Application of a MOF-based composite carbon nanofiber current collector in the preparation of a lithium-free anode lithium battery

Abstract

The present invention belongs to the technical field of lithium battery current collector materials, and particularly relates to the application of a composite carbon nanofiber current collector based on MOFs in the preparation of a lithium-free anode lithium battery. The composite carbon nanofiber current collector is a carbon fiber anode material PNCF@ZnO rich in N and ZnO, and its preparation includes the following steps: mixing MOFs and polyacrylonitrile, dissolving them with an organic substance to form a spinning solution, preparing mixed nanofibers with a spinning machine, and forming a composite carbon nanofiber current collector after carbonization. The application of the composite carbon nanofiber current collector provided by the present invention in the preparation of a lithium-free anode lithium battery realizes the stable cycling of a lithium metal battery with a lithium-free anode, and has the characteristics of low preparation cost, simple process, environmental friendliness, etc., opening up a new direction for the development of a lithium-free anode lithium battery and providing a broad application prospect for a lithium metal battery with a lithium-free anode.

Description

Technical Field

[0001] The present invention belongs to the technical field of current collector materials for lithium batteries, and particularly relates to the application of a composite carbon nanofiber current collector based on MOFs in the preparation of a lithium-free anode lithium battery. Background Art

[0002] Energy is the basis for the survival and development of human society. The industrial development of the world in the past two hundred years has led to an increasingly tense relationship among fossil energy, economy, and ecology. Energy transformation has become a global consensus. As a renewable and environmentally friendly secondary energy, electric energy has shown great utilization value. Therefore, vigorously developing electric energy storage devices is the only way to achieve energy transformation and solve energy and environmental problems, which has greatly promoted the research and development of the next-generation high-energy-density secondary energy storage batteries. As one of the important measures to improve the energy density of batteries, the application of high specific capacity anode materials has also received increasing attention. Lithium metal anodes, with their excellent theoretical specific capacity (3860 mAh / g) and the lowest redox electromotive force (-3.04V), have become an ideal candidate for the anodes of the next-generation high-density energy storage batteries. However, in practical applications, lithium metal batteries have also exposed their own defects such as low Coulombic efficiency, short service life, and safety problems. A large number of lithium dendrites will be generated during the redox reaction process of traditional lithium metal battery anodes. As the working time increases, the lithium dendrites will continue to grow and penetrate the separator, triggering safety problems. At the same time, a large amount of "dead lithium" will be formed during the repeated lithium insertion / delithium process of lithium metal anodes. These "dead lithium" will cause infinite volume expansion of the electrode, resulting in low Coulombic efficiency and reduced cycle life of the battery. How to solve a series of problems brought about by the growth of lithium dendrites is the key to constructing a more stable lithium metal anode.

[0003] So far, to address the above problems existing in lithium metal batteries, various strategies have been developed to solve the formation of lithium dendrites on the lithium anode surface by constructing a solid electrolyte interface membrane (SEI) on the lithium anode surface. Additives such as inorganic / organic molecules are added to the electrolyte to form a stable SEI on the surface of the lithium metal anode. Applying functional coatings made of materials such as covalent organic frameworks (COFs), metal organic frameworks (MOFs), polymers, and Al2O3 to the lithium metal anode can induce uniform deposition of lithium ions. Some scholars have proposed that three-dimensional anode materials represented by nickel foam and copper foam have a large contact surface with the electrolyte, providing relatively rich sites for lithium ion deposition. The space reserved inside the material effectively alleviates volume expansion, and the interconnected conductive network also reduces the local current density. Although some achievements have been made, this method does not start from the microscopic perspective to inhibit the growth of lithium dendrites. Some other scholars have proposed to capture lithium through a microsphere structure to limit its deposition and inhibit dendrite growth. The microspheres prepared by them are composites of carbon nanotubes and a porous silica protective layer, which can confine the deposited lithium within the fiber tubes and the inter-fiber voids to avoid lithium dendrites, and are very effective for controlling lithium deposition behavior. In addition, biomimetic ion gel electrolytes have the ability to rapidly transport lithium ions and can spontaneously form a particle-rich layer on the surface of the lithium metal anode, thus effectively inhibiting the growth of lithium dendrites, providing a new idea for designing high-performance metal lithium batteries using the biomimetic concept. Although the above methods can inhibit the formation of dendritic lithium dendrites to a certain extent and enhance the SEI, they lack effective lithium ion deposition sites, cannot maintain uniform deposition of lithium ions for a long time, and generally have a low Coulomb efficiency, unable to meet the requirements of long-term stable cycling of lithium metal batteries. In addition, due to the limitation of the Coulomb efficiency of the battery anode, the anodes prepared by the above methods generally have the problem of excessive lithium, resulting in the ratio of lithium ions in the positive electrode to those in the negative electrode in the lithium metal battery system being much greater than 1, making the energy density of the actual battery system much smaller than the theoretical value of the lithium metal battery.

