CN111129456B - Co-doped FeNCN/C and preparation method and application thereof - Google Patents

Abstract

The utility model provides a one-step in-situ synthesis method for preparing the Co-doped FeNCN/C compound, simplifies the complicated preparation process of the FeNCN material, and has simple equipment; meanwhile, the Co-doped FeNCN/C compound is prepared from cheap carbon-nitrogen sources (urea or cyanamide), organic iron salts and cobalt salts, and the method has the advantages of low raw material price, simple method, mild reaction temperature and low energy consumption; since FeNCN is a metastable compound and is easily reduced by ammonia gas generated by urea decomposition at high temperature, the flow rate control of argon is a very critical technique in the whole synthesis process. The decomposition temperature of the urea is 200-300 ℃, in order to ensure the smooth discharge of the redundant unreacted ammonia gas, the flow rate of the carrier gas argon is 100 sccm at the moment, when the temperature is increased to be more than 300 ℃, in order to discharge the residual ammonia gas as soon as possible so as to avoid the occurrence of a reduction reaction at high temperature, the flow rate of the carrier gas argon is increased to be 200-300 sccm, the method is simple and easy to control, the industrial batch production is easy to realize, and no by-product is generated in the reaction.

Description

A kind of Co-doped FeNCN/C and its preparation method and application

technical field

The invention belongs to the technical field of electrochemistry, and in particular relates to a Co-doped FeNCN/C and a preparation method and application thereof.

technical background

Due to the advantages of high energy density, long service life, and environmental friendliness, lithium-ion batteries have become a research hotspot in recent years and have been successfully commercialized. But lithium resources are relatively low on earth and expensive, which has become an obstacle to the continued development of lithium-ion batteries. Therefore, it is urgent to find an element with abundant reserves and similar properties to replace lithium. Sodium and lithium are elements of the same main group, and sodium has high reserves and wide distribution on the earth. Therefore, in recent years, a large number of scientific researchers have invested a lot of energy in the research of sodium-ion batteries, and sodium-ion batteries have also achieved rapid progress. development of. However, the radii of Na and Li are quite different, so volume expansion has become a major factor restricting the development of Na-ion batteries.

Carbodiimide compound is a new type of metal-organic framework compound with abundant pore structure. Among them, FeNCN has a band gap of 0 eV and has metal-like conductivity. It is a very suitable anode for sodium-ion batteries. s material. In 2016, foreign scholar Moulay T. Sougrati first reported transition metal carbodiimides as lithium-ion batteries and sodium-ion batteries, and showed excellent electrochemical performance, especially when FeNCN was used as a lithium-ion anode material, with good performance. 100 cycles at 56 mA g ^-1 , the capacity can be maintained at 500 mAh g ^-1 , and when applied to sodium-ion battery materials, the capacity can be maintained at 350 mAh g ^-1 (Angewandte Chemie International Edition, 2016, 55 : 5090-5095). At the same time, A. Eguia-Barrio also reported that MNCN (M=Fe, Co, Ni, Mn, Cu and Zn) has potential as an ion battery material (Journal of Power Sources, 2017, 367:130-137.). It can be seen that the multi-channel structure and high electrical conductivity of transition metal carbodiimide compounds demonstrate high electrochemical activity.

However, so far, FeNCN research work is less, the main problem is that its synthesis process is relatively complex and the preparation environment is also harsh. At present, the method reported in the literature is mainly the traditional coordination method. First, the precursor solution needs to be prepared in an oxygen-free environment using distilled water degassed by ammonia gas _. ) ₂ Fe(SO ₄ ) ₂ ]·6H ₂ O) aqueous solution by passing concentrated ammonia water to first obtain the ferrous ammonia complex ([Fe(NH ₃ ) ₆ ] ²⁺ ), and then adding [Fe(NH ₃ ) ₆ ] ²⁺ and H ₂ NCN were mixed in the liquid phase to prepare the complex Fe(NCNH) ₂ , and then the green Fe(NCNH) ₂ precursor was decomposed in a halide (KCl/LiCl) salt bath (390~410 ℃) to obtain Dark red FeNCN (Chemistry. 2009;15(7):1558-61). Among them, the synthesis and storage conditions of H ₂ NCN are relatively harsh, and it is easy to undergo hydrolysis at room temperature (pH < 2 or pH > 12) to generate urea, or to polymerize at high temperature (over 40 °C, pH 8-10), Generate dicyandiamide. Such harsh synthesis conditions greatly restrict the research progress of FeNCN.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a Co-doped FeNCN/C and its preparation method and application, so as to overcome the problems of complex synthesis process and harsh preparation environment existing in the prior art.

