CN116845225A - A kind of preparation method of nano silicon/graphene lithium ion battery negative electrode material - Google Patents

Abstract

A method for preparing nano-silicon/graphene lithium-ion battery negative electrode materials, belonging to the field of new energy materials and electrochemical technology. First, the silicon nanoparticles are treated with a mixed acid of HF/HNO3 to obtain the Si-H surface. Then, a variety of carbon-containing organic compounds containing double bonds or triple bonds are used to perform a hydrosilylation reaction on the surface-treated silicon nanoparticles. Finally, Graphene is directly mixed with silicon nanoparticles that have undergone hydrosilylation reaction and dried to obtain nano silicon/graphene negative electrode material. The above-mentioned preparation method of nano-silicon/graphene lithium-ion battery negative electrode material, on the one hand, uses silicon nanoparticles, which effectively suppresses the volume expansion problem of silicon. In addition, the silicon powder prepared by hydrosilylation is used for post-processing. The good monodispersity effectively avoids the occurrence of silicon agglomeration. Combined with the excellent conductivity of graphene, it effectively improves the rate performance and cycle performance of lithium-ion batteries.

Description

A kind of preparation method of nano silicon/graphene lithium ion battery negative electrode material

Technical field

The invention belongs to the technical field of new energy materials and electrochemistry, and is specifically a preparation method of nano silicon/graphene lithium ion battery negative electrode material.

Background technique

Compared with nickel-cadmium batteries, nickel-metal hydride batteries, etc., lithium-ion batteries are widely used in electric vehicles and portable electronic devices due to their advantages of high energy density, good cycle life, good safety, low self-discharge rate, no memory effect, and low pollution. It has been widely used in other aspects.

As the main storage body of lithium-ion batteries, the negative electrode material is accompanied by the insertion and extraction of lithium ions during the battery operation process. It is the key to improving battery parameters such as lithium-ion battery capacity and Coulombic efficiency, and improving cycle performance. Since Sony first commercialized lithium-ion batteries in 1991, graphite has been used as the anode material for commercial lithium-ion batteries. However, the theoretical specific capacity of graphite is only 372mAh/g, and its specific capacity is close to this theoretical value in actual commercial applications, which greatly limits the further improvement of lithium-ion battery capacity. Therefore, it is very urgent to develop and research negative electrode materials with high specific capacity.

During the process of electrochemical lithium storage, silicon and lithium can form Li12Si7, Li13Si4, Li7Si3, and Li22Si5 alloys. The theoretical specific capacity of Li22Si5 can reach as high as 4200mAh/g, which is 10 times that of graphite. In addition, the element that can alloy lithium storage (Sn , Pb, Al, Au, Pt, Zn, Cd, Ag, Mg) is the highest. In addition, silicon has a low lithium insertion potential (~0.4V vsLi/Li+). From the perspective of safety performance, the voltage platform of silicon is slightly higher than that of graphite, and surface lithium precipitation will not occur during charging. Moreover, silicon has a wide range of sources and is non-toxic and harmless. Therefore, silicon has become a research hotspot as anode material for lithium-ion batteries.

However, due to the volume expansion (up to 300%) of silicon during the charging and discharging process of lithium ions, the material pulverizes and the structure collapses, causing the electrical contact between the active material and the current collector to deteriorate, ultimately reducing the capacity of the battery. and cycle performance degrades rapidly.

To address these problems, measures such as nanometerizing silicon materials, compounding silicon materials with other materials, and combining nanometerization with compounding are currently commonly used. To nanosize silicon materials, we use synthetic nanoparticles, nanowires, nanotubes, nanofilms and other materials to reduce the volume expansion and contraction of silicon during the lithium insertion/delithiation process and reduce the negative impact on battery performance. It is reported in the literature that when the size of silicon particles is less than 10nm, the volume expansion phenomenon of silicon will disappear. The use of silicon nanoparticles below 10nm as battery negative electrode materials has aroused strong interest among researchers.

Composite silicon materials with other materials are synthesized by synthesizing silicon-compound composites, silicon-metal composites, and silicon-carbon composites. These studies can alleviate volume expansion, effectively improve the cycle performance of silicon-based anode materials, and improve Battery specific capacity, reduced irreversible capacity.

