CN114262955B

CN114262955B - Size-controllable Ni-NiO heterojunction nanoparticle doped carbon fiber, preparation method and application thereof in lithium-sulfur battery diaphragm

Info

Publication number: CN114262955B
Application number: CN202111615264.4A
Authority: CN
Inventors: 濮军; 王涛
Original assignee: Anhui Normal University
Current assignee: Anhui Normal University
Priority date: 2021-12-24
Filing date: 2021-12-24
Publication date: 2024-03-15
Anticipated expiration: 2041-12-24
Also published as: CN114262955A

Abstract

The invention provides a size-controllable Ni-NiO heterojunction nano-particle doped carbon fiber, a preparation method and application thereof in a lithium-sulfur battery diaphragm. Compared with the prior art, the preparation method provided by the invention is simple and easy to implement, high energy consumption technologies such as electrostatic spinning and the like are not needed, the nanofiber precursor can be directly prepared by stirring and standing, and the Ni-NiO heterojunction uniform particles with controllable size are generated in situ in the heat treatment process. The Ni-NiO heterojunction nanoparticle doped carbon nanofiber can play an important role in a lithium sulfur battery, and the prepared material is modified on the surface of a lithium sulfur battery diaphragm, so that the initial capacity can be remarkably improved, the shuttle effect can be restrained, and the comprehensive performance of the lithium sulfur battery can be improved.

Description

Size-controllable Ni-NiO heterojunction nanoparticle doped carbon fiber, preparation method and application thereof in lithium-sulfur battery diaphragm

Technical Field

The invention belongs to the field of battery materials, and particularly relates to a size-controllable Ni-NiO heterojunction nanoparticle doped carbon nanofiber, a preparation method and application thereof in a lithium-sulfur battery diaphragm.

Background

Lithium ion batteries have greatly promoted the development of human society as a high-efficiency energy storage device and will continue to play an important role in the future. However, conventional lithium ion batteries having lithium-rich transition metal oxide anodes and graphite cathodes in combination have had difficulty meeting the demands of high energy density and low manufacturing costs. Therefore, it is urgent to explore and develop a new type of rechargeable battery system.

The theoretical energy density of the lithium-sulfur battery is 2600Wh/Kg, which is 7-8 times of that of the traditional lithium ion battery, and the theoretical specific capacity of the sulfur simple substance in the positive electrode is 1675mAh/g, which is the solid positive electrode material with the maximum known theoretical specific capacity. The materials used for the lithium-sulfur battery have the advantages of environmental friendliness, rich storage and the like. Therefore, lithium sulfur batteries have become an ideal next-generation commercial battery. But the "shuttle effect" caused by the dissolution of polysulfide intermediates in the electrolyte during the lithium sulfur battery reaction process can lead to rapid decay of the battery's capacity. At the same time, the insulativity and slow reaction kinetics of the charge and discharge products limit the rapid charge and discharge capabilities of the battery. These severely limit the large-scale commercial application of lithium sulfur batteries.

The prior art shows that improving the separator of lithium-sulfur batteries can effectively improve the problems. Common lithium sulfur battery separators are nonpolar Polyethylene (PE) or polypropylene (PP) materials that have no inhibiting effect on polysulfide diffusion. The polar metal compound nanoparticle doped carbon nanofiber modified membrane can greatly relieve the shuttle effect (ChemNanoMat, 2016,2,937-941; J. Mater. Chem. A,2018,6,6155-6182). Among the numerous candidate materials of polar metal compounds, transition metal nickel and its compound materials are not only inexpensive, but also have extremely high capacities for adsorbing and catalyzing polysulfide conversion for soluble polysulfides.

