Electronic-grade lithium sulfide and preparation method and application thereof

Abstract

The invention discloses electronic-grade lithium sulfide as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing lithium sulfate with hydrogen under a vacuum condition, and carrying out a reduction reaction to prepare the electronic-grade lithium sulfide. According to the preparation method of the electronic-grade lithium sulfide, lithium sulfate is reduced through hydrogen, no waste gas or waste water is generated in the process, environment friendliness is achieved, unreacted hydrogen and water vapor return to the hydrogen storage tank, hydrogen can be reused, the water vapor settles to the bottom of the tank to be recycled after being condensed, the technological process is short, and the product purity is high; the method is suitable for large-scale popularization and application.

Description

Technical Field

[0001] The present invention relates to the field of material preparation technology, in particular to the field of solid-state battery positive electrode material preparation technology, and specifically to electronic-grade lithium sulfide and its preparation method and application. Background Art

[0002] High-purity lithium sulfide can be used in the preparation of new polymer functional materials and is also a potential new material for lithium-ion batteries and solid-state batteries. Its theoretical capacity is as high as 1166mAh / g, almost four times the theoretical capacity of lithium cobalt oxide, making it a strong competitor for the next generation of positive electrode materials.

[0003] The preparation methods of lithium sulfide in the prior art mainly include the reaction method of metallic lithium and sulfur, the reaction method of organic lithium and methyl mercaptan, the grinding mixing and vacuum defoaming method, the molten salt electrolysis method, the fluidized bed reactor method, the hydrothermal synthesis method, and the hydrogen sulfide reaction method. Among these preparation methods, the raw materials mainly used are expensive high-purity metallic lithium and high-purity lithium salts. Some of these methods obtain lithium sulfide products with low purity and require secondary purification, resulting in high preparation costs. They are only suitable for laboratory research and cannot be promoted on a large scale. For example, existing patents CN202411273897.5 and CN202280094992.1 use carbon reduction of strontium sulfate to prepare lithium sulfide. First, lithium sulfate is carbon-coated, and carbon monoxide and carbon react with lithium sulfate at a certain temperature to produce lithium sulfide. Carbon dioxide gas is produced during the preparation of lithium sulfide by carbon reduction, which is not friendly to the environment. At the same time, the carbon coating process is added, and the preparation process is complicated. Summary of the Invention

[0004] The main purpose of the present invention is to provide an electronic grade lithium sulfide and a preparation method and application thereof, so as to overcome the deficiencies in the prior art.

[0005] To achieve the aforementioned object of the invention, the technical solutions adopted by the present invention include:

[0006] One aspect of the present invention provides a method for preparing electronic-grade lithium sulfide, which comprises: mixing lithium sulfate and hydrogen under vacuum conditions to carry out a reduction reaction to obtain electronic-grade lithium sulfide.

[0007] Another aspect of the present invention provides electronic-grade lithium sulfide prepared by the aforementioned preparation method.

[0008] Another aspect of the present invention also provides the use of the aforementioned electronic-grade lithium sulfide in the preparation of battery positive electrode materials or the preparation of polymer functional materials.

[0009] Compared with the prior art, the present invention has at least the following advantages:

[0010] The preparation method of electronic-grade lithium sulfide provided by the present invention reduces lithium sulfate with hydrogen, and no waste gas or wastewater is generated during the process, which is environmentally friendly. Unreacted hydrogen and water vapor are returned to the hydrogen storage tank, and the hydrogen can be reused. The water vapor is condensed and settles to the bottom of the tank for recovery and treatment. The process is short, the product purity is high, and it is suitable for large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0012] Figure 1 This is an XRD analysis result diagram of electronic grade lithium sulfide prepared in Example 1 of the present invention;

[0013] Figure 2 This is an XRD analysis result diagram of electronic grade lithium sulfide prepared in Example 2 of the present invention;

[0014] Figure 3 This is an XRD analysis result diagram of electronic grade lithium sulfide prepared in Example 3 of the present invention;

