Preparation of nitrogen-doped carbon fiber encapsulated tin-cobalt alloy nanoparticle material and application thereof to lithium ion battery negative electrode

Abstract

The application specifically relates to preparation of a nitrogen-doped carbon fiber encapsulating tin-cobalt alloy nanoparticle material and application of the material to a lithium ion battery negative electrode. A CoSn@C-N composite material with CoSn alloy embedded in N-doped carbon nanofibers is prepared through electrostatic spinning and thermal reduction, and is applied to a lithium ion battery negative electrode. A large number of gaps exist between CoSn alloy particles, which can effectively reduce stress caused by Sn volume change and relieve volume expansion; complete encapsulation of highly dispersed CoSn nano-alloy particles in porous carbon fibers also provides considerable buffer space for volume expansion, carbon nanofibers not only can prevent structure fracture in the cycle process, but also are favorable for electrolyte permeation, improve mass and charge transfer capacity, and enhance reaction kinetics. The preparation method is simple in process, low in cost, and more suitable for large-scale production, and the prepared CoSn@C-N composite material has excellent cycle performance and rate performance in a lithium ion battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery electrode materials, and particularly relates to application of a nitrogen-doped carbon fiber encapsulating tin-cobalt alloy nanoparticle composite material in a lithium ion battery negative electrode. BACKGROUND

[0002] As a representative secondary energy storage device, rechargeable lithium ion batteries (LIBs) have attracted great attention. Two types of batteries have been widely used in portable electronic products, electric vehicles and large-scale energy storage systems due to their high energy density, long service life and environmental friendliness. Although commercial graphite has been widely used as an anode in LIBs, the lithium / sodium storage process of conventional graphite negative electrode materials has limitations such as small capacity, poor cycle stability and high cost, so it is particularly important to find new high-efficiency low-cost lithium / sodium storage negative electrode materials.

[0003] Studies have shown that tin (Sn) has attracted widespread attention due to its ultra-high theoretical specific capacity (4200 mAh g -1 ) and higher discharge platform than graphite and can adapt to a wider voltage operating range, thus becoming a new type of anode material. However, tin-based negative electrode materials, although having the above advantages, face challenges such as slow ion reaction kinetics and poor conductivity in practice, high processing cost and volume expansion during charging and discharging. Previous attempts have been made to alleviate volume expansion, such as doping Sn into a carbon matrix, manufacturing a core-shell structure, forming Sn-active metal (Sb, Bi, Ge) alloy / nanocomposite materials, etc. However, when ions are deintercalated, the large volume change of Sn will cause severe fragmentation and instability of the solid electrolyte interphase (SEI) film, resulting in rapid fading of capacity, so it is very meaningful to design a reasonable carbon-based carrier. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings and deficiencies of the prior art, and to provide a nitrogen-doped carbon fiber encapsulating tin-cobalt alloy nanoparticle material and a battery.

[0005] The technical solutions adopted by the present application are as follows:

[0006] The first aspect of the present application provides a nitrogen-doped carbon fiber encapsulating tin-cobalt alloy nanoparticle material, and the preparation method thereof comprises the following steps:

[0007] S1, dissolving a soluble cobalt salt and a soluble tin salt in a solvent respectively to obtain a cobalt salt solution and a tin salt solution, mixing the cobalt salt solution and the tin salt solution, and then performing a complexation reaction with sodium citrate, and finally forming CoSn(OH)6 particles with a hollow structure by etching the precursor with an alkaline solution;

[0008] S2, uniformly disperse the CoSn(OH)6 precursor with a hollow structure in N,N-dimethylformamide by ultrasonic dispersion, and continue stirring after adding polyacrylonitrile and polymethyl methacrylate to obtain a precursor solution;

[0009] S3, electrospinning the precursor solution to obtain a precursor nanofiber;

[0010] S4, obtaining a CoSn@C-N nanofiber by thermal reduction of the precursor nanofiber.

[0011] Preferably, in step S1, the soluble cobalt salt is cobalt acetate tetrahydrate, and the soluble tin salt is tin tetrachloride pentahydrate.

[0012] Preferably, in step S1, first mix the cobalt salt solution and sodium citrate uniformly, and then add the tin salt solution to the mixed solution.

