JP2014116136A - All-solid-state secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an all-solid-state secondary battery in which, when a laminated cell is prepared by a hydrostatic pressing method in a sulfide-based solid electrode body, the laminated cell is prevented from being brought into contact with an electrode end face so that fracture and film breaking of the laminated cell are not caused.SOLUTION: In an all-solid-state battery, fracture and film breaking of a laminated cell caused by a hydrostatic pressing method can be prevented by continuously increasing an electrode thickness from an electrode end part toward the center relative to a sulfide-based solid electrolyte.

Description

  The present invention relates to a solid state battery, and more particularly to an electrode body using a sulfide solid electrolyte as a solid electrolyte.

  A solid battery using an inorganic solid electrolyte is known as a lithium ion secondary battery. This solid battery includes a solid electrolyte layer containing a solid electrolyte, electrode bodies (positive electrode and negative electrode) formed on both surfaces of the solid electrolyte layer, and a current collector bonded to each electrode. In a solid battery, a solid electrolyte is generally mixed with each electrode. As one form, a sulfide-based solid electrolyte excellent in lithium ion conductivity is heavily used as the inorganic solid electrolyte.

  In a solid battery, a solid electrolyte layer exists between the positive electrode layer and the negative electrode layer, and the negative electrode layer and the solid electrolyte layer need to have an area equal to or larger than that of the positive electrode layer. The solid electrolyte layer is larger.

  Solid batteries can be made by stacking the positive electrode, negative electrode, and fixed electrolyte layers, and improving the contact between the positive electrode layer-solid electrolyte layer and negative electrode layer-solid electrolyte layer. Therefore, it is desirable to apply pressure.

If the negative electrode layer and the solid electrolyte layer are larger than the positive electrode layer at the time of pressurization, a strong force is applied to the solid electrolyte layer at the positive electrode end, or the solid electrolyte layer is greatly deformed.
On the other hand, as a technique for increasing the capacity per volume of the solid state battery, it is a common technique to improve the density of the electrodes or increase the thickness of the electrodes.

  As the density of the electrode is increased or the thickness of the electrode is increased, the stress applied to the solid electrolyte layer during pressurization increases, resulting in a problem that the solid battery is deteriorated or short-circuited.

Moreover, if a hydrostatic pressure press (CIP) method is used as a pressurization method, a high pressure that is difficult to realize with a roll press can be applied.
Cells can be pressurized by placing an electrode in the laminate and using an isostatic pressing method. However, if there is a large step at the end of the electrode, the laminate may be broken. .

  Conventionally, countermeasures have been reported for such problems that occur during pressurization. Patent Document 1 discloses a measure for providing a chamfered portion on the side edge of the positive electrode and / or the negative electrode layer against the film breakage of the solid electrolyte that occurs during lamination by roll press. When producing, the laminate which the electrode end surface contacted may be damaged. Further, Patent Document 2 discloses a measure for suppressing temperature variation in the electrode by changing the electrode layer according to the position in the electrode, but the shape is not suitable for hydrostatic press.

JP 2012-38425 A

  Against this background, the present invention prevents the end face of the electrode from coming into contact with the end surface of the laminate cell when the laminate cell is produced by a hydrostatic press method in the sulfide-based solid electrode body. An object of the present invention is to provide an all solid state secondary battery.

  As a result of diligent study by the present inventor, it was possible to prevent breakage and film breakage of the laminate cell by the hydrostatic press method by continuously increasing the electrode thickness from the end of the electrode toward the center of the sulfide-based solid electrolyte. The present invention has been completed by finding out what can be done.

  That is, the present invention includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer sandwiched between the positive electrode layer and the negative electrode layer, and the thickness of the end portions of the electrolyte layer and the positive electrode layer or the negative electrode layer is a central portion. It is characterized by being thin compared to those of.

  In addition, the thickness of the electrode layer is continuously reduced from the center of the electrode toward the end of the electrode.

The solid electrolyte is a solid electrolyte synthesized from at least lithium sulfide (Li ₂ S) and diphosphorus pentasulfide (P ₂ S ₅ ).

