CN114162803A

CN114162803A - Method for injecting phosphorus in liquid phase in hollow carbon nanospheres and red phosphorus anode material

Info

Publication number: CN114162803A
Application number: CN202111485887.4A
Authority: CN
Inventors: 李俊; 金辉乐; 王舜; 陈锡安; 卢行; 张礼杰
Original assignee: Wenzhou University
Current assignee: Wenzhou University
Priority date: 2021-12-07
Filing date: 2021-12-07
Publication date: 2022-03-11

Abstract

The invention belongs to the technical field of electrochemical materials, and particularly relates to a method for injecting phosphorus into a hollow carbon nanosphere in a liquid phase manner and a red phosphorus anode material. The invention converts the block red phosphorus into soluble small phosphorus molecules (mainly P) through the activation reaction of the red phosphorus and a nucleophilic reagent sodium ethoxide₅ ^‑And secondly is P₁₆ ^2‑And P₂₁ ^3‑Composition), then small phosphorus molecules are encapsulated in mesopores of hollow nano carbon spheres under the assistance of ultrasound, and phosphorus on the outer surfaces of the carbon spheres can be easily washed away by a polar solvent by a solution-based liquid phase phosphorus injection method. Therefore, the small phosphorus molecules can be encapsulated inside the hollow carbon nanospheres by utilizing the mesoporous confinement effect inside the hollow carbon nanospheres, and the obtained small phosphorus molecule/carbon nanosphere composite has excellent rate performance and cycling stability.

Description

Method for injecting phosphorus in liquid phase in hollow carbon nanospheres and red phosphorus anode material

Technical Field

The invention belongs to the technical field of electrochemical materials, and particularly relates to a method for injecting phosphorus into a hollow carbon nanosphere in a liquid phase manner and a red phosphorus anode material.

Background

Red phosphorus as the anode material of sodium ion battery can react with sodium to form Na₃P, and provide 2596 mAh g^-1Far exceeding any other sodium ion battery anode material currently existing. However, red phosphorus has the disadvantages of extremely low electron conductivity and severe volume expansion during charge and discharge, which results in low utilization of active materials and severe pulverization of material structure, resulting in low coulombic efficiency, unstable SEI film and rapid capacity drop during cycling. To solve the above problems, researchers have used a number of methods to compound red phosphorus with other materials to enhance the conductivity of red phosphorus and to accommodate the volume expansion of red phosphorus. At present, the commonly used composite red phosphorus comprises a high-energy ball milling method and a gas phase phosphorus injection method. The following disadvantages exist in conventional high energy ball milling: (1) an inert gas is required to be added for preventing the electrode material from being oxidized; (2) a carbon material having a specific design is destroyed, resulting in structural destruction of the carbon material, for example, a hollow carbon material having a low strength is structurally collapsed in a severe collision. Aiming at the defects of high-energy ball milling, the gas-phase phosphorus injection does not damage the structure of the carbon material and can fully utilize the porous structure of the carbon material to limit red phosphorus. However, during vapor phase phosphorus injection, white phosphorus inevitably deposits on the outside of the carbon material in the form of phosphorus oxide and crystalline phosphorus. Although white phosphorus on the outside can be easily usedEthanol or CS₂The crystallized phosphorus on the inner surface of the CNT is very stable and is not easily removed, which results in a rapid decrease in the battery capacity.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a method for injecting phosphorus into a hollow carbon nanosphere in a liquid phase and a red phosphorus anode material.

The technical scheme adopted by the invention is as follows: a method for injecting phosphorus in a liquid phase in hollow carbon nanospheres comprises the following steps: the red phosphorus is changed into small phosphorus molecules under the etching of sodium ethoxide, and the etching supernatant is taken to be mixed with the hollow nano carbon spheres for ultrasonic reaction to obtain the liquid-phase phosphorus-injected hollow nano carbon spheres.

The activation reaction of the red phosphorus and sodium ethoxide is carried out in a dimethyl sulfoxide solvent.

And heating the red phosphorus and sodium ethoxide in a dimethyl sulfoxide solvent to reflux under the protection of argon gas for activation reaction.

The hollow nano carbon ball has a sea urchin-shaped inner cavity.

The preparation process of the hollow carbon nanospheres comprises the following steps:

(1) preparing a sea urchin-shaped silicon dioxide template;

(2) carrying out amination treatment on the sea urchin-shaped silica template to obtain an aminated silica template;

(3) wrapping glucose outside the aminated silicon dioxide template, and calcining to obtain carbon spheres;

(4) and removing the silicon dioxide template in the carbon spheres to obtain the hollow nano carbon spheres.

In the step (1), cetyl pyridine bromide and urea are dissolved in water, the solution system is changed from colorless to milky white by stirring to obtain a solution system A, tetraethyl silicate and n-amyl alcohol are added and dispersed into cyclohexane to obtain a solution system B, the solution system A and the solution system B are mixed and heated to 110-130 ℃ for reaction, the mixture is cooled and centrifuged to obtain a white solid, the white solid is placed at 70-90 ℃ for 6-10h, and the mixture is calcined at 500-600 ℃ for 4-8h in the air atmosphere.

