Lithium-scandium- and sodium-scandium pnictogenes and chalcogens

Abstract

The present invention relates a new class of lithium- and sodium-rich solid-state compounds which additionally contain scandium, which significantly improves the ion conductivity. In addition, the invention relates to compositions comprising a mixture of inventive compounds and to a process for preparation of the inventive compounds. Further, the present invention relates to the use thereof as solid electrolytes or in composite cathodes in primary and secondary electro-chemical energy storage devices. The invention further relates to solid electrolytes and composite cathodes comprising the inventive compounds and compositions.

Description

[0001]

[0002] Lithium-Scandium- and Sodium-Scandium Pnictogenes and Chalcogens

[0003] Background

[0004] The invention is in the field of battery research, specifically in the field of materials research on solid-state compounds for new all-solid-state batteries.

[0005] Great hopes are currently being pinned on solid electrolyte batteries. They are expected to replace the lithium-ion batteries with liquid electrolytes that are currently used almost exclusively in electric vehicles (but also in other battery-powered devices) in the next few years. The reason for this is the significantly improved operational safety of the solid-state batteries, which do not have the problem of highly flammable liquid electrolytes based on elemental lithium. In addition, no toxic liquids are released if the cells are damaged. Thus, All-solid-state battery (ASSB) is a frontier battery technology with superior potential in incombustibility based on the thermal stability of inorganic materials, and high energy and power density over the conventional Li-ion batteries, making it the sustainable and promising alternative in electric vehicles and energy storage applications. The new batteries could be charged much faster and e-vehicles could achieve greater ranges than with their current counterparts with liquid electrolytes.

[0006] High ionic conductivities are required in the electrolytes for high-power charging and discharging. Comparatively low ionic conductivities have long been a weakness of solid-state electrolytes. Another technical problem is the complex and expensive production of solid-state electrolytes. As a core and indispensable component of ASSBs, solid-state electrolytes (SEs) require high ionic conductivity, negligible electronic conductivity, and electrochemical stability to meet theapplication demands. Therefore, numerous efforts have been devoted to develop the SEs, which has led to a variety of potential electrolyte materials represented by oxides, sulfides, polymers, and inorganic-organic hybrid electrolytes. Among them, only handful argyrodites Li6PS5X (X = Cl, Br, I), sulfides

[0007] Li10MP2Si2(M= Ge, Sn) and their derivatives exhibit excellent ionic conductivities reaching 10-2S cm-1at room temperature. Kraft et al, Inducing High Ionic Conductivity in the Lithium Superionic Argyrodites Li6+xP1–xGexS5I for All-Solid-State Batteries, Journal of the American Chemical Society 2018, 140 (47), 16330-16339; Kraft et al, Influence of Lattice Polarizability on the Ionic Conductivity in the Lithium Superionic Argyrodites Li6PS5X (X = Cl, Br, I), Journal of the American Chemical Society 2017, 139 (31), 10909-10918; Zhou et al, New Family of Argyrodite Thioantimonate Lithium Superionic Conductors, Journal of the American Chemical Society 2019, 141 (48), 19002-19013; Kamaya et al, A lithium superionic conductor, Nature Materials 2011, 10 (9), 682-686; Hori et al, Synthesis, structure, and ionic conductivity of solid solution,

[0008] Li10+δM1+δP2–δS12(M = Si, Sn). Faraday Discussions 2014, 176 (0), 83-94. The fastest Li+superionic conductor reported in solids is Li9.54[Si0.6Ge0.4]1.74P1.44S11.1Br0.3O0.6, achieving 32 mS·cm-1at room temperature. Li et al, A Lithium Superionic Conductor for Millimeter-thick Battery Electrode, Science 2023, 381 (6653), 50.

[0009] Pristine cubic NasPS4 which exhibited a conductivity of 0.2 mS cm-1as a glassceramic electrolyte which could be improved to 0.46 mS cm-1using high-purity starting materials. The derivatives NasPSe4 and NasSbS4 have a conductivity of 1-3 mS cm-1whereas the modifications Na3-xPS4-xClx(x=6.25%) reaches a conductivity of 1.14 mS cm-1. Na11Sn2PS12was reported and exhibited a very high ionic conductivity of 3.7 mS cm-1. The so far highest sodium ion conductivities were achieved in Na2.88Sb0.88W0.12S4or Na2.9Sb0.9W0.1S4with conductivity values of 32 mS cm-1and 41 mS cm-1, respectively, at room temperature. Jansen et al, J. Solid State Chem. 1992, 99, 110-119; Hayashi et al, Nat. Commun. 2012, 3, 856; A. Hayashi et al, Journal of Power Sources 2014, 258, 420-423; Zhang et al, Advanced Energy Materials 2015, 5, 1501294; Banerjee et al, Angew. Chem.Int. Ed. 2016, 55, 9634-9638; Chu et al, Sci. Rep. 2016, 6, 33733; Duchardt et al, Angew. Chem. Int. Ed. 2018, 57, 1351-1355; Zhang et al, Energy Environ. Sci.

[0010] 2018, 11, 87-93; Hayashi et al, Nat. Commun. 2019, 10, 5266; Fuchs et al, ACS Energy Letters 2020, 5, 146-151.

[0011] A high ionic conductivity not only ensures a fast Li+or Na+conduction between the anode and cathode, but also fulfils the realistic design of an ASSB for high loadings and current densities. Approaches to improve the ionic conductivity mainly focus on structure design and modifications in atomic scale.

[0012] Recently, lithium-ion conductivity in the range of 10-5to 10-4S cm-1at 50 °C has been shown for lithium arsenidotetrelates, LisTtAs4 (Tt = Si, Ge) and LiuTtAse (Tt = Si, Ge, Sn), Pfitzner etal., Dalton Trans., 2024, 53, 11257-11263. Further, several compounds comprising lithium, scandium, phosphorous and sulphur have been described recently, i.e. monoclinic and tetragonal LiScP2Se as well as Li2.925Sco.358P2Se, showing ionic conductivities of 4.5 • 10-8, 1.2 • 10-6, and 1.2 • 10-3mS cm-1at RT, respectively. Schoop et al, Zeitschrift fur anorganische und allgemeine Chemie 2018, 644, 1854-1862. Dietrich et al, Chemistry of Materials 2016, 28, 8764-8773.

[0013] Lithium- and sodium-rich pnictogens have been known for a long time, whereby the compounds LisP, LisAs, LisSb, LisBi, as well as NasP, NasAs, NasSb, NasBi are described with regard to synthesis and structural composition; and LisP, LisAs, LisSb, NasP, NasAs, NasSb, and NasBi with regard to the presence of various modifications. The compounds show very little to no lithium or sodium ion mobility as pure substances. For pnictogen compounds, for example, a value of 1 • 10-3S cm-1at ambient condition was measured for LisN on single crystals at ambient temperature, a value of 3.0(6) • 10’8S cm-1for microcrystalline powders of LisP at 50 °C, a value of 1.5(3) • 10-7S cm-1at 50 °C for LisAs, and a mainly electronic of nature for NasP. For other binaries, no values are available. U. v. Alpen, Journal of Solid State Chemistry 1979, 29, 379-392;

[0014] Wegner et al, Zeitschrift fur anorganische und allgemeine Chemie 2022, 648,e202100358; A. Pfitzner, Zeitschrift fur anorganische und allgemeine Chemie 2022, 648, e202100358; Eickhoff et al, Zeitschrift fur anorganische und allgemeine Chemie 2021, 647, 28-33.

[0015] Binary lithium- and sodium-rich chalcogens such as l_i2S, Li2Se, Li2Te, Na2S, Na2Se, and Na2Te, have also been investigated fortheir synthesis and structural properties. Among these, l_i2S and Na2S are known to have also high-pressure structural polymorphs. These binary compounds generally show intrinsic low ionic conductivity. For example, bulk l_i2S exhibits low ionic conductivity at room temperature, approximately 10-13S cm-1(Anh Tu, T.; Phuc, N. H. H.; Anh, L. T. Q.; Toan, T. V., Preparation of Li2S-Alh-Lil Composite Solid Electrolyte and Its Application in All-Solid-State Li-S Battery, Batteries 2023, 9(6), 290.). Regarding Li2Se, no ionic conductivity is directly measured and reported. However, a migration energy of 0.2-0.3 eV has been reported when Li2Se is used as a protective layer on lithium metal anodes. (Park, H.; Kim, J.; Lee, D.; Park, J.; Jo, S.; Kim, J.; Song, T.; Paik, U., Epitaxial growth of nanostructured Li2Se on lithium metal for all solid - state batteries, Advanced Science 2021, 8(11), 2004204.) Further extended investigation into Li2S-LisP system has resulted in a solid solution (Li3P)x-(Li2S)i-x for 0.33

[0016]

[0017] < x 0.75 which remains stable up to 125°C. The extracted solid solution conductivities reported to be are significantly higher than those of the pure end member phases Li2S and LisP.

[0018] (Szczuka, C.; Karasulu, B.; Groh, M. F.; Sayed, F. N.; Sherman, T. J.; Bocarsly, J. D.; Verna, S.; Menkin, S.; Emge, S. P.; Morris, A. J.; Grey, C. P., Forced Disorder in the Solid Solution Li3P— Li2S: A New Class of Fully Reduced Solid Electrolytes for Lithium Metal Anodes, Journal of the American Chemical Society 2022, 144(36), 16350-16365.) For Li2Te and Na2Te, no experimental ionic conductivity values have been reported. Study of a Na2S single crystal has revealed an activation energy of 0.59 eV. (Bertheville, B.; Low, D.; Bill, H.; Kubel, F., Ionic conductivity of Na2S single crystals between 295 and 1350 K experimental setup and first results, Journal of Physics and Chemistry of Solids 1997, 58(10), 1569-1577). Further studies on Na2Se reveal an ionic conductivity of 10–13S cm-1at room temperature. (Liu, Z.; Hu, W.; Deng, H., Chemistry of Defects in Crystalline Na2Se: Implications for the Na-Se Battery. The Journal of Physical Chemistry C 2020, 124(51), 27930-27936).

