Phosphorus-carbon composite negative electrode material, its preparation method, negative electrode and sodium-ion battery

Abstract

The present invention relates to the technical field of sodium battery materials, and discloses a phosphorus-carbon composite anode material, a preparation method thereof, an anode, and a sodium-ion battery. The phosphorus-carbon composite anode material includes carbon spheres and red phosphorus filled in the carbon spheres. The carbon spheres are composed of a carbon layer shell and a porous carbon core located inside the carbon layer shell. The red phosphorus is filled between the porous carbon core and the carbon layer shell and in the pores of the porous carbon core. The preparation method includes filling red phosphorus in the pores of the porous carbon core and between the porous carbon core and the carbon layer shell. The anode includes the above-mentioned anode material. The sodium-ion battery includes the above-mentioned anode. The composite anode material provided by the present invention can achieve excellent cycle performance of maintaining a specific capacity of 1465 mAh / g after 1000 cycles at a current density of 1 A / g.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium battery materials, and in particular, to a phosphorus-carbon composite negative electrode material, a preparation method thereof, a negative electrode, and a sodium ion battery. Background Art

[0002] Sodium ion batteries are considered potential alternatives to lithium ion batteries due to the wide distribution and rich reserves of sodium. However, the specific capacity of most of the currently commercialized hard carbon materials is less than 300 mAh / g, which greatly limits the development of sodium ion batteries. Red phosphorus can provide a specific capacity of 2596 mAh / g through an alloying reaction with sodium, making it an excellent negative electrode material for sodium ion batteries. However, the poor conductivity of red phosphorus makes it difficult to achieve its theoretical capacity. At the same time, the large volume expansion also restricts the cycle stability of red phosphorus.

[0003] In traditional technologies of carbon-coated red phosphorus, red phosphorus can only expand outward to release the impact caused by the huge volume change. At the same time, due to the poor conductivity of red phosphorus itself, the internal red phosphorus may not be able to fully exert its performance.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a phosphorus-carbon composite negative electrode material, a preparation method thereof, a negative electrode, and a sodium ion battery.

[0006] The present invention is implemented as follows:

[0007] In a first aspect, the present invention provides a phosphorus-carbon composite negative electrode material, including carbon spheres and red phosphorus filled inside the carbon spheres. The carbon spheres are composed of a carbon layer shell and a porous carbon core located inside the carbon layer shell, and the red phosphorus is filled between the porous carbon core and the carbon layer shell and in the pores of the porous carbon core.

[0008] In an optional embodiment, the mass ratio of the carbon spheres to the red phosphorus is 1:1 to 3.

[0009] In a second aspect, the present invention provides a preparation method of a phosphorus-carbon composite negative electrode material as described in the foregoing embodiment, including:

[0010] Filling red phosphorus in the pores of the porous carbon core and between the porous carbon core and the carbon layer shell.

[0011] In an optional embodiment, the method of filling red phosphorus is chemical vapor deposition.

[0012] In an optional embodiment, the method of filling red phosphorus is specifically:

[0013] After mixing the carbon spheres and red phosphorus, keep them at 500 - 800 °C under a vacuum degree < -0.08 Mpa for 1 - 4 h;

[0014] Preferably, after filling with red phosphorus, it further includes calcining the obtained material in a mixed atmosphere of hydrogen and argon at 200-400 °C for 1-5 h.

[0015] In an alternative embodiment, before filling with red phosphorus, it includes preparing carbon spheres, and the preparation method of the carbon spheres includes:

[0016] Calcine the composite polymer powder in a mixed atmosphere with an oxygen-to-inert gas volume ratio of 1-5:1 at 200-300 °C for 1-5 h; then adjust the oxygen-to-inert gas volume ratio to 1:10-20 and the temperature to 500-1000 °C and calcine for 1-5 h to obtain the calcined powder. The composite polymer powder is composed of a coated polymer coating metal coordination polymer particles. The coated polymer is at least one of polypyrrole, polyaniline, and polypyridine, and the metal coordination polymer is formed by complexing transition metal ions and organic acids;

[0017] Perform pickling on the calcined powder to remove metal oxides in the calcined powder to obtain carbon spheres;

[0018] Preferably, the pickling method is: soak the calcined powder in 0.3-0.5 mol / L hydrochloric acid and perform a water bath at 50-80 °C for 1-5 h.

