JP6462343B2 - Method for producing Li-containing composite oxide - Google Patents

Description

  The present invention relates to a method for producing a Li-containing composite oxide, and further to a solid electrolyte for an all solid-state lithium ion secondary battery using the obtained Li-containing composite oxide.

Garnet-type solid electrolytes typified by Li ₅ La ₃ Nb ₂ O ₁₂ have ion diffusion through three-dimensional pathways, chemical and thermal stability, and a wide potential window, so all-solid-state lithium ion secondary batteries (LIBs) ) Application to solid electrolyte is expected. In order to actually apply to all-solid-state LIB, high-quality single crystals with good ion diffusion paths are desired. In addition, solid / solid interface bonding is required. In general, the solid interface between the electrolyte and the active material in all-solid-type LIB tends to be in point contact, which is undesirable from the viewpoint of interfacial ion migration. In addition, when a solid electrolyte is brought into contact with the active material surface, a space charge layer is formed as a solid interface having a different chemical potential for lithium ions. As a result, lithium ions move from the solid electrolyte to the active material side, the composition of the solid electrolyte changes from the optimum composition, and a large resistance component is generated at the interface. This is a factor that hinders ion migration at the active material / solid electrolyte interface. In view of the above, it is said that the development of a laminate having a good bonding interface between the active material and the solid electrolyte at a low temperature in consideration of the heat resistance temperature of the current collector and the electrode active material and the formation method thereof are said to be urgent.

  In secondary batteries used in devices such as personal computers and mobile phones, liquid electrolytes such as organic solvents are widely used as a medium for moving ions. A battery using such a liquid electrolyte may cause problems such as leakage and ignition. In contrast, an all-solid-type LIB in which a solid electrolyte is used instead of a liquid electrolyte and all other battery elements are made of solid can be made to have a high energy density, and a ceramic in which the electrolyte is sintered. Therefore, there is no risk of ignition or leakage, and problems such as deterioration of battery performance due to corrosion hardly occur.

  Garnet-type solid electrolyte particles that are such solid electrolytes are mainly synthesized by a solid-phase reaction method (Non-patent Documents 1 and 2). However, particles produced by the solid-phase reaction method are amorphous polycrystals.

  In addition, as a method for producing the all-solid-state LIB, there is a method of forming a laminate by pressing the produced electrode and electrolyte material. However, this method has a problem that a good electrode / electrolyte interface cannot be formed. Therefore, a technique that can form a good electrode / solid electrolyte interface with a simple process is required.

Venkataraman Thangadurai, Stefan Adams, Werner Weppner, Chem. Mater., 16, 2998 (2004). Sumaletha Narayanan, Venkataraman Thangadurai, Journal of Power Sources, 196, 8085 (2011)

The present invention provides a laminate in which a Li-containing composite oxide single crystal such as a high-quality Li ₅ La ₃ Nb ₂ O ₁₂ having a good lithium ion diffusion path is directly grown from an electrode active material layer, and the laminate efficiently. A method of manufacturing is provided.

