All-solid-state batteries

Abstract

To provide an all-solid battery capable of suppressing expansion and contraction during charging and discharging.SOLUTION: An all-solid battery 1 that utilizes the deposition-dissolution reaction of metallic lithium as a negative electrode reaction includes a positive electrode current collector layer 10, a positive electrode active material layer 20, a solid electrolyte layer 30, and a negative electrode current collector layer 40 laminated in this order. The solid electrolyte layer 30 includes one or more concave portions 35. The concave portion 35 is localized on a surface of the solid electrolyte layer 30 on the side of the negative electrode current collector layer and is separated from the negative electrode current collector layer 40. The concave portion 35 is preferably larger than a solid electrolyte particle contained in the solid electrolyte layer 30.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] This disclosure relates to all-solid-state batteries. [Background technology]

[0002] In recent years, with the rapid proliferation of information-related devices and communication equipment such as personal computers, video cameras, and mobile phones, the development of batteries used as their power sources has become increasingly important. Furthermore, the automotive industry is also developing high-output, high-capacity batteries for electric vehicles and hybrid vehicles. Currently, among various types of batteries, lithium-ion batteries are attracting attention due to their high energy density.

[0003] Patent Document 1 discloses a solid electrolyte layer structure for an all-solid-state battery, comprising a plate-shaped dense body made of ceramics containing a solid electrolyte, and a porous layer made of ceramics containing the same or a different solid electrolyte as the dense body, formed by firing and integrating it onto at least one surface of the dense body. The document states that such a structure makes it possible to reduce the connection resistance at the connection interface with the electrodes.

[0004] Patent Document 2 discloses a method for manufacturing a lithium solid-state battery module. In the manufacturing of the lithium solid-state battery module, the document discloses that when the restraining pressure used to restrain the lithium solid battery is P (MPa) and the average pore radius of the solid electrolyte layer determined by the mercury intrusion method is R (μm), the condition P ≤ -5900R + 74 is satisfied. The document states that by such a manufacturing method, a lithium solid-state battery module can be obtained that suppresses the occurrence of short circuits caused by dendrites. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2008 / 059987 [Patent Document 2] Japanese Patent Publication No. 2015-156297 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In all-solid-state batteries, which utilize the deposition-dissolution reaction of metallic lithium as the reaction at the negative electrode, metallic lithium is deposited between the negative electrode current collector layer and the solid electrolyte layer during charging. Furthermore, in such all-solid-state batteries, the metallic lithium between the negative electrode current collector layer and the solid electrolyte layer dissolves during discharge. As a result, such all-solid-state batteries expand and contract with charging and discharging. This expansion and contraction reduces the contact area between the solid electrolyte and metallic lithium, which can lead to a decrease in the charge and discharge capacity of the all-solid-state battery. Moreover, repeated expansion and contraction can cause cracks and defects in the solid electrolyte layer, which can ultimately lead to internal short circuits.

[0007] The objective of this disclosure is to provide an all-solid-state battery that can suppress expansion and contraction during charging and discharging. [Means for solving the problem]

[0008] The inventors have found that the above problem can be achieved by the following means: 《Aspect 1》 This all-solid-state battery utilizes the deposition-dissolution reaction of metallic lithium as the reaction at the negative electrode. The positive electrode current collector layer, positive electrode active material layer, solid electrolyte layer, and negative electrode current collector layer are stacked in this order. The solid electrolyte layer has one or more recesses, The recess is localized on the surface of the solid electrolyte layer facing the negative electrode current collector layer and is spaced apart from the negative electrode current collector layer, in an all-solid-state battery. 《Aspect 2》 The all-solid-state battery according to embodiment 1, wherein the recess is larger than the solid electrolyte particles contained in the solid electrolyte layer. 《Aspect 3》 The all-solid-state battery according to embodiment 1 or 2, wherein the recess is dome-shaped. Appearance 4 The maximum length of the concave portion in the stacking direction of the all-solid-state battery is 2 μm to 200 μm, and the all-solid-state battery according to any one of Aspects 1 to 3. 《Aspect 5》 The maximum length of the concave portion in the plane direction of the all-solid-state battery is 2 μm to 200 μm, and the all-solid-state battery according to any one of Aspects 1 to 4. 《Aspect 6》 The solid electrolyte layer has a plurality of the concave portions, and when viewed from the stacking direction of the all-solid-state battery, the interval between the plurality of the concave portions is 2 μm to 500 μm, and the all-solid-state battery according to any one of Aspects 1 to 5. 《Aspect 7》 There is a conductive layer between the solid electrolyte layer and the negative electrode current collector layer, The conductive layer is arranged along the solid electrolyte layer such that it is separated from the negative electrode current collector layer in a portion along the concave portion and is in electrical contact with the negative electrode current collector layer in other portions. The all-solid-state battery according to any one of Aspects 1 to 6. 《Aspect 8》 The thickness of the conductive layer is 100 nm to 10 μm, and the all-solid-state battery according to Aspect 7. 《Aspect 9》 The conductive layer is a layer of a metal capable of forming an alloy with lithium or a layer of carbon, and the all-solid-state battery according to Aspect 7 or 8. 《Aspect 10》 The conductive layer contains magnesium, tin, indium, or gold, and the all-solid-state battery according to any one of Aspects 7 to 9.

Advantages of the Invention

[0009] According to the present disclosure, an all-solid-state battery capable of suppressing expansion and contraction during charge and discharge can be provided.

