JP6018930B2 - Method for producing positive electrode-solid electrolyte composite - Google Patents

Description

  The present invention relates to a method for producing a positive electrode-solid electrolyte complex, and more particularly to a method for producing a positive electrode-solid electrolyte complex 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.

  For example, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2009-193802) discloses an all-solid battery in which each of a positive electrode current collector, a positive electrode layer, a solid electrolyte layer, a negative electrode layer, and a negative electrode current collector is formed of a green compact. Has been. This green compact all solid state battery has low density of the active material layer and the electrolyte layer, and has a problem in high capacity and rate characteristics. Further, since the bonding interface is not dense, it is considered that the resistance becomes high. In addition, since each member is formed of a green compact, it is understood that a restraining means for pressing these members is required.

  Patent Document 2 (International Publication No. 2011/132627) discloses an all solid state secondary battery in which a positive electrode layer, a negative electrode layer, and a solid electrolyte layer are joined by sintering. 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 obtained green sheet laminate. In order to form an interface with high adhesion by such a simultaneous sintering method, the heat treatment temperature must be increased, and as a result, the interface resistance becomes very high, and each member has a good function inherently. It is difficult to make the best use of.

  Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2009-009897) discloses an all-solid-state thin film battery in which each of a positive electrode layer, a negative electrode layer, and a solid electrolyte layer is formed by a gas phase process. Since this thin-film all-solid battery has few active materials in the electrode, in principle, it is difficult to increase the capacity and the energy density is small. In addition, a reaction layer having a high resistance is formed at the interface during the film forming process, and sufficient capacity and rate characteristics as a battery cannot be obtained.

By the way, as a positive electrode active material layer of a lithium ion secondary battery, a lithium composite oxide sintered body plate has been proposed. For example, Patent Document 4 (Japanese Patent Laid-Open No. 2012-009193) and Patent Document 5 (Japanese Patent Laid-Open No. 2012-009194) have a layered rock salt structure, and have X-ray diffraction with respect to the diffraction intensity by the (104) plane. A lithium composite oxide sintered plate having a diffraction intensity ratio [003] / [104] of (003) plane of 2 or less is disclosed. By adopting such a configuration, in the lithium ion secondary battery, high capacity is realized while maintaining good cycle characteristics. Patent Document 6 (Japanese Patent No. 4745463) discloses a general formula: Li _p (Ni _x , Co _y , Al _z ) O ₂ (where 0.9 ≦ p ≦ 1.3, 0.6 < x ≦ 0.9, 0.1 <y ≦ 0.3, 0 ≦ z ≦ 0.2, x + y + z = 1) and a plate-like particle having a layered rock salt structure is disclosed, and (003) plane Is oriented so as to intersect the plate surface of the particles, so that high capacity and high rate characteristics can be realized simultaneously when used as a positive electrode material of a solid-state lithium secondary battery.

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 7 (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 denseness and lithium ion conductivity. ing. Patent Document 8 (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 9 (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.

JP 2009-193802 A International Publication No. 2011/132627 JP 2009-009897 A JP 2012-009193 A JP 2012-009194 A Japanese Patent No. 4745463 JP 2011-051800 A JP 2011-073962 A JP 2011-073963 A

  In general, the present inventors have laminated a plate-like positive electrode and a plate-like solid electrolyte made of a ceramic sintered body and pressurizing them while heating, thereby enabling bonding at a relatively low temperature and high resistance at the interface. In addition to suppressing the formation of the reaction layer, it has been found that the bonding area can be maximized by increasing the adhesion of the plate-like positive electrode and the plate-like solid electrolyte at the interface.

  Accordingly, an object of the present invention is to enable bonding at a relatively low temperature to suppress the formation of a high-resistance reaction layer at the interface, and to increase the adhesion between the plate-like positive electrode and the plate-like solid electrolyte at the interface, thereby increasing the bonding area. It is an object of the present invention to provide a method for producing a positive electrode-solid electrolyte composite for an all-solid-state energy storage device capable of maximizing the current.

