Lithium-sulfur battery positive electrode active material and preparation method thereof, positive electrode material, positive electrode and preparation method thereof, and lithium-sulfur battery

Abstract

The application relates to the technical field of lithium-sulfur battery positive electrode materials, and discloses a lithium-sulfur battery positive electrode active material and a preparation method thereof, a lithium-sulfur battery positive electrode material, a lithium-sulfur battery positive electrode and a preparation method thereof, and a lithium-sulfur battery. The lithium-sulfur battery positive electrode active material is a composite material, and the composite material contains graphene, elemental sulfur and carbon-coated nickel nanomaterial. The preparation method of the positive electrode active material is simple and low in cost, the prepared lithium-sulfur battery positive electrode material effectively inhibits the "shuttle effect" of polysulfide intermediate products in the battery reaction process, can catalyze the electrochemical conversion of sulfur-containing substances, provides active sites for electrochemical reactions, and improves the utilization rate of active sulfur. The lithium-sulfur battery prepared by using the positive electrode active material has high specific capacity and long cycle life.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology, specifically relating to a positive electrode active material for lithium-sulfur batteries and its preparation method, as well as a positive electrode material for lithium-sulfur batteries, a positive electrode for lithium-sulfur batteries and its preparation method, and a lithium-sulfur battery. Background Technology

[0002] With the rapid development of electric vehicles and mobile electronic devices in recent years, the energy density of lithium-ion batteries has become insufficient to meet the demands. Lithium-sulfur batteries, due to their high theoretical specific capacity (1675 mAh g⁻¹), have become a more viable alternative. -1 ) and theoretical energy density (2600Wh kg) -1 Lithium-sulfur batteries have attracted much attention as the most promising next-generation high-energy rechargeable battery system due to their advantages such as environmental friendliness, safety, non-toxicity, and low cost. However, lithium-sulfur batteries also have many drawbacks. The electronic insulating properties of sulfur at room temperature, the volume expansion of up to 80% during charging and discharging, and the "shuttle effect" caused by the dissolution of polysulfides, intermediate products of sulfur in the electrolyte, all lead to relatively low specific capacity and poor cycle performance of current lithium-sulfur batteries, thus severely restricting their practical application.

[0003] To address these issues, researchers have conducted a series of studies to suppress the migration and diffusion of polysulfide ions, thereby improving the cycle performance and charge / discharge efficiency of lithium-sulfur batteries. Among these efforts, the research focus on cathode materials falls into three main categories. The first category involves carbon / sulfur composite materials prepared using conductive carbon materials of various morphologies as a framework. For example, carbon nanotubes, graphene, and mesoporous carbon are used to store sulfur, improving the overall conductivity of the electrode and confining sulfur within the pores of the carbon material. Alternatively, the high specific surface area of ​​the carbon material can be used to limit the dissolution of lithium polysulfides, thus improving battery performance. The second category involves coating elemental sulfur with conductive polymers or using conductive polymer network frameworks to adsorb elemental sulfur. For instance, polypyrrole, polyaniline, and polythiophene are used as sulfur storage mediums. These not only limit the dissolution of lithium polysulfides but also enhance battery performance due to the activity of the conductive polymers themselves. The third category involves adding polar inorganic metal compounds (oxides, sulfides, hydroxides, nitrides, and carbides, etc.) to immobilize polysulfides through chemisorption, thereby reducing the impact of the shuttle effect on battery performance.

[0004] In recent years, the concept of "electrocatalysis" has been introduced into the field of lithium-sulfur batteries, and some transition metal nanomaterials have been shown to catalyze the electrochemical conversion of intermediate polysulfides. However, due to the high activity of transition metal nanoparticles, they are prone to aggregation or side reactions during electrochemical reactions, affecting the performance and application of these materials. For example, CN110931752A discloses a nitrogen-doped porous carbon-supported nickel-metallic lithium-sulfur battery cathode material. The preparation method of this nitrogen-doped porous carbon-supported nickel-metallic material adopts the template method and the impregnation method. This preparation method has disadvantages such as high raw material cost, low preparation efficiency, cumbersome steps, and the need for ammonia gas. Moreover, in the composite material prepared by this method, the metal particles are only dispersed on the carbon material and are in an exposed state, making them extremely prone to aggregation or oxidation, and even spontaneous combustion in air. At the same time, side reactions are prone to occur during the electrochemical reaction, leading to failure. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of poor specific capacity and cycle performance of existing lithium-sulfur batteries, and to provide a composite material containing carbon-coated nickel nanomaterials as a sulfur cathode carrier, so as to improve the specific capacity and cycle performance of lithium-sulfur batteries.

