Preparation method and use of graphite-metal organic framework (MOF) composite

Abstract

A preparation method for and application of a composite material containing graphite and MOF. The preparation method comprises: adding an amino-containing organic substance into a mixed solution, perf

Description

20 09 24 TECHNICAL FIELD

[0001] The present disclosure belongs to the field of batten' materials, and specifically relates to a preparation method and use of a graphite-metal organic framework (MOF) composite. BACKGROUND

[0002] With the advancement of internet technology, the use of more and more technical applications relies on electronic devices. The use of electronic devices requires lithium batteries with high capacity and convenient use for continuous operation. In addition, with the large-scale use of electric vehicles and other electric tools promoted by various policies in recent years, lithium batteries have become an indispensable device in social development from all walks of life to daily life. At present, anode materials in lithium-ion batteries (LIBs) mainly include: carbons, such as graphite, soft carbon, and hard carbon; or new electrode materials, such as silicon-carbon anodes or transition metal oxides. As tire market requirements on batten capacity tend to become higher and higher, LIBs with traditional anodes can no longer meet current requirements. In view of this, the preparation of new materials and use thereof in LIBs has become a research hotspot.

[0003] MOFs are crystalline frameworks with intramolecular pores, which are formed by self-assembly of metal ions or clusters with organic ligands via coordination bonds under specified conditions. This type of materials has large specific surface area (SSA) and adjustable pore size and shape, and is easy to modify. Proton-conducting and electron-conducting MOFs have shown potential application value in fuel cells, electrocatalysis, LIBs, supercapacitors, and other fields. MOFs have attracted widespread attention due to having a unique channel structure and containing transition metal elements. An electrode with MOF as an active material or as an active material carrier has been successfully prepared, and an electrode that has an active material or active material carrier prepared with MOF as a precursor has also been prepared. However, MOF, when serving as an electrode, shows slightly-lower conductivity than other electrode materials. Moreover, a preparation process of the MOF itself is relatively-complicated, which affects the morphology controllability of the MOF, makes the MOF have poor stability, and limits the wide application of MOF in electrode materials. 20 09 24

[0004] So far, the use of various MOFs as anodes for lithium batteries has been reported. However, most MOFs show the disadvantage of low capacity when used as anodes for lithium batteries. Therefore, it is of great significance to find a composite with stable structure, large SSA, wide application range, and greatly-improved charge and discharge coulombic efficiency and cycling performance. SUMMARY

[0005] The present disclosure is intended to provide a preparation method and use of a graphite-MOF composite. The composite prepared by the preparation method of the present disclosure has prominent structural stability. The composite, when used in an anode for a lithium battery, can eliminate the volume expansion effect of the lithium battery during a charging and discharging process caused by the structural collapse of an anode material due to the lithium insertion-deinsertion cycle of the lithium batten during the charging and discharging process, thereby improving the capacity and other electrochemical properties.

[0006] To achieve the above objective, the present disclosure adopts the following technical solutions:

[0007] The present disclosure provides a preparation method of a graphite-MOF composite, including the following steps:

[0008] (1) adding an amino-containing organic substance to a mixed liquid, stirring, stirring at an increased speed, adding a titanium-contaming coupling agent, and continuing stirring to obtain a suspension;

[0009] (2) subjecting the suspension to a solvothermal reaction and filtration, washing a resulting filter cake alternately with organic solvents, and conducting extraction to obtain an MOF; and

[0010] (3) grinding graphite into a powder, mixing the powder with an alcohol, shaking, adding the MOF, and continuing shaking; allowing a resulting mixture to react under reflux and then to stand, and centrifuging a resulting system; and drying a resulting precipitate to obtain the graphite-MOF composite; wherein in step (1), the mixed liquid may be obtained by mixing AA'-dimcthylfomiamidc (DMF) and methanol in a mass ratio of l:(6-9); the amino-containing organic substance may be 2-aminoterephthalic acid; a mass ratio of the amino-containing organic substance to the mixed 20 09 24 liquid is l:(3-6); the titanium-containing coupling agent may be tetrabutyl titanate (TBT); and a mass ratio of the mixed liquid to the titanium-containing coupling agent may be 1: (15-35);

[0011] in step (2), the organic solvents may be DMF and methanol.

[0012] Preferably, the DMF and methanol may both be in an anhydrous state.

[0013] Preferably, the DMF may be distilled out at 50°C to 60°C; and the methanol may be distilled out at 55°C to 65°C.

