Method for forming a metal layer on the surface of a solid ion-conducting substrate, substrate which can be produced using the method, and anode-free battery

Abstract

The invention relates to a method for forming a metal layer (i.e., a metal electric current conductor) on the surface of a solid ion-conducting substrate (for example, a lithium-ion secondary battery or a sodium-ion secondary battery), to a substrate which can be produced using the method, and to an anode-free battery. The method according to the invention allows parts of solid-state electrolyte batteries (e.g., the anode side of a solid-state electrolyte battery) to be provided in an industrially relevant scale in a quick, simple, and inexpensive manner, said parts being characterized by a homogenous electric current density and a suitability for high maximum charge and discharge currents.

Description

[0001] Method for forming a metal layer on a surface of a solid, ion-conducting substrate, substrate that can be produced by the method, and anode-free battery The invention relates to a method for forming a metal layer

[0002] (ie a metallic electrical conductor) on a surface of a solid, ion-conducting substrate (e.g. a lithium-ion secondary battery or a sodium-ion secondary battery), a substrate that can be produced by the method, and an anode-free battery. The method according to the invention makes it possible to use in industrially relevant

[0003] To provide parts for solid electrolyte batteries (e.g. the anode side of a solid electrolyte battery) on a fast, simple, and cost-effective basis. These parts are characterized by a homogeneous electrical current density and are suitable for high maximum possible charging and discharging currents. Current collectors for secondary batteries (e.g. solid-state batteries) are usually much thicker than necessary (approx. 20 μm for copper arranged on the anode side in lithium-based battery cells). The extraction of the raw material for these foils through electrolytic refining of pure copper or molten salt electrolysis for aluminum is also extremely energy-intensive. Copper foils must have a certain minimum thickness in order to meet the strength required for a roll-to-roll process, for example. Crack-related failures bring production lines to a standstill for long periods.In the past, copper foils of suitable thickness were produced using established rolling processes or electrolytically. Continuous feedback loops in quality control made it possible to achieve sufficiently homogeneous thicknesses and strengths of the produced copper foils. Other solution strategies involve coating thin and very strong electrically conductive plastic films (e.g., polyimide films) with copper. The use of the plastic film has the advantage of reducing the overall weight of the current collector, since the plastics used usually have a lower specific density than copper (e.g., specific density of the plastic film is 1.5 g / cm³). 3 compared to the specific density of copper of approximately 9 g / cm 3). On the other hand, this solution has the disadvantage that the plastic used has a poorer specific electrical conductivity than copper, thus limiting the maximum possible electrical currents with the secondary battery.

[0004] In solid-state batteries, the comparatively low ionic conductivity also requires the production of very thin ceramic separators that are permeable to metal ions (usually lithium ions or sodium ions). A suitable separator thickness is less than 50 pm. If, during battery cell production, a lithium-coated copper current collector were pressed onto the usually jagged surface of a ceramic separator as a substrate, the ceramic separator would inevitably break due to its thinness. To avoid this, it is known to apply surface-conformal current collector layers to such thin ceramic separators using atomic layer deposition (ALD), sputtering, or thermal evaporation. However, this usually requires a vacuum, which makes high-throughput production difficult or impossible. Furthermore, sputtering can only deposit layers at a rate of nm / min.This means it takes a very long time to achieve an optimal thickness of between 1 pm and 10 pm. When sputtering current collector layers (e.g. made of copper) onto ceramic or polymeric electrode materials, the growth initially occurs in islands. The coalescence of the islands to form a flat, pore-free layer is usually not achieved. Significant roughness in these layers leads to high local electrical current densities at roughness peaks. The ALD process also has the disadvantage that it is comparatively slow, and layer thicknesses in the pm range are difficult or even impossible to achieve on an industrial scale. Furthermore, this process also results in topology-conform deposition on undercut geometries and pores, which can lead to these very geometries being re-shaped and not closed. This, however, must be avoided in order to achieve the most homogeneous current density possible.Electroplating is also not practical due to the low electrical conductivity required for the solid electrolyte substrates.

[0005] It is known that solid-state batteries can only achieve a significant energy density gain as anode-free concepts. However, due to poor surface contact between a rigid, metallic copper foil and a solid electrolyte separator, it has so far been virtually impossible to implement anode-free concepts in solid-state batteries, as metallic lithium can only be deposited at small contact points between the current collector and the solid electrolyte. Thus, using a current collector foil, it is not possible to deposit a homogeneous (lithium) layer using conventional methods, but only a "forest" of lithium whiskers. A well-known approach to solving this problem and producing metallic, anode-side active materials is the production of a solid electrolyte sponge in which, for example, metallic lithium is plated. The solid electrolyte sponge has a porous layer of brittle ceramic.The disadvantage of this approach, however, is that the brittle ceramic of the solid electrolyte sponge is susceptible to mechanical damage due to the contact pressure of the foil, which increases the risk of rejects and process costs. Another approach to solving this problem involves the use of chemical vapor deposition (CVD) and physical vapor deposition (PVD), which, however, suffer from the disadvantages mentioned above. Another approach is to increase the electrical contact surface through polishing steps on the fissured ceramic layer. However, this approach does not appear to be effective given the goal of large-scale series production, as it is very cost-intensive and time-consuming.

