Modified lithium sulfide and preparation method and application thereof

Abstract

The invention discloses modified lithium sulfide and a preparation method thereof and sulfide solid electrolyte, the modified lithium sulfide provided by the invention comprises lithium sulfide and doping elements, the doping elements comprise halogen and an aluminum element, based on the total mass of the modified lithium sulfide, the doping amount of the halogen is 1.00 wt%-6.00 wt%, and the doping amount of the aluminum element is 0.05 wt%-1.50 wt%. According to the preparation method, halogen and aluminum elements are doped in lithium sulfide at the same time, so that aluminum-halogen co-doped lithium sulfide is obtained, the hydrolytic property of lithium sulfide is greatly reduced, a trace amount of water in the environment is prevented from reacting with lithium sulfide to release H2S gas and generate lithium oxide and hydroxide, the water resistance of lithium sulfide is improved, and the service life of lithium sulfide is prolonged. And the modified lithium sulfide with good water resistance can be prepared by adopting a simple solid-phase sintering method, so that the method has practical production significance.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and more specifically, to a modified lithium sulfide, its preparation method, and its application. Background Technology

[0002] Lithium sulfide is a key raw material for sulfide solid electrolytes. Existing preparation technologies can be broadly classified into: solid-phase method, solvent method, and direct reduction method.

[0003] Solid-phase method: Lithium sulfide is obtained by mechanically ball milling solid elemental sulfur and metallic lithium / lithium hydride in an inert atmosphere.

[0004] Solvent method: Lithium sulfide is prepared by reacting lithium / lithium compounds and sulfur / sulfur compounds in a solvent medium. Organic solvents or liquid ammonia are used as solvents; organic solvents are often aliphatic hydrocarbons, aromatic hydrocarbons, or ether solvents, such as ethanol, hexane, toluene, diethyl ether, tetrahydrofuran, and N-methylpyrrolidone.

[0005] Direct reduction method: Using strong reducing substances, such as carbon materials / carbon material precursors, metallic magnesium, metallic aluminum, hydrogen, carbon monoxide, etc., lithium sulfate is reduced to lithium sulfide.

[0006] Li₂S exhibits strong hydrolytic properties; upon contact with even trace amounts of moisture in the environment, it releases H₂S gas and generates oxides. Currently, common methods for synthesizing Li₂S include reacting metallic Li and elemental S under high-temperature conditions or in an organic phase, reducing Li₂SO₄ at high temperatures, and reacting H₂S gas with lithium oxides. Regardless of the method used, the water insensitivity of Li₂S must be addressed, necessitating strict control of extremely low humidity (dew point temperature < -60℃) during the production process. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned problems existing in the prior art and to provide a modified lithium sulfide, its preparation method and application.

[0008] The technical problem solved by this invention is achieved by the following technical solution.

[0009] The present invention provides a modified lithium sulfide, comprising: lithium sulfide and doping elements, the doping elements including halogen and aluminum, and based on the total mass of the modified lithium sulfide, the doping amount of halogen is 1.00wt%-6.00wt% and the doping amount of aluminum is 0.05wt%-1.50wt%.

[0010] This invention provides a method for preparing the above-mentioned modified lithium sulfide, wherein the modified lithium sulfide is prepared by solid-state sintering.

[0011] This invention provides an application of lithium sulfide, which is used as a cathode material for lithium-sulfur batteries or as a precursor for synthesizing sulfide solid electrolytes.

[0012] This invention provides a sulfide solid electrolyte, which is prepared using the modified lithium sulfide described above, or the modified lithium sulfide prepared by the above preparation method, as a precursor.

[0013] The present invention provides a battery comprising the above-described sulfide solid electrolyte.

[0014] The present invention has the following beneficial effects: This invention obtains aluminum-halogen co-doped lithium sulfide by simultaneously doping a lithium sulfide matrix with halogens and aluminum. This greatly reduces the hydrolytic properties of lithium sulfide, avoids the reaction of trace amounts of moisture in the environment with lithium sulfide to release H2S gas and generate lithium oxides and hydroxides, thereby improving air stability. As a result, lithium sulfide can be better used as a cathode material for lithium-sulfur batteries or as a raw material for synthesizing sulfide solid electrolytes in all-solid-state batteries. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 The particle size distribution diagram is shown for the modified lithium sulfide prepared in Example 1 of this invention. Figure 2 This is a SEM image of the modified lithium sulfide prepared in Example 1 of the present invention. Detailed Implementation

[0017] 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0018] The following is a detailed description of a modified lithium sulfide, its preparation method, and its applications provided by the present invention.