The present invention provides the following inventions in order to solve the above problems.
(1) A metal layer that is one of the metal components of a Li-containing composite oxide is provided on the surface of the electrode active material layer; a solution containing a starting material and a flux of the Li-containing composite oxide on the surface of the metal layer or Applying the dispersion; and heating the collector containing the solution or dispersion containing the Li-containing composite oxide starting material and flux, and then cooling the Li-containing composite electrode on the electrode active material layer A method for producing a Li-containing composite oxide, comprising : forming a composite oxide crystal layer.
(2) The Li-containing composite oxide according to the above (1), wherein the Li-containing composite oxide is a garnet type, perovskite type, LISICON (· -Li ₃ PO ₄ ) type, NASICON type, or Li- · -alumina type composite oxide A method for producing a composite oxide.
(3) The garnet-type composite oxide has a general formula of Li ₅ La ₃ M ₂ O ₁₂ (M = Nb and / or Ta) or Li _7-x La ₃ Zr _2−x M ′ _x O ₁₂ (M ′ is Nb) , Ta or Al, 0 ≦ x ≦ 2), and the method for producing a Li-containing composite oxide according to (2) above.
(4) The method for producing a Li-containing composite oxide according to (2), wherein the perovskite complex oxide is represented by the general formula (LiLn) TiO ₃ (Ln = rare metal).
(5) The LISICON type composite oxide is Li ₁₄ ZrGe ₄ O ₁₆ or a general formula Li _{1 + x} M _2−x M _x ^III P ₃ O ₁₂ (M = Ti, Zr, Ge or Hf; M ^III = Al, In or The manufacturing method of Li containing complex oxide as described in said (2) shown by Sc, 0 <= x <= 2.
(6) The Li-containing composite oxide according to any one of the above (1) to (5), wherein the starting material of the Li-containing composite oxide is an oxide, hydroxide, metal salt or alkoxide of each metal component Manufacturing method.
(7) The flux is LiOH.H ₂ O (melting point: 471 ° C.), Li ₂ CO ₃ (melting point: 720 ° C.), LiCl (melting point: 605 ° C.), LsiNO ₃ (melting point: 873 ° C.), Li ₂ SO ₄ ( Melting point: 860 ° C.), LiBO ₂ (melting point: 849 ° C.), Li ₆ B ₄ O ₉ (melting point: 754 ° C.), KOH (melting point: 406 ° C.), NaCl (melting point: 801 ° C.), KCl (melting point: 770 ° C.) ) Contains at least one selected from KNO ₃ (melting point: 334 ° C.), NaNO ₃ (melting point: 308 ° C.), K ₂ CO ₃ (melting point: 633 ° C.), Na ₂ CO ₃ (melting point: 851 ° C.) The manufacturing method of Li containing complex oxide in any one of said (1)-(6).
(8) a metal film, one of the deposited on the collector electrode active material for a secondary battery, a metal film which is one of the metal components of the Li-containing composite oxide (1) to (7) The manufacturing method of Li containing complex oxide as described in any one of.
( 9 ) The method for producing a Li-containing composite oxide according to ( 8 ), wherein the secondary battery is a lithium ion secondary battery or a sodium ion secondary battery.
( 10 ) The method for producing a Li-containing composite oxide according to (8) or (9) , wherein the metal film that is one of the metal components of the Li-containing composite oxide is Nb or Zr.
(11) A method of manufacturing a Li-containing complex oxide according to any one of the above Li-containing complex oxide is _{Li 5 La 3 Nb 2 O 12} (1) ~ (10).
(12) A method of manufacturing a Li-containing complex oxide according to any one of the above Li-containing complex oxide is _{Li 7 La 3 Zr 2 O 12} (1) ~ (10).
( 13 ) The Li-containing composite oxide crystal layer according to any one of the above (1) to ( 12 ), wherein the Li-containing composite oxide crystal layer is a stacked structure in which single crystal particles of the Li-containing composite oxide are stacked. Production method.

According to the present invention, a method for efficiently producing a Li-containing composite oxide such as a high-quality Li ₅ La ₃ Nb ₂ O ₁₂ crystal having a good lithium ion diffusion path can be provided, and the resulting Li ₅ La can be obtained. ₃ Nb ₂ O ₁₂ crystal or the like is suitable as a solid electrolyte for an all solid-state lithium ion secondary battery.

_Li formed Nb on the substrate 5 _La 3 _Nb 2 _{O 12} crystals and Nb substrate XRD pattern. _Li 5 _La 3 _Nb 2 _{O 12} crystal and Nb substrate SEM images formed Nb on the substrate. TG-DTA curve of Nb substrate. Nb substrate in-situ XRD pattern. XRD pattern of crystals grown with different retention times. SEM images of crystals grown with different retention times. XRD patterns of various crystals. SEM images of various crystals. XRD patterns of various crystals. SEM images of various crystals.

  The Li-containing composite oxide of the present invention is obtained by applying a solution or dispersion containing the starting material and the flux to the substrate surface, heating the substrate containing the applied surface, and then cooling the substrate. It is obtained by forming an oxide crystal layer.

Examples of the Li-containing composite oxide include garnet-type, perovskite-type, LISCON (.-Li ₃ PO ₄ ) -type, NASICON-type, and Li --- alumina-type composite oxides. A composite oxide is preferable, and a garnet-type composite oxide is particularly preferable.

