WO2025262054A1 - Sodium ion conductor, method for the production thereof, and use thereof - Google Patents

Abstract

The invention relates to a sodium ion conductor, in particular for use in a sodium ion or sodium solid-state battery with at least one crystal phase and more than 28 mol.% Na2O and the components SiO₂, oxides of rare earths and at least one of the components Al₂O₃, B₂O₃ and/or P₂O₅. A sodium conductivity at room temperature of more than 10^-5 S/cm can be achieved. The invention further relates to a method for producing a sodium ion conductor of this type and to the uses thereof, in particular as a component of a sodium ion battery or a sodium solid-state battery.

Description

Sodium ion conductors, methods for their production and their use

The present invention relates to a sodium ion conductor, a method for its production, and the use of the sodium ion conductor in a sodium ion battery, in particular a sodium solid-state battery.

Batteries are used in a wide variety of applications. They are indispensable in small portable electronic devices such as smartphones, tablets, and laptops, as well as on a larger scale in electric cars and stationary energy storage systems. Lithium-ion batteries are frequently used, especially in applications requiring high energy density. The extraction of lithium and other raw materials necessary for the production of these batteries, such as copper, cobalt, and manganese, is complex and sometimes associated with environmental problems.

Sodium-ion batteries are being discussed as a rational alternative. These are based on environmentally friendly raw materials with high global availability. They can be manufactured with either a liquid or a solid electrolyte. Organic liquid electrolytes generally have the disadvantage of being flammable and often toxic or environmentally harmful. Sodium batteries with water-based liquid electrolytes, which do not have this disadvantage, achieve only low energy densities and are therefore only conditionally suitable for mobile and stationary applications. Batteries with solid-state sodium ion conductors are proposed as a solution to these problems. Since these solid-state ion conductors often have insufficient conductivity at room temperature, they were used in the past in so-called thermal batteries at high temperatures (300°C or more). However, this solution is disadvantageous for both safety and cost reasons and is not suitable for mobile applications.

Two classes of materials are known from the prior art that exhibit sufficiently high sodium conductivity even at room temperature: sodium β-aluminate and NaSICon (NaI⁺ _x Zr₂SixP₃-xOI₂ and derivatives thereof). The production of these materials generally requires complex ceramic processes at high temperatures, as described, for example, in US 4049891 A. and US 3475223 A, which results in significant manufacturing effort. Particularly when manufacturing using ceramic processes, producing pore-free components for batteries is extremely difficult.

Glass-based or glass-ceramic sodium ion conductors are also known, for example from US 3829331 A or DE 2811688 A. Production via a melting process allows for large-scale manufacturing and, depending on the glass system, shaping by rolling or drawing. However, the aforementioned systems with good conductivity, such as NaSICon or β-Al₂O₃, are difficult to produce via glass melting due to their high melting temperatures. For example, US patent US 4465744 B for NaSICon describes that melting temperatures of 1600°C are necessary and the glass melt must be cooled very rapidly at 100°C/sec. In practice, these high melting temperatures lead to a lower yield due to the formation of melt remnants and uncontrolled devitrification, and also to high energy consumption.

Silicate sodium ion conductors containing rare earth elements are described in US 4097345 A and US 4223077 A. They were manufactured via a solid-state reaction. The maximum conductivities achieved were 0.1 S/cm at 200°C. However, sufficient ionic conductivities were only achieved at 200°C, not at room temperature.

Production using a solvent-based process and spray drying has also been described, see EP0151925 A2. Here too, acceptable conductivities were only achieved at 300 °C.

US patent application 2022271330 A describes a glass-ceramic ionic conductor with the composition NaxMxSixOx (M = Gd or Y, x is an integer) that exhibits a high conductivity of > ^10⁻⁴ S/cm at room temperature. However, its production requires a complex process involving various mixing and/or milling steps in organic solvents followed by a sintering step at temperatures exceeding 1000°C. The object of the present invention is therefore to provide a sodium ion conductor which has high conductivity at room temperature and allows rational large-scale production.

The object of the invention is achieved by the subject matter of the independent claims. Specific and preferred embodiments are found in the dependent claims and in the description of the present disclosure.

