Method for preparing sulfide electrolyte by multi-stage sintering and prepared sulfide electrolyte

Abstract

The method for preparing a sulfide electrolyte by multi-step sintering provided by the present invention includes the steps of sequentially subjecting a precursor material to microwave plasma sintering and muffle furnace annealing sintering to obtain a sulfide electrolyte. The present invention uses a multi-step sintering method combining microwave plasma sintering and muffle furnace sintering, which can rapidly complete the crystal nucleation and densification processes of the matrix, and ensure the uniformity of the reaction during the grain growth process, and can rapidly obtain a sulfide electrolyte material with high crystallinity, uniform bulk phase, and excellent performance.

Description

[Technical Field]

[0001] The present invention belongs to the technical field of battery electrolytes, and relates to a method for preparing a sulfide electrolyte by multi-stage sintering and the prepared sulfide electrolyte. [Background technology]

[0002] Solid electrolytes are important components of all-solid-state batteries. Among them, sulfide electrolytes have high room-temperature ionic conductivity and low electronic conductivity, as well as good mechanical properties, which are advantageous for forming good solid-solid contact interfaces between electrodes and electrolytes in all-solid-state batteries.

[0003] Sulfide electrolytes are often prepared by combining solid-state mixing and annealing / sintering. During the sintering process, an additional reaction occurs within the crystal lattice of the reactants at or near the grain boundaries. This process can be divided into three stages: the first stage is the formation of crystal nuclei within the crystal lattice of the reactants at or near the grain boundaries; the second stage is the growth of the crystal nuclei at high temperatures; and the third stage is the thickening of the product, the reaction rate slows, and finally the reaction is completed, resulting in the formation of the electrolyte material. Currently, muffle furnace sintering is used for sulfide electrolyte preparation. However, due to limitations in the heating method and the thermal conductivity of the electrolyte material, the first stage of the crystal nucleation process requires a long time, typically 4 to 48 hours, significantly affecting the efficiency of sulfide electrolyte preparation. Furthermore, muffle furnace sintering has a slow heating rate, typically 2 to 5°C / min, resulting in a long low-temperature sintering stage, which easily deforms the pores within the material, affecting the thermal conductivity and thermal uniformity of the material and resulting in uneven grain size.

[0004] Microwave plasma sintering uses microwaves to ionize gases to form plasma, which is then used as a heating source. The ambient temperature of the material in the plasma rises instantly, resulting in the rapid formation of uniform crystal nuclei, increasing the density of the material and quickly completing the first stage of the sintering process. However, microwave plasma sintering can cause heat spots and thermal runaway in the latter half of sintering due to excessively large temperature gradients within the material during the sintering process of dense materials. This can cause some material to overheat and sinter, resulting in amorphous material, which can affect the performance of the electrolyte. Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the shortcomings in the prior art, it is an object of the present invention to provide a method for preparing a sulfide electrolyte by multi-stage sintering and the prepared sulfide electrolyte. [Means for solving the problem]

[0006] One object of the present invention is achieved by the following technical solutions. A method for preparing a sulfide electrolyte by multi-stage sintering, comprising the steps of microwave plasma sintering and muffle furnace anneal sintering precursor materials in sequence to obtain a sulfide electrolyte.

[0007] The present invention uses a multi-step sintering method that combines microwave plasma sintering and muffle furnace sintering, which can quickly complete the crystal nucleation and densification processes of the green body and ensure the reaction uniformity during the crystal grain growth process, thereby quickly obtaining a sulfide electrolyte material with high crystallinity, uniform bulk phase, and excellent performance.

[0008] Preferably, the preparation of the precursor material includes a step of weighing raw materials containing lithium sulfide in a molar ratio and thoroughly mixing the raw materials to obtain the precursor material.

[0009] Preferably, the method for preparing the lithium sulfide comprises one or more of ball milling, carbothermal reduction, lithiation of sulfur-containing chemicals, sulfurization of metallic lithium nanoparticles, and interaction of lithium-containing and sulfur-containing materials.

[0010] Preferably, in preparing the precursor material, the mixing method comprises one or more of mechanical stirring, mechanical shaking, ball milling, and roll milling.

