JP6688460B2 - Positive electrode for all-solid-state lithium secondary battery, manufacturing method thereof, and all-solid-state lithium secondary battery including the same - Google Patents

Description

  The present invention relates to a lithium secondary battery electrode having a nano-hetero structure, a method for manufacturing the same, and a lithium secondary battery including the same.

  A lithium secondary battery is known as a secondary battery having a high energy density and has been conventionally used as a power source for various electronic devices. However, conventional lithium secondary batteries are not always sufficient in output characteristics, for example, discharge capacity, and there has been a demand for lithium secondary batteries having higher output characteristics.

  The electrode used in such a lithium secondary battery has conventionally been formed by mixing electrode material powder of several μm to several tens of μm with a conductive material such as carbon, a conductive auxiliary agent, a binder, a solvent, etc. Then, the paste is applied onto a current collector, dried, and pressure-molded if necessary. However, since the binder inhibits the conduction of lithium ions and electrons in the electrode manufactured using the binder, it is necessary to add a large amount of a conductive material or a conductive auxiliary agent, and such an electrode is provided as a positive electrode. The lithium secondary battery has a problem of low discharge capacity.

Japanese Unexamined Patent Application Publication No. 2014-179238 (Patent Document 1) discloses that Li ₇ La ₃ Zr ₂ O ₁₂ and LiCoO ₂ are contained in a matrix composed of one inorganic component of Li ₇ La ₃ Zr ₂ O ₁₂ and LiCoO ₂ . Lithium consisting of a nano-heterostructure in which the other inorganic component is arranged three-dimensionally and periodically and at least a part of which has a three-dimensional periodic structure having a length of one unit of a predetermined repeating structure. An electrode material for a secondary battery is disclosed, and it is also disclosed that a member for a lithium secondary battery in which these electrode materials and an electrically conductive material such as an aluminum plate are integrated can be manufactured by press molding. However, when an electrode provided with a positive electrode material composed of the nano-heterostructure and an aluminum current collector is manufactured by cold pressing, a large gap is likely to occur in the positive electrode material, variation in the discharge capacity of the battery occurs, and the stability of the battery is improved. Was sometimes lowered.

JP, 2014-179238, A

  The present invention has been made in view of the above problems of the prior art, and has an electrode having a nano-hetero structure and capable of increasing the discharge capacity of a lithium secondary battery, a method for manufacturing the electrode, and the electrode. It is intended to provide a lithium secondary battery.

The inventors of the present invention provide a nano-heterostructure powder having a predetermined three-dimensional periodic structure formed of Li ₇ La ₃ Zr ₂ O ₁₂ and LiCoO ₂ on at least a part of the surface of an aluminum current collector. After dropping the dispersion liquid and drying to dryness by natural drying to form an aggregate of the nanoheterostructure powder, after warm pressure molding a laminate including the aggregate of the nanoheterostructure powder and an aluminum current collector It was found that an electrode with improved battery stability can be obtained by subjecting the obtained pressure-molded body to annealing treatment. However, the discharge capacity of the lithium secondary battery provided with this electrode is not always sufficiently high.

  Therefore, as a result of intensive studies to achieve the above-mentioned object, the present inventors have used a nickel current collector as a current collector in the above-described method for manufacturing an electrode, thereby improving the discharge capacity of a lithium secondary battery. The inventors have found that an electrode capable of increasing the electric field can be obtained, and completed the present invention.

That is, the positive electrode for an all-solid-state lithium secondary battery of the present invention comprises Li ₇ La ₃ Zr ₂ O ₁₂ and LiCoO _{2 in} a matrix composed of one inorganic component of Li ₇ La ₃ Zr ₂ O ₁₂ and LiCoO ₂ . The other inorganic component is arranged three-dimensionally and periodically, and at least partly has a three-dimensional periodic structure in which the average value of the length of one unit of the repeating structure is 1 nm to 100 nm. A positive electrode material composed of a nanoheterostructure and having an electrode density of 1.5 to 3.5 g / cm ³ , a nickel current collector, and a thickness of 1 to 3 μm, and one surface of the positive electrode material is in contact with the positive electrode material. And a NiO layer having the other surface in contact with the nickel current collector.

Further, the all-solid-state lithium secondary battery of the present invention is characterized by including such a positive electrode of the present invention.

The method for producing a positive electrode for an all-solid-state lithium secondary battery according to the present invention comprises: Li ₇ La ₃ Zr ₂ O ₁₂ and LiCoO _{2 in} a matrix composed of one inorganic component of Li ₇ La ₃ Zr ₂ O ₁₂ and LiCoO _2. The other inorganic component is arranged three-dimensionally and periodically, and at least a part thereof has a three-dimensional periodic structure in which the average value of the length of one unit of the repeating structure is 1 nm to 100 nm. A step of dispersing the nanoheterostructure powder in a solvent, a dispersion of the nanoheterostructure powder obtained in the step is dropped onto a nickel current collector, and the nanoheterostructure powder is dried to dryness by natural drying, A step of forming an aggregate of the nanoheterostructure powder on the surface of the nickel current collector, and an aggregation of the nickel current collector and the nanoheterostructure powder obtained in the step A step of warm press-molding a laminated body composed of a body and a pressure of 500-2000 MPa at a temperature of 20-150 ° C., and a pressure-molded body obtained in the above step, under atmospheric pressure, 400-800 ° C. And a step of performing heat treatment at the temperature of 1. In such a method for producing a positive electrode for an all-solid lithium secondary battery of the present invention, it is preferable that the heat treatment of the pressure-molded body is performed in a nitrogen atmosphere.

