Double-transition metal selenide core-shell hollow nanosphere for lithium-sulfur battery positive electrode host material as well as preparation method and application of double-transition metal selenide core-shell hollow nanosphere

Abstract

The invention discloses a double-transition metal selenide core-shell hollow nanosphere for a lithium-sulfur battery positive electrode host material as well as a preparation method and application of the double-transition metal selenide core-shell hollow nanosphere, and belongs to the technical field of battery material preparation. The preparation method of the double transition metal selenide core-shell hollow nanospheres comprises the following steps: mixing a transition metal salt solution with glycerol, and heating for reaction to obtain a transition metal-glycerol precursor; adding another transition metal salt into the transition metal-glycerol precursor solution, and heating for reaction to obtain a double-transition metal core-shell hollow nanosphere precursor; and carrying out high-temperature calcination on the double-transition metal core-shell hollow nanosphere precursor and selenium powder together to obtain the double-transition metal selenide core-shell hollow nanosphere. The double transition metal selenide core-shell hollow nanosphere is used as a lithium-sulfur battery positive electrode host material, can effectively inhibit a shuttle effect caused by polysulfide, improves the utilization rate of sulfur, and remarkably improves the specific capacity, coulombic efficiency and cycling stability of a battery.

Description

Technical Field

[0001] The present invention relates to the technical field of battery material preparation, and in particular to a double transition metal selenide core-shell hollow nanosphere used as a positive electrode host material for a lithium-sulfur battery, and a preparation method and application thereof. Background Art

[0002] Lithium-sulfur (Li-S) batteries have a capacity of up to 1675 mAh g -1 Theoretical specific capacity, 2600Wh kg -1 The theoretical energy density is 3 to 5 times that of lithium-ion batteries. In addition, sulfur is abundant on earth, has low cost, and is environmentally friendly, making Li-S batteries one of the most promising next-generation high-energy-density batteries and attracting widespread attention from researchers. However, the electrochemical performance of Li-S batteries has not been fully realized to date, especially the low utilization rate of sulfur, low rate performance, and poor cycle life, which have hindered their practical application. These problems mainly stem from: (1) During the battery charge and discharge cycle, the positive electrode material severely expands in volume (≈80%), resulting in structural damage to the electrode material; (2) the intermediate polysulfide (Li 2 S n , 4≤n≤8) are easily soluble in the electrolyte, and they can easily migrate to the negative electrode and react with the negative electrode metal lithium, corroding the lithium negative electrode and causing the "shuttle effect", which leads to rapid capacity decay and reduced Coulomb efficiency of the battery; (3) sulfur and lithium sulfide (Li 2 S) have poor electrical conductivity, resulting in slow redox reaction kinetics.

[0003] In response to the above problems, researchers have solved the problems in Li-S batteries from different angles. The most proposed strategy is to introduce porous conductive carbon into the positive electrode structure, thereby reducing the volume expansion of the electrode during the cycle and accelerating the ability of electron transfer. However, due to the weak interaction between carbon and polar polysulfides, the ability of non-polar carbon materials to inhibit the "shuttle effect" of polysulfides or accelerate the conversion of polysulfides is very limited. Summary of the invention

[0004] The purpose of the present invention is to provide a double transition metal selenide core-shell hollow nanosphere for lithium-sulfur battery positive electrode host material and a preparation method and application thereof, so as to solve the problems existing in the above-mentioned prior art.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention is a method for preparing double transition metal selenide core-shell hollow nanospheres for lithium-sulfur battery positive electrode host materials, comprising the following steps:

[0007] (1) mixing a solution of a transition metal salt and glycerol, stirring under magnetic force for 2 to 6 hours, and then heating for reaction (i.e., hydrothermal reaction), washing the precipitate several times after the reaction, and vacuum drying (temperature of 50 to 80° C., time of 8 to 12 hours) to obtain a transition metal-glycerol precursor with a particle size of 300 to 500 nm;

[0008] (2) adding another transition metal salt to the solution of the transition metal-glycerol precursor and heating the solution to react (cation exchange strategy) to obtain a double transition metal core-shell hollow nanosphere precursor having a particle size of 300 to 500 nm;

[0009] (3) calcining the double transition metal core-shell hollow nanosphere precursor and selenium powder at high temperature (selenization at high temperature) to obtain the double transition metal selenide core-shell hollow nanosphere with a particle size of 300 to 500 nm.

[0010] The double transition metal selenide core-shell hollow nanosphere is a hollow nanosphere with a core-shell structure and has hierarchical porosity of micropores, mesopores and macropores.

