A method for preparing doped high ionic conductivity silver sulfide-germanium sulfide solid electrolytes in liquid phase

Abstract

This invention belongs to the technical field of solid electrolytes and discloses a method for preparing a liquid-phase doped silver-germanium sulfide solid electrolyte with high ionic conductivity. The method includes: 1) dispersing lithium sulfide and phosphorus pentasulfide in an organic solvent, heating and stirring to obtain a precursor solution containing Li3PS4; 2) mixing lithium iodide, sulfur powder, and additives with the precursor solution, heating and stirring to remove the organic solvent, and obtaining a powder; 3) sintering the powder under a protective atmosphere to obtain a silver-germanium sulfide solid electrolyte; the additives are one or more of SiS2, GeS2, SnS2, As2S3, and Sb2S3. This invention is simple, and the prepared silver-germanium sulfide electrolyte undergoes elemental doping during thermal crystallization, improving the electrolyte's ionic conductivity and air stability. This method is suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of solid-state battery solid electrolyte material technology, specifically relating to a method for preparing a liquid-phase doped high-ionic-conductivity silver-germanium sulfide solid electrolyte. Background Technology

[0002] Lithium-ion batteries are widely used in most portable electronic devices due to their high energy density and long cycle life. However, traditional lithium-ion batteries pose significant safety risks due to the use of volatile and flammable liquid electrolytes, which limits their further development. All-solid-state batteries, using solid electrolytes with excellent thermal stability and good mechanical properties, can effectively solve battery safety issues. Among various solid electrolytes, sulfide solid electrolytes possess ionic conductivity comparable to liquid electrolytes and are therefore considered a promising candidate.

[0003] Sulfur-germanium sulfide solid electrolytes (Li6PS5X, X = Cl, Br, I) are characterized by their high ionic conductivity (~10). -3 S cm -1 The good phase-forming properties of I-based sulfide solid electrolytes have been extensively studied. Although I-based sulfide solid electrolytes of the silver-germanium sulfide type have good phase-forming properties, they have been extensively studied. - / S 2- The high degree of order in lithium leads to a decrease in ionic conductivity. However, the LiI in the SEI layer formed at the interface between the I-based sulfide solid electrolyte and lithium metal plays a positive role in preventing side reactions and lithium dendrite formation. Therefore, researchers have improved the ionic conductivity by doping with soft acid metal ions with larger atomic radii. - / S 2- The disorder of the electrolyte enhances its ionic conductivity. Furthermore, based on the hard and soft acid-base theory, the binding between soft acid metals and S is stronger, thus improving the electrolyte's air stability. For example, as reported in the literature (Adv. Energy Mater. 2020, 10, 1903422), doping Li6PS5I with Sn reduced the original LPSI's room-temperature ionic conductivity to only 2.8 × 10⁻⁶. -6 S cm -1 The ionic conductivity of the doped LPSI-20Sn reaches 3.5 × 10⁻⁶. -4 Scm -1This represents an improvement of two orders of magnitude. However, currently, the only method for preparing doped I-based silver-germanium sulfide solid electrolytes, as described above, is mechanical ball milling, which often requires a ball milling phase formation process exceeding 24 hours, making it time-consuming and uneconomical. Patent CN 106684432 B describes a mechanical ball milling method for preparing Mn-doped high-ionic-conductivity sulfide solid electrolytes, but this method requires 40-60 hours of long-term ball milling. Similarly, patent CN110137565B describes a method for industrial-scale preparation involving continuous grinding, large feed volumes, and significant differences between the locally mixed material ratios and the original stoichiometric ratios, potentially resulting in a product composition that is not the designed ratio. A method was developed to pre-sinter, crush, and screen the raw materials before grinding, which can produce high-precision sulfide solid electrolytes; however, this pretreatment method significantly increases time and cost. Summary of the Invention

[0004] The technical problem this invention aims to solve is that the doping modification of argillium germanium sulfide solid electrolytes currently only involves mechanical ball milling, which is cumbersome, time-consuming, and not suitable for large-scale production. This invention provides a method for preparing doped argillium germanium sulfide solid electrolytes with high ionic conductivity in the liquid phase.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing a liquid-phase doped solid electrolyte with high ionic conductivity silver sulfide-germanium sulfide includes the following steps:

[0007] 1) Lithium sulfide and phosphorus pentasulfide are dispersed in an organic solvent and heated and stirred to react, thereby obtaining a precursor solution containing Li3PS4;

[0008] 2) Mix lithium iodide, sulfur powder and additives with a precursor solution containing Li3PS4, heat and stir to react, remove organic solvent, and obtain powder;

[0009] 3) The powder is sintered under a protective atmosphere to obtain a sulfide solid electrolyte of silver-germanium ore type.

