Sulfide-based solid-state electrolyte, its production and use, and solid-state battery cell containing this

Abstract

The invention relates to a sulfide-based solid electrolyte comprising or consisting of the general chemical formula (I): Li₆+y[S₆P₆S₆M₆]S₅Ha₆I, where M is selected from the group consisting of germanium (Ge), tin (Sn), arsenic (As), zinc (Zn), molybdenum (Mo), titanium (Ti), copper (Cu), and bismuth (Bi); x = 0.25; 0.1 < y < 0.9, and Hal is selected from the group consisting of Cl, Br, and I; with the proviso that if M is germanium (Ge) and Hal is iodide, y cannot be 0.5. The sulfide-based solid electrolyte is characterized by a low activation energy, resulting in high performance of a solid-state battery at very low temperatures, in particular down to -20°C, and thus maintaining the range of an electric vehicle (BEV) even at these very low temperatures.

Description

The invention relates to a sulfide-based solid electrolyte, its production and use, and to a solid-state battery cell comprising the same.In battery technology, lithium ion-based battery systems have become increasingly prevalent in recent years. These are distinguished in particular by their high energy density and expected long service life, so that more efficient battery configurations are possible. The high chemical reactivity and the low mass of lithium ions and their high mobility play a central role here. In all-solid-state batteries, both electrodes and the electrolyte are made of solid material. In lithium ion batteries, lithium compounds are present in all three phases of the electrochemical cell, i.e. the negative electrode, the positive electrode and the electrolyte contain lithium ions from solid-state lithium ion conductors. The general advantage of lithium-based solid-state batteries is that a liquid electrolyte, which is frequently easily flammable or toxic and tends to decompose, is replaced and an improvement in the safety and reliability of lithium-based batteries is thus possible.In particular for electric vehicles, the development of lithium-based solid-state batteries with high power output, high capacity and good (electro)chemical stability is of great interest. For high battery performance, a solid electrolyte material having good ionic conductivity is generally desirable in view of achieving as high a power output as possible of a battery.Conventional sulfidic solid electrolytes of the LGPS type (Li 10 GeP 2 S 12) and of the argyrodite type (Li 6 PS 5 Cl) usually exhibit high activation energies of 0.3 eV or more and 24 kJ mol -1 or more, respectively. For the LGPS type, these are in the range from 25-35 kJ mol of -1(1). For argyrodites, these are between 28 and 36 kJ mol -1 or about 0.29 eV (2). The activation energy represents an energetic barrier or energy difference which must be overcome by the reaction partners during a chemical reaction in order that the starting materials can react with one another. The Arrhenius equation describes the relationships in chemical kinetics on the basis of the quantitative dependence of the reaction rate constant k on the temperature. Thus, the Arrhenius equation can be used to determine the ionic conductivity as a function of the temperature. A high activation energy makes the lithium ion transport through the crystal lattice more difficult. Based on the Arrhenius equation: whereink: speed constant,A: Pre-exponential factor,k: Boltzmann factor,T: absolute temperature,Ea: Activation energymeans that the velocity constant decreases at high activation energy. The slope of the Arrhenius function thus increases as a function of temperature. It follows finally that the ionic conductivity at low temperatures decreases as the activation energy increases.Sulfide-based solid electrolyte described in the prior art therefore exhibits drastic lowering of electrochemical performance at low temperatures, e.g., -10° C. and below, due to the high activation energy of the materials.The prior art has already disclosed approaches for sulfide-based solid electrolytes to reduce the activation energy which are based on cation doping or anion doping: for example, J. Lin et al. (3) describes an argyrodite-type solid electrolyte obtained with cation doping having the chemical formula Li 6,5[ P 0,25 Si 0,25 Ge 0,25 Sb 0,25] S 5 I in which a low activation energy for lithium diffusion of -0.2 eV and a high ion conductivity at room temperature of ∼ 13 mS cm -1 were obtained. Furthermore, F. Strauss et al. (4) describes sulfide-based argyrodite-type solid electrolytes obtained with anion doping in the form of high-entropic ceramics, in particular Li 6 PS 5[ Cl 0,33 Br 0,33 I 0,33], Li 6 P[S 2,5 Se 2,5]-[ Cl 0,33 Br 0,33 I 0,33] and Li 6,5[ Ge 0,5 P 0,5]( S 2,5 Se2,5][Cl0,33Br0,33I0,33], which