Medium-entropy alloy composite cerium oxide modified diaphragm as well as preparation method and application thereof

Abstract

The invention provides a medium-entropy alloy composite cerium oxide modified diaphragm and a preparation method and application thereof.The medium-entropy alloy composite cerium oxide is composed of a medium-entropy alloy (CoNiMoIr) and CeO2, the stability of the structure is guaranteed on a semi-oxidation interface of the medium-entropy alloy (MEA) and CeO2, meanwhile, the semi-oxidation structure can promote the sulfur reduction reaction process, and the stability of the structure is improved. The alloying structure can promote the sulfur oxidation process, and cerium oxide is used as an adsorption active center to synergistically catalyze the conversion of polysulfide with MEA, so that the rate capability and cycle stability of the lithium-sulfur battery are effectively improved, and the shuttle effect problem in the lithium-sulfur battery is effectively solved.

Description

Technical Field

[0001] The invention relates to the technical field of lithium-sulfur battery diaphragm materials, in particular to a medium-entropy alloy composite cerium oxide modified diaphragm and a preparation method and application thereof. Background Art

[0002] Due to the rapid development of electronic energy storage devices and new energy vehicles, the demand for advanced energy storage devices is growing, which has promoted the rapid development of rechargeable battery systems. However, commercial lithium-ion batteries are limited by their theoretical specific capacity and energy density and cannot meet the needs of future development. In recent years, lithium-sulfur batteries have been widely used due to their high theoretical specific capacity of sulfur (1675mAh g -1 ), high theoretical specific energy (2600Wh kg -1 ), the abundant reserves of sulfur, the active material of the positive electrode, and its low cost make it one of the most promising energy storage devices. However, lithium-sulfur batteries face problems such as low conductivity of the active material S and the discharge product Li2S2 / Li2S, the "shuttle effect" caused by soluble polysulfides (LiPSs), slow redox reaction kinetics, and dendrite growth of the lithium negative electrode, resulting in poor cycle and rate performance. Among them, the "shuttle effect" of LiPSs is the biggest challenge facing the development of lithium-sulfur batteries.

[0003] By coating a layer of modified material with adsorption and catalysis on the surface of the diaphragm, the "shuttle effect" can be suppressed, the reaction kinetics of lithium-sulfur batteries can be accelerated, and the performance of lithium-sulfur batteries can be improved. Non-polar materials (such as carbon materials) were first applied on the surface of the diaphragm, which have a good adsorption effect on polysulfides. However, physical adsorption cannot prevent the fundamental shuttling problem of long-chain polysulfides.

[0004] In order to solve the above problems, the present invention combines cerium oxide with a medium-entropy alloy having good adsorption effect to improve the reaction kinetics of lithium-sulfur batteries and improve battery performance. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a medium-entropy alloy composite cerium oxide modified diaphragm and a preparation method and application thereof. The prepared medium-entropy alloy cerium oxide has a semi-oxidized structure, which together with cerium oxide and an alloy structure can adsorb, forwardly and reversely catalyze polysulfide active centers and have good lithium-sulfur battery performance.

[0006] The present invention is achieved through the following scheme:

[0007] The medium-entropy alloy composite cerium oxide modified diaphragm is composed of a diaphragm and a modified layer coated on the surface of the diaphragm, wherein the covering layer includes a conductive additive, a binder and a composite material;

[0008] The medium-entropy alloy (MEA) CeO2 composite material has a special structure. The synergistic effect between metals and between metals and cerium oxide jointly promotes the conversion of polysulfides. The catalytic active center is the medium-entropy alloy and the interface between the medium-entropy alloy and cerium oxide. These two active centers catalyze the reduction and oxidation reactions of sulfur respectively, realizing bidirectional catalysis and improving the performance of lithium-sulfur batteries, that is, better promoting the nucleation and dissociation of lithium sulfide (Li2S), preventing the uneven deposition of lithium sulfide and the accumulation of lithium sulfide from causing changes in the active center; after the medium-entropy alloy is composited with cerium oxide, due to the semi-oxidized interface, the (220) crystal plane of cerium oxide and the (111) crystal plane of the medium-entropy alloy are stably combined, and the battery has a low capacity decay rate per cycle under long cycles.