[0010] The mass ratio of lithium sulfide to phosphorus pentasulfide in step 1) is (220-240):(210-230).

[0011] The organic solvent is one or more of tetrahydrofuran, acetonitrile, ethyl acetate, and methyl ethyl ketone, preferably acetonitrile.

[0012] The amount of organic solvent used in step 1) is 200% to 1200% of the total mass of lithium sulfide and phosphorus pentasulfide powder, preferably 400% to 1000%.

[0013] The heating and stirring temperature in step 1) is 40–60°C, and the heating and stirring time is 1–72 h, preferably 8–48 h, and more preferably 8–24 h. The stirring speed is 300–1200 rpm, preferably 500–1000 rpm.

[0014] The dispersion described in step 1) is ultrasonic dispersion. The ultrasonic power is 10W to 50W, the frequency is 50Hz, and the ultrasonic dispersion time is 10 to 30 minutes.

[0015] The additive mentioned in step 2) is one or more of SiS2, GeS2, SnS2, As2S3, and Sb2S3.

[0016] The amount of additives used in step 2) is 1% to 40% of the total mass of lithium sulfide and phosphorus pentasulfide powder in step 1), the amount of lithium iodide used in step 2) is 20% to 200% of the total mass of lithium sulfide and phosphorus pentasulfide in step 1), and the amount of sulfur powder used is 1% to 7% of the total mass of lithium sulfide and phosphorus pentasulfide in step 1).

[0017] The heating and stirring temperature in step 2) is 40–60°C, and the heating and stirring time is 1–72 h, preferably 8–48 h, and more preferably 8–24 h. The stirring speed is 300–1200 rpm, preferably 500–1000 rpm.

[0018] The sintering temperature in step 3) is 400-500℃, the sintering time is 0.5-8 hours, and the heating / cooling rate is 1-3℃ / min.

[0019] Preferably, the sintering time in step 3) is 1 to 3 hours.

[0020] The removal of organic solvents mentioned in step 3) refers to heating and evaporating to dryness at a temperature of 60–80°C.

[0021] The protective atmosphere is an inert atmosphere.

[0022] After sintering, cool to room temperature.

[0023] To further ensure good internal and external contact between the sulfide solid electrolyte particles prepared by the above preparation method, the molding method is also very important. Cold pressing can effectively promote the filling of the gaps between crystalline particles by the amorphous part of the electrolyte.

[0024] The method for forming the sulfide solid electrolyte of silver-germanium sulfide type described in step 3) includes the following steps:

[0025] The sheet is formed by cold pressing: the pressure is controlled at 100-700 MPa, the cold pressing time is controlled at 5 min-30 min, and the thickness of the electrolytic sheet is controlled at 10-600 μm.

[0026] A doped silver-germanium sulfide solid electrolyte with high ionic conductivity, prepared by a liquid-phase method, is obtained using the above-mentioned preparation method.

[0027] The solid electrolyte prepared by this invention is used in lithium batteries in the form of a sheet.

[0028] The basic principle of this invention:

[0029] The method for preparing doped high ionic conductivity silver-germanium sulfide solid electrolyte by liquid phase according to the present invention first generates a complex of Li3PS4 and organic solvent in liquid phase, then adds the required proportion of additives to the solution after the first reaction to further obtain the precursor of silver-germanium sulfide electrolyte, and then further converts the precursor into silver-germanium sulfide solid electrolyte by heating and crystallizing.

[0030] The present invention has the following significant advantages:

[0031] (1) The present invention achieves the preparation of doped silver-germanium sulfide solid electrolyte through liquid phase, without the need for time-consuming mechanical ball milling process, only a simple liquid phase reaction is needed to generate Li3PS4, and then additives are introduced in proportion, and the silver-germanium sulfide solid electrolyte can be obtained after thermal crystallization.

