Si / ZnMOF composite material, preparation method thereof and application in lithium-ion batteries

Abstract

The present invention discloses a Si / ZnMOF composite material, a preparation method thereof, and an application in a lithium-ion battery. The preparation method of the Si / ZnMOF composite material comprises: uniformly mixing ZnMOF and Si, maintaining the temperature at 290-700°C for 1-4 hours under a protective atmosphere, and cooling to room temperature to obtain the Si / ZnMOF composite material; pyrolyzing the mixed ZnMOF and silicon to obtain the Si / ZnMOF composite material. The Si / ZnMOF composite material can be used as a negative electrode material for a lithium-ion battery. The electrode sheet prepared using the Si / ZnMOF composite material as the negative electrode material has greatly improved cycle stability after being assembled into a lithium-ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery negative electrode materials, and specifically relates to a Si / ZnMOF composite material, a preparation method thereof, and an application thereof in lithium-ion batteries. Background Art

[0002] Lithium-ion batteries (LIBs) are one of the most popular rechargeable batteries today due to their high energy density and long cycle life. They have become the main power source for portable electronic products and have great prospects in automotive electrification. However, existing lithium-ion battery technology has relatively low electrode capacity (372 mAh g for graphite). -1 , metal lithium oxide / phosphate is 140~170mAh g -1 ) limits the overall capacity of the battery. Silicon has a theoretical capacity of 4200mAh g -1 The discharge potential is almost close to that of graphite, and its advantages such as low cost and environmental friendliness have gradually become a research hotspot. However, silicon materials used as lithium-ion negative electrode materials have two disadvantages: poor conductivity and large volume expansion after cycling. This leads to a large capacity decay of silicon negative electrodes, seriously affecting their cycle life. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the object of the present invention is to provide a method for preparing Si / ZnMOF composite materials, which combines MOF-derived carbon materials with silicon through some simple high-temperature processes.

[0004] Another object of the present invention is to provide a Si / ZnMOF composite material obtained by the above preparation method.

[0005] Another object of the present invention is to provide an application of the above-mentioned Si / ZnMOF composite material in lithium-ion batteries to improve the charge-discharge specific capacity after ten cycles.

[0006] A method for preparing a Si / ZnMOF composite material comprises: uniformly mixing ZnMOF and Si, maintaining the temperature at 290-700° C. for 1-4 hours under a protective atmosphere, and cooling to room temperature to obtain the Si / ZnMOF composite material, wherein the ratio of ZnMOF to Si is (1-2):(1-2) by mass. The method for preparing the ZnMOF comprises the following steps: uniformly mixing terephthalic acid, triethylamine, and a first solvent to obtain a first liquid, uniformly mixing zinc acetate dihydrate and a second solvent to obtain a second liquid, mixing the first liquid and the second liquid, stirring for 2-3 hours, centrifuging, washing the solid obtained by centrifugation, and drying to obtain the ZnMOF. The ratio of the mass fraction of terephthalic acid, the volume fraction of triethylamine, and the mass fraction of zinc acetate dihydrate is (2-3):(3-4):(8-9), the unit of the mass fraction is g, and the unit of the volume fraction is mL.

[0007] In the above technical solution, the insulation temperature is 290-500°C.

[0008] In the above technical solution, ZnMOF and Si are mixed and then ground for at least 0.5 h to achieve uniform mixing of ZnMOF and Si.

[0009] In the above technical solution, the protective atmosphere is argon.

[0010] In the above technical solution, the temperature is increased from room temperature to the above 290-700° C. at a heating rate of 2-5° C. / min.

[0011] In the above technical solution, the first solvent and the second solvent are both N,N-dimethylformamide, the ratio of the volume fraction of the first solvent to the mass fraction of terephthalic acid is (180-200):(2-3), and the ratio of the volume fraction of the second solvent to the mass fraction of zinc acetate dihydrate is (250-260):(8-9).

[0012] In the above technical solution, a detergent is used to wash the solid obtained by centrifugation. The detergent is a mixture of N,N-dimethylformamide and methanol. The ratio of N,N-dimethylformamide to methanol in the detergent is (2-3):(1-2) by volume.

[0013] In the above technical solution, the drying is vacuum drying.

[0014] The Si / ZnMOF composite material is obtained by the above preparation method.

[0015] Application of Si / ZnMOF composite materials in lithium-ion batteries to improve the charge-discharge specific capacity after ten cycles.

