JPWO2019031349A1 - Electrode for lithium secondary battery and method for manufacturing the same - Google Patents

Abstract

It is an object of the present invention to provide an electrode for a lithium secondary battery, which is excellent in safety and has a sufficiently reduced internal resistance, and a method for manufacturing the same. <1> A lithium secondary battery electrode in which a porous polyamideimide (PAI) layer is laminated and integrated on the surface of an electrode active material layer, and the porous PAI layer has the following features: .. 1) The ionic conductivity of the porous PAI layer is 0.6 mS/cm or more. 2) The thickness of the porous PAI layer is more than 1 μm and less than 30 μm. <2> A dispersion containing a binder, active material particles and a solvent is applied to the surface of a metal foil that is a current collector of an electrode for a lithium secondary battery and dried to form an electrode active material layer on the metal foil. After that, a coating liquid containing PAI and a solvent is applied to the surface of the electrode active material layer to form a coating film, and then the solvent in the coating film is removed, whereby phase separation occurs in the coating film. In the method for producing an electrode for a lithium secondary battery in which the electrode active material layer and the ion-permeable porous layer are integrally laminated, the PAI is a diamine component. As a mixed solvent comprising 4,4′-diaminodiphenyl ether as a solvent, the solvent being 5 parts by mass or more and 20 parts by mass or less of an amide solvent, and 95 parts by mass or less and 80 parts by mass or more of tetraglyme (TG) (however, The total amount of the amide-based solvent and TG is 100 parts by mass), The method for producing an electrode for a lithium secondary battery.

Description

The present invention relates to a lithium secondary battery electrode having excellent safety, high capacity and good charge/discharge cycle characteristics, and a method for producing the same.

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

In order to prevent this internal short circuit, in Patent Document 1, a solution in which a heat-resistant polymer such as polyamideimide (PAI) is dissolved is applied on the positive electrode surface, and the positive electrode is dipped in a coagulating liquid containing a poor solvent for PAI. Then, a method for producing a positive electrode for a lithium secondary battery in which a porous PAI layer and a positive electrode are integrated by depositing PAI and the like and drying it is proposed. However, since the ion permeability of the porous layer made of PAI or the like produced by such a method is not sufficient, the internal resistance of the electrode becomes high, and as a result, good charge/discharge characteristics cannot be obtained. there were. Furthermore, the method for obtaining a porous layer using the coagulation liquid described above has a problem as a manufacturing method from the viewpoint of environmental compatibility since waste liquid containing a poor solvent is generated from the coagulation bath.

As a method for solving the problem of the method using such a coagulating liquid, Patent Document 2 discloses that a uniform solution containing a good solvent and a poor solvent for a heat resistant polymer such as PAI is applied to the surface of an electrode and dried to form a porous film. Methods have been proposed for forming a textured layer.

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

However, even in the electrode obtained by this method, in order to be an electrode for a lithium secondary battery that can be charged and discharged in a short time, the ion permeability is not sufficient, and the ion permeability is further improved, It was necessary to obtain a porous PAI layer having a further reduced internal resistance.

Then, this invention solves the said subject, Comprising: It is excellent in safety and it aims at providing the electrode for lithium secondary batteries which internal resistance fell sufficiently, and its manufacturing method.

The present inventors have solved the above problems by an electrode in which a PAI chemical structure is specified and a porous PAI layer obtained from the PAI solution in which the solvent composition of the PAI solution for coating is specified is laminated and integrated. It was found that the present invention has been completed.

The present invention has the following gist.