[0011] The double metal selenide in the double transition metal selenide core-shell hollow nanosphere prepared by the present invention has a strong chemical affinity for polysulfide and can effectively confine the polysulfide inside the positive electrode.

[0012] The double transition metal selenide core-shell hollow nanospheres prepared by the present invention are used as the positive electrode host material of the Li-S battery, which can significantly increase the sulfur loading of the positive electrode of the lithium-sulfur battery. The double metal selenides in the double transition metal selenide core-shell hollow nanospheres can catalyze the conversion of intermediate polysulfides, improve the redox conversion reaction kinetics of the positive electrode, and inhibit the shuttle effect, thereby improving the problem of poor cycle stability of the Li-S battery.

[0013] The double transition metal selenide core-shell hollow nanospheres prepared by the present invention have a hollow core-shell structure, which can provide a huge loading space for the positive electrode active material sulfur, greatly improve the sulfur loading of the positive electrode, and alleviate the volume expansion of the electrode during the cycle; the double transition metal selenide core-shell hollow nanospheres have strong conductivity, and can be used as a catalyst to effectively catalyze the conversion of polysulfides, improve the redox conversion reaction kinetics of the positive electrode sulfur, and therefore significantly improve the specific capacity, coulomb efficiency and cycle stability of the Li-S battery.

[0014] Furthermore, in step (1) and step (2), the transition metal salt is selected from two of iron salts, nickel salts, cobalt salts, vanadium salts and manganese salts.

[0015] Furthermore, the iron salt is selected from one of ferric nitrate, ferric sulfate and ferrous chloride; the nickel salt is selected from one of nickel nitrate, nickel sulfate, nickel chloride and nickel acetate; the cobalt salt is selected from one of cobalt nitrate, cobalt sulfate, cobalt chloride and cobalt acetate; the vanadium salt is selected from one of ammonium metavanadate, sodium vanadate and vanadium pentoxide; the manganese salt is selected from one of manganese nitrate, manganese sulfate, manganese chloride and manganese acetate.

[0016] Furthermore, in step (1), the heating reaction temperature is 150 to 200° C. and the time is 10 to 30 hours;

[0017] And / or, the mass ratio of the transition metal salt to glycerol is 1:(100-200).

[0018] Furthermore, in step (2), the heating reaction temperature is 100 to 150° C. and the time is 2 to 6 hours.

[0019] Furthermore, in step (3), the heating rate of the high temperature calcination is 2 to 10°C / min, the temperature is 300 to 500°C, and the time is 2 to 6 hours.

[0020] Furthermore, the contents of the two transition metals in the double transition metal selenide core-shell hollow nanospheres are independently 10-30wt%, and the content of selenium is 40-80wt%.

[0021] The second technical solution of the present invention: a double transition metal selenide core-shell hollow nanosphere prepared by the above preparation method.

[0022] The third technical solution of the present invention: an application of the above-mentioned double transition metal selenide core-shell hollow nanospheres as a positive electrode host material for lithium-sulfur batteries.

[0023] The fourth technical solution of the present invention: a composite sulfur positive electrode material (i.e., a lithium-sulfur battery positive electrode material), the raw materials of which include the above-mentioned double transition metal selenide core-shell hollow nanospheres and elemental sulfur.

[0024] A fifth technical solution of the present invention is a method for preparing the composite sulfur cathode material, comprising the following steps:

[0025] The double transition metal selenide core-shell hollow nanospheres are compounded with elemental sulfur to obtain the composite sulfur positive electrode material.

[0026] Furthermore, the mass ratio of the double transition metal selenide core-shell hollow nanospheres to elemental sulfur is 1:3 to 1:5;

[0027] The composite method is a high-temperature melt impregnation method or a liquid phase infiltration method; the high-temperature melt impregnation method comprises: mixing the double transition metal selenide core-shell hollow nanospheres and elemental sulfur, sealing them in a weighing bottle, heating them to 150-160° C., keeping the temperature constant for 10 hours, and cooling them to room temperature to obtain the composite sulfur positive electrode material.

