CN109920985B - Lithium-sulfur battery positive electrode material and preparation method thereof - Google Patents
Lithium-sulfur battery positive electrode material and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a lithium-sulfur battery positive electrode material, a preparation method thereof and application of the lithium-sulfur battery positive electrode material in preparation of a lithium-sulfur battery. The anode material comprises four parts, namely a nano silicon dioxide mesoporous sphere, a functional group-rich carbon coating layer, three-dimensional reticular reduced graphene oxide and sublimed sulfur. The preparation method adopts a self-assembly mode to obtain nano silicon dioxide mesoporous spheres with different sizes; melting the sublimed sulfur in the nano silicon dioxide mesoporous spheres to form a compound; the compound is reduced with graphene oxide to obtain the lithium-sulfur battery anode material. Coating a positive electrode material, a conductive agent and an adhesive on a current collector according to a mass ratio to obtain a high-performance lithium-sulfur battery positive electrode, wherein the high-performance lithium-sulfur battery positive electrode can greatly improve the cycle stability, the rate capability and the coulombic efficiency of an assembled lithium-sulfur battery; the charge-discharge performance is good, the load capacity is high, the cycle life is long, and the specific capacity is high; the requirements of the battery market on the batteries with long service life and high specific capacity are met.
Description
Technical Field
The invention relates to a battery anode material, in particular to an anode material for a lithium-sulfur battery and a preparation method thereof, belonging to the field of battery anode materials.
Background
The lithium-sulfur battery is a lithium battery with sulfur as the positive electrode and metal lithium as the negative electrode. The theoretical specific capacity of the sulfur as the positive electrode of the lithium ion battery reaches 1675mAh/g, which is an order of magnitude larger than the specific capacity of the positive electrode material of the current commercial lithium iron phosphate, lithium cobaltate and nickel cobalt manganese lithium ion battery. In addition, the elemental sulfur has rich source, low price and environmental protection, so that the lithium-sulfur battery has good commercial value. The theoretical specific capacity of the metallic lithium reaches 3861 mAh/g. The average discharge voltage of the lithium-sulfur battery is 2.15V, and therefore, the theoretical energy density of the lithium-sulfur battery is 2600Wh/Kg, which is 5 times the theoretical energy density of the lithium-ion battery, and for this reason, the lithium-sulfur battery is considered as the most potential next-generation secondary battery system. However, polysulfide generated by elemental sulfur in the electrochemical cycle process is easily dissolved in the conventional electrolyte and separated from the positive host material, and sulfur is converted into dilithium sulfide after the discharge is finished, so that the volume expansion is 8 times, and the practical application of the polysulfide is seriously influenced; therefore, it is very necessary to develop a positive electrode material for a lithium-sulfur battery having more excellent conductivity.
Disclosure of Invention
Aiming at the problems and the defects involved in the background technology, the invention aims to provide a lithium-sulfur battery positive electrode material and a preparation method thereof; the lithium-sulfur battery positive electrode material prepared by the method has excellent conductivity, and the cycle stability, rate capability and coulombic efficiency of the lithium-sulfur battery prepared by applying the lithium-sulfur battery positive electrode material to the lithium-sulfur battery positive electrode can be greatly improved; has higher practical application value.
To achieve the above object, the present invention is achieved by the following means.
The invention provides a lithium-sulfur battery positive electrode material and a preparation method thereof, and the basic idea is as follows: the invention provides a method for combining a physical barrier of a core-shell structure with a host material rich functional group to restrain polysulfide generated in a discharge process, so that the cycle life of the polysulfide is prolonged; the carbon coating and the graphene oxide synergistic effect are utilized to improve the conductivity of the lithium-sulfur battery anode material, so that the rate capability of the lithium-sulfur battery anode material is improved; the conversion of lithium polysulfide is promoted by adding transition metal elements, thereby improving the coulombic efficiency of the lithium polysulfide. The realization method comprises the following steps: the ethyl orthosilicate reacts in reaction mother liquor containing hexadecyl trimethyl ammonium bromide with different concentrations to form nano silicon dioxide mesoporous spheres with different sizes by adopting a self-assembly mode; the carbon layer coated by the nano silicon dioxide mesoporous spheres and the corresponding functional groups are accessed by utilizing the pyrolysis reaction of a carbon source under the atmosphere condition; melting sublimed sulfur in carbon-coated silicon dioxide mesoporous spheres according to a designed mass ratio to generate a carbon-coated silicon dioxide mesoporous sphere/sulfur composite material; after the composite material is compounded with graphene oxide, silicon dioxide mesoporous spheres are uniformly distributed in reduced graphene oxide nanosheets to form a three-dimensional reticular carbon-coated silicon dioxide mesoporous sphere/graphene/sulfur positive electrode material. The lithium polysulfide generated by the reaction of sulfur and lithium in the discharge process of the lithium-sulfur battery positive electrode material is bound by the method of combining the core-shell structure of the silica mesoporous spheres with the host material rich functional groups, so that the cycle life of the lithium-sulfur battery assembled by the prepared positive electrode material can be prolonged; the conductivity of the positive electrode material is improved by utilizing the synergistic effect of the carbon coating and the graphene, so that the rate capability of the lithium-sulfur battery can be improved; the transition metal element added into the cathode material can promote the conversion of lithium polysulfide, so that the coulombic efficiency of the lithium-sulfur battery can be improved.
