CN111370673A - Self-supporting lithium-sulfur battery cathode material with hierarchical structure and preparation method thereof - Google Patents

Self-supporting lithium-sulfur battery cathode material with hierarchical structure and preparation method thereof Download PDF

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CN111370673A
CN111370673A CN202010210020.7A CN202010210020A CN111370673A CN 111370673 A CN111370673 A CN 111370673A CN 202010210020 A CN202010210020 A CN 202010210020A CN 111370673 A CN111370673 A CN 111370673A
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self
sulfur
hierarchical structure
supporting
lithium
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CN111370673B (en
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吴玉程
高傲
刘家琴
张琪
闫健
胡颖
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Hefei University of Technology
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5805—Phosphides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention belongs to the technical field of new energy materials and devices, and particularly relates to a self-supporting lithium-sulfur battery cathode material with a hierarchical structure and a preparation method thereof. The preparation method comprises the following steps: uniformly coating a viscous precursor prepared from glucose, potassium hydroxide, red phosphorus and nickel acetate on a carbon paper substrate, drying, shaping and calcining at high temperature to prepare a three-dimensional hierarchical conductive carrier of carbon fiber supported porous carbon with fine nickel-phosphorus compound nanoparticles dispersed and distributed on the surface of the porous carbon; and finally, carrying out hot-melting compounding on the active sulfur and the conductive carrier to obtain the self-supporting lithium-sulfur battery positive electrode material with the hierarchical structure. The lithium-sulfur battery positive electrode material not only does not need a current collector, a conductive agent and a binder, but also can realize high load of sulfur, effectively inhibit polysulfide dissolution shuttling and relieve electrode volume expansion, so that a battery assembled based on the positive electrode material has excellent electrochemical performance.

Description

Self-supporting lithium-sulfur battery cathode material with hierarchical structure and preparation method thereof
Technical Field
The invention belongs to the technical field of new energy materials and devices, and particularly relates to a self-supporting lithium-sulfur battery cathode material with a hierarchical structure and a preparation method thereof.
Background
The social development is changing day by day, the energy demand is rapidly increased, however, fossil fuel is gradually exhausted and the environment is greatly damaged in the using process, so the demands of developing clean new energy and developing high-efficiency energy storage technology are more and more urgent. The lithium ion battery is widely concerned due to higher specific energy and good cycle performance and has been widely applied to various energy storage demonstration projects, but the energy density of the lithium ion battery is difficult to break through 300Wh kg-1Therefore, the large-scale application of the electric vehicle and the hybrid vehicle is limited. Therefore, a new generation of battery system with high energy density, long cycle life, good safety performance and low cost is needed to be developed.
The lithium-sulfur battery is a novel secondary battery using sulfur as a positive active material and metal lithium as a negative electrode, and has 1675mAh g-1And 2600Wh kg-1The theoretical specific capacity and specific energy of the lithium-sulfur battery are several times of those of the current commercial lithium ion battery, and the sulfur has the advantages of rich reserve, environmental friendliness, low price and the like, so the lithium-sulfur battery is considered to be one of the most potential-developed new-generation high-energy-density energy storage systems.
However, the lithium-sulfur battery still faces the problems of low utilization rate of active materials, rapid capacity attenuation, structural damage of electrodes and the like caused by poor conductivity of sulfur and discharge end products, dissolution shuttling of soluble intermediate products (polysulfide), volume expansion of charge and discharge electrodes and the like, and the industrial application of the lithium-sulfur battery is seriously hindered.
The sulfur positive electrode material is the most critical factor influencing the performance of the lithium-sulfur battery, and the improvement of the composition and the structure of the sulfur positive electrode material is the most main strategy for solving a plurality of problems of the lithium-sulfur battery. The main idea of sulfur anode material design and research and development is to compound sulfur and other conductive carriers to improve the electron/ion conductivity, limit the diffusion of polysulfide ions to a certain extent, buffer the volume change of electrodes during charge and discharge, and improve the reaction kinetics. The support materials for sulfur include mainly carbon materials, conductive polymers, metal oxides and other support materials. The porous carbon material has the advantages of light weight, high conductivity, large specific surface area, high pore volume, good stability and the like, the problem of poor conductivity of sulfur and discharge products is solved to a great extent by compounding the sulfur and the porous carbon, the adjustable pore channel structure also has the function of physically limiting migration and shuttling of polysulfide, and the problem of volume expansion and contraction of electrodes in the circulation process can be adapted, so that the porous carbon is considered as the optimal carrier of active sulfur.
