JP2020140963A - Solid electrolyte, all-solid secondary battery, and manufacturing method thereof - Google Patents

Abstract

To provide a solid electrolyte having high ionic conductivity.SOLUTION: A solid electrolyte includes a first solid electrolyte particles 11 and a second solid electrolyte particles 12, and the first solid electrolyte particles 11 and the second solid electrolyte particles 12 have the same crystal structure as each other, when the average particle size of the first solid electrolyte particles 11 is D1, the sintering temperature of the first solid electrolyte particles 11 is T1, the average particle size of the second solid electrolyte particles 12 is D2, and the sintering temperature of the second solid electrolyte particles 12 is T2, the relationship of D1>D2 and T1>T2 is satisfied.SELECTED DRAWING: Figure 2

Description

The present invention relates to a solid electrolyte, an all-solid secondary battery, and a method for producing the same.

Lithium-ion secondary batteries are widely used as a power source for small portable devices such as mobile phones, notebook PCs, and PDAs. Lithium-ion secondary batteries used in such small portable devices are required to be smaller, thinner, and more reliable.

As the lithium ion secondary battery, one using an organic electrolytic solution as an electrolyte and one using a solid electrolyte (so-called all-solid secondary battery) are known. Compared to lithium-ion secondary batteries that use organic electrolytes, all-solid-state secondary batteries have a higher degree of freedom in battery shape design, and it is easier to reduce the size and thickness of batteries. It has the advantage of high reliability without liquid leakage.

On the other hand, the all-solid-state secondary battery generally has lower lithium ion conductivity than the lithium ion secondary battery using an organic electrolytic solution. Therefore, the all-solid-state secondary battery has problems that the internal resistance is high and the output current is low as compared with the lithium ion secondary battery using the organic electrolytic solution.

Therefore, in an all-solid-state secondary battery, it is required to increase the ionic conductivity of lithium ions of a solid electrolyte and reduce the internal resistance (see, for example, Patent Documents 1 to 3 below).

Specifically, Patent Document 1 below describes a crystalline lithium ion conductive substance and Li ⁺ _x (B _1-y , A _y ) ^{z +} O ^2- _δ as a base material (in the formula, A is C, It is at least one element among Al, Si, Ga, Ge, In, and Sn, y satisfies 0 ≦ y <1, and z is an average valence of (B _1-y , A _y ). X, z, δ satisfy the relational expression of x + z = δ / 2), and a solid electrolyte containing the above is disclosed.

This solid electrolyte has a relatively high lithium ion conductivity and can be sintered at a low temperature of about 700 ° C. The reason is that Li ⁺ _x (B _1-y , A _y ) ^{z +} O ^2- _δ as the base material melts at a low temperature, so it is considered that it can be sintered at a low temperature similar to the melting temperature.

On the other hand, in Patent Document 2 below, a part of the crystal structure of the oxide represented by the general formula Li _p La _{(2-p) / 3} TiO ₃ (0 <p ≦ 0.5) is the firing of the oxide. It is replaced with a low melting point material having a melting point lower than the sintering temperature, or a low melting point material (Bi, Li _{2) having a} melting point lower than the sintering temperature of the oxide is added to this oxide as a main component. A solid electrolyte is disclosed which is a sintered body satisfying at least one of containing (1 or more selected from B ₄ O ₇ and Li BO ₂ ).

On the other hand, Patent Document 3 contains a solid electrolyte ceramic material having lithium ion conductivity, wherein the ceramic material contains a main constituent element of Li, La, Zr and O, and a substitution element containing at least Bi. A ceramic material comprising a garnet-type or garnet-type-like crystal single-phase substantially composed of an oxide sintered body is disclosed.

Japanese Unexamined Patent Publication No. 2013-037992 Japanese Unexamined Patent Publication No. 2013-140762 Japanese Unexamined Patent Publication No. 2015-050072

However, even with the techniques described in Patent Documents 1 to 3 described above, a solid electrolyte having high lithium ion conductivity cannot be obtained, and an all-solid secondary battery using such a solid electrolyte can obtain a sufficiently large capacity. I couldn't.

The present invention has been proposed in view of such conventional circumstances, and a solid electrolyte having high ionic conductivity and an all-solid state in which a large capacity can be obtained by using such a solid electrolyte. An object of the present invention is to provide a secondary battery and a method for manufacturing the secondary battery.

