A carbon fiber / SnO 2 Preparation method and application of nano hollow sphere composite material

Abstract

The present invention discloses a preparation method and application of a carbon fiber / SnO2 nano-hollow sphere composite material. In the technical solution of the present invention, by introducing SnO2 nano-hollow spheres into flexible carbon fibers, a flexible electrode material suitable for lithium-ion batteries is prepared. The hollow morphology of SnO2 alleviates the severe volume change of SnO2 during the charge and discharge process of the battery, and the amorphous characteristics of the material are improved through heat treatment, thereby improving the battery performance and capacity. According to the technical solution of the present invention, by using electrospinning technology combined with heat treatment, the synthesized flexible integrated electrode does not need to add a binder or a conductive agent, greatly simplifying the experimental steps, and the actually assembled and tested lithium-ion half-cells and full-cells all exhibit good performance, having broad application prospects.

Description

Technical Field

[0001] The present invention relates to a method for preparing a composite material, and in particular to a method for preparing a carbon fiber / SnO 2 The invention relates to a preparation method of a nano hollow sphere composite material and application of the material. Background Art

[0002] With the improvement of living standards, the demand and consumption of fossil energy are increasing worldwide, and the resulting problems such as fossil energy shortage and environmental pollution are becoming increasingly serious. Under such circumstances, the development and application of new clean energy is imminent. The research and application technologies of solar energy, tidal energy, and geothermal energy are gradually maturing. In turn, how to store and use these energies has become a new problem.

[0003] With the development of science and technology and the progress of commerce, society has an increasingly strong demand for lightweight and portable terminals; at the same time, areas such as space technology, national defense equipment, electronic communications, and transportation involving national security also place higher demands on energy storage devices with long-term and stable power supply.

[0004] In response to the above needs, lithium-ion batteries have emerged with their unique performance advantages and have achieved leapfrog development, and are expected to become one of the main power sources in the 21st century. Lithium-ion batteries are mainly composed of positive electrodes, negative electrodes, electrolytes and separators, among which graphite is the most commonly used negative electrode material for commercial lithium-ion batteries. However, due to the limited theoretical specific capacity of carbon (372mAhg -1 ), and the current technology is already close to this theoretical limit. Therefore, continuing to use graphite as the negative electrode material is unlikely to bring about further improvements in the energy density and power density of lithium-ion batteries. Therefore, the development of negative electrode materials with high specific capacity is crucial for the development of the next generation of lithium-ion batteries.

[0005] SnO 2 As a typical metal oxide with high theoretical lithium storage capacity (783mAhg -1 ), and it has the characteristics of good safety, low price, environmental friendliness and abundant resource reserves, making it one of the most promising negative electrode materials for lithium-ion batteries that can replace graphite.

[0006] However, the current obstacle for SnO 2 There are two main problems in practical application: On the one hand, SnO 2 During the charge and discharge cycle, there will be a large volume change, which can reach 300%, which will affect the structure of the battery and easily pulverize, resulting in poor cycle performance. On the other hand, SnO 2 There is also the general problem of poor conductivity, which leads to poor rate performance. 2The cycle stability and rate performance improvement of negative electrode materials are the key to promoting SnO 2 A crucial issue for practical application.

[0007] Among them, nano-sizing is the solution to SnO 2 An effective way to improve the cycle stability of negative electrode materials is to replace SnO 2 The preparation of nanomaterials with special structures, especially hollow nanospheres, can effectively alleviate the large volume changes during the cyclic charge and discharge process, thereby improving its cycle stability. 2 An effective way to improve conductivity is to convert SnO 2 The composite with the conductive carbon matrix can effectively improve its conductivity, thereby improving its rate performance. Therefore, combining the advantages of both, using a simple and effective method to prepare a composite structure with nano-sizing and carbon coating can effectively improve SnO 2 Performance as negative electrode material.

[0008] There have been relevant reports in this regard. For example, Chinese patent applications CN105702937A and CN105895952A both disclose a SnO 2 / C fiber preparation method; CN108649234A discloses a Pt-SnO 2 Carbon Fiber.

