Preparation method of lithium sulfide, solid-state electrolyte and solid-state battery

Abstract

The invention discloses a preparation method of lithium sulfide, a solid-state electrolyte and a solid-state battery, the lithium sulfide is used for preparing the solid-state electrolyte, and the preparation method comprises the following steps: uniformly mixing lithium sulfate, an organic carbon source and a high-molecular polymer in a solvent to obtain a mixed solution; wherein the mass ratio of the lithium sulfate to the organic carbon source is 1: (0.7-1), and the mass ratio of the organic carbon source to the high-molecular polymer is (0.7-1): (0.1-2.5); the ratio of the mass sum of the residual carbon amount of the organic carbon source and the residual carbon amount of the high-molecular polymer to the mass of the lithium sulfate is (0.2-0.25): 1; carrying out spray drying on the mixed solution to obtain a precursor material; and sintering the precursor material to obtain the product lithium sulfide. The sulfide solid electrolyte prepared by the preparation method is high in purity and low in carbon impurity content.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a method for preparing lithium sulfide, a solid electrolyte, and a solid battery. Background Technology

[0002] Lithium sulfide possesses an antifluorite crystal structure, where lithium ions migrate through tetrahedral and octahedral interstices, forming abundant transport channels. This structure allows lithium sulfide to achieve ionic conductivity close to that of liquid electrolytes (up to 10⁻⁶) at room temperature. -2 The S / cm ratio is significantly higher than that of oxide electrolytes.

[0003] Lithium sulfide is a key precursor material for the synthesis of sulfide solid electrolytes, directly affecting the ionic conductivity and battery performance of solid electrolytes, and limiting the subsequent synthesis process and product performance of sulfide solid electrolytes. In solid-state batteries, lithium sulfide, as an electrolyte material, can enable the energy density of all-solid-state lithium batteries to exceed 500 Wh / kg (while traditional lithium batteries are about 300 Wh / kg), while suppressing lithium dendrite growth and improving safety.

[0004] Among the product specifications of lithium sulfide, purity is particularly critical, significantly impacting the preparation of sulfide electrolytes. Currently, lithium sulfide production primarily relies on the solid-phase method of carbothermic reduction of lithium sulfate. However, this process generates numerous impurities, such as carbon impurities, resulting in low purity lithium sulfide and ultimately affecting the performance of sulfide solid-state electrolytes using lithium sulfide. The carbon impurities in lithium sulfide can impart a certain degree of electronic conductivity to the sulfide solid-state electrolyte, a negative characteristic that needs to be avoided for solid-state electrolytes.

[0005] Therefore, how to improve the purity of lithium sulfide is a technical problem to be solved in this field. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this application is to provide a method for preparing lithium sulfide, a solid electrolyte and a solid battery, which can effectively improve the purity of the prepared lithium sulfide.

[0007] To achieve one, some, or all of the above objectives, or other objectives, the first aspect of this application provides a method for preparing lithium sulfide, characterized in that the lithium sulfide is used to prepare a solid electrolyte, comprising the following steps:

[0008] Lithium sulfate, an organic carbon source, and a polymer are mixed uniformly in a solvent to obtain a mixture; wherein the mass ratio of lithium sulfate to the organic carbon source is 1:(0.7~1), and the mass ratio of the organic carbon source to the polymer is (0.7~1):(0.1~2.5); the ratio of the sum of the residual carbon content of the organic carbon source and the residual carbon content of the polymer to the mass of lithium sulfate is (0.2~0.25):1;

[0009] The mixture is spray-dried to obtain the precursor material;

[0010] The precursor material is sintered to obtain lithium sulfide.

[0011] Furthermore, the particle size of the precursor material is 1–10 μm;

[0012] Furthermore, the particle size of the precursor material is 1–5 μm;

[0013] Furthermore, the lithium sulfate has a particle size of less than or equal to 5 μm, and the organic carbon source has a particle size of less than or equal to 1 μm.

[0014] Furthermore, the organic carbon source includes at least one of glucose, sucrose, and citric acid; and / or, the polymer includes at least one of polyethylene glycol, polyvinyl alcohol, and polyoxyethylene.

[0015] Furthermore, the molecular weight of the polymer is less than or equal to 400.

[0016] Furthermore, the solvent is water or ethanol.

[0017] Furthermore, the inlet air temperature for the spray drying is 100℃~200℃.

[0018] Further, the step of sintering the precursor material includes:

[0019] The precursor material is placed in an inert atmosphere and heated to 800℃~900℃ at a heating rate of 3~6℃ / min, and held at that temperature for 2~12h to sinter the precursor material.

[0020] Furthermore, the ratio of the mass of the residual carbon of the organic carbon source and the residual carbon of the polymer to the mass of the lithium sulfate is (0.21~0.22):1.

[0021] A second aspect of this application provides a solid electrolyte comprising lithium sulfide prepared by the above-described method for preparing lithium sulfide.

