CN111960422A - Preparation method and application of two-dimensional silicon nanomaterial - Google Patents

Abstract

The invention discloses a preparation method and application of a two-dimensional silicon nano material, wherein the method only needs to utilize a layered compound CaSi₂And CO₂Heating at a certain temperature to allow CO to pass through₂And CaSi₂By reaction to CaCO₃And CaO, the few-layer Si nanosheets can be obtained by acid washing after the Ca is extracted, and the Si nanosheets can be used as the negative electrode of the lithium battery and show better electrochemical performance. The discharge capacity of the first ring reaches 1200 mA.h.g^‑1The first circle of charging capacity reaches 840 mA.h.g^‑1The coulombic efficiency of the first circle reaches 70 percent, and the capacity after 500 circles of circulationNo attenuation and suitability for industrialization.

Description

A kind of preparation method of two-dimensional silicon nanomaterial and its application

technical field

The invention belongs to the field of functional materials, and relates to a preparation method and application of a two-dimensional silicon nanomaterial.

Background technique

Elemental silicon has received extensive attention in the field of lithium batteries in recent years due to its high energy density, low operating potential, and abundant reserves in the earth's crust. The theoretical capacity of silicon can reach 4200 mA hg ^-1 , which is much larger than that of commercial graphite anodes (theoretical capacity ~370 mA hg ^-1 ). However, during the intercalation and delithiation process of silicon material, the volume change reaches 400%, which can easily cause the disconnection of the electrode and the formation of an unstable solid electrolyte interface (SEI) film, thus affecting the working life of the battery. Due to its ultra-thin sheet structure, two-dimensional silicon wafers can effectively release the huge stress caused by volume changes; on the other hand, the two-dimensional structure is conducive to the transport of ions and electrons, and can improve the power density of silicon anodes, which has been widely used. s concern. The use of layered Zintl compound CaSi ₂ as a raw material for the preparation of single-layer or few-layer silicon wafers is an effective approach. But the current mainstream method is still low temperature strong acid stripping method or high temperature vacuum extraction method, such as (Nakano et al., J. Am. Chem. Soc., 2012, 134, 5452-5455; An et al., ACS Nano, 2019, 13, 13690-13701, etc.). These methods require relatively harsh reaction conditions, such as low temperature, high vacuum, and long reaction time, which limit their industrialization.

Zhang et al. (Zhang et al., Nanoscale, 2018, 10, 5626-5633) of Zhejiang University obtained a Si/C composite by the reaction of CO ₂ and Mg ₂ Si and subsequent acid treatment, which showed good performance as a negative electrode lithium battery performance. The author thinks that the reaction mechanism is that Mg ₂ Si decomposes at a certain temperature to form Mg and Si, and then Mg further reacts with CO ₂ to form MgO and C. Si/C composites were obtained after acid treatment.

The existing method for preparing single-layer or few-layer Si wafers by using calcium silicide has harsh reaction conditions and large environmental pollution, which is not conducive to industrialization. The reaction between Mg ₂ Si and CO ₂ can only obtain silicon nanoparticles, but cannot form low-dimensional silicon nanomaterials with regular morphology.

SUMMARY OF THE INVENTION

Aiming at the deficiencies of the prior art, the present invention provides a preparation method and application of a two-dimensional silicon nanomaterial. The method only needs to use layered compounds CaSi ₂ and CO ₂ to heat at a certain temperature, and the method can pass CO ₂ and CO 2 . The reaction of CaSi ₂ generates CaCO ₃ and CaO. After the Ca is extracted, the few-layer Si nanosheets can be obtained by pickling. The few-layer Si nanosheets are used as the negative electrode of lithium batteries, and can show good electrochemical performance. The method has the advantages of low reaction temperature, short reaction time, easy amplification and synthesis, and is suitable for industrialization.

A preparation method of two-dimensional silicon nanomaterial, comprising the following steps:

Step 1, put 1-10g of CaSi ₂ in a horizontally placed tubular reactor, the CaSi ₂ is a Zintl compound with a layered structure;

Step 2, pass pure _CO2 or a mixed gas containing _CO2 into the tubular reaction furnace, exhaust the air in the tubular furnace, and react at 300-800 °C at a heating rate of 5-10 °C/min for 3- 10 hours;

Step 3: After the temperature is lowered to room temperature, the reacted product is washed with 10% dilute hydrochloric acid, washed with distilled water, and dried in vacuum at 70° C. to obtain two-dimensional silicon nanosheets.