<1> A lithium secondary battery electrode in which a porous PAI layer is laminated and integrated on the surface of an electrode active material layer, wherein the porous PAI layer has the following features.
1) The ionic conductivity of the porous PAI layer is 0.6 mS/cm or more.
2) The thickness of the porous PAI layer is more than 1 μm and less than 30 μm.
<2> A dispersion containing a binder, active material particles and a solvent is applied to the surface of a metal foil that is a current collector of an electrode for a lithium secondary battery and dried to form an electrode active material layer on the metal foil. After that, a coating liquid containing PAI and a solvent is applied to the surface of the electrode active material layer to form a coating film, and thereafter, the solvent in the coating film is removed, whereby phase separation occurs in the coating film. In the method for producing an electrode for a lithium secondary battery in which the ion-permeable porous layer is formed by laminating the electrode active material layer and the ion-permeable porous layer, PAI is used as a diamine component. A mixed solvent containing 4,4′-diaminodiphenyl ether (DADE) and containing 5 parts by mass or more and 20 parts by mass or less of an amide solvent and 95 parts by mass or less and 80 parts by mass or more of tetraglyme (TG). (However, the total amount of the amide-based solvent and TG is 100 parts by mass), The method for producing an electrode for a lithium secondary battery, wherein
<3> The method for producing an electrode for a lithium secondary battery, wherein the DADE content is 30 to 100 mol% based on all diamine components.

INDUSTRIAL APPLICABILITY The electrode for lithium secondary battery of the present invention has excellent ion permeability, and therefore has low internal resistance and excellent safety.
Therefore, it can be suitably used as an electrode for a lithium secondary battery that can be charged and discharged in a short time. Moreover, in the manufacturing method of the present invention, the electrode of the present invention can be easily manufactured by a simple process.

The electrode for a lithium secondary battery of the present invention is one in which a porous PAI layer is laminated and integrated on the surface of an electrode active material layer. The electrode for a lithium secondary battery is an electrode that constitutes a lithium secondary battery, and is a positive electrode in which a positive electrode active material layer is bonded to a positive electrode current collector, or a negative electrode active material layer is bonded to a negative electrode current collector. Negative electrode. The electrode active material layer is a generic term for the positive electrode active material layer and the negative electrode active material layer.

As the current collector, a metal foil such as a copper foil, a stainless foil, a nickel foil, or an 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 subjected to a surface roughening treatment or a rustproofing treatment for improving the adhesiveness to the active material layer.

The positive electrode active material layer is a layer obtained by binding the positive electrode active material particles with a binder. The material used as the positive electrode active material particles is preferably one that can store and store lithium ions, and examples thereof include those generally used as the positive electrode active material of a lithium secondary battery. For example, oxide type (LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ etc.), complex oxide type (LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ etc.), iron phosphate type (LiFePO ₄ , Li). ₂ FePO ₄ F, etc.), polymer compound-based (polyaniline, polythiophene, etc.) active material particles, and the like. Among 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 a layer obtained by binding the negative electrode active material particles with a binder. The material used as the negative electrode active material particles is preferably a material that can store and store lithium ions, and examples thereof include those generally used as the negative electrode active material of a lithium secondary battery. For example, graphite, amorphous carbon, silicon-based, tin-based active material particles and the like can be mentioned. Of these, graphite particles and silicon-based particles are preferable. Examples of the silicon-based particles include particles of silicon simple substance, silicon alloy, silicon/silicon dioxide composite, and the like. Among these silicon-based particles, particles of silicon alone (hereinafter, may be abbreviated as “silicon particles”) are preferable. Single silicon means 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, etc. are mixed in an amount of about 1 to 30% by mass. May be.

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

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

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

As the binder for binding the active material particles, for example, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, styrene-butadiene copolymer rubber, poly Examples thereof include tetrafluoroethylene, polypropylene, polyethylene, imide-based polymers and the like. Among these, polyvinylidene fluoride, styrene/butadiene copolymer rubber, and imide polymer are preferable.

For the active material layer of the positive electrode or the negative electrode, a dispersion containing a binder, active material fine particles and a solvent can be applied and dried to form an electrode active material layer on the metal foil.

In the electrode of the present invention, porous PAI having high ion permeability is laminated and integrated on the surface of the electrode active material layer.

PAI that constitutes the porous PAI layer is a polymer obtained by performing a polycondensation reaction of a tricarboxylic acid component as a raw material and a diamine component.

