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

Preparation method and application of two-dimensional silicon nanomaterial

Technical Field

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

Background

Elemental silicon materials have received much attention in the field of lithium batteries in recent years due to their high energy density, low operating potential and abundant reserves in the earth's crust. The theoretical capacity of silicon can reach 4200 mA h g^-1Is far larger than that of a commercial graphite cathode (theoretical capacity-370 mA h g)^-1). However, in the process of lithium intercalation and deintercalation, the volume change of the silicon material reaches 400%, which easily causes the disconnection of the electrode and the formation of an unstable Solid Electrolyte Interface (SEI) film, thereby affecting the working life of the battery. Due to the ultrathin lamellar structure of the two-dimensional silicon wafer, huge stress caused by volume change can be effectively released; on the other hand, the two-dimensional structure is beneficial to the transmission of ions and electrons, and can improve the power density of the silicon cathode, thereby obtaining wide attention. Using layered Zintl compounds CaSi₂Is an effective way to prepare single-layer or few-layer silicon chip. However, the mainstream methods at present are low-temperature strong acid stripping methods or high-temperature vacuum extraction methods, 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 severe reaction conditions such as low temperature, high vacuum, long reaction time, etc., which limits their industrialization.

Zhejiang university Zhang et al (Zhang et al, Nanoscale, 2018, 10, 5626-5633) utilized CO₂And Mg₂The Si reaction and subsequent acid treatment yielded Si/C composites that showed good lithium electrical performance as the negative electrode. The reaction mechanism considered by the authors is firstly Mg₂Decomposing Si at a certain temperature to form Mg and Si, and further mixing Mg with CO₂MgO and C are generated by reaction. And obtaining the Si/C composite material after acid treatment.

The existing method for preparing the single-layer or few-layer Si sheet by utilizing the calcium silicide has harsh reaction conditions and large environmental pollution, and is not beneficial to industrialization. Using Mg₂Si and CO₂The reaction can only obtain silicon nano particles, and can not form the low-dimensional silicon nano material with regular morphology.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a preparation method and application of a two-dimensional silicon nano material, and 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 can be used as the negative electrode of the lithium battery, and the good electrochemical performance can be displayed. The method has the advantages of low reaction temperature, short reaction time and easy scale-up synthesis, and is suitable for industrialization.

A preparation method of a two-dimensional silicon nano material comprises the following steps:

step 1, 1-10g of CaSi₂In the case of a horizontally arranged tube reactor, 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.

As an improvement, the CaSi weighed in the step 1₂Removing CaSi by treating with 1-3M sodium hydroxide₂Silicon as an impurity contained in the raw material.

As an improvement, the CO content in the step 2₂The mixed gas of (A) is CO₂/N₂Mixed gases or CO₂A mixed gas of/Ar; the CO is₂The content is 10-50%.

The two-dimensional silicon nanomaterial is applied to preparation of a lithium battery negative electrode material.

The first discovery of the utilization of CO₂The gas can directly extract CaSi under certain conditions₂A Ca layer in (C) to form a layered compound CaSi₂Stripping, reaction product having CaCO₃CaO and Si flakes with a small surface area.

Has the advantages that:

compared with the prior art, the preparation method and the application of the two-dimensional silicon nanomaterial have the following advantages:

the method only needs to utilize a layered compound CaSi₂And CO₂Heating and reacting at a certain temperature to generate CaCO₃And CaO, the Ca is extracted out, the two-dimensional Si nanosheets can be obtained through acid washing, the obtained few-layer Si nanosheets are used as the negative electrode of the lithium battery, the good lithium storage performance is shown, the good electrochemical performance can be shown, and the first-circle discharge capacity reaches 1200 mA.h.g^-1The first circle of charging capacity reaches 840 mA.h.g^-1And the coulomb efficiency of the first circle reaches 70 percent. In addition, the method has the advantages of low reaction temperature, short reaction time (3-5 hours), easy amplification and synthesis, and is suitable for industrialization.

Drawings

FIG. 1 is a capacity-voltage curve of a first circle of charge and discharge of a two-dimensional silicon wafer electrode;

FIG. 2 shows CaSi₂Scanning electron microscope images of the raw materials;

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

FIG. 4 shows CaSi₂And CO₂XRD pattern of the reaction product;

FIG. 5 is two-dimensional silicon wafer electrode long cycle stability data.

