Solid material suitable for use as a solid electrolyte

Abstract

Described are a solid material suitable for use as a solid electrolyte, a process for preparing said solid material, and its use for preparing a cathode or a separator for an electrochemical cell.

Description

[0001]BASF SE Carl-Bosch-Straße 38, 67056 Ludwigshafen am Rhein Germany University of Waterloo 200 University Ave W, N2L 3G1 WATERLOO Canada Solid material suitable for use as a solid electrolyte Described are a solid material suitable for use as a solid electrolyte, a process for preparing said solid material, and its use for preparing a cathode or a separator for an electrochemical cell. Tao Dai et al. (Nature Energy, https: / / doi.org / 10.1038 / s41560-023-01356-y) describe inor- ganic glass electrolytes having a composition according to the formula MAlCl4−2xOx(M = Li, Na, 0.5 < x < 1). Said electrolytes have a polymer-like viscoelasticity. Said electrolytes are obtained by reacting molten tetrachloroaluminate of Li resp. Na with antimony (III) oxide as source of oxygen. However, this process has the disadvantage of generating the toxic by- product SbCl3.Further technological background is disclosed in HU et al., NATURE COMMUNICATIONS, vol.14, no.1, 27 June 2023, XP093221712; ZHANG SHUMIN et al., JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 29 Janu- ary 2024, XP093221713; and ZHANG SHUMIN et al., NATURE COMMUNICATIONS, vol.14, no.1, 24 June 2023, XP093221715; and BASF SE 231724 TANAKA YOSHIAKI et al., ANGEWANDTE CHEMIE INTERNATIONAL EDITION, vol.62, no.13, 20 February 2023, XP093221718. Due to the wide-spread use of all solid state lithium batteries, there is an increasing demand for solid state inorganic electrolytes having high plasticity which could be processed like polymer electrolytes without sacrificing advantageous properties of ceramic electrolytes like high ion conductivity and high chemical and electrochemical stability, and which are obtainable by a facile synthesis process. It is an objective of the present disclosure to provide a solid material which may be used as a solid electrolyte for an electrochemical cell. In addition, there is provided a process for preparing said solid material, a use of said solid material as a solid electrolyte for an elec- trochemical cell, a solid structure selected from the group consisting of a cathode and a separator for an electrochemical cell, and an electrochemical cell comprising such solid structure, wherein said solid structure comprises said solid material. According to a first aspect, there is provided a solid material comprising or consisting of discrete structural units of general formula (I) A(1+n)M(3-x-y)M’xM’’yX(6+n+x-y)O2(I) wherein in each structural unit (I), independently from each other structural unit (I), A is one or more of Li, Na and K; X is one or more of F, Cl and Br; M is trivalent and is one or more of Al, Ga and Fe; M’ is tetravalent and is one or more Si, Ge, Sn and Ti; M’’ is divalent and is one or more of Zn, Fe and Mg; each of n, x and y is an integer from 0 to 2; x + y ≤ 2; 0 ≤ n + x - y ≤ 2. In the structural units according to general formula (1), the ratio of the metals (M+M’+M’’) to oxygen is 3:2, and the ratio of the alkali metals A to the metals (M + M’+M’’) is from 1:3 (when n = 0) to 1:1 (when n = 2). BASF SE 231724 The parameter n defines the amount of AX present in addition to the basis composition AM(3-x-y)M’xM’’yX(6+x-y)O2 (n = 0). When n = 2, the structural unit is saturated with X, when n is 0 or 1 it is unsaturated with X. Without wishing to be bound by any theory, it is presently assumed that the discrete struc- tural units of the general formula (I) may be considered as oligomers, i.e. short-chain poly- mers, resulting in polymer-like characteristics of the above-defined solid material. More specifically, the oligomers are trimers. Without wishing to be bound by any theory, it is presently assumed that the solid material comprising or consisting of the above-defined structural units (trimers) is in a glassy state without long-range ordering. Within the solid material [M(3-x-y)M’xM’’yX(6+n+x-y)O2](1+n)-forms an anion the charge of which is balanced by (1+n) alkali metal cations. A considerable number of alkali cations are placed in dynamic states, thus being highly exchangeable, so that the ion conductivity is enhanced compared to the precursor materials of the type AMX4 (for details see below) which have crystalline structure. Furthermore, due to configurational entropy with rotational degree of freedom the solid material shows mechanical plasticity and a decreased elastic modulus. The plasticity of the above-defined solid material is evident from the observation that upon increasing pressure the conductivity of the material increases, and the increased conductivity is retained after releasing the pressure (for details see examples section be- low). In each discrete structural unit of general formula (I), the total number n of atoms of trivalent metals M (as defined above) is at least 1 and at most 3. If the total number of atoms of trivalent metals M (as defined above) corresponds to 3, then there are no atoms of tetra- valent metals M’ (x = 0) and no atoms of divalent metals M’’ (y = 0). The preferred alkali metals A are Li and Na. The preferred trivalent metal M is Al. The preferred tetravalent metal M’ is Si. The preferred divalent metal M’’ is Zn. BASF SE 231724 The preferred halogen X is Cl. In certain cases, the discrete structural units of general formula (I) of an above-defined solid material comprise a trivalent metal M, but neither a tetravalent metal M’ (x = 0) nor a divalent metal M’’ (y = 0). Preferably, the trivalent metal M is Al. In certain cases, the discrete structural units of general formula (I) of an above-defined solid material comprise a trivalent metal M, and a tetravalent metal M’ (1 ≤ x ≤ 2) but no divalent metal M’’ (y = 0). Preferably, the trivalent metal M is Al and the tetravalent metal M’ is Si. In certain cases, the discrete structural units of general formula (I) of an above-defined solid material comprise a trivalent metal M, and a divalent metal M’’ (1 ≤ y ≤ 2) but no tetravalent metal M’ (x = 0). Preferably, the trivalent metal M is Al and the divalent metal M’’ is Zn. In certain cases, in the discrete structural units of general formula (I) of an above-defined solid material A is Li or Na; n = 2; X is Cl; M is Al; x = 0; y = 0. In certain cases, in the discrete structural units of general formula (I) of an above-defined solid material A is Li or Na; n = 2; X is Cl; M is Al; M’ is Si; M’’ is Zn; BASF SE 231724 x = 1; y = 1. In certain cases, in the discrete structural units of general formula (I) of an above-defined solid material A is Li or Na; n = 2; X is Cl; M is Al; M’’ is Zn; x = 0; y = 1. In certain cases, in the discrete structural units of general formula (I) of an above-defined solid material A is Li or Na; n = 2; X is Cl; M is Al; M’’ is Zn; x = 0; y = 2. In said solid materials with n = 2, the discrete structural units of formula (I) are isostructural to catena-octachlorotrisiloxane Si3O2Cl8 which has a structure according to entry #409627 of the database for inorganic crystal structures (ICSD). In certain cases, in the discrete structural units of general formula (I) of an above-defined solid material A is Li or Na; n = 1; BASF SE 231724 X is Cl; M is Al; x = 0; y = 0. In certain cases, in the discrete structural units of general formula (I) of an above-defined solid material A is Li or Na; n = 1 X is Cl; M is Al; M’ is Si; x = 1; y = 0. In certain cases, in the discrete structural units of general formula (I) of an above-defined solid material A is Li or Na; n = 1 X is Cl; M is Al; M’ is Si; M’’ is Zn; x = 1; y = 1. In certain cases, in the discrete structural units of general formula (I) of an above-defined solid material A is Li or Na; n = 1 BASF SE 231724 X is Cl; M is Al; M’’ is Zn; x = 0 y = 1. In certain cases, in the discrete structural units of general formula (I) of an above-defined solid material A is Li or Na; n = 0; X is Cl; M is Al; x = 0; y = 0. In certain cases, in the discrete structural units of general formula (I) of an above-defined solid material A is Li or Na; n = 0 X is Cl; M is Al; M’ is Si; x = 1; y = 0. In certain cases, in the discrete structural units of general formula (I) of an above-defined solid material A is Li or Na; n = 0 X is Cl; BASF SE 231724 M is Al; M’ is Si; x = 2; y = 0. In certain cases, in the discrete structural units of general formula (I) of an above-defined solid material A is Li or Na; n = 0 X is Cl; M is Al; M’ is Si; M’’=Zn; x = 1; y = 1. In preferred cases, in the discrete structural units of general formula (I) of an above-defined solid material A is Li or Na; X is Cl; M is Al; x = y = 0 0 ≤ n ≤ 2. Such materials are lithium aluminum oxychlorides resp. sodium aluminum oxychlorides. In certain cases lithium aluminum oxychlorides resp. sodium aluminum oxychlorides having n = 2 are preferred, because as a result of their saturation with regard to Cl, the oxidation stability is increased due to sp3-hybridization of M-Cl and M-O. BASF SE 231724 In the structural units of above-defined general formula (I) - the three atoms of metals selected from M, M’ and M’’ as defined above and the two oxygen atoms may form a chain wherein each atom of oxygen forms a single bridge connecting two atoms of the metals selected from M, M’ and M’’ as defined above - alkali metals A may be coordinated to O via dative bonds and to X via ionic bonds. When the three atoms of the metals selected from M, M’ and M’’ as defined above and the two oxygen atoms form a chain wherein each atom of oxygen forms a single bridge be- tween two atoms of metals selected from M, M’ and M’ as defined above, in the discrete structural units of the general formula (I) non-bridging oxygen atoms and double bridges of oxygen atoms are virtually not present (double bridges of oxygen atoms means that two oxygen atoms at the same time connect two atoms of metals selected from M, M’ and M’’ as defined above). The absence of non-bridging oxygen atoms and double bridges of oxygen atoms is an important difference against the materials described by Tao Dai et al. (Nature Energy, https: / / doi.org / 10.1038 / s41560-023-01356-y) which is expected to result in different prop- erties (see examples section). The oxygen atoms forming the single bridges between the three atoms of the metals se- lected from M, M’ and M’’ as defined above may form dative bonds to the alkali metal ions. When n = 2, in the structural units of above-defined general formula (I) none of the atoms of the element X forms any bridge connecting atoms of metals selected from M, M’ and M’’ as defined above . When n = 1, in the structural units of above-defined general formula (I) one of the atoms of the element X forms a bridge connecting the first and the second of the three atoms of metals selected from M, M’ and M’’ as defined above. When n = 0, in the structural units of above-defined general formula (I) one of the atoms of the element X forms a bridge connecting the first and the second of the three atoms of metals selected from M, M’ and M’’ as defined above, and a further one of the atoms of the element X forms a bridge connecting the second and the third of the three atoms of metals selected from M, M’ and M’’ as defined above. BASF SE 231724 The solid material as defined above may have a glass transition temperature in the range of from -10 °C to -100 °C, preferably -15 °C to -100 °C, as determined by differential scan- ning calorimetry (DSC). The solid material as defined above may have an ionic conductivity of 0.8 mS / cm or more, preferably 1 mS / cm or more, more preferably 1.2 mS / cm or more, in each case measured at 30 °C. The ionic conductivity is determined in the usual manner known in the field of battery materials development by means of electrochemical impedance spectroscopy (for details see examples section below). In certain cases, the solid material as defined above comprises or consists of structural units of general formula (I) selected from the group consisting of LiAl3Cl6O2, Li2Al3Cl7O2, Li3Al3Cl8O2and mixtures thereof. In certain cases, the solid material as defined above comprises or consists of structural units of general formula (I) selected from the group consisting of NaAl3Cl6O2, Na2Al3Cl7O2, Na3Al3Cl8O2 and mixtures thereof. In certain cases, the solid material further contains one or more additional constituents selected from the group consisting of - compounds AX wherein A is one or more of Li, Na and K, X is one or more of F, Cl and Br; - compounds AMX4wherein A is one or more of Li, Na and K, M is trivalent and is one or more of Al, Ga and Fe, X is one or more of F, Cl and Br; - compounds A2M4O2X10(e.g. A2M4O2Cl10) wherein A is one or more of Li, Na and K, M is trivalent and is one or more of Al, Ga and Fe, X is one or more of F, Cl and Br; BASF SE 231724 - compounds MOX wherein M is trivalent