[0019] In a first aspect, the present invention provides a modified lithium sulfide, comprising: lithium sulfide and doping elements, the doping elements including halogen and aluminum, wherein, based on the total mass of the modified lithium sulfide, the doping amount of halogen is 1.00wt%-6.00wt% and the doping amount of aluminum is 0.05wt%-1.50wt%.

[0020] In some alternative embodiments, the halogen doping amount in the modified lithium sulfide is 1.5wt%-3.5wt%, and the aluminum doping amount is 0.1wt%-0.5%.

[0021] According to the acid-base theory, Li in Li₂S + For hard acid, S 2- As a soft alkali, Li₂S has low bonding strength and is easily hydrolyzed in air. To improve the water resistance of Li₂S, this invention proposes doping the lithium sulfide matrix with halogens and aluminum. Halogen doping, as a hard alkali, can improve the water resistance of Li₂S. + and S 2- The binding strength is reduced, decreasing the exchange capacity between lithium ions and protons in water molecules in the air, thus reducing hydrolysis and degradation reactions and improving air stability. It is worth noting that by controlling the appropriate doping amounts of halogens and aluminum, the air stability of the material and the ionic conductivity of the resulting sulfide solid electrolyte can be maximized. If the doping amount is too low, the improvement in the ionic conductivity of the resulting sulfide solid electrolyte is not significant; if it is too high, impurities will appear instead of doping, leading to deterioration of electrochemical performance.

[0022] In some alternative embodiments, the halogen includes at least one of Cl, Br, and F; Preferably, the halogen includes at least one element selected from Cl and Br, and the element F.

[0023] The modified lithium sulfide provided by this invention comprises: lithium sulfide and a doping element, wherein the doping element includes halogens and aluminum. Doping with a halogen (including at least one of Cl, Br, and F) as a hard base can improve the efficiency of Li... + and S 2- This increases the bonding strength, thereby improving the water resistance of modified lithium sulfide. In some preferred embodiments, the halogen includes F element, and one or more of Cl and Br. Due to the high electronegativity of F element, the chemical bond formed between the highly electronegative F element and lithium metal ions is more polar and has a higher bond energy, thus increasing the S content in lithium sulfide. 2- It is not easily hydrolyzed, and with the assistance of Cl and Br, it can form lithium sulfide with good stability and water resistance.

[0024] In some alternative embodiments, the modified lithium sulfide has the chemical formula Li. 2+y Al x SM y N3x M is at least one of Cl, Br, and I, N is F, the aluminum content is 0.05wt%-1.50wt%, and the total content of M and N is 1.00wt%-6.00wt%.

[0025] In some optional embodiments, the particle size distribution of the modified lithium sulfide particles is as follows: D10: 0.5 μm-1.3 μm; D50: 2.0 μm-5.0 μm; D90: 7.0 μm-14.0 μm, with a specific surface area of ​​0.5-10.0 m². 2 / g.

[0026] As can be seen from the above, by simultaneously doping lithium sulfide with halogens and aluminum, aluminum-halogen co-doped lithium sulfide is obtained, which greatly reduces the hydrolytic properties of lithium sulfide and avoids the reaction of trace amounts of moisture in the environment with lithium sulfide to release H2S gas and generate lithium oxides and hydroxides, thus effectively solving the problem of lithium sulfide's poor water resistance.

[0027] Secondly, the present invention provides a method for preparing the above-mentioned modified lithium sulfide, wherein the modified lithium sulfide is prepared by solid-state sintering.

[0028] In some alternative implementations, the following steps are included: S1 After mixing the raw materials, put them into the corundum crucible; S2 involves placing the corundum crucible into a tube furnace made of corundum material for high-temperature sintering; S3 ball mills the sintered material to obtain aluminum halide-doped modified lithium sulfide.

