JP6803041B2 - Manufacturing method of positive electrode for all-solid-state battery, positive electrode for all-solid-state battery and all-solid-state battery including the positive electrode - Google Patents

Description

The present invention relates to a positive electrode active material for an all-solid-state battery containing a metal oxide having a Li ₂ MnO ₃ type crystal structure, a method for producing a positive electrode comprising the positive electrode active material, a positive electrode for an all-solid-state battery, and an all-solid-state battery including the positive electrode. ..

Among various secondary batteries being developed, the lithium ion secondary battery (LIB), which can easily obtain a high energy density, is the most promising. On the other hand, with the expansion of battery applications, large batteries such as automobile batteries and stationary batteries are attracting attention. Ensuring safety is even more important for large batteries than for small batteries. An all-solid-state lithium-ion secondary battery (hereinafter referred to as an all-solid-state battery) that uses an inorganic solid electrolyte is easier to ensure safety even if it is made larger than a LIB that uses an organic electrolyte containing a large amount of flammable solvent. , It is expected that the capacity of the active material can be used effectively.

In recent years, as a positive electrode active material, a solid solution material of Li ₂ MnO ₃ and Li M ³ O ₂ (in the formula, M ³ is a transition metal element such as Mn, Ni, Co) has attracted attention. Specific examples thereof include solid solution materials such as zLi ₂ MnO _3- (1-z) LiM ³ O ₂ (in the formula, z is the molar ratio of Li ₂ MnO ₃ to the solid solution).

For example, Patent Document 1 proposes a solid solution material using a solid solution of Li ₂ M ⁴ O ₃ and Li M ⁵ O _2, and Patent Document 2 proposes a solid solution composed of a Li-M ^5- Mn-based composite oxide. The material is disclosed. In these equations, M ⁴ is a tetravalent metal element and M ⁵ is a trivalent metal element.

Japanese Unexamined Patent Publication No. 2012-059528 Special Table 2004-538610

The solid solution materials of Patent Document 1 and Patent Document 2 are not easily activated electrochemically. Therefore, the charge / discharge reaction is not reversibly performed smoothly, and it is difficult to secure a high capacity for both the charge capacity and the discharge capacity. Such problems are particularly pronounced in all-solid-state batteries, where all electrochemical reactions are solid-state reactions that occur at the solid-solid interface.

An object of the present invention is to smoothly carry out a charging reaction and a discharging reaction in an all-solid-state battery and effectively utilize the capacity of the positive electrode active material.

One aspect of the present invention is to provide the positive electrode of an all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer intervening between the positive electrode and the negative electrode and containing an inorganic solid electrolyte exhibiting lithium ion conductivity. It ’s a manufacturing method,
(I) The process of preparing metal oxide particles and
(Ii) A step of firing the metal oxide particles in a reducing atmosphere, and
(Iii) The step of mixing the calcined particles with an inorganic solid electrolyte exhibiting lithium ion conductivity and compressing the obtained mixture to obtain the positive electrode is included.
The metal oxide has a Li ₂ MnO ₃ type crystal structure and has a formula (A): Li _{1 + x} (M ¹ _y M ² _1-y ) _1-x O ₂
(In the formula, the element M ¹ is the first metal element, the element M ² is the second metal element having a lower average valence than the first metal element, and 0 <x ≦ 1/3 and 0.5 ≦ y ≦. It is represented by 0.8.)
The first metal element contains at least Mn and contains at least Mn.
The second metal element relates to a method for producing a positive electrode for an all-solid-state battery and a positive electrode obtained by the method , which comprises at least one selected from the group consisting of Ni, Co, and Fe, and also contains at least Ni.

Another aspect of the present invention is a negative electrode containing the positive electrode, an inorganic solid electrolyte exhibiting lithium ion conductivity, and a negative electrode active material for inserting and removing lithium ions, and between the positive electrode and the negative electrode. The present invention relates to an all-solid-state battery including an intervening solid electrolyte layer containing an inorganic solid electrolyte exhibiting lithium ion conductivity.

According to the present invention, since the electrochemical activity of the positive electrode active material is enhanced, the charging reaction and the discharging reaction can be smoothly carried out, and the charging capacity and the discharging capacity can be increased.

It is a vertical cross-sectional view which shows schematic the electrode group included in the all-solid-state battery which concerns on one Embodiment of this invention.

The method for producing a positive electrode active material for an all-solid-state battery according to an embodiment of the present invention includes (i) a step of preparing metal oxide particles and (ii) a step of preparing metal oxide particles in step (i). , Including the step of firing in a reducing atmosphere.

Here, the metal oxide prepared in the step (i) has a Li ₂ MnO ₃ type crystal structure, and the formula (A): Li _{1 + x} (M ¹ _y M ² _1-y ) _1-x. O ₂ (In the formula, the element M ¹ is the first metal element, the element M ² is the second metal element having a lower average valence than the first metal element, and 0 <x ≦ 1/3 and 0.5 ≦. It is represented by (satisfying y ≦ 0.8). The first metal element (element M ¹ ) contains at least Mn, and the second metal element (element M ² ) contains at least one selected from the group consisting of Ni, Co, and Fe, and contains at least Ni. ..