[0028] The present invention discloses the following technical effects:

[0029] (1) The present invention firstly adopts a one-step hydrothermal method to prepare a transition metal-glycerol precursor with a solid sphere structure, then introduces another transition metal through a cation exchange strategy to prepare a double transition metal core-shell hollow nanosphere precursor with a hollow core-shell structure, and then successfully prepares a double transition metal selenide core-shell hollow nanosphere with a hollow core-shell structure by selenization at high temperature. When the double transition metal selenide core-shell hollow nanosphere with a hollow core-shell structure is used as a positive electrode host material of a Li-S battery, the hollow core-shell structure can provide a huge space for the positive electrode active material of the Li-S battery, greatly increase the sulfur loading, and alleviate the volume expansion of the electrode during the cycle; and the synergistic effect between the two transition metals can effectively catalyze the conversion of polysulfides generated by the Li-S battery during the cycle, improve the redox conversion kinetics, so that the problem of poor cycle stability of the Li-S battery is significantly improved, and its cycle life is extended. At a rate of 1.0C, after a long cycle of 1400 cycles, the capacity decay rate per cycle is only 0.030%.

[0030] (2) The synthesis method of the double transition metal selenide core-shell hollow nanospheres of the present invention is simple and easy, which is conducive to industrial production and can be widely used as a sulfur cathode host material in the fields of lithium-sulfur batteries.

[0031] (3) The double transition metal selenide core-shell hollow nanospheres prepared by the present invention can be used as the host material of the positive electrode of the lithium-sulfur battery, which can significantly increase the sulfur loading of the positive electrode. In addition, the double transition metal selenide can be used as a catalyst to accelerate the conversion kinetics of polysulfides generated during the charging and discharging process of the lithium-sulfur battery, and can effectively inhibit the "shuttle effect" caused by polysulfides, thereby improving the utilization rate of sulfur and significantly improving the specific capacity, coulombic efficiency and cycle stability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1This is a scanning electron microscope image of the double transition metal selenide core-shell hollow nanosphere CoVSe with a hollow core-shell structure prepared in Example 1 of the present invention;

[0034] Figure 2 A transmission electron microscope image of the double transition metal selenide core-shell hollow nanosphere CoVSe with a hollow core-shell structure prepared in Example 1 of the present invention;

[0035] Figure 3 The nitrogen adsorption-desorption curve of the double transition metal selenide core-shell hollow nanosphere CoVSe with a hollow core-shell structure prepared in Example 1 of the present invention;

[0036] Figure 4 This is a comparison chart of the rate performance of the batteries prepared in Example 5 of the present invention and Comparative Examples 1 to 2;

[0037] Figure 5 This is a comparison chart of the long cycle performance of the batteries prepared in Example 5 of the present invention and Comparative Examples 1 to 2;

[0038] Figure 6 CV comparison diagram of the batteries prepared in Example 5 of the present invention and Comparative Examples 1-2;

[0039] Figure 7 This is a scanning electron microscope image of the double transition metal selenide core-shell hollow nanospheres with a hollow core-shell structure prepared in Comparative Example 3 of the present invention;

[0040] Figure 8 This is a scanning electron microscope image of the double transition metal selenide core-shell hollow nanospheres with a hollow core-shell structure prepared in Comparative Example 4 of the present invention. DETAILED DESCRIPTION

[0041] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0042] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0043] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0044] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0045] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0046] The “parts” described in the following examples are all “parts by weight”.

[0047] Example 1

[0048] A preparation method of double transition metal selenide core-shell hollow nanosphere CoVSe with a hollow core-shell structure:

[0049] (1) 0.5 g of Co(NO 3 ) 2 6H 2 O was added into an appropriate amount of isopropanol, and a uniform solution was formed by ultrasonic and magnetic stirring at room temperature; then, 50 g of glycerol was slowly added during the magnetic stirring, and after continuous magnetic stirring for 3 h, it was transferred to a 100 mL high temperature and high pressure reactor, kept at 150 ° C for 10 h, washed several times by centrifugation with ethanol, and vacuum dried at 80 ° C for 12 h to obtain a Co-glycerol precursor with a particle size of 300-500 nm.

[0050] (2) 0.2 g of Co-glycerol precursor was added to 50 mL of anhydrous ethanol, and after ultrasonic dispersion, 0.2 g of NH 4 VO 3 , and then add an appropriate amount of ultrapure water, stir magnetically while ultrasonicating for 30 minutes. When the solution changes color, transfer it to a 100 mL high temperature and high pressure reactor, keep it at 150°C for 2 hours, filter and wash, and obtain the CoV precursor (double transition metal core-shell hollow nanosphere precursor) with a particle size of 300-500 nm.

[0051] (3) 0.6 g of selenium powder was placed at the front end of the magnetic boat, and 0.1 g of CoV precursor was placed at the end of the magnetic boat. The magnetic boat was placed in a high-temperature tube furnace for high-temperature calcination (heating rate of 5 °C / min, temperature of 450 °C, time of 2 h) to obtain double transition metal selenide core-shell hollow nanospheres CoVSe with a hollow core-shell structure, with a particle size of 300 to 500 nm.

