KR20180075520A - Polyimide solution for capacitor electrode, method for manufacturing capacitor electrode and capacitor electrode - Google Patents

Abstract

An object of the present invention is to provide a PI solution capable of forming a PI film having a fine phase separation structure and a sufficiently reduced ion resistivity. The present invention relates to a polyimide solution containing a good solvent for a polyimide and a poor solvent, wherein the polyimide has an oxyalkylene unit and / or a siloxane unit in the main chain, Meade solution.

Description

Polyimide solution for capacitor electrode, method for manufacturing capacitor electrode and capacitor electrode

The present invention relates to an electrode used in a charge storage element such as a lithium secondary battery, a lithium ion capacitor, a capacitor, and a capacitor.

When thermal runaway occurs due to overcharging or the like in an electrode used in a charge storage element such as a lithium secondary battery, scratches and / or irregularities on the surface of the electrode are caused to break the electrical insulation property of the separator in contact with the electrode, An internal short circuit may occur.

In order to prevent such an internal short circuit, by applying a solution of polyimide (hereinafter also abbreviated as " PI ") such as polyimide and polyamide imide having heat resistance to the surface of the electrode active material layer, There has been proposed a method of providing a porous PI insulating film (hereinafter sometimes abbreviated as " porous PI film "). In such a method, the electrode provided with the PI insulating film is used as a capacitor element electrode by filling the pores with an electrolyte solution to express ion conductivity. For example, in Patent Document 1, a coating film for forming a film is formed on the surface of an active material layer using a PI solution, and then the film is dipped in a coagulating bath containing a poor solvent before drying to cause phase separation of the coating film Thereby forming a porous film. Patent Document 2 proposes a method of making a porous film by using a coating liquid in which fine particles such as iron oxide, silica, and alumina are mixed as a filler in a PI solution or the like. However, the laminated electrode obtained by using these electrolytic solutions has a low adhesiveness between the active material layer and the porous film, so that the effect of preventing short circuit is not always sufficient, and there is a need to improve the safety from the viewpoint of safety of the battery. In addition, such an electrode has not sufficient stress relaxation due to a change in the volume of the active material, and thus improvement in the cycle characteristics of the electrode is not necessarily sufficient. Further, in the laminated electrode obtained by the method of inducing phase separation by using a coagulation bath containing a poor solvent such as water and / or alcohol, since the entire active material layer is in contact with the coagulation bath, the poor solvent has properties inherent to the active material layer There was a case of harm. Furthermore, with respect to this method, a waste liquid containing a poor solvent is generated from the coagulation bath, so that there is also a problem in terms of production method from the viewpoint of environmental compatibility.

As a method for solving these problems, Patent Document 3 discloses a method of forming a coating film on a surface of an electrode active material layer by using a specific solution containing PI and then drying the coating film to cause phase separation Thereby obtaining a porous PI film.

The porous PI coating described in Patent Document 3 has insufficient affinity for the electrolyte solution and the ion resistivity of the PI coating when the electrolyte is filled in the pores is not sufficiently lowered in some cases. Further, when the average pore size of the porous film is slightly larger than 2000 nm, when lithium foil or lithium aluminum alloy foil or the like is used as the negative electrode active material layer, generation of dendrites accompanied by insertion and desorption of lithium ions is sufficiently inhibited It was difficult. Moreover, it has been difficult to use this film as a polymer electrolyte.

Japanese Patent Application Laid-Open No. 11-185731 Japanese Patent Application Laid-Open No. 2011-233349 International Publication No. 2014/106954

DISCLOSURE OF THE INVENTION The present invention provides a PI solution capable of forming a PI film having a fine phase separation structure and a sufficiently reduced ion resistivity, .

The present inventors have found that the above problem is solved by forming a PI coating having a phase separation structure obtained therefrom on the electrode active material layer by using a PI solution in which the PI chemical structure and the PI solution are specified, Thereby completing the present invention.

The present invention is intended to be as follows.

≪ 1 > A PI solution containing a good solvent for a PI and a poor solvent, wherein the PI contains an oxyalkylene unit and / or a siloxane unit in the main chain, .

≪ 2 > The PI solution for a capacitor element electrode according to < 1 >, wherein the PI solution further contains a lithium salt.

&Lt; 3 &gt; A method for manufacturing a capacitor element electrode, comprising: forming a PI coating having a phase separation structure by applying a PI solution described in <1> or <2> to a surface of an active material layer and then drying.

&Lt; 4 &gt; A PI coating having a phase-separated structure is formed by applying the PI solution described in &lt; 1 &gt; or &lt; 2 &gt; to a substrate and then drying the resultant. Then, the PI coating is thermally compressed on the surface of the active material, A method for manufacturing a capacitor element electrode, comprising the step of peeling a base material.

<5> A method for manufacturing a capacitor element electrode according to <3> or <4>, wherein the PI film having a phase separation structure is a porous PI film.

<6> A method for manufacturing a capacitor element electrode according to <3> or <4>, wherein the PI coating having a phase-separated structure has at least two phases, one of the phases is a PI and at least one phase of the other phase contains an electrolyte.

<7> An electrode in which a PI film having a phase separation structure is laminated and integrated on a surface of an active material layer, wherein the PI contains an oxyalkylene unit and / or a siloxane unit in its main chain.

The PI coating having the phase separation structure obtained by applying the PI solution of the present invention to the surface of the capacitor active material layer and drying can sufficiently lower the ion resistivity of the coating and can be suitably used as a capacitor electrode excellent in safety have. The PI solution of the present invention can also be used as a solution for forming a polymer electrolyte by previously containing a lithium salt. In addition, the electrode having a PI coating formed using the PI solution of the present invention has excellent charge / discharge characteristics.

Fig. 1 is an SEM cross-sectional view of the electrode &quot; A-1 &quot; obtained in Example 9. Fig.
2 is a sectional SEM image of the porous PI coating portion of the electrode &quot; A-1 &quot; obtained in Example 9. Fig.

Hereinafter, the present invention will be described in detail.

