All-solid-state battery

Abstract

An all-solid-state battery (1A) is provided with: a power generation element (30) in which a positive electrode layer (40), a solid electrolyte layer (60), and a negative electrode layer (50) are laminated in this order along the Z direction; a positive electrode current collector (10) that is in contact with the positive electrode layer (40); and a negative electrode current collector (20) that is in contact with the negative electrode layer (50). The positive electrode layer (40) includes lateral surfaces (40b) that contact the solid electrolyte layer (60) and are angled toward the center of the positive electrode layer (40) in a direction from the positive electrode current collector (10) toward the negative electrode current collector (20). The all-solid-state battery (1A) is equipped with a non-Li-ion-conductive coating section (70) which is provided on the positive electrode current collector (10) and covers the lateral surfaces (40b). The thickness (T3) of the coating section (70) in the Z direction is thinner than the thickness (T1) of the power generation element (30) in the Z direction.

Description

All solid state battery

[0001] The present invention relates to an all-solid-state battery.

[0002] In the all-solid-state battery, the first current collector layer, the first active material layer, the second active material layer, the first solid electrolyte layer, and the second solid electrolyte layer extend outward beyond the third active material layer and the fourth active material layer to form an extension portion. An insulating resin layer is continuously provided over one surface of the first solid electrolyte layer, the side surface of the extension portion, and the other surface of the second solid electrolyte layer (see paragraph

[0043] and Figures 2 and 4 of Patent Document 1). This insulating resin layer prevents the battery from slipping off at its ends.

[0003] JP 2014-116136 A

[0004] In the all-solid-state battery as described above, when the negative electrode layer of the all-solid-state battery expands and contracts significantly, the insulating resin layer cannot follow, resulting in an increase in powder falling off from the positive electrode layer.

[0005] The problem to be solved by the present invention is to provide an all-solid-state battery capable of suppressing powder falling off from the positive electrode layer.

[0006] The present invention solves the above problem by providing a non-Li ion conductive coating portion that is provided on the positive electrode current collector and covers the side surface of the positive electrode layer, and by making the thickness of the coating portion thinner than the thickness of the power generating element.

[0007] According to the present invention, powder falling from the positive electrode layer can be suppressed.

[0008] Fig. 1 is a cross-sectional view showing an all-solid-state battery according to an embodiment of the present invention. Fig. 2 is a cross-sectional view showing an all-solid-state battery according to a first modified example of the present invention. Fig. 3 is a cross-sectional view showing an all-solid-state battery according to a second modified example of the present invention. Fig. 4 is a cross-sectional view showing an all-solid-state battery according to a third modified example of the present invention. Fig. 5 is an image diagram showing the distribution of positive electrode active material particles according to the size relationship between the particle size of positive electrode active material particles and the particle size of metal oxide particles according to an embodiment of the present invention.

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] Fig. 1 is a cross-sectional view showing an all-solid-state battery 1A according to this embodiment. As shown in Fig. 1, the all-solid-state battery 1A includes a positive electrode current collector 10, a negative electrode current collector 20, a power generating element 30 interposed therebetween, and a covering portion 70. Note that Fig. 1 illustrates only one set of positive and negative electrode current collectors 10, 20 and power generating element 30, but the all-solid-state battery 1A may include a plurality of positive and negative electrode current collectors 10, 20 sandwiching the power generating element 30 therebetween, or may include a plurality of covering portions 70 covering the power generating element 30.

[0011] The positive electrode current collector 10 is a conductive plate-like (or foil-like) member and is made of, for example, a metal or a conductive resin, although it is not particularly limited thereto. Examples of metals that can be used include aluminum, nickel, iron, stainless steel, titanium, and copper. Alternatively, a clad material of nickel and aluminum, or a clad material of copper and aluminum may also be used. Examples of conductive resins include resins in which a conductive filler is added to a non-conductive polymer material.

[0012] The negative electrode current collector 20, like the positive electrode current collector 10, is a conductive plate-like (or foil-like) member and is made of, for example, but not limited to, a metal or a conductive resin. The metal and the conductive resin may be the same materials as those used to make the positive electrode current collector 10. The material used to make the positive electrode current collector 10 and the material used to make the negative electrode current collector 20 may be the same or different.

[0013] A power generating element 30 is interposed between the positive and negative electrode current collectors 10, 20. The power generating element 30 has a positive electrode layer 40, a negative electrode layer 50, and a solid electrolyte layer 60. In the power generating element 30, the positive electrode layer 40, the solid electrolyte layer 60, and the negative electrode layer 50 are stacked in this order along the Z direction. The +Z direction in this embodiment corresponds to an example of the "first direction" in the present invention. In other words, the first direction corresponds to the stacking direction of the positive electrode layer 40, the solid electrolyte layer 60, and the negative electrode layer 50.

