Solid state ionic conductors

Abstract

The present disclosure relates to a solid state polycrystalline material with improved ionic conductivity that provides electrolyte for solid state batteries, including, inter alia, potassium ion batteries. The solid polycrystalline material is stable to atmosphere, and the preparation process is cheap and can be amplified.

Description

Technical Field

[0001] The present invention relates to a solid polycrystalline material with improved ionic conductivity, which provides an electrolyte for a solid-state battery. The solid polycrystalline material is stable to the atmosphere and has an economical and efficient preparation process. Background Art

[0002] Fast inorganic solid-state oxide ion conductors (ISOCs) with high conductivity for alkali metal ions are promising solutions for a variety of technological applications such as all-solid-state batteries, alkali metal sulfur batteries, and potentiometric gas sensors. In solid-state batteries in particular, the use of ISOCs instead of liquid ion conductors and polymer separators offers numerous advantages, such as higher thermochemical stability, a wider temperature and potential range for operating conditions, improved safety, higher energy density, and faster charging speeds. In other solid-state devices, such as potentiometric gas sensors, ISOCs can be used to replace larger, more expensive, and more power-hungry optical gas sensing solutions. The conductivity of alkali metal ions in ISOCs, the manufacturing cost, and the stability of these compounds under different operating conditions are key criteria for selecting a suitable electrolyte.

[0003] Conducting Li + ISOC has the highest conductivity among alkali metal ion conductors, with a lithium ion conductivity of 10 at room temperature. -8 to 10 -3 However, the high cost and scarcity of lithium limit the potential of such materials for large-scale technological applications such as all-solid-state batteries.

[0004] On the contrary, ISOCs, where alkali metal ions are abundant on earth, constitute a more cost-effective solution. + An example of a fast ion conductor includes the honeycomb layered tellurite K2Mg2TeO6. This material shows very high ionic conductivity of 40 mS / cm at 300°C and 0.01 mS / cm at 25°C when measured under argon. However, like most other K-ISOCs, K2Mg2TeO6 is hygroscopic and therefore needs to be stored under a protective atmosphere such as argon. Similarly, KSi2P3 is another K ion conductor candidate that also shows a high ionic conductivity of 2.6·10 -4 S / cm, but this material is also sensitive to air and moisture and therefore needs to be handled in a protective environment.

[0005] Therefore, there is still a need in the art to provide next generation inorganic fast solid state oxide electrolytes with K-ion conductivity, which ideally should be highly stable under ambient conditions, show fast K-ion conductivity over a relatively wide temperature range, and employ cost-efficient manufacturing processes, utilizing elements that are abundant and non-toxic on earth. The present application aims to meet this need by the invention disclosed herein. SUMMARY

[0006] Disclosed herein is a solid state electrolyte which constitutes a fast inorganic solid state oxide ion conductor (ISOC). The solid state electrolyte of the present disclosure is a polycrystalline potassium magnesium silicate whose structure is integrated by a co-corner polyhedral network of SiO4and MgO4moieties, thus each oxygen atom is bonded to both Si 4+ and Mg 2+ cations. The three-dimensional network of channels between the polyhedra provides a migration pathway for potassium cations present in superstoichiometric amounts. The superstoichiometry of potassium in the solid state electrolyte of the present disclosure is directly related to the increase in ionic conductivity compared to the stoichiometric analog.

[0007] Within the solid state structure of the electrolyte, the potassium cations are located at highly metastable interstitial sites, diffusing through the channels with very low activation energy barriers for migration. The lower activation energy barriers increase the potassium ion conductivity of the solid state electrolyte of the present disclosure compared to other solid state oxide electrolytes reported in the prior art, such as potassium beta-alumina solid state electrolyte (K-BASE), KAlO2and KFeO2.

[0008] Furthermore, as shown in the examples herein, the electrolyte has a K-ion conductivity at room temperature exceeding 10 -7 S / cm, and its electrochemical performance is essentially unaffected even when exposed to the atmosphere. Unlike the layered structure, the lattice in the co-corner framework of the solid state electrolyte provides exposed interstices that are too narrow to accommodate water molecules, thus enabling stability against moisture. Despite the increase in ionic conductivity, the electronic conductivity is four orders of magnitude lower. As shown in the examples herein, the electrolyte has a high densification level, which can ensure optimal performance of the particles and self-standing tapes in various applications, most notably as alkali metal ion conductive solid state electrolytes for batteries, such as potassium and / or sodium ion conductive solid state electrolytes for potassium and / or sodium batteries.

[0009] The above features, combined with the high densification level of the material, provide optimal properties for the development of solid state batteries, such as solid state alkali metal ion batteries, and in particular potassium ion batteries and / or sodium ion batteries, comprising the solid state electrolyte disclosed in the present application.

[0010] One aspect of the present application is a solid state electrolyte comprising a general formula of K2+X Mg 1-(X / 2) a potassium ion-conducting polycrystalline material of the general formula K

[0011] Another aspect of the present invention is a solid state electrolyte comprising a potassium ion-conducting polycrystalline material of the general formula K 2+X Mg 1-(X / 2) a potassium ion-conducting polycrystalline material of the general formula K

[0012] Another aspect of the present invention is a battery comprising:

[0013] an ion-conducting electrolyte layer,

[0014] a positive electrode layer, and

[0015] a negative electrode layer,

[0016] wherein at least one of the electrolyte layer, the positive electrode layer and the negative electrode layer comprises a potassium ion-conducting polycrystalline material of the general formula K 2+X Mg 1-(X / 2) a potassium ion-conducting polycrystalline material of the general formula K

[0017] Another aspect of the present invention is a potassium ion battery comprising:

[0018] a potassium ion-conducting electrolyte layer,

[0019] a positive electrode layer, and

[0020] a negative electrode layer,

[0021] wherein at least one of the electrolyte layer, the positive electrode layer and the negative electrode layer comprises a potassium ion-conducting polycrystalline material of the general formula K 2+X Mg 1-(X / 2) a potassium ion-conducting polycrystalline material of the general formula K

[0022] Another aspect of the present invention is a sensor comprising a potassium ion-conducting polycrystalline material of the general formula K 2+X Mg 1-(X / 2) a potassium ion-conducting polycrystalline material of the general formula K

[0023] Another aspect of the present invention is a sensor comprising a potassium ion-conducting polycrystalline material of the general formula K 2+X Mg 1-(X / 2) a potassium ion-conducting polycrystalline material of the general formula K

[0024] The electrochemical properties of the solid-state electrolyte allow it additional use in potential sensors for gases such as SO2. The sensitivity of a potential sensor comprising the electrolyte of the present application has been demonstrated and shows a significantly superior detection limit.

[0025] Another aspect of the present application is a method of manufacturing a solid-state electrolyte of general formula K 2+X Mg 1-(X / 2) SiO4(0.0 < x < 0.5) comprising the following successive steps:

[0026] a) mixing at least one potassium source, at least one magnesium source and at least one silicon source in a ratio to obtain a superstoichiometric potassium ratio of K:Mg:Si corresponding to (2+x):1-(x / 2):1 (0.0 < X < 0.5), thereby forming a mixture, and

[0027] b) heating the mixture to a temperature comprised between 600°C and 1000°C to obtain a sintered mixture.

[0028] The method of manufacturing the solid-state electrolyte of the present disclosure is particularly suitable for industrial scale production as it employs inexpensive and readily commercialized materials, while the sintering temperature is 850°C, far lower than the typical K-based solid-state electrolytes reported in the prior art (e.g. K-BASE, which sintering temperature is comprised between 1400-1700°C). Therefore, the more facile method of manufacturing provides a suitable implementation for the large-scale production of the solid-state electrolyte of the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1

[0030] A: X-ray diffraction pattern of KMS-2 at room temperature (25°C) under N2 atmosphere. The 2theta reflections indicate that KMS-2 adopts an orthorhombic structure at 25°C with space group Pca21.

[0031] B: Schematic representation of the orthorhombic structure of KMS-2 modeled by the VESTA software.

[0032] Figure 2

[0033] A: X-ray diffraction pattern of KMS-2 at 600°C under N2 atmosphere. The 2theta reflections indicate that KMS-2 adopts a cubic structure at 600°C with space group Fd-3m.

[0034] B: Schematic representation of the cubic structure of KMS-2 modeled by the VESTA software.

[0035] Figure 3

[0036] Comparison of the X-ray diffraction patterns of KMS-2 at 25°C (cubic Fd-3m) and at 600°C (orthorhombic Pca21) under N2.

[0037] Figure 4

[0038] A: X-ray diffraction patterns of KMS-2 under pure N2 during gradual heating from 25°C to 650°C. The X-ray diffraction pattern was recorded at 25°C and from 100°C, after each 50°C increase. Between 200°C and 250°C, a transition from the Pca21 phase to the Fd-3m phase was observed. When the temperature was increased above 250°C, the cubic phase underwent a gradual thermal expansion.

[0039] B: X-ray diffraction patterns of KMS-2 under pure N2 during gradual cooling from 650°C to 25°C. The recording temperatures of the X-ray diffraction patterns were the same as for the heating runs. As the temperature was decreased from 650°C, the cubic phase gradually contracted. Between 250°C and 200°C, a reverse phase transition occurred, i.e. the orthorhombic Pca21 lattice was exhibited.

[0040] C: X-ray diffraction patterns of KMS-2 under atmospheric air during gradual heating from 25°C to 650°C. The X-ray diffraction pattern was recorded at 25°C and from 100°C, after each 50°C increase. The 2Q reflections were the same as recorded during the similar heating run under pure N2 atmosphere.

[0041] D: X-ray diffraction patterns of KMS-2 under atmospheric air during gradual cooling from 650°C to 25°C. The recording temperatures of the X-ray diffraction patterns were the same as for the heating runs. The 2Q reflections were the same as recorded during the similar cooling run under pure N2 atmosphere.

[0042] Figure 5

[0043] A: SEM micrograph of KMS-2 at low magnification obtained by dry polishing and thermal etching (30 min at 750°C under atmospheric air) of the surface of a particle sintered at 800°C.

[0044] B: SEM micrograph of KMS-2 at high magnification obtained by dry polishing and thermal etching (30 min at 750°C under atmospheric air) of the surface of a particle sintered at 800°C.

[0045] Figure 6

[0046] Ion conductivity measurements of KMS-0, KMS-1, KMS-2, KMS-4 and KMS-5 were performed at different temperatures from 25 °C to 600 °C. The plots show that the conductivities of KMS-1, KMS-2, KMS-4 and KMS-5 are improved compared to KMS-0. This difference is most pronounced below 300 °C.

[0047] Figure 7

[0048] A: Ion conductivity measurements of KMS-2 in dry N2 and air at different temperatures from 25 °C to 600 °C. Above 200 °C, the ion conductivity of KMS-2 is essentially unaffected by moisture and / or oxygen.

[0049] B: 500 mV DC potentiostatic polarization on a Pt / KMS-2 / Pt symmetric cell at room temperature in dry N2.

[0050] Figure 8

[0051] Thermogravimetric analysis of a KMS-2 solid rod measured under argon atmosphere. The normalized mass is essentially unaffected after removal of surface moisture.

[0052] Figure 9

[0053] X-ray photoelectron spectroscopy (XPS) high-resolution binding energy spectrum measurements of KMS-2 before (A-C) and after (D-F) the aging process specified in Example 6, and after the recovery process specified in Example 6 (G-I).

[0054] A: 287-300 eV range. The spectrum shows (from left to right) discernible K2p 1 / 2 , K2p 3 / 2 and C1s peaks.

[0055] B: 1297-1309 eV range. The spectrum shows a peak corresponding to Mg1s.

[0056] C: 95-107 eV range. The spectrum shows a clear Si2p peak.

[0057] D: 287-300 eV range. The spectrum shows (from left to right) discernible K2p 1 / 2 , K2p 3 / 2 and C1s peaks.

[0058] E: 1297-1309 eV range. The peak associated with Mg1s is not present.

[0059] F: 95-107 eV range. Spectrum shows a clear Si2p peak.

[0060] G: 287-300 eV range. Spectrum shows (from left to right) discernible K2p 1 / 2 , K2p 3 / 2 and C1s peaks.

[0061] H: 1297-1309 eV range. Spectrum again shows a peak corresponding to Mg1s.

[0062] I: 95-107 eV range. Spectrum shows a clear Si2p peak.

[0063] Figure 10

[0064] Ion conductivity as a function of temperature for the "Original KMS-2", "Aged KMS-2" and "Recovered KMS-2" samples measured under dry N2, and comparison between ion conductivities. Graph shows partial recovery of ion conductivity for the "Recovered KMS-2" sample after treatment compared to the "Original KMS-2".

[0065] Figure 11

[0066] Sensitivity of the type III potentiometric SO2 sensor (O2, Au | Ag | KMS-2 | K2SO4 | Pt | Au, SO2, O2) at 500 °C as demonstrated by emf

[0067] A: Response / recovery times for a 2 ppm SO2 step change.

[0068] B: Dependence on the logarithm of SO2 concentration.

[0069] C: Schematic of sensor assembly and performance mechanism.

[0070] Figure 12

[0071] A: Galvanostatic cycling with potential limits (GCPL) measurements on a Na / KMS-2 / Na symmetric cell at 40 °C, current density of 0.1 mA / cm 2 , metal plating / stripping depth of 0.025 mAh / cm 2 .

[0072] B: GCPL measurements on a Na / KMS-2 / Na symmetric cell at 40 °C, current density of 1 mA / cm 2 , metal plating / stripping depth of 0.025 mAh / cm 2 . DETAILED DESCRIPTION

[0073] definition

[0074] The term KMS as used herein generally refers to a compound or composition of formula (I),

[0075] K 2+X Mg 1-(X / 2) SiO4(0.0 <x≤0.5)(I)

[0076] In the context of the present invention, KMS-1 refers to the compound or composition of formula (I) wherein x = 0.1, and similarly for KMS-2, KMS-3, KMS-4, and KMS-5 as referred to herein. KMS or KMS-0 are used interchangeably herein to refer to the compound K2MgSiO4 wherein x = 0.

[0077] As used herein, the term "electrolyte" refers to a substance that allows charge (i.e., current) to flow in the form of ions between the positive and negative electrodes of a battery. The KMS polycrystals disclosed herein are referred to as "solid-state electrolytes" because the compound is in a solid state within the temperature range for which it is designed for this purpose. This temperature range is 25°C to 650°C. The KMS polycrystals disclosed herein allow charge to flow in the form of ions, such as K + ions and / or Na + Flow in the form of ions.

[0078] As used herein, the term "active electrode material" refers to an electrode component that participates in an electrochemical reaction that generates or stores electrical energy. In other words, it refers to a substance or composition that allows interstitial storage and release of mobile ions, such as the positive and negative electrode materials commonly known to those skilled in the art of batteries and electrochemical cells. In contrast to active electrode materials, electrolytes (see above) do not allow any storage or release of mobile ions, but only allow the transfer / flow of such ions. Various active electrode materials suitable for practicing the present invention are defined herein.

[0079] Exemplary Na + and K + The electronic and steric similarities between ions are well known in the art. Thus, although the superstoichiometric KMS electrolyte of the present invention is described herein as being specifically potassium (K + ) ions, but it should not be understood as being applicable only to potassium ions. The superstoichiometric KMS electrolyte of the present invention can be considered as a conductor of various ions, in particular monovalent cations, such as alkali metal ions, especially sodium (Na + ) ions, this is because Na + and K + There are well-known similarities between them.

