Solid-state battery and solid electrolyte

Abstract

To provide a solid-state battery that has a high charge-discharge efficiency.SOLUTION: The present disclosure provides a solid-state battery including: a positive electrode active material layer; a negative electrode active material layer; and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer. At least one of the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer contains a solid electrolyte. The solid electrolyte contains a Li element, an Al element, an M element (M is at least one kind of B, Ga, In, and Tl), and a halogen element, and contains the halogen element as a main component of an anion.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to solid-state batteries and solid electrolytes. [Background technology]

[0002] In recent years, the development of batteries has been actively pursued. For example, in the automotive industry, development of batteries for use in electric vehicles (BEVs), plug-in hybrid vehicles (PHEVs), and hybrid electric vehicles (HEVs) is underway. Furthermore, development of components and materials for use in these batteries is also underway.

[0003] For example, Patent Document 1 discloses a lithium ion conductor containing LiBI4 as a solid electrolyte used in a battery. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-120474 Summary of the Invention [Problem to be solved by the invention]

[0005] From the viewpoint of improving battery performance, good charge-discharge efficiency (Coulomb efficiency) is required. The present disclosure has been made in view of the above-mentioned circumstances, and has as its main object to provide a solid-state battery with good charge-discharge efficiency. [Means for solving the problem]

[0006] [1] A solid-state battery having a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, at least one of the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer contains a solid electrolyte; The solid electrolyte contains a Li element, an Al element, an M element (M is at least one of B, Ga, In, and Tl), and a halogen element, and the halogen element is contained as a main component of the anion.

[0007] [2] The solid state battery according to [1], wherein in the solid electrolyte, a proportion of the M element to the total of the Al element and the M element is 10% or more and 80% or less.

[0008] [3] The solid state battery according to [1] or [2], wherein the solid electrolyte contains an I element as the halogen element.

[0009] [4] The solid state battery according to any one of [1] to [3], wherein the negative electrode active material layer contains a Si-based negative electrode active material.

[0010] [5] A solid electrolyte for use in a solid-state battery, A solid electrolyte containing Li element, Al element, M element (M is at least one of B, Ga, In and Tl), and a halogen element, and containing the halogen element as a main component of an anion. [Effects of the Invention]

[0011] The present disclosure has an effect of providing a solid-state battery with good charge / discharge efficiency. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating a solid-state battery according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] The solid-state battery and solid electrolyte according to the present disclosure will be described in detail below.

[0014] A. Solid state battery FIG. 1 is a schematic cross-sectional view illustrating a solid-state battery according to the present disclosure. Note that FIG. 1 is a schematic illustration of the solid-state battery according to the present disclosure, and the size and shape of each component are appropriately exaggerated for ease of understanding. The solid-state battery 10 shown in FIG. 1 includes a positive electrode active material layer 1, a negative electrode active material layer 2, and a solid electrolyte layer 3 disposed between the positive electrode active material layer 1 and the negative electrode active material layer 2. The solid-state battery 10 also includes a positive electrode current collector 4 that collects electrons from the positive electrode active material layer 1 and a negative electrode current collector 5 that collects electrons from the negative electrode active material layer 2. In particular, in the solid-state battery 10, at least one of the positive electrode active material layer 1, the negative electrode active material layer 2, and the solid electrolyte layer 3 contains a solid electrolyte. The solid electrolyte contains Li, Al, M (where M is at least one of B, Ga, In, and Tl), and a halogen element, and the halogen element serves as a primary anion component.

[0015] According to the present disclosure, at least one of the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer contains a predetermined solid electrolyte, resulting in a solid battery with good charge / discharge efficiency.

