CN114684825B - Preparation method and application of silica-carbon composite nanoparticles with core-shell structure - Google Patents

Abstract

The invention relates to a preparation method and application of a silica-carbon composite nanoparticle with a core-shell structure. The method prepares SiO with a core-shell by the strategies of solvent-free sol-gel, ball milling and carbon coating process _x A silicon-carbon LIB cathode with a/C @ C nano structure; the obtained nano-particles are used in a lithium battery cathode, and excellent cycle stability can be obtained. The method is solvent-free, macroscopic and controllable, and has great potential and application value in the aspect of promoting the nano engineering to approach the industrialization.

Description

Preparation method and application of silica-carbon composite nanoparticles with core-shell structure

Technical Field

The invention belongs to the field of nano materials and the field of electrochemical energy storage, and particularly relates to a silicon monoxide-carbon composite nano particle (SiO for short) with a core-shell structure as a lithium ion battery cathode material _x /C @ C) and a preparation method thereof.

Background

With the continuous advance of industrial civilization, lithium Ion Batteries (LIBs) gradually become indispensable energy storage systems in the fields of electric vehicles, aerospace, portable electronic products and the like. However, the development of a graphite negative electrode with a capacity of only 372mAh/g has been prevented from the development of LIB toward higher energy density, and therefore, the development of a more excellent LIB negative electrode is one of the keys for the development of high-performance LIB (g.li, j. -y.li, f. -s.yue, q.xu, t. -t.zuo, y _x /G/C anode toward industrial application in high energy density lithium-ion batteries[J].Nano Energy 2019,60,485-492.)。

Silicon protoxide (SiO) _x 0 < x ≦ 2) exhibits very high capacity (-2000 mAh/g) as the negative electrode of lithium ion batteries, and silicon occupies a very high natural abundance on earth. But its further practical application is limited by its inherent low conductivity and large volume expansion (-200%). The reason for this is that it has poor electron transport ability due to the presence of elemental oxygen; in addition, lithium ions inevitably cause volume expansion during the insertion of active silicon. These problems eventually evolve into serious problems of pole piece electrical contact failure, active particle exfoliation, structural cracking, etc. (j.sung, n.kim, j.ma, j.h.lee, s.h.joo, t.lee, s.chae, m.yoon, y.lee, j.hwang, s.k.kwak, j.cho, subnano-sized silicon anode video crystal growth inhibition mechanism and its application in a prototype battery pack[J].Nature Energy 2021,6,1164-1175；Y.Cui,Silicon anodes[J].Nature Energy 2021,6,995-996.)。

In the last decades, a series of pioneering works at home and abroad show that the reduction of the material size to the nanometer level and the combination with carbon is expected to solve the problems. In more detail, the nano structure not only can effectively shorten the migration distance of lithium ions in the lithiation-delithiation process, but also can slow down the stress of volume expansion. Meanwhile, the conductivity can be greatly improved through carbon coating and doping, and the exchange and utilization of electrons and lithium ions are accelerated. Improve cycling stability and extend battery life (Z.Liu, Q.Yu, Y.ZHao, R.He, M.Xu, S.Feng, S.Li, L.Zhou, L.Mai, silicon oxides: a formulating family of materials for lithium-ion batteries [ J ] chem.Soc.Rev.2019,48, 285-309).

