JP5226332B2 - Lithium secondary battery using laminate exterior material - Google Patents

Description

The present invention relates to a lithium secondary battery used for storing electricity generated by a power source of an electronic device, a power source mounted on an electric vehicle, a fuel cell, a solar cell, or the like. More specifically, the present invention relates to a lithium secondary battery that uses a laminate exterior material and is excellent in durability, safety, and workability.

A metal plate such as a stainless steel plate has been used as a case material for a sealed battery. However, since a metal plate such as a stainless steel plate is strong, it is not suitable for processing into a flat and thin shape and has a large specific gravity. Therefore, when used for a thin type battery, the energy density per unit weight of the battery is lowered.

For this reason, in recent years, a thin battery has been made using a laminate exterior material in which a metal foil and a resin film are bonded together. The laminate exterior material is lighter and more flexible than the stainless steel plate, and is therefore suitable for processing into a flat and thin shape. Furthermore, since it can be heat-sealed, the battery is easily sealed. However, the laminate exterior material has a problem that the moisture permeability is higher than that of the stainless steel plate, and the heat-sealed portion has a problem that the moisture permeability is further higher.

When the moisture permeability is high, the moisture present in the atmosphere gradually enters the battery, and in the lithium secondary battery, the lithium salt electrolyte reacts with the moisture and is hydrolyzed to generate hydrogen fluoride. As a result, deterioration occurs in the heat-sealed portion and the metal film of the laminate exterior material. This deterioration further facilitates the entry of moisture in the air into the battery, promotes the deterioration, and eventually causes liquid leakage and the battery life is exhausted.

In order to extend the battery life, water must be prevented from entering the interior as much as possible. Therefore, the hygroscopic material is housed in the synthetic resin housing together with the battery element so that the housing is completely sealed to prevent ingress of air and moisture from the outside, and even if moisture enters, it is absorbed by the hygroscopic material. A lithium secondary battery is known (for example, Patent Document 1). In this battery, the substance that can be removed is limited to moisture, and hydrogen fluoride is not removed. Therefore, if there is moisture that is not absorbed, hydrogen fluoride is generated by reacting with the lithium salt electrolyte, leading to deterioration of the exterior material.

Also known is a lithium secondary battery in which a plastic layer on the electrolyte side of an exterior bag made of a metal layer and a plastic layer, in which an electrolytic solution is enclosed, has a water permeation prevention function and an acid permeation prevention function. (For example, Patent Document 2). In this case, when the exterior bag is formed by drawing, a thin portion having a permeation prevention function may occur. In addition, because of the presence of the absorbent particles mixed in the plastic layer in order to provide the moisture permeation prevention function and the acid permeation prevention function, defects may occur in the outer bag. Therefore, it cannot be used for battery applications involving the drawing process.

Also known is a lithium secondary battery in which a hygroscopic agent is sandwiched between layers at the sealing portion of a laminate outer package made of a metal thin film and a heat-sealable resin film, and the periphery of the hygroscopic agent is sealed by heat-sealing. (For example, Patent Document 3). In this case, processing for sandwiching the hygroscopic agent in the laminate sealing part is difficult, and the adhesive strength of the sealing part is weakened. In order to maintain the adhesive strength of the sealing portion, it is necessary to increase the area of the sealing portion, which causes an increase in the amount of the laminate exterior material used and the problem of battery size. Moreover, since this battery does not have an acid absorption function, deterioration of the exterior body due to the generation of hydrogen fluoride cannot be suppressed.
JP 2000-243357 A Japanese Patent No. 3137061 JP 2003-187762 A

The present invention has been made to solve such problems, prevents moisture from entering the battery and deterioration of the exterior material due to hydrogen fluoride that can be generated inside the battery, and is excellent in workability. An object of the present invention is to provide a lithium secondary battery.

In the lithium secondary battery in which a power generation element is enclosed in a laminate outer package, the inventors of the present invention provide an inorganic particle having an acid absorption function and an inorganic particle having a water absorption function together with the power generation element. It has been found that the above object can be achieved by encapsulating an absorbent sheet having a resin layer containing.

That is, the present invention is lithium in the interior of the exterior body made of a laminated outer member made of a metal layer and a synthetic resin layer, the power generating element comprising a layer having a positive electrode material layer and the negative electrode material layer and the lithium salt electrolyte is filled In the secondary battery, an absorption sheet is enclosed inside the outer package together with the power generation element, and the absorption sheet includes inorganic particles having an acid absorption function and inorganic particles having a water absorption function. It is composed of the above resin layer, and the absorbent sheet has a total of at least 5 parts by weight of the inorganic particles having an acid absorbing function and the water absorbing function with respect to 100 parts by weight of the resin. It is a lithium secondary battery characterized by including.

