JP2000100443A - Electrode base material film for secondary battery and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a reinforced electrode base material to realize high energy density by forming a conductive thin film composed of metal or an alloy on at least one surface of a plastic film composed of resin having an acid amide bond or an acid imide bond. SOLUTION: A metallic foil such as aluminum for a positive electrode and copper for a negative electrode is laminated as a conductive thin film on at least one surface of a plastic film composed of resin having an acid amide bond and/or an acid imide bond to obtain an electrode base material film for a secondary battery. The resin having the acid amide bond contains aromatic polyamide, and the thickness of the plastic film is set to 1 to 50 μm to desirably secure necessary mechanical strength. The thickness of the conductive thin film is set to 100 nm to 10 μm to thereby prevent heating by a battery current as well as to improve the weight and volume energy density of the battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a base film used for a positive electrode or a negative electrode of a secondary battery, and a secondary battery using the same.

[0002]

2. Description of the Related Art In recent years, various devices such as a camera-integrated VTR device, an audio device, a portable computer, and a cellular phone have been reduced in size and weight, and there has been a demand for higher performance of a battery as a power supply for these devices. Is growing. Above all, development of lithium secondary batteries capable of realizing high voltage, high energy density and excellent cycle characteristics as batteries for power sources of electric vehicles has been active.

[0003] A lithium secondary battery is composed of a positive electrode active material and a negative electrode active material capable of inserting and extracting lithium ions formed on a conductive electrode substrate, and a non-aqueous electrolyte solution. A non-aqueous electrolyte was used as the electrolyte. However, batteries using non-aqueous electrolytes have the danger of leakage and ignition.In recent years, non-aqueous electrolytes have been used to improve safety. The development of polymer electrolytes in the form of particles is also underway.

In particular, in a lithium secondary battery, heat generation and ignition caused by an internal short circuit due to precipitation of lithium dendrites when a liquid electrolyte is used poses a problem, and application of a polymer electrolyte has been desired. Furthermore, as described above,
Unlike a conventional lithium secondary battery, a polymer electrolyte containing an electrolyte solution in a polymer does not require a separator, and thus can be used by joining a positive electrode and a negative electrode with a polymer electrolyte interposed therebetween. Since such a polymer electrolyte is lightweight and has shape flexibility as compared with a liquid electrolyte, for example, it is possible to make a thin film such as a sheet, and it is possible to produce a lightweight and space-saving battery. There is a point.

As the performance of secondary batteries such as lithium secondary batteries has been improved, the active material layer containing the active material and the electrolyte layer have been developed to reduce the size and weight of the batteries. Attempts have also been made to improve the conductive electrode substrate together with the improvement. Reducing the weight of the base material leads to a reduction in the weight of the secondary battery itself, that is, an improvement in the weight energy density. Therefore, a perforated substrate such as an expanded metal or a punched metal has been used. These can be freely changed in weight by changing the aperture ratio.However, if the aperture ratio is high, the strength is insufficient, and as a result, it becomes difficult to handle the battery at the time of manufacturing and the like. There is also a problem from the viewpoint of productivity, for example, the viscosity range of the coating liquid cannot be freely set in order to maintain the uniformity of the coating film after applying the coating material for forming a layer.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems in the prior art.
It is an object of the present invention to reduce the weight of a base material for a secondary battery, maintain the strength of the base material, provide a battery with a high energy density as a result, and provide an efficient manufacturing process. As a result of the study of the present inventors, the above object as a base material,
They have found that this can be achieved by reinforcing the conductive electrode substrate with a resin having an acid amide bond or an acid imide bond, and completed the present invention.

