JP6962548B2 - Polyamide-imide solution for power storage element electrodes, manufacturing method of power storage element electrodes, and power storage element electrodes - Google Patents

Description

The present invention relates to a polyamide-imide solution used for a power storage element such as a lithium secondary battery, a lithium ion capacitor, a capacitor, and a capacitor, a method for manufacturing an electrode power storage element electrode using the polyamide-imide solution, and a power storage element electrode.

In a power storage element such as a lithium secondary battery, the electrical insulation of the separator in contact with the electrode may be destroyed due to scratches or irregularities on the electrode surface. As a result, an electrical internal short circuit may occur.

In order to prevent this internal short circuit, it has been proposed to provide a protective layer made of an insulating porous film on the electrode surface. As a porous film to be a protective layer, Patent Documents 1 to 4 are formed of a water-soluble polymer (cellulose derivative, polyacrylic acid derivative, polyvinyl alcohol derivative, etc.), a fluorine-based resin, a rubber-based resin, etc. , A porous film in which pores are formed by blending a large amount of fine particles such as alumina, silicon dioxide, and zirconia into these has been proposed. As another method for forming the protective layer, Patent Documents 5 and 6 describe that a coating film for forming a protective layer is formed on the electrode surface and then immersed in a coagulation bath containing a poor solvent before drying. A method of causing phase separation of the coating film to obtain a porous protective layer has also been proposed. On the other hand, in a lithium secondary battery using a high-capacity active material such as silicon, a wound electrode body in which a positive electrode and a negative electrode are spirally wound via a separator is formed into a square (square tubular) outer can. Or, it is generally loaded inside the outer body of a laminated film to form a battery. In that case, the capacity may decrease due to repeated charging and discharging, or the thickness may increase significantly due to the swelling of the battery. In order to improve such a problem, Patent Document 7 describes that the outer surface of the active material layer of the electrode (negative electrode) is made of a PI polymer such as polyimide (PI) having excellent mechanical properties and heat resistance. A method has been proposed in which a porous layer containing a large amount of fine particles such as silicon and alumina is provided to alleviate the volume change and deformation of the electrode. However, since the electrode provided with the porous layer on the surface as described above has low adhesiveness between the active material layer and the porous layer, the effect of preventing a short circuit is not always sufficient.

As a method for solving such a problem, Patent Document 8 states that an electrode active material layer is formed on a metal foil, and then a PI precursor, polyamide-imide (PAI), etc. are formed on the surface of the electrode active material layer. A coating liquid containing the PI-based polymer and the solvent is applied to form a coating film, and then the solvent in the coating film is removed and, if necessary, thermally imidized in the coating film. A method for producing an electrode for a lithium secondary battery has been proposed by causing phase separation to form a PI porous layer. By using this method, a porous PI layer having excellent heat resistance and mechanical properties and having high adhesion to the electrode active material layer can be formed on the surface of the electrode active material layer.

International Publication No. 1997/008763 Japanese Patent No. 5071056 Japanese Patent No. 5262323 Japanese Patent No. 5370356 Japanese Patent No. 3371839 Japanese Patent No. 3593345 Japanese Unexamined Patent Publication No. 2011-233349 International Publication No. 2014/106954

However, in the method disclosed in Patent Document 8, when a PAI solution is used as the solution for forming the porous PI layer, the viscosity of this solution tends to be slightly low, and therefore when it is applied to the electrode active material layer, it tends to be slightly low. In addition, the PAI solution may permeate the porous active material layer and block the pores of the active material layer, which may reduce the ion permeability at the interface between the active material layer and the porous PAI film. , There was a point to be improved. Further, due to the low viscosity, the thickness unevenness of the coating film may easily occur, and there is a point that the coatability at the time of coating should be improved.

Therefore, the present invention solves the above-mentioned problems, and is a PAI solution having good coatability capable of forming a porous PAI film having good ion permeability, and a storage element electrode on which this film is formed. The purpose is to provide the manufacturing method.

The present inventors used a PAI solution having a specific PAI solution composition and a specific chemical structure of PAI, and laminated and integrated the resulting porous PAI film on the electrode active material layer. By doing so, it was found that the above-mentioned problems could be solved, and the present invention was completed.

