Patent Publication Number: US-2023163355-A1

Title: Method, coating device and preparation for forming functional layers of an electrochemical storage device

Description:
This nonprovisional application is a continuation of International Application No. PCT/EP2021/070490, which was filed on Jul. 22, 2021, and which claims priority to European Patent Application No. 20187223.1, which was filed on Jul. 22, 2020, and which are both herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a method and a coating device for forming functional layers of an electrochemical storage device and a preparation for forming a functional layer of an electrochemical storage device. 
     Description of the Background Art 
     Electrochemical storage devices within the meaning of the present specification are devices which are capable of storing electrical energy due to their chemical composition. For example, such devices may be batteries, particularly solid-state batteries, e.g., solid-state lithium-ion batteries or solid-state sodium ion batteries or capacitors, e.g. super-capacitors. In such solid-state batteries the charged species (e.g., lithium or sodium ions) migrating between the anode and the cathode of the battery during charging and discharging is embedded in a solid matrix (e.g., comprising an inorganic material, polymers, or a mixture of inorganic material and polymers) forming a solid-state electrolyte. 
     The above-described electrochemical storage devices are often structured into functional layers fulfilling different functions in the electrochemical storage device. The functional layers may be electrochemically active layers, i.e., they may be adapted to store or transport charged species such as ions or electrons, or they may be electrochemically passive layers (i.e., not adapted to store or transport charged species). Functional layers adapted for ion storage may be intercalation hosts, such as anode layers or cathode layers. Furthermore, functional layers configured for ion transport may be e.g., solid-state electrolytes, and functional layers adapted for electron transport may e.g., serve as a current collector. A nonlimiting example of an electrochemically passive layer is a protective layer (typically arranged on the outermost layer) that is adapted to protect the active layers e.g., from corrosion or degradation). 
     Solid-state electrolytes eliminate the use of organic flammable liquid electrolytes by replacing the liquid with a solid, which is not as easily combustible. This significantly reduces the fire hazard during use of devices powered by such solid-state electrochemical storage devices. In addition, some solid-state electrolytes are more electrochemically stable. Furthermore, solid-state electrolyte batteries do not require a separator since the structural integrity of the solid electrolyte prevents internal short-circuiting between anode and cathode. In some combinations of active materials (i.e., with the use of lithium metal) solid state electrolyte batteries can be more energy dense than state of the art batteries with liquid electrolytes. 
     Despite these advantages, manufacturing costs and manufacturing throughput of electrochemical storage devices comprising solid-state electrolytes are non-optimal when using methods of the prior art. Therefore, solid-state electrolyte batteries currently cannot compete economically with batteries using liquid electrolytes. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a method (as well as a coating device and a preparation) for generating functional layers of an electrochemical storage device which is able to reduce manufacturing times and costs compared to the methods of the prior art. 
     A first aspect of the invention relates to a method for generating functional layers of an electrochemical storage device, comprising: providing a first preparation in a first reservoir of a coating device, providing a second preparation in a second reservoir of the coating device, placing the coating device above a substrate and moving the coating device relative to the substrate along a coating direction, dispensing the first preparation from the first reservoir through a first slot of the coating device onto a coating surface of the substrate, wherein the first slot extends along a lateral axis perpendicular to the coating direction and parallel to the coating surface, and simultaneously dispensing the second preparation from the second reservoir through a second slot of the coating device onto the substrate, wherein the second slot extends along the lateral axis, wherein the first preparation and the second preparation form a curtain between the coating device and the substrate, and wherein a first functional layer of the electrochemical storage device is formed on the coating surface of the substrate from the first preparation, and a second functional layer of the electrochemical storage device is simultaneously formed on the first functional layer from the second preparation. 
     The first preparation and the second preparation jointly can form a curtain between the coating device and the substrate. 
     In particular, the coating device may comprise a coating head or nozzle comprising at least the first slot and the second slot and optionally also the first and the second reservoir (alternatively, the first and second reservoir may be disposed outside of the coating head or nozzle and in fluid connection with the first or second slot). For example, the first and the second reservoir may be formed by a cavity in the coating head or nozzle or by a manifold that is insertable in a cavity of the coating head or nozzle. The first preparation and the second preparation may be provided in the first and second reservoir by pumps which transport the first and second preparation from a separate storage reservoir into the respective first or second reservoir of the coating device, e.g., via a tubing or conduit. Of course, the coating device may comprise one or several additional reservoirs and associated slots to deposit additional functional layers of the electrochemical storage device, particularly simultaneously with the first and second functional layer. 
     The coating device is particularly moved relative to the substrate by placing the substrate (e.g., in the form of a film or web) on a conveyor belt and driving the conveyor belt such that the substrate moves below the coating head or nozzle of the coating device, wherein the coating device remains stationary. Of course, it is also possible within the scope of the invention to move the coating head or nozzle of the coating device while the substrate remains stationary. 
     In particular, the coating device can be arranged such that the first slot is arranged closer to the coating surface of the substrate than the second slot. In this manner, it is ensured that the second functional layer is formed on top of the first functional layer. 
     The first and the second preparation (and optionally the third and/or the at least one further preparation) dispensed from the first and the second slot (and optionally the third and/or the at least one further slot) of the coating device, particularly a coating die, can form layers on top of each other on a dispensing surface (also termed “slide”) of the coating device and flow down from the dispensing surface onto the coating surface of the substrate in a layered curtain. In other words, the first and the second preparation (and optionally the third and/or the at least one further preparation) are dispensed by slide curtain coating. In this manner, it is possible to generate the functional layers simultaneously. 
     Also, it may be possible to dispense the first and the second preparation from slots on a bottom side of the coating device (particularly the coating die), wherein the slots are arranged adjacent to each other, such that a layered curtain is formed from the first and the second preparation at the exit of the slots. Such a coating device particularly does not contain a dispensing surface (slide). This method is also known as “slot curtain coating” and the corresponding coating die is termed “slot die”. In contrast to slot coating, slide coating has the advantage that the number of slots and, correspondingly, the number of generated layers is not limited by geometric constraints. 
     The first preparation and the second preparation can be a liquid or a slurry, such that it can be dispensed from the respective slot of the coating device. Therein, the term slurry describes a composition comprising a liquid solvent or monomer and particles (particularly having a diameter from 1 nm and 500 μm) suspended in the liquid solvent or monomer. 
     The first preparation and the second preparation can form a curtain while being dispensed from the respective slot of the coating device onto the coating surface of the substrate. Therefore, the method described above may be described as a curtain coating method. Within the scope of the present specification, the term ‘curtain’ describes a continuous free-falling sheet of a liquid or slurry material. To obtain such a curtain, it is necessary to adjust the flow rate of the first or second preparation dispensed from the respective first or second slot, the coating speed at which the substrate moves relative to the coating device and the rheological properties (e.g. the viscosity) of the first and second preparation (particularly such that the first or second preparation exhibits a shear thinning behavior, i.e. a drop of the viscosity at increasing shear rates). 
     Advantageously, curtain coating benefits from an effect termed hydrodynamic assist: the free-falling curtain creates a pressure field at the point of impingement on the coating surface of the substrate, which allows the formation of a sufficiently thin layer (e.g., 30 μm or less, particularly 5 μm or less) without any defects at very high coating speeds (e.g. about 40 m/min to more than 2500 m/min). 
     Furthermore, the inventors found that it is possible to apply several layers of material simultaneously onto the substrate by curtain coating. Therefore, it is no longer necessary to separately process (e.g., dry or hot-press) the separate layers which significantly improves manufacturing times of the resulting electrochemical storage devices. 
     A third preparation can be provided in a third reservoir of the coating device, and wherein the third preparation is dispensed onto the substrate through a third slot of the coating device simultaneously to the first preparation and the second preparation, wherein the third preparation forms a curtain between the coating device and the substrate, and wherein a third functional layer of the electrochemical storage device is formed on the second functional layer from the third preparation. 
     The first preparation, the second preparation and the third preparation jointly can form a curtain between the coating device and the substrate. 
     At least one further preparation may be provided in a further reservoir of the coating device, wherein the further preparation is dispensed onto the substrate through a further slot of the coating device simultaneously to the first preparation, the second preparation and the third preparation, wherein the further preparation forms a curtain between the coating device and the substrate, and wherein a further functional layer of the electrochemical storage device is formed on the third functional layer from the further preparation. 
