JP6201569B2 - Solid electrolyte material and all solid state battery - Google Patents

Description

  The present invention relates to a solid electrolyte material and an all-solid battery, and more particularly to a solid electrolyte material contained in a solid electrolyte layer and an electrode layer of the all-solid battery, and an all-solid battery using the solid electrolyte material.

  In recent years, with the expansion of the market for portable electronic devices such as mobile phones, notebook computers, and digital cameras, secondary batteries have been actively developed as cordless power sources for these electronic devices. In addition, with the background of global warming and the depletion of petroleum resources, development of electric vehicles and hybrid vehicles using secondary batteries as a power source is also actively conducted.

  Under such circumstances, lithium ion secondary batteries using lithium ions as charge carriers and utilizing an electrochemical reaction associated with charge exchange are already in widespread use.

  However, in this type of lithium ion secondary battery, a liquid electrolyte (electrolytic solution) mainly composed of an organic compound is usually used as a medium for transferring ions. There is a risk of leakage from the can. Moreover, since the organic compound normally used as a liquid electrolyte is a combustible substance, sufficient safety cannot be ensured, and high temperature stability and durability are also inferior.

  For this reason, research on secondary batteries using solid electrolytes instead of liquid electrolytes has been actively conducted today.

As a technique related to a solid electrolyte, as described in Patent Document 1, a NASICON structure represented by a general formula Na _{1 + x} Zr ₂ P _3−x Si _x O ₁₂ (0 ≦ x ≦ 3) has been conventionally used. A method of forming a Na ⁺ ion conductive solid electrolyte thin film having a hydrogen atom has been proposed.

In Patent Document 1, Na is passed through a process including a process of forming a thin film of a mixed solution of raw materials on a heat-resistant substrate, a process of drying the thin film, and a process of firing the dry thin film in an oxidizing atmosphere. ^{+ An} ion conductive solid electrolyte thin film is formed. According to Patent Document 1, the Na ⁺ ion conductive solid electrolyte thin film has a composition formula: NaZr ₂ PO ₄ (SiO ₄ ) ₂ , the crystal system is monoclinic, and the ion conductivity of Na ⁺ is maximized. ing.

  Further, in Patent Document 2, in a solid electrolyte for a secondary battery composed of a composite oxide composed of lithium metal and another metal, the composite oxide was produced using a metal alkoxide and at least one lithium compound as raw materials. A solid electrolyte for a secondary battery made of an oxide obtained by firing a sol has been proposed.

In Patent Document 2, the general formula Li _1-x M _2-x M ′ _x (PO ₄ ) ₃ (where x represents 0 ≦ x <1 and M and M ′ represent Al, Ti, or Zr. ), For example, LiZr ₂ (PO ₄ ) ₃ is used for the solid electrolyte layer.

Japanese Patent Laid-Open No. 2-188803 JP 2001-143753 A (Claim 7, paragraph numbers [0051] to [0053], Table 1 etc.)

However, Patent Document 1 attempts to maximize the ionic conductivity of the Na ion conductor by adopting a single crystal system crystal structure, but does not describe the Li ⁺ ion conductor. Further, as a result of research by the present inventors, it has been found that when a Li ⁺ ion conductor having a NASICON structure is made to have a single crystal system, the ionic conductivity is extremely low.

  On the other hand, as a solid electrolyte material, a NASICON-type structure containing Zr having reduction resistance as a central metal is considered promising. However, according to the research results of the present inventors, a solid electrolyte having a NASICON-type structure containing Zr is proposed. It has been found that when materials are used and an all-solid battery is manufactured by a sintering method, it is difficult to sinter densely, and thus it is difficult to obtain stable and good ion conductivity.

However, although Patent Document 2 uses LiZr ₂ (PO ₄ ) ₃ for the solid electrolyte layer, it does not describe the sinterability of the Zr-containing oxide, and the ionic conductivity and the crystal system are not described. Have a close relationship, but there is no mention of this point. Therefore, in Patent Document 2, it is considered difficult to obtain an all-solid-state battery having a stable and good ion conductivity by densely sintering the solid electrolyte material.

  The present invention has been made in view of such circumstances, and has solid sinterability and good ionic conductivity even if it contains Zr, and this solid electrolyte material It aims at providing the sintering-type all-solid-state battery which uses this.

  In order to achieve the above object, the present inventors have conducted intensive research on a compound having a nasicon structure containing Zr as a main component as a central metal, and have a crystal system mainly composed of a rhombohedral system at room temperature. On the other hand, by causing a reversible transition with other crystal systems in the temperature range from room temperature to the firing temperature, it can be densely sintered at the firing temperature and has good ion conductivity. The knowledge that it can secure was acquired.

The present invention has been made based on such knowledge, and the solid electrolyte material according to the present invention is a solid electrolyte material in which the basic skeleton of the crystal structure has a NASICON structure, and the main component is as a central metal. Zr-containing general formula Li _x Zr ₂ (PO ₄ ) ₃ (where x is 1.1 ≦ x ≦ 2.0), and the first crystal system mainly composed of rhombohedral system is used at room temperature. And having a reversible transition between the second crystal system different from the first crystal system in the temperature range from the room temperature to the firing temperature, and being sintered at the firing temperature. It is a feature.

  In the solid electrolyte material of the present invention, it is preferable that the second crystal system includes one or more of a monoclinic system, an orthorhombic system, and a triclinic system.