[0009] Electrospinning technology is a new method for preparing one-dimensional micro-nano materials developed in recent years. It has the advantages of simple equipment, easy operation, fast and efficient. Electrospinning technology has obvious advantages in constructing one-dimensional micro-nano materials with special structures (such as nanowires, nanotubes, core-shell structures, etc.). For micro-nano structures with many pores such as tubular structures, the presence of pores enables a variety of lithium insertion / extraction mechanisms (including surface, micropore adsorption, lattice defect lithium insertion / extraction, etc.), the material capacity is larger, and the material has good flexibility during the charge / discharge cycle, is not easy to agglomerate, and can improve the cycle performance of the electrode. Therefore, the use of electrospinning technology can not only nano-size the electrode material, but also directly carbon-compound it, which greatly improves the performance of the electrode material.

[0010] On the other hand, the preparation of traditional lithium-ion battery electrodes requires the mixing of conductive agents, binders and active materials, and then coating them on current collectors. This preparation method requires the introduction of conductive agents, binders and current collectors, which not only requires precise control of the process, but also is relatively complex and increases the manufacturing cost of lithium-ion batteries; more importantly, this traditional lithium-ion battery preparation process cannot produce flexible lithium-ion batteries.

[0011] In recent years, wearable portable electronic products have become a new growth point for electronic products. The demand for miniaturization, diversity and variability of electronic products has led to an increasing demand for flexible electrodes. In this regard, electrospinning technology also has its place. It can be combined with high-temperature calcination methods to directly prepare integrated flexible films to meet current needs.

[0012] For example, Chinese patent application CN114975888A discloses a method for preparing tin or tin dioxide@hollow porous carbon nanofiber flexible electrodes by regulating the carbonization temperature, wherein a tin source precursor and PAN are added to a mixed solution formed by a thermoplastic polymer material, and a SnO@Hollow porous carbon nanofiber flexible electrode is obtained by combining electrospinning and heat treatment. 2 @HPCNFs or Sn@HPCNFs. However, this solution requires the introduction of polymer materials and the removal of polymer components by heat treatment after spinning, which will bring two serious problems: first, the preparation steps are complicated, there will be obvious changes in shape and volume during the heat treatment process, and it is difficult to maintain structural uniformity and stability, which will lead to obvious fluctuations in the quality of the obtained electrode materials; second, due to the low overall density of the product (hollow structure), the content of tin and carbon as active components of the negative electrode material is low, which will seriously affect the specific capacity of the battery and limit the application of the battery. Summary of the invention

[0013] In view of the current development direction and demand of lithium-ion batteries, the inventors proposed a technology combining hydrothermal method, electrospinning and heat treatment to obtain a hollow SnO2 coated with carbon nanofibers. 2 Nanosphere composite material, which can be used as a flexible and independent electrode of a lithium ion battery without any auxiliary additives and current collector. After testing, the composite material prepared by the present invention as a negative electrode shows good cycle stability and high capacity in semi-lithium ion batteries and full lithium ion batteries, and has broad application prospects in lithium ion batteries. The technical solution of the present invention is as follows.

[0014] In one aspect, the present invention provides a carbon fiber / SnO 2 The invention discloses a method for preparing a nano hollow sphere composite material.

[0015] In a second aspect, the present invention provides an application of the material obtained according to the first aspect of the present invention in negative electrode materials for lithium-ion batteries.

[0016] Regarding the first aspect, a carbon fiber / SnO 2 The preparation method of the nano hollow sphere composite material comprises the following steps:

[0017] S1: SiO 2The nanospheres are dispersed in a solvent, a tin source is added, and a solvothermal reaction is carried out under alkaline conditions to obtain SnO 2 @SiO 2 Core-shell structural materials;

[0018] S2: SnO 2 @SiO 2 SiO in core-shell structure materials 2 Etching to obtain SnO 2 Hollow nanospheres;

[0019] S3: Prepare polyacrylonitrile dispersion and add SnO 2 The nano hollow spheres are dispersed evenly to obtain a spinning solution, and the nano fiber membrane is obtained by electrospinning;

[0020] S4: The nanofiber membrane is heated in an air atmosphere and then carbonized in an inert gas atmosphere to obtain a carbon fiber / SnO 2 Hollow nanosphere composites.

