CN109461909B - Positive electrode material of lithium-sulfur battery and preparation method thereof - Google Patents

Positive electrode material of lithium-sulfur battery and preparation method thereof Download PDF

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CN109461909B
CN109461909B CN201811189810.0A CN201811189810A CN109461909B CN 109461909 B CN109461909 B CN 109461909B CN 201811189810 A CN201811189810 A CN 201811189810A CN 109461909 B CN109461909 B CN 109461909B
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halloysite
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韩凯
王云艳
王璐璐
贺亚灵
叶红齐
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Central South University
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Abstract

The invention provides a lithium-sulfur battery positive electrode material which comprises a matrix layer, a polymer layer wrapping the matrix layer and a core layer positioned in the matrix layer. The invention also provides a preparation method of the lithium-sulfur battery positive electrode material. According to the lithium-sulfur battery positive electrode material provided by the invention, the conductive polymer layer is coated outside the substrate layer, the core layer is filled in the substrate layer, and the physical limitation effect and the adsorption effect of chemical components of the one-dimensional pipeline of the substrate layer are utilized, so that the problems of low battery capacity, low cycle retention rate and low overall electrochemical performance caused by the shuttle effect of intermediate polysulfide ions generated in the charging and discharging processes of the lithium-sulfur battery sulfur positive electrode in the prior art are solved. The substrate layer is a halloysite layer, so that the shuttle of polysulfide ions can be inhibited from two aspects of physical limitation and chemical adsorption, and the halloysite is used as a cheap natural mineral, so that the cost of the anode can be reduced by using the halloysite as the substrate, and the popularization and the application are facilitated.

Description

Positive electrode material of lithium-sulfur battery and preparation method thereof
Technical Field
The invention belongs to the technical field of battery materials, and particularly relates to a lithium-sulfur battery positive electrode material and a preparation method thereof.
Background
With the rapid development of new energy automobiles and mobile electronic devices, batteries with higher energy density are urgently needed. In a new energy system, a lithium-sulfur battery becomes one of the most potential secondary battery systems in the next generation due to the characteristics of high theoretical specific energy (2600W · h/kg), cheap elemental sulfur, environmental friendliness and the like.
Typical lithium sulfur batteries generally employ elemental sulfur as the positive electrode and a metallic lithium plate as the negative electrode. However, lithium sulfur batteries have three major problems: (1) elemental sulfur and a discharge product lithium sulfide are used as non-conductive or low-conductive substances, and the conductivity is very poor; (2) during the charging and discharging processes of sulfur, the volume can be enlarged and reduced, and the battery can be damaged; (3) shuttling effect of intermediate lithium polysulphides, i.e. polysulphides (Li) produced by the positive electrode during charging and discharging2Sx) dissolving the intermediate in an electrolyte, andthrough the separator, diffuse toward the negative electrode, and directly react with the metallic lithium of the negative electrode, eventually resulting in irreversible loss of effective materials in the battery, degradation of battery life, and low coulombic efficiency. The three problems mentioned above, especially the shuttling effect of the intermediate lithium polysulphide, have hindered the commercialization of lithium-sulphur batteries. To solve this problem, the prior art starts with both physical limitations and chemisorption. In the aspect of physical limitation, sulfur and polysulfide are physically adsorbed and confined by carriers (such as graphene, carbon tubes and the like) with high specific surface area and pore structures for the anode; in the aspect of chemical adsorption, the carrier is further subjected to chemical modification to modify active sites so as to realize chemical adsorption.