The present invention has the following object.

<1> A PAI solution containing a good solvent and a poor solvent for PAI, wherein the PAI contains an oxyalkylene unit and / or a siloxane unit in a side chain.
<2> A method for manufacturing a power storage element electrode, which comprises a step of applying the PAI solution to the surface of an active material layer and then drying it to form a porous PAI film.
<3> An electrode in which a porous PAI film is laminated and integrated on the surface of an active material layer, and has the following characteristics.
1) The side chain of the PAI contains an oxyalkylene unit and / or a siloxane unit.
2) The average pore diameter on the surface of the porous coating is 10 nm or more and 5000 nm or less.

Since the PAI solution of the present invention has a high solution viscosity, it is difficult for the PAI solution to permeate into the electrode active material layer, the ionic resistance can be sufficiently lowered, and the coatability at the time of coating can be applied. Is good. Therefore, an electrode in which a porous PAI film obtained by applying this to the surface of the active material layer and then drying it is laminated and integrated on the surface of the active material layer is suitably used as an electrode for a power storage element having excellent safety. Can be done.

Hereinafter, the present invention will be described in detail.

The present invention uses a PAI solution. PAI is a polycondensate of a tricarboxylic acid component and a diamine component, which are raw materials.

The tricarboxylic acid component of PAI is an organic compound having three carboxyl groups (including derivatives thereof) per molecule, and at least two of the three carboxyl groups have an acid anhydride form. It is arranged at a position where it can be formed.

Examples of the tricarboxylic acid component include a benzenetricarboxylic acid component and a naphthalene tricarboxylic acid component.

Specific examples of the benzenetricarboxylic acid component include trimellitic acid, hemmellitic acid, and anhydrides thereof and monochrome rides thereof.

Specific examples of the naphthalene tricarboxylic acid component include, for example, 1,2,3-naphthalentricarboxylic acid, 1,6,7-naphthalentricarboxylic acid, 1,4,5-naphthalentricarboxylic acid, their anhydrides and their monoclonalides. Can be mentioned.

Among the tricarboxylic acid components, trimellitic acid and trimellitic anhydride chloride (TAC) are preferable.

The tricarboxylic acid component may be used alone or in combination of two or more.

In addition, some of the tricarboxylic acid components are terephthalic acid, isophthalic acid, pyromellitic acid, 3,3', 4,4'-biphenyltetracarboxylic acid, 3,3', 4,4'-benzophenone tetracarboxylic acid. Those substituted with such components may be used.

The diamine component of PAI is an organic compound having two primary amino groups (including derivatives thereof) per molecule.

Specific examples of the diamine component include, for example, 4,4'-diaminodiphenyl ether (DADE), m-phenylenediamine (MDA), p-phenylenediamine, 4,4'-diphenylmethanediamine (DMA), 4,4'-diphenyl ether. Diamine, diphenylsulfone-4,4'-diamine, diphenyl-4,4'-diamine, o-tridine, 2,4-tolylene diamine, 2,6-tolylene diamine, xylylene diamine, naphthalenediamine, and these. Diamine derivatives can be mentioned.

Among the diamine components, DADE, MDA and DMA are preferable.

The diamine component may be used alone or in combination of two or more.

PAI usually has a glass transition temperature of 200 ° C. or higher. The value measured by DSC (Differential Thermal Analysis) is used for the glass transition temperature.

The PAI may be thermoplastic or non-thermoplastic, but the aromatic PAI having the glass transition temperature described above can be preferably used.

The PAI of the present invention is a PAI containing an oxyalkylene unit and / or a siloxane unit in the side chain (hereinafter, these may be abbreviated as "PAI-M"). By doing so, it is possible to increase the viscosity of the PAI solution.

Specific examples of the oxyalkylene unit include an oxyethylene unit, an oxypropylene unit, and an oxybutylene unit. A PAI containing an oxyalkylene unit can be obtained, for example, by reacting a PAI with a diamine having an oxyalkylene unit (hereinafter, may be abbreviated as "DA-1") in a solvent.

