Preparation method and application of lithium sulfide material containing lithium polysulfide

Abstract

The invention relates to a preparation method and application of a lithium sulfide material containing lithium polysulfide. The preparation method comprises the following steps: weighing lithium hydride and powdered sulfur according to a molar ratio of 2: (1.01-1.10), dividing the lithium hydride into 2-4 parts, taking one part of lithium hydride and powdered sulfur, mixing and ball-milling, sequentially adding the rest lithium hydride, and ball-milling to obtain mixture powder containing lithium sulfide and lithium polysulfide, namely the lithium sulfide material containing lithium polysulfide. Sulfur loss caused by phosphorus pentasulfide decomposition and sulfur element volatilization in the sulfide solid electrolyte preparation and sintering process is supplemented through lithium polysulfide, and the purity and the room-temperature ionic conductivity of the sulfide solid electrolyte are improved.

Description

Technical Field

[0001] This invention belongs to the field of solid-state batteries, specifically relating to a method for preparing lithium sulfide materials containing lithium polysulfides and their applications. Background Technology

[0002] Traditionally, lithium sulfide, phosphorus pentasulfide, and lithium halides are used to prepare electrolytes. However, due to the decomposition of phosphorus pentasulfide and the volatilization of sulfur during calcination, obtaining electrolyte materials with higher ionic conductivity often requires the addition of an external sulfur source to suppress sulfur volatilization. Commonly used external sulfur sources include elemental sulfur and hydrogen sulfide. However, elemental sulfur has poor practical performance due to its molten state during calcination, and hydrogen sulfide gas is difficult to store and transport. In large-scale preparation, it cannot effectively participate in the reaction to replenish the lost sulfur in the electrolyte and is prone to component segregation, affecting batch stability. Therefore, to obtain sulfide solid electrolytes with more stable quality in large-scale preparation, it is crucial to obtain a uniform sulfur source to compensate for the sulfur loss during the sintering process of sulfide solid electrolytes.

[0003] Lithium polysulfides decompose gradually at temperatures ranging from 200 to 400°C. Short-chain Li₂S₂ / Li₂S₃ decomposes at higher temperatures, exceeding 300°C, while long-chain Li₂S₆ / Li₂S₈ decomposes at lower temperatures, beginning around 200°C, producing lithium sulfide and sulfur vapor. Replacing some lithium sulfide with polysulfides can compensate for sulfur loss during the solid-state sintering process of sulfide solid electrolytes, promote reactions between the electrolyte's raw materials, and stabilize the electrolyte's crystal structure.

[0004] This invention proposes a method for preparing lithium sulfide materials containing lithium polysulfides. By supplementing the sulfur loss caused by the decomposition of phosphorus pentasulfide and the volatilization of sulfur during the preparation and sintering process of sulfide solid electrolytes with lithium polysulfides, the purity and room temperature ionic conductivity of sulfide solid electrolytes are improved. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art by providing a method for preparing lithium sulfide materials and their applications. Currently, there are no pure lithium polysulfide materials; lithium polysulfides generally appear as byproducts of lithium sulfide, and their composition is not fixed, with no effective means for separation. This invention prepares a mixture powder containing lithium sulfide and lithium polysulfides, wherein the lithium polysulfides are mainly Li2S2 and Li2S3.

[0006] The objective of this invention can be achieved through the following methods:

[0007] This invention provides a method for preparing lithium sulfide materials containing lithium polysulfides, comprising the following steps:

[0008] Weigh lithium hydride and sulfur powder at a molar ratio of 2:1.01 to 1.10. Divide the lithium hydride into 2 to 4 parts. Take one part of lithium hydride and mix it with sulfur powder and ball mill it. Add the remaining lithium hydride in sequence and ball mill it to obtain a mixture powder containing lithium sulfide and lithium polysulfide, which is lithium sulfide material containing lithium polysulfide.

[0009] As one embodiment of the present invention, the molar ratio of lithium hydride to sulfur powder is preferably 2:1.04 to 1.10.

[0010] In one embodiment of the present invention, the ball milling speed after each addition of lithium hydride is 400-600 rpm / min, and the ball milling time is 2-5 hours. The ball milling is carried out in a vacuum ball milling jar equipped with an exhaust valve.

[0011] In one embodiment of the present invention, lithium hydride is divided into 2 to 4 parts, with the mass percentage difference between each part not exceeding 10%. For example, it can be divided into two parts, one accounting for 45% and the other for 55%; or into three parts, one accounting for 30%, one for 30%, and one for 40%. Preferably, it is divided into 2 to 4 parts with equal mass ratios. Adding the lithium source in batches allows for excess sulfur in the early stage of the reaction, generating as much lithium polysulfide as possible. Subsequent replenishment of the lithium source to the target value allows for preferential decomposition of long-chain lithium polysulfides, retaining as much of the more stable short-chain Li2S2 / Li2S3 as possible. Adding it all at once will also result in the presence of lithium polysulfides, but the content will be lower, and the improvement in effect will not be significant.

[0012] In one embodiment of the present invention, the addition of lithium hydride is carried out in a dry, inert environment.

