A method for co-production of lithium sulfide and lithium carbonate, products and applications thereof

Abstract

The application discloses a kind of lithium sulfide and lithium carbonate co-production preparation method, product and application: according to certain molar ratio, lithium sulfate and sodium sulfide are weighed, and the double decomposition reaction of two kinds of substances occurs in heated organic alcohol solvent;After reaction, the obtained suspension is separated to obtain clear night and precipitate;Evaporate the alcohol solvent in clear liquid, and then high-temperature calcination solid crude product can obtain high-purity lithium sulfide fine product;Precipitate is dissolved in water, and sodium carbonate is added to stir, and after sufficient reaction, the precipitate is collected and dried to obtain pure lithium carbonate;The obtained lithium sulfide and lithium carbonate can be applied to secondary battery.The application has the advantages of easy-to-obtain raw materials, mild reaction conditions, green environmental protection, easy mass production and convenient operation, conforms to the purpose of double carbon and the tenet of green chemistry.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of secondary batteries, and more particularly to a method for co-production of lithium sulfide and lithium carbonate, products and applications thereof. BACKGROUND

[0002] At present, the secondary battery represented by lithium ion battery (LIBs) has been widely used in communication, transportation, national defense, aerospace and other fields due to its long cycle life, high energy conversion efficiency and environmental friendliness. However, the actual energy density of lithium ion battery has approached its theoretical limit, which is difficult to meet the performance requirements of current more advanced energy storage devices.

[0003] Compared with lithium ion battery, lithium-sulfur battery has higher mass energy density (2500 Wh / kg, vs. 420 Wh / kg) and volume energy density (2800 Wh / L, vs. 1400 Wh / L), and has attracted widespread attention in recent years. As an important positive material of lithium-sulfur battery, lithium sulfide (Li2S) can be paired with lithium-free negative electrode (such as silicon, graphite, tin, etc.), which not only has good thermal stability, but also has various nanostructures (such as nanosheets, nanospheres, etc.), which can meet the actual needs of lithium-sulfur battery electrode structure. However, the existing Li2S synthesis methods each have different problems. The laboratory preparation method of lithium sulfide can be roughly divided into ball milling method, carbon thermal reduction method and mutual reaction of lithium / sulfur-containing compounds.

[0004] The ball milling method has two synthesis routes, top-down and bottom-up. The former is a physical crushing method, which means that commercial Li2S microparticles are ball milled in a ball mill to break down the large-particle microparticles into small-particle Li2S nanocrystals. The latter is a chemical synthesis method, which means that ball milling is used to promote chemical reactions between raw materials, for example, the published Chinese patent CN116216652A. Although this method can prepare Li2S on a large scale, it will introduce impurities from the ball and the ball mill, and the material dispersion is poor.

[0005] The carbon thermal reduction method is a method for reducing Li2SO4 to Li2S at high temperature using a reducing agent, where the reducing agent usually uses a carbon source (including elemental carbon or organic carbon precursor) and a metal element. Representative patents include, for example, published Chinese patents CN111628150A, CN115714169A and CN115321490A. The essential problem of this method is the emission of greenhouse gas CO2, which is contrary to the long-term development goal of green chemistry. At the same time, the non-spontaneous intrinsic factors of this method under normal temperature and pressure lead to relatively harsh reaction conditions, which will be greatly limited in the long run.

[0006] The metallothermic reduction method uses a strong reducing elemental metal to reduce lithium sulfate to prepare lithium sulfide. The raw materials are mixed by hand grinding or mechanical ball milling, then calcined for a predetermined time under an inert atmosphere. Afterwards, byproducts are separated by ethanol, and the lithium sulfide solution in ethanol is calcined at high temperature to obtain battery-grade lithium sulfide. Representative patents include CN115947313A and CN114477099A. This method has the advantages of simple operation, low temperature, instantaneous reaction, and no carbon emissions; however, the reaction is highly exothermic and excessively vigorous, making it difficult to scale up for production.

