A hollow iron phosphide / carbon nanofiber and its preparation method and application

Abstract

The present invention relates to the field of electrode material technology, and in particular to a hollow iron phosphide / carbon nanofiber, its preparation method, and application. The preparation method of the present invention comprises the following steps: S1, dissolving ferric acetylacetonate, phenylphosphonic acid, and polymethyl methacrylate in an organic solvent to obtain a core layer solution; dissolving polyacrylonitrile in an organic solvent to obtain a skin layer solution; S2, respectively loading the core layer and skin layer solutions prepared in step S1 into syringes, adopting a coaxial electrospinning method, using carbon-coated copper foil or aluminum foil as a current collector, to prepare a coaxial nanofiber membrane; S3, pre-oxidizing and then carbonizing the coaxial nanofiber membrane to obtain a hollow iron phosphide / carbon nanofiber. The present invention forms an iron phosphide-based composite material by loading iron phosphide onto carbon nanofibers, thereby improving their structural stability and conductivity, preparing hollow carbon nanofibers, increasing the specific surface area of ​​the material, increasing the active sites of the material, and thereby improving their electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and in particular to a hollow iron phosphide / carbon nanofiber and a preparation method and application thereof. Background Art

[0002] As a key component of a battery, the anode determines its performance. Ideal lithium-ion battery anode materials should be able to accommodate sufficient lithium ions, exhibit high ionic conductivity, and maintain good cycling stability. However, existing lithium-ion battery anode materials suffer from poor high-current cycling performance and low initial charge and discharge efficiency. Therefore, developing new, high-performance lithium-ion battery anode materials and modifying existing materials are current research hotspots in the field of lithium-ion battery anode materials.

[0003] Iron (Fe) is one of the most abundant elements in the earth's crust. Fe-based compounds are considered to be promising alternatives to current electrode materials due to their low cost and environmental friendliness. Among Fe-based compounds, Fe-based oxides (Fe3O4, Fe2O3) have been studied as negative electrodes for lithium-ion batteries. Although they have high specific capacity, their poor electrical conductivity and high irreversible capacity loss limit their commercial application. Compared with oxides, iron phosphide (Fe2P) has a higher electrical conductivity (0.33Scm -1 ), lower theoretical capacity loss and higher theoretical capacity of the conversion reaction. However, this high-capacity conversion process will cause a larger volume expansion of Fe2P, affecting its cycling stability. Summary of the Invention

[0004] The purpose of the present invention is to address the above-mentioned deficiencies in the prior art and to provide a hollow iron phosphide / carbon nanofiber and a preparation method and application thereof.

[0005] A method for preparing hollow iron phosphide / carbon nanofibers of the present invention comprises the following steps:

[0006] S1, dissolving ferric acetylacetonate, phenylphosphonic acid, and polymethyl methacrylate in an organic solvent to obtain a core layer solution; dissolving polyacrylonitrile in an organic solvent to obtain a skin layer solution;

[0007] S2, the core layer and skin layer solutions prepared in step S1 are respectively loaded into syringes, and a coaxial nanofiber membrane is prepared by a coaxial electrospinning method using carbon-coated copper foil or aluminum foil as a current collector;

[0008] S3. The coaxial nanofiber membrane is pre-oxidized and then carbonized to obtain hollow iron phosphide / carbon nanofibers.

[0009] Furthermore, in step S1, the molar mass ratio of ferric acetylacetonate, phenylphosphonic acid and polymethyl methacrylate is 1.5-2.5 mmol:0.75-1.25 mmol:1-1.5 g;

[0010] Furthermore, the mass volume ratio of the polymethyl methacrylate to the organic solvent is 1-1.5 g:10 ml.

[0011] Furthermore, the mass volume ratio of the polyacrylonitrile to the organic solvent is 1-1.25 g:10 ml; and the organic solvent is N,N-dimethylformamide.

[0012] Furthermore, the carbonization temperature was 650-750°C, the heating program was 5°C / min, and the time was 2 h.

