JPWO2017029899A1 - Oriented positive electrode plate for lithium secondary battery - Google Patents

Abstract

An oriented positive plate for a lithium secondary battery comprising a sintered body composed of a plurality of lithium cobalt oxide crystal grains is provided. In this oriented positive electrode plate, at least part of the crystal grains is oriented in a direction in which the (003) plane of the layered rock salt structure intersects the plate surface of the oriented positive electrode plate, and by X-ray diffraction with respect to the surface of the oriented positive electrode plate, A ratio RS of the diffraction peak intensity of the (003) plane to the diffraction peak intensity of the (104) plane is (003) plane with respect to the diffraction intensity of the (104) plane by X-ray diffraction with respect to the center position in the thickness direction of the oriented positive electrode plate. The ratio of the surface XRD peak ratio RS to the internal XRD peak ratio RI is 0.5 or less. According to this oriented positive electrode plate, it is possible to suppress the progress of cracks when external stress is applied while maintaining the ease of taking out lithium ions by orientation on the surface of the oriented positive electrode plate and the high output characteristics thereby.

Description

  The present invention relates to an oriented positive electrode plate for a lithium secondary battery.

As a positive electrode active material in a lithium secondary battery (sometimes called a lithium ion secondary battery), a material using a lithium composite oxide (lithium transition metal oxide) having a layered rock salt structure is widely known. . In this type of positive electrode active material, the diffusion of lithium ions (Li ⁺ ) therein is performed in the in-plane direction of the (003) plane (that is, any direction in a plane parallel to the (003) plane). It is known that lithium ions enter and exit from crystal planes other than the (003) plane (for example, the (101) plane or the (104) plane).

Therefore, in this type of positive electrode active material, a surface that comes into contact with the electrolyte more in a crystal plane (a plane other than the (003) plane, for example, the (101) plane or the (104) plane) on which lithium ions can enter and exit satisfactorily. Attempts have been made to improve the battery characteristics of lithium secondary batteries by exposing them to the above. For example, Patent Document 1 (WO 2010/074304), a sheet containing _Co 3 _{O 4} particles by firing a green sheet (h00) face is oriented parallel to the sheet surface including _Co 3 _{O 4} It is disclosed that a LiCoO ₂ ceramic sheet (positive electrode active material film) having a (104) plane oriented parallel to the sheet surface is produced by forming and then introducing Li. This document also describes that Bi ₂ O ₃ is further added as a grain growth promoting material to a green sheet containing Co ₃ O ₄ .

International Publication No. 2010/0704304

  When a positive electrode plate with crystal orientation aligned (hereinafter referred to as an alignment positive electrode plate) as disclosed in Patent Document 1 is applied to a lithium ion secondary battery, the lithium ion is not aligned because the alignment direction is uniform. Easy to take out and high output characteristics can be obtained. However, on the other hand, since the crystal orientation is uniform, cracks tend to progress in a specific direction, and in the product made into a plate shape, there is a problem that it is easy to crack due to external stress during handling or use as a battery material. there were.

  Inventors of the present invention have recently made a structure in which only the surface is highly oriented by deliberately randomizing the orientation inside the oriented positive electrode plate (hereinafter referred to as a surface orientation structure), thereby providing lithium by orientation on the surface of the oriented positive electrode plate. While maintaining ease of ion extraction and high output characteristics (particularly high rate characteristics), it is possible to suppress the development of cracks when external stress is applied, and therefore prevent cracking in the plate shape during use. I got the knowledge.

  Therefore, the object of the present invention is to maintain the ease of extraction of lithium ions by orientation on the surface of the oriented positive electrode plate and the high output characteristics (particularly high rate characteristics), and the development of cracks when external stress is applied. Another object of the present invention is to provide an oriented positive plate for a lithium secondary battery that can be suppressed (and therefore can prevent cracking in the shape of the plate during use).

According to one aspect of the present invention, an alignment positive electrode plate for a lithium secondary battery,
The oriented positive electrode plate is composed of a sintered body composed of a plurality of lithium cobaltate crystal grains having a layered rock salt structure, and at least a part of the plurality of lithium cobaltate crystal grains is a (003) plane having a layered rock salt structure. Is oriented in a direction intersecting the plate surface of the oriented positive electrode plate,
Surface XRD peak ratio R _{S (003} ), which is the ratio of the diffraction peak intensity of the (003) plane to the diffraction peak intensity of the (104) plane measured by X-ray diffraction with respect to the surface on at least one side of the oriented positive electrode plate. _{) / (104)} is the ratio of the diffraction intensity of the (003) plane to the diffraction intensity of the (104) plane measured by X-ray diffraction with respect to the center position in the plate thickness direction of the oriented positive electrode plate. the ratio _{R I (003) / (104)} lower than the ratio of the internal XRD peak ratio _{R I (003) /} the relative ₍₁₀₄₎ surface XRD peak ratio _{R S (003) / (104} ) R S / R _I ratio is 0.5 or less, the orientation positive electrode plate is provided.

It is a schematic cross section which shows notionally the orientation state of the surface orientation positive electrode plate by this invention. 2 is a schematic cross-sectional view conceptually showing a non-oriented state of a non-oriented positive electrode plate. FIG. It is a schematic cross section which shows notionally the orientation state of the orientation positive electrode plate orientated to the inside. It is a schematic diagram for demonstrating the determination method of the high orientation area | region of the orientation positive electrode plate in an EBSD image. It is an XRD profile acquired by the X-ray diffraction with respect to the surface of the orientation positive electrode plate produced in Example 1 (comparison). It is an XRD profile acquired by the X-ray diffraction with respect to the inside of the orientation positive electrode plate produced in Example 1 (comparison). 3 is an XRD profile obtained by X-ray diffraction with respect to the surface of the oriented positive electrode plate produced in Example 2. FIG. 3 is an XRD profile acquired by X-ray diffraction with respect to the inside of the oriented positive electrode plate produced in Example 2.

Definitions The following are definitions of parameters used to identify the oriented positive plate according to the present invention.

In this specification, “surface XRD peak ratio R _{S (003) / (104)} ” means the diffraction peak intensity (104) plane (measured by X-ray diffraction with respect to the surface on at least one side of the aligned positive electrode plate ( This is the ratio of the diffraction peak intensity (maximum height of diffraction peak) of the (003) plane to the maximum height of diffraction peak. This measurement by X-ray diffraction can be performed by using an XRD apparatus and acquiring an XRD profile when the surface of the sintered plate is irradiated with X-rays.

In this specification, “internal XRD peak ratio R _{I (003) / (104)} ” means the diffraction peak intensity (104) plane (measured by X-ray diffraction with respect to the center position in the plate thickness direction of the oriented positive electrode plate ( This is the ratio of the diffraction peak intensity (maximum height of diffraction peak) of the (003) plane to the maximum height of diffraction peak. In this X-ray diffraction measurement, the alignment positive electrode plate is polished from one side so that its thickness is ½, the central cross section of the alignment positive electrode plate is exposed, and then the center of the sintered plate is measured using an XRD apparatus. This can be done by obtaining an XRD profile when the cross section is irradiated with X-rays.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oriented positive plate for a lithium secondary battery, and particularly preferably to an oriented positive plate for an all-solid lithium secondary battery. The oriented positive plate of the present invention comprises a sintered body composed of a plurality of lithium cobalt oxide crystal grains having a layered rock salt structure. Therefore, the oriented positive plate can also be referred to as an oriented sintered plate. Although the lithium cobaltate (LiCoO ₂ ) crystal has a layered rock salt structure, in the oriented positive electrode plate of the present invention, at least a part of the plurality of lithium cobaltate crystal grains has a (003) plane of the layered rock salt structure. It is oriented in a direction that intersects the plate surface of the oriented positive electrode plate. As described above, since the in-plane direction of the (003) plane (that is, any direction in a plane parallel to the (003) plane) is the lithium ion conduction direction, this in-plane direction is defined as the plate surface of the oriented positive electrode plate. By making them intersect (that is, by reducing exposure to the surface of the (003) plane), a crystal plane (for example, (101) plane or (104) plane) in which lithium ions can enter and exit satisfactorily is obtained. More can be exposed on the surface. Typically, at least one of the (101) plane and the (104) plane of LiCoO ₂ is oriented parallel to the plate surface (provided that the thickness of the lithium cobaltate oriented positive electrode plate increases (101) plane. Orientation becomes dominant). In any case, when incorporated in a lithium secondary battery, it is possible to realize easy extraction of lithium ions due to orientation on the surface of the oriented positive electrode plate and high output characteristics (particularly high rate characteristics). .

