JP5207883B2 - Lithium battery separator and lithium battery. - Google Patents

Description

  The present invention relates to a separator for a lithium battery and a lithium battery.

A metal-air battery is a battery that uses a metal such as zinc as an active material for a negative electrode and oxygen in the air as an active material for a positive electrode. The positive electrode of an air battery includes a gas diffusion layer that takes in oxygen or air and a catalyst for promoting oxidation and reduction of oxygen in an aqueous electrolyte.
If lithium can be used as the negative electrode of such a metal-air battery, it becomes possible to realize a battery having a high energy density, but when water generated by the aqueous electrolyte in the positive electrode or battery reaction reaches the negative electrode, Lithium and moisture react and cannot maintain stable performance.
For this reason, in Patent Document 1, lithium ion conductive glass ceramics with low moisture permeability are used as the separator located between the negative electrode and the positive electrode.

  However, when the lithium ion conductive glass ceramic is in contact with the aqueous electrolyte for a long period of time, the positive electrode surface reacts with moisture, the ion conductivity decreases, and the battery performance deteriorates. there were.

JP-T-2006-503416

  The present invention provides a lithium battery separator that enables a lithium battery using an aqueous electrolyte to stably maintain good performance over a long period of time, and stably maintain good performance over a long period of time. An object of the present invention is to provide a lithium battery that can be used.

  As a result of intensive studies in view of the above problems, the present inventor has formed a protective layer having a specific thickness with respect to an aqueous electrolyte on one surface of a lithium ion conductive inorganic solid electrolyte. The present invention has been completed by finding out to solve the problem, and its specific configuration is as follows.

