Lithium-sulfur battery negative electrode protection film, preparation method and application thereof, and lithium-sulfur battery

Abstract

The invention belongs to the technical field of lithium metal batteries, and provides a lithium-sulfur battery negative electrode protection film, a preparation method and application thereof, and a lithium-sulfur battery. The lithium-sulfur battery negative electrode protection film provided by the invention comprises a carbon matrix (formed by interweaving nano carbon fibers) and an active metal compound (one or more of metal nitride, metal phosphide and metal telluride) embedded in the carbon matrix. The lithium-sulfur battery negative electrode protection film is arranged between the lithium negative electrode and the diaphragm, the lithium-sulfur battery negative electrode protection film has an independent and self-supporting structure, and compared with a scheme for pretreating and protecting the lithium negative electrode in the prior art, the lithium-sulfur battery negative electrode protection film is simple to operate and easier to industrialize. The lithium-sulfur battery negative electrode protective film provided by the invention has excellent mechanical strength, chemical stability and ionic conductivity, and can effectively inhibit the growth of lithium dendrites, protect the stability of an SEI (Solid Electrolyte Interphase) film and prolong the cycle life of a lithium negative electrode.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium metal batteries, and particularly to a negative electrode protective film for a lithium-sulfur battery, a preparation method and application thereof, and a lithium-sulfur battery. Background Art

[0002] Lithium-sulfur batteries (Li-S batteries) are regarded as important candidates for the next generation of high-energy-density batteries due to their extremely high theoretical energy density (~2600 Wh / kg) and potential cost-effectiveness. Sulfur, as the positive electrode material, has the advantages of low cost, environmental friendliness, and abundant reserves, while the high specific capacity (3860 mAh / g) of the lithium metal negative electrode greatly improves the energy density of the battery. However, despite the great promise shown by lithium-sulfur batteries, they still face a series of scientific and technological challenges in practical applications, especially the stability problem of the lithium metal negative electrode. The lithium negative electrode is prone to generating lithium dendrites and forming an unstable solid electrolyte interface (SEI), which seriously affect the battery life, safety, and performance. Therefore, the protection of the lithium metal negative electrode has become the focus of current research, and the protective film made of inorganic materials, as an effective solution, has received extensive attention.

[0003] The related prior art discloses a method for protecting the negative electrode of a lithium-sulfur battery, specifically by immersing and pre-treating the lithium negative electrode in an organic compound containing double bonds or triple bonds to form a flexible protective film on its surface to inhibit the shuttle effect and negative electrode surface passivation caused by the reaction with polysulfide ions. However, when applying the above method, the lithium negative electrode needs to be processed immediately before use each time, which is not conducive to industrial scale application. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a negative electrode protective film for a lithium-sulfur battery, a preparation method and application thereof, and a lithium-sulfur battery. The negative electrode protective film for a lithium-sulfur battery of the present invention is placed between the negative electrode lithium sheet and the separator. The negative electrode protective film for a lithium-sulfur battery has an independent and self-supporting structure. Compared with the prior art solution of pre-treating and protecting the negative electrode lithium sheet, the operation is simple and it is more suitable for industrialization.

[0005] In order to achieve the above invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a negative electrode protective film for a lithium-sulfur battery, which includes a carbon matrix and active metal compounds embedded in the carbon matrix. The carbon matrix is formed by interweaving nanofibers, and the active metal compounds are one or more of metal nitrides, metal phosphides, and metal tellurides.

[0007] Preferably, the metal nitride is titanium nitride and / or vanadium nitride; the metal phosphide is iron phosphide and / or cobalt phosphide, and the metal telluride is nickel telluride and / or cobalt telluride.

[0008] Preferably, the areal density of the film for protecting the negative electrode of the lithium-sulfur battery is 2-3 mg / cm 2 ; the thickness of the film for protecting the negative electrode of the lithium-sulfur battery is 0.01-0.15 mm.

[0009] The present invention also provides a method for preparing the film for protecting the negative electrode of the lithium-sulfur battery according to the above technical solution, comprising the following steps:

[0010] Mix a soluble metal salt, a carbon matrix precursor and a solvent to obtain a spinning solution;

[0011] Perform electrospinning on the spinning solution to obtain a nanofiber membrane containing metal ions;

[0012] Perform heat treatment on the nanofiber membrane containing metal ions to obtain the film for protecting the negative electrode of the lithium-sulfur battery.

[0013] Preferably, the carbon matrix precursor includes one or more of polyacrylonitrile, polyvinylpyrrolidone, polystyrene and polymethyl methacrylate, and the soluble metal salt includes one or more of soluble titanium salts, soluble vanadium salts, soluble iron salts, soluble cobalt salts and soluble nickel salts.

[0014] Preferably, the spinning solution further includes a pore-forming agent, and the pore-forming agent includes polystyrene.

[0015] Preferably, the electrospinning method is single-axis electrospinning or coaxial electrospinning.

