Preparation method and application of cobalt phosphide modified porous carbon nanofiber composite lithium negative electrode and carrier

Abstract

The present invention relates to the field of battery material technology and discloses a preparation method and application of a cobalt phosphide-modified porous carbon nanofiber composite lithium negative electrode and carrier. The preparation method comprises dissolving cobalt nitrate hexahydrate and polyacrylonitrile in an N,N-dimethylformamide solution, mixing and spinning to obtain a cobalt-containing precursor film, wherein the mass ratio of cobalt nitrate hexahydrate to polyacrylonitrile is 1:1.5-3.2; then soaking the film in a methanol solution for 6-24 hours, and then soaking the film in a methanol solution containing a phosphorus source for 1-2 hours, wherein the volume ratio of the phosphorus source to the methanol solution is 1:40-60; and then pre-oxidizing and pyrolyzing the film for 1-2 hours to obtain a porous nanofiber carrier for a composite lithium metal negative electrode. The nanofiber carrier has a porous structure, which facilitates rapid electrolyte transport and uniform lithium ion flux on the negative electrode surface. The negative electrode has good coulombic efficiency and a high cycle number.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a preparation method and application of a cobalt phosphide modified porous carbon nanofiber composite lithium negative electrode and a carrier. Background Art

[0002] In recent years, with the large-scale application of lithium-ion batteries in fields such as electric vehicles, consumer electronics, and energy storage power stations, their technical bottlenecks and resource constraints have become increasingly prominent. First, cobalt resources are the core element of mainstream ternary cathode materials, with 75% of the global reserves concentrated in Congo. The concentration of the supply chain has led to drastic price fluctuations, and the proportion of cathode material costs has remained above 40% for a long time. Secondly, although the energy density of commercial lithium-ion batteries has exceeded 300 Wh / kg, due to the limitations of the theoretical energy density of cathode materials, the marginal benefits of improving energy density through existing material systems have been significantly reduced. At the same time, low-temperature performance defects are particularly prominent in applications in cold regions. For example, when the temperature is below -20°C, the viscosity of traditional liquid electrolytes increases sharply, causing more severe lithium dendrite growth, posing serious safety risks to the battery.

[0003] Lithium-sulfur batteries are battery systems that store energy through multi-electron redox reactions between a sulfur cathode and a lithium anode. Their theoretical energy density reaches 2600Wh / kg, more than five times that of traditional "deintercalation" lithium-ion batteries. Currently, lithium-sulfur batteries developed by China's Zhongkepaisi Energy Storage Technology Co., Ltd. have achieved a discharge specific energy of 400Wh / kg at -20°C and can still operate in extremely cold environments of -60°C, representing low-temperature performance unattainable by current lithium-ion batteries. However, due to limitations in the conductivity of the sulfur cathode, the shuttling effect of intermediate products, and dendritic growth defects at the lithium anode, lithium-sulfur batteries have not yet been mass-produced and applied. After nearly a decade of research, significant progress has been made in the cathode of lithium-sulfur batteries, but the problems existing in the lithium anode are now a hot topic of research. During the charge and discharge process, lithium dendrites form on the lithium anode due to uneven deposition. These dendrites grow continuously as the charge and discharge process proceeds, eventually destroying the solid electrolyte interphase (SEI) film on the anode surface or puncturing the separator, leading to a decrease in battery cycle performance and even causing a short circuit, resulting in spontaneous combustion of the battery, posing a serious safety hazard. Therefore, to further improve the long-term cycle performance of lithium-sulfur batteries and accelerate the industrialization of lithium-sulfur batteries, it is imperative to develop an anode that can effectively inhibit volume expansion and dendrite growth during lithium stripping / deposition. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that lithium dendrites will be generated due to uneven deposition during the charging and discharging process of the lithium negative electrode, and will continue to grow as the charging and discharging proceeds, eventually destroying the SEI film on the surface of the negative electrode or puncturing the diaphragm, resulting in a decrease in battery cycle performance and even causing a short circuit, causing the battery to spontaneously combust, posing a serious safety hazard.