  The reason why the discharge capacity of the lithium secondary battery can be increased by the lithium secondary battery electrode of the present invention is not always clear, but the present inventors speculate as follows. That is, in the method for producing an electrode for a lithium secondary battery of the present invention, a dispersion liquid of a predetermined nano-heterostructure powder is dropped on the surface of a nickel current collector, and the nano-heterostructure powder is dried to dryness by natural drying. An aggregate of the nano-heterostructure powders stacked without any gap is formed. By performing warm pressure molding of such an aggregate of the nano-heterostructure powder, the nano-heterostructure powder is densely aggregated, and a large gap is not easily formed between the aggregated powders. It is estimated that the discharge capacity of the battery can be increased. Further, in the method for producing an electrode for a lithium secondary battery of the present invention, a nickel current collector is used as the current collector. This nickel current collector is annealed to form a crystallized NiO layer on its surface (in the present invention, an interface with the positive electrode material composed of the nanoheterostructure) by heating. In this NiO layer, the activity of the particles in the part in contact with the inorganic component of the nanoheterostructure becomes high (nonstoichiometric compound), and a solid solution state in which lithium is incorporated in the crystal lattice is formed. (Li can be dissolved in about 15% as a solid solution), the conductivity changes, the property of the semiconductor is expressed, and the electron transfer is also possible, so it is presumed that the discharge capacity of the lithium secondary battery can be increased. It

  The "average value of the length of one unit of the repeating structure" in the present invention means the average of the distances between the centers of adjacent ones of the other inorganic components arranged in the matrix composed of one inorganic component. It is a value and corresponds to the so-called periodic structure interval (d). The interval (d) of the periodic structure is obtained by small angle X-ray diffraction as follows. Further, the spherical, columnar, gyroid-shaped, or layered structure according to the present invention can be defined by a characteristic diffraction pattern measured by small-angle X-ray diffraction as follows.

  That is, by small-angle X-ray diffraction, Bragg reflection from a characteristic lattice plane of a pseudo-crystal lattice in which spherical, columnar, gyroid-shaped, layered, and other structures are periodically arranged in a matrix is observed. At that time, a diffraction peak is observed when a periodic structure is formed, and a spherical, columnar, gyroid-shaped, or layered structure should be specified from the ratio of the size (q = 2π / d) of the diffraction spectra. You can Further, the interval (d) of the periodic structure can be obtained from the peak position of the diffraction peak by the Bragg equation (nλ = 2d sin θ; λ is the X-ray wavelength, θ is the diffraction angle). Table 1 below shows the relationship between each structure and the ratio of the size (q) of the diffraction spectrum at the peak position. Note that it is not necessary to confirm all the peaks shown in Table 1, as long as the structure can be specified from the observed peaks.

  Further, such a spherical, columnar, gyroid, or layered structure can also be specified by using a transmission electron microscope (TEM), whereby the shape or periodicity can be discriminated and evaluated. it can. Furthermore, it is possible to discriminate the three-dimensionality in more detail by observing from various directions and using three-dimensional tomography.

  According to the present invention, it is possible to obtain an electrode having a nano-hetero structure and capable of increasing the discharge capacity of a lithium secondary battery.

It is a graph which shows the relationship between the pressure at the time of warm pressure molding in the reference example 1 and the comparative reference examples 1-2, and the density of the positive electrode material in the obtained pressure molding. 3 is a scanning electron micrograph showing a cross section of the pressure-molded body obtained in Comparative Reference Example 1. 3 is a scanning electron micrograph showing a cross section of the pressure-molded body obtained in Comparative Reference Example 1. 6 is a scanning electron micrograph showing a cross section of an electrode manufactured according to the method described in Patent Document 1. 3 is a scanning electron micrograph showing the analysis result of the electrode manufactured in Example 1 by energy dispersive X-ray spectroscopy. 5 is a scanning electron micrograph showing an analysis result of an electrode manufactured in Comparative Example 1 by energy dispersive X-ray spectroscopy. 5 is a scanning electron micrograph showing an analysis result of an electrode manufactured in Comparative Example 3 by energy dispersive X-ray spectroscopy. 7 is a graph showing the relationship between the thickness of the positive electrode material of the electrodes manufactured in Example 1 and Comparative Examples 1 to 6 and the discharge capacity. It is a graph which shows the relationship between the thickness of the positive electrode material of the electrode produced in Examples 2-4, and Comparative Examples 7-15 and discharge capacity.

  Hereinafter, the present invention will be described in detail with reference to its preferred embodiments.

First, the electrode for a lithium secondary battery of the present invention will be described. The electrode for a lithium secondary battery of the present _{invention, Li 7 La 3 Zr 2 O} 12 and matrix of the one inorganic component of the _{LiCoO 2 Li 7 La 3 Zr 2} O 12 and other of LiCoO ₂ of From a nanoheterostructure in which inorganic components are arranged three-dimensionally and periodically, and which has at least a part of a three-dimensional periodic structure in which the average value of the length of one unit of the repeating structure is 1 nm to 100 nm And a positive electrode material having an electrode density of 1.5 to 3.5 g / cm ³ , a nickel current collector, and a thickness of 1 to 3 μm. One surface is in contact with the positive electrode material and the other surface is And a NiO layer that is in contact with the nickel current collector.

