CN111498829A - Graphene-based silicon-carbon composite material, preparation method and application thereof, and battery - Google Patents

Graphene-based silicon-carbon composite material, preparation method and application thereof, and battery Download PDF

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CN111498829A
CN111498829A CN202010345831.8A CN202010345831A CN111498829A CN 111498829 A CN111498829 A CN 111498829A CN 202010345831 A CN202010345831 A CN 202010345831A CN 111498829 A CN111498829 A CN 111498829A
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graphene
silicon
dispersion liquid
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carbon composite
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CN111498829B (en
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郝胐
王文阁
王俊美
袁伟
李金来
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Inner Mongolia Xinminhui Nanotechnology Co ltd
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Xinao Graphene Technology Co ltd
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    • C01—INORGANIC CHEMISTRY
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Abstract

The invention provides a graphene-based silicon-carbon composite material, a preparation method and application thereof and a battery. Dispersing organic carboxylate, strong base and weak acid salt, silicon particles and graphene with positive charges in water to obtain graphene-silicon dispersion liquid; carrying out spray drying on the graphene-silicon dispersion liquid to obtain a graphene-silicon precursor; and roasting the graphene-silicon precursor in an inert environment to obtain the graphene-based silicon-carbon composite material. The graphene-based silicon-carbon composite material is prepared by a preparation method of the graphene-based silicon-carbon composite material. The battery comprises the graphene-based silicon-carbon composite material. The graphene-based silicon-carbon composite material is used for preparing a battery.

Description

Graphene-based silicon-carbon composite material, preparation method and application thereof, and battery
Technical Field
The invention relates to the technical field of batteries, in particular to a graphene-based silicon-carbon composite material, a preparation method and application thereof and a battery.
Background
With the continuous improvement of the requirement of people on the endurance mileage of electric vehicles, the graphite cathode material cannot meet the increasing specific energy requirement of power batteries, and people urgently need a cathode material with higher capacity.
Among many high-capacity negative electrode materials, the silicon material has an ultra-high specific capacity (theoretical capacity of 4200mAh/g) so that the silicon material is considered as the most potential battery negative electrode material. However, silicon as an electrode material in batteries has to face a very troublesome problem: during the charging and discharging process of the battery, the repeated lithium ion deintercalation can cause the silicon material to generate very large volume expansion, and the volume expansion rate even reaches 300 percent. This not only destroys the particle structure of the silicon material itself, but also destroys the binder and conductive agent network of the electrode, seriously destroying the cycle performance of the battery electrode.
Disclosure of Invention
The invention aims to provide a graphene-based silicon-carbon composite material, a preparation method and application thereof, and a battery, which can improve the structural stability of an electrode containing silicon materials and ensure the cycle performance of the battery.
In order to achieve the purpose, the invention provides a preparation method of a graphene-based silicon-carbon composite material. The preparation method of the graphene-based silicon-carbon composite material comprises the following steps:
step 1): dispersing organic carboxylate, strong base and weak acid salt, silicon particles, an optional carbon source and graphene with positive charges in water, so that the organic carboxylate and the strong base and weak acid salt are hydrolyzed and then subjected to condensation reaction to form a mixed gel cross-linking agent to wrap the surface of the silicon particles, and meanwhile, the mixed gel cross-linking agent and the graphene with positive charges are assembled together through electrostatic reaction to form graphene-silicon dispersion liquid;
step 2): carrying out spray drying on the graphene-silicon dispersion liquid to obtain a graphene-silicon precursor;
step 3): and roasting the graphene-silicon precursor in an inert environment, and carbonizing the mixed gel crosslinking agent to obtain the graphene-based silicon-carbon composite material.
Compared with the prior art, in the preparation method of the graphene-based silicon-carbon composite material provided by the embodiment of the invention, organic carboxylate is mixed with water to generate hydrolysis reaction, so that organic carboxylic acid is obtained. The strong base and weak acid salt can be mixed with water to generate hydrolysis reaction, and weak acid hydrogen radical ions are formed in the water. And the organic carboxylic acid and the weak acid hydrogen ions can be subjected to dehydration condensation, so that the hydrolyzed organic carboxylic acid salt and the strong base weak acid salt can be subjected to dehydration condensation reaction to form a three-dimensional network structure, and the mixed gel cross-linking agent is coated on the surface of the silicon material. Meanwhile, weak acid hydrogen ions which are not subjected to dehydration condensation reaction on the surface of the mixed gel cross-linking agent can be assembled with the graphene with positive charge through electrostatic reaction to obtain the graphene-silicon dispersion liquid.
And because the graphene with positive charges and the silicon particles wrapped with the mixed gel cross-linking agent are assembled together through an electrostatic reaction, the graphene and the silicon particles have better bonding strength, and therefore, after the graphene-silicon precursor is sintered in an inert environment, the obtained graphene-based silicon-carbon composite material has tighter bonding of silicon and graphene, so that the graphene-based silicon-carbon composite material has good structural strength.
Meanwhile, the mixed gel cross-linking agent is carbonized in the roasting process, and a thin carbon layer is formed on the surface of the silicon particles, so that on one hand, enough volume space is provided for the expansion of the silicon particles, the damage of the expansion of the silicon particles to an electrode conductive network is reduced, and the cycle performance of the battery is further ensured. On the other hand, areas of adjacent graphene sheet layers separated by silicon particles can form good conductive connection, and the graphene-based silicon-carbon composite material can be guaranteed to have good conductive performance.
The invention also provides the graphene-based silicon-carbon composite material. The graphene-based silicon-carbon composite material is prepared by the preparation method of the graphene-based silicon-carbon composite material.
Compared with the prior art, the beneficial effects of the graphene-based silicon-carbon composite material provided by the invention are the same as those of the preparation method of the graphene-based silicon-carbon composite material, and the detailed description is omitted.
The invention also provides a battery. The battery comprises the graphene-based silicon-carbon composite material.
Compared with the prior art, the beneficial effects of the electrode material provided by the invention are the same as those of the graphene-based silicon-carbon composite material, and are not repeated herein.
The invention also provides application of the graphene-based silicon-carbon composite material in preparation of batteries.