[0052] In the double transition metal selenide core-shell hollow nanospheres CoVSe with a hollow core-shell structure prepared in this example, the content of Co is 20 wt %, the content of V is 20 wt %, and the content of Se is 60 wt %.

[0053] The scanning electron microscope (SEM) image of the double transition metal selenide core-shell hollow nanosphere CoVSe with a hollow core-shell structure prepared in this example is shown in Figure 1 , transmission electron microscopy (TEM) images are shown in Figure 2 , nitrogen adsorption and desorption curve (the inset is the pore size distribution curve) see Figure 3 .

[0054] from Figures 1 to 3 It can be seen that the material prepared in this example has a hollow core-shell structure and a hierarchical porous structure of micropores, mesopores and macropores.

[0055] Example 2

[0056] A preparation method of double transition metal selenide core-shell hollow nanosphere CoVSe with a hollow core-shell structure:

[0057] (1) 0.5 g of Co(NO 3 ) 2 6H 2 O was added into an appropriate amount of isopropanol, and a uniform solution was formed by ultrasonic and magnetic stirring at room temperature; then, 100 g of glycerol was slowly added during the magnetic stirring, and after continuous magnetic stirring for 3 h, it was transferred to a 150 mL high temperature and high pressure reactor, maintained at 150 ° C for 10 h, washed several times by centrifugation with ethanol, and vacuum dried at 80 ° C for 12 h to obtain a Co-glycerol precursor with a particle size of 300 to 500 nm.

[0058] (2) 0.3 g of Co-glycerol precursor was added to 100 mL of anhydrous ethanol, and after ultrasonic dispersion, 0.6 g of NH 4 VO 3 , and then add an appropriate amount of ultrapure water, stir magnetically while ultrasonicating for 30 minutes. When the solution changes color, transfer it to a 150mL high-temperature and high-pressure reactor, keep it at 150°C for 2 hours, filter and wash, and obtain a CoV precursor (double transition metal core-shell hollow nanosphere precursor) with a particle size of 300-500nm.

[0059] (3) 0.4 g of selenium powder was placed at the front end of the magnetic boat, and 0.3 g of CoV precursor was placed at the end of the magnetic boat. The magnetic boat was placed in a high-temperature tube furnace for high-temperature calcination (heating rate of 5 °C / min, temperature of 450 °C, time of 2 h) to obtain double transition metal selenide core-shell hollow nanospheres CoVSe with a hollow core-shell structure, with a particle size of 300 to 500 nm.

[0060] In the double transition metal selenide core-shell hollow nanospheres CoVSe with a hollow core-shell structure prepared in this example, the content of Co is 30 wt %, the content of V is 30 wt %, and the content of Se is 40 wt %.

[0061] Example 3

[0062] A preparation method of double transition metal selenide core-shell hollow nanospheres FeVSe with a hollow core-shell structure:

[0063] (1) 0.5 g of Fe(NO 3 ) 2 6H 2 O was added into an appropriate amount of isopropanol, and a uniform solution was formed under ultrasonic and magnetic stirring at room temperature; then, 50 g of glycerol was slowly added during the magnetic stirring, and after continuous magnetic stirring for 3 h, it was transferred to a 100 mL high temperature and high pressure reactor, kept at 150 ° C for 10 h, washed by centrifugation with ethanol for several times, and vacuum dried at 80 ° C for 12 h to obtain a Fe-glycerol precursor with a particle size of 300-500 nm.

[0064] (2) 0.2 g of Fe-glycerol precursor was dissolved in 100 mL of anhydrous ethanol and ultrasonically dispersed uniformly. Then 0.2 g of NH 4 VO 3 Then, add an appropriate amount of ultrapure water and stir magnetically for 30 minutes while ultrasonicating. When the solution changes color, transfer it to a 150mL high-temperature and high-pressure reactor, keep it at 150°C for 2 hours, filter and wash, and obtain a FeV precursor (double transition metal core-shell hollow nanosphere precursor) with a particle size of 300-500nm.

[0065] (3) 0.6 g of selenium powder was placed at the front end of the magnetic boat, and 0.4 g of FeV precursor was placed at the end of the magnetic boat. The magnetic boat was placed in a high-temperature tube furnace for high-temperature calcination (heating rate of 5 °C / min, temperature of 450 °C, time of 2 h) to obtain double transition metal selenide core-shell hollow nanospheres FeVSe with a hollow core-shell structure, with a particle size of 300 to 500 nm.

