Patent Application
20190260012
This invention relates to a method for preparing a boron-doped carbon material, in particular, a method for making boron-doped porous carbon spheres.
Among the various electrochemical energy storage devices or equipment, lithium-ion batteries, due to their high energy density and long cycle life, have already been widely used in mobile phones and electric vehicles. With a growing demand for the technology, there is a need for a higher performance rate and cycle stability in the next generation high-performance lithium-ion batteries, especially as to the need for the anode material. Currently, graphite has been used commercially as anode material. However, it has a low theoretical capacity (372 mAh g−1) and inferior rate performance, which are keys to lithium ion battery performances. Therefore, domestic and foreign researchers have proposed a variety of anode substitutes with high lithium-ion storage capacities, such as Sn, SnO2, Si, ZnO, and various transition metal oxides. However, the materials mentioned above have problems during the lithium-insertion/extraction process, such as substantial volume changes, substantial electrode-electrolyte side reactions, and poor chemical stability of the electrode materials, thereby limiting the rate performance and cycle life of lithium-ion anode materials.
In comparison, carbon-based materials, especially porous carbon materials, have high chemical stability and abundant porous structures. As anode materials for lithium-ion batteries, carbon-based materials can absorb and store lithium ions with their abundant pore structures and large specific surface area, thereby greatly improving the lithium-ion storage capacity as compared to graphite. Relevant studies have shown that carbon-based materials doped with heteroatoms (such as nitrogen doping and boron doping) can further improve the capacity, rate performance and cycle stability of lithium-ion anode materials. Furthermore, boron doping can enhance the lithium-ion adsorption sites in the carbon materials for lithium-ion storage, thereby improving lithium-ion storage capacity, Moreover, boron-containing structural units with high chemical stability, such as BC3, BC2O and BCO2, can be introduced into the carbon skeleton structure, thus greatly improving the structural stability of carbon materials in electrochemical reactions, especially for cyclic stability under high current density.
Existing methods for preparing boron-doped porous carbon materials or graphite-doped materials include the chemical vapor deposition method, the boron source post-treatment method, and the boron source co-hydrothermal synthesis method. Problems with current methods for the preparation of boron-doped carbon-based materials, include, among others, high raw material costs, time-consuming and complicated production methods that are difficult to scale up, and low boron doping concentrations (<4-wt %). To compensate for the deficiencies in the preparation methods mentioned above, the present invention provides a simple method towards the technical problem of preparing boron-doped porous carbon spheres that is capable of in-situ boron doping and has a large-scale production potential.
The preparation method of boron-doped porous carbon spheres provided by the present invention solves the current problems of high cost, low boron doping and difficult-to-scale production, by using boric acid, carbohydrates, and silicon-based pore-forming agents as sources of boron, carbon, and a pore template, to obtain boron-doped porous carbon spheres by a self-assembly process assisted by a spray drying treatment.
The preparation mechanism and key ideas of the present invention are as follows: a precursor solution of boron-doped carbon is formed by self-assembly between the hydroxyl groups of boric acid and carbohydrates; a silicon-based pore-forming agent capable of forming a good complexation with boric acid and carbohydrates is added to the precursor solution to create pores; the precursor solution is passed through a spray drying process (aerosol-assisted) to form polydispersed nanospheres. Meanwhile, aerosol droplets formed from boron sources, carbon sources, and pore-forming agents undergo a self-assembly reaction, guided by solvent evaporation and an initial condensation polymerization reaction, to form solid spheres; porous carbon spheres, which are doped with boron in situ in high concentrations, are then obtained through a high-temperature pyrolysis process and a process for removing the pore template. As can be seen from the above description, the multidimensional structural properties of the doped porous carbon spheres obtained by the present invention can be regulated and optimized, including their external morphology (continuous production of polydispersed nanospheres can be achieved), pore structure (through the selection of pore templates and proportion control), boron doping concentrations (which can be achieved through the regulation of boric acid proportions in the precursor solution). In addition, the low cost choice of materials and the simple continuous production process mean that the boron-doped porous carbon spheres obtained by the present invention have important application potential in anode materials for lithium-ion batteries.
