Method for forming metal layer on surface of solid, ion-conducting substrate, substrate producible by this method, and anodeless battery

Abstract

The present invention relates to a method of forming a metal layer, i.e. A metal current conductor, on a surface of a solid, ion-conducting substrate, such as a lithium-ion secondary battery or a sodium-ion secondary battery, a substrate producible by the method and an anodeless battery. By means of the method according to the invention, a component of a solid-state electrolyte battery, for example the anode side of a solid-state electrolyte battery, can be provided on an industrially relevant scale in a rapid, simple and cost-effective manner, said component being characterized by a uniform current density and suitability for high maximum charge and discharge currents.

Description

Technical Field

[0001] The present invention relates to a method for forming a metal layer (i.e., a metal current conductor) on the surface of a solid-state, ion-conducting substrate (such as a lithium-ion secondary battery or a sodium-ion secondary battery), a substrate producible by this method, and an anode-free battery. By the method according to the invention, components of a solid-state electrolyte battery (such as the anode side of a solid-state electrolyte battery) can be provided in an industrially relevant scale in a fast, simple, and cost-effective manner, which components are characterized by a uniform current density and suitability for high maximum charge and discharge currents. Background Art

[0002] Current collectors for secondary batteries (such as solid-state batteries) are usually much thicker than required (for example, in the case of a lithium-based battery cell, the copper arranged on the anode side is about 20 μm). Obtaining the raw materials for these foils by electrolytic refining of pure copper or by melting electrolysis of aluminum is also very energy-consuming. The copper foils must have a certain minimum thickness, for example, to meet the strength requirements for the roll-to-roll process. Failures related to cracks can cause long downtimes of the production line. In the past, copper foils of suitable thickness were produced by a well-established rolling process (Walzprozess) or by electrolysis. By a continuous feedback loop in quality control, a sufficiently uniform thickness and strength of the produced copper foils can be achieved. Other solution strategies include coating copper on a thin and very strong conductive plastic foil (such as a polyimide foil). On the one hand, the advantage of using a plastic foil is that it reduces the total weight of the current collector because the plastics used usually have a lower specific gravity than copper (for example, the specific gravity of the plastic foil is 1.5 g / cm 3 , while the specific gravity of copper is about 9 g / cm 3 ). On the other hand, the disadvantage of this solution is that the plastics used have a worse specific conductivity than copper and thus limit the maximum possible current of the secondary battery.

[0003] For solid-state batteries, due to the relatively low ionic conductivity, it is also necessary to fabricate a very thin ceramic separator through which metal ions (usually lithium ions or sodium ions) can pass. A suitable separator thickness is less than 50 μm. If a copper current collector coated with lithium is pressed onto the surface of a generally uneven ceramic separator serving as a substrate during the battery cell manufacturing process, the ceramic separator will inevitably break due to its thin thickness. To avoid this, it is known to apply a current collector layer conforming to the surface onto such a thin ceramic separator by atomic layer deposition (ALD), sputtering techniques, or thermal evaporation. However, this generally requires a vacuum, which makes large-scale production difficult or impossible. Additionally, with sputtering techniques, the layer can only be deposited at a rate of nm / min. This requires a long time to reach an optimal thickness of 1 μm to 10 μm. When sputtering a conductor layer (e.g., made of copper) onto a ceramic or polymer electrode material, the growth initially occurs in an island-like form. These islands generally do not grow together to form a flat, pore-free layer. The significant roughness in these layers leads to a high local current density at the roughness peaks. The ALD method also has drawbacks, namely its relatively slow speed and difficulty or impossibility to achieve layer thicknesses in the μm range on a large scale. Additionally, this method forms a conformal topological deposition on undercut geometries and pores, which precisely causes these geometries to reform rather than be closed, which must be avoided to achieve as uniform a current density as possible. Similarly, due to the necessary low conductivity of the solid-state electrolyte substrate, electroplating is not suitable for use.

[0004] It is known that significant energy density gains in solid-state batteries can only be achieved with a non-anode design. However, due to the poor surface contact between the rigid metal copper foil and the solid-state electrolyte separator, it is currently almost impossible to implement a non-anode design in solid-state batteries because metallic lithium can only be deposited at small contact points between the current collector and the solid-state electrolyte. Therefore, it is not possible to deposit a uniform (lithium) layer using a conductor foil by known methods, and only a "forest" of lithium whiskers can be formed. A known method to solve this problem and fabricate the active material on the metal anode side is to fabricate a solid-state electrolyte sponge in which, for example, metallic lithium is plated. The solid-state electrolyte sponge has a porous layer made of a brittle ceramic. However, the drawback of this method is that the brittle ceramic is easily mechanically damaged due to the contact pressure of the foil, thereby increasing the risk of rejects and the cost of the method. Another approach to solving this problem is to use chemical vapor deposition (CVD) and physical vapor deposition (PVD) methods, but these methods also have the above-mentioned drawbacks. Another approach is to increase the electrical contact surface by performing a polishing step on the uneven ceramic layer. However, considering the goal of large-scale mass production, this approach does not achieve the purpose because it is costly and time-consuming.

[0005] The cyclability and durability of the lithium boundary layer at the solid electrolyte also highly depend on the local current density. When charging and discharging at high current densities, so-called voids (pores) and metallic dendrites form in the boundary layer. The latter are formed precisely where the current density is particularly high. Currently, this dendrite formation can only be prevented by reducing the local current density below a critical value. The formation of voids further reduces the available electrical contact area and leads to a positive control loop of decreasing battery performance. In addition, dendrites can also grow through the separator in ceramic cells and cause a short circuit of the cell. To avoid the problem of the critical current density that limits performance, one approach is to 3D structure the surface (e.g., by laser machining or 3D printing) or to produce a highly porous, sponge-like solid electrolyte electrode layer by mixing organic and ceramic powders and subsequent pyrolysis. Another approach is to prevent the formation of voids and dendrites by using (lithium) alloys (e.g., LiMg) and adhesion promoters or diamond nanoparticles, while leaving the surface unchanged. This includes solid electrolyte materials with a high elastic modulus (E-Modul), as low a conductivity as possible, and at the same time a high ionic conductivity, especially when the grain boundary density and pore volume are low.

