JP5271182B2 - Non-aqueous electrolyte battery adhesive and non-aqueous electrolyte battery using the same - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte adhesive and a battery using the same, and particularly to an adhesive for bonding a member constituting a non-aqueous electrolyte such as a lithium battery having improved adhesive strength. The present invention relates to a non-aqueous electrolyte battery.

  Conventionally, digital cameras and small portable electronic devices such as PDAs have been widely used, and a large-capacity lithium battery has been adopted as a power source for that purpose. These electronic devices are always required to have a minimum volume and light weight, and the batteries are required to be similarly small, light, and large capacity.

  As such a battery, a film-like lithium non-aqueous electrolyte battery has been put into practical use in recent years. The structure of this battery is shown in FIG. 1 which is a partially cutaway view and FIG. 2 which is a cross-sectional view of a cell body which is a power generation element of a lithium nonaqueous electrolyte battery. As shown in FIGS. 1 and 2, the battery 10 includes a negative electrode current collector 21, an adhesive layer 22, a negative electrode active material layer 23, an electrolyte layer 24 made of an electrolytic solution and a gelling agent, a separator 25, an electrolyte, and the like. The cell body 12 including the layer 26, the positive electrode active material layer 27, the adhesive layer 28, and the positive electrode current collector layer 29 is covered with a highly airtight exterior material 11. The electrodes connected to the cell body 12 are led out from the current collectors 21 and 29 as tab-shaped terminals 13 and 14.

  If the electrolyte containing the carbonate-based solvent that forms the electrolyte layer contained inside the battery leaks to the outside, the battery will not function, and depending on the material, there is a risk of ignition, etc. Yes, not preferred. For this purpose, high adhesive strength is required for the exterior material 11 and the exterior material 11 and the tab-like terminals 13 and 14 in consideration of the severe usage of the battery.

  Conventionally, as this exterior material, a polyamide film layer disposed on the outer surface having mechanical strength and a material such as polypropylene or polyethylene film having excellent airtightness are bonded and laminated to an aluminum foil as an intermediate layer as an inner layer. Is formed. In addition, the tab electrode led out from the current collector and the exterior material are hermetically sealed by heat seal adhesion, but the inner surface of the exterior material is an olefin-based film such as polypropylene or polyethylene film. The terminal is made of a tab electrode with a film in which an olefin film such as polyethylene or polypropylene of the same quality is heat-sealed to the tab electrode in advance, and is heat-sealed to the exterior material.

  As described above, in the lithium non-aqueous electrolyte battery, a laminated structure using a polymer film and a metal foil bonded to each other is frequently used, and these are required to maintain airtightness even under severe use conditions. However, the conventional adhesive technology has not been able to realize an adhesive technology having sufficient adhesive strength, and therefore there is a risk of leakage particularly in applications such as non-aqueous electrolyte batteries.

Further, in lithium-based non-aqueous electrolyte batteries, an organic solvent electrolyte containing a lithium salt as an electrolyte, such as LiPF ₆ , is widely used. By the way, this fluorine-containing electrolyte such as LiPF ₆ is chemically decomposed and generates HF when water is mixed into the electrolytic solution. This HF is a highly corrosive substance, which erodes the adhesive constituting the lithium battery, causes peeling of the outer packaging material, and may cause electrolyte leakage.

  The present invention was made in order to solve the problems in adhesives used in conventional lithium non-aqueous electrolyte batteries and the like, and by preventing the leakage of liquid by improving the adhesive strength of battery members joined by the adhesive. The object is to realize a non-aqueous electrolyte battery with improved performance and battery life.

The present invention relates to an adhesive for obtaining a positive electrode for a nonaqueous electrolyte battery by binding a positive electrode active material to the surface of a positive electrode current collector, and a chitosan derivative represented by Chemical Formula 1 having a deacetylation degree of 80% or more And an organic compound having at least one carboxyl group in the molecule.

