JP7850538B2 - All-solid-state battery and its manufacturing method - Google Patents

Description

This invention relates to an all-solid-state battery and a method for manufacturing the same.

In recent years, rechargeable batteries have been used in various fields. However, rechargeable batteries using electrolytes have problems such as electrolyte leakage. Therefore, development is underway on all-solid-state batteries that incorporate a solid electrolyte and other solid components (see Patent Documents 1-4).

Japanese Patent Application Publication No. 6-231796 Japanese Patent Publication No. 2011-216235 Japanese Patent Publication No. 2015-220106 Japanese Patent Publication No. 2020-166980

All-solid-state batteries are manufactured by layering multiple electrode pastes for the electrode layer and green sheets for the solid electrolyte layer, and then firing them. During this process, delamination may occur at the interface between the solid electrolyte layer and the electrode layer due to differences in elasticity between the two layers.

This invention has been made in view of the above-mentioned problems, and aims to suppress the occurrence of delamination at the interface between the solid electrolyte layer and the electrode layer.

The all-solid-state battery according to the present invention is characterized in that a plurality of first electrode layers, a solid electrolyte layer, and a second electrode layer are stacked along a first direction, the stack having a first surface on which the first electrode layer is exposed and a second surface on which the second electrode layer is exposed, a first external electrode provided on the first surface and connected to the first electrode layer, and a second external electrode provided on the second surface and connected to the second electrode layer, the first electrode layer having a first portion connected to the first external electrode and a second portion extending along a second direction from the first external electrode toward the second external electrode, the second electrode layer having a third portion connected to the second external electrode and a fourth portion extending along the second direction, the first width of the first portion along a third direction intersecting the first direction and the second direction being narrower than the second width of the second portion, and the third width of the third portion along the third direction being narrower than the fourth width of the fourth portion.

In the above-described all-solid-state battery, the first center line passing through the center of the first portion and extending along the second direction, and the second center line passing through the center of the second portion and extending along the second direction may be offset from each other.

In the above-described all-solid-state battery, the edges of the first portion and the second portion may be located on a first imaginary line extending along the second direction, and the edges of the third portion and the fourth portion may be located on a second imaginary line extending along the second direction.

In the above-described all-solid-state battery, the first width may be wider than half the second width, and the third width may be wider than half the fourth width.

In the above-described all-solid-state battery, when the thickness of the first electrode layer is T1, the thickness of the second electrode layer is T2, and the thickness of the solid electrolyte layer is T3, it is also acceptable for T1 ≥ T2 > T3.

The manufacturing method for an all-solid-state battery according to the present invention comprises the steps of: forming a laminate in which a plurality of first electrode layers, a solid electrolyte layer, and a second electrode layer are stacked along a first direction, and the laminate has a first surface on which the first electrode layer is exposed and a second surface on which the second electrode layer is exposed; firing the laminate; forming a first external electrode connected to the first electrode layer on the first surface; and forming a second external electrode connected to the second electrode layer on the second surface, wherein the first electrode layer is in contact with the first external electrode. The electrode layer has a first continuous portion and a second portion extending along a second direction from the first external electrode toward the second external electrode. The second electrode layer has a third portion connected to the second external electrode and a fourth portion extending along the second direction. The first width of the first portion along the third direction intersecting the first and second directions is narrower than the second width of the second portion, and the third width of the third portion along the third direction is narrower than the fourth width of the fourth portion.

According to the present invention, it is possible to suppress the occurrence of delamination at the interface between the solid electrolyte layer and the electrode layer.

This is an external view of an all-solid-state battery. This is a cross-sectional view along the line I-I in Figure 1. This is a plan view of the first electrode layer and its surroundings. This is a plan view of the second electrode layer and its surroundings. This diagram shows the positional relationship between the centerlines of the first electrode layer and the second electrode layer. This is a perspective view showing the positional relationship of each electrode layer in the laminate. Figure 7 is a flowchart of the manufacturing method for the all-solid-state battery according to this embodiment. Figure 8 is a plan view of the first electrode layer and its surroundings according to a comparative example. Figure 9 is a plan view of the second electrode layer and its surroundings according to the comparative example. Figure 10 is a perspective view showing the positional relationship of each electrode layer in the laminate according to the comparative example.