Combining the above two methods is currently the most widely used method. Among many matrix materials, carbon materials are sought after due to their advantages such as good electrical conductivity and small volume expansion. Compared with pure silicon materials, silicon-carbon composite materials as negative electrodes for lithium-ion batteries significantly improve battery performance. Among many carbon materials, graphene is widely used in lithium-ion batteries due to its good conductivity, large specific surface area, flexibility, chemical stability, etc. Compared with other carbon-based materials, such as graphite, carbon black, and carbon nanotubes, graphene can provide good dispersion for silicon nanoparticles, ensure the conductivity of the entire electrode structure, and help achieve high battery rates. Therefore, nano-silicon/graphene composite materials are expected to become the development direction of negative electrode materials for lithium-ion batteries.

The improvement of electrical conductivity of nano-silicon/graphene composite materials is mainly achieved through the following methods:

1. Conductive bridging: Adding graphene between nano-silicon particles and between nano-silicon particles and battery current collectors can form conductive bridging, allowing electrons to be transmitted between particles faster. This can effectively improve the electrical conductivity of composite materials.

2. Improve the conductivity of the electrode: The high conductivity of graphene can improve the overall conductivity of the electrode, thereby reducing the resistance of the electrode and increasing the power density and energy density of the electrode.

3. Increase the surface area of the electrode: The single-layer structure and high specific surface area of graphene can increase the surface area of the electrode, thereby increasing the contact area between the electrode and the electrolyte and promoting the transmission of ions.

At present, nano-silicon/graphene composite materials, as lithium-ion battery anode materials, still have shortcomings such as low specific capacity and unstable cycle performance, which affects the development of nano-silicon/graphene composite materials and lithium-ion battery anode materials and needs further improvement. These shortcomings are mainly due to the following reasons:

1. Inherent defects of nano-silicon: As a negative electrode material, current mainstream synthesis methods of nano-silicon are often unable to synthesize small-sized (such as 10nm or smaller), highly dispersible silicon particles, which are not enough to suppress the volume during the charge and discharge process. Changes, so nano-silicon will undergo aggregation, peeling and other phenomena, resulting in the breakage and falling-off of nano-silicon particles. These defects can lead to capacity fading and unstable cycling performance of the composites.

2. Process methods and parameters: The performance of nano-silicon/graphene composite materials depends largely on the selection of preparation process methods and parameters. For example, factors such as the mass ratio of graphene and nano-silicon, solvent selection during the preparation process, preparation temperature and time will all affect the performance of composite materials. Different preparation methods and parameters may lead to different defects and limitations, such as aggregation, uneven dispersion, surface oxidation, etc.

Therefore, in order to improve the cycle performance of nano-silicon/graphene composites, it is necessary to optimize the selection of process methods and parameters, and explore new preparation methods and material combinations. At the same time, it is also necessary to further study the essential mechanism of the inherent defects of nano-silicon in order to better solve these problems.

Contents of the invention

In view of the above-mentioned problems existing in the prior art, the purpose of the present invention is to design and provide a technical solution for a preparation method of nano-silicon/graphene lithium-ion battery negative electrode material, which produces a negative electrode material with high specific capacity and stable cycle performance.

The described method for preparing a nano-silicon/graphene lithium-ion battery negative electrode material is characterized by: first using a mixed acid of HF/HNO3 to treat the silicon nanoparticles to obtain a Si-H surface, and then using a variety of materials containing double The surface-treated silicon nanoparticles are hydrosilylated with carbon-containing organic matter that has a bond or a triple bond. Finally, the graphene is directly mixed with the silicon nanoparticles that have undergone the hydrosilylation reaction and dried to obtain a nano-silicon/graphene negative electrode material.

The preparation method of nano silicon/graphene lithium ion battery negative electrode material is characterized in that the method specifically includes the following steps:

1) Generation of Si-H surface of silicon nanoparticles: Dissolve 10-100mg silicon nanoparticles in 1-100ml alcohol solution, ultrasonic for 30-60 minutes, add HF/HNO3 mixed acid to the resulting solution for etching, during the etching process , the particle size decreases. After reacting for 5-10 minutes, add 10-100mL of alcohol solution to the solution, collect it by filtration with PVDF membrane, dry it under vacuum, and quickly move it to the glove box;

2) Use carbon-containing organic matter containing double bonds or triple bonds to perform a hydrosilylation reaction on the surface-treated silicon nanoparticles: In the glove box, disperse the silicon nanoparticles treated in step 1) in a layer containing double bonds or triple bonds. In a mixed solution of carbonaceous organic matter and organic solvent, the reaction solution is heated to 150-300°C until the reaction solution becomes clear;

3) Production of nano-silicon/graphene negative electrode material: Add graphene to the clear solution obtained in step 2), and evaporate the solution to dryness to obtain nano-silicon/graphene lithium-ion battery negative electrode material.