[0019] In previous studies on phosphides, a series of compounds with good to very good ionic conductivity was obtained in Li3P by formal partial replacement of monovalent lithium atoms by trivalent and tetravalent atoms. These include for instance:

[0020] a) Replacement by Al, Ga, In in the structure of Li3P leads to the general formula Li3-3x77xP (Tr= Al, Ga, In), whereby only the existence of the compound forx = 0.25 and the occurrence of various modifications is certain, i.e.

[0021] Li2.25Al0.25P = β- and ω-Li9AlP4, Li2.25Ga0.25P = β- and ω-Li9GaP4and Li2.25In0.25P = ω-Li9InP4, where ω-Li9GaP4has the highest ionic conductivity of 4.5(2) • 10’3S cm-1. Restle et al, Advanced Functional Materials 2022, 32, 2112377; Restle et al, Angewandte Chemie International Edition 2020, 59, 5665-5674; Restle et al, Chemistry of Materials 2021, 33, 2957-2966.

[0022] b) Replacement by Si, Ge, Sn in the structure of Li3P leads to the general formula Li3–4xTtxP (Tt = Si, Ge, Sn), where the existence of the compounds is only certain forx = 0.25 and x = 0.167 (1 / 6) as well as the occurrence of various modifications, i.e. forx = 0.25: Li2Si0.25P = Li8SiP4, Li2Ge0.25P = α- and β-Li8GeP4, and Li2Sn0.25P = α- and β-Li8SnP4; as well as forx = 0.167:

[0023] Li2.333Si0.167P = Li14SiP6, Li2.333Ge0.167P = Li14GeP6, and Li2.333Sn0.167P = Li14SnP6wherein Li14SiP6(=Li7 / 3Si1 / 6P) has an ionic conductivity of 1.0 10’3S cm’1. Eick-hoff et al, Chemistry of Materials 2018, 30, 6440-6448; Strangmuller et al, Journal of Materials Chemistry A 2021, 9, 15254-15268; Strangmuller et al, Journal of the American Chemical Society 2019, 141, 14200-14209; Strangmuller et al, Chemistry of Materials 2020, 32, 6925-6934; Toffoletti et al, Chemistry: a European journal 2016, 22, 17635-17645.In previous studies on phosphides, a series of compounds with good ionic conductivity were obtained in NasP by formal partial replacement of monovalent sodium atoms by tetravalent atoms. These include for instance:

[0024] c) Replacement by Ge, Sn in the structure of NasP leads to the general formula Na3–4xTtxP (Tt = Ge, Sn), where only the existence of the compound for x = 0.25 and the occurrence of various modifications is certain, i.e. forx = 0.25:

[0025] Na2Ge0.25P = Na8GeP4Eickhoff et al, Zeitschrift fur anorganische und allge-meine Chemie 2021, 647, 28-33; Botta et al, Zeitschrift fur anorganische und allgemeine Chemie 2023, 649 (20), e202300166.

[0026] EP 3828979 A1 discloses Li1.5Sco.5N as a candidate material to be used in the preparation of sulfide solid electrolytes. A method of synthesizing Li1.5Sco.5N is further disclosed in R. Niewa et al, Chem. Eur. J. 2003, 9, 4255-4259. M. van Dijk et al. Mat. Res. Bull. 1980, 15, 103-106 discloses a method of synthesizing Lio.5Sco.5S and Nao.5Sco.5S using a reaction of the binary sulphides. Neither electronic nor ionic conductivity of Li1.5Sco.5N, Lio.5Sco.5S and Nao.5Sco.5S have been measured. Other ternary compounds that formally arise by partially replacing Li or Na with Sc in the binary lithium and sodium pnictogens, LisP, LisAs, LisSb, LisBi and NasP, NasAs, NasSb, NasBi, were previously unknown. Similarly, other ternary compounds that formally arise by partially replacing Li or Na with Sc in the binary lithium and sodium chalcogens, Li2S, Li2Se, Li2Te, Na2S, Na2Se, Na2Te, were previously unknown.

[0027] There remains a need for solid-state electrolytes (SEs) with high ionic conductivity. For the application in ASSBs, it is desirable that SEs exhibit not only high ionic conductivity but also negligible electronic conductivity. Further, solid-state electrolytes with high ionic conductivity can be used for composite cathodes. Composite cathodes are cathodes composed of active materials, electronic conductive additives (typically carbon) and ionic conductive fillers, which require materials with high ionic conductivity which can provide ionic pathways.Summary of the invention

[0028] The invention relates to a new class of lithium- and sodium-rich solid-state compounds which additionally contain scandium and to compositions comprising mixtures of the inventive compounds. The invention further relates to a process for their preparation and their use as solid electrolytes or in composite cathodes in primary and secondary electrochemical energy storage devices. The invention further relates to composite cathodes and solid electrolytes containing the inventive compounds and compositions.

[0029] The inventive compounds contain scandium which significantly improves the ion conductivity of lithium- and sodium-rich binary solid-state compounds. In addition, the invention relates to a process for preparing the inventive compounds allowing for a comparatively simple preparation in comparison to the complex and expensive production of solid-state electrolytes frequently employed in the prior art.

[0030] The inventive compounds are of general formula (I) or general formula (II) or general formula (III):

[0031] A+(3-3x)Sc3+xPn3- (I)

[0032] A is selected from Li and Na,

[0033] Pn is selected from the group consisting of N, P, As, Sb and Bi,

[0034] x is in the range 0<x< 0.5

[0035] A+(2-3y)Sc3+yCh2- (II)

[0036] A is selected from Li and Na,

[0037] Ch is selected from the group consisting of S, Se and Te,

[0038] y is in the range 0<y< 0.5[A+z(m-3x)+(1-z)(n-3y)Sc3+zx+(1-z)y(D1 )m'z(D2)n'(i-z)] (III),

[0039] A is selected from Li and Na,

[0040] D1 and D2 are each selected from N, P, As, Sb, Bi, S, Se and Te, with D1 ≠ D2,

[0041] x is in the range 0 < x < 0.5,

[0042] y is in the range 0 < y < 0.5,

[0043] 0 < z < 1,

[0044] m is 2 or 3, n is 2 or 3, wherein m and n can be the same or different.

[0045] Brief description of the drawings

[0046] Figure 1a: Rietveld analysis of the powder diffraction data (Mo Kα1, λ = 0.7093 Å) of Li2.625Sc0.125Sb at 298 K. The dots show the observed intensities Yobs, the line behind the dots the calculated intensities Ycalcand the line at the bottom of the diagram the difference between the two. Vertical lines show the Bragg positions of the corresponding ternary phase.

[0047] Figure 1b: Rietveld analysis of the powder diffraction data (Mo Kai, A = 0.7093 A) of Li2.55Sco.15Sb at 298 K. The dots show the observed intensities Yobs, the line behind the dots the calculated intensities Ycalcand the line at the bottom of the diagram the difference between the two. Vertical lines show the Bragg positions of the corresponding ternary phase.

[0048] Figure 1c: Rietveld analysis of the powder diffraction data (Mo Kα1, λ = 0.7093 Å) of Li2.55Sc0.15P at 298 K. The dots show the observed intensities Yobs, the line behind the dots the calculated intensities Ycaicand the line at the bottom of the diagram the difference between the two. Vertical lines show the Bragg positions of the corresponding ternary phase.

[0049] Figure 1d: Rietveld analysis of the powder diffraction data (Mo Kα1, λ = 0.7093 Å) of Na2.55Sc0.15Sb at 298 K. The dots show the observed intensities Yobs, theline behind the dots the calculated intensities Ycalcand the line at the bottom of the diagram the difference between the two. Vertical lines show the Bragg positions of the corresponding ternary phase.

[0050] Figure 1e: Experimental X-ray powder diffraction pattern (Mo Kα1, λ = 0.7093 Å) of Li2.85Sc0.05Bi at 298 K. Vertical lines show the Bragg positions (model from Li2.55Sco.15Sb).

[0051] Figure 1f: Experimental X-ray powder diffraction pattern (Mo Kα1, λ = 0.7093 Å) of Li2.55Sc0.15Bi at 298 K. Vertical lines show the Bragg positions (model from Li2.55Sco.15Sb).

[0052] Figure 1g: Experimental X-ray powder diffraction pattern (Mo Kα1, λ = 0.7093 Å) of Li2.71Sc0.03S0.2Sb0.8 at 298 K. Vertical lines show the Bragg positions (model from Li2.55Sco.15Sb). The asterisks indicate that the peaks overlap with the Li2S impurity peak.

[0053] Figure 1h: Experimental X-ray powder diffraction pattern (Mo Kα1, λ = 0.7093 Å) of Li2.275Sc0.075S0.5Sb0.5 at 298 K. Vertical lines show the Bragg positions (model from Li2.55Sco.15Sb). The asterisks indicate that the peaks overlap with the Li2S impurity peak.

[0054] Figure 2: Nyquist plot (left) and Arrhenius plots (right) of Li2.625Sc0.125Sb (x = 0.125) and Li2.55Sc0.15Sb (x = 0.15). Nyquist plot: Li2.625Sc0.125Sb (x = 0.125, triangles in the diagram) and Li2.55Sco.15Sb (x = 0.15, squares in the diagram), measured under ion-blocking condition at 298 K. Each measurement was performed after establishing a 3 h thermal equilibrium. The semicircle coupled with the Warburg tail indicates an ionic conductive contribution from Li-ions, and the presence of an inductive tail is attributed to the cell set-up and cabling resistance. For Li2.625Sc0.125Sb (x = 0.125), fitting was performed from f= 353 Hz to 100 mHz; for Li2.55Sco.15Sb (x = 0.15), fitting was performed from f= 2037 Hz to 100 mHz. Arrhenius plots of conductivity and temperature (σLi T) for Li2.625Sc0.125Sb (x = 0.125) and Li2.55Sco.15Sb (x = 0.15) obtained in the heatingand cooling branches, respectively, with error bars for each measurement based on the standard deviation from independent measurements with three cells; the shown linear fit through both branches was used to obtain the activation energy EAPEISof 20.37 ± 0.61 kJ / mol (x = 0.125) and 21.21 ± 0.48 kJ / mol (x = 0.15), respectively.

