All-solid-state batteries

Abstract

This disclosure aims to provide an anode-free all-solid-state battery with improved discharge capacity and cycle characteristics. Furthermore, this disclosure aims to provide an anode-free all-solid-state battery that can be driven with low confinement pressure. [Solution] The present disclosure provides an all-solid-state battery comprising a positive electrode including a positive electrode active material layer, a negative electrode current collector, and a solid electrolyte layer disposed between the positive electrode and the negative electrode current collector, wherein the all-solid-state battery does not contain a negative electrode active material, lithium ions are supplied from the positive electrode active material layer by charging, a lithium metal layer as a negative electrode active material is formed on the negative electrode current collector, and the solid electrolyte layer comprises a sulfide-based solid electrolyte containing a group 12 element and having an argyrodite-type crystal structure.

Description

[Technical Field]

[0001] This disclosure relates to an all-solid-state battery with an anode-free structure. [Background technology]

[0002] To improve safety, extend lifespan, and increase energy density, the development of all-solid-state batteries is progressing, in which the electrolyte of lithium-ion batteries is replaced with a solid electrolyte. Among the many solid electrolytes, Li 10 GeP2S 12 Sulfide-based solid electrolytes, such as those mentioned above, have advantages such as high ionic conductivity similar to that of liquid electrolytes, and are soft, making it easy to achieve adhesion with active materials. Therefore, the practical application of all-solid-state batteries using sulfide-based solid electrolytes is anticipated.

[0003] On the other hand, lithium metal is attracting attention as a negative electrode material for all-solid-state batteries because its low mass per unit volume and large theoretical capacity allow for a high mass energy density (Wh / kg). However, Li 10 GeP2S 12 Sulfide-based solid electrolytes, such as those mentioned above, have a problem in that they have low stability with respect to lithium metal, making them difficult to use with lithium metal anodes.

[0004] Furthermore, when lithium metal is used as the negative electrode of a battery, batteries are generally manufactured by attaching lithium foil to a flat current collector. However, lithium is an alkali metal and highly reactive, reacting explosively with water and also with oxygen in the atmosphere, making it difficult to manufacture and use in general environments. In particular, when lithium metal is exposed to the atmosphere, oxide films such as LiOH, Li2O, and Li2CO3 are formed as a result of oxidation. When a surface oxide film is present on the surface, it acts as an insulating film, reducing electrical conductivity and hindering the smooth movement of lithium ions, leading to increased electrical resistance.

[0005] To address this problem, Patent Documents 1 to 3 disclose an anodeless all-solid-state battery in which a small amount of seed metal capable of forming an alloy with lithium, such as Ag or Zn, is deposited on the negative electrode current collector. However, such anodeless all-solid-state batteries have the problem of high costs because they require additional processes for coating and sputtering the above-mentioned metal. Furthermore, anodeless all-solid-state batteries require high confinement pressure during battery operation to prevent the growth of lithium dendrites.

[0006] To solve the above problems, the inventors conducted multifaceted research and designed an anode-free all-solid-state battery that fundamentally blocks contact between lithium metal and the atmosphere during battery assembly. This battery allows a lithium metal layer to be formed on the negative electrode current collector by lithium ions transferred from the positive electrode active material during charging after the battery is assembled. Furthermore, by using a sulfide-based solid electrolyte containing polyvalent cations as the solid electrolyte used in the anode-free all-solid-state battery, the inventors developed an anode-free all-solid-state battery with excellent discharge capacity and cycle characteristics, and capable of being driven at low confinement pressure. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2020-191202 [Patent Document 2] Japanese Patent Publication No. 2020-167146 [Patent Document 3] Japanese Patent Publication No. 2022-504134 [Patent Document 4] Japanese Patent Publication No. 2022-529975 [Overview of the project] [Problems that the invention aims to solve]

[0008] This disclosure aims to provide an anode-free all-solid-state battery with improved discharge capacity and cycle characteristics.

[0009] Moreover, the present disclosure aims to provide an anode-free all-solid-state battery that can be driven at a low confinement pressure.

Means for Solving the Problems

[0010] To achieve the above object, the present disclosure provides an all-solid-state battery including a positive electrode including a positive electrode active material layer, a negative electrode current collector, and a solid electrolyte layer disposed between the positive electrode and the negative electrode current collector, wherein the all-solid-state battery does not contain a negative electrode active material, lithium ions are supplied from the positive electrode active material layer upon charging, and a lithium metal layer serving as a negative electrode active material is formed on the negative electrode current collector, and the solid electrolyte layer includes a sulfide-based solid electrolyte containing a Group 12 element and having an argyrodite-type crystal structure.

[0011] In one embodiment, the negative electrode current collector and the solid electrolyte layer may be in direct contact.

[0012] In one embodiment, the sulfide-based solid electrolyte is represented by the chemical formula Li 7-x-2y M y PS 6-x Ha x and in the chemical formula, M is one or more elements selected from Group 12 elements, Ha is one or more elements selected from halogen elements, and 0 < x < 2.5, 0 < y < 0.45 may be satisfied.

[0013] In one embodiment, M may be Zn.

[0014] In one embodiment, the reaction product of the negative electrode current collector and the sulfide-based solid electrolyte may not be included.

[0015] In one embodiment, the all-solid-state battery may be pressurized at a pressure of 0.3 MPa or less in the direction in which the positive electrode, the negative electrode current collector, and the solid electrolyte layer are stacked.

[0016] In one embodiment, the positive electrode active material layer may include the sulfide-based solid electrolyte.

[0017] In one embodiment, the D10 of the solid electrolyte may be 0.1 to 10 μm.

[0018] In one embodiment, the D50 of the solid electrolyte may be 0.1 to 50 μm.

[0019] In one embodiment, the D90 of the solid electrolyte may be 1 to 100 μm. [Effects of the Invention]

[0020] This disclosure can provide an anode-free all-solid-state battery with improved discharge capacity and cycle characteristics.

[0021] Furthermore, this disclosure can provide an anode-free all-solid-state battery that can be driven with low constraining pressure. [Brief explanation of the drawing]

[0022] [Figure 1] This is a schematic diagram of the all-solid-state battery in Example 1. [Figure 2] This is a schematic diagram of the all-solid-state battery in Comparative Example 1. [Figure 3] Comparative Example 2 is a schematic diagram of an all-solid-state battery. [Figure 4] This figure shows the X-ray diffraction (XRD) patterns of fine and coarse powders of solid electrolytes. [Figure 5] This graph shows the discharge capacity retention rate of the all-solid-state batteries in Example 1 and Comparative Examples 1 and 2. [Modes for carrying out the invention]

[0023] The following provides a more detailed explanation of this disclosure.

[0024] Terms and words used in this specification and in the claims should not be interpreted restrictively in their usual or dictionary sense, but rather in a sense and concept consistent with the technical idea of ​​this disclosure, in accordance with the principle that inventors can appropriately define the concepts of terms in order to best describe their invention.

[0025] In order to clearly illustrate the present invention, the drawings omit parts that are not relevant to the description, and similar parts throughout the specification are denoted by similar reference numerals. Furthermore, the sizes and relative sizes of the components shown in the drawings are independent of the actual scale and may be reduced or exaggerated for clarity of explanation.

[0026] In this specification, "Dn" refers to the particle size distribution, and means the particle size at the n% point of the cumulative particle number distribution by particle size. That is, D50 is the particle size (central particle size, average particle size) at the 50% point of the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution by particle size. Alternatively, the particle size distribution may be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500), and the difference in diffraction patterns due to particle size as the particles pass through the laser beam is measured to calculate the particle size distribution.

[0027] [All-solid battery] The all-solid-state battery of this disclosure includes a positive electrode containing a positive electrode active material layer, a negative electrode current collector, and a solid electrolyte layer disposed between the positive electrode and the negative electrode current collector. The all-solid-state battery of this disclosure does not contain a negative electrode active material; lithium ions are supplied from the positive electrode active material layer during charging, and a lithium metal layer as the negative electrode active material is formed on the negative electrode current collector. The all-solid-state battery of this disclosure includes a sulfide-based solid electrolyte layer containing a group 12 element and having an argyrodite-type crystal structure. The anode-free all-solid-state battery of this disclosure, having the above configuration, can improve discharge capacity and cycle characteristics. Furthermore, the anode-free all-solid-state battery of this disclosure, having the above configuration, can be driven at a low confinement pressure.

