Lithium sulfide and preparation method and application thereof

Abstract

The invention provides lithium sulfide as well as a preparation method and application thereof. The preparation method of the lithium sulfide comprises the following steps: providing a mixed solution containing a lithium-containing compound and liquid sulfur which are uniformly mixed, and enabling the mixed solution to be in contact with a reducing gas so as to carry out a lithium sulfide synthesis reaction, after the synthesis reaction of the lithium sulfide is finished, at least removing part of sulfur in the obtained reaction mixture to obtain a crude finished product; and calcining the crude finished product to convert lithium polysulfide in the crude finished product into lithium sulfide to obtain a lithium sulfide product. According to the preparation method provided by the invention, the high-purity lithium sulfide is prepared by a one-pot method, the liquid sulfur is used as a reaction raw material and a reaction solvent, and the whole reaction process does not need to use an organic solvent; according to the method, the lithium salt conversion rate can reach 99% or above, and the purity of the obtained lithium sulfide can reach 99.99% or above; compared with the prior art, the reaction temperature is lower, and low energy consumption and high conversion rate are both considered.

Description

Technical Field

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

[0002] Lithium-sulfur batteries (Li-S) have high theoretical specific capacity (1675 mAh / g) and theoretical energy density (≈2600Wh / kg), and the raw materials have the advantages of low cost (sulfur cost ≈ $0.1 / kg) and abundant reserves. They are considered to be one of the most promising candidates for the next generation of rechargeable batteries. Lithium sulfide (Li2S) is the positive electrode material of lithium-sulfur batteries. The demand for it will be huge in the future, and all-solid-state lithium-sulfur batteries will require more lithium sulfide products. In addition, sulfide solid electrolytes have the advantages of high ionic conductivity, high energy density, low hardness and easy processing. They are the preferred materials for flexible all-solid-state batteries. Lithium sulfide (Li2S) is the key precursor material for synthesizing sulfur-based solid electrolytes and the main raw material for preparing sulfide solid electrolytes, so the market prospects are huge.

[0003] At present, the preparation methods of lithium sulfide (Li2S) can be roughly divided into solid phase ball milling method, liquid phase reaction method, high temperature / high pressure method and thermal reduction method.

[0004] The principle of the solid-phase ball milling method is to mix elemental sulfur and metallic lithium / lithium hydride under an inert atmosphere and then perform a mechanical ball milling reaction to obtain lithium sulfide. This method is relatively simple, environmentally friendly, and does not produce any waste liquid; however, it has disadvantages such as high raw material prices, low conversion rates, and difficulty in scaling up the reactor, which is not conducive to industrial production.

[0005] The principle of the liquid phase reaction method is to prepare lithium sulfide by mixing lithium / lithium-containing (organic) compounds and sulfur / sulfur-containing compounds (such as H2S, etc.) in a liquid medium. The liquid medium can be an organic solvent or liquid ammonia, wherein the organic solvent includes aliphatic hydrocarbons, aromatic hydrocarbons, alcohols or ethers, etc. This method has the advantages of full reaction and no need for high temperature treatment. The disadvantage is that the introduced organic solvent has a strong binding force with lithium sulfide and is difficult to remove. In the subsequent purification process, impurities such as lithium oxide are easily produced, the product purity is low, the preparation cost is high, and the stability of intermittent operation batches is poor.

[0006] The principle of the high temperature / high pressure method is to prepare lithium sulfide by reacting lithium / lithium-containing compounds and sulfur / sulfur-containing compounds in liquid or gas phases under the protection of an inert / reducing atmosphere at high temperature / high pressure. The advantages of this method are simple process flow, no generation of harmful gases, and a short preparation process. The disadvantages are that the working condition control is difficult and the equipment selection requirements are high, which is not conducive to industrial application.

[0007] The pyrolysis reduction method is usually prepared by reacting lithium sulfide precursors (one or more of lithium sulfate, lithium sulfite, lithium bisulfate, and lithium dithionate) with relevant reducing agents under high temperature conditions. The core step of this method is that lithium salts (such as lithium sulfate, etc.) are reduced by carbon or carbon-containing compounds (such as sugar, etc.) at high temperatures, and solid-phase ball milling is used for mixing. Its advantages are that the raw materials are easy to obtain, the operation is simple, and the crude products in the intermediate steps are convenient for storage and transportation. It is especially suitable for the one-step preparation of lithium sulfide / carbon composite materials. Its disadvantages are insufficient solid-phase reaction, high temperature and high energy, and emission of greenhouse gas carbon dioxide, and the introduction of certain metal ion impurities, which affects product quality.

[0008] In summary, the process for preparing lithium sulfide in the prior art has the disadvantages of high raw material cost, harsh high temperature and high pressure conditions, difficulty in removing organic solvents, difficulty in separating metal ions, difficulty in separating lithium oxide impurities, long purification process, high construction investment, high energy consumption and easy generation of greenhouse gases. These have caused the preparation cost of lithium sulfide to remain high, with commercial lithium sulfide reaching 12,000 yuan / kg, which has seriously restricted the research and development and industrial application development of downstream sulfide solid electrolytes and lithium-sulfur battery positive electrode materials. Therefore, it is an urgent problem for those skilled in the art to develop a low-cost, high-efficiency, safe and controllable green preparation method, and a preparation process that is easy to industrialize on a large scale. Summary of the invention

[0009] In order to solve all or part of the above technical problems, the present invention provides the following technical solutions: One of the objects of the present invention is to provide a method for preparing lithium sulfide, comprising: Providing a mixed solution containing a uniformly mixed lithium-containing compound and liquid sulfur, and contacting the mixed solution with a reducing gas to perform a lithium sulfide synthesis reaction; After the lithium sulfide synthesis reaction is completed, at least part of the sulfur in the obtained reaction mixture is removed to obtain a crude product; The crude product is calcined to convert the lithium polysulfide in the crude product into lithium sulfide to obtain a lithium sulfide product.

