Sulfide solid electrolyte and all-solid-state sodium-ion battery

Abstract

A sulfide solid electrolyte and an all-solid-state sodium-ion battery. The sulfide solid electrolyte is prepared by adopting a liquid phase synthesis method, and has a chemical formula of Na3-a-bWaMobSb1-a-bS4, where 0＜a＜0.5, and 0＜b＜0.5. As for the sulfide solid electrolyte, specific Mo element and specific W element are screened out for double doping, and compared with a sulfide solid electrolyte singly doped with molybdenum or singly doped with tungsten or doped with other elements, the sulfide solid electrolyte can effectively increase the vacancy number of Na ions, and improve the ionic conductivity of original Na3SbS4; and can also improve the electrochemical stability and air stability of the solid electrolyte. The obtained sulfide solid electrolyte has uniform doped element distribution and a low synthesis method cost, is more suitable for scale production, and lays a foundation for wide use of the sulfide solid electrolyte in industrial production.

Description

A sulfide solid electrolyte and a full solid sodium ion battery TECHNICAL FIELD

[0001] The present application relates to the field of sodium ion batteries, in particular to a sulfide solid electrolyte and a full solid sodium ion battery. BACKGROUND

[0002] Due to the wide availability and low cost of sodium resources, research on sodium batteries is accelerating. Among them, in order to overcome the safety and application limitations of NaS batteries, the use state of solid composition materials and lower temperature are necessary. For example, β-alumina and sodium ion super ionic conductor (NASICON) are classic sodium ion conductive solid electrolytes, which have the advantages of high ion conductivity, high sodium ion transmission speed and high chemical stability, especially the high ion conductivity exhibited at room temperature, which can reach more than 0.1 mS / cm, but must be sintered at a temperature higher than 1000℃ to reduce the grain boundary resistance and improve the conductivity, which is a necessary process to realize full solid battery.

[0003] Similarly, sulfide-based solid electrolytes, as a viable electrolyte, are different from oxide-based electrolytes in that they can easily form dense sulfide-based materials at room temperature under cold pressing process (so-called "room temperature pressure sintering"). The continuous development of practical full solid sodium batteries requires new sulfide-based solid electrolytes with high sodium ion conductivity. Based on the above characteristics, high-conductivity sulfide sodium ion solid electrolytes such as Na3PS4, Na4SiS4, Na3PSe4 and Na3P 0.62 As 0.38 S4, etc. with cubic Na3PS4 structure have been widely studied. However, sulfide-based solid electrolytes of this structure still have the following problems: 1) the conventional phosphorus-containing sulfide Na3PS4 material has poor chemical stability in air, not only reacts with water in the environment, but also produces toxic H2S gas, which is mixed with oxygen in dry air, causing serious practical application obstacles; 2) sulfide-based solid electrolytes are usually prepared by high-energy dry ball milling method, which has poor particle uniformity and serious particle aggregation, and often has low conductivity in practical application.

[0004] Therefore, it is necessary to provide a technical solution to solve the above problems. SUMMARY

[0005] One of the purposes of the present application is to provide a sulfide solid electrolyte to solve the problems of poor chemical stability in air and low conductivity in practical application of the current sulfide solid electrolyte for sodium batteries, in view of the deficiencies of the prior art.

[0006] In order to achieve the above object, the present application adopts the following technical solutions:

[0007] A sulfide solid electrolyte is prepared by a liquid phase synthesis method, and has a chemical formula of Na 3-a- b W a Mo b Sb 1-a-b S4, 0

[0008] Preferably, 0.01

[0009] Preferably, 0.01

[0010] Preferably, 0.1

[0011] Preferably, the sulfide solid electrolyte has a sodium ion conductivity greater than or equal to 3.0 mS / cm at room temperature of 25°C.

[0012] Preferably, the liquid phase synthesis method comprises the following steps: mixing Na3SbS4 powder and sodium thiotungstomolybdate powder to prepare an aqueous solution and stirring to perform a co-precipitation reaction; then drying under vacuum, and then heat-treating in an inert atmosphere at 200-450°C to obtain the Na 3-a-b W a Mo b Sb 1-a-b S4 sulfide solid electrolyte.

[0013] Preferably, the co-precipitation reaction is performed by heating and stirring in a water bath at 60-80°C for 4-8h; the vacuum drying temperature is 120-200°C, and the drying time is 8-15h; and the heat-treatment time is 2-12h.

[0014] Preferably, the preparation method of the Na3SbS4 powder comprises the following steps: adding Na2S, Sb2S3 and sulfur powder into deionized water, heating and stirring in a water bath at 60-80°C, filtering to obtain a homogeneous precursor aqueous solution of Na3SbS4, then adding an alcohol to perform a precipitation reaction to obtain Na3SbS4 hydrate, vacuum drying, and then heat-treating in an inert atmosphere at 200-350°C to obtain the Na3SbS4 powder.

[0015] Preferably, the preparation method of the sodium thiotungstomolybdate powder comprises the following steps: mixing sodium base, thiotungsten salt and thiomolybdenum salt into deionized water, heating and stirring in a water bath at 60-80°C to obtain a precursor solution, vacuum drying, and then heat-treating in an inert atmosphere at 200-350°C to obtain the sodium thiotungstomolybdate powder, which has a chemical formula of Na2W x Moy S4, 0 < x < 1.0, 0 < y < 1.0, and x + y = 1.

