CN111600009B

CN111600009B - Molybdenum trioxide-molybdenum dioxide heterostructure complex and preparation method and application thereof

Info

Publication number: CN111600009B
Application number: CN202010358796.3A
Authority: CN
Inventors: 宫勇吉; 陈乾; 杨伟伟; 魏怡
Original assignee: Beihang University
Current assignee: Beijing zhongruitai New Material Co.,Ltd.
Priority date: 2020-04-29
Filing date: 2020-04-29
Publication date: 2021-12-03
Anticipated expiration: 2040-04-29
Also published as: CN111600009A

Abstract

The invention discloses a molybdenum trioxide-molybdenum dioxide heterostructure complex and a preparation method and application thereof. The preparation method comprises the following steps: adding carbon paper into a reaction solution containing a molybdenum source, reacting for 10-20 h at the pH value of 2-4 and the temperature of 140-180 ℃, and cooling to obtain molybdenum trioxide growing on the carbon paper; and under the atmosphere of inert gas and hydrogen, heating the molybdenum trioxide growing on the carbon paper to 300-500 ℃ at the speed of 5-15 ℃/min, and preserving heat for 1-2 hours to obtain the molybdenum trioxide. The molybdenum trioxide-molybdenum dioxide heterostructure complex has high specific surface area and higher reaction activity. By adopting proper reaction conditions, the appearance can be effectively protected, the product yield is improved, and the cost is reduced. The molybdenum trioxide-molybdenum dioxide heterostructure complex has more active sites, so that the molybdenum trioxide-molybdenum dioxide heterostructure complex has better application performance in the field of batteries.

Description

Molybdenum trioxide-molybdenum dioxide heterostructure complex and preparation method and application thereof

Technical Field

The invention relates to the technical field of electrode materials, in particular to a molybdenum trioxide-molybdenum dioxide heterostructure complex and a preparation method and application thereof.

Background

The application field of the lithium ion battery has been rapidly expanded from the first mobile communication to various aspects including various portable electronic products, relating to life and entertainment, military, aerospace, medical treatment and communication of people, and is developing to large and medium-sized energy storage devices, power sources and the like after the lithium ion battery has been born for less than 20 years now. The great commercial success of lithium ion batteries and the promotion of the development in the above field are incomparable with any secondary battery.

The most studied and used lithium ion battery positive electrode materials at present are mainly lithium transition metal oxides, includingHexagonal layered structure material (typically LiCoO for example)₂、LiNi_0.5Mn_0.5O₂And LiNi_1/3Co_1/3Mn_1/3O₂) Spinel-structured LiMn₂O₄Lithium-rich material Li_1+xM_xM′_1-xO_2+xAnd polyanion-based positive electrode materials (such as phosphate LiFePO)₄Silicate Li₂FeSiO₄And vanadate LiNiVO₄)。

The lithium-sulfur battery is one kind of lithium battery and belongs to the field of urgent development. Lithium Sulfur Batteries (LSBs) use elemental sulfur as the positive electrode and metal lithium as the negative electrode; the reaction mechanism is different from the ion extraction mechanism of the lithium ion battery, but is an electrochemical mechanism. During discharging, the negative electrode reacts to enable lithium to lose electrons and become lithium ions, the positive electrode reacts to enable sulfur, the lithium ions and the electrons to react to generate sulfide, and the potential difference between the positive electrode and the negative electrode is the discharging voltage provided by the lithium sulfur battery. Under the action of an applied voltage, the reaction of the positive electrode and the negative electrode of the lithium-sulfur battery is carried out reversely, namely, the charging process is carried out.

The lithium-sulfur battery has ultrahigh theoretical energy density (2600Wh kg)^-1) And ultrahigh theoretical specific capacity (1675mAh g^-1) And is considered to be the most promising material for the next generation of energy storage devices. In addition, the sulfur resource is rich, the cost is low, the environment is friendly, the biocompatibility is high, and the sulfur-containing material can play a role in high-capacity energy storage application.

Disclosure of Invention

The invention provides a molybdenum trioxide-molybdenum dioxide heterostructure complex and a preparation method and application thereof.

The invention provides a preparation method of a molybdenum trioxide-molybdenum dioxide heterostructure complex, which comprises the following steps:

adding carbon paper into a reaction solution containing a molybdenum source, reacting for 10-20 h at 140-180 ℃ under the condition that the pH value is 2-4, and cooling to obtain molybdenum trioxide growing on the carbon paper; and under the atmosphere of inert gas and hydrogen, heating the molybdenum trioxide growing on the carbon paper to 300-500 ℃ at the speed of 5-15 ℃/min, and preserving heat for 1-2 hours to obtain the molybdenum trioxide.

In the preparation method of the molybdenum trioxide-molybdenum dioxide heterostructure complex, preferably, the molybdenum source comprises one or more of molybdic acid tetrahydrate, ammonium molybdate, sodium molybdate, ammonium phosphomolybdate, molybdenum acetylacetonate, and molybdenum acetate; more preferably molybdic acid tetrahydrate.