Compared with the prior art, the beneficial effects of the application of the graphene-based silicon-carbon composite material in the preparation of the battery are the same as those of the electrode material, and the details are not repeated herein.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention and not to limit the invention. In the drawings:
fig. 1 is one of the flow charts of the preparation of the graphene-based silicon-carbon composite material according to the embodiment of the present invention;
fig. 2 is a second flow chart of a preparation process of the graphene-based silicon-carbon composite material according to the embodiment of the present invention;
fig. 3 is a third flow chart of a preparation process of the graphene-based silicon-carbon composite material according to the embodiment of the present invention;
FIG. 4 is an electron microscope image of a graphene-based silicon-carbon composite material prepared according to a first embodiment of the present invention;
fig. 5 is a flow chart for preparing a button cell provided by the embodiment of the invention;
fig. 6 is a graph of electrochemical performance of a button cell.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
With the continuous improvement of the requirement of people on the endurance mileage of the electric automobile, the traditional graphite cathode material cannot meet the increasing specific energy requirement of the power battery, and people urgently need a cathode material with higher capacity.
Among the numerous high capacity negative electrode materials, the silicon material has an ultra-high input specific capacity (theoretical capacity of 4200mAh/g) so that the silicon material is considered as the most potential battery negative electrode material. However, silicon as an electrode material in batteries has to face a very troublesome problem: during the charging and discharging process of the battery, the repeated lithium ion deintercalation can cause the silicon material to generate very large volume expansion, and the volume expansion rate even reaches 300 percent. This not only destroys the particle structure of the silicon material itself, but also destroys the binder and conductive agent network of the electrode, seriously destroying the cycle performance of the battery electrode.
Embodiment one
In order to improve the structural stability of the electrode containing the silicon material and ensure the cycle performance of the battery, referring to fig. 1, the embodiment of the invention provides a preparation method of a graphene-based silicon-carbon composite material. The preparation method of the graphene-based silicon-carbon composite material comprises the following steps:
step 1): dispersing organic carboxylate, strong base weak acid salt, silicon particles and graphene with positive charges in water, so that the organic carboxylate and the strong base weak acid salt are hydrolyzed and then subjected to condensation reaction to form a mixed gel cross-linking agent to wrap the surfaces of the silicon particles; meanwhile, the mixed gel cross-linking agent and the graphene with positive charges are assembled together through electrostatic reaction to obtain the graphene-silicon dispersion liquid.
The organic carboxylic acid salt is a salt formed from an organic carboxylic acid having a carboxyl group, and the organic carboxylic acid salt is carbonized in a high-temperature environment. The kind of the organic carboxylic acid salt can be selected according to actual conditions. For example. The organic carboxylate can be sodium carboxymethyl cellulose, sodium salicylate, etc.
The strong base and weak acid salt refers to a salt generated by the reaction of strong base and weak acid. The type of the strong base and weak acid salt can be selected according to actual conditions, as long as the strong base and weak acid salt can be hydrolyzed to obtain weak acid hydrogen radical ions. For example, the acid ion in the strong base and weak acid salt may be a borate ion (B)4O7 2-)Carbonate ion (CO)3 2-) Sulfite ion (SO)3 2-) And Silicate Ion (SiO)3 2-) The strong base ion in the strong base weak acid salt can be sodium ion (Na)+) Potassium ion (K)+) Calcium ion (Ca)2+) And barium ion (Ba)2+) And the like.
The graphene having a positive charge may be graphene oxide or aminated graphene.
In this case, the organic carboxylic acid salt is dissolved in water and then undergoes hydrolysis reaction to obtain an organic carboxylic acid. Meanwhile, strong base and weak acid salt can also undergo hydrolysis reaction to form weak acid hydrogen radical ions in water. The organic carboxylic acid and the weak acid hydrogen ions can generate dehydration condensation reaction, so that the hydrolyzed organic carboxylate and the strong base weak acid salt form a three-dimensional network structure, and the mixed gel cross-linking agent is coated on the surface of the silicon material. Meanwhile, weak acid hydrogen ions which do not undergo a dehydration condensation reaction on the surface of the mixed gel cross-linking agent can be assembled with the graphene with positive charges through an electrostatic reaction to obtain the graphene-silicon dispersion liquid.
For example: when the organic carboxylate is carboxymethyl celluloseWhen the strong alkali weak acid salt is sodium borate, after the sodium carboxymethylcellulose, the sodium borate and the silicon particles are dissolved in water, the sodium carboxymethylcellulose and the sodium borate can be hydrolyzed, and then the hydrolyzed sodium carboxymethylcellulose and the sodium borate are subjected to dehydration condensation reaction to form a mixed gel cross-linking agent CMC-Na2B4O7Wrapping the surface of the silicon particles. At the same time, the mixed gel crosslinking agent CMC-Na2B4O7HB with surface not undergoing dehydration condensation reaction4O7 -The graphene-silicon dispersion liquid can be assembled with graphene with positive charges through electrostatic reaction to obtain the graphene-silicon dispersion liquid.
Step 2): and carrying out spray drying on the graphene-silicon dispersion liquid to obtain a graphene-silicon precursor. When the graphene-silicon dispersion liquid is subjected to spray drying in a spray drying mode, a granular graphene-silicon precursor can be obtained, the granularity of the graphene-silicon precursor can be controlled by controlling the pressure of a spray head and the rotating speed of an atomizer during spray drying, the phenomenon of agglomeration of the graphene-silicon precursor is avoided, and silicon granules can uniformly enter a sheet layer of graphene during subsequent roasting.
Step 3): and roasting the graphene-silicon precursor in an inert environment, and carbonizing the mixed gel crosslinking agent to obtain the graphene-based silicon-carbon composite material. It should be understood that: the temperature for the calcination may be selected according to the actual conditions, as long as the mixed gel crosslinking agent can be carbonized. The inert environment can be a nitrogen atmosphere environment or an argon atmosphere environment as long as the graphene-silicon precursor is not oxidized during roasting. At the moment, the mixed gel cross-linking agent coated on the surface of the silicon particles is carbonized in the roasting process, and a thin carbon layer is formed on the surface of the silicon particles, so that on one hand, enough volume space can be provided for the expansion of the silicon particles, the damage of the silicon expansion to an electrode conductive network is reduced, and the cycle performance of the battery is ensured; on the other hand, areas of adjacent graphene sheet layers separated by silicon particles can form good conductive connection, and the graphene-based silicon-carbon composite material can be guaranteed to have good conductive performance.
