CN105399073A - Preparation method of hollow amorphous NaFePO4 nanosphere - Google Patents

Abstract

The invention relates to the technical field of nanomaterials, in particular to a method for preparing hollow amorphous _NaFePO4 nanospheres _. In a mixed atmosphere of _H2 and Ar, _NaH2PO4 and sodium oleate are heated to 380°C to form a mixed molten Salt, then added ferrous stearate, the product was washed with water and alcohol several times to remove other salts; dried at 100°C for 12 hours. The preparation method of the hollow amorphous _NaFePO nanospheres provided by the present invention adopts a one-step salt melting method, adding ferrous stearate to the mixed molten salt of NaH ₂ PO ₄ and sodium oleate, through in situ-hard template method, prepared hollow amorphous NaFePO ₄ nanospheres, which are used as cathode materials for sodium-ion batteries, and have excellent cycle stability and high rate characteristics. The method does not need a template agent, is simple and economical, and can realize large-scale preparation.

Description

Preparation method of hollow amorphous NaFePO4 nanosphere

technical field

The invention relates to the technical field of nanometer materials, in particular to a method for preparing hollow amorphous _NaFePO4 nanospheres.

Background technique

Lithium-ion batteries (LIBs) are currently widely used due to their good cycle performance and high energy density. However, with the increasing demand, lithium-ion batteries (LIBs) are facing serious challenges due to the scarcity of lithium resources. Due to the similar electrochemical performance of Na-ion batteries to Li-ion batteries, Na-ion batteries have become the most promising substitutes for Li-ion batteries.

It has been found that polyanionic compounds, such as Na ₄ Fe ₃ (PO ₄ ) ₂ (P ₂ O ₇ ), Na ₂ FeP ₂ O ₇ and Na ₂ FePO ₄ are very promising cathode materials for sodium-ion batteries (SIBs). Although NaFePO ₄ nanomaterials have a higher theoretical capacity than other iron-based polyanionic compounds, the existing NaFePO ₄ with olivine structure is unstable and cannot be prepared by conventional methods, which also greatly reduces the capacity of crystalline NaFePO _{4 .} Attractiveness for Na-ion battery applications.

Contents of the invention

In view of the above technical problems, the present invention provides a method for preparing hollow amorphous NaFePO ₄ nanospheres, and the prepared hollow amorphous NaFePO ₄ nanospheres can be used as anode materials for sodium ion batteries.

The specific technical solutions are:

The preparation method of hollow amorphous NaFePO ₄ nanospheres, comprises the following steps:

(1) Under a mixed atmosphere of 5% H ₂ and 95% Ar by volume, heat NaH ₂ PO ₄ and sodium oleate in the reactor to 380°C to form a mixed molten salt; the mass ratio of NaH ₂ PO ₄ and sodium oleate 1:4;

(2) under the condition of continuous stirring, ferrous stearate is added in the mixed salt of step (1) gained; The massfraction of ferrous stearate accounts for 10.1% of total material;

(3) continue to react and cool to room temperature after 30 minutes;

(4) Washing the product repeatedly with water and alcohol to remove other salts;

(5) Drying at 100° C. for 12 hours.

The preparation method of the hollow amorphous _NaFePO nanospheres provided by the present invention adopts a one-step salt melting method, adding ferrous stearate to the mixed molten salt of NaH ₂ PO ₄ and sodium oleate, through in situ-hard template method, prepared hollow amorphous NaFePO ₄ nanospheres, which are used as cathode materials for sodium-ion batteries, and have excellent cycle stability and high rate characteristics. The method does not need a template agent, is simple and economical, and can realize large-scale preparation.

Description of drawings

Fig. 1 (a) is the low magnification scanning transmission electron microscope (STEM) photo of the hollow amorphous _NaFePO nanosphere prepared by embodiment 1; (b) is the low magnification of a single, enlarged nanosphere of the sample prepared by embodiment 1 Scanning transmission electron microscope (STEM) photo; (c) is a low-magnification scanning transmission electron microscope (STEM) photo of a single, enlarged nanosphere of the sample prepared in Example 1.

Figure 2 is the hollow amorphous NaFePO ₄ nanosphere sample prepared in Example 1 in Ar atmosphere, under different temperature conditions a-25 ° C, b-480 ° C, c-580 ° C, d-680 ° C, the product obtained after treatment for 2 hours The X-ray diffraction (XRD) pattern.