The garnet-type composite oxide has a general formula of Li ₅ La ₃ M ₂ O ₁₂ (M = Nb and / or Ta) or Li _7-x La ₃ Zr _2-x M ′ _x O ₁₂ (M ′ is Nb, Ta or Al, 0 ≦ x ≦ 2). Specific examples include Li ₅ La ₃ Nb ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li _7-x La ₃ Zr _2−x Nb _x O _{12, and the} like. From the viewpoint of lithium ion conductivity, Li 5 _{7-x La 3 Zr 2-} x Nb x O 12 is most preferred.

The perovskite complex oxide is represented by the general formula (LiLn) TiO ₃ (Ln = rare metal). Specific examples include Li _3x La _{(2 / 3-x)} Li _3x TiO ₃ (0.05 ≦ x ≦ 0.1), LiLa _1/3 Nb _1-x Ti _x O _{3, and the} like. From the viewpoint of ionic conductivity, Li _0.33 La _0.5 TiO ₃ or the like is preferable.

The LISICON-type composite oxide is Li ₁₄ ZrGe ₄ O ₁₆ or a general formula Li _{1 + x} M _2−x M _x ^III P ₃ O ₁₂ (M = Ti, Zr, Ge or Hf; M ^III = Al, In or Sc, 0 ≦ x ≦ 2).

The starting material for the Li-containing composite oxide is preferably an oxide, hydroxide, metal salt or alkoxide of a metal component such as Li, La, Nb, Ta, Zr, and Al. For example, examples of the Li component include lithium hydroxide and lithium carbonate, examples of the La component include lanthanum hydroxide and lanthanum oxide La ₂ O ₃ , and examples of the Nb component include niobium oxide Nb ₂ O ₅ , niobium chloride. Examples thereof include NbCl ₅ and niobium alkoxide, and examples of the Zr component include zirconia ZrO ₂ . Further, examples of the Ti component include titanium alkoxide. As the Nb, Zr, Ta, Al, and Ti components, metals themselves can also be used.

  The starting materials for these Li-containing composite oxides are blended with a quantitative ratio determined in accordance with the composition ratio of the target Li-containing composite oxide.

  The flux method is a type of crystal growth from a solution, in which the solute is dissolved in a flux (solvent) that is melted at high temperature, and the crystal is formed by utilizing the increase in supersaturation due to cooling of the solution or evaporation of the solvent. Cultivate. The target crystal can be grown at a temperature lower than the melting point, a high-quality crystal can be grown, and no special apparatus or operation is required. In the flux method, crystals are usually grown in a container such as a crucible. The flux coating method is a crystal layer (thin film) forming method that applies the principle of such a flux method. Usually, a solvent is added to the starting materials (solute and flux) filled in the crucible to prepare a solution or paste at room temperature, and this is applied to the substrate surface and heated. The applied solute is dissolved in the flux by heating, and a crystal grows on the surface of the substrate by driving the evaporation of the flux or the cooling of the solution as a driving force.

The flux method can grow high-quality single crystals with a self-form surrounded by a flat crystal plane that reflects the crystal structure in order to precipitate crystals from solution. The flux preferably contains at least one of alkali carbonate, alkali nitrate, alkali chloride, and alkali hydroxide, and includes LiOH.H ₂ O (melting point: 471 ° C.), Li ₂ CO ₃ (melting point: 720 ° C.), LiCl (melting point: 605 ° C.), LiNO ₃ (melting point: 873 ° C.), Li ₂ SO ₄ (melting point: 860 ° C.), LiBO ₂ (melting point: 849 ° C.), Li ₆ B ₄ O ₉ (melting point: 754 ° C), KOH (melting point: 406 ° C), NaCl (melting point: 801 ° C), KCl (melting point: 770 ° C)
Contains at least one selected from KNO ₃ (melting point: 334 ° C.), NaNO ₃ (melting point: 308 ° C.), K ₂ CO ₃ (melting point: 633 ° C.), Na ₂ CO ₃ (melting point: 851 ° C.) Are preferably used. Li-containing flux is also used as a Li source.