[0006] The cyclability and fatigue strength of a lithium interface on the solid electrolyte are also strongly dependent on the local electrical current density. During charging and discharging at high current densities, so-called voids (pores) and metallic dendrites form at the interface. The latter form precisely where the electrical current density is particularly high. This dendrite formation can currently only be prevented by reducing the local electrical current density below a critical value. The formation of voids further reduces the available electrical contact area, resulting in a positive feedback loop in the degradation of the battery. Furthermore, dendrites can also grow through the separator in ceramic cells and short-circuit the cell. To circumvent the problem of the performance-limiting critical electrical current density, a 3D structuring of the surface is carried out (e.g.On the one hand, highly porous, sponge-like solid electrolyte electrode layers are produced by mixing organic materials and ceramic powder followed by pyrolysis. On the other hand, void and dendrite formation is prevented while maintaining a constant surface by using (lithium) alloys (such as LiMg) and adhesion promoters or diamond nanoparticles, etc. These include solid electrolyte materials with a high modulus of elasticity, the lowest possible electrical conductivity, and simultaneously high ionic conductivity, which is particularly present when the grain boundary density and pore volume are low.

[0007] It is also known that lithium is difficult to deposit on copper foil and that lithium does not adhere well to bare copper foil. Only after lithiophilization of the copper foil through targeted oxidation of the copper surface, e.g. in a furnace under an oxygen atmosphere at high temperature and for a long time, can a thin layer of lithium be deposited on copper foil from a lithium melt. This process of lithium deposition is expensive because it has to be carried out in a protective gas atmosphere. This is the only way to ensure the quality of the lithium layer-copper foil composite for battery applications. The composite component produced in this way must then be brought into contact with the other components of the respective cell under a protective gas. This means that production can only take place, for example, in dry rooms that are expensive to operate.Any passivation of the lithium surface during processing must be prevented, as otherwise the electrical contact resistance increases significantly, and lithium oxides, hydroxides, or carbonates harden the surface and significantly increase the required contact pressure on the ceramic separator. A current approach to avoid this problem is the deliberate oxidation of the copper surface at high temperatures in air or an oxygen atmosphere. The copper oxide is then reduced by the lithium and thus serves as an adhesion promoter. It is important that the copper oxide layer is not too thick, as this in turn increases the electrical contact resistance.

[0008] For battery cell production, only selected areas of the current collectors are currently coated with active material paste in roll-to-roll processes. These coated areas are then laser cut or punched out in a subsequent step. This can burn active material or create burrs that can short-circuit the cells. Standardized film widths and lengths limit the selection of possible cell formats. Downtime during roll changes and potentially contaminated offcuts make these production processes expensive and reduce the achievable yield. Furthermore, handling the coated rolls is logistically challenging, with all the consequences this has for price and yield. Technologies are currently being developed to increase the variability of cell formats, e.g., by laser cutting the coated electrical current collectors, which is increasingly becoming the industry standard.Highly flexible plastic foils and general improvements in quality assurance in the production of copper foils are being pursued to prevent foil tearing during production. In summary, it can be stated that no process is currently known that makes it possible to produce solid electrolyte battery components (e.g., an anode side of a solid electrolyte battery) on an industrially relevant scale in a quick, simple, and cost-effective (i.e., economical) manner. These components are characterized by a homogeneous electrical current density (i.e., avoiding locally elevated electrical current densities) and are suitable for high maximum possible charging and discharging currents.

[0009] The object is achieved by the method having the features of claim 1, the solid, ion-conducting substrate having the features of claim 14 and the anode-free battery having the features of claim 19. Advantageous embodiments and further developments of the invention can be realized with features specified in dependent claims.

[0010] According to the invention, a method for forming a metal layer on a surface of a solid, ion-conducting substrate is provided, comprising the steps of: a) spraying metal particles along a spray path in the direction of a solid, ion-conducting substrate, wherein the metal particles are i) at least partially molten metal particles, or ii) solid metal particles which are heated along the spray path and / or by their impact speed on the solid ion-conducting substrate to a temperature which is higher than the melting temperature of the metal particles, whereby at least partially molten metal particles are formed; and b) allowing the at least partially molten metal particles to solidify on the solid, ion-conducting substrate, whereby a metal layer is formed which is arranged on the solid, ion-conducting substrate.

[0011] The process according to the invention makes it possible to produce solid electrolyte battery parts (e.g., an anode side of a solid electrolyte battery) on an industrially relevant scale in a rapid, simple, and cost-effective (i.e., economical) manner. These parts are characterized by a homogeneous electrical current density and a suitability for high maximum possible charging and discharging currents. The process allows the production of electrical conductors that adhere well even to rugged, 3D-structured, and sponge-like (ceramic) solid electrolyte separators.

[0012] One reason for this is that the metal particles can adapt to any surface contour upon impact, creating a very large contact area between the metal particles and the substrate. This wets a significantly larger substrate surface than with the application of a metal foil, and the formation of interface defects (such as voids, whiskers, and dendrites) is greatly reduced or even completely prevented, resulting in a more homogeneous current density distribution.

[0013] Spraying the metal particles onto the substrate also makes it possible to coat any shape of solid-state cell when using the resulting substrate in a solid-state battery. There is no waste, and the layers can be produced in the desired thicknesses, which can be made significantly thinner than before while still maintaining sufficient electrical conductivity. A saving of approximately 50% of the currently required amount of metal, such as copper or aluminum, is possible.

[0014] Furthermore, the substrate according to the invention is suitable for use as an anode-free part of a solid-state battery, i.e., metallic lithium is only deposited between the substrate and the metal layer or the at least partially oxidized metal layer (see below) during use of the solid-state battery and does not need to be processed as metallic lithium in the production process, which simplifies and makes the manufacturing process safer. In other words, so-called "low-dew point" enclosures, which would significantly increase the cost of the manufacturing process, can be dispensed with, and there is no risk of the layer conducting the electrical current being damaged (e.g., cracking) during the manufacturing process. By enabling an anode-free design, the requirement for lithium (or alternatively, Na, K, Mg, etc.) can also be significantly reduced.The metal particles can be sprayed using a method selected from the group consisting of plasma spraying, cold gas spraying, high-velocity flame spraying, flame spraying, detonation spraying, laser spraying, arc spraying, and thermal spraying according to DIN EN 657:2005. Preferably, the metal particles are sprayed using a method selected from the group consisting of plasma spraying, cold gas spraying, and arc spraying, particularly preferably using a plasma spraying method.