[0066] In the double transition metal selenide core-shell hollow nanospheres FeVSe with a hollow core-shell structure prepared in this example, the content of Fe is 20 wt %, the content of V is 20 wt %, and the content of Se is 60 wt %.

[0067] Example 4

[0068] A method for preparing double transition metal sulfide hollow nanospheres CoVS with a hollow core-shell structure:

[0069] (1) 0.5 g of Co(NO 3 ) 2 6H 2 O was added into an appropriate amount of isopropanol, and a uniform solution was formed under ultrasonic and magnetic stirring at room temperature; then, 50 g of glycerol was slowly added during the magnetic stirring, and after continuous magnetic stirring for 3 h, it was transferred to a 100 mL high temperature and high pressure reactor, maintained at 150 ° C for 10 h, washed several times by centrifugation with ethanol, and vacuum dried at 80 ° C for 12 h to obtain a Ni-glycerol precursor with a particle size of 300-500 nm.

[0070] (2) 0.2 g of Co-glycerol precursor was added to 100 mL of anhydrous ethanol, and after ultrasonic dispersion, 0.2 g of NH 4 VO 3 , and then add an appropriate amount of ultrapure water, stir magnetically while ultrasonicating for 30 minutes. When the solution changes color, transfer it to a 150mL high-temperature and high-pressure reactor, keep it at 150°C for 2 hours, filter and wash, and obtain a CoV precursor (double transition metal core-shell hollow nanosphere precursor) with a particle size of 300-500nm.

[0071] (3) 0.6 g of sulfur powder was placed at the front end of the magnetic boat, and 0.4 g of CoV precursor was placed at the end of the magnetic boat. The magnetic boat was placed in a high-temperature tube furnace for high-temperature calcination (heating rate of 5 °C / min, temperature of 450 °C, time of 2 h) to obtain double transition metal selenide core-shell hollow nanospheres CoVS with a hollow core-shell structure, with a particle size of 300 to 500 nm.

[0072] In the double transition metal selenide core-shell hollow nanospheres CoVS with a hollow core-shell structure prepared in this example, the content of Co is 20 wt %, the content of V is 20 wt %, and the content of S is 60 wt %.

[0073] Example 5

[0074] 1. Preparation method of composite sulfur positive electrode material CoVSe / S (i.e., lithium-sulfur battery positive electrode material):

[0075] The double transition metal selenide core-shell hollow nanospheres CoVSe with a hollow core-shell structure obtained in Example 1 are loaded with sulfur, and the specific steps are as follows:

[0076] (1) The double transition metal selenide core-shell hollow nanospheres CoVSe with a hollow core-shell structure obtained in Example 1 and sublimed sulfur were placed in an agate mortar at a mass ratio of 1:3 and ground for 20 min. Then, carbon disulfide (CS2) was added. 2 ) to immerse the sample and continue grinding until carbon disulfide (CS 2 ) was completely evaporated and then ground for 20 min.

[0077] (2) The ground sample in step (1) was transferred to a stainless steel reactor, heated to 155°C for 12 h, and then naturally cooled to room temperature.

[0078] (3) Grinding the sample obtained after cooling in step (2) again with an agate mortar, collecting the obtained powder sample, and obtaining a composite material CoVSe / S (i.e., a composite sulfur positive electrode material) of double transition metal selenide core-shell hollow nanospheres CoVSe with a hollow core-shell structure and sulfur.

[0079] 2. Preparation method of positive electrode sheet of lithium-sulfur battery:

[0080] (1) 0.07 g of CoVSe / S obtained in step 1, 0.02 g of acetylene black and 0.01 g of binder (PVDF) were ground in an agate mortar for 30 min, and then 0.25 mL of N-methylpyrrolidone (NMP) was added to grind into a slurry.

[0081] (2) Take 0.3 mL of the slurry prepared in step (1) and spread it evenly on a 50 cm 2 The resulting mixture was placed on an aluminum foil and vacuum dried at 60°C for 12 h to obtain a positive electrode sheet for a lithium-sulfur battery.

[0082] 3. Preparation method of lithium-sulfur battery:

[0083] (1) The positive electrode sheet of the lithium-sulfur battery obtained in step 2 is cut into a circular electrode sheet with a diameter of 14 mm, and a battery shell of model 2032 is selected to assemble the battery in a glove box filled with argon.

[0084] (2) After the battery assembled in step (1) was left to stand for 12 hours, the electrochemical performance was tested using a blue battery test system. The test results are shown in Figures 4-5 ; The assembled symmetrical cell was tested by CV to explore its catalytic performance on polysulfides. The results are shown in Figure 6 .

