A method for preparing FePS3 and electrode materials

Abstract

This invention discloses a method for preparing FePS3, which involves mechanically mixing pyrite powder, sulfur-containing small molecules, and elemental phosphorus. The thoroughly mixed powder is then calcined and cooled in two temperature stages under a protective atmosphere to obtain FePS3 nanoparticles. The first temperature stage is 200℃~300℃ for 120~240 minutes, and the second temperature stage is 400℃~600℃ for 120~180 minutes. The sulfur-containing small molecules are thiourea, thioacetamide, or a mixture of both. The molar ratio of FeS2 molecules in the pyrite powder to sulfur atoms and phosphorus atoms in the sulfur-containing small molecules is 1:3:5 to 1:1:5. This invention uses pyrite as both the iron and sulfur source, and the sulfur-containing small molecules as the second sulfur source, directly obtaining FePS3 nanoparticles through a solid-phase reaction with elemental phosphorus without additional purification. This method features a low solid-phase reaction temperature, simple process, and does not require stringent reaction conditions, making it easy to scale up for production.

Description

Technical Field

[0001] This invention relates to the field of materials synthesis technology, and specifically to a method for preparing FePS3. Background Technology

[0002] Transition metal sulfides can undergo conversion reactions with lithium ions to form elemental metals and Li₂S, thus enabling lithium ion storage and serving as anode materials for lithium-ion batteries. The sulfur content in the compound directly determines its theoretical lithium storage capacity. However, most transition metal sulfides have a maximum sulfur content of disulfides, while some transition metals exist as trisulfides and tetrasulfides, but these are difficult to prepare and have poor stability. Compared to the inertness of transition metals towards lithium, Group IV and V elements (such as tin and phosphorus) can undergo alloying reactions with lithium, providing lithium storage capacity. Therefore, if cation substitution of Group IV / V elements can be achieved in transition metal sulfides, or if ternary sulfides can be formed with Group IV / V elements, their theoretical capacity can be effectively improved.

[0003] Due to the significant differences in properties between transition metals and Group IV / V elements, the amount of cation substitution in transition metal sulfides is very limited. Among ternary sulfides, FePS3 is highly attractive due to its high sulfur content and low material cost, but its synthesis is difficult. Currently, FePS3 is mainly synthesized through a direct solid-phase method involving the reaction of elemental iron, phosphorus, and sulfur in a vacuum tube at 700°C or higher for 6 to 14 hours. This process requires strict vacuum conditions, making large-scale production difficult. A method has also been reported in the literature, using a NaCl template mixed with ferric chloride, 5 times the excess of elemental phosphorus, and 21 times the excess of elemental sulfur, followed by calcination in nitrogen. This method yields FePS3 after holding at 500°C for 180 minutes. [1] The method involves washing with deionized water to remove NaCl, thereby obtaining FePS3 nanoparticles (Salt-Templated Construction of Ultrathin Cobalt Doped Iron Thiophosphite Nanosheets toward Electrochemical Ammonia Synthesis. Small 2019,15:e1903500.). However, this method uses a large amount of chloride, which is harmful to the environment and human health. A large amount of sulfur is released as sulfur vapor during the reaction, forming harmful SO2 gas. Furthermore, washing NaCl wastes too much water. Therefore, this method is difficult to promote. Summary of the Invention

[0004] To address the above-mentioned problems, this invention researches and designs a method for preparing FePS3. The technical means employed in this invention are as follows:

[0005] A method for preparing FePS3, characterized in that: pyrite powder, sulfur-containing small molecules and elemental phosphorus are mechanically mixed, and the well mixed powder is calcined and cooled in two temperature stages under a protective atmosphere to obtain FePS3 nanopowder;

[0006] The first temperature stage is 200℃~300℃, with a holding time of 120 minutes~240 minutes; the second temperature stage is 400℃~600℃, with a holding time of 120 minutes~180 minutes; the sulfur-containing small molecules are thiourea, thioacetamide, or a mixture of both; the molar ratio of FeS2 molecules, sulfur atoms, and phosphorus atoms in the pyrite powder to sulfur-containing small molecules is 1:3:5~1:1:5, wherein the excess phosphorus is to prevent phosphorus from vaporizing during heating, which would lead to phosphorus deficiency.

[0007] The FePS3 obtained in this invention is a layered nanomaterial, and may contain a small amount of nano-carbon or graphene.

[0008] Furthermore, the pyrite powder has a particle size range of 500 to 1200 mesh.

[0009] Furthermore, the pyrite powder has a particle size range of 600-800 mesh.