In order to achieve the above object, the present invention provides the following means.
[1] The first solid electrolyte particles and the second solid electrolyte particles are included.
The first solid electrolyte particles and the second solid electrolyte particles have the same crystal structure as each other.
The average particle size of the first solid electrolyte particles is D1, the sintering temperature of the first solid electrolyte particles is T1, the average particle size of the second solid electrolyte particles is D2, and the second solid is solid. When the sintering temperature of the electrolyte particles is T2,
D1> D2,
T1> T2
A solid electrolyte characterized by satisfying the relationship of.
[2] 0.1 × D1 ≧ D2
The solid electrolyte according to the above [1], which satisfies the above-mentioned relationship.
[3] The solid electrolyte according to the above [1] or [2], wherein at least 50% or more of the surfaces of the first solid electrolyte particles are in contact with the second solid electrolyte particles. ..
[4] T1-T2 ≥ 100 ° C
The solid electrolyte according to any one of the above [1] to [3], which is characterized by satisfying the above-mentioned relationship.
[5] The solid electrolyte according to any one of the above [1] to [4], wherein the first solid electrolyte particles and the second solid electrolyte particles have different compositions from each other.
[6] The first solid electrolyte particle has a garnet structure containing Li, La, Zr, and O, and has a garnet structure.
The solid electrolyte according to any one of the above [1] to [5], wherein the second solid electrolyte particles have a garnet structure containing Li, La, Bi, and O.
[7] An all-solid-state secondary battery comprising the solid electrolyte according to any one of the above [1] to [6].
[8] A method for manufacturing an all-solid-state secondary battery using a solid electrolyte containing a first solid electrolyte particle and a second solid electrolyte particle.
The first solid electrolyte particles and the second solid electrolyte particles have the same crystal structure as each other.
The average particle size of the first solid electrolyte particles is D1, the sintering temperature of the first solid electrolyte particles is T1, the average particle size of the second solid electrolyte particles is D2, and the second solid is solid. When the sintering temperature of the electrolyte particles is T2,
D1> D2,
T1> T2
A method for manufacturing an all-solid-state secondary battery, which comprises using a solid electrolyte that satisfies the above relationship.

As described above, according to the present invention, there is provided a solid electrolyte having high ionic conductivity, an all-solid secondary battery capable of obtaining a large capacity by using such a solid electrolyte, and a method for producing the same. It is possible to do.

It is sectional drawing which shows the structure of the all-solid-state secondary battery which concerns on one Embodiment of this invention. It is a schematic diagram which shows the cross-sectional structure of the solid electrolyte included in the all-solid-state secondary battery shown in FIG. It is a graph which shows the measurement curve when the heat shrinkage behavior was measured by TMA, and the differential curve in the sintering behavior.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.
In addition, in the drawing used in the following description, in order to make the feature of the present invention easy to understand, the feature portion may be enlarged and shown for convenience. Therefore, the dimensional ratio and the like of each component described in the drawings may differ from the actual ones. Further, the materials, dimensions, etc. exemplified in the following description are examples, and the present invention is not limited thereto, and the present invention can be appropriately modified without changing the gist thereof.

(All-solid-state secondary battery)
First, as an embodiment of the present invention, for example, the all-solid-state secondary battery 1 shown in FIG. 1 will be described. Note that FIG. 1 is a cross-sectional view showing the configuration of the all-solid-state secondary battery 1.

As shown in FIG. 1, the all-solid-state secondary battery 1 of the present embodiment is an all-solid-state lithium-ion secondary battery to which the present invention is applied. Specifically, the all-solid-state secondary battery 1 contains a first electrode 2, a second electrode 3, and a solid electrolyte 4 interposed between the first electrode 2 and the second electrode 3. I have.

The all-solid-state secondary battery 1 has a laminate 5 in which the first electrode 2, the solid electrolyte 4, and the second electrode 3 are repeatedly laminated. Further, the all-solid-state secondary battery 1 includes a first connection terminal 6 electrically connected to each of the plurality of first electrodes 1 constituting the laminate 5, and a plurality of components constituting the laminate 5. Each of the second electrodes 2 is provided with a second connection terminal 7 electrically connected to the second electrode 2.

