A preparation method of a carbon-coated porous silicon negative electrode material for a lithium ion battery

Abstract

The application belongs to the technical field of new energy materials, and particularly relates to a preparation method of carbon-coated porous silicon negative electrode material for lithium ion batteries. The preparation method is characterized in that: firstly, magnesium silicide is subjected to hydrothermal reaction at high temperature, and then the product is subjected to acid pickling to remove magnesium salt and impurities, so as to obtain a light yellow powder. Then, a phenolic resin polymer is in-situ grown in an alkaline aqueous solution, and then a compact carbon shell is formed through high-temperature pyrolysis, and is uniformly coated on the porous silicon microparticles. Thus, the volume change of silicon in the cycle process can be effectively alleviated, and the cycle stability and the electrical conductivity of the composite material are improved. Meanwhile, the porous structure provides a large number of active sites for lithium ions, and helps to improve the electrochemical stability. The prepared carbon-coated porous silicon is applied to lithium ion batteries as a negative electrode material, and has a significant progress in improving the specific capacity, cycle performance and rate performance of the lithium ion batteries, and has the advantages of simple and environment-friendly process and low cost.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials technology, specifically relating to a method for preparing carbon-coated porous silicon anode materials for lithium-ion batteries. Background Technology

[0002] In recent years, with the rapid development of electric vehicles and consumer electronics, power batteries have also seen rapid growth, and lithium-ion batteries have been rapidly applied in various fields. They have attracted widespread attention and research due to their advantages such as high operating voltage, large specific capacity, long cycle life, no memory effect, low self-discharge rate, environmental friendliness, and safety. However, with the needs of development, lithium-ion batteries are trending towards higher energy density and higher safety. Currently, the most widely used lithium-ion battery anode material is commercial graphite, with a theoretical capacity of only 372 mAh / g, which cannot meet the market's ever-increasing energy density requirements. Therefore, researching lithium-ion batteries with higher energy density has become a hot topic.

[0003] Studies have found that silicon has a theoretical capacity as high as 4200 mAh / g, making it an ideal anode active material for lithium-ion batteries. However, silicon is prone to significant changes during charge and discharge, with an expansion rate as high as 300%, which easily leads to material pulverization, severely damaging the material structure. This causes the electrode active material to detach from the current collector, resulting in loss of electrical contact and a significant reduction in battery cycle life. Furthermore, due to the formation of lithium silicate, while the initial irreversible capacity is high, the repeated growth and breakage of the SEI film caused by material pulverization limits its application as an anode material for lithium-ion batteries.

[0004] To address the inherent limitations of existing silicon-based anodes in lithium-ion batteries, such as poor conductivity, researchers have discovered that coating silicon with carbon materials reduces volume change while improving the conductivity of the composite material. Alternatively, doping the voids in the silicon structure with metal particles can significantly enhance the conductivity of silicon-based materials. Furthermore, in-situ grown polymers can be uniformly dispersed on the surface of the material structure, forming a dense composite structure. The resulting composite material, after carbonization, effectively enhances the structural stability and conductivity of the material. More importantly, compared to pure silicon anodes, battery cycle performance and rate performance are greatly improved. Therefore, researching and optimizing the performance of silicon anode materials is of significant value and importance.

[0005] Chinese patent CN201911319091.4 discloses a silicon-carbon anode material for lithium-ion batteries. The method involves mixing a silicon source and an organic solvent to form a slurry, then spraying the solution into the slurry using a spray gun, adding a carbon source, and finally filtering and drying to obtain the target product. This method is complex, requires high equipment costs, is difficult to industrialize, and generates toxic industrial wastewater, polluting the environment. Importantly, the product exhibits poor cycle stability and rate performance.

[0006] Currently, the preparation of silicon-carbon anode materials can be broadly categorized into chemical synthesis, vapor deposition, and self-assembly methods. Each method has its own advantages and disadvantages. This invention employs a previously undisclosed chemical synthesis method. In a water and ethanol solution, a series of chemical reactions occur on the surface of silicon nanoparticles using carbon precursors, generating carbon-containing resins and other polymers, resulting in a silicon nanoparticle-polymer composite. The advantages of this method are its simplicity, environmental friendliness, and high microstructural stability. Summary of the Invention

[0007] The technical problem solved by this invention is to provide a method for preparing a carbon-coated porous silicon anode material for lithium-ion batteries. The technical solution adopted is as follows:

[0008] A method for preparing a carbon-coated porous silicon anode material for lithium-ion batteries includes the following steps:

[0009] Step 1: Using magnesium silicide as the silicon source, magnesium silicide and water are mixed in a certain proportion in a high-temperature reactor and hydrothermal reaction is carried out in an inert atmosphere.