The invention thus relates to a sodium ion conductor suitable for use in a sodium-ion or sodium solid-state battery, which contains at least one crystalline phase and more than 28 mol% Na₂U as well as the components SiO₂, rare earth oxides and at least one of the components Al₂O₃, B₂O₃ and/or P₂O₅. This naturally implies that the aforementioned components can be present in any combination.

The inventors recognized that such sodium ion conductors exhibit high sodium conductivity. High conductivity, as defined by the invention, is a sodium conductivity at room temperature of more than ^10⁻⁵ S/cm, advantageously more than ^10⁻⁴ S/cm. Upper limits of 0.5 S/cm or 1 S/cm can be expected.

In an advantageous embodiment, the sodium ion conductors contain at least 55 vol%, preferably at least 60 vol%, of the aforementioned crystal phase Na _5+q (R)(M) ₄ 0i2 (R=divalent, trivalent, tetravalent or pentavalent ions, M=Si and optionally P or B) as the main crystal phase, wherein q denotes the sodium excess compared to the stoichiometric composition and preferably q > 0.

This crystal phase, or more specifically the main crystal phase, can be described by the following formula:

Na⁵ _{+ q} (R)(M)⁴⁰i²±o, where R is selected from rare earth elements, aluminum, divalent ions (Mg, Ca, Sr, Ba, Zn), tetravalent ions Zr, Hf, Ti, as well as Ta or Nb, and M is selected from Si, B, and P, and the sodium excess is preferably q > 0. All elements are It is completely oxidized. Due to the different charges of the cations R and M, the O content can deviate by μ from the ideal composition.

Advantageous are the trivalent ions selected from the rare earths, aluminum and/or iron, and/or the divalent ions selected from Mg, Ca, Sr, Ba and/or Zn, and/or the tetravalent ions selected from Zr, Hf and/or Ti, and/or the pentavalent ions selected from tantalum and/or niobium. Naturally, all combinations are possible and covered by the invention.

The sodium ion conductor advantageously contains only a small amount of less conductive secondary crystal phases, or simply secondary phases, such as Na2SiO3, Nas(R)(M)3O9 and NagRMeOis.

Accordingly, an advantageous sodium ion conductor has a main crystal phase and, optionally, minor crystal phases that constitute less than 30 vol%, preferably less than 20 vol%, of the total crystal phase. Most preferably, the sodium ion conductor contains no minor phases.

According to an advantageous embodiment, the molar composition of the sodium ion conductor is given by (in mol%):

Na ₂ O 28 - 60%, advantageous 30 - 50%

RE2O3 0.1 - 15%, advantageous 1 - 10%, particularly advantageous 2 - 8%.

_SiO2 35-75%, advantageous 40-60%.

P2O5 0 - 10%, advantageous 0.1 - 8%, particularly advantageous 0.5 - 5%.

AI2O3 0 - 10%, advantageous 0- 5%.

MgO+CaO+SrO+BaO+ZnO 0 - 10%, advantageously 0- 5%.

B2O3 0 - 8%, advantageous 0 - 5%, particularly advantageous 0 - 3%

_ZrO₂ + _HfO₂ 0 - < 20 mol %, advantageous

Nb2Os+Ta2O5 0 - 10%, advantageous 0 - 5%

SO3 0-10%, advantageous 0-5%, particularly advantageous <5% F+Cl+Br+I 0 - 10%, advantageous 0- 5%, particularly advantageous < 5%

In a particularly preferred embodiment, the sodium ion conductor is free of Nb2Ü5 and/or Ta2Os.

RE2O3 represents the sum of the rare earth oxides SC2O3, Y2O3, La2Os, Ce2O3, Pr2O3, Nd2Ü3, Srr Os, EU2O3, Gd2Os, Tb2Os, Dy2O3, HO2O3, Er20s, Trri2O3, Yb2Ü3 and LU2O3, including any combinations thereof.

F, CI, Br and/or I may be present individually or in combination within the specified limits. The same applies in principle to the use of the symbol '+', which means that the elements associated with it may be present individually or in combination.

RE2O3 is preferably selected from Y2O3, Gd2Ü3, Nd2Ü3, Pr2O3, La2Ü3 and Yb2Ü3, either individually or in any combination.

It should be emphasized that the preferred areas of one component can be combined with any areas of other components. In other words, all areas for components and/or component groups included in this description can be combined with the areas for other components and/or component groups. The same applies to the selection of specific components.

