Three-phase composite sodium-storage material, and preparation method therefor and use thereof

Abstract

A three-phase composite sodium-storage material, and a preparation method therefor and the use thereof. The three-phase composite sodium-storage material is selected from any one of the structures represented by the following general formula: (FeS)x / (V3S4)y / C, where 0.2≤x≤5 and 0.2≤y≤5.

Description

Three-phase composite sodium storage materials, their preparation methods and applications

[0001] This application claims priority to Chinese patent application No. 202410991820.5, filed on July 23, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to the field of battery technology, and in particular to a three-phase composite sodium storage material, its preparation method, and its application. Background Technology

[0003] Sodium-ion batteries possess advantages such as low cost, high safety, and fast charging capability, making them promising candidates for energy storage. During the charging and discharging process of sodium-ion batteries, sodium ions migrate towards and are stored in the corresponding electrode materials. The quantity and rate of sodium ion extraction and insertion at the electrodes significantly impact the cycle stability and rate performance of the electrode materials. The cycle stability and rate performance of the electrode materials, in turn, affect the electrochemical performance of sodium-ion batteries. Summary of the Invention

[0004] This disclosure provides a three-phase composite sodium storage material, its preparation method, and its application, aiming to solve the problem of rapid degradation of electrochemical performance of sodium-ion batteries during charging and discharging.

[0005] In a first aspect, a three-phase composite sodium storage material is provided. The three-phase composite sodium storage material is selected from any one of the structures shown in the following general formula: (FeS) x / (V3S4) y / C; 0.2≤x≤5, 0.2≤y≤5.

[0006] The three-phase composite sodium storage material (FeS) provided in some embodiments of this disclosure x / (V3S4) y In / C, firstly, FeS and V3S4 can form a heterogeneous interface. At the interface, the adsorption energy required for sodium storage is lower, which makes it easier for sodium ions to be adsorbed. This can increase the amount of sodium ions stored in the three-phase composite sodium storage material.

[0007] Furthermore, (FeS) x / (V3S4) y The bulk phase of sodium-ion batteries contains numerous point, line, and surface defects, which provide abundant sodium-ion storage sites. This further enhances the amount of sodium ions stored in the three-phase composite sodium storage material, resulting in a better specific capacity. Consequently, a greater number of sodium ions are extracted and inserted into the positive and negative electrodes of the sodium-ion battery. During the charge and discharge process of the sodium-ion battery, the specific capacity of the electrode materials decreases relatively little.

[0008] Secondly, (FeS) x / (V3S4) y The bulk phase of / C contains numerous defects, which can generate a large number of free electrons and holes, thereby improving the conductivity of the three-phase composite sodium storage material and accelerating the migration rate of sodium ions; (FeS) x / (V3S4) y The numerous defects contained in the bulk phase of / C can also enhance the electrochemical dynamics of the three-phase composite sodium storage material, thus reducing the resistance to sodium ion migration.

[0009] Furthermore, (FeS) x / (V3S4) y The numerous defects in the bulk phase of / C can also provide more ion channels for sodium ion migration, which helps to accelerate the migration of sodium ions, thereby increasing the rate of sodium ion extraction and insertion at the positive and negative electrodes. This can improve the rate performance of sodium ion battery electrode materials and reduce impedance.

[0010] In addition, the carbon material in the three-phase composite sodium storage material can form a tight interfacial bond with FeS and V3S4, acting as a bridge or medium for the formation of the FeS and V3S4 heterogeneous interface, promoting the formation and stability of the heterogeneous interface. The carbon material also has good electrical conductivity, which can improve the electrochemical performance of the three-phase composite sodium storage material. Furthermore, the carbon material has good mechanical strength and ductility, which can suppress the volume expansion of the electrode material, reduce the structural damage of the electrode material, reduce the shedding of active material from the electrode material, ensure the stability of the three-phase composite sodium storage material during the charge and discharge process of the sodium-ion battery electrode material, reduce the impedance of the electrode material, and thus improve the cycle life of the sodium-ion battery.

[0011] Therefore, the synergistic effect among FeS, V3S4 and C components can improve the cycle stability and rate performance of the three-phase composite sodium storage material as an electrode material, thereby solving the problem of rapid decline in electrochemical performance of sodium-ion batteries during charge and discharge.

