Preparation method and application of lithium-sulfur battery niS2-coS2 heterojunction catalyst modified separator

Abstract

The application provides a preparation method of a lithium-sulfur battery NiS2-CoS2 heterojunction catalyst modified diaphragm and application thereof, and belongs to the technical field of lithium-sulfur battery diaphragms, in particular to the following: taking divalent nickel salt, divalent cobalt salt and thiosulfate as raw materials, dissolving in deionized water, carrying out hydrothermal reaction at 180-220 DEG C for 10-14 h, and obtaining NiS2-CoS2 heterojunction material through centrifugation and drying, and then taking the NiS2-CoS2 heterojunction material as a catalyst to modify the diaphragm. The NiS2-CoS2 heterojunction material is prepared through a one-step hydrothermal method, and is used as a catalyst for diaphragm modification, so that the diaphragm modification cost can be significantly reduced, and the method is more practical. In addition, the heterojunction is constructed between NiS2 and CoS2, an internal built-in electric field is formed in the diaphragm, electron and ion transport is promoted, lithium polysulfide conversion kinetics is promoted, the "shuttle effect" is inhibited, and the charge and discharge capacity and cycle stability of lithium-sulfur button batteries and lithium-sulfur soft package batteries are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium-sulfur battery separators, and particularly relates to a preparation method of a lithium-sulfur battery NiS2-CoS2 heterojunction catalyst modified separator and application thereof. BACKGROUND

[0002] The lithium-sulfur battery uses sulfur / carbon composite material as a positive electrode and metal lithium as a negative electrode. When the battery is discharged, the lithium negative electrode loses electrons to become lithium ions, and the sulfur positive electrode undergoes a multi-electron transfer reaction with the lithium ions to generate a plurality of polysulfides in the intermediate process, and finally converts into lithium disulfide (Li2S); when charged, the lithium ions decomposed from the Li2S migrate back to the negative electrode under the action of an electric field and deposit into metal lithium. The lithium-sulfur battery has a very high theoretical capacity of 1675 mAh / g, and the sulfur material is abundant, low in cost and less polluting, so it is a key research and development direction of the next generation of high-energy storage batteries.

[0003] The separator is a key component of the lithium-sulfur battery, and its main function is to isolate the positive electrode and the negative electrode, prevent internal short circuit, and promote the free movement of lithium ions between the electrodes. The separator of the lithium-sulfur battery is usually made of non-polar thin film polypropylene (PP). During the charging and discharging process of the lithium-sulfur battery, lithium polysulfide is divided into two types: long-chain lithium polysulfide that is easily dissolved in electrolyte, and short-chain lithium polysulfide that has low solubility and slow reaction kinetics. Due to the different characteristics of the two types of lithium polysulfide, the "shuttle effect" is generated, and the existing separator cannot inhibit this "shuttle effect" and cannot promote the conversion kinetics of lithium polysulfide, which seriously hinders the transmission of electrons and ions, thereby reducing the cycle stability and capacity of the lithium-sulfur battery. SUMMARY

[0004] In view of the above-mentioned "shuttle effect" problem existing in the existing separator, the application provides a preparation method of a lithium-sulfur battery NiS2-CoS2 heterojunction catalyst modified separator and application thereof. The NiS2-CoS2 heterojunction catalyst is prepared by a one-step hydrothermal method and coated on the separator, so that a built-in electric field is formed at the NiS2-CoS2 heterojunction interface, promoting the electron and ion transport in the separator, thereby promoting the conversion kinetics of lithium polysulfide and inhibiting the "shuttle effect".