In the step (1), the white solid is placed at 70-90 ℃ and kept for 6-10h, and then the temperature is raised to 500-600 ℃ at the temperature raising rate of 10 ℃/min.

In the step (2), the sea urchin-shaped silica template is added into toluene, heated to 50-70 ℃ under stirring, then aminopropyltriethoxysilane is added for reaction, and after the reaction is finished, the aminated silica template is obtained by centrifugation.

In the step (3), the aminated silicon dioxide template and glucose are added into water for reaction, after the reaction is finished, the yellow solid is collected to obtain yellow solid, the yellow solid is dried and ground into powder, and the powder is calcined for 1.5 to 2.5 hours at the temperature of 900 ℃ in the argon atmosphere.

The red phosphorus anode material is prepared by the method for injecting phosphorus into the hollow carbon nanospheres in a liquid phase manner.

The invention has the following beneficial effects: the invention converts the block red phosphorus into soluble small phosphorus molecules (mainly P) through the activation reaction of the red phosphorus and a nucleophilic reagent sodium ethoxide₅ ^-And secondly is P₁₆ ^2-And P₂₁ ^3-Composition), then small phosphorus molecules are encapsulated in mesopores of hollow nano carbon spheres under the assistance of ultrasound, and phosphorus on the outer surfaces of the carbon spheres can be easily washed away by a polar solvent by a solution-based liquid phase phosphorus injection method. Therefore, the small phosphorus molecules can be encapsulated inside the hollow carbon nanospheres by utilizing the mesoporous confinement effect inside the hollow carbon nanospheres, and the obtained small phosphorus molecule/carbon nanosphere composite has excellent rate performance and cycling stability.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is within the scope of the present invention for those skilled in the art to obtain other drawings based on the drawings without inventive exercise.

In FIG. 1, a, b) SEM images of silica templates of different sizes.

In fig. 2, a, b) SEM images of mesoporous hollow nanocarbon spheres with different sizes; c) TEM image of mesoporous hollow carbon nanospheres.

FIG. 3 is an X-ray diffraction pattern of a red phosphorus and silica template.

Fig. 4 is a raman spectrum of the hollow nanocarbon sphere.

In FIG. 5, a, b) SEM image of PP @ CS-0.30, c, d) TEM image and e, f) elemental distribution chart.

FIG. 6 is an X-ray diffraction pattern of a complex of red phosphorus, PP @ CS-0.17 and PP @ CS-0.30.

FIG. 7 is a Raman spectrum of a complex of red phosphorus, PP @ CS-0.17 and PP @ CS-0.30.

FIG. 8 is a nitrogen adsorption and desorption curve (a) and a BJH pore size distribution curve (b) of hollow carbon spheres and a PP @ CS-0.30 composite;

FIG. 9 shows that the voltage window of the hollow carbon nanosphere (a) and the activated carbon electrode (b) is 0.01V to 2V, and the current density is 0.1A g^-1Constant current charging and discharging curve.

FIG. 10, (a) PP @ CS-0.30 electrode at a voltage window of 0.01 to 2V and a sweep rate of 0.1 mV s^-1The constant current charging and discharging curve of (b) PP @ CS-0.30 electrode is 0.01 to 2V in voltage window, and the current density is 0.1A g^-1Constant current charging and discharging curve of (1);

FIG. 11 shows that CS (a) and AC (b) are at 0.1A g^-1The cycle stability of the following.

FIG. 12 shows PP @ CS-0.30 complex at 0.1A g^-1Cycling stability plots.

FIG. 13 shows CS and AC from 0.1 to 1A g^-1The rate performance graph of (1).

FIG. 14 is a graph of the rate performance of PP @ CS-0.30 and PP @ CS-0.17 composites.

FIG. 15 shows that CS is at 1A g^-1Lower cycling stability plot.

FIG. 16 shows the PP @ CS-0.30 and PP @ CS-0.17 complexes at 2A g^-1Cycling stability plots.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings.

The invention provides a method for injecting phosphorus into a hollow carbon nanosphere in a liquid phase, which comprises the following steps: the red phosphorus is changed into small phosphorus molecules under the etching of sodium ethoxide, and the etching supernatant is taken to be mixed with the hollow nano carbon spheres for ultrasonic reaction to obtain the liquid-phase phosphorus-injected hollow nano carbon spheres. The activation reaction of red phosphorus and nucleophilic reagent sodium ethoxide makes the block red phosphorus converted into soluble small phosphorus molecule (mainly P)₅ ^-And secondly is P₁₆ ^2-And P₂₁ ^3-Composition), then small phosphorus molecules are encapsulated in mesopores of hollow nano carbon spheres under the assistance of ultrasound, and phosphorus on the outer surfaces of the carbon spheres can be easily washed away by a polar solvent by a solution-based liquid phase phosphorus injection method. Therefore, the small phosphorus molecules can be packaged in the hollow carbon nanospheres by utilizing the mesoporous confinement effect in the hollow carbon nanospheres.

In some embodiments of the invention, the activation reaction of red phosphorus with sodium ethoxide is performed in dimethyl sulfoxide solvent.