[0012] In some embodiments, the average particle size of the three-phase composite sodium storage material ranges from 4 μm to 10 μm.

[0013] In some embodiments, the specific capacity of the three-phase composite sodium storage material is in the range of 500mAh / g to 600mAh / g after cycling for 150 to 200 cycles under a current density range of 0.8A / g to 1.2A / g.

[0014] In some embodiments, the specific capacity of the three-phase composite sodium storage material decreases by less than or equal to 25% after 1000 cycles under a current density range of 3.8 A / g to 4.2 A / g.

[0015] In some embodiments, the initial electrochemical impedance of the three-phase composite sodium storage material ranges from 0.015Ω to 0.020Ω.

[0016] Secondly, a method for preparing a three-phase composite sodium storage material is provided. The method includes: reacting an iron source and a vanadium source under alkaline conditions to obtain a first precipitate; subjecting a carbon source, the first precipitate, and a sulfur source to a hydrothermal reaction in an organic solvent to obtain a second precipitate; and calcining the second precipitate under inert gas conditions to obtain the three-phase composite sodium storage material; the three-phase composite sodium storage material is selected from any one of the structures shown in the following general formula: (FeS) x / (V3S4) y / C, 0.2≤x≤5; 0.2≤y≤5.

[0017] In some embodiments, the iron source includes at least one of ferric chloride, ferrous chloride, ferric sulfate, ferric oxalate, and ferric nitrate.

[0018] In some embodiments, the vanadium source includes at least one of vanadium chloride, vanadium oxide, and vanadium oxalate.

[0019] In some embodiments, the sulfur source includes at least one of thiourea, thioacetamide, and sulfur powder.

[0020] In some embodiments, the carbon source includes at least one of polyvinylpyrrolidone, glucose, polypyrrolidone, and polydopamine.

[0021] In some embodiments, the molar ratio of the iron source to the vanadium source ranges from 0.2 to 5.

[0022] In some embodiments, the molar ratio of the iron source to the sulfur source ranges from 2 to 5.

[0023] In some embodiments, the mass of the carbon source is 10% to 20% of the total mass of the iron source, sulfur source and vanadium source.

[0024] In some embodiments, the first precipitate comprises at least one of iron oxide, iron hydroxide, vanadium oxide, and vanadium hydroxide.

[0025] In some embodiments, the second precipitate comprises at least one of an iron-sulfur compound and a vanadium-sulfur compound.

[0026] Thirdly, the application of the aforementioned three-phase composite sodium storage material in sodium-ion battery electrode materials is provided. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 is a flowchart of a method for preparing a three-phase composite sodium storage material according to some embodiments;

[0029] Figure 2 is an X-ray diffraction pattern of the three-phase composite sodium storage material according to Example 1;

[0030] Figure 3 is a scanning electron microscope image of the three-phase composite sodium storage material according to Example 1;

[0031] Figure 4 is a scanning electron microscope image of the three-phase composite sodium storage material according to Example 1;

[0032] Figure 5 is a transmission electron microscope image of the three-phase composite sodium storage material according to Example 1;

[0033] Figure 6 is a scanning electron microscope image of the three-phase composite sodium storage material according to Example 2;

[0034] Figure 7 is a scanning electron microscope image of the sodium storage material according to Comparative Example 1;

[0035] Figure 8 is a scanning electron microscope image of the sodium storage material according to Comparative Example 2;

[0036] Figure 9 is a comparison chart of the discharge specific capacity of sodium storage materials according to Example 1, Comparative Example 1 and Comparative Example 2.

[0037] Figure 10 is a comparison of the charging specific capacity and discharging specific capacity of the three-phase composite sodium storage material according to Example 1.

[0038] Figure 11 is a comparison of the initial electrochemical impedance of the sodium storage materials according to Example 1, Comparative Example 1 and Comparative Example 2.

[0039] Figure 12 is a comparison chart of the rate performance of sodium storage materials according to Example 1, Comparative Example 1 and Comparative Example 2. Detailed Implementation

[0040] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this disclosure.

[0041] In embodiments of this disclosure, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, article, or apparatus that includes that element.

[0042] In this disclosure, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" or "for example" in this disclosure should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of terms such as "exemplary" or "for example" is intended to present the relevant concepts by way of example.