[0015] In a preferred embodiment, the metal particles are sprayed using a plasma spray process. The plasma spray process is advantageous because it produces particularly well-closed and homogeneous metal surfaces on the substrate surface. In the plasma spray process, a plasma can be ignited in a gap between an anode and a cathode using a direct voltage. An inert gas (e.g. argon gas) can flow through the aforementioned gap and is ionized, thus becoming electrically conductive. The inert gas heats up considerably. The metal II particles can be blown into the plasma, where they melt. In the plasma spray process, the metal II particles are melted in a nozzle, and the molten metal particles are sprayed towards the surface of the substrate.Preferably, the metal particles are melted in the nozzle by an inert gas plasma, particularly preferably a noble gas plasma, in particular argon plasma, optionally containing >0% vol. to 5% vol. hydrogen plasma. The hydrogen in the hydrogen plasma increases the process gas temperature and has a reducing effect, so that oxidation can be avoided or reduced.

[0016] The inert gas plasma can be generated, in particular, by applying an electrical voltage to the nozzle in the range of 1 V to 60 V in continuous operation for thermal atmospheric plasma and in the range of 100 V to 10 kV for a cold-active atmospheric plasma, with the ignition voltage optionally being at least ten times higher. For example, an ignition voltage of 15 kV can be used. After ignition, the plasma becomes electrically conductive, and only low electrical voltages (e.g., only 2-3 kV) are then required to keep it "running." Furthermore, the inert gas plasma can exit the nozzle, in particular, with a volume flow in the range of 1 l / min to 100 l / min.

[0017] It is preferred that, in the method, a spraying speed of the metal particles, a heating temperature of the metal particles, a diameter of the metal particles, a shape of the metal particles, and the spraying distance of the metal particles are selected such that bursting of the metal particles upon impact with the surface of the substrate is prevented. Preventing bursting means that the metal particles, upon impact with the surface of the substrate, do not shatter into pieces that are distributed over the surface of the substrate. Preventing bursting thus means that the particles do not shatter on the surface of the substrate, but solidify with their entire volume at the point of impact on the surface. The advantage is that a (closed) metal layer is applied to the substrate, which is formed by metal particles arranged one above and next to one another that were melted, i.e.on the substrate, they briefly took the form of liquid and intact metal droplets and solidified as intact metal droplets on the substrate without any loss of material per metal droplet. The corresponding parameters can be determined for a particular metal or metal alloy from which the metal particles are made and the respective substrate surface to be coated using a few tests. Once determined, they can then be reproducibly maintained during the process. The following also lists process parameters that can be used to prevent the metal particles from bursting on the surface of the substrate.

[0018] The metal particles can be sprayed onto the surface of the substrate at a spray speed of no more than 700 m / s, preferably no more than 500 m / s, preferably to prevent the metal particles from bursting upon impact with the surface of the substrate. A speed in this range reduces the risk of speed-related bursting of the metal particles on the surface of the substrate and also the risk of destruction of the substrate (e.g., breaking of the substrate) due to excessive kinetic energy of the metal particles. Furthermore, preferably to prevent the metal particles from bursting upon impact with the surface of the substrate, the metal particles can have a temperature before impacting the substrate and / or upon impacting the substrate that is no more than 200 K, preferably no more than 100 K, particularly preferably no more than 50 K, above a melting temperature of the metal particles.A temperature in this range reduces the risk of viscosity-related bursting of the metal particles on the surface of the substrate and also the risk of possible destruction of the substrate due to excessively high temperature of the metal particles.

[0019] In addition, the metal particles can have a maximum diameter in the range of 1 pm to 1000 pm, particularly preferably in the range of 10 pm to 100 pm, to prevent them from bursting upon impact with the surface of the substrate. The maximum diameter refers to a maximum diameter that can be determined by microscopy. A diameter in this range reduces the risk of size-related bursting of the metal particles on the surface of the substrate and also the risk of possible destruction of the substrate due to excessive kinetic energy of the metal particles.

[0020] In a preferred embodiment, the metal particles do not have a maximum diameter that is in the range of < 100 nm, optionally in the range of < 1 pm, wherein the maximum diameter refers to a maximum diameter that can be determined by microscopy.

[0021] Apart from that, the metal particles can have a substantially round shape, preferably to prevent the metal particles from bursting upon impact with the surface of the substrate, wherein an aspect ratio of a length to a width of the metal particles is preferably in the range of 1:10 to 1:1, particularly preferably 1:5 to 1:1, very particularly preferably in the range of 1:2 to 1:1, in particular in the range of 1.5:1 to 1:1, wherein the aspect ratio refers to an aspect ratio determinable by microscopy. A shape that is as round as possible can minimize the risk of the metal particles bursting on the surface of the substrate (rod-shaped particles are more likely to burst than spherical particles) and reduce the risk of possible destruction of the substrate (rod-shaped particles can cause very high local pressure, which can damage the substrate, particularly in cold gas spraying, when the head ends of the rods hit the substrate).

[0022] Furthermore, in the process, the metal particles can be sprayed over a spray path in the range of 1.5 cm to 4 cm, preferably to prevent the metal particles from bursting upon impact with the surface of the substrate. In the case of a plasma spray process, the spray path is defined by the distance between the opening of a nozzle and the surface of the substrate. The smaller the distance between the substrate surface and the nozzle, the higher the particle temperature upon impact with the substrate surface and the smaller the deposition spot on the surface. A spray path in this range can prevent the metal particles from hitting the surface of the substrate too hot or too cold, thus minimizing the risk of bursting and damaging the substrate.

