阅读说明：本技术 一种碳包覆空心二氧化硅复合材料及其制备方法 (Carbon-coated hollow silicon dioxide composite material and preparation method thereof ) 是由 李永涛 王德昊 刘豫州 施陈勇 张红光 刘利清 于 2021-03-02 设计创作，主要内容包括：本发明公开一种碳包覆空心二氧化硅复合材料及其制备方法,以聚丙烯酸为原料配制聚丙烯酸微球,再加入无水乙醇、正硅酸四乙酯、氨水,以原位生成的二氧化硅沉积到聚丙烯酸微球表面,形成二氧化硅层包覆在聚丙烯酸外部,使用去离子水将聚丙烯酸反复冲洗,直至形成空心二氧化硅微球,再加入酚醛树脂、去离子水,使酚醛树脂沉积在二氧化硅表面,实现二氧化硅和酚醛树脂比例的调控,最后将产物热解成无定形碳。与现有技术相比,本发明采用的自组装方法条件温和,步骤简单,不需要复杂昂贵的设备,有利于大规模推广,且制备的碳包覆二氧化硅复合材料充放电循环250次后放电比容量可达743mAh g～(-1),电化学性能有显著提高。(The invention discloses a carbon-coated hollow silicon dioxide composite material and a preparation method thereof, which takes polyacrylic acid as a raw material to prepare polyacrylic acid microspheres, and then absolute ethyl alcohol, tetraethyl orthosilicate and ammonia water are added to deposit silicon dioxide generated in situ toForming a silicon dioxide layer on the surface of a polyacrylic acid microsphere to cover the polyacrylic acid, repeatedly washing the polyacrylic acid by using deionized water until a hollow silicon dioxide microsphere is formed, then adding phenolic resin and deionized water to deposit the phenolic resin on the surface of the silicon dioxide, realizing the regulation and control of the proportion of the silicon dioxide and the phenolic resin, and finally pyrolyzing the product to form amorphous carbon. Compared with the prior art, the self-assembly method adopted by the invention has mild conditions, simple steps, no need of complex and expensive equipment and contribution to large-scale popularization, and the prepared carbon-coated silicon dioxide composite material has a specific discharge capacity of 743mAh g after 250 charge-discharge cycles ‑1 The electrochemical performance is obviously improved.)

1. The preparation method of the carbon-coated hollow silica composite material is characterized by comprising the following steps of:

(1) dissolving polyacrylic acid in ammonia water to prepare a solution with the mass concentration of 60-80g/L, stirring, adding absolute ethyl alcohol, and continuing stirring until the solution becomes white to obtain a polyacrylic acid microsphere mixed solution;

(2) adding absolute ethyl alcohol, deionized water and tetraethyl orthosilicate into the polyacrylic acid microsphere mixed solution obtained in the step (1), reacting for 9-12h at 30-50 ℃, washing with deionized water, filtering, and drying the precipitate to obtain hollow silicon dioxide microspheres;

(3) and (3) dispersing the hollow silica microspheres obtained in the step (2) and solid phenolic resin into deionized water, reacting for 3-5h at the temperature of 60-80 ℃ with the mass concentration of 30g/L, drying the precipitate after filtering, and carbonizing for 3-6h at the temperature of 900 ℃ in an inert atmosphere of 500-.

2. The method for preparing a carbon-coated hollow silica composite material according to claim 1, characterized in that: by weight, the hollow silica: the weight ratio of the solid phenolic resin is 100: (100-300).

3. The method for preparing a carbon-coated hollow silica composite material according to claim 1, characterized in that: the wall thickness of the hollow silicon dioxide prepared in the step (2) is 30-100 nm.

4. The method for preparing a carbon-coated hollow silica composite material according to claim 1, characterized in that: the phenolic resin in the step (3) is solid phenolic resin with the mass fraction of 95%.

5. The method for preparing a carbon-coated hollow silica composite material according to claim 1, characterized in that: the particle size of the hollow silica prepared in the step (2) is 100-400 nm.

6. The method for preparing a carbon-coated hollow silica composite material according to claim 1, characterized in that: in the step (2), the volume of the absolute ethyl alcohol is 10-15 times of that of the deionized water.

7. The method for preparing a carbon-coated hollow silica composite material according to claim 1, characterized in that: and (3) adding tetraethyl orthosilicate in the step (2) for 5 times at intervals of 1-3 h.