The tricarboxylic acid component of PAI is an organic compound having three carboxyl groups (including its derivatives) and one or more aromatic rings per molecule, and at least two carboxyl groups among the three carboxyl groups are included. The group is arranged at a position capable of forming an acid anhydride form.

Examples of the aromatic tricarboxylic acid component include a benzene tricarboxylic acid component and a naphthalene tricarboxylic acid component.

Specific examples of the benzenetricarboxylic acid component include trimellitic acid, hemimellitic acid, and their anhydrides and their monochlorides.

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

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

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

Further, a part of the tricarboxylic acid component is terephthalic acid, isophthalic acid, pyromellitic acid, 3,3',4,4'-biphenyltetracarboxylic acid, 3,3',4,4'-benzophenonetetracarboxylic acid. You may use what was substituted by the components such as.

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

The PAI diamine component forming the porous PAI layer of the present invention preferably contains DADE.
The DADE is more preferably 30 to 100 mol%, further preferably 40 to 100 mol%, and particularly preferably 50 to 100 mol% based on the total diamine component of PAI. Thus, by using DADE as the diamine component, good ion permeability can be ensured when the porous PAI layer is formed. The mechanism of the effect of including DADE is not clear, but the ether bond of DADE and the ether bond of TG, which is a poor solvent for PAI, which will be described later, interact with each other to form a homogeneous structure. It is considered that a porous structure is formed and good ion permeability is exhibited.

Specific examples of the diamine component used by copolymerizing with DADE include m-phenylenediamine (MDA), p-phenylenediamine, 4,4′-diphenylmethanediamine (DMA), 4,4′-diphenyletherdiamine, diphenylsulfone- 4,4'-diamine, diphenyl-4,4'-diamine, o-tolidine, 2,4-tolylenediamine, 2,6-tolylenediamine, xylylenediamine, naphthalenediamine, and diisocyanate derivatives thereof You can

Among these diamine components, MDA is preferable.

The diamine component used by copolymerizing with DADE may be used alone or in combination of two or more kinds.

PAI usually has a glass transition temperature of 200° C. or higher. As the glass transition temperature, a value measured by DSC (differential thermal analysis) is used.

The PAI used in the present invention can be obtained using a known method. That is, for example, use one in which the tricarboxylic acid component and the diamine component, which are raw materials, are mixed in approximately equimolar amounts, and PAI is isolated as powder from a solution obtained by polymerizing the tricarboxylic acid component and the diamine component in the mixed solvent. You can

The ionic conductivity of the porous PAI layer of the present invention needs to be 0.6 mS/cm or more. The ionic conductivity is preferably 0.7 mS/cm or more, more preferably 0.8 mS/cm or more, and further preferably 0.9 mS/cm or more. In an electrode in which a porous layer made of a heat-resistant polymer such as polyamideimide (PAI) is laminated and integrated, a porous layer exhibiting such high conductivity has not been heretofore known, and the porous PAI of the present invention is known. The layers are used as an arrowhead.

The ionic conductivity of the porous PAI layer can be obtained by an AC impedance method which is a known evaluation method. Specifically, the impedance of a cell composed of a laminated electrode impregnated with an electrolyte solution and a cell composed of a non-laminated electrode is measured, and the resistance value (Ω) of the real part in the Nyquist plot of both cells is calculated. Can be calculated from the value “A” (Ω) obtained by subtracting the resistance value of the non-laminated electrode from the following formula.
Ionic conductivity (mS/cm) = 0.1*B/(A*C)
Here, C represents the electrode area (cm ² ) and B represents the thickness (μm) of the porous PAI layer. The ionic conductivity is a value evaluated as a laminated electrode in an electrolytic solution, and is not necessarily the same value as the ionic conductivity in the bulk state of a usual polymer material.

