Positive electrode material as well as preparation method and application thereof
Patent Information
- Application Number
- CN202480015027.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-02-27
- Filing Date
- 2024-01-19
- Publication Date
- 2025-10-03
AI Technical Summary
The outflow and structural instability of LiPSs in lithium-sulfur batteries lead to low material utilization, low Coulombic efficiency and poor safety performance, and it is difficult to manufacture high-density and thick cathode materials for nanostructured electrodes.
Mo-based organometallic framework materials are sintered with lithium sources and carbon disulfide to prepare cathode materials with porous structures to form Mo-Li2S-carbon heterostructures. The rapid transfer of electrons and ions is achieved through the chemical bridge structure of Mo and carbon materials, and suppresses Outflow of LiPSs.
It improves the cycle performance and rate performance of the cathode material, maintains structural stability, enhances electrocatalytic activation and chemical absorption of Li2S, reduces impedance, and achieves more efficient lithium ion diffusion and charge transfer.
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Abstract
Description
A positive electrode material, preparation method and application thereof
[0001] CROSS-REFERENCE TO RELATED APPLICATIONS
[0002] This disclosure claims priority to application number 2023101720973, filed with the Patent Office of China on February 27, 2023, entitled “A positive electrode material, its preparation method and application,” the entire contents of which are incorporated by reference into this disclosure. Technical Field
[0003] The present disclosure relates to the technical field of lithium-sulfur batteries, and in particular to a positive electrode material, a preparation method thereof, and applications thereof. Background Art
[0004] Lithium-sulfur batteries (Li-S) are ideal energy storage devices due to their high energy density, abundant and non-toxic electrode materials, and low cost. A common Li-S battery is a Li2S cathode and a Si anode. The insulating properties of commercial Li2S lead to a large activation potential and poor material utilization. Furthermore, the dissolution of the intermediate product, lithium polysulfide (LiPSs), in the electrolyte can lead to rapid capacity decay, low Coulombic efficiency (CE), and poor battery safety, hindering the commercialization of Li-S batteries.
[0005] Sulfur (S8) and lithium sulfide (Li2S and Li2S2) are the products of sulfur electrode full charge and discharge, respectively. Their insulating properties require a large amount of conductive additives. Meanwhile, lithium polysulfide (Li2S x , 3≤x≤8)(LiPS) is a highly soluble circulating intermediate in aprotic liquid electrolytes, acting as an internal redox mediator, resulting in low battery Coulombic efficiency and rapid capacity decay. In addition, when the denser S8 is converted to Li2S during discharge, the sulfur electrode has a significant volume expansion.
[0006] Currently, the main method for preparing sulfur-containing nanocomposites is to infiltrate sulfur into nanostructured conductors to enhance their electronic and ionic conductivity. In these sulfur-containing nanocomposites, a certain amount of voids are usually retained to accommodate the volume change of sulfur. However, this method has the following disadvantages: (1) During the preparation process, the open pores of the nanostructured conductor are a necessary condition for sulfur infiltration. However, the open pores also make it difficult to retain the solvated LiPs in the electrode during cycling. (2) Because the precipitation of solvated LiPs into Li2S2 or Li2S is often uncontrollable, the expansion of the active material cannot effectively utilize the voids retained in the composite material.
[0007] In addition, most nanostructured sulfur electrodes are severely affected by their soft texture. With current manufacturing technology, it is difficult to manufacture dense and thick electrodes on metal foil current collectors.
[0008] In view of this, the present disclosure is proposed.
[0009] Summary of the Invention
[0010] The purpose of the present disclosure is to provide a cathode material, a preparation method and application thereof, aiming to effectively inhibit the outflow of LiPSs and maintain structural stability while improving the rate and cycle performance of the material.
[0011] The present disclosure is achieved as follows:
[0012] In a first aspect, the present disclosure provides a positive electrode material for a lithium-sulfur battery, the positive electrode material comprising a first shell layer, a second shell layer and a core layer, wherein the second shell layer is disposed between the first shell layer and the core layer;
[0013] The core layer includes Li2S;
[0014] The second shell includes Mo atoms or Mo-containing compounds;
[0015] The first shell includes a carbon material;
[0016] The second shell layer and the core layer together form a porous structure; the porosity of the porous structure is 1%-30%.