[0011] Preferably, in preparing the precursor material, the mixing time is 0.2 to 1 hour.

[0012] Preferably, the total sintering time for the microwave plasma sintering and the muffle furnace annealing sintering is 1.5 hours or less.

[0013] Preferably, the temperature rise rate in microwave plasma sintering is, for example, 50 to 200°C / min, the sintering temperature is 80 to 600°C, and the sintering time is 2 to 20 minutes, more preferably 5 to 15 minutes. Preferably, the discharge gas in microwave plasma sintering is nitrogen gas or argon gas.

[0014] Preferably, after the precursor material has undergone microwave plasma sintering, the product is placed directly in a muffle furnace for annealing and sintering. After the precursor material has undergone microwave plasma sintering, the product does not need to be cooled and is placed directly in a muffle furnace already set at the sintering temperature for sintering.

[0015] Preferably, the muffle furnace annealing and sintering temperature is 180 to 700°C, and the sintering time is 0.5 to 1.5 hours. More preferably, the sintering time for muffle furnace annealing and sintering is 0.5 to 1.2 hours. The atmosphere for muffle furnace annealing and sintering is an inert atmosphere.

[0016] Another object of the present invention is to provide a sulfide electrolyte prepared by the above-mentioned method for preparing a sulfide electrolyte by multi-stage sintering.

[0017] Preferably, the sulfide electrolyte has one or more of the chemical formulas shown in Formula I, Formula II, and Formula III. (100-xy)Li2S·xP2S5·yM m N n Formula I, wherein 0≦x<100, 0≦y<100, 0≦x+y<100, 0≦m<4, 0≦n<6, M is one or more of Ge, Si, Sn, and Sb, and N is one or more of Se, O, Cl, Br, and I; Li 10±l Ge 1-g G g P 2-q Q q S 12-w W w Formula II, wherein 0≦l<1, 0≦g≦1, 0≦q≦2, 0≦w<1, G is Si and / or Sn, Q is Sb, and W is one or more of O, Se, Cl, Br, and I; Li 6±l P 1-e E e S 5-s R r X 1±t Formula III, where 0≦l<1, 0≦e<1, 0≦s<2, 0≦r<1, 0≦t<1, E is one or more of Ge, Si, Sn, and Sb, R is O and / or Se, and X is one or more of Cl, Br, and I.

[0018] More preferably, in formula I, 0 <x+y<100である。

[0019] Preferably, the room temperature ionic conductivity of the sulfide electrolyte is 1×10 -4 ~1×10 -1 S / cm.

[0020] Preferably, the sulfide electrolyte is crystalline. [Effects of the Invention]

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention uses a multi-step sintering method that combines microwave plasma sintering and muffle furnace sintering, which can quickly complete the crystal nucleation and densification processes of the green body, significantly shortening the sintering time of the material and improving production efficiency. 2. The multi-step sintering method combining microwave plasma sintering and muffle furnace sintering according to the present invention ensures uniformity of the reaction during the grain growth process, which is advantageous for quickly obtaining sulfide electrolyte materials with high crystallinity and uniform bulk phase. 3. The sulfide electrolyte material prepared using the multi-step sintering method of the present invention, which combines microwave plasma sintering and muffle furnace sintering, has better electrolyte performance than sulfide electrolyte materials prepared using only microwave plasma sintering or muffle furnace sintering. 4. In the present invention, the sintering time of microwave plasma sintering is controlled to 2 to 20 minutes, and the sintering time of muffle furnace annealing sintering is controlled to 0.5 to 1.5 hours, respectively, to achieve appropriate sintering time lengths, which is more advantageous in improving the crystallinity and performance of the electrolyte material. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 shows the X-ray diffraction patterns of the Li6PS5Cl sulfide electrolytes of Example 1, Comparative Example 1, and Comparative Example 2. [Figure 2] FIG. 2 is a test graph of the room temperature ionic conductivity of the Li6PS5Cl sulfide electrolytes of Example 1, Comparative Example 1, and Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0023] The technical solutions of the present invention will be further described below through specific examples and drawings. However, it should be understood that the specific examples described herein are only used to aid in understanding the present invention and are not used to specifically limit the present invention. Furthermore, the drawings used in this specification are only used to better explain the disclosure of the present invention and do not limit the scope of protection. Unless otherwise specified, all raw materials used in the examples of the present invention are raw materials commonly used in this field, and all methods used in the examples are common methods in this field.

