A preparation method and application of lithium sulfide

Abstract

The present invention relates to the technical field of lithium battery materials, and specifically provides a method for preparing lithium sulfide and application thereof, wherein hydrogen sulfide with water content and oxygen content limited within a certain range is used as a sulfur source to react with a lithium source to prepare lithium sulfide, thereby greatly reducing the generation of lithium hydroxide or oxidative impurities, thereby facilitating the improvement of the purity of the lithium sulfide product, and can be directly used as a raw material for a sulfide solid electrolyte, thereby facilitating the improvement of the performance of the sulfide solid electrolyte.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery materials, and in particular to a preparation method and application of lithium sulfide. Background Art

[0002] In recent years, new energy technologies have been developing rapidly. Among them, all-solid-state batteries with higher energy density and better safety have attracted much attention from academia and industry. The core of all-solid-state batteries is solid electrolyte materials, among which sulfide solid electrolytes have high room temperature conductivity, which can reach 10 -4 -10 -3 S / cm, a wide electrochemical window above 5V, and strong processability are considered to be the most likely solid electrolyte material for industrialization, and have good application prospects in lithium-ion batteries.

[0003] Lithium sulfide is an important component of sulfide solid electrolytes, which affects the ionic conductivity of solid electrolytes. It is also one of the main factors that determine the performance of all-solid-state batteries. Therefore, the quality requirements for lithium sulfide materials are becoming increasingly stringent.

[0004] At present, the synthesis method of lithium sulfide mainly adopts the reaction of lithium source and sulfur source for preparation, and the preparation of lithium sulfide has high requirements for the purity of the reaction raw materials. The existing literature mainly focuses on the purity of the lithium source. For example, patents CN110475745B, CN117916194A, and EP3235787B1 require the use of high-purity lithium hydroxide as a raw material, but the literature rarely pays attention to the requirements for the quality of hydrogen sulfide. Lithium sulfide has been confirmed to be a substance that is sensitive to water and oxygen. It is easily oxidized and hydrolyzed to produce impurities. When lithium sulfide is used in solid-state batteries, the application performance is significantly affected by the impurities in the lithium sulfide raw materials. In industry, hydrogen sulfide generally comes from by-products and has complex components. At the same time, due to the high toxicity and strong corrosiveness of hydrogen sulfide, companies generally do not conduct detailed research on impurities in hydrogen sulfide.

[0005] In order to stably obtain lithium sulfide materials with high purity and good application performance in solid-state batteries, how to control the raw material indicators, especially the hydrogen sulfide raw material indicators, has become an urgent problem to be solved. Summary of the invention

[0006] Through in-depth research, the present invention finds that the water and oxygen contents in the hydrogen sulfide raw material have a significant impact on the application performance of the lithium sulfide product, especially in the late reaction period, when the water and oxygen contents in the hydrogen sulfide are high, due to the reaction balance, impurities such as LiOH and Li2O in the lithium sulfide product are difficult to be completely converted, and due to oxidation, impurities such as lithium sulfate are also high, which affects the application of the lithium sulfide product in solid-state batteries.

[0007] In order to solve the problems existing in the above-mentioned prior art, the present invention provides a method for preparing lithium sulfide, which uses hydrogen sulfide with water content and oxygen content limited to a certain range as a sulfur source to react with a lithium source to prepare lithium sulfide, thereby greatly reducing the generation of lithium hydroxide or oxidizing impurities, thereby facilitating the improvement of the purity of the lithium sulfide product, and can be directly used as a raw material for a sulfide solid electrolyte, which is beneficial to improving the performance of the sulfide solid electrolyte.

[0008] To achieve the above object, the present invention first provides a method for preparing lithium sulfide, comprising the following steps: Lithium sulfide is obtained by reacting a lithium source with hydrogen sulfide in a reactor, wherein the water content of the hydrogen sulfide is less than 70 ppm and the oxygen content is less than 200 ppm.

[0009] Furthermore, before hydrogen sulfide is introduced for reaction, an inert gas is introduced into the reactor for replacement; the inert gas is one or more of nitrogen, argon and helium.

[0010] Furthermore, the lithium source is a lithium-containing substance, specifically selected from one or more of anhydrous lithium hydroxide, potassium hydroxide monohydrate, lithium carbonate, lithium oxide, lithium nitrate, lithium chloride, lithium acetate, butyl lithium, hexyl lithium, lithium amide, alkyl lithium, and aryl lithium, and the purity of the lithium source is preferably above 99%, more preferably above 99.9%.