………化学式１

.... Chemical formula 1

  According to the present invention, a member constituting a battery such as a polymer film such as polypropylene or polyethylene having high hydrophobicity or a metal foil such as aluminum foil having high polarity can be bonded with high strength. In the non-aqueous electrolyte battery using, the leakage performance of the organic solvent is improved, and a battery having high practicality can be obtained.

FIG. Sectional drawing which shows the electric power generation element (electrode body unit) of a nonaqueous electrolyte battery. Sectional drawing of the laminated body used with the battery of this invention.

  As described above, the present invention is characterized in that the chitosan derivative represented by the chemical formula 1 (hereinafter, the chitosan derivative represented by the chemical formula 1 is abbreviated as chitosan derivative) is used for adhesion of the members constituting the battery. have.

[adhesive]
The chitosan derivative, which is the main component of the adhesive 32, is chitin, which is a naturally occurring polymer substance obtained from crusts such as crabs, shrimps and insects, or mushrooms, that is, β-poly-N-acetyl-D-glucosamine. It is obtained by glycerating chitosan, which is a polysaccharide containing an amino group having 2-amino-2-deoxy-D-glucose as a structural unit obtained by deacetylation, and forms various acids and salts to form water. It is a material that exhibits cationic properties when dissolved in. Since it is a compound having such a high reactivity, it can be bonded to either the hydrophilic material surface or the hydrophobic material surface.

Such chitosan derivatives are produced industrially, are supplied in various grades, and are commercially available.
In the present invention, a chitosan derivative having a degree of deacetylation of 80% or more is suitable. When the degree of deacetylation is lower than the above range, it becomes difficult to dissolve in water because it dissolves in water to form an aqueous solution, which is inappropriate for the present invention.
Moreover, 1000 or more and 2 million or less are preferable, and, as for a weight average molecular weight, it is more preferable that it is the range of 10,000-1 million. If the molecular weight is below this range, it is inappropriate for use in the present invention in terms of film formation of the adhesive layer. On the other hand, if the molecular weight exceeds this range, the viscosity of the aqueous solution increases. Therefore, it is inappropriate for use in the present invention in terms of handling such as workability.
As the specifications of the adhesive, it is preferable that the chitosan derivative further contains an organic compound having at least one carboxyl group in the molecule.

In the present invention, the members constituting the non-aqueous electrolyte battery are joined using an adhesive containing a chitosan derivative. As the adhesive, an aqueous solution in which the chitosan derivative is dissolved in water can be used. The concentration is preferably in the range of 0.1 to 20% by mass. When the concentration of the chitosan derivative is less than 0.1% by mass, the adhesive strength is not increased and it is not practical. On the other hand, when the concentration of the chitosan derivative exceeds the above range, the viscosity increases and handling becomes difficult.
In addition to chitosan derivatives, additives such as organic compounds having at least one carboxyl group in the molecule, rheological property improvers (thixotropic improvers), preservatives, antioxidants, etc. may be used in combination with this adhesive. Can do.

[Nonaqueous electrolyte battery]
As shown in FIGS. 1 and 2, the nonaqueous electrolyte battery suitable for applying the present invention has the following structure. That is, a positive electrode and a negative electrode are overlapped with a separator 25 inside the exterior material 11 formed using a sheet body obtained by bonding a metal foil and a polymer film with an adhesive, or flattened after winding. In this structure, the rectangular electrode body unit 12 is accommodated, and the separator 25 is impregnated with an electrolyte. The electrode body unit 12 is provided with a positive electrode current collector plate 29 on the positive electrode side surface and a negative electrode current collector plate 21 on the negative electrode side surface. The lead terminal of the positive electrode current collector plate and the lead terminal of the negative electrode current collector plate Tab terminals 13 and 14 projecting outward from the upper edge of the outer package 11 and leading out. Olefin films 15a and 15b are attached to the surfaces of these tab terminals 13 and 14, and when sealed by heat sealing using the exterior material 11, the surface of the tab terminals 13 and 14 is packaged. The material 11 is bonded in an airtight manner. As this olefin film, a modified polyolefin such as maleated polypropylene is suitable.

