A cobalt-doped flower-like montmorillonite composite material, a preparation method and application thereof

Abstract

The application provides a cobalt-doped flower-like montmorillonite composite material and a preparation method and application thereof, and belongs to the technical field of sodium ion battery electrode materials. The composite material is a flower-like material generated by cobalt doping reassembly with 2D montmorillonite nanosheets as a substrate; the content of cobalt in the composite material is 20-30%. In the application, the montmorillonite mineral material is peeled into 2D nanosheets through ultrasonic peeling with the montmorillonite mineral material as a sacrifice template, the 2D nanosheets are reassembled with cobalt ions and dimethyl imidazole at normal temperature, and then the cobalt-doped reassembled flower-like montmorillonite composite material is formed through high-temperature annealing under inert gas protection. The cobalt-doped flower-like montmorillonite composite material prepared by the method has a specific capacity of 193 mAh / g after 5000 cycles at a current density of 2 A / g when used as a half-cell sodium ion battery negative material, and exhibits excellent cycle performance; the specific capacity is more than 276 mAh / g after 100 cycles at a current density of 0.1 A / g, and the rate performance is excellent.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion battery electrode materials, and particularly relates to a cobalt-doped flower-like montmorillonite composite material as well as a preparation method and application thereof. BACKGROUND

[0002] With the exhaustion of global fossil resources and the deterioration of the environment, the demand for renewable clean energy is growing. The exploration and research of large-scale energy storage systems are the key to solving the problem of intermittent and discontinuous power supply of renewable clean energy. Lithium ion batteries (LIBs) and sodium ion batteries (SIBs) are two important energy storage systems in energy storage devices. However, lithium elements are mainly distributed in the form of ore in the earth's crust and there is a problem of uneven global distribution. In contrast, the abundance of sodium elements in the earth's crust is about 1000 times that of lithium elements and is uniformly and widely distributed in the sea. Sodium ion batteries have the advantages of green and sustainable development in large-scale energy storage applications of clean energy. The current commercial negative electrode material of lithium ion batteries is generally graphite. However, due to the larger ionic radius of sodium ions than lithium ions, the interlayer spacing of graphite is limited and is not suitable for sodium intercalation reaction.

[0003] Transition metal sulfides have excellent electrochemical performance due to their high theoretical capacity and have attracted extensive attention from researchers. Patent application CN108075128A discloses a nitrogen-doped carbon-coated cobalt-nickel sulfide / graphene composite electrode material. In the one-step carbonization and sulfidation process, the organic ligand is carbonized to form carbon, and the nitrogen element is doped into the carbon formed by the organic ligand in the sulfidation process, thereby improving the electrical conductivity and defects of the electrode material and improving the electrochemical performance. However, the relative positions of cobalt-nickel sulfide particles are fixed, and the volume expansion caused by the insertion of sodium ions during use is very serious, which may even cause the electrode to powder, thereby causing the structure of the electrode material to crack, and ultimately leading to poor rate performance and cycle stability. Due to the lack of sodium ion battery negative electrode materials with good electrochemical performance, the development of sodium ion batteries is limited. Therefore, it is urgent to develop negative electrode materials for high-performance sodium ion batteries. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides a cobalt-doped flower-like montmorillonite composite material, which can solve the problem of volume expansion of the negative electrode material during sodium intercalation / deintercalation, leading to electrode powdering. At the same time, the doping of cobalt greatly improves the electrical conductivity of montmorillonite, opening up the application of montmorillonite in sodium ion batteries.

[0005] In order to achieve the above object, the cobalt-doped flower-like montmorillonite composite material has the following characteristics: the cobalt-doped flower-like montmorillonite composite material is a flower-like material generated by cobalt doping and reassembly based on 2D montmorillonite nanosheets, and the content of cobalt in the composite material is 20-30%.

[0006] Another object of the present application is to provide a preparation method of the cobalt-doped flower-like montmorillonite composite material, comprising the following steps:

[0007] S1. Montmorillonite is added to pure water and stirred uniformly, and then ultrasonic treatment is performed, and the obtained solution is centrifuged to obtain the supernatant, which is a 2D montmorillonite nanosheet solution;

[0008] S2. Cobalt nitrate and dimethyl imidazole are added to the 2D montmorillonite nanosheet solution obtained in step S1, and uniform stirring is performed, and after washing, separation and drying, a flower-like montmorillonite organic cobalt composite material is obtained;

[0009] S3. The flower-like montmorillonite organic cobalt composite material obtained in step S2 is subjected to high-temperature annealing under a protective gas to obtain a cobalt-doped flower-like montmorillonite composite material.