[0009] The method for preparing the medium-entropy alloy cerium oxide modified diaphragm of the present invention is specifically achieved by the following steps:

[0010] (1) using chlorides of cobalt, nickel, molybdenum, iridium and cerium as metal sources and 2,5-dihydroxyterephthalic acid as an organic ligand, adding N,N-dimethylformamide (DMF) and stirring until the mixture is uniformly mixed, then transferring the mixed solution to a high temperature resistant reactor for reaction, then centrifuging the product, washing it with deionized water and ethanol several times, and then drying it at 60°C for 12 hours; finally, adding it to a tubular furnace under argon / hydrogen reduction to obtain a medium entropy alloy cerium oxide material;

[0011] Among them, the molar ratio of cobalt chloride: nickel chloride: molybdenum chloride: iridium chloride: cerium chloride: 2,5-dihydroxyterephthalic acid is 1:1:1:1:1:3.

[0012] The reaction temperature in the high temperature resistant reactor is 140°C and the reaction time is 24h.

[0013] (2) The medium-entropy alloy cerium oxide material, the conductive additive and the binder prepared in step (1) are mixed, added into a solvent N-methylpyrrolidone (NMP), stirred and dispersed evenly, and a composite material slurry is obtained.

[0014] The mass ratio of medium entropy alloy cerium oxide material: conductive additive: binder is 8:1:1;

[0015] The conductive additive is carbon nanotube, and the binder is polyvinylidene fluoride (PVDF).

[0016] (3) The composite material slurry prepared in step (2) is uniformly coated on one surface of a commercial polymer membrane substrate, and then dried in an oven at 60° C. to obtain a medium-entropy alloy cerium oxide modified membrane.

[0017] The diaphragm material prepared by the above-mentioned method for preparing the medium entropy alloy composite cerium oxide modified diaphragm still belongs to the protection scope of the present invention;

[0018] At the same time, an application of the diaphragm material in a lithium-sulfur battery is provided. The lithium-sulfur battery comprises a positive electrode, a negative electrode, a diaphragm, and an electrolyte, wherein the electrolyte has a molar concentration of 1 mol L -1 A mixed solution is prepared by lithium bistrifluoromethanesulfonimide (LiTFSI), lithium nitrate with a mass fraction of 1%, ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a volume ratio of 1:1; the negative electrode is a metal lithium sheet, and the positive electrode is a carbon nanotube / sulfur composite material, wherein the mass fraction of sulfur is 70wt%.

[0019] The beneficial effects of the present invention are as follows: Compared with the traditional unmodified diaphragm, the main advantage of the present invention is that the (MEA) CeO2 composite material has a special semi-oxidized structure, which synergizes with cerium oxide and medium entropy alloy to promote the whole process of sulfur reduction and sulfur oxidation in lithium-sulfur batteries, solves the problem of "shuttle effect" well, and greatly improves battery performance;

[0020] Specifically, the advantages of this material are:

[0021] (1) After the intermediate entropy alloy is composited with cerium oxide, the catalytic active centers are the intermediate entropy alloy and the interface between the intermediate entropy alloy and cerium oxide. These two active centers catalyze the reduction and oxidation reactions of sulfur, respectively, to achieve bidirectional catalysis. The bidirectional catalysis can better accelerate the conversion kinetics of polysulfides, that is, better promote the nucleation and dissociation of lithium sulfide (Li2S), and prevent the uneven deposition of lithium sulfide and the accumulation of lithium sulfide from causing changes in the active centers;

[0022] (2) After the intermediate entropy alloy is composited with cerium oxide, due to the semi-oxidized interface, the (220) crystal plane of cerium oxide and the (111) crystal plane of the intermediate entropy alloy are stably combined, resulting in a low capacity decay rate per cycle under long battery cycles;

[0023] (3) The performance of the soft-pack battery of the medium-entropy alloy composite cerium oxide material under high load and poor electrolyte can still maintain 1084mAh g -1 The first lap capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying creative labor, other drawings obtained based on these drawings still belong to the scope of the present invention.

