阅读说明：本技术 一种嵌锂mof/石墨烯复合修饰的功能隔膜及制备方法 (Lithium-intercalated MOF/graphene composite modified functional membrane and preparation method thereof ) 是由 熊杰 周酩杰 胡音 雷天宇 陈伟 胡安俊 王显福 于 2021-08-16 设计创作，主要内容包括：本发明提供的一种嵌锂MOF/石墨烯复合修饰的功能隔膜及制备方法,属于锂硫电池隔膜领域,包括依次设置的隔膜、由嵌锂MOF组成的致密修饰层和石墨烯导电修饰层；嵌锂MOF为锂离子嵌入MOF内部的颗粒,通过将MOF与LiTFSI在无水乙醇中搅拌12h,经离心清洗、烘干后得到；嵌锂MOF与PVDF分散至溶剂中,抽滤至隔膜上得到致密修饰层。高比表面积的MOF可有效吸附LiPSs,致密的MOF修饰层也进一步抑制穿梭效应,提高电池的容量和循环稳定性；利用MOF内部微孔,通过嵌锂处理构建锂离子传输通道,显著提高致密修饰层的锂离子通过性,提升电池的倍率性能；高导电性的石墨烯导电修饰层可提高LiPSs利用率。(The invention provides a lithium-intercalated MOF/graphene composite modified functional diaphragm and a preparation method thereof, belonging to the field of lithium-sulfur battery diaphragms and comprising a diaphragm, a compact modification layer and a graphene conductive modification layer which are sequentially arranged, wherein the compact modification layer consists of lithium-intercalated MOF; the lithium intercalated MOF is particles with lithium ions intercalated into the MOF, and is obtained by stirring the MOF and LiTFSI in absolute ethyl alcohol for 12 hours, centrifuging, cleaning and drying; and dispersing the lithium-intercalated MOF and the PVDF into a solvent, and performing suction filtration on the membrane to obtain a compact modified layer. The MOF with high specific surface area can effectively adsorb LiPSs, the shuttle effect is further inhibited by the compact MOF modification layer, and the capacity and the cycle stability of the battery are improved; the lithium ion transmission channel is constructed by utilizing the internal micropores of the MOF through lithium embedding treatment, so that the lithium ion permeability of the compact modification layer is obviously improved, and the rate capability of the battery is improved; the graphene conductive modification layer with high conductivity can improve the utilization rate of LiPSs.)

1. A functional diaphragm compositely modified by lithium intercalation MOF/graphene is characterized by comprising a diaphragm, a compact modification layer and a graphene conductive modification layer, wherein the compact modification layer is composed of the lithium intercalation MOF; the lithium intercalated MOF is a particle with lithium ions intercalated into the MOF; the loading ratio of the compact modification layer to the graphene conductive modification layer in the functional diaphragm is 4: 1-1: 4, and the thickness of the compact modification layer is larger than 1 mu m.

2. The lithium-intercalated MOF/graphene composite modified functional membrane according to claim 1, wherein the thickness of the graphene conductive modification layer is 15-30 μm.

3. The lithium intercalated MOF/graphene composite modified functional membrane according to claim 1, wherein the MOF is ZIF-67 or ZIF-8.

4. A preparation method of a functional membrane compositely modified by lithium intercalated MOF/graphene is characterized by comprising the following steps:

step 1: mixing the MOF and the LiTFSI according to the mass ratio of 300: (718-1436) and stirring for 12 hours to obtain a dispersion liquid A; centrifuging and cleaning the dispersion liquid A for many times, and drying to obtain the lithium-intercalated MOF; wherein the concentration of the MOF in the dispersion liquid A is 0.1-0.3 g/mL;

step 2: adding lithium-intercalated MOF and PVDF into DMF or NMP according to the mass ratio of 2:1, and carrying out ultrasonic treatment to obtain a dispersion liquid B; taking 1-4 mL of the dispersion liquid B, and carrying out suction filtration on the membrane to obtain a lithium-intercalated MOF modified membrane; wherein the concentration of lithium-intercalated MOF in the dispersion liquid B is 0.5 mg/mL;

and step 3: adding rGO and PVDF into DMF or NMP according to the mass ratio of 1:1, and performing ultrasonic treatment to obtain a dispersion liquid C; taking 1-4 mL of dispersion liquid C, carrying out suction filtration on the lithium-intercalated MOF modified membrane obtained in the step 2, and drying to obtain a lithium-intercalated MOF/graphene composite modified functional membrane; wherein the concentration of rGO in the dispersion C is 0.5 mg/mL.

