Carbon nanotube material filled with inorganic salt, preparation method and suction filtration device

Abstract

The invention discloses a carbon nanotube material filled with inorganic salt, a preparation method and a suction filtration device. The preparation method comprises the following steps: S1, pretreating a carbon nanotube to obtain a carbon nanotube with an opened tip; s2, adding a carbon nanotube with an opened tip into a solution containing metal salt ions, and uniformly stirring to obtain a suspension; s3, carrying out primary suction filtration on the suspension by using an internal filling suction filtration device, gradually adjusting the suction filtration pressure from normal pressure to 10 <-7 > mbar in the primary suction filtration process, and determining the secondary suction filtration pressure according to a liquid drop dropping vibration frequency curve; s4, carrying out secondary suction filtration on the suspension, and obtaining a precursor by adopting the secondary suction filtration pressure determined in the step S3; and S5, calcining the precursor in a protective atmosphere to obtain the carbon nanotube material filled with inorganic salt, the outer surface cleanliness and the product uniformity of the carbon nanotube material are obviously improved, and the carbon nanotube material has relatively high rate capability and cycling stability when being applied to a negative electrode of a lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of battery electrode materials, and particularly to a carbon nanotube material filled with inorganic salts, a preparation method thereof, and a suction filtration device. Background Art

[0002] In recent years, the annual output of new energy vehicles worldwide has been growing at a rate of doubling every year, providing a broad application market for new types of ion batteries such as lithium-ion batteries. However, the theoretical capacity of the graphite negative electrode currently used in lithium-ion batteries is only 374 mAh g -1 , which cannot meet the long-range driving needs of new energy vehicles and frequently triggers discussions about "charging anxiety". The theoretical lithium storage capacity of metal compounds can usually reach more than twice that of graphite, and it is a very promising negative electrode material for the next generation of high-energy-density lithium-ion batteries. However, the volume change of such materials during lithium deintercalation and intercalation is significant, which easily leads to serious grain agglomeration, material pulverization, and capacity attenuation, thus limiting their practical applications.

[0003] Using carbon skeleton materials for nano-confined structure design is one of the main means to solve the volume expansion problem. The rigid carbon skeleton can inhibit the free expansion of the material, so that the surface density and geometric thickness of the electrode sheet do not change significantly. In addition, the grains confined in a limited space can avoid electrochemical secondary agglomeration and maintain the original nano-structure design. For example, Chinese Patent CN103979523B discloses a method for filling cadmium sulfide inside multi-walled carbon nanotubes, where the carbon nanotubes are dispersed in a cadmium-containing solution and subjected to hydrothermal treatment, and then the outer surface of the carbon nanotubes is washed with dimethyl sulfoxide. Another example is that in Chinese Patent CN103159169B, vanadium tetrachloride is vaporized and filled into a evacuated device containing carbon nanotubes to make the gaseous vanadium tetrachloride adhere. However, in these technologies, there is still a lack of a method to pour substances inside the carbon nanotubes while avoiding the contamination of the same substances on the outer wall of the carbon nanotubes, resulting in poor uniformity of the actually produced products and unable to achieve the original effect of the carbon nanotube-filled material.

[0004] In view of the above situation, there is an urgent need to develop a method for filling substances into carbon nanotubes while keeping the outer wall of the carbon nanotubes clean, which can improve the uniformity of the product and has high rate performance and cycle stability when used as the negative electrode of a lithium-ion battery. Summary of the Invention

[0005] Aiming at the defects existing in the prior art, the purpose of the present invention is to provide a carbon nanotube material filled with inorganic salts, a preparation method thereof and a suction filtration device, which can solve the problem of lacking a method to infuse substances inside carbon nanotubes while avoiding contamination of the outer walls of carbon nanotubes with the same kind of substances, significantly improving the cleanliness of the outer surface of the carbon nanotube material filled with inorganic salts and the uniformity of the product, and the carbon nanotube material filled with inorganic salts has high rate performance and cycle stability when applied to the negative electrode of a lithium-ion battery.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] The first aspect of the present invention provides a preparation method of a carbon nanotube material filled with inorganic salts, comprising the following steps:

[0008] S1, pretreat the carbon nanotubes to obtain carbon nanotubes with opened tips;

[0009] S2, add the carbon nanotubes with opened tips into a solution containing metal salt ions, and stir evenly to obtain a suspension;

[0010] S3, perform a primary suction filtration on the suspension using an internal filling suction filtration device. During the primary suction filtration process, gradually adjust the suction filtration pressure from atmospheric pressure to 10 -7 mbar, and determine the secondary suction filtration pressure according to the liquid drop dripping vibration frequency curve;

[0011] S4, perform a secondary suction filtration on the suspension using an internal filling suction filtration device, and use the secondary suction filtration pressure determined in step S3 to obtain a precursor;

[0012] S5, calcine the precursor under a protective atmosphere to obtain a carbon nanotube material filled with inorganic salts.

