JP2001325951A - Electrode for non-aqueous electrolyte secondary battery, method for producing the same, and non-aqueous electrolyte secondary battery - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To improve battery productivity and reduce internal resistance
An electrode for a non-aqueous electrolyte secondary battery having a high output density, a method for producing the same, and a non-aqueous electrolyte secondary battery are provided. An electrode for a non-aqueous electrolyte secondary battery according to the present invention is a non-aqueous electrolyte comprising an electrode plate and a non-conductive porous film integrally formed on at least one surface of the electrode plate. The electrode for a secondary battery, wherein a portion of the electrode plate that contacts the porous membrane has a porosity of a predetermined value or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode for a non-aqueous electrolyte secondary battery which can be used for a battery of an electronic device such as a notebook computer or a small portable device or an automobile, a method for producing the same, and a non-aqueous electrolyte solution. Next battery.

[0002]

2. Description of the Related Art In recent years, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries having a high energy density per volume and weight have become mainstream as power sources for cellular phones, portable video cameras, portable information terminals and the like. It is also attracting attention as a battery for electric vehicles.

[0003] A conventional lithium ion secondary battery includes a positive electrode capable of releasing lithium ions, a negative electrode capable of storing and releasing the lithium ions released from the positive electrode, and a separator interposed between the positive electrode and the negative electrode. And an electrolyte for moving the lithium ions between the positive electrode and the negative electrode. Thus, in the conventional lithium ion secondary battery, the separator prepared separately from the positive electrode and the negative electrode,
Since the battery was sandwiched between the positive electrode and the negative electrode at the stage of assembling the battery, there was a limit in improving the productivity.

In Japanese Patent Application Laid-Open No. H11-2888412, productivity is excellent by integrally forming a porous film as a separator on the surface of a positive or negative electrode plate.

In addition, when a lithium ion secondary battery is used for an electric vehicle, it is required to provide a large amount of electric power, and the inside of the battery depends on the conductivity of the electrolyte, the membrane resistance of the separator, the resistance of the conductor, and the like. When the resistance increases, a problem of heat generation and a problem of insufficient output occur.

[0006]

Therefore, according to the present invention, an electrode for a non-aqueous electrolyte secondary battery having a low internal resistance and a high output density while improving the productivity of the battery, a method for producing the same, and a non-aqueous electrolyte It is an object to provide a liquid secondary battery.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies for the purpose of solving the above problems, and as a result, the porosity of the surface of the electrode plate forming the porous film has been reduced to a predetermined value or less. The inventors have found that the internal resistance can be reduced, and have reached the following invention.

That is, the electrode for a non-aqueous electrolyte secondary battery of the present invention comprises a non-aqueous electrolyte comprising an electrode plate and a non-conductive porous film integrally formed on at least one surface of the electrode plate. In the electrode for a liquid secondary battery, a portion of the electrode plate that contacts the porous membrane has a porosity of a predetermined value or less.

The method of manufacturing an electrode for a non-aqueous electrolyte secondary battery according to the present invention, which solves the above-mentioned problems, is directed to an electrode for forming an electrode plate holding a mixture layer containing an active material capable of releasing and occluding lithium ions. A method for producing an electrode for a non-aqueous electrolyte secondary battery, comprising: a plate forming step; and a porous film forming step of integrally forming a porous film made of a polymer material on the surface of the electrode plate. The mixture layer of the electrode plate has a porosity of a predetermined value or less.

In other words, the electrode for a non-aqueous electrolyte secondary battery of the present invention and the method for producing the same are characterized in that the porosity of the electrode plate in contact with the porous membrane is set to a predetermined value or less, so that The penetration of the membrane can be prevented, and the decrease in the effective surface area of the electrode plate due to the porous membrane can be suppressed.

Further, the present inventors have conducted research and found that after forming a porous film in advance, the porous film is integrally fused to the surface of the electrode plate to be dependent on the porosity of the mixture layer. It has been found that the internal resistance can be reduced without performing the above, and the following invention has been conceived.

That is, the electrode for a non-aqueous electrolyte secondary battery according to the present invention is an electrode manufactured by an electrode plate forming step of forming an electrode plate holding a mixture layer containing an active material capable of releasing and occluding lithium ions. The present invention is characterized in that the plate and a porous film manufactured by a porous film manufacturing process for manufacturing a porous film made of a polymer material are integrated later.

That is, since the polymer solution is not brought into contact with the electrode plate, it is possible to prevent the polymer solution from seeping into the gaps of the electrode plate and to suppress a decrease in the effective surface area of the electrode plate due to the porous membrane.

