Solid state electrolyte and solid state battery

Abstract

To provide a solid state electrolyte and a solid state battery.SOLUTION: The invention relates to a solid state electrolyte (SSE) including: a dense membrane including LLZO having a thickness of 100 μm or less; and an Sb-including coating layer having a thickness between 1 and 20 nm provided on a surface of the dense membrane. The dense membrane has a density of 90% or more of the theoretical density of the membrane, where the surface of the dense membrane onto which the coating layer is provided is substantially free of Li2CO3, where the SSE comprises a first Li-Sb alloy at the interface of the Sb-including coating layer and the LLZO-including dense membrane, where the thicknesses are as calculated from SEM images of the SSE. The invention also relates to a solid state battery (SSB) including the SSE, and to methods of producing the SSE and the SSB.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a solid electrolyte, a solid-state battery including the solid electrolyte, and a method for manufacturing the solid electrolyte and the solid-state battery. [Background technology]

[0002] Due to the need to develop safe, non-flammable, heat-resistant, and high-energy density energy storage systems, research into batteries made up of only solid components is attracting attention. In particular, cubic Li7La3Zr2O 12 The solid-state battery (SSB) using the (LLZO) garnet-type solid electrolyte has a high Li-ion conductivity of up to 1 mS / cm (room temperature) and a high conductivity of approximately 10 -8 Low electronic conductivity of 1000 S / cm (at room temperature), high thermal and mechanical stability, and Li + It has a wide electrochemical operating window of 0-6 V vs. / Li, making it particularly attractive as an energy storage technology.

[0003] However, LLZO-based SSBs still have several drawbacks that limit their application in commercial batteries. In particular, the poor wettability of LLZO to Li metal causes relatively high Li / LLZO interfacial resistance, resulting in high voltage polarization during lithium plating / stripping, and the non-uniform distribution of applied current density across the interface, which can lead to the formation of dendrites.

[0004] Dubey, Sastre et al., "Building a Better Li-Garnet Solid Electrolyte / Metallic Li Interface with Antimony," Adv. Energy Mater. 2021, 11, 2102086 (Non-Patent Document 1), discloses the use of an antimony thin film layer as an interface layer, i.e., a layer between metallic lithium of the negative electrode and LLZO solid electrolyte (SSE). A 10 nm Sb coating was applied to a 1 mm LLZO pellet. The interface resistance was 4.1 Ω cm. 2A low value of 0.64 mA / cm was reported, and analysis of the interface indicated the presence of a Li-Sb alloy as an intermediate layer. 2 The critical current density was measured to be 0.2 mA / cm 2 A low overpotential of 40-50 mV was observed at a current density of 1000 kJ / s.

[0005] However, the thickness of the LLZO SSE with the antimony (Sb) thin coating is not suitable for commercial battery cells. Furthermore, from the perspective of commercial batteries, the reported interfacial resistance is still relatively high and the critical current density is relatively low, so even if it becomes feasible to manufacture, its performance will still be limited compared to liquid electrolytes, including those in lithium-ion secondary batteries.

[0006] Therefore, it is necessary to further improve the performance of LLZO-based SSEs, particularly their performance during repeated charge / discharge cycles, performance at high temperatures, and their ability to support high currents and fast charging, while also reducing their thickness and costs. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Dubey, Sastre et al., “Building a Better Li-Garnet Solid Electrolyte / Metallic Li Interface with Antimony,” Adv. Energy Mater.2021,11,2102086. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to overcome one or more of the above-mentioned drawbacks. It is an object of the present invention to provide a solid electrolyte (SSE) for use in a solid-state battery (SSB), i.e., one having a commercially acceptable thickness and exhibiting improved performance, particularly low interfacial resistance, compared to existing SSEs for SSBs, at room temperature and at elevated temperatures, e.g., up to 75°C. It is also an object of the present invention to provide an SSE for use in a solid-state battery (SSB) that can withstand high current densities at room temperature and elevated temperatures, thereby enabling rapid charging of the SSB. It is also an object of the present invention to provide an SSE that can withstand a high number of lithium plating / stripping cycles, even at elevated temperatures.