[0006] In addition, it is known that lithium has difficulty depositing on copper foils, and lithium does not adhere well to bare copper foils. Only after the copper surface has been deliberately oxidized (e.g., at high temperature and for a long time in an oxygen atmosphere in a furnace) to make the copper foil lithiophilic can a thin lithium layer be deposited from a lithium melt on the copper foil. This lithium deposition process is costly because it has to be carried out in a protective gas atmosphere. Only in this way can the quality of the composite of the copper foil and the lithium layer for battery applications be ensured. Then, the composite component thus produced must also be brought into contact with the other components of the respective battery under a protective gas. Therefore, this production can only be carried out, for example, in a dry room with high operating costs. Any passivation of the lithium surface during processing must be avoided, otherwise the electrical contact resistance will increase significantly, and lithium oxides, hydroxides, or carbonates will harden the surface and greatly increase the necessary contact pressure on the ceramic separator. The current way to avoid this problem is to deliberately oxidize the copper surface at high temperature in air or an oxygen atmosphere. The copper oxide is then reduced by lithium and thus acts as an adhesion promoter. Importantly, the copper oxide layer should not be too thick, as this would in turn increase the electrical contact resistance.

[0007] For the production of battery cells of a battery, the active material paste is currently applied only in selected areas of the current collector in a roll-to-roll process. These coated areas are then cut or punched using a laser in the next step. This can lead to combustion of the active material or formation of burrs, which can cause short circuits in the battery cells. The standardized width and length of the foils make the choice of possible battery cell formats inflexible. The downtime when changing the rolls and the possible waste contaminated with the active material make these production processes expensive and reduce the achievable throughput. In addition, the handling of the coated rolls is logistically challenging and has all the consequences for price and throughput. Technologies are currently being developed to increase the diversity of battery cell specifications, for example by laser-cutting the coated current collector, which is gradually becoming an industrial standard. In the production of copper foils, highly flexible plastic foils are used and overall continuous improvement of quality assurance is carried out to prevent tearing of the foils during the production process.

[0008] In summary, it can be determined that there is currently no known method to provide components of a solid-state electrolyte battery (such as the anode side of a solid-state electrolyte battery) on an industrially relevant scale in a fast, simple and cost-effective (i.e., economical) manner, the components being characterized by a uniform current density (i.e., avoiding locally elevated current density) and suitability for high maximum charge and discharge currents. Summary of the Invention

[0009] The problem is solved by a method having the features of claim 1, a solid-state, ion-conducting substrate having the features of claim 14 and an anode-free battery having the features of claim 19. Advantageous embodiments and further improvements of the invention can be achieved by the features shown in the dependent claims.

[0010] According to the invention, there is provided a method for forming a metal layer on a surface of a solid-state, ion-conducting substrate, comprising the steps of:

[0011] a) spraying metal particles in the direction of the solid-state, ion-conducting substrate along a spraying distance, wherein the metal particles

[0012] i) are at least partially molten metal particles, or

[0013] ii) are solid metal particles which are heated to a temperature above the melting temperature of the metal particles along the spraying distance and / or by their impact velocity on the solid-state, ion-conducting substrate, wherein at least partially molten metal particles are produced; and

[0014] b) solidifying the at least partially molten metal particles on the solid-state, ion-conducting substrate, wherein a metal layer is produced which is arranged on the solid-state, ion-conducting substrate.

[0015] By means of the method according to the invention, components of a solid-state electrolyte cell (for example, the anode side of a solid-state electrolyte cell) can be provided in an industrial relevant scale in a fast, simple and cost-effective (i.e., economical) manner, and the components are characterized by a uniform current density and suitability for high maximum charge and discharge currents. The method is capable of producing current conductors that adhere well even on uneven, three-dimensionally structured and spongy (ceramic) solid-state electrolyte separators.

[0016] One reason is that when the metal particles impact on the substrate surface, they can adapt to any surface profile of the substrate, thereby generating a very large contact area between the metal of the metal particles and the substrate. Therefore, compared with the application of a metal foil, significantly more substrate surfaces are wetted, and the formation of interfacial defects (such as voids, whiskers and dendrites) is greatly reduced or even completely avoided, thus making the current density distribution more uniform.

[0017] By spraying metal particles onto the substrate, when the produced substrate is used in a solid-state battery, solid-state battery cells with a freely selectable shape can also be coated. This does not generate waste and layers with a desired thickness can be produced, and these layers can in particular be significantly thinner than the currently manufactured layers while still having sufficient conductivity. Approximately 50% of the amount of metal (such as copper or aluminum) currently required can be saved.

[0018] In addition, the substrate according to the invention is suitable for use as an anodeless part of a solid-state battery, that is, metallic lithium is only deposited between the substrate and a metal layer or at least partially oxidized metal layer (see below) during the use of the solid-state battery, and it is not necessary to handle it as metallic lithium during the production process, which simplifies the manufacturing method and makes it safer. In other words, the use of a so-called "low dew point" casing that would significantly increase the cost of the manufacturing method can be avoided, and there is also no risk that the current conducting layer is damaged (such as cracked) during the production process. By implementing an anodeless design, the demand for lithium (or Na, K, Mg, etc.) can also be significantly reduced.

[0019] The spraying of the metal particles can be carried out using a method selected from the group consisting of: plasma spraying method, cold gas spraying, high velocity oxy-fuel spraying, flame spraying, detonation spraying, laser spraying, arc spraying and thermal spraying according to DIN EN 657:2005. Preferably, the spraying of the metal particles is carried out using a method selected from the group consisting of: plasma spraying method, cold gas spraying and arc spraying, and particularly preferably using the plasma spraying method.