[0014] The positive electrode layer 40 is formed on the main surface of the positive electrode current collector 10. The positive electrode layer 40 has a tapered shape that narrows from the positive electrode current collector 10 toward the negative electrode current collector 20, and thus the positive electrode layer 40 has a trapezoidal cross section. The positive electrode layer 40 can be formed by, but is not particularly limited to, applying a paste containing a positive electrode active material and a binder to the main surface of the positive electrode current collector 10 and drying the paste.

[0015] The positive electrode layer 40 includes a first end face 40 a, a side face 40 b, and a second end face 40 c. The first end face 40 a is in contact with the main surface of the positive electrode current collector 10 and is a surface that is approximately parallel to the main surface of the positive electrode current collector 10.

[0016] The side surface 40b is covered by the covering portion 70. The side surface 40b is formed so as to surround the first end surface 40a and the second end surface 40c. The side surface 40b is a flat surface that inclines toward the center of the positive electrode layer 40 as it approaches the negative electrode current collector 20 from the positive electrode current collector 10. The side surface 40b is not perpendicular to the main surface of the positive electrode current collector 10.

[0017] The second end face 40c is the end face opposite to the first end face 40a. The second end face 40c is covered with the solid electrolyte layer 60. The second end face 40c is a flat surface that is approximately parallel to the main surface of the positive electrode current collector 10.

[0018] The negative electrode layer 50 is formed on the main surface of the negative electrode current collector 20. The negative electrode layer 50 in this embodiment has a rectangular cross section, but is not limited thereto, and may have a trapezoidal cross section like the positive electrode layer 40.

[0019] The negative electrode layer 50 includes a lithium metal layer 51 and an intermediate layer 52. The lithium metal layer 51 is composed of lithium metal deposited on the main surface of the negative electrode current collector 20. The volume of this lithium metal layer 51 increases as lithium metal is deposited during charging of the all-solid-state battery 1A, and decreases as lithium metal is lost (moves toward the positive electrode layer) during discharging. The intermediate layer 52 is a layer that assists the deposition of the lithium metal layer 51 and contains a material capable of absorbing and releasing lithium ions. The intermediate layer 52 may be omitted. The lithium metal layer 51 may be deposited between the intermediate layer 52 and the solid electrolyte layer 60.

[0020] The solid electrolyte layer 60 is interposed between the positive electrode layer 40 and the negative electrode layer 50. As this solid electrolyte, a solid electrolyte made of a material with low electronic conductivity can be used, such as a sulfide solid electrolyte or an oxide solid electrolyte, but it is preferable to use a sulfide solid electrolyte. The positive electrode layer 40 is not particularly limited, but can be formed by applying a paste containing a solid electrolyte and a binder onto the positive electrode layer 40 and the covering portion 70 and drying the paste.

[0021] In this embodiment, the solid electrolyte layer 60 covers the second end face 40 c and the fourth end face 70 c. This allows the lithium metal layer 51 to be deposited only in the region between the solid electrolyte layer 60 and the negative electrode current collector 20, thereby reducing stress concentration on the negative electrode layer 50 during the process of deposition and dissolution of the lithium metal layer 51.

[0022] The covering portion 70 covers the side surface 40b of the positive electrode layer 40, thereby binding the positive electrode layer 40. The covering portion 70 can prevent the positive electrode layer 40 from peeling off and the positive electrode active material from sliding off from the positive electrode layer 40. In other words, it can prevent the positive electrode layer 40 from powdering off.

[0023] The coating portion 70 is non-Li ion conductive and does not conduct lithium ions. The coating portion 70 also has electrical insulation. Because the coating portion 70 is non-Li ion conductive, lithium metal does not precipitate in the coating portion 70, and therefore, it is possible to suppress the occurrence of a short circuit between the lithium metal and the positive electrode layer 40 or the positive electrode current collector 10.

[0024] The material for forming the covering portion 70 is not particularly limited, but may be, for example, particles of a non-Li ion conductive metal oxide such as alumina or zirconia. Resin materials cannot be used because they lose slight Li ion conductivity after long-term use. Examples of such resin materials include polyimide.