The non-aqueous electrolyte secondary battery according to the present invention, which solves the above-mentioned problems, comprises an electrode body comprising a positive electrode and a negative electrode overlapped with each other, a non-aqueous electrolyte, and the electrode body and the non-aqueous electrolyte inside. And a case containing a liquid, and at least one of the positive electrode and the negative electrode,
It has an electrode plate and a non-conductive porous film integrally formed on at least one surface of the electrode plate, and a portion of the electrode plate in contact with the porous film has a porosity of not more than a predetermined value. There is a feature.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an electrode for a non-aqueous electrolyte secondary battery of the present invention, a method for producing the same, and a non-aqueous electrolyte secondary battery will be described in detail. In the following description, a lithium ion secondary battery will be described as an example of the nonaqueous electrolyte secondary battery, but the present invention is applicable to other nonaqueous electrolyte secondary batteries. Needless to say. Further, the method for producing an electrode for a non-aqueous electrolyte secondary battery of the present invention is applicable to an electric double layer capacitor or the like having an electrode in which an electrode mixture containing activated carbon as an active material is formed in a layer on the surface of a current collector. Therefore, the term “battery” in this specification includes the meaning of “capacitor”.

The electrode for a non-aqueous electrolyte secondary battery of the present invention will be described by taking an electrode for a lithium ion secondary battery as an example. The lithium ion secondary battery to which the electrode of the present embodiment can be applied can have a known battery structure such as a coin battery, a button battery, a cylindrical battery, and a square battery, and the shape is not particularly limited. Lithium ion secondary batteries generally include a positive electrode and a negative electrode containing an active material capable of transferring lithium ions, a separator that electrically insulates between the positive electrode and the negative electrode and allows lithium ions to move, It consists of a liquid and a case in which they are stored.

<Electrode for Lithium-Ion Secondary Battery> The electrode for a lithium-ion secondary battery of the present embodiment may be applied to either the positive electrode or the negative electrode. Further, the use of only one of them is not hindered, but the use of only one of them is preferable for reducing the internal resistance.

The electrode according to the present invention comprises an electrode plate capable of transmitting and receiving lithium ions and a porous film serving as a separator. The electrode plate and the porous film are integrally formed. I have. The porous film may be formed on only one side of the electrode plate, or may be formed on both sides. When the present invention is applied to a battery in which an electrode is wound, it is necessary to provide a porous film on both sides since both surfaces of the electrode need to face the other electrode and be insulated therebetween. The method for forming the electrodes will be described in the later-described electrode manufacturing method.

The electrode plate is a member for holding the active material.
As the active material of the positive electrode, a known positive electrode active material such as LiMn ₂ O ₄ can be used. In addition, as the active material of the negative electrode, a known negative electrode active material such as a carbon material can be used. Above all, it is preferable to use one made of natural graphite or artificial graphite having high crystallinity. By using such a highly crystalline carbon material, the lithium ion transfer efficiency of the negative electrode can be improved. Further, an oxide, a sulfide, or the like may be used as an active material in addition to the carbon material. Regardless of whether the electrode plate is applied to a positive electrode or a negative electrode, it is preferable to form the active material in a layer on a current collector such as a metal foil.

In this case, the portion of the electrode plate integrated with the porous film must have a porosity of not more than a predetermined value. This is because if the porosity is high, the porous membrane penetrates into the inside of the electrode plate and the effective surface area of the electrode plate decreases, so that when applied to a battery, the internal resistance of the battery increases. Here, the “predetermined value” in the electrode for a lithium ion secondary battery of the present embodiment refers to “a porosity in which the porous film does not penetrate into the electrode plate so that the effective surface area of the electrode active material is reduced and the internal resistance is increased. Is the limit value. For example, it is preferably 45% or less, which was obtained in a test performed in an example described later. In this specification, the “porosity” means the ratio of the volume of pores (voids) communicating with the outside on the side in contact with the porous membrane to the apparent volume of the electrode plate.

The porous film may be an organic substance or a mixture of an organic substance and an inorganic substance, but the organic substance is preferably made of a thermoplastic polymer. When the temperature inside the battery rises abnormally due to a short circuit or the like, the porous film made of a thermoplastic polymer can exhibit a shutdown function and prevent a short circuit current. Therefore, the safety of the battery is ensured even when the temperature inside the battery rises abnormally.

The thermoplastic polymer should be a heat-resistant polymer having a melting point of 150 ° C. or higher if it is a crystalline polymer and a glass transition temperature of 150 ° C. or higher if it is a non-crystalline polymer. Is preferred. As described above, a porous film made of a heat-resistant polymer having a melting point or a glass transition temperature of 150 ° C. or higher does not cause shrinkage or melting even at a high temperature exceeding 150 ° C. Therefore, the temperature inside the battery is 150 ° C
Even when the temperature becomes higher than this, the safety of the battery is ensured by the porous membrane.

Examples of the heat-resistant polymer include polybenzimidazole, polyimide, polyetherimide, polyamideimide, polyphenylene sulfide, polyethersulfone, polysulfone, polyetheretherketone, polymethylpentene, aramid, polyvinylidene fluoride, polyamide, It is preferably at least one of polyethylene terephthalate, polybutylene terephthalate, polyarylate, polyacetal, and polyphenylene ether (polyphenylene oxide). Among these heat-resistant polymers, those having a melting point or a glass transition temperature that are particularly high among those having a melting point or a glass transition temperature of 150 ° C. or higher. Therefore, a porous film having extremely excellent heat resistance can be obtained.

It is preferable that the porous membrane has a sponge-shaped central part and a surface part having pores having a smaller diameter than the central part.

In this porous film, the central portion is sponge-shaped, so that it has large-sized holes and high porosity. Therefore, the electrolyte (lithium ion) is extremely easy to move, and the passing property is extremely excellent.