In the present invention, a PI solution is used. Here, PI is a heat-resistant polymer having an imide bond in its main chain or a precursor thereof, and is usually obtained by polycondensing a monomer component, a diamine component, and a tetracarboxylic acid component and / or a tricarboxylic acid component. In addition to the usual PI (soluble polyimide, thermoplastic polyimide, non-thermoplastic polyimide, etc.), these PIs may contain polyimide imides (hereinafter, sometimes abbreviated as &quot; PAI &quot;), And PI precursor, and the PI precursor and PAI are preferably used. These PIs are copolymer PIs containing an oxyalkylene unit and / or a siloxane unit in the main chain and using a monomer containing an oxyalkylene unit and / or a siloxane unit as a copolymerization component.

The PI precursor is an imide bond formed by heating at a temperature of 100 캜 or higher. In the present invention, a polyamic acid (hereinafter sometimes abbreviated as &quot; PAA &quot;) is preferably used. PAA is obtained by reacting tetracarboxylic dianhydride with diamine in a solvent. On the other hand, the PAA may be partially imidized.

The PI such as the PI precursor (for example, PAA) and PAI contains an oxyalkylene unit and / or a siloxane unit in the main chain. For the PAA solution containing an oxyalkylene unit in the main chain, for example, a PI solution as disclosed in Japanese Patent No. 5944613 can be used. The patent publication is based on the following <1> and <2>, and a PI solution containing an oxyalkylene unit described in detail herein can also be used in the present invention. That is, in the present invention, the full text of the patent publication is referred to and is referred to.

<1> A porous PI film comprising a PI containing an oxyalkylene unit and having a porosity of 45 vol% or more and 95 vol% or less and an average pore size of 10 nm or more and 1000 nm or less.

&Lt; 2 &gt; A solution comprising a PI containing an oxyalkylene unit, a good solvent thereof and a poor solvent and having a poor solvent content in the above mixed solvent of 65% by mass or more and 95% by mass or less, Wherein the porous PI film is dried at a temperature of less than 350 캜 after application.

The PAA containing an oxyalkylene unit and / or a siloxane unit can be obtained by reacting tetracarboxylic dianhydride with tetra carboxylic acid dianhydride in the reaction at approximately equimolar amounts of tetracarboxylic dianhydride and diamine, A copolymer of carboxylic acid dianhydride and tetracarboxylic dianhydride not containing an oxyalkylene unit or a siloxane unit or a diamine containing an oxyalkylene unit and / or a siloxane unit as a diamine and an oxyalkylene unit By copolymerization using diamine not containing a siloxane unit, or by copolymerization using both of the tetracarboxylic acid dianhydride and the diamines described above. Here, a tetracarboxylic acid dianhydride or diamine containing an oxyalkylene unit and / or a siloxane unit is referred to as a &quot; monomer A &quot;, a tetracarboxylic acid dianhydride or diamine not containing an oxyalkylene unit or a siloxane unit, Monomer B &quot;, respectively. The tetracarboxylic acid dianhydride not containing an oxyalkylene unit or a siloxane unit is referred to as "TA", and the diamine not containing an oxyalkylene unit or a siloxane unit is referred to as "DA".

In the present invention, the monomer A does not interfere with the oxyalkylene unit and the siloxane unit in one molecule, but the monomer A generally has one oxyalkylene unit or siloxane unit . As the monomer A containing an oxyalkylene unit (hereinafter may be abbreviated as "monomer A-1" in some cases) in the monomer A, tetracarboxylic acid dianhydride containing an oxyalkylene unit (hereinafter referred to as " TA-1 ") and a diamine containing an oxyalkylene unit (hereinafter sometimes abbreviated as" DA-1 "). As the monomer A (hereinafter abbreviated as "monomer A-2" hereinafter) containing a siloxane unit in the monomer A, tetracarboxylic acid dianhydride containing a siloxane unit (hereinafter referred to as "TA- 2 &quot;), and a diamine containing a siloxane unit (hereinafter sometimes abbreviated as &quot; DA-2 &quot;). As the monomer A, one or both of the monomer A-1 and the monomer A-2 may be used, and usually one of them is used.

The PAA containing an oxyalkylene unit and / or a siloxane unit can be obtained by reacting one or two or more monomers selected from the group consisting of TA-1, DA-1, TA-2 and DA- . The PAA containing the preferred oxyalkylene unit and / or siloxane unit contains one or more monomers selected from the group consisting of DA-1 and DA-2 as monomer components.

PAA containing an oxyalkylene unit can be obtained, for example, by copolymerizing a copolymer PAA obtained by copolymerizing TA-1 and / or DA-1 with TA and / or DA (hereinafter abbreviated as "PAA-1" ).

PAA containing a siloxane unit can be obtained, for example, by copolymerization of TA-2 and / or DA-2 with TA and / or DA (hereinafter abbreviated as "PAA-2" ).

PAA-1 and PAA-2 may be mixed and used.

The PAA solution contains a mixed solvent obtained by mixing a good solvent that dissolves the solute PAA and a solvent that becomes a poor solvent in the solute. Here, the positive solvent refers to a solvent having a solubility to PAA of 1% by mass or more at 25 占 폚, and a poor solvent means a solvent having a solubility to PAA of less than 1% by mass at 25 占 폚. The poor solvent is preferably a higher boiling point than the good solvent. The proportion thereof is preferably 5 占 폚 or higher, more preferably 20 占 폚 or higher, and still more preferably 50 占 폚 or higher.

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

As the poor solvent, an ether-based solvent is preferably used. Examples of the ether solvent include diethylene glycol dimethyl ether (boiling point: 162 占 폚), triethylene glycol dimethyl ether (boiling point: 216 占 폚), tetraethylene glycol dimethyl ether (boiling point: 275 占 폚), diethylene glycol (boiling point: 244 占 폚), triethylene glycol (boiling point: 287 占 폚), tripropylene glycol (boiling point: 273 占 폚), diethylene glycol monomethyl ether : 194 占 폚), tripropylene glycol monomethyl ether (boiling point: 242 占 폚), and triethylene glycol monomethyl ether (boiling point: 249 占 폚). These may be used alone, or two or more of them may be used in combination.

