CN111244432A - Preparation and application of manganese dioxide @ sulfur @ carbon sphere positive electrode composite material with yolk-shell structure - Google Patents

Preparation and application of manganese dioxide @ sulfur @ carbon sphere positive electrode composite material with yolk-shell structure Download PDF

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CN111244432A
CN111244432A CN201811443100.6A CN201811443100A CN111244432A CN 111244432 A CN111244432 A CN 111244432A CN 201811443100 A CN201811443100 A CN 201811443100A CN 111244432 A CN111244432 A CN 111244432A
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sulfur
carbon
manganese
manganese dioxide
yolk
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CN111244432B (en
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陈剑
邵钦君
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Dalian Institute of Chemical Physics of CAS
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention provides a manganese dioxide @ sulfur @ carbon sphere positive electrode composite material with a yolk-shell structure and a preparation method and application thereof, wherein manganese dioxide with a sheet structure is taken as a core and is distributed in a cavity with a carbon sphere as a shell, sulfur is distributed between the manganese dioxide core and the carbon shell, the carbon content in the composite material is 10-30%, the manganese dioxide content is 10-30%, and the sulfur content is 40-80%; the hollow carbon spheres not only provide sufficient sulfur-carrying space, but also ensure the rapid transmission of electrons through rich point-to-point contact among the carbon spheres, the flaky manganese dioxide nuclear layer in the carbon sphere cavity has stronger chemical adsorption and conversion effects on polysulfide, the shuttle effect can be effectively inhibited by combining the physical limiting effect of the carbon layer, and the capacity retention rate, the cycle stability and the rate capability of the battery are improved.

Description

Preparation and application of manganese dioxide @ sulfur @ carbon sphere positive electrode composite material with yolk-shell structure
Technical Field
The invention belongs to the technical field of new energy, and particularly relates to preparation and application of a manganese dioxide @ sulfur @ carbon sphere positive electrode composite material with a yolk-shell structure.
Background
With the consumption of non-renewable resources such as fossil, the development and utilization of new energy resources have been accelerated, and among them, secondary batteries are playing more and more important roles as an important energy carrier. At present, the methodThe lithium ion battery has the advantages of good safety and cycling stability, low cost and the like, and is widely applied to the energy storage fields of small-sized mobile power supplies, power batteries and the like. But due to its lower theoretical specific capacity (< 300mAh g)-1) The demand of people for high specific energy batteries has not been satisfied, and therefore, it is of great importance to develop a novel secondary battery having high specific energy, long cycle life, low cost and environmental friendliness. Among them, the lithium sulfur battery attracts people's extensive attention and research by virtue of the theoretical energy density of 2600Wh/Kg, abundant raw materials, environmental friendliness, and the like.
The sulfur positive electrode material is a key component of the lithium sulfur battery, and due to the insulating property of elemental sulfur, a high-conductivity carbon material needs to be added into the positive electrode material so as to improve the utilization rate of positive electrode active substances and the rate capability of the battery. In addition, the reaction of sulfur with lithium ions during discharge is complicated and undergoes a transition from long-chain polysulfides (Li)2SxAnd x is more than 4 and less than 8), wherein the long-chain polysulfide is easily dissolved in ether electrolyte and shuttled to the side of the metallic lithium cathode through a diaphragm to be reduced in the battery circulation process, so that the lower capacity retention rate, the coulombic efficiency and the poorer circulation stability are caused, and therefore, how to relieve the shuttle effect of the polysulfide is a basic scientific problem still existing in the lithium-sulfur battery.
The Chinese patent publication No. CN 104916828A mentions that the carbon-sulfur cathode material prepared by using hollow carbon spheres as sulfur carriers solves the problem of poor cycle performance caused by shuttle of lithium polysulfide by limiting sulfur in the cavities of the carbon spheres. However, in this patent, the physical interaction between the nonpolar carbon spheres and the polar lithium polysulfide is weak, and it is difficult to efficiently adsorb the dissolved lithium polysulfide, and the occurrence of the shuttle effect cannot be effectively suppressed. Meanwhile, in the chinese invention patent of the granted publication No. CN 107887605A, it is proposed to prepare a sulfur positive electrode by using nano sulfur powder, manganese dioxide powder, carbon fiber, and carbon nanotube as slurry, although manganese dioxide plays an anchoring role for dissolved lithium polysulfide through chemical adsorption conversion, the battery can obtain better cycle stability in the first 80 cycles, but manganese dioxide with poor conductivity is easy to lose electrical contact with an insulating active substance sulfur in the cycle, and further, dissolution of lithium polysulfide cannot be effectively inhibited, so that the battery has poor long cycle performance.
