MOF-derived carbon aerogel, preparation method therefor, and the use thereof in lithium-ion battery

Abstract

The present invention relates to the technical field of lithium-ion batteries, and provided thereby are an MOF-derived carbon aerogel, a preparation method therefor, and a use thereof in a lithium-ion

Description

A MOFs-derived carbon aerogel, a preparation method thereof, and application in lithium-ion batteries Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a MOFs-derived carbon aerogel, a preparation method thereof, and application in lithium ion batteries. Background Art

[0002] The energy crisis is a major issue facing human society in the 21st century. Once fossil fuels are depleted, they cannot be replenished naturally in the short term. Lithium-ion batteries, with their long cycle life, high operating voltage, high specific energy, excellent safety, high energy density, low self-discharge, fast charge and discharge, and wide operating temperature range, have become one of the most popular energy storage methods.

[0003] The key components of lithium-ion batteries include the positive electrode, negative electrode, electrolyte, and separator. The electrochemical properties of the negative electrode are a key factor influencing the performance of lithium-ion batteries. Currently, graphite is the most commonly used negative electrode material for lithium-ion batteries. However, commercially available graphite negative electrode materials suffer from shortcomings such as low theoretical capacity, poor layered structural stability, and poor rate performance, which hinder the further development of lithium-ion batteries. Therefore, there is an urgent need to develop a negative electrode material with high stability and excellent electrochemical performance.

[0004] Summary of the Invention

[0005] In view of this, the present invention provides a MOFs-derived carbon aerogel, a preparation method thereof, and application in lithium-ion batteries. The MOFs-derived carbon aerogel provided by the present invention has excellent charge-discharge performance, high specific capacity, extremely high rate capability, and superb cycle stability.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] A method for preparing MOFs-derived carbon aerogel comprises the following steps:

[0008] A dichloromethane solution of 4,4'4"-tris(4-pyridyl)triphenylamine and a methanol solution of CdCl2 were mixed to carry out a coordination reaction to obtain [Cd(tppa)2Cl2];

[0009] The [Cd(tppa)2Cl2] is carbonized under a protective atmosphere to obtain a MOFs-derived carbon aerogel.

[0010] Preferably, the molar ratio of the 4,4'4"-tris(4-pyridyl)triphenylamine to CdCl2 is 6-8:2-3; and the temperature of the coordination reaction is room temperature.

[0011] Preferably, the method of mixing the dichloromethane solution of 4,4'4"-tris(4-pyridyl)triphenylamine and the methanol solution of CdCl2 includes method 1 or method 2; the method 1 includes the following steps: dropwise adding the dichloromethane solution of 4,4'4"-tris(4-pyridyl)triphenylamine to the methanol solution of CdCl2;

[0012] The second method comprises the following steps: placing a dichloromethane solution of 4,4'4"-tris(4-pyridyl)triphenylamine at the bottom of a reaction vessel, then adding a dichloromethane-methanol mixed solution, and then adding a methanol solution of CdCl2;

[0013] When the method of the first method is used for mixing, the coordination reaction time is 20 to 30 hours; when the method of the second method is used for mixing, the coordination reaction time is 24 to 27 days.

[0014] Preferably, the [Cd(tppa)2Cl2] is a powder crystal or a single crystal; the crystal data of the single crystal are: belonging to the monoclinic system P21 / c, and the asymmetric unit includes a Cd II ion, two ligand TPPA molecules and two chloride ions.

[0015] Preferably, the carbonization temperature is 800-1000° C., the holding time is 3-4 hours, and the protective atmosphere is nitrogen.

[0016] The present invention also provides a MOFs-derived carbon aerogel prepared by the preparation method described in the above scheme, wherein the density of the MOFs-derived carbon aerogel is 0.2 to 0.4 mg / cm 3 , the porosity is 85~95%.

[0017] The present invention also provides the use of the MOFs-derived carbon aerogel described in the above scheme as a negative electrode active material in a lithium ion battery.

[0018] The present invention also provides a lithium ion battery negative electrode, wherein the negative electrode active material used in the lithium ion battery negative electrode is the MOFs-derived carbon aerogel described in the above scheme.