[0013] Furthermore, the pre-oxidation temperature ramp was 2°C / min, with the first stage calcination at 180°C for 2 hours, and the second stage calcination at 280°C for 2 hours. No reaction occurs during the pre-oxidation phase, but the goal is to increase the mechanical strength and thermal stability of the fiber, allowing for use under high-temperature and high-strength conditions.

[0014] Furthermore, in coaxial electrospinning, the distance between the needle tip and the current collector is 20 cm, the positive high voltage is 16KV, the negative high voltage is -3kV, the outer channel solution injection speed is 0.060mm / min, the inner channel solution injection speed is 0.040-0.080mm / min, the coaxial needle size is 16G / 21G, the needle translation distance is 4.00mm, the needle translation speed is 40.00mm / min, and the roller collector receiving speed is 140.00r / min.

[0015] A hollow iron phosphide / carbon nanofiber material prepared by the above-mentioned preparation method.

[0016] A negative electrode material is obtained by directly cutting the above-mentioned hollow iron phosphide / carbon nanofiber material and using it as the negative electrode material.

[0017] A lithium battery uses the above-mentioned negative electrode material as the negative electrode.

[0018] The present invention forms an iron phosphide-based composite material by loading iron phosphide onto carbon nanofibers, thereby improving their structural stability and conductivity, preparing hollow carbon nanofibers, increasing the material's specific surface area, and increasing the material's active sites, thereby improving their electrochemical performance.

[0019] The hollow iron phosphide / carbon nanofibers prepared by the present invention can be directly used as the negative electrode of a lithium-ion battery. The carbon material is constructed into a self-supporting structure to support the active material, thereby avoiding the use of a binder that affects the rate performance and cycle stability of the prepared electrode, thereby improving the conductivity and stability of the negative electrode material.

[0020] The present invention uses a coaxial electrospinning method to prepare hollow iron phosphide / carbon nanofibers. This material has superior electrochemical performance compared to ordinary solid iron phosphide carbon nanofibers. Compared with solid fibers, the problems of severe volume expansion and particle agglomeration of ordinary solid iron phosphide fibers are overcome. Hollow fibers can further alleviate volume changes. The hollow inner cavity shortens the diffusion length of ions and provides more space to alleviate the strain caused by ion insertion / extraction, thereby improving the material's cycle performance. The hollow carbon nanofibers well confine the precursor in the cavity, not only inhibiting the free crystal growth of Fe2P particles during the synthesis process, but also effectively buffering the volume change, preventing the aggregation and re-accumulation of Fe2P during the insertion / extraction process. The hollow morphology can increase the specific surface area of ​​the material, increase the active sites, increase its capacity, and thus improve its electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the preparation method of the present invention;

[0022] Figure 2a and Figure 2b This is the SEM image of H-Fe2P@CNF prepared in Example 1;

[0023] Figure 2c and Figure 2d This is the SEM image of Fe2P@CNF prepared in Comparative Example 1;

[0024] Figure 3 XRD patterns of H-Fe2P@CNF prepared in Example 1 and Fe2P@CNF prepared in Comparative Example 1;

[0025] Figure 4 Electrochemical performance of half-cells of H-Fe2P@CNF prepared in Example 1 and Fe2P@CNF prepared in Comparative Example 1;

[0026] Figure 5 2. Pseudocapacitance comparison chart of H-Fe2P@CNF prepared in Example 1 and Fe2P@CNF prepared in Comparative Example 1;

[0027] Figure 6a A comparison chart of the lithium ion migration numbers of H-Fe2P@CNF prepared in Example 1 and Fe2P@CNF prepared in Comparative Example 1;

[0028] Figure 6bis the lithium ion diffusion coefficient of H-Fe2P@CNF prepared in Example 1 and Fe2P@CNF prepared in Comparative Example 1;

[0029] Figure 7 The XRD patterns of the products prepared in Comparative Example 2, Example 1 and Comparative Example 3 are shown;

[0030] Figure 8a 0.1Ag of the products prepared in Comparative Example 2, Example 1 and Comparative Example 3 -1 Cycling performance diagram under current density;

[0031] Figure 8b The figure is a rate performance diagram of the products prepared in Comparative Example 2, Example 1 and Comparative Example 3;

[0032] Figure 9 Thermogravimetric analysis diagrams of the products prepared in Comparative Example 2, Example 1 and Comparative Example 3;

[0033] Figure 10 The Raman spectra of the products prepared in Comparative Example 2, Example 1 and Comparative Example 3 are shown;

[0034] Figure 11 is the XRD pattern of the samples prepared in Examples 1-3;

[0035] Figure 12 Graph showing the cycle performance of the samples prepared in Examples 1-3.