[0013] Preferably, in step S1:

[0014] The carbon nanotubes are selected from single-walled carbon nanotubes, multi-walled carbon nanotubes or a mixture of single-walled and multi-walled carbon nanotubes;

[0015] The pretreatment process is as follows: disperse the carbon nanotubes in a concentrated nitric acid solution, soak them under heating conditions, and then filter and wash them with deionized water to obtain carbon nanotubes with opened tips.

[0016] Preferably, in step S2:

[0017] The solution is an alcohol solution or an aqueous solution; and / or

[0018] The metal salt is selected from one or more of nitrates, sulfates, carbonates, chlorides that are soluble in water or alcohol.

[0019] Preferably, the metal salt is selected from FeCl3·5H2O, Cr(NO3)3·9H2O, CoCl3·6H2O, NaCl, ZnSO4 or Co(NO3)2.

[0020] Preferably, in step S2:

[0021] In the solution containing metal salt ions, the concentration of metal salt ions is 0.01 - 10 mol / L; and / or

[0022] In every 100 mL of the solution, the addition amount of the carbon nanotubes with open tips ≤ 10 g; and / or

[0023] The stirring time is 10 - 4000 min.

[0024] Preferably, step S3 includes the following processes:

[0025] S31, Add the suspension to the liquid addition funnel filled with a suction filtration device. Under the action of the suction filtration pressure, the suspension drips through the filter membrane into the liquid storage tank. Use a vibration monitor and a vibration recorder to obtain the vibration frequency curve of the liquid drops during the process of adjusting the suction filtration pressure from atmospheric pressure to 10 -7 mbar.

[0026] S32, Obtain the first pressure, second pressure, third pressure, and fourth pressure corresponding to the first peak value, second peak value, third peak value, and fourth peak value of the vibration frequency of the liquid drops according to the vibration frequency curve of the liquid drops;

[0027] S33, The secondary suction filtration pressure is between the third pressure and the fourth pressure.

[0028] Preferably, in step S4, the secondary suction filtration time is 1 - 1440 min.

[0029] Preferably, the secondary suction filtration time is 30 - 360 min.

[0030] Preferably, in step S5, the protective atmosphere is nitrogen or an inert gas, the calcination temperature is 300 - 1500 °C, and the calcination time is 10 - 240 min.

[0031] Preferably, in step S5, during the calcination process, an active substance is also added or an active gas is introduced.

[0032] Preferably, the active substance is one of NaH2PO2·H2O, sulfur, and phosphorus; the mass ratio of the active substance to the precursor is 1:100 - 10:1; or

[0033] The active gas is one of hydrogen sulfide, sublimed sulfur, phosphine, sublimed phosphorus, ammonia, nitrogen, and carbon dioxide.

[0034] The second aspect of the present invention provides a carbon nanotube material filled with inorganic salts, which is prepared by using the preparation method of the carbon nanotube material filled with inorganic salts as described in the first aspect of the present invention, and inorganic salts are filled inside the carbon nanotubes; the inner cavity diameter of the carbon nanotubes is 1-20 nm, and the average particle size of the inorganic salts is 2-10 nm.

[0035] The third aspect of the present invention provides an internal filling suction filtration device used in the preparation method of the carbon nanotube material filled with inorganic salts as described in the first aspect of the present invention, including a liquid storage tank, a liquid addition hopper arranged on the liquid storage tank, a pressure control device connected to the liquid storage tank, a vacuum pump connected to the pressure control device, a vibration monitor for monitoring the vibration frequency of liquid droplets dripping in the liquid storage tank, and a vibration recorder connected to the vibration monitor; a filter membrane is arranged between the liquid storage tank and the liquid addition hopper.

[0036] Preferably, a microscope camera is further arranged on the internal filling suction filtration device for observing the water film under the filter membrane condensing into liquid droplets and dripping.

[0037] Preferably, a fixing sticker is arranged at the bottom of the liquid storage tank.

[0038] Preferably, an air extraction pipeline is arranged between the pressure control device and the liquid storage tank, an air extraction bracket is arranged below the air extraction pipeline, and a fixing strap for preventing vibration is arranged at the bottom of the air extraction bracket.

