JP7349708B2 - Coating liquid for lithium secondary battery electrodes, method for producing electrodes for lithium secondary batteries, and electrodes for lithium secondary batteries - Google Patents

Description

The present invention relates to a simple and economical method for producing an electrode for a lithium secondary battery that is highly safe and has good charge-discharge cycle characteristics.

In lithium secondary batteries, scratches or irregularities on the electrode surface may destroy the electrical insulation of the separator in contact with the electrode. As a result, electrical internal short circuits 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 surface of the electrode active material layer. For example, in Patent Documents 1 and 2, as a method for forming an ion-permeable protective layer, after forming a heat-resistant protective layer-forming coating film made of polyimide or the like on the electrode surface, and before drying, A method has been proposed in which a porous protective layer is obtained by causing phase separation within the coating film by immersing the coating in a coagulation bath containing a coagulation liquid such as water or methyl alcohol. However, since the electrode obtained by this method has low adhesion between the active material layer and the porous layer, the prevention effect against short circuits is not necessarily sufficient, and improvements are needed from the perspective of ensuring battery safety. There was something to be done. Furthermore, the ion permeability of the porous protective layer was not sufficient, and when used as an electrode, sufficient cycle characteristics could not be obtained. Furthermore, in electrodes obtained by a method of causing phase separation using a coagulating liquid such as water or methyl alcohol, the entire active material layer comes into contact with the coagulating bath, so the coagulating liquid does not impair the original characteristics of the active material layer. there were. In addition to these problems, this method also has problems as a manufacturing method from the viewpoint of environmental compatibility, since a waste liquid containing a coagulating liquid is generated from the coagulating bath.

As a method for solving such problems, Patent Document 3 describes a method for manufacturing an electrode for a lithium secondary battery, in which polyamide-imide is coated on the surface of an electrode active material layer formed on a metal foil. A coating liquid containing (PAI) and a solvent is applied to form a coating film, and then, when the solvent in the coating film is removed, the coating film is formed using the action of the poor solvent remaining in the coating film. A method of forming a heat-resistant porous PAI layer having ion permeability by causing phase separation within the PAI is disclosed, and it is stated that ether solvents such as tetraglyme and triglyme are effective as poor solvents. ing. Although this method makes it possible to form a protective layer made of porous PAI having ion permeability, it is necessary to further increase the ion permeability. In addition, it is necessary to use a large amount of expensive ether solvent, and there are points that need to be improved from the economic point of view.

On the other hand, Patent Document 4 discloses a method for obtaining a porous PAI film from a PAI solution containing an alcohol solvent as a poor solvent. With this method, a porous PAI film with high porosity can be obtained even if the amount of alcohol, which is a poor solvent, is reduced.

Patent No. 3371839 Patent No. 3593345 International Publication No. 2014-106954 JP2016-222912A

However, when a protective layer made of porous PAI for an electrode for a lithium secondary battery is formed using the porous PAI film forming solution described in Patent Document 4, sufficient ion permeability may not be obtained. However, there were points that needed to be improved in order to obtain good cycle characteristics as an electrode for lithium secondary batteries.

The present invention simply and economically produces an electrode for a lithium secondary battery in which a protective layer made of porous PAI having excellent ion permeability and good cycle characteristics is laminated and integrated with an electrode active material layer. The purpose of the present invention is to provide a coating liquid that can be used as a coating liquid, and a method of manufacturing an electrode for a lithium secondary battery using the coating liquid.

The present inventors have found that the above-mentioned problem can be solved by specifying the composition of the coating liquid for forming the protective layer, and have completed the present invention.

The purpose of the present invention is as follows.