Disclosure of Invention
The invention aims to provide preparation and application of a manganese dioxide @ sulfur @ carbon sphere positive electrode composite material with a yolk-shell structure, which synergistically plays a physical role of a carbon coating layer and a chemical adsorption conversion role of manganese dioxide through reasonable nano-structure design and construction, and effectively limits sulfur and easily soluble lithium polysulfide in a cavity of the yolk-shell, so that a shuttle effect in a sulfur positive electrode is inhibited, and the long-cycle stability of a battery is improved.
The manganese dioxide @ sulfur @ carbon sphere positive electrode composite material with the yolk-shell structure is characterized in that manganese dioxide with a sheet structure is taken as a core and is distributed in a cavity with a carbon sphere as a shell, sulfur is distributed between the manganese dioxide core and the carbon shell, the carbon content in the composite material is 10% -30%, the manganese dioxide content is 10% -30%, and the sulfur content is 40% -80%;
the yolk-shell structure manganese dioxide @ carbon sphere material has the hollow carbon sphere cavity inner diameter of 50-500 nm, the carbon layer thickness of 10-50 nm, micropores of 0-2 nm, mesopores of 2-50 nm and a specific surface area of 100-1000 m2g-1Pore volume of 0.1-2 cm3g-1。
A preparation method of manganese dioxide @ sulfur @ carbon sphere positive electrode composite material with a yolk-shell structure comprises the following steps of coating a silicon dioxide template layer on the surface of manganese carbonate, coating a phenolic resin precursor, carbonizing, etching, carrying out heat treatment and carrying out sulfur loading to obtain the material, and comprises the following steps:
(1) synthesizing manganese carbonate: the volume ratio of the components is 2: 1-3, in a mixed solvent of water and ethylene glycol or propylene glycol or glycerol or butanediol, preparing manganese carbonate by using manganese sulfate, manganese chloride or manganese nitrate or a manganese source and sodium carbonate, sodium bicarbonate or potassium carbonate or potassium bicarbonate as a precipitant, and performing suction filtration, washing and drying on a reaction product to obtain spherical manganese carbonate particles;
(2) synthesizing manganese carbonate @ silicon dioxide with a core-shell structure: dispersing manganese carbonate into a mixed solvent of water containing Cetyl Trimethyl Ammonium Bromide (CTAB), ethanol and alkali, wherein the alkali is one or more of ammonia water, aniline and benzylamine; dissolving tetraethyl orthosilicate (TEOS) by using ethanol as a solvent to prepare a solution with the TEOS content of 0.01-0.1 g/ml, dropwise adding the solution into the suspension at a constant speed of 5-20 ml/h, and performing suction filtration, washing and drying on a product to obtain silicon dioxide coated manganese carbonate nano-sphere particles with a core-shell structure;
(3) phenolic resin coated manganese carbonate @ silica: dispersing manganese carbonate @ silicon dioxide into a mixed solvent of water, ethanol and alkali containing CTAB, wherein the alkali is one or more of ammonia water, sodium hydroxide or potassium hydroxide; sequentially adding resorcinol and formaldehyde as carbon sources, generating a phenolic resin layer on the surface of the manganese carbonate @ silicon dioxide under the catalytic action of alkali, and performing suction filtration, washing and drying on the product to obtain the manganese carbonate @ silicon dioxide nano-sphere particles coated with the phenolic resin;
(4) carbonizing: putting the phenolic resin coated manganese carbonate @ silicon dioxide nanosphere particles prepared in the step (3) into a tubular furnace, and performing high-temperature pyrolysis carbonization in an argon or nitrogen atmosphere to obtain carbon coated manganese carbonate @ silicon dioxide nanosphere particles;
(5) etching: dispersing the carbon-coated manganese carbonate @ silicon dioxide material prepared in the step (4) into a concentrated sodium hydroxide aqueous solution, reacting under a heating condition, etching off a silicon dioxide template layer, reacting with manganese carbonate to generate manganese dioxide, and performing suction filtration, washing and drying on a product to obtain a hollow yolk-shell structure @ manganese dioxide carbon sphere nano material;
(6) and (3) sulfur compounding: taking the manganese dioxide @ carbon material prepared in the step (5) and sublimed sulfur according to the mass ratio of 1: 2-6, grinding, transferring into a sealed bottle, and carrying out heat treatment under an argon or nitrogen atmosphere to carry sulfur to obtain a yolk-shell structure manganese dioxide @ sulfur @ carbon sphere composite material;