Specific examples of DA-1 include ethylene glycol bis (2-aminoethyl) ether, diethylene glycol bis (2-aminoethyl) ether, triethylene glycol bis (2-aminoethyl) ether, and tetraethylene glycol bis (2-amino). Ethyl) ether, polyethylene glycol bis (2-aminoethyl) ether (PEGME), propylene glycol bis (2-aminoethyl) ether, dipropylene glycol bis (2-aminoethyl) ether, tripropylene glycol bis (2-aminoethyl) ) Ether, tetrapropylene glycol bis (2-aminoethyl) ether, polypropylene glycol bis (2-aminoethyl) ether (PPGME) and the like. Among these, those having a number average molecular weight of 300 to 5000 are preferable. These may be used alone or in combination of two or more. Of these, PEGME and PPGME are preferable. Commercially available products can be used for these compounds.

The PAI containing a siloxane unit can be obtained, for example, by reacting PAI with a diamine having a siloxane unit (hereinafter, may be abbreviated as "DA-2") in a solvent.

Specific examples of DA-2 include 1,3-bis (3-aminopropyl) -1,1,3,3-tetramethyldisiloxane and 1,3-bis (4-aminobutyl) -1,1,. 3,3-Tetramethyldisiloxane, bis (4-aminophenoxy) dimethylsilane, 1,3-bis (4-aminophenoxy) -1,1,3,3-tetramethyldisiloxane, etc., and the following general formula ( Those represented by 1) can be mentioned. These may be used alone or in combination of two or more. Among these, in the following general formula (1), R1 and R2 are trimethylene groups, R3, R4, R5 and R6 are methyl groups, and n is 3 to 100 (hereinafter, abbreviated as "DASM"). ) Is preferable, and among these, those having a number average molecular weight of 300 to 5000 are more preferable. These DASMs may be used alone or in combination of two or more. As DASM, a commercially available product can be used.

（ただし、式中ｎは１以上の整数を示す。また、Ｒ１およびＲ２は、それぞれ同一または異なった、低級アルキレン基またはフェニレン基を示し、Ｒ３、Ｒ４、Ｒ５およびＲ６は、それぞれ同一または異なった、低級アルキル基、フェニル基またはフェノキシ基を示す。）

(However, n in the formula represents an integer of 1 or more, R1 and R2 represent the same or different lower alkylene group or phenylene group, respectively, and R3, R4, R5 and R6 are the same or different, respectively. , Lower alkyl group, phenyl group or phenoxy group.)

A PAI solution containing PAI-M (hereinafter, may be abbreviated as "PAI-M solution") is a mixture of a good solvent that dissolves PAI-M, which is a solute, and a solvent that is a poor solvent for the solute. Contains the mixed solvent. Here, the good solvent means a solvent having a solubility in PAI-M of 1% by mass or more at 25 ° C., and the poor solvent means a solvent having a solubility in PAI-M of less than 1% by mass at 25 ° C. .. The poor solvent preferably has a higher boiling point than the good solvent. The boiling point difference is preferably 5 ° C. or higher, more preferably 20 ° C. or higher, and even more preferably 50 ° C. or higher.

As a good solvent, an amide solvent or a urea solvent is preferably used. Examples of the amide solvent include N-methyl-2-pyrrolidone (NMP boiling point: 202 ° C.), N, N-dimethylformamide (DMF boiling point: 153 ° C.), and N, N-dimethylacetamide (DMAc boiling point: 166 ° C.). Can be mentioned. Examples of the urea solvent include tetramethylurea (TMU boiling point: 177 ° C.) and dimethylethylene urea (boiling point: 220 ° C.). These good solvents may be used alone or in combination of two or more.

As the poor solvent, an ether solvent is preferably used. Examples of the ether solvent include diethylene glycol dimethyl ether (boiling point: 162 ° C.), triethylene glycol dimethyl ether (G3 boiling point: 216 ° C.), tetraethylene glycol dimethyl ether (G4 boiling point: 275 ° C.), diethylene glycol (boiling point: 244 ° C.), and tri. Ethylene glycol (boiling point: 287 ° C) Tripropylene glycol (boiling point: 273 ° C), diethylene glycol monomethyl ether (boiling point: 194 ° C), tripropylene glycol monomethyl ether (boiling point: 242 ° C), triethylene glycol monomethyl ether (boiling point) : 249 ° C.) and the like. These may be used alone or in combination of two or more. The blending amount of the poor solvent is preferably 15 to 95% by mass, more preferably 60 to 90% by mass, based on the total amount of the solvent. With such a solvent composition, phase separation occurs efficiently in the drying step after coating on the active material layer, and a porous PAI film having a high porosity and good ion permeability can be obtained.

