JP2014096351A - Ceramic positive electrode-solid electrolyte assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode-solid electrolyte assembly with low resistance.SOLUTION: A ceramic positive electrode-solid electrolyte assembly comprises: a plate-like positive electrode made of a ceramic sintered compact containing a positive electrode active material with a layered rock salt type structure; a solid electrolyte with lithium ion conductivity; and an interface layer positioned between the plate-like positive electrode and the solid electrolyte, and consisting of a lithium ion conductive complex oxide represented by a formula LiMoOor LiMoO.

Description

  The present invention relates to a positive electrode-solid electrolyte composite, and more particularly to a positive electrode-solid electrolyte composite for an all-solid-state energy storage device.

  In recent years, lithium ion secondary batteries have attracted attention from the viewpoint of high energy density. However, since lithium ion secondary batteries currently widely used are mainly organic electrolytes in which lithium salts are dissolved in flammable organic solvents, it is important to ensure safety against liquid leakage and the like. Yes. On the other hand, an all-solid battery using a solid electrolyte instead of an electrolytic solution has been proposed as a highly safe battery that does not require the use of a flammable organic solvent.

  Patent Document 1 (International Publication No. 2011/132627) discloses an all-solid secondary battery integrated by sintering of a positive electrode layer, a negative electrode layer, and a solid electrolyte layer. This all-solid-state secondary battery is produced by laminating green sheets of a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, and simultaneously sintering the laminate. In order to form an interface with high adhesion by such a simultaneous sintering method, the heat treatment temperature must be increased. As a result, it is difficult to maximize the good functions inherent to each member, such as composition fluctuations caused by element diffusion between layers, and formation of a reaction layer with extremely high resistance in the interface layer. It was.

Non-Patent Literature 1 (Takehisa Kato, 8 others, “Reduction of Li ₇ La ₃ Zr ₂ O ₁₂ / LiCoO ₂ resistance by interface control”, 79th Annual Meeting of the Electrochemical Society, Proceedings P93, 3C13, 2012 (March) discloses that a Li—Nb—O-based material is formed at the interface between the positive electrode and the solid electrolyte as a means for suppressing element diffusion during the heat treatment. However, it is difficult to control the composition of Li—Nb—O-based materials, and the resistance value is sensitive to a shift in composition. For this reason, it is difficult to stably form a low-resistance interface, and further control of the interface is desired.

On the other hand, as a solid electrolyte having lithium ion conductivity, a garnet-type ceramic material having a Li ₇ La ₃ Zr ₂ O ₁₂ (hereinafter referred to as LLZ) composition has attracted attention. For example, Patent Document 2 (Japanese Patent Laid-Open No. 2011-051800) discloses that the addition of Al in addition to Li, La and Zr, which are basic elements of LLZ, can improve the density and lithium ion conductivity. ing. Patent Document 3 (Japanese Patent Laid-Open No. 2011-073962) discloses that lithium ion conductivity can be further improved by adding Nb and / or Ta in addition to Li, La and Zr, which are basic elements of LLZ. ing. Patent Document 4 (Japanese Patent Laid-Open No. 2011-073963) includes Li, La, Zr, and Al, and the density can be further improved by setting the molar ratio of Li to La to 2.0 to 2.5. Is disclosed.

International Publication No. 2011-132627 JP 2011-051800 A JP 2011-073962 A JP 2011-073963 A

Takehisa Kato and 8 others, "Reduction of Li7La3Zr2O12 / LiCoO2 resistance by interface control", 79th Annual Meeting of the Electrochemical Society, Proceedings P93, 3C13, March 2012

  The inventors of the present invention have recently found that a low-resistance positive electrode-solid electrolyte composite can be provided by intentionally forming an interface having a specific composition when joining a positive electrode and a solid electrolyte.

  Accordingly, an object of the present invention is to provide a positive electrode-solid electrolyte composite having low resistance.

According to one aspect of the invention,
A plate-like positive electrode comprising a ceramic sintered body containing a positive electrode active material having a layered rock salt structure;
A solid electrolyte made of a ceramic having lithium ion conductivity;
An interfacial layer comprising a lithium ion conductive composite oxide that is interposed between the plate-like positive electrode and the solid electrolyte and represented by a chemical formula of Li ₂ MoO ₃ or Li ₄ MoO ₅ ;
A ceramic positive electrode-solid electrolyte composite is provided.