Metal oxide particles having a Li ₂ MnO ₃ type crystal structure and having a composition as described above can insert and desorb Li ions, but have low conductivity and are difficult to be electrochemically activated. Therefore, in an all-solid-state battery, it is usually difficult to reversibly and smoothly carry out the charge / discharge reaction. This is because, in an all-solid-state battery, since the solid electrolyte and the active material are bonded by point contact, the introduction of the conductive material significantly inhibits the above-mentioned interfacial reaction, and it is difficult to introduce the conductive material. Is. Such a problem does not occur in a battery including an electrolytic solution.

On the other hand, by firing the metal oxide particles in a reducing atmosphere, the electrochemical activity of the metal oxide is enhanced. As a result, even in the all-solid-state battery, the charge / discharge reaction proceeds reversibly and smoothly. The details of the mechanism by which the electrochemical activity of the metal oxide is increased are unknown, but the reduction metal ion changes the valence and ion distribution of the constituent transition metal ions, and is optimized as an active material for all-solid-state batteries. Is presumed to be. As described above, according to the manufacturing method of the present embodiment, a positive electrode active material having excellent reversibility of the charge / discharge reaction can be obtained, the charge capacity and the discharge capacity are greatly improved, and the capacity of the all-solid-state battery can be increased. is there.

The metal oxide particles having a Li ₂ MnO ₃ type crystal structure and a composition as described above are also used as a positive electrode active material in a battery provided with an electrolytic solution. Even when the metal oxide particles are fired in a reducing atmosphere, the charge capacity and the discharge capacity of the battery provided with the electrolytic solution are not significantly improved. That is, the improvement of the electrochemical activity by firing the metal oxide particles in a reducing atmosphere is a specific phenomenon seen only in the all-solid-state battery.

Hereinafter, the positive electrode active material according to the present embodiment will be described in more detail.
(Metal oxide particles)
In general, the crystal structure of Li ₂ MnO ₃ type belongs to the monoclinic layered rock salt type, has a space group C2 / m, and has LiMO type ₂ (in the formula, M is a combination of Mn and Ni, Co, etc.). The crystal structure of) belongs to the hexagonal layered rock salt type and has a space group R-3m. All of these have a layered rock salt type structure and can form a solid solution. Although the above-mentioned metal oxide has a large theoretical capacity, it has an inactive Li ₂ MnO ₃ type crystal structure as a whole, and is activated by the solid solution of the metal oxide having a LiMO ₂ type crystal structure. It is thought that.

The metal oxides containing the first metal element and the second metal element include Li ₂ M ¹ O ₃ having a Li ₂ MnO ₃ type crystal structure and the above Li MO ₂ type crystal structure from the viewpoint of increasing the capacity. A solid solution with LiM ² O ₂ having the above is promising. The solid solution of Li ₂ M ¹ O ₃ and Li M ² O ₂ can contain more Li than the total amount of the first metal element and the second metal element in terms of molar ratio. Such a solid solution has a Li ₂ MnO ₃ type crystal structure as a whole and can be represented by the above formula (A).

In the formula (A), x is 0 <x ≦ 1/3, preferably 0.10 ≦ x ≦ 0.30, and more preferably 0.14 ≦ x ≦ 0.26. When x is in such a range, the capacity of the metal oxide can be increased and charging / discharging can be stably performed.

The molar ratio y of the first metal element to the total of the first metal element and the second metal element is 0.5 ≦ y ≦ 0.8, and preferably 0.6 ≦ y ≦ 0.8. When y is in such a range, it is easy to balance the volume and the electrochemical activity.

The first metal element contained in the metal oxide may contain at least Mn, may be Mn alone, or may contain Mn and a first metal element other than Mn. Examples of the first metal element other than Mn include at least one selected from the group consisting of Ti and Zr. As the first metal element, only Mn or a combination of Mn and Ti is preferable, and among them, the first metal element is preferably composed only of Mn. The average valence of the first metal element is basically tetravalent, and may be lowered to 3.3 valence.
For the average valence of the first metal element, the metal oxide is thinly stretched using a binder or the like, the X-ray absorption spectrum at the K absorption edge of the first metal element is measured, and this X-ray absorption spectrum and the valence are known. It can be obtained by comparing with the X-ray absorption spectrum of the standard substance of the first metal element.

The molar ratio y1 of Mn in the total of the first metal element and the second metal element satisfies 0.5 ≦ y1 ≦ 0.8. If the molar ratio y1 is less than 0.5, the volume derived from Li ₂ MnO ₃ decreases and the contribution as a solid solution material cannot be obtained, and if it exceeds 0.8, the contribution of Li ₂ MnO ₃ becomes too large. Electrochemically reduced activity. From the viewpoint of the balance between the volume and the electrochemical activity, the molar ratio y1 preferably satisfies 0.6 ≦ y1 ≦ 0.8 or 0.6 ≦ y1 ≦ 0.7.