The PAI solution of the present invention can be produced, for example, by the following production method. That is, the solid PAI is dissolved in the mixed solvent to prepare a PAI solution, and then DA-1 and / or DA-2 is added to this solution and heated to about 60 ° C. to 150 ° C. to obtain PAI. It can be a PAI-M solution in which an oxyalkylene unit and / or a siloxane unit is introduced into the side chain. In this reaction, a part of the imide ring of PAI is opened by aminolysis of diamine to form an amide bond, so that the viscosity of the PAI solution can be increased while maintaining the solution state. That is, DA-1 and DA-2 act as linkers for PAI via an amide bond and contribute to increasing the viscosity, but they do not completely crosslink and gel, so that the solution state can be maintained. can. It should be noted that such a reaction can be confirmed by increasing the viscosity of the PAI solution, but it can also be confirmed by using a spectroscopic method such as NMR or IR.
The amount of DA-1 or DA-2 added is preferably 5 to 40% by mass, preferably 10 to 35% by mass, based on PAI. The solid content concentration during this reaction is preferably 10 to 20% by mass as the solid content concentration of PAI-M.

The viscosity (30 ° C.) of the PAI-M solution is preferably 10 to 100 Pa · s, more preferably 15 to 50 Pa · s. By doing so, it is possible to obtain a solution capable of forming a PAI film having good coatability and good ion permeability.

As the solid PAI, for example, commercially available PAI powder (for example, Toron 4000T series, Toron 4000TF, Toron AI-10 series manufactured by Solvay Advanced Polymers Co., Ltd.) can be used.

In order to obtain a PAI solution, a method of producing using the solid PAI as described above is preferable, but the aromatic tricarboxylic acid component and the diamine component (various diamines or diisocyanates derivatives thereof) as raw materials are substantially polymerized. A solution obtained by polymerizing the mixture in the above-mentioned mixed solvent can also be used. Further, a method in which a poor solvent is added to a solution obtained by a polymerization reaction only in a good solvent, or a method in which a good solvent is added thereto after a polymerization reaction is carried out only in a poor solvent to obtain a suspension. The PAI solution can be obtained with.

Fila can be added to the PAI-M solution. The ion permeability of the porous PAI layer can be further enhanced by the synergistic effect of the porous structure formed by blending the filler and the porous structure formed by the action of the poor solvent.

The type of filler is not limited, and organic filler, inorganic filler and a mixture thereof can be used. Specific examples of the organic filler include styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, methyl acrylate and the like alone or two or more copolymers, polytetrafluoroethylene, and the like. Examples thereof include powders made of a polymer such as a tetrafluorinated ethylene-6 fluoride propylene copolymer, a tetrafluorinated ethylene-ethylene copolymer, and a fluororesin such as polyvinylidene fluoride. The organic filler can be used alone or in combination of two or more. Examples of the inorganic filler include powders made of inorganic substances such as metal oxides, metal nitrides, metal carbides, metal hydroxides, carbonates, and sulfates. Specific examples include powders made of alumina, boehmite (aluminum oxide oxide), kaolin (aluminum silicate), silica, titanium dioxide, barium sulfate, calcium carbonate and the like. The inorganic filler can be used alone or in combination of two or more. Among these inorganic fillers, alumina powder and boehmite powder are preferable from the viewpoint of chemical stability.

The shape of the filler is not limited, and particles such as substantially spherical, plate-shaped, columnar, needle-shaped, whisker-shaped, and fibrous can be used, and substantially spherical particles are preferable. The aspect ratio of the substantially spherical particles (major axis of the particles / minor axis of the particles) is preferably 1 or more and 1.5 or less.