  Further, in the solid electrolyte material of the present invention, the second crystal system may include a mixed crystal system with the rhombohedral system.

  In this case, in the solid electrolyte material of the present invention, it is also preferable that a part of the Li is replaced with at least one of Na and K.

  Furthermore, in the solid electrolyte material of the present invention, a part of the Zr is at least one selected from Ca, Mg, Ba, Sr, Al, Sc, Y, In, Ti, Ge, Ga, and Hf. It is characterized by being substituted with the element M.

  An all solid state battery according to the present invention is an all solid state battery having a positive electrode layer on one main surface of a solid electrolyte layer and a negative electrode layer on the other main surface of the solid electrolyte layer, and at least the solid state battery. The electrolyte layer is characterized by having the solid electrolyte material described above as a main component.

  In the all solid state battery of the present invention, it is also preferable that the solid electrolyte layer and at least one of the positive electrode layer and the negative electrode layer are integrally joined by sintering.

  As a result, it is possible to obtain a sintered all-solid battery that can be densely sintered at the sintering temperature and that can ensure good ion conductivity.

  Furthermore, the all-solid-state battery according to the present invention is an all-solid-state battery having a positive electrode layer on one main surface of the solid electrolyte layer and a negative electrode layer on the other main surface of the solid electrolyte layer, The electrolyte layer and the negative electrode layer contain any of the solid electrolyte materials described above, and at least the solid electrolyte layer and the negative electrode layer are integrally joined by sintering.

  In the all solid state battery of the present invention, it is also preferable that a gel electrolyte layer is interposed between the solid electrolyte layer and the positive electrode layer.

According to the solid electrolyte material of the present invention, the basic structure Li _x Zr ₂ (PO ₄ ) _{3 in which} the basic skeleton of the crystal structure has a NASICON structure and the main component contains Zr as a central metal. (Where x is 1.1 ≦ x ≦ 2.0), and has a first crystal system mainly composed of rhombohedral system at room temperature, and in the temperature range from the room temperature to the firing temperature, Since a reversible transition occurs between the second crystal system different from the first crystal system and is sintered at the firing temperature, it can be densely sintered at the firing temperature and is excellent. A solid electrolyte material capable of ensuring ion conductivity can be obtained.

  That is, the ionic conductivity of the solid electrolyte material is affected by the resistance caused by the crystal grain boundaries of the solid electrolyte and the resistance within the crystal particles of the solid electrolyte material. Then, transition to the second crystal system in a temperature range from room temperature to the firing temperature and dense sintering at the firing temperature can reduce the resistance caused by the crystal grain boundaries. In addition, since the reversible transition occurs in the rhombohedral system having excellent ion conductivity during the process of cooling to room temperature, the resistance in the crystal grains can be reduced.

  As described above, in the present invention, a solid electrolyte material that can be densely sintered at a firing temperature and can ensure good ion conductivity can be obtained.

  The all solid state battery of the present invention is an all solid state battery having a positive electrode layer on one main surface of a solid electrolyte layer and a negative electrode layer on the other main surface of the solid electrolyte layer, Since the solid electrolyte layer is mainly composed of any of the solid electrolyte materials described above, it is possible to obtain an all-solid battery that can be densely sintered at a sintering temperature and that can ensure good ion conductivity. it can.

  The all solid state battery of the present invention is an all solid state battery having a positive electrode layer on one main surface of a solid electrolyte layer and a negative electrode layer on the other main surface of the solid electrolyte layer, and at least the solid electrolyte Since the layer and the negative electrode layer contain any one of the solid electrolyte materials described above, an all solid state battery that can be densely sintered at a sintering temperature and can secure even better ion conductivity. Can be obtained.

It is sectional drawing which shows typically one Embodiment (1st Embodiment) of the all-solid-state battery produced using the solid electrolyte material which concerns on this invention. It is sectional drawing which shows typically 2nd Embodiment of the all-solid-state battery produced using the solid electrolyte material which concerns on this invention. It is sectional drawing which shows typically the laminated sintered body of 2nd Embodiment. It is a figure which shows the X-ray spectrum in 25 degreeC-1000 degreeC of the solid electrolyte material A with a reference | standard pattern. It is a figure which shows the X-ray spectrum in 25 degreeC-1000 degreeC of the solid electrolyte material D with a reference pattern. It is a figure which shows the X-ray spectrum in 25 degreeC-1000 degreeC of the solid electrolyte material F with a reference | standard pattern. It is a figure which shows the X-ray spectrum in 25 degreeC-1000 degreeC of the solid electrolyte material G with a reference | standard pattern.

  Next, an embodiment of the present invention will be described in detail.

  In the solid electrolyte material according to the present invention, the basic skeleton of the crystal structure has a NASICON structure.

The NASICON structure can be represented by the general formula Y ₂ (XO ₄ ) ₃ and has a structure in which the vertex of the regular octahedron YO _{6 and} the vertex of the regular tetrahedron XO ₄ are shared and arranged three-dimensionally. Since it has a large void in the crystal structure and cations such as Li ions move easily, it is excellent as a medium for moving cations. Particularly, among the NASICON structure, a phosphoric acid compound in which the polyanion of regular tetrahedron XO ₄ is formed of PO ₄ is preferable because the solid electrolyte and the electrode layer can be densely and integrally sintered.