(Embodiment)
Figure 1 is an external view of the all-solid-state battery 100. As illustrated in Figure 1, the all-solid-state battery 100 comprises a stacked chip 70 having a rectangular parallelepiped shape and external electrodes 40a and 40b provided on two opposing surfaces of the stacked chip 70.

Figure 2 is a cross-sectional view taken along the line I-I in Figure 1. As illustrated in Figure 2, the laminated chip 70 has a laminate 60 in which multiple solid electrolyte layers 11, a first electrode layer 12, and a second electrode layer 14 are stacked along the first direction Z.

The laminate 60 has a first surface 60a and a second surface 60b parallel to the first direction Z. A first external electrode 40a is provided on the first surface 60a, and the first electrode layer 12 is connected to the first external electrode 40a. On the other hand, a second external electrode 40b is provided on the second surface 60b, and the second electrode layer 14 is connected to the second external electrode 40b.

Furthermore, the laminate 60 has a third surface 60c and a fourth surface 60d perpendicular to the first direction Z. The third surface 60c is the upper surface that faces upward when the all-solid-state battery 100 is mounted on the wiring board. The fourth surface 60d is the lower surface that faces downward during mounting. In this example, the outermost layer of the laminate 60 is the solid electrolyte layer 11, and both the third surface 60c and the fourth surface 60d are defined by the surface of the solid electrolyte layer 11.

Furthermore, both the first electrode layer 12 and the second electrode layer 14 are conductive layers containing both a positive electrode active material and a negative electrode active material. While the positive electrode active material is not particularly limited, here a material with an olivine-type crystal structure is used as the positive electrode active material. Examples of such positive electrode active materials include phosphates containing a transition metal and lithium. The olivine-type crystal structure is found in natural olivine and can be identified by X-ray diffraction.

Examples of electrode active materials having an olivine-type crystal structure include _LiCoPO4 containing Co. Phosphates in which the transition metal Co is replaced in this chemical formula may also be used. Here, the ratio of Li and _PO4 may vary depending on the valency. Note that Co, Mn, Fe, Ni, etc. may be used as the transition metal.

Furthermore, the negative electrode active material may be, for example, titanium oxide, lithium titanium composite oxide, lithium titanium composite phosphate, carbon, or lithium vanadium phosphate.

By using both positive and negative electrode active materials in the first electrode layer 12 and the second electrode layer 14, the similarity between the electrode layers 12 and 14 is increased. As a result, each of the first electrode layer 12 and the second electrode layer 14 functions as both a positive and negative electrode, and even if the terminals of the all-solid-state battery 100 are connected in reverse (positive and negative), it will not malfunction during short-circuit testing and will withstand actual use. This embodiment is not limited to this; the all-solid-state battery 100 may also be given polarity by forming a positive electrode layer as the first electrode layer 12 and a negative electrode layer as the second electrode layer 13.

Furthermore, when fabricating the first electrode layer 12 and the second electrode layer 14, oxide-based solid electrolyte materials and conductive additives such as carbon or metal may be added to these electrode layers. Examples of conductive additive metals include Pd, Ni, Cu, and Fe. Furthermore, alloys of these metals may be used as conductive additives.

Furthermore, the layer structure of the first electrode layer 12 and the second electrode layer 14 is not particularly limited. For example, as shown in the dotted circle, the first electrode layer 12 may be formed on both main surfaces of the first current collector layer 12b made of a conductive material. Similarly, the second electrode layer 14 may be formed on both main surfaces of the second current collector layer 14b made of a conductive material.

On the other hand, as a material for the solid electrolyte layer 11, for example, there is a phosphate-based solid electrolyte having a NASICON structure. A phosphate-based solid electrolyte having a NASICON structure has high ionic conductivity and is chemically stable in the atmosphere. The phosphate-based solid electrolyte is not particularly limited, but here a lithium-containing phosphate is used. This phosphate is, for example, based on a composite lithium phosphate salt with Ti ( _LiTi₂ ( _PO₄ ) _₃ ), and is a salt in which the Li content is partially substituted with a trivalent transition metal such as Al, Ga, In, Y, or La. Examples of such salts include Li _{-Al- M -PO4 phosphates (where M is Ge, Ti, Zr} , etc.), such as Li _1+x Al _x Ge _2-x ( _PO4 ) ₃ , Li _1+x Al _x Zr _2-x ( _PO4 ) ₃ , and Li 1+x Al x Ti ₂ -x (PO4) ₃ .

