CN114684825A

CN114684825A - Preparation method and application of silica-carbon composite nanoparticles with core-shell structure

Info

Publication number: CN114684825A
Application number: CN202210409653.XA
Authority: CN
Inventors: 张旭; 王志远; 王小梅
Original assignee: Hebei University of Technology
Current assignee: Hebei University of Technology
Priority date: 2022-04-19
Filing date: 2022-04-19
Publication date: 2022-07-01
Anticipated expiration: 2042-04-19
Also published as: CN114684825B

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_xA silicon-carbon LIB cathode with a/C @ C nano structure; the obtained nano-particles are used in the negative electrode of the lithium battery and can obtain excellent performanceExceptional cycle stability. 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 lithium ion battery cathode material with a core-shell structureSilica-carbon composite nanoparticles (hereinafter referred to as SiO)_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 automobiles, 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)_x0 < 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 rupture, 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 application in a protocol battery pack [ j.].Nature Energy 2021,6,1164-1175；Y.Cui,Silicon anodes[J].Nature Energy 2021,6,995-996.)。

A series of pioneering works at home and abroad over the last decades indicate that the reduction of the material size to the nanometer level and the combination with carbon is expected to solve the above 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 cell 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 coating by the carbon coating process improves the conductivity, the pure SiO inside the material_xThe conductivity of the substrate 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_xOften from commercially available SiO or a silicon source obtained by hydrolysis of tetraethylorthosilicate. Consequently, it is difficult to achieve carbon doping in microscopic regions, even on a nanometer scale, as is the case for SiO_xThe 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 can lead to excessive side reactions, resulting in low Initial Coulombic Efficiency (ICE). Therefore, there is an urgent need to search for a simple, solvent-free and mass-producible solution for synthesizing a silicon and carbon composite LIB anode with a more reasonable nanostructure, so as to avoid the problems of volume expansion and poor conductivity during use. Simultaneously, a green preparation method with macro and controllable capacity 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@TiO₂@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_xA 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.

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 10-500 nm; 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_xa/C powder; wherein x is more than 0 and less than or equal to 2, and when x tends to 0 valence, the components are 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_xPerforming chemical vapor deposition on the/C powder in a tube furnace at the temperature of 1200 ℃ in mixed atmosphere 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 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 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 CR 2430;

the invention has the substantive characteristics that:

one is SiO_xThe particles structurally realize carbon doping and uniform carbon coating in the nanometer field at the same time; secondly, the organosilane and the initiator are directly mixed without any solvent in the whole process, so that 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 as a solvent is a solute that is readily soluble in water, whereas here, 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 traditionally used as a solvent.

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_xa/C nano composite, and a carbon shell is accumulated on the outer surface 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 beneficial effects of the invention are as follows:

(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 fills the redundant specific surface area in the nano structure with carbon by means of the carbon coating process, 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, 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 of the invention is simple and the reaction conditions are easy to realize.

Drawings

FIG. 1 is a SiO core shell_xA structural schematic diagram of/C @ C nanoparticles;

FIG. 2 is a SiO core shell_xA preparation flow chart of/C @ C nano particles;

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_xSEM images of/C @ C nanoparticles;

FIG. 4 shows SiO core shell in example 1_xA Transmission Electron Microscope (TEM) photograph of the/C @ C nanoparticles and an elemental profile of the corresponding element; wherein FIG. 4a shows the structure of the embodiment 1Core-shell SiO_xTEM photograph of/C @ C nanoparticles, FIG. 4b is the core-shell SiO of example 1_xTEM image of/C @ C nanoparticles in HAADF, FIG. 4C is the core-shell SiO in example 1_xThe elemental profile of/C @ C nanoparticles;

FIG. 5 is SiO core shell in example 1_xThe particle size distribution diagram of the/C @ C nano particles;

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

FIG. 7 is SiO core shell in example 1_xRate 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 2 h. The reactor was moved to a drying oven and dried to obtain bulk polysilsesquioxane pellets.

(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 at 650 ℃ for 10 hours under the condition of nitrogen to obtain SiO_xC black powder.

(4) The black powder is placed in a tube furnace, and chemical vapor deposition is carried out for 4 hours at 650 ℃ in the atmosphere of mixed gas of methane and argon (volume ratio is 20: 80), so as to obtain the silica-carbon core-shell nano-particles.

