Lithium-sulfur button battery and preparation method thereof

Abstract

This application discloses a modified-diaphragm lithium-sulfur button cell and its preparation method. A P-CS-0.5 composite material is obtained by creating vacancies in CoSe2 and inducing phosphorus doping. The P-CS-0.5 composite material is then used to modify the diaphragm, and the lithium-sulfur button cell is prepared using the P-CS-0.5-modified diaphragm. The nucleation and decomposition curves of lithium sulfide show that P-CS-0.5 can catalyze the rapid nucleation and decomposition of lithium sulfide, increase the nucleation and decomposition capacity, and effectively improve the adsorption and catalytic conversion of polysulfides, thereby suppressing the shuttle effect.

Description

Technical Field

[0001] The present application relates to the technical field of battery materials, and in particular to a lithium-sulfur button battery and a preparation method thereof. Background Art

[0002] Lithium-sulfur batteries have the advantages of high theoretical specific capacity, high specific energy, abundant natural reserves of raw materials, environmental friendliness, and low preparation cost. They are the research hotspot of the next generation energy storage system. However, some defects hinder the large-scale commercial application of lithium-sulfur batteries. In lithium-sulfur batteries, the separator not only acts as an electrolyte storage, but also promotes the transfer of Li-ion batteries during the charge and discharge process. + The modified functional membrane also has a large number of active sites for the adsorption of polysulfide ions, promoting the formation of lithium polysulfide and inhibiting its shuttle to the lithium negative electrode. In addition, the functional modified separator can also induce the uniform deposition of metallic lithium, inhibit the growth of lithium dendrites, and improve the cycle performance and safety of the battery.

[0003] Various catalysts, such as oxides, carbides, nitrides, and sulfides, have inherent properties that make it difficult to meet the high catalytic performance requirements of the slow redox kinetics of sulfur. Transition metal selenides possess both sulfur-philic and lithium-philic sites. The sulfur-philic sites can effectively adsorb polysulfides, thereby mitigating the shuttle effect, while the lithium-philic sites can lower the nucleation barrier of lithium sulfide and induce uniform deposition of lithium ions on the negative electrode side. As a result, transition metal selenides have become a hot topic of research.

[0004] Based on this, the present application creates vacancies in CoSe2 and induces phosphorus doping to obtain a corresponding composite material, resulting in a P-CS-NaBH4 catalyst for use in lithium-sulfur battery separator modification. This catalyst catalyzes the rapid nucleation and decomposition of lithium sulfide, increases the nucleation and decomposition capacity, and effectively improves the adsorption and catalytic conversion of polysulfides, thereby suppressing the shuttle effect. Summary of the Invention

[0005] The purpose of the present invention is to provide a lithium-sulfur button cell and a preparation method thereof, and to prepare a P-CS-NaBH4 catalyst for use in the diaphragm modification of lithium-sulfur batteries.

[0006] The embodiment of the present application discloses a lithium-sulfur button battery, including a negative electrode (lithium sheet), a positive electrode and an electrolyte, and a modified separator.

[0007] Preferably, the positive electrode is prepared as follows: S and carbon nanotubes (CNTs) are mixed in a mass ratio of 8:2 and heated at 155°C for 16 h to obtain an S / CNT composite material; S / CNT, Super P and PVDF are added to an NMP solvent in a mass ratio of 7:2:1 to obtain a slurry; the slurry is coated on aluminum foil, placed in an oven at 50°C for 12 h, and cut into discs with a diameter of 12 mm.

[0008] Preferably, the electrolyte is a solution of 1,3-dioxolane and ethylene glycol dimethyl ether (volume ratio is 1:1) containing 0.5 M LiTFSI and LiNO3.

[0009] Preferably, the modified diaphragm preparation method comprises the following steps:

[0010] S1: Preparation of ZIF-67. Etching ZIF-67 with tannic acid to obtain a hollow structure and in-situ selenization to obtain hollow cubic CoSe2.