[0022] A third aspect of this application provides a solid-state battery, including a positive electrode, a negative electrode, and a solid electrolyte, wherein the solid electrolyte comprises lithium sulfide prepared by the above-described method for preparing lithium sulfide.

[0023] The lithium sulfide preparation method, solid electrolyte, and solid battery provided in this application utilize a mixed carbon source of organic carbon source and polymer. The uniform dispersion of lithium sulfate and carbon source is achieved through solvent mixing. Combined with the spherical precursor formed by spray drying, the problem of uneven mixing caused by point-to-point contact in the solid-phase method is solved. At the same time, through the synergistic effect of organic carbon source and polymer, the total amount of carbon source is precisely controlled, which ensures that lithium sulfate is fully reduced while avoiding excessive carbon source residue. The prepared sulfide solid electrolyte has high purity and low carbon impurity content. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] in:

[0026] Figure 1 SEM image of the precursor material obtained during the preparation process in Example 1;

[0027] Figure 2 Here is a SEM image of the precursor material obtained during the preparation process of Comparative Example 1;

[0028] Figure 3 The XRD pattern of lithium sulfide prepared in Example 1;

[0029] Figure 4 The image shows the XRD pattern of lithium sulfide prepared in Comparative Example 1. Detailed Implementation

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein in the specification of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the terms "comprising" and "having," and any variations thereof, in the specification, claims, and foregoing drawings of this application, are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the specification, claims, or foregoing drawings of this application are used to distinguish different objects, not to describe a particular order.

[0031] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0032] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings.

[0033] The lithium sulfide prepared in this application is used to prepare a solid electrolyte, so it is desirable that the product contains as few carbon impurities as possible. Since the core function of a solid electrolyte is to enable lithium-ion conduction and block electron conduction, and carbon impurities can significantly enhance the electron conduction capability of sulfide solid electrolytes, the carbon impurity content in the product must be strictly controlled. Battery-grade lithium sulfide typically requires a carbon impurity content of less than 0.1%, and reducing the impact of carbon impurities on subsequent battery performance is crucial.

[0034] In conventional preparation methods, lithium sulfide is mostly prepared via a solid-state method of carbothermic reduction of lithium sulfate, which involves mixing and sintering inorganic or organic carbon compounds with lithium sulfate as a reducing agent. The core challenge of this process lies in the precise control of the carbon source dosage: during solid-state mixing, lithium sulfate particles and carbon source particles can only achieve point-to-point contact, resulting in numerous voids in the precursor and preventing the achievement of an ideal uniform dispersion. This leads to two problems: firstly, some areas of lithium sulfate are incompletely reduced due to lack of carbon source contact, producing inorganic impurities such as Li₂O; secondly, some areas have excessive carbon source, which remains as carbon impurities after the reaction. Increasing the carbon source dosage to ensure complete reduction of lithium sulfate further exacerbates the problem of excessive carbon impurities. Therefore, how to prepare high-purity lithium sulfide with acceptable carbon impurity levels has always been a challenge in the industry.

[0035] This application embodiment combines an organic carbon source and a polymer as a comprehensive carbon source. By finely adjusting the ratio and using spray drying to form a precursor encapsulation structure in which the polymer encapsulates both lithium sulfate and the organic carbon source, the dispersion uniformity of the precursor is optimized. The polymer fills the gaps between the lithium sulfate and the organic carbon source, achieving a near-ideal uniform dispersion. The technical solution and its effects will be explained in detail below.

[0036] This application provides a method for preparing lithium sulfide, wherein the lithium sulfide is used to prepare a solid electrolyte, comprising the following steps:

[0037] S1: Lithium sulfate, an organic carbon source, and a polymer are mixed evenly in a solvent to obtain a mixture; wherein the mass ratio of lithium sulfate to the organic carbon source is 1:(0.7~1), and the mass ratio of the organic carbon source to the polymer is (0.7~1):(0.1~2.5); the ratio of the sum of the residual carbon content of the organic carbon source and the residual carbon content of the polymer to the mass of lithium sulfate is (0.2~0.25):1;

[0038] S2: Spray dry the mixture to obtain the precursor material;

[0039] S3: The precursor material is sintered to obtain lithium sulfide.

[0040] In step S1 above, lithium sulfate serves as both a lithium and sulfur source, and is reduced to lithium sulfide in the subsequent reduction reaction. An organic carbon source and a polymer are used as reducing agents, and the polymer also improves the dispersion uniformity of the mixture. The organic carbon source can be solid particles or an aqueous solution. Organic carbon sources generally have a higher residual carbon content per unit mass than some low-molecular-weight polymers, requiring less residual carbon to achieve the same contribution. If an organic carbon source is not used, and the reduction relies solely on the polymer, the residual carbon rate needs to be increased by raising the polymer's molecular weight. However, excessively high molecular weight polymers lead to a sharp increase in solution viscosity, making uniform mixing difficult and hindering the uniform dispersion of the raw materials. This, in turn, increases the impurities in the lithium sulfide product.