As can be seen from the above, in the preparation method of the graphene-based silicon carbon composite material provided by the embodiment of the invention, after hydrolysis, organic carboxylate and strong base weak acid salt undergo a dehydration condensation reaction to form a mixed gel cross-linking agent to wrap the surface of silicon particles. The mixed gel cross-linking agent can modify the surface of the silicon particles, so that weak acid hydrogen ions which do not undergo dehydration condensation reaction on the surface of the silicon particles can be assembled with the positively charged graphene through electrostatic reaction, and the positively charged graphene and the silicon particles have better bonding strength. At this time, after the graphene-silicon precursor is roasted in an inert environment, the obtained graphene-based silicon-carbon composite material has tight combination of silicon and graphene, so that the graphene-based silicon-carbon composite material has good structural strength, and the structural stability of the electrode can be improved.
Meanwhile, the baked mixed gel cross-linking agent is carbonized to form a thin carbon layer, so that an expansion space can be reserved for silicon particles in the silicon-carbon composite material, the damage of silicon expansion to an electrode conductive network is reduced, and the cycle performance of the electrode is ensured.
Therefore, when the graphene-based silicon-carbon composite material is applied to a battery electrode, the graphene-based silicon-carbon composite material can improve the structural stability of the electrode, and reduce the occurrence probability of electrode structure collapse and electrode material peeling, so that the cycle performance of the battery is improved.
As an embodiment, in order to reserve a larger expansion space for silicon particles inside the graphene-based silicon-carbon composite material, in step 1), a carbon source, organic carboxylate, strong base and weak acid salt, silicon particles, and graphene with positive charges are uniformly dispersed in water, so that the carbon source is uniformly dispersed in the graphene-silicon dispersion liquid, and the carbon source is uniformly distributed in the graphene-silicon precursor. The carbon source refers to an organic substance that can be carbonized after baking. The kind of the carbon source can be selected according to the actual situation, and the carbon source can be glucose, for example.
At the moment, in the roasting process of the graphene-silicon precursor, the carbon source and the mixed gel cross-linking agent can be carbonized together, so that a larger volume space is formed in the graphene-based silicon-carbon composite material, the damage of silicon expansion to an electrode conductive network is further reduced, and the cycle performance of the battery is ensured. Meanwhile, after the carbon source is carbonized, better conductive connection can be formed in the areas, separated by the silicon particles, of the adjacent graphene sheet layers, so that the graphene-based silicon-carbon composite material is further ensured to have good conductive performance.
As a possible implementation, see fig. 2, step 1) above: uniformly dispersing organic carboxylate, strong base and weak acid salt, silicon particles and graphene with positive charges in water, and specifically comprising the following steps:
step 1.1): and uniformly mixing the organic carboxylate solution, the strong base weak acid salt solution and the silicon dispersion liquid to obtain a first mixed dispersion liquid. The organic carboxylate solution, the strong base weak acid salt solution, and the silicon dispersion may be prepared by themselves or may be obtained by a commercially available method. At this time, the organic carboxylic acid obtained after hydrolysis of the organic carboxylic acid salt and the weak acid hydrogen ions obtained after hydrolysis of the strong base weak acid salt can be subjected to dehydration condensation, so that a crosslinking reaction is carried out to obtain a mixed gel crosslinking agent coated on the surface of the silicon particles.
And step 1.2) uniformly mixing the first mixed dispersion liquid and the graphene dispersion liquid with positive charges. It should be understood that the above-mentioned positively charged graphene dispersion liquid may be configured by itself through the positively charged graphene, or the graphene dispersion liquid may be directly purchased. At this time, weak acid hydrogen ions which are not subjected to a crosslinking reaction on the surface of the graphene surface-modified mixed gel crosslinking agent can be subjected to an electrostatic reaction with the positively charged graphene, so that silicon particles are assembled on the surface of the graphene.
As can be seen from the above, the preparation method of the graphene-based silicon-carbon composite material provided by the embodiment of the invention can be seen that the organic carboxylate, the strong base weak acid salt, the silicon particles and the positively charged graphene are dispersed in water by a step-by-step mixing method, so that the mixed gel cross-linking agent obtained by hydrolyzing the organic carboxylate and the strong base weak acid salt can be ensured to be coated on the surfaces of the silicon particles, and thus the silicon particles are modified. Then, the modified silicon particles are mixed with the positively charged graphene so that the modified silicon particles can be assembled with the positively charged graphene through an electrostatic reaction.
Specifically, in step 1.1), the organic carboxylate solution and the strong base weak acid salt solution are uniformly mixed with the silicon dispersion liquid to obtain a first mixed dispersion liquid, which includes:
and adding an organic carboxylate solution and a strong base weak acid salt solution into the silicon dispersion liquid, and uniformly stirring and dispersing to obtain the graphene-silicon dispersion liquid. The time and speed of the stirring dispersion may be selected according to actual requirements, as long as the organic carboxylate solution, the strong base weak acid salt solution and the silicon dispersion can be sufficiently mixed. At the moment, in the process that the hydrolyzed organic carboxylate and the hydrolyzed strong alkali weak acid salt water are subjected to a crosslinking reaction to form the mixed gel crosslinking agent, the formed mixed gel crosslinking agent can be fully contacted with silicon particles, so that the silicon particles can be fully wrapped by the mixed gel crosslinking agent.
Specifically, referring to fig. 3, in the step 1.2), the uniformly mixing the first mixed dispersion liquid and the positively charged graphene dispersion liquid includes:
step 1.2.1): and adding the first mixed dispersion liquid into the graphene dispersion liquid with positive charges, and stirring and mixing to obtain a second mixed dispersion liquid. It should be understood that the time for the above stirring and mixing and the speed of stirring may be selected according to actual conditions as long as the first mixed dispersion and the positively charged graphene dispersion can be uniformly mixed. For example: the stirring and mixing time can be 1-3 h, and the stirring and mixing speed is 10-50 rpm.