[0005] In order to solve the above technical problems, the technical solutions of the present invention are as follows:

[0006] In a first aspect, the present invention provides a method for preparing a cobalt phosphide-modified porous carbon nanofiber composite lithium negative electrode carrier, comprising the following steps:

[0007] S1. Dissolving cobalt nitrate hexahydrate and polyacrylonitrile in an N,N-dimethylformamide solution, mixing well, and spinning to obtain a cobalt-containing precursor film, wherein the mass ratio of cobalt nitrate hexahydrate to polyacrylonitrile is 1:1.5-3.2;

[0008] S2. Soak the cobalt-containing precursor film in a methanol solution for 6 to 24 hours;

[0009] S3. The cobalt-containing precursor film after soaking in step S2 is placed in a methanol solution containing a phosphorus source and is soaked for 1 to 2 hours, the volume ratio of the phosphorus source to the methanol solution being 1:40 to 60;

[0010] S4. The cobalt-containing precursor film after soaking in step S3 is placed in an oxygen-containing atmosphere for pre-oxidation at a temperature of 200 to 300 ℃;

[0011] S5. The product obtained in step S4 is placed in an inert gas atmosphere containing hydrogen for 1 to 2 hours to obtain a cobalt phosphide-modified porous carbon nanofiber composite lithium negative electrode carrier.

[0012] As a possible design, in step S1, 0.8-1.2 g of polyacrylonitrile is dissolved per 10 mL of N,N-dimethylformamide solution.

[0013] As a possible design, the mass ratio of cobalt nitrate hexahydrate to polyacrylonitrile in step S1 is 1:2-3.

[0014] As a possible design, the mass ratio of cobalt nitrate hexahydrate to polyacrylonitrile in step S1 is 1:2.6.

[0015] As a possible design, the soaking time in step S2 is 10 to 20 hours, and the temperature is room temperature;

[0016] As a possible design, the phosphorus source in step S3 is phytic acid.

[0017] As a possible design, the volume percentage of hydrogen in the inert gas atmosphere in step S5 is 5-10%, and the pyrolysis temperature is 800-1000°C.

[0018] In a second aspect, the present invention provides an electrode sheet, which is obtained by mixing and grinding a cobalt phosphide-modified porous carbon nanofiber composite lithium negative electrode carrier and polyvinylidene fluoride in a mass ratio of 8 to 9.5:1, then adding N-methylpyrrolidone and continuing to grind to obtain a slurry, coating the slurry into a thin sheet and drying it.

[0019] In a third aspect, the present invention provides a composite lithium negative electrode, which is assembled into a half-cell by matching an electrode sheet and metallic lithium, and then undergoing electrodeposition to insert lithium.

[0020] The beneficial effects of the present invention are:

[0021] 1. The cobalt phosphide-modified carbon nanofibers obtained by the preparation method disclosed in the present invention have a network structure, which is beneficial to the rapid transmission of the electrolyte and the uniform lithium ion flux on the negative electrode surface.

[0022] 2. Each fiber of the composite material is anchored with nanometer-sized CoP particles, which can be converted into lithium-philic elemental Co and Li3P, the effective component of the SEI film, during the first cycle of discharge, and have good performance.

[0023] 3. The negative electrode made of the cobalt phosphide-modified carbon nanofibers obtained by the preparation method disclosed in the present invention has good coulombic efficiency and a high number of cycles; the obtained cobalt phosphide-modified carbon nanofibers have a low nucleation overpotential when made into a negative electrode with metallic lithium. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 XRD patterns of the negative electrode support materials synthesized for Examples 1-4 and Comparative Example 1;

[0025] Figure 2 is the SEM image of Example 1;

[0026] Figure 3 is the SEM image of Example 2;

[0027] Figure 4 This is the SEM image of Example 3;