Brief Description of the Drawings

[0010] [Figure 1A] FIG. 1A is a schematic diagram of an all-solid-state battery 1 according to a first embodiment of the present disclosure. [Figure 1B]Figure 1B is a schematic diagram showing a state in which an all-solid-state battery 1 according to the first embodiment of this disclosure is being charged. [Figure 1C] Figure 1C is a schematic diagram showing the state of a fully charged all-solid-state battery 1 according to the first embodiment of this disclosure. [Figure 2A] Figure 2A is a schematic diagram of an all-solid-state battery 2 that differs from the embodiment of the present disclosure. [Figure 2B] Figure 2B is a schematic diagram showing a state in which an all-solid-state battery 2, different from the embodiment of the present disclosure, is being charged. [Figure 2C] Figure 2C is a schematic diagram showing a fully charged state of a solid-state battery 2, which differs from the embodiment of the present disclosure. [Figure 3A] Figure 3A is a schematic diagram of an all-solid-state battery 3 according to a second embodiment of the present disclosure. [Figure 3B] Figure 3B is a schematic diagram showing a state in which an all-solid-state battery 3 according to a second embodiment of the present disclosure is being charged. [Figure 3C] Figure 3C is a schematic diagram showing the fully charged state of the all-solid-state battery 3 according to the second embodiment of this disclosure. [Figure 4A] Figure 4A is a scanning electron microscope (SEM) image of the solid electrolyte coating layer of the all-solid-state battery of Example 1. [Figure 4B] Figure 4B is a scanning electron microscope (SEM) image of a cross-section in the stacking direction of the all-solid-state battery of Example 1 when fully charged. [Figure 5A] Figure 5A is a graph showing the relationship between the change in internal pressure and time when the all-solid-state battery of Comparative Example 1 is charged and discharged. [Figure 5B] Figure 5B is a graph showing the relationship between the change in internal pressure and time when the all-solid-state battery of Example 1 is charged and discharged. [Figure 6] Figure 6 is a graph showing the relationship between current density and charging capacity during the 1st, 4th, 7th, and 13th charge-discharge cycles when the all-solid-state batteries of Example 1 and Comparative Example 1 were repeatedly charged and discharged at 25°C while changing the C rate every 3 cycles. [Figure 7A] Figure 7A is a scanning electron microscope (SEM) image of a cross-section in the stacking direction of the all-solid-state battery of Example 1 when fully charged. [Figure 7B] Figure 7B is a scanning electron microscope (SEM) image of a cross-section in the stacking direction of the all-solid-state battery of Example 2 when fully charged. [Figure 8A] Figure 8A is a graph showing the relationship between charge / discharge capacity and the number of cycles when the all-solid-state battery of Example 1 is repeatedly charged and discharged at a predetermined C rate. [Figure 8B] Figure 8B is a graph showing the relationship between charge / discharge capacity and the number of cycles when the all-solid-state battery of Example 2 is repeatedly charged and discharged at a predetermined C rate. [Modes for carrying out the invention]

[0011] The embodiments of this disclosure will be described in detail below. However, this disclosure is not limited to the embodiments described below, and can be implemented in various modified forms within the scope of the essence of the disclosure.

[0012] The all-solid-state battery disclosed herein is an all-solid-state battery that utilizes a deposition-dissolution reaction of metallic lithium as the reaction of the negative electrode, wherein a positive electrode current collector layer, a positive electrode active material layer, a solid electrolyte layer, and a negative electrode current collector layer are stacked in this order, and the solid electrolyte layer has one or more recesses, the recesses being localized on the surface of the solid electrolyte layer on the negative electrode current collector layer side and spaced apart from the negative electrode current collector layer.

[0013] Here, "an all-solid-state battery that utilizes the deposition-dissolution reaction of metallic lithium as a reaction at the negative electrode" refers to an all-solid-state battery in which, as part of the battery reaction, metallic lithium is deposited between the solid electrolyte layer and the negative electrode current collector layer during charging and discharging, and the metallic lithium dissolves during discharge.

[0014] In the all-solid-state battery of the present disclosure, the solid electrolyte layer has one or more recesses. The recesses are localized on the surface of the solid electrolyte layer facing the negative electrode current collector layer and are spaced apart from the negative electrode current collector layer. When the all-solid-state battery of the present disclosure is charged, at least a portion of the metallic lithium deposited between the negative electrode current collector layer and the solid electrolyte layer is deposited in the recesses. Therefore, compared with an all-solid-state battery without such recesses, the increase in the thickness of the all-solid-state battery due to the metallic lithium layer formed by charging can be reduced. As a result, the expansion and contraction of the all-solid-state battery due to charging and discharging is suppressed in the all-solid-state battery of the present disclosure compared with an all-solid-state battery without such recesses.

[0015] Figure 1A is a schematic diagram of a solid-state battery 1 according to the first embodiment of this disclosure. Figure 1B is a schematic diagram showing the solid-state battery 1 according to the first embodiment of this disclosure in a charging state. Figure 1C is a schematic diagram showing the solid-state battery 1 according to the first embodiment of this disclosure when fully charged.

[0016] As shown in Figure 1A, the all-solid-state battery 1 according to the first embodiment of this disclosure is an all-solid-state battery that utilizes the deposition-dissolution reaction of metallic lithium as the reaction of the negative electrode. In a completely discharged state, the all-solid-state battery 1 has a positive electrode current collector layer 10, a positive electrode active material layer 20, a solid electrolyte layer 30, and a negative electrode current collector layer 40 stacked in this order. The solid electrolyte layer 30 has one or more (three in Figure 1A) recesses 35. The recesses 35 are localized on the surface of the solid electrolyte layer 30 facing the negative electrode current collector layer 40 and are spaced apart from the negative electrode current collector layer 40. Also, in Figure 1A, the recesses 35 have a curved shape, more specifically dome-shaped, and even more specifically hemispherical. The recesses 35 are spaced apart from the negative electrode current collector layer 40. Therefore, in a completely discharged state, a gap is formed between the recesses 35 of the solid electrolyte layer 30 and the negative electrode current collector layer 40. In the following, this void may be referred to as the "recess."

