阅读说明：本技术 包覆型结构锂硫电池自支撑正极的制备方法及应用 (Preparation method and application of self-supporting positive electrode of lithium-sulfur battery with coated structure ) 是由 曹俊 王怡 张延玉 杨东平 于 2020-05-29 设计创作，主要内容包括：本发明属于电化学领域,具体涉及一种包覆型结构锂硫电池自支撑正极的制备方法及应用。氧化石墨烯水分散液、MXene水分散液、硫源和盐酸混合搅拌,一次水热反应得到RGO/MXene-S复合水凝胶,将RGO/MXene-S复合水凝胶切片后浸入氧化石墨烯水分散液和MXene水分散液的混合水分散液中进行二次水热反应,冷冻干燥后压片,即得RGO/MXene-S@RGO/MXene复合电极。本发明利用电极中RGO和MXene的物理吸附和化学键合作用抑制了锂硫电池的穿梭效应；同时独立自支撑结构的设计,可以大大提高电池的能量密度,具有方法简单、适用性广、良好的电化学性能等优点。(The invention belongs to the field of electrochemistry, and particularly relates to a preparation method and application of a self-supporting positive electrode of a lithium-sulfur battery with a cladding structure. Mixing and stirring the graphene oxide aqueous dispersion, the MXene aqueous dispersion, a sulfur source and hydrochloric acid, carrying out a primary hydrothermal reaction to obtain RGO/MXene-S composite hydrogel, slicing the RGO/MXene-S composite hydrogel, immersing the sliced RGO/MXene-S composite hydrogel into a mixed aqueous dispersion of the graphene oxide aqueous dispersion and the MXene aqueous dispersion for a secondary hydrothermal reaction, and carrying out freeze drying and tabletting to obtain the RGO/MXene-S @ RGO/MXene composite electrode. The shuttle effect of the lithium-sulfur battery is inhibited by utilizing the physical adsorption and chemical bonding effects of RGO and MXene in the electrode; meanwhile, due to the design of the independent self-supporting structure, the energy density of the battery can be greatly improved, and the method has the advantages of simplicity, wide applicability, good electrochemical performance and the like.)

1. A preparation method of a self-supporting positive electrode of a lithium-sulfur battery with a coated structure is characterized in that graphene oxide aqueous dispersion, MXene aqueous dispersion, a sulfur source and hydrochloric acid are mixed and stirred, an RGO/MXene-S composite hydrogel is obtained through a first hydrothermal reaction, the RGO/MXene-S composite hydrogel is sliced and then immersed into mixed aqueous dispersion of the graphene oxide aqueous dispersion and the MXene aqueous dispersion for a second hydrothermal reaction, and the RGO/MXene-S @ RGO/MXene composite electrode is obtained through freeze drying and tabletting.

2. The preparation method of the self-supporting positive electrode of the lithium-sulfur battery with the coated structure according to claim 1, wherein the graphene oxide aqueous dispersion is prepared by mixing concentrated sulfuric acid, graphite, sodium nitrate and potassium permanganate, preserving heat in a water bath, adding water for dilution under an ice bath condition, adding hydrogen peroxide, washing with hydrochloric acid and deionized water, performing ultrasonic centrifugation, and taking supernatant to obtain the graphene oxide aqueous dispersion.

3. The method of claim 1, wherein the MXene aqueous dispersion is prepared by mixing Ti with the above solution₃AlC₂Adding into HF solution for etching, centrifugally washing to obtain MXene, adding dimethyl sulfoxide intercalation, dissolving the intercalated MXene in deionized water, and ultrasonically and centrifugally treating to obtain MXene water dispersion.

4. The method of claim 1, wherein the sulfur source is Na₂S₂O₃·5H₂O, the concentration of the graphene oxide aqueous dispersion is 5-10 mg/ml^-1The concentration of MXene aqueous dispersion is 5-10 mg/ml^-1。

5. The method for preparing the self-supporting positive electrode of the lithium-sulfur battery with the cladding structure according to claim 1, wherein the mass ratio of the graphene oxide aqueous dispersion to the MXene aqueous dispersion in the first hydrothermal reaction is 15-80: 10-50.