In one embodiment, the sum of the components Al₂O₃ + B₂O₃ + P₂O₅ is greater than 0.1 mol%, particularly preferably > 1 mol%. Upper limits of <30 mol%, <20 mol%, or <10 mol% can be specified. This improves glass formation during melt production.

In a particularly preferred embodiment, the ratios of the cations (all values given in cation percent) in the sodium ion conductor are such that (P-Al) ■ 0.2 + 1 < Na/R < (P-Al) ■ 0.2 + 8, preferably (P-Al) ■ 0.2 + 4 < Na/R < (P-Al) ■ 0.2 + 7. Here, R represents the metal cations R (RE, Al, Fe, Zr, Ti, Hf, Nb, Ta, Zn, Mg, Ca, Sr, Ba), and RE represents the rare earth cations. These and/or their selection have been described above. For compositions that If this condition is met, a particularly high proportion of the highly conductive Nas+q(R)(M)40i2±ö crystal phase is formed during ceramicization. With a lower Na/R ratio, phases with a lower sodium content are favored, while with a higher ratio, those with a higher sodium content are preferred. However, these crystal phases generally exhibit lower conductivity, resulting in a lower overall conductivity of the sodium-ion conductor.

It has also proven particularly advantageous if the sodium ion conductor has a ratio of Na to the sum of all metal cations R that lies between 1 and 7, preferably between 2.4 and 6.8. R represents RE, AI, Fe, Zr, Ti, Hf, Nb, Ta, Zn, Mg, Ca, Sr, Ba and/or combinations thereof.

Advantageously, the composition of the sodium ion conductors according to the invention satisfies the condition Na / (Si+P-RE-Fe-Al) < 2. It has been found that this reduces the formation of sodium-rich side phases such as the Ng phase. In this formula, '+' and '-' denote the mathematical operators, i.e., addition and subtraction.

The ratio of all metal cations R (RE, Al, Fe, Zr, Ti, Hf, Nb, Ta, Zn, Mg, Ca, Sr, Ba) to nonmetal cations M (Si, P, B), i.e., R/M, is preferably in the range between 0.1 and 0.3; the range between 0.18 and 0.28 is particularly advantageous, or in other words, 0.18 < R/M < 0.28. This achieves an optimum with respect to meltability, glass formation, and the formation of highly conductive crystal phases.

The ratio of P/Si should advantageously be less than 1, more advantageously less than 0.5, and in particular less than 0.2, since excessively high phosphorus contents lead to increased formation of secondary phases.

According to a particularly advantageous embodiment, the sodium ion conductor is essentially free of toxic or environmentally harmful components such as Sb, As, Te, V, Pb, Cd.

The term "essentially free" means that it contains at most impurities that are unavoidable in normal and economically viable production processes (e.g., due to raw materials). This means that the sodium ion conductor is specifically free of the elements mentioned. According to one embodiment, the sodium ion conductor is essentially free of toxic or environmentally harmful components such as Sb, As, Te, V, Pb, Cd and/or Ga, Ge, Ta and W, since the use of these components can lead to environmental pollution or inefficient procurement processes.

The term "essentially free" means that only impurities that are unavoidable in normal and economical processes (e.g., due to raw materials) are present.

According to another embodiment, the sodium ion conductor is essentially free of polyvalent ions, in particular free of Ce, Fe, V, Ti, Nb and Mo, since polyvalent ions can reduce the stability of the material relative to other components in a battery or can result in electronic conductivity which, when used as an electrolyte, can lead to self-discharge of the battery.

According to one embodiment, the oxygen in the sodium ion conductor can be replaced by other anions to achieve improved conductivity. These anions can be halides or sulfate ions. However, the halide content should be limited to avoid impairing stability in the presence of atmospheric conditions and/or humidity; it is therefore below 10 mol%, preferably below 5 mol%, and particularly preferably below 2 mol%. The halides are selected from the group consisting of fluorine (F), chlorine (Cl), iodine (I), and ferrous ions (Br).

The overall composition of the sodium ion conductor may differ from the composition of the Nas+q(R)(M)40i2±ö crystal phase.

In an advantageous embodiment, the sodium ion conductor consists of a glass ceramic with the main crystal phase Nas+q(R)(M)40i2±ö and a residual glass phase which has a lower melting temperature than the crystal phase and thus positively influences the sintering behavior.