[0017] In an optional embodiment, the content of Mo element is 0.01 wt%-5 wt%, and the content of Li2S is 50 wt%-90 wt%.
[0018] In an optional embodiment, in the positive electrode material, the carbon content is 0.1 wt%-30 wt%.
[0019] In an optional embodiment, the particle size of the positive electrode material is 30 nm-800 nm.
[0020] In an optional embodiment, the thickness of the first shell layer is 0.5 nm-30 nm.
[0021] In an optional embodiment, the carbon material is selected from at least one of graphene, graphene oxide, carbon nanotubes and graphite.
[0022] In an alternative embodiment, the second shell further comprises amorphous carbon.
[0023] In a second aspect, the present disclosure provides a method for preparing a positive electrode material, comprising: using a Mo-based organic metal framework material, a lithium source and carbon disulfide as raw materials to prepare a positive electrode material having the first shell layer, the second shell layer and the core layer.
[0024] In an optional embodiment, the Mo-based organic metal framework material, the lithium source and carbon disulfide are sintered at a high temperature;
[0025] Preferably, the sintering temperature is controlled to be 500°C-1200°C, and the sintering time is 0.5h-10h;
[0026] Preferably, the sintering process is carried out under an inert atmosphere.
[0027] In an optional embodiment, the molar ratio of Mo, Li and S is 0.01-5:1.5-2:1 by adjusting the amounts of Mo-based organic metal framework material, lithium source and carbon disulfide.
[0028] In an alternative embodiment, the lithium source is selected from at least one of lithium foil, lithium sheet, and lithium ribbon.
[0029] In an optional embodiment, the preparation process of the Mo-based organic metal framework material includes: utilizing a molybdenum source and an organic ligand to react, wherein the molybdenum source is molybdenum nitrate hexahydrate; and the organic ligand is 2-methylimidazole.
[0030] In an optional embodiment, the molar ratio of the molybdenum source to the organic ligand is 0.125-0.5:1;
[0031] In an optional embodiment, the reaction temperature is controlled to be 50°C-120°C, and the reaction time is 20min-40min.
[0032] In an optional embodiment, the molybdenum source solution and the organic ligand solution are mixed and reacted, the reaction solution is allowed to stand for aging, and then solid-liquid separation, washing and drying are performed in sequence;
[0033] Preferably, the aging time is 20h-28h;
[0034] Preferably, solid-liquid separation is performed by centrifugation;
[0035] Preferably, washing is performed multiple times using an organic solvent;
[0036] Preferably, the drying is carried out at 50° C. to 80° C. for 10 h to 15 h.
[0037] In a third aspect, the present disclosure provides a positive electrode plate, comprising the positive electrode material in the aforementioned embodiment or the positive electrode material prepared by any one of the preparation methods in the aforementioned embodiment.
[0038] In a fourth aspect, the present disclosure provides a lithium battery comprising the positive electrode sheet of the aforementioned embodiment.
[0039] In a fifth aspect, the present disclosure further provides an electrical device comprising the lithium battery in the aforementioned embodiment.
[0040] The present disclosure has the following beneficial effects: by providing a positive electrode material having a first shell layer, a second shell layer and a core layer, the second shell layer is arranged between the first shell layer and the core layer, and the core layer includes Li2S; the second shell layer includes Mo atoms or Mo-containing compounds, and the first shell layer includes carbon materials to form a dense Mo-Li2S-carbon material heterostructure. The special chemical bridge structure can not only enable the rapid transfer of electrons and ions in the composite material, but also achieve efficient electrocatalytic activation of Li2S; the shell-core nanostructure effectively inhibits the outflow of LiPSs and maintains its structural stability. In addition, the strong interaction between Li2S and graphene and between Li2S and Mo ensures effective chemical absorption, further inhibiting the effect of LiPSs in the nanomaterial. The structural domain restriction of LiPSs effectively inhibits the shuttle behavior of polysulfides, thereby improving the cycle performance. In addition, the positive electrode material provided by the present disclosure forms a porous structure inside the nanomaterial, which shortens the Li ion diffusion path and is conducive to the improvement of rate performance. BRIEF DESCRIPTION OF THE DRAWINGS
[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.
