CN111900373B

CN111900373B - A kind of preparation method of lithium metal battery negative electrode side separator material with anti-lithium dendrite

Info

Publication number: CN111900373B
Application number: CN202010772814.2A
Authority: CN
Inventors: 李祥村; 姜福林; 王舒婷; 贺高红; 代岩; 周长宇; 姜晓滨; 张悦; 肖武; 郑文姬
Original assignee: Dalian University of Technology
Current assignee: Dalian University of Technology
Priority date: 2020-08-04
Filing date: 2020-08-04
Publication date: 2021-08-06
Anticipated expiration: 2040-08-04
Also published as: CN111900373A

Abstract

The invention discloses a preparation method of a lithium metal battery cathode side separator material for preventing lithium dendrites. Polyacrylonitrile and a carbon nano tube are used as raw materials, a CNT @ C composite membrane material (CNT @ C interlayer material which is used as a lithium metal battery cathode side interlayer material) for preventing lithium dendrites is obtained by preparing a membrane liquid, performing solvent phase conversion, pre-oxidizing and carbonizing, and the CNT @ C interlayer material with a sponge pore structure and high conductivity is covered on a lithium sheet to protect the lithium metal battery cathode and prevent the lithium dendrites and the battery from short circuit. At 8mA h cm^‑2And 8mA cm^‑2At high plating/stripping capacity and current density, the overpotential after 500h operation of the Li/CNT @ C electrode was about 0.15V. When using LiFePO₄When the full battery is assembled as a positive electrode, the capacity retention rate of the Li/CNT @ C battery after 600 cycles is 82.5%, which shows that the CNT @ C interlayer material has good effects of retarding the growth of lithium dendrites and prolonging the cycle life of the battery.

Description

Preparation method of lithium dendrite-resistant lithium metal battery cathode side separator material

Technical Field

The invention relates to the field of lithium metal battery interlayers, in particular to a preparation method of a lithium metal battery anode side interlayer material for preventing lithium dendrites.

Background

The continuous increase in global economy has increased the demand for energy, and the reserves of fossil energy that have been explored to date are not optimistic, and the carbon dioxide produced by the combustion of fossil fuels contributes to the global warming effect. Renewable energy sources such as solar energy, tidal energy and the like can effectively reduce carbon emission and protect the environment, but the utilization of the energy sources is limited due to the characteristics of instability and intermittence. Energy storage devices have therefore gained increasing attention, particularly lithium batteries, which have developed rapidly in recent years.

Lithium batteries have been penetrated into various fields of our lives, and are utilized in the fields of mobile phones, computers and new energy automobiles which are hot in recent years. Lithium batteries can be roughly divided into lithium ion batteries and lithium metal batteries, and relatively, lithium metal batteries are more superior in safety, specific capacity, self-discharge rate and the like, but have higher technical requirements. The lithium metal battery uses metal lithium as a negative electrode, and the positive electrode generally adopts manganese dioxide and other materials, and can also adopt materials with higher theoretical specific capacity such as sulfur, oxygen and the like. With the rapid development of science and technology, the industries such as aerospace, new energy vehicles, high-speed rails, large-scale energy storage power grids and the like are also in the period of rapid development, the requirements on energy storage equipment are higher and higher, and the lithium metal battery with high energy density can well meet the requirements of people on the energy storage equipment with high energy density and high power density. Lithium metal batteries have also become a focus of recent research. However, lithium dendrites generated during the charge and discharge of the lithium metal battery seriously affect the safety and cycle stability of the battery. How to protect the metallic lithium cathode of the lithium metal battery, inhibit the formation of lithium dendrites, and ensure the service life and safety performance of the lithium metal battery becomes a key part of the research of the lithium metal battery. At present, the protection of the lithium metal battery negative electrode mainly comprises four aspects of electrolyte optimization, diaphragm modification, negative electrode structuring, interlayer addition and the like. The addition of an interlayer between the metallic lithium negative electrode and the separator is a simple and effective negative electrode protection means, and the existence of the interlayer can stabilize the surface of the metallic lithium, adjust the deposition behavior of lithium ions and act as a physical barrier to prevent the growth of lithium dendrites to the positive electrode. The method for adding the interlayer is simple in process and easy to operate, but the current interlayer material has the problems of unreasonable structural design, difficulty in amplification preparation and the like, how to design the carbon-based material with a suitable nano structure and good conductivity through structural regulation and control, and large-scale preparation of the carbon-based material have important significance in inhibiting growth of lithium dendrites and protecting lithium cathodes.