[0011] S2: The prepared CoSe2 was immersed in NaBH4 solutions of different concentrations at a mass volume ratio of 1 mg:1 ml for 30 min, washed with deionized water several times, and dried at 60 °C for 8-16 h to obtain material A;

[0012] S3: NaH2PO2 and material A in S2 are placed in the upstream and downstream of a tube furnace in a mass ratio of 1:1, respectively, and heated to obtain a P-CS-NaH2PO2 composite material;

[0013] S4 adding P-CS-NaH2PO2 composite material powder, Super P and PVDF into NMP solvent in proportion to obtain a mixed slurry;

[0014] S5 coated the slurry on the PP separator, and the material loading was about 0.5 mg / cm 2 , and then dried and cut into discs with a diameter of 19 mm to obtain the modified diaphragm.

[0015] Furthermore, the preparation method of ZIF-67 in step S1 is: Co(NO3)2·6H2O and hexadecyltrimethylammonium bromide are weighed in a mass ratio of 20:1 and added to deionized water, and stirred to obtain solution A; 2-methylimidazole is added to deionized water in proportion, and stirred to obtain solution B; solution A is poured into solution B, and stirred at high speed for 40 minutes to obtain a purple suspension; ethanol is used for centrifugal washing six times to obtain a purple substance, and dried under vacuum at 60°C to obtain ZIF-67.

[0016] Furthermore, in step S1, the preparation of CoSe2 is as follows: hollow ZIF-67 and selenium powder are placed in a crucible in a mass ratio of 1:3, and heated at 450°C for 2 h (heating rate of 2°C / min) under a H2 / Ar protective atmosphere to obtain CoSe2.

[0017] Furthermore, the heating system in step S3 is: heating at 300-400° C. for 1.5-3 h under Ar protective atmosphere.

[0018] Furthermore, in step S4, the mass ratio of the P-CS-NaH2PO2 composite material powder, Super P and PVDF is 5:4:1.

[0019] Furthermore, the drying temperature in step S4 is 45-60° C., and the drying time is 10-16 h.

[0020] The present invention has the advantage of using tannic acid to etch ZIF-67 to create a hollow structure, followed by in-situ selenization to produce a hollow cubic CoSe2 structure. Subsequently, NaBH4 is used to create vacancies and induce phosphorus doping to produce the P-CS-0.5 catalyst. P-CS-0.5 can catalyze the rapid nucleation and decomposition of lithium sulfide, increase nucleation and decomposition capacity, effectively improve polysulfide adsorption and catalytic conversion processes, and thus inhibit the shuttle effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 Shown are SEM images of the membrane materials prepared in Example 2, where (a) is the PP film and (b) is the prepared P-CS-0.5 modified membrane;

[0023] Figure 2 Shown are (a) Li2S deposition curves and (b) Li2S decomposition curves of different materials obtained in Examples 1-3: CS, CS-0.1, CS-0.5, CS-1, and P-CS-0.5;

[0024] Figure 3 Shown are the CV curves of different batteries using different materials obtained in Examples 1-3 at a scan rate of 0.1 mV s-1;

[0025] Figure 4 Shown are (a) in situ Raman spectrum and (b) Raman contour map of the P-CS-0.5 modified membrane obtained in Example 2 at 0.5°C. DETAILED DESCRIPTION

[0026] The following is a detailed description of the technical solutions in the embodiments of the present invention, with reference to the accompanying drawings. Obviously, the described embodiments are only a portion of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0027] Example 1

[0028] Preparation of S1 ZIF-67: Add 300 mg of Co(NO3)2·6H2O and 15 mg of hexadecyltrimethylammonium bromide to 20 mL of deionized water and stir to obtain solution A; add 908 mg of 2-methylimidazole to 140 mL of deionized water and stir to obtain solution B; pour solution A into solution B and stir at high speed for 40 min to obtain a purple suspension; use ethanol to wash six times by centrifugation to obtain a purple substance, and dry it at 60°C under vacuum for 12 h to obtain ZIF-67.

[0029] S2 Preparation of hollow ZIF-67: The prepared ZIF-67 was dispersed in 20 mL of ethanol, and then poured into 160 mL of a mixed solution of ethanol and deionized water containing 1 mg / mL tannic acid. The mixture was stirred at room temperature for 15 min, and the product was collected by centrifugation and washed several times with ethanol to obtain hollow structured ZIF-67.

[0030] Preparation of S3 CoSe2: Hollow ZIF-67 and selenium powder (mass ratio of 1:3) were placed in a crucible and heated at 450°C for 2 h (heating rate of 2°C / min) under H2 / Ar atmosphere to obtain CoSe2; 50 mg of the prepared CoSe2 was soaked in 50 mL of NaBH4 solution (0.1 mol / L concentration) for 30 min, then washed several times with deionized water and dried at 60°C overnight to obtain the target material (CS-0.1).