[0028] In this disclosure, "all-solid-state battery" refers to the state before the initial lithium metal deposition (initial charging) is performed on the negative electrode current collector (also called an all-solid-state battery precursor).

[0029] The all-solid-state battery may also be an all-solid-state lithium secondary battery.

[0030] Solid-state batteries are subjected to a confinement pressure during charging and discharging to prevent the growth of lithium dendrites, which can cause short circuits between the positive and negative electrodes. The confinement pressure can be applied in the direction in which the positive electrode, the negative electrode current collector, and the solid electrolyte layer positioned between the positive and negative electrode current collectors are stacked, that is, perpendicular to the plane direction of the negative electrode current collector. For example, the confinement pressure can be achieved by fixing the solid-state battery with fixtures from both the positive electrode side and the negative electrode current collector side.

[0031] High confinement pressure is typically applied to all-solid-state batteries to prevent the growth of lithium dendrites. However, all-solid-state batteries of the present disclosure that utilize a sulfide-based solid electrolyte containing divalent cations may require little to no confinement pressure.

[0032] The all-solid-state battery may be pressurized during charging and discharging at a pressure of 0.3 MPa or less, preferably 0.1 MPa or less, more preferably 0.05 MPa or less, and even more preferably 0.02 MPa or less. Thus, the anode-free all-solid-state battery of this disclosure can be driven at low constraint pressure.

[0033] In lithium secondary batteries, the negative electrode is typically formed on a negative electrode current collector. However, in the all-solid-state battery of this disclosure, the negative electrode current collector does not have metal particles or a coating layer on its surface. After assembling an anode-free battery structure using only the negative electrode current collector, lithium ions released from the positive electrode active material during charging form a lithium metal layer on the negative electrode current collector, acting as the negative electrode active material. As a result, a negative electrode with a negative electrode current collector / negative electrode active material layer configuration is formed, achieving the configuration of a normal lithium secondary battery.

[0034] In other words, the term "anode-free battery" in this disclosure is a concept that includes all batteries in which a negative electrode is not formed on the negative electrode current collector when initially assembled, and in which a negative electrode is formed on the negative electrode current collector as it is used. However, this does not exclude all solid-state batteries in this disclosure from having metal particles or a coating layer on the surface of the negative electrode current collector when initially assembled.

[0035] Furthermore, in the negative electrode of this disclosure, the form of lithium metal formed as negative electrode active material on the negative electrode current collector includes both a form in which the lithium metal is formed in layers and a structure in which the lithium metal is not formed in layers (for example, a structure in which the lithium metal is aggregated in a granular form).

[0036] In the following description, this disclosure will be based on the morphology of lithium metal layers in which lithium metal is formed in layers. However, it is clear that this description does not exclude structures in which lithium metal is not formed in layers.

[0037] <Solid electrolyte layer> The solid electrolyte layer contains a solid electrolyte. In an all-solid-state lithium secondary battery, the solid electrolyte layer can serve as an insulator and as an ion-conductive channel.

[0038] The solid electrolyte layer may have a thickness of about 50 μm or less, preferably about 15 μm to 50 μm. The thickness can have an appropriate value considering the ion conductivity, physical strength, energy density of the applied battery, etc. within the above-mentioned range. For example, in terms of ion conductivity and energy density, the thickness can be 10 μm or more, 20 μm or more, or 30 μm or more. On the other hand, in terms of physical strength, the thickness can be 50 μm or less, 45 μm or less, or 40 μm or less. Also, the solid electrolyte layer has a tensile strength of about 100 kgf / cm 2 to about 2,000 kgf / cm 2 and can have a porosity of 15 vol% or less, or about 10 vol% or less. Thus, the solid electrolyte layer according to the present disclosure can have high mechanical strength despite being a thin film.

[0039] (Solid electrolyte) The solid electrolyte may contain one or more of a sulfide-based solid electrolyte, an oxide-based solid electrolyte, and a polymer-based solid electrolyte. Preferably, the solid electrolyte contained in the all-solid-state battery of the present disclosure is a sulfide-based solid electrolyte. The solid electrolyte may be contained in the positive electrode active material layer or may be contained in the solid electrolyte layer as a separator.

[0040] The average particle size of the solid electrolyte can be controlled according to the application. By controlling the average particle size of the solid electrolyte, the ion conductivity can be improved.

[0041] The average particle size of the solid electrolyte can be controlled by changing conditions such as the rotation speed and time of a ball mill device. Thereby, solid electrolyte coarse powder with a relatively large average particle size and solid electrolyte fine powder with a relatively small average particle size can be produced.

[0042] The average particle size (D50) of the solid electrolyte is 0.1 to 50 μm, D10 is 0.1 to 10 μm, and D90 is 1 to 100 μm. The average particle size (D50) of the solid electrolyte coarse powder may be larger than the average particle size of the solid electrolyte fine powder. The average particle size of the solid electrolyte coarse powder is 5 to 50 μm, preferably 8 to 30 μm, and more preferably 10 to 20 μm. The average particle size of the solid electrolyte fine powder is 0.1 to 10 μm, preferably 0.5 to 5 μm, more preferably 1 to 3 μm, and even more preferably 1.5 to 2 μm.

[0043] The D10 of the solid electrolyte coarse powder is 0.1 to 10 μm, preferably 3 to 8 μm, and more preferably 4.5 to 8 μm. The D90 of the solid electrolyte coarse powder is 30 to 100 μm, preferably 40 to 90 μm, more preferably 50 to 80 μm, and even more preferably 56 to 70 μm.

[0044] The D10 of the solid electrolyte fine powder is 0.1 to 5 μm, preferably 0.2 to 3 μm, and more preferably 0.5 to 2 μm. The D90 of the solid electrolyte fine powder is 1 to 20 μm, preferably 3 to 15 μm, and more preferably 5 to 15 μm.

[0045] The average particle size of the sulfide-based solid electrolyte contained in the solid electrolyte layer may be larger than the average particle size of the sulfide-based solid electrolyte contained in the positive electrode active material layer. Coarse solid electrolyte powder exhibits high ionic conductivity when used in the solid electrolyte layer because it has a large average particle size and few grain boundaries per unit volume. Fine solid electrolyte powder, when used in the positive electrode active material layer, can enter the gaps between positive electrode active material particles, providing lithium ion conduction pathways to the positive electrode active material. Therefore, by making the average particle size of the sulfide-based solid electrolyte contained in the solid electrolyte layer larger than that of the sulfide-based solid electrolyte contained in the positive electrode active material layer, the discharge capacity and cycle characteristics of the all-solid-state battery can be improved.

[0046] The sulfide-based solid electrolyte is not particularly limited as long as it contains sulfur (S), and any known sulfide-based solid electrolyte can be used.

[0047] Sulfide-based solid electrolytes may have a crystalline structure. Sulfide-based solid electrolytes having a crystalline structure can promote the conduction of lithium ions and have high lithium ion conductivity.

[0048] Sulfide-based solid electrolytes may have argyrodite, nassycon, perovskite, garnet, or LGPS crystal structures. Preferably, sulfide-based solid electrolytes have an argyrodite crystal structure. Sulfide-based solid electrolytes having an argyrodite crystal structure have high stability with respect to lithium metal, making it possible to use lithium metal with a high mass energy density as a negative electrode material.

[0049] The sulfide-based solid electrolyte may be in the form of amorphous, glass, or glass-ceramic material.

[0050] Sulfide-based solid electrolytes are those that have the ionic conductivity of metals belonging to Group 1 or Group 2 of the periodic table, and may include Li-PS-based glasses and Li-PS-based glass ceramics. Non-restrictive examples of such sulfide-based solid electrolytes include Li2S-P2S5, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, and Li2S-GeS2-ZnS, and may include one or more of these. However, they are not particularly limited to these.