[0041] Weigh the raw materials according to the following proportions: the mass ratio of lithium sulfate to organic carbon source is controlled within the range of 1:(0.7~1), for example, this range can be 1:0.7, 1:0.8, 1:0.9, 1:1, etc.; the mass ratio of organic carbon source to polymer is controlled within the range of (0.7~1):(0.1~2.5), for example, this range can be 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.8, 1:1, 1:1.5, 0.9:0.2, 0. 0.9:0.5, 0.9:0.8, 0.9:1, 0.9:1.1, 0.9:1.2, 0.9:1.5, 0.9:1.8, 0.8:0.5, 0.8:0.6, 0.8:0.7, 0.8:0.8, 0.8:1, 0.8:1.5, 0.8:2, 0.8:2.2, 0.7:0.6, 0.7:0.8, 0.79:1, 0.7:1.2, 0.7:1.5, 0.7:2, 0.7:2.2, 0.7:2.5, etc. Simultaneously, ensure that the sum of the residual carbon content of the organic carbon source and the polymer is in a mass ratio of (0.2~0.25):1 to lithium sulfate. For example, this range can be 0.2:1, 0.21:1, 0.22:1, 0.23:1, 0.24:1, 0.25:1, etc. Specifically, this can be achieved by pre-measuring the residual carbon percentage of the selected organic carbon source and polymer at the sintering temperature. Measure the residual carbon mass percentage (X1) per unit mass of organic carbon source and (X2) per unit mass of polymer. Then, determine the amount of each raw material by conversion. Let the mass of the organic carbon source be Y1 and the mass of the polymer be Y2. The sum of the residual carbon mass is then X1Y1 + X2Y2. The residual carbon content can be measured through thermogravimetric analysis. Place the sample in an inert atmosphere, control the temperature through a program, and allow the sample to undergo evaporation and pyrolysis processes. The final carbonaceous residue is the residual char. The instrument records the mass change in real time, and after the mass stabilizes, calculate the residual char mass percentage.

[0042] The weighed lithium sulfate, organic carbon source, and polymer are added sequentially to the solvent and mixed using magnetic or mechanical stirring until a homogeneous, transparent mixture without obvious particles is formed, ensuring uniform dispersion of all raw materials. For example, the stirring speed is controlled at 200-300 rpm, and the stirring time is 30-60 minutes.

[0043] In step S2 above, the mixture is introduced into a spray drying device. The rotation speed of the atomizing disc is adjusted according to the viscosity and solid content of the mixture to control the droplet size, thereby controlling the particle size of the precursor after spray drying. Specific values ​​are not specifically limited herein, and those skilled in the art can set them flexibly according to actual needs. The inlet air temperature is set according to the solvent type. For an aqueous mixture, the inlet air temperature is 150~200℃; for an ethanol-based mixture, the inlet air temperature is 100~150℃, so that the sprayed droplets can be quickly dried into powder. After drying, the precursor material is collected. This precursor is a uniform, near-spherical particle, used for subsequent sintering.

[0044] In step S3 above, the precursor material is placed in a tube furnace for sintering. An inert protective gas, such as nitrogen or argon, is continuously introduced during sintering. The sintering heating process uses a segmented heating method, first heating to 800-900℃ at a rate of 3-6℃ / min and holding for 2-12 hours. After sintering, the inert gas is maintained, allowing the product to cool to room temperature with the furnace, yielding lithium sulfide. The film-forming characteristics of the polymer during spray drying allow the polymer and organic carbon source to coat the surface of lithium sulfate particles. After heat treatment, a carbon film in close contact with lithium sulfate is formed, significantly increasing the reaction contact area. Combined with control of the precursor particle size, the conversion rate can be significantly improved. Simultaneously, by controlling the ratio of lithium sulfate to organic carbon source, and the ratio of organic carbon source to polymer, the carbon source can be accurately supplemented, reducing the carbon content of the product, resulting in a higher lithium sulfide yield, lower carbon content, and higher purity. The lithium sulfide product can be further refined in particle size according to actual application requirements to obtain lithium sulfide products with different particle sizes.

[0045] The lithium sulfide prepared by the method in this embodiment uses a mixed carbon source of organic carbon source and polymer. The uniform dispersion of lithium sulfate and carbon source is achieved through solvent mixing. Combined with the spherical precursor formed by spray drying, the problem of uneven mixing caused by point-to-point contact in the solid-state method is solved. At the same time, through the synergistic effect of organic carbon source and polymer, the total amount of carbon source is precisely controlled, which ensures that lithium sulfate is fully reduced and avoids excessive carbon source residue. The prepared sulfide solid electrolyte has high purity and low carbon impurity content.