8. The method for preparing a carbon-coated hollow silica composite material according to claim 1, characterized in that: in the step (2), the reaction temperature is 40 ℃, and the reaction time is 10 hours.

9. A carbon-coated hollow silica composite material obtained by the production method according to any one of claims 1 to 8.

10. The carbon-coated hollow silica composite material as claimed in claim 9, wherein the carbon-coated hollow silica composite material has a particle size of 100-400nm and a silica content of 40-80 wt% and is used in a negative electrode material of a lithium ion battery.

Technical Field

The invention belongs to the technical field of lithium ion battery cathode materials, and particularly relates to a carbon-coated hollow silicon dioxide composite material and a preparation method thereof.

Background

Lithium ion secondary batteries are applied to fields ranging from portable devices to vehicles and energy storage due to their high energy density, long cycle life and environmentally friendly characteristics. At present, graphite is taken as a negative electrode material of a commercial lithium ion battery, and the theoretical maximum discharge capacity is only 372 mAh g^-1. The theoretical discharge capacity is low, so that the discharge capacity hardly meets the huge development requirements of portable electronic products and electric automobiles.

As a promising alternative, silicon-based materials have been used for their extremely high theoretical lithium storage capacity (4200 mAh g)^-1) And relatively low operating voltages are considered to be the most promising next generation anode materials. However, the relatively low conductivity and drastic volume change (about 300%) during repeated insertion and extraction of lithium ions result in a large decay of their practical capacity, which limits the large-scale application of silicon-based anodes.

At present, various structures have been constructed to improve the performance of lithium ion batteries, in which a hollow structure used as a negative electrode material of a lithium battery can significantly improve the performance of the lithium battery. Firstly, the cathode material with a hollow structure provides a wider space for the storage of lithium ions in the lithium battery, the surface capacity of the battery is increased to a certain extent, and the large specific surface area can effectively reduce the lithium ion transmission distance. Second, the hollow structure provides sufficient space to mitigate volume change of the material caused by insertion and separation of lithium ions, thereby effectively preventing compression and pulverization of the electrode material, so that the cycle performance of the battery is greatly improved.

In the past decades, human beings have been devoted to the modification studies of the silicon dioxide-based electrode material. On the one hand, silica is an abundant raw material on earth and therefore very low cost. On the other hand, silica-based anodes generate Li during insertion and extraction of lithium ions₂O and Li₄SiO₄It is possible to greatly buffer the volume change during the reaction, and thus has excellent cycle stability. In addition, silica has a moderate theoretical capacity (1950 mAh g)^-1) But the initial coulombic efficiency and intrinsic conductivity are low. To overcome these problems, coating carbon and fabricating nanostructures are considered to be effective methods.

In recent years, various silica nanostructures, including nanorods, nanotubes, nanosheets, hollow nanostructures, and the like, have been prepared. Yan et al (J. Colloid Interf Sci, 2011) prepared flower-like hollow porous SiO₂Nanocubes showing 919 mAh g in 30 cycles^-1Stable reversible capacity of (2). The SiO is obtained by the two-step growth method in Favors (Sci. Rep, 2014)₂Nanotubes of which structure retains 1266 mAh g after 100 cycles^-1The capacity of (c).

SiO prepared by Zhang team (ACS apple Mater Interfaces, 2018)₂ / TiO₂@ C nanoplate at 100 mA g^-1Shows 998 mAh g after 100 cycles at a current density of (1)^-1High reversible capacity of (2). Furthermore, after 400 cycles, at 2000 mA g^-1At a current density of 410 mAh g^-1High capacity of (2). Gu et al (Journal of Alloys and Compounds, 2018) prepared porous C/SiO₂Composite material of/C yolk structure and at 50 mA g^-1The current can still be obtained after 60 cyclesReach 1135 mAh g^-1Stable reversible capacity of (2).

Disclosure of Invention

In order to overcome the disadvantages and shortcomings of the prior art, the invention provides a preparation method of a carbon-coated hollow silica composite material.

Aiming at the problem that the volume expansion can occur when the silicon dioxide is used as the lithium ion battery cathode material, the method takes polyacrylic acid as a template to prepare the carbon-coated hollow-structure nano silicon dioxide spheres with good structure and uniform size, and the material is used as the cathode material to assemble the lithium ion battery, thereby improving the cycle performance, the rate capability and the energy density of the battery.