[0010] Step 2: The mixture of silicon and magnesium salts prepared by the hydrothermal reaction in Step 1 is acid-washed with hydrofluoric acid, hydrochloric acid and deionized water, and then filtered to obtain pure silicon.

[0011] Step 3: The pure silicon prepared in Step 2 is coated with hexadecyltrimethylammonium bromide (CTAB) and phenolic resin generated by condensation reaction as carbon sources. Ethanol and deionized water are added to a container. CTAB is used as a reactive agent and template agent. Ammonia water is added and stirred. After stirring, formaldehyde and resorcinol are added to the mixed solution and stirred at a constant temperature. Finally, the mixture is washed with water, filtered, and dried to obtain the phenolic-silicon composite material.

[0012] Step four: The phenolic-silicon composite material prepared in step three is pyrolyzed and carbonized at high temperature. The sample is then transferred to a high-temperature tube furnace and heated in an inert atmosphere to obtain the carbon-coated porous silicon anode material.

[0013] Preferably, in step one, the molar ratio of deionized water to magnesium silicide is 1–50:1; the hydrothermal reaction temperature in the reactor is 100–1000℃, the heating rate is 0.1–10℃ / min, and the holding time is 1–10h.

[0014] As a further preferred embodiment, the hydrothermal reaction temperature in the reactor is 700°C.

[0015] Preferably, in step two, the particle size of the pure silicon prepared is 0.05–50 μm.

[0016] Preferably, in step two, the ratio of hydrofluoric acid to deionized water is 1:10-50, the ratio of hydrochloric acid to deionized water is 1:10-50, the pickling time is 1-10 hours, and the number of pickling cycles is 3-5.

[0017] Preferably, in step three, ammonia is added and stirred for 1-5 hours; formaldehyde and m-diphenol are added and stirred at a constant temperature of 20-100°C for 1-10 hours.

[0018] Preferably, in step three, the water is washed with deionized water 3 to 5 times.

[0019] Preferably, in step four, during the heating reaction, the heating rate is 0.1–10 °C / min to 100–1000 °C, and the temperature is maintained for 0.1–10 h.

[0020] The carbon-coated porous silicon anode material is a composite material made by uniformly coating a porous silicon surface with an outer layer of phenolic resin after high-temperature carbonization. The phenolic resin is generated by the condensation reaction of formaldehyde and resorcinol in an aqueous solution at a certain temperature. Preferably, in step four, the particle size of the carbon-coated porous silicon anode material is 50–500 nm.

[0021] Preferably, the inert atmosphere of the present invention is at least one of helium, nitrogen, argon, and carbon dioxide.

[0022] The carbon-coated porous silicon nanocomposite material prepared using the above method can be used to prepare the negative electrode material for lithium-ion batteries. The electrolyte for this lithium-ion battery is any one of the following: LiPF6 dissolved in ethylene carbonate (EC) + dimethyl carbonate (DMC), LiPF6 dissolved in ethylene carbonate (EC) + diethyl carbonate (DEC), or LiPF6 dissolved in ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC). The LiPF6 concentration in the lithium-ion battery electrolyte required for assembling coin cells is 0.5–1.5 mol / L.

[0023] Compared with the prior art, the advantages of the present invention are:

[0024] This invention provides a novel method for preparing carbon-coated porous silicon. First, magnesium silicide undergoes a hydrothermal reaction at high temperature. The product is then acid-washed to remove magnesium salts and impurities, yielding a pale yellow powder. A phenolic resin polymer is then grown in situ in an alkaline aqueous solution, followed by high-temperature pyrolysis to form a dense carbon shell, which is then uniformly coated onto porous silicon microparticles. This effectively mitigates the volume change of silicon during cycling, improving cycle stability and the conductivity of the composite material. Simultaneously, the porous structure provides numerous active sites for lithium ions, contributing to enhanced electrochemical stability.

[0025] The carbon-coated porous silicon prepared by the method of this invention is used as a negative electrode material in lithium-ion batteries, which has made significant progress in improving the specific capacity, cycle performance and rate performance of lithium-ion batteries. More importantly, it proposes a new method for preparing porous silicon, which is simple, environmentally friendly and low in cost. Attached Figure Description

[0026] Figure 1 This is a SEM image of the carbon-coated silicon anode material provided in Embodiment 1 of the present invention.

[0027] Figure 2 The first charge-discharge curve of the carbon-coated silicon anode material provided in Embodiment 1 of the present invention.

[0028] Figure 3 The cycling curve of the carbon-coated silicon anode material provided in Example 1 of the present invention at a current density of 0.5 A / g. Detailed Implementation

[0029] The accompanying drawings are for illustrative purposes only; certain common knowledge and prior art may be omitted for those skilled in the art; to better explain the present invention and facilitate understanding of its technical solutions, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The water used in this embodiment is deionized water.