It is a schematic cross section which shows the structure of the ceramic positive electrode-solid electrolyte composite by this invention.

Positive - the solid electrolyte composite Figure 1, the ceramic cathode according to the invention - an example of a solid electrolyte composite body is shown schematically. A ceramic positive electrode-solid electrolyte composite 10 shown in FIG. 1 includes a plate-like positive electrode 12 and a solid electrolyte 14. The plate-like positive electrode 12 is made of a ceramic sintered body containing a positive electrode active material having a layered rock salt structure, while the solid electrolyte 14 is made of a ceramic having lithium ion conductivity. Between the plate-like positive electrode 12 and the solid electrolyte 14, there is an interface layer 16 made of a lithium ion conductive composite oxide represented by a chemical formula of Li ₂ MoO ₃ or Li ₄ MoO ₅ . That is, the plate-like positive electrode 12 and the solid electrolyte 14 are indirectly joined through the interface layer 16 having the above composition, and are not joined directly. When the plate-like positive electrode 12 and the solid electrolyte 14 are directly joined, a high-resistance layer having an unintended composition is formed on the interface through a treatment such as firing, and the interface resistance Will rise. When such a positive electrode-solid electrolyte composite having a high interface resistance is used as a battery, the internal resistance of the battery is increased, which is disadvantageous in realizing high-speed charge / discharge. In this respect, in the present invention, the interface layer 16 having the above composition is intentionally formed between the plate-like positive electrode 12 and the solid electrolyte 14, thereby effectively forming a high-resistance layer having an unintended composition. Can be avoided.

The interface layer 16 is made of a lithium ion conductive composite oxide represented by a chemical formula of Li ₂ MoO ₃ or Li ₄ MoO ₅ . With these compositions, it is easy to adopt a crystal structure in which diffusion paths of lithium ions are continuously connected, the lithium ion conductivity of the substance itself is high, and the bonding property between the positive electrode and the solid electrolyte is good. Bring. When a lithium ion secondary battery is formed by integrally bonding the positive electrode active material and the solid electrolyte while intentionally forming an interface layer having such a composition, the internal resistance is reduced while realizing good interface formation. And a high output battery is obtained.

  The interface layer 16 preferably has a thickness of 10 nm to 100 nm, more preferably 10 nm to 70 nm, and still more preferably 10 nm to 50 nm. Within these ranges, a chemically and physically stable interface layer can be formed. When the thickness is 10 nm or more, defects are unlikely to occur as a composite oxide layer, and element diffusion between the positive electrode active material and the solid electrolyte can be preferentially suppressed, resulting in a reduction in interface resistance. Can be realized effectively. Moreover, the raise of the interface resistance accompanying the increase in a diffusion distance can be suppressed as it is the thickness of 100 nm or less.

The plate-like positive electrode 12 is a plate-like material made of a ceramic sintered body containing a positive electrode active material having a layered rock salt structure. The positive electrode active material having a layered rock salt structure is preferably a lithium-transition metal composite oxide. The layered rock salt structure has the property that the redox potential decreases due to occlusion of lithium ions, and the redox potential increases due to elimination of lithium ions. Among these, a composition containing a large amount of Ni is particularly preferable. Here, the layered rock salt structure is a crystal structure in which transition metal layers other than lithium and lithium layers are alternately stacked with an oxygen atom layer interposed therebetween, that is, an ion layer and lithium ions of transition metals other than lithium. Crystal structure in which layers are alternately stacked with oxide ions (typically α-NaFeO ₂ type structure: structure in which transition metal and lithium are regularly arranged in the [111] axis direction of cubic rock salt type structure ). Typical examples of the lithium-transition metal composite oxide having a layered rock salt structure include lithium nickelate, lithium manganate, nickel / lithium manganate, nickel / lithium cobaltate, cobalt / nickel / lithium manganate, cobalt / manganese. Examples of these materials include Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Ag, Sn, and Sb. , Te, Ba, Bi, etc. may further contain one or more elements. A preferred positive electrode active material comprises as a main component a compound selected from the group consisting of lithium cobaltate, nickel-manganese-lithium cobaltate, lithium nickelate, and nickel-cobalt-lithium aluminumate. In addition to being able to obtain high output from the low internal resistance of the positive electrode-solid electrolyte complex, by using these preferred compounds, the average potential for lithium as the negative electrode can be increased, and high capacity density is also obtained. It is done.