[0019] Preferably, the negative electrode of the lithium-ion battery includes a current collector and an active material layer coated on the surface of the current collector; the components of the active material layer include a negative electrode active material, a conductive agent and a binder.

[0020] The present invention also provides a lithium ion battery, wherein the negative electrode of the lithium ion battery is the negative electrode of the lithium ion battery described in the above solution.

[0021] The present invention provides a preparation method of MOFs-derived carbon aerogel, comprising the following steps: mixing a dichloromethane solution of 4,4'4"-tris(4-pyridyl)triphenylamine and a methanol solution of CdCl2 for coordination reaction to obtain [Cd(tppa)2Cl2]; calcining the [Cd(tppa)2Cl2] under a protective atmosphere to obtain MOFs-derived carbon aerogel. The present invention first prepares [Cd(tppa)2Cl2], which is a macroporous metal organic framework material. The MOFs-derived carbon aerogel is porous and lightweight, allowing for more lithium storage space during lithium intercalation and deintercalation, and maintaining stable material properties after multiple cycles. The MOFs-derived carbon aerogel, when used as a negative electrode active material for lithium-ion batteries, exhibits excellent electrochemical performance, including ultra-long cycle life and extremely high rate capability, as well as high reversible capacity at low current densities. It holds promise as a commercially viable alternative to graphite for the next generation of lithium-ion battery negative electrode materials.

[0022] The results of the embodiment show that the MOFs-derived carbon aerogel of the present invention is used as the negative electrode active material to prepare a lithium-ion battery. The operating voltage of the obtained lithium-ion battery is between 0.01 and 3.5 V. The discharge specific capacity after 170 cycles at a current density of 0.5 A / g is as high as 500 mAh / g. At a high current density of 10 A / g, it can stably cycle 10,000 cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 shows the Cd content of MOF-ZX-4. II Ion coordination configuration diagram;

[0024] Figure 2 is the “diamond” (4,4) network diagram of MOF-ZX-4;

[0025] FIG3 is a SEM image of the MOFs-derived carbon aerogel product prepared in Example 1;

[0026] FIG4 is a CV graph of a half-cell assembled with MOFs-derived carbon aerogel in Example 2 at a scan rate of 0.1 m / s, and the test results are shown in FIG3 ;

[0027] FIG5 is a Nyquist plot of a half-cell assembled using MOFs-derived carbon aerogel in Example 2;

[0028] Figure 6 is a graph showing the rate performance of a half-cell assembled using MOFs-derived carbon aerogels in Example 2 at currents of 0.1 A / g, 0.2 A / g, 0.5 A / g, 1 A / g, 2 A / g, 5 A / g, and 0.1 A / g;

[0029] FIG7 is a graph showing the cycling performance of a half-cell assembled with MOFs-derived carbon aerogel at a current of 5 A / g in Example 2;

[0030] FIG8 is a graph showing the cycling performance of a half-cell assembled with MOFs-derived carbon aerogel at a current of 10 A / g in Example 2;

[0031] FIG9 is a graph showing the cycling performance of a half-cell assembled using MOFs-derived carbon aerogel in Example 3 at a current density of 0.5 A / g. DETAILED DESCRIPTION

[0032] The present invention provides a method for preparing MOFs-derived carbon aerogel, comprising the following steps:

[0033] A dichloromethane solution of 4,4'4"-tris(4-pyridyl)triphenylamine and a methanol solution of CdCl2 were mixed to carry out coordination reaction to obtain [Cd(tppa)2Cl2];

[0034] The [Cd(tppa)2Cl2] is carbonized under a protective atmosphere to obtain a MOFs-derived carbon aerogel.

