JP2015202998A - Garnet type oxide and production method thereof, and solid electrolyte for secondary battery and secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a garnet type oxide and a production method thereof which make it possible to produce a compact garnet type oxide, and a solid electrolyte for a secondary battery and a secondary battery which use the garnet type oxide.SOLUTION: A method of producing a garnet type oxide according to the present invention includes a burning step of heating a plurality of kinds of inorganic materials including carbonate, in a carbon dioxide gas atmosphere including carbon dioxide, up to a burning temperature and burning them.

Description

  The present invention relates to a garnet-type oxide, a method for producing the same, a solid electrolyte for a secondary battery using the same, and a secondary battery.

An oxide having a garnet-type crystal structure (for example, Li ₇ La ₃ Zr ₂ O ₁₂ ) has ionic conductivity, excellent chemical stability such as water resistance and weather resistance, and the like under high potential and low potential. Excellent electrical stability, such as being relatively difficult to decompose. For this reason, it is considered that the garnet type oxide is used as a solid electrolyte for a secondary battery.

  The crystal structure of the garnet-type oxide is roughly divided into tetragonal crystals and cubic crystals. Among these, cubic oxides have excellent ionic conductivity. Such an oxide is produced by, for example, a solid phase method (Patent Documents 1 and 2), a sol-gel method (Non-Patent Document 1), and the like.

JP 2010-102929 A JP 2011-51800 A

Masaki Matsui, Tue-Al-09, 19th, International Conference on Solid State ionics Proceedings

  However, since the heat treatment in the production process is performed in the air, carbon dioxide is easily vaporized from the carbonate used as the raw material. The vaporized gas escapes from the sintered body and prevents the oxide from being densified.

  The present invention has been made in view of such circumstances, and a method for producing a garnet-type oxide capable of producing a dense garnet-type oxide, a garnet-type oxide, and a solid electrolyte for a secondary battery using the same. It is another object of the present invention to provide a secondary battery.

  The method for producing a garnet-type oxide according to the present invention includes a main baking step of baking a plurality of types of inorganic materials including carbonate by heating to a main baking temperature in a carbon dioxide gas atmosphere including carbon dioxide. To do.

  The garnet-type oxide of the present invention is obtained by the production method described above.

  The solid electrolyte for a secondary battery of the present invention is characterized by having a garnet oxide.

  A secondary battery according to the present invention includes the above-described solid electrolyte for a secondary battery, a positive electrode, and a negative electrode.

  According to the present invention, an inorganic material having a carbonate is fired in a carbon dioxide gas atmosphere. For this reason, a dense garnet-type oxide can be produced.

FIG. 5 is an explanatory diagram showing firing conditions for producing Sample 1. 3 is a SEM (scanning electron microscope) cross-sectional photograph of a sintered body of Sample 1. FIG. 5 is an explanatory diagram showing firing conditions for producing Sample 2. 3 is a SEM cross-sectional photograph of a sintered body of Sample 2. The upper part of FIG. 5 is a plan view of the sintered body of sample 3, and the lower part of FIG. 4 is a SEM photograph of a sintered body of Sample 4. 4 is a SEM photograph of a sintered body of Sample 5. 4 is a SEM photograph of a sintered body of Sample 6.

Method of manufacturing a garnet-type oxide in accordance with an embodiment of the present invention has a main firing step of firing the inorganic material containing a carbonate (such as Li ₂ CO ₃₎ was heated at the sintering temperature. An inorganic material containing a carbonate is a raw material for a garnet-type oxide. In the main firing step, the inorganic material is fired in a carbon dioxide gas atmosphere. As an example of the carbonate, lithium carbonate is decomposed by the following formulas (1) and (2). Formula (1) illustrates the carbonate decomposition reaction in which the carbonate is decomposed, and Formula (2) illustrates the oxide decomposition reaction in which the metal oxide is decomposed.

Li ₂ CO ₃ → Li ₂ O + CO ₂ (1)
Li ₂ O → 2Li + 1 / 2O ₂ (2)
When carbon dioxide gas (CO ₂ ) is present in the atmosphere, the progress of the reaction in the right direction of formula (1) is suppressed, and the decomposition of lithium carbonate is suppressed. Generation of carbon dioxide gas from lithium carbonate is suppressed, generation of pores through which carbon dioxide gas escapes into the inorganic material is reduced, and a dense garnet-type oxide sintered body can be formed from the inorganic material.

  In the main firing step of the present invention, an inorganic material containing carbonate is heated and fired at the main firing temperature in a carbon dioxide gas atmosphere. The carbon dioxide gas atmosphere in the main firing step is an atmosphere containing carbon dioxide gas. When the total gas in the carbon dioxide gas atmosphere is 100% by volume, the concentration of carbon dioxide gas in the carbon dioxide gas atmosphere is preferably 10% by volume or more and 100% or less by volume, and 30% by volume or more and 80% by volume or less. The volume is preferably not more than volume%, particularly preferably not less than 50 volume% and not more than 70 volume%. When the carbon dioxide gas concentration is too thin, it may be difficult to suppress the progress of the carbonate decomposition reaction exemplified by the formula (1).

  The carbon dioxide gas atmosphere in the main baking step is preferably an atmosphere with little oxygen. This is because, when oxygen is present in the atmosphere, the oxide decomposition reaction exemplified by the formula (2) does not proceed easily, and metals such as Li are difficult to volatilize. The concentration of oxygen gas in the carbon dioxide gas atmosphere is preferably 0% by volume or more and 10% by volume or less, more preferably 8% by volume or less, and preferably 5% by volume or less.

  The carbon dioxide gas atmosphere in the main baking step may contain only carbon dioxide gas, or may contain an inert gas such as nitrogen gas or argon gas in addition to the carbon dioxide gas.