show a low activation energy for lithium diffusion of 0.22 eV and a high ion conductivity at room temperature of ~10-3S cm-1.However, there remains a great need to provide sulfide-based solid electrolytes that can be operated at low temperatures without losing performance.The object of the present invention is therefore to avoid the disadvantages from the prior art and to provide a sulfide-based solid electrolyte which has a suitable electrochemical performance, in particular ionic conductivity, even at low temperatures, in particular below 0° C.According to the invention, the above object is achieved by a sulfide-based solid electrolyte comprising or consisting of the general chemical formula (I): Li 6+y[ Si x P x Sb x M x] S 5 HaI formula (I), wherein M is selected from the group consisting of germanium (Ge), tin (Sn), arsenic (As), zinc (Zn), molybdenum (Mo), titanium (Ti), copper (Cu) and bismuth (Bi); x=0.25; 0.1<y<0.9 and Hal is selected from the group consisting of Cl, Br and I; with the proviso that when M is germanium (Ge) and Hal is iodine, y cannot be 0.5.Therefore, a sulfide-based solid electrolyte having the general chemical formula (I) is provided. The terms "sulfide-based solid electrolyte", "sulfide solid electrolyte" and "sulfide solid electrolyte" are intended to be synonymous and interchangeable.The sulfide-based solid electrolyte of the invention is a novel solid electrolyte in the form of a high entropy material, where multi-doping of the sulfide solid electrolyte is performed with more than 2 cations and 2 anions in almost the same stoichiometric amounts.M is selected from any one of elements selected from the group consisting of germanium (Ge), tin (Sn), arsenic (As), zinc (Zn), molybdenum (Mo), titanium (Ti), copper (Cu), and bismuth (Bi). There is always only one element selected from the above group present for M, and a plurality of elements of the group are not present simultaneously as M. M is particularly preferably selected from germanium (Ge), tin (Sn), arsenic (As), zinc (Zn) or titanium (Ti).Hal is selected from one of the elements of the group consisting of Cl, Br and I. Only 1 halide is always present, and a plurality of halides for Hal are not present simultaneously in the compound of the formula (I). More preferably, Hal = I or Cl.In formula (I), x is always 0.25 Y is 0.1 < y < 0.9.The Delaimer, provided that when M is germanium (Ge) and Hal is iodine, y cannot be 0.5, excludes the compound Li 6,5[ P 0,25 Si 0,25 Ge 0,25 Sb 0,25] S 5 I (3).According to a preferred embodiment, the general chemical formula (I) applies: 0.15<y<0.9 or 0.2<y<0.9 or 0.25<y<0.9 or 0.3<y<0.9 or 0.35<y<0.9 or 0.4<y<0.9 or 0.45<y<0.9, in particular 0.45<y<0.85 or 0.45<y<0.8.The sulfide-based solid electrolyte of the present invention has succeeded in lowering the activation energy to below about 0.2 eV. The low activation energy is achieved via a configuration having high entropy by doping the solid electrolyte with more than 2 cations and 2 anions. This low activation energy leads to a high lithium ion migration even at very low temperatures, up to about -20° C. As a result, a solid-state battery comprising the solid electrolyte can be operated (virtually) without power loss at low temperatures, in particular 0° C., in particular up to about -10° C. or even up to about -20° C.By using a solid-state battery with this high-entropy solid-state electrolyte, the range of an electrically operated vehicle (BEV, battery electric vehicle) is not reduced by falling temperatures. This makes it possible to extend the intervals for recharging an all-solid-state battery and to reduce the number of charging cycles required.The invention also relates to a process for the preparation of the high entropic solid electrolyte based on sulfide, comprising the steps of: (a) providing the starting materials of the solid electrolyte based on sulfide, preferably in the form of halide and / or sulfide salts, (b) weighing the starting materials in stoichiometric amounts according to the general formula (I) of the solid electrolyte based on sulfide of the present invention; (c) grinding the weighed amounts of the starting materials for 1 to 100 hours; (d) heating the ground mixture obtained in step (c) to a temperature in the range of 300° C. to 1000° C. for 1 to 100 h, and (e) after cooling, obtaining the sulfide-based solid electrolyte, wherein steps (b), (c), and (d) are performed in an inert gas atmosphere with exclusion of moisture or in a vacuum with exclusion of moisture.In step (a), first, the starting materials of the sulfide-based solid electrolyte are provided. These are, for example, commercially available salts, preferably in the form of halide and / or sulfide salts. According to the invention, for