Alternatively, a Li-Al-Ge- _PO4 phosphate, to which a transition metal contained in the phosphate in the first electrode layer 12 has been pre-added, may be used as the material for the solid electrolyte layer 11. For example, if the first electrode layer 12 contains a phosphate containing either Co or Li, a Li-Al-Ge- _PO4 phosphate to which Co has been pre-added may be included in the solid electrolyte layer 11. This makes it possible to suppress the elution of the transition metal from the first electrode layer 12 into the solid electrolyte layer 11.

Furthermore, a moisture-proof layer 80 is provided on the surface of the outermost solid electrolyte layer 11 of the laminate 60. The moisture-proof layer 80 is a layer of inorganic oxide containing silicon, and its role is to protect the laminate 60 from moisture in the atmosphere. Note that any of B, Bi, Zn, Ba, Li, P, Sn, Pb, Mg, and Na may be added to the moisture-proof layer 80.

The film thickness of each layer is not particularly limited, but in this embodiment, the film thickness of the first electrode layer 12 is 2 μm to 100 μm, more preferably 5 μm to 50 μm. The film thickness of the second electrode layer 14 is 2 μm to 100 μm, more preferably 5 μm to 50 μm. By adopting this range, it is possible to prevent a decrease in capacity due to thinning of each electrode layer 12 and 14, and to prevent a decrease in lamination accuracy due to thickening of each electrode layer 12 and 14. Furthermore, the film thickness of the solid electrolyte layer 11 is 2 μm to 50 μm, more preferably 5 μm to 25 μm. By adopting this range, it is possible to prevent an increase in short circuits and leakage current due to thinning of the solid electrolyte layer 11, while preventing a decrease in capacity and responsiveness due to thickening of the solid electrolyte layer 11.

Furthermore, when the film thickness of the first electrode layer 12 is T1, the film thickness of the second electrode layer 14 is T2, and the film thickness of the solid electrolyte layer 11 is T3, it is preferable that T1 ≥ T2 > T3. By reducing the film thickness T3 of the solid electrolyte layer 11 in this way, the proportion occupied by each electrode layer 12 and 14 in the all-solid-state battery increases, and the capacity of the all-solid-state battery increases. In addition, since the positive electrode material tends to have a smaller capacity than the negative electrode material, setting T1 ≥ T2 further increases the capacity of the all-solid-state battery.

Figure 3 is a plan view of the first electrode layer 12 and its surroundings. As shown in Figure 3, the first electrode layer 12 has a first portion 12x connected to the first external electrode 40a, and a second portion 12y extending from the first portion 12x along a second direction Y. The second direction Y is the direction from the first external electrode 40a to the second external electrode 40b, and is perpendicular to the first direction Z.

Figure 4 is a plan view of the second electrode layer 14 and its surroundings. As shown in Figure 4, the second electrode layer 14 has a third portion 14x connected to the second external electrode 40b and a fourth portion 14y extending from the third portion 14x along the second direction Y.

Figure 5 shows the positional relationship between the centerlines of the first electrode layer 12 and the second electrode layer 14.

The first center line P1 of the first electrode layer 12 is a straight line that passes through the center C1 of the first portion 12x in a plan view and extends along the second direction Y. The center C1 is the centroid of the rectangular first portion 12x in a plan view.

On the other hand, the second center line P2 of the second electrode layer 14 is a straight line that passes through the center C2 of the third portion 14x in a plan view and extends along the second direction Y. Note that the center C2 is the centroid of the rectangular third portion 14x in a plan view.

In this example, the first center line P1 and the second center line P2 are offset from each other along the third direction X. This allows for homogenization of the reactions within and between the electrode layers during charging and discharging.

As shown in Figure 3, the first width W1 of the first portion 12x along the third direction X, which is perpendicular to both the first direction Z and the second direction Y, is narrower than the second width W2 of the second portion 12y along the third direction X.