[0011] Furthermore, the hydrogen sulfide content is preferably 99% or more, more preferably 99.9% or more.

[0012] Furthermore, the molar ratio of hydrogen sulfide to lithium in the lithium-containing substance is (0.5-100):1.

[0013] Furthermore, the reaction temperature is 10-800° C., and after hydrogen sulfide is introduced for reaction, the reaction time is 0.5-30 hours, preferably 1-12 hours.

[0014] More specifically, a dry process lithium source is used to react with hydrogen sulfide, the reaction temperature is 120-800° C., preferably 300-700° C., and after the hydrogen sulfide is introduced, the reaction time is 0.5-20 h, preferably 1-8 h.

[0015] A wet process is adopted to react a lithium source with hydrogen sulfide, the reaction temperature is 10-220°C, preferably 30-160°C; after the hydrogen sulfide is introduced, the reaction time is 0.5-30h, preferably 1-12h; wherein the solvent used in the wet process is selected from one of n-hexane, N-methylpyrrolidone, dimethyl sulfoxide, dimethylamide, cyclopentane sulfone, toluene, ethylbenzene and xylene.

[0016] The hydrogen sulfide used in the present invention is obtained from the purification of petroleum refining tail gas, and the main impurities are alkanes, which have no obvious effect on the product quality. The purity of the final product can reach more than 98%, and the highest can reach more than 99.9%.

[0017] The present invention also provides a method for preparing a sulfide solid electrolyte, wherein the lithium sulfide prepared by the above method is prepared, and the sulfide solid electrolyte has excellent lithium ion conductivity. 5.4 PS 4.4 Cl 0.8 Br 0.8 As an example, the specific steps are as follows: Step 1, under a dry argon atmosphere, weigh the raw materials according to the composition ratio of the above solid electrolyte, place them in a ball mill, and mill them; the raw materials are lithium sulfide, phosphorus pentasulfide, lithium chloride, and lithium bromide; Step 2, under the protection of a dry inert atmosphere, heat-treating the powder obtained after ball milling in step 1, while introducing hydrogen sulfide gas during the heat treatment; Step 3: Under the protection of a dry inert atmosphere, the product after the heat treatment in step 2 is ball-milled to obtain a sulfide solid electrolyte.

[0018] Furthermore, the ball milling conditions in step 1 are: ball-to-material mass ratio is (3-10):1, rotation speed is 300-850 rpm, and ball milling time is 3-12h.

[0019] Furthermore, in step 2, the hydrogen sulfide content is 99.9%, the water content is less than 70ppm, the oxygen content is less than 200ppm, the flow rate is 1.0L / min; the heat treatment temperature is 360-550℃, and the time is 2-5h.

[0020] Furthermore, in steps 2 and 3, the inert atmosphere is argon, xenon or a mixture of argon and xenon.

[0021] Furthermore, the ball milling conditions in step 2 include: a ball-to-material mass ratio of (5-10):1, a rotation speed of 300-550 rpm, and a ball milling time of 15 h.

[0022] Furthermore, the heat treatment method in step 3 is: fill the mixed powder in a graphite sagger, and place the sagger inside the furnace core tube of a tubular furnace. While hydrogen sulfide gas is circulated in the furnace core tube at a rate of 1.0L / min, the temperature is raised to 500°C at a rate of 5°C / min, and heated for 4 hours in this state to obtain a sulfide solid electrolyte; wherein the hydrogen sulfide content used is 99.9%, the water content is less than 70ppm, and the oxygen content is less than 200ppm.

[0023] The sulfide solid electrolyte obtained above was press-formed at a pressure of 200 MPa, and then cold isostatically pressed (CP) at a pressure of 200 MPa to produce pellets with a diameter of 10 mm and a thickness of 2 mm. After the carbon paste as an electrode was directly applied to the upper and lower surfaces of the pellets according to the existing method, a heat treatment was performed at 180°C for 30 minutes to produce a sample for measuring lithium ion conductivity. The lithium ion conductivity was measured by using an AC impedance method at 25°C.