[0013] Preferably, in step S1, the alkaline solution is a 1-3 mol·L -1 Sodium hydroxide solution.

[0014] Preferably, in step S2, the mass-volume ratio of CoSn(OH)6 to N,N-dimethylformamide is 40-60:1.

[0015] Preferably, in step S2, the mass ratio of polyacrylonitrile to polymethyl methacrylate is 2-2.5:1.

[0016] Preferably, in step S3, the electrospinning is set at a distance of 13-17 cm, a voltage of 10-14 kV, and a spinning speed of 0.4-0.8 ml / h.

[0017] Preferably, in step S4, the thermal reduction specifically includes the following steps:

[0018] S4.1, pre-oxidation: heat the temperature of the tube furnace to 210-250℃ and maintain for 1-3 h to complete the pre-oxidation;

[0019] S4.2, carbonization treatment: increase the temperature of the tube furnace to 580-620℃ for carbonization treatment, and continue for 1-3 h.

[0020] The second aspect of the application provides a lithium ion battery which uses the nitrogen-doped carbon fiber encapsulating tin-cobalt alloy nanoparticle material as described above as a negative electrode material.

[0021] Preferably, the preparation method comprises the following steps: uniformly mixing CoSn@C-N nanofiber, acetylene black and sodium alginate in proportion, stirring into a paste with a solvent, and coating on a copper foil; drying, tabletting and assembling the battery to obtain the lithium ion battery.

[0022] The beneficial effects of the present application are as follows: the present application firstly uses (CH3COO)2Co·4H2O and SnCl4·5H2O as the cobalt source and tin source respectively, introduces a large number of carboxyl groups into the solution by adding C6H5Na3O7, the carboxyl groups are complexed with Co 2+ and Sn 4+ , and finally the CoSn(OH)6 precursor is formed by co-precipitation, then a certain concentration of NaOH is added for etching, and the CoSn(OH)6 precursor with a hollow structure is obtained after centrifugal washing and drying treatment; the CoSn(OH)6 is uniformly dispersed in DMF and stirred to prepare a uniform electrospinning solution, the CoSn(OH)6 hollow nanoblocks are confined in the PMMA-PAN nanofibers with smooth surfaces; after high-temperature annealing, PMMA escapes with high-temperature decomposition, and the uniformly dispersed CoSn alloy nanoparticles derived from CoSn(OH)6 are embedded in N-doped carbon nanofibers. The material structure inside the nanofiber almost retains the morphology of the CoSn(OH)6 precursor, which provides strong support for realizing high-performance composites. With the structural support and connected electron transport channels of the carbon layer, the agglomeration and fragmentation of CoSn alloy particles are significantly reduced, so the capacity attenuation degree is low. This shows that the covering effect of the carbon material effectively reduces the mechanical pressure caused by volume expansion, and the efficient conductive network, the rich pore structure and the size of the nanoparticles, together promote the dispersion of lithium ions and the rapid transfer of electric charge.

[0023] The CoSn@C-N nanofiber prepared in one embodiment of the present application, as a LIB negative electrode, can be seen that the reversible capacity of the CoSn@C-N material after 100 cycles is 612.2mAh g -1 , similarly, when the current density is 1000mA g -1 , the reversible capacity of the CoSn@C-N material after 600 cycles is 525.2mAh g -1 , the discharge capacity of CoSn@C-N under the conditions of 0.1, 0.2, 0.5, 1, 2A g -1 corresponds to 772, 713, 604, 531, 480mAh g -1 , when the current density is increased to 0.2A g -1 again, the discharge capacity is restored to 710mAh g -1 , and this capacity is maintained stable in the subsequent cycle times. The research fully shows that the electrode material used exhibits excellent rate characteristics and high reversible capacity, highlighting the advantages of the hollow nanoblock structure and stable performance. BRIEF DESCRIPTION OF DRAWINGS

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0025] Figure 1 Transmission electron microscope (TEM) images of CoSn@CN nanofibers prepared in Example 1 (a, c) and tin-carbon nanofibers prepared in Comparative Example 1 without the addition of cobalt (b, d).