[0007] The lithium / sulfur compound reaction involves reacting elemental lithium or lithium-containing compounds with elemental sulfur or sulfur-containing compounds to obtain lithium sulfide products. This reaction is diverse, as illustrated by published Chinese patents CN116354315A, CN115986112A, CN116040587A, and CN115535968A. The reactants used in this reaction (such as LiH and CS2, Li2CO3 and H2S) are generally expensive, resulting in poor economic efficiency. For example, patent CN114455549A uses relatively inexpensive LiCl and Na2S as raw materials to prepare Li2S via a metathesis reaction. While this reduces production costs, it requires a large amount of organic solvent (N-methylpyrrolidone or acetone) to wash impurities in the crude product. This method suffers from problems such as poor solvent recovery and easy decomposition and carbonization during product calcination, polluting the environment. Furthermore, this reaction is carried out at room temperature and requires both raw materials to have good solubility in the reaction solvent, making it unsuitable for certain lithium salt raw materials, such as lithium sulfate.

[0008] In summary, current laboratory methods for preparing lithium sulfide nanocrystals each have their own problems, such as high energy consumption, complex processes, high costs, poor economic benefits, and environmental pollution, which cannot meet the future requirements of the battery industry for lithium sulfide.

[0009] In addition, lithium carbonate is also an important material in the lithium battery field. Currently, it is mainly used as a raw material for preparing cathode materials for lithium-ion batteries (such as nickel-cobalt-manganese ternary cathodes, lithium iron phosphate, and lithium-rich manganese-based cathodes), and it is also a standard substance for measuring all lithium products. Currently, the main industrial methods for producing lithium carbonate are the lithium ore preparation method and the brine preparation method. For example, published Chinese patents CN116477644A, CN116443900A, and CN116639713A. The lithium ore preparation method mainly uses sulfuric acid to acidify lithium ore to obtain lithium sulfate, which is then added with sodium carbonate to obtain crude lithium carbonate. The brine preparation method involves using resin-based adsorbents to separate lithium and magnesium, followed by concentration, washing, and impurity removal to obtain a lithium-containing concentrate, and finally adding soda ash to precipitate lithium carbonate. The above methods are suitable for preparing lithium carbonate from mineral resources, and the processes are relatively mature with a relatively complete industrial chain. Summary of the Invention

[0010] Based on the above problems, the present application provides a co-production preparation method of lithium sulfide and lithium carbonate, product and application, which has the advantages of easy-to-get raw materials, mild reaction conditions, green and environmental protection, easy large-scale production and convenient operation, and meets the purpose of green chemistry.

[0011] The purpose of the present application is realized by the following technical solutions.

[0012] A co-production preparation method of lithium sulfide and lithium carbonate, comprising the following steps:

[0013] S1, under the protection of inert atmosphere, lithium sulfate and sodium sulfide are taken according to a certain molar ratio and added to an organic alcohol solution to carry out a double decomposition reaction, and after stirring for a certain time, a suspension is obtained;

[0014] S2, under the protection of inert atmosphere, the suspension obtained in step S1 is subjected to solid-liquid separation, and is separated into solid and liquid phases, and the solid precipitate and liquid supernatant are collected respectively;

[0015] S3, under the protection of inert atmosphere, the supernatant collected in step S2 is evaporated to remove the organic alcohol solution therein, and a lithium sulfide crude product is obtained;

[0016] S4, under the protection of inert atmosphere, the lithium sulfide crude product obtained in step S3 is calcined at high temperature to obtain a lithium sulfide fine product;

[0017] S5, under the protection of inert atmosphere, the precipitate collected in step S2 is dissolved in water, and then sodium carbonate powder is added and stirred to carry out a reaction, and a suspension is obtained;

[0018] S6, the suspension obtained in step S5 is subjected to solid-liquid separation, and the solid precipitate is collected and dried to obtain a pure lithium carbonate product.

[0019] Preferably, in step S1, the lithium sulfate is anhydrous lithium sulfate or water-containing lithium sulfate after water removal, the sodium sulfide is anhydrous sodium sulfide or water-containing sodium sulfide after water removal, the molar ratio of the lithium sulfate to the sodium sulfide is (3-6):1, the double decomposition reaction temperature is 35-75℃, the stirring time is 4-48h, and the stirring is mechanical stirring or magnetic stirring; the mechanical stirring speed is 200-800rpm, and the magnetic stirring speed is 300-1000rpm.

[0020] Preferably, in step S1, the organic alcohol solution is an organic alcohol treated by molecular sieve water absorption after activation, and the organic alcohol includes at least one of methanol, ethanol, propanol, isopropanol, butanol, tert-butanol, ethylene glycol, glycerol, butanediol and hexanediol; in steps S1-S5, the inert atmosphere is helium atmosphere, neon atmosphere, nitrogen atmosphere or argon atmosphere.