Currently, there are two general techniques for preparing nickel-based compound doped carbon nanofibers: the first is to directly grow nickel-based nano-particles on a carbon nanofiber finished product by means of hydrothermal, electrodeposition and the like, and for example, a literature (surface science, 2016,45,4, 132-136) published in month 4 of 2016 entitled "research on influence of sodium dodecyl sulfate on electrodeposition behavior of nickel plating on a carbon fiber surface" reports that a nickel-based nano-coating is prepared on a carbon nanofiber by electrodeposition. And secondly, preparing a fibrous nickel-containing organic precursor by spraying under high pressure by utilizing an electrostatic spinning means, and then performing high-temperature treatment to obtain the nickel-based compound nanoparticle doped carbon nanofiber material. These methods are not only complex in process but also require expensive equipment (e.g., electrochemical workstations, electrospinning instruments, etc.), with limited control over the size of nickel-based nanoparticles.

Therefore, developing a fast, simple, low-cost, particle size controllable nickel-based nanoparticle doped carbon nanofiber remains a challenge.

Disclosure of Invention

The invention aims to provide a size-controllable Ni-NiO heterojunction nano-particle doped carbon fiber and a preparation method thereof, wherein a fibrous nickel dimethylglyoxime precursor is formed by complexing precipitation of dimethylglyoxime and nickel ions, a Ni-NiO heterojunction structure is formed in situ during high-temperature carbonization and precursor oxidation, the fiber morphology is reserved, the size of the generated nickel-based particles is controlled by adjusting the calcination temperature, and the particles with the diameters of about 3-50nm are uniformly distributed on the surface of the nano-fiber without the complicated steps of carbonizing materials to form the carbon fiber and then doping the heterojunction structure.

The invention also aims to provide application of the size-controllable Ni-NiO heterojunction nanoparticle doped carbon fiber in a lithium-sulfur battery diaphragm, and the technical problems of capacity reduction, low multiplying power and the like caused by the shuttle effect of polysulfide in a lithium-sulfur battery are solved through adjustment of the reaction of the Ni-NiO heterojunction on the polysulfide. The initial capacity of the battery can be improved, the capacity decay rate of the battery in the cycle process is slowed down, and the performance of the lithium-sulfur battery is comprehensively improved.

The specific technical scheme of the invention is as follows:

the preparation method of the size-controllable Ni-NiO heterojunction nanoparticle doped carbon nanofiber comprises the following steps of:

1) Dissolving dimethylglyoxime in a solvent, and regulating the pH value to 9-13 to form a solution A;

2) Dropwise adding the solution A into a nickel source solution, stirring, standing, centrifugally separating precipitate, washing and drying;

3) Carbonizing the product obtained in the step 2) in inert gas to obtain a carbon nanofiber material doped with ultrafine Ni nano particles;

4) And 3) placing the product obtained in the step 3) in air, and performing heating oxidation treatment to obtain the size-controllable Ni-NiO heterojunction nano-particle doped carbon nano-fiber.

The solvent in the step 1) is absolute ethyl alcohol, so that the dimethylglyoxime is dissolved. The absolute ethyl alcohol is an organic solvent, has similar polarity with the dimethylglyoxime, has similar compatible effect, and can promote the dimethylglyoxime to be fully dissolved; and the ethanol is cheap and nontoxic, and other low-carbon organic solvents are not friendly to the environment and are expensive.

In the step 1), the molar concentration of the dimethylglyoxime in the solvent A is 0.011-0.081mol/L.

In step 1), the pH is adjusted to 9-13 by using an alkaline solution; the concentration of the alkaline solution is 0.2-0.8 mol/L; the alkaline solution is sodium hydroxide solution or potassium hydroxide solution.

In the step 2), the nickel source is any one of nickel chloride, nickel nitrate, nickel sulfate and nickel acetate.

In the step 2), the molar concentration of the nickel source solution is 0.001-0.005mol/L.

In the step 2), the volume ratio of the solution A to the nickel source solution is 0.05-0.1:1.

In the step 2), the dripping is carried out for 10-30 minutes, and the reaction is fully carried out by slowly dripping.

In the step 2), stirring is carried out for 10-60 minutes at normal temperature at a stirring speed of 200-800 revolutions per minute; the solvent dropped on the upper layer of the solution and the solution on the lower layer can also react rapidly by stirring, so that the pH of the whole solution is uniform, the reaction is fully carried out, nucleation is promoted, and agglomeration is prevented.