[0024] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in: (1) the purity of the prepared lithium sulfide is high, higher than 99.7%; (2) the sulfide solid electrolyte prepared by the lithium sulfide obtained by the method has an ionic conductivity of 10 -3 S / cm level, up to 10 -2 S / cm level, reaching the level of liquid commercial electrolytes, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 X-ray diffraction patterns of lithium sulfide prepared in the examples and comparative examples of the present invention (from top to bottom are examples 1-7, comparative examples 1-4). DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with specific embodiments, so that those skilled in the art can understand the present invention more comprehensively, but the present invention is not limited in any way. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0027] Example 1 A method for preparing lithium sulfide, the specific steps are as follows: 100 g of lithium hydroxide monohydrate (content 99.9%) was added to a quartz glass reactor, and 99.999% high-purity nitrogen was introduced. The temperature was raised while nitrogen was introduced to 300°C, and nitrogen was continued to be introduced until the water and oxygen contents in the reaction system were stable. The introduction of nitrogen was stopped, and hydrogen sulfide (water content 30 ppm, oxygen content 60 ppm) was introduced at a flow rate of 300 mL / min. The reaction was carried out for 6 hours. The purity of the obtained sample was determined by potentiometric titration to be 99.9%. The results are shown in Table 1.

[0028] Example 2 A method for preparing lithium sulfide, the specific steps are as follows: 100 g of lithium hydroxide monohydrate (content 99.9%) was added to a quartz glass reactor, and 99.999% high-purity nitrogen was introduced. The temperature was raised while nitrogen was introduced to 300°C, and nitrogen was continued to be introduced until the water and oxygen contents in the reaction system were stable. The introduction of nitrogen was stopped, and hydrogen sulfide (water content 70 ppm, oxygen content 200 ppm) was introduced at a flow rate of 300 mL / min. The reaction was carried out for 6 hours. The purity of the obtained sample was determined by potentiometric titration to be 99.9%. The results are shown in Table 1.

[0029] Example 3 A method for preparing lithium sulfide, the specific steps are as follows: 100 g of lithium carbonate (content 99.9%) was added to a quartz glass reactor, and 99.999% high-purity nitrogen was introduced. The temperature was raised while nitrogen was introduced to 700°C, and nitrogen was continued to be introduced until the water and oxygen contents in the reaction system were stable. The introduction of nitrogen was stopped, and hydrogen sulfide (water content 70 ppm, oxygen content 200 ppm) was introduced at a flow rate of 500 mL / min. The reaction was carried out for 4 hours. The purity of the obtained sample was determined by potentiometric titration to be 99.9%. The results are shown in Table 1.

[0030] Example 4 A method for preparing lithium sulfide, the specific steps are as follows: In a 99.999% high-purity nitrogen atmosphere, 100 g of butyl lithium and 1000 g of n-hexane were added to the reactor, and nitrogen was continued to be introduced until the water and oxygen contents in the reaction system were detected to be stable. The reaction temperature was adjusted to 30°C, and hydrogen sulfide (water content 70 ppm, oxygen content 200 ppm) was introduced at a hydrogen sulfide flow rate of 250 mL / min. The reaction time was 3 h, and a colorless solid was precipitated. The solid was filtered and washed, and the solid was vacuum dried to constant weight. The purity of the obtained sample was determined by potentiometric titration to be 99.8%. The results are shown in Table 1.

[0031] Example 5 A method for preparing lithium sulfide, the specific steps are as follows: 100 g of lithium hydroxide monohydrate (content 99.9%) was added to a quartz glass reactor, and 99.999% high-purity nitrogen was introduced. The temperature was raised while nitrogen was introduced to 120° C. Nitrogen was continued to be introduced until the water and oxygen contents in the reaction system were stable. The introduction of nitrogen was stopped, and hydrogen sulfide (water content 70 ppm, oxygen content 200 ppm) was introduced at a flow rate of 5000 mL / min. The reaction was carried out for 8 hours. The purity of the obtained sample was determined by potentiometric titration to be 99.8%. The results are shown in Table 1.

[0032] Example 6 A method for preparing lithium sulfide, the specific steps are as follows: 100 g of lithium carbonate (content 99.9%) was added to a quartz glass reactor, and 99.999% high-purity nitrogen was introduced. The temperature was raised while nitrogen was introduced to 800°C, and nitrogen was continued to be introduced until the water and oxygen contents in the reaction system were detected to be stable. The introduction of nitrogen was stopped, and hydrogen sulfide (water content 70 ppm, oxygen content 200 ppm) was introduced at a flow rate of 5000 mL / min. The reaction was carried out for 0.5 hour. The purity of the obtained sample was determined by potentiometric titration to be 99.7%. The results are shown in Table 1.