[0021] Preferably, in step S2, the solid-liquid separation method of the suspension is centrifugation or suction filtration; the centrifugation is performed at a speed of 4000-10000 rpm for 5-30 min; the suction filtration is performed by a water pump or a mechanical pump at a vacuum degree of 0.006-0.06 MPa and a filter paper with a pore size of 0.1-1.0 μm; the solid-phase precipitate is excess unreacted lithium sulfate and by-product sodium sulfate; and the solute in the liquid-phase supernatant is lithium sulfide and a small amount of lithium sulfate.

[0022] Preferably, in step S3, the method for removing the alcohol solvent includes thermal evaporation at normal pressure and vacuum evaporation at room temperature; the thermal evaporation is performed at a heating temperature of 200-500 °C for 6-48 h; the vacuum evaporation is performed at a vacuum degree of 0.001-0.05 MPa for 1-36 h; and the obtained lithium sulfide crude product contains a small amount of lithium sulfate and alcohol adsorbed in the form of an adduct, but does not need to be washed with a solvent for removal.

[0023] Preferably, in step S4, the high-temperature calcination is performed at a temperature of 400-700 °C for 6-36 h; during the calcination, the lithium sulfate in the lithium sulfide crude product is reduced to lithium sulfide by the adsorbed alcohol; and the obtained product is high-purity lithium sulfide.

[0024] Preferably, in step S5, the number of moles of sodium carbonate added is equal to the difference between the number of moles of lithium sulfate added in step S1 and the number of moles of lithium sulfide; and the reaction is performed in a room-temperature environment.

[0025] Preferably, in step S6, the solid-liquid separation is performed by centrifugation or filtration, and the drying is performed in hot air.

[0026] A lithium-containing product, characterized by comprising lithium sulfide and lithium carbonate prepared by the co-production method of lithium sulfide and lithium carbonate.

[0027] An application of a lithium-containing product, wherein lithium sulfide and lithium carbonate prepared by the co-production method of lithium sulfide and lithium carbonate are applied to the production of rechargeable batteries.

[0028] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0029] (1) The lithium sulfide synthesis of the present application uses lithium sulfate and sodium sulfide as raw materials, which are low in cost, abundant in source and can be stored in air, and can meet the requirements of large-scale industrial production.

[0030] (2) Compared with the prior art, the method provided by the present application has mild reaction conditions, and the product is easy to separate; the crude product does not need to be washed with a solvent; the single auxiliary solvent used is organic alcohol, which is low in cost and non-toxic, and can be recycled and reused, thereby greatly reducing the production cost and protecting the environment. The above advantages make the method have great potential for industrial application.

[0031] (3) The lithium carbonate synthesis of the present application is co-produced with the preparation of lithium sulfide by utilizing the by-product of lithium sulfide production, so as to reduce the cost of lithium sulfide preparation and apply the process of industrial lithium carbonate production, suitable for mass production.

[0032] (4) The lithium sulfide and lithium carbonate products obtained by the technical scheme of the present application have high purity, so as to apply the lithium sulfide and lithium carbonate to the field of battery production. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The flow chart of the co-production preparation method of lithium sulfide and lithium carbonate of the present application.

[0034] Figure 2 The XRD graph of the crude lithium sulfide product prepared in Example One of the present application.

[0035] Figure 3 The XRD graph of the solid by-product obtained in Example One of the present application.

[0036] Figure 4 The data graph of the adsorbed alcohol solvent released by the crude lithium sulfide product prepared in the present application under heating condition monitored by a mass spectrometer.

[0037] Figure 5 The XRD graph of the fine lithium sulfide product prepared in Example Two of the present application.

[0038] Figure 6 The XRD graph of the fine lithium sulfide product prepared in Example Three of the present application.

[0039] Figure 7 The XRD graph of the lithium carbonate prepared in Example Three of the present application.

[0040] Figure 8 The performance graph of the positive electrode material made of the fine lithium sulfide product prepared in the present application in the application of lithium-sulfur battery. DETAILED DESCRIPTION

[0041] In order to make the technical scheme and advantages of the present application clearer, the present application and its beneficial effects will be further described in detail below in combination with the specific embodiments and the drawings of the specification, but the embodiments of the present application are not limited thereto.

