymer slurry was dehydrated, washed with water and then dried at 80 ° C. for 20 hours to obtain a polymer powder. Η _inh of the obtained vinylidene fluoride polymer was 1.7 dl / g, and the carbonyl group content was 1.2 × 10 ⁻⁴ mol / g.

  For the polymers (7) and (8), the carbonyl group content was determined by the following method.

[Measurement of carbonyl group content]
A calibration curve is prepared by plotting the relationship between the ratio of the absorption at 1726 cm ^{−1 to} the absorption at 881 cm ^{−1 in} the IR spectrum and the carbonyl group content for a sample in which the polyvinylidene fluoride resin and the polymethyl methacrylate resin are mixed at a predetermined ratio.

After washing the sample polymer with hot water and removing unreacted monomer and homopolymer remaining in the polymer by Soxhlet extraction with benzene at 80 ° C. for 24 hours, 1747 cm ⁻¹ due to the carbonyl group in the IR spectrum. The ratio of the absorption to the absorption of 881 cm ⁻¹ is determined, and the carbonyl group content is determined from the calibration curve prepared earlier.

(Polymer (10)): P (VDF / GMA) Copolymer: η _inh = 1.8 dl / g
An autoclave with an internal volume of 2 liters was charged with 1036 g of ion-exchanged water, 0.6 g of methyl cellulose, 400 g of vinylidene fluoride, 12 g of glycidyl methacrylate, and 3.2 g of diisopropyl peroxycarbonate (IPP), and subjected to suspension polymerization at 28 ° C. for 32 hours. It was. After the polymerization was completed, the polymerization slurry was dehydrated, washed with water, and dried at 80 ° C. for 20 hours to obtain a polymer powder. Η _inh of the obtained vinylidene fluoride polymer was 1.8 dl / g.

(Polymer (11)): P (VDF / MAA / HEMA) Copolymer: η _inh = 1.9 dl / g
An autoclave with an internal volume of 2 liters was charged with 1036 g of ion-exchanged water, 0.6 g of methylcellulose, 400 g of vinylidene fluoride, 4 g of methacrylic acid, 2 g of hydroxyethyl methacrylate, and 3.2 g of diisopropyl peroxycarbonate (IPP) at 28 ° C. for 23 hours. Suspension polymerization was performed. After the polymerization was completed, the polymerization slurry was dehydrated, washed with water, and dried at 80 ° C. for 20 hours to obtain a polymer powder. Η _inh of the obtained vinylidene fluoride polymer was 1.9 dl / g.

(Examples 1-11, Comparative Examples 1-5)
<Binder>
As shown in Table 1 below, Examples 1 to 11 can be obtained by combining the above polymers (1) to (11) (Examples 1 to 11 and Comparative Example 5) or alone (Comparative Examples 1 to 4). 11 and Comparative Examples 1 to 5 were obtained. Each of the vinylidene fluoride polymers constituting the binder (hereinafter simply referred to as “binder”) exhibited the inherent viscosity (η _inh ) values shown in Table 1. In any example, with respect to a binder used in combination of two kinds of polymers at a predetermined ratio, firstly, the high molecular weight side polymer is dissolved in an organic solvent (NMP), and after the dissolution is visually confirmed, the remaining weight is determined. The coalescence was further dissolved to obtain each binder solution.

Swelling degree measurement method A binder solution (concentration: about 10% by weight) obtained by dissolving each of the above binders in N-methyl-2-pyrrolidone (NMP) is dried at 110 ° C. to obtain a cast film having a thickness of about 100 μm. It was. Separately, to the electrolyte obtained by adding 1 mol / liter LiPF ₆ to a mixed solution of 3: 5: 2 by weight ratio of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / diethyl carbonate (DEC), The cast film obtained in (1) was immersed at 80 ° C. for 7 hours to measure the weight increase, and the rate of increase was determined as the degree of swelling (%).

  The measurement results for each binder are collectively shown in Table 1 below.

<Electrode mixture>
In the solvent N-methyl-2-pyrrolidone (NMP), 2 parts by weight of each of the above binders (total amount in the case of two polymers) (in the case of two polymers, high molecular weight side polymer → low molecular weight side weight) Dissolved to form a binder solution having a concentration of about 5% by weight, and LiCoO ₂ (“Cell Seed C-5H” manufactured by Nippon Chemical Industry Co., Ltd .; average particle size = 5 μm) as a positive electrode active material. 100 parts by weight and 2 parts by weight of carbon black (“DENKA BLACK” manufactured by Denki Kagaku Kogyo Co., Ltd .; average particle size = 45 nm) as a conductive auxiliary agent are dispersed, and the total solid content concentration of the binder, the active material and the conductive auxiliary agent Was 73% by weight of electrode mixture (slurry).

<Electrode mixture layer>
The electrode mixture (slurry) was applied onto a 15 μm thick Al foil with a bar coater, dried at 90 ° C. for 10 minutes, and then at 110 ° C. for 10 minutes, and an electrode having a dry mixture basis weight of 250 g / m ² ( A mixture) layer was formed.