The porous PAI of the present invention needs to have a thickness of more than 1 μm and less than 30 μm, and preferably more than 5 μm and less than 25 μm. More preferably, it is more than 5 μm and less than 20 m. When the thickness is 1 μm or less, the insulating property of the porous PAI layer is insufficient, and the safety as an electrode may not be ensured. Further, when the thickness is 30 μm or more, the ion permeability is impaired and the internal resistance increases when used as an electrode.
The thickness of the porous PAI indicates a value calculated by acquiring an SEM image obtained by observing an electrode cross section in which the porous PAI is laminated and integrated with an electron microscope at a magnification of 500 times.

On the surface of the electrode active material layer described above, for example, a coating liquid containing PAI and a solvent is applied to form a coating film, and then the solvent in the coating film is removed to form a phase in the coating film. Separation can occur to form a porous PAI layer.

This coating liquid can be obtained by dissolving the PAI powder described above in a solvent. As the solvent used here, it is preferable to use a mixed solvent composed of an amide solvent that is a good solvent for PAI and TG (boiling point: 275° C.) that is a poor solvent for PAI. Specific examples of the amide-based solvent include N-methyl-2-pyrrolidone (NMP boiling point: 202°C), N,N-dimethylformamide (boiling point: 153°C), N,N-dimethylacetamide (DMAc boiling point: 166°C). Can be mentioned. These amide solvents may be used alone or in combination of two or more. Among these, NMP is preferable. Here, the good solvent refers to a solvent having a solubility of 1% by mass or more in PAI at 25°C. The poor solvent refers to a solvent having a PAI solubility of less than 1% by mass at 25°C.

The mixed solvent is preferably a mixed solvent composed of 5 parts by mass or more and 20 parts by mass or less of an amide solvent and 95 parts by mass or less and 80 parts by mass or more of TG, and preferably 10 parts by mass or more and 20 parts by mass or less. It is more preferable to use a mixed solvent composed of the amide solvent of (4) and 90 parts by mass or less and 80 parts by mass or more of TG. However, the mixed solvent is a mixture of both amide solvent and TG solvent so that the total amount thereof is 100 parts by mass. By using such a mixed solvent, when the coating film is dried and removed, phase separation due to the difference in boiling points of the solvents constituting the mixed solvent occurs efficiently in the coating film, and high ion permeability is obtained. The porous layer can be formed and the electrode active material layer and the porous PAI can be laminated and integrated.

Known additives such as various surfactants and organic silane coupling agents may be added to the PAI coating liquid within a range that does not impair the effects of the present invention. Further, a polymer other than PAI may be added to the PAI coating liquid within a range that does not impair the effects of the present invention. Further, if necessary, a filler such as alumina, silica, boehmite, kaolin, etc. may be added.

The PAI coating liquid is applied to the surface of the electrode active material layer, dried at 100 to 150° C., and then heat-treated at 250 to 350° C., if necessary, to form a porous PAI having good ion permeability. be able to. The porosity of the formed porous PAI can be 30 to 90% by volume. The average pore diameter of the imide porous layer can be 0.1 to 10 μm. By setting the porosity and the average pore diameter in such ranges, good ion permeability is secured. The porosity and the average pore diameter can be adjusted by selecting the type of amide solvent in the PAI coating liquid and the blending amount of TG. The porosity can also be adjusted by selecting the drying conditions.
The porosity (volume %) is calculated using the following formula when the apparent density of the imide porous layer is A (g/cm ³ ) and the true density of PAI is B (g/cm ³ ). be able to.
Porosity (volume %)=100-A* (100/B)

When applying the PAI coating liquid to the electrode surface, a method of continuously applying by a roll-to-roll method or a method of applying in a sheet-like manner can be adopted, and any method may be used. As the coating device, a die coater, a multilayer die coater, a gravure coater, a comma coater, a reverse roll coater, a doctor blade coater, or the like can be used.

In the electrode of the present invention, the coating liquid described above is applied onto a base material having releasability such as a polyester film and an aluminum foil, and dried to form a porous PAI film, which is then applied to the electrode active material. It is also possible to obtain it by laminating and integrating the above, and then peeling the base material having releasability.