example, Li 2 S, LiI, P 2 S 5, SiCl 2, Sb 2 S 3, SiS 2 and a sulfide or iodide of the metal or semimetal M are used. The salts are each preferably used in a purity of ≥98%, more preferably ≥98.5%, even more preferably ≥99.0%, in particular ≥99.5% or ≥99.9% purity.In step (b), the weighing of the starting materials is then carried out in stoichiometric amounts according to the general formula (I). The weighing is carried out under an inert gas atmosphere or under reduced pressure, i.e. without the presence of oxygen, and with exclusion of moisture. An inert gas atmosphere is, for example, an inert gas such as argon or nitrogen gas and the like. With exclusion of moisture, for example, a content of H 2 means O<0.6 ppm. Compliance with an O 2- content<0.6 ppm may also be expedient.After weighing in step (b), optionally, mixing of the starting materials can be carried out or else a direct transition can be made to step (c). If mixing is carried out, this is likewise carried out under an inert gas atmosphere or under vacuum, i.e. without the presence of oxygen, and in each case with exclusion of moisture.In the subsequent step (c), the weighed amounts of the starting materials are ground. Grinding is carried out for 1 to 100 h, for example 15 to 50 h. Any type of mill can be used for this purpose, in which grinding can be carried out under an inert gas atmosphere or under vacuum, i.e. without the presence of oxygen, and with exclusion of moisture. According to the invention, a ball mill is particularly preferably used, in particular a planetary ball mill. Particularly preferably, the grinding takes place in the range from 200 U / min to 500 U / min.Optionally, after step (c) and before step (d), the resulting ground mixture may be pressed in the form of pellets. This is preferably carried out again under an inert gas atmosphere or vacuum and with exclusion of moisture.In step (d), the ground mixture or the pellets obtained in step (c) are heated to a temperature in the range from 300° C. to 1000° C. for 1 to 100 h in an inert gas atmosphere or under vacuum and exclusion of moisture. Preference is given to using 300° C. to 800° C., in particular 300° C. to 700° C. The temperature is maintained for a period of 1 to 100 hours, particularly preferably 15 to 50 hours.After cooling, in step (e), the sulfide-based solid electrolyte is obtained. Cooling is preferably carried out by allowing the solid electrolyte based on sulfide to stand at room temperature (25° C.) in an inert gas atmosphere or under vacuum and exclusion of moisture.The form in which the sulfide-based solid electrolyte may be present is not limited any more. Preferably, the sulfide-based solid electrolyte obtained in the step (e) is subjected to another milling step to obtain a powder. Preferably, the average particle diameter (d50) of the powder is in the range of 0.1 μm to 50 μm. The grinding is preferably carried out under an inert gas atmosphere or under vacuum and with exclusion of moisture.The invention also relates to the use of the sulfide-based solid electrolyte in a solid-state battery cell.The invention also relates to an all-solid-state battery cell comprising the sulfide-based solid electrolyte according to the present invention. Preferably, the all-solid-state battery cell is a high power output cell.The all-solid-state battery cell of the present invention may be a primary battery or a secondary battery, preferably a secondary battery that can be repeatedly charged and discharged. Primary batteries can only be discharged once and cannot be recharged thereafter. Secondary batteries, which are also referred to as accumulators, are rechargeable. For example, the solid-state battery cell according to the invention can be mounted in a vehicle.For example, the sulfide-based high entropy solid electrolyte of the invention can be incorporated into solid state secondary batteries and operated at low temperatures of up to about -20°C (nearly) without causing power loss. This means that when using a solid-state battery which has the solid-state electrolyte according to the invention in an electrically operated vehicle (BEV), the range practically does not decrease as the temperature falls.A solid-state battery cell preferably has a cathode material layer, an anode material layer and an electrolyte layer arranged therebetween, wherein the sulfide-based solid-state electrolyte according to the invention is present in one, two or all three layers.The anode material layer of an all-solid-state battery cell includes, for example, at least one anode active material, and may include an all-solid electrolyte material, a conductive material, and a binder. The anode-active material layer preferably comprises the sulfide-based solid electrolyte according to the