In the step 2), the standing is normal temperature standing, and the standing time is 2-6 hours, so that the reaction is fully carried out.

In the step 2), the washing refers to respectively washing with deionized water and absolute ethyl alcohol for 3-5 times until the pH value of the supernatant is neutral.

In the step 2), the drying refers to drying for 6-12 hours at 50-60 ℃;

in the step 3), the inert atmosphere refers to one of argon, nitrogen or a mixture of the argon and the nitrogen.

In the step 3), the carbonization treatment temperature is 300-700 ℃ and the calcination time is 1-5 hours.

The heating oxidation treatment in the step 4) is carried out at the temperature of 50-300 ℃ for 1-5 hours.

According to the invention, the dimethylglyoxime and nickel ions are subjected to complexation precipitation to form a fibrous dimethylglyoxime nickel precursor, a Ni-NiO heterojunction structure is formed in situ during high-temperature carbonization and precursor oxidation, the fiber morphology is reserved, the size of the generated nickel-based particles is controlled by adjusting the calcination temperature, and the particles with diameters of about 3-50nm are uniformly distributed on the surface of the nanofiber. The carbon fiber is left by carbonizing the precursor of the dimethylglyoxime at high temperature; hydrogen bonds are present in the reaction product of dimethylglyoxime and nickel ions. This hydrogen bond connects the oxygen in the chain with the oxygen bond to form the whole polymer chain into a sheet, and since the free energy of the surface is very high, the sheet molecules are easily stacked preferentially along the c-axis to form crystals, and the growth in the a-and b-axis directions is relatively slow, so that the precipitated product grows into a fibrous shape.

The size-controllable Ni-NiO heterojunction nanoparticle doped carbon nanofiber is prepared by the method. Particles with the diameter of 3-50nm are uniformly distributed on the surface and inside of the nanofiber, the surface is of a Ni-NiO heterojunction structure, and the inside is of metallic nickel.

The invention also provides application of the size-controllable Ni-NiO heterojunction nanoparticle doped carbon nanofiber in a lithium-sulfur battery diaphragm.

The specific application method comprises the following steps:

and dispersing the size-controllable Ni-NiO heterojunction nano-particle doped carbon nano-fiber and a binder PVDF in an NMP (N-methylpyrrolidone) solvent, uniformly stirring the obtained mixed slurry, coating the mixed slurry on the surface of a diaphragm through a scraper, and carrying out vacuum drying to obtain the modified diaphragm for the lithium-sulfur battery.

The mass ratio of the size-controllable Ni-NiO heterojunction nano-particle doped carbon nano-fiber to the binder PVDF is 9:1.

The volume ratio of the binder PVDF to NMP is 1:1.

The thickness of the mixed slurry on the surface of the diaphragm is 12 mu m.

According to the size-controllable Ni-NiO heterojunction nanoparticle doped carbon nanofiber, the size-controllable Ni-NiO heterojunction nanoparticle doped carbon nanofiber is used as a diaphragm modification layer of a lithium-sulfur battery, niO outside a heterojunction interface can adsorb polysulfide through chemical bonding, and shuttling of the NiO is restrained; due to the excellent conductivity of the metal Ni in the heterojunction interface, the electron transfer between NiO and a carbon matrix is accelerated, the catalysis process of NiO on polysulfide is promoted, the slow dynamic process during polysulfide conversion is accelerated, and the utilization rate of active materials is improved. The two are cooperated to improve the initial capacity of the battery, slow down the decay rate of the capacity when the battery circulates, and comprehensively improve the performance of the lithium-sulfur battery.