[0051] Sulfide-based solid electrolytes can include a crystalline phase and an amorphous phase. The sulfide-based solid electrolyte can include a crystalline phase having an argyrodite-type crystal structure (also referred to herein as an argyrodite phase) and other phases (also referred to herein as impurity phases or unknown phases). The argyrodite-type crystal structure is preferably cubic. The other phases may be crystalline or amorphous. The other phases, regardless of whether they are crystalline or amorphous, can include Li2S phase, P2S5 phase, LiCl phase, LiBr phase, Li3PS4 phase, ZnS phase, CdS phase, HgS phase, etc. Preferably, the sulfide-based solid electrolyte does not contain or substantially does not contain impurity phases other than the argyrodite phase. That is, preferably, the sulfide-based solid electrolyte may consist only of the argyrodite phase. When the sulfide-based solid electrolyte does not contain or substantially does not contain impurity phases, lithium ion conduction is less likely to be inhibited, so the sulfide-based solid electrolyte can have a high lithium ion conductivity.

[0052] The proportion of the crystalline phase contained in the sulfide-based solid electrolyte can be evaluated quantitatively or semi-quantitatively from the XRD pattern. As one method, the proportion of the crystalline phase can be evaluated by comparing the peak intensities (height or area) of the XRD pattern.

[0053] The sulfide-based solid electrolyte has the chemical formula Li 7-x-2y M y PS 6-x Ha x and can be represented by. In the chemical formula, M is one or more elements selected from Group 12 elements, Ha is one or more elements selected from halogen elements, and 0 < x < 2.5, 0 < y < 0.45 can be satisfied. The lattice volume of the sulfide-based solid electrolyte is 940 Å 3 or more and 980 Å 3The following is possible. Such sulfide-based solid electrolytes can have high lithium-ion conductivity. By using a sulfide-based solid electrolyte with high lithium-ion conductivity in an anode-free all-solid-state battery, the discharge capacity and cycle characteristics of the all-solid-state battery can be improved. Furthermore, since the growth of lithium dendrites on the negative electrode current collector is prevented by the sulfide-based solid electrolyte with high lithium-ion conductivity, the anode-free all-solid-state battery of this disclosure can be driven at low confinement pressure.

[0054] A sulfide-based solid electrolyte according to one embodiment of the present disclosure is Li 7-x PS 6-x Ha x In this material, some of the lithium is replaced by a Group 12 element M that can become a divalent cation. The Group 12 element M that replaces lithium may be one or more selected from the group consisting of zinc (Zn), cadmium (Cd), and mercury (Hg). The ionic radius (6-coordinate) of lithium (Li) is 76 pm, while the ionic radii (6-coordinate) of zinc (Zn), cadmium (Cd), and mercury (Hg) are 74 pm, 95 pm, and 102 pm, respectively. Based on the valence of the elements, two lithium atoms may be replaced by one Group 12 element M. Substitution by a Group 12 element M can create lithium site vacancies, potentially improving lithium ion conductivity. Furthermore, substitution by a Group 12 element M can alter the lattice constant and lattice volume of the sulfide-based solid electrolyte, resulting in a crystal structure suitable for lithium ion conduction.

[0055] Furthermore, the group 12 element M, which can become a divalent cation, is Li 7-x PS 6-x Ha x A sulfide-based solid electrolyte according to one embodiment of the present disclosure can be formed by penetrating into the crystal lattice of Li. The Group 12 element M penetrating into the crystal lattice may be one or more selected from the group consisting of zinc (Zn) and cadmium (Cd). Zinc (Zn) and cadmium (Cd) may be used individually or in combination. Preferably, the Group 12 element M is zinc (Zn) and / or cadmium (Cd), and particularly preferably zinc (Zn). 7-xPS 6-x Ha x When the Group 12 element M penetrates into the crystal lattice of Ha, the lattice constant and lattice volume of the sulfide-based solid electrolyte change, and it may become possible to have a crystal structure suitable for lithium ion conduction. A sulfide-based solid electrolyte containing zinc (Zn) as the Group 12 element M has a high lithium ion conductivity. By using such a sulfide-based solid electrolyte in an anode-free all-solid-state battery, the discharge capacity and cycle characteristics of the all-solid-state battery can be improved. Further, by using such a sulfide-based solid electrolyte, the growth of lithium dendrites on the negative electrode current collector is prevented, and thus the anode-free all-solid-state battery of the present disclosure can be driven at a low constraint pressure.

[0056] When the Group 12 element M is zinc (Zn) and / or cadmium (Cd), the sulfide-based solid electrolyte can have a high crystallinity, and therefore, the sulfide-based solid electrolyte can have a high ion conductivity. This is considered to be because the ionic radius of lithium (Li) is 76 pm, and the ionic radii of zinc (Zn) and cadmium (Cd) are 74 pm and 95 pm, respectively, and the alditolite-type crystal structure is likely to be maintained even after the substitution of lithium sites by the Group 12 element M.

[0057] Chemical formula Li 7-x-2y M y PS 6-x Ha x The addition amount y of the Group 12 element M in Ha satisfies 0 < y < 0.45, preferably, y satisfies 0 < y < 0.25, more preferably, 0 < y < 0.2, even more preferably, 0 < y < 0.075, and most preferably, 0.0125 ≤ y ≤ 0.05. When y satisfies the above range, the sulfide-based solid electrolyte can have a high ion conductivity. When y is 0, no change in the crystal structure due to the substitution of the Group 12 element M is obtained, and the ion conductivity may be low. When y is 0.45 or more, the alditolite-type crystal structure of the sulfide-based solid electrolyte may not be maintained, and the ion conductivity may decrease. Also, the impurity phase that inhibits lithium ion conduction in the sulfide-based solid electrolyte increases, and the ion conductivity may decrease.

[0058] Chemical formula Li 7-x-2y M y PS 6-x Ha x The halogen (Ha) in [Li2MSiPS3O2]1-x[Li2MSiPS3Ha2]x is one or more elements selected from halogen elements. Preferably, the halogen (Ha) contains bromine (Br). More preferably, the halogen (Ha) contains chlorine (Cl) and bromine (Br). When sulfur (S) is a divalent anion, it has a stronger ability to attract lithium ions compared to monovalent halogen and can greatly inhibit the movement of lithium ions. By containing bromine (Br), the occupancy of sulfur (S) at specific sites in the argyrodite-type crystal structure decreases, the halogen occupancy at these sites increases, and the lithium ion mobility around the bromine (Br) sites can become active. As a result, the lithium ion conductivity of the sulfide-based solid electrolyte can be improved. Also, bromine (Br) can combine with Li in the sulfide-based solid electrolyte to form lithium bromide (LiBr), which is a water-absorbing substance. Lithium bromide (LiBr) can adsorb moisture that can reduce the lithium ion conductivity and improve the lithium ion conductivity of the sulfide-based solid electrolyte.

[0059] Chemical formula Li 7-x-2y M y PS 6-x Ha x The ratio x of the halogen (Ha) in [Li2MSiPS3O2]1-x[Li2MSiPS3Ha2]x satisfies 0 < x < 2.5, preferably satisfies 1.0 < x < 2.0, more preferably satisfies 1.3 ≤ x ≤ 2.0, and even more preferably satisfies 1.3 ≤ x ≤ 1.8. When x satisfies the above range, the argyrodite-type crystal structure is stabilized and the sulfide-based solid electrolyte can have high ion conductivity.

[0060] It should be noted that the formula [Li2MSiPS3O2]1-x[Li2MSiPS3Ha2]x is added for better understanding of the context in the translation of relevant content. If this is not allowed, please adjust according to the actual requirements.The ionic conductivity of sulfide-based solid electrolytes can be influenced by their crystallinity. Crystallinity can be evaluated from the XRD pattern. When other phases besides the argyrodite crystalline phase (such as crystalline or amorphous phases like Li2S, P2S5, LiCl, LiBr, Li3PS4, ZnS, CdS, and HgS) are not observed or are hardly observed in the XRD pattern, sulfide-based solid electrolytes can have high ionic conductivity.

