CN114843481A - A lithium ion anode material derived from ZIF-8 and its preparation method - Google Patents

Abstract

The invention belongs to the technical field of preparation of lithium ion battery electrode materials, and in particular relates to a lithium ion negative electrode material derived from ZIF-8 and a preparation method thereof. The material is prepared by a simple co-precipitation method and a heat treatment process. The preparation method provided by the present invention has the advantages of simple and easy operation, high material yield, high rate, stable structure, large particle dispersion coefficient, low cost, green environmental protection, etc., and the obtained ZIF-8-derived lithium ion battery negative electrode material has a uniform morphology Controllable, no agglomeration, large specific surface area, abundant central active sites, when used as an electrode material, it exhibits high discharge specific capacity and electrochemical characteristics, which can meet the requirements of preparing high-performance lithium-ion battery electrode materials.

Description

A lithium ion anode material derived from ZIF-8 and its preparation method

technical field

The invention belongs to the technical field of preparation of lithium ion battery electrode materials, in particular to a lithium ion negative electrode material derived from ZIF-8 and a preparation method thereof.

Background technique

Lithium-ion batteries have the advantages of high energy density, long cycle life and no memory effect, and have been widely used. At present, the negative electrode material of commercial lithium-ion batteries is graphite electrode, but its theoretical specific capacity is only 372mA h/g, and when the battery is charged and discharged at a high rate, the graphite electrode is prone to produce lithium dendrites, which makes the internal structure of the battery suffer. damage, leading to security issues.

As an electrode material for lithium-ion batteries, ZIF-8 has many advantages, such as abundant redox active sites, abundant resources, high yield, strong temperature adaptability, and universality, and has been concerned and studied by the majority of workers. However, the currently prepared ZIF-8 has disadvantages such as poor morphology, low yield, more impurities in the product, low mechanical strength, and poor material stability, which lead to its low capacity and poor performance during charging and discharging of lithium-ion batteries. Poor wait. Therefore, it is necessary to prepare a ZIF-8 electrode material with universal synthesis method, high yield, good stability and strong temperature adaptability.

In the prior art, the methods for preparing ZIF-8 material with micro-nano structure and achieving better electrochemical performance mainly include: hydrothermal method (solvothermal method), co-precipitation method, microwave-assisted method and the like. The preparation method has complex process, impure product, high experimental requirements, high cost and low yield, and is not suitable for large-scale production; at the same time, the prepared ZIF-8 has poor cycle stability during the lithium ion charge and discharge process. , defects such as lower capacity.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the above-mentioned problems existing in the conventional technology, and to provide a lithium ion negative electrode material derived from ZIF-8 and a preparation method thereof.

In order to realize the above-mentioned technical purpose and achieve the above-mentioned technical effect, the present invention is realized through the following technical solutions:

A preparation method of a lithium ion negative electrode material derived from ZIF-8, comprising the following steps:

1) Measure CH ₃ OH solution and deionized water according to the proportion, pour them into a mixing container and stir to form mixed solution A;

2) respectively weigh Zn(NO ₃ ) ₂ .6H ₂ O and 2-methylimidazole according to the proportions, place them in a mortar and grind them uniformly to obtain a liquid mixed medicine;

3) adding the obtained mixed medicine into mixed solution A, and rapidly dissolving under ultrasonic action to obtain mixed solution B;

4) The obtained mixed solution B is subjected to magnetic stirring to obtain a precipitate; the obtained precipitate is washed and dried, and is denoted as ZIF-8;

5) The obtained precipitate ZIF-8 is placed in a tube furnace, and in an Ar atmosphere, the lithium ion derived from ZIF-8 is obtained after heat treatment at 500 to 1000 ° C for 2 to 4 hours and naturally cooled to room temperature negative electrode material.

Further, in the above-mentioned preparation method of lithium ion negative electrode material, in step 1), the volume of CH ₃ OH solution is related to the amount of Zn(NO ₃ ) ₂ ·6H ₂ O, wherein 1mM Zn(NO ₃ ) ₂ ·6H ₂ O requires 10-30 ml _of CH3OH solution.