In some embodiments of the present invention, the red phosphorus and sodium ethoxide are heated to reflux in a dimethyl sulfoxide solvent under the protection of argon gas to perform the activation reaction.

The hollow nano carbon ball has a sea urchin-shaped inner cavity.

In some embodiments of the present invention, the preparation process of the hollow nanocarbon sphere comprises the following steps:

(1) preparing a sea urchin-shaped silicon dioxide template;

The hollow carbon nanospheres prepared by the method have the advantages that the inner hollow parts of the hollow carbon nanospheres are outwards diffused along the center and are barbed, and a unique hollow sea urchin-shaped inner structure is formed. The hollow carbon nanospheres with the unique structure can increase the contact area with small phosphorus molecules, are beneficial to shortening the transmission distance of sodium ions, and meanwhile, the sufficient inner space can accommodate the volume expansion of phosphorus.

In some embodiments of the invention, step (1) is as follows: dissolving cetyl pyridine bromide and urea in water, stirring to change a solution system from colorless to milky white to obtain a solution system A, adding tetraethyl silicate and n-amyl alcohol into cyclohexane and dispersing the tetraethyl silicate and the n-amyl alcohol into the cyclohexane to obtain a solution system B, mixing the solution system A and the solution system B, heating to 110-130 ℃, reacting, cooling, centrifuging to obtain a white solid, placing the white solid at 70-90 ℃, keeping for 6-10h, and calcining for 4-8h at 500-600 ℃ in an air atmosphere. In this step, water and cyclohexane form an emulsion due to the stabilizing effect of the surfactant cetylpyridinium bromide, and tetraethyl silicate is decomposed in the droplets, so that the formed silica template has a uniform size and is microscopically sea urchin-like by outward diffusion from the center.

In some embodiments of the present invention, in step (1), the white solid is heated to 500-600 ℃ at a heating rate of 10 ℃/min after being kept at 70-90 ℃ for 6-10 h.

In some embodiments of the invention, in step (2), the sea urchin-shaped silica template is added into toluene, heated to 50-70 ℃ under stirring, then aminopropyltriethoxysilane is added for reaction, and after the reaction is finished, the aminated silica template is obtained by centrifugation.

In some embodiments of the present invention, in step (3), the aminated silica template and glucose are added into water, the yellow solid is collected after the reaction is finished, the yellow solid is dried, ground into powder, and calcined at 900 ℃ for 1.5-2.5h in an argon atmosphere. And (3) carrying out amination on the silicon dioxide template, carrying out hydrothermal reaction on the silicon dioxide template and glucose, and carrying out polymerization reaction on amino on the surface of the silicon dioxide template and hydroxyl, aldehyde and ketone groups of the glucose to wrap the glucose on the surface of the silicon dioxide spheres. As the reaction time is prolonged, the glucose reacted on the surface of the silica is further reacted with the glucose in the solution, thereby coating a layer of organic polymer on the sea urchin-shaped silica template. The skilled person can select the reaction time and the reaction temperature by limited experimentation or by monitoring the course of the reaction. In some embodiments of the invention, the aminated silica template is reacted with glucose at 160-200 ℃ for 10-14 h.

In some embodiments of the present invention, in step (4), the silica template in the carbon sphere is removed by acid soaking or alkali soaking, and those skilled in the art can also remove the silica template in the carbon sphere by other methods. In some embodiments of the invention, 10% diluted hydrochloric acid is adopted for soaking for 10h, then deionized water is used for washing to be neutral, hollow carbon nanospheres are obtained after drying, and detection shows that the silicon dioxide template is etched cleanly and has no residue.

The small phosphorus molecule/carbon sphere compound prepared by the method for injecting phosphorus into the hollow nano carbon spheres in a liquid phase can be used as an anode material, particularly an anode material of a sodium ion battery.

The following is a preparation process of several embodiments of the present invention, and the comparison of the test results of several embodiments illustrates the optimization effect of the present invention on the prior art, which is only a preferred embodiment of the present invention, and certainly not intended to limit the scope of the present invention.

Example 1 preparation of hollow nanocarbon spheres:

(1) synthesis of sea urchin-shaped silica template

10 g of cetylpyridinium bromide (CPBr) and 6 g of urea were added to a beaker containing 300 mL of deionized water and dissolved by ultrasonic stirring at 45 ℃ so that the solution gradually changed from milky white to colorless. The colorless solution obtained above was transferred into a 1000 mL three-necked flask, and the solution changed from colorless to milky white and lasted for 10 mins under high-speed mechanical stirring at 1500 revolutions. 25 mL of tetraethyl silicate and 15 mL of n-pentanol were added to a beaker containing 300 mL of cyclohexane, stirred ultrasonically for 10 mins, and added to a three-necked flask, and stirred for 1 h. And standing for half an hour after stirring is finished, adding the obtained solution into a 50 mL reaction kettle, reacting for 6 hours at 120 ℃, naturally cooling to obtain a yellowish milky solution, collecting and centrifuging for three minutes at 10000 revolutions to obtain a white solid, and keeping for 8 hours at 80 ℃. Grinding the white product, calcining for 6 h at 550 ℃ in air atmosphere, and heating at a rate of 10 ℃/min to obtain the sea urchin-shaped silicon dioxide template.