The preparation method of nano silicon/graphene lithium ion battery negative electrode material is characterized in that in step 1): the mass fraction of HF in the HF/HNO3 mixed acid is 45-50%, and the mass fraction of HNO3 is 65-72%, the mass fraction of HF is preferably 48%, and the mass fraction of HNO3 is preferably 68%; the volume ratio of HF to HNO3 is 5-30:1, the volume ratio is preferably 10-25:1, and the volume ratio is more Preferably it is 15-20:1.

The preparation method of a nano silicon/graphene lithium ion battery negative electrode material is characterized in that in step 1): the alcohol solution is methanol, ethanol or propanol; the pore size of the PVDF membrane is 0.2- 0.3μm, and the pore diameter is preferably 0.25-0.27μm.

The described preparation method of nano silicon/graphene lithium ion battery negative electrode material is characterized in that in step 1): the weight and volume ratio of silicon nanoparticles: alcohol solution is 20-80 mg: 10-90 ml, preferably 30-70 mg : 20-80ml; more preferably 40-60mg: 30-60ml; ultrasonic time 40-50min, after reaction for 5-10min, add 20-80mL alcohol solution to the solution, preferably 40-60mL alcohol solution.

The preparation method of a nano silicon/graphene lithium ion battery negative electrode material is characterized in that in step 2): the carbon-containing organic matter containing double bonds or triple bonds is dodecene/alkyne, octadecene/ Alkyne, styrene/alkyne or fullerene, the organic solvent is toluene, chloroform or trimethylbenzene.

The preparation method of a nano silicon/graphene lithium ion battery negative electrode material is characterized in that in step 2): the carbon-containing organic matter containing double bonds or triple bonds: the volume ratio of the mixed solution of the organic solvent is 1: 10-20, the preferred volume ratio is 1:13-16; perform bubbling treatment 1.1-1.3 hours in advance.

The preparation method of nano silicon/graphene lithium ion battery negative electrode material is characterized in that in step 2): the heating temperature of the reaction solution is 180-270°C, preferably 200-250°C.

As mentioned above, silicon nanosilicon with small size and high dispersion performance is the key to composite anode materials with high specific volume and stable cycle performance. There is a lot of evidence in the academic community pointing to the good performance of nanometer-scale, highly dispersed silicon particles. However, silicon nanoparticles usually agglomerate during processing, and their excellent conductivity cannot be fully exerted after composited with graphene. performance, resulting in limited improvements in rate and cycle performance. Therefore, it is necessary to further hydrosilylation the silicon nanoparticles to obtain highly dispersible silicon nanoparticles. Graphene can further be evenly dispersed in the matrix to exert its excellent conductivity. performance. Because it is very difficult to prepare small-sized, highly dispersed silicon nanoparticles, there are very few sources of such materials in the industry. For a long time, scientific researchers have basically not carried out work in this area due to the difficulty in material preparation.

The above-mentioned preparation method of nano-silicon/graphene lithium-ion battery negative electrode material, on the one hand, uses silicon nanoparticles, which effectively suppresses the volume expansion problem of silicon. In addition, the silicon powder prepared by hydrosilylation is used for post-processing. The good monodispersity effectively avoids the occurrence of silicon agglomeration. Combined with the excellent conductivity of graphene, it effectively improves the rate performance and cycle performance of lithium-ion batteries.

Detailed ways

The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The embodiments described below are illustrative and are intended to explain the present invention and are not to be construed as limiting the present invention.

Example 1

1) Dissolve 40 mg of silicon nanoparticles in 10 mL of methanol solution and sonicate for 30 minutes. 11 mL of HF/HNO3 mixed acid (volume ratio 10:1) was added to the resulting solution for etching. During the etching process, the particle size decreased. After 5 min of reaction, 10 mL of methanol solution was added to the reaction solution. The silicon nanoparticles obtained by the reaction were collected on the PVDF membrane, washed three times with 200 mL methanol/deionized water (volume ratio 1:3), dried in a vacuum drying box for 12 hours, and then quickly transferred to the glove box.

