Nanocarbon cages, methods of making and using the same

Abstract

The application relates to the technical field of preparation of new carbon materials, and discloses a nano carbon cage and a preparation method and application thereof, the preparation method comprising the following steps: (1) physically mixing pitch and a nickel-containing compound, and then baking to obtain an intermediate product; wherein the softening point of the pitch is 130-300 DEG C; the baking temperature is 700-1200 DEG C, and the time is 60-240 min; (2) acid washing the intermediate product. The preparation method of the nano carbon cage can effectively improve the carbon yield and reduce the raw material cost by using pitch as a carbon source without using a template agent; the prepared carbon cage has high graphitization degree, thin cage wall, good specific capacity and good rate performance.

Description

Technical Field

[0001] This invention relates to the field of novel carbon material preparation technology, specifically to a nano carbon cage, its preparation method, and its application. Background Technology

[0002] As a novel type of nanomaterial, carbon nanocages are gradually emerging as a new platform for energy storage and conversion, attracting widespread attention from academia and industry in recent years. Carbon nanocages possess a unique hollow structure, exhibiting excellent electrical conductivity and wettability. Due to their special porous structure and high specific surface area, carbon nanocages have been extensively studied in the field of supercapacitor energy storage. Simultaneously, carbon nanocages also show promising application prospects as catalyst supports in electrochemistry and chemical engineering.

[0003] Currently, the main methods for preparing carbon nanocages include chemical vapor deposition, arc discharge, hard template method, plasma polymerization, and laser evaporation of graphite. The formation mechanism of carbon nanocages generally falls into two categories: one is that under high-temperature conditions, nano-metal particles catalyze the formation of cavities in carbon materials, gradually growing to form carbon nanocages; the other is that the carbon source is carbonized on the template surface to form a stable carbon-coated structure, and then the internal template is removed to obtain the carbon nanocage material. For example, the team led by Hu Zheng at Nanjing University successfully developed a series of high specific surface area carbon nanocage materials using magnesium oxide as a template and benzene as an organic carbon source. Furthermore, CN1810635A first prepares a large quantity of amorphous carbon precursors with uniformly distributed iron catalyst particles, then heat-treats the precursors to obtain hollow carbon nanocages through a solid-state reaction, and finally removes the catalyst from the hollow carbon nanocages to obtain the final product. CN108455565A physically mixes cyanamide compounds with metal acetates or metal carbonates, and obtains nitrogen-doped graphitized carbon nanocages through high-temperature carbonization and acid washing. CN110078051A uses sugars as a carbon source and potassium chloride as a template. After ball milling and high-temperature carbonization, the potassium chloride template is removed by soaking to obtain nano-carbon cage materials. CN110272035A successfully prepared nano-carbon cages with abundant pore structure and large specific surface area by calcining a rhombic dodecahedral metal-organic framework precursor.

[0004] In summary, existing methods for preparing carbon nanocages suffer from relatively complex production processes, high raw material costs, and low carbon yields, making large-scale production difficult. Furthermore, the structural regularity and uniformity of carbon nanocages prepared using existing methods need improvement. Therefore, finding a simple, low-cost, and structurally controllable preparation method is of great significance for the large-scale production and application of carbon nanocages. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of high cost, complex process, and low graphitization degree of carbon cages in the existing technology, and to provide a nano carbon cage, its preparation method and application. The preparation method of this nano carbon cage has low raw material cost, simple process, and the carbon cage obtained has a high degree of graphitization and controllable structure.

[0006] To achieve the above objectives, the present invention provides a method for preparing nano-carbon cages, the method comprising:

[0007] (1) Physically mix asphalt and nickel-containing compounds, and then calcine them to obtain an intermediate product;

[0008] The softening point of the asphalt is 130-300℃; the calcination temperature is 700-1200℃ and the time is 60-240 min.

[0009] (2) The intermediate product is acid washed.

[0010] A second aspect of the present invention provides a nano-carbon cage prepared by the above-described preparation method.

[0011] A third aspect of the present invention provides the application of the above-mentioned nano-carbon cage in lithium-ion capacitors.