[0080] Although only mobile potassium ions exist in the superstoichiometric KMS electrolyte of the present invention, mobile Na ions can be released after combining with active electrode materials containing other ions (e.g., active electrode materials containing Na). + ions, through the three-dimensional network of corner-sharing polyhedra of SiO4 and MgO4 moieties present in superstoichiometric KMS, these Na + Ions can be transported through such migration channels. Figure 12 A and 12B demonstrate this view and support that ionic conductivity is not limited to potassium ions but also applies to other ions, such as alkali metal ions, especially Na + ion.

[0081] Therefore, it should be readily understood by those skilled in the art that any reference herein to a superstoichiometric KMS electrolyte having potassium ion conductivity also refers to the same electrolyte having alkali metal ion conductivity, particularly sodium ion conductivity.

[0082] The term "space group" as used herein should have the ordinary meaning used by those skilled in the art of chemistry (especially crystallography), and is considered to refer to a crystallographic space group comprising 230 different space groups (taking into account chiral space groups). The term is well known and widely used in the art and requires no further explanation.

[0083] As used herein, the term "battery" refers to a device capable of generating electrical energy by the flow of charge between a cathode and an anode, which are separated by an electrolyte material. Cathode and anode are terms well known and commonly used by those of ordinary skill in the art and require no further explanation.

[0084] As used herein, the term "polycrystalline material" refers to a solid material composed of a plurality of individual crystals having the same crystal lattice, but wherein each crystal exhibits its own orientation in space.

[0085] The term "atmospheric air" refers to a gaseous composition consisting primarily of N2 and O2 and having a relative humidity percentage ranging from 0% to 100%. Atmospheric air is used interchangeably with ambient air.

[0086] As used herein, the terms "phase transition" and "phase change" refer equivalently to a physical process by which a solid material characterized by a well-defined crystal space group undergoes a transformation, meaning that the material as a whole adopts a different crystal space group while its chemical composition remains unchanged. As described in the present disclosure, the "phase transition" or "phase change" experienced by the KMS polycrystal is caused by external physical factors (i.e., temperature changes).

[0087] The term "potentiometric sensor" as used herein refers to a sensor used to determine the concentration of a chemical species, i.e. an analyte. Such sensors produce an output signal in the form of a potential difference between a working electrode and a reference electrode, which is mathematically related to the concentration of the target analyte in the sample. As described in the prior art, "potentiometric sensors" can be used to detect gaseous analytes, i.e. "potentiometric gas sensors".

[0088] Potentiometric gas sensors consist of two electrodes connected on either side of a solid-state electrolyte. One electrode is exposed to the gas to be measured, while the reference electrode faces a reference gas with constant concentration. In type I potentiometric gas sensors, the measured gas is converted into the main mobile ions in the solid-state electrolyte, i.e. the electrolyte should have the same substance as the gas phase. Examples of type I sensors include yttrium-stabilized zirconium (fast oxygen ion conductor) for the detection of O2.

[0089] In type II electrodes, the gaseous analyte reacts reversibly with non-mobile ions in the electrolyte, forming an intermediate, segregated or dissolved phase in the electrolyte. An equilibrium is thus established between the gas and the intermediate phase. An electrolyte made of K2CO3 for the determination of CO2 constitutes a type II sensor.

[0090] Type III sensors are described as sensors that employ a thin auxiliary layer to detect different target gas species. The sensor consists of a type II electrode and an ionic junction between the electrolyte and the auxiliary phase. The ionic junction allows the concentration of a chemical species not present in the electrolyte to be measured.

[0091] The term "M" as used herein refers to molarity or molar concentration.

[0092] The term "ball milling" as used herein refers to a mechanical process by which a solid material or a mixture composed of two or more solid materials is ground by a device known as a "ball mill". A "ball mill" as used herein comprises a hollow cylindrical shell rotating around its axis, the inside of which is partially filled with balls constituting the grinding medium. As the shell rotates, the balls are lifted on the ascending side of the shell and then fall into the solid particles. The impact of the balls on the solid particles reduces their size.

[0093] The term "pelletizing" as used herein refers to a mechanical process that includes compressing or molding a solid material into a compressed self-standing solid particle, which is a spherical, round, oval or cylindrical pellet.

[0094] The term "pulverization" as used herein refers to a mechanical process that includes using physical forces to reduce the size of a solid particle, deform or compress a solid particle.

[0095] The term “green ball” as used herein refers to the pellets obtained immediately after pressing of the material, which are not calcined or sintered. This is a commonly used term in ceramic processing and does not require further explanation.

[0096] The term “mother powder” as used herein refers to a mixture of KMS precursors, for example, with the same stoichiometric ratio, which is used to synthesize a specific compound in a specific stoichiometric ratio. This is a very commonly used term in inorganic synthesis of inorganic materials containing volatile elements.

[0097] Abbreviations of chemicals

[0098] The following chemicals are described herein: dimethoxyethane (DME), tetraethylene glycol dimethyl ether (TEGDME), diethyl carbonate (DEC), ethyl carbonate (EC), bis(trifluoromethanesulfonyl)imide (TFSI), polyethylene oxide (PEO), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyvinyl chloride (PVC), polyacrylonitrile (PAN), poly(methyl methacrylate) (PMMA), polyvinylidene fluoride (PVDF), poly(acrylic acid) (PAA), and polypropylene carbonate (PPC).

[0099] The term “BASE” as used herein refers to a β-alumina solid-state electrolyte, which has a layered crystal structure enabling fast ion transport of alkali metal species (e.g., Na and K). The structure is a polyaluminate with channels along which the ionic alkali metal species in the solid can migrate. If the structure contains sodium as the alkali metal species, it is denoted as “Na-BASE”. Likewise, the potassium-containing analogue is referred to as “K-BASE”.

[0100] The term “carnegieite” as used herein refers to sodium aluminum silicate with the molecular formula NaAlSiO4. Other structures, such as Na2CaSiO4 or Na2MgSiO4, are also referred to as carnegieite analogues in the art, as they crystallize in the same crystallographic space group as carnegieite at room temperature, namely orthorhombic Pbca. The same is true for K2MgSiO4 (KMS-0), which is a carnegieite analogue structure that crystallizes in orthorhombic Pbca at room temperature.

[0101] The term “cristobalite” as used herein refers to the mineral polymorph with the chemical formula SiO2. The crystal structure of cristobalite is cubic with space group Fd-3m.

[0102] Chemical composition and structure

[0103] One embodiment of the present disclosure provides a solid-state electrolyte comprising a general formula of K 2+X Mg 1-(X / 2)ionically conductive polycrystalline material of SiO4(0.0 < x < 0.5).

[0104] In one embodiment, the solid state electrolyte consists essentially of a potassium ionically conductive polycrystalline material of the general formula K 2+X Mg 1-(X / 2) SiO4(0.0 < x < 0.5).

[0105] One embodiment of the disclosure provides a solid state electrolyte comprising a potassium ionically conductive polycrystalline material of the general formula K 2+X Mg 1-(X / 2) SiO4(0.0 < x < 0.5).

[0106] In one embodiment, the solid state electrolyte consists essentially of a potassium ionically conductive polycrystalline material of the general formula K 2+X Mg 1-(X / 2) SiO4(0.0 < x < 0.5).

[0107] In one embodiment, X is between 0.1 and 0.5, for example between 0.1 and 0.15, for example between 0.15 and 0.2, for example between 0.2 and 0.25, for example between 0.25 and 0.3, for example between 0.3 and 0.35, for example between 0.35 and 0.4, for example between 0.4 and 0.45, for example between 0.45 and 0.5. In one embodiment, X is selected from 0.1, 0.2, 0.3, 0.4 and 0.5, including any 0.01 integer therebetween.

[0108] In one embodiment, X is 0.1. In one embodiment, X is 0.2. In one embodiment, X is 0.4.

[0109] In one embodiment, X is selected from the range of 0.2 to 0.4, preferably 0.2 or 0.4.

[0110] In one embodiment, the polycrystalline material is characterised by an orthorhombic space group at room temperature.

[0111] In one embodiment, the orthorhombic space group at room temperature is Pca21. As shown in the examples herein, X-ray diffraction analysis and subsequent computational data processing methods enable the modelling of the unit cell and estimation of interatomic distances. The KMS electrolyte adopts an orthorhombic space group at room temperature, which is a significant difference compared to triclinic nepheline, which is characterised by a Pbca crystal space group.

[0112] In one embodiment of the disclosure, the Pca21 space group of the KMS electrolyte described herein is characterised by the following lattice parameters:

[0113]

[0114] and

[0115]

[0116] In one embodiment, the KMS electrolyte described herein of space group Pca21 is characterized by the following lattice parameters:

[0117]

[0118] and

[0119]

[0120] In one embodiment, the polycrystalline material is characterized by a crystal structure comprising a corner-sharing polyhedron of non-alkali metal ions, such as a corner-sharing tetrahedron comprising SiO4and / or MgO4moieties. In one embodiment, the polycrystalline material is characterized by a corner-sharing tetrahedron comprising SiO4and / or MgO4moieties. Corner-sharing framework structures constitute a promising solution to develop new superior K + Conductors. In contrast to layered structures, the lattices in the corner-sharing frameworks of solid state electrolytes provide exposed interstices that are too narrow to accommodate water molecules, thus enabling stability against moisture. Moreover, in corner-sharing frameworks, the non-alkali metal polyhedra exhibit higher degrees of freedom, which leads to more irregular interstices, in turn increasing the interstitial site energies of alkali metal ions. The high-energy alkali metal ions in highly distorted sites show lower activation energy for migration to more symmetric coordinates through the interstices, thus ultimately increasing ionic conductivity.

[0121] In one embodiment, the polycrystalline material is characterized by a phase transition temperature of 100 °C to 1000 °C, such as 100 °C to 200 °C, such as 200 °C to 250 °C, such as 250 °C to 300 °C, such as 300 °C to 350 °C, such as 350 °C and 400 °C, such as 400 °C to 500 °C, such as 500 °C to 600 °C, such as 600 °C to 700 °C, and wherein the phase transition temperature represents a transition from an orthorhombic space group to a cubic space group.

[0122] In one embodiment, the polycrystalline material is characterized by a phase transition temperature of 200 °C to 250 °C, wherein the phase transition temperature represents a transition from an orthorhombic space group to a cubic space group. In one embodiment, the polycrystalline material is characterized by a phase transition temperature of 200 °C to 250 °C. In one embodiment, the phase transition temperature represents a transition from an orthorhombic space group to a cubic space group.

[0123] In one embodiment, the polycrystalline material is characterized by a cubic space group at 300 °C. In one of the embodiments, the cubic space group at 300 °C is Fd-3m. As shown in the examples herein, X-ray diffraction analysis and subsequent data processing with computational methods enable modeling of the unit cell and estimation of interatomic distances. The KMS polycrystalline material adopts the cubic space group Fd-3m at 300 °C.

[0124] The X-ray diffraction patterns recorded at multiple temperature values as shown in the examples herein indicate that the KMS polycrystalline material undergoes a phase transition between 200 °C and 250 °C and crystallizes into a cubic crystal structure with higher symmetry, with the space group Fd-3m, and fine lattice parameters When the temperature is further increased above the phase transition temperature, the cubic Fd-3m crystal structure expands to The phase transition temperature of the KMS polycrystalline material described herein is lower than that of other K-containing polycrystalline materials reported in the prior art, such as KAI02 and KFe02, which have phase transition temperatures of 400-550 °C and 650 °C, respectively.

[0125] In one embodiment of the present disclosure, the KMS polycrystalline material with the cubic Fd-3m crystal structure reverts to the initial orthorhombic Pca21 phase when the sample is cooled below 250 °C. As shown in the examples herein, the X-ray diffraction patterns of the KMS polycrystalline material recorded at multiple temperature values are largely independent of the atmosphere used during the study, i.e. atmospheric air or N2. The homogeneity between the X-ray diffraction patterns under N2and atmospheric air indicates that no significant phase decomposition due to the presence of O2and moisture occurs under atmospheric conditions, unlike many other fast K + conductors for which this problem has been observed. As shown in the examples herein, thermogravimetric analysis further demonstrates the stability of the KMS polycrystalline material to moisture, as no hydrated phase or uptake of moisture is observed throughout the thermal process.

[0126] Physical properties

[0127] In one embodiment of the present disclosure, the electrolyte is characterized by an alkali metal ion conductivity at room temperature (25 °C) of 1 · 10 -7 S / cm to 1 · 10 -4 S / cm.

[0128] In one embodiment of the present disclosure, the electrolyte is characterized by a potassium ion conductivity at room temperature (25 °C) of 1 · 10 -7 S / cm to 1 · 10 -4 S / cm.

[0129] In one embodiment, the potassium ion conductivity at room temperature (25 °C) is 1 · 10-7 S / cm to 1 · 10 -4 S / cm, for example 1 · 10 -7 S / cm to 5 · 10 -7 S / cm, for example 5 · 10 -7 S / cm to 1 · 10 -6 S / cm, for example 1 · 10 -6 S / cm to 5 · 10 -6 S / cm, for example 5 · 10 -6 S / cm to 1 · 10 -5 S / cm, for example 1 · 10 -5 S / cm to 5 · 10 -5 S / cm, for example 5 · 10 -5 S / cm to 1 · 10 -4 S / cm.

[0130] In one embodiment of the disclosure, the electrolyte is characterized by a potassium ion conductivity at 300 °C of 1 · 10 -7 S / cm to 1 · 10 -1 S / cm.

[0131] In one embodiment of the disclosure, the electrolyte is characterized by a potassium ion conductivity at 300 °C of 1 · 10 -7 S / cm to 1 · 10 -1 S / cm.

[0132] In one embodiment, the potassium ion conductivity at (300 °C) is 1 · 10 -7 S / cm to 1 · 10 -1 S / cm, for example 1 · 10 -7 S / cm to 1 · 10 -6 S / cm, for example 1 · 10 -6 S / cm to 1 · 10 -5 S / cm, for example 1 · 10 -5 S / cm to 1 · 10 - 4 S / cm, for example 1 · 10 -4 S / cm to 5 · 10 -4 S / cm, for example 5 · 10 -4 S / cm to 1 · 10 -3 S / cm, for example 1 · 10 -3 S / cm to 5 · 10 -3 S / cm, for example 5 · 10 -3 S / cm to 1 · 10 -2 S / cm, for example 1 · 10 -2 S / cm to 5 · 10 -2S / cm, for example 5-10 - 2 S / cm to 1-10 -1 S / cm.

[0133] In one embodiment, the electrolyte is characterized by a sodium ion conductivity at 40 °C of 1-10 -7 S / cm to 3-10 -4 S / cm.

[0134] In one embodiment, the ion conductivity is measured by electrochemical impedance spectroscopy (EIS).

[0135] In one embodiment, the electrolyte is characterized by a relative density of 90 ± 2% or higher, for example 91 ± 2% or higher, for example 92 ± 2% or higher, for example 93 ± 2% or higher, for example 94 ± 2% or higher, for example 95 ± 2% or higher, for example 96 ± 2% or higher, for example 97 ± 2% or higher, for example 98 ± 2%, preferably having a relative density of 95 ± 2%. In one embodiment, the electrolyte is characterized by a relative density of 95 ± 2%. Density is measured by gas pycnometer as shown in the examples herein. The density measurements demonstrate that the KMS solid state electrolyte has a high level of densification, which is critical to ensure optimal performance of the granules and self-standing tapes in various applications, most notably as alkali metal ion-conductive solid state electrolytes for batteries, for example potassium ion-conductive solid state electrolytes for potassium batteries.