[0009] It is a further object to provide a solid-state battery (SSB) comprising the SSE of the present invention that can withstand high energy density and high current density even when exposed to high temperatures, such as 75° C. It is yet another object to provide an SSB that can be charged quickly and in a short time, and can withstand a high number of charge / discharge cycles, and therefore has a long life. [Means for solving the problem]

[0010] A first aspect of the present invention relates to a solid state electrolyte (SSE) as set out in the accompanying claims.

[0011] The SSE comprises a dense membrane and a coating layer disposed on the surface of the dense membrane, where "disposed on the surface" as used herein means "present on the surface," and the surface refers to the most exposed surface.

[0012] The dense film is made of lithium lanthanum zirconium oxide, i.e., Li7La3Zr2O 12 (abbreviation: LLZO). LLZO may be doped LLZO. Preferably, when LLZO is doped, LLZO is aluminum-doped LLZO, i.e., Li 6.25 Al 0.25 La3Zr2O 12 (Abbreviation: Al-LLZO).

[0013] "High density" as used in the articles of the present disclosure refers to an article whose density is 90% or more of theoretical density, preferably at least 92% or more, more preferably at least 95% or more, and most preferably at least 98% or more.

[0014] For example, when the dense film is made of LLZO, the density of the dense film is 90% or more of the theoretical density of LLZO, that is, 5.1 g / cm 3 90% or more (thus, 4.59 g / cm 3 That's all.

[0015] The dense membrane has a thickness of 100 μm or less, preferably 75 μm or less, more preferably 45 μm or less, the thickness being calculated from a scanning electron microscope (SEM) image of the SSE.

[0016] The dense membrane conveniently has a thickness of 2 μm to 100 μm, preferably 3 μm to 75 μm, more preferably 5 μm to 50 μm, for example 10 μm to 45 μm, calculated from a scanning electron microscope (SEM) image of the SSE.

[0017] At least the surface of the dense membrane on which the coating layer is provided is substantially free of Li2CO3. Advantageously, at least the surface of the dense membrane on which the coating layer is provided is also substantially free of LiOH. Advantageously, at least the surface of the dense membrane on which the coating layer is provided is also substantially free of Li2O.

[0018] Here, "substantially free" means that at least 90%, preferably at least 95%, more preferably at least 98%, for example at least 99%, of the surface area is free of the respective compound.

[0019] The coating layer contains or consists essentially of antimony (Sb) and has a thickness of 1 to 20 nm, preferably 2 to 15 nm, and more preferably 5 to 10 nm, calculated from a scanning electron microscope (SEM) image of the SSE.

[0020] The SSE further comprises a first Li—Sb alloy at the interface of the coating layer comprising, or consisting essentially of, Sb and the dense film comprising, or consisting essentially of, LLZO.

[0021] The Sb-containing coating layer is conveniently provided on one side of the dense membrane, or alternatively, the Sb-containing coating layer is conveniently provided on both opposing surfaces of the dense membrane.

[0022] The critical current density of SSE is 2mA / cm at room temperature. 2 More than 2.5mA / cm 2 More preferably, 3 mA / cm 2 or more, for example, at least 3.5 mA / cm 2 It is convenient to be.

[0023] A second aspect of the present invention relates to a solid state battery (SSB) as set out in the accompanying claims.

[0024] The SSB comprises a negative electrode, a positive electrode, and an SSE according to the first aspect of the present invention. The negative electrode comprises or consists essentially of metallic lithium. The negative electrode is adjacent to a coating layer comprising or consists essentially of Sb from the SSE.

[0025] The SSB further comprises a second Li—Sb alloy at the interface between the negative electrode and the coating layer comprising or consisting essentially of Sb.

[0026] The interface resistance of the anode / SSE interface at room temperature calculated from the impedance measurement of the SSB is 6 Ω cm 2 Less than or equal to 5.5 Ω cm, preferably 2 Advantageously, the following is true:

[0027] In a third aspect of the present invention, a method for producing a solid electrolyte (SSE) is disclosed as set forth in the accompanying claims. The SSE is according to the first aspect of the present invention, i.e., comprises a dense membrane comprising or consisting essentially of LLZO, and further comprises a coating layer comprising or consisting essentially of Sb. Advantageously, the dense layer and the coating layer are as described above.

[0028] The method includes a heating operation and a deposition operation.