[0010] Montmorillonite is a typical layered aluminosilicate mineral, two silica tetrahedral sheets are sandwiched between aluminum oxide octahedral sheets, but the van der Waals force and the electrostatic force between the layers are weak, which enables the montmorillonite to form independent atomic layers after exfoliation. The sandwich-like montmorillonite is converted into 2D montmorillonite after ultrasonic exfoliation treatment, the exfoliated 2D montmorillonite nanosheet has a two-dimensional sheet shape, a large specific surface area and abundant hydroxyl groups, and can attach more ions, the reassembled flower-like structure makes the overall structure more stable, and the inlaying of cobalt particles can enhance the conductivity of inorganic minerals; at the same time, the high-temperature sintering of the composite material can completely remove the structural water of montmorillonite, and the montmorillonite loses the problem of swelling in water and can be applied in battery materials.

[0011] Preferably, in step S1, the ultrasonic frequency is 35-45 KHz, and the ultrasonic time is 5-12 h; the centrifugal speed is 5000-7000 r / min, and the centrifugal time is 5 min.

[0012] Preferably, in step S2, the molar ratio of cobalt ions to dimethyl imidazole is 1: (4-9).

[0013] Preferably, in step S3, the protective gas is high-purity argon, the high-temperature annealing temperature is 600-700℃, and the time is 1-3 h.

[0014] Preferably, in step S1, the montmorillonite in step S1 is sodium-based montmorillonite.

[0015] Preferably, the cobalt-doped flower-like montmorillonite composite material is applied to a sodium ion battery electrode material.

[0016] Compared with the prior art, the present application has the advantages of:

[0017] (1) The present application first applies montmorillonite to a sodium ion battery electrode material, and solves the problems of swelling of montmorillonite when it comes into contact with water and poor conductivity by peeling, high-temperature calcination and cobalt ion doping; ultrasonic peeling and recombination make montmorillonite have more active sites, which can load more cobalt, thereby improving the specific capacity; cobalt doping can improve the conductivity of the composite material and improve the electrochemical performance of the material.

[0018] (2) The cobalt-doped flower-like montmorillonite composite material prepared by the present application is used as a sodium ion battery negative material, which maintains a specific capacity of 193 mAh / g after 5000 cycles at a current density of 2A / g, exhibits excellent cycle performance, and maintains a specific capacity of more than 276 mAh / g after 100 cycles at a current density of 0.1A / g, and has excellent rate performance. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 XRD patterns of cobalt-doped flower-like montmorillonite, cobalt element and sodium-based montmorillonite prepared in Example 1;

[0020] Figure 2 SEM image of the cobalt-doped flower-like montmorillonite composite material prepared in Example 1;

[0021] Figure 3 TEM image of the cobalt-doped flower-like montmorillonite composite material prepared in Example 1;

[0022] Figure 4 Cycle performance graph of the cobalt-doped flower-like montmorillonite composite material prepared in Example 1 at a current density of 2A / g;

[0023] Figure 5 Cycle performance graph of the cobalt-doped flower-like montmorillonite composite material prepared in Example 1 at a current density of 0.1A / g;

[0024] Figure 6 SEM image of the montmorillonite composite cobalt element composite material prepared in Comparative Example 1;

[0025] Figure 7 SEM image of the peeled and reassembled flower-like montmorillonite composite material prepared in Comparative Example 2;

[0026] Figure 8 SEM image of the nitrogen-doped carbon cobalt material prepared in Comparative Example 3;

[0027] Figure 9 ​SEM image of sodium-based montmorillonite prepared for Comparative Example 4;

[0028] Figure 10 Cycling performance graph of cobalt-doped flower-like montmorillonite composite material prepared for Example 1, montmorillonite composite cobalt elemental composite material prepared for Comparative Example 1, exfoliated reassembled flower-like montmorillonite composite material prepared for Comparative Example 2, nitrogen-doped carbon cobalt material prepared for Comparative Example 3, and sodium-based montmorillonite prepared for Comparative Example 4 at a current density of 2A / g. DETAILED DESCRIPTION