[0006] To achieve the above objectives, the present invention provides a positive electrode active material for lithium-sulfur batteries, wherein the positive electrode active material is a composite material containing graphene, elemental sulfur, and carbon-coated nickel nanomaterials. Based on the total weight of the composite material, the content of graphene is 5-20% by weight, the content of elemental sulfur is 60-90% by weight, and the content of nickel is 0.5-10% by weight.

[0007] The inventors of this invention discovered that transition metal nanomaterials exhibit high catalytic activity towards sulfur-containing substances but poor chemical stability, while carbon nanomaterials possess good chemical stability but require further improvement in catalytic activity. Combining the two in an appropriate manner may produce new synergistic effects, enabling them to exhibit novel and unique properties. Although CN109304195A discloses a carbon-coated transition metal nanocomposite material, it is used as a catalyst for treating volatile organic compounds and does not mention the application of carbon-coated nickel nanomaterials in lithium-sulfur batteries.

[0008] A second aspect of the present invention provides a method for preparing a positive electrode active material for lithium-sulfur batteries, wherein the preparation method includes:

[0009] (1) Provide a mixture containing carbon-coated nickel nanomaterials with elemental sulfur and graphene;

[0010] (2) Under the protection of an inactive atmosphere, the mixture obtained in step (1) is subjected to high-temperature heat treatment at a melting temperature not lower than that of sulfur.

[0011] A third aspect of the present invention provides a lithium-sulfur battery cathode material, the cathode material comprising a cathode active material, a conductive agent and a binder, wherein the cathode active material is the lithium-sulfur battery cathode active material provided by the present invention.

[0012] A fourth aspect of the present invention provides a positive electrode for a lithium-sulfur battery, the positive electrode comprising a current collector and a positive electrode material coated and / or filled on the current collector, wherein the positive electrode material is the positive electrode material provided by the present invention.

[0013] The fifth aspect of the present invention provides a method for preparing a positive electrode for a lithium-sulfur battery, the method comprising coating and / or filling a slurry containing a positive electrode active material, a conductive agent, a binder, and a solvent onto a current collector, drying, and calendering or not calendering, wherein the positive electrode active material is the positive electrode active material for lithium-sulfur batteries provided by the present invention.

[0014] The sixth aspect of the present invention provides a lithium-sulfur battery, the battery comprising an electrode assembly and a non-aqueous electrolyte, the electrode assembly and the non-aqueous electrolyte being sealed within a battery casing, the electrode assembly comprising a positive electrode, a negative electrode and a separator, the separator being located between the positive electrode and the negative electrode, wherein the positive electrode is the positive electrode of the lithium-sulfur battery provided by the present invention.

[0015] The lithium-sulfur battery cathode active material provided by this invention is a composite material containing graphene, elemental sulfur, and carbon-coated nickel nanomaterials. The carbon-coated nickel nanomaterials possess a core-shell structure with tightly coated graphitized carbon layers and a metallic nickel core, preventing the agglomeration of the metallic nickel core, which could lead to spontaneous combustion in air or side reactions with intermediate products, thus improving its chemical stability. Simultaneously, the carbon-coated nickel nanomaterials have abundant mesoporous structures, which facilitates mass transfer and diffusion of reactants and products during battery reactions; in particular, they can possess multi-level mesoporous structures, thereby endowing the material with more diverse functions and making it suitable for a wider range of applications. Furthermore, the carbon-coated nickel nanomaterials can both "anchor" intermediate polysulfides through chemisorption and catalyze the electrochemical conversion of sulfur-containing substances, providing active sites for electrochemical reactions, improving the utilization rate of active sulfur, and enhancing the charge-discharge specific capacity and cycle stability of lithium-sulfur batteries prepared using the lithium-sulfur battery cathode active material of this invention.