  And in this Embodiment, the central element Y of a NASICON type structure contains Zr as a main component. Since Zr has good reduction resistance, when a solid electrolyte material containing Zr as a main component as a main component is used near the negative electrode layer or the negative electrode layer, the solid electrolyte is reduced at the potential of the negative electrode layer. This can be avoided, and damage to the charge / discharge characteristics of the all-solid-state battery can be suppressed.

  Further, in the present embodiment, the second crystal having the first crystal system mainly composed of a rhombohedral system at room temperature and different from the first crystal system in a temperature range from room temperature to the firing temperature. A reversible transition occurs between the system and the first crystal system and is sintered at the firing temperature. As a result, a solid electrolyte material that can be densely sintered at the firing temperature and can ensure good ion conductivity can be obtained.

  The ionic conductivity of the solid electrolyte material is affected by both the resistance caused by the crystal grain boundaries of the solid electrolyte and the resistance within the crystal particles of the solid electrolyte material. In this embodiment mode, the crystal system at room temperature has a first crystal system mainly composed of a rhombohedral system having good ion conductivity, and the first crystal is in a temperature range from room temperature to the firing temperature. It is transferred to a second crystal system having good sinterability different from that of the system and densely sintered at the firing temperature.

  That is, the firing temperature of the Zr-containing compound containing Zr is generally high, and it is difficult to sinter densely.

  However, as a result of intensive studies by the present inventors, there is a difference in the difficulty of sinterability depending on the crystal system even if it is a Zr-containing compound, and the sinterability is improved in crystal systems other than the rhombohedral system. And it was found that dense sintering is possible.

  Therefore, in the present embodiment, in the temperature range from room temperature to the firing temperature, the second crystal system having good sinterability different from the first crystal system mainly composed of the rhombohedral system is transferred and fired. Sintered densely at temperature. As a result, the resistance caused by the grain boundaries can be reduced, and good ion conductivity is obtained.

  In addition, the resistance in the crystal grains can be reduced by transferring from the second crystal system to the first crystal system mainly composed of the original rhombohedral system in the process of cooling from the firing temperature to room temperature. Therefore, it is possible to obtain good ionic conductivity in a wide temperature range from room temperature to high temperature.

  As described above, in the present invention, a solid electrolyte material that can be densely sintered at a firing temperature and can ensure good ion conductivity can be obtained.

  Such a second crystal system is not particularly limited as long as it is densely sintered at the firing temperature. Crystal systems other than rhombohedral systems, such as monoclinic systems, orthorhombic systems, etc. Any one or more of a crystal system and a triclinic system may be included, and a rhombohedral system and a mixed crystal system of these crystal systems may be used.

In addition, as described above, the first crystal system is included at room temperature, a reversible transition occurs between the second crystal system in the temperature range from room temperature to the firing temperature, and sintering is performed at the firing temperature. In this case, the composition of the solid electrolyte material is not particularly limited, but the main component is the general formula Li _x Zr ₂ (PO ₄ ) ₃ (where x is 1.1 ≦ x ≦ 2.0). The compounds represented can be used with preference.

  Since Li has good ionic conductivity, Li ions are normally used as a charge carrier in all solid batteries. However, when the molar ratio x of Li is less than 1.1, the Li is close to the firing temperature. Even if the temperature is raised, the transition of the crystal system becomes difficult. On the other hand, if the Li molar ratio x exceeds 2.0, a crystal system other than the rhombohedral system may be formed at room temperature.

  Even if a part of Li is replaced with another alkali metal element such as Na or K, the above-described effects of the present invention can be obtained.

  Furthermore, by replacing a part of Zr with at least one element M selected from Ca, Mg, Ba, Sr, Al, Sc, Y, In, Ti, Ge, Ga, and Hf, The system can easily be rhombohedral.

  FIG. 1 is a cross-sectional view schematically showing an embodiment of an all solid state battery according to the present invention.

  In this all-solid-state battery, a positive electrode current collector 2 is formed on one main surface of the laminated sintered body 1, and a negative electrode current collector 3 is formed on the other main surface of the laminated sintered body 1.

  The current collector material for forming the positive electrode current collector 2 and the negative electrode current collector 3 is particularly limited as long as it is a conductive material having good electron conductivity and good adhesion to the laminated sintered body 1. Instead, for example, Pt, Au, Ag, Al, Cu, stainless steel, ITO (indium tin oxide), or the like can be used.

  In the laminated sintered body 1, a positive electrode layer 5 joined to the positive electrode current collector 2 is formed on one main surface of the solid electrolyte layer 4, and a negative electrode current collector is formed on the other main surface of the solid electrolyte layer 4. A negative electrode layer 6 bonded to the body 3 is provided.

  The solid electrolyte layer 4 contains a solid electrolyte material as a main component. The positive electrode layer 5 contains a positive electrode active material, a solid electrolyte material, and a conductive agent, and the negative electrode layer 6 contains a negative electrode active material, a solid electrolyte material, and a conductive agent.

  In the present embodiment, the above-described solid electrolyte material of the present invention is used for the solid electrolyte layer 4 and the negative electrode layer 6, whereby it can be densely sintered at a firing temperature and has good ion conductivity. Can be obtained.

  Next, the manufacturing method of this all-solid-state battery is explained in full detail.

  First, a solid electrolyte material of the present invention, a binder resin such as a polyvinyl acetal resin, and an organic solvent such as ethanol are prepared, and weighed so that the solid electrolyte material, the binder resin, and the organic solvent have a predetermined weight ratio.