Nevertheless, the aligned positive electrode plate of the present invention has a surface XRD peak ratio Rs _{(003) / (104)} lower than the internal XRD peak ratio RI _{(003) / (104)} . This means that the surface of the oriented positive electrode plate has a high degree of orientation that makes it easier to extract lithium ions than the inside of the oriented positive electrode plate. In other words, the surface of the oriented positive electrode plate has a crystal surface with high lithium ion conductivity ( For example, it means that (101) plane and (104) plane) are many and lithium ions are exposed. That is, the surface XRD peak ratio R _{S (003) / (104)} is measured by X-ray diffraction with respect to the surface on at least one side of the aligned positive electrode plate, and the diffraction peak intensity (maximum height of the diffraction peak) on the (104) plane. )) Is the ratio of the diffraction peak intensity (maximum height of the diffraction peak) of the (003) plane, so that the lower the ratio, the more the (101) plane and (104) plane with higher lithium ion conductivity. It means that the alignment state is exposed (in other words, the alignment state in which the (003) plane having poor lithium ion conductivity is exposed to the surface less). The internal XRD peak ratio RI _{(003) / (104)} can also be considered in the same manner as above except that it is measured by X-ray diffraction with respect to the center position in the thickness direction of the oriented positive electrode plate. Therefore, as described above, the surface XRD peak ratio Rs _{(003) / (104)} is lower than the internal XRD peak ratio RI _{(003) / (104)} , so that the surface has more lithium ions than the inside. While a highly oriented state that is easy to take out is realized, the inside is inferior to such an oriented state (for example, non-oriented) than the surface. In order to further polarize this tendency, in the present invention, R _S / R _I which is the ratio of the surface XRD peak ratio R _{S (003) / (104) to} the internal XRD peak ratio R _{I (003) / (104)} . The ratio is limited to 0.5 or less. Thus, rather actively considerably higher that the orientation of the internal orientation positive electrode plate for an internal XRD peak ratio _{R I (003) / (104} ) surface XRD peak ratio _{R S (003) / (104} ) Can be randomized. In this way, the surface orientation structure in which only the surface is highly oriented by deliberately randomizing the orientation inside the oriented positive electrode plate makes it easy to extract lithium ions due to the orientation on the surface of the oriented positive electrode plate, and thereby high output. While maintaining the characteristics (particularly high rate characteristics), it is possible to effectively prevent cracks in the plate shape during use by suppressing the progress of cracks when external stress is applied.

In order to promote understanding of the oriented positive electrode plate of the present invention, FIGS. 1 to 3 conceptually illustrate positive electrode plates of various orientation forms. As a premise, as a typical form of a conventional lithium cobalt oxide (LiCoO ₂ ) positive electrode plate, a non-oriented form as shown in FIG. 2 and an oriented form as shown in FIG. 3 are known. . In the non-oriented positive electrode plate 20 shown in FIG. 2, a large number of crystal grains 22 are sintered so that the movable direction A of lithium ions is random. On the other hand, in the oriented positive electrode plate 30 shown in FIG. 3, a large number of crystal grains 32 cross the lithium ion movable direction A with the plate surface of the oriented positive electrode plate 30 (for example, with respect to the plate surface). It is sintered so as to be (vertical direction). On the other hand, in the surface-oriented positive electrode plate 10 according to the present invention shown in FIG. 1, the crystal grains 12 are highly oriented on the surface in the same manner as in FIG. Is low. Thus, by making the oriented positive electrode plate 30 have a surface orientation structure, it is possible to suppress the progress of cracks when external stress is applied due to the internal random orientation, and to prevent cracks in the plate shape during handling and use. Can do. On the other hand, since the surface on which the lithium ion can be easily taken out is aligned on the surface of the aligned positive electrode plate 30, high output characteristics (particularly high rate characteristics) can be maintained.

As described above, the surface alignment mode of the present invention in which the alignment level is polarized between the surface and the inside is the surface XRD peak ratio R _{S (003) / (104)} is the internal XRD peak ratio R _{I (003) /} R _S / R _I which is specified by being lower than ₍₁₀₄₎ and is the ratio of the surface XRD peak ratio R _{S (003) / (104) to} the internal XRD peak ratio R _{I (003) / (104)} The ratio is specified as a more effective surface orientation form. This R _S / R _I ratio is 0.5 or less, preferably 0.25 or less, more preferably 0.03 to 0.25, and particularly preferably 0.03 to 0.20. Further, the surface XRD peak ratio Rs _{(003) / (104)} is preferably 0.4 or less, more preferably 0.05 to 0.35, still more preferably 0.05 to 0.25, particularly preferably. It is 0.05-0.20. On the other hand, the internal XRD peak ratio RI _{(003) / (104)} is preferably 0.8 to 1.6, more preferably 1.0 to 1.6, and still more preferably 1.2 to 1.6. Especially preferably, it is 1.4 to 1.6.

  The thickness of the aligned positive electrode plate is preferably 20 μm or more, more preferably 20 to 100 μm, still more preferably 20 to 90 μm, particularly preferably 20 to 70 μm, and most preferably 20 to 60 μm. Thus, it becomes possible to produce an all-solid-state lithium battery with a high energy density because the oriented positive electrode plate is thick. Since this oriented positive electrode plate has high orientation at the surface portion as described above, it is easy to insert and remove lithium ions, and even if it is thick to some extent, highly efficient lithium ion removal and insertion is possible over the entire thickness of the oriented positive electrode plate. The capacity improvement effect brought about by the thick oriented positive electrode plate can be maximized. The ease of lithium ion desorption / insertion over the entire thickness can be desirably improved by combination with the control of the crystal grain size described later. For example, when an all-solid lithium battery is configured in combination with a solid electrolyte, lithium existing on the side of the thick oriented positive electrode plate away from the solid electrolyte can be sufficiently utilized for charging and discharging. Such an increase in capacity can greatly improve the energy density of the all-solid-state lithium battery.

The size of the orientation positive electrode plate is preferably 5 mm × 5 mm square or more, more preferably 10 mm × 10 mm to 100 mm × 100 mm square, and further preferably 10 mm × 10 mm to 50 mm × 50 mm square. preferably 25 mm ² or more, more preferably 100～10000Mm ^2, more preferably from 100~2500mm ^2.

  The average primary particle diameter of the lithium cobalt oxide crystal grains constituting the sintered body that is an oriented positive electrode plate is preferably 4 μm or more, more preferably 4 to 20 μm, still more preferably 4 to 15 μm, and particularly preferably. Is 4 to 10 μm. By appropriately increasing the particle diameter in this way, the influence (for example, decrease in lithium ion conductivity) that may occur due to random orientation (eg, non-orientation) inside is reduced, and the inside is sufficiently oriented. The same output characteristics as those obtained can be achieved. Moreover, it becomes easy to implement | achieve desired intensity | strength because a crystal grain is not too large.