Further, the surface portion having pores having a smaller pore diameter than the center portion can suppress dendrite deposition on the negative electrode. Further, since the pore diameter is small, the pore can be quickly and sufficiently closed when the temperature becomes high. Therefore, the shutdown function when the temperature of the battery becomes high can be more effectively exerted. Further, since the surface portion has a high density and is strong, the mechanical strength of the porous film can be increased.

Therefore, this porous membrane is extremely excellent in passage of electrolyte (lithium ions) and can effectively function as a shutdown function even at a high temperature. Therefore, the battery performance such as load characteristics and output characteristics of the lithium ion secondary battery can be improved, and short-circuit and abnormal heat generation can be effectively prevented. As a result, the safety of the battery becomes extremely high.

The lithium ion secondary battery to which the electrode of this embodiment is applied can have a low internal resistance and a high output density.

<Method of Manufacturing Electrode for Lithium-Ion Secondary Battery> The method of manufacturing an electrode for a lithium-ion secondary battery of this embodiment may be applied to either the positive electrode or the negative electrode, as in the case of the above-described electrodes. Similarly, the use of only one of them and not both does not hinder the use of only one of them.

The method of manufacturing an electrode according to the present embodiment includes an electrode plate forming step and a porous film forming step. The electrode plate forming step is a step of forming an electrode plate holding a mixture layer containing an active material capable of releasing and storing lithium ions. The electrode plate forming step is not particularly limited, and a known method of forming an electrode on which a porous film is not formed can be applied.

For example, as a method for forming a positive electrode, a slurry in which a positive electrode mixture obtained by mixing a positive electrode active material, a conductive material and a binder is dispersed in a dispersing material is applied to an aluminum positive electrode current collector and dried. Thereafter, press molding is performed to form a positive electrode mixture layer. As a method for forming the negative electrode, a slurry in which a negative electrode mixture obtained by mixing a negative electrode active material and a binder is dispersed in a dispersing material is applied to a copper negative electrode current collector, dried, and then press-formed by press molding. A material layer is formed.

However, when the porous film is formed by applying the polymer solution to the electrode plate in the porous film forming step described later, the porosity of the mixture layer portion of the electrode plate to which the polymer solution is applied is formed. Must be equal to or less than a predetermined value. As a method of adjusting the porosity, the method of changing the pressure and time of the press molding described above, a method of changing the physical properties such as the type of the active material, the conductive agent, the particle size, the type of the binder, and the mixing ratio, and the like Is given as an example. The meaning of the “predetermined value” will be described later.

The porous film forming step is a step of integrally forming a porous film made of a polymer material on the surface of the electrode plate. Therefore, the porous film forming step is a step including a step of manufacturing the porous film itself and a step of integrating the manufactured porous film with the electrode plate, and simultaneously forming the porous film itself and the electrode plate. And a method in which the porous membrane is manufactured independently of the electrode plate and then integrated with the electrode plate.

As a method of completing the integration of the porous film itself with the electrode plate at the same time as producing the porous film itself, a polymer coating step of coating a polymer solution obtained by dissolving a polymer material in a solvent on the surface of the electrode plate is performed. Forming a porous film from the obtained polymer solution. In this manufacturing method, the type of the polymer material is not particularly limited as long as it is soluble in a solvent, and can be selected according to a desired porous membrane. At this time, if a thermoplastic polymer is particularly used as the polymer material, the obtained porous membrane is thinner than a conventional separator and can exhibit an excellent shutdown function. Further, a solvent for dissolving the polymer material (good solvent) and a solvent that is hardly soluble in the polymer material (poor solvent) are appropriately selected depending on the polymer material used.

In particular, polymer materials include polybenzimidazole, polyimide, polyetherimide, polyamideimide, polyphenylene sulfide, polyethersulfone, polysulfone, polyetheretherketone, polymethylpentene, aramid, polyvinylidene fluoride, polyamide, At least one of polyethylene terephthalate, polybutylene terephthalate, polyarylate, polyacetal, and polyphenylene ether, and the good solvent is N-methyl-2-pyrrolidone (NM
P), dimethyl sulfoxide, dimethyl sulfamide,
Diglyme, toluene, xylene, dimethylacetamide, dichloromethane, at least one of cyclohexane and cyclohexanone, the poor solvent is water,
It is preferably at least one of alcohol, alkane and ketone.

In the polymer application step, a polymer solution prepared by dissolving a polymer material in a solvent is applied to the electrode plate obtained in the previous step. In this step, the temperature of the polymer solution, the concentration of the polymer material, and the like are not particularly limited, and can be selected according to productivity, the type of the polymer material, the amount of precipitation in a subsequent step, and the like. Further, in order to obtain a porous film having a uniform thickness, a surfactant, an antifoaming agent, a surface preparation agent, and the like may be added to the polymer solution. As such an additive, a fluorine-based or silicon-based compound which has low reactivity in a battery and is effective even with a small amount of addition is preferable. Furthermore, in order to make the shape, size and distribution of the voids of the porous membrane appropriate,
Water, alcohol, glycol, alkane, ketone and the like may be added to the polymer solution.