[0016] LiAl halide salts such as LiAlI4 have been investigated as solid electrolytes for use in solid-state batteries. However, the present inventors have found that solid-state batteries using LiAl halide salts exhibit reduced charge-discharge efficiency (cycle characteristics). Although the details are unclear, it is believed that this is due to the reductive decomposition of the LiAl halide salts caused by repeated charge-discharge cycles of the battery. After extensive research, the present inventors have found that a solid-state battery with good charge-discharge efficiency can be obtained when a solid electrolyte in which a Group 13 element other than Al is added to a LiAl halide salt is used. Although the details are unclear, it is believed that the addition of a Group 13 element other than Al forms a stable reduction product on the surface of the solid electrolyte, suppressing the reductive decomposition of the entire solid electrolyte.

[0017] 1.Solid electrolyte The solid electrolyte of the present disclosure contains Li, Al, M (where M is at least one of B, Ga, In, and Tl), and a halogen element, and contains the halogen element as a main anion component. The solid electrolyte of the present disclosure corresponds to a so-called LiAl halide salt.

[0018] The total proportion of the Li element, Al element, halogen element, and M element to all elements contained in the solid electrolyte may be 100 mol% or less. The total proportion of the Li element, Al element, halogen element, and M element is, for example, 70 mol% or more, 80 mol% or more, or 90 mol% or more.

[0019] Examples of halogen elements include F, Cl, B, and I. The solid electrolyte may contain one type of halogen element, or may contain two or more types of halogen elements. Among these, the solid electrolyte preferably contains at least I element. The halogen element is contained as the main anion component. "Contained as the main anion component" means that the proportion of the halogen element to all anion components contained in the solid electrolyte is 50 mol % or more. The proportion of the halogen element to all anion components may be 100 mol % or less.

[0020] The M element is at least one of B, Ga, In, and Tl. The solid electrolyte may contain one type of M element, or may contain two or more types of M elements. Among these, it is preferable that the solid electrolyte contains at least Ga. Furthermore, in the solid electrolyte, the ratio (molar ratio) of the M element to the total of the Al element and the M element is, for example, 10% or more, or may be 20% or more, or may be 30% or more, or may be 40% or more. On the other hand, the ratio of the M element is, for example, 80% or less, or may be 60% or less, or may be 50% or less. If the ratio of the M element is too low, the effect of suppressing the reductive decomposition of the solid electrolyte may not be sufficiently obtained. If the ratio of the M element is too high, good ionic conductivity may not be obtained.

[0021] Here, it is preferable that the solid electrolyte in the present disclosure does not contain S element (sulfur element), because this results in a solid electrolyte with good water resistance.

[0022] The composition of the solid electrolyte is, for example, LiAl 1-a M a X4 (0.1≦a≦0.8) can be mentioned. M is the above-mentioned M element, and X is the above-mentioned halogen element. a can be 0.2 or more, 0.3 or more, or 0.4 or more. On the other hand, x can be 0.7 or less, 0.6 or less, or 0.5 or less. Here, the solid electrolyte represented by the above composition can be considered as a salt in which a part of Al in a LiAl halide salt is substituted with the M element.

[0023] The melting point of the solid electrolyte is, for example, 300°C or lower, and may be 200°C or lower, or 150°C or lower. On the other hand, the melting point is, for example, 10°C or higher, and may be 50°C or higher. The melting point can be determined, for example, by differential scanning calorimetry (DSC measurement). Here, a solid electrolyte having a melting point of 100°C or lower is also called a molten salt. Note that the solid electrolyte in the present disclosure may be in a molten state or a solid state during charge and discharge.

[0024] The ionic conductivity of the solid electrolyte at 25°C is not particularly limited, but a higher value is preferable. The ionic conductivity is, for example, 1.0 × 10 -6 S / cm or more, 1.0×10 -4 S / cm or less.

[0025] The solid electrolyte may have only one crystalline phase, or may have two or more crystalline phases. In the former case, the crystalline phase represented by the above-mentioned composition may be used. In the latter case, examples include the crystalline phase represented by the above-mentioned composition, a crystalline phase of a LiAl halide such as LiAlI4, and a crystalline phase of a LiM halide such as LiGaI4.

[0026] In addition, the solid electrolyte of the present disclosure is contained in at least one of the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer in the solid battery, and may be contained in any one, two, or three of the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer.