The nanoheterostructure according to the present invention has a nanostructure such as a spherical structure, a columnar structure, a gyroid structure, and a layered structure (preferably a columnar structure, a gyroid structure, and a layered structure), and Li ₇ La ₃ With respect to the combination of Zr ₂ O ₁₂ and LiCoO ₂ , it is possible to obtain a nanoheterostructure having various arrangements, compositions, structural scales, and the like controlled. Therefore, according to the nano-heterostructure of the present invention, the effect of increasing the interface, the nano-size effect, the durability, etc. can be dramatically improved, and the utilization rate as the electrode material for a lithium secondary battery can be increased. In addition, the nanoheterostructure according to the present invention has a large reaction interface area due to the nanostructure and smooth charge transfer, thus improving output characteristics. As a result, in the lithium secondary battery including the positive electrode material made of the nanoheterostructure according to the present invention, the storage battery characteristics are dramatically improved.

Li ₇ La ₃ Zr ₂ O ₁₂ (hereinafter, abbreviated as “LLZO”) constituting the nanoheterostructure according to the present invention functions as a lithium ion conductor of a positive electrode material, and LiCoO ₂ (hereinafter, “LCO”). Abbreviated) functions as the positive electrode active material of the positive electrode material. Therefore, the nanoheterostructure according to the present invention functions as a positive electrode material for a lithium secondary battery.

  In the nano-heterostructure according to the present invention, either LLZO or LCO may form a nano-heterostructure matrix, but from the viewpoint that the discharge capacity per volume or mass of the positive electrode material can be maximized, LCO It is preferable to form a matrix. In addition, the cross-sectional diameter of the inorganic components that are three-dimensionally and periodically arranged in the matrix is 5 to 90 nm from the viewpoint that it is difficult to form a conductive path if it is too small and the interface decreases if it is too large. preferable. Further, as a ratio of LLZO and LCO, it is preferable that LLZO is 0.05 to 0.1 mol per mol of LCO. If the proportion of LLZO deviates from the above range, the discharge capacity tends to decrease.

The positive electrode material according to the present invention is composed of such a nanoheterostructure, and its density (electrode density) is 1.5 to 3.5 g / cm ³ . When the density of the positive electrode material is less than the above lower limit, the electric resistance increases or the electrode strength decreases. On the other hand, in order to obtain a positive electrode material having a density exceeding the upper limit, it is necessary to increase the molding pressure during warm pressure molding, but when the molding pressure is increased, the aggregated primary particles are destroyed and the positive electrode material is destroyed. A large number of cracks are generated inside and the electric resistance increases. Further, the density of the positive electrode material is preferably 2.5 to 3.0 g / cm ³ from the viewpoint that the electrode resistance decreases and the electrode strength increases.

  The thickness of the positive electrode material according to the present invention is not particularly limited, but is preferably 5 to 100 μm, more preferably 10 to 50 μm. When the thickness of the positive electrode material is less than the lower limit, the proportion of the positive electrode in the lithium secondary battery decreases, and the discharge capacity tends to decrease. On the other hand, when the thickness exceeds the upper limit, the lithium conductivity in the positive electrode material decreases. Tend to do.

  The nickel current collector according to the present invention is not particularly limited, and a conventionally known nickel current collector can be used. The thickness of such a nickel current collector is not particularly limited, but is preferably 50 to 1000 μm, more preferably 100 to 500 μm. If the thickness of the nickel current collector is less than the lower limit, it tends to be difficult to obtain a positive electrode material having a predetermined electrode density by warm pressure molding, while if it exceeds the upper limit, a positive electrode material is obtained. Adhesion tends to decrease. The nickel current collector can improve the adhesion with the positive electrode material by subjecting the surface of the nickel current collector to phosphoric acid treatment.

  The lithium secondary battery electrode of the present invention includes such a positive electrode material and a nickel current collector, and further includes a NiO layer between the positive electrode material and the nickel current collector. One surface of the NiO layer is in contact with the positive electrode material, and the other surface is in contact with the nickel current collector. It is considered that such a NiO layer can increase the discharge capacity of the lithium secondary battery due to the fact that it has a non-stoichiometric compound or semiconductor property and has a strong fixing function with the positive electrode material.

  The NiO layer according to the present invention has a thickness of 1 to 3 μm. When the thickness of the NiO layer is less than the lower limit, when the thickness is less than the lower limit, the function becomes small, and thus the discharge capacity of the lithium secondary battery cannot be increased. On the other hand, the NiO layer exceeding the upper limit cannot be formed by heat treatment.

  The lithium secondary battery of the present invention includes such an electrode of the present invention as a positive electrode and has a high discharge capacity. Examples of such a lithium secondary battery include a lithium secondary battery in which an electrolyte is sandwiched between the electrode of the present invention and a counter electrode. As the counter electrode and the electrolyte, known ones can be used.

Further, the discharge capacity of the lithium secondary battery of the present invention tends to depend on the thickness of the positive electrode material forming the electrode. That is,
When the thickness of the positive electrode material is 10 μm or more and less than 15 μm, the discharge capacity is 45 mAh / g or more,
When the thickness of the positive electrode material is 15 μm or more and less than 25 μm, the discharge capacity is 40 mAh / g or more,
When the thickness of the positive electrode material is 25 μm or more and less than 30 μm, the discharge capacity is 35 mAh / g or more,
When the thickness of the positive electrode material is 30 μm or more and less than 35 μm, the discharge capacity is 30 mAh / g or more,
When the thickness of the positive electrode material is 35 μm or more and less than 45 μm, the discharge capacity is 25 mAh / g or more,
When the thickness of the positive electrode material is 45 μm or more and less than 50 μm, the discharge capacity is 20 mAh / g or more,
When the thickness of the positive electrode material is 50 μm or more and less than 55 μm, the discharge capacity is 15 mAh / g or more,
When the thickness of the positive electrode material is 55 μm or more and less than 60 μm, the discharge capacity is 10 mAh / g or more,
When the thickness of the positive electrode material is 60 μm or more, the discharge capacity is 5 mAh / g or more,
Tends to be.