[0046] In some embodiments, the precursor material has a particle size of 1–10 μm. During the spray drying process in step S2, the droplet size is controlled by adjusting parameters such as the atomizing disc rotation speed and inlet air temperature, thereby ensuring that the particle size of the precursor material obtained after drying is within the range of 1–10 μm. For example, the precursor particle size can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, etc. In some embodiments, the precursor material has a particle size of 1–5 μm. Precursor materials within this particle size range have suitable specific surface area and particle morphology. During the sintering process in step S3, lithium sulfate can fully contact and react with the carbon source (including organic carbon sources and polymers), avoiding the problem of insufficient reaction inside the particles due to excessively large particle size, thereby improving the conversion rate and conversion efficiency of lithium sulfide and reducing impurity generation.

[0047] In some embodiments, the lithium sulfate has a particle size of less than or equal to 5 μm, and the organic carbon source has a particle size of less than or equal to 1 μm. The lithium sulfate and organic carbon source can be pretreated using powder refining processes such as ball milling or air jet milling to control the particle size of the lithium sulfate to less than or equal to 5 μm. For example, the particle size can be 5 μm, 4 μm, 3 μm, 2 μm, 1 μm, etc.; and the particle size of the organic carbon source can be controlled to less than or equal to 1 μm. For example, the particle size can be 1 μm, 0.8 μm, 0.5 μm, 0.3 μm, 0.1 μm, etc. In some embodiments, the organic carbon source can also be in liquid form, such as liquid glucose. Small-particle-size lithium sulfate and organic carbon source have a larger specific surface area, allowing for faster and more complete dispersion in the solvent during the solvent mixing process in step S1, forming a uniform mixture.

[0048] In some embodiments, the organic carbon source includes at least one of glucose, sucrose, and citric acid.

[0049] In some embodiments, the polymer includes at least one of polyethylene glycol, polyvinyl alcohol, and polyethylene oxide.

[0050] In some embodiments, the molecular weight of the polymer is less than or equal to 400. Exemplarily, the molecular weight can be 400, 300, 200, 100, etc., specifically selected according to the chosen polymer type and process requirements. For example, when polyethylene glycol (PEG) is used as the polymer, PEG400, etc., can be selected. The molecular weight of the polymer directly affects its dissolution rate and solution viscosity in the solvent. Polymers with a molecular weight ≤400 can dissolve rapidly in the solvent and form a low-viscosity solution, ensuring that small-particle-size lithium sulfate and organic carbon sources are fully dispersed during stirring, avoiding particle agglomeration. When the molecular weight exceeds 400, the viscosity of the mixture increases significantly, leading to uneven mixing of lithium sulfate and organic carbon source particles and the formation of localized agglomeration. Lower molecular weight polymers also facilitate control of droplets with smaller particle sizes, thereby obtaining small-particle-size precursor materials.

[0051] High molecular weight polymers with a molecular weight of 400 or less are used because their shorter molecular chains make them easier to decompose and vaporize during pyrolysis, resulting in a relatively low residual carbon content. If only these low molecular weight polymers are used as the sole carbon source, a large quantity is required to provide enough carbon for lithium sulfate reduction. However, excessive polymer content can have negative effects, such as abnormally high viscosity of the mixture, increasing the difficulty of stirring and atomization; and the generation of large amounts of gas during pyrolysis, which may affect the structural stability of the precursor. Therefore, high molecular weight polymers need to be used in conjunction with organic carbon sources.

[0052] In some embodiments, glucose is selected as the organic carbon source and PEG400 as the polymer. The preferred mass ratio of the organic carbon source to the polymer is (0.7~1):(0.2~1.1). Within this ratio range, the amount of polymer used is relatively small, avoiding the possibility of material blockage during spray drying and reducing raw material costs.

[0053] In some embodiments, the solvent is water or ethanol. Deionized water or anhydrous ethanol is readily and completely removed by drying, which helps to form smaller, more uniform precursor particles during spray drying.

[0054] In some embodiments, the inlet air temperature of the spray dryer is 100°C to 200°C.

[0055] In some embodiments, step S3 of sintering the precursor material includes:

[0056] The precursor material is placed in an inert atmosphere and heated to 800℃~900℃ at a heating rate of 3~6℃ / min, and held at this temperature for 2~12h to sinter the precursor material. Exemplarily, the heating rate can be 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, etc. The sintering temperature can be 800℃, 820℃, 840℃, 860℃, 880℃, 900℃, etc. The sintering time can be 2h, 4h, 6h, 8h, 10h, 12h, etc. At the sintering temperature of 800℃~900℃, lithium sulfate undergoes a reduction reaction with the carbon source, efficiently yielding high-purity lithium sulfide and suppressing the formation of byproducts.

[0057] In some embodiments, the ratio of the mass of the residual carbon of the organic carbon source and the residual carbon of the polymer to the mass of the lithium sulfate is (0.21~0.22):1. Exemplarily, this ratio can be 0.21:1, 0.215:1, 0.218:1, 0.22:1, etc. This range is preferred, resulting in lithium sulfide with higher purity and fewer carbon impurities.