According to the invention, a fibrous nickel dimethylglyoxime precursor is formed by complexing precipitation of dimethylglyoxime and nickel ions, and the greater the pH value is, the shorter the length of the fiber is, because the pH value is high, the surface of the precursor is surrounded by OH groups, the surface energy is low, and the growth in the C axis direction is slow. When the precursor is carbonized at high temperature, a Ni-NiO heterojunction structure is formed in situ, the fiber morphology is reserved, and the complicated steps of firstly carbonizing a material to form carbon fibers and then doping the heterojunction structure are not needed; high cost electrospinning is also unnecessary. The size of the generated nickel-based particles is controlled by adjusting the carbonization temperature, and the particles with the diameter of 3-50nm are uniformly doped in the carbon nanofiber, and NiO is formed by heating and oxidizing in the air, so that a layer of Ni-NiO heterojunction structure is formed on the surface of the nanofiber. Both the surface and the interior have particles, which are uniformly doped.

Compared with the prior art, the invention has the beneficial effects that: the Ni-NiO heterojunction uniform particles with controllable size are generated in situ, and the Ni-NiO heterojunction nano-particles doped with the carbon nano-fibers can play an important role in the lithium sulfur battery.

Drawings

FIG. 1 is an X-ray powder diffraction pattern of a Ni-NiO heterojunction nanoparticle-doped carbon nanofiber and a partial enlarged view thereof, which were obtained in example 1; a is an X-ray powder diffraction pattern, b is a partial enlarged view of the a pattern;

FIG. 2 is an SEM image of a Ni-NiO heterojunction nanoparticle-doped carbon nanofiber prepared in example 1;

FIG. 3 is a cyclic voltammetry test curve of a battery assembled with a common commercial PP separator membrane of comparative example 1 and a Ni-NiO heterojunction nanoparticle-doped carbon nanofiber prepared in example 1 as a separator modification layer;

FIG. 4 is a cycling test of a battery assembled with comparative example 1 (a battery assembled with a common commercial PP separator) and the Ni-NiO heterojunction nanoparticle-doped carbon nanofiber prepared in example 1 as a separator finish;

FIG. 5 is an SEM image of a Ni-NiO heterojunction nanoparticle-doped carbon nanofiber prepared in example 2;

FIG. 6 is a graph showing the particle size distribution of Ni-NiO heterojunction nanoparticle-doped carbon nanofibers obtained in example 2;

fig. 7 is a cycle test of a battery assembled with a common commercial PP separator as a separator finishing layer of comparative example 1 and the Ni-NiO heterojunction nanoparticle-doped carbon nanofiber prepared in example 2;

FIG. 8 is an X-ray powder diffraction pattern of the Ni-NiO heterojunction nanoparticle-doped carbon nanofibers produced in example 3;

FIG. 9 is an SEM image of a Ni-NiO heterojunction nanoparticle-doped carbon nanofiber prepared in example 3;

fig. 10 is a cycle test of a battery assembled with a common commercial PP separator as a separator finishing layer of comparative example 1 and the Ni-NiO heterojunction nanoparticle-doped carbon nanofiber prepared in example 3.

FIG. 11 is an SEM image of a Ni-NiO heterojunction nanoparticle-doped carbon nanofiber prepared in example 4;

fig. 12 is a cycle test of a battery assembled with a common commercial PP separator as a separator finishing layer of comparative example 1 and the Ni-NiO heterojunction nanoparticle-doped carbon nanofiber prepared in example 4.

FIG. 13 is an SEM image of a Ni-NiO heterojunction nanoparticle-doped carbon nanofiber prepared in example 5;

fig. 14 is a cycle test of a battery assembled with a common commercial PP separator as a separator finishing layer of comparative example 1 and the Ni-NiO heterojunction nanoparticle-doped carbon nanofiber prepared in example 5.

Detailed Description

Example 1

1) 0.278g of dimethylglyoxime was weighed out and dissolved in 24mL of absolute ethanol, and 40mL of a sodium hydroxide solution having a concentration of 0.5mol/L was added thereto, and the pH of the solution was adjusted to 13 to form a solution A.

2) 0.521g of nickel chloride hexahydrate was weighed into 700mL of deionized water to form solution B.

