CN113328201B - Lithium-sulfur battery diaphragm with functional interlayer and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of modification of lithium-sulfur battery diaphragms, and provides a lithium-sulfur battery diaphragm with a functional intermediate layer and a preparation method thereof, wherein a ZIF-8 template is firstly prepared, then in-situ synthesis of ZIF-67 is carried out on the template, then annealing is carried out under the protection of inert atmosphere, metal ions of the prepared precursor are removed by etching with sulfuric acid under high-temperature high-pressure sealing, and potassium hydroxide is used for activation under the protection of inert gas to obtain N/O-nanocages/CNTs, and finally the lithium-sulfur battery diaphragm with the functional intermediate layer is prepared, and the rich hierarchical structure of micropores and mesopores is favorable for ion migration and volume expansion for containing active substances; the N/O double doping has strong chemical affinity to polysulfide, can inhibit shuttle of polysulfide, and the in-situ growth of CNTs on the surface of a main body promotes electron migration, improves reaction kinetics and improves the utilization rate of active substances of the lithium-sulfur battery. The problems of low utilization rate and short cycle life of the existing active substances of the lithium-sulfur battery are effectively solved.

Description

A lithium-sulfur battery separator with functional intermediate layer and preparation method thereof

technical field

The invention belongs to the technical field of lithium-sulfur battery diaphragm modification, and in particular relates to a lithium-sulfur battery diaphragm with a functional intermediate layer and a preparation method thereof.

Background technique

Lithium-sulfur batteries are recognized as one of the lithium secondary battery systems with the most research value and application prospects due to their high material theoretical specific capacity and battery theoretical specific energy, as well as their economical, environmentally friendly, easy-to-obtain, and harmless advantages. one. However, at present, there are problems such as low utilization rate of active materials, low cycle life and poor safety, which seriously restrict the development of lithium-sulfur batteries. Lithium-sulfur batteries use sulfur as the positive electrode and metal lithium as the negative electrode, and the battery is charged and discharged through the rupture and regeneration of sulfur-sulfur bonds. Among them, long-chain polymers with high solubility easily diffuse into the electrolyte, resulting in irreversible capacity decay. In addition, due to the poor electrical conductivity of sulfur, it is not conducive to the capacity of the battery under high current density, and in the process of converting sulfur into polysulfide, the volume expansion will destroy the material framework, resulting in the loss of sulfur element.

As an important component of lithium-sulfur batteries, the separator is used to separate the two poles of the battery, avoid short-circuiting of the battery, and facilitate the transport of free lithium ions between the electrodes. During the discharge process of lithium-sulfur batteries, polysulfides are easily dissolved in the electrolyte, resulting in irreversible battery capacity attenuation, which seriously affects the cycle performance and Coulomb efficiency of lithium-sulfur batteries. However, existing lithium-sulfur battery separators are difficult to suppress the diffusion of polysulfides, resulting in irreversible damage to the sulfur structure of the cathode. The shortcomings of the above-mentioned separators lead to a series of problems such as poor cycle stability and low actual specific capacity of lithium-sulfur batteries. Therefore, it is urgent to develop a lithium-sulfur battery separator that can improve the cycling stability of lithium-sulfur batteries.

SUMMARY OF THE INVENTION

The present invention is carried out in order to solve the above-mentioned problems, and the purpose is to provide a lithium-sulfur battery separator with a functional intermediate layer and a preparation method thereof.