[0010] The preparation method provided by the present invention realizes the "one-pot method" to prepare high-purity lithium sulfide products, wherein the liquid sulfur is used as both a reaction raw material and a reaction solvent, and no organic solvent is required in the entire reaction process. The lithium salt conversion rate of this method is relatively high, which can reach more than 99%; and the required reaction temperature is relatively low, taking into account both low energy consumption and high conversion rate, and it is economical, which is an important path to realize the industrialization of lithium sulfide at low cost. In addition, the method provided by the present invention converts the mixed lithium polysulfide therein into lithium sulfide by calcining and purifying the crude product, and obtains a lithium sulfide product with a purity of more than 99.99%. The purification method does not require the use of organic solvents, which solves the problem that the method of using organic solvent redissolution and filtration in the prior art is prone to generate lithium oxide, resulting in a decrease in product purity.

[0011] In some embodiments, the method specifically includes: passing dry protective gas into liquid sulfur to form continuous bubbling, and adding dry lithium-containing compounds to the liquid sulfur in batches to form the mixed solution; and contacting the mixed solution with dry reducing gas to carry out the lithium sulfide synthesis reaction. The introduction of water is avoided during the entire reaction process, thereby reducing the hydrolysis of the product and improving the purity and yield of the product.

[0012] In some embodiments, the method specifically includes: under a pressure condition of 0~-0.01MPaG, the temperature of the liquid sulfur is controlled at 130°C~160°C, then a dry protective gas is introduced into the liquid sulfur to form continuous bubbling, and a dry lithium-containing compound is added to the liquid sulfur in batches to form the mixed solution; and the mixed solution is contacted with a dry reducing gas to carry out the lithium sulfide synthesis reaction.

[0013] In some typical embodiments, the amount of the protective gas introduced is 0.1-1 L / min / 100 ml of the mixed liquid, preferably 0.3-0.6 L / min / 100 ml of the mixed liquid. The protective gas includes, for example, nitrogen, but is not limited thereto. For example, a sulfur condenser is provided to control the temperature of the liquid sulfur within the range of 130° C. to 160° C.

[0014] In some embodiments, the feeding speed of the lithium-containing compound is 2-10 g / min / 100 ml of reaction solution. If the feeding speed of the lithium-containing compound is too fast, the heat generated by the dissolution of the lithium-containing compound will cause the local temperature to rise, and the material will clump, which is not conducive to dissolution; if the local temperature is too high, for example, exceeding 180°C, the vaporization amount of the solvent sulfur will increase, and the energy consumption load of the condenser will increase.

[0015] In some implementations, during the process of adding the lithium-containing compound to the liquid sulfur, the pressure of the system is controlled to be normal pressure or slightly negative pressure, and the pressure of the slightly negative pressure is less than 0 and greater than or equal to -0.01 MPaG.

[0016] In some embodiments, the reaction temperature of the lithium sulfide synthesis reaction is 130° C. to 300° C. Compared with the high temperature conditions of 600° C. or above required by the prior art, the reaction temperature of the present method is significantly lower than the temperature required by the prior art, taking into account both low energy consumption and high conversion rate.

[0017] In some embodiments, the reaction time of the lithium sulfide synthesis reaction is 1 to 5 hours. Alternatively, the water content in the tail gas generated by the reaction is detected during the reaction, and when the water content in the tail gas is less than 100 ppm, the lithium sulfide synthesis reaction is terminated.

[0018] In some embodiments, the pressure of the lithium sulfide synthesis reaction is normal pressure or slightly negative pressure, and the pressure of the slightly negative pressure is less than 0 and greater than or equal to -0.01 MPaG.

[0019] In some preferred embodiments, the pressure when the lithium-containing compound is added to the liquid sulfur and / or the pressure of the lithium sulfide synthesis reaction is preferably slightly negative pressure, because the synthesis reaction is accompanied by the by-production of water vapor, and the product and water will be hydrolyzed to generate lithium oxide and hydrogen sulfide. The slightly negative pressure helps to guide and accelerate the airflow to carry away moisture, thereby maintaining a high product yield and high purity.

[0020] In some embodiments, the reducing gas is introduced into the mixed solution at a rate of 0.1 to 1.0 L / min / 100 ml of the mixed solution, so that the mixed solution is in contact with the reducing gas, and preferably the introduction rate is 0.3 to 0.8 L / min / 100 ml of the mixed solution. If the introduction rate of the reducing gas is low, the reaction is slow, and the generated water vapor cannot be discharged smoothly, resulting in increased side reactions and reduced product yields; if the introduction rate of the reducing gas is high, the utilization rate of the reducing gas is low, and the reaction temperature rises quickly, the sulfur carried away increases, and the viscosity of the reaction system increases, resulting in uneven reaction.

[0021] In some embodiments, the mass concentration of the lithium-containing compound is 5wt%~50wt% of the total mass of the lithium-containing compound and the liquid sulfur, and preferably 10wt%~30wt%.

[0022] In some embodiments, the mixed solution does not contain an organic solvent. That is, the preparation method provided by the present invention does not require the use of an organic solvent throughout the entire process (including the synthesis process and the purification process), thereby solving the problem that the organic solution introduced in the prior art has a strong binding force with lithium sulfide, is difficult to remove, and is prone to produce impurities such as lithium oxide in the subsequent purification process.

[0023] In some embodiments, the lithium-containing compound includes one or a combination of lithium hydroxide, lithium carbonate, lithium o-benzoylsulfonyl imide, and lithium bis(fluorosulfonyl)imide, but is not limited thereto.

[0024] In some embodiments, the reducing gas includes one or a combination of hydrogen and hydrogen sulfide, but is not limited thereto.

[0025] Furthermore, in an embodiment where the reducing gas is a mixed gas of hydrogen and hydrogen sulfide, the weight proportion of the hydrogen is greater than 25%.

[0026] In some embodiments, the amount of reducing gas introduced during the lithium sulfide synthesis reaction is such that the molar ratio of the total amount of hydrogen in the reducing gas to the total amount of lithium in the lithium-containing compound is X, and when X≤1 (i.e., the total amount of reducing gas introduced during the entire reaction process is X≤1), the reaction temperature is controlled at 130° C. to 160° C. When the total amount of hydrogen introduced during the entire synthesis process is relatively insufficient, the lithium sulfide yield is about 70%.