The first connection terminal 6 is provided so as to face one side surface of the laminated body 5 and to be in contact with the end portions of the first electrodes 2 exposed from the side surface. The second connection terminal 7 is provided so as to face the other side surface of the laminated body 5 and to be in contact with the end portion of each second electrode 3 exposed from this side surface.

It is preferable to use a material having a high conductivity for the first connection terminal 6 and the second connection terminal 7. Specifically, for example, silver (Ag), palladium (Pd), gold (Au), platinum (Pt), aluminum (Al), copper (Cu), nickel (Ni), tin (Sn), gallium (Ga). ), Indium (In), alloys thereof, and the like can be used. The first connection terminal 6 and the second connection terminal 7 may be made of the same material or different materials.

In the all-solid-state secondary battery 1, one of the first electrode 2 and the second electrode 3 (the first electrode layer 2 in the present embodiment) functions as a positive electrode (hereinafter referred to as a positive electrode 2). However, one of the other (second electrode 3 in this embodiment) functions as a negative electrode (hereinafter referred to as a negative electrode 3).

As a result, in the all-solid-state secondary battery 1 of the present embodiment, charge / discharge is performed by exchanging lithium ions via the solid electrolyte 4 between the positive electrode 2 and the negative electrode 3 which are alternately laminated with the solid electrolyte 4 interposed therebetween. Is done.

The first electrode 2 and the second electrode 3 have a positive electrode and a negative electrode depending on which of the positive and negative polarities of the external terminals are connected to the first connection terminal 6 and the second connection terminal 7. It will function as either.

The positive electrode 2 has a positive electrode current collector 2a and a positive electrode active material 2b. Similarly, the negative electrode 3 has a negative electrode current collector 3a and a negative electrode active material 3b.

It is preferable to use materials having high conductivity for the positive electrode current collector 2a and the negative electrode current collector 3a. Specifically, for example, silver (Ag), palladium (Pd), gold (Au), platinum (Pt), aluminum (Al), copper (Cu), nickel (Ni), or alloys thereof can be used. it can.

Among them, copper does not easily react with the positive electrode active material 2b, the negative electrode active material 3b, and the solid electrolyte 4, so that when copper is used for the positive electrode current collector 2a and the negative electrode current collector 3a, the all-solid-state secondary battery 1 Internal resistance can be reduced. The positive electrode current collector 2a and the negative electrode current collector 3b may be made of the same material or different materials from each other.

The positive electrode active material 2b is provided on both sides of the positive electrode current collector 2a. However, when the uppermost layer or the lowermost layer of the laminated body 5 is composed of the positive electrode 2, the positive electrode 2 located in the uppermost layer or the lowermost layer is the positive electrode current collector 2a facing the negative electrode 3 on the lower layer or the upper layer side thereof. The positive electrode active material 2b is provided on only one side of the above.

Similarly, the negative electrode active material 3b is provided on both sides of the negative electrode current collector 3a. However, when the uppermost layer or the lowermost layer of the laminated body 5 is composed of the negative electrode 3, the negative electrode 3 located in the uppermost layer or the lowermost layer is the negative electrode current collector 3a facing the positive electrode 2 on the lower layer or the upper layer side thereof. The negative electrode active material 3b is provided on only one side of the above.

As the positive electrode active material 2b and the negative electrode active material 3b, an active material capable of efficiently inserting and removing lithium ions can be appropriately selected and used. Specifically, a transition metal oxide, a transition metal composite oxide, or the like can be used. More specifically, for example, lithium manganese composite oxide Li ₂ Mn _a Ma _1-a O ₃ (0.8 ≦ a ≦ 1, Ma = Co, Ni), lithium cobaltate (LiCoO ₂ ), lithium nickelate. (LiNiO _2), lithium manganese spinel (LiMn ₂ O _4), the general _formula: in _{LiNi x Co y Mn z O 2} (x + y + z = 1,0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ z ≦ 1) Represented composite metal oxide, lithium vanadium compound (LiV ₂ O ₅ ), olivine type LiMbPO ₄ (where Mb is one type selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr. Represents the above elements), Lithium vanadium phosphate (Li ₃ V ₂ (PO ₄ ) ₃ or LiVOPO ₄ ), Li ₂ MnO _3- LiMcO ₂ (Mc = Mn, Co, Ni) Li excess system solid solution, lithium titanate _{(Li 4 Ti 5 O 12)} , a composite represented by _{Li s Ni t Co u Al v} O 2 (0.9 <s <1.3,0.9 <t + u + v <1.1) A metal oxide or the like can be used.