[0016] Preferably, the atmosphere for the heat treatment is nitrogen, phosphorus-containing vapor or tellurium-containing vapor;

[0017] The phosphorus-containing vapor includes phosphorus vapor, hydrogen and argon;

[0018] The tellurium-containing vapor includes tellurium vapor, hydrogen and argon.

[0019] Preferably, the temperature of the heat treatment is 500-1500 °C and the time is 1-20 h.

[0020] The present invention also provides a lithium-sulfur battery, comprising a sulfur positive electrode, a lithium negative electrode and a separator, and the film for protecting the negative electrode of the lithium-sulfur battery according to the above technical solution or the film for protecting the negative electrode of the lithium-sulfur battery prepared by the preparation method according to the above technical solution is disposed in parallel between the lithium negative electrode and the separator.

[0021] The present invention provides a film for protecting the negative electrode of a lithium-sulfur battery.

[0022] The negative electrode protective film of the lithium-sulfur battery provided by the present invention is placed between the lithium negative electrode and the separator. The negative electrode protective film of the lithium-sulfur battery has an independent and self-supporting structure. Compared with the prior art solutions for pre-treating and protecting the negative lithium sheet, the operation is simple and it is easier to industrialize.

[0023] The negative electrode protective film of the lithium-sulfur battery provided by the present invention includes a carbon matrix, and the carbon matrix is interwoven by nanofibers; the carbon matrix has the characteristics of a layered multi-microstructure and a three-dimensional intertwined network. The microstructure includes a porous structure, a hollow structure, and a hollowed-out structure, which significantly promotes the rapid shuttling and uniform distribution of lithium ions, reduces the concentration of local current density, and inhibits the formation of lithium dendrites. In addition, active metal compounds (one or more of metal nitrides, metal phosphides, and metal tellurides) are embedded in the carbon matrix, reducing the lithium ion diffusion energy barrier, improving the lithium ion transport efficiency, and at the same time providing sufficient active sites to promote the efficient nucleation and uniform deposition of lithium, and can also inhibit lithium dendrites. Compared with the protective film wrapped by pre-treating the lithium negative electrode in the prior art, the negative electrode protective film of the lithium-sulfur battery of the present invention has excellent mechanical strength, chemical stability, and ionic conductivity, can effectively inhibit the growth of lithium dendrites, protect the stability of the SEI film, and improve the cycle life of the lithium negative electrode. Brief Description of the Drawings

[0024] Figure 1 XRD pattern of the negative electrode protective film of the lithium-sulfur battery obtained in Example 1;

[0025] Figure 2 SEM image of the negative electrode protective film of the lithium-sulfur battery obtained in Example 1;

[0026] Figure 3 TEM image of the negative electrode protective film of the lithium-sulfur battery obtained in Example 1;

[0027] Figure 4 Rate performance graphs of the lithium-protective film symmetric battery and the pure lithium-lithium symmetric battery in Example 1;

[0028] Figure 5 Cycling performance graphs of the lithium protective film symmetric battery and the pure lithium-lithium symmetric battery in Example 1;

[0029] Figure 6 Cycling performance graphs of the lithium protective film symmetric battery and the pure lithium-lithium symmetric battery in Example 1;

[0030] Figure 7 Cycling performance graph of the coin-type lithium-sulfur battery in Example 1;

[0031] Figure 8 Cycling performance graph of the soft-pack lithium-sulfur battery in Example 1. Detailed Description of the Embodiments

[0032] The present invention provides a negative electrode protective film for a lithium-sulfur battery, which comprises a carbon matrix and active metal compounds embedded in the carbon matrix. The carbon matrix is formed by interwoven nano-carbon fibers, and the active metal compounds are one or more of metal nitrides, metal phosphides and metal tellurides.

[0033] The negative electrode protective film for a lithium-sulfur battery provided by the present invention comprises a carbon matrix, and the carbon matrix is formed by interwoven nano-carbon fibers. In the present invention, the carbon matrix has the characteristics of a layered porous structure and a three-dimensional interwoven network, which can improve the utilization rate of the active substance sulfur, capture and block the shuttle of LiPSs, and accelerate the transmission of lithium ions. When applied to a lithium-sulfur battery, the lithium-sulfur battery shows a higher specific capacity and a stable long cycle life.

[0034] The negative electrode protective film for a lithium-sulfur battery provided by the present invention comprises active metal compounds embedded in the carbon matrix, and the active metal compounds are one or more of metal nitrides, metal phosphides and metal tellurides. In the present invention, the metal nitride is preferably titanium nitride and / or vanadium nitride; the metal phosphide is preferably iron phosphide and / or cobalt phosphide; the metal telluride is preferably nickel telluride and / or cobalt telluride. In the present invention, embedding active metal compounds in the carbon matrix can reduce the lithium ion diffusion energy barrier, improve the lithium ion transmission efficiency, and at the same time provide sufficient active sites to promote the efficient nucleation and uniform deposition of lithium and inhibit lithium dendrites. The embedding of active metal compounds can improve the chemical stability and interface stability of the carbon matrix, and also enhance the transmission power of lithium ions and the inhibitory ability against the growth of lithium dendrites.