  Further, the present invention is characterized in that the solid battery is packaged with an exterior material made of a laminate film.

  The present invention prevents the lamination cell from being broken and the film is cut by continuously thinning the end portions of the positive electrode layer and the electrolyte layer, and includes a solid film having a laminated film as a package with a thick electrode having a high density. A secondary battery can be manufactured.

It is sectional drawing and SEM image of the solid battery which concern on embodiment of this invention.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

<Configuration of all-solid-state battery>
First, the configuration of the solid state battery according to the present embodiment will be described with reference to FIG. A solid battery is composed of a positive electrode layer, a solid electrolyte, and a negative electrode layer.

The positive electrode layer has a sulfide-based solid electrolyte, includes at least lithium sulfide as the first component, and is phosphorus sulfide as the second component. In particular, Li ₂ S—P ₂ S ₅ is preferably used. . This sulfide-based solid electrolyte is known to have higher lithium ion conductivity than other inorganic compounds. In addition to Li ₂ S—P ₂ S ₅ , SiS ₂ , GeS ₂ , B ₂ S _3, etc. It may contain sulfide. As the solid electrolyte, an inorganic solid electrolyte to which Li ₃ PO ₄ , halogen, a halogen compound, or the like is appropriately added can be used.

The sulfide-based solid electrolyte is obtained by heating Li ₂ S and P ₂ S ₅ to a melting temperature or higher, melting and mixing them at a predetermined ratio, holding them for a predetermined time, and then rapidly cooling (melting). Quenching method). The obtained processed by mechanical milling method _{Li 2 S-P 2 S 5} .

The ratio (A) of lithium sulfide in the solid electrolyte in the positive electrode is such that 0.6 ≦ B <A ≦ 0.85 with respect to the ratio (B) of lithium sulfide in the solid electrolyte and the solid electrolyte in each of the negative electrodes. Is set to The mixing ratio of Li ₂ S—P ₂ S ₅ is 70/30 ≦ (lithium sulfide / 5 diphosphorus sulfide) ≦ 85/15 in the molar ratio of the positive electrode, and 60% in each of the solid electrolyte layer and the negative electrode. / 40 ≦ (lithium sulfide / 5 phosphorus disulfide) ≦ 75/25, the molar ratio (C) of lithium sulfide to niolin pentasulfide at the positive electrode, and lithium sulfide and 5 at each of the solid electrolyte layer and the negative electrode. The molar ratio (D) of niline sulfide is preferably set so that 60/40 ≦ D <C ≦ 85/15.

Examples of the solid electrolyte include those containing a lithium ion conductor made of an inorganic compound as the inorganic solid electrolyte in addition to the sulfide-based solid electrolyte. Examples of such lithium ion conductors include Li ₃ N, LIICON, LIPON (Li _{3 + y} PO _4−x N _x ), Thio-LISICON (Li _3.25 Ge _0.25 P _0.75 S ₄ ), Li has _{2 O-Al 2 O 3 -TiO} 2 -P 2 O 5 (LATP).

The solid electrolyte has a structure such as amorphous, glassy, crystal (crystallized glass). When the solid electrolyte is a sulfide-based solid electrolyte made of Li ₂ S—P ₂ S ₅ , the lithium ion conductivity of the amorphous body is 10 ⁻⁴ Scm ⁻¹ . On the other hand, the lithium ion conductivity of the crystalline material is 10 ⁻³ Scm ⁻¹ .

  The sulfide-based solid electrolyte in each of the positive electrode, the negative electrode, and the electrolyte layer is composed of a mixture of an amorphous material and a crystal material. The amorphous body is produced by mixing the first component and the second component of the sulfide described above and processing the mixture by a mechanical milling method. The crystalline body is produced by baking an amorphous body.

  In the positive electrode and / or the negative electrode, together with the crystalline solid electrolyte, a flexible amorphous solid electrolyte is used together, thereby preventing the generation of voids at the interface between the electrode active material and the solid electrolyte during charging and discharging.