in the step (1), the solvent is mixed, and the volume ratio of water to alcohol is 2: 1-3; the molar ratio of the manganese salt to the precipitator is 1: 1-20; adding a precipitator into a hydroalcoholic solution in which manganese salt is dissolved, and reacting for 5-60 minutes under vigorous stirring;
tetraethyl orthosilicate in the mixed solvent in the step (2): alkali: water: the ethanol molar ratio is 1: 1-5: 5-50: 100-400; dropwise adding an ethanol solution of tetraethyl orthosilicate into the suspension at a certain rate, wherein the dropwise adding speed is 5-20 ml/h;
alkali in the mixed solution in the step (3): CTAB: water: the ethanol molar ratio is 1: 1-20: 500-2000: 1000-3000, adding resorcinol into a dispersion liquid of manganese carbonate @ silicon dioxide, adding a formaldehyde solution after 5-30 minutes, and continuously stirring for 12-36 hours at the reaction temperature of 20-40 ℃;
in the step (4), the protective atmosphere is high-purity nitrogen or argon, the flow rate of the gas flow is 50-200 ml/min, the carbonization temperature is 600-900 ℃, the carbonization time is 1-10 hours, and the temperature rise rate is 1-10 ℃/min;
the concentration of the sodium hydroxide in the step (5) is 1-6 mol/L;
the protective atmosphere in the step (6) is high-purity argon or high-purity nitrogen, the flow rate of the gas flow is 20-100 ml/min, the heat treatment temperature is 140-160 ℃, and the treatment time is 12-24 hours;
the hollow carbon sphere material has the carbon sphere cavity inner diameter of 50-500 nm, the carbon layer thickness of 10-50 nm, the micropore aperture of 0-2 nm, the mesopore of 2-50 nm and the specific surface area of 100-1000 m2g-1Pore volume of 0.1-2 cm3g-1(ii) a The carbon-sulfur composite material coated with manganese dioxide comprises 10-30% of carbon, 10-30% of manganese dioxide and 40-80% of sulfur;
according to the invention, the surface of manganese carbonate is coated with the silicon dioxide sacrificial template layer and then coated with the porous carbon layer, the silicon dioxide intermediate layer is etched by the treatment of sodium hydroxide, manganese carbonate is reacted to generate manganese dioxide, and the manganese dioxide and sulfur are subjected to heat treatment to obtain the manganese dioxide @ sulfur @ carbon sphere positive electrode composite material with the yolk-shell structure.
The composite material has the advantages of low raw material cost, mature synthesis process and batch production, and can optimize the yolk-shell structure of manganese dioxide @ carbon spheres by regulating and controlling parameters of a single step so as to fully play the inhibiting effect of the composite material with the structure on the lithium polysulfide shuttling effect in sulfur anodes of different systems. The manganese dioxide @ carbon sphere material with the yolk-shell structure, which is prepared, firstly has a large cavity and an abundant internal micro-mesoporous structure, is beneficial to subsequent effective sulfur loading, provides buffer for volume expansion of sulfur, realizes high specific energy density of a battery through high sulfur loading capacity, and simultaneously, the abundant pore structure is also beneficial to infiltration of electrolyte and full contact of active substance sulfur, so that the rapid conduction of lithium ions in the interior of a positive electrode under high multiplying power is met; meanwhile, abundant point-to-point contact among the high-conductivity hollow carbon spheres ensures good electronic conductivity among particles in the positive electrode, solves the problem of low electronic conductivity after sulfur loading, and realizes charge and discharge under high multiplying power and high utilization rate of active substance sulfur. On the other hand, the flaky manganese dioxide loaded in the carbon spheres can adsorb long-chain lithium polysulfide which is a discharge intermediate product easily soluble in ether electrolyte through electrostatic action, can react with the long-chain lithium polysulfide to generate short-chain lithium polysulfide, and is finally reduced to a discharge end product lithium sulfide, so that the shuttle effect of polysulfide in the lithium-sulfur battery is relieved, the lithium cathode is protected, and meanwhile, the loss of active substances is reduced, so that the capacity retention rate of the battery is improved, and the battery has higher cycle stability. In summary, the manganese dioxide @ sulfur @ carbon sphere composite material with the yolk-shell structure has good electronic and ionic conductivity, plays an obvious role in inhibiting the shuttle effect of lithium polysulfide through the physical limitation of a carbon layer and the chemical adsorption of manganese dioxide, shows good cycle performance and rate capability when being applied to the positive electrode of a lithium-sulfur battery, and has potential possibility in the industrialization of the lithium-sulfur battery.