The preparation method of the lithium-sulfur battery anode material is characterized in that sublimed sulfur is fused into a nano silicon dioxide mesoporous sphere according to a designed mass ratio to form a compound; mixing the composite and graphene oxide according to a designed mass ratio, and reducing to obtain a lithium-sulfur battery positive electrode material; the method specifically comprises the following steps:
(1) preparation of graphene oxide
Dissolving 9 g of potassium persulfate and 9 g of phosphorus pentoxide in 15ml of concentrated sulfuric acid, adding 11 g of graphite powder, uniformly stirring, and then preserving heat at 80 ℃ for 24 hours to obtain pre-oxidized graphite slurry;
filtering the obtained pre-oxidized graphite slurry, washing the slurry by using deionized water, and then placing the slurry in an oven at the temperature of 80 ℃ for baking for 24 hours to obtain pre-oxidized graphite powder;
thirdly, adding 3 g of sodium nitrate into 255ml of concentrated sulfuric acid, completely adding the obtained pre-oxidized graphite powder after the sodium nitrate is completely dissolved, placing the whole system in a water bath kettle below 10 ℃, and carrying out the next operation after the temperature of the whole system is stabilized below 10 ℃;
fourthly, weighing 18 grams of potassium permanganate, and adding the potassium permanganate into the system for 20 times in each time of 0.9 gram, wherein the temperature of the system is always kept below 10 ℃; sealing after the addition is finished, preserving the heat for 3 hours at the temperature, transferring the mixture into a water bath kettle at 55 ℃, and intensively stirring for 5 hours to form a paste substance;
fifthly, centrifugally cleaning the obtained pasty substance by using a hydrochloric acid solution, and centrifugally cleaning the pasty substance by using deionized water to obtain graphene oxide;
(2) preparation of nano silicon dioxide mesoporous spheres
Firstly, 0.1-0.8 g of hexadecyl trimethyl ammonium bromide is put into 50ml of deionized water and fully stirred for 0.6 hour to prepare a reaction mother solution; placing the prepared reaction mother liquor in a thermostat with the temperature of 60-110 ℃ and preserving heat for 10-48 hours;
② taking out reaction mother liquor and adding tetraethoxysilane into the reaction mother liquor, wherein the proportion of the added tetraethoxysilane to the reaction mother liquor is as follows: adding 0.08-0.64 g of reaction mother liquor into every 1ml of tetraethoxysilane, magnetically stirring for 1-10 hours at normal temperature, and reacting for 10-48 hours after sealing to generate a reactant;
thirdly, carrying out suction filtration and cleaning on the generated reactant to form a paste, dispersing the paste product in 50-150 ml of deionized water, and carrying out magnetic stirring for 2 hours to form a nano silicon dioxide mesoporous sphere dispersion liquid;
(3) coating the mesoporous carbon spheres of the nano silicon dioxide and introducing corresponding functional groups
Adding 0.4 g of carbon source into the nano silicon dioxide mesoporous sphere dispersion liquid, and simultaneously adding 0.01-0.35 g of functional group-rich substance according to the introduced functional group to form a mixed liquid;
adding transition metal acetate into the mixed solution according to a molar ratio, wherein the ratio of the mixed solution to the transition metal acetate is as follows: 1: 3; then ultrasonically cleaning for 0.2-2.5 hours, uniformly mixing, and drying in an oven at 60-110 ℃ to obtain a mixture of the carbon-coated silicon dioxide mesoporous spheres rich in functional groups and transition metal acetate;
thirdly, annealing the mixture for 5 to 10 hours at 850 to 1000 ℃ under the vacuum atmosphere condition, and naturally cooling to room temperature to obtain carbon-coated nano silicon dioxide mesoporous spheres;
(4) preparation of lithium-sulfur battery cathode material
Uniformly mixing the carbon-coated nano silicon dioxide mesoporous spheres and sublimed sulfur according to the mass ratio of 1: 1-1: 6, and then preserving heat for 2-20 hours at the temperature of 150-250 ℃ under the atmosphere condition to obtain carbon-coated nano silicon dioxide mesoporous spheres/sulfur compounds;
dispersing 0.3 g of graphene oxide prepared in the step (1) and 1g of carbon-coated nano silicon dioxide mesoporous spheres/sulfur compound in 80-300 ml of deionized water, and stirring for 0.2-2 hours by using a magnetic stirrer to obtain a graphene oxide mixed solution;
thirdly, placing the obtained graphene oxide mixed solution into a drying oven at the temperature of 60-110 ℃, and preserving heat for 1-10 hours to obtain a mixed product; and (3) filtering the obtained mixed product to paste, washing with deionized water, freeze-drying for 1-15 hours to obtain the lithium-sulfur battery positive electrode material, and grinding the positive electrode material for later use.
Furthermore, the diameter of the nano silicon dioxide mesoporous sphere prepared in the step (2) is between 30 and 200 nanometers.
Further, the proportion of the added tetraethoxysilane to the reaction mother liquor in the step (2) is as follows: 0.16 g of reaction mother liquor is added per 1ml of tetraethoxysilane.
Furthermore, the concentration of the nano-silica mesoporous sphere dispersion liquid in the step (2) is 0.1mg/ml to 10 mg/ml.
Further, in the step (3), 0.4 g of carbon source is added into the nano-silica mesoporous sphere dispersion liquid, wherein the carbon source is one of gelatin and glucose; the addition amount is 0.4 g of carbon source added to each 1g of nano-silica mesoporous spheres.
Further, the transition metal acetate added in step (3) is one of nickel acetate, cobalt acetate, manganese acetate, aluminum acetate, or iron acetate.
Further, the functional group-rich substance in step (3) is one selected from glutamic acid, glycine, aspartic acid, or sodium fluoride.
Further, in the step (3), the mixture is annealed under the atmosphere condition, wherein the atmosphere is argon, argon-hydrogen mixed gas, ammonia gas or nitrogen gas, and the like, and the ratio of argon-hydrogen mixed gas is 95: 5.
further, the corresponding functional group in step (3) refers to a fluoride ion, or a carboxyl group, or a hydroxyl functional group.
The lithium-sulfur battery positive electrode material prepared by the preparation method comprises four parts, namely nano silicon dioxide mesoporous spheres, a functional group-rich carbon coating layer, three-dimensional reticular reduced graphene oxide and sublimed sulfur.
The invention also provides an application of the cathode material in the preparation of a lithium-sulfur battery.
The application process of the lithium-sulfur battery positive electrode material is generally as follows: grinding the prepared lithium-sulfur battery positive electrode material, and preparing the ground lithium-sulfur battery positive electrode material into slurry with acetylene black serving as a conductive agent and PVDF serving as an adhesive according to the mass ratio of 8:1: 1; the slurry is evenly dispersed and then evenly coated on a battery electrode aluminum foil, and the sulfur loading per unit area is 3.4mg/cm2And drying in an oven at the temperature of 60-110 ℃ to obtain the anode for assembling the lithium-sulfur battery, and assembling the button lithium-sulfur battery by using the anode of the battery.
The lithium-sulfur battery positive electrode material provided by the invention comprises four parts, namely nano silicon dioxide mesoporous spheres, a functional group-rich carbon coating layer, three-dimensional reticular reduced graphene oxide and sublimed sulfur. The positive electrode material is formed by binding lithium polysulfide generated by the reaction of sulfur and lithium in the positive electrode material of the lithium-sulfur battery in the discharge process through a method of combining a core-shell structure of a silica mesoporous sphere with a host material rich functional group, and the host material has sufficient internal space to bear S8To Li2SX(X is 1-8) volume expansion in the change process, and the carbonized gelatin and other organic matters (such as cetyl trimethyl ammonium bromide and the like) added in the preparation process can form a multi-layer carbonized network, so that the positive electrode material of the lithium-sulfur battery has excellent conductive performance. The three-dimensional graphene can provide a conductive network, can keep the stability of the whole structure, and effectively improves the long-cycle stability and the rate characteristic of the lithium-sulfur battery. The raw materials used by each part of the invention are low in price, and the synthesis route is suitable for large-scale preparation, thereby providing an effective solution for the commercial application of the lithium-sulfur battery anode material.
Compared with the prior art, the invention has the following beneficial technical effects:
1. the invention provides a novel preparation method of a composite material for a lithium-sulfur battery anode, which has the advantages of easily obtained raw materials, relatively low price and low cost; the preparation process is simple, the period is short, and the method is suitable for batch production and commercial application.