The second metal element (element M ² ) contained in the metal oxide contains at least Ni. When the second metal element contains Ni, it becomes easy to improve the stability of the crystal structure, the reduction of charge / discharge hysteresis, and the electron conductivity. The second metal element (element M ² ) may contain Co and / or Fe, and may further contain other elements. However, it is preferable that the second metal element is composed of only Ni or is a combination of Ni and Co and / or Fe. Although the details are not clear, it is presumed that these combinations increase the structural stability when Li or Li ₂ O is desorbed. The average valence of the element M ² is trivalent or less, and it may be generally divalent or more and trivalent or less.
For the average valence of the second metal element, the metal oxide is thinly stretched using a binder or the like, the X-ray absorption spectrum at the K absorption edge of the second metal element is measured, and this X-ray absorption spectrum and the valence are known. It can be obtained by comparing with the X-ray absorption spectrum of the standard substance of the second metal element.

The ratio of Ni to the second metal element is, for example, 10 to 100 mol%, preferably 40 to 80 mol% or 50 to 75 mol% (however, both include the values at both ends, and the same applies hereinafter. ). When the ratio of Ni is in such a range, it is more advantageous in terms of increasing the capacity.

When the second metal element contains Co, the ratio of Co to the second metal element is, for example, 5 to 60 mol%, preferably 15 to 50 mol% or 25 to 50 mol%. When the ratio of Co is in such a range, it is more advantageous in that the electron conductivity can be easily increased.

Among the metal oxides of the formula (A), those in which the first metal element is Mn are particularly preferable. Such a metal oxide is represented by the formula (1): Li _{1 + x} (Mn _y1 M ² _1-y1 ) _1-x O ₂ (in the formula, the elements M ² , x and y 1 are the same as described above). be able to.

In the above formulas (A) and (1), the metal oxide is described as a dioxide, but the oxygen coefficient "2" may be "2 ± δ", and the oxygen coefficient is 2 ± δ. The metal oxides of the formula (A) and the formula (1) are also included in the present embodiment. Here, δ is an excess oxygen amount or an oxygen deficiency amount, and is, for example, 0 to 0.2.

Specific examples of the metal oxides of the formulas (A) and (1) include Li _{1 + x} (Ni _0.2 Co _0.2 Mn _0.6 ) _1-x O ₂ , Li _{1 + x} (Ni _0.2 Co _0.1 Mn _0.7 ) _{1 -x} O ₂ , Li _{1 + x} (Ni _0.3 Co _0.1 Mn _0.6 ) _1-x O _{2 and the} like.

The average particle size of the metal oxide particles is, for example, 4 to 10 μm, preferably 5 to 9 μm. In the present specification, the average particle size is the median size (D ₅₀ ) in the volume-based particle size distribution measured by using a laser diffraction type particle size distribution measuring device.

Hereinafter, each step of the manufacturing method according to the present embodiment will be described.
(I) Step of preparing metal oxide particles The metal oxide particles may be commercially available if they are on the market. In addition, metal oxide particles may be synthesized from the precursor by the following method. The metal oxide particles can be obtained, for example, by calcining a mixture containing a precursor containing Li and a precursor containing a first metal element and a second metal element. The metal oxide particles obtained by firing may be washed with water or the like.

As the precursor containing Li, for example, oxides, hydroxides, carbonates, nitrates, sulfates and the like can be used, and among them, inexpensive lithium carbonate is preferably used.

As the precursor containing the first metal element and the second metal element, a mixture containing the precursor containing the first metal element and the precursor containing the second metal element may be used, and the first metal element and the first metal element may be used. Precursors containing both two metallic elements may be used. The precursor containing the first metal element and the second metal element may be a coprecipitate obtained by a coprecipitation method from a compound containing each metal element. Such a coprecipitate is preferably a hydroxide or an oxide obtained by firing a hydroxide.

When the particles of the metal oxide contain a plurality of first metal elements, a precursor containing each first metal element may be used in combination, or a precursor containing a plurality of first metal elements may be used. Similarly, when the metal oxide particles contain a plurality of second metal elements, a precursor containing each second metal element may be used in combination, or a precursor containing a plurality of second metal elements may be used. Good.

The mixture of precursors may be ground at appropriate steps.
Firing of the mixture of precursors is preferably carried out in an oxygen-containing atmosphere, specifically in the atmosphere (air) or oxygen, in order to fully develop the crystal structure of the oxide. The firing temperature is, for example, 700 to 1000 ° C. When firing is performed in multiple stages, the firing conditions for each stage may be different. As a result, particles of the metal oxide represented by the above formula (A) or the formula (1) can be obtained. The particles may be appropriately pulverized to control the particle size.