[0005] In order to achieve the above-mentioned purpose, the technical method adopted by the application is as follows:

[0006] A preparation method of a lithium-sulfur battery NiS2-CoS2 heterojunction catalyst modified separator, comprising the following steps:

[0007] Step 1, preparing a NiS2-CoS2 heterojunction material;

[0008] With bivalent nickel salt, bivalent cobalt salt and thiosulfate as raw materials, each raw material is weighed according to the molar ratio of nickel atom: cobalt atom: sulfur atom of 5-7: 2-4: 8-12, and is dissolved in deionized water to obtain a mixed solution with a nickel atom concentration of 0.08M-0.117M; the mixed solution is subjected to hydrothermal reaction at 180-220℃ for 10-14h, and after centrifugation and drying, a NiS2-CoS2 heterojunction material is obtained.

[0009] Step 2, the separator is modified with the NiS2-CoS2 heterojunction material as a catalyst.

[0010] Further, the specific process of step 2 is as follows: NiS2-CoS2 heterojunction material, conductive agent and binder are weighed according to the mass ratio of 2-3: 5-6: 2, respectively, and are added into a solvent together, and a modified slurry is obtained by ball milling, which is coated on the surface of the separator, and a lithium-sulfur battery NiS2-CoS2 heterojunction catalyst modified separator is obtained after vacuum drying.

[0011] Further, the bivalent nickel salt is at least one of nickel chloride hexahydrate, nickel sulfate, and nickel bromide.

[0012] Further, the bivalent cobalt salt is at least one of cobalt chloride hexahydrate, cobalt sulfate, and cobalt bromide.

[0013] Further, the thiosulfate is at least one of sodium thiosulfate pentahydrate and magnesium thiosulfate.

[0014] Further, the conductive agent is at least one of conductive carbon black (Super P), acetylene black, and ketjen black; the binder is polyvinylidene fluoride (PVDF); and the solvent is at least one of N-methyl pyrrolidone (NMP) and N,N-dimethylformamide (DMF).

[0015] Further, the centrifugation speed in step 1 is 7500-8500r / min, and the centrifugation is performed 3-5 times, each time for 2-4min.

[0016] The application also provides the application of the lithium-sulfur battery NiS2-CoS2 heterojunction catalyst modified separator prepared by the preparation method in lithium-sulfur button cells or lithium-sulfur soft pack batteries.

[0017] Compared with the prior art, the application has the following beneficial effects:

[0018] The application provides a preparation method and application of a lithium-sulfur battery NiS2-CoS2 heterojunction catalyst modified separator, wherein the NiS2-CoS2 heterojunction material is prepared by a one-step hydrothermal method and used as a catalyst for modifying the separator; on the one hand, the mass of the NiS2-CoS2 heterojunction material in the modified slurry is only about half of that of the conductive agent, so that the modification cost of the separator can be significantly reduced; on the other hand, the heterojunction is constructed between the NiS2 and the CoS2, and a built-in electric field is formed in the separator, so as to promote the electron and ion transport, promote the lithium polysulfide conversion kinetics, inhibit the “shuttle effect”, and improve the charge and discharge capacity and cycle stability of the lithium-sulfur button cell and lithium-sulfur soft package cell; and it is further indicated that the application can maintain excellent electrochemical performance while reducing the content of the modified material (NiS2-CoS2 heterojunction material), and is more practical. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0020] Figure 1 The XRD (X-ray diffraction) pattern of the NiS2-CoS2 heterojunction material prepared for Example 1;

[0021] Figure 2 The SEM (scanning electron microscope) pattern of the NiS2-CoS2 heterojunction material prepared for Example 1;

[0022] Figure 3 The EDS (energy spectrum analyzer) pattern of the NiS2-CoS2 heterojunction material prepared for Example 1;

[0023] Figure 4 The TEM (transmission electron microscope) pattern of the NiS2-CoS2 heterojunction material prepared for Example 1;

[0024] Figure 5 The SEM top view of the lithium-sulfur battery NiS2-CoS2 heterojunction catalyst modified separator prepared for Example 1;

[0025] Figure 6 The SEM side view of the lithium-sulfur battery NiS2-CoS2 heterojunction catalyst modified separator prepared for Example 1;

