Sulfide solid electrolyte for solid-state battery and preparation method thereof

Abstract

The present invention relates to a solid electrolyte for a solid-state battery, which is configured as a phosphorus-free solid electrolyte having a cubic silver structure. The solid electrolyte is characterized by a composition according to the total formula: Li < 6 + x > M < x > Sb < 1-y > S < 5-z > R, for x = 0 to 0.7; y = 0 to 0.7, z = 0 to 0.7, where the (semi) metal comprises M = Si, Sn, W and halogens R = I1, Cl1Brz, Br1, is applicable, and where M = W and xgt are also applicable for R = I1; 0. A method of preparation is also described.

Description

[0001] The present invention relates to a sulfide solid electrolyte for a solid-state battery. The present invention also relates to a method for preparing such a sulfide solid electrolyte.

[0002] Various types of batteries are known for storing electric power. One type among them is the so-called solid-state battery. A solid-state battery or a solid-state secondary battery contains a solid electrolyte or a solid-state electrolyte, respectively. For example, compared with a lithium-ion battery, a solid-state battery does not contain a liquid or a flammable and toxic organic solvent, which makes the solid-state battery have higher safety than a lithium-ion battery. Therefore, solid-state batteries are regarded as promising so-called next-generation batteries.

[0003] In order to improve the performance of a solid-state battery, the solid electrolyte can be modified. The aim is to further improve the ionic conductivity and the stability to lithium, which is related to the improvement of the performance and safety of the solid-state battery.

[0004] For example, a solid electrolyte having a basic general formula Li6 P S5 R is known, where R can be a halogen, such as chlorine, bromine or iodine. The disadvantage of such a conventional solid electrolyte mainly lies in the use of phosphorus. Phosphorus combines with oxygen in the air and will eventually cause the decomposition of the sulfide structure. For this reason, it is basically known from the prior art that phosphorus can be replaced by antimony, which prevents the reaction with oxygen. Therefore, an air-stable sulfide solid-state electrolyte can finally be obtained, for example, according to the general formula

[0005] Li 6+x Mx Sb 1-x S5 I, where the (semi)metal M is usually Si, Ge or Sn. The factor x is in the range of 0.1 < x < 0.7. In this case, only iodine is used as the anion to obtain the crystal structure of argyrodite having the space group F43m. For example, such a modification is described in "New Family of Argyrodite Thioantimonate Lithium Superionic Conductors" in Journal of the American Chemical Society, Vol. 141, pages 19002 to 19013, 2019. Antimony is larger than phosphorus and further improves the ionic conductivity of the composition.

[0006] The structure described therein always contains iodine as a halogen and is provided with a (semi)metal, such as especially silicon, germanium or tin. Although this new phosphorus-free sulfide solid electrolyte has improved resistance to atmospheric oxygen, the solid-state battery equipped with it still tends to short-circuit very quickly and has a low power density or energy density.

[0007] The object of the present invention is to provide a sulfide solid electrolyte for solid-state batteries which combines an increase in power compared to known solid-state electrolytes with good processability of the solid-state electrolytes.

[0008] According to the invention, this object is achieved by a solid electrolyte for solid-state batteries having the features of claim 1, in particular in the characterizing part of claim 1. Advantageous embodiments and improvements are given in the dependent claims. A method for producing such a solid electrolyte is also described. In this case, advantageous improvements also follow from the dependent subclaims.

[0009] The core of the solid electrolyte according to the invention is formed of a composition having the basic general formula:

[0010] Li 6+x M x Sb 1-y S 5-z R

[0011] For x = 0 to 0.7; y = 0 to 0.7, z = 0 to 0.7, M = Si, Sn, W and R = I1, Cl1Br z , Br1. Thus, in the case of using iodine as free radical R, the (semi)metal M is in any case tungsten, which is present in the composition in a proportion greater than 0.