[0007]

That is, the gist of the present invention is as follows.
It is present in a secondary battery electrode base film in which a conductive thin film is formed on at least one surface of a plastic film made of a resin having an acid amide bond and / or an acid imide bond. Another aspect of the present invention is directed to a secondary battery including a positive electrode and a negative electrode each having an active material layer formed on a conductive electrode substrate, and an electrolyte layer, wherein the positive electrode and / or the negative electrode are electrically conductive. A secondary battery characterized in that a resin layer made of a resin having an acid amide bond and / or an acid imide bond is formed on the back side of a substrate.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The base film of the present invention is formed by forming a thin film made of a conductive material on one or both sides of a plastic film. Usually, metals or alloys such as aluminum and copper are used as the conductive material. Examples of a method for forming a metal thin film include a metal foil laminating method, a sputtering method, and a vacuum deposition method, and any method can be used as long as the adhesiveness between the metal thin film and the plastic film is sufficient. At this time, an appropriate adhesive layer may be provided between the plastic film and the conductive thin film by using an adhesive or the like.

When the thickness of the conductive thin film is extremely small, the thickness is usually 10 nm or more, preferably 100 nm or more because heat generation due to battery current is feared due to electric resistance in the metal. . On the other hand, the upper limit is usually 1000 μm or less, preferably 10 μm, from the viewpoint of improving the weight energy density and volume energy density of the battery.
m or less.

It is necessary that the material of the plastic film contains a resin having an acid amide bond and / or an acid imide bond. Preferably, it contains a resin having an acid amide bond. Examples of the resin having an acid amide bond include various commonly used polyamide resins. Examples of such polyamide resins include aliphatic polyamides represented by various nylons and aramids (aromatic polyamides). Specifically, aliphatic polyamides such as polycapramide, polyhexamethylene adipamide, polyhexamethylene sebacamide, polyundecaneamide, poly-ω-aminoheptanoic acid, poly-ω-aminononanoic acid, and phenylenediamine and benzene Aromatic polyamides such as polycondensates with carboxylic acids can be mentioned. Preferably, it is an aromatic polyamide.

Further, a resin having an acid imide bond can be used. As the resin having an acid imide bond,
Examples include cyclized polycondensates of various tetracarboxylic anhydrides and diamines, such as polycondensates of pyromellitic anhydride and m-phenylenediamine. These resins generally have high mechanical strength at room temperature. In addition, it has a high melting point and softening point, little thermal decomposition and deterioration by heat, and high mechanical strength at high temperatures. In the battery manufacturing process, the above-mentioned characteristics are important because tension or heat is usually applied to the base material such as application, drying, reaction, and conveyance of a paint.

The weight average molecular weight of these resins is as follows:
Usually, it is about 10,000 to 1,000,000. In addition, as a material of the plastic film, a mixture of the above resin having an acid amide bond and / or an acid imide bond and another resin is used, or the plastic film has the above acid amide bond and / or an acid imide bond. A laminate in which a layer made of a resin and a layer made of another resin are stacked can also be used. In any case, the ratio of the resin having the acid amide bond and / or the acid imide bond to the entire plastic film is usually 50% by weight or more, preferably 90% by weight.
% By weight or more.

When a thermoplastic resin represented by polyethylene or polypropylene is used, the electrode itself is deformed by the application of heat during the battery manufacturing process due to low heat resistance. When a short circuit occurs and heat is generated, the electrode is thermally deformed to promote a short circuit, and thus is insufficient for use as a battery electrode base material. However, when a resin having an acid amide bond and / or an acid imide bond is used, the mechanical strength is high at both room temperature and high temperature, and it can be applied to such manufacturing and battery safety. The electrode weight can be significantly reduced as compared with the use of the metal single film. Further, polyester resin represented by PET is not preferable because the strength is not sufficient and irreversible elongation occurs particularly when tension is applied under heating.