For example, CN107403916A discloses a positive electrode material for a lithium sulfur battery, which is prepared from graphene nanoplatelets, lithium polysulfide powder, a polyimide solution and an organic carbon source aqueous solution, and is constrained by a graphene conductive network, wherein the graphene nanoplatelets of the invention have the characteristics of good dispersibility and high conductivity, and are beneficial to reducing the restacking between graphene sheet layers after modification. After the graphene nanoplatelets and the organic carbon source aqueous solution are mixed and carbonized, the generated polysulfide can be prevented from being dissolved in the electrolyte, so that the improvement of the conductivity of the positive electrode and the fixation of lithium polysulfide is facilitated, namely the cycle number of the electrode is improved, and the rate characteristic of the electrode is also improved. CN103490027B discloses a diaphragm for a lithium-sulfur battery and a preparation method thereof, wherein the diaphragm for the lithium-sulfur battery is composed of a common battery diaphragm and a porous barrier layer loaded on the common battery diaphragm, the porous barrier layer can allow lithium ions to pass through, but has blocking and adsorption effects on a lithium polysulfide intermediate formed in a sulfur positive electrode in a charging and discharging process, so that an active substance sulfur can be limited on one side of the positive electrode, irreversible capacity fading of the sulfur positive electrode due to the fact that the lithium polysulfide intermediate formed in a circulating process is dissolved in an electrolyte is prevented, and the cycle performance of the sulfur positive electrode is improved. Meanwhile, the diaphragm can weaken the shuttle effect of polysulfide to the lithium negative electrode, prevent a sulfur-containing passivation layer from being formed on the surface of the lithium negative electrode in the battery circulation process, and improve the circulation performance of the lithium negative electrode. The invention also discloses a lithium-sulfur battery using the diaphragm, and the diaphragm for the lithium-sulfur battery has the advantages of simple preparation method, easily obtained raw materials and suitability for large-scale production. However, the prior art still does not adequately solve the problem of the shuttling effect of the intermediate lithium polysulfide.
Disclosure of Invention
In order to solve the problems of low specific capacity, low cycle retention rate and low overall electrochemical performance of a battery caused by shuttle effect of lithium polysulfide serving as an intermediate product of a sulfur positive electrode in a lithium-sulfur battery in the prior art, the invention aims to provide a lithium-sulfur battery positive electrode material.
The invention also aims to provide a preparation method of the lithium-sulfur battery positive electrode material.
In order to achieve the purpose, the invention adopts the following technical scheme:
the positive electrode material of the lithium-sulfur battery comprises a substrate layer, a polymer layer wrapping the substrate layer and a core layer positioned in the substrate layer.
Preferably, the matrix layer is halloysite.
Preferably, the polymer is one of polypyrrole (PPy), Polyaniline (PANI), and poly 3, 4-ethylenedioxythiophene (PEDOT).
Preferably, the core layer is a sulfur single layer.
The preparation method of the positive electrode material of the lithium-sulfur battery is characterized by comprising the following steps:
(1) carrying out acid leaching and heat treatment on the substrate layer;
(2) dispersing the substrate layer treated in the step (1) in a solvent, adding a polymer monomer and an oxidant into the solvent, and polymerizing to obtain a semi-finished product;
(3) and (3) loading the core layer into the semi-finished product obtained in the step (2).
The purpose of the acid leaching of step (1) is to remove impurities in the matrix layer.
Preferably, the acid in step (1) is one of hydrochloric acid, sulfuric acid or oxalic acid.
More preferably, the mass fraction of the hydrochloric acid is 30-40%.
Preferably, the leaching temperature in the step (1) is 60-70 ℃, and the leaching time is 100-150 min.
Preferably, the temperature of the heat treatment in the step (1) is 200-500 ℃, and the time of the heat treatment is 2-6 h.
Preferably, the solvent in step (2) is water, and the oxidant is FeCl3One of ammonium persulfate, potassium persulfate and sodium persulfate.
Further preferably, the mass ratio of the matrix layer to the polymer monomer in step (2) is 1: (0.5-3), wherein the mass ratio of the polymer monomer to the oxidant is 1: (1-5).
Preferably, the polymerization temperature in the step (2) is 20-30 ℃ and the time is 12-24 h.
Preferably, the loading method of the core layer in the step (3) is a hot melting method, specifically: and (3) uniformly mixing the semi-finished product obtained in the step (2) with sulfur, placing the mixture in a tube furnace, and keeping the temperature of 150-200 ℃ for 10-16 hours in Ar atmosphere.
Halloysite is a natural silicate mineral and has a unique hollow tubular structure, the outer wall of the tube is composed of silica tetrahedrons, and the inner wall of the tube is an aluminum octahedron. In order to solve the problem of shuttle effect of lithium polysulfide, a one-dimensional pipeline and chemical components of halloysite can be simultaneously utilized to perform physical limitation and chemical adsorption on the lithium polysulfide, so that the performance of the battery is finally improved.