[0020] In a preferred embodiment, the spraying of the metal particles is carried out using a plasma spraying method. The plasma spraying method has advantages because it produces a particularly well - closed and uniform metal surface on the substrate surface. In the plasma spraying method, a plasma can be ignited in the gap between the anode and the cathode using a DC voltage. An inert gas (such as argon) can flow through the above - mentioned gap and be ionized, thus becoming conductive. The inert gas is significantly heated during this process. The metal particles can be blown into the plasma and melted therein. In the plasma spraying method, the metal particles are melted in the nozzle and the molten metal particles are sprayed towards the substrate surface. Preferably, the metal particles are melted in the nozzle by an inert gas plasma present in the nozzle, and the inert gas plasma is particularly preferably a noble gas plasma, especially an argon plasma, optionally containing from >0 vol% to 5 vol% of hydrogen plasma. The hydrogen in the hydrogen plasma raises the process gas temperature and has a reducing effect, thereby avoiding or reducing oxidation.

[0021] The inert gas plasma can be particularly generated by applying a voltage to the nozzle during continuous operation. For hot atmospheric plasmas, the voltage range is from 1 V to 60 V, and for cold active atmospheric plasmas, the voltage range is from 100 V to 10 kV, where the ignition voltage is optionally at least 10 times larger. For example, an ignition voltage of 15 kV can be used. After ignition, the plasma becomes conductive and only a low voltage (such as only 2 - 3 kV) is required to keep it "running".

[0022] In addition, the inert gas plasma can particularly exit the nozzle with a volume flow rate in the range of 1 l / min to 100 l / min.

[0023] Preferably, in the method, the spraying speed of the metal particles, the heating temperature of the metal particles, the diameter of the metal particles, the shape of the metal particles, and the spraying distance of the metal particles are selected to prevent the metal particles from breaking when they impact the substrate surface. Preventing breakage means that the metal particles do not break into parts distributed on the substrate surface when they impact the substrate surface. Preventing breakage means that the particles do not break on the substrate surface but solidify on the surface at the impact point with their entire volume. The advantage is that a (closed) metal layer is formed on the substrate, which is formed by metal particles that are stacked on top of each other and arranged adjacent to each other. The metal particles are melted, i.e., in the form of liquid and complete metal droplets on the substrate for a short time, and solidify on the substrate as complete metal droplets, without any material loss from each metal droplet. The respective metals or metal alloys used to form the metal particles and the corresponding parameters for each substrate surface to be coated can be determined based on a small number of tests, and then these parameters can be reproducibly maintained during the process implementation according to the measurement results. The method parameters that can be used to prevent the metal particles from breaking on the substrate surface are also listed below.

[0024] Preferably, in order to prevent the metal particles from cracking when hitting the substrate surface, the metal particles can be sprayed onto the surface of the substrate at a spraying speed of up to 700 m / s, preferably up to 500 m / s. The speed within this range reduces the risk of the metal particles cracking due to speed on the substrate surface and also reduces the risk of the substrate being damaged (e.g., the substrate cracking) due to excessive kinetic energy of the metal particles.

[0025] In addition, preferably, in order to prevent the metal particles from cracking when hitting the substrate surface, the temperature of the metal particles before hitting the substrate and / or when hitting the substrate can be at most 200 K higher than the melting temperature of the metal particles, preferably at most 100 K, and particularly preferably at most 50 K. The temperature within this range reduces the risk of the metal particles cracking due to viscosity on the substrate surface and also reduces the risk of the substrate being damaged due to excessive temperature of the metal particles.

[0026] In addition, preferably, in order to prevent the metal particles from cracking when hitting the substrate surface, the maximum diameter of the metal particles can be in the range of 1 μm to 1000 μm, particularly preferably in the range of 10 μm to 100 μm, where the maximum diameter refers to the maximum diameter measurable by a microscope. The diameter within this range reduces the risk of the metal particles cracking due to size on the substrate surface and also reduces the risk of the substrate being damaged due to excessive kinetic energy of the metal particles.

[0027] In a preferred embodiment, the maximum diameter of the metal particles is not in the range of ≤100 nm, optionally not in the range of <1 μm, where the maximum diameter refers to the maximum diameter measurable by a microscope.

[0028] In addition, preferably, in order to prevent the metal particles from cracking when hitting the substrate surface, the metal particles can have a substantially circular shape, where the aspect ratio of the length to the width of the metal particles is preferably in the range of 1:10 to 1:1, particularly preferably in the range of 1:5 to 1:1, very particularly preferably in the range of 1:2 to 1:1, especially in the range of 1.5:1 to 1:1, where the aspect ratio refers to the aspect ratio determinable by a microscope. As round a shape as possible can minimize the risk of the metal particles cracking on the substrate surface (rod-shaped particles are more likely to crack than spherical particles) and reduce the risk of the substrate being damaged (rod-shaped particles, especially in cold gas spraying, can cause very high local pressure when the head of the rod hits the substrate, and this pressure may damage the substrate).

[0029] In addition, in the method, preferably to prevent the metal particles from cracking when hitting the substrate surface, the metal particles can be sprayed at a spraying distance in the range of 1.5 cm to 4 cm, where in the case of the plasma spraying method, the spraying distance is defined by the interval from the opening of the nozzle to the substrate surface. The smaller the interval between the substrate surface and the nozzle, the higher the particle temperature when hitting the substrate surface and the smaller the deposition spot on the surface.

[0030] The spraying distance in this range can prevent the metal particles from hitting the substrate surface overheated or overcooled, thereby minimizing the risk of substrate cracking and damage.

[0031] In the method, the metal particles can be sprayed in the direction of the solid-state, ion-conducting substrate at a spraying rate (i.e., mass flow rate) in the range of ≥ 3 g of metal particles / minute, preferably in the range of 3 g to 6 g of metal particles / minute. The spraying rate in this range has been proven to be beneficial for forming a metal layer on the substrate, and the metal layer is formed by solidified molten metal particles that are stacked and arranged adjacent to each other.

[0032] The metal particles sprayed in the method may contain or consist of metal, and the metal is preferably selected from the group consisting of: copper, aluminum, gold, silver, tin, and alloys of at least one of these metals.

[0033] In a preferred embodiment, the metal particles sprayed in the method do not contain any alkali metal or any material that absorbs alkali metal, preferably do not contain the active material of the battery electrode. The advantage is that a metal layer can be formed on the surface of the solid-state, ion-conducting substrate in the form of electrode-free material (anode-free).