Step 1.2.2): and mixing the second mixed dispersion liquid by a mill to obtain the graphene-silicon dispersion liquid. The equipment used for mixing the above-mentioned mills may be selected according to actual needs. For example, the apparatus used for mill mixing may be a sand mill or a ball mill. In the same way, the mixing time of the mill also needs to be reasonably selected according to the actual situation and the applicable equipment. For example: the equipment used for mixing the mill is a ball mill, the rotating speed of the ball mill is 250 rpm-400 rpm, and the ball milling and mixing time is 3 h-4 h.
According to the preparation method of the graphene-based silicon-carbon composite material provided by the embodiment of the invention, the first mixed dispersion liquid and the graphene dispersion liquid with positive charges are stirred and mixed, so that the mixed gel cross-linking agent coated on the surfaces of silicon particles can be preliminarily combined with the graphene with positive charges, and the second mixed dispersion liquid is obtained. Then carry out the mill with the second mixed dispersion and mix, the mill mixes and can reduce the granularity of the silicon particle in the second mixed dispersion and the graphite alkene of taking the positive charge, improves the area of contact between the silicon particle of taking the positive charge and the graphite alkene for the equipment between graphite alkene of taking the positive charge and the silicon particle is more even and inseparable, guarantees that the graphite alkene base silicon carbon composite who obtains has good structural strength, and then when graphite alkene base silicon carbon composite is used for the electrode, improves the cyclicity ability of electrode. Meanwhile, the positive-charge graphene can be cut and separated by the mill mixing, so that the aggregation phenomenon of the graphene in the second mixed dispersion liquid is avoided, the uniform dispersion of the positive-charge graphene in the prepared graphene-silicon precursor is ensured, and the conductivity of the graphene-silicon precursor is further improved.
Of course, when the carbon source is uniformly dispersed in water together with the organic carboxylate, the strong base and the weak acid salt, the silicon particles and the graphene with positive charges, the step 1.2): uniformly mixing the first mixed dispersion, the positively charged graphene dispersion and the optional carbon source dispersion comprises:
and adding the first mixed dispersion liquid into the graphene dispersion liquid with positive charges, stirring and mixing, and adding the carbon source dispersion liquid to obtain a second mixed dispersion liquid.
And mixing the second mixed dispersion liquid by a mill to obtain the graphene-silicon dispersion liquid.
At this time, the carbon source dispersion liquid and the second mixed dispersion liquid may be uniformly mixed by a mill, so that the carbon source may be uniformly dispersed in the graphene-silicon dispersion liquid, and further, the carbon source may be uniformly distributed in the graphene-silicon precursor. At this time, the carbonization of the carbon source forms a uniform volume space within the graphene-based silicon-carbon composite material when the graphene-silicon precursor is fired, thereby ensuring that the silicon particles have a sufficient expansion space.
Exemplary, at step 1.2): after uniformly mixing the first mixed dispersion, the positively charged graphene dispersion, and the optional carbon source dispersion, the step 1) of dispersing the organic carboxylate, the strong base and the weak acid salt, the silicon particles, and the positively charged graphene in water further includes:
step 1.3): and heating the first mixed dispersion liquid and the graphene dispersion liquid with positive charges which are uniformly mixed. At the moment, the organic carboxylate and the strong base and weak acid salt are hydrolyzed more fully, and the formed mixed gel cross-linking agent can wrap the positively charged graphene and the silicon particles at the same time, so that the bonding strength of the silicon particles and the positively charged graphene is further improved. Meanwhile, after the mixed gel cross-linking agent coated on the surfaces of the silicon particles and the graphene is carbonized, an expansion space can be reserved for the silicon particles, and the cycle performance of the battery electrode when the graphene-based silicon-carbon composite material is used for the battery electrode is further improved.
Specifically, in order to ensure uniformity and controllability when the uniformly mixed first mixed dispersion liquid and the positively charged graphene dispersion liquid are heated, the uniformly mixed first mixed dispersion liquid and the positively charged graphene dispersion liquid may be heated by using a water bath heating method.
The temperature of the water bath heating can be selected according to actual conditions, as long as the hydrolysis degree of the organic carboxylate and the strong and weak base acid salt in the water can be improved. For example: the temperature of the water bath heating is 65-90 ℃, and the time of the water bath heating is 8-16 h.
Illustratively, in order to ensure that the silicon particles can be fully wrapped by the mixed gel cross-linking agent obtained by cross-linking after the organic carboxylate and the strong base weak acid salt are hydrolyzed, the mass fraction of the organic carboxylate in the organic carboxylate solution is 1-5%; the mass fraction of the strong base and the weak acid salt in the strong base and weak acid salt solution is 0.5 to 10 percent; the mass concentration of silicon particles in the silicon dispersion liquid is 18-20%, and the mass ratio of the organic carboxylate solution, the strong base weak acid salt solution and the silicon dispersion liquid is (10-20): (0.5-1.5): (2.5-7.5).
And the mass concentration of graphene in the graphene dispersion liquid with positive charges is 2-3.2%; the mass fraction of the carbon source in the carbon source dispersion liquid is 5-10%; and the mass ratio of the silicon dispersion liquid to the positively charged graphene dispersion liquid to the carbon source dispersion liquid is 5: (217-287): (22-42). At the moment, the silicon particles coated with the mixed gel cross-linking agent can be fully assembled on the surface of the graphene with positive charges through electrostatic reaction, so that stronger chemical bond bonding is ensured between the silicon particles and the graphene with positive charges, and the cycle performance of the graphene-based silicon-carbon composite material is improved.
Meanwhile, in order to ensure that enough space is provided on the surface of the positively charged graphene for attaching silicon particles, and avoid the aggregation of the positively charged graphene due to overlarge sheet diameter, the sheet diameter of the positively charged graphene is 6-16 um.