Generally, carbon coating is often a common means for increasing conductivity, but the role of carbon doping is often neglected. Although the electrical conductivity is improved by the coating by the carbon coating process, the pure SiO inside the material _x The conductivity of the matrix cannot be guaranteed. This results in poor electrical conductivity within the active material and results in inefficient lithium ion transport and utilization. However, for the conventional synthesis of nanoparticles, siO _x Often from commercially available SiO or a silicon source obtained by hydrolysis of tetraethoxysilane. Consequently, it is difficult to achieve carbon doping in microscopic regions, even on a nanometer scale, as is the case for SiO _x The development of the material itself is disadvantageous. Moreover, the transfer of nanostructure engineering to practical applications is still largely hampered by several other fatal defects: (1) The traditional wet chemical synthesis route has the problems of harsh conditions, complex process, low yield and the like; (2) Even if the scheme is used for practical production, the synthesis stage inevitably uses a large amount of solvent, resulting in additional energy consumption and poor environmental problems; (3) Most materials with high specific surface area will cause excessive side reactions resulting in low Initial Coulombic Efficiency (ICE). Therefore, there is an urgent need to explore a simple, solvent-free and mass-producible solution for synthesizing a nanostructure with more rational structureThe silicon and carbon composite LIB cathode can avoid the problems of volume expansion and poor conductivity in the using process. Simultaneously, a green preparation method with macroscopic quantity and controllability is developed to achieve the practical application of the nano-structure material (Z.Xiao, C.Yu, X.Lin, X.Chen, C.Zhang, H.Jiang, R.Zhang, F.Wei, tiO) ₂ as a multifunction coating layer to enhance the electrochemical performance of SiO _x @TiO ₂ @C composite as anode material[J],Nano Energy 2020,77,105082；S.Xu,J.Zhou,J.Wang,S.Pathiranage,N.Oncel,P.Robert Ilango,X.Zhang,M.Mann,X.Hou,In Situ Synthesis of Graphene-Coated Silicon Monoxide Anodes from Coal-Derived Humic Acid for High-Performance Lithium-Ion Batteries,Advanced Functional Materials 2021,31,2101645)。

Disclosure of Invention

The invention aims to provide a preparation method and application of a silica-carbon composite nanoparticle with a core-shell structure aiming at the defects of low yield, solvent requirement, low carbon content, complex process and the like of all the nanostructures synthesized by the current wet chemical method. The method prepares SiO with a core-shell by the strategies of solvent-free sol-gel, ball milling and carbon coating process _x A silicon-carbon LIB cathode with a/C @ C nano structure; the obtained nano-particles are used in a lithium battery cathode, and excellent cycle stability can be obtained. The method has the advantages of no solvent, large quantity and controllability, and has huge potential and application value in the aspect of promoting the nano engineering to approach the industrialization.

The technical scheme of the invention is as follows:

a preparation method of a silica-carbon composite nanoparticle with a core-shell structure comprises the following steps:

(1) Mixing organosilane with a catalyst, reacting for 0.1-30 hours at 10-70 ℃, and drying to obtain a polysilsesquioxane bulk material;

wherein the volume ratio of the catalyst to the organosilane is 0.01-10: 1; the organosilane is one or more of siloxane or chlorosilane; the catalyst is acetic acid, hydrochloric acid, sulfuric acid, nitric acid, ammonia water or sodium hydroxide solution;

(2) Grinding the obtained block material in a ball mill for 0.1-20 hours to obtain polysilsesquioxane nano-particles;

wherein the size of the obtained nano particles is 10-500nm; the rotating speed of the ball mill is 50-1000 r/min.

(3) Pyrolyzing polysilsesquioxane particles for 0.1-20 hours at 350-1200 ℃ in an inert atmosphere to obtain SiO _x a/C powder; wherein x is more than 0 and less than or equal to 2, and when x tends to be 0 valence, the component is closer to the silicon simple substance; when x is 2, the micro-phase is closer to silicon dioxide, and the micro-phase is the random blending of Si-O bonds and Si-Si bonds;

wherein the inert gas is one or two of nitrogen and argon.

(4) Mixing SiO _x Performing chemical vapor deposition on the/C powder in a tubular furnace in mixed atmosphere at 350-1200 ℃ for 0.1-48 hours to finally obtain the silica-carbon composite nano particles with the core-shell structure;

wherein the mixed atmosphere is a mixture of A gas and B gas; the gas A is one or more of acetylene, ethylene and methane; b gas is one or two of nitrogen and argon; and the volume fraction of the gas A is 1-72%;

the feeding amount of the organosilane is kilogram-hundred kilogram;

the organosilane is specifically one or more of 3-mercaptopropyltrimethoxysilane, vinyl triethoxysilane, vinyl trimethoxysilane, 3-aminopropyltriethoxysilane, 3-mercaptopropyltriethoxysilane, methyltrichlorosilane and trimethylchlorosilane.