[0035] In the present invention, the areal density of the negative electrode protective film for a lithium-sulfur battery is preferably 2-3 mg / cm 2 , specifically preferably 2 mg / cm 2 , 2.1 mg / cm 2 , 2.2 mg / cm 2 , 2.3 mg / cm 2 , 2.4 mg / cm 2 , 2.5 mg / cm 2 , 2.6 mg / cm 2 , 2.7 mg / cm 2 , 2.8 mg / cm 2 , 2.9 mg / cm 2 or 3 mg / cm 2 .

[0036] In the present invention, the thickness of the negative electrode protective film for a lithium-sulfur battery is preferably 0.01-0.15 mm, specifically preferably 0.01 mm, 0.05 mm, 0.1 mm or 0.15 mm.

[0037] In the present invention, the negative electrode protective film of the lithium-sulfur battery can effectively inhibit the growth of lithium dendrites, protect the stability of the SEI film, and improve the cycle life of the lithium negative electrode. Specifically: Inhibiting the growth of lithium dendrites: The negative electrode protective film of the lithium-sulfur battery promotes the uniform deposition of lithium ions on the surface of the lithium negative electrode by regulating the transport path of lithium ions, reduces the concentration of local current density, and inhibits the formation of lithium dendrites. Forming a stable interfacial layer: The negative electrode protective film of the lithium-sulfur battery can form a stable interface between the lithium metal and the electrolyte, prevent the direct contact between the electrolyte and the lithium metal, and reduce the occurrence of side reactions. Mechanical stress buffering and volume change regulation: The high mechanical strength and elastic modulus of the negative electrode protective film of the lithium-sulfur battery can effectively relieve the stress caused by the volume change of lithium during charge and discharge, and keep the electrode structure intact. By introducing a carbon matrix with flexible and self-healing properties, the long-term stability of the carbon matrix can also be improved.

[0038] The present invention also provides a preparation method of the negative electrode protective film of the lithium-sulfur battery according to the above technical solution, including the following steps:

[0039] Mix a soluble metal salt, a carbon matrix precursor, and a solvent to obtain a spinning solution;

[0040] Perform electrospinning on the spinning solution to obtain a nanofiber membrane containing metal ions;

[0041] Perform heat treatment on the nanofiber membrane containing metal ions to obtain the negative electrode protective film of the lithium-sulfur battery.

[0042] The present invention mixes a soluble metal salt, a carbon matrix precursor, and a solvent to obtain a spinning solution.

[0043] In the present invention, the soluble metal salt preferably includes one or more of soluble titanium salts, soluble vanadium salts, soluble iron salts, soluble cobalt salts, and soluble nickel salts. In the present invention, the soluble titanium salt preferably includes tetrabutyl titanate, the soluble vanadium salt preferably includes vanadium acetylacetonate, the soluble iron salt preferably includes iron acetylacetonate, the soluble cobalt salt preferably includes cobalt acetylacetonate, and the soluble nickel salt preferably includes nickel acetylacetonate.

[0044] In the present invention, the carbon matrix precursor preferably includes one or more of polyacrylonitrile, polyvinylpyrrolidone, polystyrene, and polymethyl methacrylate, and is further preferably polyacrylonitrile.

[0045] In the present invention, the solvent preferably includes one or more of N-methylpyrrolidone, tetrahydrofuran, and N,N-dimethylformamide, and is further preferably N-methylpyrrolidone.

[0046] In the present invention, the spinning solution preferably further includes a pore-forming agent, and the pore-forming agent preferably includes polystyrene.

[0047] In the present invention, the mass ratio of the soluble metal salt to the carbon matrix precursor is preferably 0.1 - 5:1 - 1.5; the dosage ratio of the soluble metal salt to the solvent is preferably 0.1 - 5 g:7 - 10 mL; the mass ratio of the soluble metal salt to the pore-forming agent is preferably 0.1 - 5:0.6 - 1.

[0048] In the present invention, when the soluble metal salt is a soluble titanium salt, the dosage ratio of the soluble titanium salt to the carbon matrix precursor is preferably 2 - 5 mL:1.2 - 1.5 g, more preferably 2 - 3 mL:1.2 - 1.5 g, and specifically preferably 3 mL:1.2 g or 2 mL:1.5 g; the volume ratio of the soluble titanium salt to the solvent is preferably 2 - 5:8 - 10, more preferably 2 - 3:8 - 10, and specifically preferably 3:8 or 2:10; the dosage ratio of the soluble titanium salt to the pore-forming agent is preferably 2 - 5 mL:1 g.