[0028] Figure 5 is the SEM image of Example 4;

[0029] Figure 6 It is the SEM picture of comparative example 1;

[0030] Figure 7 It is the SEM picture of comparative example 2;

[0031] Figure 8This is the SEM image of Comparative Example 3;

[0032] Figure 9 This is the SEM image of Comparative Example 4;

[0033] Figure 10 This is the SEM image of Comparative Example 5;

[0034] Figure 11 This is the SEM image of Comparative Example 6; DETAILED DESCRIPTION

[0035] The specific implementation methods of the present invention will be clearly and completely described below with reference to examples. Obviously, the examples described are only part of the embodiments of the present invention, rather than all the embodiments.

[0036] The present invention will be further described below in conjunction with the embodiments:

[0037] In the following examples, unless otherwise specified, the operations described are routine operations in the art.

[0038] In the following examples, unless otherwise specified, all raw materials used can be obtained through conventional commercial channels.

[0039] In the following examples, methanol and N,N-dimethylformamide (DMF) were analytical grade reagents. Phytic acid was used in the experiment in the form of a 50% by mass aqueous solution.

[0040] Example 1

[0041] (1) 1.2 g of polyacrylonitrile and 0.452 g of cobalt nitrate hexahydrate were dissolved in 12 mL of N,N-dimethylformamide (DMF) solution, and then stirred at room temperature for 12 h to obtain an electrospinning solution. The electrospinning solution was aspirated into a 10 mL plastic syringe, and electrospun at a voltage of 23 kV, a receiving distance of 20 cm, and a propulsion speed of 0.065 mm / min. The solution was then dried at 65 °C for 12 h to obtain a cobalt-loaded electrospun membrane material.

[0042] (2) Soak the cobalt-loaded electrospun membrane material in 30 mL of methanol solution for 6 h;

[0043] (3) Place the soaked electrospun membrane material in 30 mL of methanol solution containing phytic acid (methanol:phytic acid volume ratio = 60:1) and let it stand for 1 h; after standing, rinse it with methanol solution 2 to 3 times and dry it at 65 °C for 12 h;

[0044] (4) Pre-oxidation at 200 °C for 2 h in air atmosphere to obtain CoP@CNF precursor;

[0045] (5) The obtained CoP@CNF precursor was placed in a tubular furnace and calcined at 900 °C for 2 h in an argon-hydrogen mixture with a hydrogen content of 10% at a heating rate of 5 °C / min. The obtained negative electrode carrier material was labeled CoP@CNF-6.

[0046] (6) CoP@CNF-6 and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 9:1, and a certain amount of N-methylpyrrolidone (NMP) was added and ground into a uniform negative electrode slurry. The slurry was then scraped onto the surface of copper foil using a 50 μm scraper and dried at 60°C for 12 h. The scraped sample was then cut into small discs with a diameter of 14 mm using a microtome to obtain the CoP@CNF-6 negative electrode.

[0047] Example 2

[0048] (1) 1.2 g of polyacrylonitrile and 0.520 g of cobalt nitrate hexahydrate were dissolved in 12 mL of N,N-dimethylformamide (DMF) solution, and then stirred at room temperature for 12 h to obtain an electrospinning solution. The electrospinning solution was aspirated into a 10 mL plastic syringe and electrospun at a voltage of 23 kV, a receiving distance of 20 cm, and a propulsion speed of 0.065 mm / min. The solution was then dried at 65 °C for 12 h to obtain a cobalt-loaded electrospun membrane material.

[0049] (2) Soak the cobalt-loaded electrospun membrane material in 30 mL of methanol solution for 12 h;

[0050] (3) Place the soaked electrospun membrane material in 30 mL of methanol solution containing phytic acid (methanol:phytic acid volume ratio = 50:1) and let it stand for 1 h; after standing, rinse it with methanol solution 2 to 3 times and dry it at 65 °C for 12 h;

[0051] (4) Pre-oxidation at 200 °C for 2 h in air atmosphere to obtain CoP@CNF precursor;

[0052] (5) The obtained CoP@CNF precursor was placed in a tubular furnace and calcined at 900 °C for 2 h in an argon-hydrogen mixture with a hydrogen content of 10% at a heating rate of 5 °C / min. The obtained negative electrode carrier material was labeled CoP@CNF-12.

