JPH0287415A - Lithium ion electroconductive solid electrolytic sheet - Google Patents

Abstract

PURPOSE:To provide possibility of making in a thin construction, enhance producibility, uniformity, chemical stability, and flexibility, increase the electroconductivity, and enlarge the transference number of lithium ion by forming a sheet from a mixture of a highpolymer resilient substance and Li4 SiO4-Li3VO4 type solid electrolyte powder, which is dispersed in the resilient substance so that the volume fraction becomes a specified value. CONSTITUTION:Li4SiO4-Li3VO4 type solid electrolyte powder is dispersed in a highpolymer resilient substance so that the volume fraction becomes 55-95%, and the resultant mixture is turned into a sheet. Such solid electrolyte powder contains Li4 SiO4 and Li3VO4. The mix proportion shall preferably be Li4SiO4/Li3 VO4 being 1/9 thru 9/1 by mol ratio, and volume fraction of this solid electrolyte powder in the highpolymer resilient substance shall be 55-95%, favorably being 75-92%. Below 55% causes the ion electroconductivity under 1X10<-8>Scm<-1> as not suitable to practical use, while exceeding 95% causes brittle sheet of solid electrolyte, wherein the powder will easily be separated off.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a lithium ion conductive solid electrolyte sheet, and more specifically, it is suitable for use in solid batteries, solid electrochemical double layer capacitors, solid electrochromic displays, etc. The present invention relates to a lithium ion conductive solid electrolyte sheet.

[Conventional technology]

In recent years, various lithium solid-state batteries using lithium-based solid electrolytes have been put into practical use, but there is a desire to develop lithium solid-state batteries with excellent reliability that can be made smaller and thinner.

The lithium solid battery requires the use of a solid electrolyte with high lithium ion conductivity.

As such a lithium ion conductive solid electrolyte,
Li1. Inorganic solid electrolytes such as Li5N and polymer solid electrolytes such as lithium salt complexes of polyethylene oxide are known, but they have the problem of strong hygroscopicity and poor chemical stability. Furthermore, in the case of inorganic solid electrolytes, it is necessary to pelletize the inorganic powder using a high-pressure press, and the resulting pellets are also hard and brittle, making it difficult to make them thinner and causing problems such as poor productivity and uniformity. On the other hand, solid polymer electrolytes do not have sufficiently high conductivity and have a low transference number for lithium ions, so when used in batteries, polarization occurs and the voltage drops rapidly.

[Problem to be solved by the invention]

It is an object of the present invention to solve the problems of the prior art, to be able to be made thinner, to have excellent productivity, uniformity, chemical stability, and flexibility, to have high electrical conductivity, and to have a transference number of stium ions. The purpose of the present invention is to provide a lithium ion conductive solid electrolyte sheet with a large amount of lithium ion conductivity.

[Means to solve the problem]

The present invention provides LiaS gos - Lis VOd
It is characterized in that a mixture in which solid electrolyte powder is dispersed in a polymeric elastomer at a volume fraction of 55 to 95% is molded into a sheet shape.

The Li, Sin, -Li and O1-based solid electrolyte powder (hereinafter simply referred to as "solid electrolyte powder") used in the present invention is a mixture of Li4Sio, (!: Li, VOa). The mixing ratio is LiaS to, in molar ratio.
/L 13VO4=1/9 to 9/1, more preferably 2/8 to 8/2, particularly preferably 3
/7 to 515. If the mixing ratio is outside the above range, it is difficult to obtain sufficient ionic conductivity.

The details of the Li, Sio4-Li, and VOa-based solid electrolyte powders are described in "Electrochemistry and Industrial Physical Chemistry J 49 (10), 667 (1981).

The shape and particle size of these solid electrolyte powders are not particularly limited, but from the viewpoint of ease of mixing with the polymeric elastomer, those that pass through a 100 to 200 mesh (Tyler standard sieve) are preferred. preferable.