[0061] The lattice volume of sulfide-based solid electrolytes can change due to the substitution of lithium sites by group 12 elements (M). While not strictly theoretical, it is thought that the group 12 elements M exhibit divalent cationic properties, which strengthens their interaction with other anions present in the sulfide-based solid electrolyte, thus changing the lattice volume—that is, increasing or decreasing it. Such a change in lattice volume leads to a crystal structure suitable for lithium ion conduction, allowing sulfide-based solid electrolytes to have high ionic conductivity.

[0062] The lattice volume of sulfide-based solid electrolytes is 940 Å. 3 The above is 980 Å. 3 The following, preferably 950 Å 3 The above is 970 Å. 3 The following, and more preferably 954 Å 3 The above 966 Å 3 The following applies: The lattice constant and lattice volume can be evaluated from the XRD pattern. The lattice volume of a sulfide-based solid electrolyte can change depending on the firing temperature, even with the same composition. When the lattice volume satisfies the above range, lithium ion conduction in the sulfide-based solid electrolyte is promoted, and the sulfide-based solid electrolyte can have high ionic conductivity.

[0063] The ionic conductivity of a sulfide-based solid electrolyte (also referred to herein as "lithium ion conductivity") refers to the ionic conductivity at room temperature (25°C, 298K) and atmospheric pressure (1 atm), unless otherwise specified. When a sulfide-based solid electrolyte is used in an all-solid-state battery, it is practically desirable for the ionic conductivity to be 4 mS / cm or higher. The ionic conductivity of a sulfide-based solid electrolyte according to one embodiment of this disclosure is 1.5 mS / cm or higher, preferably 4 mS / cm or higher, more preferably 8 mS / cm or higher, even more preferably 10.8 mS / cm or higher, and most preferably 12 mS / cm or higher.

[0064] A sulfide-based solid electrolyte according to one embodiment of the present disclosure may be obtained by a manufacturing method comprising the steps of mixing a lithium source, a group 12 element source, a phosphorus source, a sulfur source, and a halogen source to obtain a mixture, and calcining the mixture at a temperature of 250°C to 600°C. The calcination of the mixture may be carried out under an inert atmosphere such as argon gas and nitrogen gas.

[0065] The lithium source, Group 12 element source, phosphorus source, sulfur source, and halogen source may be compounds such as sulfides, oxides, and nitrides. Lithium sulfide (Li2S) can be used as the lithium source, diphosphorus pentasulfide (P2S5) as the phosphorus source, and lithium halides (LiHa) such as lithium chloride (LiCl) and lithium bromide (LiBr) as the halogen source. For example, a sulfide can be used as the Group 12 element source. Alternatively, sulfur can be supplied from another element source. That is, one or more of the lithium source, Group 12 element source, phosphorus source, and halogen source may also serve as the sulfur source.

[0066] The firing temperature for sulfide-based solid electrolytes having an argyrodite crystal structure is preferably 350°C to 550°C, more preferably 400°C to 500°C, and even more preferably 410°C to 470°C. When the firing temperature is within the above range, the formation of the argyrodite crystal structure is promoted, and the sulfide-based solid electrolyte can have a high degree of crystallinity. This makes it possible to obtain a sulfide-based solid electrolyte with high ionic conductivity.

[0067] The solid electrolyte layer may further include a binder for the solid electrolyte layer. The binder for the solid electrolyte layer may be introduced for bonding between solid electrolytes and for bonding the solid electrolyte layer to battery elements (e.g., positive electrode, negative electrode, etc.) stacked on both sides of it.

[0068] The material for the binder in the solid electrolyte layer is not particularly limited and can be appropriately selected from the range of components used as binders for solid electrolytes in all-solid-state lithium secondary batteries. Specifically, the binder in the solid electrolyte layer may include at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinyl alcohol (PVA), carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), styrene-butadiene rubber (SBR), styrene-butadiene styrene block copolymer (SBS), nitrile butadiene rubber (NBR), fluororubber, and acrylic binders.

[0069] The solid electrolyte layer does not necessarily have to contain a binder for the solid electrolyte layer. When the solid electrolyte layer does not contain a binder for the solid electrolyte layer, the content of the solid electrolyte contained in the solid electrolyte layer can be increased, and the ionic conductivity of the solid electrolyte layer can be improved.

[0070] <Negative electrode> The negative electrode does not contain negative electrode active material before the initial lithium metal deposition (initial charging) is performed.

[0071] During charging, lithium ions are supplied from the positive electrode active material contained in the positive electrode active material layer, and a lithium metal layer, acting as the negative electrode active material, is formed on the negative electrode current collector. Specifically, when an all-solid-state battery having an anode-free battery structure is charged by applying a voltage above a certain level, lithium ions are detached from the positive electrode active material in the positive electrode. The detached lithium ions pass through the solid electrolyte layer and move to the negative electrode current collector, forming a lithium metal layer consisting purely of lithium on the negative electrode current collector, thus forming the negative electrode. This method of forming a lithium metal layer by charging has the advantage of forming a thin film layer and making it very easy to adjust the interface properties, compared to conventional negative electrodes where a lithium metal layer is sputtered onto the negative electrode current collector or where lithium foil and the negative electrode current collector are laminated.

[0072] In particular, because the anode-free battery structure prevents any exposure of lithium metal to the atmosphere during the battery assembly process, it is possible to fundamentally eliminate problems such as the formation of an oxide film on the surface due to the high reactivity of lithium itself, and the resulting reduction in the lifespan of lithium secondary batteries.

[0073] The formed lithium metal layer creates a uniform, continuous or discontinuous layer on the negative electrode current collector. For example, if the negative electrode current collector is in foil form, it may have a continuous thin film form, and if the negative electrode current collector has a three-dimensional porous structure, the lithium metal layer may be formed discontinuously. That is, a discontinuous layer means that within a specific region there are areas where the lithium metal layer is present and areas where it is not, but the areas where the lithium metal layer is absent are distributed in an island-like manner, isolated, discontinuous, or separated from the areas where the lithium compound is present, meaning that the areas where the lithium metal layer is present are distributed without continuity.

[0074] The lithium metal layer formed through this charging and discharging process has a thickness of at least 50 nm and 100 μm, preferably 1 μm and 50 μm, in order to function as a negative electrode. If the thickness is less than the above range, the battery's charge and discharge efficiency decreases sharply. Conversely, if it exceeds the above range, while the lifespan characteristics may be stable, there is a problem of a lower battery energy density.

[0075] In particular, the lithium metal layer shown in this disclosure is manufactured as an anode-free battery without lithium metal during battery assembly. Compared to conventional lithium secondary batteries assembled using lithium foil, this method prevents the formation of little to no oxide layer on the lithium metal layer during the assembly process. This prevents the degradation of battery life caused by the oxide layer.

[0076] In this disclosure, the charging range for forming the lithium metal layer is a voltage range of 2.5V to 4.5V, with a charge / discharge rate range of 0.01C to 0.2C for one charge cycle. If charging is performed below the above range, it becomes difficult to form the lithium metal layer, and conversely, if it exceeds the above range, the battery may be damaged, leading to over-discharge, after which charging and discharging may not occur properly.

[0077] The negative electrode may include a negative electrode current collector. The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the all-solid-state battery and is conductive. As the negative electrode current collector, iron, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., can be used.