[0053] (6) CoP@CNF-12 and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 9:1, and a certain amount of NMP was added to grind to form a uniform negative electrode slurry. The slurry was then scraped onto the surface of copper foil using a 50 μm scraper and dried at 60°C for 12 h. The scraped sample was then cut into small discs with a diameter of 14 mm using a microtome to obtain the CoP@CNF-12 negative electrode.

[0054] Example 3

[0055] (1) 1.2 g of polyacrylonitrile and 0.458 g of cobalt nitrate hexahydrate were dissolved in 12 mL of N,N-dimethylformamide (DMF) solution, and then stirred at room temperature for 12 h to obtain an electrospinning solution. The electrospinning solution was aspirated into a 10 mL plastic syringe and electrospun at a voltage of 23 kV, a receiving distance of 20 cm, and a propulsion speed of 0.065 mm / min. The solution was then dried at 65 °C for 12 h to obtain a cobalt-loaded electrospun membrane material.

[0056] (2) Soak the cobalt-loaded electrospun membrane material in 30 mL of methanol solution for 18 h;

[0057] (3) Place the soaked electrospun membrane material in 30 mL of methanol solution containing phytic acid (methanol:phytic acid volume ratio = 60:1) and let it stand for 1 h; after standing, rinse it with methanol solution 2 to 3 times and dry it at 65 °C for 12 h;

[0058] (4) Pre-oxidation at 200 °C for 2 h in air atmosphere to obtain CoP@CNF precursor;

[0059] (5) The obtained CoP@CNF precursor was placed in a tubular furnace and calcined at 900 °C for 2 h in an argon-hydrogen mixture with a hydrogen content of 10% at a heating rate of 5 °C / min. The obtained negative electrode carrier material was labeled CoP@CNF-18.

[0060] (6) CoP@CNF-18 and PVDF were mixed at a mass ratio of 9:1, and a certain amount of NMP was added to grind to form a uniform negative electrode slurry. The slurry was then scraped onto the surface of copper foil using a 50 μm scraper and dried at 60°C for 12 h. The scraped sample was then cut into small discs with a diameter of 14 mm using a microtome to obtain the CoP@CNF-18 negative electrode.

[0061] Example 4

[0062] (1) 1.2 g of polyacrylonitrile and 0.458 g of cobalt nitrate hexahydrate were dissolved in 12 mL of N,N-dimethylformamide (DMF) solution, and then stirred at room temperature for 12 h to obtain an electrospinning solution. The electrospinning solution was aspirated into a 10 mL plastic syringe and electrospun at a voltage of 23 kV, a receiving distance of 20 cm, and a propulsion speed of 0.065 mm / min. The solution was then dried at 65 °C for 12 h to obtain a cobalt-loaded electrospun membrane material.

[0063] (2) Soak the cobalt-loaded electrospun membrane material in 30 mL of methanol solution for 24 h;

[0064] (3) Place the soaked electrospun membrane material in 30 mL of methanol solution containing phytic acid (methanol:phytic acid volume ratio = 55:1) and let it stand for 1 h; after standing, rinse it with methanol solution 2 to 3 times and dry it at 65 °C for 12 h;

[0065] (4) Pre-oxidation at 200 °C for 2 h in air atmosphere to obtain CoP@CNF precursor;

[0066] (5) The obtained CoP@CNF precursor was placed in a tubular furnace and calcined at 900 °C for 2 h in an argon-hydrogen mixture with a hydrogen content of 10% at a heating rate of 5 °C / min. The obtained negative electrode carrier material was labeled CoP@CNF-24.

