CN100383037C - A kind of carbon material/nano-silicon composite material and its preparation method and application - Google Patents

Abstract

The invention belongs to the technical field of electrochemistry, and specifically relates to a method for preparing a carbon material/nano-silicon composite material through a mixed calcining method and the carbon material/nano-silicon composite material obtained by the method. The carbon material/nano-silicon composite material prepared by the method of the invention has a stable structure, and the average particle diameter is less than 1 mm. In the process of intercalation and deintercalation of lithium ions, since the nano-silicon particles are fixed on the surface of the carbon material and have a strong force with the surface, the agglomeration effect between a large number of nanoparticles is avoided, and the carbon material has a stable structure. , so that the lithium-ion battery has a high reversible capacity and good cycle performance. The method of the invention has strong operability and good reproducibility, and the quality of the obtained product is stable.

Description

A kind of carbon material/nano-silicon composite material and its preparation method and application

technical field

The invention belongs to the field of electrochemical technology, and specifically relates to a method for preparing carbon material/nano-silicon composite material. Nanocomposite methods for cladding. The present invention also relates to the application of the carbon material/nano-silicon composite material obtained by the above method, that is, as the negative electrode material of the lithium ion battery.

Background technique

As we all know, silicon, as a promising anode material for lithium-ion batteries, has attracted more and more attention in the industry. The main reason is that the cut-off potential of lithium insertion into silicon can not only be controlled above 0.2V, but also the reversible insertion of lithium into silicon Large, the theoretical insertion capacity reaches 4000mAh/g, which can significantly improve the capacity and safety performance of the battery. However, during the insertion and deintercalation process of lithium, the volume change is relatively large, even up to 600%, so the electrode particles are prone to pulverization and structural damage during the cycle, and the capacity drops rapidly.

At present, mainly through alloying (Netz A, et al, J Power Source.2003, 119-121: 95), carrier dispersion (Hwang S, et al, J Electrochem Solid-State Lett. 2001, 4: A97), surface Modification (Yoshio M, et al, J Electrochem Soc.2002, 149: A1598) and other methods to improve cycle performance, but these methods have not achieved significant results. It has recently been found that the use of nanoparticles can slow down the volume change during charge and discharge, improve the stability and cycle performance of the structure, and the cycle number can reach 100 times (Bensenhard J O, et al, J Power Sources.1997, 68:87). However, because the nanoparticles are prone to agglomeration, the unique effect of the nanoparticles is gradually lost, and the long-term cycle performance is still not ideal.

At the same time, carbon material, as a kind of graphite material, has excellent cycle performance when used as a negative electrode material for lithium-ion batteries, but the capacity is only close to the theoretical capacity of graphite of 372mAh/g. Obviously, its capacity needs to be further improved.

Contents of the invention

In order to overcome the above-mentioned problems in the prior art, the inventors of the present invention have carried out extensive and in-depth research in the field of carrier dispersion of nano-silicon, and found that the nano-silicon particles can be dispersed on carbon by using the mixed calcining method (mixing first, then calcining). On the surface of the material carrier, heat treatment at high temperature can improve the stability of the combination of the two, forming a carbon material/nano-silicon composite material with stable structure, uniform particle distribution, good safety, high capacity, and good reversibility of lithium intercalation and deintercalation. The carbon material/nano-silicon composite material is used as the negative electrode material of the lithium-ion battery and assembled into a lithium-ion battery.

Therefore, an object of the present invention is to provide a kind of method for preparing carbon material/nano-silicon composite material, and this method makes the nano-silicon that is uniformly dispersed on the surface of carbon material in lithium intercalation and deintercalation process, can not agglomerate, improves The reversible capacity of carbon materials, while maintaining the characteristics of excellent cycle performance of carbon materials.

Another object of the present invention is to provide a carbon material/nano-silicon composite material produced by the method of the present invention.

Another object of the present invention is to provide an application of the carbon material/nano-silicon composite material produced by the method of the present invention, and the composite material can be used as a lithium ion battery negative electrode material.