[0055] Figure 3: Nyquist plot of Li2.275Sc0.075S0.5Sb0.5, measured under ion-blocking condition at different temperatures ranging from 283 K to 343 K. Square: 283 K, circle: 298 K, triangle pointing upwards: 313 K, triangle pointing downwards: 328 K, diamond: 343 K.

[0056] Figure 4: Arrhenius plot of Li2.275Sc0.075S0.5Sb0.5, measured under ion-blocking condition at different temperatures ranging from 283 K to 343 K.

[0057] Figure 5: DC polarization measurement of Li2.275Sc0.075S0.5Sb0.5 at ion-blocking condition. The dotted lines indicate the applied potential profile corresponding to the measuring current shown in solid lines.

[0058] Detailed description

[0059] I. The inventive compounds

[0060] For applications in all-solid-state batteries, solid-state electrolytes require high ionic conductivity and negligible electronic conductivity. Nevertheless, for composite cathodes, it is advantageous to include solids that possess both high ionic and electronic conductivity. So-called mixed electronic and ionic conductors (MIECs) are valuable to act not as a blocking layer (separator), but as an additive in composite cathode, which function as solid electrolytes and electronic conductive additives and might allow to work with less or without conductive carbon at the cathode. In this invention, scandium is proposed as a substitution element for the alkali metals lithium and sodium in pnictogen systems or in chalcogen systems. One equivalent of scandium replaces three equivalents of Li or Na in the compounds.The object of the present invention is therefore to provide a new class of I ithium -and sodium-rich solid-state compounds which, based on the binary compounds, enable a high lithium or sodium ion mobility and a phase-pure production of the ternary phases Li-Sc-Pn, Na-Sc-Pn, Li-Sc-Ch and Na-Sc-Ch (Pn: pnictogen, Ch: chalcogen).

[0061] This problem is solved according to the invention by partial replacement of Li and Na by Sc according to general formula (I) (including formula (la) and formula (lb)) or general formula (II) (including formula (Ila) and formula (lib)) or general formula (III):

[0062] A+(3-3x)Sc3+xPn3-(Ia)

[0063] A is selected from Li and Na,

[0064] Pn is selected from the group consisting of P, As, Sb and Bi,

[0065] x is in the range 0<x<0.5

[0066] A+(3-3X) S c3+xP n3‘ (lb)

[0067] A is selected from Li and Na,

[0068] Pn is N,

[0069] x is in the range 0<x<0.25

[0070] A+(2-3y)SC3+yCh2‘ (Ila)

[0071] A is selected from Li and Na,

[0072] Ch is selected from the group consisting of Se and Te,

[0073] y is in the range 0<y<0.5A+(2-3y)Sc3+yCh2-(IIb)

[0074] A is selected from Li and Na,

[0075] Ch is S,

[0076] y is in the range 0<y<0.25

[0077] [A+z(m-3x)+(1-z)(n-3y)Sc3+zx+(1-z)y(D1)m-z(D2)n-(1-z)] (III),

[0078] A is selected from Li and Na,

[0079] D1 and D2 are each selected from N, P, As, Sb, Bi, S, Se and Te, with D1 ≠ D2,

[0080] x is in the range 0 < x < 0.5,

[0081] y is in the range 0 < y < 0.5,

[0082] 0 < z < 1,

[0083] m is 2 or 3, n is 2 or 3, wherein m and n can be the same or different. In formula (III), m is the charge of D1 and n is the charge of D2. Thus, m and n can have the following values:

[0084] • when D1 is selected from N, P, As, Sb and Bi, m = 3,

[0085] • when D1 is selected from S, Se and Te, m = 2,

[0086] • when D2 is selected from N, P, As, Sb and Bi, n = 3,

[0087] • when D2 is selected from S, Se and Te, n = 2.

[0088] • when D1 and D2 are selected from the same group, i.e. both D1 and D2 are selected from the Pn group, or both D1 and D2 are selected from the Ch group, m = n,

[0089] • when D1 and D2 are selected from different groups, i.e. one of D1 and D2 is selected from the Pn group, and the other is selected from the Ch group, m ≠ n.

[0090] Thus, compounds of formula (III) encompass the following combinations of elements:• (i) compounds comprising Li or Na, Sc and two different pnictogens, such as (Li3-3xScxPn1)z(Li3-3yScyPn2)i-z, wherein Pn1 and Pn2 are each selected from N, P, As, Sb and Bi, with Pn1 + Pn2, for example (Lis- 3xScxP)z(Li3-3yScySb)i-z (in this case, m = n),

[0091] • (ii) compounds comprising Li or Na, Sc and two different chalcogens (in this case, m = n), and

[0092] • (iii) compounds comprising Li or Na, Sc, one pnictogen and one chalcogen (in this case, m ≠ n).

[0093] Possibility (iii) can alternatively be described by the following formula (Illa):

[0094] [A+z(3-3x)+(1-z)(2-3y)Sc3+zx+(1-z)yPn3-zCh2-(1-z)] (IIIa),

[0095] A is selected from Li and Na,

[0096] Pn is selected from the group consisting of N, P, As, Sb and Bi,

[0097] Ch is selected from the group consisting of S, Se and Te,

[0098] x is in the range 0 < x < 0.5,

[0099] y is in the range 0 < y < 0.5,

[0100] 0 < z < 1.

[0101] Preferred are compounds of formula (I), compounds of formula (III), wherein D1 and D2 are each selected from N, P, As, Sb and Bi, and compounds of formula (III), wherein one of D1 and D2 is selected from N, P, As, Sb and Bi and the other one is selected from S, Se and Te. The inventive compounds have advantageous ionic and electronic conductivities. Therefore, a new material class with superior ion conductivity is introduced here as a promising candidate for ASSB solid electrolytes and as an additive in composite cathodes.

[0102] The present invention further relates to a solid electrolyte comprising an inventive compound (according to general formula I or II or III) or a composition comprising a mixture of two or more inventive compounds. The present invention further relates to a composite cathode comprising an inventive compound(according to general formula I or II or III) or a composition comprising a mixture of two or more inventive compounds.

[0103] A “composition comprising a mixture of two or more inventive compounds” is to be distinguished from mixed compounds of formula (III). The inventive compositions are obtained by mixing respective amounts of individual compounds after solid-state synthesis, whereas the mixed compounds of formula (III) are the solid solutions obtained either from atomic-level mixing of the inventive compounds within formula I and / or formula II, or from mixing stochiometric quantities of the elements contained in formula (III) at the beginning of solid-state synthesis.

[0104] A “solid solution” refers to a homogeneous mixture of at least two, typically two, crystalline solids with similar / same crystal lattices at an atomic level, and it is one single phase. Obtaining a solid solution by mixing compounds of formula (I) and (II) on the atomic level can be achieved for instance by ball milling and / or post annealing, resulting in bond cleavage and new bond formation, thereby achieving a single phase with variation in composition. Such procedure is described in more detail in connection with the inventive process below. In comparison, a “composition comprising a mixture of two or more inventive compounds" can have two or more substances that are mixed together but not chemically combined at an atomic level.

[0105] It is to be understood that the numerical values contained in any chemical formulae given in this application include a certain numerical range. This range can be due to unavoidable inaccuracies in the synthesis of the compounds or in the analytical determination of the molar composition of the compounds. In addition, although it is possible to obtain most of the inventive compounds as phase-pure samples, the presence of side phases is not excluded.

[0106] For instance, if the chemical composition of a prepared compound is determined by Rietveld refinement of PXRD data, deviations between the nominal composition (experimentally determined) and refined composition (result fromRietveld analysis) can arise within the standard deviations (3σ rule). In addition, the formation of undetected amorphous phases can lead to deviations between the nominal composition and the results from Rietveld analysis. Further, there can be a weight loss during a multiple-step synthesis resulting in materials not exactly matching the stochiometric amounts of elements weighted at the beginning of synthesis. Finally, it is to be understood that due to the rounding of values and the inaccuracy of the crystallographically determined composition, the indicated formulae do not always match perfectly general formula (I), (II) and (III), i.e. the molar amount of Li or Na is not always perfectly 3-3x or 2-3y, but matches this value within the standard deviations (3σ rule). The skilled person in the field of solid-state chemistry understands the range of compounds encompassed by the specific formulae given in this application.

[0107] Preferably, x is in the range 0.05 < x < 0.50, more preferably 0.05 < x < 0.25, more preferably 0.10 < x < 0.25, more preferably 0.11 < x < 0.25, more preferably 0.11 < x < 0.20, even more preferably 0.12 < x < 0.20. Preferably, y is in the range 0.05 < y < 0.50, more preferably 0.05 < y < 0.25, more preferably 0.10 < y < 0.25, more preferably 0.11 < y < 0.25, more preferably 0.11 < y < 0.20, even more preferably 0.12 < y < 0.20.

[0108] Preferably, z is in the range 0.1 < z < 0.9, more preferably 0.2 < z < 0.8. In other words, it is preferred that certain amounts of each D1 and D2 are present. For compounds of formula (III) comprising Pn and Ch, when the attribution of elements is D1 = Ch and D2 = Pn, preferably 0.1 < z < 0.6, more preferably 0.2 < z < 0.5. It is assumed that a certain minimum amount of Sc is required to achieve a sufficient ionic conductivity, whereas too high amounts of Sc can lead to the formation of impurities, such as ScSb, which is due to the dissolution limit of scandium in each general formula. We did not observe any impurities in our samples when x < 0.2.In formula (I), Pn is selected from the group consisting of N, P, As, Sb and Bi, preferably, P, As, Sb and Bi. From the viewpoint of ease of handling and toxicity, P and Sb are preferred, but to achieve high ionic conductivities, compounds wherein Pn is Sb, As or Bi can be preferred, too. Sb is particularly preferred. When Pn = N, it is preferred than A = Li because the preparation of these compounds is much easier than the preparation of compounds with Pn = N and A = Na. Furthermore, when Pn = N, it is preferred that x is in the range 0.05 <x < 0.25.