[0085] Figure 4 is the rate performance diagram; Figure 5 is the long cycle performance diagram; Figure 6 is the CV curve.

[0086] Comparative Example 1

[0087] 1. Preparation method of composite sulfur positive electrode material CoVS / S (i.e., lithium-sulfur battery positive electrode material):

[0088] The double transition metal sulfide hollow nanospheres CoVS with a hollow core-shell structure obtained in Example 4 are loaded with sulfur, and the specific steps are as follows:

[0089] (1) The double transition metal selenide core-shell hollow nanospheres CoVS with a hollow core-shell structure obtained in Example 4 and sublimed sulfur were placed in an agate mortar at a mass ratio of 1:3 and ground for 20 min, then carbon disulfide (CS 2 ) to immerse the sample and continue grinding until carbon disulfide (CS 2 ) was completely evaporated and then ground for 20 min.

[0090] (2) The ground sample in step (1) was transferred to a stainless steel reactor, heated to 155°C for 12 h, and then naturally cooled to room temperature.

[0091] (3) Grinding the sample obtained after cooling in step (2) again with an agate mortar, collecting the obtained powder sample, and obtaining a composite material CoVS / S (i.e., a composite sulfur positive electrode material) of double transition metal selenide core-shell hollow nanospheres CoVS and sulfur having a hollow core-shell structure.

[0092] 2. Preparation method of positive electrode sheet of lithium-sulfur battery:

[0093] (1) 0.07 g of CoVS / S obtained in step 1, 0.02 g of acetylene black and 0.01 g of binder (PVDF) were ground in an agate mortar for 30 min, and then 0.25 mL of N-methylpyrrolidone (NMP) was added to grind into a slurry.

[0094] (2) Take 0.3 mL of the slurry prepared in step (1) and spread it evenly on a 50 cm 2 The resulting mixture was placed on an aluminum foil and vacuum dried at 60°C for 12 h to obtain a positive electrode sheet for a lithium-sulfur battery.

[0095] 3. Preparation method of lithium-sulfur battery:

[0096] (1) The positive electrode sheet of the lithium-sulfur battery obtained in step 2 is cut into a circular electrode sheet with a diameter of 14 mm, and a battery shell of model 2032 is selected to assemble the battery in a glove box filled with argon.

[0097] (2) After the battery assembled in step (1) was left to stand for 12 hours, the electrochemical performance was tested using a blue battery test system. The test results are shown in Figures 4-5 ; The assembled symmetrical cell was tested by CV to explore its catalytic performance on polysulfides. The results are shown in Figure 6 .

[0098] Figure 4 is the rate performance diagram; Figure 5 is the long cycle performance diagram; Figure 6 is the CV curve.

[0099] Comparative Example 2

[0100] 1. Preparation method of composite sulfur positive electrode material SuperP / S (i.e. lithium-sulfur battery positive electrode material):

[0101] The common carbon material SuperP is loaded with sulfur. The specific steps are as follows:

[0102] (1) SuperP and sublimed sulfur were ground in an agate mortar at a mass ratio of 1:3 for 20 min, and then carbon disulfide (CS 2 ) to immerse the sample and continue grinding until carbon disulfide (CS 2 ) is completely evaporated and then ground for 20 minutes.

[0103] (2) The ground sample in step (1) was transferred to a stainless steel reactor, heated to 155°C for 12 h, and then naturally cooled to room temperature.

[0104] (3) Grind the sample obtained after cooling in step (2) again with an agate mortar, collect the obtained powder sample, and obtain a composite material of SuperP and sulfur, SuperP / S (i.e., composite sulfur positive electrode material).

[0105] 2. Preparation method of positive electrode sheet of lithium-sulfur battery:

[0106] (1) 0.07 g of SuperP / S obtained in step 1, 0.02 g of acetylene black and 0.01 g of binder (PVDF) were ground in an agate mortar for 30 min, and then 0.25 mL of N-methylpyrrolidone (NMP) was added to grind into a slurry.

[0107] (2) Take 0.3 mL of the slurry prepared in step (1) and apply it evenly on a 50 cm 2 The resulting mixture was placed on an aluminum foil and vacuum dried at 60°C for 12 h to obtain a positive electrode sheet for a lithium-sulfur battery.

[0108] 3. Preparation method of lithium-sulfur battery:

[0109] (1) The positive electrode sheet of the lithium-sulfur battery obtained in step 2 is cut into a circular electrode sheet with a diameter of 14 mm, and a battery shell of model 2032 is selected to assemble the battery in a glove box filled with argon.