[0025] The coating portion 70 can be formed by, but is not limited to, applying a paste containing a mixture of metal oxide particles, a binder, and the like as described above to the positive electrode current collector 10 so as to cover the side surface 40b of the positive electrode layer 40, and then drying the paste. In particular, the coating portion 70 containing the metal oxide particles as described above is formed so as to be embedded in the positive electrode layer 40 on the order of micrometers or nanometers, thereby improving the bonding strength between the coating portion 70 and the positive electrode layer 40 compared to when a resin material is used. Therefore, the coating portion 70 can continue to suppress powder shedding from the positive electrode layer 40 over the long term.

[0026] Furthermore, the size (particle diameter) of the metal oxide particles contained in the coating portion 70 is preferably smaller than the size (particle diameter) of the positive electrode active material particles. The "particle diameter" referred to here is not particularly limited, but can be calculated as follows. First, the cross section of the coating portion 70 and the positive electrode layer 40 is observed with an electron microscope. Then, when a line is drawn from one end of the particle observed in the cross section to the other, two points where the length of this line is longest are identified. The distance between these two points is then measured. This distance is measured for 100 randomly selected particles, and the average value calculated can be used as the "particle diameter."

[0027] In addition to forming the above-mentioned bite, the size of the particles contained in the coating portion 70 is smaller than the size of the particles of the positive electrode active material contained in the positive electrode layer 40, which effectively prevents the positive electrode active material from penetrating the coating layer 70 and becoming isolated from the positive electrode layer 40, making it unable to contribute to charging and discharging.

[0028] Such an effect will be specifically described with reference to Fig. 5. Fig. 5 shows the particle diameter D of the positive electrode active material particles 45 in this embodiment. ｐ and the particle diameter D of the metal oxide particles 75 ｏ 5 is an image diagram showing the distribution of the positive electrode active material 45 according to the size relationship between the particle diameter D of the metal oxide particles 75 and the particle diameter D of the metal oxide particles 75. ｏ is the particle diameter D of the positive electrode active material particles 45 ｐ This shows the case where ｏ >D ｐ ), the lower left and lower right figures show the particle diameter D of the metal oxide particles 75 ｏ is the particle diameter D of the positive electrode active material particles 45 ｐ (D ｏ <D ｐ 5 shows the positive electrode active material particles 45 and the metal oxide particles 75 before pressing, and the right and left views show the positive electrode active material particles 45 and the metal oxide particles 75 after pressing.

[0029] Therefore, as shown in the upper left and upper right diagrams of FIG. 5, the particle diameter D of the metal oxide particle 75 is ｏ is the particle diameter D of the positive electrode active material particles 45 ｐ If the distance between the positive electrode layer 40 and the coating layer 70 is larger than 1 / 2 mm, when the positive electrode layer 40 and the coating layer 70 are compressed by pressing, the positive electrode active material particles 45 having smaller particle sizes will get trapped between the metal oxide particles 75. In this case, as shown in the upper right diagram of Fig. 5 , the positive electrode active material particles 46 that have gotten trapped between the metal oxide particles 75 will be isolated from the other positive electrode active material particles 45, and the positive electrode active material particles 46 will not be able to contribute to charge and discharge.

[0030] On the other hand, as shown in the lower left and lower right diagrams of FIG. 5, the particle diameter D ｏis the particle diameter D of the positive electrode active material particles 45 ｐ If the distance is smaller than 1 / 2 mm, the positive electrode active material particles 45 are less likely to enter between the oxide particles 75 during pressing, and isolated positive electrode active material particles 46 are less likely to occur. This makes it possible to improve the charge / discharge characteristics of the all-solid-state battery 1A.

[0031] Although not particularly limited, the covering portion 70 has an annular shape and covers the entire circumference of the side surface 40b. The covering portion 70 includes a third end surface 70a, a first inner surface 70b, a fourth end surface 70c, and an outer surface 70d.

[0032] The third end face 70a is in contact with the main surface of the positive electrode current collector 10 and is a surface approximately parallel to the main surface of the positive electrode current collector 10. The first inner surface 70b is in contact with the side surface 40b and is inclined to correspond to the inclination of the side surface 40b. In other words, the first inner surface 70b is a flat surface that is inclined so as to approach the center of the positive electrode layer 40 as it approaches the negative electrode current collector 20 from the positive electrode current collector 10.

[0033] The fourth end face 70c is the end face opposite to the third end face 70a. At least a portion of the fourth end face 70c is covered with the solid electrolyte layer 60. The fourth end face 70c is a flat surface that is approximately parallel to the main surface of the positive electrode current collector 10. The outer surface 70d is the surface opposite to the first inner surface 70b and is the outer peripheral edge of the solid electrolyte layer 60.

