Disclosure of Invention
The invention aims to solve the technical problems of low specific capacity and poor cycle stability of the conventional lithium ion battery cathode material in the prior art, provides a preparation method of metal organic framework derived carbon with high specific surface area, and applies the metal organic framework derived carbon as the lithium ion battery cathode material to a lithium ion battery. Since the prepared carbon material has large specific surface area, more active sites for lithium ion storage are exposed, and lithium ion diffusion kinetics are reduced, so that high lithium storage and rate performance is realized.
In order to solve the above technical problems, an embodiment of the present invention provides a method for preparing a metal organic framework-derived carbon having a high specific surface area, including the following steps:
(1) weighing 3.856g of zinc nitrate hexahydrate and 1.152g of tetrafluoroterephthalic acid, dissolving in 80mL of absolute ethanol, and stirring to obtain a mixed solution;
(2) carrying out hydrothermal reaction on the mixed solution at 120 ℃ for 12 hours, and then sequentially carrying out immersion cleaning treatment and filtering treatment to obtain a metal organic framework material;
(3) placing the metal organic framework material in a horizontal tube furnace, carrying out carbonization treatment under the condition of continuously introducing inert gas, and then naturally cooling to room temperature to obtain a carbonized product;
(4) sequentially carrying out immersion cleaning treatment, cleaning treatment and filtering treatment on the carbonized product to obtain an acid-cleaned product;
(5) and drying the acid washing product to obtain the metal organic framework derived carbon with high specific surface area.
On the basis of the technical scheme, the invention can be further improved as follows.
Further, the immersion cleaning treatment in the step (2) is specifically immersion cleaning by sequentially using deionized water and absolute ethyl alcohol.
Further, the inert gas is argon.
Further, the carbonization treatment is specifically carried out by heating from room temperature to 800 ℃, and keeping the temperature for 4 hours.
Further, in the carbonization treatment, the temperature rise rate is 5 degrees centigrade per minute.
Further, the immersion cleaning in the step (4) is specifically performed by using a hydrochloric acid solution with a concentration of 20%, and the cleaning is specifically performed by using deionized water for 5 times.
Further, the drying treatment specifically comprises the step of drying the acid-washed product in a vacuum drying oven at 75 ℃ for 24 hours.
Further, the specific surface area of the metal organic framework derived carbon with high specific surface area is 3686m2/g。
In order to solve the technical problem, embodiments of the present invention provide an application of the metal organic framework derived carbon with a high specific surface area as a negative electrode material in the preparation of a lithium ion battery.
The invention has the beneficial effects that: the preparation method of the metal organic framework derived carbon with the high specific surface area uses fluorine in an organic raw material as a mineralizer to quickly prepare the metal organic framework material. The carbon material with ultrahigh specific surface area and pore volume is obtained by processing the metal organic framework in a high-temperature carbonization and acid washing mode, and is applied to the negative electrode of the lithium ion battery. The preparation method is simple and convenient and easy to characterize, and a large number of pores exist in the prepared carbon material with the large specific surface, so that the method is very effective in relieving volume expansion of the material in the lithium ion storage process and shortening the diffusion path of lithium ions in the material, and shows excellent electrochemical performance. When the charge-discharge current density is 0.1A/g, the battery has high specific capacity of 1304mAh/g and also has good rate capability. In addition, under the condition of 5A/g of super-high current density, the specific capacity of 233mAh/g is still kept after 4000 cycles.
Detailed Description
The principles and features of this invention are described below in conjunction with the following drawings, which are set forth by way of illustration only and are not intended to limit the scope of the invention.
Example 1
1.152g of tetrafluoroterephthalic acid and 3.856g of zinc nitrate hexahydrate were dissolved in 80mL of an ethanol solution and uniformly stirred to obtain a mixed solution. And then, carrying out hydrothermal reaction on the mixed solution at 120 ℃ for 12 hours, sequentially using deionized water and absolute ethyl alcohol for immersion cleaning, and filtering to obtain the metal organic framework precursor material. And putting the metal organic framework precursor material into a tube furnace, carbonizing the metal organic framework precursor material for 4 hours at 800 ℃ under the argon atmosphere, cooling the metal organic framework precursor material to room temperature, and taking out the sample. And after taking out, washing the sample for 24 hours by using 20% hydrochloric acid, washing the sample for 5 times by using deionized water, filtering the washed sample, and finally drying the sample in a vacuum drying oven at the temperature of 75 ℃ to obtain the metal organic framework derived carbon with high specific surface area.
