Preparation method of three-dimensional self-supporting sulfur/graphene positive electrode material and lithium-sulfur battery positive electrode

文档序号：1630035 发布日期：2020-01-14 浏览：21次中文

阅读说明：本技术 三维自支撑硫/石墨烯正极材料制备方法及锂硫电池正极 (Preparation method of three-dimensional self-supporting sulfur/graphene positive electrode material and lithium-sulfur battery positive electrode ) 是由李卿鹏汤元波于 2018-07-06 设计创作，主要内容包括：一种三维自支撑硫/石墨烯正极材料制备方法及锂硫电池正极。正极材料制备包括以下步骤：(a)制备氧化石墨烯溶液；(b)通过一步还原诱导自组装制备三维硫/石墨烯复合物正极材料。将正极材料与导电碳、聚偏氟乙烯混合制备锂硫电池正极,进而装配成电池。本发明电池在0.1、0.2、0.5、1.0和1.2 A.g-1电流下放电,膜电极比容量分别为1480、1280、1100、880和660mAh.g-1,当电流密度重新回到0.1 A.g-1时,三维硫/石墨烯凝胶膜回复比容量为1290 mAh.g-1,膜电极结构并未受到破坏,在1.5 A.g-1电流密度下循环500周后容量保持率在83.5%。(A preparation method of a three-dimensional self-supporting sulfur/graphene positive electrode material and a lithium-sulfur battery positive electrode. The preparation method of the cathode material comprises the following steps: (a) preparing a graphene oxide solution; (b) the three-dimensional sulfur/graphene composite cathode material is prepared by one-step reduction induced self-assembly. Preparing the lithium-sulfur battery anode by mixing the anode material with conductive carbon and polyvinylidene fluorideThe poles, in turn, are assembled into a battery. The battery of the invention is 0.1, 0.2, 0.5, 1.0 and 1.2A.g ‑1 Discharging under current, and the specific capacities of the membrane electrodes are 1480, 1280, 1100, 880 and 660mAh ‑1 When the current density returns to 0.1A.g ‑1 The recovery specific capacity of the three-dimensional sulfur/graphene gel film is 1290 mAh ‑1 The membrane electrode structure was not destroyed at 1.5A.g ‑1 The capacity retention rate after 500 weeks of cycling under current density was 83.5%.)

1. A preparation method of a three-dimensional self-supporting sulfur/graphene positive electrode material and a lithium-sulfur battery positive electrode are characterized in that: the positive electrode material is prepared by reducing graphene oxide to construct a porous sulfur/graphene composite structure, and comprises the following steps:

(a) preparing a graphene oxide solution: mixing graphite with NaNO₃Mixing the solid, wherein the graphite accounts for 50% ~ 65% of the solid, and NaNO₃35 percent of ~ 50 percent of solid, then adding inorganic strong protonic acid with the mixed solid content of 1000 percent to ~ 3000 percent to 3000 percent, stirring the mixture under a magnetic stirrer, stirring the mixture for 24 ~ 36 hours, then adding strong oxidant with the mixed solid content of 150 percent to ~ 200 percent, controlling the reaction temperature to be not more than 25 ℃, stirring the mixture for 0.5 ~ 1.5.5 hour, then heating the mixture to 80 ~ 100 ℃ again, continuing stirring the mixture until the magnetic stirring is failed, standing the mixture for 6 ~ 8 hours, then slowly adding deionized water with the mixed solid content of 200 percent to ~ 300 percent into the mixture, manually stirring the mixture for 2 ~ 3 hours, and then adding H with the mass fraction of 30 percent into the mixture₂O₂In which H is₂O₂The mixed solid accounts for 20 percent ~ 30 percent, stands for 24h ~ 36h and adopts 1 ~ 2mol.L^-1Washing the bottom precipitate with dilute hydrochloric acid and deionized water until no sulfate radical exists in the solution, putting the obtained graphite oxide into a dialysis bag for dialysis to remove metal ions in graphene oxide, carrying out ultrasonic treatment on the cleaned graphite oxide after one week of dialysis, and dispersing for 1 ~ 2 hours by ultrasonic to obtain a lamellar structure material;