Drawings
FIG. 1 is a scanning electron micrograph of manganese carbonate;
FIG. 2 is a transmission electron micrograph of manganese carbonate @ silica material;
FIG. 3 is a transmission electron micrograph of manganese dioxide @ carbon sphere material;
FIG. 4 is an XRD powder diffraction pattern of manganese dioxide @ carbon sphere material;
fig. 5 is a specific capacity cycling plot for the batteries of comparative example and example 1.
Detailed Description
The following examples are further illustrative of the present invention and are not intended to limit the scope of the present invention.
Comparative example 1
Adding 40ml of deionized water, 70ml of ethylene glycol and 1mmol of manganese sulfate into a beaker, uniformly stirring, quickly pouring 30ml of deionized water solution in which 10mmol of sodium bicarbonate is dissolved, violently stirring at 25 ℃ for reaction for 15min, and carrying out suction filtration, washing and drying on a white product to obtain manganese carbonate particles, wherein a scanning electron microscope image of the manganese carbonate particles is shown in figure 1;
taking 0.1g of manganese carbonate, adding 0.1g of CTAB, 5ml of deionized water, 65ml of ethanol and 1ml of concentrated ammonia water, ultrasonically dispersing for 30min, adding 20ml of ethanol solution containing 0.8ml of tetraethyl orthosilicate within two hours, continuously reacting for 4h, carrying out suction filtration, washing and drying to obtain manganese carbonate @ silicon dioxide with a core-shell structure, wherein a transmission electron microscope image of the manganese carbonate @ silicon dioxide is shown in FIG. 2;
taking 0.16g of manganese carbonate @ silicon dioxide, adding 3g of CTAB, 20ml of deionized water, 70ml of ethanol and 0.24ml of ammonia water, ultrasonically dispersing for 30min, adding 0.12g of resorcinol and 0.204ml of formaldehyde solution (37 wt%), reacting for 6h at 30 ℃, aging overnight, filtering, washing, drying, placing in a tube furnace, heating to 700 ℃ at a heating rate of 3 ℃/min under an argon atmosphere, and keeping the temperature for 3 h; putting the carbonized product into a 4mol/L sodium hydroxide aqueous solution, reacting at 60 ℃ for 24h to etch silicon dioxide, performing suction filtration, washing and drying to obtain a yolk-shell structure manganese dioxide @ carbon material, wherein a transmission electron microscope diagram and an XRD powder diffraction diagram are respectively shown in figures 3 and 4;
taking 0.5g of manganese dioxide @ carbon spheres, dispersing into 10ml of deionized water, adding 5ml of concentrated hydrochloric acid, reacting overnight, performing suction filtration, washing and drying to obtain hollow carbon spheres containing no manganese dioxide; and (3) grinding 0.1g of etched hollow carbon spheres and 0.4g of sublimed sulfur, transferring the mixture into a sealed reaction kettle, and carrying out heat treatment at 155 ℃ for 12 hours and 300 ℃ for 2 hours to obtain the hollow carbon-sulfur composite material.
