Method for producing a material or a component for a solid-state battery

Abstract

The invention relates to a method for producing a material for a solid-state battery and / or a component for a solid-state battery, and to a solid-state battery cell. In the method for producing a material (10) for a solid-state battery (30) and / or a component (20) for a solid-state battery (30), at least one starting material (1), together with a sodium source (2) and H3BO3, is heated (5) to a temperature between 600 °C and 1300 °C. The material and / or the component can be produced using a far lower temperature.

Description

[0001] Process for producing a material or component for a solid-state battery

[0002] Description

[0003] The invention relates to a method for producing a material for a solid-state battery and / or a component for a solid-state battery and a solid-state battery cell.

[0004] Solid-state sodium batteries are considered promising energy storage devices because they offer advantages over conventional lithium batteries with organic liquid electrolytes in terms of cost, material availability, and operational reliability. However, the production of such batteries is technically complex and cost-intensive.

[0005] The components of solid-state sodium batteries include the electrodes and the separator, which electrically insulates adjacent electrodes of different cells and typically serves as the solid electrolyte. These components can be produced individually or in various combinations by sintering, typically resulting in dense structures. In the case of commercially available high-temperature sodium batteries, the electrolyte is ß-alumina. For low-temperature systems, compounds known as NaSICON, which is derived from the acronym for "Na Super Ionic Conductor," are suitable, for example, materials from the NZSP (Nai) family. +x Zr2Si x P3- xOi2). These inorganic compounds can exist as glasses or crystallize in rhombohedral or monoclinic structures and exhibit very good ionic conductivity combined with very low electrical conductivity. Examples are described in the publications US 10 020 508 B2, EP2 900 594 B1, KR 101 974 848 B1, KR 102 339 641 B1, JP 5 753 852 B2, and US 8 012 633 B2. These materials are usually produced by multiple calcination steps, typically at 900 °C to 1200 °C, followed by sintering at temperatures between 1200 °C and 1300 °C to produce the dense ceramic for the desired component. Milling steps are often carried out in between. This results in considerable technical effort, high energy consumption, and high costs. The above-mentioned features and properties can be combined in any way with the claimed subject-matter, unless otherwise stated.

[0006] The publication “Liquid-phase sintering of highly Na + "Ion conducting NagZr2Si2POi2 ceramics using NasBOs additive" by Noi et al. (DOI: 10.1111 / jace.15288) describes the use of sodium borate to reduce the sintering temperature in the production of a battery component with a NaSICON compound. The additive is co-sintered with a previously prepared NaSICON powder to produce the component. The additive used is prepared using two calcination steps and intermediate milling, and must also be handled under a protective gas atmosphere.

[0007] It is the object of the invention to provide an improved method for producing a material and / or a component for a solid-state battery and an improved solid-state battery cell.

[0008] The object is achieved by the method according to claim 1 and by the solid-state battery cell according to the independent claim.

[0009] To achieve the object, a method for producing a material for a solid-state battery and / or for producing a component for a solid-state battery is used, in which at least one starting material is heated together with a sodium source and H3BO3 to a temperature between 600 °C and 1300 °C.

[0010] The process can be used, on the one hand, to produce a material for a solid-state battery, in particular a NaSICON material. The NaSICON crystal structure is created by heating. The produced material is suitable for producing a solid-state battery. The process can also be used to produce at least one component for a solid-state battery. The component is sintered upon heating and thus produced as a solid body of the desired shape. Combinations of both are possible.

[0011] In both cases, the sodium source and H3BO3 (collectively referred to as the additives according to the invention) enable a process at a significantly reduced temperature. This reduces the technical effort and the energy required, and thus the costs. The additives used can be processed in the atmosphere and are therefore comparatively easy to handle. Time- and energy-intensive production of NagBOg is not necessary. In the case of the production of a NaSICON material, the required properties such as density, ionic conductivity, and the NaSICON crystal structure are achieved even at the lower temperature.

[0012] In particular, the temperature between 600°C and 1300°C to which heating is carried out is the maximum temperature. In other words, no heating to a higher temperature occurs during the production of the material and / or component for a solid-state battery. Preferably, heating to a maximum of 1200°C is used.

[0013] The solid-state battery is, in particular, a solid-state sodium battery. A sodium source is a substance containing sodium. A substance within the meaning of the invention comprises a mixture of substances. In particular, this refers to a substance that contains sodium that is chemically available during the process. The sodium source is, in particular, an alkaline sodium compound, for example, NaOH, Na2CO3, or NaHCO3. Alkaline sodium compounds enable particularly extensive temperature reductions.

[0014] In particular, the material and / or component produced according to the invention contains less than 20%, preferably less than 10% and particularly preferably less than 5% secondary phase. In other words, the vast majority of the material and / or component, for example at least 80%, preferably at least 90% and in particular at least 95%, has the desired NaSICON crystal structure. In particular, the material and / or component produced according to the invention contains a boron concentration (g / g) of 0.2% to 0.8%, preferably 0.4% to 0.6% (before sintering). These are values ​​that apply to the examples mentioned below. Depending on the application, the optimal boron concentration can also be shifted upwards or downwards. Since boron is volatile at high temperatures, the boron concentration can decrease at high sintering temperatures. After heating orSintering at 900 °C maintains approximately the same boron concentration (corresponding to the additive concentration used according to the invention). With increasing sintering temperature, the remaining measurable boron concentration decreases continuously, and after sintering at 1260 °C, the boron content is below the detection limit. Between these temperatures, a steady decrease in the boron concentration is to be expected. The boron concentration can be determined using ion beam analysis (IBA), with particle-induced gamma quantum emission (PIGE) of boron at 718 keV being particularly suitable for analysis. The density-corrected total emission can be evaluated and compared, in particular, with the respective sample production parameters. Materials and / or components produced according to the invention can therefore be identified by their comparatively high boron concentration.