[0043] In the description of this specification, features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0044] In some embodiments, due to the inherent structural properties of the sodium-ion battery electrode material, the electrode material has low conductivity, electrochemical hysteresis, and high expansion rate. This results in a large decrease in specific capacity, poor cycle capability and rate performance during the charge and discharge process, ultimately leading to a rapid decline in the electrochemical performance of the sodium-ion battery, which affects its service life and application range.

[0045] In related technologies, sodium sulfide storage materials can be used as negative electrode materials for sodium-ion batteries. For example, the electrochemical performance of sodium-ion batteries can be improved by designing the morphology and structure of sodium sulfide storage materials. However, during the charging and discharging process of sodium-ion batteries, the electrochemical performance of sodium-ion batteries still suffers from a relatively rapid decline.

[0046] Based on this, some embodiments of this disclosure provide a three-phase composite sodium storage material. The three-phase composite sodium storage material is selected from any of the structures shown in the following general formula: (FeS) x / (V3S4) y / C; For example, 0.2≤x≤5, 0.2≤y≤5.

[0047] The three-phase composite sodium storage material (FeS) provided in some embodiments of this disclosure x / (V3S4) y In / C, firstly, FeS and V3S4 can form a heterogeneous interface. At the interface, the adsorption energy required for sodium storage is lower, which makes it easier for sodium ions to be adsorbed. This can increase the amount of sodium ions stored in the three-phase composite sodium storage material.

[0048] Furthermore, (FeS) x / (V3S4) y The bulk phase of the sodium-ion battery contains numerous point, line, and surface defects, which provide abundant sodium-ion storage sites. This further enhances the amount of sodium ions stored in the three-phase composite sodium storage material, resulting in a better specific capacity. Consequently, a greater number of sodium ions are extracted and inserted into the positive and negative electrodes of the sodium-ion battery. During the charge and discharge process of the sodium-ion battery, the specific capacity of the electrode material decreases relatively little.

[0049] Secondly, (FeS) x / (V3S4) y The bulk phase of / C contains numerous defects, which can generate a large number of free electrons and holes, thereby improving the conductivity of the three-phase composite sodium storage material and accelerating the migration rate of sodium ions; (FeS) x / (V3S4) y The numerous defects contained in the bulk phase of / C can also enhance the electrochemical dynamics of the three-phase composite sodium storage material, thus reducing the resistance to sodium ion migration.

[0050] Furthermore, (FeS) x / (V3S4) y The numerous defects in the bulk phase of / C can also provide more ion channels for sodium ion migration, which helps to accelerate the migration of sodium ions, thereby increasing the rate of sodium ion extraction and insertion at the positive and negative electrodes. This can improve the rate performance of the electrode materials of sodium-ion batteries and reduce impedance.

[0051] Furthermore, the carbon material in the three-phase composite sodium storage material has several advantages. First, it can form a tight interfacial bond with FeS and V3S4, acting as a bridge or medium for the formation of the FeS and V3S4 heterogeneous interface, thus promoting its formation and stability. Second, it has good electrical conductivity, which enhances the electrochemical performance of the three-phase composite sodium storage material. Third, it possesses good mechanical strength and ductility, which can suppress the volume expansion of the electrode material, reduce structural damage, and minimize the shedding of active material from the electrode material. This ensures the stability of the three-phase composite sodium storage material during the charge and discharge process of the sodium-ion battery, reduces the impedance of the electrode material, and ultimately improves the cycle life of the sodium-ion battery.

[0052] Therefore, the synergistic effect among FeS, V3S4 and C components can effectively improve the cycle stability and rate performance of the three-phase composite sodium storage material, thereby solving the problem of rapid decline in electrochemical performance of sodium-ion batteries during charging and discharging.

[0053] In some embodiments, the average particle size of the three-phase composite sodium storage material ranges from 4 μm to 10 μm.

[0054] For example, the average particle size of the three-phase composite sodium storage material can be 4μm, 6μm, 8μm or 10μm, etc., and there is no limit here.

[0055] When the average particle size of the three-phase composite sodium storage material is too large, for example, greater than 10 μm, it may reduce the stability of the material structure during the charging and discharging process of sodium-ion batteries. When the average particle size of the three-phase composite sodium storage material is too small, for example, less than 4 μm, it may cause the three-phase composite sodium storage material to agglomerate, affecting the performance of the three-phase composite sodium storage material and causing a decrease in battery capacity and battery cycle performance.