[0031] Preparation of S4 P-CS-0.1 composite material: NaH2PO2 and CS-0.1 with a mass ratio of 1:1 were placed upstream and downstream of a tube furnace, respectively, and heated at 350°C in an Ar atmosphere for 2 h to obtain P-CS-0.1.

[0032] Preparation of S5 modified membrane: P-CS-0.1 powder, Super P, and PVDF were added to NMP solvent at a mass ratio of 5:4:1 to obtain a mixed slurry. The slurry was coated on a PP membrane with a material loading of approximately 0.5 mg cm -2 , then dried at 50 °C for 12 h and cut into discs with a diameter of 19 mm.

[0033] Preparation of S6 cathode material: S and carbon nanotubes (CNTs) were mixed in a mass ratio of 8:2 and heated at 155°C for 16 h to obtain an S / CNT composite material. S / CNT, Super P, and PVDF were added to an NMP solvent in a mass ratio of 7:2:1 to obtain a slurry. The slurry was coated on aluminum foil, placed in an oven at 50°C for 12 h, and then cut into discs with a diameter of 12 mm.

[0034] Preparation of S7 lithium-sulfur button cell: The CR2032 button cell was assembled using the S / CNT prepared above as the positive electrode, the P-CS-0.5 modified separator as the battery separator, the lithium sheet as the negative electrode, and a 1,3-dioxolane and ethylene glycol dimethyl ether (1:1 volume ratio) solution containing 0.5 M LiTFSI and LiNO3 as the electrolyte. Example 2

[0035] Preparation of S1 ZIF-67: Add 300 mg of Co(NO3)2·6H2O and 15 mg of hexadecyltrimethylammonium bromide to 20 mL of deionized water and stir to obtain solution A; add 908 mg of 2-methylimidazole to 140 mL of deionized water and stir to obtain solution B; pour solution A into solution B and stir at high speed for 40 min to obtain a purple suspension; use ethanol to wash six times by centrifugation to obtain a purple substance, and dry it at 60°C under vacuum for 12 h to obtain ZIF-67.

[0036] S2 Preparation of hollow ZIF-67: The prepared ZIF-67 was dispersed in 20 mL of ethanol, and then poured into 160 mL of a mixed solution of ethanol and deionized water containing 1 mg / mL tannic acid. The mixture was stirred at room temperature for 15 min, and the product was collected by centrifugation and washed several times with ethanol to obtain hollow structured ZIF-67.

[0037] Preparation of S3 CoSe2: Hollow ZIF-67 and selenium powder (mass ratio of 1:3) were placed in a crucible and heated at 450°C for 2 h (heating rate of 2°C / min) under H2 / Ar atmosphere to obtain CoSe2; 50 mg of the prepared CoSe2 was soaked in 50 mL of NaBH4 solution (0.5 mol / L concentration) for 30 min, then washed several times with deionized water and dried at 60°C overnight to obtain the target material (CS-0.5).

[0038] Preparation of S4 P-CS-0.5 composite material: NaH2PO2 and CS-0.5 with a mass ratio of 1:1 were placed upstream and downstream of a tube furnace, respectively, and heated at 350°C in an Ar atmosphere for 2 h to obtain P-CS-0.5.

[0039] Preparation of S5 modified membrane: P-CS-0.5 powder, Super P, and PVDF were added to NMP solvent at a mass ratio of 5:4:1 to obtain a mixed slurry. The slurry was coated on a PP membrane with a material loading of approximately 0.5 mg cm -2 , then dried at 50 °C for 12 h and cut into discs with a diameter of 19 mm.

[0040] Preparation of S6 cathode material: S and carbon nanotubes (CNTs) were mixed in a mass ratio of 8:2 and heated at 155°C for 16 h to obtain an S / CNT composite material. S / CNT, Super P, and PVDF were added to an NMP solvent in a mass ratio of 7:2:1 to obtain a slurry. The slurry was coated on aluminum foil, placed in an oven at 50°C for 12 h, and then cut into discs with a diameter of 12 mm.