3 is a diagram showing the formation mechanism of the hollow amorphous NaFePO ₄ nanospheres prepared in Example 1.

Figure 4 is the CV curve of the hollow amorphous NaFePO ₄ nanospheres prepared in Example 1 as the positive electrode material of the sodium ion battery, the voltage window is between 1.5V-4V, the scan rate is 0.1mVs ^-1 , and 1 to 10 cycles .

Figure 5 is the hollow amorphous _NaFePO4 nanosphere prepared in Example 1 as the positive electrode material of the sodium ion battery, at a current density of 0.1C, charging and discharging under different cycle times (1st, 100th, 200th) curve. 1C = 155 mAg ^-1 .

Fig. 6 shows the cycle performance of the hollow amorphous NaFePO ₄ nanospheres prepared in Example 1 as the positive electrode material of the sodium ion battery at a current density of 0.1C.

Fig. 7 shows the rate performance of hollow amorphous NaFePO ₄ nanospheres prepared in Example 1 as anode material for sodium ion batteries at different current densities from 0.2C to 10C, 1C=155mAg ^-1 .

Fig. 8 is the Nyquist diagram of the hollow amorphous _{NaFePO 4} nanospheres prepared in Example 1 as the positive electrode material of the sodium ion battery, obtained by electrochemical impedance spectroscopy (EIS) under 20 charging states.

Fig. 9 (a) is the high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) photo of the hollow amorphous _NaFePO4 nanosphere prepared in Example 1; (b) is the high-angle image of the amorphous NaFePO4 prepared under general conditions Annular dark-field scanning transmission electron microscope (HAADF-STEM) photograph.

Figure 10 is the N ₂ adsorption-desorption curve of the hollow amorphous NaFePO ₄ nanospheres prepared in Example 1.

Figure 11 is the pore size distribution curve of the amorphous hollow NaFePO ₄ nanospheres prepared in Example 1.

Figure 12 is the N ₂ adsorption-desorption curves of amorphous NaFePO ₄ under the prepared conditions under the general conditions.

Figure 13 (a) is the selected area electron diffraction (SAED) photo of the hollow amorphous _NaFePO nanosphere prepared in Example 1; (b) is the HR-STEM photo of the hollow amorphous _NaFePO nanosphere prepared in Example 1 .

Fig. 14 is a high-angle annular dark-field scanning transmission electron micrograph of the hollow amorphous NaFePO ₄ nanosphere prepared in Example 1, including a white interface.

Figure 15 is the atomic ratio of O/P, Na/P, and Fe/P at the white section of the hollow amorphous NaFePO ₄ nanospheres in Figure 14.

Fig. 16 is the energy dispersive spectrum (EDAX spectrum) of the prepared hollow amorphous NaFePO ₄ nanospheres at points 1-3 in Fig. 14 .

Fig. 17 is an X-ray photoelectron spectrum (XPS) of Fe element in the prepared hollow amorphous NaFePO ₄ nanosphere.

Figure 18 is the Mössbauer spectrum of the as-prepared hollow amorphous NaFePO ₄ nanospheres.

Figure 19 is a-5 minutes, b-10 minutes, c-20 minutes, d-10 minutes under different reaction time conditions, low magnification scanning transmission electron microscope (STEM) photos of the prepared hollow amorphous NaFePO4 nanospheres.

Figure 20 is the energy dispersive chromatogram (EDAX) spectrum of the prepared hollow amorphous NaFePO ₄ nanospheres under different reaction time conditions a-5 minutes, b-10 minutes, c-20 minutes, d-10 minutes.

Fig. 21 is the X-ray diffraction (XRD) patterns of the prepared porous amorphous NaFePO ₄ nanospheres under different reaction time conditions a-5 minutes, b-10 minutes, c-20 minutes, d-10 minutes.

Fig. 22 is the CV curves of the prepared hollow amorphous NaFePO ₄ nanospheres at different scan rates in the voltage window of 1.5V-4V.

Figure 23 is a rate performance comparison between the as-prepared hollow amorphous NaFePO ₄ nanospheres and similar materials reported recently.