  Then, after dissolving the binder resin in an organic solvent to produce an organic vehicle, it is put into a ball mill together with a solid electrolyte material and a grinding medium such as PSZ (partially stabilized zirconia) balls, and sufficiently mixed and pulverized to obtain a solid electrolyte slurry. Is made.

  Next, a negative electrode active material, a conductive agent, and the solid electrolyte material of the present invention are prepared, and a predetermined amount of these negative electrode active material, conductive agent, and solid electrolyte material is weighed to obtain a negative electrode material.

Here, the negative electrode active material is not particularly limited. For example, Nb ₂ O ₅ , TiO ₂ , SiO, SnO, MoO ₂ , Cr ₂ O ₃ , Fe ₂ O ₃ , NiO, MnO, CoO, Cu ₂ O, CuO, WO, V ₂ O ₅ , RuO _{2 and the} like can be used alone or in combination.

  In addition, the conductive agent is not particularly limited, for example, carbonaceous fine particles such as graphite, carbon black, acetylene black, carbon fibers such as vapor grown carbon fiber, carbon nanotube, carbon nanohorn, polyaniline, polypyrrole, Conductive polymers such as polythiophene, polyacetylene, and polyacene can be used.

  Then, this negative electrode material is put into a pot mill together with the pulverization medium and the organic vehicle, and sufficiently mixed and pulverized to prepare a negative electrode slurry.

  Next, a positive electrode active material, a conductive agent, and a solid electrolyte material are prepared, and a predetermined amount of these positive electrode active material, conductive agent, and solid electrolyte material is weighed to obtain a positive electrode material.

  Then, this positive electrode material is put into a pot mill together with the pulverization medium and the organic vehicle, and sufficiently mixed and pulverized to produce a positive electrode slurry.

Here, the positive electrode active material is not particularly limited. For example, phosphoric acid compounds such as Li ₃ V ₂ (PO ₄ ) ₃ , LiFePO ₄ , LiMnPO ₄ , LiCoO ₂ , LiCo _1/3 Ni _1/3. Cobalt compounds such as Mn _1/3 O ₂ and spinel type compounds such as LiMnO ₄ and LiNi _0.5 Mn _1.5 O ₄ can be used alone or in combination.

In addition, the solid electrolyte material contained in the positive electrode layer 5 is not particularly limited, and the solid electrolyte material of the present invention described above may be used, and a solid electrolyte material different from the solid electrolyte material of the present invention may be used. May be used. However, since the positive electrode layer 5 has a higher potential than the negative electrode layer 6, there is little need to consider reduction resistance. Therefore, LiTi (PO ₄ ) ₃ , Li _1.2 Ti _1.8 Al _0.2 (PO ₄ ) _3, etc. It is preferable to use a compound having a NASICON structure using Ti having good conductivity as a central metal.

  In addition, as a electrically conductive agent, the thing similar to what was used with the negative electrode material can be used.

  Next, the solid electrolyte slurry, the negative electrode slurry, and the positive electrode slurry prepared as described above are applied onto a base film using a doctor blade method, a die coater method, a comma coater method, a screen printing method, and the like, and then molded. Processing is performed to produce a solid electrolyte layer green sheet, a negative electrode layer green sheet, and a positive electrode layer green sheet, each having a predetermined thickness.

  Next, the solid electrolyte layer green sheet, the negative electrode layer green sheet, and the positive electrode layer green sheet are peeled off from the base film, respectively, and the positive electrode layer green sheet, the solid electrolyte layer green sheet, and the negative electrode layer The green sheets are laminated one after another, thermocompression bonded at a predetermined pressure, sealed in a film container, and pressurized using a hot isostatic press, a cold isostatic press, a hydrostatic press, etc., thereby solid electrolyte A laminated structure in which the layer green sheet is sandwiched between the positive electrode layer green sheet and the negative electrode layer green sheet is prepared.

  Next, the laminated structure is degreased at a predetermined temperature and then subjected to a firing treatment, thereby producing a laminated sintered body 1 in which the positive electrode layer 5 and the negative electrode layer 6 are formed on both main surfaces of the solid electrolyte 4.

  Finally, a positive electrode current collector 2 and a negative electrode current collector 3 are formed on both main surfaces of the laminated sintered body 1 using a thin film forming method such as a sputtering method or a vacuum vapor deposition method, and then dried. After removing the adsorbed moisture from the atmosphere, it is sealed in a battery can, thereby producing an all-solid battery.

  Thus, this all solid state battery has the positive electrode layer 5 on one main surface of the solid electrolyte layer 4 and the negative electrode layer 6 on the other main surface of the solid electrolyte layer 4. Since the layer 6 contains the solid electrolyte material, it is possible to obtain an all-solid battery that can be densely sintered at the sintering temperature and that can secure even better ion conductivity.

  FIG. 2 is a cross-sectional view schematically showing a second embodiment of the all solid state battery according to the present invention.

  In the second embodiment, a gel electrolyte layer 12 containing a polymer organic material such as polymethyl acrylate resin (hereinafter referred to as “PMMA”) is formed on the surface of the positive electrode layer 11 such as metallic lithium. ing. A laminated sintered body 13 is formed on the surface of the gel electrolyte layer 12, and a negative electrode current collector 14 made of Pt or the like is further formed on the surface of the laminated sintered body 13.