2. The lithium-sulfur battery positive electrode material prepared by the invention comprises four parts, namely nano silicon dioxide mesoporous spheres, a functional group-rich carbon coating layer, three-dimensional reticular reduced graphene oxide and sublimed sulfur; preparing the positive electrode material, conductive agent acetylene black and adhesive PVDF into slurry according to the mass ratio; the slurry is uniformly coated on a current collector aluminum foil and dried to obtain the high-performance positive electrode for assembling the lithium-sulfur battery.
3. The lithium-sulfur battery manufactured by taking the prepared lithium-sulfur battery positive electrode material as the positive electrode and the commercial reason piece as the negative electrode can greatly improve the cycle stability, the rate capability and the coulombic efficiency; the charge-discharge performance is good, and the charge-discharge performance has the advantages of high load capacity, long cycle life and high specific capacity; the requirements of the battery market on the batteries with long service life and high specific capacity are met; has higher practical application value.
Drawings
Fig. 1 is a graph showing the results of specific discharge capacity and coulombic efficiency tests at 1C current for a lithium-sulfur battery prepared in example 1 according to the present invention;
fig. 2 is a graph of the specific discharge capacity and coulombic efficiency test results of the lithium-sulfur battery prepared in example 2 at a current of 1C;
fig. 3 is a graph showing the specific discharge capacity and coulombic efficiency test results of the lithium-sulfur battery prepared in example 3 at 1C current according to the present invention;
fig. 4 is a graph of the specific discharge capacity at 1C current and the coulombic efficiency test result of the lithium-sulfur battery prepared in example 4 according to the present invention;
fig. 5 is a graph of the specific discharge capacity at 1C current and coulombic efficiency test results of the lithium-sulfur battery prepared in example 5 according to the present invention;
FIG. 6 is a graph showing the results of testing specific discharge capacity at 1C current of the lithium-sulfur battery of the present invention prepared by using comparative example 1;
FIG. 7 is a graph showing the results of testing specific discharge capacity at 1C current of the lithium-sulfur battery of the present invention prepared by comparative example 2;
fig. 8 is a graph showing the results of a specific discharge capacity test at a current of 1C for a lithium-sulfur battery according to the present invention prepared using comparative example 3.
Detailed Description
The lithium-sulfur battery positive electrode material, the preparation method thereof and the application thereof in the preparation of a lithium-sulfur battery are further described in detail by the following embodiments in combination with the accompanying drawings; the exemplary embodiments of the present invention and the description thereof are provided for explaining the present invention and do not constitute any limitation to the present invention.
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
In each of the examples described below, the materials were purchased from Chengdu Chang Fermentation glass, Inc.
In the following examples, the preparation method of the graphene oxide is as follows:
dissolving 9 g of potassium persulfate and 9 g of phosphorus pentoxide in 15ml of concentrated sulfuric acid, adding 11 g of graphite powder, uniformly stirring, and then preserving heat at 80 ℃ for 24 hours to obtain pre-oxidized graphite slurry;
filtering the obtained pre-oxidized graphite slurry, washing the slurry by using deionized water, and then placing the slurry in an oven at the temperature of 80 ℃ for baking for 24 hours to obtain pre-oxidized graphite powder;
thirdly, adding 3 g of sodium nitrate into 255ml of concentrated sulfuric acid, completely adding the obtained pre-oxidized graphite powder after the sodium nitrate is completely dissolved, placing the whole system in a water bath kettle below 10 ℃, and carrying out the next operation after the temperature of the whole system is stabilized below 10 ℃;
weighing 18 g of potassium permanganate, and adding the potassium permanganate into the system for 20 times in each time of 0.9 g, wherein the temperature of the system is always kept below 10 ℃; sealing after the addition is finished, preserving the heat for 3 hours at the temperature, transferring the mixture into a water bath kettle at 55 ℃, and intensively stirring for 5 hours to form a paste substance;
fifthly, centrifugally cleaning the obtained pasty substance with a hydrochloric acid solution, and centrifugally cleaning with deionized water to obtain the graphene oxide.
Example 1
Taking 0.16 g of hexadecyl trimethyl ammonium bromide, putting the hexadecyl trimethyl ammonium bromide into 50ml of deionized water, fully stirring for 0.6 hour to prepare reaction mother liquor, and putting the prepared reaction mother liquor into a thermostat at the temperature of 80 ℃ for heat preservation for 24 hours; taking out reaction mother liquor, and adding tetraethoxysilane into the reaction mother liquor, wherein the proportion of tetraethoxysilane to the mother liquor is as follows: adding 0.3 g of reaction mother liquor into every 1ml of tetraethoxysilane, magnetically stirring for 5 hours at normal temperature, sealing and reacting for 24 hours, filtering the generated reactant after the reaction is finished, and alternately cleaning the reactant with absolute ethyl alcohol and deionized water for at least three times to obtain paste; dispersing the paste product into 80ml of deionized water, and magnetically stirring for 2 hours; to form a nano silicon dioxide mesoporous sphere dispersion liquid with the concentration of 0.1 mg/ml.
Weighing 0.4 g of gelatin, placing the gelatin in 100ml of absolute ethyl alcohol, completely dissolving the gelatin, and pouring the gelatin into the nano silicon dioxide mesoporous sphere dispersion liquid; simultaneously weighing 0.3 g of manganese acetate and 0.01g of glutamic acid, respectively adding the manganese acetate and the glutamic acid into the nano silicon dioxide mesoporous sphere dispersion liquid, and then carrying out ultrasonic cleaning for 1 hour; uniformly mixing, and drying in an oven at 80 ℃ to obtain a mixture of the carbon-coated silicon dioxide mesoporous spheres rich in functional groups and manganese acetate; and placing the mixture in a vacuum tube type atmosphere furnace for annealing treatment under the condition of argon atmosphere, keeping the annealing temperature at 850 ℃ for 10 hours, raising the temperature at 5 ℃/min, and naturally cooling to room temperature after reaction to obtain the carbon-coated nano silicon dioxide mesoporous spheres.
Mixing carbon-coated nano silicon dioxide mesoporous spheres and sublimed sulfur according to the mass ratio of 1:1, fully grinding and uniformly mixing, and then preserving heat for 20 hours at 150 ℃ to form a carbon-coated nano silicon dioxide mesoporous sphere/sulfur compound; dispersing 0.3 g of prepared graphene oxide and 1g of carbon-coated nano silicon dioxide mesoporous spheres/sulfur compound in 300ml of deionized water, stirring for 1 hour by using a magnetic stirrer to prepare graphene oxide mixed liquor with the concentration of 1mg/ml, putting the graphene oxide mixed liquor into a 60 ℃ oven, and preserving heat for 1 hour to obtain a mixed product; and (3) filtering the mixed product to paste, washing the paste with deionized water for at least three times, and freeze-drying the paste for 1 hour to form the three-dimensional network reduced graphene oxide supported carbon-coated nano silicon dioxide mesoporous sphere/sulfur cathode material with rich functional groups.