Next, a method for manufacturing the electrode for a lithium secondary battery of the present invention will be described. The method for producing an electrode for a lithium secondary battery of the present invention,
Li ₇ La ₃ Zr ₂ O ₁₂ and other inorganic components are three-dimensionally and periodically arranged among the matrix of the inorganic components of _Li 7 _La 3 _Zr 2 _{O 12} and LiCoO ₂ of one of LiCoO ₂ And the step of dispersing the nano-heterostructure powder having a three-dimensional periodic structure in at least a part of which the average value of the length of one unit of the repeating structure is 1 nm to 100 nm in a solvent (dispersion liquid preparation step ) And the dispersion liquid of the nano-heterostructure powder obtained in the step is dropped on a nickel current collector, and the nano-heterostructure powder is dried to dryness by natural drying, and the nano-hetero structure is formed on the surface of the nickel current collector. A step of forming an aggregate of the structure powder (laminate forming step), and a product including the nickel current collector obtained in the step and the aggregate of the nano-heterostructure powder. A step (warm pressure molding step) of warm pressure molding the layered body at a temperature of 20 to 150 ° C. and a pressure of 500 to 2000 MPa, and 400 to 800 ° C. to the pressure molded body obtained in the above step. And a step of performing heat treatment at a temperature (annealing step).

[Dispersion liquid preparation process]
This step is a step of dispersing the nanoheterostructure powder described below in a solvent to prepare a dispersion liquid of the nanoheterostructure powder.

  The nano-heterostructure powder used in the present invention has a matrix composed of one inorganic component of LLZO and LCO in which the other inorganic component of LLZO and LCO is arranged three-dimensionally and periodically, and repeatedly. It is a powder of a nano-heterostructure having a three-dimensional periodic structure having an average value of one unit of structure of 1 nm to 100 nm in at least a part thereof.

  Such nano-heterostructure powder can be obtained by pulverizing the nano-heterostructure manufactured according to the method described in JP-A-2014-179238. The pulverization method is not particularly limited, and examples thereof include a method using various pulverizers such as a jet mill, a roll mill, a ball mill and a mortar.

  In the present invention, the average primary particle diameter of the nanoheterostructure powder is preferably 20 to 100 nm, more preferably 30 to 60 nm. When the average primary particle diameter of the nano-heterostructure powder is less than the lower limit, the fine crystal component accompanied by an amorphous portion tends to increase, and the functions of LLZO and LCO tend to decrease. There is a tendency that only the surface of the structure powder is used and the inside cannot be used.

  The solvent used in the present invention is not particularly limited as long as it can uniformly disperse the nano-heterostructure to be used, and alcohol (eg, ethanol, propanol, butanol), ether (eg, ethyl methyl ether), ketone ( Examples thereof include methyl ethyl ketone), toluene, cyclohexane, and the like, and mixed solvents thereof.

  In the dispersion liquid of the nanoheterostructure powder used in the present invention, the concentration of the nanoheterostructure powder is preferably 0.05 to 0.5 g / ml, more preferably 0.1 to 0.3 g / ml. When the concentration of the nano-heterostructure powder is less than the lower limit, the suspended and suspended nano-heterostructure powder tends to be in a colloidal state, while when it exceeds the upper limit, the precipitated nano-heterostructure powder increases and floats. There is a tendency for a density difference to occur between the nano heterostructure powder and the nanoheterostructure powder. Therefore, when increasing the thickness of the positive electrode material, it is preferable to repeat the following laminated body forming step.

[Laminate formation process]
The step concerned forms the aggregate of the said nano-heterostructure powder on the surface of the said nickel electrical power collector demonstrated below, and produces the laminated body of the said nickel electrical power collector and the aggregate of the said nano-heterostructure powder. It is a process to do.

  First, the dispersion liquid of the nano-heterostructure powder prepared in the step is dropped on the nickel current collector. As a result, a film of the dispersion liquid of the nanoheterostructure powder is formed on the surface of the nickel current collector. Then, the film of the dispersion liquid of the nanoheterostructure powder thus formed is naturally dried to evaporate the nanoheterostructure powder to dryness. As a result, an aggregate in which the nanoheterostructure powders are stacked without a gap is formed on the surface of the nickel current collector. When an aggregate in which such nano-heterostructure powders are piled up without a gap is subjected to warm pressure molding described later, a dense positive electrode is formed with few voids, and the discharge capacity of the lithium secondary battery is increased. Is possible.

  Further, in this step, the thickness of the positive electrode material can be increased by repeatedly dropping the dispersion liquid of the nanoheterostructure powder and evaporating and drying the nanoheterostructure powder.

[Warm pressure molding process]
The step is such that the laminate of the nickel current collector and the aggregate of the nano-heterostructure powder is subjected to warm pressure molding, and the positive electrode and the nickel current collector made of the aggregate of the nano-heterostructure powder. It is a step of producing a pressure-molded body including.