The average particle size of the filler is not limited, but is preferably 0.01 μm or more and 2 μm or less. The average particle size can be measured by a measuring device based on the laser diffraction / scattering method.

The surface of the filler may be treated with a surface treatment agent such as a surfactant or a silane coupler.

The amount of the filler compounded is preferably 80/20 to 10/90, more preferably 70/30 to 20/80, in terms of the mass ratio (PAI-M / filler) of PAI-M to the solid content. ..

If necessary, known additives such as various surfactants and organic silane coupling agents may be added to the PAI solution as long as the effects of the present invention are not impaired. If necessary, polymers other than PAI may be added as long as the effects of the present invention are not impaired.

By applying the PAI-M solution to the surface of the electrode active material layer and drying at a temperature of 100 to 200 ° C., phase separation can be induced to form a porous PAI film, and the electrode active material layer can be formed. And this porous PAI coating are laminated and integrated.

As a method of applying the PAI solution to the electrode active material layer, a method of continuously applying by roll-to-roll and a method of applying in sheet form can be adopted, and any method may be used. As the coating apparatus, a known method using a die coater, a multi-layer die coater, a gravure coater, a comma coater, a reverse roll coater, a doctor blade coater, or the like can be used.

The average pore diameter on the surface of the porous PAI coating is 10 nm or more and 5000 nm or less, more preferably 20 nm or more and 3000 nm or less. By setting the average pore diameter in this way, the ion resistivity of the PAI coating can be sufficiently lowered. The average pore diameter can be confirmed by acquiring an SEM (scanning electron microscope) image of the surface of the porous PAI coating at a magnification of 5000 to 20000 and analyzing it with commercially available image processing software.

The porosity of the porous PAI coating is preferably 30 to 90% by volume, more preferably 40 to 80% by volume, and even more preferably 45 to 80% by volume. By setting the porosity in this way, good mechanical properties and good cushioning properties for stress relaxation due to the volume change of the active material are ensured at the same time. Therefore, it is possible to obtain an electrode having excellent safety and good cycle characteristics. The porosity of the porous PAI coating is a value calculated from the apparent density of the porous PAI coating and the true density (specific gravity) of the PAI constituting the coating. Specifically, the porosity (% by volume) is calculated by the following equation when the apparent density of the PAI film is A (g / cm ³ ) and the true density of PAI is B (g / cm ^3).
Porosity (% by volume) = 100-A * (100 / B)

The porous PAI coating preferably has sufficient ion permeability. That is, the ion resistivity ^{is preferably 2.5 Ωcm 2} or less. When the ion resistivity is in the above range, good charge / discharge characteristics of the lithium secondary battery using the electrode of the present invention can be ensured.
Here, the ion resistivity (Rs-PAI) of the PAI coating can be calculated by using, for example, the following method. That is, assuming that the ion resistivity of only the active material layer formed on the current collector is Rs-1, and the ion resistivity of the laminate having the porous PAI film formed on the surface thereof is Rs-2, then Rs-PAI Is calculated by subtracting Rs-1 from Rs-2.
Rs-1 and Rs-2 form a measurement cell by sequentially laminating a commercially available separator and a lithium foil as a counter electrode on their surfaces in the presence of an electrolytic solution, and form the lithium foil and the current collector. Can be determined to measure the impedance at 100 KHz at 25 ° C.

The porous PAI coating is preferably firmly adhered to the active material layer. That is, from the viewpoint of improving the safety of the battery, it is preferable that the adhesive strength between the electrode active material layer and the porous PAI coating is higher than the strength of the electrode active material layer. Whether or not the adhesive strength is higher than the strength of the electrode active material layer can be determined by whether cohesive fracture occurs or interface peeling occurs at the interface when the electrode active material layer is peeled from the PAI coating. .. When cohesive fracture occurs, it is determined that the strength of the adhesive interface is higher than the strength of the electrode active material layer. When a fragment of the active material layer adheres to a part of the surface (adhesive surface with the electrode active material layer) of the PAI film after peeling, it is determined to be cohesive fracture. In the electrode of the present invention, such a high adhesive force greatly contributes to the improvement of battery safety.

The thickness of the porous PAI coating is preferably 0.5 to 100 μm, more preferably 1 to 20 μm.