[0027] In some embodiments, the amount of reducing gas introduced during the lithium sulfide synthesis reaction makes the molar ratio of the total amount of hydrogen in the reducing gas to the total amount of lithium in the lithium-containing compound be X, and when 1<X≤10 (i.e., the total amount of reducing gas introduced during the entire reaction process is 1<X≤10), the temperature of the lithium sulfide synthesis reaction is adjusted as the amount of reducing gas introduced increases, specifically including: when X≤1, the temperature of the reaction is controlled at 130°C~160°C, when 1<X<2, the temperature of the reaction is controlled at 160~250°C, and when 2≤X≤10, the temperature of the reaction is controlled at 250~300°C. When the total amount of hydrogen introduced during the entire synthesis process is relatively sufficient, the use of gradient heating can obtain better raw material conversion rate and product yield. In the first stage (X≤1), hydrogen is insufficient, and lithium compounds and solvent sulfur will undergo intermediate reactions to generate corresponding sulfides and polysulfides. The gradient temperature rise controls the viscosity of the system to be in a good flow state; in the second stage (1<X<2), hydrogen is relatively sufficient. As the reaction depth increases, lithium compounds are consumed more, the concentration decreases, and the reaction rate gradually decreases. Properly increasing the temperature helps maintain a high reaction rate; in the third stage (2≤X≤10), heat preservation is maintained to complete the tailing reaction. By controlling the echelon temperature, the reaction rate and system viscosity can be stabilized, thereby promoting the raw material conversion rate and product yield.

[0028] In some preferred embodiments, 1<X≤10, which can obtain better raw material conversion rate and product yield.

[0029] In some embodiments, sulfur in the reaction mixture is removed by at least distillation, the vacuum degree of the distillation is 0~-0.098MPaG, and the temperature of the distillation is 250℃~450℃.

[0030] In some preferred embodiments, the vacuum degree of the distillation is -0.06 MPaG to -0.098 MPaG.

[0031] In some preferred embodiments, the distillation temperature is 250°C to 300°C.

[0032] In some embodiments, the distillation time is 2h~12h, preferably 4h~6h.

[0033] In some embodiments, the equipment used for the distillation is, for example, a double-cone drying equipment or a spray drying equipment, preferably a double-cone vacuum drying equipment.

[0034] In some embodiments, the calcination temperature is 450°C to 850°C, preferably 500°C to 700°C.

[0035] In some embodiments, the calcination is carried out in an inert atmosphere at normal pressure or under reduced pressure vacuum conditions, and the pressure of the high-temperature calcination is 0~-0.098MPaG.

[0036] In some preferred embodiments, the calcination time is 2 h to 12 h, preferably 4 h to 8 h.

[0037] In some embodiments, the method further comprises: collecting sulfur during the distillation and / or calcination process, and the collected sulfur can be used as a reaction raw material again to react, thereby realizing the cycle of the process.

[0038] In some embodiments, the calcination equipment is, for example, a roller kiln or a rotary kiln, but is not limited thereto.

[0039] In some embodiments, the method further comprises: before the calcination, crushing the crude finished product into powder, for example, crushing it into powder by rolling, so as to prevent large pieces from entering the calcination in a compacted state and affecting the purification effect.

[0040] In some embodiments, after the calcination is completed, the temperature of the purified lithium sulfide is reduced to room temperature~50°C in an inert atmosphere; the lithium sulfide product is then rolled and crushed to obtain a uniform powder of lithium sulfide; the uniform powder of lithium sulfide is subjected to air flow shear grinding and / or mechanical grinding to obtain lithium sulfide with uniform particle size; the lithium sulfide is demagnetized and then packaged under inert atmosphere protection conditions.

[0041] The second object of the present invention is to provide a lithium sulfide prepared by any of the above methods. The lithium sulfide prepared by the method meets the application standards of positive electrode materials or solid electrolyte materials in batteries.

[0042] In some embodiments, the purity of the lithium sulfide is above 99.99%; according to XRD detection, there is no lithium oxide component, and the moisture content is ≤10ppm, the total amount of metal impurities is <50ppm, the mass content of free chlorine is <10ppm, and the mass content of sulfate is <5ppm.

[0043] The third object of the present invention is to provide the use of the lithium sulfide in preparing a positive electrode for a secondary battery, a sulfide solid electrolyte or a secondary battery.

[0044] A fourth object of the present invention is to provide a positive electrode for a lithium-sulfur battery, wherein the positive electrode of the lithium sulfide battery comprises the lithium sulfide.

[0045] A fifth object of the present invention is to provide a lithium-sulfur battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode is the positive electrode for the lithium-sulfur battery.

[0046] Compared with the prior art, the present invention has at least the following beneficial effects: The method provided by the present invention realizes the "one-pot method" to prepare high-purity lithium sulfide, uses liquid sulfur as both a reaction raw material and a reaction solvent, and introduces a reducing gas into the reaction solution to reduce the by-product lithium sulfate to lithium sulfide in situ, the lithium salt conversion rate reaches more than 99%, and the selectivity is improved to more than 99%; The preparation method provided by the present invention can achieve a conversion rate of more than 99% of lithium salt under a process condition of no more than 300°C. Compared with the prior art which requires a high temperature condition of more than 600°C, the preparation method of the present invention takes into account both low energy consumption and high conversion rate. The preparation method of the present invention does not use organic solvents throughout the entire process, that is, no organic solvents are needed in the preparation stage and the purification stage, thereby avoiding the problem of carbonization of materials and introduction of lithium oxide impurities caused by side reactions in the purification process using organic solvents in the prior art; The preparation method of the present invention does not introduce oxides and metal impurities, and adopts a high-temperature calcination process to convert the byproduct lithium polysulfide into the product lithium sulfide again. The purity of the prepared lithium sulfide is higher than that of commercially available products, and the purity can reach 99.99%. XRD detection shows that there is no lithium oxide component, the water content is ≤10ppm, the total amount of metal impurities is <50ppm, wherein Na is <10ppm, Si is <20ppm, Ca is <10ppm, Mg is <10ppm, other impurity metals are <5ppm, the mass content of free chlorine is <10ppm, and the mass content of sulfate is <5ppm. Compared with the preparation method of the prior art that directly uses gas-solid reaction between lithium salt and hydrogen sulfide, the present invention creatively uses sulfur as a reaction solvent to achieve a safe and efficient control process for gas-liquid reaction; and under the same conditions, the lithium salt conversion rate is increased by more than 30%, the material transfer between equipment is easier to achieve, the batch stability is better, the reactor manufacturing cost is low, and it is easy to achieve industrial scale-up. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic diagram of the process flow for preparing high-purity lithium sulfide in one embodiment of the present invention. DETAILED DESCRIPTION