A glass-ceramic within the meaning of the present invention is understood to be, in particular, a material that is produced by melting technology and subsequently transformed into a glass-ceramic by targeted cooling and/or subsequent heat treatment ("ceramization"). The material obtained after cooling the melt preferably contains less than 30% crystalline phase and is Amorphous phases are particularly preferred. During ceramization, the degree of ceramization, and thus the ratio of amorphous phase to crystalline phase, the microstructure, and possibly the type of crystalline phase, can be controlled by appropriately selecting the time and temperature conditions.

The production of the sodium ion conductor according to the invention preferably takes place in the following steps:

1. Provision and mixing of raw materials

2. Melting of the raw materials at 1200-1650 °C, preferably at 1300-1600 °C

3. Casting and cooling of the molten glass as a casting or ribbons

4. Ceramicization

5. Cold processing of the glass ceramic or grinding to produce sodium ion-conducting powder

Grinding the glassy material followed by ceramicization is possible, but not preferred, as partial sintering of the powder can occur during ceramicization. Furthermore, it has been observed that ceramicization of castings or ribbons, in contrast to ceramicization of powder, reduces the formation of side phases.

The sodium ion conductor according to the invention can be used as a solid electrolyte, an additive to a liquid or polymer electrolyte, or as a separator in combination with liquid electrolytes. Solid electrolytes can also be used in high-temperature batteries (250°C - 350°C), for example, sodium-sulfur batteries or Na-NiCl batteries. Sodium-MeCl₂ batteries (Me = Na, Fe, Zn, and others) are possible as Ni-free alternatives.

A membrane made of the sodium ion conductor according to the invention can also be used as an ion-selective membrane for chemical processes, e.g., for chemical syntheses using electrolysis or for recycling. Its use in sensors, e.g., gas sensors, is also possible.

In a preferred embodiment, particularly as a further processed product, the sodium ion conductor is in powder form, advantageously with a particle size distribution with a dso < 100 pm, preferably < 10 pm, particularly preferably <3 pm. The sodium ion conductor or the powder described above can be used in particular for the manufacture of a sodium ion battery or a sodium solid-state battery.

This ion-conducting powder is particularly advantageous for use in the production of thin membranes as an electrolyte or separator, or as a composite with electrode material to increase the ionic conductivity of the electrodes. This can be achieved by using binders, polymers, ionic liquids, and/or by means of a hot sintering process. The production of sintered bodies with other geometries (e.g., tubular shapes) is also possible. When a sintering process is used, the sintering temperature of the sodium ion conductor according to the invention is preferably below 1050°C, and particularly preferably below 1000°C. The sintering temperature according to the present invention is understood to be the temperature at which the sodium ion-conducting powder can be sintered into sintered bodies with a density of more than 90%, preferably more than 95%, of the theoretical density.

It is also possible to use the ion-conducting powder as a starting material for a coating process to produce conductive coatings.

The material according to the invention is suitable for the large-scale production of sodium ion conductors: common raw materials such as oxides, carbonates, hydroxides, or complex raw materials such as phosphates can be used as raw materials. For melt-based production, costly grinding of the raw materials or the use of expensive nanoscale raw materials can be avoided.

In hot-process manufacturing (melting or sintering), low-melting components can be lost through evaporation or dust formation. This loss is typically compensated for by using a superstoichiometric weight. Melting is advantageous here because the surface area to volume ratio of the produced material is more favorable (i.e., lower) than in powder-based ceramic manufacturing. If the sodium ion conductor is to be used further as a powder, it is advantageous during production via a glass-ceramic route to first produce and ceramicize thin glass ribbons. Rapid cooling of these ribbons induces stresses within them, which, during subsequent milling, lead to a reduction in process time.

The grinding is preferably carried out by a dry grinding process or by water grinding followed by drying.

Sodium ion conductors, especially in powder form, can be hygroscopic, which can lead to the formation of poorly conductive hydroxides or carbonates on the surface. Therefore, the ion-conducting powder is preferably processed and stored in a dry atmosphere or under protective glass, or dried in a post-processing step after contact with (atmospheric) moisture.

The invention will be explained in more detail below using examples.

