CN103682349A - Additive-free sulfonated graphene/sulfur electrode slice and preparation method and application thereof - Google Patents

Abstract

The invention belongs to the technical field of lithium-sulfur batteries, and in particular relates to an additive-free sulfonated graphene/sulfur electrode sheet and a preparation method and application thereof. The present invention firstly modifies graphene oxide to obtain sulfonated graphene with good water solubility and conductivity; disperses sulfonated graphene in sodium thiosulfate solution, adds sulfuric acid solution, and forms sulfonated graphene through disproportionation reaction /sulfur composite; the composite is slurried with absolute ethanol as a solvent, coated on a carbon-coated aluminum foil to make a pole piece, and applied to the positive electrode of a lithium-sulfur battery. The preparation method of the invention has simple process and good reproducibility. The prepared material has excellent conductivity and certain viscosity. The production of the pole piece does not need to add conductive carbon black and binder, which can greatly improve the volumetric energy density of the positive electrode material of the lithium-sulfur battery; in addition, the intermediate product generated can be avoided Diffusion into the electrolyte reduces the occurrence of the shuttle effect and improves the cycle performance and rate performance of lithium-sulfur batteries.

Description

A kind of additive-free sulfonated graphene/sulfur electrode sheet and its preparation method and application

technical field

The invention belongs to the technical field of lithium-sulfur batteries, and in particular relates to a sulfonated graphene/sulfur electrode sheet and a preparation method and application thereof.

Background technique

Lithium-sulfur battery, using elemental sulfur (or sulfur-containing compound) as the positive electrode, metal lithium as the negative electrode, a type of metal lithium secondary battery that realizes the mutual conversion between chemical energy and electrical energy through the chemical reaction between sulfur and lithium, its theoretical ratio The capacity is 1675 mAh g ^-1 , the theoretical energy density is 2600 Wh kg ^-1 , the actual energy density can reach 300 Wh kg ^-1 at present, and it is very likely to increase to about 600 Wh kg ^-1 in the next few years. Compared with lithium-ion battery oxide electrode materials, such as lithium cobalt oxide, lithium manganese oxide, and lithium iron phosphate, sulfur-based cathode materials have unique advantages in terms of specific capacity, energy density, and power density. In addition, elemental sulfur also has the advantages of abundant reserves, low cost, environmental friendliness, and good battery safety, and can better meet the four aspects of future power battery requirements, namely high energy density, better safety, and green Environmental protection and low cost not only meet the requirements of electric vehicles (EV) for power batteries, but also meet the requirements of portable electronic products for chemical power sources of light weight, miniaturization, low cost and non-toxicity, so lithium-sulfur batteries are considered to be the most researched One of the attractive secondary battery systems.

But at present, the practical application of lithium-sulfur batteries also faces many problems, one of which is the influence of cathode materials. Elemental sulfur forms an orthorhombic crystal with S ₈ molecules in the natural state, which is an insulator of electrons and ions (5×10 ^-30 S cm ^-1 ), and the polysulfides produced by the cathode material of lithium-sulfur batteries during the discharge process are easily Soluble in organic electrolyte, this not only causes the lower active material utilization rate of lithium-sulfur batteries, but also the dissolved polysulfides will migrate to the negative electrode and be reduced to insoluble Li ₂ S ₂ /Li ₂ S and deposited on the Lithium on the negative electrode causes great damage to the electrode structure, resulting in a large decline in battery capacity and poor cycle performance, which seriously restricts the practical application of lithium-sulfur batteries. In order to solve the above problems, a lot of research has been carried out on the preparation of high-performance cathode materials in recent years. Filling the active material elemental sulfur into its nanopores to form a carbon/sulfur composite material has become an effective solution. The use of carbon skeletons can achieve composite The electron transport in the bulk phase of the material, and the strong capillary force of the nanopores of the carbon material can realize the immobilization of the active substance sulfur and the intermediate product [XL Ji, KT Lee, LF Nazar, Nat.Mater. 2009, 8 (6), 500 ]. Zhang et al. used the chemisorption of a large number of oxygen-containing groups on the surface of graphene oxide (GO) to the intermediate product to achieve the immobilization of sulfur, but the large number of oxygen-containing groups on the surface of GO destroyed the conjugated structure of graphene itself, reducing Electronic conductivity [LW Ji, MM Rao, HM Zheng, L. Zhang, YG Zhang, J. Am. Chem. Soc. 2011, 133 (46), 18522].

Contents of the invention

The purpose of the present invention is to provide a sulfonated graphene/sulfur electrode sheet with simple preparation process and excellent electrochemical performance, as well as its preparation method and application.