The invention also aims to provide the carbon-coated hollow silica composite material prepared by the method, which is used as a negative electrode material of a lithium ion battery, the nano-particles with the hollow structures can reduce volume expansion, and the carbon layer coated outside can be used as a channel for rapidly transmitting lithium ions, so that the electron conductivity is improved. The spherical structure has large mechanical stress, and the silicon dioxide structure can be prevented from being damaged.

The technology of the invention realizes that the nano silicon dioxide is coated by the phenolic resin, inhibits the volume expansion generated in the process of lithium ion insertion and extraction of the silicon dioxide and enhances the conductivity of the silicon dioxide on the one hand, and on the other hand, the hollow structure of the nano silicon dioxide can effectively relieve the volume expansion generated in the process of charging and discharging and improve the cycle stability.

The purpose of the invention is realized by the following scheme:

a preparation method of a carbon-coated hollow silicon dioxide composite material comprises the following steps:

(1) dissolving polyacrylic acid in ammonia water to prepare a solution with the mass concentration of 60-80g/L, stirring for 5 minutes, adding absolute ethyl alcohol, and continuing stirring until the solution becomes pure white to obtain a polyacrylic acid microsphere mixed solution;

(2) adding absolute ethyl alcohol, deionized water and tetraethyl orthosilicate into the polyacrylic acid microsphere mixed solution obtained in the step (1), reacting for 9-12h at 30-50 ℃, washing for 3 times by using the deionized water, and drying precipitates after filtering to obtain hollow silicon dioxide microspheres;

(3) dispersing the silicon dioxide microspheres obtained in the step (2) and solid phenolic resin into deionized water, preparing the mixture with the mass concentration of 30g/L, reacting for 3-5h at 60-80 ℃, drying the precipitate after filtering, and carbonizing for 3-6h at 900 ℃ in an inert atmosphere of 500-.

By weight, the hollow silica: the weight ratio of the solid phenolic resin is 100: (100-300).

The wall thickness of the hollow silicon dioxide prepared in the step (2) is 30-100 nm.

The phenolic resin in the step (3) is solid phenolic resin with the mass fraction of 95%.

The particle size of the nano-silica prepared in the step (2) is 100-400 nm.

In the step (2), the volume of the absolute ethyl alcohol is 10 to 15 times of that of the deionized water, and preferably 12 times of that of the deionized water.

And (3) adding tetraethyl orthosilicate in the step (2) for 5 times, wherein the interval between every two times is 1-3 hours, and preferably 2 hours.

In the step (2), the reaction temperature is preferably 40 ℃, and the reaction time is preferably 10 h.

In the step (2) and the step (3), the drying may include one of drying methods such as forced air drying, vacuum drying, freeze drying and the like.

The present invention will be described in more detail below.

(1) Dissolving polyacrylic acid in ammonia water to prepare a solution with the mass concentration of 60-80g/L, continuously stirring for 5 minutes at room temperature until the solution is colorless and transparent, adding 30mL of absolute ethyl alcohol, and continuously stirring until the solution becomes pure white to obtain a polyacrylic acid microsphere mixed solution.

The method comprises the steps of utilizing the rapid increase of the concentration of polyacrylic acid in an ammonia water solution, rapidly shrinking and agglomerating polyacrylic acid single chains, adding absolute ethyl alcohol into the solution, rapidly reducing the concentration, rapidly unfolding and breaking the shrunk single chains, and forming the polyacrylic acid microspheres.

In this step, the concentration of polyacrylic acid directly determines the particle size of the prepared microsphere, so that it needs to be uniformly mixed with ammonia water according to a certain ratio to prepare a suitable polyacrylic acid microsphere. The preferable preparation concentration is 60-80g/L, and if the concentration is too low, polyacrylic acid cannot be balled and is seriously agglomerated; if the concentration is too high, the particle size of the microspheres is too large and cannot reach the nanometer level.

In the step, anhydrous ethanol is added, one-time quick injection is needed, and if the anhydrous ethanol is added too slowly, the concentration is slowly reduced, and polyacrylic acid cannot be pelletized.