and is one or more of Al, Ga and Fe, X is one or more of F, Cl and Br. In certain cases, said additional constituents may form separate phases detectable by X- ray diffraction. More specifically, in certain cases the solid material contains a phase having the composi- tion LiCl or NaCl, and in certain cases the solid material contains a phase having the com- position LiAlCl4 or NaAlCl4. In certain preferred cases, LiAlCl4 resp. NaAlCl4 is dissolved within the trimers of formula (I) (see examples section). Specific preferred solid materials have the following composition: (i) mixture of LiAl3Cl6O2, Li2Al4O2Cl10and AlOCl resp. mixture of NaAl3Cl6O2, Na2Al4O2Cl10 and AlOCl (ii) mixture of LiAl3Cl6O2 and Li2Al3Cl7O2 resp. mixture of NaAl3Cl6O2 and Na2Al3Cl7O2 (iii) mixture of LiAl3Cl6O2, Li2Al3Cl7O2and LiCl resp. mixture of NaAl3Cl6O2, Na2Al3Cl7O2and NaCl (iv) mixture of Li2Al3Cl7O2, Li3Al3Cl8O2 and LiCl resp. mixture of Na2Al3Cl7O2, Na3Al3Cl8O2 and NaCl (v) mixture of Li2Al3Cl7O2, Li3Al3Cl8O2, LiAlCl4and LiCl resp. mixture of Na2Al3Cl7O2, Na3Al3Cl8O2, NaAlCl4and NaCl. According to a second aspect, there is provided a process for preparing a solid material according to the above-defined first aspect. Said process comprises or consist of the steps of a) providing AlCl3•6H2O as oxygen source and the precursors - AMX4 wherein A is one or more of Li, Na and K, X is one or more of F, Cl and Br, BASF SE 231724 M is trivalent and is one or more of Al, Ga and Fe; - and optionally one or more of MX3wherein - X is one or more of F, Cl and Br, - M is trivalent and is one or more of Al, Ga and Fe - M’(OR)aXb wherein - M’ is tetravalent and is one or more Si, Ge, Sn and Ti, - R is alkyl, - X is one or more of F, Cl and Br, - each of a and b is an integer from 0 to 4, - a + b = 4; A2M’’X4wherein - A is one or more of Li, Na and K, - X is one or more of F, Cl and Br, - M’’ is divalent and is one or more of Zn, Fe and Mg; b) preparing a powder mixture comprising the precursors and AlCl3•6H2O in a molar ratio according to general formula (I); c) annealing the powder mixture obtained in step b) under vacuum for 3 to 10 hours at temperatures in the range of from 180°C to 250°C and allowing re- lease of one or more of - HX wherein X is one or more of F, Cl and Br, and - ROH wherein R is alkyl, and - RX wherein R is alkyl and X is one or more of F, Cl and Br, so that a material having a composition according to general formula (I) is obtained; d) cooling down the obtained material so that a solid material having a composi- tion according to general formula (I) is obtained. The preferred alkali metals A are Li and Na. BASF SE 231724 The preferred trivalent metal M is Al. The preferred tetravalent metal M’ is Si. The preferred divalent metal M’’ is Zn. The preferred halogen X is Cl. The preferred alkyl R is ethyl. In certain cases it is preferred that in formula M’(OR)aXb 0 ≤ b ≤ 3. The preferred precursors A2M’’X4are Li2ZnCl4and Na2ZnCl4. The preferred precursors AMX4are LiAlCl4and NaAlCl4. The preferred precursor MX3 is AlCl3. Compared to the process described by Tao Dai et al. (Nature Energy, https: / / doi.org / 10.1038 / s41560-023-01356-y), the process as defined above has the major advantage that aluminum chloride hexahydrate (AlCl3•6H2O) is used as the source of oxy- gen instead of Sb2O3, so that no toxic SbCl3 is released which requires cost-intensive post- processing. AlCl3•6H2O is a suitable source of oxygen because it releases HCl upon thermal decom- position while the remaining oxygen of the water is covalently bonded to Al. In a process for preparing a solid material according to the above-defined first aspect wherein x = 0 and 1 ≤ y ≤ 2 the precursors comprise or consist of - AMX4wherein A is one or more of Li, Na and K, X is one or more of F, Cl and Br, M is trivalent and is one or more of Al, Ga and Fe; - A2M’’X4wherein A is one or more of Li, Na and K, BASF SE 231724 X is one or more of F, Cl and Br, M’’ is divalent and is one or more of Zn, Fe and Mg; - optionally MX3wherein X is one or more of F, Cl and Br, M is trivalent and is one or more of Al, Ga and Fe; and no compounds of tetravalent metals M’. The preferred alkali metals A are Li and Na. The preferred trivalent metal M is Al. The preferred divalent metal M’’ is Zn. The preferred halogen X is Cl. The preferred precursors A2M’’X4are Li2ZnCl4and Na2ZnCl4. The preferred precursors AMX4are LiAlCl4and NaAlCl4. The preferred precursor MX3 is AlCl3. In a process for preparing a solid material according to the above-defined first aspect wherein y = 0 and 1 ≤ x ≤ 2 the precursors comprise or consist of - AMX4wherein A is one or more of Li, Na and K, X is one or more of F, Cl and Br, M is trivalent and is one or more of Al, Ga and Fe; - M’(OR)aXbwherein M’ is tetravalent and is one or more Si, Ge, Sn and Ti, R is alkyl; X is one or more of F, Cl and Br, each of a and b is an integer from 0 to 4, BASF SE 231724 a + b = 4; - optionally MX3 wherein X is one or more of F, Cl and Br, M is trivalent and is one or more of Al, Ga and Fe; and no compounds of divalent metals M’’. The preferred alkali metals A are Li and Na. The preferred trivalent metal M is Al. The preferred tetravalent metal M’ is Si. The preferred halogen X is Cl. The preferred alkyl R is ethyl. The preferred precursors M’(OR)aXbare Si(OR)aClbwherein a =1 and b = 3, or a = 2 and b = 2, or a = 3 and b = 1, or a = 4 and b = 0, and in each case R is ethyl. The preferred precursors AMX4 are LiAlCl4 and NaAlCl4. The preferred precursor MX3 is AlCl3. In a process for preparing a solid material according to the above-defined first aspect wherein x = 0 and y = 0 the precursors comprise or consist of - AMX4 wherein A is one or more of Li, Na and K, X is one or more of F, Cl and Br, M is trivalent and is one or more of Al, Ga and Fe; BASF SE 231724 - optionally MX3 wherein X is one or more of F, Cl and Br, M is trivalent and is one or more of Al, Ga and Fe. and no compounds of divalent metals M’’ and tetravalent metals M’. The preferred alkali metals A are Li and Na. The preferred trivalent metal M is Al. The preferred halogen X is Cl. The preferred precursors AMX4are LiAlCl4and NaAlCl4. The preferred precursor MX3 is AlCl3. In step c), annealing is preferably carried out for two hours at 200 °C. A preferred process comprises the steps of a) providing AlCl3•6H2O as oxygen source and the precursors - AAlCl4 wherein A is one or more of Li, Na and K, - optionally AlCl3b) preparing a powder mixture comprising the precursors