A porous CuFe2S3@C nanofiber and its preparation method and sodium ion battery negative electrode material having the nanofiber

Abstract

A porous CuFe2S3@C nanofiber, a preparation method thereof, and a sodium-ion battery negative electrode material comprising the nanofiber. The preparation method comprises the following steps: S1: adding a polymer to a polystyrene solution, then adding a copper salt and an iron salt, stirring in a water bath, and then electrospinning to obtain a fiber fabric; S2: pre-calcining the fiber fabric to obtain a pre-calcined sample; and S3: sulfurizing and calcining the pre-calcined sample to obtain porous CuFe2S3@C nanofibers. The porous CuFe2S3@C nanofibers prepared by the present invention have a simple process, low energy consumption, and generally exhibit a low capacity decay rate during charge and discharge, maintaining a long cycle life and relatively stable performance, thereby improving the specific capacity and efficiency of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of novel materials and sodium ion batteries, and in particular to a porous CuFe2S3@C nanofiber and a preparation method thereof, as well as a sodium ion battery negative electrode material having the nanofiber. Background Art

[0002] Sodium-ion secondary batteries are considered to be a new type of rechargeable energy storage secondary battery that is expected to replace lithium-ion secondary batteries in the future due to their similar physical and chemical properties to lithium and their high natural abundance and low cost. They have attracted extensive attention from researchers in recent years. However, sodium ions have a larger radius than lithium ions ( vs ), slow diffusion kinetics, and significant volume changes and structural collapse during the insertion / extraction process of the electrode material, leading to problems such as short cycle life and poor rate performance. Therefore, there is an urgent need to develop and explore electrode materials with high specific capacity and excellent cycle stability to promote the ultimate practical development of sodium-ion batteries.

[0003] For sodium-ion batteries, the conductivity of the discharge product Na2S generated by metal sulfides during the charge and discharge process is higher than that of Na2O formed by metal oxides. Therefore, metal sulfides are more widely used in sodium-ion batteries. The theoretical specific capacity of copper sulfide and iron sulfide is greater than that of commercial graphite. Iron sulfide also has a synergistic energy storage mechanism of conversion reaction and insertion / extraction reaction, which is superior to copper sulfide in terms of energy storage capacity and charge and discharge rate. As a negative electrode material for sodium-ion batteries, copper sulfide generally exhibits a low capacity decay rate during the charge and discharge process, and can maintain a long cycle life and relatively stable performance. By utilizing the interaction of bimetallic materials, the development of bimetallic sulfides can better utilize the synergistic sodium storage advantages of the two metals and obtain a negative electrode material with excellent performance.

[0004] In the prior art, there are some studies on the use of Cu5FeS4 and CuFeS2 materials in the Cu-Fe-S system for sodium negative electrodes. The use of CuFe2S3 with a lower Cu content is conducive to further reducing the cost of negative electrode materials. For example, German scholars used vacuum sealing technology to heat treat copper powder, iron powder, and sulfur powder at 950°C for 4 days, and then annealed at 800°C for 8 hours to prepare CuFe2S3. The material was applied to the sodium negative electrode and showed good cycle stability. However, this method is technically complex and requires a long time for heat treatment of copper powder and iron powder under vacuum conditions, which results in high energy consumption and is not conducive to large-scale production. Summary of the Invention

[0005] The present invention aims to provide a porous CuFe2S3@C nanofiber and a preparation method thereof, as well as a sodium ion battery negative electrode material having the nanofiber, so as to improve the specific capacity and service life of the battery. The preparation method is simple.

[0006] In order to solve the above technical problems, the specific solution adopted by the present invention is a method for preparing porous CuFe2S3@C nanofibers, which specifically includes the following steps:

[0007] S1: Add the polymer to the polystyrene solution, dissolve it, then add copper salt and iron salt, stir in a water bath and perform electrospinning to obtain fiber fabric;

[0008] S2: pre-calcining the fiber fabric in an air atmosphere to obtain a pre-calcined sample;

[0009] S3: The pre-calcined sample is subjected to sulfurization calcination under a protective atmosphere to obtain porous CuFe2S3@C nanofibers.

[0010] As an optimized solution for the preparation method of the above-mentioned porous CuFe2S3@C nanofiber: the polymer is one or more of polyvinyl alcohol, polyvinyl pyrrolidone and polyacrylonitrile.

[0011] As another optimization scheme for the preparation method of the above-mentioned porous CuFe2S3@C nanofibers: the polymer is polyvinyl alcohol, the molecular weight of polyvinyl alcohol is 20,000-50,000, 2-4 g of polyvinyl alcohol is added to every 10-30 ml of polystyrene, and the particle size of PS microspheres in the polystyrene solution is 100-400 nm.