[0058] This application also provides a solid electrolyte, including lithium sulfide prepared by the method described in the foregoing embodiments. The lithium sulfide solid electrolyte of this application has low carbon impurity content, high product purity, and avoids leakage current caused by residual carbon.

[0059] This application also provides a solid-state battery, including a positive electrode, a negative electrode, and a solid electrolyte, wherein the solid electrolyte comprises lithium sulfide prepared by the aforementioned method. High-purity lithium sulfide can reduce side reactions at the electrode-electrolyte interface and optimize the electrochemical performance of the battery.

[0060] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be further described in detail below with reference to the accompanying drawings and several preferred embodiments. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Unless otherwise specified, the test methods in the following embodiments are performed under conventional conditions. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0061] The organic carbon sources (glucose, sucrose, citric acid) and polymer materials (polyethylene glycol, polyvinyl alcohol, polyoxyethylene) used in the following examples were all purchased. The residual carbon mass percentage per unit mass of organic carbon source / polymer was obtained in advance through thermogravimetric analysis, which was used to calculate the specific proportions in each example.

[0062] Example 1

[0063] Step 1: Weigh the raw materials with a mass ratio of lithium sulfate:glucose:PEG400 = 1:0.9:0.225. The sum of the residual carbon content of glucose and PEG400 should be 0.218:1 compared to the mass of lithium sulfate. Mix lithium sulfate, glucose, and PEG400 evenly in ethanol to obtain a mixture. The lithium sulfate particle size should be less than or equal to 5 μm, and the glucose particle size should be less than or equal to 1 μm. The residual carbon content of glucose should be 23% by mass, and the residual carbon content of PEG400 should be 5% by mass.

[0064] Step 2: Spray dry the mixture obtained in Step 1 at 100°C to obtain the precursor material. The particle size of the precursor material is less than or equal to 5 μm.

[0065] Step 3: Place the precursor material obtained in Step 2 in an inert atmosphere, heat it to 900℃ at a heating rate of 3℃ / min, and hold it at that temperature for 2 hours to sinter the precursor material. Then grind the product in a crusher to obtain lithium sulfide.

[0066] Example 2

[0067] Step 1: Weigh the raw materials in a mass ratio of lithium sulfate:glucose:PEG400 = 1:1:0.2. The sum of the residual carbon content of glucose and PEG400 should be 0.24:1 compared to the mass of lithium sulfate. Mix lithium sulfate, glucose, and PEG400 evenly in water to obtain a mixture. The lithium sulfate particle size should be less than or equal to 5 μm, and the glucose particle size should be less than or equal to 1 μm. The residual carbon content of glucose should be 23% by mass, and the residual carbon content of PEG400 should be 5% by mass.

[0068] Step 2: Spray dry the mixture obtained in Step 1 at 150°C to obtain the precursor material. The particle size of the precursor material is less than or equal to 10 μm.

[0069] Step 3: The precursor material obtained in Step 2 is placed in an inert atmosphere and heated to 850°C at a heating rate of 6°C / min, and held at that temperature for 12 hours to sinter the precursor material. The product is then ground in a crusher to obtain lithium sulfide.

[0070] Example 3

[0071] Step 1: Weigh the raw materials in a mass ratio of lithium sulfate:glucose:PEG400 = 1:1:0.4. The sum of the residual carbon content of glucose and PEG400 should be 0.25:1 compared to the mass of lithium sulfate. Mix lithium sulfate, glucose, and PEG400 thoroughly in ethanol to obtain a mixture. The lithium sulfate particle size should be less than or equal to 5 μm, and the glucose particle size should be less than or equal to 1 μm. The residual carbon content of glucose should be 23% by mass, and the residual carbon content of PEG400 should be 5% by mass.

[0072] Step 2: Spray dry the mixture obtained in Step 1 at 150°C to obtain the precursor material. The particle size of the precursor material is less than or equal to 10 μm.

[0073] Step 3: The precursor material obtained in Step 2 is placed in an inert atmosphere and heated to 800°C at a heating rate of 6°C / min, and held at that temperature for 12 hours to sinter the precursor material. The product is then ground in a crusher to obtain lithium sulfide.

[0074] Example 4

[0075] Step 1: Weigh the raw materials in a mass ratio of lithium sulfate:glucose:PEG400 = 1:0.7:1.04. The sum of the residual carbon content of glucose and PEG400 should be 0.21:1 compared to the mass of lithium sulfate. Mix lithium sulfate, glucose, and PEG400 thoroughly in ethanol to obtain a mixture. The lithium sulfate particle size should be less than or equal to 5 μm, and the glucose particle size should be less than or equal to 1 μm. The residual carbon content of glucose should be 23% by mass, and the residual carbon content of PEG400 should be 5% by mass.