Figure 24 (a) is a scanning transmission electron microscope (STEM) photo of the prepared hollow amorphous NaFePO ₄ nanospheres after 100 cycles at a current density of 5C; (b) is the prepared hollow amorphous NaFePO ₄ nanospheres in High Angle Annular Dark Field Scanning Transmission Electron Microscope (HAADF-STEM) photo after 100 cycles at 5C current density; (c) is the electron selection area of the as-prepared hollow amorphous _NaFePO4 nanospheres after 100 cycles at 5C current density Diffraction (SAED) photographs.

Figure 25 shows the atomic ratios of O/P, Na/P, and Fe/P at the white section in Figure 24(b) after the as-prepared hollow amorphous NaFePO ₄ nanospheres were cycled 100 times at a current density of 5C.

Figure 26 is the energy dispersive spectrum (EDAX) of the as-prepared hollow amorphous NaFePO ₄ nanospheres after 100 cycles at a current density of 5C at the white section in Figure 24(b).

Figure 27 is the X-ray diffraction (XRD) pattern of the prepared hollow amorphous NaFePO ₄ nanospheres after 100 full charge and discharge cycles.

Fig. 28 is the CV curve of the amorphous NaFePO ₄ material prepared by the general method as the positive electrode material of the sodium ion battery when the voltage window is 1.5V-4V and the scan rate is 0.1mVs ^-1 .

Figure 29 is the charge-discharge curves of the amorphous _NaFePO4 material prepared by the general method as the positive electrode material of the sodium-ion battery at a current density of 0.1C and different cycle times for the first, 100th, and 200th cycles.

Figure 30 shows the cycle performance of the amorphous NaFePO ₄ material prepared by the general method as the anode material of the sodium ion battery at a current density of 0.1C.

Figure 31 shows the rate performance of the amorphous NaFePO ₄ material prepared by the general method as the negative electrode material of the sodium ion battery at different current densities from 0.2C to 10C. 1C=155mAg ^-1 .

Fig. 32 is the Nyquist diagram of the amorphous _{NaFePO 4} material prepared by the general method as the negative electrode material of the sodium ion battery, obtained by electrochemical impedance spectroscopy (EIS) under 20 charging states.

detailed description

The following examples are further detailed descriptions of the present invention.

The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials and reagents used in the following examples can be obtained from commercial sources unless otherwise specified.

Example 1

In order to achieve the above purpose, the preparation steps of concrete hollow amorphous _NaFePO nanospheres are:

(1) Under the mixed atmosphere of 5% H2/95% Ar, add ferrous stearate to the mixed molten salt of NaH ₂ PO ₄ and sodium oleate (mass ratio 1:4) at 380°C, wherein the ferrous stearate is The mass fraction of ferrous fatty acid is about 10.1%.

(2) Cool to room temperature after reacting the above molten salt for 30 minutes.

(3) Repeated washing with water to remove other salts on the surface of the prepared material.

(4) This was dried at 100° C. for 12 hours.

The hollow amorphous _NaFePO of the present invention gained The performance of the nanosphere:

The material prepared in Example 1 was characterized using a scanning transmission electron microscope (STEM). Figure 1(a) is a STEM photo of the prepared material, and (b) and (c) are single, enlarged STEM photos of hollow nanospheres , it can be seen from the photos that hollow nanospheres with a diameter of 20nm and a shell thickness of 2nm with a relatively uniform structure were successfully prepared, and the ratio of the hollow spheres was as high as 95%.

The structural properties of the material were analyzed by XRD, and Fig. 2 shows the material prepared in Example 1 under Ar atmosphere, under different temperature conditions (a-25°C, b-480°C, c-580°C, d-680°C), The X-ray diffraction (XRD) pattern of the product obtained after treatment for 2h. As can be seen from the figure, the prepared hollow _NaFePO nanospheres have an amorphous structure, and as the heat treatment temperature of the sample increases, the characteristic diffraction peaks of crystal _NaFePO gradually appear in the XRD spectrum, which further proves that the sample prepared in Example 1 is amorphous.

To better explore the formation process of hollow amorphous _NaFePO4 nanospheres, a possible formation mechanism diagram is proposed in Figure 3. Here, the in-situ-hard template method is used, adding ferrous stearate into the mixed molten salt of NaH ₂ PO ₄ and sodium oleate, first forming iron nanospheres, and then using iron nanospheres as a template to combine with NaH ₂ PO ₄ reaction prepared hollow amorphous NaFePO ₄ nanospheres.