[0025] Figure 1 This is a scanning electron microscope image of the medium-entropy alloy composite cerium oxide material prepared in Example 1 of the present invention;

[0026] Figure 2 This is a transmission electron microscope image of the medium-entropy alloy composite cerium oxide material prepared in Example 1 of the present invention;

[0027] Figure 3 This is the XRD pattern of the medium entropy alloy composite cerium oxide prepared in Example 1 of the present invention;

[0028] Figure 4 The performance diagram of the lithium-sulfur battery with the separator modified by different materials prepared in the present invention at different rates;

[0029] Figure 5 The cycle stability performance diagram of lithium-sulfur batteries with diaphragms modified with different materials prepared in the present invention;

[0030] Figure 6 Performance diagram of soft pack battery of (MEA)CeO2 / PP under high load and poor electrolyte DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with Examples 1-3, Comparative Examples 1 and 2 and the accompanying drawings.

[0032] Example 1

[0033] (1) Preparation of medium-entropy alloy composite cerium oxide material: Cobalt chloride, nickel chloride, molybdenum chloride, iridium chloride, cerium chloride, and 2,5-dihydroxyterephthalic acid were weighed in a molar ratio of 1:1:1:1:1:1:3, and DMF was added to dissolve until the mixture was uniformly stirred. Then, the mixed solution was transferred to a high-temperature hydrothermal reactor and reacted at 140°C for 24 hours. The product was then centrifuged, washed with deionized water and anhydrous ethanol for 5 times, and then dried at 60°C for 12 hours. Finally, it was added to a tubular furnace under argon / hydrogen reduction (900°C, 2h) to obtain a medium-entropy alloy cerium oxide material.

[0034] (2) Preparation of medium-entropy alloy composite cerium oxide modified diaphragm: The medium-entropy alloy cerium oxide material obtained in step (1) is mixed with carbon nanotubes and PVDF in a mass ratio of 8:1:1 to obtain a uniform slurry; the slurry is then evenly coated on a polypropylene diaphragm using a 50 μm coater, and then dried in a vacuum oven at 60°C for 12 hours to finally obtain a composite material modified diaphragm.

[0035] (3) Preparation of positive electrode: CNTs and sulfur were mixed in a mass ratio of 7:3 and fully ground, and heat treated in an oven at 165°C for 12 h. The carbon / sulfur composite material, conductive carbon and PVDF were then added to an appropriate amount of N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 and stirred evenly. The slurry was then evenly coated on aluminum foil with a 150 μm coater, and then vacuum dried at 60°C for 12 h and cut into discs with a diameter of 14 mm to obtain the positive electrode sheet of the lithium-sulfur battery.

[0036] (4) Battery assembly: The sulfur / carbon nanotube electrode prepared above was used as the positive electrode, the metal lithium sheet was used as the negative electrode, the composite material modified diaphragm prepared above was used as the battery diaphragm, and the electrolyte was 1 mol L -1 A mixed solution of 1% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 1:1 volume ratio of ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) and 1% lithium nitrate was prepared. CR2032 button cells were assembled in an argon atmosphere glove box.

[0037] (5) Conventional battery performance test: The NEWARE test system was used to perform charge and discharge tests on the above assembled batteries, with a voltage range of 1.7 to 3V.

