Method for preparing lithium sulfide through hydrogen reduction of lithium sulfate

Abstract

The invention relates to the technical field of preparation of lithium sulfide, in particular to a method for preparing lithium sulfide through hydrogen reduction of lithium sulfate. According to the specific technical scheme, the method for preparing the lithium sulfide by reducing the lithium sulfate through the hydrogen comprises the steps that the lithium sulfate is smashed to be micron-sized and then fed into a fluidized bed reactor, then high-purity hydrogen preheated to 850 DEG C is introduced into the fluidized bed reactor from the bottom of the fluidized bed reactor, the reaction temperature is controlled to be 850 + / -20 DEG C, and the reaction time is controlled to be 5-10 min. The hydrogen reduction method is relatively low in reaction temperature (700-900 DEG C), hydrogen is used as a clean reducing agent, a reaction byproduct is only water, and the problems of insufficient purity, high energy consumption, serious environmental pollution and the like in a traditional lithium sulfide preparation method can be avoided. The introduction of the fluidized bed technology can greatly enhance the gas-solid phase heat and mass transfer efficiency, realizes the continuity and automation of the process, and is an important path for realizing the industrialization of the reaction.

Description

Technical Field

[0001] This invention relates to the field of lithium sulfide preparation technology, and specifically to a method for preparing lithium sulfide by hydrogen reduction of lithium sulfate. Background Technology

[0002] Lithium-ion batteries, with their high energy and power density, are widely studied due to their advantages such as long cycle life and low environmental pollution. Since the commercialization of lithium-ion batteries by Sony in Japan in 1991, the lithium-ion battery industry has developed rapidly and has been widely applied in various aspects of people's lives. In recent years, the rapid development of the new energy vehicle industry has also led to a continuous expansion of the demand for lithium-ion batteries. Existing research shows that traditional lithium-ion batteries use graphite as the negative electrode, lithium cobalt oxide, lithium iron phosphate, ternary materials, etc., as the positive electrode, and organic electrolytes as the intermediate electrolyte for conducting lithium ions. However, the energy density of traditional lithium-ion batteries is approaching its limit. In addition, due to the flammability, explosiveness, and volatility of the organic liquid electrolytes used in traditional lithium-ion batteries, short circuits, damage, and leakage during cycling can easily lead to fires, explosions, and other adverse events, posing a great safety hazard to human life. Therefore, it is crucial to explore a new battery system that simultaneously achieves high energy density and high safety performance.

[0003] Compared to traditional liquid lithium-ion batteries using organic electrolytes, all-solid-state lithium-ion batteries offer significant improvements in safety performance. This is primarily due to the use of non-flammable solid electrolytes, avoiding the flammability and explosion issues common in traditional liquid lithium-ion batteries. Furthermore, the compact structure of all-solid-state lithium batteries results in higher energy density (reaching over 450 kWh / kg), a significant advantage over traditional liquid lithium batteries, attracting widespread attention and becoming a major research direction for next-generation energy storage technology. As the most crucial component of all-solid-state batteries, the solid electrolyte plays an irreplaceable role in improving the cycle performance and energy density of lithium-ion batteries. It replaces the electrolyte and separator in traditional liquid batteries, conducting lithium ions between the positive and negative electrodes. Polymer solid electrolytes, oxide solid electrolytes, halide solid electrolytes, and sulfide solid electrolytes are currently the four most researched types of solid electrolytes. In comparisons of ionic conductivity, sulfide solid electrolytes stand out. Existing research has shown that sulfide solid electrolytes achieve an ionic conductivity of 10-1. -2 S·cm -1The ionic conductivity of solid-state electrolytes (SSEs) is on the order of magnitude, approaching or even exceeding that of electrolytes in traditional liquid batteries. However, in terms of ionic conductivity, the most critical parameter for evaluating electrolytes, oxide solid-state electrolytes, halide solid-state electrolytes, and polymer solid-state electrolytes all lag far behind sulfide solid-state electrolytes. Therefore, sulfide solid-state electrolytes have been extensively studied due to their high ionic conductivity. However, sulfide solid-state electrolytes also face a critical problem: cost. The high price of sulfide solid-state electrolytes hinders their application in new energy vehicles. Therefore, reducing the cost of sulfide solid-state electrolytes is crucial for their widespread adoption.

[0004] Lithium sulfide (Li2S), as a key precursor for sulfide solid electrolytes and cathode materials in lithium-sulfur batteries, plays a crucial role in next-generation high-energy-density lithium batteries. With the rapid development of the global new energy vehicle industry, the demand for high-safety, high-energy-density solid-state batteries is increasing, making the market prospects for lithium sulfide very promising.

[0005] Traditional methods for preparing lithium sulfide include:

[0006] Direct reaction method: The direct reaction of lithium metal with sulfur (2Li+S→Li2S) is simple in principle, but the raw material lithium metal is expensive and chemically active, resulting in high production costs and making it unsuitable for large-scale application.