  Typically, the positive electrode active material is a polycrystal composed of a plurality of crystal particles, and the plurality of crystal particles are preferably oriented. This orientation is preferably oriented so that the (003) plane of the layered rock salt structure intersects the plate surface (principal surface) of the plate-like positive electrode, more preferably a plane other than (003) ( For example, the (104) plane) is preferably oriented parallel to the plate surface of the plate-like positive electrode. Such an orientation facilitates insertion / removal of ions such as lithium ions, increases ion conductivity, and improves rate characteristics when a power storage element is configured. The degree of orientation in such a plate-like positive electrode is the ratio of the diffraction intensity (peak intensity) of the (103) plane to the diffraction intensity of the (104) plane in the X-ray diffraction from the plate surface of the plate-like positive electrode [003] / [ 104], and a preferable [003] / [104] ratio is 2 or less, more preferably 1 or less, and further preferably 0.5 or less. Note that such a low [003] / [104] ratio means that the ratio of the appearance of the (003) plane parallel to the plate surface in the plate surface or inside of the plate-like positive electrode is reduced.

  The plate-like positive electrode 12 is made of a ceramic sintered body containing a positive electrode active material. This ceramic sintered body may contain an optional component such as a conductive mobilizer in addition to the positive electrode active material, but it is also possible to have a configuration substantially free of such an optional component. For example, in the case of using a positive electrode active material in which crystal particles are oriented, ion mobility can be improved without using a conductive aid or the like, so that the active material filling rate can be maximized. . Accordingly, the plate-like positive electrode 12 preferably consists essentially of the positive electrode active material (consisting essential 1y of), and more preferably consists only of the positive electrode active material (consisting of).

  The plate-like positive electrode 12 and the positive electrode active material constituting the plate-like positive electrode 12 preferably have pores. The presence of pores in the plate-like positive electrode can relieve stress that may be caused by expansion or contraction associated with insertion / extraction of lithium ions due to charge / discharge. Furthermore, the generation | occurrence | production of the crack resulting from the difference in the thermal expansion coefficient produced at the time of joining and a crack is suppressed. As a result, it is possible to effectively prevent peeling at the interface that may occur when the dense plates are joined together. The positive electrode active material preferably has a porosity of 3 to 30%, more preferably 5 to 25%, and still more preferably 10 to 20%. The voidage is a volume ratio of pores (including open pores and closed pores) in the plate-like positive electrode, and is sometimes referred to as porosity, and the bulk density and true density of the plate-like positive electrode It can be calculated from

  Although the dimension of the plate-like positive electrode 12 is not particularly limited, the thickness is preferably 0.1 to 300 μm, more preferably 10 to 200 μm, and still more preferably 50 to 100 μm, from the viewpoint of the active material capacity per unit area. The size of the plate surface is preferably 0.5 mm square to 10 mm square, more preferably 1 mm square to 5 mm square, from the viewpoint of suppressing warpage in the plate surface and ease of electrode production.

  According to a preferred aspect of the present invention, a plurality of plate-like positive electrodes are prepared, and the plurality of plate-like positive electrodes are arranged in a tile shape on the plate-like solid electrolyte. Accordingly, there is an advantage that the active material can be filled in the electrode with higher density.

  The plate-like positive electrode 12 may further be provided with a current collector on the side opposite to the solid electrolyte 14. The current collector may be a film or foil formed of gold, silver, copper, aluminum, nickel or the like, and is formed by, for example, a sputtering method.