(2) Amination of sea urchin-like silica templates

1 g of sea urchin-like silica template and 200 mL of toluene were weighed into a 1000 mL round bottom flask, heated to 60 ℃ with 1000 revolutions of mechanical stirring and incubated for 0.5 h. 10 mL of aminopropyltriethoxysilane was added to the solution and stirring was continued for 10 h. Notably, the reagents and environment should be kept anhydrous during the reaction. After the reaction is finished, cooling to room temperature, centrifuging for 1 min at 10000 r, ultrasonically washing with toluene for three times, and drying in vacuum for 12 h at 80 ℃ to obtain the yellowish aminated silicon dioxide template.

(3) Synthesis of hollow nano carbon spheres

1 g of aminated silica and 8 g of glucose were weighed into a polytetrafluoroethylene reaction vessel containing 50 mL of deionized water, and ultrasonically stirred for 4 hours. The above solution was reacted at 180 ℃ for 12 h. Cooling to room temperature, taking out solid matter, collecting yellow solid, oven drying, and grinding into powder. The yellow powder was calcined at 800 ℃ for 2 h under an argon atmosphere. And (3) soaking the product in 50 mL of 10% diluted hydrochloric acid for 10 hours, washing the product with deionized water to be neutral, and preserving the temperature at 80 ℃ for 10 hours to dry to obtain the hollow carbon nanosphere, which is marked as CS.

(4) Weighing 100mg of hollow carbon nanospheres, 21.4 mg of acetylene black and 21.4 mg of polyvinylidene fluoride (PVDF) according to the mass ratio of 7:1.5:1.5, adding into the grinding bowl, and grinding until no large white particles exist. 1mL of Nitrogen Methyl Pyrrolidone (NMP) is transferred by a liquid transfer gun and added into a grinding bowl for grinding for 40-60 mins. Coating the slurry on copper film, vacuum drying at 80 deg.C for 24 hr, and cutting into round electrode slice with diameter of about 14 mm.

The following are the structural characterization test results of the silica template and the hollow carbon nanospheres:

as shown in FIG. 1, the present embodiment obtains a uniform size of a silica template, which has a size of about 240-300 nm. The silica template was found to be echinoid from the center to the outside at a size of 400 nm.

As shown in FIG. 2, the mesoporous hollow carbon nanocapsules obtained in this example have smooth surfaces without agglomeration, and the particle size of the carbon nanocapsules is about 300-360 nm. The carbon ball is hollow, the hollow part is outwards dispersed along the center, the hollow part in the carbon ball is formed by etching silicon dioxide, the hollow part on the surface of the silicon dioxide is filled by the carbon layer originally, and the inside of the carbon ball is barbed.

As shown in FIG. 3, the X-ray diffraction pattern of the sea urchin-shaped silica template showed that all the diffraction peaks in the X-ray diffraction pattern corresponded to standardized cristobalite-based silica (PDF number 71-0785). From this, it was found that the crystallinity of the product was very high and no other hetero phase was present. The hollow nanocarbon spheres show a typical X-ray diffraction (XRD) pattern in which (002) and (101) crystal planes of graphitic carbon are represented, respectively, centering around 23 ° and 43 ° 2 θ. This also proves that the silicon dioxide template in the prepared hollow nano carbon sphere is etched cleanly without residue.

As shown in FIG. 4, the hollow nanocarbon spheres showed a typical Raman spectrum at 1333 cm^-1Is the D peak of the hollow carbon nanosphere, the intensity is 2720, and the intensity is 1587 cm^-1Is the G peak of the hollow carbon nanospheres, and the intensity is 2890. Wherein I_D/I_GThe ratio of (A) to (B) is 0.941.

Example 2:

(1) weighing 50 mg of red phosphorus particles, grinding the red phosphorus particles into fine powder in a bowl, adding the fine powder into a 50 mL single-neck round-bottom flask, weighing 110 mg of sodium ethoxide, transferring 12 mL of dimethyl sulfoxide (DMSO) by using a liquid transfer gun, and adding a polytetrafluoroethylene stirrer into the round-bottom flask. Heating the mixture to 195 ℃ in an oil bath, cooling and refluxing condensed water, and reacting for 6 hours under the protection of argon. Standing after the reaction is finished, transferring the supernatant of the solution while the solution is hot, adding the supernatant into a 50 mL centrifuge tube, weighing 50 mg of the hollow carbon nanospheres prepared in the example 1, adding the hollow carbon nanospheres into the centrifuge tube, heating the hollow carbon nanospheres in an ultrasonic water bath at the temperature of 75 ℃, and carrying out ultrasonic reaction for 3 hours, wherein the name of the hollow carbon nanospheres is PP @ CS-0.17.

(2) Weighing 100mg of once phosphorus injection hollow carbon nanospheres, 21.4 mg of acetylene black and 21.4 mg of polyvinylidene fluoride (PVDF) according to the mass ratio of 7:1.5:1.5, adding into the bowl, and grinding until no large white particles exist. 1mL of Nitrogen Methyl Pyrrolidone (NMP) is transferred by a liquid transfer gun and added into a grinding bowl for grinding for 40-60 mins. Coating the slurry on copper film, vacuum drying at 80 deg.C for 24 hr, and cutting into round electrode slice with diameter of about 14 mm.