The application method is not particularly limited, and can be a spray method, a dipping method, a trowel brush method, or the like. After application, it is dried at room temperature to about 100 ° C., the flux amount is usually ^{0.01mg · cm -2 ~10mg · cm -2} .

  Next, the substrate including the coated surface is introduced into a heating furnace, preferably heated in a high oxygen partial pressure atmosphere, and then cooled to form a target crystal layer on the substrate. The obtained crystal layer is a laminated structure in which single crystal particles of Li-containing composite oxide are densely laminated.

  Heating is selected from about 500 to 1000 ° C., preferably about 700 to 900 ° C. and maintained for about 1 minute to 3 hours.

The substrate is preferably an electrode active material layer of a secondary battery. Alternatively, the substrate is preferably a metal that is one of the metal components of the Li-containing composite oxide, such as an Nb or Zr substrate. Alternatively, more preferably, the substrate is an Nb or Zr layer formed on the electrode active material. That is, for example, Li ₅ La ₃ Nb ₂ O ₁₂ crystal layer, Li ₇ La ₃ Zr ₂ O ₁₂ , Li _7-x La ₃ Zr _2−x Nb _x O ₁₂ is directly formed on the electrode active material by a flux coating method. be able to. Preferably, the substrate is an electrode active material layer of a lithium ion secondary battery or a sodium ion secondary battery. Alternatively, the substrate is a metal film that is one of the metal components of the Li-containing composite oxide formed on the electrode active material of a lithium ion secondary battery or a sodium ion secondary battery. The film is formed by a sputtering method, a vacuum evaporation method, or the like, but can be preferably formed by a sputtering method. The film thickness is usually selected from about 5 to 500 nm.

  In the sodium ion secondary battery, a carbon material such as sodium metal oxide is generally used for the positive electrode and graphite is used for the negative electrode.

  As a method for producing the all-solid-state LIB, there is a method in which the produced electrode and the electrolyte material are pressed to form a laminate. However, this method has a problem that a good electrode / electrolyte interface cannot be formed. Here, a good electrode / solid electrolyte interface can be formed by a simple process.

The Li-containing composite oxide thus obtained is particularly useful as a solid electrolyte for an all solid-state lithium ion secondary battery. That is, the all solid-state lithium ion secondary battery includes a positive electrode, a negative electrode, and a solid electrolyte that is the Li-containing composite oxide of the present invention. The positive electrode and the negative electrode can include known positive electrode active materials and negative electrode active materials used in lithium ion secondary batteries. Examples of the positive electrode active material include lithium manganese composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, lithium manganese cobalt composite oxide, and lithium phosphate compound having an olivine structure. _{LiCoO 2, LiNiO 2, LiNi 0.33} Mn 0.33 Co 0.33 O 2, LiNi 0.82 Co 0.13 Al 0.05 O 2 _{having, LiMnO 4, LiNi 0.5 Mn 1.5} O 4 having a spinel structure, LiNiPO _4, LiNiPO ₄ or the like having an olivine structure Is preferred. Examples of the negative electrode active material include carbon, metal lithium (Li), lithium titanate (nitride), and the like.

  As described above, in the present invention, when a laminated structure in which single crystal particles of a Li-containing composite oxide are densely laminated on an electrode active material layer is obtained, for example, this is used as a solid electrolyte for an all solid type It can be suitably used for a lithium ion secondary battery.

Hereinafter, the present invention will be described in more detail with reference to examples. In the following examples, the results for Li ₅ La ₃ Nb ₂ O ₁₂ are shown as an example of the Li-containing composite oxide, but the present invention is not limited to Li ₅ La ₃ Nb ₂ O ₁₂ , Moreover, it is not limited to the experimental condition selected in the Example.
Example 1
A. Conversion of Nb substrate to Li ₅ La ₃ Nb ₂ O ₁₂ crystal layer by LiOH flux (1) In order to directly form a solid electrolyte crystal layer on the active material, the heat resistance temperature of the current collector and the active material should be considered In addition to forming at low temperature, it is necessary to form the film directly while suppressing the reaction between the solute and the active material. Therefore, an Nb layer is stacked on the active material LiCoO ₂ . Nb can be used as a protective layer because it does not form a solid solution with Co. Furthermore, if the Nb source is supplied from the Nb layer, the crystal grows on the surface of the substrate, so that a dense and strong crystal layer can be produced. Here, we focused on forming a crystal layer from an Nb layer (Nb substrate) as a model experiment. The Li ₅ La ₃ Nb ₂ O ₁₂ crystal layer was prepared by using commercially available reagents LiOH · H ₂ O (special grade reagent, Wako Pure Chemical Industries) 0.295 g, La ₂ O ₃ (optical, Wako Pure Chemical Industries) 0.305 g Was used. In addition, 2.431 g of LiOH · H ₂ O was used as a flux. LiOH / H ₂ O is also used as a Li source, but here it is not handled as Li concentration, but for the sake of convenience, solute and flux are distinguished.