[0032] (2) The sulfide solid electrolyte particles prepared by the present invention are small, have good mechanical properties, and are easy to compress into tablets.

[0033] (3) Due to the presence of Li3PS4 as a precursor, beneficial elements can be added during the second-step thermal crystallization process to improve the ionic conductivity and air stability of the prepared silver-germanium sulfide solid electrolyte. Attached Figure Description

[0034] Figure 1 The Li6P sulfide solid electrolyte prepared in Example 1 is a sulfide-germanium sulfide-type electrolyte. 0.5 Sb 0.5 X-ray diffraction pattern of S5I; ICSD represents the standard XRD curve of silver sulfide-type solid electrolyte; 80℃ represents the XRD result of the powder after the solvent was evaporated at 80℃; 450℃ represents the Li6P after sintering at 450℃. 0.5 Sb 0.5 XRD results of S5I;

[0035] Figure 2The Li6P sulfide solid electrolyte prepared in Example 1 is a sulfide-germanium sulfide-type electrolyte. 0.5 Sb 0.5 Scanning electron microscope image of S5I;

[0036] Figure 3 The Li6P sulfide solid electrolyte prepared in Example 1 is a sulfide-germanium sulfide-type electrolyte. 0.5 Sb 0.5 Electrochemical impedance spectroscopy results of S5I;

[0037] Figure 4 The X-ray diffraction pattern is shown for the electrolyte prepared in Comparative Example 2, with 450℃ corresponding to the electrolyte prepared at that temperature. Detailed Implementation

[0038] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the implementation and protection scope of the present invention are not limited thereto.

[0039] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the pharmaceutical raw materials and reagents used in the following examples are commercially available products.

[0040] Example 1

[0041] This embodiment utilizes a liquid phase to prepare a doped silver-germanium sulfide-type solid electrolyte with high ionic conductivity. The preparation method includes the following steps:

[0042] 1) In a glove box, weigh 2.3g of lithium sulfide and 2.2g of phosphorus pentasulfide. Add the two chemicals to 45g of anhydrous acetonitrile and sonicate at 50W power and 50Hz frequency for 20 minutes. Then stir the sonicated solution at 50℃ for 12 hours. The solution color changes from light yellow to light blue.

[0043] 2) In a glove box, weigh 2.7g of lithium iodide, 1.7g of antimony sulfide, and 0.3g of sublimed sulfur and add them to the light blue solution after the reaction in step 1). Continue stirring the reaction at 50°C for 12 hours to obtain the solution after the reaction.

[0044] 3) Transfer the reacted solution to an open container, dry it at 80°C to remove acetonitrile, and then sinter the resulting powder at 450°C for 2 hours at a heating rate of 2°C / min. Cool it to room temperature (cooling rate of 2°C / min) to obtain crystalline silver-germanium sulfide solid electrolyte Li6P. 0.5 Sb 0.5 S5I.

[0045] Figure 1 Li6P prepared in Example 1 0.5 Sb 0.5The X-ray diffraction pattern of the S5I electrolyte shows that the prepared electrolyte exhibits characteristic peaks of argillium sulfide-type electrolytes. ICSD represents the standard XRD curve of the argillium sulfide-type solid electrolyte, 80℃ represents the XRD result of the powder after the solvent was evaporated at 80℃, and 450℃ represents the Li6P sintered at 450℃. 0.5 Sb 0.5 XRD results of S5I.

[0046] Figure 2 Li6P prepared in Example 1 0.5 Sb 0.5 Scanning electron microscope image of S5I electrolyte, showing the prepared Li6P 0.5 Sb 0.5 S5I electrolyte has a fine, sheet-like stacked structure.

[0047] Figure 3 The Li6P sulfide solid electrolyte prepared in Example 1 is a sulfide-germanium sulfide-type electrolyte. 0.5 Sb 0.5 The electrochemical impedance spectroscopy results of S5I show that the Li6P prepared in Example 1... 0.5 Sb 0.5 The impedance of the symmetrical cell assembled with S5I electrolyte is 100.3Ω, and the calculated ionic conductivity is 6.24 × 10⁻⁶. -5 S cm -1 .