[0048] The process for preparing lithium sulfide in the prior art has the problems of harsh high temperature and high pressure conditions, difficulty in removing the organic solvent, difficulty in separating metal ions, difficulty in separating lithium oxide impurities, and long purification process. In view of the deficiencies in the prior art, the inventors of this case have proposed the technical solution of the present invention after long-term research and a lot of practice. The present invention finds that a process in which liquid sulfur is mixed with lithium salt as a reaction raw material and a reducing gas is introduced for reaction can obtain a higher lithium salt conversion rate and product purity, and the entire process does not require the use of organic solvents. This solves the problems of cumbersome lithium sulfide process flow, high manufacturing cost, high impurity content, and difficulty in product purification in the prior art. The "one-pot method" provided by the present invention is used to prepare high-purity lithium sulfide with a purity that can reach the battery-grade application level, thereby overcoming the deficiencies in the prior art.

[0049] The technical solution of the present invention is further described below by specific implementation methods. Those skilled in the art should understand that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Unless otherwise specified, the functional devices used in the embodiments of the present invention are all known in the art and can be obtained commercially. The specific structures and models are not limited here.

[0050] Example 1 This embodiment provides a lithium sulfide and a preparation method thereof, the process flow is as follows Figure 1 As shown, the specific steps include: Add 80 ml of liquid sulfur to a 250 ml reactor and heat it to 150°C; introduce dry nitrogen below the liquid level of the reactor to form continuous bubbling; slowly add 50 g of anhydrous lithium hydroxide to the above sulfidation solution, maintain the internal temperature at 150°C, and stir evenly to obtain a mixed solution; Dry hydrogen is introduced into the reactor through another gas phase port on the reactor at a rate of 0.19L / min / 100ml of the mixed liquid to carry out the reaction. The molar ratio of the total amount of hydrogen in the introduced hydrogen to the total amount of lithium in the anhydrous lithium hydroxide is X. The amount of hydrogen introduced is monitored during the reaction and the reaction temperature is adjusted according to the change of X, specifically: when X≤1, the temperature is controlled at 150°C, and as the amount of hydrogen introduced increases, when X is 1<X<2, the temperature is raised to 200°C, and when X≧2, the temperature is raised to 280°C and maintained until the reaction is completed. The total amount of hydrogen introduced during the entire reaction process is X=4.5238, and the reaction time is 4h; and sampling and analyzing the moisture content in the tail gas begins at the third hour, and the reaction is completed when the moisture content in the tail gas is <50ppm; Transfer the reaction solution obtained by the reaction to a rotary evaporator while it is still hot, keep the temperature of the rotary evaporator condenser at 140° C., and the temperature of the rotary evaporator at 300° C.; gradually reduce the vacuum degree to evaporate the remaining sulfur solvent to obtain 55 g of solid lithium sulfide crude product; Under nitrogen atmosphere protection conditions, the solid lithium sulfide obtained above was ground for 3 minutes to obtain a loose and uniform powdered lithium sulfide crude product; the crude lithium sulfide was put into a sagger and vacuum calcined at 700°C in an atmosphere furnace for 4.5 hours, and the vacuum degree was controlled at -0.06MPa. After the calcination, the temperature was lowered and mechanical grinding was performed under inert atmosphere protection conditions to obtain 47.5g of high-purity lithium sulfide with uniform particle size, and the yield was 99.1%.

[0051] The high-purity lithium sulfide sample obtained above was subjected to XRD, IC, ICP, particle size and insoluble matter analysis. The analysis results are shown in Table 1.

[0052] Example 2 This embodiment provides a lithium sulfide and a preparation method thereof, which specifically comprises the following steps: Add 340 ml of liquid sulfur to a 1000 ml reactor and heat it to 145°C; introduce dry nitrogen below the liquid level of the reactor to form continuous bubbling; slowly add 100 g of lithium hydroxide monohydrate to the above sulfidation solution, maintain the internal temperature at 145°C, and stir evenly to obtain a mixed solution; A mixed gas of dry hydrogen and hydrogen sulfide is introduced into the reactor at a rate of 0.5L / min / 100ml of the mixed liquid through another gas phase port of the reactor to react, wherein the weight of hydrogen in the mixed gas accounts for 40%; the molar ratio of the total amount of hydrogen element in the introduced hydrogen to the total amount of lithium element in the anhydrous lithium hydroxide is X, and the amount of hydrogen introduced is monitored during the reaction and the reaction temperature is adjusted according to the change of X, specifically: when X≤1, the temperature is controlled at 130°C, and as the amount of hydrogen introduced increases, when X is 1<X<2, the temperature is raised to 160°C, and when X≧2, the temperature is raised to 250°C and maintained until the reaction is completed. The total amount of hydrogen introduced during the entire reaction process is X=5.38, and the reaction time is 3h; and sampling and analyzing the moisture content in the tail gas begins in the second hour, and the reaction is completed when the moisture content in the tail gas is <50ppm; The reaction solution obtained by the reaction was transferred to a rotary evaporator while hot, the temperature of the rotary evaporator condenser was maintained at 140° C., the temperature of the rotary evaporator was maintained at 300° C., the vacuum degree was gradually reduced, and the remaining sulfur solvent was evaporated to obtain 62 g of solid lithium sulfide crude product; Under the protection of a nitrogen atmosphere, the solid lithium sulfide obtained above was ground for 3 minutes to obtain a loose and uniform powdered lithium sulfide crude product; the crude lithium sulfide was put into a sagger and vacuum calcined at 850°C in an atmosphere furnace for 4 hours, and the vacuum degree was controlled at -0.065MPa. After the calcination, the temperature was lowered and mechanical grinding was performed under the protection of an inert atmosphere to obtain 53g of high-purity lithium sulfide with uniform particle size, and the yield was 96.7%.