[0029] The technical solutions of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0030] Example 1

[0031] A preparation method of a cobalt-doped flower-like montmorillonite composite material, specifically comprising the following steps:

[0032] S1. Dissolve 1g of sodium-based montmorillonite into 100ml of deionized water and stir for 2h, then perform ultrasonic exfoliation treatment, ultrasonic exfoliation at a frequency of 40KHz for 10h, centrifuge the obtained solution at a speed of 6000r / min for 5min, and take the supernatant after centrifugation, which is the exfoliated 2D montmorillonite nanosheet;

[0033] S2. Homogeneously stir 20ml of the exfoliated 2D montmorillonite nanosheet solution obtained in step S1 with 1mmol of cobalt nitrate and 8mmol of dimethylimidazole for 15min, and then stand for 5h, and after washing, separation and drying, a flower-like montmorillonite organic cobalt composite material is obtained;

[0034] S3. Perform high-temperature annealing of the flower-like montmorillonite organic cobalt composite material obtained in step S2 at 600℃ under a protective gas for 3h to obtain the cobalt-doped flower-like montmorillonite composite material.

[0035] EDS detection analysis shows that the content of cobalt in the cobalt-doped flower-like montmorillonite composite material is about 25%.

[0036] Figure 1 XRD graph of the cobalt-doped flower-like montmorillonite, cobalt element, and sodium-based montmorillonite prepared for Example 1, from which it can be seen that the cobalt-doped flower-like montmorillonite contains characteristic peaks of cobalt element and sodium-based montmorillonite, indicating that a certain amount of cobalt element is successfully doped in the flower-like montmorillonite.

[0037] Figure 2 、 3The SEM and TEM images of the cobalt-doped flower-like montmorillonite composite material prepared in Example 1 show that the composite material has a flower-like structure with granular protrusions on the surface. The TEM image shows that cobalt particles are uniformly distributed in the flower-like structure material.

[0038] Figure 4 、 5 The cycle performance graphs of the cobalt-doped flower-like montmorillonite composite material prepared in Example 1 at current densities of 2A / g and 0.1A / g show that the composite material still has a specific capacity of 193mAh / g after 5000 cycles at a current density of 2A / g. Figure 4 The cycle performance graphs of the cobalt-doped flower-like montmorillonite composite material prepared in Example 1 at current densities of 2A / g and 0.1A / g show that the composite material still has a specific capacity of 193mAh / g after 5000 cycles at a current density of 2A / g. Figure 5 The cycle performance graphs of the cobalt-doped flower-like montmorillonite composite material prepared in Example 1 at current densities of 2A / g and 0.1A / g show that the composite material still has a specific capacity of 193mAh / g after 5000 cycles at a current density of 2A / g.

[0039] Example 2

[0040] A method for preparing a cobalt-doped flower-like montmorillonite composite material, specifically comprising the following steps:

[0041] S1. Dissolve 1g of sodium-based montmorillonite in 100ml of deionized water and stir for 2h, then perform ultrasonic peeling treatment at a frequency of 40KHz for 5h. Centrifuge the obtained solution at a speed of 7000r / min for 8min, and take the supernatant as the peeled 2D montmorillonite nanosheets;

[0042] S2. Homogeneously stir 20ml of the peeled 2D montmorillonite nanosheet solution obtained in step S1 with 1mmol of cobalt nitrate and 4mmol of dimethyl imidazole for 15min, and then stand for 5h. After washing, separation and drying, the flower-like montmorillonite organic cobalt composite material is obtained;

[0043] S3. Anneal the flower-like montmorillonite organic cobalt composite material obtained in step S2 at 700℃ for 1h under a protective gas to obtain the cobalt-doped flower-like montmorillonite composite material.

[0044] Example 3

[0045] A method for preparing a cobalt-doped flower-like montmorillonite composite material, specifically comprising the following steps:

[0046] S1. Dissolve 1g of sodium-based montmorillonite in 100ml of deionized water and stir for 2h, then perform ultrasonic peeling treatment at a frequency of 40KHz for 5h. Centrifuge the obtained solution at a speed of 7000r / min for 8min, and take the supernatant as the peeled 2D montmorillonite nanosheets;

[0047] S2. The 20 ml solution of exfoliated 2D montmorillonite nanosheets obtained in step S1 was uniformly stirred with 1 mmol of cobalt nitrate and 9 mmol of dimethylimidazole for 15 min, and then left to stand for 5 h. After washing, separation and drying, a flower-shaped montmorillonite organic cobalt composite material was obtained.