  As an application object of the present invention to be bonded using the chitosan derivative of the present invention, the metal foil and the polymer film constituting the exterior material 11 are joined, the tab terminals 13 and 14 for external derivation and the exterior material 11 are joined, Examples include bonding of the electrode current collectors 21 and 29 and the active materials 23 and 27.

(Exterior material)
In a lithium nonaqueous electrolyte battery using a nonaqueous organic solvent, a laminated structure in which a metal foil and a polymer film are bonded is used as an exterior material. This is a combination of these materials in order to prevent the gas containing the organic solvent inside and outside the battery from flowing and to improve the mechanical strength. The adhesive used in this laminated structure needs to be an adhesive that is not eroded by an organic solvent, and has a hydrophilic surface such as a metal foil surface and a hydrophobic surface such as a polymer film. It is necessary to have a function capable of bonding, and as described above, a chitosan derivative is suitable.

  As shown in FIG. 3, the laminated structure of the present embodiment includes a polymer film 31, an adhesive 32 having chitosan derivatives as main components, a metal foil 33, an adhesive 34 having chitosan derivatives as main components, and a high It consists of a molecular film 35.

  The metal foil used in the present invention is a foil of a metal such as aluminum, copper, nickel, iron, stainless steel, or an alloy thereof, and the thickness thereof is not particularly limited. The range of 10-100 micrometers is preferable. The surface may be a rolled processed surface as it is, or may be roughened. By roughening the surface by sandblasting or the like, an improvement in adhesion can be expected.

The polymer film used in the present invention is preferably determined in consideration of mechanical strength, airtightness, electrical insulation, heat resistance, and the like. As materials having these characteristics, materials such as polypropylene, polyethylene, polyester, polyamide, polyimide, polyvinylidene fluoride, and polyurethane are suitable. As a laminated structure suitable for the exterior material, a laminated structure made of a polyamide film such as nylon, a metal foil, and a polyolefin film is suitable.
The surface of such a laminated structure may be the surface of the polymer material itself, but it is preferable to make it hydrophilic by oxidation treatment or the like because the adhesive strength is further improved. In addition, the adhesiveness can be further improved by modification by maleation. The thickness of the film is not limited at all, but when the structure is used in a battery, a range of 10 to 100 μm is preferable.

  As described above, the laminated structure having such a structure can be used not only for battery exterior materials but also for foods using characteristics such as moisture resistance, mechanical strength, heat resistance, deodorization, oxygen permeation prevention, and the like. It can be used for packaging exterior materials, pharmaceutical exterior materials, and the like.

This laminated structure can be manufactured as follows.
That is, first, a chitosan derivative and possibly other additives are dissolved in water on the surface of the first polymer film, and an aqueous solution is applied and dried, and a metal foil is attached to the surface. Next, similarly, an adhesive composed of a chitosan derivative is applied to the surface of the metal foil and dried, and a second polymer film is adhered to the surface. Strong adhesion can be performed by heating and pressurizing the laminate thus formed.

(Positive electrode)
The positive electrode of this embodiment is obtained by bonding a positive electrode active material to the surface of a positive electrode current collector using an adhesive. In this embodiment, an adhesive containing a chitosan derivative and an organic compound having at least one carboxyl group in the molecule is suitable as the adhesive because of its solvent resistance.
As a positive electrode material of this Embodiment, generally well-known positive electrode material can be used as a nonaqueous electrolyte battery, without receiving a restriction | limiting in particular. Specifically, for example, mixed with the lithium-containing salt as the positive electrode active material _{(LiCoO 2, LiNiO 2, LiMnO} 2, LiFeO 2 or the like) carbon powder (graphite powder, coke powder etc.) as a conductive agent and a binder And what was formed by apply | coating and drying to the positive electrode collector surface like aluminum can be used.