[0016] Si / ZnMOF composite material was used as the negative electrode material.

[0017] Application of ZnMOF in alleviating the volume change of Si during charge and discharge.

[0018] The beneficial effects of the present invention are as follows:

[0019] 1. The present invention prepares ZnMOF by a wet chemical method with one-step stirring, and pyrolyzes it with silicon to finally obtain a Si / ZnMOF composite material. The Si / ZnMOF composite material can be used as a negative electrode material for lithium-ion batteries.

[0020] 2. The cycle stability of the electrode sheets prepared with Si / ZnMOF composite materials as negative electrode materials is greatly improved after being assembled into lithium-ion batteries.

[0021] 3. Si / ZnMOF composite materials alleviate the volume change of Si during the charge and discharge process, and improve the cycle stability and specific capacity of silicon. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the XRD pattern of Si / ZnMOF composite material;

[0023] Figure 2a This is a scanning electron microscope image of the Si / ZnMOF composite material obtained in Example 1;

[0024] Figure 2b This is a scanning electron microscope image of the Si / ZnMOF composite material obtained in Example 4;

[0025] Figure 2c This is a scanning electron microscope image of the Si / ZnMOF composite material obtained in Example 6;

[0026] Figure 3 The negative electrode half-cell assembled with electrode sheets made of Si or Si / ZnMOF composite materials at 100mA g -1 Charge and discharge cycles at current density;

[0027] Figure 4 The negative electrode half-cell assembled from the electrode sheet made of the Si / ZnMOF composite material obtained in Example 1 was -1 First charge and discharge curves at current density. DETAILED DESCRIPTION

[0028] The preparation method of the Si / ZnMOF composite material of the present invention is described in detail below with reference to the accompanying drawings.

[0029] Zinc acetate dihydrate ((CH3COO)2Zn, Tianjin Kewei Co., Ltd., analytical grade);

[0030] N,N-Dimethylformamide (DMF, Tianjin Damao Chemical Reagent Factory, analytical grade);

[0031] Terephthalic acid (C8H6O4, Shanghai Luoen Reagent, purity 99%);

[0032] Triethylamine ((C2H5)3N, San Chemical Technology (Shanghai) Co., Ltd., purity ≥99.9%).

[0033] Examples 1 to 6

[0034] A method for preparing a Si / ZnMOF composite material comprises: mixing ZnMOF and Si, grinding them in an agate mortar for t2 h to achieve uniform mixing of the ZnMOF and Si, transferring the mixture to a crucible and placing the mixture in a tubular furnace, heating the mixture from room temperature (20-25°C) to T°C at a heating rate of 5°C / min under an argon environment, maintaining the temperature at T°C for t1 h, and naturally cooling the mixture to room temperature to obtain the Si / ZnMOF composite material, wherein the ratio of ZnMOF to Si is 1:1 by mass.

[0035] The method for preparing ZnMOF includes the following steps: preparing two beakers, in the first beaker, evenly mixing terephthalic acid, triethylamine and a first solvent to obtain a first liquid; in the second beaker, evenly mixing zinc acetate dihydrate and a second solvent to obtain a second liquid, mixing the first liquid and the second liquid, stirring for 2.5 hours, centrifuging, washing the solid obtained by centrifugation with a detergent, vacuum drying, and grinding to obtain ZnMOF, the ratio of the mass fraction of terephthalic acid, the volume fraction of triethylamine and the mass fraction of zinc acetate dihydrate is X, the unit of mass fraction is g, and the unit of volume fraction is mL, the first solvent and the second solvent are both N,N-dimethylformamide, the ratio of the volume fraction of the first solvent to the mass fraction of terephthalic acid is Y, and the ratio of the volume fraction of the second solvent to the mass fraction of zinc acetate dihydrate is 250:8.5.

[0036] The detergent is a mixture of N,N-dimethylformamide and methanol, and the ratio of N,N-dimethylformamide to methanol in the detergent is 2:1 by volume.

[0037] The values ​​of T, t1, t2, X and Y are shown in Table 1.

[0038] Table 1

[0039]

[0040] The Si / ZnMOF composite materials obtained in Examples 1 to 6 were tested.

[0041] A D&A X-ray diffractometer (Bruker, Germany) was used with Cu Kα radiation, an incident wavelength of λ = 0.154 nm, and an angle measurement range of 2θ = 5 to 80°. A Quanta FEG 250 environmental field emission scanning electron microscope (Environmental SEM with FEG) was used with an accelerating voltage of 15 kV.

