JP2011086558A - Scale-like inorganic solid electrolyte filler, solid electrolyte membrane containing the same, nonaqueous electrolyte secondary battery, and capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolyte membrane of high intensity and high ionic conductivity with the use of scale-like inorganic solid electrolyte. <P>SOLUTION: The scale-like inorganic electrolyte filler is endowed with lithium ionic conductivity. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a scaly inorganic solid electrolyte filler, a solid electrolyte membrane containing the same, a nonaqueous electrolyte secondary battery, and a capacitor.

In recent years, non-aqueous electrolyte secondary batteries, especially lithium secondary batteries, have been demanded from conventional portable terminal applications to larger-sized applications such as electric tools, electric bicycles, scooters, electric vehicle batteries and hybrid cars. Is growing.
Conventional separators for non-aqueous electrolyte secondary batteries for portable terminals use microporous polyolefin materials, but an excessive current flows in the separator due to a short circuit between the positive and negative electrodes. In addition, in order to prevent the reaction from accelerating and causing explosion accidents, when the micropores of the separator exceed the normal operating temperature, they clog as low as possible at the temperature exceeding the normal operating temperature, and excess current is contained in the electrolyte. Safety measures are taken by adding a shutdown function that prevents the flow of the battery.
When a non-aqueous electrolyte secondary battery, particularly a lithium secondary battery is enlarged, or when the secondary battery is disposed near an internal combustion engine such as a hybrid car, the electrolyte functions as a separator even at a high temperature. Is required. For this reason, for the purpose of preventing a short circuit between the positive electrode and the negative electrode during overcharge, there are methods of changing the positive electrode material from conventional lithium cobalt oxide to lithium manganate or adding iron phosphate.
However, in a secondary battery with a large capacity, if a short circuit occurs between the positive electrode and the negative electrode, the sudden chemical reaction occurs abruptly, so the development of a solid electrolyte battery is desired. Although a secondary battery using an inorganic solid electrolyte has high safety, there is a characteristic deterioration at the interface, and thus a battery that can withstand a long-term cycle cannot be manufactured. Further, in a secondary battery using a solid polymer electrolyte, lithium ions have low conductivity, and it is necessary to reduce the thickness in order to solve the problem. However, when the thickness is reduced, the mechanical strength is lowered, the polymer solid electrolyte is destroyed, and the positive electrode and the negative electrode are short-circuited.
In order to solve these problems, a solid electrolyte battery (Patent Document 1) containing 2 to 35% by weight of an inorganic solid electrolyte in a polymer solid electrolyte, or a lithium ion conductive glass ceramic powder in a sheet-like polymer material. There has been proposed a glass-ceramic composite electrolyte obtained by impregnating a non-aqueous electrolyte in a medium to be contained (Patent Documents 2 to 4).

Japanese Patent Laid-Open No. 10-144349 JP 2001-015164 A JP 2004-303738 A JP 2006-086102 A

However, when these inorganic solid electrolytes are in the form of particles, the thinner the electrolyte membrane, the lower the strength, and there is a problem that the positive electrode and the negative electrode are short-circuited due to destruction of the polymer solid electrolyte. Further, when the temperature in the battery rises and the polymer is melted or burned out, there arises a problem that the inorganic solid electrolyte flows and the positive electrode and the negative electrode are short-circuited. Furthermore, since the particle shape itself does not have a film-forming ability, the content cannot be increased. Moreover, even if the content can be increased, there is a problem that high ionic conductivity cannot be obtained because there are few contacts between the electrolytes.
Accordingly, an object of the present invention is to provide a solid electrolyte membrane having high strength and high ion conductivity by using a scaly inorganic solid electrolyte.

The scaly inorganic solid electrolyte filler of the present invention is characterized by having lithium ion conductivity as described in claim 1.
According to a second aspect of the present invention, in the flaky inorganic solid electrolyte filler according to the first aspect, the flaky inorganic solid electrolyte filler has an average thickness of 0.01 to 5.0 μm and an average particle diameter of 0.1. It is ˜100 μm.
Moreover, the solid electrolyte membrane of this invention contains the said scaly inorganic solid electrolyte filler of Claim 1 or Claim 2, as described in Claim 3. It is characterized by the above-mentioned.
According to a fourth aspect of the present invention, in the solid electrolyte membrane according to the third aspect, the wide surface of the scaly inorganic solid electrolyte filler is oriented so as to be perpendicular to the thickness direction of the solid electrolyte membrane. It was made to be characterized.
The present invention described in claim 5 is characterized in that in the solid electrolyte membrane according to claim 3 or 4, 0.1 to 80% by mass of a binder polymer is included with respect to the total mass of the solid electrolyte membrane. And
Moreover, the nonaqueous electrolyte secondary battery of this invention was equipped with the solid electrolyte membrane of any one of Claims 3-5 as described in Claim 6.
According to a seventh aspect of the present invention, a capacitor includes the solid electrolyte membrane according to any one of the third to fifth aspects.