[0015] In one embodiment, the temperature is below 1100°C, in particular below 1000°C, and preferably below 900°C. In one embodiment, the temperature is approximately 850°C. It is possible to reduce the temperature to 850°C and possibly even lower, particularly when producing components for a solid-state battery from intermediate products, e.g., from calcined starting materials for the production of NaSICON. Tests have shown that key properties of the produced component, such as ionic conductivity and relative density, as well as the NaSICON crystal structure, are good in this case despite the significantly reduced sintering temperature. To achieve the desired crystal structure, at least one calcination step above 1000°C is necessary using conventional methods. The same temperatures are possible when producing the NaSICON material for a solid-state battery.Analogous to what is described above, the respective temperature to which heating takes place, in particular the maximum temperature.

[0016] In principle, a very low temperature allows for significant savings in effort and costs, but at least beyond a certain point, it leads to a deterioration in the properties of the manufactured material or component. Thus, the optimum temperature depends on the specific requirements. Depending on the application, a temperature below 1100 °C, 1050 °C, 1000 °C, 950 °C, 900 °C, or a temperature of approximately 850 °C or below 850 °C may be optimal. The temperature reductions achieved by the invention are significantly greater than when using NaaBOa.

[0017] The temperature is preferably above 700°C, especially above 800°C, to achieve sufficient crystallinity, ionic conductivity, and / or density of the produced material or component. In one embodiment, NaOH is used as the sodium source. It has been shown that, among alkaline sodium sources, NaOH enables particularly high temperature reductions. Furthermore, NaOH is readily available and inexpensive.

[0018] In one embodiment, the mixing ratio of NaOH and H3BO3 (orthoboric acid) is greater than 1 mol / mol, in particular greater than 2 mol / mol, and / or less than 6 mol / mol, in particular less than 4 mol / mol. Preferably, the mixing ratio is approximately 3 mol / mol.

[0019] In particular, a mixing ratio of the additives according to the invention to NaSICON, to a starting material for producing NaSICON and / or to an intermediate for producing NaSICON is at least 0.02 g / g, in particular at least 0.04 g / g, preferably at least 0.06 g / g and / or at most 0.2 g / g, in particular at most 0.14 g / g, preferably at most 0.11 g / g. In a particularly preferred embodiment, the mixing ratio is approximately 0.05 g / g, approximately 0.071 g / g, approximately 0.107 g / g, at least 0.065 g / g and / or at most 0.08 g / g. This applies both to the production of a material for a solid-state battery and to the production of a component.

[0020] In one embodiment, a NaSICON-containing material for a solid-state battery is produced. In particular, the starting material contains reactants for producing NaSICON. For example, the starting material contains a mixture of reactants for producing NaSICON, e.g., a mixture of sodium nitrate, zirconium nitrate, tetraethyl orthosilicate, and ammonium dihydrogen phosphate for producing Na3.4Zr2Si2.4Po.60i2 (NZSiP3.4). The mixture of reactants for producing NaSICON is, in particular, such that NaSICON can be produced by sintering without the addition of further substances (complete mixture). Reactants or precursors for producing NaSICON refer to substances that can be heated together in mixed form and, in particular, also pressed to produce NaSICON in this way.It can be advantageous to perform at least one heat treatment before pressing at a temperature, for example, between 750°C and 800°C, particularly to burn off the nitrates, and typically to subsequently grind the mixture. In particular, the mixture being heated contains no further additives besides the sodium source and H3BO3. In particular, a NaSICON-containing material, preferably one consisting of NaSICON, is produced for a solid-state battery. This is also referred to as synthesis. Sintering occurs during heating, so the heating step is also referred to as sintering. Sintering creates a NaSICON crystal structure, which leads to the well-known high ionic conductivities.

[0021] Compared to conventional processes, the typically multiple calcination steps and the grinding between them are eliminated. Furthermore, the temperature is reduced.

[0022] NaSICON are substances with the formula M 1 1+2w+x-y+zM ll w M lll x(Zr, Hf) IV 2-wx-yM v y (SiO4)z(PO4)3-z. Where M 1 Well, M", M 111 and M v are suitable divalent, trivalent, or pentavalent metal cations. For example, M" Mg 2+ , Ca 2+ , Sr 2 *, Ba 2+ , Co 2+ and / or Ni 2+ For example, M 111 Al 3+ , Ga 3+ , Sc 3+ , La 3+ , Y 3+ , Gd 3+ , Sm 3+ , Lu 3+ , Fe 3+ and / or Cr 3 * For example, M v V 5+ , Nb 5+ and / or Ta 5+ Any combination is possible.

[0023] NaSICON can still produce substances with the formula Nai+xZr2Si xP3-xOi2, 0 < x < 3. It can also include substances that are structurally constructed according to the formula mentioned and in which a portion of Na, Zr, and / or Si is replaced by isovalent or equivalent elements. NaSICONs are solids. NaSICONs exhibit high conductivity for sodium ions and negligible electron conduction. Examples of NaSICONs are further Na3.4Zr2.o(SiO4)2.4(PO4)o.6 and Nai+. x Zr2(SiO4)x(PO4)3-x (0 x < 3), the latter substance also being called NZSP.

[0024] NaSICON can be produced, for example, by a solid-state reaction (SSR), by a sol-gel reaction such as a solution-assisted SSR (SA-SSR), or by coprecipitation. In conventional processes, a calcination step above 1000°C is always necessary, as otherwise the correct crystal structure of NaSICON cannot be formed. As described, this is no longer necessary due to the additives of the invention.

[0025] Alternatively or additionally, the starting material can contain intermediates for the production of NaSICON, which is described further below. In a supplementary or alternative embodiment, a component for a solid-state battery is produced. In this and other embodiments, the component is in particular a densely sintered component. The starting material can contain at least one reactant for the production of NaSICON or a mixture of reactants for the production of NaSICON, for example as described above. In this case, the synthesis of the NaSICON and the sintering of the component can take place together in one step. This is also referred to as reactive sintering. For example, this takes place to produce a separator.