  In the aligned positive electrode plate of the present invention, at least a thickness region from the surface of the aligned positive electrode plate to a depth of 2 μm is measured by an EBSD (Electron Back Scatter Diffraction) method with respect to a polished cross section perpendicular to the plate surface of the aligned positive electrode plate. It is preferably a highly oriented region in which the length in the direction parallel to the plate surface occupied by particles having an angle between the (003) plane and the plate surface of 30 ° or less is 30% or less, more preferably at least the surface of the oriented positive electrode plate. To a depth of 5 μm or 7 μm is the highly oriented region. The identification of the highly oriented region can be preferably performed as follows. That is, as schematically shown in the lower right of FIG. 4, an EBSD image is acquired using the polished cross section of the oriented positive electrode as an observation surface, and the EBSD image of the polished cross section acquired as schematically shown in the center of FIG. In (3), particles having an angle between the (003) plane and the plate plane of 30 ° or less are colored and displayed. Then, as shown in FIG. 4, a line is drawn parallel to the plate surface at an interval of 1 μm depth from the plate surface, and the length occupied by the colored portion on the line is 30% or less of the entire measurement length. In FIG. For example, in the case of the example shown in FIG. 4, the length occupied by the colored portion is 6% or less of the entire measurement length in 6 lines having a depth of 0, 1, 2, 3, 4 and 5 μm from the plate surface. In addition, in the line (bottom line) having a depth of 6 μm from the plate surface, the length occupied by the colored portion is more than 30% of the entire measurement length, so the depth from the plate surface to the depth of 5 μm It can be determined that the thickness region is a highly oriented region.

By the way, the X-ray diffraction with respect to the orientation positive electrode plate in this invention is performed paying attention to (104) plane regarding a lithium ion conduction surface. This is because the orientation positive electrode plate of the present invention typically has a maximum peak intensity of the diffraction peak on the (104) plane in the diffraction peak detected in the surface X-ray diffraction measurement. This is because of consideration. However, the aligned positive electrode plate of the present invention preferably has the maximum peak intensity of the diffraction peak on the (101) plane among the diffraction peaks detected in the surface X-ray diffraction measurement. In particular, as described above, in the aligned positive electrode plate of the present invention, it is typical that at least one of the (101) plane and the (104) plane of LiCoO ₂ is aligned parallel to the plate surface. However, when the thickness of the lithium cobaltate oriented positive electrode plate is increased, the orientation of the (101) plane becomes dominant.

  The lithium cobalt oxide oriented positive electrode plate according to the present invention is provided within the range not departing from the spirit of the present invention, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, One or more elements such as Zr, Nb, Mo, Ag, Sn, Sb, Te, Ba, Bi, Ni, Mn and the like or a form equivalent thereto (for example, partial solid solution to the surface layer of crystal grains, segregation, A trace amount may be contained by coating or adhesion).

Production Method The production of the aligned positive electrode plate according to the present invention comprises (a) preparing a green sheet comprising Co ₃ O ₄ particles, and (b) firing the green sheet at 900 to 1450 ° C. to obtain a fired intermediate. (C) The sintered intermediate is cooled to obtain a Co ₃ O ₄ oriented sintered plate containing a Co ₃ O ₄ phase, and (d) lithium is introduced into the Co ₃ O ₄ oriented sintered plate. it can.

  Hereafter, the detail of each process of a manufacturing method is demonstrated.

(A) Preparation of Green Sheet In this step (a), a green sheet having a thickness of 100 μm or less and containing Co ₃ O ₄ particles is prepared. The green sheet preferably further contains bismuth oxide (typically Bi ₂ O ₃ particles) as a grain growth promoter. The green sheets, Co ₃ O ₄ particles and bismuth oxide optionally a raw material containing (typically Bi ₂ O ₃ particles) may be made by molding into a sheet. The amount of Bi ₂ O ₃ particles added is not particularly limited, but is preferably 0.1 to 30% by weight, more preferably 1 to 30% by weight based on the total amount of Co ₃ O ₄ particles and Bi ₂ O ₃ particles. 20% by weight, more preferably 3 to 10% by weight. The volume-based D50 particle size of the Co ₃ O ₄ particles is preferably 0.1 to 2.0 μm, more preferably 0.3 to 1.2 μm. The volume-based D50 particle size of Bi ₂ O ₃ particles is preferably 0.1 to 1.0 μm, more preferably 0.2 to 0.5 μm. The thickness of the green sheet is 100 μm or less, preferably 1 to 90 μm, more preferably 5 to 60 μm. The green sheet may include CoO particles and / or Co (OH) ₂ particles in place of all or part of the Co ₃ O ₄ particles. In this case, the step (b) ), A CoO fired intermediate having the (h00) plane oriented parallel to the sheet surface can be obtained, and as a result, the same as in the case of using a green sheet containing Co ₃ O ₄ particles. In addition, a lithium cobaltate oriented sintered plate can be produced.

  Examples of a method for forming a green sheet include (i) a doctor blade method using a slurry containing raw material particles, and (ii) applying a slurry containing the raw material onto a heated drum and drying it with a scraper. (Iii) A method using a drum dryer, (iii) A slurry is applied to a heated disk surface, dried and scraped with a scraper, (iv) A clay containing raw material particles is removed. Examples include the extrusion molding method used. A particularly preferable sheet forming method is a doctor blade method. When using the doctor blade method, the slurry is applied to a flexible plate (for example, an organic polymer plate such as a PET film), and the applied slurry is dried and solidified to form a molded body, and the molded body and the board are peeled off. Thus, a green sheet may be produced. When preparing a slurry or clay before molding, inorganic particles may be dispersed in a dispersion medium, and a binder, a plasticizer, or the like may be added as appropriate. Moreover, it is preferable to prepare the slurry so that the viscosity is 500 to 4000 cP, and it is preferable to defoam under reduced pressure.

(B) Preparation of firing intermediate (firing step)
In this step (b), the green sheet is fired at 900 to 1450 ° C., and all or a part (preferably all) of the Co ₃ O ₄ particles have a (h00) plane (h is an arbitrary integer, for example, h = 2) is a fired intermediate changed to CoO oriented parallel to the sheet surface. That is, at 900 ° C. or higher (eg, 920 ° C. or higher), the Co oxide undergoes a phase transformation from a spinel structure represented by Co ₃ O ₄ at room temperature to a CoO rock salt structure. By this firing, all or a part of Co ₃ O ₄ is reduced and transformed into CoO, and the sheet is densified. The Co ₃ O ₄ particles before firing have an isotropic form, and therefore the green sheet does not initially have an orientation, but the Co ₃ O ₄ particles undergo phase transformation to CoO and undergo grain growth upon firing. Orientation occurs (hereinafter referred to as CoO oriented grain growth). In particular, in the presence of bismuth oxide (typically Bi ₂ O ₃ ), oriented grain growth of CoO is promoted. However, when the green sheet contains bismuth oxide, bismuth volatilizes and is removed from the sheet during firing. The firing temperature of the green sheet is 900 to 1450 ° C, preferably 1000 to 1300 ° C, and more preferably 1100 to 1300 ° C. The green sheet is preferably fired at the firing temperature for 1 to 20 hours, more preferably 2 to 10 hours.