  The laminated body produced in the above step is subjected to warm pressure molding. As a result, a dense positive electrode with few voids is formed, and the discharge capacity of the lithium secondary battery can be increased.

  The temperature during warm pressure molding is 20 to 150 ° C. When the temperature at the time of warm pressure molding is lower than the lower limit, the fluidity of the nano-heterostructure powder is lowered and the moldability is deteriorated. On the other hand, when the temperature is higher than the upper limit, the temperature of the molding die is kept uniform. It may not be possible, or the lubricant that adheres to the gap between the male and female of the mold may seize and cease to function. From the viewpoint of ensuring the fluidity and moldability of the nanoheterostructure, the temperature during warm pressure molding is preferably 100 to 150 ° C, more preferably 130 to 150 ° C.

  The pressure during warm pressure molding is 500 to 2000 MPa. If the pressure during warm press molding is less than the lower limit, the positive electrode material is not formed, while if it exceeds the upper limit, the density of the positive electrode material is significantly reduced. Further, from the viewpoint that a high-density positive electrode material can be obtained, the pressure during warm pressure molding is preferably 700 to 1500 MPa, more preferably 800 to 1200 MPa.

[Annealing process]
In this step, the pressure-molded body produced in the above step is subjected to heat treatment (annealing treatment) under atmospheric pressure to obtain an electrode including the positive electrode material, the nickel current collector, and the NiO layer. is there. Further, by this heat treatment (annealing treatment), the gap between the nano-heterostructure powders in the pressure-molded body can be reduced, and a positive electrode material having a predetermined electrode density can be obtained.

  The temperature of such heat treatment (annealing treatment) is preferably 400 to 800 ° C, more preferably 500 to 800 ° C, and particularly preferably 700 to 800 ° C. When the temperature of the heat treatment (annealing treatment) is lower than the lower limit, sintering in the gap between the nanoheterostructure powders (aggregation of particles) in the pressure-molded body tends not to proceed, while the upper limit is exceeded. Then, the LCO changes to another oxide, and the function of the LCO that stores lithium ions tends to disappear.

  Further, the heat treatment (annealing treatment) needs to be performed under atmospheric pressure. When the heat treatment (annealing treatment) is performed under pressure, that is, when the hot press treatment is performed, the fluidity of the nano-heterostructure powder increases, but the shape change etc. when released from the charged state does not occur. Since it becomes stable (spring back), the discharge capacity of the lithium secondary battery tends to decrease.

  The heat treatment (annealing treatment) may be performed in an oxygen atmosphere or a nitrogen atmosphere, but it is preferably performed in a nitrogen atmosphere from the viewpoint of forming a stable NiO layer.

  As described above, the nickel current collector and the assembly of the nano-heterostructures are integrated and warm-pressed to provide a dense positive electrode material, and a stable interface is provided between the nickel current collector and the positive electrode material. It is possible to obtain an electrode having the following, and it is possible to increase the discharge capacity of the lithium secondary battery.

  Hereinafter, the present invention will be described more specifically based on Examples and Comparative Examples, but the present invention is not limited to the following Examples. The nanoheterostructure powders used in Examples and Comparative Examples were prepared by the following method.

(Preparation example 1)
Nano-heterostructure powder was prepared according to the method described in JP-A-2014-179238. That is, as a block copolymer, polystyrene-b-poly (2-vinylpyridine) (PS-b-P2VP, number average molecular weight of PS component: 40.5 × 10 ³ , number average molecular weight of P2VP component: 40 × 10 ³ ) 0 0.5 g, 0.36 g of lithium salicylate (C ₆ H ₄ (OH) COOLi) as a Li ₇ La ₃ Zr ₂ O ₁₂ (LLZO) precursor (Li precursor, La precursor and Zr precursor), and tris (2). , 4-pentanedionato) lanthanum (III) hydrate _{(La (CH 3 COCHCOCH 3)} 3 · xH 2 O) 0.156g and tetrakis (2,4-pentanedionato) zirconium (IV) (Zr (CH ₃ COCHCOCH ₃ ) ₄ ) 0.1305 g and salicylic acid as LiCoO ₂ (LCO) precursor (Li precursor and Co precursor) 0.120 g of lithium (C ₆ H ₄ (OH) COOLi) and 0.234 g of cobalt carbonyl (Co (CO) ₈ ) were dissolved in 100 ml of tetrahydrofuran (THF) to obtain a raw material solution. The amount of the LLZO precursor was 0.11 mol with respect to 1 mol of the LCO precursor in this raw material solution.

  This raw material solution was placed in a heat treatment container and calcined at 600 ° C. for 25 hours in an air stream, whereby LCOs were three-dimensionally and periodically arranged in a matrix composed of LLZO, and the length of one unit of repeating structure was long. A nanoheterostructure (hereinafter abbreviated as “LCO / LLZO nanoheterostructure”) having a three-dimensional periodic structure having an average value of 1 nm to 100 nm in at least a part thereof was obtained. The LCO / LLZO nanoheterostructure was uniformly crushed in a mortar and sieved to obtain LCO / LLZO nanoheterostructure powder having a particle size of about 1 μm.