The electrode (positive electrode and negative electrode) of the present invention can form a cell by laminating a normal lithium secondary battery separator made of porous polyolefin or the like between the electrodes. The electrode of the present invention can also be used as an electrode for forming a so-called "separatorless" cell without using such a separator.

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 (negative electrode) active material layer used in the following Examples and Comparative Examples was obtained as follows.

88 parts by mass of graphite particles (average particle size 8 μm) that is a negative electrode active material, 5 parts by mass of carbon black (acetylene black) that is a conductive additive, and 7 parts by mass of PVDF that is a binder resin were added to N-methyl-2-pyrrolidone. It was uniformly dispersed in it 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 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 form a film having a thickness of 100 μm formed on the copper foil. An electrode (N-1) provided with a negative electrode active material layer was obtained.

The ionic conductivity of the electrodes obtained in the following examples and comparative examples was evaluated by the following method.

An electrode in which a porous PAI layer was laminated and integrated on the surface of N-1 was punched out into a circular shape having a diameter of 1.6 cm to form a symmetrical cell consisting of electrode/separator made of polyethylene porous membrane (thickness 20 μm)/electrode. Electrolyte solution (solvent: mixed solvent of ethylene carbonate and dimethyl carbonate mixed in a volume ratio of 1:1 and electrolyte: 1MLiPF ₆ ) is injected into a stainless steel flat cell (manufactured by Takumi Giken). To obtain a cell (C-1) for evaluation. On the other hand, in the same manner as described above, N-1 (non-laminated electrode) was used to obtain a cell (C-2) for evaluation.
The impedances of C-1 and C-2 were measured using an AC impedance measuring device (Celltest System 1470E manufactured by Solartron Analysis). The measurement conditions were as follows.
<Measurement conditions>
Measurement temperature: 25°C
Frequency range: 100mHz to 1MHz
Amplitude: ±10 mV
The resistance value (Ω) of the real part in the Nyquist plot obtained by this AC impedance measurement is obtained, and the resistance value of C-2 (R-2) is subtracted from the resistance value of C-1 (R-1). The value (A) divided by 2 was used as the resistance value (Ω) of the porous PAI layer, and the ionic conductivity of the porous PAI layer was calculated using the following formula.
Ionic conductivity (mS/cm) = 0.0391*B/A
Here, B represents the thickness (μm) of the porous PAI layer.

[Example 1]
In a dry nitrogen gas atmosphere, 0.07 mol of DADE and 0.03 mol of MDA were placed in a glass reaction vessel, NMP and 0.1 mol of triethylamine were added thereto, and the mixture was stirred to produce an NMP solution having a solid content concentration of 15% by mass. Got Thereafter, while maintaining this solution at 10° C. or lower, a 0.1 mol TAC NMP solution (solid content concentration: 20 mass %) was slowly added dropwise under stirring. After the dropping was completed, the solution was returned to room temperature and stirred for 2 hours. The obtained solution was poured into a large amount of water to cause precipitation of PAI, which was filtered and washed to obtain a yellow solid, which was then heated at 200° C. for drying and imidization. By doing so, PAI powder (AP) was obtained. The DSC Tg of AP was 285°C. Next, AP was dissolved in a mixed solvent of NMP and TG to obtain a PAI coating liquid (L-1) having a solid content concentration of 9% by mass. Here, the mixing ratio of NMP and TG was such that the amount of TG was 85 mass% with respect to the mass of the mixed solvent. L-1 was applied to the surface of the electrode (N-1) and dried at 150° C. for 20 minutes to obtain an electrode (P-1) having a 10 μm-thick porous PAI layer. The evaluation results of this porous PAI layer are shown in Table 1.

[Example 2]
An electrode (P-2) having a porous PAI layer formed was obtained in the same manner as in Example 1 except that only 0.1 mol of DADE was used as the diamine and the thickness of the porous PAI layer was 8 μm. The evaluation results of this porous PAI layer are shown in Table 1.

[Example 3]
An electrode (P-3) having a porous PAI layer formed was obtained in the same manner as in Example 1 except that "a mixture of 0.05 mol of DADE and 0.05 mol of MDA" was used as the diamine. The evaluation results of this porous PAI layer are shown in Table 1.