In the present invention, since the absorption sheet has an acid absorption function and a water absorption function, it is generated by the moisture mixed in the lithium secondary battery and the mixed moisture when it is housed inside the lithium secondary battery. Effectively absorbs hydrogen fluoride and moisture entering from the fusion part of the outer package, and hydrogen fluoride generated by the intruded moisture, and the influence of moisture and hydrogen fluoride on the power generation element, the fused part of the outer package It is possible to avoid a decrease in adhesiveness. Therefore, it is possible to provide a lithium secondary battery excellent in durability and safety, in which deterioration of the exterior body, battery heat generation, and ignition are suppressed. Moreover, since the exterior material does not include particles having an acid absorption function and particles having a water absorption function, it can be suitably formed by drawing. Therefore, the lithium secondary battery of the present invention is excellent in workability.

Hereinafter, a lithium secondary battery according to the present invention will be described in detail with reference to the drawings. In the lithium secondary battery according to the present invention, the exterior body is composed of a laminate exterior material including a metal layer and a synthetic resin layer, and a power generation element is enclosed in the exterior body. An example of a plan view of a lithium secondary battery according to the present invention is shown in FIGS. 3 and 4, reference numeral 9 denotes a laminate exterior material, which is fused by a surrounding sealing portion 10 to form an exterior body. The laminate exterior material 9 is composed of a metal layer and a synthetic resin layer. For example, the laminate exterior material 9 may have a configuration in which a nylon film, an aluminum foil, and a polyolefin film are bonded together in this order, and the polyolefin film is fused so as to be inside the exterior body. Or it seals with an adhesive agent and an exterior body is formed. As the polyolefin film, for example, a polypropylene film, a polyethylene film, a modified polyethylene film and the like can be used.

12 and 13 are a positive electrode terminal and a negative electrode terminal, respectively, and are led out from the inside of the exterior body toward the outside. Each of the positive electrode terminal and the negative electrode terminal is made of a metal material such as aluminum, copper, nickel, or stainless steel, and may have a thin plate shape or a mesh shape, respectively.

A close contact film 11 for preventing the entry of outside air can be inserted between the laminate exterior material and the positive electrode terminal and the negative electrode terminal. The adhesion film is made of a material having adhesion to the positive electrode terminal and the negative electrode terminal, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

As the shape of the exterior body formed by the laminate exterior material, for example, a pouch type and a drawing type are preferably used. In the pouch type, a laminate exterior material is formed in a bag shape, and a power generation element is accommodated in the bag. The pouch-type production method includes a method of heat-sealing four sides of two laminated outer packaging materials into a bag shape, folding a rectangular laminated outer packaging material into two at the center line, and overlapping the opposite sides. Only two sides perpendicular to the line, or the above two sides and the center line are heat sealed to form a bag, and then a power generation element is inserted from the opening and the opening is heat sealed, and a rectangular shape The laminated exterior material is heat-sealed in a pair of opposing sides without folding, and the exterior material is folded so that the heat seal portion faces the center line of the exterior material. There is a method in which one side is heat sealed to form a bag, a power generation element is inserted from the opening, and the opening is heat sealed. In the drawing type, the sealant layer side of the laminate exterior material is processed into a recess using a press and a die (drawing process), and the power generation element is stored in this recess, and another laminate exterior material is placed on the recess. Obtained by overlapping. The other laminate exterior material may or may not have a recess. In addition, there is a method in which a single rectangular laminate exterior material is used, a recess is formed on one half of the center line, or a recess is formed on each side of the center line, and the center line is folded in two. .

The power generation element in the present invention is usually used in a lithium secondary battery, and includes a positive electrode material layer, a negative electrode material layer, and a layer having a lithium salt electrolyte. For example, as shown in FIG. 1, the positive electrode material layer and the negative electrode material layer are formed on the current collectors 3 and 4, respectively, and constitute a positive electrode plate 5 and a negative electrode plate 6, respectively. The positive electrode plate 5 and the negative electrode plate 6 are laminated via a layer 7 containing a lithium salt electrolyte, for example, as shown in FIG.

The positive electrode material and the negative electrode material may contain a conductive additive, a resin, and the like together with the respective electrode active materials. Examples of the conductive aid include graphite, carbon black, carbon fiber, and metals such as nickel, aluminum, copper, and silver. Examples of the resin include fluororesin and fluororubber.

As the positive electrode active material, lithium transition metal composite oxides such as lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), and lithium manganate (LiMnO ₂ ) are used. Moreover, in order to improve the electroconductivity of these positive electrode active materials, it is preferable to further mix carbon powders, such as acetylene black and a graphite powder. As the negative electrode active material, amorphous carbonaceous materials such as soft carbon and hard carbon, and carbonaceous powders such as natural graphite are used.

The positive electrode plate 5 and the negative electrode plate 6 are formed in a thin plate shape by applying the positive electrode material 1 and the negative electrode material 2 to the positive electrode current collector 3 and the negative electrode current collector 4, respectively. As a material suitably used for each current collector, for example, an aluminum foil is used as the positive electrode current collector, and a copper foil is used as the negative electrode current collector.

In the power generation element, the positive electrode plate and the negative electrode plate are wound or laminated via a layer 7 containing an electrolyte so that the positive electrode plate and the negative electrode plate are not in direct contact with each other. As the layer 7 containing an electrolyte, a separator made of a porous resin film and impregnated with a liquid or gel lithium salt electrolyte is usually used. As the separator, for example, a porous separator made of polyethylene having lithium ion permeability and a laminated structure separator in which porous polypropylene and porous polyethylene are laminated are used. The separator softens and loses its porosity when the electrode material or the electrode plate becomes high temperature, and as a result, it also serves as a safety mechanism that can suppress the movement of lithium ions, that is, the battery reaction.