3) Slowly dripping the solution A into the solution B for 30 minutes, stirring at the stirring speed of 400 rpm Zhong Yunsu for 30 minutes, standing for 3 hours, centrifugally separating, washing with deionized water and absolute ethyl alcohol for 5 times respectively until the pH value of the supernatant is neutral, and drying at 60 ℃ for 10 hours to obtain the precursor.

4) And (3) placing the obtained precursor into a tube furnace, and calcining at 600 ℃ for 1 hour under the protection of argon to obtain the superfine Ni nano particle doped carbon nano fiber.

5) And (3) placing the obtained product in air, and calcining at 100 ℃ for 1 hour to obtain the Ni-NiO heterojunction nanoparticle modified carbon nanofiber.

Characterization of the samples of the final product by X-ray powder diffraction XRD, three characteristic peaks of Ni can be seen from the a-plot in fig. 1, the corresponding crystal planes being the (111), (200) and (220) planes, respectively, and the amorphous carbon peak. From the b-diagram in FIG. 1, it can be seen that the characteristic peaks of NiO are the (111), (200) and (220) planes, respectively, indicating that the product also contains some NiO component.

The morphology of the product was characterized by scanning electron microscope SEM, and it can be seen from fig. 2 that the obtained Ni-NiO heterojunction nanoparticles were uniformly distributed.

By analysis of the particle size on the surface of the product, it was found that the diameter of the particles ranged from 3 to 30nm, with an average diameter of 16nm.

The application of the prepared size-controllable Ni-NiO heterojunction nano-particle doped carbon nano-fiber in a lithium-sulfur battery is specifically as follows:

A. dispersing a Ni-NiO heterojunction ultrafine nanoparticle doped carbon nanofiber material and a binder PVDF in an NMP (N-methylpyrrolidone) solvent according to a mass ratio of 9:1, wherein the volume ratio of the binder PVDF to the NMP is 1:1. After being evenly stirred, the mixture is coated on the surface of a PP2500 diaphragm with the thickness of 25 mu m by a scraper, the thickness of the coating is 12 mu m, and the vacuum drying is carried out, thus obtaining the modified diaphragm for the lithium-sulfur battery.

B. The positive electrode of the lithium-sulfur battery is prepared by mixing CNT (carbon nano tube) and sulfur powder according to the mass ratio of 3:7, then mixing the mixture with acetylene black and a binder PVDF according to the mass ratio of 8:1:1, and then coating the mixture on an aluminum foil, wherein the negative electrode is a metal lithium sheet, and the electrolyte is 1mol/L LiTFSI (lithium bistrifluoromethyl sulfonic acid imide) +0.2mol/L LiNO ₃ (lithium nitrate) +DOL (1, 3-dioxolane)/DME (ethylene glycol dimethyl ether) (1/1, v/v), the separator was modified with the lithium-sulfur battery prepared in the above step A, and the assembly into a coin cell was completed in a glove box.

The battery samples were subjected to cyclic voltammetry (voltage range 1.7-2.8V, sweep rate 0.1 mV/s) and charge and discharge testing (temperature 25 ℃ C., voltage range 1.7-2.8V) for 100 cycles at 1C rate.

Comparative example 1

The comparative example is used for influencing electrochemistry and cycle performance when the modified diaphragm is applied to a lithium-sulfur battery compared with a common PP diaphragm, and comprises the following steps of:

the positive electrode of the lithium-sulfur battery is prepared by mixing CNT (carbon nano tube) and sulfur powder according to the mass ratio of 3:7, then mixing the mixture with acetylene black and a binder PVDF according to the mass ratio of 8:1:1, and then coating the mixture on an aluminum foil, wherein the negative electrode is a metal lithium sheet, and the electrolyte is 1mol/L LiTFSI (lithium bistrifluoromethyl sulfonic acid imide) +0.2mol/L LiNO ₃ (lithium nitrate) +DOL (1, 3-dioxolane)/DME (ethylene glycol dimethyl ether) (1/1, v/v), a normal PP separator was used as the separator, and a button cell of a normal PP separator was mounted in a glove box.