[0026] In conventional processes, such as those used to manufacture the separator, NaSICON is produced by repeated calcination, powdered, pressed into the desired component shape, and then sintered at temperatures between 1200 °C and 1300 °C (in the case of NZSP, for example, 1260 °C). Until now, good ionic conductivity could only be achieved at such high temperatures. The invention allows a complete mixture of reactants for producing NaSICON, together with the additives, to be sintered once at a significantly reduced temperature to produce the NaSICON component with good ionic conductivity in a single step.

[0027] In an alternative or additional embodiment, the starting material contains at least one intermediate for producing NaSICON or a mixture of intermediates for producing NaSICON. The starting material can contain a mixture of calcined reactants for producing NaSICON and / or a calcined mixture of reactants for producing NaSICON. In particular, the intermediate contains calcined powder.

[0028] In particular, an intermediate for the production of NaSICON (also referred to as a precursor) is a calcined reactant for the production of NaSICON, a mixture of calcined reactants for the production of NaSICON, or a calcined mixture of reactants for the production of NaSICON. An intermediate may already have a NaSICON crystal structure in part, but typically less than 20%, in particular less than 10%. In other words, the NaSICON crystal structure is produced by heating. In particular, the component contains a NaSICON portion which has a NaSICON crystal structure in part to more than 70%, in particular more than 90%, preferably more than 95%, and in one embodiment more than 98%. In one embodiment, a mixture of calcined powders or a calcined mixture of powders is used as the intermediate for the production of NaSICON.These are mixed with the additives according to the invention, for example, in one of the ways described below. Heating typically then follows. This can be done as a further calcination to produce the component. This typically takes place in an oxygen-containing atmosphere.

[0029] In one embodiment, the starting material contains a mixture of at least one reactant for producing NaSICON and at least one intermediate for producing NaSICON. In one embodiment, a mixed electrode, for example a mixed cathode, is produced as a component, typically sintered. In particular, a mixed electrode contains phases of different materials, as described in detail below.

[0030] In one embodiment, a starting material, preferably an intermediate for the production of NaSICON, is produced wet-chemically. Such a starting material can be fired in an additional step before heating, for example, at a temperature between 700°C and 850°C, typically at about 800°C. This can decompose nitrates, for example. Firing can produce an intermediate for the production of NaSICON.

[0031] In an alternative or additional embodiment, the starting material contains NaSICON itself. For example, the starting material can contain fully crystalline NaSICON powder. The additives according to the invention, which here serve as a sintering aid, allow the temperature to be lowered as described without the need to generate NasBO.

[0032] Any mixtures of the aforementioned constituents of the starting material are possible. In other words, the component can be produced from starting materials for the production of NaSICON, intermediates, and / or NaSICON itself. In particular, the starting material is such that NaSICON can be produced or obtained without the addition of further substances. In particular, the starting material in this embodiment does not contain NaSICON. Already produced NaSICON material, for example in powder form, is used. In particular, the NaSICON material is already produced according to the invention. Here, too, a significantly lower temperature is required compared to conventional processes.

[0033] In particular, this configuration is used to produce electrodes. Here, an active material and NaSICON, especially in powder form, are heated together with the additives according to the invention.

[0034] In a further embodiment, a component for a solid-state battery is produced, wherein the starting material contains a mixture of at least one intermediate for producing NaSICON, at least one reactant for producing NaSICON and / or NaSICON.

[0035] In one embodiment, the at least one starting material is provided in powder form. In one embodiment, the at least one starting material is mixed with the sodium source and the H3BO3, pressed into shape, and / or heated. In particular, the heating occurs after mixing and / or pressing. In this embodiment, particularly favorable starting materials can be used. Starting materials for the production of NaSICON, in particular in ground form, can be used as the starting material or starting materials. In other words, a solid-state reaction takes place.

[0036] Mixing with the sodium source and the H3BO3 can be carried out by preparing a solution of the sodium source and the H3BO3. For example, an aqueous solution is prepared. This can be mixed with the starting material. Alternatively or additionally, one or both of the additives according to the invention can also be added at least partially, and in particular completely, as a solid.

[0037] In one embodiment, a particularly aqueous solution of the additives according to the invention is prepared. An intermediate product, in particular in powder form, can be added to the solution. The solvent can be removed, in particular by evaporation or vaporization. In this way, the intermediate product can be coated with the additives according to the invention. The resulting uniform distribution of the additives according to the invention allows the production of a component to be carried out particularly advantageously. The starting material or materials can be ground together with the sodium source and the H3BO3. The grinding can be carried out dry or wet. The sodium source and / or the H3BO3 can be added in dry form or as a solution. Mixing can take place during grinding. This eliminates an additional mixing step. The starting material or materials can be slurried with a solution of the additives according to the invention.The mixture of the additives according to the invention and the starting material(s) can be dried. This can be done before and / or after slurrying. Alternatively or additionally, the starting material(s) can be wetted with a solution of the additives according to the invention.

[0038] In one embodiment, the ground starting material is pressed into shape together with the additives according to the invention and sintered into a component by heating.

[0039] In one embodiment, a separator is manufactured as a component. The separator typically comprises NaSICON. In particular, the separator is made of NaSICON. A separator can, for example, have the shape of a film or a cup.

[0040] In one embodiment, an electrode, for example a cathode, is produced as a component. The electrode can be composed of different phases. The electrode comprises, in particular, an ion-conducting phase comprising or consisting of NaSICON, and an active material, also called the active phase, for example, made of NNFM or NVP, as described further below. An electrode can also optionally have an electrically conductive phase. In particular, NaSICON and NNFM have the advantage that the lower temperature compared to the prior art reduces the occurrence of disruptive secondary phases during sintering.