Example 3:

(1) compared with the operation process of example 2, after red phosphorus reacts with sodium ethoxide and DMSO in an oil bath for 6 hours, two identical supernatant liquid are taken and added into a 50 mL centrifuge tube, 50 mg of hollow carbon nanospheres are weighed and added into the centrifuge tube, and the mixture is heated in an ultrasonic water bath at the temperature of 75 ℃, the ultrasonic reaction time is 3 hours, and the name of the mixture is PP @ CS-0.30.

(2) Weighing 100mg of secondary phosphorus injection hollow carbon nanospheres, 21.4 mg of acetylene black and 21.4 mg of PVDF according to the mass ratio of 7:1.5:1.5, adding into the grinding bowl, and grinding until no large white particles exist. 1mL of Nitrogen Methyl Pyrrolidone (NMP) is transferred by a liquid transfer gun and added into a grinding bowl for grinding for 40-60 mins. Coating the slurry on copper film, vacuum drying at 80 deg.C for 24 hr, and cutting into round electrode slice with diameter of about 14 mm.

The following are the results of the structural characterization test of PP @ CS-0.17 prepared in example 2 and PP @ CS-0.30 prepared in example 3:

as shown in FIG. 5, compared with the hollow carbon nanospheres, the morphology of the carbon nanospheres in the PP @ CS-0.30 composite is kept unchanged.

As shown in fig. 6, the X-ray diffraction pattern of commercial red phosphorus shows a sharp peak at 2 θ = 15 ° and a broad peak at 2 θ = 34 °, showing that commercial red phosphorus is a medium-range ordered structure in combination with XRD standard card (PDF No. 44-0906). The P @ CS-0.17 and PP @ CS-0.30 composites showed similar graphitic peak positions for carbon compared to the XRD pattern of RP, showing a peak at 2 θ = 15 ° and a broad peak at 34 °, indicating that the hollow carbon sphere confines small phosphorus molecules. The XRD patterns of the PP @ CS-0.17 and PP @ CS-0.30 complexes show the combination of XRD signals for hollow nanocarbon spheres and red phosphorus, but at a lower intensity, indicating that hollow nanocarbon spheres can effectively confine small phosphorus molecules in the pores.

And the structure between the hollow nano carbon spheres with different loading amounts and red phosphorus is researched through Raman spectrum. As shown in FIG. 7, red phosphorus is present at 300 and 500 cm^-1Performance ofThe composite material has strong Raman resonance peak, but the PP @ CS-0.17 and PP @ CS-0.30 composite materials do not show RP Raman resonance peak, liquid phase phosphorus injection effectively confines small phosphorus molecules in mesopores of hollow carbon nanospheres, which is beneficial to maintaining stable structure of the PP @ CS composite material in the rapid charge and discharge process.

BET tests show that the specific surface area and the pore size distribution in the hollow carbon nanospheres are greatly changed before and after the small phosphorus molecules are compounded. As shown in FIG. 8, N2 adsorption/desorption isotherms illustrate that hollow nanocarbon spheres prepared by preparing a silica template by etching show a typical IV curve, and a Brunauer-Emmett-Teller (BET) specific surface area of 623.2 cm² g^-1The pore diameter distribution of the hollow carbon nanospheres is mainly mesoporous about 6 nm. After the hollow carbon nanospheres are compounded with the small phosphorus molecules, the BET surface area of the PP @ CS-0.30 compound is sharply reduced to 185.9 cm²g^-1The result shows that most mesopores of the hollow carbon nanospheres are occupied by small phosphorus molecules. Accordingly, the pore volume of the PP @ CS-0.30 composite is from 0.606 cm of the hollow nanocarbon sphere³ g^-1Quickly reduced to 0.25 cm³ g^-1. The micropores of the hollow nano carbon spheres can effectively limit the small phosphorus molecules, the small phosphorus molecules are wrapped in the holes of the carbon spheres, and meanwhile, the small phosphorus molecules cannot completely fill the internal gaps of the carbon spheres, so that the part of space plays a vital role in buffering stress in the charge and discharge process of the battery.

Thermogravimetric analysis (TGA) was performed in a nitrogen atmosphere to measure the phosphorus content of the P @ CS-0.17 and PP @ CS-0.30 complexes as shown in FIG. 9. The phosphorus contents of the PP @ CS-0.17 and PP @ CS-0.30 complexes were 17% and 30%, respectively, as determined by thermogravimetric analysis. It is worth mentioning that compared with PP @ CS-0.17, the sublimation temperature of the PP @ CS-0.30 composite is slightly reduced and increased, which is probably caused by the high volume ratio of the nanoparticles, and this also indicates that the sizes of the red phosphorus nanoparticles in the mesopores of the hollow carbon nanospheres with different loading amounts are different.

