Method for preparing gradient distribution of transition metal sulfides in sulfur-based composite material

Abstract

The invention discloses a method for preparing transition metal sulfides distributed in a sulfur-based composite material in a gradient manner, and belongs to the technical field of chemical power sources. When the sulfur-based composite material is prepared by a chemical reaction method, a self-assembly reaction occurs. Wherein the transition metal ions are continuously reduced along with the proceeding of the reaction, and the concentration is in a decreasing trend. The transition metal sulfide nanoparticles are distributed in the composite material in a gradient manner along with the proceeding of the reaction, so that the material core with slow dynamics can be compounded with more transition metal sulfides, and the gradient distribution catalyst can well fix sulfur and has very strong catalytic property on the conversion reaction of polysulfides; the shuttling of polysulfide is inhibited to a great extent. According to the technology, the negative influence of a polysulfide shuttle effect on battery circulation is greatly relieved, so that the performance of the battery is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical power sources, and in particular relates to a method for preparing a transition metal sulfide gradiently distributed in a sulfur-based composite material. Background Art

[0002] As the dominant type of secondary battery in the energy storage market, lithium-ion batteries have experienced a boom in development and growth. In the past few decades, they have covered almost every aspect of life, from handheld electronic devices to all-electric vehicles and even micro smart grids. As the demand for energy storage increases in the future, lithium-ion batteries cannot meet the growing demand due to their density limitations (400Wh / kg). Lithium-sulfur (Li-S) batteries have become a candidate battery for the new generation of energy storage systems due to their high energy density (2600Wh / kg), low cost and environmental friendliness. In recent years, they have become a research hotspot in the field of scientific research.

[0003] Despite its great advantages, the charging and discharging of lithium-sulfur batteries is a multi-electron transfer process, and the positive electrode material is a solid-liquid dual-phase conversion process. In the discharge state, sulfur is gradually reduced to soluble lithium polysulfide and enters the electrolyte. Driven by multiple factors such as concentration gradient, some LiPSs (Li2S n ,4≤n≤8) detach from the cathode skeleton and diffuse into the electrolyte. Lithium metal has strong reducing properties. When long-chain LiPSs diffuse into the negative electrode area, they are reduced to short-chain LiPSs, and some of them return to the cathode area to form a "shuttle effect". In addition, dissolved LiPSs increase the viscosity of the electrolyte and slow down the transport of lithium ions. This seriously affects the cycle stability and practical application of lithium-sulfur batteries.

[0004] In this regard, this patent proposes a method for preparing a sulfur-based composite material with a gradient distribution of transition metal sulfides. This method adds a sulfur solution to a carbon suspension containing a certain transition metal at a uniform speed. As the reaction proceeds, the transition metal sulfide nanoparticles are gradiently distributed in the composite material, which helps to limit the diffusion of polysulfides and promote redox reactions. This innovative method alleviates the negative impact of the polysulfide shuttle effect on battery cycles and significantly improves battery performance; it simplifies the preparation process of carbon-sulfur-doped positive electrode materials, making this technology easy to achieve large-scale production. Summary of the invention

[0005] The present invention aims to solve the technical problems existing in the above-mentioned background technology and provides a method for preparing a transition metal sulfide gradiently distributed in a sulfur-based composite material.

[0006] The present invention adopts the following technical solution: a method for preparing a transition metal sulfide gradient distribution in a sulfur-based composite material, comprising the following steps:

[0007] Step 1, stirring and mixing a predetermined proportion of carbon material, a transition metal ion compound, an acidic reagent and a dispersant to form a carbon material suspension;

[0008] Step 2, adding solution A to the carbon material suspension, where solution A generates nano-sulfur in an acidic environment, which is compounded with the carbon material in the carbon material suspension, and also generates transition metal sulfide with the transition metal ions in the carbon material suspension;

[0009] Step 3: As the reaction proceeds, the concentration of transition metal ions in the carbon material suspension gradually decreases, and the transition metal sulfide is distributed in the sulfur-based composite material in a gradient manner.