Disclosure of Invention

Aiming at the problems, the invention provides a preparation method of a lithium metal battery negative electrode side separation layer material for preventing lithium dendrite. Polyacrylonitrile and carbon nano tubes are used as raw materials, a membrane layer is prepared, and a lithium dendrite-preventing lithium metal battery negative electrode side spacer material (CNT @ C) is obtained through solvent phase conversion, pre-oxidation and carbonization, so that a lithium metal battery negative electrode is protected. The CNT @ C interlayer material with the sponge pore structure and high conductivity covers the lithium sheet, so that the deposition of lithium is more uniform, and the CNT @ C interlayer can be used as a physical barrier to hinder the growth of lithium dendrites. Experiments prove that the CNT @ C interlayer can effectively slow down the polarization phenomenon, so that the cycle performance of the battery is more stable, and the large-scale production can be realized.

In order to achieve the above purpose, the invention provides the following technical scheme:

a preparation method of a lithium dendrite-preventing lithium metal battery negative electrode side separator material comprises the following steps:

1) preparation of CNT @ PAN composite membrane material

Polyacrylonitrile (PAN) and N, N-Dimethylformamide (DMF) were added and mixed, and Carbon Nanotubes (CNT) were added after stirring. Then placing the mixture into an oil bath pan, and stirring the mixture for 8 to 12 hours at the temperature of between 60 and 80 ℃ to form uniform and viscous black casting solution. And (3) after the casting solution is cooled to room temperature, coating the casting solution on a dry and clean glass plate by using an automatic coating machine to form a liquid film. Quickly transferring the glass plate into a gel bath, forming a CNT @ PAN composite film based on a phase inversion principle, soaking for 20-24h, taking out, drying, transferring into a vacuum drying oven, and carrying out vacuum drying; in the casting solution, the mass ratio of polyacrylonitrile, N-dimethylformamide and carbon nanotubes is 1:12: 1-5: 12:5, for example, 1 g: 12 g: 1g, the network cross-linked pore structure interlayer material cannot be prepared beyond the proportion range;

2) preparation of CNT @ C composite film material

And transferring the dried CNT @ PAN composite film into a muffle furnace, carrying out pre-oxidation treatment, transferring the pre-oxidized film into a tubular furnace, and carrying out high-temperature carbonization to obtain a CNT @ C composite film material, namely a CNT @ C composite carbon film interlayer material, which is called CNT @ C interlayer material for short, and is used as a lithium metal battery cathode side interlayer material for preventing lithium dendrites.

Further, in the step 1), the stirring time of the mixture of polyacrylonitrile and N, N-dimethylformamide is not less than 30 min.

Further, in the step 1), the thickness of the liquid film obtained by the automatic coating machine is 150-250 μm.

Further, in step 1), the gel bath is n-pentanol.

Further, in step 1), the vacuum drying conditions are as follows: the drying temperature is 70-90 ℃, and the drying time is 3-5 h.

Further, in step 2), the pre-oxidation conditions are as follows: raising the temperature from room temperature to the pre-oxidation temperature at the temperature raising rate of 2-3 ℃ for min^-1The pre-oxidation temperature is 200-300 ℃, the constant temperature time is 2h, and finally the temperature is naturally reduced.

Further, in step 2), the carbonization conditions are as follows: heating from room temperature to carbonization temperature in inert gas atmosphere at a heating rate of 4-6 deg.C for min^-1The carbonization temperature is 700-.

The beneficial effects of the invention include:

the invention takes polyacrylonitrile and carbon nano tubes as raw materials, and obtains the CNT @ C interlayer material by preparing a film layer, solvent phase conversion, pre-oxidation and carbonization. The CNT @ C film layer material has a sponge pore structure and high conductivity. The CNT @ C film layer is covered on the lithium sheet, so that the deposition of lithium can be more uniform, and the CNT @ C interlayer plays a role of a physical barrier and can effectively prevent the generation of lithium dendrites.

The invention solves the problem of dendritic crystal growth of lithium metal batteries by adding the interlayer, has simple and effective process flow and realizes large-scale production. The CNT @ C barrier material has good conductivity while inhibiting the growth of lithium dendrites. In the lithium copper battery, the addition of the CNT @ C interlayer enables the metal lithium negative electrode to have more stable stripping capacity; the lithium-lithium symmetrical battery is 8mA h cm^-2And 8mA cm^-2The Li/CNT @ C electrode had an overpotential of only about 0.15V after 500 hours of operation, while the pure lithium electrode cell failed after about 200 hours of operation; in the presence of LiFePO₄In the full cell of the positive electrode, the capacity retention rate of the Li/CNT @ C cell after 600 times of operation is 82.5%, and the pure lithium negative electrode has a more obvious overcharge phenomenon at the 100 th cycle. The experiment result shows that the CNT @ C interlayer material can be used as a negative electrode side interlayer of a lithium metal battery, so that the polarization phenomenon is slowed down, the metal lithium negative electrode is effectively protected under high current density, and the cycling stability and the service life of the battery are improved.

