Preparation method and application of lithium sulfide

Abstract

The invention provides a preparation method and application of lithium sulfide. The preparation method comprises the following steps: reacting a lithium source with a sulfur source; the lithium source is a solid lithium-containing substance with the purity of 99% or above and the whiteness of 86 or above; the solid lithium-containing substance is selected from one or more of anhydrous lithium hydroxide, lithium hydroxide monohydrate, lithium carbonate, lithium chloride, lithium bromide and lithium nitrate. According to the method, a solid lithium-containing substance with the purity of 99% or above and the whiteness of 86 or above is used as a lithium source and reacts with a sulfur source, and the ionic conductivity value of the Li6PS5Cl solid electrolyte prepared from the obtained lithium sulfide is stable. Experimental results show that the ionic conductivity can stably reach more than 2mS / cm.

Description

Technical Field

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

[0002] In recent years, with the rapid development of new energy electric vehicles, the problems of short battery life, long charging times, and poor safety of traditional liquid lithium-ion batteries have gradually become apparent, hindering the further development of the electric vehicle market. All-solid-state batteries, due to their use of non-flammable solid electrolytes, can effectively address safety issues and significantly increase battery energy density through the use of lithium anodes. They also have a wide operating temperature range, excellent safety, and long cycle life, making them considered one of the most promising battery technologies. Among them, sulfide solid electrolytes, as a key component of all-solid-state batteries, have become the most promising technology route due to their high ionic conductivity, easy processing, and good electrochemical stability.

[0003] The ionic conductivity of the solid electrolyte directly determines the charge and discharge rate and power density of solid-state batteries, and is a crucial parameter for solid-state battery performance. Whether its room-temperature ionic conductivity reaches 1mS / cm is one of the core indicators that determine its commercialization. However, when preparing solid electrolytes, the ionic conductivity of the electrolyte obtained by the reaction is sometimes low and the value is unstable, which seriously affects the charge and discharge capacity and rate performance of solid-state batteries, greatly limiting their application. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a method for preparing lithium sulfide and its application. The method uses a solid lithium-containing material with a purity of more than 99% and a whiteness of more than 86 to react with a sulfur source to prepare lithium sulfide having a high ionic conductivity and a stable value of more than 2mS / cm.

[0005] Lithium sources such as high-white lithium hydroxide not only have fewer impurities, but also have high crystallinity and fewer microstructural defects. When synthesizing lithium sulfide, the reaction is more uniform, avoiding local over-reaction or unreacted areas. When preparing downstream sulfide solid electrolytes, it helps to reduce grain boundary resistance and improve ion conduction efficiency.

[0006] The present invention provides a method for preparing lithium sulfide, comprising reacting a lithium source and a sulfur source;

[0007] The lithium source is a solid lithium-containing material with a purity of more than 99% and a whiteness of more than 86;

[0008] The solid lithium-containing material is selected from one or more of anhydrous lithium hydroxide, lithium hydroxide monohydrate, lithium carbonate, lithium chloride, lithium bromide and lithium nitrate.

[0009] Preferably, the whiteness of the lithium source is 86.5-94.

[0010] Preferably, the sulfur source is selected from one or more of hydrogen sulfide, carbon disulfide, ammonium sulfide and sodium sulfide.

[0011] Preferably, the molar ratio of lithium in the lithium source to sulfur in the sulfur source is 1:(0.5-80).

[0012] Preferably, the reaction temperature is 35 to 750° C., and the reaction time is 1 to 13 hours.

[0013] Preferably, the reaction is a dry reaction;

[0014] The temperature of the dry reaction is 350-750°C. When the reaction temperature is lower than 350°C, amorphous or low-crystallinity lithium sulfide is easily generated, and the reaction is incomplete. When the reaction temperature is higher than 750°C, the grains of the lithium sulfide sample will coarsen, reducing its specific surface area, and high corrosion resistance requirements will be placed on the equipment. The reaction time is 1-8h. When the reaction time is less than 1h, the problem of raw material residue is likely to occur. When the reaction time exceeds 8h, the lithium sulfide grains will grow excessively and the specific surface area will decrease, thereby affecting the performance of downstream applications.