<1> A coating liquid used for laminating a protective layer on an electrode active material of a lithium secondary battery electrode , which has the following characteristics.
1) The solute consists of PAI.
2) The solvent is a mixed solvent of a good solvent and a poor solvent for PAI, and the poor solvent is ethylene carbonate and/or propylene carbonate.
3) Contains filler.
<2> A method for manufacturing an electrode for a lithium secondary battery, in which the coating liquid is applied to the surface of an electrode active material layer formed on a metal foil to form a coating film, and then, When the solvent in the coating film is removed, the action of ethylene carbonate or propylene carbonate remaining in the coating film is used to cause phase separation within the coating film, resulting in a protection made of porous PAI having ion permeability. A method for producing an electrode for a lithium secondary battery, the method comprising forming a layer.
<3> A protective layer made of porous PAI containing filler is formed on the surface of the electrode active material layer formed on the metal foil, and ethylene carbonate and/or propylene carbonate remains in the protective layer. The content thereof is 0.01% by mass or more and 10% by mass or less based on the mass of the protective layer, and the ionic resistance increase rate based on the protective layer is 20% or less. Electrodes for lithium secondary batteries.

The electrode for a lithium secondary battery on which a protective layer is formed, which is obtained using the coating liquid of the present invention, has excellent ion permeability and therefore has good cycle characteristics.

Using the coating liquid of the present invention, a protective layer having ion permeability is formed on the surface of the electrode active material layer formed on the metal foil. An electrode for a lithium secondary battery is an electrode that constitutes a lithium ion 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 bonded to a negative electrode current collector. refers to the negative electrode. The electrode active material layer is a general term for the positive electrode active material layer and the negative electrode active material layer. Note that from the viewpoint of improving the safety of the lithium secondary battery, the protective layer is preferably formed on the negative electrode active material layer. By doing so, it is possible to suppress the generation of lithium dendrites (acicular crystals of metallic lithium) on the surface of the negative electrode active material. This lithium dendrite may cause an electrical short circuit.

As the metal foil, metal foils such as copper foil, stainless steel foil, nickel foil, and aluminum foil can be used. The metal foil acts as an electrode for a lithium secondary battery, and 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 roughening treatment or rust prevention treatment to improve adhesion to the active material layer.

The positive electrode active material layer is a layer obtained by binding positive electrode active material particles with a resin binder. The material used as the positive electrode active material particles is preferably one that can occlude and store lithium ions, and examples thereof include materials commonly used as positive electrode active materials for power storage elements. For example, oxide type (LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ etc.), composite oxide type, iron phosphate type (LiFePO ₄ , Li ₂ FePO ₄ F etc.), polymer compound type (polyaniline, polythiophene etc.) Examples of active material particles include: Among these, LiCoO ₂ , LiNiO ₂ and LiFePO ₄ are preferred. The positive electrode active material layer contains about 1 to 30% by mass of conductive additives such as carbon (graphite, carbon black, etc.) particles and metal (silver, copper, nickel, etc.) particles in order to reduce its internal resistance. You can leave it there.

The negative electrode active material layer is 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 that can occlude and store lithium ions, and includes materials commonly used as negative electrode active materials for power storage elements. Examples include graphite, amorphous carbon, silicon-based, tin-based active material particles, and the like. Among these, graphite particles and silicon-based particles are preferred. Examples of silicon-based particles include particles of simple silicon, silicon alloys, and silicon/silicon dioxide composites. Here, simple silicon refers to crystalline or amorphous silicon with a purity of 95% by mass or more. The negative electrode active material layer contains about 1 to 30% by mass of conductive additives such as carbon (graphite, carbon black, etc.) particles and metal (silver, copper, nickel, etc.) particles in order to reduce its internal resistance. You can leave it there.

The average particle diameter of the active material particles and the conductive additive is preferably 50 μm or less for both the positive electrode and the negative electrode, and more preferably 10 μm or less. If the average particle diameter is too small, binding by the resin binder becomes difficult, so it 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 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-butadiene copolymer. Known resin binders can be mentioned, such as polyester, polytetrafluoroethylene, polypropylene, polyethylene, polyimide, and polyamideimide.

PAI forming the protective layer is a polymer obtained by performing a polycondensation reaction between 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) and one or more aromatic rings per molecule, and among the three carboxyl groups, at least two carboxyl groups The group is placed in a position where it can form an acid anhydride form.

Examples of the aromatic tricarboxylic acid component include a benzenetricarboxylic acid component and a naphthalenetricarboxylic acid component.