[0041] A separator and, optionally, also an electrode can be produced particularly advantageously in a single step from at least one intermediate and / or at least one reactant for producing NaSICON. In conventional processes, a NaSICON powder was applied to a previously produced separator and then calcined and sintered. The invention enables direct production from reactants for producing NaSICON, intermediates for producing NaSICON, and / or NaSICON, thus reducing the number of process steps.

[0042] In one embodiment, the component comprises an electrode and a separator. In one embodiment, the electrode and separator are heated together and thus manufactured together in a single step.

[0043] In other words, the separator and electrode, for example the cathode, are produced in a single step. Production can be carried out from NaSICON or starting materials for producing NaSICON. Production of the electrode and the separator in a single step means that the sintered form of the electrode and the sintered form of the separator are produced in a single heating process. In particular, no electrode is present before heating. In particular, no separator is present before heating. In particular, the electrode and separator are arranged directly adjacent. In particular, a contact surface is present at which the separator and the electrode make surface-to-surface contact. In particular, the separator and the electrode are firmly connected to one another at the contact surface. The connection is preferably produced by a sintering process caused by the shared heating.

[0044] The separator is a component for the spatial and electrical separation of the electrodes, but which has ion-conducting properties. In conventional batteries, for example Li-ion batteries, the separator is a film impregnated with a liquid electrolyte. The separator according to the invention typically consists of an ion-conducting ceramic, i.e., the solid electrolyte. The electrode can be a cathode or, particularly in the case of a symmetrical solid-state battery, an anode. The electrode comprises, in particular, an active material. In particular, the electrode comprises NVP (Na x V2P30i2) or preferably at least one layered oxide such as NNFM (NaO,6?[FeO,iNio,iMno,8]O2), a sodium manganese oxide with nickel and iron (Na x [Feo,iNio,iMno,8]02 or Nao.67[Ni0.33Mn0.67]02 or with Co, as in Na[Nio,33Mn0.33Coo,33]02, Na x CoO2 (general: Na xMÜ2 with M = Mn, Ni, Co, Fe, Mg or a mixture of 2 or 3 of the elements) or oxides with a tunnel structure, such as NaO,6i[FeO,34Tio,39MnO,27]O2. Similar to the metal in the oxide structures, the V in NVP can also be substituted, e.g., with Al, Fe, Ti or similar. A general notation, for example, can be Na3V2- x M x (PO4)3 with x typically between 0 and 1. Deviations are possible. Due to the reduced temperature, the different phases of the electrode can be heated together. This allows for new material combinations.

[0045] In one embodiment, in particular before heating, a material is applied to a body or a material, thus enabling joint heating. For example, a starting material for producing the separator can be applied to a starting material for producing an electrode, or vice versa. Alternatively, the starting material for producing the separator can be applied to a prefabricated electrode or an electrode precursor. Analogously, a starting material for producing the electrode can be applied to a prefabricated separator or a separator precursor. A precursor of a respective component is a not yet fully sintered component, which can then be densely sintered and which preferably already has a certain dimensional stability. For example, a slip can be applied.The application can be carried out, for example, by film casting, vacuum slip casting, roller coating or printing processes such as screen printing.

[0046] In conventional processes, the ceramic electrolyte or separator is first produced by sintering at temperatures above 1200 °C. The desired cathode active material is then applied to the finished electrolyte. Further calcination removes additives such as solvents or organic binders, establishing good contact between the electrolyte and the active material. The production of electrolyte and electrode in a single step has not yet been possible for most electrode active materials, as the necessary sintering of the electrolyte above 1200 °C would decompose the electrode's active material or render it unusable by reacting with the electrolyte. This is especially true for layered oxides, which exhibit higher capacity than NVP and are also cheaper and less toxic.

[0047] In one embodiment, a half-cell, i.e., a system consisting of a separator and an electrode, is produced as the component. In one embodiment, a full cell, i.e., a system consisting of a separator and two electrodes, typically arranged on opposite sides of the separator, is produced as the component. In particular, the full cell is a symmetrical cell, i.e., a cell in which the anode and cathode are identical, preferably containing NVP or NNFM.

[0048] Each of the described components can be produced from NaSICON, at least one intermediate for producing NaSICON, and / or at least one reactant for producing NaSICON. Particularly advantageous for achieving the object when producing an electrode and / or a component comprising a separator and an electrode is the use of at least one intermediate for producing NaSICON and / or NaSICON.

[0049] In one embodiment, a component for a solid-state battery is produced. In particular, the component is a solid-state battery cell that comprises or consists of a separator and two electrodes. In particular, the electrodes are arranged on both sides of the separator and / or on opposite sides of the separator.

[0050] In one embodiment, the solid-state battery cell is a symmetrical solid-state battery cell with two electrodes. The electrodes can be of the same type. In particular, the electrodes have the same composition. In particular, the cathode and anode are constructed in the same way. In particular, both electrodes comprise the same NaSICON material. In a further embodiment, an anode comprises an anode active material and a cathode comprises a cathode active material, wherein the anode active material and the cathode active material are different and, in particular, each comprise different NaSICON compounds.

[0051] In one embodiment, the heating takes place in an oxygen-containing atmosphere. The atmosphere can be oxygen. In particular, however, an air atmosphere can be used. In other words, the heating is a calcination. This takes place in particular for producing NaSICON-containing material for a solid-state battery and / or a component from at least one intermediate product and / or at least one reactant for producing NaSICON. In addition to the above-described saving of the series of work steps and the temperature reduction, the need for an inert gas atmosphere, e.g., an argon atmosphere, is also eliminated. The technical complexity is thus further reduced. The above-described production of a component comprising a separator and an electrode can also take place in an oxygen-containing atmosphere.This is particularly possible when using NNFM as electrode active material, even when producing the component from at least one intermediate and / or at least one reactant for producing NaSICON.