[0034] In this embodiment, the covering portion 70 covers only the positive electrode layer 40 and does not cover other parts of the power generating element 30. Therefore, the thickness T ３ is the thickness T of the positive electrode layer 40 ２ is substantially the same as (T ３ =T ２ ) In this embodiment, the thickness is the thickness in the Z direction.

[0035] As shown in the following modified example 1, the thickness T ３ is the thickness T of the positive electrode layer 40 ２ It may be thicker (T ３ >T ２ 2 is a cross-sectional view showing an all-solid-state battery 1B according to a first modification. In this first modification, the thickness T ３ is the thickness T of the positive electrode layer 40２ It is thicker (T ３ >T ２ ), the covering portion 70 has a protruding portion 71 that protrudes further in the +Z direction than the second end surface 40 c of the positive electrode layer 40 .

[0036] The solid electrolyte layer 60 of this first modified example has a shape that follows the surface of the protrusion 71, and specifically has a first portion 61 formed on the second end face 40 c of the positive electrode layer 40 and a second portion 62 formed on the fourth end face 70 c of the protrusion 71.

[0037] Thickness T of the second portion 62 ５ is the thickness T of the first portion 61 ４ The second portion 62 is located outside the first portion 61 and forms the outer periphery of the solid electrolyte layer 60. Because the second portion 62 is thin, the amount of exposed side surface of the second portion 62 can be reduced compared to, for example, the solid electrolyte layer 60 of the embodiment shown in FIG. 1 . This can reduce powder falling off from the solid electrolyte layer 60.

[0038] Returning to FIG. 1, the thickness T of the covering portion 70 ３ is the thickness T of the power generating element 30 １ is smaller than (T ３ <T １ ). As a result, the covering portion 70 is not formed continuously over the entire side surface of the power generating element 30 in the Z direction, and the covering portion 70 is not in contact with the negative electrode current collector 20. The negative electrode layer 50 includes a lithium metal layer whose thickness increases or decreases significantly with the charging or discharging of the all-solid-state battery 1A. Therefore, the distance between the positive and negative electrode current collectors 10, 20 varies significantly with the increase or decrease in the thickness of the lithium metal layer. For this reason, the covering portion may break without being able to keep up with the fluctuation in the distance between the positive and negative electrode current collectors 10, 20. In contrast, in the all-solid-state battery 1A of this embodiment, the thickness T ３ is the thickness T of the power generating element 30 １ Since the distance between the positive and negative electrode current collectors 10 and 20 is smaller than the above, the breakage of the covering portion 70 can be prevented without being affected by an increase or decrease in the distance between the positive and negative electrode current collectors 10 and 20 .

[0039] In particular, the covering portion 70 in this embodiment does not contact the side surface of the negative electrode layer 50. If the covering portion were also formed on the side surface of the lithium metal layer, the covering portion could break due to an increase or decrease in the thickness of the lithium metal layer, but in this embodiment, such breakage of the covering portion 70 can be prevented.

[0040] In the present embodiment, the inner surface of the covering portion 70 is made up of the first inner surface 70b, and the entire inner surface of the covering portion 70 is in contact with the positive electrode layer 40, but this is not limiting. As shown in the second modified example below, a part of the inner surface of the covering portion 70 may be separated from the positive electrode layer 40.

[0041] 3 is a cross-sectional view showing an all-solid-state battery 1C according to a second modified example. In this all-solid-state battery 1C, the inner surface of the covering portion 70 includes a second inner surface 70e in addition to a first inner surface 70b. The second inner surface 70e is connected to the first inner surface 70b from the solid electrolyte layer 60 side (the +Z direction side) and is spaced apart from the side surface 40b of the positive electrode layer 40. In this embodiment, the second inner surface 70e is inclined so as to move away from the center of the positive electrode layer 40 as it approaches the negative electrode current collector 20 from the positive electrode current collector 10.

[0042] In this second modified example, the solid electrolyte layer 60 includes an intervening portion 63 interposed between the side surface 40 b and the second inner surface 70 e. The intervening portion 63 increases the contact area between the solid electrolyte layer 60 and the positive electrode layer 40, and also provides an anchoring effect. This makes it possible to suppress peeling between the solid electrolyte layer 60 and the positive electrode layer 40. Furthermore, increasing the contact area between the solid electrolyte layer 60 and the positive electrode layer 40 also alleviates current concentration at the interface between the solid electrolyte layer 60 and the positive electrode layer 40.

