JP6909409B2 - Sulfide-based all-solid-state battery - Google Patents

Description

The present invention relates to a sulfide-based all-solid-state battery containing a sulfide-based solid electrolyte.

In recent years, secondary batteries typified by lithium ion batteries have been used as vehicle drive power sources for electric vehicles (EVs), hybrid vehicles (HVs), plug-in hybrid vehicles (PHVs), and the like. In a lithium ion battery, charge and discharge are performed by moving lithium ions, which are electrolyte ions, back and forth between the positive and negative electrodes, and based on the electrochemical reaction when lithium ions are released from the negative electrode active material and stored in the positive electrode active material. Current can be taken out to an external circuit. Conventionally, a liquid non-aqueous electrolyte solution has been mainly used as the electrolyte, but the non-aqueous electrolyte solution is safe because it is flammable while it can form a good reaction interface when it gets wet with an active material. There are still issues left. Therefore, the practical application of an all-solid-state battery using a solid solid electrolyte is being energetically promoted (see, for example, Patent Documents 1 and 2).

There are roughly two types of solid electrolytes known: oxide-based solid electrolytes and sulfide-based solid electrolytes. Oxide-based solid electrolytes are generally easy to handle because they are excellent in chemical stability, but have a problem of low ionic conductivity. On the other hand, the sulfide-based solid electrolyte has excellent ionic conductivity, but tends to be chemically unstable, and has the property of reacting with moisture in the atmosphere to decompose or unintentionally reacting with other elements. There is. For example, the sulfur (S) component contained in the sulfide-based solid electrolyte reacts with copper (Cu) or the like, which is widely used as a negative electrode current collector, due to fluctuations in the temperature environment or voltage environment, and reacts with CuS or the like. Things can be deposited. This causes problems such as a decrease in capacity due to consumption of the solid electrolyte and a short circuit of the solid electrolyte layer.

JP 2015-005421 JP 2015-069848

For example, in Patent Document 1, in an all-solid-state battery containing a sulfide-based solid electrolyte material in the negative electrode active material layer, a conductive film containing a carbon material is provided on the surface of a negative electrode current collector whose surface roughness is appropriately adjusted. Is disclosed. As a result, it is possible to suppress the reaction between Cu of the current collector and S of the solid electrolyte material even in a high temperature environment or a voltage fluctuation environment while suppressing damage to the conductive film due to the rough surface of the current collector. It is stated that. Further, Patent Document 2 discloses that in an all-solid-state battery containing a sulfide-based solid electrolyte material in the negative electrode active material layer, a conductive element is sputtered and coded on the surface of a Cu foil as a negative electrode current collector. ing. It is also described that this also suppresses the reaction between Cu in the current collector and S in the solid electrolyte material, and suppresses a decrease in capacity due to consumption of the solid electrolyte.

However, according to the study by the present inventors, it has been found that when a conductive film containing a carbon material is formed on the current collector, lithium ions are occluded in the carbon material and the irreversible capacity increases. In addition, spatter is disadvantageous in terms of productivity, and there is room for improvement.
The present invention has been made in view of this point, and an object of the present invention is to provide a sulfide-based all-solid-state battery capable of both suppressing the formation of reaction products that deteriorate the battery performance and reducing the irreversible capacity. To provide.

The sulfide-based all-solid-state battery disclosed herein includes a positive electrode, a solid electrolyte layer, and a negative electrode, and the negative electrode is a current collector containing at least one of copper (Cu), iron (Fe), and nickel (Ni). And a negative electrode active material layer containing a sulfide solid electrolyte material and a negative electrode active material, and a conductive intermediate layer arranged between the current collector and the negative electrode active material layer. The conductive intermediate layer contains a mayenite type compound.

The mayenite-type compound may have high electron conductivity comparable to that of a metal, but has no reactivity with lithium ions and does not occlude and consume lithium ions. Therefore, by forming the conductive intermediate layer using the mayenite type compound, the generation of irreversible capacitance due to the conductive intermediate layer is prevented, and the conductivity between the negative electrode active material layer and the current collector is enhanced. be able to. Further, the conductive intermediate layer containing the mayenite type compound is advantageous in that it can be easily formed as having high electron conductivity by a coating method or the like without being limited to the sputtering method. Further, the mayenite type compound has high thermal stability up to about 300 ° C. and withstand voltage characteristics, and there is little concern about damage. Therefore, it is possible to preferably suppress metal elements such as Cu, Fe, and Ni constituting the current collector from diffusing as the environmental temperature and voltage rise and reacting with S contained in the solid electrolyte material. According to the technique disclosed herein, a sulfide-based all-solid-state battery capable of both suppressing the formation of reaction products that deteriorate the battery performance and reducing the irreversible capacity is realized.