5. The preparation method of the lithium-intercalated MOF/graphene composite modified functional membrane according to claim 4, wherein the centrifugal cleaning in the step 1 is carried out for 3 times by using absolute ethyl alcohol at a rotating speed of 6000-10000 rpm for 10-15 min.

6. The preparation method of the lithium-intercalated MOF/graphene composite modified functional membrane according to claim 4, wherein the drying conditions in the step 1 and the step 3 are both vacuum drying at 80-100 ℃ for 12-24 h.

7. The preparation method of the lithium-intercalated MOF/graphene composite modified functional membrane according to claim 4, wherein the duration of the ultrasonic treatment in the step 2 and the step 3 is 1-3 h.

8. The preparation method of the lithium-intercalated MOF/graphene composite modified functional membrane according to claim 4, characterized in thatAnd the suction filtration area in the step 2 and the step 3 is 10-30 cm²。

Technical Field

The invention belongs to the field of lithium-sulfur battery diaphragms, and particularly relates to a lithium-intercalated MOF/graphene composite modified functional diaphragm and a preparation method thereof.

Background

Long-chain polysulfide compounds (LiPSs) generated in the discharging process of the lithium-sulfur (Li-S) battery have strong solubility, and can cause a shuttle effect to cause rapid capacity attenuation. Aiming at the challenge, the polar material with chemical adsorption effect on the LiPSs is introduced to be used as the diaphragm modification layer, so that the diffusion of the LiPSs can be effectively reduced, and the battery performance is improved. In addition, the polar adsorption material and the conductive carbon material are combined to form a composite modification layer, so that the conversion of adsorbed LiPSs can be accelerated, and the battery capacity is further improved. However, although the dense modification layer formed by the polar material can effectively block the LiPSs, the dense modification layer can also slow down Li lithium ion transmission, which causes a significant capacity reduction of the battery at high rate. Therefore, it is necessary to develop a new strategy to obtain a separator modification layer having good lithium ion transport ability and LiPSs blocking effect.

Metal Organic Frameworks (MOFs) have gained a breakthrough in various research areas as an emerging porous material. In Li-S batteries, the metal active sites in the MOF have a strong polar adsorption effect on the LiPSs. In addition, the MOF particles have extremely high specific surface area, which is beneficial to fully exposing the adsorption active sites, and therefore, the MOF particles are used as a membrane modification layer to block the shuttling effect of LiPSs. However, because a dense modification layer formed by the MOF particles has an inhibition effect on lithium ion transport, the rate performance of the Li-S battery based on the MOF modified membrane is not ideal enough, and the application potential of the MOF material in the Li-S battery is yet to be explored.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a lithium-intercalated MOF/graphene composite modified functional diaphragm and a preparation method thereof, which are used for pre-intercalating lithium ions into the internal pores of the MOF to form a transmission channel, so that the shuttle effect is inhibited and the rapid transmission of the lithium ions in a battery is ensured.

A functional diaphragm compositely modified by lithium intercalation MOF/graphene is characterized by comprising a diaphragm, a compact modification layer and a graphene conductive modification layer, wherein the compact modification layer is composed of the lithium intercalation MOF; the lithium intercalation MOF is particles with lithium ions intercalated into the MOF and is obtained by carrying out pre-intercalation treatment on the MOF; the loading ratio of the compact modification layer to the graphene conductive modification layer in the functional diaphragm is 4: 1-1: 4, and the thickness of the compact modification layer is larger than 1 mu m.

Further, the thickness of the graphene conductive modification layer is 15-30 μm.

Further, the MOF is ZIF-67 or ZIF-8.

Further, the lithium intercalated MOF is 900nm in size.