  Since the electrolyte filler of the present invention and the electrolyte membrane using the same use a scaly inorganic solid electrolyte, the electrolyte filler itself has a film forming ability, and an electrolyte membrane can be formed with almost no binder. Therefore, the solid electrolyte content can be increased and the ionic conductivity can be improved. Moreover, since it is scaly, the electrolyte is arranged in parallel to the film surface. Therefore, the strength in the direction perpendicular to the film is improved, and the contact of each electrolyte filler is performed on the surface, so that the ionic conductivity can be improved. By using scale-like inorganic solid electrolytes for these reasons, a solid electrolyte membrane having high strength and high ionic conductivity can be provided.

Explanatory drawing of a short resistance measuring device

Hereinafter, embodiments of the present invention will be described in detail.
The scaly inorganic solid electrolyte filler of the present invention has lithium ion conductivity.
The inorganic solid electrolyte is not particularly limited as long as it can conduct lithium ions. For example, Li ₃ N, LiTi ₂ (PO ₄ ) ₃ , Li-βAl ₂ O ₃ , LiI, LiI-Li ₂ S-P ₂ O ₅ , LiI-Li ₂ S-B ₂ S ₃ , LiI-Li ₃ N-LiOH, Li ₂ O-B ₂ O ₃ , Li ₂ O-V ₂ O ₃ -SiO ₂ , LiTaO ₃ , Li ₂ S -SiS ₂ -Li ₃ PO _4, can be selected _{LiI-Li 2 S-P 2} S 5, Li-Ge-P-S inorganic solid electrolytes such. These may be used alone or in combination. These electrolytes may be amorphous or crystalline.

About the shape of the filler used for this invention, what is the scale shape provided with the wide surface of the front and back is sufficient.
Moreover, although there is no restriction | limiting in particular about the dimension, It is preferable that it is an average thickness of 0.01-5.0 micrometers and an average particle diameter of 0.1-100 micrometers. If the average thickness exceeds 5.0 μm, the solid electrolyte membrane described later may be uneven, or a protrusion may be formed. If the average particle diameter exceeds 100 μm, a problem may occur for the same reason. On the other hand, when the average thickness is less than 0.01 μm, the productivity of the inorganic solid electrolyte may be extremely deteriorated, which is not practical. On the other hand, when the average particle size is less than 0.1 μm, the strength may be lowered, and the productivity is extremely deteriorated, which is not practical. In the present specification, the average thickness of the flaky filler refers to extracting at least 100 flaky fillers, measuring the thickness of these flaky fillers using a scanning electron microscope (SEM), This is the value obtained by dividing the total by the number of sheets to be measured. In the present specification, the average particle size of the scaly filler is a particle size (D50) corresponding to 50% of the cumulative mass percentage in the particle size distribution measured based on the laser diffraction scattering method.

The filler may be coated with a coupling agent in order to increase the affinity with the binder. A typical example of the coupling agent is a silane coupling agent. The silane coupling agent varies depending on the resin used, but vinyl silane, epoxy silane, methacryloxy silane, and amino silane are preferable. These silane coupling agents may be used alone or in combination.
Examples of vinyl silane include vinyl trichlorosilane, vinyl trimethoxy silane, vinyl triethoxy silane and the like. Examples of the epoxy silane include 2- (3,4 epoxycyclohexyl) ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 3-glycidoxypropyltriethoxysilane. Can be illustrated. Examples of methacryloxysilane include 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, and 3-methacryloxypropyltriethoxysilane. As aminosilane, N-2 (aminoethyl) 3-aminopropylmethyldimethoxysilane, N-2 (aminoethyl) 3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, Examples thereof include 3-triethoxysilyl-N- (1,3-dimethyl-butylidene) propylamine and N-phenyl-3-aminopropyltrimethoxysilane.
It is preferable that the content rate of a silane coupling agent is 0.01 mass%-5.0 mass% with respect to the whole mass. When the amount is less than 0.01% by mass, it is difficult to obtain sufficient affinity with the polymer as a binder. On the other hand, when the content exceeds 5.0% by mass, a reaction between coupling agents occurs, which impairs the affinity between the filler and the polymer, and increases the cost.