     The first preparation, the second preparation, the third preparation and the at least one further preparation jointly can form a curtain between the coating device and the substrate. 
     The first preparation and the second preparation (and particularly also the third preparation and the at least one further preparation) may exhibit a shear thinning behavior, i.e., a drop of viscosity at increasing shear rates. 
     The first preparation and the second preparation (and particularly also the third preparation and the at least one further preparation) can comprise the same solvent or the same polymerizable monomer at the same concentration such that no diffusion occurs at an interface of the first preparation and the second preparation (particularly any of the first, second, third and at least one further preparation), particularly in the resulting functional layer of the electrochemical storage device. In certain embodiments, the first preparation and the second preparation (and particularly also the third preparation and the at least one further preparation) comprise the same salt composition at the same concentration, such that no diffusion occurs at an interface of the first preparation and the second preparation (particularly any of the first, second, third and at least one further preparation). 
     This particularly reduces diffusion gradients in the generated functional layers after deposition on the substrate, and, combined with the laminar flow during curtain coating, reduces mixing between the layers to a minimum and thus improves the quality of the interface of the resulting functional layers, improving the quality of the electrochemical storage device. 
     The first functional layer, the second functional layer, the third functional layer and/or the at least one further functional layer can form a solid-state electrolyte of the electrochemical storage device. 
     The solid-state electrolyte can comprise an inorganic solid electrolyte, e.g., a ceramic or glass material. Such an inorganic solid-state electrolyte may comprise lithium or sodium in its stoichiometric composition. 
     The inorganic solid electrolyte can be selected from the group including or consisting of LiPON, LiI, Li 3 N, Li-β″-Al 2 O 3 , Li 3X La 2/3-X□1/3-2X TiO 3  (LLTO, perovskite), Li 3 OCl (anti-perovskite), Li 14 ZnGe 4 O 16  (LiSICON), Li 1.3 Ti 1.7 Al 0.3 (PO 4 ) 3  (NaSICON type), Li 7 La 3 Zr 2 O 12  (garnet), Thio-LiSICON, Li 6 PS 5 X (wherein X designates Cl, Br or I), argyrodites, and Li 10 MP 2 S 12 , (wherein M designates Ge or Sn). 
     The solid-state electrolyte can comprise a polymer electrolyte, wherein particularly the solid-state electrolyte comprises a mixture of a polymer and a metal ion salt, more particularly a lithium salt or a sodium salt. 
     The polymer electrolyte can comprise a mixture of a polymer and a metal salt, a mixture of different polymers, a block-co polymer or a single ion conducting polymer electrolyte, particularly a lithium polymer salt. 
     The polymer electrolyte can comprise a polyether, in particular polyethylene oxide (PEO) or polypropylene oxide (PPO), a polysiloxane, a polycarbonate, a polyester, a polynitrile, a polyalcohol, a polyamine or poly(bis-(methoxyethoxyethoxide)phosphazene (MEEP). 
     The polymer electrolyte can comprise a metal ion salt, particularly LiBF 4 , LiClO 4 , LiPF 6 , LiAsF 6 , LiCF 3 SO 3  (lithium trifluoromethanesulfonate (LiTf)), or LiN(CF 3 SO 2 ) 2  (lithium bis (trifluoromethanesulfonyl)imide (LiTFSI)). 
     The polymer electrolyte can comprise a metal ion salt, particularly NaBF 4 , NaClO 4 , NaPF 6 , NaAsF 6 , NaCF 3 SO 3  (sodium trifluoromethanesulfonate), or NaN(CF 3 SO 2 ) 2  (sodium bis (trifluoromethanesulfonyl)imide). 
     The polymer electrolyte can comprise a mixture of a polymer and a metal salt, particularly a mixture of polyethyleneoxide and LiBF 4 , a mixture of polyethyleneoxide and LiClO 4 , a mixture of polyethyleneoxide and LiPF 6 , a mixture of polyethyleneoxide and LiAsF 6 , a mixture of polyethyleneoxide and LiCF 3 SO 3 , a mixture of polyethyleneoxide and LiN(CF 3 SO 2 ) 2 , a mixture of polypropyleneoxide and LiClO 4 , a mixture of poly(bis-(methoxyethoxyethoxide)phosphazene and LiCF 3 SO 3  or a mixture of a polysilicone and LiN(CF 3 SO 2 ) 2 . 
     The polymer electrolyte can comprise a functional-group-to-charge-carrier ratio (e.g., Ethylene Oxide to Lithium) ratio from 5:1 to 50:1. In other words, the functional group of the polymer is 5 to 50 times more apparent than the metal ion of the salt which is the charge carrier. 
     The first preparation, the second preparation, the third preparation and/or the at least one further preparation can comprise a polymer, particularly polyethyleneoxide (PEO), polyvinylidenfluorid (PVdF), polyacrylic acid (PAA), carboxymethylcellulose (CMC), styrenebutadiene rubber (SBR), poly(tetrafluoroethylene) (PTFE), polyethylene (PE), polystyrene (PS), polypropylene (PP), gelatin, starch, agar-agar, alginate, amylose, arabic gum, carrageenan, caseine, chitosan, (carbonyl-beta) cyclodextrines, ethylene propylene diene monomer rubber (EPDM), gellan gum, guar gum, karaya gum, cellulose, pectine, PEDOT-PSS, poly(methyl acrylate) (PMA), poly (vinyl alcohol) (PVA), poly (vinyl acetate) (PVAc), polyacrylonitrile (PAN), polyisoprene (PIpr), polyaniline (PANi), polyimide (PI), polyurethane (PU), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), tara gum, tragacanth gum, TRD202A or xanthan gum. 
     By adding polymers to the respective preparation, it is possible to provide a binder, tune the rheological properties of the preparation and particularly provide a solid ion conductor to obtain a solid-state electrolyte layer. 
     The first functional layer, the second functional layer, the third functional layer or the at least one further functional layer can form a cathode or an anode of the electrochemical storage device. 
     The first functional layer, the second functional layer, the third functional layer or the at least one further functional layer can form an electron transport medium, particularly a current collector, of the electrochemical storage device. 
     The first functional layer, the second functional layer, the third functional layer or the at least one further functional layer can form a protective layer of the electrochemical storage device. In certain embodiments, the protective layer is air-impermeable and/or water-impermeable, wherein particularly the protective layer is a top layer or a bottom layer of the stack of functional layers (i.e., the protective layer is coated onto the substrate as the first (bottom) functional layer or the last (top) functional layer). This advantageously protects the other functional layers from moisture and/or air, thereby preventing malfunctioning of the electrochemical storage device and improving its shelf-life. 
     The first preparation, the second preparation, the third preparation and/or the at least one further preparation can comprise a solvent. This solvent particularly evaporates after formation of the respective functional layer resulting in an increased solid content of the electrochemical storage device. 
     The solvent can comprise or consist of water, acetonitrile, N-methyl-2-pyrrolidone, an alcohol, particularly ethanol or methanol, or tetrahydrofuran. 
     The first preparation, the second preparation, the third preparation and/or the at least one further preparation can comprise a polymerizable monomer, wherein particularly polymerization of the monomer is facilitated or initiated by metal ions. Alternatively, polymerization of the monomer can be initiated by electromagnetic radiation of a certain wavelength (e.g., photopolymerization) or by the addition of radicals (radical polymerization). The polymerizable monomer may serve as the solvent, particularly to suspend the particles to form a slurry, or the monomer may be provided in addition to a solvent. A preparation comprising a polymerizable monomer has the advantage that a subsequent solvent evaporation step may be omitted and replaced by a polymerization step which can significantly accelerate manufacture of the electrochemical storage device. 
     Polymerization of the polymerizable monomer can be initiated subsequently to forming the first functional layer, the second functional layer, the third functional layer and/or the at least one further functional layer on the coating surface of the substrate. 
     The first preparation, the second preparation, the third preparation and/or the at least one further preparation can comprise a metal ion host, particularly a conversion material or intercalation material. In particular, a functional layer comprising such a metal ion host may serve as an anode or a cathode of the electrochemical storage device. 
     The metal ion host can comprise or consist of a cathode active material, particularly lithium nickel manganese cobalt oxide (Li—NMC, e.g., Li a Ni x Mn y Co z O 2 ), lithium iron phosphate (LFP, LiFePO 4 ), lithium nickel cobalt aluminium oxide (Li—NCA, e.g. Li a Ni x Co y Al z O z ), lithium cobalt oxide (LCO, LiCoO 2 ), or lithium manganese oxide (LMO, LiMn 2 O 4 ). 
     The metal ion host can comprise or consist of an anode active material, particularly graphite, silicon, lithium titanate (LTO, Li 4 Ti 5 O 12 ) or titanium oxide (TiO 2 ). 
     The first preparation, the second preparation, the third preparation and/or the at least one further preparation can comprise a precursor capable of forming a metal ion host, particularly a conversion material or intercalation material. The metal ion host may be formed from the precursor by a chemical reaction which is initiated or automatically occurs after forming the respective functional layer of the electrochemical storage device by curtain coating. For example, the precursor may be a nitrate, a carbonate or a hydroxide. 
     The first preparation, the second preparation, the third preparation and/or the at least one further preparation can comprise a solid ion conductor, particularly comprising an inorganic material (e.g. a ceramic or glass material) or a polymer electrolyte. 
     The first preparation, the second preparation, the third preparation and/or the at least one further preparation can comprise a precursor capable of forming a solid ion conductor, particularly comprising an inorganic material (e.g. a ceramic or glassy/amorphous material) or a polymer electrolyte. The solid ion conductor may be formed from the precursor by a chemical reaction which is initiated or automatically occurs after forming the respective functional layer of the electrochemical storage device by curtain coating. In case of a polymer electrolyte, this chemical reaction may be a polymerization reaction and the precursor may be a monomer capable of forming the polymer by polymerization. Alternatively, in particular, the precursor may be a nitrate, a carbonate or a hydroxide. 
     The first preparation, the second preparation, the third preparation and/or the at least one further preparation can comprise a solid electronic conductor, particularly comprising a metal (e.g. aluminum or copper) or carbon (e.g. carbon black). 