[0021] The solvent used in step S1 is a mixture of deionized water and ethanol in a volume ratio of (0.3-2):(0.6-1.4).

[0022] Preferably, the SiO in step S1 2 The nanospheres are prepared by hydrolysis of ammonia water and tetraethyl orthosilicate in ethanol. For example, they can be prepared in the following manner:

[0023] 60 ml of anhydrous ethanol, 3 ml of ammonia water and 1 ml of deionized water were added to a 100 ml flask and stirred to mix evenly. Then 2.3 ml of tetraethyl orthosilicate (TEOS) was slowly added thereto using a liquid gun and stirred at a constant temperature of 20 ° C for 6 h. The obtained product was centrifuged, washed three times with deionized water and ethanol respectively, and finally dried in vacuum at 60 ° C for 12 h to obtain SiO 2 Nanospheres.

[0024] Preferably, the tin source in step S1 is a soluble tetravalent tin salt, most preferably K 2 SnO 3 or SnCl 4 .

[0025] Preferably, the alkaline condition of the solvothermal reaction is weakly alkaline, which is achieved by adding a weak base, most preferably by adding urea.

[0026] Solvothermal reaction of SiO 2 The ratio of SnO to tin source is not limited. 2 Capable of coating SiO 2 Preferably, SiO 2, the mass ratio of tin source and urea is 1:(1-6):(0.6-2).

[0027] In step S1, the solvent thermal reaction temperature is not required, and the usual solvent thermal reaction conditions can be achieved. A higher reaction temperature can accelerate the reaction, but is not conducive to the particle size control of the product, so the most preferred reaction condition is to keep the temperature at about 120-180°C for 8-30h.

[0028] In step S2, NaOH is used to etch for 6-12 hours in an oil bath at 45-70°C to completely remove SiO 2 There is no requirement for the concentration of NaOH, but 0.5-2 mol / L is generally preferred.

[0029] Preferably, the molecular weight of polyacrylonitrile in step S3 is between about 1,000,000 and 1,800,000. Polyacrylonitrile can be dispersed in any organic solvent suitable for subsequent electrospinning, preferably in N,N-dimethylformamide.

[0030] In step S3, polyacrylonitrile and SnO 2 The mass ratio of the hollow nanospheres is (1-10):1, which controls the ratio of polyacrylonitrile to SnO 2 The mass ratio of C / Sn can be controlled to obtain a negative electrode material with good conductivity and high specific capacity.

[0031] In step S3, electrospinning can be performed according to the product carbon fiber / SnO 2 The requirements of the nano hollow sphere composite material reasonably determine its conditions, such as the injection speed of the spinning solution and the rotation speed of the drum. Preferably, the electrospinning conditions can be: voltage 10-18kV, receiving distance 18cm, the rotation speed of the drum receiving device 420-500rpm, and the spinning solution flow rate 0.2-0.3mL / min.

[0032] In step S4, the purpose of heating in air atmosphere is pre-oxidation to fix the molecular orientation, and the condition is to increase the temperature from room temperature to 230-280°C at a rate of 1°C / min, and keep the temperature for 3-5h, and then cool it down naturally.

[0033] In step S4, the purpose of carbonization is to heat and promote the decomposition of polyacrylonitrile to obtain carbon nanofibers CNFs. The carbonization conditions are to heat from room temperature to 530-660°C for 3 hours at a rate of 1-3°C / min under an inert atmosphere (preferably a high-purity nitrogen atmosphere), and then cool naturally. In addition, it is found through testing that the obtained carbonized film has amorphous characteristics. Compared with crystalline materials, the permeation channels in amorphous materials are more conducive to the diffusion of lithium ions.

[0034] Regarding the second aspect, the carbon fiber / SnO prepared according to the above scheme 2 Nano hollow sphere composite materials can be used as battery negative electrodes, especially as flexible electrodes, in batteries such as lithium-ion batteries.