  In the laminated sintered body 13, the solid electrolyte layer 15 and the negative electrode layer 16 are integrally joined by sintering, the solid electrolyte layer 15 is joined to the gel electrolyte layer 12, and the negative electrode layer 16 is joined to the negative electrode current collector layer 14. It is joined to.

  Thus, by bonding the gel electrolyte layer 12 having better ion conductivity to the solid electrolyte layer 15, larger ionic conductivity can be obtained.

  The all solid state battery of the second embodiment can be easily manufactured as follows.

  That is, a green sheet for a solid electrolyte layer and a green sheet for a negative electrode layer are produced by the same method and procedure as in the first embodiment, and a laminated structure is produced by laminating both, and then the laminated structure is fired. Then, as shown in FIG. 3, the laminated sintered body 13 in which the solid electrolyte layer 15 and the negative electrode layer 16 are integrally joined is obtained.

  Next, after forming the negative electrode current collector layer 14 on the negative electrode layer 16 of the laminated sintered body 13 using a thin film forming method such as sputtering, a gel electrolyte containing a cation such as Li ion is formed on the positive electrode layer 11. The gel electrolyte layer 12 is formed by coating, the gel electrolyte layer 12 and the solid electrolyte layer 15 are joined, and sealed in a battery can, whereby an all-solid battery is manufactured.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible in the range which does not deviate from a summary. For example, in the above embodiment, the solid electrolyte layers 4 and 15 are formed of a single green sheet for a solid electrolyte layer, but may have a multilayer structure of two or more layers.

  In each of the above embodiments, the solid electrolyte material of the present invention is used for both the solid electrolyte layers 4 and 15 and the negative electrode layers 6 and 16, but it may be used as a material constituting the vicinity of the negative electrode layers 6 and 16. Even if it is used only for the solid electrolyte layers 4 and 15 disposed in the vicinity of the negative electrode layers 6 and 16, or it is used only for the negative electrode layers 6 and 16, the intended object of the present invention can be achieved. it can.

  In addition, the solid electrolyte slurry, the positive electrode slurry, and the negative electrode slurry are prepared using a ball mill in the above embodiment, but a viscomill method, a sand mill method, a high-pressure homogenizer method, a kneader dispersion method, or the like is used. May be. Moreover, you may add phthalic acid esters, such as dioctyl phthalate and diisononyl phthalate, as a plasticizer to each of these slurries.

  Next, examples of the present invention will be specifically described.

[Evaluation of solid electrolyte materials]
(Production of solid electrolyte material)
Li ₂ CO ₃ , Na ₂ CO ₃ , ZrO ₂ , CaCO ₃ , and NH ₄ H ₂ PO ₄ were prepared as raw materials, and predetermined amounts of these raw materials were weighed so as to have compositions A to G shown in Table 1. .

  Next, these weighed products were put into a polyethylene pot mill and mixed for 16 hours to obtain a mixed powder.

  Then, a heat treatment was performed at a temperature of 500 ° C. for 1 hour in an air atmosphere, and further a heat treatment was performed at 800 ° C. for 6 hours to remove volatile components in the raw material powder.

  Next, the raw material powder from which these volatile components have been removed is put into a polyethylene pot mill together with pure water and PSZ balls, and the pot mill is rotated at a rotation speed of 150 rpm for 16 hours, and then heated to 120 ° C. The dried water was removed by drying on the hot plate to obtain a dry powder.

  Subsequently, this dry powder was heat-treated at a temperature of 1200 ° C. for 20 hours in an air atmosphere to prepare heat-treated powders A to G.

Next, the heat treated powders A to G were pressed at a pressure of 50 kN / cm ² to produce a molded body having a diameter of 10 mm and a thickness of 500 to 1000 μm.

  Next, this molded body was subjected to a firing treatment in a nitrogen atmosphere at a temperature of 1000 ° C. for 2 hours to produce solid electrolyte materials A to G.

  In addition, since these solid electrolyte materials A to G are not collapsed into powder after firing and sintered while maintaining the shape of the molded body, the sintering temperature of these solid electrolyte materials A to G is 1000 ° C. or less. It was confirmed that.

(Identification of crystal system)
Each sample of the solid electrolyte materials A to G is sealed in a Pt container, and an X-ray diffractometer is used. The scanning speed is 4.0 ° / min and the angular range is 10 ° to 50 °, and the temperature is 25 ° C. The temperature is raised from 1000 ° C. to 1000 ° C., then the temperature is lowered from 1000 ° C. to 25 ° C., X-ray diffraction spectra at 25 ° C., 500 ° C., and 1000 ° C. are measured at the time of temperature rise, An X-ray diffraction spectrum at 25 ° C. was measured.

  FIG. 4 shows an X-ray diffraction spectrum of the solid electrolyte material A at each temperature together with a reference pattern. The horizontal axis represents the diffraction angle 2θ (°), and the vertical axis represents the X-ray intensity (au).

  In the figure, A1 to A3 indicate X-ray diffraction spectra at 25 ° C., 500 ° C., and 1000 ° C. when the temperature is raised, and A4 and A5 indicate X-ray diffraction spectra at 900 ° C. and 25 ° C. when the temperature is lowered, respectively. .