  The main baking temperature in the main baking step may be a temperature at which a garnet-type crystal structure can be formed by a solid phase reaction. The inorganic material may be fired at a main firing temperature higher than the melting point of the carbonate. When the inorganic material is fired at a main firing temperature higher than the melting point of the carbonate, the carbonate melts to become a liquid phase on the surface of the inorganic material, and the particles of the inorganic material are well bonded to form a dense sintered body. It is because it becomes easy to obtain.

On the other hand, by setting the main firing temperature to a temperature higher than the melting point of the carbonate, the energy state of the carbonate is increased, and the carbonate decomposition reaction and the oxide decomposition reaction exemplified by the formulas (1) and (2). Advances, and CO ₂ and O ₂ are generated and pores are easily formed. However, even at this high temperature, by performing the main baking step at the main baking temperature in a carbon dioxide gas atmosphere, the progress of the carbonate decomposition reaction can be effectively suppressed, and the suppression of CO ₂ generation and pore generation can be suppressed. Can be suppressed. In addition, the carbonate particle surface is coated with a liquid phase to increase the CO ₂ partial pressure inside the particle, thereby suppressing the carbonate decomposition reaction exemplified by the formula (1) and suppressing the generation of CO ₂ . In addition, the oxide decomposition reaction subsequent to the carbonate decomposition reaction can be suppressed, and there is an effect of suppressing O ₂ generation.

  Lithium carbonate is preferably used as the carbonate. The melting point of lithium carbonate is 723 ° C. When lithium carbonate is used as the carbonate, the main firing temperature is preferably higher than 723 ° C, and more preferably 1100 to 1300 ° C. The main firing temperature is, for example, preferably 724 ° C. or higher and 1400 ° C. or lower, preferably 730 ° C. or higher and 1380 ° C. or lower, and more preferably 750 ° C. or higher and 1350 ° C. or lower. When the main firing temperature is lower than the melting point of lithium carbonate, the lithium carbonate does not melt and it may be difficult to produce a garnet-type oxide. If the main calcination temperature is excessively high, Li is likely to be volatilized and the composition of the compound may be shifted.

  When the garnet-type oxide produced by the method for producing a garnet-type oxide of the present invention is used for a solid electrolyte of a secondary battery, the carbonate as the raw material of the garnet-type oxide is occluded and released by the electrode. It is preferable to include a metal element of a metal ion. For example, when a garnet-type oxide is used for a lithium ion secondary battery or a solid electrolyte of a lithium secondary battery, the carbonate may contain lithium carbonate. When a garnet type oxide is used for a solid electrolyte of a sodium ion secondary battery or a sodium secondary battery, the carbonate may contain sodium carbonate, and the garnet type oxide is used for a solid electrolyte of a calcium ion secondary battery. In some cases, the carbonate may contain calcium carbonate, and when the garnet-type oxide is used for the solid electrolyte of the magnesium ion secondary battery, the carbonate may contain magnesium carbonate.

  In the main firing step of the present invention, the inorganic material is preferably fired in a relatively short time in order to suppress the generation of carbon dioxide gas. In order to fire the inorganic material in a relatively short time, it may be fired at a high temperature. The higher the main baking temperature, the shorter the baking time at the main baking temperature.

  In the main baking step of the present invention, the baking time for baking the inorganic material at the main baking temperature is preferably 60 minutes or less, more preferably 30 minutes or less, and preferably 5 minutes or less. Further, in order to reliably form the garnet-type oxide, the firing time for firing the inorganic material at the main firing temperature is preferably 1 minute or longer, more preferably 3 minutes or longer, and preferably 4 minutes or longer. It is desirable that

  The relationship between the main baking temperature and the baking time at the main baking temperature is preferably shown in the hatched range shown in Chemical Formula 1 below. In this case, a dense garnet oxide with few defects such as Li can be obtained.

  Further, the rate of temperature increase to the main firing temperature is preferably 5 ° C./min or more, more preferably 5 to 1350 ° C./min, and further preferably 50 ° C./min or more. Most preferably, it is 100 ° C./min or more. If the rate of temperature rise is too slow, carbon dioxide gas may volatilize from lithium carbonate while the temperature is raised to the main firing temperature, and pores may be generated in the sintered body.

  The inorganic material may be transferred from the atmosphere at a temperature lower than the main baking temperature to the atmosphere at the main baking temperature, or after the inorganic material is put into an atmosphere at a temperature lower than the main baking temperature, The temperature may be increased to reach the main firing temperature.

  A carbon dioxide gas atmosphere is preferable before the temperature of the atmosphere becomes higher than the melting point of the carbonate. When the temperature of the atmosphere becomes higher than the melting point of the carbonate, the surface of the carbonate becomes a liquid phase. The carbonate in the liquid phase is likely to undergo a carbonate decomposition reaction exemplified by the right reaction of Formula (1) in an atmosphere that does not contain carbon dioxide gas. Therefore, from the time when the carbonate is in a relatively low temperature before becoming a liquid phase, the inorganic material is baked in a carbon dioxide gas atmosphere until the carbonate becomes a liquid phase until it becomes a liquid phase. Make the reaction difficult to proceed. Thereby, carbon dioxide gas production from the carbonate is suppressed, and the carbonate can form a dense crystal structure as a heterogeneous phase. Therefore, it is preferable that a heterogeneous phase precipitates in the main firing step. The heterogeneous phase preferably has a carbonate. The solid electrolyte of the present invention preferably contains a garnet-type oxide as a main component and includes a heterogeneous phase between particles. This heterogeneous phase acts as an adhesive to form a solid electrolyte having a high sintered density. It is preferable that the heterogeneous phase in the solid electrolyte of the present invention mainly comprises carbonate. A heterogeneous phase is a phase in a different state from the particles. In the main firing step, the particle central portion maintains a solid state, but the particle surface becomes a liquid state, and a different phase is precipitated between the particles. Thereby, in the main baking step, the particle surface becomes a liquid phase by heating in carbon dioxide gas to promote liquid phase sintering. This produces a dense garnet-type oxide sintered body with almost no voids so that the particles are connected in a different phase.