[0049] In the present invention, when the soluble metal salt is a soluble vanadium salt, the mass ratio of the soluble vanadium salt to the carbon matrix precursor is preferably 0.2 - 0.5:1.5, specifically preferably 0.2:1.5, 0.3:1.5, 0.4:1.5 or 0.5:1.5; the dosage ratio of the soluble vanadium salt to the solvent is preferably 0.2 - 0.5 g:10 mL, specifically preferably 0.2 g:10 mL, 0.3 g:10 mL, 0.4 g:10 mL or 0.5 g:10 mL; the mass ratio of the soluble vanadium salt to the pore-forming agent is preferably 0.2 - 0.5:1, specifically preferably 0.2:1, 0.3:1, 0.4:1 or 0.5:1.

[0050] In the present invention, when the soluble metal salt is a soluble iron salt, the mass ratio of the soluble iron salt to the carbon matrix precursor is preferably 0.1 - 0.5:1, specifically preferably 0.1:1, 0.2:1, 0.3:1, 0.4:1 or 0.5:1; the dosage ratio of the soluble iron salt to the solvent is preferably 0.1 - 0.5 g:8 mL, specifically preferably 0.1 g:8 mL, 0.2 g:8 mL, 0.3 g:8 mL, 0.4 g:8 mL or 0.5 g:8 mL; the mass ratio of the soluble iron salt to the pore-forming agent is preferably 0.1 - 0.5:0.6, specifically preferably 0.1:0.6, 0.2:0.6, 0.3:0.6, 0.4:0.6 or 0.5:0.6.

[0051] In the present invention, when the soluble metal salt is a soluble cobalt salt, the mass ratio of the soluble cobalt salt to the carbon matrix precursor is preferably 0.2 - 0.35:1, specifically preferably 0.2:1, 0.25:1, 0.3:1 or 0.35:1; the dosage ratio of the soluble cobalt salt to the solvent is preferably 0.2 - 0.35 g:7 - 8 mL, specifically preferably 0.2 g:8 mL or 0.35 mg:7 mL; the mass ratio of the soluble cobalt salt to the pore-forming agent is preferably 0.2 - 0.35:0.6 - 0.8, specifically preferably 0.2:0.6 or 0.35:0.8.

[0052] In the present invention, when the soluble metal salt is a soluble nickel salt, the mass ratio of the soluble nickel salt to the carbon matrix precursor is preferably 0.3 - 0.5:1, specifically preferably 0.3:1, 0.35:1, 0.4:1, 0.45:1 or 0.5:1; the dosage ratio of the soluble cobalt salt to the solvent is preferably 0.3 - 0.5 g:7 mL, specifically preferably 0.3 g:7 mL, 0.35 g:7 mL, 0.4 g:7 mL, 0.45 g:7 mL or 0.5 g:7 mL; the mass ratio of the soluble cobalt salt to the pore-forming agent is preferably 0.3 - 0.5:0.8, specifically preferably 0.3:0.8, 0.35:0.8, 0.4:0.8, 0.45:0.8 or 0.5:0.8.

[0053] In the present invention, the mixing of the soluble metal salt, the carbon matrix precursor and the solvent is preferably carried out under stirring; the mixing temperature of the soluble metal salt, the carbon matrix precursor and the solvent is preferably room temperature, and the time is preferably 6 - 12 h, specifically preferably 6 h, 8 h, 10 h or 12 h.

[0054] After obtaining the spinning solution, the present invention electrospins the spinning solution to obtain a nanofiber membrane containing metal ions.

[0055] In the present invention, the electrospinning method is preferably single-axis electrospinning or coaxial electrospinning.

[0056] In the present invention, the parameters of the single-axis electrospinning include: the voltage is preferably 15 - 20 kV, specifically preferably 15 kV, 16 kV, 17 kV, 18 kV, 19 kV or 20 kV; the distance between the needle and the receiver is preferably 15 - 20 cm, specifically preferably 15 cm, 16 cm, 17 cm, 18 cm, 19 cm or 20 cm; the receiver is preferably an aluminum foil.

[0057] In the present invention, the parameters of the coaxial electrospinning include: the voltage is preferably 15 - 20 kV, specifically preferably 15 kV, 16 kV, 17 kV, 18 kV, 19 kV or 20 kV; the distance between the needle and the receiver is preferably 15 - 20 cm, specifically preferably 15 cm, 16 cm, 17 cm, 18 cm, 19 cm or 20 cm; the receiver is preferably aluminum foil.

[0058] After obtaining the nanofiber membrane containing metal ions, the present invention subjects the nanofiber membrane containing metal ions to heat treatment to obtain the lithium-sulfur battery negative electrode protective film.

[0059] In the present invention, the atmosphere for the heat treatment is preferably nitrogen, phosphorus-containing vapor or tellurium-containing vapor.

[0060] In the present invention, when the atmosphere for the heat treatment is preferably nitrogen, the nitrogen is preferably high-purity nitrogen; the active compound in the lithium-sulfur battery negative electrode protective film is a metal nitride.