[0053] The high-purity lithium sulfide sample obtained above was subjected to XRD, IC, ICP, particle size and insoluble matter analysis, and the analysis structure is shown in Table 1.

[0054] Example 3 This embodiment provides a lithium sulfide and a preparation method thereof, which specifically comprises the following steps: Add 250 ml of liquid sulfur to a 1000 ml reactor and heat it to 160°C; introduce dry nitrogen below the liquid level of the reactor to form continuous bubbling; slowly add 100 g of anhydrous lithium carbonate to the above sulfidation solution, maintain the internal temperature at 160°C, and stir evenly to obtain a mixed solution; Dry hydrogen sulfide gas is introduced into the reactor through another gas phase port of the reactor at a rate of 1L / min / 100ml of the mixed liquid to react, the molar ratio of the total amount of hydrogen element in the introduced hydrogen to the total amount of lithium element in the anhydrous lithium hydroxide is X, the amount of hydrogen introduced is monitored during the reaction and the reaction temperature is adjusted according to the change of X, specifically: when X≤1, the temperature is controlled at 160°C, as the amount of hydrogen introduced increases and X is 1<X<2, the temperature is raised to 250°C, when X≧2, the temperature is raised to 300°C and maintained until the reaction is completed, the total amount of hydrogen introduced during the entire reaction process is X=2.64, and the reaction time is 1h; and sampling and analyzing the moisture content in the tail gas begins at 40min, and the reaction is completed when the moisture content in the tail gas is <50ppm; The reaction solution obtained by the reaction was transferred to a rotary evaporator while hot, the temperature of the rotary evaporator condenser was maintained at 140° C., the temperature of the rotary evaporator was maintained at 300° C., the vacuum degree was gradually reduced, the remaining sulfur solvent was evaporated, and finally 69 g of solid lithium sulfide crude product was obtained at 300° C.; Under the protection of a nitrogen atmosphere, the solid lithium sulfide obtained above was ground for 3 minutes to obtain a loose and uniform powdered lithium sulfide crude product; the crude lithium sulfide was put into a sagger and vacuum calcined at 450°C in an atmosphere furnace for 5 hours, and the vacuum degree was controlled at -0.075MPa. After the calcination, the temperature was lowered and mechanical grinding was performed under the protection of an inert atmosphere to obtain 60.5g of high-purity lithium sulfide with uniform particle size, and the yield was 97.3%.

[0055] The high-purity lithium sulfide sample obtained above was subjected to XRD, IC, ICP, particle size and insoluble matter analysis, and the analysis structure is shown in Table 1.

[0056] Example 4 This embodiment provides a lithium sulfide and a preparation method thereof, which specifically comprises the following steps: Add 80 ml of liquid sulfur to a 250 ml reactor and heat it to 150°C; introduce dry nitrogen below the liquid level of the reactor to form continuous bubbling; slowly add 50 g of anhydrous lithium hydroxide to the above sulfidation solution, maintain the internal temperature at 150°C, and stir evenly to obtain a mixed solution; Dry hydrogen was introduced into the reactor through another gas phase port on the reactor at a rate of 0.19 L / min / 100 ml of the mixed solution to carry out the reaction, the reaction temperature was controlled at 280° C., and the molar ratio X of the total amount of hydrogen in the hydrogen introduced to the total amount of lithium in the anhydrous lithium hydroxide during the entire reaction was 4.5238, the reaction was continued for 4 hours, and the reaction was terminated; The reaction solution obtained by the reaction was transferred to a rotary evaporator while hot, and the temperature of the rotary evaporator condenser was maintained at 140° C. The temperature of the rotary evaporator was 300° C., and the vacuum degree was gradually reduced to evaporate the remaining sulfur solvent to obtain 55 g of solid lithium sulfide crude product; Under the protection of a nitrogen atmosphere, the solid lithium sulfide obtained above was ground for 3 minutes to obtain a loose and uniform powdered lithium sulfide crude product; the crude lithium sulfide was put into a sagger and vacuum calcined at 700°C in an atmosphere furnace for 4.5 hours, and the vacuum degree was controlled at -0.06MPa. After the calcination, the temperature was lowered and mechanical grinding was performed under the protection of an inert atmosphere to obtain 46.1g of high-purity lithium sulfide with uniform particle size, and the yield was 96.2%.

[0057] The high-purity lithium sulfide sample obtained above was subjected to XRD, IC, ICP, particle size and insoluble matter analysis. The analysis results are shown in Table 1.

[0058] Example 5 Example 5 is basically the same as Example 1, except that Example 5 maintains a slightly negative pressure state during the synthesis reaction, and the reactor pressure is -0.01 MPaG. After calcination and purification, 47.85 g of high-purity lithium sulfide with uniform particle size is obtained, and the yield is 99.9%.

[0059] The high-purity lithium sulfide sample obtained above was subjected to XRD, IC, ICP, particle size and insoluble matter analysis. The analysis results are shown in Table 1.