(b) dissolving a sulfur source in the graphene oxide aqueous solution prepared in step (a) in advance, wherein the sulfur source is a sulfur sourceThe sulfur source proportion is 97 percent ~ 99.2.2 percent, the graphene oxide solution proportion is 0.8 percent ~ 3 percent, the mixture is stirred for 10 ~ 30min under the ice bath condition, and then the mixture is added with the solid content of 900 percent and the concentration of 0.024 ~ 0.03.03 mol.L^-1Reacting the dilute hydrochloric acid aqueous solution for 6 ~ 8h under ice bath condition, centrifuging and collecting the obtained suspension, washing with deionized water, re-dispersing the collected product into 20 ~ 30mL of deionized water to form brown sulfur oxide/graphene composite colloid, namely a precursor, taking 1 ~ 2mol.L^-1Adding the sodium ascorbate solution into the compound colloid, wherein the adding amount is 50% ~ 60% of the solid mixture, performing ultrasonic dispersion for 10 ~ 30min, placing the mixture in an air-blast drying oven at 95 ~ 105 and 105 ℃ for standing reaction for 1.5 ~ 2.5.5 h to obtain the sulfur/graphene compound hydrogel, washing and freeze-drying the hydrogel to obtain compound aerogel, and rolling the aerogel by using a roll-to-roll machine to obtain the flexible self-supporting three-dimensional sulfur/graphene anode material.

2. The preparation method of the three-dimensional self-supporting sulfur/graphene positive electrode material and the lithium-sulfur battery positive electrode according to claim 1, wherein the preparation method comprises the following steps: the graphite in the step (a) has the particle size of less than 30 mu m, the content of more than 95wt% and the carbon content of 99.85 wt%.

3. The preparation method of the three-dimensional self-supporting sulfur/graphene positive electrode material and the lithium-sulfur battery positive electrode according to claim 1, wherein the preparation method comprises the following steps: the inorganic strong protonic acid in the step (a) is concentrated sulfuric acid, fuming nitric acid or a mixture thereof with the weight percent of 95-98 percent.

4. The preparation method of the three-dimensional self-supporting sulfur/graphene positive electrode material and the lithium-sulfur battery positive electrode according to claim 1, wherein the preparation method comprises the following steps: the strong oxidant in the step (a) is one of potassium permanganate and potassium perchlorate.

5. The preparation method of the three-dimensional self-supporting sulfur/graphene positive electrode material and the lithium-sulfur battery positive electrode according to claim 1, wherein the preparation method comprises the following steps: the sulfur source in the step (b) is one of sodium thiosulfate pentahydrate, sodium sulfate, sodium sulfite and sodium sulfide.

6. The preparation method of the three-dimensional self-supporting sulfur/graphene positive electrode material and the lithium-sulfur battery positive electrode according to claim 1, wherein the preparation method comprises the following steps: the sulfur/graphene anode material is a sulfur/graphene composite material with 50-80 wt% of sulfur loading.

7. The preparation method of the three-dimensional self-supporting sulfur/graphene positive electrode material and the lithium-sulfur battery positive electrode according to claim 1, wherein the preparation method comprises the following steps: the size of sulfur particles in the sulfur/graphene anode material is 10-30 nm.