The electrode active material layer on which the porous PAI film is laminated is a layer formed on the current collector of the power storage element (for example, lithium secondary battery) electrode of the present invention, and is a positive electrode active material layer and a negative electrode active material layer. It is a general term for.

As the current collector, a metal foil such as copper foil, stainless steel foil, nickel foil, or aluminum foil can be used. Aluminum foil is preferably used for the positive electrode, and copper foil is preferably used for the negative electrode. The thickness of these metal foils is preferably 5 to 50 μm, more preferably 9 to 18 μm. The surface of these metal foils may be roughened or rust-proofed to improve the adhesiveness with the active material layer.

The positive electrode active material layer is, for example, a layer obtained by binding positive electrode active material particles with a resin binder. As the material used as the positive electrode active material particles, those capable of storing and storing lithium ions are preferable, and for example, oxide-based (LiCoO ₂ , LiNiO _2, etc.), iron phosphate-based (LiFePO _4, etc.), and polymer compound-based (LiFePO 4, etc.) Active material particles such as polyaniline, polythiophene, etc.) can be mentioned. Of these, LiCoO ₂ , LiNiO ₂ , and LiFePO ₄ are preferable. In order to reduce the internal resistance of the positive electrode active material layer, conductive particles such as carbon (graphite, carbon black, etc.) particles and metal (silver, copper, nickel, etc.) particles are blended in an amount of about 1 to 30% by mass. May be.

The negative electrode active material layer is, for example, a layer obtained by binding negative electrode active material particles with a resin binder. As the material used as the negative electrode active material particles, those capable of storing and storing lithium ions are preferable, and examples thereof include active material particles such as graphite, amorphous carbon, silicon-based, and tin-based particles. Of these, graphite particles and silicon-based particles are preferable. Examples of the silicon-based particles include particles such as elemental silicon, a silicon alloy, and a silicon-silicon dioxide composite. Among these silicon-based particles, particles of simple substance silicon are preferable. Elemental silicon refers to crystalline or amorphous silicon having a purity of 95% by mass or more. In order to reduce the internal resistance of the negative electrode active material layer, conductive particles such as carbon (graphite, carbon black, etc.) particles and metal (silver, copper, nickel, etc.) particles are blended in an amount of about 1 to 30% by mass. May be. Further, as the negative electrode active material layer, a lithium foil or a lithium alloy foil can be used.

The particle size of the active material particles and the conductive particles is preferably 50 μm or less for both the positive electrode and the negative electrode, and more preferably 10 μm or less. If the particle size is too small, it will be difficult to bind with a resin binder, so the particle size is usually 0.1 μm or more, preferably 0.5 μm or more.

The porosity of the electrode active material layer is preferably 5 to 50% by volume, more preferably 10 to 40% by volume for both the positive electrode and the negative electrode.

The layer thickness of the electrode active material layer is usually about 20 to 200 μm.

Examples of the resin binder for binding the active material particles include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and styrene. Examples thereof include butadiene copolymer rubber (SBR), polytetrafluoroethylene, polypropylene, polyethylene, PAI and the like. Of these, PVDF, SBR and PAI are preferable.

As the laminate in which the active material layer is formed on the current collector as described above, a commercially available product can be used, but for example, it can be produced by a known method as follows.

That is, a dispersion containing the above-mentioned binder, active material particles, and a solvent (hereinafter, may be abbreviated as "active material dispersion") is applied to the surface of a metal foil which is a current collector, and then dried. An electrode active material layer can be formed on the metal foil.

Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the examples.

The electrode active material layer (for the negative electrode) formed on the current collector used in the following Examples and Comparative Examples was obtained as follows.

88 parts by mass of graphite particles (average particle size 8 μm) which is a negative electrode active material, 5 parts by mass of carbon black (acetylene black) which is a conductive auxiliary agent, and 7 parts by mass of PVDF which is a binder resin are uniformly dispersed in NMP. A negative electrode active material dispersion having a solid content concentration of 25% by mass was obtained. This dispersion was applied to a copper foil having a thickness of 18 μm, which is a negative electrode current collector, and the obtained coating film was dried at 150 ° C. for 20 minutes and then hot-pressed to obtain a negative electrode active material layer having a thickness of 50 μm. ..