[0042] The present application proposes a co-production preparation method of lithium sulfide and lithium carbonate, as shown in Figure 1 The specific steps include the following:

[0043] S1, under the protection of inert atmosphere, lithium sulfate and sodium sulfide are weighed according to a certain molar ratio and added to an organic alcohol solution for a double decomposition reaction, and a suspension is obtained after a certain time of stirring.

[0044] In this step, the lithium sulfate can use anhydrous lithium sulfate or water-containing lithium sulfate after water removal, the sodium sulfide can use anhydrous sodium sulfide or water-containing sodium sulfide after water removal. The molar ratio of lithium sulfate and sodium sulfide is (3-6):1, the temperature of the metathesis reaction is 35-75℃, the stirring time is 4-48h, the stirring is mechanical stirring or magnetic stirring; the speed of mechanical stirring is 200-800rpm; the speed of magnetic stirring is 300-1000rpm.

[0045] The water removal treatment step of the water-containing lithium sulfate is: under the protection of inert atmosphere, the water-containing lithium sulfate is heated by rotary evaporation or tube furnace, the heating temperature is 50-300℃, the heating time is 1-40h, to obtain anhydrous lithium sulfate. More preferably, the rotary evaporation heating temperature is 80-200℃, the heating time is 2-8h; the tube furnace heating temperature is 60-180℃, the heating time is 2-10h.

[0046] The water removal treatment step of the water-containing sodium sulfide is: under the protection of inert atmosphere, the water-containing sodium sulfide is heated by rotary evaporation or tube furnace, the heating temperature is 85-500℃, the heating time is 3-48h, to obtain anhydrous sodium sulfide. More preferably, the rotary evaporation heating temperature is 85-150℃, the heating time is 3-10h; the tube furnace heating temperature is 200-350℃, the heating time is 12-24h.

[0047] In this step, the inert atmosphere uses helium atmosphere or neon atmosphere or nitrogen atmosphere or argon atmosphere. The organic alcohol solution is an organic alcohol treated by activated molecular sieve water absorption, and the organic alcohol includes at least one of methanol, ethanol, propanol, isopropanol, butanol, tert-butanol, ethylene glycol, glycerol, butanediol and hexanediol.

[0048] In this step, the equation of the metathesis reaction of lithium sulfate and sodium sulfide in the organic alcohol solution is:

[0049] Li2SO4(sol)+Na2S(sol)→Li2S(sol)+Na2SO4(↓)

[0050] Li2SO4(sol)+Na2SO4(sol)→2LiNaSO4(sol)

[0051] In the formula, Li2SO4 represents lithium sulfate, Na2S represents sodium sulfide, Li2S represents lithium sulfide, Na2SO4 represents sodium sulfate, and LiNaSO4 represents sodium lithium sulfate.

[0052] S2, under the protection of inert atmosphere, the suspension obtained in step S1 is subjected to solid-liquid separation to separate into solid phase and liquid phase, and the solid phase precipitate (i.e. solid by-product) and the liquid phase solution are collected respectively.

[0053] In this step, the inert atmosphere is helium atmosphere, neon atmosphere, nitrogen atmosphere or argon atmosphere. The method for solid-liquid separation of the suspension is centrifugation or suction filtration. The centrifugation is performed at a speed of 4000-10000 rpm for 5-30 min. The suction filtration is performed by water pump or mechanical pump at a vacuum degree of 0.006-0.06 MPa and a filter paper pore size of 0.1-1.0 μm. The solid phase precipitate is excess unreacted lithium sulfate and by-product sodium sulfate (lithium).

[0054] S3, under the protection of inert atmosphere, the solution collected in step S2 is subjected to evaporation to remove the organic alcohol solution to obtain lithium sulfide crude product.

[0055] In this step, the inert atmosphere is helium atmosphere, neon atmosphere, nitrogen atmosphere or argon atmosphere. The method for removing the alcohol solvent includes thermal evaporation at normal pressure and vacuum evaporation at room temperature. The thermal evaporation is performed at a heating temperature of 200-500 °C for 6-48 h. The vacuum evaporation is performed at a vacuum degree of 0.001-0.05 MPa for 1-36 h. The obtained lithium sulfide crude product contains trace amount of lithium sulfate and adsorbed alcohol in the form of adduct, and does not need to be subjected to solvent washing for removal.

