CN108565406B - Lithium ion battery composite material and preparation method of composite electrode thereof - Google Patents

Lithium ion battery composite material and preparation method of composite electrode thereof Download PDF

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CN108565406B
CN108565406B CN201810019135.0A CN201810019135A CN108565406B CN 108565406 B CN108565406 B CN 108565406B CN 201810019135 A CN201810019135 A CN 201810019135A CN 108565406 B CN108565406 B CN 108565406B
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graphene quantum
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lithium ion
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孔丽娟
张德仁
张宝凤
徐子福
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Amprius Wuxi Co ltd
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    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
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    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
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    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
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    • Y02E60/10—Energy storage using batteries

Abstract

The invention relates to a lithium ion battery composite material and a preparation method of a composite electrode thereof.A nano-silicon is added into a dopamine hydrochloride solution to form a polydopamine wrapping layer on the surface of a silicon; and simultaneously, preparing the graphene quantum dots by a one-step solvothermal method, and doping the graphene quantum dots into a sodium alginate binder to prepare the composite electrode material. According to the invention, the poly-dopamine wrapping layer can buffer the huge volume expansion of the silicon spheres, and the stability of the silicon-based negative electrode material is effectively improved. The doping of the graphene quantum dots enables the binder layer to have higher mechanical property and elastic property, so that the graphene quantum dots have more lasting swelling property in electrolyte, and can play a reversible buffering role for huge volume change of silicon after multiple cycles, thereby ensuring the structural integrity of the electrode in the charging and discharging process. Meanwhile, the graphene quantum dots have certain conductivity, so that the conductivity of the binder layer is improved. Therefore, the electrode shows good electrochemical performance and can be widely used for various high-capacity lithium ion batteries.

Description

Lithium ion battery composite material and preparation method of composite electrode thereof
Technical Field
The invention relates to a lithium ion battery composite material and a preparation method of a composite electrode thereof, belonging to the technical field of lithium ion batteries
Background
The development of modern economy is mainly based on fossil energy. However, in the 21 st century, half of the resources on which economies depend are rapidly lost. Due to energy shortages, electrochemical energy storage technologies including batteries, fuel cells, electrochemical capacitors, etc. have been emerging. Among these energy conversion devices, a lithium ion battery having advantages of high energy density, long cycle life, environmental friendliness, no memory effect, and the like will play a significant role. With the improvement of living standard and technical progress, people put higher requirements on the performance of lithium ion batteries.
The commercial lithium ion battery cathode material is mainly graphite, but has low lithium storage capacity (372mA h g)-1) It is difficult to meet the requirements of high-performance lithium ion batteries. Currently, silicon has the highest theoretical lithium storage capacity (4200mA h g)-1) The negative electrode material (2) is about ten times the capacity of the graphite electrode. In addition, the lithiation reaction voltage platform of the silicon is 0.2-0.3V and higher than a graphite electrode (less than 0.1V), so that the formation of lithium dendrites can be avoided, and the safety problem generated in the charging and discharging process is reduced. However, there is a process for converting silicon-based materials to negative electrode materials for lithium ion batteries on a large scale. This is due to the very unstable cycling performance of the silicon negative electrode, the very low intrinsic electron conductivity and the lithium ion diffusion coefficient. The biggest challenge faced by the silicon cathode in the using process is that the material generates huge volume change in the charging and discharging processes, and the volume change reaches 400%. Such a large volume effect will cause a series of problems (Wu H, Cui Y. designing nanostructured Si antibodies for high energy batteries. Nano Today, 2012, 7(5):414-429), which are typical: the electrode material is easy to be pulverized and fall off, and is separated from a current collector, so that the reversible capacity of the battery is reduced, and the cycle performance is poor; the stable SEI film is difficult to form on the surface of the electrode material, and a new and unstable SEI film is formed by the reaction of a continuously formed fresh fracture surface and the electrolyte, so that the electrode material and the electrolyte are greatly consumed, the specific capacity is rapidly reduced, and the coulombic efficiency is reduced. In addition, the electron conductivity of the electrode material is very low, and the electrode material cannot effectively participate in the charge and discharge process, resulting in the attenuation of the battery capacity.
