JP2000090731A - Solid state ion conductive composition, and manufacture of molding comprising it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid state ion conductive composition that has high cation transport number and does not cause problem such as liquid leakage when it is used for electrolyte of such as a battery, and a manufacturing method for a molding comprising this. SOLUTION: In a manufacturing method of a molding comprising solid state ion conductive composition, the solid state ion conductive composition formed by mixing polyether based macromolecule and polyvinyl alcohol cross-linked through boron is used, alkali metallic salt of boric acid or mixture of hydroxide of boric acid and alkali metal is added to mixing solution composed of polyether based macromolecule and polyvinyl alcohol for solation, and this sol is molded and dried.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid ion conductive composition for conducting alkali metal ions and a method for producing a molded article comprising the same, and mainly relates to an electrolyte such as a lithium ion battery, a positive electrode binder, or an electrochromic material. The present invention relates to a solid ion-conductive composition used for devices and the like, and a method for producing a molded article comprising the composition.

[0002]

2. Description of the Related Art Most of ion-conductive materials conventionally used are liquids obtained by dissolving an electrolyte salt in an organic solvent. For example, LiClO ₄ , LiBF ₄ , Li
A solution in which an electrolyte salt such as PF ₆ or LiN (CF ₃ SO ₂ ) ₂ is dissolved in an organic solvent having a high dielectric constant is used. However, batteries using such an organic solvent-based electrolyte may leak out the organic solvent, and have a problem in reliability.

In order to solve this problem, a gel electrolyte in which a polyvinylidene fluoride polymer is swollen with an organic solvent has been used, and commercialization of a battery using this gel electrolyte has started. Have been. The use of this gel electrolyte reduces the possibility of liquid leakage, but does not completely eliminate the possibility of liquid leakage, and further improvement in reliability is desired.

Further, carbon is used as a negative electrode material of a lithium ion secondary battery using such an organic solvent-based or gel-based electrolyte. The reason why lithium metal, which can be expected to increase battery capacity, is not used as the material of the negative electrode is that by repeatedly charging and discharging a battery using an organic solvent-based or gel-based electrolyte, dendrites are formed on the lithium metal surface of the negative electrode. The generation of dendritic crystals of so-called lithium metal is mentioned. The occurrence of dendrite causes problems such as a decrease in battery capacity, and thus it has been difficult to use lithium metal for the negative electrode of a battery using an organic solvent-based or gel-based electrolyte.

Further, the conventional organic solvent-based or gel-based electrolyte has a problem that the cation transport number is low. For example, the cation transport number in an organic solvent-based electrolyte is at most about 0.5. When the cation transport number of the electrolyte is low, the polarization of the electrolyte is likely to occur, and the resistance in the battery increases due to the IR drop as the battery.
There is a demand for an improvement in the cation transport number of the electrolyte.

For the purpose of solving the problem of the leakage of the organic solvent and the generation of dendrites, a solid polymer electrolyte containing no or almost no organic solvent has been studied. Solid polymer electrolytes using vinylidene fluoride polymers have been reported. However, the cation transport number of these solid polymer electrolytes is even lower than that of organic solvent or gel electrolytes, and is at most about 0.2.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a solid ionic conductive material which has a high cation transport number and does not cause a problem such as liquid leakage when used for an electrolyte such as a battery. An object of the present invention is to provide a composition and a method for producing a molded article comprising the composition.

[0008]

This problem is solved by a solid ionic conductive composition comprising a mixture of a polyether polymer and polyvinyl alcohol crosslinked with boron. Also, an alkali metal salt of boric acid or a mixture of boric acid and a hydroxide of an alkali metal is added to a mixed solution comprising a polyether polymer and polyvinyl alcohol to form a sol, and then the sol is formed and dried. The problem is solved by a method for producing a molded article comprising a solid ion conductive composition.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The polyether polymer in the solid ion conductive composition of the present invention is an ion conductive polymer having an ether structure in the main chain and / or the side chain. Examples of such a polyether polymer include polyethylene oxide (hereinafter, referred to as PEO), polypropylene oxide (PPO), and the like. The molecular weight of the polyether polymer is not particularly limited. For example, when PEO is used as the polyether polymer,
The range is from 10,000 to 10,000.

[0010] The polyvinyl alcohol crosslinked with boron in the solid ion conductive composition of the present invention is:
It is obtained by adding an alkali metal salt of boric acid or a mixture of boric acid and a hydroxide of an alkali metal to a solution of polyvinyl alcohol (hereinafter referred to as PVA).

The above-mentioned PVA is a resin obtained by saponifying polyvinyl acetate, and includes partially saponified polyvinyl acetate having a low degree of saponification, and those obtained by subjecting PVA to a treatment such as formalization. Although the molecular weight of the PVA is not particularly limited, for example, 2000 to 1,000,000
00 range.