As an improvement, the CaSi ₂ weighed in step 1 needs to be treated with sodium hydroxide with a concentration of 1-3 M to remove the impurity silicon contained in the purchased CaSi ₂ raw materials.

As an improvement, the mixed gas containing CO ₂ in step 2 is a mixed gas of CO ₂ /N ₂ or a mixed gas of CO ₂ /Ar; the CO ₂ content is 10%-50%.

The application of the above-mentioned two-dimensional silicon nanomaterials in the preparation of negative electrode materials for lithium batteries.

For the first time, it was found that the Ca layer in CaSi ₂ can be directly extracted by CO ₂ gas under certain conditions, so that the layered compound CaSi ₂ can be peeled off. The reaction products are CaCO ₃ , CaO and Si sheets with less surface oxygen.

Beneficial effects:

Compared with the prior art, the preparation method and application of a two-dimensional silicon nanomaterial of the present invention have the following advantages:

The method only needs to use layered compounds CaSi ₂ and CO ₂ to heat and react at a certain temperature to generate CaCO ₃ and CaO. After the Ca is extracted, two-dimensional Si nanosheets can be obtained by pickling. As the negative electrode of lithium battery, it shows good lithium storage performance and good electrochemical performance. The first cycle discharge capacity reaches 1200 mA•h•g ^-1 , and the first cycle charge capacity reaches 840 mA•h•g ^-1 , the Coulomb efficiency of the first lap reaches 70%. In addition, this method has the advantages of low reaction temperature, short reaction time (3-5 hours), easy amplification and synthesis, and is suitable for industrialization.

Description of drawings

Figure 1 is the capacity-voltage curve of the first cycle of charge and discharge of the two-dimensional silicon wafer electrode;

Fig. ₂ is the scanning electron microscope image of CaSi raw material;

Fig. 3 is the scanning electron microscope image of the obtained two-dimensional silicon wafer of the present invention;

Fig. 4 is the XRD pattern of the reaction product of CaSi ₂ and CO ₂ ;

Figure 5 shows the long-cycle stability data of the two-dimensional silicon wafer electrode.

Detailed ways

Example 1

A preparation method of two-dimensional silicon nanomaterial, comprising the following steps:

Step 1, 5 grams of CaSi ₂ is treated with 1-3 M sodium hydroxide to remove the impurity silicon contained in the purchased CaSi ₂ raw material, and placed in a flat tubular reactor.

Step 2: Passing CO ₂ /Ar mixed gas (20% volume fraction of CO ₂ ) into the tubular reaction furnace to exhaust the air in the tubular furnace, and at a heating rate of 5-10 ° C/min, the temperature is increased to 700 ° C React for 3 hours.

In step 3, after the temperature drops to room temperature, the obtained product is washed with 1 M dilute hydrochloric acid, washed with distilled water, and dried to obtain two-dimensional silicon nanosheets.

The above-mentioned two-dimensional silicon nanosheets are used to prepare battery anode materials, and the specific steps are as follows:

Step 4: Disperse the two-dimensional silicon nanosheets obtained in the third step in distilled water for further ultrasonic dispersion for half an hour, coat polydopamine by solution polymerization, and then dry the product and heat treatment at 800 °C under an argon atmosphere for 4 hours to coat the carbon layer.

Step 5: The silicon wafer-carbon composite material obtained in the fourth step, conductive graphite, and sodium carboxymethyl cellulose (CMC) are made into a slurry in a mass ratio of 8:1:1, and coated on copper foil, 100 ℃ vacuum drying overnight to prepare battery electrode sheets. A button-type lithium battery CR2025 was used as a simulated battery, the electrolyte composition was 1 M LiPF6 (acetate carbonate:diethyl carbonate=1:1 volume ratio), and a polypropylene film was used as a separator. The lithium sheet is the counter electrode.