[0056] By setting the average particle size range of the three-phase composite sodium storage material to 4μm to 10μm, the stability of the three-phase composite sodium storage material structure can be improved, which is conducive to the diffusion of sodium ions and thus improves the electrochemical performance of sodium-ion batteries.

[0057] In some embodiments, the specific capacity of the three-phase composite sodium storage material ranges from 500 mAh / g to 600 mAh / g after 150 to 200 cycles at a current density of 0.8 A / g to 1.2 A / g. Specific capacity refers to the amount of electricity that can be released per unit weight of battery or active material, and is an important indicator of battery performance.

[0058] For example, after cycling 150 to 200 times at a current density of 1 A / g, the specific capacity of the three-phase composite sodium storage material can be 500 mAh / g, 520 mAh / g, 550 mAh / g, 560 mAh / g, 580 mAh / g, or 600 mAh / g, etc., without any limitation.

[0059] Therefore, the three-phase composite sodium storage material provided in the embodiments of this disclosure has a high specific capacity.

[0060] In some embodiments, the specific capacity of the three-phase composite sodium storage material decreases by less than or equal to 25% after 1000 cycles under a current density range of 3.8 A / g to 4.2 A / g. Cycling performance refers to the effect of the number of charge-discharge cycles on the specific capacity by charging and discharging the battery at a certain current density. In other words, after 1000 cycles under a current density range of 3.8 A / g to 4.2 A / g, the specific capacity of the three-phase composite sodium storage material remains above 75% of its initial specific capacity.

[0061] For example, the specific capacity of a three-phase composite sodium storage material decreases by 25%, 20%, 15%, or 10% after 1000 cycles under a current density of 4 A / g, and no limit is set here.

[0062] Based on this scheme, the three-phase composite sodium storage material provided in some embodiments of this disclosure can maintain a high specific capacity after multiple cycles at a high current density, indicating that the three-phase composite sodium storage material has good cycle stability and alleviates the disadvantage of rapid decline in electrochemical performance of sodium-ion batteries during charging and discharging.

[0063] In some embodiments, the initial electrochemical impedance of the three-phase composite sodium storage material ranges from 0.015Ω to 0.020Ω.

[0064] For example, the initial electrochemical impedance of the three-phase composite sodium storage material is 0.015Ω, 0.016Ω, 0.017Ω, 0.018Ω, 0.019Ω or 0.020Ω, etc., and there is no limit here.

[0065] Based on this scheme, the three-phase composite sodium storage material provided in some embodiments of this disclosure has a smaller initial electrochemical impedance. During the charging and discharging process of sodium-ion batteries, the insertion and extraction of sodium ions are easier, reducing the obstacles to electrochemical reactions and helping to maintain the stability of the electrochemical performance of sodium-ion batteries. This alleviates the disadvantage that the electrochemical performance of sodium-ion batteries decreases rapidly during charging and discharging.

[0066] Some embodiments of this disclosure also provide a method for preparing a three-phase composite sodium storage material, as shown in Figure 1. The method for preparing the three-phase composite sodium storage material includes steps S1 to S3.

[0067] S1. Under alkaline conditions, the iron source and vanadium source are reacted to obtain the first precipitate.

[0068] For example, sodium hydroxide solution can be used under alkaline conditions.

[0069] For example, the iron source provides the element iron, and the iron source includes at least one of ferric chloride, ferrous chloride, ferric sulfate, ferric oxalate, and ferric nitrate.

[0070] For example, a vanadium source provides the element vanadium, and the vanadium source includes at least one of vanadium chloride, vanadium oxide, and vanadium oxalate.

[0071] For example, the molar ratio of iron source to vanadium source ranges from 0.2 to 5.

[0072] For example, the molar ratio of iron source to vanadium source can be 0.2, 1.0, 1.8, 2.4, 3.2, 4.0 or 5, etc., and there are no restrictions here.

[0073] Iron in the iron source reacts with sulfur to form FeS, while vanadium in the vanadium source reacts with sulfur to form V3S4. FeS and V3S4 have different crystal structures and electrochemical properties. When the molar ratio of iron to vanadium is small, such as less than 0.2, or large, such as greater than 5, the imbalance caused by this difference will be aggravated, leading to a decrease in the overall structural stability of the three-phase composite sodium storage material.