In recent years, researchers find that metal phosphide has dual functions of chemisorption and catalytic conversion on soluble polysulfide, the polysulfide is firmly fixed by the chemisorption, and the high-efficiency conversion of the polysulfide is promoted by the catalytic activity of the metal phosphide, so that the stable trapping-diffusion-catalytic conversion process of the polysulfide on the surface of an electrode material is realized, and the shuttle effect problem of a lithium-sulfur battery can be efficiently solved.
At present, most of lithium-sulfur battery positive electrode materials are in a powder form, and are required to be mixed with a conductive agent (Super-P and the like) and a binder (PVDF and the like) and coated on a current collector when a battery is assembled, so that good contact between an active material and the current collector is ensured. However, the conductive agent, the binder and the current collector do not contribute to the capacity in the battery, thereby causing a reduction in the overall energy density of the battery, and the use of the electrochemically inert binder may also cause undesirable side reactions, mask reactive active sites, increase the internal resistance of the electrode, thereby reducing the active sulfur utilization and the electron/ion kinetics. Therefore, the structure of the traditional positive electrode material is optimized and reformed, the active material and the flexible current collector are integrally designed, a conductive agent and a binder are not needed, and the development of the novel self-supporting sulfur positive electrode material becomes the focus of attention of domestic and foreign scholars.
Disclosure of Invention
The invention aims to provide a self-supporting lithium-sulfur battery positive electrode material with a hierarchical structure and a preparation method thereof. Preparing precursor slurry by taking four raw materials of glucose, potassium hydroxide, red phosphorus and nickel acetate as solutes and water as a solvent, uniformly coating the precursor slurry on a carbon paper substrate, drying, shaping and calcining at high temperature to prepare a three-dimensional hierarchical conductive carrier of carbon fiber supported porous carbon with fine nickel-phosphorus compound nanoparticles dispersed and distributed on the surface of the porous carbon; and finally, carrying out hot-melting compounding on the active sulfur and the conductive carrier to obtain the self-supporting lithium-sulfur battery positive electrode material with the hierarchical structure. The self-supporting lithium-sulfur battery cathode material with the hierarchical structure can realize high load of sulfur, efficiently inhibit polysulfide dissolution shuttling and relieve electrode volume expansion, so that the battery assembled based on the cathode material has the advantages of high specific capacity, long cycle life, good rate performance and the like.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a self-supporting lithium-sulfur battery cathode material with a hierarchical structure is composed of active sulfur and a self-supporting conductive carrier with a hierarchical structure, wherein the self-supporting conductive carrier with the hierarchical structure takes a carbon fiber network as a conductive framework, and fine nickel-phosphorus compound nanoparticles are dispersed and distributed on the surface of the carbon fiber coated with porous carbon.
As a preferred technical scheme of the invention, in the self-supporting conductive carrier with the hierarchical structure, the nickel-phosphorus compound dispersed and distributed on the surface of the porous carbon is Ni12P5，Ni12P5Diameter of the nanoparticles<100nm。
A preparation method of a self-supporting lithium-sulfur battery cathode material with a hierarchical structure comprises the following steps:
(1) preparing a viscous precursor by taking four raw materials of glucose, potassium hydroxide, red phosphorus and nickel acetate as solutes and water as a solvent according to a certain proportion;
(2) uniformly coating the prepared viscous precursor on a carbon paper substrate by taking the carbon paper as the substrate, and drying and shaping;
(3) carrying out high-temperature calcination carbonization on the dried and shaped carbon paper and the coating layer, cleaning and drying to prepare a hierarchical-structure self-supporting conductive carrier of carbon fiber supported porous carbon with fine nickel-phosphorus compound nanoparticles dispersed and distributed on the surface of the porous carbon;
(4) and carrying out hot-melting compounding on the self-supporting conductive carrier with the hierarchical structure and elemental sulfur to prepare the self-supporting lithium-sulfur battery cathode material with the hierarchical structure.