  The green sheet thickness of 100 μm or less contributes to the CoO grain growth. That is, in a green sheet having a thickness of 100 μm or less, the amount of material present in the thickness direction is extremely small compared to the in-plane direction (the direction perpendicular to the thickness direction). For this reason, in the initial stage where there are a plurality of grains in the thickness direction, grains grow in random directions. On the other hand, when the grain growth proceeds and the material in the thickness direction is consumed, the grain growth direction is limited to a two-dimensional direction in the sheet surface (hereinafter referred to as a plane direction). This reliably promotes grain growth in the surface direction. In particular, even when the green sheet is formed as thin as possible (for example, several μm or less) or the green sheet is relatively thick (up to about 100 μm, for example, about 20 μm), the grain growth is promoted as much as possible. By doing so, grain growth in the surface direction can be surely promoted. In any case, at the time of firing, only the particles having the crystal plane with the lowest surface energy in the plane of the green sheet are selectively grown in a flat shape (plate shape) in the plane direction. As a result, by firing the green sheet, CoO plate-like crystal grains having a large aspect ratio and oriented so that the (h00) plane is parallel to the plate face of the grains are oriented with the (h00) plane parallel to the sheet plane. Thus, a fired intermediate formed by bonding in the plane direction at the grain boundary part is obtained.

  The green sheet is preferably placed on a setter that has been embossed during firing. This is particularly preferable in that only the surface of the oriented positive electrode plate is highly oriented and the orientation inside the oriented positive electrode plate is easily randomized. As for the height of the protrusion which the setter which gave embossing has, 50-500 micrometers is preferable, More preferably, it is 100-400 micrometers, More preferably, it is 100-300 micrometers. The setter is preferably made of at least one ceramic material selected from the group consisting of zirconia, yttria stabilized zirconia (YSZ), alumina, mullite and cordierite, and more preferably made of zirconia.

(C) Preparation of oriented sintered plate (cooling process)
This step (c) is a temperature lowering step performed subsequent to the firing in the step (b) (that is, from the firing temperature). That is, in step (c), the temperature of the calcined intermediate is lowered so as to return to Co ₃ O ₄ (from the calcining temperature in step (b)) to obtain a Co ₃ O ₄ oriented sintered plate containing a Co ₃ O ₄ phase. obtain. It is particularly preferable that the Co ₃ O ₄ oriented sintered plate contains partially remaining CoO in that only the surface of the oriented positive plate is highly oriented and the orientation inside the oriented positive plate is easily randomized. For this purpose, it is preferable to lower the temperature of the calcined intermediate at a relatively high rate, more preferably 200 ° C./h or more, further preferably 200 to 500 ° C./h, particularly preferably 250 to 400 ° C./h. h, most preferably the temperature is lowered at a rate of 250 to 350 ° C./h.

In this step (c), CoO is oxidized to Co ₃ O ₄ in the process of lowering the temperature of the calcined intermediate. At that time, since the alignment direction of CoO is taken over in the _Co 3 _{O 4,} (h00) face is oriented _Co 3 _{O 4} crystal particles are obtained in parallel with the plate surface of the particles. As a result, an independent plate-like sheet composed of a large number of Co ₃ O ₄ particles oriented so that the (h00) plane is parallel to the sheet surface is formed. An “independent” sheet refers to a sheet that can be handled as a single unit independently of other supports after firing. That is, the “independent” sheet does not include a sheet that is fixed to another support (substrate or the like) by firing and integrated with the support (unseparable or difficult to separate). In this way, a self-supporting oriented sintered plate is obtained in which a large number of grains oriented such that the (h00) plane is parallel to the grain plane. This self-supporting plate can be a dense ceramic sheet in which a large number of particles as described above are bonded without gaps.

(D) Introduction of lithium In this step (d), lithium is introduced into the Co ₃ O ₄ oriented sintered plate to form a lithium cobaltate oriented sintered plate made of LiCoO ₂ . The introduction of lithium is preferably performed by reacting a Co ₃ O ₄ oriented sintered plate with a lithium compound. Examples of lithium compounds for introducing lithium include (i) lithium hydroxide, (ii) various lithium salts such as lithium carbonate, lithium nitrate, lithium acetate, lithium chloride, lithium oxalate, and lithium citrate, (iii) Examples include lithium alkoxides such as lithium methoxide and lithium ethoxide, and lithium carbonate and lithium hydroxide are particularly preferable. Conditions for introducing lithium, for example, the mixing ratio, heating temperature, heating time, atmosphere, and the like may be appropriately set in consideration of the melting point, decomposition temperature, reactivity, etc. of the material used as the lithium source, and are not particularly limited. For example, lithium can be introduced into the Co ₃ O ₄ oriented sintered plate by placing a predetermined amount of lithium carbonate on the (h00) oriented Co ₃ O ₄ oriented sintered plate and heating. Lithium carbonate may be placed by placing it on a molded body sheet in the form of a lithium-containing sheet containing lithium carbonate, but the Co ₃ O ₄ oriented sintered plate is placed from above and below the lithium-containing sheet. In order to produce a thick oriented sintered plate, not only can lithium be sufficiently introduced, but only the surface of the oriented positive plate is highly oriented and the orientation inside the oriented positive plate is easily randomized. Particularly preferred in terms. The lithium-containing sheet is preferably obtained by slurrying lithium carbonate and subjecting it to tape molding, and the tape molding method is the same as the method described in the step (a) described above. Good. What is necessary is just to determine suitably the thickness of a lithium containing sheet | seat so that the amount of lithium carbonate in which the said Li / Co ratio becomes a desired value may be given, for example, it is 20-60 micrometers. Alternatively, as another method, a predetermined amount of slurry in which LiOH powder is dispersed is applied to a (h00) oriented Co ₃ O ₄ oriented sintered plate, dried, and then heated to form Co ₃ O ₄ particles. Lithium may be introduced. In any method, the heating temperature is preferably 700 to 900 ° C., and it is preferable to perform heating at a temperature within this range for 2 to 30 hours. The amount of the lithium compound attached to the Co ₃ O ₄ oriented sintered plate is the Li / Co ratio (that is, the molar ratio of the amount of Li contained in the lithium compound to the amount of Co contained in the Co ₃ O ₄ oriented sintered plate). It is preferably 1.0 or more, more preferably 1.0 to 4.0, and still more preferably 1.2 to 3.0. Even when there is too much Li, there is no problem since the excess Li volatilizes and disappears with heating. This lithium introduction step may be repeated a plurality of times. The lithium cobalt oxide oriented sintered plate thus obtained is obtained by aligning at least one of the (101) plane and the (104) plane of LiCoO ₂ in parallel with the plate plane.

The lithium cobalt oxide oriented sintered plate thus obtained is obtained by aligning at least one of the (101) plane and the (104) plane of LiCoO ₂ in parallel with the plate plane. Therefore, the (101) plane and the (104) plane where lithium ions enter and exit well are aligned so as to be parallel to the plate surface of the oriented sintered plate. For this reason, when a battery is constructed using this oriented sintered plate as a positive electrode active material, the exposure (contact) of the surface to the electrolyte is increased, and the (003) surface (lithium ion of the surface) of the plate is increased. The exposure ratio of the surface not suitable for going in and out is extremely low. Therefore, for example, when a lithium cobaltate oriented sintered plate is used as a positive electrode material for a solid lithium secondary battery, high capacity and high rate characteristics can be achieved simultaneously.

