JP5113685B2 - Electrochemical element separator - Google Patents

Description

  The present invention relates to a separator for an electrochemical element.

  A lithium ion secondary battery, which is one of the electrochemical elements, has a feature of high energy density, and is widely used as a power source for portable electric devices such as mobile phones, portable music players, and notebook personal computers. . In addition, the use of lithium-ion secondary batteries is expanding in large-sized devices such as electric bicycles, hybrid vehicles, and electric vehicles. For this reason, lithium ion secondary batteries are required to have high capacity and charge / discharge characteristics at a large current. However, since lithium ion secondary batteries are non-aqueous batteries, they emit smoke compared to aqueous batteries. It is known that there is a high risk of ignition, rupture, etc., and improvement in safety is also required.

  In a lithium ion secondary battery, the risk of smoking increases due to temperature rise due to external heat, overcharge, internal short circuit, external short circuit, and the like. These can be prevented to some extent by an external protection circuit. In addition, the polyolefin resin porous film used as a separator for lithium ion secondary batteries melts around 120 ° C., and the pores are blocked to block current and ion flow, thereby increasing the temperature of the battery. It is suppressed. This is called a shutdown function. However, when the temperature rises due to external heat or when a chemical reaction occurs inside the battery due to the temperature rise, the battery temperature further rises even if the shutdown function works. The porous film contracted, causing an internal short circuit, which could cause ignition.

  As described above, it is difficult to suppress the ignition of the battery by the shutdown function of the separator. In addition, with the increase in capacity of batteries, the increase in current during charging and discharging is also progressing, and in order to suppress the Joule heat generated at that time, it is also necessary to lower the resistance value of the separator impregnated with the electrolyte. It has become. For this reason, metal oxide fine particles were used for the purpose of suppressing the ignition of the battery by lowering the resistance value while making it difficult to cause an internal short circuit by raising the heat shrinkage temperature than the porous film of polyolefin resin. Separator has been developed. In this separator, the pore diameter is controlled by the metal oxide fine particles, and it is possible to suppress internal short circuit, improve heat resistance, and lower the resistance value.

  For example, a separator having a microporous pseudoboehmite layer obtained as a porous film by mixing pseudoboehmite and a binder, drying and peeling after coating on a separately prepared film has been proposed (for example, patents) Reference 1). However, although this separator has an improved heat shrink temperature, when forming a microporous pseudo boehmite layer, in the case of an aqueous system, a water-soluble binder such as polyvinyl alcohol, polyethylene oxide, and polyvinylpyrrolidone is used in combination with an ultraviolet curable resin. In the case of alcohol, polyvinyl butyral is used as a binder, so that these polymers adhere to the surface of the pseudo boehmite and impede the wettability of the electrolytic solution, and the resistance value of the separator deteriorates. There were drawbacks. Moreover, since powder fall and a crack are easy to occur, there was a problem that it was difficult to take out alone as a winding-type separator, and handling at the time of battery manufacture was bad.

  Also proposed is a separator having a porous inorganic coating on and in the nonwoven fabric, the inorganic coating having aluminum (Al), silicon (Si) and / or zirconium (Zr) oxide particles. (For example, refer to Patent Document 2). Although this separator uses non-woven fabric as a base material, handling is improved, but other metal oxides are detected by silica fine particles generated by the sol-gel method. Drops and cracks are likely to occur, which leads to the generation of pinholes and causes internal short circuits, making it difficult to be a useful separator.

Furthermore, AlO (OH) or Al 2 _{O 3} · _H compound represented by the 2 _O separator particles or aluminum oxide as a main component (boehmite) is contained in the void of the nonwoven fabric have been disclosed (e.g., patent References 3 and 4). In these separators, boehmite and aluminum oxide are filled in the gaps using binders such as carboxymethyl cellulose, ethylene vinyl alcohol copolymer latex, polyvinyl butyral, etc., and polymer fine particles are included in order to develop a shutdown function. Therefore, the resistance value as a separator tends to increase, which is a problem.