The solid electrolyte 14 is made of a ceramic having lithium ion conductivity. Preferred examples of the lithium ion conductive inorganic solid electrolyte are selected from the group consisting of garnet-type or garnet-like ceramic materials, perovskite-type ceramic materials, NASICON-type phosphate ceramics or glass ceramic materials, and nitride-based ceramic materials. There is at least one kind. Of these, garnet type, perovskite type, and NASICON type are preferable. Examples of garnet ceramic material, Li-La-Zr-O-based material _{(specifically,} such as _{Li 7 La 3 Zr 2 O 12} ), the Li-La-Ta-O-based material (specifically, Li ₇ La ₃ Ta ₂ O ₁₂ ) and those described in Patent Documents 2 to 4 can also be used. Among _them, material mainly composed of Li ₇ La ₃ Zr _{2 O 12} is preferable. It is because it does not react with the lithium metal as the negative electrode and high ionic conductivity is obtained. Examples of the perovskite-based ceramic material include Li—La—Ti—O based materials (specifically, LiLa _1-x Ti _x O ₃ (0.04 ≦ x ≦ 0.14) and the like). Examples of phosphoric acid-based ceramic materials include Li-Al-Ti-PO, Li-Al-Ge-PO, and Li-Al-Ti-Si-PO (specifically, Li _{1 + x + y al x Ti 2-x Si y} P 3-y O 12 (0 ≦ x ≦ 0.4,0 <y ≦ 0.6) , and the like). Among these, Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ is preferable because of high ion conductivity. Examples of nitride ceramic materials include Li ₁₃ N, LiPON, and the like.

  Particularly preferred solid electrolyte 14 is (i) a composite oxide composed of at least Li, La, Zr and O and has a garnet-type or garnet-like crystal structure, and (ii) composed of at least Li, Al, Ge, P and O. And (iii) selected from the group consisting of a composite oxide having at least Li, La, Ti and O and having a perovskite crystal structure. These solid electrolytes have high lithium ion conductivity, and can constitute a positive electrode-solid electrolyte complex without impairing material properties due to the effect of the interface layer. The most preferable solid electrolyte is a composite oxide composed of at least Li, La, Zr and O, and has a garnet-type or garnet-like crystal structure, and contains at least one element selected from Al and Mg as an additive, A part of Zr is substituted with at least one element selected from Ta and Nb. The solid electrolyte having this composition can provide a dense ceramic with high lithium ion conductivity, and is excellent in chemical stability with the negative electrode.

A garnet-type or garnet-like crystal structure including Li, La, Zr, and O is called an LLZ crystal structure, and is an X-ray diffraction file No. of CSD (Cambridge Structural Database). It has an XRD pattern similar to 422259 (Li ₇ La ₃ Zr ₂ O ₁₂ ). In addition, No. Compared to 422259, the constituent elements are different and the Li concentration in the ceramics may be different, so the diffraction angle and the diffraction intensity ratio may be different. The molar ratio Li / La of Li to La is preferably 2.0 or more and 2.5 or less, and the molar ratio Zr / La to La is preferably 0.5 or more and 0.67 or less. This garnet-type or garnet-like type crystal structure may further comprise Nb and / or Ta. That is, by replacing a part of Zr of LLZ with one or both of Nb and Ta, the conductivity can be improved as compared with that before the substitution. The substitution amount (molar ratio) of Zr with Nb and / or Ta is preferably set such that the molar ratio of (Nb + Ta) / La is 0.03 or more and 0.20 or less. The garnet-based oxide sintered body preferably further contains Al and / or Mg, and these elements may exist in the crystal lattice or may exist in other than the crystal lattice. The addition amount of Al is preferably 0.01 to 1% by mass of the sintered body, and the molar ratio Al / La to La is preferably 0.008 to 0.12. The addition amount of Mg is preferably 0.01 to 1% by mass or more, and more preferably 0.05 to 0.30% by mass. It is preferable that the molar ratio Mg / La of Mg to La is 0.0016 to 0.07. Such LLZ-based ceramics can be manufactured according to a known technique as described in Patent Documents 2 to 4, or by appropriately modifying it.

  The shape and dimensions of the solid electrolyte 14 are not particularly limited, and may be, for example, a plate shape. The thickness is preferably 0.005 mm to 5 mm, more preferably 0, from the viewpoint of charge / discharge rate characteristics and mechanical strength. 0.005 mm to 2 mm, more preferably 0.01 to 1 mm, and the size of the plate surface is preferably 0.2 mm square to 500 mm square, more preferably 0.5 mm square from the viewpoint of charge / discharge capacity and mechanical strength. ~ 100 mm square.

