A method for synthesizing nanoscale lithium sulfide

Abstract

The application provides a synthesis method of nanoscale lithium sulfide, and relates to the technical field of lithium sulfide synthesis. The synthesis method comprises the following steps: stirring and dissolving lithium sulfide raw materials in an alcohol solvent to obtain a lithium sulfide alcohol solution; evaporating and crystallizing the lithium sulfide alcohol solution and drying to obtain lithium sulfide crystals; mixing the lithium sulfide crystals with a sulfur source, and sintering at 550 DEG C-850 DEG C to obtain nanoscale lithium sulfide. The nanoscale lithium sulfide is directly synthesized by a solid-phase sintering method in one step, the operation method is simple, the cost is low, and the nanoscale lithium sulfide can be mass-produced in an industrialized manner.

Description

Technical Field

[0001] This invention relates to the field of lithium sulfide synthesis technology, and more particularly to a method for synthesizing nanoscale lithium sulfide. Background Technology

[0002] Since its invention, lithium-ion batteries have been widely used in portable electronic devices such as cameras, laptops, mobile phones, and power tools due to their high cycle life and high energy density. In recent years, with the continuous upgrading of lithium-ion batteries, they have even been applied to the new energy vehicle sector. However, with the rapid development of the new energy vehicle industry, issues such as vehicle range, charging time, and safety have become key factors restricting its further development. Therefore, developing next-generation battery technologies with high energy density is particularly important. Lithium-sulfur batteries and all-solid-state batteries are considered among the most promising directions in future battery technology due to their high energy density. Lithium sulfide, as the active cathode material of lithium-sulfur batteries and a key raw material for synthesizing solid electrolytes, has broad market demand and application prospects, attracting widespread attention.

[0003] According to reports, lithium sulfide, as the cathode material for lithium-sulfur batteries, needs a purity of over 99.9% to help reduce the adverse effects of impurities on battery performance, decrease capacity decay, and extend cycle life. Furthermore, the particle size of lithium sulfide should be at the nanometer level. Nanoscale lithium sulfide has a larger specific surface area, which is beneficial for the contact between the electrolyte and the electrode, effectively promoting the insertion and extraction of lithium ions, thereby improving the lithium ion transport rate and the battery's charge-discharge performance. For the currently popular sulfide-based all-solid-state batteries, the ionic conductivity of lithium sulfide in the solid electrolyte plays a crucial role and is one of the key factors determining the performance of all-solid-state batteries. Therefore, the quality requirements for lithium sulfide materials are extremely high, especially its purity and particle size, which have a significant impact on battery performance.

[0004] Existing methods for preparing lithium sulfide have several shortcomings. Many methods fail to produce high-purity lithium sulfide products, and the high moisture content during the reaction process leads to product agglomeration and large particle sizes. Furthermore, the production processes are complex, requiring sophisticated equipment and hindering large-scale production. Currently, the preparation of nanoscale lithium sulfide mainly relies on wet ball milling technology. This method not only demands sophisticated equipment and involves cumbersome operations, but also yields low-purity lithium sulfide at high costs. Therefore, there is an urgent need to provide a solution to address these issues. Summary of the Invention

[0005] The purpose of this invention is to provide a method for synthesizing nanoscale lithium sulfide.

[0006] The present invention provides a method for synthesizing nano-sized lithium sulfide, comprising: dissolving lithium sulfide raw material in an alcohol solvent by stirring and separating to obtain a lithium sulfide alcohol solution; evaporating and crystallizing the lithium sulfide alcohol solution and drying to obtain lithium sulfide crystals; mixing the lithium sulfide crystals with a sulfur source and calcining at 550℃-850℃ to obtain nano-sized lithium sulfide.

[0007] Optionally, the alcohol solvent includes one of ethanol, methanol, ethylene glycol, propylene glycol, isopropanol, and n-butanol.

[0008] Optionally, the lithium sulfide raw material includes industrially produced lithium sulfide products and lithium sulfide products containing impurities.

[0009] Optionally, the lithium sulfide alcohol solution can be evaporated and crystallized at 100℃-150℃.