[0007] Carbothermic reduction method: Lithium sulfate reacts with carbon powder at high temperature (Li2SO4+4C→Li2S+4CO). Although the raw material cost is relatively low, the reaction temperature needs to be as high as 1100℃ or above, and it is easy to produce by-products (such as Li2O, Li2CO3), resulting in low product purity (usually below 99%), and accompanied by a large amount of carbon dioxide emissions.

[0008] Solvent method and high temperature and high pressure method: Although these methods can obtain high purity, they either use flammable and explosive organic solvents or have extremely high equipment requirements and low single-batch output, making it difficult to meet the needs of large-scale industrial production.

[0009] Therefore, traditional lithium sulfide preparation methods suffer from problems such as insufficient purity, high energy consumption, and significant environmental pollution, necessitating the development of an efficient and clean large-scale production process. Summary of the Invention

[0010] To address the shortcomings of existing technologies, this invention provides a method for preparing lithium sulfide by hydrogen reduction of lithium sulfate.

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] This invention discloses a method for preparing lithium sulfide by hydrogen reduction of lithium sulfate. The lithium sulfate is pulverized to the micron level and fed into a fluidized bed reactor. Then, high-purity hydrogen gas preheated to 850°C is introduced into the fluidized bed reactor from the bottom. The reaction temperature is controlled at 850±20°C and the reaction time is 5-10 min.

[0013] Preferably, the top of the fluidized bed reactor is connected to a gas separation unit, and the separated gas is sent into the fluidized bed reactor.

[0014] Preferably, a closed spiral cooler is connected to the outlet of the fluidized bed reactor to cool the material to room temperature under the protection of argon gas.

[0015] Preferably, the material cooled by the closed spiral cooler is sent into a glove box and sealed under an inert atmosphere.

[0016] Preferably, a gas distribution plate is provided at the bottom of the fluidized bed reactor, through which hydrogen gas, after preheating, enters the fluidized bed reactor.

[0017] Preferably, the purity of the hydrogen is ≥99.999%, and the purity of the lithium sulfate is ≥99.5%.

[0018] The present invention has the following beneficial effects:

[0019] 1. This invention employs a hydrogen reduction method (Li₂SO₄ + 4H₂ → Li₂S + 4H₂O), which has a relatively low reaction temperature (700-900℃). Furthermore, hydrogen acts as a clean reducing agent, and the only byproduct is water, thus avoiding the problems of insufficient purity, high energy consumption, and significant environmental pollution associated with traditional lithium sulfide preparation methods. The introduction of fluidized bed technology greatly enhances the gas-solid phase heat and mass transfer efficiency, enabling continuous and automated processes, and is a crucial pathway to the industrialization of this reaction.

[0020] 2. The lithium sulfate fluidized bed hydrogen reduction process utilizes hydrogen as a reducing agent to reduce lithium sulfate (Li₂SO₄) to high-purity lithium sulfide in a fluidized bed reactor. Compared with the traditional carbothermal reduction method, this method has significant advantages such as high product purity (up to 99.9% or more), lower reaction temperature, no carbon dioxide emissions, and suitability for continuous large-scale production. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Unless otherwise specified, the technical means used in the implementation examples are conventional means well known to those skilled in the art.

[0023] The core reaction of the lithium sulfate fluidized bed hydrogen reduction process disclosed in this invention is:

[0024] Li2SO4(s)+4H2(g)→Li2S(s)+4H2O(g)(ΔH>0)

[0025] This reaction is endothermic and requires high temperature. The reaction temperature needs to be controlled between 700℃ and 900℃. If the temperature is too low, the reduction reaction will be incomplete; if the temperature is too high (>1000℃), it may cause Li2S to melt (melting point about 938℃) or decompose, and may also trigger complex side reactions of lithium sulfate decomposition products.

[0026] Thermodynamic analysis shows that increasing the partial pressure of hydrogen gas favors the forward reaction. Therefore, this invention uses excess hydrogen gas (with a pressure of 0.2-0.3 MPa) to improve the conversion rate and reaction rate of lithium sulfate, achieving a lithium sulfate conversion rate of 99.999%.

[0027] This invention employs a three-step reduction fluidized bed process to prepare lithium sulfide, the specific process of which is as follows:

[0028] 1. Raw material pretreatment section:

[0029] Battery-grade lithium sulfate raw material (purity ≥99.5%) is subjected to micron-level ultrafine grinding using an air jet mill to ensure uniform particle size, which is beneficial to fluidization quality and reaction rate. The processed lithium sulfate powder is then continuously and stably fed into the main reaction zone of the fluidized bed reactor through a closed screw feeder and a star feed valve.

[0030] 1.1 Reduction Reaction Section:

[0031] Pretreated lithium sulfate powder enters the fluidized bed reactor. High-purity hydrogen gas (purity ≥99.999%) is preheated by an electric heater (to 850℃) and then fed into the bed from the bottom of the reactor through a gas distribution plate. Under the action of the distribution plate, the hydrogen gas forms a uniform gas flow, causing the lithium sulfate solid particles to be suspended and fluidized (i.e., in a suspended state), achieving sufficient contact and mixing between the gas and solid phases. An electromagnetic heating furnace is installed outside the fluidized bed reactor to provide the heat required for the reaction, and the temperature of the reaction zone is precisely controlled at 850±20℃ through thermocouples and a control system.

