All-solid-state battery

Abstract

The purpose of the present invention is to provide an anode-free all-solid-state battery having improved discharge capacity and cycle characteristics. In addition, the purpose of the present invention is to provide an anode-free all-solid-state battery that can be driven at a low confining pressure. The present invention 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, whereby 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.

Description

All-solid-state battery

[0001] The present invention relates to an all-solid-state battery with an anode-free structure.

[0002] This application claims priority based on Japanese application No. 2024-231223 filed on December 26, 2024, and all contents disclosed in the specification of said application are incorporated into this application.

[0003] The development of all-solid-state batteries, which replace the liquid electrolyte in lithium-ion batteries with a solid electrolyte, is underway to achieve high safety, extended lifespan, and higher energy density. Among the numerous solid electrolytes, sulfide-based solid electrolytes such as Li10GeP2S12 possess high ionic conductivity comparable to that of liquid electrolytes and have the advantage of being soft, making it easy to achieve adhesion with active materials; therefore, the practical application of all-solid-state batteries utilizing sulfide-based solid electrolytes is anticipated.

[0004] Meanwhile, lithium metal is attracting attention as an anode 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, sulfide-based solid electrolytes such as Li10GeP2S12 have low stability with respect to lithium metal, which poses a problem in that they are difficult to use with lithium metal anodes.

[0005] Furthermore, when lithium metal is used as the negative electrode, the battery is generally manufactured by attaching lithium foil to a planar current collector; however, since lithium is an alkali metal with high reactivity, it reacts explosively with water and also reacts with oxygen in the atmosphere, presenting a disadvantage that makes manufacturing and use difficult 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, it acts as an insulating layer, lowering electrical conductivity and hindering the smooth movement of lithium ions, leading to a problem of increased electrical resistance.

[0006] To resolve this problem, Patent Documents 1 to 3 disclose an anode-less 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 a negative electrode current collector. However, such an anode-less all-solid-state battery has the problem of high cost because additional processes are required to coat and sputter the metal. In addition, the anode-less all-solid-state battery requires high restraint pressure during battery operation to prevent the growth of lithium dendrites.

[0007] To solve the above problem, the inventors, through multifaceted research, designed an anode-free all-solid-state battery capable of forming a lithium metal layer on a negative electrode current collector by lithium ions transferred from the positive electrode active material by charging after assembling the battery, in order to fundamentally block contact between lithium metal and the atmosphere during battery assembly. In addition, by using a sulfide-based solid electrolyte containing polyvalent cations as the solid electrolyte used in the anode-free all-solid-state battery, an anode-free all-solid-state battery was developed that has excellent discharge capacity and cycle characteristics and can also be operated at a low confinement pressure.

[0008] [Prior Art Literature]

[0009] [Patent Literature]

[0010] Patent Document 1: Japanese Patent Publication No. 2020-191202

[0011] Patent Document 2: Japanese Patent Publication No. 2020-167146

[0012] Patent Document 3: Japanese Patent Publication No. 2022-504134

[0013] Patent Document 4: Japanese Patent Publication No. 2022-529975

[0014] The present invention aims to provide an anode-free all-solid-state battery with improved discharge capacity and cycle characteristics.

[0015] In addition, the present invention aims to provide an anode-free all-solid-state battery capable of operating at low confinement pressure.

[0016] To achieve the above objective, the present invention,

[0017] A solid-state battery comprising a positive electrode including a positive active material layer, a negative electrode current collector, and a solid electrolyte layer disposed between the positive electrode and the negative electrode current collector,

[0018] The above-mentioned all-solid-state battery does not include a negative electrode active material, and

[0019] Lithium ions are supplied from the positive active material layer by charging, and a lithium metal layer as a negative active material is formed on the negative current collector, and

[0020] The present invention provides an all-solid-state battery in which the solid electrolyte layer comprises a sulfide-based solid electrolyte containing a Group 12 element and having an argylodite-type crystal structure.

[0021] In one embodiment, the negative current collector and the solid electrolyte layer may be in direct contact.

[0022] In one embodiment, the sulfide-based solid electrolyte is represented by the chemical formula Li7-x-2yMyPS6-xHax, and

[0023] In the above chemical formula,

[0024] The above M is one or more elements selected from Group 12 elements, and

[0025] The above Ha is one or more elements selected from halogen elements, and

[0026] It can satisfy 0 < x < 2.5 and 0 < y < 0.45.

[0027] In one embodiment, the above M may be Zn.

[0028] In one embodiment, the reaction product of the cathode current collector and the sulfide-based solid electrolyte may not be included.

[0029] In one embodiment, the all-solid-state battery may be pressurized to 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.

[0030] In one embodiment, the positive active material layer may include the sulfide-based solid electrolyte.

[0031] In one embodiment, the D10 of the solid electrolyte may be 0.1 to 10 μm.

[0032] In one embodiment, the D50 of the solid electrolyte may be 0.1 to 50 μm.

[0033] In one embodiment, the D90 of the solid electrolyte may be 1 to 100 μm.

[0034] The present invention can provide an anode-free all-solid-state battery with improved discharge capacity and cycle characteristics.

[0035] In addition, the present invention can provide an anode-free all-solid-state battery capable of operating at low confinement pressure.

[0036] Figure 1 is a schematic diagram of an all-solid-state battery of Example 1.

[0037] Figure 2 is a schematic diagram of the all-solid-state battery of Comparative Example 1.

[0038] Figure 3 is a schematic diagram of the all-solid-state battery of Comparative Example 2.

[0039] Figure 4 is a diagram showing the X-ray diffraction (XRD) patterns of fine and coarse powders of a solid electrolyte.

[0040] Figure 5 is a graph showing the discharge capacity retention rate of the all-solid-state batteries of Example 1, Comparative Example 1, and Comparative Example 2.

[0041] The present invention will be described in more detail below.

[0042] Terms and words used in this specification and claims shall not be interpreted as being limited to their ordinary or dictionary meanings, and shall be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe their invention.

[0043] In the drawings, parts unrelated to the description have been omitted to clearly explain the invention, and similar parts throughout the specification have been given similar reference numerals. Additionally, the sizes and relative sizes of the components shown in the drawings are not related to the actual scale and may be reduced or exaggerated for clarity of explanation.

[0044] In this specification, 'Dn' represents a particle size distribution and refers to the particle size at the n% point of the cumulative distribution of the number of particles by particle size. That is, D50 is the particle size (center particle size, average particle size) at the 50% point of the cumulative distribution of the number of particles by particle size, D90 is the particle size at the 90% point of the cumulative distribution of the number of particles by particle size, and D10 is the particle size at the 10% point of the cumulative distribution of the number of particles by particle size. Meanwhile, the particle size distribution can be measured using a laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500), and the difference in the diffraction pattern due to particle size when the particle passes through the laser beam is measured to calculate the particle size distribution.