[0026] Figure 2 (ac)SEM image, (df)TEM image, (j)HRTEM image, (h)SAED image and (i)EDS Mapping image of the CoSn@CN nanofiber material prepared in Example 1;

[0027] Figure 3 (a) X-ray diffraction pattern of CoSn@CN nanofibers prepared in Example 1; (b) X-ray diffraction pattern of tin-carbon nanofibers prepared without cobalt in Comparative Example 1.

[0028] Figure 4 The CoSn@CN nanofiber anode material prepared in Example 1 and the tin-carbon nanofiber prepared without cobalt element in Comparative Example 1, when used as anodes in lithium-ion batteries at a low current of 100 mA g, showed performance. -1 (a) and 1000mA g -1 (b) and (c) the cycle stability test results at different current densities. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0030] Example 1:

[0031] A method for preparing a high-performance lithium storage anode material using nitrogen-doped carbon fiber-encapsulated tin-cobalt alloy nanoparticles, comprising the following steps:

[0032] S1: 3 mmol of cobalt acetate and 3 mmol of sodium citrate were weighed and uniformly dissolved in 45 ml of deionized water, respectively, and were denoted as solution A and solution B. Solution B was added dropwise to solution A, and a magnetic stirrer was used to form a uniform mixed solution. Then, 3 mmol of tin tetrachloride pentahydrate was uniformly dissolved in 15 ml of ethanol solution, and was denoted as solution C. Solution C was added dropwise to the above-mentioned mixed solution of A and B to form a uniform solution D. Then, 15 ml of a 2 mol / L NaOH solution was added dropwise to solution D under magnetic stirring in a 25°C water bath for 2 h. Then, 60 ml of a 8 mol / L NaOH solution was added, and the reaction was carried out for 15 min to obtain a precursor, cobalt tin hydroxide CoSn(OH)6. -1 -1

[0033] S2: 500 mg of CoSn(OH)6was dissolved in 10 ml of N, N-dimethylformamide (DMF), and ultrasonic dispersion treatment was performed for 1 h.

[0034] S3: 0.9 g of polyacrylonitrile (PAN) and 0.4 g of polymethyl methacrylate (PMMA) were sequentially added to the solution, and magnetic stirring was performed for 24 h to prepare a uniform precursor solution.

[0035] S4: The solution was loaded into a 10 mL plastic syringe, and electrospinning was performed. During the electrospinning, the distance was set to 15 cm, the voltage was set to 12 kV, and the spinning speed was set to 0.6 ml / h.

[0036] S5: The precursor nanofiber was subjected to pre-oxidation and carbonization treatment in a tube furnace. During the process, the temperature was increased to 230°C at a rate of 2°C / min, and the pre-oxidation was completed by maintaining the temperature for 2 h.

[0037] S6: Subsequently, the temperature was increased to 600°C at a rate of 2°C / min for carbonization treatment, and the process was continued for 2 h to obtain the final product, CoSn@C-N nanofiber material.

[0038] S7: The CoSn@C-N nanofiber material, acetylene black, and sodium alginate were mixed in a mass ratio of 7:2:1, and an appropriate amount of ultrapure water was added. The mixture was continuously stirred to form a paste, which was coated onto a copper foil. The copper foil was dried, pressed into a sheet, and assembled into a battery to obtain a lithium ion battery.

[0039] Comparative Example 1

[0040] The preparation process of this comparative example was substantially the same as that of Example 1, except that no cobalt element was introduced in step S1, and tin nanofiber (Sn@C-N) was synthesized.

[0041] ​​Sn nanofiber (Sn@C-N) material, acetylene black and sodium alginate were mixed in a mass ratio of 7:2:1, and then a proper amount of ultrapure water was added. The mixture was continuously stirred into a paste, which was coated on a copper foil. The copper foil was dried, pressed into a sheet, and assembled into a battery to obtain a lithium ion battery.