     The solid electronic conductor can comprise electrically conductive fibers, particularly carbon nanotubes. These electrically conductive fibers simultaneously serve as an electron conductor and improve the rheological properties (viscosity) of the preparation, resulting in improved stability of the curtain during coating. 
     The first preparation, the second preparation, the third preparation and/or the at least one further preparation can comprise a surfactant. 
     The first functional layer can form a cathode or an anode and the second functional layer can form a solid-state electrolyte of the electrochemical storage device. 
     The first preparation, the second preparation, the third preparation and/or the at least one further preparation can comprise a low-shear viscosity of 1 mPa s to 100000 mPa s, particularly 100 mPa s to 1000 mPa s. 
     The first preparation, the second preparation, the third preparation and/or the at least one further preparation can comprise lithium ions or sodium ions. 
     The first preparation, the second preparation, the third preparation and/or the at least one further preparation can comprise a liquid metal, particularly liquid lithium, liquid gallium, or a mixture of liquid lithium and liquid gallium (resulting in an alloy), or metal particles (particularly resulting in a metal paste). Advantageously, lithium and gallium have a relatively low melting temperature which facilitates manufacturing. The metal particularly forms an electronic conductor, such as a current collector, as well as a host for metal ions (e.g. wherein the ions form a deposit on the metal layer). Forming a current collector by the method according to the present invention has the advantage that a very thin (e.g. 5 μm or less) current collector layer can be formed in contrast to method of the prior art, resulting in improved quality of the electrochemical storage device. In case of a combined current collector and metal ion host, the thickness of the electrochemical storage device can be further reduced. 
     The first preparation, the second preparation, the third preparation and/or the at least one further preparation can comprise a liquid metal, particularly liquid lithium, liquid gallium or a mixture of liquid lithium and liquid gallium, wherein the preparation is heated prior to and/or during dispensing onto the coating surface of the substrate. 
     The first preparation, the second preparation, the third preparation and/or the at least one further preparation can comprise a first polymer having a molecular weight from 1000 g mol −1  to 100000 g mol −1  and a second polymer having a molecular weight from 300000 g mol −1  to 1200000 g mol −1 . In particular, this bimodal size distribution allows to obtain optimal rheological properties and at the same time provides optimal conditions for a polymer electrolyte of a solid-state electrochemical storage device. It also allows higher solid contents of the preparations and therefore shorter drying times. 
     The coating device, particularly the coating head or the nozzle, can comprise a dispensing surface configured to receive the first and the second preparation (and optionally the third and/or the at least one further preparation) dispensed from the first and the second slot (and optionally the third and/or the at least one further slot) of the coating device, particularly wherein the first preparation and the second preparation (and optionally the third preparation and the at least one further preparation) form layers on top of each other on the dispensing surface, wherein the layers form a layered curtain between the coating device and the coating surface of the substrate. 
     The first reservoir and the first slot, the second reservoir and the second slot, the third reservoir and the third slot and/or the at least one further reservoir and the at least one further slot can be divided into a first section and a second section along the lateral axis, wherein the first section and the second section are physically separated, preventing flow of the respective preparation between the first and the second section. In particular, the first section forms an end section of the respective reservoir along the lateral axis. 
     The first reservoir and the first slot, the second reservoir and the second slot, the third reservoir and the third slot and/or the at least one further reservoir and the at least one further slot further can comprise a third section which is physically separated from the first section and the second section, wherein particularly the second section is arranged between the first section and the third section, wherein the first section and the second section form opposite end sections of the respective reservoir along the lateral axis. 
     For example, physical separation between the sections may be obtained by integral walls of the coating head or nozzle separating the sections of the respective reservoir, by placing separate manifolds in the respective sections of a recess in the coating head or nozzle or by inserting separators into the respective reservoir. 
     The first, the second, the third or the at least one further preparation can be provided in the first section of the respective reservoir at a first flow rate and the second preparation is provided in the second section of the respective reservoir at a second flow rate, such that the functional layer formed by the respective preparation dispensed from the first section of the respective slot comprises a greater thickness perpendicular to the coating surface than the functional layer formed by the respective preparation dispensed from the second section of the respective slot, particularly wherein the first flow rate is greater than the second flow rate. 
     The dispensing surface can comprise a recess comprising a width along the lateral axis corresponding to the width of the first section of the respective reservoir and the respective slot, wherein particularly the recess extends from the respective slot along the entire dispensing surface in the coating direction. In particular, a depth of the recess perpendicular to the dispensing surface corresponds to the thickness difference between the functional layer formed by the respective preparation dispensed from the first section and the functional layer formed by the respective preparation dispensed from the second section. 
     The first, the second, the third or the at least one further preparation can be provided in the third section of the respective reservoir at a third flow rate, such that the functional layer formed by the respective preparation dispensed from the third section of the respective slot comprises a greater thickness perpendicular to the coating surface than the functional layer formed by the respective preparation dispensed from the second section of the respective slot, wherein particularly the third flow rate is equal to the first flow rate and the thickness of the functional layer formed by the respective preparation dispensed from the third section is equal to the thickness of the functional layer formed by the respective preparation dispensed from the first section. 
     The dispensing surface can comprise a recess comprising a width along the lateral axis corresponding to the width of the third section of the respective reservoir and the respective slot, wherein particularly the recess extends from the respective slot along the entire dispensing surface in the coating direction. In particular, a depth of the recess perpendicular to the dispensing surface corresponds to the thickness difference between the functional layer formed by the respective preparation dispensed from the third section and the functional layer formed by the respective preparation dispensed from the second section. 
     The second preparation can be provided in the first section at a first flow rate and the second preparation is provided in the second section at a second flow rate, such that the second functional layer formed by the second preparation dispensed from the first section of the second slot comprises a greater thickness perpendicular to the coating surface than the second functional layer formed by the second preparation dispensed from the second section of the second slot. In particular, the first slot comprises a width extending along the lateral axis which is equal to the width of the second section of the second slot, particularly such that the first functional layer formed by the first preparation is embedded by the second functional layer formed by the second preparation. 
     The second preparation can be provided in the third section of the second reservoir at a third flow rate, such that the functional layer formed by the second preparation dispensed from the third section of the second slot comprises a greater thickness perpendicular to the coating surface than the functional layer formed by the second preparation dispensed from the second section of the second slot, wherein particularly the third flow rate is equal to the first flow rate and the thickness of the functional layer formed by the second preparation dispensed from the third section is equal to the thickness of the functional layer formed by the second preparation dispensed from the first section. 
     Providing the preparations in the different sections of the respective reservoir at different flow rates as described above, can be used to laterally embed an adjacent functional layer applied through a separate slot or form interconnections between functional layers, particularly if this slot comprises a width which is equal to the width of the second (middle) section. The flow rate necessary to obtain a pre-defined thickness depends on the width of the slot along the lateral axis. By means of the optional recess in the dispensing surface corresponding to the width of the first and/or third section, a lower functional layer can be embedded by an upper functional layer while maintaining a plain surface of the upper layer, which is advantageous for deposition of further layers on the upper layer. 
     The first or second preparation can be dispensed from the first section and a further preparation is dispensed from the second section, such that the first or second preparation and the further preparation are arranged in a pre-defined pattern on the coating surface of the substrate to jointly form the first or second functional layer of the electrochemical storage device. 
     For instance, this may be applied to laterally embed a solid electrolyte of a solid electrolyte battery e.g. by a layer of active material (anode or cathode) or by a protective layer or to form interconnections between layers in a single manufacturing step. 
     Of course, the reservoirs and associated slots can be divided into additional sections (besides the first, the second and the third section) to obtain certain patterns of the functional layers and allow interconnection between layers. 
     The functional layers can be chemically, thermally, optically, or mechanically excited to change the composition and/or the structure of the functional layers. 
     The first preparation, the second preparation, the third preparation and/or the at least one further preparation can comprise a solvent, wherein the solvent is evaporated subsequently to forming the functional layers on the coating surface of the substrate. 