  By the way, as a separator used for an electrochemical element called a capacitor such as an electric double layer capacitor, an electrolytic capacitor, or a solid electrolytic capacitor, a paper separator mainly composed of fibers obtained by beating a solvent-spun cellulose fiber or a regenerated cellulose fiber. Is used (for example, see Patent Documents 5 to 8). Paper separators are not only advantageous in terms of cost, but also have a large porosity and stable pore diameter, and furthermore, due to the surface properties of cellulose fibers, the affinity for the electrolyte is very high. The resistance value of the separator impregnated with was very low, and had the effect of reducing the internal resistance of the electrochemical element.

However, in recent years, as with the technological trend of lithium ion secondary batteries, capacitors are also required to have higher capacities. As a result, miniaturization of the electrode active material has progressed, and paper separators in which pores are formed by cellulose fibers have caused a situation of inducing an internal short circuit, and a separator having a smaller pore diameter is required. In addition, in the case of an electric double layer capacitor, it is necessary to heat at the time of manufacturing the capacitor in order to remove adsorbed water from activated carbon having a high specific surface area and surface active materials used for electrodes, but a paper separator has heat resistance. Because it is low, the adsorbed water on the cellulose fiber cannot be sufficiently dehydrated, and there is a problem that the remaining adsorbed water deteriorates the characteristics of the electric double layer capacitor, and a separator with excellent heat resistance is required. Has been.
JP-T-2001-527274 JP 2005-536658 Gazette JP 2007-157723 A JP 2008-4439 A JP-A-5-267103 JP-A-11-168033 JP 2000-3834 A JP 2005-327935 A

  An object of the present invention is to provide a separator for an electrochemical device that has excellent heat resistance, good handling, and a small pore diameter.

  As a result of intensive studies to solve the above-mentioned problems, (1) a separator for an electrochemical device in which an aluminum oxide having a dispersed aggregation diameter of less than 1 μm and a microfibrillated cellulose are filled between fiber matrices; In addition, the present inventors have found a separator for an electrochemical element in which aluminum oxide, aluminum hydroxide oxide, and microfibrillated cellulose are filled, and a dispersion aggregate diameter of an aggregate structure composed of aluminum oxide and aluminum hydroxide oxide is less than 1 μm.

  The separator for electrochemical devices of the present invention has excellent heat resistance, good handling, and controls the pore size to submicron size compared to conventional polyethylene porous films and paper separators. Therefore, it is possible to suppress the internal short circuit of the electrochemical element, improve the yield during production, and further improve the characteristics of the electrochemical element.

  The separator (1) for an electrochemical element of the present invention is formed by filling aluminum fiber having a dispersed aggregation diameter of less than 1 μm and microfibrillated cellulose between fiber matrices. The separator (2) for an electrochemical element of the present invention is formed by filling an agglomerated structure composed of aluminum oxide having a dispersed aggregation diameter of less than 1 μm and aluminum hydroxide oxide and a microfibrillated cellulose between fiber matrices.

  The fiber matrix is a fiber assembly including organic fibers, inorganic fibers and the like. Examples of organic fibers include polyethylene terephthalate, polybutylene terephthalate and derivatives thereof, aromatic polyester, polyester such as wholly aromatic polyester, polyolefin, acrylic, polyacetal, polycarbonate, aliphatic polyketone, aromatic polyketone, aliphatic polyamide, aromatic Polyamide, wholly aromatic polyamide, polyimide, polyamideimide, polyphenylene sulfide, polybenzimidazole, polyetheretherketone, polyethersulfone, poly (para-phenylenebenzobisthiazole), poly (para-phenylene-2,6-benzobis Oxazole), polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyurethane, and polyvinyl chloride. Such as cellulose fibers and the like to. Examples of inorganic fibers include inorganic fibers made of glass, alumina, silica, zirconia, silicon carbide, and various ceramics. These fibers may be divided and fibrillated. Two or more kinds of fibers can also be used. Polyester fibers can be preferably used because they are materials that have a high degree of freedom in fiber length and fiber diameter and are easy to handle, and polyethylene terephthalate fibers are particularly preferably used. Furthermore, a heat-fusible fiber having a core-sheath structure is also known as a polyester fiber, and when this is used, a thermoplastic fiber matrix can be formed, and workability can be greatly improved.