The present invention provides a kind of method for preparing carbon material/nano-silicon composite material on the one hand, the concrete steps of this method are as follows:

(1) Ultrasonic dispersion: add carbon material and nano-silicon into the organic solvent, stir evenly at room temperature (1 minute-24 hours), and then continue to ultrasonically disperse for a certain period of time (1 minute-24 hours), so that the nano-silicon is uniform Dispersed in the carbon material carrier. Here, the weight ratio of the carbon material to the nano-silicon is 1-100:1, and the amount of the organic solvent is 0.01-100 times the total weight of the carbon material and the nano-carbon.

(2) Drying: heating the mixed liquid obtained in step (1) to 20-100° C., stirring continuously for 5 minutes to 96 hours to evaporate the organic solvent to obtain dry carbon material/nano-silicon powder.

(3) Calcining: Calcining the mixed powder obtained in step (2) at 100-1200° C. for 1 minute to 96 hours in an inert or reducing atmosphere.

Another aspect of the present invention provides a carbon material/nano-silicon composite material, wherein the carbon material is artificial graphite, natural graphite or low-temperature amorphous carbon, the average particle diameter of the carbon material is 0.01 to 1000 microns, and the particle diameter of the nano-silicon is 1~500 nanometers. The particle size of the composite material is 0.1-1000 microns.

These and other objects, features and advantages of the present invention will become more apparent after reading the entire specification in conjunction with the accompanying drawings.

Detailed description of the invention

In the carbon material/nano-silicon composite material preparation method of the present invention, the carbon material in step (1) is artificial graphite, natural graphite or low-temperature amorphous carbon, and the average particle size of the carbon material is 0.01-1000 microns.

In the carbon material/nano-silicon composite material preparation method of the present invention, step (1) involves ultrasonic dispersion of nano-silicon. The nano-silicon used in this step can be industrial-grade nano-silicon or high-purity silicon. In terms of cost, industrial grade nano silicon is preferred. The particle size of nano-silicon is within the range of 1 nm-500 nm, preferably 5 nm-200 nm, more preferably 10 nm-100 nm. The shape of nano-silicon can be nanosphere, nanowire, nanorod, nanofiber, nanotube, etc., preferably nanosphere. The particle size of the carbon material used in this step is preferably 0.1 micron to 20 micron, more preferably 2 micron to 15 micron. The amount of the support carbon material is 1-100 grams, preferably 8-50 grams, more preferably 10-30 grams per gram of nano-silicon. The ultrasonic time is 1 minute-24 hours, preferably 2 hours-20 hours, and more preferably controlled at 6-12 hours. The organic solvents used in this step include low-level volatile organic solvents such as methanol, ethanol or ether. The dosage of the organic solvent is 0.01-100 times of the total weight of the carbon material and the nano-silicon. Preferably 1-50 times.

In the carbon material/nano-silicon composite material preparation method of the present invention, step (2) involves drying the mixed liquid obtained in step (1). The volatilization temperature depends on the type of organic solvent used. Taking methanol as an example, the volatilization temperature is controlled at 10-30°C. Stirring is kept during the volatilization of the organic solvent, and the volatilization time is controlled at 5 minutes to 96 hours, preferably 30 minutes to 48 hours, more preferably 6 hours to 24 hours.

In the method for preparing silicon/carbon core-shell nanocomposites of the present invention, step (3) involves high-temperature calcination of the carbon material/nano-silicon dry powder obtained in step (2). The calcining temperature in this step is 100-1200°C, preferably 400-900°C. The calcination is carried out under the condition of an inert atmosphere (such as Ar, Ne, He, Xe, N ₂ or a reducing atmosphere (such as H ₂ /Ar mixed gas). The calcination time can be 1 minute to 96 hours, preferably 1 hour to 24 hours. After High-temperature calcination improves the stability of the combination of nano-silicon and carbon material supports.

The expression "composite material" used in the term "carbon material/nano-silicon composite material" in the present invention means that nano-silicon is uniformly dispersed on the surface of the carbon material to form a coating structure during the ultrasonic dispersion process of the present invention. After fully dispersed, after drying process, the obtained carbon material/nano-silicon dry powder is calcined at high temperature to improve the stability of the combination of nano-silicon and carbon material carrier, and obtain a stable composite material. This composite material can be used as a negative electrode material for lithium-ion batteries. When lithium ions are intercalated and deintercalated, since the nanoparticles are dispersed on the surface of the carbon material and have a strong force with the surface, the interaction between a large number of nanoparticles is avoided. At the same time, because the carbon material has a stable structure, the composite material with this structure has high reversible capacity and good cycle performance.