[0042] Microscopic characterisation

[0043] The following are the microcharacterizations of the different means for synthesizing large-scale tin monoxide nanosheet composite graphene high-performance lithium storage materials by surfactant adsorption:

[0044] Figure 1 The scanning electron microscope (TEM) images (a) (c) of the CoSn@C-N nanofiber prepared in Example 1 and the scanning electron microscope images (b) (d) of the Sn@C-N prepared without adding cobalt element in Comparative Example 1. The transmission electron microscope images (TEM) of the CoSn@C-N, Sn@C-N composite materials can be clearly seen from the figure that the two substances are wrapped by carbon nanofibers. From the figure, it can be seen that the carbon fiber surface is relatively smooth, and the alloy particles are uniformly wrapped inside the carbon fiber. It can be clearly observed that the CoSn alloy particles are completely wrapped by one by one carbon fibers with a diameter of about 150 nm, and the size is uniform, which indicates the successful use of the sample spinning technology. From the figure, it can be seen that the Sn particles formed are about 1 μm in size, and are tightly wrapped by part of the carbon nanofiber, but are not completely wrapped. It shows that the SnO2 particles cannot enter the inside of the spinning fiber, and cannot take advantage of the advantages of the carbon fiber structure. Figure 1 (a) and (c) can see that the surface of the carbon fiber is relatively smooth, and the alloy particles are uniformly wrapped inside the carbon fiber. It can be clearly observed that the CoSn alloy particles are completely wrapped by one by one carbon fibers with a diameter of about 150 nm, and the size is uniform, which indicates the successful use of the sample spinning technology. From the figure, it can be seen that the Sn particles formed are about 1 μm in size, and are tightly wrapped by part of the carbon nanofiber, but are not completely wrapped. It shows that the SnO2 particles cannot enter the inside of the spinning fiber, and cannot take advantage of the advantages of the carbon fiber structure. Figure 1 (b) (d) shows that Sn@C-N presents a large particle nanosphere wrapped by spinning. It can be seen from the figure that the size of the Sn particles formed is about 1 μm, and is tightly wrapped by part of the carbon nanofiber, but is not completely wrapped. It shows that the SnO2 particles cannot enter the inside of the spinning fiber, and cannot take advantage of the advantages of the carbon fiber structure.

[0045] Figure 2Figure (ac) shows the SEM, TEM, HRTEM, SAED, and EDS mapping images of the CoSn@CN nanofiber material prepared in Example 1. The images show that the CoSn bimetallic particles exhibit an irregular circular shape with a diameter of approximately 60 nm, completely embedded within an amorphous carbon layer. The spacing of the crystal fringes was measured to be 0.22 nm, pointing to the (111) crystal plane of the hexagonal CoSn particles. Furthermore, two other crystal planes, (102) and (220), were confirmed by selected area electron diffraction (SEAD) rings. This matches the diffraction peaks detected in X-rays. Figure (i) shows the elemental distribution of the CoSn@CN material, indicating that the CoSn alloy particles are uniformly dispersed at the edges and center of the sample, while C and N elements are mainly distributed in the outer layer. This phenomenon verifies that the CoSn bimetallic compound particles are completely encapsulated by amorphous nitrogen-doped carbon material, forming a characteristic hollow nanostructure.

[0046] Figure 3 X-ray diffraction (XRD) pattern of CoSn@CN nanofibers prepared in Example 1 (a) and X-ray diffraction (XRD) pattern of tin-carbon nanofibers prepared in Comparative Example 1 without the addition of cobalt (b).

[0047] Electrochemical performance characterisation

[0048] Figure 4 The CoSn@CN nanofiber anode material prepared in Example 1 and the tin-carbon nanofiber prepared without cobalt element in Comparative Example 1, when used as anodes in lithium-ion batteries at a low current of 100 mA g, showed performance. -1 (a) and 1000mA g -1 (b) and (c) the cycle stability test results of CoSn@CN and Sn@CN materials at different current densities. -1 It can be seen that the reversible capacity of the CoSn@CN material after 100 cycles is 612.2 mAh g. -1 Superior to Sn@CN material (473.1 mAh g) -1 Similarly, at a current density of 1000 mA g -1 The results show that the reversible capacity of the CoSn@CN material after 600 cycles is 525.2 mAh g. -1 Superior to Sn@CN material (337.1mAh g) -1 ).