Next, the solid electrolyte membrane containing the scale-like inorganic solid electrolyte filler will be described.
In order to obtain a solid electrolyte membrane, a scaly inorganic solid electrolyte filler is stirred and mixed uniformly in a resin binder dispersed or dissolved in a solvent, and this liquid is formed into a film by a casting method or a coating method, or extrusion molding, After molding by injection molding or the like, vacuum drying is performed. In this process, the wide surface of the scaly inorganic solid electrolyte filler is oriented perpendicular to the thickness direction of the sheet. Further, roll forming can be performed to adjust the thickness.

As the binder to be added to the solid electrolyte membrane, a polyolefin material such as polyethylene or polypropylene, a fluororesin such as polytetrafluoroethylene, polychlorotrifluoroethylene, or polyvinylidene fluoride, or a polymer material such as polyamide or polyester polyacrylate is used. be able to.
Further, when a polymer solid electrolyte is used as a binder, for example, a known polymer material such as polyethylene oxide, polypropylene oxide, polyethyleneimine, etc., as a solute, for example, lithium trifluoromethanesulfonate LiCF ₃ SO ₃ , lithium hexafluorophosphate LiPF ₆ , lithium tetrafluoroborate LiBF ₄ , lithium perchlorate LiClO ₄ , lithium trifluoromethanesulfonate imidolithium LiN (CF ₃ SO ₂ ) _{2 and the} like can be used. Further, when adding a solute, a solvent that dissolves the solute may be added, and the polymer solid electrolyte may be used in the form of a gel. As such a solvent, for example, propylene carbonate, ethylene carbonate, γ-butyrolactone, butylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate, diethyl carbonate and the like can be used.
The binder is preferably 0.1 to 80% by mass with respect to the mass of the entire electrolyte membrane. This is because if it is 0.1% by mass or less, it does not function as a binder for the inorganic solid electrolyte filler and the strength decreases. If it is 80% by mass or more, the number of contacts of the inorganic solid electrolyte filler is reduced, and the ionic conductivity is lowered. More preferably, it is 1-50 mass%, More preferably, it is 2-10 mass%.
Furthermore, inorganic fibers or inorganic fiber nonwoven fabrics may be added or used for the purpose of reinforcing the solid electrolyte membrane. When inorganic fibers or inorganic fiber nonwoven fabrics are used, the mass thereof is preferably 10% by mass or less with respect to the electrolyte membrane. If it is 10% by mass or more, the number of contacts of the inorganic solid electrolyte filler is reduced, and the ionic conductivity is lowered. The inorganic fiber or the inorganic fiber nonwoven fabric is not particularly limited as long as it does not affect the battery or the capacitor. For example, ceramics such as silica and alumina, glass, and the like can be used.
In the solid electrolyte membrane, it is preferable to orient the wide surface of the scaly inorganic solid electrolyte filler so as to be perpendicular to the thickness direction of the solid electrolyte membrane. This is because the wide surface of the filler is arranged so as to partially overlap in the thickness direction, so that the dendrite growth path can be meandered.
In order to ensure the function as a solid electrolyte membrane, the thickness is preferably 100 μm, more preferably 20 μm or less.

The solid electrolyte membrane of the present invention can be used as a known non-aqueous electrolyte secondary battery or capacitor electrolyte membrane or separator.
Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In addition, unless it exceeds the gist of the present invention, it is not limited to the following examples.

NH ₄ H ₂ PO ₄ , Al (PO ₃ ) ₃ , Li ₂ CO ₃ , SiO ₂ , TiO ₂ are used as raw materials, and these are 35.0% P ₂ O ₅ and Al ₂ O in mol% in terms of oxide. Weighed ₃ to 7.5%, Li ₂ O 15.0%, TiO ₂ 38.0%, SiO ₂ 4.5% and mixed uniformly, then placed in the dissolution tank and heated for 2 hours with stirring at 1600 ° C. did. A nozzle was placed in the dissolution tank, and thin glass was produced while air was blown from the nozzle, and the thin glass was continuously drawn out by a roller. Glass having an average thickness of 0.4 μm was obtained by changing the amount of air blown and the number of roller rotations. Thereafter, pulverization and classification were performed to obtain scaly glass having an average particle diameter of 10 μm. For the pulverization, a jet mill type pulverizer (product name “Lab Jet LJ” (manufactured by Nippon Pneumatic Co., Ltd.)) was used. Further, the particle size was adjusted by sieving and classification. For the sifting classification, an electromagnetic sieve shaker (product name “RETSCHSIEVESHAKER, type VIBRO” (manufactured by RETSCH Co., Ltd.) was used, and a sieve was appropriately selected according to the intended particle size distribution. The measurement was performed using a measuring apparatus (product name “Microtrack (registered trademark) HRA” (manufactured by Nikkiso Co., Ltd.)).
Furthermore, this flaky glass was heat-treated at 950 ° C. for 12 hours to give the desired ionic conductivity, thereby obtaining a flaky inorganic solid electrolyte filler. The ionic conductivity of the scaly inorganic solid electrolyte filler was 1 × 10 ⁻³ S · cm ⁻¹ at room temperature.
Next, 0.8% by weight of polyimide resin varnish `` Rika Coat PN-20 '' (solid content 20 wt%) manufactured by Shin Nippon Rika Co., Ltd., 99% by weight of dehydrated N-methyl-2-pyrrolidone, 0.2% by weight of polyethylene glycol After the polyimide resin varnish was dissolved in N-methyl-2-pyrrolidone at 60 ° C., polyethylene glycol was added to obtain a completely and completely compatible resin solution. To 100 g of this resin solution, 29 g of a scale-like inorganic solid electrolyte filler was added and stirred and mixed so as to be uniform. This liquid was formed into a film by a casting method and then vacuum-dried to prepare a scale-like glass-resin composite film that was a solid electrolyte film. The thickness of the obtained solid electrolyte membrane was about 20 μm.