[0017] As shown in Figure 1B, when the all-solid-state battery 1 according to the first embodiment of this disclosure is charged, lithium ions (Li +Lithium ions (Li) move from the positive electrode active material layer 20 side to the negative electrode current collector layer 40 side through the solid electrolyte layer 30. + ) is an electron (e) at or near the interface between the solid electrolyte layer 30 and the negative electrode current collector layer 40. - It receives ions and generates metallic lithium. This generation of metallic lithium is particularly likely to occur at the edge of the recess 35 at the interface between the solid electrolyte layer 30 and the negative electrode current collector layer 40. In Figure 1B, the black arrows indicate the movement of lithium ions, and the white arrows indicate the movement of electrons.

[0018] Then, as shown in Figure 1C, when the all-solid-state battery 1 according to the first embodiment of this disclosure is fully charged, a metallic lithium layer 50 is formed at the interface between the solid electrolyte layer 30 and the negative electrode current collector layer 40 so as to at least partially fill the recess 35.

[0019] Thus, in the all-solid-state battery 1 according to the first embodiment of this disclosure, at least a portion of the metallic lithium generated between the negative electrode current collector layer 40 and the solid electrolyte layer 30 is deposited in the recess 35. Therefore, the thickness of the all-solid-state battery 1 due to the metallic lithium layer 50 formed by charging can be reduced. In other words, the expansion and contraction of the all-solid-state battery 1 due to charging and discharging can be suppressed.

[0020] Figures 1A-C are not intended to limit the all-solid-state batteries of this disclosure.

[0021] In contrast, in the all-solid-state battery 2, which differs from the embodiments of this disclosure, the expansion and contraction of the all-solid-state battery 2 due to charging and discharging is significant.

[0022] Figure 2A is a schematic diagram of a solid-state battery 2 different from that of the embodiments of this disclosure. Figure 2B is a schematic diagram showing a solid-state battery 2 different from that of the embodiments of this disclosure in a charging state. Figure 2C is a schematic diagram showing a solid-state battery 2 different from that of the embodiments of this disclosure when fully charged.

[0023] As shown in Figure 2A, the all-solid-state battery 2, which differs from the embodiments of this disclosure, is an all-solid-state battery 2 that utilizes a deposition-dissolution reaction of metallic lithium as the reaction of the negative electrode, similar to the all-solid-state battery 1 according to the first embodiment of this disclosure. In the all-solid-state battery 2, when fully discharged, the positive electrode current collector layer 10, the positive electrode active material layer 20, the solid electrolyte layer 30, and the negative electrode current collector layer 40 are stacked in this order. However, in the all-solid-state battery 2, which differs from the embodiments, the solid electrolyte layer 30 does not have a recess 35.

[0024] As shown in Figure 2B, when a solid-state battery 2 different from the embodiment of this disclosure is charged, lithium ions (Li + Lithium ions (Li) move from the positive electrode active material layer 20 side to the negative electrode current collector layer 40 side through the solid electrolyte layer 30. + ) is an electron (e) at or near the interface between the solid electrolyte layer 30 and the negative electrode current collector layer 40. - It receives ) and produces metallic lithium. In Figure 2B, the black arrows show the movement of lithium ions, and the white arrows show the movement of electrons.

[0025] As shown in Figure 2C, in the fully charged state of the all-solid-state battery 2, which differs from the embodiment of this disclosure, a metallic lithium layer 50 is formed at the interface between the negative electrode current collector layer 40 and the solid electrolyte layer 30. Here, the all-solid-state battery 2, which differs from the embodiment of this disclosure, does not have a recess 35. Therefore, compared to the all-solid-state battery 1 according to the first embodiment of this disclosure, the thickness of the metallic lithium layer 50 formed at the interface between the negative electrode current collector layer 40 and the solid electrolyte layer 30 is larger.

[0026] Figures 2A-C are not intended to limit the all-solid-state batteries of this disclosure.

[0027] Thus, in the all-solid-state battery 1 according to the first embodiment of this disclosure, at least a portion of the metallic lithium deposited between the negative electrode current collector layer 40 and the solid electrolyte layer 30 is deposited in the recess 35. Therefore, compared to an all-solid-state battery 2 that does not have such a recess 35, the increase in the thickness of the all-solid-state battery 1 due to the metallic lithium layer 50 formed by charging can be reduced. In other words, the all-solid-state battery 1 according to the first embodiment of this disclosure has reduced increase or decrease in thickness due to charging and discharging compared to an all-solid-state battery 2 different from the embodiment of this disclosure.

[0028] Positive electrode current collector layer All-solid-state batteries typically have a positive electrode current collector layer that collects current from the positive electrode active material layer.

[0029] As the positive electrode current collector layer, known metal or carbon materials usable as current collector layers for all-solid-state batteries can be used. Examples of metals include metallic materials containing one or more elements selected from the group consisting of copper, nickel, aluminum, vanadium, gold, platinum, magnesium, iron, titanium, cobalt, chromium, zinc, germanium, and indium. Examples of carbon materials include any conductive carbon material, such as carbon.

[0030] Examples of materials for the positive electrode current collector layer include stainless steel, aluminum, nickel, iron, titanium, and carbon.

[0031] The form of the positive electrode current collector layer is not particularly limited and can take various forms such as foil-like or mesh-like shapes.

[0032] 《Cathode active material layer》 The positive electrode active material layer contains a positive electrode active material and may also contain optional components such as a solid electrolyte, a conductive additive, and a binder.