(Configuration 1)
A separator for a lithium battery, wherein a first protective layer that is stable against an aqueous electrolyte is formed on one surface of a lithium ion conductive inorganic solid electrolyte with a thickness of 5 μm or less.
(Configuration 2)
The lithium battery separator according to Configuration 1, wherein the first protective layer has a solubility in water of 0.8 or less.
(Configuration 3)
A non-aqueous electrolyte or Li metal-stable second protective layer having a thickness of less than 100 nm is formed on the surface opposite to the surface on which the first protective layer of the lithium ion conductive inorganic solid electrolyte is formed. The separator for lithium batteries according to Configuration 1 or 2.
(Configuration 4)
The lithium battery separator according to any one of configurations 1 to 3, wherein the first protective layer is selected from a Li composite metal oxide layer, a metal oxide layer, a metal layer, and a fluoride layer.
(Configuration 5)
5. The lithium battery separator according to any one of configurations 3 and 4, wherein the second protective layer is selected from a Li composite metal oxide layer, a metal layer, a nitride layer, a fluoride layer, and a phosphide layer.
(Configuration 6)
Li composite metal oxide layer, metal layer, nitride layer, fluoride layer in which the second protective layer has an ion conductivity accompanying ion migration using an active Li metal electrode of 1 × 10 ⁻¹⁰ S / cm or more The separator for lithium batteries in any one of the structures 3 to 5 chosen from a phosphide layer.
(Configuration 7)
The lithium battery separator according to any one of configurations 1 to 6, wherein the lithium ion conductive inorganic solid electrolyte has a thickness of 500 μm or less.
(Configuration 8)
The lithium ion conductive inorganic solid electrolyte is:
Li _{1 + x + z} M _x (Ge _1−y Ti _y ) _2−x Si _z P _3−z O ₁₂ (where 0 ≦ x ≦ 0.8, 0 ≦ y ≦ 1.0, 0 ≦ z ≦ 0.6, The separator for lithium batteries according to any one of Structures 1 to 7, which contains a crystal of one or more selected from M = Al and Ga.
(Configuration 9)
The lithium ion conductive inorganic solid electrolyte is formed by forming a slurry containing a lithium ion conductive inorganic solid electrolyte powder, a binder, and a solvent into a green sheet, and sintering the green sheet. To 8. The lithium battery separator according to any one of 1 to 8.
(Configuration 10)
The separator for a lithium ion battery according to any one of configurations 3 to 7, wherein the first protective layer or the second protective layer is formed by a coating method or a vapor phase method.
(Configuration 11)
A separator in which a first protective layer stable to an aqueous electrolyte is formed on one surface of a lithium ion conductive inorganic solid electrolyte with a thickness of 5 μm or less;
A positive electrode including an aqueous electrolyte and located on a side of the separator on which the first protective layer is formed;
A negative electrode containing metal Li and located on the opposite side of the positive electrode through the separator;
A lithium battery.
(Configuration 12)
The lithium battery according to Configuration 11, wherein the first protective layer has a solubility in water of 0.8 or less.
(Configuration 13)
A second protective layer that is stable to a non-aqueous electrolyte or Li metal is formed with a thickness of less than 100 nm on the surface opposite to the surface on which the first protective layer of the lithium ion conductive inorganic solid electrolyte is formed. The lithium battery according to Configuration 11 or 12, wherein:
(Configuration 14)
The lithium battery according to any one of constitutions 11 to 13, wherein the first protective layer is selected from a Li composite metal oxide layer, a metal oxide layer, a metal layer, and a fluoride layer.
(Configuration 15)
The lithium battery according to any one of the structures 13 and 14, wherein the second protective layer is selected from a Li composite metal oxide layer, a metal layer, a nitride layer, a fluoride layer, and a phosphide layer.
(Configuration 16)
The second protective layer includes a Li composite metal oxide layer, a metal oxide layer, a metal layer, and a fluoride layer, each having a resistance value against ion migration using an active Li metal electrode of 1 × 10 ⁻¹⁰ S / cm or more. The lithium battery according to any one of the structures 13 to 15 selected.
(Configuration 17)
The lithium battery according to any one of configurations 11 to 16, wherein a thickness of the lithium ion conductive inorganic solid electrolyte is 500 μm or less.
(Configuration 18)
The lithium ion conductive inorganic solid electrolyte is
Li _{1 + x + z} M _x (Ge _1−y Ti _y ) _2−x Si _z P _3−z O ₁₂ (where 0 ≦ x ≦ 0.8, 0 ≦ y ≦ 1.0, 0 ≦ z ≦ 0.6, The lithium battery according to any one of the constitutions 11 to 17 containing a crystal of one or more selected from M = Al and Ga.
(Configuration 19)
The lithium ion conductive inorganic solid electrolyte is formed by forming a slurry containing a lithium ion conductive inorganic solid electrolyte powder, a binder, and a solvent into a green sheet, and sintering the green sheet. To 18. The lithium battery according to any one of 18 to 18.
(Configuration 20)
The lithium battery according to any one of Structures 13 to 19, wherein the first protective layer or the second protective layer is formed by a coating method or a vapor phase method.

The separator for a lithium battery of the present invention can prevent moisture from reaching the negative electrode, and can maintain high ion conductivity for a long period without deterioration of the surface even when in contact with an aqueous electrolyte for a long period of time.
Therefore, the lithium battery using the separator of the present invention can maintain good performance for a long time.

The separator of the present invention is preferably a lithium ion conductive inorganic solid electrolyte because it is difficult to permeate moisture and is required to have high ionic conductivity.
Examples of the inorganic solid electrolyte include crystals having a perovskite structure having lithium ion conductivity such as Li ₃ N, LISICON, La _0.55 Li _0.35 TiO ₃ , LiTi ₂ P ₃ O ₁₂ , LiPON having a NASICON type structure. Lithium / phosphorus sulfide glass or the like can be used, but it has high lithium ion conductivity and relatively high chemical stability. Therefore, Li _{1 + x + z} M _x (Ge _1-y Ti _y ) _2- xSi _z P _3-z O ₁₂ (where 0 ≦ x ≦ 0.8, 0 ≦ y ≦ 1.0, 0 ≦ z ≦ 0.6, M = Al, Ga, one selected from A material containing the above crystal) is preferable.
For example _{Li 1 + x + z M x} (Ge 1-y Ti y) 2-x Si z P 3-z O 12 ( where, 0 ≦ x ≦ 0.8,0 ≦ y ≦ 1.0,0 ≦ z ≦ 0.6 , M = Al or one selected from Al and Ga) is advantageous because it has substantially no or very few vacancies and crystal grain boundaries that inhibit ionic conduction.