Grinding the prepared cathode material, mixing with acetylene black and PVDF according to a mass ratio of 8:1:1, preparing into slurry; uniformly dispersed in NMP, and uniformly coated on aluminum foil of battery electrode, wherein the sulfur loading per unit area is about 3.4mg/cm2Drying the lithium-sulfur battery in an oven at 80 ℃ for 5 hours to obtain a positive electrode for assembling the lithium-sulfur battery; and assembling the dried cut pieces into a 2032 button cell. The specific capacity of the test result reaches 1410mAh/g under the condition of 0.1C multiplying power charging and discharging, and 0.2C reaches 1280 mAh/g; the first circle of discharge under 1C reaches 1100mAh/g, the long circulation is 100 circles 823mAh/g, and 200 circles 729 mAh/g. As shown in fig. 1.
Example 2
Taking 0.1 g of hexadecyl trimethyl ammonium bromide, putting the hexadecyl trimethyl ammonium bromide into 50ml of deionized water, stirring for 0.6 hour to prepare reaction mother liquor, and putting the prepared reaction mother liquor into a thermostat at 60 ℃ for heat preservation for 48 hours; taking out reaction mother liquor, and adding tetraethoxysilane into the reaction mother liquor, wherein the proportion of tetraethoxysilane to the reaction mother liquor is as follows: adding 0.08 g of tetraethoxysilane into every 1ml of tetraethoxysilane, magnetically stirring for 1 hour at normal temperature, sealing and reacting for 10 hours to generate a reactant after the reaction is finished; carrying out suction filtration on the generated reactant, and alternately cleaning the reactant for at least three times by using absolute ethyl alcohol and deionized water to form a paste; dispersing the paste product into 50ml of deionized water, and magnetically stirring for 2 hours; forming nano silicon dioxide mesoporous sphere dispersion liquid; the concentration was 10 mg/ml.
Weighing 0.4 g of glucose in 100ml of absolute ethyl alcohol, and pouring the glucose into the nano silicon dioxide mesoporous sphere dispersion liquid after completely dissolving; simultaneously weighing 0.01g of nickel acetate and 0.35 g of glycine, respectively adding the nickel acetate and the glycine into the nano silicon dioxide mesoporous sphere dispersion liquid, and then carrying out ultrasonic cleaning for 0.2 hour; uniformly mixing, and drying in a 60 ℃ drying oven to obtain a mixture of the carbon-coated silicon dioxide mesoporous spheres rich in functional groups and nickel acetate; and (3) annealing the mixture in a vacuum tube type atmosphere furnace under the condition of ammonia atmosphere, keeping the annealing temperature at 1000 ℃ for 5 hours, raising the temperature at 5 ℃/min, and naturally cooling to room temperature after reaction to obtain the carbon-coated nano silicon dioxide mesoporous spheres.
Mixing carbon-coated nano silicon dioxide mesoporous spheres and sublimed sulfur according to the mass ratio of 1:3, fully grinding and mixing, and then preserving the heat for 16 hours at 170 ℃ to form the carbon-coated nano silicon dioxide mesoporous sphere/sulfur compound. Dispersing 0.3 g of the prepared graphene oxide and 1g of the carbon-coated nano silicon dioxide mesoporous spheres/sulfur compound in 80ml of deionized water, stirring for 0.2 h by using a magnetic stirrer to prepare a graphene oxide mixed solution with the concentration of 1mg/ml, putting the graphene oxide mixed solution into an oven at 80 ℃, and preserving heat for 10 h to obtain a mixed product; and (3) filtering the mixed product into paste, washing the paste with deionized water for at least three times, filtering the paste into paste, and freeze-drying the paste for 15 hours to form the three-dimensional network reduced graphene oxide supported carbon-coated nano silicon dioxide mesoporous sphere/sulfur cathode material.
Grinding the prepared cathode material, mixing with acetylene black and PVDF according to a mass ratio of 8:1:1, uniformly dispersed in NMP and uniformly coated on a battery-grade aluminum foil, and the sulfur loading per unit area is about 3.4mg/cm2Drying the lithium-sulfur battery in an oven at 80 ℃ for 5 hours to obtain a positive electrode for assembling the lithium-sulfur battery; and assembling the dried cut pieces into a 2032 button cell. The test result shows that the specific capacity reaches 1426mAh/g under the condition of 0.1C multiplying power charging and discharging, and the specific capacity reaches 1300mAh/g under the condition of 0.2C multiplying power charging and discharging. The first circle of the discharge reaches 1080mAh/g under 1C, the long cycle of 100 circles is 811mAh/g, and the long cycle of 200 circles is 702mAh/g, as shown in FIG. 2.
Example 3
Taking 0.25 g of hexadecyl trimethyl ammonium bromide, putting the hexadecyl trimethyl ammonium bromide into 50ml of deionized water, stirring for 0.6 hour to prepare reaction mother liquor, and putting the prepared reaction mother liquor into a thermostat with the temperature of 90 ℃ for heat preservation for 30 hours; taking out the reaction mother liquor, and adding tetraethoxysilane into the reaction mother liquor, wherein the proportion of tetraethoxysilane to the reaction mother liquor is as follows: adding 0.64 g of reaction mother liquor into every 1ml of tetraethoxysilane, magnetically stirring for 10 hours at normal temperature, sealing and reacting for 38 hours to generate a reactant after the reaction is finished; carrying out suction filtration on the generated reactant, and alternately cleaning the reactant for at least three times by using absolute ethyl alcohol and deionized water to form a paste; dispersing the paste product into 150ml of deionized water, and magnetically stirring for 2 hours; forming the nano silicon dioxide mesoporous sphere dispersion liquid. The concentration is 8mg/ml.
Weighing 0.4 g of glucose in 100ml of absolute ethyl alcohol, and pouring the glucose into the nano silicon dioxide mesoporous sphere dispersion liquid after completely dissolving; simultaneously weighing 0.3 g of cobalt acetate and 0.35 g of aspartic acid, respectively adding the cobalt acetate and the aspartic acid into the nano silicon dioxide mesoporous sphere dispersion liquid, and then carrying out ultrasonic cleaning for 2.5 hours; drying in a drying oven at 110 ℃ to obtain a mixture of the carbon-coated silicon dioxide mesoporous spheres rich in functional groups and cobalt acetate; and placing the mixture in a vacuum tube type atmosphere furnace for annealing treatment under the condition of argon atmosphere, keeping the annealing temperature of 900 ℃ for 10 hours, raising the temperature at the speed of 5 ℃/min, and naturally cooling to room temperature after reaction to obtain the carbon-coated nano silicon dioxide mesoporous spheres.