[0056] S4, under the protection of inert atmosphere, the lithium sulfide crude product obtained in step S3 is subjected to high temperature calcination to obtain lithium sulfide fine product.

[0057] In this step, the inert atmosphere is helium atmosphere, neon atmosphere, nitrogen atmosphere or argon atmosphere. The high temperature calcination is performed at a temperature of 400-700 °C for 6-36 h. During the calcination process, the lithium sulfate in the lithium sulfide crude product is reduced to lithium sulfide by the adsorbed alcohol, and the obtained product is high purity lithium sulfide fine product.

[0058] S5, under the protection of inert atmosphere, the precipitate collected in step S2 is dissolved in water, then sodium carbonate powder is added, and the reaction is performed by stirring to obtain a suspension.

[0059] In this step, the inert atmosphere is helium atmosphere, neon atmosphere, nitrogen atmosphere or argon atmosphere. The amount of sodium carbonate added is equal to the difference between the amount of lithium sulfate added in step S1 and the amount of lithium sulfide. The reaction is performed at room temperature.

[0060] In this step, the sodium carbonate reacts with sodium sulfate (lithium) in the solution:

[0061] xLiNaSO4(sol) + yLi2SO4(sol) + zNa2CO3(sol) → zLi2CO3(↓) + (x+y)Na2SO4(sol)

[0062] wherein Na2CO3 represents sodium carbonate, Li2CO3 represents lithium carbonate, and x, y, z represent chemical formula coefficients.

[0063] S6, performing solid-liquid separation on the suspension obtained in step S5, collecting the solid precipitate, and drying to obtain pure lithium carbonate product. The solid-liquid separation is performed by centrifugation or filtration, and the drying is performed in hot air.

[0064] The present application also provides a lithium-containing product comprising lithium sulfide and lithium carbonate prepared by the above-mentioned co-production method.

[0065] The present application also provides an application of a lithium-containing product, wherein the lithium sulfide and lithium carbonate prepared by the above-mentioned co-production method are applied to the production of rechargeable batteries.

[0066] The co-production method of lithium sulfide and lithium carbonate according to the present application will be described in detail below with reference to specific examples.

[0067] Example 1

[0068] A co-production method of lithium sulfide and lithium carbonate, comprising the following steps:

[0069] S1, in an argon atmosphere glove box, lithium sulfate anhydrous (Li2SO4) and sodium sulfide (Na2S) raw materials are weighed according to a molar ratio of 6:1, i.e. 339.5 mg of sodium sulfide and 2869.6 mg of lithium sulfate are weighed; then 15 ml of methanol solution is added, and continuous mechanical stirring is performed at 40°C for 4h at a speed of 800 rpm, and a white suspension is obtained after the complete double decomposition reaction; wherein the double decomposition reaction of sodium sulfide and lithium sulfate in the alcohol solution is as follows:

[0070] 6Li2SO4(sol) + Na2S(sol) → Li2S(sol) + Na2SO4(↓) + 5Li2SO4(sol)

[0071] 5Li2SO4(sol) + Na2SO4(sol) → 2LiNaSO4(sol) + 4Li2SO4(sol)

[0072] S2, under the protection of argon atmosphere, the suspension is transferred to a centrifuge for solid-liquid separation, the centrifuge speed is set to 10000 rpm, and the time is 5 min, and the solid by-product and the clear liquid are collected respectively.

[0073] S3, under the protection of argon atmosphere, the supernatant obtained in step S2 was transferred to a conical flask, which was placed on a heating table, and a distillation device was connected to start distillation; the temperature of the heating table was set to 250°C, and the temperature was kept constant for 48 h, until the alcohol solution was evaporated to dryness, to obtain the crude lithium sulfide product.

[0074] S4, under the protection of argon atmosphere, the crude lithium sulfide product was transferred to a porcelain boat, which was transferred to a tube furnace under the protection of argon, and the temperature was set to increase at a rate of 2°C / min, and the temperature was increased to 400°C, and the temperature was kept constant for 36 h, to obtain the fine lithium sulfide product

[0075] S5, under the protection of argon atmosphere, 3.0 g of the solid by-product collected in step S2 was dissolved in 10 ml of ultrapure water, then 2.31 g of sodium carbonate powder was added, and the mixture was stirred to react, to obtain a suspension.