  The fiber matrix can be produced by a wet papermaking method, an electrospinning method, a melt blown method, a flash spinning method, a spunbond method, a card method, a combination of these, and the like. The fiber matrix is subjected to a confounding process such as a needle punch and a water jet, a calendar process, a thermal calendar process, and a heat treatment as necessary. The wet papermaking method is a method in which fibers are dispersed in water and homogenized, and this is made with a net or the like, but if a thinner and more uniform fiber matrix is required, formation by the wet papermaking method is required. It is advantageous.

The thickness of the fiber matrix is preferably 15 to 120 μm, and more preferably 25 to 70 μm. If the thickness is less than 15 μm, pinholes may be generated, and an internal short circuit may easily occur. When the thickness exceeds 120 μm, the battery capacity may be reduced. The density of the fiber matrix is preferably ^{0.10~0.40g / cm 3, 0.15~0.30g / cm} 3 is more preferable. When the density is less than 0.10 g / cm ³ , the mechanical strength of the fiber matrix may be extremely reduced. When the density exceeds 0.40 g / cm ³ , the porosity is reduced and the internal resistance of the separator is reduced. May increase.

  The microfibrillated cellulose refers to a cellulosic fiber having a portion where a whisker is generated on the surface of the fiber, and a cellulosic fiber having fine fibers in which the fiber itself is very finely divided mainly in a direction parallel to the fiber axis. The fiber diameter of at least a part of the whiskers or the divided fine fibers is preferably 5 μm or less, and more preferably 1 μm or less.

  As the microfibrillated cellulose, those obtained by mechanically pulverizing, chemically pulverizing, enzymatically pulverizing, bacterial cellulose, and the like, which are highly crystalline and highly oriented cellulose-based materials can be used. Cellulosic materials include: wood pulp, straw, cocoon, straw, kenaf, bamboo, linter, bagasse, esparto, sugarcane and other plant fibers, cellulose regenerated fibers such as rayon fiber, acetate and other semisynthetic fibers, lyocell fiber, plants And fibers obtained from parenchyma cells. The plant parenchyma can be obtained by crushing the internal parenchyma of the stem, the mesophyll of the leaf, the fruit and the like. In addition, juice squeezed from fruit, sugar beet, sugar cane, etc. discharged from food processing factories, sugar factories and the like can be used. Fibers can be obtained by applying a pulping treatment for producing pulp from wood to plant parenchymal cells. These cellulosic materials may be used alone or in combinations of two or more.

  The aspect ratio (fiber length / fiber diameter) of the microfibrillated cellulose is distributed in the range of 20 or more and 100000 or less, and the Canadian standard freeness (JIS P8121) is preferably 500 ml or less, and 200 ml or less. Is more preferable. Further, those having a mass average fiber length in the range of 0.1 mm to 2 mm are preferred.

  Aluminum oxide can be obtained by a method obtained by sintering aluminum hydroxide, aluminum nitrate, aluminum sulfate or the like after sintering at a high temperature, a method obtained by burning aluminum chloride, or the like. It is preferable to use aluminum oxide with a high content of α-alumina having high hardness because the porosity can be maintained when calendering is performed.

  In the present invention (1), the aluminum oxide filled between the fiber matrices forms a porous film. The particle size of the aluminum oxide is deeply related to the porosity of the film, particularly the pore diameter and the porosity. Yes. The porosity depends on the dispersion aggregation diameter that can be measured optically when aluminum oxide is dispersed. The dispersion aggregation diameter of aluminum oxide is less than 1 μm, more preferably from 50 nm to less than 1 μm, and further preferably from 0.1 μm to 0.8 μm. When the dispersion aggregation diameter is 1 μm or more, the pore diameter becomes too large, and it is not suitable as a separator for an electrochemical device. On the other hand, if it is smaller than 50 nm, the porosity may be lost and the porosity may be lowered.