[0036] Figure 13a This is a picture of the bending of the hollow iron phosphide / carbon nanofiber prepared in Example 1;

[0037] Figure 13b This is a picture of the bending of the hollow iron phosphide / carbon nanofiber prepared in Comparative Example 4. DETAILED DESCRIPTION

[0038] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0039] Example 1

[0040] The preparation method of hollow iron phosphide / carbon nanofiber of the present invention is as follows Figure 1 shown.

[0041] The experimental steps are as follows:

[0042] (1) Dissolve ferric acetylacetonate, phenylphosphonic acid, and polymethyl methacrylate in N,N-dimethylformamide and stir at 60°C for 12 hours to obtain a core layer solution;

[0043] (2) Dissolve polyacrylonitrile in N,N-dimethylformamide and stir at 60°C for 12 h to obtain a cortex solution;

[0044] (3) using a coaxial electrospinning method, using the core layer solution obtained in step (1) as the inner channel solution, the skin layer solution obtained in step (2) as the outer channel solution, using carbon-coated copper foil as the current collector, and spinning using an electrospinning machine;

[0045] (4) vacuum drying the spinning precursor obtained in step (3) and transferring it to a muffle furnace, and calcining it at high temperature for a period of time to obtain a pretreated product;

[0046] (5) The product obtained in step (4) is transferred to a tubular furnace and calcined at high temperature for a period of time to obtain hollow iron phosphide / carbon nanofiber H-Fe2P@CNF.

[0047] The molar ratio of ferric acetylacetonate, the molar ratio of phenylphosphonic acid, the mass of polymethyl methacrylate and the volume ratio of N,N-dimethylformamide in step (1) is 2 mmol:1 mmol:1.25 g:10 ml.

[0048] The mass of polyacrylonitrile in step (2) and the volume ratio of N,N-dimethylformamide are 1.25 g:10 ml.

[0049] The electrospinning parameters in step (3) are set as follows: the distance between the needle tip and the current collector is 20 cm, the positive high voltage is 16 kV, the negative high voltage is -3 kV, the outer channel solution injection speed is 0.060 mm / min, the inner channel solution injection speed is 0.050 mm / min, the coaxial needle size is 16G / 21G, the needle translation distance is 4.00 mm, the needle translation speed is 40.00 mm / min, and the drum collector receiving speed is 140.00 r / min.

[0050] The temperature rise program in step (4) is 2°C / min, the first stage calcination temperature is 180°C, the calcination time is 2h, and the second stage calcination temperature is 280°C, the calcination time is 2h.

[0051] The temperature rise program in step (5) is 5°C / min, the calcination temperature under nitrogen atmosphere is 700°C, and the calcination time is 3h.

[0052] Example 2

[0053] In step (1), the molar ratio of ferric acetylacetonate to phenylphosphonic acid was changed from 2 to 1.0, and the other steps were the same as in Example 1 to prepare hollow iron phosphide / carbon nanofiber H-Fe2P@CNF-1.0.

[0054] Example 3

[0055] In step (1), the molar ratio of ferric acetylacetonate to phenylphosphonic acid was changed from 2 to 1.5, and the other steps were the same as in Example 1 to prepare hollow iron phosphide / carbon nanofiber H-Fe2P@CNF-1.5.

[0056] Comparative Example 1

[0057] (1) Ferric acetylacetonate, phenylphosphonic acid, polymethyl methacrylate, and polyacrylonitrile were dissolved in N,N-dimethylformamide and stirred at 60°C for 12 hours to obtain a comparative spinning solution.