[0052] This is also possible if a different electrode active material is used, such as NVP. However, if particularly high demands are placed on the properties of the component, it is advantageous to produce NaSICON in a first step, preferably in an oxygen-containing atmosphere, and then to produce the component comprising the NaSICON and the active material in a subsequent second step under an inert gas atmosphere, e.g., an argon atmosphere. The process is similar for bonding the ion-conducting ceramic to the cathode active material.

[0053] A further aspect of the invention is a solid-state battery cell that can be produced or is produced by the method according to the invention. The solid-state battery cell comprises a separator and two electrodes. The electrodes can be of the same type and / or have the same composition. The electrodes can be made of the same material or materials and / or have the same structure. In particular, the electrodes are mixed electrodes. In particular, the cell is constructed analogously to a rocking-chair battery cell (conventional lithium-ion battery cell). In particular, the active material is not or not fully sodiated. All features, configurations, and advantages of the aspect of the invention mentioned above apply analogously to this aspect, and vice versa.

[0054] In one embodiment, at least one of the electrodes comprises NNFM, typically as the active material. In particular, at least one of the electrodes further contains NaSICON as an ion-conducting phase. In one embodiment, the separator comprises NaSICON. In particular, the separator is made of NaSICON. The separator is preferably manufactured according to the invention.

[0055] In one embodiment, at least one of the electrodes, for example the cathode, in particular both electrodes, comprises NNFM and NaSICON. In other words, these are mixed electrodes such as a mixed cathode. In particular, the mixed electrode is produced using the method according to the invention. In one embodiment, one of the two electrodes is made of sodium. In a mixed electrode, particles of NaSICON and the selected active material, e.g., NNFM, are present side by side. To produce a mixed electrode, reactants for producing NaSICON, intermediates for producing NaSICON, or crystalline NaSICON, in particular in powder form, can be mixed with the active material, preferably likewise as a powder, and heated. In other words, they are mixed and sintered together. The reactants, intermediates, or NaSICON are admixed with the additives according to the invention before heating.In particular, in this way, starting from respective powders, production can be carried out in a single sintering step.

[0056] A further aspect of the invention is a method for producing a material and / or a component for a solid-state battery, in which at least one starting material is heated together with a sodium source and an acid, in particular an inorganic acid, to a temperature between 600°C and 1300°C. In addition to H3BO3, HNO3, H3PO4, HCl, H2SO4, or H2SO3 can be used as the acid, for example. All features, configurations, and advantages of the aforementioned aspect of the invention apply analogously to this aspect.

[0057] All of the features, configurations and embodiments mentioned in this application can be combined with one another in any way, unless otherwise stated.

[0058] Below, exemplary embodiments of the invention are explained in more detail with reference to experiments and figures. Features of the exemplary embodiments can be combined individually or in multiples with the claimed subject matter, unless otherwise stated. The claimed scope of protection is not limited to the exemplary embodiments.

[0059] They show:

[0060] Fig. 1 : X-ray diffractogram of different samples,

[0061] Fig. 2: further X-ray diffractogram of different samples,

[0062] Fig. 3: schematic representation of a solid-state battery cell,

[0063] Fig. 4: X-ray diffractogram of different samples,

[0064] Fig. 5: Charge-discharge curves of a battery cell,

[0065] Fig: 6: schematic representation of a component of a solid-state battery cell, Fig. 7: a schematic sequence of a method according to the invention,

[0066] Fig. 8: Charging cycles of another battery cell over time, as well as

[0067] Fig. 9: Charge-discharge curves of the other battery cell.

[0068] Experiment 1

[0069] Na3.4Zr2Si2.4Po.60i2 (NZSiP3.4) was prepared according to the solution-assisted solid-state reaction described in the publication “Na3Zr2(SiO4)2(PO4) prepared by a solution-assisted solid state reaction” by Naqash, S., et al., (Solid State Ionics, 2017, 302: pp. 83-91) by dissolving stoichiometric amounts of sodium nitrate (NaNO3), zirconium nitrate (ZrO(NO3)2), tetraethyl orthosilicate (Si(OC2H6)4), and ammonium dihydrogen phosphate (NH4H2PO4) (molar ratio 3.4 / 2 / 2.4 / 0.6) in deionized water. The formed gel was thoroughly dried at 85 °C, ground to a fine powder, and ground in an electric mortar. well mixed. The resulting powder is a complete mixture of reactants for the production of NaSICON.

[0070] The powder was then calcined in air at 800 °C for 4 hours. The calcined powder was ball-milled in ethanol for 72 hours in a tumbler mixer using ZrO2 grinding balls (diameters 3 mm and 5 mm) to achieve a d50 particle size of < 3 pm or approximately 3 pm. The milled powder was finally dried to obtain an intermediate for the production of NaSICON. The intermediate for the production of NaSICON corresponds to a calcined mixture of starting materials for the production of NaSICON.

[0071] In Experiment 1a, sodium hydroxide (NaOH) and orthoboric acid (H3BO3) were used as additives, each in powder form. These were dissolved in deionized water in a molar ratio of 75% NaOH and 25% H3BO3, corresponding to 3 mol / mol. The intermediate for the preparation of NaSICON was added to the NaOH / HsBOs solution with stirring. The mixing ratio was 0.71 g of additives for 10 g of intermediate. The solvent (water) was evaporated with continuous stirring on a magnetic stirrer hotplate to coat the intermediate for the preparation of NaSICON with the additives of the invention. The dried powder was pulverized in an agate hand mortar and pressed at a pressure of 100 MPa into cylindrical pellets with a diameter of 13 mm. For comparison, the intermediate without the additives was also pressed at 100 MPa into pellets with a diameter of 13 mm. Alternatively, pellets can also be pressed at higher pressures, e.g. 200 MPa.Instead of pellets, any components for a solid-state battery can be produced in the same way. The pellets are then heated, or sintered.