The glass ceramic is mol% based on oxide,
Li ₂ O 10~25%, and Al ₂ O ₃ and / or _Ga 2 _O 3 _0.5~15%, and TiO ₂ and / or _GeO 2 25 to 50%, and SiO ₂ 0 to 15%, and P ₂ O ₅ 26-40%
It can obtain by making the raw glass containing each of these components, and precipitating a crystal | crystallization from a glass phase by heat-processing at 600 to 1000 degreeC for 1 to 24 hours. Here, the “oxide standard” means that oxides, nitrates, etc. used as raw materials of glass constituent components are all decomposed and changed into oxides when melted, and each component contained in the glass is converted into an oxide. In this method, the composition is represented by an oxide.

The inorganic solid electrolyte of the present invention may use the above-mentioned glass ceramics in bulk form, or a slurry containing lithium ion conductive inorganic solid electrolyte powder, a binder, and a solvent is prepared, and a doctor blade method, a calendar method, etc. A green sheet formed by a method may be used, and the green sheet may be sintered. The lithium ion conductive inorganic solid electrolyte powder for producing the green sheet includes lithium ion conductive ceramic powder, lithium ion conductive glass ceramic powder, lithium ion conductive glass powder, or lithium after sintering. An inorganic powder exhibiting ion conductivity (for example, an original glass powder of lithium ion conductive glass ceramics) can be used. These may be used alone or in combination.
Use of the method of sintering the green sheet is advantageous because it requires little or no material to be processed into a thin plate after sintering.

A first protective layer that is stable against the aqueous electrolyte is provided on one surface of the lithium ion conductive inorganic solid electrolyte. This protective layer prevents direct contact between the aqueous electrolyte and the inorganic solid electrolyte, and prevents the separator surface from deteriorating.
However, if the thickness of the first protective layer is excessively thick, the lithium ion conductivity of the separator is lowered and the performance of the battery is lowered. Therefore, the thickness needs to be 5 μm or less. In order to further suppress the decrease in ion conductivity of the separator, the thickness of the first protective layer is preferably 3 μm or less, and most preferably 1 μm or less.
On the other hand, if the thickness of the first protective layer is excessively thin, the protective layer is likely to be destroyed due to an external factor. Therefore, the thickness is preferably 1 nm or more, more preferably 3 nm or more, and 5 nm. The above is most preferable.

  “Stable to aqueous electrolyte” means that the solubility in water is not more than a specific value. Solubility in water: Add material powder to pure water at room temperature, dissolve the material powder using a stirrer, etc., adjust the supersaturated aqueous solution, take out 100 g of the aqueous solution, and measure the weight of the substance after drying the aqueous solution Can be calculated. In the present invention, if the solubility of the first protective layer in water is 0.8 or less, the first protective layer dissolves in the aqueous electrolyte within the expected use period of the battery even if the thickness is 5 μm or less. Thus, the surface of the separator can be protected without exposing the surface. For more reliable protection, the solubility of the first protective layer in water is more preferably 0.3 or less, and most preferably 0.1 or less.

  The first protective layer is preferably a layer having a solubility in water as defined above and made of a material having lithium ion conductivity, and is a Li composite metal oxide layer, a metal oxide layer, a metal layer. Preferably, at least one selected from fluoride layers is used. For example, Li complex metal oxides include lithium titanate, lithium manganate, iron iron phosphate, lithium aluminate, lithium germanate, lithium niobate, lithium silicate, lithium tantalate, lithium vanadate, and oxidation as metal oxide. Aluminum, silicon oxide, titanium oxide, vanadium oxide, iron oxide, zinc oxide, calcium oxide, copper oxide, magnesium oxide, calcium titanate, metals include aluminum, silicon, titanium, vanadium, manganese, iron, copper, tantalum, Examples of zinc, zirconium, tungsten, and fluoride include aluminum fluoride, calcium fluoride, iron fluoride, nickel fluoride, and copper fluoride. It is considered that when an aqueous electrolyte in which a lithium salt is dissolved contacts a protective layer made of these materials, Li enters and lithium ion conductivity is obtained.