[0015] Preferably, the reaction is a wet reaction;

[0016] The temperature of the wet reaction is 35 to 210°C. When the reaction temperature is lower than 35°C, the reaction rate is slow, which will significantly extend the reaction time. Impurities are easily wrapped in lithium sulfide particles and are difficult to separate. When the reaction temperature is higher than 210°C, side reactions will intensify, resulting in reduced product purity and higher requirements for equipment corrosion resistance. The time is 2 to 13h. When the reaction time is less than 2h, the reaction raw materials cannot be fully converted and the yield is reduced. When the reaction time is higher than 13h, long-term stirring will cause particle aggregation, increase the risk of oxidation, generate impurities such as Li2SO3 / Li2SO4, and increase production costs.

[0017] Preferably, the solvent used in the wet reaction is selected from one or more of tetrahydrofuran, ethylene glycol dimethyl ether, 1,4-dioxane, n-hexane, cyclohexane, N-methylpyrrolidone, dimethylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, sulfolane, methanol, ethanol, isopropanol, ethylene glycol, toluene, ethylbenzene and xylene. The appropriate solvent should be selected by comprehensively considering factors such as the solubility, boiling point, toxicity, chemical stability and economy of the solvent.

[0018] Preferably, the purity of the sulfur source is above 99%.

[0019] The present invention provides a solid electrolyte for lithium-ion batteries, and the raw materials for preparing the solid electrolyte include lithium sulfide prepared by the preparation method described in the above technical solution.

[0020] The present invention provides a method for preparing lithium sulfide, comprising reacting a lithium source with a sulfur source; the lithium source is a solid lithium-containing material with a purity of 99% or greater and a whiteness of 86 or greater; the solid lithium-containing material is selected from one or more of anhydrous lithium hydroxide, lithium hydroxide monohydrate, lithium carbonate, lithium chloride, lithium bromide, and lithium nitrate. This method uses a solid lithium-containing material with a purity of 99% or greater and a whiteness of 86 or greater as the lithium source, and reacts it with a sulfur source. The resulting Li6PS5Cl solid electrolyte exhibits stable ionic conductivity. Experimental results demonstrate that the ionic conductivity can consistently reach above 2 mS / cm. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the XRD spectrum of lithium sulfide prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0022] The present invention provides a method for preparing lithium sulfide, comprising reacting a lithium source and a sulfur source;

[0023] The lithium source is a solid lithium-containing material with a purity of more than 99% and a whiteness of more than 86;

[0024] The solid lithium-containing material is selected from one or more of anhydrous lithium hydroxide, lithium hydroxide monohydrate, lithium carbonate, lithium chloride, lithium bromide and lithium nitrate.

[0025] The present invention uses a solid lithium source with a purity of more than 99% and a whiteness of more than 86 to react with a sulfur source to prepare lithium sulfide for preparing a sulfide solid electrolyte. The ionic conductivity of the lithium sulfide solid electrolyte can stably reach more than 2mS / cm, meeting the requirements of commercial applications. When the purity of the lithium source reaches more than 99%, the whiteness is determined to be a key indicator affecting the stability of the ionic conductivity.

[0026] In the present invention, the whiteness of the lithium source is preferably 86-94, more preferably 86.5-94.

[0027] The lithium source is selected from one or more of anhydrous lithium hydroxide with a purity of 99% and a whiteness of 86.1, lithium carbonate with a purity of 99% and a whiteness of 88.3, anhydrous lithium hydroxide with a purity of 99.5% and a whiteness of 91.8, anhydrous lithium hydroxide with a purity of 99.5% and a whiteness of 92.1, lithium chloride with a purity of 99% and a whiteness of 86.7, anhydrous lithium hydroxide with a purity of 99.5% and a whiteness of 93.4, anhydrous lithium hydroxide with a purity of 99.5% and a whiteness of 91.5, and lithium hydroxide monohydrate with a purity of 99% and a whiteness of 89.2.

[0028] The sulfur source in the present invention is selected from one or more of hydrogen sulfide, carbon disulfide, ammonium sulfide, and sodium sulfide. The sulfur source preferably has a purity of 99% or greater, more preferably 99.9% or greater. The flow rate of the hydrogen sulfide is 1 to 17 L / min.

[0029] In the present invention, the molar ratio of lithium in the lithium source to sulfur in the sulfur source is 1:(0.5-80). Specifically, it can be 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, 1:21, 1:22, 1:23, 1:24, 1:25, 1:26, 1:27, 1:28, 1:29, 1:30, 1:31, 1:32, 1:33, 1:34, 1:35, 1:36, 1:7, 1:8, 1:9, 1:40, 1:41, 1:42, 1:43, 1:44, 1:45, 1:46, 1:47, 1:8, 1:49, 1:50, 1:51, 1:52, 1:53, 1:54, 1:55, 1:56, 1:57, 1:58, 1:59, 1:60, 1:61, 1:62, 1:63, 1:64, 1:65, 1:66, 1:67, 1:68, 1:69, 1:70, 1:71, 1:72, 1:73, 1:74, 1:75, 1:76, 1:77, 1:78, 1:79, or 1:80.