As a preferred technical scheme of the invention, in the preparation method of the self-supporting lithium-sulfur battery cathode material with the hierarchical structure:
in the step (1), four raw materials of glucose, potassium hydroxide, red phosphorus and nickel acetate are used as solutes, water is used as a solvent to prepare a solution, the mass ratio of the four solutes is 5: 2-4, and part of the solvent is heated, stirred and evaporated at 50-60 ℃ to prepare viscous precursor slurry.
In the step (2), the carbon paper is common commercial carbon fiber paper, the drying temperature is 50-70 ℃, the drying time is 12-24 hours, and the coating amount of the dried and shaped precursor on the carbon paper is 6-12 mg/cm2。
Calcining the shaped carbon paper and the coating layer at high temperature under the protection of inert atmosphere, carbonizing, cleaning and drying, wherein the inert atmosphere is argon, the calcining temperature is 700-1000 ℃, the calcining time is 3-6 h, the heating rate is 3-8 ℃/min, then sequentially cleaning by using dilute hydrochloric acid and deionized water, the concentration of the dilute hydrochloric acid is 1-2 mol/L, and vacuum drying is carried out at 60-80 ℃ for 6-12 h; the area mass of the porous carbon and the nickel-phosphorus compound nanoparticles on the surface of the porous carbon in the self-supporting conductive carrier obtained by the preparation method is 3-6 mg/cm2。
And (4) carrying out hot melting compounding on the self-supporting conductive carrier with the hierarchical structure and elemental sulfur under the protection of inert atmosphere, wherein the inert atmosphere is argon, the hot melting temperature is 150-160 ℃, the hot melting time is 12-24 hours, and then heating to 170 ℃ to remove surface sulfur, so that the area capacity of sulfur in the prepared self-supporting lithium-sulfur battery positive electrode material with the hierarchical structure is controlled to be 2-6 mg/cm2。
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a self-supporting lithium-sulfur battery anode material with a hierarchical structure, which is characterized in that a carbon fiber (paper) supporting flexible conductive framework is used as a substrate to construct a carbon fiber/porous carbon/metal phosphide hierarchical structure self-supporting conductive network, the carbon fiber/porous carbon/metal phosphide hierarchical structure self-supporting conductive network is further used as a conductive carrier to be compounded with sulfur, and the carbon fiber conductivity, the high sulfur loading/sulfur limiting capacity of the porous carbon and the adsorption-catalysis effect of metal phosphide on soluble polysulfide are simultaneously exerted, so that the high loading of active sulfur is realized, the dissolution shuttling of polysulfide is effectively inhibited, and the volume expansion of an electrode is relieved. In addition, the battery assembled by the lithium-sulfur battery positive electrode material does not need to use a current collector, a conductive agent and a binder. The lithium-sulfur battery assembled based on the self-supporting sulfur cathode material with the hierarchical structure has the advantages of high sulfur carrying capacity, high specific capacity, long cycle life, good rate capability and the like. In addition, the preparation method of the self-supporting lithium-sulfur battery cathode material with the hierarchical structure is simple in process, low in cost, environment-friendly and suitable for large-scale industrial application.
Drawings
Fig. 1 is an SEM image of the plain commercial carbon fiber paper of example 1.
Fig. 2 is an SEM topography of the hierarchical self-supporting conductive support prepared in example 1.
Fig. 3 is an XRD curve of the self-supporting conductive support of the hierarchical structure prepared in example 1 and comparative example 1.
Fig. 4 is a pore size distribution curve of the self-supporting conductive support of a hierarchical structure prepared in example 1.
Fig. 5 is an SEM morphology of the graded-structure self-supporting lithium sulfur battery cathode material prepared in example 1.
Fig. 6 is an SEM morphology of the hierarchical self-supporting conductive support prepared in comparative example 1.
Fig. 7 is a constant current charge and discharge cycle test result at 0.5C rate of the battery assembled based on the prepared hierarchical self-supporting sulfur positive electrode material in example 1 and comparative example 1.
Fig. 8 is a charge and discharge voltage characteristic curve of a battery assembled based on the prepared hierarchical self-supporting sulfur cathode material in example 1, cycled at 0.5C rate for various times.
Fig. 9 shows the results of the cycle charge and discharge test at different rates for the battery assembled based on the prepared graded-structure self-supporting sulfur positive electrode material in example 1.
Fig. 10 is the long cycle charge and discharge test results at 1C rate for the battery assembled based on the prepared hierarchical self-supporting sulfur positive electrode material in example 1.