Figure ₂ is a scanning electron microscope image of the CaSi raw material used in this example, from which it can be seen that it has a block-like morphology. After reacting with _CO at a certain temperature, the XRD of the obtained product is shown in Figure 4. It can be seen that To generate CaO and CaCO ₃ . The CaO here is obtained from the decomposition _of CaCO3. When the product was washed with dilute hydrochloric acid, as shown by the scanning electron microscope in FIG. 3 , a two-dimensional sheet-like structure of Si material was obtained, indicating that the method of the present invention successfully achieved the peeling of CaSi ₂ .

The two-dimensional silicon nanosheets obtained in Example 1 were used to make the negative electrode material of the lithium battery, and the performance was tested. The data obtained are shown in FIG. 1 . It can be seen from Fig. 1 that the discharge specific capacity is as high as 1200 mA hg ^-1 in the first cycle, and the charge specific capacity is 850 mAh g ^-1 .

Example 2

Under the condition that other steps remain unchanged, the CO ₂ /Ar gas in step 2 is replaced with pure CO ₂ gas, and the reaction is carried out at 500 ° C for 3 hours. The electrochemical performance of the obtained material is basically the same as that of Example 1.

Example 3

Under the condition that other steps remain unchanged, the _CO2 /Ar gas in step 2 is replaced with pure CO2/N2 mixed gas, and the reaction is carried out at 600 °C for 5 hours. The electrochemical performance of the obtained material is basically the same as that of Example 1.

Comparative ratio

Zhang et al. (Zhang et al., Nanoscale, 2018, 10, 5626-5633) of Zhejiang University obtained a Si/C composite by the reaction of CO ₂ and Mg ₂ Si and subsequent acid treatment, which showed good performance as a negative electrode lithium battery performance. The author thinks that the reaction mechanism is that Mg ₂ Si decomposes at a certain temperature to form Mg and Si, and then Mg further reacts with CO ₂ to form MgO and C. Si/C composites were obtained after acid treatment.

The reaction mechanism of the above comparative example is completely different from ours, and the obtained material has no fixed morphology, and has poor cycle performance as an electrode material for lithium batteries. After 100 cycles, the capacity retention rate is less than 70%. The 2D silicon material we obtained is very stable, and the capacity increases after 500 cycles, as shown in Figure 5.

The above are only preferred specific embodiments of the present invention, and the protection scope of the present invention is not limited thereto. Any person skilled in the art can obviously obtain the simplicity of the technical solution within the technical scope disclosed in the present invention. Variations or equivalent substitutions fall within the protection scope of the present invention.

Claims (5)

1. A preparation method of a two-dimensional silicon nano material is characterized by comprising the following steps:

step 1, 1-10g of CaSi₂As for the horizontally placed tubesIn a reactor of the formula, the CaSi₂Is a Zintl compound with a layered structure;

step 2, introducing pure CO into the tubular reaction furnace₂Or containing CO₂Exhausting the air in the tube furnace, and reacting at 300-800 ℃ for 3-10 hours at the heating rate of 5-10 ℃/min;

and 3, after the temperature is reduced to the room temperature, washing the reaction product by using 10% dilute hydrochloric acid, washing by using distilled water, and drying in vacuum at 70 ℃ to obtain the two-dimensional silicon nanosheet.

2. The method as claimed in claim 1, wherein the CaSi weighed in step 1 is used as the raw material₂Treatment with 1-3M sodium hydroxide is required.

3. The method as claimed in claim 1, wherein the step 2 comprises CO₂The mixed gas of (A) is CO₂/N₂Mixed gases or CO₂A mixed gas of/Ar; the CO is₂The content is 10-50%.

4. Use of the two-dimensional silicon nanomaterial prepared according to claim 1 for preparing a negative electrode material for a lithium battery.

5. The application of claim 4, wherein the two-dimensional silicon nanosheets are dispersed in distilled water, ultrasonically dispersed for half an hour, coated with polydopamine by a solution polymerization method, dried, and then placed in an argon atmosphere for heat treatment at 800 ℃ for 4 hours to coat a carbon layer, so as to obtain the silicon wafer-carbon composite material; preparing a silicon wafer-carbon composite material, conductive graphite and sodium carboxymethylcellulose into slurry according to the mass ratio of 8:1:1, coating the slurry on a copper foil, and carrying out vacuum drying at 100 ℃ overnight to prepare the battery electrode plate.

Images