     The functional layers can be dried subsequently to forming the functional layers on the coating surface of the substrate. 
     The functional layers can be exposed to an electric field and/or a magnetic field during drying the functional layers. In particular, this results in the formation of a conductivity network in a solid electrolyte functional layer (e.g. by formation of lithium ion channels) with a defined morphology and directionality, which improves the quality of the electrochemical storage device. 
     At least two adjacent functional layers can be cross-linked subsequently to forming the functional layers on the coating surface of the substrate. In other words, the interface of the adjacent layers is linked by a chemical reaction between the chemical groups of the layers resulting in increased mechanical stability, and particularly less subsequent chemical reactions between the layers and/or improved ion conductivity through the interface of the layers. 
     Pressure and/or heat can be applied to the functional layers subsequently to forming the functional layers on the coating surface of the substrate. 
     The functional layers can be calendered subsequently to forming the functional layers on the coating surface of the substrate. Calendering can be performed by passing the stack of functional layers between two rollers separated by a small gap with or without additional heating, resulting in compaction of the layers. 
     A chemical reaction can occur in at least one of the functional layers subsequently to forming the functional layers on the coating surface of the substrate, wherein particularly the chemical reaction involves polymerization of the monomer, forming a metal ion host from a precursor, forming a solid ion conductor from a precursor, or forming a solid electronic conductor from a precursor. 
     The functional layers can be sintered subsequently to forming the functional layers on the coating surface of the substrate, particularly by applying heat, radiation (e.g. infrared radiation, light, for instance laser light or microwaves). 
     The substrate can be removed from the functional layers subsequently to forming the functional layers on the coating surface of the substrate. In other words, the substrate is used as a sacrificial layer, which is delaminated or otherwise removed after curtain coating the functional layers of the electrochemical storage device. This has the advantage that the overall weight of the electrochemical storage device is reduced. Furthermore, removing the rigid substrate allows to adapt the shape of the functional layer stack of the electrochemical storage device, or even realize a flexible electrochemical storage device depending on the used components of the functional layers, for example to integrate the electrochemical storage device in textiles or wearable devices. 
     The first preparation, the second preparation, the third preparation or the at least one further preparation can comprise a polymer, wherein the first preparation and/or the second preparation is dispensed onto the coating surface of the substrate at a temperature above the melting point of the polymer. Therein, in particular, the first preparation, the second preparation, the third preparation and/or the at least one further preparation does not contain a solvent. Using such a solvent-free preparation, a functional layer with a high solid content can be formed by cooling (resulting in solidification of the polymer) instead of evaporating the solvent, which improves the speed of the manufacturing method. 
     A second aspect of the invention relates to a coating device for generating functional layers of an electrochemical storage device comprising a first reservoir for receiving a first preparation, a first slot for dispensing the first preparation from the first reservoir onto a coating surface of a substrate, such that the first preparation forms a curtain between the coating device and the substrate during dispensing the first preparation onto the coating surface, a second reservoir for receiving a second preparation, a second slot extending parallel to the first slot for dispensing the second preparation from the second reservoir onto the coating surface simultaneously to the first preparation, such that the second preparation forms a curtain between the coating device and the coating surface during dispensing the second preparation onto the coating surface, wherein the coating device is configured to be placed above the substrate and moved relative to the substrate along a coating direction. 
     The first slot and the second slot can be configured and arranged such that a first functional layer of the electrochemical storage device can be formed on the coating surface from the first preparation, and a second functional layer of the electrochemical storage device can be formed simultaneously (with the first functional layer) on the first functional layer from the second preparation. 
     The coating device can comprise a third reservoir for receiving a third preparation, a third slot for dispensing the third preparation from the third reservoir onto the coating surface of the substrate, such that the third preparation forms a curtain between the coating device and the substrate during dispensing the third preparation onto the coating surface, particularly wherein the third slot is configured and arranged such that a third functional layer of the electrochemical storage device can be formed simultaneously with the first and second functional layer on the second functional layer. 
     The coating device can comprise at least one further reservoir for receiving a further preparation, at least one further slot for dispensing the further preparation from the further reservoir onto the coating surface of the substrate, such that the further preparation forms a curtain between the coating device and the substrate during dispensing the further preparation onto the coating surface, particularly wherein the at least one further slot is configured and arranged such that a further functional layer of the electrochemical storage device can be formed simultaneously with the first, the second (and optionally the third) functional layer, more particularly on the third functional layer. 
     The coating device, particularly the coating head or the nozzle, can comprise a dispensing surface configured to receive the first and the second preparation (and optionally the third and/or the at least one further preparation) dispensed from the first and the second slot (and optionally the third and/or the at least one further slot) of the coating device, particularly wherein the dispensing surface is arrangeable such that the first preparation and the second preparation (and optionally the third preparation and the at least one further preparation) form layers on top of each other on the dispensing surface and that the layers form a layered curtain between the coating device and the coating surface of the substrate. In this manner, it is possible to generate the functional layers simultaneously. 
     The coating device may comprise a coating head or nozzle comprising at least the first slot, the second slot, the third slot and/or the at least one further slot and optionally also the first reservoir, the second reservoir, the third reservoir and/or the at least one further reservoir (alternatively, the first, the second, the third and/or the at least one further reservoir may be disposed outside of the coating head or nozzle and in fluid connection with the respective first, second, third or further slot). For example, the first, the second, the third and/or the at least one further reservoir may be formed by a cavity in the coating head or nozzle or by a manifold that is insertable in a cavity of the coating head or nozzle. The first preparation, the second preparation, the third preparation and/or the fourth preparation may be provided in the respective first, second, third or further reservoir by pumps which transport the respective preparation from a separate storage reservoir into the respective reservoir of the coating device, e.g. via a tubing or conduit. 
     The coating device may comprise edge guides configured to prevent neck formation of the curtain between the coating device and the coating surface of the substrate. Therein, thinning of the curtain along the lateral axis as a result of surface tension is termed ‘neck formation’. In particular, the edge guides comprise or consist of tabs or plates extending from both lateral ends of the dispensing surface in a vertical direction towards the coating surface. 
     The coating device may comprise a conveyor mechanism, e.g. a conveyor belt, configured to move the substrate (e.g. in the form of a film or web) relative to the coating device, particularly relative to the coating head or nozzle, against the coating direction, wherein the coating device, particularly the coating head or nozzle, remains stationary. In particular, in case the substrate is a web, a film or a foil, the substrate can be moved itself without an additional conveyor belt. 
     The coating device may comprises an actuator configured to move the coating head or nozzle relative to the substrate along the coating direction. 
     The first reservoir, the second reservoir, the third reservoir and/or the further reservoir can comprise a respective pump inlet for connecting a pump to the respective reservoir, such that a preparation may be provided in the respective reservoir by means of the pump. The pump inlets of the first, second, third and/or further reservoir may be connected to the same pump or separate pumps. 
     The coating device can comprise at least one pump connected to the pump inlet of the first reservoir, the second reservoir, the third reservoir and/or the further reservoir. 
     The first reservoir (and also the first slot), the second reservoir (and also the second slot), the third reservoir (and also the third slot) and/or the further reservoir (and also the further slot) can be divided into a (respective) first section and a (respective) second section along the lateral axis, wherein the first section and the second section are physically separated. Therein, in particular, the first reservoir, the second reservoir, the third reservoir and/or the at least one further reservoir comprises a first pump inlet connected to the first section and a second pump inlet connected to the second section, wherein the first pump inlet and the second pump inlet are configured to be connected to respective pumps to provide respective preparations in the first section and the second section. In particular, the first section forms a first end section of the first, second, third or further reservoir along the lateral axis. In other words, the first section is limited by a wall forming an end of the respective first, second, third or further reservoir along the lateral axis. 
     The first reservoir, the second reservoir, the third reservoir and/or the further reservoir can comprise a third section, wherein the second section is arranged between the first section and the third section along the lateral axis. In particular, the third section forms a second end section of the respective reservoir opposite the first end section. In particular, the respective reservoir comprises a third pump inlet connected to the third section. 