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

Specific examples of naphthalenetricarboxylic acid components include 1,2,3-naphthalenetricarboxylic acid, 1,6,7-naphthalenetricarboxylic acid, 1,4,5-naphthalenetricarboxylic acid, their anhydrides, and their monochlorides. can be mentioned.

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

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

In addition, some of the tricarboxylic acid components are terephthalic acid, isophthalic acid, pyromellitic acid, 3,3',4,4'-biphenyltetracarboxylic acid, and 3,3',4,4'-benzophenonetetracarboxylic acid. Those substituted with other components may also be used.

The diamine component of PAI is an organic compound having two primary amino groups (including derivatives thereof) and one or more aromatic rings per molecule.

Specific examples of aromatic diamine components include 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-tolydine, 2,4-tolylene diamine, 2,6-tolylene diamine, xylylene diamine, naphthalene diamine, and their diisocyanate derivatives.

Among the aromatic diamine components, DADE, MDA and DMA are preferred.

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

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

The coating liquid of the present invention contains a mixed solvent consisting of a good solvent and a poor solvent for PAI. Here, a good solvent is a solvent whose solubility for PAI at 25°C is 1% by mass or more, and a poor solvent is a solvent whose solubility for PAI at 25°C is less than 1% by mass. It is about.

As the good solvent used in the present invention, it is preferable to use an amide solvent. Examples of the amide solvent include N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide, and N,N-dimethylacetamide. The amide solvents may be used alone or in combination of two or more. Among these, NMP is preferred.

The poor solvent used in the present invention needs to be ethylene carbonate and/or propylene carbonate (ester solvent).

The content of ethylene carbonate and/or propylene carbonate in the mixed solvent is preferably 1% by mass or more and less than 70% by mass, and preferably 5% by mass or more and 60% by mass or less, based on the total solvent mass. More preferred. By setting the solvent composition as described above, when the coating film obtained from the PAI coating liquid is dried and solidified, the ethylene carbonate or propylene carbonate (poor solvent) remaining in the coating film can efficiently interact with each other. Separation can occur and form a porous PAI with high porosity. Note that the PAI solution used here is a uniform solution. A homogeneous solution refers to a solution that is transparent to visible light.
By using such a uniform solution, a uniform phase separation phenomenon is induced during drying of the coating film. Therefore, for example, a microphase-separated, non-uniform PAI solution as disclosed in JP-A No. 2007-269575 is not preferred.

The coating liquid of the present invention requires a filler to be blended into the PAI solution. By doing so, it is possible to ensure good ion permeability of the formed protective layer. That is, a protective layer having good ion permeability can be obtained due to the synergistic effect of the porous structure of PAI formed by the action of the poor solvent and the porous structure formed by blending the filler.

There is no restriction on the type of filler, and organic fillers, inorganic fillers, mixtures thereof, etc. can be used. Specific examples of organic fillers include styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, copolymers of two or more of them, polytetrafluoroethylene, Examples include powders made of polymers such as fluororesins such as tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, and polyvinylidene fluoride. Organic fillers can be used alone or in combination of two or more. Specific 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, silica, titanium dioxide, barium sulfate, calcium carbonate, and the like. Inorganic fillers can be used alone or in combination of two or more. Among these inorganic fillers, alumina and boehmite are preferred from the viewpoint of chemical stability.

There is no restriction on the shape of the filler, and substantially spherical, plate-like, columnar, needle-like, whisker-like, and fibrous particles can be used, with substantially spherical particles being preferred. The aspect ratio (major axis of particle/minor axis of particle) of the approximately spherical particles is preferably 1 or more and 1.5 or less.

There is no limit to the average particle diameter of the filler, but it is preferably 0.01 μm or more and 2 μm or less. The average particle diameter can be measured using a measuring device based on 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.

There is no limit to the amount of filler added, but it is usually 10 to 95% by weight, preferably 20 to 90% by weight, based on the total weight of PAI and filler.