Further, it is preferable to dissolve a salt in the polymer solution. By this salt, pores through which lithium ions can pass are easily formed in the porous membrane. As a result, a porous film having excellent lithium ion permeability can be easily formed on the electrode.

The salt is not particularly limited in its kind, but is preferably a lithium salt, particularly lithium chloride, lithium nitrate, lithium iodide, lithium tetrafluoroborate, lithium bistrifluortomethylsulfonylimide, and 6-fluoride. It is preferably at least one of lithium arsenate. Since these lithium salts have excellent solubility in a solvent, the pore size can be controlled by the amount of the salt added.

The concentration of the lithium salt is preferably from 5% by weight to 20% by weight based on the polymer material. If the concentration of the lithium salt is less than 5%, the pores of the formed porous membrane become too small, and the permeability of lithium ions deteriorates. as a result,
It becomes difficult to obtain excellent battery performance, for example, it becomes difficult to obtain high output characteristics. On the other hand, if the concentration exceeds 20%, the pores of the porous film become too large, and the shutdown function and the like of the porous film deteriorate. As a result, it is difficult to obtain excellent battery performance, for example, it is difficult to obtain high safety within the allowable range.

The coating method of the polymer solution can be selected from known coating methods such as a blade coater, a roll coater, a knife coater and a die coater according to the shape of the electrode plate. In these coating methods, the polymer solution is preferably a high-viscosity solution, since the polymer solution easily replaces the air in the gaps in the electrode plate. For example, polyethylene terephthalate (P
When ET) is used, a high-viscosity polymer solution can be obtained if the amount of dissolution is 10 to 40% by weight (solid content) based on the entire polymer solution. The viscosity of the polymer solution may be increased by adding a thickener or the like.

In addition to the above-mentioned coating method, the electrode plate can be coated by dipping in a polymer solution. In this coating method, it is preferable to use a polymer solution having a low viscosity in order to improve the liquid shortage when the electrode plate is pulled up from the polymer solution. For example, when PET is used as a polymer material, a polymer solution having a low viscosity can be obtained by setting the amount of dissolution to 10% by weight or less based on the entire polymer solution.

As a method of forming the applied polymer solution into a porous film, (1) a method in which the polymer material is exposed to a poor solvent of the polymer material to separate and precipitate the polymer material, and There is a method in which a substance for forming is mixed to form a film and then removed from the film.

The method of -1 for phase separation using a poor solvent for a polymer material is to expose an electrode plate coated with a polymer solution to the poor solvent for a polymer material after a polymer coating step. The method includes a polymer deposition step of depositing a polymer material to form a porous film, and a drying step of drying an electrode plate which deposits the polymer material to form a porous film. The solvent for dissolving the polymer material is not only a good solvent for the polymer material but also a mixed solvent of a good solvent for the polymer material, a poor solvent for the polymer material, and a solvent having a higher boiling point than the good solvent. Is preferred. This is because the porosity of the porous film can be increased and the film resistance can be reduced.

In the polymer coating step, the polymer solution obtained by dissolving the polymer material in a mixed solvent of a good solvent for the polymer material and a poor solvent for the polymer material and having a boiling point higher than the good solvent is applied to the electrode plate. And then drying the electrode plate on which the polymer solution has been applied to separate the applied polymer solution into phases to form a porous film. In this case, since the high-molecular material having a lower boiling point evaporates from the good solvent in the drying step, the ratio of the poor solvent relatively increases, and the polymer material undergoes phase separation, whereby a porous film can be formed.

In the method of -2, in which a substance which forms pores is previously mixed in a polymer solution to form a film and then removed from the inside of the film, the substance which forms pores may be a salt dissolved in the polymer solution described above. preferable. By this salt, pores through which lithium ions can pass are easily formed in the porous membrane. As a result, when the salt is removed by an operation such as extraction with a solvent, a porous membrane having excellent lithium ion permeability can be easily formed on the electrode. The salt is not particularly limited, but is preferably used at the salt and concentration described above.

As described above, the porosity of the electrode plate to which the electrode manufacturing method having the polymer coating step of coating the polymer solution on the surface of the electrode plate is required to be not more than a predetermined value. Here, the "predetermined value" in the method for manufacturing an electrode for a lithium ion secondary battery of the present embodiment is "the effective surface area of the electrode plate when the polymer solution is brought into contact with the surface of the electrode plate when the polymer solution is brought into contact with the surface of the electrode plate. Is the limit value at which the internal resistance does not increase without penetrating to the extent that it decreases, and varies not only with the polymer, the solvent in which the polymer is dissolved, the composition of the electrode, etc., but is also affected by the viscosity of the polymer solution. Value. Above all, it is greatly affected by the viscosity of the polymer solution. As a result of experiments in Examples described later, when the porosity of the electrode plate is X (%) and the viscosity of the polymer solution is Y (cP), X <0. 0029Y
It turned out that it is preferable to satisfy the relationship of +42.0. The viscosity Y is a viscosity at the time of application and is greatly affected by the temperature. Therefore, from the viewpoint of stabilizing the viscosity, the temperature at the time of applying the polymer solution is preferably adjusted to a constant temperature. For example, in the combination of the above-mentioned preferable polymer solution and polymer solution, 120 to 13
It is preferable to control the temperature to about 0 ° C. In this case, if possible from the viewpoint of improving productivity, it is preferable to lower the porosity of the electrode plate rather than increase the viscosity of the polymer solution. The predetermined value is particularly preferably 45%. Although the lower limit of the predetermined value is not particularly set, it is considered that if the porosity is too low, the area where the electrolytic solution comes into contact with the active material is reduced, so that the efficiency of the battery is reduced. However, it is considered that an ordinary electrode plate forming step such as the above-described electrode plate manufacturing method does not form an electrode plate having a low porosity so as to cause inconvenience.

