阅读说明：本技术 全固体二次电池 (All-solid-state secondary battery ) 是由 竹内启子 上野哲也 矶道岳步 于 2019-03-22 设计创作，主要内容包括：本发明提供一种全固体二次电池,其中,具备正极活性物质层、负极活性物质层、以及位于它们之间的固体电解质层,上述正极活性物质层和上述负极活性物质层中的至少一方具有磷酸钒锂,上述固体电解质层具有磷酸锆锂,在具有上述磷酸钒锂的上述正极活性物质层或上述负极活性物质层与上述固体电解质层之间,具备：第一中间层,其具有含锆的磷酸钒锂,位于上述正极活性物质层或上述负极活性物质层侧；和第二中间层,其具有含钒的磷酸锆锂,位于上述固体电解质层侧。(The present invention provides an all-solid-state secondary battery including a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer located therebetween, wherein at least one of the positive electrode active material layer and the negative electrode active material layer includes lithium vanadium phosphate, the solid electrolyte layer includes lithium zirconium phosphate, and the all-solid-state secondary battery includes: a first intermediate layer having lithium vanadium phosphate containing zirconium and located on the positive electrode active material layer side or the negative electrode active material layer side; and a second intermediate layer having lithium zirconium phosphate containing vanadium, which is located on the side of the solid electrolyte layer.)

1. An all-solid secondary battery in which,

comprises a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer interposed therebetween,

at least one of the positive electrode active material layer and the negative electrode active material layer has lithium vanadium phosphate,

the solid electrolyte layer has a lithium zirconium phosphate,

the solid electrolyte layer is provided between the positive electrode active material layer or the negative electrode active material layer having the lithium vanadium phosphate and the solid electrolyte layer, and includes:

a first intermediate layer having lithium vanadium phosphate containing zirconium, which is located on the positive electrode active material layer side or the negative electrode active material layer side; and

a second intermediate layer having lithium zirconium phosphate containing vanadium, on the solid electrolyte layer side.

2. The all-solid secondary battery according to claim 1, wherein,

the first intermediate layer and the second intermediate layer have a concentration gradient of zirconium and a concentration gradient of vanadium.

3. The all-solid secondary battery according to claim 1 or 2, wherein,

the first intermediate layer satisfies: zirconium content/(zirconium content + vanadium content) >0.1, and

the thickness of the first intermediate layer is 0.1 [ mu ] m or more.

4. The all-solid secondary battery according to any one of claims 1 to 3,

the second intermediate layer satisfies: zirconium content/(zirconium content + vanadium content) < 0.9, and

the thickness of the second intermediate layer is 0.1 [ mu ] m or more.

5. The all-solid secondary battery according to any one of claims 1 to 4,

the solid electrolyte layer satisfies: zirconium content/(zirconium content + vanadium content) is not less than 0.9

The thickness of the solid electrolyte layer is 0.1 [ mu ] m or more.

6. The all-solid secondary battery according to any one of claims 1 to 5,

in the first intermediate layer, the average particle diameter D1 is 0.03 to 2 μm.

7. The all-solid secondary battery according to any one of claims 1 to 6,

in the second intermediate layer, the average particle diameter D2 is 0.03 to 2 μm.

Technical Field

The present invention relates to an all-solid secondary battery.

This application claims priority from Japanese patent application laid-open in Japan as filed on 29.3.2018, Japanese patent application laid-open No. 2018-063522, the contents of which are incorporated herein by reference.

Background

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

As lithium ion secondary batteries, batteries using an organic electrolytic solution as an electrolyte and batteries using a solid electrolyte are known. A lithium ion secondary battery (all-solid-state secondary battery) using a solid electrolyte as an electrolyte has a higher degree of freedom in designing the shape of the battery than a lithium ion secondary battery using an organic electrolytic solution, and is easy to realize downsizing or thinning of the battery size. In addition, the electrolyte does not leak, and the like, and has an advantage of high reliability.

In all-solid secondary batteries, an oxide-based solid electrolyte that is stable in air can be used. By using the oxide-based solid electrolyte, each member to be each layer of the all-solid-state secondary battery can be laminated and then fired at the same time. This enables industrial mass production of all-solid-state secondary batteries. However, since the dissimilar materials are fired simultaneously, it is difficult to join the positive electrode layer and the negative electrode layer constituting the all-solid-state secondary battery and the solid electrolyte layer. In addition, there are also problems as follows: the peeling occurs at the interface between the positive electrode layer and the solid electrolyte when the positive electrode layer and the negative electrode layer expand and contract in accordance with the charge and discharge of the all-solid secondary battery, and the cycle characteristics deteriorate.