[0035] In the present invention, a dichloromethane solution of 4,4'4"-tris(4-pyridyl)triphenylamine and a methanol solution of CdCl2 are mixed for coordination reaction to obtain [Cd(tppa)2Cl2]. In the present invention, the English name of the 4,4'4"-tris(4-pyridyl)triphenylamine is tris(4-(pyridin-4-yl)phenyl)amine, abbreviated as tppa; the molar ratio of the 4,4'4"-tris(4-pyridyl)triphenylamine and CdCl2 is preferably 6-8:2-3, more preferably 6:2; the concentration of the dichloromethane solution of the 4,4'4"-tris(4-pyridyl)triphenylamine is preferably 0.075-0.013 mol / L, more preferably 0.01mol / L; the concentration of the methanol solution of CdCl2 is preferably 0.0025-0.005mol / L, more preferably 0.003-0.004mol / L; the method of mixing the dichloromethane solution of 4,4'4"-tris(4-pyridyl)triphenylamine and the methanol solution of CdCl2 includes method 1 or method 2; the method 1 includes the following steps: mixing the dichloromethane solution of 4,4'4"-tris(4-pyridyl)triphenylamine Add dropwise to a methanol solution of CdCl2; in the present invention, the methanol solution of CdCl2 is preferably placed in a conical flask first, and then a dichloromethane solution of 4,4'4"-tris(4-pyridyl)triphenylamine is added dropwise through a constant pressure dropping funnel; the second method comprises the following steps: placing a dichloromethane solution of 4,4'4"-tris(4-pyridyl)triphenylamine at the bottom of a reaction vessel, then adding a dichloromethane-methanol mixed solution, and then adding a methanol solution of CdCl2; the volume ratio of dichloromethane to methanol in the dichloromethane-methanol mixed solution is preferably 1:1, and the volume ratio of the dichloromethane solution of 4,4'4"-tris(4-pyridyl)triphenylamine to the dichloromethane-methanol mixed solution is preferably 6-8:8-10; the reaction vessel is preferably a test tube. In the present invention, the first method is used for the synthesis of powder crystals, which meets the requirements of rapid industrialization, and the second method can cultivate a white block single crystal structure suitable for X-ray structure analysis.

[0036] In the present invention, the temperature of the coordination reaction is preferably room temperature. When the mixing method is adopted, the time of the coordination reaction is preferably 20 to 30 hours, specifically, the obtained mixed liquid is first stirred at room temperature for 8 to 13 hours, and then allowed to stand for reaction for 12 to 17 hours; when the mixing method is adopted, the time of the coordination reaction is preferably 24 to 28 days, specifically, the obtained mixed liquid is sealed and allowed to stand for reaction.

[0037] After the coordination reaction is completed, the present invention preferably filters the obtained mother liquor, washes the obtained precipitate and then dries it to obtain [Cd(tppa)2Cl2] (denoted as MOF-ZX-4); the washing detergent is preferably ethanol, the drying temperature is preferably 70°C, and the MOF-ZX-4 obtained after drying is a white powder.

[0038] In the present invention, the [Cd(tppa)2Cl2] is a powder crystal or a single crystal; the crystal data of the single crystal are: belonging to the monoclinic system P21 / c, and the asymmetric unit includes a Cd II ion, two ligand TPPA molecules and two chloride ions.

[0039] After obtaining [Cd(tppa)2Cl2], the present invention carbonizes the [Cd(tppa)2Cl2] under a protective atmosphere to produce a MOF-derived carbon aerogel. In the present invention, the carbonization temperature is preferably 800-1000°C, more preferably 800-900°C, the heating rate to the carbonization temperature is preferably 5°C / min, and the carbonization holding time is preferably 3-4 hours, more preferably 3-3.5 hours. The protective atmosphere is preferably nitrogen, and the carbonization is preferably performed in a tube furnace. After carbonization, the aerogel is allowed to cool naturally to room temperature.

[0040] The present invention also provides a MOFs-derived carbon aerogel prepared by the preparation method described in the above scheme, wherein the density of the MOFs-derived carbon aerogel is preferably 0.2 to 0.4 mg / cm 3 , the porosity is preferably 85 to 95%.

[0041] The present invention also provides the use of the MOF-derived carbon aerogel described in the above-mentioned solution as a negative electrode active material in a lithium-ion battery. The MOF-derived carbon aerogel provided by the present invention is lightweight and porous. As a negative electrode active material for lithium-ion batteries, it exhibits excellent electrochemical performance, good cycle stability, high rate capability, and high reversible capacity at low current densities. It is expected to replace graphite as a negative electrode material for the next generation of lithium-ion batteries.