[0014] Preferably, in step (1), the stirring may be first conducted for 10 min to 30 min at a temperature of 15°C to 35°C and a stirring speed of 500 r / min to 800 r / min.

[0015] Preferably, in step (1), the stirring at an increased speed may be conducted at 1,000 r / min to 1,500 r / min, and then the stirring may be further conducted for 10 min to 30 min.

[0016] More preferably, in step (1), a mass ratio of the mixed liquid to the titanium-containing coupling agent may be 1:(20-30).

[0017]

[0018] Preferably, in step (2), the washing may be conducted alternately with DMF and methanol 3 to 5 times.

[0019] Preferably, in step (2), the solvothermal reaction may be conducted at 130°C to 150°C for 24 h to 72 h.

[0020] Preferably, in step (2), the extraction may be conducted with a Soxhlet extractor.

[0021] Preferably, in step (3), the graphite may be ground into a powder of 100 to 200 mesh.

[0022] Preferably, in step (3), the alcohol may be anhydrous methanol.

[0023] Preferably, in step (3), a mass ratio of the graphite to the alcohol may be 1:(10-20).

[0024] More preferably, in step (3), a mass ratio of the graphite to the alcohol may be 1:(15-20).

[0025] Preferably, in step (3), a mass ratio of the MOF to the alcohol may be 1:(10-20).

[0026] More preferably, in step (3), a mass ratio of the MOF to the alcohol may be 1:(15-20).

[0027] Preferably, in step (3), the shaking may refer to ultrasonic shaking; and the ultrasonic shaking may be first conducted for 20 min to 40 min and further conducted for 20 min to 40 min.

[0028] Preferably, in step (3), the resulting mixture may react under reflux at 60°C to 70°C for 12 h to 18 h; and the standing may be conducted for 12 h to 18 h.

[0029] The present disclosure also provides a graphite-MOF composite prepared by the preparation method described above, and the graphite-MOF composite has a specific capacity of 460 20 09 24 mAh / g to 495 mAh / g, a porosity of 32% to 37%, and an SSA of 2.7 m2 / g to 3.5 m2 / g.

[0030] The present disclosure also provides a negative electrode sheet, including the graphite-MOF composite described above.

[0031] Hie present disclosure also provides a preparation method of the negative electrode sheet, including the following steps:

[0032] mixing the graphite-MOF composite with acetylene black, and conducting ball-milling to obtain a mixture; mixing the mixture, PVDF, and N-methylpyrrolidone (NMP) to obtain a slurry-; and coating and drying the slurry to obtain the negative electrode sheet.

[0033] Preferably, a weight ratio of the graphite-MOF composite to the acetylene black may be 1:(0.1-0.3).

[0034] Preferably, the ball-milling may be conducted for 10 min to 20 min at a rotational speed of 3,000 r / min to 6,000 r / min.

[0035] Preferably, the mixture, PVDF, and NMP may have a mass ratio of 1:(0.1-0.15):(0.1-0.5).

[0036] The present disclosure also provides a battery including the negative electrode sheet described above.

[0037] Advantages of the present disclosure:

[0038] 1. The present disclosure uses the prepared graphite-MOF composite (graphite-coated MOF) as a basic structure for anode materials, which exhibits prominent structural stability. The composite, when used in an anode for a lithium battery, can eliminate the volume expansion effect of the lithium battery- during a charging and discharging process caused by the structural collapse of an anode material due to the lithium insertion-deinsertion cycle of the lithium battery' during the charging and discharging process (volume expansion will lead to the collapse of a material structure and the deterioration of electrochemical properties), thereby improving the capacity and other electrochemical properties.

[0039] 2. The composite designed in the present disclosure not only exhibits better charge and discharge capacity and conductivity than graphite, but also has the excellent structural stability of MOF.

[0040] 3. The present disclosure introduces NFb’ into an MOF, which not only enhances the electron density of a material such that the conductivity of the material is increased to some extent, but also provides lithium insertion sites such that the charge and discharge capacity of the material is 4 20 09 24 significantly increased. The composite of the present disclosure has an initial specific discharge capacity as high as 492.3 mAh / g and a capacity- retention as high as 96.6%. BRIEF DESCRIPTION OF DRAWINGS

[0041] FIG. 1 is an X-ray diffraction (XRD) pattern of the graphite-MOF composite prepared in Example 1; and

[0042] FIG. 2 is a transmission electron microscopy (TEM) image of the graphite-MOF composite prepared in Example 1. DETAILED DESCRIPTION

[0043] In order to have a thorough understanding of the present disclosure, preferred experimental schemes of the present disclosure are described below with reference to examples to further illustrate the characteristics and advantages of the present disclosure. Any change or modification made without departing from the subject of the present disclosure can be understood by those skilled in the art. The protection scope of the present disclosure is determined by the claims.