[0039] The beneficial effects of the present invention are as follows:

[0040] 1. The present invention uses a unique internal filling suction filtration device to achieve the injection of substances inside the carbon nanotubes while avoiding the contamination of the outer wall of the carbon nanotubes with the same kind of substances. This method has universality in filling materials inside the carbon nanotubes, and the cleanliness of the outer surface of the carbon nanotubes, the product uniformity, and the large-scale preparation performance are all significantly improved;

[0041] 2. The carbon nanotube material filled with inorganic salts obtained by using the method of the present invention has a clean outer surface, and lithium storage active nanocrystals are uniformly filled inside. The size of the nanocrystals restricted in the inner cavity of the carbon nanotubes is not larger than the inner cavity diameter of the carbon nanotubes, and the volume expansion during lithium insertion is inhibited, thereby significantly improving the rate performance and cycle performance;

[0042] 3. The preparation method of the carbon nanotube material filled with inorganic salts of the present invention can save raw materials, has low cost, and the process is controllable, and is suitable for large-scale production. Description of the Drawings

[0043] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments read in conjunction with the accompanying drawings:

[0044] Figure 1 Schematic flow chart of the preparation method of the carbon nanotube material filled with inorganic salt of the present invention;

[0045] Figure 2 Schematic diagram of the liquid drop dripping frequency curve during the first suction filtration process of the present invention;

[0046] Figure 3 Schematic structural diagram of the internal filling suction filtration device used in the preparation method of the carbon nanotube material filled with inorganic salt of the present invention;

[0047] Figure 4 Low-magnification TEM image of the carbon nanotube material filled with cobalt phosphide prepared in Example 1 of the present invention;

[0048] Figure 5 High-magnification TEM image of the carbon nanotube material filled with cobalt phosphide prepared in Example 1 of the present invention;

[0049] Figure 6 Rate performance curve of the carbon nanotube material filled with cobalt phosphide prepared in Example 1 of the present invention as a lithium-ion negative electrode material;

[0050] Figure 7 Cycling performance curve of the carbon nanotube material filled with cobalt phosphide prepared in Example 1 of the present invention as a lithium-ion negative electrode material. Detailed Description of the Invention

[0051] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form.

[0052] Combined with Figure 1 As shown, a preparation method of a carbon nanotube material filled with inorganic salt provided by the present invention includes the following steps:

[0053] S1, pretreat the carbon nanotubes to obtain carbon nanotubes with opened tips;

[0054] Specifically, the carbon nanotubes are selected from single-walled carbon nanotubes, multi-walled carbon nanotubes, or a mixture of single-walled and multi-walled carbon nanotubes. In a preferred embodiment, multi-walled carbon nanotubes can be used; the above carbon nanotubes are pretreated: the carbon nanotubes are dispersed in a concentrated nitric acid solution, soaked for a period of time under heating conditions, and then filtered and washed with deionized water to obtain carbon nanotubes with opened tips. Here, the carbon nanotubes with opened tips can be either open at one end or open at both ends, and preferably carbon nanotubes open at both ends

[0055] The inner cavity diameter of the carbon nanotubes used above is 1 to 20 nm, preferably 5 to 10 nm; the length is 20 to 200,000 nm; preferably the length is 100 to 1000 nm.

[0056] S2. Add the carbon nanotubes with opened tips to a solution containing metal salt ions, and obtain a suspension after stirring evenly.

[0057] Specifically, first prepare a solution containing metal salt ions: the metal salt is selected from one or several of nitrates, sulfates, carbonates, and chlorides that are soluble in water or alcohol, such as FeCl3·5H2O, Cr(NO3)3·9H2O, CoCl3·6H2O, NaCl, ZnSO4, or Co(NO3)2, etc.; the solution is an alcohol solution or an aqueous solution; the solution containing metal salt ions can be an aqueous sodium chloride solution, an aqueous zinc sulfate solution, a cobalt nitrate ethanol solution, etc. Among the solutions containing metal salt ions, the concentration of metal salt ions is 0.01 to 10 mol / L; the addition amount of the carbon nanotubes with opened tips per 100 mL of the solution ≤ 10 g.

[0058] After that, add the carbon nanotubes with opened tips to the solution containing metal salt ions, and obtain a suspension after stirring evenly. The stirring time is 10 to 4000 min.

[0059] S3. Use an inner filling suction filtration device to perform a primary suction filtration on the suspension. During the primary suction filtration process, the suction filtration pressure is gradually adjusted from atmospheric pressure to 10 -7 mbar, and determine the secondary suction filtration pressure according to the liquid drop dripping vibration frequency curve.

[0060] Step S3 includes the following processes:

[0061] S31. Add the suspension to the liquid addition hopper of the inner filling suction filtration device for a primary suction filtration. During this process, the suction filtration pressure starts to be gradually adjusted from atmospheric pressure to 10 -7 mbar. The suspension drips onto the liquid storage tank through the filter membrane under the action of the suction filtration pressure. Use a vibration monitor and a vibration recorder to obtain the liquid drop dripping vibration frequency curve during the process of adjusting the suction filtration pressure from atmospheric pressure to 10 -7 mbar.