(Reference example 1)
The LCO / LLZO nanoheterostructure powder obtained in Preparation Example 1 was uniformly dispersed in ethanol so that the concentration of the LCO / LLZO nanoheterostructure powder would be 0.17 g / ml. A predetermined amount of the LCO / LLZO nanoheterostructure powder ethanol dispersion was used as a nickel current collector (a pure metal nickel plate (manufactured by Niraco Co., Ltd.)) with a diameter of 14 mm and a thickness of 500 μm so that the thickness of the obtained positive electrode material was 50 μm. (Which has been processed into 1.) and then naturally dried in a draft (normal temperature (15 to 25 ° C.)) for 6 hours to evaporate the LCO / LLZO nanoheterostructure powder to dryness, and to obtain the nickel current collector. A predetermined amount of the LCO / LLZO nanoheterostructure powder aggregate was formed on the surface of the.

  Next, the laminated body composed of the thus obtained nickel current collector and the LCO / LLZO nanoheterostructure powder aggregate was placed under conditions of a temperature of 150 ° C., a pressure of 500 MPa, 1000 MPa, or 1500 MPa. Warm pressure molding was performed for 2 seconds to prepare a pressure molded body including a positive electrode material made of the LCO / LLZO nanoheterostructure having a thickness of 50 μm and the nickel current collector. FIG. 1 shows the results of measuring the density of the positive electrode material in the obtained pressure-molded body and plotting it against the pressure during warm pressure molding.

(Comparative Reference Example 1)
An aluminum current collector (a pure metal aluminum plate (manufactured by Niraco Co., Ltd.) processed into a diameter of 14 mm and a thickness of 500 μm) is used as a current collector, and the pressure during warm pressure molding is 300 MPa, 500 MPa, 1000 MPa, In the same manner as in Reference Example 1 except that the pressure was changed to 1500 PMa or 2000 MPa, a pressure molded body including a positive electrode material made of the LCO / LLZO nanoheterostructure having a thickness of 50 μm and the aluminum current collector was produced. FIG. 1 shows the results of measuring the density of the positive electrode material in the obtained pressure-molded body and plotting it against the pressure during warm pressure molding.

  Further, the cross section of the obtained pressure-molded body was observed with a scanning electron microscope (SEM). The result is shown in FIG. 2A. Further, FIG. 2B is an enlarged view of the white line in FIG. 2A. As is clear from the results shown in FIGS. 2A and 2B, cracks were observed in the positive electrode material in the obtained pressure-molded body.

  On the other hand, in FIG. 2C, according to the method described in JP-A-2014-179238, an aluminum current collector is put into a mold, and LCO / LLZO nanoheterostructure powder is filled on the aluminum current collector, followed by cold pressing. The scanning electron microscope (SEM) photograph of the cross section of the produced electrode is shown. As is clear from the results shown in FIG. 2C, gaps having a size of 50 to 100 μm were observed between the LCO / LLZO nanoheterostructure powders in the positive electrode material in the obtained electrode.

(Comparative Reference Example 2)
A stainless steel (SUS316) current collector (stainless steel SUS316 steel plate (manufactured by Niraco Co., Ltd.) processed to have a diameter of 14 mm and a thickness of 500 μm) is used as a current collector, and the pressure during warm pressure forming is 300 MPa, 500 MPa, In the same manner as in Reference Example 1 except that the pressure was changed to 1000 MPa or 2000 MPa, a pressure-molded body including a positive electrode material made of the LCO / LLZO nanoheterostructure having a thickness of 50 μm and the stainless current collector was produced. FIG. 1 shows the results of measuring the density of the positive electrode material in the obtained pressure-molded body and plotting it against the pressure during warm pressure molding.

As is clear from the results shown in FIG. 1, it was found that there is a suitable range and optimum value for the pressure during warm pressure molding regardless of which collector is used. For example, when a nickel current collector is used, the LCO / LLZO nanoheterostructure having an electrode density of 1.5 to 3.5 g / cm ³ is formed by performing warm pressure molding at a pressure of 500 to 1500 MPa. It was found that a positive electrode material was obtained.

(Example 1)
The concentration of the LCO / LLZO nanoheterostructure powder in the ethanol dispersion of the LCO / LLZO nanoheterostructure powder was changed to 0.085 g / ml so that the thickness of the obtained positive electrode material was 25 μm and the predetermined amount of the above was used. A laminate comprising the nickel current collector and the LCO / LLZO nanoheterostructure powder aggregate was prepared in the same manner as in Reference Example 1 except that the ethanol dispersion of the LCO / LLZO nanoheterostructure powder was added dropwise.

Next, the laminated body thus obtained was subjected to warm pressure molding for 1 to 2 seconds under the conditions of a temperature of 150 ° C. and a pressure of 900 MPa, and the positive electrode material composed of the LCO / LLZO nanoheterostructure and the nickel. A pressure molded body including a current collector was produced. The obtained pressure-molded body was subjected to a heat treatment (annealing treatment) at 750 ° C. for 12 hours in a nitrogen atmosphere to obtain an electrode including the positive electrode material having a thickness of 25 μm and the nickel current collector. When the density of the positive electrode material in this electrode was measured, it was 3.0 g / cm ³ .

  The electrode thus obtained was subjected to energy dispersive X-ray (EDX) spectroscopy using a scanning electron microscope (SEM). FIG. 3 shows the result of mapping the element distribution of each inorganic component in the cross section of the electrode. From the results shown in FIG. 3, it was found that a NiO layer having a thickness of 1 to 3 μm was formed between the positive electrode material and the nickel current collector. Further, the distribution of La, Zr, and Co was uneven in the positive electrode material.