[0010] Optionally, the lithium sulfide alcohol solution can be evaporated and crystallized in an ultrasonic environment.

[0011] Alternatively, the lithium sulfide alcohol solution can be evaporated and crystallized in an evaporation reactor, a continuous oscillating baffle crystallizer, a vertical conical crystallizer, or a rotary evaporator.

[0012] Optionally, after evaporation and crystallization, the product can be dried at 200℃-350℃.

[0013] Alternatively, drying can be carried out under a vacuum or inert atmosphere.

[0014] Optionally, the product is dried for 5-10 hours after evaporation and crystallization.

[0015] Optionally, the crystals can be evaporated and then dried to a constant weight.

[0016] Optionally, the sulfur source includes one of elemental sulfur, thiols, thiophenols, thioethers, thiocarboxylic acids, thioamides, and thiocyanates.

[0017] Optionally, the thiol compound includes isobutanol thio, ethylenedithiol, or dodecathiol.

[0018] Optionally, the thiophenolic compound includes toluenethiophenol or naphthiophenol.

[0019] Optionally, the thioether compound includes dibenzyl thioether or diethyl thioether.

[0020] Optionally, the thiocarboxylic acid compound includes thiobenzoic acid.

[0021] Optionally, the thioamide compound includes thiourea or thioacetamide.

[0022] Optionally, the thiocyanate compound includes ammonium thiocyanate.

[0023] Alternatively, the lithium sulfide crystals are mixed with the sulfur source in a pulverizer, high-speed mixer, ball mill, or roller mill.

[0024] Optionally, the mass ratio of lithium sulfide to sulfur source is 100:(5-30).

[0025] Optionally, lithium sulfide crystals are mixed with a sulfur source and ground to a particle size of 50nm-1000nm.

[0026] Optionally, after mixing, the temperature is increased to 550℃-850℃ at a rate of 2℃ / min-20℃ / min for firing.

[0027] Optionally, the mixture can be fired at 550℃-850℃ for 2-5 hours.

[0028] Alternatively, nano-sized lithium sulfide can be obtained by calcining at 550℃-850℃ and then cooling to room temperature.

[0029] Optionally, the particle size of the nano-sized lithium sulfide is 200nm-800nm.

[0030] Alternatively, the firing process can be carried out in an inert gas at 550°C-850°C.

[0031] Optionally, the inert gas includes nitrogen, helium, or argon.

[0032] Optionally, the flow rate of the inert gas is 2 mL / s to 8 mL / s.

[0033] Alternatively, the firing process can be carried out in an inert gas at 550℃-850℃ and 0.8atm.-1.5atm.

[0034] Optionally, the firing is carried out in a vacuum environment of 550℃-850℃, and the vacuum degree of the vacuum environment is greater than 0.08MPa.

[0035] The method for synthesizing nano-sized lithium sulfide provided by this invention has at least one of the following beneficial technical effects compared with the prior art:

[0036] 1. Nanoscale lithium sulfide can be directly synthesized in one step via solid-state sintering. The operation method is simple, low-cost, and can be mass-produced industrially.

[0037] 2. By dissolving lithium sulfide raw materials in an alcohol solvent, not only can lithium sulfide be purified, but more uniform nucleation sites can also be formed during evaporation, drying and recrystallization, thereby promoting the precipitation of more fine lithium sulfide crystals.

[0038] 3. The addition of lithium sulfide can effectively suppress the formation of organolithium compounds during sintering, effectively avoid the generation of impurities, and ensure the purity of lithium sulfide nanoparticles. Attached Figure Description

[0039] Figure 1 A flowchart illustrating a method for synthesizing nanoscale lithium sulfide provided by this invention;

[0040] Figure 2 The X-ray diffraction patterns of lithium sulfide in Examples 1 to 3 of this invention are shown below.

[0041] Figure 3 This is a SEM image of the nano-sized lithium sulfide prepared in Example 1 of the present invention;

[0042] Figure 4 This is a SEM image of the nano-sized lithium sulfide prepared in Example 2 of the present invention;

[0043] Figure 5 This is a SEM image of the nano-sized lithium sulfide prepared in Example 3 of the present invention;

[0044] Figure 6 The X-ray diffraction pattern of the nanoscale lithium sulfide prepared in Comparative Example 1 of this invention is shown.