Further, when the functional membrane is applied to a lithium-sulfur battery, the side of the functional membrane with the lithium intercalation MOF/graphene composite modification faces to the positive electrode.

A method for preparing a lithium-intercalated MOF/graphene composite modified functional membrane is characterized by comprising the following steps:

step 1: mixing MOF and lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) according to a mass ratio of 300: (718-1436) and stirring for 12 hours to obtain a dispersion liquid A; centrifuging and cleaning the dispersion liquid A for many times, and drying to obtain lithium-intercalated MOF (Li-MOF); wherein the concentration of the MOF in the dispersion liquid A is 0.1-0.3 g/mL;

step 2: adding the lithium-intercalated MOF and polyvinylidene fluoride (PVDF) into N, N-Dimethylformamide (DMF) or N-methylpyrrolidone (NMP) according to the mass ratio of 2:1, and carrying out ultrasonic treatment to obtain a dispersion liquid B; then, taking 1-4 mL of the dispersion liquid B, and carrying out suction filtration on the membrane to obtain a lithium-intercalated MOF modified membrane; wherein the concentration of lithium-intercalated MOF in the dispersion liquid B is 0.5 mg/mL;

and step 3: adding reduced graphene oxide (rGO) and PVDF into DMF or NMP according to the mass ratio of 1:1, and performing ultrasonic treatment to obtain a dispersion liquid C; then, taking 1-4 mL of dispersion liquid C, carrying out suction filtration on the lithium intercalation MOF modified membrane obtained in the step 2, and drying to obtain a lithium intercalation MOF/graphene composite (Li-MOF/rGO) modified functional membrane; wherein the concentration of rGO in the dispersion C is 0.5 mg/mL.

Further, the centrifugal cleaning in the step 1 is carried out for 3 times by using absolute ethyl alcohol and carrying out centrifugal cleaning for 10-15 min at the rotating speed of 6000-10000 rpm.

Further, the drying conditions in the step 1 and the step 3 are vacuum drying at 80-100 ℃ for 12-24 h.

Further, the duration of ultrasonic treatment in the step 2 and the step 3 is 1-3 h.

Further, the suction filtration area in the step 2 and the step 3 is 10-30 cm²。

Compared with the prior art, the invention has the following beneficial effects:

1. the invention provides a lithium-intercalated MOF/graphene composite modified functional diaphragm which is obtained by sequentially preparing a compact modified layer consisting of lithium-intercalated MOF and a graphene conductive modified layer on the surface of the diaphragm; the specific surface area of the MOF is extremely high, fully exposed active metal sites can effectively adsorb LiPSs, and meanwhile, a compact MOF modification layer can further inhibit a shuttle effect, so that the capacity and the cycle stability of the battery are improved; the lithium ion transmission channel is constructed by utilizing the internal micropores of the MOF through lithium embedding treatment, so that the lithium ion permeability of the compact modification layer can be obviously improved, and the rate capability of the battery is improved; in addition, the graphene conductive modification layer tightly attached to the compact modification layer can enhance the conductivity of the functional diaphragm, promote the adsorption-blocked LiPSs to further discharge, and improve the utilization rate of the LiPSs;

2. the preparation process of the functional diaphragm compositely modified by the lithium-intercalated MOF/graphene has the advantages of simplicity and convenience and easiness in large-scale production, is suitable for application scenes of button batteries and soft package batteries, and can remarkably improve the capacity, the multiplying power and the cycling stability of Li-S batteries.

Drawings

FIG. 1 is an SEM picture of Li-MOF obtained in example 1 of the present invention;

FIG. 2 is a representation of Li-MOF obtained in example 1 of the present invention; wherein (a) is an XRD pattern of Li-MOF, MOF and LiTFSI; (b) the Raman test chart of Li-MOF, MOF and LiTFSI is shown; (c) BET test patterns of Li-MOF and MOF are shown; (d) is a graph comparing the pore size distribution of Li-MOF and MOF;

FIG. 3 is an SEM image of a dense modification layer on the surface of a membrane obtained in example 1 of the present invention;

FIG. 4 is an SEM image of a lithium-intercalated MOF/graphene composite modified functional membrane obtained in example 1 of the present invention;

FIG. 5 is a sectional SEM image of a lithium-intercalated MOF/graphene composite modified functional membrane obtained in example 1 of the invention;

fig. 6 is a graph comparing constant current discharge rate and cycle performance of Li-S batteries obtained in example 1, example 2, example 3 and comparative example of the present invention.