(Negative electrode)
In the negative electrode of this embodiment, a negative electrode active material is bonded to the surface of a negative electrode current collector using an adhesive. In this embodiment, an adhesive containing a chitosan derivative and an organic compound having at least one carboxyl group in the molecule is suitable as the adhesive because of its solvent resistance.
As the negative electrode material of the present embodiment, a generally known negative electrode material as a nonaqueous electrolyte battery can be used without any particular limitation as in the case of the positive electrode described above. For example, the negative electrode plate may be formed by mixing graphite powder as a negative electrode active material with a binder, and applying and drying the negative electrode current collector surface such as copper.

(Separator)
The separator prevents the positive electrode and the negative electrode from coming into direct contact and short-circuits in the battery, and a known material can be used in the nonaqueous electrolyte battery. Specifically, it is made of a porous polymer film such as polyolefin or paper. As this porous polymer film, a film made of polyethylene, polypropylene, or the like is preferable because it is not affected by the electrolyte. The separator is formed in a size slightly larger than that of the positive electrode or the negative electrode, and its end portion extends outward from the end portion of the positive electrode or the negative electrode so that the two electrodes do not come into contact with each other.

  In this separator, an electrolyte is filled in a portion of the porous membrane sandwiched between the positive electrode and the negative electrode so that ion conduction is sufficiently performed between the positive electrode and the negative electrode.

(Electrolytes)
As the nonaqueous electrolyte of the present embodiment, a gel containing a nonaqueous solvent and a nonaqueous electrolyte substance is used.
Examples of the solvent for the nonaqueous electrolytic solution include organic solvents such as ethylene carbonate and propylene carbonate, or dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, and the like. Examples of the electrolyte that is a solute of the nonaqueous electrolytic solution include LiPF ₆ , LiClO ₄ , and LiCF ₃ SO ₃ .

(Tab terminal part)
As described above, the tab terminal is a terminal derived from the positive and negative electrode collectors, and has a structure derived from the sealing joint interface of the exterior material to the outside. The tab terminals 13 and 14 are made of a metal foil such as aluminum or nickel. Even if the exterior material is heat-sealed, the tab terminals 13 and 14 have an airtight adhesion between the tab terminal and the exterior material. Since it does not occur, it is preferable that the polymer films 15a and 15b are bonded in advance to the surfaces of the tab terminals 13 and 14, respectively. Adhesion between the tab terminal and the polymer films 15a and 15b is preferably performed with an adhesive using the chitosan derivative of the present embodiment in order to prevent leakage.

  The nonaqueous electrolyte battery of the present embodiment has the above-described structure, and when bonding is performed with an adhesive in this structure, the organic compound has at least one carboxyl group in the molecule and a chitosan derivative as the adhesive. It is preferable to use an adhesive containing, in order to improve leakage resistance and improve battery life.

(Method for producing non-aqueous electrolyte battery)
This non-aqueous electrolyte battery can be manufactured as follows.
(1) Production of electrode body unit A positive electrode current collector plate and a negative electrode current collector plate are produced by cutting a conductive metal foil into a predetermined shape. The positive electrode is prepared by mixing a positive electrode active material, a conductive agent, and a binder and applying the mixture to the surface of the positive electrode current collector plate. The negative electrode is prepared by mixing a negative electrode active material and a binder and applying the mixture to the surface of the negative electrode current collector plate. In this positive and negative electrode, an adhesive containing a chitosan derivative and an organic compound having at least one carboxyl group in the molecule is preferably used for the bond between the active material and the current collector. The separator is produced by cutting a polyolefin-based porous film into a predetermined shape. A plurality of these positive electrodes, separators, and negative electrodes are overlapped to form an electrode body unit.
Moreover, a long positive electrode, a separator, a negative electrode, and a 2nd separator can be wound in a coil shape, and this can be compressed flatly to make an electrode body unit.