[0019] In an alternative embodiment, the transition metal ions are at least one of manganese, iron, nickel, and cobalt, and the organic acid is at least one of trimesic acid, terephthalic acid, biphenyl dicarboxylic acid, and 1,4-naphthalene dicarboxylic acid.

[0020] In an alternative embodiment, the preparation method of the composite polymer powder includes:

[0021] Disperse the metal coordination polymer and the monomer for synthesizing the coated polymer in a solution, then add an initiator to the solution and react fully. After the reaction ends, obtain a solid-liquid mixture, and extract the solid substance in the solid-liquid mixture to obtain the composite polymer;

[0022] Preferably, grind the composite polymer to obtain the composite polymer powder;

[0023] Preferably, the initiator is ammonium persulfate;

[0024] Preferably, the ratio of the coated polymer to the metal coordination polymer is 5-0.5:1;

[0025] Alternatively, the ratio of the monomer of the coated polymer to the metal coordination polymer is 25-50:0.5.

[0026] In a third aspect, the present invention provides a negative electrode, including the negative electrode material as described in the foregoing embodiments or the negative electrode material prepared by the preparation method of any one of the foregoing embodiments.

[0027] In a fourth aspect, the present invention provides a sodium-ion battery, including a negative electrode as described in the foregoing embodiments.

[0028] The present invention has the following beneficial effects:

[0029] Since red phosphorus is filled in the pores of the porous core and between the core and the shell, the red phosphorus expands inside the carbon sphere. Its outward expansion is restricted by the carbon layer shell and the outward expansion is buffered. When expanding inward, the presence of the porous core provides a buffer for its inward expansion. Therefore, the phosphorus-carbon composite negative electrode material provided in this application can effectively inhibit the structural rupture caused by the huge volume change of red phosphorus, avoid the large loss of active sites, and improve the cycle stability. Experiments prove that the phosphorus-carbon composite material provided in the embodiments of this application has better cycle stability and rate performance, and can achieve an excellent cycle performance of maintaining a specific capacity of 1465 mAh / g after 1000 cycles at a current density of 1 A / g. Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0031] Figure 1 Schematic diagram of the synthesis route of the phosphorus-carbon composite negative electrode material provided in this application;

[0032] Figure 2 Rate performance graph of the phosphorus-carbon composite negative electrode material prepared in Example 1;

[0033] Figure 3 Cycle performance graph of the phosphorus-carbon composite negative electrode material prepared in Example 1;

[0034] Figure 4 Transmission electron microscope image of the phosphorus-carbon composite negative electrode material prepared in Example 1. Detailed Embodiments

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0036] The phosphorus-carbon composite negative electrode material, its preparation method, negative electrode, and sodium-ion battery provided in the embodiments of the present invention will be specifically described below.

[0037] As Figure 1 shown, the phosphorus-carbon composite anode material provided by the embodiment of the present invention includes carbon spheres and red phosphorus filled in the carbon spheres. The carbon spheres are composed of a carbon layer shell and a porous carbon core located inside the carbon layer shell, and the red phosphorus is filled between the porous carbon core and the carbon layer shell and in the pores of the porous carbon core.

[0038] For the above phosphorus-carbon composite anode material, since the red phosphorus is filled in the pores of the porous inner core and between the inner core and the outer shell, the red phosphorus expands inside the carbon sphere. Its outward expansion is restricted by the carbon layer shell and the outward expansion is buffered. When expanding inward, the presence of the porous inner core provides a buffer for its inward expansion. Therefore, the phosphorus-carbon composite anode material provided by this application can effectively inhibit the structural rupture caused by the huge volume change of red phosphorus, avoid a large loss of active sites, and improve the cycle stability. Experiments prove that the phosphorus-carbon composite material provided by the embodiment of this application has better cycle stability and rate performance, and can achieve an excellent cycle performance of maintaining a specific capacity of 1465 mAh / g after cycling 1000 times at a current density of 1 A / g.