In the prior art, a scholars firstly increases the inner diameter of a tube cavity of the halloysite through acid etching, then fills sulfur into the tube cavity of the halloysite by adopting a liquid-phase chemical deposition method and a heat treatment two-step method to form a halloysite/sulfur composite material, and then prepares a lithium-sulfur battery positive plate based on the halloysite. However, such treatment is limited in that since halloysite does not have conductivity and is not favorable for electron transport, the battery capacity and the cycle retention rate are low, and the overall electrochemical performance is to be improved.
The invention has the advantages of
1. According to the lithium-sulfur battery positive electrode material provided by the invention, the conductive polymer layer is coated outside the substrate layer, the core layer is filled in the substrate layer, and the physical limiting function and the chemical component adsorption function of the one-dimensional pipeline of the substrate layer are utilized, so that the problems that in the prior art, the specific capacity and the cycle retention rate of a battery are lower and the overall electrochemical performance is low due to the shuttle effect of intermediate product polysulfide ions generated in the charging and discharging processes of the lithium-sulfur battery positive electrode are solved;
2. in the lithium-sulfur battery positive electrode material provided by the invention, the substrate layer is the halloysite layer, so that the shuttle of polysulfide ions can be inhibited from two aspects of physical limitation and chemical adsorption, the halloysite is used as a cheap natural mineral, the cost of the positive electrode can be reduced by using the halloysite as the substrate, and the popularization and the application are facilitated;
3. according to the preparation method provided by the invention, the conductive polymer is coated on the surface of the halloysite, and then sulfur is loaded, so that the problem that the halloysite is not conductive is solved skillfully;
4. the first discharge specific capacity of the lithium-sulfur battery cathode material prepared by the method is 786.9mAh g under the multiplying power of 0.1C-1After 100 cycles, the cycle retention rate is as high as 71.8%.
Drawings
Fig. 1 is a schematic structural view of a positive electrode material for a lithium sulfur battery.
FIG. 2 is a scanning electron micrograph of untreated halloysite.
Fig. 3 is a scanning electron microscope image of the lithium sulfur battery cathode material prepared in example 2.
Fig. 4 is the results of the battery rate performance test of example 2.
Fig. 5 is the results of the battery rate performance test of example 5.
Fig. 6 is the result of the battery rate performance test of comparative example 1.
Fig. 7 shows the results of the battery cycle performance test of example 2.
Fig. 8 is the results of the battery cycle performance test of example 5.
Fig. 9 is the result of the battery cycle performance test of comparative example 1.
Detailed Description
The following are specific embodiments of the present invention and are further described with reference to the accompanying drawings, but the present invention is not limited to these embodiments.
Example 1
The positive electrode material of the lithium-sulfur battery comprises a substrate layer, a polymer layer wrapping the substrate layer and a core layer positioned in the substrate layer. As shown in fig. 1, wherein 1 is a substrate layer, 2 is a polymer layer, and 3 is a core layer.
The substrate layer is halloysite, the polymer is one of polypyrrole (PPy), Polyaniline (PANI) and poly 3, 4-ethylenedioxythiophene (PEDOT), and the core layer is a sulfur simple substance layer.
FIG. 2 is a Scanning Electron Microscope (SEM) image of untreated halloysite, from which it can be seen that the halloysite has smooth outer walls and hollow tubes.
Example 2
The preparation method of the positive electrode material of the lithium-sulfur battery comprises the following steps:
(1) carrying out acid leaching on halloysite and then carrying out heat treatment, wherein the heat treatment specifically comprises the following steps:
adding 10g of natural halloysite solid powder into a solution consisting of 28ml of concentrated hydrochloric acid with the mass fraction of 38% and 7ml of deionized water, reacting for 120min at 70 ℃, then centrifugally washing, filtering to obtain a solid, placing the solid in an oven at 80 ℃ for drying for 24h to obtain acid-leached and purified halloysite powder, placing the purified halloysite powder in a tubular furnace under the argon atmosphere, preserving heat at 300 ℃ for 3h, and cooling at the heating rate of 5 ℃/min to obtain the heat-treated halloysite powder.
(2) Dispersing the halloysite treated in the step (1) in a solvent, adding the polymer and an oxidant into the solvent, and polymerizing to obtain a semi-finished product, wherein the semi-finished product specifically comprises the following components:
adding 0.1g of halloysite treated in the step (1) into 90ml of deionized water, performing ultrasonic treatment at room temperature for 10min, adding 100 mu L of pyrrole, stirring for 10min to obtain a suspension, and taking 0.15g of FeCl3Dissolving in 10ml deionized water, adding FeCl3And dripping the solution into the suspension, stirring at room temperature for 24h, and carrying out centrifugal separation, washing and drying on the liquid to obtain the PPy-coated halloysite powder.