Fig. 11 is a result of a cyclic charge and discharge test of batteries assembled based on the prepared hierarchical self-supporting sulfur positive electrode material in examples 1, 5 and 6 at different sulfur loadings.
Detailed Description
The present invention provides a graded-structure self-supporting lithium-sulfur battery positive electrode material and a preparation method thereof, which are described in further detail below with reference to the following examples and accompanying drawings.
Example 1
The embodiment provides a self-supporting lithium-sulfur battery cathode material with a hierarchical structure, which consists of active sulfur and a self-supporting conductive carrier with the hierarchical structure, wherein the self-supporting conductive carrier with the hierarchical structure takes a carbon fiber network as a conductive framework, the surface of the carbon fiber is coated with porous carbon, and fine nickel-phosphorus compound nanoparticles are dispersed and distributed on the surface of the porous carbon.
The embodiment provides a preparation method of a self-supporting lithium-sulfur battery cathode material with a hierarchical structure, which comprises the following steps:
(1) glucose, potassium hydroxide, red phosphorus and nickel acetate are used as solutes, water is used as a solvent to prepare a solution, the mass ratio of the four solutes is 5: 2, and partial solvent is evaporated by heating and stirring at 60 ℃ to prepare a viscous precursor.
(2) Using common commercial carbon paper as a substrate, uniformly coating the prepared precursor on the carbon paper substrate, and drying and shaping, wherein the coating amount of the precursor is 8mg/cm2The drying temperature is 60 ℃, and the drying time is 12 h.
(3) And (3) carrying out high-temperature calcination carbonization on the shaped carbon paper and the coating layer under the protection of argon atmosphere, wherein the calcination temperature is 900 ℃, the calcination time is 4h, and the heating rate is 4 ℃/min. Then sequentially washing with dilute hydrochloric acid and deionized water and drying in vacuum to prepare the self-supporting conductive carrier with the hierarchical structure, wherein the concentration of the dilute hydrochloric acid is 1mol/L, the drying temperature is 70 ℃, the drying time is 12h, and the porous carbon and the surface thereof areThe area loading of the nickel-phosphorus compound nano particles is 4mg/cm2。
(4) Carrying out hot melting compounding on the self-supporting conductive carrier with the hierarchical structure and elemental sulfur under the protection of argon atmosphere, wherein the hot melting temperature is 155 ℃, the hot melting time is 12 hours, then heating to 170 ℃ to remove surface sulfur, and finally controlling the area loading of sulfur to be 4mg/cm2。
Referring to fig. 1, the figure shows the SEM morphology of the common commercial carbon fiber paper used in this embodiment, and it can be seen that the carbon paper is formed into a three-dimensional network structure by interleaving carbon fibers, wherein the carbon fibers have a diameter of 8 to 10 μm, have the characteristics of high mechanical strength, good conductivity, strong durability, etc., and serve as a self-supporting conductive skeleton in the self-supporting conductive carrier with the hierarchical structure. Referring to fig. 2 and fig. 3, wherein fig. 2 is an SEM image of the self-supporting conductive carrier with a hierarchical structure prepared in the present embodiment, and fig. 3 is an XRD curve thereof, it can be seen that the self-supporting conductive carrier with a hierarchical structure uses a carbon fiber network as a conductive framework, the surface of the carbon fiber is coated with a porous carbon, and a large amount of fine Ni is dispersed and distributed on the surface of the porous carbon12P5Nanoparticles of which Ni12P5Diameter of the nanoparticles<100nm, which can reach 10-100 nm. Referring to fig. 4, the porous carbon has a well-developed mesoporous-macroporous hierarchical porous structure, so that the mesoporous-macroporous hierarchical porous carbon and the surface thereof are dispersed with a large amount of fine Ni12P5The nanoparticles enable the self-supporting conductive carrier of the hierarchical structure to have a high specific surface area. Referring to fig. 5, after the active sulfur and the self-supporting conductive carrier with the hierarchical structure are hot-melted and compounded, elemental sulfur is uniformly filled in the mesoporous-macroporous hierarchical pores of the porous carbon, and is not accumulated on the surface thereof.