A mixed reagent of LiOH.H ₂ O and La ₂ O ₃ was applied on an Nb substrate (10 × 15 mm). After that, it was covered and installed in the electric furnace. The temperature was raised to 500 ° C at 8.3 ° C / min and held at that temperature for 0-10 hours. After the holding, it was cooled to 100 ° C at 200 ° C / hour and then allowed to cool to room temperature. After that, the crucible was taken out from the electric furnace and immersed in warm water to dissolve and remove the flux.
(2) A Li ₅ La ₃ Nb ₂ O ₁₂ crystal layer was produced using a LiOH flux at a holding temperature of 500 ° C. The XRD pattern of the produced crystal layer is shown in FIG. In FIG. 1, (a) is a crystal formed on an Nb substrate with a holding time of 10 hours, (b) is an untreated Nb substrate, and (c) is Li ₅ La ₃ Nb ₂ O ₁₂ ICDD PDF 73-7390 The XRD pattern is shown. In the XRD pattern, diffraction lines attributed to Nb and Li ₅ La ₃ Nb ₂ O ₁₂ were detected. As a result, it was confirmed that the produced crystal layer was Li ₅ La ₃ Nb ₂ O ₁₂ . Figure 2 shows SEM images of the untreated Nb substrate (a) and the crystal layers ((b) and (c)) produced at a holding temperature of 10 hours. A crystal layer consisting of self-developed polyhedral crystals could be formed on the Nb substrate surface. The produced crystal layer was firmly bonded to the substrate. This is probably because the Nb source was supplied from the Nb substrate. From the cross-sectional image, it was confirmed that the crystal layer was composed of one crystal in the thickness direction. In addition, since crystals are densely accumulated, it is considered that crystals grow on the substrate surface.
(3) In order to consider the crystal growth process on the substrate surface, TG-DTA analysis of the Nb substrate and the XRD pattern with respect to temperature change were investigated. In both cases, the temperature was raised to 500 ° C at a heating rate of 500 ° C / hour. The results are shown in FIGS. 4A shows an Nb substrate, and FIG. 4B shows Nb ₂ O ₅ ICDD PDF 03-0514.

In TG-DTA analysis, the weight of the Nb substrate increased with heating. In addition, in-situ XRD analysis confirmed diffraction lines resulting from the formation of Nb ₂ O ₅ at 461-499 ° C. Considering the melting point of the flux (462 ° C) and these results, the Nb source is considered to be an oxide film formed on the surface by heating.
(4) Next, Fig. 5 shows the XRD pattern of the crystal layer produced by changing the holding time from 10 hours to no holding or from 1 hour holding. Without retention (a), Li ₅ La ₃ Nb ₂ O _{12 was} slightly produced, but LiLa ₂ NbO ₆ was produced as the main phase. At a retention time of 1 hour (b), LiLa ₂ NbO ₆ became a by-product and Li ₅ La ₃ Nb ₂ O ₁₂ was produced as the main phase. At a retention time of 10 hours (c), the diffraction lines attributed to LiLa ₂ NbO ₆ disappeared and only Li ₅ La ₃ Nb ₂ O ₁₂ was produced (↓: Nb substrate). From this, it is considered that the Li ₅ La ₃ Nb ₂ O ₁₂ crystal layer is generated via LiLa ₂ NbO ₆ . (d) shows LiLa ₂ NbO ₆ ICDD PDF and (e) shows Li ₅ La ₃ Nb ₂ O ₁₂ ICDD PDF.