8. The preparation method of the three-dimensional self-supporting sulfur/graphene positive electrode material and the lithium-sulfur battery positive electrode as claimed in claim 1 are characterized in that the lithium-sulfur battery positive electrode comprises a positive electrode active material, a conductive agent and a binder, wherein the positive electrode active material is a flexible self-supporting three-dimensional sulfur/graphene positive electrode material, the conductive agent is conductive carbon, the binder is polyvinylidene fluoride (PVDF), the positive electrode active material is punched into a small disc with the diameter of 15mm ~ 20mm by a punching machine, the small disc is directly used as the positive electrode material, the positive electrode active material is weighed according to the proportion of 7 parts of the positive electrode active material, 2 parts of the conductive carbon and 1 part of the PVDF (PVDF), 5 ~ 6 parts of the PVDF is dissolved into 95 ~ 96 parts of polyvinylpyrrolidone (NMP) to form a solution with the mass fraction of 5 ~ 6%, the conductive carbon and the positive electrode active material are added into the solution to be uniformly stirred in vacuum, finally, the mixed slurry is uniformly coated on an aluminum foil by a 100 ~ 200 μm wet film preparation device, the solution is dried at ~ 70 ℃, and the positive electrode plate of the lithium-sulfur battery is punched by a drying machine at 70 ℃.

Technical Field

The invention relates to the technical field of lithium-sulfur batteries, in particular to a preparation method of a three-dimensional self-supporting sulfur/graphene positive electrode material and a lithium-sulfur battery positive electrode prepared by the same.

Background

At present, commercial lithium ion batteries cannot meet the increasing requirement of long-distance running after once charging of electric automobiles, and the development of a novel high-energy density battery system has very important significance. Lithium sulfur batteries are currently an ideal candidate for replacing commercial lithium ion batteries due to their high energy density. The lithium-sulfur battery is a battery system with sulfur as a positive electrode material and lithium as a negative electrode material. Since elemental sulfur has an extremely high theoretical capacity (1675 mAh. g.)^-15-10 times of the traditional anode material), and the energy density can reach 2500Wh^-1Meanwhile, the sulfur has a series of advantages of no toxicity, environmental friendliness, wide raw material source, low cost and the like. Therefore, the lithium-sulfur battery is expected to be the next generation of energy storage system with great development prospect, and will play a key role in the development of emerging advanced technologies such as pure electric vehicles.

Although lithium sulfur batteries have the potential to replace the current commercial lithium ion batteries, the development of the batteries is challenged by the complex electrochemical process during charging and discharging. First, elemental sulfur and solid sulfide (Li)₂S and Li₂S₂) The low electronic conductivity and lithium ion conductivity increase the intrinsic impedance of the lithium-sulfur battery, thereby preventing the effective utilization of the active material of the positive electrode material and reducing the coulombic efficiency. Secondly, the elemental sulfur undergoes complete lithium intercalation to form Li₂During S, the corresponding volume change is up to 80%. Such a large volume change may cause pulverization of the positive active material of the battery and separation from the current collector when the lithium-sulfur battery is charged and discharged. In addition, during charging and discharging, the higher-order polysulfide Li is formed₂S_x（4<x is less than or equal to 8) is soluble in the electrolyte. Under the combined action of concentration difference and electric field force, these polysulfides can shuttle between positive and negative electrodes of the battery, i.e. "shuttle effect". Shuttling of such polysulfides can result in: (1) the soluble polysulphide migrates from the positive electrode to the lithium metal negative electrode,directly chemically reacting with metallic lithium to irreversibly form Li passivating the metallic lithium cathode₂S, resulting in irreversible loss of the positive electrode active material; (2) polysulfide transferred to the negative electrode is partially reduced and then transferred back to the positive electrode, electrochemical oxidation reaction is continuously carried out on the positive electrode, internal energy loss is caused, and the coulomb efficiency of the battery is reduced; (3) during the charging and discharging processes, polysulfide is dissolved and re-deposited on the positive electrode and the negative electrode, the micro appearance of the electrode is changed, and the cycle life of the battery is shortened; (4) self-discharge occurs upon standing. Several of the above problems all reduce the performance of the battery, mainly manifested by poor cycling performance and coulombic efficiency, low practical specific capacity and safety problems.