Detailed Description

Example 1

A preparation method of a two-dimensional silicon nano material comprises the following steps:

step 1, 5 g of CaSi₂With hydrogen hydroxide in a concentration of 1-3MSodium treatment to remove CaSi₂Impurity silicon contained in the raw material is placed in a horizontally placed tubular reaction furnace.

Step 2, introducing CO into the tubular reaction furnace₂Mixed gas of/Ar (20% volume fraction CO)₂) Exhausting the air in the tube furnace, and heating to 700 ℃ at the heating rate of 5-10 ℃/min for reacting for 3 hours.

And 3, after the temperature is reduced to the room temperature, washing the obtained product with 1M dilute hydrochloric acid, washing with distilled water, and drying to obtain the two-dimensional silicon nanosheet.

The two-dimensional silicon nanosheet is used for preparing a battery cathode material, and the specific steps are as follows:

and 4, dispersing the two-dimensional silicon nanosheets obtained in the step 3 in distilled water for further ultrasonic dispersion for half an hour, coating polydopamine by a solution polymerization method, drying the product, and performing heat treatment at 800 ℃ for 4 hours in an argon atmosphere to coat a carbon layer.

And 5, preparing the silicon wafer-carbon composite material obtained in the step 4, conductive graphite and sodium carboxymethyl cellulose (CMC) into slurry according to the mass ratio of 8:1:1, coating the slurry on a copper foil, and performing vacuum drying at 100 ℃ overnight to prepare the electrode plate of the battery. A lithium button cell CR2025 was used as the simulated cell, the electrolyte composition was 1M LiPF6 (acetic carbonate: diethyl carbonate =1:1 volume ratio), and a polypropylene membrane was used as the separator. The lithium sheet is a counter electrode.

FIG. 2 shows CaSi used in the present example₂The raw material can be seen in a scanning electron microscope image in a blocky shape by being mixed with CO₂XRD of the product obtained after the reaction at a certain temperature is shown in figure 4, and the generation of CaO and CaCO can be seen₃. CaO here is made of CaCO₃Decomposing the obtained product. After the product is washed by dilute hydrochloric acid, a two-dimensional sheet-shaped Si material is obtained as shown by a scanning electron microscope in figure 3, which shows that the treatment by the method of the invention successfully realizes CaSi₂Peeling off.

The two-dimensional silicon nanosheet obtained in example 1 was used to prepare a negative electrode material for a lithium battery, and performance testing was performed, with the data shown in fig. 1. As can be seen from FIG. 1, the first-turn specific discharge capacityUp to 1200 mA h g^-1Specific charging capacity of 850 mA h g^-1。

Example 2

In the case of unchanged other steps, the CO in step 2 is added₂Conversion of/Ar gas to pure CO₂The gases were reacted at 500 ℃ for 3 hours, and the electrochemical properties of the resulting material were substantially the same as those of example 1.

Example 3

In the case of unchanged other steps, the CO in step 2 is added₂the/Ar gas is changed into pure CO2/N2 mixed gas, and the reaction is carried out for 5 hours at the temperature of 600 ℃, and the electrochemical performance of the obtained material is basically the same as that of the embodiment 1.

Comparative example

Zhejiang university Zhang et al (Zhang et al, Nanoscale, 2018, 10, 5626-5633) utilized CO₂And Mg₂The Si reaction and subsequent acid treatment yielded Si/C composites that showed good lithium electrical performance as the negative electrode. The reaction mechanism considered by the authors is firstly Mg₂Decomposing Si at a certain temperature to form Mg and Si, and further mixing Mg with CO₂MgO and C are generated by reaction. And obtaining the Si/C composite material after acid treatment.

The reaction mechanism of the comparative example is completely different from that of the comparative example, the obtained material has no fixed morphology, the cycle performance of the electrode material of the lithium battery is poor, and the capacity retention rate is less than 70% after 100 cycles. The two-dimensional silicon material obtained by the method has very good stability, and the capacity is increased after 500 cycles, as shown in figure 5.

The above description is only a preferred embodiment of the present invention, and the scope of the present invention is not limited thereto, and any simple modifications or equivalent substitutions of the technical solutions that can be obviously obtained by those skilled in the art within the technical scope of the present invention are within the 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.

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