[0033] Example 7 A method for preparing lithium sulfide, the specific steps are as follows: In a 99.999% high-purity nitrogen atmosphere, 100 g of butyl lithium and 1000 g of N-methyl pyrrolidone were added to the reactor, and nitrogen was continued to be introduced until the water and oxygen contents in the reaction system were detected to be stable. The reaction temperature was adjusted to 160°C, and hydrogen sulfide (water content 70 ppm, oxygen content 200 ppm) was introduced at a hydrogen sulfide flow rate of 1600 mL / min. The reaction time was 30 h, and a colorless solid was precipitated. The solid was filtered and washed, and the solid was vacuum dried to constant weight. The purity of the obtained sample was determined by potentiometric titration to be 99.7%. The results are shown in Table 1.

[0034] Comparative Example 1 A method for preparing lithium sulfide, the specific steps are as follows: 100 g of lithium hydroxide monohydrate (content 99.9%) was added to a quartz glass reactor, and 99.999% high-purity nitrogen was introduced. The temperature was raised while nitrogen was introduced to 300° C. Nitrogen was continued to be introduced until the water and oxygen contents in the reaction system were detected to be stable. The introduction of nitrogen was stopped, and hydrogen sulfide (water content 80 ppm, oxygen content 220 ppm) was introduced at a flow rate of 300 mL / min. The reaction was carried out for 6 hours. The purity of the obtained sample was determined by potentiometric titration to be 98.1%. The results are shown in Table 1.

[0035] Comparative Example 2 A method for preparing lithium sulfide, the specific steps are as follows: 100 g of lithium carbonate (content 99.9%) was added to a quartz glass reactor, and 99.999% high-purity nitrogen was introduced. The temperature was raised while nitrogen was introduced to 700° C. Nitrogen was continued to be introduced until the water and oxygen contents in the reaction system were stable and the oxygen content was below 300 ppm. The introduction of nitrogen was stopped, and hydrogen sulfide (water content 80 ppm, oxygen content 220 ppm) was introduced at a flow rate of 500 mL / min. The reaction was carried out for 4 hours. The purity of the obtained sample was determined by potentiometric titration to be 98.2%. The results are shown in Table 1.

[0036] Comparative Example 3 A method for preparing lithium sulfide, the specific steps are as follows: 100 g of lithium hydroxide monohydrate (content 99.9%) was added to a quartz glass reactor, and 99.999% high-purity nitrogen was introduced. The temperature was raised while nitrogen was introduced to 300° C. Nitrogen was continued to be introduced until the water and oxygen contents in the reaction system were detected to be stable. The introduction of nitrogen was stopped, and hydrogen sulfide (water content 70 ppm, oxygen content 220 ppm) was introduced at a flow rate of 300 mL / min. The reaction was carried out for 6 hours. The purity of the obtained sample was determined by potentiometric titration to be 98.6%. The results are shown in Table 1.

[0037] Comparative Example 4 A method for preparing lithium sulfide, the specific steps are as follows: 100 g of lithium hydroxide monohydrate (content 99.9%) was added to a quartz glass reactor, and 99.999% high-purity nitrogen was introduced. The temperature was raised while nitrogen was introduced to 300° C. Nitrogen was continued to be introduced until the water and oxygen contents in the reaction system were detected to be stable. The introduction of nitrogen was stopped, and hydrogen sulfide (water content 80 ppm, oxygen content 200 ppm) was introduced at a flow rate of 300 mL / min. The reaction was carried out for 6 hours. The purity of the obtained sample was determined by potentiometric titration to be 98.5%. The results are shown in Table 1.

[0038] The inventors tested the lithium sulfide prepared in the embodiment and the comparative example, and the X-ray diffraction patterns thereof are as follows: Figure 1 As shown, from top to bottom are Examples 1-7 and Comparative Examples 1-4, Figure 1 It can be seen that the synthesized samples are all single-phase lithium sulfide.

[0039] Application Examples The lithium sulfide prepared in the examples and comparative examples was used as a raw material to prepare a sulfide solid electrolyte by the following method, and its lithium ion conductivity was further measured. 5.4 PS 4.4 Cl 0.8 Br 0.8 As an example, lithium sulfide powder, phosphorus pentasulfide powder, lithium chloride powder and lithium bromide powder were weighed in a glove box according to their elemental composition to a total amount of 60 g, 300 g of zirconium oxide balls were sealed in a 1 L ball mill jar, and ground with a ball mill at a speed of 500 rpm for 6 h.