invention, for example in a proportion of from 0.1 to 80% by volume. The anode material layer may further include a conductive material selected from carbon black, graphitized carbon black, graphite, carbon nanotubes, and carbon nanofibers, or combinations thereof. In addition, the anode material layer may include a binder such as polyvinylidene fluoride (PVDF). The thickness of the anode material layer is preferably in a range of 0.1 μm to 1000 μm.The cathode material layer of an all-solid-state battery cell includes, for example, at least one cathode active material, and may include an all-solid electrolyte material, a conductive material, and a binder. The cathode-active material layer preferably comprises the sulfide-based solid electrolyte according to the invention, for example in a proportion of from 0.1 to 80% by volume. For example, a cathode active material may comprise LiCoO 2, LiNiO 2 or Li y Ni (1-p-w) M p N w O 2 where 0.8≤y≤1.2, 0≤p≤0.33, 0≤w≤0.33, where M and N are selected from Mn, Co, Al. Further, a conductive material and a binder are present as in the anode material layer. The thickness of the cathode material layer is preferably in the range from 0.1 μm to 1000 μm.The electrolyte layer of a solid-state battery cell is present between the cathode material layer and the anode material layer, and enables ion conduction. The electrolyte layer preferably contains the sulfide-based solid electrolyte according to the invention, which is present in a proportion of 10 to 100% by volume. The thickness of the electrolyte layer is preferably in the range from 0.1 μm to 1000 μm, for example in the range from 0.1 μm to 300 μm.The all-solid-state battery cell has a separator which spatially and electrically separates the anode and cathode from one another. According to a preferred embodiment, the separator of the all-solid-state battery cell comprises a sulfide-based all-solid electrolyte.It is further preferred that the particle size (d50) of the sulfide-based solid electrolyte of the cathode composition is smaller than the particle size (d50) of the cathode active material. Further, it is preferable that the particle size (d50) of the sulfide-based solid electrolyte used in the cathode composition is smaller than the particle size (d50) of the sulfide-based solid electrolyte used for the separator.The invention also relates to a vehicle having one or more all-solid-state battery cells, the range of which remains virtually constant at temperatures of up to -20° C. The sulfide-based solid electrolyte has low activation energy, which leads to high performance of the solid-state battery at very low temperatures, in particular up to -20° C., and thereby keeps the range of an electric vehicle (BEV) almost constant even at these very low temperatures.The sulfide-based solid electrolyte has particularly good properties and can therefore be used particularly advantageously in solid-state battery cells even at very low temperatures.Production Example:Sulfide-based solid electrolyte materials of the present invention represented by the formula (I) were prepared by a mechanical ball mill and then solid-state reaction at elevated temperatures as described below.For this purpose, Li 2 S (99.9%+ purity), P 2 S 5(98 %+ purity), LiCl (98%+ purity), SiCl 2(98 %+ purity), Sb 2 S 3(98 %+ purity) and SnS 2(99,9 %+ purity) were weighed in stoichiometric amounts in an argon gas-filled glove box containing <0.6 ppm of H 2 O and <0.6 ppm of O 2. The weighed chemicals were mixed and placed in a zirconia planetary ball mill, a Premium 7 Series Pulverizer from Fa. Fritsch, ground for 40 hours. The ground powder was formed into cylindrical pellets in a glove box filled with argon gas. The pellets were filled into fused silica vials and evacuated to <10 Pa. The sealed ampoules were heated from 25°C to 500°C, and the temperature was then maintained for 15 hours. After the reaction, the ampoules were naturally cooled to room temperature, and the desired sulfide-based solid electrolyte was obtained.List of Literature:(1) Kamaya, N., et al.: "A lithium superionic conductor" in Nature Materials, 10, 2011, 682-686; (2) Adeli, P., et al.: "Boosting solid-state diffusivity and conductivity in lithium superionic argyrodites by halide substitution" in Angew. Chem. Int. Ed., 2019, 58, 8681-8686; (3) J. Lin et al.: "A High-Entropy Multicationic Substituted Lithium Argyrodite Superionic Solid Electrolyte", ACS Materials Lett., 2022, 4, 2187-2194; and (4) F. Strauss et al.: "High-Entropy Polyanionic Lithium Superionic Conductors", ACS Materials Lett. 2022, 4, 418-423.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Cited Non-Patent LiteratureKamaya, N., et al.: "A lithium super ionic conductor" in Nature Materials, 10, 2011, 682-686