[0012] This solid electrolyte enables solid-state batteries with high power, high power density and at the same time very high safety, since short circuits and the formation of toxic gases, such as in conventional batteries, are prevented.

[0013] Advantageously, the sulfide solid electrolytes according to the present invention describe a new class of phosphorus-free sulfide solid electrolytes having a cubic argyrite structure and having increased chemical and electrochemical properties compared to known argyrite structures.

[0014] A very advantageous embodiment of the sulfide solid electrolyte according to the invention can be that the (semi)metal is silicon or tin, wherein, in this case, the factor z is zero, so that five parts of sulfur are always present. Furthermore, this leads to the fact that chlorine or bromine always appear alone, in a stoichiometric ratio of 1, wherein iodine is excluded in any case. In this case, the factors x and y are identical and lie in the range between 0 and 0.6, so that even with a value of 0 there are variants which contain no silicon or tin at all.

[0015] Another very advantageous design of the sulfide solid electrolyte according to the invention can provide that the free radical, i.e. the halogen, is always iodine, as already stated as a special case of the main claim. In this case, the metal M according to claim 1 will be tungsten in a stoichiometric ratio greater than 0. A preferred embodiment of the material also provides that if the factor z=0, the sulfur is always present in a stoichiometric ratio of 5, and the factors x and y are equal and between 0.05 and 0.2.

[0016] The solid electrolyte thus has a structure which uses iodine and tungsten, which replace the hitherto customary (semi)metals and which, together with iodine, offer high ionic conductivity with correspondingly good stability towards air, moisture and lithium.

[0017] Another very advantageous design of the sulfide solid electrolyte according to the present invention can also provide that it is over-halogenated. Therefore, in this case, the free radicals contain more than one halogen, whose common stoichiometric ratio is greater than 1. Therefore, in this case, the factor y will be 0, the factors x and z will be the same, and in the value range of 0.1 to 0.7. Due to this over-halogenation, especially when (semi) metals are not used at all according to its very advantageous improvement scheme, the ionic conductivity increases sharply due to the expansion of the cubic crystal structure in the solid electrolyte material. The simultaneous use of bromine and chlorine in a common stoichiometric ratio greater than 1 achieves a sharp increase in ionic conductivity by reducing the activation energy of lithium diffusion. The activation energy value can be reduced to below 0.2eV by over-halogenation, while the standard values ​​are generally in the order of 0.28eV and 0.35eV.

[0018] Therefore, in particular this overhalation leads to materials that are highly efficient and very stable with respect to ambient conditions and have very high ionic conductivity.

[0019] The method for preparing a sulfide solid electrolyte comprises the following steps. First, the raw materials are mechanically mixed into a glassy or amorphous powder mixture. Depending on the desired composition, the raw materials include:

[0020] Lithium sulfide (Li2S);

[0021] Antimony (III) sulfide or (V) antimony sulfide (SbS3, Sb2S5), wherein both oxidation states can be used here;

[0022] Silicon disulfide (SiS2), tin (IV) sulfide (SnS2) and / or tungsten (IV) sulfide (WS2); and

[0023] Lithium chloride (LiCl), lithium bromide (LiBr) and / or lithium iodide (LiI).

[0024] In the next step, the amorphous powder mixture is then heated at a temperature between 470° C. and 580° C. for 1 to 7 days in an argon atmosphere, or at a temperature between 400° C. and 600° C. for 1 to 7 days under static or dynamic vacuum. By heating the glassy amorphous powder, a crystalline structure is obtained from the mixture.

[0025] The new solid electrolytes can therefore be prepared by classical synthesis routes. The preparation of the new solid electrolytes is therefore simple and reliable, as the processes are known and can be reliably carried out in existing plants.