  The primary particle diameter of aluminum oxide is preferably 3 nm or more and less than 1 μm, more preferably 8 nm or more and 0.8 μm or less. When the primary particle diameter is less than 3 nm, the aggregation of the primary particles may be too strong, and the porous property of the aggregated structure may be lost in the separator for electrochemical devices. In addition, when the primary particle diameter is 1 μm or more, the gap between the particles widens and the pore diameter of the separator increases, which may cause an internal short circuit. In addition, the particles are not retained between the fiber matrices and function as a separator. The aluminum oxide may be lost or the aluminum oxide may be easily precipitated and separated in the dispersion containing the aluminum oxide.

Aluminum hydroxide oxide is a general term for hydrous alumina that appears when aluminum hydroxide is thermally decomposed between 300 ° C. and 800 ° C., and is present in the natural world as boehmite. Since aluminum hydroxide oxide is obtained as a fine plate-like crystal having a thickness of several nm to several tens of nm, it has a high specific surface area and has a hydroxyl group on the surface, and thus has hydrophilicity. . The primary particle diameter of the aluminum hydroxide oxide used in the present invention is preferably 1 to 20 nm, and more preferably 2 to 15 nm. The specific surface area is preferably 100 m ² / g or more.

  Aluminum hydroxide oxide has softer particles than aluminum oxide, and by using it together with aluminum oxide, the packing form can be changed by applying pressure during calendering, etc., so the pore size as a separator is controlled. And a higher performance separator can be obtained.

  In the present invention (2), the aluminum oxide and the aluminum hydroxide oxide filled between the fiber matrices form a porous film, but the dispersed aggregate diameter of the aggregate structure composed of the aluminum oxide and the aluminum hydroxide oxide is this. It is deeply related to the porous property of the porous membrane, particularly the pore diameter and porosity. The dispersion aggregate diameter of the aggregate structure is less than 1 μm, more preferably 50 nm or more and less than 1 μm, and further preferably 0.1 μm or more and 0.8 μm or less. When the dispersion aggregation diameter is 1 μm or more, the pore diameter becomes too large, and it is not suitable as a separator for an electrochemical device. On the other hand, if it is smaller than 50 nm, the porosity may be lost and the porosity may be lowered.

  In the separator for an electrochemical element in which aluminum oxide and microfibrillated cellulose are filled between the fiber matrix, the content of aluminum oxide with respect to the fiber matrix is 100% by mass to 800% by mass, preferably 200% by mass to 600% by mass. % Or less, more preferably 250 mass% or more and 500 mass% or less. When the content of aluminum oxide is less than 100% by mass, the pore diameter may increase and internal short circuit may be easily caused. When the content of aluminum oxide exceeds 800% by mass, the porosity may decrease and the porosity may be lost.

  Further, the content of microfibrillated cellulose with respect to aluminum oxide is preferably 0.01% by mass or more and 5% by mass or less, more preferably 0.02% by mass or more and 2% by mass or less, and 0.05% by mass or more and 1% by mass. The following is more preferable. When the content of the microfibrillated cellulose is less than 0.01% by mass, the aluminum oxide may not be sufficiently retained in the fiber matrix, and the aluminum oxide may be detached from the separator. When the amount exceeds 5% by mass, the aggregate structure of aluminum oxide may become too large, and the aluminum oxide becomes difficult to penetrate between the fiber matrices, so that the aluminum oxide cannot interact with the fiber matrix. May be detached from the fiber matrix.

  In the separator for an electrochemical element filled with aluminum oxide, aluminum hydroxide oxide and microfibrillated cellulose, the total content of aluminum hydroxide oxide and aluminum oxide with respect to the fiber matrix is 100% by mass or more and 800% by mass or less. Preferably, 200 mass% or more and 600 mass% or less are more preferable, and 250 mass% or more and 500 mass% or less are further more preferable. When the total content is less than 100% by mass, the pore diameter may be increased and internal short circuit may be easily caused. If the total content exceeds 800% by mass, the porosity may decrease and the porosity may be lost.