(Ii) Step of firing metal oxide particles in a reducing atmosphere Next, by firing metal oxide particles in a reducing atmosphere, partial reduction of the first metal element and the second metal element is performed. .. It is considered that this optimizes the ion distribution and lattice constant change of the first metal element and the second metal element.

The reducing atmosphere may be, for example, a reduced pressure atmosphere or an inert gas atmosphere. As the inert gas, a rare gas such as nitrogen or argon can be used. Above all, by heating the metal oxide particles in a nitrogen atmosphere, the reduction of the metal oxide particles tends to proceed appropriately. As a result, the surface state of the metal oxide particles can be made suitable for the solid-phase reaction peculiar to the all-solid-state battery.

The heating temperature in the reducing atmosphere may be any temperature at which appropriate reduction proceeds, but it is preferable to bake the metal oxide particles at 600 ° C. to 850 ° C., and it is possible to bake at 750 ° C. to 800 ° C. More preferred.

The heating time in the reducing atmosphere may be any time as long as the appropriate reduction proceeds, but it is preferable to heat and reduce the metal oxide particles over 1 hour or more, and 3 hours or more (for example, 3 to 3 to 3). It is more preferable to perform heating for 20 hours) or 5 hours or more (for example, 5 to 20 hours).

By analyzing the metal oxide powder calcined in the reducing atmosphere by X-ray diffraction measurement (XRD), the degree of oxidation of a transition metal such as Ni can be estimated. Specifically, as the reduction of the transition metal such as Ni progresses, the sum of the lattice volume and the occupancy of the transition metal in the cation position of the Li ₂ MnO ₃ structure relatively increases.

(Iii) Step of obtaining a positive electrode Next, the particles of the metal oxide after firing in a reducing atmosphere are mixed with an inorganic solid electrolyte exhibiting lithium ion conductivity, and the obtained mixture is compressed for an all-solid-state battery. Make a positive electrode. From the viewpoint of suppressing the oxidation of the metal oxide particles after firing, it is advantageous to shorten the period until the metal oxide particles are mixed with the inorganic solid electrolyte and compression-molded as much as possible. For example, the contact period with the atmosphere (air) may be limited to a predetermined time (for example, 1 hour). Further, the particles of the metal oxide after firing may be stored in an inert gas atmosphere until they are mixed with the inorganic solid electrolyte and compression molded. The dew point of the inert gas atmosphere may be −35 ° C. or lower (for example, −40 ° C. or lower).

The method for mixing the metal oxide particles and the inorganic solid electrolyte is not particularly limited, but it is preferable to mix them in a dry manner. The method of compressing the obtained mixture to obtain a positive electrode is also not particularly limited, but it is preferable to apply pressure a plurality of times while gradually increasing the pressure. At this time, the maximum load is preferably set to, for example, 490 MPa or more.

The positive electrode usually includes a positive electrode current collector and a positive electrode mixture supported on the positive electrode current collector. The positive electrode mixture is a mixture containing a positive electrode active material and an inorganic solid electrolyte, and may contain other components used for the positive electrode of an all-solid-state battery. The positive electrode active material contains particles of a metal oxide represented by the above formula (A) or formula (1) after being calcined in a reducing atmosphere.

The inorganic solid electrolyte is not particularly limited as long as it exhibits lithium ion conductivity, and an inorganic solid electrolyte such as that used for the solid electrolyte layer in an all-solid-state battery can be used. The crystalline state of the inorganic solid electrolyte is not particularly limited, and it may be either crystalline or amorphous. As the inorganic solid electrolyte, sulfide (sulfide-based inorganic solid electrolyte) is preferable. From the viewpoint of high resistance to reductive decomposition, sulfides containing Li and P are particularly preferable. As the sulfide, for example, Li ₇ P ₃ S ₁₁ , Li ₃ PS ₄ , Li ₁₀ GeP ₂ S ₁₂ , Li ₆ PS ₅ X (X is selected from the group consisting of F, Cl, Br, I and At). It is at least one kind.) And so on. One of these solid electrolytes may be used alone, or two or more thereof may be used in combination, if necessary.

The ratio of the inorganic solid electrolyte to the total amount of the positive electrode active material and the inorganic solid electrolyte is preferably 5 to 40% by mass, and more preferably 10 to 40% by mass. When the proportion of the inorganic solid electrolyte is in such a range, it is easy to secure high lithium ion conductivity of the positive electrode.

Examples of the positive electrode current collector include a metal foil, a plate-like body, and an aggregate of powder. The metal foil may be an electrolytic foil, an etched foil, or the like. Examples of the material of the positive electrode current collector include aluminum, magnesium, stainless steel, titanium, iron, cobalt, zinc, tin, and alloys thereof.

[All-solid-state battery]
Next, the all-solid-state battery according to the embodiment of the present invention will be described. The all-solid-state battery includes the positive electrode, the negative electrode, and a solid electrolyte layer interposed between them.