The sulfur positive electrode, the lithium negative electrode and 1M LiTFSI/DOL + DME (volume ratio of DOL to DME is 1: 1) prepared in the above way are added with 2 wt% LiNO3) And assembling 2032 button lithium-sulfur batteries with the electrolyte and carrying out charge and discharge tests, wherein the test voltage window is 1.7-2.8V.
Comparative example 1
For comparison, the self-supporting lithium-sulfur battery cathode material with the hierarchical structure provided by the invention can realize high loading and high-efficiency inhibition of active sulfurAnd (3) preparing a polysulfide dissolution shuttle to improve the electrochemical performance, wherein the method for preparing the self-supporting lithium-sulfur battery cathode material with the hierarchical structure in the comparative example is basically the same as that in the example 1, except that the product after high-temperature calcination in the step (3) is not washed by dilute hydrochloric acid, but is washed by aqua regia, then washed by deionized water and dried. The finally prepared self-supporting lithium-sulfur battery cathode material with the hierarchical structure does not contain nickel-phosphorus compound (Ni)12P5) Nanoparticles (see fig. 3).
Then, a sulfur positive electrode, a lithium negative electrode and 1M LiTFSI/DOL + DME (volume ratio of DOL to DME is 1: 1) prepared in the same manner as the comparative example, 2 wt% LiNO was added3) And (3) assembling 2032 button cells by using the electrolyte, and carrying out charge and discharge tests, wherein the test voltage window is 1.7-2.8V.
Referring to fig. 6, which is a self-supporting conductive carrier with a hierarchical structure and without nickel-phosphorus nanoparticles prepared in comparative example 1, it can be seen that the conductive carrier uses a carbon fiber network as a conductive skeleton, the surface of the carbon fiber is coated with porous carbon, but the surface of the porous carbon does not have Ni dispersed and distributed12P5And (3) nanoparticles.
Referring to fig. 7, the initial discharge capacity of the battery assembled by the self-supporting lithium-sulfur battery cathode material based on the hierarchical structure in example 1 is 1082mAh g at 0.5C rate-1The circulation is 200 circles and 884mAh g is still kept-1The discharge capacity and the capacity retention rate are 81.7 percent; the self-supporting conductive support of the hierarchical structure prepared in comparative example 1 did not contain the polar nickel phosphorus compound nanoparticles, and the initial discharge capacity of the battery based on the self-supporting lithium sulfur battery positive electrode material of the hierarchical structure was 1004mAh g at 0.5C rate-1The discharge capacity of 200 cycles is 719mAh g-1The capacity retention rate was 71.6%.
Referring to fig. 8, the charge and discharge voltage characteristics of the battery assembled based on the self-supporting lithium-sulfur battery cathode material with the hierarchical structure in example 1 are shown at 0.5C for 1 cycle (1st), 50 cycles (50th), 100 cycles (100th) and 200 cycles (200th), all of which include two discharge stages and one charge stage of 2.35V and 2.10V, and the cycle is repeatedThe capacity retention rate after 200 cycles was 81.7%, indicating that the lithium-sulfur battery in example 1 has a higher sulfur loading (4 mg/cm)2) And good reversibility is shown in the process of repeated charge and discharge, which shows that the positive electrode material can effectively inhibit polysulfide shuttling, and avoids the loss of active sulfur on the positive electrode side and the rapid capacity attenuation.
Referring to fig. 9, which shows the results of the rate performance test of the lithium-sulfur batteries in example 1 and comparative example 1, the lithium-sulfur batteries were charged and discharged at rates of 0.1C, 0.2C, 0.5C, 1C, 2C, 3C and 5C, respectively, and the discharge capacity of the lithium-sulfur battery in example 1 was 1401mAh/g at a low rate of 0.1C and was still as high as 535mAh/g at a high rate of 5C. In contrast, the lithium sulfur cell of comparative example 1 had a discharge capacity of 1356mAh/g at a low rate of 0.1C and only 452mAh/g at a high rate of 5C, indicating that the rate performance of the cell of comparative example 1 is significantly lower than that of the cell of example 1.