[0023] In the process, the metal particles can be sprayed toward the solid, ion-conducting substrate at a spray rate (i.e., a mass flow) in the range of > 3 g of metal particles per minute, preferably 3 g to 6 g of metal particles per minute. A spray rate in this range has proven advantageous for forming a metal layer on the substrate, which is formed by solidified, molten metal particles arranged one above the other and next to one another.

[0024] The metal particles sprayed in the process may contain or consist of a metal, wherein the metal is preferably selected from the group consisting of copper, aluminum, gold, silver, tin and an alloy of at least one of these metals.

[0025] In a preferred embodiment, the metal particles sprayed in the process contain no alkali metal and no alkali metal-absorbing material, preferably no active material of a battery electrode. The advantage is that the metal layer can be formed on the surface of the solid, ion-conducting substrate in an electrode material-free (anode-free) form. The metal layer produced in the process can have a layer thickness, in a direction perpendicular to the surface of the metal layer, in the range of 0.1 μm to 50 μm, preferably in the range of 0.2 μm to 20 μm, particularly preferably 0.5 μm to 10 μm, in particular 1 μm to 2 μm.

[0026] Furthermore, the metal layer produced in the process can be porous, preferably having a porosity in the range of >0 to 30%, with the porosity preferably referring to a porosity that can be determined by SEM or X-ray tomography. Determination by SEM can be carried out, for example, by sawing and ion beam polishing the metal layer, followed by viewing the metal layer in the SEM.

[0027] In a preferred embodiment, the metal layer produced in the process does not have a layer containing or consisting of solidified particles having a maximum diameter in the range of < 100 nm, optionally in the range of < 1 pm.

[0028] In a further preferred embodiment, the metal layer produced in the process has no oxygen-conducting properties, optionally no gas-conducting properties.

[0029] In a preferred embodiment, the method comprises the following steps before step a): a) spraying metal particles, preferably the same metal particles as in step a) of the method, along a spray path in the direction of a surface of the solid, ion-conducting substrate, wherein the metal particles are i) at least partially molten metal particles, or ii) solid metal particles which are heated along the spray path and / or by their impact speed on the solid, ion-conducting substrate to a temperature which is higher than the melting temperature of the metal particles, whereby at least partially molten metal particles are formed; and b) at least partially oxidizing the metal particles at least in regions along the spray path, preferably by contacting the metal particles with a gas which contains or consists of oxygen, in particular with air, whereby at least partially oxidized metal particles are formed;and c) allowing the at least partially oxidized, at least partially molten metal particles to solidify on the solid, ion-conducting substrate, thereby forming an at least partially oxidized metal layer arranged on the solid, ion-conducting substrate, wherein the at least partially oxidized metal layer particularly preferably makes planar contact with the solid, ion-conducting substrate.

[0030] The advantage of this embodiment is that an at least partially oxidized metal layer is created between the surface of the substrate and the metal layer. This metal layer can have a stronger binding effect (affinity) to lithium metal or sodium metal. For example, it is known that lithium metal has a stronger bonding strength to copper oxide than to metallic copper. The copper oxide can form a lithiophilic boundary layer, which promotes the deposition of lithium during use of the substrate in a solid-state battery and which establishes high mechanical strength and low electrical contact resistance, which in turn establishes high mechanical adhesion of the electrochemically active metal layer to be deposited to the metal layer (i.e., to the sprayed-on current collector) and also establishes a low electrical contact resistance there.

[0031] The produced, at least partially oxidized metal layer can have, in a direction perpendicular to the partially oxidized metal layer, a thickness in the range of 10 nm to 1.5 pm, preferably 15 nm to 1.0 pm.

[0032] 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 a porosity that can be determined via SEM or X-ray tomography.

[0033] In a further preferred embodiment, the substrate is moved relative to a device used for spraying and heating the metal particles. The substrate is preferably transported on a moving belt, and the metal layer is continuously applied to the substrate, wherein, particularly preferably, a metal oxide layer that is at least partially oxidized is continuously applied to the substrate before the metal layer is applied. It is preferred that a relative speed in the range from 0.1 m / s to 1 m / s is maintained between the substrate and the device. The relative movement from the substrate to the device is preferably a translational movement. It is further preferred that a plurality of nozzles, which are preferably arranged next to one another on at least one comb, are used to spray the metal particles.The use of at least one comb with multiple nozzles has the advantage of allowing a large substrate surface to be coated quickly. The nozzles can also be arranged in a staggered arrangement in two or more rows on the at least one comb.

[0034] The substrate is preferably configured as a flat substrate, preferably as a flat layer, particularly preferably as a flat film. Furthermore, it is preferred that the metal layer, optionally a metal layer that is at least partially oxidized, is applied at least partially to one of the two flat sides of the flat substrate (e.g., the top or bottom of the flat substrate).

[0035] The substrate (without the metal layer or partially oxidized metal layer) can have a surface with a surface roughness Rz in the range of 0 to 100 pm, whereby the surface roughness preferably refers to a surface roughness determinable according to DIN EN ISO 25178. The surface roughness can refer to a surface roughness that can be determined by confocal microscopy, atomic force microscopy, or stylus profilometry.

[0036] Furthermore, the substrate may contain or consist of an ion-conducting material selected from the group consisting of lithium-conducting ceramic material, sodium-conducting ceramic material, magnesium-conducting ceramic material, potassium-conducting ceramic material, zinc-conducting ceramic material, aluminum-conducting ceramic material, and combinations thereof. It is preferred that the substrate contains or consists of a ceramic ion-conducting material, preferably a material selected from the group consisting of LLZO, LATP, LAGP, NZSP, NASICON, ß-aluminate, and combinations thereof, wherein LLZO is optionally Li6.4La3Zr1.4Tao.60i2.