(Negative electrode)
The negative electrode usually includes a negative electrode current collector and a negative electrode mixture supported on the negative electrode current collector. The negative electrode mixture is a mixture containing a negative electrode active material and an inorganic solid electrolyte. The negative electrode can be manufactured according to the case of the positive electrode.

The negative electrode active material is not particularly limited as long as lithium ions can be inserted and removed, and known negative electrode active materials used in LIB can be used. For example, in addition to a carbonaceous material capable of inserting and removing lithium ions, simple substances, alloys, or compounds of metals and semimetals capable of inserting and removing lithium ions can be mentioned. Examples of the carbonaceous material include graphite, hard carbon, and amorphous carbon. Examples of simple substances and alloys of metals and semimetals include lithium metals and alloys, simple substances of Si, and SiO. Examples of the compound include oxides, sulfides, nitrides, hydrates, silicides (lithium silicide and the like) and the like. Examples of the oxide include titanium oxide and silicon oxide. As the negative electrode active material, one type may be used alone, or two or more types may be used in combination. For example, a silicon oxide and a carbonaceous material may be used in combination.

In addition to the negative electrode active material, the negative electrode may contain other components used for the negative electrode in the all-solid-state battery. As in the case of the positive electrode, from the viewpoint of enhancing the lithium ion conductivity in the negative electrode, the negative electrode preferably contains an inorganic solid electrolyte exhibiting lithium ion conductivity together with the negative electrode active material. As such an inorganic solid electrolyte, it can be appropriately selected from those exemplified for the positive electrode. The ratio of the inorganic solid electrolyte to the total amount of the negative electrode active material and the inorganic solid electrolyte can be appropriately selected from the range described as the ratio of the inorganic solid electrolyte to the total amount of the positive electrode active material and the inorganic solid electrolyte.

Examples of the form of the negative electrode current collector include those described for the positive electrode current collector. Examples of the material of the negative electrode current collector include copper, nickel, stainless steel, titanium, and alloys thereof.

(Solid electrolyte layer)
The solid electrolyte layer interposed between the positive electrode and the negative electrode contains an inorganic solid electrolyte exhibiting lithium ion conductivity. The thickness of the solid electrolyte layer is, for example, 20 to 200 μm. Examples of such an inorganic solid electrolyte include the inorganic solid electrolyte exemplified for the positive electrode, and sulfide is preferable.

The solid electrolyte layer can be formed by compressing the inorganic solid electrolyte. The solid electrolyte layer can optionally contain additives used in the solid electrolyte layer of the all-solid-state battery.

FIG. 1 is a vertical cross-sectional view schematically showing a group of electrodes included in the all-solid-state battery according to the present embodiment. The electrode group 1 included in the all-solid-state battery includes a positive electrode 2, a negative electrode 4, and a solid electrolyte layer 3 interposed between them. The positive electrode 2 includes a positive electrode current collector 2b and a positive electrode mixture layer 2a supported on the current collector 2b. The negative electrode 4 includes a negative electrode current collector 4b and a negative electrode mixture layer 4a supported on the current collector 4b. The positive electrode 2 and the negative electrode 4 are arranged so that the positive electrode mixture layer 2a and the negative electrode mixture layer 4a face each other. The solid electrolyte layer 3 is arranged between the positive electrode mixture layer 2a and the negative electrode mixture layer 4a. The solid electrolyte layer 3 contains a lithium ion conductive inorganic solid electrolyte.

The positive electrode mixture layer 2a, the negative electrode mixture layer 4a, and the solid electrolyte layer 3 in FIG. 1 have a disk shape having substantially the same size, and are laminated with the solid electrolyte layer 3 sandwiched between them. Is forming. An insulator 5 is mounted on the side surface of the laminate 6 so as to cover the side surface of the negative electrode mixture layer 4a and the side surface of the solid electrolyte layer 3 on the negative electrode mixture layer 4a side. The positive electrode current collector 2b and the negative electrode current collector 4b are circular metal foils having a size larger than that of the positive electrode mixture layer 2a and the negative electrode mixture layer 4a. The positive electrode current collector 2b and the negative electrode current collector 4b are formed so as to have substantially the same size as the laminated body 6 with the insulator 5 attached.

The all-solid-state battery can be manufactured by housing the electrode group in a cell case. One end of a lead is connected to the positive electrode and the negative electrode of the electrode group, respectively. The other end of the lead is electrically connected to an external terminal exposed to the outside of the cell case.

The all-solid-state battery is not limited to the example shown in FIG. 1, and may be of various types such as a round type, a cylindrical type, a square type, and a thin layer flat type. The electrode group may include a plurality of positive electrodes and / or a plurality of negative electrodes.