[0004] Developing lithium metal batteries with a lithium-free anode can greatly improve the energy density of lithium metal batteries and is a strong candidate for the next generation of high-energy density energy storage devices. To solve the serious lithium dendrite growth problem at the anode, most previous solutions have been to use high-cost, highly flammable organic electrolytes with high-concentration, mixed lithium salts instead of commercial dilute electrolytes. Although this type of solution strategy has achieved stable cycling of lithium-free organic batteries, the large use of high-cost lithium salts and flammable organic solvents poses new challenges to the cost control and production process of the battery. Summary of the Invention

[0005] In view of the above problems, the object of the present invention is to provide an application of a MOF-based composite carbon nanofiber current collector in the preparation of a lithium-free anode lithium battery, which can effectively inhibit the formation of lithium dendrites, generate a stable electrode / electrolyte interface phase (SEI), and further achieve long-term stable cycling in a lithium metal battery system with a high-energy density lithium-free anode.

[0006] The technical content of the present invention is as follows:

[0007] The present invention provides an application of a MOF-based composite carbon nanofiber current collector in the preparation of a lithium-free anode lithium battery;

[0008] The composite carbon nanofiber current collector is a carbon fiber negative electrode material PNCF@ZnO rich in N and ZnO, and its preparation includes the following steps: mixing MOFs and polyacrylonitrile (PAN), dissolving them with an organic substance to form a spinning solution, preparing mixed nanofibers with a spinning machine, and forming a composite carbon nanofiber current collector after carbonization;

[0009] The mixing mass ratio of the MOFs and polyacrylonitrile (PAN) is (0.6~0.8):1;

[0010] The concentration of the spinning solution is 0.1~0.2 g / mL;

[0011] The spinning conditions of the spinning machine are that the voltage is 11~13 Kv and the spinning flow rate is 0.8~1.2 mL / h;

[0012] The carbonization conditions are calcination at 600 - 700 °C for 1 h;

[0013] The preparation of the MOFs includes the following steps: ultrasonically dissolving adenine and 4,4-biphenyldicarboxylic acid (BPDC) to obtain solution A and solution B respectively, ultrasonically dissolving zinc acetate and polyvinylpyrrolidone (PVP, Mv = 28000 - 32000) to obtain solution C, mixing solutions A, B, and C, then adding an organic solvent, methanol, and deionized water, stirring at room temperature, and then centrifuging to obtain a white powder. After washing it successively with DMF, deionized water, and methanol, it is dried in an oven to obtain Bio-MOF-100 nanoparticles;

[0014] The use concentration of adenine in solution A is 0.015~0.02 g / mL;

[0015] The use concentration of 4,4-biphenyldicarboxylic acid (BPDC) in solution B is 0.015~0.025 g / mL;

[0016] The use concentration of zinc acetate in solution C is 0.006~0.008 g / mL;

[0017] The concentration of cetyltrimethylammonium bromide used in the solution C is 0.6 - 0.75 g / mL.

[0018] The beneficial effects of the present invention are as follows:

[0019] The application of the MOF-based composite carbon nanofiber current collector of the present invention in the preparation of a lithium-free anode lithium battery. The composite carbon nanofiber current collector is a fiber material prepared by electrospinning MOFs and polyacrylonitrile, and is used for the preparation of a lithium-free anode lithium battery. The polymer fiber film doped with MOFs is used as a three-dimensional current collector of a lithium metal battery after high-temperature carbonization. The rich and uniformly distributed zinc oxide nanoparticles derived from MOFs can provide good nucleation sites for lithium metal, and cooperate with the hierarchical pore structure, thereby providing a stable site for the deposition and stripping of metallic lithium, effectively inhibiting the formation of lithium dendrites, and generating a stable electrode / electrolyte interface phase (SEI). Furthermore, long-term stable cycling can be achieved in a lithium metal battery system with a high energy density lithium-free anode. The application of the composite carbon nanofiber current collector provided by the present invention in the preparation of a lithium-free anode lithium battery realizes the stable cycling of a lithium metal battery with a lithium-free anode, which has the characteristics of low preparation cost, simple process, environmental friendliness, etc., opens up a new direction for the development of lithium metal batteries with a lithium-free anode, and provides a broad application prospect for lithium metal batteries with a lithium-free anode. Description of the Drawings