Manufacturing Method The ceramic positive electrode-solid electrolyte composite of the present invention is formed so that an interface layer made of a lithium ion conductive composite oxide represented by the chemical formula of Li ₂ MoO ₃ or Li ₄ MoO ₅ is formed at the interface. It can be manufactured by any method for joining the electrode-like positive electrode to the solid electrolyte.

For example, the interface layer is formed by forming a ceramic bulk body having a desired composition and performing sputtering using the bulk body as a sputtering target, thereby forming the interface layer having the above composition on the positive electrode or the solid electrolyte. It can be preferably performed. Alternatively, an interface can be formed by a method in which a Mo metal film is formed on a Li-containing solid electrolyte by sputtering or the like, and heat-treated at a temperature lower than the decomposition temperature of the solid electrolyte in an oxidizing atmosphere to obtain an interface layer having the above composition. In this case, since only the surface composition of the solid electrolyte is changed to Li ₂ MoO ₃ or Li ₄ MoO ₅ , the characteristics of the solid electrolyte are not deteriorated.

The plate-like positive electrode and the solid electrolyte are joined by stacking the positive electrode and the solid electrolyte so as to sandwich the interface layer having a composition of Li ₂ MoO ₃ or Li ₄ MoO ₅ formed on the positive electrode or the solid electrolyte, and joining them by hot pressing. This can be preferably performed. Normally, when hot press bonding is attempted without intentionally forming the interface layer, the constituent elements of the positive electrode and the solid electrolyte are interdiffused to provide a high resistance interface, but the interface layer according to the present invention is interposed. As a result, these undesirable diffusions are suppressed, and a good low resistance interface is formed between the positive electrode active material and the solid electrolyte.

It is also possible to form the interface layer simultaneously with the joining of the plate-like positive electrode and the solid electrolyte. For example, a Mo metal film is formed on a plate-like positive electrode, the Mo metal film is oxidized in an oxidizing atmosphere, and an aerosol deposition method, a powder jet deposition method, a thermal spraying method, or the like is applied on the obtained Mo oxide film. Forming an interfacial layer having a composition of Li ₂ MoO ₃ or Li ₄ MoO ₅ while joining a plate-like positive electrode to the solid electrolyte by forming a solid electrolyte film containing Li in bulk and performing heat treatment Can do.

  The present invention is more specifically described by the following examples.

Example 1: Production of NCA ceramic plate An NCA ceramic plate used as a plate-like positive electrode in the present invention was produced by the following procedure.

(1) Slurry preparation 81.6 parts by weight of Ni (OH) ₂ powder (manufactured by Kojundo Chemical Laboratory Co., Ltd.), 15.0 parts by weight of Co (OH) ₂ powder (manufactured by Wako Pure Chemical Industries, Ltd.), and Al _A raw material powder was prepared by weighing 3.4 parts by weight of ₂ O ₃ .H ₂ O powder (manufactured by SASOL). Next, 97.3 parts by weight of pure water, 0.4 part by weight of a dispersant (manufactured by NOF Corporation: Part No. AKM-0521), 0.2 weight of 1-octanol (made by Katayama Chemical Co., Ltd.) as an antifoaming agent Part and a binder (Nippon Vinegar Poval Co., Ltd. product: PV3) 2.0 parts by weight was produced. The vehicle and raw material powder thus obtained were mixed and pulverized in a wet manner to prepare a slurry. This mixing and pulverization was performed by treating for 24 hours with a ball mill using zirconia balls having a diameter of 2 mm and then treating with a bead mill using zirconia beads having a diameter of 0.1 mm for 40 minutes.

(2) Granulation The obtained slurry was put into a two-fluid nozzle type spray dryer to form a granulated body. By appropriately adjusting parameters such as the spray pressure of the spray dryer, the nozzle diameter, and the circulating air volume, it is possible to form granulated bodies of various sizes.