[0044] If no specific conditions arc specified in the examples of the present disclosure, conventional conditions or the conditions recommended by a manufacturer will be adopted. All of the raw materials, reagents, or the like which are not specified with manufacturers are conventional commercially-available products.

[0045] Example 1

[0046] A preparation method of a graphite-MOF composite was provided in this example, including the following steps:

[0047] (1) anhydrous DMF and anhydrous methanol were distilled out at 50°C and 55°C, respectively, and then mixed in a ratio of 1:6 to obtain a mixed liquid;

[0048] (2) 2-aminoterephthalic acid was added in a mass-to-vol time ratio of 1:3, and a resulting mixture was stirred for 10 min at a stirring speed of 500 r / min and a temperature of 15°C; and the stirring speed was increased to 1,000 r / min, then TBT was added in a volume ratio of 1:15, and a resulting mixture was further stirred for 10 min to obtain a suspension;

[0049] (3) the suspension was transferred to a dry hydrothermal reactor, and a solvothermal reaction was conducted at 130°C for 24 h; then a product of the solvothermal reaction was filtered 20 09 24 out and washed alternately with anhydrous DMF and anhydrous methanol, each 3 times; and extraction was conducted with a Soxhlet extractor to obtain a white-solid MOF; and

[0050] (4) graphite was ground into a powder (which was sieved through a 100-mesh sieve), the powder was mixed with anhydrous methanol in a mass-volume ratio of 1:10, and a resulting mixture was ultrasonically shaken for 20 min; then the white-solid MOF was added in a mass-volume ratio of 1:10, and a resulting mixture was further ultrasonically shaken for 20 min; a resulting mixture reacted under reflux at 60°C for 12 h, then stood for 12 h, and then centrifuged; and a resulting filter cake was dried to obtain the graphite-MOF composite (graphite-coated MOF).

[0051] A preparation method of a negative electrode sheet was provided in this example, including the following steps: the graphite-MOF composite was mixed with acetylene black in a weight ratio of 1:0.1, and a resulting mixture was then ball-milled at 3,000 r / min for 10 min; a resulting mixture powder was mixed with PVDF and NMP in a ratio of 1:0.1:0.1 to obtain a slurry; and the slurry- was coated and dried to obtain the negative electrode sheet.

[0052] Example 2

[0053] A preparation method of a graphite-MOF composite was provided in this example, including the following steps:

[0054] (1) anhydrous DMF and anhydrous methanol were distilled out at 50°C and 60°C, respectively, and then mixed in a ratio of 1:7 to obtain a mixed liquid;

[0055] (2) 2-aminoterephthalic acid was added in a mass-to-volume ratio of 1:5, and a resulting mixture was stirred for 20 min at a stirring speed of 700 r / min and a temperature of 20°C; and the stirring speed was increased to 1,200 r / min, then TBT was added in a volume ratio of 1:25, and a resulting mixture was further stirred for 20 min to obtain a suspension;

[0056] (3) the suspension was transferred to a dry hydrothermal reactor, and a solvothermal reaction was conducted at 140°C for 48 h; then a product of the solvothermal reaction was filtered out and washed alternately with anhydrous DMF and anhydrous methanol, each 3 times; and extraction was conducted with a Soxhlet extractor to obtain a white-solid MOF; and

[0057] (4) graphite was ground into a powder (which was sieved through a 150-mesh sieve), the powder was mixed with anhydrous methanol in a mass-volume ratio of 1:15, and a resulting mixture was ultrasonically shaken for 30 min; then the white-solid MOF was added in a mass-volume ratio of 1:15, and a resulting mixture was further ultrasonically shaken for 30 min; a resulting mixture 6 20 09 24 reacted under reflux at 65 °C for 15 h, then stood for 15 h, and then centrifuged; and a resulting filter cake was dried to obtain the graphite-MOF composite (graphite-coated MOF).