[0016] The second object of the present application is to provide a solid-state sodium battery, comprising a positive electrode sheet, a negative electrode sheet, and a solid-state electrolyte film interposed between the positive electrode sheet and the negative electrode sheet, wherein the solid-state electrolyte film is a solid-state electrolyte film made of the sulfide solid-state electrolyte described above; the positive electrode sheet contains or does not contain the sulfide solid-state electrolyte described above; and the negative electrode sheet contains or does not contain the sulfide solid-state electrolyte described above.

[0017] The sulfide solid-state electrolyte provided by the present application screens specific Mo and W elements, and the Na3SbS4 is doped with Mo-W double elements. The inventors found that, compared with other elements, on the one hand, Mo and W elements can effectively increase the vacancy number of Na ions, and can effectively improve the ionic conductivity of Na3SbS4; on the other hand, through Mo-W double element doping, the electrochemical stability of the electrolyte can be further improved, and the air stability of the solid-state electrolyte is further improved, and the probability of reaction with moisture in the air is reduced, which lays a foundation for the solid-state electrolyte to be widely used in industrial production. In addition, the inventors found through experiments that, compared with the conventional solid-phase synthesis method, the Mo-W double elements need to be prepared by the liquid-phase synthesis method, so that the uniformity of the distribution of the two doping elements can be ensured, and the solid-state electrolyte with uniform particle size and small agglomeration can be prepared, which can effectively improve the ionic conductivity of Na 3-a-b W a Mo b Sb 1-a-b S4 sulfide solid-state electrolyte. BRIEF DESCRIPTION OF DRAWINGS

[0018] FIG. 1 is an SEM image of the solid-state electrolyte of Example 3 of the present application.

[0019] FIG. 2 is an SEM image of the solid-state electrolyte of Comparative Example 4 of the present application.

[0020] FIG. 3 is an XRD image of the solid-state electrolyte of Example 3 and Comparative Examples 1 and 4 of the present application.

[0021] FIG. 4 is a Raman image of the solid-state electrolyte of Example 3 and Comparative Example 1 of the present application.

[0022] FIG. 5 is an XRD image of the solid-state electrolyte of Comparative Example 1 of the present application after air exposure for 6 hours.

[0023] FIG. 6 is an XRD image of the solid-state electrolyte of Example 3 of the present application after air exposure for 6 hours. DETAILED DESCRIPTION

[0024] In order to make the technical solutions and advantages of the present application clearer, the present application and its beneficial effects will be described in further detail below with reference to specific embodiments and the accompanying drawings of the specification, but the embodiments of the present application are not limited thereto.

[0025] Generally speaking, the ion conductivity of the conventional sulfide solid-state electrolyte doped with some transition metal elements can be improved to 0.1 mS / cm or higher, but even if the composition of each element is changed, the ion conductivity of the currently preferred state of the experiment can only be improved to 0.8 mS / cm at most to 3 mS / cm, although it has shown several times growth compared with 0.1 mS / cm, but in the current background of pursuing fast charging and other applications, the ion conductivity of 1 mS / cm is still insufficient to meet the needs of users.

[0026] Based on this, the present inventors have provided a sulfide solid-state electrolyte, which is prepared by a liquid phase synthesis method and has a chemical formula of Na 3-a-b W a Mo b Sb 1-a-b S4, 0

[0027] Through in-depth research, it is found that, compared with the sulfide solid-state electrolyte doped with molybdenum or tungsten or other elements, the sulfide solid-state electrolyte obtained by the present application is doped with tungsten and molybdenum, and the preparation method and the content of each element are controlled, so that the distribution of the doped elements is uniform, the vacancy number of Na ions can be effectively increased, the ion conductivity of the original Na3SbS4 can be improved, the electrochemical stability and air stability of the solid-state electrolyte can be improved, and the electrolyte synthesis method provided by the present application has low cost and is more suitable for large-scale production, thereby laying a foundation for the wide application of the solid-state electrolyte in industrial production.

[0028] Among them, the content of tungsten can be 0

[0029] The content of molybdenum can be 0

[0030] Correspondingly, according to the specific values of a and b, the content ranges of Na and Sb are adjusted, so that the sulfide solid-state electrolyte of the present application is Na 3-a-b W a Mob Sb 1-a-b S4.

[0031] The values of a and b are controlled in the above range, so that the doping amounts of a and b are avoided to be too much, and the contents of Sb and Na are affected, thereby affecting the structural stability of the sulfide solid electrolyte.

[0032] Preferably, for the content of tungsten, a is preferably 0.01≤a≤0.25; for the content of molybdenum, b is 0.01≤b≤0.25.

[0033] More preferably, for the content of tungsten, a is 0.01

[0034] In addition, it is found that the values of a and b are simultaneously controlled to satisfy 0.1≤a+b≤0.3 and 0≤b-a≤0.1, which can further improve the ionic conductivity of the solid electrolyte, and can also improve the oxidation resistance of the solid electrolyte, widen the potential window, and have more excellent performance.