[0109] Particularly preferred compounds of the present invention are compounds of formula (I), wherein A = Li or Na, Pn = Sb and x is in the range 0.05 < x < 0.50, more preferably 0.10 < x < 0.50, more preferably 0.11< x < 0.50, more preferably 0.11< x < 0.25, more preferably 0.11< x < 0.20 (e.g., Li2.625Sco.i25Sb, Li2.55Sco.15Sb, Na2.55Sco.15Sb). These compounds show exceptional high ionic conductivities.

[0110] Further preferred compounds of the present invention are compounds of formula (I), wherein A = Li or Na, Pn = Bi and x is in the range 0.025 < x < 0.50, more preferably 0.03 <x < 0.20, more preferably 0.05 <x < 0.15, e.g.

[0111] Li2.85Sc0.05Bi, Li2.55Sco.15Bi, Na2.85Sc0.05Bi, and Na2.55Sco.15Bi.

[0112] Further preferred compounds of the present invention are compounds of formula (Illa), wherein A = Li or Na, one of D1 and D2 = Ch, preferably S or Se, more preferably S; and the other one of D1 and D2 = Pn, preferably Sb, As or Bi, more preferably Sb. Particularly preferably, one of D1 and D2 is S and the other one is Sb. When the attribution of elements is D1 = Ch and D2 = Pn, z is preferably in the range of 0.1 to 0.6, more preferably 0.2 to 0.5. In these preferred compounds, the molar ratio of Sc, i.e. zx+(1-z)y is in the range 0 < zx+(1-z)y < 0.5, more preferably 0 < zx+(1-z)y < 0.25, more preferably 0 < zx+(1-z)y < 0.1, more preferably 0.025 < zx+(1-z)y < 0.1, more preferably 0.025 < zx+(1-z)y < 0.08, more preferably 0.03 < zx+(1-z)y < 0.075, e.g. Li2.7iSco.o3So.2Sbo.8 andLi2.275Sc0.075S0.5Sb0.5- These compounds show high ionic and electronic conductivities.

[0113] Preferably, the inventive compounds have ionic conductivities above 0.1 mS / cm, more preferably above 0.25 mS / cm, more preferably above 0.3 mS / cm, more preferably above 0.5 mS / cm, more preferably above 1 mS / cm, more preferably above 5 mS / cm, more preferably above 10 mS / cm, more preferably above 20 mS / cm, more preferably above 30 mS / cm, as determined by electrochemical impedance spectroscopy (EIS) according to the experimental part below. These high ionic conductivities are preferable both for the use as solid-state electrolytes and the use in composite cathodes.

[0114] Preferably, the inventive compounds have electronic conductivities below 10 mS / cm, preferably below 5 mS / cm, as determined by direct-current (DC) polarization method according to the experimental part below.

[0115] Preferably, for use as solid-state electrolytes, the inventive compounds have electronic conductivities below 1 x 10’1mS / cm, more preferably below 1 x 10’2mS / cm, as determined by direct-current (DC) polarization method according to the experimental part below.

[0116] Preferably, for use in composite cathodes, the inventive compounds have electronic conductivities above 0.05 mS / cm, more preferably above 0.1 mS / cm, more preferably above 0.15 mS / cm, more preferably above 1 mS / cm, more preferable above 2 mS / cm, more preferable above 2.5 mS / cm, more preferable above 4 mS / cm. Preferably, for use in composite cathodes, the inventive compounds have mixed ionic and electronic conductivities above 0.05 mS / cm, more preferably above 0.1 mS / cm, more preferably above 0.15 mS / cm, more preferably above 1 mS / cm, more preferable above 2 mS / cm, more preferable above 2.5 mS / cm, more preferable above 4 mS / cm. The term “mixed ionic and electronic conductivities above” means that both the ionic and the electronic conductivity is higher than the indicated lower limit. For instance, the term “mixedionic and electronic conductivities above 0.05 mS / cm” is synonymous to “ionic conductivity above 0.05 mS / cm and electronic conductivity above 0.05 mS / cm”.

[0117] For use in composite cathodes, it is preferable that the electronic conductivity is comparable with the ionic conductivity so as to reach a balance for ionic and electronic conduction. Further, the ionic and the electronic conductivity of the inventive compounds should be compatible with the cathode active material. Compounds of the present invention exhibiting both high ionic and electronic conductivities, which can be named “Mixed Ionic and Electronic Conductors (MIEC)”, are particularly suitable for composite cathodes as they can serve dual functions in composite cathodes, acting as 1) solid electrolyte (require high ionic conductivity) and 2) conductive additive (require high electronic conductivity). Because of the dual functions within a single material, enhancing the energy density can be expected, as well as reduction of different interfacial boundaries due to the use of single material.

[0118] Preferably, the inventive compounds have activation energies below 75 kJ / mol, more preferably below 50 kJ / mol, more preferably below 40 kJ / mol, more preferably below 35 kJ / mol, more preferably below 30 kJ / mol, as determined by electrochemical impedance spectroscopy (EIS) according to the experimental part below.

[0119] For applications in all-solid-state batteries, solid-state electrolytes require high ionic conductivity, and negligible electronic conductivity. Further advantageous properties are a high thermal stability and electrochemical stability. For composite cathodes, it is advantageous to have solids that possess both high ionic and electronic conductivity.

[0120] The different possible combinations of elements are described in more detail in the following.I. a. The

[0121]

[0122] lithium-scandium-;

[0123] The incorporation of scandium into the Li-rich pnictide system leads to the formation of solid solutions for x < 0.5, preferably x < 0.25, with tunable ionic and electronic conductivities that depend on the scandium content. Therefore, materials with specific conductivity properties can be effectively designed by the controlled incorporation of Sc into the known pnictide system.

[0124] Li2.55Sco.15Sb possesses an ionic conductivity of 42(6) mS cm-1at 298 K, with an activation energy of 21.2 (5) kJ mol-1. Li2.625Sco.i25Sb possesses an ionic conductivity of 50(5) mS cm-1at 298 K, with an activation energy of 20.4(6) kJ mol-1. Thus, these compounds represent the highest ionic conductivity among reported lithium-ion conductors. The high ionic conductivity can be explained by the formation of vacancies created by scandium substitution.

[0125] Li2.55Sco.15Sb maintains the structure of the parent compound β-Li₃Sb, in which Sc3+ions occupy the tetrahedral voids of the Sb anion arrangement, creating vacancies by removing lithium ions from the octahedral site. Driven by the vacancy mechanism, these resulting vacancies facilitate Li+ion transport by creating effective ion diffusion pathways, thus leading to enhanced ionic conductivity.

[0126] Preferably, for compounds of formula (I), wherein A = Li and Pn = Sb, x is in the range 0.05 < x < 0.50, more preferably 0.10 < x < 0.50, more preferably 0.11 < x < 0.50, more preferably 0.11 < x < 0.25, more preferably 0.11 < x < 0.20, even more preferably 0.12 <x < 0.20.

[0127] I.b. Formula (I) - The

[0128]

[0129] lithium-scandium-i

[0130]

[0131] Li2.55Sco.15P possesses an ionic conductivity of 0.25(1) mS cm-1at 298 K, with an activation energy of 33.8(6) kJ mol-1. The high ionic conductivity can be explained by the structural changes in the crystal structure induced by scandium substitution. Through substitution of Li with Sc in the hexagonal LisP structure, a hexagonal-to-cubic phase transition occurs, providing a desired multidimensional diffusion pathway. Additionally, the structural disorder induced by scan-dium incorporation further favours the ionic mobility. As a result, the ionic conductivity can be increased significantly, up to several orders of magnitude. For instance, Li2.55Sco.15P shows an ionic conductivity of 0.25(1) mS cm-1in comparison to an ionic conductivity of 3.0(6) • 10’5mS cm-1as published for microcrystalline powders of LisP at 50 °C.

[0132] Preferably, in compounds of formula (I), wherein A = Li, and Pn = P, x is in the range 0.05 < x < 0.25, more preferably 0.10 < x < 0.20, for example Li2.55Sco.15P.

[0133] I.c. Formula (I) - The systems lithium-scandium-nitrogen, lithium-scandium-arsenic and lithium-scandium-bismuth

[0134] Due to the ease of handling and toxicity, in the experimental part of this invention, compounds comprising P and Sb have been prepared. However, to achieve high ionic conductivities, compounds wherein Pn is N, As or Bi are preferred, too. By the partial replacement of lithium by scandium in LisN, LisAs and LisBi, the creation of advantageous diffusion pathways can be achieved, providing compounds of formula (I) with high ionic conductivities.

[0135] Preferably, in compounds of formula (I), wherein A = Li, and Pn = As or Bi, x is in the range 0.025 < x < 0.50, more preferably 0.025 < x < 0.25, more preferably 0.05 < x < 0.20, more preferably 0.05 < x < 0.15, for example Li2.55Sco.15As, Li2.625SCo.125AS, Li2.85SC0.05AS, Li2.55SC0.i5AS, Li2.55SC0.i5Bi, Li2.625SCo.125Bi, Li2.85Sc0.05Bi or Li2.55Sco.15Bi.

[0136] Preferably, in compounds of formula (I), wherein A = Li and Pn = N, x is in the range 0.05 < x < 0.25, more preferably 0.10 < x < 0.20.

[0137] I.d. Formula (I) - The system sodium-scandium-antimony

[0138] Na2.55Sco.15Sb possesses an ionic conductivity of 1.6 mS cm-1at 298 K, with an activation energy of 27.1(4) kJ mol-1. The high ionic conductivity can be explained by the structural changes in the crystal structure induced by scandium substitution. The high-pressure cubic polymorph of NasSb is stabilized by theternary element substitution, and the resulting structural disorder enhances the overall ionic conductivity, as electrochemical investigation on NasSb reveals that it is predominantly an electronic conductor (oe- = 7.3x1 O’6S cm-1at 298 K). The resulting phase transition and structural disorder favour the ionic conductivity by forming a desired three-dimensional diffusion pathway for Na-ions migrating through adjacent tetrahedral and octahedral voids in the fee lattice of Sb atoms, which is superior to the two-dimensional diffusion pathway exhibited by the pristine NasSb with a hexagonal lattice.