[0012] The present invention provides a method for preparing nano-carbon cages, using pitch and nickel-containing compounds as raw materials. An intermediate product is obtained through physical mixing. During calcination, the pitch carbonizes, and the nickel-containing compound pyrolyzes. The reduced nickel atoms act as catalysts and templates, resulting in uniform carbon coating on the nickel atoms. Finally, metallic nickel is removed from the initial product by acid washing, and a thin-layer nano-carbon cage material is obtained after drying. Using pitch and nickel-containing compounds as raw materials has several advantages. First, it eliminates the need for nano-templating agents during preparation, significantly reducing raw material costs. Using pitch as a carbon source also improves carbon yield. Second, using pitch as a raw material facilitates increased graphitization of the carbon cage, and the thinner cage walls of the nano-carbon cages are beneficial for their application as negative electrodes in lithium-ion capacitors, improving specific capacitance and rate performance. Attached Figure Description

[0013] Figure 1 These are transmission electron microscope images of the carbon nanocages prepared in Example 1;

[0014] Figure 2 This is the Raman spectrum of the nano-carbon cage prepared in Example 1;

[0015] Figure 3 This is the XRD pattern of the nano-carbon cage prepared in Example 1;

[0016] Figure 4 The half-cell rate cycling curve of the negative electrode made of nano-carbon cage S1 is shown.

[0017] Figure 5 The half-cell rate cycling curve of the negative electrode made of nano-carbon cage S2.

[0018] Figure 6 This is the half-cell rate cycling curve of the negative electrode made of nanomaterial DS1. Detailed Implementation

[0019] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0020] The first aspect of this invention provides a method for preparing nano-carbon cages, the method comprising:

[0021] (1) Physically mix asphalt and nickel-containing compounds, and then calcine them to obtain an intermediate product;

[0022] The softening point of the asphalt is 130-300℃; the calcination temperature is 700-1200℃ and the time is 60-240 min.

[0023] (2) The intermediate product is acid washed.

[0024] In this invention, asphalt with a softening point of 130-300℃ is physically and uniformly mixed and dispersed with a nickel-containing compound. Then, nickel is removed from the intermediate product by acid washing. The resulting nano-carbon cages have a higher degree of graphitization and thinner cage walls, which is beneficial for improving specific capacity and rate performance. The reason for this is likely that asphalt with a softening point of 130-300℃ has a larger molecular weight, making it difficult to form a dense multilayered coating structure during pyrolysis, resulting in fewer carbon layers. In the physical mixing process described in this invention, the asphalt and the nickel-containing compound undergo virtually no chemical changes, allowing nickel to be uniformly dispersed in the asphalt. In contrast, existing technologies using small-molecule organic compounds as carbon sources typically result in denser coatings, more carbon layers, difficulty in acid washing of nickel ions, and low carbon yield.

[0025] In addition, the preparation method provided by this invention uses asphalt, a by-product of petrochemicals, as raw material, and does not require the use of nanotemplating agents during the preparation process, which greatly reduces the cost of raw materials; using asphalt as a carbon source is beneficial to improving the carbon production rate.

[0026] In this invention, the term "asphalt" has the conventional definition in the art and can be petroleum asphalt and / or coal tar pitch.

[0027] In some preferred embodiments of the present invention, the asphalt is ultra-high temperature asphalt, and the softening point of the asphalt is 200-280℃. Using the above-mentioned preferred asphalt raw materials is beneficial to obtaining nano-carbon cages with fewer carbon layers, which is further beneficial to improving capacity and rate performance.

[0028] Preferably, the content of quinoline-insoluble matter in the asphalt does not exceed 10 wt%. In this invention, the content of quinoline-insoluble matter is determined by the GB / T2293-80 method.

[0029] According to some preferred embodiments of the present invention, the asphalt includes carbon, hydrogen, oxygen, and optionally nitrogen and sulfur elements. Based on the total amount of the asphalt, the content of element C is not less than 90 wt%, the content of element H is not more than 10 wt%, the content of element O is not more than 1 wt%, the content of element N is not more than 1 wt%, and the content of element sulfur is not more than 1 wt%. Those skilled in the art will understand that the asphalt may also contain other impurity elements, such as metallic elements.