In order to achieve the object of the present invention, the method provided by the present invention is:

A preparation method of Co-doped FeNCN/C, comprising the following steps:

1) Add 1.0~3.0 g analytically pure urea or cyanamide, 1.0 g organic acid iron salt and 0.1~0.2 g cobalt acetate tetrahydrate into 10~30 mL deionized water, stir for 0.5-2 h to prepare iron salt The complex of , marked as solution A;

2) Freeze solution A at -30 °C for 1.5-2.5 h, and then dry it in a vacuum freeze dryer for 20-30 h to obtain flake precursor B;

3) Place the sheet precursor B in a tube furnace, the protective atmosphere is argon, the flow rate of argon is 50-100 sccm, and the temperature is increased to 300°C at a rapid rate of 10-15°C/min, and the flow rate of argon is increased. Adjust to 200 ~ 300 sccm, keep warm for 1 hour, then heat up to 400-650 °C at a slow rate of 3-10 °C/min, and keep it for 0.5 ~ 2 h, after the insulation is completed, continue to pass argon gas to natural cooling After reaching room temperature, the flow rate of argon gas was 300 sccm to obtain the final product Co-doped FeNCN/C.

The organic acid iron salt in the above step 1) is ferric ammonium oxalate or ferric ammonium citrate.

Co-doped FeNCN/C prepared by the above preparation method.

The application of the above-mentioned Co-doped FeNCN/C in the anode material of sodium ion battery.

Compared with the prior art, the beneficial effects of the present invention are as follows:

1. The present invention proposes a one-step in-situ synthesis method to prepare Co-doped FeNCN/C composites, which simplifies the tedious preparation process of FeNCN materials and has simple equipment; Organic iron salts and cobalt salts are used to prepare Co-doped FeNCN/C composites, the raw materials are cheap, the method is simple, the reaction temperature is relatively mild, and the energy consumption is low.

2. Since FeNCN is a metastable compound, it is easily reduced by ammonia generated by urea decomposition at high temperature, so the flow rate control of argon is a very critical technology in the whole synthesis process. The decomposition temperature of urea is at 200 to 300 ℃, in order to ensure the smooth discharge of unnecessary unreacted ammonia gas, the flow velocity of the carrier gas argon of the present invention is 100sccm. The residual ammonia gas is discharged to avoid reduction reaction at high temperature, and the flow rate of carrier gas argon is increased to 200-300 sccm. The method is simple and easy to control, and it is easy to realize industrial mass production, and the reaction has no by-products.

3. The product prepared by the present invention is doped with Co, which increases the defects in FeNCN and provides additional active sites, which is beneficial to increase the energy storage capacity of FeNCN, thereby improving the electrochemical performance of the product. Therefore, this material is used. The prepared negative electrode material of the sodium ion battery has good conductivity, good energy storage performance, and fast charge transfer speed, which is beneficial to realize fast charge and discharge.

Description of drawings

Fig. 1 is the XRD pattern of embodiment 1 product;

Fig. 2 is the FTIR figure of embodiment 1 product;

Fig. 3 is the SEM image of embodiment 1 product;

Fig. 4 is the TEM image of the product of Example 1

Figure 5 is a rate performance diagram of the product of Example 1 prepared as a negative electrode material for a sodium ion battery.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

The reaction principle of the invention is as follows: using urea and cyanamide as carbon source and nitrogen source, and organic iron salt as iron source to prepare Co-doped FeNCN/C composite.

Example 1:

A preparation method of Co-doped FeNCN/C, comprising the following steps:

1) Add 1.0 g of analytically pure urea, 1.0 g of ferric ammonium oxalate, and 0.1 g of cobalt acetate tetrahydrate into 10 mL of deionized water, and stir for 1 h to prepare a complex of iron salt and cobalt salt, marked as A;

2) The solution A was frozen at -30 °C for 2 h, and then dried in a vacuum freeze dryer for 24 h to obtain the flake precursor B.

3) Put product B in a tube furnace, the protective atmosphere is argon gas, the argon gas flow rate is 100 sccm, and the temperature is increased to 300 ℃ at a rapid rate of 10 °C/min, the argon gas flow rate is adjusted to 200 sccm, and the temperature is maintained. After 1 hour, the temperature was raised to 500 °C at a slow rate of 5 °C/min, and kept for 1 h. After the insulation was completed, argon gas was continued to cool to room temperature naturally, and the flow rate of argon gas was 300 sccm to obtain the final product Co-doped. HeteroFeNCN/C.