By subjecting the products to cyclic voltammetry, it can be seen from fig. 3 that the potential difference (Δv) between the second reduction peak and the main oxidation peak of the two cells, respectively, is 0.27V less than that of the comparative example, indicating that the material modified on the separator can effectively promote the transformation kinetics of the redox reaction occurring when the cells are charged and discharged.

By performing charge and discharge tests on the two batteries assembled in example 1 and comparative example 1, it can be seen from fig. 4 that the initial specific discharge capacity of the prepared separator modified battery is 931.4 mAh/g at a discharge rate of 1C, and the initial specific discharge capacity of the comparative example is 754.5mAh/g, because the modified material on the separator can not only chemisorb polysulfide dissolved in the electrolyte, but also promote transformation of the reduction phase thereof, and the utilization rate of the active material is improved. The common PP separator of the comparative sample battery can not provide adsorption and catalysis, and can not promote the utilization of active materials in initial discharge. After 100 circles of circulation, the specific capacity of the modified diaphragm battery is 716.5mAh/g, the specific capacity of the comparison sample is 449.6mAh/g, the capacity retention rate of the comparison sample is 76.9 percent, and the capacity retention rate is obviously higher than that of the comparison sample of 59.6 percent.

Example 2

1) 0.278g of dimethylglyoxime was weighed out and dissolved in 24mL of absolute ethanol, and 40mL of potassium hydroxide solution having a concentration of 0.8 mol/L was added thereto, and the pH of the solution was adjusted to 13 to form a solution A.

3) Slowly dripping the solution A into the solution B for 30 minutes, uniformly stirring for 30 minutes at a stirring speed of 400 revolutions per minute, standing for 3 hours, centrifugally separating, washing with deionized water and absolute ethyl alcohol for 5 times respectively until the pH value of the supernatant is neutral, and drying at 60 ℃ for 10 hours to obtain the precursor.

4) And (3) placing the obtained precursor into a tube furnace, and calcining at 700 ℃ for 1 hour under the protection of argon to obtain the superfine Ni nano particle doped carbon nano fiber.

The morphology of the product was characterized by scanning electron microscope SEM, and it can be seen from fig. 5 that the obtained Ni-NiO heterojunction nanoparticles were uniformly distributed on the surface of the nanofiber.

By analysis of the particle size on the surface of the product, it can be seen from FIG. 6 that the particles have diameters in the range of 20-50nm and an average diameter of 29nm. Comparative example 1 the average particle diameter obtained at a calcination temperature of 600 c, the particle diameter increased at a calcination temperature of 700 c. Because at higher temperatures the nickel metal particles will grow further and agglomerate with other particles beside, resulting in an increase of the particle size. By utilizing the phenomenon, the size of the Ni-NiO heterojunction nano-particles on the surface of the carbon nano-fiber can be regulated and controlled by regulating the calcination temperature.

A. dispersing a Ni-NiO heterojunction ultrafine nanoparticle doped carbon nanofiber material and a binder PVDF in an NMP (N-methylpyrrolidone) solvent according to a mass ratio of 9:1, uniformly stirring, coating the mixture on the surface of a PP2500 membrane with a thickness of 25 mu m by a scraper, coating the coating with a thickness of 12 mu m, and vacuum drying to obtain the modified membrane for the lithium-sulfur battery.

B. The anode of the lithium-sulfur battery is prepared by mixing CNT (carbon nano tube) and sulfur powder according to the mass ratio of 3:7, then mixing the mixture with acetylene black and a binder PVDF according to the mass ratio of 8:1:1, and then coating the mixture on an aluminum foil to prepare the lithium-sulfur battery, wherein the cathode is a metal lithium sheet, the electrolyte is 1mol/L LiTFSI (lithium bis (trifluoromethylsulfonate imide)), 0.2mol/L LiNO3 (lithium nitrate) +DOL (1, 3-dioxolane)/DME (ethylene glycol dimethyl ether) (1/1, v/v), and the diaphragm is modified by using the prepared lithium-sulfur battery, so that the assembly of the button battery is completed in a glove box.