and AlCl3•6H2O in a molar ratio according to general formula (I) c) annealing the powder mixture obtained in step b) under vacuum for 3 to 10 hours at temperatures in the range of from 180°C to 250°C and allowing release of HCl, so that a material having a composition according to general formula (I) is obtained d) cooling down the obtained material so that a solid material having a composition according to general formula (I) is obtained. A solid material according to the above-defined first aspect resp. obtained by the process according to the above-defined second aspect can be used as a solid electrolyte for an electrochemical cell. Herein the solid electrolyte may form a component of a solid structure BASF SE 231724 for an electrochemical cell, wherein said solid structure is selected from the group consist- ing of cathode and separator. Accordingly, a solid material according to the above-defined first aspect resp. obtained by the process according to the above-defined second aspect can be used (if necessary in combination with additional components) for producing a solid structure for an electrochemical cell, such as a cathode or a separator. Thus, the present disclosure further provides the use of a solid material according to the above-defined first aspect resp. obtained by the process according to the above- defined second aspect as a solid electrolyte for an electrochemical cell. Regarding specific and preferred solid materials according to the above-defined first aspect resp. obtained by the process according to the above-defined second aspect, the same applies as disclosed above in the context of the first aspect. More specifically, the present disclosure further provides the use of a solid material accord- ing to the above-defined first aspect resp. obtained by the process according to the above- defined second aspect as a component of a solid structure for an electrochemical cell, wherein said solid structure is selected from the group consisting of cathode and separator. In the context of the present disclosure, the electrode where during discharging a net neg- ative charge occurs is called the anode and the electrode where during discharging a net positive charge occurs is called the cathode. Suitable electrochemically active cathode ma- terials and suitable electrochemically active anode materials are known in the art. The cath- ode of a solid-state electrochemical cell usually comprises beside an active cathode mate- rial as a further component a solid electrolyte. Said solid electrolyte may be a solid material according to the above-defined first aspect resp. obtained by the process according to the above-defined second aspect. In an electrochemical cell, a separator electronically separates a cathode and an anode from each other. In a solid-state electrochemical cell, the separator comprises a solid elec- trolyte. Said solid electrolyte may be a solid material according to the above-defined first aspect resp. obtained by the process according to the above-defined second aspect. The present disclosure further provides a solid structure for an electrochemical cell, wherein the solid structure is selected from the group consisting of cathode and separator, wherein the solid structure for an electrochemical cell comprises a solid material according to the above-defined first aspect resp. obtained by the process according to the above- defined second aspect. BASF SE 231724 In certain cases, said solid structure is a cathode. Such cathode may comprise a mixture comprising one or more cathode active materials and a solid material according to the above-defined first aspect resp. obtained by the process according to the above-defined second aspect. Further constituents of said mixture are one or more selected from the group consisting of electron conducting materials and binding agents. In certain cases, said cathode comprises a cathode active material having a redox potential of 3.3 V or more vs. Li+ / Li, preferably of 4 V or more (cathode active material of the “4 V class”). Due to its favorable oxidation stability, a solid material according to the above- defined first aspect resp. obtained by the process according to the above-defined second aspect may be applied as a solid electrolyte in direct contact with a cathode active material having a redox potential of 4 V or more, more preferably of 4.3 V or more, most preferably of 4.5 V or more vs. Li+ / Li. Regarding specific and preferred solid materials according to the above-defined first aspect resp. obtained by the process according to the above-de- fined second aspect, the same applies as disclosed above in the context of the first aspect. For application with a cathode active material having a redox potential of 4 V or more, especially of 4.3 V or more or even 4.5 V or more vs. Li+ / Li, lithium aluminum oxychlorides resp. sodium aluminum oxychlorides having n = 2 are preferred, because as a result of their saturation with regard to Cl, the oxidation stability is increased due to sp3-hybridization of M-Cl and M-O. For instance, a solid material according to the above-defined first aspect resp. obtained by the process according to the above-defined second aspect may form a layer covering par- ticles of one or more cathode active materials. For instance, a solid material according to the above-defined first aspect resp. obtained by the process according to the above-defined second aspect may form a matrix wherein par- ticles of one or more cathode active materials are embedded. More specifically, in such cathode, a solid material according to the above-defined first aspect resp. obtained by the process according to the above-defined second aspect may form a coating on the surface of the cathode active material which may protect the solid electrolyte material of the separator layer of an electrochemical cell comprising such cath- ode from being oxidized by the cathode active material. BASF SE 231724 A cathode as described herein may comprise - a solid material according to the above-defined first aspect resp. obtained by the process according to the above-defined second aspect in a total amount of from 1 %to 50 %, more preferably of from 10 % to 30 %, further preferably of from 15 % to 25 %, relative to the total mass of the cathode - cathode active materials in a total amount of from 50 % to 99 %, more preferably of from 70 % to 97 %, relative to the total mass of the cathode - optionally, electron conducting materials in a total amount of from 