Drawings

FIG. 1 is an electron micrograph of the CNT @ C composite film material prepared in example 1.

Figure 2 is a schematic representation of the CNT @ C separator prepared in example 1 as a negative electrode protection.

Figure 3 is a graph of coulombic efficiencies for the assembled CNT @ C spacer-added lithium copper half cell and pure lithium electrode lithium copper half cell of example 1.

Fig. 4 is a graph of the charge and discharge curves of the assembled CNT @ C interlayer-added lithium copper half cell and pure lithium electrode lithium copper half cell of example 1.

Fig. 5 is a graph of the constant current voltage of the assembled pure lithium electrode symmetric cell of example 1 and the symmetric cell containing the CNT @ C barrier.

FIG. 6 shows LiFePO assembled according to example 1₄Lithium metal battery cycle performance diagram with pure lithium or Li/CNT @ C as cathode.

FIG. 7 shows LiFePO assembled according to example 1₄Lithium metal battery charge-discharge curve using pure lithium or Li/CNT @ C as anode and cathodeFigure (a).

Detailed Description

The following is a detailed description of specific embodiments of the present invention with reference to specific examples, but the present invention is not limited to the examples. Unless otherwise specified, the methods are conventional methods, and raw materials and instruments used in the methods are commercially available.

Example 1

1) Preparation of CNT @ PAN composite membrane material

Weighing 1g of Polyacrylonitrile (PAN), placing the Polyacrylonitrile (PAN) into a silk mouth bottle, adding 12g N, N-Dimethylformamide (DMF), stirring for 30min, adding 1g of Carbon Nano Tube (CNT), wherein the mass ratio of the materials of the N, N-dimethylformamide, the carbon nano tube and the polyacrylonitrile is 12: 1: 1. and (3) placing the screw bottle in an oil bath pot, and stirring for 8-12h at the temperature of 60-80 ℃ to form uniform and viscous black casting solution. And after the casting solution is cooled to room temperature, coating the casting solution on a dry and clean glass plate by using an automatic coating machine to form a liquid film with the thickness of 200 mu m. And (3) quickly transferring the glass plate into n-amyl alcohol, forming the CNT @ PAN composite film based on the phase inversion principle, taking out and airing after soaking for 24 hours, transferring the film into a vacuum drying oven, and performing vacuum drying for 4 hours at 90 ℃ to remove the residual n-amyl alcohol in the film. The mass ratio of polyacrylonitrile, N-dimethylformamide and carbon nanotubes is 1:12: 1-5: 12: 5. The network cross-linked pore structure barrier layer material with the structure cannot be prepared beyond the proportion range.

2) Preparation of CNT @ C composite film material

The dried CNT @ PAN film was transferred to a muffle furnace at 2 ℃ for min^-1The temperature rising rate is increased to 250 ℃, and the temperature is kept for 2 hours, thus completing the pre-oxidation treatment. Naturally cooling, transferring the pre-oxidized film to a tube furnace for high-temperature carbonization, and carrying out carbonization at 5 ℃ for min in argon atmosphere^-1The temperature rise rate is increased to 800 ℃, the temperature is kept for 1h, and the CNT @ C composite film material with the thickness of about 150 mu m, namely the CNT @ C composite carbon film interlayer material (CNT @ C interlayer), is obtained after natural temperature reduction, and figure 1 is an electron microscope image of the prepared CNT @ C composite film material with the sponge pore structure, and the network cross-linked pore structure of the material improves the conductivity of the material.

The test batteries are all CR2025 button batteries, the assembly process is carried out in a glove box in argon atmosphere, the diameters of lithium sheets are 16mm, the diaphragm is Celgard 2325, namely a polypropylene (PP)/Polyethylene (PE)/polypropylene (PP) three-layer composite diaphragm, and the electrolyte is ether lithium sulfur battery electrolyte (1M LiTFSI-DOL: DME (1:1) + 1% LiNO3) which takes lithium bistrifluoromethanesulfonylimide (LiTFSI), 1, 3-Dioxolane (DOL) and ethylene glycol dimethyl ether (DME) as main components. The adding position of the CNT @ C interlayer is positioned between the lithium sheet and the diaphragm in the assembling process of the lithium copper half battery, the lithium symmetric battery and the lithium-iron phosphate lithium battery.

FIG. 2 is a schematic diagram of the CNT @ C barrier layer prepared in this example as a negative electrode protection, and the three-dimensional structure of the CNT @ C barrier layer and the lithium sheet can be visually seen.

Fig. 3 is a graph of the coulombic efficiencies of the assembled lithium copper half cell with the CNT @ C interlayer and the pure lithium electrode lithium copper half cell of the embodiment, the coulombic efficiency of the cell with the CNT @ C interlayer still remains 98.76% after 60 cycles, and the coulombic efficiency of the pure lithium negative electrode cell fluctuates sharply.