Patent document 1 describes the following: by interposing an appropriate firing assistant between the interface of the positive electrode layer and the solid electrolyte layer and the interface of the negative electrode layer and the solid electrolyte layer, mechanical bonding becomes firm, and by making bonding of the layers firm, mechanical stress is enhanced.

[ Prior art documents ]

Patent document

Patent document 1: japanese patent laid-open publication No. 2011-

Disclosure of Invention

[ problem to be solved by the invention ]

However, as described in patent document 1, when the bonding of the respective layers is strengthened only by designing the sintering aid, a sufficient bonding state cannot be achieved. This is because the sintering aid is destroyed by repeated charge and discharge, and peeling between the positive electrode layer and the negative electrode layer and the solid electrolyte layer may occur. Therefore, further improvement in cycle characteristics is required for all-solid secondary batteries.

The present invention has been made in view of the above-described problems, and an object thereof is to provide an all-solid secondary battery having improved adhesion at the interface between a solid electrolyte layer and a negative electrode layer or a positive electrode layer and excellent cycle characteristics.

[ solution for solving problems ]

In order to solve the above technical problems, the present invention provides the following technical solutions.

(1) An all-solid secondary battery according to a first aspect includes a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer located therebetween, wherein at least one of the positive electrode active material layer and the negative electrode active material layer has lithium vanadium phosphate, the solid electrolyte layer has lithium zirconium phosphate, and the all-solid secondary battery includes, between the positive electrode active material layer or the negative electrode active material layer having the lithium vanadium phosphate and the solid electrolyte layer: a first intermediate layer having lithium vanadium phosphate containing zirconium, which is located on the positive electrode active material layer side or the negative electrode active material layer side; and a second intermediate layer having lithium zirconium phosphate containing vanadium, on the solid electrolyte layer side.

(2) In the all-solid secondary battery according to the above aspect, the first intermediate layer and the second intermediate layer may have a concentration gradient of zirconium and a concentration gradient of vanadium.

(3) The first intermediate layer in the all-solid secondary battery of the above-described aspect may satisfy: the zirconium content/(zirconium content + vanadium content) >0.1, and the thickness of the first intermediate layer is 0.1 μm or more.

(4) The second intermediate layer in the all-solid secondary battery of the above-described aspect may satisfy: the zirconium content/(zirconium content + vanadium content) < 0.9, and the thickness of the second intermediate layer is 0.1 μm or more.

(5) The solid electrolyte layer in the all-solid-state secondary battery of the above-described aspect may satisfy: the zirconium content/(zirconium content + vanadium content) is not less than 0.9, and the thickness of the solid electrolyte layer is not less than 0.1 μm.

(6) In the first intermediate layer of the all-solid-state secondary battery according to the above aspect, the average particle diameter D1 may be 0.03 to 2 μm.

(7) In the second intermediate layer of the all-solid-state secondary battery according to the above aspect, the average particle diameter D2 may be 0.03 to 2 μm.

[ Effect of the invention ]

The all-solid-state secondary battery of the above embodiment is excellent in cycle characteristics during charge and discharge.

Drawings

Fig. 1 is a schematic cross-sectional view of the all-solid secondary battery of the present embodiment.

Fig. 2 is a schematic cross-sectional view of the entire solid-state secondary battery according to the present embodiment, with the main portions thereof enlarged.

Fig. 3 is a Scanning Electron Microscope (SEM) image of the vicinity of the negative electrode of the all-solid-state secondary battery according to the present embodiment after enlargement.

Fig. 4 is a result of acquiring a line profile containing an element by an energy dispersive X-ray spectrometer (EDS) from a field of view of the SEM image measured in fig. 3.

Fig. 5 is a schematic view of a Transmission Electron Microscope (TEM) image obtained by enlarging the vicinity of the negative electrode of the all-solid-state secondary battery according to the present embodiment.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. In the drawings used in the following description, a part to be a feature may be enlarged for convenience of understanding the feature of the present invention. Therefore, the dimensional ratios of the respective components shown in the drawings and the like may be different from those in reality. The materials, dimensions, and the like exemplified in the following description are merely examples, and the present invention is not limited thereto, and can be appropriately modified and implemented within a range not changing the gist thereof.