According to one aspect of the present invention, there is provided a method for producing a positive electrode-solid electrolyte composite for an all-solid-state energy storage device, comprising:
Laminating a plate-like positive electrode made of a ceramic sintered body containing a positive electrode active material and a plate-like solid electrolyte made of a ceramic sintered body having ion conductivity to obtain a laminate;
Subjecting the laminate to heating and pressurizing simultaneously to integrate the positive electrode and the solid electrolyte by solid phase reaction; and
A method is provided comprising.

It is the image which observed the cross section of the composite_body | complex obtained in Example 3 by SEM at 1000 time magnification. It is the image which observed the cross section of the composite_body | complex obtained in Example 3 by SEM at the magnification of 5000 time.

Method for Producing Positive Electrode-Solid Electrolyte Complex The method according to the present invention is a method for producing a positive electrode-solid electrolyte complex for an all-solid-state energy storage device. In the present specification, the all solid state storage element is not particularly limited as long as it is an element capable of storing electricity using a solid electrolyte instead of an electrolytic solution, and various capacitors such as a lithium ion capacitor and an electric double layer capacitor, lithium Various secondary batteries such as an ion secondary battery are included. Therefore, the positive electrode-solid electrolyte composite produced by the method of the present invention can be obtained by further providing a suitable negative electrode according to the application and, if desired, a positive electrode current collector and / or a negative electrode current collector. Can function as. For example, when activated carbon is used for the negative electrode, it can function as a capacitor such as a lithium ion capacitor.

  The production method according to the present invention includes a step of obtaining a laminated body by laminating a plate-like positive electrode and a plate-like solid electrolyte, and a step of simultaneously applying heating and pressure to the laminated body and integrating them by a solid phase reaction. The plate-like positive electrode is made of a ceramic sintered body containing a positive electrode active material. The plate-like solid electrolyte is made of a ceramic sintered body having ion conductivity. Thus, since both the plate-like positive electrode and the plate-like solid electrolyte used in the present invention are composed of a ceramic sintered body, they are not a green compact, a green sheet, and a vapor-phase synthetic thin film. In the method of the present invention, the positive electrode and the solid electrolyte can be integrated by solid-phase reaction by simultaneously heating and pressing the laminate of the plate-like positive electrode and the plate-like solid electrolyte made of the ceramic sintered body. it can. The bonding between the sintered ceramics does not require the sintering of powders as required for the lamination of green sheets, thus suppressing the generation of a high-resistance reaction layer that can occur between highly active dissimilar powders. be able to. In addition, the firing temperature can be lowered by simultaneous heating and pressurization as compared with the case of joining by heating alone. Thereby, the production | generation of the highly resistant reaction layer which can be formed in the temperature range with a high sintering temperature can be suppressed. Moreover, the adhesiveness of the joint interface of the composite obtained by simultaneous heating and pressurization is surprisingly high. Thus, according to the method of the present invention, it is possible to bond at a relatively low temperature to suppress the formation of a high-resistance reaction layer at the interface, and to improve the adhesion between the plate-like positive electrode and the plate-like solid electrolyte at the interface. It can be increased to maximize the bonding area. By using the positive electrode-solid electrolyte composite having such characteristics, it is possible to provide an all-solid-state energy storage device having an extremely high capacity while being thin.

  The heating and pressurization according to the present invention are performed at the same time, and may include a stage of pressurization while heating, and there may be a deviation in the timing of heating and pressurization. Examples of methods for performing heating and pressurization simultaneously include hot press method (HP), hot isostatic press method (HIP), and discharge plasma sintering method (SPS). Is preferable because the hot pressing method (HP) is preferable.

Heating is preferably performed at a temperature of 600 to 800 ° C, more preferably 650 to 750 ° C, and even more preferably 675 to 725 ° C. Pressurization is preferably carried out at a pressure of 5~3000kgf / cm ^2, more preferably 500~2500kgf / cm ^2, more preferably 1000~2000kgf / cm ^2. Moreover, it is preferable that the time to reach the target pressure is 0.1 to 10 hours, more preferably 1 to 7 hours, and still more preferably 3 to 5 hours. Furthermore, it is preferable that the timing of the pressurization start is after the end of the temperature raising process in the firing profile. Heating and pressing are preferably performed for 0.05 to 10 hours, more preferably 1 to 8 hours, and further preferably 2 to 5 hours. Within such a range, the generation of a high-resistance reaction layer at the interface can be more reliably suppressed, and the adhesion between the plate-like positive electrode and the plate-like solid electrolyte at the interface can be further enhanced.