(E) Mg coating treatment If desired, an Mg coating treatment may be further performed. This step (e) is a step of attaching an Mg-containing compound to the oriented sintered plate and firing it if necessary, and may be the step (e1) performed prior to the step (d) or the step (d). It is good also as a process (e2) performed after. Specifically, when the Mg-containing compound is attached prior to the step (d), the subsequent firing can be performed by the firing in the step (d). On the other hand, when the Mg-containing compound is deposited after the step (d), firing is separately performed thereafter. That is, in the step (e), the Mg-containing compound is attached to the Co ₃ O ₄ oriented sintered plate prior to the step (d) (e1), or the Mg-containing lithium cobaltate oriented sintered plate is added after the step (d). What is necessary is just to carry out by any of the process (e2) of baking the said lithium cobaltate oriented sintered board to which the compound was made to adhere and to which this Mg containing compound was attached. In this way, the Mg-containing compound is attached to the LiCoO ₂ oriented sintered plate or its precursor Co ₃ O ₄ oriented sintered plate (hereinafter, both may be collectively referred to as “oriented sintered plate”). By performing firing or the like, it is possible to provide a LiCoO ₂ oriented sintered plate in which the grain boundaries interposed in the plate thickness direction are significantly reduced. In other words, when Mg-containing compounds are attached to the oriented sintered plate and fired, crystal growth occurs in such a way that the grain boundaries move between domains with high consistency, and is single crystallization in the plate thickness direction? Or a crystal structure close to that is realized. Thus, the grain boundaries interposed in the plate thickness direction can be significantly reduced (desirably such grain boundaries are eliminated). When grain boundaries are present in the plate thickness direction, lithium ion conductivity in the plate thickness direction may be reduced, but lithium ion conductivity in the plate thickness direction is improved by significantly reducing such grain boundaries. Therefore, by using such a LiCoO ₂ oriented sintered plate as a positive electrode active material for a lithium secondary battery, battery performance (particularly rate characteristics) can be improved.

  The Mg-containing compound is preferably a compound that can give MgO by firing. Preferred examples of Mg-containing compounds include magnesium acetate, magnesium nitrate, magnesium chloride, magnesium hydroxide, magnesium carbonate, magnesium sulfate, and magnesium diethoxide, and any combination thereof, particularly preferably magnesium acetate. is there.

The Mg-containing compound is preferably provided in at least one form selected from the group consisting of a solution or slurry containing the Mg-containing compound, a sheet containing the Mg-containing compound, and a powder of the Mg-containing compound, more preferably It is the form of the aqueous solution (for example, magnesium acetate aqueous solution) containing a Mg containing compound. Therefore, the adhesion of the Mg-containing compound to the oriented sintered plate may be appropriately performed by a known method according to the supply form of the Mg-containing compound. For example, in the case of the form of a solution or slurry, the oriented sintered body is immersed in the solution or slurry containing the Mg-containing compound and then dried, or the solution or slurry is applied to the oriented sintered body and thereafter The drying may be performed. In this case, the concentration of the aqueous solution containing the Mg-containing compound (eg, magnesium acetate aqueous solution) is not particularly limited, but is preferably 0.01 to 2 mol / L, more preferably 0.05 to 1 mol / L. In the case of a sheet form, a sheet containing an Mg-containing compound may be placed on the oriented sintered body. In the case of a powder form, the Mg-containing compound powder may be placed on the oriented sintered body as it is or in the form of a paste. In any method, the amount of Mg-containing compound attached to the oriented sintered body is not particularly limited. For example, a desired effect can be obtained without impairing the basic composition of LiCoO ₂ constituting the oriented sintered body. A minute amount is preferable, for example, 0.01 to 5 mol% is preferable with respect to LiCoO ₂ , and 0.05 to ₂ mol% is more preferable. Moreover, when adding a Mg containing compound, you may add another compound simultaneously, for example, when Li is added simultaneously, an effect will be accelerated | stimulated more. Although the presence form of Li is not specifically limited, For example, providing lithium hydroxide or lithium carbonate in any form of aqueous solution, powder, or a tape form is mentioned.

  The firing in the step (d2) is preferably performed at a firing temperature of 400 to 950 ° C, preferably 500 to 950 ° C, more preferably 500 to 900 ° C, and further preferably 600 to 900 ° C. This firing is preferably carried out at the firing temperature for 1 to 20 hours, more preferably 2 to 10 hours. The firing atmosphere is not particularly limited, but may be performed in an oxidizing atmosphere such as an air atmosphere.

  As described above, the lithium cobalt oxide oriented sintered plate is made of Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, and Sr without departing from the spirit of the present invention. , Y, Zr, Nb, Mo, Ag, Sn, Sb, Te, Ba, Bi, Ni, Mn, W and the like may be contained, and the addition of such an element is the process described above. Any one of (a) to (e) (typically in step (a) or step (d)) may be performed. In the case where the additive element is segregated only on the surface of the plate or only adhered, for example, after the step (d) or (e2), the additive element may be further coated and heat-treated.

  The present invention is more specifically described by the following examples.

Example 1 (Comparison)
(1) Production of LiCoO ₂ oriented sintered plate For comparison, an LiCoO ₂ oriented sintered plate having a thickness of about 40 μm oriented to the inside was produced by the following procedure.

(1a) a green sheet produced Co ₃ O ₄ raw material powder (volume basis D50 particle size 0.3 [mu] m, Seido Chemical Industry Co., Ltd.) at a rate of 5 wt% to _Bi 2 _{O 3} (by volume D50 particle size 0.3 [mu] m , Manufactured by Taiyo Mining Co., Ltd.) to obtain a mixed powder. 100 parts by weight of the mixed powder, 100 parts by weight of a dispersion medium (toluene: isopropanol = 1: 1), 10 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), and a plasticizer (DOP) : 4 parts by weight of Di (2-ethylhexyl) phthalate (manufactured by Kurokin Kasei Co., Ltd.) and 2 parts by weight of a dispersant (product name: Leodol SP-O30, manufactured by Kao Corporation) were mixed. The mixture was defoamed by stirring under reduced pressure and adjusted to a viscosity of 4000 cP. The viscosity was measured with an LVT viscometer manufactured by Brookfield. The slurry prepared as described above was formed into a sheet shape on a PET film so that the thickness after drying was 35 μm by a doctor blade method to obtain a green sheet.

(1b) Preparation of oriented sintered plate A green sheet peeled off from a PET film was cut into a 40 mm square with a cutter, and a zirconia setter (dimension 90 mm square, height 1 mm) embossed with a projection height of 300 μm After placing at the center and firing at 1300 ° C. for 5 hours, the temperature was decreased at a temperature decrease rate of 50 ° C./h, and the portion not welded to the setter was taken out as a Co ₃ O ₄ oriented sintered plate.

(1c) Introduction of Lithium LiOH · H ₂ O powder (manufactured by Wako Pure Chemical Industries, Ltd.) was pulverized to 1 μm or less with a jet mill to prepare a slurry dispersed in ethanol. This slurry was applied to the oriented sintered plate so that Li / Co = 1.3, and dried. Then, it placed on zirconia setters, to obtain a LiCoO ₂ oriented sintered plate by 20 hours of heat treatment at 840 ° C. in air.

(2) Various evaluations The following evaluation was performed on the LiCoO ₂ oriented sintered plate thus prepared. The results are shown in Table 1.

(2a) Confirmation of orientation on the surface by XRD measurement In order to confirm that the target crystal plane ((104) plane) is oriented parallel to the plate surface on the surface of the LiCoO ₂ oriented sintered plate, XRD (X-ray diffraction) measurement was performed. Specifically, using an XRD apparatus (manufactured by Rigaku Corporation, Geiger Flex RAD-IB), an XRD profile was measured when the surface of the sintered plate was irradiated with X-rays. The obtained XRD profile was as shown in FIG. 5A. From this XRD profile, the ratio I (003) / I (104) of the diffraction intensity (peak height) by the (003) plane to the diffraction intensity (peak height) by the (104) plane is obtained, and this is calculated as the surface XRD peak ratio R _{S (003) / (104)} .