In the method of the present invention, due to the use of the ultrasonic dispersion method, the nano-silicon is uniformly dispersed on the surface of the carbon material carrier in a short period of time. After the organic solvent is volatilized, the stability of the combination of the nano-silicon and the carbon material carrier is improved by high-temperature calcination, and the final product is obtained. The obtained carbon material/nano-silicon composite material has a stable structure and uniform dispersion, and improves the reversible capacity of the composite material while maintaining the excellent cycle performance of the carrier carbon material.

The carbon material/nano-silicon composite material prepared by the invention has a stable structure, and the nanoparticles are dispersed on the surface of the carbon material, avoiding the agglomeration effect among a large number of nanoparticles, and making the lithium-ion battery have high reversible capacity and good cycle performance. In addition, the particle size is uniform and the dispersion is good. Finally, the method of the invention has strong operability and good reproducibility, and the quality of the prepared product is stable.

Description of drawings

Figure 1 is a comparison of the cycle performance of Comparative Example 1 and Example 1.

Fig. 2 is a scanning electron microscope (SEM) photo of the carbon material/nano-silicon composite material obtained in Example 1 of the present invention.

Detailed ways

The present invention is described in more detail below by referring to comparative examples and examples, but the protection scope of the present invention is not limited to these examples.

Comparative example 1

SSG (modified natural graphite, Hunan Loudi Huiyu Technology Co., Ltd. product) without doped nano-silicon was used as the working electrode, 1mol/L LiPF ₆ EC-DEC (volume ratio 1:1) was used as the electrolyte solution, and metal lithium was The counter electrode constitutes a two-electrode simulated battery, the weight percentage of SSG, carbon black, and PVDF in the working electrode is 70:20:10, and the charge and discharge current density is 0.24mA/cm ² . The initial charging capacity is 299.8mAh/g, and after 20 cycles, due to the full activation of the electrode, the capacity is 120% of the initial capacity, which is close to the theoretical capacity of graphite materials.

Example 1

Add 3.0 g of SSG and 0.3 g of nano-silicon into 50 mL of anhydrous methanol, stir at room temperature for 12 hours, and then continuously ultrasonically disperse for 12 hours, so that the nano-silicon is uniformly dispersed in the carbon material carrier. Then slowly raise the temperature to 30° C., and continue to stir for about 24 hours to volatilize the anhydrous methanol to obtain a carbon material/nano-silicon dry powder. The powder was calcined at 600° C. for 6 hours in an inert atmosphere to obtain a black carbon material/nano-silicon composite material.

The electrochemical performance test of the obtained carbon material/nano-silicon composite is as follows. The carbon material/nano-silicon composite material is used as the working electrode, EC-DEC (volume ratio 1:1) of 1mol/L LiPF ₆ is used as the electrolyte solution, and metal lithium is used as the counter electrode to form a two-electrode simulated battery. The carbon material/ The weight percentage of nano-silicon composite material, carbon black and PVDF is 70:20:10, and the charge and discharge current density is 0.24mA/cm ² . The first charge capacity was measured to be 562.1mAh/g, and the capacity remained at 100% of the initial capacity after 20 cycles.

Comparative example 2

CMS (artificial graphite, product of Shanghai Shanshan Technology Co., Ltd.) without doped nano-silicon is used as the working electrode, 1mol/L LiPF ₆ EC-DEC (volume ratio 1:1) is used as the electrolyte solution, and metal lithium is used as the counter electrode. Two-electrode simulated battery, the weight percentage of CMS, carbon black and PVDF in the working electrode is 70:20:10, and the charge and discharge current density is 0.24mA/cm ² . The initial charging capacity is 280mAh/g, and the capacity after 20 cycles is 99% of the initial capacity.