Using the CR2032 sodium ion button-type simulated battery, the prepared hollow amorphous _NaFePO4 nanosphere was used as the negative electrode material, polypropylene was used as the separator, and 1 mole per liter of _NaPF6 in ethyl carbonate and diethyl carbonate solution was used as the electrolyte , the volume ratio of ethyl carbonate and diethyl carbonate is 1:1, and the electrochemical performance test is carried out. The prepared sample was mixed with conductive agent acetylene black, and polytetrafluoroethylene was used as a binder to make a battery positive electrode. The mass ratio of sample: conductive agent: binder was 65:20:15. Cyclic voltammetry tests were performed on a CHI660A electrochemical workstation. Fig. 4 is the CV curve of the material prepared in Example 1 as the negative electrode material of the sodium ion battery, with a voltage window of 1.5V-4V, a scan rate of 0.1mVs ^-1 , and 1-10 cycles. It can be seen from this curve that there is a pair of current peaks at 2.86 and 2.32 V, which represent the extraction and intercalation of the Na-ion battery, respectively. At the same time, the CV curves of the as-prepared samples remained almost unchanged during different cycle periods, which indicated that the as-prepared materials had stable and reversible electrochemical properties.

The battery test system ArbinBT-2000 was used to conduct charge and discharge performance tests under different current densities (1C=155mAg-1) within the voltage range of 1.5-4V. Figure 5 is the charge-discharge curve of the sample. In the charge-discharge curves, the deintercalation/intercalation of Na ions is on a smooth curve, which once again confirms the amorphous structure of our prepared materials. The initial charge and discharge capacities are 154.0 and 152.1mAhg ^-1 , and after 100 and 200 charges and discharges, the initial charge and discharge capacities are 167.4 and 154.6mAhg ^-1 respectively, and the Coulombic efficiency is as high as 98.7%. In addition, the first, hundredth and two hundredth cycles of the charge and discharge curves are very similar, which indicates that the electrochemical process of this material is very stable.

Figure 6 reflects the cycle performance of the prepared material at a current density of 0.1C (1C=155mAhg ^-1 ). After 300 cycles, its capacity decays from 152 to 144.3mAhg ^-1 , and the cycle stability of this NaFePO ₄ nanosphere is better than other reported NaFePO ₄ nanomaterials.

In addition, it can be seen from Fig. 7 that the as-prepared material exhibits better rate capability in the range of charge-discharge rate from 0.1 to 10C. When the current rate is 0.2, 0.5, 1, 2, 5 and 10C, its average specific capacity is 147.8, 138.3, 124.6, 107.2, 88.1 and 67.4mAhg ^-1 , respectively. After the high-rate charge-discharge cycle, the current density was reduced to 0.2C, and the specific capacity of the material recovered to 147.8mAhg ^-1 .

Fig. 8 is a Nyquist diagram obtained by electrochemical impedance spectroscopy (EIS) testing of the prepared material, which is composed of a small semicircle in the high frequency range, a small circular arc in the intermediate frequency range and an inclined straight line in the low frequency range. The high frequency region reflects the sodium ion diffusion resistance (Rsf) on the electrode surface, the intermediate frequency region reflects the charge transfer resistance (Rct) at the electrode/electrolyte interface, and the low frequency range reflects the diffusion resistance of sodium ions in the material (Zw) . It can be seen from the equivalent circuit diagram that NaFePO ₄ hollow nanospheres have a small Rct value, indicating that the unique hollow structure of the material itself makes it have a small charge transfer resistance and high conductivity. At the same time, the relationship between the Warburg coefficient (σ) and the sodium ion diffusion material can be expressed by the formula D _Na ⁺ =1/σ ^{2 .21} . The diffusion coefficient of NaFePO ₄ hollow nanospheres is greater than that of nanoparticles, so the hollow sphere structure is also conducive to the improvement of electrical conductivity and the diffusion of solid sodium ions.

It can be seen from Figure 9a that the prepared hollow amorphous NaFePO ₄ nanospheres can be uniformly dispersed in water; while it can be seen from Figure 9b that the prepared amorphous NaFePO ₄ has no specific structural morphology under general conditions.