[0136] In one embodiment, the electrolyte is characterized by an electronic conductivity at room temperature (25 °C) of 1-10 -10 S / cm to 1-10 -6 S / cm.

[0137] In one embodiment, the electronic conductivity at room temperature (25 °C) is 1-10 -10 S / cm to 1-10 -6 S / cm, for example 1-10 -10 S / cm to 1-10 -9 S / cm, for example 1-10 -9 S / cm to 1-10 -8 S / cm, for example 1-10 -8 S / cm to 1-10 - 7 S / cm, for example 1-10 -7 S / cm to 1-10 -6 S / cm.

[0138] In one embodiment, the electrolyte is characterized by an electronic conductivity at 300 °C of 1-10 -10 S / cm to 1-10-6 S / cm.

[0139] In one embodiment, the electronic conductivity at 300°C is 1 · 10 -10 S / cm to 1 · 10 -6 S / cm, for example 1 · 10 -10 S / cm to 1 · 10 -9 S / cm, for example 1 · 10 -9 S / cm to 1 · 10 -8 S / cm, for example 1 · 10 -8 S / cm to 1 · 10 -7 S / cm, for example 1 · 10 -7 S / cm to 1 · 10 -6 S / cm.

[0140] In one embodiment, the electronic conductivity is measured by chronoamperometry at 500 mV, although other ways known to the skilled person can also be employed.

[0141] As shown in the examples herein, the ionic conductivity of K hyperstoichiometric KMS-1, KMS-2, KMS-4 and KMS-5 is higher than that of the stoichiometric counterpart KMS-0 at temperatures of 300°C or lower. It is thus shown that the addition of a hyperstoichiometric amount of potassium can improve the K ionic conductivity. As shown in the examples herein, the temperature dependence of the ionic conductivity values of KMS-1, KMS-2 and KMS-4 indicates that the K + migration activation energy (0.36 eV) is lower than the analogous value for the stoichiometric KMS-0 (0.47 eV). Despite the higher K ionic conductivity, KMS-2 exhibits an electronic conductivity of ~5 · 10 -9 S / cm, which is about four orders of magnitude lower than the former parameter, as shown in the examples herein. Thus, the K + migration number is close to 1, which is a desirable property for the development of potassium ion batteries with solid state electrolytes.

[0142] Use in sensors

[0143] One embodiment of the present disclosure provides the electrolyte of the present disclosure for use as a component in a sensor. Thus, one embodiment of the present disclosure is an electrolyte of general formula K 2+X Mg 1-(X / 2) SiO4(0 < x < 0.5) for use as a component in a sensor, for example a potentiometric sensor. One embodiment of the present disclosure is a sensor comprising an electrolyte of general formula K 2+X Mg 1-(X / 2) SiO4(0 < x < 0.5).

[0144] In one embodiment, the sensor is a potentiometric sensor. In one embodiment, the sensor is a Type III potentiometric sensor.

[0145] In one embodiment, the sensor is used to sense a gas, for example a gas selected from the group consisting of SO2, SO3, NO, NO2, CO, and CO2. In one embodiment, the sensor is used to sense SO2. As shown in the examples herein, a Type III potentiometric solid-state gas sensor for the detection of SO2 (equilibrated from synthetic air) was developed using KMS-2 as the electrolyte, a combination of porous K2SO4 layer and porous Pt layer as the auxiliary sensing electrode, a combination of KMS-2 surface exposed to air (under porous silver) and porous silver layer as the reference electrode (O2, Au | Ag | K 2.2 Mg 0.9 SiO4| K2SO4| Ag | Pt, SO2, O2). The working principle of the electrode of the present disclosure involves a thermodynamic equilibrium via Equation (I) below between the solid-state electrolyte, SO2 in the gas, and the porous auxiliary sensing electrode (Pt + K2SO4 in this example):

[0146]

[0147] According to Equation (II), another thermodynamic equilibrium is established between the solid-state electrolyte, O2 in the gas, and the porous reference electrode (Ag here) on the silver-coated surface of the solid-state electrolyte:

[0148]

[0149] The establishment of the above thermodynamic equilibria fixes the K + chemical potential at the solid-state electrolyte surface at the electrolyte / sensing electrode and electrolyte / reference electrode interfaces and creates a chemical potential difference between the two electrodes. This chemical potential can be measured in the form of electrical potential via the Nernst equation (Equation (III)):

[0150]

[0151] The solid-state electrolyte layer (KMS-2 in the examples herein) provides K + for the above thermodynamic equilibrium reactions (Equations I and II). The K +The high ionic conductivity of the substance is a requirement for establishing the above thermodynamic equilibrium reaction and the fast response time and stable sensing signal that follows, which is consistent with a Nernstian response (Equation III). As shown in the examples herein, a potentiometric SO2 sensor constructed with the electrolyte of the present disclosure is able to determine SO2 in the concentration range of 0-10 ppm at 500 °C with a sensitivity of 74-89 mV / dec, and a response / recovery time of 2 to 120 minutes.

[0152] Use in batteries

[0153] One embodiment of the present disclosure provides an electrolyte of the general formula K 2+X Mg 1-(X / 2) Use of an electrolyte of the general formula K

[0154] In one embodiment, the battery is an alkali metal ion-conducting battery, such as a sodium ion battery or a potassium ion battery.

[0155] One embodiment of the present disclosure provides a battery comprising:

[0156] an ion-conducting electrolyte layer,

[0157] a positive electrode layer,

[0158] a negative electrode layer, and

[0159] wherein at least one of the electrolyte layer, the positive electrode layer, and the negative electrode layer comprises an ion-conducting polycrystalline material of the general formula K 2+X Mg 1-(X / 2) SiO4(0 < x < 0.5).

[0160] In one embodiment of the present disclosure, the conductive polycrystalline material is capable of conducting alkali metal ions, such as having alkali metal ion conductivity. In one embodiment, the conductive polycrystalline material has potassium ion conductivity and / or sodium ion conductivity.

[0161] In one embodiment of the present disclosure, the battery comprising an ion-conducting polycrystalline material of the general formula K 2+X Mg 1-(X / 2) SiO4(0 < x < 0.5) is an alkali metal ion battery, such as a potassium ion battery and / or a sodium ion battery. In some embodiments of the present disclosure, the battery can be a hybrid alkali metal ion battery, such as capable of conducting and intercalating two or more alkali metal ions, preferably wherein the two or more alkali metal ions comprise at least sodium and potassium.

[0162] In one embodiment of the disclosure, the alkali metal ion battery is a potassium ion battery.

[0163] One embodiment of the disclosure provides a potassium ion battery comprising:

[0164] a potassium ion-conductive electrolyte layer,

[0165] a positive electrode layer,

[0166] a negative electrode layer, and

[0167] wherein at least one of the electrolyte layer, the positive electrode layer, and the negative electrode layer comprises a potassium ion-conductive polycrystalline material of general formula K 2+X Mg 1-(X / 2) SiO4(0 < x < 0.5).

[0168] The electrochemical properties of the solid-state electrolytes of the disclosure shown in the examples herein, i.e. ionic and electronic conductivity, densification, and stability to environmental conditions, provide an optimal framework for the development of alkali metal ion batteries, such as K-ion batteries.

[0169] In one embodiment, the ion-conductive electrolyte layer is a solid-state ion-conductive electrolyte layer. In one embodiment, the potassium ion-conductive electrolyte layer is a solid-state potassium ion-conductive electrolyte layer. In one embodiment, the ion-conductive electrolyte layer is a liquid-state ion-conductive electrolyte layer. In one embodiment, the potassium ion-conductive electrolyte layer is a liquid-state potassium ion-conductive electrolyte layer. In one embodiment, the ion-conductive electrolyte layer is a solid / liquid hybrid ion-conductive electrolyte layer. In one embodiment, the potassium ion-conductive electrolyte layer is a solid / liquid hybrid potassium ion-conductive electrolyte layer.

[0170] In one embodiment, the ion-conductive electrolyte layer is formed between the positive electrode layer and the negative electrode layer.

[0171] In one embodiment, the potassium ion-conductive electrolyte layer is formed between the positive electrode layer and the negative electrode layer.

[0172] In one embodiment, the solid ion-conducting electrolyte layer comprises one of the following: an inorganic solid electrolyte, a liquid electrolyte, a solid polymer electrolyte, and any of the foregoing, or a mixture thereof, in combination with the KMS electrolyte of the present disclosure to form a composite material. In one embodiment, the solid ion-conducting electrolyte comprises the KMS electrolyte of the present disclosure, used alone or as part of a composite material with at least one selected from an inorganic solid electrolyte, a liquid electrolyte, and a solid polymer electrolyte. In one embodiment, the solid potassium ion-conducting electrolyte layer comprises one of the following: an inorganic solid electrolyte, a liquid electrolyte, a solid polymer electrolyte, and any of the foregoing, or a mixture thereof, in combination with the KMS electrolyte of the present disclosure to form a composite material. In one embodiment, the solid ion-conducting electrolyte layer comprises an inorganic solid electrolyte. In one embodiment, the solid potassium ion-conducting electrolyte layer comprises a liquid electrolyte. In one embodiment, the solid ion-conducting electrolyte layer comprises an inorganic solid electrolyte. In one embodiment, the solid potassium ion-conducting electrolyte layer comprises a liquid electrolyte. In one embodiment, the solid ion-conducting electrolyte layer comprises a solid polymer electrolyte.

[0173] In one embodiment, the solid potassium ion conducting electrolyte layer comprises a solid polymer electrolyte.

[0174] In one embodiment, a battery according to the present disclosure comprises an inorganic solid electrolyte selected from the group consisting of K-BASE, K2MgSiO4, KAlO2, KFeO2, KGaO2, K 0.7 Sr 0.15 GaO2 KAlSiO4, K2CaSiO4, K2Mg2TeO6, K2ZnSiO4, K2Si2P3, K2Sb5P2O 10 , K 2.92 Sb 0.92 W 0.08 S4, K 0.59 Mg 0.53 Sb 0.47 O2, K3SbS4, K 1.9 Fe 1.95 P 0.05 O4, K 1.9 Pb 0.05 AlO2, K 0.405 Bi 0.865 AsO4、K 0.4 Cd 0.3 FeO2, K2Fe4O7, K 1.6 Zn 0.8 Ti 7.2 O 16 , K 0.72 In 0.72Sn 0.28 O2, KBiO3, K3Sc(MoO4)3, KMgPO4, K2MgV2O7, K2Mg2Si2O7, K2CaP2O7, K2ZnGeO4, K2Mg2(MoO4)3, K4Mg(WO4)3, K2CaPO4F, Li7La3Zr2O 12 (LLZO), Li 5.1 Ga 0.32 La3Zr 2.25 O 13 , Li 6.25 Ga 0.25 La3Zr2O 12 , Li x La y TiO3(0.07 < x < 0.13; y = (2 / 3) - x) (LLTO), Li 0.45 La 0.48 TiO3, Li5La3X2O 12 (X = Nb or Ta), Li x PO y N z (3 < x < 3.2; 3 < y < 3.5; 0 < z < 0.5; 3 < (y + z) < 4), Li 3.13 PO 1.69 N 1.39 , Li 0.98 PO 2.55 N 0.50 , Li3PO4, La (1+x) Al x Ti (2-x) (PO4)3(0 < x < 2) (LATP), Li 1.3 Al 0.4 Ti 1.7 (PO4)3, Li 10 GeP2S 12 , Li7P3S 11 , Na-BASE, NaM2(PO4)3(M = Ge, Ti, Zr), Na 1+x Zr2Si x P 3-x O 12 (0 < X < 3), Na2MgSiO4, Na2CaSiO4, Na2ZnSiO4, Na2Mg2TeO6, Na2Mg2ZnO6, Na3PS4, Na4SiS4, Na3PSe4, Na 10 SnP2S 12 , Na3SbS4, and any combination thereof.

[0175] In one embodiment, the battery according to the present disclosure comprises an inorganic solid-state electrolyte selected from the group consisting of K-BASE, K2MgSiO4, KAlSiO4, K2CaSiO4, K2Si2P3, K 2.92 Sb 0.92 W 0.08 S4, K3SbS4, Na-BASE, Na 1+x Zr2Si x P 3-x O 12 (0≤X≤3), Na2MgSiO4, and Na2CaSiO4, and any combination thereof.

[0176] In one embodiment, the battery according to the present disclosure comprises a liquid electrolyte selected from the group consisting of ether electrolytes such as (AN(SO2F)2 in DME) or (ACF3SO3 in TEGDME); ester electrolytes such as (APF6 in EC / DMC), (APF6 in PC), or (AN(SO2F)2 in EC / DEC), ATFSI in tetraethylene glycol dimethyl ether, where (A = K, Li, or Na); and aqueous electrolytes such as (1M KNO3 per 0.01M HNO3), (1M KNO3 pH = 2), 0.5M K2SO4, 0.1M KCl, 22M KCF3SO3, 3M KCl, 30M KFSI, or 1M KOH, or mixtures thereof. In one embodiment, the battery according to the present disclosure comprises the liquid electrolyte ATFSI in tetraethylene glycol dimethyl ether, where (A = K, Li, or Na).

[0177] In one embodiment, the battery according to the present disclosure comprises a solid state polymer electrolyte selected from the group consisting of (KTFSI+PEO), PEO-KAg4I5, PEO-KBrO3, PPC-KFSI, PEO-KFSI, PVP+PVA+KBrO3, PVC+KBrO3, PAN-KI, PMMA-KPF6, PVA-KCl, (KTFSI+PEO).(LiTFSI+PEO), PEO-LiAg4I5, PEO-LiBrO3, PPC-LiFSI, PEO-LiFSI, PVP+PVA+LiBrO3, PVC+LiBrO3, PAN-Lii, PMMA-LiPF6, PVA-LiCl, (LiTFSI+PEO).(NaTFSI+PEO), PEO-NaAg4I5, PEO-NaBrO3, PPC-NaFSI, PEO-NaFSI, PVP+PVA+NaBrO3, PVC+NaBrO3, PAN-NaI, PMMA-NaPF6, PVA-NaCl, (NaTFSI+PEO) and any combination thereof. In one embodiment, the battery according to the present disclosure comprises a solid state polymer electrolyte (KTFSI+PEO).

[0178] In one embodiment, the battery according to the present disclosure comprises a cathode layer selected from the group consisting of a solid state cathode layer, a liquid cathode layer and a solid-liquid hybrid cathode layer.