The present invention provides a preparation method of a lithium-sulfur battery separator with a functional intermediate layer, which has the characteristics of including the following steps: Step S1, weigh 5g-15g of Zn(NO ₃ ) ₂ ·6H ₂ O and dissolve it in 100ml In ~400ml methanol, 5g ~ 15g of 2-methylimidazole was weighed and dissolved in 100ml ~ 400ml methanol, the two solutions were mixed to obtain the first mixed product, and the first mixed product was subjected to centrifugal washing to obtain the second mixed product after centrifugal washing. a mixed product, and then the first mixed product after centrifugation and washing is dried to obtain a white powder, which is marked as ZIF-8; in step S2, 0.5g-1g of ZIF-8 and 0.5g-1g of Co(NO ₃ ) ₂ ·6H are weighed ₂ O is placed in 100ml~200mL methanol, marked as solution A, 0.5g~1g of 2-methylimidazole is weighed and dissolved in 50ml~100mL methanol, marked as solution B, and solution A is mixed with solution B to obtain the first solution. The second mixed product is subjected to centrifugal washing to obtain the second mixed product after centrifugal washing, and then the second mixed product after centrifugal washing is dried to obtain a light purple powder, which is marked as ZIF-8@ZIF- 67; Step S3, placing ZIF-8@ZIF-67 in a tube furnace for high-temperature pyrolysis treatment, using an inert atmosphere, and keeping the temperature at 600°C to 1000°C for 1 hour to 5 hours to obtain an intermediate product; Step S4, in At 50℃～150℃, use 1M～5M H ₂ SO ₄ solution to etch the intermediate product. After etching for 10h～24h, black powder is obtained, and the black powder is placed in a tube furnace for high temperature pyrolysis treatment. Using an inert atmosphere, adding potassium hydroxide to activate and keeping at a temperature of 600 ° C ~ 1000 ° C for 0.5 h ~ 2 h to obtain N/O-nano cage/CNT; Step S5, N/O-nano cage/CNT and polyvinylidene fluoride are mixed Ethylene is mixed and ground in a mass ratio of 5:1 to 10:1. The grinding time is 30min to 1.5h. 1mL to 5mL of N-methylpyrrolidone is added dropwise to form a slurry, and then the slurry is applied to a commercial diaphragm. and drying it to obtain a lithium-sulfur battery separator with a functional intermediate layer.

In the preparation method of the lithium-sulfur battery separator with a functional intermediate layer provided by the present invention, it may also have the following characteristics: wherein, in step S1, the drying temperature is 50°C to 150°C, and the drying time is 1 day to 2 days.

The method for preparing a lithium-sulfur battery separator with a functional intermediate layer provided by the present invention may also have the following features: wherein, in step S2, the drying temperature is 50°C to 150°C, and the drying time is 1 day to 2 days.

In the preparation method of the lithium-sulfur battery separator with a functional intermediate layer provided by the present invention, it may also have the following characteristics: wherein, in step S5, the drying temperature is 50°C-100°C, and the drying time is 6h-12h.

The invention also provides a lithium-sulfur battery separator with a functional intermediate layer.

The role and effect of the invention

According to the preparation method of a lithium-sulfur battery separator with a functional intermediate layer involved in the present invention, a ZIF-8 template is firstly prepared, then ZIF-67 is synthesized in-situ on the template, and then under the protection of an inert atmosphere at a certain temperature After annealing, the prepared precursor was etched with sulfuric acid to remove metal ions under the condition of high temperature and high pressure sealing, and finally activated with potassium hydroxide under the protection of inert gas at a certain temperature to obtain N/O-nano cage/CNT. The designed structure of the cage is anchored by carbon nanotubes, which are derived from the coupled structure of ZIF-8@ZIF-67 because ZIF-8@ZIF-67 is a layered structure with abundant microporous and mesoporous structures structure, which is conducive to ion migration and accommodates the volume expansion of active materials, and the double doping of N/O has a strong chemical affinity for polysulfides, which can inhibit the shuttle of polysulfides, so it can avoid the loss of active materials and improve the The utilization rate of the active material of lithium-sulfur battery, thereby improving the service life of lithium-sulfur battery. In addition, the in situ growth of CNTs on the host surface promotes electron transfer and improves reaction kinetics. To sum up, the lithium-sulfur battery separator with a functional intermediate layer prepared by the method for preparing a lithium-sulfur battery separator with a functional intermediate layer involved in the present invention enables the lithium-sulfur battery to have good rate and long cycle performance.