[0029] The heating operation involves heating a dense film comprising or consisting essentially of LLZO to a temperature between 700° C. and 1000° C., preferably between 800° C. and 900° C. The heating is carried out in an inert atmosphere, preferably an inert atmosphere comprising or consisting essentially of argon.

[0030] The heating operation at least partially, preferably substantially completely, removes impurities present on the surface of the dense film. Examples of such impurities include Li2CO3, LiOH, Li2O, and especially Li2CO3. In other words, the heating operation advantageously results in a dense film having a substantially clean surface. The inventors surprisingly discovered that in the absence of Li2CO3, even the presence of some Li2O significantly increases the critical current density of the SSE. While not wishing to be bound by any theory, the inventors believe that Li2CO3 adversely affects lithium plating / stripping performance, significantly negatively affecting the critical current density and the number of lithium plating / stripping cycles that the SSE can withstand, while only negatively affecting the interfacial resistance.

[0031] The deposition operation includes depositing a coating layer containing or consisting essentially of Sb on the surface of the dense film, which is substantially free of Li2CO3. The coating layer has a thickness as described above, i.e., a thickness of 1 to 20 nm. During the deposition step, a first Li-Sb alloy is formed at the interface between the dense film containing or consisting essentially of LLZO and the coating layer containing or consisting essentially of Sb.

[0032] Deposition of the coating layer comprising or consisting essentially of Sb can be carried out by methods known in the art. The coating layer is conveniently deposited by radio frequency (RF) magnetron sputtering. When RF magnetron sputtering is used to deposit the coating layer, sputtering is conveniently carried out in an inert atmosphere. The inert atmosphere conveniently comprises or consists essentially of argon.

[0033] In a fourth aspect of the present invention, a method for producing a solid-state battery (SSB) as set forth in the accompanying claims is disclosed. The SSB is according to the second aspect of the present invention, i.e., advantageously comprises an anode, a cathode, and an SSE according to the first aspect of the present invention or obtained by the third aspect of the present invention. The SSE advantageously comprises a dense film as described above and a coating layer comprising or consisting essentially of Sb as described above, the coating layer being provided on one side of the dense film.

[0034] A method for producing an SSB includes the steps of providing a pre-SSB, isostatically pressing the pre-SSB, and heating the pre-SSB.

[0035] The pre-SSB is provided by providing an anode and a cathode on either side of an SSE, where the anode comprises or consists essentially of metallic lithium and is provided adjacent to the anode with a coating layer comprising or consisting essentially of Sb.

[0036] The pre-SSB is hydrostatically pressurized to a pressure of at least 10 MPa. It is understood that the applied pressure is selected depending on the pressure that the components of the pre-SSB, particularly the dense membrane of the SSE, can withstand. In particular, the applicable pressure increases as the thickness of the dense membrane of the SSE increases. For example, when the thickness of the dense membrane is about 45 μm, a pressure of 50 to 75 MPa, preferably 65 to 71 MPa, is applied.

[0037] The pre-SSB is isostatically pressed to obtain a green SSB. The green SSB is heated to a temperature of 150°C to 500°C, preferably 200°C to 300°C. The heating operation is carried out in an inert atmosphere. The inert atmosphere is conveniently an atmosphere containing or consisting essentially of argon.

[0038] During the heating step, a second Li—Sb alloy is formed at the interface between the negative electrode comprising, or consisting essentially of, lithium metal and the coating layer comprising, or consisting essentially of Sb.

[0039] Advantages of the present invention include, but are not limited to, that the solid-state battery has low interfacial resistance between its anode and solid electrolyte, and very high critical current density (CCD) upon cycling at room temperature and at elevated temperatures up to 75° C. Without wishing to be bound by any theory, the inventors believe that the presence of the first Li—Sb alloy and the second Li—Sb alloy forms a uniform interface, thereby contributing to reducing the interfacial resistance and increasing the CCD.