A liquid electrolyte (electrolytic solution) can be obtained by dissolving a lithium salt electrolyte in a non-aqueous solvent. The gel electrolyte is obtained by holding the liquid electrolyte in a polymer compound.

Examples of the non-aqueous solvent include carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, 1,3-dioxolane, Examples include cyclic ethers such as 4-methyldioxolane, lactones such as γ-butyrolactone, and sulfolane. 3-methyl sulfolane, dimethoxyethane, diethoxyethane, ethoxymethoxyethane, ethyl diglyme and the like can also be used.

Any electrolyte may be used as long as it dissolves in a non-aqueous solvent to generate lithium ions, and one kind may be used alone, or two or more kinds may be mixed and used. For example, lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium perchlorate (LiClO ₄ ), lithium trifluoromethanesulfonate ( LiCF3SO _3), bis (trifluoromethanesulfonyl) imide lithium _{(LiN (SO 2 CF 3)} 2), tris (trifluoromethanesulfonyl) methyl lithium _{(LiC (SO 2 CF 3)} 3), four lithium chloride aluminate (LiAlCl ₄ ) Or lithium hexafluorosilicate (LiSiF ₆ ).

Examples of the polymer compound used in the gel electrolyte include a fluorine-based polymer compound such as polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene, a crosslinked product containing polyethylene oxide or polyethylene oxide, and the like. Examples include ether polymer compounds, polyacrylonitrile, and the like.

In the lithium secondary battery of the present invention, an absorption sheet is enclosed in an exterior body together with a power generation element. The absorbent sheet is composed of one or more resin layers including inorganic particles having an acid absorbing function and inorganic particles having a water absorbing function. The absorbent sheet may be composed of a single resin layer containing inorganic particles having an acid absorbing function and inorganic particles having a water absorbing function, or a resin layer containing inorganic particles having an acid absorbing function And a laminate of a resin layer containing inorganic particles having a water absorption function. The absorbent sheet contains at least 5 parts by weight in total of inorganic particles having an acid-absorbing function and inorganic particles having a water-absorbing function with respect to 100 parts by weight of the resin. The total amount of the inorganic particles is preferably 200 parts by weight or less, and more preferably 10 to 150 parts by weight with respect to 100 parts by weight of the resin. When the total amount is too small, a sufficient absorption function cannot be obtained, and when it is too large, film formability may be deteriorated. In addition, the inorganic particles having the acid absorption function and the water absorption function are the same as those having both absorption functions, as illustrated below. There may be inorganic particles. In the former case, the amount of each of the inorganic particles having an acid absorbing function and the inorganic particles having a water absorbing function is preferably 2.5 parts by weight or more with respect to 100 parts by weight of the resin. Preferably it is 5 parts by weight or more.

As the inorganic particles having a function of absorbing water, any material having moisture absorption properties can be used, but those having a small volume change and state change due to moisture absorption are preferable, for example, metal oxide, zeolite, Examples thereof include calcined hydrotalcite, hydrotalcite oxide, magnesium sulfate (0 to 3 hydrate), phosphorus pentoxide, and calcium chloride. Preferably, metal oxide, zeolite, calcined hydrotalcite, hydrotalcite oxide and magnesium sulfate (0 to 3 hydrate), more preferably zeolite, calcined hydrotalcite, hydrotalcite oxide and Magnesium sulfate (0-3 hydrate). One kind of inorganic particles having a water absorption function may be used alone, or a plurality of kinds may be mixed and used.

It is preferable to use the material having the hygroscopic property as described above in a dehydrated and dried state below the decomposition temperature of each substance. Hydrotalcite has low hygroscopicity, but the calcined hydrotalcite calcined at 300 ° C. or lower and the hydrotalcite oxide calcined at 300 ° C. or higher are in a dehydrated state and the hygroscopic property is improved. Suitable for use as a desiccant.

The inorganic particles having an absorption function of acid, metal carbonate, hydrotalcite, calcined hydrotalcite, although hydrotalcite oxides, preferably hydrotalcite, calcined hydrotalcite, hydrotalcite It is an oxide. One kind of inorganic particles having an acid absorption function may be used alone, or a plurality of kinds may be mixed and used.

As the resin used for the absorbent sheet, any resin can be used as long as it is resistant to the electrolytic solution. However, polyethylene, polypropylene, polymethylpentene, a copolymer of ethylene and butene, a copolymer of ethylene and propylene can be used. Copolymers, ionomers, modified polyethylene, modified polypropylene, ethylene-vinyl acetate copolymers and ethylene-vinyl alcohol copolymers are preferred. One kind of the resin may be used alone, or a plurality of kinds may be mixed and used.

The thickness of the absorbent sheet is appropriately determined depending on the blending amount of the inorganic particles having an acid absorbing function and the inorganic particles having a water absorbing function and the period in which the function of the absorbent sheet is desired to be maintained. Although it is necessary to consider the influence on the thickness of the lithium secondary battery, it is preferably 10 to 1000 μm, more preferably 20 to 100 μm.