[0045] [All-solid-state battery]

[0046] The all-solid-state battery of the present invention comprises 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. The all-solid-state battery of the present invention does not include a negative electrode active material, and lithium ions are supplied from the positive electrode active material layer by charging, so that a lithium metal layer as a negative electrode active material is formed on the negative electrode current collector. The all-solid-state battery of the present invention comprises a solid electrolyte layer containing a Group 12 element and a sulfide-based solid electrolyte having an argyrodite-type crystal structure. The anode-free all-solid-state battery of the present invention can improve discharge capacity and cycle characteristics by having the above configuration. Furthermore, the anode-free all-solid-state battery of the present invention can be operated at a low confinement pressure by having the above configuration.

[0047] Meanwhile, in the present invention, an all-solid-state battery refers to a state prior to the first deposition of lithium metal (first charge) on the negative electrode current collector (also referred to as an all-solid-state battery precursor).

[0048] The all-solid-state battery can be an all-solid-state lithium secondary battery.

[0049] In an all-solid-state battery, a restraining pressure is applied during charging and discharging to prevent the growth of lithium dendrites, which can cause a short circuit between the positive and negative electrodes. The restraining pressure can be applied in a direction perpendicular to the plane direction of the negative current collector, that is, the direction in which the positive electrode, the negative current collector, and the solid electrolyte layer placed between the positive and negative current collectors are stacked. For example, the restraining pressure can be achieved by fixing the all-solid-state battery with a jig from both the positive side and the negative current collector side.

[0050] Typically, a large confining pressure is applied to an all-solid-state battery to prevent the growth of lithium dendrites. However, the all-solid-state battery of the present invention, which uses a sulfide-based solid electrolyte containing divalent cations, may require almost no confining pressure.

[0051] The all-solid-state battery may be pressurized to 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 during charging and discharging. In this way, the anode-free all-solid-state battery of the present invention can be operated at a low confining pressure.

[0052] In a lithium secondary battery, the negative electrode is typically formed on a negative current collector. However, in the all-solid-state battery of the present invention, the negative current collector does not have metal particles or a coating layer on its surface, and is assembled into an anode-free battery structure using only the negative current collector. Then, lithium ions released from the positive active material upon charging form a lithium metal layer as a negative active material on the negative current collector. As a result, a negative electrode having a structure of a negative current collector / negative active material layer is formed, thereby enabling the configuration of a conventional lithium secondary battery.

[0053] In other words, the term "anode-free battery" in the present invention encompasses all types of batteries, including those in which a negative electrode is not formed on the negative current collector at the time of initial assembly, and in which a negative electrode may be formed on the negative current collector as a result of use. However, the all-solid-state battery of the present invention is not limited to having metal particles or a coating layer on the surface of the negative current collector at the time of initial assembly.

[0054] In addition, in the cathode of the present invention, the form of the lithium metal formed as a cathode active material on the cathode 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 the form of particles).

[0055] Hereinafter, the present invention is described based on the form of a lithium metal layer formed by a lithium metal. However, it is clear that this description does not exclude structures in which the lithium metal is not formed by a layer.

[0056] <Solid Electrolyte Layer>

[0057] The solid electrolyte layer contains a solid electrolyte. The solid electrolyte layer can serve as an insulator and function as an ion-conducting channel in an all-solid-state lithium secondary battery.

[0058] The solid electrolyte layer may have a thickness of about 50 μm or less, preferably about 15 μm to 50 μm. Within the aforementioned range, the thickness may be appropriately determined by considering ionic conductivity, physical strength, and the energy density of the applied battery. For example, in terms of ionic conductivity or energy density, the thickness may be 10 μm or more, 20 μm or more, or 30 μm or more. Meanwhile, in terms of physical strength, the thickness may be 50 μm or less, 45 μm or less, or 40 μm or less. In addition, while having the aforementioned thickness range, the solid electrolyte layer may have a tensile strength of about 100 kgf / cm² to about 2,000 kgf / cm². Furthermore, the solid electrolyte layer may have a porosity of 15 vol% or less or about 10 vol% or less. Thus, the solid electrolyte layer according to the present invention can have high mechanical strength despite being a thin film.

[0059] (Solid electrolyte)

[0060] The solid electrolyte may include one or more of a sulfide-based solid electrolyte, an oxide-based solid electrolyte, and a polymer-based solid electrolyte. Preferably, the solid electrolyte included in the all-solid-state battery of the present invention is a sulfide-based solid electrolyte. The solid electrolyte may be included in the positive electrode active material layer or in the solid electrolyte layer serving as a separator.

[0061] The average particle size of solid electrolytes can be controlled depending on the application. By controlling the average particle size of solid electrolytes, ionic conductivity can be improved.

[0062] The average particle size of the solid electrolyte can be controlled by changing conditions such as the rotational speed and time of the ball mill device, for example. Accordingly, it is possible to produce solid electrolyte coarse powder with a relatively large average particle size and solid electrolyte fine powder with a relatively small average particle size.

[0063] The average particle size (D50) of the solid electrolyte may be 0.1 to 50 μm, D10 may be 0.1 to 10 μm, and D90 may be 1 to 100 μm. The average particle size (D50) of the solid electrolyte coarse particles may be larger than the average particle size of the solid electrolyte fine particles. The average particle size of the solid electrolyte coarse particles 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 particles 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.

[0064] The D10 of the solid electrolyte particles is 1 to 10 μm, preferably 3 to 8 μm, and more preferably 4.5 to 8 μm. The D90 of the solid electrolyte particles is 30 to 100 μm, preferably 40 to 90 μm, more preferably 50 to 80 μm, and even more preferably 56 to 70 μm.

[0065] 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.

[0066] The average particle size of the sulfide-based solid electrolyte included in the solid electrolyte layer may be larger than the average particle size of the sulfide-based solid electrolyte included in the positive electrode active material layer. Since coarse solid electrolyte particles have a large average particle size and fewer grain boundaries per unit volume, they can exhibit high ionic conductivity when used in the solid electrolyte layer. When fine solid electrolyte particles are used in the positive electrode active material layer, they can enter the gaps between the positive electrode active material particles, thereby providing a lithium ion conduction pathway to the positive electrode active material. Therefore, by making the average particle size of the sulfide-based solid electrolyte included in the solid electrolyte layer larger than the average particle size of the sulfide-based solid electrolyte included in the positive electrode active material layer, the discharge capacity and cycle characteristics of the all-solid-state battery can be improved.

[0067] As long as the sulfide-based solid electrolyte contains sulfur (S), there are no particular restrictions, and known sulfide-based solid electrolytes may be used.

[0068] Sulfide-based solid electrolytes can have a crystalline structure. Sulfide-based solid electrolytes having a crystalline structure promote the conduction of lithium ions, thereby enabling high lithium ion conductivity.

[0069] Sulfide-based solid electrolytes can have crystal structures of the azirodite, NASICON, perovskite, garnet, or LGPS type. Preferably, the sulfide-based solid electrolyte has an azirodite crystal structure. Since sulfide-based solid electrolytes having an azirodite crystal structure exhibit high stability with respect to lithium metal, they enable the use of lithium metal with a high mass energy density as a negative electrode material.