[0040] Consequently, such an improved anode / SSE interface also has the benefit of increasing the number of charge / discharge cycles that the battery can withstand before failure, thereby extending the battery's lifespan, even under high current densities (due to the high CCD). Aspects of the invention will now be described in more detail with reference to the accompanying drawings, in which like reference numerals denote like features, and in which: [Brief explanation of the drawings]

[0041] [Figure 1] 1 shows a schematic diagram of a first solid electrolyte (SSE) of the present invention. [Figure 2] 1 illustrates a second SSE of the present invention. [Figure 3] 2 shows a schematic diagram of a first solid-state battery (SSB) of the present invention including the first SSE of FIG. 1. [Figure 4] 3 shows a schematic diagram of a second SSB of the present invention, including the second SSE of FIG. 2; [Figure 5A] 1 shows an SEM image of the surface of the first LLZO-containing dense film. [Figure 5B] 1 shows an SEM image of a cross section of a first LLZO-containing dense film. [Figure 6] 1 shows an SEM image of a cross section of a second LLZO-containing dense film. [Figure 7] The composition of the dense films as determined by X-ray photoelectron spectroscopy (XPS) is shown, expressed as atomic concentration of O 1s as a function of sputtering time / depth of XPS analysis. [Figure 8] 1 shows impedance measurements of lithium symmetric cells with a reference SSE and a first inventive SSE at room temperature. [Figure 9] 1 shows impedance measurements at 75° C. of lithium symmetric cells with a reference SSE and a first inventive SSE. [Figure 10] 1 shows the cell potential and current density as a function of time for a lithium symmetric cell with a first inventive SSE at room temperature. [Figure 11] 1 shows the cell potential and current density as a function of capacity for a lithium symmetric cell with a first inventive SSE at 75° C. [Figure 12] 1 shows the cell potential and current density as a function of time for a lithium symmetric cell equipped with a second inventive SSE at 75° C. [Figure 13] 1 shows the cell potential of a lithium symmetric cell with a first inventive SSE at 75° C. as a function of time and number of charge / discharge cycles. [Figure 14A] 1 shows the cell potential as a function of time under galvanostatic cycling of a reference control cell at 75° C. for up to 25 hours. [Figure 14B] 1 shows the cell potential as a function of time under galvanostatic cycling for a lithium symmetric cell equipped with a first inventive SSE at 75° C. for up to 25 hours. [Figure 15A] A cross-sectional SEM image of a reference control cell after 25 hours of galvanostatic cycling is shown. [Figure 15B]1 shows a cross-sectional SEM image of a lithium symmetric cell with a first inventive SSE after 900 hours of galvanostatic cycling. DETAILED DESCRIPTION OF THE INVENTION

[0042] Figure 1 shows a schematic diagram of a solid electrolyte 1 according to the present disclosure. The SSE 1 comprises a dense membrane 2 comprising, or consisting essentially of, LLZO and a coating layer 3 comprising, or consisting essentially of Sb. Advantageously, the coating layer consists of Sb.

[0043] The dense film 2 advantageously has a thickness of 5-50 μm, for example 15 μm-45 μm. Such dense films can be produced by methods known in the art. Particular methods include preparing a slurry containing the optionally doped LLZO, tape-casting the slurry, removing the binder from the slurry (annealing), and sintering the green film to densify it. Advantageously, the sintering comprises or essentially consists of ultra-rapid sintering (UFS). Advantageously, the (ultra-rapid) sintering is carried out in an inert atmosphere, thereby limiting the formation of carbon-containing contaminants, such as Li2CO3, at the surface of the film.

[0044] Advantageously, the surface of the dense film that interfaces with the coating layer 3 comprising or consisting essentially of Sb is free of Li2CO3. Furthermore, the surface is advantageously free of LiOH and / or Li2O.

[0045] The surface roughness of the dense film is advantageously a few nanometers, in other words, if the dense film is 45 μm thick, then its thickness will be between 44.998 μm and 45.002 μm, depending on the location at which the thickness is measured on the surface.

[0046] The thickness of the Sb-containing coating layer 3 is conveniently 1 to 20 nm, preferably 5 to 10 nm.

[0047] The SSE 1 further comprises a first Li—Sb alloy 5 at the interface between the dense film 2 , in particular the lithium contained in the dense film 2 , and the Sb-containing coating layer 3 .

[0048] Advantageously, the first Li—Sb alloy 5 comprises or consists essentially of LiSb. Although the Li—Sb alloy may further comprise LiSb, the inventors believe that deposition of the coating layer 3 on the dense film 2 is rate-limited by the dissolution and solid-state diffusion of Li from the LLZO contained in the dense film 2 into the Sb-containing coating layer 3, resulting in the formation of primarily LiSb.