And applied to lithium-sulfur batteries, it not only ensures ultra-high conductivity, but also improves the quality of active materials on the pole piece, and due to the sheet structure of graphene and the existence of sulfonate groups, it alleviates the volume expansion of sulfur during charge and discharge. problems, and limit the dissolution of sulfur and intermediate products into the electrolyte, making the material have excellent electrochemical performance.

The preparation method of the additive-free sulfonated graphene/sulfur electrode sheet that the present invention proposes, concrete steps are as follows:

a, the synthesis of sulfonated graphene, the specific steps are: disperse 300-400 mg graphene oxide in 300-400 ml deionized water, ultrasonic 2-3 h; after pretreatment, sulfonation, post-treatment three processes, Promptly obtain sulfonated graphene;

Wherein, the pretreatment process is as follows: use 5%-10% sodium carbonate solution to adjust the pH of the graphene oxide dispersion to 9-10, and then add 75-100 ml of 0.03-0.04g/ml sodium borohydride solution; Stir the above mixed solution at 80-100 ℃ for 3-4 h, then centrifuge, wash with a large amount of water until neutral, and obtain a partially reduced graphene oxide product, redisperse the product in 30-40 ml deionized water, and ultrasonically 2 -3h;

Described sulfonation process is as follows:

First prepare the diazonium salt of benzenesulfonic acid: in a 100 ml beaker, add 0.8-1.2 g p-aminobenzenesulfonic acid crystals, add 8-12 ml 2%-5% NaOH solution, dissolve it in a hot water bath, cool to At room temperature, add 0.3-0.5 g of sodium nitrite and 2-4 ml of water into a solution and cool it to 0-5°C in an ice-water bath. After dissolving, mix 1-2 ml of concentrated hydrochloric acid with 4-6 ml of The solution made of water is slowly added dropwise to the above mixture, and the obtained mixture solution is dropped in batches into a beaker filled with 6-7 ml of ice-cold water and 1-1.6 ml of concentrated sulfuric acid, keeping the temperature below 5°C (above 0°C), after the dropwise addition is completed, check with starch-potassium iodide test paper, and place it in an ice-water bath for 15-20 minutes to obtain diazonium benzenesulfonate;

Add the prepared benzenesulfonic acid diazonium salt solution to the partially reduced graphene oxide dispersion obtained in the above pretreatment process, stir in an ice-water bath for 2-3 h, then centrifuge, wash with a large amount of water until neutral, and obtain sulfonate Acidified graphene oxide, redisperse the product in 300-400 ml deionized water, ultrasonic 2-3 h;

The post-treatment process is as follows: add 8-10 ml of hydrazine hydrate to the above-mentioned sulfonated graphene oxide dispersion, reflux at 80-100 ° C for 20-30 h, then filter, wash with a large amount of water, and the product is heated at 60-70 ° C Under vacuum drying, obtain sulfonated reduced graphene, referred to as sulfonated graphene;

b, Synthesis of sulfonated graphene/sulfur composites, the specific steps are: disperse 80-120 mg sulfonated graphene in 100-150 ml 0.1-0.2 mol/L sodium thiosulfate solution, and sonicate at room temperature for 1 -2 h, then slowly add 100-150 ml of 0.1-0.2 mol/L sulfuric acid solution dropwise at a rate of 1-2 ml min ^-1 , continue to stir for 1-2 h, filter, and wash with a large amount of water, at 60-70 ℃ in a vacuum oven for 10-12 h to obtain a sulfonated graphene/sulfur (PhSO ₃ -RG/S) composite;

c. The preparation of lithium-sulfur battery electrode sheet, the specific steps are: use sulfonated graphene/sulfur composite as electrode material, absolute ethanol as dispersant, carbon-coated aluminum foil as substrate, and prepare lithium by coating Sulfur battery positive electrode sheet.

The method of the invention has the advantages of simple process, good reproducibility, and uniform distribution of the prepared material structure. Compared with the prior art, the beneficial effects of the present invention are reflected in:

The material itself has excellent electrical conductivity and a certain degree of viscosity. There is no need to add conductive carbon black and binders during the production of the pole piece, so the quality of the active material on the pole piece is much higher than that of other research materials. Quality, greatly improving the volumetric energy density of lithium-sulfur battery cathode materials. In addition, the modified sulfonated graphene sheet can not only coat more elemental sulfur, but also alleviate the volume expansion of sulfur during the discharge process, avoiding the diffusion of the generated intermediate products into the electrolyte, thereby reducing the The occurrence of the shuttle effect greatly improves the cycle performance and rate performance of lithium-sulfur batteries.

Description of drawings

Figure 1 is a scanning electron microscope and a transmission electron microscope photo of the product. Among them, a and c are the SEM images and TEM images of PhSO ₃ -RG, and c and d are the SEM images and TEM images of PhSO ₃ -RG/S.