[0016] Furthermore, the preparation method of the positive electrode active material for lithium-sulfur batteries according to the present invention involves mixing a core-shell structured carbon-coated nickel nanocomposite material (the shell being an oxygen-doped graphitized carbon coating layer, and the core being metallic nickel nanoparticles) with graphene and elemental sulfur, followed by high-temperature melting to obtain the positive electrode active material for lithium-sulfur batteries. The particle size and pore size of the carbon-coated nickel nanomaterial can be artificially controlled, making it suitable for large-scale industrial production. The preparation method of the positive electrode active material for lithium-sulfur batteries according to the present invention is simple and low-cost. The obtained positive electrode active material effectively suppresses the "shuttle effect" of polysulfide ion intermediates in the battery reaction process, while catalyzing the electrochemical conversion of sulfur-containing substances, providing active sites for the electrochemical reaction, and improving the utilization rate of active sulfur. Lithium-sulfur batteries using the positive electrode active material of the present invention exhibit high specific capacity and long cycle life. Attached Figure Description

[0017] Figure 1 This is a SEM image of the carbon-coated nickel nanomaterial / graphene-sulfur composite positive electrode active material prepared in Example 1;

[0018] Figure 2 The image shows the XRD pattern of the carbon-coated nickel nanomaterial / graphene-sulfur composite positive electrode active material prepared in Example 1.

[0019] Figure 3 This is a comparison chart of the cycle performance of lithium-sulfur batteries prepared in Examples 1-4. Detailed Implementation

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] According to the present invention, the positive electrode active material of the lithium-sulfur battery is a composite material containing graphene, elemental sulfur and carbon-coated nickel nanomaterials. Based on the total weight of the composite material, the content of graphene is 5-20% by weight, the content of elemental sulfur is 60-90% by weight, and the content of nickel is 0.5-10% by weight.

[0022] According to the present invention, preferably, based on the total weight of the composite material, the graphene content is 8-20% by weight, the elemental sulfur content is 70-90% by weight, and the nickel content is 1-8% by weight.

[0023] According to the present invention, the positive electrode active material of the lithium-sulfur battery is a composite material containing graphene, elemental sulfur, and carbon-coated nickel nanomaterials. Based on the total weight of the composite material, the graphene content is 5-20% by weight, the elemental sulfur content is 60-90% by weight, and the carbon-coated nickel nanomaterial content is 1-20% by weight. Preferably, based on the total weight of the composite material, the graphene content is 8-20% by weight, the elemental sulfur content is 70-90% by weight, and the carbon-coated nickel nanomaterial content is 1-10% by weight.

[0024] According to the present invention, the carbon-coated nickel nanomaterial is a carbon-coated nickel nanoparticle, which contains a metallic nickel core and a graphitized carbon coating layer covering the surface of the metallic nickel core. The metallic nickel is the core of the carbon-coated nickel nanomaterial, and the surface of the metallic nickel core is coated with the graphitized carbon coating layer.

[0025] In this invention, the term "metallic nickel" refers to nickel with a valence state of zero.

[0026] In this invention, the term "graphitized carbon coating" refers to a carbon structure with a layered structure that can be clearly observed under a high-resolution transmission electron microscope, rather than an amorphous structure, and with an interlayer spacing of approximately 0.34 nm. The carbon-coated nickel nanoparticles are spherical or near-spherical.

[0027] In this invention, the term "mesopore" is defined as a pore with a diameter in the range of 2-50 nm. A pore with a diameter less than 2 nm is defined as a micropore, and a pore with a diameter greater than 50 nm is defined as a macropore.

[0028] The term "mesopore distribution peak" refers to the mesopore distribution peak on the pore distribution curve obtained by calculating the desorption curve according to the Barrett-Joyner-Halenda (BJH) method.

[0029] According to the present invention, the metallic nickel comprises a face-centered cubic lattice structure and / or a hexagonal close-packed lattice structure. The lattice structure of the metallic nickel can be determined by XRD characterization.

[0030] According to the present invention, the pore size of the carbon-coated nickel nanomaterial has at least one mesoporous peak. Preferably, the pore size of the carbon-coated nickel nanomaterial has two mesoporous distribution peaks, and the two mesoporous distribution peaks correspond to a first most probable pore size and a second most probable pore size, respectively. The first most probable pore size is smaller than the second most probable pore size, and the first most probable pore size is 2-5 nanometers, while the second most probable pore size is 8-12 nanometers.

[0031] According to the present invention, the mesopore volume of the carbon-coated nickel nanomaterial accounts for more than 50% of the total pore volume, preferably more than 80%; more preferably, the mesopore volume of the carbon-coated nickel nanomaterial is 0.05-1.25 cm³. 3 / g.

[0032] According to the present invention, based on the total amount of the carbon-coated nickel nanoparticles, the nickel content can be 30-80% by weight, preferably 60-80% by weight; the carbon content can be 20-70% by weight, preferably 20-40% by weight.