  If the content of aluminum hydroxide oxide with respect to the sum of aluminum hydroxide oxide and aluminum oxide exceeds 90% by mass, the ability of aluminum hydroxide to retain aluminum hydroxide oxide may decrease, and particles may be detached from the separator. Therefore, it is preferable to set it as 90 mass% or less, and 85 mass% or less is more preferable. Further, the content of the microfibrillated cellulose with respect to the total of aluminum hydroxide oxide and aluminum oxide is preferably 0.01% by mass or more and 5% by mass or less, more preferably 0.02% by mass or more and 2% by mass or less. More preferably, the content is in the range of 05% by mass to 1% by mass. When the content of microfibrillated cellulose is less than 0.01% by mass, the aluminum matrix and the aluminum hydroxide oxide are not sufficiently retained in the fiber matrix, and the particles may be detached from the fiber matrix. When it exceeds 5 mass%, the aggregate structure of aluminum oxide and aluminum hydroxide oxide becomes large and difficult to enter between the fiber matrices, and may be detached from the fiber matrix.

  The manufacturing method of the separator for electrochemical devices of this invention is demonstrated. Aluminum oxide or aluminum oxide and aluminum hydroxide oxide are dispersed in water and further dispersed after an acid such as nitric acid, sulfuric acid or acetic acid or a basic substance such as ammonia is added. It is mixed with fibrillated cellulose at the time of dispersion or after dispersion to obtain a dispersion. The obtained dispersion is applied to or impregnated into a fiber matrix and then dried to form a sheet. In the obtained sheet-like material, excess voids are removed by calendering, and aluminum oxide or aluminum oxide and aluminum hydroxide oxide are filled together with microfibrillated cellulose between the fiber matrix to form a separator for an electrochemical device. . The linear pressure during the calendar process is preferably 4.9 to 20 MPa, and more preferably 7.8 to 15 MPa. Heat may be applied during the calendar process.

  Calendering promotes adhesion between high hardness aluminum oxide and organic fibrillated cellulose and between aluminum oxide and fiber matrix, and the aluminum oxide and fibrillated cellulose are closely packed, resulting in high porosity. While having it, a highly uniform separator showing a fine pore diameter can be obtained. As described above, aluminum hydroxide oxide is soft and easily adhered, and the pore diameter of the separator for an electrochemical element can be controlled.

The thickness of the separator for electrochemical elements of the present invention is preferably 15 μm or more and 70 μm or less, and more preferably 20 μm or more and 60 μm or less. If the thickness is less than 15 μm, pinholes are likely to be formed, and an internal short circuit may occur. When the thickness exceeds 70 μm, the resistance value of the separator portion increases, Joule heat is generated, and energy loss may occur, and the volume of the electrochemical element increases to include an electrode active material per unit volume. The amount may decrease and the element capacity may also decrease. Moreover, the density of the separator for electrochemical elements is preferably 0.2 g / cm ³ or more and 1.6 g / cm ³ or less, and more preferably 0.8 g / cm ³ or more and 1.4 g / cm ³ or less. If the density is less than 0.2 g / cm ³ , the contained aluminum oxide or aluminum hydroxide oxide is small, the pore diameter becomes large and internal short circuit may be easily caused, and the density may be 1.6 g / cm ³ . If it exceeds, sufficient porosity cannot be maintained, and the resistance value of the separator may increase.

  EXAMPLES Next, although an Example demonstrates this invention still in detail, this invention is not limited to these at all.

<Preparation of dispersions A to D (type I)>
A mixed solution was prepared according to the formulation shown in Table 3. The aluminum oxide used is shown in Tables 1 and 2. This mixed liquid was put into a polypropylene container together with zirconia beads, and dispersed for 2 hours with a paint conditioner (manufactured by Red Devil) to prepare dispersions A to D.

<Preparation of dispersions E to F (type II)>
A mixed solution was prepared according to the formulation shown in Table 4. Tables 1 and 2 show the aluminum hydroxide oxide and aluminum oxide used. This mixed liquid was put into a polypropylene container together with zirconia beads, and dispersed for 2 hours with a paint conditioner (manufactured by Red Devil) to prepare dispersions E to F.