[0076] Step 2: Spray dry the mixture obtained in Step 1 at 100°C to obtain the precursor material. The particle size of the precursor material is less than or equal to 5 μm.

[0077] Step 3: Place the precursor material obtained in Step 2 in an inert atmosphere, heat it to 850°C at a heating rate of 5°C / min, and hold it at that temperature for 6 hours to sinter the precursor material. Then grind the product in a crusher to obtain lithium sulfide.

[0078] Example 5

[0079] Step 1: Weigh the raw materials in a mass ratio of lithium sulfate:glucose:PEG400 = 1:0.8:0.68. The sum of the residual carbon content of glucose and PEG400 should be 0.22:1 in mass of lithium sulfate. Mix lithium sulfate, glucose, and PEG400 evenly in ethanol to obtain a mixture. The particle size of lithium sulfate should be less than or equal to 5 μm, and the particle size of glucose should be less than or equal to 1 μm. The residual carbon content of glucose should be 23% by mass, and the residual carbon content of PEG400 should be 5% by mass.

[0080] Step 2: Spray dry the mixture obtained in Step 1 at 100°C to obtain the precursor material with a particle size of 5 μm.

[0081] Step 3: Place the precursor material obtained in Step 2 in an inert atmosphere, heat it to 900℃ at a heating rate of 5℃ / min, and hold it at that temperature for 6 hours to sinter the precursor material. Then grind the product in a crusher to obtain lithium sulfide.

[0082] Example 6

[0083] Step 1: Weigh the raw materials with a mass ratio of lithium sulfate:sucrose:polyvinyl alcohol = 1:0.9:1.12. The sum of the residual carbon content of sucrose and polyvinyl alcohol is 0.218:1 in mass ratio to lithium sulfate. Mix lithium sulfate, sucrose, and polyvinyl alcohol evenly in ethanol to obtain a mixture. The lithium sulfate particle size is less than or equal to 5 μm, and the sucrose particle size is less than or equal to 1 μm. The residual carbon content of sucrose is 18% by mass, and the residual carbon content of polyvinyl alcohol is 5% by mass.

[0084] Step 2: Spray dry the mixture obtained in Step 1 at 100°C to obtain the precursor material with a particle size of 5 μm.

[0085] Step 3: Place the precursor material obtained in Step 2 in an inert atmosphere, heat it to 900℃ at a heating rate of 5℃ / min, and hold it at that temperature for 6 hours to sinter the precursor material. Then grind the product in a crusher to obtain lithium sulfide.

[0086] Example 7

[0087] Step 1: Weigh the raw materials with a mass ratio of lithium sulfate:citric acid:polyoxyethylene = 1:1:2.36. The sum of the residual carbon content of citric acid and polyoxyethylene and the mass ratio of lithium sulfate are 0.218:1. Mix lithium sulfate, citric acid, and polyoxyethylene in ethanol until homogeneous to obtain a mixture. The particle size of lithium sulfate is less than or equal to 5 μm, and the particle size of citric acid is less than or equal to 1 μm. The residual carbon content of citric acid is 10% by mass, and the residual carbon content of polyoxyethylene is 5% by mass.

[0088] Step 2: Spray dry the mixture obtained in Step 1 at 100°C to obtain the precursor material with a particle size of 5 μm.

[0089] Step 3: Place the precursor material obtained in Step 2 in an inert atmosphere, heat it to 900℃ at a heating rate of 5℃ / min, and hold it at that temperature for 6 hours to sinter the precursor material. Then grind the product in a crusher to obtain lithium sulfide.

[0090] Comparative Example 1

[0091] Step 1: Weigh the raw materials with a mass ratio of lithium sulfate: glucose = 1:0.95, mix the lithium sulfate and glucose evenly in ethanol to obtain a mixture; wherein, the lithium sulfate and glucose are the same type as in Example 1; the mass ratio of the residual carbon of glucose to the mass of lithium sulfate is 0.218:1.

[0092] Step 2: Spray dry the mixture obtained in Step 1 at 100°C to obtain the precursor material. The particle size of the precursor material is less than or equal to 5 μm.

[0093] Step 3: Place the precursor material obtained in Step 2 in an inert atmosphere, heat it to 900℃ at a heating rate of 3℃ / min, and hold it at that temperature for 2 hours to sinter the precursor material. Then grind the product in a crusher to obtain lithium sulfide.

[0094] Comparative Example 2

[0095] Step 1: Weigh the raw materials with a mass ratio of lithium sulfate:PEG400 = 1:4.36, and the mass ratio of residual carbon of PEG400 to lithium sulfate is 0.218:1. Mix the lithium sulfate and PEG400 evenly in ethanol to obtain a mixture; wherein the particle size of lithium sulfate is less than or equal to 5μm; and the mass percentage of residual carbon of PEG400 is 5%.

[0096] Step 2: Spray dry the mixture obtained in Step 1 at 100°C to obtain the precursor material. The particle size of the precursor material is less than or equal to 5 μm.