[0010] Furthermore, the protective atmosphere is nitrogen, argon, or a mixture of both.

[0011] An electrode material comprising the material prepared by the FePS3 preparation method described in this invention.

[0012] Compared with existing technologies, the FePS3 preparation method of the present invention has the following advantages:

[0013] 1. Using pyrite (FeS2) as the iron and sulfur source and sulfur-containing small molecules as the second sulfur source, FePS3 nanopowder is directly obtained through solid-phase reaction with elemental phosphorus. The raw material sources are abundant, and my country has abundant reserves of pyrite which are widely distributed.

[0014] 2. This method has a low solid-phase reaction temperature, simple process, does not require stringent reaction conditions, does not require complex equipment, and is easy to scale up for production;

[0015] 3. The sulfur source is stable and controllable during the reaction, and there is no need to add a significant excess of sulfur source;

[0016] 4. Impurities are controllable. Possible impurity elements are C, N, and H. During the reaction, some are discharged as NH3 gas, and the remaining part exists as nano-carbon, which can improve the conductivity of the main material and is beneficial to its battery performance. No additional purification treatment is required. Attached Figure Description

[0017] Figure 1This is a comparison between the X-ray diffraction pattern of pyrite powder used in Example 1 of the present invention and the standard pattern of FeS2.

[0018] Figure 2 This is a comparison between the X-ray diffraction pattern of the FePS3 powder synthesized in Example 1 of this invention and the standard FePS3 pattern.

[0019] Figure 3 This is a scanning electron microscope image of the FePS3 powder synthesized in Example 1 of this invention.

[0020] Figure 4 The X-ray diffraction pattern of the FePS3 powder synthesized in Example 2 of this invention is compared with the standard FePS3 pattern.

[0021] Figure 5 This is a scanning electron microscope image of the FePS3 powder synthesized in Example 2 of this invention.

[0022] Figure 6 The X-ray diffraction pattern of the FePS3 powder synthesized in Example 3 of this invention is compared with the standard FePS3 pattern.

[0023] Figure 7 This is a scanning electron microscope image of the FePS3 powder synthesized in Example 3 of this invention.

[0024] Figure 8 This is a comparison of the X-ray diffraction pattern of the sample prepared in Comparative Example 1 of this invention with the standard FeS2 pattern.

[0025] Figure 9 This is a comparison of the X-ray diffraction pattern of the sample prepared in Comparative Example 2 of this invention with the standard patterns of FeS2 and P4S7. Detailed Implementation

[0026] Example 1: Synthesis of FePS3 using thiourea as the second sulfur source

[0027] In this example, 30 grams of 800-mesh pyrite powder, 57 grams of thiourea, and 38.75 grams of elemental phosphorus (FeS2, with a sulfur to phosphorus molar ratio of 1:3:5 in thiourea) were mechanically mixed using a mixer. The mixed powder was then heated in a nitrogen atmosphere. The heating program was as follows: nitrogen was pre-purged into a tube furnace for 30 minutes, the temperature was increased to 200°C at a rate of 5°C / min and held for 240 minutes, then increased to 600°C at the same rate and held for 180 minutes. The mixture was then cooled with the furnace to obtain a black powder sample. X-ray diffraction (XRD) tests on the pyrite raw material and the synthesized powder showed that the pyrite raw material used had an FeS2 structure (…). Figure 1 The prepared powder has a FePS3 structure ( Figure 2Scanning electron microscopy (SEM) images show that the prepared powder is a layered nanomaterial encapsulated by an ultrathin carbon film. Figure 3 The carbon film is formed because thiourea produces some solid products during its thermal decomposition as a second sulfur source, including carbon, ammonium sulfide, and a small amount of elemental sulfur. The carbon cannot be further thermally decomposed or participate in the reaction, so it coats the surface of the products to form a carbon film.

[0028] Example 2: Synthesis of FePS3 using thioacetamide as the second sulfur source

[0029] In this example, 30 g of 800-mesh pyrite powder, 18.75 g of thiourea, and 38.7 g of elemental phosphorus (FeS2, the molar ratio of sulfur to phosphorus atoms in thiourea is 1:1:5) were mechanically mixed using a mixer. The mixed powder was then heated in an argon atmosphere. The heating program was as follows: nitrogen gas was pre-purged into the tube furnace for 30 min, the temperature was increased to 300 °C at a rate of 5 °C / min and held for 120 min, then increased to 400 °C at the same rate and held for 120 min, followed by furnace cooling to obtain a black powder sample. XRD characterization of the sample showed that the obtained sample had a FePS3 structure (…). Figure 4 SEM results showed that the prepared powder was a layered nanomaterial, and the ultrathin carbon film in Example 1 was almost invisible. Figure 5 Unlike thiourea, the thermal decomposition of thioacetamide produces no solid products. The carbon elements in the process escape from the reaction system as CH4 gas in an oxygen-free environment with the nitrogen or argon atmosphere and cannot be coated on the product surface. Therefore, no ultrathin carbon film was observed during the characterization process.