<Preparation of dispersions G to L (type III)>
A mixed solution was prepared according to the formulation shown in Table 5. Tables 1 and 2 show the aluminum hydroxide oxide and aluminum oxide used. This mixed liquid was put into a polypropylene container together with zirconia beads, and dispersed for 2 hours with a paint conditioner (manufactured by Red Devil) to prepare dispersions G to L.

<Preparation of dispersions M to O (type IV)>
A mixed solution was prepared according to the formulation shown in Table 6. Tables 1 and 2 show the aluminum hydroxide oxide and aluminum oxide used. This mixed solution was put into a polypropylene container together with zirconia beads, and dispersed for 2 hours with a paint conditioner (manufactured by Red Devil) to prepare dispersions M to O.

<Preparation of dispersions P to R (type V)>
A mixed solution was prepared according to the formulation shown in Table 7. Tables 1 and 2 show the aluminum hydroxide oxide and aluminum oxide used. This mixed liquid was put into a polypropylene container together with zirconia beads, and dispersed for 2 hours with a paint conditioner (manufactured by Red Devil) to prepare dispersions P to R.

<Measurement of dispersion aggregation diameter>
Each dispersion was diluted 200 times with ion-exchanged water, and the dispersion aggregate diameter was measured using a submicron particle meter (product name; model N4, manufactured by Coulter Co.). Table 1 shows the results.

<Production of fiber matrix (α) to (γ)>
Fibers were mixed together in the formulations shown in Tables 8 to 10, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. The papermaking slurry was made up by a wet papermaking method using a circular paper machine, and the core-sheath polyester fiber was adhered by a cylinder dryer at 120 ° C. to develop the strength, thereby producing a fiber matrix made of nonwoven fabric. Table 11 shows the basis weight and density of each fiber matrix.

<Examples 1 to 21>
In the combinations shown in Tables 12 to 14, the dispersion liquid was applied to the fiber matrix and dried, and then treated with a thermal calendar heated to 180 ° C. The linear pressure of the thermal calendar roll was 14.7 MPa. In addition, the thickness, density, porosity, air permeability, maximum pore diameter, average pore diameter, shape change at 180 ° C, change in water, change in ethanol, change due to bending and stretching, Tables 12 to 14 show the dispersion aggregation diameter when redispersed.

<Thickness and density>
It measured based on JIS C2111.

<Porosity>
The obtained sheet (mass: W _all ) was put in water, and mass reduction (ΔW) due to buoyancy was measured. Taking the specific gravity of water at room temperature as 1, ΔW is converted as the volume of solid content (V _oc ) in the sheet, and the void ratio in the sheet is measured from the difference between the total volume of the sheet (V _all ) and V _oc did. In addition, the thing which does not get wet with water with a hydrophobic film was measured using ethanol.

<Air permeability>
Measured using a Oken air permeability smoothness tester.

<Maximum pore size and average pore size>
Based on the bubble point method prescribed | regulated to ASTMF316-86, it measured using the porosimeter II by Coulter.

<Shape change at 180 ° C>
The separator was heated at 180 ° C. for 3 hours, and the shape change was visually observed.

<Changes in water>
The separator was placed in ion-exchanged water and allowed to stand at room temperature for 12 hours, and the presence or absence of particles from the separator was visually observed. When the ion-exchanged water became cloudy with particles desorbed from the separator, it was judged as “with desorption”.

<Change in ethanol>
The separator was placed in ethanol and allowed to stand at room temperature for 12 hours, and the presence or absence of particles from the separator was visually observed. When ethanol became cloudy with particles detached from the separator, it was judged as “with desorption”.

<Change due to bending and stretching>
The operation of taking out a 10 cm × 5 cm separator, folding it in the center and then folding it to the opposite side was repeated twice. The shape change at the stage of folding the separator was visually observed to show the state.

<Measurement of dispersion aggregate diameter when re-dispersing separator>
100 parts by mass of ion-exchanged water was added to 100 parts by mass of the separator, placed in a polypropylene container together with zirconia beads, and dispersed with a paint conditioner (manufactured by Red Devil) for 2 hours. The dispersion was diluted 200 times with ion-exchanged water, and the dispersion agglomerated diameter was measured using a submicron particle meter (product name; model N4, manufactured by Coulter). Table 1 shows the results.