(2) Adding absolute ethyl alcohol, deionized water and tetraethyl orthosilicate into the polyacrylic acid microsphere mixed solution obtained in the step (1), reacting for 9-12h at 30-50 ℃, washing for 3 times by using the deionized water, and drying precipitates after filtering to obtain hollow silicon dioxide microspheres;

in this step, the amount of deionized water directly affects the hydrolysis rate of tetraethyl orthosilicate, preferably 2mL of deionized water, if the amount of deionized water is too small, tetraethyl orthosilicate cannot be completely hydrolyzed; if the amount of the deionized water is too much, the hydrolysis speed is too high, and the polyacrylic acid microspheres cannot be coated with the deionized water in time.

In this step, tetraethyl orthosilicate is injected preferably 5 times at 2h intervals. A small amount of the tetraethyl orthosilicate can be ensured to be uniformly coated by multiple injections, and the agglomeration phenomenon is reduced.

In the step, the polyacrylic acid microspheres have monodispersity, have a large number of hydroxyl groups on the surfaces, and can adsorb tetraethoxysilane on the surfaces of the microspheres to form uniform silicon dioxide shells.

In this step, the reaction temperature is preferably 40 ℃ and the reaction time is preferably 10 hours, which otherwise may result in poor coating effect.

In the step, a large amount of deionized water is used for repeatedly washing for 3 times, and the polyacrylic acid template needs to be thoroughly washed away, so that pure hollow silicon dioxide microspheres are obtained.

(3) And (3) adding the silicon dioxide microspheres obtained in the step (2) and solid phenolic resin into deionized water to prepare a solution with the mass concentration of 30g/L, reacting for 3-5h at the temperature of 60-80 ℃, drying the precipitate after filtering, and carbonizing for 3-6h at the temperature of 900 ℃ in an inert atmosphere to obtain the carbon-coated hollow silicon dioxide composite material.

In this step, the mass ratio of silica to solid phenolic resin is 100: (100-300).

The carbonization atmosphere in this step is not critical and must be argon, and other inert gases such as nitrogen may be used instead. The carbonization temperature is required to be in the range of 500-900 ℃ and the time is 3-5h, if the temperature or the time is too low, the carbonization is incomplete, and if the temperature or the time is too high, the production cost is increased, and on the other hand, the carbon structure is unstable.

In the step, the hydrothermal reaction temperature is 60-80 ℃, preferably 70 ℃, and the reaction time is preferably 4h, otherwise, the coating effect of the phenolic resin is not obvious.

The carbon-coated hollow silicon dioxide composite material prepared by the method has monodispersity, the particle size is between 100 and 400nm, and the content range of the silicon dioxide is 40-80 wt%. Can be applied to the cathode material of the lithium ion battery.

Compared with the prior art, the invention has the following characteristics and beneficial effects:

(1) the carbon-coated hollow silicon dioxide prepared by the invention has a hollow structure, the particle size is uniformly distributed, the carbon-coated hollow silicon dioxide is highly dispersed, the volume expansion is effectively inhibited, and compared with pure silicon dioxide and pure carbon, the carbon-coated hollow silicon dioxide has higher unreal performance and rate capability when being used as a lithium ion battery cathode material. Has good application prospect.

(2) In the preparation process of the carbon-coated hollow silica, the polyacrylic acid is used as the template, the phenolic resin is used as the carbon source, the raw materials are large in amount, cheap and easily available, the preparation process is simple and environment-friendly, and a large amount of discharged toxic and harmful gas and waste liquid are avoided, so that the resource is saved and the environment is protected.

Drawings

FIG. 1 is an SEM image of carbon-coated silica prepared in example 2 of the present invention;

FIG. 2 is an SEM photograph of silica prepared in example 4 of the present invention.

Detailed Description

The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto.

Example 1

Dissolving 100mg of polyacrylic acid in 1.5mL of ammonia water, stirring for 5 minutes, adding 30mL of absolute ethyl alcohol, and continuing stirring until the solution becomes pure white to obtain the polyacrylic acid microspheres. Adding 24mL of absolute ethyl alcohol, 2mL of deionized water and 1.5mL of tetraethyl orthosilicate into a polyacrylic acid solution, reacting for 10h at 40 ℃, washing for 3 times by using the deionized water, filtering, and drying a precipitate to obtain hollow silicon dioxide microspheres;

adding 100mg of silicon dioxide microspheres and 100mg of solid phenolic resin into deionized water, reacting for 4 hours at 70 ℃, filtering, drying the precipitate, and carbonizing for 5 hours at 800 ℃ in an inert atmosphere to obtain the carbon-coated hollow silicon dioxide composite material.