The blending amount of the poor solvent in the mixed solvent is preferably 15 to 95 mass%, more preferably 60 to 90 mass%, with respect to the mass of the mixed solvent. By doing so, phase separation is efficiently performed in the drying step after application to the substrate.

As the PAA-1 solution, tetracarboxylic acid dianhydride (a mixture of TA-1 and TA, or TA alone) as a monomer and diamine (a mixture of DA-1 and DA, or DA only) A solution obtained by polymerizing in a mixed solvent at a temperature of 10 to 70 占 폚 can be used.

TA-1 is a tetracarboxylic dianhydride containing an oxyalkylene unit. Specific examples of TA-1 include ethylene glycol bisanhydrotrimellitate (TMEG), diethylene glycol bisanhydrotrimellitate, triethylene glycol bisanhydrotrimellitate, tetraethylene glycol Bisanhydrotrimellitate, polyethylene glycol biscyanhydrotrimellitate, propylene glycol biscyanhydrotrimellitate, dipropylene glycol biscyanhydrotrimellitate, tripropylene glycol bisanhydrotrimetate, (DA-1), which will be described later, in addition to the poly (ethylene glycol) aniline, melitate, tetrapropylene glycol bisanhydrotrimellitate and polypropylene glycol bisanhydrotrimellitate, And an anhydrous trimellitic acid amide-forming reaction That is, there may be mentioned acid dianhydride having two amide bond. These may be used alone, or two or more of them may be used in combination. Of these, TMEG is preferable. These compounds are commercially available products and can be prepared by known methods.

The TA is not particularly limited as long as it is a tetracarboxylic acid dianhydride not containing an oxyalkylene unit or a siloxane unit. Specific examples of TA include pyromellitic dianhydride (PMDA), 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,3,3', 4'-biphenyl Tetracarboxylic dianhydride, 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, and 3,3', 4,4'-diphenylsulfone tetracarboxylic acid dianhydride And the like. These may be used alone, or two or more of them may be used in combination. Of these, at least one compound selected from the group consisting of PMDA and BPDA is preferable. These compounds are commercially available products and can be prepared by known methods.

DA-1 is a diamine containing an oxyalkylene unit. Specific examples of DA-1 include ethylene glycol bis (2-aminoethyl) ether, diethylene glycol bis (2-aminoethyl) ether, triethylene glycol bis Propylene glycol bis (2-aminoethyl) ether, dipropylene glycol bis (2-aminoethyl) ether, glycerol bis (2-aminoethyl) ether, polyethylene glycol bis Ether, tripropylene glycol bis (2-aminoethyl) ether, tetrapropylene glycol bis (2-aminoethyl) ether and polypropylene glycol bis (2-aminoethyl) ether (PPGME) have. These may be used alone, or two or more of them may be used in combination. Of these, PPGME is preferred. These compounds are commercially available products and can be prepared by known methods. For example, PPGME is available as Zephamine D2000 (number average molecular weight 2000: Huntsman).

DA is not particularly limited as long as it is a diamine not containing an oxyalkylene unit or a siloxane unit. Specific examples of DA include 4,4'-diaminodiphenyl ether (DADE), 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 2,2-bis (4-aminophenoxy) phenyl] propane (BAPP), 4,4'-diaminodiphenylmethane, 2,2-bis [4- Propene, p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, 1,4-bis (4-aminophenoxy) benzene, 1,3- ) Benzene, 1,3-bis (3-aminophenoxy) benzene, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis (trifluoromethyl) (4-aminophenoxy) biphenyl, 3,3'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, bis [4- ] Sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, and 4,4'-diaminodiphenyl sulfide. These may be used alone, or two or more of them may be used in combination. Of these, at least one compound selected from the group consisting of DADE and BAPP is preferable. These compounds are commercially available products and can be prepared by known methods.

As the PAA-2 solution, tetracarboxylic acid dianhydride (a mixture of TA-2 and TA, or TA alone) as a monomer and diamine (a mixture of DA-2 and DA or DA alone) A solution obtained by polymerizing in a mixed solvent at a temperature of 10 to 70 占 폚 can be used.

TA-2 is a tetracarboxylic dianhydride containing a siloxane unit. Specific examples of TA-2 include 1,3-bis (3,4-dicarboxyphenyl) -1,1,3,3-tetramethyldisiloxane dianhydride, 1,3-bis (3,4- Phenyl) -1,1,3,3-tetraethylsiloxane dianhydride, bis (3,4-dicarboxyphenyl) dimethylpolysiloxane dianhydride, bis (3,4-dicarboxyphenyl) diethylpolysiloxane dianhydride Water and the like. These may be used alone, or two or more of them may be used in combination. These compounds are commercially available products and can be prepared by known methods.

DA-2 is a diamine containing a siloxane unit. Specific examples of DA-2 include 1,3-bis (3-aminopropyl) -1,1,3,3-tetramethyldisiloxane, 1,3-bis (4-aminobutyl) , 3-tetramethyldisiloxane, 1,3-bis (4-aminophenoxy) -1,1,3,3-tetramethyldisiloxane, and a compound represented by the following formula (1) have. These may be used alone, or two or more of them may be used in combination. A compound wherein R ¹ and R ² are a trimethylene group, R ³ , R ⁴ , R ⁵ and R ⁶ are methyl groups and n is 3 to 100, and mixtures thereof (hereinafter, DASM "), and among these, compounds having a number average molecular weight of 300 to 5000 and mixtures thereof are more preferable. On the other hand, DA-2 can be a commercially available product and can be produced by a known method. For example, DASM is available as KF-8010 (number average molecular weight 860: manufactured by Shin-Etsu Chemical Co., Ltd.).

R ¹ and R ² are the same or different and each represents a lower alkylene group or a phenylene group, and R ³ , R ⁴ , R ^5, and R ⁵ are the same or different, R ⁶ are the same or different and each represents a lower alkyl group, a phenyl group or a phenoxy group.

