All-solid-state batteries

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

[Technical Field]

[0001] This invention relates to an all-solid-state battery. [Background technology]

[0002] In an 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 and fourth active material layers, forming an extended portion. Furthermore, an insulating resin layer is continuously provided across one side surface of the first solid electrolyte layer, the side surface of the extended portion, and the other side surface of the second solid electrolyte layer (Patent Document 1, paragraph

[0043] , and Figures 2 and 4). This insulating resin layer suppresses slippage at the ends of the battery. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-4697 [Overview of the project] [Problems that the invention aims to solve]

[0004] In all-solid-state batteries as described above, there is a problem in that when the negative electrode layer of the all-solid-state battery expands and contracts significantly, the insulating resin layer cannot keep up, resulting in increased powder shedding from the positive electrode layer.

[0005] The problem that this invention aims to solve is to provide an all-solid-state battery that can suppress powder shedding from the positive electrode layer. [Means for solving the problem]

[0006] The present invention solves the above problem by providing a non-Li ion conductive coating portion that is attached to the positive electrode current collector, in contact with and covering the side surface of the positive electrode layer, and making the thickness of the coating portion thinner than the thickness of the power generation element. [Effects of the Invention]

[0007] According to the present invention, powder shedding from the positive electrode layer can be suppressed. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a cross-sectional view showing an all-solid-state battery according to an embodiment of the present invention. [Figure 2] Figure 2 is a cross-sectional view showing an all-solid-state battery in a first modified example of the present invention. [Figure 3] Figure 3 is a cross-sectional view showing an all-solid-state battery in a second modified example of the present invention. [Figure 4] Figure 4 is a cross-sectional view showing an all-solid-state battery in a third modified example of the present invention. [Figure 5] Figure 5 is an illustrative diagram showing the distribution of positive electrode active material particles according to the relative sizes of the positive electrode active material particles and the metal oxide particles in an embodiment of the present invention. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below with reference to the drawings.

[0010] Figure 1 is a cross-sectional view showing an all-solid-state battery 1A in this embodiment. As shown in Figure 1, the all-solid-state battery 1A comprises a positive electrode current collector 10, a negative electrode current collector 20, a power generation element 30 interposed between them, and a covering portion 70. In Figure 1, one set of positive and negative electrode current collectors 10, 20 and power generation element 30 is shown, but the all-solid-state battery 1A may have multiple positive and negative electrode current collectors 10, 20 with the power generation element 30 sandwiched in between, and may also have multiple covering portions 70 that cover the power generation element 30.

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

[0012] The negative electrode current collector 20 is, like the positive electrode current collector 10, a plate-shaped (or foil-shaped) member having conductivity, and although not particularly limited, for example, it is composed of a metal or a resin having conductivity. As the metal and the resin having conductivity, the same materials as those constituting the above-described positive electrode current collector 10 can be used. Note that the material constituting the positive electrode current collector 10 and the material constituting the negative electrode current collector 20 may be the same or different.

[0013] A power generation element 30 is interposed between the positive and negative electrode current collectors 10 and 20. This power generation element 30 has a positive electrode layer 40, a negative electrode layer 50, and a solid electrolyte layer 60. In this power generation element 30, the positive electrode layer 40, the solid electrolyte layer 60, and the negative electrode layer 50 are laminated in this order along the Z direction. The +Z direction in the present embodiment corresponds to an example of the "first direction" in the present invention. That is, the first direction corresponds to the lamination 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. This positive electrode layer 40 has a tapered shape that becomes narrower as it approaches the negative electrode current collector 20 from the positive electrode current collector 10. As a result, the positive electrode layer 40 has a trapezoidal cross section. This positive electrode layer 40 is not particularly limited, but can be formed by 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] This positive electrode layer 40 includes a first end face 40a, a side face 40b, and a second end face 40c. The first end face 40a is in contact with the main surface of the positive electrode current collector 10 and is a plane substantially parallel to the main surface of the positive electrode current collector 10.