Researchers have made many attempts to improve the electrochemical performance of silicon anodes, wherein the "composite" method is simple and the selection of composite materials is wide, and has been developed as the main modification method of silicon anodes. In addition, extensive research and repeated experiments show that the compounding and optimization of the active material not only affects the performance of the lithium battery, but also the stability of the electrode structure is important. Among them, especially for materials having a large volume effect, as an essential component of the electrode, the selection and optimization of the binder are important. Conventional binders have not been satisfactory. Therefore, the patent explores a lithium ion battery composite material and a preparation method of a composite electrode thereof, and the lithium ion battery composite material is used for improving the electrochemical performance of a silicon-based negative electrode.
Disclosure of Invention
The invention aims to provide a lithium ion battery composite material and a preparation method of a composite electrode thereof, which are used for improving the electrochemical performance of a silicon-based negative electrode. The preparation method comprises the steps of adding nano silicon spheres into a dopamine hydrochloride solution to form a polydopamine wrapping layer on the surfaces of the silicon spheres, preparing graphene quantum dots with uniform size, good dispersibility and good water solubility by a one-step solvothermal method, and doping the graphene quantum dots into a sodium alginate binder to prepare the composite electrode material.
In order to achieve the purpose, the technical scheme provided by the invention is as follows:
a lithium ion battery composite electrode coats a layer of polydopamine with strong adhesion on the surface of a negative electrode material of the electrode, and simultaneously uses graphene quantum dots to modify a binder, wherein the preparation method comprises the following steps:
1) preparing solid graphene quantum dots:
weighing graphite oxide GO powder, mixing with N, N-Dimethylformamide (DMF) to obtain a mixed suspension, ultrasonically dispersing uniformly, transferring to a reaction kettle, and carrying out hydrothermal reaction for a certain time; cooling the mixed solution to room temperature, performing suction filtration by using a microporous filter membrane to obtain brown filtrate, performing rotary evaporation to remove a DMF solvent, dissolving in deionized water, dialyzing by using a 3000Da molecular weight dialysis bag, and finally freeze-drying the solution in the bag to obtain solid graphene quantum dots;
2) preparing a graphene quantum dot modified binder:
dispersing binder powder by using deionized water, stirring to be homogeneous, adding the graphene quantum dots prepared in the step 1), continuously dispersing, and stirring for one day to obtain a modified binder for later use;
3) preparing hydrophilic nano silicon:
dispersing nano silicon in a mixed solution of hydrogen peroxide, ammonia water and deionized water, heating for reaction for a certain time, performing centrifugal separation, and drying to obtain hydrophilic nano silicon;
4) preparing a polydopamine/nano-silicon compound:
sequentially dissolving the hydrophilic nano-silicon prepared in the step 3) and dopamine hydrochloride in deionized water, vigorously stirring at room temperature, dropwise adding ammonium persulfate into the mixed solution, continuously stirring for a certain time after adding, centrifugally separating, washing with deionized water, and drying to obtain a polydopamine/nano-silicon compound;
5) preparing a composite electrode:
mixing and grinding the polydopamine/nano-silicon compound obtained in the step 4) and acetylene black for half an hour, then mixing and dispersing the mixture with a modified binder in deionized water, magnetically stirring to obtain slurry, and uniformly coating the slurry on the surface of copper foil to obtain the lithium ion battery negative plate.
In the step 1), the concentration of a mixed suspension formed by graphite oxide GO powder and N, N-dimethylformamide is 5-50 mg/ml, and ultrasonic dispersion is carried out for 0.5-2 hours.
In the step 1), the high-temperature pyrolysis temperature and time of the hydrothermal reaction are respectively 150-300 ℃ and 2-10 h, and the post-treatment comprises suction filtration, deionized water washing, dialysis and freeze drying.
The adhesive in the step 2) is sodium alginate.
The particle size of the nano silicon in the step 3) is 50-200 nm; the solvent used for the hydrophilic nano-silicon treatment is a mixed solution of hydrogen peroxide, ammonia water and deionized water; the volume ratio of the hydrogen peroxide to the ammonia water is 10: 1-1: 1, the volume ratio of the ammonia water to the water is 1:6, and the heating time is 0.5-1 h.
Mixing the hydrophilic nano-silicon and the dopamine hydrochloride in the step 4) according to the mass ratio of 1: 0.8-1: 1.6, stirring for 2 hours, adding the dopamine hydrochloride and the ammonium persulfate according to the mass-volume ratio of 1 g/(10-60) ml, fully stirring for 3-6 hours, and carrying out polymerization reaction on the dopamine under an initiator to uniformly coat on the surface of the nano-silicon.