[0048] Example 2

[0049] This embodiment utilizes a liquid phase to prepare a doped silver-germanium sulfide-type solid electrolyte with high ionic conductivity. The preparation method includes the following steps:

[0050] 1) In a glove box, weigh 2.3g of lithium sulfide and 2.2g of phosphorus pentasulfide. Add the two chemicals to 45g of anhydrous acetonitrile and sonicate at 50W power and 50Hz frequency for 20 minutes. Then stir the sonicated solution at 50℃ for 12 hours. The solution color changes from light yellow to light blue.

[0051] 2) In a glove box, weigh 2.7g of lithium iodide, 1.3g of arsenic sulfide, and 0.3g of sublimed sulfur and add them to the light blue solution after the reaction in step 1). Continue stirring the reaction at 50°C for 12 hours to obtain the solution after the reaction.

[0052] 3) The reacted solution was transferred to a petri dish, dried at 80°C to remove acetonitrile, and the resulting powder was sintered at 450°C for 2 hours with a heating / cooling rate of 2°C / min to obtain crystalline As-doped silver-germanium sulfide solid electrolyte. The ionic conductivity was measured to be 8.53 × 10⁻⁶ using the above method. -5 S cm -1 .

[0053] Example 3

[0054] This embodiment utilizes a liquid phase to prepare a doped silver-germanium sulfide-type solid electrolyte with high ionic conductivity. The preparation method includes the following steps:

[0055] 1) In a glove box, weigh 2.3g of lithium sulfide and 2.2g of phosphorus pentasulfide. Add the two chemicals to 45g of anhydrous acetonitrile and sonicate at 50W power and 50Hz frequency for 20 minutes. Then stir the sonicated solution at 50℃ for 12 hours. The solution color changes from light yellow to light blue.

[0056] 2) In a glove box, weigh 2.7g of lithium iodide, 1.0g of antimony sulfide, and 0.2g of sublimed sulfur and add them to the light blue solution after the reaction in step 1). Continue stirring the reaction at 50°C for 12 hours to obtain the solution after the reaction.

[0057] 3) The reacted solution was transferred to a petri dish, dried at 80℃ to remove acetonitrile, and the resulting powder was sintered at 450℃ for 2 hours with a heating / cooling rate of 2℃ / min to obtain crystalline Sb-doped silver-germanium sulfide solid electrolyte. The ionic conductivity was measured to be 5.24 × 10⁻⁶. -5 S cm -1 .

[0058] Comparative Example 1

[0059] This embodiment utilizes a liquid-phase method to prepare a sulfide solid electrolyte of silver-germanium sulfide type, and the preparation method includes the following steps:

[0060] 1) In a glove box, weigh 2.3g of lithium sulfide and 2.2g of phosphorus pentasulfide. Add the two chemicals to 45g of anhydrous acetonitrile and sonicate at 50W power and 50Hz frequency for 20 minutes. Then stir the sonicated solution at 50℃ for 12 hours. The solution color changes from light yellow to light blue.

[0061] 2) In a glove box, weigh 2.66g of LiI and add it to the light blue solution after the reaction in step 1). Continue stirring the reaction at 50℃ for 12 hours to obtain the solution after the reaction.

[0062] 3) The solution after reaction was transferred to a petri dish, dried at 80°C to remove acetonitrile, and the resulting powder was sintered at 450°C for 2 hours with a heating / cooling rate of 2°C / min to obtain crystalline silver-germanium sulfide solid electrolyte Li6PS5I.

[0063] The Li6PS5I electrolyte prepared by the above method was assembled into a symmetric cell using the same process described above, and the ionic conductivity was measured to be 1.94 × 10⁻⁶. -6 S cm -1 This further proves that the liquid-phase doping method described above can improve the ionic conductivity of the prepared silver-germanium sulfide solid electrolyte.

[0064] Comparative Example 2

[0065] This embodiment utilizes a liquid-phase method to prepare a doped silver-germanium sulfide solid electrolyte, the preparation method of which includes the following steps:

[0066] 1) In a glove box, weigh 2.3g lithium sulfide, 2.2g phosphorus pentasulfide, 2.7g lithium iodide, 0.7g cadmium sulfide, and 0.3g sublimed sulfur. Add the five chemicals to 45g anhydrous acetonitrile and sonicate at 50W power and 50Hz frequency for 20 minutes. Then, stir the sonicated solution at 50℃ for 24 hours.