[0061] In the present invention, the phosphorus-containing vapor preferably includes phosphorus vapor, hydrogen and argon. In the present invention, the volume ratio of phosphorus vapor, hydrogen and argon in the phosphorus-containing vapor is preferably 1:1:9. In the present invention, when the atmosphere for the heat treatment is phosphorus-containing vapor, the active compound in the lithium-sulfur battery negative electrode protective film is a metal phosphide.

[0062] In the present invention, the tellurium-containing vapor preferably includes tellurium vapor, hydrogen and argon. In the present invention, the volume ratio of tellurium vapor, hydrogen and argon in the tellurium-containing vapor is preferably 1:1:9. In the present invention, when the atmosphere for the heat treatment is tellurium-containing vapor, the active compound in the lithium-sulfur battery negative electrode protective film is a metal telluride.

[0063] In the present invention, the temperature for the heat treatment is preferably 500 - 1500 °C, specifically preferably 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C, 1100 °C, 1200 °C, 1300 °C, 1400 °C or 1500 °C; the time is preferably 1 - 20 h, specifically preferably 1 h, 3 h, 6 h, 9 h, 12 h, 15 h, 18 h or 20 h.

[0064] The present invention also provides a lithium-sulfur battery, including a sulfur positive electrode, a lithium negative electrode and a separator, and the lithium-sulfur battery negative electrode protective film described in the above technical solution or the lithium-sulfur battery negative electrode protective film prepared by the preparation method described in the above technical solution is disposed in parallel between the lithium negative electrode and the separator.

[0065] The lithium-sulfur battery provided by the present invention includes a sulfur positive electrode.

[0066] The lithium-sulfur battery provided by the present invention includes a lithium negative electrode.

[0067] The lithium-sulfur battery provided by the present invention includes a separator, and the separator is preferably a polypropylene (PP) separator, a polyethylene (PE) separator, a polyimide (PI) separator or a composite material separator.

[0068] In the present invention, the negative electrode and the separator are arranged in parallel with the lithium-sulfur battery negative electrode protective film described in the above technical solution or the lithium-sulfur battery negative electrode protective film prepared by the preparation method described in the above technical solution.

[0069] In the present invention, applying the lithium-sulfur battery negative electrode protective film to the lithium-sulfur battery can significantly improve the lithium ion transport kinetics of the lithium-sulfur battery, induce uniform lithium nucleation and deposition, inhibit the formation of lithium dendrites, and further extend the cycle life of the lithium-sulfur battery, especially showing excellent stability under high rate conditions. The lithium-sulfur battery negative electrode protective film of the present invention provides an effective solution for developing high-power and long-life lithium-sulfur batteries and has broad application prospects.

[0070] The following will describe in detail the lithium-sulfur battery negative electrode protective film provided by the present invention, its preparation method and application, and the lithium-sulfur battery in conjunction with embodiments, but they cannot be understood as limiting the protection scope of the present invention.

[0071] Example 1

[0072] 3 mL of tetrabutyl titanate, 1.2 g of polyacrylonitrile, and 8 mL of N-methylpyrrolidone were stirred and dissolved at room temperature for 6 hours to obtain a spinning solution. A titanium ion-containing nanofiber membrane was synthesized by single-axis electrospinning (voltage: 17 kV, distance between the needle and the receiver: 20 cm, receiver: aluminum foil). The collected nanofiber membrane was treated at 1000 °C for 3 h in an atmosphere of high-purity nitrogen to obtain a titanium nitride-based carbon nanofiber membrane, which is the lithium-sulfur battery negative electrode protective film with a thickness of 0.1 mm. Among them, the areal density of the titanium nitride-based carbon nanofiber membrane is 2-3 mg / cm 2 .

[0073] The obtained titanium nitride-based carbon nanofiber membrane was cut into a circular pole piece with a diameter of 15.6 mm as the lithium metal negative electrode protective film. A button-type lithium-sulfur battery was assembled in the order of sulfur positive electrode, separator, lithium metal negative electrode protective film, and metal lithium negative electrode, matching with a commercial lithium-sulfur battery electrolyte. A button-type lithium-sulfur battery was assembled in the order of sulfur positive electrode, separator, and metal lithium negative electrode, matching with a commercial lithium-sulfur battery electrolyte, as a control group button-type lithium-sulfur battery.

[0074] The obtained titanium nitride-based carbon nanofiber film was cut into circular electrodes with a diameter of 15.6 mm as the lithium metal anode protective film, and a lithium-protective film symmetric cell was assembled in the order of metallic lithium, the lithium-sulfur battery anode protective film, the separator, the lithium metal anode protective film, and metallic lithium. Without using the lithium-sulfur battery anode protective film, a pure lithium-lithium symmetric cell was assembled.