Plate positive electrode for use in a plate-like positive electrode present invention is made of a ceramic sintered body containing a positive electrode active material. The positive electrode active material is not particularly limited as long as it can function as an active material in the positive electrode of the all-solid-state energy storage device, but is preferably a lithium-transition metal composite oxide. The positive electrode active material, particularly the lithium-transition metal composite oxide preferably has a layered rock salt structure or a spinel structure, and more preferably has a layered rock salt structure. The layered rock salt structure has a property that the oxidation-reduction potential decreases due to occlusion of lithium ions and the oxidation-reduction potential increases due to elimination of lithium ions, and 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 in between (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 the like. One or more elements such as Sb, Te, Ba, Bi and the like may be further included.

That is, the lithium-transition metal composite oxide is Li _x M1O ₂ or Li _x (M1, M2) O ₂ (where 0.5 <x <1.10, M1 is a group consisting of Ni, Mn, and Co) At least one transition metal element selected from the group consisting of Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Ag, Sn , Sb, Te, Ba and Bi, which is at least one element selected from the group consisting of, and more preferably Li _x (M1, M2) O ₂ and M1 Is Ni and Co, M2 is at least one composition selected from the group consisting of Mg, Al and Zr, more preferably Li _x (M1, M2) O ₂ , where M1 is Ni and Co And M2 is Al. The proportion of Ni in the total amount of M1 and M2 is preferably 0.6 or more in atomic ratio. Any of such compositions can take a layered rock salt structure. A ceramic having a Li _x (Ni, Co, Al) O ₂ -based composition in which M1 is Ni and Co and M2 is Al may be referred to as NCA ceramics. Particularly preferred NCA ceramics have the general formula: Li _p (Ni _x , Co _y , Al _z ) O ₂ (where 0.9 ≦ p ≦ 1.3, 0.6 <x ≦ 0.9, 0.1 <Y ≦ 0.3, 0 ≦ z ≦ 0.2, x + y + z = 1), and has a layered rock salt structure.

  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. This facilitates insertion / removal of ions such as lithium ions, and improves the 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) by the (003) plane to the diffraction intensity by the (003) 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 is made of a ceramic sintered body containing a positive electrode active material. This ceramic sintered body may contain optional components such as a conductive additive and a binder in addition to the positive electrode active material, but it is also possible to have a configuration substantially free of such optional components. . 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 preferably consists essentially of only the positive electrode active material, and more preferably consists only of the positive electrode active material.

The plate-like positive electrode and the positive electrode active material constituting the plate-like positive electrode 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. Moreover, (8.0 × ¹⁰ -6 at NCA ceramics example described later, in the LLZ ceramic 4.0 × ^{10 -6)} difference in thermal expansion coefficient caused during bonding suppressing generation of cracks and cracks due to. 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

The positive electrode active material having such pores is preferably produced from positive electrode active material precursor particles prepared in advance. The positive electrode active material precursor particles are preferably precursor particles that can become a positive electrode active material containing a lithium-transition metal composite oxide having a layered rock salt structure by introducing lithium. Particularly preferred positive electrode active material precursor particles are formed in a substantially spherical shape, and a large number of voids are substantially uniformly provided therein, the average particle diameter D50 (volume basis) is 0.5 to 5 μm, and the specific surface area is 3 ~25m a ² / g, relative tap density is a value obtained by dividing the tap density by the theoretical density of 0.25 to 0.4. When such conditions are satisfied, when the positive electrode active material is generated through the subsequent molding step and firing step (lithium introduction step), the firing environment is stabilized and the lithium introduction (diffusion) state is made uniform, Thereby, the internal fine structure is made as uniform as possible. In addition, the shape stability and crystallographic synthesis degree of the positive electrode active material that is the final object are improved.