[0027] 2.Cathode active material layer The positive electrode active material layer contains at least a positive electrode active material.

[0028] The positive electrode active material may be, for example, an oxide active material. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and LiNi 0.8 Co 0.15 Al 0.05 Examples of the active material include rock salt layer type active materials such as O2, spinel type active materials such as LiMn2O4, and olivine type active materials such as LiFePO4. Sulfur (S) may also be used as the positive electrode active material.

[0029] The positive electrode active material is, for example, in the form of particles. 50 ) is, for example, 0.5 μm or more and 50 μm or less. 50) refers to the volume cumulative particle size measured by a laser diffraction / scattering particle size distribution analyzer. The proportion of the positive electrode active material in the positive electrode active material layer is, for example, 50% by weight or more and 80% by weight or less.

[0030] The positive electrode active material layer may contain at least one of an electrolyte, a conductive material, and a binder, as necessary. The positive electrode active material layer preferably contains the solid electrolyte described in "1. Solid Electrolyte" as the electrolyte. The positive electrode active material may also contain an electrolyte (another electrolyte) other than the above-mentioned solid electrolyte. The other electrolytes are described in "4. Solid Electrolyte Layer." The proportion of the solid electrolyte in the positive electrode active material layer is, for example, 30% by weight or more and 80% by weight or less.

[0031] Examples of the conductive material include carbon materials. Examples of the carbon material include particulate carbon materials such as acetylene black (AB) and ketjen black (KB), and fibrous carbon materials such as carbon fiber, carbon nanotubes (CNT), and carbon nanofibers (CNF). The proportion of the conductive material in the positive electrode active material layer is, for example, 0.01% by weight or more and 10% by weight or less.

[0032] The thickness of the positive electrode active material layer is not particularly limited, but is, for example, 0.1 μm or more and 1000 μm or less.

[0033] 3.Negative electrode active material layer The negative electrode active material layer contains at least a negative electrode active material.

[0034] Examples of negative electrode active materials include Si-based active materials. Si-based active materials are active materials containing Si element. Examples of Si-based active materials include simple Si, Si alloys, and Si oxides. The Si alloy preferably contains Si element as a main component. The proportion of Si element in the Si alloy is, for example, 50 mol% or more, or may be 70 mol% or more, or even 90 mol% or more. On the other hand, the proportion of Si element in the Si alloy is, for example, 99 mol% or less. Examples of Si alloys include Si-Al based alloys, Si-Sn based alloys, Si-In based alloys, Si-Ag based alloys, Si-Pb based alloys, Si-Sb based alloys, Si-Bi based alloys, Si-Mg based alloys, Si-Ca based alloys, Si-Ge based alloys, and Si-Pb based alloys. The Si alloy may be a binary alloy or a multi-component alloy of 3 or more components. Examples of Si oxides include SiO.

[0035] The Si-based active material may have a diamond-type crystalline phase, a clathrate I crystalline phase, or a clathrate II crystalline phase. In the clathrate I or II crystalline phase, multiple Si elements form a polyhedron (cage) containing pentagons or hexagons. This polyhedron has spaces inside that can encapsulate metal ions such as Li ions, thereby suppressing volumetric changes during charging and discharging. The Si-based active material may also have voids inside the primary particles. These voids can suppress volumetric changes in the active material and cracking of the negative electrode active material layer. The porosity is not particularly limited, but is, for example, 4% or more and 40% or less. The presence of voids in the primary particles and the porosity can be confirmed by observation with a scanning electron microscope (SEM).

[0036] The negative electrode active material layer may contain at least one of an electrolyte, a conductive material, and a binder, as needed. The conductive material and binder are the same as those described in "2. Positive electrode active material layer." The negative electrode active material layer preferably contains the solid electrolyte described in "1. Solid electrolyte" as the electrolyte. The negative electrode active material layer may also contain other electrolytes as the electrolyte. The proportion of the solid electrolyte and other electrolytes are the same as those described in "2. Positive electrode active material layer."