[0030] Example 3: Synthesis of FePS3 using a mixture of thiourea and thioacetamide as a second sulfur source.

[0031] In this example, 30 g of 700-mesh pyrite powder, 19 g of thiourea, 19 g of thioacetamide, and 38.75 g of elemental phosphorus (FeS2, the molar ratio of sulfur atoms to phosphorus atoms in thiourea is 1:2:5) were mechanically mixed using a mixer. The mixed powder was then heated in an argon atmosphere. The heating program was as follows: nitrogen gas was pre-purged into the tube furnace for 30 min, the temperature was increased to 250 °C at a rate of 5 °C / min and held for 180 min, then increased to 500 °C at the same rate and held for 150 min, followed by furnace cooling to obtain a black powder sample. XRD characterization of the sample showed that the obtained sample had a FePS3 structure (…). Figure 6 SEM results showed that the prepared powder was a layered nanomaterial. Figure 7 ), and accompanied by a small amount of ultrathin carbon film.

[0032] Comparative Example 1 used thiourea as the second sulfur source and calcined it only at temperatures above 600 degrees Celsius.

[0033] In this example, 30 g of 800-mesh pyrite powder, 57 g of thiourea, and 38.75 g of elemental phosphorus (FeS2, with a sulfur to phosphorus molar ratio of 1:3:5 in thiourea) were mechanically mixed using a mixer. The mixed powder was then heated in a nitrogen atmosphere. The heating program was as follows: nitrogen was pre-purged into a tube furnace for 30 min, the temperature was increased to 700 °C at a rate of 5 °C / min and held for 420 min, followed by furnace cooling to obtain a black powder sample. X-ray diffraction (XRD) was performed on the synthesized black powder. The tests showed that the main component of the black powder was FeS2 (… Figure 8 FePS3 was not generated because the excessively high temperature caused elemental phosphorus to vaporize and escape from the reaction system as phosphorus vapor.

[0034] Comparative Example 2 used thiourea as the second sulfur source and calcined it only at temperatures below 310°C.

[0035] In this example, 30 g of 800-mesh pyrite powder, 57 g of thiourea, and 38.75 g of elemental phosphorus (FeS2, with a sulfur to phosphorus atom molar ratio of 1:3:5 in thiourea) were mechanically mixed using a mixer. The mixed powder was then heated in a nitrogen atmosphere. The heating program was as follows: nitrogen was pre-purged into a tube furnace for 30 min, the temperature was increased to 180 °C at a rate of 5 °C / min and held for 360 min, followed by furnace cooling to obtain a black powder sample. X-ray diffraction (XRD) was performed on the synthesized black powder. The tests showed that the main component of the black powder was a mixture of FeS2 and phosphorus-sulfur compounds. Figure 9 FePS3 was not generated because the temperature was too low, which only caused phosphorus and sulfur to combine and react, and FeS2 did not participate in the reaction.

[0036] 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 FePS3, characterized in that: Pyrite powder, sulfur-containing small molecules and elemental phosphorus are mechanically mixed. The well-mixed powder is then calcined and cooled in two temperature stages under a protective atmosphere to obtain FePS3 nanopowder. The first temperature stage is 200℃~300℃, with a holding time of 120 minutes~240 minutes; the second temperature stage is 400℃~600℃, with a holding time of 120 minutes~180 minutes; the sulfur-containing small molecules are thiourea, thioacetamide, or a mixture of both; the molar ratio of FeS2 molecules, sulfur atoms, and phosphorus atoms in the sulfur-containing small molecules in the pyrite powder is 1:(1~3):

5.

2. The method for preparing FePS3 according to claim 1, characterized in that: Pyrite powder, with a particle size range of 500~1200 mesh.

3. The method for preparing FePS3 according to claim 2, characterized in that: Pyrite powder, with a particle size range of 600~800 mesh.

4. The method for preparing FePS3 according to claim 1, characterized in that: The protective atmosphere is nitrogen, argon, or a mixture of both.

5. An electrode material, characterized in that: The material comprises the FePS3 prepared by the preparation method according to any one of claims 1 to 4.

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