Preferably, the first width W1 is wider than half the second width W2. This increases the amount of the first electrode layer 12 connected to the first external electrode 40a, thereby reducing the electrical resistance between the first electrode layer 12 and the first external electrode 40a. More preferably, the first width W1 is wider than two-thirds of the second width W2, and even more preferably, the first width W1 is wider than three-quarters of the second width W2. This stabilizes the connectivity between the first external electrode 40a and the first electrode layer 12, ensures the shortest possible electron conduction distance, suppresses internal resistance, and improves charge-discharge characteristics.

Furthermore, in this example, the edges of the first portion 12x and the second portion 12y are located on the first imaginary line L1 extending along the second direction Y.

Furthermore, as shown in Figure 4, the third width W3 of the third portion 14x along the third direction X is narrower than the fourth width W4 of the fourth portion 14y along the third direction X.

Furthermore, it is preferable that the third width W3 is wider than half the fourth width W4. This increases the amount of the second electrode layer 14 in the portion connected to the second external electrode 40b, thereby reducing the electrical resistance between the second electrode layer 14 and the second external electrode 40b. More preferably, the third width W3 is wider than two-thirds of the fourth width W4, and even more preferably, the third width W3 is wider than three-quarters of the fourth width W4. This stabilizes the connectivity between the second external electrode 40b and the second electrode layer 14, ensures the shortest possible electron conduction distance, suppresses internal resistance, and improves charge-discharge characteristics.

In this example, the edges of the third portion 14x and the fourth portion 14y are located on a second virtual line L2 that extends along the second direction Y.

Figure 6 is a perspective view showing the positional relationship of each electrode layer 12 and 14 in the laminate 60.

As shown in Figure 6, the first portion 12x of the first electrode layer 12 is exposed to the first surface 60a, and the third portion 14x of the second electrode layer 14 is exposed to the second surface 60b.

According to the embodiment described above, as shown in Figure 3, by making the first width W1 narrower than the second width W2, the area of the first electrode layer 12 exposed on the first surface 60a can be reduced. If a large portion of the first electrode layer 12 is exposed on the first surface 60a, the difference in the elastic moduli of the first electrode layer 12 and the solid electrolyte layer 11 becomes prominent on the first surface 60a, causing delamination to occur at the interface between the first electrode layer 12 and the solid electrolyte layer 11, starting from the first surface 60a. In this embodiment, since the area of the first electrode layer 12 exposed on the first surface 60a can be reduced as described above, the occurrence of delamination at the interface between the first electrode layer 12 and the solid electrolyte layer 11 can be suppressed.

Similarly, as shown in Figure 4, by making the third width W3 narrower than the fourth width W4, the area of the second electrode layer 14 exposed on the second surface 60b can be reduced. As a result, delamination at the interface between the second electrode layer 14 and the solid electrolyte layer 11, starting from the first surface 60b, can be suppressed.

Furthermore, as shown in Figure 3, the edges of the first portion 12x and the second portion 12y of the first electrode layer 12 are located on the first imaginary line L1. While delamination often occurs at the corners of the first electrode layer 12, this structure prevents the formation of extra corners on the first imaginary line L1, thus more effectively preventing delamination of the first electrode layer 12.

Similarly, as shown in Figure 4, since the edges of the third portion 14x and the fourth portion 14y of the second electrode layer 14 are located on the second imaginary line L2, no extra corners of the second electrode layer 14 are formed on the second imaginary line L2, and peeling of the second electrode layer 14 can be prevented even more effectively.

Next, the manufacturing method of the all-solid-state battery according to this embodiment will be described. Figure 7 is a flowchart of the manufacturing method of the all-solid-state battery according to this embodiment.

(Ceramic raw material powder manufacturing process)
First, a powder of the phosphate-based solid electrolyte constituting the solid electrolyte layer 11 is prepared. For example, the powder of the phosphate-based solid electrolyte constituting the solid electrolyte layer 11 can be prepared by mixing raw materials and additives and using a solid-phase synthesis method. The obtained powder can be adjusted to a desired average particle size by dry grinding. For example, the desired average particle size can be adjusted using a planetary ball mill with 5 mmφ _ZrO2 balls.

The additives include sintering aids. For example, any of the following glass components can be used as sintering aids: Li-B-O compounds, Li-Si-O compounds, Li-C-O compounds, Li-S-O compounds, and Li-P-O compounds.