[0042] FIG1 is a graph showing the cycle performance test results of the positive electrode materials prepared in Examples and Comparative Examples;
[0043] FIG2 is a graph showing the rate performance test results of the positive electrode materials prepared in the embodiment and the comparative example. DETAILED DESCRIPTION
[0044] The embodiments of the present disclosure will be described in detail below with reference to the examples. However, those skilled in the art will appreciate that the following examples are intended only to illustrate the present disclosure and should not be construed as limiting the scope of the present disclosure. Where specific conditions are not specified in the examples, the experiments were performed under conventional conditions or the conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, all are commercially available conventional products.
[0045] The endpoints of the ranges and any values disclosed in this disclosure 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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.
[0046] The present disclosure provides a method for preparing a core-shell structure lithium-sulfur battery cathode material, comprising the following steps:
[0047] S1. Preparation of Mo-based organic metal framework materials
[0048] Mo-based organic metal framework materials are prepared by reacting molybdenum sources with organic ligands. During the reaction, molybdenum and organic ligands combine to form organic metal framework materials.
[0049] In some embodiments, the molybdenum source is molybdenum nitrate hexahydrate and the organic ligand is 2-methylimidazole, but the present invention is not limited thereto. The molar ratio of the molybdenum source to the organic ligand is 0.125-0.5:1. Controlling the ratio of the molybdenum source to the organic ligand within this range is preferred to maximize utilization of the molybdenum source and further enhance the electrochemical performance of the product.
[0050] Specifically, the molar ratio of the molybdenum source to the organic ligand can be 0.125:1, 0.150:1, 0.200:1, 0.250:1, 0.300:1, 0.350:1, 0.400:1, 0.450:1, 0.500:1, etc.
[0051] In some embodiments, the reaction temperature is controlled to be 50° C.-120° C., and the reaction time is 20 min-40 min. By controlling the reaction temperature and reaction time, the reaction is fully carried out and the utilization rate of raw materials is improved. Specifically, the reaction temperature can be 50° C., 70° C., 90° C., 100° C., 120° C., etc., and the reaction time can be 20 min, 30 min, 40 min, etc.
[0052] In some embodiments, a molybdenum source solution and an organic ligand solution are mixed and reacted. That is, the molybdenum source is first dissolved to obtain a molybdenum source solution, and the organic ligand is dissolved to obtain an organic ligand solution, and then the molybdenum source solution and the organic ligand solution are mixed and reacted. The solvent used to dissolve the molybdenum source and the organic ligand is not limited and can be a common organic alcohol, such as ethanol. After the reaction of the molybdenum source solution and the organic ligand solution is completed, the resulting mixture is allowed to stand for aging, and then solid-liquid separation, washing, and drying are performed in sequence to obtain a pure Mo-based organic metal framework material.
[0053] In some embodiments, the aging time is 20-28 hours. The long aging time allows the solid material to fully settle. The aging time can be 20 hours, 23 hours, 25 hours, 28 hours, etc. The aging temperature can be room temperature, such as about 25°C.
[0054] In some embodiments, solid-liquid separation may be performed by centrifugation, but is not limited thereto. Conventional filtration may also be used for solid-liquid separation.
[0055] In some embodiments, washing can be performed multiple times using an organic solvent, such as using anhydrous methanol for multiple washings, and the number of washing times can be 3 times or more.
[0056] In some embodiments, drying is performed at 50° C. to 80° C. for 10 to 15 hours to fully remove the solvent on the surface. Specifically, the drying temperature can be 50° C., 55° C., 60° C., 65° C., 70° C., 75° C., 80° C., etc., and the drying time can be 10 hours, 12 hours, 14 hours, 15 hours, etc.