[0062] Combined with Figure 2 、 Figure 3 As shown, after adding the suspension to the liquid addition hopper of the inner filling suction filtration device, at 10 3At atmospheric pressure of mbar, the liquid naturally flows down rapidly through the filter membrane. Along with the natural sedimentation of carbon nanotubes under gravity, a carbon nanotube layer with a certain thickness is formed on the upper surface of the filter membrane. There is still a small amount of clear solution above it. At this time, the dripping vibration frequency of the liquid droplet reaches the first valley value. By gradually adjusting the vacuum degree in the liquid storage tank through the pressure control device, the solution above the carbon nanotube layer will flow down at a faster speed. At this time, the dripping vibration frequency of the liquid droplet reaches the first peak value. Along with the flowing down of the solution above the carbon nanotube layer, the carbon nanotube layer thins under the pressure difference and gradually becomes a denser layer, which prevents the solution above it from continuously flowing down until it is completely drained. At this time, the dripping vibration frequency of the liquid droplet reaches the second valley value. By increasing the vacuum degree in the liquid storage tank again, the remaining solution above the carbon nanotube layer will penetrate through the carbon nanotube layer and flow down. The dripping vibration frequency of the liquid droplet reaches the second peak value. As the solution is drained, the dripping vibration frequency of the liquid droplet reaches the third valley value. At this time, a carbon nanotube layer with a very thin thickness and no water traces on it is formed above the filter membrane. This carbon nanotube layer at this time is composed of intertwined nanotubes and a water film on the grid formed by the intertwined carbon nanotube walls. By continuing to increase the vacuum degree, there will be a phenomenon of a small amount of liquid droplets condensing and dripping. At this time, when looking down at the film layer formed by carbon nanotubes from the top, it will change from a matte texture to a texture that is easy to reflect light and shiny. The dripping vibration frequency of the liquid droplet reaches the third peak value; the film layer composed of the carbon nanotube layer is composed of intertwined carbon nanotubes and a small amount of solution poured into the inner cavity of the carbon nanotubes. These small amounts of solution are affected by nano-scale capillary forces and will only be pumped out when the vacuum degree is extremely high. Therefore, when continuing to increase the vacuum degree to pump it out, at this time the dripping vibration frequency of the liquid droplet reaches the fourth peak value. After that, continue to increase the vacuum degree until the suction filtration pressure is adjusted to 10 -7 mbar, and one suction filtration ends. During the above process, the dripping vibration frequency of the liquid droplet is monitored by a vibration monitor and recorded by a vibration recorder, so as to obtain the dripping vibration frequency curve of the liquid droplet during the process of adjusting the suction filtration pressure from atmospheric pressure to 10 -7 mbar; the product obtained by this suction filtration is discarded.

[0063] During the regulation of the suction filtration pressure in one suction filtration process, it should be as slow as possible according to the actual situation, or the rate parameter of the pressure change during multiple suction filtrations should be regulated to observe four relatively obvious peak values.

[0064] S32, Obtain the first pressure, second pressure, third pressure, and fourth pressure corresponding to the first peak value, second peak value, third peak value, and fourth peak value of the liquid droplet dripping vibration frequency according to the liquid droplet dripping vibration frequency curve;

[0065] S33, The secondary suction filtration pressure is between the third pressure and the fourth pressure to ensure that the liquid inside the carbon nanotubes is retained, and at the same time, there is no residual liquid outside the carbon nanotubes.

[0066] S4. Use an internal filling suction filtration device to perform secondary suction filtration on the suspension, and adopt the secondary suction filtration pressure determined in step S3 to obtain a precursor, that is, carbon nanotubes filled with a metal salt ion solution; wherein the secondary suction filtration time is adjustable between 1 and 1440 min, preferably adjustable between 30 and 360 min.

[0067] S5. Calcinate the precursor under a protective atmosphere to obtain a carbon nanotube material filled with inorganic salts.

[0068] Specifically, place the precursor in a closed heating furnace and calcinate it under a protective atmosphere, and then obtain a carbon nanotube material filled with inorganic salts after cooling. Among them, the protective atmosphere is nitrogen or an inert gas (such as argon, etc.), the calcination temperature is 300 - 1500 °C, and the calcination time is 10 - 240 min.

[0069] During this process, an active substance or an active gas can also be added into the heating furnace; wherein, the active substance is one of NaH2PO2·H2O, sulfur, and phosphorus; the mass ratio of the active substance to the precursor is 1:100 - 10:1. The active gas is one of hydrogen sulfide, sublimed sulfur, phosphine, sublimed phosphorus, ammonia, nitrogen, and carbon dioxide.