[0030] More preferably, based on the total amount of the asphalt, the content of C element is 92-98 wt%, the content of H element is 1-6 wt%, the content of O element is 0.1-0.5 wt%, the content of N element is 0-0.5 wt%, and the content of sulfur element is 0-1 wt%. Using the asphalt with the above-preferred composition as a carbon source is beneficial to reducing the specific surface area within the micropores of the carbon cage and to improving the carbon cage yield.

[0031] In this invention, the composition of asphalt is obtained by elemental analysis.

[0032] According to some preferred embodiments of the present invention, the mass ratio of the asphalt to the nickel-containing compound is 1:(1-8), for example, it can be a typical but not limiting mass ratio such as 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, or a range between the two. Preferably, the mass ratio of the asphalt to the nickel-containing compound is 1:(3-6). In the above preferred cases, it is beneficial to obtain a carbon cage with a regular structure and a suitable specific surface area. Further application in lithium-ion capacitors can achieve better electrochemical performance, possessing both excellent capacitance and rate performance.

[0033] The present invention does not have any special requirements for the specific operation and conditions of the physical mixing in step (1). As long as it can facilitate the uniform mixing of asphalt and nickel-containing compounds, it can be carried out in a conventional manner in the art.

[0034] According to some preferred embodiments of the present invention, the physical mixing method includes mixing the asphalt, the nickel-containing compound, and an optional dispersant under stirring and / or ball milling conditions.

[0035] More preferably, the physical mixing method includes: premixing the asphalt, nickel-containing compound, and optional dispersant under stirring conditions, and then ball milling the premixed mixture. Using the above preferred embodiment helps to uniformly disperse the nickel-containing compound in the asphalt, which is beneficial to improving the regularity and uniformity of the obtained nano-carbon cage structure, and further enabling it to have higher capacity and better rate performance when applied in lithium-ion capacitors.

[0036] According to the present invention, preferably, the dispersant is selected from methanol and / or ethanol, and more preferably ethanol.

[0037] Preferably, the ratio of the amount of dispersant to the total mass of the asphalt and nickel-containing compound is 2-15:1, more preferably 5-10:1.

[0038] According to the present invention, preferably, the premixing temperature is 60-90°C, more preferably 70-80°C, and the time is 1-5 hours, more preferably 2-4 hours.

[0039] Preferably, the premixing process further includes solid-liquid separation and drying steps to remove residual dispersant. The solid-liquid separation and drying steps can be performed using methods conventional in the art, and the present invention is not particularly limited in this regard. For example, filtration, vacuum filtration, centrifugation, etc., can be used for the solid-liquid separation.

[0040] In this invention, the ball milling can be performed using a planetary ball mill. Preferably, the ball milling conditions include: a milling speed of 300-500 rpm, more preferably 350-450 rpm, and a milling time of 5-20 h, more preferably 8-12 h.

[0041] The present invention has a wide range of choices for the specific types of nickel-containing compounds. Preferably, the nickel-containing compounds are selected from inorganic salts of nickel, preferably from at least one of nickel acetate, nickel nitrate, nickel chloride and basic nickel carbonate, and more preferably from basic nickel carbonate.

[0042] According to the present invention, during the roasting process described in step (1), the pitch is carbonized, the nickel-containing compound is pyrolyzed, and the reduced nickel atoms act as a catalyst and template, so that carbon is uniformly coated on the outside of the nickel atoms.

[0043] According to some preferred embodiments of the present invention, the calcination conditions include: a heating rate of 1-10℃ / min, a calcination temperature of 700-1200℃, preferably 800-1000℃; and a time of 60-240min, preferably 60-120min.

[0044] According to the present invention, preferably, the calcination is carried out under an inert atmosphere, which is preferably provided by nitrogen.

[0045] According to the present invention, metallic nickel in the precursor is removed by acid washing in step (2) to form a hollow nano-carbon cage. The specific operation and conditions of the acid washing can be selected according to actual needs, as long as the above-mentioned effect can be achieved. The inventors of the present invention have found in their research that asphalt with a softening point of 130-300℃ does not easily form a dense multi-layered coating structure during pyrolysis, resulting in fewer carbon layers and easier removal of nickel ions by acid washing.