[0067] (6) CoP@CNF-24 and PVDF were mixed at a mass ratio of 9:1, and a certain amount of NMP was added to grind to form a uniform negative electrode slurry. The slurry was then scraped onto the surface of copper foil using a 50 μm scraper and dried at 60°C for 12 h. The scraped sample was then cut into small discs with a diameter of 14 mm using a microtome to obtain the CoP@CNF-24 negative electrode.

[0068] Comparative Example 1

[0069] (1) Add 1.2 g of polyacrylonitrile to 12 mL of DMF solution and stir at room temperature for 12 h to obtain an electrospinning solution. The electrospinning solution was aspirated into a 10 mL plastic syringe and electrospun at a voltage of 23 KV, a receiving distance of 20 cm, and a propulsion speed of 0.065 mm / min to prepare a cobalt-free precursor film.

[0070] (2) The cobalt-free precursor film was dried at 65°C for 12 h, heated to 200°C in an air atmosphere for pre-oxidation for 2 h, and then placed in a tube furnace and calcined at 900°C for 2 h in an argon-hydrogen mixture with a hydrogen content of 10% at a heating rate of 5°C / min. The resulting negative electrode carrier material was labeled CNF.

[0071] (3) CNF and PVDF were mixed at a mass ratio of 9:1, and a certain amount of NMP was added to grind into a uniform slurry. The slurry was then applied to the surface of copper foil using a 50 μm scraper and dried at 60°C for 12 h. The slurry was then cut into small discs with a diameter of 14 mm using a microtome to obtain the CNF negative electrode.

[0072] Comparative Example 2

[0073] (1) 1.2 g of polyacrylonitrile was added to 12 mL of DMF solution and then stirred at room temperature for 12 h to obtain an electrospinning solution. The electrospinning solution was aspirated into a 10 mL plastic syringe and electrospun at a voltage of 23 KV, a receiving distance of 20 cm, and a propulsion speed of 0.065 mm / min to prepare a cobalt-free precursor film.

[0074] (2) The cobalt-free precursor film was dried at 65°C for 12 h, then immersed in 30 mL of methanol for 18 h, rinsed 2-3 times, and dried at 65°C for 18 h.

[0075] (3) The precursor film after soaking was pre-oxidized at 200 °C in an air atmosphere for 2 h, and then placed in a tubular furnace and calcined at 900 °C for 2 h in an argon-hydrogen mixture with a hydrogen content of 10% at a heating rate of 5 °C / min. The obtained negative electrode carrier material was labeled CNF-methanol.

[0076] Comparative Example 3

[0077] (1) 1.2 g of polyacrylonitrile and 0.458 g of cobalt nitrate hexahydrate were added to 12 mL of DMF solution, and then stirred at room temperature for 12 h to obtain an electrospinning solution. The electrospinning solution was aspirated into a 10 mL plastic syringe and electrospun at a voltage of 23 KV, a receiving distance of 20 cm, and a propulsion speed of 0.065 mm / min to prepare a cobalt-containing precursor film.

[0078] (2) The cobalt-containing precursor film was dried at 65 °C for 12 h and then pre-oxidized at 200 °C in air for 2 h. It was then placed in a tubular furnace and calcined at 900 °C for 2 h in an argon-hydrogen mixture with a hydrogen content of 10% at a heating rate of 5 °C / min. The resulting negative electrode carrier material was labeled Co-CNF.

[0079] Comparative Example 4

[0080] (1) 1.2 g of polyacrylonitrile and 0.458 g of cobalt nitrate hexahydrate were added to 12 mL of DMF solution, and then stirred at room temperature for 12 h to obtain an electrospinning solution. The electrospinning solution was aspirated into a 10 mL plastic syringe and electrospun at a voltage of 23 KV, a receiving distance of 20 cm, and a propulsion speed of 0.065 mm / min to prepare a cobalt-containing precursor film.