[0075] The obtained titanium nitride-based carbon nanofiber film was cut into rectangular electrodes with a size of 45 mm×58 mm as the lithium metal anode protective film, and a soft-pack lithium-sulfur battery was assembled in the order of the sulfur cathode, the separator, the lithium metal anode protective film, and the metallic lithium anode, matching with a commercial lithium-sulfur battery electrolyte.

[0076] Figure 1 XRD pattern of the lithium-sulfur battery anode protective film obtained in Example 1. From Figure 1 it can be seen that: the diffraction peak positions of the synthesized material coincide with those of the standard card of TiN (PDF#38-1420). The three strong diffraction peaks located at 36.6°, 42.6°, and 61.8° correspond to the (111), (200), and (220) crystal planes of TiN, respectively.

[0077] Figure 2 SEM image of the lithium-sulfur battery anode protective film obtained in Example 1. From Figure 2 it can be seen that: the material presents one-dimensional nanofibers, which are a randomly oriented nanofiber intertwined network structure with a diameter of about 100 nm. The fibers intersect and connect with each other to form a carbon conductive network, which is beneficial to the conduction of electrons.

[0078] Figure 3 TEM image of the lithium-sulfur battery anode protective film obtained in Example 1; From Figure 3 it can be seen that: a large number of metal nanoparticles are embedded in the fibers, which is beneficial to the adsorption and catalysis of polysulfides.

[0079] The lithium plating / stripping kinetics of the lithium-sulfur battery anode protective film obtained in Example 1 was studied by galvanostatic charge-discharge (GCD) measurement. At a stripping / plating capacity of 1 mAh / cm 2 the rate performance of TiN-Li at different current densities from 0.5 mA / cm 2 to 5 mA / cm 2 was studied, and the results are as Figure 4 shown. Figure 4 Rate performance graphs of the lithium-protective film symmetric cell and the pure lithium-lithium symmetric cell in Example 1. From Figure 4 it can be seen that: at 0.5 mA / cm 2At the electroplating current density, the deposition curve of TiN-Li is smooth and stable, and the initial nucleation overpotential is low, indicating that its deposition process is uniform and dense. As the current density increases, TiN-Li exhibits a low nucleation overpotential, showing efficient and stable stripping / plating behavior.

[0080] Figure 5 Figure 4 shows the cycling performance of the lithium protective film symmetric battery and the pure lithium-lithium symmetric battery in Example 1. From Figure 5 it can be seen that even when the current density and plating / stripping capacity are upgraded to 1 mA / cm 2 , TiN-Li can still achieve an ultra-low overpotential and stable long-term cycling, and the overpotential shows a downward trend at time intervals of 400 h, 700 h, 1300 h, and 1500 h, indicating that TiN has excellent Li + affinity and strong Li + transport kinetics.

[0081] Figure 6 Figure 4 shows the cycling performance of the lithium protective film symmetric battery and the pure lithium-lithium symmetric battery in Example 1. From Figure 6 it can be seen that even at a plating capacity of 2 mA / cm 2 , TiN-Li can still stably cycle for 1400 hours at the current density and maintain an ultra-low overpotential. These remarkable cycling plating / stripping performances directly demonstrate the excellent ability of TiN to regulate Li + deposition and diffusion, thus significantly inhibiting the growth of lithium dendrites.

[0082] Figure 7 Figure 5 shows the cycling performance of the coin-type lithium-sulfur battery in Example 1. From Figure 7 it can be seen that at 2C, both show good cycling retention ability, and the capacity retention rate can almost reach 95%.

[0083] Figure 8 Figure 6 shows the cycling performance of the pouch-type lithium-sulfur battery in Example 1. From Figure 8 it can be seen that the battery still has a high specific capacity after cycling 20 times at a current of 36 mA, showing its potential in flexible Li-S batteries and practical applications.

[0084] For the assembled coin-type lithium-sulfur battery and the control coin-type lithium-sulfur battery, at a current density of 0.1C, the initial discharge specific capacities are 1436.3 mAh / g and 979.42 mAh / g, respectively.

[0085] Example 2

[0086] 2 mL of tetrabutyl titanate, 300 mg of vanadyl acetylacetonate, 1.5 g of polyacrylonitrile, 1 g of polystyrene, and 10 mL of N-methylpyrrolidone were stirred and dissolved at room temperature for 6 h to obtain a spinning solution. A nanofiber membrane containing titanium and vanadium ions was synthesized by coaxial electrospinning (voltage: 17 kV, distance between the needle and the receiver: 20 cm, receiver: aluminum foil). The collected nanofiber membrane was treated at 1000 °C for 3 h in a high-purity nitrogen atmosphere to obtain a titanium nitride-vanadium nitride-based carbon nanofiber membrane, which is the negative electrode protective film for a lithium-sulfur battery with a thickness of 0.1 mm. Among them, the areal density of the titanium nitride-vanadium nitride-based carbon nanofiber membrane is 2-3 mg / cm 2 .