[0033] There are no particular restrictions on the type of positive electrode active material; any material usable as an active material for all-solid-state batteries can be used. Examples of positive electrode active materials include LiCoO2 and LiNi. x Co 1-xO2(0 < x < 1), LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiMnO2, hetero-element-substituted Li-Mn spinel (e.g., LiMn 1.5 Ni 0.5 O4, LiMn 1.5 Al 0.5 O4, LiMn 1.5 Mg 0.5 O4, LiMn 1.5 Co 0.5 O4, LiMn 1.5 Fe 0.5 O4, and LiMn 1.5 Zn 0.5 O4, etc.), lithium titanate (e.g., Li4Ti5O 12 ), lithium metal phosphate (e.g., LiFePO4, LiMnPO4, LiCoPO4, and LiNiPO4, etc.), lithium compounds such as LiCoN, Li2SiO3, and Li4SiO4, transition metal oxides (e.g., V2O5, and MoO3, etc.), etc. can be mentioned.

[0034] The shape of the positive electrode active material is not particularly limited, but it may be particulate.

[0035] A coating layer containing a lithium ion conductive oxide may be formed on the surface of the positive electrode active material. This is because the reaction between the positive electrode active material and the solid electrolyte can be suppressed.

[0036] Examples of the lithium ion conductive oxide include, for example, LiNbO3, Li4Ti5O 12 , and Li3PO4, etc. The thickness of the coating layer is, for example, 0.1 nm or more, and may be 1 nm or more. On the other hand, the thickness of the coating layer is, for example, 100 nm or less, and may be 20 nm or less. The coverage rate of the coating layer on the surface of the positive electrode active material is, for example, 70% or more, and may be 90% or more.

[0037] Examples of the solid electrolyte include solid electrolytes that can be incorporated into the solid electrolyte layer described later.

[0038] The content of the solid electrolyte in the positive electrode active material layer is not particularly limited, but may be in the range of, for example, 1% to 80% by mass when the total mass of the positive electrode active material layer is 100% by mass.

[0039] As conductive additives, known materials can be used, such as carbon materials and metal particles. As carbon materials, for example, at least one selected from the group consisting of carbon black such as acetylene black and furnace black, VGCF, carbon nanotubes, and carbon nanofibers can be used, and in particular, from the viewpoint of electronic conductivity, at least one selected from the group consisting of VGCF, carbon nanotubes, and carbon nanofibers may be used. As metal particles, examples include nickel, copper, iron, and stainless steel particles.

[0040] The content of conductive additives in the positive electrode active material layer is not particularly limited.

[0041] As the binder, you may use the one mentioned above for the solid electrolyte layer. The positive electrode active material layer can be manufactured by known methods, such as the following methods, but the manufacturing method is not particularly limited.

[0042] A slurry is prepared by dispersing the positive electrode active material, solid electrolyte, and optionally conductive additives and binders in a dispersion medium. This slurry is then coated onto the positive electrode current collector layer, dried, and pressed.

[0043] 《Solid electrolyte layer》 The solid electrolyte layer contains a solid electrolyte.

[0044] The solid electrolyte is preferably an inorganic solid electrolyte. Examples of inorganic solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, and nitride solid electrolytes.

[0045] Sulfide solid electrolytes typically contain Li and S elements. Furthermore, it is preferable that sulfide solid electrolytes contain at least one of P, Ge, Sn, and Si elements. In addition, sulfide solid electrolytes may contain at least one halogen element (e.g., F, Cl, Br, I).

[0046] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-P2S5-GeS2, Li2S-P2S5-SnS2, Li2S-P2S5-SiS2, Li2S-P2S5-LiI, Li2S-P2S5-LiI-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z. m S n (where m and n are positive numbers, and Z is one of Ge, Zn, or Ga.) Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (wherein x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, or In.) These are some examples. The above description of "Li2S-P2S5" means a material made using a raw material composition containing Li2S and P2S5, and the same applies to other descriptions.

[0047] The solid electrolyte may be glass, glass ceramics, or a crystalline material. Glass can be obtained by amorphous treatment of the raw material composition (e.g., a mixture of Li2S and P2S5). Examples of amorphous treatment include mechanical milling. Mechanical milling may be dry or wet, but the latter is preferred because it prevents the raw material composition from adhering to the walls of containers, etc. Glass ceramics can be obtained by heat treatment of glass. Crystalline materials can be obtained, for example, by solid-phase reaction treatment of the raw material composition.

[0048] The solid electrolyte is preferably particulate. The average particle size (D50) of the solid electrolyte is, for example, 0.01 μm or larger. On the other hand, the average particle size (D50) of the solid electrolyte may be, for example, 10 μm or less, or even 5 μm or less. The lithium ion conductivity of the solid electrolyte at 25°C is, for example, 1 × 10⁻⁶. -4 S / cm or more, 1 × 10 -3 It is preferable that the ratio is S / cm or higher.

[0049] The solid electrolyte content in the solid electrolyte layer is, for example, 70% by weight or more, and may be 90% by weight or more.

[0050] The solid electrolyte layer may contain a binder as needed. The binder may be, but is not limited to, materials such as polyvinylidene fluoride (PVdF), carboxymethylcellulose (CMC), butadiene rubber (BR), or styrene-butadiene rubber (SBR), or a combination thereof.

[0051] The thickness of the solid electrolyte layer is not particularly limited as long as it is thick enough to form a recess. The thickness of the solid electrolyte layer may be, for example, 10 μm to 1000 μm. The thickness of the solid electrolyte layer may be 10 μm or more, 10 μm or more, 10 μm or more, or 10 μm or more, and may be 1000 μm or less, 1000 μm or less, 1000 μm or less, or 1000 μm or less.