[0070] Sulfide-based solid electrolytes can be in the form of amorphous, glass, or glass ceramics.

[0071] Sulfide-based solid electrolytes are those having the ionic conductivity of metals belonging to Group 1 or Group 2 of the periodic table, and may include Li-PS-based glass or Li-PS-based glass ceramics. Non-limiting 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, Li2S-GeS2-ZnS, etc., and may include one or more of these. However, they are not particularly limited to these.

[0072] Sulfide-based solid electrolytes may include crystalline and amorphous phases. Sulfide-based solid electrolytes may include a crystalline phase having an azirodite-type crystal structure (also referred to herein as the azirodite phase) and other phases (also referred to herein as impurity phases or unknown phases). The azirodite-type crystal structure is preferably cubic. The other phase may be a crystalline phase or an amorphous phase. Regardless of whether it is a crystalline or amorphous phase, the other phase may include Li2S phase, P2S5 phase, LiCl phase, LiBr phase, Li3PS4 phase, ZnS phase, CdS phase, and HgS phase, etc. Preferably, the sulfide-based solid electrolyte does not include or substantially does not include an impurity phase other than the azirodite phase. That is, preferably, the sulfide-based solid electrolyte may consist only of the azirodite phase. When a sulfide-based solid electrolyte does not contain or substantially does not contain an impurity phase, lithium ion conduction is not easily inhibited, so the sulfide-based solid electrolyte can have a high lithium ion conductivity.

[0073] The proportion of the crystalline phase contained in a 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.

[0074] Sulfide-based solid electrolytes have the chemical formula Li 7-x-2y M y PS 6-x Ha x It can be represented as follows. 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 and 0 < y < 0.45 can be satisfied. The lattice volume of the sulfide-based solid electrolyte is 940 Å. 3 Above 980Å 3 The following may be possible. Such a sulfide-based solid electrolyte may have high lithium ion conductivity. By using a sulfide-based solid electrolyte having 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. In addition, since the growth of lithium dendrites on the negative electrode current collector is prevented by the sulfide-based solid electrolyte having high lithium ion conductivity, the anode-free all-solid-state battery of the present invention can be operated at a low confining pressure.

[0075] A sulfide-based solid electrolyte according to one embodiment of the present invention is Li 7-x PS 6-x Ha xA portion of the lithium in the structure is substituted with a Group 12 element (M) that can become a divalent cation. The Group 12 element (M) substituting the 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, and 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 substituted with one Group 12 element (M). Substitution by the Group 12 element (M) creates lithium site vacancies, which can improve lithium ion conductivity. Additionally, substitution by the Group 12 element (M) changes the lattice constant and lattice volume of the sulfide-based solid electrolyte, allowing it to have a crystal structure suitable for lithium ion conduction.

[0076] In addition, a sulfide-based solid electrolyte according to one embodiment of the present invention comprises a Group 12 element (M) capable of becoming a divalent cation, Li 7-x PS 6-x Ha x It can be formed by intruding into the crystal lattice. The Group 12 element (M) intruding 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 alone or in combination. Preferably, the Group 12 element (M) is zinc (Zn) and / or cadmium (Cd), and particularly preferably is zinc (Zn). Li 7-x PS 6-x Ha xThe intrusion of a Group 12 element (M) into the crystal lattice changes the lattice constant and lattice volume of the sulfide-based solid electrolyte, thereby enabling it 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 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. Furthermore, by using such a sulfide-based solid electrolyte, the growth of lithium dendrites on the negative electrode current collector is prevented, so the anode-free all-solid-state battery of the present invention can be operated at a low confinement pressure.

[0077] When the Group 12 element (M) is zinc (Zn) and / or cadmium (Cd), the sulfide-based solid electrolyte may have a high degree of crystallinity, and as a result, the sulfide-based solid electrolyte may have a high ionic conductivity. This is thought to be because the ionic radius of lithium (Li) is 76 pm, and the ionic radii of zinc (Zn) and cadmium (Cd) are close to values ​​of 74 pm and 95 pm, respectively, so the azyrodite-type crystal structure is easily maintained even after the substitution of lithium sites by the Group 12 element (M).

[0078] Chemical formula Li 7-x-2y M y PS 6-x Ha xThe amount y of the Group 12 element (M) added in the above range satisfies 0 < y < 0.45, preferably 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 ionic conductivity. When y is 0, the change in the crystal structure due to the substitution of the Group 12 element (M) is not obtained, so the ionic conductivity may be low. When y is 0.45 or higher, the azirodite-type crystal structure of the sulfide-based solid electrolyte cannot be maintained, and the ionic conductivity may decrease. In addition, the impurity phase that inhibits lithium ion conduction in the sulfide-based solid electrolyte increases, and the ionic conductivity may decrease.

[0079] Chemical formula Li 7-x-2y M y PS 6-x Ha x The halogen (Ha) in the above is one or more elements selected from halogen elements. Preferably, the halogen (Ha) includes bromine (Br). More preferably, the halogen (Ha) includes chlorine (Cl) and bromine (Br). When sulfur (S) is a divalent anion, it has a stronger attractive force for lithium ions compared to monovalent halogens, which can significantly inhibit the movement of lithium ions. By including bromine (Br), the occupancy of sulfur (S) at specific sites in the azirodite-type crystal structure is lowered, the occupancy of halogen at those sites is increased, and the mobility of lithium ions around the bromine (Br) sites can be made more active. As a result, the lithium ion conductivity of the sulfide-based solid electrolyte can be improved. In addition, bromine (Br) can combine with Li in the sulfide-based solid electrolyte to form lithium bromide (LiBr), which is an absorbent material. Lithium bromide (LiBr) can improve the lithium ion conductivity of sulfide-based solid electrolytes by adsorbing moisture that can reduce lithium ion conductivity.

[0080] Chemical formula Li 7-x-2y M y PS 6-x Ha x The ratio x of the halogen (Ha) in the above range satisfies 0 < x < 2.5, preferably 1.0 < x < 2.0, more preferably 1.3 ≤ x ≤ 2.0, and even more preferably 1.3 ≤ x ≤ 1.8. When x satisfies the above range, the azirodite-type crystal structure is stabilized, and the sulfide-based solid electrolyte can have high ionic conductivity.

[0081] The ionic conductivity of sulfide-based solid electrolytes can be influenced by the degree of crystallization of the sulfide-based solid electrolytes. The degree of crystallization can be evaluated from the XRD pattern. In the XRD pattern, if phases other than the argyrodite crystalline phase (crystalline or amorphous phases such as Li2S, P2S5, LiCl, LiBr, Li3PS4, ZnS, CdS, and HgS) are not observed or are hardly observed, the sulfide-based solid electrolyte may have high ionic conductivity.