[0046] According to some preferred embodiments of the present invention, the pickling in step (2) includes: contacting the precursor with an acid solution, and then washing and drying.

[0047] Preferably, H + The molar mass ratio of the acid solution to the intermediate product is (1-4):1, preferably (2-3):1.

[0048] Preferably, the contact temperature is 60-120℃, more preferably 90-105℃; the contact time is 2-12h, more preferably 4-8h.

[0049] Preferably, the acid solution is an aqueous solution of an inorganic acid and / or an organic acid, more preferably hydrochloric acid. The concentration of the acid solution can be 0.5-2 mol / L, preferably 0.8-1.5 mol / L.

[0050] In this invention, the washing is used to remove residual acid, and various water washing methods in the art capable of washing the carbon nanocages to neutrality can be applied to this invention. The drying is used to remove water from the carbon nanocages, and drying can also be carried out using conventional methods.

[0051] A second aspect of the present invention provides a nano-carbon cage prepared by the above-described preparation method.

[0052] According to the present invention, the nano-carbon cages prepared by the above preparation method have a hollow cage-like structure and a high degree of graphitization of the cage walls, and are characterized by Raman spectroscopy.

[0053] Preferably, in the Raman curve of the nano-carbon cage, I D / I G Less than 1, preferably 0.8-0.95.

[0054] In this invention, the Raman curve is obtained by Raman spectroscopy, with an excitation wavelength of 532 nm.

[0055] Under the above-mentioned preferred conditions, it is beneficial to use nano-carbon cages as the negative electrode of lithium-ion capacitors, thereby improving specific capacity and rate performance.

[0056] Preferably, the specific surface area of ​​the nano-carbon cage is 150-600 m². 2 / g, preferably 300-500m 2 / g.

[0057] In this invention, the specific surface area of ​​the sample was determined by a Quantachrome AS-6B analyzer, and the specific surface area of ​​the material was obtained by the Brunauer-Emmett-Taller (BET) method.

[0058] According to the present invention, by using pitch as a carbon source, the graphitization degree of the carbon cage is improved, and the resulting nano-carbon cage has a thinner cage wall. When applied to the negative electrode of a lithium-ion capacitor, this facilitates the insertion and extraction of lithium ions, thereby improving specific capacity and rate performance. Preferably, the average number of carbon layers in the cage wall of the nano-carbon cage is 2-5 layers, more preferably 2-3 layers. In contrast, the average number of carbon layers in nano-carbon cages generally prepared in the prior art is greater than 5.

[0059] Preferably, the average diameter of the nano-carbon cage is 3-10 nm, and more preferably 6-8 nm.

[0060] In this invention, the diameter of the nano-carbon cage and the average number of carbon layers in the cage wall are determined by high-resolution transmission electron microscopy (HRTEM). The HRTEM used in this invention is a JEM-2100 (HRTEM) (Japan Electronics Corporation), and the HRTEM testing conditions are: accelerating voltage of 200 kV. Specifically, the diameter and number of carbon layers of 10 carbon cages within the field of view are statistically analyzed, and their average values ​​are calculated to obtain the diameter of the nano-carbon cage and the average number of carbon layers in the cage wall.

[0061] A third aspect of the present invention provides the application of the above-mentioned nano-carbon cage in lithium-ion capacitors.

[0062] Compared to lithium-ion battery anodes, lithium-ion capacitor anodes do not require a charge / discharge platform, and therefore have higher requirements for specific capacity and rate performance to match the performance of the cathode. The nano-carbon cage provided by this invention can be used alone as a lithium-ion capacitor anode, or it can be combined with other anode active materials to form a composite anode in lithium-ion capacitors; this invention does not impose any particular limitations on this. The nano-carbon cage provided by this invention has a high degree of graphitization and thinner cage walls, resulting in high specific capacity and excellent rate performance when applied to lithium-ion capacitors.

[0063] The present invention will be described in detail below through embodiments.

[0064] Unless otherwise specified, all raw materials used in the following embodiments are commercially available.

[0065] The high-resolution transmission electron microscope (HRTEM) used in this invention is model JEM-2100 (HRTEM) (Nippon Electron Ltd.), and the high-resolution transmission electron microscope test conditions are: accelerating voltage of 200kV.