[ all-solid-state secondary battery ]

Fig. 1 is a schematic cross-sectional view of an all-solid secondary battery 10 of the present embodiment. The all-solid secondary battery 10 has at least one first electrode layer 1, at least one second electrode layer 2, and a solid electrolyte layer 3 sandwiched between the first electrode layer 1 and the second electrode layer 2. The first electrode layer 1, the solid electrolyte layer 3, and the second electrode layer 2 are sequentially stacked to form a stacked body 4. The first electrode layers 1 are connected to terminal electrodes 5 arranged on one end side, and the second electrode layers 2 are connected to terminal electrodes 6 arranged on the other end side.

One of the first electrode layer 1 and the second electrode layer 2 functions as a positive electrode layer, and the other functions as a negative electrode layer. For convenience of understanding, the first electrode layer 1 is referred to as a positive electrode layer 1, and the second electrode layer 2 is referred to as a negative electrode layer 2.

As shown in fig. 1, positive electrode layers 1 and negative electrode layers 2 are alternately laminated via solid electrolyte layers 3. The all-solid-state secondary battery 10 is charged and discharged by the transfer of ions between the positive electrode layer 1 and the negative electrode layer 2 through the solid electrolyte layer 3.

As shown in fig. 1, the positive electrode layer 1 has: a positive electrode current collector layer 1A containing a positive electrode current collector, and a positive electrode active material layer 1B containing a positive electrode active material. The negative electrode layer 2 has: an anode current collector layer 2A containing an anode current collector, and an anode active material layer 2B containing an anode active material.

As the positive electrode collector layer 1A and the negative electrode collector layer 2A, materials having high conductivity can be used. For example, silver, palladium, gold, platinum, aluminum, copper, nickel, or the like is preferably used for the positive electrode collector layer 1A and the negative electrode collector layer 2A. Among these, copper is less likely to react with the positive electrode active material, the negative electrode active material, and the solid electrolyte. If copper is used for the positive electrode collector layer 1A and the negative electrode collector layer 2A, the internal resistance (internal resistance) of the all-solid secondary battery 10 can be reduced. The positive electrode collector layer 1A and the negative electrode collector layer 2A may be made of the same material or different materials.

The positive electrode collector layer 1A and the negative electrode collector layer 2A may contain a positive electrode active material and a negative electrode active material, respectively. The content ratio of the active material contained in each current collector layer is not particularly limited as long as the active material functions as a current collector. For example, the volume ratio of the positive electrode current collector/positive electrode active material or the negative electrode current collector/negative electrode active material is preferably in the range of 90/10 to 70/30.

Since the positive electrode collector layer 1A and the negative electrode collector layer 2A contain the positive electrode active material and the negative electrode active material, respectively, the adhesion between the positive electrode collector layer 1A and the positive electrode active material layer 1B and the adhesion between the negative electrode collector layer 2A and the negative electrode active material layer 2B are improved.

The positive electrode active material layer 1B is formed on one surface or both surfaces of the positive electrode current collector layer 1A. For example, in the case where the positive electrode layer 1 is formed on the uppermost layer in the stacking direction of the stacked body 4, the positive electrode layer 1 and the negative electrode layer 2 are not opposed to each other on the uppermost layer. Therefore, in the positive electrode layer 1 located at the uppermost layer, the positive electrode active material layer 1B may be present only on the lower side in the stacking direction. On the other hand, from the viewpoint of moderating the stress applied to the positive electrode current collector layer 1A, the positive electrode active material layers 1B are preferably provided on both surfaces of the positive electrode current collector layer 1A.

The negative electrode active material layer 2B is also formed on one surface or both surfaces of the negative electrode current collector layer 2A, as in the positive electrode active material layer 1B. In the case where the negative electrode layer 2 is formed on the lowermost layer in the stacking direction of the stacked body 4, the negative electrode active material layer 2B may be present only on the upper side in the stacking direction in the negative electrode layer 2 located on the lowermost layer with respect to the positive electrode layer 1 and the negative electrode layer 2. On the other hand, from the viewpoint of moderating the stress applied to the negative electrode current collector layer 2A, the negative electrode active material layers 2B are preferably provided on both surfaces of the negative electrode current collector layer 2A.

Fig. 2 is an enlarged schematic cross-sectional view of a main portion M of the all-solid secondary battery 10 according to the present embodiment. Fig. 2 corresponds to a main portion M surrounded by a dotted line in fig. 1.

As shown in fig. 2, the solid electrolyte layer 3 is located between the positive electrode active material layer 1B and the negative electrode active material layer 2B. A first intermediate layer 7 and a second intermediate layer 8 are present between the positive electrode active material layer 1B and the negative electrode active material layer 2B and the solid electrolyte layer 3.