Taking 0.1g of the electrolyte, adding 0.02g of conductive carbon and 0.267g of 5% polyvinylidene fluoride (PVDF) solution, taking N-methylpyrrolidone as a solvent, grinding for 1h, then using a 200-micron scraper to scrape and coat a carbon-coated aluminum foil to form a film, drying at 60 ℃ overnight, slicing, weighing, carrying out vacuum drying at 55 ℃ for 24h, taking the electrode piece as a positive electrode, a lithium piece as a negative electrode, Celgard2500 as a diaphragm, taking 1M bis (trifluoromethylsulfonyl) lithium imide solution (LITFSI) as an electrolyte, 0.2M lithium nitrate as an additive, taking a mixed solution (volume ratio is 1:1) of 1, 3-Dioxolane (DOL) and dimethyl ether (DME) as a solvent, assembling a battery, and carrying out charge and discharge test at the rate of 0.05-2C; under the multiplying power of 1C, the charge-discharge capacity of the first circle is 1120 mAh/g; after 500 weeks of circulation, the capacity is 265 mAh/g; the specific capacity cycling profile of the comparative example cell is shown in figure 5.
Example 1
The process for preparing the manganese dioxide @ carbon material with the yolk-shell structure is the same as the comparative example, 0.1g of manganese dioxide @ carbon material is taken and ground with 0.4g of sublimed sulfur, the ground material is transferred into a sealed reaction kettle and is subjected to heat treatment at 155 ℃ for 12 hours and heat treatment at 300 ℃ for 2 hours, so that the @ manganese dioxide sulfur @ carbon composite material with the yolk-shell structure is obtained, the carbon content in the composite material is 24.9 percent, the manganese dioxide content is 12.6 percent, the sulfur content is 62.5 percent, the inner diameter of a hollow carbon ball cavity is 500nm, the thickness of a carbon layer is 30nm, and the specific surface area is 598m2g-1Pore volume of 0.584cm3g-1The subsequent pole piece coating and battery assembly tests are the same as the comparative examples.
It can be seen from FIG. 1 that the particle size of manganese carbonate is 600+100nm, from which it can be seen that the manganese carbonate pellet has a uniform particle size.
As can be seen from FIG. 2, the manganese carbonate @ silicon dioxide with a core-shell structure is stable in form and uniform in particle size, wherein the thickness of the silicon dioxide coating layer is 50+10 nm;
it can be seen from fig. 3 that the manganese dioxide @ carbon sphere material with the yolk-shell structure has sufficient cavities inside, can fully carry sulfur and provides buffer for volume expansion of sulfur. In addition, rich pores in the carbon layer can provide a sufficient path for the immersion of sulfur in subsequent heat treatment, so that the sulfur can be fully immersed in the cavity, and a stable passage can be provided for the immersion of subsequent electrolyte, so that higher ion conductivity is ensured, and the battery has better rate performance;
as can be seen from the XRD powder diffraction pattern of the manganese dioxide @ carbon material in fig. 4, the crystal form of the coated manganese dioxide is δ (JCPDS No.43-1456), and as can be seen from the transmission electron microscope pattern in fig. 3, the δ -type flaky manganese dioxide in the core region has a perfect and uniform form and a high internal porosity, and can effectively inhibit the dissolution and shuttle effects of lithium polysulfide by adsorption and chemical conversion of lithium polysulfide, thereby improving the cycle performance of the battery, and the manganese dioxide has a good conductivity, and the structure thereof does not affect the immersion of the electrolyte, so the rate performance of the battery is not affected.
The specific capacity cycling diagram of the battery is shown in fig. 5, and it can be seen from the diagram that compared with a hollow carbon-sulfur material containing no manganese dioxide, the capacity retention rate of the manganese dioxide @ sulfur @ carbon sphere positive electrode material with a yolk-shell structure is obviously improved, and under the multiplying power of 1C, the specific capacity of 506mAh/g still exists after 500 cycles, while the capacity of the comparative hollow carbon-sulfur material is only 265mAh/g, and the capacity decay rate is reduced from 0.207% to 0.063% per cycle, which indicates that the dissolution of polysulfide by manganese dioxide is effectively inhibited, and the cycling stability of the battery is improved.