(3) Heat treatment (temporary firing)
The obtained granule was heat-treated at 1100 ° C. for 3 hours (atmospheric atmosphere) to form a composite oxide of nickel, cobalt, and aluminum ((Ni _0.8 , Co _0.15 , Al _0.05 ) O). Positive electrode active material precursor particles, which are particles, were obtained. When the obtained positive electrode active material precursor particles were analyzed as shown below, the average particle diameter D50 (volume basis) was 2.3 μm, the specific surface area was 12 m ² / g, and the relative tap density was 0.00. 3.
<Average particle diameter D50>
By dispersing a powder sample of positive electrode active material precursor particles using water as a dispersion medium into a laser diffraction / scattering particle size distribution measuring apparatus (model number “LA-700” manufactured by Horiba, Ltd.), an average is obtained. The particle size D50 (volume basis) was measured.
<Relative tap density>
After tapping the measuring cylinder containing the powder sample of the positive electrode active material precursor particles 200 times using a commercially available tap density measuring device, the tap density is calculated by calculating (powder weight) / (powder bulk volume). Asked. Thereafter, the relative tap density [dimensional value] was calculated by dividing the obtained tap density by the theoretical density.

(4) Molding 100 parts by weight of the obtained positive electrode active material precursor particle powder, 50 parts by weight of a dispersion medium (xylene: butanol = 1: 1), polyvinyl butyral as a binder (manufactured by Sekisui Chemical Co., Ltd .: product number BM-2) )) 10 parts by weight, DOP as a plasticizer (Di (2-ethylhexyl) phthalate: manufactured by Kurokin Kasei Co., Ltd.), and a dispersant (product name “Reodol SPO-30” manufactured by Kao Corporation) 3 parts by weight are weighed, pre-kneaded in a mortar, and then kneaded using a tri-roll to measure a molding slurry having a viscosity of 2000 to 3000 cP (measured using a Brookfield LVT viscometer). Prepared. A sheet having a thickness of 50 μm was formed by the doctor blade method using the molding slurry thus obtained. By punching the dried sheet, a 1 mm square green sheet molded body was obtained.

(5) Firing (Lithium introduction)
The 1 mm square green sheet molded body obtained as described above was heat-treated at 900 ° C. in an air atmosphere, whereby the molded body was degreased and pre-fired. The temperature of the green body preliminary firing is lower than the above-described heat treatment (granulated body preliminary firing) temperature. This is because lithium is uniformly diffused and reacted during the subsequent main firing by suppressing the progress of sintering between the internal particles during the temporary firing of the molded body.

On the other hand, an ethanol dispersion of lithium hydroxide was prepared as follows. First, LiOH.H ₂ O powder (manufactured by Wako Pure Chemical Industries, Ltd.) was pulverized using a jet mill so as to have a visual particle diameter of 1 to 5 μm by observation with an electron microscope. What added this powder in the ratio of 1 weight part with respect to 100 weight part of ethanol (made by Katayama Chemical Co., Ltd.) was disperse | distributed until it became impossible to confirm powder visually by an ultrasonic wave.

A solution obtained by spraying a predetermined amount of the ethanol dispersion of lithium hydroxide with an airbrush onto both surfaces of the calcined molded body is heat-treated at 750 ° C. for 10 hours (oxygen atmosphere), whereby Li (Ni _0.8 , An NCA ceramic plate having a composition of Co _0.15 , Al _0.05 ) O ₂ was obtained as a plate-like positive electrode. When the obtained plate-like positive electrode was analyzed by the procedure shown below, the porosity was 15%, the open pore ratio was 95%, and the diffraction intensity (peak intensity) ratio [003] / [104] was 0.5. there were.
<Porosity>
The porosity is a value calculated from the relative density (porosity = 1−relative density). The relative density is a value obtained by dividing the bulk density obtained by the Archimedes method by the true density obtained using a pycnometer. In the measurement of the bulk density, the sample was boiled in water in order to sufficiently expel the air present in the voids.
<Open pore ratio>
The open pore ratio is a value obtained by calculation from the closed porosity and the total porosity (open pore ratio = open pores / total pores = open pores / (open pores + closed pores)). The closed porosity is obtained from the apparent density measured by the Archimedes method. The total porosity is determined from the bulk density measured by the Archimedes method.
<Diffraction intensity (peak intensity) ratio>
The diffraction intensity (peak intensity) ratio is measured by placing a ceramic plate for a positive electrode active material layer processed to a size of about φ5 to 10 mm in a sample folder for XRD measurement, and an XRD apparatus (product name “RINT, manufactured by Rigaku Corporation”). -TTRIII ") was used to measure the XRD profile when the surface of the plate-shaped positive electrode was irradiated with X-rays, and the diffraction intensity (003) plane relative to the (104) plane diffraction intensity (peak height) ( This was done by determining the ratio of peak height. According to this measuring method, a diffraction profile can be obtained from a crystal plane parallel to the crystal plane of the plate plane, that is, a crystal plane oriented in the plate plane direction.