[0058] (2) using an electrospinning method and using a carbon-coated copper foil as a current collector, the comparative example spinning solution obtained in step (1) is spun using an electrospinning machine to obtain a precursor E;

[0059] (3) vacuum drying the spinning precursor obtained in step (2) and transferring it to a muffle furnace, and calcining it at high temperature for a period of time to obtain a pretreated product F;

[0060] (4) The product F obtained in step (3) is transferred to a tubular furnace and calcined at high temperature for a period of time to obtain iron phosphide nanofibers Fe2P@CNF.

[0061] The volume ratio of the moles of ferric acetylacetonate, the moles of phenylphosphonic acid, the mass of polyacrylonitrile and N,N-dimethylformamide in step (1) is 2 mmol:1 mmol:1.25 g:10 ml.

[0062] The electrospinning parameters in step (2) are set as follows: the distance between the needle tip and the current collector is 20 cm, the positive high voltage is 16 kV, the negative high voltage is -3 kV, the solution injection speed is 0.060 mm / min, the axis needle size is 21 G, the needle translation distance is 4.00 mm, the needle translation speed is 40.00 mm / min, and the roller collector receiving speed is 140.00 r / min.

[0063] The temperature rise program in step (3) is 2°C / min, the first stage calcination temperature is 180°C, the calcination time is 2h, and the second stage calcination temperature is 280°C, the calcination time is 2h.

[0064] The temperature rise program in step (4) is 5°C / min, the calcination temperature is 600-800°C, and the calcination time is 3h.

[0065] Comparative Example 2

[0066] The calcination temperature in step (5) of Example 1 was changed from 700°C to 600°C, and the rest was the same as Example 1.

[0067] Comparative Example 3

[0068] The calcination temperature in step (5) of Example 1 was changed from 700°C to 800°C, and the rest was the same as Example 1.

[0069] Comparative Example 4

[0070] The ratio of ferric acetylacetonate, phenylphosphonic acid and polymethyl methacrylate was 3 mmol:1.5 mmol:1.25 g, and the rest was the same as in Example 1. The hollow iron phosphide / carbon nanofibers obtained had poor toughness and were easily broken under stress.

[0071] Material characterization and testing: XRD was performed using a Rigaku / MiniFlex 600 desktop X-ray diffractometer; Raman analysis was performed using a DXR2 XI laser confocal Raman spectrometer; SEM was performed using an SU8010 field-emission electron microscope; STEM was performed using a FEI-Tecnai G2F30 field-emission transmission electron microscope; TG was performed using a TG209 F3 thermogravimetric analyzer; and XPS was performed using an EscalabXi+ X-ray photoelectron spectrometer. Half-cell and full-cell testing was performed using a Landdt test system (LANDdt V5.9K, Wuhan Landdt Electronics Co., Ltd.).

[0072] Figure 2a and Figure 2b This is the SEM image of H-Fe2P@CNF prepared in Example 1;

[0073] Figure 2c and Figure 2d This is the SEM image of Fe2P@CNF prepared in Comparative Example 1;

[0074] SEM images reveal a distinct hollow fiber morphology, with distinct pores on the fiber surface. These pores are formed by the thermal decomposition of the core (polymethyl methacrylate) into gas that permeates the shell (carbonized polyacrylonitrile). A comparison of the morphologies of H-Fe2P@CNF and Fe2P@CNF reveals no significant particle agglomeration on the H-Fe2P@CNF surface, while Fe2P@CNF exhibits significant particle agglomeration. This suggests that particle aggregation is suppressed during the formation of hollow carbon nanofibers.

[0075] Figure 3 Figure 2 shows the XRD patterns of H-Fe2P@CNF and Fe2P@CNF. We found that all samples have several typical diffraction peaks at 40.5°, 44.4°, 47.4°, 53.1°, and 54.3°, corresponding to the diffraction of Fe2P (JCPDS#85-1725) (111), (201), (210), (002), and (300) crystal planes, indicating that Fe2P was generated.