[0035] However, it should be noted that the present inventors have found that, after optimization, the element components of the present application, in combination with the liquid phase synthesis method, can ensure the uniformity of the distribution of the doped elements, so as to prepare a solid electrolyte with uniform particle size and small agglomeration. Although the powder mixing method of the solid phase synthesis method is simpler, the prepared particles often have poor uniformity, and the distribution of the doped elements in the particles is not uniform. Even if the improvement method of small particle size and increased mixing time is used in the solid phase synthesis method, the sulfide solid electrolyte obtained still has limited improvement in ionic conductivity.

[0036] The sulfide solid electrolyte obtained by the present application has a sodium ion conductivity of greater than or equal to 3.0 mS / cm at 25℃ room temperature, and can exhibit a sodium ion conductivity of greater than 12 mS / cm after regulating the composition of tungsten and molybdenum. Compared with existing sulfide solid electrolytes, the sodium ion conductivity is greatly improved, which provides more application directions for the practical application of sodium batteries.

[0037] Specifically, the chemical formula of the sulfide solid electrolyte of the present application includes but is not limited to Na 2.95 W 0.025 Mo 0.025 Sb 0.95 S4, Na2.9 W 0.06 Mo 0.04 Sb 0.9 S4, Na 2.9 W 0.08 Mo 0.02 Sb 0.9 S4, Na 2.85 W 0.09 Mo 0.06 Sb 0.85 S4, Na 2.85 W 0.012 Mo 0.03 Sb 0.85 S4, Na 2.7 W 0.2 Mo 0.1 Sb 0.7 S4, Na 2.5 W 0.4 Mo 0.1 Sb 0.5 S4, Na 2.5 W 0.1 Mo 0.5 Sb 0.5 S4.

[0038] Specifically, the liquid phase synthesis method is as follows: Na3SbS4 powder and sodium thiotungstate powder are mixed, configured into an aqueous solution, and stirred to perform a co-precipitation reaction; then, after drying under vacuum, heat treatment is performed in an inert atmosphere at 200-450 DEG C to obtain Na 3-a-b W a Mo b Sb 1-a-b S4 sulfide solid electrolyte.

[0039] The liquid phase synthesis method provided by the application uses a multi-step liquid phase synthesis method to synthesize, Na3SbS4 powder and sodium thiotungstate powder are first prepared into an aqueous solution and then mixed and stirred to perform a co-precipitation reaction, which can realize uniform mixing of doped elements at the atomic level, and further ensure the uniformity of subsequent doping; then, through heat treatment at a suitable temperature, the crystal water can be well removed, the crystallization strength of the material is improved, the stability of the structure is ensured, and more vacancies are provided for Na ions.

[0040] The temperature of the heat treatment can be 200-250℃, 250-300℃, 300-350℃, 350-400℃ or 400-450℃. Controlling the temperature of the heat treatment within the above range can meet the requirement of removing the crystal water, and will not damage the overall structure of the solid electrolyte, ensuring the air stability in practical application. Preferably, the temperature of the heat treatment can be 200-350℃. Because the preparation method in the early stage of the application is mixing in liquid phase, the uniformity of the distribution of the doping elements is ensured, so that the structure of the solid electrolyte after removing the crystal water is more stable under the same heat treatment temperature.

[0041] In some embodiments, the conditions of the co-precipitation reaction are heating and stirring in a water bath at 60-80℃ for 4-8h; the vacuum drying temperature is 120-200℃, and the drying time is 8-15h; and the heat treatment time is 2-12h.

[0042] Controlling the water bath temperature of the co-precipitation to 60-80℃ and carrying out the reaction for 4-8h can ensure that the elements can be fully mixed and doped, and greatly avoid the situation of particle agglomeration during the doping process, fully ensuring the uniformity of the components.

[0043] Because the application is prepared by using a multi-step liquid phase synthesis method, a large amount of water is used as a solvent, so before the heat treatment, vacuum drying is carried out to remove the water, which can ensure the effect of removing the crystal water in the subsequent heat treatment and the uniformity of the components.

[0044] In some embodiments, the preparation method of the Na3SbS4 powder is: adding Na2S, Sb2S3 and sulfur powder into deionized water, heating and stirring in a water bath at 60-80℃, filtering to obtain a homogeneous precursor aqueous solution of Na3SbS4, then adding an alcohol to carry out a precipitation reaction, the alcohol can be preferably isopropyl alcohol to obtain Na3SbS4 hydrate, vacuum drying, and then heat treatment in an inert atmosphere at 200-350℃ to obtain Na3SbS4 powder.

[0045] In some embodiments, the preparation method of the sodium thiotungstomolybdate powder is: mixing sodium base, thiotungsten salt and thiomolybdenum salt and adding into deionized water, heating and stirring in a water bath at 60-80℃ to obtain a precursor solution, vacuum drying, and then heat treatment in an inert atmosphere at 200-350℃ to obtain sodium thiotungstomolybdate powder, the chemical formula is Na2W x Mo y S4, 0

[0046] In addition, the precursor raw materials Na3SbS4 powder and sodium thio tungsten molybdate powder used in the present application are both prepared by liquid phase synthesis method, which can better control the components and regulate the particle morphology and size of the two precursors, so that the co-precipitation of the two precursors can realize the uniform mixing of metal elements at the atomic level when the sulfide solid electrolyte is prepared by subsequent liquid phase, and the uniformity of the material components is better ensured.