The battery sample was subjected to a charge-discharge test for 100 cycles at a temperature of 25℃and a voltage in the range of 1.7-2.8V.

As can be seen from fig. 7, the separator-modified battery of example 2 has an initial discharge specific capacity of 901.6mAh/g and a capacity retention rate of 70.9% after 100 cycles, which is better than that of the conventional PP separator battery of the comparative example.

Example 3

1) 0.595g of dimethylglyoxime was weighed out and dissolved in 27mL of absolute ethanol, 45mL of a sodium hydroxide solution having a concentration of 0.6 mol/L was added thereto, and the pH of the solution was adjusted to 13 to form a solution A.

2) 0.318g of nickel chloride hexahydrate was weighed into 800mL of deionized water to form solution B.

3) Slowly dripping the solution A into the solution B for 30 minutes, stirring for 20 minutes at the stirring speed of 500 revolutions per minute Zhong Yunsu, and standing for 4 hours to obtain a precursor.

5) And (3) placing the obtained product in air, and calcining at 300 ℃ for 2 hours to obtain the Ni-NiO heterojunction nanoparticle modified carbon nanofiber.

Characterization of samples of the final product by X-ray powder diffraction XRD, it can be seen from fig. 8 that the product composition obtained consisted mainly of Ni and NiO. Comparative example 1, the content of NiO component was significantly increased after the calcination temperature and time in air were increased.

The morphology of the product was characterized by scanning electron microscope SEM, and it can be seen from fig. 9 that the obtained Ni-NiO heterojunction nanoparticles were uniformly distributed.

A. dispersing the Ni-NiO heterojunction ultrafine nanoparticle doped carbon nanofiber material and a binder PVDF in an NMP (N-methylpyrrolidone) solvent according to a mass ratio of 9:1, uniformly stirring, coating the mixture on the surface of a PP2500 membrane with a thickness of 25 mu m by a scraper, wherein the thickness of the coating is 12 mu m, and drying in vacuum to obtain the modified membrane for the lithium-sulfur battery.

The battery samples were subjected to a charge-discharge test for 100 cycles at a temperature of 25℃and a voltage in the range of 1.7-2.8V.

The separator-modified battery of example 3 was compared with comparative example 1, and by performing charge and discharge tests on both batteries assembled in example 3 and comparative example 1, it can be seen from fig. 10 that the initial discharge specific capacity of the separator-modified battery was 804.7mAh/g, and the capacity retention rate after 100 cycles was 70.1%, which is better than that of the comparative general PP separator battery.

Example 4

1) 0.189g of dimethylglyoxime was weighed out and dissolved in 12mL of absolute ethanol, and 20mL of a sodium hydroxide solution having a concentration of 0.5mol/L was added thereto to adjust the pH of the solution to 12, thereby forming a solution A.

2) 0.261g of nickel chloride hexahydrate was weighed into 600mL of deionized water to form solution B.

3) Slowly dripping the solution A into the solution B for 30 minutes, stirring for 20 minutes at the stirring speed of 400 rpm Zhong Yunsu, and standing for 2 hours to obtain a precursor.

The morphology of the product was characterized by scanning electron microscope SEM, and it can be seen from fig. 11 that the obtained ni—nio heterojunction nanoparticles were uniformly distributed, the nanoparticle size morphology was not significantly different from example 1, but the length of the carbon fiber was increased.

The separator-modified battery of example 4 was compared with comparative example 1, and by performing charge and discharge tests on both batteries assembled in example 4 and comparative example 1, it can be seen from fig. 12 that the initial discharge specific capacity of the separator-modified battery was 970.8mAh/g, and the capacity retention rate after 100 cycles was 66.8%, which is better than that of the conventional PP separator battery of comparative example.

Example 5

1) 0.2g of dimethylglyoxime was weighed out and dissolved in 12mL of absolute ethanol, and 40mL of a sodium hydroxide solution having a concentration of 0.5mol/L was added thereto, and the pH of the solution was adjusted to 13 to form a solution A.