In order to improve the conductivity and stability of the sulfur cathode material and reduce the problems of low utilization rate of active substances and poor cycle performance of a battery caused by poor conductivity of sulfur, the composite material prepared by compounding the sulfur and the conductive material is used as a main improvement means. Many conductive materials are available for compounding with sulfur, including conductive carbon materials, high molecular polymers, metal oxides, and the like. Such as: carrying out melt compounding on the highly ordered mesoporous carbon and elemental sulfur; sulfur-coated reduced graphene oxide sheets; sulfur, boron and other heterogeneous atoms, or metal oxide (mainly Ti) with strong chemical bonding effect with polysulfide added into electrode_xO₂、MnO₂Etc.), sulfides (e.g., WS)₂、Co_xS), nitrides (e.g., TiN, VN), and the like. Although these additives and polysulfides have a strong effect on improving the cycling stability of the electrode material, they are ultimately inactive components of the electrode and are not conducive to improving the energy density performance of lithium sulfur batteries.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a preparation method of a three-dimensional self-supporting sulfur/graphene positive electrode material and a lithium sulfur battery positive electrode, wherein a porous sulfur/graphene composite structure is constructed by reducing and oxidizing graphene, so that polysulfide can be subjected to physical and chemical adsorption, the shuttle effect of the lithium sulfur battery is solved, the problem of stacking of reduced and oxidized graphene sheets can be avoided, and the lithium sulfur battery positive electrode with high energy density and excellent cycle performance is obtained.

In order to achieve the above object, the positive electrode material of the present invention is prepared by reducing graphene oxide to form a porous sulfur/graphene composite structure, and includes the following steps:

(a) preparing a graphene oxide solution: mixing graphite with NaNO₃Mixing the solid, wherein the graphite accounts for 50% ~ 65% of the solid, and NaNO ₃35 percent of ~ 50 percent of solid, then adding inorganic strong protonic acid with the mixed solid content of 1000 percent to ~ 3000 percent to 3000 percent, stirring the mixture under a magnetic stirrer, stirring the mixture for 24 ~ 36 hours, then adding strong oxidant with the mixed solid content of 150 percent to ~ 200 percent, controlling the reaction temperature to be not more than 25 ℃, stirring the mixture for 0.5 ~ 1.5.5 hour, then heating the mixture to 80 ~ 100 ℃ again, continuing stirring the mixture until the magnetic stirring is failed, standing the mixture for 6 ~ 8 hours, then slowly adding deionized water with the mixed solid content of 200 percent to ~ 300 percent into the mixture, manually stirring the mixture for 2 ~ 3 hours, and then adding H with the mass fraction of 30 percent into the mixture₂O₂In which H is₂O₂The mixed solid accounts for 20 percent ~ 30 percent, stands for 24h ~ 36h and adopts 1 ~ 2mol.L^-1Washing the bottom precipitate with dilute hydrochloric acid and deionized water until no sulfate radical exists in the solution, putting the obtained graphite oxide into a dialysis bag for dialysis to remove metal ions in graphene oxide, carrying out ultrasonic treatment on the cleaned graphite oxide after one week of dialysis, and dispersing for 1 ~ 2 hours by ultrasonic to obtain a lamellar structure material;

(b) dissolving a sulfur source in the graphene oxide aqueous solution prepared in advance in the step (a), wherein the proportion of the sulfur source is 97 percent ~ 99.2.2 percent, the proportion of the graphene oxide solution is 0.8 percent ~ 3 percent, stirring for 10 ~ 30min under the ice bath condition, and then adding a solid with the concentration of 900 percent of 0.024 ~ 0.03.03 mol.L^-1Reacting the dilute hydrochloric acid aqueous solution for 6 ~ 8h under ice bath condition, centrifuging and collecting the obtained suspension, washing with deionized water, re-dispersing the collected product into 20 ~ 30mL of deionized water to form brown sulfur oxide/graphene composite colloid, namely a precursor, taking 1 ~ 2mol.L^-1Adding sodium ascorbate solution into the above compound colloid in an amount of 50% ~ 60% of the solid mixture, ultrasonic dispersing for 10 ~ 30min, and standing at 95%Standing in an air-blast drying oven at ~ 105 ℃ for 1.5 ~ 2.5.5 h to react to obtain the sulfur/graphene composite hydrogel, washing and freeze-drying the hydrogel to obtain composite aerogel, and rolling the aerogel by using a roller machine to obtain the flexible self-supporting three-dimensional sulfur/graphene anode material.