It is sectional drawing which showed schematic the structure of the sulfide-based all-solid-state battery which concerns on one Embodiment. It is a figure explaining the state of the Cu diffusion test in an Example. It is a graph which shows the time-dependent change of the resistance of the electrode plate of each example in a Cu diffusion test. It is an electron microscope image of the cross section of the electrode plate of each example after a Cu diffusion test.

Hereinafter, preferred embodiments of the present invention will be described. Matters other than those specifically mentioned in the present specification and necessary for carrying out the present invention can be grasped as design matters of those skilled in the art based on the prior art in the art. The present invention can be carried out based on the contents disclosed in the present specification and common general technical knowledge in the art. In this specification, the notation "X to Y" indicating a numerical range means X or more and Y or less.

FIG. 1 is a cross-sectional view schematically showing the structure of a sulfide-based all-solid-state battery (hereinafter, may be simply referred to as “all-solid-state battery”) 1 according to the embodiment. The all-solid-state battery 1 is a secondary battery that can be repeatedly charged and discharged, and is, for example, a lithium ion battery. The all-solid-state battery 1 disclosed herein includes a negative electrode 10, a solid electrolyte layer 20, and a positive electrode 30. The negative electrode 10, the solid electrolyte layer 20, and the positive electrode 30 are power generation elements, and are housed in a battery case (not shown) and sealed. Hereinafter, each component will be described.

The solid electrolyte layer 20 mainly contains a solid electrolyte material. The solid electrolyte layer 20 may contain a binder, if necessary. In this case, for example, the solid electrolyte layer 20 is formed by applying a solid electrolyte paste obtained by kneading a powdery solid electrolyte material and a binder in an appropriate dispersion medium to the surface of the base material and drying the solid electrolyte layer 20. It can be easily produced. The base material referred to here may be a carrier sheet such as a polyethylene terephthalate (PET) film, or may be a surface such as a negative electrode 10 or a positive electrode 30 described later.
Further, in the present specification, "mainly" means that the component is contained in an amount of 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, unless otherwise specified. For example, it may be an embodiment containing 80% by mass or more.

As the solid electrolyte material, for example, various compounds having lithium ion conductivity but not electron conductivity can be preferably used. Such solid electrolyte material, specifically, for _{example, Li 2 S-SiS 2,} LiI-Li 2 S-SiS 2, LiI-Li 2 S-P 2 S 5, LiI-Li 2 S-B _{2 S 3, Li 3 PO 4} -Li 2 S-Si 2 S, Li 3 PO 4 -Li 2 S-SiS 2, LiPO 4 -Li 2 S-SiS, LiI-Li 2 S-P 2 O 5, LiI -Li ₃ PO ₄ -P ₂ S ₅ , LiI-Li ₃ PS _4- LiBr, Li _{2 SP 2} S ₅ , Li _{2 SP 2} S ₅ -Li I-Li Br and Li _{2 SP 2} S ₅ Amorphous sulfides such as −GeS _{2 , Li 2} O−B ₂ O ₃ −P ₂ O ₅ , Li ₂ O−SiO ₂ , Li ₂ O−B ₂ O ₃ , and Li ₂ O−B ₂ O ₃ Amorphous oxides such as −ZnO, crystalline sulfides such as _{Li 10} GeP ₂ S _{12 , Li 1.3} Al _0.3 Ti _0.7 (PO ₄ ) ₃ , Li _{1 + x + y} A ¹ _x Ti _2-x Si _y P _3-y O ₁₂ (A ¹ is Al or Ga, 0 ≦ x ≦ 0.4, 0 <y ≦ 0.6), [(A ² _1/2 Li _1/2 ) _1-z C _z ] TiO ₃ (A ² is La, Pr, Nd, or Sm, C is Sr or Ba, 0 ≦ z ≦ 0.5), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li Crystalline oxides such as ₆ BaLa ₂ Ta ₂ O ₁₂ and Li _3.6 Si _0.6 P _0.4 O _{4 , crystalline acid nitrides such as Li 3} PO _{(4-3 / 2w)} N _w (w <1), Li crystalline nitride such as ₃ N, _{and, LiI, LiI-Al 2 O} 3, and Li ₃ crystalline iodide such as N-LiI-LiOH and the like. Among them, a sulfide-based solid electrolyte material can be preferably used because it has excellent lithium ion conductivity, and a sulfide-based solid electrolyte material made of amorphous sulfide can be particularly preferably used.