     The first section and/or the third section of the second slot can extend beyond the first slot along the lateral axis, such that the second functional layer can be formed laterally with respect of the first functional layer, in particular thereby embedding the first functional layer. In other words, the second slot has a greater width than the first slot. 
     The coating device can comprise a first pump connected to the first pump inlet, which is connected to the first section of the first, the second, the third and/or the at least one further reservoir and a second pump connected to the second pump inlet, which is connected to the second section of the first, the second, the third and/or the at least one further reservoir. In particular, the coating device comprises a third pump connected to the third pump inlet which is connected to the third section of the first, the second, the third and/or the at least one further reservoir. 
     Using this setup, different preparations can be provided in the sections of the reservoirs and dispensed from the associated slot sections to obtain a functional layer comprising a pre-defined pattern of materials, e.g. embedding certain layers or forming interconnections between layers. 
     The coating device can comprise a pump controller configured to set a first flow rate of the first pump and a second flow rate of the second pump, particularly such that the functional layer formed by the respective preparation dispensed from the first section of the respective slot comprises a greater thickness perpendicular to the coating surface than the functional layer formed by the preparation, particularly the second preparation, dispensed from the second section of the respective slot. 
     The dispensing surface can comprise a recess comprising a width along the lateral axis corresponding to the width of the first section of the respective reservoir and the respective slot, wherein particularly the recess extends from the respective slot along the entire dispensing surface in the coating direction. This allows to obtain an upper functional layer embedding a lower functional layer while maintaining a plain surface of the upper functional layer in case the depth of the recess corresponds to the difference in thickness of the functional layer dispensed from the first section of the respective slot and the functional layer dispensed from the second section of the respective slot. 
     The coating device can further comprise a third pump connected to the third pump inlet connected to the third section of the first, the second, the third and/or the at least one further reservoir, wherein the pump controller is configured to set a third flow rate of the third pump, particularly such that the functional layer formed by the respective preparation dispensed from the third section of the respective slot comprises a greater thickness perpendicular to the coating surface than the functional layer formed by the preparation dispensed from the second section of the respective slot, wherein particularly the third flow rate is equal to the first flow rate. Alternatively, in certain embodiments, the first pump is further connected to the third pump inlet connected to the third section of the first, the second, the third or the at least one further reservoir (in addition to the first pump inlet connected to the first section), particularly such that the functional layers formed by the preparation dispensed from the first section and the third section comprise the same thickness. 
     The dispensing surface can comprise a recess comprising a width along the lateral axis corresponding to the width of the third section of the respective reservoir and the respective slot, wherein particularly the recess extends from the respective slot along the entire dispensing surface in the coating direction. This allows to obtain an upper functional layer embedding a lower functional layer while maintaining a plain surface of the upper functional layer in case the depth of the recess corresponds to the difference in thickness of the functional layer dispensed from the third section of the respective slot and the functional layer dispensed from the second section of the respective slot. 
     The coating device can comprise a first pump connected to the first pump inlet, which is connected to the first section of the second reservoir and a second pump connected to the second pump inlet, which is connected to the second section of the second reservoir, wherein the coating device comprises a pump controller configured to set a first flow rate of the first pump and a second flow rate of the second pump, such that the functional layer formed by the second preparation dispensed from the first section of the respective slot comprises a greater thickness perpendicular to the coating surface than the functional layer formed by the second preparation dispensed from the second section, wherein particularly the first slot comprises a width extending along the lateral axis which is equal to the width of the second section of the second slot, particularly such that the first functional layer formed by the first preparation is embedded by the second functional layer formed by the second preparation. 
     The above-described examples with a divided reservoir (and slot) allow to apply different preparations in one functional layer of the electrochemical storage device in a pre-defined pattern. For instance, this may be applied to laterally embed a solid electrolyte of a solid electrolyte battery e.g. by a layer of active material (anode or cathode) or by a protective layer or form interconnections between two layers which are separated by a further layer in a single manufacturing step. Alternatively, it is possible to apply the preparations from the different sections at different flow rates. For example, a higher flow rate may be applied in the outer (first and/or third) section(s) of the respective reservoir) than in the middle (second) section. This can be used to laterally embed a previous functional layer applied through a separate slot, particularly if this slot comprises a width which is equal to the width of the second (middle) section. 
     A third aspect of the invention relates to a preparation (i.e., the first, the second, the third or the at least one further preparation mentioned above) for forming a functional layer of an electrochemical storage device. 
     The preparation can exhibit a shear thinning behavior, i.e., a drop of viscosity at increasing shear rates. 
     The preparation may be a liquid or a slurry. 
     The preparation can comprise a solvent. 
     The preparation can comprise a polymerizable monomer, wherein particularly polymerization of the monomer is initiated or facilitated by metal ions, more particularly lithium ions. Alternatively, polymerization of the monomer can be initiated by electromagnetic radiation of a certain wavelength (e.g. photopolymerization) or by the addition of radicals (radical polymerization). 
     The preparation can comprise a metal ion host or a precursor capable of forming a metal ion host, particularly a conversion material or intercalation material. 
     The preparation can comprise a solid ion conductor or a precursor capable of forming a solid ion conductor, particularly comprising an inorganic material comprising metal ions, more particularly lithium ions or sodium ions. 
     The preparation can comprise a solid electronic conductor or a precursor capable of forming a solid electronic conductor particularly comprising a metal or carbon. 
     The preparation can comprise a low-shear viscosity of 1 mPa s to 100000 mPa s, particularly 100 mPa s to 1000 mPa s, such that the preparation is capable of forming a curtain between a coating device and a coating surface of a substrate when the preparation is dispensed from a slot of the coating device onto the coating surface. 
     The preparation can comprise a first polymer having a molecular weight from 1000 g mol −1  to 100000 g mol −1  and a second polymer having a molecular weight from 300000 g mol −1  to 1200000 g mol −1 . In particular, this bimodal size distribution allows to obtain optimal rheological properties and at the same time provide optimal conditions for a polymer electrolyte of a solid-state electrochemical storage device. It also allows higher solid contents of the preparations and therefore shorter drying times. 
     The preparation can comprise a polymer, particularly polyethyleneoxide (PEO), polyvinylidenfluorid (PVdF), polyacrylic acid (PAA), carboxymethylcellulose (CMC), styrenebutadiene rubber (SBR), poly(tetrafluoroethylene) (PTFE), polyethylene (PE), polystyrene (PS), polypropylene (PP), gelatin, starch, agar-agar, alginate, amylose, arabic gum, carrageenan, caseine, chitosan, (carbonyl-beta) cyclodextrines, ethylene propylene diene monomer rubber (EPDM), gellan gum, guar gum, karaya gum, cellulose, pectine, PEDOT-PSS, poly(methyl acrylate) (PMA), poly (vinyl alcohol) (PVA), poly (vinyl acetate) (PVAc), polyacrylonitrile (PAN), polyisoprene (Plpr), polyaniline (PANi), polyimide (PI), polyurethane (PU), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), tara gum, tragacanth gum, TRD202A or xanthan gum. 
     By adding polymers to the preparation, it is possible to provide a binder, tune the rheological properties of the preparation and particularly also provide a solid ion conductor to obtain a solid-state electrolyte layer. 
     The preparation can comprise a solvent. This solvent particularly evaporates after formation of the respective functional layer resulting in an increased solid content of the electrochemical storage device. In certain embodiments, the solvent comprises or consists of water, acetonitrile, N-methyl-2-pyrrolidone, an alcohol, particularly ethanol or methanol, or tetrahydrofuran. 
     The preparation can comprise a polymerizable monomer, wherein particularly polymerization of the monomer is facilitated or initiated by metal ions. The polymerizable monomer may serve as the solvent, particularly to suspend the particles to form a slurry, or the monomer may be provided in addition to a solvent. A preparation comprising a polymerizable monomer has the advantage that a subsequent solvent evaporation step may be omitted and replaced by a polymerization step which can significantly accelerate manufacture of the electrochemical storage device. 
     The preparation can comprise a metal ion host, particularly a conversion material or intercalation material. In particular, a functional layer comprising such a metal ion host may serve as an anode or a cathode of the electrochemical storage device. 
     The metal ion host can comprise or consist of a cathode active material, particularly lithium nickel manganese cobalt oxide (Li—NMC, e.g. Li a Ni x Mn y Co z O 2 ), lithium iron phosphate (LFP, LiFePO 4 ), nickel cobalt aluminium oxide (Li—NCA, e.g. Li a Ni x Co y Al z O z ), lithium cobalt oxide (LCO, LiCoO 2 ), or lithium manganese oxide (LMO, LiMn 2 O 4 ). 
     The metal ion host can comprise or consist of an anode active material, particularly graphite, silicon, lithium titanate (LTO, Li 4 Ti 5 O 12 ) or titanium oxide (TiO 2 ). 