[0067] 2) Transfer the reaction solution to a petri dish, dry it at 80°C to remove acetonitrile, and then sinter the resulting powder at 450°C for 2 hours with a heating / cooling rate of 2°C / min.

[0068] Figure 4 The X-ray diffraction pattern of the powder prepared in Comparative Example 2 shows that the peak intensity of the silver sulfide-germanium sulfide electrolyte is weak and there are obvious impurity peaks of cadmium sulfide, indicating that the doping was unsuccessful. This comparative example illustrates the importance of the first step of the method of the present invention in preparing the Li3PS4 precursor.

[0069] Table 1 summarizes the doping results of the embodiments listed in this invention.

[0070] Table 1. Doping results of Examples 1-3 and Comparative Example 2.

[0071] Example Example 1 Example 2 Example 3 Comparative Example 2 Doping results success success success fail

[0072] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a liquid-phase doped solid electrolyte of high ionic conductivity silver-germanium sulfide type, characterized in that: Includes the following steps: 1) Lithium sulfide and phosphorus pentasulfide are dispersed in an organic solvent and reacted by heating and stirring to obtain a precursor solution containing Li3PS4; the dispersion in step 1) is ultrasonic dispersion; 2) Mix lithium iodide, sulfur powder and additives with a precursor solution containing Li3PS4, heat and stir to react, remove organic solvent, and obtain powder; 3) The powder is sintered under a protective atmosphere to obtain a sulfide solid electrolyte of silver-germanium ore type; Step 2) The additive is one or more of SiS2, GeS2, SnS2, As2S3, and Sb2S3; The mass ratio of lithium sulfide to phosphorus pentasulfide in step 1) is (220~240):(210~230). The organic solvent is one or more of tetrahydrofuran, acetonitrile, ethyl acetate, and methyl ethyl ketone; The amount of organic solvent used in step 1) is 400% to 1000% of the total mass of lithium sulfide and phosphorus pentasulfide powder; The amount of additives used in step 2) is 1% to 40% of the total mass of lithium sulfide and phosphorus pentasulfide powder in step 1), the amount of lithium iodide used in step 2) is 20% to 200% of the total mass of lithium sulfide and phosphorus pentasulfide in step 1), and the amount of sulfur powder used is 1% to 7% of the total mass of lithium sulfide and phosphorus pentasulfide in step 1). The heating and stirring temperature in step 1) is 40~60℃, and the heating and stirring time is 8~48h; The heating and stirring temperature in step 2) is 40~60℃, and the heating and stirring time is 8~48h; Step 3) The sintering temperature is 400~500℃, the sintering time is 1~3 hours, and the sintering heating rate is 1~3℃ / min; After sintering, cool to room temperature; the cooling rate is 1~3℃ / min.

2. The method for preparing a liquid-phase doped high-ionic-conductivity silver-germanium sulfide solid electrolyte according to claim 1, characterized in that: The organic solvent is acetonitrile.

3. The method for preparing a liquid-phase doped high-ionic-conductivity silver-germanium sulfide solid electrolyte according to claim 1, characterized in that: The stirring speed in step 1) is 300~1200 rpm; the stirring speed in step 2) is 300~1200 rpm.

4. The method for preparing a liquid-phase doped high-ionic-conductivity silver-germanium sulfide solid electrolyte according to claim 1, characterized in that: After cooling to room temperature, it will be shaped. The forming process involves cold pressing to form sheets, wherein the pressure is controlled at 100~700MPa, the cold pressing time is 5min~30min, and the thickness of the electrolytic sheet is controlled at 10~600μm.

5. A doped high ionic conductivity silver-germanium sulfide solid electrolyte prepared by the method described in any one of claims 1 to 4.

6. The application of the doped high ionic conductivity silver-germanium sulfide solid electrolyte according to claim 5, characterized in that: The doped high-ionic-conductivity silver-germanium sulfide solid electrolyte is used in lithium batteries.

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