As the solid electrolyte, a semi-solid polymer electrolyte such as polyethylene oxide containing a lithium salt, polypropylene oxide, polyvinylidene fluoride, or polyacrylonitrile can also be used.
The thickness of the solid electrolyte layer 20 is not particularly limited. It is exemplified that the thickness of the solid electrolyte layer 20 is, for example, 20 μm or more and 200 μm or less, typically 100 μm or less, for example, 50 μm or less.

The binder is the same as the binder used for forming the bulk layer of this type of battery (that is, the solid electrolyte layer 20 formed from the powder material, the negative electrode active material layer 14, and the positive electrode active material layer 34). Can be adopted as appropriate. For example, vinyl resins such as vinyl acetate copolymers, vinyl halide resins such as polyvinyl fluoride and vinylidene fluoride (PVdF), ethylene resins such as polytetrafluoroethylene, polytrifluoroethylene and polyethylene, and polyethylene oxide (PEO). ) And other polyalkylene oxides, ethyl cellulose and other cellulose resins, acrylic resins, nitrile rubbers, butyl rubbers, polybutadiene rubbers, styrene butadiene rubbers (SBR), polysulfide rubbers, fluororubbers, acrylonitrile butadiene rubbers and other rubbers and other polymer materials. It can be preferably adopted. The proportion of binder in the bulk layer of this type of battery is not strictly limited, for example, assuming that the layer constituent material is 100% by mass, 10% by mass or less is appropriate, 5% by mass or less is preferable, and 3% by mass or less. Is more preferable.

The negative electrode 10 includes a negative electrode current collector 12, a negative electrode active material layer 14, and a conductive intermediate layer 16 arranged between the negative electrode current collector 12 and the negative electrode active material layer 14. Each of these layers is fixed to each other.
As the negative electrode current collector 12, a metal sheet having good electron conductivity can be preferably used, for example, copper (Cu), nickel (Ni), iron (Fe), and these and other elements. Metal foils such as alloys (eg, SUS steel) are suitable. Among them, copper such as Cu foil is preferably used as the negative electrode current collector 12 from the viewpoint that reaction unevenness is unlikely to occur in the battery reaction due to its high electron conductivity and heat dissipation is good due to its high thermal conductivity. be able to. The thickness of the current collector 12 is not particularly limited because it depends on the dimensions of the active material layer 14 and the like, but is preferably 5 μm or more and 500 μm or less, and more preferably 10 μm or more and 100 μm or less.

The conductive intermediate layer 16 mainly contains a mayenite type compound. Although not limited to this, the conductive intermediate layer 16 can further contain a binder, if necessary, and for example, a powdery mayenite-type compound and a binder are suitable as a dispersion medium. It can be easily produced by applying the intermediate layer paste kneaded in the medium to the surface of the negative electrode current collector 12 and drying it. The binder and its proportions may be similar to those described in the column of solid electrolyte layer 20 described above.

Characteristic mayenite type compound in the all-solid-state cell disclosed herein is a compound derived from cement minerals produced in Mayen region of Germany, the general formula: 12AeO · 7Al 2 _{O 3;} a representative composition represented by Have. In addition, Ae in the formula is at least one kind selected from the group 2 element of the periodic table, and typically contains at least one kind of calcium (Ca) and strontium (Sr). Any one of the elements Ae may be contained alone, or two or more of them may be contained in combination. Of these, a form containing Ca is preferable. When two or more elements are contained as Ae, it is preferable that Ca is contained at the highest content (for example, exceeding 50 atm%).