(Comparative Example 1)
The LCO / LLZO nanoheterostructure having a thickness of 20 μm was prepared in the same manner as in Example 1 except that a predetermined amount of the ethanol dispersion of the LCO / LLZO nanoheterostructure powder was added dropwise so that the obtained positive electrode material had a thickness of 20 μm. A pressure-molded body including a positive electrode material having a body and the nickel current collector was produced. In Comparative Example 1, the pressure-molded body was used as an electrode without heat treatment (annealing treatment). When the density of the positive electrode material in this electrode was measured, it was 3.0 g / cm ³ .

  The electrode thus obtained was subjected to energy dispersive X-ray (EDX) spectroscopy using a scanning electron microscope (SEM). FIG. 4 shows the result of mapping the element distribution of each inorganic component in the cross section of the electrode. From the results shown in FIG. 4, the NiO layer was not formed between the positive electrode material and the nickel current collector. Further, the inorganic component was uniformly distributed in the positive electrode material.

(Comparative example 2)
A pressure-molded body including the positive electrode material made of the LCO / LLZO nanoheterostructure and the nickel current collector prepared in the same manner as in Example 1 was placed under a nitrogen atmosphere at 750 ° C. and 4.9 MPa (50 kgf / cm ^2). The hot press treatment was performed for 3 hours under the conditions of 1) to obtain an electrode including the positive electrode material having a thickness of 20 μm and the nickel current collector. When the density of the positive electrode material in this electrode was measured, it was 3.3 g / cm ³ .

(Comparative example 3)
In the same manner as in Example 1 except that a predetermined amount of the ethanol dispersion of the LCO / LLZO nanoheterostructure powder was dropped so that the thickness of the obtained positive electrode material was 20 μm, the nickel current collector and the LCO / A laminated body including an aggregate of LLZO nanoheterostructure powder was produced. This laminated body was subjected to a hot press treatment under a nitrogen atmosphere at 750 ° C. and 4.9 MPa (50 kgf / cm ² ) for 3 hours to obtain a positive electrode material made of the LCO / LLZO nanoheterostructure having a thickness of 20 μm and the nickel. An electrode provided with a current collector was obtained. When the density of the positive electrode material in this electrode was measured, it was 3.2 g / cm ³ .

  The electrode thus obtained was subjected to energy dispersive X-ray (EDX) spectroscopy using a scanning electron microscope (SEM). FIG. 5 shows the result of mapping the element distribution of each inorganic component in the cross section of the electrode. From the results shown in FIG. 5, no NiO layer was formed between the positive electrode material and the nickel current collector. Further, the inorganic component was uniformly distributed in the positive electrode material.

(Comparative Examples 4-5)
The thickness was the same as in Comparative Example 3 except that the pressure during hot press treatment was changed to 5.9 MPa (60 kgf / cm ² ) (Comparative Example 4) or 12.7 MPa (130 kgf / cm ² ) (Comparative Example 5). An electrode having a positive electrode material composed of the LCO / LLZO nanoheterostructure of 20 μm and the nickel current collector was obtained. When the density of the positive electrode material in these electrodes was measured, they were 3.4 g / cm ³ (Comparative Example 4) and 3.6 g / cm ³ (Comparative Example 5).

(Comparative example 6)
A predetermined amount of the LCO / LLZO nanoheterostructure powder ethanol dispersion was added dropwise so that the thickness of the obtained positive electrode material was 30 μm, and the pressure during hot pressing was changed to 5.9 MPa (60 kgf / cm ² ). An electrode including a positive electrode material made of the LCO / LLZO nanoheterostructure having a thickness of 30 μm and the nickel current collector was obtained in the same manner as in Comparative Example 3 except for the above. When the density of the positive electrode material in this electrode was measured, it was 3.3 g / cm ³ .

(Example 2)
An electrode including a positive electrode material composed of the LCO / LLZO nanoheterostructure having a thickness of 25 μm and the nickel current collector was obtained in the same manner as in Example 1 except that the pressure during warm pressure molding was changed to 1000 MPa. . When the density of the positive electrode material in this electrode was measured, it was 3.0 g / cm ³ .

(Examples 3 to 4)
Same as Example 2 except that a predetermined amount of the LCO / LLZO nanoheterostructure powder ethanol dispersion was dropped so that the thickness of the obtained positive electrode material was 45 μm (Example 3) or 60 μm (Example 4). Then, an electrode including a positive electrode material composed of the LCO / LLZO nanoheterostructure having a predetermined thickness and the nickel current collector was obtained. When the density of the positive electrode material in these electrodes was measured, it was 2.9 g / cm ³ (Example 3) and 2.8 g / cm ³ (Example 4).

(Comparative Example 7)
An aluminum current collector was used as a current collector, and a positive electrode material composed of the LCO / LLZO nanoheterostructure having a thickness of 25 μm was prepared in the same manner as in Example 2 except that the pressure during warm press molding was changed to 500 MPa. An electrode including the aluminum current collector was obtained. When the density of the positive electrode material in this electrode was measured, it was 3.7 g / cm ³ .

(Comparative Examples 8 to 11)
A predetermined amount of the LCO / LLZO nanoheterostructure powder so that the thickness of the obtained positive electrode material is 10 μm (Comparative Example 8), 20 μm (Comparative Example 9), 35 μm (Comparative Example 10) or 40 μm (Comparative Example 11). An electrode including the positive electrode material made of the LCO / LLZO nanoheterostructure having a predetermined thickness and the aluminum current collector was obtained in the same manner as in Comparative Example 7 except that the ethanol dispersion liquid of Example 1 was dropped. When the density of the positive electrode material in these electrodes was measured, it was 3.8 g / cm ³ (Comparative Example 8), 3.8 g / cm ³ (Comparative Example 9), 3.7 g / cm ³ (Comparative Example 10), It was 3.6 g / cm ³ (Comparative Example 11).