[0052] The solid electrolyte layer can be manufactured by known methods, such as the following methods, but the manufacturing method is not particularly limited.

[0053] A slurry is prepared by dispersing a solid electrolyte and, as appropriate, a binder in a dispersion medium. This slurry is then coated onto a substrate, dried, and pressed.

[0054] <Recessed area> The all-solid electrolyte layer of the present disclosure has one or more recesses. The recesses are localized on the surface of the solid electrolyte layer facing the negative electrode current collector layer and are spaced apart from the negative electrode current collector layer.

[0055] The recess can be larger than the solid electrolyte particles contained in the solid electrolyte layer.

[0056] Furthermore, when a solid-state battery is charged, metallic lithium may be unevenly deposited between the negative electrode current collector layer and the solid electrolyte layer. This uneven deposition of metallic lithium applies uneven stress to the solid electrolyte layer, which can lead to cracking of the solid electrolyte layer and cause an internal short circuit in the solid-state battery. From the viewpoint of suppressing such problems, it is preferable that the recess has a curved shape. When the recess has a curved shape, the stress applied to the surface of the recess by the metallic lithium deposited in the recess during charging of the solid-state battery is more easily dispersed.

[0057] Specific examples of shapes in which the recess has a curved surface include, but are not limited to, a dome shape, and more specifically, a hemispherical shape or an elongated sphere shape.

[0058] The maximum length of the stacking direction of the all-solid-state battery from the curved surface of the recess to the negative electrode current collector layer is preferably 2 μm to 200 μm. If the maximum length of the stacking direction of the all-solid-state battery in the recess is 2 μm or more, the amount of metallic lithium stored in the recess can be significantly increased. On the other hand, if the maximum length of the stacking direction of the all-solid-state battery in the recess is 200 μm or less, the thickness of the solid electrolyte layer can be reduced. Also, depending on the thickness of the solid electrolyte layer, forming a recess in the solid electrolyte layer tends to reduce the strength of the solid electrolyte layer. If the maximum length of the stacking direction of the all-solid-state battery in the recess is 200 μm or less, the strength of the solid electrolyte layer can be particularly maintained.

[0059] From the viewpoint of ensuring sufficient storage capacity of metallic lithium in the recesses, reducing the thickness of the solid electrolyte layer, and maintaining the strength of the solid electrolyte layer, it is particularly preferable that the maximum length of the recesses in the stacking direction of the all-solid-state battery be 2 μm to 150 μm.

[0060] The maximum length of the recess in the stacking direction of the all-solid-state battery may be 2 μm or more, 10 μm or more, 20 μm or more, or 50 μm or more, and may be 150 μm or less, 120 μm or less, 100 μm or less, or 80 μm or less.

[0061] From a similar viewpoint, the maximum length in the planar direction of the recessed all-solid-state battery is preferably 2 μm to 200 μm, and particularly preferably 2 μm to 150 μm. Furthermore, the maximum length in the planar direction of the recessed all-solid-state battery may be 2 μm or more, 10 μm or more, 20 μm or more, or 50 μm or more, and may be 150 μm or less, 120 μm or less, 100 μm or less, or 80 μm or less.

[0062] The solid electrolyte layer preferably has multiple recesses, and when viewed from the stacking direction of the all-solid-state battery, the spacing between the multiple recesses is preferably 2 μm to 500 μm. Note that the spacing between the multiple recesses refers to the shortest distance between the edges of adjacent recesses.

[0063] When the spacing between multiple recesses is 2 μm or more, it is easier to partition the recesses during manufacturing, making molding easier. Furthermore, when the spacing between multiple recesses is 500 μm or less, the amount of metallic lithium that can be stored can be increased.

[0064] From the viewpoint of ease of forming recesses during manufacturing and the amount of metallic lithium that can be stored, the spacing between multiple recesses is particularly preferably 2 μm to 400 μm.

[0065] The spacing between multiple recesses may be 2 μm or more, 50 μm or more, 100 μm or more, or 200 μm or more, and may be 500 μm or less, 450 μm or less, 400 μm or less, or 350 μm or less.

[0066] The recesses can be formed, for example, by placing a mold on a pre-formed solid electrolyte layer and pressing it, but the method is not limited to this. Any mold capable of forming recesses can be used, such as a metal mesh.

[0067] Conductive layer The all-solid-state battery of the present disclosure preferably further has a conductive layer between the solid electrolyte layer and the negative electrode current collector layer. Here, the conductive layer is arranged along the solid electrolyte layer such that it is spaced apart from the negative electrode current collector layer in portions along the recesses and in other portions electrically in contact with the negative electrode current collector layer.

[0068] When recesses are provided in the solid electrolyte layer, metallic lithium deposits in these recesses during charging of the all-solid-state battery. This deposit of metallic lithium is particularly likely to occur at the edges of the recesses at the interface between the solid electrolyte layer and the negative electrode current collector layer, as shown in Figure 1B. When metallic lithium deposits at the edges of the recesses, it is also likely to deposit at the interface between the portion of the solid electrolyte layer without recesses and the negative electrode current collector layer.

[0069] In this regard, when the conductive layer described above is placed between the solid electrolyte layer and the negative electrode current collector layer, metallic lithium is more likely to precipitate on the side of the recess surface closer to the positive electrode active material layer than at the edge of the recess. This is because electrons can move from the negative electrode current collector layer to the conductive layer, allowing lithium ions moving through the solid electrolyte layer to receive electrons on the side of the recess surface closer to the positive electrode active material layer. Such a location could be, for example, near the apex of the dome if the recess is dome-shaped.