[0033] According to the present invention, the carbon-coated nickel nanoparticles may also contain oxygen, possibly formed in the graphitized carbon coating layer during the preparation of the carbon-coated nickel nanomaterials, and present in various forms. Based on the total amount of the carbon-coated nickel nanoparticles, the oxygen content can be less than 15% by weight, preferably 0.5-10% by weight. In this invention, the oxygen content in the carbon-coated nickel nanoparticles is determined by elemental analysis, and the nickel content is the normalized content after deducting carbon and oxygen.

[0034] According to the present invention, the average thickness of the graphitized carbon coating layer in the carbon-coated nickel nanoparticles can be 0.3-6 nm, preferably 0.3-3 nm. The average particle size of the metallic nickel core is 1-200 nm, preferably 3-100 nm. The average particle size of the carbon-coated nickel nanoparticles is 1-200 nm, preferably 3-100 nm, more preferably 4-50 nm. In the present invention, the average thickness of the graphitized carbon coating layer, the average particle size of the metallic nickel core, and the average particle size of the carbon-coated nickel nanoparticles are determined by transmission electron microscopy.

[0035] According to the present invention, the preparation method of the carbon-coated nickel nanoparticles can be obtained by referring to methods well known to those skilled in the art, such as the method disclosed in patent document CN109304195A, which will not be described in detail here.

[0036] According to the present invention, in a preferred embodiment, the surface of the metallic nickel core of the carbon-coated nickel nanomaterial is tightly coated with a graphitized carbon coating layer to prevent the occurrence of side reactions of metallic nickel during the electrochemical reaction process, thereby affecting the performance of the lithium-sulfur battery electrode.

[0037] The tightness of the graphitized carbon coating reflects the proportion of metallic nickel isolated from the external environment by the graphitized carbon coating, which can be characterized by high-resolution transmission electron microscopy (HRTEM) analysis, nickel content analysis, and acid washing experiment results. Preferably, the acid washing loss rate of the carbon-coated nickel nanomaterial is less than 50%, and more preferably less than 40%. The "acid washing loss rate" refers to the proportion of nickel lost from the prepared carbon-coated nickel nanomaterial after acid washing. It reflects the tightness of the graphitized carbon layer's coating on the metallic nickel core. A higher acid washing loss rate indicates a lower tightness of the surface graphitized carbon layer's coating on the metallic nickel core, and a lower acid washing loss rate indicates a higher tightness of the surface graphitized carbon coating on the metallic nickel core. The measurement and calculation methods for the acid washing loss rate can refer to the definition in CN109304195A.

[0038] According to the present invention, the method for preparing the positive electrode active material of the lithium-sulfur battery includes:

[0039] (1) Provide a mixture containing carbon-coated nickel nanomaterials with elemental sulfur and graphene;

[0040] (2) Under the protection of an inactive atmosphere, the mixture obtained in step (1) is subjected to high-temperature heat treatment at a melting temperature not lower than that of sulfur.

[0041] According to the present invention, in step (1), the amount of carbon-coated nickel nanomaterials, elemental sulfur, and graphene used in the resulting mixture is such that, based on the total weight of the mixture, the content of graphene is 5-20% by weight, the content of elemental sulfur is 60-90% by weight, and the content of nickel is 0.5-10% by weight; preferably, the content of graphene is 8-20% by weight, the content of elemental sulfur is 70-90% by weight, and the content of nickel is 1-8% by weight.

[0042] According to the present invention, in step (1), the amount of carbon-coated nickel nanomaterials, elemental sulfur, and graphene used in the resulting mixture is such that, based on the total weight of the mixture, the content of graphene is 5-20% by weight, the content of elemental sulfur is 60-90% by weight, and the content of carbon-coated nickel nanomaterials is 1-20% by weight; preferably, the content of graphene is 8-20% by weight, the content of elemental sulfur is 70-90% by weight, and the content of carbon-coated nickel nanomaterials is 1-10% by weight.

[0043] According to the present invention, the mixture can be obtained by mixing and grinding carbon-coated nickel nanomaterials with elemental sulfur and graphene.

[0044] According to the present invention, in step (2), the high-temperature heat treatment is carried out at a temperature not lower than the melting temperature of sulfur, so that elemental sulfur is in a molten state and can be uniformly dispersed on the graphene conductive network. Preferably, the high-temperature heat treatment can be carried out at a temperature of 120-200°C, more preferably, the high-temperature heat treatment can be carried out at a temperature of 120-180°C. The duration of the high-temperature heat treatment can be 1-48 hours, preferably 8-40 hours, more preferably 10-30 hours, and even more preferably 12-20 hours. The high-temperature heat treatment is carried out in a closed reactor, for example, in a common high-pressure reactor.