Description of drawings

Fig. 1 is the X-ray (XRD) spectrum of N/O-nano cage/CNT prepared in the embodiment of the present invention 1;

Fig. 2 is the scanning electron microscope (SEM) figure under different wavelengths of N/O-nano cage/CNT prepared in the embodiment of the present invention 1;

Fig. 3 is the cyclic voltammetry (CV) curve of the lithium-sulfur battery separator battery with functional intermediate layer prepared in Example 1 of the present invention and the commercial separator battery prepared in Example 3 at different scan rates;

Fig. 4 is the lithium ion reaction kinetics of the lithium-sulfur battery separator battery with functional intermediate layer prepared in Example 1 of the present invention and the commercial separator battery prepared in Example 3;

Fig. 5 is the lithium-sulfur battery separator battery with functional intermediate layer prepared in Example 1 of the present invention and the commercial separator battery prepared in Example 3 Long cycle performance graphs at different rates; and

Fig. 6 is the impedance test chart of the lithium-sulfur battery separator battery with a functional intermediate layer prepared in Example 2 of the present invention and the commercial separator battery prepared in Example 3 before and after cycling.

Detailed ways

In order to make the technical means, creative features, achievement goals and effects realized by the present invention easy to understand, a lithium-sulfur battery separator with a functional intermediate layer of the present invention and a preparation method thereof are described in detail below in conjunction with the embodiments and the accompanying drawings.

Unless otherwise specified, the raw materials and reagents used in the present invention are all from common commercial sources.

A preparation method of a lithium-sulfur battery separator with a functional intermediate layer provided by the present invention includes the following steps:

Step S1, weigh 5g～15g of Zn(NO ₃ ) ₂ ·6H ₂ O and dissolve in 100ml～400ml of methanol, weigh 5g～15g of 2-methylimidazole and dissolve in 100ml～400ml of methanol, mix the two The solutions are mixed to obtain the first mixed product, the first mixed product is subjected to centrifugal washing to obtain the first mixed product after centrifugal washing, and then the first mixed product after the centrifugal washing is dried to obtain a white powder, which is marked as ZIF-8 ;

In this step, the drying temperature is 50°C to 150°C, and the drying time is 1 day to 2 days.

Step S2, weigh 0.5g～1g of the ZIF-8 and 0.5g～1g Co(NO ₃ ) ₂ ·6H ₂ O into 100ml～200mL methanol, marked as solution A, weigh 0.5g～1g 2- The methylimidazole was dissolved in 50ml to 100mL of methanol, marked as solution B, the solution A was mixed with the solution B to obtain a second mixed product, and the second mixed product was subjected to centrifugal washing to obtain a solution after centrifugal washing. The second mixed product is then dried to obtain a light purple powder, which is labeled as ZIF-8@ZIF-67;

In this step, the drying temperature is 50°C to 150°C, and the drying time is 1 day to 2 days.

Step S3, placing the ZIF-8@ZIF-67 in a tube furnace for high-temperature pyrolysis treatment, using an inert atmosphere, and keeping the temperature at 600°C～1000°C for 1h～5h to obtain an intermediate product;

Step S4, using a 1M-5M H ₂ SO ₄ solution at 50° C. to 150° C. to etch the intermediate product, and after etching for 10 h to 24 h, a black powder is obtained, and the black powder is placed in a tubular Perform high-temperature pyrolysis treatment in a furnace, use an inert atmosphere, add potassium hydroxide for activation, and keep at a temperature of 600 ° C ~ 1000 ° C for 0.5 h ~ 2 h to obtain N/O-nano cage/CNT;

Step S5, the N/O-nano cage/CNT and the polyvinylidene fluoride are mixed and ground in a mass ratio of 5: 1 to 10: 1, the grinding time is 30 min to 1.5 h, and 1 mL to 5 mL of N is added dropwise. -Methylpyrrolidone is prepared into a slurry, and the slurry is then coated on a commercial separator and dried to obtain a lithium-sulfur battery separator (modified separator) with a functional intermediate layer.

In this step, the drying temperature is 50°C to 100°C, and the drying time is 6h to 12h.