(3) Loading the core layer in the semi-finished product obtained in the step (2), specifically:
and (3) uniformly mixing 0.07g of sublimed sulfur powder and 0.03g of the PPy-coated halloysite powder obtained in the step (2), placing the mixture in a tube furnace, and keeping the temperature at 155 ℃ for 12 hours in an argon atmosphere to obtain the S/PPy-coated halloysite mixed material, wherein the scanning electron microscope result is shown in figure 3, the originally smooth outer wall of the halloysite is not difficult to find to be rough, a large amount of additional substances are attached to the outer wall of the halloysite, and the pipeline is filled with the mixture.
The weight ratio of halloysite, polymer and sulfur in this example was 1: 1: (7/3).
Example 3
The preparation method of the positive electrode material of the lithium-sulfur battery comprises the following steps:
(1) carrying out acid leaching on halloysite and then carrying out heat treatment, wherein the heat treatment specifically comprises the following steps:
adding 10g of natural halloysite solid powder into a solution consisting of 28ml of concentrated hydrochloric acid with the mass fraction of 38% and 7ml of deionized water, reacting for 120min at 70 ℃, then centrifugally washing, filtering to obtain a solid, placing the solid in an oven at 80 ℃ for drying for 24h to obtain acid-leached and purified halloysite powder, placing the purified halloysite powder in a tubular furnace under the argon atmosphere, preserving heat at 300 ℃ for 3h, and cooling at the heating rate of 5 ℃/min to obtain the heat-treated halloysite powder.
(2) Dispersing the halloysite treated in the step (1) in a solvent, adding the polymer and an oxidant into the solvent, and polymerizing to obtain a semi-finished product, wherein the semi-finished product specifically comprises the following components:
adding 0.1g of halloysite treated in the step (1) into 90ml of deionized water, performing ultrasonic treatment at room temperature for 10min, adding 120 mu L of aniline, stirring for 10min to obtain a suspension, and taking 0.1mol L of aniline-1Adding 240 mu L of HCl into the suspension, dissolving 0.2g of ammonium persulfate in 5mL of water, dripping the ammonium persulfate solution into the suspension, stirring at room temperature for 24h, and performing centrifugal separation, washing and drying on the liquid to obtain PANI-coated halloysite powder.
(3) Loading the core layer in the semi-finished product obtained in the step (2), specifically:
and (3) uniformly mixing 0.07g of sublimed sulfur powder and 0.03g of the PANI coated halloysite powder obtained in the step (2), placing the mixture in a tube furnace, and keeping the temperature at 155 ℃ for 12 hours in an argon atmosphere to obtain the S/PANI coated halloysite mixed material.
The weight ratio of halloysite, polymer and sulfur in this example was 1: 1: (7/3).
Example 4
The preparation method of the positive electrode material of the lithium-sulfur battery comprises the following steps:
(1) carrying out acid leaching on halloysite and then carrying out heat treatment, wherein the heat treatment specifically comprises the following steps:
adding 10g of natural halloysite solid powder into a solution consisting of 28ml of concentrated hydrochloric acid with the mass fraction of 38% and 7ml of deionized water, reacting for 120min at 70 ℃, then centrifugally washing, filtering to obtain a solid, placing the solid in an oven at 80 ℃ for drying for 24h to obtain acid-leached and purified halloysite powder, placing the purified halloysite powder in a tubular furnace under the argon atmosphere, preserving heat at 300 ℃ for 3h, and cooling at the heating rate of 5 ℃/min to obtain the heat-treated halloysite powder.
(2) Dispersing the halloysite treated in the step (1) in a solvent, adding the polymer and an oxidant into the solvent, and polymerizing to obtain a semi-finished product, wherein the semi-finished product specifically comprises the following components:
adding 0.1g of halloysite treated in the step (1) into 90mL of deionized water, performing ultrasonic treatment for 10min at room temperature, adding 120 mu LPEDOT, stirring for 10min to obtain a suspension, dissolving 0.12g of camphorsulfonic acid in 5mL of water, adding the suspension, dissolving 0.6g of ammonium persulfate in 5mL of water, dripping the ammonium persulfate solution into the suspension, stirring for 24h at room temperature, and performing centrifugal separation, washing and drying on the liquid to obtain the PEDOT-coated halloysite powder.