[0097] Step 3: Place the precursor material obtained in Step 2 in an inert atmosphere, heat it to 900℃ at a heating rate of 3℃ / min, and hold it at that temperature for 2 hours to sinter the precursor material. Then grind the product in a crusher to obtain lithium sulfide.

[0098] Comparative Example 3

[0099] Step 1: Weigh the raw materials with a mass ratio of lithium sulfate: glucose: PEG400 = 1:0.9:0.225. The ratio of the sum of the residual carbon content of glucose and PEG400 to the mass of lithium sulfate is 0.218:1. Mix lithium sulfate, glucose, and PEG400 evenly in ethanol to obtain a mixture. The particle size of lithium sulfate is less than or equal to 5 μm, and the particle size of glucose is less than or equal to 1 μm. The residual carbon content per unit mass of glucose and per unit mass of polyethylene glycol PEG400 are calculated in advance by thermogravimetric analysis.

[0100] Step 2: Stir and dry the mixture obtained in Step 1 to obtain the precursor material;

[0101] Step 3: Place the precursor material obtained in Step 2 in an inert atmosphere, heat it to 900℃ at a heating rate of 3℃ / min, and hold it at that temperature for 2 hours to sinter the precursor material. Then grind the product in a crusher to obtain lithium sulfide.

[0102] Comparative Example 4

[0103] Step 1: Weigh the raw materials with a mass ratio of lithium sulfate: glucose: PEG400 = 1:0.9:0.225. The ratio of the sum of the residual carbon content of glucose and PEG400 to the mass of lithium sulfate is 0.218:1. Mix lithium sulfate, glucose, and PEG400 evenly in ethanol to obtain a mixture. The particle size of lithium sulfate is less than or equal to 5 μm, and the particle size of glucose is less than or equal to 1 μm. The residual carbon content per unit mass of glucose and per unit mass of polyethylene glycol PEG400 are calculated in advance by thermogravimetric analysis.

[0104] Step 2: Spray dry the mixture obtained in Step 1 at 100°C to obtain the precursor material. The particle size of the precursor material is less than or equal to 5 μm.

[0105] Step 3: Place the precursor material obtained in Step 2 in an inert atmosphere, heat it to 700℃ at a heating rate of 3℃ / min, and hold it at that temperature for 2 hours to sinter the precursor material. Then grind the product in a crusher to obtain lithium sulfide.

[0106] The purity of Li₂S and the carbon impurity content were tested for the lithium sulfides prepared in the above examples and comparative examples. The purity of Li₂S was tested using ICP-MS (inductively coupled plasma mass spectrometry), and the carbon impurity content was tested using a high-frequency infrared carbon-sulfur analyzer. The test results are listed in Table 1. SEM analysis was performed on the precursor materials obtained in some examples. The SEM image of the precursor material obtained in Example 1 is shown below. Figure 1As shown; SEM images of the precursor materials obtained during the preparation process of Comparative Example 1 are shown below. Figure 2 As shown. XRD tests were performed on lithium sulfide prepared in some examples, with the XRD pattern of lithium sulfide prepared in Example 1 shown below. Figure 3 As shown, the XRD pattern of lithium sulfide prepared in Comparative Example 1 is as follows. Figure 4 As shown.

[0107] Table 1

[0108] serial number <![CDATA[Li2S purity / %]]> Carbon impurity content / % Example 1 99.9 0.065 Example 2 99.8 0.08 Example 3 99.7 0.09 Example 4 99.8 0.06 Example 5 99.8 0.05 Example 6 99.6 0.09 Example 7 99.7 0.09 Comparative Example 1 97.7 1.1 Comparative Example 2 93 1.6 Comparative Example 3 98.4 1.0 Comparative Example 4 88 1.8

[0109] As shown in Table 1, the lithium sulfide prepared in each example exhibits high purity and low carbon impurities. This is due to the film-forming properties of the polymer during spray drying, which allows the polymer and organic carbon source to coat the surface of lithium sulfate particles. After heat treatment, a carbon film in close contact with lithium sulfate is formed, greatly increasing the reaction contact area. Combined with the control of precursor particle size, the conversion rate can be significantly improved. Simultaneously, by controlling the ratio of lithium sulfate to organic carbon source, and the ratio of organic carbon source to polymer, the carbon source can be accurately supplemented, reducing the carbon content of the product, resulting in higher lithium sulfide yield, lower carbon content, and higher purity. In Comparative Example 1, only an organic carbon source was used, leading to a decrease in Li₂S purity and an increase in the proportion of carbon impurities. The possible reason is the lack of dispersion by the polymer, resulting in uneven mixing of glucose and lithium sulfate, and localized carbon source aggregation leading to insufficient reduction. In Comparative Example 2, only a high-molecular-weight polymer was used, resulting in a decrease in Li₂S purity and an increase in the proportion of carbon impurities. The possible reason is that PEG400 has a low residual carbon rate, requiring a large addition to meet the reduction requirements. However, excessive polymer not only leads to excessively high viscosity and poor dispersibility of the mixture, but also causes excessive gas production during pyrolysis, damaging the precursor structure and ultimately resulting in insufficient reduction and carbon impurity accumulation. In Comparative Example 3, conventional stirring and drying were used. Since stirring and drying cannot form spherical precursors, the raw materials easily agglomerate, leading to insufficient contact between the carbon source and lithium sulfate during sintering, resulting in poor purity and carbon impurities. In Comparative Example 4, the sintering temperature was lower, resulting in insufficient consumption of the carbon source, a decrease in Li₂S purity, and an increase in residual carbon content.