The application of the silica-carbon composite nano particle with the core-shell structure is used as a negative electrode material of a lithium ion battery.

The structure of the lithium ion battery is as follows: the button cell is assembled by a positive plate, a diaphragm, a negative plate, a gasket, a spring piece and a negative plate in sequence, and is filled with a proper amount of electrolyte;

wherein, the positive plate is a lithium plate; the negative plate is a working electrode; the working electrode is prepared by mixing the obtained nano particles, a conductive agent and a binder in a mass ratio of 7.5:1:1.5, mixing into slurry, coating the slurry on a copper foil, drying and cutting into pieces to obtain the copper foil;

the loading capacity of the unit area of the pole piece is 0.5-2.5 mg cm ^-2 ；

The conductive agent is acetylene black or Surper P; the adhesive is sodium alginate or carboxymethyl cellulose; the diaphragm model is Celgard 2400;

the electrolyte is obtained by dissolving lithium hexafluorophosphate in ethyl methyl carbonate, dimethyl carbonate and ethylene carbonate in equal volume ratio, and the concentration is 0.5-2.5 mol/L.

The button cell is CR2032, CR2016 or CR2430;

the invention has the substantive characteristics that:

one is SiO _x The particles structurally realize carbon doping and uniform carbon coating in the nanometer field at the same time; secondly, the organic silane and the initiator are directly mixed without any solvent in the whole process, the preparation of kilogram-level nano materials can be realized, and the preparation process can not cause environmental pollution, which is a characteristic that most nano materials do not have.

The catalyst of the present invention is a solution, which contains water, but the role of water here should be considered as part of the reactants, not as a solvent; this is due to the premise that water is used as a solvent, where the solute is readily soluble in water, whereas the organosilane is poorly soluble in water; all hydrolysis reactions, including organosilanes, require the presence of water. Thus, water should be considered herein as part of the reactants; moreover, the proportion of water is very low in the overall system and is not as solvent in the traditional sense.

The reaction mechanism is as follows: the organosilane is weakly hydrolyzed in the initiator, a small amount of organosilane is hydrolyzed and is released to methanol or ethanol, the intersolubility of the system is increased, and the hydrolysis is further promoted to obtain the polysilsesquioxane fast body. Grinding the block polysilsesquioxane into polysilsesquioxane nano-particles in a high-speed ball milling state by using a ball mill, and pyrolyzing the obtained particles to generate SiO _x /C nano compositeAnd a carbon shell is accumulated on the outer surface of the composite after the composite is subjected to chemical vapor deposition. The lithium ion battery anode material is applied to a lithium ion battery cathode and shows excellent electrochemical performance.

The invention has the beneficial effects that:

(1) The resulting product can adequately cope with the huge volume expansion and low conductivity due to the synergistic effect of carbon doping and encapsulation, maintain structural integrity and promote efficient transport of electrons and ions.

(2) The conventional nano structure is not favorable for the stability of the battery because of large specific surface area. The invention utilizes the carbon coating process to fill the redundant specific surface area in the nano structure with carbon, thereby weakening the unfavorable electrode/electrolyte contact area and reducing the excessive consumption of lithium ions to the maximum extent.

(3) Aiming at the problem that the carbon content of the traditional route is difficult to control, the invention can obtain products with different carbon contents through the time of vapor deposition, thereby achieving the purpose of controllable preparation.

(4) The granules according to the invention exhibit good powder properties, such as a narrow particle size distribution, a low specific surface area and good mechanical strength, making them advantageous for processing.

(5) For the traditional commercial SiO, the conductivity is not good because of no carbon doping. The invention can realize carbon doping with nanometer scale, increase electrochemical performance, and show high specific capacity (1200 mAh/g) and high coulombic efficiency (71.4%), and the capacity is more than 3 times of that of the traditional cathode (as shown in figure 6).

The LIB cathode material has the following preparation advantages:

(1) The traditional method for synthesizing the nano material uses a large amount of solvent, which causes potential pollution, energy waste and other problems. The whole process of the invention does not involve the use of any solvent, and is green, environment-friendly and pollution-free;

(2) The traditional synthetic route has the problems of harsh conditions, complex process, low yield and the like, and the synthetic process is simple and the reaction conditions are easy to realize.