[0037] Furthermore, it is preferred that the substrate contains or consists of a glassy ion-conducting material, preferably a material selected from the group consisting of UPON, inorganic glass, organic glass, and combinations thereof. The substrate can, for example, contain or consist of a material selected from the group consisting of lithium lanthanum zirconium oxide (LiyLaoZryO ), lithium aluminum titanium phosphate (Lii +x AlxTi2-x(PO4)3), lithium aluminum germanium phosphate (Lii.3Alo.3Gei.7(PO4)3), sodium zirconium silicate phosphate (NasZrSiyPO), lithium phosphorus oxynitrite (Li3.6PO3.4N06) and combinations thereof.

[0038] In an optional embodiment, the substrate is heated in the process, preferably to a temperature in the range of 150 °C to 300 °C. Heating the substrate can prevent damage to the substrate (e.g., formation of cracks in the substrate and / or delamination in the joining interface).

[0039] In a preferred embodiment, the solid, ion-conducting substrate does not contain any active material of a battery electrode.

[0040] The process is particularly suitable for use in anode-free systems. In this case, the cathode material must contain the electrochemically active material to be deposited on the anode.

[0041] The method according to the invention forms or produces a metal layer (i.e., a current collector) on the surface of a solid, ion-conducting substrate. The method according to the invention is material-agnostic and (when the substrate is used in a battery cell) cell-agnostic.

[0042] The solid, ion-conducting substrate may be a substrate selected from one of the following substrates:

[0043] - a cathode infiltrated with solid electrolyte material;

[0044] - an anode infiltrated with solid electrolyte material;

[0045] - a cathode layer containing a solid, ion-conducting material, wherein the cathode layer is preferably a free-standing cathode layer, particularly preferably a free-standing cathode layer which has been freed from impurities (e.g. binder and conductive carbon black) by means of laser technology;

[0046] - an anode layer containing a solid, ion-conducting material, wherein the anode layer is preferably a free-standing cathode layer, particularly preferably a free-standing cathode layer which has been freed from impurities (e.g. binder and conductive carbon black) by means of laser technology;

[0047] - a composite (or mixture) of solid electrolyte material and cathode material (optionally sintered);

[0048] - a composite (or mixture) of solid electrolyte material and anode material (optionally sintered);

[0049] - a solid electrolyte material infiltrated with active material (cathode material); and

[0050] - a solid electrolyte material infiltrated with anode material.

[0051] In a preferred embodiment, the method further comprises the following steps: i) applying a layer containing or consisting of an alkali metal and / or alkaline earth metal, preferably containing or consisting of sodium and / or lithium, to a surface of the solid, ion-conducting substrate which is opposite to the surface of the solid, ion-conducting substrate on which the metal layer has been arranged (optionally also an at least partially oxidized metal layer has been arranged);and ii) connecting a negative pole of a power source to the metal layer, connecting a positive pole of the power source to the layer applied in step i) and applying an electrical voltage to the negative pole and to the positive pole, wherein a layer containing or consisting of an alkali metal and / or alkaline earth metal (in particular in elemental form) is deposited between the metal layer and the solid, ion-conducting substrate (optionally between an at least partially oxidized metal layer arranged on the substrate and the solid, ion-conducting substrate);

[0052] According to the invention, a solid, ion-conducting substrate is further provided, wherein a metal layer is arranged at least in regions on a surface of the substrate, characterized in that the metal layer is formed by solidified molten metal particles arranged one above the other and next to one another.

[0053] The substrate according to the invention can be produced quickly, easily, and inexpensively (i.e., economically) and can be used as the anode side of a solid electrolyte battery. The substrate has a topology-conforming metal layer that significantly increases the contact surface to the substrate and thus reduces variances in current density along the planar interface between the substrate and the metal layer. The substrate according to the invention is thus characterized by a homogeneous electrical current density and suitability for high maximum possible charging and discharging currents.

[0054] The solid, ion-conducting substrate can have a surface roughness Rz in the range of 0 to 100 pm on the surface on which the metal layer is arranged, at least in some regions (preferably without the metal layer, i.e., in the uncoated state). The surface roughness preferably refers to a surface roughness determinable in accordance with DIN EN ISO 25178. The surface roughness can refer to a surface roughness that can be determined using confocal microscopy, atomic force microscopy, or stylus profilometry.

[0055] In a preferred embodiment, an at least partially oxidized metal layer is arranged between the substrate and the metal layer, which is formed by solidified, molten, at least partially oxidized metal particles arranged one above the other and next to one another, wherein the at least partially oxidized metal layer preferably contacts the substrate and the metal layer over a large area.

[0056] The substrate can be designed as a flat substrate, preferably as a flat layer, particularly preferably as a flat film, wherein the metal layer, optionally also a metal layer oxidized at least in regions, is applied at least in regions to one of the two flat sides of the flat substrate.

[0057] In the substrate according to the invention, a layer containing or consisting of an alkali metal and / or alkaline earth metal can be deposited between the metal layer and the solid, ion-conducting substrate (optionally between an at least partially oxidized metal layer of the substrate and the solid, ion-conducting substrate), wherein the layer preferably contains or consists of sodium and / or lithium (in particular in elemental form).

[0058] Furthermore, the substrate may have been produced by the process according to the invention.

[0059] According to the invention, an anode-free battery, preferably an anode-free secondary battery, is also provided, which contains a substrate according to the invention. Preferably, one side of the substrate on whose surface the metal layer is arranged is an anode side of the battery.

[0060] The subject matter of the invention will be explained in more detail with reference to the following examples and the following figures, without wishing to restrict it to the specific embodiments shown here.

[0061] Figure 1 schematically shows an embodiment of the method according to the invention using a plasma spray process. Molten metal particles 3 are sprayed via a nozzle 5 of a plasma spray device through a spray path 4 onto a solid, ion-conducting substrate 2.