[0047] In addition, because the precursor raw materials used in the present application are Na3SbS4 powder and Na2W x Mo y S4 powder, W and Mo will not be mixed with Sb elements first, which will affect the overall crystal structure of the solid electrolyte. Compared with the way of mixing molybdenum sulfide, tungsten sulfide, antimony sulfide and sodium sulfide as raw materials respectively, the present application can make tungsten and molybdenum better doped into the crystal structure on the basis of Na3SbS4, and the obtained solid electrolyte is more stable, and the air stability is also better.

[0048] In addition, the present application also provides a solid-state sodium battery, which comprises a positive electrode sheet, a negative electrode sheet and a solid-state electrolyte film interposed between the positive electrode sheet and the negative electrode sheet, the solid-state electrolyte film is a solid-state electrolyte film prepared from the above-mentioned sulfide solid electrolyte, and the positive electrode sheet contains or does not contain the above-mentioned sulfide solid electrolyte; the negative electrode sheet contains or does not contain the above-mentioned sulfide solid electrolyte. The preparation method of the solid-state electrolyte film can refer to the existing solid-state electrolyte film preparation method, such as wet preparation or dry preparation, which will not be described here.

[0049] Preferably, the thickness of the solid electrolyte film is 10 μm to 2000 μm, and more preferably in the range of 50 μm to 200 μm. If the solid electrolyte film is too thin, the mechanical strength will be reduced, and it is easy to be damaged. In addition, the occurrence of internal short circuit is also easier.

[0050] The positive electrode sheet specifically comprises a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector. The positive electrode active material in the positive electrode active material layer can be a conventional positive electrode active material for sodium ion battery, such as one or more of layered transition metal sodium oxide, polyanion positive electrode material and prussian positive electrode material. The layered transition metal sodium oxide can be a layered transition metal sodium oxide doped with Li, Mg, Zn, Ca, Al, V, Cr, Mn, Fe, Ti, Zr, Sn, Ru, Nb, Co, Ni and the like, which will not be described in detail here. The positive electrode current collector can be various materials suitable for being used as a positive electrode current collector of a sodium ion battery in the art, for example, the positive electrode current collector can include but is not limited to metal foil and the like, and more specifically can include but is not limited to aluminum foil and the like.

[0051] The positive electrode active material layer also includes commonly used binders, conductive agents, etc., the binder includes but is not limited to at least one of SBR, PAA, PI, PAN, PVDF, and the conductive agent includes but is not limited to at least one or more of carbon black (such as Super-P, KS-6), VGCF, multi-walled CNT, and single-walled CNT, which will not be described in detail here.

[0052] Specifically, the preparation method of the positive electrode sheet can be prepared according to the conventional preparation of the positive electrode sheet, such as the following method: the positive electrode active material, the conductive agent, and the binder are proportionally prepared into a slurry, and then coated, rolled, and die-cut at a certain area density to obtain the positive electrode sheet. In the slurry, the positive electrode active material can account for 70wt%-90wt%, the conductive agent can account for 0.05wt%-5wt%, and the binder can account for 0.5wt%-5wt%. In addition, in order to further increase the ionic conductivity of the full solid-state sodium ion battery, the sulfide solid-state electrolyte of the application can also be added to the positive electrode active material layer, and the content can account for 5wt%-25wt%.

[0053] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode active material in the negative electrode active material layer can be one or more of soft carbon, hard carbon, carbon fiber, mesocarbon microbeads, tin-based material, oxide-type negative electrode material, or other metals capable of forming an alloy with sodium, etc. Among them, the carbon-based negative electrode material can be selected from one or more of soft carbon, hard carbon, carbon fiber, and mesocarbon microbeads; the tin-based material can be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. The negative electrode current collector is usually a structure or part that collects current. The negative electrode current collector can be various materials suitable for use as a sodium ion battery negative electrode current collector in the art, for example, the negative electrode current collector can include but is not limited to a metal foil, and more specifically can include but is not limited to an aluminum foil and a copper foil, etc.

[0054] The commonly used negative electrode active material is hard carbon material, which has a large interlayer spacing and is easy for sodium ions to intercalate and deintercalate. In addition, for the convenience of experimental detection, a sodium sheet can also be directly used as a negative electrode to further assemble a full solid-state sodium ion battery. For other selection and settings in the negative electrode sheet, reference can be made to the conventional negative electrode sheet for sodium ion batteries. For example, the negative electrode active material layer also includes commonly used binders, conductive agents, etc., the proportion of each substance can be 65wt%-95wt% for the negative electrode active material, 0.05wt%-5wt% for the conductive agent, and 0.5wt%-5wt% for the binder. In addition, in order to further increase the ionic conductivity of the full solid-state sodium ion battery, the sulfide solid-state electrolyte of the application can also be added to the negative electrode active material layer, and the content can account for 5wt%-25wt%.