[0024] In the following examples and comparative examples, the room temperature ionic conductivity was tested as follows. The test was performed using a Solartron 1470E electrochemical workstation in the UK. The lithium ion conductivity of the bulk material was tested in AC impedance mode. The test conditions were 10 6 Hz~10 -2 Hz, amplitude 15mV.

[0025] Before the AC impedance test, the sample needed to be pretreated. The thickness t of the solid electrolyte sample and the electrical resistance R at room temperature were measured, and the lithium ion conductivity of the sample at room temperature was calculated using the formula σ = t / (R·S). Here, σ is the electrical conductivity (unit: S / cm), t is the thickness of the test sample (unit: cm), R is the electrical resistance (unit: Ω), and S is the area of ​​the test sample (unit: cm). 2 )

[0026] In the following examples and comparative examples, the microwaves used in the microwave plasma sintering process had a power of 2 kW and a frequency of 2.45 GHz.

[0027] Example 1 Dried sulfur powder and lithium hydride powder were mixed in a 1:2 ratio and placed in a ball mill pot. The mixture was ball milled at room temperature for 24 hours at 100 rpm to obtain lithium sulfide powder. Lithium sulfide, diphosphorus pentasulfide, and lithium chloride were weighed in a molar ratio and mechanically stirred at 200 rpm for 20 minutes to obtain a precursor material. The precursor material was subjected to microwave plasma sintering at 500°C for 5 minutes (heating rate: 100°C / min). The microwave plasma sintered product was then directly transferred to a muffle furnace at 550°C for 1 hour and sintered under argon gas for both microwave plasma sintering and muffle furnace sintering to obtain a Li6PS5Cl electrolyte. The resulting Li6PS5Cl electrolyte exhibited high crystallinity, and its X-ray diffraction pattern is shown in Figure 1. The room-temperature ionic conductivity was 3.6 mS / cm, and the test results are shown in Figure 2.

[0028] Example 2 Li2S was prepared by the interaction of a lithium-containing compound and a sulfur-containing compound. Specifically, metallic lithium and elemental sulfur were dissolved in diethyl ether, an organic solvent, in a 2.1:1 ratio by mass, mixed, and then distilled under reduced pressure to produce Li2S. Lithium sulfide, germanium disulfide, and diphosphorus pentasulfide were weighed out in a molar ratio and mechanically stirred at 300 rpm for 15 minutes to obtain a precursor material. The precursor material was subjected to microwave plasma sintering at 550°C for 10 minutes (heating rate: 100°C / min). The microwave plasma sintered product was then directly transferred to a muffle furnace at 620°C and sintered for 1 hour. The atmosphere for both the microwave plasma sintering and the muffle furnace sintering was nitrogen gas. Li 10 GeP2S 12 The electrolyte was obtained. 10 GeP2S 12 The electrolyte had a high degree of crystallinity and an ionic conductivity of 6.3 mS / cm at room temperature.

[0029] Example 3 Li2S was prepared by carbothermal reduction. Specifically, anhydrous lithium sulfate, glucose, and hard carbon were mixed in a mass ratio of 1:2:5 and heated to 900 °C under a hydrogen gas atmosphere to produce Li2S. Lithium sulfide and diphosphorus pentasulfide were weighed in a molar ratio and ball milled at 500 rpm for 1 hour to obtain a precursor material. The precursor material was subjected to microwave plasma sintering at 150 °C for 5 minutes (heating rate: 100 °C / min). The microwave plasma sintered product was then directly transferred to a muffle furnace at 230 °C and sintered for 0.5 hours. Both the microwave plasma sintering and muffle furnace sintering atmospheres were nitrogen gas, yielding a Li3PS4 electrolyte. The prepared Li3PS4 electrolyte had high crystallinity and a room-temperature ionic conductivity of 0.4 mS / cm.