Particularly, in the PAA containing only the oxyalkylene unit in the oxyalkylene unit or the siloxane unit, when one of TA-1 and DA-1 is used as the monomer A-1 containing an oxyalkylene unit, TA (Copolymerization ratio) of -1 or DA-1 is preferably 0.5 to 20 mol%, and more preferably 1 to 10 mol%. The mol% representing the copolymerization ratio refers to a value calculated according to the following formula. In the case of using both of TA-1 and DA-1, the amount of use (copolymerization ratio) is preferably 0.5 to 20 mol%, more preferably 1 to 10 mol%.

Also, in the PAA containing only the siloxane unit out of the oxyalkylene unit or the siloxane unit, when TA-2 or DA-2 is used as the monomer A-2 containing the siloxane unit, TA-2 Or the amount of DA-2 (copolymerization ratio) is preferably 0.5 to 20 mol%, more preferably 1 to 10 mol%. The mol% representing the copolymerization ratio refers to a value calculated according to the following formula. In the case of using both of TA-2 and DA-2, the amount of use (copolymerization ratio) is preferably 0.5 to 20 mol%, more preferably 1 to 10 mol%.

The amount (copolymerization ratio) of TA-1, TA-2, DA-1 and DA-2 in the PAA containing both the oxyalkylene unit and the siloxane unit is preferably 0.5 to 20 mol% , More preferably from 1 to 10 mol%.

As described above, in the copolymerized PAA, the copolymerization ratio of the monomer containing oxyalkylene unit or siloxane unit is preferably 0.5 to 20 mol% based on the above formula, More preferably 10 mol%. That is, in the PAA containing oxyalkylene unit and / or siloxane unit, at least one of the amounts (copolymerization ratios) of TA-1, DA-1, TA-2 and DA- (Copolymerization ratio) is preferably within the above range.

Although an example of PAA has been described above, a method similar to that of PAA can be used for PIs other than PAA, for example, availability PI and / or PAI. The same applies to the preferable amount (copolymerization ratio) of the monomer containing an oxyalkylene unit or a siloxane unit.

For example, as the PAI solution, a PAI solution as disclosed in JP-A-2016-145300 can be used. The publication discloses the following <1> and <2>, and a PAI solution containing an oxyalkylene unit described in detail herein can also be used in the present invention. That is, in the present invention, the full text of the above publication is referred to and is referred to.

<1> A porous PAI obtained by a dry polycrystalline process, comprising PAI containing an oxyalkylene unit and having a porosity of 20 vol% or more and 95 vol% or less, an average pore diameter of 10 nm or more and 1000 nm or less PAI film.

&Lt; 2 &gt; A method for producing a porous PAI film, comprising applying a solution containing an oxyalkylene unit, a good solvent thereof and a poor solvent onto a substrate, and drying the resultant at a temperature of 200 DEG C or lower.

In the present invention, PAI containing a siloxane unit may also be used. This is a copolymerized PAI obtained by copolymerizing the tricarboxylic acid component, the DA-2 and the DA.

The PI solution can be obtained by a method in which a solution is obtained by polymerization reaction in a good solvent and then a poor solvent is added thereto, a method in which a suspension is obtained by polymerization reaction in a poor solvent, and then a good solvent is added thereto.

The concentration of PI in the PI solution is preferably 3 to 45% by mass, and more preferably 5 to 40% by mass.

The viscosity of the PI solution at 30 캜 is preferably in the range of 0.01 to 100 Pa · s, more preferably 0.1 to 50 Pa · s.

If necessary, various additives such as various surfactants and / or silane coupling agents may be added to the PI solution to the extent that the effect of the present invention is not impaired. If necessary, a polymer other than PI may be added to the PI solution within a range that does not impair the effect of the present invention.

In order to integrate the electrode active material layer with the porous PI coating, a PI solution may be coated on the surface of the electrode active material layer and dried to form a porous PI coating by causing phase separation. Further, the PI solution is coated on a substrate (e.g., a release film such as a polyester film) and dried to cause phase separation to form a porous PI film, which is then thermally compressed And then the substrate (releasing film) is peeled off, so that the laminated body can be integrated. In the case of thermocompression bonding, an adhesive may be applied to the surface of the porous PI coating in a dotted pattern, followed by thermocompression bonding with the electrode active material layer. On the other hand, for the application of the adhesive on the spot, for example, the methods disclosed in JP-A-2003-151638, WO-A-2014/014118 and JP-A-2016-42454 can be used.

As a method of applying the PI solution to the electrode active material layer, a method of continuously applying the PI solution by roll-to-roll and a method of applying the sheet may be employed, and any method may be employed. The coating apparatus can be carried out by a known method using a die coater, a multilayer die coater, a gravure coater, a comma coater, a reverse roll coater, a doctor blade coater or the like.

In the case where the PI precursor solution is used as the PI solution, the drying step includes a step 1 in which a solvent contained in the coating film is volatilized to induce phase separation to form a porous PAA coating, and a step 1 in which the porous PAA coating is heat- Thereby forming a porous PI film. The temperature of Step 1 is preferably about 100 to 200 占 폚, and the temperature of Step 2 is preferably less than 350 占 폚, for example, 200 to 320 占 폚. On the other hand, when PI other than PI precursor such as soluble polyimide or PAI is used, step 2 is not required. Further, in the step 2, the copolymerized PAA need not be imidized to 100%, and a copolymerized PAA component that is not imidized may remain. Here, the imidization ratio can be adjusted by selecting drying conditions, heat imidization conditions, and the like.

The PI used in the present invention preferably has a Tg of 150 DEG C or higher, more preferably 200 DEG C or higher. By doing so, it is possible to secure good heat resistance. On the other hand, Tg can be a value measured by DSC (differential thermal analysis).

The average pore diameter of the porous PI coating is preferably 10 nm or more and 2000 nm or less, more preferably 20 nm or more and 1300 nm or less, and more preferably 20 nm or more and 1000 nm or less. By performing the average pore size in this way, the ion resistivity of the PI coating can be sufficiently lowered, and the PI coating can be used as the polymer electrolyte. On the other hand, the average pore diameter is determined by obtaining a SEM (scanning electron microscope) image of the cross section of the porous PI coating at a magnification of 5000 to 20000 times and separating the pore and PI portions by commercially available image processing software .