1 % to 5%, more preferably from 1 % to 2 %, relative to the total mass of the cathode. - optionally, binding agents in a total amount of from 0.1 % to 3 %, relative to the total mass of the cathode. Typical electron-conducting materials are those comprising or consisting of elemental car- bon, e g. carbon black and graphite. Typical binding agents are polytetrafluoroethylene (PTFE), poly(vinylidenefluroride) (PVDF), styrene-butadiene rubber (SBR), polyisobutene, polyethylene vinyl acetate), polyacrylonitrile butadiene). Suitable electrochemically active cathode materials (cathode active materials) are known in the art, for example - Lithium iron phosphate - Cathode active materials selected from the group consisting of materials having a composition according to general formula (II) Li1+t[CoxMnyNizMu]1-tO2 (II) wherein 0 ≤ x ≤ 1 0 ≤ y ≤ 1 0 ≤ z ≤ 1 0 ≤ u ≤ 0.15 M if present is one or more elements selected from the group consisting of Al, Mg, Ba, B, and transition metals other than Ni, Co, and Mn, x + y + z > 0 x + y + z + u = 1 BASF SE 231724 -0.05 ≤ t ≤ 0.2; The cathode active material is most preferably selected from the group consisting of - LiCoO2, - lithium nickel cobalt manganese oxides (so called “NCM”), and - spinel lithium nickel manganese oxide. Advantageously, the cathode active materials are those having a redox potential of 4 V or more vs. Li+ / Li (cathode active material of the “4 V class”), which enable obtaining a high cell voltage may be used, since the solid material according to the above-defined first as- pect resp. obtained by the process according to the above-defined second aspect is stable in the presence of cathode active materials having such high redox potential. The form of the solid structure for an electrochemical cell, in particular for a solid-state lithium battery, depends in particular on the form of the electrochemical cell itself. The present disclosure further provides an electrochemical cell comprising a solid material according to the above-defined first aspect resp. obtained by the process according to the above-defined second aspect. In said electrochemical cell, the solid material according to the above-defined first aspect resp. obtained by the process according to the above-de- fined second aspect may form a component of one or more solid structures selected from the group consisting of cathode, and separator. Preferably, in said electrochemical cell the solid material according to the above-defined first aspect resp. obtained by the process according to the above-defined second aspect is not in direct contact with metallic lithium, in order to prevent undesired interaction. The above-defined electrochemical cell may be a rechargeable electrochemical cell com- prising the following constituents α) at least one anode, ß) at least one cathode, γ) at least one separator, wherein at least one of the constituents selected from the group consisting of cathode and separator comprises a solid material according to the above-defined first aspect resp. ob- tained by the process according to the above-defined second aspect. BASF SE 231724 Suitable electrochemically active cathode materials and suitable electrochemically active anode materials are known in the art. Exemplary cathode active materials are disclosed above. In an electrochemical cell as described above the anode α) may comprise graphitic carbon, metallic lithium or a metal alloy comprising lithium as the anode active material. Electrochemical cells as described above may be alkali metal ion cells, especially lithium- ion cells or sodium ion cells. In lithium-ion cells, the charge transport is effected by Li+ions. In sodium-ion cells, the charge transport is effected by Na+ions. The electrochemical cell may have a disc-like or a prismatic shape. The electrochemical cells can include a housing that can be from steel or aluminum. A plurality of electrochemical cells as described above may be combined to a solid-state battery, which has both solid electrodes and solid electrolytes. A further aspect of the pre- sent disclosure refers to batteries, more specifically to an alkali metal ion battery, in partic- ular to a lithium-ion battery comprising at least one electrochemical cell as described above, for example two or more electrochemical cells as described above. Electrochemical cells as described above can be combined with one another in alkali metal ion batteries, for example in series connection or in parallel connection. Series connection is preferred. The electrochemical cells resp. batteries described herein can be used for making or oper- ating cars, computers, personal digital assistants, mobile telephones, watches, camcord- ers, digital cameras, thermometers, calculators, laptop BIOS, communication equipment or remote car locks, and stationary applications such as energy storage devices for power plants. A further aspect of this disclosure is a method of making or operating cars, comput- ers, personal digital assistants, mobile telephones, watches, camcorders, digital cameras, thermometers, calculators, laptop BIOS, communication equipment, remote car locks, and stationary applications such as energy storage devices for power plants by employing at least one inventive battery or at least one inventive electrochemical cell. A further aspect of the present disclosure is the use of the electrochemical cell as described above in motor vehicles, bicycles operated by electric motor, robots, aircraft (for example unmanned aerial vehicles including drones), ships or stationary energy stores. The present disclosure further provides a device comprising at least one inventive electro- chemical cell as described above. Preferred are mobile devices such as are vehicles, for example automobiles, bicycles, aircraft, or water vehicles such as boats or ships. Other BASF SE 231724 examples of mobile devices are those which are portable, for example computers, espe- cially laptops, telephones or electrical power tools, for example from the construction sec- tor, especially drills, battery-driven screwdrivers or battery-driven tackers. The invention is illustrated further by the following examples which are not limiting. Examples Five powder mixtures of the oxygen source AlCl3•6H2O, and the precursors LiAlCl4 and optionally AlCl3in different molar ratios according to general formula (I) (see table 1) were ground together and annealed under vacuum at 200°C for two hours allowing release of HCl, and subsequently cooled down. The