Wherein the mass ratio of the polydopamine/nano-silicon composite, the acetylene black, the graphene quantum dots and the binder is (75-80): 10, (1-2.5): 8-9.
The composite electrode of the lithium ion battery is prepared by taking water as a solvent, then the composite electrode is assembled into a button type half battery in a glove box, and the electrochemical performance of the button type half battery is tested.
The nano silicon spheres are coated by the polydopamine, and the polydopamine molecular structure has higher strength due to the existence of aromatic functional groups; in addition, the interface adhesive force between the coating layer and the nano silicon is very strong through covalent bonds and other intramolecular interactions, so that the volume expansion effect can be buffered by the coating layer, and the stability of the silicon-based negative electrode material is effectively improved. In addition, the polydopamine contains phenol and indole-like functional groups, so that the coating layer has high hydrophilicity and secondary reaction activity, and the composite material coated with dopamine for the first time has hydrophilicity and continuous reaction activity. The method for preparing the graphene quantum dots by the one-step solvothermal method is simple, raw materials are cheap and easy to obtain, the surfaces of the prepared graphene quantum dots contain a large number of oxygen-containing groups (epoxy groups and hydroxyl groups are on the surfaces of the graphene quantum dots, and carboxyl groups are on the edges of the graphene quantum dots), the water solubility is good, and the prepared graphene quantum dots can be uniformly distributed in a sodium alginate adhesive layer. The sodium alginate is added into the sodium alginate, so that the conductivity of the adhesive can be enhanced, the transmission of charges in an electrode is accelerated, and the rapid electron and charge transfer can be realized by easily coupling the electronic energy levels of a silicon semiconductor. In addition, the hydrogen bonding enables the adhesive layer to have better elasticity, mechanical property and swelling property, and the structural integrity of the electrode is still maintained after the silicon material is subjected to repeated volume expansion. Importantly, the existence of the edge groups causes the edge groups of the graphene sheets to be mutually wound and protruded to form a certain spatial structure, so that the graphene sheets have rich channels for conveying the electrolyte, and the diffusion coefficient of lithium ions is greatly improved. The electrode material exhibits high capacity, good rate characteristics and cycling stability.
Compared with the prior art, the invention has the following remarkable advantages:
(1) the method for preparing the graphene quantum dots by the one-step solvothermal method is simple, efficient, low in cost and cheap and easily available in raw materials. The prepared graphene quantum dot is small in size, the surface of the graphene quantum dot contains a large number of oxygen-containing groups (epoxy groups and hydroxyl groups are on the surface of the graphene quantum dot, and carboxyl groups are on the edge of the graphene quantum dot), and the graphene quantum dot is good in water solubility, so that the graphene quantum dot is uniformly dispersed in a binder layer.
(2) The nano silicon ball is coated by the polydopamine, the polydopamine molecular structure has higher strength due to the existence of aromatic functional groups, and in addition, the interface adhesive force between the coating layer and the nano silicon is very strong through covalent bonds and other intramolecular interactions, so the volume expansion effect can be buffered, and the stability of the silicon-based negative electrode material can be effectively improved by the coating layer. In addition, the polydopamine contains phenol and indole-like functional groups, so that the coating layer has high hydrophilicity and secondary reaction activity, and the composite material coated with dopamine for the first time has hydrophilicity and continuous reaction activity.
(3) The doping of the graphene quantum dots enables the surface of the adhesive layer to have a very dense microstructure without macropores. Some groups exist at the edge of the graphene quantum dot, so that strong hydrogen bonding action occurs between a graphene sheet in the quantum dot and sodium alginate groups, so that the sodium alginate binder has higher mechanical property and elastic property, and has more lasting swelling property in an electrolyte, and can play a reversible buffering role for huge volume change of silicon after multiple cycles, thereby ensuring the structural integrity of the electrode in the charging and discharging process. Meanwhile, the graphene quantum dots have certain conductivity, and the interaction between the graphene quantum dots and sodium alginate groups enhances the jumping of lithium ions between adjacent groups, so that the conductivity of the binder layer is improved. The electrode thus exhibits high capacity, good rate characteristics and cycling stability.