[0039] Preferably, the mass ratio of the carbon spheres to the red phosphorus is 1:1 to 3 (such as 1:1, 1:2 or 1:3), and the ratio is particularly preferably around 1:3, such as 1:2.5 to 3.5.

[0040] The phosphorus-carbon composite anode material composed of the carbon spheres and the red phosphorus with the above mass ratio has more excellent electrochemical performance.

[0041] The preparation method of the above phosphorus-carbon composite anode material provided by the embodiment of this application includes:

[0042] Filling red phosphorus in the pores of the porous carbon core and between the porous carbon core and the carbon layer shell.

[0043] As Figure 1 shown, the specific preparation method is:

[0044] S1. Prepare composite polymer powder

[0045] Disperse the metal coordination polymer and the monomers (at least one of pyrrole, aniline and pyridine) for synthesizing the coating polymer in an ethanol solution, then add an initiator to the ethanol solution, and react for 8 to 12 h (such as 8 h, 10 h or 12 h) in a constant temperature water bath at 70 to 90 °C (such as 70 °C, 80 °C or 90 °C) until the reaction is sufficient. After the reaction, obtain a solid-liquid mixture, filter it, extract the solid substance in the solid-liquid mixture, and then rinse it twice with ethanol and deionized water respectively, and dry it at 70 to 90 °C (such as 70 °C, 80 °C or 90 °C) to obtain the composite polymer;

[0046] The composite polymer is ground to obtain a composite polymer powder, which is composed of a coated polymer coating metal coordination polymer particles.

[0047] The above metal coordination polymer is formed by complexing transition metal ions and organic acids.

[0048] Preferably, the transition metal ions are at least one of manganese, iron, nickel and cobalt, and the organic acid is at least one of trimellitic acid, terephthalic acid, biphenyl dicarboxylic acid and 1,4-naphthalene dicarboxylic acid.

[0049] Preferably, the initiator is ammonium persulfate; further, the mass ratio of the initiator to the monomer is 1 / 1000 - 1 / 100:1, particularly preferably around 1 / 100:1, such as 1 / 200 - 1 / 100:1.

[0050] Preferably, to ensure that the prepared carbon spheres have a stable structure and an appropriate internal space size, the ratio of the coated polymer to the metal coordination polymer is 0.5 - 5:1 (such as 0.5:1, 1:1, 2:1, 3:1 or 5:1). This ratio relationship is just the ratio relationship that satisfies the reaction, without raw material residue.

[0051] Alternatively, the ratio of the monomer of the coated polymer to the metal coordination polymer is 25 - 50:0.5 (such as 25:0.5, 35:0.5 or 50:0.5). This ratio relationship is the ratio relationship when the coated polymer is in excess. Usually, in actual production, the coated polymer is added in excess.

[0052] S2. Preparation of carbon spheres

[0053] The composite polymer powder is calcined in a mixed atmosphere with an oxygen to inert gas volume ratio of 1 - 5:1 (such as 1:1, 2:1, 3:1 or 5:1) at 200 - 300 °C (such as 200 °C, 250 °C or 300 °C) for 1 - 5 h (such as 1 h, 2 h, 3 h or 5 h); then the oxygen to inert gas volume ratio is adjusted to 1:10 - 20 (such as 1:10, 1:12, 1:15 or 1:20), and the temperature is 500 - 1000 °C (such as 500 °C, 800 °C or 1000 °C) and calcined for 1 - 5 h (such as 1 h, 2 h, 3 h or 5 h) to obtain the calcined powder.