[0081] (2) The cobalt-containing precursor film was dried at 65°C for 12 h, then immersed in 30 mL of methanol for 18 h, and then dried at 65°C for 24 h;

[0082] (3) The precursor film after soaking was pre-oxidized at 200 °C in air atmosphere for 2 h, and then placed in a tube furnace and calcined at 900 °C for 2 h in an argon-hydrogen mixture with a hydrogen content of 10% at a heating rate of 5 °C / min. The obtained negative electrode carrier material was labeled Co-CNF-methanol.

[0083] Comparative Example 5

[0084] (1) 1.2 g of polyacrylonitrile and 0.458 g of nickel nitrate hexahydrate were added to 12 mL of DMF solution, and then stirred at room temperature for 12 h to obtain an electrospinning solution. The electrospinning solution was aspirated into a 10 mL plastic syringe and electrospun at a voltage of 23 KV, a receiving distance of 20 cm, and a propulsion speed of 0.065 mm / min to prepare a cobalt-containing precursor film.

[0085] (2) The cobalt-containing precursor film was dried at 65°C for 12 h, then immersed in 30 mL of methanol for 18 h, and then dried at 65°C for 24 h;

[0086] (3) The precursor film after soaking was pre-oxidized at 200 °C in an air atmosphere for 2 h, and then placed in a tubular furnace and calcined at 900 °C for 2 h in an argon-hydrogen mixture with a hydrogen content of 10% at a heating rate of 5 °C / min. The obtained negative electrode carrier material was labeled Ni-CNF-methanol.

[0087] Comparative Example 6

[0088] (1) 1.2 g of polyacrylonitrile and 0.458 g of ferric chloride were added to 12 mL of DMF solution and then stirred at room temperature for 12 h to obtain an electrospinning solution. The electrospinning solution was aspirated into a 10 mL plastic syringe and electrospun at a voltage of 23 KV, a receiving distance of 20 cm, and a propulsion speed of 0.065 mm / min to prepare a cobalt-containing precursor film.

[0089] (2) The cobalt-containing precursor film was dried at 65°C for 12 h, then immersed in 30 mL of methanol for 18 h, and then dried at 65°C for 24 h;

[0090] (3) The precursor film after soaking was pre-oxidized at 200 °C in an air atmosphere for 2 h, and then placed in a tubular furnace and calcined at 900 °C for 2 h in an argon-hydrogen mixture with a hydrogen content of 10% at a heating rate of 5 °C / min. The resulting negative electrode carrier material was labeled Fe-CNF-methanol.

[0091] 1. XRD analysis of Examples 1-4 and Comparative Example 1

[0092] Figure 1The XRD patterns of the negative electrode support materials synthesized in Examples 1-4 and Comparative Example 1 show that the materials in Examples 1-4 exhibit diffraction peaks at 2θ≈31.6, 35.3°, 36.3°, 46.2°, 48.1°, 52.2°, 56.0°, and 56.7°, corresponding to the (0 1 1), (2 0 0), (1 1 2), (2 1 1), (1 0 3), (0 2 0), and (3 0 1) crystal planes of CoP, respectively. Furthermore, the broad peak at 2θ≈20-30° is attributed to the diffraction peak of carbon in the composite material, indicating that CoP@CNF was successfully synthesized. However, the figure also shows that the intensity of the CoP characteristic peak gradually increases with the immersion time of the cobalt-containing precursor film in the methanol solution, indicating that the relative content of CoP in the composite material is also increasing. In contrast, the material in Comparative Example 1 only showed a carbon peak at 2θ≈20~30°, indicating that the cobalt-free precursor film was successfully converted into CNF after carbonization.