The specific technical protocol of the present invention is:
A method for preparing boron-doped porous carbon spheres is provided, comprising the following steps:
(1) dissolving and mixing a carbohydrate carbon source and boric acid (boron source) in water at desired proportions to form a transparent solution;
(2) adding and mixing a silicon-based pore-forming agent to the solution from step (1) to form a precursor solution for the boron-doped porous carbon spheres;
(3) spray drying (aerosol-assisted)the precursor solution obtained in step (2), wherein the precursor solution undergoes a hydroxyl-guided self-assembly and polycondensation process during the spraying and heating process, thereby obtaining solid precursor particles of the boron-doped porous carbon spheres.
(4) heating the solid precursor particles obtained in step (3) to 600° C.˜1000° C. in an inert atmosphere to obtain a mixture in which a pore template SiO2 is embedded in a boron-doped carbon spheres.
(5) removing the silicon-based pore-forming agent from the mixture obtained in step (4), thereby obtaining the boron-doped porous carbon spheres.
Optimally, the carbohydrate carbon source mentioned above is selected from one or more of the following: glucose, sucrose, maltose, chitosan and soluble starch, wherein the boric acid to carbohydrate mass ratio is0.1:100˜1:1.
Optimally, the silicon-based pore-forming agent is selected from one or more of tetraethyl orthosilicate (TEOS), nano-silica (SiO2) and sodium silicate, wherein the mass ratio of the silicon-based pore-forming agent to carbohydrate is 5:1˜1:10.
Optimally, the heating temperature of the spray drying process is 300° C.˜600° C.
Optimally, the aerosol in the spray drying process is a droplet carrying gas, wherein the gas is one of or more of nitrogen gas and/or argon gas, wherein the gas flow rate is 0˜50 L/min.
Optimally, the inert atmosphere in step 4) is one of or both nitrogen gas and/or argon gas.
Optimally, the high-temperature pyrolysis heating temperature is 600˜1000° C., wherein the heating rate is 0.5° C./min˜15° C./min, and wherein the holding time is 0 h˜6 h.
Optimally, the silicon-based pore-forming agent is removed using a hydrofluoric acid or sodium hydroxide washing method, wherein the washing liquid is one or more of a 1%˜10% hydrofluoric acid solution and/or a 0.5 mol/L˜5 mol/L sodium hydroxide, wherein the washing temperature is 25° C.˜60° C., wherein the washing method includes centrifugation and/or suction filtration.
Optimally, the temperature of the drying process in step 5) is 50° C.˜120° C. In another aspect, the present invention relates to boron-doped porous carbon spheres prepared using the method above.
The significant advantages of the present invention are as follows:
(1) The present invention has a significant economic advantage because the boron source and carbon source used, the boric acid and carbohydrate, are low in cost as compared to existing methods for preparing boron-doped carbon materials, which use expensive raw materials such as sodium borohydride and boron chloride;
(2) the present invention provides a method using an (aerosol-assisted) spray drying treatment method, which is a simple process that can be realized for continuous production, and has significant advantages for industrial application;
(3) the boron-doped porous carbon spheres made using the present invention is obtained by a molecular precursor self-assembly reaction, wherein the boron doping quantity and pore structure can be controlled by adjusting the ratio of the carbon source, boron source, and pore-forming agent in the precursor solution, thereby obtaining boron-doped porous carbon spheres to different applications; and
(4) the boron-doped porous carbon spheres prepared with the method herein have the advantages such as having high specific surface areas; the boron is capable of being doped in-situ; a high boron doping amount; structures that can be controlled; and high carbon structural stability, all of which have important application value in the field of lithium-ion batteries.
The following combination of drawings and specific examples further elaborates the advantages of the present invention.