Assemble the battery and test: Grind multi-walled carbon nanotubes (MWCNT) and sublimed sulfur at a mass ratio of 1:1 to 1:5 for 0.5h to 1h, then dropwise add 1 to 5mL of carbon disulfide to fully dissolve, and grind for 0.5h ~1h, after fully mixing, transfer it into an ampere tube and seal it in a nitrogen atmosphere, and react at 150°C to 160°C for 8h to 10h to obtain an S/C cathode material. Mix and grind the obtained S/C cathode material with acetylene black and polyvinylidene fluoride in a mass ratio of 8:1:1 until completely mixed, and add 1-5 mL of N-methylpyrrolidone to obtain a black uniform slurry , and then coat it on aluminum foil, put it into a blast drying oven and dry it at 60 °C to obtain the positive electrode piece of the battery, and finally press the positive electrode shell, positive electrode piece, and lithium-sulfur battery separator with a functional intermediate layer in the glove box. (modified separator), lithium sheets, gaskets, shrapnel, and negative electrode shells are assembled in sequence to form a lithium-sulfur battery. The electrochemical performance of the prepared lithium-sulfur battery was tested by the electrochemical workstation and the blue electric test system.

<Example 1>

The present embodiment specifically describes the preparation method of the lithium-sulfur battery separator with the functional intermediate layer, which specifically includes the following steps:

Step S1, take 5g of Zn(NO ₃ ) ₂ ·6H ₂ O and dissolve it in 150ml of methanol, take 6g of 2-methylimidazole and dissolve it in 150ml of methanol, and place these two solutions in a constant temperature water bath (50° C.). ) and stirred for 1 h. Then the two solutions were mixed and stirred for 18h, then centrifuged at 8000r/min for 5min, washed 4 times with methanol, and finally put into a blast drying oven and dried at 80°C for 1 day to obtain a white powder (marked as ZIF-8).

Step S2, take 0.6 g of dry white powder ZIF-8 and 0.5 g of Co(NO ₃ ) ₂ ·6H ₂ O, disperse in 150 mL of methanol and sonicate for 1 h (marked as solution A), 0.6 g of 2-methylimidazole Dissolved in 100 mL of methanol (marked as solution B), poured solution B into solution A, mixed and stirred for 1 h, centrifuged at 8000 r/min for 5 min, washed with methanol 4 times, and finally put it into a blast drying oven Drying at 80°C for 1 day gave a light purple powder (labeled as ZIF-8@ZIF-67).

In step S3, the prepared light purple powder ZIF-8@ZIF-67 is placed in a tube furnace for high-temperature pyrolysis treatment, and an argon atmosphere is used, and the temperature is kept at 700 °C for 2 hours, and the heating rate is 1 °C min ^-1 .

Step S4, using _{2M H2SO4} solution at 100°C to etch the product prepared in step S3, after 12h of etching, black powder is obtained, which is placed in a tube furnace for high temperature pyrolysis treatment, A nitrogen atmosphere was used, potassium hydroxide was added for activation and the temperature was kept at 600 °C for 0.5 h, and the heating rate was 5 °C min ^-1 . Finally, N/O-nanocages/CNTs were obtained.

Step S5, the N/O-nano cage/CNT and polyvinylidene fluoride (PVDF) are mixed and ground at a ratio of 8:1, the grinding time is 1 h, and 2 mL of N-methylpyrrolidone (NMP) is added dropwise to prepare a slurry After 8 hours, a lithium-sulfur battery separator (modified separator) with a functional intermediate layer was obtained.

Assemble the battery and test: Grind multi-walled carbon nanotubes (MWCNT) and sublimated sulfur at a mass ratio of 1:3 for 1 h, then dropwise add 2 mL of carbon disulfide to fully dissolve it, and grind for 1 h. After mixing well, transfer it to a In an ampere tube and sealed in a nitrogen atmosphere, the S/C cathode material was obtained by reacting at 155° C. for 10 hours. The obtained S/C cathode material was mixed and ground with acetylene black and polyvinylidene fluoride in a mass ratio of 8:1:1 until completely mixed, and 2 mL of N-methylpyrrolidone was added to obtain a black uniform slurry. Coat it on aluminum foil, put it into a blast drying oven and dry it at 60°C to obtain the positive electrode piece of the battery, and finally press the positive electrode shell, the positive electrode piece, and the lithium-sulfur battery separator with a functional intermediate layer in the glove box (modified). The lithium-sulfur battery is assembled in the sequence of lithium sheet, gasket, shrapnel, and negative electrode shell. The electrochemical performance of the prepared lithium-sulfur battery was tested by electrochemical workstation and blue electricity test system.