[0015] Figure 4 This is an XRD analysis result diagram of electronic grade lithium sulfide prepared in Example 4 of the present invention;

[0016] Figure 5 This is an XRD analysis result diagram of electronic grade lithium sulfide prepared in Example 5 of the present invention;

[0017] Figure 6 This is an XRD analysis result diagram of electronic grade lithium sulfide prepared in Example 6 of the present invention;

[0018] Figure 7 This is an XRD analysis result diagram of electronic grade lithium sulfide prepared in Example 7 of the present invention;

[0019] Figure 8 This is the XRD analysis result of lithium sulfide prepared in Comparative Example 1;

[0020] Figure 9 This is the XRD analysis result of lithium sulfide prepared in Comparative Example 2. DETAILED DESCRIPTION

[0021] The present invention will be more fully understood by reading the following detailed description. However, it should be understood that the detailed description disclosed below is merely exemplary of the present invention, and that the present invention may be embodied in a variety of forms. Therefore, the specific functional details disclosed herein should not be construed as limiting, but rather as a basis for the claims and as a representative basis for teaching those skilled in the art to variously employ the present invention in virtually any appropriately detailed embodiment.

[0022] As one aspect of the technical solution of the present invention, a method for preparing electronic-grade lithium sulfide includes: mixing lithium sulfate and hydrogen under vacuum conditions to carry out a reduction reaction to obtain electronic-grade lithium sulfide.

[0023] In some embodiments, the preparation method includes: placing lithium sulfate in a vacuum reaction chamber, introducing hydrogen gas, and causing the lithium sulfate and hydrogen gas to undergo the reduction reaction to produce electronic grade lithium sulfide.

[0024] In some preferred embodiments, the preparation method comprises: placing lithium sulfate in a crucible, placing the crucible in a tube furnace, evacuating the tube furnace, and then introducing hydrogen to carry out the reduction reaction to produce electronic grade lithium sulfide.

[0025] In some more preferred embodiments, the purity of the lithium sulfate is above 99%.

[0026] In some more preferred embodiments, the reduction reaction temperature is 600-800° C., and the reduction reaction time is 2-8 hours.

[0027] In some more preferred embodiments, the crucible comprises an aluminum oxide corundum crucible.

[0028] In some more preferred embodiments, the preparation method further comprises: drying the lithium sulfate and the crucible before placing them in the tube furnace. Furthermore, the drying temperature is 80-180° C., and the drying time is 60-200 min.

[0029] In some more preferred embodiments, the preparation method further comprises: dehydrating the hydrogen with concentrated sulfuric acid before passing the hydrogen into the tube furnace.

[0030] In some more preferred embodiments, the flow rate of hydrogen is 0.5-2 L / min.

[0031] In some more preferred embodiments, the heating rate of the tube furnace is 6-10° C. / min.

[0032] In some more preferred embodiments, the outlet of the tube furnace is connected to a hydrogen storage tank, so that the hydrogen at the outlet of the tube furnace can enter the hydrogen storage tank for further recycling.

[0033] In some more preferred embodiments, after the reduction reaction is completed, the temperature is lowered and the resulting electronic-grade lithium sulfide is subjected to high-energy ball milling to obtain lithium sulfide products of varying particle sizes. The milling jar and balls of the high-energy ball mill are both made of corundum. The use of corundum prevents corrosion of the equipment by the lithium sulfide product.

[0034] The chemical equation of the reduction reaction is as follows:

[0035] Li2SO4+4H2==Li2S+4H2O

[0036] As can be seen from the above equation, lithium sulfate and hydrogen undergo an oxidation-reduction reaction to generate lithium sulfide and water. The purity of lithium sulfide is determined by lithium sulfate. If high-purity lithium sulfate is used, the product obtained is high-purity lithium sulfide. The reaction temperature is high during the reaction, and H2O turns into water vapor and can be returned to the recovery tank along with the hydrogen. The entire preparation process is green and environmentally friendly.