[0045] Figure 7 The X-ray diffraction pattern of the nanoscale lithium sulfide prepared in Comparative Example 2 of this invention;

[0046] Figure 8 The X-ray diffraction pattern of the nanoscale lithium sulfide prepared in Comparative Example 3 of this invention is shown.

[0047] Figure 9 These are comparative appearance diagrams of Embodiment 1 and Comparative Examples 1 to 3 of the present invention. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0049] See Figure 1 This invention provides a method for synthesizing nanoscale lithium sulfide, comprising the following steps:

[0050] S1. Lithium sulfide raw material is dissolved in an alcohol solvent by stirring and then separated to obtain lithium sulfide alcohol solution;

[0051] S2. Evaporate and crystallize the lithium sulfide alcohol solution and dry it to obtain lithium sulfide crystals;

[0052] S3. After mixing lithium sulfide crystals with a sulfur source, nano-sized lithium sulfide is obtained by calcining at 550℃-850℃.

[0053] In fact, the synthesis method provided by the present invention can purify lithium sulfide in lithium sulfide raw materials by utilizing the good solubility of lithium sulfide in alcohol solvents. At the same time, solid lithium sulfide crystals are obtained by evaporation and crystallization, and nano-sized sulfide materials are obtained by one-time sintering process after being fully mixed with sulfur source.

[0054] In fact, the alcohol solvent used in step S1 includes one of ethanol, methanol, ethylene glycol, propylene glycol, isopropanol, and n-butanol. Dissolving the lithium sulfide raw material in the alcohol solvent allows for the separation of insoluble substances and yields a pure lithium sulfide alcohol solution. Specifically, to improve the dissolution rate of the lithium sulfide raw material during stirring separation, commonly used solubilizing methods in the art, such as stirring, shaking, and heating, can be employed.

[0055] In some embodiments, the lithium sulfide raw material used in step S1 includes industrially produced lithium sulfide products or lithium sulfide products containing impurities. In fact, the method provided by this invention can not only purify lithium sulfide products but also reduce their particle size; for example, it can convert micron-sized lithium sulfide into nano-sized lithium sulfide. Specifically, when the lithium sulfide raw material is a lithium sulfide product containing impurities, the impurities can be lithium carbonate, lithium sulfate, lithium hydroxide, lithium oxide, or other lithium compounds.

[0056] In some embodiments, the alcohol solvent used in step S1 is necessary to dissolve the lithium sulfide in the lithium sulfide raw material. In fact, when impurities in the lithium sulfide raw material are insoluble in the alcohol solvent, an excess of alcohol solvent can be added to improve purification efficiency and reduce the concentration of lithium sulfide in the alcohol solution to obtain fine lithium sulfide crystals. In some embodiments, after the lithium sulfide raw material is dissolved in the alcohol solvent by stirring in step S1, common solid-liquid separation methods such as vacuum filtration and filtration can be used to separate the lithium sulfide alcohol solution.

[0057] In practice, during step S2, the lithium sulfide alcohol solution can be evaporated and crystallized at temperatures below 150°C. This not only promotes the precipitation of lithium sulfide crystals but also inhibits crystal growth, resulting in the accumulation of a large number of fine and uniformly distributed lithium sulfide particles during the evaporation process. Specifically, to balance the evaporation crystallization rate and crystal morphology, evaporation crystallization can be carried out at temperatures between 100°C and 150°C.

[0058] In some embodiments, during step S2, ultrasonic treatment can be added during the evaporation and crystallization process to allow the lithium sulfide alcohol solution to be evaporated and crystallized under ultrasonic conditions. In fact, by performing ultrasonic treatment, the ultrasonic cavitation effect can be effectively utilized to further reduce the nucleation size, promote the formation of more nucleation particles, and inhibit in-situ crystal growth.

[0059] Specifically, in industrial applications, step S2 can be performed by evaporating and crystallizing the lithium sulfide alcohol solution in an evaporating reactor, a continuous oscillating baffle crystallizer, a vertical conical crystallizer, or a rotary evaporator. In practice, existing industrial evaporation equipment can be used to evaporate and crystallize the lithium sulfide alcohol solution, while also allowing for the recovery and reuse of the obtained alcohol solvent.