[0139] Preferably, for compounds of formula (I), wherein A = Na and Pn = Sb, x is in the range 0.05 < x < 0.50, more preferably 0.10 < x < 0.50, more preferably 0.11 < x < 0.50, more preferably 0.11 < x < 0.25, more preferably 0.11 < x < 0.20, for example Na2.55Sco.15Sb or Na2.625Sco.i25Sb.

[0140] I.e. Formula (I) - The system sodium-scandium-phosphorous, sodium-scan-dium-arsenic and sodium-scandium-bismuth

[0141] Due to the ease of handling and toxicity, in the experimental part of this invention, compounds comprising P and Sb have been prepared. However, to achieve high ionic conductivities, compounds wherein Pn is As or Bi are preferred, too. By the partial replacement of sodium by scandium in NasP, NasAs and NasBi, the creation of advantageous diffusion pathways can be achieved, providing compounds of formula (I) with high ionic conductivities.

[0142] Preferably, in compounds of formula (I), wherein A = Na, and Pn = P, As or Bi, x is in the range 0.025 < x < 0.50, more preferably 0.025 < x < 0.25, more preferably 0.05 < x < 0.20, more preferably 0.05 < x < 0.15, for example Na2.55Sco.15As, Na2.625SCo.125AS, Na2.85SC0.05AS, Na2.55SC0.i5AS, Na2.55SC0.i5Bi, Na2.625SCo.125Bi, Na2.85Sc0.05Bi or Na2.55Sco.15Bi.

[0143] Preferably, in compounds of formula (I), wherein A = Na and Pn = P, x is in the range 0.05 <x < 0.25, more preferably 0.10 <x < 0.20, e.g. Na2.55Sco.15P or Na2.625Sco.125P.l.f. Formula (I) - The system sodium-scandium-nitroqen

[0144] To achieve high ionic conductivities, compounds wherein A = Na and Pn = N can be advantageous. By the partial replacement of sodium by scandium in NasN, the creation of advantageous diffusion pathways can be achieved, providing compounds of formula (I) with high ionic conductivities. However, due to the complexity of synthesis for the system sodium-scandium-nitrogen, this system is less preferred than the system lithium-scandium-nitrogen, where synthesis is much easier.

[0145] Preferably, in compounds of formula (I), wherein A = Na, and Pn = N, x is in the range 0.05 < x < 0.25, more preferably 0.10 < x < 0.20.

[0146] I.g. Formula (II)

[0147] As explained for several inventive compounds above, a high ionic conductivity is obtained by the partial replacement of lithium / sodium by scandium in binary lithium or sodium pnictogens. The incorporation of scandium results in phase transitions and / or the creation of vacancies in the crystal structure and these structural changes provide effective ion diffusion pathways. Additionally, the structural disorder induced by scandium incorporation further favours the ionic mobility. An analogous effect can be achieved by the partial replacement of lithium / sodium by scandium in Li2S, Li2Se, Li2Te, Na2S, Na2Se and Na2Te, providing compounds of formula (II) with high ionic conductivities, which are promising materials for ASSB solid electrolytes or as an additive in composite cathodes.

[0148] Preferably, in compounds of formula (II), Ch is selected from the group consisting of Se and Te. Preferably, in compounds of formula (II), y is in the range 0.05 < y< 0.25, more preferably 0.10 < y < 0.20.

[0149] In compounds of formula (II), wherein Ch is selected from the group consisting of Se and Te, y is in the range 0 < y < 0.5, preferably 0.05 < y < 0.25, more preferably 0.10 < y< 0.20.Preferably, in compounds of formula (II), wherein Ch is S, y is in the range 0.05 < y < 0.25, more preferably 0.10 < y < 0.20.

[0150] I.h. Formula (III)

[0151] Compounds of formula (III) represent mixed compounds, which are formally a mixture consisting of z amount of [A+(m-3x)Sc3+x(D1 )m-] and (1-z) amount of [A+(n-3y)Sc3+y(D2)n‘], with 0 < z < 1 (according to formula I and II, whereas here D1 and D2 are selected from the set of Pn group and Ch group), resulting in the convergent general formula (III):

[0152] [A+z(m-3x)+(1-z)(n-3y)Sc3+zx+(1-z)y(D1 )m'z(D2)n'(i-z)] (III),

[0153] A is selected from Li and Na,

[0154] D1 and D2 are each selected from N, P, As, Sb, Bi, S, Se and Te, with D1 ≠ D2,

[0155] x is in the range 0 < x < 0.5,

[0156] y is in the range 0 < y < 0.5,

[0157] 0 < z < 1,

[0158] m is 2 or 3, n is 2 or 3, wherein m and n can be the same or different.

[0159] Compounds of formula (III) are obtained either from mixing of the inventive compounds at an atomic-level within formula I and / or formula II, or from stochio-metric quantities of the elements contained in formula (III) and subsequent solid-state synthesis, e.g. by the inventive process. Compounds of formula (III) are to be distinguished from inventive compositions comprising two or more inventive compounds. These compositions are obtained by mixing respective amounts of individual compounds after solid-state synthesis but mixing is not at an atomic level.It is to be understood that the absolute values x and y can only be determined if the synthesis is mixing of the inventive compounds at an atomic-level within formula (I) and / or formula (II). However, when the synthesis starts from stochio-metric quantities of the elements contained in formula (III) and subsequent solid-state synthesis, the absolute values x and y cannot be determined, but only the sum of the amounts of x and y. In other words, the conditions (a) x is in the range 0 < x < 0.5, and (b) y is in the range 0 < y < 0.5 will be replaced by the following condition: zx+(1-z)y is in the range 0 < zx+(1-z)y < 0.5.

[0160] [A+z(m-3x)+(1-z)(n-3y)Sc3+zx+(1-z)y(D1 )m'z(D2)n'(i-z)] (III),

[0161] A is selected from Li and Na,

[0162] D1 and D2 are each selected from N, P, As, Sb, Bi, S, Se and Te, with D1 ≠ D2,

[0163] zx+(1 -z)y is in the range 0 < zx+(1 -z)y < 0.5

[0164] 0 < z < 1,

[0165] m is 2 or 3, n is 2 or 3, wherein m and n can be the same or different.

[0166] It is to be understood that any indications in this application regarding the preferred chemical composition, such as preferred values forx and y and preferred elements for A, D (Pn or Ch), which are stated in connection with compounds of formula (I) and (II), are applicable also to compounds of formula (III). In addition, specific preferable compounds of formula (III) fulfil one or more of the following features:

[0167] • D1 is Ch, i.e. selected from the group consisting of S, Se and Te, more preferably S and Se, more preferably S; and D2 is Pn, i.e. selected from the group consisting of N, P, As, Sb and Bi, more preferably Sb, As and Bi, more preferably Sb. Particularly preferably, D1 is S and D2 is Sb. Accordingly, preferably, m is 2 and n is 3. It is understood that the attribution of elements Pn and Ch to either D1 or D2 is arbitrary.• When D1 = Ch and D2 = Pn, z is preferably in the range of 0.1 to 0.6, more preferably 0.2 to 0.5.

[0168] • zx+(1 -z)y is in the range 0.025 < zx+(1 -z)y < 0.1, more preferably 0.025 < zx+(1 -z)y < 0.08, more preferably 0.03 < zx+(1 -z)y < 0.075.

[0169] In the examples of this application, compounds Li2.7iSco.o3So.2Sbo.8 and Li2.275Sc0.075S0.5Sb0.5 according to formula (III) were prepared. Formally, these compounds are a mixture of compounds according to formula (I) and (II). For instance, Li2.7iSco.o3So.2Sbo.8 is a compound according to general formula (III), with A = Li; D1 = S, D2 =Sb, m = 2, n = 3; z = 0.8, x+4y = 0.15. Alternatively, Li2.7iSco.o3So.2Sbo.8 can formally be described as a mixture consisting of 0.2 (i.e. z) amount of Li(2-3y)ScyS (corresponding to Formula (II) with A = Li, Ch = S, 0 < y < 0.5), and 0.8 (i.e. 1-z) amount of Li(3-3x)ScxSb (corresponding to Formula (I) with A = Li, Pn = Sb, 0 < x < 0.5). As described above, the absolute values of x and y cannot always be determined, but the sum of the amounts of x and y, i.e. zx+(1-z)y, fulfilling the requirement 0 < zx+(1-z)y < 0.5.

[0170] II. The inventive process

[0171] The invention also relates to a process for the preparation of solid-state compounds of the general formula (I) or (II) or (III), as defined above. The compounds can be obtained by either heating the corresponding elements (in the form of powders, pieces or chunks) (method A) or ball milling of the elements and subsequent annealing of powders or pellets (methods B, C and D). For preparing compounds of formula (I) or (III) with Pn = N, N2 can be used as the nitrogen source, but this requires a corresponding adjustment of the reaction system. Thus, for the nitrogen-containing compounds, preferably LisN and / or ScN, more preferably LisN, is used as the precursor instead of the corresponding elements. For preparing compounds of formula (III), starting materials can be either elements following the methods A, B, C or D, or precursors derived from the inventive compounds of formula (I) and / or formula (II). In the latter case,compounds of formula (I) and / or formula (II)) are used as starting materials instead of the corresponding elements in step 1.

[0172] The inventive process comprises the following steps:

[0173] 1. Mixing starting materials containing stoichiometric quantities of the elements contained in formula (I), formula (II) or formula (III) in an inert gas atmosphere to obtain a mixture,

[0174] The starting materials used in step 1 can be the respective chemical elements, e.g. elemental lithium, elemental scandium and elemental antimony. Using the elements as starting material is preferred for compounds of formula (II) and for compounds of formula (I), wherein Pn + N. For compounds of formula (I), wherein Pn = N, the starting materials are preferably solid compounds comprising the required elements. For instance, for nitrogen-containing compounds, preferably LisN and / or ScN, more preferably LisN, is used as starting material. For preparing compounds of formula (III), the starting materials can be the respective chemical elements or solid compounds comprising the required elements. In addition, for compounds of formula (III), the starting materials can be compounds of formula (I) and / or (II). It is to be understood that different kinds of starting materials can be combined, e.g. for preparing a compound comprising Li, Sc and N, elemental Sc can be combined with LisN.