[0072] Table 1 shows the exact sintering parameters and the resulting densities (relative density as a percentage of the maximum achievable density) and ionic conductivities after sintering. The pressing force was applied uniaxially in each case. The measurement temperature refers to the ionic conductivity.

[0073] Sintering temperature in measuring temperature ion conductivity relative pressing force

[0074] °C in °C (a total ) m mS / cm density without additives

[0075] 15kN (uni) 1260 23 4.46 98% with additives

[0076] 15kN (uni) 1050 23 3.66 93%

[0077] 15kN (uni) 1000 23.3 3.65 94%

[0078] 15kN (uni) 950 23.3 3.48 98%

[0079] 15kN (uni) 900 20 2.33 96%

[0080] 15kN (uni) 850 23.5 1 .38 92%

[0081] 30kN (uni) 850 23.8 1.65 93%

[0082] The maximum density achieved is at 950°C, with very high ionic conductivity. Good densities and ionic conductivities are also achieved at lower temperatures. Overall, it can be seen that the additives according to the invention can reduce the sintering temperature by several hundred degrees Celsius.

[0083] Figure 1 shows an X-ray diffractogram of the various samples produced by conventional and inventive processes. The diffraction angle in 2° is plotted on the x-axis, and the intensity in arbitrary units is plotted on the y-axis. The intermediates for the preparation of NaSICON were each prepared using SA-SSR after calcination for 4 hours. A stands for the intermediate without the inventive additives and without further heating. B to H stand for the materials or components produced by further heating. Each was heated (sintered) for 6 hours. B stands for sintering at 900 °C without the inventive additives (conventional process at reduced temperature). H stands for sintering at 1260 °C without the inventive additives (conventional process). C to G stand for the materials or components produced with the inventive additives.C stands for sintering at 850 °C; D stands for sintering at 900 °C; E stands for sintering at 950 °C; F stands for sintering at 1000 °C; G stands for sintering at 1050 °C.

[0084] It is evident that A has a completely different crystal structure. It contains less than 5% or less than 1% as the NaSICON phase. B shows a poor result. Thus, simply reducing the temperature without additives does not produce the desired NaSICON phase. Only approximately 20% is present as the NaSICON phase; the influence of the secondary phase is strong. The peaks marked with a diamond (#) indicate a Na2ZrSiO? phase. C to G are all comparable to H, i.e., the NaSICON phase produced by the conventional process. The peaks marked with an asterisk (*) indicate a ZrO2 secondary phase. However, this can never be completely avoided and is not very present here. At least 99% is present as the desired NaSICON phase.

[0085] The reduced temperature during sintering of components is likely due, at least in part, to liquid-phase sintering caused by the additives used. Gaps are closed by a forming melt. Reactive sintering is also assumed, which occurs particularly during the formation of the crystal structure during the production of NaSICON.

[0086] In modifications of the experiments, mixing ratios of 0.036 g / g and 0.142 g / g achieved lower ionic conductivities. Consequently, mixing ratios between 0.036 g / g and 0.142 g / g are preferable. However, even with unfavorable mixing ratios, the achieved ionic conductivities are still much better than without the additives according to the invention. The mixing ratios mentioned here and above show particularly good results when using NaOH. With other sodium sources, slightly modified mixing ratios can achieve optimal results. In Experiment 1b, H3BO3 was added during the preparation of the mixture of reactants, particularly in the form of a gel, for example, using SA-SSR. The addition took place simultaneously with sodium and / or zirconium nitrate. This eliminates the need for the additive to be subsequently mixed with the intermediate for the production of NaSICON.

[0087] Table 2 shows the sintering parameters analogous to Table 1 above. Reference is made to the above explanations. Unless otherwise stated, sintering was carried out for 6 h in each case. In one case, an isostatic pressure was applied in addition to the uniaxial force.

[0088] Sintering temperature in measuring temperature ionic conductivity Relative

[0089] Press force

[0090] °C in °C (a total ) in mS / cm density 15kN uni 1260 23 0.78 88%

[0091] 15kN uni 1150 25 2.68 92.5%

[0092] 15kN uni 1100 25 2.44 94%

[0093] 15kN uni 1050 23 1 ,94 96%

[0094] 29n0n0n0hb U a n r i is + O 1050 1.83 95%

[0095] 15kN uni 1000 23.3 1.52 97.5%

[0096] 15kN uni 950 23.3 1 .10 97%

[0097] 15kN uni 900 20 0.82 96%

[0098] 30kN uni 850 23.8 0.60 89%

[0099] Due to the different manufacturing processes, the resulting NaSICON compound may have a different composition. A general structural formula can be as follows: Na 1+x+2y Zr2Si x P 3 x y B y O 12i WOwhere an optimal window for y is between 0.1 and 0.4 and preferably between 0.2 and 0.3, corresponding to the boron concentration of the additive according to the invention. The numbers for the initial weight are calculated as if boron were incorporated into the NaSICON structure. During sintering, however, a boron-containing secondary phase can also occur, which forms at the grain boundary and is not incorporated into the crystal structure. Rather, the structural formula given is the molar element distribution in the entire material and not necessarily a chemical structural formula of the phase(s) present. Depending on the requirements, for example with regard to the conductivity of the NaSICON compound, x can be between 1.4 and 2.2, preferably between 1.6 and 2.0.It is shown that the correct NaSICON phase is formed even at low temperatures (850 °C), although the density and ionic conductivity do not quite reach those achieved in Experiment 1a.

[0100] Experiment 2

[0101] The starting materials Na2CO3, ZrSiO4, SiO2, and NH4H2PO4 were weighed in stoichiometric ratios and ground in ethanol in a planetary ball mill equipped with ZrO2 grinding balls. This resulted in a mixture of reactants for the production of NaSICON. The additives according to the invention were added to the ground powder in a molar ratio of 3 mol NaOH per mol H3BO3. 0.071 g of the additive mixture was added per gram of ground powder. The resulting powder was pressed into pellets and sintered (900 °C or 1050 °C).