Detailed Description

The technical scheme of the invention is detailed below by combining the accompanying drawings and the embodiment.

Example 1

The embodiment prepares a lithium-intercalated MOF/graphene composite modified functional membrane, and specifically comprises the following steps:

step 1: 0.87g of Co (NO)₃)₂·6H₂Adding O and 1.97g of 2-methylimidazole into 50mL of methanol according to the mass ratio of 145:493, and stirring for 12 hours to obtain a reaction product; centrifugally cleaning the reaction product with deionized water for 2 times, centrifugally cleaning with absolute ethyl alcohol for 2 times to obtain a precipitate, and then drying in vacuum at 80 ℃ for 12 hours to obtain MOF ZIF-67;

step 2: adding 3g of ZIF-67 and 7.18g of LiTFSI into 10mL of absolute ethanol, and stirring for 12 hours to obtain a dispersion A; centrifugally cleaning the dispersion liquid A for 3 times by using absolute ethyl alcohol, and then drying for 12h in vacuum at 80 ℃ to obtain lithium-intercalated MOF (Li-MOF);

step 3, adding 50mg of the lithium intercalation MOF and 25mg of PVDF into 100mL of DMF, and carrying out ultrasonic treatment for 1h to obtain a dispersion liquid B; then 2mL of dispersion B was filtered under suction to an area of 13.8cm²To obtain a lithium-intercalated MOF-modified separatorA film;

step 4, adding 50mg of rGO and 50mg of PVDF into 100mL of DMF, and carrying out ultrasonic treatment for 1h to obtain a dispersion liquid C; and then, carrying out suction filtration on 2mL of dispersion liquid C to the membrane modified by the lithium intercalation MOF obtained in the step 3, and finally, carrying out vacuum drying for 12h at 80 ℃ to obtain the functional membrane modified by the Li-MOF/rGO composite.

A series of representations are made on the Li-MOF obtained in step 2 of the present example, and an SEM image is shown in FIG. 1, which shows that the Li-MOF has a regular rhombic dodecahedron structure; as can be seen from the XRD patterns of Li-MOF with MOF and LiTFSI shown in fig. 2(a), no LiTFSI diffraction peak was observed in Li-MOF, indicating that the Li-MOF surface does not contain unwashed LiTFSI precursor, and Li is present only inside MOF; as shown in FIG. 2(b), it is understood from the Raman test chart of Li-MOF, MOF and LiTFSI that the MOF is located at 679cm^-1The imidazole ring of (1) shifts to 684cm after lithium intercalation^-1Indicating that the atomic distance of Li-MOF is increased, proving that Li is successfully embedded into MOF; the BET test plots of Li-MOF and MOF shown in FIG. 2(c) show that the specific surface area of the internal micropores of MOF is reduced after intercalation of Li, and also demonstrate that Li intercalation occupies the internal space; according to the comparison graph of the internal pore size distribution of MOF before and after lithium intercalation calculated according to the BET test result, as shown in FIG. 2(d), it can be known that the total volume of micropores 1nm after Li intercalation is reduced, which indicates that the internal space of MOF is reduced after Li intercalation.

The SEM image of the compact modification layer on the surface of the separator obtained in step 3 of this example is shown in fig. 3, which shows that the compact modification layer composed of Li-MOF is relatively compact.

The SEM image and the cross-sectional SEM image of the Li-MOF/rGO composite modified functional membrane obtained in this example are shown in fig. 4 and 5, respectively, and it can be seen that the dense modification layer is dense, the thickness is about 1 μm, and the graphene conductive modification layer is fluffy, and the thickness is 17.3 μm.

