A silicon-carbon anode material and its preparation method

Abstract

The present invention relates to the technical field of lithium-ion batteries, and discloses a silicon-carbon anode material and a preparation method thereof. The silicon-carbon anode material is obtained by coating modified carbon nanotubes and silicon materials; the modified carbon nanotubes refer to carbon nanotubes bonded with pyrene compounds; the pyrene compounds account for 3-30% of the total weight of the carbon nanotubes, and the modified carbon nanotubes account for 1-15% of the total weight of the silicon-carbon anode material. The silicon-carbon anode material obtained by the present invention is a silicon composite material coated with carbon nanotubes modified with pyrene compounds. It can enable the carbon nanotubes and silicon particles to be uniformly compounded, and a uniform conductive network structure can be constructed between the carbon nanotubes and the silicon particles, thereby forming a strong silicon-carbon interface interaction force, and further obtaining a negative electrode material with excellent cycling performance; in addition, the silicon-carbon anode material obtained by the present invention has the advantages of being simple, easy to operate, and low in energy consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and more specifically, to a silicon-carbon anode material and a preparation method thereof. Background Art

[0002] In recent years, with the rapid development of new energy vehicles and portable electronic products, higher energy density requirements have been put forward for lithium-ion batteries. Currently, the anode materials of commercial lithium-ion batteries are mainly graphitized carbon materials, which have good electrical conductivity, a good layered structure, are suitable for the insertion and extraction of lithium ions, and have a good voltage platform, with a charge-discharge efficiency of more than 90%. However, the biggest drawback of graphitized carbon anode materials is their low theoretical specific capacity (372 mAh / g), which cannot meet the growing demand for the energy density of lithium-ion batteries.

[0003] Compared with traditional commercial graphitized carbon anode materials, silicon anode materials are expected to replace carbon anode materials as the next-generation high-energy density lithium-ion battery anode materials due to their high theoretical specific capacity (4200 mAh / g, Li 22 Si5). At the same time, silicon used as an anode material in lithium-ion batteries also has advantages such as a low lithium insertion potential (0.4 V vs Li / Li+), abundant raw materials, and environmental friendliness. However, due to the huge volume change of silicon during the lithium deinsertion / insertion process, the electrochemical performance of silicon anodes rapidly decays, and the cycle life is short, which further restricts their practical applications.

[0004] In response to the poor electrical conductivity and volume expansion effect of silicon anode materials, many improvement methods, including nanostructured silicon and its dimensional design, and silicon composites and their structure design, have been reported. Carbon nanotubes have good flexibility and high electron conductivity, can form a developed conductive network on silicon particles, establish highly conductive and durable links, ensure the effective transmission of electrons between active particles, and at the same time buffer the volume expansion during the lithium deinsertion / insertion process of silicon, avoiding its pulverization and resulting in capacity decay.

[0005] Patents with publication numbers CN115663131A, CN113871587A, CN110400930A, and CN114361427A have all reported carbon nanotube-coated silicon anode materials. However, the methods of introducing carbon nanotubes are basically direct introduction or depositing carbon nanotubes on the surface of silicon particles by CVD method, which is difficult to ensure the uniformity of the composite of carbon nanotubes and silicon, which will affect the electron conductivity between active particles, and the weak binding force between the silicon-carbon surface makes the composite material fall off from the current collector during the lithium deinsertion / insertion process, resulting in a rapid decay of the specific capacity. Summary of the Invention

[0006] <Technical Problems to be Solved by the Invention>

[0007] To solve the problems existing in the prior art, namely, poor dispersion of carbon nanotubes in silicon particles and weak binding force.

[0008] <The technical solution adopted by the present invention>

[0009] In view of the above technical problems, the object of the present invention is to provide a silicon-carbon anode material and a preparation method thereof. The silicon-carbon anode material obtained by the present invention is a composite material in which carbon nanotubes modified with pyrene compounds coat silicon, which can make the carbon nanotubes and silicon particles uniformly composite, and a uniform conductive network structure can be constructed between the carbon nanotubes among the silicon particles, thereby forming a strong silicon-carbon interface interaction force, and further obtaining an anode material with excellent cycle performance; in addition, the silicon-carbon anode material obtained by the present invention has the advantages of being simple, easy to operate, and low energy consumption.

[0010] The specific content is as follows:

[0011] First, the present invention provides a silicon-carbon anode material, which is obtained by coating a modified carbon nanotube and a silicon material;

[0012] The modified carbon nanotube means that a pyrene compound is bonded to the carbon nanotube;

[0013] The pyrene compound accounts for 3-30% of the total weight of the carbon nanotubes, and the modified carbon nanotubes account for 1-15% of the total weight of the silicon-carbon anode material.