Drawings
Fig. 1 is a TEM image of the graphene quantum dot prepared in example 1 of the present invention.
Fig. 2 is an SEM picture of the poly-dopamine coated silicon spheres prepared in example 1 of the present invention.
FIG. 3 shows the composite electrode and pure nano-silicon spheres prepared in example 1 of the present invention at 100mA g-1Photographs of the cycling performance at current density.
Fig. 4 is a photograph of the rate capability of the composite electrode prepared in example 1 of the present invention and pure nano silicon spheres under different current densities.
Detailed Description
The present invention will be further described with reference to the following specific examples.
The experimental procedures, in which specific conditions are not noted in the following examples, are generally carried out under conventional conditions or conditions recommended by the manufacturers. The term "room temperature" and "normal pressure" as used herein refer to the temperature and pressure during normal operation, generally 25 ℃ and one atmosphere.
In the following examples, the electrode used for electrochemical tests of the cell was a copper foil (diameter: 15mm, thickness: 0.02mm), and a half cell was used as a test object. The electrochemical test is a new Weier system, the operating voltage is 0.001-2.5V, and the charging and discharging multiplying power is 50, 100, 200, 500, 1000, 1500, 2000mA g-1Current density of 100mAg during circulation-1。
Example 1
A preparation method of a composite electrode of a lithium ion battery comprises the following steps:
1) weighing 1g of graphite oxide powder, mixing with 80ml of N, N-dimethylformamide, ultrasonically dispersing for 1h, transferring to a 100ml reaction kettle, and carrying out hydrothermal reaction at 220 ℃ for 8 h. Cooling the mixed solution to room temperature, performing suction filtration by using a microporous filter membrane to obtain brown filtrate, performing rotary evaporation to remove a DMF solvent, dissolving in deionized water, dialyzing by using a 3000Da molecular weight dialysis bag, and finally freeze-drying the solution in the bag to obtain solid graphene quantum dots;
2) dispersing nano silicon into a mixed solution of 100mL of deionized water, 20mL of hydrogen peroxide and 20mL of ammonia water, heating in a water bath at 95 ℃ for reaction for 30min, performing centrifugal separation, and drying to obtain hydrophilic nano silicon powder;
3) sequentially dissolving 0.5g of hydrophilic nano-silicon and 0.5g of dopamine hydrochloride in 100ml of deionized water, vigorously stirring at room temperature for 2 hours, dropwise adding 15ml of ammonium persulfate into the mixed solution, continuously stirring for 5 hours after the addition is finished, performing centrifugal separation, washing with deionized water, and drying to obtain a polydopamine/nano-silicon compound;
4) dispersing 1g of 2000cP sodium alginate powder by using 50ml of deionized water, stirring to be homogeneous, adding 235mg of prepared graphene quantum dots, continuously dispersing, and stirring for one day to obtain a modified binder for later use;
5) mixing and grinding 0.3g of the prepared polydopamine-coated silicon composite material and 37.5mg of acetylene black for half an hour, then dispersing the mixture in 1.594ml of the modified binder prepared in the step 4), magnetically stirring to obtain slurry, uniformly coating the slurry on the surface of copper foil, performing vacuum drying and slicing to obtain a battery piece with the diameter of 15mm, taking the battery piece as a positive electrode and a metal lithium piece as a negative electrode, adopting 1MLiPF6/EC, EMC, DMC (1:1:1in vol) + 2% VC electrolyte and a polypropylene microporous membrane as a diaphragm, assembling a button half battery in a glove box, and testing the charge and discharge performance of the button half battery.