obtained lithium aluminum oxychlorides (LAOCs) (i) to (v) were subject to structural analysis, measurement of ionic conductivity and electrochemical tests. Structural analysis Fig.1 shows the synthesis route of LAOC and structure models of the trimers Tb0, Tb1and Tb2. The superscript of Tbxdenotes the number of bridging Cl. There are three possible configurations of anionic trimer: monovalent with two bridging Cl (Tb2), divalent with one bridging Cl (Tb1) and trivalent without bridging Cl (Tb0). The structures can be transformed one into the other by adding or subtracting LiCl. Tb2and Tb1structures are derived from known poly-chloroaluminates, and the structure of Tb0corresponds to the structure of the Si3O2Cl8molecule. The trimer Tb0is saturated with chlorine, while Tb1and Tb2are not. Table 1 shows the composition of the obtained lithium aluminum oxychlorides as deter- mined by XRD, X-ray pair distribution function (PDF) analysis, FT-IR and X-ray absorption spectroscopy (XAS). The absence of hydrogen was confirmed by1H-NMR measurement (not shown). BASF SE 231724 Table 1 LAOC No. Reactants Producti 3 LiAlCl4 5 AlCl3 AlCl3•H2O mixture of LiAl3Cl6O2, Li2Al4O2Cl10 and AlOClii 4.5 LiAlCl43.5 AlCl3 AlCl3•H2O mixture of LiAl3Cl6O2 and Li2Al3Cl7O2iii 6 LiAlCl4 2 AlCl3 AlCl3•H2O mixture of LiAl3Cl6O2, Li2Al3Cl7O2 and LiCliv 8 LiAlCl4 AlCl3•H2O mixture of Li2Al3Cl7O2, Li3Al3Cl8O2 and LiClv 9 LiAlCl4 AlCl3•H2O Mixture of Li2Al3Cl7O2, Li3Al3Cl8O2, LiAlCl4 and LiClX-ray diffraction patterns are displayed in Fig.2. Peaks attributed to the tetrameric lithium oxychloride Li2Al4O2Cl10 (herein referred to as Tet, not according to the invention) appear when the Li / Al ratio is below 0.5, and LiCl peaks come up when the Li / Al ratio is above 0.5. The absence of Tet in LAOC(ii), (iii) and (iv) was also confirmed by FTIR (Fig. 3). The materials having the lowest crystallinity, i.e. LAOC(ii) and (v), show the highest conductivity (see table 2 below and Fig.4). In LAOC(v), LiAlCl4 appears to be ‘dissolved’ within the trimers like a salt in an ionic liquid. Without wishing to be bound by theory, it is assumed that the dissolved LiAlCl4prevents phase separation of LiCl, and at elevated temperatures (>150°C) which are present during material preparation LiAlCl4 plays a role as plasticizer that increases the flowability of visco- plastic Trimers. Due to metastability, LAOC(v) does not release LiCl even at room temper- ature. But since LiAlCl4is a crystalline solid, it is phase-separated after harsh mechanical grinding, resulting in increased LiCl and LiAlCl4peaks (not shown). With more LiAlCl4con- tent (ratio Li / Al =0.92 ratio), LiAlCl4 is phase-separated in orthorhombic structure (Pmn21). LiAlCl4(Pmn21) has tetrahedral Li sites different from the original LiAlCl4(P121 / c1), having octahedral Li sites. Fig.5 displays the simulated trimer Tb1that contains bridging as well as non-bridging Cl. It is notable that the distances between Al-Al and O-Cl are shortened due to bridging. To investigate the structure in detail, X-ray synchrotron pair-distribution-function (PDF) analysis was conducted. Fig.6 presents X-ray synchrotron pair-distribution-function anal- ysis of LAOC(ii) and (v) as well as the simulated plot of LAOC(v) The simulated pair-distri- bution-function of LAOC(v) whose structure is generated from density functional theory (DFT) relaxation and ab-initio molecular dynamics (AIMD) matches decently with experi- mental data. LAOC(ii) shows notable peaks only up to 4.5 Å within Trimer length scale and BASF SE 231724 LAOC(v) shows only LiCl peaks above the range. The LiCl peaks in LAOC(v) occur be- cause of the grinding of the material in sample preparation which results in phase-separa- tion of LiCl. Since LAOC(ii) has more bridging Cl than (v), the signals from Al-Al and O-Cl are shifted to a shorter distance for LAOC(ii), compared to LAOC(v). At the peak corre- sponding to Cl-Cl (around 3.5 Å), due to the phase-separated LiCl the intensity of LAOC(v) becomes much larger compared to LAOC(ii). In the experimental X-ray synchrotron PDF, no peak is observed around 2.5~2.6 Å (Fig.6). Especially in PDF for LAOC(v), there is no signal in between 2.33~2.98 Å range (the three small bumps in between are considered as Fourier wiggles). Thus, LAOC(ii) and LAOC (v) have negligible double bridging oxygen. Fig.7 presents XAS of the oxygen K-edge for LAOC (ii), (iv) and (v), and for comparison for LiAlO2and Li5AlO4. XAS peaks of LAOC showed up at 539 eV which is same with Al2O3and it indicates the absence of non-bridging oxygen. Due to the increased number of non- bridging oxygen in LiAlO2 and Li5AlO4 the energy of the XAS peak is lower (536.8 eV resp. 535.3 eV). The absence of triple bonded O-Al3is confirmed by FTIR. Signals at 680 cm-1and 808 cm-1which correspond to triple bonded O in the tetramer Li2Al4O2Cl10(Tet) disappear in the FTIR of LAOC(ii). Additionally, based on PDF, there is no peak at 2.65 Å that corresponds to Al- Al distance of triple bonded oxygen. Thus, glassy LAOC has negligible triple bonded oxy- gen. Fig.8 shows the temperature-dependent heat capacity (determined by DSC) of LiAlCl4 and LAOC(i), (ii) and (iv). In general, the temperature dependency of a solid is originated from thermal vibration because all the atoms are fixed to their own position. Though LAOC(i) presents a similar tendency with crystalline LiAlCl4, LAOC(ii) and (iv) exhibit a glass transi- tion temperature (Tg) at around -15 °C. Glass transitions occur when the material can ex- plore various structural configurations in the potential energy landscape. The configura- tional entropy generally originates from the rotational degree of freedom like in organic polymers. In LAOC, the terminal -AlCl3could have rotational degree of freedom with non- bridged Cl as presented in Fig.5. The rotational motion occurred particularly in the glassy LAOCs in contrast to crystalline Tet that did not show glass transition although it has ter- minal –AlCl3. The emergence of configurational entropy implies its potential of facile struc- ture rearrangement at room temperature, which allows for increased alkali metal ion con- ductivity (see below). Upon preparing the LAOCs, oxygen is introduced to LiAlCl4 by the decomposition of H2O BASF SE 231724 from AlCl3•6H2O. In contrast to lithium chloride hydrate that releases H2O upon heating, aluminum chloride hydrate tends to release HCl with decomposition: - AlCl3•H2O ^ AlCl2(OH) + HCl Thus, it is reasonable to consider that all the O atoms