[0076] The reaction of sodium carbonate with sodium sulfate in an alcohol solution is as follows:

[0077] 2LiNaSO4(sol)+4Li2SO4(sol)+5Na2CO3(sol)→5Li2CO3(↓)+6Na2SO4(sol)

[0078] S6, the suspension obtained in step S5 was subjected to solid-liquid separation, and the solid was collected and dried to obtain 1.36 g of lithium carbonate powder.

[0079] Example Two

[0080] A method for co-production of lithium sulfide and lithium carbonate, comprising the following steps:

[0081] S1, in a nitrogen atmosphere glove box, anhydrous lithium sulfate (Li2SO4) and sodium sulfide (Na2S) raw materials were weighed according to a molar ratio of 3:1, i.e. 181.1 mg of sodium sulfide and 1434.8 mg of lithium sulfate were weighed; then 15 ml of ethanol solution was added, and the mixture was continuously mechanically stirred at 35°C for 36 h at a speed of 200 rpm, to fully carry out the double decomposition reaction and obtain a white suspension; wherein the double decomposition reaction of sodium sulfide and lithium sulfate in an alcohol solution is as follows:

[0082] 3Li2SO4(sol)+Na2S(sol)→Li2S(sol)+Na2SO4(↓)+2Li2SO4(↓)

[0083] 2Li2SO4(sol)+Na2SO4(sol)→2LiNaSO4(sol)+Li2SO4(sol)

[0084] S2, under the protection of nitrogen atmosphere, the suspension was transferred to a centrifuge for solid-liquid separation, the centrifuge was set to rotate at a speed of 6000 rpm for 25 min, and the solid by-product and the supernatant were collected separately.

[0085] S3, under the protection of nitrogen atmosphere, the clear solution obtained in step S2 is transferred to a conical flask, placed on a heating table, and connected to a distillation device to start distillation; the temperature of the heating table is set to 500°C, and the temperature is kept constant for 6h, until the alcohol solution is evaporated to dryness, to obtain a crude lithium sulfide product.

[0086] S4, under the protection of nitrogen atmosphere, the crude lithium sulfide product is transferred to a porcelain boat and transferred to a tube furnace under argon protection, and the temperature is set to rise at a rate of 2°C / min, and the temperature is raised to 700°C, and the temperature is kept constant for 12h, to obtain a fine lithium sulfide product.

[0087] S5, under the protection of nitrogen atmosphere, 1.57g of solid by-product collected in step S2 is dissolved in 8ml of ultrapure water, then 0.92g of sodium carbonate powder is added, and the mixture is stirred to react, to obtain a suspension.

[0088] The reaction of sodium carbonate with sodium sulfate (lithium) in alcohol solution is:

[0089] 2LiNaSO4(sol) + Li2SO4(sol) + 2Na2CO3(sol) → 2Li2CO3(↓) + 3Na2SO4(sol)

[0090] S6, the suspension obtained in step S5 is subjected to solid-liquid separation, and the solid is collected and dried to obtain 0.55g of lithium carbonate powder.

[0091] Example Three

[0092] A co-production method for preparing lithium sulfide and lithium carbonate, comprising the following steps:

[0093] S1, in a neon atmosphere glove box, lithium sulfate (Li2SO4) and sodium sulfide (Na2S) raw materials are weighed according to a molar ratio of 5:1, i.e. 339.5mg of sodium sulfide and 2391.4mg of lithium sulfate are weighed; then 15ml of isopropyl alcohol solution is added, and the mixture is continuously stirred at 75°C for 48h at a speed of 450rpm, to obtain a white suspension; wherein the metathesis reaction of sodium sulfide and lithium sulfate in alcohol solution is:

[0094] 5Li2SO4(sol) + Na2S(sol) → Li2S(sol) + Na2SO4(↓) + 4Li2SO4(↓)

[0095] 4Li2SO4(sol) + Na2SO4(sol) → 2LiNaSO4(sol) + 3Li2SO4(↓)

[0096] S2, under neon gas atmosphere, the suspension was transferred to a centrifuge for solid-liquid separation, the centrifuge was set at 4000 rpm for 30 min, and the solid by-product and the supernatant were collected.

[0097] S3, under argon gas atmosphere, the supernatant obtained in step S2 was transferred to a conical flask, which was placed on a heating table, and a distillation device was connected to start distillation; the heating table was set at 200°C for 48 h, and the alcohol solution was evaporated to obtain the lithium sulfide crude product.