This embodiment is a preferred embodiment in which,
the poly dopamine layer is uniformly coated on the surface of the nano silicon sphere, the thickness of the poly dopamine layer is about 10nm, the silicon surface is effectively prevented from being directly contacted with electrolyte molecules, and the loss of active ingredients of the electrode caused by the reaction of silicon and the electrolyte is reduced. Meanwhile, the wrapping layer has good mechanical strength and can bring a certain buffering effect for the huge volume change of the silicon spheres. The average transverse size of the graphene quantum dots prepared by the solvothermal method is 4nm, and the average thickness of the graphene quantum dots is 1.2nm, which shows that 1-3 layers of the graphene quantum dots have a structure similar to graphene. In addition, due to the very small size and good water solubility of the graphene quantum dots, the doping of the graphene quantum dots enables the surface of the binder layer to have a very dense microstructure without macropores. Some groups exist at the edge of the graphene quantum dot, so that strong hydrogen bonding action occurs between a graphene sheet in the quantum dot and sodium alginate groups, so that the sodium alginate binder has higher mechanical property and elastic property, and has more lasting swelling property in an electrolyte, and can play a reversible buffering role for huge volume change of silicon after multiple cycles, thereby ensuring the structural integrity of the electrode in the charging and discharging process. Meanwhile, the graphene quantum dots have certain conductivity, and the interaction between the graphene quantum dots and sodium alginate groups enhances the jumping of lithium ions between adjacent groups, so that the conductivity of the binder layer is improved. The study showed that the composite electrode was at 100mA g-1The reversible capacity is kept at 2427.68mA h g after the circulation of 100 circles under the current density-1Furthermore, at 2000mA g-1、2500mA g-1、4200mA g-1The discharge specific capacity under high rate is 2326.35mA h g-1、2187.43mA h g-1、1978.24mA h g-1。
Fig. 1 is a TEM image of the graphene quantum dot prepared in example 1 of the present invention. According to the analysis of a transmission electron microscope image, the graphene quantum dots are almost not agglomerated and are approximately of a two-dimensional sheet structure. The particle size distribution obtained by using image generation software shows that the size distribution range of graphene sheets in the graphene quantum dots is 2-7 nm, and the average size is 4 nm. Thus, the graphene quantum dots with uniform size and good dispersibility are successfully prepared.
Fig. 2 is an SEM picture of the poly-dopamine coated silicon spheres prepared in example 1 of the present invention. The silicon spheres are spherical and are 50-200 nm in size, the silicon spheres are wrapped into a cluster by polydopamine, a specific area is enlarged, a layer of 'film' is obviously arranged on the periphery of each silicon sphere, and the polydopamine is formed on the surface of each silicon sphere in situ in the synthesis process, so that the exposed silicon spheres cannot be seen.
FIG. 3 shows that the composite electrode and pure nano-silicon spheres prepared in example 1 of the present invention are at 100mA g-1Photographs of the cycling performance at current density. Initially, the specific capacity of pure nano-silicon material decays rapidly, and after several turns, the capacity becomes almost 0. This is because, during the charging and discharging process, silicon undergoes large volume changes repeatedly, the electrode material is pulverized, a stable SEI film is hardly formed on the surface, and a new, unstable SEI film is formed by the reaction of a fresh fracture surface that is continuously formed with the electrolyte, resulting in a large amount of consumption of the electrode material and the electrolyte. As the number of cycles increases, the loss of electrode active material increases, and the specific capacity of the cycle decreases continuously, leaving only 4.6% of the second cycle after 100 cycles. Under the same condition, the specific capacity of the composite electrode after 100 circles is 2427.68mA hg-1The capacity fade per cycle is only 0.36% on average.
FIG. 4 shows different current densities of the composite electrode prepared in example 1 of the present invention and pure nano-silicon spheresMagnification performance photograph of the following. When the current density reaches 1000mA g-1The specific discharge capacity of the composite electrode is 2584.5mA h g-1The specific capacity retention rate is about 72%, and the pure silicon electrode has only 5.2% under the same condition. At 2000mA g-1、2500mA g-1、4200mAg-1The discharge specific capacity under high rate is 2326.35mA h g-1、2187.43mA h g-1、1978.24mA h g-1. The result shows that the composite electrode has good high-rate performance. The obvious improvement of the rate capability benefits from the introduction of polydopamine and graphene quantum dots.