[Example 4]
An electrode (P-4) having a porous PAI layer formed was obtained in the same manner as in Example 1 except that "a mixture of DADE 0.03 mol and MDA 0.07 mol" was used as the diamine. The evaluation results of this porous PAI layer are shown in Table 1.

[Example 5]
An electrode (P-4) having a porous PAI layer formed was obtained in the same manner as in Example 1 except that DMAc was used as the amide solvent and the thickness of the porous PAI layer was 6 μm. The evaluation results of this porous PAI layer are shown in Table 1.

[Example 6]
An electrode (P-6) having a porous PAI layer formed was obtained in the same manner as in Example 1 except that "a mixture of 0.05 mol of DADE and 0.05 mol of DMA" was used as the diamine. The evaluation results of this porous PAI layer are shown in Table 1.

[Example 7]
An electrode (P-7) having a porous PAI layer formed was obtained in the same manner as in Example 1 except that the thickness of the porous PAI was 15 μm. The evaluation results of this porous PAI layer are shown in Table 1.

[Example 8]
An electrode (P-8) having a porous PAI layer formed was obtained in the same manner as in Example 1 except that the TG amount of the mixed solvent was 82% by mass with respect to the mixed solvent mass. The evaluation results of this porous PAI layer are shown in Table 1.

[Example 9]
An electrode (P-9) on which a porous PAI layer was formed in the same manner as in Example 1 except that the TG amount of the mixed solvent was 82% by mass relative to the mixed solvent mass, and the thickness of the porous PAI layer was 15 μm. ) Got. The evaluation results of this porous PAI layer are shown in Table 1.

[Example 10]
An electrode (P-10) having a porous PAI layer formed was obtained in the same manner as in Example 1 except that the TG amount of the mixed solvent was 87% by mass with respect to the mixed solvent mass. The evaluation results of this porous PAI layer are shown in Table 1.

[Comparative Example 1]
An electrode (R-1) having a porous PAI layer formed was obtained in the same manner as in Example 1 except that "a mixture of 0.01 mol of DADE and 0.09 mol of MDA" was used as the diamine. The evaluation results of this porous PAI layer are shown in Table 1.

[Comparative example 2]
An electrode (R-2) having a porous PAI layer formed was obtained in the same manner as in Example 1 except that "a mixture of 0.01 mol of DADE and 0.09 mol of DMA" was used as the diamine. The evaluation results of this porous PAI layer are shown in Table 1.

[Comparative Example 3]
An electrode on which a porous PAI layer was formed in the same manner as in Example 1 except that "a mixture of 0.01 mol of DADE and 0.09 mol of MDA" was used as the diamine and the thickness of the porous PAI layer was 6 μm. R-3) was obtained. The evaluation results of this porous PAI layer are shown in Table 1.

[Comparative Example 4]
An electrode (R-4) having a porous PAI layer formed was obtained in the same manner as in Example 1 except that the TG amount of the mixed solvent was 75% by mass with respect to the mixed solvent mass. The evaluation results of this porous PAI layer are shown in Table 1.

[Comparative Example 5]
An electrode (R-5) having a porous PAI layer formed was obtained in the same manner as in Example 1 except that the TG amount of the mixed solvent was 65% by mass with respect to the mixed solvent mass. The evaluation results of this porous PAI layer are shown in Table 1.

[Comparative Example 6]
An electrode (R-6) having a porous PAI layer formed was obtained in the same manner as in Example 1 except that the thickness of the porous PAI layer was 35 μm. The evaluation results of this porous PAI layer are shown in Table 1.

[Comparative Example 7]
An electrode (R-7) having a porous PAI layer formed was obtained in the same manner as in Example 1 except that only 0.1 mol of DADE was used as the diamine and the thickness of the porous PAI layer was 35 μm. The evaluation results of this porous PAI layer are shown in Table 1.