[0030] Example 4 Li2S was prepared by ball milling and the interaction of lithium-containing compounds with sulfur-containing compounds. Specifically, metallic lithium and elemental sulfur were dissolved in tetrahydrofuran, an organic solvent, in a 2.2:1 ratio by mass. The mixture was ball milled at 200 rpm for 24 hours, followed by vacuum distillation to obtain Li2S. Lithium sulfide, diphosphorus pentasulfide, and lithium iodide were weighed in a molar ratio and mechanically stirred at 100 rpm for 10 minutes. The mixture was then ball milled at 500 rpm for 30 minutes to obtain a precursor material. The precursor material was subjected to microwave plasma sintering at 100 °C for 5 minutes (heating rate: 100 °C / min). The microwave plasma sintered product was then directly transferred to a muffle furnace at 200 °C and sintered for 0.6 hours. Both the microwave plasma sintering and muffle furnace sintering atmospheres were argon gas, yielding Li7P2S8I electrolyte. The prepared Li7P2S8I electrolyte had high crystallinity and room temperature ionic conductivity of 1.2 mS / cm.

[0031] Example 5 Li2S was prepared by ball milling. Specifically, dry sulfur powder and lithium hydride powder were mixed in a 1:2 ratio and placed in a ball mill pot. The mixture was ball milled at room temperature for 12 hours at 500 rpm to obtain Li2S. Lithium sulfide, diphosphorus pentasulfide, and lithium chloride were weighed out in molar ratios and roll milled at 300 rpm for 1 hour to obtain a precursor material. The precursor material was subjected to microwave plasma sintering at 490 °C for 6 minutes (heating rate: 100 °C / min). The microwave plasma sintered product was then directly transferred to a muffle furnace at 550 °C and sintered for 1 hour. The atmosphere for both microwave plasma sintering and muffle furnace sintering was nitrogen gas. Li2S was obtained. 5.4 PS 4.4 Cl 1.6 The electrolyte was obtained. 5.4 PS 4.4 Cl 1.6 The electrolyte had a high degree of crystallinity and an ionic conductivity of 8.2 mS / cm at room temperature.

[0032] Example 6 Li2S was prepared by ball milling. Specifically, dry sulfur powder and lithium hydride powder were mixed in a mass ratio of 1:2.5, placed in a ball mill pot, and ball milled at room temperature for 24 hours at 300 rpm to obtain lithium sulfide. Lithium sulfide and diphosphorus pentasulfide were weighed out in a molar ratio and mechanically stirred at 200 rpm for 10 minutes. The mixture was then subjected to high-energy ball milling at 500 rpm for 30 minutes to obtain a precursor material. The precursor material was subjected to microwave plasma sintering at 120 °C for 5 minutes (heating rate: 100 °C / min). The microwave plasma sintered product was then directly transferred to a muffle furnace at 260 °C and sintered for 0.5 hours. The atmosphere for both the microwave plasma sintering and the muffle furnace sintering was argon gas, resulting in Li7P3S. 11 The electrolyte was obtained. 11 The electrolyte had a high degree of crystallinity and an ionic conductivity of 1.2 mS / cm at room temperature.

[0033] Example 7 Li2S was prepared by ball milling and the interaction of lithium-containing and sulfur-containing substances. Specifically, metallic lithium and elemental sulfur were dissolved in tetrahydrofuran in a 2.2:1 ratio by mass. The mixture was mixed for 24 hours at 200 rpm using ball milling, followed by vacuum distillation to obtain lithium sulfide. Lithium sulfide, diphosphorus pentasulfide, lithium chloride, and diphosphorus pentoxide were weighed in a molar ratio and mechanically shaken at 200 rpm for 30 minutes to obtain a precursor material. The precursor material was subjected to microwave plasma sintering at 520 °C for 7 minutes (heating rate: 100 °C / min). The microwave plasma sintered product was then directly transferred to a muffle furnace at 570 °C and sintered for 1 hour. The atmosphere for both the microwave plasma sintering and the muffle furnace sintering was argon gas, yielding Li6PS. 4.8 O 0.2 The prepared Li6PS electrolyte was obtained. 4.8 O 0.2 The Cl electrolyte had a high degree of crystallinity and an ionic conductivity of 15.2 mS / cm at room temperature.