The boric acid includes, for example, orthoboric acid, metaboric acid, tetraboric acid and the like. Examples of the alkali metal ion of boric acid alkali metal salt and alkali metal hydroxide include lithium ion, sodium ion and potassium ion. As an alkali metal salt of boric acid, LiBO ₂ is preferably used in consideration of ionic conductivity, cation transport number and the like, and a mixture of boric acid and an alkali metal hydroxide is H _3.
A mixture of BO ₃ and LiOH is preferably used.

The weight ratio of the polyether polymer to the PVA (PVA / polyether polymer) in the solid ion conductive composition of the present invention is not particularly limited, but is, for example, in the range of 0.001 to 1000. And preferably in the range of 0.1 to 100. When the weight ratio of the polyether polymer and PVA is less than 0.001, the number of alkali metal ions is reduced, and the ionic conductivity is reduced.
If it exceeds 1,000, the ionic conductivity of PEO cannot be utilized.

The amount of the alkali metal borate added to the solid ion conductive composition of the present invention is not particularly limited, but may be, for example, 1 to 25 parts by weight per 100 parts by weight of PVA.
Parts by weight, preferably 5 to 10 parts by weight. If the amount of the alkali metal salt of boric acid is less than 1 part by weight, the concentration of the alkali metal ion will be low, and the ionic conductivity will decrease. If the amount of the boric acid alkali metal salt exceeds 25 parts by weight, the boric acid alkali metal salt remains as an impurity, which adversely affects the cycle characteristics of the battery.

The amount of boric acid added to the solid ionic conductive composition of the present invention is not particularly limited.
The amount is 1.5 to 40 parts by weight, preferably 7 to 15 parts by weight, based on 100 parts by weight of PVA. The amount of the alkali metal hydroxide added to the solid ion conductive composition of the present invention is not particularly limited.
0.5 to 15 parts by weight based on 100 parts by weight of VA,
Preferably it is 2 to 10 parts by weight. If the amount of the alkali metal hydroxide added is less than 0.5 part by weight, the concentration of the alkali metal ion will be low, and the ionic conductivity will decrease. If the amount of the alkali metal hydroxide exceeds 15 parts by weight, the alkali metal hydroxide remains as an impurity, which adversely affects the cycle characteristics of the battery.

The solid ionic conductive composition of the present invention includes:
Propylene carbonate (hereinafter referred to as PC), ethylene carbonate, diethyl carbonate,
A small amount of a highly polar organic solvent such as dimethoxyethane, dimethylsulfoxide and dimethylformamide may be added. These plasticizers improve the ionic conductivity by lowering the Tg of the polyether-based polymer and promoting the movement of alkali metal ions.

The amount of the plasticizer is 500 parts by weight or less, preferably 300 parts by weight or less, based on 100 parts by weight of the mixture of the polyether polymer and the boron-crosslinked PVA. When the amount of the plasticizer exceeds 500 parts by weight,
When the solid ion conductive composition to which the plasticizer is added is used as an electrolyte of a battery, the battery may leak, and if lithium metal is used for the negative electrode of the battery, Dendrite is generated on the lithium metal surface.

The solid ion-conductive composition of the present invention may further contain, if necessary, additives such as a modifier, a colorant, an antioxidant and other resins, and the like. You may add in the range which does not impair the characteristic of a thing.

Next, a method for producing a molded article comprising the solid ion conductive composition of the present invention will be described. First, a polyether polymer and PVA are dissolved in a solvent.
To this mixed solution, an alkali metal salt of boric acid or a mixture of boric acid and an alkali metal hydroxide is added within the above-mentioned range, and a mixed solution of a polyether polymer and PVA is added to the sol. To Next, the sol is formed into a desired shape, for example, by casting it into a mold, and dried. Further, if necessary, the molded product after drying may be impregnated with a plasticizer. As the solvent, for example, water, alcohols, methyl ethyl ketone and the like can be used,
Among them, water is preferably used.

In addition to the above-mentioned method, it is obtained by adding an alkali metal salt of boric acid or a mixture of boric acid and an alkali metal hydroxide to a mixed solution comprising a polyether polymer and PVA. A method of mixing a sol with another resin, molding the mixture, and drying the mixture may be used. Further, a sol obtained by adding an alkali metal salt of boric acid or a mixture of boric acid and a hydroxide of an alkali metal to a mixed solution comprising a polyether polymer and PVA is formed into an appropriate form and dried. Then, this is extruder,
It is also possible to use a method of forming pellets using a pelletizer or the like and molding the pellets by an extrusion molding method, an injection molding method, or the like.