[0014] Second, the present invention provides a preparation method of the aforementioned silicon-carbon anode material, including the following steps:

[0015] The modified carbon nanotubes and the silicon material are blended in an organic solvent, and the silicon-carbon anode material is obtained through grinding, filtration, washing, and drying.

[0016] <The beneficial effects achieved by the present invention>

[0017] (1) In the present invention, the pyrene compound is modified on the surface of the carbon nanotubes to obtain modified carbon nanotubes; due to the strong interaction force between the pyrene compound and the carbon nanotubes through π-π stacking, a uniform conductive network structure is formed between the silicon particles; the carbon nanotubes obtained by the present invention establish highly conductive and durable links between the silicon particles.

[0018] (2) For the modified carbon nanotubes obtained by the present invention, the network structure intertwined between the silicon particles not only ensures the effective transmission between the active particles, but also the flexible carbon nanotubes can buffer the volume expansion of silicon during the lithium insertion and extraction process, avoiding its pulverization and resulting in capacity attenuation.

[0019] (3) The modified carbon nanotubes obtained in the present invention can increase the charge transfer rate, promote the formation of a SEI layer on the surface of the active material by the electrolyte at a relatively high potential, prevent further decomposition of the electrolyte, and reduce the irreversible consumption of lithium ions. Description of the Drawings

[0020] Figure 1 SEM image of the silicon-carbon negative electrode material prepared in Example 3;

[0021] Figure 2 SEM image of the carbon nanotube-coated silicon composite material prepared in Comparative Example 1;

[0022] Figure 3 Impedance comparison diagram of the composite materials prepared in Example 3 and Comparative Example 1;

[0023] Figure 4 Cycling performance diagram of the silicon-carbon negative electrode material prepared in Example 3 at a current density of 1 A / g. Detailed Embodiments

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0025] <Technical Solution>

[0026] First, the present invention provides a silicon-carbon negative electrode material, which is obtained by coating modified carbon nanotubes and silicon materials;

[0027] The modified carbon nanotubes refer to carbon nanotubes bonded with pyrene compounds;

[0028] The pyrene compounds account for 3-30% of the total weight of the carbon nanotubes, and the modified carbon nanotubes account for 1-15% of the total weight of the silicon-carbon negative electrode material.

[0029] Further, the carbon nanotubes are single-walled or multi-walled carbon nanotubes with a diameter ranging from 2 to 50 nm.

[0030] Further, the pyrene compounds include at least one of pyrene, 1-hydroxypyrene, 1,6-dihydroxypyrene, 1,3-diaminopyrene, pyrenebutanoic acid, 3-hydroxypyrene, and 1-nitropyrene.

[0031] Further, the particle size range of the silicon material is 10-500 nm.

[0032] Further, the preparation method of the modified carbon nanotubes includes the following steps:

[0033] After the carbon nanotubes are treated with acid, they are added to the dispersion of pyrene compounds, and the modified carbon nanotubes are obtained through blending, washing, and drying.

[0034] The acid-treated carbon nanotubes can interact with the functional groups on the surface of silicon particles, which is beneficial to the formation of a stable SEI layer and reduces the collapse and shedding during cycling.

[0035] Furthermore, the acid includes at least one of concentrated sulfuric acid, concentrated nitric acid, concentrated hydrochloric acid, and concentrated sulfuric acid.

[0036] Furthermore, the acid treatment temperature is 70 - 120 °C, and the time is 1 - 6 h. Preferably, the acid treatment temperature is 70 - 100 °C, and the time is 1 - 4 h.

[0037] Furthermore, the solvent in the pyrene compound dispersion includes at least one of water, methanol, ethanol, ethylene glycol, isopropyl alcohol, n-butanol, and ethyl acetate; and / or, the mass ratio of the solvent to the carbon nanotubes is 10 - 50:1.

[0038] Furthermore, the molar ratio of hydrogen ions in the acid to the carbon nanotubes is 5 - 20:1 - 6.

[0039] Furthermore, during the blending process, an ultrasonic treatment method can be adopted, the ultrasonic time is 0.5 - 2 h; the stirring time is 1 - 6 h.

[0040] Furthermore, vacuum drying can be selected for drying, the temperature is 60 - 150 °C, and the drying time is 6 - 24 h. Preferably, the temperature is 80 - 110 °C, and the time is 6 - 15 h.

[0041] Second, the present invention provides a preparation method of the silicon-carbon negative electrode material mentioned above, including the following steps:

[0042] The modified carbon nanotubes and silicon materials are blended in an organic solvent, and the silicon-carbon negative electrode material is obtained through grinding, filtering, washing, and drying.