Drawings

FIG. 1 is a SiO core shell _x of/C @ C nanoparticlesA schematic structural diagram;

FIG. 2 is a SiO core shell _x A preparation flow chart of the/C @ C nano particle;

FIG. 3 is a Scanning Electron Microscope (SEM) picture of each product of the synthesis procedure of example 1, wherein FIG. 3a is a Scanning Electron Microscope (SEM) picture of the bulk polysilsesquioxane of example 1. FIG. 3b is the SiO core shell of example 1 _x SEM image of/C @ C nanoparticles;

FIG. 4 is SiO core shell in example 1 _x Transmission Electron Microscope (TEM) photograph of/C @ C nanoparticles and elemental profile of the corresponding elements; wherein, FIG. 4a shows SiO core shell in example 1 _x TEM photograph of/C @ C nanoparticles, FIG. 4b is core-shell SiO in example 1 _x TEM photo of/C @ C nanoparticles under HAADF, FIG. 4c is core-shell SiO in example 1 _x The elemental profile of/C @ C nanoparticles;

FIG. 5 shows SiO core shell in example 1 _x The particle size distribution diagram of the/C @ C nano particle;

FIG. 6 is SiO core shell in example 1 _x The cycling performance of/C @ C nanoparticles;

FIG. 7 shows SiO core shell in example 1 _x Rate capability of/C @ C nanoparticles.

Detailed Description

The present invention is further illustrated by the following specific examples, but the scope of the present invention is not limited to the following examples.

Example 1:

(1) 5kg of 3-aminopropyltriethoxysilane with 80g of ammonia (20 wt.%) were placed in the reactor and allowed to stand at 15 ℃ for 2h. The reactor was moved to a drying oven and dried to obtain bulk polysilsesquioxane particles.

(2) And (3) putting the large polysilsesquioxane particles into a ball mill, and carrying out ball milling for 1h at 100 revolutions per minute to obtain the polysilsesquioxane nano particles.

(3) Putting polysilsesquioxane nano-particles into a tube furnace, carbonizing the polysilsesquioxane nano-particles for 10 hours at 650 ℃ under the condition of nitrogen to obtain SiO _x C black powder.

(4) The black powder was placed in a tube furnace and subjected to chemical vapor deposition at 650 ℃ for 4 hours under an atmosphere of a mixed gas of methane and argon (volume ratio 20).

The silica-carbon core-shell nanoparticles obtained in this example are taken as an example. FIG. 1 is a schematic cross-sectional view of the nanoparticle obtained, the interior of this core-shell structure being a mixed SiO _x And carbon, the outside being coated with a carbon layer. FIG. 2 shows a flow diagram of the synthesis; FIG. 3a shows an SEM image of a bulk polysilsesquioxane, the particles having a size of tens of microns; FIG. 3b is the final product, with a silica-carbon core shell nanoparticle size of only about 100 nm and uniform particle distribution;

FIG. 4 is a SiO core shell _x TEM and elemental profile of/C @ C nanoparticles, FIG. 4a demonstrates that the size of the nanoparticles is around 100 nm; FIG. 4b clearly identifies shell coating at the boundaries of the particles; fig. 4C shows the distribution diagram of Si, O, C elements, it can be seen that the distribution of each element is very uniform, and it can be seen from the overlay of these three elements that the nanoparticles are coated by a uniform carbon shell;

FIG. 5 is SiO core shell _x The particle size distribution diagram of the/C @ C nano particles is narrow, and the average size of the particles is 93.0nm; the core-shell SiO prepared in the example _x the/C @ C nano particles are assembled into a button cell, and the electrochemical performance of the button cell is tested.