In the separator of the present invention, a second protective layer that is stable to a non-aqueous electrolyte or Li metal is formed on the surface opposite to the surface on which the first protective layer of the lithium ion conductive inorganic solid electrolyte is formed. It is preferable. The negative electrode side of the lithium-air battery is in direct contact with Li metal or with a nonaqueous electrolyte. This second protective layer allows the inorganic solid electrolyte and Li metal or the inorganic solid electrolyte and the non-aqueous electrolyte to react with each other, making it difficult for the lithium ion conductivity to decrease, and is stable and favorable over a long period of time. A lithium battery capable of maintaining excellent performance can be manufactured.
However, if the thickness of the second protective layer is excessively large, the lithium ion conductivity of the separator is lowered and the performance of the battery is lowered. Therefore, the thickness is preferably 100 nm or less. In order to further suppress the decrease in ion conductivity of the separator, the thickness of the second protective layer is preferably 80 nm or less, and most preferably 50 nm or less.
On the other hand, if the thickness of the second protective layer is excessively thin, the protective layer is likely to be destroyed due to an external factor. Therefore, the thickness is preferably 1 nm or more, more preferably 3 nm or more, and 5 nm. The above is most preferable.

“Stable to non-aqueous electrolyte or Li metal” means that the chemical reaction is moderate with respect to either the non-aqueous electrolyte or Li metal, and is specifically defined as follows.
Sample membranes are prepared on both sides of the lithium ion conductive solid electrolyte, and Li metal / sample membrane / solid electrolyte / sample membrane / Li metal, or Li metal / non-aqueous electrolyte using Li metal of the active electrode / Sample membrane / solid electrolyte / sample membrane / nonaqueous electrolyte / Li metal test cell was prepared, and the resistance value of the separator against lithium ion migration at 25 ° C. was measured. After holding for a week, the resistance value of the separator is measured in the same manner, and the resistance value is within 4 times the initial resistance value.

  The protective layer that can be applied to the second protective layer is preferably at least one selected from a Li composite metal oxide layer, a metal layer, a nitride layer, a fluoride layer, and a phosphide layer. This is because the layer made of these materials is stable to a non-aqueous electrolyte or Li metal as described above. For example, Li composite metal oxides include lithium titanate, lithium manganate, iron iron phosphate, lithium aluminate. , Lithium germanate, lithium niobate, lithium silicate, lithium tantalate, lithium vanadate, metals include aluminum oxide, silicon oxide, titanium oxide, vanadium oxide, iron oxide, zinc oxide, calcium oxide, copper oxide, magnesium oxide, Aluminum phosphate, nitride as silicon nitride, titanium nitride, fluoride as aluminum fluoride, calcium fluoride, iron fluoride, nickel fluoride, copper fluoride, lithium hexafluoride, LiTFSI, phosphide as phosphide Examples include aluminum, manganese phosphide, iron phosphide, cobalt phosphide, and zinc phosphide. It is considered that when a non-aqueous electrolyte in which a lithium salt is dissolved or Li metal comes into contact with a protective layer made of these materials, Li enters and lithium ion conductivity is obtained.

As described above, the second protective layer is stable to the non-aqueous electrolyte or Li metal and is a layer made of a material having lithium ion conductivity, so that the discharge current of the lithium battery can be easily increased. . Therefore, in order to make it easy for the lithium battery using the separator of the present invention to obtain a large discharge current, the second protective layer has an ion conductivity of 1 × 10 ⁻¹⁰ S / cm accompanying ion migration using the active Li metal electrode. Preferably, it is 1 × 10 ⁻⁸ S / cm or more, and more preferably 1 × 10 ⁻⁶ S / cm or more.

  The first protective layer or the second protective layer can be formed by a coating method or a vapor phase method.