  You may perform a temporary baking process before a main baking process. The pre-baking step is a step of pre-baking the inorganic material at a pre-baking temperature lower than the main baking temperature. This is because organic substances such as a binder contained in the inorganic material are burned off during temporary firing. The pre-baking temperature is preferably a temperature at which the organic matter is burned off, for example, preferably from 300 ° C. to less than 723 ° C., more preferably from 400 ° C. to 720 ° C., and more preferably from 500 ° C. to 700 ° C. The following is desirable. When the calcination temperature is too low, the organic matter remains, and a gas derived from the organic matter is generated at the time of subsequent firing at the main firing temperature, which may make it difficult to obtain a dense crystal structure.

  The atmosphere of the pre-baking step may be a carbon dioxide gas atmosphere containing carbon dioxide gas, or a general atmosphere containing no or almost no carbon dioxide gas. When the carbon dioxide gas atmosphere is set in the preliminary baking step, the concentration of carbon dioxide gas contained in the atmosphere may be changed with respect to the carbon dioxide gas atmosphere in the main baking step. The general atmosphere refers to an atmosphere containing no or almost no carbon dioxide gas, and examples thereof include an atmosphere containing oxygen gas, air, and water vapor.

  The atmosphere of the pre-baking step is preferably an oxygen-containing atmosphere, for example, air. This is because organic substances such as a binder react with oxygen in the air and easily burn out.

  The inorganic material fired in the main firing step is a raw material for the garnet oxide.

  This inorganic material has a carbonate. Carbonate is a salt formed from an element constituting garnet-type oxide and carbonic acid. The carbonate may contain at least one selected from the group of lithium carbonate, sodium carbonate, calcium carbonate, and magnesium carbonate, for example.

The compounding ratio of the carbonate in the inorganic material varies depending on the composition of the target garnet oxide. The inorganic material to be fired may include an oxide of a constituent element contained in the target garnet-type oxide. For example, when the garnet-type oxide is a lithium-containing garnet-type oxide containing lithium, the oxide that can be contained in the inorganic material is Li ₂ O, a Group 2 element (for example, Mg, Ca, Sr, Ba, Ra), lanthanoid elements, Y, Sc, Ti, Zr, Hf, oxides having at least one of V, Nb, Ta, Mo, V, and Al. Among these, at least one selected from the group consisting of CaO, SrO, BaO, Nd ₂ O ₃ , ZrO ₂ , NbO ₂ , TaO ₂ , and Al ₂ O ₃ is preferable, and further La ₂ O ₃ , ZrO ₂ , Li ₂ Oxides such as O, Al ₂ O ₃ , NbO ₂ , CaO, SrO, TaO ₂ are preferable.

  The carbonate may form particles alone, or may be mixed with an oxide other than the carbonate-derived element, which is a constituent element of a garnet-type oxide, to form particles. In addition, oxides of constituent elements other than carbonate-derived elements may form separate particles for each constituent element, or plural kinds may be mixed with each other to form particles.

  When the total amount of the inorganic material is 100% by mass, and the carbonate is 25% by mass or more, the carbon dioxide gas atmosphere is used as the atmosphere in the main firing step, whereby the right side reaction of the formula (1) of the carbonate is performed. The significance of suppressing carbon dioxide gas volatilization by suppressing the exemplified carbonate decomposition reaction is great.

  Before performing the main firing step, a molding step for forming a molded body by adding a binder to the inorganic material to form a slurry, and a temporary firing step for prefiring the molded body at a preliminary firing temperature lower than the main firing temperature, It is good to do.

  It is preferable to add a binder and, if necessary, a solvent to the inorganic material to form a slurry, and the slurry is formed into a sheet to form a sheet-like molded body. When the slurry is formed into a sheet shape, a method such as doctor blade can be employed. As the binder, it is preferable to use an organic substance which is effective with a small amount of PVB (polyvinyl butyral), acrylic resin, etc., does not react with the material, does not emit a toxic gas during decomposition, and has no residual ash. As the solvent, toluene, butanol or the like is preferably used. In this case, in order to use the garnet-type oxide as a solid electrolyte of the secondary battery, the thickness of the sheet-like molded body is preferably 50 to 500 μm.

  Alternatively, the inorganic material may be formed into a molded body by adding pressure without adding a binder. When obtaining a molded body by pressurization, it can be formed into a molded body by cold isotropic molding (CIP), hot isotropic molding (HIP), mold molding, hot pressing or the like. In this case, in order to use the garnet type oxide as the solid electrolyte of the secondary battery, the thickness of the molded body is preferably 10 μm or more and 10000 μm or less.