(Comparative Example 12)
An electrode including the positive electrode material made of the LCO / LLZO nanoheterostructure having a thickness of 25 μm and the stainless current collector was obtained in the same manner as in Example 2 except that a stainless (SUS316) current collector was used as the current collector. It was When the density of the positive electrode material in this electrode was measured, it was 3.0 g / cm ³ .

(Comparative Examples 13 to 15)
A predetermined amount of the ethanol dispersion of the LCO / LLZO nanoheterostructure powder was added dropwise so that the thickness of the obtained positive electrode material was 20 μm (Comparative Example 13), 35 μm (Comparative Example 14) or 50 μm (Comparative Example 15). An electrode including a positive electrode material made of the LCO / LLZO nanoheterostructure having a predetermined thickness and the stainless current collector was obtained in the same manner as in Comparative Example 7 except for the above. When the density of the positive electrode material in these electrodes was measured, it was 3.1 g / cm ³ (Comparative Example 13), 3.0 g / cm ³ (Comparative Example 14), and 2.9 g / cm ³ (Comparative Example 15). there were.

<Discharge capacity measurement>
Each of the electrodes obtained in Examples and Comparative Examples was used as a positive electrode, and a lithium metal foil (φ14 mm × 0.4 mm) was used as a negative electrode. With these electrodes, polyethylene oxide (PEO) was converted into lithium-bis (trifluoromethanesulfonyl) imide ( A polymer electrolyte (φ14 mm × 1 mm) doped with LiTFSI) was sandwiched to prepare a battery cell. The discharge capacity of this battery cell was measured by cyclic voltammetry (CV) in the range of 3 V to 4.2 V at a scan rate of 0.05 mV / sec, and the results plotted against the thickness of the positive electrode material of the obtained electrode were obtained. It shows in FIGS.

  As is clear from the results shown in FIG. 6, when Example 1 and Comparative Example 1 are compared, it is found that the discharge capacity is increased to about double by performing the annealing treatment after the warm pressure forming. It was Further, when the annealing treatment is performed after the warm pressure molding (Example 1), the hot pressing treatment is performed after the warm pressure molding (Comparative example 2) and the warm pressure molding and the annealing treatment are performed. It was found that the discharge capacity was larger than that in the case where hot press treatment was applied instead of (Comparative Examples 3 to 6).

  Further, as is clear from the results shown in FIG. 7, when comparing the same positive electrode material thickness, when a nickel current collector is used as a current collector (Examples 2 to 4), an aluminum current collector is used. It was found that the discharge capacity was larger than that in the case (Comparative Examples 7 to 11) and the case in which the stainless current collector was used (Comparative Examples 13 to 15).

  As described above, according to the present invention, an electrode can be formed by integrating a positive electrode material composed of a nanoheterostructure and a nickel current collector, and the interface between the positive electrode material and the nickel current collector is stable. Can be obtained.

  Therefore, the electrode of the present invention is useful as a positive electrode material for an all-solid-state lithium secondary battery in which the electrolyte is solid.

Claims (4)

Li ₇ La ₃ Zr ₂ O ₁₂ and other inorganic components are three-dimensionally and periodically arranged among the matrix of the inorganic components of _Li 7 _La 3 _Zr 2 _{O 12} and LiCoO ₂ of one of LiCoO ₂ The nanoheterostructure has at least a part of a three-dimensional periodic structure in which the average value of the length of one unit of the repeating structure is 1 nm to 100 nm, and the electrode density is 1.5 to 3. A positive electrode material having a weight of 5 g / cm ³ ,
A nickel current collector,
A NiO layer having a thickness of 1 to 3 μm, one surface of which contacts the positive electrode material and the other surface of which contacts the nickel current collector;
A positive electrode for an all-solid-state lithium secondary battery, comprising: An all-solid-state lithium secondary battery comprising the positive electrode according to claim 1. Li ₇ La ₃ Zr ₂ O ₁₂ and other inorganic components are three-dimensionally and periodically arranged among the matrix of the inorganic components of _Li 7 _La 3 _Zr 2 _{O 12} and LiCoO ₂ of one of LiCoO ₂ And a step of dispersing a nano-heterostructure powder having a three-dimensional periodic structure having an average value of the length of one unit of the repeating structure of 1 nm to 100 nm in at least a part in a solvent,
The dispersion liquid of the nanoheterostructure powder obtained in the step is dropped on a nickel current collector, and the nanoheterostructure powder is dried to dryness by natural drying, and the nanoheterostructure powder is formed on the surface of the nickel current collector. Forming an aggregate of
A step of warm press-molding a laminate comprising the nickel current collector obtained in the step and an assembly of the nano-heterostructure powder at a temperature of 20 to 150 ° C. and a pressure of 500 to 2000 MPa;
A step of subjecting the pressure-molded body obtained in the above step to a heat treatment at a temperature of 400 to 800 ° C. under atmospheric pressure;
A method for producing a positive electrode for an all-solid-state lithium secondary battery, comprising: The method for producing a positive electrode for an all-solid lithium secondary battery according to claim 3, wherein the heat treatment of the pressure molded body is performed in a nitrogen atmosphere.