Example 2
Preparing manganese carbonate in the same comparison example;
taking 0.1g of manganese carbonate, adding 0.1g of CTAB, 5ml of deionized water, 65ml of ethanol and 1ml of concentrated ammonia water, ultrasonically dispersing for 30min, adding 20ml of ethanol solution containing 0.4ml of tetraethyl orthosilicate within two hours, continuously reacting for 4h, and performing suction filtration, washing and drying to obtain manganese carbonate @ silicon dioxide with a core-shell structure;
the same comparative example is used for preparing a yolk-shell structure manganese dioxide @ carbon material, subsequent sulfur dipping, pole piece coating and battery assembly tests are the same as example 1, the content of carbon in the composite material is 23.5%, the content of manganese dioxide is 13.1%, the content of sulfur is 63.4%, the inner diameter of a hollow carbon ball cavity is 400nm, the thickness of a carbon layer is 30nm, and the specific surface area is 548m2g-1Pore volume of 0.474cm3g-1。
The manganese dioxide @ carbon sphere composite material with the yolk-shell structure is subjected to XRD (X-ray diffraction), scanning electron microscope and transmission electron microscope tests and battery specific capacity tests, and the results of the battery specific capacity tests show that TEOS (tetraethyl orthosilicate) feeding is reduced, the thickness of a silicon dioxide coating layer is reduced, the ion transmission distance is shortened, the rate capability of the battery is improved, but due to the reduction of the pore volume, sufficient sulfur-carrying space cannot be provided, and the utilization rate and the cycling stability of active materials of the battery are low.
Example 3
Preparing manganese carbonate in the same comparison example;
taking 0.1g of manganese carbonate, adding 0.1g of CTAB, 5ml of deionized water, 65ml of ethanol and 1ml of concentrated ammonia water, ultrasonically dispersing for 30min, adding 20ml of ethanol solution containing 1.2ml of tetraethyl orthosilicate within two hours, continuously reacting for 4h, and performing suction filtration, washing and drying to obtain manganese carbonate @ silicon dioxide with a core-shell structure;
the same comparative example is used for preparing a yolk-shell structure manganese dioxide @ carbon material, subsequent sulfur immersion, pole piece coating and battery assembly tests are the same as example 1, the content of carbon in the composite material is 24.7 percent, the content of manganese dioxide is 13.4 percent, the content of sulfur is 61.9 percent, the inner diameter of a hollow carbon ball cavity is 600nm, the thickness of a carbon layer is 25nm, and the specific surface area is 462m2g-1Pore volume of 0.758cm3g-1。
The manganese dioxide @ carbon sphere composite material with the yolk-shell structure is subjected to XRD (X-ray diffraction), scanning electron microscope and transmission electron microscope tests and battery specific capacity tests, and the results show that the thickness of a silicon dioxide coating layer is increased by increasing the TEOS feeding amount, and an extremely sufficient space is provided for sulfur carrying, but due to the fact that the distance between a carbon layer and manganese dioxide is lengthened, ion transmission and electron transmission channels in the material are blocked, the rate performance of the battery is poor, and the stability performance of the battery under long circulation is poor.
Example 4
Preparing manganese dioxide @ silicon dioxide with a core-shell structure in the same comparison example;
taking 0.16g of manganese carbonate @ silicon dioxide, adding 3g of CTAB, 20ml of deionized water, 70ml of ethanol and 0.12ml of strong ammonia water, ultrasonically dispersing for 30min, adding 0.06g of resorcinol and 0.102ml of formaldehyde solution (37 wt%), reacting at 30 ℃ for 6h, then aging overnight, filtering, washing and drying;
the same comparative example is used for preparing a yolk-shell structure manganese dioxide @ carbon ball material, subsequent sulfur dipping, pole piece coating and battery assembly tests are the same as example 1, the content of carbon in the composite material is 13.4 percent, the content of manganese dioxide is 25.4 percent, the content of sulfur is 61.2 percent, the inner diameter of a hollow carbon ball cavity is 500nm, the thickness of a carbon layer is 15nm, and the specific surface area is 362m2g-1Pore volume of 0.624cm3g-1。
The manganese dioxide @ carbon sphere composite material with the yolk-shell structure is subjected to XRD (X-ray diffraction), scanning electron microscope and transmission electron microscope tests and battery specific capacity tests, and the results show that the thickness of a carbon layer is reduced due to the reduction of the feeding of resorcinol and formaldehyde, the uniformity of the morphology of the material is reduced although the subsequent sulfur is favorably immersed in a cavity area of the composite material, some granular carbon layers are damaged, the physical limiting effect of the carbon layer is lost, and the cycle stability and the capacity retention rate of the anode composite material are reduced due to the continuous dissolution of sulfur in the cycle process.