[0078] In particular, it is preferable that the negative electrode current collector of this disclosure does not react with the sulfide-based solid electrolyte. In other words, it is preferable that the all-solid-state battery of this disclosure does not contain reaction products between the negative electrode current collector and the sulfide-based solid electrolyte. The absence of reaction products between the negative electrode current collector and the sulfide-based solid electrolyte can be confirmed, for example, by observing a cross-section of the all-solid-state battery with a scanning electron microscope (SEM) or transmission electron microscope (TEM). The absence of the above reaction products may also be confirmed using XRD measurement. Before the initial lithium metal deposition (initial charging), the negative electrode current collector and the sulfide-based solid electrolyte may be in direct contact. Also, after the battery is discharged, the lithium metal as the negative electrode active material moves to the positive electrode side, and there is little or no negative electrode active material on the negative electrode current collector. If a side reaction occurs between the negative electrode current collector and the sulfide-based solid electrolyte, by-products such as hydrogen sulfide may be generated, which may adversely affect the performance of the all-solid-state battery. To prevent such side reactions, the negative electrode current collector preferably has high stability with respect to the sulfide-based solid electrolyte. Since the negative electrode current collector does not react with the sulfide-based solid electrolyte, the anode-free all-solid-state battery of this disclosure can improve discharge capacity and cycle characteristics. Furthermore, since the negative electrode current collector does not react with the sulfide-based solid electrolyte and does not generate side reaction products, the anode-free all-solid-state battery of this disclosure can be driven at a low confinement pressure.

[0079] The negative electrode current collector may have a thickness of 3 μm or more and 500 μm or less.

[0080] The negative electrode current collector may take various forms, such as films, sheets, foils, nets, porous materials, foams, or nonwoven fabrics, all of which have fine irregularities formed on their surface.

[0081] The negative electrode current collector may be in direct contact with the solid electrolyte layer. The negative electrode current collector may be in direct contact with the sulfide-based solid electrolyte contained in the solid electrolyte layer. Direct contact between the negative electrode current collector and the solid electrolyte layer, without an intermediate layer, can reduce the thickness of the all-solid-state battery and improve its volumetric energy density. This increases the amount of active material that can be installed and prevents the growth of lithium dendrites, thereby improving the discharge capacity and cycle characteristics of the all-solid-state battery. Furthermore, the all-solid-state battery can be driven with low confinement pressure.

[0082] The negative electrode current collector does not have to be in direct contact with the solid electrolyte layer. An intermediate layer may be formed between the negative electrode current collector and the solid electrolyte layer. When an intermediate layer is formed, the lithium metal layer is formed on the negative electrode current collector by lithium ions supplied from the positive electrode active material layer passing through the intermediate layer. In other words, during charging, the lithium metal layer is formed between the negative electrode current collector and the intermediate layer.

[0083] Here, the intermediate layer can be any material that allows lithium ions to be smoothly transported, and may be a lithium-ion conductive polymer and / or a material used for inorganic solid electrolytes, and may further contain a lithium salt if necessary.

[0084] The intermediate layer may contain a metal that forms an alloy with lithium. Examples of metals that form an alloy with lithium include germanium, tin, zinc, indium, gallium, antimony, lead, gold, silver, aluminum, platinum, and palladium.

[0085] The lithium-ion conductive polymer may be one selected from the group consisting of polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), or a mixture of two or more of these, but is not limited thereto. Any polymer having lithium-ion conductivity can be used without restriction.

[0086] When using lithium-ion conductive polymers, additional substances used for this purpose may be included to further increase lithium-ion conductivity.

[0087] For example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 The material may further contain lithium salts such as LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiSCN, LiC(CF3SO2)3, (CF3SO2)2NLi, (FSO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate, and lithium imide.

[0088] The inorganic solid electrolyte is a ceramic-based material, and may be crystalline or amorphous. Thio-LISICON(Li 3.25 Ge 0.25 P 0.75 S4), Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, Li3PS4, Li7P3S 11 , Li2O-B2O3, Li2O-B2O3-P2O5, Li2O-V2O5-SiO2, Li2O-B2O3, Li3PO4, Li2O-Li2WO4-B2O3, LiPON, LiBON, Li2O-SiO2, LiI, Li3N, Li5La3Ta2O 12 Li7La3Zr2O 12 Li6BaLa2Ta2O 12 Li3PO (4-3 / 2w) Nw(where w < 1), Li 3.6 Si 0.6 P 0.4 Inorganic solid electrolytes such as O4 are possible. When using an inorganic solid electrolyte, lithium salts may be further included if necessary.

[0089] Inorganic solid electrolytes can be mixed with known substances such as binders and applied in the form of thick films through slurry coating. If necessary, they can also be applied in the form of thin films through deposition processes such as sputtering. The slurry coating method used can be appropriately selected based on the coating method, drying method, and solvent content mentioned for lithium-ion conductive polymers.

[0090] The aforementioned intermediate layer containing a lithium-ion conductive polymer and / or an inorganic solid electrolyte can increase the lithium-ion transfer rate, thereby facilitating the formation of the lithium metal layer, while simultaneously suppressing or preventing the formation of lithium dendrites that occur when the lithium metal layer / negative electrode current collector is used as the negative electrode.

[0091] To ensure the above effect, it is necessary to limit the thickness of the intermediate layer.

[0092] A lower intermediate layer thickness is advantageous for the battery's output characteristics. However, if it is not formed to a certain thickness or greater, it is not possible to suppress the side reactions between lithium and electrolyte that subsequently form on the negative electrode current collector, and furthermore, it is not possible to effectively block dendrite growth. In this disclosure, the intermediate layer thickness is preferably 10 nm or more and 50 μm or less. If the intermediate layer thickness is less than the above range, it is not possible to effectively suppress the side reactions and exothermic reactions between lithium and electrolyte that increase under conditions such as overcharging or high-temperature storage, and thus safety improvements cannot be achieved. If it exceeds the above range, the thickness of the all-solid-state battery increases, and the volumetric energy density of the all-solid-state battery may decrease.

[0093] <Positive electrode> The positive electrode may include a positive electrode active material layer and a positive electrode current collector.

[0094] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes to the positive electrode or battery and has high conductivity. For example, it may include at least one selected from the group consisting of iron, stainless steel, copper, aluminum, nickel, titanium, and calcined carbon, and specifically may include aluminum. The positive electrode current collector may include a carbon-based conductive material and a binder, and may further include a primer layer coated on the surface of the positive electrode current collector. This can greatly improve the bonding force and electrical conductivity between the positive electrode active material layer and the current collector.

[0095] The positive electrode active material layer can be arranged on at least one surface of the positive electrode current collector. Specifically, the positive electrode active material layer can be arranged on one or both surfaces of the positive electrode current collector.

[0096] The positive electrode active material layer may contain the positive electrode active material. In the anode-free battery structure of this disclosure, the lithium source for forming the lithium metal layer is the positive electrode active material, and the positive electrode active material contains lithium. That is, when the lithium ions of the positive electrode active material are charged within a specific voltage range, the lithium ions are desorbed to form a lithium metal layer on the negative electrode current collector.

[0097] The positive electrode active material can be any material that is suitable for use as a positive electrode active material in a lithium-ion secondary battery. Positive electrode active materials include layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides including O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMn2O4, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-x M xNi-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, P, Mg, Ca, Zr, Ti, Ru, Nb, W, B, Si, Na, K, Mo, V or Ga, and x = 0.01 to 0.3); chemical formula LiMn 1-x M x Lithium manganese composite oxide represented by O2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiNi x Mn 2-x Lithium manganese composite oxide with a spinel structure represented by O4; LiMn2O4 in which part of Li in the chemical formula is substituted with alkaline earth metal ions; disulfide compound; LiMn x Fe 1-x PO4 (0 ≦ x ≦ 0.9); It can contain Fe2(MoO4)3, etc. However, it is not limited to these only.