Mixing carbon-coated nano silicon dioxide mesoporous spheres and sublimed sulfur according to the mass ratio of 1: 4, fully grinding and mixing, and then preserving heat for 10 hours at 190 ℃ to form a carbon-coated nano silicon dioxide mesoporous sphere/sulfur compound; dispersing 0.3 g of prepared graphene oxide and 1g of carbon-coated nano silicon dioxide mesoporous spheres in 200ml of deionized water, stirring for 2 hours by using a magnetic stirrer to prepare graphene oxide mixed liquor with the concentration of 1mg/ml, putting the graphene oxide mixed liquor into a 60 ℃ oven, and preserving heat for 10 hours to obtain a mixed product; and (3) filtering the mixture into paste, washing the paste with deionized water for at least three times, and freeze-drying the paste for 15 hours to form the three-dimensional network reduced graphene oxide supported carbon-coated nano silicon dioxide mesoporous spheres/sulfur cathode material.
Grinding the prepared cathode material, mixing with acetylene black and PVDF according to a mass ratio of 8:1:1, uniformly dispersed in NMP and uniformly coated on a battery-grade aluminum foil, and the sulfur loading per unit area is about 3.4mg/cm2Drying the lithium-sulfur battery in an oven at 80 ℃ for 5 hours to obtain a positive electrode for assembling the lithium-sulfur battery; and assembling the dried cut pieces into a 2032 button cell. The test result shows that the specific capacity reaches 1425mAh/g under the condition of 0.1C multiplying power charging and discharging, and the specific capacity reaches 1296mAh/g under the condition of 0.2C multiplying power charging and discharging. The discharge of the first circle under 1C reaches 1096mAh/g, the discharge of the long circulation of 100 circles is 812mAh/g, and the discharge of 200 circles is 715 mAh/g; as shown in fig. 3.
Example 4
Taking 0.65 g of hexadecyl trimethyl ammonium bromide, putting the hexadecyl trimethyl ammonium bromide into 50ml of deionized water, stirring for 0.6 hour to prepare reaction mother liquor, and putting the prepared reaction mother liquor into a thermostat with the temperature of 100 ℃ for heat preservation for 40 hours; taking out reaction mother liquor, and adding tetraethoxysilane into the reaction mother liquor, wherein the proportion of tetraethoxysilane to the reaction mother liquor is as follows: adding 0.50 g of reaction mother liquor into every 1ml of tetraethoxysilane, magnetically stirring for 8 hours at normal temperature, sealing and reacting for 42 hours to generate a reactant after the reaction is finished; carrying out suction filtration on the generated reactant, and alternately cleaning the reactant for at least three times by using absolute ethyl alcohol and deionized water to form a paste; dispersing the paste product into 100ml of deionized water, and magnetically stirring for 2 hours; to form nano silicon dioxide mesoporous sphere dispersion liquid with the concentration of 5 mg/ml.
Weighing 0.4 g of gelatin in 100ml of absolute ethyl alcohol, and pouring the gelatin into the nano silicon dioxide mesoporous sphere dispersion liquid after completely dissolving; simultaneously weighing 0.2 g of ferric acetate and 0.15 g of sodium fluoride, respectively adding the ferric acetate and the sodium fluoride into the nano silicon dioxide mesoporous sphere dispersion liquid, and then carrying out ultrasonic cleaning for 1.5 hours; drying in an oven at 80 ℃ to obtain a mixture of the carbon-coated silica mesoporous spheres rich in functional groups and ferric acetate; and placing the mixture in a vacuum tube type atmosphere furnace for annealing under the atmosphere of argon-hydrogen mixed gas, wherein the argon-hydrogen mixed gas ratio is 95: 5; and (3) keeping the annealing temperature of 900 ℃ for 7 hours, raising the temperature at the speed of 5 ℃/min, and naturally cooling to room temperature after reaction to obtain the carbon-coated nano silicon dioxide mesoporous spheres.
Mixing carbon-coated nano silicon dioxide mesoporous spheres and sublimed sulfur according to the mass ratio of 1: 5, fully grinding and mixing, and then preserving heat for 16 hours at 190 ℃ to form the carbon-coated nano silicon dioxide mesoporous sphere/sulfur compound. Dispersing 0.3 g of prepared graphene oxide and 1g of carbon-coated nano silicon dioxide mesoporous spheres/sulfur compound in 300ml of deionized water, stirring for 1.5 hours by using a magnetic stirrer to prepare a graphene oxide mixed solution with the concentration of 1mg/ml, putting the graphene oxide mixed solution into a 70 ℃ oven, and preserving heat for 9 hours to obtain a mixed product; and (3) filtering the mixed product to paste, washing the paste with deionized water for at least three times, and freeze-drying the paste for 10 hours to form the three-dimensional network reduced graphene oxide supported carbon-coated nano silicon dioxide mesoporous sphere/sulfur cathode material with rich functional groups.
Grinding the prepared cathode material, mixing with acetylene black and PVDF according to a mass ratio of 8:1:1, uniformly dispersed in NMP and uniformly coated on a battery-grade aluminum foil, and the sulfur loading per unit area is about 3.4mg/cm2Drying the lithium-sulfur battery in an oven at 80 ℃ for 5 hours to obtain a positive electrode for assembling the lithium-sulfur battery; and assembling the dried cut pieces into a 2032 button cell. The test result shows that the specific capacity reaches 1431mAh/g under the charge-discharge multiplying power of 0.1C, and 0.2C reaches 1305 mAh/g.The discharge of the first circle under 1C reaches 1093mAh/g, the discharge of the first circle under long circulation of 100 circles is 809mAh/g, and the discharge of the first circle under long circulation of 200 circles is 719 mAh/g; as shown in fig. 4.
Example 5
Taking 0.8 g of hexadecyl trimethyl ammonium bromide, putting the hexadecyl trimethyl ammonium bromide into 50ml of deionized water, stirring for 0.6 hour to prepare reaction mother liquor, and putting the prepared reaction mother liquor into a thermostat with the temperature of 110 ℃ for heat preservation for 10 hours; taking out reaction mother liquor, and adding tetraethoxysilane into the reaction mother liquor, wherein the proportion of tetraethoxysilane to the reaction mother liquor is as follows: adding 0.64 g of reaction mother liquor into every 1ml of tetraethoxysilane, magnetically stirring for 10 hours at normal temperature, sealing and reacting for 48 hours to generate a reactant after the reaction is finished; carrying out suction filtration on the generated reactant, and alternately cleaning the reactant for at least three times by using absolute ethyl alcohol and deionized water to form a paste; dispersing the paste product into 150ml of deionized water, and stirring for 2 hours by using a magnetic stirrer; to form the nano silicon dioxide mesoporous sphere dispersion liquid with the concentration of 6 mg/ml.
Weighing 0.4 g of gelatin in 100ml of absolute ethyl alcohol, and pouring the gelatin into the nano silicon dioxide mesoporous sphere dispersion liquid after completely dissolving; weighing 0.3 g of aluminum acetate and 0.25 g of glutamic acid, respectively adding the aluminum acetate and the glutamic acid into the nano silicon dioxide mesoporous sphere dispersion liquid, and then carrying out ultrasonic cleaning for 1 hour; drying in an oven at 80 ℃ to obtain a mixture of the carbon-coated silica mesoporous spheres rich in functional groups and aluminum acetate; and (3) annealing the mixture in a vacuum tube furnace under the argon atmosphere condition, keeping the annealing temperature of 950 ℃ for 8 hours, raising the temperature at the speed of 5 ℃/min, and naturally cooling to room temperature after reaction to obtain the carbon-coated nano silicon dioxide mesoporous spheres.