Example 2
1) Weighing 1.6g of graphite oxide powder, mixing with 80ml of N, N-dimethylformamide, ultrasonically dispersing for 1h, transferring to a 100ml reaction kettle, and carrying out hydrothermal reaction at 200 ℃ for 8 h. Cooling the mixed solution to room temperature, performing suction filtration by using a microporous filter membrane to obtain brown filtrate, performing rotary evaporation to remove a DMF solvent, dissolving in deionized water, dialyzing by using a 3000Da molecular weight dialysis bag, and finally freeze-drying the solution in the bag to obtain solid graphene quantum dots;
2) dispersing nano silicon into a mixed solution of 100mL of deionized water, 40mL of hydrogen peroxide and 20mL of ammonia water, heating in a water bath at 95 ℃ for reaction for 30min, performing centrifugal separation, and drying to obtain hydrophilic nano silicon powder;
3) sequentially dissolving 0.5g of hydrophilic nano-silicon and 0.5g of dopamine hydrochloride in 100ml of deionized water, vigorously stirring at room temperature for 2 hours, dropwise adding 20ml of ammonium persulfate into the mixed solution, continuously stirring for 5 hours after the addition is finished, performing centrifugal separation, washing with deionized water, and drying to obtain a polydopamine/nano-silicon compound;
4) dispersing 1g of 2000cP sodium alginate powder by using 50ml of deionized water, stirring to be homogeneous, adding 235mg of prepared graphene quantum dots, continuously dispersing, and stirring for one day to obtain the modified binder for later use.
5) Mixing and grinding 0.3g of the prepared polydopamine-coated silicon composite material and 37.5mg of acetylene black for half an hour, then dispersing the mixture in 1.594ml of the modified binder prepared in the step 4), magnetically stirring to obtain slurry, uniformly coating the slurry on the surface of copper foil, performing vacuum drying and slicing to obtain a battery piece with the diameter of 15mm, taking the battery piece as a positive electrode and a metal lithium piece as a negative electrode, adopting 1MLiPF6/EC, EMC, DMC (1:1:1in vol) + 2% VC electrolyte and a polypropylene microporous membrane as a diaphragm, assembling a button half battery in a glove box, and testing the charge and discharge performance of the button half battery.
Through tests, the performance of the silicon-based composite electrode prepared in the embodiment is close to that of the silicon-based composite electrode obtained in the embodiment 1.
Example 3
1) Weighing 1.6g of graphite oxide powder, mixing with 80ml of N, N-dimethylformamide, ultrasonically dispersing for 1h, transferring to a 100ml reaction kettle, and carrying out hydrothermal reaction at 200 ℃ for 8 h. Cooling the mixed solution to room temperature, performing suction filtration by using a microporous filter membrane to obtain brown filtrate, performing rotary evaporation to remove a DMF solvent, dissolving in deionized water, dialyzing by using a 3000Da molecular weight dialysis bag, and finally freeze-drying the solution in the bag to obtain solid graphene quantum dots;
2) dispersing nano silicon into a mixed solution of 100mL of deionized water, 40mL of hydrogen peroxide and 20mL of ammonia water, heating in a water bath at 95 ℃ for 40min, performing centrifugal separation, and drying to obtain hydrophilic nano silicon powder;
3) sequentially dissolving 0.5g of hydrophilic nano-silicon and 0.6g of dopamine hydrochloride in 100ml of deionized water, vigorously stirring at room temperature for 2 hours, dropwise adding 20ml of ammonium persulfate into the mixed solution, continuously stirring for 5 hours after the addition is finished, performing centrifugal separation, washing with deionized water, and drying to obtain a polydopamine/nano-silicon compound;
4) dispersing 1g of 2000cP sodium alginate powder by using 50ml of deionized water, stirring to be homogeneous, adding 235mg of prepared graphene quantum dots, continuously dispersing, and stirring for one day to obtain the modified binder for later use.
5) Mixing and grinding 0.3g of the prepared polydopamine-coated silicon composite material and 37.5mg of acetylene black for half an hour, then dispersing the mixture in a modified binder prepared by 1.594ml 4), magnetically stirring to obtain slurry, uniformly coating the slurry on the surface of copper foil, drying in vacuum, and slicing to obtain a battery piece with the diameter of 15mm, wherein the battery piece is taken as a positive electrode, a metal lithium piece is taken as a negative electrode, 1M LiPF6/EC, EMC, DMC (1:1:1in vol) + 2% VC electrolyte and a polypropylene microporous membrane are taken as a diaphragm, assembling a button half battery in a glove box, and testing the charge and discharge performance of the button half battery.
Through tests, the performance of the silicon-based composite electrode prepared in the embodiment is close to that of the silicon-based composite electrode obtained in the embodiment 1.