     The preparation can comprise a precursor capable of forming a metal ion host, particularly a conversion material or intercalation material. The metal ion host may be formed from the precursor by a chemical reaction which is initiated or automatically occurs after forming the respective functional layer of the electrochemical storage device by curtain coating. For example, the precursor may be a nitrate, a carbonate or a hydroxide. 
     The preparation can comprise a solid ion conductor, particularly comprising an inorganic material (e.g. a ceramic or glass material) or a polymer electrolyte. 
     The preparation can comprise a precursor capable of forming a solid ion conductor, particularly comprising an inorganic material (e.g. a ceramic or glass material) or a polymer electrolyte. The solid ion conductor may be formed from the precursor by a chemical reaction which is initiated or automatically occurs after forming the respective functional layer of the electrochemical storage device by curtain coating. In case of a polymer electrolyte, this chemical reaction may be a polymerization reaction and the precursor may be a monomer capable of forming the polymer by polymerization. Alternatively, in particular, the precursor may be a nitrate, a carbonate or a hydroxide. 
     The preparation can comprise a solid electronic conductor, particularly comprising a metal (e.g. aluminum or copper) or carbon (e.g. carbon black). In certain embodiments, the solid electronic conductor comprises electrically conductive fibers, particularly carbon nanotubes. These electrically conductive fibers simultaneously serve as an electron conductor and improve the rheological properties (viscosity) of the preparation, resulting in improved stability of the curtain during coating. 
     The preparation can comprise a surfactant. 
     The preparation can comprise lithium ions or sodium ions. 
     The preparation can comprise a liquid metal, particularly liquid lithium, liquid gallium or a mixture of liquid lithium and liquid gallium, or metal particles (particularly resulting in a metal paste). The metal particularly forms an electronic conductor, such as a current collector. Forming a current collector by the method according to the present invention has the advantage that a very thin (e.g. 30 μm or less, particularly 5 μm or less) current collector layer can be formed in contrast to method of the prior art, resulting in improved quality of the electrochemical storage device. 
     Wherever alternatives for single separable features are laid out herein as examples and/or embodiments, it is to be understood that such alternatives may be combined freely to form discrete embodiments of the invention disclosed herein. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes, combinations, and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein: 
         FIG.  1    shows a cross-sectional view of a part of a coating device according to an embodiment of the invention in a plane parallel to the coating direction; 
         FIG.  2    shows a schematic partially cut-away perspective view of a part of a coating device according to an embodiment of the invention and the curtain and functional layers formed during the method according to the invention; 
         FIG.  3    shows a schematic perspective view of a coating device according to an embodiment of the invention with divided manifolds and associated pump inlets; 
         FIG.  4    shows a schematic perspective view of a coating device according to an embodiment of the invention and the curtain and functional layers formed during a first embodiment of the method according to the invention; 
         FIG.  5    shows a sectional view of the functional layers perpendicular to the coating direction, the functional layers having been formed according to the embodiment of the method depicted in  FIG.  4   ; 
         FIG.  6    shows a schematic perspective view of a coating device according to an embodiment of the invention and the curtain and functional layers formed during a second embodiment of the method according to the invention; and 
         FIG.  7    shows a sectional view of the functional layers perpendicular to the coating direction, the functional layers having been formed according to the embodiment of the method depicted in  FIG.  6   . 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    shows a cross-sectional view of a coating head  4  of a coating device  1  according to an embodiment of the invention in a plane parallel to a coating direction C, and  FIG.  2    shows a corresponding perspective view of the coating head  4 . As shown in  FIGS.  1  and  2   , the coating head  4  comprises a first reservoir  10 , a second reservoir  20  and a third reservoir  30  for respectively receiving a first preparation P 1 , a second preparation P 2  and a third preparation P 3 . In the depicted example, the reservoirs  10 ,  20 ,  30  are formed by cylindrical cavities in a main body of the coating head  4 , the cavities extending along a lateral axis L which is to be arranged perpendicular to the coating direction C when performing the method according to the invention. The reservoirs  10 ,  20 ,  30  each branch into an associated slot  11 ,  21 ,  31  in a dispensing surface  2  or slide of the coating head  4 . The dispensing surface  2  comprises a convexly curved section  2   a  at which a lip  3  is arranged which forms the bottom end of the coating head  4  in the arrangement shown in  FIGS.  1  and  2   . 
     According to an embodiment of the curtain coating method according to the invention, a first preparation P 1  is provided in the first reservoir  10 , a second preparation P 2  is provided in the second reservoir  20  and a third preparation P 3  is provided in the third reservoir  30  through respective pump inlets (not shown in  FIG.  1   , e.g. see  FIG.  3   ) in the reservoirs  10 ,  20 ,  30 , which are connected to a respective pump. By generating a flow of the respective preparations P 1 , P 2 , P 3 , the preparations P 1 , P 2 , P 3  are dispensed from the slots  11 ,  21 ,  31 , and, due to the tilted arrangement of the coating head  4  flow downwards on the dispensing surface  2  towards the curved section  2   a  and the lip  3 . 
     At the position of the first slot  11 , the second preparation P 2  forms a layer on top of the first preparation P 1  being dispensed from the first slot  11 . In a similar manner at the position of the second slot  21 , the third preparation P 3  forms a layer on the second preparation P 2  being dispensed from the second slot  21 . Provided that the composition and the rheological properties of the first preparation P 1 , the second preparation P 2 , and the third preparation P 3  are set accordingly, and that a laminar flow occurs, these layers formed on top of the dispensing surface  2  are not mixed and form a layered curtain composed of a first segment  310  from the first preparation P 1 , a second segment  320  from the second preparation P 2  and a third segment  330  from the third preparation P 3 , the curtain flowing down from the lip  3  of the coating head  4  onto a coating surface  210  of a substrate  200 . 
     The substrate  200  is moved against the coating direction C relative to the coating head  4 , for instance by a conveyor mechanism. Thereby, the functional layers  110 ,  120 ,  130  are formed on top of each other on the coating surface  210 . 
     In particular, the first preparation P 1 , the second preparation P 2  and the third preparation P 3  are slurries having appropriate rheological properties (i.e. an appropriate viscosity and preferably shear thinning behavior) to be used for curtain coating. To obtain a stable curtain, the flow rate of the preparations P 1 , P 2 , P 3  as well as the coating speed at which the substrate  200  moves relative to the coating head  4  against the coating direction C have to be appropriately set. 
     In particular, the coating head  4  comprises edge guides formed by tabs extending from both lateral edges of the lip  3  towards the coating surface  210  in the vertical direction to guide the edges of the curtain  310 ,  320 ,  330  and prevent neck formation. 
     The functional layers  110 ,  120 ,  130  of the electrochemical storage device may be, for example, a cathode  110 , a solid-state electrolyte  120  and an anode  130  of a solid-state metal ion battery, e.g., a solid-state lithium ion battery or a solid-state sodium ion battery. According to this example, the first preparation P 1  contains a metal ion host (conversion or intercalation material) suitable for forming a cathode of a solid-state ion battery, e.g. NMC, LFP, NCA, LCO, or LMO). The second preparation P 2  contains a solid ion conductor, for instance an inorganic matrix containing metal ions, a polymer electrolyte such as a mixture of a polymer and a metal ion salt, or a mixture of an inorganic matrix containing metal salt and a polymer electrolyte. The third preparation P 3  contains a metal ion host suitable for forming an anode of the solid-state ion battery, such as graphite, silicon, LTO or TiO 2 . 
     Alternatively, to form a solid electronic conductor, such as a current collector layer, the dispensed preparation may, e.g., contain metals or carbon black. 
     To tune the rheological properties of the first preparation P 1 , the second preparation P 2  and the third preparation P 3 , these preparations may contain polymers, particularly a mixture of two polymers of different molecular weights. 
     In addition, the preparations P 1 , P 2 , P 3  may contain solvents or polymerizable monomers, and optionally surfactants. 
     The described curtain coating method has the advantage that several very thin (e.g. &lt;30 μm) layers of an electrochemical storage device can be formed simultaneously at high coating speeds (e.g., 40 m/min to 2500 m/min), which significantly improves manufacturing times of electrochemical storage devices, such as solid-state ion batteries. 
     An exemplary protocol for generating a slurry preparation according to the invention to form a solid electrolyte layer is as follows: 2.67 g of PEO (M v  600 000) are dissolved in 77 g Acetonitrile. 1.67 g of LiTFSI are added and stirred with a spatula. 12 g of LLZO powder (d mean  400 nm) is added and stirred again with a spatula. These mass ratios are particularly chosen to result in approximately even volumetric parts of ceramic and polymer within the dried films. The EO:Li molar ratio is 10.4:1. The total solid content of the slurry is 17.5 wt % (m PEO +m LiTFSI +m LLZO )/m total . The low shear steady state viscosity is around 130 mPas. 
     Furthermore, an exemplary protocol for generating a slurry preparation according to the invention to form a cathode layer is as follows: 6 g Acetonitrile, 0.25 g PEO (M v  35 000), 0.167 g PEO (M v  600 000), 0.27 g LiTFSI, 1.1 g LFP (Host) (d mean  1 micron), 0.1375 carbon black (60 nm). 
     Following curtain coating, a number of post processing steps may be performed on the stack of functional layers, particularly the following steps:
         1) Evaporation of the solvent   2) Drying   3) cross-linking   4) hot-pressing   5) calendaring   6) initiating chemical reactions between components of the functional layers   7) sintering   8) initiating further chemical reactions between components of the functional layers   9) pressuring       