[0042] Figure 1 The XRD simulation data card of silicon and the XRD patterns of the Si / ZnMOF composite materials obtained in Examples 1, 4 and 6 are shown. It can be clearly seen from the figure that the Si / ZnMOF composite materials obtained in Examples 1, 4 and 6 all have sharp diffraction peaks, indicating that the Si / ZnMOF composite materials still have a crystalline structure after being heated at 300°C, 500°C and 700°C. The diffraction peaks in the Si / ZnMOF composite materials can correspond one-to-one with the diffraction peaks of silicon (JCPDS card No.75-0589), indicating that Si and ZnMOF have indeed formed a composite material, and the characteristic peaks of Si are still retained after pyrolysis. No crystalline carbon (graphite) peaks were found in the Si / ZnMOF composite materials, indicating that the carbon therein may be amorphous, and its peaks are covered by the crystal peaks of MOF.

[0043] Figure 2a This is a scanning electron microscope image (SEM) of the Si / ZnMOF composite material obtained in Example 1. It can be seen that smaller block-shaped particles are distributed on the smooth block silicon. The size distribution of the small particles is uneven, and the size itself ranges from 1 to 2 μm.

[0044] Figure 2b This is a scanning electron microscope (SEM) image of the Si / ZnMOF composite material obtained in Example 4. The silicon is surrounded by rough porous agglomerates.

[0045] Figure 2c This is a scanning electron microscope (SEM) image of the Si / ZnMOF composite material obtained in Example 6, showing some flaky substances distributed around the silicon.

[0046] Electrode sheets were prepared by mixing the negative electrode material with the conductive agent acetylene black and the binder PVDF in a mass ratio of 5:3:2. The preparation process was as follows: 0.02 g of PVDF was placed in a small beaker, 1.0 mL of NMP was added dropwise, and the beaker was placed on a magnetic stirrer to thoroughly stir and dissolve. The negative electrode material and acetylene black were then added, and stirring continued for 3 hours to form a black, viscous slurry. The slurry was then coated onto copper foil to form a coating with a thickness of 1.65 mm. After vacuum drying at 60°C, the coating was punched into 14 mm diameter discs to form the electrode sheets.

[0047] The prepared electrode sheet served as the working electrode, and metallic lithium served as the reference and counter electrodes. The electrolyte was KLE-HV4701 high-voltage button cell electrolyte from Xianghe Kunlun Chemical Co., Ltd., the battery separator was Gelgard 2300, and the battery case was an LIR 2032 button cell. In a glove box filled with high-purity argon, the negative electrode half-cell was assembled in the following order: positive electrode case, electrode sheet, 40 μL electrolyte, separator, 40 μL electrolyte, lithium sheet, gasket, spring, and negative electrode case.

[0048] The negative electrode half-cell was subjected to a constant current charge-discharge cycle test. The test was performed on a LAND CT2001A battery cycle test system. The negative electrode was charged and discharged using a constant current method with a voltage range of 0.01 to 3.0 V and a current density of 100 mA g -1 , the ambient temperature is kept constant at 25℃.

[0049] The above-mentioned negative electrode material is Si, one of the Si / ZnMOF composite materials obtained in Examples 1, 4 and 6, Figure 3 The negative electrode half-cell assembled with electrode sheets made of different negative electrode materials is subjected to a current density of 100 mA g -1 The charge-discharge cycle curves for the Si / ZnMOF anode are shown in Figure 1. The figure shows that both Si and Si / ZnMOF composites have high initial capacities. However, due to the incorporation of MOF materials into the Si / ZnMOF composites, the mass of Si, the active material, becomes 50% of the mass of the anode material in a pure Si anode. Therefore, the initial capacity of the Si / ZnMOF composite is lower than that of the pure Si anode. However, after the first dozen or so weeks of capacity decay, the capacity of the Si / ZnMOF composites is higher than that of Si.

[0050] The first discharge capacity of silicon as a negative electrode material can reach 2219.3 mAh g -1 After 20 cycles of charge and discharge, the silicon capacity gradually stabilized. After 100 cycles, the discharge capacity was only 222.9 mAh g -1 As the number of cycles increases, the specific capacity of silicon also shows a slow growth trend. After 250 cycles, the discharge specific capacity can reach 353.2mAh g -1 .