[0060] In fact, drying after evaporation and crystallization in step S2 can further improve the cleanliness and dryness of lithium sulfide crystals, effectively preventing the formation of organolithium compounds during subsequent sintering and improving the purity of nano-sized lithium sulfide products. Specifically, drying can be carried out at 200℃-350℃ for 5-10 hours until constant weight is achieved. Alternatively, drying can be performed under vacuum or an inert atmosphere.

[0061] In fact, after adding the sulfur source in step S3, the sulfur source melts and covers the surface of the lithium sulfide crystals during the heating and sintering process. This not only effectively inhibits the further growth of lithium sulfide crystals, but also effectively inhibits the formation of organolithium compounds, thus avoiding the generation of impurities during high-temperature sintering. Specifically, in step S3, the mass ratio of lithium sulfide to sulfur source is 100:(5-30).

[0062] Specifically, the sulfur source used includes one of the following: elemental sulfur, thiols, thiophenols, thioethers, thiocarboxylic acids, thioamides, and thiocyanates. Further, thiols include isobutanol thiosulfate, ethylenedithiol, or dodecanethiol; thiophenols include toluenethiophenol or naphthiophenol; thioethers include dibenzyl sulfide or diethyl sulfide; thiocarboxylic acids include thiobenzoic acid; thioamides include thiourea or thioacetamide; and thiocyanates include ammonium thiocyanate.

[0063] In some embodiments, lithium sulfide crystals can be mixed with a sulfur source during step S3. This improves the uniformity of sulfur source dispersion, which in turn facilitates the melting of the sulfur source and its coverage of the lithium sulfide crystals during high-temperature sintering. Specifically, the lithium sulfide crystals and sulfur source can be ground and mixed in equipment such as a pulverizer, high-speed mixer, ball mill, or roller mill to achieve a particle size of 50nm-1000nm.

[0064] In practice, in step S3, the mixed lithium sulfide crystals and sulfur source are heated to 550℃-850℃ at a rate of 2℃ / min-20℃ / min for 2h-5h, and then cooled to room temperature to obtain nanoscale lithium sulfide with a size of 200nm-800nm. In some embodiments, calcination can be carried out at 550℃-850℃ in an inert gas (including nitrogen, helium, or argon) at 0.8atm.-1.5atm., and the flow rate of the inert gas can be controlled at 2mL / s-8mL / s. In some embodiments, calcination can also be carried out in a vacuum environment (vacuum degree greater than 0.08MPa) at 550℃-850℃.

[0065] Example 1

[0066] This embodiment 1 provides a method for synthesizing nanoscale lithium sulfide, including the following steps:

[0067] S1. Add 100g of deteriorated lithium sulfide raw material containing impurities (impurities are lithium carbonate, lithium sulfate, lithium hydroxide, and lithium oxide) to 5000mL of anhydrous ethanol, stir to dissolve, and then filter to separate the lithium sulfide alcohol solution.

[0068] S2. The lithium sulfide alcohol solution was concentrated and crystallized by rotary evaporation at 120°C and anhydrous ethanol was recovered. The resulting crystals were transferred to a vacuum oven at 250°C and kept at that temperature for 8 hours. The crystals were then cooled to room temperature in the oven to obtain lithium sulfide crystals.

[0069] S3. After thoroughly mixing lithium sulfide crystals with 30% sulfur by mass in a mixer, the mixture is loaded into a crucible and heated to 600℃ at a rate of 10℃ / min in an argon flow of 5mL / s. The mixture is then held at this temperature for 2 hours and cooled to room temperature in the furnace to obtain lithium sulfide with a primary particle size of 500nm.

[0070] Example 2

[0071] This embodiment 2 provides a method for synthesizing nanoscale lithium sulfide, including the following steps:

[0072] S0. 278.6g of lithium sulfate monohydrate and 261.4g of glucose were mixed evenly in a mixer at a speed of 28000rpm and then loaded into an alumina crucible. The crucible was then transferred to a tube furnace and heated to 850℃ at a rate of 5℃ / min under an argon atmosphere and calcined at a constant temperature for 5h. After cooling to room temperature with the furnace, the crucible was transferred to a glove box with a water oxygen content of less than 0.1ppm and the material in the crucible was ground to obtain lithium sulfide raw material.