Examples of compositions of sodium ion conductor materials according to the invention can be found in Table 1 (all values in mol percent). Examples 1-11 represent sodium ion conductors according to the invention, while examples V1-V6 are comparative examples.

The abbreviation RE2O3 stands for the sum of the rare earth oxides: SC2O3, Y2O3, La2Os, Ce2O3, Pr2Os, Nd2Ü3, Srri2O3, EU2O3, Gd2Os, Tb2Os, Dy2Os, HO2O3, Er2Os, Trri2O3, _Yb2O3 and _LU2O3 . Preferably, RE2O3 is selected from Y2O3, Gd2Ü3, Nd2O3, Pr2Os, La2Ü3 and Yb2Ü3 or combinations thereof.

The materials listed in Table 1 were melted and homogenized using raw materials commonly used in the glass industry at temperatures of approximately 1350 °C to 1650 °C. Castings were made from the molten material and then annealed in a cooling oven at the temperatures specified in the table, allowing the material to cool to room temperature. Test samples for ceramic coating were then prepared from these castings. Alternatively, the molten material was poured between two rotating rollers to produce ribbons, which were subsequently ceramic coated. For the ceramization processes, one- or two-stage programs were used, as specified in Table 1. In two-stage programs, the starting glass samples are first heated from room temperature to a nucleation temperature above T_{_g} and held there for a sufficient time for nucleation. The samples are then heated to the ceramization temperature and held there as well. In one-stage programs, the samples are heated directly to the crystallization temperature and held there.

Holding times for (optional) nucleation range from 0 min to 24 h, advantageously up to 6 h, followed by a ceramization step of 5 min to 48 h, advantageously 30 min to 12 h. Holding times can also be replaced by slow heating rates.

The crystal phases of the ceramicized samples were determined using X-ray diffraction (XRD). The crystal phases listed in Table 1 were identified by X-ray diffraction measurements on a Panalytical X’Pert Pro diffractometer (Almelo, Netherlands). CuKa radiation (X = 1.5060 A) generated via a Ni filter was used as the X-ray source. Standard X-ray diffraction measurements on both powder and solid samples were performed under a Bragg-Brentano geometry (0-20°). The X-ray diffraction patterns were measured between 10° and 100° (20° angles). The measurements were performed on ground sample material.

In the crystal phases, Ns _q stands for Nas+q(R)(M)40i2, Ng for NagRESieOis, N3 for NasRESisOg.

A distinction was made between the main crystal phase and the secondary crystal phase, with the main crystal phase being defined as the crystal phase whose proportion is the largest in relation to all crystal phases.

In examples 3-6, 9-11 and in the comparison examples V5, V7-V9, the proportion of the main crystal phase, as well as all crystal phases present in the glass ceramic, was additionally determined using a Riedveld analysis.

The conductivity of samples from Examples 3-7 was also determined at room temperature. For this purpose, the sample is sputtered on both sides with a gold layer and measured at room temperature using electrochemical impedance spectroscopy (EIS). The total conductivity is measured. The specified total conductivity is composed of the conductivity of the ion-conducting crystallites ("grain conductivity") and a grain boundary contribution, which exhibits a lower conductivity. The grain boundary contribution includes both the (lower) conductivity of an amorphous phase and, in the case of sintered bodies, the pores. Unless explicitly stated otherwise, in the context of this invention, conductivity or room-temperature conductivity refers to the total conductivity at room temperature.

The abbreviation "n.b." stands for "not determined".

Examples 1-11 according to the invention all show the ion-conducting phase _Na⁵⁺ q(R)(M) _₄O₂ as the main crystal phase. Any secondary phases present are detectable only in small quantities in the XRD measurements. The measured conductivities at room temperature range between 5 x ^10⁻⁵ S/cm and 3.4 x ^10⁻³ S/cm.

Ribbons were also produced from the composition in Example 7 by pouring the molten glass onto two counter-rotating metal rollers. The ribbons were ceramicized according to the temperature program specified in Table 1, then ground into a powder with a particle size of approximately 1 pm. This powder was then used to produce pellets, which were sintered at 900–1000°C. The conductivity of the pellets was in the range of ^10⁻³ S/cm for all samples, and the density was >90% of the theoretical density.