[0087] The obtained titanium nitride-vanadium nitride-based carbon nanofiber membrane was cut into circular electrodes with a diameter of 15.6 mm as the lithium metal negative electrode protective film. A button lithium-sulfur battery was assembled in the order of sulfur positive electrode, separator, lithium metal negative electrode protective film, and lithium metal negative electrode, matching a commercial lithium-sulfur battery electrolyte. When assembling the button lithium-sulfur battery, at a current density of 0.1 C, the initial discharge specific capacity can reach 1417.28 mAh / g.

[0088] Example 3

[0089] 200 mg of ferric acetylacetonate, 1.0 g of polyacrylonitrile, 8 mL of N-methylpyrrolidone, and 0.6 g of polystyrene were stirred and dissolved at room temperature for 8 h to obtain a spinning solution. A nanofiber membrane containing iron ions was synthesized by single-axis electrospinning (voltage: 17 kV, distance between the needle and the receiver: 20 cm, receiver: aluminum foil). The collected nanofiber membrane was treated at 850 °C for 2 h in a mixed atmosphere of phosphorus vapor / high-purity hydrogen / argon (volume ratio of phosphorus vapor, high-purity hydrogen, and argon: 1:1:9) to obtain an iron phosphide-based carbon nanofiber membrane, which is the negative electrode protective film for a lithium-sulfur battery with a thickness of 0.1 mm. Among them, the areal density of the iron phosphide-based carbon nanofiber membrane is 2-3 mg / cm 2 .

[0090] The obtained iron phosphide-based carbon nanofiber membrane was cut into circular electrodes with a diameter of 15.6 mm as the lithium metal negative electrode protective film. A lithium-protective film symmetric battery was assembled in the order of lithium metal, lithium-sulfur battery negative electrode protective film, separator, lithium metal negative electrode protective film, and lithium metal. A pure lithium-lithium symmetric battery was assembled without using the lithium-sulfur battery negative electrode protective film.

[0091] Secondly, a button lithium-sulfur battery was assembled in the order of sulfur positive electrode, separator, protective film, and lithium metal negative electrode, matching a commercial lithium-sulfur battery electrolyte. When assembling the button lithium-sulfur battery, at a current density of 0.1 C, the initial discharge specific capacity can reach 1408.86 mAh / g.

[0092] Example 4

[0093] 200 mg of cobalt acetylacetonate, 1.0 g of polyacrylonitrile, 8 mL of N-methylpyrrolidone, 0.6 g of polystyrene, stirred and dissolved at room temperature for 8 h to obtain a spinning solution. A cobalt ion-containing nanofiber membrane was synthesized by uniaxial electrospinning (voltage: 17 kV, distance between the needle and the receiver: 20 cm, receiver: aluminum foil). The collected nanofiber membrane was treated at 850 °C for 2 h in a mixed atmosphere of phosphorus vapor / high-purity hydrogen / argon (volume ratio of phosphorus vapor, high-purity hydrogen and argon: 1:1:9) to obtain a cobalt phosphide-based carbon nanofiber membrane, which is the negative electrode protective film for a lithium-sulfur battery, with a thickness of 0.1 mm. Among them, the areal density of the cobalt phosphide-based carbon nanofiber membrane is 2-3 mg / cm 2 。

[0094] The obtained cobalt phosphide-based carbon nanofiber membrane was cut into circular electrodes with a diameter of 15.6 mm as the lithium metal negative electrode protective film, and a lithium protective film symmetric cell was assembled in the order of metal lithium, lithium-sulfur battery negative electrode protective film, separator, lithium metal negative electrode protective film, and metal lithium. A pure lithium-lithium symmetric cell was assembled without using the lithium-sulfur battery negative electrode protective film.

[0095] Secondly, a coin-type lithium-sulfur battery was assembled in the order of sulfur positive electrode, separator, protective film, and metal lithium negative electrode, matching a commercial lithium-sulfur battery electrolyte. When assembling the coin-type lithium-sulfur battery, at a current density of 0.1 C, the initial discharge specific capacity can reach 1391.41 mAh / g.

[0096] Example 5

[0097] 350 mg of nickel acetylacetonate, 1.0 g of polyacrylonitrile, 7 mL of N-methylpyrrolidone, 0.8 g of polystyrene, stirred and dissolved at room temperature for 8 h to obtain a spinning solution. A nickel ion-containing nanofiber membrane was synthesized by uniaxial electrospinning (voltage: 17 kV, distance between the needle and the receiver: 20 cm, receiver: aluminum foil). The collected nanofiber membrane was treated at 600 °C for 10 h in a mixed atmosphere of tellurium vapor / high-purity hydrogen / argon (volume ratio of tellurium vapor, high-purity hydrogen and argon: 1:1:9) to obtain a nickel telluride-based carbon nanofiber membrane, which is the negative electrode protective film for a lithium-sulfur battery, with a thickness of 0.1 mm. Among them, the areal density of the nickel telluride-based carbon nanofiber membrane is 2-3 mg / cm 2 。

[0098] The obtained nickel telluride-based carbon nanofiber membrane was cut into circular electrodes with a diameter of 15.6 mm as the lithium metal negative electrode protective film, and a coin-type lithium-sulfur battery was assembled in the order of sulfur positive electrode, separator, lithium metal negative electrode protective film, and metal lithium negative electrode, matching a commercial lithium-sulfur battery electrolyte. When assembling the coin-type lithium-sulfur battery, at a current density of 0.1 C, the initial discharge specific capacity can reach 1354.37 mAh / g.