[0038] Example 2

[0039] (1) Preparation of medium-entropy alloy MEA material: Cobalt chloride, nickel chloride, molybdenum chloride, iridium chloride, and 2,5-dihydroxyterephthalic acid were weighed in a molar ratio of 1:1:1:1:3, and DMF was added to dissolve until the mixture was stirred and mixed evenly. Then, the mixed solution was transferred to a high-temperature hydrothermal reactor and reacted at 140°C for 24 hours. The product was then centrifuged, washed with deionized water and anhydrous ethanol 5 times, and then dried at 60°C for 12 hours. Finally, it was added to a tubular furnace under argon / hydrogen reduction to obtain a medium-entropy alloy MEA.

[0040] (2) Preparation of medium entropy alloy MEA material modified diaphragm: The MEA material obtained in step (1) was mixed with carbon nanotubes and PVDF in a ratio of 8:1:1 to obtain a uniform slurry. The slurry was then evenly coated on the polypropylene diaphragm using a 50 μm coater, and then dried in a vacuum oven at 60°C for 12 hours. Finally, a MEA modified diaphragm was obtained.

[0041] (3) Battery assembly: The sulfur / carbon nanotube electrode prepared above was used as the positive electrode, the metal lithium sheet was used as the negative electrode, the MEA material modified diaphragm prepared above was used as the battery diaphragm, and the electrolyte was a 1 mol L -1A mixed solution of 1% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 1:1 volume ratio of ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) and 1% lithium nitrate was prepared. CR2032 button cells were assembled in an argon atmosphere glove box.

[0042] (4) Conventional battery performance test: The NEWARE test system was used to perform charge and discharge tests on the above assembled batteries, with a voltage range of 1.7 to 3V.

[0043] Example 3

[0044] (1) Preparation of cerium oxide CeO2 material: Weigh cerium chloride and 2,5-dihydroxyterephthalic acid in a molar ratio of 1:3, add DMF to dissolve and mix until uniform. Then, transfer the mixed solution to a high-temperature hydrothermal reactor and react at 140°C for 24 hours. Then centrifuge the product, wash it with deionized water and anhydrous ethanol 5 times, and then dry it at 60°C for 12 hours; finally, add it to a tube furnace under an argon / hydrogen atmosphere to obtain cerium oxide CeO2.

[0045] (2) Preparation of cerium oxide CeO2 material modified membrane: The CeO2 material obtained in step (1) was mixed with carbon nanotubes and PVDF in a ratio of 8:1:1 to obtain a uniform slurry. The slurry was then evenly coated on a polypropylene membrane using a 50 μm coater, and then dried in a vacuum oven at 60°C for 12 hours. Finally, a CeO2 modified membrane was obtained.

[0046] (3) Battery assembly: The sulfur / carbon nanotube electrode prepared above was used as the positive electrode, the metal lithium sheet was used as the negative electrode, the CeO2 material modified diaphragm prepared above was used as the battery diaphragm, and the electrolyte was 1 mol L -1 A mixed solution of lithium bistrifluoromethanesulfonimide (LiTFSI), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a volume ratio of 1:1 and lithium nitrate with a mass fraction of 1% was prepared; CR2032 button batteries were assembled in a glove box with an argon atmosphere.

[0047] (4) Conventional battery performance test: The NEWARE test system was used to perform charge and discharge tests on the above assembled batteries, with a voltage range of 1.7 to 3V.

[0048] Comparative Example 1

[0049] (1) Preparation of carbon nanotube modified membrane: carbon nanotubes and PVDF were mixed at a ratio of 9:1 to obtain a uniform slurry. The slurry was then evenly coated on a polypropylene membrane using a 50 μm coater, and then dried in a vacuum oven at 60°C for 12 h to obtain a carbon nanotube modified membrane.

[0050] (2) Battery assembly: The sulfur / carbon nanotube electrode prepared above is used as the positive electrode, the metal lithium sheet is used as the negative electrode, the carbon nanotube material modified diaphragm prepared above is used as the battery diaphragm, and the electrolyte is 1 mol L -1 A mixed solution of 1% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 1:1 volume ratio of ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) and 1% lithium nitrate was prepared. CR2032 button cells were assembled in an argon atmosphere glove box.