[0029] In some optional embodiments, the following steps are included: mixing anhydrous lithium sulfate powder, AlF3 and M source, and sintering under a reducing atmosphere to obtain modified lithium sulfide; Preferably, the purity of anhydrous lithium sulfate is ≥99.9%, and the M source includes chlorides of element M; Preferably, the mass ratio of anhydrous lithium sulfate, AlF3, and M source is 100:(0.1-3.5):(0.1-3.0); Preferably, the sintering process is as follows: the temperature is increased from room temperature to 800-1000℃ at a heating rate of 2-10℃ / min, held at 800-1000℃ for 3-8 hours, and then naturally cooled to room temperature. Preferably, in the sintering process, the reducing atmosphere is one or more of H2, CO, and NH3 as the reducing gas, and one or more of He, N2, and Ar as the carrier gas; Preferably, the process further includes: after high-temperature sintering, ball milling is performed, wherein the ball-to-material ratio of the ball milling process is 8:1-8:3, the ball milling speed is 400rpm-800rpm, and the ball milling time is 2h-8h.

[0030] In the preparation process of the modified lithium sulfide described above, anhydrous lithium sulfate, AlF3, and M source are used as raw materials. After mixing the raw materials, sintering is performed under a reducing atmosphere to obtain modified lithium sulfide. Anhydrous lithium sulfate is widely available and relatively inexpensive. It is reduced to lithium sulfide at high temperatures, and aluminum and halogen elements are incorporated into the lithium sulfide matrix, resulting in modified lithium sulfide with uniformly distributed doped elements. Due to the poor stability of lithium sulfide, aluminum oxide is not selected as a raw material. AlF3 can simultaneously increase both F and aluminum elements, making it a preferred raw material for preparing modified lithium sulfide. In addition, chlorides of raw materials containing Cl and Br are preferred. Sintering after mixing the selected raw materials can minimize the impact of impurities on the performance of lithium sulfide.

[0031] In some alternative embodiments, the following steps are included: mixing high-purity lithium sulfide powder, AlF3 and M source, and sintering under a protective gas atmosphere to obtain modified lithium sulfide; Preferably, the purity of high-purity lithium sulfide is ≥99.9%, and the M source includes chlorides of the M element; Preferably, the molar ratio of high-purity lithium sulfide, AlF3, and M source is 100:(0.5-1.5):(0.2-1.0).

[0032] Preferably, the sintering process is as follows: the temperature is increased from room temperature to 800-1000℃ at a heating rate of 2-10℃ / min, held at 800-1000℃ for 3-8 hours, and then naturally cooled to room temperature. Preferably, during the sintering process, the protective gas atmosphere is selected from one or more of He, N2, and Ar; Preferably, the process further includes: after high-temperature sintering, ball milling is performed, wherein the ball-to-material ratio of the ball milling process is 8:1-8:3, the ball milling speed is 400rpm-800rpm, and the ball milling time is 2h-8h.

[0033] In the preparation process of the above-mentioned modified lithium sulfide, high-purity lithium sulfide, AlF3, and M source are used as raw materials. After the raw materials are mixed, they are sintered under a protective gas atmosphere to obtain modified lithium sulfide. High-purity lithium sulfide is relatively expensive, but it has high purity. In the preparation process, aluminum and halogens are doped into the lithium sulfide matrix to obtain modified lithium sulfide with uniform distribution of doped elements.

[0034] Thirdly, the present invention provides an application of lithium sulfide, which is used as a cathode material for lithium-sulfur batteries or as a precursor for synthesizing sulfide solid electrolytes.

[0035] This invention provides a modified lithium sulfide, which can be used as a cathode material for lithium-sulfur batteries or as a precursor for synthesizing sulfide solid electrolytes. The modified lithium sulfide provided by this invention is obtained through aluminum halide co-doping, which significantly reduces the hydrolytic properties of lithium sulfide and improves its air stability. Using it as a cathode material for lithium-sulfur batteries or as a precursor for synthesizing sulfide solid electrolytes can reduce the stringent requirements for a dry environment (low humidity workshop, anhydrous solvent) in the preparation of sulfide solid electrolytes, thus reducing equipment investment and energy consumption. Furthermore, because the modified lithium sulfide contains dopant elements, the amount of some raw materials required in the preparation of sulfide solid electrolytes can be reduced.

[0036] Fourthly, the present invention provides a sulfide solid electrolyte, which is prepared using the modified lithium sulfide described above, or the modified lithium sulfide prepared by the above preparation method, as a precursor.