[0030] Example 1

[0031] A method for preparing a carbon-coated porous silicon anode material for lithium-ion batteries, comprising the following steps:

[0032] Weigh 2g of magnesium silicide on an electronic balance and pour it into a clean reaction vessel. Then, take 3mL of water with a small dropper and add it to the reaction vessel.

[0033] Nitrogen gas is introduced into the above-mentioned reactor, and the residual air in the reactor is purged for a certain period of time.

[0034] After sealing the reactor, heat it to 700°C in a high-temperature furnace at a heating rate of 5°C / min and hold it at that temperature for 3 hours.

[0035] After the high-temperature reaction, the mixture was placed in a 500mL beaker, and an appropriate amount of deionized water, 10mL of hydrochloric acid, and 3mL of hydrofluoric acid were added. The mixture was stirred for 3 hours.

[0036] After acid washing, let it stand for 30 minutes to settle, pour out the supernatant solution, add an appropriate amount of deionized water, and wash for 20 minutes.

[0037] Continue washing with water until the water is clear, then filter and dry to obtain a pale yellow powder;

[0038] Take 0.5g of pale yellow powder and 0.3g of hexadecyltrimethylammonium bromide (CTAB), pour them into a 100mL beaker, add 50mL of deionized water, then add 2.5mL of ammonia water and 15mL of anhydrous ethanol in a fume hood, and stir for 2 hours;

[0039] After stirring, add 1.5 mL of formaldehyde and 0.5 g of m-diphenol to the fume hood and stir at a constant temperature of 30°C for 6 hours.

[0040] After stirring at a constant temperature, the mixture was allowed to stand and settle for 30 minutes. The upper white solution was then discarded. An appropriate amount of water was added, and the mixture was washed three times. The solid was then filtered and dried at 60°C for 12 hours.

[0041] The dried powder was collected and argon gas was introduced into a high-temperature tube furnace to raise the temperature to 800°C at a rate of 2°C / min, and then held at that temperature for 4 hours. Finally, carbon-coated porous silicon anode material was obtained, which was denoted as porous Si@C-1 anode material.

[0042] Example 2

[0043] Weigh 2g of magnesium silicide on an electronic balance and pour it into a clean reaction vessel. Then, use a small dropper to take 3mL of water and add it to the reaction vessel.

[0044] Nitrogen gas was introduced into the above-mentioned reactor, and the residual air in the reactor was purged for a certain period of time.

[0045] After sealing the reactor, heat it to 600°C in a high-temperature furnace at a heating rate of 5°C / min and hold it at that temperature for 3 hours.

[0046] Other aspects not mentioned are the same as in Example 1. The final carbon-coated porous silicon anode material is obtained, with a particle size of denoted as porous Si@C-2 anode material.

[0047] Example 3

[0048] Weigh 2g of magnesium silicide on an electronic balance and pour it into a clean reaction vessel. Then, use a small dropper to take 3mL of water and add it to the reaction vessel.

[0049] Nitrogen gas was introduced into the above-mentioned reactor, and the residual air in the reactor was purged for a certain period of time.

[0050] After sealing the reactor, heat it to 800°C in a high-temperature furnace at a rate of 5°C / min and hold it at that temperature for 3 hours.

[0051] Other aspects not mentioned are the same as in Example 1. The final product is a carbon-coated porous silicon anode material, denoted as porous Si@C-3 anode material.

[0052] Experimental data shows that when the reaction temperature in the reactor is 600℃, 700℃, and 800℃, the silicon yields are 86.1%, 94.4%, and 72.2%, respectively, proving that the silicon yield is highest at 700℃. Furthermore, comparing the performance of porous Si@C-1, Si@C-2, and porous Si@C-3 anode materials prepared at different reaction temperatures, it was found that at a reaction temperature of 700℃, porous Si@C-1 exhibits the highest initial discharge capacity of 2547 mAh / g and an initial coulombic efficiency of 85%, with a capacity decay rate of only 0.59% per cycle.

[0053] from Figure 1 Scanning electron microscope (SEM) images of carbon-coated silicon composite materials show that the particle size distribution of the carbon-coated silicon composite materials is 50-500 nm, and the different particle sizes are beneficial to improving the tap density of the material.

[0054] In the preparation of the negative electrode sheet, the negative electrode material is used as the active material, PAA is used as the binder, and conductive acetylene black is added in a ratio of active material:acetylene black:PAA = 7:2:1. An appropriate amount of deionized water is added to a mortar, and the mixture is ground and dispersed evenly to form a slurry. The slurry is then evenly coated onto copper foil and dried in an oven at 60℃ for 12 hours. After drying, it is rolled and sliced ​​to obtain a circular electrode sheet with a diameter of 12 mm. The average loading of this porous Si@C-1 composite negative electrode material is approximately 0.8-1.2 mg / cm³. -2 .