       FIGS.  3  to  7    show further examples of the coating device  1  and the curtain coating method according to the invention which can be advantageously used to generate structured functional layers  110 ,  120 ,  130  of an electrochemical storage device. 
       FIG.  3    is a semitransparent perspective view of a coating head  4 , where only one reservoir  10  and the associated slot  11  has been drawn for simplicity (however, this arrangement can be used in coating heads containing three or even more reservoirs and slots). In the embodiment according to  FIG.  3   , the reservoir  10  is formed by three physically separated manifolds, resulting in a first section  10   a , a second section  10   b  and a third section  10   c , which are arranged along the lateral axis L, the second section  10   b  forming a middle section, and the first section  10   a  and the third section  10   c  forming opposite end sections. The first section  10   a  comprises a first pump inlet  13   a , the second section  10   b  comprises a second pump inlet  13   b  and the third section  10   c  comprises a third pump inlet  13   c , each being configured to be connected to a pump, such that a respective preparation P 1 , P 2 , P 3 , P 4  can be provided in the respective section  10   a ,  10   b ,  10   c  of the reservoir  10 . 
     In  FIG.  4   , a coating head  4  is depicted, wherein the first reservoir  10  is divided into a first section  10   a  (extending along the lateral axis over the width X 1 ), a second section  10   b  (extending along the lateral axis L over the width X 2 ) and a third section  10   c  (extending along the lateral axis L over the width X 3 ) similar to  FIG.  3   . 
     A first preparation P 1  is dispensed from the first section  10   a  and the third section  10   c  of the first slot  11 , and a further preparation P 4  is simultaneously dispensed from the second section  10   b  of the first slot  11 . Further, simultaneously, the first preparation P 1  is dispensed from the second slot  21  over the whole width X 1 +X 2 +X 3  of the second slot  21 . 
     As shown in  FIG.  5   , the curtain coating process depicted in  FIG.  4    results in a structured first functional layer  110 , wherein the first preparation P 1  laterally embeds the further preparation P 4 , and a uniform second functional layer  120  formed from the first preparation. For example, the first preparation P 1  may form an active material of the electrochemical storage device and the further preparation P 4  may form a solid-state electrolyte which is protected from ingress of moisture and air by the active material. 
       FIG.  6    shows a further embodiment of the coating device  1 , wherein the second reservoir  20  and the corresponding second slot  21  are separated into a first section  20   a  having a width X 1  along the lateral axis L, a second section  20   b  having a width X 2  along the lateral axis L and a third section  20   c  having a width X 3  along the lateral axis L. This can be realized, for example, by separate manifolds as shown in  FIG.  3   . The sections  20   a ,  20   b ,  20   c  each comprise an associated pump inlet  13   a ,  13   b ,  13   c  (not shown in  FIG.  6   ) branching off from a side of the second reservoir  20  opposite the slot  21 , similar to the embodiment shown in  FIG.  3   . 
     The dispensing surface  2  of the coating device  1  comprises a recess  2   b  aligned with the first section  20   a  of the second slot  21  and comprising a width along the lateral axis L corresponding to the width X 1  of the first section  20   a  of the second slot  21 , wherein the recess  2   b  extends from the second slot  21  along the entire dispensing surface  2  in the coating direction C. Furthermore, the dispensing surface  2  comprises a further recess aligned with the third section  20   c  and comprising a width along the lateral axis L corresponding to the width X 3  of the third section  20   c.    
     By means of the pump or pumps connected to the first pump inlet  13   a  and the third pump inlet  13   c  (see  FIG.  3   ), the second preparation P 2  is provided in the first section  20   a  and the third section  20   c  at a first flow rate, and by means of the pump connected to the second pump inlet  13   b  (see  FIG.  3   ) the second preparation P 2  is provided in the second section  20   b  at a second flow rate, such that a thicker layer of the second preparation P 2  is deposited on the substrate  200  along the width X 1  and X 3  than along the width X 2 . Simultaneously, the first preparation P 1  is dispensed from the first slot  11  connected to the first reservoir  10 , wherein the first slot  11  has a width w which is equal to the width X 2  of the second section  20   b  of the second reservoir  20  and second slot  21 . 
     The resulting pattern of materials deposited on the substrate  200  by the curtain coating method depicted in  FIG.  6    is shown in  FIG.  7   . Similar to the result shown in  FIG.  5   , the first functional layer  110  consists of a core of the first preparation P 1  along the width X 2  flanked laterally by two sections where the second preparation P 2  is deposited (along the width X 1  and the width X 3 ). The second functional layer  120  is a uniform layer of the second preparation P 2  over the entire width X 1 +X 2 +X 3 . The uniform upper surface of the second functional layer  120  is due to the recesses  2   b  of the dispensing surface  2 , the depth of which (perpendicular to the dispensing surface  2 ) is equal to the thickness of the first functional layer  110  in this case, compensating for the additional volume of the second preparation P 2  dispensed from the first section  20   a  and the third section  20   c  of the second slot  21 . Similar to the above-discussed result shown in  FIG.  5   , the first preparation P 1  may form an active material of the electrochemical storage device and the second preparation P 2  may form a solid-state electrolyte which is protected from ingress of moisture and air by the active material. 
     In particular, to ensure that the second preparation P 2  is deposited along the width X 1  and X 3  at a thickness equal to the sum of the thickness of the layer of the first preparation P 1  and the second preparation along the width X 2  in a direction perpendicular to the lateral axis L, the flow rates f P1,X2 , f P2,X1 , f P2,X2  and f P2,X3  can be set according to the following formula: 
     