The PAI solid content concentration in the PAI coating liquid is preferably 1 to 50% by mass, more preferably 2 to 30% by mass.

If necessary, known additives such as various surfactants and silane couplers, polymers other than PAI, solvents other than ethylene carbonate or propylene carbonate, etc. may be added to the PAI coating liquid within a range that does not impair the effects of the present invention. May be added.

The PAI coating liquid obtained as described above is applied to the surface of the electrode active material layer and dried at 100 to 180°C, thereby making use of the effect of the poor solvent remaining in the coating film. By causing phase separation to occur, a protective layer made of porous PAI with good ion permeability can be formed. There is no limit to the thickness of the protective layer, but it is preferably 1 to 20 μm, more preferably 2 to 10 μm.

The ion permeability of the protective layer can be determined by, for example, calculating the ionic resistivity before and after laminating the protective layer, and determining the ratio (ion resistance increase rate) of the ionic resistivity of the laminated electrode to the pre-laminated electrode (P-1). It can be evaluated by The ionic resistance increase rate of the present invention is preferably 20% or less, more preferably 15% or less.
By doing so, good cycle characteristics can be ensured when used as a lithium secondary battery.

Preferably, a trace amount of ethylene carbonate or propylene carbonate remains in the protective layer thus obtained. The residual rate of ethylene carbonate or propylene carbonate is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 5% by mass or less, based on the mass of the protective layer. preferable.

When applying the PAI coating liquid, a continuous roll-to-roll coating method or a sheet-wise coating method can be employed, and either method may be used. As a coating device, a die coater, a multilayer die coater, a gravure coater, a comma coater, a reverse roll coater, a doctor blade coater, etc. can be used.

A polyolefin resin layer is formed on the surface of the protective layer of the electrode obtained using the PAI coating liquid of the present invention by depositing polyolefin resin particles made of polyethylene resin, polypropylene resin, ethylene-propylene copolymer resin, etc. be able to. By doing this, when the battery abnormally heats up due to a short circuit between the electrodes, the resin particles melt and block the current path, making it possible to shut down the current flowing through the battery, further increasing safety. I can do it. The melting point of the polyolefin resin particles is preferably 140°C or lower. Further, the thickness of the deposited polyolefin resin layer is preferably 10 to 25 μm.

As described above, the electrode of the present invention can be easily manufactured by a simple process.

EXAMPLES The present invention will be explained in more detail below with reference to Examples. Note that the present invention is not limited to the examples.

Electrodes used in the following examples and comparative examples were obtained as follows.

88 parts by mass of graphite particles (average particle diameter 8 μm) as a negative electrode active material, 5 parts by mass of carbon black (acetylene black) as a conductive agent, and 7 parts by mass of PVDF as a binder resin were combined with N-methyl-2-pyrrolidone. 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 with a thickness of 18 μm, which is a negative electrode current collector, and the resulting coating film was dried at 150°C for 20 minutes, and then hot pressed, so that the thickness of the film formed on the copper foil was 100 μm. An electrode (P-1) provided with a negative electrode active material layer was obtained.

The characteristics of the electrodes obtained in the following Examples and Comparative Examples were evaluated by the following methods.

(1) Ion permeability
An electrode was punched out into a circular shape with a diameter of 16 mm, a separator made of a porous polyethylene film and lithium foil were sequentially laminated, and this was housed in a coin-shaped outer container made of stainless steel. An electrolytic solution (solvent: a mixed solvent of ethylene carbonate and dimethyl carbonate mixed at a volume ratio of 1:1, electrolyte: 1 MLiPF ₆ ) was injected into the outer container, and a stainless steel A cap was placed and fixed, and the battery can was sealed to obtain a cell for evaluation. Using this cell, the ionic resistivity before and after lamination of the protective layer was calculated from the impedance at 100 KHz at 25°C, and the ratio of the ionic resistivity of the laminated electrode to the pre-laminated electrode (P-1) (ion resistance increase The ion permeability was evaluated by determining the
(2) Cycle characteristics Using the test cell obtained above, measurement temperature: 30°C, voltage range: 0.01 to 2V, charging current and discharging current: 500 mA/g - repeated charging and discharging conditions of the electrode active material layer. The battery was charged and discharged, and the cycle characteristics were evaluated by determining the ratio of the 20th discharge capacity to the 2nd discharge capacity (discharge capacity retention rate).
(3) Residual solvent content Using 5 mg of the sample scraped from the protective layer, the temperature was measured before and after the temperature was raised from room temperature (20°C) to 300°C using a differential thermal/thermogravimeter (Thermo plus EVO2 manufactured by Rigaku Co., Ltd.). The rate of decrease in the mass of the protective layer was measured, and the residual solvent content was calculated.