The specific surface of the sample was measured using the nitrogen adsorption-desorption technique, and the sample was heated to 200 °C for 180 min to degas before the measurement. The nitrogen adsorption-desorption results are shown in Figure 10. The specific surface area of the sample is large, reaching 120.4m ² g ^-1 , and the average pore size of the hollow nanospheres is 2.5nm, as shown in Figure 11. Figure 12 is the N ₂ adsorption-desorption curve of amorphous NaFePO ₄ prepared under general conditions. At this time, the specific surface area of the sample is 25.3 m ² g ^-1 , which is much smaller than that of the hollow nanospheres prepared in Example 1.

The SAED and HR-STEM photos of the samples were obtained by FEITecnaiG2F20S-Twin transmission electron microscope. Before the STEM test, the surface of the sample was coated on a copper grid coated with an amorphous carbon film. From the SAED photo in Figure 13(a), it can be seen that only halos can be observed on the diffraction pattern, while no lattice diffraction fringes are seen in the HR-STEM photo in Figure 13(b), which further verifies that the prepared The amorphous structure of the material.

It can be determined from Figure 14 and Figure 15 that the Na/Fe/P/O ratio of the prepared sample is about 1:1:1:4. Through the Oxford energy spectrometer, the system error is within ±2 at.%, and the EDAX spectrum of the product is obtained, as shown in Figure 16. It can be seen from Figure 14 that only the signal peaks of Na, Fe, O, P, and Cu appear in the spectrum, and the Cu peak is the base peak without any impurity peaks.

The electronic state of the sample surface was determined by X-ray photoelectron spectrometer, Perkin-Elmer PHI5000CESCA, AlKα. The Fe2p _3/2 peak appears at the binding energy of 710.7eV, indicating that Fe is +2 in the hollow amorphous NaFePO ₄ nanospheres, as shown in Figure 17.

As shown in Figure 18, the valence state of iron in the prepared sample was further determined to be +2 by performing the determination of the Mössbauer spectrum on the sample.

In order to determine the experimental mechanism of the reaction, experiments under different reaction time conditions were carried out, and the corresponding STEM, EDAX characterization and XRD tests are shown in Figure 19, Figure 20, and Figure 21, respectively. When the reaction time is 5 minutes, a solid spherical structure appears, and it can be concluded from EDAX and XRD analysis that the solid spherical substance here is crystalline iron. The existence of elemental iron is conducive to the thermal decomposition of iron stearate to form elemental iron and reducing agents such as C, CO, _H2 , and the existence of these reducing agents will promote the formation of iron nanospheres. When the reaction time increased to 10min, a small amount of hollow NaFePO ₄ nanospheres appeared, which indicated that Fe nanospheres had started to react with NaH ₂ PO ₄ .

As the reaction progressed, the number of hollow NaFePO ₄ nanospheres increased rapidly, and the number of solid Fe nanospheres decreased sharply. When the reaction time was 30 min, all the solid spheres were transformed into hollow spheres, as shown in Figures 19 and 20. Further increasing the reaction time to 2 h did not change the morphology significantly. According to the corresponding XRD measurement shown in Figure 21, as the reaction time increases, the characteristic peaks of the crystalline iron element gradually become weaker, and finally no characteristic peaks appear. These results suggest that the reaction proceeds in two steps:

(1) Ferrous stearate decomposes to form Fe nanospheres (C ₃₆ H ₇₀ FeO ₄ →Fe+4CO+35H ₂ +32C)

(2) Fe nanospheres and NaH ₂ PO ₄ form NaFePO ₄ (Fe+NaH ₂ PO ₄ →NaFePO ₄ +H ₂ )

In order to investigate the influence of the pseudocapacitive behavior of the hollow amorphous NaFePO ₄ nanospheres on their electrochemical performance, the CV curves were measured at different scan rates of 0.1-10mVs-1, as shown in Figure 22. When the scanning speed was increased, the redox peak did not disappear into a regular rectangular shape, which indicated that the pseudocapacitive behavior of the as-prepared samples might exist but not so obvious.

Figure 23 compares the rate performance between hollow amorphous _NaFePO4 nanospheres and similar materials reported recently, and found that it is significantly better than other similar materials.

Figure 24 is a STEM photo of hollow amorphous NaFePO ₄ nanospheres after 100 cycles at 5C, and no significant change in structure was found, which indicates that hollow amorphous NaFePO ₄ nanospheres have extremely good structural stability.