[0102] Figure 2 shows an X-ray diffractogram of the various samples (for the axes, see Figure 1 above), which were produced using conventional and inventive processes. The reactants for the production of NaSICON were each prepared using SSR. Each sample was heated (sintered) for 6 hours. A represents the mixture of reactants without the inventive additives and sintered at 1260 °C (conventional process). B represents sintering at 1050 °C with the inventive additives. C represents sintering at 900 °C with the inventive additives. The peaks marked with an asterisk (*) indicate a ZrO2 secondary phase, as in Figure 1.

[0103] It has been shown that even here, at significantly lower sintering temperatures, the correct crystal structure of the NASICON phase can be obtained with a single heat treatment, along with good densification and ionic conductivity. This is achieved by means of a solid-state reaction (SSR). In this case, at least 90%, and in particular at least 95%, is present as the desired NaSICON phase. In addition, approximately 2-3% may be present as a secondary ZrO2 phase.

[0104] Figure 3 shows a simplified, schematic, and not-to-scale representation of a solid-state battery cell 35. Since a solid-state battery 30 can also consist of a single solid-state battery cell 35, Figure 3 also shows a solid-state battery 30. Typically, however, a solid-state battery 30 contains a plurality of solid-state battery cells 35, which are connected in series or parallel. These cells can be connected to one another via a current collector, for example in the form of a copper foil.

[0105] The solid-state battery cell 35 contains two electrodes 21 arranged on opposite sides of the separator 22. It is thus a full cell. The separator 22 acts as a solid electrolyte and is ion-conductive, but not or only very slightly electron-conductive (electrically conductive).

[0106] The solid-state battery cell 35 can be symmetrical and comprise NNFM (NaO,67[FeO,iNiO,iMnO,8]O2) as the active material of the electrodes 21. The electrode 21 can be an anode or a cathode. These can have the same or different structures. For example, a Na metal anode can be present. The solid electrolyte or separator 22 consists in particular of NaSICON. The solid-state battery cell 35 was manufactured in particular according to Experiment 3 and sintered in one step.

[0107] Experiment 3

[0108] To produce a free-standing or single electrode 21, the active material NNFM was arranged together with reactants for producing NaSICON and / or intermediates for producing NaSICON together with the additives according to the invention and sintered together at 900 °C.

[0109] Figure 4 shows an X-ray diffractogram of the various samples (for the axes, see the analogously constructed Figure 1 above) produced by conventional and inventive processes. A stands for crystalline active material NNFM. B stands for a mixture of reactants for the production of NaSICON with the additives according to the invention and sintering at 900 °C. C stands for a mixture of reactants for the production of NaSICON with the additives according to the invention and NNFM and sintering at 900 °C. D stands for the mixture of an intermediate for the production of NaSICON (in particular a calcined intermediate according to SA-SSR, see Experiment 1) with the additives according to the invention and NNFM and sintering at 900 °C. Sintering, i.e. heating, takes place for 6 hours in each case. The peaks marked with an asterisk * indicate a ZrO2 secondary phase, as already shown in Figure 1.

[0110] It has been shown that at the lower sintering temperature, the correct crystal structure of the NASICON phase and the NNFM phase can be obtained with a single heat treatment, as well as good densification. This is possible, for example, using solid-state reaction (SSR). In this case, a total of at least 90%, and in particular at least 95%, is present as the desired NaSICON phase and NNFM phase.

[0111] Experiment 4

[0112] To produce the electrodes 21, the active material NNFM was combined with reactants for producing NaSICON or intermediates for producing NaSICON, along with the additives according to the invention. To produce the electrolyte or separator 22, reactants for producing NaSICON or intermediates for producing NaSICON were combined with the additives according to the invention. The respective mixtures were arranged in the sequence shown in Figure 3 and sintered together to obtain the solid-state battery cell 35 in a single sintering step.

[0113] Figure 5 shows a diagram of the charging and discharging of a symmetrical battery cell produced using the method according to the invention. This is the battery cell from Figure 3. The first charge 1 stL is marked. In the smaller diagram, the efficiency Eff is plotted against the cycle number ZN. It shows that the battery cell was successfully charged and discharged multiple times with very good coulombic efficiency above 97%.

[0114] Experiment 5

[0115] To produce an electrode 21, the active material NNFM was arranged together with reactants for producing NaSICON or intermediates for producing NaSICON, together with the additives according to the invention. To produce the electrolyte or separator 22, reactants for producing NaSICON or intermediates for producing NaSICON were arranged together with the additives according to the invention. The respective mixtures were arranged as shown in Figure 6 and sintered together. In a further step, metallic sodium can be applied to the separator 22 as a further electrode 21, in particular as an anode, to obtain a solid-state battery cell.

[0116] Figure 7 schematically shows a process according to the invention. A starting material 1, a sodium source 2, and H3BO3 are mixed. The mixture is then heated 5 together. This results in a material 10 for a solid-state battery and / or a component 20 for a solid-state battery.

[0117] Figures 8 and 9 show diagrams of the charging and discharging of a battery cell produced using the method according to the invention. This is the battery cell from Figure 6, namely a full cell with a sodium anode, a separator made of NaSICON produced using the additives according to the invention, and a mixed electrode (cathode) made of NNFM and NaSICON produced using the additives according to the invention. The cathode and the separator were produced together in a single step. Figure 8 shows the charging cycles over time, and Figure 9 shows a representation analogous to Figure 5. It can be seen that the battery cell could be successfully charged and discharged multiple times.

[0118] In one embodiment, heating takes place over a period of at least 2 hours, in particular at least 3 hours, and / or less than 6 hours, in particular less than 5 hours. Due to the additives according to the invention, longer heating is not necessary.