[0055] Transfer the prepared electrode sheets into an inert atmosphere glove box and prepare the coin cell assembly components: negative electrode shell, lithium metal sheet, separator, gasket, spring sheet, positive electrode shell, electrolyte, in addition to the pressing mold, pipette and insulated tweezers.

[0056] A coin cell was assembled using a lithium foil as the counter electrode, a polypropylene microporous membrane as the separator, and 1 mol / L LiPF6 dissolved in ethylene carbonate (EC) + dimethyl carbonate (DMC) (volume ratio 1:1) as the electrolyte. The assembly was performed in a glove box filled with argon atmosphere (O2 < 0.1 ppm, H2O < 0.1 ppm) and allowed to stand at room temperature for 24 hours after assembly. Charge-discharge cycle tests were then conducted on the coin cell: the charge-discharge cutoff voltage was 0.01-1.50 V. The first three cycles were performed at a rate of 0.1 Ag. -1 The battery was activated using a current density of 0.5 Ag. -1 Long-cycle testing was conducted on the current density. From Figure 2 The initial charge-discharge curve of the carbon-coated silicon composite material shows that its initial discharge capacity is 2547 mAh / g and its initial coulombic efficiency is 85%.

[0057] from Figure 3The cycling curves of the carbon-coated silicon composite material at a current density of 0.5 A / g show that the carbon-coated silicon composite material has excellent cycling performance.

[0058] The rate performance of the negative electrode material prepared in Example 1 was tested, and the results are shown in Table 1.

[0059] Table 1 compares the performance of porous Si@C-1 anode materials under different current densities.

[0060]

[0061] During testing, the current density was gradually increased from a small value (0.1 A / g to 2 A / g) and then decreased back to 0.1 A / g. The data in Table 1 show that the porous Si@C-1 anode material prepared in Example 1 can maintain good performance in terms of reversible discharge specific capacity, charge-discharge cycle capacity decay rate, and coulombic efficiency.

[0062] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for preparing a carbon-coated porous silicon anode material for lithium-ion batteries, characterized in that, Includes the following steps: Step 1: Using magnesium silicide as the silicon source, magnesium silicide and deionized water are mixed in a certain proportion in a high-temperature reactor and subjected to a hydrothermal reaction in an inert atmosphere; wherein, the molar ratio of deionized water to magnesium silicide is 1-50:1; the hydrothermal reaction temperature in the reactor is 600-1000℃, the heating rate is 0.1-10℃ / min, and the holding time is 1-10h. Step 2: The mixture of silicon and magnesium salts prepared by the hydrothermal reaction in Step 1 is acid-washed with hydrofluoric acid, hydrochloric acid and deionized water, and filtered to obtain pure silicon. The particle size of the pure silicon is 0.05-50 μm. The ratio of hydrofluoric acid to deionized water is 1:10-50, the ratio of hydrochloric acid to deionized water is 1:10-50, the acid washing time is 1-10 h, and the number of acid washings is 3-5. Step 3: The pure silicon prepared in Step 2 is coated with phenolic resin generated by condensation reaction as carbon source. Ethanol and deionized water are added to a container, and hexadecyltrimethylammonium bromide is added as a reactive agent and template agent. Ammonia water is added and stirred. After stirring, formaldehyde and resorcinol are added to the mixed solution and stirred at a constant temperature. Finally, the mixture is washed with water, filtered, and dried to obtain phenolic-silicon composite material. Ammonia water is added and stirred for 1-5 hours. Formaldehyde and resorcinol are added and stirred at a constant temperature of 20-100°C for 1-10 hours. Step four involves high-temperature pyrolysis carbonization of the phenolic-silicon composite material prepared in step three, transferring the sample to a high-temperature tube furnace, and heating the reaction in an inert atmosphere to obtain the carbon-coated porous silicon anode material. During the heating reaction, the heating rate is 0.1–10 °C / min, the temperature is raised to 800–1000 °C, and held for 0.1–10 h to obtain a carbon-coated porous silicon anode material with a particle size of 50–500 nm.

2. The method for preparing a carbon-coated porous silicon anode material for lithium-ion batteries according to claim 1, characterized in that, The hydrothermal reaction temperature in the reactor is 700℃.

3. The method for preparing a carbon-coated porous silicon anode material for lithium-ion batteries according to claim 1, characterized in that, In step three, the water is washed with deionized water 3 to 5 times.

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