The present embodiment of the method for preparing boron-doped porous carbon spheres is carried out according to the following steps: 1.8 g of glucose and 1.24 g of boric acid were measured and dissolved in 15 mL of deionized water and stirred until complete dissolution; 4.2 g of tetraethyl orthosilicate, 2 mL of 0.1 mol/L hydrochloric acid, and 15 mL of ethanol were added in sequence and the mixture was stirred for 1 h to form a precursor solution; then the precursor solution was carried by nitrogen into the aerosol-assisted spray drying unit at a temperature of 450° C.; the carrier nitrogen flow was controlled at 500 mL/min; and the solid products obtained were heated to 900° C. in a tubular furnace at a heating rate of 8° C./min in nitrogen and remained insulated for 3 hours; the carbonized products were washed by centrifugation with 10% hydrofluoric acid and deionized water three times, and then dried for 10 hours at 80° C. to obtain the boron-doped porous carbon spheres in this example.
The present invention provides a method for preparing undoped porous carbon spheres in order to ascertain the effect of boron doping on the structure of carbon materials: 1.8 g of glucose was measured and dissolved in 15 mL of deionized water and stirred to complete dissolution; 4.2 g of tetraethyl orthosilicate, 2 mL of 0.1 mol/L hydrochloric acid, and 15 mL of ethanol were added in sequence, and the mixture was stirred for 1 h to form a precursor solution; then the precursor solution was carried by nitrogen into the aerosol-assisted spray drying unit at a temperature of 450° C.; the carrier nitrogen flow was controlled at 500 mL/min; and the solid products obtained were heated to 900° C. in a tubular furnace at a heating rate of 8° C./min in nitrogen and remained insulated for 3 hours; the carbonized products were washed by centrifugation with 10% hydrofluoric acid and deionized water three times, and then dried for 10 hours at 80° C. to obtain the undoped porous carbon spheres in Comparative Example 1.
1.8 g of sucrose and 1.8 g of boric acid were measured and dissolved in 15 mL of deionized water and stirred until complete dissolution; 4.2 g of tetraethyl orthosilicate, 2 mL of 0.1 mol/L hydrochloric acid, and 15 mL of ethanol were added in sequence, and the mixture was stirred for 1 h to form a precursor solution; then the precursor solution was carried by nitrogen into the aerosol-assisted spray drying unit at a temperature of 450° C.; the carrier nitrogen flow was controlled at 500 mL/min; the solid products obtained were heated to 900° C. in a tubular furnace at a heating rate of 8° C./min in nitrogen and remained insulated for 3 hours; and the carbonized products were washed by centrifugation with 10% hydrofluoric acid and deionized water three times, and then dried for 10 hours at 80° C. to obtain the boron-doped porous carbon spheres in this example. XPS analysis shows that the boron concentration of the boron-doped porous carbon spheres was 4.5%.
1.8 g of soluble starch and 1.24 g of boric acid was measured and dissolved in 15 mL of deionized water and stirred until complete dissolution; 4.2 g of tetraethyl orthosilicate, 2 mL of 0.1 mol/L hydrochloric acid, and 15 mL of ethanol were added in sequence and the mixture was stirred for 1 h to form a precursor solution; then the precursor solution was carried by nitrogen into the aerosol-assisted spray drying unit at a temperature of 450° C.; the carrier nitrogen flow was controlled at 500 mL/min; the solid products obtained were heated to 900° C. in a tubular furnace at a heating rate of 8° C./min in nitrogen and remained insulated for 3 hours; and the carbonized products were washed by centrifugation with 10% hydrofluoric acid and deionized water three times, and then dried for 10 hours at 80° C. to obtain the boron-doped porous carbon spheres in this example. XPS analysis shows that the boron concentration of the boron-doped porous carbon spheres was 3.2%.
1.8 g of glucose and 1.24 g of boric acid were measured and dissolved in 15 mL of deionized water and stirred until complete dissolution; 15 g of a nano-SiO2 solution (the solvent was water, the SiO2 nanoparticle size was 15 nm ˜20 nm, and the mass fraction was 30%) were stirred for 1 h to form a precursor solution; then the precursor solution was carried by nitrogen into the aerosol-assisted spray drying unit at a temperature of 450° C.; the carrier nitrogen flow was controlled at 500 mL/min; the solid products obtained were heated to 900° C. in a tubular furnace at a heating rate of 8° C./min in nitrogen and remained insulated for 3 hours; and the carbonized products were washed by centrifugation with 10% hydrofluoric acid and deionized water three times, and then dried for 10 hours at 80° C. to obtain the boron-doped porous carbon spheres in this example. XPS analysis shows that the boron concentration of the boron-doped porous carbon spheres was 2.5%.