[0057] S2. Sintering
[0058] Mo-based metal-organic frameworks (Mo-MOFs) are synthesized by sintering a Mo-based metal-organic framework (MOF) with a lithium source and carbon disulfide (CS2). Mo-MOFs with a certain stoichiometry react with lithium and CS2 to form porous Li2S-Mo nanostructures and Li2S-C nanostructures. The resulting composite material has a first shell, a second shell, and a core. The second shell comprises Li2S, which is located between the first and core shells. The core layer contains Mo atoms or Mo-containing compounds, while the first shell comprises carbon. This creates a dense Mo-Li2S-carbon heterostructure. The unique chemical bridge structure not only enables rapid electron and ion transfer within the composite, but also enables efficient electrocatalytic activation of Li2S.
[0059] It should be noted that this porous core-shell nanostructure design provides channels for the electrolyte to penetrate into the hollow regions within the material during long-term cycling. This increases the apparent lithium-ion diffusion coefficient of the particles, improves the first coulombic efficiency, and enhances rate performance, promising fast lithium-ion diffusion and charge transfer rates while maintaining good structural integrity. The strong interactions between Li2S and carbon materials (such as graphene) and between Li2S and Mo ensure effective chemical absorption, further suppressing the effect of LiPSs in the nanoshell core-shell structure material and effectively inhibiting the dissolution of LiPSs into the electrolyte. The uniform doping of Mo nanocrystals and the uniform coating of graphene nanolayers give it high electrochemical activity, which has great application prospects in the realization of both Li-S batteries and sulfur-based lithium batteries.
[0060] In some embodiments, the sintering temperature is 500°C-1200°C, and the sintering time is 0.5h-10h, so that the reaction can be fully carried out to form a core-shell nanostructured positive electrode material. The sintering process can be carried out under an inert atmosphere, and Mo-MOFs reacts with metallic Li under an inert gas atmosphere to form Li2S-Mo porous nanocomponents, avoiding the introduction of impurities. Specifically, the sintering temperature can be 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, etc., and the sintering time can be 0.5h, 1.0h, 3.0h, 5.0h, 8.0h, 10.0h, etc.
[0061] In some embodiments, by regulating the amounts of Mo-based organic metal framework material, lithium source, and carbon disulfide, the molar ratio of Mo, Li, and S is 0.01-5:1.5-2:1. It is preferable to control the amount of each raw material within the above range to introduce a suitable amount of Mo, which is beneficial to improving the rate and cycle performance of the material. If the amount of Mo exceeds the above range, it is not conducive to improving the rate and cycle performance. Specifically, the molar ratio of Mo, Li, and S can be 0.01:1.5:1, 0.1:1.5:1, 1.0:1.6:1, 2.0:1.7:1, 3.0:1.8:1, 4.0:1.9:1, 5.0:2.0:1, etc.
[0062] In some embodiments, the lithium source is selected from at least one of lithium foil, lithium sheet, and lithium ribbon, and may be any one or more of the above.
[0063] An embodiment of the present disclosure provides a positive electrode material, which includes a first shell layer, a second shell layer and a core layer, wherein the second shell layer is arranged between the first shell layer and the core layer, the core layer includes Li2S, the second shell layer includes Mo atoms or Mo-containing compounds, and the first shell layer includes a carbon material; the second shell layer and the core layer together constitute a porous structure, and the porosity of the porous structure is 1%-30%.
[0064] It should be noted that the embodiment of the present disclosure uses Mo-based MOFs as nanocrystalline cores embedded in the Li2S matrix. During the calcination process in an inert atmosphere, the organic ligands in the MOFs are converted into carbon and nitrogen compound gases and water is volatilized, thereby forming a porous structure inside the nanomaterial. This porous structure shortens the Li ion diffusion path, which is conducive to the improvement of rate performance.
[0065] Specifically, the porosity is obtained by conventional testing methods and is the volume ratio of pores. The porosity can be 1%, 5%, 10%, 15%, 20%, 25%, 30%, etc.