[0040] The mixed powder is filled in a graphite sagger, and the sagger is placed inside the furnace core tube of a tubular furnace. While hydrogen sulfide gas is circulated in the furnace core tube at a rate of 1.0 L / min, the temperature is raised to 500°C at a rate of 5°C / min, and heated in this state for 4 hours to obtain a sulfide solid electrolyte; The hydrogen sulfide content used is 99.9%, the water content is less than 70ppm, and the oxygen content is less than 200ppm.

[0041] The sulfide solid electrolyte was press-formed at a pressure of 200 MPa, and then cold isostatically pressed (CIP) at a pressure of 200 MPa to produce pellets with a diameter of 10 mm and a thickness of 2-5 mm.

[0042] After coating the upper and lower surfaces of the pellet with a carbon paste as an electrode, the pellet was heat treated at 180°C for 30 minutes to prepare a sample for measuring lithium ion conductivity. The lithium ion conductivity was measured by an alternating current impedance method at 25°C.

[0043] The above operations were all carried out in a glove box that was purged with fully dry argon (dew point below -60°C). The final lithium ion conductivity data of the sulfide solid electrolyte are shown in Table 1.

[0044] Table 1 Purity of lithium sulfide prepared in Examples and Comparative Examples and lithium ion conductivity of sulfide solid electrolytes From the above results, it can be seen that the water content and oxygen content in hydrogen sulfide have an important influence on the purity of the product. When the water content is higher than 70 ppm and the oxygen content is higher than 200 ppm, the purity of the obtained lithium sulfide is significantly reduced, which in turn affects the ionic conductivity of the sulfide solid electrolyte prepared downstream. The ionic conductivity of the solid electrolyte obtained in the embodiment is significantly better than that in the comparative example.

[0045] The present invention illustrates the detailed process equipment and process flow of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed process equipment and process flow, that is, it does not mean that the present invention must rely on the above-mentioned detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing lithium sulfide, comprising the step of reacting a lithium source with hydrogen sulfide, characterized in that: The water content of the hydrogen sulfide is less than 70 ppm, and the oxygen content is less than 200 ppm.

2. According to claim 1, it is characterized in that: Before introducing hydrogen sulfide for reaction, an inert gas is introduced for replacement, and the inert gas is one or more of nitrogen, argon and helium.

3. The method for preparing lithium sulfide according to claim 1, characterized in that: The lithium source is a lithium-containing substance selected from one or more of anhydrous lithium hydroxide, potassium hydroxide monohydrate, lithium carbonate, lithium oxide, lithium nitrate, lithium chloride, lithium acetate, butyl lithium, hexyl lithium, lithium amide, alkyl lithium, and aryl lithium.

4. The method for preparing lithium sulfide according to claim 1, characterized in that: The purity of lithium source is above 99.9%; the content of hydrogen sulfide is above 99.9%.

5. The method for preparing lithium sulfide according to claim 1, characterized in that: The molar ratio of hydrogen sulfide to lithium in the lithium-containing substance is (0.5-100):

1.

6. The method for preparing lithium sulfide according to claim 1, characterized in that: The reaction temperature is 10-800°C, and the reaction time is 0.5-30 hours.

7. The method for preparing lithium sulfide according to claim 6, characterized in that: When a dry lithium source is used to react with hydrogen sulfide, the reaction temperature is 300-700° C. and the reaction time is 1-8 hours.

8. The method for preparing lithium sulfide according to claim 6, characterized in that: When a wet process is used to react a lithium source with hydrogen sulfide, the reaction temperature is 10-220° C. and the reaction time is 0.5-30 hours; the solvent used in the wet process is selected from one of n-hexane, N-methylpyrrolidone, dimethyl sulfoxide, dimethylamide, cyclopentane, toluene, ethylbenzene and xylene.

9. The method for preparing lithium sulfide according to claim 8, characterized in that: When a wet process lithium source is used to react with hydrogen sulfide, the reaction temperature is 30-160° C. and the reaction time is 1-12 hours.

10. A solid electrolyte for lithium ion batteries, characterized in that: Prepared by using lithium sulfide obtained by the method according to any one of claims 1 to 9.

Images