[0037] Using the modified lithium sulfide provided by this invention as a precursor, various sulfide solid electrolytes with different compositions can be prepared, such as LPS, LPSC, LGPS, and chloride-rich LPSC (e.g., Li). 5.4 PS 4.4 Cl 1.6 )wait.

[0038] For example, using the modified lithium sulfide, phosphorus pentasulfide, and lithium chloride as raw materials, a sulfide solid electrolyte Li6PS5Cl was prepared by mixing and sintering them in a specific ratio. The dual doping of halogen and aluminum elements in the modified lithium sulfide can increase the ion mixing ratio within the Li6PS5Cl crystal lattice, expand the ion channels, and thus improve the ionic conductivity and lithium stability of the Li6PS5Cl electrolyte system. Furthermore, larger-sized trace Al... 3+ To maintain charge balance, the partial substitution of higher-valence P ion sites in the sulfide Li6PS5Cl generates additional lithium vacancies during its preparation. These lattice defects cause slight lattice distortion, broadening the lithium content range. + The migration channel reduced Li + The improved migration energy enhances the lithium-ion conductivity. Furthermore, the improved water resistance of modified lithium sulfide allows for stable existence, resulting in high batch stability during the preparation of the solid electrolyte LiPSX. Its ionic conductivity is also significantly superior to that of LiPSX materials synthesized from conventional lithium sulfide.

[0039] Fifthly, the present invention provides a battery comprising the above-described sulfide solid electrolyte.

[0040] The present invention will be further described below with reference to embodiments.

[0041] Example 1 50g of anhydrous lithium sulfate (Li₂SO₄) with a purity of 99.9%, 0.5g of AlF₃, and 0.2g of anhydrous lithium chloride were ball-milled and mixed, then placed in an alumina crucible. The alumina crucible was placed in an alumina tube furnace, and nitrogen gas was introduced at a flow rate of 2L / min for 60 minutes to remove oxygen. After oxygen removal, the temperature was increased, and hydrogen gas was introduced into the tube at a flow rate of 2L / min. The heating curve was set to increase the temperature from room temperature to 950℃ at a rate of 5℃ / min, and then held at 950℃ for 6 hours before naturally cooling to room temperature. The reduced material was transferred to an agate-lined ball mill jar with a ball-to-material ratio of 8:1. The sealed ball mill jar was placed on a ball mill at a speed of 400 rpm for 8 hours to obtain aluminum halide-doped modified lithium sulfide. The particle size of the modified lithium sulfide prepared in Example 1 was tested using a dry particle size distribution method. The test results are shown in [link to relevant documentation]. Figure 1 The particle size distribution is as follows: D10: 0.778 μm; D50: 2.809 μm; D90: 12.86 μm, with a specific surface area of ​​4.3 m². 2 / g. See SEM image of modified lithium sulfide. Figure 2 .

[0042] The following are the preparation conditions and test results of Examples 1-4 and Comparative Examples 1-3. Among them, the test method for air stability is as follows: 1g of modified lithium sulfide was weighed and placed in a 1000mL sealed container after drying in a dry room with a dew point of -20℃. The concentration of hydrogen sulfide in the sealed container was measured after 1 hour.

[0043]

[0044] As can be seen from the table above, compared with pure lithium sulfide, modified lithium sulfide doped only with halogens, or modified lithium sulfide doped only with aluminum, the aluminum halide co-doped lithium sulfide prepared using the embodiments of the present invention has significantly improved air stability.

[0045] The XRF test results of the products prepared in the examples and comparative examples are shown in the table below:

[0046] As can be seen from the table above, the aluminum halide co-doped lithium sulfide prepared by the embodiments of the present invention contains Al and F elements, as well as Cl or Br in its lithium sulfide matrix, indicating that the present invention successfully doped Al and halogen elements into the lithium sulfide matrix.

[0047] Using the modified lithium sulfide prepared in Examples 1-4, the pure lithium sulfide prepared in Comparative Examples 1-3, the modified lithium sulfide doped only with halogens, or the modified lithium sulfide doped only with aluminum as raw materials, they were mixed with phosphorus pentasulfide and lithium chloride and sintered to prepare the sulfide solid electrolyte Li6PS5Cl. The ionic conductivity obtained is shown in the table below:

[0048] As can be seen from the table above, compared with Li6PS5Cl prepared from pure lithium sulfide, modified lithium sulfide doped only with halogens, or modified lithium sulfide doped only with aluminum, the Li6PS5Cl prepared from aluminum halide co-doped lithium sulfide prepared according to the embodiments of the present invention has a higher ionic conductivity than Li6PS5Cl prepared from pure lithium sulfide, modified lithium sulfide doped only with halogens, or modified lithium sulfide doped only with aluminum.