  New Nippon Rika Co., Ltd. polyimide resin varnish “Rika Coat PN-20” (solid content 20 wt%) 2.5 wt%, dehydrated N-methyl-2-pyrrolidone 97 wt%, polyethylene glycol 0.5 wt% After weighing out and dissolving the polyimide resin varnish in N-methyl-2-pyrrolidone at 60 ° C., polyethylene glycol was added to obtain a completely and completely compatible resin solution. To 100 g of this resin solution, 27 g of a scaly inorganic solid electrolyte filler obtained by the same method as in Example 1 was added and stirred and mixed so as to be uniform. This solution was formed into a film by a casting method and then vacuum-dried to produce a solid electrolyte membrane. The thickness of the obtained solid electrolyte membrane was about 20 μm.

Titanium oxide TiO ₂ , lithium carbonate Li ₂ CO ₃ and ammonium phosphate (NH ₄ ) H ₂ PO ₄ were mixed as raw materials, and this mixture was heated and melted at 1200 ° C. for 2 hours while stirring the glass melt. A nozzle was placed in the dissolution tank, and thin glass was produced while air was blown from the nozzle, and the thin glass was continuously drawn out by a roller. Glass having an average thickness of 0.4 μm was obtained by changing the amount of air blown and the number of roller rotations. Thereafter, pulverization and classification were performed in the same manner as in Example 1 to obtain a glass flake having an average particle diameter of 10 μm. The ionic conductivity of the glass flakes was 2 × 10 ⁻⁴ S · cm ⁻¹ at room temperature.
Next, a polymer of polyethylene oxide and polypropylene oxide to which LiPF ₆ is added as a Li salt is uniformly mixed at a ratio of 80:20 with ethanol as a solvent to a solid content of 30% by mass, and a polymer solid electrolyte solution is obtained. Produced. To 100 g of this solution, 30 g of a flaky inorganic solid electrolyte filler was added, stirred and mixed so as to be uniform, formed into a film by a casting method, and then vacuum dried to produce a solid electrolyte film. The obtained scaly glass-polymer solid electrolyte composite membrane had a thickness of about 20 μm.

A glass short fiber having the composition of C glass shown in Table 1 and having an average diameter of 0.7 μm and an average length of about 3 mm is introduced into a pulper for unraveling the fiber, and it is sufficient in an aqueous solution adjusted to pH 2.5 with sulfuric acid. The slurry for glass making (glass fiber dispersion) was prepared. Using this slurry as a raw material, a glass fiber nonwoven fabric was obtained using a wet papermaking machine. The obtained glass fiber nonwoven fabric had a thickness of 20 μm and a basis weight of 5 g / m ² .

注：Ｒ₂Ｏは、Ｎａ₂ＯとＫ₂Ｏの合計を表す。

Note: R ₂ O represents the total of Na ₂ O and K ₂ O.

  The glass fiber nonwoven fabric was cut into a size of 10 cm × 10 cm, placed on a PET (polyethylene terephthalate) film, and impregnated with 10 g of the glass flake-resin composite solution used in Example 1 from above. The glass nonwoven fabric impregnated with the resin solution was dried in vacuum for 1 hour and then peeled off from the PET film. The thickness of the obtained glass fiber nonwoven fabric-flaky glass-resin composite film was about 30 μm.