(Green sheet manufacturing process)
Next, the obtained powder is uniformly dispersed in an aqueous solvent or organic solvent together with a binder, dispersant, and plasticizer, etc., and wet grinding is performed to obtain a solid electrolyte slurry having the desired average particle size. At this time, a bead mill, wet jet mill, various kneaders, high-pressure homogenizer, etc. can be used, and a bead mill is preferred from the viewpoint that particle size distribution adjustment and dispersion can be performed simultaneously.

Then, a binder is added to the obtained solid electrolyte slurry to obtain a solid electrolyte paste. By coating with the solid electrolyte paste, a green sheet for the solid electrolyte layer 11 is obtained. The coating method is not particularly limited, and methods such as slot die coating, reverse coating, gravure coating, bar coating, and doctor blade coating can be used. The particle size distribution after wet grinding can be measured, for example, using a laser diffraction measuring device employing laser diffraction scattering.

(Process for preparing electrode layer paste)
Next, an electrode layer paste is prepared for creating the first electrode layer 12 and the second electrode layer 14. For example, the positive electrode active material, the negative electrode active material, and the solid electrolyte material are highly dispersed using a bead mill or the like to produce a ceramic paste consisting only of ceramic particles. Alternatively, a carbon paste containing carbon particles such as carbon black may be prepared and mixed with the ceramic paste.

(Lamination process)
Next, an electrode layer paste is printed on one main surface of a green sheet. Then, 150 of the printed green sheets are stacked alternately and offset, and the resulting laminate 60 is cut to a predetermined size using a dicer. The top and bottom layers of the laminate 60 are green sheets.

(Firing process)
Next, the laminate 60 is fired in a firing atmosphere containing oxygen. To suppress the loss of carbon material contained in the electrode layer paste, it is preferable to set the oxygen partial pressure of the firing atmosphere to 2 × ^10⁻¹³ atm or less. On the other hand, to suppress the melting of the phosphate-based solid electrolyte, it is preferable to set the oxygen partial pressure to 5 × ^10⁻²² atm or more.

Subsequently, the first external electrode 40a and the second external electrode 40b are formed by applying metal paste to each surface 60a and 60b of the laminate 60 and baking it. Alternatively, the first external electrode 40a and the second external electrode 40b may be formed by sputtering or plating.

Furthermore, the thickness of the first electrode layer 12 after firing is 14 μm, and the thickness of the second electrode layer 14 is 10 μm. Also, the thickness of the solid electrolyte layer 11 after firing is 8 μm.

(Coating process)
Next, a solution of tetraalkoxysilane dissolved in dibutyl ether or a dibutyl ether-based solvent is applied to the third to sixth surfaces 60c to 60f of the laminate 60. Then, the moisture-proof layer 80 is obtained by heating the solution to a temperature of about 100°C to 150°C. With the above steps, the basic structure of the all-solid-state battery 100 is completed.

(Comparative example)
Figure 8 is a plan view of the first electrode layer 12 and its surroundings according to the comparative example. As shown in Figure 8, in the comparative example, the first electrode layer 12 is rectangular in plan view. Therefore, compared to the embodiment in Figure 3, the area of the first electrode layer 12 exposed to the first surface 60a increases in the comparative example. As a result, the difference in the elastic moduli of the first electrode layer 12 and the solid electrolyte layer 11 becomes more pronounced on the first surface 60a, increasing the likelihood of delamination occurring at the interface between the first electrode layer 12 and the solid electrolyte layer 11, starting from the first surface 60a.

Figure 9 is a plan view of the second electrode layer 14 and its surroundings according to the comparative example. As shown in Figure 9, the second electrode layer 14 according to the comparative example is rectangular in plan view, similar to the first electrode layer 12. Therefore, for the same reasons as with the first electrode layer 12 in Figure 8, there is a higher possibility of delamination occurring at the interface between the second electrode layer 14 and the solid electrolyte layer 11, starting from the second surface 60b.

Figure 10 is a perspective view showing the positional relationship of each electrode layer in the laminate according to the comparative example. As shown in Figure 10, in the comparative example, the first electrode layer 12 is exposed on the first surface 60a, and the second electrode layer 14 is exposed on the second surface 60b.