According to the preparation method of the molybdenum trioxide-molybdenum dioxide heterostructure complex, the volume density of the carbon paper is preferably 0.5-0.9 g/cm³The porosity is 70-80%, and the air permeability is 1500-3000 ml.mm/(cm)²Hr · mmAq); the resistivity is 2 to 3m omega cm, and the thermal expansion coefficient is (0.5 to 1) × 10^-6/℃。

Preferably, the carbon paper satisfies at least one of the following characteristics:

(1) the bulk density of the carbon paper is 0.78g/cm³；

(2) The porosity was 75%;

(3) the air permeability is 2000 ml.mm/(cm)²·hr·mmAq)；

(4) The resistivity is 2.5m omega cm;

(5) coefficient of thermal expansion of-0.8X 10^-6/℃。

According to the preparation method of the molybdenum trioxide-molybdenum dioxide heterostructure complex, preferably, the reaction solution containing the molybdenum source further comprises nitric acid;

the mass volume ratio of the molybdenum source to the nitric acid is 1g: (1-5) mL; more preferably 1g: 3mL, wherein the nitric acid can adopt concentrated nitric acid with the concentration of 60-70% (for example, 68%).

According to the preparation method of the molybdenum trioxide-molybdenum dioxide heterostructure complex, the pH value is preferably 3-3.5.

According to the preparation method of the molybdenum trioxide-molybdenum dioxide heterostructure complex, the mass concentration of the molybdenum source in the reaction solution is preferably 0.1 g/(50-100) mL.

According to the preparation method of the molybdenum trioxide-molybdenum dioxide heterostructure complex, carbon paper is preferably added into a reaction solution containing a molybdenum source, the reaction is carried out for 10-15 hours at 160 ℃, and molybdenum trioxide growing on the carbon paper is obtained after cooling.

According to the preparation method of the molybdenum trioxide-molybdenum dioxide heterostructure complex, the molybdenum trioxide growing on the carbon paper is preferably heated to 350-400 ℃ at a rate of 5-15 ℃/min in an inert gas and hydrogen atmosphere, and the temperature is kept for 1-2 hours.

According to the preparation method of the molybdenum trioxide-molybdenum dioxide heterostructure complex, preferably, a molybdenum source is added into deionized water and stirred, nitric acid is added and stirred, and then carbon paper is added; the mass volume ratio of the molybdenum source to the deionized water is 0.1g (50-99) mL.

In another aspect, the invention provides a molybdenum trioxide-molybdenum dioxide heterostructure complex.

A molybdenum trioxide-molybdenum dioxide heterostructure complex is formed by directly growing a molybdenum trioxide-molybdenum dioxide heterostructure on carbon paper.

Preferably, the molar ratio of the molybdenum trioxide to the molybdenum dioxide is (3-4): 2.

preferably, the band gap of the molybdenum trioxide-molybdenum dioxide heterostructure is 0.65-0.80 eV per 1cm²The mass of the molybdenum trioxide and molybdenum dioxide heterostructure growing on the carbon paper is 0.3-0.6 mg; more preferably, the band gap is 0.70 to 0.75 eV.

The molybdenum trioxide-molybdenum dioxide heterostructure complex is preferably prepared by the preparation method of any one of the technical schemes.

The third aspect of the present invention provides an application of the molybdenum trioxide-molybdenum dioxide heterostructure complex in any one of the above technical schemes to a positive electrode plate of a lithium-sulfur battery.

Specifically, in the application of the positive electrode for the lithium-sulfur battery, the positive electrode piece of the lithium-sulfur battery takes the molybdenum trioxide-molybdenum dioxide heterostructure complex as a positive electrode piece substrate.

The fourth aspect of the present invention provides a method for preparing the positive electrode plate of the lithium-sulfur battery, including the following steps:

and (3) taking the molybdenum trioxide-molybdenum dioxide heterostructure complex as a positive pole piece substrate, and dropwise adding positive slurry to the surface of the substrate to obtain the composite material.

The positive electrode slurry comprises a positive electrode active material, and the positive electrode active material comprises one or more of dilithium octasulfide, dilithium hexasulfide, dilithium tetrasulfide, lithium sulfide and sulfur.

The invention also provides a lithium-sulfur battery which comprises the positive pole piece.

The invention also provides an electronic device comprising the lithium-sulfur battery of the invention.

The electronic device of the present invention includes electronic devices in general in the art, such as a notebook computer, a mobile phone, an electric motorcycle, an electric car, an electric toy, and the like.

The preparation method adopted by the invention has the advantages of simple process steps, environmental protection, easily obtained reaction raw materials, easily controlled reaction conditions, good repeatability, high yield up to 95 percent, low cost and better large-scale application potential.

The molybdenum trioxide-molybdenum dioxide heterostructure composite material provided by the invention grows on carbon paper, so that the specific surface area of the material can be effectively improved, and the material can have higher reactivity. By adopting proper annealing temperature, the appearance can be effectively protected and the synthesis purpose can be achieved. In the composite material, a transition interface exists between molybdenum trioxide and molybdenum dioxide in the molybdenum trioxide-molybdenum dioxide heterostructure compound, so that the molybdenum trioxide-molybdenum dioxide heterostructure has more active sites compared with other heterostructure materials with sharp interfaces.