[0042] The present invention also provides a lithium-ion battery negative electrode, wherein the negative electrode active material used in the lithium-ion battery negative electrode is the MOFs-derived carbon aerogel described in the above scheme; in the present invention, the lithium-ion battery negative electrode preferably includes a current collector and an active material layer coated on the surface of the current collector; the components of the active material layer preferably include a negative electrode active material, a conductive agent, and a binder; the conductive agent is preferably acetylene black, and the binder is preferably polyvinylidene fluoride (PVDF); the mass ratio of the negative electrode active material, the conductive agent, and the binder is preferably 7:1:2; the present invention has no special requirements for the type of the current collector, and any material familiar to those skilled in the art can be used, such as copper foil. In the present invention, when the negative electrode is a 12 cm diameter disc, the loading amount of the negative electrode active material in the lithium-ion battery negative electrode is preferably 1 to 2 mg / disc.

[0043] The present invention has no special requirements for the preparation method of the negative electrode of the lithium ion battery, and a method familiar to those skilled in the art can be used. For example, after mixing the negative electrode active material, the conductive agent and the binder, an appropriate amount of N-methylpyrrolidone solvent is added and mixed evenly, and the resulting slurry is coated on the surface of the current collector and then dried.

[0044] The present invention also provides a lithium-ion battery, the negative electrode of which is the negative electrode of the lithium-ion battery described in the above scheme; in the present invention, the lithium-ion battery includes a positive electrode, a negative electrode, a separator and an electrolyte. The present invention has no special requirements for the types of the positive electrode, separator and electrolyte, and those familiar to those skilled in the art can be used; in a specific embodiment of the present invention, the positive electrode is preferably a lithium sheet, the separator is preferably Celgard 2500, the electrolyte is preferably a LiPF6 solution, the solvent of the electrolyte is preferably a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC), and the volume ratio of EC and DMC in the mixed solvent is preferably 3:7 or 1:1; the concentration of LiPF6 in the electrolyte is preferably 1 mol / L; additives can also be added to the electrolyte, and the additive is preferably fluoroethylene carbonate (FEC), and the mass fraction of FEC in the electrolyte is preferably 5%.

[0045] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0046] Example 1

[0047] 0.6 mmol of tppa and 0.2 mmol of CdCl₂ were dissolved in 60 mL of dichloromethane and 60 mL of methanol, respectively, to obtain a clear solution. The CdCl₂ methanol solution was poured into a conical flask, and the tppa dichloromethane solution was slowly added dropwise to the methanol solution using a constant pressure dropping funnel. The mixture was stirred at room temperature for 8 hours. After standing for 12 hours, the white precipitate was collected by filtration and washed three times with 10 mL of ethanol. The white powder was dried at 70°C to obtain MOF-ZX-4 with a yield of approximately 60%. The white MOF-ZX-4 was placed in a tubular furnace and heated to 800°C at a rate of 5°C / min under a nitrogen atmosphere. The mixture was then kept at this temperature for 3 hours and then cooled naturally to room temperature to obtain the MOF-derived carbon aerogel product.

[0048] In addition, MOF-ZX-4 single crystals were prepared for structural analysis. The single crystal preparation method was as follows: the ligand 4,4'4"-tris(4-pyridyl)triphenylamine (tppa, 0.06 mmol) was dissolved in dichloromethane (6 mL) and placed at the bottom of a test tube. 8 mL of a dichloromethane / methanol mixed solution (volume ratio of 1:1) was carefully added, and then a methanol solution (6 mL) of CdCl2 (0.02 mmol) was added on top. The tube was sealed and allowed to stand for 24 days. White block-like single crystals suitable for X-ray structural analysis precipitated on the wall of the test tube.

[0049] The mother liquor after the reaction was filtered, washed with ethanol (10 ml) three times, and vacuum dried to obtain MOF-ZX-4 single crystals with a yield of ∼30%.