[0035] Preferably, the carbon fiber / SnO 2 The hollow nanosphere composite material can be directly used as the negative electrode of the battery after optional cutting and drying as required, without adding other components such as conductive agent and / or binder.

[0036] The technical solution of the present invention is to 2 The nano hollow spheres are introduced into the flexible carbon fiber to prepare the negative electrode material suitable for lithium ion batteries, especially without the need to add additional conductive agents and binders, and are suitable for use as flexible electrodes. 2 The hollow morphology effectively alleviates the SnO 2 The serious volume change improves the electrical conductivity of the material and improves the amorphous properties of the material through heat treatment, which is beneficial to improving battery performance and capacity.

[0037] The technical solution of the present invention utilizes electrospinning technology combined with heat treatment to synthesize flexible integrated electrodes without the need to add binders or conductive agents, which greatly simplifies the experimental steps. The lithium-ion half-cells and full-cells actually assembled and tested have shown good performance, confirming their excellent practical applicability and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is the SiO obtained in Example 1 2 SEM images of nanospheres;

[0039] Figure 2 The SnO obtained in Example 1 2 @SiO 2 SEM image of core-shell structure material;

[0040] Figure 3 The SnO obtained in Example 1 2 SEM image of hollow nanospheres;

[0041] Figure 4 The carbon fiber / SnO obtained in Example 1 2 SEM image of the nano hollow sphere composite material;

[0042] Figure 5 The carbon fiber / SnO obtained in Example 1 2 XRD pattern of hollow nanosphere composites;

[0043] Figure 6 The carbon fiber / SnO obtained in Example 1 2 Raman images of hollow nanosphere composites;

[0044] Figure 7 The carbon fiber / SnO obtained in Example 1 2 XPS full spectrum of nano hollow sphere composite material;

[0045] Figure 8 The carbon fiber / SnO obtained in Example 1 2 Sn 3d high-resolution XPS spectrum of the hollow nanosphere composite material;

[0046] Fig. 9 The carbon fiber / SnO obtained in Example 1 2 C1s high-resolution XPS spectrum of the hollow nanosphere composite material;

[0047] Fig.10 The carbon fiber / SnO obtained in Example 1 2 N1s high-resolution XPS spectrum of the hollow nanosphere composite material;

[0048] Fig.11 The carbon fiber / SnO obtained in Example 1 2 O1s high-resolution XPS spectrum of hollow nanosphere composites;

[0049] Fig.12 The carbon fiber / SnO obtained in Example 1 2 TGA curve of nano hollow sphere composite material;

[0050] Fig.13 The cyclic voltammetry curve of the half-cell assembled in Example 2;

[0051] Fig.14 The half-cell assembled for Example 2 was subjected to a current density of 0.1 Ag. -1 Cyclic performance curve below;

[0052] Fig.15 is a charge / discharge curve diagram of a full battery assembled in Example 3;

[0053] Fig.16 It is a rate performance curve diagram of the full battery assembled in Example 3 at different currents. DETAILED DESCRIPTION

[0054] In order to better explain the present invention, the present invention is explained and illustrated through the following specific implementation modes.

[0055] Example 1

[0056] A carbon fiber / SnO2 The preparation method of the nano hollow sphere composite material comprises the following steps:

[0057] S1: Add 60 ml of anhydrous ethanol, 3 ml of ammonia water, and 1 ml of water into a 100 ml flask, stir and mix evenly, then slowly add 2.3 ml of tetraethyl orthosilicate (TEOS) with a liquid gun, and stir at a constant temperature of 20 ° C for 6 h. Wash the sample with water and ethanol for 3 times, centrifuge and vacuum dry at 60 ° C for 12 h to obtain SiO 2 Nanospheres. Figure 1 For the SiO 2 SEM image of nanospheres.