(3) Loading the core layer in the semi-finished product obtained in the step (2), specifically:
and (3) uniformly mixing 0.07g of sublimed sulfur powder and 0.03g of PEDOT-coated halloysite powder obtained in the step (2), placing the mixture in a tube furnace, and keeping the temperature at 155 ℃ for 12 hours in an argon atmosphere to obtain the S/PEDOT-coated halloysite mixed material.
The weight ratio of halloysite, polymer and sulfur in this example was 1: 1: (7/3).
Example 5
The preparation method of the positive electrode material of the lithium-sulfur battery comprises the following steps:
(1) carrying out acid leaching on halloysite and then carrying out heat treatment, wherein the heat treatment specifically comprises the following steps:
adding 10g of natural halloysite solid powder into a solution consisting of 28ml of concentrated hydrochloric acid with the mass fraction of 38% and 7ml of deionized water, reacting for 120min at 70 ℃, then centrifugally washing, filtering to obtain a solid, placing the solid in an oven at 80 ℃ for drying for 24h to obtain acid-leached and purified halloysite powder, placing the purified halloysite powder in a tubular furnace under the argon atmosphere, preserving heat at 300 ℃ for 3h, and cooling at the heating rate of 5 ℃/min to obtain the heat-treated halloysite powder.
(2) Dispersing the halloysite treated in the step (1) in a solvent, adding the polymer and an oxidant into the solvent, and polymerizing to obtain a semi-finished product, wherein the semi-finished product specifically comprises the following components:
adding 0.1g of halloysite treated in the step (1) into 90ml of deionized water, performing ultrasonic treatment at room temperature for 10min, adding 200 mu L of pyrrole, stirring for 10min to obtain a suspension, and taking 0.3g of FeCl3Dissolving in 10ml of deionized water, dripping FeCl3 solution into the suspension, stirring at room temperature for 24h, and carrying out centrifugal separation, washing and drying on the liquid to obtain the PPy-coated halloysite powder.
(3) Loading the core layer in the semi-finished product obtained in the step (2), specifically:
and (3) uniformly mixing 0.07g of sublimed sulfur powder and 0.03g of the halloysite powder coated by the PPy obtained in the step (2), placing the mixture in a tube furnace, and keeping the temperature at 155 ℃ for 12 hours in an argon atmosphere to obtain the halloysite mixed material coated by the S/PPy.
The weight ratio of halloysite, polymer and sulfur in this example was 1: 2: (7/3).
Example 6
The preparation method of the positive electrode material of the lithium-sulfur battery comprises the following steps:
(1) carrying out acid leaching on halloysite and then carrying out heat treatment, wherein the heat treatment specifically comprises the following steps:
adding 10g of natural halloysite solid powder into a solution consisting of 28ml of concentrated hydrochloric acid with the mass fraction of 38% and 7ml of deionized water, reacting for 120min at 70 ℃, then centrifugally washing, filtering to obtain a solid, placing the solid in an oven at 80 ℃ for drying for 24h to obtain acid-leached and purified halloysite powder, placing the purified halloysite powder in a tubular furnace under the argon atmosphere, preserving heat at 300 ℃ for 3h, and cooling at the heating rate of 5 ℃/min to obtain the heat-treated halloysite powder.
(2) Dispersing the halloysite treated in the step (1) in a solvent, adding the polymer and an oxidant into the solvent, and polymerizing to obtain a semi-finished product, wherein the semi-finished product specifically comprises the following components:
adding 0.1g of halloysite treated in the step (1) into 90ml of deionized water, performing ultrasonic treatment at room temperature for 10min, adding 240 mu L of aniline, stirring for 10min to obtain a suspension, and taking 0.1mol L of aniline-1Adding 480 mu L of HCl into the suspension, dissolving 0.4g of ammonium persulfate into 5mL of water, dripping the ammonium persulfate solution into the suspension, stirring at room temperature for 24h, and performing centrifugal separation, washing and drying on the liquid to obtain PANI-coated halloysite powder.