Figure 2 is the electrochemical cycle diagram of the product PhSO ₃ -RG/S and the conventional material GO/S at a discharge current of 0.2 C.

Fig. 3 is a diagram of the electrochemical rate performance of the products PhSO ₃ -RG/S and GO/S. The tested currents are 0.035 C, 0.1 C, 0.2 C, 0.3 C, 0.4 C, 0.035 C, respectively.

Detailed ways

Below through embodiment, the scheme of the present invention is described further in detail.

Example 1

1. The synthesis steps of acidified graphene are as follows: disperse 300-400 mg graphene oxide in 300-400 ml deionized water, and sonicate for 2-3 h. It can be obtained after three processes of pretreatment, sulfonation and posttreatment. in:

The pretreatment process is as follows: use 5%-10% sodium carbonate solution to adjust the pH of the graphene oxide dispersion described in a to 9-10, and then add 75-100 ml of 0.03-0.04 g/ml sodium borohydride solution , the above mixed solution was stirred at 80-100 ℃ for 3-4 h, then centrifuged, washed with a large amount of water until neutral, and the partially reduced graphene oxide product was obtained, and the product was redispersed in 30-40 ml deionized water, ultrasonically 2-3h.

The sulfonation process is as follows: first, diazonium benzenesulfonate is prepared. In a 100 ml beaker, add 0.8-1.2 g p-aminobenzenesulfonic acid crystals, add 8-12 ml 2%-5% NaOH solution, dissolve it in a hot water bath, cool to room temperature, add 0.3-0.5 g nitrous acid The solution made of sodium and 2-4 ml of water is cooled to 0-5°C in an ice-water bath. After dissolving, slowly add the solution made of 1-2 ml of concentrated hydrochloric acid and 4-6 ml of water under continuous stirring. Into the above mixed solution, drop the obtained mixture solution in batches into a beaker filled with 6-7 ml of ice-cold water and 1-1.6 ml of concentrated sulfuric acid, keep the temperature below 5°C, and after the addition is completed, use starch-potassium iodide After the test paper is tested, place it in an ice-water bath for 15-20 minutes to obtain diazonium benzenesulfonate. Add the prepared benzenesulfonic acid diazonium salt solution to the partially reduced graphene oxide dispersion obtained in the above pretreatment process, stir in an ice-water bath for 2-3 h, then centrifuge, wash with a large amount of water until neutral, and then obtain Sulfonated graphene oxide, redisperse the product in 300-400 ml deionized water, and sonicate for 2-3 h.

The post-treatment process is as follows: 8-10 ml of hydrazine hydrate is added to the above-mentioned sulfonated graphene oxide dispersion, refluxed at 80-100 °C for 20-30 h, then filtered, washed with a large amount of water, and the product is vacuum-dried at 60-70 °C , to obtain sulfonated reduced graphene, referred to as sulfonated graphene.

2. The synthesis steps of the sulfonated graphene/sulfur complex are as follows: disperse 80-120 mg of sulfonated graphene in 100-150 ml of 0.1-0.2 mol/L sodium thiosulfate solution, and sonicate at room temperature for 1-2 h, then slowly add 100-150 ml 0.1-0.2 mol/L sulfuric acid solution dropwise at a rate of 1-2 ml min ^-1 , continue to stir for 1-2 h, filter, wash with a large amount of water, and store at 60-70 ℃ After drying in a vacuum oven for 10-12 h, the sulfonated graphene/sulfur (PhSO ₃ -RG/S) composite can be obtained.

3. The obtained sulfonated graphene/sulfur composite material is made into a positive electrode of a lithium-sulfur battery, and the steps are as follows: using the sulfonated graphene/sulfur composite as an electrode material, absolute ethanol as a dispersant, and carbon-coated aluminum foil As a substrate, the positive electrode of a lithium-sulfur battery is prepared by coating.

Result description:

Accompanying drawing 1 illustrates that sulfonated graphene has a pleated sheet structure, and sulfur grows in situ on the surface or between layers of sulfonated graphene through redox reactions, and the overall structure is not damaged, and it is still a pleated structure, but after compounding The shape is more plump than before.

Comparative example 1

GO/S electrodes were prepared by combining graphene oxide (GO) and S according to a method for preparing positive electrodes of lithium-sulfur batteries as described in claims 1 and 2.

Result description:

(a) Figure 2 illustrates that under the same test conditions, the PhSO ₃ -RG/S composite exhibits better cycle life and better cycle stability;

(b) Figure 3 shows that under the same test conditions, the PhSO ₃ -RG/S composite exhibits better rate performance.