[0055] When the sulfide solid electrolyte of the application is added to both the positive electrode sheet and the negative electrode sheet, and then a solid electrolyte membrane is formed, a full solid sodium ion battery is formed, and the electrochemical performance and air stability of the battery are higher.

[0056] In order to make the technical solutions and advantages of the application clearer, the application and its beneficial effects will be described in further detail below in combination with specific embodiments and the drawings of the specification, but the embodiments of the application are not limited thereto.

[0057] Embodiment 1

[0058] A sulfide solid electrolyte is prepared by a liquid phase synthesis method, and has a chemical formula of Na 2.95 W 0.025 Mo 0.025 Sb 0.95 S4.

[0059] The specific preparation steps of the liquid phase synthesis method are as follows:

[0060] 1) The preparation method of Na3SbS4 powder is as follows: Na2S, Sb2S3 and sulfur powder are added to deionized water according to the stoichiometric ratio (molar ratio of 3:1:2), heated and stirred in a water bath at 70°C for 6h, filtered to remove antimony sulfide and other residual substances, to obtain a homogeneous precursor aqueous solution of Na3SbS4, then isopropanol is added for precipitation reaction to obtain Na3SbS4·9H2O, dried at 160°C under vacuum for 12h, then heat treated at 270°C under Ar atmosphere for 6h to obtain Na3SbS4 powder;

[0061] 2) The preparation method of sodium thiotungstomolybdate powder is as follows: NaOH, (NH4)2WS4 and (NH4)2MoS4 are mixed according to the stoichiometric ratio (molar ratio of 4:1:1), then added to deionized water, heated and stirred in a water bath at 70°C for 6h to obtain a precursor solution, dried at 160°C under vacuum for 12h, then heat treated at 270°C under Ar atmosphere for 6h to obtain Na2W 0.5 Mo 0.5 S4 powder;

[0062] 3) Na3SbS4 powder and Na2W 0.5 Mo 0.5 S4 powder are weighed and mixed according to the stoichiometric ratio (molar ratio of 19:1), then added to deionized water to prepare an aqueous solution, heated and stirred in a water bath at 70°C for 6h for co-precipitation reaction; then dried at 160°C under vacuum for 12h, heat treated at 270°C under Ar atmosphere for 6h to obtain Na 2.95 W 0.025 Mo 0.025 Sb0.95 S4, the sulfur compound solid-state electrolyte of the present application.

[0063] Example 2

[0064] Different from Example 1, the chemical formula of the sulfur compound solid-state electrolyte of the present application is Na 2.95 W 0.01 Mo 0.04 Sb 0.95 S4, the sulfur compound solid-state electrolyte of the present application.

[0065] Example 3

[0066] Different from Example 1, the chemical formula of the sulfur compound solid-state electrolyte of the present application is Na 2.9 W 0.04 Mo 0.06 Sb 0.9 S4, the sulfur compound solid-state electrolyte of the present application.

[0067] Example 4

[0068] Different from Example 1, the chemical formula of the sulfur compound solid-state electrolyte of the present application is Na 2.9 W 0.02 Mo 0.08 Sb 0.9 S4, the sulfur compound solid-state electrolyte of the present application.

[0069] Example 5

[0070] Different from Example 1, the chemical formula of the sulfur compound solid-state electrolyte of the present application is Na 2.9 W 0.06 Mo 0.04 Sb 0.9 S4, the sulfur compound solid-state electrolyte of the present application.

[0071] Example 6

[0072] Different from Example 1, the chemical formula of the sulfur compound solid-state electrolyte of the present application is Na 2.85 W 0.06 Mo 0.09 Sb 0.85 S4, the sulfur compound solid-state electrolyte of the present application.

[0073] Example 7

[0074] Different from example 1, the chemical formula of the sulfide solid electrolyte of the present example is Na 2.85 W 0.03 Mo 0.12 Sb 0.85 S4, the adding amount of each element can be adjusted according to the different molar ratio, which can be referred to example 1, and will not be repeated here.

[0075] Example 8

[0076] Different from example 1, the chemical formula of the sulfide solid electrolyte of the present example is Na 2.85 W 0.005 Mo 0.145 Sb 0.85 S4, the adding amount of each element can be adjusted according to the different molar ratio, which can be referred to example 1, and will not be repeated here.

[0077] Example 9

[0078] Different from example 1, the chemical formula of the sulfide solid electrolyte of the present example is Na 2.85 W 0.09 Mo 0.06 Sb 0.85 S4, the adding amount of each element can be adjusted according to the different molar ratio, which can be referred to example 1, and will not be repeated here.

[0079] Example 10

[0080] Different from example 1, the chemical formula of the sulfide solid electrolyte of the present example is Na 2.7 W 0.15 Mo 0.15 Sb 0.7 S4, the adding amount of each element can be adjusted according to the different molar ratio, which can be referred to example 1, and will not be repeated here.

[0081] Example 11

[0082] Different from example 1, the chemical formula of the sulfide solid electrolyte of the present example is Na 2.7 W 0.1 Mo 0.2 Sb 0.7 S4, the adding amount of each element can be adjusted according to the different molar ratio, which can be referred to example 1, and will not be repeated here.