The garnet-type oxide obtained by the method for producing a garnet-type oxide of the present invention is preferably a lithium-containing garnet-type oxide. In this case, a lithium-containing garnet-type oxide, basic composition is _{Li x A y B 3-y} M 2 O 12, and a relative density to the theoretical density of 70% or higher, conductivity is 1.0 × It is good that it is 10 ⁻⁵ (Scm ⁻¹ ) or more. However, A is any one or more of group 2 elements (for example, Mg, Ca, Sr, Ba, Cs), B is any one or more of lanthanoid elements and Y, Sc, and y is 0 or more and 3 or less. When an integer, x = 7 + y, M is one or more of Ti, Zr, and Hf, and when x = 5 + y, M is any one or more of V, Nb, and Ta. Of these, A is preferably Ca, Sr, Ba or the like, B is preferably La or Nd, and M is preferably Zr, Nb, Ta or the like. The lithium-containing garnet-type oxide, it is more preferable basic composition is _{Li x A y La 3-y} Zr 2 O 12 and _{Li x A y La 3-y} Nb 2 O 12. As the lithium-containing garnet-type oxide, in addition to this, (Na _1-x Li _x ) _y M ₂ Fe ₃ O ₁₂ (where M is an element that can take an oxidation number +6 state (S, Se, Te, 1 or more of Po), 0.3 ≦ x ≦ 1.0, 2.5 ≦ y ≦ 3.0), and Ca ₃ LiMV ₃ O ₁₂ (where M is Co, Ni, Fe, Mn) 1 or more of them), Ca ₃ Li _x Nb _{(1.5 + x)} Ga _(3.5-2x) O ₁₂ (where x is 0.24 ≦ x ≦ 0.60), and the like. The “basic composition” is intended to include those that differ by 20%, 10%, etc. with respect to the content of each element of this composition. For example, “what the basic composition is Li ₇ La ₃ Zr ₂ O ₁₂ ” is generally the same as the composition, for example, the composition is Li _7.2 La ₃ Zr ₂ O _12.2 or the composition is Li _6.8 La. It is intended to include those that are ₃ Zr ₂ O _11.8 .

In the case where the basic composition of the lithium-containing garnet-type oxide is Li _x A _y La _{3 -y} Zr ₂ O ₁₂ , x is preferably 7 or more and 9 or less, and more preferably 8 or less. Moreover, y is preferably 0 or more and 2 or less, and more preferably 1 or less. Of these, the basic composition of x = 7 and y = 0 is preferably Li ₇ La ₃ Zr ₂ O ₁₂ . At this time, the relative density with respect to the theoretical density is 70 (%) or more, more preferably 90 (%) or more, and still more preferably 92 (%) or more. Further, the conductivity is 1.0 × 10 ⁻⁵ S / cm or more, and more preferably 1.0 × 10 ⁻⁴ S / cm or more. If the conductivity is 1.0 × 10 ⁻⁴ S / cm or more, the battery performance can be further improved.

In the case where the basic composition of the lithium-containing garnet-type oxide is Li _x A _y La _{3 -y} Nb ₂ O ₁₂ , x is preferably 5 or more and 7 or less, and more preferably 6 or less. Moreover, y is preferably 0 or more and 2 or less, and more preferably 1 or less. Of these, the basic composition of x = 5 and y = 0 is preferably Li ₅ La ₃ Nb ₂ O ₁₂ . At this time, the relative density with respect to the theoretical density is 70 (%) or more, more preferably 90 (%) or more, and still more preferably 92 (%) or more. The conductivity is 1.0 × 10 ⁻⁵ or more.

According to the method for producing a garnet-type oxide of the present invention, a metal-deficient garnet-type oxide such as Li having a lower Li content than the basic composition may be obtained. For example, when producing a lithium-containing garnet-type oxide having a basic composition of Li ₇ La ₃ Zr ₂ O ₁₂ , the lithium-containing garnet-type oxide in which the Li content x is 7> x with respect to La3 mol May be obtained. For example, 1 <x <7 may be sufficient, and 2 <x <7, 3 <x <7 may be sufficient.

The garnet oxide obtained by the method for producing a garnet oxide of the present invention can be used as a solid electrolyte of a secondary battery. When the garnet type oxide obtained by the manufacturing method of the garnet type oxide of this invention is a lithium containing garnet type oxide, this lithium containing garnet type oxide can be used as a solid electrolyte of a lithium ion secondary battery. . The solid electrolyte of the lithium ion secondary battery is interposed between the positive electrode and the negative electrode and conducts lithium ions.

  The garnet-type oxide of the present invention is used as a solid electrolyte for secondary batteries, a battery solid electrolyte using lithium metal as a negative electrode, a battery using this solid electrolyte as a diaphragm, or a positive electrode active on both sides of a current collector. There are applications such as a battery (bipolar battery) used for the electrolyte layer having a structure in which a plurality of electrolyte layers sandwiched between bipolar electrodes in which a substance and a negative electrode active material are arranged are stacked in series.

  When using the garnet type oxide obtained by the manufacturing method of the garnet type oxide of this invention as an electrolyte or a diaphragm, it is preferable that the density of a garnet type oxide is high. When the density is high, there are few gaps between the garnet-type oxides, and it is possible to prevent the possibility of short circuit or liquid leakage.

  Specifically, when the garnet type oxide is used for the solid electrolyte for the secondary battery, the relative density of the garnet type oxide is preferably 70% or more and 98% or less, and more preferably 90% or more and 95% or less. It is preferable. When the density is low, lithium dendrite grows in the gaps of the garnet-type oxide, which may cause a short circuit or not function as a diaphragm.

  The garnet-type oxide obtained by the method for producing a garnet-type oxide of the present invention may be either a cubic crystal or a tetragonal crystal, but the cubic crystal has higher ion conductivity and is suitable as a solid electrolyte for a secondary battery. Used.

  The secondary battery of the present invention includes a positive electrode having a positive electrode active material capable of occluding and releasing metal ions, a negative electrode having a negative electrode active material capable of occluding and releasing metal ions, a garnet-type oxide as a solid electrolyte, Is provided. Examples of the metal ions include lithium ions and sodium ions.

