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 capable of being 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 in the all-solid-state battery, without containing a negative electrode active material, lithium ions are supplied from the positive electrode active material layer by charging to allow a lithium metal layer as a negative electrode active material to be formed on the negative electrode current collector, and the solid electrolyte layer includes a sulfide-based solid electrolyte containing a group 2 element and having an argyrodite-type crystal structure.

Description

All-solid-state batteries

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

[0002] This application claims priority to Japanese Application No. 2023-221548, filed December 27, 2023, the entire disclosure of which is incorporated herein by reference.

[0003] To achieve high-density, long-life, and high-energy density, the development of all-solid-state batteries is underway, replacing the electrolyte of lithium-ion batteries with solid electrolytes. Among the numerous solid electrolytes, Li 10 GeP2S 12 Sulfide-based solid electrolytes have the advantage of high ionic conductivity close to that of electrolytes and are soft, making it easy to obtain adhesion with active materials. Therefore, the practical application of all-solid-state batteries using sulfide-based solid electrolytes is anticipated.

[0004] Meanwhile, lithium metal is attracting attention as an anode material for all-solid-state batteries because it can increase the mass energy density (Wh / kg) due to its low mass per unit volume and large theoretical capacity. However, Li 10 GeP2S 12 Sulfide-based solid electrolytes have the problem of low stability toward lithium metal, making them difficult to use with lithium metal negative electrodes.

[0005] In addition, when lithium metal is used as a battery negative electrode, a battery is generally manufactured by attaching lithium foil on a flat current collector, but since lithium is an alkali metal and is highly reactive, it reacts explosively with water and also reacts with oxygen in the air, so there is a disadvantage in that it is difficult to manufacture and use in a general environment. In particular, when lithium metal is exposed to the air, an oxide film such as LiOH, Li2O, Li2CO3, etc. is formed as a result of oxidation. When a surface oxide film exists on the surface, the oxide film acts as an insulating film, lowering the electrical conductivity and hindering the smooth movement of lithium ions, causing a problem of increased electrical resistance.

[0006] To address this issue, Patent Documents 1 to 3 disclose an anode-less all-solid-state battery that deposits a trace amount of a seed metal capable of forming an alloy with lithium, such as Ag or Zn, on a negative electrode current collector. However, such an anode-less all-solid-state battery has the problem of high cost because it requires an additional process for coating and sputtering the metal. Furthermore, an anode-less all-solid-state battery requires a high confining pressure to be applied during battery operation to prevent the growth of lithium dendrites.

[0007] To solve the above problem, the inventors of the present invention conducted comprehensive research and designed an anode-free all-solid-state battery that can form a lithium metal layer on a negative electrode current collector by lithium ions transferred from a 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 a polyvalent cation as the solid electrolyte used in the anode-free all-solid-state battery, the inventors developed an anode-free all-solid-state battery that has excellent discharge capacity and cycle characteristics and can be operated at a low confining pressure.

[0008] The purpose of the present invention is to provide an anode-free all-solid-state battery with improved discharge capacity and cycle characteristics.

[0009] In addition, the present invention aims to provide an anode-free all-solid-state battery that can be driven at a low confining pressure.

[0010] To achieve the above purpose, the present invention,

[0011] 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,

[0012] The above all-solid-state battery does not contain a negative electrode active material,

[0013] By charging, lithium ions are supplied from the positive electrode active material layer, and a lithium metal layer as a negative electrode active material is formed on the negative electrode current collector.

[0014] An all-solid-state battery is provided, wherein the solid electrolyte layer includes a sulfide-based solid electrolyte containing a Group 2 element and having an argylodite-type crystal structure.

[0015] In one embodiment, the negative electrode current collector and the solid electrolyte layer can be in direct contact.

[0016] In one embodiment,

[0017] The above sulfide-based solid electrolyte has the chemical formula Li 7-x-2y M y PS 6-x Ha x is displayed as,

[0018] In the above chemical formula,

[0019] The above M is one or more elements selected from the second group elements,

[0020] The above Ha is one or more elements selected from halogen elements,

[0021] It can satisfy 0<x<2.5, 0<y<0.45.

[0022] In one embodiment, M may be Ca.

[0023] In one embodiment, the reaction product of the negative electrode current collector and the sulfide-based solid electrolyte may not be contained.

[0024] 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 laminated.

[0025] In one embodiment, the positive electrode active material layer may include the sulfide-based solid electrolyte.

[0026] In one embodiment, the average particle diameter of the sulfide-based solid electrolyte included in the solid electrolyte layer may be larger than the average particle diameter of the sulfide-based solid electrolyte included in the positive electrode active material layer.

[0027] In one embodiment, the Group 2 element may be present at the 48h site of the argyrodite-type crystal structure.

[0028] The present invention can provide an anode-free all-solid-state battery with improved discharge capacity and cycle characteristics.

[0029] In addition, the present invention can provide an anode-free all-solid-state battery that can be driven at a low confinement pressure.

[0030] Figure 1 is a schematic diagram of the all-solid-state batteries of Examples 1 to 3.

[0031] Figure 2 is a schematic diagram of the all-solid-state battery of Comparative Example 1.

[0032] Figure 3 is a schematic diagram of the all-solid-state battery of Comparative Example 2.

[0033] FIG. 4 is a drawing showing X-ray diffraction (XRD) patterns of solid electrolytes of Manufacturing Examples 1 and 2, and Comparative Manufacturing Examples 1 and 2.

[0034] Figure 5 is a graph showing the discharge capacity retention rate of the all-solid-state batteries of Examples 1 to 4 and Comparative Examples 1 and 2.

[0035] Figure 6 is a graph showing the discharge capacity retention rate of the all-solid-state batteries of Examples 1 to 4, Comparative Examples 1 and 2.

[0036] Figure 7 is an SEM image showing the calcium distribution in the all-solid-state battery of Example 1.

[0037] Figure 8 is a graph showing an SEM image (left) and calcium line analysis results (right) of the negative electrode current collector side of the all-solid-state battery of Example 1 after the first charge.

[0038] Hereinafter, the present invention will be described in more detail.

[0039] The terms and words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to best explain his or her invention.

[0040] In the drawings, parts irrelevant to the description are omitted to clearly illustrate the present invention, and similar parts are designated with similar reference numerals throughout the specification. Furthermore, the sizes and relative sizes of components depicted in the drawings are not necessarily to scale and may be reduced or exaggerated for clarity of explanation.

[0041] In this specification, 'Dn' means particle size distribution, and means particle size at the n% point of the cumulative distribution of particle numbers by particle size. That is, D50 is the particle size (center particle diameter, average particle diameter) at the 50% point of the cumulative distribution of particle numbers by particle size, D90 is the particle size at the 90% point of the cumulative distribution of particle numbers by particle size, and D10 is the particle size at the 10% point of the cumulative distribution of particle numbers by particle size. Meanwhile, the particle size distribution can be measured using the laser diffraction method. Specifically, after the powder to be measured is dispersed 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 diffraction pattern due to particle size when the particle passes through the laser beam is measured to calculate the particle size distribution.

[0042] [All-solid-state battery]

[0043] 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, and 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 2 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 driven at a low confining pressure by having the above configuration.

[0044] Meanwhile, in the present invention, the all-solid-state battery means a state before the first lithium metal deposition (first charge) on the negative electrode current collector (also called an all-solid-state battery precursor).

[0045] All-solid-state batteries can also be all-solid-state lithium secondary batteries.

[0046] In order to prevent the growth of lithium dendrites, an all-solid-state battery is subjected to a confining pressure during charging and discharging. The confining pressure can be applied in a direction perpendicular to the direction in which the positive electrode, the negative electrode current collector, and the solid electrolyte layer disposed between the positive and negative electrode current collectors are laminated, i.e., in a direction perpendicular to the plane direction of the negative electrode current collector. For example, the confining pressure can be achieved by fixing the positive electrode and negative electrode current collector sides of the all-solid-state battery with jigs from both sides.