[0041] Preparation of S7 lithium-sulfur button cell: The CR2032 button cell was assembled using the S / CNT prepared above as the positive electrode, the P-CS-0.5 modified separator as the battery separator, the lithium sheet as the negative electrode, and a 1,3-dioxolane and ethylene glycol dimethyl ether (1:1 volume ratio) solution containing 0.5 M LiTFSI and LiNO3 as the electrolyte. Example 3

[0042] Preparation of S1 ZIF-67: Add 300 mg of Co(NO3)2·6H2O and 15 mg of hexadecyltrimethylammonium bromide to 20 mL of deionized water and stir to obtain solution A; add 908 mg of 2-methylimidazole to 140 mL of deionized water and stir to obtain solution B; pour solution A into solution B and stir at high speed for 40 min to obtain a purple suspension; use ethanol to wash six times by centrifugation to obtain a purple substance, and dry it at 60°C under vacuum for 12 h to obtain ZIF-67.

[0043] S2 Preparation of hollow ZIF-67: The prepared ZIF-67 was dispersed in 20 mL of ethanol, and then poured into 160 mL of a mixed solution of ethanol and deionized water containing 1 mg / mL tannic acid. The mixture was stirred at room temperature for 15 min, and the product was collected by centrifugation and washed several times with ethanol to obtain hollow structured ZIF-67.

[0044] Preparation of S3 CoSe2: Hollow ZIF-67 and selenium powder (mass ratio of 1:3) were placed in a crucible and heated at 450°C for 2 h (heating rate of 2°C / min) under H2 / Ar atmosphere to obtain CoSe2; 50 mg of the prepared CoSe2 was soaked in 50 mL of NaBH4 solution (1 mol / L concentration) for 30 min, then washed several times with deionized water and dried at 60°C overnight to obtain the target material (CS-1).

[0045] Preparation of S4 P-CS-1 composite material: NaH2PO2 and CS-1 with a mass ratio of 1:1 were placed upstream and downstream of a tube furnace, respectively, and heated at 350°C in an Ar atmosphere for 2 h to obtain P-CS-1.

[0046] Preparation of S5 modified membrane: P-CS-1 powder, Super P, and PVDF were added to NMP solvent at a mass ratio of 5:4:1 to obtain a mixed slurry. The slurry was coated on a PP membrane with a material loading of approximately 0.5 mg cm -2 , then dried at 50 °C for 12 h and cut into discs with a diameter of 19 mm.

[0047] Preparation of S6 cathode material: S and carbon nanotubes (CNTs) were mixed in a mass ratio of 8:2 and heated at 155°C for 16 h to obtain an S / CNT composite material. S / CNT, Super P, and PVDF were added to an NMP solvent in a mass ratio of 7:2:1 to obtain a slurry. The slurry was coated on aluminum foil, placed in an oven at 50°C for 12 h, and then cut into discs with a diameter of 12 mm.

[0048] Preparation of S7 lithium-sulfur button cell: The CR2032 button cell was assembled using the S / CNT prepared above as the positive electrode, the P-CS-0.5 modified separator as the battery separator, the lithium sheet as the negative electrode, and a 1,3-dioxolane and ethylene glycol dimethyl ether (1:1 volume ratio) solution containing 0.5 M LiTFSI and LiNO3 as the electrolyte.

[0049] The membrane material prepared in Example 2 was characterized using SEM. Figure 1 As shown in (a) and (b), the original PP separator is filled with numerous pores, which are much larger than polysulfides, making it difficult to effectively block polysulfides and inhibit the shuttling effect. However, after the P-CS-0.5 material is evenly coated on the PP separator, the original pores are completely covered, physically hindering the passage of polysulfides.

[0050] The material was dropped onto carbon paper as the positive electrode and Li2S8 solution was used as the electrolyte to assemble the battery and conduct the Li2S nucleation and decomposition experiments. Figure 2As shown, the battery based on the P-CS-0.5 modified separator can promote the rapid nucleation of Li2S and deliver 119 mAh g -1 The Li2S deposition capacity and 434.1 mAh g -1 The decomposition capacity of P-CS-0.5 is higher than that of other materials, indicating that the P-CS-0.5 modified separator can effectively promote the nucleation and decomposition of Li2S.

[0051] By 0.1 mV s -1 The CV curve under the scanning rate is used to evaluate the reaction kinetics of the battery, such as Figure 3 As shown in the figure, the P-CS-0.5 modified membrane exhibits the largest peak current and peak area, and its oxidation peak is located at the lowest potential, indicating that the redox kinetics of polysulfides are significantly enhanced.