(2) Impregnation of electrolytic solution A nonaqueous solvent, a nonaqueous electrolyte, and optionally a gelling agent are added and blended to adjust the electrolytic solution. By immersing the electrode body unit in the electrolytic solution, the electrolytic solution can be impregnated. When the viscosity of the electrolytic solution is high, it takes a long time for the electrode body unit to be impregnated with a sufficient amount of the electrolytic solution. In such a case, the impregnation can be efficiently performed by disposing the electrode body unit in a container that can be depressurized, injecting the electrolytic solution into the container after depressurizing.

(3) Exterior material After that, a laminated body having a first polymer film, a metal foil, and a second polymer film is disposed so as to enclose the electrode body unit impregnated with the electrolytic solution, and the polymer film is disposed on the surface. The laminated film is sealed in a state where the tab-shaped lead terminal led out from the electrode body unit is sandwiched. This sealing can be performed by heat sealing when the opposite surfaces of the laminate film are polymer films, which are heated and bonded. On the other hand, if the opposing surface is a metal foil, sealing can be performed using an adhesive.

  The impregnation step (2) may be performed before the separator is overlaid with the positive electrode and the negative electrode, or after the porous film is overlaid with the positive electrode plate and the negative electrode plate to form the electrode body unit. Also good.

A non-aqueous electrolyte battery can be produced by the above manufacturing method.

  Hereinafter, the present invention will be described with reference to examples and comparative examples.

Example 1
In order to confirm the effect of the adhesive of the present invention, an adhesive mainly composed of a chitosan derivative (World Rock (registered trademark) X-SC01: solid content 5.0%) is applied in advance to the surface of the nickel foil and dried. Then, a maleated polypropylene film was adhered to the surface by heat sealing to prepare a 50 × 5 mm peel test piece.

(Comparative Example 1)
A peel test piece was prepared in the same manner as in the above example, except that Worldlock (registered trademark) X-SC02 and a solid content of 1.0% were used as the adhesive.

(Peel test)
About the peeling test piece created in the said Example 1 and the comparative example, force was applied to nickel foil and a polypropylene film, and peeling strength was measured at the speed | rate of the tensile rate of 100 mm / min.
As a result, the peel strength of the comparative peel test piece was 720 g / 5 mm. On the other hand, the peeling test piece of this example was 930 g / 5 mm, peeling of the adhesive portion was not observed, and the film was broken.

(Hydrofluoric acid immersion test)
The peel test pieces of Examples and Comparative Examples were immersed in a 1.0% hydrofluoric acid aqueous solution for 30 minutes, and the peel test was performed.
As a result, in the peel test piece of Example 1, no peel was observed in all 10 peel test pieces, while in the peel test piece of the comparative example, 10 peel test pieces did not peel. There were only 6 samples.

(Reference Example 1)
A non-aqueous electrolyte battery having a battery capacity of 150 mAh was produced according to the following specifications.

  Aluminum foil was used for the positive electrode current collector plate, and copper foil was used for the negative electrode current collector plate. From these current collector plates, an aluminum foil tab terminal was connected to the positive electrode, and a nickel foil tab terminal was connected to the negative electrode. A maleated polypropylene film was bonded to the surface of the tab terminal of the aluminum foil and nickel foil using an adhesive containing chitosan.

The positive electrode is a mixture of LiCoO ₂ powder as a positive electrode active material, carbon powder (Ketjen Black) as a conductive agent, and PVdF powder as a binder in a weight ratio of 90: 3: 2: 5. Was made into a slurry, applied to the surface of the positive electrode current collector plate, and vacuum heat-treated. The area of the positive electrode was 52 cm ² and its thickness was 80 μm.