[0083] Example 12

[0084] Different from example 1, the chemical formula of the sulfide solid electrolyte of the present example is Na 2.7 W 0.2 Mo0.1 Sb 0.7 S4, according to the different adjustment of the content of each element molar ratio can be prepared, see example 1, here no more.

[0085] Example 13

[0086] Unlike example 1, the chemical formula of the sulfide solid electrolyte of the present embodiment is Na 2.6 W 0.05 Mo 0.35 Sb 0.6 S4, according to the different adjustment of the content of each element molar ratio can be prepared, see example 1, here no more.

[0087] Example 14

[0088] Unlike example 1, the chemical formula of the sulfide solid electrolyte of the present embodiment is Na 2.5 W 0.05 Mo 0.45 Sb 0.5 S4, according to the different adjustment of the content of each element molar ratio can be prepared, see example 1, here no more.

[0089] Example 15

[0090] Unlike example 1, the chemical formula of the sulfide solid electrolyte of the present embodiment is Na 2.5 W 0.45 Mo 0.05 Sb 0.5 S4, according to the different adjustment of the content of each element molar ratio can be prepared, see example 1, here no more.

[0091] Comparative example 1

[0092] Unlike example 1, the chemical formula of the sulfide solid electrolyte of the present embodiment is Na3SbS4, that is, no tungsten and molybdenum doped elements, directly through the liquid phase synthesis of Na3SbS4 can be seen in example 1, here no more.

[0093] Comparative example 2

[0094] Unlike example 1, the chemical formula of the sulfide solid electrolyte of the present embodiment is Na 2.9 W 0.1 Sb 0.9 S4, according to the different adjustment of the content of each element molar ratio can be prepared, see example 1, here no more.

[0095] Comparative example 3

[0096] Different from example 1, the chemical formula of the sulfide solid-state electrolyte of the present example is Na 2.9 Mo 0.1 Sb 0.9 S4, the adding amount of each element can be adjusted according to the different molar ratio, which can be referred to example 1, and will not be repeated here.

[0097] Comparative example 4

[0098] Different from example 3, the preparation method of the present comparative example is different. The chemical formula of the sulfide solid-state electrolyte of the present comparative example is Na 2.9 W 0.04 Mo 0.06 Sb 0.9 S4, the preparation method of which is as follows:

[0099] Under the inert gas atmosphere, the raw materials of Na2S, Sb2S3, MoS2, WS2 and sulfur powder are weighed and mixed according to the required components, and then are fully ground in an agate mortar. After grinding, the powder is recovered and heat treated at 270℃ for 6h under Ar gas atmosphere. The Na 2.9 W 0.04 Mo 0.06 Sb 0.9 S4 solid-state electrolyte is obtained.

[0100] Comparative example 5

[0101] Different from example 1, the chemical formula of the sulfide solid-state electrolyte of the present example is Na 2.9 Mn 0.04 Mo 0.06 Sb 0.9 S4, the adding amount of each element can be adjusted according to the different molar ratio, which can be referred to example 1, and will not be repeated here.

[0102] Comparative example 6

[0103] Different from example 1, the chemical formula of the sulfide solid-state electrolyte of the present example is Na 2.9 W 0.04 Mg 0.06 Sb 0.9 S4, the adding amount of each element can be adjusted according to the different molar ratio, which can be referred to example 1, and will not be repeated here.

[0104] The chemical formula of the sulfide solid-state electrolyte obtained from the above examples 1-15 and comparative examples 1-6 is arranged, and the sodium ion conductivity is tested at room temperature of about 25 degrees.

[0105] The sodium ion conductivity was tested using impedance spectroscopy, a symmetrical battery blocking method. The electrolyte sheet was prepared using a Ti rod as the current collector under a pressure of 3 tons, and the ion conductivity of the solid electrolyte was measured using electrochemical impedance spectroscopy (EIS). Data were collected from 3 MHz to 10 Hz using an impedance analyzer (EC-Lab) and an applied AC voltage of 10–25 mV. Measurements were performed at various temperatures, including 25 degrees Celsius. Sodium ion conductivity (σ) was calculated using the following formula: σ (mS / cm) = T / (R×A)

[0106] In the above formula, T is the thickness of the electrolyte sheet (cm), and A is the area of ​​the electrolyte sheet (cm²). 2 R is the resistance (mS) obtained through electrochemical impedance spectroscopy. -1 ).

[0107] The test results are shown in Table 1 below.

[0108] Table 1

[0109] As can be seen from the above test results, the solid electrolyte prepared by the present invention, through dual doping with Mo and W and combined with liquid-phase synthesis, can obtain a solid electrolyte with uniform doping and high particle size uniformity, providing more vacancies for sodium ions and improving the sodium ion conductivity of the solid electrolyte.

[0110] Furthermore, the comparison of Examples 1-15 shows that controlling the proportions of tungsten and molybdenum within the range of 0.01-0.2% avoids the problem of reduced Sb proportion due to excessive doping of both, which could affect the structure of the solid electrolyte and thus ensure the subsequent sodium ion conductivity. Preferably, controlling the sum of tungsten and molybdenum doping amounts between 0.1-0.3% results in a higher ionic conductivity of the solid electrolyte; simultaneously, controlling the molybdenum doping amount to be greater than the tungsten doping amount can further improve the ionic conductivity of the solid electrolyte. This may be because the differences in atomic mass and atomic structure between tungsten and molybdenum cause them to exhibit different supports for the crystal structure of the solid electrolyte during doping, thereby improving the ionic conductivity of the solid electrolyte.