At least one of the positive electrode active material layer 1B and the negative electrode active material layer 2B has lithium vanadium phosphate. Preferably, at least one of the positive electrode active material layer 1B and the negative electrode active material layer 2B has lithium vanadium phosphate as a main component. As lithium vanadium phosphate, Li may be used₃V₂(PO₄)₃、LiVOPO₄And the like. In the positive electrode active material layer 1B and the negative electrode active material layer 2B, lithium ions are inserted or desorbed during charge and discharge.

The solid electrolyte layer 3 has lithium zirconium phosphate. Preferably, the solid electrolyte layer 3 has lithium zirconium phosphate as a main component. As the lithium zirconium phosphate, LiZr can be used₂(PO₄)₃And the like. The solid electrolyte layer 3 is responsible for the conduction of lithium ions between the positive electrode layer 1 and the negative electrode layer 2.

In fig. 2, the following is assumed: the positive electrode active material layer 1B and the negative electrode active material layer 2B each contain lithium vanadium phosphate, and a first intermediate layer 7 and a second intermediate layer 8 are provided between the positive electrode active material layer 1B and the solid electrolyte layer 3 and between the negative electrode active material layer 2B and the solid electrolyte layer 3. However, it may be: the first intermediate layer 7 and the second intermediate layer 8 are provided only between the positive electrode active material layer 1B and the solid electrolyte layer 3 or between the negative electrode active material layer 2B and the solid electrolyte layer 3. The first intermediate layer 7 and the second intermediate layer 8 located between the positive electrode active material layer 1B and the solid electrolyte layer 3 and the first intermediate layer 7 and the second intermediate layer 8 located between the negative electrode active material layer 2B and the solid electrolyte layer 3 are not necessarily the same, and the thicknesses, the proportions of the constituent elements, and the like may be different.

The first intermediate layer 7 is located closer to the positive electrode active material layer 1B or the negative electrode active material layer 2B than the second intermediate layer 8, and the second intermediate layer 8 is located closer to the solid electrolyte layer 3 than the first intermediate layer 7. The first intermediate layer 7 and the second intermediate layer 8 strengthen the bonding at the interface between the first intermediate layer 7 and the second intermediate layer 8, and reduce the difference in expansion and contraction between the positive electrode active material layer 1B or the negative electrode active material layer 2B and the solid electrolyte layer 3 during charge and discharge. That is, the first intermediate layer 7 and the second intermediate layer 8 suppress interfacial separation caused by expansion and contraction during charge and discharge, and improve the cycle characteristics of the all-solid secondary battery 10.

The first intermediate layer 7 has lithium vanadium phosphate containing zirconium (i.e., part of vanadium in lithium vanadium phosphate is replaced with zirconium). Preferably, the first intermediate layer 7 has lithium vanadium phosphate containing zirconium as a main component. The crystal structure of the zirconium-containing lithium vanadium phosphate is similar to that of the lithium vanadium phosphate contained in the adjacent positive electrode active material layer 1B or negative electrode active material layer 2B, and the purpose thereof is to firmly bond the first intermediate layer 7 and the adjacent positive electrode active material layer 1B or negative electrode active material layer 2B.

The second intermediate layer 8 has lithium zirconium phosphate containing vanadium (i.e., part of zirconium in lithium zirconium phosphate is replaced with vanadium). Preferably, the second intermediate layer 8 has vanadium-containing lithium zirconium phosphate as a main component. The crystal structure of the vanadium-containing lithium zirconium phosphate is similar to that of the lithium zirconium phosphate contained in the adjacent solid electrolyte layer 3, with the object of firmly bonding the second intermediate layer 8 and the adjacent solid electrolyte layer 3.

Fig. 3 is a Scanning Electron Microscope (SEM) image of the entire solid-state secondary battery 10 according to the present embodiment, with the vicinity of the negative electrode enlarged. As shown in fig. 3, the difference between the first intermediate layer 7 and the second intermediate layer 8 can be confirmed by SEM images. In the case where the main component of the first intermediate layer 7 is lithium vanadium phosphate containing zirconium and the main component of the second intermediate layer 8 is lithium zirconium phosphate containing vanadium, the difference in crystal structure between the first intermediate layer 7 and the second intermediate layer 8 can be clearly recognized by X-ray analysis, electron beam analysis, or the like. That is, the interface between the first intermediate layer 7 and the second intermediate layer 8 can be clearly recognized by X-ray analysis, electron beam analysis, or the like. In addition, using a Transmission Electron Microscope (TEM), the interface between the first intermediate layer 7 and the second intermediate layer 8 can be recognized according to the difference in crystal structure.