And the particle size of the silicon particles is 50 nm-1 um, so that the silicon particles have a large specific surface area, and meanwhile, the distance between the silicon particles and the graphene with positive charges can be ensured to be small, the bonding strength between the silicon particles and the graphene with positive charges is ensured, and the cycle performance of the graphene-based silicon-carbon composite material is ensured.
As a possible implementation manner, the graphene dispersion liquid with positive charge is obtained according to the following method:
carrying out ultrasonic dispersion on the graphene with positive charges in water. At the moment, the positively charged graphene can be uniformly dispersed in water under the action of ultrasonic dispersion, so that the phenomenon of agglomeration of the graphene is avoided.
The time of the ultrasonic dispersion can be selected according to actual conditions, as long as the positively charged graphene can be uniformly dispersed in water. For example, the time for the ultrasonic dispersion may be 1 to 2 hours.
Of course, in order to reduce the surface tension of the positively charged graphene and prevent the positively charged graphene from agglomerating in the subsequent mixing process, the dispersant and the positively charged graphene may be ultrasonically dispersed in water at the same time. It is to be understood that the above-mentioned dispersing agent may be selected according to the actual circumstances, and for example, the above-mentioned dispersing agent may be polyvinylpyrrolidone.
The mass ratio of the positively charged graphene to the dispersant to the water can be selected according to actual needs. For example: the mass ratio of the positively charged graphene to the dispersant to the water is 7: 0.07: (210-280).
At this time, the dispersant can modify the graphene with positive charges, reduce the interfacial tension of the graphene with positive charges, and ensure the dispersion uniformity of the graphene.
As an example, in order to avoid agglomeration of the graphene-silicon precursor obtained by spray drying, the pressure of a spray head during spray drying is 0.1 to 0.4mPa, the rotation speed of an atomizer during spray drying is 2 to 8rpm/min, and the temperature of spray drying is 220 to 280 ℃.
Meanwhile, firing the graphene-silicon precursor in an inert environment includes: and under an inert atmosphere, heating to 900-1200 ℃ at a heating rate of 5 ℃/min, and then preserving heat for 60-180 min to obtain the graphene-based silicon-carbon composite material.
Example one
The embodiment of the invention provides a preparation method of a graphene-based silicon-carbon composite material. The preparation method of the graphene-based silicon-carbon composite material comprises the following steps:
the first step is as follows: preparing a sodium carboxymethylcellulose solution with the mass concentration of 1%.
Preparing a sodium borate solution with the mass concentration of 5%.
A silicon dispersion having a mass concentration of 20% was prepared.
7g of graphene oxide and 0.07g of polyvinylpyrrolidone (PVP) were dispersed in 210g of water, and ultrasonically dispersed for 2 hours to obtain a graphene dispersion liquid. Among them, graphene is purchased from Jinnlite and polyvinylpyrrolidone is purchased from Shanghai test plant.
1g of glucose was dispersed in 20ml of pure water to obtain a glucose dispersion.
And secondly, placing 5g of silicon dispersion liquid into a 50m L beaker, then adding 15g of sodium carboxymethylcellulose solution and 1g of sodium borate solution into the beaker, and uniformly stirring to ensure that the hydrolyzed sodium carboxymethylcellulose and the hydrolyzed sodium borate undergo a dehydration condensation reaction to form a mixed gel cross-linking agent to wrap the surfaces of the silicon particles to obtain a first mixed dispersion liquid, wherein the sodium carboxymethylcellulose is purchased from Mecline.
The third step: dropwise adding the first mixed dispersion liquid into the graphene oxide dispersion liquid, stirring and dispersing for two hours to enable hydrogen borate ions which do not undergo a dehydration condensation reaction in the mixed gel cross-linking agent to be assembled with the graphene oxide through an electrostatic reaction, and then adding the glucose dispersion liquid into the graphene oxide dispersion liquid to obtain a second mixed dispersion liquid.
The fourth step: and ball-milling the second mixed dispersion liquid in a ball mill at the rotating speed of 300rpm for 3h, and then carrying out water bath on the ball-milled second mixed dispersion liquid in a water bath kettle at the temperature of 85 ℃ for 12 h to obtain the graphene-silicon dispersion liquid.
The fifth step: and (3) carrying out spray drying on the graphene-silicon dispersion liquid at the temperature of 260 ℃ under the pressure of 0.3mPa and the rotating speed of 3rpm/min to obtain the graphene-silicon precursor.
And a sixth step: and heating the graphene-silicon precursor to 1200 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, and preserving the heat for 120min to obtain the graphene-based silicon-carbon composite material.
Fig. 4 shows an SEM image of the graphene-based silicon-carbon composite material prepared in the first example. As can be seen from fig. 4, the silicon particles wrapped by the thin carbon layer are uniformly deposited on the graphene sheet layer, and meanwhile, the regions between the layers of the graphene oxide, which are not separated by the silicon particles, form very good conductive connection, so that the transmission of electrons from bottom to top is not affected, and the conductive performance of the graphene-based silicon-carbon composite material is ensured. And the tight bonding force also enables the silicon particles to be more firmly pinned in the interlayer of the graphene, prevents the volume expansion of the silicon particles, and ensures the cycle performance of the graphene-based silicon-carbon composite material.
Example 2
The embodiment of the invention provides a preparation method of a graphene-based silicon-carbon composite material. The preparation method of the graphene-based silicon-carbon composite material comprises the following steps:
the first step is as follows: preparing a sodium carboxymethylcellulose solution with the mass concentration of 5%.
Preparing a sodium borate solution with the mass concentration of 0.5%.
A silicon dispersion having a mass concentration of 18% was prepared.
Taking 7g of graphene oxide and 0.07g of polyvinylpyrrolidone (PVP) to be dispersed in 280g of water, and performing ultrasonic dispersion for 2 hours to obtain a graphene oxide dispersion liquid. The graphene oxide is purchased from element six in Changzhou, and the polyvinylpyrrolidone is purchased from Shanghai test factory.
2g of glucose was dispersed in 20ml of pure water to obtain a glucose dispersion.