And when the material is used as a lithium-sulfur battery positive electrode material, a pole piece blanking machine can be used for cutting the molybdenum trioxide-molybdenum dioxide heterostructure complex, and the material can be directly used as a battery positive electrode piece, so that the traditional coating process is omitted. The complex has stronger adsorption effect on the lithium polysulfide of the active substance of the positive electrode, reduces the loss of sulfur in the cycle process of the lithium-sulfur battery, and greatly improves the cycle performance.

Drawings

FIG. 1 is an SEM image of molybdenum trioxide from example 1;

FIG. 2 is an SEM image of a molybdenum trioxide-molybdenum dioxide heterostructure composite of example 1;

FIG. 3 is an XRD pattern of a molybdenum trioxide-molybdenum dioxide heterostructure complex of example 1;

FIG. 4 is an XPS plot of a molybdenum trioxide-molybdenum dioxide heterostructure complex of example 1;

FIG. 5-1 is a photograph comparing the dilithium sulfide solution (left) and the dilithium sulfide solution after adding carbon paper (right) in test example 1;

FIG. 5-2 is a photograph showing the results of testing the lithium polysulfide adsorption capacity of the molybdenum trioxide-molybdenum dioxide heterostructure complexes of examples 1-4 in Experimental example 1;

fig. 6 is a graph showing the results of cycle performance tests of the lithium sulfur batteries of example 11 and comparative example 2 in test example 2;

fig. 7 is a graph showing the results of rate performance tests of the lithium sulfur batteries of example 11 and comparative example 2 in experimental example 2.

Detailed Description

In order to make the objects, features and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

adding carbon paper into a reaction solution containing a molybdenum source, reacting at 140-180 ℃ for 10-20 h, and cooling to obtain molybdenum trioxide growing on the carbon paper; and under the atmosphere of inert gas and hydrogen, heating the molybdenum trioxide growing on the carbon paper to 300-500 ℃ at the speed of 5-15 ℃/min, and preserving heat for 1-2 hours to obtain the molybdenum trioxide.

The inventor finds that when the preparation is carried out under the conditions, the carbon paper is added under the hydrothermal condition of the pH value of 2-4, molybdenum trioxide can be nucleated on the surface of the carbon paper, a cluster-shaped appearance is obtained, and the specific surface area of the material is increased. And annealing is carried out at the temperature of 300-500 ℃, so that the molybdenum trioxide-molybdenum dioxide heterostructure is effectively synthesized.

In the invention, the inert gas can be one or more of inert gases conventional in the art, such as nitrogen, argon, helium and the like; the inert gas and hydrogen atmosphere of the present invention may be a nitrogen and hydrogen atmosphere, an argon and hydrogen atmosphere, a helium and hydrogen atmosphere.

According to the preparation method of the molybdenum trioxide-molybdenum dioxide heterostructure complex, the volume density of the carbon paper is preferably 0.5-0.9 g/cm³The porosity is 70-80%, and the air permeability is 1500-3000 ml.mm/(cm)²Hr · mmAq); the resistivity is 2 to 3m omega cm, and the thermal expansion coefficient is- (0.5 to 1) × 10^-6/℃。

The carbon paper which meets the parameters can be used for obtaining the molybdenum trioxide-molybdenum dioxide heterostructure complex with more stable performance. In the present application, the thermal expansion coefficient is an in-plane thermal expansion coefficient measured at 25 to 100 ℃.

(1) the bulk density of the carbon paper is 0.78g/cm³；

(2) The porosity was 75%;

(3) the air permeability is 2000ml & mm/(cm2 & hr & mmAq);

(4) the resistivity is 2.5m omega cm;

(5) coefficient of thermal expansion of-0.8X 10^-6/℃。

In the above feature, the carbon paper may satisfy only one of the above features, or 2 to 5 of the above features, and the present invention is not particularly limited thereto. The source of the carbon paper is not particularly limited, and the carbon paper can be prepared by adopting a method acceptable in the field or obtained by a commercial channel; such as available from shanghai hesen electric limited.

The carbon paper has the size of (2-5) cm x (1-3) cm.

The molybdenum source has the advantages of friendly reaction system and high reaction efficiency, and particularly, the molybdenum trioxide nanosheet synthesized by adopting molybdic acid tetrahydrate has smaller thickness.

the mass volume ratio of the molybdenum source to the nitric acid is 1g: (1-5) mL; more preferably 1g: 3 mL. Wherein, the nitric acid can adopt concentrated nitric acid with the concentration of 60-70% (for example, nitric acid with the concentration of 68%).

By adopting the mass-to-volume ratio, verification proves that molybdenum trioxide with larger specific surface area can be obtained, so that a molybdenum trioxide-molybdenum dioxide heterostructure complex with larger specific surface area can be obtained.

According to the preparation method of the molybdenum trioxide-molybdenum dioxide heterostructure complex, the pH value is preferably 3-3.5. The verification proves that under the specific pH value condition, the product yield is higher and can exceed 88%.

The inventors found that at the above-mentioned mass concentration ratio range, the synthesized molybdenum trioxide sheet layer was thinner.