2) 0.261g of nickel acetate tetrahydrate was weighed out and dissolved in 600mL of deionized water to form solution B.

3) Slowly dripping the solution A into the solution B for 30 minutes, stirring at a stirring speed of 400 revolutions per minute, uniformly stirring for 20 minutes, and standing for 3 hours to obtain a precursor.

4) And (3) placing the obtained precursor into a tube furnace, and calcining at 500 ℃ for 1 hour under the protection of argon to obtain the superfine Ni nano particle doped carbon nano fiber.

5) And (3) placing the obtained product in air, and calcining at 50 ℃ for 1 hour to obtain the Ni-NiO heterojunction nanoparticle modified carbon nanofiber.

The morphology of the product was characterized by scanning electron microscope SEM, and it can be seen from fig. 13 that the distribution of the ni—nio heterojunction nanoparticles on the obtained carbon nanofibers was uniform. It may be that the nickel acetate organic mass lowers the surface energy of the C-axis and the length of the fiber decreases.

As can be seen from fig. 14, the separator-modified battery of example 5 had an initial specific discharge capacity of 844.2mAh/g at a discharge rate of 1C, and the comparative example had an initial specific discharge capacity of 754.5mAh/g, as compared with comparative example 1. After 100 cycles, the specific capacity of the modified diaphragm cell is 663.0 mAh/g, the specific capacity of the comparison sample is 449.6mAh/g, the capacity retention rate of the former is 78.5 percent, and the capacity retention rate is obviously higher than that of the latter of 59.6 percent.

Claims

1. The preparation method of the size-controllable Ni-NiO heterojunction nanoparticle doped carbon fiber is characterized by comprising the following steps of:

4) Placing the product obtained in the step 3) in air, and performing heating oxidation treatment to obtain the size-controllable Ni-NiO heterojunction nano-particle doped carbon nano-fiber;

the solvent in the step 1) is absolute ethyl alcohol;

in the step 3), the carbonization treatment temperature is 300-700 ℃ and the calcination time is 1-5 hours;

the size-controllable Ni-NiO heterojunction nano-particles are doped with carbon nano-fibers, and particles with diameters of 3-50 and nm are uniformly distributed on the surface and inside of the nano-fibers, wherein the surface is of a Ni-NiO heterojunction structure, and the inside is of metallic nickel.

2. The preparation method according to claim 1, wherein in step 1), the molar concentration of dimethylglyoxime in the solution A is 0.011-0.081mol/L.

3. The method according to claim 1 or 2, wherein in step 2), the nickel source is any one of nickel chloride, nickel nitrate, nickel sulfate and nickel acetate.

4. The method according to claim 1 or 2, wherein in step 2), the molar concentration of the nickel source solution is 0.001 to 0.005mol/L.

5. The method according to claim 1, wherein in step 2), the volume ratio of the solution a to the nickel source solution is 0.05-0.1:1.

6. the method according to claim 4, wherein in step 2), the volume ratio of the solution A to the nickel source solution is 0.05-0.1:1.

7. the method according to claim 1, wherein the thermal oxidation treatment in step 4) is performed at a temperature of 50 to 300 ℃ for a treatment time of 1 to 5 hours.

8. The method according to claim 5, wherein the heat oxidation treatment in step 4) is performed at a temperature of 50 to 300℃for a treatment time of 1 to 5 hours.

9. The size-controllable Ni-NiO heterojunction nano-particle doped carbon nanofiber prepared by the preparation method of any one of claims 1-8, wherein particles with diameters of 3-50 and nm are uniformly distributed on the surface and inside of the nanofiber, the surface is of a Ni-NiO heterojunction structure, and the inside is of metallic nickel.

10. Use of size-controllable Ni-NiO heterojunction nanoparticle-doped carbon nanofibers prepared by the preparation method of any one of claims 1-8, for lithium-sulfur battery separators.