[0058] S2: 0.05 g SiO 2 The nanospheres were dispersed in a mixed solvent consisting of 3 mL of deionized water and 3 mL of anhydrous ethanol, stirred evenly, and then 0.15 g of tin source K was added under continuous stirring. 2 SnO 3 ·3H 2 O and 0.045g urea, after ultrasonic dispersion for 30min, the obtained mixed solution was transferred into a high-pressure reactor, kept at 150℃ for 24h, and the product was taken out after cooling to room temperature, and washed alternately with deionized water and ethanol for 3 times. After centrifugation, the solid product was vacuum dried at 60℃ for 12h to obtain SnO 2 @SiO 2 Core-shell structural materials. Figure 2 For the SnO 2 @SiO 2 SEM image of core-shell structure material.

[0059] S3: Take 400 mg SnO 2 @SiO 2 The core-shell structure material was added to a 2 mol / L NaOH solution and stirred in an oil bath at 50 °C for 8 h. 2 @SiO 2 SiO in core-shell structure materials 2 After the reaction is completed, it is washed with deionized water until neutral, and vacuum dried at 60 ° C for 12 h to obtain SnO 2 Hollow nanospheres. Figure 3 To obtain SnO 2 SEM image of hollow nanospheres.

[0060] S4: Take a 10 ml round-bottom flask, add 9 g N,N-dimethylformamide and 1 g polyacrylonitrile with a molecular weight of 1300000 in sequence, and stir magnetically at 50 °C for 12 h; take 5 g of the above solution, add 200 mg of SnO obtained in step S2 2The hollow nanospheres were ultrasonically dispersed at 90°C for 2 hours and then magnetically stirred for 12 hours to form a viscous liquid. The liquid was added to a syringe equipped with a 12-gauge needle, and the electrospinning parameters were set as follows: voltage of 15 kV, vertical distance between the spinneret and the receiving plate of 18 cm, rotation speed of the aluminum foil-wrapped drum receiving device of 460 rpm, spinning solution flow rate of 0.2 mL / min, and the nanofiber membrane was obtained after electrospinning for 3 hours.

[0061] S5: The nanofiber membrane is placed in a box furnace, and the temperature is raised from room temperature to 250°C for 3 hours at a rate of 1°C / min in an air atmosphere, and then the temperature is naturally lowered to obtain a pre-oxidized nanofiber membrane; the nanofiber membrane is then placed in a tubular carbonization furnace and carbonized in a high-purity nitrogen atmosphere. The specific conditions are as follows: the temperature is raised from room temperature to 600°C for 3 hours at a rate of 1°C / min, and the sample is taken out after the temperature is naturally lowered to room temperature, thus obtaining a carbon fiber / SnO 2 Hollow nanosphere composites. Figure 4 The structural features of the composite material are shown.

[0062] Combination Figure 1-Figure 3 , the SiO obtained in this example 2 The nanospheres are full and round in shape, with good size consistency; Figure 2 It can be clearly seen that SnO 2 @SiO 2 The good morphology and size of these intermediate products provide excellent SnO 2 The hollow nanospheres provide a basis for SnO 2 The D50 particle size of the nano hollow spheres is between 280-300nm.

[0063] from Figure 4 It can be seen that the carbon fiber / SnO obtained in Example 1 2 The nanofibers of the nano hollow sphere composite material are continuously and randomly distributed, showing a complete carbon fiber network structure. In addition, there are a large number of particles inside the carbon fiber, showing a relatively uniform dispersion feature, which proves that SnO 2 Hollow nanospheres have been successfully incorporated into carbon fibers.

[0064] In order to detect the performance of the composite material obtained in Example 1, XRD, XPS, TG and other methods were used to characterize and analyze it.

[0065] PAN electrospinning will be graphitized after high temperature carbonization, so it has a great influence on the carbon fiber / SnO 2 The nano hollow sphere composite material was subjected to XRD test. The results are shown in Figure 5 As shown, the diffraction peak at around 24.4° corresponds to the (002) crystal plane of graphite, which is a typical feature of amorphous carbon. Figure 5 SnO is not shown in 2 The characteristic peak of SnO 2 The above results show that after high-temperature carbonization, PAN is successfully graphitized to form carbon fibers.

[0066] Furthermore, Raman spectroscopy was used for testing, such as Figure 6 As shown, at 1348cm -1 and 1582cm -1 There are two obvious peaks near the material, corresponding to the disordered D band and the graphite G band, and I D / I G =1.05, indicating that the material has a more disordered structure, which is consistent with the XRD results, indicating that PAN is graphitized to form carbon fibers.