[0099] Example 6

[0100] 350 mg of cobalt acetylacetonate, 1.0 g of polyacrylonitrile, 7 mL of N-methylpyrrolidone, and 0.8 g of polystyrene were stirred and dissolved at room temperature for 8 h to obtain a spinning solution. A nanofiber membrane containing cobalt ions was synthesized by uniaxial electrospinning (voltage: 17 kV, distance between the needle and the receiver: 20 cm, receiver: aluminum foil). The collected nanofiber membrane was treated in a mixed atmosphere of tellurium vapor / high-purity hydrogen / argon (volume ratio of tellurium vapor, high-purity hydrogen, and argon: 1:1:9) at 650 °C for 10 h to obtain a cobalt telluride-based carbon nanofiber membrane, which is the negative electrode protective film for a lithium-sulfur battery, with a thickness of 0.1 mm. The areal density of the cobalt telluride-based carbon nanofiber membrane is 2 - 3 mg / cm 2 。

[0101] The obtained cobalt telluride-based carbon nanofiber membrane was cut into rectangular electrodes with a diameter of 45 mm × 58 mm as the lithium metal negative electrode protective film, and a soft-pack lithium-sulfur battery was assembled in the order of a sulfur positive electrode, a separator, the lithium metal negative electrode protective film, and a lithium metal negative electrode, matching a commercial lithium-sulfur battery electrolyte. A coin-type lithium-sulfur battery was assembled, and at a current density of 0.1 C, the initial discharge specific capacity could reach 1374.19 mAh / g.

[0102] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A negative electrode protective film for a lithium-sulfur battery, comprising a carbon matrix, and an active metal compound embedded in the carbon matrix, wherein the carbon matrix is ​​interwoven with nanocarbon fibers, and the active metal compound is one or more of a metal nitride, a metal phosphide and a metal telluride.

2. The negative electrode protective film for lithium-sulfur batteries according to claim 1, characterized in that: The metal nitride is titanium nitride and / or vanadium nitride; the metal phosphide is iron phosphide and / or cobalt phosphide; and the metal telluride is nickel telluride and / or cobalt telluride.

3. The negative electrode protective film for lithium-sulfur batteries according to claim 1, characterized in that: The surface density of the negative electrode protective film of the lithium-sulfur battery is 2 to 3 mg / cm 2 ; The thickness of the negative electrode protective film of the lithium-sulfur battery is 0.01 to 0.15 mm.

4. The method for preparing a negative electrode protective film for a lithium-sulfur battery according to any one of claims 1 to 3, characterized in that: The following steps are involved: mixing a soluble metal salt, a carbon matrix precursor and a solvent to obtain a spinning solution; Electrospinning the spinning solution to obtain a nanofiber membrane containing metal ions; The metal ion-containing nanofiber membrane is heat-treated to obtain the lithium-sulfur battery negative electrode protective membrane.

5. The preparation method according to claim 4, characterized in that: The carbon matrix precursor includes one or more of polyacrylonitrile, polyvinyl pyrrolidone, polystyrene and polymethyl methacrylate, and the soluble metal salt includes one or more of soluble titanium salt, soluble vanadium salt, soluble iron salt, soluble cobalt salt and soluble nickel salt.

6. The preparation method according to claim 4, characterized in that: The spinning solution further comprises a porogen, and the porogen comprises polystyrene.

7. The preparation method according to claim 4, characterized in that: The electrospinning method is uniaxial electrospinning or coaxial electrospinning.

8. The preparation method according to claim 4, characterized in that: The atmosphere of the thermal treatment is nitrogen, phosphorus-containing vapor or tellurium-containing vapor; The phosphorus-containing vapor includes phosphorus vapor, hydrogen and argon; The tellurium-containing vapor includes tellurium vapor, hydrogen gas and argon gas.

9. The preparation method according to claim 4 or 8, characterized in that: The heat treatment temperature is 500-1500° C. and the time is 1-20 hours.

10. A lithium-sulfur battery, comprising a sulfur positive electrode, a lithium negative electrode and a separator, wherein the lithium-sulfur battery negative electrode protective film according to any one of claims 1 to 3 or the lithium-sulfur battery negative electrode protective film prepared by the preparation method according to any one of claims 4 to 9 is arranged in parallel between the lithium negative electrode and the separator.

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