[0012] As another optimization scheme for the preparation method of the above-mentioned porous CuFe2S3@C nanofibers: the molar ratio of the added amounts of the copper salt and the iron salt is 1:2.

[0013] As another optimization scheme for the preparation method of the above-mentioned porous CuFe2S3@C nanofibers: the copper salt is one or both of copper nitrate and copper acetate, and the iron salt is one or more of ferric nitrate, ferric acetate and ferric acetylacetonate.

[0014] As another optimization scheme for the preparation method of the above-mentioned porous CuFe2S3@C nanofibers: the voltage of electrospinning is 15-25 kV, the spinning speed is 0.0002-0.002 mm / s, and the distance between the needle tip and the receiver is 10-20 cm.

[0015] As another optimization scheme for the preparation method of the above-mentioned porous CuFe2S3@C nanofibers: the pre-calcination temperature is 250-300°C, and the pre-calcination time is 2-5 hours.

[0016] As another optimization scheme for the preparation method of the above-mentioned porous CuFe2S3@C nanofibers: the sulfiding substance used in the sulfidation calcination is one or both of thioacetamide and sulfur powder, and the mass ratio of the sulfiding substance to the pre-burned sample in step S2 is 5 to 15:1; the calcination temperature is 600 to 800°C, the calcination time is 2 to 5 hours, and the heating rate is 1 to 10°C / min.

[0017] A porous CuFe2S3@C nanofiber is prepared by the above preparation method.

[0018] A sodium ion battery negative electrode material comprises the above-mentioned porous CuFe2S3@C nanofiber, acetylene black, polyvinylidene fluoride and N-methyl-2-pyrrolidone.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] In the present invention, polymers, copper salts and iron salts are added to a polystyrene solution and stirred. CuFe2S3@C nanofibers are prepared by electrospinning technology and precise control of the copper / iron ratio. Cu has good electrical conductivity and Fe has good electrochemical properties. The synergistic effect between the two metals can obtain a negative electrode material with high power and high capacity, which helps to improve the performance of sodium ion batteries and expand the application range of the material. In addition, a polystyrene solution with a suitable particle size and a one-step vulcanization technology are used to prepare CuFe2S3@C nanofibers with optimal pore size. The polystyrene template can uniformly adsorb metal ions, ensure uniform contact of Cu and Fe ions in the precursor, and ensure uniform reaction of Cu, Fe ions and sulfur in the subsequent vulcanization process to avoid the formation of impurity phases. The CuFe2S3 in the present invention belongs to a conversion sodium storage mechanism. Compared with the alloy sodium storage mechanism with larger volume expansion in the prior art, its volume change is small, and the protective effect of the porous structure is more obvious. While achieving uniform distribution of metal particles on the surface of the carbon matrix, the porous structure inside it can alleviate the material pulverization problem caused by volume expansion during the cycle. In addition, the porous carbon matrix can effectively inhibit the "polysulfide shuttle" effect during the sodium ion battery reaction process. The present invention does not require high-end equipment and complex operating techniques, is safe and environmentally friendly, has relatively low cost, and meets green requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the SEM image of CuFe2S3@C nanofibers prepared in Example 1 of the present invention;

[0022] Figure 2 This is the SEM image of CuFe2S3@C nanofibers prepared in Example 1 of the present invention;

[0023] Figure 3This is the mapping diagram of CuFe2S3@C nanofibers prepared in Example 1 of the present invention;

[0024] Figure 4 This is the XRD pattern of CuFe2S3@C nanofibers prepared in Example 1 of the present invention;

[0025] Figure 5 This is a test diagram of the cycling performance of the CuFe2S3@C nanofibers prepared in Example 1 of the present invention as a negative electrode material for sodium ion batteries;

[0026] Figure 6 This is a rate performance test diagram of the CuFe2S3@C nanofibers prepared in Example 1 of the present invention as a negative electrode material for sodium ion batteries;

[0027] Figure 7 This is the SEM image of CuFe2S3@C nanofibers prepared in Example 3 of the present invention;

[0028] Figure 8 This is the XRD pattern of CuFe2S3@C nanofibers prepared in Example 4 of the present invention;

[0029] Figure 9 This is the XRD pattern of CuFe2S3@C nanofibers prepared in Example 5 of the present invention;

[0030] Figure 10 The performance test comparison chart of Example 1, Comparative Examples 1 and 2 is shown. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described in detail below. Parts of the present invention that are not described and disclosed in detail in the following description should be understood as existing technologies known or should be known to those skilled in the art.