[0026] A particularly advantageous design of the method for preparing the novel solid electrolyte can also provide that the particle size of the lithium sulfide is selected to be correspondingly small, for example of the order of magnitude of less than 3 μm. The particle size can particularly preferably be less than 1 μm. By controlling the particle size of the lithium sulfide as a raw material, the final particle size of the synthesized solid electrolyte can be influenced accordingly. The smaller the particle size of the lithium sulfide, the smaller the particle size of the solid electrolyte. The above-mentioned sizes are therefore ideal for achieving high stability and good functionality of the solid electrolyte.

[0027] Further advantageous embodiments of the solid electrolyte according to the invention also result from the exemplary embodiments of the material, which will be described in more detail below with reference to the drawings.

[0028] in:

[0029] Figure 1 A tabular list of different compositions is shown.

[0030] exist Figure 1 In the diagram of FIG. 1 , possible compositions of solid electrolytes for solid-state batteries are shown in four separate tables. The compositions in the table describe the materials available in the first column on the far left using formulas and factors x, y, z. In the next column, different values ​​of the factor x are given, which is identical to the factor y or z, depending on the composition. The other columns show the raw materials for preparing the material. In this case, antimony sulfide is always listed here as antimony (V) sulfide, but antimony (III) sulfide can also be used, in which case the antimony (III) sulfide must be appropriately adjusted according to the prescribed proportions. In the two upper tables, silicon sulfide is in each case specified as the raw material for the (semi)metal M and in the lower table as tungsten sulfide. No (semi)metal is required for the lower table. In each case, the required lithium halide is listed in the rightmost column of the three upper tables and in the two right columns of the next table. In each case, the amounts of the individual raw materials should be given in moles.

[0031] For example, according to the last row of the table above, the total formula is Li 6.6 Sb 0.4 Si 0.6A pure example of a solid electrolyte of S5Cl1 is 1.434 mol Li2S; 0.642 mol Sb2S3; 0.523 mol SiS2 and 0.401 mol LiCl are required. These starting amounts can be adjusted to each other in appropriate proportions, i.e. increased or decreased, and mixed as required. The mixture of amorphous glass powders is then heated in an argon atmosphere, for example at 470°C to 580°C for 1 to 7 days to obtain the crystalline structure of the solid electrolyte.

[0032] This will occur similarly for other compositions.

Claims

1. A sulfide solid electrolyte for a solid-state battery, the sulfide solid electrolyte being configured as a phosphorus-free solid electrolyte having a cubic silver structure, Features Composition according to the general formula: Li 6+x M x Sb 1-y S 5-z R For x = 0 to 0.7; y = 0 to 0.7, z = 0 to 0.7, where the (semi)metal contains M = Si, Sn, W and halogen R = I1, Cl1 Br z , Br1, then it applies, and where, for the case of R=I1, it is also applicable that M=W and x>0.

2. The sulfide solid electrolyte according to claim 1, It is characterized in that For the case where M=Si, Sn, R==Cl1 Br z , Br1, and wherein z=0 and x=y also apply, wherein x=0 to 0.

6.

3. The sulfide solid electrolyte according to claim 1, It is characterized in that For the case where R = I1, M = W and x > 0 applies z=0 and x=y, where x=0.05 to 0.

2.

4. The sulfide solid electrolyte according to claim 1, It is characterized in that For R = Cl1 Br z In case of y=0 and x=z, where x=0.1 to 0.

7.

5. The sulfide solid electrolyte according to claim 4, It is characterized in that The composition does not contain a metal or a semimetal M.

6. A method for preparing a solid electrolyte according to any one of claims 1 to 5, It is characterized by the following steps: Mixed raw materials Li2S and SbS3 or Sb2S5 and SiS2, SnS2 and / or WS2 and LiCl, LiBr and / or LiI A glassy amorphous powder mixture, heating the amorphous powder mixture to a temperature between 470°C and 580°C in an argon atmosphere, or The amorphous powder mixture is heated at a temperature of 400°C to 600°C under static or dynamic vacuum. 1 to 7 days respectively.

7. The method according to claim 6, It is characterized in that Li2S with a particle size of less than 3 μm, preferably less than 1 μm, is used.

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