[0082] The lattice volume of a sulfide-based solid electrolyte can change due to the substitution of lithium sites by a Group 12 element (M). Although not bound by theory, it is thought that as the Group 12 element (M) exhibits the characteristics of a divalent cation, the interaction with other anions present in the sulfide-based solid electrolyte becomes stronger, causing the lattice volume to change, that is, to increase or decrease. Such a change in lattice volume leads to a crystal structure suitable for lithium ion conduction, allowing the sulfide-based solid electrolyte to have high ionic conductivity.

[0083] The lattice volume of sulfide-based solid electrolytes is 940 Å. 3 Above 980Å 3 Less than, preferably 950 Å 3 Above 970Å 3 Less than, and more preferably 954 Å 3 Above 966Å 3The following describes the lattice constant and lattice volume. Lattice volume of a sulfide-based solid electrolyte can vary depending on the calcination 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, allowing the sulfide-based solid electrolyte to have a high ionic conductivity.

[0084] The ionic conductivity of a sulfide-based solid electrolyte (also referred to as "lithium ionic conductivity" in this specification) refers to the ionic conductivity at room temperature (25°C, 298K) and atmospheric pressure (1 atm), unless otherwise specifically stated. When a sulfide-based solid electrolyte is used in an all-solid-state battery, it is practical to have an ionic conductivity of 4 mS / cm or higher. The ionic conductivity of a sulfide-based solid electrolyte according to one embodiment of the present invention 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.

[0085] A sulfide-based solid electrolyte according to one embodiment of the present invention can 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.

[0086] The lithium source, the Group 12 element source, the phosphorus source, the sulfur source, and the halogen source may be compounds such as sulfides, oxides, or nitrides. Lithium sulfide (Li2S) may be used as the lithium source, phosphorus pentasulfide (P2S5) as the phosphorus source, and lithium halides (LiHa), such as lithium chloride (LiCl) and lithium bromide (LiBr), may be used as the halogen source. For example, sulfides may be used as the Group 12 element source. Alternatively, sulfur may be supplied from other element sources. That is, one or more of the lithium source, the Group 12 element source, the phosphorus source, and the halogen source may serve as the sulfur source.

[0087] For a sulfide-based solid electrolyte having an azirodite-type crystal structure, the calcination temperature 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 calcination temperature satisfies the above range, the formation of an azirodite-type crystal structure is promoted, and the sulfide-based solid electrolyte can have a high degree of crystallinity. Accordingly, a sulfide-based solid electrolyte having high ionic conductivity can be obtained.

[0088] 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 between the solid electrolyte layer and battery elements (e.g., positive electrode, negative electrode, etc.) stacked on both sides thereof.

[0089] The material of the binder for the solid electrolyte layer is not particularly limited and can be appropriately selected within the range of components used as binders for the solid electrolyte in an all-solid-state lithium secondary battery. Specifically, the binder for the solid electrolyte layer may include at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, 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.

[0090] The solid electrolyte layer does not need to include a binder for the solid electrolyte layer. When the solid electrolyte layer does not include a binder for the solid electrolyte layer, the content of the solid electrolyte contained in the solid electrolyte layer can be increased, thereby improving the ionic conductivity of the solid electrolyte layer.

[0091] <Cathode>

[0092] The cathode does not contain cathode active material before the first lithium metal deposition (first charge).

[0093] By charging, lithium ions are supplied from the positive active material contained in the positive active material layer, and a lithium metal layer as a negative active material is formed on the negative current collector. Specifically, when a voltage above a certain level is applied to charge an all-solid-state battery having an anode-free battery structure, lithium ions are released from the positive active material within the positive electrode, and the released lithium ions pass through the solid electrolyte layer and move toward the negative current collector side to form a lithium metal layer consisting purely of lithium on the negative current collector, thereby forming the negative electrode. Compared to conventional negative electrodes in which a lithium metal layer is sputtered onto the negative current collector or a lithium foil is laminated with the negative current collector, the formation of the lithium metal layer by such charging has the advantage of being able to form a thin film layer, making it very easy to control interface characteristics.

[0094] In particular, since it is formed with an anode-free battery structure and thus completely prevents the exposure of lithium metal to the atmosphere during the battery assembly process, problems such as the formation of an oxide film on the surface due to the high reactivity of lithium itself and the resulting degradation of the lifespan of the lithium secondary battery can be fundamentally eliminated.

[0095] The formed lithium metal layer forms a uniform and continuous or discontinuous layer on the negative electrode current collector. For example, if the negative electrode current collector is in the form of a foil, 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, the discontinuous layer is distributed discontinuously, so that within a specific region, there are regions where the lithium metal layer exists and regions where it does not exist, but the regions where the lithium metal layer does not exist are distributed to isolate, disconnect, or separate the regions where the lithium compound exists, such as in an island shape, so that the regions where the lithium metal layer exists are distributed without continuity.

[0096] The lithium metal layer formed through such charging and discharging has a thickness of at least 50 nm and 100 μm or less, preferably 1 μm or more and 50 μm or less, in order to function as a negative electrode. If the thickness is less than the above range, the charging and discharging efficiency of the battery decreases rapidly, and conversely, if it exceeds the above range, the lifespan characteristics are stable, but there is a problem that the energy density of the battery is lowered.

[0097] In particular, the lithium metal layer disclosed in the present invention is manufactured as an anode-free battery without lithium metal during battery assembly, so that, compared to conventional lithium secondary batteries assembled using lithium foil, no or almost no oxide layer is formed on the lithium metal layer during the assembly process. Accordingly, the degradation of battery life caused by the oxide layer can be prevented.

[0098] In the present invention, the charging range for forming a lithium metal layer is a single charge performed in a voltage range of 2.5V to 4.5V and a charge / discharge rate range of 0.01C to 0.2C. If the charging is performed below the above range, it becomes difficult to form a lithium metal layer, and conversely, if it exceeds the above range, damage to the battery occurs, and after over-discharge occurs, the charging and discharging are not performed properly.

[0099] The negative electrode may include a negative current collector. The negative current collector only needs to be conductive and not cause chemical changes in the all-solid-state battery, and is not particularly limited. As a negative current collector, iron, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment such as carbon, nickel, titanium, silver, etc. may be used.

[0100] In particular, it is preferable that the negative electrode current collector of the present invention does not react with the sulfide-based solid electrolyte. In other words, it is preferable that the all-solid-state battery of the present invention does not contain reaction products between the negative electrode current collector and the sulfide-based solid electrolyte. That the negative electrode current collector does not contain reaction products can be confirmed, for example, by observing a cross-section of the all-solid-state battery using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). It may also be confirmed that the reaction products are not contained by using XRD measurements. Before the first lithium metal deposition (first charge) is performed, the negative electrode current collector and the sulfide-based solid electrolyte may be in direct contact. Furthermore, after the battery is discharged, the lithium metal acting as the negative electrode active material migrates to the positive electrode side, resulting in almost no or no negative electrode active material remaining 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 are generated, which may have an adverse effect on the performance of the all-solid-state battery. To prevent such side reactions, it is desirable for the negative electrode current collector to have 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 the present invention can improve discharge capacity and cycle characteristics. Furthermore, since the negative electrode current collector does not react with the sulfide-based solid electrolyte and thus does not generate side reaction products, the anode-free all-solid-state battery of the present invention can be operated at a low confinement pressure.