According to the preparation method of the molybdenum trioxide-molybdenum dioxide heterostructure complex, carbon paper is preferably added into a reaction solution containing a molybdenum source, the reaction is carried out for 10-15 hours at 160 ℃ under the condition that the pH value is 2-4, and molybdenum trioxide growing on the carbon paper is obtained after cooling.

According to the preparation method of the molybdenum trioxide-molybdenum dioxide heterostructure complex, the molybdenum trioxide growing on the carbon paper is preferably heated to 350-400 ℃ at a rate of 5-15 ℃/min in an inert gas and hydrogen atmosphere, and the temperature is kept for 1-2 hours. The molybdenum trioxide-molybdenum dioxide heterostructure complex obtained under the control of the parameters has complete morphology and high material active area, and the yield of the product can be further improved; when the pH value of the system is 3-3.5 during the hydrothermal reaction, the product yield can reach 95%.

preferably, the band gap of the molybdenum trioxide-molybdenum dioxide heterostructure is 0.65-0.80 eV per 1cm²The mass of the molybdenum trioxide and molybdenum dioxide heterostructure growing on the carbon paper is 0.3-0.6 mg;

more preferably, the band gap is 0.70 to 0.75 eV.

The positive pole piece of the lithium-sulfur battery can also comprise a positive active material layer, and the positive active material layer can comprise the molybdenum trioxide-molybdenum dioxide heterostructure complex. The positive electrode active material layer of the present invention may further include a binder, a conductive agent, and sulfur powder.

In the present invention, the positive electrode current collector is not particularly limited as long as the object of the present invention can be achieved, and for example, may be a copper foil, an aluminum foil, or the like, and preferably an aluminum foil.

In the present invention, the conductive agent may be selected from conductive agents commonly used in the art, for example, the conductive agent includes at least one of carbon black, ketjen black, acetylene black, and carbon nanotubes. These conductive agents may be used alone or in combination of two or more. The content of the conductive agent is not particularly limited, and a conventional content may be used. For example, the content of the conductive agent may be 0.5 to 10 wt% of the positive electrode active material layer.

In the present invention, the binder may be selected from binders commonly used in the art, for example, the binder includes at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and polytetrafluoroethylene. These binders may be used alone or in combination of two or more. The binder content is not particularly limited, and for example, the binder content may be 0.5 to 10 wt% of the positive electrode active material layer.

The invention provides a lithium-sulfur battery, which comprises the positive pole piece. A lithium sulfur battery may include the positive electrode tab, the negative electrode tab, a separator, and an electrolyte.

In the present invention, the negative electrode sheet is not particularly limited, and may be any negative electrode sheet known in the art. For example, the negative electrode sheet is a lithium sheet.

In the present invention, the electrolyte is not particularly limited, and the electrolyte may be any one of a gel state, a solid state, and a liquid state. The present invention is not limited to the electrolytic solution as long as the object of the present invention can be achieved. For example, the liquid electrolyte includes a lithium salt and a nonaqueous solvent.

The lithium salt is not limited at all, and for example, the lithium salt may be selected from LiPF₆、LiBF₄、LiAsF₆、LiClO₄、LiB(C₆H₅)₄、LiCH₃SO₃、LiCF₃SO₃、LiN(SO₂CF₃)₂、LiC(SO₂CF₃)₃And LiPO₂F₂At least one of (1). These lithium salts may be used alone or in combination of two or more. For example, LiPF is used as lithium salt₆。

The nonaqueous solvent is not limited at all, and may be selected from at least one of carbonate compounds, carboxylate compounds, ether compounds, nitrile compounds, and other organic solvents, for example.

For example, the carbonate compound may be selected from diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), Vinyl Ethylene Carbonate (VEC), fluoroethylene carbonate (FEC), 1, 2-difluoroethylene carbonate, 1, 2-trifluoroethylene carbonate, 1,2, 2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1, 2-difluoro-1-methylethylene carbonate, 1, 2-trifluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1, 2-difluoro-1-methylethylene carbonate, 1, 2-trifluoro-2-methylethylene carbonate, 1-fluoro-2-methylethylene carbonate, and mixtures thereof, At least one of trifluoromethyl ethylene carbonate. These nonaqueous solvents may be used alone or in combination of two or more.

The separator is not particularly limited, and for example, the separator includes a polymer or inorganic substance formed of a material stable to the electrolyte of the present invention, or the like.

For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a film or a composite film having a porous structure, and the material of the substrate layer may be at least one selected from polyethylene, polypropylene, polyethylene terephthalate and polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is disposed on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

For example, the inorganic layer includes inorganic particles and a binder, and the inorganic particles are not particularly limited and may be, for example, at least one selected from the group consisting of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is not particularly limited, and may be, for example, one or a combination of several selected from polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer comprises a polymer, and the material of the polymer comprises at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

It will be understood by those skilled in the art that the foregoing description of the present invention is by way of example only, and not by way of limitation.

Example 1

The present example provides a molybdenum trioxide-molybdenum dioxide heterostructure composite and a method of making the same.