[0119] In one embodiment, heating occurs only once. This can be the case, in particular, when producing a NaSICON-containing material using a starting material containing reactants for producing NaSICON or when producing a component for a solid-state battery using a starting material containing NaSICON. A double or even more frequent heating or sintering is not necessary due to the additives according to the invention.

[0120] In one embodiment, the starting material is such that it has a sodium content that corresponds stoichiometrically to the sodium contained in the NaSICON to be produced. In other words, the starting material is such that it is stoichiometrically suitable for producing NaSICON - at least in terms of sodium content. Since the sodium source is also added, more sodium is used overall than is stoichiometrically necessary for producing NaSICON. In one embodiment, the sodium content in a mixture of the starting material and the sodium source is superstoichiometric for producing NaSICON. In one embodiment, the ionic conductivity of the NaSICON-containing material or component produced is greater than 1 mS / cm at 25°C, in particular greater than 1.2 mS / cm and preferably greater than 1.5 mS / cm, particularly preferably greater than 1.8 mS / cm.In some embodiments, the ionic conductivity of the produced NaSICON-containing material or component is greater than 2 mS / cm, in particular greater than 2.5 mS / cm, and preferably greater than 3 mS / cm. As described, a particularly high ionic conductivity can be achieved due to the additives according to the invention. In a particularly preferred embodiment, the ionic conductivity is greater than 0.5 mS / cm and less than 3 mS / cm.

[0121] In one embodiment, heating is carried out in such a way that no melt is produced. This means that the starting material(s) are not completely or even largely melted. This applies, for example, to the use of calcined reactants for the production of NaSICON, as described in Experiment 1 above. In particular, heating is carried out to a temperature below the melting temperature of the starting material(s) used. The additives according to the invention are independent of this and can melt completely or partially.

[0122] In one embodiment, Na2CO3 and NH4H2PO4 are used and / or reactive sintering is performed. This may result in partial and / or temporary melting of the starting materials and / or decomposition products of the starting materials.

[0123] In one embodiment, the produced material is largely crystalline. In particular, at least 80%, preferably at least 90%, and especially at least 95% of the produced material has a NaSICON crystal structure.

[0124] In one embodiment, the NaSICON-containing phase of the produced component is largely crystalline. The component can comprise different materials. Typically, one of these is NaSICON or at least contains NaSICON. This material is largely crystalline in this embodiment. Therefore, no glass phase is produced in this embodiment, or only a negligible amount of glass phase is produced. In particular, a proportion of at least 80%, preferably at least 90%, and in particular at least 95% of the NaSICON-containing phase of the component has a NaSICON crystal structure.

[0125] In one embodiment, the mixing ratio of the sodium source and H3BO3 is greater than 1 mol Na / mol H3BO3, in particular greater than 2 mol Na / mol H3BO3 and / or less than 6 mol Na / mol H3BO3, in particular less than 4 mol Na / mol H3BO3. Preferably, the mixing ratio is approximately 3 mol Na / mol H3BO3. This superstoichiometric sodium dosage has proven optimal for achieving high ionic conductivity and high relative density.

[0126] List of reference symbols

[0127] Source material 1

[0128] Sodium source 2

[0129] Heating 5

[0130] Material 10

[0131] Component 20

[0132] Electrode 21

[0133] Separator 22

[0134] Solid-state battery 30

[0135] Solid-state battery cell 35

[0136] First load 1 st L

[0137] Efficiency Eff

[0138] Cycle No. ZN

[0139] time

Claims

Claims 1. A method for producing a material (10) for a solid-state battery (30) and / or a component (20) for a solid-state battery (30), in which at least one starting material (1) is heated together with a sodium source (2) and H3BO3 to a temperature between 600 °C and 1300 °C (5).

2. Process according to claim 1, characterized in that the temperature is below 1100 °C, in particular below 1000 °C and preferably below 900 °C.

3. Process according to one of the preceding claims, characterized in that NaOH is used as the sodium source (2).

4. Method according to one of the preceding claims, characterized in that a NaSICON-containing material (10) for a solid-state battery (30) is produced, wherein the starting material (1) contains reactants for producing NaSICON.

5. Method according to one of the preceding claims, characterized in that a component (20) for a solid-state battery (30) is produced, wherein the starting material (1) contains at least one reactant for producing NaSICON.

6. Method according to one of the preceding claims, characterized in that a component (20) for a solid-state battery (30) is produced, wherein the starting material (1) contains at least one intermediate product for the production of NaSICON.

7. Method according to one of the preceding claims, characterized in that a component (20) for a solid-state battery (30) is produced, wherein the starting material (1) contains NaSICON.

8. Method according to one of the preceding claims, characterized in that the at least one starting material (1) is in powder form, is mixed with the sodium source (2) and the H3BO3, is pressed into shape and is then heated (5).Method according to one of the preceding claims, characterized in that an electrode (21) or a separator (22) is produced as the component (20). Method according to one of the preceding claims, characterized in that the component (20) comprises an electrode (21) and a separator (22), wherein the electrode (21) and the separator (22) are heated together (5) and are thus produced together in one step. Method according to one of the preceding claims, characterized in that a component (20) for a solid-state battery (30) is produced, wherein the component (20) is a solid-state battery cell (35) comprising a separator (22) and two electrodes (21). Method according to the preceding claim, characterized in that the solid-state battery cell (35) is a symmetrical solid-state battery cell (35) with two electrodes (21) of the same type.Method according to one of the preceding claims, characterized in that the heating (5) takes place in an oxygen-containing atmosphere. A solid-state battery cell (35) produced according to the method according to one of the preceding claims, comprising a separator (22) and two electrodes (21). A solid-state battery cell (35) according to the preceding claim, characterized in that at least one of the two electrodes (21) comprises NNFM and NaSICON and / or the separator (22) comprises NaSICON. A solid-state battery cell (35) according to one of the two preceding claims, characterized in that one of the two electrodes (21) is made of sodium.

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