[0101] The cathode current collector can have a thickness of 3㎛ or more and 500㎛ or less.

[0102] The cathode current collector may be in various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric with fine irregularities formed on its surface.

[0103] The negative electrode current collector can come into direct contact with the solid electrolyte layer. The negative electrode current collector can come into direct contact with the sulfide-based solid electrolyte contained in the solid electrolyte layer. By bringing the negative electrode current collector and the solid electrolyte layer into direct contact without an intermediary layer, the thickness of the all-solid-state battery can be reduced, thereby improving the volumetric energy density of the all-solid-state battery. Since the amount of active material that can be mounted increases and the growth of lithium dendrites is prevented, the discharge capacity and cycle characteristics of the all-solid-state battery can be improved. In addition, the all-solid-state battery can be operated at a low confinement pressure.

[0104] The negative electrode current collector does not need 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. If an intermediate layer is formed, a lithium metal layer is formed on the negative electrode current collector as lithium ions supplied from the positive electrode active material layer pass through the intermediate layer. In other words, a lithium metal layer is formed between the negative electrode current collector and the intermediate layer during charging.

[0105] Here, the intermediate layer can be any material capable of smoothly transporting lithium ions, and may use a material used in lithium ion-conducting polymers and / or inorganic solid electrolytes, and may further include a lithium salt if necessary.

[0106] The intermediate layer may include 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, palladium, etc.

[0107] As a lithium ion conductive polymer, it may be composed of, for example, any 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, and any polymer having lithium ion conductivity may be used without limitation.

[0108] When using lithium ion conductive polymers, additional materials used for this purpose may be included to further increase lithium ion conductivity.

[0109] For example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 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 may be further included.

[0110] Inorganic solid electrolytes are ceramic-based materials, and crystalline or amorphous materials may be used, such as 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, Li5La3Ta2O12 , Li7La3Zr2O 12 , Li6BaLa2Ta2O 12 , Li3PO (4-3 / 2 w) N w (w<1), Li 3.6 Si 0.6 P 0.4 Inorganic solid electrolytes such as O4 are possible. In this case, when using an inorganic solid electrolyte, lithium salts may be additionally included if necessary.

[0111] Inorganic solid electrolytes can be mixed with known materials such as binders and applied in the form of a thick film through slurry coating. Additionally, if necessary, they can be applied in the form of a thin film through deposition processes such as sputtering. The slurry coating method used can be appropriately selected based on the coating method, drying method, and solvent mentioned in the section on lithium-ion conductive polymers.

[0112] An intermediate layer comprising the aforementioned lithium ion-conducting polymer and / or inorganic solid electrolyte can increase the transport rate of lithium ions to facilitate the formation of a lithium metal layer, while simultaneously securing the effect of suppressing or preventing the formation of lithium dendrites that occur when a lithium metal layer / negative current collector is used as a negative electrode.

[0113] To secure the above effect, it is necessary to limit the thickness of the intermediate layer.

[0114] Although a thinner intermediate layer is advantageous for the output characteristics of the battery, if it is not formed with a thickness greater than a certain level, it cannot suppress the side reaction between lithium and the electrolyte formed on the negative electrode current collector, and it cannot effectively block dendrite growth. In the present invention, the thickness of the intermediate layer may preferably be 10 nm or more and 50 μm or less. If the thickness of the intermediate layer is less than the above range, it cannot effectively suppress the side reaction and exothermic reaction between lithium and the electrolyte that increase under conditions such as overcharging or high-temperature storage, and thus safety improvement cannot be achieved. Furthermore, 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.

[0115] <Bipolar>

[0116] The positive electrode may include a positive electrode active material layer and a positive electrode current collector.

[0117] The positive current collector is not particularly limited as long as it does not cause chemical changes in the positive electrode or battery and has high conductivity, and may include at least one material selected from the group consisting of, for example, iron, stainless steel, copper, aluminum, nickel, titanium, and calcined carbon, and specifically may include aluminum. The positive current collector may further include a primer layer coated on the surface of the positive current collector, comprising a carbon-based conductive material and a binder. Accordingly, the bonding strength and electrical conductivity between the positive active material layer and the current collector can be significantly improved.

[0118] The positive active material layer may be disposed on at least one surface of the positive current collector. Specifically, the positive active material layer may be disposed on one or both surfaces of the positive current collector.

[0119] The positive active material layer may include a positive active material. In the anode-free battery structure of the present invention, the lithium source for forming the lithium metal layer is the positive active material, and the positive active material contains lithium. That is, when the lithium ions of the positive active material are charged within a specific voltage range, the lithium ions detach to form a lithium metal layer on the negative current collector.

[0120] The positive electrode active material may be used without restriction as long as it is suitable for use as a positive electrode active material for a lithium-ion secondary battery. The positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides including O4 (x is 0–0.33), LiMnO3, LiMn2O3, LiMn2O4, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (M=Co, Mn, Al, Cu, Fe, P, Mg, Ca, Zr, Ti, Ru, Nb, W, B, Si, Na, K, Mo, V or Ga, x=0.01–0.3); chemical formula LiMn 1-x M x Lithium manganese composite oxide represented as O2 (M=Co, Ni, Fe, Cr, Zn or Ta, x=0.01–0.1) or Li2Mn3MO8 (M=Fe, Co, Ni, Cu or Zn); LiNi x Mn 2-x Lithium manganese complex oxide with a spinel structure represented by O4; LiMn2O4 in which part of the Li in the chemical formula is substituted with alkaline earth metal ions; disulfide compound; LiMn x Fe 1-x It may include PO4 (0≤x≤0.9); Fe2(MoO4)3, etc. However, it is not limited to these alone.

[0121] The cathode active material is Li 1+x M y O 2+z It may include, and M may 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 may be 0≤x≤5, 0<y≤2, and 0≤z≤2. Specifically, the 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, LiFePO 4, 0.5 Li2MnO 3·0.5 Li[Mn 0.4 Ni 0.3 Co 0.3 It may include at least one selected from the group consisting of ]O2. Preferably, the 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 0.05It may include any one of ]O2. The cathode active material is Li 1+x M y O 2+z From including, lithium can be sufficiently supplied to the cathode, and Li 1+x M y O 2+z Since it exhibits electrochemical activity after the first cycle without causing a degradation in the overall performance of the battery, 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 It may be in the form of a secondary particle formed by combining or assembling primary particles, or alternatively, it may be in the form of a single particle.

[0122] The positive active material may be included in the positive active material layer in an amount of 50% to 95% by weight, specifically 60% to 90% by weight.

[0123] In addition, the average particle size of the positive electrode active material is 1 μm or more and 30 μm or less, and according to one embodiment, 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 capacity characteristics of the battery are excellent.

[0124] The positive active material layer may further include a positive conductive material.