[0098] The positive electrode active material can contain Li 1+x M y O 2+z where M can be at least one element selected from the group consisting of Ni, Co, Mn, Fe, P, Al, Mg, Ca, Zr, Zn, Ti, Ru, Nb, W, B, Si, Na, K, Mo, and V, and 0 ≦ x ≦ 5, 0 < y ≦ 2, 0 ≦ z ≦ 2. Specifically, the above Li 1+x M y O 2+z is LiCoO2, LiNiO2, LiMnO2, Li[Ni 0.5 C o0.3 Mn 0.2 O2, Li[Ni 0.6 Co 0.2 Mn 0.2 O2, Li[Ni 0.7 Co 0.1 Mn 0.2 O2, Li[Ni 0.8 Co 0.1 Mn 0.1 O2, Li[Ni 0.9 Co 0.05 Mn 0.05 O2, LiMn2O4, LiFePO4、0.5 Li2MnO3·0.5Li[Mn 0.4 Ni 0.3 Co 0.3 O2 can include at least any one selected from the group consisting of. Preferably, the above Li 1+x M y O 2+z is the above Li[Ni 0.6 Co 0.2 Mn 0.2 O2, Li[Ni 0.7 Co 0.1 Mn 0.2 O2, Li[Ni 0.8 Co 0.1 Mn 0.1 O2, Li[Ni 0.9 Co 0.05 Mn 0.05 O2. Since the positive electrode active material contains Li 1+x M y O 2+z , lithium can be sufficiently supplied to the negative electrode, and Li 1+x M y O 2+z does not cause a decrease in the overall performance of the battery and shows electrochemical activity after the first cycle, so the loss of battery capacity due to the irreversible capacity of the negative electrode can be eliminated. The above Li 1+x M y O 2+z can be in the form of secondary particles formed by binding or granulating primary particles, and in contrast, it can also be in the form of single particles.

[0099] The positive electrode active material can be contained in the positive electrode active material layer at 50% to 95% by weight, specifically 60% to 90% by weight.

[0100] Also, the average particle size of the positive electrode active material is 1 μm or more and 30 μm or less. According to one embodiment, it is 8 μm or more and 12 μm or less. When the average particle size of the positive electrode active material is within the above range, the battery has excellent capacity characteristics.

[0101] The positive electrode active material layer can further include a positive electrode conductive material.

[0102] The positive electrode conductive material is not particularly limited as long as it does not cause a chemical change in the positive electrode or battery and is conductive. For example, the positive electrode conductive material may include one or more mixtures of conductive materials selected from graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; graphene; conductive fibers such as carbon nanofibers and carbon nanotubes; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0103] The positive electrode conductive material can be included in the positive electrode active material layer at a concentration of 1% to 30% by weight.

[0104] The positive electrode active material layer may further contain a positive electrode binder.

[0105] The positive electrode binder is not particularly limited as long as it contains components that are useful for bonding the positive electrode active material, positive electrode conductive material, etc., and for bonding to the current collector. Specifically, it may include at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinyl alcohol (PVA), carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, polyvinylpyrrolidone, polytetrafluoroethylene (PTFE), polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), styrene-butadiene rubber (SBR), and fluororubber.

[0106] The positive electrode binder can be contained within the positive electrode active material layer in an amount of 1% to 30% by weight.

[0107] The positive electrode active material layer may contain one or more additives as needed, such as oxidation stabilizers, reduction stabilizers, flame retardants, heat stabilizers, and anti-fogging agents.

[0108] The positive electrode active material layer may further contain a sulfide-based solid electrolyte. The sulfide-based solid electrolyte contained in the positive electrode active material layer may have the same composition as the sulfide-based solid electrolyte contained in the solid electrolyte layer, or it may have a different composition.

[0109] The positive electrode active material layer may contain a sulfide-based solid electrolyte in an amount of 5% to 60% by weight, specifically 10% to 40% by weight.

[0110] The average particle size of the positive electrode active material may be larger than the average particle size of the solid electrolyte particles contained in the positive electrode active material layer. In this case, the solid electrolyte particles can enter the gaps between the positive electrode active material particles, providing lithium ion conduction pathways to the positive electrode active material.

[0111] This disclosure provides a secondary battery having the structure described above. This disclosure also provides a battery module including a secondary battery as a unit battery, a battery pack including a battery module, and a device including a battery pack as a power source. Specific examples of the device include, but are not limited to, power tools driven by electric motors; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; and power systems.

[0112] The following examples illustrate the present invention, but these examples are merely illustrative. It will be obvious to those skilled in the art that various modifications and alterations are possible within the scope of the present invention and the technical concept, and that such variations and alterations will naturally fall within the scope of the appended claims.

[0113] (Synthesis of solid electrolytes) Manufacturing Example 1 The raw materials used are lithium sulfide (Li2S, Mitsuwa Chemical), phosphorus pentasulfide (P2S5, Aldrich), zinc sulfide (ZnS, High Purity Chemical), lithium chloride (LiCl, Aldrich), and lithium bromide (LiBr, Aldrich), and the composition is Li 5.4-2y M y PS 4.4 Cl 1.0 Br 0.6 The mixture was weighed and mixed in a mortar and pestle in an Ar gas-flowing glove box to obtain a mixed powder (with an amount of Group 12 element M, y = 0.025). This mixed powder was placed in a ZrO2 pot along with ZrO2 balls to obtain a sealed pot. This sealed pot was placed in a planetary ball mill apparatus and ball milling was performed at 380 rpm for 20 hours. After that, the pot was opened in a glove box and the powder was collected. This powder was placed in a carbon crucible, sealed, and then calcined at 430°C for 8 hours while flowing Ar gas. The calcined powder was ground in a mortar and pestle for 10 minutes to obtain a crude solid electrolyte powder containing the divalent cation of zinc (Zn), a Group 12 element.

[0114] Manufacturing Example 2 The coarse solid electrolyte powder containing divalent cations obtained in Production Example 1 was placed in a ZrO2 pot together with ZrO2 balls and anisole solvent, and wet grinding was performed at 250 rpm for 1 hour to obtain fine solid electrolyte powder containing divalent cations.

[0115] Comparative Manufacturing Example 1 A solid electrolyte crude powder free of divalent cations was obtained in the same manner as in Example 1, except that zinc sulfide (ZnS, high-purity chemicals) was not used. The composition of the solid electrolyte obtained in Comparative Production Example 1 was Li 5.4 PS 4.4 Cl 1.0 Br 0.6 That was the case.

[0116] Comparative Manufacturing Example 2 The solid electrolyte coarse powder, which does not contain divalent cations, obtained in Comparative Production Example 1 was placed in a ZrO2 pot together with ZrO2 balls and anisole solvent, and wet grinding was performed at 250 rpm for 1 hour to obtain solid electrolyte fine powder, which does not contain divalent cations.

[0117] Comparative Manufacturing Example 3 The coarse solid electrolyte powder containing divalent cations obtained in Production Example 1 was placed in a ZrO2 pot together with ZrO2 balls and anisole solvent, and wet grinding was performed at 250 rpm for 5 hours to obtain fine solid electrolyte powder containing divalent cations.

[0118] [evaluation] The following evaluations were performed using the obtained solid electrolyte.

[0119] (XRD measurement) A predetermined amount of solid electrolyte was placed in a sealed holder within an Ar gas-flow glove box, and XRD measurements were performed. The lattice constant, lattice volume, and full width at half maximum (FWHM) were calculated from the obtained XRD (X-ray diffraction) patterns. The FWHM was calculated from the (311) plane crystal peak of the argyrodite-type crystal structure observed around 2θ = 30° in Figure 4.

[0120] The measuring equipment and conditions are as follows: • X-ray diffractometer: Rigaku Smartlab ·Radiation source: Cu-Kα radiation (λ=1.5418Å) Voltage: 45kV ·Current: 200mA • Scan range (2θ): 10-60° Step size: 0.01°

[0121] (Particle size distribution measurement) A solid electrolyte dispersion solution was prepared by adding a solid electrolyte to a heptane solvent and using Span 80 as a dispersant. The particle size distribution of this dispersion solution was measured using a Mastersizer 3000 particle size analyzer. The refractive index of the solid electrolyte was assumed to be 2.16 for data analysis.

[0122] (Ionic conductivity measurement) A predetermined amount of solid electrolyte was placed inside a Machor tube, and the Machor tube and pellet molding jig (upper and lower press pins) were combined and press-formed at approximately 370 MPa using a single-screw press. Subsequently, a predetermined amount of gold powder was placed on both sides of the pellet, and then press-formed at approximately 554 MPa using a single-screw press to obtain a Machor tube cell. The obtained Machor tube cell was placed in an electrochemical measurement jig cell, and pressurized to 80 MPa using a torque wrench to obtain an ion conductivity measurement cell. The obtained ion conductivity measurement cell was connected to an impedance measuring device, and the resistance value of the solid electrolyte pellet was measured at room temperature (298 K) and atmospheric pressure (1 atm) to derive the ion conductivity [mS / cm] of the solid electrolyte.