[0049] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A modified lithium sulfide, characterized in that, include: Lithium sulfide and doping elements, the doping elements including halogens and aluminum, wherein the doping amount of halogens is 1.00wt%-6.00wt% and the doping amount of aluminum is 0.05wt%-1.50wt% based on the total mass of the modified lithium sulfide.

2. The modified lithium sulfide according to claim 1, characterized in that, The halogen includes at least one of Cl, Br, and F; Preferably, the halogen includes at least one element selected from Cl and Br, and the element F.

3. The modified lithium sulfide according to claim 1, characterized in that, The modified lithium sulfide has the chemical formula Li. 2+ y Al x SM y N 3x M is at least one of Cl and Br, N is F, the aluminum content is 0.05wt%-1.50wt%, and the total content of doping elements M and N is 1.00wt%-6.00wt%.

4. The modified lithium sulfide according to any one of claims 1-3, characterized in that, The modified lithium sulfide particles have the following particle size distribution: D10: 0.5μm-1.3μm; D50: 2.0μm-5.0μm; D90: 7.0μm-14.0μm, with a specific surface area of ​​0.5-10.0m². 2 / g.

5. A method for preparing modified lithium sulfide according to any one of claims 1-4, characterized in that, The modified lithium sulfide was prepared by solid-state sintering.

6. The preparation method according to claim 5, characterized in that, Includes the following steps: Anhydrous lithium sulfate powder, AlF3 and M source were mixed and sintered under a reducing atmosphere to obtain the modified lithium sulfide. Preferably, the anhydrous lithium sulfate has a purity of ≥99.9%, and the M source includes chlorides of element M; Preferably, the mass ratio of anhydrous lithium sulfate, AlF3, and M source is 100:(0.1-3.5):(0.1-3.0); Preferably, the sintering process is as follows: the temperature is increased from room temperature to 800-1000℃ at a heating rate of 2-10℃ / min, held at 800-1000℃ for 3-8 hours, and then naturally cooled to room temperature. Preferably, in the sintering process, the reducing atmosphere is one or more of H2, CO, and NH3 as the reducing gas, and one or more of He, N2, and Ar as the carrier gas; Preferably, the process further includes: after high-temperature sintering, ball milling is performed, wherein the ball-to-material ratio of the ball milling process is 8:1-8:3, the ball milling speed is 400rpm-800rpm, and the ball milling time is 2h-8h.

7. The preparation method according to claim 5, characterized in that, Includes the following steps: High-purity lithium sulfide powder, AlF3 and M source are mixed and sintered under a protective gas atmosphere to obtain the modified lithium sulfide. Preferably, the high-purity lithium sulfide has a purity of ≥99.9%, and the M source includes chlorides of the M element; Preferably, the mass ratio of high-purity lithium sulfide, AlF3, and M source is 100:(0.5-1.5):(0.2-1.0); Preferably, the sintering process is as follows: the temperature is increased from room temperature to 800-1000℃ at a heating rate of 2-10℃ / min, held at 800-1000℃ for 3-8 hours, and then naturally cooled to room temperature. Preferably, in the sintering process, the protective gas atmosphere is selected from one or more of He, N2, and Ar; Preferably, the process further includes: after high-temperature sintering, ball milling is performed, wherein the ball-to-material ratio of the ball milling process is 8:1-8:3, the ball milling speed is 400rpm-800rpm, and the ball milling time is 2h-8h.

8. An application of modified lithium sulfide, characterized in that, The modified lithium sulfide is used as a precursor for lithium-sulfur battery cathode materials or for synthesizing sulfide solid electrolytes, wherein the modified lithium sulfide is the modified lithium sulfide according to any one of claims 1-4.

9. A sulfide solid electrolyte, characterized in that, It is prepared using modified lithium sulfide as a precursor according to any one of claims 1-4.

10. A battery, characterized in that, Includes the sulfide solid electrolyte as described in claim 9.

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