[0074] Based on this scheme, by adjusting the molar ratio of iron and vanadium sources within a suitable range, the relative contents of FeS and V3S4 in the three-phase composite sodium storage material can be controlled. Firstly, this can improve the overall stability of the three-phase composite sodium storage material structure. Secondly, FeS and V3S4 can form a heterogeneous interface, and the adsorption energy required for sodium storage at the interface is relatively low, which makes it easier for sodium ions to be adsorbed at the interface, thereby improving the sodium storage capacity of the three-phase composite sodium storage material, improving ion transport performance, and thus increasing the specific capacity of the three-phase composite sodium storage material, thereby improving the cycle stability and rate performance of sodium-ion battery electrode materials.

[0075] In some embodiments, the first precipitate comprises at least one of iron oxide, iron hydroxide, vanadium oxide, and vanadium hydroxide.

[0076] Iron oxides, iron hydroxides, vanadium oxides, and vanadium hydroxides all exhibit good compatibility with sulfur and carbon source components, which is beneficial for subsequent hydrothermal reactions and the formation of structurally stable three-phase composite sodium storage materials.

[0077] S2. In an organic solvent, a carbon source, a first precipitate, and a sulfur source are subjected to a hydrothermal reaction to obtain a second precipitate.

[0078] For example, the carbon source provides carbon elements and can be an organic compound. For instance, the carbon source includes at least one of polyvinylpyrrolidone, glucose, polypyrrolidone, and polydopamine. As described above, carbon materials can form tight interfacial bonds with FeS and V3S4, and can also promote the formation and stabilization of heterogeneous interfaces.

[0079] For example, a sulfur source provides sulfur, including at least one of thiourea, thioacetamide, and sulfur powder. The sulfur source forms sulfides with iron and vanadium, enabling better recombination of FeS and V3S4 and facilitating the formation of heterogeneous interfaces.

[0080] For example, an organic solvent such as ethylene glycol.

[0081] In some embodiments, the molar ratio of the iron source to the sulfur source ranges from 2 to 5.

[0082] For example, the molar ratio of iron source to sulfur source can be 2, 3, 4 or 5, etc., and there is no limit here.

[0083] In some embodiments, the mass of the carbon source is 10% to 20% of the total mass of the iron source, sulfur source and vanadium source.

[0084] For example, the mass of the carbon source can be 10%, 12%, 14%, 16%, 18%, or 20% of the total mass of the iron, sulfur, and vanadium sources, etc., without any restrictions.

[0085] Based on the above introduction about iron, carbon, and sulfur sources, it can be seen that by adjusting the molar ratio of iron, carbon, and sulfur sources, a more stable heterogeneous interface can be formed between FeS and V3S4, thereby improving the electrochemical performance of sodium-ion batteries.

[0086] In some embodiments, the second precipitate comprises at least one of an iron-sulfur compound and a vanadium-sulfur compound.

[0087] Iron-sulfur compounds and vanadium-sulfur compounds have stable crystal structures that can maintain structural integrity during charge and discharge, thus improving the cycle stability of sodium-ion batteries. Moreover, when combined with carbon sources, iron-sulfur compounds and vanadium-sulfur compounds can form stable composite material structures, which is beneficial for forming structurally stable three-phase composite sodium storage materials.

[0088] S3. Under inert gas conditions, the second precipitate is calcined to obtain a three-phase composite sodium storage material.

[0089] During the calcination process, the organic matter in the second precipitate is pyrolyzed to generate carbon materials, which are then embedded into the structure of the sulfides. At the same time, calcination also causes solid-phase reactions between the sulfides, forming a more stable three-phase composite sodium storage material.

[0090] For example, the three-phase composite sodium storage material is selected from any of the structures shown in the following general formula: (FeS) x / (V3S4) y / C; For example, 0.2≤x≤5, 0.2≤y≤5.

[0091] The three-phase composite sodium storage material obtained by some embodiments of this disclosure provides abundant sodium ion storage sites and provides more migration pathways for sodium ions.

[0092] Some embodiments of this disclosure also provide an application of the above-described three-phase composite sodium storage material in sodium-ion battery electrode materials.

[0093] The following describes in more detail the preparation methods of three-phase composite sodium storage materials provided in some embodiments of this disclosure, with reference to the accompanying drawings.