In the mayenite type compound, for example, a cage-like structure having a diameter of about 0.4 nm composed of ^{Ae 2+} (Ca ²⁺ ), Al ³⁺ , and O ^{2- is three-dimensionally linked.} It has a characteristic crystal structure. The skeletons that make up this cage are positively charged, forming 12 cages per unit cell. ^{One oxygen ion (O2-} ) is introduced into 1/6 of this cage in order to satisfy the electrical neutrality condition of the crystal. That is, it can be said that the myenite compound is an oxide ion-encapsulating aluminosilicate. The oxygen ions in the cage have properties that are chemically different from the other oxygen ions that make up the skeleton, and therefore the oxygen ions in the cage are particularly called free oxygen ions. Then, the mayenite type compound is not normally exhibit electron conductivity, a part or all of the free oxygen ions electrons by replacing with such anions (e ^{- -)} and hydride ion (H) Electron conductivity is imparted. As an example, when free oxygen ions are replaced with hydride ions, permanent electrical conductivity is exhibited by irradiation with ultraviolet rays. Further, when free oxygen ions are replaced with electrons, they become stable electrides (electrons) at room temperature, and metallic electrical conductivity is exhibited. In the electrode material disclosed herein, the mayenite-type compound may be a conductive mayenite-type compound in which free oxygen ions are substituted with anions, and more preferably an electride in which free oxygen ions are substituted with electrons. ..

In the above mayenite type compound, the ratio of the elements Ae and Al may vary within the range in which the cage structure which is the skeleton of the crystal lattice is maintained. The molar ratio of Ae to Al is preferably in the range of, for example, 13: 12-11: 16. Further, the elements Ae and Al may be partially or wholly replaced with other elements as long as the cage structure is maintained.

The thickness of the conductive intermediate layer 16 is not particularly limited. Considering the increase in electrical resistance and bulk of the conductive intermediate layer 16, it is preferable that the conductive intermediate layer 16 is as thin as possible. For example, a through hole having a size that allows current collector constituent ions and the like to pass through the conductive intermediate layer 16. It is preferable that the thickness is such that Specifically, the thickness of the conductive intermediate layer 16 (which is the average thickness; the same applies hereinafter) may be, for example, about 100 nm or more, and may be about 50 μm or less, for example, about 10 μm or less. As an example, when the conductive intermediate layer 16 is formed as a dense film by a thin film forming method such as a plating method, a sputtering method, a vapor deposition method, or a liquid phase method, the thickness is about 100 nm to several μm (for example, 100 nm to 3 μm). It may be. As another example, when the conductive intermediate layer 16 is formed as a relatively coarse film by a printing method using a powder-containing paste, a coating method, or the like, the thickness is several μm to 10 μm (for example, 3 to 10 μm). ) It should be about. In this case, as the mayenite type compound, it is preferable to use a powder having an average particle size of about 0.1 to 5 μm.

The negative electrode active material layer 14 mainly contains the negative electrode active material, and further contains a sulfide-based solid electrolyte material. Although not limited to this, the negative electrode active material layer 14 may further contain a binder if necessary, and for example, it may be combined with a powdery negative electrode active material material and a sulfide-based solid electrolyte material. A negative electrode paste obtained by kneading the coating agent in an appropriate dispersion medium can be easily prepared by applying it to the surface of the conductive intermediate layer 16 and drying it. The binder and its proportions may be similar to those described in the column of solid electrolyte layer 20 described above.

The negative electrode active material may be any material that can reversibly occlude and release the charge carrier. Such a negative electrode active material has no clear limitation with the positive electrode active material described later, and the charge / discharge potentials show relatively noble potentials by comparing the charge / discharge potentials of the two types of active materials. A material having a relatively low potential can be used as a positive electrode active material, and a material having a relatively low potential can be used as a negative electrode active material. Typical negative electrode active material materials include carbon materials such as graphite (graphite), non-graphitized carbon (hard carbon), easily graphitized carbon (soft carbon), and carbon nanotubes, lithium titanate, and phosphorus. Oxides such as lithium metal acid, vanadium oxide and molybdenum oxide, titanium sulfide, lithium cobalt nitride, lithium silicon oxide, lithium metal (Li), silicon (Si) and tin (Sn) and their oxides (eg, for example. SiO, SnO ₂ ), lithium alloys (eg, LiM ¹ , M ¹ are C, Sn, Si, Al, Ge, Sb, or P), lithium-storable intermetallic compounds (eg, Mg _x M ² and M ^3). _y Sb, M ² is Sn, Ge, or Sb, M ³ is In, Cu, or Mn), and derivatives and complexes thereof. Among them, graphite-based materials such as natural graphite (stone ink) and artificial graphite can be preferably used from the viewpoint of energy density. As the graphite-based material, those in which amorphous carbon is arranged on at least a part of the surface can be preferably used. More preferably, almost the entire surface of the granular carbon is coated with an amorphous carbon film.