[0110] Depend on Figure 1 and Figure 2 SEM characterization analysis of the precursor materials showed that... Figure 1 The image shows the precursor of Example 1 as an SEM image. It can be seen that it has a regular spherical structure with uniform particle size distribution, dense surface and no obvious agglomeration. Figure 2 The image shows the precursor SEM image of Comparative Example 1. Although the particles are spherical, their surfaces are rough and there is obvious local aggregation. Glucose and lithium sulfate are unevenly dispersed in the mixture, and after drying, they are prone to particle aggregation, which directly affects the reaction efficiency during subsequent sintering.

[0111] Depend on Figure 3 and Figure 4 XRD pattern analysis of lithium sulfide shows that... Figure 3 The XRD pattern of lithium sulfide in Example 1 shows that its diffraction peaks correspond perfectly to the standard card of Li2S. The peaks are sharp and there are no obvious impurity peaks, indicating that the product is pure phase Li2S with a complete crystal structure. Figure 4 The image shows the XRD pattern of lithium sulfide in Comparative Example 1. Although the main diffraction peak corresponds to Li2S, there are many impurity peaks, indicating low purity.

[0112] In summary, the lithium sulfide prepared by the method of this application has high purity and low carbon impurity content, and its various performance indicators can meet the requirements for use in sulfide solid electrolytes.

[0113] Obviously, the embodiments described above are only some embodiments of this application, not all embodiments. The accompanying drawings show preferred embodiments of this application, but do not limit the patent scope of this application. This application can be implemented in many different forms; rather, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing specific embodiments, or make equivalent substitutions for some of the technical features. Any equivalent structures made using the content of this application's specification and drawings, directly or indirectly applied to other related technical fields, are similarly within the scope of patent protection of this application.

Claims

1. A method for preparing lithium sulfide, characterized in that, The lithium sulfide is used to prepare a solid electrolyte, including the following steps: Lithium sulfate, an organic carbon source, and a polymer are mixed uniformly in a solvent to obtain a mixture; wherein the mass ratio of lithium sulfate to the organic carbon source is 1:(0.7~1), and the mass ratio of the organic carbon source to the polymer is (0.7~1):(0.1~2.5); the ratio of the sum of the residual carbon content of the organic carbon source and the residual carbon content of the polymer to the mass of lithium sulfate is (0.2~0.25):1; The mixture is spray-dried to obtain the precursor material; The precursor material is sintered to obtain lithium sulfide.

2. The method for preparing lithium sulfide as described in claim 1, characterized in that, The precursor material has a particle size of 1 to 10 μm; and / or, the lithium sulfate has a particle size of less than or equal to 5 μm, and the organic carbon source has a particle size of less than or equal to 1 μm.

3. The method for preparing lithium sulfide as described in claim 1, characterized in that, The organic carbon source includes at least one of glucose, sucrose, and citric acid; and / or, the polymer includes at least one of polyethylene glycol, polyvinyl alcohol, and polyoxyethylene.

4. The method for preparing lithium sulfide as described in claim 1, characterized in that, The molecular weight of the polymer is less than or equal to 400.

5. The method for preparing lithium sulfide as described in claim 1, characterized in that, The solvent is water or ethanol.

6. The method for preparing lithium sulfide as described in claim 1, characterized in that, The inlet air temperature for the spray dryer is 100℃~200℃.

7. The method for preparing lithium sulfide according to claim 1, characterized in that, The step of sintering the precursor material includes: The precursor material is placed in an inert atmosphere and heated to 800℃~900℃ at a heating rate of 3~6℃ / min, and held at that temperature for 2~12h to sinter the precursor material.

8. The method for preparing lithium sulfide as described in claim 1, characterized in that, The ratio of the mass of the residual carbon of the organic carbon source and the residual carbon of the polymer to the mass of the lithium sulfate is (0.21~0.22):

1.

9. A solid electrolyte, characterized in that, Lithium sulfide prepared by the method for preparing lithium sulfide as described in any one of claims 1-8.

10. A solid-state battery, comprising a positive electrode, a negative electrode, and a solid electrolyte, characterized in that, The solid electrolyte includes lithium sulfide prepared by the method for preparing lithium sulfide as described in any one of claims 1-8.

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