Fig. 6 shows SEM images of Li ₅ La ₃ Nb ₂ O ₁₂ crystal layers fabricated at each retention time. Without retention (a), polyhedral crystals were partially formed, and with a retention time of 1 hour (b), the number of polyhedral crystals increased. At a holding time of 10 hours (c), the polyhedral crystal completely occupied the substrate surface, and the individual crystal size increased.
(5) Consider the crystal layer formation process from the above results. The Nb substrate surface is covered with an oxide film at around 450 ℃. When the temperature is raised to 500 ° C., the solute reacts in the melted flack to form LiLa ₂ NbO ₆ on the substrate surface, and then Li ₅ La ₃ Nb ₂ O ₁₂ starts to be generated. The generated Li ₅ La ₃ Nb ₂ O ₁₂ crystal grows in the flux, and a dense Li ₅ La ₃ Nb ₂ O ₁₂ crystal layer is formed on the substrate surface. That is, after the Li ₅ La ₃ Nb ₂ O ₁₂ crystal is formed on the substrate surface, it is considered that each crystal is Ostwald ripened in the flux.
B. Preparation of Li ₅ La ₃ Nb ₂ O ₁₂ Crystal Layer on Active Material from LiOH Flux (1) Preparation of Li ₅ La ₃ Nb ₂ O ₁₂ Crystal Layer on Active Material ₂ O (special grade reagent, Wako Pure Chemical Industries) and La ₂ O ₃ (optical, Wako Pure Chemical Industries) were used. LiCoO ₂ used as a commercially available positive electrode material was used as the active material. As the Nb source, an Nb layer formed by sputtering on LiCoO ₂ was used. The sputtering conditions were a back pressure of 2.0 × 10 ⁻³ Pa, an output of 300 W, an argon flow rate of 3.0 sccm, a discharge Ar gas pressure of 0.67 Pa, and a discharge time of 5 hours. In addition, LiOH · H ₂ O was selected as the flux. LiOH · H ₂ O (0.295 g) and La ₂ O ₃ (0.305 g) were used. In addition, 2.431 g of LiOH · H ₂ O as a flux was dry mixed and applied onto LiCoO ₂ pellets coated with Nb. In the electric furnace, the temperature was raised to 500 ° C at about 8.3 ° C / min and held at that temperature for 10 hours. After completion of the holding, it was cooled to 100 ° C. at 200 ° C./hour and further allowed to cool to room temperature. After that, it was removed from the electric furnace and immersed in warm water to dissolve and remove the flux.
(2) FIG. 7 shows an XRD pattern of untreated LiCoO ₂ pellets, after Nb sputtering and after crystal layer formation. In FIG. 7, (a) to (e) are: (a) Li ₅ La ₃ Nb ₂ O ₁₂ / LiCoO ₂ (Run No. 2-11), (b) Nb / LiCoO ₂ , (c) LiCoO ₂ , d) Li ₅ La ₃ Nb ₂ O ₁₂ ICDD PDF and (e) LiLa ₂ NbO ₆ ICDD PDF 40-0895. The diffraction lines attributed to Nb were confirmed from the XRD pattern after Nb sputtering. Moreover, from the XRD pattern after Nb layer conversion, it was confirmed that Li ₅ La ₃ Nb ₂ O ₁₂ was produced as the main phase, but LiLa ₂ NbO ₆ was produced as a byproduct. FIG. 8 shows SEM images of untreated LiCoO ₂ pellets, Nb after sputtering, and after crystal layer formation. After sputtering, it was confirmed that an Nb film was formed on the LiCoO ₂ surface. In addition, it was confirmed from the SEM image after Nb layer conversion that a crystal layer composed of self-developed polyhedral crystals could be densely formed. The individual crystals constituting the crystal layer were surrounded by {110} and {211} planes in the same manner as the crystal layer on the substrate. In FIG. 8, (a) to (d) show (a) LiCoO ₂ , (b) Nb / LiCoO ₂ and ((c) and (d)) Li ₅ La ₃ Nb ₂ O ₁₂ crystal layer / LiCoO ₂ . Show.