In order to enhance the lithium ion conductivity in the negative electrode active material layer 14, in other words, for the purpose of increasing the conduction path of lithium ions, the negative electrode active material layer 14 preferably contains a solid electrolyte material composed of sulfide. be able to. The sulfide-based solid electrolyte material made of sulfide may be the solid electrolyte material made of amorphous sulfide or crystalline sulfide described in the above column of solid electrolyte layer 20. When the solid electrolyte layer 20 is composed of a sulfide-based solid electrolyte material, the negative electrode active material layer 14 may contain the same or the same solid electrolyte material as the sulfide-based solid electrolyte material constituting the solid electrolyte layer 20. preferable. The ratio of the solid electrolyte material contained in the negative electrode active material layer 14 can be, for example, 60% by mass or less, preferably 50% by mass or less, when the total of the active material material and the solid electrolyte material is 100% by mass. , 40% by mass or less is more preferable. The proportion of the solid electrolyte material is preferably 10% by mass or more, preferably 20% by mass or more, and more preferably 30% by mass or more. A high-resistance reaction layer may be formed at the interface between the negative electrode active material and the solid electrolyte, and the interface resistance may increase. Therefore, in order to suppress such an event, the particles constituting the negative electrode active material may be coated with a crystalline oxide having lithium ion conductivity.

The thickness of the negative electrode active material layer 14 is not particularly limited. In an all-solid-state battery for which a large current is instantly supplied, the thickness of the negative electrode active material layer 14 is preferably thick as long as the electrical resistance does not become too high. For example, the thickness of the negative electrode active material layer 14 can be, for example, 50 μm or more and 300 μm or less, typically 200 μm or less, for example 100 μm or less.

The positive electrode 30 includes a positive electrode current collector 32 and a positive electrode active material layer 34 fixed on the positive electrode current collector 32. As the positive electrode current collector 32, a metal sheet having good conductivity can be preferably used, and for example, a metal foil such as aluminum or an iron alloy (for example, various SUS steels) is suitable. The positive electrode active material layer 34 contains the positive electrode active material as a main component, and may further contain a solid electrolyte material. Although not limited to this, the positive electrode active material layer 34 may further contain a binder, if necessary, and includes, for example, a powdery positive electrode active material material, a solid electrolyte material, and a binder. Can be easily produced by applying a positive electrode paste obtained by kneading in an appropriate dispersion medium to the surface of the positive electrode current collector 32 and drying the mixture. The binder and its proportions may be similar to those described in the column of solid electrolyte layer 20 described above.

The positive electrode active material may be any material that can reversibly store and release charge carriers. Preferable examples of the positive electrode active material of the all-solid lithium secondary battery include lithium nickel-containing composite oxide, lithium cobalt-containing composite oxide, lithium nickel cobalt-containing composite oxide, lithium manganese-containing composite oxide, and lithium nickel cobalt manganese-containing. Examples thereof include lithium transition metal composite oxides such as composite oxides. From the viewpoint of high durability, a so-called 4V class positive electrode active material such as a layered lithium nickel cobalt manganese-containing composite oxide having an operating potential of 4.2V or less based on metallic lithium is preferable. From the viewpoint of achieving high output at one time, a so-called 5V class cathode such as lithium nickel manganese oxide having a spinel structure having an operating potential exceeding 4.2V and about 5.2V or less based on metallic lithium is used. Active material is preferred.