[0066] In this invention, the specific surface area of ​​the sample was determined by a Quantachrome AS-6B analyzer, and the specific surface area of ​​the material was obtained by the Brunauer-Emmett-Taller (BET) method.

[0067] Raman curves are obtained by Raman spectroscopy, with specific test conditions including an excitation wavelength of 532 nm.

[0068] The X-ray diffraction (XRD) test conditions in this invention are: Cu target, Kα rays (wavelength λ = 0.154 nm), tube voltage of 40 kV, tube current of 200 mA, and scanning speed of 5° / min.

[0069] In this invention, the negative electrode performance of the thin-layer nano-carbon cage material was obtained by testing it under different current densities using the Wuhan Landian testing system.

[0070] Example 1

[0071] The ultra-high temperature petroleum asphalt powder used in this embodiment has the following composition: carbon content of 93.3%, oxygen content of 0.21%, sulfur content of 0.77%, hydrogen content of 5.51%, and the remainder being impurity elements; the content of quinoline insoluble matter is ≤10wt%, and the softening point is 280℃.

[0072] 1g of ultra-high temperature asphalt powder, 3g of basic nickel carbonate, and 50mL of anhydrous ethanol were mixed and heated under reflux at 80℃ for 4h. After filtration, the mixture was dried in an oven. The dried mixture was transferred to a ball mill jar and ball-milled at 400 rpm for 12h using a planetary ball mill. The ball-milled powder was poured into a ceramic crucible and placed in a tube furnace. Under nitrogen protection, the temperature was increased to 800℃ at a rate of 5℃ / min and calcined at this temperature for 2h. Finally, the mixture was allowed to cool naturally to room temperature to obtain a black intermediate product.

[0073] The intermediate product was then added to 50 mL of deionized water and stirred until homogeneous. A hydrochloric acid solution (1 mol / L concentration) with a molar mass twice that of the intermediate product was then added. The mixture was subsequently heated to 105 °C and stirred for 8 hours. After cooling to room temperature, the mixture was filtered and washed with water until neutral. It was then placed in an oven and dried overnight to obtain a thin-layer nano-carbon cage material S1. Its physicochemical properties are shown in Table 1.

[0074] Figure 1 This is a TEM image of nano-carbon cage S1, obtained through... Figure 1It can be seen that the nano-carbon cage has a hollow cage-like structure; the Raman curve and XRD curve are as follows: Figure 2 and Figure 3 As shown, this indicates that the material has a high degree of graphitization.

[0075] Example 2

[0076] The ultra-high temperature petroleum asphalt powder used in this embodiment has the following composition: carbon content of 93.3%, oxygen content of 0.21%, sulfur content of 0.77%, hydrogen content of 5.51%, and the remainder being impurity elements; the content of quinoline insoluble matter is ≤10wt%, and the softening point is 280℃.

[0077] 1g of ultra-high temperature asphalt powder, 4g of basic nickel carbonate, and 50mL of anhydrous ethanol were mixed and heated under reflux at 80℃ for 4h. After filtration, the mixture was dried in an oven. The dried mixture was transferred to a ball mill jar and ball-milled at 450 rpm for 8h using a planetary ball mill. The ball-milled powder was poured into a ceramic crucible and then placed in a tube furnace. Under nitrogen protection, the temperature was increased to 900℃ at a rate of 5℃ / min and calcined at a constant temperature for 2h. Finally, it was naturally cooled to room temperature to obtain a black intermediate product.

[0078] The intermediate product was then added to 50 mL of deionized water and stirred until homogeneous. A hydrochloric acid solution (1 mol / L concentration) with a molar mass twice that of the intermediate product was then added. The mixture was subsequently heated to 105 °C and stirred for 8 hours. After cooling to room temperature, the mixture was filtered and washed with water until neutral. It was then placed in an oven and dried overnight to obtain the thin-layer carbon nanocage material S2. Its physicochemical properties are shown in Table 1.

[0079] Example 3

[0080] The ultra-high temperature petroleum asphalt powder used in this embodiment has the following composition: carbon content of 93.3%, oxygen content of 0.21%, sulfur content of 0.77%, hydrogen content of 5.51%, the remainder being impurity elements, quinoline insoluble content ≤10wt%, and softening point of 280℃.