[0098] S4, under neon gas atmosphere, the lithium sulfide crude product was transferred to a porcelain boat, which was transferred to a tube furnace under argon gas atmosphere, and the temperature was set to increase at a rate of 5°C / min and then to 600°C for 6 h to obtain the lithium sulfide fine product.

[0099] S5, under neon gas atmosphere, 2.53 g of the solid by-product collected in step S2 was dissolved in 5 ml of ultrapure water, and then 1.84 g of sodium carbonate powder was added, and the mixture was stirred to obtain a suspension.

[0100] The reaction of sodium carbonate with sodium sulfate (lithium) in an alcohol solution is as follows:

[0101] 2LiNaSO4(sol) + 3Li2SO4(sol) + 4Na2CO3(sol) → 4Li2CO3(↓) + 5Na2SO4(sol)

[0102] S6, the suspension obtained in step S5 was subjected to solid-liquid separation, and the solid was collected and dried to obtain 1.09 g of lithium carbonate powder.

[0103] The lithium sulfide prepared in Examples 1 to 3 was characterized. The characterization results are shown in Figures 2 to 6 .

[0104] From Figure 2 The XRD results of the lithium sulfide crude product in the corresponding Example 1 showed that it contained a small amount of lithium sulfate (Li2SO4) impurity peak, which could be attributed to the weak solubility of Li2SO4 in alcohol, which was partially retained in the alcohol solution of lithium sulfide. From Figure 3 The XRD results of the solid by-product in the corresponding Example 1 showed that it contained lithium sulfate and sodium lithium sulfate. From Figure 5 and Figure 6 The XRD results of the lithium sulfide fine product in the corresponding Examples 2 and 3 showed that the final lithium sulfide prepared by the present application had high purity and no impurities. According to the fact that lithium sulfate can be prepared into lithium sulfide by carbothermal reduction, the disappearance of lithium sulfate in the crude product stage after calcination can be attributed to the fact that the residual ethanol in the lithium sulfide reduces the lithium sulfate impurities to lithium sulfide during high-temperature calcination, thereby obtaining high-purity lithium sulfide. Figure 4is the data of the tail gas of the crude lithium sulfide product after pyrolysis mass spectrometry detection, it can be seen that the ethanol signal in the tail gas significantly increases (from 4.4 x 10 -11 to 4.1 x 10 -10 mbar), proving the small amount of residual ethanol in the crude product.

[0105] From Figure 7 The corresponding lithium carbonate XRD results in Example Three can be seen that the lithium carbonate prepared by the present application has high purity and no impurities.

[0106] From Figure 8 The battery performance data graph can be seen that the self-made lithium sulfide and commercial lithium sulfide respectively assembled button cells have equivalent cycle performance at 0.5C rate. Therefore, the battery-grade lithium sulfide synthesized by the present application has good application prospect in lithium-sulfur batteries.

[0107] Compared with the existing technology for preparing lithium sulfide based on a metathesis reaction, the method provided by the present application benefits from the poor solubility of lithium sulfate in alcohol solution at room temperature, so that the residual lithium sulfate in the crude lithium sulfide product does not need to be removed by additional solvent washing, but is reduced to lithium sulfide by the residual alcohol at the high-temperature calcination stage, and finally high-purity lithium sulfide is obtained; the preparation of lithium carbonate combines the by-product of lithium sulfide production, which is consistent with the existing preparation technology based on lithium sulfate in industry, greatly improving the material utilization value. At the same time, by referring to the industrial production technology of lithium carbonate, the by-products of lithium sulfate and sodium sulfate can be further processed to obtain battery-grade lithium carbonate, thereby greatly improving the economic benefits of the entire process. The present application has the advantages of simple technical process, low energy consumption, no carbon emission, no greenhouse gas emission, recyclable auxiliary solvents, auxiliary reagents and by-products, simple and green process, no need for expensive instruments and equipment, and easy large-scale industrial production.

[0108] Although the functions and working processes of the present application have been described above in combination with the drawings, the present application is not limited to the specific functions and working processes described above, and the above specific embodiments are only illustrative and not limiting. Those skilled in the art can make many forms under the inspiration of the present application without departing from the purpose of the present application and the scope protected by the claims, and these all belong to the protection of the present application.