<Example 2>

The present embodiment specifically describes the preparation method of the lithium-sulfur battery separator with the functional intermediate layer, which specifically includes the following steps:

Step S1, take 6g of Zn(NO ₃ ) ₂ ·6H ₂ O and dissolve it in 200ml of methanol, take 8g of 2-methylimidazole and dissolve it in 200ml of methanol, and place these two solutions in a constant temperature water bath (50° C.). ) and stirred for 1 h. Then the two solutions were mixed and stirred for 18h, then centrifuged at 8000r/min for 5min, washed 4 times with methanol, and finally put into a blast drying oven and dried at 80°C for 1 day to obtain a white powder (marked as ZIF-8).

Step S2, take 0.6 g of dry white powder ZIF-8 and 0.7 g of Co(NO ₃ ) ₂ ·6H ₂ O and disperse them in 200 mL of methanol and sonicate for 2 h (marked as solution A), 0.6 g of 2-methylimidazole Dissolved in 100 mL of methanol (marked as solution B), poured solution B into solution A, mixed and stirred for 1 h, centrifuged at 8000 r/min for 5 min, washed with methanol 4 times, and finally put it into a blast drying oven Drying at 80°C for 1 day gave a light purple powder (labeled as ZIF-8@ZIF-67).

In step S3, the prepared light purple powder ZIF-8@ZIF-67 is placed in a tube furnace for high-temperature pyrolysis treatment, and an argon atmosphere is used, and the temperature is kept at 800 °C for 2 hours, and the heating rate is 3 °C min ^-1 .

_In step S4, using 3M _H2SO4 solution at 100°C, the product prepared in step S3 is etched, and after 12h of etching, black powder is obtained, which is placed in a tube furnace for high temperature pyrolysis treatment, A nitrogen atmosphere was used, potassium hydroxide was added for activation and the temperature was kept at 800 °C for 1 h, and the heating rate was 8 °C min ^-1 . Finally, N/O-nanocages/CNTs were obtained.

Step S5, mix and grind N/O-nano-cage/CNT and polyvinylidene fluoride (PVDF) at a ratio of 8:1, the grinding time is 1 h, drop 2 mL of NMP into a slurry, and then apply it to the slurry with a spatula. On the commercial separator, and put it into a blast drying oven to dry at 60° C., and after 8 h, a lithium-sulfur battery separator (modified separator) with a functional intermediate layer was obtained.

Assemble the battery and test: Grind multi-walled carbon nanotubes (MWCNT) and sublimated sulfur at a mass ratio of 1:3 for 1 h, then dropwise add 2 mL of carbon disulfide to fully dissolve it, and grind for 1 h. After mixing well, transfer it to a In an ampere tube and sealed in a nitrogen atmosphere, the S/C cathode material was obtained by reacting at 155° C. for 10 hours. The obtained S/C cathode material was mixed and ground with acetylene black and polyvinylidene fluoride in a mass ratio of 8:1:1 until completely mixed, and 2 mL of N-methylpyrrolidone was added to obtain a black uniform slurry. Coat it on aluminum foil, put it into a blast drying oven and dry it at 60°C to obtain the positive electrode piece of the battery, and finally press the positive electrode shell, the positive electrode piece, and the lithium-sulfur battery separator with a functional intermediate layer in the glove box (modified). The lithium-sulfur battery is assembled in the sequence of lithium sheet, gasket, shrapnel, and negative electrode shell. The electrochemical performance of the prepared lithium-sulfur battery was tested by electrochemical workstation and blue electricity test system.