  Preferably, the positive electrode active material includes (a) a granulated body containing a large number of plate-like particles of transition metal hydroxide constituting the main raw material of the lithium composite oxide and having a large number of voids provided therein substantially uniformly. A granulating step, and (b) a heat treatment step of forming the positive electrode active material precursor particles by heat-treating the granulated body, and (c) forming a large number of positive electrode active material precursor particles into a predetermined shape. Thus, the molded body is produced by a method having a molding step, and (d) a firing step of firing the compact to produce a lithium composite oxide. The granulation step (a) is preferably a step of forming a granulated body by spray drying a slurry prepared by mixing raw material powder containing a transition metal hydroxide while being pulverized wet. In particular, spray drying using a two-fluid nozzle system can be suitably used. The raw material powder may contain nickel and cobalt hydroxides as transition metal hydroxides. The raw material powder may contain a metal compound other than a transition metal such as an aluminum oxide hydrate or an aluminum hydroxide. The lithium compound can be added at the time of molding or before firing after molding. That is, for example, the lithium compound can be added to the molding slurry described above together with the positive electrode active material precursor particles during molding. Alternatively, a compact that does not contain a lithium compound is temporarily calcined (molded calcined), and then a mixture of the calcined compact and the lithium compound is calcined (main calcining) in two stages (lithium Step) may be performed.

  The dimension of the plate-shaped positive electrode is not particularly limited, but 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 surface is preferably 0.2 mm × 0.2 mm to 10 mm × 10 mm, more preferably 0.5 mm × 0.5 mm to 2 mm × 2 mm from the viewpoint of warpage suppression in the plate surface and ease of electrode production. is there.

  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 may further be provided with a current collector on the side opposite to the solid electrolyte. 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.

Plate-shaped solid electrolyte The plate-shaped solid electrolyte is made of a ceramic sintered body having ion conductivity. As long as charge can be transferred to and from the positive electrode, ions to be conducted are not particularly limited, and may be lithium ions, sodium ions, hydroxide ions, etc., but a preferable solid electrolyte is lithium. It is an inorganic solid electrolyte having ionic conductivity.

Preferable examples of the lithium ion conductive inorganic solid electrolyte include at least one selected from the group consisting of garnet-based ceramic materials, nitride-based ceramic materials, perovskite-based ceramic materials, and phosphate-based ceramic materials. 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 ) can be used, and those described in JP 2011-051800 A, JP 2011-073962 A, and JP 2011-073963 A can also be used. Examples of nitride ceramic materials include Li ₃ N, LiPON, and the like. Examples of the perovskite-based ceramic material include Li-La-Zr-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).

A particularly preferred lithium ion conductive inorganic solid electrolyte is a garnet-based ceramic material in that no reaction occurs even when it is in direct contact with negative electrode lithium. In particular, an oxide sintered body having a garnet type or a garnet type-like crystal structure containing Li, La, Zr and O is excellent in sinterability and easily densified, and has high ionic conductivity. Therefore, it is preferable. A garnet-type or garnet-like crystal structure of this type of composition is called an LLZ crystal structure, and is referred to as 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 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 known methods as described in JP 2011-051800 A, JP 2011-073962 A and JP 2011-073963, or appropriately modified. Can be performed.

  The dimensions of the plate-like solid electrolyte are not particularly limited, but the thickness is preferably 0.005 mm to 5 mm, more preferably 0.01 mm to 2 mm, and still more preferably 0.05, from the viewpoints of charge / discharge rate characteristics and mechanical strength. From the viewpoint of charge / discharge capacity and mechanical strength, 0.2 mm × 0.2 mm to 500 mm × 500 mm is preferable, and 0.5 mm × 0.5 mm to 100 mm × 100 mm is more preferable. It is.

In order to reduce the interfacial resistance between the plate-like positive electrode active material and the plate-like solid electrolyte, the plate-like positive electrode active material and the plate-like solid electrolyte are subjected to a solid phase reaction on the plate-like positive electrode active material or on the plate-like solid electrolyte. Forming a layer made of an element (for example, a thin film made of metal Nb, Ta, Ti or a compound thereof having a thickness of several tens of nanometers or less) that reduces the resistance of the reaction layer formed when integrating with It may be left. The formation method in the case of the Nb compound is not particularly limited, but may be formed by a liquid phase method such as a sputtering method, a vapor phase method such as a CVD method, a sol-gel method, or a coating pyrolysis method. Further, after forming a metal Nb film, it may be compounded by atmospheric heat treatment or the like. For example, in the case of an oxide, it may be formed by once forming a layer made of metal Nb and then heat-treating in an oxidizing atmosphere, or by directly forming a layer made of Nb oxide (for example, Nb ₂ O ₅ ). Also good.