[0047] To prevent the growth of lithium dendrites, a large confining pressure is typically applied to all-solid-state batteries. However, the all-solid-state battery of the present invention, which utilizes a sulfide-based solid electrolyte containing divalent cations, may require almost no confining pressure.

[0048] The all-solid-state battery may be pressurized 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 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.

[0049] The negative electrode of a lithium secondary battery is typically formed on a negative electrode current collector. However, in the present invention, an anode-free battery structure is assembled using only a negative electrode current collector without metal particles or a coating layer on its surface. Then, lithium ions released from the positive electrode active material upon charging form a lithium metal layer as a negative electrode active material on the negative electrode current collector. As a result, an anode having a configuration of a negative electrode current collector / negative electrode active material layer is formed, forming a configuration typical of a lithium secondary battery.

[0050] That is, the anode-free battery in the present invention is a concept that includes both an anode-free battery in which a negative electrode is not formed on the negative electrode collector when first assembled, and a battery in which a negative electrode is formed on the negative electrode collector during use and thus a negative electrode is present.

[0051] In addition, in the negative electrode of the present invention, the form of the lithium metal formed as the negative electrode active material on the negative electrode current collector includes both a form in which the lithium metal is formed as a layer and a structure in which the lithium metal is not formed as a layer (for example, a structure in which the lithium metal is agglomerated in the form of particles).

[0052] Hereinafter, the present invention will be described based on the form of a lithium metal layer in which lithium metal is formed as a layer, but it is clear that this description does not exclude a structure in which lithium metal is not formed as a layer.

[0053] Solid electrolyte layer

[0054] The solid electrolyte layer contains a solid electrolyte. The solid electrolyte layer can function as an insulator and an ion-conducting channel in an all-solid-state lithium secondary battery.

[0055] The solid electrolyte layer may have a thickness of about 50 μm or less, and preferably about 15 μm to 50 μm. The thickness may be appropriate within the aforementioned range, taking into consideration ionic conductivity, physical strength, and the energy density of the battery to be applied. 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, the solid electrolyte layer may have a tensile strength of about 100 kgf / cm2 to about 2,000 kgf / cm2 along with the thickness range. In addition, the solid electrolyte layer may have a porosity of 15 vol% or less or about 10 vol% or less. In this way, the solid electrolyte layer according to the present invention may have high mechanical strength despite being a thin film.

[0056] (solid electrolyte)

[0057] 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 as a separator.

[0058] 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.

[0059] The average particle size and particle size distribution of the solid electrolyte can be controlled, for example, by changing conditions such as the rotation speed and time of the ball mill device. Accordingly, it is possible to produce solid electrolyte coarse powder having a relatively large average particle size, solid electrolyte fine powder having a relatively small average particle size, and solid electrolyte ultra-coarse powder having a wider particle size distribution than the solid electrolyte coarse powder. For example, solid electrolyte coarse powder and solid electrolyte ultra-coarse powder can be produced separately by controlling the grinding time of the ball mill device.

[0060] The average particle size 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, and more preferably 1 to 3 μm.

[0061] The average particle size of the solid electrolyte coarse powder may be the same as the average particle size of the solid electrolyte coarse powder. That is, 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 D10 of the solid electrolyte coarse powder is smaller than the D10 of the solid electrolyte coarse powder, and the D90 of the solid electrolyte coarse powder is larger than the D90 of the solid electrolyte coarse powder. The D10 of the solid electrolyte coarse powder is 1 to 6 μm, preferably 2 to 5 μm. The D10 of the solid electrolyte coarse powder is 3 to 8 μm, preferably 4 to 7 μm. The D90 of the solid electrolyte coarse powder is 100 to 500 μm, preferably 200 to 400 μm. The D90 of the solid electrolyte coarse powder is 30 to 100 μm, preferably 40 to 80 μm.

[0062] 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 the solid electrolyte coarse powder and the solid electrolyte ultra-fine powder have a large average particle size and few grain boundaries per unit volume, they can exhibit high ionic conductivity when used in the solid electrolyte layer. The solid electrolyte fine powder can enter the gaps between the positive electrode active material particles when used in the positive electrode active material layer, thereby providing a lithium ion conduction path 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.

[0063] The particle size distribution of the solid electrolyte can affect the discharge capacity and cycle characteristics of the all-solid-state battery. The narrower the particle size distribution of the solid electrolyte, for example, the smaller the (D90-D10) / D50, the more uniform lithium conduction during charge and discharge, which can maintain a high discharge capacity. If the particle size distribution of the solid electrolyte is wide, lithium conduction during charge and discharge becomes uneven, which can lower the discharge capacity. (D90-D10) / D50 is 1 to 30, preferably 1 to 10, and more preferably 1 to 5. By controlling the particle size distribution of the solid electrolyte within the above range in addition to the average particle size, the discharge capacity and cycle characteristics of the all-solid-state battery can be further improved.

[0064] There are no particular restrictions on the sulfide-based solid electrolyte as long as it contains sulfur (S), and any known sulfide-based solid electrolyte can be used.

[0065] Sulfide-based solid electrolytes may have a crystal structure. Sulfide-based solid electrolytes with a crystal structure can promote lithium ion conduction and achieve high lithium ion conductivity.

[0066] The sulfide-based solid electrolyte may have an argyrodite-type, NASICON-type, perovskite-type, garnet-type, or LGPS-type crystal structure. Preferably, the sulfide-based solid electrolyte has an argyrodite-type crystal structure. A sulfide-based solid electrolyte having an argyrodite-type crystal structure has high stability toward lithium metal, enabling the use of lithium metal with a high mass energy density as an anode material.

[0067] The sulfide-based solid electrolyte may be in the form of amorphous, glass, or glass ceramic.

[0068] The sulfide-based solid electrolyte has the ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and may include a Li-PS-based glass or a Li-PS-based glass ceramic. 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, the present invention is not particularly limited to these.

[0069] The sulfide-based solid electrolyte may include a crystalline phase and an amorphous phase. The sulfide-based solid electrolyte may 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 an impurity phase or an unknown phase). The argyrodite-type crystal structure is preferably a cubic system. The other phase may be a crystalline phase or an amorphous phase. The other phase may include a Li2S phase, a P2S5 phase, a LiCl phase, a LiBr phase, a Li3PS4 phase, a MgS phase, a CaS phase, a SrS phase, a BaS phase, a CaBr2 phase, etc., regardless of whether it is a crystalline phase or an amorphous phase. Preferably, the sulfide-based solid electrolyte does not include or substantially does not include an impurity phase other than the argyrodite phase. That is, preferably, the sulfide-based solid electrolyte may be composed only of the argyrodite phase. Since lithium ion conduction is not easily inhibited when the sulfide-based solid electrolyte does not contain or substantially does not contain an impurity phase, the sulfide-based solid electrolyte can have high lithium ion conductivity.

[0070] The ratio of crystalline phases contained in a sulfide-based solid electrolyte can be quantitatively or semi-quantitatively evaluated from XRD patterns. One method is to compare the peak intensities (height or area) of the XRD patterns to evaluate the ratio of crystalline phases.

[0071] The sulfide-based solid electrolyte has the chemical formula Li 7-x-2y M y PS 6-x Ha x It can be expressed as. In the chemical formula, M is one or more elements selected from Group 2 elements, Ha is one or more elements selected from halogen elements, and can satisfy 0<x<2.5, 0<y<0.45. The lattice volume of the sulfide-based solid electrolyte is 950Å. 3 More than 980Å 3It may be below. Ha may include Br. 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.

[0072] A sulfide-based solid electrolyte according to one embodiment of the present invention comprises Li 7-x PS 6-x Ha x A portion of the lithium in can be substituted with a Group 2 element (M) that can become a divalent cation. The Group 2 element (M) substituting for lithium may be at least one selected from the group consisting of magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). The ionic radius (6-coordination) of lithium (Li) is 90 pm, and the ionic radii (6-coordination) of magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba) are 86 pm, 114 pm, 132 pm, and 149 pm, respectively. Based on the valence of the elements, two lithiums can be substituted with one Group 2 element (M). Substitution by the Group 2 element (M) creates lithium site vacancies, which can improve lithium ion conductivity. In addition, the lattice constant and lattice volume of the sulfide-based solid electrolyte can be changed by substitution with a Group 2 element (M), thereby obtaining a crystal structure suitable for lithium ion conduction.