[0045] According to the present invention, in step (2), the high-temperature heat treatment is carried out in an inactive atmosphere, which is an atmosphere formed by group zero gas and / or nitrogen, wherein the group zero gas may be, for example, argon.

[0046] According to the present invention, in a preferred embodiment, after the high-temperature heat treatment in step (2), the obtained reaction product is naturally cooled to room temperature and ground into powder to obtain the composite material of the present invention.

[0047] According to the present invention, the lithium-sulfur battery cathode material contains a cathode active material, a conductive agent and a binder, wherein the cathode active material is the lithium-sulfur battery cathode active material provided by the present invention.

[0048] According to the present invention, the positive electrode of the lithium-sulfur battery includes a current collector and a positive electrode material coated and / or filled on the current collector, wherein the positive electrode material is the positive electrode material described in the present invention.

[0049] According to the present invention, the method for preparing the positive electrode of the lithium-sulfur battery includes coating and / or filling a slurry containing a positive electrode active material, a conductive agent, a binder, and a solvent onto a current collector, drying, and calendering or not calendering, wherein the positive electrode active material is the positive electrode active material of the lithium-sulfur battery provided by the present invention.

[0050] According to the present invention, the lithium-sulfur battery includes an electrode assembly and a non-aqueous electrolyte, the electrode assembly and the non-aqueous electrolyte being sealed within a battery casing. The electrode assembly includes a positive electrode, a negative electrode and a separator, the separator being located between the positive electrode and the negative electrode, wherein the positive electrode is the positive electrode of the lithium-sulfur battery provided by the present invention.

[0051] Since this invention only relates to improvements on the positive electrode active material in existing lithium-sulfur cathode materials, there are no particular limitations on other components and structures of lithium-sulfur batteries.

[0052] For example, for the positive electrode of a lithium-sulfur battery, the binder of the positive electrode material described in this invention can be any binder known in the art that can be used in lithium-sulfur batteries. It can be selected from one or more of fluorinated resins and / or polyolefin compounds, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and styrene-butadiene rubber. Based on the weight of the positive electrode active material, the content of the binder can be 0.01-15% by weight. The content and type of conductive agent in the positive electrode material described in this invention are well known to those skilled in the art; for example, based on the positive electrode active material, the content of the conductive agent is generally 0-30% by weight. The conductive agent can be selected from one or more of conductive carbon black (Super-P), acetylene black, nickel powder, copper powder, and conductive graphite. The current collector can be various current collectors known to those skilled in the art, such as aluminum foil, copper foil, and nickel-plated steel strip; this invention uses aluminum foil as the current collector.

[0053] In the lithium-sulfur battery, metallic lithium sheets can be directly used as the negative electrode.

[0054] The electrolyte for lithium-sulfur batteries can be any electrolyte commonly used in the field. The ratio of the injected volume of the electrolyte to the mass of the active material sulfur is generally 1-40 μL / mg, and the concentration of the electrolyte is generally 0.2-8.0 mol / L.

[0055] The separator has electrical insulation and liquid retention properties, is disposed between the positive and negative electrodes, and is sealed together with the positive and negative electrodes and the electrolyte in the battery casing. The separator can be any type of separator commonly used in the art, such as a composite membrane made by welding or bonding together polyethylene, polypropylene, modified polyethylene felt, modified polypropylene felt, ultrafine glass fiber felt, vinylon felt, or nylon felt with wettable polyolefin microporous membranes from various known manufacturers and brands.

[0056] The present invention will be described in detail below through embodiments.

[0057] XRD is used to obtain information such as the composition of materials and the structure or morphology of atoms or molecules inside the materials. The XRD diffractometer used is an XRD-6000 X-ray powder diffractometer (Shimadzu, Japan). The XRD test conditions are: Cu target, Kα rays (wavelength λ = 0.154 nm), tube voltage of 40 kV, tube current of 200 mA, and scanning speed of 10° (2θ) / min.

[0058] The surface morphology of the material was characterized using scanning electron microscopy (SEM). A Hitachi S-4800 cold field scanning emission microscope (SEM) was used. The SEM testing conditions were: the powder sample was fixed on the sample stage with conductive adhesive for observation, and the accelerating voltage was 5 kV. The surface morphology of the material was also characterized using high-resolution transmission electron microscopy (HRTEM). A JEM-2100 (Nippon Electron Ltd.) was used. The HRTEM testing conditions were: accelerating voltage 200 kV. The particle size of the nanoparticles in the sample was measured from the electron microscope images.