Further, in the above-mentioned preparation method of lithium ion negative electrode material, in step 1), the volume of the deionized water is 2-6 times the volume of CH ₃ OH.

Further, in the above-mentioned preparation method of lithium ion negative electrode material, in step 2), the 2-methylimidazole acts as a Zn ²⁺ ligand in the reaction process, wherein Zn(NO ₃ ) ₂ ·6H ₂ O and The molar ratio of 2-methylimidazole is 1:2-6.

Further, in the above-mentioned preparation method of lithium ion negative electrode material, in step 2), the time of the ultrasonic action is 5-10 minutes.

Further, in the above-mentioned preparation method of lithium ion negative electrode material, in step 3), the determination basis for the dissolution is: the solution becomes turbid due to the rapid coordination between the ions after the ions are hydrolyzed.

Further, in the above-mentioned preparation method of lithium ion negative electrode material, in step 4), the rotational speed during the magnetic stirring is 300-700 r/min.

Further, in the above-mentioned preparation method of lithium ion negative electrode material, in step 4), the washing solution used in the washing is CH ₃ OH solution, and the washing times are 2 to 4 times.

Further, in the above-mentioned preparation method of lithium ion negative electrode material, in step 4), the obtained drying is carried out in a vacuum drying oven, the drying temperature is 50-80° C., and the drying time is 12-24 h.

A lithium ion negative electrode material derived from ZIF-8, which is prepared according to the above-mentioned preparation method of a lithium ion negative electrode material.

The beneficial effects of the present invention are:

1. The raw materials used are rich in sources, low in cost, environmentally friendly, safe and pollution-free, the synthesis method is simple and easy to operate, the yield is high, and has a good application prospect for lithium ion batteries.

2. The ZIF-8-derived lithium ion anode material was prepared by a simple co-precipitation method and heat treatment process. During this process, due to the hydrolysis reaction of Zn ²⁺ and 2-methylimidazole, it has a strong coordination function, And because of the addition of the aqueous solution, the hydrolysis rate of the ions in the solution can be accelerated in a short time; secondly, by adjusting the ratio of the reactants, the yield of the product can be effectively improved, and the microscopic morphology can be made more uniform, for the efficient preparation of high-performance lithium The anode materials for ion batteries provide a universal preparation route.

3. The ZIF-8-derived lithium ion anode material prepared by this method has a skeleton structure, which can not only provide a higher specific surface area, thereby increasing the contact area between the electrode material and the electrolyte, which is conducive to the rapid transmission of ions; and The structure can play a supporting role and is not easy to collapse during the charge-discharge cycle, so it exhibits high specific capacity and good cycle stability as a ZIF-8-derived lithium-ion battery anode material.

Of course, it is not necessary for any product implementing the present invention to achieve all of the above advantages simultaneously.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings used in the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without any creative effort.

FIG. 1 is a state diagram of mixed solution B after ultrasonic dissolution in Example 1. FIG.

2 is the SEM images of the lithium-ion battery negative electrode material obtained in Example 1 (heated at 700° C., denoted as ZNC-700) under different magnifications;

Fig. 3 is the EIS curve diagram of the ZNC-700 electrode material obtained in Example 1;

4 is a schematic diagram of the electrochemical performance of the ZNC-700 electrode material obtained in Example 1 as a negative electrode of a lithium ion battery: (a) CV curve; (b) GCD curve;

5 is a graph showing the cycle stability of the ZNC-700 electrode material obtained in Example 1 at a current density of 500 mA/g;

6 is a state diagram of mixed solution B after ultrasonic dissolving in Example 2;

7 is the SEM images of the lithium-ion battery negative electrode material (heated at 800° C., denoted as ZNC-800) obtained in Example 2 under different magnifications;

Fig. 8 is the EIS curve diagram of the ZNC-800 electrode material obtained in Example 2;

9 is a schematic diagram of the electrochemical performance of the ZNC-800 electrode material obtained in Example 2 as a negative electrode of a lithium ion battery: (a) CV curve; (b) GCD curve;

10 is a schematic diagram of the cycle performance of the ZNC-800 electrode material obtained in Example 2 at a current density of 500 mA/g.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Compared with the common use of methanol as the organic solvent to carry out the standing reaction for a long time (12-36h), the invention adopts the mixed solution of deionized water and methanol with stronger polarity as the solvent, which can accelerate the hydrolysis reaction of the metal complex. resulting in rapid precipitation. The invention obtains the desired target electrode material by co-precipitation method, has the advantages of simple and easy operation, low reaction temperature, rapid synthesis and high yield, large material dispersion coefficient without agglomeration, and can provide higher specific surface area and central activity site, so that the lithium intercalation/delithiation reaction can occur better and show better lithium battery performance.