(2b) Confirmation of internal orientation by XRD measurement In order to confirm that the target crystal plane ((104) plane) is oriented parallel to the plate surface inside the LiCoO ₂ oriented sintered plate, XRD (X-ray diffraction) measurement was performed. Specifically, the oriented sintered plate was polished from one side so that its thickness was ½, and the central cross section of the oriented sintered plate was exposed. Using an XRD apparatus (manufactured by Rigaku Corporation, Geiger Flex RAD-IB), an XRD profile was measured when X-rays were irradiated to the central cross section of the sintered plate. The obtained XRD profile was as shown in FIG. 5B. From this XRD profile, the ratio I (003) / I (104) of the diffraction intensity (peak height) by the (003) plane to the diffraction intensity (peak height) by the (104) plane is obtained, and this is calculated as the internal XRD peak ratio R. _{I (003) / (104)} .

(2c) Confirmation of the average primary particle diameter About the LiCoO ₂ oriented sintered plate, the fracture surface was scanned using a scanning electron microscope (SEM, JSM-6610LV, manufactured by JEOL), the acceleration voltage was 15 kV, and the entire fracture surface was in the field of view. Observation was performed at a magnification of entering. In the obtained SEM observation image, the diameter of the circumscribed circle when the circumscribed circle was drawn was determined for each of the observed primary particles. And the average value of the diameter of the obtained circumscribed circle was made into the average primary particle diameter.

(2d) Confirmation of orientation range in the cross-sectional direction About the LiCoO ₂ oriented sintered plate, the cross-section polisher (CP) was polished so that the cross-section of the sintered plate could be observed, and the polished cross-section (cross-section perpendicular to the plate surface) The crystal orientation of the primary particles was observed using the EBSD method. From this observation result, a line is drawn parallel to the plate surface at a depth of 1 μm from the plate surface, and the length occupied by particles having an angle between the (003) plane and the plate surface of 30 ° or less on the line is 30% or less. When it was, it was defined as being oriented, and the depth of the orientation range from the surface was determined. This series of methods was performed in the same procedure as the preferred method described above with reference to FIG.

(2e) Confirmation of bending strength The strength of the LiCoO ₂ oriented sintered plate was measured by a simple bending test. Specifically, the oriented sintered plate was cut into a size of 10 mm × 3 mm, placed on a pedestal installed with an interval of 8 mm, and the amount of load to break by applying a load to the central portion was determined. The test was performed five times, and the average value was defined as the load capacity.

(2f) Production and Evaluation of Battery (2f-1) Production of Positive Electrode A LiCoO ₂ oriented sintered plate was fixed to a stainless steel current collector plate with an epoxy-based conductive adhesive in which conductive carbon was dispersed to produce a positive electrode. .

(2f-2) Production of solid electrolyte layer A lithium phosphate sintered compact target having a diameter of 4 inches (about 10 cm) was prepared. Using this target, sputtering was performed using a sputtering apparatus (SPF-430H, manufactured by Canon Anelva) with an RF magnetron method so that the gas type N ₂ was 0.2 Pa, the output was 0.2 kW, and the film thickness was 3 μm. . Thus, a LiPON-based solid electrolyte sputtered film having a thickness of 3 μm was formed on the positive electrode plate.

(2f-3) Production of all-solid lithium battery An Au film having a thickness of 500 mm was formed on the solid electrolyte layer by sputtering using an ion sputtering apparatus (JFC-1500, manufactured by JEOL Ltd.). Next, the vapor deposition which provides Li thin film on Au film | membrane was performed using the vacuum vapor deposition apparatus (The Sanyu Electronics make, carbon coater SVC-700). In this way, a unit cell was produced in which a Li vapor deposition film having a thickness of 3.5 μm was formed on the solid electrolyte sputtered film. By placing stainless steel as the negative electrode current collector on the Li negative electrode layer of the unit cell, press-pressing using a hot plate at 200 ° C., and encapsulating it in an exterior material made of an Al laminate film in an Ar atmosphere An all solid lithium battery was obtained.

(2f-4) Battery evaluation The obtained all-solid lithium battery was charged at a constant current until the battery voltage became 4.0V at a current value of (i) 0.1C rate, and then (ii) the battery voltage was set to 4.0V. Under the current condition of maintaining at a constant voltage, charging was performed at a constant voltage until the current value decreased to 1/10 (0.01 C), and then the operation was stopped for 10 minutes. Subsequently, (iii) a constant current was discharged until the battery voltage reached 3.0 V at a current value of 0.02 C rate, and then rested for 10 minutes. The discharge capacity obtained at this time was set to W _1. By repeating the same charge and discharge as the above (i) to (iii) except that the discharge rate was changed to the 0.1 C rate, the discharge capacity at that time was set as W _2, and W ₂ was divided by W ₁ . Rate characteristics were obtained. This measurement was carried out at 25 ° C.

Example 2
(1) by the following procedure Preparation of LiCoO ₂ oriented sintered plate, only the surface to prepare a LiCoO ₂ oriented sintered plate of approximately 40μm thickness were highly oriented.

(1a) a green sheet produced Co ₃ O ₄ raw material powder (volume basis D50 particle size 0.3 [mu] m, Seido Chemical Industry Co., Ltd.) at a rate of 5 wt% to _Bi 2 _{O 3} (by volume D50 particle size 0.3 [mu] m , Manufactured by Taiyo Mining Co., Ltd.) to obtain a mixed powder. 100 parts by weight of the mixed powder, 100 parts by weight of a dispersion medium (toluene: isopropanol = 1: 1), 10 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), and a plasticizer (DOP) : Di (2-ethylhexyl) phthalate , and Kurogane Kasei Co., Ltd.) 4 parts by weight, dispersing agent (product name RHEODOL _{SP-O 30,} were mixed and Kao _{Corporation) 2} parts by weight. The mixture was defoamed by stirring under reduced pressure and adjusted to a viscosity of 4000 cP. The viscosity was measured with an LVT viscometer manufactured by Brookfield. The slurry prepared as described above was formed into a sheet shape on a PET film so that the thickness after drying was 35 μm by a doctor blade method to obtain a green sheet.

(1b) Preparation of oriented sintered plate A green sheet peeled off from a PET film was cut into a 40 mm square with a cutter, and a zirconia setter (dimension 90 mm square, height 1 mm) embossed with a projection height of 300 μm After placing at the center and firing at 1300 ° C. for 5 hours, the temperature was decreased at a temperature decrease rate of 300 ° C./h, and the portion not welded to the setter was taken out as a Co ₃ O ₄ oriented sintered plate.

(1c) Introduction of lithium (1c-1) Preparation of lithium sheet 100 parts by weight of Li ₂ CO ₃ raw material powder (volume basis D50 particle size 2.5 μm, manufactured by Honjo Chemical) and binder (polyvinyl butyral: product number BM-2, 5 parts by weight of Sekisui Chemical Co., Ltd., 2 parts by weight of a plasticizer (DOP: Di (2-ethylhexyl) phthalate, manufactured by Kurokin Kasei Co., Ltd.), and a dispersant (product name: Leodol SP-O ₃₀ , Kao Corporation) 2 parts by weight) were mixed. The mixture was defoamed by stirring under reduced pressure and adjusted to a viscosity of 4000 cP. The viscosity was measured with an LVT viscometer manufactured by Brookfield. The slurry prepared as described above was formed into a sheet shape on a PET film so that the thickness after drying was 25 μm by a doctor blade method to obtain a green sheet.

(1c-2) Introduction of lithium The Co ₃ O ₄ oriented sintered plate produced in (1b) is the lithium sheet produced in (1c-1), with the Li / Co ratio being 1.3. The sample was sandwiched and placed on a zirconia setter and heat-treated at 840 ° C. for 20 hours in the air to obtain a LiCoO ₂ oriented sintered plate.