Example 2: Production of LLZ ceramics LLZ ceramics used as a solid electrolyte in the present invention were produced by the following procedure.

Lithium hydroxide (Kanto Chemical Co., Inc.), lanthanum hydroxide (Shin-Etsu Chemical Co., Ltd.), zirconium oxide (Tosoh Corp.), and tantalum oxide were prepared as raw material components for preparing the raw material for firing. These powders are weighed and blended so as to be LiOH: La (OH) ₃ : ZrO ₂ : Ta ₂ O ₅ = 7: 3: 1.625: 0.1875, and mixed by a laika machine to be a raw material for firing. Got.

  As the first firing step, the firing raw material was placed in an alumina crucible, heated at 600 ° C./hour in the air atmosphere, and held at 900 ° C. for 6 hours.

As a second firing step, γ-Al ₂ O ₃ is added to the powder obtained in the first firing step so that the Al concentration is 0.08 wt%, and this powder and cobblestone are mixed to form a vibration mill. And milled for 3 hours. After pulverizing this pulverized powder, the obtained powder was press-molded at about 100 MPa using a mold into pellets. The obtained pellets are placed on a magnesia setter, and the whole setter is placed in a magnesia sheath, heated at 200 ° C./hour in an Ar atmosphere, and held at 1000 ° C. for 36 hours to obtain 35 mm × 18 mm. A sintered body having a size of 11 mm and a thickness of 11 mm was obtained, and a LLZ ceramic plate having a size of 10 mm × 10 mm and a thickness of 1 mm was obtained as a solid electrolyte. The Ar atmosphere was prepared by depressurizing the furnace having a capacity of about 3 L in advance and replacing it with Ar gas having a purity of 99.99% or more, and then introducing Ar into the electric furnace at a flow rate of 2 L / min. .

After polishing the upper and lower surfaces of the obtained sintered body sample, various evaluations and measurements shown below were performed. When the X-ray diffraction measurement of the sintered body sample was performed, an X-ray diffraction file No. of CSD (Cambridge Structural Database) was obtained. A crystal structure similar to 422259 (Li ₇ La ₃ Zr ₂ O ₁₂ ) was obtained. From this, it was confirmed that the obtained sample has the characteristics of the LLZ crystal structure. Further, in order to grasp the Al and Mg contents of the sintered body sample, when chemical analysis was performed by inductively coupled plasma emission analysis (ICP analysis), the Al content was 0.08 wt% and the Mg content was 0.07 wt. %Met.

Example 3: Preparation of interface layer Lithium carbonate (Honjo Chemical) and molybdenum oxide (Kanto Chemical) powders were weighed to have a composition of Li ₂ MoO ₃ and mixed dry. The obtained mixed powder was formed into a pellet and fired at 650 ° C. for 12 hours in an air atmosphere to produce a Li ₂ MoO ₃ sintered body. Using the synthesized sintered body as a target, a 0.05 μm film was formed as an interface layer on the solid electrolyte by magnetron sputtering. Thus, an LLZ ceramic plate (solid electrolyte) with an interface layer was obtained.