Referring to fig. 10, when the lithium-sulfur battery in example 1 is charged and discharged at a constant current of 1C for 500 cycles, the discharge capacity of the first cycle of the battery is 964mAh/g, the discharge capacity can still reach 583mAh/g after 500 cycles of long-cycle charging and discharging, the capacity retention rate is 60.5%, and the coulomb efficiency is maintained at more than 98.7%. It is demonstrated that the lithium sulfur battery of example 1 also has very good cycle charge and discharge stability at a higher rate of 1C. Compared with the prior art, the lithium-sulfur battery in the comparative example 1 has the advantages that under the same test conditions, the capacity is obviously and rapidly attenuated, the capacity is attenuated to 409mAh/g from 892mAh/g after 500 times of cyclic charge and discharge, the capacity retention rate is only 45.9%, the attenuation rate is obviously increased, and the poor cyclic stability is shown.
The battery performance test results show that: the self-supporting lithium-sulfur battery positive electrode material with the hierarchical structure provided by the invention has excellent electrochemical performance, wherein the staggered carbon fiber network structure is used as a conductive skeleton substrate, the mesoporous-macroporous hierarchical porous carbon structure on the surface of the carbon fiber can realize high load of active sulfur, efficiently inhibit polysulfide dissolution shuttling and relieve electrode volume expansion, and in addition, fine polar Ni which is dispersedly distributed on the surface of the porous carbon12P5The particles can perform the functions of chemical adsorption and catalytic conversion on dissolved polysulfide, thereby further realizing the function of the catalystThe shuttle effect is inhibited, and the specific capacity, the rate capability and the cycling stability of the sulfur anode material are improved. Therefore, the self-supporting lithium-sulfur battery cathode material with the hierarchical structure can be successfully applied to lithium-sulfur batteries, and is simple in overall preparation process, low in cost, environment-friendly and suitable for large-scale industrial application.
Example 2
The preparation method of this example is the same as example 1, except that the mass ratio of glucose, potassium hydroxide, red phosphorus and nickel acetate in step (1) is adjusted to 5: 4: 2, and other implementation conditions are not changed. Compared with the embodiment 1, the battery capacity, rate performance and cycling stability assembled by the self-supporting lithium-sulfur battery cathode material based on the hierarchical structure prepared by the embodiment are basically kept unchanged, and the initial discharge capacity at 0.5C rate is up to 1080mAh g-1878mAh g is still kept after 200 cycles of circulation-1The capacity retention rate was 81.3%.
Example 3
The preparation method of this example is the same as example 1, except that the coating amount of the dried precursor in the step (2) is 10mg/cm2Other implementation conditions are unchanged. Compared with example 1, the battery capacity, rate performance and cycling stability assembled by the self-supporting lithium-sulfur battery cathode material based on the hierarchical structure prepared by the embodiment are reduced, and the initial discharge capacity at 0.5C rate is up to 1007mAh g-1712mAh g is still maintained after 200 cycles-1The capacity retention rate is 70.7%, mainly because when the precursor loading is large in this embodiment, the etching pore-forming effect of potassium hydroxide on carbon during high-temperature calcination is poor, and the porous carbon and the surface Ni thereof are12P5An increase in the area loading of the particles results in a corresponding decrease in the energy density of the battery.
Example 4
The preparation method of this example is the same as example 1, except that the high-temperature calcination temperature in step (3) is 750 ℃, and other implementation conditions are not changed. Compared with example 1, the battery assembled by the self-supporting lithium-sulfur battery cathode material based on the hierarchical structure prepared by the embodiment has reduced capacity, and the initial discharge capacity at 0.5C rate is as high as1016mAh g-1769mAh g is still kept after 200 cycles-1. In addition, the rate performance and cycle stability of the battery in this embodiment are also reduced accordingly.
Example 5
The preparation method of this example is the same as example 1, except that the area loading of sulfur in step (4) is 6mg/cm2Other implementation conditions are unchanged. Compared with example 1, please refer to fig. 11, the specific capacity of the battery assembled by the self-supporting lithium-sulfur battery cathode material based on the hierarchical structure prepared in this example is greatly reduced, and the initial discharge capacity at 0.5C rate is only 858mAhg-1619mAh g is still kept after 200 cycles of circulation-1The capacity retention rate was 72%. In addition, the rate performance and cycle stability of the battery in this embodiment are also reduced accordingly.