Fig. 4 is a result of acquiring a line profile containing an element by an energy dispersive X-ray spectrometer (EDS) from a field of view of the SEM image measured in fig. 3. Fig. 4(a) is a view showing measurement sites, and a line profile is measured in this order from the negative electrode current collector layer 2A to the negative electrode active material layer 2B, the first intermediate layer 7, the second intermediate layer 8, and the solid electrolyte layer 3. Fig. 4(b) is the detected zirconium content/(zirconium content + vanadium content).

In the line profile shown in fig. 4, the first intermediate layer 7 corresponds to a portion having a crystal structure of lithium vanadium phosphate among portions satisfying the zirconium content/(zirconium content + vanadium content) > 0.1. The zirconium content and the vanadium content measured by EDS can be converted into the composition ratio at each portion of the first intermediate layer 7.

For example, in the presence of Li_αV_βZr_γ(PO₄)₃When the composition of the first intermediate layer 7 is expressed, the above formula can be converted to γ/(β + γ)>0.1. In addition, for example, in the use of Li_αV_βZr_γOPO₄When the composition of the first intermediate layer 7 is expressed, it can be similarly converted into γ/(β + γ)>0.1。

The second intermediate layer 8 corresponds to a portion having a crystal structure of zirconium lithium phosphate in a portion satisfying a zirconium content/(zirconium content + vanadium content) < 0.9. In addition, the negative electrode active material layer 2B corresponds to a portion having a zirconium content/(zirconium content + vanadium content) of not more than 0.1, and the solid electrolyte layer 3 corresponds to a portion having a zirconium content/(zirconium content + vanadium content) of not less than 0.9.

The zirconium content and the vanadium content measured by EDS can be converted into the composition ratio of the second intermediate layer 8, the negative electrode active material layer 2B, and the solid electrolyte layer 3.

For example, in the presence of Li_αV_βZr_γ(PO₄)₃In the case of the composition of the second intermediate layer 8, the above formula can be expressed in terms of γ/(β + γ) < 0.9, and the negative electrode active material layer 2B and the solid electrolyte layer 3 can be expressed in the same manner, the negative electrode active material layer 2B corresponds to a portion of γ/(β + γ) ≦ 0.1, and the solid electrolyte layer 3 corresponds to γ/(β + γ) ≧ 0.9.

As shown in the region showing the first intermediate layer 7 and the second intermediate layer 8 in the line profile of fig. 4, the first intermediate layer 7 and the second intermediate layer 8 preferably have a concentration gradient of zirconium and a concentration gradient of vanadium inside. By having a concentration gradient inside, rapid changes in the zirconium concentration and vanadium concentration at the interface between the first intermediate layer 7 and the second intermediate layer 8 can be suppressed, and the adhesion at the interface can be improved. In addition, it is preferable that the zirconium concentration and the vanadium concentration between the first intermediate layer 7 and the cathode active material layer 1B or the anode active material layer 2B continuously change rather than rapidly change. Preferably, the zirconium concentration and the vanadium concentration between the second intermediate layer 8 and the solid electrolyte layer 3 also continuously change.

Preferably, the concentration gradient of zirconium and vanadium at the interface between the positive electrode active material layer 1B or the negative electrode active material layer 2B and the first intermediate layer 7 and at the interface between the solid electrolyte layer 3 and the second intermediate layer 8 is small. In addition, it is preferable that the concentration gradient of zirconium and vanadium at the interface between the first intermediate layer 7 and the second intermediate layer 8 is large.

The thickness of the first intermediate layer 7 is preferably 0.1 μm or more, more preferably 1.0 μm or more, and further preferably 2.0 μm or more. The thickness of the first intermediate layer 7 is preferably 10.0 μm or less, and more preferably 5.0 μm or less.

The first intermediate layer 7 is a layer having a similar crystal structure to the positive electrode active material layer 1B or the negative electrode active material layer 2B, but the first intermediate layer 7 is different from the positive electrode active material layer 1B or the negative electrode active material layer 2B in that it contains zirconium. Therefore, the lithium ions in and out of the first intermediate layer 7 are smaller than in the positive electrode active material layer 1B or the negative electrode active material layer 2B. Further, the expansion and contraction at the time of charge and discharge of the first intermediate layer 7 is smaller than that of the positive electrode active material layer 1B or the negative electrode active material layer 2B.