  On the other hand, the solid electrolyte layer receives only the stress accompanying the volume change from the positive electrode and the negative electrode during the charge / discharge process, and the volume change of the solid electrolyte itself hardly occurs. For this reason, many crystalline solid electrolytes whose ionic conductivity is larger than an amorphous solid electrolyte are used for a solid electrolyte layer.

  Thus, a large amount of amorphous solid electrolyte is contained in the positive electrode and / or negative electrode, and a large amount of crystalline solid electrolyte is contained in the solid electrolyte layer, so that high lithium ion conductivity is maintained while maintaining high lithium ion conductivity. Generation of voids in the active material-solid electrolyte during discharge can be prevented.

  When the ratio (A) of the amorphous body in the solid electrolyte in the positive electrode and the negative electrode is less than 0.5, the ratio of the amorphous body is decreased, and the electrode active material is associated with charge / discharge of the battery. Expands and contracts to form voids between the electrode active material and the solid electrolyte. When the ratio exceeds 0.9, the proportion of the crystalline material decreases and the discharge capacity decreases.

  The positive electrode active material is not particularly limited as long as it is a material capable of reversibly occluding and releasing lithium ions. For example, lithium cobalt oxide (LCO), lithium nickelate, lithium nickel cobaltate, nickel cobalt aluminum acid Lithium (hereinafter also referred to as “NCA”), nickel cobalt lithium manganate (hereinafter also referred to as “NCM”), lithium manganate, lithium iron phosphate, nickel sulfide, copper sulfide, sulfur , Iron oxide, vanadium oxide and the like. These positive electrode active materials may be used independently and 2 or more types may be used together.

The positive electrode active material is preferably a lithium salt of a transition metal oxide having a layered rock salt type structure, among the examples of the positive electrode active materials listed above. “Layered” as used herein means a thin sheet-like shape, and “rock salt structure” refers to a sodium chloride structure, which is a kind of crystal structure, and includes cations and anions. Each of the face-centered cubic lattices formed by each indicates a structure that is shifted from each other by a half of the edge of the unit lattice. As a lithium salt of a transition metal oxide having such a layered rock salt structure, for example, Li _1-x-yz Ni _x Co _y Al _z O ₂ (NCA) or Li _1-x-yz Ni _x Co _y Mn _z O ₂ (NCM) (0 <x <1, 0 <y <1, 0 <z <1, and x + y + z <1) is represented by a lithium salt of a ternary transition metal oxide. Can be mentioned.

  The positive electrode layer binder is, for example, a nonpolar resin having no polar functional group. Therefore, the positive electrode layer binder is inactive to highly reactive solid electrolytes, particularly sulfide-based solid electrolytes. The positive electrode layer binder preferably includes the first binder described above. Since the electrolyte of the solid battery is a highly reactive sulfide-based solid electrolyte, the positive electrode layer binder is a nonpolar resin.

  The ratio of the content of the sulfide-based solid electrolyte, the positive electrode active material, the positive electrode layer conductive material, and the positive electrode layer binder in the positive electrode is not particularly limited. For example, the sulfide-based solid electrolyte is 20 to 50% by mass with respect to the total mass of the positive electrode layer, the positive electrode active material is 45 to 75% by mass with respect to the total mass of the positive electrode layer, and the positive electrode layer conductive material is the total mass of the positive electrode layer. 1-10 mass% with respect to the mass, and the positive electrode layer binder is 0.5-4 mass% with respect to the total mass of the positive electrode layer.

  The electrolyte layer includes a sulfide-based solid electrolyte and an electrolyte binder. The electrolyte binder is a nonpolar resin having no polar functional group. Accordingly, the electrolyte binder is inactive to highly reactive solid electrolytes, particularly sulfide-based solid electrolytes.

  The negative electrode layer includes a negative electrode active material, a negative electrode binder, and a solid electrolyte. As the negative electrode binder, the binder described above is included. The binder of the negative electrode layer interdiffuses with the binder of the electrolyte layer, and firmly adheres the negative electrode layer and the electrolyte layer.

  Examples of the negative electrode active material include graphite-based active material graphite such as artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, and natural graphite coated with artificial graphite.