[0052] In situ Raman spectroscopy was used to monitor the transformation behavior of polysulfides during discharge and charge. Figure 4 As shown in the figure, the peaks at 202, 402, and 451 cm-1 Raman shifts are attributed to the polysulfides that appear during the charge and discharge process. The weak Raman signals indicate that the polysulfides are rapidly catalytically converted, proving that the P-CS-0.5 modified membrane effectively suppresses the shuttle effect.

[0053] This implementation mode is only an illustrative description of this patent and does not limit its scope of protection. People skilled in the art may also make partial changes to it. As long as it does not exceed the spirit of this patent, it will be regarded as an equivalent replacement of this patent and will be within the scope of protection of this patent.

Claims

1. A lithium-sulfur button battery, characterized in that: The invention comprises a negative electrode, a positive electrode, an electrolyte, and a modified diaphragm; the negative electrode is a lithium sheet, and the preparation method of the modified diaphragm comprises the following steps: S1: Preparation of ZIF-67. Etching ZIF-67 with tannic acid to obtain a hollow structure and in-situ selenization to obtain hollow cubic CoSe2. S2: The prepared CoSe2 was immersed in NaBH4 solutions of different concentrations at a mass volume ratio of 1 mg:1 ml for 30 min, washed with deionized water several times, and dried at 60 ° C for 8-16 h to obtain material A; S3: NaH2PO2 and material A in S2 are placed in the upstream and downstream of a tube furnace in a mass ratio of 1:1, respectively, and heated to obtain a P-CS-NaH2PO2 composite material; S4 adding P-CS-NaH2PO2 composite material powder, Super P and PVDF into NMP solvent in proportion to obtain a mixed slurry; S5 coated the slurry on the PP separator, and the material loading was about 0.5 mg / cm 2 , and then dried and cut into discs with a diameter of 19 mm to obtain the modified diaphragm.

2. The lithium-sulfur button cell according to claim 1, characterized in that The positive electrode was prepared by mixing S and carbon nanotubes (CNTs) in a mass ratio of 8:2 and heating at 155°C for 16 h to obtain an S / CNT composite material; adding S / CNT, Super P, and PVDF in a mass ratio of 7:2:1 to an NMP solvent to obtain a slurry; coating the slurry on aluminum foil, placing it in a 50°C oven for 12 h, and cutting it into discs with a diameter of 12 mm.

3. The lithium-sulfur button cell according to claim 1, characterized in that The electrolyte is a 1,3-dioxolane and ethylene glycol dimethyl ether solution containing 0.5 M LiTFSI and LiNO 3 , and the volume ratio of the 1,3-dioxolane to the ethylene glycol dimethyl ether solution is 1:

1.

4. The lithium-sulfur button cell according to claim 1, characterized in that: The preparation method of ZIF-67 in step S1 is as follows: Co(NO3)2·6H2O and hexadecyltrimethylammonium bromide are weighed in a mass ratio of 20:1, added to deionized water, and stirred to obtain solution A; 2-methylimidazole is added to deionized water in a certain proportion, and stirred to obtain solution B; solution A is poured into solution B, and stirred at high speed for 40 minutes to obtain a purple suspension; The product was washed by centrifugation six times with ethanol to obtain a purple substance, which was then dried under vacuum at 60°C to obtain ZIF-67.

5. The lithium-sulfur button cell according to claim 1, characterized in that: Preparation of CoSe2 in step S1: hollow ZIF-67 and selenium powder are placed in a crucible in a mass ratio of 1:3, and heated at 450°C for 2 h under a H2 / Ar protective atmosphere at a heating rate of 2°C / min to obtain CoSe2.

6. The lithium-sulfur button cell according to claim 1, characterized in that The heating system in step S3 is: heating at 300-400° C. for 1.5-3 h under Ar protective atmosphere.

7. The lithium-sulfur button cell according to claim 1, characterized in that: In step S4, the mass ratio of the P-CS-NaH2PO2 composite material powder, Super P and PVDF is 5:4:

1.

8. The lithium-sulfur button cell according to claim 1, wherein The drying temperature in step S5 is 45-60° C., and the drying time is 10-16 h.

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