[0066] In some embodiments, in the entire positive electrode material, the content of Mo is 0.01wt%-5wt%, the content of Li2S is 50wt%-90wt%, and the content of carbon is 0.1wt%-30wt%. By controlling the amount of Mo and carbon introduced, the electrochemical activity of the product is maintained at a good level, which is conducive to reducing impedance. Specifically, in the entire positive electrode material, the content of Mo can be 0.01wt%, 0.1wt%, 1.0wt%, 2.0wt%, 3.0wt%, 4.0wt%, 5.0wt%, etc., the content of Li2S can be 50wt%, 60wt%, 70wt%, 80wt%, 90wt%, etc., and the content of carbon can be 0.1wt%, 0.5wt%, 1.0wt%, 5.0wt%, 10.0wt%, 15.0wt%, 20.0wt%, 25.0wt%, 30.0wt%.
[0067] In some embodiments, the particle size of the positive electrode material is 30 nm to 800 nm, and the thickness of the first shell layer is 0.5 nm to 30 nm. Specifically, the particle size of the positive electrode material can be 30 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, etc., and the thickness of the first shell layer can be 0.5 nm, 5.0 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, etc.
[0068] In some embodiments, the carbon material in the first shell layer is selected from at least one of graphene, graphene oxide, carbon nanotubes, and graphite, and may be any one or more of the above.
[0069] In some embodiments, the second shell layer may further include amorphous carbon, the specific type of which is not limited, such as carbon black, activated carbon, or a mixed form of carbon materials.
[0070] It should be added that the positive electrode material provided in the embodiment of the present disclosure can be prepared by the preparation method provided in the embodiment of the present disclosure. Mo-Li2S-graphene is used as an example to illustrate the advantages of the positive electrode material provided in the embodiment of the present disclosure:
[0071] (1) All three components from the lithium thermal reaction are connected by chemical bonds between Mo-S and CS. Through the strong chemical interactions between its components, a dense Mo-Li2S-graphene heterostructure is formed. The special chemical bridge structure not only enables the rapid transfer of electrons and ions in the composite material, but also achieves efficient electrocatalytic activation of Li2S. The inventors found that the transition metal Mo can make the electrocatalytic effect of Li2S better, thereby making the activation potential between the charge overpotential and catalytic activation of Mo-Li2S-graphene lower (only 2.43V). Both reduced graphene and Mo can promote the initial activation of Li2S.
[0072] (2) In the Mo-Li2S-graphene nanoshell core structure, the active Li2S is wrapped by the graphene shell, thus maintaining its good structural integrity. The core-shell nanostructure effectively inhibits the outflow of LiPSs and maintains its structural stability. In addition, the strong interaction between Li2S and graphene and between Li2S and Mo ensures effective chemical absorption, further inhibiting the role of LiPSs in nanomaterials. The structural domain restriction of LiPSs effectively inhibits the shuttle behavior of polysulfides, thereby improving the cycle performance.
[0073] (3) The uniform doping of Mo nanocrystals and the uniform coating of graphene nanolayers are beneficial to improving the diffusion of lithium ions and the charge transfer speed, making it have higher electrochemical activity, thereby helping to reduce impedance.
[0074] The embodiments of the present disclosure provide a positive electrode sheet comprising the aforementioned positive electrode material or the positive electrode material prepared by the aforementioned preparation method. This positive electrode material can be used to prepare a positive electrode sheet using conventional methods. By improving the structure and composition of the positive electrode material, the resulting positive electrode sheet can be endowed with superior electrochemical performance. In actual operation, the preparation process of the positive electrode sheet is generally as follows: first, the positive electrode material of the embodiments of the present disclosure is mixed with a binder and a conductive agent to obtain a positive electrode slurry; the positive electrode slurry is applied to at least one side of a positive electrode current collector, and dried to form a coating.
[0075] The present disclosure also provides a lithium battery comprising the aforementioned positive electrode sheet, and further comprising a negative electrode, an electrolyte, a separator, etc., to form a complete battery structure. The negative electrode may be of any type, including but not limited to a Si-C negative electrode.