And secondly, placing 2.5g of silicon dispersion liquid into a 50m L beaker, then adding 10g of sodium carboxymethyl cellulose solution and 0.5g of sodium borate solution into the beaker, and uniformly stirring to ensure that the hydrolyzed sodium carboxymethyl cellulose and the hydrolyzed sodium borate undergo a dehydration condensation reaction to form a mixed gel cross-linking agent to wrap the surface of the silicon particles, thereby obtaining the first mixed dispersion liquid, wherein the sodium carboxymethyl cellulose is purchased from Mecline.
The third step: dropwise adding the first mixed dispersion liquid into the graphene oxide dispersion liquid, stirring and dispersing for two hours, assembling boric acid hydrogen ions which do not undergo dehydration condensation reaction in the mixed gel cross-linking agent and the graphene oxide through electrostatic reaction, and then adding the glucose dispersion liquid into the graphene oxide dispersion liquid to obtain a second mixed dispersion liquid.
The fourth step: and ball-milling the second mixed dispersion liquid in a ball mill at the rotating speed of 250rpm for 4 hours, and then carrying out water bath on the obtained dispersion liquid in a water bath kettle at the temperature of 90 ℃ for 6 hours to obtain the graphene-silicon dispersion liquid.
The fifth step: and (3) carrying out spray drying on the graphene-silicon dispersion liquid at the temperature of 220 ℃ under the pressure of 0.1mPa and the rotating speed of 8rpm/min to obtain the graphene-silicon precursor.
And a sixth step: and heating the graphene-silicon precursor to 900 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, and preserving the temperature for 180min to obtain the graphene-based silicon-carbon composite material.
Example 3
The embodiment of the invention provides a preparation method of a graphene-based silicon-carbon composite material. The preparation method of the graphene-based silicon-carbon composite material comprises the following steps:
the first step is as follows: preparing a sodium carboxymethylcellulose solution with the mass concentration of 3%.
Preparing a sodium borate solution with the mass concentration of 10%.
A silicon dispersion having a mass concentration of 19% was prepared.
Graphene oxide (7 g) and polyvinylpyrrolidone (0.07 g, polyvinylpyrrolidone (PVP) in 250g of water were ultrasonically dispersed for 2 hours to obtain a graphene dispersion. The graphene oxide is purchased from Shandong Yuhuang new energy, and the polyvinylpyrrolidone is purchased from Shanghai trial plant.
1.5g of glucose was dispersed in 20ml of pure water to obtain a glucose dispersion.
And secondly, placing 7.5g of silicon dispersion liquid into a 50m L beaker, then adding 20g of sodium carboxymethylcellulose solution and 1.5g of sodium borate solution into the beaker, and uniformly stirring to ensure that the hydrolyzed sodium carboxymethylcellulose and the hydrolyzed sodium borate undergo a dehydration condensation reaction to form a mixed gel cross-linking agent to wrap the surface of the silicon particles, thereby obtaining the first mixed dispersion liquid, wherein the sodium carboxymethylcellulose is purchased from national reagents.
The third step: dropwise adding the first mixed dispersion liquid into the graphene oxide dispersion liquid, stirring and dispersing for two hours, assembling boric acid hydrogen ions which do not undergo dehydration condensation reaction in the mixed gel cross-linking agent and the graphene oxide through electrostatic reaction, and then adding the glucose dispersion liquid into the graphene dispersion liquid to obtain a second mixed dispersion liquid.
The fourth step: and ball-milling the second mixed dispersion liquid in a ball mill at the rotating speed of 400rpm for 1h, and then carrying out water bath on the obtained dispersion liquid in a water bath kettle at the temperature of 65 ℃ for 16h to obtain the graphene-silicon dispersion liquid.
The fifth step: and (3) carrying out spray drying on the graphene-silicon dispersion liquid at the pressure of 0.4mPa and the rotating speed of 5rpm/min at 280 ℃ to obtain the graphene-silicon precursor.
And a sixth step: and heating the graphene-silicon precursor to 1000 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, and preserving the heat for 120min to obtain the graphene-based silicon-carbon composite material.
Comparative example 1
The embodiment of the invention provides a preparation method of a graphene-based silicon-carbon composite material. The preparation method of the graphene-based silicon-carbon composite material comprises the following steps:
the first step is as follows: preparing a sodium carboxymethylcellulose solution with the mass concentration of 1%.
A silicon dispersion having a mass concentration of 20% was prepared.
7g of graphene oxide and 0.07g of polyvinylpyrrolidone (PVP) were dispersed in 210g of water, and ultrasonically dispersed for 2 hours to obtain a graphene dispersion liquid.
1g of glucose was dispersed in 20ml of pure water to obtain a glucose dispersion.
The second step is that: and (3) putting 5g of the silicon dispersion liquid into a 50ml beaker, adding 15g of the sodium carboxymethyl cellulose solution into the beaker, and uniformly stirring and dispersing to enable the sodium carboxymethyl cellulose solution to wrap the surface of the silicon particles to obtain a first mixed dispersion liquid.
The third step: dropwise adding the first mixed dispersion liquid into the graphene oxide dispersion liquid, stirring and dispersing for two hours, combining hydrolyzed sodium carboxymethyl cellulose and graphene oxide together, and then adding the glucose dispersion liquid into the graphene oxide dispersion liquid to obtain a second mixed dispersion liquid.
The fourth step: and ball-milling the second mixed dispersion liquid in a ball mill at the rotating speed of 300rpm for 3 hours, and then carrying out water bath on the obtained dispersion liquid in a water bath kettle at the temperature of 85 ℃ for 12 hours to obtain the graphene-silicon dispersion liquid on the surface of the silicon particles.
The fifth step: and (3) carrying out spray drying on the graphene-silicon dispersion liquid at the temperature of 260 ℃ under the pressure of 0.3mPa and the rotating speed of 3rpm/min to obtain the graphene-silicon precursor.
And a sixth step: and heating the graphene-silicon precursor to 1200 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, and preserving the heat for 120min to obtain the graphene-based silicon-carbon composite material.