[0034] The metal layer produced in the method may have a layer thickness in the range of 0.1 μm to 50 μm in the direction perpendicular to the surface of the metal layer, preferably in the range of 0.2 μm to 20 μm, particularly preferably in the range of 0.5 μm to 10 μm, especially in the range of 1 μm to 2 μm.

[0035] In addition, the metal layer produced in the method can be porous, preferably having a porosity in the range of > 0 to 30%, where the porosity preferably refers to the porosity that can be measured by SEM or X-ray tomography. The measurement by SEM can be carried out, for example, by sawing and ion beam polishing the metal layer and then observing the metal layer in the SEM.

[0036] In a preferred embodiment, the metal layer produced in the method does not have a layer or a layer composed of solidified particles with a maximum diameter in the range of ≤ 100 nm, optionally in the range of < 1 μm.

[0037] In a further preferred embodiment, the metal layer produced in the method does not have oxygen-conducting properties and optionally does not have gas-conducting properties.

[0038] In a preferred embodiment, the method comprises the following steps before step a):

[0039] a) Spraying metal particles in the direction of the surface of a solid, ion-conducting substrate along a spraying distance, preferably the same metal particles as in step a) of the method, wherein the metal particles

[0040] i) are at least partially molten metal particles, or

[0041] ii) are solid metal particles which are heated to a temperature above the melting temperature of the metal particles along the spraying distance and / or by their impact velocity on the solid, ion-conducting substrate, wherein at least partially molten metal particles are produced; and

[0042] b) At least partially oxidizing the metal particles at least locally along the spraying distance, preferably by contacting the metal particles with a gas containing or consisting of oxygen (in particular air), wherein at least partially oxidized metal particles are produced; and

[0043] c) Solidifying the at least partially oxidized, at least partially molten metal particles on the solid, ion-conducting substrate, wherein an at least partially oxidized metal layer arranged on the solid, ion-conducting substrate is produced, wherein the at least partially oxidized metal layer particularly preferably contacts the solid, ion-conducting substrate in a planar manner.

[0044] The advantage of this embodiment is that an at least partially oxidized metal layer is produced between the substrate surface and the metal layer. This can have a higher binding effect (affinity) for lithium metal or sodium metal. For example, it is known that the binding strength of lithium metal to copper oxide is higher than that to metallic copper. Copper oxide can form a lithiophilic boundary layer, which is beneficial for the deposition of lithium when using the substrate in a solid-state battery and establishes high mechanical strength and low electrical contact resistance, which in turn establishes high mechanical adhesion and low electrical contact resistance between the electrochemically active metal layer to be deposited and the metal layer (i.e., the sprayed current collector).

[0045] The produced at least partially oxidized metal layer can have a thickness in the range of 10 nm to 1.5 μm in a direction perpendicular to the at least partially oxidized metal layer, preferably in the range of 15 nm to 1.0 μm.

[0046] Furthermore, the produced at least partially oxidized metal layer can be porous, preferably having a porosity in the range of >0 to 30%, wherein the porosity preferably refers to the porosity that can be measured by SEM or X-ray tomography.

[0047] In a further preferred embodiment, the substrate is moved relative to the device for spraying and heating the metal particles. Preferably, the substrate is conveyed on a moving belt and the metal layer is continuously applied to the substrate, wherein in particular preferably an at least partially oxidized metal oxide layer is continuously applied to the substrate before applying the metal layer. Preferably, the relative speed between the substrate and the device is maintained in the range of 0.1 m / s to 1 m / s. The relative movement from the substrate to the device is preferably a translational movement. Further preferably, a plurality of nozzles are used to spray the metal particles, and the nozzles are preferably arranged adjacent to each other on at least one comb structure (Kamm). The advantage of using at least one comb structure with a plurality of nozzles is that a large-area substrate surface can be coated quickly. The nozzles can also be arranged on at least one comb structure in a staggered arrangement in two or more rows.

[0048] The substrate is preferably designed as a flat substrate, preferably designed as a flat layer, and particularly preferably designed as a flat film. In addition, preferably the metal layer (optionally an at least partially oxidized metal layer) is at least partially applied to one of the two flat sides of the flat substrate (e.g., the top side or the bottom side of the flat substrate).

[0049] The substrate (without a metal layer or a partially oxidized metal layer) can have a surface with a surface roughness Rz in the range of 0 to 100 μm, wherein the surface roughness preferably refers to the surface roughness determinable according to DIN EN ISO 25178. The surface roughness can refer to the surface roughness measurable by confocal microscopy, atomic force microscopy, or stylus profilometry.

[0050] In addition, the substrate can comprise or consist of an ion-conducting material selected from the group consisting of: lithium-conducting ceramic materials, sodium-conducting ceramic materials, magnesium-conducting ceramic materials, potassium-conducting ceramic materials, zinc-conducting ceramic materials, aluminum-conducting ceramic materials, and combinations thereof.

[0051] Preferably, the substrate comprises or consists of a ceramic ion-conducting material, preferably a material selected from the group consisting of: LLZO, LATP, LAGP, NZSP, NASICON, β-aluminates, and combinations thereof, wherein LLZO is optionally Li 6.4 La 3 Zr 1,4 Ta 0.6 O 12 。

[0052] In addition, it is preferred that the substrate comprises or consists of a glassy ion-conducting material, preferably a material selected from the group consisting of: LiPON, inorganic glass, organic glass, and combinations thereof. The substrate may for example comprise or consist of a material selected from the group consisting of: lithium lanthanum zirconium oxide (Li 7 La 3 Zr 2 O 12 ), lithium aluminum titanium phosphate (Li 1+x Al x Ti 2-x (PO 4 ) 3 ), lithium aluminum germanium phosphate (Li 1.3 Al 0.3 Ge 1.7 (PO 4 ) 3 ), sodium zirconium silicate phosphate (Na 3 Zr 2 Si 2 PO 12 ), lithium phosphorus oxynitrite (Li 3.6 PO 3.4 N 0.6 ) and combinations thereof.