[0043] Furthermore, the organic solvent includes at least one of ethanol, methanol, or ether.

[0044] Furthermore, one of ball milling, sand milling, or disk milling is selected for grinding; and / or one of vacuum drying, flash evaporation, spraying, freeze drying, or microwave drying is selected for drying.

[0045] Using the silicon-carbon negative electrode material prepared in this application, a button cell is prepared in sequence. The functional groups on the pyrene compound can interact with the binder sodium carboxymethyl cellulose, while reducing the amount of the binder (non-active component), enhancing the interaction force between the active material and the current collector, and improving the cycle life of the entire electrode.

[0046] <Example>

[0047] Example 1

[0048] Add 2 g of multi-walled carbon nanotubes with a diameter of 15 nm to a concentrated nitric acid solution containing 2 mol of hydrogen ions, stir and react at 80 °C for 2 h. Add the reacted carbon nanotubes to distilled water, then filter, wash, and dry at 80 °C to obtain acid-treated carbon nanotube A;

[0049] Dissolve 0.2 g of 1-hydroxypyrene in 90 ml of ethanol, add 1.8 g of carbon nanotube A, sonicate for 1 h, react under stirring for 3 h, then wash, filter, and vacuum dry at 90 °C for 12 h to obtain a carbon nanotube material B modified with a hydroxypyrene compound;

[0050] Mix 1.2 g of the modified carbon nanotube B with 6.8 g of silicon material with a size of 100 nm in ethanol, ball mill at a speed of 450 r / min for 4 h, then filter, wash, and dry to obtain a carbon-silicon composite material.

[0051] Example 2

[0052] Add 2 g of multi-walled carbon nanotube material with a diameter of 15 nm to a concentrated nitric acid solution containing 2 mol of hydrogen ions, stir and react at 80 °C for 2 h. Add the reacted carbon nanotubes to distilled water, then filter, wash, and dry at 80 °C to obtain acid-treated carbon nanotube A;

[0053] Dissolve 0.3 g of 1-hydroxypyrene in 60 ml of ethanol, add 1.2 g of carbon nanotube A, sonicate for 1 h, react under stirring for 3 h, then wash, filter, and vacuum dry at 90 °C for 12 h to obtain a carbon nanotube material B modified with a hydroxypyrene compound;

[0054] Mix 1 g of the modified carbon nanotube B with 19 g of silicon material with a size of 100 nm in ethanol, ball mill at a speed of 450 r / min for 4 h, then filter, wash, and dry to obtain a carbon-silicon composite material.

[0055] Example 3

[0056] Add 2 g of multi-walled carbon nanotube material with a diameter of 15 nm to a concentrated nitric acid solution containing 2 mol of hydrogen ions, stir and react at 80 °C for 2 h. Add the reacted carbon nanotubes to distilled water, then filter, wash, and dry at 80 °C to obtain acid-treated carbon nanotube A;

[0057] Dissolve 0.3 g of 1-hydroxypyrene in 35 ml of ethanol, add 0.7 g of carbon nanotube A, sonicate for 1 h, react under stirring for 3 h, then wash, filter, and dry in vacuum at 90 °C for 12 h to obtain carbon nanotube material B modified with hydroxypyrene compounds;

[0058] Mix 1 g of the modified carbon nanotube B with 9 g of silicon material with a size of 100 nm in ethanol, and ball mill at a speed of 450 r / min for 4 h, then filter, wash, and dry to obtain a carbon-silicon composite material.

[0059] Example 4

[0060] The difference between this example and Example 1 is that the acid is concentrated sulfuric acid.

[0061] Example 5

[0062] The difference between this example and Example 1 is that in carbon nanotube B, the parameters for vacuum drying are 110 °C and 8 h.

[0063] Example 6

[0064] The difference between this example and Example 1 is that 1-hydroxypyrene is replaced with 1-nitropyrene.

[0065] Example 7

[0066] The difference between this example and Example 1 is that 1-nitropyrene is replaced with 1,6-dinitropyrene.

[0067] <Comparative Example>

[0068] Add 2 g of multi-walled carbon nanotube material with a diameter of 15 nm to a concentrated nitric acid solution containing 2 mol of hydrogen ions, stir and react at 80 °C for 2 h, add the reacted carbon nanotubes to distilled water, then filter, wash, and dry at 80 °C to obtain acid-treated carbon nanotube A;

[0069] Mix 1 g of the modified carbon nanotube A with 9 g of silicon material with a size of 100 nm in ethanol, and ball mill at a speed of 450 r / min for 4 h, then filter, wash, and dry to obtain a carbon nanotube-coated silicon composite material.