[0067] In order to analyze the carbon fiber / SnO 2 The chemical composition and structure of the nano hollow sphere composite material were tested and peak calculated using XPS for its elemental composition and possible functional groups.

[0068] Figure 7 It is the full XPS spectrum of the composite material, which shows the presence of elements such as Sn, C, N and O in the composite material.

[0069] The composition of the composite material can be analyzed in detail by high-resolution XPS spectra, such as Figure 8-Figure 11 , corresponding to the Sn3d spectrum, C 1s spectrum, N 1s spectrum and O1s spectrum respectively. Figure 8 In the experiment, two obvious peaks at 486.8eV and 495.3eV were detected, which is consistent with the SnO 2 Sn 3d 5 / 2 and Sn 3d 3 / 2 The binding energy corresponds to . Fig. 9 In the graph, there are two peaks at binding energies of 284.6 eV and 286.3 eV, which are attributed to carbon atoms in CC and Sn-OC bonds, respectively. Fig.10 In the figure, the high-resolution N1s peak can be further divided into three different peaks at 398.5, 400 and 400.9 eV, which are attributed to pyridinic nitrogen, pyrrolic nitrogen and graphitic nitrogen, respectively. The different forms of nitrogen atoms indicate that a large number of defects are introduced into nanocarbon fibers, which is beneficial to the improvement of the performance of lithium-ion batteries. Fig.11 In the graph, O 1s has three peaks at 530.8, 531.9 and 532.8 eV, corresponding to SnO 2 , C=O, O=CO or CO and H 2 O in O.

[0070] By TGA analysis, such as Fig.12 As shown in the figure, the prepared composite material has two weight loss processes during the heating process. The first weight loss process occurs below 350℃, mainly because the material loses adsorbed water. The second weight loss process occurs between 350℃ and 480℃, because the nanocarbon fibers are oxidized to CO 2 The final curve stabilizes at around 49%, and the remaining substance is SnO 2 , which indicates that SnO 2 The content is about 49%.

[0071] Example 2

[0072] Based on Example 1, the obtained carbon fiber / SnO 2 The hollow nanosphere composite material is assembled into a half-cell. The specific scheme is as follows.

[0073] S6: The carbon fiber / SnO obtained in Example 1 2 The nano hollow sphere composite material was processed into a disc with a diameter of 14 mm using a grinding tool, and dried in a blast drying oven to obtain an electrode sheet, and its weight was weighed. No binder and conductive agent were used in this step.

[0074] S7: The electrode sheet obtained in S6 is used as the negative electrode and the metal lithium sheet is used as the counter electrode to form a CR2025 button battery. The electrolyte is 1 mol / L LiPF 6 Dissolved in a mixed solution of EC / DEC with a volume ratio of 1:1, and the separator uses Celgard2325 microporous film.

[0075] The prepared half-cell was placed and dried for two days, and then its electrical performance was tested.

[0076] Fig.13 The cyclic voltammetry curve of the half-cell obtained in this example is shown. In the first cycle, an obvious reduction peak can be observed at about 0.87 V, which is due to the formation of the SEI film and the SnO 2 The reduction peak at 0.35 V and the oxidation peak at 0.6 V can be attributed to the alloying of metal Sn and the conversion of Li x Sn delithiation reaction, Sn to SnO was observed around 1.2V 2 The oxidation peak of SnO 2 The conversion to Sn is reversible. The second and subsequent CV curves are highly overlapped, indicating that the composite material prepared by the present invention has good stability and reversibility as an electrode material.

[0077] Fig.14The half-cell obtained in this embodiment has a current density of 0.1A. -1 The cycle performance curve below shows that when the current density increases to 0.1A -1 The electrode material still maintains 692.7 mAh g after 350 cycles. -1 The reversible capacity and Coulombic efficiency are about 100%, indicating the excellent cycling performance of the material. Fig.14 It also shows that the capacity of the anode material decays slightly in its first 60 cycles and then remains stable after 110 cycles. 2 Similar phenomena are often observed for electrodes with high Li-ion conductivity, which is attributed to the reversible formation of a polymer gel layer by electrolyte decomposition and improved lithium ion reversibility upon long cycling.