[0123] [Evaluation Results] (crystalline phase) Table 1 shows the evaluation results of the crystalline phase (crystal structure) identified from the XRD patterns obtained by XRD measurement. Figure 4 shows the measured XRD patterns. As can be seen from Table 1 and Figure 4, the solid electrolytes obtained in Production Examples 1 and 2 and Comparative Examples 1 and 2 showed almost no impurity phases (also called unknown phases), and consisted almost entirely of peaks of the argyrodite phase. Sulfide-based solid electrolytes with an argyrodite-type crystalline structure that had little to no impurity phases were obtained. Sulfide-based solid electrolytes with high crystallinity can promote lithium ion hopping conduction and contribute to an increase in ionic conductivity.

[0124] [Table 1]

[0125] (Lattice volume) The lattice constants derived from the XRD patterns were in the range of 9.8750 Å to 9.8755 Å in fabrication examples 1 and 2, and the lattice volume was 962.9 Å. 3 From 963.1 Å 3The range was as follows. On the other hand, in comparative production examples 1 and 2, in which the lithium sites of the sulfide-based solid electrolyte were not substituted with group 12 element M, the lattice constant was in the range of 9.9467 Å to 9.9470 Å, and the lattice volume was 984.1 Å. 3 From 984.2 Å 3 The results were within this range. It was shown that substituting the lithium sites of the argyrodite-type crystal structure with group 12 element M reduced the crystal volume by approximately 2.1%. Although not bound by theory, it is thought that the crystal volume of the sulfide-based solid electrolyte changed because one of the two lithium sites was substituted with group 12 element M, and the other became a lithium vacancy. The lithium vacancy is thought to serve as a pathway for lithium ion hopping conduction, contributing to an increase in ionic conductivity. In addition, the group 12 element M substituted at the lithium site may have a divalent state, and its ability to attract anions around the group 12 element M site may change compared to monovalent lithium ions. This is thought to change the crystal volume of the sulfide-based solid electrolyte, resulting in a structure suitable for lithium ion hopping conduction.

[0126] The full width at half maximum (FWHM) of the (311) plane crystal peak in the argyrodite crystal structure was 0.06° in production examples 1 and 2. In contrast, it was 0.08° in comparative production examples 1 and 2. Production examples 1 and 2, which are solid electrolytes containing divalent cations, have a smaller FWHM. A smaller FWHM corresponds to a larger crystallite size and is thought to contribute to an increase in ionic conductivity. Furthermore, it was found that the crystallinity and crystal size of the solid electrolyte did not change during the pulverization process from coarse powder to fine powder.

[0127] (particle size distribution) Table 2 shows the particle size distribution measurement results. The average particle size D50 was 15.6 μm for the solid electrolyte coarse powder containing divalent cations in Production Example 1, and 1.68 μm for the solid electrolyte fine powder containing divalent cations in Production Example 2. In addition, it was 14.7 μm for the solid electrolyte coarse powder without divalent cations in Comparative Production Example 1, and 1.42 μm for the solid electrolyte fine powder without divalent cations in Comparative Production Example 2. It was confirmed that the solid electrolyte coarse powder could be pulverized into solid electrolyte fine powder by additional wet grinding. In addition, it was 1.2 μm for the solid electrolyte fine powder containing divalent cations in Comparative Production Example 3.

[0128] The average particle size D10 was 4.85 μm for the solid electrolyte coarse powder containing divalent cations in Production Example 1, and 0.71 μm for the solid electrolyte fine powder containing divalent cations in Production Example 2. Furthermore, it was 4.03 μm for the solid electrolyte coarse powder without divalent cations in Comparative Production Example 1, and 0.73 μm for the solid electrolyte fine powder without divalent cations in Comparative Production Example 2. Finally, it was 0.71 μm for the solid electrolyte fine powder containing divalent cations in Comparative Production Example 3.

[0129] The average particle size D90 was 59.2 μm for the solid electrolyte crude powder containing divalent cations in Production Example 1, and 5.09 μm for the solid electrolyte fine powder containing divalent cations in Production Example 2. Furthermore, it was 55.7 μm for the solid electrolyte crude powder without divalent cations in Comparative Production Example 1, and 4.86 μm for the solid electrolyte fine powder without divalent cations in Comparative Production Example 2. Finally, it was 3.09 μm for the solid electrolyte fine powder containing divalent cations in Comparative Production Example 3.

[0130] [Table 2]

[0131] (Ionic conductivity) Table 1 shows the results of ionic conductivity measurements. The coarse solid electrolyte powder containing divalent cations in Production Example 1 had an ionic conductivity of 12.98 mS / cm, while the fine solid electrolyte powder containing divalent cations in Production Example 2 had an ionic conductivity of 4.30 mS / cm. Furthermore, the coarse solid electrolyte powder without divalent cations in Comparative Production Example 1 had an ionic conductivity of 9.91 mS / cm, and the fine solid electrolyte powder without divalent cations in Comparative Production Example 2 had an ionic conductivity of 3.3 mS / cm. The fine solid electrolyte powder containing divalent cations in Comparative Production Example 3 had an ionic conductivity of 2.5 mS / cm. Regardless of the presence or absence of divalent cations, the coarse solid electrolyte powder had a higher ionic conductivity than the fine solid electrolyte powder. This is likely because the coarse solid electrolyte powder has fewer grain boundaries per unit volume. Regardless of the average particle size of the solid electrolyte, solid electrolytes containing divalent cations had a higher ionic conductivity than solid electrolytes without divalent cations. Even with the presence of divalent cations, excessively small particle sizes of the solid electrolyte generated impurities, leading to a decrease in ionic conductivity.

[0132] Example 1 90 mg of the solid electrolyte crude powder containing divalent cations obtained in Production Example 1 was weighed, placed in a molding jig, and pressure molded at 110 MPa for 1 minute to obtain solid electrolyte pellets.

[0133] An NCM-based positive electrode active material with a Ni content of 80 mol%, a solid electrolyte fine powder containing divalent cations obtained in Production Example 2, and a conductive material were weighed in a mass ratio of 60:35:5. These were mixed to obtain a positive electrode mixture.

[0134] After placing 17 mg of positive electrode mixture on one surface of a solid electrolyte pellet, a SUS press pin of a molding jig was pressed against it to flatten it, and then it was pressure-molded at 110 MPa for 1 minute to obtain a positive electrode active material layer formed on the solid electrolyte layer. A SUS plate as a positive electrode current collector was placed on the positive electrode active material layer, and a SUS plate as a negative electrode current collector was placed so as to be in direct contact with the solid electrolyte layer on the opposite side of the positive electrode active material layer. This was pressure-molded at 554 MPa for 1 minute to obtain a laminate. The obtained laminate was combined with a SUS press pin to fabricate a Macol tube cell. The obtained Macol tube cell was placed in a battery cell, and a low confinement pressure of approximately 0.1 MPa was applied to obtain an all-solid-state battery. In other words, the all-solid-state battery of Example 1 contains solid electrolyte coarse powder containing divalent cations in the solid electrolyte layer and solid electrolyte fine powder containing divalent cations in the positive electrode active material layer.

[0135] Figure 1 shows the all-solid-state battery of Example 1. As shown in Figure 1, the negative electrode current collector 1 and the solid electrolyte layer 2 containing a solid electrolyte with divalent cations are in direct contact. The all-solid-state battery of Example 1 is in the state of a battery precursor before the first charge and does not contain a negative electrode active material layer. The all-solid-state battery of Example 1 is an all-solid-state battery with an anode-free structure. By charging and discharging the all-solid-state battery with an anode-free structure, lithium precipitates and dissolves between the negative electrode current collector 1 and the solid electrolyte layer 2 containing the solid electrolyte, allowing it to operate as an all-solid-state battery.