If the thickness of the first intermediate layer 7 is too thin, the concentration gradient of zirconium and vanadium in the first intermediate layer 7 becomes large. As a result, the effect of mitigating the difference in expansion and contraction between the first intermediate layer 7 and the second intermediate layer 8, and between the first intermediate layer 7 and the positive electrode active material layer 1B or the negative electrode active material layer 2B, during charge and discharge of the all-solid secondary battery 10 is reduced. If the thickness of the first intermediate layer 7 is excessively thick, the size of the all-solid secondary battery 10 becomes excessively large.

The thickness of the second intermediate layer 8 is preferably 0.1 μm or more, more preferably 1.0 μm or more, and further preferably 2.0 μm or more. The thickness of the second intermediate layer 8 is preferably 10.0 μm or less, and more preferably 5.0 μm or less.

The second intermediate layer 8 is a layer having a similar crystal structure to the solid electrolyte layer 3, but the second intermediate layer 8 is different from the solid electrolyte layer 3 in that it contains vanadium. Therefore, the lithium ions enter and exit from the second intermediate layer 8, and expansion and contraction occur during charge and discharge of the all-solid secondary battery 10.

If the thickness of the second intermediate layer 8 is too thin, the concentration gradient of zirconium and vanadium in the second intermediate layer 8 becomes large. As a result, the effect of mitigating the difference in expansion and contraction between the first intermediate layer 7 and the second intermediate layer 8, and between the second intermediate layer 8 and the solid electrolyte layer 3 during charge and discharge of the all-solid secondary battery 10 is reduced. If the thickness of the second intermediate layer 8 is excessively thick, the size of the all-solid secondary battery 10 is excessively large.

The thickness of the solid electrolyte layer 3 is preferably 0.1 μm or more, more preferably 1.0 μm or more, and still more preferably 3 μm or more. If the thickness of the solid electrolyte layer 3 is thin, the solid electrolyte layer 3 cannot ensure sufficient insulation, and a short circuit is likely to occur between the positive electrode layer 1 and the negative electrode layer 2.

The thickness of the first intermediate layer 7, the thickness of the second intermediate layer 8, and the thickness of the solid electrolyte layer 3 were obtained from SEM images and SEM-EDS spectral profiles. The boundary between the first intermediate layer 7 and the second intermediate layer 8 is determined from the SEM image. Next, the thicknesses of the first intermediate layer 7, the second intermediate layer 8, and the solid electrolyte layer 3 were measured by measuring the thicknesses in a range in which the composition ratio (zirconium content/(zirconium content + vanadium content)) measured from the line profile was within a predetermined range.

Fig. 5 is a schematic view of a Transmission Electron Microscope (TEM) image obtained by enlarging the vicinity of the negative electrode of the all-solid secondary battery 10 according to the present embodiment. In the all-solid secondary battery 10 of the present embodiment, since the amount of electron transmission differs for each crystal orientation, the grain boundaries of the layers of the first intermediate layer 7, the second intermediate layer 8, the negative electrode active material layer 2B, and the solid electrolyte 3 can be distinguished from the TEM image.

The area of the crystal grain obtained by directly measuring the TEM image is divided by the observation magnification of the TEM image to obtain the cross-sectional area C of the crystal grain. Further, assuming that the outline of the crystal grain is a circle, the diameter D of the crystal grain can be obtained by using the sectional area C of the crystal grain according to a formula for obtaining the area of the circle. Specifically, the diameter D of the crystal grain can be obtained by calculation of √ (4C/pi) ═ D.

The average value of the diameters D of the crystal grains of 30 or more first intermediate layers 7 and second intermediate layers 8 was obtained by measuring the diameters D by the above-described method, and the average values were defined as the average particle diameter D1 of the first intermediate layer 7 and the average particle diameter D2 of the second intermediate layer 8.

The average particle diameter D1 of the first intermediate layer 7 is preferably 0.03 to 2 μm. If the average particle diameter D1 of the first intermediate layer 7 exceeds 2 μm, the strength of the first intermediate layer 7 is lowered, and the cycle characteristics are lowered, which is not preferable. Further, if the average particle diameter of the first intermediate layer 7 is less than 0.03 μm, the strength is also decreased, and the cycle characteristics are also decreased, which is not preferable.

The average particle diameter D2 of the second intermediate layer 8 is preferably 0.03 to 2 μm. If the average particle diameter of the second intermediate layer 8 exceeds 2 μm, the strength of the second intermediate layer 8 is lowered, and the cycle characteristics are lowered, which is not preferable. Further, if the average particle diameter of the second intermediate layer 8 is less than 0.03 μm, the strength is also decreased, and the cycle characteristics are also decreased, which is not preferable.