The comparative examples serve to illustrate individual aspects of the invention and are presented in Table 2. In comparative example V1, no rare earth elements are present; although a crystal phase isostructural to Nas+q(R)(M) ₄ Oi2 is formed (here designated as Nsq(Fe)), the presence of polyvalent iron ions results in low reduction stability and increased electronic conductivity. Furthermore, the amount of this crystal phase is insufficient for good conductivity.

Comparative examples V2-V4 demonstrate the importance of the dopants P2O5, Al2O3, and B2O3, the sum of which should not be zero. In all cases, the desired crystal phase forms as the main crystal phase, but not in sufficient quantity, and significant amounts of secondary phases are formed. Comparative example V5 illustrates that the ratio of metal ions to non-metal ions should preferably be less than 0.28, otherwise other crystal phases such as the less conductive phase NagGdSieOis will be formed.

In comparative example V6, the ratio of the Na/R components lies outside the preferred range. This also leads to the main crystal phase being the NagGdSieOis phase and not, as desired, the Nas+q(R)(M)40i2 phase.

Comparative example V7 has an excessively high P/Si ratio of more than 0.2, which leads to the formation of detrimental NasGdSisOg.

In examples V8 and V9, the less conductive crystal phase Ng is formed due to the cation ratio of Na/(Si+P-RE-Fe-Al) > 2, and consequently, the required conductivity of > ^10⁻⁵ S/cm is not achieved. However, by using a different ceramicization process (usually involving longer holding times), these compositions can be transformed into a glass-ceramic with higher proportions of the N₅q crystal phase, thus increasing the conductivity accordingly.

Table 1: Examples of implementation

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Table 2: Comparison examples (continued)

Table 2: Comparison examples (continued)

Table 2: Comparison examples (continued)

The invention is described below with reference to a figure.

Fig. 1 shows a graphical representation of the sodium ion conductivity (Y-axis, "Conductivity [S/cm]") of various glass-ceramic compositions as a function of their respective N5 volume percent in the crystal phase (X-axis, "N5").

[Vol.%]“). As can be seen, a conductivity of at least ^10⁻⁵ S/cm is required. An N5 volume percentage of 55 vol% or more is required, preferably an N5 volume percentage of more than 60 vol% is provided.

The values shown in the graph of Fig. 1 can be found in the following table:

Claims

Patent claims 1. Sodium ion conductor, especially for use in a sodium ion or sodium solid-state battery, comprising at least one crystalline phase and more than 28 mol% Na2Ü, as well as the components SiC>2, rare earth oxides and at least one of the components Al2O3, B2O3 and/or P2O5. 2. Sodium ion conductor according to claim 1 having a sodium conductivity at room temperature of more than ^10⁻⁵ S/cm, preferably more than ^10⁻⁴ S/cm, particularly preferably more than ^10⁻⁵ S/cm to 1 S/cm or more than ^10⁻⁵ S/cm to 0.5 S/cm. 3. Sodium ion conductor according to at least one of the preceding claims, wherein at least 55 vol%, preferably at least 60 vol% of the crystal phase Na _5+q (R)(M) ₄ 0i2 (R=divalent, trivalent, tetravalent or pentavalent ions, M=Si and optionally P or B) is contained as the main crystal phase and preferably q > 0. 4. Sodium ion conductor according to claim 3, wherein the trivalent ions are selected from the rare earth elements, aluminum and/or iron and/or wherein the divalent ions are selected from Mg, Ca, Sr, Ba and/or Zn and/or wherein the tetravalent ions are selected from Zr, Hf and/or Ti and/or wherein the pentavalent ions are selected from tantalum and/or niobium. 5. Sodium ion conductor according to at least one of the preceding claims, comprising at least one main crystal phase and minor crystal phases comprising less than 30 vol%, preferably less than 20 vol%, of the total crystal phase; preferably the sodium ion conductor has no minor crystal phases. 6. Sodium ion conductor according to at least one of the preceding claims comprising (in mol%): _Na2O28 - 60% preferably 30-50% RE2Ü3 0.1 - 15%, preferably 1 - 10%, particularly preferably 2 - 8%. _SiO2 35-75%, preferably 40-60% P2O5 0 - 10%, preferably 0.1 - 8%, particularly preferably 0.5 - 5% AI2O3 0 - 10%, preferably 0- 5% MgO+CaO+SrO+ BaO+ZnO 0 - 10%, preferably 0 - 5% B2O3 0 - 8%, preferably 0 - 5% _ZrO₂ + _HfO₂ 0 - < 20 mol %, preferably < 15 mol %, Nb2Os+Ta2O5 0 - 10%, preferably 0 - 5%, particularly preferably free of Nb2Ü5 and/or Ta2Os, where RE2O3 represents the sum of the rare earth oxides. 7. Sodium ion conductor according to at least one of the preceding claims, wherein the rare earth oxides RE2O3 are selected from Y2O3, Gd ₂ O ₃ , Nd ₂ O ₃ , Pr2O3, La2Ü3 and Yb2Ü3 or combinations thereof. 8. Sodium ion conductor according to at least one of the preceding claims, comprising Al2O3+P2O5+B2O3 >0.1 mol%, preferably > 1 mol% and particularly preferably <30 mol% or <20 mol% or <10 mol%. 9. Sodium ion conductor according to at least one of the preceding claims, wherein the cation ratio (P-Al) ■ 0.2 + 1 < Na/R < (P-Al) ■ 0.2 + 8, preferably (P-Al) ■ 0.2 + 4 < Na/R < (P-Al) ■ 0.2 + 7, wherein R represents the metal- Cations (RE, AI, Fe, Zr, Ti, Hf, Nb, Ta, Zn, Mg, Ca, Sr, Ba) and RE stands for the rare earth cations, preferably selected from Y2O3, Gd2Ü3, Nd ₂ O ₃ , Pr2O3, La2Ü3 and Yb2Ü3 and/or combinations thereof. 10. Sodium ion conductor according to at least one of the preceding claims, wherein the ratio of Na to the sum of all cations R is: 1 < Na/R < 7, preferably 2.4 < Na/R < 6.8, where R stands for RE, AI, Fe, Zr, Ti, Hf, Nb, Ta, Zn, Mg, Ca, Sr, Ba and/or combinations thereof. 11. Sodium ion conductors according to at least one of the preceding ones, where for the contained cations Na / (Si+P-RE-Fe-Al) < 2. 12. Sodium ion conductor according to at least one of the preceding claims, wherein the ratio of metal cations R to non-metal cations M is: 0.1 < R/M < 0.3; preferably 0.18 < R/M < 0.28, where R represents RE, AI, Fe, Zr, Ti, Hf, Nb, Ta, Zn, Mg, Ca, Sr, Ba and M represents Si, P, B and/or combinations thereof. 13. Sodium ion conductor according to one of the preceding claims, characterized in that P/Si < 1, preferably P/Si < 0.5, particularly preferably P/Si < 0.2. 14. Sodium ion conductor according to at least one of the preceding claims, which is substantially free of Sb, As, Te, V, Pb or Cd, of polyvalent ions and/or of Ga, Ge, Ta or W. 15. Sodium ion conductor according to at least one of the preceding claims, containing less than 10 mol% of oxygen of various anions, in particular containing less than 10 mol% of halides, preferably < 5 mol%, particularly preferably < 2 mol%. 16. A glass-ceramic sodium ion conductor according to at least one of the preceding ones, which contains or consists of at least one main crystal phase Nas+q(R)(M)40i2±ö and a residual glass phase, wherein the The residual glass phase has a lower melting temperature than the main crystal phase. 17. A method for producing a sodium ion conductor according to one of the preceding claims, comprising a melting process, preferably with the following steps: Provision and mixing of raw materials, Melting of raw materials at 1200-1650°C, preferably at 1300-1600°C, casting and cooling of the glass melt as castings or ribbons, ceramicization, Cold processing of the glass ceramic or grinding to produce sodium ion-conducting powder. 18. Sodium ion-conducting powder consisting of or comprising a sodium ion conductor according to at least one of claims 1-16, wherein the powder has a sintering temperature of less than 1050°C, preferably less than 1000°C. 19. Use of the sodium ion conductor according to at least one of claims 1-16 as a component of a sodium ion battery or a sodium solid-state battery or as an ion-selective membrane or as a sensor. 20. Use of the sodium ion conductor according to at least one of claims 1-16 or of a sodium ion-conducting powder according to claim 18 for the manufacture of a sodium ion battery or a sodium solid-state battery. [The text abruptly ends here, so the translation stops as well.]