In the polymer application step, the electrode plate is immersed in an organic solvent in which the polymer material is dissolved, and in the polymer deposition step, it is immersed in water, alcohol, alkane, ketone, or the like. It must be resistant to these solutions. In the electrode plate forming step,
The method for forming the active material on the current collector plate is generally a method of suspending the active material with a binder and applying the suspension on the current collector plate. At this time, the binder preferably comprises a water-soluble polymer material having a hydroxyl group and a crosslinking agent having a functional group which reacts with the hydroxyl group.

A binder comprising a water-soluble polymer material having a hydroxyl group and a cross-linking agent having a functional group which reacts with the hydroxyl group can be used for a high-temperature organic solvent, water, alcohol, alkane, ketone and the like. And the non-solubility, it is possible to improve the resistance of the electrodes integrally formed with the porous membrane to the solution. In the electrode using the crosslinked binder, the organic solvent resistance and the water resistance are compatible, the selection range of the solution used in the polymer coating step and the polymer deposition step is widened, and the quality control of the porous film is controlled. There is an advantage that it becomes easy.

The type of the cross-linking agent is not particularly limited, but is preferably at least one of a silane coupling agent, a titanium coupling agent, a urea formalin resin, a methylolmelamine resin, glyoxal, and tannic acid. . These crosslinking agents have a functional group having excellent reactivity with a hydroxyl group contained in the water-soluble polymer, and can crosslink the water-soluble polymer with good crosslinkability. Above all, it is desirable to use a water-soluble polymer material having excellent organic solvent resistance and to use a binder obtained by crosslinking a hydroxyl group portion of the water-soluble polymer material using a silane coupling agent.

The water-soluble polymer material is not particularly limited in its kind, but is preferably at least one of carboxymethyl cellulose, methyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylate and polyethylene oxide. These water-soluble polymer materials are particularly excellent in organic solvent resistance, and can improve the resistance of the electrode, in which the porous film is integrally formed, to the organic solvent.

The amount of the crosslinking agent added to the water-soluble polymer material is preferably an amount having at least the same number of hydrolyzable groups as the number of hydroxyl groups contained in the water-soluble polymer.

By selecting the amount of the crosslinking agent to be added, the hydrophilic group (hydroxyl group) contained in the water-soluble polymer material is selected.
Can be subjected to a crosslinking reaction. Therefore, the resistance of the binder to an organic solvent, water, alcohol, alkane, ketone and the like can be further improved.

Specifically, carboxylmethyl cellulose
Su: C₆H₇O₂(OH)₂OCH ₂COONa to Shira
Coupling agent: H₂NC₃H₆Si (OC₂H₅)
₃If adding carboxymethyl cellulose
Molecular weight of ose sodium salt is 242, dissolved in water
The number of hydroxyl groups in is 3 while the silane coupling agent
Whether the molecular weight of the compound is 221 and the number of hydrolyzable groups is 3
The addition amount of the silane coupling agent is carboxy
(221/3) / (242
/3)=0.91 times or more.

The method of manufacturing the porous film independently of the electrode plate and then integrating the same with the electrode plate includes the steps of forming the porous film and integrating the formed porous film on the electrode plate. Consists of

As a method of forming a porous film, a method of stretching a polymer thin film, which is a known method, or the above-described method is used.
In the methods (1) and (2), there is a method in which a porous film is not formed on the electrode plate, but is formed in another flat plate, and then a peeling step of peeling the porous film is performed.

As a method of integrating the porous film thus formed on the electrode plate, a method of melting or dissolving the surface of the porous film and pressing the porous film on the electrode plate is exemplified.
In this case, when the viscosity of the melted or dissolved porous membrane surface is low, it may be necessary to reduce the porosity of the electrode plate to a predetermined value or less as in the above-described method.

The method for manufacturing an electrode according to the present embodiment is excellent in productivity. Further, the lithium ion secondary battery to which the electrode manufactured by the method for manufacturing an electrode according to the present embodiment is applied can have low internal resistance and high output density.

<Lithium Ion Secondary Battery> The lithium ion secondary battery of the present embodiment has an electrode body formed by laminating a positive electrode and a negative electrode, a nonaqueous electrolyte, and the electrode body and the nonaqueous electrolyte therein. A non-aqueous electrolyte secondary battery having a case enclosing the same, wherein at least one of the positive electrode and the negative electrode is a non-conductive material integrally formed on a surface of at least one of an electrode plate and the electrode plate. A porosity of a portion of the electrode plate in contact with the porous film is equal to or less than a predetermined value.