       
         
           
             
               
                 
                   f 
                   
                     
                       P 
                       ⁢ 
                       2 
                     
                     , 
                     
                       X 
                       ⁢ 
                       1 
                     
                   
                 
                 
                   X 
                   ⁢ 
                   1 
                 
               
               = 
               
                 
                   
                     f 
                     
                       
                         P 
                         ⁢ 
                         2 
                       
                       , 
                         
                       3 
                     
                   
                   
                     X 
                     ⁢ 
                     3 
                   
                 
                 = 
                 
                   
                     
                       f 
                       
                         
                           P 
                           ⁢ 
                           2 
                         
                         , 
                         
                           X 
                           ⁢ 
                           2 
                         
                       
                     
                     
                       X 
                       ⁢ 
                       2 
                     
                   
                   + 
                   
                     
                       f 
                       
                         
                           P 
                           ⁢ 
                           1 
                         
                         , 
                         
                           X 
                           ⁢ 
                           2 
                         
                       
                     
                     
                       X 
                       ⁢ 
                       2 
                     
                   
                 
               
             
             , 
           
         
       
     
     where f P1,X2  indicates the flow (volume per unit of time) of the first preparation along the width X 2 , f P2,X1  indicates the flow of the second preparation along the width X 1 , f P2,X2  indicates the flow of the second preparation along the width X 2 , and f P2,X3  indicates the flow of the second preparation along the width X 3 . 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.