[0054] During the calcination process, the wrapped polymer finally pyrolyzes and carbonizes to form the outermost carbon shell. The internal metal coordination polymer forms an oxide shell layer due to the action of oxygen, and the metal ions gather outward. The organic small molecules are oxidized into gases such as carbon dioxide and volatilize, leaving cavities. Finally, the carbon molecules wrapped on the outer layer diffuse inward due to the concentration gradient to form carbon spheres and wrap the internal nano-scale oxides therein.

[0055] The calcined powder is pickled with acid to remove metal oxides in the calcined powder to obtain carbon spheres.

[0056] Preferably, the pickling method is as follows: the calcined powder is immersed in hydrochloric acid with a concentration of 0.3 - 0.5 mol / L (such as 0.3 mol / L, 0.4 mol / L or 0.5 mol / L) and water-bathed at 50 - 80 °C (such as 50 °C, 70 °C or 80 °C) for 1 - 5 h (such as 1 h, 2 h, 3 h or 5 h).

[0057] S3. Filling red phosphorus

[0058] Red phosphorus is filled between the porous carbon core and the carbon layer shell and into the pores of the porous carbon core by chemical vapor deposition.

[0059] Specifically, the filling method is to mix the carbon spheres and red phosphorus according to a mass ratio of 1:1 - 3 (such as 1:1, 1:2 or 1:3), and then keep them at 500 - 800 °C (such as 500 °C, 600 °C or 800 °C) under a vacuum degree of < -0.08 Mpa for 1 - 4 h (such as 1 h, 2 h, 3 h or 4 h) to complete the filling of red phosphorus.

[0060] Preferably, after filling red phosphorus, it further includes calcining the obtained material in a mixed atmosphere of hydrogen and argon at 200 - 400 °C (such as 200 °C, 300 °C or 400 °C) for 1 - 5 h (such as 1 h, 2 h, 3 h or 5 h). The function of this step of calcining is to remove white phosphorus in the material.

[0061] Preferably, the volume ratio of hydrogen to argon is 1:18 - 20 (such as 1:18, 1:19 or 1:20).

[0062] The negative electrode provided by the embodiment of the present application includes the negative electrode material provided by the embodiment of the present application or the negative electrode material prepared by the preparation method provided by the embodiment of the present application.

[0063] The sodium ion battery provided by the embodiment of the present application includes the negative electrode provided by the embodiment of the present application.

[0064] The features and properties of the present invention will be further described in detail below in conjunction with embodiments.

[0065] Example 1

[0066] Weigh 0.5 g of metal-organic framework (Mn-BTC) and 25 g of pyrrole, disperse them in 150 ml of ethanol to prepare solution A. Weigh 0.25 g of ammonium persulfate, dissolve it in 10 ml of deionized water, and then add it to solution A. Keep the mixture in a water bath at 80 °C for 10 h. Then, filter the above mixture and wash it twice with ethanol and deionized water respectively. After drying at 80 °C and grinding, the metal-organic framework coated with polypyrrole is obtained. Place the ground material in a tube furnace and calcine it at 280 °C for 3 h in a mixed atmosphere of oxygen and argon (volume ratio 3:1), and then calcine it at 800 °C for 3 h in a mixed atmosphere of oxygen and argon (volume ratio 1:19). Add the sintered powder and hydrochloric acid with a concentration of 0.4 mol / L to a beaker at a ratio of 1 ml / mg, keep it in a water bath at 60 °C for 2 h, then filter out the solid substance and dry it to obtain carbon spheres. Mix the carbon spheres and red phosphorus at a mass ratio of 1:3, place them in a tube furnace, keep the temperature at 550 °C and the vacuum degree < -0.08 Mpa for 3 h, and then calcine them at 300 °C for 3 h in a mixed atmosphere of hydrogen and argon (volume ratio 1:19) to obtain the phosphorus-carbon composite material.