[0034] Example 8 Li2S was prepared by ball milling. Specifically, dry sulfur powder and lithium hydride powder were mixed in a 1:2 ratio and placed in a ball mill pot. The mixture was ball milled at room temperature at 100 rpm for 24 hours to obtain lithium sulfide. Lithium sulfide, diphosphorus pentasulfide, lithium chloride, and lithium bromide were weighed out in molar ratios and mechanically stirred at 200 rpm for 30 minutes to obtain a precursor material. The precursor material was subjected to microwave plasma sintering at 480 °C for 8 minutes (heating rate: 100 °C / min). The microwave plasma sintered product was then directly transferred to a muffle furnace at 530 °C and sintered for 0.8 hours. The atmosphere for both the microwave plasma sintering and the muffle furnace sintering was argon gas, and Li6PS5Cl was obtained. 0.5 Br 0.5 The electrolyte was obtained. 0.5 Br 0.5 The electrolyte had a high degree of crystallinity and an ionic conductivity of 10.2 mS / cm at room temperature.

[0035] Example 9 Li2S was prepared by sulfurization of metallic lithium nanoparticles. Specifically, metallic lithium nanoparticles were dispersed in a tetrahydrofuran-n-hexane medium, and a mixture of hydrogen sulfide and argon gas was passed through the dispersion for 24 hours to obtain lithium sulfide. Lithium sulfide, diphosphorus pentasulfide, lithium chloride, and diphosphorus pentoxide were weighed in a molar ratio and mechanically stirred at 300 rpm for 10 minutes. The mixture was then ball-milled at 400 rpm for 30 minutes to obtain a precursor material. The precursor material was subjected to microwave plasma sintering at 480 °C for 9 minutes (heating rate: 100 °C / min). The microwave plasma sintered product was then directly transferred to a muffle furnace at 560 °C and sintered for 0.9 hours. The atmosphere for both the microwave plasma sintering and the muffle furnace sintering was argon gas. Li2S was obtained. 5.4 PS 4.2 O 0.2 Cl 1.6 The electrolyte was obtained. 5.4 PS 4.2 O 0.2 Cl 1.6 The electrolyte had a high degree of crystallinity and an ionic conductivity of 12 mS / cm at room temperature.

[0036] Example 10 Li2S was prepared by the interaction of lithium-containing and sulfur-containing materials. Specifically, metallic lithium and elemental sulfur were dissolved in toluene in a 2.1:1 ratio, mixed, and then distilled under reduced pressure to produce lithium sulfide. Lithium sulfide, phosphorus pentasulfide, germanium disulfide, and lithium iodide were weighed out in molar ratios and mechanically stirred at 200 rpm for 10 minutes, followed by ball milling at 400 rpm for 40 minutes to obtain a precursor material. The precursor material was subjected to microwave plasma sintering at 400 °C for 8 minutes (heating rate: 100 °C / min). The microwave plasma sintered product was then directly transferred to a muffle furnace at 540 °C and sintered for 1 hour. The atmosphere for both the microwave plasma sintering and the muffle furnace sintering was argon gas. Li 6.6 P 0.4 Ge 0.6 The S5I electrolyte was obtained. 6.6 P 0.4 Ge0.6 The S5I electrolyte had a high degree of crystallinity and an ionic conductivity of 18 mS / cm at room temperature.

[0037] Comparative Example 1 The chemical formula of this sulfide electrolyte material is Li6PS5Cl. Its preparation method differs from that of Example 1 in that the precursor material was directly sintered in a muffle furnace at 550°C for 1 hour without undergoing microwave plasma sintering. The presence of a large amount of intermediate product phases in the prepared product phase indicates that the sample had low crystallinity and the sintering reaction was incomplete. The X-ray diffraction pattern is shown in Figure 1. The room-temperature ionic conductivity was 1.7 mS / cm, and the grain boundary impedance was large. The test results are shown in Figure 2.

[0038] Comparative Example 2 The chemical formula of this sulfide electrolyte material in Comparative Example 1 is Li6PS5Cl. Its preparation method differs from that in Example 1 in that the precursor material was sintered entirely by microwave plasma sintering at 500°C for 1 hour, without undergoing muffle furnace sintering. The prepared product had low crystallinity and contained many heterogeneous phases. Its X-ray diffraction pattern is shown in Figure 1. The room temperature ionic conductivity was 1.5 mS / cm, and the grain boundary impedance was large. The test results are shown in Figure 2.