Example 2

Dissolving 100mg of polyacrylic acid in 1.5mL of ammonia water, stirring for 5 minutes, adding 30mL of absolute ethyl alcohol, and continuing stirring until the solution becomes pure white to obtain the polyacrylic acid microspheres. Adding 24mL of absolute ethyl alcohol, 2mL of deionized water and 1.5mL of tetraethyl orthosilicate into a polyacrylic acid solution, reacting for 10h at 40 ℃, washing for 3 times by using the deionized water, filtering, and drying a precipitate to obtain hollow silicon dioxide microspheres;

adding 100mg of silicon dioxide microspheres and 200mg of solid phenolic resin into deionized water, reacting for 4 hours at 70 ℃, filtering, drying the precipitate, and carbonizing for 5 hours at 800 ℃ in an inert atmosphere to obtain the carbon-coated hollow silicon dioxide composite material.

Example 3

Dissolving 100mg of polyacrylic acid in 1.5mL of ammonia water, stirring for 5 minutes, adding 30mL of absolute ethyl alcohol, and continuing stirring until the solution becomes pure white to obtain the polyacrylic acid microspheres. Adding 24mL of absolute ethyl alcohol, 2mL of deionized water and 1.5mL of tetraethyl orthosilicate into a polyacrylic acid solution, reacting for 10h at 40 ℃, washing for 3 times by using the deionized water, filtering, and drying a precipitate to obtain hollow silicon dioxide microspheres;

adding 100mg of silicon dioxide microspheres and 300mg of solid phenolic resin into deionized water, reacting for 4 hours at 70 ℃, filtering, drying the precipitate, and carbonizing for 5 hours at 800 ℃ in an inert atmosphere to obtain the carbon-coated hollow silicon dioxide composite material.

Example 4

Dissolving 100mg of polyacrylic acid in 1.5mL of ammonia water, stirring for 5 minutes, adding 30mL of absolute ethyl alcohol, and continuing stirring until the solution becomes pure white to obtain the polyacrylic acid microspheres. Adding 24mL of absolute ethyl alcohol, 2mL of deionized water and 1.5mL of tetraethyl orthosilicate into a polyacrylic acid solution, reacting for 10h at 40 ℃, washing for 3 times by using the deionized water, filtering, and drying a precipitate to obtain hollow silicon dioxide microspheres;

the prepared carbon-coated hollow silica composite material is applied to a lithium ion battery cathode material, and electrochemical test and material characterization are carried out, and the results are shown in table 1 and figures 1-2.

The morphology and size of the inventive samples were tested by scanning electron microscopy (SEM, FEI Quanta FEG 650).

The battery adopts a half-battery assembly scheme, the battery model is CR2032, the positive electrode material comprises 70 wt% of active substance, 20 wt% of conductive carbon black (Super P) and 10 wt% of binder (sodium carboxymethylcellulose), wherein the active substance is the prepared embodiment. The lithium sheet is used as a counter electrode, and the electrolyte is LiPF with the concentration of 1mol/L₆As the solute, the solvent is prepared from Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of 1:1: 1. The assembly of the lithium-ion half-cell was completed in an argon-protected glove box. The novalr cell test system is used for testing the battery with 200mA g in a voltage range of 0.01-3.0V^-1The constant current cyclic charge and discharge test is performed on the current density.

Example 4 is a silica material without a carbon layer coating.

TABLE 1 cyclability of materials of the examples

Table 1 illustrates: silica uncoated with carbon Material at 200mA g^-1Current density of 100 cycles of discharge specific capacity only left a quarter of the initial specific capacity, whereas the carbon material coated example was 200mA g^-1Current density lower cycle 1The material has higher specific discharge capacity after 00 times. Therefore, the carbon-coated hollow silica composite material prepared by the invention has more excellent energy storage effect.

FIG. 1 is an SEM image of carbon-coated silica prepared in example 2 of the present invention. The figure shows that the carbon-coated hollow silica has uniform appearance and good dispersibility.

FIG. 2 is an SEM photograph of silica prepared in example 4 of the present invention. As can be seen from the figure, the hollow silica has the advantages of spherical shape, no fracture, uniform size and particularly good dispersity.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, and simplifications are intended to be included in the scope of the present invention.