<Production of electric double layer capacitor>
Using activated carbon powder (specific surface area 2000 m ² / g) as an electrode active material, positive and negative electrodes are prepared, laminated through separators produced in the meantime, dried at 180 ° C. for 10 hours, and then coated with polyethylene-coated aluminum foil It was stored in a storage bag, and an electrolytic solution was injected and sealed to produce an electric double layer capacitor. As the electrolytic solution, a 1.5 mol / liter triethylmethylammonium tetrafluoroborate propylene carbonate solution was used. The manufactured electric double layer capacitor was charged and discharged to confirm operation, and the internal resistance and leakage current were measured. The results are given in Table 15.

<Production of lithium ion secondary battery>
95 parts by mass of graphite as a negative electrode active material and 5 parts by mass of polyvinylidene fluoride (PVDF) as a binder are mixed using N-methyl-2-pyrrolidone as a solvent, applied onto a 10 μm thick copper foil and dried. A negative electrode was produced. Next, 85 parts by mass of lithium cobaltate as a positive electrode active material, 10 parts by mass of acetylene black, and 5 parts by mass of PVDF were mixed using N-methyl-2-pyrrolidone as a solvent, applied onto an aluminum foil having a thickness of 15 μm, and dried. Thus, a positive electrode was produced.

  The two electrodes were laminated via a separator and dried at 180 ° C. for 2 hours, and then stored in a polyethylene-coated aluminum foil storage bag, and the electrolyte was injected and sealed to produce a lithium ion secondary battery. As the electrolytic solution, an ethylene carbonate / diethyl carbonate composite (1: 1 volume conversion) solution of 1 mol / liter lithium hexafluorophosphate was used. The produced lithium ion secondary battery had an initial capacity of 460 mAh. After charging / discharging this 500 times at 0.5 C, the capacity was measured again to determine the capacity retention rate (capacity after 500 charging / discharging / initial capacity × 100). The results are shown in Table 15.

<Preparation of Comparative Dispersion (A)>
The mixed liquid was put into a polypropylene container together with zirconia beads with the formulation shown in Table 16, and dispersed for 2 hours with a paint conditioner (manufactured by Red Devil) to prepare a comparative dispersion liquid (A).

<Preparation of Comparative Dispersion (B)>
A mixed solution prepared according to the formulation shown in Table 17 is placed in a polypropylene container together with zirconia beads, dispersed with a paint conditioner (manufactured by Red Devil) for 2 hours, and further a urethane latex (trade name; Bondic 1910NE, manufactured by DIC, solid A comparative dispersion (B) was prepared by adding and mixing 100 g of a partial concentration of 40% by mass.

<Preparation of Comparative Dispersion (C)>
The mixed solution prepared with the formulation shown in Table 18 is placed in a polypropylene container together with zirconia beads, dispersed with a paint conditioner (manufactured by Red Devil) for 2 hours, and further 34.7 g of tetraethoxysilane is added and mixed for comparative dispersion. A liquid (C) was produced.

<Preparation of Comparative Dispersion (D)>
A mixed solution prepared according to the formulation shown in Table 19 was placed in a polypropylene container together with zirconia beads, and dispersed for 2 hours with a paint conditioner (manufactured by Red Devil) to prepare a comparative dispersion (D).

<Preparation of Comparative Dispersion (E)>
A mixed solution prepared according to the formulation shown in Table 20 was placed in a polypropylene container together with zirconia beads and dispersed with a paint conditioner (manufactured by Red Devil) for 2 hours to prepare a comparative dispersion (E).

<Preparation of Comparative Dispersion (F)>
A mixed liquid prepared according to the formulation shown in Table 21 was placed in a polypropylene container together with zirconia beads, and dispersed for 2 hours with a paint conditioner (manufactured by Red Devil) to prepare a comparative dispersion liquid (F).

<Preparation of Comparative Dispersion (G)>
A mixed solution prepared according to the formulation shown in Table 22 was placed in a polypropylene container together with zirconia beads and dispersed with a paint conditioner (manufactured by Red Devil) for 2 hours to prepare a comparative dispersion (G).