[0076] Comparative Example 2, Example 1, and Comparative Example 3 were subjected to XRD tests on H-Fe2P@CNF samples prepared at calcination temperatures of 600, 700, and 800°C. Figure 7 The XRD patterns show that the diffraction peaks for the samples fired at all three temperatures correspond to those of Fe2P (JCPDS#85-1725). Furthermore, significant differences in the diffraction peak intensities are observed: the characteristic peak intensity increases with increasing calcination temperature, indicating a gradual increase in crystallinity.

[0077] A hollow iron phosphide / carbon nanofiber as a lithium ion battery negative electrode assembly half / full battery and a material testing method, comprising the following steps:

[0078] Half-cell assembly: The prepared hollow iron phosphide / carbon nanofiber / iron phosphide carbon nanofiber was cut into Φ10 cm original sheets as the negative electrode, Φ12 cm lithium metal sheet as the negative electrode, Φ16 cm PP as the separator, 1.0 M LiPF6 in EC:DMC:EMC=1:1:1 (Vol) as the electrolyte, and a model 2032 battery shell was used for battery assembly.

[0079] Full battery assembly: The prepared hollow iron phosphide / carbon nanofiber / iron phosphide carbon nanofiber was cut into Φ10 cm original sheets as the negative electrode, Φ10 cm commercial lithium iron phosphate was used as the positive electrode, Φ16 cm PP was used as the separator, 1.0 M LiPF6 in EC:DMC:EMC=1:1:1 (Vol) was used as the electrolyte, and the battery was assembled using a battery shell of model 2032.

[0080] Operating conditions: The active mass of the assembled button cell electrode is approximately 0.70 mg, the electrolyte dosage is 40 μL, and the battery needs to be left to stand for 12 hours after assembly and tested at room temperature.

[0081] Figure 4 The figure shows the comparison of the cycle performance and rate performance of H-Fe2P@CNF and Fe2P@CNF. Figure 4 It can be seen that H-Fe2P@CNF shows the most stable cycling performance. -1 The capacity is still as high as 649.6 mAh g after 100 cycles at a current density of -1 , which is about 95.3% of the initial specific capacity (stable at the third cycle); while Fe2P@CNF at 0.1Ag -1 The capacity is 457.3 mA h g after 100 cycles at a current density of -1 , which is about 90.9% of the initial specific capacity (stable at the third cycle).

[0082] H-Fe2P@CNF also showed the best rate performance when the applied current density was between 0.1 and 5Ag. -1 When the specific capacities of H-Fe2P@CNF varied within the range of 1.5, 2.5, 3.5, 4.9, and 3.6 mAh g, respectively. -1 , which are all higher than the specific capacity of Fe2P@CNF at various current densities. This shows that the morphology of the hollow fiber exposes more active sites, which is conducive to the improvement of capacity, while less particle agglomeration improves the cycling performance.

[0083] Figure 5 The CV curves of H-Fe2P@CNF and Fe2P@CNF were tested at a scan rate of 0.2 to 1.0 mV s-1 to explore the kinetic behavior of the two materials. As shown in the figure, as the scan rate increases, the peak current gradually increases and slightly shifts, indicating that the material is relatively stable during this process and only a slight polarization phenomenon occurs. The b values ​​of the two electrodes were calculated. The b values ​​of the two materials are close to 1, and the corresponding b value of H-Fe2P@CNF is greater than the b value of Fe2P@CNF, indicating that the electrochemical behavior in H-Fe2P@CNF is mainly pseudocapacitive, and the pseudocapacitive contribution is greater than that in Fe2P@CNF, which further explains its rapid reaction kinetics. The pseudocapacitive contribution and diffusion-controlled capacity contribution of the two materials are compared. Figure 5 As shown in c and d, with the increase of scan rate, the capacitance contribution gradually increases, and at the same scan rate, the pseudocapacitance contribution of H-Fe2P@CNF is greater than that of Fe2P@CNF, indicating that H-Fe2P@CNF has a faster reaction kinetic process, which can be attributed to the more active sites in the hollow porous structure and the effect of confining Fe2P to the inner wall of the fiber and inhibiting agglomeration.

[0084] Figure 6a and Figure 6b The lithium ion diffusion number and coefficient of H-Fe2P@CNF and Fe2P@CNF materials were measured by GITT in order to explore the effect of the introduction of hollow structure on the kinetics.