[0070] For the carbon nanotube material filled with inorganic salts prepared above, its carbon nanotubes and the inorganic salts filled inside; the inner cavity diameter of the carbon nanotubes is 1 - 20 nm (preferably 5 - 10 nm), the length is 20 - 200000 nm (preferably 100 - 1000 nm), and the average particle size of the inorganic salts is 2 - 10 nm (preferably 4 - 8 nm).

[0071] The carbon nanotube material filled with inorganic salts prepared above can be used as the negative electrode material of a lithium-ion battery.

[0072] All the reagents and raw materials used above are commercially available.

[0073] Combined with Figure 3As shown in the figure, the internal filling suction filtration device used in the preparation method of the above carbon nanotube material filled with inorganic salts includes a liquid storage tank 3, a liquid addition hopper 1 provided on the liquid storage tank 3, a pressure control device 8 connected to the liquid storage tank 3, a vacuum pump 9 connected to the pressure control device 8, a vibration monitor 5 for monitoring the vibration frequency of liquid droplets dripping in the liquid storage tank 3, and a vibration recorder 6 connected to the vibration monitor 5. The liquid addition hopper 1 is used to hold the suspension; a filter membrane 2 is provided between the liquid storage tank 3 and the liquid addition hopper 1, which is used to filter and separate carbon nanotubes and the solution; the liquid storage tank 3 is used to store the separated solution. The vacuum pump 9 is used to provide a vacuum negative pressure; the pressure control device 8 is used to make the negative pressure provided by the vacuum pump 9 easy to regulate. The vibration monitor 5 is used to monitor the vibration caused by the dripping of liquid droplets in the liquid storage tank 3, and the vibration recorder 6 is used to record the vibration frequency monitored by the vibration monitor 5.

[0074] Combined with Figure 3 As shown in the figure, a microscopic camera 4 is also provided on the internal filling suction filtration device for observing the water film on the lower side of the filter membrane 2 to condense into liquid droplets and drip.

[0075] Combined with Figure 3 As shown in the figure, a fixed sticker 10 is provided at the bottom of the liquid storage tank 3 to ensure the stability of the liquid storage tank 3.

[0076] Combined with Figure 3 As shown in the figure, an air extraction pipeline 7 is provided between the pressure control device 8 and the liquid storage tank 3. An air extraction support is provided below the air extraction pipeline 7, and a fixed strap 11 for preventing vibration is provided at the bottom of the air extraction support to ensure that the vibration caused by the vacuum pump 9 and the pressure control device 8 will not be transmitted to the liquid storage tank 3 through the air extraction pipeline 7 to cause abnormal recording of the vibration recorder 6.

[0077] The carbon nanotube material filled with inorganic salts, the preparation method and the suction filtration device of the present invention will be further introduced below with specific examples.

[0078] Example 1

[0079] The preparation method of the carbon nanotube material filled with inorganic salts in this example adopts the following steps:

[0080] (1) 0.1 g of multi-walled carbon nanotubes are dispersed in 20 mL of concentrated nitric acid solution, heated to 120 °C and soaked for 12 hours, and filtered and washed 3 times with deionized water to obtain carbon nanotubes with opened tips.

[0081] (2) 0.1 g of multi-walled carbon nanotubes with opened tips and 1.4 g of Co(NO3)3·6H2O are dispersed in 20 mL of deionized water to form a suspension, and stirred at 60 °C for 12 hours.

[0082] (3) First suction filtration, take 10 mL of the suspension and put it into the carbon nanotube internal filling suction filtration device, and slowly adjust the suction filtration pressure from normal pressure to 10-7 mbar and monitor the vibration frequency of the liquid drops falling. It is observed that the last two peaks appear at 10 -4 mbar and 3*10 - 5 mbar.

[0083] (4) Secondary filtration. Take another 10 mL of the suspension and adjust the filtration pressure to 7*10 -5 mbar to obtain the precursor, i.e., the carbon nanotube material filled with Co(NO3)2·6H2O inside.

[0084] (5) Calcinate 80 mg of the precursor and 1 g of NaH2PO2·H2O at 350 °C for 2 hours under an Ar flow, so that NaH2PO2·H2O decomposes to release PH3 and reacts with Co(NO3)2·6H2O to generate cobalt phosphide (CoP), and obtain the carbon nanotube material filled with cobalt phosphide inside;

[0085] In the above-prepared carbon nanotube material filled with cobalt phosphide, the inner cavity diameter of the carbon nanotubes is about 10 nm, the length is 150 nm to 10000 nm, and the average particle size of cobalt phosphide is 9 nm.

[0086] Figure 4 For the low-magnification transmission electron microscope (TEM) image of the obtained carbon nanotube material filled with cobalt phosphide, it can be seen that a large amount of material is filled in the inner cavity of the carbon nanotubes, and at the same time, the outer wall of the carbon nanotubes is smooth.