In the above examples, the fluorine ion in tetrafluoroterephthalic acid was used as a mineralizer to promote crystallization of the metal-organic framework material; the carbon material containing zinc oxide is produced by the metal organic framework material in the high-temperature carbonization process, and the specific surface area is 3686m by utilizing the reaction of hydrochloric acid and zinc oxide2Carbon material per g.
In order to test the specific capacity, rate capability and cycle performance of the metal organic framework derived carbon with high specific surface area, the metal organic framework derived carbon with high specific surface area is used as a negative electrode in a lithium ion battery to assemble a button battery, and the process is as follows: drying the metal organic framework derived carbon in a vacuum oven at 75 ℃ for 6 hours; then, respectively weighing metal organic framework derived carbon, conductive carbon black and polyvinylidene fluoride according to the mass ratio of 8:1:1, mixing with a proper amount of N-methyl pyrrolidone, grinding into electrode slurry, coating the electrode slurry on an aluminum foil, drying for 24 hours in a vacuum oven at 75 ℃, and cutting into electrode slices with the diameter of 14 mm by using a slicing machine; celgard2400 is used as a separator, metal lithium is used as another electrode, a dimethyl carbonate/diethyl carbonate/ethylene carbonate solution containing 1mol/L lithium hexafluorophosphate is used as an electrolyte, a mixed solution of dimethyl carbonate, diethyl carbonate and ethylene carbonate in a ratio of 1:1:1 is used as a solution, 1mol/L lithium hexafluorophosphate is used as a solute, and the electrolyte and an electrode plate are assembled together to form the lithium-ion button half-cell.
The lithium ion button half cell is subjected to electrochemical performance test on a cell test system of a CT2001A model and an electrochemical workstation of a CH604E model, and the voltage range of the lithium ion button half cell is 0.01-3V.
Fig. 1 is an SEM image of a metal organic framework-derived carbon having a high specific surface area obtained by the method of this example, and it can be seen that the carbon material exhibits a rough porous structure.
Fig. 2 is an N2 adsorption-desorption curve of the metal organic framework-derived carbon with a high specific surface area obtained by the method of the present embodiment, and the curve has a significant hysteresis loop due to the existence of a large number of mesopores; furthermore, the rapid rise of the curve over a small pressure range indicates that the material is rich in a microporous structure; specific surface area of metal organic framework derived carbon found by BET method 3686m2/g。
FIG. 3 is a Raman diagram of the metal-organic framework derived carbon having a high specific surface area obtained by the method of this example, and it can be seen that the Raman diagram is located at 1580cm-1And 1340cm-1The two characteristic peaks in (a) represent that the metal organic framework derived carbon is amorphous carbon.
Fig. 4 shows that the metal organic framework derived carbon with high specific surface area obtained by the method of the present embodiment is used as a lithium ion battery negative electrode active material, and has a cycle performance curve with a current density of 5A/g, and after 4000 cycles, the specific capacity is stabilized at 233mAh/g, and the lithium ion battery negative electrode active material has good cycle stability.
Fig. 5 is a rate performance curve of the metal organic framework derived carbon with high specific surface area obtained by the method of the present embodiment as a negative electrode active material of a lithium ion battery under different current densities, and when the current densities are 0.1, 0.2, 0.5, 1, 2, 5, and 10A/g, the battery has specific capacities of 1304, 1171, 980, 825, 704, 501, and 370mAh/g, and has excellent rate performance.
Fig. 6 is a CV curve measured on an electrochemical workstation of a model CH604E, in which the metal organic framework-derived carbon with high specific surface area obtained by the method of the present embodiment is used as a negative electrode active material of a lithium ion battery, an irreversible peak appears in the first turn due to SEI formation, and the curve maintains a good coincidence in the subsequent tests, indicating that the stability is good.