Fig. 4 is a charging and discharging curve diagram of the assembled lithium copper half-cell with the CNT @ C interlayer added and the lithium copper half-cell with the pure lithium electrode in the embodiment, the charging curve of the pure lithium negative electrode has obvious voltage fluctuation, the cell voltage with the CNT @ C interlayer added is stable, and the metal lithium negative electrode has more stable stripping capacity.

FIG. 5 is a graph of the constant current voltage of a pure lithium electrode symmetric cell assembled according to this example and a symmetric cell containing a CNT @ C separator at 8mA h cm^-2And 8mA cm^-2When operated at high plating/stripping capacities and current densities, the overpotential of the symmetrical cell containing the CNT @ C barrier layer was only about 0.15V after 500 hours, whereas the pure lithium electrode cell failed after about 200 hours of operation.

FIG. 6 shows the LiFePO used in the present example₄The cycle performance diagram of the lithium metal battery taking pure lithium or Li/CNT @ C as the cathode is taken as the anode, the specific capacity of the pure lithium cathode battery is rapidly reduced when the battery is cycled under the current density of 0.5C, the coulombic efficiency is severely attenuated when the battery is cycled at the 120 th cycle, and the initial capacity of the Li/CNT @ C battery is 141.5mA h g^-1The operation can be carried out for 600 cycles relatively stably.

FIG. 7 shows an assembly of LiFePO according to the present embodiment₄The lithium metal battery is taken as a positive electrode, pure lithium or Li/CNT @ C is taken as a negative electrode, the charge-discharge curve change of the battery added with the Li/CNT @ C interlayer is obviously smaller than that of the pure lithium negative electrode, and the pure lithium negative electrode has obvious overcharge phenomenon at the 100 th cycle.

The CNT @ C film layer material provided by the invention has good conductivity while inhibiting the generation of lithium dendrites. The addition of the CNT @ C barrier layer significantly improves the electrochemical performance of the lithium metal battery.

Finally, it should be noted that: the above embodiment is only one implementation of the present invention, and is not to be construed as limiting the scope of the present invention. The present invention is not limited to the embodiments described above, and various modifications and changes may be made without departing from the scope of the present invention.

Claims

1. a preparation method of the lithium metal battery negative electrode side interlayer material of anti-lithium dendrite, is characterized in that, comprises the steps:

1) Preparation of CNT@PAN composite membrane material

Mix polyacrylonitrile PAN and N,N-dimethylformamide DMF, add carbon nanotubes CNT after stirring, then put it in an oil bath, and stir at 60-80 ° C for 8-12 hours to form a uniform, viscous After the casting liquid is cooled to room temperature, use an automatic coating machine to coat the casting liquid on a dry and clean glass plate to form a liquid film, and quickly transfer the glass plate to the gel bath. The CNT@PAN composite film is formed according to the conversion principle. After soaking for 20-24 hours, it is taken out to dry, and then transferred to a vacuum drying box for vacuum drying; polyacrylonitrile, N,N-dimethylformaldehyde in the casting liquid The material mass ratio of amide and carbon nanotubes is 1:12:1～5:12:5;

2) Preparation of CNT@C composite film material

The dried CNT@PAN composite film was transferred to a muffle furnace for pre-oxidation treatment, and then the pre-oxidized film was transferred to a tube furnace for high-temperature carbonization to obtain a CNT@C composite carbon film interlayer material.

2. The preparation method according to claim 1, wherein in step 1), the stirring time of the mixture of polyacrylonitrile and N,N-dimethylformamide is not less than 30min.

3. The preparation method according to claim 1, wherein in step 1), the thickness of the liquid film obtained by the automatic coating machine is 150-250 μm.

4. The preparation method according to claim 1, characterized in that: in step 1), the gel bath is n-amyl alcohol.

5 . The preparation method according to claim 1 , wherein in step 1), the vacuum drying conditions are: drying temperature 70-90° C. and drying time 3-5 h. 6 .

6. preparation method according to claim 1, is characterized in that: in step 2), described pre-oxidation condition is: from room temperature to pre-oxidation temperature, temperature rise rate is 2-3 ℃ of min ^-1 , pre-oxidation The temperature is 200-300℃, the constant temperature is 2h, and finally the temperature is naturally cooled.

7. preparation method according to claim 1, is characterized in that: in step 2), described carbonization condition is: under inert gas atmosphere, be raised to carbonization temperature from room temperature, and heating rate is 4-6 ℃ of min ^-1 , the carbonization temperature is 700-900 ℃, the constant temperature time is 1h, and finally the temperature is naturally cooled.