[0030] In the present invention, the reaction temperature is 35 to 750° C., and the reaction time is 1 to 13 hours.

[0031] The reaction described in the present invention is a dry reaction, and the temperature of the dry reaction is 350-750°C. When the reaction temperature is lower than 350°C, amorphous or low-crystallinity lithium sulfide is easily generated, and the reaction is incomplete; when the reaction temperature is higher than 750°C, the grains of the lithium sulfide sample will coarsen, reducing its specific surface area, and high corrosion resistance requirements will be placed on the equipment; the reaction time is 1-8h. When the reaction time is less than 1h, the problem of raw material residue is likely to occur; and when the reaction time exceeds 8h, the lithium sulfide grains will grow excessively, the specific surface area will decrease, and thus affect the downstream application performance.

[0032] Preferably, the reaction is a wet reaction;

[0033] The temperature of the wet reaction is preferably 35-210°C. When the reaction temperature is lower than 35°C, the reaction rate is slow, which will significantly extend the reaction time. Impurities are easily wrapped in lithium sulfide particles and are difficult to separate. When the reaction temperature is higher than 210°C, side reactions will intensify, resulting in reduced product purity and higher requirements for equipment corrosion resistance. The reaction time is preferably 2-13h. When the reaction time is less than 2h, the reaction raw materials cannot be fully converted and the yield is reduced. When the reaction time is higher than 13h, long-term stirring will cause particle aggregation, increase the risk of oxidation, generate impurities such as Li2SO3 / Li2SO4, and increase production costs.

[0034] Preferably, the solvent used in the wet reaction is selected from one or more of tetrahydrofuran, ethylene glycol dimethyl ether, 1,4-dioxane, n-hexane, cyclohexane, N-methylpyrrolidone, dimethylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, sulfolane, methanol, ethanol, isopropanol, ethylene glycol, toluene, ethylbenzene and xylene. The appropriate solvent should be selected by comprehensively considering factors such as the solubility, boiling point, toxicity, chemical stability and economy of the solvent.

[0035] Preferably, the purity of the sulfur source is above 99%.

[0036] The present invention provides a solid electrolyte for lithium-ion batteries, and the raw materials for preparing the solid electrolyte include lithium sulfide prepared by the preparation method described in the above technical solution.

[0037] The solid electrolyte composed of Li6PS5Cl was prepared by referring to the method for preparing a solid electrolyte in patent CN119735171A. The specific steps are as follows:

[0038] Step 1: Under a dry argon atmosphere, weigh raw materials according to the composition ratio of the above solid electrolyte and place them in a ball mill; the raw materials are lithium sulfide, phosphorus pentasulfide, and lithium chloride;

[0039] Step 2: heat-treating the powder obtained after ball milling in step 1 under the protection of a dry inert atmosphere, while introducing an inert gas; the inert gas includes but is not limited to one of high-purity nitrogen and argon;

[0040] 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.

[0041] Furthermore, the ball milling conditions in step 1 are: ball-to-material mass ratio is (3-10):1, rotation speed is 500-1000 rpm, and ball milling time is 5-12 h.

[0042] Furthermore, the heat treatment equipment in step 2 can be selected from a muffle furnace or a tube furnace, with a treatment temperature of 400-600° C. and a treatment time of 4-12 hours.

[0043] The sulfide solid electrolyte obtained above was press-formed at a pressure of 300 MPa and then cold isostatically pressed (CP) at a pressure of 200 MPa to produce pellets with a diameter of 8 mm and a thickness of 1 mm. Following conventional methods, the pellets were directly surface-sprayed with gold for 30 seconds and then heat-treated at 180°C for 30 minutes to prepare samples for lithium ion conductivity measurement. Lithium ion conductivity was measured using an AC impedance spectroscopy method at 25°C.

[0044] In order to further illustrate the present invention, the preparation method of lithium sulfide and its application provided by the present invention are described in detail below with reference to the examples, but they should not be construed as limiting the scope of protection of the present invention.

[0045] The whiteness was measured using an UltraScan PRO HunterLab colorimeter.