[0087] Figure 5 For Figure 4 the further enlarged image, the cobalt phosphide grains are restricted in the inner cavity of the carbon nanotubes and cannot grow excessively, which is more conducive to the rapid insertion of lithium ions when used as the anode material for lithium-ion batteries.

[0088] Use a 2032 coin cell for the electrochemical performance test. Mix 80% by mass of the material obtained in Example 1, 10% by mass of conductive carbon black (Super P), and 10% by mass of polyvinylidene fluoride (PVDF) with an appropriate amount of N-methylpyrrolidone (NMP) solvent, grind and stir to form a slurry, and then coat it on a copper foil by a doctor blade to obtain a working electrode. The counter electrode and the separator are a lithium foil and a polypropylene membrane (Celgard 2400) respectively. The base liquid of the electrolyte is a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) with a volume ratio of 1:1 added with 5% by mass of fluoroethylene carbonate (FEC), and the electrolyte is lithium hexafluorophosphate (LiPF6) with a concentration of 1 mole / liter. The charge and discharge performance test of the battery is carried out on a Wuhan Blue Electric test system (LAND-CT2001C).

[0089] As Figure 6As shown, it is the test result of the rate performance of the button cell with the carbon nanotube material filled with cobalt phosphide obtained in Example 1. At a current density of 0.2 A / g, the discharge specific capacitance of the material can reach 1024 mAh / g; at a large current density of 10 A / g, the capacity can reach more than 464 mAh / g.

[0090] As Figure 7 shown, it is the test result of the cycle performance of the button cell with the carbon nanotube material filled with cobalt phosphide obtained in Example 1. At a current density of 2 A / g, the material can stably cycle 300 times, and the capacity retention rate reaches 93.8%.

[0091] Example 2

[0092] The preparation method of the carbon nanotube material filled with inorganic salts in this example adopts the following steps:

[0093] (1) Disperse 0.1 g of multi-walled carbon nanotubes in 20 mL of concentrated nitric acid solution, heat to 120 °C and keep for 12 hours, filter and wash 3 times with deionized water to obtain carbon nanotubes with opened tips.

[0094] (2) Disperse 0.1 g of multi-walled carbon nanotubes with opened tips and 2.2 g of FeCl3·5H2O in 20 mL of deionized water to make a suspension, and stir at 60 °C for 12 hours.

[0095] (3) Perform primary suction filtration. Take 10 mL of the suspension and put it into the carbon nanotube internal filling suction filtration device. Slowly adjust the suction filtration pressure from normal pressure to 10 -7 mbar and monitor the vibration frequency of the liquid drop dripping. Observe the positions where the last two peaks appear at 10 -4 mbar and 10 - 5 mbar.

[0096] (4) Perform secondary suction filtration. Take another 10 mL of the suspension and adjust the suction filtration pressure to between the positions where the last two peaks appear to obtain a precursor, that is, a carbon nanotube material filled with FeCl3·5H2O.

[0097] (5) Calcinate 80 mg of the precursor and 0.8 g of sulfur powder at 600 °C for 2 hours under an Ar flow to obtain a carbon nanotube material filled with iron sulfide.

[0098] In the above-prepared carbon nanotube material filled with iron sulfide, the inner cavity diameter of the carbon nanotube is 10 nm, the length is 150 nm to 10000 nm, and the average particle size of the iron sulfide is 9 nm.

[0099] Example 3

[0100] The preparation method of the carbon nanotube material filled with inorganic salts in this example adopts the following steps:

[0101] (1) 0.1 g of multi-walled carbon nanotubes was dispersed in 20 mL of concentrated nitric acid solution, heated to 120 °C and maintained for 12 hours, and then filtered and washed three times with deionized water to obtain carbon nanotubes with opened tips.

[0102] (2) Subsequently, 0.1 g of the multi-walled carbon nanotubes with opened tips and 1 g of Cr(NO3)3·9H2O were dispersed in 20 mL of deionized water to form a suspension, and stirred at 60 °C for 12 hours.

[0103] (3) For the first filtration, 10 mL of the suspension was placed into the carbon nanotube inner filling filtration device, and the filtration pressure was slowly adjusted from atmospheric pressure to 10 -7 mbar and the vibration frequency of the liquid droplets was monitored. The positions where the last two peaks appeared were observed at 5*10 -4 mbar and 10 - 6 mbar.

[0104] (4) For the second filtration, another 10 mL of the suspension was taken, and the filtration pressure was adjusted to be between the positions where the last two peaks appeared to obtain a precursor, namely, the carbon nanotube material with Cr(NO3)3·9H2O filled inside.