6. The preparation method of the self-supporting positive electrode of the lithium-sulfur battery with the cladding structure according to claim 1, wherein the ratio of the graphene oxide aqueous dispersion to the sulfur source in the first hydrothermal reaction is 3-8: 350-560, the graphene oxide aqueous dispersion is calculated by ml, and the sulfur source is calculated by mg.

7. The method for preparing the self-supporting positive electrode of the lithium-sulfur battery with the cladding structure as claimed in claim 1, wherein the ratio of the sulfur source to the hydrochloric acid is 350-560: 5-15, the sulfur source is measured by mg, and the hydrochloric acid is measured by ml.

8. The method for preparing the self-supporting positive electrode of the lithium-sulfur battery with the cladding structure according to claim 1, wherein the mass ratio of the graphene oxide aqueous dispersion to the MXene aqueous dispersion in the mixed aqueous dispersion of the graphene oxide aqueous dispersion and the MXene aqueous dispersion is 5-20: 5-20.

9. The method for preparing the self-supporting positive electrode of the lithium-sulfur battery with the coating structure according to claim 1, wherein the temperature of the first hydrothermal reaction is 90-160 ℃, the time of the first hydrothermal reaction is 8-12h, the temperature of the second hydrothermal reaction is 90-160 ℃, and the time of the second hydrothermal reaction is 8-12 h.

10. The application of the self-supporting positive electrode of the lithium-sulfur battery with the coating structure obtained by the preparation method of any one of claims 1 to 9 is characterized in that a negative electrode is placed in a negative electrode shell, then a diaphragm is added, an electrolyte is dropwise added, then an RGO/MXene-S @ RGO/MXene composite electrode is placed, then a gasket and an elastic sheet are added, a positive electrode shell is covered, and finally a packaging machine is used for sealing to obtain the lithium-sulfur battery.

Technical Field

The invention belongs to the field of electrochemistry, and particularly relates to a preparation method and application of a self-supporting positive electrode of a lithium-sulfur battery with a cladding structure.

Background

The current human society depends on the use of fossil fuel which has the characteristics of non-regeneration, environmental pollution and the like, so that the energy crisis and the environmental problem caused by the fossil fuel become two major problems faced by people. Therefore, the development of green clean energy such as solar energy, wind energy, geothermal energy and tidal energy is gradually becoming a trend of current social development. However, these renewable energy sources are periodic and intermittent, and therefore, in order to realize continuous supply of energy, an appropriate energy storage system is required to store energy. Based on this, rechargeable secondary batteries having high energy density, such as lead-acid batteries, nickel-hydrogen batteries, nickel-cadmium batteries, lithium ion batteries, and the like, have been developed. Among them, lithium ion batteries have been used as lithium cobaltate (LiCoO) for the past thirty years, because of their relatively superior energy density₂) And graphite as the positive and negative electrodes, respectively, are widely used in consumer electronics products. However, the currently used transition metal oxides have low theoretical capacity and high cost, which greatly limits the application of the conventional lithium ion batteries in the fields of emerging electric vehicles and unmanned aerial vehicles. Therefore, the development of a rechargeable battery with higher energy density is increasingly important. The electrochemical conversion mechanism of the lithium-sulfur battery, which is one of lithium ion batteries, relates to a reaction process of two electrons, and the energy density of the lithium-sulfur battery is as high as 2567 Wh.kg^-1Theoretical specific capacity up to 1675mAh g^-1. Meanwhile, the elemental sulfur has the advantages of abundant reserves, low price, environmental friendliness and the like. Therefore, lithium-sulfur batteries are one of the research hotspots in the current battery field.

The electrode of the conventional lithium sulfur battery is generally prepared by a slurry coating method, i.e., an electrode material, a conductive additive and a binder are dispersed in an organic solvent to prepare a slurry, and then the slurry is coated on a metal current collector. However, the electrode prepared by the method is easy to cause the anode material to fall off in the deformation process of repeated bending and the like of the electrode, so that the performance of the battery is attenuated. In addition, the non-electrochemical active materials such as the conductive agent, the binder and the metal current collector occupy certain electrode mass, so that the overall mass of the battery is increased, and the energy density of the lithium-sulfur battery is reduced. Therefore, the preparation of independent self-supporting electrode materials without binder and other non-electrochemical active components is one of the key approaches for improving the overall performance of the lithium-sulfur battery. In addition, lithium polysulfide generated in the charging and discharging processes of the lithium-sulfur battery is easily dissolved in organic electrolyte to form a shuttle effect, so that the problems of low coulombic efficiency, fast capacity attenuation, high self-discharge rate and the like are caused.