[0050] The single crystal structure of MOF-ZX-4 was analyzed. The results showed that the space group of MOF-ZX-4 belongs to the monoclinic system P21 / c, and the asymmetric unit includes a Cd II ion, two ligand TPPA molecules and two chloride ions.

[0051] Figure 1 shows the Cd content of MOF-ZX-4. II Ion coordination configuration diagram, each Cd II The ion is coordinated with four nitrogen atoms from different TPPA molecules and two chloride ions to form an octahedral coordination configuration. The Cd-N coordination bond length in the equatorial plane is and the axial Cd-Cl coordination bond length reaches Therefore, Cd II There is an obvious Jahn-Teller effect in ions.

[0052] Figure 2 shows the "diamond" (4,4) network diagram of MOF-ZX-4. According to Figure 2, although the TPPA molecule has three nitrogen atoms, only two nitrogen atoms participate in the coordination during the assembly process, that is, each TPPA ligand bridges two Cd IIions, resulting in a two-dimensional "diamond" (4,4) network with a lattice size of The pore size reaches the nanometer level.

[0053] FIG3 is an SEM image of the obtained MOFs-derived carbon aerogel product. As can be seen from FIG3 , the MOFs-derived carbon aerogel product has a sheet-like structure, a small number of layers, and a thin thickness. The surface is very flat and smooth, and presents a translucent silk-like appearance.

[0054] Example 2

[0055] In this embodiment, the electrochemical properties of the electrode materials were tested using a half-cell. The half-cell mainly consisted of five parts: a positive electrode, a negative electrode, a separator, an electrolyte, and a battery case. The positive electrode was a lithium sheet, the negative electrode was a mixed material consisting of MOF-ZX-4 derived carbon aerogel, acetylene black, and a binder, the separator was Celgard 2500, the electrolyte in the electrolyte was 1 mol / L LiPF6, and the solvent was a mixed solvent of EC and DMC (volume ratio of 3:7).

[0056] The negative electrode was prepared as follows:

[0057] (1) The MOFs-derived carbon aerogel prepared in Example 1, acetylene black, and PVDF were mixed in a mass ratio of 7:1:2, and an appropriate amount of N-methylpyrrolidone solvent was added to mix them uniformly to obtain a slurry;

[0058] (2) The slurry was evenly coated on the copper foil using a coater, dried in a vacuum oven at 70°C for 10 h, and then cut into electrode sheets with a diameter of 12 cm. After weighing, the sheets were placed in a glove box containing an inert gas to assemble the battery.

[0059] CV testing of the assembled half-cell was performed using a Shanghai Chenhua CHI660E electrochemical workstation at a scan rate of 0.1 m / s. The test results are shown in Figure 4. The results in Figure 4 show that, except for the irreversible process of the electrode material in the first scan (mainly attributed to the formation of the SEI film and the decomposition of the electrolyte), there was no significant change in the second and third cycles, demonstrating good cycling stability and reversibility.

[0060] The assembled half-cell was tested using an electrochemical impedance spectroscopy (EIS) spectrometer (CHI660E) from a Shanghai Chenhua electrochemical workstation. The results are shown in Figure 5. In Figure 5, the AC impedance spectroscopy image is composed of a semicircle and a straight line. The diameter of the semicircle represents the ease of charge transfer during the electrochemical reaction within the battery, while the straight line represents the ease of lithium ion diffusion within the electrode material. The results in Figure 5 indicate that the impedance (Re+Rsf+Rst) value is slightly below 300, indicating a relatively high impedance value.

[0061] The rate performance of the half-cell was tested on a blue electric test system at currents of 0.1A / g, 0.2A / g, 0.5A / g, 1A / g, 2A / g, 5A / g, and 0.1A / g, and the test results are shown in FIG6 . The results in FIG6 show that the half-cell assembled with the MOFs-derived carbon aerogel of the present invention can maintain a rate of 200 mAh g at a high current of 5A. -1 The reversible specific capacity can be restored to 600 mAh g when the current density returns to 0.1 A. -1 , indicating that the structure of the material remains intact after a large current passes through it, showing excellent rate performance.