Comparative example 1:

100mg of Activated Carbon (AC), 21.4 mg of acetylene black and 21.4 mg of PVDF are weighed according to the mass ratio of 7:1.5:1.5 and added into the bowl, and the bowl is ground until no large white particles exist. 1mL of Nitrogen Methyl Pyrrolidone (NMP) is transferred by a liquid transfer gun and added into a grinding bowl for grinding for 40-60 mins. Coating the slurry on copper film, vacuum drying at 80 deg.C for 24 hr, and cutting into round electrode slice with diameter of about 14 mm.

The following are the results of the study of the battery performance of the electrode sheets prepared in examples 1 to 3 and comparative example 1:

FIG. 9 shows the current density at 0.1A g^-1The corresponding constant current discharge (GDC) curves of the hollow carbon nanospheres and the activated carbon electrodes. As shown in fig. 9a, the first relatively flat discharge plateau occurs between 1-1.5V during the first discharge cycle of the hollow nanocarbon sphere electrode, where about 40% of the initial capacity is provided, mainly due to electrolyte decomposition. Between 0 and 0.6V a steep slope of a steep length occurs, providing about 60% of the initial capacity. In the following discharging process, a fine platform appears below 0.25V, which is the capacity provided by the residual functional groups on the surface of the hollow carbon nanospheres after annealing at 800 ℃. The initial discharge capacity of the hollow carbon nanospheres is 1017 mAh g^-1The initial coulombic efficiency was only 11.9%, which is mainly due to electrode instability, consuming electrolyte on the surface of the hollow nanocarbon sphere to form SEI layer. Although the initial coulombic efficiency of the hollow nanocarbon sphere electrode is relatively low, it shows excellent cycle stability, which is mainly attributed to the fact that the diffusion distance of sodium ions is shortened by the structure of the internal and internal cavities of the unique conductive network in the hollow carbon sphere. In comparison, the Activated Carbon (AC) electrode, when discharged in the first cycle, presents a first steeper discharge plateau between 0.9 and 1.5V, where it provides about 30% of its initial capacity, mainly due to electrolyte decomposition. Between 0 and 0.5V a steep slope of a steep length occurs, providing about 70% of the initial capacity. During the subsequent discharge process, a fine plateau below 0.2V appears, which is longer than the plateau of the hollow nanocarbon spheres and therefore provides more capacity, mainly because the activity is higher after the higher annealing temperature treatment, the graphite level is higher, but the interlayer spacing is larger than that of graphite, and sodium ions can be intercalated, and thus the capacity is higher.

In FIG. 10a, the PP @ CS-0.30 electrode was swept at a rate of 0.1 mV s^-1The voltage window is 0.The CV diagram of 01-2V shows the first sharp reduction peak at 1.4V during the first discharge cycle, and the small phosphorus molecule is further embedded with sodium corresponding to the discharge plateau of FIG. 10 b. At 0.8V a large package of reduction peaks occurs, mainly due to decomposition of the electrolyte. At the first cathodic scan, a sharp peak at 0.52V appears, and little charging plateau is evident after the first turn, corresponding to the first turn charging plateau of fig. 10 b.

FIG. 10b shows the current density at 0.1A g^-1PP @ CS-0.30 electrode constant current discharge (GDC) curve. The initial discharge capacity of the PP @ CS-0.30 electrode is 2338 mAh g^-1The coulomb efficiency is 72%, which is mainly due to the small phosphorus molecules that can effectively wash off the outer surface of the carbon sphere, the hollow carbon sphere is beneficial to the full contact between the small phosphorus molecules and the electrolyte, the phosphorus can be utilized to the maximum degree, and the diffusion distance of the sodium ions and the transmission distance of the electrons can be shortened. However, the volume expansion of the small phosphorus molecules in the PP @ CS-0.30 complex during charging and discharging results in rapid capacity fade and poor cycle stability.

To further study the sodium storage performance of the carbon spheres, as shown in FIG. 11, at 0.1A g^-1The cycling stability of the hollow carbon nanospheres and the activated carbon electrode to the sodium ion battery was tested at the current density of (a). Specifically, the empty nanocarbon spheres were cycled at 35 cycles, and then at 0.1A g^-1The current is 122 mA h g^-1The capacity retention was only 77.8%. However, the activated carbon electrode was subjected to 35 cycles of the cycle stability test at the same current density, which also provided 132 mAh g^-1The capacity retention ratio of (2) was 80.5%. The cycle performance test proves that the sodium storage mechanism of the activated carbon electrode is different from that of the hollow nano carbon sphere due to the high graphitization degree of the activated carbon electrode, so the capacity contribution of the activated carbon electrode is also different.

As shown in FIG. 12, the PP @ CS-0.30 composite electrode was at 0.1A g^-1Cycling stability plot at low current density. The initial discharge capacity of the PP @ CS-0.30 electrode is 2338 mAh g^-1Accordingly, the initial coulombic efficiency was 72%. The volume change of the small phosphorus molecules in the sodium intercalation and sodium desorption processes causes the instability of an SEI film on the surface of an electrode, so that the charge-discharge balance cannot be quickly achievedThus, the discharge capacity of the PP @ CS-0.30 electrode decays rapidly during the first five initial cycles. As coulombic efficiency approaches 100%, the cell tends to stabilize with little capacity loss in the next 70 cycles.