Here, at least one of the positive electrode and the negative electrode is the above-described electrode or an electrode manufactured by the above-described electrode manufacturing method. Other configurations are not particularly limited, and known configurations can be used.

The lithium ion secondary battery of the present embodiment is
It can have low internal resistance and high output density.

[0061]

The present invention will now be described more specifically with reference to examples.

(Production Method of Test Lithium Ion Secondary Battery) Each lithium ion secondary battery for test of the present example and the comparative example has a structure as schematically shown in FIG.
The coin-type lithium ion secondary battery includes a positive electrode 1 capable of releasing lithium ions, a negative electrode 2 made of a carbon material capable of occluding and releasing lithium ions released from the positive electrode 1, and electrolytes 3 and 3. The positive electrode 1, the negative electrode 2, and the non-aqueous electrolyte 3 are sealed in a positive electrode case 4 and a negative electrode case 5 made of stainless steel via a gasket 6 made of polypropylene.

The positive electrode 1 has a positive electrode active material layer 1 containing LiMn ₂ O ₄ on a positive electrode current collector 1 a made of aluminum.
b is an electrode. The negative electrode 2 is an electrode having a negative electrode active material layer 2b made of a carbon material on a negative electrode current collector 2a made of a copper foil, and integrally having a porous film 2c instead of a separator on a surface facing the positive electrode 1. is there. The non-aqueous electrolyte 3 is obtained by mixing a solvent obtained by mixing ethylene carbonate and diethyl carbonate at a predetermined ratio with LiPF ₆ as an electrolyte.
Was dissolved at a concentration of 1 mol / liter.

The negative electrode 2 is formed as follows.

<Examples 1 to 3 and Comparative Examples 1 to 3> [Electrode plate forming step] Artificial graphite powder was prepared as a carbon material, and was mixed with polyvinylidene fluoride (PVDF) at a predetermined ratio and a predetermined amount of NMP. By mixing, a paste-like negative electrode mixture was obtained. Next, this negative electrode mixture was applied to the copper foil 2a using a blade coater. The NMP in the mixture was volatilized and removed by drying the applied mixture for a negative electrode in a high-temperature bath, thereby solidifying the mixture. Lastly, the solidified negative electrode mixture is press-formed so that the densities are as shown in Table 1, respectively, so that the carbon material negative electrode active material layer 2b is formed on the negative electrode current collector 2a made of copper foil. To obtain a negative electrode plate.

[Polymer Coating Step] Polyethylene terephthalate prepared as a polymer material was dissolved in NMP to obtain a polymer solution. Here, the dissolved amount of polyethylene terephthalate was dissolved in the entire polymer solution at the concentrations shown in Table 1, respectively. The viscosity of the polymer solution was as shown in Table 1. In this step, the polymer solution was applied to the negative electrode plate using a blade coater.
At this time, in the electrode plates of each comparative example, a portion where the polymer solution was replaced with air in the pores of the negative electrode plate and permeated into the electrode plate was observed.

[Polymer Deposition Step] The negative electrode plate coated with the polymer solution was immersed in warm water of 40 ° C. for 1 minute. Hot water is a liquid that is hardly soluble in polyethylene terephthalate. As a result, the polymer solution on the surface of the negative electrode plate gelled, and polyethylene terephthalate was uniformly precipitated in the polymer solution.

[Drying Step] Hot air at 80 ° C. was blown onto the negative electrode plate obtained in the polymer precipitation step to dry the applied polymer solution. As a result, the polyethylene terephthalate precipitated in the polymer deposition step was left as a porous film on the negative electrode plate. Thus, the negative electrode 2 integrally having the porous film 2c was obtained. Example 1 as an example
SEM of the cross section of the porous film formed on the surface of the electrode plate of -1
The photograph is shown in FIG.

<Example 4-1> A porous film was formed on a release film instead of an electrode plate under the same conditions and steps as in Example 1 described above, and the formed porous film was peeled from the release film. The resulting material was fused on an electrode plate press-formed so that the mixture layer had the density shown in Table 1, to produce a negative electrode, and a battery was produced using the negative electrode. 220 ° C fusion by heater
The porous film was thermally fused to the electrode end by heating for 10 seconds.

<Example 4-2> The solvent for dissolving PET in [Polymer coating step] in Example 4-1 was NM.
88: 1 volume ratio between P (good solvent) and dodecane (poor solvent)
Negative electrode 2 was prepared in the same process as in Example 4-1 except that the mixed solvent of No. 2 was used.

<Example 4-3> The solvent for dissolving PET in [Polymer coating step] in Example 4-1 was NM.
88: 1 volume ratio between P (good solvent) and dodecane (poor solvent)
Negative electrode 2 was prepared in the same manner as in Example 4-1 except that the mixed solvent of No. 2 was not used and the [polymer deposition step] was omitted.

(Calculation of Porosity) Before forming a porous film on the surface, the porosity of each of the negative electrodes of Examples and Comparative Examples was measured. The porosity was measured by a mercury intrusion method.

Table 1 shows the results.