[0179] In one embodiment, the cathode layer is a solid state cathode layer comprising:

[0180] a. a carbonaceous material, such as carbon black;

[0181] b. a binder, such as PVDF or PAA;

[0182] c. at least one inorganic solid state electrolyte selected from the group consisting of K-BASE, K2MgSiO4, KAlO2, KFeO2, KGaO2, K 0.7 Sr 0.15 GaO2KAlSiO4, K2CaSiO4, K2Mg2TeO6, K2ZnSiO4, K2Si2P3, K2Sb5P2O 10 , K 2.92 Sb 0.92 W 0.08 S4, K 0.59 Mg 0.53 Sb 0.47 O2, K3SbS4, K 1.9 Fe 1.95 P 0.05 O4, K 1.9 Pb 0.05 AlO2, K0.405 Bi 0.865 AsO4、K 0.4 CD 0.3 FeO2、K2Fe4O7、K 1.6 Zn 0.8 Ti 7.2 The 16 、K 0.72 In 0.72 Sn 0.28 O2、KBiO3、K3Sc(MoO4)3、KMgPO4、K2MgV2O7、K2Mg2Si2O7、K2CaP2O7、K2ZnGeO4、K2Mg2(MoO4)3、K4Mg(WO4)3、K2CaPO4F、Li7La3Zr2O 12 (LLZO), Li 5.1 Ga 0.32 La3Zr 2.25 The 13 、Li 6.25 Ga 0.25 La3Zr2O 12 、Li x The y TiO3(LLTO)(0.07≤x≤0.13;y±0.05=(2 / 3)-x)、Li 0.45 The 0.48 TiO3、Li5La3X2O 12 (X=Nb or Ta), Li x PO y N z (3.0≤x≤3.2;3.0≤y≤3.5;0.0≤z≤0.5;3≤(y+z)≤4)、Li 3.13 PO 1.69 N 1.39 、Li 0.98 PO 2.55 N 0.50 、Li3PO4、La 1+x Al x Ti 2-x (PO4)3(0≤x≤2)、Li 1.3 Al 0.4 Ti 1.7 (PO4)3、Li 10 GeP2S 12 、Li7P3S 11 、Na-BASE、NaM2(PO4)3(M=Ge、Ti、Zr)、Na 1+x Zr2Si x P 3-x The 12(0 < x < 3), Na2MgSi04, Na2CaSi04, Na2ZnSi04, Na2Mg2Te06, Na2Mg2Zn06, Na3PS4, Na4SiS4, Na3PSe4, Na 10 SnP2S 12 and Na3SbS4;

[0183] d. active electrode material comprising one or more of:

[0184] i. sulfur-based cathode material selected from the group consisting of pure sulfur, K2S x (x = 1, 2, 3, 5), Na2S x (x = 1, 2, 3, 5), Li2S x (x = 1, 2, 3, 5) and PAN-S, preferably K2S x (x = 1, 2, 3, 5) and / or PAN-S;

[0185] ii. inorganic-based cathode material selected from the group consisting of K2Ni2Te06, K3Co02, K 0.3 Mn02, K2FeSi04, KFeSi04, K2CoNiTe06, KFeP04F, K2Ni02, K2CuP207, K2FeSi04, KFeSi206, KMnP04, K2FeGe04, KVP207, K 0.71 Cu[Fe(CN)6] 0.72 ·3.7H20, K 0.6 Ni 1.2 Fe(CN)6·3.6H20, K2Fe II [Fe II (CN)6]·2H20, Fe III [Fe III (CN)6], K2NiFe(CN)6·1.2H20, K 1.85 Fe 0.33 Mn 0.67 [Fe(CN)6] 0.98 ·0.77H20, K 0.22 V 1.74 O 4.37 ·0.82H20,

[0186] KM II Fe III (CN)6(M = Mn, Fe, Co, Ni, Zn), NaCo02, NaNi02, NaMn02,

[0187] NaFe02, Na 7 / 9 Cu 2 / 9 Fe1 / 9 Mn 2 / 3 O2, Na3V2(PO4)3, Na2VTi(PO4)3, Na 0.66 Mn 0.66 Ti 0.34 O2, Na 0.44 MnO2, Na2LiV2(PO4)3, Li4Ti5O 12 , LiFePO4, LiMn2O4, LiNiMnCoO2, LiNiCoAlO2, LiCoO2, preferably K2Ni2TeO6, K2FeSiO4, and KFeSi2O6; and

[0188] iii. organic cathode materials selected from A 2+x C6O6 (0 < X < 4), (A = Na, K, Li).

[0189] In one embodiment, the cathode layer is a liquid cathode layer comprising one or more sulfur-type cathode materials as active electrode material, said sulfur-type cathode materials being selected from pure sulfur, K2S x (x = 1, 2, 3, 5), Na2S x (x = 1, 2, 3, 5), Li2S x (x = 1, 2, 3, 5), preferably K2S x (x = 1, 2, 3, 5), optionally in combination with a liquid electrolyte selected from ether electrolytes, such as AN(SO2F)2 in DME or ACF3SO3 in TEGDME; ester electrolytes, such as APF6 in EC / DMC, APF6 in PC, or AN(SO2F)2 in EC / DEC, ATFSI in tetraethylene glycol dimethyl ether; and aqueous electrolytes, such as 1 M KNO3 per 0.01 M HNO3, 1 M KNO3 pH = 2, 0.5 M K2SO4, 0.1 M KCl, 22 M KCF3SO3, 3 M KCl, 30 M KFSI, or 1 M KOH, wherein (A = K, Li, or Na).

[0190] In one embodiment, the cathode layer is a hybrid cathode layer comprising any combination of a solid cathode layer as defined above and a liquid cathode layer as defined above.

[0191] In one embodiment, the anode layer is selected from a solid anode layer, a liquid anode layer, and a hybrid anode layer.

[0192] In one embodiment, the anode layer is a solid anode layer comprising one or more of:

[0193] a) a metal selected from K, Li, Na, Al or alloys thereof, preferably K or ternary K-Na-Li alloys; and

[0194] b) a carbon-based negative electrode selected from graphite and hard carbon;

[0195] c) a silicon-based negative electrode selected from silicon, crystalline silicene or zintle (potassium silicide, sodium silicide, lithium silicide and calcium silicide).

[0196] In one embodiment, the negative electrode layer is a liquid negative electrode layer comprising one or more of: a metal selected from K, Li, Na, Al or alloys thereof, preferably K or ternary K-Na-Li alloys.

[0197] In one embodiment, the negative electrode layer is a hybrid negative electrode layer comprising any combination of a solid negative electrode layer as defined above and a liquid negative electrode layer as defined above.

[0198] In one embodiment, the positive electrode layer is a solid positive electrode layer and the negative electrode layer is a solid negative electrode layer.

[0199] Sensors

[0200] One embodiment of the present disclosure provides a sensor comprising a potassium ion-conducting polycrystalline material as described herein. One embodiment of the present disclosure is that the sensor comprises a potassium ion-conducting polycrystalline material of the general formula K 2+X Mg 1-(X / 2) SiO4(0.0 < x < 0.5).

[0201] In one embodiment, the sensor of the present disclosure is suitable for detecting a gas selected from SO2, SO3, NO, NO2, CO and CO2. In one embodiment, the sensor of the present disclosure is suitable for detecting SO2.

[0202] In one embodiment, the sensor of the present disclosure is a potentiometric sensor, for example a Type III potentiometric sensor.

[0203] In one embodiment, the sensor of the present disclosure has a sensitivity of 74-89 mV / dec at 500 °C. The sensitivity of the potentiometric sensor integrated with electrolyte is 10 times higher than the sensitivity of the prior art sensor employing lithium lanthanum zirconium oxide (LLZO).

[0204] In one embodiment, the sensor of the present disclosure has a detection limit of 1-10 ppm, for example 2 ppm, for example 4 ppm, for example 6 ppm, for example 8 ppm, for example 10 ppm, for example any concentration between 1 and 10 ppm, of SO2 at 500 °C.

[0205] In one embodiment, the sensor of the present disclosure has a response / recovery time for SO2 of 2 to 120 minutes, for example 2 to 3 minutes, for example 3 to 5 minutes, for example 5 to 15 minutes, for example 15 to 45 minutes, for example 45 to 120 minutes at 500 °C.

[0206] Manufacture

[0207] One embodiment of the present disclosure provides a method of manufacturing a solid state electrolyte, the method comprising the following sequential steps:

[0208] a. mixing at least one potassium source, at least one magnesium source, and at least one silicon source in a ratio to obtain a superstoichiometric potassium ratio of K:Mg:Si corresponding to (2+X):1-(X / 2):1 (0.0 < X < 0.5), thereby forming a mixture, and

[0209] b. heating the mixture to a first temperature of 600 °C to 1000 °C to obtain a sintered mixture.

[0210] The solid state electrolyte of the present disclosure can be made from inexpensive, abundant, and non-toxic starting materials. The method of manufacturing the solid state electrolyte of the present disclosure provides a universal and common procedure to obtain all stoichiometries within the given interval of “x” in Formula (I). The variation in stoichiometry can be achieved by adjusting the relative ratio between the starting materials K2CO3, SiO2, and MgO at the beginning of the process.

[0211] In one embodiment, the method of manufacturing the solid state electrolyte of the present disclosure further comprises a step of ball milling the mixture prior to step b. For example, in one embodiment, the oxide precursors can be mixed in ethanol and then wet milled by a planetary ball mill using a milling cup and milling balls made of zirconia at 150 rpm for 2 to 12 hours, for example 4 to 8 hours, for example 6 hours. Alternative solvents for ball milling include water, isopropanol, methanol, ethyl acetate, and cyclohexane.

[0212] In one embodiment of the present disclosure, the method of manufacturing the solid state electrolyte of the present disclosure further comprises, after step b, the steps of: pulverizing the sintered mixture into a fine powder, granulating the fine powder, and heating the granulated powder to a second temperature of 600 °C to 1000 °C. The step of pulverizing the sintered mixture into a fine powder can employ the ball milling procedure described above.

[0213] In one embodiment, the steps of pulverizing, granulating, and heating to a second temperature are repeated at least 3 times, for example any one of 4 times, for example 5 times, for example 6, 7, 8, 9, and 10 times.

[0214] In one embodiment, the first temperature and the second temperature are temperatures lower than 1000 °C, for example lower than 950 °C, for example lower than 900 °C, for example lower than 850 °C, for example lower than 800 °C.

[0215] In one embodiment, the first temperature and the second temperature are temperatures lower than 850 °C.

[0216] In one embodiment, the second temperature is a temperature lower than 1000 °C, for example lower than 950 °C, for example lower than 900 °C, for example lower than 850 °C, for example lower than 800 °C, for example lower than 750 °C, for example lower than 700 °C, for example lower than 650 °C. In one embodiment, the first temperature in step b is lower than 850 °C, for example lower than 800 °C. Furthermore, the first temperature and the second temperature are lower than the typical sintering temperature of K-based solid state electrolytes reported in the prior art (e.g. K-BASE, which has a sintering temperature of 1400-1700 °C). Thus, the more facile manufacturing process makes the solid state electrolyte of the present disclosure amenable to large scale production.

[0217] In one embodiment, the granulation step in the manufacturing process of the solid state electrolyte of the present disclosure is performed by applying a uniaxial pressure of 50 MPa to 100 Mpa, for example 50 MPa to 60 MPa, for example 60 MPa to 70 MPa, for example 70 MPa to 80 MPa, for example 80 MPa to 90 MPa, for example 90 MPa to 100 MPa, preferably 70 MPa to 90 MPa. In one embodiment, the granulation step in the manufacturing process of the solid state electrolyte of the present disclosure is performed by applying a uniaxial pressure of 70 MPa to 90 MPa.

[0218] In one embodiment, the at least one potassium source is a potassium salt or a potassium oxide, for example selected from the group consisting of KF, KC1, KBr, KI, KNO3, K2CO3, K3PO4, K2SO4, KClO4, KClO3, K2O and KOH.

[0219] In one embodiment, the at least one potassium source is K2CO3 or K2O.

[0220] In one embodiment, the at least one magnesium source is a magnesium salt or a magnesium oxide, for example selected from the group consisting of MgF2, MgCl2, MgBr2, MgI2, Mg(NO3)2, MgCO3, Mg3(PO4)2, MgSO4, Mg(ClO4)2, Mg(ClO3)2, MgO and Mg(OH)2.

[0221] In one embodiment, the at least one magnesium source is MgO.

[0222] In one embodiment, the at least one silicon source is a halide of silicon or an oxide of silicon, for example selected from the group consisting of SiCl4 and SiO2.

[0223] In one embodiment of the disclosure, the at least one silicon source is SiCl4and / or SiO2.

[0224] In one embodiment, the method of manufacturing the solid-state electrolyte of the disclosure is performed in an ambient atmosphere.

[0225] In one embodiment, the method of manufacturing the solid-state electrolyte of the disclosure is performed in an inert atmosphere, for example, an inert atmosphere consisting essentially of nitrogen, argon, or a mixture thereof. In one embodiment, the method of manufacturing the solid-state electrolyte of the disclosure is performed in an inert atmosphere, for example, an inert atmosphere consisting essentially of nitrogen. In one embodiment, the method of manufacturing the solid-state electrolyte of the disclosure is performed in an inert atmosphere, for example, an inert atmosphere consisting essentially of argon.

[0226] Examples

[0227] Example 1: Synthesis of KMS solid-state electrolyte by solid-state method

[0228] The stoichiometric amounts of the starting materials K2CO3 (Sigma-Aldrich Corporation, supplier product number: 342890), MgO (Riedel-de Haen®, Sigma-Aldrich Corporation, supplier product number: 1.02600.1000), and SiO2 (Sigma-Aldrich Corporation, supplier product number: 209619) were adjusted accordingly to provide KMS solid-state electrolytes of different compositions, as determined by the value of “X” in Formula (I).

[0229] Table 1. Stoichiometric amounts of starting materials for synthesis of various KMS solid-state electrolytes.

[0230] X value [K2CO3 (mol)] MgO (mol) SiO2(mol) 0.1 2.1 0.95 1 0.2 2.2 0.90 1 0.3 2.3 0.85 1 0.4 2.4 0.80 1 0.5 2.5 0.75 1

[0231] Method

[0232] ​The KMS solid state electrolyte was synthesized using a solid state method. Oxide precursors K2CO3, MgO and SiO2 were mixed in ethanol and wet milled by a planetary ball mill (Retsch Planetary ball mill PM 400) using zirconia made cups and balls at 150 rpm for 6 hours. Subsequently, the milled slurry was dried and the resulting powder was granulated using a uniaxial press (70 MPa) in order to have a better contact and inter-diffusion between the powder particles during the calcination process. The green pellets were calcined in air at 600 °C for 24 hours. After that, the calcined pellets were crushed (with a mortar and pestle), milled (150 rpm for 6 hours), granulated and calcined again three times by the above procedure. In the subsequent repetitions, the calcination temperature was increased to 700 °C and 800 °C, respectively. Moreover, during the calcination process, the pellets were embedded in a mother powder inside an alumina crucible with a lid, regardless of the temperature, in order to prevent the evaporation of potassium from the sample. After calcination at 800 °C and subsequent crushing and milling of the sample, the resulting powder was uniaxially pressed (90 MPa) into pellets with the preferred size (solid state electrolyte) and then cold isostatic pressed (300 MPa) and finally sintered at 850 °C for 20 hours in air. During the sintering process, the solid state electrolyte should be embedded in a mother powder inside an alumina crucible with a lid, in order to prevent the evaporation of potassium from the sample.

[0233] Example 2: Phase transition study on KMS-2 by X-ray diffraction pattern analysis

[0234] Materials and methods

[0235] X-ray diffraction patterns of KMS-2 crushed pellets were recorded at different temperatures from 25 °C to 650 °C under N2 and atmospheric air, respectively (Figures A-D). The samples measured under atmospheric air conditions were crushed and then stored in a capped bottle at room temperature under atmospheric conditions (relative humidity 30-40%) for 60 days before the measurement. The samples measured under N2 were first vacuum packed inside a moisture-proof bag and then crushed before the XRD characterization was immediately performed. Figure 4

[0236] The X-ray diffraction analysis was performed on the powder samples. The diffraction patterns were Rietveld refined using the FullProf software suite to determine the crystallographic parameters and to perform the phase analysis. The crystal structure schematic and the interatomic distance estimation were achieved by the VESTA software. The X-ray diffraction analysis was performed on the powder samples. The diffraction patterns were Rietveld refined using the FullProf software suite to determine the crystallographic parameters and to perform the phase analysis. The crystal structure schematic and the interatomic distance estimation were achieved by the VESTA software.