The porosity of the porous PI coating is preferably 30 to 90% by volume, more preferably 40 to 80% by volume, still more preferably 45 to 80% by volume. By setting the porosity in this manner, good mechanical properties and good cushioning for stress relaxation accompanying changes in the volume of the active material are secured at the same time. Therefore, an electrode having excellent safety and good cycle characteristics can be obtained. The porosity of the porous PI coating is a value calculated from the apparent density of the porous PI coating and the true density (specific gravity) of the PI constituting the coating. Specifically, the porosity (volume%) is calculated by the following formula when the apparent density of the PI coating is A (g / cm ³ ) and the true density of PI is B (g / cm ³ ).

It is preferable that the porous PI coating strongly adheres to the active material layer. That is, from the viewpoint of improving the safety of the battery, it is preferable that the bonding strength between the electrode active material layer and the porous PI coating is higher than that of the electrode active material layer. Whether or not the bonding strength is higher than the strength of the electrode active material layer can be judged as to whether cohesion failure or interface peeling occurs at the interface when the electrode active material layer is peeled from the PI coating. It is determined that the strength of the bonding interface is higher than the strength of the electrode active material layer when cohesive failure occurs. It is determined that cohesive failure occurs when a piece of the active material layer adheres to a part of the surface of the PI coating after peeling (surface of adhesion to the electrode active material layer). In the electrode of the present invention, such a high adhesive force greatly contributes to the improvement of the safety of the battery.

The thickness of the porous PI coating is preferably 0.5 to 100 mu m, more preferably 1 to 20 mu m.

The porous PI coating may be either insulating or conductive. When the porous PI coating is insulative, this layer is suitable because it also functions as a separator for preventing electrical contact between the positive electrode and the negative electrode of a charge storage element (for example, a lithium secondary battery). When the porous PI coating is made conductive, conductive particles such as carbon (graphite or carbon black) particles and / or metal (silver, copper, nickel, etc.) It may be added to the coating. From the viewpoint of ensuring the cushion property and adhesion of the porous PI coating, the blending amount of these conductive particles is preferably 20 mass% or less.

The porous PI film formed on the surface of the electrode is formed by using a known electrolyte (a solvent such as ethylene carbonate and dimethyl carbonate, a lithium salt such as LiPF _6, etc.) in the pore portion, Dissolved solution) is charged. As a result, the ionic conductivity is developed and can be used as a capacitor element electrode. In this way, the capacitor electrode in which the porous PI film is formed may be a film having ion conductivity at the time of cell formation, but it is preferable that an electrolyte is contained in part or all of the pore portion in advance and a coating having ionic conductivity The film may be abbreviated as &quot; polymer electrolyte PI film &quot;). In order to do so, the solution containing the electrolyte may be impregnated into the porous PI film and filled in the pores. Such a method is known, and for example, a method as described in Electrochimica Acta 45 (2000) 1347-1360, Electrochimica Acta 204 (2016) 176-182 may be used. The solution containing the electrolyte may contain, for example, a &quot; gelling polymer &quot; as disclosed in Japanese Patent Application Laid-Open No. 2006-289985. Further, by using a solution containing an electrolyte such as a lithium salt (this solution may be abbreviated as &quot; PI-L solution &quot; in some cases) in the PI solution for forming a porous film, PI coating can be obtained. That is, a PI coating having a phase separation structure and having at least two phases by coating and drying the PI-L solution on the surface of the electrode active material layer, wherein one side of the PI coating is PI and at least one phase of the other side is electrolyzed (Solid or liquid) containing the fluorine-containing compound (s).

Specific lithium salt of the PI-L solution examples, there may be mentioned the _{LiCl, LiBr, LiI, LiClO 4} , LiBF 4, LiAsF 6, LiPF 6, LiCF 3 SO 3, LiN (CF 3 SO 2) 2. These may be used alone, or two or more of them may be used in combination. Among these, LiPF ₆ and LiN (CF ₃ SO ₂ ) ₂ are preferable. The content of the lithium salt is preferably 5 to 200% by mass, more preferably 20 to 150% by mass with respect to the mass of the poor solvent in the PI solution. By coating a solution having such a composition on the surface of the electrode active material layer and drying it, a polymer electrolyte PI film can be obtained. On the other hand, in the polymer electrolyte PI film, a part of the solvent (good solvent and poor solvent) in the PI-L solution may remain in the polymer electrolyte PI film in a form solvated with the lithium salt.

(To the electrolytic solution filled in the pores), the porous PI film, and the polymer electrolyte PI film is, ions are ion resistivity which is an index of conductivity, and 5Ωcm ² or less is preferable, and more preferably not more than 4Ωcm ^2, 3Ωcm ² is more preferably not more than Do. When the ion resistivity is within the above range, good charge / discharge characteristics of the lithium secondary battery using the electrode of the present invention can be secured. The ion resistivity (Rs-PI) of these PI coatings can be calculated, for example, by the following method. That is, assuming that the ion resistivity of only the active material layer filled with the electrolyte formed on the current collector is Rs-1, and the ion resistivity of the laminate having the PI coating formed thereon is Rs-2, Rs- By subtracting 1 from this value. Rs-1 and Rs-2 can be determined by forming a measuring cell using a lithium foil and the current collector as electrodes, using a commercially available separator as required, and measuring the impedance at 100 KHz at 25 deg. have.

An electrode active material layer in which a PI film having a phase separation structure is laminated is a layer formed on a current collector of a capacitor element (for example, a lithium secondary battery) of the present invention, and is a generic name of a positive electrode active material layer and a negative electrode active material layer.

As the current collector, a metal foil such as copper foil, stainless foil, nickel foil or aluminum foil can be used. An aluminum foil is preferably used for the anode, and a copper foil is preferably used for the cathode. The thickness of these metal foils is preferably 5 to 50 mu m, more preferably 9 to 18 mu m. The surface of these metal foils may be roughened and / or rust-proofed to improve adhesion 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 particle, it is preferable that the lithium ion storage material can absorb and store lithium ions. Examples of the material include oxide-based (LiCoO ₂ , LiNiO ₂ ), iron phosphate (LiFePO _4, etc.) Polythiophene, and the like). Of these, LiCoO ₂ , LiNiO ₂ , and LiFePO ₄ are preferable. The positive electrode active material layer may contain about 1 to 30 mass% of conductive particles such as carbon (graphite, carbon black, etc.) particles and / or metal (silver, copper, nickel, etc.) particles in order to lower the internal resistance .