  About the electrode mixture (slurry) obtained as described above using the binders of Examples 1 to 8 and Comparative Examples 1 to 4, respectively, the slurry viscosity (mPa · s) and the electrode (mixture) layer The peel strength (gf / 10 mm) was measured by the following method. The results are summarized in Table 1 below.

・ Viscosity measurement method The viscosity of the electrode mixture slurry was measured at 30 ° C. using 0.5 ml of the electrode mixture slurry using an E-type viscometer (“RE-80R” rotor 3 ° × R14 manufactured by Toki Sangyo Co., Ltd.). Measured with Table 1 shows the measured values of each electrode mixture slurry at a rotor rotational speed of 5 rpm.

・ Peel strength measurement method The upper surface of the electrode formed by coating and a plastic plate (made of acrylic resin, thickness 5 mm) are bonded together, and a 90 degree peel test is performed in accordance with JIS K-6854 to determine the peel strength. It was.

(Reference example)
A combination of the polymer (2) and the polymer (5) giving the same composition as in Example 2 above was poured into NMP at the same time, and when dissolution was attempted, it was considered to be a high molecular weight polymer (5). Insoluble matter was seen. Using the binder solution (concentration: about 10 or 5% by weight) containing the undissolved material thus obtained, the degree of swelling, the electrode mixture slurry viscosity, and the electrode (mixture) layer were the same as in the above examples. The peel strength was measured.

The measurement results for the above Examples, Comparative Examples and Reference Examples are summarized in Table 1 below.

As shown from the results in Table 1 above, the medium to high molecular weight vinylidene fluoride homopolymer (A) (polymers (1) to (3) and (9)) of the present invention is the main component, Ultra-high molecular weight vinylidene fluoride polymer (B) (polymers (5) to (8) and (10) to (11), of which polymers (7), (8) and (10) to (11) are The binder obtained in combination with an adhesive functional group) exhibits good non-aqueous electrolyte resistance with a low degree of swelling, and compared to a vinylidene fluoride polymer alone having an equivalent η _inh. It shows a good balance between low electrode mix slurry viscosity (ie good application processability) and high peel strength (ie good adhesion to the current collector substrate).

  As described above, according to the present invention, a non-aqueous electric system comprising a vinylidene fluoride homopolymer (A) of medium to high vinylidene fluoride as a main component and combined with a relatively small amount of an ultrahigh molecular weight vinylidene fluoride polymer. A binder for forming a chemical element electrode is provided. By using this binder, an electrode mixture having good application processability at the time of electrode formation, and by applying and drying this on a current collecting substrate, good adhesion to the current collecting substrate. Further, a non-aqueous electrochemical device including the electrode is provided.

The fragmentary sectional view of the electrode structure employ | adopted as a non-aqueous battery. 1 is a partially exploded perspective view of a non-aqueous solvent secondary battery that can be configured according to the present invention. 1 is a cross-sectional view of the structure of an embodiment of an electric double layer capacitor that can be configured in accordance with the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 5 Casing (5a: bottom part, 5b: rim)
6 Gasket 7 Safety valve 8 Top plate 10 Electrode structure 11 Current collector 12a, 12b Electrode mixture layer 21, 22 Polarized electrode 23 Separator 24 Cap 25 Can 26 Electrolyte 27 Packing

Claims (11)

A vinylidene fluoride homopolymer (A) having an inherent viscosity of 0.5 to 1.5 dl / g; and a vinylidene fluoride polymer (B) having an inherent viscosity of 1.4 times or more that of the polymer (A); A binder for forming a non-aqueous electrochemical element electrode in which the ratio of the polymer (A) to the total amount of the polymers (A) and (B) is in the range of 60 to 98% by weight. The binder according to claim 1, wherein the inherent viscosity of the vinylidene fluoride homopolymer (A) is 1.0 to 1.3 dl / g. The binder according to claim 1 or 2, wherein the vinylidene fluoride polymer (B) is a vinylidene fluoride homopolymer. The binder according to claim 1 or 2, wherein the vinylidene fluoride polymer (B) is a vinylidene fluoride copolymer. The binder according to claim 4, wherein the vinylidene fluoride polymer (B) is a vinylidene fluoride copolymer having a functional group. The binder according to claim 5, wherein the functional group of the vinylidene fluoride polymer (B) is selected from at least one of a carboxyl group, an epoxy group, a hydroxyl group, and a carbonyl group. Both the polymers (A) and (B) are polymers obtained by suspension polymerization in an aqueous medium, The binder according to any one of claims 1 to 6. An electrode mixture obtained by dissolving the binder according to any one of claims 1 to 7 in an organic solvent and further dispersing a powder electrode material. The electrode composite according to claim 8, wherein the powder electrode material is dispersed in a binder solution formed by dissolving the polymer (A) after the polymer (B) is substantially completely dissolved in the organic solvent. Agent. The electrode obtained by apply | coating the electrode mixture of Claim 8 or 9 on a collector. A non-aqueous electrochemical element comprising a non-aqueous electrolyte disposed between a pair of electrodes, wherein at least one of the pair of electrodes comprises the electrode according to claim 10.

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