(Evaluation of discharge capacity ratio) The discharge capacity of each lithium secondary battery of each example was measured as follows.
After charging at a constant current of 1 mA / cm ^{2 and} a constant voltage of 4.2 V for a total of 4 hours, 0.2 mA / cm ² and 4.0 mA / cm ²
Discharge was performed at a constant current of cm ² . Discharge current 4.0 mA /
The value obtained by dividing the discharge capacity of the discharge capacity when the discharge current 0.2 mA / cm ² when the cm ² and the discharge capacity ratio at large current discharge, and the results are shown in Table 1. As is clear from the results, all of the lithium secondary batteries of the examples show a large discharge capacity ratio of 0.8 or more, and the discharge capacity ratio further increases with a decrease in the porosity of the active material. Was observed. On the other hand, the lithium secondary batteries of Comparative Examples all had a low discharge capacity of about 0.66.

(Evaluation of Safety) The lithium ion secondary batteries of Examples and Comparative Examples were subjected to an overcharge test at a constant current of 1 mA / cm ² and a charge amount of 300%.
As a result, in each of the batteries, no battery short-circuit occurred and the battery temperature peaked at 140 ° C., ignited, and calmed without bursting. This is considered to be because the porous film did not shrink and melt even by the heat generated by overcharging.

(Measurement of Internal Resistance) The internal resistance of the test batteries of each of the examples and comparative examples was measured. Table 1 shows the results. FIG. 2 is a graph showing the relationship between the porosity and the internal resistance of the negative electrode mixture layer, and the relationship between the viscosity and the internal resistance of the polymer solution applied to the electrode plate surface.

[0077]

[Table 1]

As is evident from Table 1, the test batteries of the examples exhibited a significant reduction in internal resistance as compared with the test batteries of the comparative examples. As is clear from FIG. 2, the internal resistance decreases as the porosity of the negative electrode mixture layer decreases and as the viscosity of the polymer solution applied to the electrode plate increases. When the porosity is 45% or less, there is an effect of lowering the internal resistance at any viscosity of the polymer solution. The porosity is 44% or less as a range where a more remarkable effect is obtained, and 43% or less as a range where a more remarkable effect is obtained. When the porosity is set to 42% or less, a remarkably low internal resistance is exhibited even with the lowest viscosity of 700 cP. According to the study of the present inventors, the porosity of a general negative electrode mixture layer is 48% or more, and furthermore, it is not well known that the electrode plate and the separator (porous membrane) are integrated, so the present Example The effect of lowering the internal resistance is difficult to predict for those skilled in the art.

The relationship between the porosity of the electrode plate surface and the internal resistance of the battery in the viscosity of each of the polymer solutions was examined closely, and the inflection point at which the internal resistance began to decrease was determined by the maximum porosity at which the effect was recognized. There was. The inflection points are respectively porosity 43.8 when the viscosity of the polymer solution is 700 cP.
%, Example 2-1 having a porosity of 45.3% when the viscosity of the polymer solution is 1000 cP, and Example 3- having a porosity of 446.2% when the viscosity of the polymer solution is 1500 cP. It was one. From these three points, an approximate expression of X = 0.0029Y + 42.0 was obtained by the least squares method (FIG. 3). X represents the porosity (%), and Y represents the concentration (cP) of the polymer solution. Therefore, the range in which the effect occurs is as follows: X <0.0029Y + 4
2.0 is a range that satisfies the relationship of 2.0.

Further, in Examples 4-1 to 3, the porosity and the viscosity of the polymer solution are almost the same as those of Comparative Example 1-1, but the internal resistance is larger than that of Comparative Example 1-1. Reduction was observed. This is because the electrodes of Examples 4-1, 2, and 3 were formed by a method in which the porous film formed as a separate body was later fused, so that the polymer did not infiltrate into the mixture layer, so that the mixture was not mixed. It is considered that this was because the infiltration of the electrolyte into the inside was not prevented.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view schematically showing a structure of a lithium ion secondary battery subjected to a test as an example and a comparative example.

FIG. 2 shows the internal resistance, the porosity of the mixture layer, and the viscosity of the polymer solution applied to the electrode plate surface for each of the lithium ion secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 3. 3 is a graph showing the relationship.

FIG. 3 shows the relationship between the porosity of the mixture layer and the viscosity of the polymer solution applied to the electrode plate surface for each of the lithium ion secondary batteries of Examples 1-1, 2-1 and 3-1. It is a graph shown.

FIG. 4 is a cross-sectional view of a porous film formed on a negative electrode of the lithium ion secondary battery of Example 1-1.
It is a photograph taken at a magnification of 1000 times by EM.