[0014] Even for PET films and the like which have been insufficient for use from the viewpoint of heat resistance in the past, by forming a composite film in which the above-mentioned resin films are bonded together, it is possible to obtain an intermediate property between the two films. it can. If the thickness of the plastic film is too small, the strength of the resin layer itself becomes weak, and furthermore, the handling tends to be difficult in production, so that it is usually 1 μm or more, preferably 5 μm or more.
μm or more, and more preferably 10 μm. Conversely, if it is too large, the volume energy density and weight energy density of the battery will decrease, so that it is usually 50 μm or less, preferably 30
μm or less, more preferably 20 μm or less. The ratio of the thickness of the plastic film to the total thickness of the base film is 以下 or less, preferably ２〜 to ８, as compared with the case where the plastic portion is replaced with the same material as the conductive thin film. The ratio is preferably about 10 to 99%, and more preferably 30 to 95%.

The base film of the present invention may be provided with a plurality of holes communicating between the front and back surfaces of the film, such as a punched metal. Thereby, the weight of the substrate can be further reduced, and the adhesiveness between the active material layer and the substrate can be improved. The base film of the present invention is formed by forming a conductive thin film on one or both sides of a plastic film, and is used as a base material of a positive electrode and / or a negative electrode of a secondary battery. The thin film is in contact with the active material layer.

Hereinafter, a secondary battery using the substrate film of the present invention will be described. The secondary battery of the present invention, a positive electrode and a negative electrode formed by forming an active material layer on a conductive electrode substrate,
And an electrolyte layer provided between them, and a positive electrode and / or
Alternatively, a resin layer having an acid amide bond and / or an acid imide bond is provided on the back surface of the conductive electrode substrate of the negative electrode.
In this case, the conductive electrode substrate corresponds to the conductive thin film,
The resin layer corresponds to the plastic film.

As the conductive electrode substrate of the positive electrode, various metals described as the conductive thin film can be used, but aluminum is preferably used. The same applies to the conductive electrode substrate of the negative electrode, but copper is preferable. Preliminarily roughening the surface of the conductive electrode substrate on the active material layer side is a preferable method because the effect of binding to the active material layer is improved. Examples of the surface roughening method include blasting and rolling with a rough surface roll, and a method using a polishing cloth, a grinding stone, emery buff, a wire brush equipped with a steel wire, etc. to which the abrasive particles are fixed. Mechanical polishing, electrolytic polishing, chemical polishing, and the like.

Incidentally, another layer such as a primer layer may be present between the conductive electrode base material and the active material for the purpose of enhancing the adhesiveness as required. For the material used for the active material layer of the positive electrode or the negative electrode, the material used for the electrolyte layer, and the packaging material for packaging them, conventionally known materials can be used.Here, examples of the lithium secondary battery are given. explain.

Active materials capable of inserting and extracting lithium ions used for the positive electrode of a lithium secondary battery include Fe, Co,
Examples include various inorganic compounds such as oxides of transition metals such as Ni and Mn, composite oxides with lithium, and sulfides. Specifically, transition metal oxide powders such as MnO, V ₂ O ₅ , V ₆ O ₁₃ and TiO ₂ , composite oxide powders of lithium and transition metal such as lithium nickelate and lithium cobaltate, TiS ₂ , Transition metal sulfide powder such as FeS can be used. Further, organic compounds such as a conductive polymer such as polyaniline can also be used. Of course, the above-mentioned inorganic compounds and organic compounds may be used as a mixture.

As the active material capable of inserting and extracting lithium ions used for the negative electrode, a carbonaceous material such as Li metal, graphite and coke can be used. These positive electrodes,
The particle size of the active material of the negative electrode may be appropriately selected in consideration of other components of the battery, but is usually 1 to 30 μm, and particularly preferably 5 to 25 μm because battery characteristics are good.

In the active material layer, if necessary, a binder,
It can contain a conductive substance and various additives. The binder needs to be stable to an electrolytic solution or the like, and is desired to have weather resistance, chemical resistance, heat resistance, flame retardancy, and the like. Further, a material having excellent ion conductivity is desirable, and examples thereof include a cross-linkable polyethylene oxide resin.
More preferably, a resin obtained by introducing an acryl group, a methacryl group, or the like into the terminal of the polyethylene oxide resin and cross-linking by heat, ultraviolet light, or the like is desirable. The weight ratio of the active material to the binder is usually 60/40 or more, preferably 80/20 or more, and is usually 99/1 or less, preferably 98/2 or less.