[0237] Results

[0238] X-ray diffraction patterns

[0239] Figure 1 ​X-ray diffraction patterns in A indicate that KMS-2 adopts an orthorhombic structure at room temperature with space group Pca21 Figure 1 B), which is different from the typical low-temperature structure of the orthorhombic Pbca crystallized triclinic nepheline analogues. As the temperature increases, KMS-2 undergoes a phase transition between 200 °C and 250 °C, crystallizing into a cubic crystal structure with high symmetry, space group Fd-3m Figure 2 A and 2B), with fine lattice parameters of Figure 3 2Θ reflection contrasts of the two crystal structures are shown.

[0240] As expected, the high-temperature KMS-2 cubic triclinic nepheline analog structure expands as the temperature increases from 250 °C to 650 °C, and the refined lattice parameter also increases accordingly to Upon cooling in both atmospheres Figure 4 B and 4D), the high-temperature KMS-2 cubic triclinic nepheline analog structure reversibly shrinks, and the lattice parameter “a” returns to the original value, i.e. When the temperature is further reduced below 250 °C, the crystal phase changes to an orthorhombic Pca21 crystal structure. The transition temperature observed in this study is significantly lower than that reported for KAlO2 and KFeO2 (400-550 °C and 650 °C, respectively). Compared with KAlO2 and KFeO2, the lower phase transition temperature will result in a relatively higher ionic conductivity for KMS-2, especially at the standard operating temperature of K-based solid-state battery applications (~ 300 °C) and potential solid-state gas sensors (~ 500 °C).

[0241] As shown in Figure 4 A-D, the X-ray diffraction patterns obtained in ambient air at different temperatures are very similar to those obtained in N2 atmosphere, indicating that there is no apparent phase decomposition due to O2 and moisture in the atmosphere, which is a problem observed in many other fast K + conductors.

[0242] CONCLUSION

[0243] KMS-2 exhibits an orthorhombic Pca21 phase at room temperature and undergoes a reversible phase transition to a cubic phase Fd-3m between 200 °C and 250 °C. Compared with previously reported solid-state electrolytes, the lower phase transition temperature makes it have a relatively higher ionic conductivity at low temperatures. KMS-2 is a stable potassium ion-conducting electrolyte alternative that can be used in atmospheric environments, as it does not undergo any structural changes when exposed to moisture and / or O2.

[0244] Example 3: Microstructure and density analysis of KMS-2

[0245] Materials and methods

[0246] Microstructural characterization was performed using a scanning electron microscope (SEM) (ZEISS Merlin, Carl Zeiss, Germany). The sample surface was dry polished and subjected to thermal etching in air at 750 °C for 30 minutes. Micrographs were acquired using a combination of secondary and in-lens electron signals, and an acceleration voltage (UEHT) of 2-5 kV.

[0247] Density measurements were performed by a Micromeritics AccuPyc 1340 gas pycnometer under helium at 25 °C.

[0248] Results

[0249] Figure 5 A-B show scanning electron microscope (SEM) images at different magnifications of the KMS-2 surface of the particles sintered at 800 °C (dry polished and thermally etched in air at 750 °C for 30 minutes). The pictures show that even at this relatively low sintering temperature, the particles have a high degree of densification, which indicates that the pores and holes in the material are almost quantitatively eliminated. This observation is also supported by the density measurement obtained by the gas pycnometer, which shows a relative density of 95 ± 2 %, with a value of 2.28 ± 0.01 g / cm 3 .

[0250] Conclusions

[0251] The analysis of KMS-2 by SEM and density measurements clearly indicates that it has a high level of densification, which is essential to ensure the best performance of the particles and self-standing tapes in various applications, most notably as potassium ion-conducting solid-state electrolytes for potassium batteries.

[0252] Example 4: Electrochemical characterization of KMS-1, KMS-2, KMS-4 and KMS-5 and comparison with KMS-0

[0253] Materials and methods

[0254] To electrochemically characterize the KMS, dense sintered pellets with a diameter and thickness of ~10 mm and 1-2 mm, respectively, were prepared. Pt was coated on both sides of the pellets as K-blocking electrodes. The ionic conductivity of the samples was measured by electrochemical impedance spectroscopy (EIS) using a Solarton 1260 impedance analyzer in a two-electrode configuration, with an AC amplitude of 50 mV, in the frequency range of 0.06 Hz to 1 MHz, under open-circuit conditions. During the measurements, the samples were squeezed between two Pt meshes and a small external load was applied to provide better contact. The test chamber was placed inside a closed-tube furnace, under N2(p02= 3-10 -5 The measurements were performed under dry N2(dry protective atmosphere, relative humidity at inlet 2-4%), air (relative humidity at inlet 30-40%) and wet air (relative humidity at inlet higher than 90%). Measurements were performed on 4-8 samples under each temperature and atmosphere combination, and the average was taken as the conductivity. To evaluate the electronic conductivity, the same samples were also analyzed at room temperature under dry N2using 500 mV DC potentiostatic polarization method (chronoamperometry).

[0255] Results

[0256] Figure 6 Ionic conductivity measurements are presented for KMS-0, KMS-1, KMS-2, KMS-4 and KMS-5. By changing the chemical composition from stoichiometric KMS-0 to potassium hyperstoichiometric and magnesium deficient KMS-1, KMS-2, KMS-4 and KMS-5, an increase in ionic conductivity with increasing “x” value was observed, especially at temperatures below 300 °C. Moreover, the temperature dependence of the conductivity values indicates a significantly lower activation energy for K + The activation energy related to the transport kinetics is 0.36 eV.

[0257] Figure 7 A shows a comparison between the ionic conductivity of Pt / KMS-2 / Pt symmetric cells under dry N2(dry protective atmosphere, relative humidity at inlet 2-4%) and air (ambient conditions, relative humidity 30-40%). KMS-2 exhibits high ionic conductivity under dry N2, up to 5-10 -5 S / cm and 2-10 -2 S / cm at room temperature and 300 °C, respectively. The temperature dependence of the ionic conductivity of KMS-2 (measured under N2) was found to have a relatively low activation energy of 0.36 eV. Such a level of conductivity is achieved without the use of non-abundant elements such as Sb and Te or metals with multiple ionization states such as Fe. While KMS-2 exhibits a competitive level of ionic conductivity compared to standard K-BASE (potassium beta alumina solid state electrolyte), it sintered at only 850 °C, which is significantly lower than the typical sintering temperature of K-BASE (1400-1700 °C), making it a cheaper and more scalable alternative for industrial applications.

[0258] Figure 7B shows the DC potentiostatic polarization results of Pt / KMS-2 / Pt cell under dry N2at room temperature. The measurement results were used to evaluate the electronic conductivity of KMS-2 sample. KMS-2 exhibits very low electronic conductivity of ~5 · 10 -9 S / cm, which is about four orders of magnitude lower than the ion conductivity measured at room temperature, so K + The transference number is close to 1. Ion transference number close to 1 is a necessary feature to develop potassium ion batteries with solid-state electrolytes.

[0259] Conclusion

[0260] The ion conductivity of KMS-2 is higher than the conductivity of the classic potassium ion-conducting solid-state electrolytes (e.g. K-BASE) reported in the literature. Therefore, these data suggest that KMS has the potential to be a fast K + conductor. Moreover, this material can be processed and handled under atmospheric air, while many previously reported fast solid-state K + conductors (e.g. K2Mg2TeO6, KSi2P3, or K3SbS4) cannot do this.

[0261] Example 5: Thermogravimetric analysis of KMS-2

[0262] Materials and methods

[0263] KMS-2 was subjected to thermogravimetric analysis (TG analyzer (STA409 CD - simultaneous TG-DSC) NETZSCH-GmbH, Germany) under Ar atmosphere by applying a heating rate of 10 °C / min from 25 °C to 700 °C, a dwell time at 700 °C, and a cooling rate of 10 °C / min from 700 °C to 25 °C.

[0264] Results

[0265] Figure 8 The thermogravimetric analysis plot shown reveals the thermal behavior of KMS-2. The plot shows that during the entire initial heating process, there is a significant decrease in mass, which can be attributed to the removal of surface moisture and decomposition of the hydrated phase. This trend continues up to 200 °C. Thereafter, the rate of mass reduction slows down. As the temperature is further increased to 700 °C, the rate of mass reduction tends to stabilize. The observed stable mass at 700 °C indicates that the sample has reached a thermodynamic steady state. Upon cooling the sample from 700 °C to room temperature, no significant mass gain is observed.

[0266] Conclusion

[0267] The constant weight of the KMS-2 sample throughout the thermogravimetric analysis demonstrates the stability of the sample and the absence of hydrated phase formation and water uptake.

[0268] ​Example 6: Stability under ambient conditions

[0269] Materials and methods

[0270] Prior to characterisation, the sintered particles of KMS-2 (original KMS) were first vacuum packed with moisture barrier bags. A set of sintered particles stored at room temperature in air (relative humidity 30-40%) for 60 days prior to measurement (aged KMS-2) and another set of aged KMS-2 samples heat treated at 600°C for 24 hours under dry N2(recovered KMS-2) were analysed using X-ray photoelectron spectroscopy (XPS). XPS analysis was performed using an ESCALAB 250Xi X-ray photoelectron spectroscopy microprobe (Thermo Fisher Scientific, East Grinstead, UK) using a monochromatic Al-Ka (1486.6 eV) X-ray source with a spot size of 300 pm at 90° to the surface. A dual beam source in the form of a combined ion / electron gun was used for charge compensation. Sputter depth profiling was performed using a single atom Ar + ion beam at a kinetic energy of 1000 eV. For each step, the etching time was 5 seconds and 5-6 etching steps were performed during the depth profiling. The elemental composition of the surface was determined by survey spectra between 0-1350 eV. High resolution binding energy spectra of K 2p 1 / 2 / K 2p 3 / 2 (288-304 eV), Mg1s (1296-1309 eV) and Si2p (95-110 eV) were also obtained for further characterisation. Prior to each measurement, the peak position on the spectrum was calibrated by analysing the Au4f 7 / 2 (84.0 eV) peak obtained from the surface of a gold foil.

[0271] Results

[0272] As Figure 9 shown, the spectra show peaks related to the binding energies of K + , Mg 2+ and Si 4+ . The peaks in the energy ranges 290-294 eV, 294-297 eV, 1300-1306 eV and 98-106 eV are related to the binding energies of K2p 1 / 2 , K2p 3 / 2 , Mg1s and Si2p, respectively. Indeed, in the aged KMS-2 samples, Figure 9E), the Mg1s peak is almost absent, indicating the presence of a thin K-rich / Si-rich layer on the surface. The change in surface composition could be caused by the formation of an amorphous hydrated phase, as previously reported for similar filled cristobalite silicates. Notably, after the recovery process, an increase in the Mg content on the surface is observed, as shown in the spectrum of the recovered KMS-2 ( Figure 9 H). The reappearance of the Mg1s peak indicates that the surface composition has been partially reformed during the recovery process. Considering the mobility of all ions in this composition, this phenomenon is likely due to the K + Downward diffusion and subsequent surface dissolution of the surface-separated phase.

[0273] like Figure 10 As shown in Figure 2, the surface of KMS-2 material undergoes slight degradation when exposed to atmospheric air, which can be significantly reversed by heat treatment at 600 °C for 24 h under N2. Figure 9 In addition to aging the aged KMS-2 sample in sintered pellet form for 60 days at room temperature, it was also exposed to humid air for an additional 300 hours to exacerbate degradation. Following this enhanced degradation process, the aged KMS-2 sample was then subjected to a heat-treatment recovery process. This is likely due to the formation of an amorphous or hydrated phase on the KMS-2 surface during aging, resulting in a thin layer with low ionic conductivity that can be partially recovered by the secondary heat treatment. However, this differs from the performance recovery of layered structures, where moisture sensitivity can be reduced by heat treatment / drying at high temperatures, thereby reducing the interlayer spacing. It should be noted that the performance of non-oxide superionic conductors (such as Na3SbS4) has also been reported to recover from degraded hydrated phases by secondary heat treatment at 200°C under vacuum, although the mechanism of this behavior is unclear.

[0274] in conclusion

[0275] The structural behavior of the KMS-2 solid electrolyte suggests that this compound could potentially be used in ceramic processing techniques under ambient laboratory conditions, with subsequent degradation effects reversed by heat treating the material in an environment with low moisture content.

[0276] Example 7: Potential Sensing of SO2

[0277] Materials and methods

[0278] A type III potentiometric solid-state gas sensor (O2, Au | Ag | KMS-2 | K2SO4 | Pt | Au, SO2, O2) for the detection of SO2 (equilibrated from synthetic air) was developed using KMS-2 as electrolyte; a porous K2SO4 layer combined with a porous Pt layer as auxiliary sensing electrode; and a KMS-2 surface exposed to air (underneath the porous silver, see below) combined with a porous silver layer as reference electrode, as shown in the scheme in C. Figure 11 In a type III potentiometric gas sensor, the target gas (here SO2) is in thermodynamic equilibrium with the ionic species (here SO42- immobilized in K2SO4) inside the auxiliary sensing electrode. 2-

[0279] Results

[0280] Figure 11 A and 1 IB show the relationship between electromotive force (emf) and SO2 concentration at 500 °C, the emf response / recovery time for a 2 ppm SO2 step change, and a schematic of the potentiometric sensing mechanism for SO2, respectively. The sensor showed a sensitivity of 74-89 mV / dec in the SO2 concentration range of 0-10 ppm at 500 °C, which is in good agreement with the theoretical sensitivity (77 mV / dec) based on a two-electron reaction following the Nernst equation (Eq. III).

[0281] Conclusion

[0282] Compared to a type III potentiometric sensor based on lithium lanthanum zirconium oxide (LLZO) electrolyte and a similar sulfate sensing electrode, the sensor in this study showed similar or higher sensitivity (10 times higher) and comparable response / recovery time (2-120 min) in the same temperature and SO2 concentration range.

[0283] Example 8: Symmetric cell cycling - metal electrode plating / de-plating

[0284] Materials and methods

[0285] The ability of metal electrode plating / de-plating is one of the key indicators for solid state electrolytes in all-solid-state battery or semi-solid-state battery applications. This test is typically performed by galvanostatic cycling with potential limits (GCPL) on a symmetric cell made by sandwiching a solid state electrolyte between two metal electrodes containing metal ions suitable for conduction through the electrolyte solid state electrolyte.

[0286] ​The goal of this measurement was to verify two key features crucial for battery applications: a) the transport of alkali metal ions through the electrolyte; and b) the ability of alkali metals to bind to or dissociate from the battery electrodes during operation. To this end, a 1 cm diameter, 120 μm thick KMS-2 disk was sandwiched between two sheets of sodium foil to create a symmetric Na / KMS-2 / Na cell. This cell was then assembled into a CR2032 coin cell in an argon-filled glove box, where oxygen and moisture levels were below 0.1 ppm.

[0287] Here, the Na electrode is selected as the electrode to determine the alkali metal ions (Na + and K + The assembled symmetric coin cells were analyzed outside the glove box at 40 °C using a BioLogic VMP3 multichannel potentiostat (BioLogic Science Instruments) according to the manufacturer's instructions and the GCPL method.

[0288] During the charging (electroplating) process, metal ions from the electrolyte adhere to the surface of the sodium electrode under the influence of an applied electric field. The metal ions are reduced by electrons provided by the external circuit (generated by an external power source) and deposited on the surface of the metal anode. As more ions are deposited, the metal anode layer becomes thicker, and electrical energy is stored in the form of chemical potential energy.