[0081] 1g of ultra-high temperature asphalt powder, 6g of basic nickel carbonate, and 50mL of anhydrous ethanol were mixed and heated under reflux at 80℃ for 4h. After filtration, the mixture was dried in an oven. The dried mixture was transferred to a ball mill jar and ball-milled at 400 rpm for 8h using a planetary ball mill. The ball-milled powder was poured into a ceramic crucible and then placed in a tube furnace. Under nitrogen protection, the temperature was increased to 1000℃ at a rate of 5℃ / min and calcined at a constant temperature for 2h. Finally, it was naturally cooled to room temperature to obtain a black intermediate product.

[0082] The intermediate product was then added to 50 mL of deionized water and stirred until homogeneous. A hydrochloric acid solution (1 mol / L concentration) with a molar mass twice that of the intermediate product was then added. The mixture was subsequently heated to 105 °C and stirred for 8 hours. After cooling to room temperature, the mixture was filtered and washed with water until neutral. It was then placed in an oven and dried overnight to obtain the thin-layer carbon nanocage material S3. Its physicochemical properties are shown in Table 1.

[0083] Example 4

[0084] The method of Example 1 was followed, except that the calcination conditions included: heating to 1100°C at a heating rate of 5°C / min under nitrogen protection, and calcining at a constant temperature for 2 hours. The prepared nano-carbon cage material was designated S4, and its physicochemical properties are shown in Table 1.

[0085] Example 5

[0086] The asphalt powder used in this embodiment has the following composition: carbon content of 92.27%, oxygen content of 0.24%, sulfur content of 0.32%, hydrogen content of 7.17%, and the remainder being impurity elements; the content of quinoline insoluble matter is ≤5wt%, and the softening point is 150℃.

[0087] The method of Example 1 was followed, except that the above-mentioned asphalt powder was used instead of the ultra-high temperature asphalt powder in Example 1. The carbon cage material prepared was designated as S5, and its physicochemical properties are shown in Table 1.

[0088] Example 6

[0089] The ultra-high temperature petroleum asphalt powder used in this embodiment has the following composition: carbon content of 93.3%, oxygen content of 0.21%, sulfur content of 0.77%, hydrogen content of 5.51%, and the remainder being impurity elements; the content of quinoline insoluble matter is ≤10wt%, and the softening point is 280℃.

[0090] 1g of ultra-high temperature asphalt powder and 3g of basic nickel carbonate were ground and mixed, and then placed in a tube furnace. Under the protection of nitrogen, the temperature was raised to 800℃ at a heating rate of 5℃ / min, and calcined at a constant temperature for 2 hours. Finally, the mixture was naturally cooled to room temperature to obtain a black intermediate product.

[0091] The intermediate product was then added to 50 mL of deionized water and stirred until homogeneous. A hydrochloric acid solution (1 mol / L concentration) with a molar mass twice that of the intermediate product was then added. The mixture was subsequently heated to 105 °C and stirred for 8 hours. After cooling to room temperature, the mixture was filtered and washed with water until neutral. It was then placed in an oven and dried overnight to obtain the thin-layer carbon nanocage material S6. Its physicochemical properties are shown in Table 1.

[0092] Comparative Example 1

[0093] The ultra-high temperature asphalt powder used in this comparative example is the same as that used in Example 1.

[0094] 1 g of ultra-high temperature asphalt powder was placed in a tubular calcining furnace. Under nitrogen protection, the temperature was increased to 800 °C at a heating rate of 5 °C / min, and calcined at this temperature for 2 hours. Finally, it was naturally cooled to room temperature to obtain the final product, denoted as DS1. Its physicochemical properties are shown in Table 1. TEM characterization showed that this material does not have a cage-like structure.

[0095] Comparative Example 2

[0096] The asphalt used in this comparative example is sulfonated asphalt powder, with the following composition: carbon content of 40.24 wt%, oxygen content of 17.87 wt%, sulfur content of 1.4 wt%, hydrogen content of 3.82 wt%, and the remainder being impurity elements. The content of quinoline insoluble matter is ≤20 wt%, and the softening point is 120℃.