The conductive substance is not particularly limited as long as it is a substance capable of imparting conductivity by mixing an appropriate amount of a compound powder capable of inserting and extracting lithium, and carbon-based powders such as acetylene black, carbon black and graphite can be used. And a metal powder that is stable at the electrode potential used. The DBP oil absorption of these conductive substances is preferably 120 cc / 100 g or more, particularly preferably 150 cc / 100 g or more because the electrolyte retains the electrolyte.

Next, the electrolyte layer used in the lithium secondary battery will be described. The electrolyte layer may be made of an electrolytic solution or a polymer electrolyte. In the former case, it is preferable that the positive electrode and the negative electrode are arranged with a separator such as a porous film made of polyethylene or the like interposed therebetween, and that the whole is impregnated with an electrolytic solution.

Examples of the latter polymer electrolyte include a polymer in which an electrolyte is contained in a polymer to form a gel, and a polymer in which a conductive polymer is used. Both the former and the latter are preferably non-aqueous electrolytes, which generally use a non-aqueous solvent in which a supporting electrolyte, which is a lithium salt, is dissolved. is there.

As the supporting electrolyte, LiPF ₆ , L
iAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCl
O ₄ , Lil, LiBr, LiCl, LiAlCl, L
iHF ₂ , LiSCN, LiSO ₃ CF _{2 and the} like. Among them, LiPF ₆ and LiClO ₄ are particularly preferable. The content of these supporting electrolytes in the electrolytic solution is generally 0.5 to 2.5 mol / l.

The non-aqueous solvent in which the electrolyte is dissolved is not particularly limited, but a solvent having a relatively high dielectric constant is preferably used. Specifically, cyclic carbonates such as ethylene carbonate and propylene carbonate, acyclic carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, glymes such as tetrahydrofuran, 2-methyltetrahydrofuran and dimethoxyethane, γ-butyl lactone and the like Lactones,
One or a mixture of two or more of sulfur compounds such as sulfolane and nitriles such as acetonitrile can be mentioned. Of these, especially ethylene carbonate,
One or more mixed solutions selected from cyclic carbonates such as propylene carbonate, and non-cyclic carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferred.

In the case of a gel polymer electrolyte, the above-mentioned electrolyte solution is impregnated with a polymer such as polyethylene oxide, polypropylene oxide, a crosslinked isocyanate of polyethylene oxide, phenylene oxide, phenylene sulfide polymer, or the like. A gel electrolyte can be obtained by applying a polymerization treatment such as ultraviolet curing or thermal curing after applying an electrolytic solution containing the above monomer on the electrode.

The above-mentioned active material layer, electrolyte layer, and in some cases, the primer layer are usually formed by coating. In particular, the electrode is usually formed by applying a paint containing the material of the active material layer thereon and drying it while running the long base film. In a secondary battery using a polymer electrolyte such as a lithium ion complex-containing polymer electrolyte, a plasticizer-containing polymer electrolyte, a gel polymer electrolyte, or a completely solid electrolyte, the problems of adhesion and adhesion between the constituent layers are as follows. This has a great effect on battery performance as compared to the case of a lithium ion battery called a normal liquid system. As these coating methods, together with the wet-on-dry method in which each layer is applied for each constituent layer and then post-processed and superimposed as described above, a multi-layer state is simultaneously formed and applied in a liquid state. Examples of the method include a multi-layer simultaneous application method and a so-called sequential wet-on-wet method in which another layer is overcoated on a sufficiently wet coating layer without any post-treatment. In particular, multilayer simultaneous coating method, sequential wet-
The on-wet method is preferable because the variation in battery performance related to internal impedance and charge / discharge can be significantly reduced. In the method of manufacturing a battery according to the present invention, these methods may be appropriately used depending on the productivity and battery performance.