[0125] The positive electrode conductive material is not particularly limited as long as it is conductive and does not cause chemical changes in the positive electrode or battery. For example, the positive electrode conductive material may include one or more mixtures 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, thermal black; graphene; conductive fibers such as carbon nanofibers and carbon nanotubes; fluorinated carbon; metal powder such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0126] The positive electrode conductive material may be included in the positive electrode active material layer in an amount of 1% to 30% by weight.

[0127] The positive active material layer may further include a positive binder.

[0128] The anode binder is not particularly limited as long as it is a component that helps in the bonding of the anode active material, anode conductive material, etc., and bonding to the current collector, and specifically, it may include at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinylpyrrolidone, polytetrafluoroethylene (PTFE), polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), styrene-butadiene rubber (SBR), and fluororubber.

[0129] The positive binder may be included in the positive active material layer in an amount of 1% to 30% by weight.

[0130] The positive active material layer may include one or more additives, such as an oxidation stabilizing additive, a reduction stabilizing additive, a flame retardant, a heat stabilizer, and an antifogging agent, as needed.

[0131] The positive electrode active material layer may further include a sulfide-based solid electrolyte. The sulfide-based solid electrolyte included in the positive electrode active material layer may have the same composition as the sulfide-based solid electrolyte included in the solid electrolyte layer, or may have a different composition.

[0132] The positive 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.

[0133] The average particle size of the positive electrode active material may be larger than the average particle size of the solid electrolyte particles included 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, thereby providing a lithium ion conduction pathway to the positive electrode active material.

[0134] The present invention provides a secondary battery having the structure described above. In addition, the present invention provides a battery module including the secondary battery as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of the device include, but are not limited to, a power tool driven by receiving power from an electric motor; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), etc.; an electric two-wheeled vehicle including an electric bicycle (E-bike) or an electric scooter (E-scooter); an electric golf cart; and a power system.

[0135] Hereinafter, preferred embodiments are described to facilitate understanding of the present invention. However, the following embodiments are merely examples of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present invention, and that such variations and modifications fall within the scope of the appended claims.

[0136] (Synthesis of Solid Electrolytes)

[0137] Preparation Example 1

[0138] Using lithium sulfide (Li2S, Mitsuwa Chemical product), phosphorus pentasulfide (P2S5, Aldrich product), zinc sulfide (ZnS, Japan Pure Chemical product), lithium chloride (LiCl, Aldrich product), and lithium bromide (LiBr, Aldrich product) as raw materials, the composition is Li 5.4-2y M y PS 4.4 Cl 1.0 Br 0.6 A mixed powder was obtained by weighing and mortar-and-mortar mixing in an Ar gas glove box so that the amount of added Group 12 element (M) was y=0.025. This mixed powder was placed in a ZrO2 pot together with ZrO2 balls to obtain a sealed pot. This sealed pot was installed in a planetary ball mill device and ball milling was performed at 380 rpm for 20 hours, after which the pot was opened in a glove box to recover the powder. This powder was placed in a carbon crucible and sealed, and then calcined at 430°C for 8 hours while flowing Ar gas. The calcined powder was ground in a mortar for 10 minutes to obtain a solid electrolyte coarse powder containing divalent cations of zinc (Zn), a Group 12 element.

[0139] Preparation Example 2

[0140] The solid electrolyte coarse powder containing divalent cations obtained in Preparation 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 a solid electrolyte fine powder containing divalent cations.

[0141] Comparative Manufacturing Example 1

[0142] A solid electrolyte composition not containing divalent cations was obtained in the same manner as in Example 1, except that zinc sulfide (ZnS, manufactured by Japan Pure Chemical) was not used. The composition of the solid electrolyte obtained in Comparative Preparation Example 1 was Li 5.4 PS 4.4 Cl 1.0 Br 0.6 It was.

[0143] Comparative Manufacturing Example 2

[0144] The coarse solid electrolyte powder not containing divalent cations obtained in Comparative Preparation 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 not containing divalent cations.

[0145] Comparative Manufacturing Example 3

[0146] The solid electrolyte coarse powder containing divalent cations obtained in Preparation 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 solid electrolyte fine powder containing divalent cations.

[0147] [evaluation]

[0148] Using the obtained solid electrolyte, the following evaluation was conducted.

[0149] (XRD measurement)

[0150] A predetermined amount of solid electrolyte was placed in a sealed holder inside an Ar gas glove box, and XRD measurements were performed. From the obtained XRD (X-ray diffraction) pattern, the lattice constant, lattice volume, and full width at half maximum were calculated. The full width at half maximum was calculated from the (311) plane crystal peak of the azirodite-type crystal structure observed around 2θ=30° in Fig. 4.

[0151] The measuring device and conditions are as follows.

[0152] · X-ray diffraction device: Rigaku Smartlab

[0153] · Source: Cu-Kα line (λ=1.5418Å)

[0154] · Voltage: 45kV

[0155] · Current: 200mA

[0156] · Scan range (2θ): 10-60°

[0157] · Step size: 0.01°

[0158] (Particle size distribution measurement)

[0159] A solid electrolyte was added to a heptane solvent, and a solid electrolyte dispersion solution was prepared using Span 80 as a dispersant. The particle size distribution was measured using a Mastersizer 3000 particle size measuring device with this dispersion solution. Data analysis was performed with the refractive index of the solid electrolyte set to 2.16.

[0160] (Ion conductivity measurement)

[0161] A predetermined amount of solid electrolyte MACOR ® A Mako pipe was placed inside the pipe, and the Mako pipe and pellet forming jig (upper press pin and lower press pin) were combined and press-formed at approximately 370 MPa using a single-axis press. After that, 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-axis press to obtain a Mako pipe cell. The obtained Mako pipe cell was installed in a jig cell for electrochemical measurement, and an ion conductivity measurement cell was obtained by applying pressure up to 80 MPa using a torque wrench. 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.

[0162] [Evaluation Results]

[0163] (Decision)

[0164] Table 1 shows the evaluation results of the crystal phases (crystal structures) classified from the XRD patterns obtained by XRD measurement. Additionally, the measured XRD patterns are shown in Figure 4. As can be seen from Table 1 and Figure 4, the solid electrolytes obtained in Preparation Example 1, Preparation Example 2, Comparative Preparation Example 1, and Comparative Preparation Example 2 showed almost no impurity phase (also called an unknown phase), and mostly consisted of peaks of the azirodite phase. Sulfide-based solid electrolytes having an azirodite-type crystal structure with no impurity phase or almost no impurity phase were obtained. Sulfide-based solid electrolytes with a high degree of crystallinity can promote the hopping conduction of lithium ions and contribute to an increase in ion conductivity.