Graphene is a single-layer two-dimensional carbon material, and the special structure of graphene enables the graphene to have a large specific surface area, high mechanical properties and good electrical and thermal conductivity. Moreover, Graphene Oxide (GO) and Reduced Graphene Oxide (RGO), which are derivatives of graphene, can be used as basic structural units to assemble graphene macroscopic materials, including one-dimensional graphene nanowires/nanofibers, two-dimensional graphene films/graphene papers, three-dimensional graphene foams, and the like. Due to the special structure, the graphene macrostructures generally have higher conductivity and mechanical property, so that the graphene macrostructures can be directly used for preparing a self-supporting positive electrode of a lithium-sulfur battery and applied to the lithium-sulfur battery so as to meet the requirement of the modern electronic information era on development of flexible electronic equipment. Besides graphene, the novel two-dimensional material MXene is a novel transition metal carbide two-dimensional crystal, and has the advantages of good conductivity, low ion diffusion resistance, low open-circuit voltage and high storage capacity. Therefore, MXene has also been the subject of major research in recent years from the building of electrodes for supported lithium sulfur batteries. However, the problem of self-aggregation of graphene and MXene in the process of preparing an electrode still needs to be solved.

Disclosure of Invention

The invention aims to provide a preparation method of a self-supporting positive electrode of a lithium-sulfur battery with a cladding structure, which can effectively inhibit sheet layer agglomeration, the prepared self-supporting positive electrode of the lithium-sulfur battery with the cladding structure does not need to add a traditional binder and a traditional current collector, improves the energy density of the battery, realizes the physical and chemical double inhibition of the shuttling effect of lithium polysulfide of an electrode discharge product, and has the advantages of simple method, wide applicability, good electrochemical performance and the like.

The preparation method of the self-supporting anode of the lithium-sulfur battery with the coating structure comprises the steps of mixing and stirring graphene oxide aqueous dispersion, MXene aqueous dispersion, a sulfur source and hydrochloric acid, carrying out a first hydrothermal reaction to obtain RGO/MXene-S composite hydrogel, slicing the RGO/MXene-S composite hydrogel, immersing the sliced RGO/MXene-S composite hydrogel into mixed aqueous dispersion of the graphene oxide aqueous dispersion and the MXene aqueous dispersion to carry out a second hydrothermal reaction, and carrying out freeze drying and tabletting to obtain the RGO/MXene-S @ RGO/MXene composite electrode.

The preparation method of the graphene oxide aqueous dispersion comprises the steps of mixing concentrated sulfuric acid, graphite, sodium nitrate and potassium permanganate, preserving heat in a water bath, adding water for dilution under the ice bath condition, adding hydrogen peroxide, washing with hydrochloric acid and deionized water, performing ultrasonic centrifugation, and taking supernate to obtain the two-dimensional layered graphene oxide aqueous dispersion.

The ratio of concentrated sulfuric acid, graphite, sodium nitrate, potassium permanganate and hydrogen peroxide is 70-90: 1.5-3: 1.5-3: 7-9: 15-20, wherein the concentrated sulfuric acid and the hydrogen peroxide are counted by ml, the graphite, the sodium nitrate and the potassium permanganate are counted by g, and the concentration of the concentrated sulfuric acid is 18.4 mol/L; the heat preservation temperature is 35-45 ℃, and the heat preservation time is 50-70 min.

The MXene aqueous dispersion is prepared by mixing Ti₃AlC₂Adding into HF solution for etching, centrifuging and washing to obtain MXene, adding dimethyl sulfoxide (DMSO) intercalation, dissolving the intercalated MXene in deionized water, and ultrasonically centrifuging to obtain MXene water dispersion.

The Ti₃AlC₂And HF in a ratio of 1-3: 30 to 50, Ti₃AlC₂In g, HF in ml; the etching temperature is 35-55 ℃, and the etching time is 18-24 h.

The ratio of MXene to dimethyl sulfoxide is 0.5-2: 50-200, wherein MXene is calculated by g, and dimethyl sulfoxide is calculated by ml.