[Comparative Example 8]
An electrode (R-8) having a porous PAI layer formed was obtained in the same manner as in Example 1 except that only 0.1 mol of DMA was used as the diamine. The evaluation results of this porous PAI layer are shown in Table 1.

[Comparative Example 9]
An electrode (R-9) having a porous PAI layer formed was obtained in the same manner as in Example 1 except that only 0.1 mol of MDA was used as the diamine. The evaluation results of this porous PAI layer are shown in Table 1.

[Comparative Example 10]
An electrode (R-10) having a porous PAI layer formed was obtained in the same manner as in Example 1 except that TG of the mixed solvent was triethylene glycol dimethyl ether (TRG). The evaluation results of this porous PAI layer are shown in Table 1.

[Comparative Example 11]
An electrode (R-11) on which a porous PAI layer was formed was obtained in the same manner as in Example 1 except that TG of the mixed solvent was diethylene glycol dimethyl ether (DG). The evaluation results of this porous PAI layer are shown in Table 1.

[Comparative Example 12]
An electrode (R-12) having a porous PAI layer formed was obtained in the same manner as in Example 1 except that NMP was the only solvent for dissolving the AP obtained in Example 1. The evaluation results of this porous PAI layer are shown in Table 1.

[Comparative Example 13]
An electrode (R-13) on which a porous PAI layer was formed was obtained in the same manner as in Example 1 except that "a mixture of DADE 0.02 mol and MDA 0.08 mol" was used as the diamine. The evaluation results of this porous PAI layer are shown in Table 1.

[Comparative Example 14]
An electrode (R-14) having a porous PAI layer formed was obtained in the same manner as in Example 1 except that "a mixture of 0.02 mol of DADE and 0.08 mol of DMA" was used as the diamine. The evaluation results of this porous PAI layer are shown in Table 1.

As described above in Examples and Comparative Examples, the resistance of the porous PAI layer of the present invention having a specific ionic conductivity and thickness is sufficiently reduced, and therefore, an electrode in which these layers are laminated and integrated is formed. Can be suitably used as an electrode for a lithium secondary battery with improved safety. Further, it is understood that this effect can provide good cycle characteristics. Further, according to the manufacturing method of the present invention, it is possible to manufacture an electrode having excellent safety by a simple process having high environmental compatibility.

Since the lithium secondary battery electrode of the present invention has a sufficiently low internal resistance, it can be suitably used as an electrode for a lithium secondary battery which can be charged and discharged in a short time and has high safety. According to the manufacturing method of the present invention, an electrode having excellent safety can be manufactured by a simple process having high environmental compatibility.

Claims (3)

An electrode for a lithium secondary battery in which a porous polyamideimide (PAI) layer is laminated and integrated on the surface of an electrode active material layer, wherein the porous PAI layer has the following features.
1) The ionic conductivity of the porous PAI layer is 0.6 mS/cm or more.
2) The thickness of the porous PAI layer is more than 1 μm and less than 30 μm. On the surface of the metal foil that is the current collector of the lithium secondary battery electrode, a dispersion containing a binder, active material particles and a solvent is applied and dried to form an electrode active material layer on the metal foil, and then, A coating liquid containing PAI and a solvent is applied to the surface of the electrode active material layer to form a coating film, and then the solvent in the coating film is removed to cause phase separation in the coating film. In the method for producing an electrode for a lithium secondary battery in which an ion-permeable porous layer is formed by stacking and integrating the electrode active material layer and the ion-permeable porous layer, PAI is used as a diamine component in an amount of 4,4. A mixed solvent containing ′-diaminodiphenyl ether (DADE), the solvent being 5 parts by mass or more and 20 parts by mass or less of an amide solvent, and 95 parts by mass or less and 80 parts by mass or more of tetraglyme (TG) (however, The total amount of the amide solvent and TG is 100 parts by mass), The method for producing an electrode for a lithium secondary battery according to claim 1, wherein The method for producing an electrode for a lithium secondary battery according to claim 2, wherein the content of DADE is 30 to 100 mol% based on all diamine components.