[0070] When metallic lithium is deposited on the side of the recessed surface closer to the positive electrode active material layer, metallic lithium tends to deposit preferentially in the space within the recess. Therefore, the deposition of metallic lithium at the interface between the portion of the solid electrolyte layer where no recess is formed and the negative electrode current collector layer can be reduced. Consequently, by arranging a conductive layer, expansion and contraction during charging and discharging of the all-solid-state battery can be further suppressed.

[0071] Let's explain this in more detail using Figures 3A-C.

[0072] Figure 3A is a schematic diagram of a solid-state battery 3 according to a second embodiment of the present disclosure. Figure 3B is a schematic diagram showing the solid-state battery 3 according to a second embodiment of the present disclosure in a charging state. Figure 3C is a schematic diagram showing the solid-state battery 3 according to a second embodiment of the present disclosure in a fully charged state.

[0073] As shown in Figure 3A, the all-solid-state battery 3 according to the second embodiment of this disclosure has a conductive layer 60 between the solid electrolyte layer 30 and the negative electrode current collector layer 40. The conductive layer 60 is arranged along the solid electrolyte layer 30 such that it is spaced apart from the negative electrode current collector layer 40 in the portion along the recess 35 and in electrical contact with the negative electrode current collector layer 40 in the other portions. Therefore, the all-solid-state battery 3 according to the second embodiment of this disclosure has a gap between the portion of the conductive layer 60 along the recess 35 and the negative electrode current collector layer 40. The rest has the same structure as the all-solid-state battery 1 according to the first embodiment of this disclosure shown in Figure 1A.

[0074] As shown in Figure 3B, when the all-solid-state battery 3 according to the second embodiment of this disclosure is charged, lithium ions (Li + Lithium ions (Li) move from the positive electrode active material layer 20 side to the negative electrode current collector layer 40 side through the solid electrolyte layer 30. + ) is the part of the recess 35 near the positive electrode active material layer 20 side where electrons (e) that have moved through the conductive layer 60 - It receives ) and generates metallic lithium. In this process, the metallic lithium is deposited not between the conductive layer 60 and the solid electrolyte layer 30, but in the void between the conductive layer 60 and the negative electrode current collector layer. In Figure 3B, the black arrows indicate the movement of lithium ions, and the white arrows indicate the movement of electrons.

[0075] Then, as shown in Figure 3C, when the all-solid-state battery 3 according to the second embodiment of this disclosure is fully charged, a metallic lithium layer 50 is formed at the interface between the conductive layer 60 and the negative electrode current collector layer 40 so as to at least partially fill the recess 35.

[0076] The thickness of the conductive layer is preferably 100 nm to 10 μm. When the thickness of the conductive layer is 100 nm or more, unevenness is less likely to occur in the conductive layer, and the contact between the conductive layer and the negative electrode current collector layer can be particularly improved. On the other hand, when the thickness of the conductive layer is 10 μm or less, the resistivity of the conductive layer can be particularly low.

[0077] The thickness of the conductive layer may be 100 nm or more, 200 nm or more, 500 nm or more, or 1 μm or more, and may be 10 μm or less, 5 μm or less, 3 μm or less, or 1 μm or less.

[0078] The conductive layer can be made from any conductive material suitable for use in all-solid-state batteries.

[0079] The conductive layer may be, for example, a layer of metal that can form an alloy with lithium, or a layer of carbon. Examples of metals that can form an alloy with lithium include, but are not limited to, magnesium, tin, indium, or gold. Therefore, the conductive layer may contain magnesium, tin, indium, or gold.

[0080] The conductive layer may be formed, for example, by coating a substrate with a slurry in which metal powder and a binder are dispersed in a dispersion medium. The conductive layer formed on the substrate may be transferred to the solid electrolyte layer. The conductive layer may also be formed by resistance heating deposition, sputtering, or the like.

[0081] Negative electrode current collector layer The material of the negative electrode current collector layer may be a material that does not alloy with lithium, such as stainless steel, copper, and nickel. The negative electrode current collector layer can take the form of foil or plate. [Examples]

[0082] Examples 1 and 2, and Comparative Example 1 The all-solid-state batteries of Examples 1 and 2, and Comparative Example 1 were prepared as follows.

[0083] <Example 1> A positive electrode mixture was obtained by mixing positive electrode active material (Li3NiCoMnO6) powder, sulfide solid electrolyte (Li2S-P2S5) powder, and a conductive additive (carbon material).

[0084] The above solid electrolyte powder was dispersed in a dispersion medium to form a slurry. This slurry was coated onto a stainless steel foil substrate to form a solid electrolyte coating layer with a thickness of 50 μm. Next, a nickel mesh was placed on the stainless steel foil side and pressed at 98 MPa. Then, the stainless steel foil and nickel mesh were peeled off from the solid electrolyte coating layer. Multiple recesses were formed on the side of the solid electrolyte coating layer where the stainless steel foil had been placed.

[0085] The nickel mesh used was an ultra-high-precision nickel mesh with 150 mesh count, a mesh opening of 114 μm, a wire diameter of 55 μm, and a thickness of 43 μm. The mesh opening defines the spacing between recesses, the wire diameter defines the width of each recess, and the thickness defines the height of each recess.

[0086] In a glove box under an Ar atmosphere, the above-mentioned sulfide solid electrolyte powder was placed in a cylindrical container and pressed with 1 ton of pressure to form a solid electrolyte layer. Subsequently, a solid electrolyte coating layer was placed through one opening of the container, with the side without the recess facing the solid electrolyte layer, and pressed with 1 ton of pressure.