In order to enhance the lithium ion conductivity in the positive electrode active material layer 34, the positive electrode active material layer 34 can preferably contain a solid electrolyte material as described above. In this case, the solid electrolyte material contained in the positive electrode active material layer 34 is preferably the same type or the same material as the solid electrolyte material constituting the solid electrolyte layer 20. The ratio of the solid electrolyte material contained in the positive electrode active material layer 34 can be, for example, 60% by mass or less, preferably 50% by mass or less, when the total of the active material material and the solid electrolyte material is 100% by mass. , 40% by mass or less is more preferable. The proportion of the solid electrolyte material is preferably 10% by mass or more, preferably 20% by mass or more, and more preferably 30% by mass or more. A high-resistance reaction layer may be formed at the interface between the positive electrode active material and the solid electrolyte, and the interface resistance may increase. Therefore, in order to suppress such an event, the particles constituting the positive electrode active material may be coated with a crystalline oxide having lithium ion conductivity.

The thickness of the positive electrode active material layer 34 is not particularly limited. In an all-solid-state battery for which a large current is instantly supplied, the thickness of the negative electrode active material layer 14 is preferably thick as long as the electrical resistance does not become too high. For example, the thickness of the positive electrode active material layer 34 can be, for example, 50 μm or more and 300 μm or less, typically 200 μm or less, for example 100 μm or less.

The power generation element configured as described above is housed in a battery case (not shown) and sealed, so that decomposition / deterioration of the solid electrolyte material due to unintended water content or oxidation is suppressed. The form of the battery case is not limited, and may be a square type (rectangular parallelepiped type), a cylindrical type, or a laminated pack type, and the material thereof is metal, reinforced plastic, laminated sheet of metal leaf and resin sheet, etc. It may be. The battery case may be provided with, for example, a positive electrode external connection terminal and a negative electrode external connection terminal that communicate the inside and the outside of the battery case, and these positive and negative external connection terminals are a positive electrode current collector 32 and a negative electrode current collector, respectively. It can be electrically connected to 12. As a result, electric power can be extracted from the power generation element to the external load.

Further, when the all-solid-state battery is a bulk type all-solid-state battery in which each of the above layers is made of a powder material, the purpose is to reduce the interfacial resistance between the particles constituting the powder material and to achieve a high energy density. For the purpose of realizing this, compressive stress may be applied in the stacking direction of each layer (direction orthogonal to the current collector). Such compressive stress may be, for example, about 0.1 MPa or more, preferably 1 MPa or more, more preferably 2 MPa or more, particularly preferably 5 MPa or more, and for example, 10 MPa or more. The upper limit of the compressive stress is not particularly limited, and for example, it can be appropriately set according to the maximum stress that can be applied to the all-solid-state battery 1 by the compressive stress application device or the like to be used. Such an average restraining pressure can be, for example, about 50 MPa or less, for example, 20 MPa or less. Such a high compressive stress can be about 5 to 10 times or more the compressive stress of a liquid-based secondary battery using a non-aqueous electrolytic solution.

Here, in an all-solid-state battery not provided with the conductive intermediate layer 16, when a voltage is applied while the negative electrode active material layer 14 contains a sulfide-based solid electrolyte material and the power generation element is pressurized, negative electrode current collection is performed. The body and the sulfur (S) component derived from the sulfide-based solid electrolyte material contained in the negative electrode active material layer 14 react at the interface to form a reaction product (for example, a sulfide such as CuS, FeS, NiS). obtain. Further, since the solid electrolyte material in the negative electrode active material layer 14 is decomposed, the electron conductivity and the electrochemical reaction of the negative electrode active material layer 14 are hindered. Further, this reaction product may diffuse into the negative electrode active material layer 14 and eventually into the solid electrolyte layer 20. Then, for example, copper sulfide (for example, CuS) can react with lithium ions, which are charge carriers, according to the following equation to consume the charge carriers and reduce the battery performance.
_{^{CuS + 2Li + → Li 2 S}} + Cu
Further, since copper sulfide is excellent in electron conductivity, it should be avoided because if it diffuses into the solid electrolyte layer 20, it may impair the electrical insulation property of the solid electrolyte layer 20 and cause a short circuit.

On the other hand, in the all-solid-state battery disclosed here, a conductive intermediate layer 16 containing a mayenite compound is arranged between the negative electrode current collector 12 and the negative electrode active material layer 14. Therefore, even if a voltage is applied while the all-solid-state battery is pressurized, the conductive intermediate layer 16 preferably prevents contact between the negative electrode current collector 12 and the negative electrode active material layer 14, and thus the negative electrode. The reaction between the current collector 12 and the negative electrode active material layer 14 is prevented. This preferably suppresses problems such as consumption of the above-mentioned charge carrier and solid electrolyte material, deterioration of battery performance, and short circuit of the solid electrolyte layer 20. Further, since the mayenite compound is a material having excellent electron conductivity, the electric resistance between the negative electrode current collector 12 and the negative electrode active material layer 14 can be suppressed low.