[0051] (3) Conventional battery performance test: The NEWARE test system was used to perform charge and discharge tests on the above assembled batteries, with a voltage range of 1.7 to 3V.

[0052] Comparative Example 2

[0053] (1) Battery assembly: The sulfur / carbon nanotube electrode prepared above was used as the positive electrode, the metal lithium sheet was used as the negative electrode, the polypropylene separator was used as the battery separator, and the electrolyte was a 1 mol L -1 A mixed solution of 1% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 1:1 volume ratio of ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) and 1% lithium nitrate was prepared. CR2032 button cells were assembled in an argon atmosphere glove box.

[0054] (2) Conventional battery performance test: The NEWARE test system was used to perform charge and discharge tests on the above assembled batteries, with a voltage range of 1.7 to 3V.

[0055] The above-described embodiments are merely preferred embodiments of the present invention, and should not be construed as limiting the patent scope of the present invention. Various improvements may be made without departing from the concept of the present invention, and still fall within the scope of protection of the present invention.

Claims

1. A method for preparing a medium entropy alloy composite cerium oxide modified diaphragm, characterized in that: The following steps are involved: Step S1: mixing cobalt chloride, nickel chloride, molybdenum chloride, iridium chloride, cerium chloride, 2,5-dihydroxyterephthalic acid and N,N-dimethylformamide, stirring evenly, adding them into the carbon tube solution, mixing and dispersing evenly to obtain a mixed solution; Step S2: transferring the mixed solution prepared in step S1 to a high temperature resistant hydrothermal reactor, centrifuging, washing and drying with deionized water after the reaction, and then adding the dried material into a tubular furnace with argon / hydrogen gas to calcine to obtain a composite material; Step S3: Mix the composite material obtained in step S2 with a conductive agent and a binder, add them into N-methylpyrrolidone to obtain a uniform slurry, then evenly coat the slurry on a commercial diaphragm, and vacuum dry at 55-65°C to obtain a medium-entropy cerium oxide composite material modified diaphragm.

2. The method for preparing the medium-entropy alloy composite cerium oxide modified diaphragm according to claim 1, characterized in that: In step S1, the molar ratio of cobalt chloride:nickel chloride:molybdenum chloride:iridium chloride:cerium chloride:2,5-dihydroxyterephthalic acid is 1:1:1:1:1:

3.

3. The method for preparing the medium entropy alloy composite cerium oxide modified diaphragm according to claim 1, characterized in that: In step S2, the hydrothermal reaction temperature is 135°C-145°C, and the reaction time is 24 hours.

4. The method for preparing the medium entropy alloy composite cerium oxide modified diaphragm according to claim 1, characterized in that: In step S2, the temperature in the tube furnace is 900°C and the time is 2 hours.

5. The method for preparing the medium entropy alloy composite cerium oxide modified diaphragm according to claim 1, characterized in that: The commercial membrane in step S3 is any one of cellulose membrane, polyethylene membrane, polypropylene membrane, aramid membrane, polyester membrane, Celgard2400 and Celgard2500.

6. The method for preparing the medium entropy alloy composite cerium oxide modified diaphragm according to claim 1, characterized in that: In step S3, the conductive agent is carbon nanotubes, and the binder is polyvinylidene fluoride.

7. A diaphragm material prepared by the method for preparing a medium-entropy alloy composite cerium oxide modified diaphragm as described in any one of claims 1 to 6.

8. Application of the diaphragm material according to claim 7 in a lithium-sulfur battery, characterized in that: The negative electrode of the lithium-sulfur battery is a metal lithium sheet, and the positive electrode is a carbon nanotube / sulfur composite material, in which the mass fraction of sulfur is 70wt%; the electrolyte is a concentration of 1molL -1 A mixed solution of lithium bistrifluoromethanesulfonimide, 1,3-dioxolane and ethylene glycol dimethyl ether in a volume ratio of 1:1 and lithium nitrate with a mass fraction of 1%.

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