have to bridge at least two Al via covalent bonding, and no non-bridging oxygen exists. Thermogravimetric analysis (not shown) revealed that the thermal degradation point of LAOC is much higher than that of LiAlCl4. LAOC(v) containing the Cl-saturated Trimer Tb0has higher decomposition temperature (~592℃) than LAOC(ii) containing Cl-unsaturated trimers Tb2and Tb1(~487℃). Ionic conductivity The ionic conductivity was measured by electrical impedance spectroscopy (EIS). Gener- ally, ~100 mg of the powder was placed between two titanium rods and pressed into a 10 mm diameter pellet by a hydraulic press in an Ar-filled glovebox. EIS experiments were performed with 100 mV constant voltage within a frequency range of 1 MHz to 100 mHz using a VMP3 potentiostat / galvanostat (BioLogic). Fig.4 shows the Li ion conductivity of lithium aluminum (oxy-)chlorides as a function of the structure and composition. Ball-milling of crystalline LiAlCl4already increases the conduc- tivity of LiAlCl4 by about one order of magnitude, compared to untreated crystalline Li AlCl4. Then, with the introduction of oxygen, a new crystalline structure based on the Li2Al4O2Cl10 tetramer (Tet, not according to the invention) occurs which is derived from Ag2Al4O2Cl10. Further increasing the oxygen content results in formation of trimers having 3:2 ratio of aluminum and oxygen (cf. table 1 above), and loss of crystallinity, so that the material ex- hibits a glassy state. As the content of LiCl increases from n = 0 to n =1 resp. n = 2, the trimer structure is transformed from Tb2to Tb1resp. Tb0(cf. fig.4). LAOC(i) which is a mixed phase of Tet and Tb2(cf. table 1 above) exhibits increased con- ductivity (~10-1mS / cm) compared to Tet. LAOC(ii) having 1:1 ratio of Tb2and Tb1has the highest conductivity (1.3 mS / cm) of the tested LAOCs. LAOC(iii) and (iv) have a lower ion conductivity due to the increasing fraction of released LiCl, which implies the higher ther- modynamic stability of Tb2compared to Tb1and Tb0at room temperature. As mentioned BASF SE 231724 above, it is assumed that the LiAlCl4 present in LAOC (v) acts as plasticizer that suppresses release of LiCl, thus resulting in an increase of conductivity compared to LAOC(iv) which does not contain LiAlCl4. The ionic conductivities (in each case measured at 30°C) of the trimeric lithium aluminum oxychlorides according to the invention and the comparison materials LiAlCl4 (untreated), ball-milled LiAlCl4 and Li2Al4O2Cl10 are compiled in table 2: Table 2 composition Ionic conductivity / mS / cm LiAlCl4 (untreated), 10-3ball-milled LiAlCl4 10-2Li2Al4O2Cl10 10-2LAOC(i) 10-1LAOC(ii) 1.3 LAOC(iii) 1 LAOC(iv) 0.5 LAOC(v) 1.2 For particulate LAOC(ii) the development of the ion conductivity with increasing pressure was studied. LiAlCl4(untreated), ball-milled (BM) LiAlCl4and Li6PS5Cl were studied for comparison. The ion conductivity was measured as a function of increasing pressure up to 85 MPa, and again after releasing pressure to 1.8 MPa (experimental setup shown as insert in Fig.9). Fig 9 shows a plot of the ion conductivity normalized to the ion conductivity of the material at 85 MPa. The slope of the conductivity with increasing pressure is related to the elastic modulus affecting the contact area between the particles. Different from LiAlCl4and Li6PS5Cl whose increase of the conductivity is still not saturated at 85 MPa, the increase of the conductivity of LAOC(ii) is saturated at 60 MPa. The earlier saturation represents the lower elastic modulus of LAOC(ii). After releasing the pressure, LAOC(ii) maintains the in- creased conductivity because of its plasticity, while the comparison materials loose a cer- tain degree of their conductivity at 85 MPa after releasing the pressure due to their elasticity. The slopes of the normalized ion conductivity in the low pressure (20 to 40 MPa) range are: LiAlCl4(untreated): 1.0, LiAlCl4(ball milled): 1.13, Li6PS5Cl: 1.14, LAOC(ii): 2.41, indicating that the elastic modulus of LAOC(ii) is lower than half of those of the comparison materials. BASF SE 231724 Thus, the plasticity of LAOC could eliminate the issues originating from the necessity of applying high-pressure during cell fabrication and operation of all solid state batteries. Arrhenius plots of the ion conductivity of LAOC (i), (ii) and (v) as well as of LiAlCl4(un- treated), and ball-milled (BM) LiAlCl4for comparison are shown in fig.10. It is notable that the ion conductivity of LAOC(ii) and (v) is enhanced about three orders from crystalline (Cr) LiAlCl4. Interestingly, the Arrhenius plots of LAOC(ii) and LAOC(v) are linear in overall range (80 °C to -60 °C) even though they undergo a glass transition at around -15℃. This is a disparate feature of the inorganic oligomer electrolyte, compared to organic electrolytes. Without wishing to be bound by theory, it implies that Li+ion migration in lithium aluminum oxychlorides arises from vibrational motion as in ceramic solid state electrolytes, rather than from configurational motion. The activation energies determined from the Arrhenius plot are: LiAlCl4 (untreated): 0.475 eV, LiAlCl4 (ball milled: 0.473 eV, LAOC(i): 0.417 eV, LAOC(ii): 0.471 eV, LAOC(v): 0.459 eV. Electrochemical tests The oxidation stability of LAOC(ii) and LAOC(v) (cf. table 1) was studied by linear sweep voltammetry (scan rate 0.1 mV / s). The lithium aluminum oxychlorides show different oxidation behavior depending on the de- gree of Cl saturation (as defined by subscript n in formula (I)) (Fig.11). For LAOC(ii) oxi- dation appears from 3.7 V and amplifies at 4.3 V, similar to LiAlCl4, while oxidation of LAOC(v) starts only at 4.4 V. The higher oxidation potential of LAOC(v) is attributed to the saturation of trimer Tb0with Cl, due to sp3-hybridization of Al-Cl and Al-O in trimer Tb0. An all solid state battery having a cathode composite composed of 80 wt% NCM85 (LiNi0.85Co0.1Mn0.05O2) and 20 wt% LAOC(v) (cf. Table 1) coated by a layer of LAOC(v), a separator made of Li6PS5Cl and an anode comprising a Li-In alloy was subjected to charge- discharge tests at 0.2 C. It shows high coulomb efficiency over more than 200 cycles with 4.3 V (Fig.12 and Fig 13) and even with 4.6 V (Fig.14 and Fig.15). Fig.16 displays the rate capability with 4.3 V. The cell run at 0.1C (206 mAh / g) approached the maximum capacity of NCM85 (210 mAh / g). After the rate capability test, long-term charge-discharge at 0.5C was tested and confirmed the excellent electrochemical stability of LAOC(v) (Fig.17).