  A positive electrode used for a secondary battery has a positive electrode active material that can occlude and release metal ions. The positive electrode has a current collector and a positive electrode active material layer bound to the surface of the current collector.

  The positive electrode current collector is not particularly limited as long as it is a metal that can withstand a voltage suitable for the active material to be used. A current collector refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharge or charging of a secondary battery. As the current collector, at least one selected from silver, copper, gold, aluminum, stainless steel, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel A metal material such as steel can be exemplified. The current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. When the current collector is in the form of foil, sheet or film, the thickness is preferably in the range of 1 μm to 100 μm.

The positive electrode active material layer includes a positive electrode active material and, if necessary, a binder and / or a conductive aid. As the positive electrode active material, a material that can occlude and release metal ions can be used. When the metal ion is a lithium ion, the layered compound Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1) is used as the positive electrode active material. , D is at least selected from Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La 1, 1.7 ≦ f ≦ 2.1), Li ₂ MnO ₃ or the like. The ratio of b: c: d in the general formula is 0.5: 0.2: 0.3, 1/3: 1/3: 1/3, 0.75: 0.10: 0.15. 0: 0: 1, 1: 0: 0, and 0: 1: 0.

That is, specific examples of the lithium metal composite oxide having a layered rock salt structure include LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _{0. .5} Mn _0.5 O ₂ , LiNi _0.75 Co _0.1 Mn _0.15 O ₂ , LiMnO ₂ , LiNiO ₂ , and LiCoO ₂ may be at least one kind. The positive electrode active material is composed of a mixture of a lithium metal composite oxide having a layered rock salt structure and a spinel such as LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₄ , LiMn _1.5 Ni _0.5 O _4. For example, there is Li ₂ MnO ₃ —LiCoO ₂ . Examples of the positive electrode active material include polyanionic compounds represented by LiMPO ₄ , LiMVO _4, or Li ₂ MSiO ₄ (wherein M is selected from at least one of Co, Ni, Mn, and Fe). be able to. Furthermore, as the positive electrode active material, tavorite compound (the M a transition metal) LiMPO ₄ F, such as LiFePO ₄ F represented by, Limbo ₃ such LiFeBO ₃ (M is a transition metal) include borate-based compound represented by be able to. Any metal oxide used as the positive electrode active material may have the above composition formula as a basic composition, and a metal in which the metal contained in the basic composition is replaced with another metal can also be used. Further, as the positive electrode active material, a positive electrode active material that does not contain lithium ions contributing to charge / discharge, for example, sulfur alone (S), a compound in which sulfur and carbon are combined, a metal sulfide such as TiS ₂ , V ₂ O, etc. ₅ , oxides such as MnO ₂ , polyaniline and anthraquinone, compounds containing these aromatics in the chemical structure, conjugated materials such as conjugated diacetate-based organic substances, and lithium such as FeF ₃ are structured according to the amount of mobile ions It is also possible to use a material that exhibits an electric capacity with a conversion reaction that changes and other known materials. Further, a compound having a stable radical such as nitroxide, nitronyl nitroxide, galvinoxyl, phenoxyl, etc. may be adopted as the positive electrode active material. When using a positive electrode active material that does not contain lithium, it is necessary to add ions to the positive electrode and / or the negative electrode in advance by a known method. Here, in order to add the ion, a metal or a compound containing the ion may be used.

  Any metal oxide used as the positive electrode active material may have the above composition formula as a basic composition, and a metal element included in the basic composition may be replaced with another metal element, and Mg, etc. Other metal elements may be added to the basic composition to form a metal oxide. Moreover, when using these positive electrode active materials, you may coat inorganic materials, such as an oxide, as a buffer layer between the surface and solid electrolyte.

  The binder serves to bind the active material and the conductive additive to the surface of the current collector. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, and alkoxysilyl group-containing resins. be able to.

  Moreover, you may employ | adopt the polymer which has a hydrophilic group as a binder. Examples of the hydrophilic group of the polymer having a hydrophilic group include a phosphate group such as a carboxyl group, a sulfo group, a silanol group, an amino group, a hydroxyl group, and a phosphate group. Among them, a polymer containing a carboxyl group in the molecule such as polyacrylic acid (PAA), carboxymethyl cellulose (CMC) and polymethacrylic acid, or a polymer containing a sulfo group such as poly (p-styrenesulfonic acid) is preferable.

  A polymer containing many carboxyl groups and / or sulfo groups such as polyacrylic acid or a copolymer of acrylic acid and vinyl sulfonic acid becomes water-soluble. Therefore, the polymer having a hydrophilic group is preferably a water-soluble polymer, and a polymer containing a plurality of carboxyl groups and / or sulfo groups in one molecule is preferable.

  A polymer containing a carboxyl group in the molecule can be produced by, for example, a method of polymerizing an acid monomer or adding a carboxyl group to the polymer. Acid monomers include acrylic acid, methacrylic acid, vinyl benzoic acid, crotonic acid, pentenoic acid, angelic acid, tiglic acid, etc., acid monomers having one carboxyl group in the molecule, itaconic acid, mesaconic acid, citraconic acid, fumaric acid , Maleic acid, 2-pentenedioic acid, methylene succinic acid, allyl malonic acid, isopropylidene succinic acid, 2,4-hexadiene diacid, acetylenedicarboxylic acid, etc., acid monomers having two or more carboxyl groups in the molecule Is done. A copolymer obtained by polymerizing two or more kinds of monomers selected from these may be used.