<Preparation of Comparative Dispersion (H)>
A mixed liquid prepared according to the formulation shown in Table 23 was placed in a polypropylene container together with zirconia beads, and dispersed for 2 hours with a paint conditioner (manufactured by Red Devil) to prepare a comparative dispersion liquid (H).

<Preparation of Comparative Dispersion (I)>
A mixed liquid prepared according to the formulation shown in Table 24 was placed in a polypropylene container together with zirconia beads, and dispersed for 2 hours with a paint conditioner (manufactured by Red Devil) to prepare a comparative dispersion liquid (I).

<Preparation of Comparative Dispersion (J)>
A mixed liquid prepared according to the formulation shown in Table 25 was placed in a polypropylene container together with zirconia beads, and dispersed for 2 hours with a paint conditioner (manufactured by Red Devil) to prepare a comparative dispersion liquid (J).

<Comparative Example 1>
A commercially available cellulose separator was used as the electrochemical device separator of Comparative Example 1.

<Comparative example 2>
A commercially available polyethylene porous membrane separator was used as the electrochemical device separator of Comparative Example 2.

<Comparative Examples 3-12>
In the combinations shown in Tables 26 to 27, the comparative dispersion liquid was applied to the fiber matrix and dried, and then treated with a thermal calendar heated to 180 ° C. to obtain separators of Comparative Examples 3 to 12. The linear pressure of the thermal calendar roll was 14.7 MPa.

  Thickness, density, porosity, air permeability, maximum pore diameter, average pore diameter, shape change at 180 ° C., change in water, change in ethanol, change due to bending and stretching, separator of the comparative example obtained Tables 26 to 27 show the dispersion agglomerate diameters when re-dispersed. Further, using the separator of the comparative example, evaluation as an electric double layer capacitor separator and a lithium ion secondary battery separator was performed in the same manner as in the example, and the results are given in Table 28.

  The separators for electrochemical elements of Examples 1 to 21 have excellent heat resistance (change in shape at 180 ° C.) and good handling (change in water, change in ethanol, change due to bending and stretching) ) Furthermore, the pore diameter was small (maximum pore diameter, average pore diameter). The electric double layer capacitor and the lithium ion secondary battery using the separators for electrochemical elements of Examples 1 to 21 operated stably without causing an internal short circuit.

  In the electrochemical element separator of Comparative Example 1, the internal resistance could be kept low, but the leakage current was large. The electrochemical device separator of Comparative Example 2 showed a change in shape at 180 ° C., had no heat resistance, and the electric double layer capacitor and the lithium ion secondary battery did not operate. In the electrochemical device separator of Comparative Example 3, since the binder was used when filling the fiber matrix with aluminum oxide or aluminum hydroxide oxide, the internal resistance increased. In the separators for electrochemical elements of Comparative Examples 4 and 5, detachment of powder was observed, and the electrochemical elements did not operate stably.

  The separator for an electrochemical element of Comparative Example 6 in which a fiber matrix is filled with aluminum hydroxide oxide and microfibrillated cellulose shows powder detachment, a large pore diameter, and the electrochemical element operates stably. I did not. In the separator for an electrochemical element of Comparative Example 7, since microfibrillated cellulose was not contained, aluminum oxide could not be retained, the pore diameter was increased, and the electrochemical element did not operate stably. In the separators for electrochemical elements of Comparative Examples 8 to 12, since the dispersion aggregation diameter exceeds 1 μm, the pore diameter increases or the powder is detached, causing an internal short circuit. Didn't work.

  An electrochemical device having heat resistance, low internal resistance, and excellent repeatability can be produced using the separator of the present invention.

Claims (2)

  A separator for an electrochemical element, in which aluminum oxide having a dispersed aggregation diameter of less than 1 μm and a microfibrillated cellulose are filled between fiber matrices.   A separator for an electrochemical element, in which an aluminum oxide, an aluminum hydroxide oxide, and a microfibrillated cellulose are filled between fiber matrices, and a dispersed aggregate diameter of an aggregate structure composed of aluminum oxide and aluminum hydroxide oxide is less than 1 μm.