[0062] Figure 2 schematically shows an embodiment of the method according to the invention using a plasma spray process, in which the substrate is moved relative to the plasma spray device. Via a nozzle 5 of a plasma spray device, molten metal particles 3 are sprayed over a spray path 4 onto a solid, ion-conducting substrate 2, which is transported on a moving belt 7, with the moving belt being moved over rollers 6. Figure 3A shows an ion-conducting, ceramic substrate 2 from the prior art, onto which a rigid, metallic copper foil 10 and lithium metal 8 have been applied during operation of a solid-state battery containing the substrate.It is illustrated that when the substrate 2 is used in a solid-state battery, deposition of lithium metal 8 in the space between the substrate and the copper foil occurs only locally, namely at the points where the substrate 2 contacts the rigid, metallic copper foil 10. This creates a heterogeneous current density distribution, resulting in high local current densities and preventing high overall currents. High local current densities are to be avoided and lead to damage; high (homogeneously distributed) overall current densities are to be welcomed and lead to high battery performance.

[0063] Figure 3B shows an ion-conducting, ceramic substrate according to the invention, to which copper particles were applied using the method according to the invention, and the resulting deposition of lithium metal 9 during operation of a solid-state battery containing the substrate 2. It is illustrated that when the substrate 2 is used in a solid-state battery, deposition of lithium metal 9 in the space between the substrate 2 and the copper layer 1 occurs not only locally, but across the entire surface, namely over the entire area on which the substrate 2 contacts the copper layer 1. This creates a very homogeneous current density distribution and enables high currents and thus charging and discharging power with a low and evenly distributed local current density.

[0064] Figure 4 shows a scanning electron microscope (SEM) image of a substrate according to the invention. A metal layer of copper (copper pad) is applied to the front side of a solid, ion-conducting substrate (here: a sodium beta-aluminate ceramic layer) using a plasma spray process.

[0065] Figure 5 shows an SEM image of a cross-section of another substrate according to the invention. The cross-section was generated using an ion beam. An alkali metal layer (here: sodium metal layer) is electrochemically deposited between the sodium beta-aluminate ceramic layer and the copper pad of the substrate from Figure 4.

[0066] Figure 6 shows an SEM image of a cross-section of the substrate according to the invention from Figure 4. The cross-section was created using an ion beam (FIB section). The extremely close and positive surface contact and the good quality of the wetting of the ceramic surface with copper can be seen.

[0067] Figure 7 shows an enlargement of a section of Figure 6. The extremely close and form-fitting surface contact and the good quality of the wetting of the ceramic surface with copper can be seen even better in Figure 7 than in Figure 6. Such a wetting quality of the ceramic surface with copper is usually only achievable in common foil processes by extreme external pressure, which would, however, lead to the destruction of the ceramic.

[0068] Figure 8 shows an SEM image of a non-inventive substrate produced from a substrate according to the invention as shown in Figure 5 by removing the copper layer with a needle. Figure 8 shows that the deposition of the sodium metal layer worked well not only at the FIB cut locations, but also over a large area beneath the entire copper layer.

[0069] Example 1 - Method for forming a copper layer on a surface of a solid, ion-conducting ceramic substrate

[0070] In this example, the metal particles are sprayed onto the surface of an ion-conducting substrate using a plasma spray process.

[0071] Copper particles with a diameter of approximately 10 pm are melted in a thermal plasma at a temperature of 1085 °C and sprayed at a speed of 500 m / s and a spray rate of 5 g / min over a distance of 30 cm onto an ion-conducting, ceramic substrate (optionally preheated to a temperature of 200 °C). Using the temperature of 1085 °C ensures that the copper particles impact the substrate surface at a sufficiently hot surface temperature, that they are subjected to sufficiently high deformation, and adhere particularly well to the substrate surface.

[0072] A continuous layer of solidified, molten meta II particles forms on the surface of the substrate. The resulting layer has a thickness of 10 μm and a porosity of less than 30%. Porosity preferably refers to a porosity determined by SEM or X-ray tomography. The low porosity results in a higher electrical conductivity of the layer.

[0073] In certain circumstances, it may be advantageous to deposit a layer with a higher porosity on the substrate, as higher porosity allows for a larger buffer volume for lithium storage during cycling and can improve the mechanical adhesion of lithium to the layer (improved mechanical stability). Higher porosity can be achieved, for example, by using a smaller amount of metal particles and / or metal particles with a larger diameter.

[0074] Example 2 - Process for producing substrates according to the invention

[0075] First, a substrate according to the invention was produced in which a copper layer (copper pad) was deposited on a surface on the front side of a sodium beta-aluminate ceramic layer by means of a plasma spray process (see Figure 4).

[0076] Subsequently, a layer of sodium metal was pressed onto the back of the inventive substrate (approx. 2.5 MPa). A negative pole of a battery cycler was then applied to the copper layer (copper pad) on the front side of the sodium beta-aluminate ceramic layer, and a positive pole of the battery cycler was applied to the sodium metal layer on the back of the sodium beta-aluminate ceramic layer. At a voltage of approximately 27 mV, sodium ions were transported through the ion-conducting ceramic at approximately 2 pA for approximately 10 hours. The sodium ions received electrons back on the anode side, and dense metallic sodium formed at the interface between the sprayed-on copper and the ion-conducting ceramic. An SEM cross-sectional image of the inventive substrate produced in this way is shown in Figure 5. Figure 5 shows the deposited metallic sodium as an intermediate layer between the copper layer and the sodium beta-aluminate ceramic layer.The achieved thickness of 10 pm corresponds to the deposition thickness required in real batteries. The deposition is extremely dense and uniform.

[0077] The deposition quality is significantly better than in recent publications on anode-free systems, such as those by 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.; see Figure 2c.