As for the particle diameter of the inorganic particles having an acid absorption function and the water absorption function, any particle diameter can be used as long as it can achieve a desired film thickness. Preferably, it is 0.01-100 micrometers, More preferably, it is 0.1-30 micrometers.

The arrangement | positioning location of the absorption sheet in the lithium secondary battery of this invention will not be restrict | limited especially if it is an inside of an exterior body. For example, as illustrated in FIG. 5, it is preferable that two sheets of the absorbing sheet 14 are disposed so as to sandwich the power generation element 8, but one sheet may be disposed on only one of them. In addition, as shown in FIG. 6, the absorbent sheet 14 may be processed into a cylindrical shape so as to include the power generation element 8. 7-9 is sectional drawing which shows the example of the arrangement | positioning location of an absorption sheet when enclosing the absorption sheet 14 in the inside of an exterior body. FIG. 7 shows an example in which the power generation element 8 is disposed between the power generation elements 8. As shown in FIG. 8, you may arrange | position the positive electrode terminal 12 or the negative electrode terminal 13 in the vicinity of the part derived | led-out to the exterior of a laminate exterior body. Further, as shown in FIG. 9, a combination of the arrangement in FIG. 7 and the arrangement in FIG. 8 may be used.

The absorbent sheet 14 is disposed inside the exterior body, and preferably also disposed in the sealing portion 10 of the laminate exterior body. In this case, an absorption sheet is arrange | positioned at at least one part of a sealing part, More preferably, all the parts of a sealing part. Examples thereof are shown in FIGS. As shown in FIG. 10, one absorbent sheet may be used for one sealing part, and as shown in FIG. 11, two absorbent sheets may be used for one sealing part. It is possible to efficiently reduce the amount of moisture entering from the sealing part by arranging the absorbent sheet also at the sealing part of the exterior body, the influence of hydrogen fluoride on the power generation element, and the decrease in adhesion at the sealing part Can be avoided for a long time.

The absorbent sheet in the present invention may be one in which a resin is crosslinked by radiation. As the radiation, electron beams and gamma rays are preferably used. By cross-linking the resin, heat resistance is improved, and even when the temperature of the lithium secondary battery becomes high, inorganic particles having an acid absorbing function and inorganic particles having a water absorbing function are safely maintained. be able to.

Further, the absorbent sheet in the present invention may be one in which both surfaces or one of the surfaces is embossed. By increasing the surface area by embossing, the absorption rate of hydrogen fluoride and moisture inside the battery can be increased. In addition, when the absorbent sheet is disposed in the sealing portion, the uneven structure formed by the embossing process serves as a discharge port for air, electrolyte, etc. existing in the heat-sealing portion when heat-sealing with the exterior material. Therefore, it is possible to reduce the occurrence of poor adhesion at the fusion part.

The absorbent sheet in the present invention may have a pressure-sensitive adhesive layer or an adhesive layer on both sides or either side. By having the pressure-sensitive adhesive layer or the adhesive layer, the lithium secondary battery can be manufactured by adhering the absorbent sheet to the laminate exterior material with a pressure-sensitive adhesive or the like. Therefore, the arrangement position of the absorbent sheet can be fixed. Misalignment of the absorbent sheet in the manufacturing process of the secondary battery can be prevented.

In the present invention, the absorbent sheet is composed of inorganic particles having an acid absorption function, inorganic particles having a water absorption function, and resins, such as single-screw, twin-screw, and four-screw extruders, pressure kneaders, Banbury mixers, and the like. It is possible to produce by pelletizing by melting and kneading using a known kneader, and subjecting the obtained pellet to a film forming apparatus such as a T-die extrusion molding apparatus or an inflation molding apparatus. In addition, an absorbent sheet can be formed without pelletization by directly connecting an extruder or a kneader used for pelletization to a film forming apparatus or via a gear pump.

The absorbent sheet thus obtained is placed in a laminate outer package together with a power generation element, the absorbent sheet is sandwiched between sealing portions of the outer package as desired, and the outer package is heat sealed so that the positive electrode terminal and the negative electrode terminal protrude from the outer package. By sealing with, for example, a lithium secondary battery can be manufactured.

The absorption sheet in the present invention can be used for an electric double layer capacitor in addition to a lithium secondary battery.

EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to the following examples.

(1) Production of Absorbing Sheet After the resin and inorganic particles having the blending amounts shown in Table 1 were melt-kneaded with a twin screw extruder (PCM-46 twin screw extruder manufactured by Ikekai Co., Ltd.) equipped with a quantitative feed, T Films having film thicknesses shown in Table 1 were obtained using a die (manufactured by Toshiba Machine Co., Ltd.). The obtained film was stored in a dry room having a dew point temperature of −50 ° C. or lower.