The solid electrolyte powder contains An to improve conductivity.
, O:1, etc. can be added. The addition ratio of this dielectric is 5% of the total amount of solid electrolyte powder and dielectric.
It is preferably 0 mol% or less, more preferably 10 mol% or less, particularly preferably 2 to 5 mol%.

Examples of the elastic polymer used in the present invention include l
, 4-polybutadiene, natural rubber, polyisoprene, 5
BRSNBR, EPDM, E'PM.

Urethane rubber, polyester rubber, chloroprene rubber, epichlorohydrin rubber, silicone rubber, styrene-butadiene-styrene block copolymer (SBS),
Styrene-isoprene-styrene flock copolymer (S
IS), styrene-ethylene-butylene-styrene block copolymer (SEBS), butyl rubber, phosphazene rubber, polyethylene, polypropylene, polyethylene oxide, polypropylene oxide, polystyrene, vinyl chloride, ethylene-ethyl acetate copolymer, 1゜2- Examples include polybutadiene, epoxy resins, phenolic resins, methyl methacrylate, and mixtures thereof. Among these, thermoplastic materials such as SBS, SIS, 5EBS, and 1,2-polybutadiene are preferable from the viewpoint of adhesion with electrode materials and solid electrolyte, and more preferably those having ASTM-A hardness from the viewpoint of flexibility. 90 or less 6 Also, from the standpoint of heat resistance of solid electrolyte powder, 150°C
It is preferable to have the following moldability, and it is particularly preferable to contain 50% by volume or more of an elastic polymer that does not contain unsaturated bonds. If the volume fraction of such an elastic polymer is less than 50%, the decomposition voltage and electron transport number of the obtained solid electrolyte sheet may deteriorate.

The polymer elastomer contains polymers such as polyethylene oxide, polypropylene oxide, polysiloxane, and polyphosphazene, and Li, in order to improve conductivity.
Cl0a, Li5CN, LiBH4, LiBF4, L
It is preferable to mix a solid polymer electrolyte consisting of a complex with a lithium salt such as iCFzSOs or LiAsFb. The mixing ratio of the polymer electrolyte is preferably a weight fraction of elastomer polymer/solid polymer electrolyte=9/1 to 1/9.

Note that the solid polymer electrolyte is treated as an elastic polymer.

In the mixture of the solid electrolyte powder and the polymer elastic body used in the present invention, the volume fraction of the solid electrolyte powder in the polymer elastic body is 55 to 95%, preferably 75 to 92%.

If the volume fraction of the solid electrolyte powder is less than 55%, the ionic conductivity will be less than l The sheet becomes brittle and the solid electrolyte powder easily falls off.

A method for obtaining the mixture includes, for example, a method of kneading a polymer solution in which a polymer elastomer is dissolved in a solvent, solid electrolyte powder, etc. using a ball mill or the like. In this method, there is little heat generation during kneading, and there is almost no contact with the atmosphere during kneading, so that deterioration and decomposition of the solid electrolyte powder due to moisture, oxygen, etc. is unlikely to occur.

Examples of solvents used in this case include saturated hydrocarbons that do not absorb water and do not react with the solid electrolyte powder, such as n-hexane, n-heptane, n-octane, cyclohexane, benzene, toluene, xylene, ethyl acetate, trichlene, etc. Examples include hydrocarbon solvents, aromatic hydrocarbon solvents, halogenated hydrocarbon solvents, and ester solvents.

The lithium ion conductive solid electrolyte sheet of the present invention is obtained by molding the solvent-containing slurry obtained as described above into a sheet shape. There is no particular restriction on the method of forming the solid electrolyte sheet into a sheet, but in order to improve the strength of the solid electrolyte sheet, for example, the openings of the mesh body may be filled with the mixture,
It can be obtained by drying.