2) In the glove box, disperse the silicon nanoparticles treated in step 1) in a mixed solution of dodecene and trimethylbenzene (volume ratio is 1:10), and heat the reaction solution to 165°C until the reaction The solution becomes clear.

3) Add 10 mg of graphene to the clear solution obtained in step 2), and evaporate the solution to dryness to obtain nano silicon/graphene lithium ion battery negative electrode material.

Example 2

1) Dissolve 50 mg of silicon nanoparticles in 10 mL of methanol solution and sonicate for 30 minutes. 11 mL of HF/HNO3 mixed acid (volume ratio 15:1) was added to the resulting solution. During the etching process, the particle size decreased. After 8 min of reaction, 30 mL of methanol solution was added to the reaction solution. The silicon nanoparticles obtained by the reaction were collected on the PVDF membrane, washed three times with 200 mL methanol/deionized water (volume ratio 1:3), dried in a vacuum drying box for 15 hours, and then quickly transferred to the glove box.

2) In the glove box, disperse the silicon nanoparticles treated in step 1) in a mixed solution of dodecene and toluene (volume ratio is 1:15), heat the reaction solution to 185°C, and use a heating jacket to Heating was performed until the reaction solution became clear.

3) Add 30 mg of graphene to the clear solution obtained in step 2), and evaporate the solution to dryness to obtain nano silicon/graphene lithium ion battery negative electrode material.

Example 3

1) Dissolve 50 mg of silicon nanoparticles in 10 mL of methanol solution and sonicate for 30 minutes. 11 mL of HF/HNO3 mixed acid (volume ratio 20:1) was added to the resulting solution. During the etching process, the particle size decreased. After 10 min of reaction, 50 mL of methanol solution was added to the reaction solution. The silicon nanoparticles obtained by the reaction were collected on the PVDF membrane, washed three times with 200 mL methanol/deionized water (volume ratio 1:3), dried in a vacuum drying box for 12 hours, and then quickly transferred to the glove box.

2) In the glove box, disperse the silicon nanoparticles treated in step 1) in a mixed solution of styrene and chloroform (volume ratio 1:10~20), heat the reaction solution to 175°C, and use a heating jacket to It is heated until the reaction solution becomes clear.

3) Add 20 mg of graphene to the clear solution obtained in step 2), and evaporate the solution to dryness to obtain nano silicon/graphene lithium ion battery negative electrode material.

The beneficial effects of the present invention are further demonstrated below through corresponding experimental data.

In Example 1, a composite material of silicon nanoparticles and graphene was synthesized and used as anode material for lithium ion batteries. Compared with traditional graphite anodes, this composite material performs better in terms of rate performance and cycle performance. This composite material is able to achieve a capacity of up to 1178 mA h/g, while traditional graphite anodes can only achieve a capacity of 312 mA h/g. After 100 cycles, the capacity of the composite material still remains at 990 mA h/g, with a capacity retention rate of 84%, while the graphite anode is 267 mA h/g, with a capacity retention rate of 85%. This shows that silicon nanoparticles and graphene composites have excellent cycle performance compared to traditional graphite anodes. In addition, the composite material can still achieve a capacity of up to 850 mAh/g at high rate (2C), and the capacity remains at 765 mAh/g at high rate (10C). After 100 cycles, the capacity retention rate is still 81%, indicating that the silicon nanoparticles and graphene composite have excellent rate performance. The beneficial effects described in the present invention can also be achieved by performing the same experiment as Example 2 and Example 3.

In Embodiment 2, the composite material of silicon nanoparticles and graphene is used as the negative electrode material of the lithium ion battery, which can effectively suppress the volume expansion of silicon during the intercalation/extraction process of lithium ions. The volume expansion of the composite was only 8.5%, compared with 143% for the micron-sized silicon anode. After 100 cycles, the capacity retention rate of the micron-sized silicon anode was only 50%, which shows that silicon nanoparticles and graphene composites can effectively suppress the volume expansion of silicon and provide better cycle stability. The same experiment as in Example 1 and Example 3 can also achieve the beneficial effects described in the present invention.

In Example 3, the solvent dispersion performance of the composite material was tested. Dissolve 100 mg of the composite material of silicon nanoparticles and graphene in 100 ml of toluene solvent. After ultrasonic oscillation for two minutes, the solution becomes clear. The solution mixture can pass through PVDF filter paper with a pore size of 0.2 micron under pressurized conditions and remains a clear solution. . For comparison, 100 mg of a mixture of micron-sized silicon particles and graphene was dissolved in 100 ml of toluene solvent. After ultrasonic vibration for two minutes, the solution became turbid. The solution mixture could not pass through the PVDF filter paper with a pore size of 0.2 micron under pressurized conditions. A chaotic solution. This experiment shows that the composite material has good solution dispersion properties for silicon particles. The same experiment as in Example 1 and Example 2 can also achieve the beneficial effects described in the present invention.