[0037] Due to the active nature of lithium sulfide, it is extremely easy to hydrolyze in the air and is particularly difficult to purify. The reduction product is stirred and dissolved with sufficient ethanol at a dissolution temperature of 30-60°C for 1-3 hours, and then filtered. The undissolved precipitate is returned to the lithium sulfate raw material for recovery and reduction. The filtrate is used to recover ethanol using a rotary evaporator, and the crystalline product is an electronic-grade lithium sulfide product.

[0038] As another aspect of the technical solution of the present invention, it relates to electronic-grade lithium sulfide prepared by the aforementioned preparation method.

[0039] As another aspect of the technical solution of the present invention, it involves the use of the aforementioned electronic-grade lithium sulfide in the preparation of battery positive electrode materials or the preparation of polymer functional materials.

[0040] In summary, the present invention discloses a green and clean method for preparing electronic-grade lithium sulfide. After drying, the lithium sulfate is heated in a vacuum tube furnace by introducing hydrogen. A reduction reaction occurs at a certain temperature, followed by natural cooling to room temperature to obtain electronic-grade lithium sulfide. This method has a short process flow, a high-purity product, and is suitable for large-scale application. The hydrogen reduction of lithium sulfate produces no waste gas or wastewater, making it environmentally friendly. Unreacted hydrogen and water vapor are returned to the hydrogen storage tank, where the hydrogen can be reused, while the water vapor condenses and settles to the bottom of the tank for recovery.

[0041] The present invention is further illustrated by way of examples below, but the invention is not limited to the scope of the examples. The reagents and raw materials used in the following examples are commercially available, and the experimental methods where specific conditions are not specified are generally carried out under conventional conditions or according to the conditions recommended by the respective manufacturers.

[0042] Example 1

[0043] Dry the alumina crucible and weighed high-purity lithium sulfate (purity of 99%) at 180°C for 150 minutes, put them in a vacuum tube furnace, and install a sealing ring. Close the air inlet valve, connect the air outlet to a vacuum pump for vacuuming, wait for the vacuum pump to stabilize, close the air outlet valve, connect the air inlet valve to the hydrogen cylinder, slowly open the air inlet valve and the cylinder valve to pass hydrogen, open the air outlet valve after the vacuum pump reaches normal pressure, remove oxygen, pass hydrogen for 5 minutes, and the tube furnace is purged with hydrogen. The flow rate of hydrogen is controlled at 0.5L / min, and the vacuum tube furnace heating program is set. The vacuum tube furnace heating rate is 6°C / min, heated at 800°C for 8 hours, then cooled to room temperature, the sample is taken out and high-energy ball milled for 20 minutes, then dissolved in ethanol at 60°C with stirring for 6 hours, filtered, and the filtrate is recovered by rotary evaporator to recover ethanol. The crystalline product is an electronic grade lithium sulfide product. The XRD analysis results are shown in the table. Figure 1 .

[0044] Example 2

[0045] Dry the alumina crucible and weighed high-purity lithium sulfate (purity of 99%) at 80°C for 200 minutes, put them in a vacuum tube furnace, and install a sealing ring. Close the air inlet valve, connect the air outlet to a vacuum pump for vacuuming, wait for the vacuum pump to stabilize, close the air outlet valve, connect the air inlet valve to the hydrogen cylinder, slowly open the air inlet valve and the cylinder valve to pass hydrogen, open the air outlet valve after the vacuum pump reaches normal pressure, remove oxygen, pass hydrogen for 5 minutes, and the tube furnace is purged with hydrogen. The flow rate of hydrogen is controlled at 1.5L / min, and the vacuum tube furnace heating program is set. The vacuum tube furnace heating rate is 8°C / min, heated at 600°C for 8 hours, then cooled to room temperature, removed the sample and high-energy ball milled for 20 minutes, then dissolved in ethanol at 30°C with stirring for 1 hour, filtered, and the filtrate is recovered by rotary evaporator to recover ethanol. The crystalline product is an electronic grade lithium sulfide product. The XRD analysis results are shown in Figure 2 .