The sulfur source is Na₂S₂O₃·5H₂O。

The concentration of the hydrochloric acid is 0.5-1 mol/L.

The concentration of the graphene oxide aqueous dispersion is 5-10 mg/ml^-1。

The concentration of the MXene aqueous dispersion is 5-10 mg/ml^-1。

The mass ratio of the graphene oxide aqueous dispersion to the MXene aqueous dispersion in the first hydrothermal reaction is 15-80: 10-50.

The ratio of the graphene oxide aqueous dispersion to the sulfur source in the one-time hydrothermal reaction is 3-8: 350-560, the graphene oxide aqueous dispersion is calculated by ml, and the sulfur source is calculated by mg.

The mixture ratio of the sulfur source to the hydrochloric acid is 350-560: 5-15, the sulfur source is measured by mg, and the hydrochloric acid is measured by ml.

The mass ratio of the graphene oxide aqueous dispersion to the MXene aqueous dispersion in the mixed aqueous dispersion of the graphene oxide aqueous dispersion and the MXene aqueous dispersion is 5-20: 5-20.

The temperature of the first hydrothermal reaction is 90-160 ℃, and the time of the first hydrothermal reaction is 8-12 h.

The temperature of the secondary hydrothermal reaction is 90-160 ℃, and the time of the secondary hydrothermal reaction is 8-12 h.

The freeze drying temperature is-80 deg.C to-60 deg.C, and the freeze drying time is 20-24 h.

The mass of MXene in the RGO/MXene-S @ RGO/MXene composite electrode is 3-8% of the total mass of the RGO/MXene-S @ RGO/MXene composite electrode.

The application of the self-supporting positive electrode of the lithium-sulfur battery with the coating structure obtained by the preparation method is that the negative electrode is placed in a negative electrode shell, then the diaphragm is added, the electrolyte is dripped, the RGO/MXene-S @ RGO/MXene composite electrode is placed, then the gasket and the elastic sheet are added, the positive electrode shell is covered, and finally the sealing machine is used for sealing, so that the lithium-sulfur battery is obtained.

The negative electrode is a metal lithium sheet.

The diaphragm is a celgard film.

The preparation method of the electrolyte comprises the steps of dissolving lithium trifluoromethanesulfonimide in a mixed solvent of dioxolane and ethylene glycol dimethyl ether, and adding lithium nitrate to prepare the electrolyte.

The application of the self-supporting positive electrode of the lithium-sulfur battery with the coating structure obtained by the preparation method is that the self-supporting electrode slice is cut into a proper size after the RGM-S @ RGM composite electrode is pressed into a sheet; a lithium sheet is taken as a negative electrode, a celgard film is taken as a diaphragm, lithium trifluoromethanesulfonylimide (LiTFSI) is dissolved in a mixed solvent of Dioxolane (DOL) and ethylene glycol dimethyl ether (DME) in a volume ratio of 1:1, lithium nitrate accounting for 1 wt% of the total mass of the electrolyte is added to prepare the electrolyte, and the electrolyte is assembled into the button cell in a glove box.

The self-supporting positive electrode of the lithium-sulfur battery with the coating structure is a self-supporting positive electrode of a lithium-sulfur battery with a pie structure.

The preparation method of the self-supporting positive electrode of the lithium-sulfur battery with the coated structure comprises the steps of mixing GO water dispersion and MXene water dispersion, and adding Na₂S₂O₃·5H₂Taking O as a sulfur source, then dropwise adding hydrochloric acid, uniformly stirring, and generating sulfur in situ; then the mixed solution is put into a hydrothermal reaction kettle to obtain RGO/MXene-S composite hydrogel through primary hydrothermal; and further slicing the RGO/MXene-S composite hydrogel, soaking the sliced RGO/MXene-S composite hydrogel in a mixed water dispersion of GO water dispersion and MXene water dispersion, putting the soaked RGO/MXene-S composite hydrogel into a hydrothermal reaction kettle for secondary hydrothermal treatment, freeze-drying the hydrothermal reaction kettle, and tabletting the hydrothermal reaction kettle to obtain the pie-structured self-supporting composite electrode RGO/MXene-S @ RGO/MXene (RGM-S @ RGM).

The diameter of the self-supporting positive electrode of the lithium-sulfur battery with the cladding structure is 1.2-1.4 cm.