(terminal electrode)

As shown in fig. 1, the terminal electrodes 5 and 6 are formed in contact with the side surfaces (exposed surfaces of the end surfaces of the positive electrode layer 1 and the negative electrode layer 2) of the laminate 4. The terminal electrodes 5 and 6 are connected to external terminals and are responsible for the transfer of electrons to and from the laminate 4.

The terminal electrodes 5 and 6 are preferably made of a material having high electrical conductivity. The material of the terminal electrodes 5 and 6 is not particularly limited, and for example, silver, gold, platinum, aluminum, copper, tin, nickel, gallium, indium, an alloy thereof, or the like can be used.

[ method for producing all-solid-state Secondary Battery ]

(formation of laminate)

After the paste constituting each layer is prepared, green sheets (green sheets) are prepared by applying and drying the paste, and the laminate 4 can be prepared by applying pressure and temperature and performing thermocompression bonding. That is, the method for manufacturing the laminate 4 includes the steps of: a step of producing a paste of each material constituting the laminate 4 (paste production step), a step of applying and drying the paste to produce green sheets (green sheet production step), a step of laminating the green sheets to form a laminate (lamination step), and a step of thermally press-bonding the laminate (thermal press-bonding step). After the hot press bonding step is completed, the laminate is fired and cooled.

< paste preparation Process >

In the paste preparation step, the respective materials of the positive electrode collector layer 1A, the positive electrode active material layer 1B, the solid electrolyte layer 3, the negative electrode active material layer 2B, and the negative electrode collector layer 2A constituting the laminate 4 are prepared into a paste.

The method for forming the paste from each material is not particularly limited. Examples thereof include: a method of mixing powders of the respective materials with a carrier to obtain a paste. The carrier contains a solvent, a binder, and the like. Then, a paste for positive electrode collector layer 1A, a paste for positive electrode active material layer 1B, a paste for solid electrolyte layer 3, a paste for negative electrode active material layer 2B, and a paste for negative electrode collector layer 2A were prepared.

< Green sheet production Process >

Next, a green sheet was produced. The prepared paste is applied to a substrate such as a PET (polyethylene terephthalate) film, dried as necessary, and then the substrate is peeled off, thereby obtaining a green sheet. The method for applying the paste to the substrate is not particularly limited. Known methods such as screen printing, coating, transfer printing, doctor blading and the like can be used.

< laminating step >

Next, the produced green sheets are stacked in a desired order and in a desired number of layers to form a stacked sheet. When the green sheets are stacked, alignment, cutting, and the like of the green sheets are performed as necessary. For example, when a parallel type battery is manufactured, it is preferable that the green sheets are stacked by aligning (aligning) the end face of the positive electrode collector layer and the end face of the negative electrode collector layer so as not to coincide with each other.

The following positive electrode active material layer unit and negative electrode active material layer unit may be prepared, and a laminated sheet may be prepared by laminating them.

First, the solid electrolyte layer 3 is applied with paste by a doctor blade method onto a substrate such as a PET film and dried to form a sheet-like solid electrolyte layer 3. Next, the positive electrode active material layer 1B is printed with paste on the solid electrolyte layer 3 by screen printing and dried to form the positive electrode active material layer 1B. Next, the positive electrode collector layer 1A was printed with paste on the positive electrode active material layer 1B by screen printing and dried to form the positive electrode collector layer 1A. Further, the positive electrode active material layer 1B is formed by printing paste for the positive electrode active material layer 1B on the positive electrode current collector layer 1A by screen printing and drying the paste.

Then, the PET film was peeled off, whereby a positive electrode active material layer unit was obtained in which the solid electrolyte layer 3/the positive electrode active material layer 1B/the positive electrode current collector layer 1A/the positive electrode active material layer 1B were sequentially laminated. Through the same procedure, a negative electrode active material layer unit in which the solid electrolyte layer 3, the negative electrode active material layer 2B, the negative electrode current collector layer 2A, and the negative electrode active material layer 2B are sequentially laminated can be obtained.

Next, the positive electrode active material layer unit and the negative electrode active material layer unit are alternately stacked one by one. At this time, the solid electrolyte layer 3 of the positive electrode active material layer unit and the negative electrode active material layer 2B of the negative electrode active material layer unit are laminated so as to be in contact with each other, or the positive electrode active material layer 1B of the positive electrode active material layer unit and the solid electrolyte layer 3 of the negative electrode active material layer unit are laminated so as to be in contact with each other. Thus, positive electrode active material layer 1B/positive electrode current collector layer 1A/positive electrode active material layer 1B/solid electrolyte layer 3/negative electrode active material layer 2B/negative electrode current collector layer 2A/negative electrode active material layer 2B/solid electrolyte layer 3 were laminated in this order.