[0059] The pore structure properties of the material were detected using the BET test method. Specifically, a Quantachrome AS-6B analyzer was used for measurement. The specific surface area of ​​the material was obtained by the Brunauer-Emmett-Taller (BET) method, and the pore distribution curve was calculated from the desorption curve using the Barrett-Joyner-Halenda (BJH) method.

[0060] Analysis of carbon (C), hydrogen (H), and oxygen (O) was performed on an Elementar Micro Cube elemental analyzer. The specific operating procedures and conditions were as follows: 1-2 mg of sample was weighed into a tin cup, placed in the autosampler tray, and introduced into the combustion tube through a ball valve for combustion at 1000℃ (helium purging was used to remove atmospheric interference during sample introduction). The combusted gas was then reduced with copper to form carbon dioxide and water. The mixed gas was separated by three desorption columns and sequentially detected by a TCD detector. Oxygen analysis utilized high-temperature decomposition; under the action of a carbon catalyst, oxygen in the sample was converted to CO, which was then detected by a TCD detector.

[0061] The proportions of different metallic elements were determined using an X-ray fluorescence spectrometer (XRF). The content of each metallic element in the composite material was calculated from the known total content of carbon, hydrogen, and oxygen. The X-ray fluorescence spectrometer (XRF) used in this invention was a Rigaku 3013 X-ray fluorescence spectrometer, and the X-ray fluorescence spectroscopy analysis test conditions were: a scan time of 100 s and an air atmosphere.

[0062] Preparation Example 1

[0063] This preparation example illustrates the preparation of carbon-coated nickel nanomaterials.

[0064] Carbon-coated nickel nanomaterials were prepared according to the method disclosed in Example 1 of CN109304195A. The specific physicochemical characterization results are detailed in CN109304195A.

[0065] Example 1

[0066] This embodiment illustrates the preparation of the positive electrode active material for lithium-sulfur batteries.

[0067] Preparation of the positive electrode active material: The carbon-coated nickel nanomaterials obtained in Preparation Example 1, commercially available graphene material, and elemental sulfur powder were weighed separately according to a mass ratio of 5%:15%:80%, ground, and mixed evenly. The resulting mixture was placed in a reaction vessel under an argon protective atmosphere and treated at 160°C for 12 hours. The SEM and XRD data of the positive electrode active material are shown below. Figure 1 and Figure 2 As shown.

[0068] Example 2

[0069] This embodiment illustrates the preparation of the positive electrode active material for lithium-sulfur batteries.

[0070] Preparation of the positive electrode active material: The carbon-coated nickel nanomaterials obtained in Preparation Example 1, commercially available graphene material, and elemental sulfur powder were weighed separately according to a mass ratio of 3%:17%:80%, ground, and mixed evenly. The resulting mixture was placed in a reaction vessel under an argon protective atmosphere and treated at 160°C for 12 hours.

[0071] Example 3

[0072] This embodiment illustrates the preparation of the positive electrode active material for lithium-sulfur batteries.

[0073] Preparation of the positive electrode active material: The carbon-coated nickel nanomaterials obtained in Preparation Example 1, commercially available graphene material, and elemental sulfur powder were weighed separately according to a mass ratio of 7%:13%:80%, ground, and mixed evenly. The resulting mixture was placed in a reaction vessel under an argon protective atmosphere and treated at 160°C for 12 hours.

[0074] Example 4

[0075] This embodiment illustrates the preparation of the positive electrode active material for lithium-sulfur batteries.

[0076] Preparation of positive electrode active material: The carbon-coated nickel nanomaterials obtained in Preparation Example 1, commercially available graphene material, and elemental sulfur powder were weighed separately according to a mass ratio of 10%:10%:80%, ground, and mixed evenly. The resulting mixture was placed in a reaction vessel under an argon protective atmosphere and treated at 160°C for 12 hours.

[0077] Experimental Examples 1-4

[0078] This experimental example illustrates the preparation of lithium-sulfur batteries.