C. As described above, under the above conditions, Li ₅ La ₃ Nb ₂ O ₁₂ crystals were grown by the flux method. The holding temperature and holding time used for crystal growth are about 500 ° C for about 10 hours, compared with the conventional solid-phase reaction method (950 ° C, 24 hours) (J. Am. Ceram. Sos., 88, 411 (2005)). We were able to significantly reduce the temperature and time. The formation phase, crystal size and morphology depended greatly on the flux and holding temperature. The grown crystal was a polyhedral crystal with a flat crystal plane and developed self-shape. The crystal was surrounded by {110} and {221} faces. The lattice constant, crystal density, face angle, and lattice spacing of the grown crystal were almost the same as the literature values. Crystals grown under the same conditions were found to have sharp diffraction patterns and ordered atomic arrangements by TEM observation. From the above, it can be said that the crystal grown by low temperature flux is a high quality single crystal. High quality single crystals could be grown because the LiOH flux sufficiently dissolved the solute and the crystals grew. The number of crystals in the thickness direction forming the crystal layer was one. Furthermore, the crystal layer formation process on the substrate surface was considered. In the temperature rising and holding process, the Nb substrate surface changes in phase in the order of Nb, Nb ₂ O ₅ and LiLa ₂ NbO ₆ , and finally a Li ₅ La ₃ Nb ₂ O ₁₂ crystal layer is formed. In the holding process, it is considered that individual Li ₅ La ₃ Nb ₂ O ₁₂ crystals are Ostwald-ripened. In addition, a Li ₅ La ₃ Nb ₂ O ₁ crystal layer could be formed on the active material LiCoO ₂ based on the crystal layer formation conditions on the Nb substrate. From the above results, the solid electrolyte Li ₅ La ₃ Nb ₂ O ₁₂ crystal (layer) grown and produced by the flux method and the flux coating method can be suitably used for an all-solid-state lithium ion secondary battery.
Example 2
A. Conversion of Ta substrate to Li ₅ La ₃ Ta ₂ O ₁₂ crystal layer by LiOH flux A Ta layer is laminated on the active material LiCoO ₂ . Ta can be used as a protective layer because it does not form a solid solution with Co. Furthermore, if a Ta source is supplied from the Ta layer, the crystal grows on the surface of the substrate, so that a dense and strong crystal layer can be produced.
(1) Li ₅ La ₃ Ta ₂ O ₁₂ crystal layer on the active material was prepared using commercially available reagents such as LiOH · H ₂ O (special grade reagent, Wako Pure Chemical Industries), La ₂ O ₃ (optical, Hikari Pure Chemical Industries) was used. LiCoO ₂ used as a commercially available positive electrode material was used as the active material. As the Ta source, a Ta layer formed by sputtering on LiCoO ₂ was used. The sputtering conditions were a back pressure of 2.0 × 10 ^-3 Pa, an output of 150 W, an argon flow rate of 3.0 sccm, a discharge Ar gas pressure of 0.67 Pa, and a discharge time of 15 minutes. In addition, LiOH · H ₂ O was selected as the flux. LiOH · H ₂ O (0.093 g) and La ₂ O ₃ (0.188 g) were used. In addition, 1.610 g of LiOH · H ₂ O as a flux was dry-mixed and applied onto Ta-coated LiCoO ₂ pellets. In the electric furnace, the temperature was raised to 500 ° C at about 8.3 ° C / min and held at that temperature for 10 hours. After the holding, it was cooled to 100 ° C at 200 ° C / hour and then allowed to cool to room temperature. Thereafter, the flux was removed from the electric furnace and immersed in warm water to dissolve and remove the flux.
(2) FIG. 9 shows the XRD pattern after the crystal layer is formed. In FIG. 9, (a) to (d) are: (a) Li ₅ La ₃ Ta ₂ O ₁₂ / LiCoO ₂ , (b) LiCoO ₂ , (c) Li ₅ La ₃ Ta ₂ O ₁₂ ICDD PDF 45-0110 , (D) La ₂ Li _0.5 Co _0.5 O ₄ ICDD PDF 89-4701. From the XRD pattern after Ta layer conversion, it was confirmed that La ₂ Li _0.5 Co _0.5 O ₄ was formed as a by-product, but Li ₅ La ₃ Ta ₂ O ₁₂ was formed as the main phase. The SEM images after forming the crystal layer are shown in FIGS. 10 (a) and 10 (b). From the SEM image after the Ta layer conversion, it was confirmed that the crystal layer composed of polyhedral crystals with self-development was densely formed .