The coating device is not particularly limited,
In the case of multi-layer simultaneous application, each paste is formed into a multi-layer state in a liquid (semi-solid) state, and is then placed on a support to realize multi-layer simultaneous application. This includes
Although slide coating and extrusion type die coating are mentioned, the extrusion method is preferable in consideration of the paste viscosity and the applied film thickness.

Further, in the case of multi-layer coating by the sequential wet-on-wet method, almost the same performance is obtained as compared with that produced by the above-mentioned multi-layer simultaneous coating method. In this method, in addition to the extrusion die method, a reverse roll, a gravure, a knife coater, a kiss coater, a microgravure, a knife coater, a rod coater, a blade coater, and the like, if possible, the application method is not limited at all. Further, a variety of coating methods can be used in combination as compared with the multilayer simultaneous method. Further, depending on the wet state and viscosity of the lower layer, another layer in a wet state, which has been applied to another support, may be transfer-laminated and applied as an upper layer. The shape of the secondary battery of the present invention is cylindrical, box, paper, card,
Various shapes such as a circular shape can be used.

[0031]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.

[Preparation of paint for positive electrode]

Table 1 Composition Lithium cobaltate (Cellseed C10 manufactured by Nippon Chemical Industry) 92.0 wt% Acetylene black (Denka Black manufactured by Denki Kagaku Kogyo) 4.0 wt% Polyvinylidene fluoride (KF polymer manufactured by Kureha) 4.0 wt% N-methyl -2-Pyrrolidone (Mitsubishi Chemical) 67.0 wt%

The material having the above composition was kneaded with a kneader for 2 hours to obtain a positive electrode paint.

[Preparation of paint for negative electrode]

[Table 2] Composition Coke (MBC manufactured by Mitsubishi Chemical) 92.0 wt% Polyvinylidene fluoride (KF polymer manufactured by Kureha) 8.0 wt% N-methyl-2-pyrrolidone (Mitsubishi Chemical) 67.0 wt%

The material having the above composition was kneaded with a kneader for 2 hours to obtain a negative electrode paint.

[0036]

[Paste for Polymer Electrolyte] Binder (Photomer 4050, manufactured by Henkel) 20 wt% Binder (polyethylene oxide) 2.0 wt% Lithium perchlorate 15.0 wt% Polymerization initiator (Trignox 42, manufactured by Akuzo Nobel) 0.5 wt % Solvent (Mitsubishi Chemical's propylene carbonate) 100.0wt%

The materials having the above composition were mixed, stirred and dissolved to obtain a paste for a polymer electrolyte.

[0038]

[Table 4] [Base film] Base film for positive electrode: Aluminum / aramid film 6 µm / 10 µm thick Base film for positive electrode: Aluminum / polypropylene film 6 µm / 10 µm thick Base film for positive electrode: Aluminum film 16 µm thick Base for negative electrode Material film: copper / aramid film 6 μm / 10 μm thickness Negative substrate film: copper / polypropylene film 6 μm / 10 μm thickness Negative substrate film: copper film 16 μm thickness The aramid resin used above is p-phenylenediamine-based It is a polycondensate (weight average molecular weight of 20,000 to 30,000) of a compound and a terephthalic acid compound, and has the following properties.

[0039]

[Table 5] Young's modulus: 1100/1600 kgf / mm ² (the former shows the value in the vertical direction, and the latter shows the value in the lateral direction. The same applies hereinafter). Tensile strength: 60/70 kgf / mm ² Tensile elongation: 50/30 kgf / mm ² Heat shrinkage: 0% (100 ° C), 0.1% (200 ° C)

Example 1 and Comparative Examples 1 and 2 A state in which a tension of 0.2 (kg / cm width) was applied to each of the long base material films for positive electrode and negative electrode shown in Table 1. Then, the positive electrode paint and the negative electrode paint were applied on a metal surface on each base film by an extrusion die coating method, and dried at 120 ° C. Each of the obtained electrode sheets was compacted by a roll press having a linear pressure of 300 kgf / cm, and then cut into a predetermined shape. After the polymer electrolyte paste was applied on the electrode and cured by ultraviolet rays to form a gel polymer electrolyte layer, the two electrolyte layers were bonded together to obtain a thin film lithium secondary battery. At this time, the thicknesses of the positive electrode, the negative electrode, and the electrolyte layer were 100 μm, 100 μm, and 50 μm, respectively.