Examples of the network include woven or nonwoven fabrics made of insulating materials such as cellulose, polyethylene terephthalate, nylon 6, nylon 66, polypropylene, polyethylene, zeolite, and glass. The aperture ratio of these net-like bodies is suitably in the range of 35 to 65%. The aperture ratio is defined as the ratio of the total aperture area per unit area of the mesh. If the aperture ratio is less than 35%, the conductivity of the solid electrolyte sheet will be small, and if the aperture ratio is less than 6.
If it exceeds 5%, the effect of maintaining the strength as a solid electrolyte sheet cannot be obtained. Also, the specific surface area of these networks is 5
The appropriate range is 0 to 1000n(/g). In the case of nonwoven fabric, the appropriate basis weight is 5 to 50g/rrf. Taking into consideration, the range is preferably 10 to 1508 m, and the average area per opening is 6 x 10-3 to 9
x 10-”mm” and the width between adjacent openings is 20
~120 μm is preferred.

As a method for filling the openings of the net-like body with the mixture, for example, the net-like body is immersed in a slurry in which solid electrolyte powder and polymeric elastomer are mixed in the solvent, and the slurry is sufficiently attached to the net-like body. An example of this method is to fill the opening with a blade, roll, or the like made of hard rubber, plastic, metal, etc., and remove the excessively adhered slurry. The solid content concentration in the slurry at this time is preferably 3
It is 0 to 80% by weight.

The slurry filled in the openings of the mesh in this way is
For example, it is dried at 20 to 30°C, preferably in an inert gas atmosphere, to obtain the lithium ion conductive solid electrolyte sheet of the present invention.

In order to improve adhesion with the electrode layer, conductivity, polarizability, capacity, etc. when used in a solid-state battery, the solid electrolyte sheet is coated with 5 to 25% of each on both the upper and lower sides of the net-like body or on one side.
It is preferred to have a mixture layer of .mu.m.

According to the above method, it is possible to obtain solid electrolyte sheets with extremely high thickness accuracy because the mesh is used as the base material, and because these sheets have excellent flexibility and can be manufactured continuously, they have a large surface area. solid electrolyte sheets can be easily obtained.

The thickness of the lithium ion conductive solid electrolyte sheet of the present invention obtained in this way is preferably 10 to 250 μm. If the thickness of the sheet is less than 10 μm, it will easily tear and will not maintain its strength. Moreover, when the thickness exceeds 250 μm, the conductivity decreases from lXl0 to 6. It is likely to be less than Scl'.

In the lithium ion conductive solid electrolyte sheet of the present invention, for example, modified rosin, rosin derivative,
A rosin-based tackifier, aromatic tackifier, or terpene-based tackifier such as a terpene resin, a coumaron-indene resin, or a phenol-modified coumaron-indene resin can also be included.

〔Example〕

EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited thereto. In addition, in the examples, parts mean parts by weight.

Example 1 Li2Cox, VtOs and Sin were prepared in a molar ratio of Li, Co, :Vzo, :SiO□=1. 'l:
After weighing to give a ratio of 0.370.4 and vacuum drying at 200° C. for 12 hours, n-hexane was added and mixed in a mortar for 1 hour. This mixture was dried under reduced pressure at 80°C for 24 hours, and then calcined at 650°C for 3 hours using a Matsufuru furnace. Thereafter, it was cooled to room temperature under a nitrogen stream, and the calcined product was ground with a mortar to form a powder. Furthermore, the powder was fired at 800°C for 24 hours using a Matsufuru furnace,
Cool to room temperature under a nitrogen stream and crush with a mortar to obtain Li,
5iO4-L i, VO, (7) Mixture powder (L ia
S i 04 /L i 3 V O4= 4 /
6C molar ratio)) was obtained. The resulting mixture powder was passed through a Tyler standard sieve to obtain a particle size of 200 mesh or less.