[0165] [Table 1]

[0166]

[0167] (Lattice volume)

[0168] The lattice constant derived from the XRD pattern in Preparation Examples 1 and 2 is in the range of 9.8750 Å to 9.8755 Å, and the lattice volume is 962.9 Å. 3 at 963.1Å 3 It was within the range. Meanwhile, in Comparative Preparation Examples 1 and 2, in which lithium sites of the sulfide-based solid electrolyte are not substituted by a Group 12 element (M), the lattice constant is in the range of 9.9467 Å to 9.9470 Å, and the lattice volume is 984.1 Å. 3 at 984.2Å 3It was within the range. It was found that substituting lithium sites in an azirodite-type crystal structure with a 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 as one of the two lithium sites was substituted with a Group 12 element (M) and the other became a lithium void. The lithium void is thought to serve as a pathway for lithium ion hopping conduction, contributing to an increase in ion conductivity. Furthermore, the Group 12 element (M) substituted in the lithium site can have a divalent charge, which can change the attractive force of anions around the Group 12 element (M) site compared to monovalent lithium ions. Accordingly, it is thought that the crystal volume of the sulfide-based solid electrolyte changed, resulting in a structure suitable for lithium ion hopping conduction.

[0169] The full width at half maximum of the (311) plane crystal peak of the azirodite crystal structure was 0.06° in Preparation Examples 1 and 2. On the other hand, it was 0.08° in Comparative Preparation Examples 1 and 2. The full width at half maximum is small in Preparation Examples 1 and 2, which are solid electrolytes containing divalent cations. It is thought that the small full width at half maximum corresponds to a large crystallite size and contributes to an increase in ionic conductivity. Furthermore, it was found that the crystallinity and crystal size of the solid electrolyte do not change due to the pulverization process from coarse powder to fine powder.

[0170] (Particle size distribution)

[0171] The results of the particle size distribution measurement are shown in Table 2. The average particle size D50 was 15.6 μm for the coarse solid electrolyte powder containing divalent cations of Preparation Example 1 and 1.68 μm for the fine solid electrolyte powder containing divalent cations of Preparation Example 2. Additionally, it was 14.7 μm for the coarse solid electrolyte powder not containing divalent cations of Comparative Preparation Example 1 and 1.42 μm for the fine solid electrolyte powder not containing divalent cations of Comparative Preparation Example 2. It was confirmed that the coarse solid electrolyte powder could be finely ground into fine solid electrolyte powder by additional wet grinding. Furthermore, it was 1.2 μm for the fine solid electrolyte powder containing divalent cations of Comparative Preparation Example 3.

[0172] The average particle size D10 was 4.85 μm in the coarse solid electrolyte powder containing divalent cations of Preparation Example 1 and 0.71 μm in the fine solid electrolyte powder containing divalent cations of Preparation Example 2. In addition, it was 4.03 μm in the coarse solid electrolyte powder not containing divalent cations of Comparative Preparation Example 1 and 0.73 μm in the fine solid electrolyte powder not containing divalent cations of Comparative Preparation Example 2. Furthermore, it was 0.71 μm in the fine solid electrolyte powder containing divalent cations of Comparative Preparation Example 3.

[0173] The average particle size D90 was 59.2 μm in the coarse solid electrolyte powder containing divalent cations of Preparation Example 1 and 5.09 μm in the fine solid electrolyte powder containing divalent cations of Preparation Example 2. In addition, it was 55.7 μm in the coarse solid electrolyte powder not containing divalent cations of Comparative Preparation Example 1 and 4.86 μm in the fine solid electrolyte powder not containing divalent cations of Comparative Preparation Example 2. Furthermore, it was 3.09 μm in the fine solid electrolyte powder containing divalent cations of Comparative Preparation Example 3.

[0174] [Table 2]

[0175]

[0176] (Ionic conductivity)

[0177] The measurement results of ionic conductivity are shown in Table 1. The ionic conductivity was 12.98 mS / cm for the solid electrolyte coarse powder containing divalent cations of Preparation Example 1 and 4.30 mS / cm for the solid electrolyte fine powder containing divalent cations of Preparation Example 2. Additionally, the ionic conductivity was 9.91 mS / cm for the solid electrolyte coarse powder not containing divalent cations of Comparative Preparation Example 1 and 3.3 mS / cm for the solid electrolyte fine powder not containing divalent cations of Comparative Preparation Example 2. Furthermore, the ionic conductivity was 2.5 mS / cm for the solid electrolyte fine powder containing divalent cations of Comparative Preparation Example 3. Regardless of the presence or absence of divalent cations, the ionic conductivity of the solid electrolyte coarse powder was higher than that of the solid electrolyte fine powder. It is believed that the ionic conductivity is higher when using the solid electrolyte coarse powder because there are fewer grain boundaries per unit volume. Regardless of the average particle size of the solid electrolyte, the solid electrolyte containing divalent cations had a higher ionic conductivity than the solid electrolyte not containing divalent cations. Even if divalent cations were included, if the particle size of the solid electrolyte was made too small, impurities were generated and the ionic conductivity decreased.

[0178] Example 1

[0179] 90 mg of solid electrolyte powder containing divalent cations obtained in Preparation Example 1 was weighed, placed in a molding jig, and pressurized at 110 MPa for 1 minute to obtain a solid electrolyte pellet.

[0180] An NCM-based cathode active material with a Ni content of 80 mol%, fine powder of a solid electrolyte containing divalent cations obtained in Preparation Example 2, and a conductive material were weighed in a mass ratio of 60:35:5. These were mixed to obtain a cathode composite.

[0181] 17 mg of a positive composite was placed on one side of a solid electrolyte pellet, then flattened by pressing with a SUS press pin of a molding jig, and then pressure-molded at 110 MPa for 1 minute to obtain a positive active material layer formed on the solid electrolyte layer. A SUS plate was provided on the positive active material layer as a positive current collector, and a SUS plate was provided as a negative current collector to be in direct contact with the solid electrolyte layer opposite to the positive active material layer. This was pressure-molded at 554 MPa for 1 minute to obtain a laminate. A Mako pipe cell was fabricated by combining the obtained laminate with a SUS press pin. The obtained Mako pipe cell was installed in a battery cell, and a low confining pressure of about 0.1 MPa was applied to obtain an all-solid-state battery. That is, the all-solid-state battery of Example 1 contains a solid electrolyte coarse powder containing divalent cations in the solid electrolyte layer, and a solid electrolyte fine powder containing divalent cations in the positive active material layer.

[0182] The all-solid-state battery of Example 1 is shown in FIG. 1. As shown in FIG. 1, a negative electrode current collector (1) and a solid electrolyte layer (2) containing a solid electrolyte containing divalent cations are in direct contact. The all-solid-state battery of Example 1 is in a battery precursor state before the first charge and does not contain a negative electrode active material layer. The all-solid-state battery of Example 1 is an anode-free all-solid-state battery. By charging and discharging the anode-free all-solid-state battery, lithium is precipitated and dissolved between the negative electrode current collector (1) and the solid electrolyte layer (2) containing the solid electrolyte, so that it can operate as an all-solid-state battery.