  As a method using a coating method, after preparing an inorganic solid electrolyte, a slurry composed of a powder of a material constituting the protective layer, a binder, a solvent, and the like is prepared, applied to the surface of the inorganic solid electrolyte, and fired. Moreover, it may be produced by applying a slurry for preparing a protective layer on the surface of the original glass of the lithium ion conductive crystallized glass, followed by baking to crystallize the original glass and baking the protective layer. .

  As a method using a gas phase method, a sputtering method, a vapor deposition method, an ion plating method, a PVD method exemplified by a laser ablation method, a CVD method exemplified by a thermal CVD, a plasma CVD method, etc., a plasma spraying method, etc. The thermal spray thin film formation process exemplified can be used.

When the thickness of the lithium ion conductive inorganic solid electrolyte is large, it is difficult to increase the discharge current, and the battery capacity per unit volume is small. Therefore, the thickness of the lithium ion conductive inorganic solid electrolyte is 500 μm or less. Is preferably 400 μm or less, and most preferably 300 μm or less.
On the other hand, when the thickness is small, the mechanical strength is reduced and the positive electrode and the negative electrode are easily short-circuited. Therefore, the thickness of the lithium ion conductive inorganic solid electrolyte is preferably 20 μm or more, more preferably 30 μm or more. 40 μm or more is most preferable.

A lithium battery can be produced by disposing a positive electrode on the side where the first protective layer of the separator of the present invention is formed and a negative electrode containing metal Li on the opposite side of the positive electrode through the separator.
The positive electrode can employ a configuration used in a metal-air battery, and includes an aqueous electrolyte, a gas diffusion layer that takes in oxygen or air, and a catalyst for promoting oxidation and reduction of oxygen.
In addition to Li metal, the negative electrode may contain a non-aqueous electrolyte as required.

  Hereinafter, the lithium battery separator and the lithium battery according to the present invention will be described with specific examples.

[Preparation of Lithium Ion Conductive Glass Ceramic Glass]
As raw materials, H ₃ PO ₄ , Al (PO ₃ ) ₃ , Li ₂ CO ₃ , SiO ₂ manufactured by Nichetsu Co., Ltd., and TiO ₂ manufactured by Sakai Chemical Industry Co., Ltd. were used. These are mol% in terms of oxide, P ₂ O ₅ is 35.0%, Al ₂ O ₃ is 7.5%, Li ₂ O is 15.0%, TiO ₂ is 38.0%, and SiO ₂ is 4 After being weighed so as to have a composition of 0.5% and mixed uniformly, it was put in a platinum pot and heated and melted for 3 hours with stirring at a temperature of 1500 ° C. in an electric furnace to obtain a glass melt. Thereafter, the glass melt was rapidly cooled by dropping it into running water at room temperature while heating from a platinum pipe attached to the pot, to obtain an original glass of lithium ion conductive glass ceramics.

When this glass was crystallized in an electric furnace at 1000 ° C. and the lithium ion conductivity was measured, it was 1.3 × 10 ⁻³ Scm ⁻¹ at room temperature. The measurement of lithium ion conductivity was calculated by complex impedance measurement by the AC two-terminal method using an impedance analyzer SI-1260 manufactured by Solartron. Further, the precipitated crystal phase was measured using a powder X-ray diffractometer manufactured by Philips, and Li _{1 + x + z} Al _x Ti _2−x Si _z P _3−z O ₁₂ (0 ≦ x ≦ 0.4, 0 < It was confirmed that z ≦ 0.6) was the main crystal phase.

  The above original glass is pulverized by a jet mill manufactured by Kurimoto Steel Works, then placed in a ball mill using ethanol as a solvent, and wet pulverized to have an average particle size of 0.7 μm, a maximum particle size of 2 μm, and an average particle size of 0.5 μm. Two types of oxide glass powders having a maximum particle size of 1 μm were obtained. The particle size was measured using a laser diffraction / scattering particle size distribution measuring device LS100 manufactured by Beckman Coulter. Distilled water was used as the dispersion medium.