[0078] The overpotential of only 27 mV during the electrochemical deposition of the sodium metal layer between the copper layer and the sodium beta-aluminate ceramic layer indicates extremely good surface contact between the copper layer and the ceramic layer prior to the electrochemical deposition of the sodium metal layer as an intermediate layer. This extremely good surface contact is evident in the cross-sections of the inventive substrates shown in Figures 6 and 7.

[0079] Example 3 - Checking the surface area of ​​the alkali metal layer deposition

[0080] In order to check the surface area of ​​the electrochemical deposition of the alkali metal layer (here: sodium metal layer), a substrate according to the invention was first produced in which a copper layer (copper pad) was deposited on a surface on the front side of a sodium beta-aluminate ceramic layer by means of a plasma spray process (see Figure 4).

[0081] Subsequently, as described above, a sodium metal layer was electrochemically deposited between the copper layer and the sodium beta-aluminate ceramic layer (see Figure 5). After deposition of the sodium metal layer, the copper layer previously deposited using the plasma spray process was (re)removed with a needle. It was shown that the deposition of the sodium metal layer worked well not only at the FIB cut locations, but also over a large area beneath the entire copper layer (see Figure 8).

[0082] 1: Metal layer (e.g. copper layer);

[0083] 2: solid, ion-conducting substrate;

[0084] 3: metal particles;

[0085] 4: Spray section;

[0086] 5: Nozzle of a plasma spray device;

[0087] 6: Roller(s) for moving the substrate on a moving belt;

[0088] 7: moving belt for transporting the substrate;

[0089] 8: Lithium metal, deposited at points;

[0090] 9: Lithium metal, deposited in a flat layer;

[0091] 10: rigid, metallic copper layer.

Claims

Patent claims Method for forming a metal layer on a surface of a solid, ion-conducting substrate, comprising the steps of: a) spraying metal particles along a spray path in the direction of a solid, ion-conducting substrate, wherein the metal particles are i) at least partially molten metal particles, or ii) solid metal particles which are heated along the spray path and / or by their impact speed on the solid ion-conducting substrate to a temperature which is higher than the melting temperature of the metal particles, whereby at least partially molten metal particles are formed; and b) allowing the at least partially molten metal particles to solidify on the solid, ion-conducting substrate, whereby a metal layer is formed which is arranged on the solid, ion-conducting substrate.Method according to the preceding claim, characterized in that the spraying of the metal particles is carried out by means of a method selected from the group consisting of plasma spray methods, cold gas spraying, high-velocity flame spraying, flame spraying, detonation spraying, laser spraying, arc spraying and thermal spraying according to DIN EN 657:2005, preferably by means of a method selected from the group consisting of plasma spray methods, cold gas spraying and arc spraying, particularly preferably by means of a plasma spray method. Method according to one of the preceding claims, characterized in that the spraying of the metal particles takes place by means of a plasma spray process, wherein the metal particles are melted in a nozzle and the molten metal particles are sprayed in the direction of the surface of the substrate, wherein the metal particles are preferably melted in the nozzle by an inert gas plasma, particularly preferably a noble gas plasma, in particular argon plasma, optionally containing >0% vol.% to 5 vol.% hydrogen plasma, wherein the inert gas plasma is generated in particular i) by applying an electrical voltage to the nozzle in the range from 1 V to 60 V in continuous operation for thermal atmospheric plasma and in the range from 100 V to 10 kV for a cold-active atmospheric plasma, wherein the ignition voltage is optionally at least a factor of 10 higher; and / or ii) exits the nozzle with a volume flow in the range from 1 l / min to 100 l / min.Method according to one of the preceding claims, characterized in that a spray speed of the metal particles, a heating temperature of the metal particles, a diameter of the metal particles, a shape of the metal particles, and the spray distance of the metal particles are selected such that bursting of the metal particles upon impact with the surface of the substrate is prevented. Method according to one of the preceding claims, characterized in that the metal particles, preferably to prevent bursting of the metal particles upon impact with the surface of the substrate, i) are sprayed onto the surface of the substrate at a spray speed of a maximum of 700 m / s, preferably a maximum of 500 m / s; and / or. ii) before impacting the substrate and / or upon impacting the substrate have a temperature which is at most 200 K, preferably at most 100 K, particularly preferably at most 50 K, above a melting temperature of the meta I I particles; and / or iii) have a maximum diameter in the range from 1 pm to 1000 pm, particularly preferably in the range from 10 pm to 100 pm, wherein the maximum diameter refers to a maximum diameter determinable by microscopy; and / or iv) do not have a maximum diameter which is in the range of < 100 nm, optionally in the range of < 1 pm;and / or v) have a substantially round shape, wherein an aspect ratio of a length to a width of the metal particles is preferably in the range from 1:10 to 1:1, particularly preferably 1:5 to 1:1, very particularly preferably in the range from 1:2 to 1:1, in particular in the range from 1.5:1 to 1:1, wherein the aspect ratio refers to an aspect ratio determinable by microscopy;and / or vi) are sprayed over a spray path in the range of 1.5 cm to 4 cm, wherein the spray path in the case of a plasma spray process is defined by a distance from an opening of a nozzle to the surface of the substrate. Method according to one of the preceding claims, characterized in that the metal particles are sprayed in the direction of the solid, ion-conducting substrate at a spray rate in the range of > 3 g of metal particles per minute, preferably 3 g to 6 g of metal particles per minute. Method according to one of the preceding claims, characterized in that the metal particles i) contain or consist of a metal, wherein the metal is preferably selected from the group consisting of copper; Aluminum, gold, silver, tin, and an alloy of at least one of these metals; and / or ii) contain no alkali metal and no alkali metal-absorbing material, preferably no active material of a battery electrode.