The lithium ion battery is tested based on a button cell, and is assembled according to the sequence of a positive plate shell, a positive plate, a diaphragm, a negative plate, a gasket, a spring piece and a negative plate shell, and is filled with electrolyte;

the positive plate is a lithium plate; the negative plate is a working electrode; the working electrode is prepared by mixing the obtained nano particles, a conductive agent and a binder in a mass ratio of 7.5:1:1.5, mixing into slurry, coating the slurry on a copper foil, drying and cutting into pieces to obtain the copper foil;

the loading capacity of the unit area of the pole piece is 1.0mg cm ^-2 ；

The conductive agent is acetylene black; the adhesive is sodium alginate; the diaphragm model is Celgard 2400;

the electrolyte is obtained by dissolving lithium hexafluorophosphate in a solvent, wherein the solvent is methyl ethyl carbonate, dimethyl carbonate and ethylene carbonate in equal volume ratio; the concentration of the electrolyte is 1.0mol/L; the addition amount of the electrolyte is 100 mu L;

the button cell is CR2032;

FIG. 6 is SiO _x The cycling performance of the/C @ C nanoparticle, reversible capacity, was 1050mAh/g, exhibiting a high specific capacity (about 900 mAh/g) even after 70 cycles. The cycle performance is measured at 0.01-3.0V (vs. Li/Li) using LAND CT-2001A battery test system ⁺ ) The constant current charge and discharge test is carried out under the voltage window of (1), and the current density is 0.1 ag ^-1 。

FIG. 7 shows SiO _x Rate capability of/C @ C nanoparticles, the battery has a high capacity of 300mAh/g even at high current densities of 5A/g. The multiplying power performance is measured at 0.01-3.0V (vs. Li/Li) by using a battery test system of LAND CT-2001A ⁺ ) Is tested at a current density of 0.1 ag ^-1 、0.2A g ^-1 、0.5A g ^-1 、1.0A g ^-1 、2.0A g ^-1 、5.0A g ^-1 Next, 5 constant current charge and discharge cycles were continuously and respectively performed.

SiO _x The reversible capacity of the/C @ C nano particle reaches 1050mAh/g, which is almost 3 times of the capacity (372 mAh/g) of the current commercial graphite cathode; and can be realized at 5.0 ag ^-1 The rapid charge and discharge under high current density can fully charge the lithium ion battery in only 4 minutes, and the requirement of the lithium ion battery on rapid charge in the future can be met.

Example 2:

(1) 3-aminopropyltriethoxysilane (2.5 kg), 3-mercaptopropyltriethoxysilane (2.5 kg) and 100g acetic acid (15 wt.%) were placed in the reactor and left to stand at 60 ℃ for 4h. The reactor was moved to a drying oven and dried to obtain bulk polysilsesquioxane particles.

(2) And (3) putting the large polysilsesquioxane particles into a ball mill, and carrying out ball milling for 1h at 100 revolutions per minute to obtain the polysilsesquioxane nano particles.

(3) Polysilsesquioxane nanoparticles are placed in a tube furnace under nitrogenCarbonizing at 1200 deg.C for 4 hr to obtain SiO _x C black powder.

(4) The black powder was placed in a tube furnace and chemical vapor deposition was performed at 1200 ℃ for 6 hours under a mixed gas atmosphere of ethylene and nitrogen (volume ratio 35).

Example 3:

(1) 1kg of each of 3-mercaptopropyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, 3-aminopropyltriethoxysilane and 3-mercaptopropyltriethoxysilane was charged into a reactor together with 150g of sodium hydroxide solution (15 wt.%) and allowed to stand at room temperature for 4 hours. The reactor was moved to a drying oven and dried to obtain bulk polysilsesquioxane particles.

(2) And (3) putting the large polysilsesquioxane particles into a ball mill, and carrying out ball milling for 6 hours at 200 revolutions per minute to obtain the polysilsesquioxane nano particles.

(3) Placing polysilsesquioxane nano particles in a tube furnace, carbonizing the polysilsesquioxane nano particles for 3 hours at 800 ℃ under the condition of argon gas to obtain SiO _x C black powder.

(4) The black powder was placed in a tube furnace and chemical vapor deposition was performed at 700 ℃ for 6 hours under a mixed gas atmosphere of ethylene and nitrogen (volume ratio 35).