[0032] A method for preparing porous CuFe2S3@C nanofibers specifically comprises the following steps:

[0033] S1: Add the polymer to the polystyrene solution, dissolve it, then add copper salt and iron salt, stir in a water bath and perform electrospinning to obtain fiber fabric;

[0034] The polymer is one or more of polyvinyl alcohol, polyvinyl pyrrolidone and polyacrylonitrile.

[0035] The polymer is polyvinyl alcohol, the molecular weight of the polyvinyl alcohol is 20,000-50,000, 2-4g of polyvinyl alcohol is added to every 10-30ml of polystyrene, and the particle size of the PS microspheres in the polystyrene solution is 100-400nm.

[0036] The molar ratio of the added amounts of the copper salt and the iron salt is 1:2.

[0037] The copper salt is one or both of copper nitrate and copper acetate, and the iron salt is one or more of iron nitrate, iron acetate and iron acetylacetonate.

[0038] S2: pre-calcining the fiber fabric in an air atmosphere to obtain a pre-calcined sample;

[0039] The voltage of electrospinning is 15 to 25 kV, the spinning speed is 0.0002 to 0.002 mm / s, and the distance between the needle tip and the receiver is 10 to 20 cm.

[0040] The pre-firing temperature is 250-300°C, and the pre-firing time is 2-5 hours.

[0041] S3: The pre-calcined sample is subjected to sulfurization calcination under a protective atmosphere to obtain porous CuFe2S3@C nanofibers.

[0042] The sulfiding material used in the sulfidation calcination is one or both of thioacetamide and sulfur powder, and the mass ratio of the sulfiding material to the pre-calcined sample in step S2 is 5-15:1; the calcination temperature is 600-800°C, the calcination time is 2-5h, and the heating rate is 1-10°C / min.

[0043] A porous CuFe2S3@C nanofiber is prepared by the above preparation method.

[0044] A sodium ion battery negative electrode material comprises the above-mentioned porous CuFe2S3@C nanofiber, acetylene black, polyvinylidene fluoride and N-methyl-2-pyrrolidone.

[0045] The present invention is described in detail below through a number of embodiments:

[0046] Example 1

[0047] Preparation of porous CuFe2S3@C nanofibers: 3g of polyvinyl alcohol was added to a mixture of 10mL of polystyrene solution (150-200nm particle size) and 10mL of deionized water, and stirred at 80°C in a water bath for 2h. After the solution cooled, 0.26g of Cu(Ac)2 and 1.07g of Fe(NO3)3 were added to the polystyrene solution, followed by stirring for 24h to yield a viscous solution. The solution was then poured into a 20mL syringe, adjusting the distance between the syringe tip and the receiver. Under a voltage of 20kV, the solution was extruded from the syringe tip at a rate of 0.0002mm / s and sprayed onto the receiver, where it was spun into a fiber fabric. The collected fiber fabric was pre-calcined at 260°C in an air furnace for 3h. The pre-calcined sample was then calcined with thioacetamide at a mass ratio of 1:10 at 700°C under an argon atmosphere for 3h to yield porous CuFe2S3@C nanofibers.

[0048] Electrode preparation, battery assembly and testing: The porous CuFe2S3@C nanofibers, acetylene black and polyvinylidene fluoride prepared above were dispersed in N-methyl-2-pyrrolidone solvent at a mass ratio of 7:2:1 to form a uniform slurry. Then, the slurry was evenly coated on the copper foil and vacuum dried at 100°C for 12 hours to complete the preparation of the electrode. Then, the copper foil was cut into disc electrodes with a diameter of 1.2 cm, and CR-2032 coin-type batteries were assembled in an argon-filled glove box for electrochemical performance testing. NaPF6 was then dissolved in diethylene glycol dimethyl ether solution as an electrolyte, and constant current charge / discharge was measured on the new test system. The performance test diagram is as follows Figure 5 、 Figure 6 shown.

[0049] Example 2

[0050] A sodium ion battery negative electrode material is provided. In the preparation method of porous CuFe2S3@C nanofibers, polyvinyl alcohol is added as a polymer into a polystyrene solution. Other preparation methods are the same as those in Example 1.

[0051] Example 3

[0052] A sodium ion battery negative electrode material, in the preparation method of porous CuFe2S3@C nanofibers, the particle size of PS microspheres in the polystyrene solution is 300-400 nm, and the other preparation methods of the porous CuFe2S3@C nanofibers are the same as those in Example 1. Figure 7 , which is a SEM image of the CuFe2S3@C nanofibers prepared by the preparation method of this embodiment.