8. The method according to any one of the preceding claims, characterized in that the metal layer produced i) has a layer thickness, in a direction perpendicular to the surface of the metal layer, in the range from 0.1 pm to 50 pm, preferably in the range from 0.2 pm to 20 pm, particularly preferably 0.5 pm to 10 pm, in particular 1 pm to 2 pm; and / or ii) is porous, preferably has a porosity in the range from >0 to 30%, wherein the porosity preferably refers to a porosity determinable via SEM or X-ray tomography; and / or iii) does not have a layer that contains or consists of solidified particles having a maximum diameter in the range of <100 nm, optionally in the range of <1 pm; and / or iv) does not have any oxygen-conducting properties, optionally no gas-conducting properties.

9. Method according to one of the preceding claims, characterized in that the method comprises the following steps before step a): a) spraying metal particles, preferably the same metal particles as in step a) of the method, along a spray path in the direction of a surface of the solid, ion-conducting substrate, wherein the metal particles are i) at least partially molten metal particles, or ii) solid metal particles which are molten along the spray path and / or by their impact speed on the solid, ion-conducting substrate, are heated to a temperature which is higher than the melting temperature of the metal particles, whereby at least partially molten metal particles are formed; and b) at least partially oxidizing the metal particles at least in regions along the spray path, preferably by contacting the metal particles with a gas which contains or consists of oxygen, in particular with air, whereby at least partially oxidized metal particles are formed; and c) allowing the at least partially oxidized, at least partially molten metal particles to solidify on the solid, ion-conducting substrate, whereby an at least partially oxidized metal layer is formed which is arranged on the solid, ion-conducting substrate, wherein the at least partially oxidized metal layer particularly preferably contacts the solid, ion-conducting substrate over its entire surface;wherein the at least partially oxidized metal layer produced particularly preferably has, in a direction perpendicular to the partially oxidized metal layer, a thickness in the range from 10 nm to 1.5 pm, preferably 15 nm to 1.0 pm, and / or is porous, preferably has a porosity in the range from >0 to 30%, wherein the porosity preferably refers to a porosity that can be determined via SEM or X-ray tomography. Method according to one of the preceding claims, characterized in that the solid, ion-conducting substrate is moved relative to a device that is used for spraying and heating the metal particles, wherein preferably i) the substrate is transported on a moving belt and the metal layer is continuously applied to the substrate, wherein preferably before the application of the metal layer, a metal oxide layer that is at least partially oxidized is continuously applied to the substrate; and / or; ii) a relative speed between the substrate and the device in the range of 0.1 m / s to 1 m / s is maintained; and / or iii) several nozzles are used to spray the metal particles, which nozzles are preferably arranged next to one another on at least one comb. Method according to one of the preceding claims, characterized in that the solid, ion-conducting substrate i) is designed as a flat substrate, preferably as a flat layer, particularly preferably as a flat film, wherein the metal layer, optionally a metal layer that is at least partially oxidized, is applied at least partially 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 pm to 100 pm, wherein the surface roughness preferably refers to a 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 material, sodium-conducting ceramic material, magnesium-conducting ceramic material, potassium-conducting ceramic material, zinc-conducting ceramic material, aluminum-conducting ceramic material, and combinations thereof; and / or iv) contains or consists of a ceramic ion-conducting material, preferably a material selected from the group consisting of LLZO, LATP, LAGP, NZSP, NASICON, ß-aluminate, and combinations thereof, wherein LLZO is optionally; Liß, 4La3Zri,4Tao, eOi2; and / or v) contains or consists of a glassy ion-conducting material, preferably a material selected from the group consisting of UPON, 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 any active material of a battery electrode. 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 solid electrolyte material; - an anode infiltrated with solid electrolyte material; - a cathode layer containing a solid, ion-conducting material, wherein the cathode layer is preferably a free-standing cathode layer, particularly preferably a free-standing cathode layer which has been freed from impurities by means of laser technology; - an anode layer containing a solid, ion-conducting material, wherein the anode layer is preferably a free-standing cathode layer, particularly preferably a free-standing cathode layer which has been freed from impurities by means of laser technology; - a composite of solid electrolyte material and cathode material, optionally sintered; - a composite of solid electrolyte material and anode material, optionally sintered; - a solid electrolyte material infiltrated with active material; and - a solid electrolyte material infiltrated with anode material. A method according to any one of the preceding claims, characterized in that the method further comprises the following steps: i) applying a layer containing or consisting of an alkali metal and / or alkaline earth metal, preferably containing or consisting of sodium and / or lithium, to a surface of the solid, ion-conducting substrate opposite the surface of the solid, ion-conducting substrate onto which the metal layer was applied; and ii) connecting a negative pole of a power source to the metal layer, connecting a positive pole of the power source to the layer applied in step i), and applying an electrical voltage to the negative pole and to the positive pole, wherein a layer containing or consisting of an alkali metal and / or alkaline earth metal is deposited between the metal layer and the solid, ion-conducting substrate.A solid, ion-conducting substrate, wherein a metal layer is arranged at least partially on a surface of the substrate, characterized in that the metal layer is formed by solidified, molten metal particles arranged one above and next to one another. The substrate according to claim 14, characterized in that an at least partially oxidized metal layer is arranged between the substrate and the metal layer, which is formed by solidified, molten, at least partially oxidized metal particles arranged one above and next to one another, wherein the at least partially oxidized metal layer preferably makes planar contact with the substrate and the metal layer.Substrate according to one of claims 14 or 15, characterized in that the substrate is designed as a flat substrate, preferably as a flat layer, particularly preferably as a flat film, wherein the metal layer, optionally also an at least partially oxidized metal layer, is applied at least partially to one of the two flat sides of the flat substrate.

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

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

19. Anode-free battery, preferably anode-free secondary battery, comprising a substrate according to any one of claims 14 to 18, wherein a side of the substrate on whose surface the metal layer is arranged is preferably an anode side of the battery.

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