  According to the present invention, a method for efficiently producing a high-quality active material / solid electrolyte interface having an interface in which a good positive electrode active material and a solid electrolyte are directly bonded is formed and a lithium ion diffusion path is good at the interface. Can provide.

Claims (13)

A metal layer that is one of the metal components of the Li-containing composite oxide is provided on the surface of the electrode active material layer; a solution or dispersion containing the starting starting material and the flux of the Li-containing composite oxide on the surface of the metal layer. And applying a Li-containing composite oxide on the electrode active material layer by heating and then cooling the current collector including the surface on which the solution or dispersion containing the Li-containing composite oxide starting material and flux is applied Forming a crystal layer ; and a method for producing a Li-containing composite oxide. 2. The Li-containing composite oxide according to claim 1, wherein the Li-containing composite oxide is a garnet-type, perovskite-type, RISICON (• -Li ₃ PO ₄ ) -type, NASICON-type, or Li- • -alumina-type composite oxide. Production method. The garnet-type composite oxide has a general formula of Li ₅ La ₃ M ₂ O ₁₂ (M = Nb and / or Ta) or Li _7-x La ₃ Zr _2-x M ′ _x O ₁₂ (M ′ is Nb, Ta or The manufacturing method of Li containing complex oxide of Claim 2 shown by Al, 0 <= x <= 2. The method for producing a Li-containing composite oxide according to claim 2, wherein the perovskite complex oxide is represented by a general formula (LiLn) TiO ₃ (Ln = rare metal). The LISICON type complex oxide is Li ₁₄ ZrGe ₄ O ₁₆ or the general formula Li _{1 + x} M _2−x M _x ^III P ₃ O ₁₂ (M = Ti, Zr, Ge or Hf; M ^III = Al, In or Sc, 0 The manufacturing method of Li containing complex oxide of Claim 2 shown by <= x <= 2).   The method for producing a Li-containing composite oxide according to any one of claims 1 to 5, wherein the starting material of the Li-containing composite oxide is an oxide, hydroxide, metal salt or alkoxide of each metal component. The flux is LiOH.H ₂ O (melting point: 471 ° C.), Li ₂ CO ₃ (melting point: 720 ° C.), LiCl (melting point: 605 ° C.), LiNO ₃ (melting point: 873 ° C.), Li ₂ SO ₄ (melting point: 860 ° C), LiBO ₂ (melting point: 849 ° C), Li ₆ B ₄ O ₉ (melting point: 754 ° C), KOH (melting point: 406 ° C), NaCl (melting point: 801 ° C), KCl (melting point: 770 ° C)
A claim containing at least one selected from KNO ₃ (melting point: 334 ° C.), NaNO ₃ (melting point: 308 ° C.), K ₂ CO ₃ (melting point: 633 ° C.), Na ₂ CO ₃ (melting point: 851 ° C.) Item 7. The method for producing a Li-containing composite oxide according to any one of Items 1 to 6. Metal films were deposited on the collector electrode active material for a secondary battery, Li according to any one of claims 1 to 7 which is a metal film which is one of the metal components of the Li-containing complex oxide A method for producing a composite oxide. The method for producing a Li-containing composite oxide according to claim 8 , wherein the secondary battery is a lithium ion secondary battery or a sodium ion secondary battery. The method for producing a Li-containing composite oxide according to claim 8 or 9 , wherein the metal film that is one of the metal components of the Li-containing composite oxide is Nb or Zr. Method for producing a Li-containing complex oxide according to any one of claims. 1 to 10 Li-containing complex oxide is _{Li 5 La 3 Nb 2 O 12} . Method for producing a Li-containing complex oxide according to any one of claims. 1 to 10 Li-containing complex oxide is _{Li 7 La 3 Zr 2 O 12} . The method for producing a Li-containing composite oxide according to any one of claims 1 to 12 , wherein the Li-containing composite oxide crystal layer is a stacked structure in which single crystal particles of the Li-containing composite oxide are stacked.