(2) Preparation of test piece 1 (Preparation of a test piece in which the absorbent sheet is disposed only inside the test piece)
A test piece having the configuration shown in FIG. 12 was produced as follows. The following operations were performed in a dry room having a dew point temperature of −50 ° C. or lower. First, a laminate exterior material (aluminum laminate foil for lithium-ion batteries, manufactured by Showa Denko Packaging Co., Ltd., a laminate having an aluminum foil between a nylon film and a polyolefin film), a recess has a width of 30 mm and a length of 50 mm. Using a metal mold and a press machine (lamination film forming test machine, manufactured by Hosen Co., Ltd.) having a depth of 3.5 mm, the pressure is 5 MPa so that the sealant layer side (polyolefin film side) is concave. Drawing was performed under the condition of a pressing speed of 1 s / 100 mm. A separator (manufactured by Celgard Co., Ltd.) folded into a recess of the drawn laminate exterior material (9a) and having a width of 28 mm and a length of 48 mm sandwiched between two absorbent sheets having a width of 28 mm and a length of 48 mm (15 ). The laminated exterior material (9) that is not drawn and cut to a width of 40 mm and a length of 60 mm and the drawn laminated exterior material (9a) are overlapped so that the respective sealant layers face each other. It was heat-sealed under conditions of 5 mm width, 200 ° C., 1 MPa, and 5 seconds to form a bag. 3 ml of an electrolytic solution (manufactured by Kishida Chemical Co., Ltd.) in which ethylene carbonate, dimethyl carbonate and diethyl carbonate are mixed at a volume ratio of 1: 1: 1 and lithium hexafluorophosphate is dissolved to 1 mol / L. After injecting from the opening and impregnating the separator under reduced pressure, the opening was heat-sealed under the conditions of 5 mm width, 200 ° C., 1 MPa, and 5 seconds to obtain a test piece.

(3) Preparation of test piece 2 (Preparation of a test piece in which an absorbent sheet is arranged in the test piece and in the sealing portion)
A test piece having the configuration shown in FIG. 13 was produced as follows. The following operations were performed in a dry room having a dew point temperature of −50 ° C. or lower. First, a laminate exterior material (aluminum laminate foil for lithium-ion batteries, manufactured by Showa Denko Packaging Co., Ltd., a laminate having an aluminum foil between a nylon film and a polyolefin film), a recess has a width of 30 mm and a length of 50 mm. Using a metal mold and a press machine (lamination film forming test machine, manufactured by Hosen Co., Ltd.) having a depth of 3.5 mm, the pressure is 5 MPa so that the sealant layer side (polyolefin film side) is concave. Drawing was performed under the condition of a pressing speed of 1 s / 100 mm. A separator (manufactured by Celgard Co., Ltd.) folded into a recess of the drawn laminate exterior material (9a) and having a width of 28 mm and a length of 48 mm sandwiched between two absorbent sheets having a width of 28 mm and a length of 48 mm (15 ). A laminate exterior material (9) that has been cut to a width of 40 mm and a length of 60 mm and the stretched laminate exterior material (9a) are overlapped so that the respective sealant layers face each other, and are placed on any three sides. In addition, an absorbent sheet (14) cut to a width of 5 mm and a length of 55 mm is sandwiched between the laminated laminate materials that overlap each other, and the above three sides are 5 mm wide, heat sealed under the conditions of 200 ° C., 1 MPa, and 5 seconds. And formed into a bag shape. 3 ml of an electrolytic solution (manufactured by Kishida Chemical Co., Ltd.) in which ethylene carbonate, dimethyl carbonate and diethyl carbonate are mixed at a volume ratio of 1: 1: 1 and lithium hexafluorophosphate is dissolved to 1 mol / L. After injecting from the opening and impregnating the separator under reduced pressure, the absorbent sheet (14) having a width of 5 mm and a length of 55 mm is sandwiched in the opening, and the opening is heated to 5 mm in width at 200 ° C., 1 MPa for 5 seconds. The test piece was sealed.

Example 1
15 parts by weight of hydrotalcite (DHT-4A, manufactured by Kyowa Chemical Industry Co., Ltd.) is used as inorganic particles having an acid absorption function, and stainless steel sieve having an opening of 20 μm is used as inorganic particles having a water absorption function (As One Co., Ltd.) Using 15 parts by weight of magnesium sulfate sulfate (MG-0K-100, manufactured by Ako Kasei Co., Ltd.) classified by an electromagnetic sieve shaker (AS200 DIGIT, manufactured by ASONE Co., Ltd.) equipped with a resin. 100 parts by weight of polypropylene (PP, Prime Polypropylene F-744NP, manufactured by Prime Polymer Co., Ltd.) was used, and an absorption sheet having a thickness of 50 μm was obtained according to the preparation of the absorption sheet. Using the obtained absorbent sheet, a test piece was prepared according to Preparation 1 of the test piece.

Example 2
A test piece was prepared in the same manner as in Example 1 except that the amounts of hydrotalcite and magnesium sulfate were each changed to 30 parts by weight.

Example 3
A test piece was prepared in the same manner as in Example 1 except that zeolite (Molecular Sieve 4A powder, manufactured by Sakai Kogyo Co., Ltd.) was used as inorganic particles having a water absorption function.