[0073] In addition, the sulfide-based solid electrolyte according to one embodiment of the present invention comprises a second group element (M) that can be a divalent cation, Li 7-x PS 6-x Ha xIt can be formed by invading into the crystal lattice. The second group element (M) invading into the crystal lattice may be at least one selected from the group consisting of magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba) may be used alone or in combination. Preferably, the second group element (M) is magnesium (Mg) or calcium (Ca). Li 7-x PS 6-x Ha x The lattice constant and lattice volume of a sulfide-based solid electrolyte change due to the intrusion of a Group 2 element (M) into the crystal lattice, thereby providing a crystal structure suitable for lithium ion conduction. A sulfide-based solid electrolyte containing calcium (Ca) as a Group 2 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. In addition, by using such a sulfide-based solid electrolyte, the growth of lithium dendrites on the negative electrode current collector is prevented, so that the anode-free all-solid-state battery of the present invention can be operated at a low confining pressure.

[0074] The Group 2 element (M) can be located in the pore site of the sulfide-based solid electrolyte having an argyrodite-type crystal structure. Since the Group 2 element (M) is located in the pore site of the argyrodite-type crystal structure, at least a portion of the Group 2 element (M) can move out of the pore site during charge / discharge of the all-solid-state battery. A portion of the Group 2 element (M) that has moved out of the pore site can be deposited at the interface between the negative electrode current collector and the solid electrolyte layer, and / or the interface between the positive electrode active material layer and the solid electrolyte layer. In addition, a portion of the Group 2 element (M) that has moved out of the pore site can return to the original pore site or another pore site. In the all-solid-state battery of the present invention, since the amount y of the Group 2 element (M) added to the sulfide-based solid electrolyte is small, even if the Group 2 element (M) has moved out of the pore site, the argyrodite-type crystal structure of the sulfide-based solid electrolyte can be maintained. The Group 2 element (M) can move as a carrier in the all-solid-state battery together with lithium during charging and discharging of the all-solid-state battery. The position of the Group 2 element (M) can be determined by a measurement technique known to those skilled in the art, such as neutron diffraction analysis.

[0075] Preferably, the Group 2 element (M) is magnesium (Mg) and / or calcium (Ca), and particularly preferably calcium (Ca). When the Group 2 element (M) is magnesium (Mg) and / or calcium (Ca), the sulfide-based solid electrolyte can have a high crystallinity, and thus the sulfide-based solid electrolyte can have a high ionic conductivity. This is thought to be because the ionic radius of lithium (Li) is 90 pm and the ionic radii of magnesium (Mg) and calcium (Ca) are 86 pm and 114 pm, respectively, which are close values, so that the argyrodite-type crystal structure is likely to be maintained even after substitution by the Group 2 element (M).

[0076] Chemical formula Li 7-x-2y M y PS 6-x Ha xThe addition amount y of the Group 2 element (M) in satisfies 0 < y < 0.45, preferably satisfies 0 < y < 0.1, more preferably satisfies 0.005 ≤ y ≤ 0.04, and even more preferably satisfies 0.01 ≤ y ≤ 0.03. When y satisfies the above range, the sulfide-based solid electrolyte can have high ionic conductivity. When y is 0, the change in crystal structure due to the substitution of the Group 2 element (M) may not be obtained, and thus the ionic conductivity may be low. When y is 0.45 or more, the argyrodite-type crystal structure of the sulfide-based solid electrolyte cannot be maintained, and the ionic conductivity may be low. In addition, the impurity phase that inhibits lithium ion conduction in the sulfide-based solid electrolyte may increase, and thus the ionic conductivity may be low.

[0077] Chemical formula Li 7-x-2y M y PS 6-x Ha x The halogen (Ha) in is at least one element selected from halogen elements. Preferably, the halogen (Ha) includes chlorine (Cl) and / or bromine (Br). When sulfur (S) is a divalent anion, it has a stronger attraction force for lithium ions than a monovalent halogen, and thus can significantly inhibit the movement of lithium ions. By including bromine (Br), the occupancy rate of sulfur (S) at a specific site in the argyrodite-type crystal structure is lowered, so that the halogen increases and the lithium ion mobility around the bromine (Br) site can become active. As a result, the lithium ion conductivity 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 adsorb moisture, which can lower the lithium ion conductivity, and thus can improve the lithium ion conductivity of the sulfide-based solid electrolyte.

[0078] Chemical formula Li 7-x-2y M y PS 6-x Ha xThe ratio x of halogen (Ha) in satisfies 0<x<2.5, preferably satisfies 1.0<x<2.0, and more preferably satisfies 1.3<x<1.8. When x satisfies the above range, the argyrodite-type crystal structure is stabilized, so that the sulfide-based solid electrolyte can have high ionic conductivity.

[0079] The Group 2 element (M) included in the sulfide-based solid electrolyte can move during operation of the all-solid-state battery. Preferably, the Group 2 element (M) included in the sulfide-based solid electrolyte can move in the form of a divalent cation.

[0080] At least a portion of the Group 2 element (M) can migrate toward the negative electrode during charging of the all-solid-state battery and can be deposited at the interface between the negative electrode current collector and the solid electrolyte layer. If a separate intermediate layer exists between the negative electrode current collector and the solid electrolyte layer, the Group 2 element (M) can be deposited at the interface between the negative electrode current collector and the intermediate layer. A portion of the Group 2 element (M) can also be deposited within the intermediate layer.

[0081] At least a portion of the Group 2 element (M) can migrate toward the positive electrode during discharge of the all-solid-state battery and can be deposited at the interface between the positive electrode active material layer and the solid electrolyte layer. If a separate intermediate layer exists between the positive electrode active material layer and the solid electrolyte layer, the Group 2 element (M) can be deposited at the interface between the positive electrode current collector and the intermediate layer. A portion of the Group 2 element (M) can also be deposited within the intermediate layer.

[0082] The Group 2 element (M) can be deposited at each interface in the form of one or more selected from the group consisting of the Group 2 element (M) alone, an alloy with lithium, and a compound containing the Group 2 element (M). By depositing the Group 2 element (M) at each interface during charge and discharge, the adhesion at each interface is improved, and an ion conduction path and / or an electric conduction path spanning each interface is maintained. Accordingly, the all-solid-state battery of the present invention has improved discharge capacity and cycle characteristics. In addition, the all-solid-state battery of the present invention can be charged and discharged without a high confining pressure of several MPa or more required during operation of a conventional all-solid-state battery.

[0083] It is preferable that the Group 2 element (M) be present at the 48h site of the argyrodite-type crystal structure. A portion of the Group 2 element (M) present at the 48h site of the argyrodite-type crystal structure can migrate to the negative electrode side during charging of the all-solid-state battery and to the positive electrode side during discharging of the all-solid-state battery without destroying the argyrodite-type crystal structure.

[0084] The alloy of group 2 elements (M) and lithium is MLi x (1≤x≤2) may be included. Preferably, the alloy of the Group 2 element (M) and lithium is CaLi x (1≤x≤2) may be included. More preferably, the alloy of the Group 2 element (M) and lithium may include at least one selected from the group consisting of CaLi and CaLi2. In addition, it may include CaLi3 and Ca3Li.

[0085] Compounds of Group 2 elements (M) and lithium may include compounds of calcium and lithium. Additionally, compounds of magnesium and lithium may be included.

[0086] The ionic conductivity of a sulfide-based solid electrolyte can be affected by the degree of crystallinity of the sulfide-based solid electrolyte. The degree of crystallinity can be evaluated from an XRD pattern. In the XRD pattern, if no or only amorphous phases other than the argyrodite crystal phase (crystalline phases or amorphous phases such as Li2S phase, P2S5 phase, LiCl phase, LiBr phase, Li3PS4 phase, MgS phase, CaS phase, SrS phase, and BaS phase) are observed, the sulfide-based solid electrolyte can have high ionic conductivity.