There is no clear distinction between the positive electrode active material 2b and the negative electrode active material 3b, and the potentials of the two types of compounds are compared, and the compound showing a more noble potential is used as the positive electrode active material 2b to show a lower potential. The compound can be used as the negative electrode active material 3b.

Further, the positive electrode current collector 2a and the negative electrode current collector 3a may contain the positive electrode active material 2b and the negative electrode active material 3b, respectively. The content ratio of the active materials 2b and 3b contained in the respective current collectors 2a and 3a is not particularly limited as long as it functions as a current collector, but for example, a positive electrode current collector / positive electrode active material or a negative electrode current collector. It is preferable that the body / negative electrode active material is in the range of 90/10 to 70/30 in volume ratio, respectively.

Since the positive electrode current collector 2a and the negative electrode current collector 3a contain the positive electrode active material 2b and the negative electrode active material 3b, respectively, the adhesion between the positive electrode current collector 2a and the positive electrode active material 2b constituting the positive electrode 2 is determined. The adhesion between the negative electrode current collector 3a constituting the negative electrode 3 and the negative electrode active material 3b is improved.

Further, the positive electrode 2 and the negative electrode 3 may contain, for example, a conductive auxiliary agent or a binder together with the positive electrode active material 2b and the negative electrode active material 3b described above.

As the solid electrolyte 4, a material having low electron conductivity and high lithium ion conductivity can be appropriately selected and used. Specifically, for example, a compound having a garnet-type crystal structure such as Li _6.4 Al _0.2 La ₃ Zr ₂ O ₁₂ (LLZO), Li ₅ La ₃ Bi ₂ O ₁₂ , LLZO + LiBO ₂ , and Li _{1 .3} NASICON such as Al _0.3 Ti _1.7 (PO ₄ ) ₃ (LATP), LiZr ₂ (PO ₄ ) ₃ (LZP), Li _1.1 Y _0.1 Zr _1.9 (PO ₄ ) _3. A compound having a perovskite type crystal structure such as a compound having a type crystal structure, Li _0.29 La _0.57 TiO ₃ , Li _0.45 La _0.57 Ti _0.95 O _3, and the like can be used.

(Manufacturing method of all-solid-state secondary battery)
Next, a method for manufacturing the all-solid-state secondary battery 1 will be described.
When manufacturing the all-solid-state secondary battery 1, first, the laminated body 5 is manufactured. As a method for producing the laminated body 5, a simultaneous firing method or a sequential firing method can be used.

The co-fired method is a method in which the materials forming each layer are laminated and then the laminated body 5 is produced by batch firing. The sequential firing method is a method in which firing is performed each time each layer is formed.

When the simultaneous firing method is used, the laminated body 5 can be produced with fewer work steps than when the sequential firing method is used. Further, when the co-fired method is used, the obtained laminated body 5 becomes denser than when the sequential firing method is used. Therefore, in the present embodiment, a case where the laminated body 5 is produced by using the co-fired method will be described as an example.

When the laminated body 5 is produced by the co-fired method, a step of preparing a paste of each material constituting the laminated body 5, a step of applying and drying the paste to prepare a green sheet, and a step of laminating the green sheet are performed. It has a step of forming a laminated sheet and simultaneously firing the laminated sheet.

Specifically, first, each material of the positive electrode current collector 2a, the positive electrode active material 2b, the solid electrolyte 4, the negative electrode active material 3b, and the negative electrode current collector 3a constituting the laminate 5 is made into a paste.

The method for making each material into a paste is not particularly limited, and for example, a method of mixing powders of each material with a vehicle to obtain a paste is used. Here, vehicle is a general term for media in the liquid phase. Vehicles include solvents and binders.

Using such a method, a paste for the positive electrode current collector 2a, a paste for the positive electrode active material 2b, a paste for the solid electrolyte 4, a paste for the negative electrode active material 3b, and a paste for the negative electrode current collector 3a can be obtained. Make.