As a method of adding an alkali metal salt of boric acid or a mixture of boric acid and a hydroxide of an alkali metal to a mixed solution comprising a polyether polymer and PVA, for example, an alkali metal salt of boric acid is used. Or adding a mixture of boric acid and a hydroxide of an alkali metal to a mixed solution comprising a polyether polymer and PVA and dissolving it, an alkali metal salt of boric acid, or a hydroxide of boric acid and an alkali metal Is added to a mixed solution comprising a polyether polymer and PVA. Above all, in order to make the crosslinking density of the boron-crosslinked PVA uniform, an aqueous solution of an alkali metal salt of boric acid or a mixture of boric acid and an alkali metal hydroxide is mixed with a mixed solution of a polyether polymer and PVA. It is preferable to use the addition method. The concentration of the aqueous solution of boric acid or borate is not particularly limited, but is, for example, 1 to 5% by weight.

In the present invention, the polyether polymer and P
Solification of the mixed solution comprising VA occurs simultaneously with the addition of boric acid or a borate, and is usually performed at normal temperature and pressure. The casting in the present invention refers to a sol obtained by adding an alkali metal salt of boric acid or a mixture of boric acid and an alkali metal hydroxide to a mixed solution comprising a polyether polymer and PVA. Into the desired shape and pressurize, heat,
It is also possible to perform cooling or the like. The mold used for casting is not particularly limited, and a variety of shapes can be obtained by using various molds.

The drying in the present invention is an operation of removing a solvent from a cast sol to obtain a molded product. Examples of the method include a method by heating, a method by heating under reduced pressure, and a method by vacuum drying. And the like.

The shape of the molded article made of the solid ion-conductive composition of the present invention is not particularly limited, but may be various shapes such as a film, a tube and a fiber depending on the molding method. It is possible.

Such a solid ion conductive composition exhibits a high cation transport number because an alkali metal salt of boron-crosslinked PVA is used as an electrolyte salt. The following can be considered as a reason for this. When an alkali metal salt of boron-crosslinked PVA is used as an electrolyte salt,
The boron-crosslinked PVA becomes a polymer anion, and the mobility of the anion in the solid ion-conductive composition is extremely lower than the mobility of the cation. On the other hand, the mobility of the cation (alkali metal ion) in the solid ion conductive composition is almost the same as that using the conventional electrolyte salt, so that the cation transport number is lower than that using the conventional electrolyte salt. It rises relatively.

The solid ionic conductive composition of the present invention does not contain any organic solvent or contains a very small amount of organic solvent. Even when used as an electrolyte, a battery or the like does not cause liquid leakage, and even when lithium metal is used for the negative electrode of the battery, no dendrite is generated on the surface of the lithium metal.

Further, in the method for producing a molded article comprising the solid ion conductive composition, an alkali metal salt of boric acid is added to a mixed solution comprising a polyether polymer and PVA;
Alternatively, a mixture of boric acid and an alkali metal hydroxide is added to form a sol, and then the sol is formed and dried. It is possible to obtain a molded product that does not cause liquid leakage and that does not generate dendrites on the surface of lithium metal even when used as an electrolyte of a battery in which lithium metal is used for the negative electrode, at low cost and easily. it can.

[0028]

Embodiments are described below. (Example 1) 3 parts by weight of PEO (molecular weight 200), PVA
140 parts by weight (molecular weight 90,000) were dissolved in 1000 parts by weight of water. Then, 40 parts by weight of LiBO _{2 was} added to water 1
000 parts by weight, and this aqueous solution was added to an aqueous solution of a polyether polymer and PVA. The sol-formed mixed solution was cast on a petri dish, and then dried at 50 ° C. for 50 hours in an argon gas atmosphere, and further dried at room temperature under vacuum for 50 hours to remove water, and a solid ion conductive composition having a thickness of 100 μm was obtained. A thin film was obtained.

Examples 2 to 6 PEO and LiBO ₂
Example 1 was repeated except that the compounding amount of was changed as shown in Table 1.
Was carried out in the same manner as described above to obtain a thin film of the solid ion-conductive composition having a thickness of 100 μm. (Examples 7 to 10) The molecular weight of PEO was 4,000,000
0, the molecular weight of PVA was changed to 2,000, PEO,
The same procedure as in Example 1 was carried out except that the amounts of PVA and LiBO ₂ were changed as shown in Table 1, and the thickness was 100 μm.
A thin film of the solid ion conductive composition was obtained.