Example 4
Both calcined hydrotalcite (DTH-4C, manufactured by Kyowa Chemical Industry Co., Ltd.) is used as inorganic particles having acid absorbing function and water absorbing function, and the blending amount is 30 parts by weight. A test piece was prepared in the same manner as in Example 1.

Example 5
Hydrotalcite oxide (KW-2200, manufactured by Kyowa Chemical Industry Co., Ltd.) is used as both inorganic particles having acid absorbing function and water absorbing function, and the blending amount is 30 parts by weight. A test piece was prepared in the same manner as in Example 1.

Example 6
A test piece was prepared in the same manner as in Example 1 except that modified polypropylene (Admer QF551, manufactured by Mitsui Chemicals, Inc.) was used as the resin.

Example 7
A test piece was prepared in the same manner as in Example 1 except that an ethylene-vinyl acetate copolymer (Evaflex P1007, Mitsui DuPont Chemical Co., Ltd.) was used as the resin.

Example 8
A test piece was prepared in the same manner as in Example 1 except that an ethylene-vinyl alcohol copolymer (Eval F101B, manufactured by Kuraray Co., Ltd.) was used as the resin.

Example 9
A test piece was prepared in the same manner as in Example 1 except that low-density polyethylene (LDPE, Neozex 0234CL, manufactured by Prime Polymer Co., Ltd.) was used as the resin.

Example 10
A test piece was prepared in the same manner as in Example 1 except that polymethylpentene (TPX DX845, manufactured by Mitsui Chemicals, Inc.) was used as the resin.

Example 11
30 parts by weight of hydrotalcite (DHT-4A, manufactured by Kyowa Chemical Industry Co., Ltd.) as inorganic particles having an acid absorption function and 100 parts by weight of polypropylene (PP, Prime Polypro F-744NP, manufactured by Prime Polymer Co., Ltd.) as a resin The hydrotalcite-dispersed polypropylene sheet having a film thickness of 25 μm was produced according to the production of the absorbent sheet. In addition, 0 hydrate magnesium sulfate classified with an electromagnetic sieve shaker (AS200 DIGIT, manufactured by ASONE Corporation) equipped with a 20-μm-aperture stainless steel sieve (manufactured by ASONE Corporation) as inorganic particles having a water absorbing function. (MG-0K-100, manufactured by Ako Kasei Co., Ltd.) 30 parts by weight, 100 parts by weight of the polypropylene as a resin were used, and a magnesium sulfate-dispersed polypropylene sheet having a thickness of 25 μm was prepared according to the preparation of the absorbent sheet. . The obtained two sheets were heat laminated with a laminator (manufactured by Taisei Laminator Co., Ltd., FL750) under the conditions of 0.5 MPa, 180 ° C. and 1 m / min to produce an absorption sheet having a thickness of 50 μm. Using this absorbent sheet, a test piece was prepared according to Preparation 1 of the test piece.

Example 12
Using the same absorbent sheet as in Example 1, a test piece was prepared according to Test piece preparation 2.

Example 13
Using the same absorbent sheet as in Example 2, a test piece was prepared according to Test piece preparation 2.

Example 14
Using the same absorbent sheet as in Example 3, a test piece was prepared according to Test piece preparation 2.

Example 15
Using the same absorbent sheet as in Example 4, a test piece was prepared according to Test piece preparation 2.

Example 16
Using the same absorbent sheet as in Example 5, a test piece was prepared according to Test piece preparation 2.

Comparative Example 1
A test piece was prepared in the same manner as in Example 1 except that inorganic particles having an acid absorbing function and inorganic particles having a water absorbing function were not used.

Comparative Example 2
A test piece was prepared in the same manner as in Example 1 except that 30 parts by weight of magnesium sulfate was used as inorganic particles having a water absorption function without mixing inorganic particles having an acid absorption function.

Comparative Example 3
A test piece was prepared in the same manner as in Example 1 except that 30 parts by weight of hydrotalcite was used as inorganic particles having an acid absorption function without mixing inorganic particles having a water absorption function.

Comparative Example 4
A test piece was prepared according to Preparation 1 of a test piece without using an absorbent sheet.

Comparative Example 5
The hydrotalcite-dispersed polypropylene sheet side of the absorbent sheet produced in Example 11 was placed on the sealant layer side of the aluminum laminate foil for a lithium ion battery in Preparation 1 of the test piece with a laminator (FL750, manufactured by Taisei Laminator Co., Ltd.). Heat lamination was performed under conditions of 5 MPa, 180 ° C., and 1 m / min to obtain an aluminum laminate foil having an acid / water absorption function. A test piece was prepared according to Preparation 1 of a test piece, except that the obtained aluminum laminate foil was used as a laminate outer packaging material and no absorbent sheet was used.

Comparative Example 6
The absorbent sheet produced in Example 1 was applied to the sealant layer side of the aluminum laminate foil for lithium ion batteries in Preparation 1 of the test piece with a laminator (FL750, manufactured by Taisei Laminator Co., Ltd.) at 0.5 MPa, 180 ° C., 1 m / min. The aluminum laminate foil having an acid / water absorption function was obtained by heating and laminating under the conditions described above. A test piece was prepared according to Preparation 1 of a test piece, except that the obtained aluminum laminate foil was used as a laminate outer packaging material and no absorbent sheet was used.