Meanwhile, the multiplying power performance of the hollow carbon nanospheres and the activated carbon electrodes under different current densities is compared. As shown in fig. 13, the hollow nanocarbon sphere electrodes were at 0.1, 0.2, 0.5, 1 and 0.1A g^-1The reversible discharge capacities at current densities of 131, 96, 67, 42 and 89 mA hr g, respectively^-1. Correspondingly, at 0.1, 0.2, 0.5, 1 and 0.1A g^-1The reversible discharge capacities of the activated carbon electrodes were 168, 107, 78, 53 and 89 mAh g at the current densities of (A)^-1. By combining the above analysis, the reversible discharge capacity of the hollow carbon nanospheres and the activated carbon electrodes is different under the same current density: the hollow carbon nanospheres have a fine platform below 0.25V, which is the capacity provided by the reaction of surface residual functional groups and sodium ions after the hollow carbon nanospheres are annealed at 800 ℃, but the activated carbon electrodes have a fine platform below 0.2V, which is longer than the platform of the hollow carbon nanospheres, so that more capacity is provided, mainly because the activity is higher in graphite degree after being treated at a higher annealing temperature, but the interlayer spacing is larger than that of graphite, and sodium ions can be embedded, so that the capacity is higher.

The rate performance of PP @ CS-0.30 and PP @ CS-0.17 composite electrodes at different current densities was tested. As shown in FIG. 14, the PP @ CS-0.30 composite electrodes were at 0.1, 1, 2, 4, 6, 8 and 1A g^-1Exhibits excellent reversible discharge capacities at current densities of 1761, 907, 712, 609, 516, 426 and 705 mA h g, respectively^-1. Correspondingly, the reversible discharge capacities of the PP @ CS-0.17 composite electrodes were 1023, 715, 471, 418, 378, 322 and 562 mAh g^-1. During the initial low current charge and discharge process, the battery is unstable, resulting in low initial coulombic efficiency of the battery. Compared with PP @ CS-0.17, PP @ CS-0.17 shows relatively stable sodium intercalation behavior at the same current density even though the rate performance of the PP @ CS-0.30 composite electrode is better. The excellent rate performance of the PP @ CS compound is mainly attributed to the fact that small phosphorus molecules are limited in hollow nanometerIn the mesopores on the inner sea bladder-shaped surface of the carbon spheres, the inner cavity provides a larger contact area with red phosphorus, and the transmission distance of sodium ions is shortened.

Fig. 15 is a cycle stability test of hollow nanocarbon sphere electrodes at high current. Specifically, the hollow nano carbon ball electrode is 0.1A g^-1Is activated for 10 cycles, the initial coulombic efficiency is only 13.5%. But increasing the current density to 1A g^-1In time, after 300 cycles, the liquid can still maintain 55 mA h g^-1The capacity retention rate is as high as 84.1%, and the capacity hardly decays after the battery is stabilized.

FIG. 16a shows PP @ CS-0.30 and PP @ CS-0.17 composite electrodes at 2A g^-1Graph of cycling stability at high current density. First at 0.1A g^-1The initial reversible discharge capacity of the PP @ CS-0.30 electrode is 1863 mAh g^-1Accordingly, the initial coulombic efficiency was 68.9%. Then increasing the current density to 2A g^-1The PP @ CS-0.30 electrode contributed 1058 mAh g^-1The reversible discharge capacity of the lithium secondary battery can still be maintained to 536 mAh g after 300 cycles of deep circulation^-1The capacity retention rate was 50.7%, and the capacity loss rate per cycle was 0.1%. For comparison, the PP @ CS-0.17 complex with a smaller load was at 0.1A g^-1The initial reversible discharge capacity at a small current density of 1716 mAh g^-1Initial coulombic efficiency of 72.5%, and further increase the current density to 2A g^-1Then, 534 mAh g is shown^-1The reversible discharge capacity of the lithium secondary battery can still be kept to 470 mAh g after 300 cycles of deep circulation^-1The capacity retention rate was 88%, and the capacity loss rate per cycle was 0.04%. As can be seen from fig. 16, the PP @ CS-0.30 composite with a larger phosphorus loading has a higher discharge capacity than PP @ CS-0.17, but decays faster, mainly inside the hollow nanocarbon spheres, and the larger the phosphorus loading requires a larger volume space for phosphorus volume expansion, so the larger the space inside the hollow nanocarbon spheres, the smaller the PP @ CS-0.17 loading, and therefore the smaller the capacity decay rate. As shown in FIG. 16b, the impedance plots of PP @ CS-0.30 and PP @ CS-0.17, PP @ CS-0.30 is smaller than PP @ CS-0.17, so PP @ CS-0.30 is at either magnificationThe performance and the cycling stability are better than PP @ CS-0.17. Even at 2A g^-1At high current densities, but PP @ CS-0.30 and PP @ CS-0.17 were still able to contribute 536 mAh g after 300 cycles^-1And 470 mAh g^-1The reversible discharge capacity is mainly benefited from liquid phase phosphorus injection to change a red phosphorus block into small phosphorus molecules, the limited range is limited in the mesopores of the hollow nano carbon spheres under the assistance of ultrasound, the unique hollow sea urchin-shaped interior of the carbon spheres increases the contact area with the small phosphorus molecules, the sodium ion transmission distance is shortened, and meanwhile, the sufficient internal space can accommodate the volume expansion of phosphorus.