Specific embodiments of the present invention are as follows:

Example 1

First, measure 30ml of CH ₃ OH solution and 150ml of deionized water, place them together in a 200ml beaker to form mixed solution A, add a magnetic stirring bar to stir on a magnetic stirring table, and then weigh 0.52 g of Zn( NO ₃ ) ₂ ·6H ₂ O and 0.72 g of 2-methylimidazole were placed in a mortar, fully ground to make them evenly mixed, the mixed medicine was slowly added to the mixed solution A and sonicated for 5 min under the action of an ultrasonic machine to make The mixed medicine was fully dissolved to obtain mixed solution B. At this time, mixed solution B had become turbid (as shown in Figure 1). Then, mixed solution B was placed on a magnetic stirring table and stirred at a speed of 600 r/min for 8 hours. The precipitate was centrifuged, filtered, and washed 3 times with CH ₃ OH solution. The washed precipitate was collected, placed in a vacuum drying box, and dried in vacuum at 60 °C for 12 h to obtain ZIF-8. Finally, ZIF-8 was placed in a tube furnace, calcined at 700°C for 2h at a heating rate of 5°C/min in an argon atmosphere, and then naturally cooled to room temperature to obtain lithium derived from ZIF-8. Ion negative electrode material, denoted as ZNC-700.

This embodiment adopts a simple co-precipitation method and heat treatment process. After washing and drying the obtained white precipitate, the target product is obtained by further heat treatment. The experimental steps are simple, the repeatability is high, the experimental conditions are highly controllable, and the experimental method has good universality. The obtained ZNC-700 has a uniform morphology (as shown in Figure 2) and a size of about 1-2 microns. Due to the special structure of ZIF-8 after heat treatment, the material has a high specific surface area, good dispersion, stable structure and is not easy to collapse. , thereby providing more electrochemically active sites, which can improve the electrochemical reaction kinetics of the electrode material, shorten the ion transport path, improve the lithium storage performance of the material, and help the electrode material to achieve higher capacity and cycle stability.

The application of the ZNC-700 lithium ion battery electrode material obtained in this example in the energy storage system is as follows: assemble a button battery, and test its lithium storage electrochemical performance. The prepared ZNC-700 was used as the active material, the conductive carbon black (SP) was used as the conductive agent, and the polyvinylidene fluoride (PVDF) was used as the binder, which was weighed according to the mass ratio of 80:10:10, a total of 100 mg, and a certain amount was added. The dispersant N-methylpyrrolidone (NMP) was used to prepare electrode slurry. The slurry was stirred on a magnetic stirrer for 12 hours to make it evenly mixed. Then, the slurry was evenly coated on the copper foil, and then placed in a vacuum drying oven for drying at 60 °C for 12 hours. After drying, the slurry is cut into small discs of equal size under a microtome, which is the prepared working electrode. A button-type half-cell was assembled under the battery packaging machine by taking the working electrode with suitable load, Li sheet, separator, and electrolyte.