1.8 g of maltose and 1.24 g of boric acid were measured and dissolved in 15 mL of deionized water and stirred until complete dissolution; 4.2 g of tetraethyl orthosilicate, 2 mL of 0.1 mol/L hydrochloric acid, and 15 mL of ethanol were added in sequence and the mixture was stirred for 1 h to form a precursor solution; then the precursor solution was carried by nitrogen into the aerosol-assisted spray drying unit at a temperature of 450° C.; the carrier nitrogen flow was controlled at 500 mL/min; the solid products obtained were heated to 600° C. in a tubular furnace at a heating rate of 2° C./min in nitrogen and remained insulated for 3 hours; and the carbonized products were washed by centrifugation with 10% hydrofluoric acid and deionized water three times, and then dried for 10 hours at 80° C. to obtain the boron-doped porous carbon spheres in this example. XPS analysis shows that the boron concentration of the boron-doped porous carbon spheres was 5.3%.
1.8 g of soluble starch and 0.6 g of boric acid were measured and dissolved in 15 mL of deionized water and stirred until complete dissolution; 15 g of a nano-SiO2 solution (the solvent was water, the SiO2 nanoparticle size was 15 nm˜20 nm, and the mass fraction was 30%) were added in sequence and the mixture was stirred for 1 h to form a precursor solution; then the precursor solution was carried by nitrogen into the aerosol-assisted spray drying unit at a temperature of 450° C.; the carrier nitrogen flow was controlled at 500 mL/min; the resulting solid products were heated to 1000° C. in a tubular furnace at a heating rate of 8° C./min in nitrogen and remained insulated for 3 hours; and the resulting carbonized products were washed by centrifugation with a 5 mol/L sodium hydroxide solution and deionized water three times, and then dried for 10 hours at 80° C. to obtain the boron-doped porous carbon spheres in this example. XPS analysis shows that the boron concentration of the boron-doped porous carbon spheres was 0.8%.
1.8 g of glucose and 1.24 g of boric acid were measured and dissolved in 15 mL of deionized water and stirred until complete dissolution; 4.2 g of tetraethyl orthosilicate, 2 mL of 0.1 mol/L hydrochloric acid, and 15 mL of ethanol were added in sequence and the mixture was stirred for 1 h to form a precursor solution; then the precursor solution was carried by nitrogen into the aerosol-assisted spray drying unit at a temperature of 300° C.; the carrier nitrogen flow was controlled at 1 L/min; the resulting solid products were heated to 800° C. in a tubular furnace at a heating rate of 5° C./min in nitrogen and remained insulated for 3 hours; and the carbonized products obtained were washed by centrifugation with 10% hydrofluoric acid and deionized water three times, and then dried for 10 hours at 80° C. to obtain the boron-doped porous carbon spheres in this example. XPS analysis shows that the boron concentration of the boron-doped porous carbon spheres was 3.6%.
1.8 g of sucrose and 1.24 g of boric acid were measured and dissolved in 15 mL of deionized water and stirred until complete dissolution; 8.4 g of tetraethyl orthosilicate, 4 mL of 0.1 mol/L hydrochloric acid, and 30 mL of ethanol were added in sequence, and the mixture was stirred for 1 h to form a precursor solution; then the precursor solution was carried by nitrogen into the aerosol-assisted spray drying unit at a temperature of 450° C.; the carrier nitrogen flow was controlled at 500 mL/min; the solid products obtained were heated to 900° C. in a tubular furnace at a heating rate of 8° C./min in nitrogen and remained insulated for 3 hours; and the carbonized products obtained were washed by centrifugation with 10% hydrofluoric acid and deionized water three times, and then dried for 10 hours at 80° C. to obtain the boron-doped porous carbon spheres in this example. XPS analysis shows that the boron concentration of the boron-doped porous carbon spheres was 2.6%.