[0053] In an optional embodiment, the substrate is heated in the method, preferably to a temperature in the range of 150 °C to 300 °C. Heating the substrate can prevent damage to the substrate (such as forming cracks in the substrate and / or delamination occurring at the connection interface).

[0054] In a preferred embodiment, the solid, ion-conducting substrate does not contain any active materials of battery electrodes.

[0055] The method is particularly suitable for use in an anode-free system. In this case, the cathode material must contain the electrochemically active material to be deposited on the anode.

[0056] By the method according to the present invention, a metal layer (i.e., a current collector) is formed or produced on the surface of the solid, ion-conducting substrate. The method according to the present invention is material-independent and (when the substrate is used in a battery cell) battery-cell-type-independent.

[0057] The solid, ion-conducting substrate may be a substrate selected from one of the following substrates:

[0058] - A cathode infiltrated with a solid electrolyte material;

[0059] - An anode infiltrated with a solid electrolyte material;

[0060] - A cathode layer containing a solid-state, ion-conducting material, wherein the cathode layer is preferably a free-standing cathode layer, particularly preferably a free-standing cathode layer from which impurities (such as binders and conductive carbon black) have been removed by laser technology;

[0061] - An anode layer containing a solid-state, ion-conducting material, wherein the anode layer is preferably a free-standing anode layer, particularly preferably a free-standing anode layer from which impurities (such as binders and conductive carbon black) have been removed by laser technology;

[0062] - A composition (or mixture) of a solid-state electrolyte material and a cathode material, optionally sintered;

[0063] - A composition (or mixture) of a solid-state electrolyte material and an anode material, optionally sintered;

[0064] - A solid-state electrolyte material infiltrated with an active material (cathode material); and

[0065] - A solid-state electrolyte material infiltrated with an anode material.

[0066] In a preferred embodiment, the method further comprises the following steps:

[0067] i) Applying a layer containing an alkali metal and / or an alkaline earth metal or consisting thereof, preferably a layer containing sodium and / or lithium or consisting thereof, to the surface of the solid-state, ion-conducting substrate, the surface being opposite to the surface of the solid-state, ion-conducting substrate on which a metal layer (optionally also at least partially oxidized metal layer) is arranged; and

[0068] ii) Connecting the negative pole of a power source to the metal layer, connecting the positive pole of the power source to the layer applied in step i), and applying a voltage to the negative and positive poles, wherein a layer containing an alkali metal and / or an alkaline earth metal (especially in elemental form) or consisting thereof is deposited between the metal layer and the solid-state, ion-conducting substrate (optionally between the at least partially oxidized metal layer arranged on the substrate and the solid-state, ion-conducting substrate).

[0069] According to the present invention, there is also provided a solid-state, ion-conducting substrate, wherein a metal layer is at least locally arranged on the surface of the substrate, characterized in that the metal layer is formed by solidified molten metal particles which are stacked on top of each other and arranged adjacent to each other.

[0070] The substrate according to the present invention can be produced quickly, simply and cost-effectively (i.e., economically), and can be used as the anode side of a solid-state electrolyte battery. The substrate has a metal layer with a conformal topology, which significantly increases the contact surface with the substrate, thereby reducing the change in current density along the flat interface between the substrate and the metal layer. Therefore, the substrate according to the present invention is characterized by a uniform current density and applicability to high maximum charge and discharge currents.

[0071] The solid, ion-conducting substrate may have a surface roughness Rz in the range from 0 to 100 μm on the surface at least partially provided with a metal layer (preferably without a metal layer, i.e., in the uncoated state). The surface roughness preferably refers to the surface roughness determinable according to DIN EN ISO 25178. The surface roughness may refer to the surface roughness determinable by confocal microscopy, atomic force microscopy or stylus profilometry.

[0072] In a preferred embodiment, at least partially oxidized metal layer is arranged between the substrate and the metal layer, which is formed by solidified, melted, at least partially oxidized metal particles stacked on top of each other and arranged adjacent to each other, wherein the at least partially oxidized metal layer preferably contacts the substrate and the metal layer in a planar manner.

[0073] The substrate may be designed as a flat substrate, preferably a flat layer, particularly preferably a flat film, wherein the metal layer, optionally at least partially oxidized metal layer, is applied at least partially to one of the two flat sides of the flat substrate.

[0074] In the substrate according to the invention, a layer comprising and / or consisting of an alkali metal and / or an alkaline earth metal may be deposited between the metal layer and the solid, ion-conducting substrate (optionally, between the at least partially oxidized metal layer of the substrate and the solid, ion-conducting substrate), wherein the layer preferably comprises and / or consists of sodium and / or lithium (especially in elemental form).

[0075] Furthermore, the substrate can be produced by the method according to the invention.

[0076] According to the invention, an anode-free battery, preferably an anode-free secondary battery, comprising the substrate according to the invention is also provided. Preferably, the side of the substrate provided with the metal layer on its surface is the anode side of the battery. Description of the Drawings

[0077] The subject matter of the invention will be explained in more detail with reference to the following examples and drawings, but is not intended to be limited to the specific embodiments shown herein.

[0078] Figure 1 An embodiment of the method according to the invention using a plasma spraying method is schematically shown. Through the nozzle 5 of the plasma spraying device, the molten metal particles 3 are sprayed onto the solid, ion-conducting substrate 2 within the spraying distance 4 through the nozzle 5.

[0079] Figure 2An embodiment of the method according to the invention using a plasma spraying method is schematically shown, in which the substrate is moved relative to the plasma spraying device. Through the nozzle 5 of the plasma spraying device, the molten metal particles 3 are sprayed along the spraying distance 4 within the nozzle 5 onto the solid, ion-conducting substrate 2 conveyed on the moving belt 7, wherein the moving belt moves on the rollers 6.