[0094] Example 1

[0095] The preparation method of the three-phase composite sodium storage material includes steps S11 to S13.

[0096] S11. Add 4g of sodium hydroxide to 100ml of deionized water. After the sodium hydroxide dissolves, add 2mmol of ferric chloride and 6mmol of vanadium chloride. Stir for 30 minutes and let stand for 2 hours. Centrifuge to obtain the lower precipitate and then dry to obtain the first precipitate.

[0097] Ferric chloride is the iron source, and vanadium chloride is the vanadium source.

[0098] The first precipitate is a white precipitate.

[0099] S12. Dissolve 1g of polyvinylpyrrolidone in 50ml of ethylene glycol solvent and stir for 30 minutes. Add 200mg of the first precipitate and 400mg of thiourea and stir for 30 minutes. Then add the mixture to a reaction vessel and keep it at 200℃ in a constant temperature oven for 24 hours. After the reaction solution cools, centrifuge and wash it. After vacuum drying, the second precipitate is obtained.

[0100] Polyvinylpyrrolidone is used as the carbon source, ethylene glycol as the organic solvent, and thiourea as the sulfur source.

[0101] The second precipitate is a black precipitate.

[0102] S13. Place 150 mg of the second precipitate in an argon-protected tubular furnace and treat it at 500°C for 3 hours to obtain FeS / V3S4 / C three-phase composite sodium storage material.

[0103] Figure 2 shows the X-ray diffraction pattern of the three-phase composite sodium storage material of Example 1. As can be seen from Figure 2, all diffraction peaks can be identified as FeS / V3S4, and no other impurity peaks appear, indicating that the FeS and V3S4 in the three-phase composite sodium storage material synthesized in Example 1 have high purity.

[0104] Figures 3 and 4 are scanning electron microscope images of the three-phase composite sodium storage material of Example 1. Figures 3 and 4 are taken from different positions of the three-phase composite sodium storage material. From Figures 3 and 4, it can be seen that the morphology of the three-phase composite sodium storage material is cauliflower-shaped, and the average particle size is 4μm to 10μm.

[0105] Figure 5 is a transmission electron microscope image of the three-phase composite sodium storage material of Example 1. From Figure 5, the grain boundary L1 of FeS and V3S4 can be clearly seen, that is, there is an organic combination of two different substances. From the atomic end, the two substances have an interaction relationship. In addition, from the morphology of the monomer and the morphology of the composite, FeS and V3S4 are not mixed. After the formation of FeS / V3S4 composite, the morphology changed significantly. This is due to the difference in lattice growth between the two during the synthesis process, which led to the change in morphology.

[0106] Example 2

[0107] The preparation method of the three-phase composite sodium storage material in Example 2 is the same as that in Example 1, except that 2 mmol of ferric chloride is replaced with 1 mmol of ferric chloride and 6 mmol of vanadium chloride is replaced with 9 mmol of vanadium chloride, so as to obtain the (FeS)2 / (V3S4)6 / C three-phase composite sodium storage material.

[0108] Figure 6 is a scanning electron microscope image of the three-phase composite sodium storage material of Example 2. As shown in Figure 6, the morphology of (FeS)2 / (V3S4)6 / C is cauliflower-like, with an average particle size of 4μm to 10μm.

[0109] Example 3

[0110] The preparation method of the three-phase composite sodium storage material in Example 3 is the same as that in Example 1, except that 2 mmol of ferric chloride is replaced with 3 mmol of ferric chloride and 6 mmol of vanadium chloride is replaced with 3 mmol of vanadium chloride, so as to obtain the (FeS)3 / V3S4 / C three-phase composite sodium storage material.

[0111] Comparative Example 1

[0112] Comparative Example 1 provides a sodium storage material, the preparation process of which includes steps R1 to R3.

[0113] R1. Add 4g of sodium hydroxide to 100ml of deionized water. After the sodium hydroxide dissolves, add 4mmol of ferric chloride. Stir slowly for 30 minutes and let stand for 2 hours. Centrifuge to obtain the lower precipitate, and then dry to obtain a white precursor powder.

[0114] R2. Dissolve 1g of polyvinylpyrrolidone in 50ml of ethylene glycol solvent. After stirring vigorously for 30 minutes, add 200mg of white precursor powder and 400mg of thiourea. After stirring for 30 minutes, add to the reaction vessel and keep the reaction at 200℃ in a constant temperature oven for 24 hours. After the reaction solution cools, centrifuge and wash, and vacuum dry to obtain a black powder.