[0175] The particles of the obtained mixture can be in any suitable shape, e.g. the obtained mixture can be a mixture of powder particles, a mixture of pieces or a mixture of chunks.

[0176] Optionally, the inventive process comprises one of the following steps 2a, 2b and 2c:

[0177] 2a. Grinding the mixture obtained in step 1 in a ball mill under an inert gas atmosphere to obtain a ground powder (method B), or2b. Pressing the mixture obtained in step 1 into pellets (compacts) under an inert gas atmosphere (method C), or

[0178] 2c. Grinding the mixture obtained in step 1 in a ball mill under an inert gas atmosphere to obtain a ground powder and subsequently, pressing the obtained ground powder into pellets (compacts) under an inert gas atmosphere (method D).

[0179] Preferably, the inventive process comprises the following step 3 after step 1, after step 2a, after step 2b or after step 2c:

[0180] 3. Heating the mixture obtained in step 1 (Method A2) or the pellets or the ground powder obtained in step 2 to temperatures between 400°C and 900°C for a period of a few hours to 10 days in an inert gas atmosphere. Preferably, when the heating period is finished, the sample is rapidly quenched, e.g. within 1 to 10 seconds, for instance by putting the hot crucibles containing the product into water at room temperature.

[0181] High-temperature sintering in step 3, preferably followed by rapid quenching, provides a phase-pure synthesis condition and relatively high crystallinity for the desired phases. However, for most compounds, step 1 is sufficient to obtain the desired phase (Method A1). The preliminary ball milling process allows for a pre-reaction of the elements into reactive mixtures of reactants and educts.

[0182] In this application, the term “period of a few hours to 10 days” means that heating is performed for a period of 1 hour to 10 days. As described below, preferably, the heating in step 3 is carried out for a duration of 1 day to 8 days, more preferably 2 days to 6 days, more preferably 2 days to 4 days. For instance, the heating in step 3 is carried out for a duration of 3 days. When compounds of formula (III) are prepared by using compounds of formula (I) or (II) as starting materials in step 1, thorough milling is required before the heating step, i.e. in this case, either step 2a or step 2c is mandatory, followed by step 3. In other words,in this case, compounds of formula (III) are prepared according to method B or D.

[0183] The term “powder” means fine, small particles of a material with a typical size range of less than 100 pm, preferably particles with an average diameter of 1 pm to 100 pm, which can be determined by laser diffraction, dynamic light scattering (DLS) or sieve analysis.

[0184] The term “pieces” means particles larger than powder particles, i.e. particles of a material larger than 100 pm, preferably particles with an average diameter of 100 pm to 10 mm, preferably 1 mm to 10 mm, which can be determined for instance by sieve analysis.

[0185] The term “chunks” means particles larger than pieces, i.e. particles of a material larger than 10 mm, preferably particles with an average diameter of 10 mm to 1 cm, which can be determined for instance by sieve analysis.

[0186] Thus, method A1 comprises the following steps:

[0187] - Mixing the starting materials containing stoichiometric quantities of the elements in an inert gas atmosphere to obtain a mixture.

[0188] Thus, method A2 comprises the following steps:

[0189] - Mixing the starting materials containing stoichiometric quantities of the elements in an inert gas atmosphere to obtain a mixture,

[0190] - Heating the mixture, e.g. powder / pieces / chunk mixture, to temperatures between 400°C and 900°C for a period of a few hours to 10 days in an inert gas atmosphere.

[0191] Thus, method B comprises the following steps:

[0192] - Mixing the starting materials containing stoichiometric quantities of the elements in an inert gas atmosphere to obtain a mixture,- Grinding the mixture in a ball mill under an inert gas atmosphere to obtain a ground powder, and

[0193] - Heating the ground powder to temperatures between 400°C and 900°C for a period of a few hours to 10 days in an inert gas atmosphere.

[0194] Thus, method C comprises the following steps:

[0195] - Mixing the starting materials containing stoichiometric quantities of the elements, preferably in the form of powders, in an inert gas atmosphere to obtain a mixture,

[0196] - Pressing the resulting mixture, preferably powder mixture, into pellets (compacts) under an inert gas atmosphere, and

[0197] - Heating the pellets to temperatures between 400°C and 900°C for a period of a few hours to 10 days in an inert gas atmosphere.

[0198] In method C, the mixture obtained in step 1 is preferably a powder mixture to facilitate pressing the mixture into pellets.

[0199] Method D combines the steps of methods B and C. Preferably, the inventive process comprises method D, i.e. step 2c.

[0200] The process according to the invention provides good phase purity of the crystalline compounds and enables simple process control.

[0201] Step 1

[0202] In step 1, starting materials containing stoichiometric quantities of the elements contained in formula (I), formula (II) or formula (III) are mixed in an inert gas atmosphere. As described above, the starting materials can be the chemical elements or compounds comprising the respective elements. In many cases, the inventive compounds can be synthesized directly from the elements. Suitableinert gases are known to the skilled person and preferably, step 1 is performed under argon atmosphere.

[0203] Step 2

[0204] In one variant of step 2 (step 2a), the (powder) mixture obtained in step 1 is ground in a ball mill under an inert gas atmosphere. Preferably, a high-energy mechanical ball milling process is used. A suitable grinding speed is 300 - 400 rpm, e.g. 350 rpm, and a suitable grinding time is 18-36 h. Preferably, grinding intervals of around 10 min alternate with around 5 min breaks. Suitable milling conditions and a suitable ball mill are known to the skilled person and for instance, a tungsten carbide milling set can be used.

[0205] In one variant of step 2 (step 2b), the (powder) mixture obtained in step 1 is pressed into pellets (compacts) under an inert gas atmosphere. The size and shape of the pellets is not limited, but for instance, disk-shaped pellets with a diameter of 5 to 15 mm, e.g. 10 mm, are suitable, corresponding to a pellet mass of several hundred milligrams to several grams. A suitable press for preparing the pellets is known to the skilled person and for instance, a hydraulic press with a pressure of 250 to 350 MPa and a pressure time for 0.5 to 2 minutes can be used.

[0206] In one variant of step 2 (step 2c), the (powder) mixture obtained in step 1 is first ground, as described for step 2a above, and then pressed into pellets, as described for step 2b above.

[0207] Suitable inert gases are known to the skilled person and preferably, step 2 is performed under argon atmosphere.

[0208] Step 3

[0209] In step 3, either the mixture from step 1 is directly heated to temperatures between 400°C and 900°C for a period of a few hours to 10 days in an inert gas atmosphere, or the pellets or the ground powder obtained in step 2 are heatedto temperatures between 400°C and 900°C for a period of a few hours to 10 days in an inert gas atmosphere.

[0210] Suitable inert gases are known to the skilled person and preferably, step 3 is performed under argon atmosphere. Further, suitable equipment for this step is known to the skilled person. For instance, the pellets / powder can be loaded into suitable containers, e.g. sealed tantalum crucibles, and the sealed containers are heated in a suitable furnace, e.g. within evacuated quartz reaction tubes in a tube furnace.

[0211] Preferably, the heating in step 3 is carried out at a temperature between 500°C and 900°C, more preferably between 600°C and 900°C, more preferably between 700°C and 900°C, more preferably between 750°C and 850°C. For instance, the heating in step 3 is carried out around 800°C. Preferably, the heating in step 3 is carried out for a duration of 1 day to 8 days, more preferably 2 days to 6 days, more preferably 2 days to 4 days. For instance, the heating in step 3 is carried out for a duration of 3 days. Preferably, at the end of the heating duration, the obtained compounds are rapidly quenched, e.g. by quenching the hot tantalum crucibles in water.

[0212] III. The inventive use

[0213] The solid-state compounds of general formula (I), general formula (II) and general formula (III) according to the invention, as described above, can preferably be used as lithium-ion electrolytes, particularly as lithium-ion electrolytes for primary and secondary electrochemical energy storage devices, or in composite cathodes for primary and secondary electrochemical energy storage devices; or can preferably be used as sodium-ion electrolytes, particularly as sodium-ion electrolytes for primary and secondary electrochemical energy storage devices or in composite cathodes for primary and secondary electrochemical energy storage devices.“Lithium-ion electrolytes” and “sodium-ion electrolytes” are ionic conductive materials used in lithium-ion batteries to transport lithium ions between the anode and cathode during charging and discharging. While typical electrolytes of the prior art are often liquid or gel-like and typically consist of lithium or sodium salts dissolved in organic solvents, the lithium-ion electrolytes and sodium-ion electrolytes of the present invention are solid electrolytes.

[0214] “Composite cathodes” are cathodes composed of active materials, electronic conductive additives and ionic conductive fillers such as solid-state electrolytes which can provide ionic pathways. Composite cathodes are used as the positive electrode (cathode) in primary and secondary electrochemical energy storage devices.

[0215] “Primary electrochemical energy storage devices” are non-rechargeable batteries designed for single use. They store energy chemically and convert it to electrical energy during discharge. Once depleted, they cannot be recharged. A preferred example according to the present invention are primary ASSBs.

[0216] “Secondary electrochemical energy storage devices” are rechargeable batteries that can undergo multiple charge and discharge cycles. They store energy chemically and are designed for repeated use. A preferred example according to the present invention are secondary ASSBs.

[0217] All-solid-state batteries (ASSBs) are batteries that use solid electrolytes instead of liquid or gel electrolytes to transport ions between the anode and cathode. This design offers improved safety, higher energy density, and better thermal stability compared to conventional batteries.

[0218] Preferably, the inventive compounds are used as solid electrolytes or in composite cathodes in ASSBs in electric vehicles and other energy storage applications.Examples

[0219] I. Synthesis of materials

[0220] Example 1. Preparation of the compound Li3-3xScxSb, with x = 0.125.