[0080] Figure 3 A shows an ion-conducting ceramic substrate 2 of the prior art, on which a rigid metal copper foil 10 is applied, and lithium metal 8 during the operation of a solid-state battery comprising the substrate. It is shown in the figure that when the substrate 2 is used in a solid-state battery, the deposition of lithium metal 8 in the space between the substrate and the copper foil only occurs locally, i.e., at the points where the substrate 2 contacts the rigid metal copper foil 10. This results in a non-uniform current density distribution, leading to a high local current density and preventing a high total current. A high local current density is to be avoided and causes damage, while a high (uniformly distributed) overall current density is desired and enables high battery performance.

[0081] Figure 3 B shows an ion-conducting ceramic substrate according to the invention, on which copper particles are applied according to the method of the invention, and the deposition of lithium metal 9 obtained during the operation of a solid-state battery comprising the substrate 2. It is shown in the figure that when the substrate 2 is used in a solid-state battery, the deposition of lithium metal 9 in the space between the substrate and the copper foil occurs not only locally but comprehensively, i.e., over the entire surface where the substrate 2 contacts the copper layer 1. This results in a very uniform current density distribution and enables a high current to be generated, thereby enabling charging and discharging at a lower and uniformly distributed local current density.

[0082] Figure 4 A scanning electron microscope (SEM) image of a substrate according to the invention is shown. A copper metal layer (copper pad) is applied to the front side of a solid, ion-conducting substrate (here a β-aluminum sodium ceramic layer) using a plasma spraying method.

[0083] Figure 5 A cross-sectional SEM image of another substrate according to the invention is shown. This cross-section is produced by ion rays. An alkali metal layer (here a sodium metal layer) is electrochemically deposited here between the β-aluminum sodium ceramic layer and the copper pad of the substrate shown. Figure 4

[0084] Figure 6 Figure 4 Shows A cross-sectional SEM image of the substrate according to the invention in. This cross-section is produced by ion rays (FIB-cutting). An extremely tight and conforming surface contact between the ceramic surface and the copper and good wetting quality can be seen.

[0085] Figure 7 shows an enlarged view of a part of Figure 6 . Compared with Figure 6 , Figure 7 shows an extremely tight and conformal surface contact between the ceramic surface and copper and a good wetting quality. This wetting quality between the ceramic surface and copper can usually only be achieved by applying extremely high external pressure in common foil methods, but this will cause damage to the ceramic.

[0086] Figure 8 shows an SEM image of a substrate that is not the substrate of the present invention, which is produced by removing the copper layer from the substrate according to the present invention shown in Figure 5 using a needle. As can be seen from Figure 8 , the deposition of the sodium metal layer proceeds well not only at the FIB cutting position but also in a large area under the entire copper layer. Detailed Description

[0087] Example 1 - Method for forming a copper layer on the surface of a solid-state, ion-conducting ceramic substrate

[0088] In this example, metal particles are sprayed onto the surface of the ion-conducting substrate using a plasma spraying method.

[0089] Copper particles with a diameter of about 10 μm are melted in a thermal plasma at a temperature of 1085 °C and sprayed onto the ion-conducting ceramic substrate at a speed of 500 m / s and a spraying rate of 5 g / min over a distance of 30 cm (optionally preheating the substrate to a temperature of 200 °C). By using a temperature of 1085 °C, copper particles with a sufficiently high surface temperature can impact the substrate surface, causing it to undergo sufficient deformation and adhere particularly well flatly to the substrate surface.

[0090] A closed layer formed by solidified, melted metal particles is generated on the substrate surface. The generated layer has a thickness of 10 μm and a porosity of less than 30%. The porosity preferably refers to the porosity that can be measured by SEM or X-ray tomography. The low porosity results in a higher electrical conductivity of the layer.

[0091] Depositing a layer with a higher porosity on the substrate may be useful because the higher porosity can provide a larger buffer volume for lithium storage during the cycling process and can improve the mechanical adhesion of lithium to the layer (improving mechanical stability). The higher porosity can be achieved, for example, by using a smaller amount of metal particles and / or metal particles with a larger diameter.

[0092] Example 2 - Method for producing a substrate according to the present invention

[0093] First, a substrate according to the present invention was prepared, in which a copper layer (copper pad) was deposited on the surface of the front side of the β-aluminum sodium ceramic layer by a plasma spraying method (see Figure 4 ).

[0094] Subsequently, a layer of sodium metal was laminated onto the back side of the substrate according to the present invention (about 2.5 MPa). Then, the negative electrode of the battery cycler was placed on the copper layer (copper pad) on the front side of the β-aluminum sodium ceramic layer, and the positive electrode of the battery cycler was placed on the sodium metal layer on the back side of the β-aluminum sodium ceramic layer. At a voltage of about 27 mV, sodium ions passed through the ion-conducting ceramic at about 2 μA for a duration of about 10 hours. The sodium ions received electrons on the anode side and formed a dense layer of metallic sodium at the interface between the sprayed copper and the ion-conducting ceramic. The SEM cross-sectional view of the substrate according to the present invention produced in this way is shown in Figure 5 . Figure 5 It shows the deposited metallic sodium as an intermediate layer between the copper layer and the β-aluminum sodium ceramic layer. The achieved thickness of 10 μm corresponds to the layer thickness required for deposition in an actual battery. The deposition is very dense and uniform.

[0095] The deposition quality is significantly better than that of recent publications on anode-free systems (e.g., Lee, Yong-Gun et al., "High-energy long-cycling all-solid-state lithium metal batteries enabled by silver–carbon composite anodes." Nature Energy 5.4 (2020): 299-308.; compare Figure 2 c).

[0096] During the electrochemical deposition of the sodium metal layer between the copper layer and the β-aluminum sodium ceramic layer, the overvoltage is only 27 mV, indicating excellent surface contact between the copper layer and the ceramic layer before the electrochemical deposition of the sodium metal layer as an intermediate layer. In Figure 6 and Figure 7 , this extremely good surface contact can be seen from the cross-section of the substrate of the present invention shown.

[0097] Example 3 - Checking the flatness of the alkali metal layer deposition

[0098] To check the flatness of the electrochemical deposition of the alkali metal layer (here: sodium metal layer), first, a substrate according to the present invention was prepared, in which a copper layer (copper pad) was deposited on the surface of the front side of the β-aluminum sodium ceramic layer by a plasma spraying method (see Figure 4 ).