[0060] Example 6 This embodiment provides a lithium sulfide and a preparation method thereof, which specifically comprises the following steps: Add 80 ml of liquid sulfur to a 250 ml reactor and heat it to 150°C; introduce dry nitrogen below the liquid level of the reactor to form continuous bubbling; slowly add 10 g of anhydrous lithium hydroxide (lithium salt concentration 5 wt%) to the above sulfidation solution, maintain the internal temperature at 150°C, and stir evenly to obtain a mixed solution; Dry hydrogen is introduced into the reactor at a rate of 0.19L / min / 100ml of the mixed solution through another gas phase port on the reactor to react. The molar ratio of the total amount of hydrogen in the introduced hydrogen to the total amount of lithium in the anhydrous lithium hydroxide is X. The amount of hydrogen introduced is monitored during the reaction and the reaction temperature is adjusted according to the change of X. Specifically, when X≤1, the temperature is controlled at 150°C. As the amount of hydrogen introduced increases, when X is 1<X<2, the temperature is raised to 200°C. When X≧2, the temperature is raised to 280°C and maintained until the reaction is completed. The total amount of hydrogen introduced during the entire reaction process is X=4.5238, and the reaction time is 4h. Samples are taken and analyzed for moisture content in the tail gas at the third hour. When the moisture content in the tail gas is <50ppm, the reaction is completed. The reaction process maintains a slightly negative pressure state, and the reactor pressure is -0.01MPaG. The reaction solution obtained by the reaction was transferred to a rotary evaporator while hot, the temperature of the rotary evaporator condenser was maintained at 140° C., the temperature of the rotary evaporator was maintained at 300° C., the vacuum degree was gradually reduced, and the remaining sulfur solvent was evaporated to obtain 10.5 g of solid lithium sulfide crude product; Under the protection of a nitrogen atmosphere, the solid lithium sulfide obtained above was ground for 3 minutes to obtain a loose and uniform powdered lithium sulfide crude product; the crude lithium sulfide was put into a sagger and vacuum calcined at 700°C in an atmosphere furnace for 4.5 hours, and the vacuum degree was controlled at -0.06MPa. After the calcination, the temperature was lowered and mechanical grinding was performed under the protection of an inert atmosphere to obtain 9.55g of high-purity lithium sulfide with uniform particle size, and the yield was 99.5%.

[0061] The high-purity lithium sulfide sample obtained above was subjected to XRD, IC, ICP, particle size and insoluble matter analysis. The analysis results are shown in Table 1.

[0062] Example 7 This embodiment provides a lithium sulfide and a preparation method thereof, which specifically comprises the following steps: Add 80 ml of liquid sulfur to a 250 ml reactor and heat it to 150°C; introduce dry nitrogen below the liquid level of the reactor to form continuous bubbling; slowly add 200 g of anhydrous lithium hydroxide (lithium salt concentration 50 wt%) to the above sulfidation solution, maintain the internal temperature at 150°C, and stir evenly to obtain a mixed solution; Dry hydrogen is introduced into the reactor at a rate of 0.19L / min / 100ml of the mixed solution through another gas phase port on the reactor to react. The molar ratio of the total amount of hydrogen in the introduced hydrogen to the total amount of lithium in the anhydrous lithium hydroxide is X. The amount of hydrogen introduced is monitored during the reaction and the reaction temperature is adjusted according to the change of X. Specifically, when X≤1, the temperature is controlled at 150°C. As the amount of hydrogen introduced increases, when X is 1<X<2, the temperature is raised to 200°C. When X≧2, the temperature is raised to 280°C and maintained until the reaction is completed. The total amount of hydrogen introduced during the entire reaction process is X=4.5238, and the reaction time is 4h. Samples are taken and analyzed for moisture content in the tail gas at the third hour. When the moisture content in the tail gas is <50ppm, the reaction is completed. The reaction process maintains a slightly negative pressure state, and the reactor pressure is -0.01MPaG. The reaction solution obtained by the reaction was transferred to a rotary evaporator while hot, the temperature of the rotary evaporator condenser was maintained at 140° C., the temperature of the rotary evaporator was maintained at 300° C., the vacuum degree was gradually reduced, and the remaining sulfur solvent was evaporated to obtain 225 g of solid lithium sulfide crude product; Under the protection of a nitrogen atmosphere, the solid lithium sulfide obtained above was ground for 3 minutes to obtain a loose and uniform powdered lithium sulfide crude product; the crude lithium sulfide was put into a sagger and vacuum calcined at 700°C in an atmosphere furnace for 4.5 hours, and the vacuum degree was controlled at -0.06MPa. After the calcination, the temperature was lowered and mechanical grinding was performed under the protection of an inert atmosphere to obtain 177.3g of high-purity lithium sulfide with uniform particle size, and the yield was 92.5%.

[0063] The high-purity lithium sulfide sample obtained above was subjected to XRD, IC, ICP, particle size and insoluble matter analysis. The analysis results are shown in Table 1.

[0064] Comparative Example 1 Comparative Example 1 provides a method for preparing lithium sulfide using anhydrous lithium carbonate and hydrogen sulfide gas as raw materials, which specifically comprises the following steps: Add 100 g of anhydrous lithium carbonate to a 1000 ml reactor protected by an inert atmosphere, raise the temperature to 160° C., and introduce dry hydrogen sulfide gas into the reactor through the gas phase port at a rate of 800 ml / min to carry out the reaction; control the temperature at 160° C. for the first 20 min, control the temperature at 250° C. for the 20th to 40th min, and control the temperature at 300° C. for the 40th to 60th min. Stop the reaction after 1 h to obtain 75.5 g of solid crude lithium sulfide.

[0065] The solid lithium sulfide obtained above was ground for 3 minutes under nitrogen atmosphere protection conditions to obtain loose and uniform powdery lithium sulfide crude product; the crude lithium sulfide was put into a sagger and vacuum calcined at 750°C in an atmosphere furnace for 5 hours, and the vacuum degree was controlled at -0.075MPa. After the calcination, the temperature was lowered and mechanical grinding was performed under inert atmosphere protection conditions to obtain 72g of a mixed reaction liquid of lithium sulfide and lithium carbonate with uniform particle size. The sample was subjected to XRD, IC, ICP, particle size and insoluble matter analysis, and the lithium sulfide yield was 64.5%.

