A mxene edge-grown metal sulfide composite material and a preparation method and application thereof

Abstract

The application discloses a kind of MXene edge growth metal sulfide composite material and its preparation method and application, and belong to electrochemical energy storage field.The preparation method of the composite material includes the following steps: MXene, metal anion salt, thiourea and polyvinylpyrrolidone are dissolved in water and glycol mixed solution, and MXene edge growth metal sulfide composite material is obtained by one-step hydrothermal method.The composite material uses two-dimensional MXene as conductive substrate, and metal sulfide is uniformly loaded on the edge, forms a "fishing net" structure, and the material synthesis operation is simple, and the repeatability is strong.The exposed surface of MXene as conductive substrate can improve the electronic conduction of S, and also can inhibit the volume expansion of S.The "fishing net" structure can physically limit polysulfide, and metal sulfide can be used as S species conversion catalyst, accelerate the conversion reaction of S species, reduce polysulfide dissolution, inhibit shuttle effect, so as to make it as room temperature Na-S battery multifunctional S catalytic carrier material show more excellent sodium storage performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of electrochemical energy storage, and particularly relates to a MXene edge-grown metal sulfide composite material and a preparation method and application thereof. BACKGROUND

[0002] Lithium-ion batteries (LIBs) are widely used in portable devices, electric vehicles, smart grids and other fields as energy storage and power systems. However, the scarcity and uneven distribution of lithium resources inevitably restrict the large-scale application of LIBs. Among many electrochemical energy storage systems, sodium batteries are expected to become the most promising alternative to lithium batteries due to the higher sodium reserves than lithium on earth. Among them, room-temperature sodium-sulfur (Na-S) batteries based on multi-electron conversion reactions exhibit ultra-high theoretical energy density (1274 Wh / kg), and the raw materials are abundant in nature (sodium abundance is about 25670 ppm, sulfur abundance is about 953 ppm), low in price (metallic sodium: 230,000 yuan / ton), and environmentally friendly, making them have strong competitiveness in the field of large-scale safe energy storage.

[0003] Similar to Li-S batteries, Na-S batteries also face some challenges, such as fast capacity decay, low sulfur utilization, and poor reversible capacity. These problems are usually caused by a variety of factors including poor electrical conductivity of sulfur and its discharge products, slow reaction kinetics of solid sulfur and sodium, "shuttle effect" caused by dissolution / diffusion of polysulfides in electrolyte, and huge volume expansion (~260%) during charge / discharge process. An ideal S carrier material should not only provide high electronic conductivity, increase chemical adsorption of sodium polysulfide, but also have catalyst function to accelerate the conversion reaction of sodium polysulfide, improve its reaction kinetics, and thus realize efficient utilization of S positive electrode and high performance. Therefore, developing a multifunctional S catalyst carrier material with high electrical conductivity, high adsorption capacity, high catalytic activity, high specific surface area and high stability is the key to promoting the commercialization of high-performance room-temperature Na-S batteries for large-scale energy storage. For this purpose, we propose a MXene edge-grown metal sulfide composite material and a preparation method thereof, and its application as an efficient S host in room-temperature Na-S batteries. SUMMARY

[0004] The present application aims to overcome the above-mentioned deficiencies existing in the prior art, and provides a MXene edge-grown metal sulfide composite material and a preparation method and application thereof. The positive and negative charge attraction characteristics are used to make metal anion salt preferentially adsorbed on the positively charged MXene edge. A multifunctional catalyst for in-situ growth of metal sulfide on the MXene edge is designed and constructed. The catalyst is used as a host catalyst material for a sulfur positive electrode of a room-temperature sodium-sulfur battery. Based on the two-dimensional high-conductivity exposed polar surface of MXene, the conductivity of sulfur species can be improved, the volume expansion can be buffered, the physical and chemical adsorption of polysulfides can be increased, and the two-dimensional metal sulfide with high catalytic activity on the MXene edge can further realize the physical and chemical confinement of polysulfides, while accelerating the catalytic conversion of sodium polysulfide, thereby effectively preventing the shuttle effect of sodium polysulfide and improving the specific capacity and cycle life of the room-temperature Na-S battery.

[0005] The object of the present application is achieved by the following technical solutions:

[0006] A preparation method of a MXene edge-grown metal sulfide composite material, comprising the following steps:

[0007] (1) MXene, metal anion salt, thiourea and polyvinylpyrrolidone are added to 10 mL of water and 20 mL of ethylene glycol in a mass ratio of 1:(5-20):(20-100):(1-5), and a mixed solution is formed after ultrasonic stirring for 30 minutes.