[0110] (2) After the battery assembled in step (1) was left to stand for 12 hours, the electrochemical performance was tested using a blue battery test system. The test results are shown in Figures 4-5 ; The assembled symmetrical cell was tested by CV to explore its catalytic performance on polysulfides. The results are shown in Figure 6 .

[0111] Figure 4 is the rate performance diagram; Figure 5 is the long cycle performance diagram; Figure 6 is the CV curve.

[0112] from Figure 4 It can be seen that the rate performance of CoVSe / S prepared in Example 5 is significantly better than that of CoVS / S (prepared in Comparative Example 1) and the ordinary carbon material SuperP (prepared in Comparative Example 2).

[0113] from Figure 5 It can be seen that the long cycle performance of CoVSe / S prepared in Example 5 is significantly better than that of CoVS / S and ordinary carbon material Super P; at a rate of 1.0C and after 1400 cycles, its capacity decay rate per cycle is only 0.030%, which solves the problem of poor cycle stability of existing lithium-sulfur batteries and greatly extends the cycle life of lithium-sulfur batteries.

[0114] from Figure 6 It can be seen that the current density of the double transition metal selenide core-shell hollow nanospheres CoVSe with a hollow core-shell structure is significantly greater than that of the transition double metal sulfide hollow nanospheres CoVS with a core-shell structure, and has obvious redox peaks, while the ordinary carbon material Super P does not have it, indicating that the double transition metal selenide core-shell hollow nanospheres CoVSe with a hollow core-shell structure have an electrochemical catalytic effect on polysulfides, which can improve the redox conversion kinetics of polysulfides and improve the electrochemical performance of lithium-sulfur batteries.

[0115] Comparative Example 3

[0116] A method for preparing double transition metal selenide core-shell hollow nanospheres CoVSe with a hollow core-shell structure is consistent with the method in Example 1, except that glycerol is replaced by ethylene glycol.

[0117] (1) 0.5 g of Co(NO 3 ) 2 6H 2O was added into an appropriate amount of isopropanol, and a uniform solution was formed by ultrasonic and magnetic stirring at room temperature; then, 50 g of ethylene glycol was slowly added during the magnetic stirring, and after continuous magnetic stirring for 3 hours, it was transferred to a 100 mL high temperature and high pressure reactor, maintained at 150° C. for 10 hours, washed several times by centrifugation with ethanol, and vacuum dried at 80° C. for 12 hours to obtain a Co-ethylene glycol precursor with a particle size of 300 to 500 nm.

[0118] (2) Add 0.2 g of Co-ethylene glycol precursor to an appropriate amount of anhydrous ethanol, disperse it evenly by ultrasonication, and then add 0.2 g of NH 4 VO 3 , and then add an appropriate amount of ultrapure water, stir magnetically while ultrasonicating for 30 minutes. When the solution changes color, transfer it to a 100 mL high temperature and high pressure reactor, keep it at 150°C for 2 hours, filter and wash, and obtain the CoV precursor (double transition metal core-shell hollow nanosphere precursor) with a particle size of 300-500 nm.

[0119] (3) 0.6 g of selenium powder was placed at the front end of the magnetic boat, and 0.1 g of CoV precursor was placed at the end of the magnetic boat. The magnetic boat was placed in a high-temperature tube furnace for high-temperature calcination (heating rate of 5 °C / min, temperature of 450 °C, time of 2 h) to obtain double transition metal selenide core-shell hollow nanospheres CoVSe with a hollow core-shell structure, with a particle size of 300 to 500 nm.

[0120] In the double transition metal selenide core-shell hollow nanospheres CoVSe with a hollow core-shell structure prepared in this comparative example, the content of Co is 20 wt %, the content of V is 20 wt %, and the content of Se is 60 wt %.

[0121] The microscopic morphology of the double transition metal selenide core-shell hollow nanosphere CoVSe with a hollow core-shell structure prepared in this comparative example is shown in FIG. Figure 7 .

[0122] As can be seen from FIG. 7 , the difference between the CoVSe prepared in this comparative example and the CoVSe prepared in Example 1 is that the spherical shape is irregular in morphology, and the irregular morphology will lead to poor cycle stability when it is used as a battery electrode.

[0123] Comparative Example 4

[0124] A method for preparing double transition metal selenide core-shell hollow nanospheres CoVSe with a hollow core-shell structure is consistent with the method in Example 1, except that glycerol is replaced by oleic acid.