[0087] The lattice volume of sulfide-based solid electrolytes can change due to the substitution of lithium sites by Group 2 elements (M). Although not bound by theory, it is thought that the Group 2 elements (M) exhibit divalent cation properties, which strengthens their interaction with other anions present in the sulfide-based solid electrolyte, thereby changing, i.e., increasing or decreasing, the lattice volume. This change in lattice volume leads to a crystal structure suitable for lithium ion conduction, enabling the sulfide-based solid electrolyte to have high ionic conductivity.

[0088] The lattice volume of the sulfide-based solid electrolyte is 950Å. 3 More than 980Å 3 Below, preferably 958Å 3 More than 966Å 3 or less, more preferably 960Å 3 More than 964Å 3 Below, and more preferably 961Å 3 More than 963Å 3 Below. Lattice constant and lattice volume can be evaluated from XRD patterns. The lattice volume of a sulfide-based solid electrolyte can vary depending on the sintering temperature even if the composition is the same. 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.

[0089] 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, 298 K) 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 preferable that the ionic conductivity is 4 mS / cm or more. The ionic conductivity of the sulfide-based solid electrolyte according to one embodiment of the present invention is 2 mS / cm or more, preferably 4 mS / cm or more, more preferably 10.8 mS / cm or more, still more preferably 12 mS / cm or more, and most preferably 13 mS / cm or more.

[0090] A sulfide-based solid electrolyte according to one embodiment of the present invention can be obtained by a manufacturing method including a step of mixing a lithium source, a Group 2 element source, phosphorus, a sulfur source, and a halogen source to obtain a mixture, and a step of calcining the mixture at a temperature of 250°C to 600°C. The calcination of the mixture can be performed under an inert atmosphere such as argon gas or nitrogen gas.

[0091] The lithium source, Group 2 element source, phosphorus, 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) can be used as the phosphorus source, and lithium halides (LiHa) such as lithium chloride (LiCl) and lithium bromide (LiBr) can be used as the halogen source. For example, sulfide can be used as the Group 2 element source. Alternatively, sulfur can be supplied from another element source. That is, one or more of the lithium source, Group 2 element source, phosphorus, and halogen source can also serve as a sulfur source.

[0092] The sintering temperature is preferably 350°C to 550°C, more preferably 400°C to 500°C, and even more preferably 410°C to 470°C for a sulfide-based solid electrolyte having an argyrodite-type crystal structure. When the sintering temperature satisfies the above range, the formation of an argyrodite-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.

[0093] 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 the solid electrolyte and the solid electrolyte layer and battery elements (e.g., a positive electrode, a negative electrode, etc.) laminated on both sides thereof.

[0094] The material of the binder for the solid electrolyte layer is not particularly limited, and may be appropriately selected from the range of components used as a binder 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, polyvinyl pyrrolidone, 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.

[0095] 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.

[0096] <Cathode>

[0097] The negative electrode does not contain negative active material before the first lithium metal deposition (first charge).

[0098] By charging, lithium ions are supplied from the positive active material contained in the positive active material layer, and a lithium metal layer as the negative active material is formed on the negative electrode current collector. Specifically, when a voltage above a certain level is applied to an all-solid-state battery having an anode-free battery structure to charge, lithium ions are released from the positive active material in the positive electrode, and the released lithium ions pass through the solid electrolyte layer and move toward the negative electrode current collector, forming a lithium metal layer composed purely of lithium on the negative electrode current collector to form the negative electrode. The formation of the lithium metal layer by charging in this way has the advantage of being able to form a thin film layer, making it very easy to control the interface characteristics, compared to the negative electrode of the prior art that sputters a lithium metal layer on the negative electrode current collector or laminates a lithium foil and the negative electrode current collector.

[0099] In particular, since the battery is formed with an anode-free battery structure, there is no exposure of lithium metal to the atmosphere during the battery assembly process, and thus problems such as formation of an oxide film on the surface due to the high reactivity of lithium itself and the resulting reduction in the lifespan of the lithium secondary battery can be fundamentally eliminated.

[0100] The formed lithium metal layer forms a uniform, continuous or discontinuous layer on the negative electrode current collector. For example, when the negative electrode current collector is in the form of a foil, it can have a continuous thin film form, and when the negative electrode current collector has a three-dimensional porous structure, the lithium metal layer may be formed discontinuously. In other words, the discontinuous layer is a form in which the lithium metal layer is present and the region where it is not present exist within a specific region, but the region where the lithium metal layer is not present is distributed so as to isolate, disconnect or separate the region where the lithium compound is present like an island shape, meaning that the region where the lithium metal layer is present is distributed without continuity.

[0101] The lithium metal layer formed through such charge / discharge cycles has a thickness of at least 50 nm and no more than 100 μm, preferably 1 μm to 50 μm, in order to function as a negative electrode. If the thickness is less than the above range, the charge / discharge efficiency of the battery decreases rapidly, and conversely, if it exceeds the above range, the life characteristics are stable, but there is a problem that the energy density of the battery decreases.

[0102] 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 a lithium secondary battery assembled using conventional lithium foil, no or little 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.

[0103] In the present invention, the charging range for forming a lithium metal layer is a single charge of 0.01 to 0.2 C in a voltage range of 4.5 V to 2.5 V. If the charging is performed below the above range, it becomes difficult to form a lithium metal layer, and conversely, if the charging exceeds the above range, the battery is damaged, over-discharge occurs, and charging and discharging are not performed properly.

[0104] The negative electrode may include a negative current collector. The negative current collector may be any material that does not cause chemical changes in the all-solid-state battery and is conductive, and is not particularly limited. Examples of negative current collectors include iron, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0105] In particular, it is preferable that the negative electrode 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 a reaction product between the negative electrode collector and the sulfide-based solid electrolyte. The absence of a reaction product between the negative electrode collector and the sulfide-based solid electrolyte 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). The absence of the reaction product can also be confirmed using XRD measurement. Before the first lithium metal deposition (first charge), the negative electrode collector and the sulfide-based solid electrolyte may be in direct contact. Furthermore, after the battery is discharged, the lithium metal as the negative electrode active material migrates to the positive electrode side, resulting in little or no negative electrode active material on the negative electrode collector. If a side reaction occurs between the negative electrode 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, it is desirable for the negative electrode current collector to have high stability against 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 confining pressure.

[0106] The negative electrode current collector may have a thickness of 3㎛ to 500㎛.

[0107] The negative electrode current collector may be formed in various forms, such as a film, sheet, foil, net, porous body, foam, or non-woven fabric having fine irregularities on the surface.

[0108] The negative electrode current collector can be in direct contact with the solid electrolyte layer. The negative electrode current collector can be in direct contact with the sulfide-based solid electrolyte contained in the solid electrolyte layer. Since the negative electrode current collector and the solid electrolyte layer are in direct contact without an intervening layer, the thickness of the all-solid-state battery can be reduced, thereby improving the volumetric energy density of the all-solid-state battery. The amount of active material that can be loaded is increased, and the growth of lithium dendrites is prevented, thereby improving the discharge capacity and cycle characteristics of the all-solid-state battery. Furthermore, the all-solid-state battery can be operated at a low confining pressure.

[0109] 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 this intermediate layer is formed, the 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. That is, during charging, a lithium metal layer is formed between the negative electrode current collector and the intermediate layer.

[0110] Here, the intermediate layer can be any material that can smoothly conduct lithium ions, and a material used in a lithium ion conductive polymer and / or an inorganic solid electrolyte may be used, and if necessary, a lithium salt may be further included.

[0111] 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, and palladium.

[0112] As a lithium ion conductive polymer, for example, it may be composed of one selected from the group consisting of polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-hexafluoro propylene (PVDF-HFP), or a mixture of two or more thereof, but is not limited thereto, and any polymer having lithium ion conductivity may be used without limitation.

[0113] When using a lithium ion conductive polymer, additional materials used for this purpose may be included to further increase lithium ion conductivity.