[0078] Example 3

[0079] Based on Example 1, the obtained carbon fiber / SnO 2 The nano hollow sphere composite material is prepared into an electrode and assembled into a full battery, and the specific scheme is as follows.

[0080] S6: The carbon fiber / SnO obtained in Example 1 2 The nano hollow sphere composite material was processed into a disc with a diameter of 14 mm using a grinding tool, and dried in a blast drying oven to obtain an electrode sheet, and its weight was weighed. No binder and conductive agent were used in this step.

[0081] S7: The obtained electrode is used as the negative electrode of the battery with LiCoO 2 As the positive electrode material, it is used to form a CR2025 button battery. The electrolyte is 1mol / L LiPF 6 The mixture was dissolved in a 1:1 volume ratio EC / DEC solution. The separator used Celgard2325 microporous membrane. The assembly was carried out in a glove box filled with protective atmosphere (Ar). 2 <1ppm, H 2 O<1ppm.

[0082] After the prepared battery was laid flat and dried for two days, it was tested that it could light a small desk lamp. The electrical performance was tested using a battery testing system and an electrochemical workstation.

[0083] Fig.15 The charge / discharge curve of the full battery assembled in Example 3 is shown in Figure 1. The voltage range is 1.2-4.2V for electrochemical performance testing. Its first discharge and charge capacities can reach 456.3 and 455.9 mAh g, respectively. -1 After 20 cycles, the discharge and charge capacities were 365.1 and 350.6 mAh g respectively. -1

[0084] Fig.16 The rate performance of the full battery assembled in Example 3 at different currents is shown in Figure 2. -1 At current densities of 1.3, 1.7, 2.1, 3.3, and 2.2 mAh g -1 . In 1Ag -1 The reversible capacity was 154.4 mAh g -1 It is worth noting that when the current density returns to 0.05A g -1 When the capacity is restored to 405.1mAh g -1 , proving that the assembled full battery has good rate performance.

[0085] Example 4

[0086] A carbon fiber / SnO 2 The preparation method of the nano hollow sphere composite material comprises the following steps:

[0087] S1: 1g SiO 2 The nanospheres were dispersed in a mixed solvent consisting of 6 mL of deionized water and 3 mL of anhydrous ethanol, stirred evenly, and then 5 g of tin source SnCl was added under continuous stirring. 4 and 1.5 g urea, ultrasonically dispersed for 30 min, and then the obtained mixed solution was transferred into a high-pressure reactor, kept at 180 ° C for 8 h, and the product was taken out after cooling to room temperature, and washed alternately with deionized water and ethanol for 3 times. After centrifugation, the solid product was vacuum dried at 60 ° C for 6 h to obtain SnO 2 @SiO 2 Core-shell structural materials.

[0088] S2: Take 2g SnO 2 @SiO 2 The core-shell structure material was added to a 2 mol / L NaOH solution and stirred in an oil bath at 70 °C for 12 h. 2 @SiO 2 SiO in core-shell structure materials 2 After the reaction is completed, it is washed with deionized water until neutral, and vacuum dried at 50 ° C for 8 h to obtain SnO 2 Hollow nanospheres.

[0089] S3: Take a 50 ml round-bottom flask, add 20 g N,N-dimethylformamide and 6 g polyacrylonitrile with a molecular weight of 1800000 in sequence, and stir magnetically at 60 ° C for 7 h; take 16 g of the above solution, add 0.8 g of SnO obtained in step S2 2The nano hollow spheres were ultrasonically dispersed at 70°C for 2 hours and then magnetically stirred for 6 hours to form a viscous liquid. The liquid was added to a syringe equipped with a 12-gauge needle, and the electrospinning parameters were set as follows: voltage of 10 kV, vertical distance between the spinneret and the receiving plate of 18 cm, rotation speed of the aluminum foil-wrapped drum receiving device of 500 rpm, spinning solution flow rate of 0.3 mL / min, and electrospinning for 2.5 hours to obtain a nanofiber membrane.