[0125] (1) 0.5 g of Co(NO 3 ) 2 6H 2O was added into an appropriate amount of ethylene glycol, and ultrasonic and magnetic stirring were performed at room temperature to form a uniform solution; then, 50 g of oleic acid was slowly added during the magnetic stirring, and the mixture was continuously magnetically stirred for 3 h, then transferred to a 100 mL high temperature and high pressure reactor, maintained at 150 ° C for 10 h, washed by centrifugation with ethanol for several times, and vacuum dried at 80 ° C for 12 h to obtain a Co-oleic acid precursor with a particle size of 300 to 500 nm.

[0126] (2) Add 0.2 g of Co-oleic acid precursor to an appropriate amount of anhydrous ethanol, disperse it evenly by ultrasonication, and then add 0.2 g of NH 4 VO 3 , and then add an appropriate amount of ultrapure water, stir magnetically while ultrasonicating for 30 minutes. When the solution changes color, transfer it to a 100 mL high temperature and high pressure reactor, keep it at 150°C for 2 hours, filter and wash, and obtain the CoV precursor (double transition metal core-shell hollow nanosphere precursor) with a particle size of 300-500 nm.

[0127] (3) 0.6 g of selenium powder was placed at the front end of the magnetic boat, and 0.1 g of CoV precursor was placed at the end of the magnetic boat. The magnetic boat was placed in a high-temperature tube furnace for high-temperature calcination (heating rate of 5 °C / min, temperature of 450 °C, time of 2 h) to obtain double transition metal selenide core-shell hollow nanospheres CoVSe with a hollow core-shell structure, with a particle size of 300 to 500 nm.

[0128] In the double transition metal selenide core-shell hollow nanospheres CoVSe with a hollow core-shell structure prepared in this comparative example, the content of Co is 20 wt %, the content of V is 20 wt %, and the content of Se is 60 wt %.

[0129] The microscopic morphology of the double transition metal selenide core-shell hollow nanosphere CoVSe with a hollow core-shell structure prepared in this comparative example is shown in FIG. Figure 8 ,

[0130] from Figure 8 It can be seen that the difference between the CoVSe prepared in this comparative example and the CoVSe prepared in Example 1 is that the inner wall of the spherical core-shell is thicker. Due to the high viscosity and density of oleic acid, the hollow spheres are severely adhered to each other, resulting in poor cycle stability when used as a battery electrode.

[0131] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing double transition metal selenide core-shell hollow nanospheres for lithium-sulfur battery positive electrode host materials, characterized in that: The following steps are involved: (1) mixing a solution of a transition metal salt and glycerol, heating and reacting the mixture to obtain a transition metal-glycerol precursor; (2) adding another transition metal salt to the solution of the transition metal-glycerol precursor, heating and reacting, to obtain a double transition metal core-shell hollow nanosphere precursor; (3) calcining the double transition metal core-shell hollow nanosphere precursor and selenium powder at high temperature to obtain the double transition metal selenide core-shell hollow nanosphere.

2. The preparation method according to claim 1, characterized in that: In step (1) and step (2), the transition metal salt is selected from two of iron salts, nickel salts, cobalt salts, vanadium salts and manganese salts.

3. The preparation method according to claim 1, characterized in that: In step (1), the heating reaction temperature is 150-200° C. and the time is 10-30 hours; And / or, the mass ratio of the transition metal salt to glycerol is 1:(100-200).

4. The preparation method according to claim 1, characterized in that: In step (2), the heating reaction temperature is 100-150° C. and the time is 2-6 hours.

5. The preparation method according to claim 1, characterized in that: In step (3), the heating rate of the high temperature calcination is 2 to 10°C / min, the temperature is 300 to 500°C, and the time is 2 to 6 hours.

6. The preparation method according to claim 1, characterized in that: The contents of the two transition metals in the double transition metal selenide core-shell hollow nanospheres are independently 10-30 wt %, and the content of selenium is 40-80 wt %.

7. Double transition metal selenide core-shell hollow nanospheres prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the double transition metal selenide core-shell hollow nanospheres according to claim 7 as a positive electrode host material for a lithium-sulfur battery.

9. A composite sulfur positive electrode material, characterized in that: The raw materials include the double transition metal selenide core-shell hollow nanospheres as described in claim 7 and elemental sulfur.

10. A method for preparing the composite sulfur positive electrode material according to claim 9, characterized in that: The following steps are involved: The double transition metal selenide core-shell hollow nanospheres are compounded with elemental sulfur to obtain the composite sulfur positive electrode material.

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