Further, the reference pattern is a crystal pattern of a JCPDS (Joint Committee on Power Diffraction Standards) card, and the reference pattern LZPr is a rhombohedral pattern (No. 01-072-7742) of LiZr ₂ (PO ₄ ) ₃ , The reference pattern LZPm is a monoclinic pattern (No. 01-070-5819) of LiZr ₂ (PO ₄ ) ₃ , and the reference pattern Pt is a Pt pattern (No. 08-004-0802).

  As is apparent from FIG. 4, the patterns A1 and A2 substantially coincide with the rhombohedral pattern (reference pattern LZPr) of LZPr, and the crystal system is rhombohedral at 25 ° C. and 500 ° C. when the temperature is raised. It was found to be crystalline.

  In addition, the pattern A3 has a lower X-ray intensity than the rhombohedral pattern, and almost coincides with the monoclinic pattern (reference pattern LZPm) of LZPm. At 1000 ° C., the crystal system becomes monoclinic. It has metastasized.

  The patterns A4 and A5 substantially coincide with the rhombohedral pattern (reference pattern LZPr) of LZPr, and the crystal system is again rhombohedral at 900 ° C. and 25 ° C. when the temperature is lowered.

  That is, the solid electrolyte material A has a rhombohedral system at room temperature, but transitions to a monoclinic system in the course of reaching the firing temperature, and reversibly returns to the rhombohedral system when the temperature is lowered from the firing temperature to room temperature. I understood that.

  Although not shown, the solid electrolyte materials B and C are rhombohedral at room temperature as well as the solid electrolyte material A, but transition to a monoclinic system in the course of reaching the firing temperature. It was confirmed that the rhombohedral system reversibly returned to room temperature.

  FIG. 5 shows an X-ray diffraction spectrum of the solid electrolyte material D at each temperature together with a reference pattern. The horizontal axis represents the diffraction angle 2θ (°), and the vertical axis represents the X-ray intensity (au).

  In the figure, D1 to D3 indicate X-ray diffraction spectra at 25 ° C., 500 ° C., and 1000 ° C. when the temperature is raised, and D4 and D5 indicate X-ray diffraction spectra at 900 ° C. and 25 ° C. when the temperature is lowered, respectively. . The reference pattern is the same as in FIG.

  As is apparent from FIG. 5, the patterns D1 and D2 substantially coincide with the rhombohedral pattern (reference pattern LZPr) of LZPr, and the crystal system is rhombohedral at 25 ° C. and 500 ° C. when the temperature is raised. It was found to be crystalline.

  Further, the pattern D3 has a lower X-ray intensity than the rhombohedral pattern, although the degree of difference is different from the pattern A3 of the solid electrolyte material A, and is different from the monoclinic pattern (reference pattern LZPm) of LZPm. The crystal system is almost coincident, and at 1000 ° C., the crystal system transitions to a monoclinic system.

  The pattern D4 and the pattern D5 substantially coincide with the rhombohedral pattern (reference pattern LZPr) of LZPr, and the crystal system is again rhombohedral at 900 ° C. and 25 ° C. when the temperature is lowered. That is, like the solid electrolyte material A, the solid electrolyte material D is rhombohedral at room temperature, but transitions to a monoclinic system in the course of reaching the sintering temperature, and reversible when the temperature is lowered from the sintering temperature to room temperature. It turned out that it returned to rhombohedral system.

  FIG. 6 shows an X-ray diffraction spectrum of the solid electrolyte material F at each temperature together with a reference pattern. The horizontal axis represents the diffraction angle 2θ (°), and the vertical axis represents the X-ray intensity (au).

  In the figure, F1 to F3 indicate X-ray diffraction spectra at 25 ° C., 500 ° C., and 1000 ° C. at the time of temperature increase, respectively, and F4 and F5 indicate X-ray diffraction spectra at 900 ° C. and 25 ° C. at the time of temperature decrease, respectively. . The reference pattern is the same as in FIG.

  As is apparent from FIG. 6, the patterns F1 to F3 substantially coincide with the rhombohedral pattern (reference pattern LZPr) of LZPr, and the rhombohedral pattern (reference) of the patterns F4 and F5 also. The pattern LZPr) is substantially the same.

  That is, it was found that the solid electrolyte material F maintains the rhombohedral system from room temperature to the sintering temperature, and no crystal system transition occurs.

  FIG. 7 shows the X-ray diffraction spectrum of the solid electrolyte material G at each temperature together with a reference pattern. The horizontal axis represents the diffraction angle 2θ (°), and the vertical axis represents the X-ray intensity (au).

  In the figure, G1 to G3 indicate X-ray diffraction spectra at 25 ° C., 500 ° C., and 1000 ° C. when the temperature rises, respectively, and G4 and G5 indicate X-ray diffraction spectra at 900 ° C. and 25 ° C. when the temperature decreases, respectively. . The reference pattern is the same as in FIG.

  As is apparent from FIG. 7, the patterns G1 and G2 substantially coincide with the triclinic pattern of LZPr (reference pattern LZPt), and the crystal system is triclinic at 25 ° C. and 500 ° C. when the temperature is raised. It was found to be crystalline.

  Further, the pattern G3 has a lower X-ray intensity than the triclinic pattern and substantially matches the monoclinic pattern (reference pattern LZPm) of LZPm. At 1000 ° C., the crystal system becomes monoclinic. It has metastasized. The patterns G4 and G5 substantially coincide with the triclinic pattern of LZPr (reference pattern LZPt), and the crystal system is again triclinic at 900 ° C. and 25 ° C. when the temperature is lowered.