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_xAnd 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 shows the final product, which has a size of the silica-carbon core-shell nanoparticle of only about 100 nm and a uniform particle distributionFirstly, performing primary filtration;

FIG. 4 is a SiO core shell_xTEM and elemental distribution 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 the 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 the three elements that the nanoparticles are coated by a uniform carbon shell;

FIG. 5 is a core-shell SiO_xThe particle size distribution diagram of the/C @ C nano particles is narrow, and the average size of the particles is 93.0 nm; the core-shell SiO prepared in the example_xthe/C @ C nanoparticles were assembled into button cells and tested for electrochemical performance.

The lithium ion battery is tested based on a button cell, and is assembled by a positive plate shell, a positive plate, a diaphragm, a negative plate, a gasket, a spring piece and a negative plate shell in sequence, 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, the conductive agent and the adhesive 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 ethyl methyl carbonate, dimethyl carbonate and ethylene carbonate in equal volume ratio; the concentration of the electrolyte is 1.0 mol/L; the addition amount of the electrolyte is 100 mu L;

the button cell is CR 2032;

FIG. 6 is SiO_xThe cycling performance of the/C @ C nanoparticles, reversible capacity 1050mAh/g, exhibited high specific capacity (about 900mAh/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⁺) Constant current charge and discharge under the voltage windowElectric test, Current Density 0.1A g^-1。

FIG. 7 shows SiO_xRate capability of/C @ C nanoparticles, the battery has a high capacity of 300mAh/g even at a high current density 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⁺) Was tested at a current density of 0.1A g^-1、0.2A g^-1、0.5A g^-1、1.0A g^-1、2.0A g^-1、5.0A g^-1Next, 5 constant current charge and discharge cycles were continuously and respectively performed.

SiO_xThe reversible capacity of the/C @ C nano particles reaches 1050mAh/g, which is almost 3 times of the capacity (372mAh/g) of the current commercial graphite cathode; and may be implemented at 5.0A g^-1The rapid charge and discharge under high current density can fully charge the lithium ion battery in only 4 minutes, which can also meet the requirement of the rapid charge of the lithium ion battery in the future.

Example 2:

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

(3) Putting polysilsesquioxane nano-particles into a tube furnace, carbonizing for 4 hours at 1200 ℃ under the condition of nitrogen to obtain SiO_xC black powder.

(4) The black powder was placed in a tube furnace and chemical vapor deposition was carried out at 1200 ℃ for 6 hours in a mixed gas atmosphere of ethylene and nitrogen (volume ratio 35: 65) to obtain a silica-carbon core-shell nanoparticle.

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_xC black powder.

(4) The black powder was placed in a tube furnace and chemical vapor deposition was carried out at 700 ℃ for 6 hours in a mixed gas atmosphere of ethylene and nitrogen (volume ratio 35: 65) to obtain a silica-carbon core-shell nanoparticle.

Example 4:

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

(4) And (2) placing the black powder in a tube furnace, and carrying out chemical vapor deposition for 2 hours at 700 ℃ in the atmosphere of mixed gas of methane, acetylene and argon (the volume ratio is 10: 10: 80) to obtain the silica-carbon core-shell nano particles.

The invention is not the best known technology.

Claims

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

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

(3) pyrolyzing polysilsesquioxane particles for 0.1-20 hours at 350-1200 ℃ in an inert atmosphere to obtain SiO_xa/C powder; wherein, the inert gas is one or two of nitrogen and argon;

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 1-72%.

2. The method for preparing silica-carbon composite nanoparticles with core-shell structure according to claim 1, wherein the amount of organosilane is in the range of kilogram to hundred kilogram.

3. 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.

4. 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.

5. The use of the silica-carbon composite nanoparticles with core-shell structure according to claim 4, wherein 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。

6. The use of the silica-carbon composite nanoparticles having a core-shell structure according to claim 5, 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 an equal volume ratio, and the concentration of the electrolyte is 0.5-2.5 mol/L.

7. The use of silica-carbon composite nanoparticles having core-shell structure according to claim 5, wherein the button cell is of type CR2032, CR2016 or CR 2430.