[0032] To promote a complete reaction, a circulating fluidized bed mode can be adopted. The unreacted hydrogen and water vapor mixture is discharged from the top of the fluidized bed reactor and enters the gas separation unit (i.e., gas-liquid separator). The separated hydrogen is replenished and circulated back to the inlet of the fluidized bed reactor, realizing the efficient utilization of hydrogen.

[0033] 2. Product processing and purification section:

[0034] The resulting lithium sulfide solid particles are discharged from the outlet at the middle or end of the fluidized bed reactor. Because Li₂S is highly hygroscopic and oxidizable, the hot material must immediately enter a closed spiral cooler and be cooled to room temperature under argon-filled protection. The cooled product is then placed in a glove box (inert atmosphere protection) and sealed with argon for storage and transportation.

[0035] 3. Exhaust gas treatment section:

[0036] The exhaust gas produced by the reaction (mainly water vapor and excess hydrogen) is cooled by a condenser, and the condensate is collected and treated. Most of the non-condensable gases (mainly hydrogen) are returned to the system for recycling, and a small amount of purge gas is sent to a burner for treatment or purified and recovered by PSA (pressure swing adsorption).

[0037] The structure of the fluidized bed reactor in this invention is as follows:

[0038] Fluidized bed reactor structure: A multi-stage fluidized bed or circulating fluidized bed is employed, with internal baffles or cyclone separators to reduce gas backmixing, enhance the plug flow effect, and ensure uniform material residence time distribution, thereby improving conversion rate. The fluidized bed reactor lining should be made of high-purity alumina refractory material, effectively resisting the erosion of Li₂SO₄-Li₂S melt.

[0039] Material selection: The parts of the fluidized bed reactor that come into contact with high-temperature materials should be made of high-temperature resistant alloys (such as 310S stainless steel) or lined with refractory materials to withstand the corrosion and reducing environment of high-temperature hydrogen.

[0040] Gas distribution plate: A perforated plate or nozzle-type distribution plate is used to ensure uniform gas distribution and prevent material from falling and clogging the gas distribution plate.

[0041] Sealing system: The entire feeding, reaction and discharge system must operate under strict sealing conditions. It usually adopts a combination of sealing methods such as mechanical seals and nitrogen protection seals to prevent air and moisture from entering.

[0042] Control system: Adopting an advanced DCS (Distributed Control System) or PLC (Programmable Logic Controller) system, it performs precise automatic control of key parameters such as temperature, pressure, hydrogen flow rate, and material level to ensure operational safety and product stability.

[0043] The specifications and technical requirements of the equipment used in this invention are shown in Table 1 below.

[0044] Table 1. Main Equipment Specifications and Technical Requirements

[0045] Equipment Name Specifications and technical requirements fluidized bed reactor Φ2000×10000mm, 310S stainless steel / alumina lining, design temperature 1000℃ electric heater Electric heating, power 300kW, maximum preheating temperature 900℃ screw feeder Twin-screw extruder, argon-sealed, feeding accuracy ±1%. Spiral cooler Spiral type, jacketed water cooling, with argon protection Exhaust gas treatment system Condenser, gas-liquid separator, PSA hydrogen recovery unit glove box The oxygen content in the water is all <0.1ppm.

[0046] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing lithium sulfide by hydrogen reduction of lithium sulfate, characterized in that: After lithium sulfate is pulverized to the micron level, it is fed into a fluidized bed reactor. Then, high-purity hydrogen gas preheated to 850℃ is introduced into the fluidized bed reactor from the bottom. The reaction temperature is controlled at 850±20℃ and the reaction time is 5-10 min.

2. The method for preparing lithium sulfide by hydrogen reduction of lithium sulfate according to claim 1, characterized in that: The top of the fluidized bed reactor is connected to a gas separation unit, and the separated gas is sent into the fluidized bed reactor.

3. The method for preparing lithium sulfide by hydrogen reduction of lithium sulfate according to claim 1, characterized in that: The fluidized bed reactor is connected to a closed spiral cooler at the outlet, which cools the material to room temperature under the protection of argon gas.

4. The method for preparing lithium sulfide by hydrogen reduction of lithium sulfate according to claim 3, characterized in that: The material cooled by the closed spiral cooler is sent into a glove box and sealed under an inert atmosphere.

5. The method for preparing lithium sulfide by hydrogen reduction of lithium sulfate according to claim 1, characterized in that: The fluidized bed reactor is equipped with a gas distribution plate at the bottom. After hydrogen is preheated, it enters the fluidized bed reactor through the gas distribution plate.

6. The method for preparing lithium sulfide by hydrogen reduction of lithium sulfate according to claim 1, characterized in that: The purity of the hydrogen is ≥99.999%, and the purity of the lithium sulfate is ≥99.5%.