[0067] Example 2

[0068] This example is basically the same as Example 1, except that:

[0069] Weigh 0.5 g of metal-organic framework (Mn-BTC) and 50 g of pyrrole, disperse them in 200 ml of ethanol to prepare solution A. Weigh 0.5 g of ammonium persulfate, dissolve it in 10 ml of deionized water, and then add it to solution A. Keep the mixture in a water bath at 80 °C for 10 h.

[0070] Example 3

[0071] This example is basically the same as Example 1, except that:

[0072] Weigh 0.5 g of metal-organic framework (Mn-BTC) and 25 g of pyrrole, disperse them in 150 ml of ethanol to prepare solution A. Weigh 0.025 g of ammonium persulfate, dissolve it in 10 ml of deionized water, and then add it to solution A. Keep the mixture in a water bath at 80 °C for 10 h.

[0073] Example 4

[0074] This example is basically the same as Example 1, except that:

[0075] The metal-organic framework used in this example is Ni-BTC.

[0076] Example 5

[0077] This example is basically the same as Example 1, except that:

[0078] The metal coordination polymer used in this example is Mn-BDC.

[0079] Example 6

[0080] This example is basically the same as Example 1, except that:

[0081] It is replaced with an equal amount of aniline used in this example.

[0082] Example 7

[0083] This example is basically the same as Example 1, except that:

[0084] It is replaced with an equal amount of pyridine used in this example.

[0085] Example 8

[0086] This example is basically the same as Example 1, except that:

[0087] The mass ratio of carbon spheres to red phosphorus is 1:1.

[0088] Comparative Example

[0089] The experimental steps in this example are basically the same as those in Example 1, except that:

[0090] The carbon spheres are replaced with an equal amount of Ketjenblack.

[0091] Experimental Example 1

[0092] The phosphorus-carbon composite materials prepared in the above examples and comparative examples are selected to assemble coin cells for testing the electrochemical performance. In the fabrication of coin cells, a sodium metal sheet is selected as the counter electrode, and a propylene carbonate (PC) solution containing 1.0 M NaPF 6 and 3.0% FEC is used as the electrolyte. The negative electrode uses N-methylpyrrolidone (NMP) as the solvent, and 90 wt% active material, 5 wt% acetylene black, and 5 wt% polyvinylidene fluoride (PVDF) are mixed evenly, coated on aluminum foil, and placed in a vacuum drying oven at 80 °C for vacuum drying for 12 h. After the baked electrode sheet is roll-pressed and cut into 12 mm circular pieces and weighed, it is placed in a vacuum glove box for coin cell assembly.

[0093] The experimental results are recorded in Table 1 and Figure 2 and Figure 3 in.

[0094] Table 1 Test Results of Each Example and Comparative Example

[0095]

[0096]

[0097] As can be seen from the above table, the negative electrode materials prepared in the embodiments of the present application all have good electrochemical performance. In the comparative example, Ketjen black with a porous structure was used to replace the carbon spheres in Example 1. During the preparation process, red phosphorus would also fill into the pores of Ketjen black. Comparing Example 1 with the comparative example, the effect of Example 1 is significantly better, indicating that using the carbon spheres provided in the present application to prepare the carbon-phosphorus composite material can achieve better technical effects compared with the existing ordinary porous structure carbon as the preparation raw material.

[0098] Figure 2 Fig. is the rate performance graph of the phosphorus-carbon composite negative electrode material prepared in Example 1, and the test voltage range is 0.01 - 1.5V. At a current density of 0.2 A·g -1 , the material exhibits a specific capacity of 1650 mAh / g. When the current density increases to 5 A / g, the material still exhibits a specific capacity of 1290 mAh / g, demonstrating excellent rate performance. In addition, when the current density returns to 0.2 A·g -1 , the specific capacity of the material returns to 1645 mAh / g, showing good stability.

[0099] Figure 3 Fig. is the cycle performance graph of the prepared phosphorus-carbon composite negative electrode material. After 1000 cycles at a current density of 1 A·g -1 , the reversible specific capacity can still remain at 88.7%, showing good cycle stability.