  For example, a polymer composed of a copolymer of acrylic acid and itaconic acid as described in JP-A-2013-065493, and containing an acid anhydride group formed by condensation of carboxyl groups in the molecule It is also preferable to use as a binder. The structure derived from a highly acidic monomer having two or more carboxyl groups in one molecule is believed to facilitate trapping of metal ions such as lithium ions before the electrolytic solution decomposition reaction occurs during charging. Furthermore, the acidity is not excessively increased because there are more carboxyl groups and the acidity is higher than polyacrylic acid and polymethacrylic acid, and a predetermined amount of the carboxyl groups are changed to acid anhydride groups. Therefore, a secondary battery having a negative electrode formed using this binder has improved initial efficiency and improved input / output characteristics.

  The mixing ratio of the binder in the positive electrode active material layer is preferably a mass ratio of positive electrode active material: binder = 1: 0.005 to 1: 0.3. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density of the electrode is lowered.

  The conductive assistant is added to increase the conductivity of the electrode. Therefore, the conductive auxiliary agent may be added arbitrarily when the electrode conductivity is insufficient, and may not be added when the electrode conductivity is sufficiently excellent. The conductive auxiliary agent may be any chemically inert electronic high conductor, such as carbon black, graphite, acetylene black, ketjen black (registered trademark), vapor grown carbon fiber (Vapor Grown Carbon). Fiber: VGCF) and various metal particles are exemplified. These conductive assistants can be added to the active material layer alone or in combination of two or more.

  The blending ratio of the binder in the positive electrode active material layer is preferably a mass ratio of positive electrode active material: binder = 1: 0.05 to 1: 0.5. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density of the electrode is lowered.

  The negative electrode used for the secondary battery of the present invention has a current collector and a negative electrode active material layer bound to the surface of the current collector. The negative electrode active material layer includes a negative electrode active material and, if necessary, a binder and / or a conductive aid.

As the negative electrode active material, a material capable of occluding and releasing metal ions can be used. Accordingly, there is no particular limitation as long as it is a simple substance, alloy, or compound that can occlude and release metal ions. For example, when the metal ion is lithium ion, the negative electrode active material is Li, group 14 elements such as carbon, silicon, germanium, and tin, group 13 elements such as aluminum and indium, group 12 elements such as zinc and cadmium, antimony A group 15 element such as bismuth, an alkaline earth metal such as magnesium or calcium, and a group 11 element such as silver or gold may be used alone. Specific examples of alloys or compounds include tin-based materials such as Ag-Sn alloy, Cu-Sn alloy, Co-Sn alloy, carbon-based material, SiO _x disproportionate to silicon simple substance and silicon dioxide (0.3≤ Examples thereof include silicon-based materials such as x ≦ 1.6), silicon alone, or a composite of a silicon-based material and a carbon-based material. The carbon-based material is not particularly limited, and examples thereof include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. In addition, as the negative electrode active material, oxides such as Nb ₂ O ₅ , TiO ₂ , Li ₄ Ti ₅ O ₁₂ , WO ₂ , MoO ₂ , Fe ₂ O ₃ , or Li _3-x M _x N (M = A nitride represented by (Co, Ni, Cu) may be employed. One or more of these materials can be used as the negative electrode active material. In this specification, when lithium is used as the negative electrode active material, it is referred to as a lithium secondary battery, and when a material other than lithium is used as the negative electrode active material, it is referred to as a lithium ion secondary battery.

  The negative electrode current collector is not particularly limited as long as it is a metal that can withstand a voltage suitable for the active material to be used, and for example, the one described for the positive electrode current collector can be adopted. As the negative electrode binder and the conductive additive, those described for the positive electrode can be adopted.

  As a method for forming the active material layer on the surface of the current collector, a conventionally known method such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method is used. An active material may be applied to the surface of the electric body. Specifically, an active material layer-forming composition containing an active material and, if necessary, a binder and a conductive aid is prepared, and an appropriate solvent is added to the composition to make a paste, and then the collection is performed. After applying to the surface of the electric body, it is dried. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. In order to increase the electrode density, the dried product may be compressed.

  The shape of the secondary battery is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a laminate shape can be adopted.

  The secondary battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy from a lithium ion secondary battery for all or a part of its power source, and may be, for example, an electric vehicle or a hybrid vehicle. Examples of the lithium ion secondary battery include various home electric appliances, office equipment, industrial equipment, and the like driven by batteries, such as personal computers and portable communication devices, in addition to vehicles. Furthermore, lithium ion secondary batteries can be used for wind power generation, solar power generation, hydroelectric power generation and other power system power storage devices and power smoothing devices, power supplies for ships, etc. and / or power supplies for auxiliary equipment, aircraft, spacecraft, etc. Power source for power and / or auxiliary equipment, auxiliary power source for vehicles not using electricity as a power source, power source for mobile home robots, power source for system backup, power source for uninterruptible power supply, for electric vehicles You may use for the electrical storage apparatus which stores temporarily the electric power required for charge in a charging station.

  As mentioned above, although embodiment of electrolyte solution was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

(Sample 1)
As a molding process, Li ₂ CO ₃ , La ₂ O ₃ and ZrO ₂ are used as raw materials, and a ball mill (product name planetary type, manufactured by Fritsch Japan Co., Ltd.) with a blending ratio that is a stoichiometric ratio of Li ₇ La ₃ Zr ₂ O ₁₂ is used. By mixing with a ball mill P-7), an inorganic material was obtained. 8 parts by mass of PVB (polyvinyl butyral) as a binder and 300 parts by mass of a toluene and butanol mixed solution (toluene: butanol = 1: 1 volume ratio) as a solvent are added to 100 parts by mass of an inorganic material. Were kneaded to obtain a slurry. The slurry was formed into a sheet having a thickness of 100 μm by a doctor blade method to obtain a sheet molded body.

  The following temporary firing step and main firing step were performed on the sheet molded body. In the preliminary firing step and the main firing step, the sheet molded body was fired under the firing conditions shown in FIG.