[0051] The Si / ZnMOF composite material obtained in Example 1 showed a relatively excellent cycle specific capacity, with an initial capacity of 1661.5 mAh g -1 After experiencing capacity decay for more than a dozen cycles, the specific capacity of the Si / ZnMOF composite material began to increase continuously. After 100 cycles, the discharge specific capacity reached 420.5 mAh g -1, which is 1.9 times that of silicon electrode. After 250 cycles, the discharge capacity is 666.7 mAh g -1 .

[0052] The Si / ZnMOF composite material obtained in Example 4 has a discharge capacity of 273.5 mAh g after 100 charge-discharge cycles. -1 After 250 charge and discharge cycles, the discharge capacity can reach 477.9 mAh g -1 .

[0053] Compared to the Si / ZnMOF composite material obtained in Example 1, the Si / ZnMOF composite material obtained in Example 4 did not exhibit a higher specific capacity. This may be due to structural defects in the Si / ZnMOF composite material formed after pyrolysis at 500°C, resulting in an unstable skeleton that cannot withstand multiple charge and discharge cycles. However, after experiencing capacity decay over a dozen cycles, the Si / ZnMOF composite material obtained in Example 4 still exhibited a higher specific capacity as a negative electrode material than pure silicon.

[0054] The cycle specific capacity of the Si / ZnMOF composite material obtained in Example 6 as the negative electrode material is similar to that of pure silicon as the negative electrode material.

[0055] The data obtained from the above test are shown in Table 2.

[0056] Table 2

[0057]

[0058] The Si / ZnMOF composite material (Example 1) exhibits a higher specific capacity after several weeks of cycling. This may be because after pyrolysis, the Si / ZnMOF composite material simply removes surface water and other solvents, and the main framework of the Si / ZnMOF composite material is not damaged. This may be able to alleviate the volume change of Si during the charge and discharge process to a certain extent, and thus can withstand more cyclic charge and discharge reactions and maintain a relatively stable specific capacity growth process.

[0059] Figure 4 The Si / ZnMOF composite material (Example 1) is -1 The first charge-discharge curve under current density. As can be seen from the figure, the material has a charge-discharge platform in the range of 0.01 to 0.5V. In this range, the voltage changes slowly with the capacity, and most of the capacity is concentrated in this voltage range.

[0060] The above is an exemplary description of the present invention. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by other skilled in the art without expending creative labor falls within the scope of protection of the present invention.

Claims

1. An application of a Si / ZnMOF composite material in a lithium-ion battery to improve the charge-discharge capacity after ten cycles, characterized in that: The preparation method of the Si / ZnMOF composite material comprises: uniformly mixing ZnMOF and Si, maintaining the temperature at 290-500° C. for 1-4 hours under a protective atmosphere, and cooling to room temperature to obtain the Si / ZnMOF composite material, wherein the ratio of ZnMOF to Si is (1-2):(1-2) by mass. The method for preparing ZnMOF comprises the following steps: uniformly mixing terephthalic acid, triethylamine, and a first solvent to obtain a first liquid, uniformly mixing zinc acetate dihydrate and a second solvent to obtain a second liquid, mixing the first liquid and the second liquid, stirring for 2-3 hours, centrifuging, washing the solid obtained by centrifugation, and drying to obtain the ZnMOF. The ratio of the mass fraction of terephthalic acid, the volume fraction of triethylamine, and the mass fraction of zinc acetate dihydrate is (2-3):(3-4):(8-9), the unit of the mass fraction is g, and the unit of the volume fraction is mL.

2. The use according to claim 1, characterized in that After mixing ZnMOF and Si, they are ground for at least 0.5 h to achieve uniform mixing of ZnMOF and Si, and the protective atmosphere is argon.

3. The use according to claim 1, characterized in that The temperature is raised from room temperature to the temperature of 290-500° C. at a heating rate of 2-5° C. / min.

4. The use according to claim 1, characterized in that The first solvent and the second solvent are both N,N-dimethylformamide, the ratio of the volume fraction of the first solvent to the mass fraction of terephthalic acid is (180-200):(2-3), and the ratio of the volume fraction of the second solvent to the mass fraction of zinc acetate dihydrate is (250-260):(8-9).

5. The use according to claim 1, characterized in that The solid obtained by centrifugation is washed with a detergent, wherein the detergent is a mixture of N,N-dimethylformamide and methanol, and the ratio of N,N-dimethylformamide to methanol in the detergent is (2-3):(1-2) by volume.

6. The use according to claim 1, characterized in that The drying is vacuum drying.

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