The method comprises the following specific steps:

(1) synthesis of molybdenum trioxide nanosheet

Adding 0.1g of ammonium molybdate tetrahydrate into a 100mL of polytetrafluoroethylene liner, adding 60mL of deionized water, stirring for 10min, adding 0.3mL of nitric acid, adjusting the pH value to 3, stirring for 30min, adding 4cm by 2cm of carbon paper, sealing the mixture in a hydrothermal reaction kettle, transferring the hydrothermal reaction kettle to an oven, reacting for 12h at 160 ℃, then cooling the mixed solution for 24h at normal temperature, and respectively cleaning the obtained solution with deionized water and ethanol for three times for later use to obtain white molybdenum trioxide growing on the carbon paper with the thickness of about 10 nm.

The SEM image of the white molybdenum trioxide grown on the carbon paper prepared in the step is shown in the attached figure 1.

The volume density of the carbon paper is 0.78g/cm³Porosity of 75%, air permeability of 2000 ml.mm/(cm)²Hr. mmAq), resistivity of 2.5 m.OMEGA.cm, coefficient of thermal expansion-0.8X 10^-6/℃。

(2) Preparation of molybdenum trioxide-molybdenum dioxide heterostructure complex

And placing the obtained molybdenum trioxide in a tubular furnace, heating to 400 ℃ at the speed of 10 ℃ per minute in the atmosphere of hydrogen and argon mixed gas, keeping the temperature at 400 ℃ for one hour, cooling to room temperature after the reaction is finished, taking out a sample, and finally obtaining the molybdenum trioxide-molybdenum dioxide heterostructure complex.

The SEM image of the molybdenum trioxide-molybdenum dioxide heterostructure complex prepared in the step is shown in the attached figure 2. As can be seen from the comparison of FIG. 1 and FIG. 2, the morphology of the molybdenum trioxide-molybdenum dioxide heterostructure complex is not significantly changed after the annealing in step (2).

XRD patterns of the molybdenum trioxide prepared in the step (1) and the molybdenum trioxide-molybdenum dioxide heterostructure prepared in the step (2) are shown in figure 3, and it can be seen that after annealing, the molybdenum trioxide-molybdenum dioxide heterostructure XRD is MoO before the retention₃MoO is increased on the premise of peak₂The peak of (marked by a ×) in the figure.

XPS (XPS) graphs of the molybdenum trioxide prepared in the step (1) and the molybdenum trioxide-molybdenum dioxide heterostructure prepared in the step (2) are shown in the attached figure 4, and Mo can be seen⁴⁺And Mo⁶⁺Peak of (2).

The molybdenum trioxide-molybdenum dioxide heterostructure complex yield of this example was calculated to be 95%.

Example 2

The present example provides a molybdenum trioxide-molybdenum dioxide heterostructure composite and a method of making the same. The difference from the example 1 is that in the hydrothermal synthesis in the step (1), the pH value is adjusted to 2, and the molybdenum source is sodium molybdate.

The molybdenum trioxide-molybdenum dioxide heterostructure complex yield of this example was calculated to be 85%.

Example 3

The present example provides a molybdenum trioxide-molybdenum dioxide heterostructure composite and a method of making the same. The difference from example 1 is that the annealing in step (2) is carried out at a temperature of 300 ℃ for one hour.

The molybdenum trioxide-molybdenum dioxide heterostructure complex yield of this example was calculated to be 90%.

Example 4

The present example provides a molybdenum trioxide-molybdenum dioxide heterostructure composite and a method of making the same. The difference from example 1 is that the annealing in step (2) is carried out at a temperature of 500 ℃ for one hour.

The molybdenum trioxide-molybdenum dioxide heterostructure complex yield of this example was calculated to be 88%.

Example 5

The present example provides a molybdenum trioxide-molybdenum dioxide heterostructure composite and a method of making the same. The difference from example 1 is that in the hydrothermal synthesis of step (1), the pH value is adjusted to 3.5.

The molybdenum trioxide-molybdenum dioxide heterostructure complex yield of this example was calculated to be 92%.

Example 6

The present example provides a molybdenum trioxide-molybdenum dioxide heterostructure composite and a method of making the same. The difference from example 1 is that in the hydrothermal synthesis of step (1), the pH value is adjusted to 4.

The molybdenum trioxide-molybdenum dioxide heterostructure complex yield of this example was calculated to be 89%.

Example 7

This example provides a positive electrode plate for a lithium-sulfur battery, using the molybdenum trioxide-molybdenum dioxide heterostructure composite of example 1.

0.0699g of lithium sulfide and 0.3366g of sulfur were mixed in 5ml of the electrolyte and stirred at 60 ℃ for 24h to give a homogeneous solution of dilithium octasulfide. And then, cutting the molybdenum trioxide-molybdenum dioxide heterostructure complex of the embodiment 1 into a wafer with the diameter of 14mm by using a pole piece punching machine to be used as a substrate of the positive pole piece of the button lithium-sulfur battery, and dropwise adding 12.5 microliters of lithium octasulfide solution on the surface of the wafer to finally obtain the positive pole of the lithium-sulfur battery.