<Example 3>

Assemble the battery and test: Grind multi-walled carbon nanotubes (MWCNT) and sublimated sulfur at a mass ratio of 1:3 for 1 h, then add 2 mL of carbon disulfide dropwise to fully dissolve it, and grind for 1 h. After mixing well, transfer it to a In an ampere tube and sealed in a nitrogen atmosphere, the S/C cathode material was obtained by reacting at 155° C. for 10 hours. The obtained S/C cathode material was mixed and ground with acetylene black and polyvinylidene fluoride in a mass ratio of 8:1:1 until it was completely mixed, and 2 mL of N-methylpyrrolidone was added to obtain a black uniform slurry. Coat it on aluminum foil, put it into a blast drying oven and dry it at 60°C to get the positive electrode piece of the battery, and finally press the positive electrode shell, positive electrode piece, commercial separator, lithium sheet, gasket, shrapnel in the glove box. Sequential assembly of the negative shells into a lithium-sulfur battery. The electrochemical performance of the prepared lithium-sulfur battery was tested by electrochemical workstation and blue electricity test system.

<Test example>

The N/O-nano-cage/CNT prepared in Example 1 was used with an X-ray diffractometer, and the detection results are shown in FIG. 1 .

FIG. 1 is an X-ray (XRD) pattern of N/O-nanocages/CNTs prepared in Example 1 of the present invention.

As shown in Fig. 1, the peaks of N/O-nanocages/CNTs around 26° and 44° correspond to the (002) and (100) diffractions of low graphitized carbon, which originate from ZIF-8@ZIF-67 carbonization.

The N/O-nano cage/CNT prepared in Example 1 was detected with a scanning electron microscope, and the detection results are shown in Figure 2.

Figure 2(a, b, c) are respectively the scanning electron microscope (SEM) images of the N/O-nano cage/CNT prepared in Example 1 of the present invention at 1 μm, 500 nm and 100 nm.

As shown in Fig. 2(a,b), ZIF-8@ZIF-67 and ZIF-8 exhibit similar rhombic dodecahedron structure and particle size, indicating that the epitaxial growth of ZIF-67 layer is very thin. As shown in Fig. 2(c), the tubular morphology of the nanocages surface can also be found in the high-magnification SEM image, indicating that the synthesized material is indeed N/O-nanocages/CNTs.

The lithium-sulfur battery diaphragm (modified diaphragm) battery with a functional intermediate layer prepared in Example 1 and the commercial diaphragm battery prepared in Example 3 were electrochemically tested with an electrochemical workstation and a blue electricity test system. The results are shown in Figure 3-6.

Figure 3(a) shows the lithium-sulfur battery separator (modified separator) battery with a functional intermediate layer prepared in Example 1 of the present invention and the commercial separator battery prepared in Example 3 at a scan rate of 0.1mV s-1 Figure 3(b) is the cyclic voltammetry (CV) curve of the commercial separator battery prepared in Example 3 at a scan rate of 0.1-0.5mV s-1, Figure 3 (c) is a cyclic voltammetry (CV) diagram of the lithium-sulfur battery separator (modified separator) battery with a functional intermediate layer prepared in Example 1 of the present invention at a scan rate of 0.1-0.5mV s-1.

As shown in Figure 3(a), a reduction peak appears at 2.3 and 2.03V, respectively, and the corresponding processes are the solid-liquid conversion process of cyclic sulfur into long-chain polysulfides and the conversion of long-chain polysulfides into short-chain polysulfides, respectively. Liquid-liquid conversion process of chain polysulfides. An oxidation peak appeared at 2.37V, and the corresponding process was the conversion of short-chain polysulfides to long-chain polysulfides/active material sulfur. For commercial separator cells, a small spike at the oxidation peak position is due to the slow conversion of short-chain polysulfides to long-chain polysulfides. Since the coating of the separator will lead to an increase in the thickness of the film, in order to determine whether the mobility of lithium ions is affected, we carried out a test of the kinetics of the lithium ion reaction, as shown in Fig. 3(b,c), at 0.1- The CV test performed in the scan rate range of 0.5 mV s ^-1 clearly shows that the redox current of the lithium-sulfur battery separator battery with the functional interlayer is larger, which is beneficial to the catalytic conversion of polysulfides in the battery to improve the insulation material. Deposition reduces the polarization voltage.

4 is the lithium ion reaction kinetics of the lithium-sulfur battery separator (modified separator) battery with a functional intermediate layer prepared in Example 1 of the present invention and the commercial separator battery prepared in Example 3.