[0087] Subsequently, the positive electrode mixture was poured from the other end of the container opening and pressed with 6 tons of pressure to form the positive electrode active material layer. Furthermore, aluminum foil was placed on top of the positive electrode active material layer as the positive electrode current collector layer. In addition, metallic lithium foil and copper foil as the negative electrode current collector layer were poured in that order from one end of the container opening, i.e., the side where the positive electrode active material layer was not placed, and pressed with 1 ton of pressure. This formed a laminate having the positive electrode current collector layer, positive electrode active material layer, solid electrolyte layer, solid electrolyte coating layer, metallic lithium layer, and negative electrode current collector layer in that order.

[0088] Finally, the all-solid-state battery of Example 1 was prepared by constraining this laminate at 10 MPa with respect to its stacking direction and sealing it in a desiccator.

[0089] <Example 2> An all-solid-state battery of Example 2 was prepared in the same manner as in Example 1, except that a conductive layer was formed on the solid electrolyte coating layer during the preparation of the all-solid-state battery.

[0090] The conductive layer was formed as follows: Magnesium powder, a binder (styrene-butadiene rubber), and a solvent (mesitylene and dibutyl ether) were mixed and coated onto a stainless steel foil substrate. This was then transferred to the side of the solid electrolyte coating layer where the recesses were formed to form the conductive layer.

[0091] <Comparative Example 1> A solid-state battery for Comparative Example 1 was prepared in the same manner as in Example 1, except that a solid electrolyte coating layer with recesses was not formed.

[0092] <test> (Scanning electron microscope observation, part 1) The surface of the coated separator with recesses formed during the manufacturing of the all-solid-state battery in Example 1 was observed using a scanning electron microscope (SEM). As shown in Figure 4A, regular recesses were formed on the surface of the solid electrolyte coating layer.

[0093] Furthermore, a cross-section of the all-solid-state battery of Example 1 in the stacking direction in the charged state was observed using a scanning electron microscope (SEM). As shown in Figure 4B, in the all-solid-state battery of Example 1 in the charged state, a metallic lithium layer was formed between the solid electrolyte coating layer and the negative electrode current collector layer. The metallic lithium layer was present both in the recesses of the solid electrolyte coating layer and between the non-recessed portions of the solid electrolyte coating layer and the negative electrode current collector layer.

[0094] (Charge / Discharge Test) The all-solid-state batteries of Example 1 and Comparative Example 1 were subjected to charging and discharging, and the change in internal pressure during charging and discharging of each all-solid-state battery was measured.

[0095] Figure 5A is a graph showing the relationship between the change in internal pressure and time during the charging and discharging of the all-solid-state battery of Comparative Example 1. Figure 5B is a graph showing the relationship between the change in internal pressure and time during the charging and discharging of the all-solid-state battery of Example 1. Note that in Figures 5A and 5B, the internal pressure at the start of discharge differs between Comparative Example 1 and Example 1. This is due to the fluctuation range when the all-solid-state battery is placed in the measuring device, and the confinement pressure of the all-solid-state batteries of Comparative Example 1 and Example 1 is the same.

[0096] During discharge in a solid-state battery, metallic lithium dissolves to form lithium ions, reducing the thickness of the metallic lithium layer or causing it to disappear. Simultaneously, the reaction between the positive electrode active material and lithium ions increases the thickness of the positive electrode active material layer. Conversely, during charging in a solid-state battery, lithium ions are released from the positive electrode active material layer, reducing its thickness. At the same time, lithium ions between the solid electrolyte layer and the negative electrode current collector layer accept electrons to become metallic lithium, creating a metallic lithium layer.

[0097] As shown in Figure 5A, the all-solid-state battery of Comparative Example 1 gradually decreases in internal pressure during discharge. This is because the decrease in the overall thickness of the all-solid-state battery due to the decrease or disappearance of the metallic lithium layer during discharge exceeds the increase in the thickness of the positive electrode active material layer due to the reaction between the positive electrode active material and lithium ions.

[0098] Conversely, as shown in Figure 5A, the internal pressure of the all-solid-state battery in Comparative Example 1 gradually increases when charged. This is because the increase in the overall thickness of the all-solid-state battery due to the formation of the metallic lithium layer outweighs the decrease in the thickness of the positive electrode active material layer due to the release of lithium ions from the positive electrode active material layer.

[0099] As shown above, the all-solid-state battery in Comparative Example 1 exhibits large increases and decreases in internal pressure due to charging and discharging.

[0100] In contrast, as shown in Figure 5B, in the all-solid-state battery of Example 1, the internal pressure gradually decreases for a while after the start of discharge, but gradually increases during the discharge. The reason why the internal pressure gradually decreases for a while after the start of discharge is that for a while after the start of discharge, the thickness of the metallic lithium layer decreases as the part of the metallic lithium in contact with the negative electrode current collector layer and its surroundings begin to dissolve, but this decrease in thickness exceeds the increase in the thickness of the positive electrode active material layer due to the reaction between the positive electrode active material and lithium ions. The reason why the internal pressure gradually increases during the discharge is that during the discharge, the part of the metallic lithium that is not stored in the recesses disappears, and thereafter the metallic lithium in the recesses dissolves, but since the dissolution of metallic lithium in the recesses does not affect the overall thickness of the all-solid-state battery, the increase in the thickness of the positive electrode active material layer due to the reaction between the positive electrode active material and lithium ions becomes dominant, and the overall thickness of the all-solid-state battery increases.

[0101] Furthermore, as shown in Figure 5B, during charging of the all-solid-state battery in Example 1, the internal pressure decreases for a while after charging begins, but gradually increases during discharge. This is because the opposite phenomenon to the one observed during discharge of the all-solid-state battery in Example 1 is occurring.

[0102] In contrast to Comparative Example 1, where the internal pressure of the all-solid-state battery changed due to charging and discharging was 0.31 MPa / mAh, the internal pressure of Example 1 changed due to charging and discharging was 0.043 MPa / mAh.