[0039] Comparative Example 3 The chemical formula of this sulfide electrolyte material in Comparative Example was Li6PS5Cl, and its preparation method differed from that in Example 1 in that the precursor material was directly sintered in a muffle furnace at 550°C for 4 hours without going through a microwave plasma sintering process. The sintering reaction was complete, and the room temperature ionic conductivity of the Li6PS5Cl prepared by muffle furnace sintering was 3.0 mS / cm.

[0040] Comparative Example 4 The sulfide electrolyte material of this comparative example has the chemical formula Li6PS5Cl. Its preparation method differs from that of Example 1 in that the precursor material was sintered entirely by microwave plasma sintering at 500°C for 5 minutes, without undergoing muffle furnace sintering. A large amount of intermediate product phase was present in the prepared product, indicating that the sintering reaction had not progressed completely. The room temperature ionic conductivity of the prepared Li6PS5Cl was 0.9 mS / cm.

[0041] Comparative Example 5 The sulfide electrolyte material of this comparative example has the chemical formula Li6PS5Cl, and its preparation method differs from that of Example 1 in that the precursor material was sintered entirely by microwave plasma sintering at 500°C for 30 minutes without undergoing muffle furnace sintering. The sintering reaction was complete, and the room temperature ionic conductivity of the prepared Li6PS5Cl was 2.4 mS / cm.

[0042] Each aspect, embodiment, and feature of the present invention is intended in all respects to be illustrative and not limiting, the scope of which is defined solely by the claims. Other embodiments, modifications, and uses will be apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0043] In the preparation method of the present invention, the order of each step is not limited to the order listed, and any change in the order of each step made by a person skilled in the art without any creative effort is also included in the scope of protection of the present invention. In addition, two or more steps or operations may be performed simultaneously.

[0044] Finally, it should be noted that the specific examples described in this specification are merely illustrative of the present invention and do not limit the embodiments of the present invention. Those skilled in the art to which the present invention pertains may make various modifications and additions to the specific examples described, or replace them with similar forms, and it is not necessary or possible to list all embodiments here. Those obvious modifications and variations derived from the essential spirit of the present invention still fall within the protection scope of the present invention, and interpreting them as any additional restrictions would also be contrary to the spirit of the present invention.

Claims

1. A method for producing a precursor material, comprising the steps of: weighing raw materials containing lithium sulfide in a molar ratio; and thoroughly mixing the raw materials, The precursor material is microwave plasma sintered, the discharge gas of the microwave plasma sintering is nitrogen gas or argon gas, the sintering temperature is 80 to 600°C, and the sintering time is 2 to 20 minutes; The precursor material is subjected to microwave plasma sintering, and then the resulting product is directly placed in a muffle furnace for annealing and sintering, the muffle furnace annealing and sintering temperature is 180-700°C, and the sintering time is 0.5-1.5 hours to obtain a sulfide electrolyte; In preparing the precursor material, the mixing method includes one or more of mechanical stirring, mechanical shaking, ball milling, and roll milling, and the mixing time is 0.2 to 1 hour; The sulfide electrolyte has the chemical formula shown in Formula III: Li ６±ｌ P １－ｅ E ｅ S ５－ｓ R ｒ X １±ｔ Formula III wherein 0≦l<1, 0≦e<1, 0≦s<2, 0≦r<1, 0≦t<1, E is one or more of Ge, Si, Sn, and Sb, R is O and / or Se, and X is one or more of Cl, Br, and I.

2. 2. The method for preparing a sulfide electrolyte by multi-stage sintering according to claim 1, wherein the method for preparing lithium sulfide includes one or more of the following: ball milling, carbothermal reduction, lithiation of sulfur-containing chemicals, sulfurization of metallic lithium nanoparticles, and interaction of lithium-containing and sulfur-containing materials.

3. 2. The method for preparing a sulfide electrolyte by multi-stage sintering according to claim 1, wherein the total sintering time of the microwave plasma sintering and the muffle furnace annealing sintering is 1.5 hours or less.

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