[Production of green sheets]
An oxide glass having an average particle size of 0.5 μm was dispersed and mixed with an acrylic binder, a dispersant, and an antifoaming agent using water as a solvent to prepare an electrolyte slurry. The slurry was decompressed to remove bubbles, and then shaped using a doctor blade and dried to prepare an electrolyte green sheet having a thickness of 40 μm. The acrylic binder was 10 wt%, the antifoaming agent and the dispersant were 0.2 to 0.3 wt%, respectively, and the rest was oxide glass. The content of the oxide glass contained in the electrolyte green sheet was 89.5 wt%.

[Preparation of lithium ion solid electrolyte]
Eight green sheets were laminated and pressed with a heated roll press to obtain a laminated laminate. The laminated body bonded together was pressed at room temperature using CIP (cold isostatic pressing) to be densified. This laminate was placed on a quartz glass plate and heated to 600 ° C. in an electric furnace to remove organic substances such as a binder and a dispersant in the laminate.
The green sheet from which the organic matter had been removed was sandwiched between the quartz glass plates and sintered by heat treatment at 1010 ° C. for 40 minutes in an electric furnace to obtain a lithium ion conductive inorganic solid electrolyte. The thickness of the obtained lithium ion conductive inorganic solid electrolyte was 270 μm.
Moreover, when confirmed by the X-ray diffraction method, the main crystal phase is Li _{1 + x + y} Al _x Ti _2−x Si _y P _3−y O ₁₂ (0 ≦ x ≦ 0.4, 0 <y ≦ 0.6). It was confirmed that the ionic conductivity was determined by measuring impedance, and it was 3.2 × 10 ⁻⁴ Scm ⁻¹ , and it was confirmed that a thin plate-like solid electrolyte having high ionic conductivity was obtained. .

[Preparation of first protective layer]
The first protective layer was formed on the solid electrolyte by using the following coating method or vapor phase growth method. The thickness of the protective layer produced was masked on a part of the solid electrolyte, a region where the protective layer was not formed was produced, and the step between the solid electrolyte and the protective layer was used as the film thickness, and ν view (Zygo) was used. Measured. The thickness of the protective layer was determined from the distance from the solid electrolyte surface to the uppermost point in the vicinity of the edge, with the edge of the step obtained by masking as the measurement position.
In Examples 1 to 7 below, the first protective layer is prepared on both sides of the solid electrolyte for the stability evaluation with respect to the aqueous electrolyte, but when used as an actual lithium battery separator, the following method is used. The first protective layer may be formed only on the surface that is applied and becomes the positive electrode side. For each material to be applied to the first protective layer, the material powder is poured into pure water at room temperature, and the material powder is dissolved with stirring for 12 hours using a magnetic stirrer to obtain a supersaturated aqueous solution. Adjusted. The weight of the aqueous solution and the weight of the substance after drying the aqueous solution were measured and calculated. Solubility was rounded off to the third decimal place.

[Example 1]
A slurry in which lithium iron phosphate (manufactured by Japan Alliance Technology Co., Ltd.) was adjusted to an average particle size of 25 nm by wet pulverization using ethanol was prepared. This slurry was applied to both surfaces of the solid electrolyte by spin coating. The solid electrolyte coated with this lithium iron phosphate was adjusted to an argon atmosphere in an electric furnace and heat-treated at 550 ° C. for 1 hour.

[Example 2]
In the same manner as in Example 1, a slurry in which lithium manganate (manufactured by Honjo Chemical) was adjusted to an average particle size of 16 nm was applied to both surfaces of the solid electrolyte by spin coating. The electrolyte was heat-treated for 1 hour at 530 ° C. in air using an electric furnace.

[Example 3]
In the same manner as in Example 1, a slurry prepared by adjusting lithium aluminate (manufactured by High-Purity Chemical) to an average particle size of 48 nm was applied to both surfaces of the solid electrolyte by spin coating. The solid electrolyte coated with lithium aluminate was heat-treated in an atmosphere at 600 ° C. for 1 hour using an electric furnace.