  A second binder can be included in the negative electrode layer. The second binder is firmly bound to the negative electrode current collector through a hydrogen bond. However, the binding property between the negative electrode layer and the electrolyte layer may not be sufficient with the second binder alone. On the other hand, as one of the embodiments, it can be mechanically and more firmly bound to the electrolyte layer by an isostatic press.

  The negative electrode current collector may be any conductor as long as it is a conductor, and is composed of, for example, copper, stainless steel, nickel-plated steel, or the like. In addition, you may add a well-known additive etc. to said each layer suitably.

<Method for manufacturing solid battery>
Next, an example of a method for manufacturing a solid battery will be described. First, a first binder, a second binder, an adhesive layer conductive material, and a first solvent for dissolving the first binder and the second binder. An adhesive layer coating solution containing is produced. Here, examples of the first solvent include amide solvents such as NMP (N-methylpyrrolidone), DMF (N, N-dimethylformamide), N, N-dimethylacetamide, and alkyls such as butyl acetate and ethyl acetate. Examples include ester solvents, ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, ether solvents such as tetrahydrofuran and diethyl ether, alcohol solvents such as methanol, ethanol, and isopropyl alcohol.

  Next, the adhesive layer coating solution is applied onto the positive electrode current collector and dried. In addition, an adhesive layer coating solution may be applied onto a substrate such as a desktop screen printing machine and dried to form an adhesive film, and the adhesive film may be pressure-bonded to the positive electrode current collector.

  Next, a positive electrode layer coating solution containing a sulfide-based solid electrolyte, a positive electrode active material, a positive electrode layer conductive material, and a second solvent for dissolving the positive electrode layer binder is generated. The second solvent dissolves the positive electrode layer binder (first binder) but does not dissolve the second binder. The second solvent is specifically a nonpolar solvent, and examples thereof include aromatic hydrocarbons such as xylene, toluene, and ethylbenzene, and aliphatic hydrocarbons such as pentane, hexane, and heptane. Next, the positive electrode layer coating solution is applied onto the adhesive layer and dried to produce a positive electrode layer.

  Further, since the second solvent does not dissolve the second binder, the second binder in the adhesive layer swells in the positive electrode layer when the positive electrode layer coating solution is applied onto the adhesive layer. Is prevented. This prevents the sulfide solid electrolyte in the positive electrode layer 3 from being deteriorated by the second binder. Through the above steps, a positive electrode current collector and a positive electrode structure including a positive electrode layer are generated.

  On the other hand, a negative electrode layer coating solution containing a first binder, a second binder, a negative electrode active material, a sulfide-based solid electrolyte, and a second solvent is generated. When the negative electrode layer does not contain a sulfide-based solid electrolyte, a first solvent (polar solvent) can be used. Next, the negative electrode layer coating solution is applied onto the negative electrode current collector and dried to produce a negative electrode layer. Thereby, a negative electrode structure is produced.

  Next, an electrolyte layer coating solution containing a sulfide-based solid electrolyte, an electrolyte binder, and a second solvent is generated. The second solvent dissolves the electrolyte binder (first binder), but does not dissolve the second binder. Next, the electrolyte layer coating solution is applied onto the negative electrode layer and dried to produce an electrolyte layer. Thereby, since the 1st binder in a negative electrode layer melt | dissolves in an electrolyte layer because it melt | dissolves in a 2nd solvent, the binding with an electrolyte layer and a negative electrode layer becomes stronger. Further, since the second solvent does not dissolve the second binder, the second binder in the negative electrode swells in the electrolyte layer when the electrolyte layer coating solution is applied onto the negative electrode layer. It is prevented. This prevents the sulfide-based solid electrolyte in the electrolyte layer from being deteriorated by the second binder.

  Subsequently, a solid battery is produced | generated by crimping | bonding the positive electrode structure and the sheet | seat which consists of an electrolyte layer and a negative electrode structure. Thus, in this embodiment, since each layer of a solid battery is produced | generated by coating, the area of each layer can be enlarged easily. That is, in this embodiment, a large-capacity solid battery can be easily manufactured.