Comparative example No. two
The embodiment of the invention provides a preparation method of a graphene-based silicon-carbon composite material. The preparation method of the graphene-based silicon-carbon composite material comprises the following steps:
the first step is as follows: and (3) dispersing 7g of graphene oxide in 0.07g of PVP aqueous dispersion, and performing ultrasonic dispersion for 2h to obtain a graphene dispersion.
1g of glucose was dispersed in 20-40ml of pure water to obtain a glucose dispersion.
A silicon dispersion having a mass concentration of 20% was prepared.
The second step is that: dropwise adding 5g of silicon dispersion liquid into the graphene oxide dispersion liquid, stirring and dispersing for two hours to assemble silicon particles on the surface of graphene oxide, and adding glucose dispersion liquid into the graphene oxide dispersion liquid to obtain a mixed dispersion liquid.
The third step: and ball-milling the mixed dispersion liquid in a ball mill at the rotating speed of 300rpm for 3h, and then carrying out water bath on the obtained dispersion liquid in a water bath kettle at the temperature of 85 ℃ for 12 h to obtain the graphene-silicon dispersion liquid.
The fourth step: and (3) carrying out spray drying on the graphene-silicon dispersion liquid at the temperature of 260 ℃ under the pressure of 0.3mPa and the rotating speed of 3rpm/min to obtain the graphene-silicon precursor.
The fifth step: and heating the graphene-silicon precursor to 1200 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, and preserving the heat for 120min to obtain the graphene-based silicon-carbon composite material.
Embodiment two
The embodiment of the invention provides a graphene-based silicon-carbon composite material. The graphene-based silicon-carbon composite material is prepared by the preparation method of the graphene-based silicon-carbon composite material.
Compared with the prior art, the beneficial effects of the graphene-based silicon-carbon composite material provided by the embodiment of the invention are the same as those of the preparation method of the graphene-based silicon-carbon composite material, and are not repeated herein.
Embodiment four
The embodiment of the invention provides a battery. The battery comprises the electrode material.
Compared with the prior art, the beneficial effects of the battery provided by the embodiment of the invention are the same as those of the graphene-based silicon-carbon composite material, and are not repeated herein.
Further, the negative electrode of the battery comprises the graphene-based silicon-carbon composite material.
Embodiment five
The embodiment of the invention provides application of a graphene-based silicon-carbon composite material in preparation of a battery.
Compared with the prior art, the beneficial effects of the application of the graphene-based silicon-carbon composite material in the preparation of the battery provided by the embodiment of the invention are the same as those of the graphene-based silicon-carbon composite material, and are not repeated herein.
Further, the negative electrode material of the battery comprises the graphene-based silicon-carbon composite material.
Furthermore, the battery is an automobile battery.
Embodiment six
The embodiment of the invention provides a manufacturing method of a button cell, as shown in fig. 5, the manufacturing method of the button cell comprises the following steps:
step S100: preparing silicon-carbon anode slurry: and dispersing the graphene-based silicon-carbon composite material, acetylene black, styrene-butadiene rubber and carboxymethyl cellulose mixture in N-methyl pyrrolidone according to the mass ratio of 8:1:1, and uniformly mixing to obtain silicon-carbon cathode slurry. The graphene-silicon composite material is the graphene-based silicon-carbon composite material prepared in the second example, the first comparative example or the second comparative example.
Step S200: and uniformly coating the silicon-carbon negative electrode slurry on a copper foil current collector, drying under a vacuum condition, and rolling until the compacted density is 1.3g/cm3 to obtain a negative electrode plate.
And S300, assembling the button cell in a glove box in an argon atmosphere by using a lithium metal sheet as a counter electrode, a polypropylene membrane as a diaphragm and 1 mol/L L iPF6 solution as electrolyte, wherein the solvent of the L iPF6 solution is a mixed solution of ethylene carbonate and dimethyl carbonate in a volume ratio of 1: 1.
Performing electrochemical performance test on the button cell, wherein the electrochemical performance test result is shown in fig. 6, and a curve a in fig. 6 is an electrochemical performance curve of a cell prepared by using the graphene-based silicon-carbon composite material obtained in the first embodiment; curve B is the electrochemical performance curve of a battery made from the graphene-based silicon-carbon composite material obtained in comparative example i; curve C is the electrochemical performance curve for a cell made using the graphene-based silicon-carbon composite material obtained in comparative example two.
Referring to the curve a in fig. 6, it can be seen that the first discharge of the battery prepared from the graphene-based silicon-carbon composite material obtained in the first embodiment reaches 650mAh/g, the discharge capacity retention rate at 0.5C reaches 90.8% (200 cycles), and the capacity at 0.5C is stabilized at 500 mAh/g.
Referring to curve B in fig. 6, it can be seen that the first discharge specific capacity of the battery prepared from the graphene-based silicon-carbon composite material obtained in the comparative example is about 620mAh/g, and the 0.5C capacity retention rate is 85.6% (cycle 200 weeks).
Referring to curve C in fig. 6, it can be seen that the cycle retention of the battery manufactured using the graphene-based silicon-carbon composite obtained in comparative example 2 was only 51.9% (cycle 200 weeks).
Therefore, the cycle performance and stability of the battery prepared from the graphene-based silicon-carbon composite material obtained in the second embodiment are far higher than those of the batteries prepared from the graphene-based silicon-carbon composite materials obtained in the first and second comparative examples. While example two differs from comparative examples one and two only in that the hybrid gel crosslinker CMC-Na was used in example two2B4O7As a crosslinking agent, only CMC was used as a crosslinking agent in comparative example one, and no crosslinking agent was used in comparative example two.
Therefore, the mixed gel cross-linking agent is used as the cross-linking agent, so that the acting force between the silicon particles and the graphene can be improved, the silicon particles can be more firmly adsorbed on the surface of the graphene, and the cycle performance of the battery can be improved. In the foregoing description of embodiments, the particular features, structures, materials, or characteristics may be combined in any suitable manner in any one or more embodiments or examples.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.