For the negative electrode, graphite powder as the negative electrode active material and fluororesin as the binder are mixed at a weight ratio of 95: 5, and the mixture is slurried and applied to the surface of the negative electrode current collector plate. It was prepared by heat treatment. The area of the negative electrode plate was 58 cm ² , and the thickness was 65 μm.
A porous film made of polypropylene was used for the separator.

  Then, the positive electrode, the separator, and the negative electrode were overlapped to produce an electrode body unit.

As the non-aqueous electrolyte, a solution in which 1 mol / L of LiPF ₆ was dissolved in a mixed solvent of 5: 5 in a volume ratio of ethylene carbonate (EC) and diethyl carbonate (DEC) was used.

  Then, an aluminum laminate film in which a polyamide film and a polypropylene film are laminated and coated is folded using a 5% by mass aqueous solution of chitosan on an aluminum foil so as to sandwich the electrode body unit, and three sides (upper edge and both side edges) are folded. Part) was heat sealed to form an exterior body, and 3 ml of the above impregnation solution was injected. In addition, when sealing the upper edge part, it sealed in the state which pinched | interposed the lead terminal and the lead terminal.

(Comparative Example 2)
A nonaqueous electrolyte battery was produced in the same manner as in Example 1 except that a modified SEBS adhesive (World Rock (registered trademark) X-P004) was used as the adhesive.

(Leakage test)
A discharge test was performed by applying a load of 3.8 V to each of the batteries of Reference Example 1 and Comparative Example 2 in a constant temperature and humidity chamber having a temperature of 40 ° C. and a humidity of 90%. As a result, in the battery of Reference Example 1, no abnormality was observed even in 7 days in all of the 10 sample batteries. On the other hand, in the battery of Comparative Example 2, liquid leakage was observed for 3 out of 10 samples.

(Modification)
In the foregoing, the application of the adhesive of the present invention to a nonaqueous electrolyte battery has been mainly described. This is because the adhesive of the present invention is particularly excellent in resistance to non-aqueous electrolytes, but the adhesive of the present invention has sufficient adhesive ability as compared with ordinary adhesives. The present invention can also be applied as an adhesive other than the nonaqueous electrolyte battery, for example, a fuel cell.

DESCRIPTION OF SYMBOLS 10 ... Nonaqueous electrolyte battery 11 ... Exterior material 12 ... Power generation element (electrode body unit)
DESCRIPTION OF SYMBOLS 13, 14 ... Tab-shaped terminal 21 ... Negative electrode collector 22 ... Adhesive layer 23 ... Negative electrode active material layer 24 ... Electrolyte layer containing electrolyte solution 25 ... Separator 26 ... Electrolyte layer 27 ... Positive electrode active material layer 28 ... Adhesive layer DESCRIPTION OF SYMBOLS 29 ... Positive electrode collector layer 31 ... 1st polymer film 32 ... Adhesive 33 ... Metal foil 34 ... Adhesive 35 ... Polymer film

Claims (3)

An adhesive for binding a positive electrode active material to the surface of a positive electrode current collector to obtain a positive electrode for a non-aqueous electrolyte battery, wherein the deacetylation degree represented by the chemical formula 1 is 80% or more and in the molecule An adhesive comprising an organic compound having at least one carboxyl group.

.... Chemical formula 1 A positive electrode active material is formed on the surface of the positive electrode current collector using an adhesive containing a chitosan derivative represented by Chemical Formula 1 having a deacetylation degree of 80% or more and an organic compound having at least one carboxyl group in the molecule. A positive electrode for a non-aqueous electrolyte battery, characterized by being bonded.

.... Chemical formula 1 A positive electrode active material is formed on the surface of the positive electrode current collector using an adhesive containing a chitosan derivative represented by Chemical Formula 1 having a deacetylation degree of 80% or more and an organic compound having at least one carboxyl group in the molecule. A non-aqueous electrolyte battery using a bonded battery as a positive electrode.

.... Chemical formula 1

Images