[Example 4]
After applying a copper oxide coating material for spin coating (manufactured by High-Purity Chemical) on both sides of the solid electrolyte by a spin coating method, heat treatment in the atmosphere is performed using an electric furnace at 100 ° C. for 1 hour and then at 550 ° C. for 1 hour. gave.

[Example 5]
Magnesium oxide coating material for spin coating (manufactured by High-Purity Chemical) was applied to the solid electrolyte in the same manner as in Example 4 and subjected to heat treatment.

[Example 6]
A titanium thin film was formed on both sides of the solid electrolyte by using an ion plating method with a titanium target.

[Example 7]
In the same manner as in Example 1, a slurry prepared by adjusting nickel fluoride (manufactured by high purity chemical) to an average particle size of 37 nm was applied to both surfaces of the solid electrolyte by spin coating. The solid electrolyte coated with nickel fluoride was heat-treated at 300 ° C. for 1 hour in an argon atmosphere in an electric furnace.

[Comparative Example 1]
Stability evaluation was performed using the above-mentioned solid electrolyte without providing a protective layer.

[Evaluation of long-term stability of separator in aqueous electrolyte]
A PTFE microporous membrane (75 μm) hydrophilized on both surfaces of the solid electrolyte from which the first protective layer was produced as described above was impregnated with a 0.5M lithium nitrate aqueous solution. It was pressed against a solid electrolyte with a SUS electrode holder with a 0.2 kgf spring, sealed in a cell, stored at 40 ° C. for 12 hours, and then involved in lithium ion conduction by AC impedance measurement at room temperature. Measured resistance. The cell was stored at 40 ° C. for 1 week, and AC impedance measurement was performed again. A protective layer is not formed and the increase in resistance value is within 20% after storage for 12 hours and after storage for 1 week, based on the resistance value of the above solid electrolyte not affected by the aqueous electrolyte. ◯, 20% to 40% or less Δ, more than 40% or those that do not maintain the shape is ×. The results are shown in Table 1.

From the above results, it can be seen that the separator of the present invention in which the first protective layer is formed has little decrease in lithium ion conductivity even if it is indirectly in the aqueous electrolyte for a long time.

[Production of Second Protective Layer]
The second protective layer was produced on the solid electrolyte by using the following coating method or vapor phase growth method. The thickness of the protective layer produced was masked on a part of the solid electrolyte, a region where the protective layer was not formed was produced, and the step between the solid electrolyte and the protective layer was used as the film thickness, and ν view (Zygo) was used. Measured. In Examples 8 to 11 below, the second protective layer is prepared on both sides of the solid electrolyte for the stability evaluation with respect to the nonaqueous electrolytic solution or Li metal. When used as an actual lithium battery separator, The second protective layer may be formed on a surface opposite to the surface on which the first protective layer is formed by applying the method described in (1).

[Example 8]
In the same manner as in Example 1, a slurry in which lithium titanate (manufactured by Ishihara Sangyo Co., Ltd.) was adjusted to an average particle size of 15 nm was applied to both surfaces of the solid electrolyte by spin coating. The electrolyte coated with the lithium titanate was heat-treated in the atmosphere at 550 ° C. for 1 hour using an electric furnace.

[Example 9]
A titanium oxide coating material for spin coating (manufactured by High-Purity Chemical) was applied to the solid electrolyte in the same manner as in Example 4 and heat-treated.

[Example 10]
A titanium nitride thin film was formed on both surfaces of the solid electrolyte by an ion plating method using a titanium target and introducing nitrogen gas.

[Example 11]
In the same manner as in Example 1, a slurry in which cobalt phosphide (manufactured by High Purity Chemical) was adjusted to an average particle size of 50 nm was applied to the solid electrolyte by the dipping method. The solid electrolyte coated with the cobalt phosphide was vacuum dried at 200 ° C.

[Comparative Example 2]
In the same manner as in Example 9, titanium oxide was applied to both surfaces of the electrolyte and subjected to heat treatment. The coating amount at this time was five times that of Example 9.

[Comparative Example 3]
The above-mentioned solid electrolyte that does not provide the second protective layer was used.