(3) Loading the core layer in the semi-finished product obtained in the step (2), specifically:
and (3) uniformly mixing 0.07g of sublimed sulfur powder and 0.03g of the PANI coated halloysite powder obtained in the step (2), placing the mixture in a tube furnace, and keeping the temperature at 155 ℃ for 12 hours in an argon atmosphere to obtain the S/PANI coated halloysite mixed material.
The weight ratio of halloysite, polymer and sulfur in this example was 1: 2: (7/3).
Example 7
The preparation method of the positive electrode material of the lithium-sulfur battery comprises the following steps:
(1) carrying out acid leaching on halloysite and then carrying out heat treatment, wherein the heat treatment specifically comprises the following steps:
adding 10g of natural halloysite solid powder into a solution consisting of 28ml of concentrated hydrochloric acid with the mass fraction of 38% and 7ml of deionized water, reacting for 120min at 70 ℃, then centrifugally washing, filtering to obtain a solid, placing the solid in an oven at 80 ℃ for drying for 24h to obtain acid-leached and purified halloysite powder, placing the purified halloysite powder in a tubular furnace under the argon atmosphere, preserving heat at 300 ℃ for 3h, and cooling at the heating rate of 5 ℃/min to obtain the heat-treated halloysite powder.
(2) Dispersing the halloysite treated in the step (1) in a solvent, adding the polymer and an oxidant into the solvent, and polymerizing to obtain a semi-finished product, wherein the semi-finished product specifically comprises the following components:
adding 0.1g of halloysite treated in the step (1) into 90mL of deionized water, performing ultrasonic treatment for 10min at room temperature, adding 240 mu LPEDOT, stirring for 10min to obtain a suspension, dissolving 0.24g of camphorsulfonic acid in 5mL of water, adding the suspension, dissolving 1.2g of ammonium persulfate in 5mL of water, dropping the ammonium persulfate solution into the suspension, stirring for 24h at room temperature, and performing centrifugal separation, washing and drying on the liquid to obtain the PEDOT-coated halloysite powder.
(3) Loading the core layer in the semi-finished product obtained in the step (2), specifically:
and (3) uniformly mixing 0.07g of sublimed sulfur powder and 0.03g of PEDOT-coated halloysite powder obtained in the step (2), placing the mixture in a tube furnace, and keeping the temperature at 155 ℃ for 12 hours in an argon atmosphere to obtain the S/PEDOT-coated halloysite mixed material.
The weight ratio of halloysite, polymer and sulfur in this example was 1: 2: (7/3).
Example 8
The embodiment provides a preparation method of an electrode material, and particularly provides an application of a lithium-sulfur battery positive electrode material in the battery positive electrode material, which comprises the following steps: grinding the lithium-sulfur battery positive electrode material and the conductive agent uniformly according to the mass ratio of 7:2, adding the binder, stirring for 24 hours at room temperature to obtain slurry, uniformly coating the slurry on an aluminum foil by a coating method, drying and slicing to obtain the halloysite positive electrode material.
The conductive agent is Super-P, and the binder is PVDF/NMP and NMP 250 mu L.
Comparative example 1
The preparation method of the positive electrode material of the lithium-sulfur battery comprises the following steps:
(1) carrying out acid leaching on halloysite and then carrying out heat treatment, wherein the heat treatment specifically comprises the following steps:
adding 10g of natural halloysite solid powder into a solution consisting of 28ml of concentrated hydrochloric acid with the mass fraction of 38% and 7ml of deionized water, reacting for 120min at 70 ℃, then centrifugally washing, filtering to obtain a solid, placing the solid in an oven at 80 ℃ for drying for 24h to obtain acid-leached and purified halloysite powder, placing the purified halloysite powder in a tubular furnace under the argon atmosphere, preserving heat at 300 ℃ for 3h, and cooling at the heating rate of 5 ℃/min to obtain the heat-treated halloysite powder.
(2) Loading the core layer in the semi-finished product obtained in the step (1), wherein the loading specifically comprises the following steps:
and (2) uniformly mixing 0.07g of sublimed sulfur powder and 0.03g of semi-finished product powder obtained in the step (1), placing the mixture in a tube furnace, and keeping the temperature at 155 ℃ for 12 hours under the argon atmosphere to obtain the S/halloysite mixed material.
The weight ratio of halloysite, polymer and sulfur in this example was 1: (7/3).