<Example 1>
A PAI solution was prepared according to the description in Patent Document 4. That is, PAI powder (glass transition temperature 280°C) obtained by copolymerizing TAC, DADE and MDA (copolymerization molar ratio: DADE/MDA = 7/3), from NMP and ethylene carbonate. A homogeneous PAI solution (L-1) with a PAI solid content concentration of 13% by mass was obtained by dissolving it in a mixed solvent (mass ratio NMP/ethylene carbonate = 60/40) at 30°C. To this solution, the mixed solvent and commercially available spherical alumina powder (average particle size: 0.2 μm) were added and mixed in a ball mill to obtain a PAI coating liquid (L-2).
The solid content concentration of L-2 was 25% by mass, and the mass ratio of PAI to alumina was PAI/alumina = 40/60. L-2 was applied to the surface of the electrode (P-1) and dried at 150° C. for 20 minutes to obtain an electrode (P-2) on which a protective layer with a thickness of 5 μm was formed. The ionic resistance increase rate of P-2 was 13%, and the discharge capacity retention rate was 95% or more. Ethylene carbonate remained in the protective layer, and its content was 4.3% by mass based on the mass of the protective layer.

<Example 2>
A PAI coating liquid (L-3) was obtained in the same manner as in Example 1, except that the mass ratio of PAI and alumina was set to PAI/alumina = 30/70. L-3 was applied to the surface of the electrode (P-1) and dried at 150° C. for 20 minutes to obtain an electrode (P-3) on which a protective layer with a thickness of 5 μm was formed. The ionic resistance increase rate of P-3 was 11%, and the discharge capacity retention rate was 95% or more. Ethylene carbonate remained in the protective layer, and its content was 2.8% by mass based on the mass of the protective layer.

<Example 3>
A PAI coating liquid (L-4) was obtained in the same manner as in Example 1, except that the mass ratio of PAI and alumina was set to PAI/alumina = 50/50. L-4 was applied to the surface of the electrode (P-1) and dried at 150° C. for 20 minutes to obtain an electrode (P-4) on which a protective layer with a thickness of 5 μm was formed. The ionic resistance increase rate of P-4 was 17%, and the discharge capacity retention rate was 95% or more. Ethylene carbonate remained in the protective layer, and its content was 3.9% by mass based on the mass of the protective layer.

<Example 4>
A PAI coating liquid (L-5) was obtained in the same manner as in Example 1 except that propylene carbonate was used instead of ethylene carbonate. L-5 was applied to the surface of the electrode (P-1) and dried at 150° C. for 20 minutes to obtain an electrode (P-5) on which a protective layer with a thickness of 5 μm was formed. The ionic resistance increase rate of P-5 was 15%, and the discharge capacity retention rate was 95% or more. Propylene carbonate remained in the protective layer, and its content was 4.1% by mass based on the mass of the protective layer.

<Example 5>
Same as Example 1 except that the mixed solvent of NMP and ethylene carbonate was changed to a mixed solvent of NMP, ethylene carbonate, and propylene carbonate (mass ratio NMP/ethylene carbonate/propylene carbonate = 60/20/20). A PAI coating liquid (L-6) was obtained. L-6 was applied to the surface of the electrode (P-1) and dried at 150° C. for 20 minutes to obtain an electrode (P-6) on which a protective layer with a thickness of 5 μm was formed. The ionic resistance increase rate of P-6 was 18%, and the discharge capacity retention rate was 95% or more. Ethylene carbonate and propylene carbonate remained in the protective layer, and the content thereof was 3.9% by mass based on the mass of the protective layer.