The invention relates to a preparation method of a self-supporting positive electrode of a lithium-sulfur battery with a cladding structure and a preparation method of the lithium-sulfur battery, which comprises the following specific steps:

(1) preparation of MXene aqueous dispersion:

taking 1-3g MAX (Ti)₃AlC₂) Mixing with 30-50ml HF, dividing into two parts, placing in two centrifuge tubes, subjecting the centrifuge tubes to constant temperature hydrothermal treatment at 35-55 deg.C for 18-24h to successfully etch Al phase in MAX (due to HF is highly toxic, the whole process needs to be carried out in fume cupboard), taking out the centrifuge tubes, centrifuging the liquid in the tubes with deionized water (8000r/min, 5min), pouring the centrifuged supernatant into calcium hydroxide solution, precipitating, washing for multiple times until pH is close to neutral, and vacuum washing at 60-90 deg.CDrying for 8-15h, cooling to room temperature, taking out, weighing 0.5-2g of powder, dissolving in 50-200ml of dimethyl sulfoxide in a beaker, introducing argon gas into the beaker, placing in a thermocouple, magnetically stirring at constant temperature for 18-26h at normal temperature, centrifuging for 4-5 times after stirring, pouring out supernatant, dissolving precipitate in 200ml of distilled water, performing ultrasonic treatment for 1-4h, centrifuging for 30-60min at 3500r/min, and taking supernatant to obtain Ti₂C₃MXene aqueous dispersion.

(2) Preparing GO aqueous dispersion:

firstly, 1.5-3g of graphite is dispersed into 70-90ml of concentrated sulfuric acid, stirred for 30-40min at room temperature, and then 1.5-3g of NaNO is slowly added₃Before adding, the mixed solution is placed in an ice bath environment, stirred for 30-40min, and then 7-9g KMnO is added into the solution₄And the adding process is very slow to prevent danger, the GO water dispersion is stirred for 30-40min after the GO water dispersion is added, then the solution is placed at 35-45 ℃ for heat preservation for 50-70min, then distilled water is added for dilution under the ice bath condition, then 15-20ml of hydrogen peroxide is added, the solution is washed by acid washing water, ultrasonic treatment is carried out for 10-12h, then the solution is centrifuged for 30-40min at 3500 + 4500r/min, and the GO water dispersion is obtained by taking the supernatant.

(3) The preparation method of the RGM-S @ RGM composite electrode comprises the following steps:

the concentration of GO water dispersion is 5-10 mg/ml^-1The concentration of MXene aqueous dispersion is 5-10 mg/ml^-1Dripping 2-5ml MXene aqueous dispersion into 3-8ml GO aqueous dispersion, stirring for 20-40min, and adding 350-560mg Na₂S₂O₃·5H₂O, followed by dropwise addition of 5-15ml of HCl (0.5-1 mol. L)^-1) And after mixing and stirring for 1-2h, transferring the mixed solution into a reaction kettle, and carrying out hydrothermal reaction for 8-12h at the temperature of 90-160 ℃. And after the reaction is finished, taking out the obtained RGO/MXene-S composite hydrogel, slicing, placing the obtained independent self-supporting wafer in water for soaking for 3-6h, removing acid in the wafer, and then carrying out secondary hydrothermal treatment. The secondary hydrothermal method comprises the following steps: soaking the prepared independent self-supporting sheet in a mixed solution of 1-2ml of GO water dispersion and 1-2ml of MXene water dispersion, and then continuously putting the mixture into a reaction kettle for hydrothermal reaction at the temperature of 90-160 ℃ for 8-12 h. After the secondary hydrothermal treatment, the obtained RGM-S @ RGM composite hydrogel is placed at-8Freeze drying at 0-60 deg.C for 20-24 hr, compacting to obtain composite electrode, and cutting the diameter of the composite electrode to 1.2-1.4cm to obtain the final product.