Example of detection
Using the positive electrode materials for lithium sulfur batteries prepared in examples 2 and 4 and comparative examples 1 and 2, electrode materials corresponding to the numbers were prepared by the electrode material preparation method provided in example 8.
The electrode material was paired with lithium metal using a Celgard separator at 1mol L-1LiTFSI/(DOL+DME)(V/V＝1:1)/1％LiNO3And assembling the electrolyte into a 2016 button cell battery to carry out multiplying power and cycle performance tests. The results are shown in Table 1.
TABLE 1 Battery test data
Figure BDA0001827213910000081
As can be seen from Table 1, when the amount of pyrrole added was 50%, the initial specific discharge capacity of the synthesized PPy/halloysite mixed material was 786.9mAh g at 0.1C rate-1After 100 cycles, the cycle retention rate is 71.8%; when the pyrrole addition amount is 67 percent, the first discharge specific capacity of the synthesized PPy/halloysite mixed material is 947.8mAh g under the multiplying power of 0.1C-1After 100 cycles, the capacity retention rate was 53.2%. Compared with the halloysite, the first discharge specific capacity and the cycle retention rate of the battery prepared from the halloysite mixed material coated by the conductive polymer are improved, which shows that the conductivity of the halloysite is improved on the basis of keeping the original structure and chemical components of the halloysite by the coated conductive polymer, so that the performance of the battery is improved.
Fig. 4 to 6 are results of battery rate performance tests of example 2, example 5 and comparative example 1, respectively, and it can be seen that rate performance of examples 2 and 5 is superior to that of the comparative example, and battery discharge capacity prepared from the halloysite mixed material coated by the conductive polymer is good in recovery.
Fig. 7 to 9 are results of cycle performance tests of the batteries of example 2, example 5 and comparative example 1, respectively, and it can be seen that the cycle performance of examples 2 and 5 is superior to that of the comparative example, and the batteries prepared from the halloysite mixed material coated with the conductive polymer have stable cycle curves and high capacity retention rate.
The foregoing detailed description has described the principal features and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the above-described embodiments, and variations and modifications of the present invention may be made without departing from the spirit and scope of the invention. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (6)

1. The positive electrode material of the lithium-sulfur battery is characterized by comprising a matrix layer, a polymer layer wrapping the matrix layer and a core layer positioned in the matrix layer;
the substrate layer is halloysite;
the polymer is one of polypyrrole (PPy), Polyaniline (PANI) and poly 3, 4-ethylenedioxythiophene (PEDOT);
the core layer is a sulfur single layer;
the preparation method of the lithium-sulfur battery positive electrode material comprises the following steps:
(1) carrying out acid leaching and heat treatment on the substrate layer;
(2) dispersing the substrate layer treated in the step (1) in a solvent, adding a polymer monomer and an oxidant into the solvent, and polymerizing to obtain a semi-finished product;
(3) loading the core layer into the semi-finished product obtained in the step (2);
in the step (3), the method for loading the core layer is a hot melting method: uniformly mixing the semi-finished product obtained in the step (2) with sulfur, placing the mixture in a tube furnace, and keeping the temperature of 150-200 ℃ for 10-16 h under Ar atmosphere;
in the step (2), the mass ratio of the matrix layer to the polymer monomer is 1: (0.5-3), wherein the mass ratio of the polymer monomer to the oxidant is 1: (1-5).
2. The positive electrode material for a lithium-sulfur battery according to claim 1, wherein the acid in step (1) is one of hydrochloric acid, sulfuric acid and oxalic acid.
3. The positive electrode material for a lithium-sulfur battery according to claim 1, wherein the leaching temperature in step (1) is 60 to 70 ℃, and the leaching time is 100 to 150 min.
4. The positive electrode material for a lithium-sulfur battery according to claim 1, wherein the heat treatment temperature in step (1) is 200 to 500 ℃ and the heat treatment time is 2 to 6 hours.
5. The positive electrode material for lithium-sulfur battery according to claim 1, wherein the solvent in step (2) is water, and the oxidant is FeCl3One of ammonium persulfate, potassium persulfate and sodium persulfate.
6. The positive electrode material for a lithium-sulfur battery according to claim 1, wherein the polymerization temperature in step (2) is 20 to 30 ℃ and the polymerization time is 12 to 24 hours.
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