[0114] For example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiSCN, LiC(CF3SO2)3, (CF3SO2)2NLi, (FSO2)2NLi, lithium chloroborane, lithium lower aliphatic carbonates, lithium tetraphenylborate, lithium imide, etc. may be further included.

[0115] Inorganic solid electrolyte is a ceramic material, and crystalline or amorphous material may be used, and 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. When using an inorganic solid electrolyte, lithium salt may be additionally included if necessary.

[0116] Inorganic solid electrolytes can be mixed with known substances, such as binders, and applied as thick films through slurry coating. Furthermore, if necessary, thin film applications can be achieved 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.

[0117] The intermediate layer including the aforementioned lithium ion conductive polymer and / or inorganic solid electrolyte can simultaneously secure the effect of increasing the transfer rate of lithium ions to facilitate the formation of a lithium metal layer, and at the same time suppressing or preventing the formation of lithium dendrites that occur when the lithium metal layer / negative electrode current collector is used as a negative electrode.

[0118] To achieve the above effect, it is necessary to limit the thickness of the intermediate layer.

[0119] The thinner the intermediate layer, the more advantageous it is for the output characteristics of the battery. However, if it is not formed to a thickness greater than a certain thickness, it is impossible to suppress the side reaction between lithium and the electrolyte formed on the negative electrode current collector thereafter, and it is also impossible to effectively block dendrite growth. In the present invention, the thickness of the intermediate layer may be preferably 10 nm to 50 μm. If the thickness of the intermediate layer is less than the above range, it is impossible to effectively suppress the side reaction and exothermic reaction between lithium and the electrolyte, which increase under conditions such as overcharge or high-temperature storage, and thus safety improvement cannot be achieved. In addition, 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.

[0120] <Bipolar>

[0121] The positive electrode may include a positive electrode active material layer and a positive electrode current collector.

[0122] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the positive electrode or the 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, it may include aluminum. The positive electrode current collector includes 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. Accordingly, the bonding force and electrical conductivity of the positive electrode active material layer and the current collector can be significantly improved.

[0123] The positive electrode active material layer may be disposed on at least one surface of the positive electrode current collector. Specifically, the positive electrode active material layer may be disposed on one or both surfaces of the positive electrode current collector.

[0124] The positive electrode active material layer may include a positive electrode active material. In the anode-free battery structure of the present invention, the lithium source for forming the lithium metal layer is the positive electrode active material, and the positive electrode active material includes lithium. That is, when charging within a specific voltage range, the lithium ions of the positive electrode active material are released to form a lithium metal layer on the negative electrode current collector.

[0125] The cathode active material can be used without limitation as long as it can be used as a cathode active material of a lithium ion secondary battery. The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO2), 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; chemical formula LiNi 1-x M x Ni-site 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 by 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 composite oxide with spinel structure represented by O4; LiMn2O4 in which some of the Li in the chemical formula is replaced by alkaline earth metal ions; disulfide compound; LiMn x Fe 1-xIt may include PO4(0≤x≤0.9); Fe2(MoO4)3, etc., but is not limited to these.

[0126] The cathode active material is Li 1+x M y O 2+z , 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 0≤x≤5, 0<y≤2, 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 Li2MnO30.5Li[Mn 0.4 Ni 0.3 Co 0.3 ]O2 may include at least one selected from the group consisting of. 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 0.9Co 0.05 Mn 0.05 ]O2 may contain any one of the cathode active materials. The cathode active material may be Li 1+x M y O 2+z From including, lithium can be sufficiently supplied to the negative electrode, and Li 1+x M y O 2+z The loss of battery capacity due to the irreversible capacity of the negative electrode can be eliminated by showing electrochemical activity after the first cycle without causing a decrease in the overall performance of the battery. 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.

[0127] The positive electrode active material may be included in the positive electrode active material layer in an amount of 50 wt% to 95 wt%, specifically 60 wt% to 90 wt%.

[0128] Additionally, the average particle size of the positive electrode active material is 1 to 30 μm, and in one embodiment, 8 to 12 μm. When the average particle size of the positive electrode active material is within the above range, the capacity characteristics of the battery are excellent.

[0129] The positive electrode active material layer may further include a positive electrode conductive material.

[0130] The cathode conductive material is not particularly limited as long as it does not cause a chemical change in the cathode or the battery and has conductivity. For example, the cathode conductive material may include one or a mixture of two or more selected from the following conductive materials: 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, etc.; 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 polyphenylene derivatives.

[0131] The positive electrode conductive material may be included in the positive electrode active material layer at 1 wt% to 30 wt%.

[0132] The positive electrode active material layer may further include a positive electrode binder.

[0133] The positive electrode binder is not particularly limited as long as it is a component that helps in binding the positive electrode active material, the positive electrode conductive material, etc., and binding to the current collector, and specifically, may include at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene (PTFE), polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), styrene-butadiene rubber (SBR), and fluororubber.

[0134] The positive electrode binder may be included in the positive electrode active material layer at 1 wt% to 30 wt%.

[0135] The positive electrode active material layer may, if necessary, 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.

[0136] 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.

[0137] The positive electrode active material layer may contain 5 wt% to 60 wt% of a sulfide-based solid electrolyte, specifically 10 wt% to 40 wt%.

[0138] The average particle size of the positive electrode active material may be larger than the average particle size of the solid electrolyte contained in the positive electrode active material layer. In this case, the solid electrolyte can enter the gaps between the positive electrode active material particles, thereby providing a lithium ion conduction path to the positive electrode active material.

[0139] The present invention provides a secondary battery having the structure described above. In addition, the present invention provides a battery module including a secondary battery as a unit battery, a battery pack including the battery module, and a device including the battery pack as a power source. At this time, specific examples of the device include, but are not limited to, a power tool driven by 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) and an electric scooter (E-scooter); an electric golf cart; and a power system.

[0140] Hereinafter, preferred embodiments will be described to facilitate understanding of the present invention. However, the following embodiments are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various modifications and variations are possible within the scope and technical spirit of the present invention. It is also natural that such modifications and variations fall within the scope of the claims.

[0141] (Synthesis of solid electrolyte)

[0142] Manufacturing Example 1

[0143] Using lithium sulfide (Li2S, Mitsuwa Chemical product), diphosphorus pentasulfide (P2S5, Aldrich product), calcium sulfide (CaS, 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 (The amount of the Group 2 element (M) added was y = 0.025) to obtain a mixed powder by weighing and mortar mixing in an Ar gas glove box. 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 the glove box to recover the powder. This powder was placed in a carbon crucible, sealed, and then fired at 430°C for 8 hours while flowing Ar gas. The fired powder was pulverized in a mortar for 10 minutes to obtain a solid electrolyte coarse powder containing divalent cations.

[0144] Manufacturing Example 2

[0145] The solid electrolyte powder containing a divalent cation obtained in Manufacturing Example 1 was placed in a ZrO2 pot together with ZrO2 balls and anisole solvent, and wet milling was performed at 250 rpm for 1 hour to obtain a solid electrolyte powder containing a divalent cation.

[0146] Manufacturing Example 3

[0147] A solid electrolyte powder containing a divalent cation was obtained in the same manner as in Manufacturing Example 1, except that the sintered powder was ground for 1 minute.

[0148] Comparative Manufacturing Example 1

[0149] A solid electrolyte powder containing no divalent cations was obtained in the same manner as in Example 1, except that calcium sulfide (CaS, Japan Pure Chemical) was not used. The composition of the solid electrolyte obtained in Comparative Manufacturing Example 1 was Li 5.4 PS 4.4 Cl 1.0 Br 0.6 It was.

[0150] Comparative Manufacturing Example 2

[0151] The solid electrolyte fine powder not containing a divalent cation obtained in Comparative Manufacturing Example 1 was placed in a ZrO2 pot together with ZrO2 balls and anisole solvent, and wet milling was performed at 250 rpm for 1 hour to obtain a solid electrolyte fine powder not containing a divalent cation.

[0152] [evaluation]

[0153] Using the obtained solid electrolyte, the following evaluation was conducted.