Example 6
The preparation method of this example is the same as example 1, except that the area loading of sulfur in step (4) is 2mg/cm2Other implementation conditions are unchanged. Compared with example 1, please refer to fig. 11, the specific capacity of the battery assembled by the self-supporting lithium-sulfur battery cathode material based on the hierarchical structure prepared in this example is improved, and the initial discharge capacity at 0.5C rate is up to 1246mAhg-1And the discharge capacity after 200 cycles is 1010mAh g-1The capacity retention rate was 81%. In addition, the rate performance and the cycling stability of the battery in the embodiment are also slightly improved correspondingly. However, the reduction of the sulfur area loading can cause the reduction of the overall energy density of the battery, and the practical application is limited.
The foregoing is merely exemplary and illustrative of the principles of the present invention and various modifications, additions and substitutions of the specific embodiments described herein may be made by those skilled in the art without departing from the principles of the present invention or exceeding the scope of the claims set forth herein.

Claims (7)

1. The lithium-sulfur battery positive electrode material is characterized by consisting of active sulfur and a hierarchical structure self-supporting conductive carrier, wherein the hierarchical structure self-supporting conductive carrier takes a carbon fiber network as a conductive framework, the surface of the carbon fiber is coated with porous carbon, and fine nickel-phosphorus compound nanoparticles are dispersed and distributed on the surface of the porous carbon.
2. The self-supporting lithium-sulfur battery positive electrode material with a hierarchical structure as claimed in claim 1, wherein the nickel-phosphorus compound dispersed on the surface of the porous carbon is Ni12P5，Ni12P5Diameter of the nanoparticles<100nm。
3. A method for preparing a self-supporting lithium-sulfur battery positive electrode material with a hierarchical structure according to claim 1 or 2, comprising the steps of:
(1) preparing a viscous precursor by taking four raw materials of glucose, potassium hydroxide, red phosphorus and nickel acetate as solutes and water as a solvent according to a certain proportion;
(2) uniformly coating the prepared viscous precursor on a carbon paper substrate by taking the carbon paper as the substrate, and drying and shaping;
(3) carrying out high-temperature calcination carbonization on the dried and shaped carbon paper and the coating layer, cleaning and drying to prepare a hierarchical-structure self-supporting conductive carrier of carbon fiber supported porous carbon with fine nickel-phosphorus compound nanoparticles dispersed and distributed on the surface of the porous carbon;
(4) and carrying out hot-melting compounding on the self-supporting conductive carrier with the hierarchical structure and elemental sulfur to prepare the self-supporting lithium-sulfur battery cathode material with the hierarchical structure.
4. The preparation method according to claim 3, wherein in the step (1), four raw materials of glucose, potassium hydroxide, red phosphorus and nickel acetate are used as solutes, water is used as a solvent to prepare a solution, the mass ratio of the four solutes is 5: 2-4, and part of the solvent is heated, stirred and evaporated at 50-60 ℃ to prepare the viscous precursor slurry.
5. The preparation method according to claim 3, wherein the carbon paper in the step (2) is common commercial carbon fiber paper, the drying temperature is 50-70 ℃, and the drying temperature isThe drying time is 12-24 h, and the coating amount of the dried and shaped precursor on the carbon paper is 6-12 mg/cm2。
6. The preparation method according to claim 3, wherein in the step (3), the shaped carbon paper and the coating layer are subjected to high-temperature calcination carbonization under the protection of inert atmosphere, and are cleaned and dried, wherein the inert atmosphere is argon, the calcination temperature is 700-1000 ℃, the calcination time is 3-6 h, and the temperature rise rate is 3-8 ℃/min; then sequentially washing with dilute hydrochloric acid and deionized water, wherein the concentration of the dilute hydrochloric acid is 1-2 mol/L, and vacuum drying at 60-80 ℃ for 6-12 h; the area mass of the porous carbon and the nickel-phosphorus compound nanoparticles on the surface of the porous carbon in the self-supporting conductive carrier obtained by the preparation method is 3-6 mg/cm2。
7. The preparation method of claim 3, wherein in the step (4), the self-supporting conductive carrier with the hierarchical structure is subjected to hot-melting compounding with elemental sulfur under the protection of inert atmosphere, wherein the inert atmosphere is argon, the hot-melting temperature is 150-160 ℃, the hot-melting time is 12-24 h, and then the temperature is raised to 170 ℃ to remove surface sulfur, so that the area loading of sulfur in the prepared self-supporting lithium-sulfur battery positive electrode material with the hierarchical structure is controlled to be 2-6 mg/cm2。
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