[0115] R3 and 150 mg of black powder were placed in an argon-protected tube furnace and treated at 500°C for 3 hours to obtain (FeS)4 / C sodium storage material.

[0116] Figure 7 is a scanning electron microscope image of the sodium storage material of Comparative Example 1. As shown in Figure 7, the sodium storage material has a spherical morphology with an average particle size of 1 μm to 5 μm.

[0117] Comparative Example 2

[0118] Comparative Example 2 provides another sodium storage material, the preparation process of which includes steps P1 to P3.

[0119] P1. Add 4g of sodium hydroxide to 100ml of deionized water. After dissolving, add 12mmol of vanadium chloride. Stir slowly for 30 minutes, let stand for 2 hours, centrifuge to obtain the lower precipitate, and then dry to obtain a white precursor powder.

[0120] P2. Dissolve 1g of polyvinylpyrrolidone in 50ml of ethylene glycol solvent. After stirring vigorously for 30 minutes, add 200mg of white precursor powder and 400mg of thiourea. After stirring for 30 minutes, add to the reaction vessel and keep the reaction at 200℃ in a constant temperature oven for 24 hours. After the reaction solution cools, centrifuge and wash, and vacuum dry to obtain a black powder.

[0121] P3. Finally, 150 mg of black powder was placed in an argon-protected tube furnace and treated at 500°C for 3 hours to obtain (V3S4)4 / C sodium storage material.

[0122] Figure 8 is a scanning electron microscope image of the sodium storage material of Comparative Example 2. As shown in Figure 8, the sodium storage material has a spherical morphology and is aggregated together, with an average particle size of 1 μm to 5 μm.

[0123] The following section presents the performance testing data for sodium storage materials.

[0124] Test 1: The sodium storage materials obtained in Example 1, Comparative Example 1 and Comparative Example 2 were cycled 150 to 200 times at a current density of 1 A / g to obtain the specific capacity of different sodium storage materials. The results are shown in Figure 9.

[0125] As can be seen from Figure 9, the sodium storage material (FeS)4 / C in Comparative Example 1 has a high specific capacity but a large decay, while the sodium storage material (V3S4)4 / C in Comparative Example 2 has stable performance but a low specific capacity. The three-phase composite sodium storage material in Example 1 has high specific capacity and high stability. After 170 cycles, the specific capacity ranges from 500 mAh / g to 600 mAh / g.

[0126] Test 2: The charging specific capacity and discharging specific capacity of the three-phase composite sodium storage material obtained in Example 1 were measured after cycling at a current density of 4 A / g for 1000 cycles. The results are shown in Figure 10.

[0127] As can be seen from Figure 10, after 1000 cycles at a current density of 4 A / g, the specific capacity of the three-phase composite sodium storage material decreased by 24%, but 76% of the specific capacity remained, indicating that the three-phase composite sodium storage material provided in some embodiments of this disclosure has good cycling stability.

[0128] Test 3: The sodium storage materials obtained in Example 1, Comparative Example 1 and Comparative Example 2 were subjected to initial electrochemical impedance spectroscopy tests at a test frequency of 0.05 Hz to 105 Hz and a carbon content of 10% to 15%. The results are shown in Figure 11.

[0129] As can be seen from Figure 11, the initial electrochemical impedance of the three-phase composite sodium storage material obtained in Example 1 can be represented by the diameter of the real part of the impedance in the semicircle in Figure 11, that is, the difference between the final value of the real part of the impedance (0.028Ω) and the initial value of the real part of the impedance (0.01Ω). The initial electrochemical impedance of the three-phase composite sodium storage material is 0.018Ω, which is lower than the initial electrochemical impedance of the sodium storage material obtained in Comparative Example 1 and Comparative Example 2. This shows that the three-phase composite sodium storage material provided in some embodiments of this disclosure improves the stability of the electrochemical performance of sodium-ion batteries.

[0130] Test 4: The sodium storage materials obtained in Example 1, Comparative Example 1 and Comparative Example 2 were subjected to step rate performance tests. The specific capacity at current densities of 0.2 A / g, 0.5 A / g, 1 A / g and 2 A / g is shown in Figure 12.