[0154] (XRD measurement)

[0155] A predetermined amount of solid electrolyte was placed in a sealed holder in an Ar gas glove box and XRD measurements were performed. The lattice constant, lattice volume, and half-width were calculated from the obtained XRD (X-ray diffraction) pattern. The half-width was calculated from the (311) plane crystal peak of the argyrodite-type crystal structure observed around 2θ=30° in Fig. 4.

[0156] The measuring device and conditions are as follows.

[0157] ·X-ray diffraction device: Rigaku Smartlab

[0158] ·Source: Cu-Kα line (λ=1.5418Å)

[0159] ·Voltage: 45kV

[0160] Current: 200mA

[0161] ·Scan range (2θ): 10-60˚

[0162] ·Step size: 0.01˚

[0163] (Particle size distribution measurement)

[0164] A solid electrolyte dispersion was prepared by dissolving the solid electrolyte in a heptane solvent and using Span 80 as a dispersant. The particle size distribution of this dispersion was measured using a Mastersizer 3000 particle size measuring device. Data analysis was performed using a refractive index of 2.16 for the solid electrolyte.

[0165] (Ionic conductivity measurement)

[0166] A certain amount of solid electrolyte is added to MACOR ® ) was placed inside the pipe, and the Mako pipe and the pellet forming jig (upper press pin and lower press pin) were combined and press-formed at approximately 370 MPa using a uniaxial press machine. 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 uniaxial press machine to obtain a Mako pipe cell. The obtained Mako pipe cell was installed in a jig cell for electrochemical measurement, and pressurized to 80 MPa using a torque wrench to obtain an ionic conductivity measurement cell. The obtained ionic conductivity measurement cell was connected to an impedance measurement 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 ionic conductivity [mS / cm] of the solid electrolyte.

[0167] (neutron diffraction measurements)

[0168] A predetermined amount of solid electrolyte was placed in a neutron diffraction measurement device, and neutron diffraction measurements were performed. From the obtained neutron diffraction patterns, the crystal structure was determined using the crystal structure analysis program Z-Rietveld, and the lattice constant, elemental positions, occupancy rates, and atomic displacement parameters were calculated.

[0169] The measuring device and conditions are as follows.

[0170] ·Neutron diffraction device: J-PARC BL09 SPICA, High Energy Accelerator Research Organization

[0171] Neutron source: TOF (Time of Fly) type

[0172] ·Sample amount: Approximately 0.6g

[0173] ·Measurement d range: 0.3-3.7Å [Evaluation results]

[0174] (Decision)

[0175] The evaluation results of the crystal phase (crystal structure) classified from the XRD pattern by XRD measurement are shown in Table 1. In addition, the measured XRD pattern is shown in Fig. 4. As can be seen from Table 1 and Fig. 4, in the solid electrolytes obtained in Manufacturing Examples 1, 2, Comparative Manufacturing Examples 1, and 2, almost no impurity phase (also called an unknown phase) was observed, and mostly only peaks of the argyrodite phase were observed. A sulfide-based solid electrolyte having an argyrodite-type crystal structure with no or almost no impurity phase was obtained. A sulfide-based solid electrolyte with a high degree of crystallinity can contribute to increasing ionic conductivity by promoting hopping conduction of lithium ions.

[0176] (Grid volume)

[0177] The lattice constant derived from the XRD pattern is in the range of 9.8698Å to 9.8700Å in Manufacturing Examples 1 and 2, and the lattice volume is 961.4Å. 3 at 961.5Å 3 Meanwhile, in comparative manufacturing examples 1 and 2 in which the lithium site of the sulfide-based solid electrolyte is not replaced by a group 2 element (M), the lattice constant is in the range of 9.9467Å to 9.9470Å, and the lattice volume is 984.1Å. 3 ∼984.2Å 3It was in the range of. By substituting the lithium site of the argyrodite-type crystal structure with a Group 2 element (M), the crystal volume was found to decrease by approximately 2.3%. 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 the Group 2 element (M) and the other became a lithium vacancy. The lithium vacancy is thought to serve as a path for the hopping conduction of lithium ions, thereby contributing to the increase in ionic conductivity. In addition, the Group 2 element (M) substituted for the lithium site may have a divalent charge, and thus, compared to a monovalent lithium ion, the force that further attracts the anions around the Group 2 element (M) site may change. Accordingly, it is thought that the crystal volume of the sulfide-based solid electrolyte changed, resulting in a structure suitable for the hopping conduction of lithium ions.

[0178] The half-width of the (311) plane crystal peak of the argyrodite 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. In Preparation Examples 1 and 2, which are solid electrolytes containing divalent cations, the half-width is small. It is thought that the small half-width corresponds to a large crystallite size and contributes to the increase in ionic conductivity. In addition, it was found that the crystallinity and crystal size of the solid electrolyte did not change due to the micronization process.

[0179]

[0180] (particle size distribution)

[0181] The particle size distribution measurement results are shown in Table 2. The average particle diameter D50 was 15.1 μm in the solid electrolyte coarse powder containing divalent cations of Production Example 1, 1.66 μm in the solid electrolyte fine powder containing divalent cations of Production Example 2, and 14.5 μm in the solid electrolyte ultrafine powder containing divalent cations of Production Example 3. In addition, it was 14.7 μm in the solid electrolyte coarse powder not containing divalent cations of Comparative Production Example 1, and 1.42 μm in the solid electrolyte fine powder not containing divalent cations of 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.

[0182]

[0183] (ionic conductivity)

[0184] The results of the measurement of ionic conductivity are shown in Table 1. It was 13.24 mS / cm in the solid electrolyte coarse powder containing divalent cations of Preparation Example 1, 4.32 mS / cm in the solid electrolyte fine powder containing divalent cations of Preparation Example 2, and 13.20 mS / cm in the solid electrolyte ultrafine powder containing divalent cations of Preparation Example 3. In addition, it was 9.91 mS / cm in the solid electrolyte coarse powder not containing divalent cations of Comparative Preparation Example 1, and 3.3 mS / cm in the solid electrolyte fine powder not containing divalent cations of Comparative Preparation Example 2. Regardless of the presence or absence of divalent cations, the solid electrolyte coarse powder had higher ionic conductivity than the solid electrolyte fine powder. It is thought that the ionic conductivity is high when the solid electrolyte coarse powder is used 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 higher ionic conductivity than the solid electrolyte not containing divalent cations.

[0185] (neutron diffraction measurements)

[0186] The results of neutron diffraction measurements are shown in Tables 3 and 4. Table 3 shows the results of crystal structure analysis of the solid electrolyte powder of Manufacturing Example 1. Table 4 shows the results of crystal structure analysis of the solid electrolyte powder of Comparative Manufacturing Example 1. In each table, a site is represented by a combination of numbers and English notation. The numbers indicate the number of positions where an element can be placed in the crystal structure, and the English notation indicates the symmetry defined in the crystallography of the site, with a, b, c, d… in order of increasing crystallinity. g indicates the occupancy rate of each site. x, y, and z are parameters determined by the site, and the values ​​represent the positions where elements are located as ratios of lattice constants in the x, y, and z directions. B iso is the atomic displacement parameter, which represents the distribution of displacement due to thermal vibration of atoms.

[0187] As shown in Table 3, in the solid electrolyte powder of Manufacturing Example 1, it was confirmed that calcium (Ca) existed at the 48h site of the argyrodite type crystal structure. The occupancy rate of calcium (Ca) at the 48h site, g, was 0.003±0.002. When the amount of the Group 2 element (M) added to the solid electrolyte powder of Manufacturing Example 1 having a crystal structure is calculated, it becomes 0.036±0.024, and the input addition amount (y=0.025) falls within that range. Since the solid electrolyte powder of Comparative Manufacturing Example 1 does not use calcium in the raw material, calcium (Ca) did not appear in the analysis results of Table 4.

[0188]

[0189]

[0190] Example 1

[0191] 90 mg of the solid electrolyte powder containing divalent cations obtained in Manufacturing Example 1 was weighed, placed in a molding jig, and pressurized at 110 MPa for 1 minute to obtain a solid electrolyte pellet.