[0037] The thickness of the negative electrode active material layer is not particularly limited, but is, for example, 0.1 μm or more and 1000 μm or less.

[0038] 4.Solid electrolyte layer The solid electrolyte layer is a layer disposed between the positive electrode active material layer and the negative electrode active material layer, and contains at least a solid electrolyte. The solid electrolyte layer preferably contains the solid electrolyte described in "1. Solid Electrolyte."

[0039] The solid electrolyte layer may also contain other electrolytes, such as inorganic solid electrolytes such as sulfide solid electrolytes. The sulfide solid electrolyte preferably contains sulfur (S) as the main anion element.

[0040] The sulfide solid electrolyte preferably contains Li, X (X is at least one of P, Sn, Al, Zn, In, Ge, Si, Sb, Ga, and Bi), and S. The sulfide solid electrolyte may also contain a halogen element such as F, Cl, Br, or I. In the sulfide solid electrolyte, a portion of the S element may be substituted with O.

[0041] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-GeS2, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-P2S5-LiI-LiBr, 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. Z is Ge, Zn, or Ga.), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, and In.)

[0042] Other electrolytes include, for example, organic solid electrolytes such as gel electrolytes and electrolytic solutions, which may be any of materials conventionally known in the field of batteries.

[0043] The solid electrolyte layer may contain a binder as needed. The binder is the same as that described in "2. Positive electrode active material layer." The thickness of the solid electrolyte layer is not particularly limited, but is, for example, 0.1 μm or more and 1000 μm or less.

[0044] 5. Other configurations The solid-state battery according to the present disclosure preferably includes a positive electrode current collector that collects current from the positive electrode active material layer and a negative electrode current collector that collects current from the negative electrode active material layer. Examples of materials for the positive electrode current collector include stainless steel, aluminum, nickel, iron, titanium, and carbon. Examples of materials for the negative electrode current collector include stainless steel, copper, nickel, and carbon.

[0045] The solid-state battery according to the present disclosure may further include a restraining jig that applies a restraining pressure to the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer in the thickness direction. The restraining pressure is, for example, 0.1 MPa or more, or may be 1 MPa or more, or may be 5 MPa or more. On the other hand, the restraining pressure is, for example, 100 MPa or less, or may be 50 MPa or less, or may be 20 MPa or less.

[0046] 6. Solid state battery The type of solid-state battery in the present disclosure is not particularly limited, but is typically a lithium-ion battery. The solid-state battery in the present disclosure may be a semi-solid-state battery or an all-solid-state battery. Generally, a solid-state battery in which the entire electrolyte constituting the solid electrolyte layer is made of an inorganic solid electrolyte is referred to as an all-solid-state battery. The solid-state battery in the present disclosure may be a primary battery or a secondary battery, but a secondary battery is preferred. This is because it can be repeatedly charged and discharged, making it useful as, for example, an in-vehicle battery.

[0047] Examples of applications of solid-state batteries include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, they are preferably used as driving power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). Solid-state batteries may also be used as power sources for mobile objects other than vehicles (for example, railways, ships, and aircraft), and may also be used as power sources for electrical appliances such as information processing devices.

[0048] B. Solid electrolyte The present disclosure also provides a solid electrolyte for use in a solid-state battery, the solid electrolyte containing Li, Al, M (where M is at least one of B, Ga, In, and Tl), and a halogen element, with the halogen element being the main component of the anion. The solid-state battery and the solid electrolyte are the same as those described in "A. Solid-state battery."

[0049] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0050] [Example 1] (Preparation of solid electrolyte) A total of 10 g of LiI and AlI3 were weighed as raw materials, and 100 g of heptane was weighed. These were placed in a Fritsch ball mill (size: 500 ml, balls used: 5 mm ZrO2) and ball milled at 300 rpm for 20 hours. This yielded LiAlI4. Furthermore, LiI and GaCl3 were used as raw materials and ball milled in the same manner as above to yield LiGaI4. The resulting LiAlI4 and LiGaI4 were weighed out to a molar ratio of 90:10 and ball milled. This yielded LiAl 0.9 Ga 0.1 A solid electrolyte having the composition of I4 was obtained.