[0016] The side face 40b is covered by the covering portion 70. The side face 40b is formed so as to surround the first end face 40a and the second end face 40c. This side face 40b is a plane that slopes 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. This side face 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 on the opposite side of the first end face 40a. This second end face 40c is covered by the solid electrolyte layer 60. The second end face 40c is a plane substantially 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] [[ID=,16]]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 with the charging of the all-solid-state battery 1A, while decreasing as lithium metal disappears (moves to the positive electrode layer side) with discharging. The intermediate layer 52 is a layer for assisting the deposition of the lithium metal layer 51 and contains a material capable of occluding and releasing lithium ions. This intermediate layer 52 may be omitted. Note that 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 the solid electrolyte, a solid electrolyte made of a material with low electronic conductivity can be used, for example, a sulfide solid electrolyte or an oxide solid electrolyte can be used, but the use of a sulfide solid electrolyte is preferred. The positive electrode layer 40 is not particularly limited, but it can be formed by applying a paste containing a solid electrolyte or binder onto the positive electrode layer 40 and the coating portion 70, and then drying the paste.

[0021] In this embodiment, the solid electrolyte layer 60 covers the second end face 40c and the fourth end face 70c. 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 mitigating stress concentration on the negative electrode layer 50 during the deposition and dissolution process of the lithium metal layer 51.

[0022] The covering portion 70 secures the positive electrode layer 40 by covering the side surface 40b of the positive electrode layer 40. This covering portion 70 can suppress peeling of the positive electrode layer 40 and the sliding off of the positive electrode active material from the positive electrode layer 40. In other words, it can suppress powder shedding from the positive electrode layer 40.

[0023] The coating portion 70 is non-Li ion conductive and does not conduct lithium ions. Furthermore, this coating portion 70 also has electrical insulating properties. Because the coating portion 70 is non-Li ion conductive, lithium metal does not deposit in the coating portion 70, thus suppressing the occurrence of short circuits between the lithium metal and the positive electrode layer 40 or the positive electrode current collector 10.

[0024] The material constituting the coating portion 70 is not particularly limited, but for example, particles of non-Li ion conductive metal oxides such as alumina and zirconia can be used. However, resin materials cannot be used because they acquire slight Li ion conductivity after long-term use. Examples of such resin materials include polyimide.

[0025] The coating portion 70 is not particularly limited, but it can be formed by applying a paste, which is a mixture of metal oxide particles and a binder as described above, onto 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, since the coating portion 70 containing the metal oxide particles described above is formed to interlock with the positive electrode layer 40 on the order of micrometers or nanometers, the bonding strength between the coating portion 70 and the positive electrode layer 40 can be improved compared to when a resin material is used. Therefore, the coating portion 70 can continuously suppress powder shedding from the positive electrode layer 40 over the long term.

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

[0027] In addition to forming the aforementioned interlocking, this effectively prevents the positive electrode active material from penetrating the coating layer 70 and becoming isolated from the positive electrode layer 40, as the size of the particles contained in the coating 70 is smaller than the size of the positive electrode active material particles contained in the positive electrode layer 40.

[0028] These effects will be explained in detail using Figure 5. Figure 5 shows the particle size D of the positive electrode active material particles 45 in this embodiment. p And the particle size D of metal oxide particles 75 o This is an illustrative diagram showing the distribution of the positive electrode active material 45 according to the relative sizes of the particles. The upper left and upper right diagrams of Figure 5 show the particle size D of the metal oxide particles 75. o The particle size D of the positive electrode active material particles 45 p This shows the case where it is greater than (D o >Dp ) The upper left and lower left figures show the particle size D of the metal oxide particles 75 o is smaller than the particle size D of the positive electrode active material particles 45 p . (D o < D p ). The positive electrode layer 40 and the coating layer 70 are usually used after being pressed. The upper left and lower left figures of FIG. 5 show the positive electrode active material particles 45 and the metal oxide particles 75 before pressing, and the upper right and lower right figures show the positive electrode active material particles 45 and the metal oxide particles 75 after pressing.

[0029] The particles with a smaller particle size will get into the space between the particles with a larger particle size. Therefore, as shown in the upper left and upper right figures of FIG. 5, when the particle size D of the metal oxide particles 75 o is larger than the particle size D of the positive electrode active material particles 45 p , when the positive electrode layer 40 and the coating layer 70 are compressed by pressing, the positive electrode active material particles 45 with a smaller particle size will get into the space between the metal oxide particles 75. Then, as shown in the upper right figure of FIG. 5, the positive electrode active material particles 46 that have got into the space between the metal oxide particles 75 will be isolated from other positive electrode active material particles 45, and the positive electrode active material particles 46 will no longer be able to contribute to charge and discharge.