  First, the sheet compact was placed in an electric furnace (manufactured by Koyo Thermo System Co., Ltd.) in an air atmosphere. The atmosphere in the electric furnace was raised from normal temperature at a heating rate of 10 ° C./min (first heating step). When the atmosphere in the electric furnace reached 600 ° C., it was maintained at 600 ° C. for 30 minutes to perform preliminary firing (temporary firing step).

  Next, the temperature inside the electric furnace was raised (second temperature raising step). The temperature rising rate at this time was 10 ° C./min. When the temperature reached 1100 ° C., the temperature was maintained at 1100 ° C. for 1 hour (main firing step). Thereafter, the inside of the furnace was allowed to cool (temperature lowering step). The rate of temperature drop during cooling was 20 ° C./min.

  The atmosphere during firing was an air atmosphere during the first temperature raising step and the temporary firing step. The air atmosphere contains 78% by volume: nitrogen and 21% by volume: oxygen as main components when the entire air is 100% by volume. The carbon dioxide gas atmosphere was switched to after the pre-baking step, and the carbon dioxide gas atmosphere was used between the second temperature raising step and the main baking step (in the air atmosphere ratio up to 600 ° C., the amount of air was 100 ml / min, 600 The carbon dioxide flow rate is 1 L / min in the temperature range between 0 ° C. and 700 ° C., and the carbon dioxide flow rate is 50 mL / min at temperatures above 700 ° C.). The component ratio of the carbon dioxide gas atmosphere was 100% by volume of carbon dioxide gas when the entire atmosphere was 100% by volume. Simultaneously with the completion of the main firing step at 1100 ° C., the carbon dioxide gas atmosphere was switched to the air atmosphere, and the temperature lowering step was performed in the air atmosphere.

The sintered body obtained as described above was a cubic lithium-containing garnet-type oxide having a basic composition of Li ₇ La ₃ Zr ₂ O ₁₂ . The obtained lithium-containing garnet-type oxide was subjected to elemental mass spectrometry by an inductively coupled plasma method (ICP). The results are shown in Table 1. The relative density of the lithium-containing garnet-type oxide was 93%.
Further, an SEM (scanning electron microscope) photograph of the lithium-containing garnet-type oxide is shown in FIG. As shown in FIG. 2, the garnet-type oxide hardly had any pores.

(Sample 2)
A sheet molded body similar to the sheet molded body of Sample 1 was prepared. The sheet compact was fired under the firing conditions shown in FIG. Among the firing conditions shown in FIG. 3, the temperature condition is the same as the firing condition of Sample 1. On the other hand, the atmosphere during firing was changed as follows.

  The atmosphere in the electric furnace during firing was an air atmosphere in the first temperature raising step, the temporary firing step, the second temperature raising step, and the temperature lowering step. Only the main baking step maintained at the main baking temperature of 1100 ° C. was made a carbon dioxide gas atmosphere. The component ratio of the air atmosphere and the carbon dioxide gas atmosphere is the same as that of the sample 1.

The obtained sintered body was a cubic lithium-containing garnet-type oxide having a basic composition of Li ₇ La ₃ Zr ₂ O ₁₂ , and element mass spectrometry was performed on this with an inductively coupled plasma method (ICP). The results are shown in Table 1. The relative density of the lithium-containing garnet oxide was measured and found to be 50%. Moreover, the SEM (scanning electron microscope) photograph of the lithium containing garnet-type oxide was shown in FIG.

(Sample 3)
A sheet molded body similar to the sheet molded body of Sample 1 was prepared. The sheet compact was fired under predetermined firing conditions. Among these firing conditions, the temperature condition is the same as the firing condition of Sample 1. However, the atmosphere during firing was an air atmosphere.

The obtained sintered body was a cubic lithium-containing garnet-type oxide having a basic composition of Li ₇ La ₃ Zr ₂ O ₁₂ . About this, element mass spectrometry was performed by the inductively coupled plasma method (ICP). The results are shown in Table 1. Moreover, it was 35% when the relative density of the lithium containing garnet-type oxide was measured. Moreover, the front view of the fired body is shown in the upper part of FIG. 5, and the lower part of FIG. 5 shows an SEM (scanning electron microscope) photograph of the lithium-containing garnet-type oxide.

  When comparing samples 1 to 3, as shown in Table 1, sample 1 had the highest density. Further, as shown in the upper part of FIG. 5, the sample 3 was very fragile and collapsed as soon as an external force was applied. As shown in the lower part of FIG. 5, fairly large cavities were observed between the particles, and the particles did not have a dense structure. On the other hand, in Sample 2, the relative density was low, and a plurality of pores were observed as shown in FIG.

  The amount of Li in each of samples 1 to 3 was smaller than the basic composition.

  From the above, Sample 1 was fired in the carbon dioxide gas atmosphere not only at the main firing temperature at 1100 ° C. but also during the second temperature raising step up to the main firing temperature, so that a dense garnet crystal structure was obtained. It was.

(Sample 4)
The same sheet molded body as the sheet molded body of Sample 1 was prepared, and this was subjected to a main firing step. In the main baking step, the main baking temperature is 1250 ° C., the rate of temperature increase from the temporary baking temperature of 600 ° C. to the main baking temperature of 1250 ° C. is 1250 ° C./min, and the baking time of the main baking temperature at 1250 ° C. is 4 The sheet molded body was baked under the same conditions as in Sample 1 except that the sample was used.