[0066] Comparative Example 2 Comparative Document 2 provides a method for preparing lithium sulfide using solid sulfur powder and anhydrous lithium hydroxide as raw materials, which specifically includes the following steps: Add 155g of sulfur powder and 192g of anhydrous lithium hydroxide to a 500ml reactor protected by an inert atmosphere, mix them evenly at room temperature, then heat to 300°C and react for 4h, and finally obtain 250g of solid lithium sulfide crude product at 300°C; Under nitrogen atmosphere protection conditions, the solid lithium sulfide crude product obtained above was ground for 3 minutes to obtain a loose and uniform powdery lithium sulfide crude product; the lithium sulfide crude product was put into a sagger and vacuum calcined at 700°C in an atmosphere furnace for 5 hours, and the vacuum degree was controlled at -0.075MPa. After the calcination, the temperature was lowered and mechanical grinding was performed under inert atmosphere protection conditions to obtain 240g of a mixed reaction liquid of lithium sulfide and lithium sulfate with uniform particle size. The sample was subjected to XRD, IC, ICP, particle size and insoluble matter analysis, and the lithium sulfide yield was 70%.

[0067] Comparative Example 3 Comparative Example 3 uses anhydrous ethanol to purify lithium sulfide, which specifically includes the following steps: 55 g of solid crude lithium sulfide No. 1 was obtained by the same synthesis method and sulfur evaporation method as in Example 1. Under nitrogen atmosphere protection conditions, the solid crude lithium sulfide No. 1 obtained above was dissolved with 2 L of anhydrous ethanol, and insoluble matter was filtered out after dissolution; the anhydrous ethanol was removed under vacuum conditions at 150 ° C to obtain a crude lithium sulfide No. 2; the crude lithium sulfide No. 2 was ground for 3 min to obtain a loose and uniform crude lithium sulfide No. 3; the crude lithium sulfide No. 3 was loaded into a sagger, and vacuum calcined at 700 ° C in an atmosphere furnace for 4.5 h, controlling the vacuum degree at -0.06 MPa, and after calcination, the temperature was lowered and mechanical grinding was performed under inert atmosphere protection conditions to obtain 40 g of a lithium sulfide sample with uniform particle size, with a yield of 83.4%.

[0068] The lithium sulfide samples obtained above were subjected to XRD, IC, ICP, particle size and insoluble matter analyses. The analysis results are shown in Table 1.

[0069] The lithium sulfide products obtained in the above examples and comparative preparation examples were characterized and their yields were calculated. The results are shown in Table 1. Among them, the test method is: Moisture: Tested using Karl Fischer Coulometry; Impurity metal content: quantitative analysis using ICP-OES instrument; Free chlorine and sulfate content: tested using ion chromatography, column model Thermo Fisher AS22 anion analysis column 4×250mm; 150mmol / L sulfuric acid solution was used as the inhibitory solution; eluent preparation steps: 1) first prepare the buffer solution (mother liquor): 4.5428g NaHCO3, 8.4813g Na2CO3, add 200mL distilled water to dissolve, ultrasonically dissolve, and filter; 2) Prepare the mobile phase: take 20mL mother liquor, 1380g distilled water, 600ml acetonitrile, stir and mix, and set aside.

[0070] Table 1 Performance Characterization Parameters of Lithium Sulfide Products Prepared in Examples and Comparative Examples

[0071] From Table 1 we can see: (1) The method for preparing high-purity lithium sulfide by the "one-pot method" provided by the present invention has a high yield of lithium sulfide, the highest yield can reach more than 99.9%, and the comprehensive yield is greater than 92%. The purity of the Li2S product is high, and the purity can reach 99.995% by the deduction method. Water ≤10ppm, SO4 2- ≤5ppm, the mass content of free chlorine is <10ppm, Na <10ppm, Si <20ppm, Ca <10ppm, Mg <10ppm, and other impurity metals are all <10ppm, which meets the application standards in electrolyte.

[0072] (2) From the comparison of the results of Example 1 and Example 4, it can be seen that when the gradient temperature is not increased, the product yield decreases by 2.9%, and the ethanol insoluble matter increases significantly after the reaction. The possible reason is that the constant temperature operation causes the viscosity of the system to change significantly before and after the reaction, causing some side reactions.

[0073] (3) By comparing the results of Example 1 and Example 5, it can be seen that when the reaction is carried out under slightly negative pressure, the product yield is increased by 0.8%, and the ethanol insoluble matter after the reaction is significantly reduced. The possible reason is that the slightly negative pressure promotes the evaporation of by-product water, reduces the chance of by-product water contacting the product, reduces the risk of product hydrolysis, and improves the product yield and purity.

[0074] (4) The lithium salt concentrations in Examples 1, 6 and 7 are 20wt%, 5wt% and 50wt% respectively. It can be seen from these three examples that the lithium salt concentration has an impact on the output, purity and yield of the product. Although the product purity and yield are acceptable at low concentrations, the output is too low. Although the product output is increased at high concentrations, the quality is reduced, which increases the difficulty of controlling the purification process. The present invention has systematically studied and found that the mass concentration of the lithium-containing compound is better when it is 10wt% to 30wt% of the total mass of the lithium-containing compound and liquid sulfur.

[0075] (5) By comparing Example 3 with Comparative Example 1, it can be seen that when liquid sulfur is not used as a solvent, the product yield of the reaction of hydrogen sulfide and lithium carbonate under the same process conditions decreases by 32.8%. The product purity is low due to the incomplete reaction of lithium carbonate and the occurrence of some side reactions. In particular, the ethanol insoluble matter reaches 850 ppm, which is mainly due to the difficulty in separating the residual lithium carbonate from lithium sulfide, and the content of other metal ions and anionic impurities is also relatively high.

[0076] (6) By comparing Example 1 and Comparative Example 2, it can be seen that when no reducing gas is introduced, the sulfate content in the reaction product reaches 35.74%, indicating that a large amount of lithium sulfate is generated by the reaction of sulfur and lithium hydroxide; high-purity lithium sulfide cannot be obtained using the same purification process.

[0077] (7) By comparing Example 1 and Comparative Example 3, it can be seen that when the purification scheme of re-dissolving with anhydrous ethanol and filtering is adopted after the reaction is completed, and the same calcination process is adopted, the prepared lithium sulfide is tested to have an ethanol insoluble matter of up to 3500ppm. According to XRD analysis, the ethanol insoluble matter is mainly lithium oxide. This may be related to the fact that ethanol and lithium sulfide have certain side reactions at high temperatures, and finally produce lithium oxide.