[0046] Example 1

[0047] In a quartz glass reactor protected by an argon atmosphere, 100 g of anhydrous lithium hydroxide with a purity of 99% and a whiteness of 86.1 was added, the temperature was raised to 350°C, and hydrogen sulfide with a content of 99.9% was introduced at a hydrogen sulfide flow rate of 17 L / min. The reaction was carried out for 8 hours. The XRD pattern of the obtained lithium sulfide sample is shown as follows: Figure 1 shown.

[0048] Example 2

[0049] In a quartz glass reactor protected by an argon atmosphere, 100 g of lithium carbonate with a purity of 99% and a whiteness of 88.3 was added, the temperature was raised to 750°C, and hydrogen sulfide with a content of 99.9% was introduced at a hydrogen sulfide flow rate of 11 L / min. The reaction was carried out for 1 hour. The obtained sample was lithium sulfide.

[0050] Example 3

[0051] In a quartz glass reactor protected by an argon atmosphere, 100 g of anhydrous lithium hydroxide with a purity of 99.5% and a whiteness of 91.8 was added, the temperature was raised to 550°C, and hydrogen sulfide with a content of 99.9% was introduced at a hydrogen sulfide flow rate of 2 L / min. The reaction was carried out for 4 hours. The resulting sample was lithium sulfide.

[0052] Example 4

[0053] In a quartz glass reactor protected by an argon atmosphere, 100 g of anhydrous lithium hydroxide with a purity of 99.5% and a whiteness of 92.1 was added, the temperature was raised to 550°C, and hydrogen sulfide with a content of 99.9% was introduced at a hydrogen sulfide flow rate of 2 L / min. The reaction was carried out for 4 hours. The resulting sample was lithium sulfide.

[0054] Example 5

[0055] Under the protection of an argon atmosphere, 100 g of lithium chloride with a purity of 99% and a whiteness of 86.7 was weighed and dissolved in 1 L of anhydrous ethanol. 92 g of anhydrous sodium sulfide was weighed and dissolved in 500 mL of anhydrous ethanol. The two solutions were mixed and stirred. The reaction temperature was set to 35°C and the reaction time was 13 h to obtain a suspension. The filtrate was evaporated to dryness and washed with N-methylpyrrolidone, filtered, and washed three times. The solid product was vacuum dried to obtain a lithium sulfide product. The experiment was carried out in a glove box with an argon atmosphere, and the obtained sample was lithium sulfide.

[0056] Example 6

[0057] In a stainless steel reactor under argon atmosphere, 100 g of anhydrous lithium hydroxide with a purity of 99.5% and a whiteness of 93.4 and 500 g of xylene were added, the temperature was raised to 120° C., and hydrogen sulfide with a content of 99.9% was introduced at a hydrogen sulfide flow rate of 1 L / min. After reacting for 7 hours, the reaction was filtered to obtain a sample of lithium sulfide.

[0058] Example 7

[0059] In a stainless steel reactor protected by an argon atmosphere, 100 g of anhydrous lithium hydroxide with a purity of 99.5% and a whiteness of 91.5 and 500 g of xylene were added, the temperature was raised to 120° C., and hydrogen sulfide with a content of 99.9% was introduced at a hydrogen sulfide flow rate of 1 L / min. After reacting for 7 hours, the reaction was filtered to obtain a sample of lithium sulfide.

[0060] Example 8

[0061] In a stainless steel reactor under argon atmosphere, 100 g of lithium hydroxide monohydrate with a purity of 99% and a whiteness of 89.2 and 500 g of N-methylpyrrolidone were added, the temperature was raised to 210° C., and hydrogen sulfide with a content of 99.9% was introduced at a flow rate of 4 L / min. After reacting for 2 hours, the reaction was filtered to obtain a lithium sulfide sample.

[0062] Comparative Example 1

[0063] In a quartz glass reactor protected by an argon atmosphere, 100 g of anhydrous lithium hydroxide with a purity of 99% and a whiteness of 82.8 was added, the temperature was raised to 350°C, and hydrogen sulfide with a content of 99.9% was introduced at a hydrogen sulfide flow rate of 17 L / min. The reaction was carried out for 8 hours. The obtained sample was lithium sulfide.

[0064] Comparative Example 2

[0065] 100 g of lithium carbonate with a purity of 99% and a whiteness of 80.2 was added to a quartz glass reactor under argon atmosphere, the temperature was raised to 750°C, and hydrogen sulfide with a content of 99.9% was introduced at a hydrogen sulfide flow rate of 11 L / min. The reaction was carried out for 1 hour. The obtained sample was lithium sulfide.