Mixing carbon-coated nano silicon dioxide mesoporous spheres and sublimed sulfur according to the mass ratio of 1:6, fully grinding and mixing, and then preserving heat for 16 hours at 190 ℃ to form the carbon-coated nano silicon dioxide mesoporous sphere/sulfur compound. Dispersing 0.3 g of prepared graphene oxide and 1g of carbon-coated nano silicon dioxide mesoporous spheres/sulfur compound in 300ml of deionized water, stirring for 2 hours by using a magnetic stirrer to prepare graphene oxide mixed liquor with the concentration of 1mg/ml, putting the graphene oxide mixed liquor into a 60 ℃ oven, and preserving heat for 10 hours to obtain a mixed product; and (3) filtering the mixture into paste, washing the paste with deionized water for at least three times, and freeze-drying the paste for 6 hours to form the three-dimensional network reduced graphene oxide supported carbon-coated nano silicon dioxide mesoporous spheres/sulfur cathode material.
Grinding the prepared cathode material, mixing with acetylene black and PVDF according to a mass ratio of 8:1:1, uniformly dispersed in NMP and uniformly coated on a battery-grade aluminum foil, and the sulfur loading per unit area is about 3.4mg/cm2Drying the lithium-sulfur battery in an oven at 80 ℃ for 5 hours to obtain a positive electrode for assembling the lithium-sulfur battery; and assembling the dried cut pieces into a 2032 button cell. The test result shows that the specific capacity reaches 1433mAh/g under the charge-discharge multiplying power of 0.1C, and the specific capacity reaches 1306mAh/g under the charging-discharging multiplying power of 0.2C. The first circle of discharge under 1C reaches 1102mAh/g, the long circulation of 100 circles is 820mAh/g, and the 200 circles are 701mAh/g, as shown in FIG. 5.
Comparative example 1
The carbon coating operation was not performed, i.e., no carbon source was added in the preparation, and the remaining operation and use parameters were the same as in example 1.
Taking 0.16 g of hexadecyl trimethyl ammonium bromide, putting the hexadecyl trimethyl ammonium bromide into 50ml of deionized water, stirring for 0.6 hour to prepare reaction mother liquor, and putting the prepared reaction mother liquor into a thermostat at 80 ℃ for heat preservation for 24 hours; taking out reaction mother liquor, and adding tetraethoxysilane into the reaction mother liquor, wherein the proportion of tetraethoxysilane to the reaction mother liquor is as follows: adding 0.3 g of reaction mother liquor into every 1ml of tetraethoxysilane, magnetically stirring for 5 hours at normal temperature, sealing, reacting for 24 hours, and filtering the generated reactant after the reaction is finished; alternately cleaning the paste with absolute ethyl alcohol and deionized water for at least three times; dispersing the paste product into 80ml of deionized water, and stirring for 2 hours by using a magnetic stirrer; to form a nano silicon dioxide mesoporous sphere dispersion liquid with the concentration of 0.1 mg/ml.
Weighing 0.3 g of manganese acetate and 0.01g of glutamic acid, respectively adding into the nano silicon dioxide mesoporous sphere dispersion liquid, and then carrying out ultrasonic cleaning for 1 hour; uniformly mixing, and drying in an oven at 80 ℃ to obtain a mixture of the silicon dioxide mesoporous spheres rich in functional groups and manganese acetate; and placing the mixture in a tubular atmosphere furnace for annealing under the argon atmosphere condition, keeping the annealing temperature at 850 ℃ for 10 hours, raising the temperature at the speed of 5 ℃/min, and naturally cooling to room temperature after reaction to obtain the nano silicon dioxide mesoporous spheres.
Mixing nano silicon dioxide mesoporous spheres and sublimed sulfur according to the mass ratio of 1:1, fully grinding and mixing, and then preserving heat for 20 hours at 150 ℃ to form the nano silicon dioxide mesoporous sphere/sulfur compound. Dispersing 0.3 g of prepared graphene oxide and 1g of nano silicon dioxide mesoporous sphere/sulfur compound in 300ml of deionized water, stirring for 1 hour by using a magnetic stirrer to prepare graphene oxide dispersion liquid with the concentration of 1mg/ml, putting the graphene oxide dispersion liquid into a 60 ℃ oven, and preserving heat for 1 hour to obtain a mixed product; filtering the mixed product to paste, and washing the paste with deionized water for at least three times; and freeze-drying for 1 hour to form the three-dimensional network reduced graphene oxide supported nano silicon dioxide mesoporous sphere/sulfur positive electrode material rich in functional groups.
Grinding the prepared cathode material, mixing with acetylene black and PVDF according to a mass ratio of 8:1:1, preparing into slurry, uniformly dispersing the slurry in NMP, and uniformly coating the slurry on a battery-grade aluminum foil, wherein the sulfur loading per unit area is about 3.4mg/cm2And drying the lithium sulfur battery in an oven at 80 ℃ for 5 hours to obtain a positive electrode for assembling the lithium sulfur battery, and assembling the dried cut pieces into a 2032 button battery. The test result 1C shows that the first-cycle discharge reaches 620mAh/g, and the long-cycle 200-cycle discharge reaches 380mAh/g, as shown in FIG. 6.
Comparative example 2
The operation of doping the transition metal element was not performed, that is, the transition metal element was not added in the preparation, and the remaining operation and use parameters were the same as those of example 1.
Taking 0.16 g of hexadecyl trimethyl ammonium bromide, putting the hexadecyl trimethyl ammonium bromide into 50ml of deionized water, stirring for 0.6 hour to prepare reaction mother liquor, and putting the prepared reaction mother liquor into a thermostat at 80 ℃ for heat preservation for 24 hours; taking out the reaction mother liquor, and adding tetraethoxysilane into the reaction mother liquor, wherein the proportion of tetraethoxysilane to the reaction mother liquor is as follows: adding 0.3 g of reaction mother liquor into every 1ml of tetraethoxysilane, magnetically stirring for 5 hours at normal temperature, sealing, reacting for 24 hours, and filtering the generated reactant after the reaction is finished; alternately cleaning with anhydrous alcohol and deionized water for at least three times to obtain paste; dispersing the pasty product into 80ml of deionized water, and stirring for 2 hours by using a magnetic stirrer; to form a nano silicon dioxide mesoporous sphere dispersion liquid with the concentration of 0.1 mg/ml.