<Example>
Next, examples of the present embodiment will be described. In addition, all the operations in the following Examples and Comparative Examples were performed in a dry room having a dew point temperature of −55 ° C. or lower.
[Generation of adhesive layer]
Adhesive layer conductive material graphite (Timcal KS-4, the same applies hereinafter) and acetylene black (electrochemical industry, the same applies hereinafter), and styrene thermoplastic elastomer as the first binder (hereinafter referred to as the binder) A) (Asahi Kasei S.E.E 1611, the same shall apply hereinafter) and acid-modified PVDF (hereinafter referred to as Binder B) (Kureha KF 9200, same shall apply hereinafter) as the second binder 60: 10: 15: 15 Weighed at a mass% ratio. Then, these materials and an appropriate amount of NMP were put into a planetary mixer and stirred at 3000 rpm for 5 minutes to produce an adhesive layer coating solution.

[Generation of positive electrode current collector]
Next, an aluminum foil current collector having a thickness of 20 μm was placed as a positive electrode current collector on a desktop screen printer (manufactured by Neurong Seimitsu Kogyo Co., Ltd., the same shall apply hereinafter), and an adhesive layer coating solution was applied using a 400 mesh screen. It coated on the aluminum foil electrical power collector. Thereafter, the positive electrode current collector coated with the adhesive layer coating solution was vacuum-dried at 80 ° C. for 12 hours. Thereby, an adhesive layer was formed on the positive electrode current collector. The thickness of the adhesive layer after drying was 7 μm.

[Creation of positive electrode layer]
Lithium cobaltate (LiCoO ₂ ) as a positive electrode active material, Li ₂ S—P ₂ S ₅ (80:20 mol%) as a sulfide-based solid electrolyte, and amorphous carbon powder (Ketjen black) They were weighed at a ratio of 40/10% by weight and mixed using a planetary mixer.

The sulfide-based solid electrolyte was formed from a mixture of an amorphous body and a crystalline body at a ratio (weight%) of 20:80. The amorphous body is produced by performing mechanical milling treatment (MM treatment) of Li ₂ S—P ₂ S ₅ (80:20 mol%) at 200 rpm for 30 minutes, and the crystalline body is amorphous in nitrogen. It was prepared by performing a baking treatment at 205 ° C. for 1 hour.

  Next, a xylene solution in which the binder A as the positive electrode layer binder is dissolved is added to the mixed powder so that the binder A is 1.0% by mass with respect to the total mass of the mixed powder. A primary mixed solution was prepared. Furthermore, a secondary mixed solution was generated by adding an appropriate amount of dehydrated xylene for viscosity adjustment to this mixed solution. Furthermore, in order to improve the dispersibility of the mixed powder, a zirconia ball having a diameter of 5 mm is changed into a secondary mixed solution so that the space, the mixed powder, and the zirconia ball each occupy 1/3 of the total volume of the kneading container. I put it in. The tertiary mixture produced in this way was put into a planetary mixer and stirred at 3000 rpm for 3 minutes to produce a positive electrode layer coating solution.

  Subsequently, the sheet | seat which consists of a positive electrode electrical power collector and an adhesion layer was mounted in the desk screen printer, and the positive electrode layer coating liquid was coated on the sheet | seat using a 150 micrometer metal mask. Then, after drying the sheet | seat with which the positive electrode layer coating liquid was coated with a 40 degreeC hotplate for 10 minutes, it was vacuum-dried at 40 degreeC for 12 hours. Thereby, a positive electrode layer was formed on the adhesive layer. The total thickness of the positive electrode current collector, the adhesive layer, and the positive electrode layer after drying was around 165 μm.

  Subsequently, the sheet | seat which consists of a positive electrode electrical power collector, an contact bonding layer, and a positive electrode layer was rolled using the roll press machine with a roll gap of 10 micrometers, and the positive electrode structure was produced | generated. The thickness of the positive electrode structure was around 120 μm.

[Formation of negative electrode layer]
Graphite powder as a negative electrode active material (dried at 80 ° C. for 24 hours), binder A as a first binder, and binder C (polyamic acid type as a second binder) Polyimide resin Hitachi Chemical HCI1000S) was weighed at a mass% ratio of 94.5: 0.5: 5.0. Then, these materials and an appropriate amount of NMP were put into a rotation and revolution mixer, stirred for 3 minutes at 3000 rpm, and then subjected to defoaming treatment for 1 minute to produce a negative electrode layer coating solution.