In this system, Li sheet was also used as negative electrode, ZNC-700 was used as working electrode, LiPF ₆ was used as electrolyte, and polypropylene microporous membrane was used as separator to test the electrochemical performance of ZNC-700 electrode material in lithium-ion battery. Among them, Figure 3 is the EIS curve of the battery, and the equivalent resistance of the battery is smaller. Figure 4(a) shows the cyclic voltammetry (CV) curves of the first three circles of the electrode material. The voltage window is 0.01-3.0V. It can be seen from the image that the curves have a high degree of overlap and obvious redox peaks, indicating that ZNC -700 undergoes a more sufficient redox reaction, which can provide more electronic active sites; Figure 4(b) is the charge-discharge rate performance diagram of the electrode material, after 50mA/g, 100mA/g, 200mA/g After the charge and discharge of g, 500mA/g, 1mA/g, and 50mA/g, the capacity retention rate is still very high, indicating that the electrode material has good rate performance during the cycle charge and discharge process. As shown in the figure, the battery was tested with a constant current charge-discharge cycle at a current density of 500 mA/g. After 200 cycles of testing, the discharge specific capacity reached a maximum of 564.1 mA h/g, and the capacity retention rate reached about 88.1%, indicating that the The material has good cycle stability.

Example 2

First, measure 60ml of CH ₃ OH solution and 180ml of deionized water, and place them together in a 300ml beaker to form mixed solution A, add a magnetic stirring bar to stir on a magnetic stirring table, and then weigh 1.04 g of Zn( NO ₃ ) ₂ ·6H ₂ O and 1.15 g of 2-methylimidazole were placed in a mortar, fully ground to make them evenly mixed, the mixed drug was slowly added to the mixed solution A and sonicated for 5 min under the action of an ultrasonic machine to make The mixed medicine was fully dissolved to obtain mixed solution B. At this time, mixed solution B had become turbid (as shown in Figure 6), and then mixed solution B was placed on the magnetic stirring table and stirred at a speed of 600 r/min for 8 hours. The precipitate was centrifuged, filtered, and washed 3 times with CH ₃ OH solution. The washed precipitate was collected, placed in a vacuum drying box, and dried in vacuum at 60 °C for 12 h to obtain ZIF-8. Finally, ZIF-8 was placed in a tube furnace, calcined at 800 °C for 2 h at a heating rate of 5 °C/min in an argon atmosphere, and then naturally cooled to room temperature to obtain lithium derived from ZIF-8. Ion negative electrode material, denoted as ZNC-800.

This embodiment adopts a simple co-precipitation method and heat treatment process. Compared with Example 1, the synthesis steps are similar. The material properties are optimized by changing the ratio and concentration of the reactants and adjusting the heat treatment temperature. The experimental steps are simple and have good repeatability and controllability. The morphology of the obtained ZNC-800 is more uniform than that of the ZNC-800 in Example 1 (as shown in Figure 7).

The application of the ZNC-800 lithium ion battery electrode material obtained in this example in the energy storage system is as follows: assemble a button battery, and test its lithium storage electrochemical performance. The prepared ZNC-800 was used as the active material, the conductive carbon black (SP) was used as the conductive agent, and the polyvinylidene fluoride (PVDF) was used as the binder, which was weighed according to the mass ratio of 80:10:10, a total of 100 mg, and a certain amount was added. The dispersant N-methylpyrrolidone (NMP) was used to prepare electrode slurry. The slurry was stirred on a magnetic stirrer for 12 hours to make it evenly mixed. Then, the slurry was evenly coated on the copper foil, and then placed in a vacuum drying oven for drying at 60 °C for 12 hours. After drying, the slurry is cut into small discs of equal size under a microtome, which is the prepared working electrode. A button-type half-cell was assembled under the battery packaging machine by taking the working electrode with suitable load, Li sheet, separator, and electrolyte.

In this system, Li sheet was used as negative electrode, ZNC-800 was used as working electrode, LiPF ₆ was used as electrolyte, and polypropylene microporous membrane was used as separator to test the electrochemical performance of ZNC-800 electrode material in Li-ion battery. Among them, Figure 8 is the EIS curve of the battery. It can be seen that the lithium ion battery assembled with the electrode materials synthesized under the above conditions has a small equivalent resistance due to the sufficient infiltration of the electrolyte in the electrochemical reaction. Figure 9(a) shows the cyclic voltammetry (CV) curves of the first three circles of the electrode material. The voltage window is 0.01-3.0V. It can be seen from the image that the curves have a high degree of overlap and obvious redox peaks, indicating that ZNC Sufficient redox reaction occurred at -800, and the material reaction was relatively sufficient; Figure 9(b) is the charge-discharge rate performance diagram of the electrode material. After charging and discharging at current densities of /g and 50 mA/g, the capacity retention rate is still very high, indicating that the electrode material has good rate performance during the cyclic charge and discharge process. As shown in Figure 10, the battery was tested with a constant current charge-discharge cycle at a current density of 500 mA/g. After 300 cycles of the test, the discharge specific capacity reached a maximum of 365.2 mA h/g, and the capacity retention rate reached about 73.1%. The material has good cycle stability.