[0020] Figure 1 It is the electron microscope scanning images of the bio-MOF-100 nanoparticles, fiber films and PNCF@ZnO prepared by the present invention;

[0021] Figure 2 It is the XRD pattern of the bio-MOF-100, and the XRD and XPS patterns of PNCF@ZnO prepared by the present invention;

[0022] Figure 3 It is the test result diagram of the electrochemical performance of the lithium-current collector half cell prepared by the present invention;

[0023] Figure 4 It is the test result diagram of the electrochemical performance of the pre-lithiated assembled lithium iron phosphate full cell prepared by the present invention. Detailed Embodiments

[0024] The following further describes the present invention in detail through specific implementation cases and the description of the drawings. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the protection scope of the present invention. After reading the present invention, various equivalent forms of modification of the present invention fall within the scope defined by the appended claims of this application.

[0025] Unless otherwise specified, all raw materials and reagents of the present invention are raw materials and reagents in the conventional market.

[0026] Example 1

[0027] Preparation of a MOF-based Composite Carbon Nanofiber Current Collector

[0028] 1) Dissolve 0.304 g of adenine and 0.48 g of BPDC separately in 20 mL of DMF by ultrasonic dissolution for standby. Dissolve 0.156 g of zinc acetate and 12.5 g of PVP in 20 mL of DMF by ultrasonic dissolution for standby. Mix the above three solutions, then add 20 mL of DMF, 5 mL of methanol and 1 mL of deionized water, and stir at room temperature for 18 hours;

[0029] After the reaction stops, centrifuge at 900 r / min for 3 min to obtain a white powder. Wash it successively with DMF, deionized water and methanol, and then dry it in an oven to obtain bio-MOF-100 nanoparticles;

[0030] 2) Take 1.5 g of the bio-MOF-100 synthesized in step 1) and 2.5 g of PAN and mix them to dissolve in 20 mL of DMF to form a light yellow homogeneous solution. Transfer the orange-yellow transparent solution into a 20 mL medical syringe, load it into the Genas electrostatic spinning system, use a needle with a model of 25G (outer diameter 0.5 mm, inner diameter 0.31 mm), and perform electrospinning under the conditions of 11 Kv voltage and 0.8 mL / h flow rate. Each membrane consumes 0.7 mL of solution;

[0031] Place the prepared fiber film in a 60 °C forced-air drying oven and dry it overnight, and then calcine it at high temperature in a nitrogen atmosphere. Calcine it at 700 °C for 1 h, with a heating rate of 1.5 °C / min. Name the calcined black carbon fiber product PNCF@ZnO, and cut it into discs with a diameter of 12 mm for use as a lithium-free anode.

[0032] As Figure 1 shown Figure 1 a is the SEM image of bio-MOF-100 nanoparticles, indicating that the morphology of bio-MOF-100 is uniform, with a diameter of about 500 nm; Figure 1 b is the SEM image of the fiber film, indicating that the fibers are uniform, with a diameter of about 2 µm; Figure 1 c is the SEM image of the black carbon fiber product PNCF@ZnO, indicating that the fiber structure remains intact after carbonization.

[0033] As Figure 2 shown, from Figure 2 a, it can be seen that the X-ray diffraction pattern shows that bio-MOF-100 exhibits strong crystal characteristic peaks. From Figure 2It can be seen from b that after carbonization, the fibers show obvious amorphous carbon peaks and characteristic peaks of zinc oxide. From Figure 2 The X-ray photoelectron spectra of c, e, d, and f can further show that PNCF@ZnO contains a large amount of pyridine N, pyrrole N, and graphitic N doping, and has abundant ZnO, with good lithium affinity..