[0078] The present invention also verifies that the high-purity lithium sulfide prepared in the above embodiment is used to prepare a positive electrode for a lithium-sulfur battery and is used to assemble a lithium-sulfur battery, and the obtained battery has excellent performance; the present invention also uses the high-purity lithium sulfide prepared in the above embodiment to prepare a solid electrolyte, and uses it to assemble a lithium-sulfur battery, and the obtained battery has excellent performance.

[0079] In addition, the present invention also verifies that the lithium sulfide products when the lithium-containing compound is lithium o-benzoylsulfonyl imide and lithium bis(fluorosulfonyl)imide have achieved the same effects as the above embodiments.

[0080] The "one-pot method" for preparing high-purity lithium sulfide provided by the present invention overcomes the industry pain points of long lithium sulfide preparation process, difficult material transfer, difficult amplification equipment selection, difficult impurity separation, low product yield, and high manufacturing cost. Sulfur is selected as both a reaction solvent and a sulfur source, which simplifies the process flow, improves the product yield, is suitable for industrial transformation, and the obtained product has high purity and low three wastes. It is a safe, green, environmentally friendly, and low-cost method for preparing high-purity lithium sulfide, and has good application prospects.

[0081] The various aspects, embodiments, features and examples of the present invention should be considered as illustrative in all aspects and are not intended to limit the present invention, the scope of the present invention is defined only by the claims. Other embodiments, modifications and uses will be apparent to those skilled in the art without departing from the spirit and scope of the claimed invention.

[0082] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments with other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0083] Although the present invention has been described with reference to illustrative embodiments, it will be appreciated by those skilled in the art that various other changes, omissions and / or additions may be made without departing from the spirit and scope of the present invention and that the elements of the embodiments may be replaced by substantial equivalents. In addition, many modifications may be made without departing from the scope of the present invention to adapt specific circumstances or materials to the teachings of the present invention. Therefore, it is not intended herein to limit the present invention to the disclosed specific embodiments for performing the present invention, but it is intended that the present invention will include all embodiments within the scope of the appended claims. In addition, unless specifically stated, any use of the terms first, second, etc. does not indicate any order or importance, but rather uses the terms first, second, etc. to distinguish one element from another element.

Claims

1. A method for preparing lithium sulfide, characterized in that: include: Providing a mixed solution containing a uniformly mixed lithium-containing compound and liquid sulfur, and contacting the mixed solution with a reducing gas to perform a lithium sulfide synthesis reaction; After the lithium sulfide synthesis reaction is completed, at least part of the sulfur in the obtained reaction mixture is removed to obtain a crude product; The crude product is calcined to convert the lithium polysulfide in the crude product into lithium sulfide to obtain a lithium sulfide product.

2. The preparation method according to claim 1, characterized in that: Specifically include: A dry protective gas is introduced into liquid sulfur to form continuous bubbling, and a dry lithium-containing compound is added into the liquid sulfur in batches to form the mixed solution; and the mixed solution is contacted with a dry reducing gas to carry out the lithium sulfide synthesis reaction.

3. The preparation method according to claim 1, characterized in that: The reaction temperature of the lithium sulfide synthesis reaction is 130°C to 300°C; and / or, the reaction time of the lithium sulfide synthesis reaction is 1 to 5 hours; and / or, the pressure of the lithium sulfide synthesis reaction is 0 to -0.01 MPaG; and / or, passing the reducing gas into the mixed solution at a rate of 0.1 to 1.0 L / min / 100 ml of the mixed solution, so that the mixed solution is in contact with the reducing gas; And / or, the mass concentration of the lithium-containing compound is 5wt% to 50wt% of the total mass of the lithium-containing compound and the liquid sulfur; And / or, the lithium-containing compound includes one or more of lithium hydroxide, lithium carbonate, lithium o-benzoylsulfonyl imide, and lithium bis(fluorosulfonyl)imide, and the reducing gas includes hydrogen and / or hydrogen sulfide.

4. The preparation method according to claim 1, characterized in that: The amount of reducing gas introduced during the lithium sulfide synthesis reaction is such that the molar ratio of the total amount of hydrogen in the reducing gas to the total amount of lithium in the lithium-containing compound is X; When X≤1, the reaction temperature is controlled at 130°C to 160°C; When 1<X≤10, the temperature of the lithium sulfide synthesis reaction is adjusted as the amount of reducing gas introduced increases, specifically including: when X≤1, the temperature of the reaction is controlled at 130℃~160℃, when 1<X<2, the temperature of the reaction is controlled at 160~250℃, and when 2≤X≤10, the temperature of the reaction is controlled at 250~300℃.

5. The preparation method according to claim 4, characterized in that: 1＜X≤10。 6. The preparation method according to claim 1, characterized in that: Specifically include: At least one distillation method is used to remove sulfur from the reaction mixture, wherein the vacuum degree of the distillation is 0 to -0.098 MPaG and the temperature is 250° C. to 450° C.; And / or, the calcination temperature is 450°C~850°C; and / or, the calcination time is 2~12h; and / or, the calcination is carried out in an inert atmosphere at normal pressure or under reduced pressure vacuum conditions, and the calcination pressure is 0~-0.098MPaG.

7. A lithium sulfide, characterized in that: It is prepared by the method described in any one of claims 1 to 6; Preferably, the purity of the lithium sulfide is above 99.99%; according to XRD detection, there is no lithium oxide component, and the moisture content is ≤10ppm, the total amount of metal impurities is <50ppm, the mass content of free chlorine is <10ppm, and the mass content of sulfate is <5ppm.

8. Use of the lithium sulfide according to claim 7 in preparing a positive electrode for a secondary battery, a sulfide solid electrolyte or a secondary battery.

9. A positive electrode for a lithium-sulfur battery, characterized in that: Including the lithium sulfide as described in claim 7.

10. A lithium-sulfur battery comprising a positive electrode, a negative electrode and an electrolyte, characterized in that: The positive electrode is the positive electrode for a lithium-sulfur battery according to claim 9.

Images