[0079] Preparation of the positive electrode and battery assembly: 1) Preparation of the positive electrode sheet: The lithium-sulfur battery positive electrode active material obtained in Examples 1-4, the conductive agent Super-P, and the NMP solution of the binder PVDF were mixed at a mass ratio of 8:1:1. The specific method is as follows: the dried positive electrode active material and the conductive agent were ground in a mortar for 15 minutes. After grinding evenly, PVDF solution (mass fraction 5%) was added according to the ratio, and the mixture was stirred on a magnetic stirrer for 6 hours. The resulting paste was evenly coated on current collector aluminum foil, carbon cloth, or carbon paper, and then dried in a vacuum drying oven at 60°C for 20 hours for later use. 2) Battery assembly: The dried electrode was made into a circular electrode sheet with a diameter of 12 mm; and held under a pressure of 8 MPa for 30-180 seconds to obtain the lithium-sulfur battery positive electrode. Using lithium metal as the negative electrode and a Celgard membrane as the separator, 1 mol / L lithium bis(trifluoromethanesulfonyl)imide was selected as the electrolyte, and 1% lithium nitrate was used as an additive. The solvent volume ratio of DOL (1,3-dioxolane):DME (ethylene glycol dimethyl ether) was 1:1, and CR2032 type coin cells were assembled. The amount of electrolyte added was 20 times (by mass) of elemental sulfur. The entire battery assembly was completed in a glove box, and lithium-sulfur batteries A1-A4 were prepared respectively.

[0080] Routine battery performance testing: The batteries were charged and discharged using a LAND CT2001A charge / discharge tester from Wuhan Lanbo Electronics Co., Ltd., with a charge / discharge voltage range of 1.7 to 2.8V. Specific capacity tests were performed on the assembled lithium-sulfur batteries at 0.2C, 0.5C, and 1C rates, and cycle performance tests were conducted at 1C rate. The results are as follows: Figure 3 As shown.

[0081] The lithium-sulfur battery A1 prepared using Example 1 achieved a discharge specific capacity of 1012 mAh / g at 0.2C rate, 783 mAh / g at 0.5C rate, and 699 mAh / g at 1C rate.

[0082] The lithium-sulfur battery A2 prepared using Example 2 achieved a discharge specific capacity of 1088 mAh / g at 0.2C rate, 759 mAh / g at 0.5C rate, and 678 mAh / g at 1C rate.

[0083] The lithium-sulfur battery A3 prepared using Example 3 achieved a discharge specific capacity of 1083 mAh / g at 0.2C rate, 822 mAh / g at 0.5C rate, and 725 mAh / g at 1C rate.

[0084] The lithium-sulfur battery A4 prepared using Example 4 achieved a discharge specific capacity of 1061 mAh / g at 0.2C rate, 818 mAh / g at 0.5C rate, and 752 mAh / g at 1C rate.

[0085] Comparative Experiment Example 1

[0086] Commercially available graphene material (purchased from Zhongke Times Nano Technology Co., Ltd., grade 170104) and elemental sulfur powder were weighed separately at a mass ratio of 20%:80%, ground, and mixed evenly. The resulting mixture was placed in a reactor under an argon protective atmosphere and treated at 160°C for 12 hours to obtain a conventional graphene-sulfur cathode material. The cathode was prepared, the battery was assembled, and the battery performance was tested according to the methods in Examples 1-4. The results showed that the lithium-sulfur battery obtained using the conventional graphene-sulfur cathode material achieved a discharge specific capacity of 1065 mAh / g at 0.2C rate; 691 mAh / g at 0.5C rate; and 602 mAh / g at 1C rate.

[0087] Analysis of the above data shows that the lithium-sulfur battery prepared using the positive electrode active material described in this invention has high specific capacity and long cycle life.

[0088] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A positive electrode active material for lithium-sulfur batteries, characterized in that, The positive electrode active material is a composite material containing graphene, elemental sulfur, and carbon-coated nickel nanomaterials. Based on the total weight of the composite material, the graphene content is 8-15% by weight, the elemental sulfur content is 80-90% by weight, and the nickel content is 0.5-10% by weight. The carbon-coated nickel nanomaterials exhibit a dual mesopore distribution peak, with each peak corresponding to a first most probable pore size and a second most probable pore size, respectively. The first most probable pore size is smaller than the second most probable pore size, and the first most probable pore size is 2-5 nanometers, while the second most probable pore size is 8-12 nanometers. The mesopore volume of the carbon-coated nickel nanomaterials accounts for more than 50% of the total pore volume. The mesopore volume of the carbon-coated nickel nanomaterials is 0.05-1.25 cm³. 3 / g; based on the total weight of the composite material, the content of the carbon-coated nickel nanomaterial is 5-10% by weight%. The carbon-coated nickel nanomaterial is a carbon-coated nickel nanoparticle, comprising a metallic nickel core and a graphitized carbon coating layer covering the surface of the metallic nickel core; the carbon-coated nickel nanoparticle is spherical or near-spherical; the graphitized carbon coating layer contains oxygen, with the oxygen content being less than 15% by weight based on the total amount of the carbon-coated nickel nanoparticle; the nickel content is 74.28-80% by weight based on the total amount of the carbon-coated nickel nanomaterial; and the carbon content is 20-24.29% by weight. The acid pickling loss rate of the carbon-coated nickel nanomaterial is less than 50%; Pickling loss rate = [1 - (mass fraction of nickel in the pickled carbon-coated nickel nanomaterial × mass of the pickled carbon-coated nickel nanomaterial) ÷ ​​(mass fraction of nickel in the carbon-coated nickel nanomaterial to be pickled × mass of the carbon-coated nickel nanomaterial to be pickled)] × 100%; The pickling conditions were as follows: 1 g of sample was added to 20 mL of sulfuric acid aqueous solution, and the sample was treated at 90 °C for 8 h. The concentration of the sulfuric acid aqueous solution was 1 mol / L. The sample was then washed with deionized water until neutral, dried, weighed, analyzed, and the pickling loss rate was calculated.