[0030] On the other hand, as shown in the lower left and lower right figures of FIG. 5, when the particle size D of the metal oxide particles 75 o is smaller than the particle size D of the positive electrode active material particles 45 p , it is difficult for the positive electrode active material particles 45 to get into the space between the oxide particles during pressing, and it is difficult to generate isolated positive electrode active material particles 46. Therefore, the charge and discharge characteristics of the all-solid-state battery 1A can be improved.

[0031] This coating part 70 is not particularly limited, but has an annular shape and covers the entire circumference of the side surface 40b. This coating part 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 substantially 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. That is, this first inner surface 70b is a plane that is inclined 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 the third end face 70a. At least a portion of this fourth end face 70c is covered by the solid electrolyte layer 60. The fourth end face 70c is a plane substantially 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 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 generation element 30. Therefore, the thickness T3 of the covering portion 70 is substantially the same as the thickness T2 of the positive electrode layer 40 (T3 = T2). Note that the thickness in this embodiment is the thickness in the Z direction.

[0035] Furthermore, as shown in the following modified example 1, the thickness T3 of the covering portion 70 may be made thicker than the thickness T2 of the positive electrode layer 40 (T3>T2). Figure 2 is a cross-sectional view showing the all-solid-state battery 1B in the first modified example. In this first modified example, the thickness T3 of the covering portion 70 is thicker than the thickness T2 of the positive electrode layer 40 (T3>T2), and the covering portion 70 is provided with a protruding portion 71 that protrudes in the +Z direction from the second end face 40c of the positive electrode layer 40.

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

[0037] The thickness T5 of the second part 62 is smaller than the thickness T4 of the first part 61. The second part 62 is located outside the first part 61 and constitutes the outer peripheral portion of the solid electrolyte layer 60. Since the second part 62 is thin, for example, compared with the solid electrolyte layer 60 in the embodiment shown in FIG. 1, the exposed amount of the side surface of the second part 62 can be reduced. Thereby, powder falling from the solid electrolyte layer 60 can be reduced.

[0038] Returning to FIG. 1, the thickness T3 of the coating portion 70 is smaller than the thickness T1 of the power generation element 30 (T3 < T1). Thereby, the coating portion 70 is not continuously formed on the entire side surface of the power generation element 30 in the Z direction, and the coating portion 70 does not contact the negative electrode current collector 20. Since the negative electrode layer 50 includes a lithium metal layer whose thickness greatly increases and decreases with the charge and discharge of the all-solid-state battery 1A, the distance between the positive and negative electrode current collectors 10 and 20 greatly varies with the increase and decrease of the thickness of the lithium metal layer. For this reason, the coating portion may break because it cannot follow the variation in the distance between the positive and negative electrode current collectors 10 and 20. On the other hand, in the all-solid-state battery 1A of the present embodiment, since the thickness T3 of the coating portion 70 is smaller than the thickness T1 of the power generation element 30, it is not affected by the increase and decrease in the distance between the positive and negative electrode current collectors 10 and 20, and breakage of the coating portion 70 can be prevented.

[0039] In particular, the coating portion 70 in the present embodiment does not contact the side surface of the negative electrode layer 50. If the coating portion is also formed on the side surface of the lithium metal layer, the coating portion may break due to the increase and decrease in the thickness of the lithium metal layer. However, in the present embodiment, breakage of such a coating portion 70 can be prevented.

[0040] Note that in the present embodiment, the inner surface of the coating portion 70 is composed of the first inner surface 70b, and the entire inner surface of the coating portion 70 contacts the positive electrode layer 40, but it is not limited thereto. As shown in the following second modification example, a part of the inner surface of the coating portion 70 may be separated from the positive electrode layer 40.

[0041] Figure 3 is a cross-sectional view showing a solid-state battery 1C in a second modified example. In this solid-state battery 1C, the inner surface of the covering portion 70 includes a second inner surface 70e in addition to the first inner surface 70b. The second inner surface 70e is connected to the first inner surface 70b from the solid electrolyte layer 60 side (+Z direction side) and is separated from the side surface 40b of the positive electrode layer 40. In this embodiment, the second inner surface 70e is inclined 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 between the side surface 40b and the second inner surface 70e. This 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. Therefore, delamination between the solid electrolyte layer 60 and the positive electrode layer 40 can be suppressed. Furthermore, by increasing the contact area between the solid electrolyte layer 60 and the positive electrode layer 40, current concentration at the interface between the solid electrolyte layer 60 and the positive electrode layer 40 can also be mitigated.