  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 0.3. Met.
<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>
For the measurement of the diffraction intensity (peak intensity) ratio, a ceramic plate for a positive electrode active material layer processed to a size of about φ5 to 10 mm is placed on a sample folder for XRD measurement, and an XRD apparatus (product name “RINT, manufactured by Rigaku Corporation”) is used. -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 ceramic plate An LLZ ceramic plate used as a plate-like solid electrolyte in the present invention was 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. Place the obtained pellets on a magnesia setter, place the setter in a magnesia sheath as shown in Table 1, raise the temperature at 200 ° C./hour in an Ar atmosphere, and hold at 1000 ° C. for 36 hours. Thus, a sintered body having a size of 35 mm × 18 mm and a thickness of 11 mm was obtained, and an LLZ ceramic plate having a size of 10 mm × 10 mm and a thickness of 1 mm was obtained as a plate-like solid electrolyte. As the Ar atmosphere, the inside of the furnace having a capacity of about 3 L was evacuated in advance, and then Ar gas having a purity of 99.99% or more was flowed into the electric furnace at 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: Production of NCA / LLZ composite by hot pressing 1 mm square NCA ceramics plate 1 mm square produced in Example 1 on 10 mm square LLZ ceramics plate produced in Example 2 9 were arranged so as to be in 3 rows and 3 columns. The upper and lower surfaces of this array were sandwiched between Pt foils for preventing adhesion to a firing jig, and fired at 700 ° C. for 5 hours under a pressure of 2000 kgf / cm ² with a hot press to obtain an NCA / LLZ composite. When the cross section of the obtained composite was observed by SEM at a magnification of 1000 times and 5000 times, the images shown in FIGS. 1 and 2 were obtained, respectively. As can be seen from these figures, in the obtained composite, no peeling or the like is observed at the interface between the NCA ceramic plate (plate-like positive electrode) 1 and the LLZ ceramic plate (plate-like solid electrolyte) 2, and the adhesion is extremely good. Was confirmed to be high. It was also confirmed that the NCA ceramic plate (plate-like positive electrode) 1 has a large number of pores. Furthermore, no reaction-like layer that could be high resistance at the interface was observed.

Example 4 Production of Coin Cell A positive electrode current collector (thickness: 500 Å) was formed by sputtering an Au film on the NCA ceramic plate of the NCA / LLZ composite produced in Example 3. 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 / LLZ / Li joined body thus obtained was assembled in a stainless steel CR2032 case to obtain a coin cell.

Example 5 (Comparison): Preparation of NCA / LLZ Composite and Coin Cell by Sintering Green Powder A green compact of powder obtained by pulverizing the NCA ceramics plate prepared in Example 1 to an average particle size of 0.1 μm, and an example The LLZ ceramic plate produced in No. 2 was prepared as a green compact that was pulverized to an average particle size of 0.1 μm. These green compacts were stacked and fired at 900 ° C. for 5 hours to produce an NCA / LLZ composite as a comparative sample. As a result of cross-sectional observation of this comparative sample, it was confirmed that both the NCA portion and the LLZ portion were sufficiently densified, and the NCA portion and the LLZ portion were joined. A coin cell as a comparative sample was produced using the obtained NCA / LLZ composite in the same manner as in Example 4.

Example 6: Impedance evaluation and rate characteristic evaluation The coin cell produced in Examples 4 and 5 is taken out into the atmosphere, and an electrochemical measurement system (a combination of a potentio / galvano stud and a frequency response analyzer manufactured by Solartron) is used, and a frequency of 1 MHz to AC impedance measurement was performed at 0.01 Hz and a voltage of 10 mV. The obtained arc of the impedance curve was fitted using analysis software (Zview 2 manufactured by Scribner Associates, Inc.) to obtain an impedance resistance value. As a result, the impedance of the sample according to the present invention obtained in Example 4 was 1500 Ω · cm ² , while the impedance of the comparative sample obtained in Example 5 was 5000000 Ω · cm ² . Thus, in the coin cell using the NCA / LLZ composite produced by the method of the present invention, the impedance of the produced battery was significantly lower than that of the comparative sample NCA / LLZ composite. Moreover, in the battery using the NCA / LLZ composite of the present invention, the rate characteristics during charge / discharge were good.