[0053] Example 4

[0054] A sodium ion battery negative electrode material, wherein the calcination temperature in the preparation method of porous CuFe2S3@C nanofiber is 600°C, and the other preparation methods in the preparation method of porous CuFe2S3@C nanofiber are the same as those in Example 1. Figure 8 , which is the XRD pattern of CuFe2S3@C nanofibers prepared by the preparation method of this embodiment.

[0055] Example 5

[0056] A sodium ion battery negative electrode material, wherein the calcination temperature in the preparation method of porous CuFe2S3@C nanofiber is 800°C, and the other preparation methods in the preparation method of porous CuFe2S3@C nanofiber are the same as those in Example 1. Figure 9 , which is the XRD pattern of CuFe2S3@C nanofibers prepared by the preparation method of this embodiment.

[0057] Example 6

[0058] A sodium ion battery negative electrode material, in the preparation method of porous CuFe2S3@C nanofibers, the electrospinning voltage is 16 kV, the spinning speed is 0.002 mm / s, the distance between the needle tip and the receiver is 17 cm, and the other preparation methods are the same as those in Example 1.

[0059] Example 7

[0060] A sodium ion battery negative electrode material was prepared by adding 2 g of polyvinyl alcohol to a polystyrene solution in a porous CuFe2S3@C nanofiber preparation method. The other preparation methods were the same as those in Example 1. However, due to the small amount of polyvinyl alcohol added, the fibers could not be spun into a fabric in this example.

[0061] Example 8

[0062] A sodium ion battery negative electrode material is prepared by adding 4 g of polyvinyl alcohol to a polystyrene solution in the method for preparing porous CuFe2S3@C nanofibers. Other preparation methods are the same as those in Example 1.

[0063] Example 9

[0064] A sodium ion battery negative electrode material is prepared by using sulfur powder for sulfurization during the sulfurization and calcination process of porous CuFe2S3@C nanofibers. Other preparation methods are the same as those in Example 1.

[0065] Comparative Example 1

[0066] First, 3g of polyvinyl alcohol was added to a mixture of 10mL of polystyrene solution (150-200nm particle size) and 10mL of deionized water, and stirred in a water bath at 80°C for 2h. After the solution cooled, 1.07g of Fe(NO₃)₃ was added to the polystyrene solution and stirred for 24h to produce a viscous solution. The solution was then poured into a 20mL syringe, adjusting the distance between the syringe tip and the receiver. Under a voltage of 20kV, the solution was extruded from the syringe tip at a rate of 0.0002mm / s and sprayed onto the receiver, where it was spun into a fiber fabric. The collected fiber fabric was pre-calcined at 260°C in an air furnace for 3h. The pre-calcined sample was then calcined with thioacetamide at a mass ratio of 1:10 at 700°C under an argon atmosphere for 3h to produce monometallic sulfide FeₐS₈@C nanofibers.

[0067] Electrode preparation, battery assembly, and testing: The prepared monometallic sulfide Fe7S8@C nanofibers, acetylene black, and polyvinylidene fluoride were dispersed in a 9:2:1 mass ratio in N-methyl-2-pyrrolidone solvent to form a uniform slurry. The slurry was then evenly coated on a copper foil and vacuum-dried at 100°C for 12 hours to complete the electrode preparation. The copper foil was then cut into 1.2 cm diameter disc electrodes and assembled into CR-2032 coin-type cells in an argon-filled glove box for electrochemical performance testing. NaPF6 was then dissolved in diethylene glycol dimethyl ether solution as the electrolyte, and constant current charge / discharge measurements were performed on a novel test system to measure its performance.

[0068] After testing, the capacity was only 251 mAh g after 800 cycles at a current density of 5 A g-1. -1 , the retention rate is 64.9%.

[0069] Comparative Example 2

[0070] 3g of polyvinyl alcohol was first added to a mixture of 10mL of a polystyrene solution with a particle size of 150-200nm and 10mL of deionized water, and stirred in a water bath at 80°C for 2h. After the solution cooled, 0.26g of Cu(Ac)2 was added to the polystyrene solution and stirred for 24h to produce a viscous solution. The solution was then poured into a 20mL syringe, adjusting the distance between the syringe tip and the receiver. Under a voltage of 20kV, the solution was extruded from the syringe tip at a rate of 0.0002mm / s and sprayed onto the receiver, where it was spun into a fiber fabric. The collected fiber fabric was pre-calcined at 260°C in an air furnace for 3h. The pre-calcined sample was then calcined with thioacetamide at a mass ratio of 1:10 at 700°C under an argon atmosphere for 3h to produce monometallic sulfide Cu9S5@C nanofibers.