[0111] In addition, the solid electrolytes in Example 3, Comparative Example 1 and Comparative Example 4 were characterized by SEM electron microscopy, XRD and Raman, as shown in Figures 1 to 4.

[0112] As can be seen from the Raman spectrum in Figure 4, at a wavelength of approximately 470 cm⁻¹ -1 and 450cm -1 WS4 appeared at each location2- and MoS4 2- The characteristic peaks of the solid-state electrolyte of the present application are doped with tungsten and molybdenum elements.

[0113] As can be seen from the SEM images of Figures 1 and 2, the solid-state electrolyte particles prepared by the liquid phase synthesis method of the present application are uniform and have less agglomeration, which verifies the reason why the solid-state electrolyte exhibits excellent sodium ion conductivity. The solid-state electrolyte prepared by the conventional solid phase synthesis method has relatively large particles and more agglomeration.

[0114] As can be seen from the XRD image of Figure 3, the intensity of the characteristic peaks of the solid-state electrolyte of the present application is higher than that of Comparative Example 1 and Comparative Example 4. It can be concluded that the solid-state electrolyte obtained by the liquid phase method has higher crystallinity, and there is no unreacted raw material and other by-products, and the purity of the raw material is higher.

[0115] To further verify the advantages of W-Mo double doping in the present application, the stability of the solid-state electrolyte with different components in air was compared. Figure 5 shows the XRD image of the solid-state electrolyte with the components of Comparative Example 1 of the present application after air exposure for 6 hours. As can be seen from the figure, after the W single-doped electrolyte is exposed to air, it is easy to absorb moisture in the air, the crystallinity of the material decreases, and some by-products are generated.

[0116] Figure 6 is the XRD image of the solid-state electrolyte of Example 3 of the present application after air exposure for 6 hours. Compared with the W single-doped electrolyte, the W-Mo double-doped electrolyte material still maintains good crystallinity even after exposure for 6 hours, without obvious crystal change and by-product generation. Through the above comparison, it can be further illustrated that the W-Mo double doping can improve the air stability of the electrolyte material.

[0117] To further verify the advantages of the present application, the Na 2.9 W 0.04 Mo 0.06 Sb 0.9 S4 solid-state electrolyte in Example 3 was taken as an example, and the advantages of the liquid phase synthesis method were further explored by changing the preparation conditions, as shown in the following Comparative Examples 16-29.

[0118] Example 16

[0119] Different from Example 3, the heat treatment condition in the preparation step 3) is heat treatment at 200℃ for 6h in Ar atmosphere, and the rest is described in Example 3, which is not repeated here.

[0120] Example 17

[0121] The difference between Example 3 is that in the preparation step 3), the heat treatment condition is heat treatment at 330℃ for 6h in Ar atmosphere, and the rest is described in Example 3, which is not repeated here.

[0122] Example 18

[0123] The difference between Example 3 is that in the preparation step 3), the heat treatment condition is heat treatment at 450℃ for 6h in Ar atmosphere, and the rest is described in Example 3, which is not repeated here.

[0124] Example 19

[0125] The difference between Example 3 is that in the preparation step 3), the heat treatment condition is heat treatment at 330℃ for 2h in Ar atmosphere, and the rest is described in Example 3, which is not repeated here.

[0126] Example 20

[0127] The difference between Example 3 is that in the preparation step 3), the heat treatment condition is heat treatment at 270℃ for 12h in Ar atmosphere, and the rest is described in Example 3, which is not repeated here.

[0128] Example 21

[0129] The difference between Example 3 is that in the preparation step 3), after the co-precipitation reaction, the heat treatment is carried out after drying at 80℃ under vacuum for 12h, and the rest is described in Example 3, which is not repeated here.

[0130] Example 22

[0131] The difference between Example 3 is that in the preparation step 3), the temperature of water bath heating is 40℃, and the rest is described in Example 3, which is not repeated here.

[0132] Example 23

[0133] The difference between Example 3 is that in the preparation step 2), the temperature of water bath heating during the preparation of sodium thiotungstomolybdate powder is 40℃, and the rest is described in Example 3, which is not repeated here.

[0134] Example 24

[0135] The difference between Example 3 is that in the preparation step 2), the heat treatment condition during the preparation of sodium thiotungstomolybdate powder is heat treatment at 200℃ for 6h in Ar atmosphere, and the rest is described in Example 3, which is not repeated here.

[0136] Example 25

[0137] The difference between Example 3 is that in the preparation step 2), the heat treatment condition during the preparation of sodium thiotungstomolybdate powder is heat treatment at 330℃ for 6h in Ar atmosphere, and the rest is described in Example 3, which is not repeated here.

[0138] Example 26

[0139] Different from Example 3, in the preparation step 2), the sodium thiotungstomolybdate powder is prepared by a solid phase synthesis method, which can be seen in the solid phase synthesis method in Comparative Example 4, and the rest can be seen in Example 3, which will not be repeated here.