  Next, a copper foil current collector having a thickness of 16 μm was prepared as a negative electrode current collector, and a negative electrode layer coating solution was applied onto the copper foil current collector using a blade. The thickness (gap) of the negative electrode layer coating solution on the copper foil current collector was around 150 μm.

  The sheet coated with the negative electrode layer coating solution was stored in a dryer heated to 80 ° C. and dried for 20 minutes. Then, the sheet | seat which consists of a negative electrode electrical power collector and a negative electrode layer was rolled using the roll press machine with a roll gap of 10 micrometers, and the negative electrode structure was produced | generated. The thickness of the negative electrode structure was about 100 μm. Further, the rolled sheet was vacuum heated at 300 ° C. for 2 hours. As a result, a negative electrode layer in which the binder C was imidized was generated.

[Creation of electrolyte layer]
Li ₂ S—P ₂ S ₅ (80:20 mol%) as a sulfide-based solid electrolyte, xylene solution of binder A (electrolyte binder) + mass of binder A is amorphous powder The primary mixed solution was adjusted by adding so as to be 1% by mass. Furthermore, a secondary mixed solution was generated by adding an appropriate amount of dehydrated xylene for viscosity adjustment to the primary mixed solution. Furthermore, in order to improve the dispersibility of the mixed powder, a zirconia ball having a diameter of 5 mm is changed into a secondary mixed solution so that the space, the mixed powder, and the zirconia ball each occupy 1/3 of the total volume of the kneading container. I put it in. The tertiary mixed solution thus produced was put into a planetary mixer and stirred at 200 rpm for 30 minutes to produce an electrolyte layer coating solution.

  Next, the negative electrode structure was placed on a desktop screen printer, and an electrolyte layer coating solution was applied onto the negative electrode structure using a 200 μm metal mask. Thereafter, the sheet coated with the electrolyte layer coating solution was dried on a hot plate at 40 ° C. for 10 minutes and then vacuum dried at 40 ° C. for 12 hours. As a result, an electrolyte layer was formed on the negative electrode structure. The thickness of the electrolyte layer after drying was around 130 μm.

[Production of solid battery]
The sheet consisting of the negative electrode structure and the electrolyte layer and the positive electrode structure are each punched out with a Thomson blade, and the electrolyte layer of the sheet and the positive electrode layer of the positive electrode structure are overlapped and placed in an aluminum laminate film. Sealed and packed. Then, after hydrostatic pressure press (CIP) (manufactured by Nishimura Ceramics Co., Ltd.) using a hydrostatic pressure press machine at a molding pressure of 50 MPa for 10 minutes, a cell was prepared, and then the laminate cross section was checked with an SEM for breakage. Was observed. The results are shown in Table 1.

  As can be seen from Table 1, when the electrode end portion was thinned (that is, increased in height from the end portion toward the center), no breakage was observed in the solid electrolyte layer and the laminate.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes and modifications within the scope of the technical idea described in the claims. Of course, these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Positive electrode layer 2 Solid electrolyte layer 3 Negative electrode layer

Claims (4)

  A positive electrode layer, a negative electrode layer, and a solid electrolyte layer sandwiched between the positive electrode layer and the negative electrode layer, and the thicknesses of the end portions of the electrolyte layer and the positive electrode layer or the negative electrode layer are compared with those of the central portion. All-solid-state secondary battery characterized by its thinness.   2. The all-solid-state secondary battery according to claim 1, wherein the thickness of the electrode layer is continuously reduced from the center of the electrode toward the end of the electrode. The all-solid-state secondary battery according to claim 2, wherein the solid electrolyte is a solid electrolyte synthesized from at least lithium sulfide (Li ₂ S) and diphosphorus pentasulfide (P ₂ S ₅ ).   The all-solid-state secondary battery according to any one of claims 1 to 3, wherein the all-solid-state secondary battery is packaged with an exterior material made of a laminate film.