[0058] A preparation method of a negative electrode sheet was provided in this example, including the following steps: the graphite-MOF composite (graphite-coated MOF) was mixed with acetylene black in a weight ratio of 1:0.2, and a resulting mixture was then ball-milled at 4,500 r / min for 15 min; a resulting mixture powder was mixed with PVDF and NMP in a ratio of 1:0.12:0.3 to obtain a slurry; and the slurry was coated and dried to obtain the negative electrode sheet.

[0059] Example 3

[0060] A preparation method of a graphite-MOF composite was provided in this example, including the following steps:

[0061] (1) anhydrous DMF and anhydrous methanol were distilled out at 60°C and 65°C, respectively, and then mixed in a ratio of 1:9 to obtain a mixed liquid;

[0062] (2) 2-aminoterephthalic acid w as added in a mass-to-volume ratio of 1:6, and a resulting mixture was stirred for 30 min at a stirring speed of 800 r / min and a temperature of 35°C; and the stirring speed was increased to 1,500 r / min, then TBT was added in a volume ratio of 1:35, and a resulting mixture was further stirred for 30 min to obtain a suspension;

[0063] (3) the suspension was transferred to a dry hydrothermal reactor, and a solvothermal reaction was conducted at 150°C for 72 h; then a product of the solvothermal reaction w as filtered out and washed alternately with anhydrous DMF and anhydrous methanol, each 3 times; and extraction was conducted with a Soxhlet extractor to obtain a white-solid MOF; and

[0064] (4) graphite was ground into a powder (which was sieved through a 200-mesh sieve), the powder was mixed with anhydrous methanol in a mass-volume ratio of 1:20, and a resulting mixture was ultrasonically shaken for 40 min; then the white-solid MOF was added in a mass-volume ratio of 1:20, and a resulting mixture was further ultrasonically shaken for 40 min; a resulting mixture reacted under reflux at 70°C for 18 h, then stood for 18 h, and then centrifuged; and a resulting filter cake was dried to obtain the graphite-MOF composite (graphite-coated MOF).

[0065] A preparation method of a negative electrode sheet w as provided in this example, including the following steps: the graphite-MOF composite was mixed with acetylene black in a weight ratio of 1:0.3, and a resulting mixture was then ball-milled at 6,000 r / min for 20 min; a resulting mixture powder was mixed with PVDF and NMP in a ratio of 1:0.15:0.5 to obtain a slurry; and the shiny was 7 20 09 24 coated and dried to obtain the negative electrode sheet.

[0066] Comparative Example 1

[0067] A preparation method of an anode material for a titanium-based MOF LIB was provided, including the following steps: 2.5-dihydroxytcrcphthalic acid (DHTA) was dispersed in an / -propanol solution, a resulting solution was added dropwise to a solution of titanium tetraisopropoxide in acetonitrile to obtain an orange-brown slurry at room temperature, and the slurry was stirred for 30 min; then the slurry was transferred to a Teflon high-pressure reactor, heated to 120°C, and kept at the temperature for 24 h to obtain a dark-red crystal; and the crystal was then filtered out by suction filtration in an air atmosphere, washed 3 times with each of DMF and ethanol, and dried under vacuum to obtain the electrode material.

[0068] Comparative Example 2

[0069] A preparation method of a graphite-MOF composite was provided, including the following steps: commercial graphite was ground into a powder, the powder was mixed with anhydrous methanol in a mass-volume ratio of 1:20, and a resulting mixture was ultrasonically shaken for 40 min; then the MOF obtained in Comparative Example 1 was added in a mass-volume ratio of 1:20, and a resulting mixture was further ultrasonically shaken for 40 min; a resulting mixture reacted under reflux at 70°C for 18 h, then stood for 18 h, and then centrifuged; and a resulting filter cake was dried to obtain a graphite-coated MOF.

[0070] Performance test:

[0071] Hie anode materials (graphite-MOF composites) prepared in Examples 1 to 3 and the anode materials prepared in the Comparative Examples 1 to 2 were used to prepare negative electrode sheets, and a lithium sheet was used as a positive electrode to assemble button batteries. The initial discharge test was conducted at a rate of 1 C, and results were shown in Table 1 and Table 2. It can be seen from Table I that, at a rate of I C, the graphite-MOF composites of the present disclosure show a higher initial specific discharge capacity than that of the MOF materials of Comparative Examples 1 and 2; and the Example 2 shows an initial specific discharge capacity of 492.3 mAh / g, while the Comparative Example 1 shows an initial specific dischaige capacity only of 333.1 mAh / g and the Comparative Example 2 shows an initial specific discharge capacity only of 367.2 mAh / g. It can be seen from Table 2 that, at a rate of 1 C, the graphite-MOF composites of the present disclosure show a longer cycling life than that of the MOF materials of the comparative 8 examples; and after 1,600 cycles at 1 C, the Example 2 shows a capacity retention of 96.6%, while the Comparative Examples 1 to 2 show a capacity retention only of 92.8% and 90.2%, respectively.