[0085] According to the formula:

[0086]

[0087] (VM, MB, mB and S represent molar volume, material molecular weight, mass of active material and active surface area respectively) The calculated lithium ion diffusion coefficient is as follows Figure 6b The results show that the lithium ion diffusion coefficient of H-Fe2P@CNF is significantly higher than that of Fe2P@CNF during the lithium insertion / delithiation process.

[0088] The cycle performance of the materials prepared in Example 1, Comparative Example 2 and Comparative Example 3 is as follows: Figure 8a As shown. Figure 8a It can be seen that the H-Fe2P sample at 700℃ has a -1 After 100 cycles, the discharge capacity is 649.6 mAg g -1 , the capacity retention rate is as high as 96.9%; 600℃ and 800℃ at 0.1A g -1 The results showed that 473.5 mAg g -1 , 607.5mAg g -1 The discharge specific capacity and capacity retention rates of 87.8% and 66.5% are obtained. This may be due to the smaller particles of the sample at 600℃. + The diffusion path inside the particles is short; the 800℃ sample has coarse particles, which leads to the + The diffusion pathways of Li + It is difficult to carry out reversible intercalation and deintercalation inside large grains, and irreversible lithium loss is serious, resulting in rapid capacity decay and poor cycle performance of the sample at this sintering temperature.

[0089] Figure 8b The rate performance of the samples of Example 1, Comparative Example 2 and Comparative Example 3 at different sintering temperatures is shown in FIG. Figure 8b It can be seen that the sample at 700℃ has excellent rate performance. -1 The current density is as high as 351.6 mAg g -1 The specific capacity of the sample at 800℃ is poor, 5A g -1 The specific capacity is only 263.2 mAg g -1 , and return to 0.1Ag -1 During charge and discharge, the capacity decreases rapidly; the discharge capacity of the sample at 600℃ is not high, and is lower than that of the sample at 700℃. This indicates that the sintering temperature is too high, which may cause coarse grains and Li + Diffusion is hindered, which is not conducive to the material's rate performance; when the sintering temperature is too low, agglomeration and some unreacted reactants may occur, resulting in lower capacity.

[0090] Figure 9 The thermogravimetric analysis diagrams of H-Fe2P@CNF and Fe2P@CNF are shown. Figure 9 It can be seen that the contents of Fe2P in H-Fe2P@CNF and Fe2P@CNF are almost the same (difference of 0.66%), indicating that the introduction of the hollow structure does not affect the content of Fe2P.

[0091] Figure 10The Raman spectra of H-Fe2P@CNF and Fe2P@CNF, the D peak represents sp 3 Defect structure composed of hybrid carbon atoms, G peak represents sp 2 The graphite carbon structure of the hybrid arrangement is quantified by the relative degree of the D peak and the peak, i.e., I D / I G The results show that the I D / I G The value is 1.38, which is higher than 1.04 of Fe2P@CNF, indicating that sp 3 There are more hybrid carbons, more defects and disordered structures, which also means more active sites, which is conducive to the improvement of electrochemical performance.

[0092] Figure 11 XRD patterns of samples prepared in Examples 1-3 at different feed ratios (samples prepared at ferrous acetylacetonate to phenylphosphonic acid ratios of 1.0, 1.5, and 2.0, respectively, are labeled H-Fe2P@CNF-1.0, H-Fe2P@CNF-1.5, and H-Fe2P@CNF-2.0). Observation of the XRD patterns reveals the following conclusions: the phase of sample H-Fe2P@CNF-1.0 is not Fe2P, suggesting that Fe2P cannot be formed at a ferrous acetylacetonate to phenylphosphonic acid ratio of 1.0. The crystallinity of sample H-Fe2P@CNF-1.5 is inferior to that of sample H-Fe2P@CNF-2.0, suggesting that the Fe2P content at a ferrous acetylacetonate to phenylphosphonic acid ratio of 2.0 is higher than that at a ratio of 1.5.