[0008] (2) The mixed solution is added to a 50 mL polytetrafluoroethylene liner, and sealed in a stainless steel reaction kettle. The reaction kettle is incubated in an oven at 180-220 DEG C for 12-48 hours. After cooling to room temperature, the precipitate is washed with water and anhydrous ethanol for 3 times each, and the final precipitate is freeze-dried to obtain a MXene edge-grown metal sulfide composite material.

[0009] Preferably, the MXene in step (1) is one or more of Ti3C2T x , Ti2CT x , Mo2CT x , V2CT x or V4C3T x .

[0010] Preferably, the metal anion salt in step (1) is one or more of ammonium molybdate tetrahydrate, ammonium perrhenate, ammonium vanadate, vanadium acetylacetone, ammonium tungstate, iron acetylacetone, cobalt acetylacetone, nickel acetylacetone, manganese acetylacetone, copper acetylacetone or sodium stannate.

[0011] The present application simultaneously provides a MXene edge-grown metal sulfide composite material obtained by the above-mentioned preparation method.

[0012] The application also provides application of the MXene edge-grown metal sulfide composite material as an S carrier to manufacture a mixed S electrode and in a room-temperature sodium-sulfur battery.

[0013] The manufacturing application is as follows:

[0014] (1) The MXene edge-grown metal sulfide composite material, S powder, a conductive agent and a binder are ground and mixed according to a mass ratio of 2:5:2:1, an appropriate amount of deionized water or NMP is added dropwise, and the obtained slurry is uniformly applied to the rough surface of a copper current collector and vacuum-dried at 60-120 DEG C to obtain a Na-S battery composite S electrode.

[0015] (2) The above composite S electrode is used as a positive electrode of a Na-S battery, metallic sodium is used as a negative electrode, an electrolyte is 1M NaSO3CF3 dissolved in DEGDME solvent or 1M NaPF6 dissolved in DEGDME solvent or 1M NaPF6 dissolved in DME solvent, and a separator is a double-layer separator of glass fiber GF / D and Celgard2325, wherein the Celgard2325 separator is close to the composite S electrode, and a CR2032 button-type room-temperature Na-S battery is assembled in sequence.

[0016] Preferably, the conductive agent in step (1) is one or more of conductive carbon black, graphene, MXene or carbon nanotubes.

[0017] Preferably, the binder in step (1) is one or more of polyvinylidene fluoride, polyacrylic acid, polytetrafluoroethylene, polyvinyl alcohol, carboxymethyl cellulose or sodium alginate.

[0018] Advantages and beneficial effects of the application:

[0019] (1) The application proposes a new heterostructure construction strategy based on MXene, uses the positive and negative charge attraction characteristics to make metal anion salts preferentially adsorbed on the positively charged MXene edges, designs and constructs MXene edge in-situ grown metal sulfide composite materials through a one-step hydrothermal method, the strategy is simple to operate and has strong repeatability, and meanwhile has MXene and metal element adjustability.

[0020] (2) The MXene edge-grown metal sulfide composite material exposes a rich active surface based on MXene, so that the exposed MXene surface contacts more S particles and S species in the reaction process, improves the overall structural stability and electronic conductivity, and also inhibits the volume expansion in the S reaction process.

[0021] (3) The MXene edge-grown metal sulfide composite material, the metal sulfide grown on the edge of the MXene is like a lead sinker of a fishing net, so that the MXene is like a fishing net, can physically limit the capture of polysulfides, thereby inhibiting the shuttle effect of polysulfides, in addition, the metal sulfide grown on the edge of the MXene can also act as a catalyst for the conversion of S species, accelerating the conversion reaction of S species to Na2S, reducing the dissolution of polysulfides, and further inhibiting the shuttle effect. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a transmission electron microscope image of the MoS2@MXene composite material synthesized in Example 1 and its corresponding element distribution map;

[0023] Figure 2 is an X-ray diffraction spectrum of the MoS2@MXene composite material synthesized in Example 1;

[0024] Figure 3 is a transmission electron microscope image of the ReS2@MXene composite material synthesized in Example 5;

[0025] Figure 4 is a transmission electron microscope image of the CoS2@MXene composite material synthesized in Example 6;

[0026] Figure 5 is a rate performance graph of the S / MoS2@MXene electrode prepared in Example 7 and the pure S electrode prepared in Comparative Example 4 at a current density of 0.2, 0.5, 1, 2 and 5 A / g, respectively;