Example 5
Preparing manganese dioxide @ silicon dioxide with a core-shell structure in the same comparison example;
taking 0.16g of manganese carbonate @ silicon dioxide, adding 3g of CTAB, 20ml of deionized water, 70ml of ethanol and 0.48ml of strong ammonia water, ultrasonically dispersing for 30min, adding 0.24g of resorcinol and 0.408ml of formaldehyde solution (37 wt%), reacting at 30 ℃ for 6h, then aging overnight, filtering, washing and drying;
the same comparative example is used for preparing a yolk-shell structure manganese dioxide @ carbon ball material, subsequent sulfur dipping, pole piece coating and battery assembly tests are the same as example 1, the content of carbon in the composite material is 30.5 percent, the content of manganese dioxide is 8.6 percent, the content of sulfur is 60.9 percent, the inner diameter of a hollow carbon ball cavity is 500nm, the thickness of a carbon layer is 45nm, and the specific surface area is 685m2g-1Pore volume of 0.560cm3g-1。
The manganese dioxide @ carbon sphere composite material with the yolk-shell structure is subjected to XRD (X-ray diffraction), scanning electron microscope, transmission electron microscope test and battery specific capacity test, and the results show that the thickness of a carbon layer is increased due to the increase of the feeding amount of resorcinol and formaldehyde, the complete coating of manganese dioxide is ensured, but the subsequent full immersion of sulfur is hindered by a thicker carbon layer, so that more regional deposition of part of sulfur on the outer surface of the carbon layer is caused, and the part of sulfur is firstly dissolved out in the subsequent circulating process, so that the irreversible specific capacity loss is greatly caused, and the capacity retention rate and the circulating stability of the battery are poor.

Claims (10)

1. A manganese dioxide @ sulfur @ carbon sphere positive electrode composite material with a yolk-shell structure is characterized in that: the manganese dioxide @ sulfur @ carbon sphere composite material takes manganese dioxide with a sheet structure as a core and is distributed in a cavity with a carbon sphere as a shell, sulfur is distributed between the manganese dioxide core and the carbon shell, the carbon content of the composite material is 10% -30%, the manganese dioxide content is 10% -30%, and the sulfur content is 40% -80%.
2. The yolk-shell structured manganese dioxide @ sulfur @ carbon sphere material of claim 1,
the yolk-shell structure manganese dioxide @ carbon sphere material has the hollow carbon sphere cavity inner diameter of 50-500 nm, the carbon layer thickness of 10-50 nm, micropores of 0-2 nm, mesopores of 2-50 nm and a specific surface area of 100-1000 m2g-1Pore volume of 0.1-2 cm3g-1。
3. A method for preparing manganese dioxide @ sulfur @ carbon sphere material with yolk-shell structure as claimed in claim 1, which comprises the following steps:
(1) synthesizing manganese carbonate: in a volume ratio of 2: 1-3, in a mixed solvent of water and one or more than two of ethylene glycol, propylene glycol, glycerol and butanediol, taking one or more than two of manganese sulfate, manganese chloride and manganese nitrate as a manganese source, taking one or more than two of sodium carbonate, sodium bicarbonate, potassium carbonate or potassium bicarbonate as a precipitator, preparing manganese carbonate, and performing suction filtration, washing and drying on a reaction product to obtain spherical manganese carbonate particles;
(2) synthesizing manganese carbonate @ silicon dioxide with a core-shell structure: dispersing manganese carbonate into a mixed solvent of water containing Cetyl Trimethyl Ammonium Bromide (CTAB), ethanol and alkali, wherein the alkali is one or more of ammonia water, aniline and benzylamine; dissolving tetraethyl orthosilicate (TEOS) by using ethanol as a solvent to prepare a solution with the TEOS content of 0.01-0.1 g/ml, dropwise adding the solution into the suspension at a constant speed of 5-20 ml/h, and performing suction filtration, washing and drying on a product to obtain silicon dioxide coated manganese carbonate nano-sphere particles with a core-shell structure;