Claims

BASF SE 231724 Claims:

1. Solid material comprising discrete structural units of general formula (I) A(1+n)M(3-x-y)M’xM’’yX(6+n+x-y)O2(I) wherein in each structural unit (I), independently from each other structural unit (I), A is one or more of Li, Na and K; X is one or more of F, Cl and Br; M is trivalent and is one or more of Al, Ga and Fe; M’ is tetravalent and is one or more Si, Ge, Sn and Ti; M’’ is divalent and is one or more of Zn, Fe and Mg; each of n, x and y is an integer from 0 to 2; x + y ≤ 2; 0 ≤ n + x - y ≤ 2.

2. Solid material according to claim 1, wherein in the units of general formula (I) - the three atoms of metals selected from M, M’ and M’’ and the two oxygen atoms form a chain wherein each atom of oxygen forms a single bridge con- necting two atoms of the metals selected from M, M’ and M’’, - alkali metals A are coordinated to O via dative bonds and to X via ionic bonds.

3. Solid material according to claim 1 or 2, wherein in the units of general formula (I) - one of the atoms of the element X forms a bridge connecting the first and the second of the three atoms of metals selected from M, M’ and M’’, and - optionally a further one of the atoms of the element X forms a bridge connect- ing the second and the third of the three atoms of metals selected from M, M’ and M’’.BASF SE 231724 4. Solid material according to claim 1, further comprising one or more constituents se- lected from the group consisting of - compounds AX wherein A is one or more of Li, Na and K, X is one or more of F, Cl and Br; - compounds AMX4 wherein A is one or more of Li, Na and K, M is trivalent and is one or more of Al, Ga and Fe X is one or more of F, Cl and Br; - compounds A2M4O2X10 wherein A is one or more of Li, Na and K, M is trivalent and is one or more of Al, Ga and Fe, X is one or more of F, Cl and Br; - compounds MOX wherein M is trivalent and is one or more of Al, Ga and Fe, X is one or more of F, Cl and Br.

5. Solid material according to any preceding claim, wherein the material has a glass transition temperature in the range of from -10 °C to -100 °C.

6. Solid material according to any preceding claim, wherein the solid material has an ionic conductivity of 0.8 mS or more, preferably 1 mS or more at 30 °C.

7. Solid material according to any preceding claim, wherein A is one or more of Li and Na X is Cl M is AlBASF SE 231724 x = y = 0 0 ≤ n ≤ 2.

8. Solid material according to claim 7, comprising structural units of general formula (I) selected from - the group consisting of LiAl3Cl6O2, Li2Al3Cl7O2, Li3Al3Cl8O2 and mixtures thereof or - the group consisting of NaAl3Cl6O2, Na2Al3Cl7O2, Na3Al3Cl8O2and mixtures thereof.

9. Process for preparing a material according to any of claims 1 to 7, comprising the steps of a) providing AlCl3•6H2O as oxygen source and the precursors - AMX4 wherein A is one or more of Li, Na and K, X is one or more of F, Cl and Br, M is trivalent and is one or more of Al, Ga and Fe; - and optionally one or more of MX3wherein - X is one or more of F, Cl and Br, - M is trivalent and is one or more of Al, Ga and Fe; M’(OR)aXb wherein - M’ is tetravalent and is one or more Si, Ge, Sn and Ti, - R is alkyl, - X is one or more of F, Cl and Br, - each of a and b is an integer from 0 to 4, - a + b = 4;BASF SE 231724 A2M’’X4 wherein - A is one or more of Li, Na and K, - X is one or more of F, Cl and Br, - M’’ is divalent and is one or more of Zn, Fe and Mg; b) preparing a powder mixture comprising the precursors and AlCl3•6H2O in a molar ratio according to general formula (I); c) annealing the powder mixture obtained in step b) under vacuum for 3 to 10 hours at temperatures in the range of from 180°C to 250°C and allowing re- lease one or more of - HX wherein X is one or more of F, Cl and Br, and - ROH wherein R is alkyl, and - RX wherein R is alkyl and X is one or more of F, Cl and Br, so that a material having a composition according to general formula (I) is obtained; d) cooling down the obtained material so that a solid material having a composi- tion according to general formula (I) is obtained.

10. Process according to claim 9, wherein - the precursors provided in step a) are one or more of LiAlCl4 and NaAlCl4 and optionally AlCl3, and / or - the mixture prepared in step b) comprises and AlCl3•6H2O and one or more of LiAlCl4 and NaAlCl4, and optionally AlCl3, and / or - step c) comprises annealing for 2 hours at 200°C 11. A solid structure for an electrochemical cell, wherein said solid structure is selected from the group consisting of cathode and separator, wherein the solid structure for an electrochemical cell comprises a solid material according to any of claims 1 to 8.

12. An electrochemical cell comprising a solid structure as defined in claim 11.BASF SE 231724 13. Electrochemical cell according to claim 11 or 12, said electrochemical cell having a cathode comprising a cathode active material having a redox potential of 3.3 V or more vs. Li+ / Li and a solid material according to any of claims 1 to 8, wherein the cathode active material cathode active material is preferably selected from the group consisting of lithium iron phosphate and materials having a composition according to general formula (II) Li1+t[CoxMnyNizMu]1-tO2(II) wherein 0 ≤ x ≤ 1 0 ≤ y ≤ 1 0 ≤ z ≤ 1 0 ≤ u ≤ 0.15 M if present is one or more elements selected from the group consisting of Al, Mg, Ba, B, and transition metals other than Ni, Co, and Mn, x + y + z > 0 x + y + z + u = 1 -0.05 ≤ t ≤ 0.

2.

14. Use of a solid material according to any of claims 1 to 8 for preparing a solid structure for an electrochemical cell, wherein said solid structure is selected from the group consisting of cathode and separator.

15. Use of a solid material according to any of claims 1 to 8 as solid electrolyte for an electrochemical cell.

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