Comparative Example 7
The hydrotalcite-dispersed polypropylene sheet and the magnesium sulfate-dispersed polypropylene sheet produced in Example 11 were superposed without being heat-laminated, and this was used as an absorbent sheet. A test piece was produced according to Preparation 1 of the test piece.

Comparative Example 8
A test piece was prepared in the same manner as in Example 1 except that the amount of hydrotalcite and magnesium sulfate in Example 1 was changed to 0.5 parts by weight.

Comparative Example 9
Using the same absorbent sheet as in Example 1, a test piece was prepared according to Preparation 2 of the test piece. However, the absorbent sheet was not arranged inside the test piece, and the test piece was placed only at the sealing portion. Produced.

Reliability test The test piece prepared above was left in a constant temperature and humidity chamber at 60 ° C. and 95% RH for 30 days, and then the appearance was visually observed and the hydrogen fluoride of the electrolyte solution in the test piece was observed. Concentration and water content were measured. In addition, as shown below, the water content was measured by the Karl Fischer method, and the hydrogen fluoride content was measured by an ion chromatography method. Test results are shown in Tables 2-4.

Measurement of moisture content Karl Fischer capacity titration apparatus (manufactured by Hiranuma Sangyo Co., Ltd.) in a gas-substituted glove box (SG-1000 manufactured by ASONE CORPORATION) with a dew point of −50 ° C. or less substituted with argon gas AQV-300).

Measurement of hydrogen fluoride content Lithium hexafluorophosphate (LiPF ₆ ) used as an electrolyte is weak in moisture in a salt state and reacts with water to produce hydrogen fluoride. Phosphate anion (PF ₆ ⁻ ) does not react with water. Therefore, by utilizing the property that lithium hexafluorophosphate (LiPF ₆ ) is stable in dilute aqueous solution, impurities are removed from 1 ml of electrolytic solution using a pure water production apparatus (Elix-UV3 manufactured by Nihon Millipore Corporation). The solution diluted to 100 ml with pure water was eluted with a suppressor-type ion chromatography (IC-2001, manufactured by Tosoh Corporation) using an anionic organic acid analysis column (superIC-AZ manufactured by Tosoh Corporation). As a liquid, an aqueous solution in which 2.0 mmol / L NaHCO ₃ and 3.0 mmol / L Na ₂ CO ₃ were mixed was used, and measurement was performed at a flow rate of 1.5 ml / min.

As shown in Tables 2 and 3, none of the examples 1 to 11 in which the absorbent sheets were arranged in the test pieces had any change in appearance, and the hydrogen fluoride concentration and water content were initial. Lower than the value. This result shows that when the absorbent sheet according to the present invention is placed inside an exterior body made of a laminate exterior material, it is effective in improving the characteristics of the battery, and therefore a lithium secondary battery excellent in durability and safety can be provided. .

On the other hand, in Comparative Examples 1 and 4 in which the absorbent sheet was not disposed in the test piece, corrosion of the aluminum foil of the exterior material and peeling of the sealing portion occurred, resulting in liquid leakage. In Comparative Example 2 in which the inorganic particles having an acid absorption function were not mixed, the effect of suppressing the increase in the water content was observed, but swelling was observed in the appearance observation. This is presumed to be due to the influence of hydrogen fluoride generated by acting on lithium hexafluorophosphate, which is an electrolyte, before moisture that has entered from the outside of the test piece is absorbed by the absorbent sheet. Further, in Comparative Example 3 in which the inorganic particles having a water absorbing function were not mixed, the effect of suppressing the increase in the concentration of hydrogen fluoride was seen as compared with Comparative Examples 1 and 4, but the corrosion of the aluminum foil Further, peeling of the sealing portion occurred and liquid leakage occurred.

In Comparative Examples 5 and 6 in which the absorbent sheet was not disposed in the test piece but was bonded to the sealant layer side of the laminate exterior material, corrosion of the aluminum foil and liquid leakage from the sealing portion were observed. This is because the magnesium foil particles and hydrotalcite particles in the absorbent sheet in which the interface between the aluminum foil of the laminate exterior material and the aluminum foil and the resin layer thereon is bonded to the laminate exterior material during the drawing process The reason is that the defect was caused by the damage.

In Comparative Example 7 in which the hydrotalcite-dispersed polypropylene sheet and the magnesium sulfate-dispersed polypropylene sheet were used without bonding, liquid leakage and swelling were not observed, but the hydrogen fluoride concentration and the water content were the initial values. The result was equivalent or slightly higher. When the absorbent sheet of Example 11 in which the hydrotalcite-dispersed polypropylene sheet and the magnesium sulfate-dispersed polypropylene sheet were bonded together, the hydrogen fluoride concentration and the water content were lower than the initial values. This is presumed to be because the diffusion efficiency of hydrogen fluoride and water vapor into the absorption sheet is increased by providing both the acid and water absorption functions in the same sheet. From these results, it was found that by using an absorbent sheet having an acid and water absorption function in the same sheet, the absorption efficiency of acid and water was improved, and it was effective in improving battery characteristics.