[0049] In summary, by a simple electrospinning technique and thermal reduction strategy, CoSn@C-N carbon-based composite materials embedded with N-doped carbon nanofibers are prepared and applied to lithium-ion batteries and sodium-ion battery anodes. The structural design of CoSn@C-N nanofibers provides certain advantages for lithium / sodium storage reactions. First, the introduction of non-active metal Co matrix and its voids in the hollow block CoSn alloy can effectively reduce the stress caused by the volume change of Sn and effectively alleviate the volume expansion. In addition, the highly dispersed CoSn nanoscale alloy particles are completely encapsulated in the porous carbon fibers, which also provides considerable buffer space for volume expansion. Carbon nanofibers not only prevent structural rupture during the cycling process, but also facilitate the penetration of electrolyte, enhance the mass and charge transfer capacity, and enhance the reaction kinetics. Compared with existing reports, the preparation method of the application is simple, low in cost, and more suitable for large-scale production. The CoSn@C-N composite material prepared has excellent cycle performance and rate performance in lithium-ion batteries and sodium-ion batteries.

[0050] The above disclosure is only the preferred embodiment of the application, and of course cannot limit the scope of the right of the application, so the equivalent changes made according to the claims of the application still belong to the scope covered by the application.

Claims

1. A nitrogen-doped carbon fiber encapsulating tin-cobalt alloy nanoparticle material, characterized by, The preparation method comprises the following steps: S1, the soluble cobalt salt, soluble tin salt is dissolved in solvent respectively to obtain cobalt salt solution and tin salt solution, the cobalt salt solution and tin salt solution are mixed, and complexation reaction occurs through sodium citrate, then the precursor is etched by using alkaline solution, and finally the CoSn (OH) 6 particles with hollow structure are formed; S2, the CoSn (OH) 6 precursor with hollow structure is uniformly dispersed in N, N-dimethylformamide by ultrasonic dispersion, and then polyacrylonitrile and polymethyl methacrylate are added to continue stirring to obtain a precursor solution; S3, the precursor solution is electrospun to obtain a precursor nanofiber; S4, the precursor nanofiber is obtained by thermal reduction to obtain CoSn@C-N nanofiber; In step S1, the cobalt salt solution and sodium citrate are mixed uniformly, and then the tin salt solution is added into the mixed solution; In step S2, the mass-volume ratio of CoSn (OH) 6 and N, N-dimethylformamide is 40-60:

1. 2.The nitrogen-doped carbon fiber encapsulated tin-cobalt alloy nanoparticle material of claim 1, wherein: In step S1, the soluble cobalt salt is cobalt acetate tetrahydrate, and the soluble tin salt is tin tetrachloride pentahydrate. 3.The nitrogen-doped carbon fiber encapsulated tin-cobalt alloy nanoparticle material of claim 1, wherein: In step S1, the alkaline solution is a 1-3 mol L -1 of sodium hydroxide solution.

4. The nitrogen-doped carbon fiber encapsulated tin-cobalt alloy nanoparticle material of claim 1, wherein: In step S2, the mass ratio of polyacrylonitrile to polymethyl methacrylate is 2-2.5:

1.

5. The nitrogen-doped carbon fiber encapsulated tin-cobalt alloy nanoparticle material of claim 1, wherein: In step S3, the electrospinning is set to a distance of 13-17 cm, a voltage of 10-14 kV, and a spinning speed of 0.4-0.8 ml / h.

6. The nitrogen-doped carbon fiber encapsulated tin-cobalt alloy nanoparticle material of claim 1, wherein: In step S4, the thermal reduction comprises the following steps: S4.1, pre-oxidation: heating the temperature of the tube furnace to 210-250 DEG C and maintaining for 1-3 h to complete the pre-oxidation; S4.2, carbonization treatment: the temperature of the tube furnace is raised to 580-620 DEG C for carbonization treatment, and the temperature is maintained for 1-3 h.

7. A lithium-ion battery, characterized by: The nitrogen-doped carbon fiber encapsulating tin-cobalt alloy nanoparticle material is used as the negative electrode material.

8. The lithium-ion battery of claim 7, wherein, The preparation method comprises the following steps: the CoSn@C-N nanofiber, acetylene black and sodium alginate are mixed uniformly in proportion, a solvent is added to stir into a paste, and the paste is coated on a copper foil;The copper foil is dried, pressed into a sheet, and assembled into a battery to obtain the lithium ion battery.

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