Weighing 0.4 g of gelatin in 100ml of absolute ethyl alcohol, and pouring the gelatin into the nano silicon dioxide mesoporous sphere dispersion liquid after completely dissolving; simultaneously weighing 0.01g of glutamic acid, adding the glutamic acid into the nano silicon dioxide mesoporous sphere dispersion liquid, and then carrying out ultrasonic cleaning for 1 hour; uniformly mixing, and drying in an oven at 80 ℃ to obtain a functional group-rich carbon-coated silica mesoporous sphere mixture; and placing the mixture in a vacuum tube type atmosphere furnace for annealing under the condition of argon atmosphere, keeping the annealing temperature at 850 ℃ for 10 hours, raising the temperature at 5 ℃/min, and naturally cooling to room temperature after reaction to obtain the carbon-coated nano silicon dioxide mesoporous spheres.
Mixing carbon-coated nano silicon dioxide mesoporous spheres and sublimed sulfur according to the mass ratio of 1:1, fully grinding and mixing, and then preserving heat for 20 hours at 150 ℃ to form the carbon-coated nano silicon dioxide mesoporous sphere/sulfur compound. Dispersing 0.3 g of prepared graphene oxide and 1g of carbon-coated nano silicon dioxide mesoporous spheres/sulfur compound in 300ml of deionized water, stirring for 1 hour by using a magnetic stirrer to prepare graphene oxide mixed liquor with the concentration of 1mg/ml, putting the graphene oxide mixed liquor into a 60 ℃ oven, and preserving heat for 1 hour to obtain a mixed product; filtering the mixed product to paste, and washing the paste with deionized water for at least three times; and freeze-drying for 1 hour to form the three-dimensional network reduced graphene oxide supported carbon-coated nano silicon dioxide mesoporous sphere/sulfur cathode material with rich functional groups.
Grinding the prepared cathode material, mixing with acetylene black and PVDF according to a mass ratio of 8:1:1, preparing into slurry, uniformly dispersing the slurry in NMP, and uniformly coating the slurry on a battery-grade aluminum foil, wherein the sulfur loading per unit area is about 3.4mg/cm2And drying the lithium sulfur battery in an oven at 80 ℃ for 5 hours to obtain a positive electrode for assembling the lithium sulfur battery, and assembling the dried cut pieces into a 2032 button battery. The specific capacity of the test result under 1C multiplying power charge and discharge is 802mAh/g, and the specific capacity is 160mAh/g after 200 circles of long circulation, as shown in figure 7.
Comparative example 3
Graphene oxide compounding operation is not performed, namely, graphene oxide is not added in the preparation, and the rest of operation and use parameters are the same as those in the example 1.
Taking 0.16 g of hexadecyl trimethyl ammonium bromide, putting the hexadecyl trimethyl ammonium bromide into 50ml of deionized water, stirring for 0.6 hour to prepare reaction mother liquor, and putting the prepared reaction mother liquor into a thermostat at 80 ℃ for heat preservation for 24 hours; taking out reaction mother liquor, and adding tetraethoxysilane into the reaction mother liquor, wherein the proportion of tetraethoxysilane to the reaction mother liquor is as follows: adding 0.3 g of reaction mother liquor into every 1ml of tetraethoxysilane, magnetically stirring for 5 hours at normal temperature, sealing and reacting for 24 hours, filtering the generated reactant after the reaction is finished, and alternately cleaning the reactant for at least three times by using absolute ethyl alcohol and deionized water to obtain paste; dispersing the pasty product into 80ml of deionized water, and stirring for 2 hours by using a magnetic stirrer; to form a nano silicon dioxide mesoporous sphere dispersion liquid with the concentration of 0.1 mg/ml.
Weighing 0.4 g of gelatin in 100ml of absolute ethyl alcohol, and pouring the gelatin into the nano silicon dioxide mesoporous sphere dispersion liquid after completely dissolving; simultaneously weighing 0.3 g of manganese acetate and 0.01g of glutamic acid, respectively adding the manganese acetate and the glutamic acid into the nano silicon dioxide mesoporous sphere dispersion liquid, and then carrying out ultrasonic cleaning for 1 hour; uniformly mixing, and drying in an oven at 80 ℃ to obtain a functional group-rich carbon-coated silica mesoporous sphere mixture; and placing the mixture in a vacuum tube type atmosphere furnace for annealing in an argon atmosphere, keeping the annealing temperature at 850 ℃ for 10 hours, raising the temperature at 5 ℃/min, and naturally cooling to room temperature after reaction to obtain the carbon-coated nano silicon dioxide mesoporous spheres.
Mixing carbon-coated nano silicon dioxide mesoporous spheres and sublimed sulfur according to the mass ratio of 1:1, fully grinding and mixing, and then preserving heat for 20 hours at 150 ℃ to form the carbon-coated nano silicon dioxide mesoporous sphere/sulfur compound. Grinding the prepared cathode material, mixing with acetylene black and PVDF according to a mass ratio of 8:1:1, preparing into slurry, uniformly dispersing the slurry in NMP, and uniformly coating the slurry on a battery-grade aluminum foil, wherein the sulfur loading per unit area is about 3.4mg/cm2And drying the lithium sulfur battery in an oven at 80 ℃ for 5 hours to obtain a positive electrode for assembling the lithium sulfur battery, and assembling the dried cut pieces into a 2032 button battery. The specific capacity of the material under the charge and discharge of the 1C multiplying power is 563mAh/g, and the specific capacity is 200 circles of 312mAh/g in long circulation, as shown in figure 8.
Through the above examples, the present invention provides four parts included in the positive electrode material for a lithium-sulfur battery: the nano silicon dioxide mesoporous spheres can inhibit the volume expansion of sulfur, and can well play a role in binding lithium polysulfide through the electronegativity of oxygen ions; the carbon layer coated by the carbon rich in functional groups has the function of further stabilizing the structure of the nano silicon dioxide spheres, can improve the conductivity of the nano silicon dioxide spheres, is beneficial to the transfer of electrons in the charge and discharge processes, and improves the rate capability of the battery; the transition metal element can play a good role in catalyzing the conversion between lithium polysulfide and sulfur, so that the conversion efficiency and the utilization rate of active substances are improved, and the rate capability and the specific capacity of the whole battery are further improved; the three-dimensional mesh-shaped reduced graphene oxide can provide sufficient space volume, a good conductive network and a lithium ion transmission medium, so that the stability and rate characteristic of the battery are improved, the internal resistance of the battery is reduced, and the working efficiency of the battery is improved.
The button cells prepared in examples 1 to 5 and comparative examples 1 to 3 above were tested on a blue cell tester in a constant current charge and discharge test with test currents of 0.1C, 0.2C and 1C rate, respectively, at room temperature, and with cycle numbers of 100 and 200 cycles, respectively.
As can be seen from the data of the above embodiments, the present invention achieves the following beneficial technical effects: the lithium-sulfur battery prepared by the electrode material provided by the invention has higher electrochemical performance, and particularly compared with the comparative example without carbon coating, or without transition metal elements and or without the compounding of three-dimensional graphene oxide, the carbon coating can obviously improve the conductivity of the electrode material; the doping of the transition metal element can obviously improve the rate capability and the cycle life of the material; the cycle life of the battery can be effectively prolonged by compounding the three-dimensional graphene oxide.