[0010] Preferably, the carbon material is a mixture of one or more of granular carbon, one-dimensional carbon and two-dimensional carbon; the transition metal ion compound is chloride or sulfide of transition metal; the acidic reagent is hydrochloric acid, sulfuric acid, acetic acid or citric acid; the dispersant is an ionic surfactant, a nonionic surfactant, a compound surfactant or other surfactant among surfactants; the solution A is a solution of soluble polysulfide and elemental sulfur;

[0011] The granular carbon is carbon black; the one-dimensional carbon is carbon fiber, carbon nanotube, carbon nanowire; the two-dimensional carbon is graphene; the ionic surfactant includes: cationic surfactant, anionic surfactant, amphoteric surfactant; the soluble polysulfide is sodium sulfide, sodium thiosulfate, ammonium sulfide.

[0012] Preferably, the mass ratio of the carbon material to the transition metal ion compound is 2-1000:1, the proportion of the dispersant to the carbon is 0.1-5%wt; the number of revolutions during the stirring process of the carbon material suspension is 100-10000rpm / min, and the stirring time is 10-2000min; the number of revolutions when adding solution A is 100-13000rpm / min, and the stirring time is 10-2000min.

[0013] Preferably, it is used in lithium metal batteries, lithium ion batteries, sodium ion batteries, sodium metal batteries, potassium ion batteries, and potassium metal batteries.

[0014] Beneficial effects of the present invention: Compared with traditional transition metal sulfide-doped and distributed carbon-sulfur cathode composite materials, the gradient-distributed transition metal sulfide nanoparticles in this patent can more effectively promote the redox of polysulfides, thereby greatly improving the electrochemical performance of the electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a capacity-voltage curve diagram of Example 1. DETAILED DESCRIPTION

[0016] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0017] Embodiment 1

[0018] The present embodiment discloses a method for preparing a transition metal sulfide gradient distribution in a sulfur-based composite material, and prepares a FeS gradient distribution in a sulfur-based composite material. First, 10g of acetylene black and 0.5g of sodium dodecyl sulfate are dissolved in 200ml of deionized water to form a carbon suspension, and 5ml of saturated ferric chloride solution and 5ml of hydrochloric acid are added at the same time, and stirred at a low speed (300rpm / min) for 10 minutes to ensure that the material is fully mixed. 160g of sodium thiosulfate and 40g of sulfur are dissolved in 500ml of deionized water and stirred at a low speed (400rpm / min) for 10 minutes to fully mix. Subsequently, solution A is added to the carbon suspension at a certain rate (15ml / min), and the speed is increased to 800rpm / min for continuous stirring. Finally, a FeS nanoparticle gradient distribution with superior performance in a carbon-sulfur positive electrode material is obtained, and this material is used as the positive electrode, and metal lithium is used as the negative electrode to assemble a Li-S battery soft pack. This sulfur-based material with a gradient distribution of FeS nanoparticles is conducive to the catalytic conversion of polysulfides, improves the conversion kinetics, and enhances the coulombic efficiency and long cycle capacity of the battery. At a current density of 0.1C, the first discharge specific capacity reached 959mAh / g. Figure 1 shown.

[0019] Embodiment 2

[0020] The present embodiment discloses a method for preparing a transition metal sulfide gradient distribution in a sulfur-based composite material, and a CoS nanoparticle gradient distribution in a sulfur-based composite material is prepared. First, 15g of graphene and 0.45g of hexadecyltrimethylammonium bromide are dissolved in 300ml of deionized water to form a carbon suspension, and 5ml of saturated cobalt chloride solution and 5ml of hydrochloric acid are added at the same time, and stirred at a low speed (300rpm / min) for 10 minutes to ensure that the material is fully mixed. 90g of sodium sulfide and 60g of sulfur are dissolved in 500ml of deionized water, and stirred at a low speed (300rpm / min) for 10 minutes to fully mix. Subsequently, solution A is added to the carbon suspension at a certain rate (15ml / min), and the speed is increased to 800rpm / min and continuously stirred. A carbon-sulfur positive electrode material with superior performance is obtained. Using this material as the positive electrode, metallic lithium is used as the negative electrode to assemble a Li-S battery soft pack. The gradient distribution of CoS nanoparticles in sulfur-based materials is beneficial to the catalytic conversion of polysulfides, improves the conversion kinetics, and enhances the coulombic efficiency and long cycle capacity of the battery. At a current density of 0.1C, the Li-S battery can remain stable for 70 cycles, and the coulombic efficiency after 50 cycles remains at 98.1%.