Next, a green sheet is prepared. The green sheet is obtained by applying a paste prepared for each material on a base material such as PET (polyethylene terephthalate) film, drying it if necessary, and then peeling off the base material. .. The method of applying the paste is not particularly limited, and for example, known methods such as screen printing, application, transfer, and doctor blade can be used.

Next, the green sheets produced for each material are stacked in a desired order and the number of layers to prepare a laminated sheet. When laminating green sheets, alignment and cutting are performed as necessary. For example, when manufacturing a parallel type or serial parallel type battery, it is possible to align the end faces of the positive electrode current collector 2a and the end faces of the negative electrode current collector 3a so that they do not match, and stack the green sheets. preferable.

Further, the laminated sheet may be produced by producing a positive electrode unit and a negative electrode unit and using a method of laminating these units.

Specifically, first, a paste for the solid electrolyte 4 is applied onto a base material such as a PET film by the doctor blade method, and dried to form a sheet-shaped solid electrolyte 4.

Next, the paste for the positive electrode active material 2b is printed on the solid electrolyte 4 by screen printing and dried to form the positive electrode active material 2b.

Next, the paste for the positive electrode current collector 2a is printed on the positive electrode active material 2b by screen printing and dried to form the positive electrode current collector 2a.

Next, the paste for the positive electrode active material 2b is printed on the positive electrode current collector 2a by screen printing and dried to form the positive electrode active material 2b.

Then, the PET film is peeled off to obtain a positive electrode unit. The positive electrode unit is a laminated sheet in which a solid electrolyte 4, a positive electrode active material 2b, a positive electrode current collector 2a, and a positive electrode active material 2b are laminated in this order.

Further, the negative electrode unit is manufactured by the same procedure. The negative electrode unit is a laminated sheet in which a solid electrolyte 4, a negative electrode active material 3b, a negative electrode current collector 3a, and a negative electrode active material 3b are laminated in this order.

Next, the positive electrode unit and the negative electrode unit are laminated. At this time, the solid electrolyte 4 of the positive electrode unit and the negative electrode active material 3b of the negative electrode unit are laminated so as to face each other. Alternatively, the positive electrode active material 2b of the positive electrode unit and the solid electrolyte 4 of the negative electrode unit are laminated so as to face each other.

As a result, the positive electrode active material 2b, the positive electrode current collector 2a, the positive electrode active material layer 2b, the solid electrolyte 4, the negative electrode active material 3b, the negative electrode current collector 3a, the negative electrode active material layer 3b, and the solid electrolyte 4 are in this order. A laminated laminated sheet is obtained.

When laminating the positive electrode unit and the negative electrode unit, the positive electrode current collector 2a of the positive electrode unit and the negative electrode current collector 3a of the negative electrode unit are laminated while being alternately shifted. Further, by alternately shifting the positive electrode unit and the negative electrode unit, a laminated sheet is produced while stacking the sheets for the solid electrolyte 3 on the portion where the solid electrolyte 4 does not exist.

Next, the produced laminated sheets are collectively crimped. The crimping is preferably performed while heating. The heating temperature during crimping is, for example, 40 to 95 ° C.

Next, the crimped laminated sheets are collectively removed and co-fired to obtain a laminated body 5 made of a sintered body. Debye of the laminated sheet is performed, for example, by heating to 300 to 800 ° C. in a nitrogen atmosphere. The debuy time is, for example, 0.1 to 10 hours. The laminated sheet is fired, for example, by heating to 600 to 1000 ° C. in a nitrogen atmosphere. The firing time is, for example, 0.1 to 3 hours.

The produced laminate 5 may be placed in a cylindrical container together with an abrasive such as alumina (Al ₂ O ₃ ) for barrel polishing. As a result, the corners of the laminated body 5 can be chamfered, and as another polishing method, the laminated body 5 may be polished by sandblasting. This polishing method is preferable because only a specific part can be polished.

Next, the first connection terminal 6 and the second connection terminal 7 are formed on the side surfaces of the produced laminated body 5 facing each other. The first connection terminal 6 and the second connection terminal 7 can be formed by means such as sputtering.
By going through the above steps, the all-solid-state secondary battery 1 can be manufactured.