[0289] During discharge (stripping), the reverse process occurs: the metal in the electrode layer is oxidized and diffuses into the electrolyte layer, releasing electrons to the external circuit. The flow of electrons in the external circuit can be used as electrical work.

[0290] Successful plating and stripping are crucial to achieving reversible charge and discharge cycles within solid-state batteries.

[0291] The metal plating / stripping cycle was carried out at a current density of 0.1 mA / cm 2 and 1mA / cm 2 and the potential range is from -1V to 1V. Figure 12 A and 12B show the metal plating / stripping depth of 0.025 mAh / cm, respectively. 2 (The current density is 0.1 mA / cm 2 ) and 0.25mAh / cm 2 (The current density is 1 mA / cm 2 ) . In both cases, stable and reproducible metal plating / stripping cycling performance, low overpotential, and low interfacial resistance were observed within the experimental timeframe (30.000 s), supporting the potential of KMS-2 as a solid electrolyte for various solid-state or semi-solid-state battery applications.

[0292] Item

[0293] 1. A solid-state electrolyte comprising a potassium ion-conducting polycrystalline material of general formula K 2+X Mg 1-(X / 2) SiO4(0.0 < x < 0.5).

[0294] 2. The solid-state electrolyte according to item 1, consisting essentially of a potassium ion-conducting polycrystalline material of general formula K 2+X Mg 1-(X / 2) SiO4(0.0 < x < 0.5).

[0295] 3. The electrolyte according to any one of items 1 or 2, wherein X is selected from 0.1, 0.2, 0.3, 0.4 and 0.5

[0296] 4. The electrolyte according to any one of the preceding items, wherein X is selected from 0.2 to 0.4, preferably 0.2 or 0.4.

[0297] 5. The electrolyte according to any one of the preceding items, wherein the polycrystalline material is characterized by an orthorhombic space group at room temperature.

[0298] 6. The electrolyte according to item 5, wherein the orthorhombic space group is Pca21 at room temperature.

[0299] 7. The electrolyte according to item 6, wherein the space group Pca21 is characterized by the following lattice parameters:

[0300]

[0301] and

[0302]

[0303] 8. The electrolyte according to any one of items 6 to 7, wherein the space group Pca21 is characterized by the following lattice parameters:

[0304]

[0305] and

[0306]

[0307] 9. The electrolyte according to any one of the preceding items, wherein the polycrystalline material is characterized by a crystal structure comprising a corner-sharing polyhedron of non-alkali metal ions, such as a corner-sharing tetrahedron comprising SiO4 and / or MgO4 moieties.

[0308] 10. The electrolyte according to any of the preceding items, wherein the polycrystalline material is characterized by a phase transition temperature in the range of 100 °C to 1000 °C, such as 100 °C to 200 °C, such as 200 °C to 250 °C, such as 250 °C to 300 °C, such as 300 °C to 350 °C, such as 350 °C to 400 °C, such as 400 °C to 500 °C, such as 500 °C to 600 °C, such as 600 °C to 700 °C, and wherein the phase transition temperature represents a transition from an orthorhombic space group to a cubic space group.

[0309] 11. The electrolyte according to any of the preceding items, wherein the polycrystalline material is characterized by a phase transition temperature in the range of 200 °C to 250 °C, and wherein the phase transition temperature represents a transition from an orthorhombic space group to a cubic space group.

[0310] 12. The electrolyte according to any of the preceding items, characterized by a potassium ion conductivity at room temperature (25 °C) in the range of 1 · 10 -7 S / cm to 1 · 10 -4 S / cm, when measured by electrochemical impedance spectroscopy (EIS).

[0311] 13. The electrolyte according to any of the preceding items, wherein the polycrystalline material is characterized by a cubic space group at 300 °C, wherein the cubic space group is Fd-3m.

[0312] 14. The electrolyte according to any of the preceding items, characterized by a potassium ion conductivity at 300 °C in the range of 1 · 10 -7 S / cm to 1 · 10 -1 S / cm, when measured by electrochemical impedance spectroscopy (EIS).

[0313] 15. The electrolyte according to any of the preceding items, characterized by a relative density of 90 ± 2% or more, such as 91 ± 2% or more, such as 92 ± 2% or more, such as 93 ± 2% or more, such as 94 ± 2% or more, such as 95 ± 2% or more, such as 96 ± 2% or more, such as 97 ± 2% or more, such as 98 ± 2%, preferably a relative density of 95 ± 2%.

[0314] 16. The electrolyte according to any of the preceding items, characterized by an electronic conductivity at room temperature (25 °C) in the range of 1 · 10 -10 S / cm to 1 · 10 -6 S / cm, when measured by chronoamperometry at 500 mV.

[0315] 17. The electrolyte according to any of the preceding items, characterized by an electronic conductivity at 300 °C in the range of 1 · 10-10 1 · 10 -6 S / cm.

[0316] 18. The electrolyte according to any one of the preceding items for use as a component in a sensor.

[0317] 19. The electrolyte according to item 18, wherein the sensor is a potentiometric sensor.

[0318] 20. The electrolyte according to any one of items 18 to 19, wherein the sensor is for sensing a gas, such as a gas selected from the group consisting of SO2, SO3, NO, NO2, CO and CO2.

[0319] 21. A potassium-ion battery comprising:

[0320] a potassium-ion conductive electrolyte layer,

[0321] a positive electrode layer,

[0322] a negative electrode layer, and

[0323] wherein at least one of the electrolyte layer, the positive electrode layer and the negative electrode layer comprises the potassium-ion conductive polycrystalline material of any one of items 1 to 17.

[0324] 22. The battery according to item 21, wherein the potassium-ion conductive electrolyte layer is formed between the positive electrode layer and the negative electrode layer.

[0325] 23. The battery according to any one of items 21 to 22, wherein the potassium-ion conductive electrolyte layer is a solid-state potassium-ion conductive electrolyte layer.

[0326] 24. The battery according to item 23, wherein the solid-state potassium-ion conductive electrolyte layer comprises at least one selected from the group consisting of an inorganic solid-state electrolyte, a liquid-state electrolyte, a solid-state polymer electrolyte and a composite formed by combining any one of the aforementioned with the KMS electrolyte of any one of items 1 to 17.

[0327] 25. The battery according to item 24, wherein the inorganic solid-state electrolyte is selected from the group consisting of K-BASE, K2MgSiO4, KAlO2, KFeO2, KGaO2, K 0.7 Sr 0.15 GaO2 KAlSiO4, K2CaSiO4, K2Mg2TeO6, K2ZnSiO4, K2Si2P3, K2Sb5P2O 10 , K 2.92 Sb 0.92 W 0.08 S4, K 0.59 Mg 0.53 Sb 0.47O2、K3SbS4、K 1.9 Fe 1.95 P 0.05 O4、K 1.9 Pb 0.05 AlO2、K 0.405 Bi 0.865 AsO4、K 0.4 CD 0.3 FeO2、K2Fe4O7、K 1.6 Zn 0.8 Ti 7.2 The 16 、K 0.72 In 0.72 Sn 0.28 O2、KBiO3、K3Sc(MoO4)3、KMgPO4、K2MgV2O7、K2Mg2Si2O7、K2CaP2O7、K2ZnGeO4、K2Mg2(MoO4)3、K4Mg(WO4)3、K2CaPO4F、Li7La3Zr2O 12 (LLZO), Li 5.1 Ga 0.32 La3Zr 2.25 The 13 、Li 6.25 Ga 0.25 La3Zr2O 12 、Li x The y TiO3(LLTO)(0.07≤x≤0.13;y±0.05=(2 / 3)-x)、Li 0.45 The 0.48 TiO3、Li5La3X2O 12 (X=Nb or Ta), Li x PO y N z (3.0≤x≤3.2;3.0≤y≤3.5;0.0≤z≤0.5;3≤(y+z)≤4)、Li 3.13 PO 1.69 N 1.39 、Li 0.98 PO 2.55 N 0.50 、Li3PO4、La 1+x Al x Ti 2-x (PO4)3(0≤x≤2)、Li 1.3 Al 0.4 Ti 1.7 (PO4)3、Li 10 GeP2S 12 、Li7P3S 11, Na-BASE, NaM2(PO4)3 (M = Ge, Ti, Zr), Na 1+x Zr2Si x P 3-x O 12 (0 < X < 3), Na2MgSiO4, Na2CaSiO4, Na2ZnSiO4, Na2Mg2TeO6, Na2Mg2ZnO6, Na3PS4, Na4SiS4, Na3PSe4, Na 10 SnP2S 12 and Na3SbS4.

[0328] 26. The battery of any one of items 24 to 25, wherein the inorganic solid-state electrolyte is selected from K-BASE, K2MgSiO4, KAlSiO4, K2CaSiO4, K2Si2P3, K 2.92 Sb 0.92 W 0.08 S4, K3SbS4, Na-BASE, Na 1+x Zr2Si x P 3-x O 12 (0 < X < 3), Na2MgSiO4, and Na2CaSiO4.

[0329] 27. The battery of item 24, wherein the liquid electrolyte is selected from ether electrolytes such as (AN(SO2F)2 in DME) or (ACF3SO3 in TEGDME); ester electrolytes such as (APF6 in EC / DMC), (APF6 in PC), or (AN(SO2F)2 in EC / DEC), ATFSI in tetraethylene glycol dimethyl ether; and aqueous electrolytes such as (1M KNO3 per 0.01M HNO3), (1M KNO3 pH = 2), 0.5M K2SO4, 0.1M KCl, 22M KCF3SO3, 3M KCl, 30M KFSI, or 1M KOH, where (A = K, Li, or Na).

[0330] 28. The battery according to item 24, wherein the solid-state polymer electrolyte is selected from (KTFSI+PEO), PEO-KAg4I5, PEO-KBrO3, PPC-KFSI, PEO-KFSI, PVP+PVA+KBrO3, PVC+KBrO3, PAN-KI, PMMA-KPF6, PVA-KCI, (LiTFSI+PEO), PEO-LiAg4I5, PEO-LiBrO3, PPC-LiFSI, PEO-LiFSI, PVP+PVA+LiBrO3, PVC+LiBrO3, PAN-Lil, PMMA-LiPF6, PVA-LiCI, (NaTFSI+PEO), PEO-NaAg4I5, PEO-NaBrO3, PPC-NaFSI, PEO-NaFSI, PVP+PVA+NaBrO3, PVC+NaBrO3, PAN-Nal, PMMA-NaPF6, PVA-NaCI, for example preferably (KTFSI+PEO), (LiTFSI+PEO) or (NaTFSI+PEO).

[0331] 29. The battery according to any one of items 21 to 28, wherein the positive electrode layer is selected from a solid-state positive electrode layer, a liquid-state positive electrode layer and a hybrid positive electrode layer.

[0332] 30. The battery according to item 29, wherein the positive electrode layer is a solid-state positive electrode layer comprising:

[0333] a. a carbonaceous material, for example carbon black,

[0334] b. a binder, for example PVDF or PAA,

[0335] c. at least one inorganic solid-state electrolyte selected from K-BASE, K2MgSiO4, KAlO2, KFeO2, KGaO2, K 0.7 Sr 0.15 GaO2 KAlSiO4, K2CaSiO4, K2Mg2TeO6, K2ZnSiO4, K2Si2P3, K2Sb5P2O 10 , K 2.92 Sb 0.92 W 0.08 S4, K 0.59 Mg 0.53 Sb 0.47 O2, K3SbS4, K 1.9 Fe 1.95 P 0.05 O4, K 1.9 Pb 0.05 AlO2, K 0.405 Bi 0.865 AsO4, K0.4 Cd 0.3 FeO2, K2Fe4O7, K 1.6 Zn 0.8 Ti 7.2 O 16 , K 0.72 In 0.72 Sn 0.28 O2, KBiO3, K3Sc(MoO4)3, KMgPO4, K2MgV2O7, K2Mg2Si2O7, K2CaP2O7, K2ZnGeO4, K2Mg2(MoO4)3, K4Mg(WO4)3, K2CaPO4F, Li7La3Zr2O 12 (LLZO), Li 5.1 Ga 0.32 La3Zr 2.25 O 13 , Li 6.25 Ga 0.25 La3Zr2O 12 , Li x La y TiO3(LLTO) (0.07≤x≤0.13; y±0.05=(2 / 3)-x), Li 0.45 La 0.48 TiO3, Li5La3X2O 12 (X=Nb or Ta), Li x PO y N z (3.0≤x≤3.2; 3.0≤y≤3.5; 0.0≤z≤0.5; 3≤(y+z)≤4), Li 3.13 PO 1.69 N 1.39 , Li 0.98 PO 2.55 N 0.50 , Li3PO4, La 1+x Al x Ti 2-x (PO4)3(0≤x≤2), Li 1.3 Al 0.4 Ti 1.7 (PO4)3, Li 10 GeP2S 12 , Li7P3S 11 , Na-BASE, NaM2(PO4)3 (M=Ge, Ti, Zr), Na 1+x Zr2Si x P 3-x O 12(0 < x < 3), Na2MgSi04, Na2CaSi04, Na2ZnSi04, Na2Mg2Te06, Na2Mg2Zn06, Na3PS4, Na4SiS4, Na3PSe4, Na 10 SnP2S 12 and Na3SbS4;

[0336] d. active electrode material comprising one or more of:

[0337] i. sulfur-based cathode material selected from pure sulfur, K2S x (x = 1, 2, 3, 5), Na2S x (x = 1, 2, 3, 5), Li2S x (x = 1, 2, 3, 5) and PAN-S, preferably K2S x (x = 1, 2, 3, 5) and / or PAN-S; and / or

[0338] ii. inorganic-based cathode material selected from K2Ni2Te06, K3Co02, K 0.3 Mn02, K2FeSi04, KFeSi04, K2CoNiTe06, KFeP04F, K2Ni02, K2CuP207, K2FeSi04, KFeSi206, KMnP04, K2FeGe04, KVP207, K 0.71 Cu[Fe(CN)6] 0.72 ·3.7H20, K 0.6 Ni 1.2 Fe(CN)6·3.6H20, K2Fe II [Fe II (CN)6]·2H20, Fe III [Fe III (CN)6], K2NiFe(CN)6·1.2H20, K 1.85 Fe 0.33 Mn 0.67 [Fe(CN)6] 0.98 ·0.77H20, K 0.22 V 1.74 O 4.37 ·0.82H20,

[0339] KM II Fe III (CN)6(M = Mn, Fe, Co, Ni and Zn), NaCo02, NaNi02, NaMn02,

[0340] NaFe02, Na 7 / 9 Cu 2 / 9 Fe1 / 9 Mn 2 / 3 O2, Na3V2(PO4)3, Na2VTi(PO4)3, Na 0.66 Mn 0.66 Ti 0.34 O2, Na 0.44 MnO2, Na2LiV2(PO4)3, Li4Ti5O 12 , LiFePO4, LiMn2O4, LiNiMnCoO2, LiNiCoAlO2, LiCoO2, preferably K2Ni2TeO6, K2FeSiO4, and KFeSi2O6; and / or

[0341] iii. organic cathode materials selected from A 2+x C6O6 (0 < X < 4), (A = Na, K, Li).