Next, 4.8 parts of a styrene-butadiene-styrene block copolymer (specific gravity: 0.96, manufactured by Japan Synthetic Rubber Co., Ltd., TR-2000) as a polymeric elastomer was dissolved in toluene, and the polymeric elastomer solution was dissolved. Obtained. To this polymeric elastomer solution, 95.2 parts of the Li, S+04-t, iiVO mixture powder (specific gravity 2.13) obtained above was added and kneaded for 2 hours in a ball mill to reduce the solid content concentration. A 50% by weight slurry was prepared.

Next, using a nylon woven fabric with a thickness of 50 μm, an average area per opening of 5.5×10-”mff1”, and a width of 50 μm between adjacent openings, this woven fabric was immersed in the slurry. After applying the mixture to the surface of the woven fabric, the woven fabric is sandwiched between fluororubber blades.
The mixture was allowed to fill the openings of the fabric while applying sufficient clamping force. The obtained sheet was thoroughly dried in an elastomer polymer to remove toluene, and a lithium ion conductive solid electrolyte sheet with a volume fraction of solid electrolyte powder in the elastomer polymer of 90% and a thickness of 70 μm was obtained. Obtained.

The obtained solid electrolyte sheet was sandwiched between two electrodes made of lithium metal plates, and a minute DC voltage that hardly caused polarization was applied at the electrode interface, and the DC resistance of the sheet was measured to determine the ionic conductivity. I asked for it.

Next, electronic conductivity was measured by Wagner's polarization method using graphite as a positive electrode and lithium as a negative electrode.

Further, in order to examine chemical stability, the obtained solid electrolyte sheet was left in air at 25° C. and 50% relative humidity for 12 hours, and then the ionic conductivity was determined in the same manner as described above.

The results are shown in Table 1.

Example 2 In Example 1, a styrene-butadiene-styrene block copolymer (specific gravity: 0.96) was used as the polymer elastomer.
, manufactured by Nippon Synthetic Rubber Co., Ltd., TR-2000), and 4.7 parts of Li, Si0. -L i,V
Oa (7) 91.6 parts of mixed powder and 3.0 parts of Alto's.
A slurry with a solid content concentration of 50% by weight was obtained in the same manner as in Example 1, except that 1 part (specific gravity: 3.96) was used, and the slurry was filled into the opening of a nylon woven fabric in the same manner as in Example 1. A lithium ion conductive solid electrolyte sheet having a volume fraction of 90% and a thickness of 70 μm was obtained.

The obtained solid electrolyte sheet was tested in the same manner as in Example 1, and the results are shown in Table 1.

Example 3 In Example 1, a styrene-butadiene-styrene block copolymer (specific gravity: 0.96) was used as the polymer elastomer.
, manufactured by Japan Synthetic Rubber Co., Ltd., TR-2000) 2.4 parts and polyethylene oxide and LiCl0. complex (ethylene oxide repeating unit/L i Cj! Oa
(mol)=0.2) polymer solid electrolyte 2.4
The solid content concentration was 5 parts in the same manner as in Example 1 except that 5 parts were used.
A 0% by weight slurry was obtained and filled into the openings of a nylon woven fabric in the same manner as in Example 1 to obtain a lithium ion conductive solid electrolyte sheet with a volume fraction of 90% and a thickness of 70 μm.

The obtained solid electrolyte sheet was tested in the same manner as in Example 1, and the results are shown in Table 1.

Below is a table with blank spaces [Effects of the Invention] The lithium ion conductive electrolyte sheet of the present invention is chemically stable, has excellent productivity, uniformity, and flexibility, can be made thin, and has high conductivity. Because of its large lithium ion transport number, it is useful as a material for electrochemical devices such as electrolyte sheets for solid micro batteries, electrochromic displays, and electric double layer capacitors.

Claims (1)

[Claims] (1) A lithium ion conductive solid electrolyte characterized by forming a mixture of Li_4SiO_4-Li_3VO_4-based solid electrolyte powder into an elastic polymer material at a volume fraction of 55 to 95% into a sheet shape. sheet.