[Example]
Hereinafter, the present invention will be specifically described based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Example 1
The all-solid-state battery shown in FIG. 1 was produced by the following procedure.
(1) Synthesis of positive electrode active material (i) step Ni (NO ₃₎ to prepare the metal oxide particles _{2 · 9H 2 O, Co (} NO 3) 2 · 6H 2 O, and MnCl ₂ · 4H ₂ O , Ni: Co: Mn were used in an amount such that the atomic ratio was 2: 1: 7, and dissolved in distilled water to prepare an aqueous precursor solution. This precursor aqueous solution was added dropwise to a sodium hydroxide aqueous solution kept at 20 ° C. in a constant temperature bath over several hours to form a Ni—Co—Mn coprecipitate. The obtained coprecipitate was taken out from a constant temperature bath, and the coprecipitate was aged by stirring at room temperature for 2 days while blowing air. The coprecipitate was then filtered off and washed with distilled water to remove sodium hydroxide.

An amount of lithium carbonate such that the Li / (Ni + Co + Mn) ratio was 1.7 was dispersed in distilled water. The obtained dispersion and the coprecipitate were placed in a mixer and stirred. The resulting mixture was dried at 50 ° C. for 2 days. The dried product was mechanically pulverized and then calcined in the air at 900 ° C. for 5 hours to synthesize the desired metal oxide particles a1.

From the XRD pattern of the metal oxide particles a1, the metal oxide particles a1 consist of a monoclinic Li ₂ MnO type ₃ unit cell (space group C2 / m) single phase, and are a Li ₂ MnO _3- LiM ² O ₂ solid solution. It was confirmed that. No impurities were found in the XRD pattern. The composition of the metal oxide a1 analyzed from the XRD pattern was Li _{1 + x} (Ni _0.2 Co _0.1 Mn _0.7 ) _1-x O ₂ (x = 0.25).

(Ii) Step of firing metal oxide particles in a reducing atmosphere Metal oxide particles a1 are introduced into a vacuum gas replacement furnace (KDF-75, Denken Hydental Co., Ltd.), and the temperature is 750 ° C. in a nitrogen stream. The metal oxide particles were reduced by firing in

(Iii) Step of obtaining a positive electrode (positive electrode mixture layer 2a) Metal oxide particles a1 and Li ₂ S (70 mol%) −P ₂ S ₅ (30 mol) after reduction treatment stored at a dew point of −40 ° C. in a nitrogen stream. %) The solid solution was used in a mass ratio of 7: 3 and mixed well in a dairy pot to give a mixture. 20 mg of the mixture was packed in a layer on the solid electrolyte layer 3 in the cylindrical die described later, and pressed three times in the order of 376 MPa, 752 MPa, and 1050 MPa in the thickness direction of the layer to obtain a positive electrode ( A positive electrode mixture layer 2a) was produced.

(2) Fabrication of all-solid-state battery (a) Fabrication of solid electrolyte layer 3 A cylindrical mold (inner diameter 10 mm, height 30 mm) made of cold die steel (SKD) is erected and installed, and a bottom plate is placed on the bottom of the cylindrical mold. I inserted a short pin. In this state, 50 mg of a lithium ion conductive solid electrolyte Li ₂ S (70 mol%) -P ₂ S ₅ (30 mol%) solid solution (composition: Li ₇ P ₃ S ₁₁ ) is packed in a layer in a cylindrical mold. did. Then, a long columnar pin having a size matching the inner diameter of the cylindrical die is inserted into the inside from the top of the cylindrical die, and the solid electrolyte layer is pressed once at a pressure of 188 MPa in the thickness direction of the layer. 3 was prepared.

(B) Preparation of Negative Electrode Mixture Layer 4a Graphite and a solid solution of Li ₂ S (70 mol%) -P ₂ S ₅ (30 mol%) were thoroughly mixed in a mortar using a mass ratio of 6: 4. 16 mg of the obtained mixture was layered on the solid electrolyte layer 3 in the cylindrical mold prepared in (a). Then, the negative electrode mixture layer 4a was produced by pressurizing and pressing three times in the thickness direction of the layer. The pressure of the pressure press was 188 MPa each time.

Next, the short pin was taken out with the cylindrical mold turned upside down, the short pin was inserted into the negative electrode mixture layer 4a side, and the cylindrical mold was arranged so that the short pin became the bottom. Next, the solid electrolyte layer 3 and the negative electrode mixture layer 4a were pressed from the solid electrolyte layer 3 side using a long pin. In this way, a space surrounded by the inner wall of the cylindrical mold was formed on the solid electrolyte layer 3 on the side opposite to the negative electrode mixture layer 4a.

(C) Preparation of Positive Electrode Mixture Layer 2a As described in (iii) of (1) above, a positive electrode mixture layer 2a was prepared on the solid electrolyte layer 3 in the cylindrical mold.