[0021] Embodiment 3

[0022] This embodiment discloses a method for preparing a transition metal sulfide gradient distribution in a sulfur-based composite material, and prepares a MnS gradient distribution in a sulfur-based composite material. First, 20g of carbon nanotubes and 0.8g of polyvinyl pyrrolidone are dissolved in 400ml of deionized water to form a carbon suspension, and 10ml of saturated manganese sulfate solution and 5ml of sulfuric acid are added at the same time, and stirred at a low speed (300rpm / min) for 10 minutes to ensure that the materials are fully mixed. 100g of ammonium sulfide and 50g of sulfur are dissolved in 600ml of deionized water and stirred at a low speed (300rpm / min) for 10 minutes to fully mix. Subsequently, sodium thiosulfate solution is added to the carbon suspension at a certain rate (15ml / min), and the speed is increased to 800rpm / min for continuous stirring. This material is used as the positive electrode, and metal lithium is used as the negative electrode to assemble a Li-S battery soft pack. This MnS nanoparticle gradient distribution in the sulfur-based material is beneficial to the catalytic conversion of polysulfides, improves the conversion kinetics, and improves the coulombic efficiency and long cycle capacity of the battery. At a current density of 0.1C, the Li-S battery can remain stable for 100 cycles.

[0023] The above is a detailed introduction to a method for preparing a transition metal sulfide gradient distribution in a sulfur-based composite material provided by the present invention. It is worth noting that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical details described in the aforementioned embodiments, or to make equivalent replacements for some of the technical features therein. Any equivalent replacements, modifications, etc. made within the core ideas and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a transition metal sulfide gradient distribution in a sulfur-based composite material, characterized in that: The following steps are involved: Step 1, stirring and mixing a predetermined proportion of carbon material, a transition metal ion compound, an acidic reagent and a dispersant to form a carbon material suspension; Step 2, adding solution A to the carbon material suspension, where solution A generates nano-sulfur in an acidic environment, which is compounded with the carbon material in the carbon material suspension, and also generates transition metal sulfide with the transition metal ions in the carbon material suspension; Step 3: As the reaction proceeds, the concentration of transition metal ions in the carbon material suspension gradually decreases, and the transition metal sulfide is distributed in the sulfur-based composite material in a gradient manner.

2. A method for preparing a transition metal sulfide gradient distribution in a sulfur-based composite material according to claim 1, characterized in that: The carbon material is a mixture of one or more of granular carbon, one-dimensional carbon and two-dimensional carbon; the transition metal ion compound is chloride or sulfide of transition metal; the acidic reagent is hydrochloric acid, sulfuric acid, acetic acid or citric acid; the dispersant is an ionic surfactant, a non-ionic surfactant, a compound surfactant or other surfactant among surfactants; the solution A is a solution of soluble polysulfide and elemental sulfur; The particulate carbon is carbon black; The one-dimensional carbon is carbon fiber, carbon nanotube, or carbon nanowire; The two-dimensional carbon is graphene; The ionic surfactants include: cationic surfactants, anionic surfactants, and amphoteric surfactants; The soluble polysulfide is sodium sulfide, sodium thiosulfate, and ammonium sulfide.

3. A method for preparing a transition metal sulfide gradient distribution in a sulfur-based composite material according to claim 2, characterized in that: The mass ratio of the carbon material to the transition metal ion compound is 2-1000:1, and the proportion of the dispersant to the carbon is 0.1-5%wt; the number of revolutions during the stirring process of the carbon material suspension is 100-10000rpm / min, and the stirring time is 10-2000min; the number of revolutions when adding solution A is 100-13000rpm / min, and the stirring time is 10-2000min.

4. The method for preparing a transition metal sulfide gradient distribution in a sulfur-based composite material according to claim 1, characterized in that: Used in lithium metal batteries, lithium ion batteries, sodium ion batteries, sodium metal batteries, potassium ion batteries, and potassium metal batteries.

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