Meanwhile, the results of the related tests of examples 1 to 3 and comparative example 1 can be concluded as follows:

the hollow nano carbon spheres with the inner surface in the shape of sea urchins are prepared by utilizing a silicon dioxide template method, the hollow nano carbon spheres and the active carbon are used as electrode materials for a sodium ion battery, and experimental data show that the simple hollow nano carbon spheres are used for storing energy, so that the commercial prospect challenge is huge due to the low capacity of the hollow nano carbon spheres. However, the hollow nano carbon sphere has a unique hollow sea urchin-shaped internal structure and is very stable in a large-current charging and discharging process, so that the carbon material with the unique structure is compounded with other high-theoretical-capacity substances to be used as an energy storage material, so that the hollow nano carbon sphere is a judicious choice.

The invention further converts red phosphorus into soluble small phosphorus molecules by etching through a liquid phase method, and then ultrasonically compounds the soluble small phosphorus molecules with the hollow nano carbon spheres. Because the unique structure of the hollow nano carbon sphere can increase the contact area with small phosphorus molecules, the transmission distance of sodium ions can be shortened, and meanwhile, the sufficient internal space can accommodate the volume expansion of phosphorus, the PP @ CS-0.30 electrode is 2A g^-1The current density of the current can still be maintained to 536 mAh g after 300 cycles of deep circulation^-1The reversible capacity of (2) has a capacity retention of 50.7% and a capacity loss rate per cycle of only 0.1%.

The above disclosure is only for the purpose of illustrating the preferred embodiments of the present invention, and it is therefore to be understood that the invention is not limited by the scope of the appended claims.

Claims

1. a method for liquid phase injection of phosphorus in hollow nano carbon spheres, is characterized in that: it comprises the following steps: red phosphorus becomes small phosphorus molecule under the etching of sodium ethoxide, takes etching supernatant and hollow nanometer The carbon spheres are mixed with ultrasonic reaction to obtain liquid-phase phosphorus-injected hollow nano-carbon spheres.

2 . The method for liquid phase injection of phosphorus in hollow carbon nanospheres according to claim 1 , wherein the activation reaction of the red phosphorus and sodium ethoxide is carried out in a dimethyl sulfoxide solvent. 3 .

3. the method for liquid phase injection of phosphorus in hollow carbon nanospheres according to claim 2, is characterized in that: described red phosphorus, sodium ethoxide in dimethyl sulfoxide solvent, under argon protection, are heated to The activation reaction was carried out by refluxing.

4 . The method for liquid-phase injection of phosphorus in hollow carbon nanospheres according to claim 1 , wherein the cavity inside the hollow carbon nanospheres is sea urchin-shaped. 5 .

5. The method for liquid phase injection of phosphorus in hollow carbon nanospheres according to claim 4, wherein the preparation process of the hollow carbon nanospheres comprises the following steps:

(1) Preparation of sea urchin-like silica template;

(2) Amination of the sea urchin-shaped silica template to obtain an aminated silica template;

(3) Glucose is wrapped around the aminated silica template and calcined to obtain carbon spheres;

(4) Removing the silica template in the carbon spheres to obtain hollow nano-carbon spheres.

6. The method for liquid phase injection of phosphorus in hollow carbon nanospheres according to claim 5, characterized in that: in step (1), cetylpyridinium bromide and urea are dissolved in water, and the solution system is stirred by stirring From colorless to milky white, solution system A is obtained, tetraethyl silicate and n-amyl alcohol are added and dispersed in cyclohexane to obtain solution system B, solution system A and solution system B are mixed and heated to 110-130 React at ℃, centrifuge to obtain a white solid after cooling, and keep the white solid at 70-90 ℃ for 6-10 hours, and calcinate at 500-600 ℃ for 4-8 hours in an air atmosphere.

7. The method for liquid-phase injection of phosphorus in hollow carbon nanospheres according to claim 6, wherein in step (1), the white solid is placed at 70-90°C for 6-10h and then kept at 10°C/ The heating rate of min was heated to 500-600 °C.

8 . The method for liquid phase injection of phosphorus into hollow carbon nanospheres according to claim 5 , wherein in step (2), the sea urchin-shaped silica template is added to toluene, and heated to 50 ℃ under stirring. 9 . -70°C, then adding aminopropyltriethoxysilane to react, and centrifuging to obtain an aminated silica template after the reaction.

9 . The method for liquid phase injection of phosphorus into hollow carbon nanospheres according to claim 5 , wherein in step (3), the aminated silica template and glucose are added to the water to react, and after the reaction is completed, the The solid was collected to obtain a yellow solid, which was dried and ground into powder, and calcined at 700-900° C. for 1.5-2.5 h in an argon atmosphere.

10. The red phosphorus anode material prepared by the method of liquid-phase phosphorus injection in hollow carbon nanospheres according to any one of claims 1-9.