[0093] Figure 12 The H-Fe2P@CNF prepared with different feed ratios in Examples 1-3 (the samples prepared with the ratio of ferric acetylacetonate to phenylphosphonic acid of 1.0, 1.5, and 2.0 are respectively recorded as H-Fe2P@CNF-1.0, H-Fe2P@CNF-1.5, and H-Fe2P@CNF-2.0) is heated to 0.1Ag. -1 Cycling performance diagram at current density of . Figure 11 It can be seen that with the increase of the ratio of ferric acetylacetonate and phenylphosphonic acid, the capacity of the H-Fe2P@CNF-2.0 sample prepared in Example 1 is the highest, because the content of Fe2P in the sample is the highest.

[0094] Figure 13a This is a picture of the bending of the hollow iron phosphide / carbon nanofiber prepared in Example 1; Figure 13b This is a picture of the bending of the hollow iron phosphide / carbon nanofiber prepared in comparative example 4; it can be seen from the figure that the hollow iron phosphide / carbon nanofiber prepared in Example 1 has good toughness and does not break after bending; the hollow iron phosphide / carbon nanofiber prepared in comparative example 4 has poor toughness and is easily broken when subjected to stress.

[0095] Any matters not mentioned above shall be subject to the existing technology.

[0096] Although some specific embodiments of the present invention have been described in detail through examples, those skilled in the art should understand that the above examples are for illustration only and are not intended to limit the scope of the present invention. Those skilled in the art of the present invention may make various modifications or additions to the described specific embodiments or replace them in similar ways, but they will not deviate from the direction of the present invention or exceed the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent replacements, improvements, etc. made to the above embodiments based on the technical essence of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing hollow iron phosphide / carbon nanofibers, characterized in that: The steps include: S1, dissolving ferric acetylacetonate, phenylphosphonic acid, and polymethyl methacrylate in an organic solvent to obtain a core layer solution; dissolving polyacrylonitrile in an organic solvent to obtain a skin layer solution; S2, the core layer and skin layer solutions prepared in step S1 are respectively loaded into syringes, and a coaxial nanofiber membrane is prepared by a coaxial electrospinning method using carbon-coated copper foil or aluminum foil as a current collector; S3, pre-oxidizing and then carbonizing the coaxial nanofiber membrane to obtain hollow iron phosphide / carbon nanofibers; In step S1, the molar mass ratio of ferric acetylacetonate, phenylphosphonic acid and polymethyl methacrylate is 1.5-2.5 mmol: 0.75-1.25 mmol: 1-1.5 g; The carbonization temperature was 650-750 °C, the heating rate was 5 °C / min, and the time was 2 h.

2. The preparation method according to claim 1, wherein: The mass volume ratio of the polymethyl methacrylate to the organic solvent is 1-1.5 g: 10 ml.

3. The preparation method according to claim 1, wherein: The mass volume ratio of the polyacrylonitrile to the organic solvent is 1-1.25 g: 10 ml; the organic solvent is N,N-dimethylformamide.

4. The preparation method according to claim 1, wherein: The temperature program of pre-oxidation was 2 ℃ / min, the first stage calcination temperature was 180 ℃, the calcination time was 2 h, and the second stage calcination temperature was 280 ℃, the calcination time was 2 h.

5. The preparation method according to claim 1, wherein: In coaxial electrospinning, the distance between the needle tip and the current collector is 20 cm, the positive high voltage is 16 kV, the negative high voltage is -3 kV, the outer channel solution injection speed is 0.060 mm / min, the inner channel solution injection speed is 0.040-0.080 mm / min, the coaxial needle size is 16G / 21G, the needle translation distance is 4.00 mm, the needle translation speed is 40.00 mm / min, and the roller collector receiving speed is 140.00 r / min.

6. A hollow iron phosphide / carbon nanofiber material prepared by the preparation method according to any one of claims 1 to 5.

7. A negative electrode material, characterized in that: The hollow iron phosphide / carbon nanofiber material according to claim 6 is directly cut and used as the negative electrode material.

8. A lithium battery, characterized in that: The negative electrode material as claimed in claim 7 is used as the negative electrode.

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