[0062] The cycling stability of the half-cell at high current was tested in the Blue Electric test system. Figure 7 shows the cycling performance of the MOF-ZX-4 derived carbon aerogel at 5A / g, and Figure 8 shows the cycling performance of the MOF-ZX-4 derived carbon aerogel at 10A / g. As can be seen from Figures 7 and 8, the capacity can be maintained at 100 mAh g after 5000 cycles at a current density of 5A / g. -1 Even at a current density of 10 A / g, the discharge capacity can reach 30 mAh / g after 10,000 cycles.

[0063] Example 3

[0064] The structure of the lithium-ion battery in this embodiment is essentially the same as that in Example 1, except for a slight difference in the electrolyte composition. The electrolyte in this embodiment is 1 mol / L LiPF6, and the solvent is a mixture of EC and DMC (1:1 by volume), with 5% FEC additive.

[0065] The electrochemical performance of the half-cell was tested using a blue electric test system. A constant current test was performed at a current density of 0.5 A / g under the conditions of 0.01-3.5 V. The test results are shown in Figure 9. The results in Figure 9 show that the reversible capacity of the half-cell of this embodiment can reach 500 mAh g after 170 cycles at a current density of 0.5 A / g. -1 .

[0066] The results of the above examples show that the MOFs-derived carbon aerogel prepared by the present invention using MOF-ZX-4 as a precursor is used as an active material in the negative electrode of a lithium-ion battery, and has good lithium-ion battery charge and discharge performance, high discharge specific capacity, extremely high rate performance and super strong cycle stability.

[0067] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A preparation method of an MOFs-derived carbon aerogel, comprising following steps: mixing a dichloromethane solution of tris(4-(pyridin-4-yl)phenyl)amine and a methanol solution of CdCl2 for coordination reaction to obtain [Cd(tppa)2Cl2]; andperforming carbonization of the [Cd(tppa)2Cl2] under a protective atmosphere to obtain the MOFs-derived carbon aerogel.

2. The preparation method according to claim 1, wherein a molar ratio of the tris(4-(pyridin-4-yl)phenyl)amine to CdCl2 is 6-8:2-3, a temperature of the coordination reaction is room temperature.

3. The preparation method according to claim 1, wherein a mode of mixing the dichloromethane solution of tris(4-(pyridin-4-yl)phenyl)amine and the methanol solution of CdCl2 comprises a first mode or a second mode; the first mode comprises following steps: dropwise adding the dichloromethane solution of tris(4-(pyridin-4-yl)phenyl)amine into the methanol solution of CdCl2; the second mode comprises following steps: putting the dichloromethane solution of tris(4-(pyridin-4-yl)phenyl)amine at a bottom of a reaction vessel, then adding a dichloromethanemethanol mixed solution, and then adding the methanol solution of CdCl2;when a method of the first mode is used for mixing, a duration of the coordination reaction is 20-30 h; and when a method of the second mode is used for mixing, a duration of the coordination reaction is 24-27 days.

4. The preparation method according to claim 1, wherein the [Cd(tppa)2Cl2] is a powder crystal or a single crystal; crystal data of the single ciystal is: belonging to monoclinic system P2i / c, and an asymmetric unit comprises one Cd11 ion, two ligand tppa molecules and two chloride ions.

5. The preparation method according to claim 1, wherein a temperature of the carbonization is 800-1000°C and a heat preservation duration is 3-4 h; and the protective atmosphere is nitrogen.

6. An MOFs-derived carbon aerogel prepared by the preparation method according to any one of claims 1-5.

7. An application of the MOF-derived carbon aerogel according to claim 6 as an anode active material in lithium ion batteries.

8. A lithium ion batteiy anode, wherein an anode active material used by the lithium ion battery anode is the MOFs-derived carbon aerogel according to claim 6.

9. The lithium ion battery anode according to claim 8, wherein the lithium ion battery anode comprises a current collector and an active material layer coated on a surface of the current collector; and compositions of the active material layer comprise an anode active material, a conductive agent and a binder.

10. A lithium ion batteiy, wherein an anode of the lithium ion battery is the lithium ion batteiy anode according to claim 8 or 9.

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