Example 8

The only difference from example 7 is that the molybdenum trioxide-molybdenum dioxide heterostructure complex of example 1 was replaced with the molybdenum trioxide-molybdenum dioxide heterostructure complex of example 2.

Example 9

The only difference from example 7 is that the molybdenum trioxide-molybdenum dioxide heterostructure complex of example 1 was replaced with the molybdenum trioxide-molybdenum dioxide heterostructure complex of example 3.

Example 10

The only difference from example 7 is that the molybdenum trioxide-molybdenum dioxide heterostructure complex of example 1 was replaced with the molybdenum trioxide-molybdenum dioxide heterostructure complex of example 4.

Example 11

This example provides a lithium-sulfur battery, in which the positive electrode sheet of example 7 is used as a positive electrode, a lithium sheet is used as a negative electrode, a polypropylene porous membrane (Celgard 2400) is used as a semipermeable membrane, 1M lithium bistrifluoromethylenesulfonamide is used as an electrolyte salt, 1, 3-Dioxolane (DOL) and ethylene glycol dimethyl ether (DME) (v/v ═ 1:1) are used as mixed solvents, and 1% of LiNO is added₃. The whole assembly process is completed in the glove box, and the oxygen content and the water content are both controlled to be less than or equal to 0.1ppm in the assembly process.

Example 12

The only difference from example 11 is that the positive electrode tab of example 7 was replaced with the positive electrode tab of example 8.

Example 13

The only difference from example 11 is that the positive electrode sheet of example 7 was replaced with the positive electrode sheet of example 9.

Example 14

The only difference from example 11 is that the positive electrode sheet of example 7 was replaced with the positive electrode sheet of example 10.

Comparative example 1

The present comparative example provides a lithium sulfur battery.

Positive pole piece: 0.0699g of lithium sulfide and 0.3366g of sulfur were mixed in 5ml of the electrolyte and stirred at 60 ℃ for 24h to give a homogeneous solution of dilithium octasulfide. And cutting the carbon paper into a wafer with the diameter of 14mm by using a pole piece die cutter to serve as the anode substrate of the button type lithium-sulfur battery, and dropwise adding 12.5 microliters of lithium octasulfide solution on the surface of the wafer to finally obtain the anode of the lithium-sulfur battery.

Lithium sheet is used as a negative electrode, a polypropylene porous membrane (Celgard 2400) is used as a semipermeable membrane, 1M lithium bistrifluoromethylenesulfonamide is used as electrolyte salt, 1, 3-Dioxolane (DOL) and ethylene glycol dimethyl ether (DME) (v/v is 1:1) are used as mixed solvents, and 1% of LiNO is added into the electrolyte₃. The whole assembly process is completed in the glove box, and the oxygen content and the water content are both controlled to be less than or equal to 0.1ppm in the assembly process.

Comparative example 2

This comparative example provides a lithium Sulfur battery prepared by replacing the molybdenum trioxide-molybdenum dioxide heterostructure composite material of example 1 employed with a molybdenum dioxide-molybdenum nitride heterostructure material as disclosed In the In-Situ chemical nickel depletion move 2-Mo2N Binary Nanobelts as Multifunctional Interlayer for Fast-kinetic Li-Sulfur Batteries, by the following steps, In comparison with example 9:

dissolving 0.48g of molybdenum powder in 10ml of 30% hydrogen peroxide, adding 60ml of deionized water, stirring for 40 minutes, pouring the light yellow transparent solution into a 100ml polytetrafluoroethylene liner, filling the liner into an autoclave, and reacting in an oven for 6 hours at 180 ℃. And after the reaction is finished, collecting the sample by vacuum filtration, washing the sample by water and ethanol for multiple times, and finally drying the sample in a vacuum furnace at the temperature of 80 ℃ for 12 hours to obtain a molybdenum trioxide sample. Annealing the obtained molybdenum trioxide sample for 2h under the condition of 500 ℃ ammonia gas, cooling to room temperature, and passivating for 12h under the mixed gas of oxygen/nitrogen (10%/90%), thereby obtaining the molybdenum dioxide-molybdenum nitride heterostructure material.

Test example 1

The present test example provides a test of the lithium polysulfide adsorption capacity of the molybdenum trioxide-molybdenum dioxide heterostructure composites of examples 1 to 4.

The experimental method comprises the following steps: a10 mM solution of dilithium tetrasulfide was prepared. Mixing lithium sulfide and sulfur according to a molar ratio of 1: 3 is dissolved in the electrolyte and stirred at 60 ℃ for 24h to obtain a yellowish uniform dilithium tetrasulfide solution, 5 parts are taken out and filled into vials.

Then, the molybdenum trioxide-molybdenum dioxide heterostructure complexes of the embodiments 1 to 4 with the same area are respectively placed into a small bottle filled with a dilithium tetrasulfide solution, carbon paper with the same area is placed into a small bottle filled with the dilithium tetrasulfide solution, after 6 hours of adsorption, the color change of the solution in 5 small bottles is observed, and the more obvious yellow fading is, which indicates that the sample has better adsorption effect on lithium polysulfide.

The experimental results are as follows:

as shown in fig. 5-1, 5-2 and table 1.