[0105] (5) 80 mg of the precursor was calcined at 800 °C for 2 hours under an Ar flow to obtain the carbon nanotube material with chromium oxide filled inside.

[0106] In the above-prepared carbon nanotube material with chromium oxide filled inside, the inner cavity diameter of the carbon nanotubes is 10 nm, the length is 150 nm to 10000 nm, and the average particle size of the chromium oxide is 9 nm.

[0107] Example 4

[0108] The preparation method of the carbon nanotube material with inorganic salt filled inside in this example adopts the following steps:

[0109] (1) 0.1 g of multi-walled carbon nanotubes was dispersed in 20 mL of concentrated nitric acid solution, heated to 120 °C and maintained for 12 hours, and then filtered and washed three times with deionized water to obtain carbon nanotubes with opened tips.

[0110] (2) 0.1 g of the multi-walled carbon nanotubes with opened tips and 1.4 g of CoCl3·6H2O were dispersed in 20 mL of ethanol to form a suspension, and stirred at 60 °C for 12 hours.

[0111] (3) 10 mL of the suspension was placed into the carbon nanotube inner filling filtration device, and the filtration pressure was slowly adjusted from atmospheric pressure to 10 - 7 mbar and the vibration frequency of the liquid droplets was monitored. The positions where the last two peaks appeared were observed at 10-3 mbar and 10 -5 mbar.

[0112] (4) Take another 10 mL of the suspension, adjust the suction filtration pressure to between the last two peak appearances, and obtain the precursor, i.e., the carbon nanotube material with CoCl3·6H2O filled inside.

[0113] (5) Calcinate 80 mg of the precursor at 1050 °C for 2 hours under an Ar flow, decompose CoCl3·6H2O and react it with part of the carbon on the inner wall of the carbon nanotubes to obtain the carbon nanotube material with metallic cobalt filled inside.

[0114] In the above-prepared carbon nanotube material with cobalt phosphide filled inside, the inner cavity diameter of the carbon nanotubes is 10 nm, the length is 150 nm to 10000 nm, and the average particle size of the cobalt phosphide is 9 nm.

[0115] Comparative example

[0116] The preparation method of the carbon nanotube material with inorganic salts filled inside in this comparative example adopts the following steps:

[0117] (1) Disperse 0.1 g of multi-walled carbon nanotubes in 20 mL of concentrated nitric acid solution, heat to 120 °C and keep for 12 hours, filter and wash 3 times with deionized water to obtain the carbon nanotubes with the tips opened.

[0118] (2) Subsequently, disperse 0.1 g of the multi-walled carbon nanotubes with the tips opened and 1.4 g of Co(NO3)3·6H2O in 20 mL of deionized water to make a suspension, and stir at 60 °C for 12 hours.

[0119] (3) Take 10 mL of the suspension and put it into the carbon nanotube inner filling suction filtration device, slowly adjust the suction filtration pressure from atmospheric pressure to 10 - 7 mbar and monitor the droplet vibration frequency. It is observed that the last two peaks appear at 10 -4 mbar and 3*10 -5 mbar.

[0120] (4) Take another 10 mL of the suspension, adjust the suction filtration pressure to 1*10 -3 mbar to obtain the precursor with carbon nanotubes filled inside and the outer wall contaminated with Co(NO3)2·6H2O solution.

[0121] (5) Calcinate 80 mg of the precursor and 1 g of NaH2PO2·H2O at 350 °C for 2 hours under an Ar flow, decompose NaH2PO2·H2O to release PH3 and react it with Co(NO3)2·6H2O to generate cobalt phosphide (CoP), and obtain the carbon nanotube material with cobalt phosphide filled inside, with cobalt phosphide attached to its outer wall.

[0122] In summary, the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the gist and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a carbon nanotube material filled with inorganic salts, characterized in that, The following steps are involved: S1, pre-treating the carbon nanotubes to obtain carbon nanotubes with open tips; S2, adding the carbon nanotube with the tip opened into a solution containing metal salt ions, and stirring to obtain a suspension; S3. Use an internal filling suction filtration device to perform a primary suction filtration on the suspension. During the primary suction filtration process, gradually adjust the suction filtration pressure from atmospheric pressure to 10 -7 mbar, and determine the secondary suction filtration pressure according to the liquid drop vibration frequency curve; S4, performing secondary filtration on the suspension using an internal filling filtration device, using the secondary filtration pressure determined in step S3 to obtain a precursor; S5, calcining the precursor under a protective atmosphere to obtain a carbon nanotube material filled with an inorganic salt.