Comparative Example 1 PEO (Molecular Weight 5000) 1
00 parts by weight and 13 parts by weight of LiClO ₄ were dissolved in 1000 parts by weight of acetonitrile, and this solution was cast on a petri dish, and then dried at 50 ° C. for 50 hours in an argon gas atmosphere and further dried at room temperature under vacuum for 50 hours to remove water. This was removed to obtain a thin film of the solid ionic conductive composition having a thickness of 100 μm.

(Comparative Examples 2 and 3) A thin film of a solid ionic conductive composition having a thickness of 100 μm was prepared in the same manner as in Comparative Example 1 except that the kind and the amount of the electrolyte salt were changed as shown in Table 2. I got

The ionic conductivity and cation transport number of the thin films of the solid ionic conductive compositions of Examples 1 to 10 and Comparative Examples 1 to 3 were measured by the following methods. The results are shown in Tables 1 and 2.

(Ion conductivity) The ion conductivity is measured by
The ionic conductivity was determined by measuring the AC impedance of the sample using the measurement holder shown in FIG. Under an argon gas atmosphere, a circular sample 1 having an outer diameter of 20 mm was cut out of a thin film of the solid ion-conductive composition, and this sample 1 was sandwiched between stainless steel electrodes 2 and 3, and this was cut into a stainless steel having a hole for inserting an electrode. The electrode 3 was placed in a holder 4, and further covered with a Teflon cover 6 provided with a spring 5 inside the electrode 3, and pressure was applied to the electrode 3 by the spring 5. A conducting wire was extended from the screw 7 and the screw 8 which are electrically connected to the electrodes 2 and 3, and the AC impedance was measured. Similarly, a circular sample having an outer diameter of 20 mm was cut out from the thin film of the solid ion-conductive composition, the circular sample was immersed in PC for 120 minutes, and the ionic conductivity of the sample impregnated with PC was determined.

(Cation transport number) A sample having an outer diameter of 20 mm was cut out from a thin film of the solid ion conductive composition, and a Li foil having an outer diameter of 20 mm and a thickness of 200 μm was pressed on both surfaces of the sample to obtain a test piece. . A lead wire was extended from the Li foil, and the cation transport number of this test piece was measured by a direct current method.

[0035]

[Table 1]

[0036]

[Table 2]

From these results, the thin film of the solid ionic conductive composition of the example using the boron-crosslinked PVA showed a better cation transport number than the thin film of the solid ionic conductive composition of the comparative example. You can see that it is.

[0038]

As described above, in the solid ion conductive composition of the present invention, since the boron-crosslinked PVA is used, the solid ion conductive composition using the conventional electrolyte salt is not used. It shows a higher cation transport number. When the solid ion conductive composition of the present invention is used as an electrolyte of a battery, it is possible to prevent an increase in resistance in the battery.

Further, even when the solid ion conductive composition of the present invention is used as an electrolyte for a battery, the battery does not leak. Further, even when lithium is used for the negative electrode of the battery, no dendrite is generated on the surface of the lithium metal, so that a reduction in battery capacity due to the dendrite and a short circuit between the negative electrode and the positive electrode can be prevented. Therefore, the solid ion conductive composition of the present invention is expected to be applied to various devices including a lithium ion primary battery and a lithium ion secondary battery.

Further, in the method for producing a molded article comprising the solid ion conductive composition of the present invention, the alkali metal salt of boric acid or boric acid is added to a mixed solution comprising a polyether polymer and PVA. And a mixture of a hydroxide of an alkali metal and adding the mixture to form a sol. Then, the sol is formed and dried, so that it exhibits a high cation transport number. A molded product that does not occur and that does not generate dendrites on the surface of lithium metal even when used as an electrolyte of a battery in which lithium is used for the negative electrode can be obtained inexpensively and easily.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a measurement holder used for measuring ion conductivity.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroyuki Miyata 1-5-1, Kiba, Koto-ku, Tokyo Inside Fujikura Co., Ltd. (72) Inventor Masayoshi Watanabe 30-3-401F, Oimatsu-cho, Nishi-ku, Yokohama-shi, Kanagawa F Term (reference) 4J002 BE02X CH00W CH02W DE056 DK006 FD146 GQ02 5H029 AJ05 AJ12 AL06 AL12 AM00 AM03 AM04 AM07 AM16 CJ02 CJ08 CJ11 EJ03 EJ13

Claims (2)

[Claims] 1. A solid ion conductive composition comprising a mixture of a polyether polymer and polyvinyl alcohol crosslinked with boron. 2. An alkali metal salt of boric acid is added to a mixed solution comprising a polyether polymer and polyvinyl alcohol,
Alternatively, a method for producing a molded product comprising a solid ion conductive composition, comprising adding a mixture of boric acid and an alkali metal hydroxide to form a sol, then molding and drying the sol.