[0136] Comparative Example 1 A solid-state battery was obtained in the same manner as in Example 1, except that in the step of obtaining the solid electrolyte pellet, the solid electrolyte crude powder without divalent cations obtained in Comparative Production Example 1 was used instead of the solid electrolyte crude powder containing divalent cations obtained in Production Example 1, and in the step of obtaining the positive electrode mixture, the solid electrolyte fine powder without divalent cations obtained in Comparative Production Example 2 was used instead of the solid electrolyte fine powder containing divalent cations obtained in Production Example 2. In other words, as shown in Figure 2, the solid-state battery of Comparative Example 1 contains solid electrolyte crude powder without divalent cations in the solid electrolyte layer 5 and solid electrolyte fine powder without divalent cations in the positive electrode active material layer 3.

[0137] Comparative Example 2 In the process of obtaining the all-solid-state battery, an Ag-C intermediate layer was placed on the solid electrolyte layer opposite to the positive electrode active material layer, a SUS plate as a negative electrode current collector was placed on the Ag-C intermediate layer, and a confinement pressure of approximately 4 MPa was applied. The restraint pressure was the same as in Comparative Example 1. The Ag-C intermediate layer was prepared by dissolving a predetermined amount of Ag and C (carbon black) in N-methylpyrrolidone with 7 wt% PVDF added, and then coating it onto the SUS plate. In other words, as shown in Figure 3, the all-solid-state battery of Comparative Example 2 contains solid electrolyte coarse powder that does not contain divalent cations in the solid electrolyte layer 5, solid electrolyte fine powder that does not contain divalent cations in the positive electrode active material layer 3, and an intermediate layer 6 is placed between the solid electrolyte layer 5 and the negative electrode current collector 1.

[0138] [All-Solid-State Battery Evaluation] (Charge / Discharge Test) The obtained all-solid-state batteries were subjected to charge-discharge tests at 25°C. The voltage range was 4.25V-3.0V, the charging conditions were CC(0.05C)-CV(0.01C cutoff), and the discharging conditions were CC(0.05C). The charge capacity and discharge capacity were determined from the obtained charge-discharge curves. Furthermore, the discharge capacity retention rate (%) at 25°C under the charging conditions CC(0.05C)-CV(0.01C) and the discharging conditions CC(0.05C) was derived according to the following formula.

[0139] Discharge capacity in each cycle / Discharge capacity in the first cycle × 100

[0140] [Evaluation Results] (All-solid battery characteristics) The relative ratio of the initial discharge capacity of the all-solid-state battery capacity of Example 1 to the all-solid-state battery capacity of Comparative Example 1 was 101%. Thus, the all-solid-state battery of Example 1, which includes a sulfide-based solid electrolyte layer containing a group 12 element and having an argyrodite-type crystal structure, was able to achieve a higher discharge capacity than the all-solid-state battery of Comparative Example 1, which does not include the sulfide-based solid electrolyte of this disclosure.

[0141] Figure 5 is a graph showing the discharge capacity retention rate of the all-solid-state batteries in Example 1 and Comparative Examples 1 and 2. The discharge capacity retention rate in the third cycle was 99.4% for Example 1, 78.8% for Comparative Example 1, and 92.4% for Comparative Example 2. The discharge capacity retention rate at the 7th cycle was 98.6% for Example 1 and 85.7% for Comparative Example 2. In Comparative Example 1, the discharge capacity decreased sharply after 4 cycles, making it impossible to measure the discharge capacity. Unlike Comparative Example 1, Comparative Example 2 has an intermediate layer 6 installed between the solid electrolyte layer 5 and the negative electrode current collector 1. It is thought that Comparative Example 2 showed better cycle characteristics than Comparative Example 1 because the intermediate layer 6 suppressed the growth of lithium dendrites.

[0142] Thus, the all-solid-state battery of Example 1, which includes a sulfide-based solid electrolyte having a group 12 element and an argyrodite-type crystal structure in its solid electrolyte layer, was able to achieve improved cycle characteristics compared to the all-solid-state batteries of Comparative Examples 1 and 2, which do not include the sulfide-based solid electrolyte of this disclosure.

[0143] The all-solid-state battery of Example 1 contains solid electrolyte crude powder containing divalent cations in its solid electrolyte layer, i.e., the solid electrolyte crude powder of Production Example 1. The all-solid-state battery of Comparative Example 1 contains solid electrolyte crude powder that does not contain divalent cations in its solid electrolyte layer, i.e., the solid electrolyte crude powder of Comparative Example Production Example 1. As shown in Table 1, the solid electrolyte crude powder of Production Example 1 exhibits an ionic conductivity approximately 1.3 times higher than that of the solid electrolyte crude powder of Comparative Example Production Example 1. As shown in Figure 5, the all-solid-state battery of Example 1 exhibited superior cycle characteristics compared to the all-solid-state battery of Comparative Example 1. The superior cycle characteristics of the all-solid-state battery of Example 1 are thought to be due to the high ionic conductivity of the solid electrolyte crude powder containing divalent cations.

[0144] Furthermore, during charging and discharging of solid-state batteries, high confinement pressure is typically applied to suppress the growth of lithium dendrites on the negative electrode current collector. However, as can be seen from Figure 5, the all-solid-state battery of Example 1, which was subjected to a low confinement pressure of approximately 0.1 MPa, exhibited superior cycle characteristics compared to the all-solid-state battery of Comparative Example 2, which was subjected to a high confinement pressure of approximately 4 MPa. This is thought to be due to the use of a solid electrolyte containing divalent cations in both the solid electrolyte layer and the positive electrode active material layer. Thus, the all-solid-state battery of this disclosure can be driven at low confinement pressure.

[0145] Although this disclosure has been described above with reference to limited embodiments and drawings, it is understood that this disclosure is not limited thereto and that various modifications and variations are possible within the equivalent scope of the technical concept and the appended claims by persons with ordinary skill in the art to which this disclosure pertains. [Explanation of symbols]

[0146] 1 Negative electrode current collector 2. Solid electrolyte layer containing a solid electrolyte containing a divalent cation. 3 Cathode active material layer 4 Positive electrode current collector 5. Solid electrolyte layer containing a solid electrolyte that does not contain divalent cations. 6. Mesopotamian

Claims

1. An all-solid-state battery comprising a positive electrode containing a positive electrode active material layer, a negative electrode current collector, and a solid electrolyte layer disposed between the positive electrode and the negative electrode current collector, The aforementioned all-solid-state battery does not contain a negative electrode active material. During charging, lithium ions are supplied from the positive electrode active material layer, and a lithium metal layer, acting as the negative electrode active material, is formed on the negative electrode current collector. An all-solid-state battery, wherein the solid electrolyte layer contains a sulfide-based solid electrolyte having a group 12 element and an argyrodite-type crystal structure.

2. The all-solid-state battery according to claim 1, wherein the negative electrode current collector and the solid electrolyte layer are in direct contact.

3. The aforementioned sulfide-based solid electrolyte has the chemical formula Li ７－ｘ－２ｙ M ｙ PS ６－ｘ Ha ｘ It is represented as, In the above chemical formula, The aforementioned M is one or more elements selected from the Group 12 elements, The Ha is one or more elements selected from halogen elements, The all-solid-state battery according to claim 1, satisfying 0 < x < 2.5 and 0 < y < 0.

45.

4. The all-solid-state battery according to claim 3, wherein M is Zn.

5. The all-solid-state battery according to claim 1, wherein it does not contain reaction products between the negative electrode current collector and the sulfide-based solid electrolyte.

6. The all-solid-state battery according to claim 1, wherein the all-solid-state battery is pressurized at a pressure of 0.3 MPa or less in the direction in which the positive electrode, the negative electrode current collector, and the solid electrolyte layer are stacked.

7. The all-solid-state battery according to claim 1, wherein the positive electrode active material layer includes the sulfide-based solid electrolyte.

8. The all-solid-state battery according to claim 1, wherein the D10 of the solid electrolyte is 0.1 to 10 μm.

9. The all-solid-state battery according to claim 1, wherein the D50 of the solid electrolyte is 0.1 to 50 μm.

10. The all-solid-state battery according to claim 1, wherein the D90 of the solid electrolyte is 1 to 100 μm.

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