2. The preparation method of the carbon nanotube material filled with inorganic salts as described in claim 1, characterized in that, In step S1: The carbon nanotubes are selected from single-walled carbon nanotubes, multi-walled carbon nanotubes or single-walled and multi-walled mixed carbon nanotubes; The pretreatment process is as follows: the carbon nanotubes are dispersed in a concentrated nitric acid solution, immersed under heating conditions, filtered and washed with deionized water to obtain the carbon nanotubes with opened tips.

3. The preparation method of the carbon nanotube material filled with inorganic salts as described in claim 1, characterized in that, In step S2: The solution is an alcohol solution or an aqueous solution; and / or The metal salt is selected from one or more of nitrates, sulfates, carbonates and chlorides soluble in water or alcohol.

4. The preparation method of the carbon nanotube material filled with inorganic salts as described in claim 3, characterized in that, The metal salt is selected from FeCl3·5H2O, Cr(NO3)3·9H2O, CoCl3·6H2O, NaCl, ZnSO4 or Co(NO3)2.

5. The preparation method of the carbon nanotube material filled with inorganic salts as described in claim 1, characterized in that, In step S2: In the solution containing metal salt ions, the concentration of metal salt ions is 0.01 to 10 mol / L; and / or In every 100 mL of solution, the amount of the carbon nanotubes with open tips added is ≤ 10 g; and / or The stirring time is 10 to 4000 minutes.

6. The preparation method of the carbon nanotube material filled with inorganic salts as described in claim 1, characterized in that, The step S3 includes the following process: S31. Add the suspension into the liquid addition hopper filled with a suction filtration device. Under the action of the suction filtration pressure, the suspension drips onto the liquid storage tank through the filter membrane, and a vibration frequency curve of the liquid droplet dripping is obtained by using a vibration monitor and a vibration recorder during the process of adjusting the suction filtration pressure from atmospheric pressure to 10 -7 mbar; S32, obtaining a first pressure, a second pressure, a third pressure, and a fourth pressure corresponding to a first peak value, a second peak value, a third peak value, and a fourth peak value of the droplet drop vibration frequency according to the droplet drop vibration frequency curve; S33, the secondary filtration pressure is between the third pressure and the fourth pressure.

7. The preparation method of the carbon nanotube material filled with inorganic salts as described in claim 1, characterized in that, In the step S4, the secondary filtration time is 1 to 1440 minutes.

8. The preparation method of the carbon nanotube material filled with inorganic salts as claimed in claim 7, characterized in that, The secondary filtration time is 30 to 360 minutes.

9. The preparation method of the carbon nanotube material filled with inorganic salts as described in claim 1, characterized in that, In the step S5, the protective atmosphere is nitrogen or an inert gas, the calcination temperature is 300 to 1500° C., and the calcination time is 10 to 240 minutes.

10. The preparation method of the carbon nanotube material filled with inorganic salts as described in claim 1, characterized in that, In the step S5, during the calcination process, active substances are added or active gases are introduced.

11. The preparation method of the carbon nanotube material filled with inorganic salts as described in claim 10, characterized in that, The active substance is one of NaH2PO2·H2O, sulfur and phosphorus; the mass ratio of the active substance to the precursor is 1:100 to 10:1; or The active gas is one of hydrogen sulfide, sublimated sulfur, phosphine, sublimated phosphorus, ammonia, nitrogen and carbon dioxide.

12. A carbon nanotube material filled with inorganic salts, which is prepared by using the preparation method of the carbon nanotube material filled with inorganic salts according to any one of claims 1-11, and is characterized in that, The interior of the carbon nanotube is filled with inorganic salt; the inner cavity diameter of the carbon nanotube is 1-20nm, and the average particle size of the inorganic salt is 2-10nm.

13. An internal filling suction filtration device used in the preparation method of a carbon nanotube material filled with inorganic salts as described in any one of claims 1-11, characterized in that, It includes a liquid storage tank, a liquid adding hopper arranged on the liquid storage tank, a pressure control device connected to the liquid storage tank, a vacuum pump connected to the pressure control device, a vibration monitor for monitoring the vibration frequency of droplets falling in the liquid storage tank, and a vibration recorder connected to the vibration monitor; a filter membrane is arranged between the liquid storage tank and the liquid adding hopper.

14. The internal filling suction filtration device according to claim 13, characterized in that, A microscopic camera is also provided on the internal filling suction filtration device for observing the condensation of the water film on the lower side of the filter membrane into droplets and dripping.

15. The internal filling suction filtration device according to claim 13, characterized in that, A fixing sticker is provided at the bottom of the liquid storage tank.

16. The internal filling suction filtration device according to claim 13, characterized in that, An air extraction pipeline is provided between the pressure control device and the liquid storage tank. An air extraction support is provided below the air extraction pipeline, and a fixing strap for preventing vibration is provided at the bottom of the air extraction support.

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