As shown in Figure 4, the lithium-sulfur battery separator (modified separator) battery with a functional intermediate layer has a relatively obvious improvement in the mobility of lithium ions, because the doping of N/O elements increases the interaction with lithium inside the battery. The adsorption of ions acts as a bridge to a certain level to accelerate the transfer of lithium ions and reduce the internal impedance of the battery to a certain extent.

Figure 5(a) is a graph showing the long-term cycle performance of the lithium-sulfur battery separator (modified separator) battery with a functional intermediate layer prepared in Example 1 of the present invention and the commercial separator battery prepared in Example 3 at 1C , Figure 5(b) is the long cycle performance diagram of the lithium-sulfur battery separator (modified separator) battery with a functional intermediate layer prepared in Example 1 of the present invention at a rate of 2C, and Figure 5(c) is the present invention. The lithium-sulfur battery separator (modified separator) battery with a functional intermediate layer prepared in Example 1 was tested at 0.1C, 0.2C, 0.3C, 0.5C, 1C, 2C, 0.5C, 0.3C and 0.1C. performance test chart.

As shown in Fig. 5(a), the lithium-sulfur battery separator (modified separator) battery with a functional interlayer at 1C has an initial specific capacity of 1000mAh g ^-1 and a specific capacity of 450mAh g ^-1 after 1000 cycles, with each The decay rate of the ring is 0.05%, and the sulfur usage rate of the lithium-sulfur battery separator (modified separator) battery with a functional intermediate layer has reached 59.7%, which has been greatly improved. While the initial specific capacity of the commercial separator battery is 800 mAh g ^-1 , only 400 mAh g ^-1 of specific capacity remains after 500 cycles, with a decay rate of 0.1% per cycle. After that, the long-cycle performance test was carried out at 2C. As shown in Figure 5(b), the lithium-sulfur battery separator (modified separator) battery with a functional intermediate layer has an initial specific capacity of 600mAh g ^-1 at 2C rate, After 1000 cycles, there is still 400mAh g ^-1 specific capacity remaining, and the decay rate per cycle is 0.03%. As shown in Figure 5(c), the performances tested at 0.1, 0.2, 0.3, 0.5, 1, 2, 0.5, 0.3, and 0.1C rates show a great improvement in specific capacity compared to commercial separator batteries. It can be found that the lithium-sulfur battery separator (modified separator) battery with functional interlayer has good rate capability and reversible cycling performance.

Figure 6(a) is a graph of impedance test before cycling between the lithium-sulfur battery separator (modified separator) battery with a functional intermediate layer prepared in Example 2 of the present invention and the commercial separator battery prepared in Example 3. 6(b) is the impedance test diagram of the lithium-sulfur battery separator (modified separator) battery with a functional intermediate layer prepared in Example 2 of the present invention and the commercial separator battery prepared in Example 3 after 200 cycles.

As shown in Fig. 6(a), the lithium-sulfur battery separator (modified separator) battery with a functional interlayer before battery cycling has smaller ohmic resistance and charge transfer resistance, due to the relatively high electrical conductivity of carbon materials, phase Higher charge transfer compared to commercial separators results in reduced overall cell impedance. As shown in Figure 6(b), the electrochemical impedance test was performed after 200 cycles, and the ohmic impedance and charge transfer of both the lithium-sulfur battery separator (modified separator) battery with a functional interlayer and the commercial separator battery could be found. The impedances are reduced because the contact between the interfaces is more compact during the battery cycle, which is conducive to the transfer of charges, and the functional interlayer accelerates the migration of lithium ions to reduce the internal resistance of the battery to a certain extent.