[0027] Figure 6 is a cycle stability graph of the S / MoS2@MXene electrode prepared in Example 7 at a current density of 2 A / g;

[0028] Figure 7 is a transmission electron microscope image of the MXene double-face-grown MoS2 composite material synthesized in Comparative Example 1;

[0029] Figure 8 is a transmission electron microscope image of the MXene double-face-grown MoS2 composite material synthesized in Comparative Example 2;

[0030] Figure 9 is a transmission electron microscope image of the MXene double-face-grown MoS2 composite material synthesized in Comparative Example 3. DETAILED DESCRIPTION

[0031] In order to make the above-mentioned purposes and advantages of the present application clear and easy to understand, the technical solutions in the embodiments of the present application will be described in detail below with reference to the drawings in the embodiments of the present application, but the present application is not limited to the specific embodiments. The materials, if not specifically stated, can be obtained by commercial means.

[0032] Example 1:

[0033] This example provides a synthesis and characterization analysis of MXene edge growth metal sulfide composite material, the specific synthesis process is as follows:

[0034] (1) 20 mg of Ti3C2T x MXene, 123.6 mg of ammonium molybdate tetrahydrate, 865 mg of thiourea and 25 mg of polyvinylpyrrolidone were added into 10 mL of water and 20 mL of ethylene glycol, and a mixed solution was formed after ultrasonic stirring for 30 minutes.

[0035] (2) The above mixed solution was added into a 50 mL polytetrafluoroethylene liner, and sealed in a stainless steel reaction kettle, and incubated in an oven at 200°C for 24 hours. After cooling to room temperature, the precipitate was washed with water and anhydrous ethanol for 3 times, and the final precipitate was freeze-dried to obtain MXene edge growth metal sulfide composite material (MoS2@MXene).

[0036] Figure 1 The transmission electron microscopy image of the MoS2@MXene composite material synthesized in this example and its corresponding element distribution map. From Figure 1 It can be seen that the synthesized MoS2@MXene composite material presents a lace-like structure, that is, MoS2 nanosheets grow around the edges of MXene, the size of MoS2 nanosheets is about 30-80 nm, and the size of MXene nanosheets is about 0.5-1 μm, and the element distribution map further confirms this lace-like structure, S and Mo elements are mainly distributed at the edge position of MXene, and Ti represents Ti3C2T x MXene.

[0037] Figure 2 The X-ray diffraction spectrum of the MoS2@MXene composite material synthesized in this example. From Figure 2 It can be seen that the XRD diffraction peak of the composite material can be indexed to the (101) and (110) crystal planes of MoS2 (PDF #77-0341).

[0038] Example 2:

[0039] The preparation method is the same as described in Example 1, except that:

[0040] In step (1), the addition amount of MXene, ammonium molybdate tetrahydrate, thiourea and polyvinylpyrrolidone is 20 mg, 247.2 mg, 1730 mg and 50 mg, respectively, and other conditions and parameters are carried out according to Example 1.

[0041] Example 3:

[0042] The preparation method is the same as that described in Example 1, except that:

[0043] In step (2), the hydrothermal reaction temperature is 220°C, and other conditions and parameters are as in Example 1.

[0044] Example 4:

[0045] The preparation method is the same as that described in Example 1, except that:

[0046] In step (2), the hydrothermal reaction temperature is 180°C, and other conditions and parameters are as in Example 1.

[0047] Example 5:

[0048] The preparation method is the same as that described in Example 1, except that:

[0049] In step (1), ammonium molybdate tetrahydrate was replaced with 268 mg of perrhenate ammonium, and other conditions and parameters were carried out as in Example 1.

[0050] Figure 3 Transmission electron microscopy (TEM) image of the synthesized ReS2@MXene composite material in this example. From Figure 3 It can be seen that the synthesized ReS2@MXene composite material also exhibits a lace-like structure, with ReS2 nanosheets growing around the edge of MXene.

[0051] Example 6:

[0052] The preparation method is the same as that described in Example 1, except that:

[0053] In step (1), ammonium molybdate tetrahydrate was replaced with 259 mg of cobalt acetylacetonate, and other conditions and parameters were performed as in Example 1.

[0054] Figure 4 Transmission electron microscopy (TEM) image of the synthesized CoS2@MXene composite material in this example. From Figure 4 It can be seen that the synthesized CoS2@MXene composite material also exhibits a lace-like structure, with CoS2 particles growing around the edge of MXene. The CoS2 particles scattered on the surface of MXene may be due to the fact that this is a defect location of MXene, and they preferentially adsorb cobalt ions and grow in situ.