[0046] Example 3

[0047] Dry the alumina crucible and weighed high-purity lithium sulfate (purity of 99%) at 100°C for 120 minutes, put them in a vacuum tube furnace, and install a sealing ring. Close the air inlet valve, connect the air outlet to a vacuum pump for vacuuming, wait for the vacuum pump to stabilize, close the air outlet valve, connect the air inlet valve to the hydrogen cylinder, slowly open the air inlet valve and the cylinder valve to pass hydrogen, open the air outlet valve after the vacuum pump reaches normal pressure, remove oxygen, pass hydrogen for 5 minutes, and the tube furnace is purged with hydrogen. The flow rate of hydrogen is controlled at 1.5L / min, and the vacuum tube furnace heating program is set. The vacuum tube furnace heating rate is 8°C / min, heated at 700°C for 6 hours, then cooled to room temperature, the sample is taken out and high-energy ball milled for 20 minutes, then dissolved in ethanol at 50°C with stirring for 2 hours, filtered, and the filtrate is recovered by rotary evaporator to recover ethanol. The crystalline product is an electronic grade lithium sulfide product. The XRD analysis results are shown in Figure 3 .

[0048] Example 4

[0049] Dry the alumina crucible and weighed high-purity lithium sulfate (purity of 99%) at 80°C for 60 minutes, put them in a vacuum tube furnace, and install a sealing ring. Close the air inlet valve, connect the air outlet to a vacuum pump for vacuuming, wait for the vacuum pump to stabilize, close the air outlet valve, connect the air inlet valve to the hydrogen cylinder, slowly open the air inlet valve and the cylinder valve to pass hydrogen, open the air outlet valve after the vacuum pump reaches normal pressure, remove oxygen, pass hydrogen for 5 minutes, and the tube furnace is purged with hydrogen. The flow rate of hydrogen is controlled at 1.0L / min, and the vacuum tube furnace heating program is set. The vacuum tube furnace heating rate is 6°C / min, heated at 750°C for 4 hours, then cooled to room temperature, the sample is taken out and high-energy ball milled for 20 minutes, then dissolved in ethanol at 40°C with stirring for 5 hours, filtered, and the filtrate is used to recover ethanol using a rotary evaporator. The crystalline product is an electronic grade lithium sulfide product. The XRD analysis results are shown in the table. Figure 4 .

[0050] Example 5

[0051] Dry the alumina crucible and weighed high-purity lithium sulfate (purity of 99%) at 180°C for 30 minutes, put them in a vacuum tube furnace, and install a sealing ring. Close the air inlet valve, connect the air outlet to a vacuum pump for vacuuming, wait for the vacuum pump to stabilize, close the air outlet valve, connect the air inlet valve to the hydrogen cylinder, slowly open the air inlet valve and the cylinder valve to pass hydrogen, open the air outlet valve after the vacuum pump reaches normal pressure, remove oxygen, pass hydrogen for 5 minutes, and the tube furnace is purged with hydrogen. The flow rate of hydrogen is controlled at 1.0L / min, and the vacuum tube furnace heating program is set. The vacuum tube furnace heating rate is 8°C / min, heated at 750°C for 4 hours, then cooled to room temperature, the sample is taken out and high-energy ball milled for 20 minutes, then dissolved in ethanol at 40°C with stirring for 3 hours, filtered, and the filtrate is recovered by rotary evaporator to recover ethanol. The crystalline product is an electronic grade lithium sulfide product. The XRD analysis results are shown in Figure 5 .

[0052] Example 6

[0053] Dry the alumina crucible and weighed high-purity lithium sulfate (purity of 99%) at 120°C for 50 minutes, put them in a vacuum tube furnace, and install a sealing ring. Close the air inlet valve, connect the air outlet to a vacuum pump for vacuuming, wait for the vacuum pump to stabilize, close the air outlet valve, connect the air inlet valve to the hydrogen cylinder, slowly open the air inlet valve and the cylinder valve to pass hydrogen, open the air outlet valve after the vacuum pump reaches normal pressure, remove oxygen, pass hydrogen for 5 minutes, and the tube furnace is purged with hydrogen. The flow rate of hydrogen is controlled at 0.8L / min, and the vacuum tube furnace heating program is set. The vacuum tube furnace heating rate is 10°C / min, heated at 800°C for 7 hours, then cooled to room temperature, removed the sample and high-energy ball milled for 20 minutes, then dissolved in ethanol at 40°C with stirring for 2 hours, filtered, and the filtrate is recovered by rotary evaporator to recover ethanol. The crystalline product is an electronic grade lithium sulfide product. The XRD analysis results are shown in the table. Figure 6 .