Example 4
1) Weighing 1g of graphite oxide powder, mixing with 80ml of N, N-dimethylformamide, ultrasonically dispersing for 1h, transferring to a 100ml reaction kettle, and carrying out hydrothermal reaction at 240 ℃ for 6 h. Cooling the mixed solution to room temperature, performing suction filtration by using a microporous filter membrane to obtain brown filtrate, performing rotary evaporation to remove a DMF solvent, dissolving in deionized water, dialyzing by using a 3000Da molecular weight dialysis bag, and finally freeze-drying the solution in the bag to obtain solid graphene quantum dots;
2) dispersing nano silicon into a mixed solution of 100mL of deionized water, 60mL of hydrogen peroxide and 20mL of ammonia water, heating in a water bath at 95 ℃ for reaction for 30min, performing centrifugal separation, and drying to obtain hydrophilic nano silicon powder;
3) sequentially dissolving 0.5g of hydrophilic nano-silicon and 0.6g of dopamine hydrochloride in 100ml of deionized water, vigorously stirring at room temperature for 2 hours, dropwise adding 25ml of ammonium persulfate into the mixed solution, continuously stirring for 5 hours after the addition is finished, performing centrifugal separation, washing with deionized water, and drying to obtain a polydopamine/nano-silicon compound;
4) dispersing 1g of 2000cP sodium alginate powder by using 50ml of deionized water, stirring to be homogeneous, adding 235mg of prepared graphene quantum dots, continuously dispersing, and stirring for one day to obtain the modified binder for later use.
5) Mixing and grinding 0.3g of the prepared polydopamine-coated silicon composite material and 37.5mg of acetylene black for half an hour, then dispersing the mixture in 1.5ml of the modified binder prepared in the step 4), magnetically stirring to obtain slurry, uniformly coating the slurry on the surface of copper foil, performing vacuum drying and slicing to obtain a battery piece with the diameter of 15mm, taking the battery piece as a positive electrode and a metal lithium piece as a negative electrode, adopting 1M LiPF6/EC, EMC, DMC (1:1:1in vol) + 2% VC electrolyte and a polypropylene microporous membrane as a diaphragm, assembling a button type half battery in a glove box, and testing the charge and discharge performance of the button type half battery.
Through tests, the performance of the silicon-based composite electrode prepared in the embodiment is close to that of the silicon-based composite electrode obtained in the embodiment 1.
Example 5
1) Weighing 2.4g of graphite oxide powder, mixing with 80ml of N, N-dimethylformamide, ultrasonically dispersing for 1h, transferring to a 100ml reaction kettle, and carrying out hydrothermal reaction at 280 ℃ for 6 h. Cooling the mixed solution to room temperature, performing suction filtration by using a microporous filter membrane to obtain brown filtrate, performing rotary evaporation to remove a DMF solvent, dissolving in deionized water, dialyzing by using a 3000Da molecular weight dialysis bag, and finally freeze-drying the solution in the bag to obtain solid graphene quantum dots;
2) dispersing nano silicon into a mixed solution of 100mL of deionized water, 30mL of hydrogen peroxide and 20mL of ammonia water, heating in a water bath at 95 ℃ for reaction for 30min, performing centrifugal separation, and drying to obtain hydrophilic nano silicon powder;
3) sequentially dissolving 0.5g of hydrophilic nano-silicon and 0.7g of dopamine hydrochloride in 100ml of deionized water, vigorously stirring at room temperature for 2 hours, dropwise adding 21ml of ammonium persulfate into the mixed solution, continuously stirring for 5 hours after the addition is finished, performing centrifugal separation, washing with deionized water, and drying to obtain a polydopamine/nano-silicon compound;
4) dispersing 1g of 2000cP sodium alginate powder by using 50ml of deionized water, stirring to be homogeneous, adding 235mg of prepared graphene quantum dots, continuously dispersing, and stirring for one day to obtain the modified binder for later use.
5) Mixing and grinding 0.3g of the prepared polydopamine-coated silicon composite material and 37.5mg of acetylene black for half an hour, then dispersing the mixture in 1.594ml of the modified binder prepared in the step 4), magnetically stirring to obtain slurry, uniformly coating the slurry on the surface of copper foil, performing vacuum drying and slicing to obtain a battery piece with the diameter of 15mm, taking the battery piece as a positive electrode and a metal lithium piece as a negative electrode, adopting 1MLiPF6/EC, EMC, DMC (1:1:1in vol) + 2% VC electrolyte and a polypropylene microporous membrane as a diaphragm, assembling a button half battery in a glove box, and testing the charge and discharge performance of the button half battery.