[0097] 1g of sulfonated pitch powder, 3g of basic nickel carbonate, and 50mL of anhydrous ethanol were mixed and heated and stirred at 80℃ for 4h. After filtration, the mixture was placed in an oven to dry. The mixture was then poured into a ceramic crucible and placed in a tube furnace. Under nitrogen protection, the temperature was increased to 800℃ at a rate of 5℃ / min, and calcined at this temperature for 2h. Finally, the mixture was allowed to cool naturally to room temperature to obtain a black intermediate product.

[0098] The intermediate product was then added to 50 mL of deionized water and stirred until homogeneous. A hydrochloric acid solution (1 mol / L concentration) with a molar mass twice that of the intermediate product was then added. The mixture was subsequently heated to 105 °C and stirred for 8 h. After cooling to room temperature, the mixture was filtered and washed with water until neutral. It was then placed in an oven and dried overnight to obtain the carbon material DS2. Its physicochemical properties are shown in Table 1. TEM characterization revealed that the material does not possess a cage-like structure.

[0099] Table 1

[0100] serial number <![CDATA[Specific surface area m 2 / g]]> Average number of carbon layers in cage wall Average diameter nm <![CDATA[Raman I D / I G > S1 357.4 3 6 0.83 S2 508.6 2 8 0.93 S3 431.7 2 8 0.95 S4 279.3 2 7 0.98 S5 340.5 4 8 0.98 S6 287.6 3 6 0.85 DS1 2.36 - - 0.99 DS2 342.4 - - 0.99

[0101] Application examples

[0102] The carbon material, acetylene black, and polyvinylidene fluoride prepared in the above examples and comparative examples were mixed in a mass ratio of 8:1:1, and 400 mg of N-methylpyrrolidone was added. The mixture was then thoroughly mixed using a homogenizer. The slurry was then coated onto a copper foil current collector and dried in a vacuum oven at 80°C to obtain the negative electrode of a lithium-ion capacitor. Using a lithium metal sheet as the counter electrode, a 2032-type button cell was fabricated in a glove box. A standard Celgard 2400 separator was used, and the electrolyte was LiPF6 / ethylene carbonate (EC): diethyl carbonate (DEC) (EC:DEC = 1:1, 5 wt% fluoroethylene carbonate FEC). The prepared half-cell was allowed to stand for 3 hours, and its performance was then tested using a blue-light testing system. The test conditions were: charge and discharge tests were conducted at room temperature at current densities of 0.1 A / g, 1 A / g, and 10 A / g, with a test voltage range of 0-3 V. The results are shown in Table 2.

[0103] Among them, the rate-of-use curve of S1 is as follows: Figure 4 As shown, the curve of the S2 multiplier cycle is as follows: Figure 5 As shown, the curve of DS1 rate cycle is as follows: Figure 6 As shown.

[0104] Table 2

[0105]

[0106] Combining the results in Tables 1 and 2, it can be seen that the nano-carbon cages prepared by the method provided in this invention have a high specific surface area, a high degree of graphitization, a small average number of cage wall layers, and thinner cage walls. Using these nano-carbon cages as anode materials, S1, S2, and S3 prepared under preferred conditions all exhibit high specific capacity and excellent rate performance. Comparative Example 2 uses sulfonated pitch with a low softening point as a raw material to prepare carbon materials. Due to its high heteroatom content, it can achieve a specific capacity comparable to that of Example 1 at a current density of 0.1 A / g, but its capacity is insufficient at higher current densities.

[0107] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing nano-carbon cages, characterized in that, The method includes: (1) Physically mix asphalt and nickel-containing compounds, and then calcine them to obtain an intermediate product; The softening point of the asphalt is 130-300℃; the calcination conditions include: a heating rate of 1-10℃ / min, a calcination temperature of 800-1000℃, and a calcination time of 60-120min. (2) The intermediate product is acid washed; The physical mixing method includes: premixing the asphalt, nickel-containing compound, and optional dispersant under stirring conditions, and then ball milling the premixed mixture; The nickel-containing compound is selected from inorganic salts of nickel.