[0103] (Short-circuit test) The all-solid-state batteries of Example 1 and Comparative Example 1 were charged and discharged at a temperature of 25°C with varying C rates. Specifically, for each all-solid-state battery, charging and discharging were performed at 0.1C for cycles 1-3, 1.0C for cycles 4-6, 2.0C for cycles 7-12, and 3.0C for cycle 13. The charge capacity as a function of current density was then measured for charge and discharge cycles 1, 4, 7, and 13.

[0104] The measurement results are shown in Figure 6.

[0105] As shown in Figure 6, the all-solid-state battery of Example 1 did not short-circuit even after repeated charging and discharging, but the all-solid-state battery of Comparative Example 1 short-circuited after only 4 cycles, i.e., when the C rate was changed to 1.0C.

[0106] (Scanning electron microscope observation, part 2) The cross-sections of the stacking direction of the all-solid-state batteries in Examples 1 and 2, after being discharged under a constraint of 2.4 MPa and then charged, were observed using a scanning electron microscope (SEM).

[0107] Figure 7A is a scanning electron microscope (SEM) image of a cross-section in the stacking direction of the all-solid-state battery of Example 1 when fully charged. It is also a scanning electron microscope (SEM) image of a cross-section in the stacking direction of the all-solid-state battery of Example 2 when fully charged.

[0108] As shown in Figure 7A, in the all-solid-state battery of Example 1, metallic lithium was deposited from the interface between the solid electrolyte layer and the negative electrode current collector layer, rather than from the recess, and then grew along the negative electrode current collector layer toward the recess.

[0109] In contrast, as shown in Figure 7B, in the all-solid-state battery of Example 2, metallic lithium was preferentially deposited from within the recessed areas.

[0110] (Durability test) For the all-solid-state batteries of Examples 1 and 2, repeated charging and discharging were performed at a predetermined C rate, and the change in charge / discharge capacity with respect to the number of cycles was measured.

[0111] The measurement results are shown in Figures 8A and 8B.

[0112] Figure 8A is a graph showing the relationship between charge / discharge capacity and cycle count when the all-solid-state battery of Example 1 is repeatedly charged and discharged at a predetermined C rate. Figure 8B is a graph showing the relationship between charge / discharge capacity and cycle count when the all-solid-state battery of Example 2 is repeatedly charged and discharged at a predetermined C rate. In each graph, white circles represent charging capacity and black circles represent discharging capacity.

[0113] As shown in Figure 8A, in the all-solid-state battery of Example 1, the charge and discharge capacity decreased as the number of cycles increased. Furthermore, as shown in Figure 8A, in the all-solid-state battery of Example 1, the discharge capacity was smaller than the charge capacity even within the same cycle. This is thought to be because, as shown in Figure 7A, a portion of the metallic lithium grew towards the recessed side along the negative electrode current collector layer and did not come into contact with the solid electrolyte layer, resulting in less contribution to the battery reaction.

[0114] On the other hand, as shown in Figure 8B, the all-solid-state battery of Example 2 did not show a significant decrease in charge / discharge capacity even as the number of cycles increased. In particular, there was no significant difference between the charge capacity and discharge capacity within the same cycle. Note that the reason why there are no white circles in Figure 8B from the second cycle onward is that they almost completely overlap with the black circles. [Explanation of Symbols]

[0115] 1, 2, and 3 All-solid-state batteries 10 Positive electrode current collector layer 20 Cathode active material layer 30 Solid electrolyte layer 35 recess 40 Negative electrode current collector layer 50 Metallic Lithium Layer 60. Conductive layer

Claims

1. This all-solid-state battery utilizes the deposition-dissolution reaction of metallic lithium as the reaction at the negative electrode. The positive electrode current collector layer, positive electrode active material layer, solid electrolyte layer, and negative electrode current collector layer are stacked in this order. The solid electrolyte layer has a plurality of recesses, The recess is localized on the surface of the solid electrolyte layer facing the negative electrode current collector layer, and is spaced apart from the negative electrode current collector layer. When fully charged, metallic lithium is deposited not only in the recess but also below the recess and between the negative electrode current collector layer and the solid electrolyte layer. The plurality of recesses are spaced apart from each other. The aforementioned interval is 2 μm or more when viewed from the stacking direction of the all-solid-state battery. Characterized by, All-solid-state battery.

2. The all-solid-state battery according to claim 1, wherein the recess is larger than the solid electrolyte particles contained in the solid electrolyte layer.

3. The all-solid-state battery according to claim 1 or 2, wherein the recess is dome-shaped.

4. The all-solid-state battery according to any one of claims 1 to 3, wherein the maximum length of the recess in the stacking direction of the all-solid-state battery is 2 μm to 200 μm.

5. The all-solid-state battery according to any one of claims 1 to 4, wherein the maximum length of the recess in the planar direction of the all-solid-state battery is 2 μm to 200 μm.

6. The all-solid-state battery according to any one of claims 1 to 5, wherein the interval is 500 μm or less.

7. A conductive layer is provided between the solid electrolyte layer and the negative electrode current collector layer. The conductive layer is arranged along the solid electrolyte layer such that it is spaced apart from the negative electrode current collector layer in the portion along the recess, and in other portions is in electrical contact with the negative electrode current collector layer. All-solid-state battery according to any one of claims 1 to 6.

8. The all-solid-state battery according to claim 7, wherein the thickness of the conductive layer is 100 nm to 10 μm.

9. The all-solid-state battery according to claim 7 or 8, wherein the conductive layer is a layer of metal capable of forming an alloy with Li, or a layer of carbon.

10. The all-solid-state battery according to any one of claims 7 to 9, wherein the conductive layer contains Mg, Sn, In, or Au.

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