[0048] S3. The flower-shaped montmorillonite organic cobalt composite material obtained in step S2 was annealed at 600°C for 1 h under a protective gas to obtain the cobalt-doped flower-shaped montmorillonite composite material.

[0049] Comparative Example 1

[0050] The present comparative example provides a method for preparing a montmorillonite composite cobalt elemental composite material, which specifically comprises the following steps:

[0051] S1. 0.5 g of sodium-based montmorillonite was dissolved in 20 ml of deionized water, and then uniformly stirred with 1 mmol of cobalt nitrate and 8 mmol of dimethylimidazole for 15 min. After standing for 5 h, the solution was washed, separated and dried to obtain a montmorillonite organic cobalt composite material.

[0052] S2. The montmorillonite organic cobalt composite material obtained in step S2 was annealed at 600°C for 3 h under a protective gas to obtain the cobalt-doped montmorillonite composite material.

[0053] Figure 6 The SEM image of the cobalt-doped montmorillonite composite material prepared in Comparative Example 1 is shown in the figure. As can be seen from the figure, the unexfoliated montmorillonite has a multi-layer structure, and many cobalt elements are not incorporated into the montmorillonite, but are self-polymerized into small particles on the surface.

[0054] Comparative Example 2

[0055] The present comparative example provides a method for preparing a flower-shaped montmorillonite composite material, which specifically comprises the following steps:

[0056] S1. 1 g of sodium-based montmorillonite was dissolved in 100 ml of deionized water and stirred for 2 h, and then subjected to ultrasonic exfoliation treatment at a frequency of 40 KHz for 10 h. The obtained solution was centrifuged at a speed of 6000 r / min for 5 min, and the supernatant was taken after centrifugation, which was the exfoliated 2D montmorillonite nanosheet solution.

[0057] S2. 100 mg of cetyltrimethylammonium bromide was dissolved in 50 ml of the 2D montmorillonite nanosheet solution, and stirred for 15 min. After washing, separation and drying, a flower-shaped montmorillonite material was obtained.

[0058] Figure 7 The SEM image of the flower-shaped montmorillonite material prepared in Comparative Example 2 is shown in the figure. As can be seen from the figure, the surface of the flower-shaped material is smooth, and no cobalt particles are protruding.

[0059] Comparative Example 3

[0060] The present comparative example provides a preparation method of a nitrogen-doped carbon cobalt material, specifically comprising the following steps:

[0061] S1. Dissolve 1 mmol of cobalt nitrate and 8 mmol of dimethylimidazole into 20 ml of deionized water respectively, mix and stir for 15 min, then stand for 5 h, and after washing, separation and drying, obtain the organic cobalt composite material;

[0062] S2. The organic cobalt composite material obtained in step S1 is annealed at 600°C for 3 h under a protective gas to obtain the nitrogen-doped carbon cobalt material.

[0063] Figure 8 The SEM image of the nitrogen-doped carbon cobalt material prepared for Comparative Example 3. As can be seen from the figure, without the addition of montmorillonite, cobalt grows into a sheet structure.

[0064] Comparative Example 4

[0065] The present comparative example provides a preparation method of a montmorillonite composite material, specifically comprising the following steps:

[0066] S1. Anneal 1 g of sodium-based montmorillonite at 600°C for 3 h under a protective gas to obtain the montmorillonite composite material

[0067] Figure 9 The SEM image of the montmorillonite material prepared for Comparative Example 4. As can be seen from the figure, the montmorillonite is a block material.