[0183] Comparative Example 1

[0184] A solid-state battery was obtained in the same manner as in Example 1, except that in the step of obtaining a solid electrolyte pellet, the solid electrolyte coarse powder obtained in Comparative Example 1 that does not contain divalent cations was used instead of the solid electrolyte coarse powder containing divalent cations obtained in Preparation Example 1, and in the step of obtaining an anode mixture, the solid electrolyte fine powder obtained in Comparative Example 2 that does not contain divalent cations was used instead of the solid electrolyte fine powder containing divalent cations obtained in Preparation Example 2. That is, the solid-state battery of Comparative Example 1 includes solid electrolyte coarse powder that does not contain divalent cations in the solid electrolyte layer (5) and solid electrolyte fine powder that does not contain divalent cations in the anode active material layer (3), as shown in FIG. 2.

[0185] Comparative Example 2

[0186] In the step of obtaining an all-solid-state battery, an Ag-C intermediate layer was provided on a solid electrolyte layer opposite to the positive active material layer, a SUS plate was provided as a negative current collector on the Ag-C intermediate layer, and a restraining pressure of about 4 MPa was applied; except for these steps, an all-solid-state battery was obtained in the same manner as 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 a SUS plate. That is, as shown in FIG. 3, the all-solid-state battery of Comparative Example 2 includes a solid electrolyte coarse powder that does not contain divalent cations in the solid electrolyte layer (5), a solid electrolyte fine powder that does not contain divalent cations in the positive active material layer (3), and an intermediate layer (6) is provided between the solid electrolyte layer (5) and the negative current collector (1).

[0187] [All-solid-state battery evaluation]

[0188] (Charge / Discharge Test)

[0189] A charge-discharge test was performed at 25°C using the obtained all-solid-state battery. The voltage range was set to 4.25V-3.0V, the charging conditions to CC(0.05C)-CV(0.01C cutoff), and the discharging conditions to CC(0.05C). The charge capacity and discharge capacity were determined from the obtained charge-discharge curves. In addition, the discharge capacity retention rate (%) at 25°C under charging conditions CC(0.05C)-CV(0.01C) and discharging conditions CC(0.05C) was derived by the following formula.

[0190] Discharge capacity in each cycle / Discharge capacity in the first cycle × 100

[0191] [Evaluation Results]

[0192] (All-solid-state battery characteristics)

[0193] The relative ratio of the initial discharge capacity of the all-solid-state battery of Example 1 to the capacity of the all-solid-state battery 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 azirodite-type crystal structure, was able to increase the discharge capacity compared to the all-solid-state battery of Comparative Example 1, which does not include the sulfide-based solid electrolyte of the present invention.

[0194] Figure 5 is a graph showing the discharge capacity retention rate of the all-solid-state batteries of Example 1, Comparative Example 1, and Comparative Example 2.

[0195] The discharge capacity retention rate in the third cycle was 99.4% in Example 1, 78.8% in Comparative Example 1, and 92.4% in Comparative Example 2.

[0196] The discharge capacity retention rate at the 7th cycle was 98.6% in Example 1 and 85.7% in Comparative Example 2. In Comparative Example 1, the discharge capacity dropped sharply after 4 cycles, making it impossible to measure the discharge capacity. Unlike Comparative Example 1, Comparative Example 2 has an intermediate layer (6) between the solid electrolyte layer (5) and the negative current collector (1). Since the intermediate layer (6) suppressed the growth of lithium dendrites, it is believed that Comparative Example 2 exhibited better cycle characteristics than Comparative Example 1.

[0197] 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 azirodite-type crystal structure, was able to improve 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 the present invention.

[0198] The all-solid-state battery of Example 1 comprises a solid electrolyte component containing divalent cations in the solid electrolyte layer, i.e., the solid electrolyte component of Preparation Example 1, and the all-solid-state battery of Comparative Example 1 comprises a solid electrolyte component that does not contain divalent cations in the solid electrolyte layer, i.e., the solid electrolyte component of Comparative Preparation Example 1. As shown in Table 1, the solid electrolyte component of Preparation Example 1 exhibits an ionic conductivity approximately 1.3 times higher than that of the solid electrolyte component of Comparative Preparation Example 1. As shown in Fig. 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 component containing divalent cations.

[0199] In addition, typically, during the charging and discharging of a solid-state battery, a high confining pressure is applied to suppress the growth of lithium dendrites on the negative electrode current collector. However, as can be seen from FIG. 5, the all-solid-state battery of Example 1, to which a low confining pressure of about 0.1 MPa was applied, exhibited superior cycle characteristics compared to the all-solid-state battery of Comparative Example 2, to which a high confining pressure of about 4 MPa was applied. This is thought to be due to the use of a solid electrolyte containing divalent cations in the solid electrolyte layer and the positive active material layer. Thus, the all-solid-state battery of the present invention can be operated at a low confining pressure.

[0200] Although the present invention has been described above with reference to limited embodiments and drawings, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical spirit and claims of the present invention by those skilled in the art to which the present invention belongs.

[0201] [Explanation of the symbol]

[0202] 1: Cathode current collector

[0203] 2: Solid electrolyte layer containing a solid electrolyte containing divalent cations

[0204] 3: Positive active material layer

[0205] 4: Positive current collector

[0206] 5: Solid electrolyte layer containing a solid electrolyte that does not contain divalent cations

[0207] 6: Middle layer

Claims

1. An all-solid-state battery comprising a positive electrode including a positive 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 above-mentioned all-solid-state battery does not include a negative electrode active material, and Lithium ions are supplied from the positive active material layer by charging, and a lithium metal layer as a negative active material is formed on the negative current collector, and An all-solid-state battery in which the above-mentioned solid electrolyte layer comprises a sulfide-based solid electrolyte containing a Group 12 element and having an azirodite-type crystal structure.

2. In Paragraph 1, All-solid-state battery in which the above-mentioned negative current collector and the above-mentioned solid electrolyte layer are in direct contact.

3. In Paragraph 1, The above sulfide-based solid electrolyte has the chemical formula Li 7-x-2y M y PS 6-x Ha x It is displayed as, In the above chemical formula, The above M is one or more elements selected from Group 12 elements, and The above Ha is one or more elements selected from halogen elements, and Satisfying 0<x<2.5, 0<y<0.45, All-solid-state battery.

4. In Paragraph 3, All-solid-state battery in which M is Zn.

5. In Paragraph 1, An all-solid-state battery that does not contain the reaction product of the above-mentioned negative current collector and the above-mentioned sulfide-based solid electrolyte.

6. In Paragraph 1, A solid-state battery in which the above-described solid-state battery is pressurized to 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. In Paragraph 1, An all-solid-state battery in which the positive electrode active material layer comprises the sulfide-based solid electrolyte.

8. In Paragraph 1, All-solid-state battery, wherein D10 of the above-mentioned solid electrolyte is 0.1 to 10 μm.

9. In Paragraph 1, An all-solid-state battery in which the D50 of the above-mentioned solid electrolyte is 0.1 to 50 μm.

10. In Paragraph 1, An all-solid-state battery in which the D90 of the above-mentioned solid electrolyte is 1 to 100 μm.

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