[0073] S1. Add lithium sulfide raw material to 5000 mL of anhydrous ethanol, stir to dissolve, and then filter to separate and obtain lithium sulfide alcohol solution.

[0074] S2. The lithium sulfide alcohol solution was concentrated and crystallized by rotary evaporation at 120°C and anhydrous ethanol was recovered. The resulting crystals were transferred to a vacuum oven at 250°C and kept at that temperature for 8 hours. The crystals were then cooled to room temperature in the oven to obtain lithium sulfide crystals.

[0075] S3. After thoroughly mixing lithium sulfide crystals with 30% sulfur by mass in a mixer, the mixture is loaded into a crucible and heated to 600°C at a rate of 10°C / min in a vacuum environment and sintered at that temperature for 2 hours. After cooling to room temperature in the furnace, lithium sulfide with a primary particle size of 200 nm is obtained.

[0076] Example 3

[0077] This embodiment 3 provides a method for synthesizing nanoscale lithium sulfide, including the following steps:

[0078] S0. 300g of anhydrous lithium sulfate powder with an average particle size of 0.1μm was loaded into an alumina boat, and heated to 780℃ at a rate of 10℃ / min in a mixed atmosphere of hydrogen and carbon monoxide and held for 5h. After cooling to room temperature in the furnace, the alumina boat was transferred to a glove box with a water oxygen content of less than 0.1ppm to grind the material in the crucible to obtain lithium sulfide raw material.

[0079] S1. Add lithium sulfide raw material to 5000 mL of anhydrous methanol, stir to dissolve, and then filter to separate lithium sulfide alcohol solution.

[0080] S2. The lithium sulfide alcohol solution was concentrated and crystallized by rotary evaporation at 120°C and anhydrous methanol was recovered. The resulting crystals were transferred to a vacuum oven at 250°C and kept at that temperature for 8 hours. The crystals were then cooled to room temperature in the oven to obtain lithium sulfide crystals.

[0081] S3. After thoroughly mixing lithium sulfide crystals with 10% thiourea by mass in a mixer, the mixture is loaded into a crucible and heated to 600°C at a rate of 10°C / min in a vacuum environment and sintered at that temperature for 2 hours. After cooling to room temperature in the furnace, lithium sulfide with a primary particle size of 800 nm is obtained.

[0082] Comparative Example 1

[0083] Comparative Example 1 provides a method for synthesizing nano-sized lithium sulfide, which differs from Example 1 in that the method involves heating in a vacuum oven at 350°C for 8 hours in step S2.

[0084] Comparative Example 2

[0085] Comparative Example 2 provides a method for synthesizing nanoscale lithium sulfide, which differs from Example 1 in that the amount of elemental sulfur added in step S3 is 10%.

[0086] Comparative Example 3

[0087] Comparative Example 3 provides a method for synthesizing nanoscale lithium sulfide, which differs from Example 1 in that the crystals obtained in step S2 are not dried.

[0088] Structural characterization

[0089] The nanoscale lithium sulfide prepared in Examples 1 to 3 was characterized by XRD as follows: Figure 2 As shown, SEM characterization was performed as follows: Figures 3 to 5 As shown. From Figure 2 As can be seen from the data, compared with the lithium sulfide standard card (77-2145), the nano-sized lithium sulfide prepared in Examples 1 to 3 is a pure phase of lithium sulfide, while from... Figures 3 to 5 As can be seen from the examples, the lithium sulfide synthesized in Examples 1 to 3 has a nanoscale structure.

[0090] The nanoscale lithium sulfide in Comparative Examples 1 to 3 were characterized by XRD as follows: Figures 6 to 8 As shown, the appearance of the nano-sized lithium sulfide prepared in Example 1 and Comparative Examples 1 to 3 is compared. Figure 9 As shown.