[0051] (Preparation of evaluation battery) Using the above-mentioned solid electrolyte, a solid battery as shown in FIG. 1 was fabricated as a battery for evaluation. The negative electrode active material layer used was a layer containing a Si-based negative electrode active material (simple Si), a binder (PVdF-based binder), the above-mentioned solid electrolyte, and a conductive material (VGCF). The positive electrode active material layer used was a layer containing a positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 A layer containing 02, a binder (PVdF-based binder), the above solid electrolyte, and a conductive material (VGCF) was used. The solid electrolyte layer was a layer containing a binder (butadiene rubber) and the above solid electrolyte. An Al foil was used as the positive electrode current collector, and a Ni foil was used as the negative electrode current collector. The test battery was constrained under a pressure of 6 N.

[0052] [Examples 2 to 4] LiAlI4 and LiGaI4 were mixed in molar ratios of 80:20, 60:40, and 20:80, respectively, to obtain solid electrolytes having the compositions shown in Table 1. A battery for evaluation was fabricated in the same manner as in Example 1, except that this solid electrolyte was used.

[0053] [Comparative Examples 1 to 2] A test battery was fabricated in the same manner as in Example 1, except that LiAlI4 or LiGaI4 was used as the solid electrolyte instead of the above solid electrolyte.

[0054] [Reference example] A battery for evaluation was fabricated in the same manner as in Example 1, except that a sulfide solid electrolyte (Li2S-P2S5-based sulfide solid electrolyte) was used as the solid electrolyte instead of the above solid electrolyte.

[0055] [evaluation] (Charge / discharge efficiency) Each test battery was subjected to 50 CCCV cycles at a charge / discharge rate of 1 / 3C at room temperature. The ratio of the discharge capacity after 5 cycles to the initial discharge capacity and the ratio of the discharge capacity after 50 cycles were calculated as the "charge / discharge efficiency." The results are shown in Table 1.

[0056] [Table 1]

[0057] As shown in Table 1, the solid-state batteries of Examples 1 to 3 exhibited better charge-discharge efficiency after 5 cycles than Comparative Example 1 and Comparative Example 2, and particularly showed good charge-discharge efficiency even after 50 cycles. This suggests that in the solid-state batteries of the present disclosure, decomposition of the solid electrolyte during battery charge-discharge is suppressed. Furthermore, sulfide solid electrolytes such as those used in the Reference Example are known to be less susceptible to oxidation-reduction reactions and to exhibit good ionic conductivity. On the other hand, sulfide solid electrolytes tend to have poor water resistance due to the sulfur content. In contrast, the solid-state batteries of Examples 1 to 3 were confirmed to exhibit charge-discharge efficiency equivalent to or better than that of the solid-state battery of the Reference Example, and their lack of sulfur element suggests good water resistance. [Explanation of symbols]

[0058] 1...Cathode active material layer 2...Negative electrode active material layer 3...Solid electrolyte layer 4...Positive electrode current collector 5...Negative electrode current collector 10...Solid state battery

Claims

1. A solid-state battery having a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, at least one of the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer contains a solid electrolyte; a solid-state battery, wherein the solid electrolyte contains a Li element, an Al element, an M element (M is at least one of B, Ga, In, and Tl), and a halogen element, and the halogen element is contained as a main component of an anion; , solid state battery.

2. 2. The solid-state battery according to claim 1, wherein in the solid electrolyte, a ratio of the M element to the total of the Al element and the M element is 10% or more and 80% or less.

3. The solid-state battery according to claim 1 , wherein the solid electrolyte contains an I element as the halogen element.

4. The solid state battery according to claim 1 , wherein the negative electrode active material layer contains a Si-based negative electrode active material.

5. A solid electrolyte for use in a solid-state battery, A solid electrolyte containing Li, Al, M (wherein M is at least one of B, Ga, In, and Tl), and a halogen element, wherein the halogen element is a main component of an anion.

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