[0043] Furthermore, in this second modified example, the edge 40d of the positive electrode layer 40 is located outside the edge 70f on the second inner surface 70e side of the fourth end face 70c when viewed in a plan view 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 edge of the positive electrode layer 40 can be improved, and damage to the positive electrode layer 40 can be suppressed.

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

[0045] In this embodiment, the density D1 of the fourth portion 74 is higher than the density D2 of the third portion 73. This improves the strength of the outer periphery of the covering portion 70, thereby suppressing damage to the covering portion 70. The method for creating such a density difference is not particularly limited, but the density of the fourth portion 74 may be increased by compressing it with pressure, or the difference may be created by using different materials for the material constituting the fourth portion 74 and the material constituting the third portion 73.

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

[0047] Figure 4 is a cross-sectional view showing a solid-state battery 1D in a third modified example. In this solid-state battery 1D, a mixed portion 80 is formed between the positive electrode layer 40 and the coating portion 70, in which the materials constituting the positive electrode layer 40 and the materials constituting the coating portion 70 are mixed.

[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 covering portion to the positive electrode current collector 10 so as to partially overlap with the paste for forming the positive electrode layer 40, and then drying both pastes.

[0049] The presence of such a mixed portion 80 between the positive electrode layer 40 and the coating portion 70 improves the bonding between the positive electrode layer 40 and the coating portion 70, thereby suppressing powder shedding from the positive electrode layer 40. [Explanation of Symbols]

[0050] 1A~1D…All solid state battery 10...Positive electrode current collector 20...Negative electrode current collector 30…Power generation element 40…Positive electrode layer 50... Negative electrode layer 60…Solid electrolyte layer 70... Covering part 80…Mixed part

Claims

1. A power generation element in which a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are stacked in this order along the first direction, A positive electrode current collector in contact with the positive electrode layer, A solid-state battery comprising a negative electrode current collector in contact with the negative electrode layer, The positive electrode layer is in contact with the solid electrolyte layer and includes a side surface that slopes toward the center of the positive electrode layer as it approaches the negative electrode current collector from the positive electrode current collector. The all-solid-state battery is provided on the positive electrode current collector and is in contact with and covering the side surface, and further comprises a non-Li ion conductive coating portion, The thickness of the covering portion in the first direction is thinner than the thickness of the power generation element in the first direction. The covering portion is an all-solid-state battery including a first inner surface that is in surface contact with the side surface.

2. In the all-solid-state battery described in claim 1, The positive electrode layer is The first end face that contacts the positive electrode current collector, Including a second end face located opposite to the first end face, The aforementioned covering portion is The third end surface that contacts the positive electrode current collector, Including a fourth end face located opposite to the third end face, The solid electrolyte layer covers the second end face and the fourth end face of the all-solid-state battery.

3. In the all-solid-state battery according to claim 2, The thickness of the coating portion in the first direction is greater than the thickness of the positive electrode layer in the first direction. The solid electrolyte layer is The first portion in contact with the second end face, Including the second portion in contact with the fourth end face, A solid-state battery in which the thickness of the second portion in the first direction is thinner than the thickness of the first portion in the first direction.

4. In the all-solid-state battery according to claim 2, The aforementioned covering portion is The first inner surface is inclined to correspond to the inclination of the side surface, The first inner surface includes a second inner surface connected from the solid electrolyte layer side and separated from the side surface, The solid electrolyte layer is an all-solid-state battery that includes an intervening portion between the side surface and the second inner surface.

5. In the all-solid-state battery according to claim 4, A solid-state battery in which the edge of the positive electrode layer is located outside the edge of the second inner surface of the fourth end face in a plan view from the first direction.

6. In the all-solid-state battery described in claim 1, The aforementioned covering portion is The third portion in contact with the aforementioned side surface, A fourth portion located outside the third portion and in contact with the positive electrode current collector, An all-solid-state battery in which the density of the fourth portion is higher than the density of the third portion.

7. In the all-solid-state battery described in claim 1, The all-solid-state battery further comprises a mixed portion located between the positive electrode layer and the coating portion, in which the material constituting the positive electrode layer and the material constituting the coating portion are mixed.

8. In the all-solid-state battery according to any one of claims 1 to 7, The first inner surface is inclined to correspond to the inclination of the side surface in a solid-state battery.

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