[0221] For Li3-3xScxSb, the starting materials Li, Sc and Sb are weighed in a stoichiometric ratio forx = 0.125 under an argon inert gas atmosphere and ground in a ball mill (e.g. Retsch PM100 planetary ball mill, 350 rpm, 18 h, 10 min interval, 5 min break) using a tungsten carbide grinding set (50 mL vessel with 3 WC balls, 0 15 mm). The reactive mixture obtained is pressed with a hydraulic press (Specac Atlas 15T) under a pressure of 294.2 MPa (3 T) for 5 min to form pellets of approx. 0.5 g with a diameter of 10 mm and then filled into tantalum crucibles, which were sealed in an electric arc furnace (Edmund Buhler MAM1). The crucibles thus obtained are enclosed in evacuated quartz reaction tubes and heated in a tube furnace (e.g. HTM Reetz Loba 1200-42-600-1 -OW with a EUROTHERM S 14083 temperature controller) at 870 °C for 48 hours, followed by quenching of the hot Ta crucibles in water. After crushing the broken blocks, a gray-black powder is obtained. Phase-pure compounds are obtained. The sample was analysed with PXRD (Figure 1a).

[0222] Example 2. Preparation of the compound Li3-3xScxSb, with x = 0.15.

[0223] For Li3-3xScxSb, the starting materials Li, Sc and Sb are weighed in a stoichiometric ratio forx = 0.15 under an argon inert gas atmosphere and ground in a ball mill (e.g. Retsch PM100 planetary ball mill, 350 rpm, 18 h, 10 min interval, 5 min break) using a tungsten carbide grinding set (50 mL vessel with 3 WC balls, 0 15 mm). The reactive mixture obtained is pressed with a hydraulic press (Specac Atlas 15T) under a pressure of 294.2 MPa (3 T) for 5 min to form pellets of approx. 0.5 g with a diameter of 10 mm and then filled into tantalum crucibles, which were sealed in an electric arc furnace (Edmund Buhler MAM1). The crucibles thus obtained are enclosed in evacuated quartz reaction tubes and heated in a tube furnace (e.g. HTM Reetz Loba 1200-42-600-1 -OW with aEUROTHERM S 14083 temperature controller) at 870 °C for 48 hours, followed by quenching of the hot Ta crucibles in water. After crushing the broken blocks, a gray-black powder is obtained. Phase-pure compounds are obtained. The sample was analysed with PXRD (Figure 1b).

[0224] Example 3. Preparation of the compound Li3.3xScxP, with x = 0.15.

[0225] For Li3-3xScxP, the starting materials Li, Sc and P are weighed in a stoichiometric ratio for x = 0.15 under an argon inert gas atmosphere and ground in a ball mill (e.g. Retsch PM100 planetary ball mill, 350 rpm, 18 h, 10 min interval, 5 min break) using a tungsten carbide grinding set (50 mL vessel with 3 WC balls, 0 15 mm). The reactive mixture obtained is pressed with a hydraulic press (Specac Atlas 15T) under a pressure of 294.2 MPa (3 T) for 5 min to form pellets of approx. 0.5 g with a diameter of 10 mm and then filled into tantalum crucibles, which were sealed in an electric arc furnace (Edmund Buhler MAM1). The crucibles thus obtained are enclosed in evacuated quartz reaction tubes and heated in a tube furnace (e.g. HTM Reetz Loba 1200-42-600-1 -OW with a EUROTHERM S 14083 temperature controller) at 800 °C for 48 hours, followed by quenching of the hot Ta crucibles in water. After crushing the broken blocks, a reddish-brown powder is obtained. Phase-pure compounds are obtained. The sample was analysed with PXRD (Figure 1c).

[0226] Example 4. Preparation of the compound Na3-3xScxSb, with x = 0.15.

[0227] For Na3-3xScxSb, the starting materials Na, Sc and Sb are weighed in a stoichiometric ratio for x = 0.15 under an argon inert gas atmosphere and ground in a ball mill (e.g. Retsch PM100 planetary ball mill, 350 rpm, 18 h, 10 min interval, 5 min break) using a tungsten carbide grinding set (50 mL vessel with 3 WC balls, 0 15 mm). The reactive mixture obtained is pressed with a hydraulic press (Specac Atlas 15T) under a pressure of 294.2 MPa (3 T) for 5 min to form pellets of approx. 0.5 g with a diameter of 10 mm and then filled into tantalum crucibles, which were sealed in an electric arc furnace (Edmund Buhler MAM1). The crucibles thus obtained are enclosed in evacuated quartz reaction tubesand heated in a tube furnace (e.g. HTM Reetz Loba 1200-42-600-1 -OW with a EUROTHERM S 14083 temperature controller) at 870 °C for 48 hours, followed by quenching of the hot Ta crucibles in water. After crushing the broken blocks, a gray-black powder is obtained. Phase-pure compounds are obtained. The sample was analysed with PXRD (Figure 1d).

[0228] Example 5. Preparation of the compound Li3-3xScxBi, with x = 0.05.

[0229] Example 5 was prepared in the same way as Examples 1 to 4 via a two-step solid-state synthesis route. After ball milling of stoichiometric amounts of the corresponding elements and pressing the obtained mixture into pellets, high temperature heating (800°C for 24 hours) was performed, followed by quenching. The sample was analysed with PXRD (Figure 1e).

[0230] Example 6. Preparation of the compound Li3-3xScxBi, with x = 0.15.

[0231] Example 6 was prepared in the same way as Examples 1 to 4 via a two-step solid-state synthesis route. After ball milling of stoichiometric amounts of the corresponding elements and pressing the obtained mixture into pellets, high temperature heating (800°C for 24 hours) was performed, followed by quenching. The sample was analysed with PXRD (Figure 1f).

[0232] Example 7. Preparation of the compound Li2.71Sc0.03S0.2Sb0.8[Li2.8-0.6(x+4y)Sc0.2(x+4y)SzSb(1-z)(D1 = S, m = 2; D2 = Sb, n = 3; z = 0.2, x+4y = 0.15, zx+(1-z)y = 0.03)].

[0233] Example 7 was prepared in the same way as Examples 1 to 4 via a two-step solid-state synthesis route. After ball milling of stoichiometric amounts of the corresponding elements and pressing the obtained mixture into pellets, high temperature heating (800°C for 48 hours) was performed, followed by quenching. The sample was analysed with PXRD (Figure 1g).Example 8. Preparation of the compound Li2.275Sc0.075S0.5Sb0.5[Li2.5-1.5(x+y)Sc0.5(x+y)SzSb(1-z)(D1 = S, m = 2; D2 = Sb, n = 3; z = 0.5, x+y = 0.15, zx+(1-z)y = 0.075)].

[0234] Example 8 was prepared in the same way as Examples 1 to 4 via a two-step solid-state synthesis route. After ball milling of stoichiometric amounts of the corresponding elements and pressing the obtained mixture into pellets, high temperature heating (800°C for 48 hours) was performed, followed by quenching. The sample was analysed with PXRD (Figure 1h).

[0235] II. Analytical methods

[0236] Powder X-ray diffraction

[0237] Examples 1-8 were analysed by PXRD. Powder diffraction data were collected on a STOE Stadi P diffractometer (Ge(111) monochromator, Mo Ka radiation, 0.7093 A) with a Dectris MYTHEN 1 K detector in Debye-Scherrer geometry at room temperature. Samples were sealed in glass capillaries (Ø0.3 mm) by wax for measurement. Raw data were processed with the WinXPOW software.

[0238] Examples 5 and 6 yielded phase-pure samples. Li2.85Sc0.05Bi crystallizes in a cubic lattice with space group of F m -3 m (no. 225). The lattice parameter is indexed to be a = 6.702(2) Å at 293 K (see Figure 1e). Li2.55Sc0.15Bi also adopts a cubic lattice with space group of F m -3 m (no. 225), with an indexed lattice parameter of a = 6.7374(6) Å at 293 K (see Figure 1f). A structural model of Li2.55Sc0.15Sb is employed for visual comparison and confirmation of the crystal structure.

[0239] As outlined in Table A, a comparison of lattice parameters was made among the as-synthesized compounds and the parent compound LisBi, showing a difference in the lattice parameter by Sc substitution, thereby confirming the successful synthesis of Li2.85Sc0.05Bi and Li2.55Sc0.15Bi.Table A. Comparison of lattice parameters of as-synthesized compounds of formula (I) and the parent compound Li3Bi. Of note, these compounds crystallize in the same space group F m -3 m (no. 225).

[0240] Compounds Lattice parameter a (Å)

[0241] Li3Bi (ICSD 58797) 6.7220

[0242] Li3Bi (in-house PXRD measurement) 6.719(4)

[0243] Li2.85Sc0.05Bi 6.702(2)

[0244]

[0245] Li2.55Sc0.15Bi 6.7374(6)

[0246] For Example 7 (Li2.71Sc0.03S0.2Sb0.8), synthesis resulted in the desired phase, but a small amount of Li2S as a side phase is present. The compound crystallizes in a cubic lattice with space group of F m -3 m (no. 225). The lattice parameter is indexed to be a = 6.5800(2) Å at 293 K (see Figure 1g).

[0247] For Example 8 (Li2.275Sc0.075S0.5Sb0.5), synthesis resulted in the desired phase, albeit with the presence of side phase Li2S. The compound crystallizes in a cu-bic lattice with space group of F m -3 m (no. 225). The lattice parameter is indexed to be a = 6.6219(4) A at 293 K (see Figure 1 h).

[0248] For Examples 7 and 8, a structural model of Li2.55Sco.15Sb is employed for visual comparison and confirmation of the crystal structure. As shown in Table B, the synthesized Li2.7iSco.o3So.2Sbo.8 and Li2.275Sc0.075S0.5Sb0.5 exhibit larger lattice parameters compared to that of binaries, presenting a lattice enlargement in the solid solution and the formation of the quaternary phases.

[0249] Table B. Comparison of lattice parameters of as-synthesized solid solutions and the parent compound Li2S and cubic-Li3Sb. Of note, these compounds crystallize in the same space group F m -3 m (no. 225).