Claims (10)

1. A preparation method of a graphene-based silicon-carbon composite material is characterized by comprising the following steps:
step 1): dispersing organic carboxylate, strong base weak acid salt, silicon particles, an optional carbon source and graphene with positive charges in water, so that the organic carboxylate and the strong base weak acid salt are hydrolyzed and then subjected to condensation reaction to form a mixed gel cross-linking agent to wrap the surface of the silicon particles, and meanwhile, the mixed gel cross-linking agent and the graphene with positive charges are assembled together through electrostatic reaction to obtain graphene-silicon dispersion liquid;
step 2): carrying out spray drying on the graphene-silicon dispersion liquid to obtain a graphene-silicon precursor;
step 3): and roasting the graphene-silicon precursor in an inert environment, and carbonizing the mixed gel crosslinking agent to obtain the graphene-based silicon-carbon composite material.
2. The method of preparing graphene-based silicon-carbon composite according to claim 1, wherein the step 1) of dispersing the organic carboxylate, the strong base and the weak acid salt, the silicon particles, the optional carbon source and the positively charged graphene in water comprises:
step 1.1): uniformly mixing an organic carboxylate solution, a strong base weak acid salt solution and a silicon dispersion liquid to obtain a first mixed dispersion liquid;
step 1.2): and uniformly mixing the first mixed dispersion liquid, the graphene dispersion liquid with positive charges and an optional carbon source dispersion liquid.
3. The method for preparing graphene-based silicon-carbon composite material according to claim 2, wherein the step 1.1) of uniformly mixing organic carboxylate solution and strong base weak acid salt solution with silicon dispersion liquid comprises:
adding an organic carboxylate solution and a strong base weak acid salt solution into the silicon dispersion liquid, and uniformly stirring and dispersing;
and/or the presence of a gas in the gas,
in the step 1.2), the uniformly mixing the first mixed dispersion liquid, the positively-charged graphene dispersion liquid, and the optional carbon source dispersion liquid includes:
step 1.2.1): adding the first mixed dispersion liquid into a graphene dispersion liquid with positive charges, stirring and mixing, and adding a carbon source dispersion liquid to obtain a second mixed dispersion liquid;
step 1.2.2): mixing the second mixed dispersion liquid by a mill to obtain graphene-silicon dispersion liquid;
preferably, in the step 1.2.1), the stirring and mixing time is 1-3 h, and the stirring and mixing speed is 10-50 rpm;
preferably, in the step 1.2.2), the mill mixing is performed in a ball mill, the rotation speed of the ball mill is 250rpm to 400rpm, and the mixing time of the mill is 1h to 4 h.
4. The method for preparing graphene-based silicon-carbon composite material according to claim 2 or 3, wherein, in the step 1.2), after uniformly mixing the first mixed dispersion, the positively-charged graphene dispersion and the optional carbon source dispersion, the step 1) of dispersing organic carboxylate, strong alkali weak acid salt, silicon particles, optional carbon source and positively-charged graphene in water further comprises:
step 1.3): heating the uniformly mixed first mixed dispersion, the positively charged graphene dispersion and the optional carbon source dispersion;
preferably, the first mixed dispersion liquid, the positively-charged graphene dispersion liquid and the optional carbon source dispersion liquid which are uniformly mixed are heated by a water bath heating method;
further preferably, the temperature of the water bath heating is 65-90 ℃, and the time of the water bath heating is 6-16 h.
5. The preparation method of the graphene-based silicon-carbon composite material according to any one of claims 2 to 4, wherein the mass fraction of the organic carboxylate in the organic carboxylate solution is 1% to 5%;
the mass fraction of the strong base and weak acid salt in the strong base and weak acid salt solution is 0.5-10%;
the mass concentration of silicon particles in the silicon dispersion liquid is 18-20%;
the mass ratio of the organic carboxylate solution, the strong base weak acid salt solution and the silicon dispersion liquid is (10-20): (0.5-1.5): (2.5-7.5);
and/or the presence of a gas in the gas,
the mass concentration of graphene in the positively charged graphene dispersion liquid is 2% -3.2%;
the mass concentration of the carbon source in the carbon source dispersion liquid is 5-10%;
and the mass ratio of the silicon dispersion liquid to the positively charged graphene dispersion liquid to the carbon source dispersion liquid is 5: (217-287): (22-42);
and/or the presence of a gas in the gas,
the organic carboxylate comprises sodium carboxymethyl cellulose;
the strong base weak acid salt comprises sodium borate;
the positively charged graphene comprises graphene oxide;
the carbon source comprises glucose;
and/or the presence of a gas in the gas,
the particle size of the silicon particles is 50 nm-1 um; the sheet diameter of the graphene with positive charges is 6 u-16 um.
6. The preparation method of the graphene-based silicon-carbon composite material according to any one of claims 2 to 5, wherein the positively charged graphene dispersion liquid is obtained by the following method:
carrying out ultrasonic dispersion on the graphene with positive charges and an optional dispersant in water;
preferably, the mass ratio of the positively charged graphene, the dispersant and the water is 7: 0.07: (210-280);
preferably, the dispersant comprises polyvinylpyrrolidone;
preferably, the time of ultrasonic dispersion is 1-2 h.
7. The preparation method of the graphene-based silicon-carbon composite material according to any one of claims 1 to 5, wherein in the step 2), the pressure of a spray head during spray drying is 0.1 to 0.4mPa, the rotation speed of an atomizer during spray drying is 2 to 8rpm/min, and the temperature of the spray drying is 220 to 280 ℃; and/or the presence of a gas in the gas,
in the step 3), firing the graphene-silicon precursor in an inert environment comprises:
under the inert atmosphere, the graphene-silicon precursor is heated to 900-1200 ℃ at the heating rate of 5 ℃/min, and then the temperature is kept for 60-180 min.
8. The graphene-based silicon-carbon composite material is characterized by being prepared by the preparation method of the graphene-based silicon-carbon composite material according to any one of claims 1 to 7.
9. A battery comprising the graphene-based silicon carbon composite material of claim 8;
preferably the negative electrode material of the battery comprises the graphene-based silicon-carbon composite according to claim 8.
10. Use of the graphene-based silicon-carbon composite material according to claim 8 in the preparation of a battery;
preferably the negative electrode material of the battery comprises the graphene-based silicon-carbon composite material according to claim 8;
more preferably, the battery is an automotive battery.
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