The characteristics of the electrodes obtained in the following examples and comparative examples were evaluated by the following methods.

The electrode was punched into a circle having a diameter of 16 mm, and a separator made of a polyethylene porous film and a lithium foil were laminated in this order on the surface side of the porous PAI coating film, and this was stored in a stainless coin-shaped outer container. An electrolytic solution (solvent: a mixed solvent in which ethylene carbonate and dimethyl carbonate are mixed at a volume ratio of 1: 1; electrolyte: 1MLiPF ₆ ) is injected into the outer container, and the outer container is made of stainless steel via packing. The cell was obtained by covering it with a cap and fixing it, and sealing the battery can. Using this cell, the ion resistivity (Rs-PAI) was calculated by measuring the impedance at 100 KHz by the method described above.

<Example 1>
PAI powder obtained by copolymerizing TAC with DADE and MDA (copolymerization molar ratio: DADE / MDA = 7/3) (Toron 4000T-HV manufactured by Solvent Advanced Polymers Co., Ltd., glass transition temperature 280 ° C.) Was dissolved in a mixed solvent consisting of NMP and G4 (mass ratio NMP / G4 = 30/70) at 80 ° C. to obtain a uniform PAI solution (S-0) having a solid content concentration of PAI of 15% by mass. Obtained. Next, PPGME (number average molecular weight 2000: Jeffamine D2000 manufactured by Huntsman) equivalent to 24% by mass with respect to the mass of PAI was added to this PAI solution, and the mixture was reacted at 80 ° C. for 4 hours under stirring to provide a uniform solid content. A PAI solution (S-1) having a concentration of 18.0% by mass was obtained. The viscosity of S-1 was 34.5 Pa · s at 30 ° C.

<Example 2>
The same procedure as in Example 1 was carried out except that the amount of PPGME added was 12% by mass with respect to the mass of PAI, to obtain a uniform PAI solution (S-2) having a solid content concentration of 16.5% by mass. .. The viscosity of S-2 was 11.7 Pa · s at 30 ° C.

<Example 3>
Example 1 except that DASM (number average molecular weight 860: KF-8010 manufactured by Shin-Etsu Chemical Co., Ltd.) equivalent to 6% by mass with respect to the mass of PAI was used in the PAI solution (S-0) obtained in Example 1. In the same manner as above, a uniform PAI solution (S-3) having a solid content concentration of 15.8% by mass was obtained. The viscosity of S-3 was 10.5 Pa · s at 30 ° C.

<Example 4>
To the PAI solution (S-2) obtained in Example 2, commercially available spherical alumina (average particle size: 0.5 μm) equivalent to 40% by mass with respect to the PAI mass was added, and the mixture was kneaded and mixed with a ball mill to solidify. A PAI suspension (S-4) having a particle concentration of 19.8% by mass was obtained.

<Comparative example 1>
PAI powder obtained by copolymerizing TAC with DADE and MDA (copolymerization molar ratio: DADE / MDA = 7/3) (Toron 4000T-HV manufactured by Solvent Advanced Polymers Co., Ltd., glass transition temperature 280 ° C.) Was dissolved in a mixed solvent consisting of NMP and G4 (mass ratio NMP / G4 = 30/70) at 80 ° C., and a uniform PAI solution (S-5) having a solid content concentration of PAI of 16.5% by mass was dissolved. ) Was obtained. The viscosity of S-5 was 8.6 Pa · s at 30 ° C.