[0099] Subsequently, a sodium metal layer was electrochemically deposited between the copper layer and the β-aluminum sodium ceramic layer according to the above method (seeFigure 5 )。

[0100] After the deposition of the sodium metal layer, the copper layer previously deposited by the plasma spraying method is removed again with a needle. It has been shown that the deposition of the sodium metal layer proceeds well not only at the FIB cutting position but also in a large area under the entire copper layer (see Figure 8 )。

[0101] List of Reference Numerals

[0102] 1: Metal layer (such as a copper layer);

[0103] 2: Solid-state, ion-conducting substrate;

[0104] 3: Metal particles;

[0105] 4: Spraying distance;

[0106] 5: Nozzle of the plasma spraying device;

[0107] 6: Roller for moving the substrate on the moving belt;

[0108] 7: Moving belt for transporting the substrate;

[0109] 8: Lithium metal deposited in a dot pattern;

[0110] 9: Lithium metal deposited flatly;

[0111] 10: Rigid metal copper layer.

Claims

1. A method for forming a metal layer on the surface of a solid, ion-conducting substrate, comprising the steps of: a) spraying metal particles in the direction of the solid, ion-conducting substrate along a spraying distance, wherein the metal particles i) are at least partially molten metal particles, or ii) are solid metal particles that are heated to a temperature above the melting temperature of the metal particles along the spraying distance and / or by their impact velocity on the solid, ion-conducting substrate, wherein at least partially molten metal particles are produced; and b) solidifying the at least partially molten metal particles on the solid, ion-conducting substrate, wherein a metal layer disposed on the solid, ion-conducting substrate is produced.

2. The method according to the preceding claim, characterized in that the spraying of the metal particles is carried out using a method selected from the group consisting of: plasma spraying method, cold gas spraying, high velocity oxy-fuel spraying, flame spraying, detonation spraying, laser spraying, arc spraying and thermal spraying according to DIN EN 657:2005, preferably using a method selected from the group consisting of: plasma spraying method, cold gas spraying and arc spraying, particularly preferably using the plasma spraying method.

3. The method according to any one of the preceding claims, characterized in that the spraying of the metal particles is carried out using the plasma spraying method, wherein the metal particles are melted in a nozzle and the molten metal particles are sprayed in the direction of the substrate surface, wherein the metal particles are preferably melted in the nozzle by an inert gas plasma present in the nozzle, the inert gas plasma being particularly preferably a noble gas plasma, especially an argon plasma, optionally containing >0 vol% to 5 vol% of hydrogen plasma, wherein the inert gas plasma is particularly i) generated by applying a voltage to the nozzle in continuous operation, the voltage range being 1 V to 60 V for a hot atmospheric plasma and 100 V to 10 kV for a cold active atmospheric plasma, wherein the ignition voltage is optionally at least 10 times greater; and / or ii) exits the nozzle with a volume flow rate in the range of 1 l / min to 100 l / min.

4. The method according to any one of the preceding claims, characterized in that the spraying speed of the metal particles, the heating temperature of the metal particles, the diameter of the metal particles, the shape of the metal particles and the spraying distance of the metal particles are selected to prevent the metal particles from breaking when they impact the substrate surface.

5. The method according to any one of the preceding claims, characterized in that preferably in order to prevent the metal particles from breaking when they impact the substrate surface, the metal particles i) are sprayed onto the surface of the substrate at a spraying speed of at most 700 m / s, preferably at most 500 m / s; and / or ii) have a temperature that is at most 200 K, preferably at most 100 K, particularly preferably at most 50 K higher than the melting temperature of the metal particles before and / or when they impact the substrate; and / or iii) have a maximum diameter in the range of 1 μm to 1000 μm, particularly preferably 10 μm to in the range of 100 μm, where the maximum diameter refers to the maximum diameter measurable by a microscope; and / or iv) having a maximum diameter not in the range of ≤ 100 nm, optionally not in the range of < 1 μm; and / or v) having a substantially circular shape, where the aspect ratio of the length to the width of the metal particles is preferably in the range of 1:10 to 1:1, particularly preferably in the range of 1:5 to 1:1, very particularly preferably in the range of 1:2 to 1:1, especially in the range of 1.5:1 to 1:1, where the aspect ratio refers to the aspect ratio determinable by a microscope; and / or vi) being sprayed at a spraying distance in the range of 1.5 cm to 4 cm, where in the case of the plasma spraying method, the spraying distance is defined as the distance from the opening of the nozzle to the surface of the substrate.

6. The method according to any one of the preceding claims, characterized in that the metal particles are sprayed in the direction of the solid, ion-conducting substrate at a spraying rate in the range of ≥ 3 g of metal particles / minute, preferably in the range of 3 g to 6 g of metal particles / minute.

7. The method according to any one of the preceding claims, characterized in that the metal particles i) contain a metal or consist of a metal, where the metal is preferably selected from the group consisting of: copper, aluminum, gold, silver, tin, and alloys of at least one of these metals; and / or ii) do not contain alkali metals and do not contain materials that absorb alkali metals, preferably do not contain active materials for battery electrodes.

8. The method according to any one of the preceding claims, characterized in that the produced metal layer i) has a layer thickness in the range of 0.1 μm to 50 μm in the direction perpendicular to the surface of the metal layer, preferably in the range of 0.2 μm to 20 μm, particularly preferably in the range of 0.5 μm to 10 μm, especially in the range of 1 μm to 2 μm; and / or ii) is porous, preferably having a porosity in the range of > 0 to 30%, where the porosity preferably refers to the porosity determinable by SEM or X-ray tomography; and / or iii) does not have a layer containing solidified particles with a maximum diameter in the range of ≤ 100 nm, optionally in the range of < 1 μm, or is not composed of such a layer; and / or iv) does not have oxygen-conducting properties, optionally does not have gas-conducting properties.