[0040] P. Adeli et al.: "Boosting solid-state diffusivity and conductivity in lithium superionic argyrodites by halide substitution" in Angew. Chem. Int. Ed., 2019, 58, 8681-8686

[0040] J. Lin et al.: "A High-Entropy Multicationic Substituted Lithium Argyrodite Superionic Solid Electrolyte", ACS Materials Lett., 2022, 4, 2187-2194

[0040] Strauss, F., et al., "High-Entropy Polyanionic Lithium Super ionic Conductors," ACS Materials Lett. 2022, 4, 418-423

[0040]

Claims

A sulfide-based solid electrolyte comprising or consisting of the general chemical formula (I): Li 6+y[ Si x P x Sb x M x] S 5 HaI formula (I), wherein M is selected from the group consisting of germanium (Ge), tin (Sn), arsenic (As), zinc (Zn), molybdenum (Mo), titanium (Ti), copper (Cu), and bismuth (Bi); x = 0.25; 0.1 < y < 0.9, and Hal is selected from the group consisting of Cl, Br, and I; with the proviso that when M is germanium (Ge) and Hal is iodine, y cannot be 0.5.Solid electrolyte according to Claim 1, characterized in that M is selected from the group consisting of germanium (Ge), tin (Sn), arsenic (As), zinc (Zn) or titanium (Ti).Solid electrolyte according to Claim 1 or 2, characterized in that Hal is selected from I or Cl.Solid electrolyte according to one of the preceding claims 1 to 3, characterized in that the following applies in the general chemical formula (I): 0.15 < y < 0.9 or 0.2 < y < 0.9 or 0.25 < y < 0.9 or 0.3 < y < 0.9 or 0.35 < y < 0.9 or 0.4 < y < 0.9 or 0.45 < y < 0.9, in particular 0.45 < y < 0.85 or 0.45 < y < 0.8.Solid electrolyte according to one of the preceding claims 1 to 4, characterized in that the solid electrolyte has an activation energy of less than 0.2 eV.A process for the production of the sulfide-based solid electrolyte according to any one of claims 1 to 5, comprising the steps of: (a) providing the starting materials of the sulfide-based solid electrolyte, preferably in the form of halide and / or sulfide salts, (b) weighing the starting materials in stoichiometric amounts according to the general formula (I) of claim 1; (c) grinding the weighed amounts of the starting materials for 1 to 100 hours; (d) heating the ground mixture obtained in step (c) to a temperature in the range of 300° C. to 1000° C. for 1 to 100 h, and (e) after cooling, obtaining the sulfide-based solid electrolyte, wherein steps (b), (c), and (d) are performed in an inert gas atmosphere with exclusion of moisture or in a vacuum with exclusion of moisture.Process according to Claim 6, characterized in that, after step (b) and before step (c), the starting materials are mixed under an inert gas atmosphere and moisture exclusion or in vacuo with moisture exclusion, and / or, after step (c) and before step (d), the ground mixture obtained is pressed into the form of pellets under an inert gas atmosphere with moisture exclusion or in vacuo with moisture exclusion.Use of the sulfide-based solid electrolyte according to any one of claims 1 to 5 in a solid-state battery cell that can be operated up to temperatures of -20°C, in particular without power loss.An all-solid-state battery cell comprising the sulfide-based solid electrolyte according to any one of claims 1 to 5, wherein the all-solid-state battery cell is specifically a high power output cell.The all-solid-state battery cell according to claim 9, characterized in that the all-solid-state battery cell includes a cathode material layer, an anode material layer, and an electrolyte layer interposed therebetween, wherein the sulfide-based all-solid electrolyte according to any one of claims 1 to 5 is present in one, two, or all of three layers.The all-solid-state battery cell according to claim 9 or 10, in the form of a primary battery or a secondary battery.Vehicle comprising one or more solid-state battery cells according to any one of claims 9 to 11, wherein its range remains constant at temperatures of up to -20°C.