TABLE 1

	Adsorption test results (color of solution)
		Example 1	Near colorless
Example 2	Deep yellow
		Example 3	Light yellow
Example 4	Light yellow

As shown in FIG. 5-1, the color of the prepared dilithium sulfide solution (left) and the color of the dilithium sulfide solution after adding the carbon paper (right) are compared. It can be seen that the solution color changed to near orange upon addition of the carbon paper.

As can be seen from fig. 5-2, the color of the solution containing the molybdenum trioxide-molybdenum dioxide heterostructures of examples 1 to 4 faded from the color of the dilithium sulfide solution containing the carbon paper (in fig. 5-2, example 3, example 1, and example 4 are shown in order from the left) at the same adsorption time, and it is understood that the molybdenum trioxide-molybdenum dioxide heterostructures of examples 1 to 4 have excellent lithium polysulfide adsorption ability, and it is also possible to assume without any doubt that the molybdenum trioxide-molybdenum dioxide heterostructures of examples 1 to 4 have a large specific surface area.

The fading of the dilithium tetrasulfide solution after the test in example 1 is most obvious, which shows that the molybdenum trioxide-molybdenum dioxide heterostructure complex generated under the synthesis condition in example 1 has stronger adsorption capacity, and the molybdenum trioxide-molybdenum dioxide heterostructure complex can be assuredly presumed to have larger specific surface area compared with examples 2-4.

Meanwhile, for the lithium sulfur battery, the inhibition of the shuttling effect of lithium polysulfide is one of the important approaches for solving the cycling stability of the lithium sulfur battery. The stronger the adsorption capacity to lithium polysulfide is, the shuttle effect of lithium polysulfide can be reduced in the battery cycle, and the performance of the lithium sulfur battery can be improved.

Test example 2

The test examples provide cycle performance tests and rate performance tests for the lithium sulfur batteries of examples 11-14.

The experimental method comprises the following steps: the electrochemical performance test adopts a standard CR2025 button cell;

and (3) testing the cycle performance: the lithium sulfur batteries prepared in examples 11 to 14 and comparative examples 1 to 2 were tested at 25 ℃ for system current density 1C (1C: 800mA g) in constant current blue CT2001A^-1) And the charging voltage range is 1.8V-2.8V, full-charge and full-discharge cycle test is carried out until the cycle reaches 300 circles, and the test is finished, and experimental data are recorded to compare the capacity attenuation of the battery.

And (3) rate performance test:

the lithium sulfur batteries prepared in examples 11 to 14 and comparative examples 1 to 2 were tested at 25 ℃ in a constant current blue CT2001A test system at a current density of 0.1C-10C (1C ═ 800mA g)^-1) And the charging voltage range is 1.8V-2.8V, full-filling and full-discharging cycle tests are carried out, 10 cycles are carried out at each multiplying power until the final cycle is repeated to 0.1C, the test is finished, and experimental data are recorded.

The experimental results are as follows: as shown in tables 2 and 3.

TABLE 2

As shown In Table 2, wherein the comparison of the cycle performance of the lithium-Sulfur battery of example 9 with that of examples 10, 11, 12 and 1 is shown In FIG. 6, the performance of comparative example 2 In Table 2 is derived from the corresponding document In-Situ-electrochemical calibration Derivative MoO2-Mo2N Binary Nanobelts as Multifunctional Interlayer for Fast-kinetic Li-Sulfur Batteries.

From fig. 6, it can be seen that the specific capacity of the lithium-sulfur battery adopting the molybdenum trioxide-molybdenum dioxide heterostructure complex provided by the invention is significantly improved compared with that of a lithium-sulfur battery adopting pure carbon paper. And the lithium-sulfur battery of example 11 has the most excellent performance, the specific capacity can reach 900, and a lower decay rate is maintained, which has obvious advantages compared with comparative example 2.

TABLE 3

As shown in Table 3, the rate capability of the lithium-sulfur battery of example 11 was comparable to that of the battery of example 12,

Comparison of example 13, example 14, comparative example 1 As shown In FIG. 7, comparative example 2 In Table 3 is performed from the corresponding In-Situ chemical differentiation Derivative MoO2-Mo2N Binary Nanobelts as multifunctionality Interlayer for Fast-kinetic Li-sulfurfuel Batteries. As can be seen from fig. 7, cycling is performed at different test rates, and it can be seen that the performance of the molybdenum trioxide-molybdenum dioxide heterostructure composite provided by the present invention as a sulfur carrier is higher than that of a lithium sulfur battery made of pure carbon paper at each rate, and the molybdenum trioxide-molybdenum dioxide heterostructure composite has better stability, and the performance advantage is more obvious at high rate. The rapid charge and discharge performance of the molybdenum trioxide-molybdenum dioxide heterostructure is obviously improved compared with the prior art, and a thought is provided for the development of the rapid charge technology.

Therefore, the molybdenum trioxide-molybdenum dioxide heterostructure complex provided by the invention has a higher specific surface area and more active sites, so that the molybdenum trioxide-molybdenum dioxide heterostructure complex can be applied to a lithium-sulfur battery, the sulfur loss is reduced, the shuttle effect is reduced, and the cycle performance of the battery is improved.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.