[0026] Figure 7 The 0.2C cycle performance diagram of the lithium-sulfur button cell corresponding to Example 1 and Comparative Example 1;

[0027] Figure 8 Figure for the rapid rate cycling performance of lithium-sulfur button cells corresponding to Example 1 and Comparative Example 1;

[0028] Figure 9 Figure for the 0.2C first cycle specific capacity of lithium-sulfur pouch cells corresponding to Example 1. DETAILED DESCRIPTION

[0029] In order to further understand the present application, the preferred embodiments of the present application are described below in conjunction with examples, but it should be understood that these descriptions are only intended to further illustrate the features and advantages of the present application, and are not intended to limit the scope of the claims of the present application. All raw materials of the present application are not particularly limited in source, and can be purchased on the market or prepared according to conventional methods well known to those skilled in the art.

[0030] Example 1

[0031] In this example, a lithium-sulfur battery NiS2-CoS2 heterojunction catalyst modified separator was prepared, including the following steps:

[0032] Step 1, preparation of NiS2-CoS2 heterojunction material;

[0033] 0.793 g of nickel chloride hexahydrate, 0.397 g of cobalt chloride hexahydrate, and 1.24 g of sodium thiosulfate pentahydrate were weighed respectively, mixed, and then placed in 60 mL of deionized water. The mixture was stirred at 900 r / min for 10 min until completely dissolved to obtain a mixed solution. The mixed solution was transferred to an autoclave and subjected to hydrothermal reaction at 200℃ for 12 h. Then, the solution was centrifuged four times at 8000 r / min for 3 min each time. The first centrifugation was after the hydrothermal reaction, the second and third centrifugations required the addition of deionized water, and the fourth centrifugation required the addition of anhydrous ethanol. The obtained powder after centrifugation was dried in a vacuum oven at 80℃ to obtain the NiS2-CoS2 heterojunction material;

[0034] Step 2, modification of the separator with the NiS2-CoS2 heterojunction material as catalyst;

[0035] 0.24 g of NiS2-CoS2 heterojunction material, 0.56 g of Super P, and 0.2 g of PVDF were weighed respectively; 0.2 g of PVDF was first mixed with 4 mL of NMP, and homogenized for 6 min until completely dissolved to obtain a PVDF slurry; then 0.56 g of Super P and 4 mL of NMP were added to the PVDF slurry, and ball-milled for 10 min, then 0.24 g of NiS2-CoS2 heterojunction material and 4 mL of NMP were added, and ball-milled for 15 min again to obtain a modified slurry; then the modified slurry was coated on the surface of a commercial celgard-2500 separator by using a doctor blade, and placed in a vacuum oven at 45°C for 10 h, and the dried NiS2-CoS2 heterojunction catalyst modified separator for lithium-sulfur batteries was obtained.

[0036] Figure 1 The XRD pattern of the NiS2-CoS2 heterojunction material obtained in this example showed that the NiS2-CoS2 heterojunction material was a stable Pa-3 cubic phase structure, and the diffraction peaks were consistent with the standard PDF card results of NiS2 and CoS2.

[0037] Figure 2 The SEM image of the NiS2-CoS2 heterojunction material obtained in this example showed that the micro-morphology of the NiS2-CoS2 heterojunction material was an irregular spherical structure with a large number of stacked wrinkles on the surface, and the size was in the micron level.

[0038] Figure 3 The EDS image of the NiS2-CoS2 heterojunction material obtained in this example showed that the elements S, Ni, and Co in the NiS2-CoS2 heterojunction material were uniformly distributed.

[0039] Figure 4 The TEM image of the NiS2-CoS2 heterojunction material obtained in this example showed that the lattice spacing of the (210) crystal plane of NiS2 was 0.257 nm, the lattice spacing of the (111) crystal plane of CoS2 was 0.322 nm, and a heterostructure was formed between NiS2 and CoS2.