2. The positive electrode active material for lithium-sulfur batteries according to claim 1, wherein, Based on the total weight of the composite material, the nickel content is 1-8% by weight.

3. The positive electrode active material for lithium-sulfur batteries according to claim 1 or 2, wherein, The metallic nickel comprises a face-centered cubic lattice structure and / or a hexagonal close-packed lattice structure.

4. The positive electrode active material for lithium-sulfur batteries according to claim 1, wherein, The mesopore volume of the carbon-coated nickel nanomaterial accounts for more than 80% of the total pore volume.

5. The positive electrode active material for lithium-sulfur batteries according to claim 3, wherein, The average thickness of the graphitized carbon coating is 0.3-6 nm; The average particle size of the metallic nickel core is 1-200 nm; The average particle size of the carbon-coated nickel nanoparticles is 1-200 nm.

6. The positive electrode active material for lithium-sulfur batteries according to claim 5, wherein, The average thickness of the graphitized carbon coating layer is 0.3-3 nm; The average particle size of the metallic nickel core is 3-100 nm; The average particle size of the carbon-coated nickel nanoparticles is 3-100 nm.

7. The lithium-sulfur battery positive electrode active material according to claim 6, wherein, The average particle size of the carbon-coated nickel nanoparticles is 4-50 nm.

8. The method for preparing the positive electrode active material of a lithium-sulfur battery according to any one of claims 1-7, characterized in that, The preparation method includes: (1) Provide a mixture containing carbon-coated nickel nanomaterials with elemental sulfur and graphene; (2) Under the protection of an inactive atmosphere, the mixture obtained in step (1) is subjected to high-temperature heat treatment at a melting temperature not lower than that of sulfur.

9. The preparation method according to claim 8, wherein, In step (2), the high-temperature heat treatment is carried out at a temperature of 120-200°C; the duration of the high-temperature heat treatment is 1-48 hours.

10. The preparation method according to claim 9, wherein, In step (2), the duration of the high-temperature heat treatment is 8-40 hours.

11. The preparation method according to claim 10, wherein, In step (2), the duration of the high-temperature heat treatment is 10-30 hours.

12. The preparation method according to claim 11, wherein, In step (2), the duration of the high-temperature heat treatment is 12-20 hours.

13. The preparation method according to claim 8, wherein, In step (2), the inactive atmosphere is an atmosphere formed by argon and / or nitrogen.

14. A lithium-sulfur battery cathode material, the cathode material comprising a cathode active material, a conductive agent, and a binder, characterized in that, The positive electrode active material is the lithium-sulfur battery positive electrode active material according to any one of claims 1-7.

15. A lithium-sulfur battery positive electrode, the positive electrode comprising a current collector and a positive electrode material coated and / or filled on the current collector, characterized in that, The cathode material is the cathode material as described in claim 14.

16. A method for preparing a lithium-sulfur battery positive electrode, the method comprising coating and / or filling a slurry containing a positive electrode active material, a conductive agent, a binder, and a solvent onto a current collector, drying, and calendering or not calendering, characterized in that, The positive electrode active material is the lithium-sulfur battery positive electrode active material according to any one of claims 1-7.

17. A lithium-sulfur battery, comprising an electrode assembly and a non-aqueous electrolyte, the electrode assembly and the non-aqueous electrolyte being sealed within a battery casing, the electrode assembly comprising a positive electrode, a negative electrode, and a separator, the separator being located between the positive and negative electrodes, characterized in that... The positive electrode is the lithium-sulfur battery positive electrode according to claim 15 or the lithium-sulfur battery positive electrode prepared according to the method of claim 16.

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