The negative electrode active material layer is, for example, a layer obtained by binding negative electrode active material particles with a resin binder. The material used as the negative electrode active material particles is preferably one capable of storing lithium ions, and examples thereof include graphite, amorphous carbon, silicon, and tin-based active material particles. Of these, graphite particles and silicon-based particles are preferable. Examples of the silicon-based particles include particles of silicon, a silicon alloy, a silicon-silicon dioxide composite, and the like. Of these silicon-based particles, particles of silicon alone are preferable. Silicon group refers to crystalline or amorphous silicon having a purity of 95 mass% or more. The negative electrode active material layer may contain about 1 to 30 mass% of conductive particles such as carbon (graphite, carbon black, etc.) particles and / or metal (silver, copper, nickel, etc.) particles in order to lower the internal resistance . Lithium foil and lithium alloy foil can be used as the negative electrode active material layer.

The particle size of the active material particles and the conductive particles is preferably 50 占 퐉 or less and more preferably 10 占 퐉 or less in both the positive electrode and the negative electrode. The particle diameter is usually 0.1 μm or more, preferably 0.5 μm or more, because binding with a resin binder becomes difficult even if it is too small.

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

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

As the resin binder for binding the active material particles described above, for example, polyvinylidene fluoride (PVDF), a vinylidene fluoride hexafluoropropylene copolymer, a vinylidene fluoride tetrafluoroethylene copolymer, Styrene-butadiene copolymer rubber (SBR), polytetrafluoroethylene, polypropylene, polyethylene, PI, and the like. Of these, PVDF, SBR and PI are preferred.

A commercially available product can be used as the laminate having the active material layer formed on the collector as described above. For example, a commercially available product may be used.

That is, a dispersion containing the above-described binder, active material particles and a solvent (hereinafter sometimes abbreviated as "active material dispersion") is applied to the surface of the metal foil as a current collector and dried to form an electrode active material layer .

Example

Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to the examples.

The electrode active material layers (for positive electrode and negative electrode) formed on the current collector used in the following examples and comparative examples were obtained as follows.

(Cathode active material layer)

86 parts by mass of LiFePO ₄ particles (average particle diameter 0.5 μm) as a positive electrode active material, 8 parts by mass of carbon black (acetylene black) as a conductive additive and 6 parts by mass of PVDF as a binder resin were uniformly dispersed in NMP to prepare a positive electrode active material dispersion . This dispersion was applied to an aluminum foil having a thickness of 15 m as a cathode current collector, and the obtained coating film was dried at 130 DEG C for 10 minutes and then hot-pressed to obtain a cathode active material layer having a thickness of 50 mu m.

(Negative electrode active material layer-1)

85 parts by mass of graphite particles (average particle diameter 8 占 퐉) as a negative electrode active material, 5 parts by mass of carbon black (acetylene black) as a conductive additive and 10 parts by mass of PI as a binder resin were uniformly dispersed in NMP, Thereby obtaining an anode active material dispersion. This dispersion was applied to a copper foil having a thickness of 18 mu m as an anode current collector. The obtained coating film was dried at 120 DEG C for 10 minutes, heat-treated at 300 DEG C for 60 minutes, and hot pressed to obtain a negative electrode active material layer having a thickness of 50 mu m. On the other hand, "U Imide Varnish CR" manufactured by Unitika Co., Ltd. was used as the PI.

(Anode active material layer-2)

98 parts by mass of graphite particles (average particle diameter 8 占 퐉) as negative active material, 1 part by mass of carboxymethyl cellulose and 1 part by mass of SBR as a binder resin were uniformly dispersed in water to obtain a negative electrode active material dispersion having a solid content concentration of 25% by mass. This dispersion was applied to a copper foil having a thickness of 10 占 퐉 as an anode current collector, and the obtained coating film was dried at 120 占 폚 for 10 minutes and then hot-pressed to obtain a negative electrode active material layer having a thickness of 40 占 퐉.

(Evaluation method of electrode)

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

The electrode was punched out in a circle having a diameter of 16 mm, and a separator made of a porous film made of polyethylene and a lithium foil were sequentially laminated on the porous PI coating side of the porous polyimide film and housed in a coin-shaped external container made of stainless steel. An electrolytic solution (a 1M LiPF ₆ solution in which a solvent mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 1: 1 in volume ratio was mixed as a solvent) was injected into the outer container, and a stainless steel cap was put on the outer container through a packing And the battery can was sealed to obtain a cell for evaluation. Using this cell, the ion resistivity (Rs-PI) was calculated by measuring the impedance at 100 KHz by the above-described method. The discharge capacity and cycle characteristics were evaluated using these cells.

&Lt; Example 1 &gt;

0.97 mol of DADE and 0.03 mol of PPGME (number average molecular weight 2000: Pammin D2000 manufactured by Huntsman), DMAc and a mixed solvent of tetraethylene glycol dimethyl ether (DMAc / tetra The mixing ratio of ethylene glycol dimethyl ether was 2/8 by mass ratio) and stirred to dissolve the diamine component. While the solution was cooled to 30 占 폚 or lower with a jacket, 1.01 mole of PMDA was gradually added and polymerization reaction was carried out at 40 占 폚 for 5 hours to obtain a copolymerized PAA solution (P-1: solid content concentration of 15 mass% ).

&Lt; Example 2 &gt;

A copolymerized PAA solution (P-2) was obtained in the same manner as in Example 1 except that "DADE: 0.97 mole" was changed to "DADE: 0.8 mole and BAPP: 0.17 mole".

&Lt; Example 3 &gt;

A copolymerized PAA solution (P-3) was obtained in the same manner as in Example 1 except that "PMDA: 1.01 mole" was changed to "0.81 mole of PMDA and 0.20 mole of BPDA".

<Example 4>

Copolymerized PAA solution (P-4) was obtained in the same manner as in Example 1 except that "PMDA: 1.01 mole" was changed to "BPDA: 1.01 mole".