[0049] SSE1 has a critical current density (CCD) of 2 mA / cm at room temperature. 2 More than 3mA / cm, preferably 3mA / cm 2 That's the best case scenario.

[0050] SSE1 has a CCD current of 30mA / cm at 75℃. 2 More than 50mA / cm 2 More preferably, 60 mA / cm 2 For example, 70mA / cm 2 It is convenient to be.

[0051] The SSE1, shown schematically in FIG. 1, is particularly suitable for use in solid-state batteries (SSBs) that include a negative electrode that includes, or consists essentially of, metallic lithium.

[0052] 2 shows a schematic representation of a further SSE 10 of the present invention, including the dense film 2 described above. Coating layers 3, 4 comprising or consisting essentially of Sb are provided on both sides of the dense film 2, with first Li—Sb alloys 5, 6 present at the interfaces of each coating layer 3, 4 and the dense film 2. The coating layers 3, 4 and the first Li—Sb alloys 5, 6 are as described above with respect to FIG.

[0053] The SSE 10 shown schematically in FIG. 2 is particularly suitable for use in a symmetric cell for performance analysis of the SSE, for example, a symmetric cell including two electrodes comprising, or consisting essentially of, metallic lithium.

[0054] 3 shows a schematic diagram of a solid-state battery 11 of the present invention. The SSB 11 includes the SSE 1 of FIG. 1. An anode 7 including or consisting essentially of metallic lithium is present adjacent to the Sb coating layer 3. A second Li—Sb alloy 9 is present at the interface between the anode 7, particularly the metallic lithium contained therein, and the Sb coating layer 3.

[0055] The negative electrode 7 can be any metallic lithium containing negative electrode known in the art. Conveniently, the negative electrode consists of metallic lithium.

[0056] The second Li-Sb alloy 9 conveniently comprises or consists essentially of Li2Sb. The Li-Sb alloy may further comprise Li3Sb.

[0057] SSB 11 further includes a positive electrode 8 disposed adjacent to the surface of dense film 2 opposite the surface adjacent Sb coating layer 3. The positive electrode can be any positive electrode known in the art, particularly any positive electrode known in the art for use in lithium-ion (secondary) batteries.

[0058] Figure 4 shows a schematic diagram of a symmetric cell under test, e.g., a lithium symmetric cell. The symmetric cell 12 includes the SSE 10 of Figure 2 and two electrodes 7, 13 comprising or consisting essentially of metallic lithium disposed adjacent to the coating layers 3, 4. A second Li-Sb alloy 14 is present at the interface between the second electrode 13, particularly the metallic lithium contained therein, and the adjacent Sb coating layer 4.

[0059] Although an increase in critical current density (CCD) is expected when compared to thicker LLZO-based SSEs, such as 1 mm thick LLZO pellets, the inventors have surprisingly found that the increase achieved with the LLZO-containing SSEs of the present invention significantly exceeds expectations: While a 2-fold increase was expected based on data known in the art, the inventors have achieved at least a 4-fold increase, and even a 5.5-fold increase.

[0060] Without wishing to be bound by any theory, the inventors believe that this performance improvement (increased CCD) is achieved by using an LLZO-containing dense film that is not only substantially free of Li2CO3 at the surface that interfaces with the Sb-containing coating, but also by improving the deposition of an antimony-containing layer on the surface of the LLZO-containing dense film, which results in a more uniform interface and a more optimal Li-Sb alloy at the interface.

[0061] Example To test the performance of the solid electrolyte (SSE) of the present invention, lithium symmetric cells were prepared using two of the LLZO-containing SSEs of the present invention. Lithium symmetric cells were also prepared using a reference LLZO SSE. The reference LLZO SSE consisted of a 45 μm-thick dense LLZO film. The SSE of the present invention contained a 15 μm- or 45 μm-thick dense LLZO film with a 10 nm antimony (Sb) coating on both sides.

[0062] Dense, thick LLZO films were fabricated by mixing 4.3 mL of a solvent containing 5 vol% isopropanol, 87 vol% ethanol, and 8 vol% 1-propanol, 0.408 mL of plasticizer, and 0.43 g of surfactant. For 45 μm-thick dense LLZO films, 3 g of aluminum-doped LLZO powder was added to the mixture, while for 15 μm-thick dense LLZO films, a mixture of 3 g of aluminum-doped LLZO and 7 wt% Li2CO3 was added.