[0091] from Figure 6 and Figure 9 As can be seen from the results, lithium carbonate impurities were present in the lithium sulfide prepared in Comparative Example 1, and the product was agglomerated and brownish-yellow. This is because after the drying temperature was increased, ethanol reacted with lithium sulfide to generate lithium hydroxide, and during the calcination process, lithium hydroxide reacted with elemental sulfur to generate lithium carbonate. At the same time, the volatilization of ethanol inside made it difficult to ensure that lithium sulfide grew in the desired direction during the subsequent calcination process, resulting in agglomeration and making it difficult to obtain high-purity nanoscale sulfides.

[0092] from Figure 7 and Figure 9 As can be seen, the lithium sulfide prepared in Comparative Example 2 is similar to that in Comparative Example 1, both of which have lithium carbonate impurity phases and the products are agglomerated and brownish-gray. This is because the reduced amount of sulfur added failed to effectively inhibit the reaction between ethanol and lithium sulfide, resulting in the formation of organolithium impurity phases, which are then calcined to form lithium carbonate.

[0093] from Figure 8 and Figure 9 As can be seen from the data, the lithium sulfide prepared in Comparative Example 3 did not undergo deep ethanol removal, which resulted in the inability of ethanol to be discharged quickly during the heating process, leading to carbonization. This resulted in a blackish-gray product, making it difficult to obtain high-purity nano-sized lithium sulfide.

[0094] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations fall within the scope and spirit of the invention as set forth in the claims. Furthermore, the invention described herein may have other embodiments and can be implemented or carried out in various ways.

Claims

1. A method for synthesizing nanoscale lithium sulfide, characterized in that, include: Lithium sulfide raw material is dissolved in an alcohol solvent by stirring to obtain a lithium sulfide alcohol solution. The alcohol solvent includes one of ethanol, methanol, ethylene glycol, propylene glycol, isopropanol, and n-butanol. The lithium sulfide raw material is a lithium sulfide product containing impurities. The lithium sulfide alcohol solution is evaporated and crystallized at 120°C and dried at 250°C to obtain lithium sulfide crystals. The lithium sulfide crystals are mixed with 30 wt% of a sulfur source and calcined at 550°C-850°C to obtain nano-sized lithium sulfide. The sulfur source is one of elemental sulfur, thiourea, thioacetamide, and ammonium thiocyanate.

2. The synthesis method according to claim 1, characterized in that, Evaporation and crystallization of lithium sulfide alcohol solution in an ultrasonic environment; and / or evaporation and crystallization of lithium sulfide alcohol solution in an evaporation reactor, a continuous oscillating baffle crystallizer, a vertical conical crystallizer, or a rotary evaporator.

3. The synthesis method according to claim 1, characterized in that, Drying is carried out under vacuum or inert atmosphere; and / or, after evaporation and crystallization, drying is carried out for 5-10 hours; and / or, after evaporation and crystallization, drying is carried out to constant weight.

4. The synthesis method according to claim 1, characterized in that, Lithium sulfide crystals are mixed with a sulfur source in a pulverizer, high-speed mixer, ball mill, or roller mill; and / or, lithium sulfide crystals are mixed with a sulfur source and ground to a particle size of 50 nm-1000 nm.

5. The synthesis method according to claim 1, characterized in that, After mixing, the mixture is heated to 550℃-850℃ at a rate of 2℃ / min-20℃ / min for calcination; and / or, after mixing, it is calcined at 550℃-850℃ for 2h-5h; and / or, after calcination at 550℃-850℃, it is cooled to room temperature to obtain nano-sized lithium sulfide; and / or, the particle size of the nano-sized lithium sulfide is 200nm-800nm.

6. The synthesis method according to claim 1, characterized in that, The firing process is carried out in an inert gas at 550℃-850℃; wherein the inert gas includes nitrogen, helium or argon, and / or the flow rate of the inert gas is 2mL / s-8mL / s; and / or the firing process is carried out in an inert gas at 550℃-850℃ and 0.8atm.-1.5atm.

7. The synthesis method according to claim 1, characterized in that, The firing process is carried out in a vacuum environment at 550℃-850℃, and the vacuum degree of the vacuum environment is greater than 0.08MPa.

Images