Example 4:

(1) 5kg of vinyltrimethoxysilane and 100g of hydrochloric acid (5 wt.%) were placed in the reactor and allowed to stand at 55 ℃ for 10h. The reactor was moved to a drying oven and dried to obtain bulk polysilsesquioxane particles.

(2) And (3) putting the large polysilsesquioxane particles into a ball mill, and performing ball milling for 6 hours at 200 revolutions per minute to obtain the polysilsesquioxane nano particles.

(3) Putting polysilsesquioxane nano particles into a tube furnace, carbonizing the polysilsesquioxane nano particles for 0.5 hour at 1000 ℃ under the condition of argon to obtain SiO _x C black powder.

(4) The black powder was placed in a tube furnace and subjected to chemical vapor deposition at 700 ℃ for 2 hours under a mixed gas atmosphere of methane, acetylene, argon (volume ratio 10.

The invention is not the best known technology.

Claims (6)

1. A preparation method of a silica-carbon composite nanoparticle with a core-shell structure is characterized by comprising the following steps:

(1) Mixing organosilane with a catalyst, reacting for 0.1-30 hours at 10-70 ℃, and drying to obtain a polysilsesquioxane bulk material;

wherein the volume ratio of the catalyst to the organosilane is 0.01-10: 1; the organosilane is one or more of siloxane or chlorosilane; the catalyst is acetic acid, hydrochloric acid, sulfuric acid, nitric acid, ammonia water or sodium hydroxide solution;

(2) Grinding the obtained block material in a ball mill for 0.1-20 hours to obtain polysilsesquioxane nano-particles;

wherein the size of the obtained nano particles is 10-500nm; the rotating speed of the ball mill is 50-1000 r/min;

(3) Pyrolyzing polysilsesquioxane particles for 1-6 hours at 350-1200 ℃ in an inert atmosphere to obtain SiO _x a/C powder; wherein, the inert gas is one or two of nitrogen and argon;

(4) Mixing SiO _x Performing chemical vapor deposition on the/C powder in a tubular furnace at the temperature of 350-1200 ℃ in mixed atmosphere for 2-6 hours to finally obtain the silica-carbon composite nano particles with the core-shell structure;

wherein the mixed atmosphere is a mixture of gas A and gas B; the gas A is one or more of acetylene, ethylene and methane; b gas is one or two of nitrogen and argon; and the volume fraction of the gas A is 20-35%.

2. The method for preparing silica-carbon composite nanoparticles having core-shell structure according to claim 1, wherein the organosilane is one or more selected from 3-mercaptopropyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-mercaptopropyltriethoxysilane, methyltrichlorosilane and trimethylchlorosilane.

3. The use of the silica-carbon composite nanoparticles having a core-shell structure according to claim 1, characterized by being used as a negative electrode material for lithium ion batteries.

4. The use of the silica-carbon composite nanoparticles with core-shell structure according to claim 3, wherein the structure of the lithium ion battery is as follows: the battery is formed by assembling a button cell according to the sequence of a positive plate shell, a positive plate, a diaphragm, a negative plate, a gasket, a spring piece and a negative plate shell, and is filled with a proper amount of electrolyte;

wherein, the positive plate is a lithium plate; the negative plate is a working electrode; the working electrode is prepared by mixing the obtained nano particles, a conductive agent and a binder in a mass ratio of 7.5:1:1.5, mixing into slurry, coating the slurry on a copper foil, drying and cutting into pieces to obtain the copper foil; the loading capacity of the unit area of the pole piece is 0.5-2.5 mg cm ^- ²。

5. The use of the silica-carbon composite nanoparticles having a core-shell structure according to claim 4, wherein the conductive agent is acetylene black or Surper P; the adhesive is sodium alginate or carboxymethyl cellulose; the diaphragm model is Celgard 2400;

the electrolyte is obtained by dissolving lithium hexafluorophosphate in ethyl methyl carbonate, dimethyl carbonate and ethylene carbonate in equal volume ratio, and the concentration is 0.5-2.5 mol/L.

6. The use of silica-carbon composite nanoparticles with core-shell structure according to claim 4, wherein the button cell is CR2032, CR2016 or CR2430.

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