The above two examples show that the electrochemical energy storage performance of ZIF-8-derived lithium ion anode materials can be further optimized by adjusting the solution solubility, element ratio and heat treatment temperature. The ability of the material to de/intercalate lithium is related to the specific surface area. The above results show that the ZIF-8-derived lithium-ion anode materials prepared by a simple co-precipitation method and heat treatment process have good energy storage performance and application prospects as lithium-ion battery electrode materials.

The above-disclosed preferred embodiments of the present invention are provided only to help illustrate the present invention. The preferred embodiments do not exhaust all the details, nor do they limit the invention to specific embodiments only. Obviously, many modifications and variations are possible in light of the content of this specification. The present specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is to be limited only by the claims and their full scope and equivalents.

Claims (10)

1. A preparation method of a ZIF-8-derived lithium ion negative electrode material is characterized by comprising the following steps of:

1) measuring CH according to the ratio ₃ Pouring the OH solution and deionized water into a mixing container, and stirring to form a mixed solution A;

2) weighing Zn (NO) according to the proportion ₃ ) ₂ ·6H ₂ Placing O and 2-methylimidazole in a mortar for grinding uniformly to obtain a liquid mixed medicine;

3) adding the obtained mixed medicine into the mixed solution A, and quickly dissolving under the action of ultrasound to obtain a mixed solution B;

4) magnetically stirring the obtained mixed solution B to obtain a precipitate; washing and drying the obtained precipitate, and marking as ZIF-8;

5) and (3) placing the obtained precipitate ZIF-8 in a tubular furnace, carrying out heat treatment at 500-1000 ℃ for 2-4 h in an Ar atmosphere environment, and naturally cooling to room temperature to obtain the ZIF-8-derived lithium ion negative electrode material.

2. The method for producing a lithium-ion negative electrode material according to claim 1, characterized in that: in the step 1), the step (A) is carried out,CH ₃ OH solution volume and Zn (NO) ₃ ) ₂ ·6H ₂ The amount of O, 1mM Zn (NO) ₃ ) ₂ ·6H ₂ O needs 10 to 30mlCH ₃ And (4) OH solution.

3. The method for producing a lithium-ion negative electrode material according to claim 1, characterized in that: in the step 1), the volume of the deionized water is CH ₃ 2-6 times of OH volume.

4. The method for producing a lithium-ion negative electrode material according to claim 1, characterized in that: in step 2), the 2-methylimidazole is taken as Zn in the reaction process ²⁺ Ligand, in which Zn (NO) ₃ ) ₂ ·6H ₂ The molar ratio of O to 2-methylimidazole is 1: 2-6.

5. The method for producing a lithium-ion negative electrode material according to claim 1, characterized in that: in the step 2), the time of the ultrasonic action is 5-10 mi.

6. The method for producing a lithium-ion negative electrode material according to claim 1, characterized in that: in step 3), the basis for determining dissolution is as follows: the solution becomes turbid due to rapid coordination between the ions after hydrolysis of the ions.

7. The method for producing a lithium-ion negative electrode material according to claim 1, characterized in that: in the step 4), the rotating speed during magnetic stirring is 300-700 r/min.

8. The method for producing a lithium-ion negative electrode material according to claim 1, characterized in that: in the step 4), the washing liquid used for washing is CH ₃ And (4) washing with the OH solution for 2-4 times.

9. The method for producing a lithium-ion negative electrode material according to claim 1, characterized in that: in the step 4), the drying is carried out in a vacuum drying oven, the drying temperature is 50-80 ℃, and the drying time is 12-24 hours.

10. A ZIF-8-derived lithium ion negative electrode material prepared according to the method for preparing a lithium ion negative electrode material of any one of claims 1 to 9.

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