(D) Assembly of an all-solid-state battery A cylindrical laminate 6 in a state in which the solid electrolyte layer 3 is sandwiched between the positive electrode mixture layer 2a and the negative electrode mixture layer 4a formed as in (a) to (c). Removed from the mold. An insulator 5 (inner diameter 11 mm, height 50 μm) having a hole in the center was arranged on one surface of a copper foil (length 20 mm × width 20 mm, thickness 100 μm) as the negative electrode current collector 4b. Then, the laminated body 6 (outer diameter 10 mm) was housed in the hole of the insulator 5 so that the negative electrode mixture layer 4a was in contact with the negative electrode current collector 4b. Next, the electrode group 1 was produced by arranging an aluminum foil (length 20 mm × width 20 mm, thickness 20 μm) as the positive electrode current collector 2b on the positive electrode mixture layer 2a of the laminated body 6. The insulator 5 is arranged so as to suppress contact between the negative electrode mixture layer 4a and the negative electrode current collector 4b and the positive electrode mixture layer 2a and the positive electrode current collector 2b.

The electrode group 1 was housed in a laminated cell having a negative electrode lead and a positive electrode lead, and the gas in the cell was sealed while being sucked by a vacuum pump. In this way, an all-solid-state battery was produced.

(3) Evaluation The charge capacity and discharge capacity of the all-solid-state battery were measured.
The all-solid-state battery was maintained at 25 ° C. in a constant temperature bath and pressurized at 58.8 MPa. In this state, the battery was charged with a current of 0.02 mA / cm ^{2 to} a final charge voltage of 4.7 V, and then discharged with a current of 0.05 mA / cm ^{2 to} a final discharge voltage of 2.0 V. The charge capacity and discharge capacity (initial discharge capacity) at this time were determined.

Comparative Example 1
An all-solid-state battery was produced and evaluated in the same manner as in Example 1 except that the metal oxide particles a1 were not calcined (reduced) in a nitrogen stream.

Example 2
An all-solid-state battery was produced and evaluated in the same manner as in Example 1 except that the temperature of firing (reduction treatment) of the metal oxide particles a1 in a nitrogen stream was changed to 800 ° C.

Example 3
_{Ni (NO 3) 2 · 9H} 2 O, Co (NO 3) 2 · 6H 2 O, and _{MnCl 2 · 4H 2 O, Ni} : Co: atomic ratio of Mn 2: 2: 6 to become such an amount To prepare an aqueous precursor solution by dissolving it in distilled water. This precursor aqueous solution was added dropwise to a sodium hydroxide aqueous solution kept at 20 ° C. in a constant temperature bath over several hours to form a Ni—Co—Mn coprecipitate. The obtained coprecipitate was taken out from a constant temperature bath, and the coprecipitate was aged by stirring at room temperature for 2 days while blowing air. The coprecipitate was then filtered off and washed with distilled water to remove sodium hydroxide.

An amount of lithium carbonate such that the Li / (Ni + Co + Mn) ratio was 1.7 was dispersed in distilled water. The obtained dispersion and the coprecipitate were placed in a mixer and stirred. The resulting mixture was dried at 50 ° C. for 2 days. The dried product was mechanically pulverized and then calcined in the air at 900 ° C. for 5 hours to synthesize the desired metal oxide particles a2.

From the XRD pattern of the metal oxide particles a2, the metal oxide particles a2 consist of a monoclinic Li ₂ MnO type ₃ unit cell (space group C2 / m) single phase, and are a Li ₂ MnO _3- LiM ² O ₂ solid solution. It was confirmed that. No impurities were found in the XRD pattern. The composition of the metal oxide particles a2 analyzed from the XRD pattern was Li _{1 + x} (Ni _0.2 Co _0.2 Mn _0.6 ) _1-x O ₂ (x = 0.26).

An all-solid-state battery was produced and evaluated in the same manner as in Example 1 except that the metal oxide particles a2 were used instead of the metal oxide particles a1.

Comparative Example 2
An all-solid-state battery was produced and evaluated in the same manner as in Example 3 except that the metal oxide particles a2 were not calcined (reduced) in a nitrogen stream.

Example 4
An all-solid-state battery was produced and evaluated in the same manner as in Example 3 except that the temperature of firing (reduction treatment) of the metal oxide particles a2 in a nitrogen stream was changed to 800 ° C.

Reference example 1
A non-aqueous electrolyte secondary battery was prepared by the following procedure.
The reduction-treated metal oxide particles a1 obtained in Example 1 and Denka Black are mixed at a mass ratio of 3: 1 and a small amount of polytetrafluoroethylene is added, and the obtained dry mixture is sheeted. A positive electrode sheet was prepared by molding into a shape. Next, the positive electrode sheet punched to a diameter of 10 mm was pressure-bonded to an aluminum mesh having a diameter of 15 mm at 12 MPa.

A joint body of a positive electrode sheet and an aluminum mesh was inserted into a measuring jig, and a separator impregnated with a non-aqueous electrolytic solution and a glass non-woven fabric were placed on the joint. The non-aqueous electrolyte solution was prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent having a volume ratio of ethylene carbonate and dimethyl carbonate of 3: 7. Next, a metallic lithium foil was placed on the glass non-woven fabric, and the measuring jig was covered with a weight and a spring to form a secondary battery.