[0076] The embodiments of the present disclosure further provide an electrical device, which includes the above-mentioned lithium battery and may also include other structures such as electrical appliances, and the types of electrical appliances are not limited.
[0077] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.
[0078] Example 1
[0079] This embodiment provides a method for preparing a positive electrode material, comprising the following steps:
[0080] (1) Prepare 0.4 mol / L 2-methylimidazolol solution (solvent is ethanol) and 0.05 mol / L hexahydrate molybdenum nitrate alcohol solution (solvent is ethanol). Then quickly add the 2-methylimidazolol solution to the hexahydrate molybdenum nitrate alcohol solution, control the molar ratio of hexahydrate molybdenum nitrate alcohol to 2-methylimidazolol to be 0.3:1, and stir at 80°C for 30 minutes to obtain a uniformly mixed solution A. The solution A is allowed to stand at room temperature (25°C, the same below) for 25 hours, the obtained product is precipitated and centrifuged, washed three times with anhydrous methanol, and dried in an oven at 60°C for 15 hours to obtain a Mo-based organic metal framework material.
[0081] (2) Mo-MOFs, lithium foil, and CS2 were placed in a tubular furnace. By controlling the amount of Mo-MOFs, lithium source, and carbon disulfide, the molar ratio of Mo, Li, and S was made to be 2:1.8:1. The mixture was sintered at 800°C for 5 h, and nitrogen was introduced during the reaction.
[0082] Core-shell structure formation mechanism: Mo-Li2S-graphene core-shell nanostructures were successfully prepared through a two-stage lithium-sulfur thermal reaction. First, a certain stoichiometric amount of molybdenum disulfide completely reacted with metallic lithium in an Ar atmosphere to form a Li2S-Mo nanocomponent. Then, excess molten Li further reacted with carbon disulfide to produce another Li2S-C nanostructure. Based on the above reaction sequence, the resulting composite material has the Li2S-Mo nanocomponent wrapped by the Li2S-C nanostructure, thus forming a Mo-Li2S-graphene core-shell structure. This in situ grown nanocore-shell design is expected to achieve fast conductivity and redox activation, as well as good structural integrity, and achieve good electrochemical performance in lithium batteries and S-based lithium batteries.
[0083] Example 2
[0084] This embodiment provides a method for preparing a positive electrode material, comprising the following steps:
[0085] (1) Prepare 0.9 mol / L 2-methylimidazolol solution (solvent is ethanol) and 0.1 mol / L hexahydrate molybdenum nitrate alcohol solution (solvent is ethanol). Then quickly add the 2-methylimidazolol solution to the hexahydrate molybdenum nitrate alcohol solution, control the molar ratio of hexahydrate molybdenum nitrate alcohol to 2-methylimidazolol to be 0.125:1, and stir at 50°C for 40 minutes to obtain a uniformly mixed solution A. The solution A is allowed to stand at room temperature for 20 hours, the obtained product is precipitated and centrifuged, washed three times with anhydrous methanol, and dried in an oven at 50°C for 15 hours to obtain a Mo-based organic metal framework material.
[0086] (2) Mo-MOFs, lithium foil, and CS2 were placed in a tubular furnace. By controlling the amount of Mo-MOFs, lithium source, and carbon disulfide, the molar ratio of Mo, Li, and S was made to be 0.01:1.5:1. The mixture was sintered at 500°C for 10 h, and nitrogen was introduced during the reaction.
[0087] Example 3
[0088] This embodiment provides a method for preparing a positive electrode material, comprising the following steps:
[0089] (1) Prepare 0.9 mol / L 2-methylimidazolol solution (solvent is ethanol) and 0.1 mol / L hexahydrate molybdenum nitrate alcohol solution (solvent is ethanol). Then quickly add the 2-methylimidazolol solution to the hexahydrate molybdenum nitrate alcohol solution, control the molar ratio of hexahydrate molybdenum nitrate alcohol to 2-methylimidazolol to be 0.5:1, and stir at 120°C for 20 minutes to obtain a uniformly mixed solution A. Let solution A stand at room temperature for 28 hours, precipitate the obtained product by centrifugation, wash it three times with anhydrous methanol, and dry it in an oven at 80°C for 15 hours to obtain a Mo-based organic metal framework material.