[0063] The LLZO-containing mixture was then ball-milled at 165 rpm for 18 hours to obtain a suspension. Two milliliters of binder solution (a 30:70 weight ratio mixture of polyvinyl butyral and isopropanol) was then added to the suspension, followed by ball-milling at 200 rpm for 2 hours to obtain a homogeneous slurry. The homogeneous slurry was then tape-cast onto a glass plate at a speed of 1 mm / s using a doctor blade with a 400 μm opening for the 45 μm high-density LLZO film and a 150 μm opening for the 15 μm high-density LLZO film.

[0064] The tape-cast layer was air-dried for 30 minutes, peeled off from the glass substrate, and cut into 10 mm diameter disks by laser cutting.

[0065] The LLZO membrane disk was sandwiched between a flat alumina plate and a microporous alumina plate and annealed in a muffle furnace under oxygen flow at 150°C for 2 hours, then at 400°C for 2 hours and at 600°C for 2 hours, with a heating rate of 300°C / hour, to remove the binder, followed by natural cooling.

[0066] After annealing, the LLZO films were sintered to obtain dense films. Sintering was performed by ultrafast sintering (UFS) in an argon-filled glove box. The films were placed in a graphite container sandwiched between two boron nitride plates. The entire stack was placed in a carbon felt slit in the UFS apparatus. Sintering was performed at 1200 °C for 50 seconds for the 45 μm films and at 1150 °C for 50 seconds for the 15 μm films.

[0067] Figures 5A and 5B show scanning electron microscope (SEM) images of the surface and cross section of a 45 μm LLZO film. Figure 5A clearly shows the absence of pinholes on the surface, and Figure 5B clearly shows that a highly uniform and dense (i.e., low porosity) LLZO film was obtained.

[0068] Figure 6 shows an SEM image of a cross section of a 15 μm LLZO film, and it is again clear that the film is very uniform and dense (i.e., low porosity).

[0069] One 15 μm LLZO film and two 45 μm LLZO films were heated at 900 °C for 10 min in an argon-filled glove box to remove impurities. Figure 7 shows the composition of the dense film, measured by X-ray photoelectron spectroscopy (XPS), expressed as the atomic concentration of O 1s as a function of sputtering time / depth in the XPS analysis. The dense film is shown after UFS but before heating (A) and after UFS and heating (B). Before heating, Li2O is detected at low sputtering depths (near the surface), with almost no Li2CO3 detected. After heating, the amount of Li2O as an impurity is reduced throughout the entire film depth (thickness), with only trace amounts detected deep within the dense film. While not wishing to be bound by any theory, the inventors believe that Li2O is reintegrated into the LLZO structure during the heat treatment.

[0070] A reference lithium symmetric cell was prepared by placing 3 mm diameter lithium disks on either side of a 45 μm LLZO film, vacuum sealing the Li / LLZO / Li stack in a latex container, and then isostatically pressing at 71 MPa for several minutes.

[0071] Two lithium symmetric cells equipped with the SSE of the present invention were prepared by sputtering a 10 nm Sb coating layer (3 mm diameter) on both sides of a 15 μm LLZO film and a 45 μm LLZO film using an Sb target (purchased from Plasmaterials) at an argon flow rate of 50 sccm by radio frequency magnetron sputtering (sputtering equipment: Orion, AJA International Inc.). The thickness of the Sb coating layer was adjusted by measuring the deposition rate with a quartz crystal microbalance (QCM) and adjusting the deposition time accordingly.

[0072] Next, 3 mm diameter lithium disks were placed on both sides of the Sb-LLZO film, and the Li / Sb-LLZO / Li stack was vacuum-sealed in a latex container. The stack was then isostatically pressed for several minutes. For the 45 μm LLZO film, a pressure of 71 MPa was applied. For the 15 μm LLZO film, a pressure of 10 MPa was applied.

[0073] All three lithium symmetric cells were then heated to 250° C. on a hotplate inside an argon-filled glove box for 1 hour.