[0140] Example 27

[0141] Different from Example 3, in the preparation step 1), the Na3SbS4 powder is prepared by a solid phase synthesis method, which can be seen in the solid phase synthesis method in Comparative Example 4, and the rest can be seen in Example 3, which will not be repeated here.

[0142] Example 28

[0143] Different from Example 3, in the preparation steps 1) and 2), the Na3SbS4 powder and the sodium thiotungstomolybdate powder are both prepared by a solid phase synthesis method, which can be seen in the solid phase synthesis method in Comparative Example 4, and the rest can be seen in Example 3, which will not be repeated here.

[0144] Example 29

[0145] Different from Example 3, in the preparation step 3), after the coprecipitation reaction, the heat treatment is directly performed without the vacuum drying treatment step, and the rest can be seen in Example 3, which will not be repeated here.

[0146] The sulfide solid-state electrolyte obtained in the above Examples 16-29 is tested for sodium ion conductivity at room temperature of about 25 degrees, and the test results are shown in Table 2 below.

[0147] Table 2

[0148] As can be seen from the test results in Table 2, the sodium thiotungstomolybdate powder and the Na3SbS4 powder are both prepared by a liquid phase synthesis method, which is more conducive to improving the sodium ion conductivity of the subsequent solid-state electrolyte, which is mainly because the precursor is also prepared by a liquid phase synthesis method, which can control the components and regulate the morphology and size of the particles, so that the subsequent tungsten and molybdenum doping is more easily uniformly mixed at the atomic level.

[0149] As can be seen from the above, the sulfide solid-state electrolyte provided by the present application effectively improves the problems of poor air stability and ion conductivity that cannot meet the requirements of wide application of conventional sulfide solid-state electrolytes, and can achieve a higher sodium ion conductivity under optimization and regulation.

[0150] Those skilled in the art can make various modifications and variations to the above embodiments based on the disclosure and teachings of this specification. Therefore, the present application should not be limited to the above specific embodiments, and any obvious modifications, replacements or variations made by those skilled in the art based on the present application shall fall within the scope of the present application. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation on the present application.

Claims

1. A sulfide solid-state electrolyte, characterized by, It is made by liquid phase synthesis, and its chemical formula is Na 3-a-b W a Mo b Sb 1-a-b S4, 0 < a < 0.5, 0 < b < 0.

5.

2. The sulfide solid-state electrolyte according to claim 1, characterized by, 0.01≤a≤0.25, 0.01≤b≤0.

25.

3. The sulfide solid-state electrolyte according to claim 2, characterized by, 0.01 4. The sulfide solid-state electrolyte according to claim 3, characterized by, 0.1≤a+b≤0.3, and 0≤b-a≤0.

1.

5. The sulfide solid-state electrolyte according to any one of claims 1 to 4, characterized by, The sodium ion conductivity is greater than or equal to 3.0 mS / cm at room temperature of 25℃.

6. The sulfide solid-state electrolyte of claim 1, wherein, The liquid phase synthesis method is prepared by mixing Na3SbS4 powder and sodium thiotungstate-molybdate powder, configuring into an aqueous solution and stirring to carry out a coprecipitation reaction; then dried under vacuum, and heat treated at 200-450°C in an inert atmosphere to obtain Na 3-a-b W a Mo b Sb 1-a-b S4 sulfide solid-state electrolyte.

7. The sulfide solid-state electrolyte according to claim 6, characterized in that, The co-precipitation reaction is performed by heating and stirring in a water bath at 60-80℃ for 4-8h; the vacuum drying temperature is 120-200℃, and the drying time is 8-15h; the heat treatment time is 2-12h.

8. The sulfide solid-state electrolyte of claim 6, wherein, The Na3SbS4 powder is prepared by adding Na2S, Sb2S3 and sulfur powder into deionized water, heating and stirring in a water bath at 60-80℃, filtering to obtain a homogeneous precursor aqueous solution of Na3SbS4, then adding alcohol to perform a precipitation reaction to obtain Na3SbS4 hydrate, vacuum drying, and then heat treatment in an inert atmosphere at 200-350℃ to obtain Na3SbS4 powder.

9. The sulfide solid-state electrolyte of claim 6, wherein, The preparation method of the sodium thiotungstomolybdate powder comprises the following steps: mixing sodium base, thiotungsten salt and thiomolybdenum salt into deionized water, heating and stirring in a water bath at 60-80°C to obtain a precursor solution, vacuum drying, and then heat treating at 200-350°C in an inert atmosphere to obtain the sodium thiotungstomolybdate powder with the chemical formula Na2W x Mo y S4, 0 < x ≤ 1.0, 0 < y ≤ 1.0, and x + y = 1.

10. A full solid-state sodium-ion battery comprising a positive electrode sheet, a negative electrode sheet, and a solid-state electrolyte film interposed between the positive electrode sheet and the negative electrode sheet, characterized by, The solid-state electrolyte film is a solid-state electrolyte film prepared from the sulfide solid-state electrolyte according to any one of claims 1-9; the positive electrode sheet contains or does not contain the sulfide solid-state electrolyte according to any one of claims 1-9; and the negative electrode sheet contains or does not contain the sulfide solid-state electrolyte according to any one of claims 1-9.

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