Figure 25 is the elemental composition test at the white section in the STEM photo of hollow amorphous NaFePO ₄ nanospheres after 100 cycles at 5C. It can be determined that the Na/Fe/P/O ratio of the as-prepared samples is approximately 1:1:1:4, which further confirms the excellent structural stability of the as-prepared products. It can be seen from Figure 26 that after the hollow amorphous NaFePO4 nanospheres were cycled 100 times at 5C, only the signal peaks of Na, Fe, O, P, and Cu appeared in the EDAX spectrum, and the Cu peak was the base peak. Does not contain any impurity peaks, such as Cl elements.

From the XRD pattern shown in Figure 27, it can be seen that after 100 cycles of charging and discharging, there is no new phase in the corresponding pattern, which proves that the NaFePO ₄ electrode has an amorphous structure throughout the charging and discharging process, and these results indicate that it has a long cycle Hollow amorphous _NaFePO4 nanospheres with long lifetime and high rate capability exhibit excellent sodium storage performance during fast charge and discharge.

In order to confirm the influence of the hollow nanostructure on the electrochemical performance, the electrochemical performance test was carried out on the conventional amorphous NaFePO ₄ nanoparticles as shown in Figure 28. Conventional amorphous _NaFePO4 electrodes also exhibit similar charging/discharging behaviors as hollow amorphous _NaFePO4 nanospheres. However, the initial discharge capacity of conventional NaFePO ₄ electrodes at a current density of 0.1C is only 125.3 mAh g ⁻¹ , which is significantly lower than that of hollow amorphous NaFePO ₄ nanospheres as shown in Figure 29. The discharge capacity of the traditional electrode drops sharply during the cycle, and the capacity is only 65mAhg ^-1 at the end of 200 cycles as shown in Figure 30. When discharged at a current density of 2C, the reversible capacity of the conventional electrode decays rapidly during the cycle, and finally its reversible capacity is only 51mAhg ^-1 , as shown in Figure 31, which further confirms the hollow structure of the hollow amorphous NaFePO ₄ nanospheres essential for its good electrochemistry.

Fig. 32 is a Nyquist diagram obtained by electrochemical impedance spectroscopy (EIS) testing of amorphous NaFePO ₄ materials prepared by traditional methods. This figure is similar to the Nyquist figure of the sample prepared in Example 1, but its corresponding diffusion resistance, contact resistance, etc. are significantly higher than that of the hollow amorphous NaFePO ₄ nanosphere.

The invention adopts a simple one-step molten salt method to successfully prepare hollow amorphous NaFePO ₄ nanospheres. The method is relatively mild and low in cost, and is suitable for large-scale preparation of hollow amorphous NaFePO ₄ nanospheres. At the same time, we discussed its reaction process and the formation mechanism of nanospheres, which will provide ideas for the research of hollow nanostructure materials. The stable structure of hollow amorphous _NaFePO4 nanospheres enables them to exhibit extremely good performance, maintaining high capacity after 300 cycles, and still exhibiting excellent rate capability at current densities as high as 10C. This also provides an idea for the research of NaFePO ₄ -based cathode materials for sodium-ion batteries.

Although the embodiments of the present invention have been shown and described, those skilled in the art can understand that various changes, modifications and substitutions can be made to these embodiments without departing from the principle and spirit of the present invention. and modifications, the scope of the invention is defined by the appended claims and their equivalents.

Claims (2)

1. hollow non-crystalline state NaFePO ₄the preparation method of nanometer ball, is characterized in that, comprises the following steps:

(1) at volume 5%H ₂with under the mixed atmosphere of 95%Ar, by NaH in reactor ₂pO ₄be heated to 380 DEG C with sodium oleate and form fused salt mixt;

(2) under the condition of Keep agitation, in stearic acid ferrous iron being added the mixing salt of step (1) gained;

(3) continue reaction and be cooled to room temperature after 30 minutes;

(4) product is repeatedly washed remove other salinities with alcohol wash;

(5) at 100 DEG C dry 12 hours.

2. hollow non-crystalline state NaFePO according to claim 1 ₄the preparation method of nanometer ball, is characterized in that, described NaH ₂pO ₄be 1:4 with the mass ratio of sodium oleate; The massfraction of stearic acid ferrous iron accounts for 10.1% of total material.