&Lt; Example 5 &gt;

A copolymerized PAA solution (P-5) was obtained in the same manner as in Example 1 except that "DADE: 0.97 mole, PPGME: 0.03 mole" was changed to "DADE: 0.94 mole, PPGME: 0.06 mole".

&Lt; Example 6 &gt;

Except that the mixing ratio of the mixed solvent (DMAc / tetraethylene glycol dimethyl ether) was 1/9 by mass ratio, and the solid content concentration of the copolymerized PAA solution was 10 mass%, copolymerized PAA To obtain a solution (P-6).

&Lt; Example 7 &gt;

The same procedure as in Example 2 was carried out except that the mixing ratio of the mixed solvent (DMAc / tetraethylene glycol dimethyl ether) was 1/9 by mass ratio and the solid content concentration of the copolymerized PAA solution was 10 mass% To obtain a solution (P-7).

&Lt; Example 8 &gt;

0.97 mol of DADE and 0.03 mol of DASM (number average molecular weight of about 860: KF-8010, manufactured by Shin-Etsu Chemical Co., Ltd.), DMAc and tetraethylene glycol dimethyl ether in a nitrogen atmosphere, / Tetraethylene glycol dimethyl ether was added in a mass ratio of 3/7) and the mixture was stirred. 1.03 mol of PMDA was slowly added to this solution at room temperature, and polymerization reaction was carried out at 60 占 폚 for 5 hours to obtain a copolymerized PAA solution (P-8: solid content concentration of 16% by mass) into which a siloxane unit was introduced.

&Lt; Example 9 &gt;

The P-1 obtained in Example 1 was coated on the surface of the negative electrode active material layer-1, dried at 130 占 폚 for 10 minutes, and heat-treated at 250 占 폚 for 60 minutes under a nitrogen atmosphere to obtain a porous PI coating having a thickness of 15 占 퐉, (Negative electrode) &quot; A-1 &quot; formed on the surface of layer-1 was obtained. The porous PI coating was firmly adhered to the surface of the negative electrode active material layer. The SEM image of the section of the cathode "A-1" and the SEM image of the section of the PI coating section are shown in FIGS. 1 and 2, respectively. By the image processing software, the pore portion and the PI portion were analyzed and analyzed. As a result, the average pore size of the porous PI film was 450 nm. The porosity was 65% by volume.

Using a cathode "A-1", a cell was prepared by the above-mentioned method and the ion resistivity was measured. The Rs-PI of the porous PI coating was 2.8? Cm ² . This cell was used to perform a charge-discharge cycle in which the battery was charged to 2.5 V at a constant current of 0.1 C at 30 캜 and discharged to 0.03 V. As a result, the initial discharge capacity of the cathode "A-1" was 310 [mAh / g-active material] and the discharge capacity after 10 cycles was 232 [mAh / g-active material], confirming a high initial discharge capacity and a good cycle characteristic . On the other hand, the voltage represents a voltage with respect to the ionization potential of lithium.

&Lt; Example 10 &gt;

An electrode (negative electrode) &quot; A-2 &quot;, in which a porous PI film having a thickness of 10 탆 was formed on the surface of the negative electrode active material layer, was obtained in the same manner as in Example 9. The average pore diameter of the porous PI film of the cathode "A-2" was 360 nm, and Rs-PI was 2.6 Ωcm ² .

&Lt; Example 11 &gt;

An electrode (negative electrode) &quot; A-3 &quot;, in which a porous PI film having a thickness of 8 탆 was formed on the surface of the negative electrode active material layer, was obtained in the same manner as in Example 9. The average pore diameter of the porous PI film of the cathode "A-3" was 560 nm, and the Rs-PI was 2.9? Cm ² .

&Lt; Example 12 &gt;

An electrode (negative electrode) &quot; A-4 &quot;, in which a porous PI film having a thickness of 8 m was formed on the surface of the negative electrode active material layer, was obtained in the same manner as in Example 9. The average pore diameter of the porous PI film of the cathode "A-4" was 880 nm, and the Rs-PI was 2.5 Ωcm ² .

&Lt; Example 13 &gt;

An electrode (negative electrode) &quot; A-5 &quot;, in which a porous PI film having a thickness of 10 탆 was formed on the surface of the negative electrode active material layer, was obtained in the same manner as in Example 9. The average pore diameter of the porous PI film of the cathode "A-5" was 670 nm, and Rs-PI was 2.9? Cm ² .

&Lt; Example 14 &gt;

An electrode (negative electrode) &quot; A-6 &quot;, in which a porous PI film having a thickness of 4 탆 was formed on the surface of the negative electrode active material layer, was obtained in the same manner as in Example 9. The average pore diameter of the porous PI coating of the negative electrode "A-6" was 270 nm, and Rs-PI was 2.1 Ωcm ² .

&Lt; Example 15 &gt;

An electrode (cathode) &quot; A-7 &quot;, in which a porous PI film having a thickness of 4 탆 was formed on the surface of the negative electrode active material layer, was obtained in the same manner as in Example 9 by using P-7 obtained in Example 7. The average pore diameter of the porous PI film of the cathode "A-7" was 310 nm, and Rs-PI was 2.4 Ωcm ² .

&Lt; Example 16 &gt;

P-1 obtained in Example 1 was coated on the surface of the aluminum foil with a release layer, dried at 130 占 폚 for 10 minutes, and heat-treated at 250 占 폚 for 60 minutes in a nitrogen atmosphere to obtain a porous PI film having a thickness of 7 占 퐉, Thereby obtaining a laminate formed on the surface. The porous PI film and the negative electrode active material layer-2 were thermocompression bonded at 200 占 폚 and then the aluminum foil was peeled off so that the porous PI film was bonded to the electrode (negative electrode) &quot; A- 8 &quot;. The average pore diameter of the porous PI film of the cathode "A-8" was 370 nm, and the Rs-PI was 2.7 Ωcm ² .