Example 2

Add 3.0 g of the above CMS and 0.25 g of nano-silicon into 50 mL of anhydrous methanol, stir at room temperature for 12 hours, and then continuously ultrasonically disperse for 12 hours, so that the nano-silicon is uniformly dispersed in the carbon material carrier. Then slowly raise the temperature to 30° C., and continue to stir for about 24 hours to volatilize the anhydrous methanol to obtain a carbon material/nano-silicon dry powder. The powder was calcined at 800° C. for 2 hours in an inert atmosphere to obtain a black carbon material/nano-silicon composite material. The electrochemical performance test of the carbon material/nano-silicon composite material is the same as in Example 1. The first charge capacity was measured to be 525.7mAh/g, and the capacity remained at 100% of the initial capacity after 20 cycles.

Comparative example 3

Using MCMB (artificial graphite, product of Osaka Gas Co., Ltd., Japan) without doped nano-silicon as the working electrode, 1mol/L LiPF ₆ EC-DEC (volume ratio 1:1) as the electrolyte solution, and lithium metal as the counter electrode to form two The electrode simulates a battery, the weight percentage of CMS, carbon black, and PVDF in the working electrode is 70:20:10, and the charge and discharge current density is 0.24 mA/cm ² . The initial charging capacity is 286mAh/g, and the capacity after 20 cycles is 99% of the initial capacity.

Example 3

Add 3.0 g of the above MCMB and 0.6 g of nano-silicon into 50 mL of anhydrous methanol, stir at room temperature for 12 hours, and then continuously ultrasonically disperse for 12 hours, so that the nano-silicon is uniformly dispersed in the carbon material carrier. Then slowly raise the temperature to 30° C., and continue to stir for about 24 hours to volatilize the anhydrous methanol to obtain a carbon material/nano-silicon dry powder. The powder was calcined at 400° C. for 12 hours in an inert atmosphere to obtain a black carbon material/nano-silicon composite material. The electrochemical performance test of the carbon material/nano-silicon composite material is the same as in Example 1. The first charge capacity was measured to be 634.6mAh/g, and the capacity remained at 100% of the initial capacity after 20 cycles.

Claims (8)

1. method for preparing carbon material and nano silicon composite materials is characterized in that concrete steps are as follows:

(1) ultra-sonic dispersion: carbon material and nano-silicon are added in the organic solvent, stir, and then continuous ultrasound disperseed 1 minute-24 hours, nano-silicon is dispersed in the carbon material carrier, wherein, the weight ratio of carbon material and nano-silicon is 1-100: 1, and consumption of organic solvent is carbon material and nano-sized carbon gross weight 0.01-100 a times;

(2) drying: will be warming up to 20-100 ℃ in step (1) the gained mixing liquid, continuously stirring 5 minutes-96 hours makes the organic solvent volatilization clean, obtains carbon material/nano-silicon dried powder;

(3) calcining: the mixed powder of step (2) gained was calcined 1 minute～96 hours under 100～1200 ℃ in inert atmosphere or reducing atmosphere.

2. method according to claim 1 is characterized in that used carbon material is synthetic graphite, natural graphite or low temperature decolorizing carbon in the step (1), and the median size of carbon material is 0.01 ~ 1000 micron.

3. method according to claim 1, the particle diameter that it is characterized in that used nano-silicon in the step (1) is 1nm-500nm.

4. according to the described method of claim 1, it is characterized in that organic solvent used in the step (1) is methyl alcohol, ethanol or ether.

5. method according to claim 1 is characterized in that ultrasonic time is 2 hours-20 hours in the step (1).

6. method according to claim 1 is characterized in that the organic solvent volatilization time was controlled at 30 minutes-48 hours in the step (2).

7. carbon material and nano silicon composite materials that obtains according to the described method of one of claim 1-6, for be dispersed in the clad structure that carbon material surface forms by nano-silicon, wherein the median size of carbon material is 0.01 ~ 1000 micron, the particle diameter of nano-silicon is 1 ~ 500 nanometer, and the particle diameter of matrix material is 0.1～1000 micron.

8. carbon material and nano silicon composite materials as claimed in claim 7 is as the application of lithium ion battery negative material.

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