[0034] Example 2

[0035] Preparation of a MOF-based composite carbon nanofiber current collector

[0036] 1) Dissolve 0.32 g of adenine and 0.30 g of BPDC in 20 mL of DMF respectively and set aside after ultrasonic dissolution. Dissolve 0.12 g of zinc acetate and 13.5 g of PVP in 20 mL of DMF and set aside after ultrasonic dissolution. Mix the above three solutions, then add 20 mL of DMF, 5 mL of methanol, and 1 mL of deionized water, and stir at room temperature for 18 hours;

[0037] After the reaction stops, centrifuge at 900 r / min for 3 min to obtain a white powder. Wash it successively with DMF, deionized water, and methanol, and then dry it in an oven to obtain bio-MOF-100 nanoparticles;

[0038] 2) Take 1.6 g of the bio-MOF-100 synthesized in step 1) and 2.0 g of PAN and mix them to dissolve in 20 mL of DMF to form a light yellow homogeneous solution. Transfer the orange-yellow transparent solution into a 20 mL medical syringe, load it into the Jienasi electrospinning system, use a needle with a model of 25G (outer diameter 0.5 mm, inner diameter 0.31 mm), and carry out electrospinning under the conditions of a voltage of 12 Kv and a flow rate of 1.0 mL / h. Each membrane consumes 0.7 mL of solution;

[0039] Place the prepared fiber film in a 60°C forced-air drying oven and dry it overnight, and then calcine it at high temperature in a nitrogen atmosphere. Calcine it at 600°C for 1 h, with a heating rate of 1.5°C / min. Name the calcined black carbon fiber product PNCF@ZnO, and cut it into discs with a diameter of 12 mm for use as a lithium-free anode.

[0040] Example 3

[0041] Preparation of a MOF-based composite carbon nanofiber current collector

[0042] 1) Dissolve 0.40 g of adenine and 0.40 g of BPDC in 20 mL of DMF respectively and set aside after ultrasonic dissolution. Dissolve 0.156 g of zinc acetate and 12.5 g of PVP in 20 mL of DMF and set aside after ultrasonic dissolution. Mix the above three solutions, then add 20 mL of DMF, 5 mL of methanol, and 1 mL of deionized water, and stir at room temperature for 18 hours;

[0043] After the reaction stopped, it was centrifuged at 900 r / min for 3 min to obtain a white powder. After washing it successively with DMF, deionized water and methanol, it was dried in an oven to obtain bio-MOF-100 nanoparticles;

[0044] 2) 0.85 g of the bio-MOF-100 synthesized in step 1) and 1.15 g of PAN were mixed and dissolved in 20 mL of DMF to form a light yellow homogeneous solution. The orange-yellow transparent solution was transferred into a 20 mL medical syringe, loaded into the Jienasi electrospinning system, and a needle with a model of 25G (outer diameter 0.5 mm, inner diameter 0.31 mm) was used. Electrospinning was carried out under the conditions of a voltage of 13 Kv and a flow rate of 1.2 mL / h, and each membrane consumed 0.7 mL of the solution;

[0045] The prepared fiber film was placed in a 60 °C air blast drying oven and dried overnight, and then calcined at high temperature under a nitrogen atmosphere. It was calcined at 700 °C for 1 h, and the heating rate was 1.5 °C / min. The calcined black carbon fiber product was named PNCF@ZnO and cut into discs with a diameter of 12 mm for use as a lithium-free anode.

[0046] Experimental Example

[0047] The black carbon fiber product PNCF@ZnO three-dimensional current collector prepared in Example 1 was used for the electrochemical performance test of a lithium-current collector half-cell and the electrochemical performance test of a lithium-free anode full cell loaded with lithium iron phosphate:

[0048] 1. Lithium-current collector half-cell: The three-dimensional current collector PNCF@ZnO was cut into a pole piece with a diameter of 12 mm. A lithium sheet was used as the counter electrode, a mixture of 1 mol / L lithium bis(trifluoromethanesulfonyl)imide and DOL and DME (volume ratio 1:1) was used as the electrolyte, and the separator was a common PP separator. A lithium-current collector CR2032 type button half-cell was assembled in a glove box (Ar% > 99.99%, O2 < 0.1 ppm, H2O < 0.1 ppm). The stability at different current densities and different deposition capacities was tested by the constant current charge-discharge method. For comparison, a blank copper foil or a carbon fiber obtained by carbonizing a blank spun fabric was used as the current collector for testing and comparison. The results are analyzed as follows:

[0049] As Figure 3As shown in (a), (c), and (d), when ordinary copper foil or carbon fiber is used as the current collector, the cycle life of lithium metal deposition / stripping is only less than 100 cycles or 200 cycles, far less than that of the PNCF@ZnO current collector material prepared in the present invention. The PNCF@ZnO current collector material prepared in Example 1 can stably cycle more than 1000 cycles. And the Coulomb efficiency of the PNCF@ZnO current collector material prepared in the present invention can be maintained at a relatively high level during lithium metal deposition / stripping. The average Coulomb efficiency in the first 1000 cycles is 99.02%. Even under the more stringent test conditions of 3 mAh cm -2 and 3 mAh cm -2 , the PNCF@ZnO current collector material prepared in the present invention can still stably cycle more than 400 cycles, still far superior to copper foil or carbon fiber current collectors.

[0050] To further illustrate that the PNCF@ZnO material can induce uniform deposition of lithium metal as a three-dimensional current collector, the lithium-current collector half-cell was disassembled after electrochemical cycling, and the deposition of lithium metal on the current collector was tested by scanning electron microscopy:

[0051] As Figure 3 shown in (b), when the PNCF@ZnO prepared in the present invention is used as the current collector, lithium metal can be very uniformly deposited on the entire current collector, with a uniform and smooth surface and no lithium dendrite formation.

[0052] 2. Assembling a lithium iron phosphate full cell after prelithiation: Commercial LiFePO4, carbon black as the conductive agent, and PVDF as the binder were mixed in an amount of 150 mg: 18.7 mg: 18.7 mg, and then adjusted into a slurry with 0.4 mL of N-methylpyrrolidone, uniformly coated on the aluminum foil, transferred to a vacuum drying oven at 55 °C for drying after the slurry was slightly dried, and cut into a current collector with a diameter of 12 mm;

[0053] In a glove box under an argon atmosphere, lithium iron phosphate was used as the positive electrode, lithium-free PNCF@ZnO as the current collector, a PP separator, and a mixture of 1 mol / L lithium bis(trifluoromethanesulfonyl)imide and DOL and DME (volume ratio 1:1) as the electrolyte to assemble a CR2032 type button cell. The test voltage range was 2~4.2 V. The test results are as Figure 4 shown. It can be seen that the lithium-free negative electrode cell assembled with the three-dimensional current collector PNCF@ZnO prepared in the present invention can stably cycle 100 cycles, and the capacity retention rate after 100 cycles is 79.8%.

[0054] The above tests fully demonstrate that the three-dimensional current collector PNCF@ZnO for protecting lithium metal anodes of the present invention has excellent effects, can effectively solve the problem of lithium dendrites in lithium metal batteries, and when used in lithium metal batteries with lithium-free anodes, it shows broad application prospects.

Claims

1. Application of a MOF-based composite carbon nanofiber current collector in the preparation of a lithium-free anode lithium battery, characterized in that, The composite carbon nanofiber current collector is a carbon fiber negative electrode material PNCF@ZnO rich in N and ZnO, and its preparation includes the following steps: Mix MOFs and polyacrylonitrile, dissolve them with an organic substance to form a spinning solution, prepare mixed nanofibers with a spinning machine, and form a composite carbon nanofiber current collector after carbonization; The mixing mass ratio of the MOFs and polyacrylonitrile is (0.6~0.8):1; The preparation of the MOFs includes the following steps: Ultrasonically dissolve adenine and 4,4-biphenyldicarboxylic acid to obtain solution A and solution B respectively, ultrasonically dissolve zinc acetate and cetyltrimethylammonium bromide to obtain solution C, mix solutions A, B, and C, then add an organic solvent, methanol, and deionized water, stir at room temperature, and then centrifuge to obtain a white powder. Wash it successively with DMF, deionized water, and methanol, and then dry it in an oven to obtain Bio-MOF-100 nanoparticles.

2. The application of the MOF-based composite carbon nanofiber current collector according to claim 1 in the preparation of a lithium-free anode lithium battery, characterized in that, The concentration of the spinning solution is 0.1~0.2 g / mL.

3. Use of the MOF-based composite carbon nanofiber current collector according to claim 1 in the preparation of a lithium-free anode lithium battery, characterized in that, The spinning conditions of the spinning machine are that the voltage is 11~13 Kv and the spinning flow rate is 0.8~1.2 mL / h.

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