Table 1 shows the number of samples that could be initially charged / discharged for the 20 batteries obtained. Table 1 also shows the discharge capacity ratio of each example when the initial discharge capacity of the battery of Example 1 was set to 100. Here, the charge is 0.
The results obtained when the discharge was performed at 2C (the amount of current that fully charges in 5 hours) and the discharge was performed at 0.2C and 1C are shown. In addition, for each of the samples for which initial charge and discharge were possible,
Table 1 shows the number of samples that achieved a discharge capacity retention ratio of 80% after the charge / discharge cycle test at 0.2C.

Further, Table 1 shows the battery weight ratio when the average weight (positive / negative electrodes and electrolyte) of 20 batteries using the conventional electrode substrate (Comparative Example 2) is set to 100. As is clear from Table 1, it can be seen that Example 1 and Comparative Example 2 show almost the same battery performance. However, in the case of Comparative Example 1, even when a metal thin film was provided on a polypropylene resin, the ratio of sufficiently exhibiting battery performance was extremely reduced. It is considered that this is because the substrate was deformed by heating and drying while applying tension during application, and the bonding of the positive electrode, the electrolyte, and the negative electrode was non-uniform in the plane. In addition, it is considered that the deformation causes a crack in the metal thin film, which affects the electron conductivity of the current collector.
Comparing Example 1 with Comparative Example 2, it can be seen that even if the charge and discharge capacities of the batteries are the same, using a plastic substrate with a metal thin film is more effective in reducing battery weight.

[0043]

[Table 6]

[0044]

[Table 7]

[0045]

The weight of the substrate film of the present invention is 1/2 to 1/8 of that of a conventional substrate consisting of a metal film alone.
Since it can be reduced to the extent, the weight energy density of the battery can be improved. In particular, in the case of a battery having a large amount of electrodes and a high capacity as used in electric vehicles and the like, the effect of reducing the weight of the base material is particularly large. Further, the resin film has a higher elasticity than the metal film, so that the resin film is easy to handle at the time of manufacturing the battery. Furthermore, since the resin having an acid amide bond or an acid imide bond used in the present invention has excellent heat resistance and mechanical strength, it can solve the problem of thermal deformation during the manufacturing process and has uniform in-layer adhesion. It is possible to make batteries with small variations. Further, this makes it possible to greatly improve the cycle characteristics of the battery. Therefore, it greatly contributes to both the production aspect and the performance aspect of the battery.

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Claims (6)

[Claims] An electrode substrate film for a secondary battery, comprising a plastic film made of a resin having an acid amide bond and / or an acid imide bond, on at least one surface of which a conductive thin film is formed. 2. The plastic film has a thickness of 1-50.
The electrode substrate film for a secondary battery according to claim 1, which has a thickness of μm. 3. The conductive thin film has a thickness of 100 nm or more and 10 or more.
The electrode substrate film for a secondary battery according to claim 1, wherein the thickness is not more than μm. 4. The plastic film is made of a resin having an acid amide bond, and the resin having the acid amide bond is
The electrode substrate film for a secondary battery according to claim 1, further comprising an aromatic polyamide. 5. A secondary battery using the electrode substrate film according to claim 1. 6. A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte layer each having an active material layer formed on a conductive electrode substrate, and a positive electrode and / or a negative electrode on the back side of the conductive electrode substrate. A secondary battery comprising a resin layer formed of a resin having an acid amide bond and / or an acid imide bond.