Example 2:

A preparation method of Co-doped FeNCN/C, comprising the following steps:

1) Add 2.0 g of analytically pure cyanamide, 1.0 g of ferric ammonium citrate, and 0.2 g of cobalt acetate tetrahydrate into 20 mL of deionized water, and stir for 2 h to prepare a complex of iron salts, which is marked as solution A;

2) The solution A was frozen at -30 °C for 2 h, and then dried in a vacuum freeze dryer for 24 h to obtain the flake precursor B.

3) The product B was placed in a tube furnace, the protective atmosphere was argon, and the argon flow rate was 100 sccm. After the temperature was raised to 300 ℃ at a rapid rate of 12 ℃/min, the argon gas flow rate was adjusted to 200 sccm, and the temperature was kept for 1 hour, and then heated to 450 °C at a slow rate of 3 °C/min and held for 2 h to obtain the final product Co-doped FeNCN/C.

The above embodiment 1 is the best embodiment, and the product obtained in embodiment 1 is analyzed:

Through XRD characterization analysis, the XRD pattern and FTIR pattern of the Co-doped FeNCN/C composite prepared in Example 1 are compared with the standard FeNCN material structure diagram, and it is determined that the FeNCN prepared by the method provided by the present invention has carbodiimide Structure of organic functional groups.

The product C was analyzed by Japan Rigaku D/max2000PC X-ray diffractometer. The XRD of the obtained product is shown in Figure 1. It can be seen from the figure that the diffraction peak of the product is consistent with the standard card CSD-No.419223, and the FTIR test of the prepared product shows that Contains N=C=N functional group, which is a characteristic functional group of carbodiimide compounds (Fig. 2). The sample was observed with the S4800 field emission electron microscope produced by Japan Rigaku and the FEI transmission electron microscope in the United States. It can be seen from the accompanying drawings 3 and 4 that the product is a Co-doped worm-like structure grown on the carbon film. Hetero FeCN ₂ structure, the product morphology is uniform, and the continuity is good.

The product obtained in Example 1 was prepared into a button-type sodium-ion battery, and the specific encapsulation steps were as follows: the active powder, the conductive agent (Super P), the binder carboxymethyl cellulose CMC and the styrene-butadiene rubber SBR were in a mass ratio of After the ratio of 8:1:0.5:0.5 is uniformly ground, a slurry is prepared, and the slurry is evenly coated on the copper foil with a film applicator, and then dried in a vacuum drying oven at 80°C for 12 hours. After that, the electrode sheets were assembled into sodium-ion half-cells. As can be seen from Figure 5, the battery was tested with a constant current charge and discharge using Xinwei electrochemical workstation. The capacity of the battery to charge and discharge. The test current density is 0.1A/g, and the capacity can reach 700 mAh/g. When the current density increases to 20 A/g, the capacity is still as high as 220 mAh/g. It is a high-performance high-power sodium-ion battery negative electrode Material.

The above-mentioned embodiments only represent several embodiments of the present utility model, and the descriptions thereof are specific and detailed, but should not be construed as a limitation on the scope of the utility model patent. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for this utility model shall be subject to the appended claims.

Claims (3)

1. a preparation method of Co-doped FeNCN/C, is characterized in that, comprises the following steps: 1) Add 1.0~3.0 g analytically pure urea or cyanamide, 1.0 g organic acid iron salt and 0.1~0.2 g cobalt acetate tetrahydrate into 10~30 mL deionized water, stir for 0.5-2 h to prepare iron salt The complex of , marked as solution A; 2) Freeze solution A at -30 °C for 1.5-2.5 h, and then dry it in a vacuum freeze dryer for 20-30 h to obtain flake precursor B; 3) The sheet precursor B is placed in a tube furnace, the protective atmosphere is argon, the flow rate of argon is 50-100 sccm, and the temperature is increased to 300 °C at a rapid rate of 10-15 °C/min. The gas flow rate was adjusted to 200-300 sccm, kept for 1 hour, then heated to 400-650 °C at a slow rate of 3-10 °C/min, and kept for 0.5-2 h. After the insulation was completed, continue to pass argon gas. After cooling to room temperature naturally, the flow rate of argon gas was 300 sccm to obtain the final product Co-doped FeNCN/C. 2 . The preparation method of Co-doped FeNCN/C according to claim 1 , wherein the organic acid iron salt in 1) is ferric ammonium oxalate or ferric ammonium citrate. 3 . 3. Co-doped FeNCN/C prepared according to the preparation method of claim 1 or 2.

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