[0074] The interfacial resistance was measured by impedance measurements using a Biologic MTZ-35 analyzer. Figure 8 shows the results of impedance measurements at room temperature, and Figure 9 shows the results of impedance measurements at 75°C, for a reference control cell 20 containing a 45 μm LLZO film and a control cell 21 of the invention. From these impedance measurements, the interfacial resistance can be calculated by multiplying the measured interfacial impedance by the area of ​​the sample. A smaller area under the impedance curve indicates a lower interfacial resistance. At both temperatures, it is clear that the cell of the invention has a significantly lower interfacial resistance than the reference cell: 5.35 Ω·cm at room temperature. 2 34.8 Ω cm 2 , 0.129 Ω cm at 75°C 2 0.948 Ω cm 2 A low interfacial resistance is a measure of high battery performance.

[0075] The critical current density (CCD) was also measured at room temperature and at 75°C. CCD is the highest current density that can be sustained before the SSE breaks down, and is the current density at which a battery cell can withstand charge-discharge cycles without cell failure. CCD is measured by measuring the capacity limit of a symmetric cell to 0.1 mAh / cm. 2 Repeated charging and discharging at a current step of 0.1 mA / cm 2 ~Maximum value 100mA / cm 2 The voltage was increased stepwise to 100 V and measured until a short circuit occurred.

[0076] Figure 10 shows the cell potential and current density at room temperature for a symmetric cell with an SSE of the present invention containing a 45 μm LLZO film. The current density at failure just before 8 hours of charge and discharge was 3.62 mA / cm. 2Figure 11 shows the cell potential and current density as a function of capacity at 75°C for a control cell with an SSE of the present invention containing a 45 μm LLZO film and a reference cell. It is clear that the cell with the SSE of the present invention fails at a higher capacity and has a significantly higher current density at failure (CCD): 70 mA / cm 2 , while the reference cell has a current of 16 mA / cm 2 is.

[0077] FIG. 12 shows the cell potential and current density at 75° C. for a symmetric cell with an SSE of the present invention containing a 15 μm LLZO film, with a CCD of 1.2 mA / cm 2 This indicates that

[0078] A lithium symmetric cell containing the SSE of the present invention, which includes a 45 μm LLZO film, was also subjected to cycling tests. Galvanostatic cycling was performed at a temperature of 75° C. and a current of 4 mA / cm. 2 (high) current rate of 1mAh / cm 2 Figure 13 shows the results up to approximately 3500 cycles (approximately 1800 hours), and it is clear that very stable behavior is maintained up to about 1730 cycles.

[0079] A reference lithium symmetric cell was also subjected to galvanostatic cycling under the same conditions. Figures 14A and 14B show the results up to 25 hours of cycling for the reference cell and the lithium symmetric cell containing the SSE of the present invention with a 45 μm LLZO film, respectively. It is clear that the reference cell already failed after 15 hours of testing. To evaluate the difference in cycle duration to failure (15 hours vs. nearly 1800 hours), a cross-sectional SEM image of the failed reference cell (after 25 hours) ( Figure 15A ) was compared with a cross-sectional SEM image of the lithium symmetric cell containing the SSE of the present invention with a 45 μm LLZO film after 900 hours of cycling ( Figure 15B ). It is clear that voids formed in the reference cell after 25 hours of cycling, whereas no voids formed in the SSE of the present invention even after 900 hours of cycling.

[0080] The inventors believe that the Li-Sb alloy present at both the metallic Li / Sb coating interface and the Sb coating / LLZO interface improves electronic conductivity and allows for efficient and uniform transfer of Li ions between metallic lithium and LLZO, thereby reducing vacancy formation at the metallic lithium / SSE interface. [Explanation of symbols]

[0081] 1.Solid electrolyte 2.High density membrane 3. Sb-containing coating layer 4. Sb-containing coating layer 5. First Li-Sb alloy 6. First Li-Sb alloy 7. Metallic lithium-containing anode 8.Positive electrode 9. Second Li-Sb alloy 10.Solid electrolyte 11. Solid state battery 12. Solid state battery 13. Metallic lithium-containing positive electrode 14. Second Li-Sb alloy 20. Impedance measurement relative to a reference control cell 21. Impedance measurements for symmetric cells of the present invention

Claims

1. A solid electrolyte (SSE) (1, 10) comprising a dense film (2) containing lithium lanthanum zirconium oxide (LLZO) and a coating layer (3, 4) containing antimony (Sb) provided on the surface of the dense film (2), wherein the dense film (2) has a density of 90% or more of the theoretical density of the film, the coating layer (3, 4) containing Sb has a thickness of 1 to 20 nm, and the dense film (2) has a thickness of 100 μm or less, and at least the surface of the dense film (2) on which the coating layer is provided is substantially Li ２ CO ３ and the SSE (1, 10) contains a first Li—Sb alloy (5, 6) at an interface between the Sb-containing coating layer (3, 4) and the high-density film (2) containing LLZO, wherein the thickness is a value calculated from a scanning electron microscope (SEM) image of the SSE (1, 10).