(Sample 5)
The same sheet molded body as the sheet molded body of Sample 1 was prepared, and this was subjected to a main firing step. In the main baking step, the main baking temperature is 1300 ° C., the rate of temperature increase from the temporary baking temperature of 600 ° C. to the main baking temperature of 1300 ° C. is 1300 ° C./min, and the baking time of the main baking temperature at 1300 ° C. is 3 The sheet molded body was baked under the same conditions as in Sample 1 except that the sample was used.

(Sample 6)
The same sheet molded body as the sheet molded body of Sample 1 was prepared, and this was subjected to a main firing step. In the main baking step, the main baking temperature is 1350 ° C., the rate of temperature increase from the temporary baking temperature of 600 ° C. to the main baking temperature of 1350 ° C. is 1350 ° C./min, and the baking time of the main baking temperature at 1350 ° C. is 1 The sheet molded body was baked under the same conditions as in Sample 1 except that the sample was used.

Samples 4 to 6 obtained above were all cubic lithium-containing garnet-type oxides having a basic composition of Li ₇ La ₃ Zr ₂ O ₁₂ . These were subjected to elemental analysis by ICP, density measurement, and SEM observation. The results of elemental analysis and relative density are shown in Table 2. The SEM photographs are shown in FIGS. 6 to 8 in order for Samples 4 to 6.

From these results, when the main baking temperature is 1250 ° C. to 1350 ° C. (samples 4 to 6), the main baking temperature is higher than when the main baking temperature is 1100 ° C. (sample 1, Table 1). However, the residual amount of Li was large. This is presumably because the firing time at the main firing temperature was shortened to 1 to 4 minutes, so that the production of CO ₂ from lithium carbonate was suppressed. When the main firing temperature was 1250 ° C. and 1300 ° C., the amount of remaining Li was large, and when it was 1350 ° C., the amount of remaining Li in the sintered body decreased. In particular, when the temperature was 1300 ° C., almost the same amount of Li remained as the Li theoretical ratio of the basic composition Li ₇ La ₃ Zr ₂ O ₁₂ , and almost no Li volatilized.

  In FIGS. 6 and 8, only the side surface of the sintered body is observed. In FIG. 7, the side surface of the sintered body and the flat surface thereon are observed. As shown in FIGS. 6 to 8, when the main firing temperature was 1250 ° C., many pores of about 5 μm were observed in the sintered body. At the main firing temperature of 1300 ° C., the pores almost disappeared. When the main firing temperature was 1350 ° C., there were almost no pores.

  As described above, the sintered body was almost densified and the amount of Li volatilization was small under the firing conditions of 1300 ° C. for 3 minutes. It has been found that by performing rapid firing in a carbon dioxide gas atmosphere under these conditions, the sintered body is densified and effective in suppressing Li deficiency.

Claims (18)

  A method for producing a garnet-type oxide, comprising a main baking step of baking a plurality of types of inorganic materials including a carbonate by heating to a main baking temperature in a carbon dioxide gas atmosphere including carbon dioxide.   The method for producing a garnet-type oxide according to claim 1, wherein a heterogeneous phase having a role of adhering particles is precipitated in the main firing step.   The method for producing a garnet-type oxide according to claim 2, wherein the hetero phase includes a carbonate.   The said calcination temperature is a manufacturing method of the garnet-type oxide of any one of Claims 1-3 higher than melting | fusing point of carbonate. Prior to the main firing step, there is a temperature raising step for raising the temperature from a temperature lower than the melting point of the carbonate in a carbon dioxide gas atmosphere to the main firing temperature,
The method for producing a garnet-type oxide according to any one of claims 1 to 4, wherein in the temperature raising step, the inorganic material is fired in the carbon dioxide gas atmosphere.   The said carbonate is a manufacturing method of the garnet-type oxide of any one of Claims 1-5 which consists of lithium carbonate.   The said baking temperature is 1100-1300 degreeC, The manufacturing method of the garnet-type oxide of Claim 6. The method for producing a garnet-type oxide according to claim 6 or 7, wherein a relationship between the main baking temperature and a baking time at the main baking temperature is indicated by a hatching range shown in Chemical Formula 1 below.
  The method for producing a garnet-type oxide according to any one of claims 1 to 8, wherein a rate of temperature rise to the main firing temperature is 5 to 1350 ° C / min.   The concentration of carbon dioxide gas in the carbon dioxide gas atmosphere is 10% by volume or more and 100% volume or less when the total gas in the carbon dioxide gas atmosphere is 100% by volume. The manufacturing method of the garnet-type oxide as described in a term.   Before performing the main firing step, a molding step in which a binder is added to the inorganic material to form a slurry to form a molded body, and a temporary firing step in which the molded body is temporarily fired at a temperature at which the binder is burned off. The manufacturing method of the garnet-type oxide of any one of Claims 1-10 performed.   The method for producing a garnet-type oxide according to any one of claims 1 to 11, wherein a temperature of the pre-baking in the pre-baking step is 300 ° C or higher and 723 ° C or lower. Basic composition _{Li x A y B 3-y} M 2 O 12 ( where, A is any one or more of the second group elements, B is a lanthanoid element and Y, any one or more of Sc, y is 0 or more When the integer is 3 or less and x = 7 + y, M is any one or more of Ti, Zr, and Hf, and when x = 5 + y, M is any one or more of V, Nb, and Ta. The method for producing a garnet oxide according to any one of claims 1 to 9.   A garnet-type oxide obtained by the production method according to claim 1.   The garnet-type oxide according to claim 14, which has a relative density of 70 or more and 98 or less.   The garnet-type oxide according to claim 14 or 15, which is a cubic crystal.   A solid electrolyte for a secondary battery comprising the garnet-type oxide according to any one of claims 14 to 16.   A secondary battery comprising the solid electrolyte for a secondary battery according to claim 17, a positive electrode, and a negative electrode.