&Lt; Example 17 &gt;

P-1 obtained in Example 1 was applied to the surface of the positive electrode active material layer, dried at 130 占 폚 for 10 minutes, and heat-treated at 200 占 폚 for 60 minutes in a nitrogen atmosphere to obtain a porous PI coating having a thickness of 12 占 퐉. (Positive electrode) &quot; A-9 &quot; formed on the surface was obtained. The average pore diameter of the PI coating of the anode "A-9" was 920 nm.

A cell was prepared by using the positive electrode "A-9" in the manner described above, and the ion resistivity was measured. The Rs-PI of the PI coating was 3.0 Ωcm ² . This cell was used to carry out a charge-discharge cycle in which the battery was charged to 4.5 V at a constant current of 0.1 C at 30 캜 and discharged to 3.0 V at a constant current of 0.1 C. As a result, the initial discharge capacity of the anode "A-9" became 146 [mAh / g-active material] and the discharge capacity after 10 cycles became 159 [mAh / g-active material], confirming a high initial discharge capacity and a good cycle characteristic . On the other hand, the voltage represents a voltage with respect to the ionization potential of lithium.

&Lt; Example 18 &gt;

P-1 obtained in Example 1 was applied to the surface of the positive electrode active material layer and dried at 150 ° C for 10 minutes to obtain a porous PI film having a thickness of 4 μm as an electrode (positive electrode) "A-10" formed on the surface of the positive electrode active material layer &Lt; / RTI &gt; The average pore diameter of the PI coating of the anode "A-10" was 540 nm, and Rs-PI was 1.8 Ωcm ² .

&Lt; Example 19 &gt;

P-8 obtained in Example 8 was applied to the surface of the negative electrode active material layer-1, dried at 150 占 폚 for 10 minutes, and heat-treated at 250 占 폚 for 60 minutes in a nitrogen atmosphere to form a porous PI coating having a thickness of 3 占 퐉, (Negative electrode) &quot; A-11 &quot; The average pore diameter of the PI coating of the negative electrode "A-11" was 1200 nm, and the Rs-PI was 2.5 Ωcm ² .

&Lt; Example 20 &gt;

A PAI solution was obtained in accordance with the method described in Example 1 of JP-A-2016-145300. That is, 0.96 mole of trimellitic anhydride (TMA), 1 mole of 4,4'-diphenylmethane diisocyanate (MDI), 1 mole of polytetramethylene glycol ( Molecular weight 1000): 0.04 mol, NMP was added and stirred. The resulting solution was heated to 200 DEG C and reacted for 7 hours and then cooled to obtain a PAI solution into which an oxytetramethylene unit was introduced. To this solution, tetraethylene glycol dimethyl ether was added, and an oxyalkylene unit To thereby obtain the introduced copolymerized PAI solution (P-9: 11 mass%). The mass ratio of tetraethylene glycol dimethyl ether in this solution was 70 mass% with respect to the mixed solvent (NMP and tetraethylene glycol dimethyl ether).

&Lt; Example 21 &gt;

P-9 obtained in Example 20 was applied to the surface of the negative electrode active material layer-1, dried at 150 占 폚 for 10 minutes, and heat-treated at 250 占 폚 for 60 minutes in a nitrogen atmosphere to form a porous PI coating having a thickness of 3 占 퐉, (Negative electrode) &quot; A-12 &quot; The average pore diameter of the PI coating of the cathode "A-12" was 1800 nm, and the Rs-PI was 2.8? Cm ² .

&Lt; Comparative Example 1 &

PAA solution (R-1) was obtained in the same manner as in Example 1 except that "DADE: 0.97 mol, PPGME: 0.03 mol" was changed to "DADE: 1.00 mol".

&Lt; Comparative Example 2 &

(Negative electrode) &quot; B-1 &quot;, in which a porous PI film having a thickness of 15 탆 was formed on the surface of the negative electrode active material layer, was obtained in the same manner as in Example 9. The average pore diameter of the PI coating of the negative electrode "B-1" was 3200 nm, and the Rs-PI exceeded 10 Ωcm ² .

&Lt; Comparative Example 3 &

(Negative electrode) &quot; B-2 &quot;, in which a porous PI film having a thickness of 4 탆 was formed on the surface of the negative electrode active material layer, was obtained in the same manner as in Example 9. The average pore diameter of the PI coating of the negative electrode "B-2" was 3100 nm, and the Rs-PI exceeded 10 Ωcm ² .

As shown in the examples and comparative examples, the capacitor electrode of the present invention, such as a lithium secondary battery, has a porous structure in which an oxyalkylene unit or a siloxane unit having a small average pore size and high affinity for an electrolyte, The ionic resistivity of the PI coating is low. Therefore, it can be suitably used as a capacitor electrode such as a lithium secondary battery and a lithium ion capacitor having excellent safety, high discharge capacity and good cycle characteristics.

The PI solution of the present invention is useful for the production of electrodes used in electrical storage devices such as lithium secondary batteries, lithium ion capacitors, capacitors, and capacitors.

Claims (7)

A polyimide solution containing a good solvent for a polyimide and a poor solvent, wherein the polyimide contains an oxyalkylene unit and / or a siloxane unit in the main chain. The method according to claim 1,
A polyimide solution for a capacitor electrode, characterized in that the polyimide solution further contains a lithium salt. A method for manufacturing a capacitor element electrode comprising the step of forming a polyimide coating having a phase separation structure by applying the polyimide solution according to claim 1 or 2 onto a surface of an active material layer and then drying. A process for producing a polyimide film, comprising: forming a polyimide film having a phase-separated structure by applying the polyimide solution according to claim 1 or 2 to a substrate and drying the film; then thermally bonding the polyimide film to the surface of the active material, A method for manufacturing a capacitor element electrode, comprising the step of peeling a base material. The method according to claim 3 or 4,
Wherein the polyimide coating having a phase separation structure is a porous polyimide coating. The method according to claim 3 or 4,
Wherein the polyimide coating having a phase separation structure has at least two phases, one of the phases is a polyimide, and at least one phase of the other phase contains an electrolyte. An electrode in which a polyimide film having a phase separation structure is laminated and integrated on a surface of an active material layer, wherein the polyimide contains an oxyalkylene unit and / or a siloxane unit in its main chain.

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