By the way, as shown in an enlarged manner in FIG. 2, the solid electrolyte 4 of the present embodiment includes the first solid electrolyte particles 11 and the second solid electrolyte particles 12, and these first solid electrolyte particles 11 and The second solid electrolyte particle 12 has a densified structure. Note that FIG. 2 is a schematic view showing a cross-sectional structure of the solid electrolyte 4.

Specifically, in the solid electrolyte 4 of the present embodiment, the first solid electrolyte particles 11 and the second solid electrolyte particles 12 have the same crystal structure as each other. Further, the average particle size of the first solid electrolyte particles 11 is D1, the sintering temperature of the first solid electrolyte particles 11 is T1, the average particle size of the second solid electrolyte particles 12 is D2, and the second When the sintering temperature of the solid electrolyte particles 12 is T2, the relationships of the following formulas (1) and (2) are satisfied.
D1> D2 ... (1)
T1> T2 ... (2)

Here, regarding the average particle diameters D1 and D2 of the solid electrolyte particles 11 and 12, the cross section of the solid electrolyte 4 is cut out, the grain boundaries are highlighted by annealing treatment, chemical etching, or the like, and then a scanning electron microscope (SEM) is performed. Observe by. In the observation image obtained at this time, the solid electrolyte particles 11 and 12 are discriminated. When the compositions of the solid electrolyte particles 11 and 12 are different, they can be distinguished by using energy dispersive X-ray analysis (EDS). Then, the average particle diameters D1 and D2 of the solid electrolyte particles 11 and 12 are measured. Specifically, the longest diameters of the solid electrolyte particles 11 and 12 are measured, the longest diameters of all the solid electrolyte particles 11 and 12 are measured as much as possible in the observation field, and then the average value of the solid electrolyte particles 11 is used. , 12 average particle diameters D1 and D2 were determined.

When the compositions of the solid electrolyte particles 11 and 12 are the same, a histogram may be created from the result of image processing, the solid electrolyte particles 11 and 12 may be distinguished from the result, and the average particle diameters D1 and D2 may be obtained.

As for the sintering temperatures T1 and T2 of the solid electrolyte particles 11 and 12, as shown in FIG. 3, a molded product having the same composition as the material constituting the solid electrolyte particles 11 and 12 was prepared and thermomechanical analysis (TMA) was performed. ) Measured the heat shrinkage behavior. At this time, the peak value of the differential curve (DTMA) in the sintering behavior was set to the sintering temperatures T1 and T2 of the solid electrolyte particles 11 and 12. Note that FIG. 3 is a graph showing a measurement curve (TMA) when the heat shrinkage behavior is measured by TMA and a differential curve (DTMA) in the sintering behavior.

The all-solid-state secondary battery 1 of the present embodiment has such a configuration, so that the solid electrolyte 4 sintered at a high temperature can be fired at a low temperature, a solid having a small porosity and a high lithium ion conductivity. It is possible to obtain the electrolyte 4. Further, in the all-solid-state secondary battery 1 using the solid electrolyte 4, it is possible to obtain a sufficiently large capacity.

The reason why the above effect is obtained is not necessarily clear, but it is considered to be due to the following action. That is, in the solid electrolyte 4 of the present embodiment, the average particle size D2 of the second solid electrolyte particles 12 is smaller than the average particle size D1 of the first solid electrolyte particles 11 (D1> D2). The second solid electrolyte particles 12 are likely to be present between the solid electrolyte particles 11 of the above. As a result, the laminated body 5 having a high filling rate can be produced, and the porosity can be reduced during the above-mentioned sintering.

The porosity is observed by a scanning electron microscope (SEM) after cutting out a cross section of the solid electrolyte 4 and making the grain boundaries stand out by annealing treatment or chemical etching. From the observation image obtained at this time, the area E1 occupied by the solid electrolyte particles 11 and 12 and the other area E2 were calculated, and the porosity was determined. That is, the porosity is a value [%] obtained by {E2 / (E1 + E2)} × 100.

Further, in the solid electrolyte 4 of the present embodiment, the sintering temperature T2 of the second solid electrolyte particles 12 is smaller than the sintering temperature T1 of the first solid electrolyte particles 11 (T1> T2), so that this solid is solid. In the process of raising the temperature to sinter the electrolyte 5, the sintering temperature T2 of the second solid electrolyte particles 12 is first reached. Further, by maintaining the temperature, the second solid electrolyte particles 12 first start sintering. Further, the firing temperature is preferably set between the sintering temperature T1 of the first solid electrolyte particles 11 and the sintering temperature T2 of the second solid electrolyte particles 12.