Although embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the invention as described in the claims.

11: Solid electrolyte layer 12: First electrode layer 12b: First current collector layer 12x: First portion 12y: Second portion 14: Second electrode layer 14b: Second current collector layer 14x: Third portion 14y: Fourth portion 40a: First external electrode 40b: Second external electrode 60: Laminate 60a-60f: First to sixth surfaces 70: Laminate chip 80: Moisture-proof layer 100: All-solid-state battery

Claims (5)

A laminate is a sintered body comprising a first electrode layer, a solid electrolyte layer, and a second electrode layer, each stacked in multiple layers along a first direction, with a first surface on which the first electrode layer is exposed and a second surface on which the second electrode layer is exposed and facing the first surface.
A first external electrode provided on the first surface and connected to the first electrode layer,
It has a second external electrode provided on the second surface and connected to the second electrode layer,
The first electrode layer has a first portion connected to the first external electrode and a second portion extending along a second direction from the first external electrode toward the second external electrode.
The second electrode layer has a third portion connected to the second external electrode and a fourth portion extending along the second direction.
The first width of the first portion along a third direction intersecting each of the first and second directions is narrower than the second width of the second portion, and the third width of the third portion along the third direction is narrower than the fourth width of the fourth portion.
A first center line passing through the center of the first portion and extending along the second direction, and a second center line passing through the center of the second portion and extending along the second direction are offset from each other.
The first width is wider than half the second width.
A solid-state battery characterized in that the third width is wider than half the fourth width . The edges of the first portion and the second portion are located on a first imaginary line extending along the second direction,
The all-solid-state battery according to claim 1, characterized in that the edges of the third portion and the fourth portion are located on a second imaginary line extending along the second direction. The all-solid-state battery according to claim 1 or 2, characterized in that when the thickness of the first electrode layer is T1, the thickness of the second electrode layer is T2, and the thickness of the solid electrolyte layer is T3, T1 ≥ T2 > T3. A laminate is a sintered body comprising a first electrode layer, a solid electrolyte layer, and a second electrode layer, each stacked in multiple layers along a first direction, with a first surface on which the first electrode layer is exposed and a second surface on which the second electrode layer is exposed and facing the first surface.
A first external electrode provided on the first surface and connected to the first electrode layer,
It has a second external electrode provided on the second surface and connected to the second electrode layer,
The first electrode layer has a first portion connected to the first external electrode and a second portion extending along a second direction from the first external electrode toward the second external electrode.
The second electrode layer has a third portion connected to the second external electrode and a fourth portion extending along the second direction.
The first width of the first portion along a third direction intersecting each of the first and second directions is narrower than the second width of the second portion, and the third width of the third portion along the third direction is narrower than the fourth width of the fourth portion.
A first center line passing through the center of the first portion and extending along the second direction, and a second center line passing through the center of the second portion and extending along the second direction are offset from each other.
An all-solid-state battery characterized in that, when the thickness of the first electrode layer is T1, the thickness of the second electrode layer is T2, and the thickness of the solid electrolyte layer is T3, T1 ≥ T2 > T3. A step of forming a laminate that is a sintered body, wherein a first electrode layer, a solid electrolyte layer, and a second electrode layer are each stacked in a plurality along a first direction, and the laminate has a first surface on which the first electrode layer is exposed and a second surface on which the second electrode layer is exposed and facing the first surface.
The process involves forming a first external electrode connected to the first electrode layer on the first surface,
The process includes the step of forming a second external electrode connected to the second electrode layer on the second surface,
The first electrode layer has a first portion connected to the first external electrode and a second portion extending along a second direction from the first external electrode toward the second external electrode.
The second electrode layer has a third portion connected to the second external electrode and a fourth portion extending along the second direction.
The first width of the first portion along a third direction intersecting each of the first and second directions is narrower than the second width of the second portion, and the third width of the third portion along the third direction is narrower than the fourth width of the fourth portion.
A first center line passing through the center of the first portion and extending along the second direction, and a second center line passing through the center of the second portion and extending along the second direction are offset from each other.
The first width is wider than half the second width.
A method for manufacturing an all-solid-state battery, characterized in that the third width is wider than half the fourth width .