Through tests, the performance of the silicon-based composite electrode prepared in the embodiment is close to that of the silicon-based composite electrode obtained in the embodiment 1.
The above description is only a preferred embodiment of the present invention, and should not be taken as limiting the invention in any way, and any person skilled in the art can make any simple modification, equivalent replacement, and improvement on the above embodiment without departing from the technical spirit of the present invention, and still fall within the protection scope of the technical solution of the present invention.

Claims (7)

1. A lithium ion battery composite electrode is characterized in that: the preparation method comprises the following steps of coating a layer of polydopamine with strong adhesion on the surface of a negative electrode material of an electrode, and modifying a binder by using graphene quantum dots, wherein the preparation method comprises the following steps:
1) preparing solid graphene quantum dots:
weighing graphite oxide GO powder, mixing with N, N-dimethylformamide to obtain a mixed suspension, ultrasonically dispersing uniformly, transferring to a reaction kettle, and carrying out hydrothermal reaction for a certain time; cooling the mixed solution to room temperature, performing suction filtration by using a microporous filter membrane to obtain brown filtrate, performing rotary evaporation to remove a DMF solvent, dissolving in deionized water, dialyzing by using a 3000Da molecular weight dialysis bag, and finally freeze-drying the solution in the bag to obtain solid graphene quantum dots;
2) preparing a graphene quantum dot modified binder:
dispersing binder powder by using deionized water, stirring to be homogeneous, adding the graphene quantum dots prepared in the step 1), continuously dispersing, and stirring for one day to obtain a modified binder for later use;
3) preparing hydrophilic nano silicon:
dispersing nano silicon in a mixed solution of hydrogen peroxide, ammonia water and deionized water, heating for reaction for a certain time, performing centrifugal separation, and drying to obtain hydrophilic nano silicon;
4) preparing a polydopamine/nano-silicon compound:
sequentially dissolving the hydrophilic nano-silicon prepared in the step 3) and dopamine hydrochloride in deionized water, vigorously stirring at room temperature, dropwise adding ammonium persulfate into the mixed solution, continuously stirring for a certain time after adding, centrifugally separating, washing with deionized water, and drying to obtain a polydopamine/nano-silicon compound;
5) preparing a composite electrode:
mixing and grinding the polydopamine/nano-silicon compound obtained in the step 4) and acetylene black for half an hour, then mixing and dispersing the mixture with a modified binder in deionized water, magnetically stirring to obtain slurry, and uniformly coating the slurry on the surface of copper foil to obtain the lithium ion battery negative plate.
2. The lithium ion battery composite electrode of claim 1, wherein: in the step 1), the concentration of a mixed suspension formed by graphite oxide GO powder and N, N-dimethylformamide is 5-50 mg/ml, and ultrasonic dispersion is carried out for 0.5-2 hours.
3. The lithium ion battery composite electrode of claim 1, wherein: in the step 1), the high-temperature pyrolysis temperature and time of the hydrothermal reaction are respectively 150-300 ℃ and 2-10 h.
4. The lithium ion battery composite electrode of claim 1, wherein: the adhesive in the step 2) is sodium alginate.
5. The lithium ion battery composite electrode of claim 1, wherein: the particle size of the nano silicon in the step 3) is 50-200 nm; the solvent used for the hydrophilic nano-silicon treatment is a mixed solution of hydrogen peroxide, ammonia water and deionized water; the volume ratio of the hydrogen peroxide to the ammonia water is 10: 1-1: 1, the volume ratio of the ammonia water to the water is 1:6, and the heating time is 0.5-1 h.
6. The lithium ion battery composite electrode of claim 1, wherein: mixing the hydrophilic nano-silicon and the dopamine hydrochloride in the step 4) according to the mass ratio of 1: 0.8-1: 1.6, stirring for 2 hours, adding the dopamine hydrochloride and the ammonium persulfate according to the mass-volume ratio of 1 g/(10-60) ml, fully stirring for 3-6 hours, and carrying out polymerization reaction on the dopamine under an initiator to uniformly coat on the surface of the nano-silicon.
7. The lithium ion battery composite electrode of claim 1, wherein: the mass ratio of the polydopamine/nano-silicon composite to the acetylene black to the graphene quantum dots to the binder is (75-80): 10, (1-2.5): 8-9.
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