2. The preparation method according to claim 1, wherein, The asphalt is petroleum asphalt and / or coal tar pitch.

3. The preparation method according to claim 1, wherein, The softening point of the asphalt is 200-280℃.

4. The preparation method according to claim 1, wherein, The content of quinoline insolubles in the asphalt does not exceed 10 wt%.

5. The preparation method according to claim 1, wherein, The asphalt contains carbon, hydrogen, oxygen, and optional nitrogen and sulfur elements. Based on the total amount of the asphalt, the content of C element is not less than 90 wt%, the content of H element is not more than 10 wt%, the content of O element is not more than 1 wt%, the content of N element is not more than 1 wt%, and the content of sulfur element is not more than 1 wt%.

6. The preparation method according to claim 5, wherein, Based on the total amount of the asphalt, the content of C element is 92-98wt%, the content of H element is 1-6wt%, the content of O element is 0.1-0.5wt%, the content of N element is 0-0.5wt%, and the content of sulfur element is 0-1wt%.

7. The preparation method according to claim 1, wherein, The mass ratio of the asphalt to the nickel-containing compound is 1:(1-8).

8. The preparation method according to claim 7, wherein, The mass ratio of the asphalt to the nickel-containing compound is 1:(3-6).

9. The preparation method according to claim 1, wherein, The dispersant is selected from methanol and / or ethanol.

10. The preparation method according to claim 9, wherein, The dispersant is ethanol.

11. The preparation method according to claim 1, wherein, The ratio of the amount of dispersant to the total mass of the asphalt and nickel-containing compound is 2-15:

1.

12. The preparation method according to claim 11, wherein, The ratio of the amount of dispersant to the total mass of the asphalt and nickel-containing compound is 5-10:

1.

13. The preparation method according to claim 1, wherein, The premixing temperature is 60-90℃, and the time is 1-5h.

14. The preparation method according to claim 1, wherein, The conditions for ball milling include: a ball milling speed of 300-500 rpm and a milling time of 8-20 h.

15. The preparation method according to claim 14, wherein, The conditions for ball milling include: a ball milling speed of 350-450 rpm and a milling time of 8-12 hours.

16. The preparation method according to claim 1, wherein, The nickel-containing compound is selected from at least one of nickel acetate, nickel nitrate, nickel chloride, and basic nickel carbonate.

17. The preparation method according to claim 16, wherein, The nickel-containing compound is basic nickel carbonate.

18. The preparation method according to claim 1, wherein, The calcination is carried out under an inert atmosphere.

19. The preparation method according to claim 18, wherein, The inert atmosphere is provided by nitrogen.

20. The preparation method according to claim 1, wherein, The pickling in step (2) includes: contacting the intermediate product with acid, followed by washing with water and drying.

21. The preparation method according to claim 20, wherein, With H + The molar ratio of the acid solution to the intermediate product is (1-4):

1.

22. The preparation method according to claim 20, wherein, The contact temperature is 60-120℃; the contact time is 2-12h.

23. The preparation method according to claim 22, wherein, The contact temperature is 90-105℃; the contact time is 4-8 hours.

24. The preparation method according to claim 20, wherein, The acid solution is an aqueous solution of inorganic acid and / or organic acid.

25. The preparation method according to claim 24, wherein, The acid solution is hydrochloric acid.

26. The nano-carbon cage prepared by the preparation method according to any one of claims 1-25.

27. The nano-carbon cage according to claim 26, wherein, The specific surface area of ​​the nano-carbon cage is 150-600 m². 2 / g.

28. The nanocarbon cage according to claim 26, wherein, The average number of carbon layers in the cage wall of the nano-carbon cage is 2-5.

29. The nano-carbon cage according to claim 28, wherein, The average number of carbon layers in the cage wall of the nano-carbon cage is 2-3 layers.

30. The nano-carbon cage according to claim 26, wherein, The average diameter of the nano-carbon cage is 3-10 nm.

31. The nanocarbon cage according to claim 30, wherein, The average diameter of the nano-carbon cage is 6-8 nm.

32. The nano-carbon cage according to claim 26, wherein, In the Raman curve of the nano-carbon cage, I D / I G Less than 1.

33. The application of the nano-carbon cage according to any one of claims 26-32 in lithium-ion capacitors.

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