JP2018078030A - Electrolyte and all-solid-state secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the ionic conductivity of an electrolyte. An electrolyte including an ionic conductive material and a solid electrolyte, the solid electrolyte including an oxide-based inorganic solid electrolyte, and a volume ratio of the solid electrolyte to the ionic conductive material is 1.5 or more and 2.5 or less. An electrolyte in which the porosity of the electrolyte is 30% or less, the solid electrolyte is, for example, LLZ, and the ionic conductive material is, for example, a glyme complex, or an all-solid secondary battery having the electrolyte, the positive electrode, and the negative electrode. Thereby, the ionic conductivity of the electrolyte can be improved. [Selection diagram] Figure 1

Description

  The present invention relates to an electrolyte and an all-solid secondary battery.

  Patent Document 1 discloses a room temperature molten salt as a solid ionic conductor in which a room temperature molten salt and an insulating inorganic particle are combined and mixed at a predetermined ratio so that the room temperature molten salt does not bleed and presents a solid powder. And a solid ion conductor containing insulating inorganic particles, a solid electrolyte membrane formed by compression molding a solid ion conductive material containing the solid ion conductor, and a solid electrolyte layer containing the solid ion conductor An all-solid lithium secondary battery is disclosed.

JP 2011-119158 A

  Depending on the ratio between the room temperature molten salt and the insulating inorganic particles, the porosity of the solid ionic conductor must be controlled in order to improve the ionic conductivity of the solid ionic conductor. There is no description. An object of this invention is to improve the ionic conductivity of a solid ionic conductor.

  The features of the present invention for solving the above problems are as follows, for example.

  An electrolyte including an ionic conductive material and a solid electrolyte, wherein the solid electrolyte includes an oxide-based inorganic solid electrolyte, and the volume ratio of the solid electrolyte to the ionic conductive material is 1.5 to 2.5, An electrolyte having a rate of 30% or less.

  According to the present invention, the ionic conductivity of the solid ionic conductor can be improved. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is sectional drawing of the all-solid-state secondary battery which concerns on one Embodiment of this invention. It is sectional drawing of the principal part of the all-solid-state secondary battery which concerns on one Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various modifications by those skilled in the art are within the scope of the technical idea disclosed in this specification. Changes and modifications are possible. In all the drawings for explaining the present invention, components having the same function are denoted by the same reference numerals, and repeated description thereof may be omitted.

  In this specification, a lithium ion secondary battery will be described as an example of an all-solid secondary battery. However, the technical idea of the present invention is not only a lithium ion secondary battery but also a sodium ion secondary battery, a magnesium ion secondary battery. The present invention can also be applied to batteries, aluminum ion secondary batteries, and the like.

  FIG. 1 is a cross-sectional view of an all solid state secondary battery according to an embodiment of the present invention. As shown in FIG. 1, the all solid state secondary battery 100 includes a positive electrode 70, a negative electrode 80, a battery case 30, and an electrolyte layer 50. The battery case 30 houses the electrolyte layer 50, the positive electrode 70, and the negative electrode 80. The material of the battery case 30 can be selected from materials that are corrosion resistant to non-aqueous electrolytes, such as aluminum, stainless steel, and nickel-plated steel.

  In the all-solid-state secondary battery 100, an electrode body composed of the positive electrode 70, the electrolyte layer 50, and the negative electrode 80 is laminated. The positive electrode 70 includes the positive electrode current collector 10 and the positive electrode mixture layer 40. A positive electrode mixture layer 40 is formed on both surfaces of the positive electrode current collector 10. The negative electrode 80 includes a negative electrode current collector 20 and a negative electrode mixture layer 60. Negative electrode mixture layers 60 are formed on both surfaces of the negative electrode current collector 20. The positive electrode current collector 10 and the negative electrode current collector 20 protrude outside the battery case 30, and the plurality of protruding positive electrode current collectors 10 and the plurality of negative electrode current collectors 20 are bonded together by, for example, ultrasonic bonding. Thus, a parallel connection is formed in the all solid state secondary battery 100.

  The positive electrode mixture layer 40, the electrolyte layer 50, the negative electrode mixture layer 60, and the interconnector may be laminated to form a series connection in the all-solid secondary battery 100. In this case, the interconnector has high electron conductivity, no ionic conductivity, the surface contacting the negative electrode mixture layer 60 and the positive electrode mixture layer 40 does not exhibit a redox reaction depending on the respective potentials, It is preferable. Materials that can be used for the interconnector include materials that can be used for the following positive electrode current collector 10 and negative electrode current collector 20. Specific examples include aluminum foil and SUS foil. Alternatively, the positive electrode current collector 10 and the negative electrode current collector 20 can be bonded together by clad molding and electron conductive slurry.