[0055] Example 7:

[0056] This embodiment provides a method for preparing a composite S electrode and testing the performance of a room-temperature Na-S battery. The detailed operation procedure is as follows:

[0057] (1) The MoS2@MXene dry powder obtained in Example 1 was used as the S carrier catalyst material. It was mixed with S powder, conductive carbon black and polyacrylic acid binder in a mass ratio of 2:5:2:1. Then, an appropriate amount of deionized water was added and the mixture was ground into a paste in an agate mortar. The paste was then coated onto the rough surface of copper foil using a coating machine. After drying in an oven at 60°C for 12 hours, the paste was cut into round pieces with a diameter of 14 mm and pressed at a pressure of 6 MPa for 1 minute to obtain a composite S electrode sheet (S / MoS2@MXene).

[0058] (2) Assemble a 2032 button cell in a glove box. The electrolyte is 1M NaSO3CF3 dissolved in DEGDME. The separators are GF / D and Celgard 2325. The Celgard 2325 separator is placed near the S / MoS2@MXene electrode. Sodium metal is used as the negative electrode.

[0059] (3) The button cell assembled in step (2) is tested for performance in the Xinwei Battery Test System. The battery charge and discharge voltage range is 0.4 to 3V. The current density for rate performance testing is 0.2, 0.5, 1, 2, 5 and 0.2A / g. Its cycle performance is 700 cycles at a current density of 2A / g.

[0060] like Figure 5 As shown, the rate performance test conditions for the S / MoS2@MXene electrode were 10 cycles each at 0.2, 0.5, 1, 2 and 5 A / g. The discharge specific capacity of the battery in the first cycle at each rate was 1559, 1181, 1162, 1130 and 830 mAh / g, respectively. The test was finally returned to 0.2 A / g, and the discharge specific capacity was 1256 mAh / g, demonstrating excellent rate performance.

[0061] like Figure 6 As shown, the S / MoS2@MXene battery can maintain a reversible specific capacity of 1163.2 mAh / g after 700 cycles at a current density of 2 A / g, with a capacity retention of approximately 93.4%.

[0062] Comparative Example 1:

[0063] This example provides the synthesis and characterization of a comparative material (MXene double-sided grown metal sulfide) of an MXene edge-grown metal sulfide composite. The specific synthesis process is the same as the preparation method described in Example 1, except that:

[0064] In step (1), the amounts of water and ethylene glycol used were 4 mL and 26 mL, respectively, and other conditions and parameters were as in Example 1.

[0065] like Figure 7As shown, the MXene double-sided grown MoS2 composite material synthesized in this example exhibits a different structure from the MXene edge-grown MoS2 composite material. Under these conditions, the synthesized MoS2 no longer grows in situ only at the edge of the MXene, but grows on the entire surface of the MXene. However, this reduces the electrical conductivity and toughness of the MXene, which is detrimental to the electron transport and structural stability of the S species.

[0066] Comparative Example 2:

[0067] This example provides the synthesis and characterization of another comparative material (MXene double-sided grown metal sulfide) of MXene edge-grown metal sulfide composites. The specific synthesis process is the same as the preparation method described in Example 1, except that:

[0068] In step (1), the amounts of water and ethylene glycol used are 0 mL and 30 mL, respectively, and other conditions and parameters are the same as in Example 1.

[0069] like Figure 8 As shown, the structure of the MXene double-sided MoS2 composite material synthesized in this example is the same as that in Comparative Example 1, both of which have MoS2 grown on the surface of MXene. The difference lies in the size and morphology of the MoS2 nanosheets. The MoS2 nanosheets in this example are smaller and tend to aggregate into spheres on the MXene surface. It can also be seen that the different addition ratios of water and ethylene glycol are crucial to the control of structural morphology.

[0070] Comparative Example 3:

[0071] To further demonstrate the versatility of the strategy of in-situ growth of metal sulfide composite materials at the edges of MXene by utilizing the negatively charged surface and positively charged edge properties of MXene, this example modifies the surface of MXene with a positive charge and provides the synthesis and characterization of a comparative material (MXene double-sided metal sulfide growth) for MXene edge-grown metal sulfide composite materials. The specific synthesis process is the same as the preparation method described in Example 1, except that:

[0072] In step (1), MXene is positively charged PDDA-modified MXene. The modification process involves adding the original MXene to 5 mL of a 20% polydimethylammonium chloride (PDDA) solution with a molecular weight of 100,000-200,000. After stirring and ultrasonic dispersion, the PDDA-modified MXene is obtained by centrifugation. Other conditions and parameters are as described in Example 1.