[0192] An NCM-based cathode active material with a Ni content of 80 mol% and a solid electrolyte powder containing divalent cations obtained in Manufacturing Example 2 and a conductive agent were weighed at a mass ratio of 60:35:5. These were mixed to obtain a cathode mixture.

[0193] 17 mg of a positive electrode mixture was placed on one side of a solid electrolyte pellet, and then pressed flat with a SUS press pin of a molding jig, followed by pressurization at 110 MPa for 1 minute to obtain a positive electrode active material layer formed on a solid electrolyte layer. A SUS plate as a positive electrode current collector was provided on the positive electrode active material layer, and a SUS plate as an anode current collector was provided on the solid electrolyte layer on the opposite side of the positive electrode active material layer so as to be in direct contact with it. This was pressurized at 554 MPa for 1 minute to obtain a laminate. The obtained laminate was combined with a SUS press pin to produce a Mako pipe cell. The obtained Mako pipe cell was installed in a battery cell, and a low confining pressure of about 0.005 MPa was applied to obtain an all-solid-state battery. That is, the all-solid-state battery of Example 1 includes a solid electrolyte coarse powder containing a divalent cation in the solid electrolyte layer (2), and a solid electrolyte fine powder containing a divalent cation in the positive electrode active material layer.

[0194] The all-solid-state battery of Example 1 is shown in Fig. 1. As shown in Fig. 1, the negative electrode current collector (1) and the solid electrolyte layer (2) including 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 include 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.

[0195] Example 2

[0196] In the step of obtaining a solid electrolyte pellet, an all-solid-state battery was obtained in the same manner as in Example 1, except that the solid electrolyte fine powder containing a divalent cation obtained in Production Example 2 was used instead of the solid electrolyte coarse powder containing a divalent cation obtained in Production Example 1. That is, the all-solid-state battery of Example 2 includes a solid electrolyte fine powder containing a divalent cation in the solid electrolyte layer (2) and the positive electrode active material layer (3).

[0197] Example 3

[0198] In the step of obtaining an all-solid-state battery, an all-solid-state battery was obtained in the same manner as in Example 1, except that a confining pressure of about 8 MPa was applied instead of a confining pressure of about 0.005 MPa.

[0199] Example 4

[0200] In the step of obtaining a solid electrolyte pellet, an all-solid-state battery was obtained in the same manner as in Example 1, except that the solid electrolyte pellet containing a divalent cation obtained in Production Example 3 was used instead of the solid electrolyte pellet containing a divalent cation obtained in Production Example 1. That is, the all-solid-state battery of Example 4 contains a solid electrolyte pellet containing a divalent cation in the solid electrolyte layer (2), and a solid electrolyte fine powder containing a divalent cation in the positive electrode active material layer (3).

[0201] Comparative Example 1

[0202] In the step of obtaining a solid electrolyte pellet, instead of the solid electrolyte coarse powder containing a divalent cation obtained in Manufacturing Example 1, the solid electrolyte coarse powder not containing a divalent cation obtained in Comparative Manufacturing Example 1 was used, and in the step of obtaining a positive electrode mixture, instead of the solid electrolyte fine powder containing a divalent cation obtained in Manufacturing Example 2, the solid electrolyte fine powder not containing a divalent cation obtained in Comparative Manufacturing Example 2 was used, with the exception that an all-solid-state battery was obtained in the same manner as in Example 1. That is, as shown in Fig. 2, the all-solid-state battery of Comparative Example 1 includes a solid electrolyte coarse powder not containing a divalent cation in the solid electrolyte layer (5), and includes a solid electrolyte fine powder not containing a divalent cation in the positive electrode active material layer (3).

[0203] Comparative Example 2

[0204] In the step of obtaining an all-solid-state battery, an Ag-C intermediate layer was formed on the solid electrolyte layer opposite to the positive active material layer, an SUS plate as an anode current collector was formed on the Ag-C intermediate layer, and a restraining pressure of about 4 MPa was applied, except that an all-solid-state battery was obtained in the same manner as in Comparative Example 1. The Ag-C intermediate layer was prepared by dissolving predetermined amounts of Ag and C (carbon black) in N-methyl pyrrolidone to which 7 wt% of PVDF was added, and then applying the resultant mixture on the SUS plate. That is, the all-solid-state battery of Comparative Example 2, as shown in Fig. 3, includes a solid electrolyte coarse powder that does not contain a divalent cation in the solid electrolyte layer (5), includes a solid electrolyte fine powder that does not contain a divalent cation in the positive active material layer (3), and an intermediate layer (6) is formed between the solid electrolyte layer (5) and the anode current collector (1).

[0205] [All-Solid State Battery Evaluation]

[0206] (charge / discharge test)

[0207] Charge-discharge tests were performed at 25°C using the obtained all-solid-state battery. The voltage range was 4.25 V - 3.0 V, the charge condition was CC (0.05 C) - CV (0.01 C cutoff), and the discharge condition was CC (0.05 C). The charge and discharge capacities were obtained from the obtained charge-discharge curves. In addition, the discharge capacity retention rate (%) at 25°C under the charge condition CC (0.05 C) - CV (0.01 C) and the discharge condition CC (0.05 C) was derived using the following equation.

[0208] Discharge capacity in each cycle / Discharge capacity in the first cycle × 100

[0209] [Evaluation Results]

[0210] (All-solid-state battery characteristics)

[0211] The initial discharge capacity relative ratio of the all-solid-state battery capacity of Example 1 to the all-solid-state battery capacity of Comparative Example 1 was 103%.

[0212] The initial discharge capacity relative ratio of the all-solid-state battery capacity of Example 2 to the all-solid-state battery capacity of Comparative Example 1 was 103%.

[0213] The initial discharge capacity relative ratio of the all-solid-state battery capacity of Example 3 to the all-solid-state battery capacity of Comparative Example 1 was 101%.

[0214] In this way, the all-solid-state batteries of Examples 1 to 3, in which the solid electrolyte layer contains a Group 2 element and also includes a sulfide-based solid electrolyte having an argyrodite-type crystal structure, were 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.

[0215] Figures 5 and 6 are graphs showing the discharge capacity retention rates of the all-solid-state batteries of Examples 1 to 4 and Comparative Examples 1 and 2. Figures 5 and 6 have different vertical axis scales.

[0216] The discharge capacity retention rate in the third cycle was 99.5% in Example 1, 99.2% in Example 2, 99.2% in Example 3, 97.9% in Example 4, 78.8% in Comparative Example 1, and 92.4% in Comparative Example 2.

[0217] The discharge capacity retention rate at the 8th cycle was 98.6% in Example 1, 65.5% in Example 4, and 84.2% in Comparative Example 2. In Example 4, the discharge capacity decreased after 4 cycles. The solid electrolyte coarse powder used in the solid electrolyte layer of Example 4 has the same average particle size as the solid electrolyte coarse powder used in Example 1, but has a wider particle size distribution. It is thought that this wide particle size distribution leads to uneven lithium ion conduction during charge and discharge, for example, by worsening the smoothness of the surface of the solid electrolyte layer, thereby decreasing the discharge capacity. In Comparative Example 1, the discharge capacity decreased rapidly after 4 cycles, making it impossible to measure the discharge capacity. Unlike Comparative Example 1, Comparative Example 2 has an intermediate layer (6) provided between the solid electrolyte layer (5) and the negative electrode current collector (1). It is thought that Comparative Example 2 exhibited better cycle characteristics than Comparative Example 1 because the intermediate layer (6) suppressed the growth of lithium dendrites.

[0218] In this way, the all-solid-state batteries of Examples 1 to 3, in which the solid electrolyte layer contains a Group 2 element and includes a sulfide-based solid electrolyte having an argyrodite-type crystal structure, were 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. The all-solid-state battery of Example 4 was able to improve cycle characteristics compared to the all-solid-state batteries of Comparative Examples 1 and 2, at a low cycle number.