[0090] S4: The nanofiber membrane is placed in a box furnace, and the temperature is raised from room temperature to 280°C at a rate of 1°C / min in an air atmosphere for 4 hours, and then the temperature is naturally lowered to obtain a pre-oxidized nanofiber membrane; the nanofiber membrane is then placed in a tubular carbonization furnace and carbonized in a high-purity nitrogen atmosphere. The specific conditions are as follows: the temperature is raised from room temperature to 600°C at a rate of 3°C / min for 3 hours, and the sample is taken out after the temperature is naturally lowered to room temperature, thus obtaining a carbon fiber / SnO 2 Hollow nanosphere composites.

Claims

1. A carbon fiber / SnO 2 Preparation method of nano hollow sphere composite material, It is characterized in that The preparation method comprises: S1: SiO 2 The nanospheres are dispersed in a solvent, a tin source is added, and a solvothermal reaction is carried out under alkaline conditions to obtain SnO 2 @ SiO 2 Core-shell structural materials; S2: The SnO 2 @SiO 2 SiO in core-shell structure materials 2 Etching to obtain SnO 2 Hollow nanospheres; S3: Prepare polyacrylonitrile dispersion, add the SnO 2 The nano hollow spheres are dispersed evenly to obtain a spinning solution, and the nano fiber membrane is obtained by electrospinning; the molecular weight of the polyacrylonitrile is between 1000000 and 1800000, the polyacrylonitrile is dispersed in N,N-dimethylformamide, the polyacrylonitrile and the SnO 2 The mass ratio of the hollow nanospheres is (2.5-10):1; S4: heating the nanofiber membrane in an air atmosphere, and then carbonizing it in an inert gas atmosphere to obtain a carbon fiber / SnO 2 Hollow nanosphere composites; In S4, the heating condition is to increase the temperature from room temperature to 230-280°C at a rate of 1°C / min, keep the temperature for 3-5 hours, and then cool down naturally; the carbonization condition is to increase the temperature from room temperature to 530-600°C at a rate of 1-3°C / min in a high-purity nitrogen atmosphere, keep the temperature for 3 hours, and then cool down naturally.

2. A carbon fiber / SnO according to claim 1 2 Preparation method of nano hollow sphere composite material, It is characterized in that In S1, the solvent is a mixture of deionized water and ethanol in a volume ratio of (0.3-2): (0.6-1.4); the SiO 2 The nanospheres are prepared by hydrolysis of ammonia water and ethyl orthosilicate in ethanol.

3. A carbon fiber / SnO according to claim 1 2 Preparation method of nano hollow sphere composite material, It is characterized in that In S1, the tin source is K 2 SnO 3 or SnCl 4 The alkaline condition is achieved by adding urea, and the SiO 2 , the mass ratio of tin source and urea is 1:(1-6):(0.6-2).

4. A carbon fiber / SnO according to claim 1 2 Preparation method of nano hollow sphere composite material, It is characterized in that In S1, the solvent thermal reaction condition is to keep the temperature at 120-180°C for 8-30h.

5. A carbon fiber / SnO according to claim 1 2 Preparation method of nano hollow sphere composite material, It is characterized in that In S2, the etching is performed using NaOH in an oil bath at 45-70°C for 6-12 hours.

6. A carbon fiber / SnO according to claim 1 2 Preparation method of nano hollow sphere composite material, It is characterized in that In S3, the electrospinning conditions are as follows: voltage 10-18 kV, receiving distance 18 cm, rotation speed of the drum receiving device 420-500 rpm, and spinning solution flow rate 0.2-0.3 mL / min.

7. Carbon fiber / SnO obtained by any one of the preparation methods of claims 1 to 6 2 Nano hollow sphere composite material, application as battery negative electrode.

8. The use according to claim 7, It is characterized in that The carbon fiber / SnO 2 The nano hollow sphere composite material is directly used as the negative electrode of the battery without adding a conductive agent and / or a binder.

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