Example 4: Production of NCA / LLZ composite by hot pressing The thickness of 1 mm square produced in Example 1 was formed on the interface layer of the LLZ ceramic plate with an interface layer having a thickness of 1 mm processed in 10 mm square obtained in Example 3. Nine 50 μm thick NCA ceramic plates were arranged in 3 rows and 3 columns. The upper and lower surfaces of this array are sandwiched between Pt foils for preventing adhesion to a firing jig, fired at 700 ° C. for 5 hours by hot pressing at a pressure of 2000 kgf / cm ² , and an NCA / LLZ composite (with an interface layer) ) In the obtained composite, peeling or the like was not observed at the interface between the NCA ceramic plate (plate-like positive electrode) and the LLZ ceramic plate (solid electrolyte), and it was confirmed that the adhesion was extremely high. It was also confirmed that the NCA ceramic plate (plate-like positive electrode) has a large number of pores.

  For comparison, an NCA / LLZ as a comparative sample was used in the same manner as above except that an LLZ ceramic plate having no interface layer as prepared in Example 2 was used instead of the LLZ ceramic plate with an interface layer. A composite (no interfacial layer) was prepared.

Example 5: Preparation of coin cell and evaluation of internal resistance A positive electrode current collector (thickness: 500 angstroms) was formed by sputtering an Au film on the surface of the NCA ceramic plate of the NCA / LLZ composite produced in Example 4. Formed. Next, in a glove box in an Ar atmosphere, lithium metal was melt bonded to the plate surface of the LLZ ceramic plate at 200 ° C. to obtain a negative electrode. The Au / NCA / interface layer / LLZ / Li joined body and the Au / NCA / LLZ / Li joined body thus obtained were incorporated into a stainless steel CR2032 case to form a coin cell.

In order to measure resistance, the coin cell is taken out into the atmosphere and an AC impedance is measured at a frequency of 1 MHz to 0.01 Hz and a voltage of 10 mV using an electrochemical measurement system (combination of potentiometer / galvano stud and frequency response analyzer manufactured by Solartron). Measurements were made. The arc of the obtained impedance curve was fitted using analysis software (Zview 2 manufactured by Scribner Associates, Inc.), and the interface resistance value was calculated. As a result, when the resistance value of the comparative sample having no interface layer is set to 100 (relative value), the interface resistance value of the sample having the interface layer of Li ₂ MoO ₃ according to the present invention is 0.5 (relative value). Met. In this way, a positive electrode-solid electrolyte composite having a low internal resistance is formed by intentionally forming a lithium ion conductive material capable of suppressing element diffusion at the interface, rather than simply joining the positive electrode and the solid electrolyte. Can realize a solid state battery.

Claims (6)

A plate-like positive electrode comprising a ceramic sintered body containing a positive electrode active material having a layered rock salt structure;
A solid electrolyte made of a ceramic having lithium ion conductivity;
An interfacial layer comprising a lithium ion conductive composite oxide that is interposed between the plate-like positive electrode and the solid electrolyte and represented by a chemical formula of Li ₂ MoO ₃ or Li ₄ MoO ₅ ;
A ceramic positive electrode-solid electrolyte composite comprising:   The ceramic positive electrode-solid electrolyte composite according to claim 1, wherein the interface layer has a thickness of 10 nm to 100 nm.   The positive electrode active material comprises, as a main component, a compound selected from the group consisting of lithium cobaltate, nickel-manganese-lithium cobaltate, lithium nickelate, and nickel-cobalt-lithium aluminum oxide. The ceramic positive electrode-solid electrolyte composite as described.   The ceramic positive electrode-solid electrolyte composite according to any one of claims 1 to 3, wherein the positive electrode active material is a polycrystal formed of a plurality of crystal particles, and the plurality of crystal particles are oriented.   The solid electrolyte is composed of at least Li, La, Zr and O, and is composed of a complex oxide having a garnet type or garnet-like crystal structure, at least Li, Al, Ge, P and O, and has a NASICON type crystal structure. The ceramic positive electrode according to any one of claims 1 to 4, wherein the ceramic positive electrode is selected from the group consisting of a complex oxide and a complex oxide composed of at least Li, La, Ti, and O and having a perovskite crystal structure. Solid electrolyte composite.   The solid electrolyte is composed of at least Li, La, Zr and O, and is a complex oxide having a garnet-type or garnet-like crystal structure, containing at least one element selected from Al and Mg as an additive; and The ceramic positive electrode-solid electrolyte composite according to any one of claims 1 to 5, wherein a part of Zr is substituted with at least one element selected from Ta and Nb.

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