Further, conventionally, a layer containing a carbonaceous material may be provided on the surface of the current collector as the conductive intermediate layer 16. A carbonaceous material is a preferable material in terms of forming an electron conduction path, but has a drawback of increasing an irreversible capacity in that it absorbs lithium ions. On the other hand, the mayenite compound does not occlude lithium ion, which is a charge carrier, unlike a carbonaceous material, for example. Therefore, in the technique disclosed herein, the problem of capacity reduction due to the conductive intermediate layer 16 occluding the charge carrier does not occur.
That is, the technique disclosed herein realizes a sulfide-based all-solid-state battery capable of both suppressing the formation of reaction products that deteriorate the battery performance and reducing the irreversible capacity.

Since the formation of the above reaction products is promoted in a high temperature environment, the above characteristics may be exposed to a high temperature environment that is stored outdoors or installed together with a high temperature heating device such as an engine. It is easy to find in all-solid-state batteries for applications. Further, both suppression of such reduction in battery performance and reduction in irreversible capacity are particularly required for all-solid-state batteries used in applications where high battery performance such as high energy density is required for a long period of time. Therefore, the non-aqueous electrolyte secondary battery disclosed herein can be particularly preferably used as a main battery for driving a motor mounted on a vehicle such as a plug-in hybrid vehicle, a hybrid vehicle, or an electric vehicle. can.

Hereinafter, as a specific example, electrodes provided in the sulfide-based all-solid-state battery disclosed herein were produced, and their characteristics were evaluated. It should be noted that the present invention is not intended to be limited to those shown in such specific examples.

(Example 1)
A copper foil was used as the current collector, and the copper foil was allowed to hold an electrode layer containing a sulfide solid electrolyte to form the electrode plate of Example 1. As the sulfide-based solid electrolyte, 10LiI-15LiBr-85 (0.75Li ₂ S-0.25P ₂ S ₅ ) powder having an average particle size of 2 μm was used. The electrode material is a sulfide-based solid electrolyte for the purpose of promoting the reaction between the current collector and the sulfide-based solid electrolyte and for the purpose of confirming that the reaction product diffuses in the solid electrolyte layer. Was used at a ratio of 100%, and no negative electrode active material was blended. Further, PVdF was blended as a binder in a proportion of 5% by mass in the sulfide solid electrolyte powder to form an electrode layer (here, a solid electrolyte (SE) layer) having a thickness of about 300 to 350 μm.

(Example 2)
Further, a copper foil was used as the current collector, an intermediate layer was provided on the surface of the copper foil, and then an electrode layer similar to that of Example 1 was formed on the intermediate layer to form an electrode plate of Example 2. As the intermediate layer material, mayenite powder having an average particle diameter of 5 μm was used, and an intermediate layer having a thickness of 40 μm was formed in the same manner as the formation of the SE layer. Here, in order to make an example in which the diffusion of copper (Cu) as a current collector material by the intermediate layer is more reliably suppressed, the thickness of the intermediate layer is set to be as thick as about 40 μm.

(Cu diffusion test)
The electrode plates of Examples 1 and 2 prepared in this manner were sandwiched between two SUS plates as shown in FIG. 2, and hot-pressed at 250 ° C. to apply a pressure of 10 MPa in the thickness direction was applied for 1 hour. .. At the same time, the resistance between the SUS plates was measured over time to examine the change in the electron conductivity of the SE layer. The pressurization of 10 MPa imitates a restraining load for reducing the internal resistance of the battery. Heating to 250 ° C. is carried out to promote the reaction between the current collector and the solid electrolyte component. The results of the obtained resistance measurement are shown in FIG.