[0054] Example 7

[0055] Dry the alumina crucible and weighed high-purity lithium sulfate (purity of 99%) at 160°C for 160 minutes, put them in a vacuum tube furnace, and install a sealing ring. Close the air inlet valve, connect the air outlet to a vacuum pump for vacuuming, wait for the vacuum pump to stabilize, close the air outlet valve, connect the air inlet valve to the hydrogen cylinder, slowly open the air inlet valve and the cylinder valve to pass hydrogen, open the air outlet valve after the vacuum pump reaches normal pressure, remove oxygen, pass hydrogen for 5 minutes, and the tube furnace is purged with hydrogen. The flow rate of hydrogen is controlled at 2L / min, and the vacuum tube furnace heating program is set. The vacuum tube furnace heating rate is 6°C / min, heated at 750°C for 8 hours, then cooled to room temperature, the sample is taken out and high-energy ball milled for 20 minutes, then dissolved in ethanol at 40°C with stirring for 2.5 hours, filtered, and the filtrate is recovered by rotary evaporator to recover ethanol. The crystalline product is an electronic grade lithium sulfide product. The XRD analysis results are shown in the table. Figure 7 .

[0056] Comparative Example 1

[0057] Compared with Example 1, the difference is that the heating temperature of the vacuum tube furnace is 550°C. In addition to lithium sulfide, the crystalline product also contains a large amount of lithium sulfate. The XRD analysis results are shown in Figure 8 .

[0058] Comparative Example 2

[0059] Compared with Example 1, the difference is that no vacuum is performed. In addition to lithium sulfide, the crystalline product also contains a large amount of lithium sulfate. The XRD analysis results are shown in Figure 9 .

[0060] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments using other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0061] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for preparing electronic grade lithium sulfide, characterized in that: include: Under vacuum conditions, lithium sulfate is mixed with hydrogen to undergo a reduction reaction to produce electronic grade lithium sulfide.

2. The preparation method according to claim 1, characterized in that include: Lithium sulfate is placed in a vacuum reaction chamber, and hydrogen is introduced to cause the lithium sulfate and hydrogen to undergo the reduction reaction to produce electronic grade lithium sulfide.

3. The preparation method according to claim 2, characterized in that include: Lithium sulfate is placed in a crucible, the crucible is placed in a tube furnace, the tube furnace is evacuated, and then hydrogen is introduced to perform the reduction reaction to prepare electronic grade lithium sulfide.

4. The preparation method according to claim 3, characterized in that The purity of the lithium sulfate is above 99%; And / or, the reduction reaction temperature is 600-800° C., and the reduction reaction time is 2-8 hours; And / or, the crucible comprises an aluminum oxide corundum crucible.

5. The preparation method according to claim 3, characterized in that Also includes: The lithium sulfate and the crucible are dried before being placed in a tube furnace. Preferably, the drying temperature is 80-180° C. and the drying time is 30-200 min.

6. The preparation method according to claim 3, characterized in that Also includes: The hydrogen is dehydrated with concentrated sulfuric acid before being introduced into the tube furnace.

7. The preparation method according to claim 3, characterized in that The flow rate of the hydrogen is 0.5-2 L / min.

8. The preparation method according to claim 3, characterized in that The heating rate of the tube furnace is 6-10°C / min.

9. Electronic grade lithium sulfide prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the electronic grade lithium sulfide according to claim 9 in preparing battery positive electrode materials or polymer functional materials.

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