[0219] The all-solid-state batteries of Examples 1 and 3 include a solid electrolyte coarse powder containing a divalent cation in the solid electrolyte layer, i.e., the solid electrolyte coarse powder of Preparation Example 1; the all-solid-state battery of Example 2 includes a solid electrolyte fine powder containing a divalent cation in the solid electrolyte layer, i.e., the solid electrolyte fine powder of Preparation Example 2; and the all-solid-state battery of Example 4 includes a solid electrolyte super-coarse powder containing a divalent cation in the solid electrolyte layer, i.e., the solid electrolyte super-coarse powder of Preparation Example 3. As shown in Table 1, the solid electrolyte coarse powder of Preparation Example 1 and the solid electrolyte super-coarse powder of Preparation Example 3 exhibit ionic conductivities that are about three times higher than those of the solid electrolyte fine powder of Preparation Example 2. As shown in Fig. 6, the all-solid-state battery of Example 1 exhibited superior cycle characteristics than the all-solid-state battery of Example 2. The excellent 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 coarse powder containing divalent cations. The all-solid-state battery of Example 4, despite including a solid electrolyte coarse powder with high ionic conductivity, exhibits inferior cycle characteristics to the all-solid-state battery of Example 2. This is thought to be because the large particles, such as aggregates, contained in the solid electrolyte coarse powder of Example 4, which has a wide particle size distribution, deteriorate the surface smoothness of the solid electrolyte layer, resulting in uneven lithium ion conduction during charge and discharge. Normally, during charge and discharge 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. 6, the all-solid-state battery of Example 1, to which a confining pressure of about 0.005 MPa was applied, exhibited superior discharge capacity and cycle characteristics to the all-solid-state battery of Example 3, to which a confining pressure of about 8 MPa was applied. This is believed to be due to the use of a solid electrolyte containing divalent cations in the solid electrolyte layer and the positive electrode active material layer. Thus, the all-solid-state battery of the present invention can be operated at a low confining pressure.

[0220] Figure 7 is an SEM image showing the calcium distribution in the all-solid-state battery of Example 1. The left image of Figure 7 shows a cross-sectional view of the all-solid-state battery before the first charge. The center image of Figure 7 shows a cross-sectional view of the all-solid-state battery after the first charge. The right image of Figure 7 shows a cross-sectional view of the all-solid-state battery after the first discharge. Calcium (Ca) appears white in each SEM image. For SEM observation, the negative electrode current collector was removed.

[0221] As can be seen from the image on the left side of Fig. 7, before the first charge of the all-solid-state battery, calcium (Ca) contained in the solid electrolyte layer is distributed throughout the solid electrolyte layer. However, it should be noted that the white spots observed in the region where the current collector is removed are derived from calcium (Ca) in the inward direction of the solid electrolyte layer, and that calcium (Ca) does not exist in the region where the current collector is removed.

[0222] As can be seen from the image in the center of Fig. 7, after the first charge of the all-solid-state battery, some of the calcium (Ca) moved to the interface between the negative electrode collector and the solid electrolyte layer. As can be seen from the image on the right side of Fig. 7, after the first discharge of the all-solid-state battery, some of the calcium (Ca) moved to the interface between the positive electrode active material layer (also called the 'positive electrode layer') and the solid electrolyte layer. Even during the second and subsequent charge / discharge cycles, calcium moved to the interface between the negative electrode collector and the solid electrolyte layer during charging, and moved to the interface between the positive electrode active material layer and the solid electrolyte layer during discharge. In this way, it was suggested that in the all-solid-state battery of the anode-free structure of Example 1, calcium (Ca), a Group 2 element, moved between the electrodes together with lithium, a charge carrier.

[0223] Figure 8 is a graph showing an SEM image (left) and calcium line analysis results (right) of the negative electrode current collector side of the all-solid-state battery of Example 1 after the first charge. For SEM observation, the negative electrode current collector was stripped.

[0224] As can be seen from the image on the left side of Fig. 8, after the first charge of the all-solid-state battery, precipitates were formed between the negative electrode collector and the solid electrolyte layer. The results of a linear analysis (SEM-EDX analysis) of calcium across the solid electrolyte layer, precipitates, and negative electrode collector are shown in the image on the right side of Fig. 8. It can be seen that calcium (Ca) is distributed across the solid electrolyte layer and the precipitates. In particular, it can be seen that calcium (Ca) exists in large quantities at the interface between the precipitates and the negative electrode collector. It is thought that the adhesion between the negative electrode collector and the solid electrolyte layer was improved by forming the precipitates between the precipitates and the negative electrode collector.

[0225] Since lithium is formed between the negative electrode current collector and the solid electrolyte layer when the anode-free all-solid-state battery is charged, the precipitate shown in Fig. 8 is thought to contain lithium. Furthermore, from the SEM-EDX analysis, the precipitate shown in Fig. 8 is thought to contain simple calcium (Ca), or an alloy or compound of calcium (Ca) and lithium. In particular, since calcium (Ca) exists on the negative electrode current collector side in the precipitate, it is thought that the calcium (Ca) contained in the precipitate improves the adhesion / adhesion between the negative electrode current collector and the solid electrolyte layer via the precipitate. As a result, it is thought that the all-solid-state battery of Example 1 has excellent discharge capacity and cycle characteristics, and drivability at low confining pressure. Although further analysis is required, it is thought that the precipitate formed between the positive electrode active material layer and the solid electrolyte layer when the all-solid-state battery is discharged also has the same form and characteristics as the precipitate formed between the negative electrode current collector and the solid electrolyte layer.

[0226] In a conventional anode-free battery, the ion conduction path and / or the electrical conduction path between the anode current collector and the solid electrolyte layer are destroyed by lithium-containing precipitates such as lithium metal formed between the anode current collector and the solid electrolyte layer after charging, resulting in a decrease in ion conductivity and a decrease in cycle characteristics. However, in the all-solid-state battery of the present invention, a Group 2 element contained in the solid electrolyte layer is deposited between the anode current collector and the solid electrolyte layer during charging, thereby improving the adhesion therebetween, and thus can maintain high discharge capacity and cycle characteristics. Furthermore, in the all-solid-state battery of the present invention, a Group 2 element contained in the solid electrolyte layer is deposited between the cathode active material layer and the solid electrolyte layer during discharge, thereby improving the adhesion therebetween, and thus can maintain high discharge capacity and cycle characteristics. Furthermore, in the all-solid-state battery of the present invention, the adhesion between the solid electrolyte layer and the electrode is improved by the deposit containing the Group 2 element, and thus can be operated at a low confining pressure of about 0.005 MPa or the like.

[0227] Above, although the present invention has been described through 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 equivalent to the technical idea and claims of the present invention by a person having ordinary knowledge in the technical field to which the present invention pertains.

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 all-solid-state battery does not contain a negative electrode active material, By charging, lithium ions are supplied from the positive electrode active material layer, and a lithium metal layer as a negative electrode active material is formed on the negative electrode current collector. An all-solid-state battery, wherein the solid electrolyte layer comprises a sulfide-based solid electrolyte containing a Group 2 element and having an argyrodite-type crystal structure.

2. In paragraph 1, An all-solid-state battery in which the negative electrode collector and the 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 is displayed as, In the above chemical formula, The above M is at least one element selected from the Group 2 elements, The above Ha is at least one element selected from halogen elements, Satisfying 0<x<2.5, 0<y<0.45, All-solid-state battery.

4. In paragraph 3, An all-solid-state battery wherein M is Ca.

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

6. In paragraph 1, An all-solid-state battery, wherein the above-mentioned 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 laminated.

7. In paragraph 1, An all-solid-state battery, wherein the positive electrode active material layer includes the sulfide-based solid electrolyte.

8. In paragraph 1, An all-solid-state battery, wherein the average particle diameter of the sulfide-based solid electrolyte included in the solid electrolyte layer is larger than the average particle diameter of the sulfide-based solid electrolyte included in the positive electrode active material layer.

9. In paragraph 1, An all-solid-state battery, wherein the above-mentioned Group 2 element is present at the 48h site of the above-mentioned argyrodite-type crystal structure.

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