[0250] Compounds Lattice parameter a (Å) Li2S (ICSD 56023) 5.7200

[0251]

[0252] cubic-Li3Sb (ICSD 44900) 6.5590cubic-Li3Sb (in-house PXRD measurement) 6.5694(7)

[0253] Li2.71Sc0.03S0.2Sb0.86.5800(2)

[0254]

[0255] Li2.275Sc0.075S0.5Sb0.56.6219(4)

[0256] Electrochemical Impedance Spectroscopy (EIS) and Direct-Current (DC) Polarization Methods

[0257] For the compounds prepared in Examples 1-4, the ionic conductivity was determined by electrochemical impedance spectroscopy (EIS) in RHD CompreCell (Model no.: 840324). The powdered samples (300 - 500 mg) were separately placed between two stainless-steel dies and pressed into pellets with a diameter of 6 mm and a thickness between 5.3 to 8.7 mm by applying a pressure of 381.3 MPa for approximately 5 min, leading to a compact density of ~ 85%. The above processes were performed in an Ar-filled glove box (MBraun) to exclude the impact of air and moisture. Subsequently, the RHD cell was enclosed in an in-house designed metal clamping system to ensure good contact of the cell and an air-tight atmosphere. The corresponding fabrication pressure was set at 150 MPa by fastening the screws of three springs. Prior to EIS measurements, the cell rested for 12 h to allow for thermal equilibration.

[0258] The impedance data were collected by Bio-Logic potentiostat (VSP-300) in a frequency range from 3 MHz to 100 mHz at a potential perturbation of ±10 mV. Data were analyzed by using the software EC-Lab (V 11.36). The measurements were performed in an Ar-filled glovebox at 25 °C. The electronic conductivity was determined with the same set-up using a potentiostatic direct-current (DC) polarization applying voltages of 50, 100, and 150 mV for 7 h each. For determining the activation energy of lithium- and sodium-ion conduction, the cell temperature was set to 10, 25, 40, 55 and 70 °C using a climate chamber (ESPEC, Lil-114). EIS measurements were performed during heating and cooling cycles. Temperature-dependent EIS measurements were carried out inside the glovebox. All data were obtained from three independently measured cells, andthe reported errors represent the standard deviation of conductivities obtained for these three cells.

[0259] For the compound prepared in Example 8, the ionic and electronic conductivity was determined. The ionic conductivity of Li2.275Sc0.075Sb0.5S0.5is determined to be 10.3 mS / cm from temperature-dependent PEIS measurements (Potenti-ostatic Electrochemical Impedance Spectroscopy) with the same method as Examples 1-4. The results are shown in Figures 3 and 4. Although the sample contains a small amount of Li2S, its contribution to the overall ionic conductivity can be neglected, as the ionic conductivity of Li2S is reported to be negligible (J. Maier et al, Adv. Funct. Mater. 2019, 29, 1807688).

[0260] The electronic conductivity of Li2.275Sc0.075Sb0.5S0.5(Li2.55Sc0.15SSb) was evaluated by DC-CA measurements (Direct-current (DC)-Chronoamperometry (CA)) with the same method as Examples 1-4, yielding a value of 2.6 mS / cm. The results are shown in Figures 5.

[0261] The obtained Nyquist and Arrhenius plots for Examples 1 and 2 are shown in Figure 2. The obtained Nyquist and Arrhenius plots for Example 8 are shown in Figures 3 and 4, and the obtained DC-CA plot for Example 8 is shown in Figure 5. The obtained values for ionic conductivity, electronic conductivity and activation energy are summarized in Table 1 below.

[0262] Table 1: Properties of inventive compounds.

[0263] Ex. Compound ionic conductivity electronic activation (mS / cm) at room conductivity energy temperature (mS / cm) at EAPEISroom temper(kJ / mol) ature

[0264] 1 Li2.625Sc0.125Sb 50(5) 4.18 20.4(6) (x = 0.125, Pn = Sb)

[0265] 2 Li2.55Sc0.15Sb 42(6) 0.203 21.2(5) (x = 0.15, Pn = Sb)

[0266] 3 Li2.55Sc0.15P 0.25(1) 2.8(9) x 10-533.8(6) (x = 0.15, Pn = P)

[0267] 4 Na2.55Sc0.15Sb 1.63 4.04 x 10-327.1(4)

[0268]

[0269] (x = 0.15, Pn = Sb)8 Li2.275Sc0.075Sb0.5S0.510.3 2.6 21

[0270] (z = 0.5, zx+(1-z)y =

[0271] 0.075, Ch = S, Pn =

[0272]

[0273] Sb)

[0274] Examples 3 and 4 show high ionic conductivity and negligible electronic conductivity. Thus, these compounds are promising materials for ASSB solid electrolytes. Examples 1 and 2 show comparably high ionic and electronic conductivity, making them promising candidates for use in composite cathodes. The use of materials with mixed and comparably high ionic and electronic conductivities in composite cathodes is particularly advantageous as it enhances the power densities for a thick cathode configuration, mitigates the additional interfacial resistance while reducing the need for a large portion of carbon, which has been reported to be detrimental in ASSBs. In comparison to scandium free binary parent compounds, an increase in ionic conductivity by several orders of magnitude is achieved (for instance, Li2.55Sco.15P shows an ionic conductivity of 0.25(1) mS cm-1in comparison to an ionic conductivity of 3.0(6) • 10’5mS cm-1as published for microcrystalline powders of LisP at 50 °C). In comparison to the quaternary compound Li2.925Sco.358P2Se, an increase in ionic conductivity by several orders of magnitude is achieved (Li2.55Sc0.15P shows an ionic conductivity of 0.25(1) mS cm-1in comparison to an ionic conductivity of 1.2 • 10-3mS cm-1as published for Li2.925Sc0.358P2S6). The ionic conductivity obtained for Example 3 comprising phosphorous is slightly lower than for Examples 1, 2 and 4 comprising antimony.

[0275] Example 8 shows a potential for being mixed ionic-electronic conductor (MIEC), benefiting from its high ionic and electronic conductivities.

[0276] The high ionic conductivity and low activation energy barrier of inventive examples further underscore their potential for use in ASSBs, particularly under low temperatures.

Claims

C LAI M S1. A compound of formula (I), formula (II) or formula (III):A+(3-3x)Sc3+xPn3- (I)A is selected from Li and Na,Pn is selected from the group consisting of N, P, As, Sb and Bi, x is in the range 0 < x < 0.5,A+(2-3y)Sc3+yCh2- (II)A is selected from Li and Na,Ch is selected from the group consisting of S, Se and Te, y is in the range 0 < y < 0.5.[A+z(m-3x)+(1-z)(n-3y)Sc3+zx+(1-z)y(D1)m-z(D2)n-(1-z)] (III),A is selected from Li and Na,D1 and D2 are each selected from N, P, As, Sb, Bi, S, Se and Te, with D1 ≠ D2,x is in the range 0 < x < 0.5,y is in the range 0 < y < 0.5,0 < z < 1,m is 2 or 3, n is 2 or 3, wherein m and n can be the same or different.

2. The compound according to claim 1, whereinx is in the range 0.05 < x < 0.50, preferably 0.05 < x < 0.25, more preferably 0.10 < x < 0.25, more preferably 0.11 < x < 0.25, more preferably 0.11 < x < 0.20, and / ory is in the range 0.05 < y < 0.50, preferably 0.05 < y < 0.25, more preferably 0.10 < y < 0.25, more preferably 0.11 < y < 0.25, more preferably 0.11 < y < 0.20.

3. The compound according to claim 1 or 2, wherein the compound is of formula (I), and Pn is selected from the group consisting of P, As, Sb and Bi, more preferably Sb, As and Bi, more preferably Sb.

4. The compound according to any of claims 1 to 3, wherein the compound is of formula (I), A = Li or Na, Pn = Sb and x is in the range 0.05 < x < 0.50, more preferably 0.10 <x < 0.50, more preferably 0.11< x < 0.50, more preferably 0.11 < x < 0.25, more preferably 0.11 < x < 0.20.

5. The compound according to claim 4, which is selected from the group consisting of Li2.625Sco.i25Sb, Li2.55Sco.15Sb and Na2.55Sco.15Sb.

6. The compound according to any of claims 1 to 3, wherein the compound is of formula (I), A = Li or Na, Pn = P and x is in the range 0.05 < x < 0.50, more preferably 0.05 <x < 0.25, more preferably 0.10 <x < 0.20.

7. The compound according to claim 6, which is selected from the group consisting of Li2.55Sco.15P and Na2.55Sco.15P.

8. The compound according to any of claim 1 to 7, wherein the compound has an ionic conductivity above 0.1 mS / cm, preferably above 0.25 mS cm-1, as determined by electrochemical impedance spectroscopy (EIS).

9. The compound according to any of claim 1 to 8, wherein the compound has an activation energy below 75 kJ mol-1, preferably below 35 kJ mol-1, as determined by electrochemical impedance spectroscopy (EIS).

10. The compound according to any of claim 1 to 9, wherein the compound has an electronic conductivity below 10 mS / cm, preferably below 5 mS / cm, as determined by direct-current (DC) polarization method.

11. A composition comprising a mixture of two or more compounds according to any of claims 1 to 10.

12. A solid electrolyte or an additive in a composite cathode comprising a compound according to any of claims 1 to 10 or a composition according to claim 11.

13. A process for the preparation of a compound according to any of claims 1 to 10 comprising the following steps:

1. Mixing starting materials containing stoichiometric quantities of the elements contained in formula (I), formula (II) or formula (III) in an inert gas atmosphere to obtain a mixture,2a. optionally, grinding the powder mixture obtained in step 1 in a ball mill under an inert gas atmosphere to obtain a ground powder, or 2b. optionally, pressing the mixture obtained in step 1 into pellets under an inert gas atmosphere, or2c. optionally, grinding the mixture obtained in step 1 in a ball mill under an inert gas atmosphere to obtain a ground powder and subsequently, pressing the obtained ground powder into pellets under an inert gas atmosphere, and3. Heating the mixture obtained in step 1 or the pellets or the ground powder obtained in step 2 to temperatures between 400°C and 900°C for a period of a few hours to 10 days in an inert gas atmosphere.

14. The process according to claim 13, wherein the heating in step 3 is carried out at a temperature between 700°C and 900°C for a duration of 2 days to 4 days.

15. Use of a compound according to any of claims 1 to 10 or of the composition according to claim 11 as a solid electrolyte or as an additive in a composite cathode in primary or secondary electrochemical energy storage devices, particularly in all-solid-state batteries (ASSBs).

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