(3) phenolic resin coated manganese carbonate @ silica: dispersing manganese carbonate @ silicon dioxide into a mixed solvent of water, ethanol and alkali containing CTAB, wherein the alkali is one or more of ammonia water, sodium hydroxide or potassium hydroxide; sequentially adding resorcinol and formaldehyde as carbon sources, generating a phenolic resin layer on the surface of the manganese carbonate @ silicon dioxide under the catalytic action of alkali, and performing suction filtration, washing and drying on the product to obtain the manganese carbonate @ silicon dioxide nano-sphere particles coated with the phenolic resin;
(4) carbonizing: putting the phenolic resin coated manganese carbonate @ silicon dioxide nanosphere particles prepared in the step (3) into a tubular furnace, and performing high-temperature pyrolysis carbonization in the atmosphere of argon and/or nitrogen to obtain carbon coated manganese carbonate @ silicon dioxide nanosphere particles;
(5) etching: dispersing the carbon-coated manganese carbonate @ silicon dioxide material prepared in the step (4) into a concentrated sodium hydroxide aqueous solution, reacting under a heating condition, etching off a silicon dioxide template layer, reacting with manganese carbonate to generate manganese dioxide, and performing suction filtration, washing and drying on a product to obtain a hollow yolk-shell structure @ manganese dioxide carbon sphere nano material;
(6) and (3) sulfur compounding: taking the manganese dioxide @ carbon material prepared in the step (5) and sublimed sulfur according to the mass ratio of 1: 2-6, transferring the mixture into a sealed bottle, and carrying out heat treatment under the atmosphere of argon and/or nitrogen to carry sulfur to obtain the manganese dioxide @ sulfur @ carbon sphere composite material with the yolk-shell structure.
4. The preparation method of the manganese dioxide @ sulfur @ carbon sphere cathode material with the yolk-shell structure as claimed in claim 3, wherein the volume ratio of water to alcohol in the mixed solvent in the step (1) is 2: 1-3; the molar ratio of the manganese salt to the precipitator is 1: 1-20; and adding the precipitator into the hydroalcoholic solution in which the manganese salt is dissolved, and reacting for 5-60 minutes under vigorous stirring.
5. The method for preparing manganese dioxide @ sulfur @ carbon sphere positive electrode material with the yolk-shell structure as claimed in claim 3, wherein tetraethyl orthosilicate is used in the mixed solvent in the step (2): cetyl trimethylammonium bromide: alkali: water: the ethanol molar ratio is 1: 1-5: 20-50: 5-50: 100-400; and dropwise adding the ethanol solution of tetraethyl orthosilicate into the suspension at a certain rate, wherein the dropwise adding speed is 5-20 ml/h.
6. The method for preparing manganese dioxide @ sulfur @ carbon cathode material of yolk-shell structure as claimed in claim 3, wherein the alkali in the mixed solution in the step (3): CTAB: water: the ethanol molar ratio is 1: 1-20: 500-2000: 1000-3000, adding resorcinol into a dispersion of manganese carbonate @ silicon dioxide, and adding a formaldehyde solution after 5-30 minutes, wherein the mass ratio of resorcinol: the molar ratio of the formaldehyde is 1: 1-5, and the stirring is continued for 12-36 hours, wherein the reaction temperature is 20-40 ℃.
7. The preparation method of the manganese dioxide @ sulfur @ carbon cathode material with the yolk-shell structure as claimed in claim 3, wherein the protective atmosphere in the step (4) is high-purity nitrogen and/or argon, the gas flow rate is 50-200 ml/min, the carbonization temperature is 600-900 ℃, the carbonization time is 1-10 hours, and the temperature rise rate from room temperature to the carbonization temperature is 1-10 ℃/min.
8. The preparation method of the manganese dioxide @ sulfur @ carbon cathode material with the yolk-shell structure as claimed in claim 3, wherein the concentration of sodium hydroxide in the step (5) is 1-6 mol/L.
9. The preparation method of the manganese dioxide @ sulfur @ carbon cathode material with the yolk-shell structure as claimed in claim 3, wherein the protective atmosphere in the step (6) is high-purity argon and/or high-purity nitrogen, the gas flow rate is 20-100 ml/min, the heat treatment temperature is 140-160 ℃, and the treatment time is 12-24 hours.
10. Use of a yolk-shell structured manganese dioxide @ sulfur @ carbon sphere material as claimed in claim 1 or 2, wherein: the manganese dioxide @ sulfur @ carbon sphere composite material is used as a positive electrode material and applied to a lithium-sulfur battery.
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