In addition, the lithium-sulfur battery manufactured by the lithium-sulfur battery anode material provided by the invention has the advantages of simple manufacturing process, low cost, excellent performance, higher specific capacity and cycle life, and great marketization application potential. The electrode material provided by the present invention is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A preparation method for a lithium-sulfur battery anode material is characterized in that sublimed sulfur is fused into a nano silicon dioxide mesoporous sphere according to a designed mass ratio to form a compound; mixing the composite with graphene oxide according to a designed mass ratio, and reducing to obtain a lithium-sulfur battery positive electrode material; the method specifically comprises the following steps:
(1) preparation of graphene oxide
Dissolving 9 g of potassium persulfate and 9 g of phosphorus pentoxide in 15ml of concentrated sulfuric acid, and adding 11 g of graphite powder; stirring uniformly, and then preserving heat for 24 hours at 80 ℃ to obtain pre-oxidized graphite slurry;
filtering the pre-oxidized graphite slurry, washing with deionized water, and baking in an oven at 80 ℃ for 24 hours to obtain pre-oxidized graphite powder;
thirdly, adding 3 g of sodium nitrate into 255ml of concentrated sulfuric acid, and completely dissolving the sodium nitrate to obtain pre-oxidized graphite powder; the whole system is placed in a water bath kettle below 10 ℃, and the next operation is carried out after the temperature of the whole system is stabilized below 10 ℃;
weighing 18 g of potassium permanganate, and adding the potassium permanganate into the system for 20 times according to 0.9 g; the temperature of the system is always kept below 10 ℃, the system is sealed after the addition is finished, the system is transferred to a water bath kettle at 55 ℃ after the temperature of the system is kept for 3 hours, and the system is intensively stirred for 5 hours to form a paste substance;
fifthly, centrifugally cleaning the pasty substance by using a hydrochloric acid solution, and centrifugally cleaning the pasty substance by using deionized water to obtain graphene oxide;
(2) preparation of nano silicon dioxide mesoporous spheres
Firstly, 0.1-0.8 g of hexadecyl trimethyl ammonium bromide is put into 50ml of deionized water and fully stirred for 0.6 hour to prepare a reaction mother solution; placing the prepared reaction mother liquor in a thermostat with the temperature of 60-110 ℃ and preserving heat for 10-48 hours;
② taking out reaction mother liquor and adding tetraethoxysilane into the reaction mother liquor, wherein the proportion of the added tetraethoxysilane to the reaction mother liquor is as follows: adding 0.08-0.64 g of reaction mother liquor into every 1ml of tetraethoxysilane, magnetically stirring for 1-10 hours at normal temperature, and reacting for 10-48 hours after sealing to generate a reactant;
thirdly, carrying out suction filtration and cleaning on the generated reactant to obtain a paste, dispersing the paste product in 50-150 ml of deionized water, and carrying out magnetic stirring for 2 hours to form a nano silicon dioxide mesoporous sphere dispersion liquid;
(3) coating the mesoporous carbon spheres of the nano silicon dioxide and introducing corresponding functional groups
Adding 0.4 g of carbon source into the nano silicon dioxide mesoporous sphere dispersion liquid, and simultaneously adding 0.01-0.35 g of functional group-rich substance according to the introduced functional group to form a mixed liquid;
secondly, adding transition metal acetate into the mixed solution according to a molar ratio, wherein the ratio of the mixed solution to the transition metal acetate is as follows: 1: 3; then ultrasonically cleaning for 0.2-2.5 hours, uniformly mixing, and drying in an oven at 60-110 ℃ to obtain a mixture of the carbon-coated nano silicon dioxide mesoporous spheres rich in functional groups and transition metal acetate;
thirdly, annealing the mixture for 5 to 10 hours at 850 to 1000 ℃ under the vacuum atmosphere condition; naturally cooling to room temperature to obtain carbon-coated nano silicon dioxide mesoporous spheres;
(4) preparation of positive electrode material of lithium-sulfur battery
Uniformly mixing the carbon-coated nano silicon dioxide mesoporous spheres and sublimed sulfur according to the mass ratio of 1: 1-1: 6, and then preserving heat for 2-20 hours at the temperature of 150-250 ℃ under the atmosphere condition to obtain carbon-coated nano silicon dioxide mesoporous spheres/sulfur compounds;
dispersing 0.3 g of graphene oxide prepared in the step (1) and 1g of carbon-coated nano silicon dioxide mesoporous spheres/sulfur compound in 80-300 ml of deionized water, and stirring for 0.2-2 hours by using a magnetic stirrer to obtain a graphene oxide mixed solution;
thirdly, placing the obtained graphene oxide mixed solution into a drying oven at the temperature of 60-110 ℃, and preserving heat for 1-10 hours to obtain a mixed product; filtering the mixed product to paste, washing with deionized water, and freeze-drying for 1-15 hours to obtain the lithium-sulfur battery positive electrode material; grinding the mixture to be ready for use.
2. The method for preparing a positive electrode material for a lithium-sulfur battery according to claim 1, wherein the diameter of the nano-silica mesoporous spheres prepared in the step (2) is between 30 and 200 nm.
3. The method for preparing a positive electrode material for a lithium sulfur battery according to claim 1 or 2, wherein the concentration of the nano-silica mesoporous sphere dispersion in the step (2) is 0.1mg/ml to 10 mg/ml.
4. The method for preparing a positive electrode material for a lithium sulfur battery according to claim 1, wherein the ratio of the added tetraethoxysilane to the reaction mother liquor in the step (2) is as follows: 0.16 g of reaction mother liquor is added per 1ml of tetraethoxysilane.
5. The method for preparing a positive electrode material for a lithium-sulfur battery according to claim 1, wherein 0.4 g of a carbon source is added to the dispersion liquid of the nano-silica mesoporous spheres in the step (3), wherein the carbon source is one of gelatin and glucose; the addition amount is 0.4 g of carbon source added to each 1g of nano-silica mesoporous spheres.
6. The method for preparing a positive electrode material for a lithium sulfur battery according to claim 1, wherein the added transition metal acetate in the step (3) is one of nickel, cobalt, manganese, aluminum or iron.
7. The method of claim 1, wherein the functional group-rich material in step (3) is one selected from glutamic acid, glycine, aspartic acid, and sodium fluoride.
8. The method for preparing a positive electrode material for a lithium-sulfur battery according to claim 1, wherein the mixture in the step (3) is annealed under an atmosphere condition of argon, argon-hydrogen mixture, ammonia or nitrogen; wherein the argon-hydrogen mixed gas proportion is 95: 5.
9. the positive electrode material for the lithium-sulfur battery prepared by the preparation method of any one of claims 1 to 8 comprises nano-silica mesoporous spheres, a functional group-rich carbon coating layer, three-dimensional network reduced graphene oxide and sublimed sulfur.
10. Use of the positive electrode material for lithium-sulfur batteries prepared by the preparation method according to any one of claims 1 to 9 in the preparation of lithium-sulfur batteries.
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