[0342] 31. The battery according to item 29, wherein the cathode layer is a liquid cathode layer comprising one or more sulfur-type cathode materials as active electrode material, selected from pure sulfur, K2S x (x = 1, 2, 3, 5), Na2S x (x = 1, 2, 3, 5), Li2S x (x = 1, 2, 3, 5), preferably K2S x (x = 1, 2, 3, 5), optionally in combination with a liquid electrolyte selected from ether electrolytes, such as AN(SO2F)2 in DME or ACF3SO3 in TEGDME; ester electrolytes, such as APF6 in EC / DMC, APF6 in PC, or AN(SO2F)2 in EC / DEC, ATFSI in tetraethylene glycol dimethyl ether; and aqueous electrolytes, such as 1M KNO3 per 0.01M HNO3, 1M KNO3 pH = 2, 0.5M K2SO4, 0.1M KCl, 22M KCF3SO3, 3M KCl, 30M KFSI, or 1M KOH, wherein (A = K, Li, or Na).

[0343] 32. The battery according to item 29, wherein the cathode layer is a hybrid cathode layer comprising any combination of a solid-state cathode layer as defined in item 30 and a liquid cathode layer as defined in item 31.

[0344] 33. The battery according to any one of items 21 to 32, wherein the anode layer is selected from a solid-state anode layer, a liquid anode layer, and a hybrid anode layer.

[0345] 34. The battery according to item 33, wherein the anode layer is a solid-state anode layer comprising one or more of:

[0346] a) a metal selected from K, Li, Na, Al or alloys thereof, preferably K or ternary K-Na-Li alloys,

[0347] b) a carbon-based negative electrode selected from graphite and hard carbon, and

[0348] c) a silicon-based negative electrode selected from silicon, crystalline silicene or zintle (potassium silicide, sodium silicide, lithium silicide and calcium silicide).

[0349] 35. The battery according to item 33, wherein the negative electrode layer is a liquid negative electrode layer comprising one or more of:

[0350] a metal selected from K, Li, Na, Al or alloys thereof, preferably K or ternary K-Na-Li alloys.

[0351] 36. The battery according to item 33, wherein the negative electrode layer is a hybrid negative electrode layer comprising any combination of a solid-state negative electrode layer as defined in item 34 and a liquid negative electrode layer as defined in item 35.

[0352] 37. The battery according to any one of items 21 to 36, wherein the positive electrode layer is a solid-state positive electrode layer and the negative electrode layer is a solid-state negative electrode layer.

[0353] 38. A sensor comprising the ionically conductive polycrystalline material of any one of items 1 to 17.

[0354] 39. The sensor according to item 38, wherein the sensor is adapted to detect a gas selected from SO2, SO3, NO, NO2, CO and CO2.

[0355] 40. The sensor according to any one of items 38 to 39, wherein the sensor is a potentiometric sensor, such as a Type III potentiometric sensor.

[0356] 41. The sensor according to any one of items 38 to 40, wherein the sensor has a sensitivity of 74-89 mV / dec at 500 °C.

[0357] 42. The sensor according to any one of items 38 to 41, wherein the sensor has a detection limit for SO2 of 1-10 ppm at 500 °C.

[0358] 43. The sensor according to any one of items 38 to 42, wherein the sensor has a response / recovery time for SO2 of 2 to 120 minutes at 500 °C.

[0359] 44. A method of manufacturing a solid-state electrolyte according to any one of items 1 to 17, the method comprising the following consecutive steps:

[0360] a. mixing at least one potassium source, at least one magnesium source and at least one silicon source in a ratio to obtain a superstoichiometric potassium ratio corresponding to (2+X): 1-(X / 2): 1 (0.0 < X < 0.5) of K:Mg:Si, thereby forming a mixture, and

[0361] b. heating the mixture to a first temperature of 600 °C to 1000 °C to obtain a sintered mixture.

[0362] 45. The method according to item 44, further comprising the step of ball milling the mixture prior to step b.

[0363] 46. The method according to any one of items 44 to 45, further comprising the step of pulverizing the sintered mixture into a fine powder after step b., granulating the fine powder, and heating the granulated powder to a second temperature of 600 °C to 1000 °C.

[0364] 47. The method according to item 46, wherein the steps of pulverizing, granulating and heating are repeated at least 3 times, such as 4 times, such as 5 times, such as any one of 6, 7, 8, 9 and 10 times.

[0365] 48. The method according to any one of items 44 to 47, wherein the first and second temperatures are temperatures below 1000 °C, such as below 950 °C, such as below 900 °C, such as below 850 °C, such as below 800 °C.

[0366] 49. The method according to item 48, wherein the first and second temperatures are temperatures below 850 °C.

[0367] 50. The method according to any one of items 46 to 49, wherein the granulation is performed by applying a uniaxial pressure of 50 MPa to 100 MPa, preferably 70 MPa to 90 MPa.

[0368] 51. The method according to any one of items 44 to 50, wherein the at least one potassium source is a potassium salt or a potassium oxide, such as selected from the group consisting of KF, KC1, KBr, KI, KNO3, K2CO3, K3PO4, K2SO4, KClO4, KClO3, K2O and KOH.

[0369] 52. The method according to any one of items 44 to 51, wherein the at least one potassium source is K2CO3 or K2O.

[0370] 53. The method of any one of items 44 to 52, wherein the at least one magnesium source is a magnesium salt or a magnesium oxide, for example selected from the group consisting of MgF2, MgCl2, MgBr2, MgI2, Mg(N03)2, MgC03, Mg3(P04)2, MgS04, Mg(CI04)2, Mg(CI03)2, MgO, and Mg(OH)2.

[0371] 54. The method of any one of items 53 to 62, wherein the at least one magnesium source is MgO.

[0372] 55. The method of any one of items 44 to 54, wherein the at least one silicon source is a halide of silicon or an oxide of silicon, for example selected from the group consisting of SiCl4and Si02.

[0373] 56. The method of any one of items 44 to 55, wherein the at least one silicon source is SiCl4and Si02.

[0374] 57. The method of any one of items 44 to 56, wherein the method is performed under ambient conditions.

[0375] 58. The method of any one of items 44 to 56, wherein the method is performed in an inert atmosphere, for example an inert atmosphere consisting essentially of nitrogen or argon.

[0376] Item 2

[0377] 1. A solid-state electrolyte comprising a potassium ion-conducting polycrystalline material of the general formula K 2+X Mg 1-(X / 2) Si04(0.0 < x < 0.5).

[0378] 2. The solid-state electrolyte of item 1, consisting essentially of a potassium ion-conducting polycrystalline material of the general formula K 2+X Mg 1-(X / 2) Si04(0.0 < x < 0.5), wherein X is selected from the group consisting of 0.1, 0.2, 0.3, 0.4, and 0.5.

[0379] 3. The electrolyte of any one of the preceding items, wherein the polycrystalline material is characterized by an orthorhombic space group at room temperature, wherein the orthorhombic space group is Pca21 at room temperature, characterized by the following lattice parameters:

[0380]

[0381] and

[0382]

[0383] 4. The electrolyte according to any one of the preceding items, wherein the polycrystalline material is characterized by a crystal structure comprising corner polyhedra of non-alkali metal ions, such as corner tetrahedra comprising SiO4 and / or MgO4 moieties.

[0384] 5. The electrolyte according to any one of the preceding items, wherein the polycrystalline material is characterized by a phase transition temperature in the range of 200 °C to 250 °C, and wherein the phase transition temperature represents a transition from an orthorhombic space group to a cubic space group.

[0385] 6. The electrolyte according to any one of the preceding items, wherein the polycrystalline material is characterized by a cubic space group at 300 °C, wherein the cubic space group is Fd-3m.

[0386] 7. The electrolyte according to any one of the preceding items, characterized by a potassium ion conductivity at room temperature (25 °C) in the range of 1 · 10 -5 S / cm to 1 · 10 -4 S / cm.

[0387] 8. The electrolyte according to any one of the preceding items, characterized by a potassium ion conductivity at 300 °C in the range of 1 · 10 -4 S / cm to 1 · 10 -1 S / cm.

[0388] 9. The electrolyte according to any one of the preceding items, characterized by a relative density of 95 ± 2 % or more.

[0389] 10. The electrolyte according to any one of the preceding items, characterized by an electronic conductivity at room temperature (25 °C) in the range of 1 · 10 -10 S / cm to 1 · 10 -6 S / cm, when measured by chronoamperometry at 500 mV.

[0390] 11. The electrolyte according to any one of the preceding items, for use as a component in a sensor, wherein the sensor is used for sensing a gas, such as a gas selected from the group consisting of SO2, SO3, NO, NO2, CO and CO2.

[0391] 12. A method of manufacturing a solid-state electrolyte according to any one of items 1 to 10, the method comprising the following consecutive steps:

[0392] a. mixing at least one potassium source selected from K2CO3 or K2O, at least one magnesium source which is MgO, and at least one silicon source selected from SiCl4 and SiO2 in a ratio to obtain a superstoichiometric potassium ratio corresponding to (2+X):1-(X / 2):1 (0.0 < X < 0.5) of K:Mg:Si, thereby forming a mixture, and

[0393] b. heating the mixture to a first temperature of 600 °C to 1000 °C to obtain a sintered mixture.

[0394] 13. The method of item 12, further comprising the following steps after step b.: comminuting the sintered mixture using a planetary ball mill with a cup and balls made of zirconium oxide at a rotation speed of 150 rpm for 6 hours to a fine powder, granulating the fine powder, and heating the granulated powder to a second temperature of 600 °C to 1000 °C, wherein the steps of comminuting, granulating and heating are repeated at least 3 times, and wherein the first and second temperatures are temperatures lower than 850 °C.

[0395] 14. A potassium ion battery comprising:

[0396] a potassium ion-conducting electrolyte layer,

[0397] a positive electrode layer,

[0398] a negative electrode layer, and

[0399] wherein at least one of the electrolyte layer, the positive electrode layer and the negative electrode layer comprises the potassium ion-conducting polycrystalline material of any one of items 1 to 10.

[0400] 15. A potential sensor comprising the potassium ion-conducting polycrystalline material of any one of items 1 to 10, wherein the sensor is suitable for detecting a gas selected from the group consisting of SO2, SO3, NO, NO2, CO and CO2, wherein the sensor is characterized by a detection limit for SO2 of 1-10 ppm at 500 °C.

Claims

1. A solid electrolyte comprising an ion-conductive polycrystalline material with the general formula K 1-(X / 2) Mg 1-(X / 2) SiO4 (0.0 < x ≤ 0.5).

2. The solid electrolyte according to claim 1, which mainly consists of an ion-conductive polycrystalline material with the general formula K 2+X Mg 1-(X / 2) SiO4 (0.0 < x ≤ 0.5).

3. The electrolyte according to any one of claims 1 or 2, wherein X is selected from 0.1, 0.2, 0.3, 0.4 and 0.

5.

4. The electrolyte according to any one of the preceding claims, wherein X is selected from 0.2 to 0.4, preferably 0.2 or 0.

4.

5. The electrolyte of any one of the preceding claims, wherein the polycrystalline material is characterized by an orthorhombic space group at room temperature. The electrolyte according to claim 5 , wherein the orthorhombic space group is Pca21 at room temperature.

7. The electrolyte of claim 6, wherein the space group Pca21 is characterized by the following lattice parameters: To 11.1, to 5.50, and To 15.

6.

8. The electrolyte according to any one of claims 6 to 7, wherein the space group Pca21 is characterized by the following lattice parameters: and 9. An electrolyte according to any one of the preceding claims, wherein the polycrystalline material is characterised by a crystal structure comprising corner-sharing polyhedra of non-alkali metal ions, such as corner-sharing tetrahedra comprising SiO4 and / or MgO4 moieties.

10. The electrolyte of any one of the preceding claims, wherein the polycrystalline material is characterized by a phase transition temperature of 100°C to 1000°C, such as 100°C to 200°C, such as 200°C to 250°C, such as 250°C to 300°C, such as 300°C to 350°C, such as 350°C to 400°C, such as 400°C to 500°C, such as 500°C to 600°C, such as 600°C to 700°C, and wherein the phase transition temperature represents a transition from an orthorhombic space group to a cubic space group.

11. The electrolyte of any one of the preceding claims, wherein the polycrystalline material is characterized by a phase transition temperature of 200°C to 250°C, and wherein the phase transition temperature represents a transition from an orthorhombic space group to a cubic space group.

12. The electrolyte according to any one of the preceding claims, characterized in that The potassium ion conductivity at room temperature (25°C) was 1·10 -7 S / cm to 1·10 -4 S / cm.

13. The electrolyte of any preceding claim, wherein the polycrystalline material is characterized by a cubic space group at 300°C, wherein the cubic space group is Fd-3m.

14. The electrolyte according to any one of the preceding claims, characterized in that The potassium ion conductivity at 300°C was 1·10 -7 S / cm to 1·10 -1 S / cm.

15. The electrolyte according to any one of the preceding claims, characterized in that The relative density is 90±2% or higher, such as 91±2% or higher, such as 92±2% or higher, such as 93±2% or higher, such as 94±2% or higher, such as 95±2% or higher, such as 96±2% or higher, such as 97±2% or higher, such as 98±2%, and the preferred relative density is 95±2%.

16. The electrolyte according to any one of the preceding claims, characterized in that The electronic conductivity at room temperature (25°C) is 1·10 -10 S / cm to 1·10 -6 S / cm.

17. The electrolyte according to any one of the preceding claims, characterized in that The electronic conductivity at 300 °C was 1·10 when measured by chronoamperometry at 500 mV. -10 S / cm to 1·10 -6 S / cm.

18. An electrolyte according to any one of the preceding claims, wherein the ion-conducting polycrystalline material is alkali metal ion-conducting, such as potassium ion-conducting and / or sodium ion-conducting.

19. The electrolyte of any preceding claim, wherein the ion-conducting polycrystalline material is potassium-ion-conducting.

20. The electrolyte of any preceding claim, wherein the ion-conducting polycrystalline material is sodium-ion conductive.

21. Use of an electrolyte according to any one of the preceding claims as a component in a sensor.

22. Use according to claim 21, wherein the sensor is a potentiometric sensor.

23. Use according to any one of claims 21 to 22, wherein the sensor is for sensing a gas, such as a gas selected from SO2, SO3, NO, NO2, CO and CO2.

24. A battery comprising: an ion-conducting electrolyte layer, positive electrode layer, negative electrode layer, and At least one of the electrolyte layer, the positive electrode layer and the negative electrode layer comprises the conductive polycrystalline material according to any one of claims 1 to 20.

25. The battery of claim 24, wherein the conductive polycrystalline material is potassium ion conductive and / or sodium ion conductive.

26. The battery according to any one of claims 24 to 25, wherein the battery is a potassium ion battery or a sodium ion battery.

27. The battery of claim 26, wherein the battery is a potassium ion battery.

28. The battery of claim 26, wherein the battery is a sodium ion battery.

29. The battery of claim 27, wherein the battery comprises: an ion-conducting electrolyte layer, which is a potassium ion-conducting electrolyte layer, positive electrode layer, negative electrode layer, and At least one of the electrolyte layer, the positive electrode layer and the negative electrode layer comprises the ion-conducting polycrystalline material according to any one of claims 1 to 20. 30 . The battery according to claim 24 , wherein the ion-conductive electrolyte layer is formed between the positive electrode layer and the negative electrode layer.

31. The battery according to any one of claims 24 to 30, wherein the ion-conducting electrolyte layer is a solid ion-conducting electrolyte layer, such as the KMS electrolyte according to any one of claims 1 to 20.

32. The battery according to claim 31, wherein the solid ion-conducting electrolyte layer comprises at least one selected from the group consisting of an inorganic solid electrolyte, a liquid electrolyte, a solid polymer electrolyte, the KMS electrolyte of any one of claims 1 to 20, and a composite material formed by combining any one of the foregoing with the KMS electrolyte of any one of claims 1 to 20.