[0043] In the second modified example, the edge 40d of the positive electrode layer 40 is located outward from the edge 70f of the fourth end face 70c on the second inner surface 70e side in a plan view seen from the Z direction. By satisfying this positional relationship between the edge 40d of the positive electrode layer 40 and the edge 70f of the fourth end face 70c, the strength of the end of the positive electrode layer 40 can be improved and breakage of the positive electrode layer 40 can be suppressed.

[0044] 1 , the covering portion 70 includes a third portion 73 in contact with the side surface 40 b of the positive electrode layer 40 and a fourth portion 74 in contact with the positive electrode current collector 10. The fourth portion 74 is located outside the third portion 73 and forms the outer periphery of the covering portion 70.

[0045] In this embodiment, the density D of the fourth portion 74 １ is the density D of the third portion 73 ２ This makes it possible to improve the strength of the outer periphery of the covering portion 70, thereby suppressing breakage of the covering portion 70. The method for imparting the density difference as described above is not particularly limited, but the density may be increased by compressing the fourth portion 74 by applying pressure or the like, or the density difference may be imparted by using different materials for the fourth portion 74 and the third portion 73.

[0046] In this embodiment, the interface between the positive electrode layer 40 and the covering portion 70 is clearly defined, but the interface does not have to be clearly defined, as in the third modified example described below.

[0047] 4 is a cross-sectional view showing an all-solid-state battery 1D according to a third modification. In this all-solid-state battery 1D, a mixed portion 80 in which the material constituting the positive electrode layer 40 and the material constituting the covering portion 70 are mixed is formed between the positive electrode layer 40 and the covering portion 70.

[0048] The mixed portion 80 can be formed by applying a paste for forming the positive electrode layer 40 to the positive electrode current collector 10, applying a paste for forming the coating portion to the positive electrode current collector 10 so that it partially overlaps with the paste for forming the positive electrode layer 40, and then drying both pastes.

[0049] By having such a mixed portion 80 interposed between the positive electrode layer 40 and the coating portion 70, the adhesion between the positive electrode layer 40 and the coating portion 70 can be improved, and powder falling off from the positive electrode layer 40 can be suppressed.

[0050] 1A to 1D... All-solid-state battery 10... Positive electrode current collector 20... Negative electrode current collector 30... Power generating element 40... Positive electrode layer 50... Negative electrode layer 60... Solid electrolyte layer 70... Covering portion 80... Mixed portion

Claims

1. An all-solid-state battery comprising: a power generating element having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer stacked in this order along a first direction; a positive electrode current collector in contact with the positive electrode layer; and a negative electrode current collector in contact with the negative electrode layer, wherein the positive electrode layer is in contact with the solid electrolyte layer and includes a side surface that slopes toward a center of the positive electrode layer as it approaches from the positive electrode current collector to the negative electrode current collector, and the all-solid-state battery further comprises a non-Li ion conductive coating portion provided on the positive electrode current collector to cover the side surface, and the thickness of the coating portion in the first direction is thinner than the thickness of the power generating element in the first direction.

2. An all-solid-state battery as defined in claim 1, wherein the positive electrode layer includes a first end face in contact with the positive electrode current collector and a second end face located opposite the first end face, the covering portion includes a third end face in contact with the positive electrode current collector and a fourth end face located opposite the third end face, and the solid electrolyte layer covers the second end face and the fourth end face.

3. An all-solid-state battery as defined in claim 2, wherein the thickness of the covering portion in the first direction is greater than the thickness of the positive electrode layer in the first direction, and the solid electrolyte layer includes a first portion in contact with the second end face and a second portion in contact with the fourth end face, and the thickness of the second portion in the first direction is smaller than the thickness of the second portion in the first direction.

4. An all-solid-state battery as described in claim 2, wherein the covering portion includes a first inner surface that is in contact with the side surface and is inclined to correspond to the inclination of the side surface, and a second inner surface that is connected to the first inner surface from the solid electrolyte layer side and is spaced apart from the side surface, and the solid electrolyte layer includes an intervening portion that is interposed between the side surface and the second inner surface.

5. An all-solid-state battery according to claim 4, wherein an edge of the positive electrode layer is located outside an edge of the fourth end face on the second inner surface side in a plan view seen from the first direction.

6. An all-solid-state battery as claimed in claim 1, wherein the covering portion includes a third portion in contact with the side surface, and a fourth portion located outside the third portion and in contact with the positive electrode current collector, and the density of the fourth portion is higher than the density of the third portion.

7. The all-solid-state battery according to claim 1, further comprising a mixture portion located between the positive electrode layer and the covering portion, in which the material constituting the positive electrode layer and the material constituting the covering portion are mixed.

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