[0090] (2) Mo-MOFs, lithium foil, and CS2 were placed in a tubular furnace. By controlling the amount of Mo-MOFs, lithium source, and carbon disulfide, the molar ratio of Mo, Li, and S was made to be 5:2.0:1. The mixture was sintered at 1200°C for 0.5h, and nitrogen was introduced during the reaction.
[0091] Example 4
[0092] The only difference from Example 1 is that the molar ratio of Mo, Li and S is 2:2:1.
[0093] Example 5
[0094] The only difference from Example 1 is that the molar ratio of Mo, Li and S is 2:1:1.
[0095] Comparative Example 1
[0096] The only difference from Example 1 is that Mo-MOFs is not used for the reaction, but MoS2 is used instead. The specific steps are as follows:
[0097] MoS2, lithium foil and CS2 are placed in a tubular furnace. The amount of MoS2, lithium source and carbon disulfide is controlled to control the molar ratio of Mo, Li and S to be 2:1.8:1. Sintered at 800°C for 5 hours, and nitrogen is introduced during the reaction.
[0098] Comparative Example 2
[0099] The only difference from Example 1 is that the metal Mo in Mo-MOFs is replaced by an equimolar amount of Co.
[0100] Test Example 1
[0101] The performance of the positive electrode materials prepared in the examples and comparative examples was tested. The cycle performance test results are shown in Figure 1, and the rate performance test results are shown in Figure 2. The materials obtained by lithium thermal reaction have significant differences in cycle and rate performance. The synthesis scheme using Mo-MOF as raw material has obvious advantages. This is mainly because during the inert atmosphere calcination process, the organic ligands in Mo-MOF are converted into carbon and nitrogen compound gases and water is volatilized, thereby forming a porous structure within the nanomaterial. This porous structure shortens the Li ion diffusion path, which is conducive to improving the rate performance.
[0102] Test method: The obtained positive electrode material is assembled with the Si-C negative electrode to make a 604062 type soft-pack battery. After preparation, conventional formation is performed. The formed battery is charged and discharged at a rate of 1C at room temperature (25°C) within the voltage range of 1.5-2.8V. The capacity retention rate is recorded after 1500 cycles.
[0103] As can be seen from Figures 1 and 2, the positive electrode material prepared in the embodiment of the present disclosure has better cycle performance and rate performance than the comparative example, and the introduction of molybdenum in the form of MOFs material is beneficial to further improve the comprehensive performance of the material compared with conventional raw materials.
[0104] Test Example 2
[0105] Test Example 1 A Mo-Li2S-graphene nanoshell core-shell structure of a positive electrode material was prepared. This porous core-shell nanostructure design provides a channel for the electrolyte to infiltrate into the hollow area inside the material during a long cycle. The apparent lithium ion diffusion coefficient of the particles increases, the first coulombic efficiency is improved, and the rate performance is improved. It is expected to achieve fast lithium ion diffusion and charge transfer speeds while maintaining good structural integrity. The strong interaction between Li2S and graphene and between Li2S and Mo ensures effective chemical absorption, further inhibits the effect of LiPSs in the nanoshell core-shell structure material, and effectively inhibits the dissolution of LiPSs into the electrolyte. The uniform doping of Mo nanocrystals and the uniform coating of graphene nanolayers give it high electrochemical activity, which has good application prospects in the realization of Li-S batteries and S-based lithium batteries.
[0106] The above are merely preferred embodiments of the present disclosure and are not intended to limit the present disclosure. Those skilled in the art will readily appreciate that various modifications and variations of the present disclosure are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present disclosure shall be included within the scope of protection of the present disclosure. Industrial Applicability
[0107] The present invention discloses a lithium-sulfur battery positive electrode material with a core-shell structure that can be prepared by sintering a Mo-based organic metal framework material, a lithium source, and carbon disulfide (CS2). The process is convenient to operate, does not require harsh process conditions, can significantly improve the rate and cycle performance of the material, and has excellent industrial applicability.