[Evaluation of long-term stability of second protective layer against non-aqueous electrolyte or Li metal]
The surfaces were wetted with a non-aqueous electrolyte on both surfaces of the solid electrolytes prepared as in Examples 8 to 9 and Comparative Example 2. Then, what stuck Li metal foil on the SUS electrode holding | suppressing with a spring was pressed on both surfaces of electrolyte.
In Examples 10 to 11 and Comparative Example 3, a material obtained by bonding Li metal on a SUS electrode holder with a spring was pressed against both surfaces of the electrolyte.
After the cell was prepared, it was stored at 40 ° C. for 12 hours and stored at 40 ° C. for 1 week, and then the resistance value involved in lithium ion conduction was measured by an AC impedance method at room temperature. The resistance value of the solid electrolyte itself measured in advance is subtracted from the measured value to obtain the ionic conductivity of the protective layer. If the ionic conductivity is 1 × 10 ⁻⁶ S / cm or less, 1 × 10 ^{A value of −8} to 1 × 10 ⁻¹⁰ S / cm or more was evaluated as Δ, and a value higher than that was evaluated as ×. The results are shown in Table 2.

From the above results, it can be seen that the separator of the present invention in which the second protective layer is formed has little decrease in lithium ion conductivity even if it is indirect for a long time with a non-aqueous electrolyte or Li metal.

[Example 12]
(Production of Li-air battery)
The first protective layer described in Example 1 and the second protective layer described in Example 8 were formed on the surface of the solid electrolyte. On top of the first protective layer, LiNO ₃ , 0.5M aqueous solution and Pt mesh electrode were disposed, and the second protective layer was wetted with a non-aqueous electrolyte and then pressed against a Li metal negative electrode. After storing at room temperature for 1 day, a discharge test was conducted at a discharge current of 0.25 mA / cm ² . As a result, 98% of the theoretical value obtained from the Li metal capacity was discharged, and the discharge time was about 10 days.

[Comparative Example 4]
A battery production and discharge test were performed in the same manner as in Example 12, except that the protective layer of Example 10 was formed only on the negative electrode side of the solid electrolyte and the protective layer was not formed on the positive electrode side. The discharge capacity was 55% of the theoretical value obtained from the Li metal capacity.

[Comparative Example 5]
A battery was produced and a discharge test was conducted in the same manner as in Example 12 using a solid electrolyte without providing the first protective layer and the second protective layer. The discharge capacity was 10% of the theoretical value obtained from the Li metal capacity.

  It can be seen that the lithium battery of the present invention has a sufficient discharge capacity even if it has the first protective layer and the second protective layer on the surface of the solid electrolyte. And since the above-mentioned Example has little fall of ion conductivity also for a long period of time, the stable performance can be maintained over a long period of time.

Claims (2)

Li _{1 + x + z} M _x (Ge _1−y Ti _y ) _2−x Si _z P _3−z O ₁₂ (where 0 ≦ x ≦ 0.8, 0 ≦ y ≦ 1.0, 0 ≦ z ≦ 0.6, M = one or more selected from Al and Ga), and one surface of a lithium ion conductive inorganic solid electrolyte having a thickness of 500 μm or less has a solubility in water of 0.8 or less and phosphoric acid A first protective layer selected from lithium iron, lithium manganate, lithium aluminate, copper oxide, magnesium oxide, titanium, nickel fluoride is formed with a thickness of 10 nm or more and 5 μm or less ;
A non-aqueous electrolyte selected from lithium titanate, titanium oxide, titanium nitride, and cobalt phosphide or Li metal is formed on the surface of the lithium ion conductive inorganic solid electrolyte opposite to the surface on which the first protective layer is formed. A stable second protective layer is formed with a thickness of less than 100 nm;
A lithium- air battery separator , wherein the second protective layer has a lithium ion conductivity of 1 × 10 ⁻¹⁰ S / cm or more . The lithium ion conductive inorganic solid electrolyte is obtained by forming a green sheet by forming a slurry containing a lithium ion conductive inorganic solid electrolyte powder, a binder, and a solvent, and sintering the green sheet. The separator for lithium air batteries according to 1 .