[0070] <Test Example>

[0071] Use the composite materials prepared in Examples 1-3 and the comparative example as the anode materials of lithium-ion batteries to assemble button cells. The specific method is as follows:

[0072] The composite materials prepared in Examples 1-3 and the comparative example were used as the anode materials of the battery. They were homogenized with conductive carbon black and sodium carboxymethyl cellulose binder in a ratio of 8:1:1. The slurry was coated on copper foil with a scraper and then dried in a vacuum drying oven for 12 h. The copper foil loaded with the electrode material was cut into button cell electrode sheets (12 mm) using a punching machine; a lithium metal sheet was used as the counter electrode, and a button cell was assembled in a glove box. After the assembled battery was left stationary for 12 h, various electrochemical performances were tested.

[0073] SEM image

[0074] Figure 1 SEM image of the silicon-carbon anode material prepared in Example 3.

[0075] Figure 1 It shows that the carbon nanotubes modified with pyrene compounds form a uniformly intertwined conductive network between the silicon particles, promoting the effective transmission of electrons between the active particles and effectively buffering the volume expansion of silicon during charge and discharge.

[0076] Figure 2 SEM image of the carbon nanotube-coated silicon composite material prepared in the comparative example.

[0077] Figure 2 It shows that a large number of carbon nanotubes are wound together and cannot form an effective electron transport channel.

[0078] Impedance comparison chart

[0079] Figure 3 Impedance comparison chart of the composite materials prepared in Example 3 and Comparative Example 1.

[0080] Figure 3 Explanation: The electrochemical impedance value of the silicon material coated with carbon nanotubes modified with pyrene compounds is significantly smaller than that of the carbon nanotube-coated silicon composite material. The modification with pyrene compounds effectively enhances the charge transfer in the electrode.

[0081] Cycling performance chart

[0082] Figure 4 Cycling performance chart of the silicon-carbon composite material prepared in Example 3 at a current density of 1 A / g.

[0083] Figure 4 It shows that after cycling 300 times at a current density of 1 A / g, the composite anode material still has a reversible specific capacity of 1300 mAh / g, indicating that the prepared anode material has excellent cycling performance.

[0084] Measurement results of the first efficiency and specific capacity

[0085] The results are shown in Table 1.

[0086] Table 1 Electrochemical measurement results of each example

[0087]

[0088] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. Silicon-carbon negative electrode material, characterized in that, It is obtained by coating modified carbon nanotubes and silicon materials; Modified carbon nanotubes refer to carbon nanotubes bonded with pyrene compounds; The pyrene compounds account for 3-30% of the total weight of the carbon nanotubes, and the modified carbon nanotubes account for 1-15% of the total weight of the silicon-carbon anode material; The pyrene compounds include at least one of 1-hydroxypyrene, 1,6-dihydroxypyrene, and 3-hydroxypyrene; The preparation method of the modified carbon nanotubes includes the following steps: After the carbon nanotubes are treated with acid, they are added to the pyrene compound dispersion liquid, and the modified carbon nanotubes are obtained through blending, washing, and drying; The preparation method of the silicon-carbon anode material includes the following steps: The modified carbon nanotubes and the silicon material are blended in an organic solvent, and the silicon-carbon anode material is obtained through grinding, filtration, washing, and drying.

2. The silicon-carbon negative electrode material according to claim 1, characterized in that, The acid includes at least one of concentrated sulfuric acid, concentrated nitric acid, and concentrated hydrochloric acid.

3. The silicon-carbon negative electrode material according to claim 1, characterized in that, The acid treatment temperature is 70-120 °C, and the time is 1-6 h.

4. The silicon-carbon negative electrode material according to claim 1, characterized in that, The solvent in the pyrene compound dispersion liquid includes at least one of methanol, ethanol, ethylene glycol, isopropyl alcohol, n-butanol, and ethyl acetate.

5. The silicon-carbon negative electrode material according to any one of claims 1 to 4, characterized in that, The mass ratio of the solvent in the dispersion liquid to the carbon nanotubes is 10-50:

1.

6. The silicon-carbon negative electrode material according to any one of claims 1 to 4, characterized in that, The molar ratio of hydrogen ions in the acid to the carbon nanotubes is 5-20:1-6.

7. The silicon-carbon negative electrode material according to claim 1, characterized in that, The organic solvent includes at least one of ethanol, methanol, or diethyl ether; and / or the grinding selects one of ball milling, sand milling, and disk milling; and / or the drying selects one of vacuum drying, flash evaporation, spraying, freeze drying, and microwave drying.

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