2. The SSE (1, 10) of claim 1, wherein the dense membrane (2) has a thickness of 5 to 50 μm.

3. The SSE (1, 10) of claim 1, wherein the Sb-containing coating layer (3, 4) has a thickness of 5 to 10 nm.

4. The SSE (1, 10) of claim 1, wherein the Sb-containing coating layer (3) is provided on one side of the dense membrane (2).

5. 2. The SSE (1, 10) of claim 1, wherein the LLZO is doped LLZO, preferably aluminum-doped LLZO.

6. The critical current density at room temperature is 2 mA / cm ２ More than 3mA / cm ２ The SSE (1, 10) according to claim 1 .

7. A solid-state battery (SSB) (11, 12) comprising the SSE (1, 10) of claim 1, an anode (7) comprising metallic lithium, and a cathode (8, 13), wherein the anode (7) is adjacent to the coating layer (3) comprising Sb, and the solid-state battery (SSB) (11, 12) comprises a second Li-Sb alloy (9) at the interface between the anode (7) and the coating layer (3) comprising Sb of the SSE (1, 10).

8. The interface resistance of the negative electrode-SSE interface at room temperature is 6 Ω cm as calculated from the impedance measurement of the SSB. ２ 8. The SSB (11, 12) according to claim 7, wherein:

9. 1. A method for producing a solid electrolyte (SSE) (1, 10) comprising a dense membrane (2) comprising LLZO and a coating layer (3, 4) comprising Sb, the method comprising: A step of heating a high density film (2) containing Li-LLZO to a temperature of 700°C to 1000°C in an inert atmosphere, wherein the high density film (2) has a density of 90% or more of the theoretical density of the film, and the thickness of the high density film (2) is 100 μm or less as calculated from an SEM image of the high density film (2), thereby ２ CO ３ obtaining a dense membrane (2) having a surface substantially free of -Li ２ CO ３ depositing a coating layer (3, 4) containing Sb on the surface of the dense film (2) that is substantially free of Sb, thereby obtaining the SSE (1, 10), wherein the Sb-containing coating layer (3, 4) has a thickness of 1 to 20 nm as calculated from an SEM image of the SSE (1, 10); The method is characterized in that the deposition of the Sb-containing coating layer (3, 4) forms a first Li—Sb alloy (5, 6) at the interface between the Sb-containing coating layer (3, 4) and the dense film (2) comprising LLZO.

10. 10. The method of claim 9, wherein the Sb-containing coating layers (3, 4) are deposited by radio frequency (RF) magnetron sputtering.

11. The method of claim 10, wherein the RF magnetron sputtering is performed in an inert atmosphere.

12. The method of claim 9, wherein the dense film (2) is heated at a temperature between 800°C and 900°C.

13. 10. The method of claim 9, wherein the LLZO is doped LLZO, preferably aluminum doped LLZO.

14. A method for producing a solid-state battery (SSB) (11, 12) including the SSE (1) according to claim 1 or the SSE (1) obtained by the method according to claim 9, wherein the coating layer containing Sb is provided on one side of the high-density film (2), - providing a negative electrode containing metallic lithium and a positive electrode on both sides of the SSE, the negative electrode being adjacent to the Sb-containing coating layer of the SSE, thereby obtaining a pre-SSB; - isostatically pressing said pre-SSB at a pressure of at least 10 MPa, thereby obtaining a green SSB; and - heating the green SSB to a temperature of 150°C to 500°C in an inert atmosphere, thereby forming a second Li-Sb alloy at the interface between the negative electrode and the Sb-containing coating layer of the SSE, to obtain an SSB.

15. 15. The method of claim 14, wherein the green SSB is heated to a temperature of 200°C to 300°C.

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