<Example 5>
The S-1 obtained in Example 1 was applied to the surface of the negative electrode active material layer and dried at 130 ° C. for 10 minutes to form an electrode having a PAI film having a thickness of 11 μm formed on the surface of the negative electrode active material layer. Negative electrode) "AN-1" was obtained. The coatability at the time of coating was extremely good. This porous PAI coating was firmly adhered to the surface of the negative electrode active material layer. The average pore diameter (surface) of the porous PAI coating was 2100 nm, and the porosity was 61% by volume.
When a cell was prepared by the above method using the negative electrode "AN-1" and the ion resistivity was measured, the Rs-PAI of this PAI coating was ^{2.2 Ωcm 2.}

<Example 6>
An electrode (negative electrode) "AN-2" in which a PAI film having a thickness of 12 μm was formed on the surface of the negative electrode active material layer was obtained in the same manner as in Example 5 except that S-2 was used as the PAI solution. rice field. The coatability at the time of coating was good. This porous PAI coating was firmly adhered to the surface of the negative electrode active material layer. The average pore diameter (surface) of the porous PAI coating was 2200 nm, and the porosity was 62% by volume. When a cell was prepared by the above method using the negative electrode "AN-2" and the ion resistivity was measured, the Rs-PAI of this PAI coating was ^{2.4 Ωcm 2.}

<Example 7>
An electrode (negative electrode) "AN-3" in which a PAI film having a thickness of 13 μm was formed on the surface of the negative electrode active material layer was obtained in the same manner as in Example 5 except that S-3 was used as the PAI solution. rice field. The coatability at the time of coating was good. This porous PAI coating was firmly adhered to the surface of the negative electrode active material layer. The average pore diameter (surface) of the porous PAI coating was 2500 nm, and the porosity was 61% by volume. When a cell was prepared by the above method using the negative electrode "AN-3" and the ion resistivity was measured, the Rs-PAI of this PAI coating was ^{2.3 Ωcm 2.}

<Example 8>
Electrode (negative electrode) "AN-4" in which a PAI film having a thickness of 11 μm was formed on the surface of the negative electrode active material layer in the same manner as in Example 5 except that S-4 was used as the PAI suspension. Got The coatability at the time of coating was good. This porous PAI coating was firmly adhered to the surface of the negative electrode active material layer. The average pore diameter (surface) of the porous PAI coating was 1500 nm, and the porosity was 68% by volume. When a cell was prepared by the above method using the negative electrode "AN-4" and the ion resistivity was measured, the Rs-PAI of this PAI coating was ^{1.9 Ωcm 2.}

<Comparative example 2>
An electrode (negative electrode) "AN-5" in which a PAI film having a thickness of 12 μm was formed on the surface of the negative electrode active material layer was obtained in the same manner as in Example 5 except that S-5 was used as the PAI solution. rice field. At the time of application, a part of the PAI solution sometimes flowed to the peripheral portion of the active material layer. This porous PAI coating was firmly adhered to the surface of the negative electrode active material layer. The average pore diameter (surface) of the porous PAI coating was 1900 nm, and the porosity was 60% by volume. When a cell was prepared by the above method using the negative electrode "AN-5" and the ion resistivity was measured, the Rs-PAI of this PAI coating was ^{2.9 Ωcm 2.}

As shown in Examples and Comparative Examples, the PAI solution of the present invention has a high viscosity and therefore has good coatability. Further, by using this, the porous PAI coating film formed on the electrode active material has a low ion resistivity and can secure good ion permeability.

Since the PAI solution of the present invention has a high viscosity, the coatability is good, and the porous PAI film obtained from this is excellent in ion permeability. Therefore, an electrode in which a porous PAI film obtained by applying this to the surface of the active material layer and then drying it is laminated and integrated on the surface of the active material layer is suitably used as an electrode for a power storage element having excellent safety. Can be done.

Claims (3)

A polyamide-imide solution containing a good solvent and a poor solvent for polyamide-imide, wherein the oxyalkylene unit and / or the siloxane unit is introduced into the side chain of the polyamide-imide via an amide bond. A featured polyamide-imide solution. A polyamide-imide containing an oxyalkylene unit and / or a siloxane unit in the side chain and a polyamide-imide solution containing a good solvent and a poor solvent for the polyamide-imide are applied to the surface of the active material layer and then dried to make them porous. A method for manufacturing a power storage element electrode, which comprises a step of forming a polyamide-imide film. An electrode in which a porous polyamide-imide film is laminated and integrated on the surface of an active material layer, and has the following characteristics.
1) The side chain of the polyamide-imide contains an oxyalkylene unit and / or a siloxane unit.
2) The average pore diameter of the surface of the porous polyamide-imide coating is 10 nm or more and 5000 nm or less.