Action and effect of the embodiment

According to the preparation method of a lithium-sulfur battery separator with a functional intermediate layer involved in the above embodiment, a ZIF-8 template is first prepared, then ZIF-67 is synthesized in-situ on the template, and then under the protection of an inert atmosphere at a certain temperature annealed under the condition of high temperature and high pressure, the prepared precursor was etched with sulfuric acid to remove metal ions under the condition of high temperature and high pressure, and finally activated with potassium hydroxide under the protection of inert gas at a certain temperature to obtain N/O-nanocages/CNTs. The designed structure of the nanocages is anchored by carbon nanotubes, which are derived from the coupled structure of ZIF-8@ZIF-67, because ZIF-8@ZIF-67 is a component with abundant microporous and mesoporous structures. The layered structure is conducive to ion migration and accommodates the volume expansion of active materials, and the double doping of N/O has a strong chemical affinity for polysulfides, which can inhibit the shuttle of polysulfides, so it can avoid the loss of active materials, Improve the utilization rate of the active material of the lithium-sulfur battery, thereby improving the service life of the lithium-sulfur battery. In addition, the in situ growth of CNTs on the host surface promotes electron transfer and improves reaction kinetics. To sum up, the lithium-sulfur battery separator with a functional intermediate layer prepared by the method for preparing a lithium-sulfur battery separator with a functional intermediate layer according to the present invention enables the lithium-sulfur battery to have good rate and long cycle performance.

The above-mentioned embodiments are preferred cases of the present invention, and are not intended to limit the protection scope of the present invention.

Claims (5)

1. a preparation method of the lithium-sulfur battery separator with functional intermediate layer, is characterized in that, comprises the following steps: Step S1, weigh 5g～15g of Zn(NO ₃ ) ₂ ·6H ₂ O and dissolve in 100ml～400ml of methanol, weigh 5g～15g of 2-methylimidazole and dissolve in 100ml～400ml of methanol, mix the two The solution is mixed to obtain a first mixed product, the first mixed product is subjected to centrifugal washing to obtain the first mixed product after centrifugal washing, and then the first mixed product after centrifugal washing is dried to obtain a white powder, which is marked as ZIF -8; Step S2, weigh 0.5g～1g of the ZIF-8 and 0.5g～1g Co(NO ₃ ) ₂ ·6H ₂ O in 100ml～200mL methanol, marked as solution A, weigh 0.5g～1g 2- Methylimidazole is dissolved in 50ml to 100mL of methanol, marked as solution B, the solution A is mixed with the solution B to obtain a second mixed product, and the second mixed product is subjected to centrifugal washing to obtain a centrifugally washed solution. The second mixed product, and then the second mixed product after the centrifugal washing is dried to obtain a light purple powder, which is marked as ZIF-8@ZIF-67; Step S3, placing the ZIF-8@ZIF-67 in a tube furnace for high-temperature pyrolysis treatment, using an inert atmosphere, and keeping the temperature at 600°C～1000°C for 1h～5h to obtain an intermediate product; Step S4, using a 1M-5M H ₂ SO ₄ solution at 50° C. to 150° C. to etch the intermediate product, and after etching for 10 h to 24 h, a black powder is obtained, and the black powder is placed in a tubular Perform high-temperature pyrolysis treatment in a furnace, use an inert atmosphere, add potassium hydroxide for activation, and keep at a temperature of 600 ° C ~ 1000 ° C for 0.5 h ~ 2 h to obtain N/O-nano cage/CNT; Step S5, mixing and grinding the N/O-nano cage/CNT and polyvinylidene fluoride in a mass ratio of 5:1-10:1, the grinding time is 30min-1.5h, and dripping 1mL-5mL of N -Methylpyrrolidone is prepared into a slurry, and the slurry is then coated on a commercial separator and dried to obtain a lithium-sulfur battery separator with a functional intermediate layer. 2. the preparation method of the lithium-sulfur battery separator with functional intermediate layer according to claim 1, is characterized in that: Wherein, in step S1, the drying temperature is 50°C to 150°C, and the drying time is 1 day to 2 days. 3. the preparation method of the lithium-sulfur battery separator with functional intermediate layer according to claim 1, is characterized in that: Wherein, in step S2, the drying temperature is 50°C to 150°C, and the drying time is 1 day to 2 days. 4. the preparation method of the lithium-sulfur battery separator with functional intermediate layer according to claim 1, is characterized in that: Wherein, in step S5, the drying temperature is 50°C-100°C, and the drying time is 6h-12h. 5. A lithium-sulfur battery separator with a functional intermediate layer, wherein the lithium-sulfur battery separator with a functional intermediate layer is composed of the lithium-sulfur battery with a functional intermediate layer according to any one of claims 1-4. The preparation method of the diaphragm is prepared.

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