(2) for various evaluation thus fabricated LiCoO ₂ surface oriented sintered plate was evaluated in the same manner as in Example 1. The results are shown in Table 1 and FIGS. 6A and 6B. As a result, the XRD peak ratio on the surface is similar to that in Example 1 (Comparative Example), but it can be seen that the value of the internal XRD peak ratio is large and only the surface is a highly oriented sintered plate. In this surface-oriented sintered plate, the rate characteristics when it was made into a battery maintained the same high value as in Example 1 (Comparative Example), and in addition, it was confirmed that the physical strength was greatly improved. It was. The improvement in physical strength greatly affects the ease of handling during battery production, and has a good effect on improving efficiency by simplifying the handling equipment and reducing the incidence of defects due to breakage of the sintered plate. In this example, the diffraction peak intensity on the (101) plane is the maximum in the XRD diffraction profile. This indicates that the (101) plane is the most exposed, and the (101) plane is a plane where lithium ions are more likely to enter and exit as compared to the (104) plane, which has a positive effect on the rate characteristics. It is thought to be given.

Example 3
(1) by the following procedure Preparation of LiCoO ₂ oriented sintered plate, only the surface is highly oriented, and to prepare a LiCoO ₂ oriented sintered plate of about 40μm thickness larger primary particle size.

(1a) a green sheet produced Co ₃ O ₄ raw material powder (volume basis D50 particle size 0.3 [mu] m, Seido Chemical Industry Co., Ltd.) at a rate of 5 wt% to _Bi 2 _{O 3} (by volume D50 particle size 0.3 [mu] m , Manufactured by Taiyo Mining Co., Ltd.) to obtain a mixed powder. 100 parts by weight of the mixed powder, 100 parts by weight of a dispersion medium (toluene: isopropanol = 1: 1), 10 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), and a plasticizer (DOP) : 4 parts by weight of Di (2-ethylhexyl) phthalate (manufactured by Kurokin Kasei Co., Ltd.) and 2 parts by weight of a dispersant (product name: Leodol SP-O ₃₀ , manufactured by Kao Corporation) were mixed. The mixture was defoamed by stirring under reduced pressure and adjusted to a viscosity of 4000 cP. The viscosity was measured with an LVT viscometer manufactured by Brookfield. The slurry prepared as described above was formed into a sheet shape on a PET film so that the thickness after drying was 35 μm by a doctor blade method to obtain a green sheet.

(1b) Preparation of oriented sintered plate A green sheet peeled off from a PET film was cut into a 40 mm square with a cutter, and a zirconia setter (dimension 90 mm square, height 1 mm) embossed with a projection height of 300 μm After placing at the center and firing at 1300 ° C. for 5 hours, the temperature was decreased at a temperature decrease rate of 300 ° C./h, and the portion not welded to the setter was taken out as a Co ₃ O ₄ oriented sintered plate.

(1c) Introduction of lithium (1c-1) Preparation of lithium sheet Li ₂ CO ₃ raw material powder (volume basis D50 particle size 2.5 μm, manufactured by Honjo Chemical) ₁₀₀ parts by weight and binder (polyvinyl butyral: product number BM-2, ₅ parts by weight of Sekisui Chemical Co., Ltd., plasticizer (DOP: Di (2-ethylhexyl) phthalate, manufactured by Kurokin Kasei Co., Ltd.), ₂ parts by weight of dispersant (product name: Leodol SP-O ₃₀ , Kao Corporation) ₂ parts by weight were mixed. The mixture was defoamed by stirring under reduced pressure and adjusted to a viscosity of 4000 cP. The viscosity was measured with an LVT viscometer manufactured by Brookfield. The slurry prepared as described above was formed into a sheet shape on a PET film so that the thickness after drying was 25 μm by a doctor blade method to obtain a green sheet.

(1c-2) Introduction of lithium The Co ₃ O ₄ oriented sintered plate produced in (1b) is the lithium sheet produced in (1c-1), with the Li / Co ratio being 1.3. The sample was sandwiched and placed on a zirconia setter and heat-treated at 840 ° C. for 20 hours in the air to obtain a LiCoO ₂ oriented sintered plate.

(1c-3) Magnesium addition heat treatment The LiCoO ₂ oriented sintered plate produced in (1c-2) was immersed in a 0.5 mol / L magnesium acetate aqueous solution and then dried. Thus, the LiCoO ₂ oriented sintered plate to which magnesium acetate was adhered was heat-treated at 700 ° C. for 5 hours in the air.

(2) for various evaluation thus fabricated LiCoO ₂ surface oriented sintered plate was evaluated in the same manner as in Example 1. The results are shown in Table 1. As shown in Table 1, it can be seen that only the surface is a highly oriented sintered plate. Furthermore, it was confirmed that the average primary particle size was increased at this level. In this surface-oriented sintered plate, it was confirmed that the rate characteristics when it was made into a battery maintained the same high value as in Example 1 (Comparative Example), and in addition, the physical strength was greatly improved. . In this example, it was also confirmed that the diffraction peak intensity on the (101) plane was the maximum.

Example 4 (Comparison)
(1) Production of LiCoO ₂ oriented sintered plate For comparison, the thickness of the green sheet after drying was 18 μm, and the procedure was the same as in Example 1 (Comparative Example) until approximately 20 μm thick. An oriented LiCoO ₂ oriented sintered plate was produced.

(2) for various evaluation thus fabricated LiCoO ₂ surface oriented sintered plate was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 5
(1) by the same procedure as in Example 2 except that thickness after drying of manufacturing a green sheet of LiCoO ₂ oriented sintered plate was set to be 18 [mu] m, LiCoO ₂ orientation only surface of about 20μm thick it was highly oriented A sintered plate was produced.

(2) for various evaluation thus fabricated LiCoO ₂ surface oriented sintered plate was evaluated in the same manner as in Example 1. The results are shown in Table 1. As shown in Table 1, it can be seen that only the surface is a highly oriented sintered plate. In this surface-oriented sintered plate, the rate characteristics when it was made into a battery maintained a high value almost equivalent to that of Example 4 (Comparative Example), and in addition, it was confirmed that the physical strength was greatly improved. It was.

Example 6
(1) Preparation of LiCoO ₂ oriented sintered plate The same procedure as in Example 2 except that the thickness of the green sheet after drying was 50 μm and (1c-2) the lithium introduction step was repeated twice. Thus, a LiCoO ₂ oriented sintered plate in which only the surface having a thickness of about 50 μm was highly oriented was produced.

(2) for various evaluation thus fabricated LiCoO ₂ surface oriented sintered plate was evaluated in the same manner as in Example 1. The results are shown in Table 1. As shown in Table 1, it can be seen that only the surface is a highly oriented sintered plate. Even with this surface-oriented sintered plate, the rate characteristics when it was made into a battery maintained a high value, and in addition, it was confirmed that the physical strength was high.

Example 7
(1) by the same procedure as Preparation Example 6 of LiCoO ₂ oriented sintered plate, only the surface to prepare a LiCoO ₂ oriented sintered plate of about 50μm thick it was highly oriented.

(2) Production of Battery Using Ionic Liquid Using the LiCoO ₂ oriented sintered plate thus produced, a battery using an ionic liquid as an electrolyte was produced as follows. That is, a commercially available coin cell case was prepared, and the sintered plate (positive electrode), the negative electrode made of lithium metal foil, the negative electrode current collector plate made of stainless steel, the plate spring for pressurization made of stainless steel, and the resin separator were sintered. A coin cell was fabricated by placing the assembly in the order of plate-separator-negative electrode plate-negative electrode current collector plate-pressurization plate spring, and filling and sealing this assembly with an electrolytic solution using an ionic liquid. The ionic liquid electrolyte uses 1-methyl-1-propylpyrrolidinium cation (P13) as the cation of the ionic liquid that is the solvent, bis (fluorosulfonyl) imide anion (FSI) as the anion, and the electrolyte. It was prepared by mixing bis (fluorosulfonyl) imide lithium salt (LiFSI) to a concentration of 0.4M.