The Li-MOF/rGO composite modified functional diaphragm obtained in the embodiment is used for assembling a button battery, lithium metal is used as a negative electrode, the sulfur content is 66.7%, and the sulfur load is 1.2mg/cm²The C/S composite material is a positive electrode, one side of the functional diaphragm, which is compositely modified by Li-MOF/rGO, faces the positive electrode, and constant-current charge-discharge multiplying power cycle test is carried out.

Example 2

In the embodiment, a lithium-intercalated MOF/graphene composite modified functional membrane is prepared, and compared with the step 1, the difference is only that the volume of the dispersion liquid B which is filtered on the membrane in the step 3 is adjusted from 2mL to 4 mL; the remaining steps were unchanged.

The functional diaphragm compositely modified by the lithium-intercalated MOF/graphene obtained in the embodiment is used for assembling a button battery, lithium metal is used as a negative electrode, the sulfur content is 66.7%, and the sulfur load is 1.2mg/cm²The C/S composite material is a positive electrode, one side of the functional diaphragm, which is subjected to lithium-intercalated MOF/graphene composite modification, faces the positive electrode, and constant-current charge-discharge multiplying power cycle test is carried out.

Example 3

In the present example, a lithium intercalation MOF/graphene composite modified functional membrane was prepared, and the difference between the steps of the method and the example 1 is only that the volume of the dispersion C which was suction filtered onto the lithium intercalation MOF modified membrane in the step 4 was adjusted from 2mL to 1 mL; the remaining steps were unchanged.

The functional diaphragm compositely modified by lithium-intercalated MOF/graphene obtained in the embodiment is used for assembling a soft package battery, lithium metal is used as a negative electrode, the sulfur content is 66.7%, and the sulfur load is 1.2mg/cm²The C/S composite material is a positive electrode, one side of the functional diaphragm, which is subjected to lithium-intercalated MOF/graphene composite modification, faces the positive electrode, and constant-current charge-discharge multiplying power cycle test is carried out.

Comparative example

The comparative example used an unmodified separator to assemble a coin cell, and lithium metal as the negative electrode, sulfur content 66.7%, and sulfur loading 1.2mg/cm²The C/S composite material is used as the anode, and constant-current charge-discharge multiplying power cycle test is carried out.

A comparative graph of constant current discharge rate and cycle performance of Li-S coin cells obtained in inventive example 1, example 2, example 3 and comparative example is shown in fig. 6. The Li-S battery obtained in example 1 has a capacity of 1374mAh/g at a current density of 0.2C, the capacity is kept at 742mAh/g after the current is increased to 2C, the current density returns to 0.5C after the battery is cycled for 10 circles under a large current, and the battery capacity is restored to 956mAh/g, so that good rate reversibility is shown. The Li-S battery obtained in example 2 has a capacity of 987mAh/g at a current density of 0.2C, the capacity is kept at 520mAh/g after the current is increased to 2C, the current density returns to 0.5C after the battery is cycled for 10 circles under a large current, and the battery capacity is restored to 728mAh/g, so that good rate reversibility is shown. The Li-S battery obtained in example 3 has a capacity of 1008mAh/g at a current density of 0.2C, the capacity is kept at 504mAh/g after the current is increased to 2C, the current density returns to 0.5C after the battery is circulated for 10 circles under a large current, and the battery capacity is restored to 632mAh/g, so that good rate reversibility is shown. The Li-S battery obtained in the comparative example has the capacity of only 691mAh/g at the current density of 0.2C, the capacity of only 353mAh/g is remained after the current is increased to 2C, the battery capacity is obviously lower than that of the Li-S button battery with the functional diaphragm embedded with the lithium MOF/graphene composite modification, the current density returns to 0.5C again after 10 cycles of circulation under the large current, the battery capacity returns to 521mAh/g, and the poor rate reversibility is also shown. In conclusion, the rate performance of the Li-S battery using the lithium-intercalated MOF/graphene composite modified diaphragm is obviously superior to that of the Li-S battery using a common diaphragm, and the lithium-intercalated MOF/graphene composite modified diaphragm has an adsorption effect on polysulfide, can inhibit a shuttle effect, improves the lithium ion transmission performance of the battery, reduces polarization under high rate, and can obviously improve the rate and cycle performance of the Li-S battery.