[0093] 2. Micromorphology of Examples 1-4

[0094] Figure 2-5 The SEM images of the negative electrode carrier samples of Examples 1-4 respectively show that after the cobalt precursor film is immersed in methanol and phytic acid solution and carbonized at high temperature, a network structure of interwoven fibers with a diameter of 1 μm is obtained, which will be beneficial to the rapid transmission of the electrolyte and the uniform lithium ion flux on the negative electrode surface in the subsequent process. Secondly, after magnifying the image, it was found that CoP particles with a diameter of nanometers were anchored in each fiber of the composite material, which were converted into lithium-philic elemental Co and Li3P, the effective component of the SEI film, during the first cycle of discharge. In addition, obvious pore structures can be seen on the surface and cross-section of the fibers of Examples 1-4, and as the immersion time of the cobalt precursor film in the methanol solution increases ( Figures 2 to 5 ) and increase.

[0095] 3. Microscopic morphology of comparative examples 1-6

[0096] Comparative Example 1 is a CNF carbon fiber obtained by directly calcining a cobalt-free precursor film at high temperature. Figure 6 It can be seen that the fiber diameter is about 1 μm, and its surface is smooth and has no pore structure, which indicates that the generation of the pore structure in the embodiment has nothing to do with the PAN raw material.

[0097] Comparative Example 2 is a CNF-methanol fiber obtained by immersing the cobalt-free precursor film in methanol for 18 hours and then carbonizing it. Figure 7 It can be seen that the fiber surface is smooth and no pore structure is generated at all, indicating that the pore structure in the embodiment may be related to cobalt nitrate.

[0098] Comparative Example 3 is a CNF-Co fiber obtained by directly carbonizing a cobalt-containing precursor film at high temperature. Figure 8 It can be seen that only uniformly distributed nanoparticles appear on the fiber surface, and no pore structure is generated. It is speculated that the particles should be the cobalt precursor film that reduces cobalt nitrate to elemental cobalt during the carbonization process.

[0099] Comparative Example 4 considered the effects of methanol immersion and cobalt nitrate at the same time, and soaked the cobalt-containing precursor film in methanol for 18 hours and then carbonized it to obtain CNF-Co-methanol fiber. Figure 9 It can be seen that nanoparticles and obvious pore structures appear on the surface of the resulting material, and their size is close to that of the nanoparticles. Therefore, it can be determined that the formation of the pore structure in CoP@CNF is related to the slow dissolution of cobalt nitrate during the immersion of the cobalt precursor film in methanol solution.

[0100] Comparative Example 5 used nickel nitrate hexahydrate instead of cobalt nitrate hexahydrate and analyzed the changes in fiber morphology. Figure 10 It can be seen that no pore structure is observed on the surface of Ni-CNF-methanol except for scattered particles, indicating that it is impossible to form pores on the fiber surface using ferric nitrate nonahydrate as the raw material.

[0101] Comparative Example 6: Fe-CNF-methanol fiber was prepared by replacing cobalt nitrate hexahydrate with ferric chloride. Figure 11 It can be seen that a small amount of pore structure appears on the fiber surface, indicating that pores can also be formed on the fiber surface using ferric chloride as raw material. However, due to the difference in its solubility in methanol, the pore structure is not as obvious as when cobalt nitrate hexahydrate is used as raw material.

[0102] 4. Electrochemical testing and analysis

[0103] The electrode sheets prepared in Examples 1-4 and Comparative Example 1 were paired with commercial lithium sheets and assembled into CR2032 Li / Cu half-cells in a glove box maintained at a water and oxygen content below 0.1 ppm. The electrolyte consisted of 1 mol / L lithium trifluoromethylsulfonyl imide (LiTFSI) dissolved in a 1:1 volume ratio of 1,3-dioxolane (DOL) and dimethoxymethane (DME). The additive was 0.2 mol / L LiNO₃, used in an amount of 60 µL.