[0100] Experimental Example 2

[0101] The microscopic morphology of the negative electrode material prepared in Example 1 was photographed. As Figure 4 shown, it can be seen from the figure that the negative electrode material prepared by the preparation method provided in the embodiments of the present application is spherical particles, with a porous inner core inside the particles, and red phosphorus is filled between the porous inner core and the carbon layer outer shell.

[0102] In summary, for the phosphorus-carbon composite negative electrode material provided in the present application, since red phosphorus is filled in the pores of the porous inner core and between the inner core and the outer shell, red phosphorus expands inside the carbon spheres. Its outward expansion is restricted by the carbon layer outer shell and the outward expansion is buffered. When expanding inward, the presence of the porous inner core provides a buffer for its inward expansion. Therefore, the phosphorus-carbon composite negative electrode material provided in the present application can effectively inhibit the structural rupture caused by the huge volume change of red phosphorus, avoid a large loss of active sites, and improve the cycle stability.

[0103] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a phosphorus-carbon composite anode material, characterized in that, it includes: Preparing carbon spheres, and the preparation method of the carbon spheres includes: Placing the composite polymer powder in a mixed atmosphere with a volume ratio of oxygen to inert gas of 1-5:1 and calcining at 200-300°C for 1-5 h; then adjusting the volume ratio of oxygen to inert gas to 1:10-20 and the temperature to 500-1000°C and calcining for 1-5 h to obtain the calcined powder. The composite polymer powder is composed of a coating polymer coating metal coordination polymer particles. The coating polymer is at least one of polypyrrole, polyaniline and polypyridine, and the metal coordination polymer is formed by complexing transition metal ions and organic acids; Performing pickling on the calcined powder to remove metal oxides in the calcined powder to obtain the carbon spheres. The carbon spheres are composed of a carbon layer shell and a porous carbon core located inside the carbon layer shell; Filling red phosphorus in the pores of the porous carbon core and between the porous carbon core and the carbon layer shell.

2. The preparation method according to claim 1, characterized in that, the mass ratio of the carbon spheres to red phosphorus is 1:1-3.

3. The preparation method according to claim 1, characterized in that, the method of filling red phosphorus is chemical vapor deposition.

4. The preparation method according to claim 3, characterized in that, the specific method of filling red phosphorus is: After mixing the carbon spheres and the red phosphorus, keep them at 500-800°C under a vacuum of <-0.08 Mpa for 1-4 h.

5. The preparation method according to claim 1, characterized in that, after filling red phosphorus, it further includes calcining the obtained material in a mixed atmosphere of hydrogen and argon at 200-400°C for 1-5 h.

6. The preparation method according to claim 1, characterized in that, the pickling method is: soaking the calcined powder in 0.3-0.5 mol / L hydrochloric acid and performing water bath at 50-80°C for 1-5 h.

7. The preparation method according to claim 6, characterized in that, the transition metal ions are at least one of manganese, iron, nickel and cobalt, and the organic acid is at least one of trimellitic acid, terephthalic acid, biphenyl dicarboxylic acid and 1,4-naphthalene dicarboxylic acid.

8. The preparation method according to claim 1, characterized in that, the preparation method of the composite polymer powder includes: Dispersing the metal coordination polymer and the monomers for synthesizing the coating polymer in a solution, then adding an initiator to the solution, fully reacting, and obtaining a solid-liquid mixture after the reaction ends. Extracting the solid substance in the solid-liquid mixture to obtain the composite polymer.

9. The preparation method according to claim 8, characterized in that, grinding the composite polymer to obtain the composite polymer powder.

10. The preparation method according to claim 8, characterized in that, the initiator is ammonium persulfate.

11. The preparation method according to claim 8, characterized in that, the ratio of the coating polymer to the metal coordination polymer is 0.5-5:

1.

12. The preparation method according to claim 8, characterized in that, the ratio of the monomers of the coating polymer to the metal coordination polymer is 25-50:0.5.

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