(3) Various evaluations About the battery using the ionic liquid electrolyte produced in this way, the battery evaluation similar to Example 1 was performed. The results are shown in Table 1. As shown in Table 1, even when an ionic liquid is used for the electrolyte, the rate characteristics when it is made into a battery maintain a high value, and the oriented sintered plate of the present invention is also applied to a battery using the ionic liquid. It was confirmed that it can be suitably applied.

(Other embodiments)
The present invention is not limited to the above-described embodiments, and various modifications or changes can be made without departing from the scope of the present invention.

  In the above embodiment, the example in which the lithium cobaltate oriented positive electrode plate according to the present invention is combined with the solid electrolyte has been mainly described. However, the lithium cobaltate oriented positive plate can obtain the above-described effects even when applied to other battery configurations. Can do. For example, the lithium cobalt oxide oriented positive electrode plate according to the present invention can be used for a lithium ion battery using an ionic liquid, a polymer electrolyte, a gel electrolyte, a liquid electrolyte, etc. in addition to a solid electrolyte as an electrolyte.

  The solid electrolyte layer is preferably composed of a lithium phosphate oxynitride (LiPON) ceramic material which is one of oxide ceramic materials. The thickness of the solid electrolyte layer is preferably thin from the viewpoint of improving lithium ion conductivity, but can be appropriately set in consideration of reliability during charge / discharge (defect suppression, separator function, cracks, etc.). . The thickness of the solid electrolyte layer is preferably, for example, 0.1 to 10 μm, more preferably 0.2 to 8.0 μm, still more preferably 0.3 to 7.0 μm, and particularly preferably 0.5 to 6.0 μm. It is.

  A sputtering method is preferably used as a film forming method for depositing a solid electrolyte layer made of a ceramic material on the surface of the positive electrode on the solid electrolyte side. At this time, the thickness of the solid electrolyte layer can be adjusted by controlling the film formation conditions (for example, the film formation time) in the sputtering method. Even when the positive electrode plate is formed into a battery by forming a solid electrolyte layer made of LiPON on the surface by a sputtering method, it does not easily cause a problem in battery performance.

LiPON is a group of compounds represented by the composition of Li _2.9 PO _3.3 N _0.46 . For example, Li _a PO _b N _c (wherein a is 2 to 4, b is 3 to 5 , C is 0.1 to 0.9). Therefore, the formation of the LiPON-based solid electrolyte layer by sputtering is performed by using a lithium phosphate sintered body target as a Li source, a P source and an O source, and introducing N ₂ as a gas species as an N source. Follow the instructions below. The sputtering method is not particularly limited, but the RF magnetron method is preferable. Further, a film forming method such as an MOCVD method, a sol-gel method, an aerosol deposition method, or a screen printing method can be used instead of the sputtering method.

The solid electrolyte layer may be made of an oxide ceramic material other than the LiPON ceramic material. Examples of oxide ceramic materials other than LiPON ceramic materials include at least selected from the group consisting of garnet ceramic materials, nitride ceramic materials, perovskite ceramic materials, phosphate ceramic materials, and zeolite materials. One kind is mentioned. As an example of the garnet-based ceramic material, a Li—La—Zr—O-based material (for example, Li ₇ La ₃ Zr ₂ O ₁₂ ) or a Li—La—Ta—O-based material can also be used. Examples of perovskite ceramic materials, LiLa-Ti-O-based material (e.g. _{LiLa 1-x Ti x O 3} (0.04 ≦ x ≦ 0.14)) can be mentioned. Examples of phosphate-based ceramic material, Li-Al-Ti-P -O, Li-Al-Ge-P-O, and Li-Al-Ti-Si- P-O ( e.g. _{Li 1 + x + y Al x} Ti 2 _{-x Si y P 3-y O} 12 (0 ≦ x ≦ 0.4,0 <y ≦ 0.6)) and the like.

The solid electrolyte layer may be made of a sulfide-based material. Examples of sulfide-based materials include Li ₂ S—P ₂ S ₅ system, LiI—Li ₂ S—P ₂ S ₅ system, LiI—Li ₂ S—B ₂ S ₃₂ system, or LiI—Li ₂ S—SiS _2. A material selected from a solid electrolyte of the system, thiolithicone, Li ₁₀ GeP ₂ S _{12 and the} like can be used. Since the sulfide-based material is relatively soft, a solid electrolyte layer can be formed by pressing and pressing the sulfide-based material powder on the surface of the positive electrode plate to form a battery. More specifically, a sheet of sulfide-based material powder using a binder or the like is laminated on the positive electrode plate and pressed, or a slurry in which sulfide-based material powder is dispersed is applied to the positive electrode plate. The solid electrolyte layer can be formed by pressing after drying.

The electrolyte layer may be composed of an ionic liquid. The ionic liquid is also called a room temperature molten salt, and is a salt composed of a combination of a cation and an anion. Examples of the ionic liquid include an ionic liquid containing a quaternary ammonium cation and an ionic liquid containing an imidazolium cation.

Claims (10)

An orientation positive electrode plate for a lithium secondary battery,
The oriented positive electrode plate is composed of a sintered body composed of a plurality of lithium cobaltate crystal grains having a layered rock salt structure, and at least a part of the plurality of lithium cobaltate crystal grains is a (003) plane having a layered rock salt structure. Is oriented in a direction intersecting the plate surface of the oriented positive electrode plate,
Surface XRD peak ratio R _{S (003} ), which is the ratio of the diffraction peak intensity of the (003) plane to the diffraction peak intensity of the (104) plane measured by X-ray diffraction with respect to the surface on at least one side of the oriented positive electrode plate. _{) / (104)} is the ratio of the diffraction intensity of the (003) plane to the diffraction intensity of the (104) plane measured by X-ray diffraction with respect to the center position in the plate thickness direction of the oriented positive electrode plate. the ratio _{R I (003) / (104)} lower than the ratio of the internal XRD peak ratio _{R I (003) /} the relative ₍₁₀₄₎ surface XRD peak ratio _{R S (003) / (104} ) R S / R _I ratio is 0.5 or less, the orientation positive electrode plate. The oriented positive electrode plate according to claim 1, wherein the R _S / R _I ratio is 0.25 or less. The oriented positive electrode plate according to claim 1 or 2, wherein the surface XRD peak ratio Rs _{(003) / (104)} is 0.4 or less. The oriented positive electrode plate according to claim 3, wherein the internal XRD peak ratio RI _{(003) / (104)} is 0.8 to 1.6.   The alignment positive electrode plate as described in any one of Claims 1-4 whose thickness of the said alignment positive electrode plate is 20 micrometers or more.   The alignment positive electrode plate as described in any one of Claims 1-5 whose thickness of the said alignment positive electrode plate is 20-60 micrometers.   The oriented positive electrode plate according to any one of claims 1 to 6, wherein an average primary particle diameter of the lithium cobalt oxide crystal grains is 4 µm or more.   The oriented positive electrode plate according to claim 7, wherein the average primary particle diameter is 4 to 20 μm.   At least a thickness region from the surface of the aligned positive electrode plate to a depth of 2 μm is measured by an EBSD method with respect to a polishing cross section perpendicular to the plate surface of the aligned positive electrode plate. The angle between the (003) plane and the plate surface is 30. The oriented positive electrode plate according to any one of claims 1 to 8, which is a highly oriented region in which a length in a direction parallel to a plate surface occupied by particles of less than or equal to ° is 30% or less. The oriented positive electrode plate according to any one of claims 1 to 9, wherein a peak intensity of a diffraction peak of the (101) plane is maximum among diffraction peaks detected in the surface X-ray diffraction measurement.