  FIG. 2 is a cross-sectional view of a main part of an all solid state secondary battery according to an embodiment of the present invention. The electrode body has a positive electrode mixture layer 40, an electrolyte layer 50, and a negative electrode mixture layer 60. The positive electrode mixture layer 40 includes a positive electrode active material 42, a positive electrode conductive agent 43 intended to improve the conductivity of the positive electrode mixture layer 40, and a positive electrode binder for binding them. The negative electrode mixture layer 60 includes a negative electrode active material 62, a negative electrode conductive agent 63 intended to improve the conductivity of the negative electrode mixture layer 60, and a negative electrode binder for binding them. The electrolyte layer 50 includes an electrolyte binder 53 and an electrolyte 55. The electrolyte 55 includes inorganic particles 51 and an ion conductive material 52.

  The positive electrode conductive agent 43 or the negative electrode conductive agent 63 may be referred to as an electrode conductive material. The positive electrode binder or the negative electrode binder may be referred to as an electrode binder.

<Electrode conductive material>
Electrode conductive material manufactured from conductive fibers (for example, vapor-grown carbon, carbon nanotubes, pitch (by-products such as petroleum, coal, coal tar, etc.) and carbonized at high temperature, and acrylic fibers. Carbon fiber etc.) are preferably used. Further, the positive electrode conductive agent 43 may be a material having a lower electrical resistivity than the positive electrode active material, and a material that does not oxidize and dissolve at the charge / discharge potential (usually 2.5 to 4.5 V) of the positive electrode. Good. For example, corrosion resistant metals (such as titanium and gold), carbides (such as SiC and WC), and nitrides (such as Si3N4 and BN) can be used. A carbon material having a high specific surface area (for example, carbon black or activated carbon) can be used, but is not limited thereto.

<Electrode binder>
Examples of the electrode binder include, but are not limited to, styrene-butadiene rubber, carboxymethyl cellulose, polyvinylidene fluoride (PVDF), and a mixture thereof.

<Positive electrode active material 42>
As the material of the positive electrode active material 42, for example, a lithium composite oxide containing a transition metal is preferable, and specific examples include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , Li _4. Mn ₅ O ₁₂ , Li ₂ Mn ₃ MO ₈ (M = Fe, Co, Ni, Cu, Zn), Li _1-x M _x Mn ₂ O ₄ (M = Mg, B, Al, Fe, Co, Ni, Cr, Zn, Ca, x = 0.01 to 0.1), LiMn _2−x M _x O ₂ (M = Co, Ni, Fe, Cr, Zn, Ta, x = 0.01 to 0.2) _{, LiCo 1-x M x O} 2 (M = Ni, Fe, Mn, x = 0.01~0.2), LiNi 1-x M x O 2 (M = Mn, Fe, Co, Al, Ga, Ca, Mg, x = 0.01 to 0.2), LiNi _{1− x-y Mn x Co y O} 2 (x = 0.1~0.8, y = 0.1~0.8, x + y = 0.1~0.9), LiFeO 2, LiFePO 4, LiMnPO 4 , etc. However, it is not limited to this.

<Positive electrode current collector 10>
The positive electrode current collector 10 is preferably a low-resistance conductor having heat resistance that can withstand the heating during the secondary battery manufacturing process and the operating temperature of the secondary battery, but is not limited thereto. For example, metal foil (thickness of 10 μm or more and 100 μm or less), perforated metal foil (thickness of 10 μm or more and 100 μm or less, pore diameter of 0.1 mm or more and 10 mm or less), expanded metal, foamed metal plate, glassy carbon plate and the like can be mentioned. Moreover, as a metal seed | species, aluminum, stainless steel, titanium, a noble metal (for example, gold, silver, platinum) etc. can be used.

<Positive electrode 70>
A positive electrode slurry in which a positive electrode active material 42, a positive electrode conductive agent 43, a positive electrode binder, and an organic solvent are mixed is attached to the positive electrode current collector 10 by a doctor blade method, a dipping method, or a spray method, and then the organic solvent is dried. Then, the positive electrode 70 can be produced by pressure forming with a roll press. In addition, a plurality of positive electrode mixture layers 40 can be laminated on the positive electrode current collector 10 by performing a plurality of times from application to drying.

<Negative electrode active material 62>
As a material of the negative electrode active material 62, for example, a carbon-based material (for example, graphite, graphitizable carbon material, amorphous carbon material), a conductive polymer material (for example, polyacene, polyparaphenylene, polyaniline, polyacetylene), A lithium composite oxide (eg, lithium titanate: Li ₄ Ti ₅ O ₁₂ ), metal lithium, or a metal alloyed with lithium (eg, aluminum, silicon, tin) can be used, but is not limited thereto.