The configured secondary battery was maintained at 25 ° C. in a thermostat, at a current 0.05 mA / cm ^2, and charged to a charge termination voltage 4.8 V, then at a current 0.05 mA / cm ^2, discharge It was discharged to a final voltage of 2.0 V. The charge capacity and discharge capacity (initial discharge capacity) at this time were determined.

Reference example 2
Similar to Reference Example 1, a non-aqueous electrolyte secondary battery was prepared and evaluated, except that the metal oxide particles a1 which had not been subjected to the reduction treatment were used as in Comparative Example 1.

Table 1 shows the evaluation results of Examples 1 to 4, Comparative Examples 1 and 2, and Reference Examples 1 and 2.

As shown in Table 1, in Examples 1 to 4, the charge / discharge capacity could be dramatically increased as compared with Comparative Examples 1 and 2. On the other hand, there was no significant difference in charge / discharge capacity between Reference Example 1 and Reference Example 2 using the same positive electrode active material as in Example 1 and Comparative Example 1. From this, it can be understood that the dramatic increase in charge / discharge capacity is a phenomenon peculiar to all-solid-state batteries.

The production method according to the present invention provides a positive electrode active material or a positive electrode capable of drawing out a high capacity with high electrochemical activity even in an all-solid-state battery in which an intersolid-state reaction proceeds. It is useful for increasing the capacity.

1: Electrode group 2: Positive electrode, 2a: Positive electrode mixture layer, 2b: Positive electrode current collector 3: Solid electrolyte layer 4: Negative electrode, 4a: Negative electrode mixture layer, 4b: Negative electrode current collector, 5: Insulation Body, 6: Laminate

Claims (9)

A method for producing the positive electrode of an all-solid-state battery, comprising a positive electrode, a negative electrode, and a solid electrolyte layer intervening between the positive electrode and the negative electrode and containing an inorganic solid electrolyte exhibiting lithium ion conductivity.
(I) The process of preparing metal oxide particles and
(Ii) A step of firing the metal oxide particles in a reducing atmosphere, and
The particles after (iii) the calcining is mixed with an inorganic solid electrolytes having lithium ion conductivity, wherein the step of obtaining the positive electrode by compressing the resulting mixture, and
The metal oxide has a Li ₂ MnO ₃ type crystal structure and has a formula (A): Li _{1 + x} (M ¹ _y M ² _1-y ) _1-x O ₂
(In the formula, the element M ¹ is the first metal element, the element M ² is the second metal element having a lower average valence than the first metal element, and 0 <x ≦ 1/3 and 0.5 ≦ y ≦. It is represented by 0.8.)
The first metal element contains at least Mn and contains at least Mn.
A method for producing a positive electrode for an all-solid-state battery, wherein the second metal element contains at least one selected from the group consisting of Ni, Co, and Fe, and also contains at least Ni. The method for producing a positive electrode for an all-solid-state battery according to claim 1, wherein in the step (ii), the reducing atmosphere is a nitrogen atmosphere. The method for producing a positive electrode for an all-solid-state battery according to claim 1 or 2, wherein in the step (ii), the particles are fired at a temperature of 600 ° C. to 850 ° C. in the reducing atmosphere. The method for producing a positive electrode for an all-solid-state battery according to any one of claims 1 to 3, wherein in the step (ii), the particles are calcined in the reducing atmosphere for 1 hour or more. The step (i) is
Step a of obtaining a first precursor containing the first metal element and the second metal element by the coprecipitation method, and
A step b of mixing the first precursor and the second precursor in a dispersion containing the first precursor and the second precursor containing Li.
The step c of drying the mixture obtained in the step b and
The method for producing a positive electrode for an all-solid-state battery according to any one of claims 1 to 4, further comprising a step d of firing the dried product obtained in the step c in an atmosphere containing oxygen. The positive electrode active material contains the particles after firing, and contains the particles.
The all-solid-state battery according to any one of claims 1 to 5, wherein in the positive electrode, the ratio of the inorganic solid electrolyte to the total amount of the positive electrode active material and the inorganic solid electrolyte is 10 to 40% by mass. Manufacturing method of positive electrode for. A positive electrode for an all-solid-state battery obtained by the production method according to any one of claims 1 to 6 . The positive electrode according to claim 7 and
A negative electrode containing an inorganic solid electrolyte exhibiting lithium ion conductivity and a negative electrode active material that inserts and desorbs lithium ions.
An all-solid-state battery comprising a solid electrolyte layer comprising an inorganic solid electrolyte exhibiting lithium ion conductivity, which is interposed between the positive electrode and the negative electrode. The all-solid-state battery according to claim 8 , wherein the inorganic solid electrolyte is a sulfide.

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