Claims

1. A preparation method of a molybdenum trioxide-molybdenum dioxide heterostructure complex is characterized by comprising the following steps:

adding carbon paper into a reaction solution containing a molybdenum source, reacting for 10-20 h at 140-180 ℃ under the condition that the pH value is 2-4, and cooling to obtain molybdenum trioxide growing on the carbon paper; heating the molybdenum trioxide growing on the carbon paper to 300-500 ℃ at a speed of 5-15 ℃/min in an inert gas and hydrogen atmosphere, and preserving heat for 1-2 hours to obtain the molybdenum trioxide;

the molybdenum source comprises one or more of molybdic acid tetrahydrate, ammonium molybdate, sodium molybdate, ammonium phosphomolybdate, molybdenum trioxide, molybdenum acetylacetonate, and molybdenum acetate; the mass concentration of the molybdenum source in the reaction solution is 0.1 g/(50-100) mL;

the molybdenum trioxide-molybdenum dioxide heterostructure complex is applied to a positive pole piece substrate of a lithium-sulfur battery.

2. The method of claim 1, wherein the molybdenum source is molybdic acid tetrahydrate.

3. The method according to claim 1, wherein the pH is 3 to 3.5.

4. The production method according to claim 1, characterized in that the reaction solution containing a molybdenum source further comprises nitric acid; the mass volume ratio of the molybdenum source to the nitric acid is 1g: (1-5) mL.

5. The preparation method according to claim 4, wherein the mass-to-volume ratio of the molybdenum source to the nitric acid is 1g: 3 mL.

6. The production method according to claim 2, wherein the reaction solution containing a molybdenum source further comprises nitric acid; the mass volume ratio of the molybdenum source to the nitric acid is 1g: (1-5) mL.

7. The preparation method according to claim 6, wherein the mass-to-volume ratio of the molybdenum source to the nitric acid is 1g: 3 mL.

8. The method of any one of claims 1-4, wherein the carbon paper has a bulk density of 0.5 to 0.9g/cm³The porosity is 70-80%, and the air permeability is 1500-3000 ml.mm/(cm)²Hr · mmAq); the resistivity is 2 to 3M omega cm, and the thermal expansion coefficient is (0.5 to 1) × 10^-6/℃。

9. The method of manufacturing according to claim 8, wherein the carbon paper satisfies at least one of the following characteristics:

(1) the bulk density of the carbon paper is 0.78g/cm³；

(2) The porosity was 75%;

(3) the air permeability is 2000 ml.mm/(cm)²·hr·mmAq)；

(4) The resistivity is 2.5m omega cm;

(5) coefficient of thermal expansion of-0.8X 10^-6/℃。

10. The method of claim 6, wherein the carbon paper has a bulk density of 0.5 to 0.9g/cm³The porosity is 70-80%, and the air permeability is 1500-3000 ml.mm/(cm)²Hr · mmAq); the resistivity is 2 to 3M omega cm, and the thermal expansion coefficient is (0.5 to 1) × 10^-6/℃。

11. The method of manufacturing according to claim 10, wherein the carbon paper satisfies at least one of the following characteristics:

(1) the bulk density of the carbon paper is 0.78g/cm³；

(2) The porosity was 75%;

(3) the air permeability is 2000 ml.mm/(cm)²·hr·mmAq)；

(4) The resistivity is 2.5m omega cm;

(5) coefficient of thermal expansion of-0.8X 10^-6/℃。

12. A molybdenum trioxide-molybdenum dioxide heterostructure complex is characterized in that a molybdenum trioxide-molybdenum dioxide heterostructure directly grows on carbon paper; prepared by the method of any one of claims 1 to 5.

13. The molybdenum trioxide-molybdenum dioxide heterostructure complex of claim 12, wherein the molar ratio of molybdenum trioxide to molybdenum dioxide is (3-4): 2; and/or the band gap of the molybdenum trioxide-molybdenum dioxide heterostructure is 0.65-0.80 eV per 1cm²The mass of the molybdenum trioxide and molybdenum dioxide heterostructure growing on the carbon paper is 0.3-0.6 mg.

14. The molybdenum trioxide-molybdenum dioxide heterostructure complex of claim 13, wherein the molybdenum trioxide-molybdenum dioxide heterostructure has an energy bandgap of 0.70 to 0.75 eV.

15. A positive pole piece of a lithium-sulfur battery is characterized in that the molybdenum trioxide-molybdenum dioxide heterostructure complex of claim 12 or 13 is used as a positive pole piece substrate.

16. The method for preparing the positive pole piece of claim 15 is characterized in that the molybdenum trioxide-molybdenum dioxide heterostructure complex is used as a positive pole piece substrate, and positive pole slurry is dripped on the surface of the substrate to obtain the positive pole piece; the positive electrode slurry comprises a positive electrode active material, and the positive electrode active material comprises one or more of dilithium octasulfide, dilithium hexasulfide, dilithium tetrasulfide, lithium sulfide and sulfur.

17. A lithium-sulfur battery comprising the positive electrode sheet according to claim 15.

18. An electronic device comprising the lithium-sulfur battery according to claim 17.