[0131] As shown in Figure 12, at a current density of 0.2 A / g, the specific capacity of the three-phase composite sodium storage material in Example 1 ranges from 600 mAh / g to 700 mAh / g; at a current density of 0.5 A / g, the specific capacity ranges from 550 mAh / g to 650 mAh / g; at a current density of 1 A / g, the specific capacity ranges from 550 mAh / g to 600 mAh / g; and at a current density of 2 A / g, the specific capacity ranges from 480 mAh / g to 550 mAh / g. Therefore, the three-phase composite sodium storage material obtained in Example 1 has a high specific capacity, indicating that the three-phase composite sodium storage materials provided in some embodiments of this disclosure have good rate performance.

[0132] The above are merely specific embodiments of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A three-phase composite sodium storage material, wherein, The three-phase composite sodium storage material is selected from any one of the structures shown in the following general formula: (FeS) x / (V3S4) y / C; wherein, 0.2≤x≤5, 0.2≤y≤5.

2. The triphasic composite material for sodium storage according to claim 1, wherein, The average particle size of the three-phase composite sodium storage material ranges from 4 μm to 10 μm.

3. The triphasic composite material for sodium storage according to claim 1 or 2, wherein, The specific capacity of the three-phase composite sodium storage material ranges from 500 mAh / g to 600 mAh / g after 150 cycles to 200 cycles at a current density ranging from 0.8 A / g to 1.2 A / g.

4. The triphasic composite material for sodium storage according to claim 1 or 2, wherein, The specific capacity of the three-phase composite sodium storage material decreases by less than or equal to 25% after 1000 cycles at a current density ranging from 3.8 A / g to 4.2 A / g.

5. The triphasic composite material for sodium storage according to claim 1 or 2, wherein, The initial electrochemical impedance of the three-phase composite sodium storage material ranges from 0.015 Ω to 0.020 Ω.

6. A method for preparing a three-phase composite sodium storage material, comprising: reacting an iron source and a vanadium source under alkaline conditions to obtain a first precipitate; performing a hydrothermal reaction on a carbon source, the first precipitate, and a sulfur source in an organic solvent to obtain a second precipitate; and The second precipitate is calcined under inert gas conditions to obtain the three-phase composite sodium storage material; wherein the three-phase composite sodium storage material is selected from any one of the structures shown in the following general formula: (FeS) x / (V3S4) y / C; wherein 0.2≤x≤5, 0.2≤y≤5.

7. The method of preparing a triphasic composite material for sodium storage according to claim 6, wherein, The iron source includes at least one of ferric chloride, ferrous chloride, ferric sulfate, ferric oxalate, and ferric nitrate.

8. The method of producing a triphasic composite material for sodium storage according to claim 6 or 7, wherein, The vanadium source includes at least one of vanadium chloride, vanadium oxide, and vanadium oxalate.

9. The method of producing a three-phase composite material for sodium storage according to any one of claims 6 to 8, wherein The sulfur source includes at least one of thiourea, thioacetamide, and sulfur powder.

10. The method of producing a three-phase composite material for sodium storage according to any one of claims 6 to 9, wherein The carbon source includes at least one of polyvinylpyrrolidone, glucose, polypyrrolidone, and polydopamine.

11. The method of producing a three-phase composite material for sodium storage according to any one of claims 6 to 10, wherein The molar ratio of the iron source to the vanadium source ranges from 0.2 to 5.

12. The method of preparing a triphasic composite material for sodium storage according to any one of claims 6 to 11, wherein, The molar ratio of the iron source to the sulfur source ranges from 2 to 5.

13. The method of producing a three-phase composite material for sodium storage according to any one of claims 6 to 12, wherein The mass of the carbon source is 10% to 20% of the total mass of the iron source, the sulfur source, and the vanadium source.

14. The method of producing a three-phase composite material for sodium storage according to any one of claims 6 to 13, wherein The first precipitate includes at least one of an iron oxide, an iron hydroxide, a vanadium oxide, and a vanadium hydroxide.

15. The method of preparing a triphasic composite material for sodium storage according to any one of claims 6 to 14, wherein, The second precipitate includes at least one of an iron-sulfur compound and a vanadium-sulfur compound.

16. Use of the three-phase composite sodium storage material according to any one of claims 1 to 5 as an electrode material for a sodium-ion battery.

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