1.8 g of glucose and 0.9 g of boric acid were measured and dissolved in 15 mL of deionized water and stirred until complete dissolution; 2.1 g of tetraethyl orthosilicate, 1 mL of 0.1 mol/L hydrochloric acid, and 8 mL of ethanol were added in sequence, and the mixture was stirred for 1 h to form a precursor solution; then the precursor solution was carried by nitrogen into the aerosol-assisted spray drying unit at a temperature of 450° C.; the carrier nitrogen flow was controlled at 500 mL/min; the resulting solid products were heated to 1000° C. in a tubular furnace at a heating rate of 5° C./min in nitrogen and remained insulated for 3 hours; and the carbonized products obtained were washed by centrifugation with 10% hydrofluoric acid and deionized water three times, and then dried for 10 hours at 80° C. to obtain the boron-doped porous carbon spheres in this example. XPS analysis shows that the boron concentration of the boron-doped porous carbon spheres was 2.3%.
3.6 g of sucrose and 3.6 g of boric acid were measured and dissolved in 30 mL of deionized water and stirred until complete dissolution; 30 g of a nano-SiO2 solution (the solvent was water, the Si02 nanoparticle size was 15nm-20 nm, and the mass fraction was 30%) were added in sequence, and the mixture was stirred for 1 h to form a precursor solution; then the precursor solution was carried by nitrogen into the aerosol-assisted spray drying unit at a temperature of 500° C.; the carrier nitrogen flow was controlled at 2 mL/min; the resulting solid products were heated to 900° C. in a tubular furnace at a heating rate of 8° C./min in nitrogen and remained insulated for 3 hours; and the resulting carbonized products were washed by centrifugation with a 5 mol/L sodium hydroxide solution and deionized water three times, and then dried for 10 hours at 80° C. to obtain the boron-doped porous carbon spheres in this example. XPS analysis showed that the boron concentration of the boron-doped porous carbon spheres was 3.8%.
The structure and properties of the boron-doped porous carbon spheres obtained from Example 1 were analysed: analytic methods include Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, low-temperature N2 adsorption, and X-ray photoelectron spectroscopy to determine the degree of graphitization, microscopic morphology, pore structure parameters, stability of carbon structures and amount of boron doping of the porous graphite material obtained in Example 1. The specific procedures were as follows:
The boron-doped porous carbon spheres obtained in Example 1 were used as anode materials for lithium-ion batteries. The performance test methods were as follows: using a lithium wafer as an electrode, and the boron-doped porous carbon spheres as the active material of the working electrode, a CR2032 button battery was assembled to test the performance of the spheres as anode materials for lithium-ion batteries. The method for preparing the working electrodes was as follows: the boron-doped porous carbon spheres, carbon black and PVDF were dissolved in NMP in a mass ratio of 7:1.5:1.5 and ground into a uniform paste, after which the paste was coated onto copper foil and dried in vacuum at 80° C. for 12 hours to obtain the working electrode plates. The dried plates were cut into circular sheets, maintaining an active material density of 0.5 mg cm−2-1 mg cm−2. The button cells were assembled with fresh lithium linings in a glove box. The electrolyte was 1 M LiPF6 (the solvent was ethylene carbonate and diethyl carbonate, 1:1), and a Whatman fiberglass membrane was used as the diaphragm. The cyclic voltammetric characteristic curves and the constant current-constant voltage charge/discharge curves of the battery were tested in a voltage range of 0.01 V˜3.0 V vs. Li/Li+. The results of the analysis are as follows:
It should be noted that the examples of the present invention can be readily implemented and do not impose any limitations on the present invention whatsoever. Any person of ordinary skill in the art may use the technical content disclosed above to enhance it or modify it to an equivalently effective embodiment. Any modification or equivalent change or enhancement to the above embodiments based on the technical essence of the present invention and does not exceed the technical scheme of the present invention shall be within the scope of the technical scheme of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201610298107.8 | May 2016 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2017/083134 | 5/5/2017 | WO | 00 |