[0068] Application Example

[0069] The composite materials prepared in Examples 1-3 and Comparative Examples 1-4, conductive agent (Super P) and carboxymethyl cellulose (CMC) are mixed in a mass ratio of 7:2:1, and a proper amount of ultrapure water is added to form a slurry, which is coated on a copper foil using a doctor blade or a four-sided coating device to prepare a negative electrode sheet. The coated copper foil is placed in a drying oven at 80°C for 12 h, and then the coated copper foil is cut into small round pieces with a diameter of 12 mm, and is placed in a glove box to assemble into a button cell (CR2032). The prepared composite material is used as the working electrode, and a sodium block is used as the counter electrode to test its electrochemical performance, wherein the separator is Whatman GF / A, and the electrolyte system is 1M NaClO4 solute and ethylene carbonate (EC)+dimethyl carbonate (DMC)+5%FEC solvent, and the volume ratio of EC and DMC is 1:1.

[0070] The assembled button cell was subjected to electrochemical performance test, and the test instrument used in the electrochemical performance test was as follows: a LANHE-CT2001A type multi-channel battery test system produced by Wuhan Lantian Electronics Co., Ltd., the static time was 12 h, the voltage window range was 0.01-3.0 V, the current density range was 2000 mA g -1 , and the cycle number range was 100-5000 times.

[0071] The cycle performance of the composite materials prepared in Examples 1-3 and Comparative Examples 1-4 at a current density of 2 A / g is shown in Table 1.

[0072] Table 1 Cycle performance at a current density of 2 A / g

[0073]

[0074] From Figure 10 It can be seen from Table 1 that the cobalt-doped flower-like montmorillonite composite material provided by the embodiments of the present application has excellent cycle performance, and the specific capacity is all above 185 mAh / g after 1000 cycles at a current density of 2 A / g. Comparative Example 1 is a montmorillonite composite cobalt elemental material, and because many cobalt elements are not incorporated into the montmorillonite, the specific capacity is 74 mAh / g after 1000 cycles. Comparative Example 2 is a flower-like montmorillonite composite material, and because it is not doped with cobalt, the specific capacity is only 64 mAh / g. Comparative Example 3 is a cobalt material doped with nitrogen, and the specific capacity is 120 mAh / g. Comparative Example 4 is a blocky montmorillonite material, and the specific capacity is only 21.1 mAh / g.

[0075] Although the embodiments of the present application have been shown and described, it can be understood by those of ordinary skill in the art that various changes, modifications, replacements and variations can be made to these embodiments without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. Use of a cobalt-doped flower-like montmorillonite composite material as a negative electrode material for sodium-ion half-batteries, characterized in that, The cobalt-doped flower-like montmorillonite composite material is a flower-like material generated by cobalt doping reassembly with 2D montmorillonite nanosheet as a substrate; the content of cobalt in the composite material is 20-30%; The preparation method of the cobalt-doped flower-like montmorillonite composite material comprises the following steps: S1. Montmorillonite is added to pure water and stirred uniformly, and then ultrasonic treatment is performed; the obtained solution is centrifuged, and the supernatant is taken as a 2D montmorillonite nanosheet solution after peeling; S2. Cobalt nitrate and dimethyl imidazole are added to the 2D montmorillonite nanosheet solution obtained in step S1, and uniformly stirred and mixed; after washing, separation and drying, a flower-like montmorillonite organic cobalt composite material is obtained; S3. The flower-like montmorillonite organic cobalt composite material obtained in step S2 is subjected to high-temperature annealing under a protective gas to obtain a cobalt-doped flower-like montmorillonite composite material; the high-temperature annealing temperature is 600-700 DEG C, and the annealing time is 1-3 h.

2. The use of a cobalt-doped flower-like montmorillonite composite material as claimed in claim 1 in a sodium-ion half-battery negative electrode material, characterized in that, In step S1, the ultrasonic frequency is 35-45 KHz, the ultrasonic time is 5-12 h, the centrifugal speed is 5000-7000 r / min, and the centrifugal time is 5-10 min.

3. The use of a cobalt-doped flower-like montmorillonite composite material as claimed in claim 1 in a sodium-ion half-battery negative electrode material, characterized in that, In step S2, the molar ratio of cobalt ions to dimethyl imidazole is 1: (4-9).

4. The use of a cobalt-doped flower-like montmorillonite composite material as claimed in claim 1 in a sodium-ion half-battery negative electrode material, characterized in that, In step S3, the protective gas is high-purity argon.

5. The use of a cobalt-doped flower-like montmorillonite composite material according to claim 1 as a negative electrode material for sodium-ion half-batteries, characterized in that, In step S1, the montmorillonite is sodium-based montmorillonite.

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