As a result, the second solid electrolyte particles 12 act like glue in the process of sintering, and the solid electrolyte 5 is densified while involving the first solid electrolyte particles 11. By these densification actions, a high-density solid electrolyte 5 can be obtained.

Further, since the first solid electrolyte particles 11 and the second solid electrolyte particles 12 have the same crystal structure, a bond is formed at the interface between the first solid electrolyte particles 11 and the second solid electrolyte particles 12. It becomes easy and the grain boundary resistance can be lowered.

This makes it possible to obtain the solid electrolyte 5 having high lithium ion conductivity. Further, in the all-solid-state secondary battery 1 using the solid electrolyte 5, it is possible to obtain a sufficiently large capacity. Further, by the method for manufacturing the all-solid-state secondary battery 1 using the solid electrolyte 5, it is possible to manufacture the all-solid-state secondary battery having a sufficiently large capacity.

Here, the average particle size of the solid electrolyte particles 11 of the present embodiment is 0.2 ≦ D1 ≦ 10 μm, preferably 0.5 ≦ D1 ≦ 5.0 μm, and more preferably 1.0 ≦ D1 ≦ 1.2 μm. is there.

On the other hand, the average particle size of the solid electrolyte particles 12 of the present embodiment is 0.01 ≦ D2 ≦ 2.0 μm, preferably 0.03 ≦ D2 ≦ 1.5 μm, and more preferably 0.05 ≦ D2 ≦ 1.0 μm. Is.

Further, it is preferable that the solid electrolyte 4 of the present embodiment further satisfies the relationship of the following formula (3).
0.1 × D1 ≧ D2… (3)

When the relationship of the above formula (3) is satisfied, the second solid electrolyte particles 12 are likely to be present between the first solid electrolyte particles 11, and the above effects can be further easily obtained.

Further, it is preferable that the solid electrolyte 4 of the present embodiment further satisfies the relationship of the following formula (4).
T1-T2 ≥ 100 ° C ... (4)

When the relationship of the above formula (4) is satisfied, the second solid electrolyte particles 12 are likely to be present between the first solid electrolyte particles 11, and the above effects can be further easily obtained.

Further, in the solid electrolyte 4 of the present embodiment, it is preferable that at least 50% or more of the surface of the first solid electrolyte particles 11 is in contact with the second solid electrolyte particles 12.

Here, the contact ratio is observed by a scanning electron microscope (SEM) after cutting out a cross section of the solid electrolyte 4 and highlighting the grain boundaries by annealing treatment or chemical etching. From the observation image obtained at this time, 20 nearby first solid electrolyte particles 11 were selected, the interfacial peripheral length L1 of each first solid electrolyte particle 11 and the first of each first solid electrolyte particle. The interface circumference L2 of the portion in contact with the solid electrolyte particles of 2 was calculated, and the contact ratio thereof was determined. That is, the contact rate is the average value [%] of the values obtained by (L2 / L1) × 100.

Further, it is preferable that the first solid electrolyte particles 11 and the second solid electrolyte particles 12 have different compositions from each other. As a result, the solid electrolyte 4 sintered at a high temperature can be fired at a low temperature, and the solid electrolyte 4 having a small porosity and high lithium ion conductivity can be obtained.

The first solid electrolyte particle 11 preferably has a garnet structure containing Li, La, Zr, and O, and the second solid electrolyte particle 12 preferably has a garnet structure containing Li, La, Bi, and O. Specifically, Li _6.4 Al _0.2 La ₃ Zr ₂ O ₁₂ having a garnet-type crystal structure is used as the first solid electrolyte particles 11, and the garnet-type particles 12 are of the garnet type. It is preferable to use Li ₅ La ₃ Bi ₂ O ₁₂ having a crystal structure.

As a result, the solid electrolyte 4 sintered at a high temperature can be fired at a low temperature, and the solid electrolyte 4 having a small porosity and high lithium ion conductivity can be obtained.