  That is, the solid electrolyte material F is triclinic at room temperature, but transitions to the monoclinic system in the course of reaching the sintering temperature, and reversibly becomes triclinic when the temperature is lowered from the sintering temperature to room temperature. I found it back.

(Sinterability evaluation)
About solid electrolyte material A-F, based on Numerical formula (1), volume shrinkage ratio (eta) before and behind sintering was calculated | required from the molded object volume X before baking, and the sintered compact volume Y after baking, and sinterability was evaluated.

η = {(X−Y) / X} × 100 (1)
(Ion conductivity evaluation)
Sputtering was performed on both main surfaces of the solid electrolyte materials A to G using Pt as a target material to form a pair of upper and lower electrodes.

  Then, using an impedance analyzer (Solartron, 1255B), applying a voltage of 0.1 to 1 MHz and a voltage of 100 mV, measuring the impedance Z at room temperature (25 ° C.), and measuring the impedance Z from this impedance Z σ was determined and the ionic conductivity was evaluated.

  Table 1 shows the composition, volume shrinkage η, ionic conductivity σ, and crystal system of each sample of the solid electrolyte materials A to G.

In Sample No. F, the crystal system of the solid electrolyte material has not changed in the temperature range from room temperature to the firing temperature. Therefore, the volume shrinkage η is as low as 10%, the sinterability is poor, and the ionic conductivity σ is also low. It was found to be as low as 1 × 10 ⁻⁷ S / cm and poor in ionic conductivity.

Sample No. G has a volume shrinkage η of 30%, and the crystal system is a monoclinic system that has good sinterability at the firing temperature, but is triclinic that has poor ion conductivity at room temperature. Therefore, the ionic conductivity σ was as low as 1.0 × 10 ⁻⁸ S / cm.

In contrast, sample numbers A to E have a reversible transition between the rhombohedral system and the monoclinic system in the crystal system of the solid electrolyte material in the temperature range from room temperature to the firing temperature. The volume shrinkage η is 24 to 32% and good sinterability can be obtained, and the ionic conductivity σ is 3.0 × 10 ⁻⁶ to 8 × 10 ⁻⁶ S / cm and the ionic conductivity σ. It was found that the internal resistance was small.

  That is, a reversible transition occurs in the process from room temperature to the sintering temperature, so that the sinterability is improved, and since the crystal system is a rhombohedral system at room temperature, the ionic conductivity σ is large and the internal resistance is low. I found out that I can do it.

[All-solid battery evaluation]
(Preparation of green sheet for solid electrolyte layer)
First, solid electrolyte materials A to G were prepared, polyvinyl acetal resin as a binder resin, and ethanol as an organic solvent.

  Then, these solid electrolyte materials A to G, polyvinyl acetal resin and ethanol were weighed so that solid electrolyte material: polyvinyl acetal resin: ethanol = 100: 15: 140 by weight ratio.

  Next, after the polyvinyl acetal resin was dissolved in ethanol to prepare an organic vehicle, the organic vehicle was put into a ball mill together with the solid electrolyte material and the PSZ balls, mixed well, and the PSZ balls were removed. 7 solid electrolyte slurry was prepared.

  Next, using the doctor blade method, each solid electrolyte slurry was coated on a polyethylene terephthalate (PET) film, dried on a hot plate heated to a temperature of 40 ° C., and molded to a thickness of 10 μm. The sample was cut into length: 25 mm and width: 25 mm, thereby producing solid electrolyte layer green sheets of sample numbers 1 to 7.

(Preparation of negative electrode layer green sheet)
P _0.2 Nb _1.80 O ₅ was prepared as a negative electrode active material, acetylene black and solid electrolyte materials A to G were prepared as a conductive agent.

  Next, an organic vehicle was prepared in the same manner as described above so that the negative electrode active material, polyvinyl acetal resin, and ethanol were in a weight ratio of negative electrode material: polyvinyl acetal resin: ethanol = 100: 15: 140, and then the negative electrode material was pulverized. The medium and the organic vehicle were put together in a pot mill and mixed and pulverized sufficiently to prepare negative electrode active material slurries of sample numbers 1 to 7.

  Next, carbon black is prepared as a conductive agent, and the organic vehicle is prepared in the same manner as described above so that the conductive agent, polyvinyl acetal resin, and ethanol are in a weight ratio of conductive material: polyvinyl acetal resin: ethanol = 100: 15: 140. After the production, the negative electrode material was put into a pot mill together with a grinding medium and the organic vehicle, and sufficiently mixed and ground to prepare a conductive agent slurry.

  Next, the negative electrode active material slurry, the solid electrolyte slurries of Sample Nos. 1 to 7 described above, and the conductive agent are negative electrode active material slurry: solid electrolyte slurry: conductive agent slurry = 60: 35: 5 by weight ratio. , Negative electrode active material slurry, solid electrolyte slurry, conductive agent slurry are weighed, and these weighed materials are put into a pot mill together with a grinding medium and the above organic vehicle, and sufficiently mixed and pulverized to produce negative electrode slurries of sample numbers 1 to 7 did.

  Thereafter, using the same doctor blade method as described above, the negative electrode slurry of Sample Nos. 1 to 7 was subjected to a molding process, and negative electrode layer green sheets of Sample Nos. 1 to 7 having a thickness of 10 μm were produced.