[0071] Electrode preparation, battery assembly, and testing: The monometallic sulfide Cu9S5@C nanofibers, acetylene black, and polyvinylidene fluoride prepared above were dispersed in an N-methyl-2-pyrrolidone solvent at a mass ratio of 9:2:1 to form a uniform slurry. The slurry was then evenly coated on a copper foil and vacuum-dried at 100°C for 12 hours to complete the electrode preparation. The copper foil was then cut into 1.2 cm diameter disc electrodes and assembled into CR-2032 coin-type cells in an argon-filled glove box for electrochemical performance testing. NaPF6 was then dissolved in a diethylene glycol dimethyl ether solution as the electrolyte, and constant current charge / discharge measurements were performed on a novel test system to measure its performance.

[0072] After testing, at 5A g- 1 After 800 cycles at a current density of 1.5, the capacity is only 251 mAh g -1 , the retention rate is 94.7%.

[0073] In summary, if Figure 1-4 and Figure 10 As shown in the figure, CuFe2S3@C nanofibers were prepared by electrospinning technology and precise control of the copper / iron ratio. Compared with the single metal sulfides Fe7S8 and Cu9S5 obtained by adding only Fe or Cu, the CuFe2S3@C prepared by the present invention has better cycle stability and rate performance. -1 The capacity retention rate was as high as 100% (388.8 mAh g) after 800 cycles at a current density of -1 ), the synergistic effect between the two metals helps to improve the performance of sodium-ion batteries, expand the application range of materials, and has good application prospects. The use of PS microsphere solution with appropriate particle size and one-step sulfurization technology to prepare CuFe2S3@C nanofibers with optimal pore size can achieve uniform distribution of metal particles on the surface of the carbon matrix. At the same time, the internal porous structure can alleviate the problem of material pulverization caused by volume expansion during the cycle. The porous carbon matrix can effectively inhibit the "polysulfide shuttle" effect during the sodium-ion battery reaction. The preparation process is simple, safe and environmentally friendly, with relatively low cost, and meets green requirements.

Claims

1. A method for preparing porous CuFe2S3@C nanofibers, characterized by: The specific steps include: S1: Add the polymer to the polystyrene solution, dissolve it, then add copper salt and iron salt, stir in a water bath and perform electrospinning to obtain fiber fabric; The polymer is polyvinyl alcohol, the molecular weight of polyvinyl alcohol is 20,000-50,000, 2-4 g of polyvinyl alcohol is added to every 10-30 ml of polystyrene, and the particle size of the PS microspheres in the polystyrene solution is 100-400 nm; S2: pre-calcining the fiber fabric in an air atmosphere to obtain a pre-calcined sample; S3: The pre-calcined sample is subjected to sulfurization calcination under a protective atmosphere to obtain porous CuFe2S3@C nanofibers.

2. The method for preparing porous CuFe2S3@C nanofibers according to claim 1, wherein: The molar ratio of the added amounts of the copper salt and the iron salt is 1:

2.

3. The method for preparing porous CuFe2S3@C nanofibers according to claim 1, wherein: The copper salt is one or both of copper nitrate and copper acetate, and the iron salt is one or more of iron nitrate, iron acetate and iron acetylacetonate.

4. The method for preparing porous CuFe2S3@C nanofibers according to claim 1, wherein: The voltage of electrospinning is 15~25kV, the spinning speed is 0.0002~0.002 mm / s, and the distance between the needle tip and the receiver is 10~20cm.

5. The method for preparing porous CuFe2S3@C nanofibers according to claim 1, wherein: The pre-firing temperature is 250~300℃ and the pre-firing time is 2~5h.

6. The method for preparing porous CuFe2S3@C nanofibers according to claim 1, wherein: The sulfiding material used in the sulfidation calcination is one or both of thioacetamide and sulfur powder, and the mass ratio of the sulfiding material to the pre-calcined sample in step S2 is 5-15:1; the calcination temperature is 600-800°C, the calcination time is 2-5h, and the heating rate is 1-10°C / min.

7. A porous CuFe2S3@C nanofiber, characterized by: The invention is prepared by the preparation method of any one of claims 1 to 6.

8. A sodium ion battery negative electrode material, characterized in that: The method comprises the porous CuFe2S3@C nanofiber according to claim 7, acetylene black, polyvinylidene fluoride and N-methyl-2-pyrrolidone.

Images