In Comparative Example 8, the amount of inorganic particles having an acid absorbing function and water absorbing function in the absorbing layer is less than the range of the present invention. Absorbing function was insufficient and liquid leakage occurred.

Examples 12-16 arrange | position an absorption sheet also in the sealing part of a laminate exterior body. As shown in Table 4, in Examples 12 to 16, it was confirmed that the hydrogen fluoride concentration and the moisture content reduction effect were better than those of Examples 1 to 11 in which the absorbent sheet was disposed only in the test piece. .

On the other hand, in Comparative Example 9 in which the absorbent sheet was arranged only at the sealing portion of the exterior body, an effect of suppressing an increase in the hydrogen fluoride concentration and the water content was slightly seen, but swelling was seen in the appearance observation. This is due to moisture entering from the outside and absorption effect at the sealing portion of hydrogen fluoride generated inside, but it is generated by the initial moisture content or a small amount of moisture entering through the absorbent sheet. This is probably because of the influence of hydrogen fluoride.

It is sectional drawing which shows an example of the positive (negative) electrode plate of the lithium secondary battery concerning this invention. It is sectional drawing which shows an example of the electric power generation element of the lithium secondary battery concerning this invention. It is a top view which shows an example of the lithium secondary battery concerning this invention. It is a top view which shows an example of the lithium secondary battery concerning this invention. It is a perspective view which shows an example of use of the absorption sheet concerning this invention. It is a perspective view which shows an example of use of the absorption sheet concerning this invention. It is sectional drawing which shows an example of the lithium secondary battery of this invention. It is sectional drawing which shows an example of the lithium secondary battery of this invention. It is sectional drawing which shows an example of the lithium secondary battery of this invention. It is sectional drawing which shows an example of the lithium secondary battery of this invention. It is sectional drawing which shows an example of the lithium secondary battery of this invention. It is a perspective view which shows preparation of the test piece according to preparation 1 of a test piece. It is a perspective view which shows preparation of the test piece according to preparation 2 of a test piece.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode material 2 Negative electrode material 3 Positive electrode collector 4 Negative electrode collector 5 Positive electrode plate 6 Negative electrode plate 7 Electrolyte-containing layer 8 Power generation element 9 Laminate exterior material 9a Drawing-processed laminate exterior material 10 Sealing portion 11 Adhesion film 12 Positive electrode terminal 13 Negative electrode terminal 14 Absorbent sheet 15 Laminate of absorbent sheet and separator

Claims (9)

Inside the metal layer with a synthetic resin layer laminated outer member in configured the outer package, in the lithium secondary battery power generating element is sealed including a layer having a positive electrode material layer and the negative electrode material layer and the lithium salt electrolyte, the absorbent sheet together with the power generating element into the package body is sealed, the absorbent sheet is composed of one or more resin layer containing inorganic particles having an absorption function of the inorganic particles and water with the absorption capability of the acid The absorbent sheet contains at least 5 parts by weight in total of the inorganic particles having an acid-absorbing function and the inorganic particles having a water-absorbing function with respect to 100 parts by weight of the resin. Lithium secondary battery. The lithium secondary battery according to claim 1, wherein the exterior body has a sealing portion, and at least a part of the sealing portion is sealed via the absorbent sheet. 3. The lithium according to claim 1, wherein the layer containing a lithium salt electrolyte is a porous resin film impregnated with an electrolyte solution or a gel electrolyte in which a lithium salt electrolyte is dissolved in a non-aqueous solvent. Secondary battery. The absorbent sheet is composed of a single resin layer containing inorganic particles having an acid absorbing function and inorganic particles having a water absorbing function, or a resin layer containing inorganic particles having an acid absorbing function and water The lithium secondary battery of any one of Claims 1-3 comprised by the laminated body with the resin layer containing the inorganic particle which has an absorption function. Inorganic particles Gaha hydrotalcite having an absorption function of the acid, the calcined hydrotalcite and one or more selected from the group consisting of hydrotalcite oxide, inorganic particles having a water absorption function, zeolites, baking The lithium secondary battery according to any one of claims 1 to 4, wherein the lithium secondary battery is one or more selected from the group consisting of hydrotalcite, hydrotalcite oxide, and 0 to 3 hydrate magnesium sulfate. The resin in the absorbent sheet is polyethylene, polypropylene, a copolymer of ethylene and butene, a copolymer of ethylene and propylene, a polymethylpentene, a copolymer of ethylene and vinyl acetate, and a copolymer of ethylene and vinyl alcohol. The lithium secondary battery according to claim 1, comprising one or more selected from the group consisting of a coalescence, an ionomer, a modified polyethylene, and a modified polypropylene. The lithium secondary battery according to claim 1, wherein the absorption sheet is subjected to a radiation crosslinking treatment. The lithium secondary battery according to any one of claims 1 to 7, wherein either one or both surfaces of the absorbent sheet are embossed. The lithium secondary battery according to any one of claims 1 to 8, wherein a pressure-sensitive adhesive layer or an adhesive layer is formed on both surfaces or one of the surfaces of the absorbent sheet.

Images