The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person familiar with the technical field can, within the technical scope disclosed in the present invention, according to the technical solution of the present invention and its Equivalent substitutions or changes of the inventive concept shall be included in the protection scope of the present invention.

Claims (8)

1. A preparation method of a nano silicon/graphene lithium ion battery anode material is characterized by comprising the following steps: firstly, treating silicon nano particles by using mixed acid of HF/HNO3 to obtain Si-H surfaces, then, carrying out hydrosilylation reaction on the silicon nano particles subjected to surface treatment by using various carbon-containing organic matters containing double bonds or triple bonds, and finally, directly mixing graphene with the silicon nano particles subjected to hydrosilylation reaction, and drying to obtain the nano silicon/graphene anode material.

2. The preparation method of the nano silicon/graphene lithium ion battery anode material as claimed in claim 1, which is characterized by comprising the following steps:

1) Production of Si-H surface of silicon nanoparticles: dissolving 10-100mg of silicon nano particles in 1-100mL of alcohol solution, carrying out ultrasonic treatment for 30-60min, adding HF/HNO3 mixed acid into the obtained solution for etching, reducing the particle size in the etching process, reacting for 5-10min, adding 10-100mL of alcohol solution into the solution, filtering and collecting a PVDF film, and rapidly moving into a glove box after vacuum drying;

2) Hydrosilylation of surface treated silicon nanoparticles with carbon containing organics containing double or triple bonds: dispersing the nano silicon particles treated in the step 1) in a mixed solution of a carbon-containing organic matter containing double bonds or triple bonds and an organic solvent in a glove box, and heating the reaction solution to 150-300 ℃ until the reaction solution becomes clear;

3) Production of nano silicon/graphene anode material: and 2) adding graphene into the clear solution obtained in the step 2), and evaporating the solution to dryness to obtain the nano silicon/graphene lithium ion battery anode material.

3. The method for preparing the nano silicon/graphene lithium ion battery anode material as claimed in claim 2, wherein in step 1): the mass fraction of HF in the HF/HNO3 mixed acid is 45-50%, the mass fraction of HNO3 is 65-72%, the mass fraction of HF is preferably 48%, and the mass fraction of HNO3 is preferably 68%; the volume ratio of HF to HNO3 is 5-30: 1, preferably 10-25: 1, more preferably 15-20:1.

4. the method for preparing the nano silicon/graphene lithium ion battery anode material as claimed in claim 2, wherein in step 1): the alcohol solution is methanol, ethanol or propanol; the aperture of the PVDF membrane is 0.2-0.3 μm, and the aperture is preferably 0.25-0.27 μm.

5. The method for preparing the nano silicon/graphene lithium ion battery anode material as claimed in claim 2, wherein in step 1): the weight volume ratio of the silicon nano-particles to the alcohol solution is 20-80mg:10-90ml, preferably 30-70mg:20-80ml; more preferably 40-60mg:30-60ml; after the ultrasonic treatment is carried out for 40-50min and the reaction is carried out for 5-10min, 20-80mL of alcohol solution, preferably 40-60mL of alcohol solution, is added into the solution.

6. The method for preparing the nano silicon/graphene lithium ion battery anode material as claimed in claim 2, wherein in the step 2): the carbon-containing organic matter containing double bond or triple bond is dodecene/alkyne, octadecene/alkyne, styrene/alkyne or fullerene, and the organic solvent is toluene, chloroform or trimethylbenzene.

7. The method for preparing the nano silicon/graphene lithium ion battery anode material as claimed in claim 2, wherein in the step 2): the carbon-containing organic matter containing double bond or triple bond: the volume ratio of the mixed solution of the organic solvents is 1:10-20, and the preferred volume ratio is 1:13-16; bubbling treatment is carried out 1.1-1.3h in advance.

8. The method for preparing the nano silicon/graphene lithium ion battery anode material as claimed in claim 2, wherein in the step 2): the reaction solution is heated to a temperature of 180 to 270 ℃, preferably 200 to 250 ℃.