(Comparative Example 1)
NH ₄ H ₂ PO ₄ , Al (PO ₃ ) ₃ , Li ₂ CO ₃ , SiO ₂ , TiO ₂ are used as raw materials, and these are 35.0% P ₂ O ₅ and Al ₂ O in mol% in terms of oxide. ₃ is 7.5%, Li ₂ O is 15.0%, TiO ₂ is 38.0%, SiO ₂ is 4.5% and weighed and mixed uniformly, then placed in the dissolution vessel, stirring the glass melt at 1600 ° C It was melted by heating for 2 hours. Thereafter, the glass melt was directly cast into water to obtain a mother glass. The mother glass was heat-treated at 950 ° C. for 12 hours, and then pulverized and classified using the same apparatus as in Example 1 to obtain a flaky glass substrate having an average particle diameter of 10 μm.
Further, in the same manner as in Example 1, a powdery glass-resin mixed solution was prepared using a resin solution using a polyimide resin varnish, formed into a film by a casting method, and then vacuum-dried to obtain a scaly glass-resin composite film. Produced. The thickness of the obtained powdery glass-resin composite film was about 50 μm.

(Comparative Example 2)
Using the powdery glass-resin mixed solution obtained in the same manner as in Comparative Example 1, film formation was attempted by a casting method, but a film having a thickness of about 20 μm could not be formed.

(Comparative Example 3)
A powdery glass was obtained in the same manner as in Comparative Example 1. Furthermore, it carried out similarly to Example 2, and produced the powdery glass-resin mixed solution using the resin solution using the polyimide resin varnish. Film formation was attempted by a casting method, but a film having a thickness of about 50 μm could not be formed.

  The following tests were performed on the glass-resin composite films prepared in Examples 1 to 4 and Comparative Example 1. The results of the test are shown in Table 3.

(Tensile strength measurement)
A proton conductive membrane was cut into a width of 20 mm and a length of 80 mm to prepare a test piece, and pulled at a chuck interval of 30 mm at a speed of 10 mm / min, and the load (N) at break was measured. The tensile strength (MPa) was calculated by dividing this by the measured values of the sample thickness and width. Here, the sample thickness was measured with a micrometer.

(Short resistance measurement)
A schematic diagram of the apparatus used for measuring the short-circuit resistance is shown in FIG. The resin film 1 was sandwiched from above and below by a stainless steel cylinder 2 having a diameter of 50 mm, and a load of 0.14 kg / cm ² was applied using a spring 3. The upper and lower stainless steel cylinders 2 are electrically insulated by heat-resistant insulating plates 4. The upper stainless steel cylinder 2 has a curved surface so that the separator can be removed when pressurized. This was placed in a programmed high temperature bath with a voltage of 3.0 V, and the temperature was raised from room temperature to 400 ° C. in 10 hours. When the resin porous lipid film has a high temperature at which it dissolves or burns, pressure is applied between the positive and negative electrodes, and the electrolyte flows or is exhausted, causing both electrodes to short-circuit. Whether or not a short circuit occurred was judged by the resistance measuring instrument 5, and the short circuit resistance was evaluated at the temperature at which the short circuit occurred.

  As is clear from the results of the above examples and comparative examples, in Examples 1 to 4 according to the present invention, a film can be formed even if the content of the inorganic solid electrolyte is large. It turns out that a film | membrane cannot be formed when content increases. Moreover, compared with Comparative Examples 1-3, Examples 1-4 are understood that intensity | strength and ionic conductivity are improving, and also the short circuit temperature is improving.

DESCRIPTION OF SYMBOLS 1 Resin film 2 Stainless steel cylinder 3 Spring 4 Heat-resistant insulating board 5 Resistance measuring device

Claims (7)

  A scaly inorganic solid electrolyte filler characterized by having lithium ion conductivity.   The flaky inorganic solid electrolyte filler according to claim 1, wherein the flaky inorganic solid electrolyte filler has an average thickness of 0.01 to 5.0 µm and an average particle diameter of 0.1 to 100 µm.   A solid electrolyte membrane comprising the scale-like inorganic solid electrolyte filler according to claim 1 or 2.   The solid electrolyte membrane according to claim 3, wherein a wide surface of the scaly inorganic solid electrolyte filler is oriented so as to be perpendicular to a thickness direction of the solid electrolyte membrane.   5. The solid electrolyte membrane according to claim 3, comprising 0.1 to 80% by mass of a binder polymer based on a total mass of the solid electrolyte membrane.   A nonaqueous electrolyte secondary battery comprising the solid electrolyte membrane according to any one of claims 3 to 5.   A capacitor comprising the solid electrolyte membrane according to claim 3.

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