Wherein the graphite in the step (a) has the particle size of less than 30 mu m, the content of more than 95wt% and the carbon content of 99.85 wt%.

Wherein the inorganic strong protonic acid in the step (a) is concentrated sulfuric acid, fuming nitric acid or a mixture thereof with the weight percent of 95-98%.

Wherein, the strong oxidant in the step (a) is one of potassium permanganate and potassium perchlorate.

Wherein the sulfur source in the step (b) is one of sodium thiosulfate pentahydrate, sodium sulfate, sodium sulfite and sodium sulfide.

The sulfur/graphene anode material is a sulfur/graphene composite material with 50-80 wt% of sulfur loading.

The size of sulfur particles in the sulfur/graphene anode material is 10-30 nm.

The positive electrode of the lithium-sulfur battery comprises a positive active material, a conductive agent and a binder, wherein the positive active material is a flexible self-supporting three-dimensional sulfur/graphene positive electrode material, the conductive agent is conductive carbon, the binder is polyvinylidene fluoride (PVDF), the positive active material is punched into a small wafer with the diameter of 15mm ~ 20mm by a punching machine, then the wafer is directly used as a positive electrode material and is weighed according to the proportion of 7 parts of the positive active material, 2 parts of the conductive carbon and 1 part of the polyvinylidene fluoride (PVDF), then 5 ~ 6 parts of the PVDF is dissolved into 95 ~ 96 parts of the polyvinylpyrrolidone (NMP) to form a solution with the mass fraction of 5 ~ 6%, then the conductive carbon and the positive active material are added into the solution and are uniformly stirred in a vacuum manner, finally the mixed slurry is uniformly coated on an aluminum foil by a 100 ~ 200 mu m wet film preparation device, the aluminum foil is dried at the temperature of 50 ℃ and ~ 70 ℃, and the dried pole piece is punched into a positive electrode piece of the lithium-sulfur battery.

Compared with the prior art, the provided positive electrode material comprises graphene oxide and an additiveElemental sulfur particles are uniformly distributed on the surface of the graphene oxide, and graphene oxide sheets are mutually crosslinked to form a continuous channel capable of providing electron transfer, so that the overall electron conductivity of the electrode can be improved. The sulfur nano particles and the graphene oxide in the cathode material form good contact through S-O bonds, and the S-O bonds have great effects on limiting polysulfide in a circulation process and relieving a shuttle effect, so that the cycle life of an electrode is prolonged. Experimental results show that the lithium-sulfur battery prepared from the lithium-sulfur battery cathode material provided by the invention has excellent cycle performance and rate performance. At 1.5A.g^-1The specific capacity of the electrode is 740mAh.g under current^-1After 200 cycles, the discharge capacity retention rate was 94%, after 300 cycles, the discharge capacity retention rate was 84%, and after 500 cycles, the discharge capacity retention rate was 83.5%. The cell is at 0.1, 0.2, 0.5, 1.0 and 1.2A.g^-1Discharging under current, and the specific capacity of the membrane electrode is 1480, 1280, 1100, 880 and 660mAh^-1. When the current density returns to 0.1A.g^-1The recovery specific capacity of the three-dimensional sulfur/graphene gel film is 1290 mAh.g^-1The result shows that the structure of the membrane electrode is not greatly damaged after the battery pole piece is impacted by large current density.

Drawings

Fig. 1 is a scanning electron microscope picture of the lithium sulfur battery positive electrode material in example 1 of the present invention: wherein: (a) a scanning electron microscope picture at the nanometer level, and (b) a scanning electron microscope picture at the micrometer level.