[0040] The SEM top view and the SEM side view of the lithium-sulfur battery NiS2-CoS2 heterojunction catalyst modified separator obtained in this example are shown in Figure 5 and Figure 6 It can be seen that the distribution of NiS2-CoS2 heterojunction material, Super P, and PVDF in the coating on the surface of the separator is relatively uniform, and the coating thickness is 10 μm.

[0041] Comparative Example 1

[0042] The commercial celgard-2500 separator without any modification was used in this comparative example.

[0043] Lithium-sulfur button cells were prepared based on the diaphragms obtained in Example 1 and Comparative Example 1, and electrochemical performance tests were performed, specifically:

[0044] 1) Preparation method of lithium-sulfur button battery:

[0045] The lithium-sulfur button battery consists of a battery shell, a positive electrode, a diaphragm, a negative electrode, a spring, a gasket and an electrolyte; wherein, the positive electrode is an electrode sheet made of a sulfur / carbon composite material; the negative electrode is a lithium sheet; the diaphragm is the lithium-sulfur battery NiS2-CoS2 heterojunction catalyst modified diaphragm obtained in Example 1 or the commercial celgard-2500 diaphragm without any modification in Comparative Example 1; the spring is an open-pore convex stainless steel sheet; the gasket is a 0.5 mm thick stainless steel sheet; the electrolyte contains 1% LiNO3, 1M LiTFSI (lithium bistrifluoromethanesulfonimide), and a DOL / DME (1,3-dioxolane / ethylene glycol dimethyl ether) mixed ether organic solution with a volume ratio of 1:1; the lithium-sulfur button battery is assembled in a glove box with a water and oxygen content of less than 0.1 ppm.

[0046] 2) The lithium-sulfur button cells prepared based on the diaphragms obtained in Example 1 and Comparative Example 1 were subjected to 0.2C and fast rate cycle performance tests. The test results are shown in Table 1. Figure 7 and Figure 8 As shown, it can be seen that the first-cycle 0.1C discharge capacity of the lithium-sulfur button battery prepared by the commercial celgard-2500 diaphragm without any modification obtained in comparative example 1 is 1146.9 mAh / g, while the first-cycle 0.1C discharge capacity of the lithium-sulfur button battery prepared by the lithium-sulfur battery NiS2-CoS2 heterojunction catalyst modified diaphragm obtained in Example 1 can be increased to 1337.4 mAh / g, and the corresponding lithium-sulfur button battery in Example 1 has a large discharge capacity at currents of 0.1C, 0.2C, 0.3C, 0.5C and 1C, and can reach a discharge capacity close to 0.3C when the current reaches 2C and recovers to 0.2C, reflecting excellent reversible cycle characteristics and cycle stability, and showing the potential to inhibit the shuttle effect, promote the conversion kinetics of lithium polysulfide, and slow down battery attenuation.

[0047] A lithium-sulfur soft-pack battery was prepared based on the NiS2-CoS2 heterojunction catalyst-modified diaphragm obtained in Example 1, and the electrochemical performance test was carried out, specifically:

[0048] 1) Preparation method of lithium-sulfur soft pack battery:

[0049] The lithium-sulfur soft package battery is composed of a sulfur positive electrode, a separator, a lithium negative electrode and an electrolyte, and is packaged by using an aluminum plastic film; wherein the positive electrode adopts single-sided coating of sulfur / carbon composite material, the overall size is 50mmx70mm, and there is a 10mm wide positive electrode active coating-free area in the 70mm long side for welding the positive electrode aluminum tab, so that the effective area is 50mmx60mm, and the sulfur loading of a single pole piece is 4.25mg / cm 2 ; the size of the lithium negative electrode is slightly larger than that of the positive electrode, specifically 55mmx70mm; the separator adopts the lithium-sulfur battery NiS2-CoS2 heterojunction catalyst modified separator obtained in Example 1, and the specific size is 55mmx70mm; the amount of electrolyte E / S is 8μL / mg.