Comparative example 1
1.152g of terephthalic acid and 3.856g of zinc nitrate hexahydrate were dissolved in 80mL of N, N-dimethylformamide and stirred uniformly to obtain a mixed solution. And then, carrying out hydrothermal reaction on the mixed solution at 120 ℃ for 12 hours, sequentially using deionized water and absolute ethyl alcohol for immersion cleaning, and filtering to obtain the metal organic framework precursor material. And putting the metal organic framework precursor material into a tube furnace, carbonizing the metal organic framework precursor material for 4 hours at 800 ℃ under the argon atmosphere, cooling the metal organic framework precursor material to room temperature, and taking out the sample. And taking out the sample, washing the sample for 24 hours by using 20% hydrochloric acid, washing the sample for 5 times by using deionized water, filtering the sample, and finally drying the sample in a vacuum drying oven at the temperature of 75 ℃ to obtain the metal organic framework derived carbon.
The assembly process of the battery is as follows: respectively weighing metal organic framework derived carbon, conductive carbon black and polyvinylidene fluoride according to the mass ratio of 8:1:1, mixing with a proper amount of N-methyl pyrrolidone, grinding into electrode slurry, coating the electrode slurry on a copper foil, drying in a vacuum oven at 75 ℃ for 24 hours, and cutting into electrode slices with the diameter of 14 mm by using a slicing machine; celgard2400 is used as a diaphragm, metal lithium is used as another electrode, dimethyl carbonate/diethyl carbonate/ethylene carbonate solution containing 1mol/L lithium hexafluorophosphate is used as electrolyte, wherein the volume ratio of dimethyl carbonate, diethyl carbonate and ethylene carbonate is 1:1:1, and the electrolyte and an electrode plate are jointly assembled into the lithium-ion button half-cell.
The processes of comparative example 1 and example 1 are substantially the same, except that comparative example 1 employs a fluorine-free raw material and a co-precipitation method to prepare a metal organic framework-derived carbon. Compared with the metal organic framework derived carbon prepared in example 1, the specific surface area is lower, and the cycling stability is poorer.
Comparative example 2
1.152g of tetrafluoroterephthalic acid and 3.856g of zinc nitrate hexahydrate were dissolved in 80mL of an ethanol solution and uniformly stirred to obtain a mixed solution. And then, carrying out hydrothermal reaction on the mixed solution at 120 ℃ for 12 hours, sequentially using deionized water and absolute ethyl alcohol for immersion cleaning, and filtering to obtain the metal organic framework precursor material. And putting the metal organic framework precursor material into a tubular furnace, and carbonizing at 800 ℃ for 4 hours under an argon atmosphere to obtain the metal organic framework derived carbon.
The process of comparative example 2 is substantially the same as that of example 1 except that comparative example 2 has not been washed with hydrochloric acid. The specific surface area of the metal organic framework derived carbon obtained by the method is 278m2It can be seen that the specific surface area of the metal organic framework derived carbon is greatly reduced without washing with hydrochloric acid.
According to the preparation method of the metal organic framework derived carbon with the high specific surface area, zinc nitrate and tetrafluoroterephthalic acid are used as precursors, ethanol is used as a solvent, a metal organic framework material is synthesized through a hydrothermal method, wherein fluorine in the raw materials can be used as a mineralizer, the crystallinity is increased, the growth of metal organic framework derived crystals is promoted, the metal organic framework derived crystals are carbonized at high temperature, and hydrochloric acid washing and subsequent drying treatment are used to obtain the porous carbon with the ultrahigh specific surface area. The preparation method is simple in preparation process, simple and convenient to operate and convenient to characterize, and the electrode plates can be prepared and assembled into the CR2032 lithium ion button cell for electrochemical performance test. When the charge-discharge current density is 0.1A/g, the battery has high specific capacity of 1304 mAh/g. In addition, the rate test and the cycle test also show good electrochemical performance and excellent stability.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.