[0073] like Figure 9As shown, the MoS2 nanosheets synthesized in this example will grow in situ on both sides of the MXene surface. This is because the MXene surface is also preferentially adsorbed with molybdate anions after being modified with positive charge, so that the MoS2 nanosheets grow on the entire surface. This further confirms the universality of the strategy of growing metal sulfide composite materials in situ at the edge of MXene by utilizing the negatively charged edge of the MXene surface and the attraction between positive and negative charges.

[0074] Comparative Example 4:

[0075] This example provides the preparation and electrochemical performance characterization of a comparative electrode (pure S electrode) for the S / MoS2@MXene electrode. The specific preparation process is the same as that described in Example 7, except that:

[0076] In step (1), S powder, conductive carbon black and polyacrylic acid binder are mixed evenly in a mass ratio of 7:2:1. Other conditions and parameters are carried out as in Example 7. The assembly of the room temperature Na-S battery is also the same as in Example 7.

[0077] Figure 5 The data shown is the rate performance of the pure S electrode fabricated in this example at current densities of 0.2-5 A / g. Compared with the rate performance of the S / MoS2@MXene electrode in Example 7, it can be seen that using the MXene edge-grown metal sulfide composite material (MoS2@MXene) as the S support catalyst significantly improves the performance of the room temperature Na-S battery. This indicates that this special structure can suppress the dissolution shuttle of captured sodium polysulfides and act as a catalyst to accelerate the conversion reaction of polysulfides, thereby significantly improving the S sodium storage performance.

[0078] 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 an MXene edge-grown metal sulfide composite material, comprising the following steps: (1) Add MXene, metal anion salt, thiourea and polyvinylpyrrolidone to 10 mL of water and 20 mL of ethylene glycol in a mass ratio of 1:(5-20):(20-100):(1-5), and stir ultrasonically for 30 minutes to form a mixed solution; (2) Add the above mixed solution into a 50 mL polytetrafluoroethylene liner and seal it in a stainless steel reactor. Keep it in an oven at 180-220℃ for 12-48 hours. After cooling to room temperature, wash the precipitate three times each with water and anhydrous ethanol by centrifugation. Then freeze-dry the final precipitate to obtain the MXene edge-grown metal sulfide composite material.

2. The method according to claim 1, characterized in that... The MXene is Ti3C2T x Ti2CT x Mo2CT x V2CT x Or V4C3T x One or more of them.

3. The method according to claim 1, characterized in that... The metal anionic salt is one or more of the following: ammonium molybdate tetrahydrate, ammonium perrhenate, ammonium vanadium oxide, vanadium acetylacetonate, ammonium tungstate, iron acetylacetonate, cobalt acetylacetonate, nickel acetylacetonate, manganese acetylacetonate, copper acetylacetonate, or sodium stannate.

4. The MXene edge-grown metal sulfide composite material obtained by the method of any one of claims 1-3.

5. The application of the MXene edge-grown metal sulfide composite material of claim 4 in the preparation of composite S electrodes and room-temperature Na-S batteries.

6. The application according to claim 5, characterized in that, The composite S electrode is fabricated as follows: MXene edge-grown metal sulfide composite material, S powder, conductive agent and binder are ground and mixed in a mass ratio of 2:5:2:1, an appropriate amount of deionized water or NMP is added dropwise, and the mixture is stirred evenly. The resulting slurry is evenly coated on the rough surface of the copper current collector and vacuum dried at 60-120℃ to obtain the Na-S battery composite S electrode.

7. The application according to claim 6, characterized in that... The conductive agent is one or more of conductive carbon black, graphene, MXene, or carbon nanotubes.

8. The application according to claim 6, characterized in that... The adhesive is one or more of polyvinylidene fluoride, polyacrylic acid, polytetrafluoroethylene, polyvinyl alcohol, carboxymethyl cellulose, or sodium alginate.

9. A room temperature Na-S battery, characterized in that, The composite S-electrode sheet obtained by the method described in any one of claims 6-8 is assembled, the counter electrode is metallic sodium, the electrolyte is 1M NaSO3CF3 dissolved in DEGDME solvent or 1M NaPF6 dissolved in DEGDME solvent or 1M NaPF6 dissolved in DME solvent, and the separator is a double-layer separator made of glass fiber GF / D and Celgard 2325, wherein the Celgard 2325 separator is located on the side close to the composite S-electrode.

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