FIG. 2 is a scanning electron microscope photograph of the positive electrode material of the lithium sulfur battery in comparative example 1 of the present invention: wherein: (a) 20 micron scanning electron microscope pictures, (b) 2 micron scanning electron microscope pictures, and (c) nanometer scanning electron microscope pictures.

Fig. 3 is a cyclic voltammogram of the lithium-sulfur battery of example 1 of the present invention.

FIG. 4 (a) is a graph of rate performance of the lithium sulfur battery of example 1 of the present invention; FIGS. 4 (b), (c), (d) are lithium sulfur prepared in example 1, respectivelyThe battery is 1.0, 1.5, 2.0A.g^-1And (4) a cycle performance graph.

Detailed Description

In order that the invention may be readily understood, reference will now be made in detail to the specific embodiments. The specific embodiments described herein are merely illustrative and explanatory of the invention and do not restrict the invention.

Unless otherwise defined, all terms of art used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.

Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available. All reagent grades were analytical grade.

As shown in fig. 1, 2, 3, and 4, the positive electrode material of the present invention is prepared by reducing graphene oxide to form a porous sulfur/graphene composite structure, and includes the following steps:

(a) preparing a graphene oxide solution: mixing graphite with NaNO₃Mixing the solid, wherein the graphite accounts for 50% ~ 65% of the solid, and NaNO ₃35 percent of ~ 50 percent of solid, then adding inorganic strong protonic acid with the mixed solid content of 1000 percent to ~ 3000 percent to 3000 percent, stirring the mixture under a magnetic stirrer, stirring the mixture for 24 ~ 36 hours, then adding strong oxidant with the mixed solid content of 150 percent to ~ 200 percent, controlling the reaction temperature to be not more than 25 ℃, stirring the mixture for 0.5 ~ 1.5.5 hour, then heating the mixture to 80 ~ 100 ℃ again, continuing stirring the mixture until the magnetic stirring is failed, standing the mixture for 6 ~ 8 hours, then slowly adding deionized water with the mixed solid content of 200 percent to ~ 300 percent into the mixture, manually stirring the mixture for 2 ~ 3 hours, and then adding H with the mass fraction of 30 percent into the mixture₂O₂In which H is₂O₂The mixed solid accounts for 20 percent ~ 30 percent, stands for 24h ~ 36h and adopts 1 ~ 2mol.L^-1Washing the bottom precipitate with dilute hydrochloric acid and deionized water until no sulfate radical is contained in the solution, dialyzing the obtained graphite oxide in a dialysis bag to remove metal ions in graphene oxide, performing ultrasonic treatment on the cleaned graphite oxide after one week of dialysis, and dispersing for 1 ~ 2h to obtain a layerA sheet-like structural material;

(b) dissolving a sulfur source in the graphene oxide aqueous solution prepared in advance in the step (a), wherein the proportion of the sulfur source is 97 percent ~ 99.2.2 percent, the proportion of the graphene oxide solution is 0.8 percent ~ 3 percent, stirring for 10 ~ 30min under the ice bath condition, and then adding a solid with the concentration of 900 percent of 0.024 ~ 0.03.03 mol.L^-1Reacting the dilute hydrochloric acid aqueous solution for 6 ~ 8h under ice bath condition, centrifuging and collecting the obtained suspension, washing with deionized water, re-dispersing the collected product into 20 ~ 30mL of deionized water to form brown sulfur oxide/graphene composite colloid, namely a precursor, taking 1 ~ 2mol.L^-1Adding the sodium ascorbate solution into the compound colloid, wherein the adding amount is 50% ~ 60% of the solid mixture, performing ultrasonic dispersion for 10 ~ 30min, placing the mixture in an air-blast drying oven at 95 ~ 105 and 105 ℃ for standing reaction for 1.5 ~ 2.5.5 h to obtain the sulfur/graphene compound hydrogel, washing and freeze-drying the hydrogel to obtain compound aerogel, and rolling the aerogel by using a roll-to-roll machine to obtain the flexible self-supporting three-dimensional sulfur/graphene anode material.