In a high temperature environment, copper (Cu), which is a current collector material, easily diffuses and may cause a side reaction with sulfur (S) contained in the SE layer. Therefore, with respect to the electrode plates of Examples 1 and 2 after hot pressing, the cross section in the thickness direction is observed with an electron microscope, and the (a) surface of the SE layer, (b) the center in the thickness direction, and (c) collection. Quantitative analysis of the constituent elements was performed on the electron side. These results are shown in FIG. 4 and Table 1 below. The area surrounded by the square in the observation image of FIG. 4 (Example 1) is the area where the quantitative analysis was performed. In (Example 2), as illustrated by one square, the cross-sectional region without voids is selected as the quantitative analysis region.

As shown in FIG. 3, it was found that the electrode plate of Example 1 began to decrease in resistance within a few minutes under a high temperature and pressurization environment of 250 ° C., and exhibited electron conductivity, that is, a short circuit. From this, it is considered that in the electrode plate of Example 1, Cu used as a current collector at a high temperature diffused into the SE layer to form copper sulfide (for example, CuS) which is a good electric conductor. On the other hand, the electrode plate of Example 2 did not show a significant change in resistance even when held for 1 hour in a high temperature and pressurization environment of 250 ° C., and the electrical insulation property inherent in the SE layer could be maintained. all right.

As shown in FIG. 4, from the microscopic observation of the electrode plate, the SE layer in the electrode plate of Example 1 showed a clear discoloration in the region from the end on the side in contact with the Cu foil to about 191 μm. As shown in Table 1, in the SE layer of the electrode plate of Example 1, more than 50% by mass of Cu was detected from the vicinity of the Cu foil to the vicinity of the center in the thickness direction, and a large amount of Cu was diffused in the discolored region. It turned out that there was.
On the other hand, with respect to the electrode plate of Example 2, no significant change was observed in the SE layer by microscopic observation, and Cu was not detected in the SE layer by qualitative analysis. This result is in good agreement with the result of resistance measurement.
From the above, in the electrode plate of Example 2, the mayenite layer, which is an intermediate layer formed on the surface of the current collector, suppressed the diffusion of Cu even in a high temperature environment of 250 ° C. and prevented the SE layer from being short-circuited. Was confirmed.

For reference, in the electrode plate without the mayenite layer of Example 1, a large amount of CuS was formed up to a position of 191 μm from the electrode plate with a holding time of 1 hour. The diffusion rate of Cu under such conditions is 0.053 μm / s. As an example, assuming that the thickness of the negative electrode active material layer in a standard all-solid-state battery is 40 μm and the thickness of the solid electrolyte layer is 15 μm, such a battery becomes a positive electrode in about 17 minutes when the diffusion rate of Cu is applied. It will be reached. Therefore, it was found that by providing the mayenite layer on the surface of the current collector, it is possible to prevent a short circuit of the all-solid-state battery, which is short-circuited in 17 minutes in a high temperature environment of 250 ° C.

The effects of the present invention have been described in detail above, but the above examples are merely examples. Various modifications and modifications of the above-mentioned specific examples can be applied to the invention disclosed here. For example, in the example shown in FIG. 1, the all-solid-state battery 1 includes only one power generation element, each of which is composed of a stack of a negative electrode 10, a solid electrolyte layer 20, and a positive electrode 30. However, the configuration of the all-solid-state battery 1 is not limited to this. For example, the all-solid-state battery 1 includes a conductive intermediate layer 16 and a negative electrode active material layer 14 on both sides of the negative electrode current collector 12, and a positive electrode active material layer 34 on both sides of the positive electrode current collector 32, and a plurality of negative electrodes. It may be configured to electrically insulate between the 10 and the positive electrode 30 by a plurality of solid electrolyte layers 20. In other words, the all-solid-state battery 1 may include a plurality of power generation elements in a stacked state. Thereby, the high-capacity all-solid-state battery 1 can be easily realized.

1 Sulfide-based all-solid-state battery 10 Negative electrode 12 Negative electrode current collector 14 Negative electrode active material layer 16 Conductive intermediate layer 20 Solid electrolyte layer 30 Positive electrode

Claims (1)

With positive electrode, solid electrolyte layer and negative electrode,
The negative electrode is
With a current collector containing at least one of copper, iron and nickel,
A negative electrode active material layer containing a sulfide solid electrolyte material and a negative electrode active material,
Includes a conductive intermediate layer disposed between the current collector and the negative electrode active material layer.
The conductive intermediate layer is a sulfide-based all-solid-state battery containing a mayenite-type compound.

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