[0013] This invention involves mixing one part of lithium hydride with all the sulfur powder and then adding the mixture to a vacuum ball mill jar equipped with an exhaust valve for ball milling, causing the two to react and generate lithium polysulfides. After ball milling, the remaining lithium hydride is added to the ball mill jar in the original batches for ball milling to ensure complete reaction.

[0014] In the obtained lithium sulfide material containing lithium polysulfides, the molar ratio of Li to S is 2:1.01 to 1.10.

[0015] This invention provides an application of the lithium sulfide material containing lithium polysulfides in the preparation of sulfide solid electrolytes.

[0016] This invention provides a method for preparing a sulfide solid electrolyte, comprising the following steps:

[0017] Lithium sulfide material containing lithium polysulfides, phosphorus pentasulfide, and lithium chloride are mixed and ball-milled. The milled product is then taken out, pressed into tablets, and sintered to obtain a sulfide solid electrolyte.

[0018] In one embodiment of the present invention, the ball mill rotation speed is 400-600 rpm / min and the time is 2-5 h.

[0019] As one embodiment of the present invention, the sintering temperature is 450-550°C and the time is 2-4 hours.

[0020] As one embodiment of the present invention, the obtained sulfide solid electrolyte powder is a silver-germanium sulfide type sulfide solid electrolyte, such as Li 5.5 PS 4.5 Cl 1.5 Based on the molar ratio of Li to S in the obtained lithium sulfide material containing lithium polysulfides, it was weighed and prepared with phosphorus pentasulfide and lithium chloride according to the proportions of a sulfide solid electrolyte of silver-germanium sulfide type.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) Sulfur loss occurs during the solid-phase sintering process of sulfide solid electrolytes. Replenishing this sulfur using an external sulfur source is ineffective, especially during large-scale production. The external sulfur source cannot effectively participate in the reaction to replenish the lost sulfur, and it easily causes component segregation, affecting batch stability. The lithium sulfide material preparation method of this invention can prepare lithium sulfide materials containing lithium polysulfides. Using this lithium sulfide material to prepare sulfide solid electrolytes can alleviate sulfur loss during the high-temperature solid-phase sintering process of the electrolyte.

[0023] (2) The process of releasing elemental sulfur through the heating and decomposition of lithium polysulfide replenishes the loss of elemental sulfur in situ during the solid-phase sintering reaction of the electrolyte, preventing elemental segregation during the electrolyte sintering process, while retaining some lithium polysulfide to directly enter the electrolyte crystal through the solid-phase reaction to improve the electrolyte performance.

[0024] (3) Improve the batch consistency of materials in the large-scale preparation of sulfide solid electrolytes, effectively prevent component segregation during electrolyte sintering, and improve electrolyte purity and ionic conductivity. Attached Figure Description

[0025] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0026] Figure 1 The XRD pattern of lithium sulfide prepared in Example 1;

[0027] Figure 2 Characterization of the lithium sulfide Raman test data prepared in Example 1 and Comparative Example 1;

[0028] Figure 3 The XRD pattern of lithium sulfide prepared in Comparative Example 1 is shown. Detailed Implementation

[0029] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following examples are implemented under the premise of the technical solution of the present invention, providing detailed implementation methods and specific operating procedures, which will help those skilled in the art to further understand the present invention. It should be noted that the scope of protection of the present invention is not limited to the following embodiments; any adjustments and improvements made under the concept of the present invention are all within the scope of protection of the present invention.

[0030] Example 1

[0031] This embodiment prepares a lithium sulfide material, and the specific steps are as follows:

[0032] 1) Weigh 5g (0.625mol) of lithium hydride and 31.2g (0.975mol) of sulfur powder, mix them, and add them to a ball mill jar with an exhaust valve. Then, ball mill at 500rpm / min for 3h.

[0033] 2) After ball milling, open the lid in a dry, inert environment and add another 5g (0.625mol) of lithium hydride. Ball mill at 500rpm / min for 3h, then add another 5g (0.625mol) of lithium hydride and ball mill at 500rpm / min for 3h (the total amount of lithium hydride to sulfur powder molar ratio is 2:1.04, and the lithium hydride is added in three equal portions).

[0034] 3) The above ball-milled product was sieved to obtain 42.3 g of a mixture powder containing lithium sulfide and lithium polysulfide (XRD pattern as shown). Figure 1 As shown, the Raman test data characterization is as follows: Figure 2 (as shown);

[0035] 4) Weigh 27.57g of the above mixture powder, 33.34g of phosphorus pentasulfide, and 19.07g of lithium chloride, mix them evenly, and place them in a sealed ball mill jar. Ball mill at 500rpm / min for 3h.

[0036] 5) After the ball milling product is taken out and pressed into tablets (pressure of 300MPa), it is sintered, kept at 480℃ for 2h and then cooled to room temperature. The sintered product is taken out and crushed to obtain sulfide solid electrolyte powder of silver-germanium sulfide type.

[0037] Example 2

[0038] The operation in this embodiment is the same as in embodiment 1, except that the total amount of lithium hydride to the molar ratio of sulfur powder is 2:1.01.