<Negative electrode current collector 20>
Similarly to the positive electrode current collector 10, the negative electrode current collector 20 is desirably a low-resistance conductor having heat resistance capable of withstanding the heating during the secondary battery manufacturing process and the operating temperature of the secondary battery. Not limited to. For example, metal foil (thickness of 10 μm or more and 100 μm or less), perforated metal foil (thickness of 10 μm or more and 100 μm or less, pore diameter of 0.1 mm or more and 10 mm or less), expanded metal, foamed metal plate, glassy carbon plate and the like can be mentioned. Moreover, as a metal seed | species, copper, stainless steel, titanium, nickel, a noble metal (for example, gold, silver, platinum) etc. can be used.

<Negative electrode 80>
A negative electrode slurry in which a positive electrode active material 42, a negative electrode conductive agent 63, and an organic solvent containing a trace amount of water are mixed is attached to the negative electrode current collector 20 and the negative electrode surface of the interconnector 90 by a doctor blade method, a dipping method, a spray method, or the like. After making it dry, an organic solvent is dried and a negative electrode can be produced by press-molding with a roll press. In addition, a plurality of negative electrode mixture layers 60 can be laminated on the negative electrode current collector 20 by performing a plurality of times from application to drying.

<Inorganic particles 51>
When an oxide-based inorganic solid electrolyte is used as the inorganic particles 51, an electrolyte layer having high ion conductivity can be obtained. For example, Li _{5 + X} La ₃ (Zr _X , A _2−X ) O ₁₂ (wherein A is from the group consisting of Sc, Ti, C, Y, Nb, Hf, Ta, Al, Si, Ga, Ge, Sn). One or more selected elements, X is 1.4 ≦ X ≦ 2), Li _{1 + X} Al _X Ti _2-X (PO ₄ ) ₃ (X is 0 ≦ X ≦ 1), Li _3X La _{2/3 X} TiO ₃ (X is 0 ≦ X ≦ 2/3) and the like. These have high ionic conductivity at room temperature and high electrochemical stability.

As the inorganic particles 51, from the viewpoint of electrochemical stability, insulating particles that are insoluble in an organic solvent such as an ionic liquid or glyme may be added. For example, silica (SiO ₂ ) particles, γ-alumina (Al ₂ O ₃ ) particles, ceria (CeO ₂ ) particles, and zirconia (ZrO ₂ ) particles can be preferably used. Further, other known metal oxide particles may be used.

  The volume ratio of the inorganic particles 51 to the ion conductive material 52 is 1.5 to 2.5, preferably 1.7 to 2.3, and more preferably 1.9 to 2.1.

<Ion conductive material 52>
The ionic conductive material 52 is an ionic liquid or a mixture of glymes and lithium salts that exhibit similar properties to the ionic liquid.

  As the ionic liquid, a known ionic liquid that functions as an electrolyte can be used. From the viewpoint of ionic conductivity (conductivity), N, N-diethyl-N-methyl-N- (2-methoxyethyl) is particularly preferable. Ammonium bis (trifluoromethanesulfonyl) imide (DEME-TFSI) can be preferably used.

Glymes (R—O (CH ₂ CH ₂ O) n—R ′ (R and R ′ are saturated hydrocarbons, n is an integer), a generic name for symmetric glycol diethers) are similar to ionic liquids Known glymes exhibiting properties can be used, but from the viewpoint of ion conductivity (conductivity), tetraglyme (tetraethylene dimethyl glycol, G4), triglyme (triethylene glycol dimethyl ether, G3), pentag lime (penta Ethylene glycol dimethyl ether (G5) and hexaglyme (hexaethylene glycol dimethyl ether, G6) can be preferably used.

Examples of the lithium _{salt, LiPF 6, LiBF 4, LiClO} 4, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, lithium bis oxalate borate (LiBOB), and lithium imide salt (e.g., lithium Bis (fluorosulfonyl) imide, LiFSI) or the like can be preferably used. These lithium salts may be used alone or in combination.

<Electrolyte binder 53>
As the electrolyte binder 53, a fluorine-based resin is preferably used. PVDF and PTFE are preferably used as the fluorine-based resin. By using PVDF or PTFE, the adhesion between the electrolyte layer 50 and the electrode current collector is improved, so that the battery performance is improved.

<Electrolyte 55>
The electrolyte 55 is configured by supporting the ion conductive material 52 on the inorganic particles 51. Examples of the method for producing the electrolyte 55 include the following methods. The ionic conductive material 52 and the inorganic particles 51 are mixed at a specific volume ratio, and an organic solvent such as methanol is added and mixed to prepare a slurry of the electrolyte 55. Thereafter, the slurry is spread on a petri dish, and the organic solvent is distilled off to obtain a powder of the electrolyte 55.