In summary, the present invention modifies graphene oxide through the three processes of pre-reduction, sulfonation, and post-treatment to obtain sulfonated graphene with good water solubility and conductivity, and use it as a sulfur carrier. Redox reaction grows sulfur in situ on its surface or between layers. Due to the super high conductivity and viscosity of the material itself, absolute ethanol is used as a dispersant without adding conductive agents and binders. Thin-layer-coated aluminum foil is used as the substrate, and PhSO ₃ -RG/S electrodes are prepared and applied in lithium-sulfur batteries, which greatly improves the volumetric energy density of lithium-sulfur battery cathode materials. In addition, the modified sulfonated graphene sheet can not only coat more elemental sulfur, but also alleviate the volume expansion of sulfur during the discharge process, avoiding the diffusion of the generated intermediate products into the electrolyte, thereby reducing the The occurrence of the shuttle effect greatly improves the cycle life, cycle stability and rate performance of lithium-sulfur batteries.

Claims (3)

1. a preparation method who exempts from sulfonated Graphene/sulfur electrode sheet of additive, is characterized in that concrete steps are as follows:

A, sulfonated Graphene synthetic, concrete steps are: 300-400 mg graphene oxide is dispersed in 300-400 ml deionized water to ultrasonic 2-3 h; Through preliminary treatment, sulfonated, three processes of reprocessing, obtain sulfonated Graphene;

Wherein:

Described pretreated process is as follows: with the sodium carbonate liquor of 5%-10%, by graphene oxide dispersion liquid pH furnishing 9-10, then add the sodium borohydride solution of 75-100 ml 0.03-0.04g/ml; Above-mentioned mixed liquor is stirred at 80-100 ℃ to 3-4 h, then centrifugal, massive laundering, to neutral, obtains the graphite oxide ene product of partial reduction, product is dispersed in 30-40 ml deionized water again to ultrasonic 2-3 h;

Described Sulfonated process is as follows:

First prepare benzene sulfonic acid diazol: in 100 ml beakers, add 0.8-1.2 g sulfanilic acid crystal, the NaOH solution that adds 8-12 ml 2%-5%, hot bath is dissolved, be chilled to room temperature, the solution that adds 0.3-0.5 g natrium nitrosum and 2-4 ml water to be made into is chilled to 0-5 ℃ with ice-water bath, after dissolving, under constantly stirring, the solution that 1-2 ml concentrated hydrochloric acid and 4-6 ml water are made into is slowly added drop-wise in above-mentioned mixed liquor, the mixture solution obtaining is splashed in batches in the beaker that 6-7 ml ice cold water and the 1-1.6 ml concentrated sulfuric acid are housed, temperature is remained on below 5 ℃, wait dropwising with after the check of starch-kalium iodide test paper, in ice-water bath, place 15-20 min, obtain benzene sulfonic acid diazol,

The benzene sulfonic acid diazonium salt solution of preparation is joined in the graphene oxide dispersion liquid of the partial reduction obtaining in above-mentioned preprocessing process, under ice-water bath, stir 2-3 h, then centrifugal, massive laundering is to neutral, obtain Sulfonated graphene oxide, product is dispersed in 300-400 ml deionized water again to ultrasonic 2-3 h;

The process of described reprocessing is as follows: 8-10 ml hydrazine hydrate is joined in above-mentioned Sulfonated graphene oxide dispersion liquid, and the 20-30 h that refluxes at 80-100 ℃, then filters, massive laundering, product vacuumize at 60-70 ℃, obtains Sulfonated reduced graphene, is called for short sulfonated graphene;

B, sulfonated graphene/sulfur compound synthetic, concrete steps are: 80-120 mg sulfonated graphene is dispersed in the hypo solution of 100-150 ml 0.1-0.2 mol/L, and ultrasonic 1-2 h under room temperature, then with 1-2 ml min ^-1speed slowly drip wherein the sulfuric acid solution of 100-150 ml 0.1-0.2 mol/L, continue to stir 1-2 h, filter, massive laundering, in the vacuum drying oven of 60-70 ℃, dry 10-12 h, obtains sulfonated graphene/sulfur compound;

C, the preparation of lithium-sulfur cell electrode slice, concrete steps are: using sulfonated graphene/sulfur compound as electrode material, absolute ethyl alcohol is as dispersant, and the coated aluminium foil of carbon is as substrate, and the mode by coating prepares lithium-sulfur cell electrode slice.

2. the sulfonated Graphene/sulfur electrode sheet of exempting from additive being prepared by preparation method described in claim 1.

3. the application of sulfonated Graphene/sulfur electrode sheet of exempting from additive as claimed in claim 2 in lithium-sulfur cell.

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