(Production of laminated sintered body)
The solid electrolyte layer green sheet and the negative electrode layer green sheet were each peeled from the PET film, and three negative electrode layer green sheets were sequentially laminated on the 20 solid electrolyte layer green sheets. This was sandwiched between two stainless steel plates heated to 60 ° C., thermocompression bonded at a pressure of 98 MPa (1000 kg / cm ² ), sealed in a polyethylene film container, and isotropically pressurized at a hydrostatic pressure of 180 MPa. The laminate structure of sample numbers 1 to 7 in which the green sheet for the negative electrode layer was laminated on the solid electrolyte layer green sheet was produced by pressing with a press.

Next, this laminated structure was cut into a length of 10 mm and a width of 10 mm, sandwiched between two porous setters, and fired in a state of being pressurized at a pressure of 0.2 MPa (2 kg / cm ² ). That is, after performing a degreasing process at a temperature of 500 ° C. in a nitrogen atmosphere containing 1 vol% oxygen, a baking process was performed at a temperature of 1000 ° C. for 2 hours in a nitrogen atmosphere. A laminated sintered body was produced.

(Completion of all-solid battery)
Sputtering was performed on the negative electrode of the laminated sintered body using Pt as a target material, and a negative electrode current collector was produced on one main surface of the laminated sintered body.

  On the other hand, a gel electrolyte made of PMMA containing Li ions is applied to the surface of the metal Li serving as the positive electrode layer, the gel electrolyte and the solid electrolyte are joined, and then sealed in a battery can having a diameter of 20 mm and a thickness of 3.2 mm. Thus, all solid state batteries of sample numbers 1 to 7 were produced.

(Evaluation of discharge capacity)
Each sample No. 1-7 is charged with a constant current of 40 μA until it reaches a voltage of 1.4 V, held for 5 hours, then left for several hours until the voltage becomes constant, and this charge / discharge cycle is repeated twice. After the second charge / discharge cycle, the discharge capacity was measured.

  Table 2 shows the solid electrolyte materials contained in the solid electrolyte layer and the negative electrode layer of each sample Nos. 1 to 7 and the discharge capacity.

  As is apparent from Table 2, sample No. 6 has a rhombohedral crystal system at both room temperature and firing temperature, so that the discharge capacity is 5 mAh / g. It became extremely low and proved difficult to use practically.

  In Sample No. 7, since the solid electrolyte layer and the negative electrode layer are triclinic crystals whose room temperature crystal system is inferior in ionic conductivity, the discharge capacity becomes extremely low at 2 mAh / g, making it difficult to use practically. It turns out that.

  In contrast, Sample Nos. 1 to 5 have a rhombohedral system at room temperature, and a reversible transition occurs between the rhombohedral system and the monoclinic system in the temperature range from room temperature to the firing temperature. Therefore, it was found that the solid electrolyte material has good sinterability and good ion conductivity, and as a result, a large discharge capacity of 90 mAh / g or more can be obtained.

  A solid electrolyte material having good sinterability and good ionic conductivity even if Zr is contained in the central metal, and a sintered all-solid battery using this solid electrolyte material are realized.

4 Solid Electrolyte Layer 5 Positive Electrode Layer 6 Negative Electrode Layer 11 Positive Electrode Layer 12 Gel Electrolyte Layer 15 Solid Electrolyte Layer 16 Negative Electrode Layer

Claims (9)

A solid electrolyte material in which the basic skeleton of the crystal structure has a NASICON structure,
The main component is represented by the general formula Li _x Zr ₂ (PO ₄ ) ₃ (where x is 1.1 ≦ x ≦ 2.0) containing Zr as a central metal ,
It has a first crystal system mainly composed of a rhombohedral system at room temperature and is reversible between a second crystal system different from the first crystal system in a temperature range from the room temperature to the firing temperature. Metastasis occurs,
A solid electrolyte material obtained by sintering at the firing temperature.   The solid electrolyte material according to claim 1, wherein the second crystal system includes at least one of a monoclinic system, an orthorhombic system, and a triclinic system.   The solid electrolyte material according to claim 1, wherein the second crystal system includes a mixed crystal system with the rhombohedral system. The solid electrolyte material according to any one of claims 1 to 3, wherein a part of the Li is substituted with at least one of Na and K. A part of the Zr is substituted with at least one element M selected from Ca, Mg, Ba, Sr, Al, Sc, Y, In, Ti, Ge, Ga, and Hf. The solid electrolyte material according to any one of claims 1 to 4 . An all-solid battery having a positive electrode layer on one main surface of the solid electrolyte layer and a negative electrode layer on the other main surface of the solid electrolyte layer,
An all-solid-state battery characterized in that at least the solid electrolyte layer is composed mainly of the solid electrolyte material according to any one of claims 1 to 5 . The all solid state battery according to claim 6 , wherein at least one of the solid electrolyte layer, the positive electrode layer, and the negative electrode layer is integrally joined by sintering. An all-solid battery having a positive electrode layer on one main surface of the solid electrolyte layer and a negative electrode layer on the other main surface of the solid electrolyte layer,
At least the solid electrolyte layer and the negative electrode layer contain the solid electrolyte material according to any one of claims 1 to 7 , and at least the solid electrolyte layer and the negative electrode layer are integrally joined by sintering. All-solid-state battery characterized by having. 9. The all solid state battery according to claim 8 , wherein a gel electrolyte layer is interposed between the solid electrolyte layer and the positive electrode layer.

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