33. The battery according to claim 32, wherein the inorganic solid electrolyte is selected from K-BASE, K2MgSiO4, KAlO2, KFeO2, KGaO2, K 0.7 Sr 0.15 GaO2 KAlSiO4, K2CaSiO4, K2Mg2TeO6, K2ZnSiO4, K2Si2P3, K2Sb5P2O 10 , K 2.92 Sb 0.92 W 0.08 S4, K 0.59 Mg 0.53 Sb 0.47 O2, K3SbS4, K 1.9 Fe 1.95 P 0.05 O4, K 1.9 Pb 0.05 AlO2, K 0.405 Bi 0.865 AsO4、K 0.4 Cd 0.3 FeO2, K2Fe4O7, K 1.6 Zn 0.8 Ti 7.2 O 16 , K 0.72 In 0.72 Sn 0.28 O2, KBiO3, K3Sc(MoO4)3, KMgPO4, K2MgV2O7, K2Mg2Si2O7, K2CaP2O7, K2ZnGeO4, K2Mg2(MoO4)3, K4Mg(WO4)3, K2CaPO4F, Li7La3Zr2O 12 (LLZO), Li 5.1 Ga 0.32 La3Zr 2.25 O 13 、Li 6.25 Ga 0.25 La3Zr2O 12 、Li x La y TiO3(LLTO)(0.07≤x≤0.13;y±0.05=(2 / 3)-x), Li 0.45 La 0.48 TiO3、Li5La3X2O 12 (X=Nb or Ta), Li x PO y N z (3.0≤x≤3.2; 3.0≤y≤3.5; 0.0≤z≤0.5; 3≤(y+z)≤4), Li 3.13 PO 1.69 N 1.39 、 Li 0.98 PO 2.55 N 0.50 、 Li3PO4、 La 1+x Al x Ti 2-x (PO4)3 (0 ≤ x ≤ 2), Li 1.3 Al 0.4 Ti 1.7 (PO4)3, Li 10 GeP2S 12 、 Li7P3S 11 、 Na - BASE, NaM2(PO4)3 (M = Ge, Ti, Zr), Na 1+x Zr2Si x P 3-x O<^ 12 (0 ≤ X ≤ 3), Na2MgSiO4, Na2CaSiO4, Na2ZnSiO4, Na2Mg2TeO6, Na2Mg2ZnO6, Na3PS4, Na4SiS4, Na3PSe4, Na 10 SnP2S 12 and Na3SbS4.

34. The battery according to any one of claims 32 to 33, wherein the inorganic solid electrolyte is selected from K-BASE, K2MgSiO4, KAlSiO4, K2CaSiO4, K2Si2P3, K 2.92 Sb 0.92 W 0.08 S4, K3SbS4, Na-BASE, Na 1+x Zr2Si x P 3-x O 12 (0 < X < 3), Na2MgSiO4 and Na2CaSiO4.

35. A battery according to claim 32, wherein the liquid electrolyte is selected from ether electrolytes such as (AN(SO2F)2 in DME) or (ACF3SO3 in TEGDME); ester electrolytes such as (APF6 in EC / DMC), (APF6 in PC) or (AN(SO2F)2 in EC / DEC), ATFSI in tetraethylene glycol dimethyl ether; and aqueous electrolytes such as (1M KNO3 per 0.01M HNO3), (1M KNO3 pH=2), 0.5M K2SO4, 0.1M KCl, 22M KCF3SO3, 3M KCl, 30M KFSI or 1M KOH, wherein (A=K, Li or Na).

36. The battery of claim 32, wherein the solid polymer electrolyte is selected from the group consisting of (KTFSI+PEO), PEO-KAg4I5, PEO-KBrO3, PPC-KFSI, PEO-KFSI, PVP+PVA+KBrO3, PVC+KBrO3, PAN-KI, PMMA-KPF6, PVA-KCl, (LiTFSI+PEO), PEO-LiAg4I5, PEO-LiBrO3, PPC-LiFSI, PEO-LiFSI, PVP+PVA+Li BrO3, PVC+LiBrO3, PAN-LiI, PMMA-LiPF6, PVA-LiCl, (NaTFSI+PEO), PEO-NaAg4I5, PEO-NaBrO3, PPC-NaFSI, PEO-NaFSI, PVP+PVA+NaBrO3, PVC+NaBrO3, PAN-NaI, PMMA-NaPF6, PVA-NaCl, for example, preferably (KTFSI+PEO), (LiTFSI+PEO) or (NaTFSI+PEO).

37. The battery of any one of claims 24 to 36, wherein the cathode layer is selected from a solid cathode layer, a liquid cathode layer, and a hybrid cathode layer.

38. The battery of claim 37, wherein the cathode layer is a solid-state cathode layer comprising: a. carbonaceous materials, such as carbon black; and / or b. a binder such as PVDF or PAA; and / or c. At least one inorganic solid electrolyte selected from the following: K-BASE, K2MgSiO4, KAlO2, KFeO2, KGaO2, K 0.7 Sr 0.15 GaO2 KAlSiO4, K2CaSiO4, K2Mg2TeO6, K2ZnSiO4, K2Si2P3, K2Sb5P2O 10 , K 2.92 Sb 0.92 W 0.08 S4, K 0.59 Mg 0.53 Sb 0.47 O2, K3SbS4, K 1.9 Fe 1.95 P 0.05 O4, K 1.9 Pb 0.05 AlO2, K 0.405 Bi 0.865 AsO4、K 0.4 Cd 0.3 FeO2, K2Fe4O7, K 1.6 Zn 0.8 Ti 7.2 O 16 , K 0.72 In 0.72 Sn 0.28 O2, KBiO3, K3Sc(MoO4)3, KMgPO4, K2MgV2O7, K2Mg2Si2O7, K2CaP2O7, K2ZnGeO4, K2Mg2(MoO4)3, K4Mg(WO4)3, K2CaPO4F, Li7La3Zr2O 12 (LLZO), Li 5.1 Ga 0.32 La3Zr 2.25 O 13 、Li 6.25 Ga 0.25 La3Zr2O 12 、Li x La y TiO3(LLTO)(0.07≤x≤0.13;y±0.05=(2 / 3)-x), Li 0.45 La 0.48 TiO3、Li5La3X2O 12 (X=Nb or Ta), Li x PO y N z (3.0≤x≤3.2; 3.0≤y≤3.5; 0.0≤z≤0.5; 3≤(y+z)≤4), Li 3.13 PO 1.69 N 1.39 , Li 0.98 PO 2.55 N 0.50 , Li3PO4, La 1+x Al x Ti 2-x (PO4)3 (0 ≤ x ≤ 2), Li 1.3 Al 0.4 Ti 1.7 (PO4)3, Li 10 GeP2S 12 , Li7P3S 11 , Na-BASE, NaM2(PO4)3 (M = Ge, Ti, Zr), Na 1+x Zr2Si x P 3-x O 12 (0 ≤ X ≤ 3), Na2MgSiO4, Na2CaSiO4, Na2ZnSiO4, Na2Mg2TeO6, Na2Mg2ZnO6, Na3PS4, Na4SiS4, Na3PSe4, Na 10 SnP2S 12 and Na3SbS4; d. Active electrode materials, comprising one or more of the following: i. Sulfur-type positive electrode material, which is selected from pure sulfur, K2S x (x=1、2、3、5), Na2S x (x=1, 2, 3, 5), Li2S x (x=1, 2, 3, 5) and PAN-S, preferably K2S x (x=1, 2, 3, 5) and / or PAN-S; and / or ii. Inorganic cathode material selected from K2Ni2TeO6, K3CoO2, K 0.3 MnO2, K2FeSiO4, KFeSiO4, K2CoNiTeO6, KFePO4F, K2NiO2, K2CuP2O7, K2FeSiO4, KFeSi2O6, KMnPO4, K2FeGeO4, KVP2O7, K 0.71 Cu[Fe(CN)6] 0.72 ·3.7H2O、K 0.6 Nor 1.2 Fe(CN)6·3.6H2O、 K2Fe II [Fe II (CN)6]·2H2O、Fe III [Fe III (CN)6]、K2NiFe(CN)6·1.2H2O、 K 1.85 Fe 0.33 Mn 0.67 [Fe(CN)6] 0.98 ·0.77H2O、K 0.22 In 1.74 About 4.37 ·0.82H2O, KM II Fe III (CN)6(M=Mn, Fe, Co, Ni and Zn), NaCoO2, NaNiO2, NaMnO2, NaFeO2、Na 7 / 9 Cu 2 / 9 Feb 1 / 9 Mr 2 / 3 O2、Na3V2(PO4)3、Na2VTi(PO4)3、 Na 0.66 Mn 0.66 Ti 0.34 O2、Na 0.44 MnO2, Na2LiV2(PO4)3, Li4Ti5O 12 , LiFePO4, LiMn2O4, LiNiMnCoO2, LiNiCoAlO2, LiCoO2, preferably K2Ni2TeO6, K2FeSiO4 and KFeSi2O6; and / or iii. Organic cathode material selected from A 2+x C6O6(0 <X<4),(A=Na、K、 Li).

39. The battery according to claim 37, wherein the positive electrode layer is a liquid positive electrode layer, which comprises one or more sulfur-based positive electrode materials as active electrode materials, wherein the sulfur-based positive electrode materials are selected from pure sulfur, K2S x (x=1、2、3、5), Na2S x (x=1, 2, 3, 5), Li2S x (x=1, 2, 3, 5), preferably K2S x (x=1, 2, 3, 5), which are optionally combined with a liquid electrolyte, wherein the liquid electrolyte is selected from ether electrolytes, such as (AN(SO2F)2 in DME) or (ACF3SO3 in TEGDME); ester electrolytes, such as (APF6 in EC / DMC), (APF6 in PC) or (AN(SO2F)2 in EC / DEC), ATFSI in tetraethylene glycol dimethyl ether; and aqueous electrolytes, such as (1M KNO3 per 0.01M HNO3), (1M KNO3 pH=2), 0.5M K2SO4, 0.1MKCl, 22M KCF3SO3, 3M KCl, 30M KFSI or 1M KOH, wherein (A=K, Li or Na).

40. The battery according to claim 37, wherein the positive electrode layer is a hybrid positive electrode layer comprising any combination of a solid positive electrode layer as defined in claim 38 and a liquid positive electrode layer as defined in claim 39.

41. The battery of any one of claims 24 to 40, wherein the negative electrode layer is selected from the group consisting of a solid negative electrode layer, a liquid negative electrode layer, and a hybrid negative electrode layer.

42. The battery of claim 41 , wherein the negative electrode layer is a solid-state negative electrode layer comprising one or more of: a) a metal selected from K, Li, Na, Al or alloys thereof, preferably K or a ternary K-Na-Li alloy; and / or b) a carbon-type negative electrode selected from graphite and hard carbon; and / or c) A silicon-type negative electrode selected from silicon, crystalline silicene or zintle (potassium silicide, sodium silicide, lithium silicide and calcium silicide).

43. The battery of claim 41 , wherein the negative electrode layer is a liquid negative electrode layer comprising one or more of: The metal is selected from K, Li, Na, Al or alloys thereof, preferably K or a ternary K-Na-Li alloy.

44. The battery according to claim 41, wherein the negative electrode layer is a hybrid negative electrode layer, which comprises any combination of the solid negative electrode layer defined in claim 42 and the liquid negative electrode layer defined in claim 43.

45. The battery according to any one of claims 24 to 44, wherein the positive electrode layer is a solid positive electrode layer and the negative electrode layer is a solid negative electrode layer.

46. A sensor comprising the ion-conductive polycrystalline material according to any one of claims 1 to 20.

47. The sensor according to claim 46, wherein the sensor is suitable for detecting gases selected from SO2, SO3, NO, NO2, CO, and CO2.

48. The sensor according to any one of claims 46 to 47, wherein the sensor is a potentiometric sensor, such as a type III potentiometric sensor.

49. The sensor according to any one of claims 46 to 48, wherein the sensitivity of the sensor at 500 °C is 74 - 89 mV / dec.

50. The sensor according to any one of claims 46 to 49, wherein the detection limit of the sensor for SO2 at 500 °C is 1 - 10 ppm.

51. The sensor according to any one of claims 46 to 50, wherein the response / recovery time of the sensor for SO2 at 500 °C is 2 to 120 minutes.

52. The sensor according to any one of claims 46 to 50, wherein the response and / or recovery time of the sensor for SO2 at 500 °C is 2 to 120 minutes.

53. A method of manufacturing the solid electrolyte according to any one of claims 1 to 20, the method comprising the following consecutive steps: a. Mixing at least one potassium source, at least one magnesium source, and at least one silicon source in a certain ratio to obtain a super-stoichiometric potassium ratio of K:Mg:Si corresponding to (2 + X):1 - (X / 2):1 (0.0 < X ≤ 0.5), thereby forming a mixture, and b. Heating the mixture to a first temperature of 600 °C to 1000 °C to obtain a sintered mixture.

54. The method according to claim 53, further comprising a step of ball-milling the mixture before step b.

55. The method according to any one of claims 53 to 54, further comprising a step of crushing the sintered mixture into fine powder after step b, granulating the fine powder, and heating the granulated powder to a second temperature of 600 °C to 1000 °C.

56. The method according to claim 55, wherein the steps of crushing, granulating, and heating are repeated at least 3 times, such as 4 times, such as 5 times, such as any one of 6, 7, 8, 9, and 10 times.

57. The method according to any one of claims 53 to 56, wherein the first temperature and the second temperature are temperatures below 1000 °C, such as below 950 °C, such as below 900 °C, such as below ​ 59. The method according to any one of claims 55 to 58, wherein granulation is performed by applying a uniaxial pressure of 50 to 100 MPa, preferably 70 to 90 MPa.

60. The method according to any one of claims 53 to 59, wherein the at least one potassium source is a potassium salt or potassium oxide, for example selected from KF, KCl, KBr, KI, KNO3, K2CO3, K3PO4, K2SO4, KClO4, KClO3, K2O and KOH.

61. The method of any one of claims 53 to 60, wherein the at least one potassium source is K2CO3 or K2O.

62. The method of any one of claims 53 to 61, wherein the at least one magnesium source is a magnesium salt or magnesium oxide, for example selected from MgF2, MgCl2, MgBr2, MgI2, Mg(NO3)2, MgCO3, Mg3(PO4)2, MgSO4, Mg(ClO4)2, Mg(ClO3)2, MgO and Mg(OH)2.

63. The method of any one of claims 53 to 62, wherein the at least one magnesium source is MgO.

64. The method according to any one of claims 53 to 63, wherein the at least one silicon source is a silicon halide or a silicon oxide, for example selected from SiCl4 and SiO2.

65. The method of any one of claims 53 to 64, wherein the at least one silicon source is SiCl4 and SiO2.

66. The method of any one of claims 53 to 65, wherein the method is performed under ambient conditions.

67. The method according to any one of claims 53 to 65, wherein the method is carried out in an inert atmosphere, such as an inert atmosphere consisting mainly of nitrogen or argon.

68. Use of the electrolyte according to any one of claims 1 to 20 as a component in a battery.

69. Use according to claim 68, wherein the battery is a solid-state battery or a semi-solid-state battery.

70. The use according to claim 69, wherein the battery is a solid-state battery.

71. Use according to any one of claims 68 to 70, wherein the battery is an alkali metal ion conducting battery, such as a sodium ion battery or a potassium ion battery.

72. The use according to any one of claims 68 to 71, wherein the battery is a potassium ion battery.

73. Use according to any one of claims 68 to 71, wherein the battery is a sodium ion battery.

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