  The porosity of the electrolyte is desirably 30% or less, preferably 10% or less, and more preferably 5% or less.

<Electrolyte layer 50>
As a method for producing the electrolyte layer 50, there are a method of compression molding the powder of the electrolyte 55 into a pellet using a molding die or the like, and a method of adding and mixing the electrolyte binder 53 to the powder of the electrolyte 55 to form a sheet. By adding and mixing the powder of the electrolyte binder 53 to the electrolyte 55, a highly flexible electrolyte layer 50 (electrolyte sheet) can be produced. Alternatively, the electrolyte layer 50 can be produced by adding and mixing a solution of a binder in which the electrolyte binder 53 is dissolved in the dispersion solvent to the electrolyte 55 and distilling off the dispersion solvent.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to these Examples.

A solid electrolyte was produced as follows using tetraglyme-LiTFSI as an ion conductive material and Li _6.75 La ₃ Zr _1.75 Nb _0.25 O ₁₂ (LLZ) particles as inorganic particles.

Tetraglyme and LiTFSI were mixed at a molar ratio of 1: 1, and the mixture was stirred at room temperature for 30 minutes or more using a stirrer to prepare an ion conductive material. Li ₂ CO ₃ , La (OH) ₃ , ZrO ₂ , Nb ₂ O ₅ are used as raw materials, and the charge ratio is the stoichiometric composition ratio of LLZ (in terms of molar ratio: Li: La: Zr: Nb = 6.75: 3). : 1.75: 0.25). After uniformly mixing, LLZ powder was obtained by firing at 950 ° C. for 12 hours. The obtained LLZ powder was compression molded with a uniaxial molding machine of φ10 mm, and further CIP molded at 180 MPa to produce a green compact.

  A solid electrolyte was produced by filling the produced green compact with the previously produced ion conductive material. At this time, the volume ratio of the solid electrolyte to the ionic conductive material was 2.

The resistance of the obtained solid electrolyte was evaluated by an AC impedance method (applied voltage: 10 mV, measurement frequency: 10 ^{6 to 1} Hz), and the ionic conductivity was calculated. As a result, it was 5 mS / cm. The porosity calculated from the dimensions and weight was 0%.

[Comparative Example 1]
In Example 1, SiO ₂ particles were used as inorganic particles. Other than that was carried out similarly to Example 1, and produced the solid electrolyte sheet.

The resistance of the obtained solid electrolyte sheet was evaluated by an alternating current impedance method (applied voltage: 10 mV, measurement frequency: 10 ^{6 to 1} Hz), and the ionic conductivity was calculated. As a result, it was 0.1 mS / cm. The porosity calculated from the dimensions and weight was 30%.

[Comparative Example 2]
LLZ particles were used as the inorganic particles, and the volume ratio of the solid electrolyte to the ionic conductive material was set to 1. Other than that was carried out similarly to Example 1, and produced the solid electrolyte sheet.

The resistance of the obtained solid electrolyte sheet was evaluated by an alternating current impedance method (applied voltage: 10 mV, measurement frequency: 10 ^{6 to 1} Hz), and the ionic conductivity was calculated. As a result, it was 0.1 mS / cm. The porosity calculated from the dimensions and weight was 30%.

<Discussion>
In Example 1, Comparative Example 1 to Comparative Example 2, the volume ratio of the inorganic particles 51 to the ionic conductive material 52 is 1.5 to 2.5 and the porosity of the electrolyte 55 is 30% or less. A solid electrolyte sheet with high conductivity is obtained.

DESCRIPTION OF SYMBOLS 10 Positive electrode collector 20 Negative electrode collector 30 Battery case 40 Positive electrode mixture layer 42 Positive electrode active material 43 Positive electrode conductive agent 50 Electrolyte layer 51 Inorganic particle 52 Ion conductive material 53 Electrolyte binder 55 Electrolyte 60 Negative electrode mixture layer 62 Negative electrode active material 63 Negative electrode conductive agent 70 Positive electrode 80 Negative electrode 90 Interconnector 100 All-solid-state secondary battery

Claims (4)

An electrolyte including an ionic conductive material and a solid electrolyte,
The solid electrolyte includes an oxide-based inorganic solid electrolyte,
The volume ratio of the solid electrolyte to the ionic conductive material is 1.5 or more and 2.5 or less,
An electrolyte having a porosity of 30% or less. The electrolyte of claim 1,
The electrolyte in which the solid electrolyte is LLZ. The electrolyte of claim 1,
The electrolyte in which the ionic conductive material is a glyme complex.   An all solid state secondary battery comprising the electrolyte according to claim 1, a positive electrode, and a negative electrode.

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