[0039] Example 3

[0040] The operation in this embodiment is the same as in embodiment 1, except that the total amount of lithium hydride to the molar ratio of sulfur powder is 2:1.1.

[0041] Comparative Example 1

[0042] 1) Weigh 15g of lithium hydride and 31.2g of sulfur powder (the total amount of lithium hydride to the molar ratio of sulfur powder is 2:1.04, mix them and add them to a ball mill jar with an exhaust valve. Ball mill at 500rpm / min for 3h.

[0043] 2) The above ball-milled product was sieved to obtain 39.2 g of lithium sulfide powder (XRD pattern as shown). Figure 3 As shown, the Raman test data characterization is as follows: Figure 2 (as shown);

[0044] 3) Weigh 27.57g of the above lithium sulfide, 33.34g of phosphorus pentasulfide and 19.07g of lithium chloride, mix them evenly and place them in a sealed ball mill jar, and ball mill at 500rpm / min for 3h.

[0045] 4) The ball-milled product was taken out, pressed into tablets, and sintered. After being kept at 480°C for 2 hours, it was cooled to room temperature. The sintered product was then taken out and crushed to obtain sulfide solid electrolyte powder of silver-germanium sulfide type.

[0046] Comparative Example 2

[0047] The operation of this comparative example is the same as in Example 1, except that the molar ratio of total lithium hydride to sulfur powder is 2:1.15. An excessively high sulfur powder ratio will result in an excessively high content of long-chain lithium polysulfides, with only a small improvement in performance. Further increasing this ratio will lead to residual sulfur in the electrolyte, exacerbating damage to the electrolyte preparation equipment.

[0048] Comparative Example 3

[0049] The operation of this comparative example is the same as that of Example 1, except that: 27.57g of a mixture of lithium hydride and sulfur powder (molar ratio of lithium hydride to sulfur powder is 2:1.03), 33.34g of phosphorus pentasulfide, and 19.07g of lithium chloride were directly mixed and ball-milled to prepare a sulfide solid electrolyte. Direct mixing in this comparative example cannot yield a pure electrolyte phase, and the reaction of lithium hydride produces hydrogen gas, making the direct mixing process for electrolyte preparation hazardous.

[0050] Performance testing:

[0051] The crystal structures of lithium sulfide and sulfide solid electrolyte were tested using X-ray diffraction (XRD), the particle size distribution of lithium sulfide was tested using a laser particle size analyzer, and the room temperature ionic conductivity of sulfide solid electrolyte was tested by assembling a symmetrical mold battery.

[0052] Table 1 Summary of test data for each embodiment and comparative example

[0053]

[0054]

[0055] This invention adds the lithium source in batches, by Figure 2 Raman spectroscopy revealed a higher concentration of lithium polysulfides generated, whereas a single addition resulted in a lower concentration of lithium polysulfides in the resulting lithium sulfide material. The increased concentration of lithium polysulfides helps mitigate the negative impact of sulfur loss during the high-temperature solid-phase sintering of the electrolyte, thereby improving the electrolyte's ionic conductivity.

[0056] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a lithium sulfide material containing lithium polysulfides, characterized in that, Includes the following steps: Weigh lithium hydride and sulfur powder at a molar ratio of 2:1.01 to 1.

10. Divide the lithium hydride into 2 to 4 parts. Take one part of lithium hydride and mix it with sulfur powder and ball mill it. Add the remaining lithium hydride in sequence and ball mill it to obtain a mixture powder containing lithium sulfide and lithium polysulfide, which is lithium sulfide material containing lithium polysulfide.

2. The method for preparing lithium sulfide materials containing lithium polysulfides according to claim 1, characterized in that, After each addition of lithium hydride, the ball milling speed is 400-600 rpm / min, and the ball milling time is 2-5 h.

3. The method for preparing lithium sulfide material containing lithium polysulfides according to claim 1, characterized in that, Lithium hydride is divided into 2 to 4 parts by mass ratio.

4. The method for preparing lithium sulfide materials containing lithium polysulfides according to claim 1, characterized in that, The addition of lithium hydride was carried out in a dry, inert environment.

5. The application of a lithium sulfide material obtained by the preparation method as described in claim 1 in the preparation of sulfide solid electrolytes.

6. A method for preparing a sulfide solid electrolyte, characterized in that, Includes the following steps: The lithium sulfide material obtained by the preparation method described in claim 1, phosphorus pentasulfide, and lithium chloride are mixed and ball-milled. The milled product is taken out, pressed into tablets, and sintered to obtain the sulfide solid electrolyte.

7. The preparation method according to claim 6, characterized in that, The ball milling speed is 400-600 rpm / min, and the time is 2-5 hours.

8. The preparation method according to claim 6, characterized in that, As one embodiment of the present invention, the sintering temperature is 450-550°C and the time is 2-4 hours.

9. The preparation method according to claim 6, characterized in that, The obtained sulfide solid electrolyte powder is a sulfide solid electrolyte of the silver-germanium sulfide type.

10. The preparation method according to claim 9, characterized in that, The solid electrolyte of silver-germanium sulfide is Li 5.5 PS 4.5 Cl 1.5 .

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