(4) Assembling the lithium-sulfur battery:

the whole battery assembly process is carried out in a glove box, the positive electrode is a prepared RGM-S @ RGM composite electrode, the negative electrode adopts a metal lithium sheet, a celgard film is used as a diaphragm, and the electrolyte is prepared by dissolving lithium trifluoromethanesulfonimide (LiTFSI) in a mixed solvent of Dioxolane (DOL) and ethylene glycol dimethyl ether (DME) in a volume ratio of 1:1 and adding lithium nitrate accounting for 1 wt% of the total mass of the electrolyte. The assembly sequence of the battery is started from a negative electrode shell in sequence, then a metal lithium sheet is placed into the negative electrode shell by using tweezers, then a diaphragm is added, electrolyte is dropwise added, the prepared RGM-S @ RGM composite electrode is placed, then a gasket and an elastic sheet are added, a positive electrode shell is covered, and finally a packaging machine is used for sealing.

The RGM-S @ RGM composite electrode is prepared by a two-step hydrothermal method, the shuttling effect of polysulfide is inhibited by utilizing the synergistic effect of RGO and MXene, and the content of non-electrochemical active ingredients can be reduced by designing an independent self-supporting structure of the electrode, so that the energy density of the battery is greatly improved.

The invention has the following beneficial effects:

the RGM-S @ RGM composite electrode with a pie structure is prepared by a two-step hydrothermal method, a traditional binder and a traditional current collector are not required to be added, the electrode can be used as an independent self-supporting electrode, the quality of active substances in the electrode is effectively improved, and the energy density of a battery is improved.

In the preparation process of the electrode, RGO and MXene in the electrode can be used as interlayer fillers in the compounding process, so that the agglomeration of lamella can be effectively inhibited; the special 'pie' structure of the electrode can effectively inhibit the polysulfide from dissolving into the electrolyte; the large specific surface area of the RGO in the electrode can realize the physical adsorption and fixation of the RGO on sulfur and polysulfide, and MXene can form chemical bonds with the sulfur and the polysulfide so as to effectively inhibit the shuttle effect of the polysulfide. The synergistic effect of the two components and the special structure of the electrode play the roles of effectively fixing sulfur and lithium polysulfide.

In conclusion, the independent self-supporting RGM-S @ RGM composite electrode with a pie structure is prepared by a two-step hydrothermal method, and the special structure of the electrode effectively inhibits the dissolution of lithium polysulfide; the shuttle effect of the lithium-sulfur battery is further inhibited by utilizing the physical adsorption and chemical bonding effects of RGO and MXene in the electrode; meanwhile, due to the design of the independent self-supporting structure, the energy density of the battery can be greatly improved. The method has the advantages of simplicity, wide applicability, good electrochemical performance and the like.

Drawings

FIG. 1a is a flow chart of the preparation of an RGM-S @ RGM composite electrode.

FIG. 1b is an optical photograph of an RGO/MXene-S composite electrode.

FIG. 1c is an optical photograph of the RGM-S @ RGM composite electrode after freeze-drying.

FIG. 1d is an optical photograph of the RGM-S @ RGM composite electrode after compression.

FIG. 2 is an SEM image of the inner and outer boundaries of an RGM-S @ RGM composite electrode "pie" structure.

FIG. 3 is an XRD pattern of S, MXene, RGO-S, RGO/MXene-S, and RGM-S @ RGM.

FIG. 4 is an XPS fine map of C, O, S, Ti elements in an RGM-S @ RGM composite electrode.

FIG. 5 is an optical photograph of the sulfur fixation experiment of the RGO-S composite electrode, the RGO/MXene-S composite electrode and the RGM-S @ RGM composite electrode.

FIG. 6a is a plot of cyclic voltammetry measurements for a lithium sulfur cell assembled with an RGM-S @ RGM composite electrode.

FIG. 6b is a first cycle charge-discharge diagram of a lithium sulfur battery based on an RGO-S composite electrode, an RGO/MXene-S composite electrode, and an RGM-S @ RGM composite electrode, respectively.

FIG. 6c is a graph of the rate of lithium sulfur cells based on RGO-S composite electrode, RGO/MXene-S composite electrode, and RGM-S @ RGM composite electrode, respectively.

FIG. 6d is a plot of the AC impedance of a lithium sulfur battery based on an RGO-S composite electrode, an RGO/MXene-S composite electrode, and an RGM-S @ RGM composite electrode, respectively.

FIG. 6e is a 300-cycle plot of a lithium sulfur battery based on an RGO-S composite electrode, an RGO/MXene-S composite electrode, and an RGM-S @ RGM composite electrode, respectively.

Detailed Description

The present invention is further described below with reference to examples.