[0104] (1) Analysis of Coulombic efficiency performance test results of Li / / Cu half-cell

[0105] The Li / / Cu half-cells assembled in Examples 1-4 and Comparative Example 1 were sandwiched between three stainless steel electrodes, and rate performance tests were performed using a Newwell battery test system at 30°C. The test voltage range was 0.1-1.0 V, and the current density and deposition capacity were 1 mA / cm 2 and 1mAh / cm 2The coulombic efficiency test results of the Li / / Cu half-cell are as follows: the initial coulombic efficiency of CNF in Comparative Example 1 under the above conditions is 90%, which decays to 60% after 40 cycles. In comparison, the coulombic efficiency and cycle number of the CoP@CNF-6, CoP@CNF-12, CoP@CNF-18 and CoP@CNF-24 composite negative electrodes in Examples 1-4 are better than those in Comparative Example 1, and the current density and deposition capacity of CoP@CNF-18 are 1 mA / cm 2 and 1mAh / cm 2 The number of cycles under the highest level can reach 120.

[0106] The above are only preferred embodiments of the present invention and are not intended to limit the present invention in any form. Although the present invention is disclosed in terms of preferred embodiments, they are not intended to limit the present invention. Those skilled in the art can make changes and modifications to the above technical contents without departing from the scope of the technical solution of the present invention to form equivalent embodiments of equivalent changes. However, any simple modifications, equivalent changes and modifications to the above embodiments based on their technical essence without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a cobalt phosphide modified porous carbon nanofiber composite lithium negative electrode carrier, characterized in that: The preparation method comprises the following steps: S1. Dissolving cobalt nitrate hexahydrate and polyacrylonitrile in an N,N-dimethylformamide solution, mixing well, and spinning to obtain a cobalt-containing precursor film, wherein the mass ratio of cobalt nitrate hexahydrate to polyacrylonitrile is 1:1.5-3.2; S2. Soak the cobalt-containing precursor film in a methanol solution for 6 to 24 hours; S3. The cobalt-containing precursor film after soaking in step S2 is placed in a methanol solution containing a phosphorus source and is soaked for 1 to 2 hours, the volume ratio of the phosphorus source to the methanol solution being 1:40 to 60; S4. The cobalt-containing precursor film after soaking in step S3 is placed in an oxygen atmosphere for pre-oxidation at a temperature of 200 to 300 ℃; S5. The product obtained in step S4 is placed in an inert gas atmosphere containing hydrogen and pyrolyzed for 1 to 2 hours to obtain a cobalt phosphide-modified porous carbon nanofiber composite lithium negative electrode carrier; In step S5, the volume percentage of hydrogen in the inert gas atmosphere is 5-10%, and the pyrolysis temperature is 800-1000°C.

2. The method for preparing a negative electrode carrier according to claim 1, characterized in that: In step S1, 0.8-1.2 g of polyacrylonitrile is dissolved in every 10 mL of N,N-dimethylformamide solution.

3. The method for preparing a negative electrode carrier according to claim 1, characterized in that: In step S1, the mass ratio of cobalt nitrate hexahydrate to polyacrylonitrile is 1:2-3.

4. The method for preparing a negative electrode carrier according to claim 1, characterized in that: In step S2, the cobalt-containing precursor film is immersed in a methanol solution for 10 to 20 hours.

5. The method for preparing a negative electrode carrier according to claim 1, characterized in that: In step S3, the phosphorus source is phytic acid.

6. The cobalt phosphide modified porous carbon nanofiber composite lithium negative electrode carrier obtained by the preparation method according to any one of claims 1 to 5, characterized in that: The negative electrode carrier has a network structure.

7. An electrode sheet, characterized in that: The negative electrode carrier according to claim 6 and polyvinylidene fluoride are mixed and ground in a mass ratio of 8 to 9.5:1, and then N-methylpyrrolidone is added and further ground to obtain a slurry. The slurry is coated into a thin sheet and then dried.

8. A composite lithium negative electrode, characterized in that The electrode sheet according to claim 7 and metallic lithium are matched to assemble a half-cell, and then lithium is inserted by electrodeposition.

9. Use of the negative electrode carrier according to claim 6, the electrode sheet according to claim 7 or the composite lithium negative electrode according to claim 8 in the preparation of a lithium-sulfur battery.

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