<Example 6>
A PAI coating liquid (L-7) was obtained in the same manner as in Example 1, except that commercially available boehmite powder (average particle size: 0.5 μm) was used as the alumina powder. L-7 was applied to the surface of the electrode (P-1) and dried at 160° C. for 20 minutes to obtain an electrode (P-7) on which a protective layer with a thickness of 5 μm was formed. The ionic resistance increase rate of P-7 was 17%, and the discharge capacity retention rate was 95% or more. Ethylene carbonate remained in the protective layer, and its content was 4.3% by mass based on the mass of the protective layer.

<Example 7>
The process was carried out in the same manner as in Example 1, except that the drying temperature when applying L-2 used in Example 1 to the surface of the electrode (P-1) was 170°C, and a protective layer with a thickness of 5 μm was formed. An electrode (P-8) was obtained. The ionic resistance increase rate of P-8 was 13%, and the discharge capacity retention rate was 95% or more. Ethylene carbonate remained in the protective layer, and its content was 0.8% by mass based on the mass of the protective layer.

<Comparative example 1>
A PAI coating liquid (M-1) was obtained in the same manner as in Example 1, except that only NMP was used as a solvent for dissolving the PAI powder. M-1 was applied to the surface of the electrode (P-1) and dried at 150° C. for 20 minutes to obtain an electrode (R-1) on which a protective layer with a thickness of 4 μm was formed. The ionic resistance increase rate of R-1 was 26%, and the discharge capacity retention rate was 91%.

<Comparative example 2>
By applying L-1, which does not contain alumina, to the surface of the electrode (P-1) and drying it at 150°C for 20 minutes, an electrode (R-2) on which a protective layer with a thickness of 5 μm is formed is obtained. Ta. The ionic resistance increase rate of R-2 was 33%, and the discharge capacity retention rate was 86%. Ethylene carbonate remained in the protective layer, and its content was 5.2% by mass based on the mass of the protective layer.

As shown in the Examples and Comparative Examples above, the electrode for lithium secondary batteries obtained using the coating liquid of the present invention has a protective layer containing ethylene carbonate or propylene carbonate, which is a poor solvent, and a filler. It can be seen that since pores can be formed by a synergistic effect, good ion permeability of the electrode in which the porous PAI layer is laminated and integrated can be ensured. Furthermore, it is understood that this effect allows good cycle characteristics to be obtained. Further, according to the manufacturing method of the present invention, an electrode with excellent safety can be manufactured with a simple process that is highly environmentally compatible.

Using the coating liquid of the present invention, it is possible to form a heat-resistant protective layer with excellent ion permeability on the active material layer of an electrode for lithium secondary batteries. It can be suitably used as an electrode for secondary batteries.

Claims (3)

A coating liquid used for laminating a protective layer on an electrode active material layer of a lithium secondary battery electrode , which has the following characteristics.
1) The solute consists of polyamideimide (PAI).
2) The solvent is a mixed solvent of a good solvent and a poor solvent for PAI, and the poor solvent is ethylene carbonate and/or propylene carbonate.
3) Contains filler. A method for producing an electrode for a lithium secondary battery, the method comprising: applying the coating liquid according to claim 1 to the surface of an electrode active material layer formed on a metal foil to form a coating film; , When removing the solvent in the coating film, phase separation is caused within the coating film by utilizing the action of ethylene carbonate or propylene carbonate remaining in the coating film, resulting in a porous PAI having ion permeability. A method for producing an electrode for a lithium secondary battery, the method comprising forming a protective layer. A protective layer made of porous PAI containing filler is formed on the surface of the electrode active material layer formed on the metal foil, and ethylene carbonate and/or propylene carbonate remain in the protective layer. , the content of the secondary lithium is 0.01% by mass or more and 10% by mass or less based on the mass of the protective layer, and the ionic resistance increase rate based on the protective layer is 20% or less. Electrodes for batteries.