When the positive electrode active material layer unit and the negative electrode active material layer unit are laminated, the units are alternately laminated so that the positive electrode collector layer 1A of the positive electrode active material layer unit extends only to one end surface and the negative electrode collector layer 2A of the negative electrode active material layer unit extends only to the other surface. Sheets for the solid electrolyte layer 3 having a predetermined thickness are further stacked on both surfaces of the stacked unit to produce a stacked sheet.

< thermal compression bonding Process >

Next, the produced laminated sheets are collectively thermocompression bonded. The pressure bonding is preferably performed while heating. The heating temperature during the pressure bonding is not particularly limited, and is, for example, 40 to 95 ℃.

The produced laminated sheet can be cut into a laminate 4 of an unfired laminated all-solid battery using a cutting device.

The laminated all-solid battery 11 is manufactured by binder removal and firing of the laminated body 4 of the laminated all-solid battery. The binder removal and firing may be performed, for example, in a nitrogen atmosphere at a temperature of 600 to 900 ℃. The holding time for binder removal and firing is, for example, 0.1 to 6 hours.

(Cooling of laminate)

The laminate 4 after the predetermined firing time is subjected to a two-stage cooling process in stages. The two-stage cooling process is carried out by the following steps. First, in the first process, the temperature is lowered from the firing temperature to the first cooling temperature. Then, in the second process, the first cooling temperature is maintained for a predetermined time. Finally, in the third process, the cooling is rapidly performed from the first cooling temperature to room temperature. The conditions of the cooling process are not particularly limited, and examples thereof include: the material is once cooled from a firing temperature of 900 ℃ to a first cooling temperature of 800 ℃, held at the first cooling temperature of 800 ℃ for a predetermined time, and then cooled to room temperature.

Through this step, thermal diffusion of zirconium from the solid electrolyte layer 3 to the positive electrode active material layer 1B or the negative electrode active material layer 2B occurs, and thermal diffusion of vanadium from the positive electrode active material layer 1B or the negative electrode active material layer 2B to the solid electrolyte layer 3 occurs, thereby forming the first intermediate layer 7 and the second intermediate layer 8. By changing the first cooling temperature and the holding time at the first cooling temperature, the concentration gradient of zirconium or vanadium in the first intermediate layer 7 and the second intermediate layer 8 can be freely adjusted.

The first intermediate layer 7 and the second intermediate layer 8 may be formed as follows: a layer in which the constituent elements are adjusted in advance is separately prepared and inserted between the solid electrolyte layer 3 and the positive electrode active material layer 1B or the negative electrode active material layer 2B.

By forming the terminal electrodes 5 and 6 at the end portions of the laminate 4 produced in the above-described steps, an all-solid-state lithium-ion secondary battery can be produced. The terminal electrodes 5 and 6 can be formed by a method such as sputtering of Au.

As described above, the all-solid secondary battery 10 of the present embodiment has the first intermediate layer 7 and the second intermediate layer 8, and therefore, the solid electrolyte layer 3 and the cathode active material layer 1B or the anode active material layer 2B are strongly bonded. In addition, during charging and discharging of the all-solid secondary battery 10, the entrance and exit of lithium ions change in stages in the order of the positive electrode active material layer 1B or the negative electrode active material layer 2B/the first intermediate layer 7/the second intermediate layer 8, and the difference in expansion and contraction at the interface of each layer during charging and discharging becomes small. The first intermediate layer 7 has smaller expansion and shrinkage than the positive electrode active material layer 1B or the negative electrode active material layer 2B, and the second intermediate layer 8 expands and shrinks unlike the solid electrolyte layer 3. Therefore, the all-solid-state secondary battery 10 of the present embodiment suppresses the occurrence of interfacial separation due to expansion and contraction during charge and discharge, and has excellent cycle characteristics.

When the first intermediate layer 7 and the second intermediate layer 8 have a composition gradient with respect to zirconium and vanadium, respectively, a difference in expansion and contraction rates occurs in the first intermediate layer 7 and the second intermediate layer 8. The expansion and contraction rate is high on the side close to the positive electrode active material layer 1B or the negative electrode active material layer 2B; on the side close to the solid electrolyte layer 3 side, the expansion and contraction rate is small; thereby enabling further suppression of peeling.

As described above, the embodiments of the present invention have been described in detail with reference to the drawings, but the configurations of the embodiments and the combinations thereof are merely examples, and additions, omissions, substitutions, and other modifications of the configurations may be made without departing from the spirit of the present invention.