[0050] 2) The first cycle charge-discharge specific capacity test of the obtained lithium-sulfur soft package battery is carried out, and the test results are shown in Figure 9 It can be seen that the 0.1C first cycle charge-discharge capacity of the lithium-sulfur soft package battery using the lithium-sulfur battery NiS2-CoS2 heterojunction catalyst modified separator obtained in Example 1 is 1063.1mAh / g and 1024.8mAh / g respectively, which has effectiveness and practicability.

[0051] Example 2

[0052] In this embodiment, a lithium-sulfur battery NiS2-CoS2 heterojunction catalyst modified separator is prepared, and the difference compared with Example 1 is that the hydrothermal reaction condition in step 1 is adjusted to be reacted at 180℃ for 14h; other steps are completely the same.

[0053] Example 3

[0054] In this embodiment, a lithium-sulfur battery NiS2-CoS2 heterojunction catalyst modified separator is prepared, and the difference compared with Example 1 is that the hydrothermal reaction condition in step 1 is adjusted to be reacted at 220℃ for 10h; other steps are completely the same.

[0055] The above examples are for better further understanding of the present application, and do not limit the best embodiments, and do not constitute a limitation on the content and protection scope of the present application, and any person under the inspiration of the present application or the combination of the present application with other existing technical features can obtain any product same or similar to the present application, which is within the protection scope of the present application.

Claims

1. A method for preparing a NiS2-CoS2 heterojunction catalyst modified diaphragm for a lithium-sulfur battery, characterized in that: The following steps are involved: Step 1, preparing NiS2-CoS2 heterojunction material; Using divalent nickel salt, divalent cobalt salt and thiosulfate as raw materials, the raw materials are weighed according to a molar ratio of nickel atoms: cobalt atoms: sulfur atoms of 5-7:2-4:8-12, and dissolved in deionized water to obtain a mixed solution with a nickel atom concentration of 0.08M-0.117M; the mixed solution is subjected to a hydrothermal reaction at 180-220°C for 10-14h, and after centrifugation and drying, a NiS2-CoS2 heterojunction material is obtained; Step 2: Using NiS2-CoS2 heterojunction material as a catalyst, the diaphragm is modified. The specific process is as follows: NiS2-CoS2 heterojunction material, conductive agent and binder are weighed respectively in a mass ratio of 2-3:5-6:2, added together to a solvent, and ball milled to obtain a modified slurry, which is applied to the surface of the diaphragm. After vacuum drying, a NiS2-CoS2 heterojunction catalyst-modified diaphragm for a lithium-sulfur battery is obtained.

2. The method for preparing a NiS2-CoS2 heterojunction catalyst modified diaphragm for a lithium-sulfur battery according to claim 1, characterized in that: The divalent nickel salt is at least one of nickel chloride hexahydrate, nickel sulfate, and nickel bromide.

3. The method for preparing a NiS2-CoS2 heterojunction catalyst modified diaphragm for a lithium-sulfur battery according to claim 1, characterized in that: The divalent cobalt salt is at least one of cobalt chloride hexahydrate, cobalt sulfate, and cobalt bromide.

4. The method for preparing a NiS2-CoS2 heterojunction catalyst modified diaphragm for a lithium-sulfur battery according to claim 1, characterized in that: The thiosulfate is at least one of sodium thiosulfate pentahydrate and magnesium thiosulfate.

5. The method for preparing a NiS2-CoS2 heterojunction catalyst modified diaphragm for a lithium-sulfur battery according to claim 1, characterized in that: The conductive agent is at least one of conductive carbon black, acetylene black, and Ketjen black; the binder is polyvinylidene fluoride; and the solvent is at least one of N-methylpyrrolidone and N,N-dimethylformamide.

6. Use of the lithium-sulfur battery NiS2-CoS2 heterojunction catalyst modified diaphragm obtained by the preparation method according to any one of claims 1 to 5 in lithium-sulfur button cells or lithium-sulfur soft-pack batteries.

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