The present invention is not necessarily limited to that of the above embodiment, and various modifications can be made without departing from the spirit of the present invention. That is, each configuration and a combination thereof in the above embodiment are only examples, and it is possible to add, omit, replace, and make other changes to the configuration within a range that does not deviate from the gist of the present invention. ..

Hereinafter, the effects of the present invention will be made clearer by examples. The present invention is not limited to the following examples, and can be appropriately modified and implemented without changing the gist thereof.

(Examples 1 to 14 and Comparative Examples 1 to 6)
As shown in Table 1 below, the solid electrolytes of Examples 1 to 14 and Comparative Examples 1 to 6 were actually prepared, and the contact rate, porosity, and ionic conductivity of each solid electrolyte were measured. In addition, an all-solid-state secondary battery using each solid electrolyte was prepared, and the capacity of each battery was measured. The results are summarized in Table 1 below.

An all-solid secondary battery is a simultaneous firing method in which sheets of a solid electrolyte layer, a positive electrode current collector, a positive electrode active material, a solid electrolyte, a negative electrode active material, a negative electrode current collector, and a solid electrolyte are laminated in this order. To prepare a laminated body.

Copper or palladium was used for the positive electrode current collector and the negative electrode current collector, and Li ₃ V ₂ (PO ₄ ) ₃ was mainly used for the positive electrode active material and the negative electrode active material.

Then, the first connection terminal and the second connection terminal were attached to the laminated body to prepare an all-solid-state lithium ion secondary battery.

As shown in Table 1, it can be seen that the solid electrolytes of Examples 1 to 14 have a smaller porosity and higher lithium ion conductivity than the solid electrolytes of Comparative Examples 1 to 6. Further, the all-solid-state secondary battery using the solid electrolytes of Examples 1 to 14 obtained a larger capacity than the all-solid-state secondary battery using the solid electrolytes of Comparative Examples 1 to 6.

1 ... All-solid secondary battery 2 ... First electrode (positive electrode) 2a ... Positive electrode current collector 2b ... Positive electrode active material 3 ... Second electrode (negative electrode) 3a ... Negative electrode current collector 3b ... Negative electrode active material 4 ... Solid Electrode 5 ... Laminate 6 ... First connection terminal 7 ... Second connection terminal 11 ... First solid electrolyte particles 12 ... Second solid electrolyte particles

Claims (8)

Containing a first solid electrolyte particle and a second solid electrolyte particle,
The first solid electrolyte particles and the second solid electrolyte particles have the same crystal structure as each other.
The average particle size of the first solid electrolyte particles is D1, the sintering temperature of the first solid electrolyte particles is T1, the average particle size of the second solid electrolyte particles is D2, and the second solid is solid. When the sintering temperature of the electrolyte particles is T2,
D1> D2,
T1> T2
A solid electrolyte characterized by satisfying the relationship of. 0.1 × D1 ≧ D2
The solid electrolyte according to claim 1, wherein the relationship is satisfied. The solid electrolyte according to claim 1 or 2, wherein at least 50% or more of the surfaces of the first solid electrolyte particles are in contact with the second solid electrolyte particles. T1-T2 ≥ 100 ° C
The solid electrolyte according to any one of claims 1 to 3, wherein the solid electrolyte satisfies the above-mentioned relationship. The solid electrolyte according to any one of claims 1 to 4, wherein the first solid electrolyte particles and the second solid electrolyte particles have different compositions from each other. The first solid electrolyte particle has a garnet structure containing Li, La, Zr, and O, and has a garnet structure.
The solid electrolyte according to any one of claims 1 to 5, wherein the second solid electrolyte particles have a garnet structure containing Li, La, Bi, and O. An all-solid-state secondary battery comprising the solid electrolyte according to any one of claims 1 to 6. A method for manufacturing an all-solid-state secondary battery using a solid electrolyte containing a first solid electrolyte particle and a second solid electrolyte particle.
The first solid electrolyte particles and the second solid electrolyte particles have the same crystal structure as each other.
The average particle size of the first solid electrolyte particles is D1, the sintering temperature of the first solid electrolyte particles is T1, the average particle size of the second solid electrolyte particles is D2, and the second solid is solid. When the sintering temperature of the electrolyte particles is T2,
D1> D2,
T1> T2
A method for manufacturing an all-solid-state secondary battery, which comprises using a solid electrolyte that satisfies the above relationship.

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