Claims
1. A positive electrode material for a lithium-sulfur battery, characterized in that: The positive electrode material comprises a first shell layer, a second shell layer and a core layer, wherein the second shell layer is arranged between the first shell layer and the core layer; The core layer includes Li2S; The second shell layer includes Mo atoms or Mo-containing compounds; The first shell layer comprises a carbon material; The second shell layer and the core layer together form a porous structure; the porosity of the porous structure is 1%-30%.
2. The positive electrode material according to claim 1, characterized in that In the positive electrode material, the content of Mo element is 0.01wt%-5wt%, and the content of Li2S is 50wt%-90wt%.
3. The positive electrode material according to claim 1 or 2, characterized in that In the positive electrode material, the carbon content is 0.1wt%-30wt%.
4. The positive electrode material according to any one of claims 1 to 3, characterized in that The particle size of the positive electrode material is 30nm-800nm.
5. The positive electrode material according to any one of claims 1 to 4, characterized in that The thickness of the first shell layer is 0.5 nm-30 nm.
6. The positive electrode material according to any one of claims 1 to 5, characterized in that The carbon material in the first shell layer is selected from at least one of graphene, graphene oxide, carbon nanotubes and graphite.
7. The positive electrode material according to any one of claims 1 to 6, characterized in that The second shell layer also includes amorphous carbon.
8. A method for preparing the positive electrode material according to any one of claims 1 to 7, characterized in that: The method comprises: using Mo-based organic metal framework material, lithium source and carbon disulfide as raw materials to prepare a positive electrode material having the first shell layer, the second shell layer and the core layer.
9. The preparation method according to claim 8, characterized in that: The method comprises: sintering a Mo-based organic metal framework material, a lithium source and carbon disulfide at a high temperature; Preferably, the sintering temperature is controlled to be 500°C-1200°C, and the sintering time is 0.5h-10h; Preferably, the sintering process is carried out under an inert atmosphere.
10. The preparation method according to claim 8 or 9, characterized in that: The molar ratio of Mo, Li and S is adjusted to 0.01-5:1.5-2:1 by regulating the dosage of Mo-based organic metal framework material, lithium source and carbon disulfide.
11. The preparation method according to any one of claims 8 to 10, characterized in that: The lithium source is selected from at least one of lithium foil, lithium sheet and lithium ribbon.
12. The preparation method according to any one of claims 8 to 11, characterized in that: The preparation process of the Mo-based organic metal framework material comprises: utilizing a molybdenum source and an organic ligand to react, wherein the molybdenum source is molybdenum nitrate hexahydrate; and the organic ligand is 2-methylimidazole.
13. The preparation method according to claim 12, characterized in that: The molar ratio of the molybdenum source to the organic ligand is 0.125-0.5:
1.
14. The preparation method according to claim 12 or 13, characterized in that: The reaction temperature of the molybdenum source and the organic ligand is controlled to be 50° C.-120° C., and the reaction time is controlled to be 20 min-40 min.
15. The preparation method according to any one of claims 12 to 14, characterized in that: The molybdenum source solution and the organic ligand solution are mixed and reacted, and the resulting solution is allowed to stand for aging, and then solid-liquid separation, washing and drying are performed in sequence; Preferably, the static aging time is 20h-28h; Preferably, centrifugal separation is used for solid-liquid separation; Preferably, the washing is performed multiple times using an organic solvent; Preferably, the drying is carried out at 50° C.-80° C. for 10 h-15 h.
16. A positive electrode plate, characterized in that: The invention comprises the positive electrode material according to any one of claims 1 to 7 or the positive electrode material prepared by the preparation method according to any one of claims 8 to 15.
17. A lithium battery, characterized in that: Including the positive electrode sheet as described in claim 16.
18. An electrical device, characterized in that: Including the lithium battery as described in claim 17.