Claims (24)

A method for producing a positive electrode-solid electrolyte composite for an all-solid-state energy storage device, comprising:
Laminating a plate-like positive electrode made of a ceramic sintered body containing a positive electrode active material and a plate-like solid electrolyte made of a ceramic sintered body having ion conductivity to obtain a laminate;
Subjecting the laminate to heating and pressurizing simultaneously to integrate the positive electrode and the solid electrolyte by solid phase reaction; and
Ri name contains,
The method, wherein the positive electrode consists only of the positive electrode active material .   The method according to claim 1, wherein the heating and pressing are performed by a hot press method. The method according to claim 1, wherein the heating and pressurization are performed at a temperature of 600 to 800 ° C. and a pressure of 5 to 3000 kgf / cm ² . The method according to claim 1, wherein the heating and pressurization are performed at a temperature of 600 to 750 ° C. and a pressure of 500 to 2500 kgf / cm ² . The method according to any one of claims 1 to 3 , wherein the heating and pressurization are performed at a temperature of 675 to 725 ° C and a pressure of 5 to 3000 kgf / cm ² . The method according to claim 1, wherein the heating and pressurization are performed at a temperature of 675 to 725 ° C. and a pressure of 1000 to 2000 kgf / cm ² .   The method according to any one of claims 1 to 6, wherein the heating and pressurization are performed for 0.05 to 10 hours. The method according to any one of claims 1 to 7 , wherein the positive electrode active material is a lithium-transition metal composite oxide. The method according to any one of claims 1 to 8 , wherein the positive electrode active material has a layered rock salt structure or a spinel structure. The method according to any one of claims 1 to 9 , wherein the positive electrode active material has a layered rock salt structure. The lithium-transition metal-based composite oxide is Li _x M1O ₂ or Li _x (M1, M2) O ₂ (wherein 0.5 <x <1.10, M1 is a group consisting of Ni, Mn, and Co). At least one selected transition metal element, M2 is Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Ag, Sn, The method according to any one of claims 8 to 10 , which has a composition represented by (at least one element selected from the group consisting of Sb, Te, Ba and Bi). The composition of the lithium-transition metal composite oxide is represented by Li _x (M1, M2) O ₂ , M1 is Ni and Co, and M2 is at least one selected from the group consisting of Mg, Al and Zr. The method of claim 11 , wherein: The method according to claim 11 or 12 , wherein a composition of the lithium-transition metal-based composite oxide is represented by Li _x (M1, M2) O ₂ , M1 is Ni and Co, and M2 is Al. The method according to any one of claims 11 to 13 , wherein the proportion of Ni in the total amount of M1 and M2 is 0.6 or more in atomic ratio. The method according to any one of claims 1 to 14 , wherein the positive electrode active material is a polycrystal composed of a plurality of crystal particles, and the plurality of crystal particles are oriented. The positive active material has a porosity, the method according to any one of claims 1 to 15. The method according to claim 16 , wherein the positive electrode active material has a porosity of 3 to 30%. The method according to claim 16 or 17 , wherein the volume ratio of open pores to all pores is 70% or more. Wherein the solid electrolyte has lithium-ion conductivity, the method according to any one of claims 1 to 18. The method according to any one of claims 1 to 19 , wherein the solid electrolyte is a garnet-based ceramic material. 21. The method according to claim 20 , wherein the garnet-based ceramic material is an oxide sintered body having a garnet-type or garnet-like crystal structure including at least Li, La, Zr, and O. The method according to claim 21 , wherein the garnet-type or garnet-like crystal structure further comprises Nb and / or Ta. The method according to claim 21 or 22 , wherein the oxide sintered body further contains Al and / or Mg. The method according to any one of claims 1 to 23 , wherein a plurality of the 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.