[0072] Table 1 Performance of button batteries prepared from the graphite-MOF composites Item Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Initial specific discharge capacity (mAh / g) 461.9 492.3 462.1 333.1 367.2 Initial charge and discharge efficiency (%) 93.8 93.9 93.9 82.2 84.5 20 09 24 Table 2 Cycling performance of full batteries prepared from the graphite-MOF composites Item Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Discharge capacity retention (%) after 1,600 cycles at IC 95.9 96.6 93.3 92.8 90.2

[0073] FIG. 1 is an XRD pattern of the graphite-MOF composite, which reflects the characteristic peaks of the composite. FIG. 2 is a TEM image of the graphite-MOF composite, showing a bulk morphology.

[0074] The preparation method and use of a graphite-MOF composite provided in the present disclosure are described in detail above, and specific examples are used herein to illustrate the principle and implementation of the present disclosure. The examples are illustrated above merely to help understand the method and core ideas thereof (including the optimal mode) of the present disclosure and allow any person skilled in the art to practice the present disclosure, including manufacturing and using any device or system and implementing any combined method. It should be noted that several improvements and modifications may be made by persons of ordinary skill in the art without departing from the principle of the present disclosure, and these improvements and modifications should also fall within the protection scope of the present disclosure. The protection scope of the present disclosure is defined by the claims and may encompass other examples that 9 those skilled in the art can think of. If these other examples have structural elements that are not different from the literal expression in the claims or include equivalent structural elements that are not substantially different from the literal expression in the claims, they should also be included in the scope of the claims. 20 09 24 io

Claims

20 09 241. A preparation method of a graphite-metal organic framework (MOF) composite, comprising the following steps:(1) adding an amino-containing organic substance to a mixed liquid, stirring, stirring at an increased speed, adding a titanium-containing coupling agent, and continuing stirring to obtain a suspension;(2) subjecting the suspension to a solvothermal reaction and filtration, washing a resulting filter cake alternately with organic solvents, and conducting extraction to obtain an MOF; and(3) grinding graphite into a powder, mixing the powder with an alcohol, shaking, adding the MOF, and continuing shaking; allowing a resulting mixture to react under reflux and then to stand, and centrifuging a resulting system; drying a resulting precipitate to obtain the graphite-MOF composite;wherein in step (1), the mixed liquid is obtained by mixing AJV-dimethylformamide (DMF) and methanol in a mass ratio of l:(6-9); the amino-containing organic substance is 2-aminoterephthalic acid; a mass ratio of the amino-containing organic substance to the mixed liquid is l:(3-6); the titanium-containing coupling agent is tetrabutyl titanate (TBT); and a mass ratio of the mixed liquid to the titanium-containing coupling agent is l:(15-35);in step (2), the organic solvents are DMF and methanol.

2. The preparation method according to claim 1, wherein the stirring is first conducted for 10 min to 30 min at a temperature of 15°C to 35°C and a stirring speed of 500 r / min to 800 r / min in step (1); and in step (1), the stirring at the increased speed is conducted at 1,000 r / min to 1,500 r / min, and then the stirring is further conducted for 10 min to 30 min.

3. The preparation method according to claim 1, wherein the alcohol in step (3) is anhydrous methanol; a mass ratio of the graphite to the alcohol is 1:(10-20); and in step (3), a mass ratio of the MOF to the alcohol is 1:(10-20).

4. The preparation method according to claim 1, wherein the solvothermal reaction in step (2) is conducted at 130°C to 150°C for 24 h to 72 h; in step (3), the resulting mixture reacts under reflux at 60°C to 70°C for 12 h to 18 h, and is left to stand for 12 h to 18 h5. A graphite-MOF composite prepared by the preparation method according to any one of claims 1 to 4, wherein the graphite-MOF composite has a specific capacity of 460 mAh / g to 495 mAh / g, a porosity of 32% to 37%, and a specific surface area (SSA) of 2.7 m2 / g to 3.5 m2 / g.

6. A negative electrode sheet comprising the graphite-MOF composite according to claim 5.20 09 24

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