[Explanation of symbols]

1: positive electrode 1a: positive electrode current collector 1b: positive electrode active material layer
2: negative electrode 2a: negative electrode current collector 2b: negative electrode active material layer 2
c: Porous membrane 3: Non-aqueous electrolyte 4: Positive case 5: Negative case 6: Gasket

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[Procedure amendment]

[Submission date] May 19, 2000 (2005.1.
9)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 4

[Correction method] Change

[Correction contents]

FIG. 4

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hosokawa ▲ Toku ▼ 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside Denso Co., Ltd. (72) Inventor Gaku Yamada 1-1-1, Showa-cho, Kariya-shi, Aichi Stock F term in company DENSO (reference) 5H021 AA06 BB01 BB11 BB13 CC05 EE02 HH00 HH10 5H029 AJ02 AJ14 AK03 AL06 AM03 AM05 AM07 BJ13 CJ02 CJ06 CJ08 CJ22 DJ08 DJ13 EJ12 HJ10 HJ12 5H050 AA07 GA12 GA22 HA10 HA12

Claims (13)

[Claims] An electrode for a non-aqueous electrolyte secondary battery comprising an electrode plate and a non-conductive porous film integrally formed on at least one surface of the electrode plate, wherein the electrode plate An electrode for a non-aqueous electrolyte secondary battery, wherein a portion in contact with the porous membrane has a porosity of not more than a predetermined value. 2. The electrode plate has a mixture layer containing an active material capable of releasing and occluding lithium ions on a surface portion thereof, and the porous film is formed on a surface of the mixture layer. 3. The electrode for a non-aqueous electrolyte secondary battery according to 1.). 3. An electrode plate forming step of forming an electrode plate holding a mixture layer containing an active material capable of releasing and occluding lithium ions, and a porous film made of a polymer material being integrally formed on the surface of the electrode plate. A method for producing an electrode for a non-aqueous electrolyte secondary battery, comprising: forming a porous film to form a non-aqueous electrolyte secondary battery, wherein the mixture layer of the electrode plate has a porosity of a predetermined value or less. Of producing a non-aqueous electrolyte secondary battery electrode. 4. The step of forming a porous film, the step of applying a polymer solution in which the polymer material is dissolved in a solvent to a surface of the electrode plate; and the step of coating the polymer solution with the electrode. Exposing the plate to a poor solvent for the polymer material to deposit the polymer material to form a porous film; and drying the electrode plate to deposit the polymer material to form a porous film. The method for producing an electrode for a non-aqueous electrolyte secondary battery according to claim 3, comprising the steps of: 5. The method for producing an electrode for a non-aqueous electrolyte secondary battery according to claim 4, wherein the solvent is a mixed solvent of a good solvent for the polymer material and a poor solvent for the polymer material. 6. The step of forming a porous film, comprising: disposing a polymer solution obtained by dissolving the polymer material in a mixed solvent of a good solvent for the polymer material and a poor solvent for the polymer material on the surface of the electrode plate. 4. The method according to claim 3, comprising: a polymer application step of applying the polymer solution; and a drying step of drying the electrode plate on which the polymer solution is applied, and phase-separating the applied polymer solution to form a porous film. Method for producing an electrode for a non-aqueous electrolyte secondary battery. 7. The method according to claim 1, wherein the predetermined value is X (%), and the viscosity when the polymer solution is applied to the electrode plate in the polymer application step is Y (cP). The method for producing an electrode for a non-aqueous electrolyte secondary battery according to any one of claims 4 to 6, wherein the relationship of <0.0029Y + 42.0 is satisfied. 8. An electrode plate manufactured by an electrode plate forming step of forming an electrode plate holding an mixture layer containing an active material capable of releasing and occluding lithium ions, and a porous film made of a polymer material. A method for producing an electrode for a non-aqueous electrolyte secondary battery, wherein a porous membrane produced by a porous membrane production step is integrated later. 9. The step of producing a porous film, comprising: applying a polymer solution obtained by dissolving the polymer material in a solvent to a surface of a flat plate; A polymer deposition step of depositing the applied polymer material by exposing it to a poor solvent for the polymer material to form a porous film, and drying the flat plate formed by depositing the polymer material and forming the porous film. The method for producing an electrode for a non-aqueous electrolyte secondary battery according to claim 8, comprising: a step of separating the porous film from the flat plate. 10. The method for producing an electrode for a non-aqueous electrolyte secondary battery according to claim 9, wherein the solvent is a mixed solvent of a good solvent for the polymer material and a poor solvent for the polymer material. 11. The method of manufacturing a porous film, comprising: dissolving the polymer material in a mixed solvent of a good solvent for the polymer material, a poor solvent for the polymer material, and a solvent having a higher boiling point than the good solvent. A polymer coating step of applying a polymer solution to the surface of a flat plate, and a drying step of drying the flat plate to which the polymer solution has been applied and separating the applied polymer solution into a porous film by phase separation. The method for producing an electrode for a non-aqueous electrolyte secondary battery according to claim 8, comprising a peeling step of peeling the porous film from the flat plate. 12. The method according to claim 8, wherein the step of integrating the electrode plate and the porous film is a step of melting a part or all of the surface of the porous film and fusing the surface to the electrode plate. A method for producing an electrode for a non-aqueous electrolyte secondary battery according to any of the above items. 13. A non-aqueous electrolyte secondary battery comprising: an electrode body formed by stacking a positive electrode and a negative electrode; a non-aqueous electrolyte; and a case containing the electrode body and the non-aqueous electrolyte therein. Wherein at least one of the positive electrode and the negative electrode has an electrode plate and a non-conductive porous film formed integrally on at least one surface of the electrode plate, and the porous material of the electrode plate A non-aqueous electrolyte secondary battery, wherein a porosity of a portion in contact with the membrane is not more than a predetermined value.