9. The method according to any one of the preceding claims, characterized in that before step a), the method includes the following steps: a) spraying metal particles in the direction of the surface of the solid, ion-conducting substrate along the spraying distance, preferably the same metal particles as in method step a), where the metal particles i) are at least partially molten metal particles, or ii) are solid metal particles that are heated to a temperature higher than the melting temperature of the metal particles along the spraying distance and / or by their impact velocity on the solid, ion-conducting substrate, where at least partially molten metal particles are produced; and ​ b) at least partially oxidize the metal particles at least locally along the spraying distance, preferably by contacting the metal particles with a gas containing or consisting of oxygen, in particular air, wherein at least partially oxidized metal particles are produced; and c) solidify the at least partially oxidized and at least partially molten metal particles on a solid, ion-conducting substrate, wherein an at least partially oxidized metal layer disposed on the solid, ion-conducting substrate is produced, wherein the at least partially oxidized metal layer particularly preferably contacts the solid, ion-conducting substrate in a planar manner; wherein the at least partially oxidized metal layer produced particularly preferably has a thickness in the range of 10 nm to 1.5 μm in a direction perpendicular to the partially oxidized metal layer, preferably having a thickness in the range of 15 nm to 1.0 μm; and / or is porous, preferably having a porosity in the range of >0 to 30%, wherein the porosity preferably refers to the porosity that can be determined by SEM or X-ray tomography.

10. The method according to one of the preceding claims, characterized in that the solid, ion-conducting substrate is moved relative to the device for spraying and heating the metal particles, wherein preferably i) the substrate is conveyed on a moving belt and the metal layer is continuously applied to the substrate, wherein preferably an at least partially oxidized metal oxide layer is continuously applied to the substrate before applying the metal layer; and / or ii) the relative speed between the substrate and the device is maintained in the range of 0.1 m / s to 1 m / s; and / or iii) a plurality of nozzles are used to spray the metal particles, and the nozzles are preferably arranged adjacent to each other on at least one comb-like structure.

11. The method according to one of the preceding claims, characterized in that the solid, ion-conducting substrate i) is designed as a flat substrate, preferably a flat layer, particularly preferably a flat film, wherein the metal layer, optionally an at least partially oxidized metal layer, is at least partially applied to one of the two flat sides of the flat substrate; and / or ii) has a surface with a surface roughness Rz in the range of 0 to 100 μm, wherein the surface roughness preferably refers to the surface roughness that can be determined according to DIN EN ISO 25178; and / or iii) contains or consists of an ion-conducting material selected from the group consisting of: lithium-conducting ceramic materials, sodium-conducting ceramic materials, magnesium-conducting ceramic materials, potassium-conducting ceramic materials, zinc-conducting ceramic materials, aluminum-conducting ceramic materials, and combinations thereof; and / or iv) comprising or consisting of a ceramic ion-conducting material, preferably a material selected from the group consisting of: LLZO, LATP, LAGP, NZSP, NASICON, β-aluminates, and combinations thereof, wherein LLZO is optionally Li 6.4 La 3 Zr 1,4 Ta 0.6 O 12 ; and / or v) contains or consists of a glassy ion-conducting material, preferably a material selected from the group consisting of: LiPON, inorganic glass, organic glass, and combinations thereof; and / or vi) is heated or not heated, optionally heated to a temperature in the range of 150 °C to 300 °C; and / or vii) does not contain active materials for battery electrodes.

12. The method according to one of the preceding claims, characterized in that the solid, ion-conducting substrate is a substrate selected from the group consisting of the following substrates: - a cathode infiltrated with a solid electrolyte material; - an anode infiltrated with a solid electrolyte material; - A cathode layer containing a solid, ion-conductive material, wherein the cathode layer is preferably an independent cathode layer, and particularly preferably an independent cathode layer from which impurities are removed by laser technology; - An anode layer containing a solid, ion-conductive material, wherein the anode layer is preferably an independent anode layer, and particularly preferably an independent anode layer from which impurities are removed by laser technology; - A composition of a solid electrolyte material and a cathode material, optionally sintered; - A composition of a solid electrolyte material and an anode material, optionally sintered; - A solid electrolyte material infiltrated with an active material; and - A solid electrolyte material infiltrated with an anode material.

13. The method according to any one of the preceding claims, characterized in that the method further comprises the following steps: i) applying a layer containing an alkali metal and / or an alkaline earth metal or consisting thereof, preferably a layer containing sodium and / or lithium or consisting thereof, to the surface of the solid, ion-conductive substrate, the surface being opposite to the surface of the solid, ion-conductive substrate on which the metal layer is disposed; and ii) connecting the negative electrode of a power source to the metal layer, connecting the positive electrode of the power source to the layer applied in step i), and applying a voltage to the negative and positive electrodes, wherein a layer containing an alkali metal and / or an alkaline earth metal or consisting thereof is deposited between the metal layer and the solid, ion-conductive substrate.

14. A solid, ion-conductive substrate, wherein a metal layer is at least partially disposed on the surface of the substrate, characterized in that the metal layer is formed by solidified molten metal particles that are stacked and adjacent to each other.

15. The substrate according to claim 14, characterized in that a at least partially oxidized metal layer is disposed between the substrate and the metal layer, which is formed by solidified, molten, at least partially oxidized metal particles that are stacked and adjacent to each other, wherein the at least partially oxidized metal layer preferably contacts the substrate and the metal layer in a planar manner.

16. The substrate according to claim 14 or 15, characterized in that the substrate is designed as a flat substrate, preferably a flat layer, and particularly preferably a flat film, wherein the metal layer, optionally the at least partially oxidized metal layer, is at least partially applied to one of the two flat sides of the flat substrate.

17. The substrate according to any one of claims 14 to 16, characterized in that a layer containing an alkali metal and / or an alkaline earth metal or consisting thereof is deposited between the metal layer and the solid, ion-conductive substrate, wherein the layer preferably contains sodium and / or lithium or consists thereof.

18. The substrate according to any one of claims 14 to 17, characterized in that the substrate is produced by the method according to any one of claims 1 to 13.

19. An anode-free battery, preferably an anode-free secondary battery, comprising the substrate according to any one of claims 14 to 18, wherein the side of the substrate on which the metal layer is disposed is preferably the anode side of the battery.

Images