Claims

1. A method for the co-production of lithium sulfide and lithium carbonate, characterized in that, Includes the following steps: S1. Under an inert atmosphere, weigh lithium sulfate and sodium sulfide at a molar ratio of (3-6):1, add them to an organic alcohol solution for a metathesis reaction at a temperature of 35℃-75℃ and stir for 4-48 h to obtain a suspension; S2. Under an inert atmosphere, perform solid-liquid separation on the suspension obtained in step S1 to separate it into two phases, and collect the solid precipitate and the clear liquid phase respectively; wherein, the solid-liquid separation is performed by centrifugation or vacuum filtration at a speed of 4000-10000 rpm for 5-30 min; S3. Under an inert atmosphere, the clear liquid collected in step S2 is evaporated to remove the organic alcohol solution, and a crude lithium sulfide product is obtained. The crude lithium sulfide product contains trace amounts of lithium sulfate and alcohols adsorbed in the form of adducts. S4. Under an inert atmosphere, the crude lithium sulfide product obtained in step S3 is calcined at 400~700℃ for 6~36h. During the calcination process, the lithium sulfate in the crude lithium sulfide product is reduced to lithium sulfide by the adsorbed alcohol, and high-purity lithium sulfide product is obtained. S5. Under an inert atmosphere, the precipitate collected in step S2 is dissolved in water, and then sodium carbonate powder is added. The number of moles of sodium carbonate added is equal to the difference between the number of moles of lithium sulfate and lithium sulfide added in step S1. The mixture is stirred thoroughly at room temperature to obtain a suspension. S6. The suspension obtained in step S5 is subjected to solid-liquid separation, the solid precipitate is collected, and after drying, pure lithium carbonate product is obtained.

2. The method for co-producing lithium sulfide and lithium carbonate according to claim 1, characterized in that, In step S1, the lithium sulfate is anhydrous lithium sulfate or hydrous lithium sulfate that has undergone dehydration treatment. The dehydration treatment is carried out under an inert atmosphere by rotary evaporation or tube furnace heating. The rotary evaporation heating temperature is 80~200℃ and the heating time is 2~8h; the tube furnace heating temperature is 60~180℃ and the heating time is 2~10h. The sodium sulfide is anhydrous sodium sulfide or hydrated sodium sulfide that has undergone dehydration treatment. The dehydration treatment is carried out under an inert atmosphere by rotary evaporation or tubular furnace heating. The rotary evaporation heating temperature is 85~150℃ and the heating time is 3~10h; the tubular furnace heating temperature is 200~350℃ and the heating time is 12~24h. The stirring is mechanical stirring or magnetic stirring. The speed of mechanical stirring is 200~800 rpm, and the speed of magnetic stirring is 300~1000 rpm.

3. The method for co-producing lithium sulfide and lithium carbonate according to claim 1, characterized in that, In step S1, the organic alcohol solution is an organic alcohol that has undergone water absorption treatment by activated molecular sieves. The organic alcohol includes at least one of methanol, ethanol, propanol, isopropanol, butanol, tert-butanol, ethylene glycol, glycerol, butanediol, and hexanediol. In steps S1-S5, the inert atmosphere is a helium atmosphere, a neon atmosphere, a nitrogen atmosphere, or an argon atmosphere.

4. The method for co-producing lithium sulfide and lithium carbonate according to claim 1, characterized in that, In step S2, the filtration is performed by a water pump or a mechanical pump, with a vacuum degree of 0.006~0.06MPa and a filter paper pore size of 0.1~1.0μm; the solid precipitate is excess unreacted lithium sulfate and byproduct sodium lithium sulfate, and the solute in the clear liquid phase is lithium sulfide and trace amounts of lithium sulfate.

5. The method for co-producing lithium sulfide and lithium carbonate according to claim 1, characterized in that, The method for removing the organic alcohol solution in step S3 includes thermal evaporation under normal pressure and vacuum evaporation at room temperature; the heating temperature for thermal evaporation is 200~500℃ and the time is 6~48h; the vacuum degree for vacuum evaporation is 0.001~0.05MPa and the time is 1~36h.

6. The method for co-producing lithium sulfide and lithium carbonate according to claim 1, characterized in that, In step S6, solid-liquid separation is performed by centrifugation or filtration, and drying is carried out in hot air.

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