[0066] Comparative Example 3

[0067] Under the protection of an argon atmosphere, 100 g of lithium chloride with a purity of 99% and a whiteness of 75.6 was weighed and dissolved in 1 L of anhydrous ethanol. 92 g of anhydrous sodium sulfide was weighed and dissolved in 500 mL of anhydrous ethanol. The two solutions were mixed and stirred. The reaction temperature was set to 35°C and the reaction time was 13 h to obtain a suspension. The filtrate was evaporated to dryness and washed with N-methylpyrrolidone, filtered, and washed three times. The solid product was vacuum dried to obtain a lithium sulfide product. The experiment was carried out in a glove box with an argon atmosphere, and the obtained sample was lithium sulfide.

[0068] Application Examples

[0069] Using the lithium sulfide prepared in the examples and comparative examples as a raw material, a solid electrolyte having a composition of Li6PS5C1 was manufactured by the following method, and its ionic conductivity was measured.

[0070] Based on the elemental composition of Li6PS5Cl1, lithium sulfide powder, phosphorus pentasulfide powder (99.9%, Aldrich), and lithium chloride powder (99.9%, Aldrich) were weighed in a glove box to a total of 50g. Zirconia balls (300g) were added and sealed in a 1L ball mill. The mixture was milled at 800 rpm for 8 hours. The resulting precursor powder was sintered in a muffle furnace at 450°C for 8 hours. The resulting Li6PS5Cl powder was then packaged and stored in a glove box (O2 <0.1ppm, H2O <0.1ppm).

[0071] The sulfide solid electrolyte obtained above was press-formed at a pressure of 300 MPa and then cold isostatically pressed (CP) at a pressure of 200 MPa to produce pellets with a diameter of 8 mm and a thickness of 1 mm. Following conventional methods, the pellets were directly surface-sprayed with gold for 30 seconds and then heat-treated at 180°C for 30 minutes to prepare samples for lithium ion conductivity measurement. Lithium ion conductivity was measured using an AC impedance spectroscopy method at 25°C.

[0072] The final measured lithium ion conductivity data of the sulfide solid electrolyte are shown in Table 1.

[0073] Table 1

[0074]

[0075]

[0076] As shown in the above examples, when the purity of the lithium source reaches above 99%, the ionic conductivity of lithium sulfide and then solid electrolyte prepared from it still fluctuates significantly. When the whiteness reaches above 86, the ionic conductivity can reach above 2mS / cm, which has commercial application value. For the same lithium source, higher purity corresponds to higher ionic conductivity of the corresponding solid electrolyte, and for lithium source of the same purity, higher whiteness corresponds to higher ionic conductivity.

[0077] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing lithium sulfide, comprising reacting a lithium source and a sulfur source; The lithium source is a solid lithium-containing material with a purity of more than 99% and a whiteness of more than 86; The solid lithium-containing material is selected from one or more of anhydrous lithium hydroxide, lithium hydroxide monohydrate, lithium carbonate, lithium chloride, lithium bromide and lithium nitrate.

2. The preparation method according to claim 1, characterized in that The whiteness of the lithium source is 86.5-94.

3. The preparation method according to claim 1, characterized in that The sulfur source is selected from one or more of hydrogen sulfide, carbon disulfide, ammonium sulfide and sodium sulfide.

4. The preparation method according to claim 1, characterized in that The molar ratio of lithium in the lithium source to sulfur in the sulfur source is 1:(0.5 to 80).

5. The preparation method according to claim 1, characterized in that The reaction temperature is 35 to 750° C., and the reaction time is 1 to 13 hours.

6. The preparation method according to claim 1, characterized in that The reaction is a dry process. The dry reaction temperature is 350-750°C and the reaction time is 1-8 hours.

7. The preparation method according to claim 1, characterized in that The reaction is a wet process reaction; The temperature of the wet reaction is 35 to 210° C., and the time is 2 to 13 hours.

8. The preparation method according to claim 7, characterized in that The solvent used in the wet reaction is selected from one or more of tetrahydrofuran, ethylene glycol dimethyl ether, 1,4-dioxane, n-hexane, cyclohexane, N-methylpyrrolidone, dimethylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, sulfolane, methanol, ethanol, isopropanol, ethylene glycol, toluene, ethylbenzene and xylene.

9. The preparation method according to claim 1, characterized in that The purity of the sulfur source is above 99%.

10. A solid electrolyte for lithium-ion batteries, wherein the raw materials for preparation include lithium sulfide prepared by the preparation method according to any one of claims 1 to 9.

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