A three-dimensional porous silicon@carbon nanosphere structural material using lithium nitrate as a template and a lithium supplement and a preparation method thereof, a lithium ion battery negative electrode and a battery
By preparing three-dimensional porous silicon@carbon nanosphere structures and using lithium nitrate as a template and lithium replenishing agent, the problems of volume expansion and poor stability of silicon anode materials in lithium-ion batteries were solved, thereby improving battery performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ANHUI NORMAL UNIV
- Filing Date
- 2024-08-30
- Publication Date
- 2026-07-07
Smart Images
Figure CN119133388B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the technical field of silicon anode materials for lithium-ion batteries, specifically relating to a three-dimensional porous silicon@carbon nanosphere structure material with lithium nitrate as a template and lithium replenishing agent, its preparation method, lithium-ion battery anode, and battery. Background Technology
[0002] Due to the depletion of fossil fuels and the aggravation of environmental pollution, rechargeable lithium-ion batteries have attracted widespread attention for their long cycle life and high energy density, and can be used in various applications such as portable electronics, electric vehicles and renewable energy storage. Silicon has a low lithium absorption potential and a high theoretical capacity, making it a very promising anode material for next-generation lithium-ion batteries.
[0003] However, silicon, as an anode material, typically undergoes significant volume changes during Li alloying and dealloying, leading to severe fragmentation of the active material. The continuous formation of an unstable solid-electrolyte interface causes rapid capacity decay of the silicon anode during cycling, limiting its practical application.
[0004] A patent published on July 27, 2018, with publication number CN 108336311 A, discloses a method for preparing a silicon-carbon anode material doped with silver particles. The method involves preparing a silicon slurry, preparing a dopamine-coated silicon-carbon material, preparing a precursor powder, and heat treatment to complete the preparation of the silver-doped silicon-carbon anode material. This method uses dopamine as the carbon source for coating the silicon-carbon material. The pH of the solution is adjusted using tris(hydroxymethyl)aminomethane, allowing dopamine to self-polymerize into polydopamine in an alkaline solution, which then coats the surface of the silicon-carbon material. The coating effect is uniform, and the thickness of the carbon coating layer can be precisely controlled by adjusting the amount of dopamine used to achieve the best coating effect. The carbon coating layer can effectively alleviate the volume expansion of nano-silicon. Utilizing the reducing properties of dopamine, metallic silver particles are doped outside the coating layer to improve the material's conductivity and reduce electrode polarization, resulting in good cycle performance and rate performance. However, according to its embodiments, the initial charge capacity is low, and the initial efficiency and cycle performance are poor. Summary of the Invention
[0005] The purpose of this invention is to provide a three-dimensional porous silicon@carbon nanosphere structure material with lithium nitrate as a template and lithium supplement, and its preparation method. SiO2 microspheres are prepared using inexpensive raw materials, porous Si is obtained through a magnesothermic reduction method, and then, through a template method, calcination, washing, and drying, a three-dimensional Si@C nanosphere structure material with lithium nitrate as a template and lithium supplement is obtained. This invention addresses the technical challenges of silicon-based materials as electrode materials, such as easy volume expansion and poor cycle stability, by providing a low-cost, high-yield, and novel method for preparing nanomaterials.
[0006] Another objective of this invention is to provide a lithium-ion battery anode, which is prepared using the above-mentioned three-dimensional porous silicon@carbon nanosphere structure material.
[0007] The final objective of this invention is to provide a lithium-ion battery prepared using the aforementioned lithium-ion battery negative electrode. This addresses the technical challenges of electrode materials exhibiting easy volume expansion and poor cycle stability.
[0008] The specific technical solution of this invention is as follows:
[0009] A method for preparing a three-dimensional porous silicon@carbon nanosphere structured material using lithium nitrate as a template and lithium supplementer, specifically comprising:
[0010] 1) Under magnetic stirring, porous Si nanospheres and tris(hydroxymethyl)aminomethane were dispersed in water, and the pH was adjusted with hydrochloric acid solution. Dopamine hydrochloride was added, and finally lithium nitrate was added to react.
[0011] 2) The product from step 1) was calcined in a protective atmosphere, washed and dried to obtain a three-dimensional porous Si@C nanosphere structure material.
[0012] In step 1), the ratio of porous Si nanospheres to water is 0.001–0.004 g / mL, preferably 0.002 g / mL; the ratio of tris(hydroxymethyl)aminomethane to water is 0.15–0.25 mol / L, the pH is adjusted to 8–9 with hydrochloric acid solution, the ratio of dopamine hydrochloride to water is 0.005–0.007 mol / L, and the lithium nitrate to water ratio is 0.05–0.07 mol / L, using a template method. Considering battery performance, the lithium nitrate to water ratio is 0.05–0.07 mol / L; preferably: the ratio of tris(hydroxymethyl)aminomethane to water is 0.2 mol / L, the pH is adjusted to 8.5, the ratio of dopamine hydrochloride to water is 0.006 mol / L, and the ratio of lithium nitrate to water is 0.06 mol / L.
[0013] In step 1), the reaction refers to a reaction time of 20-30 hours, preferably 24 hours, and a reaction temperature of room temperature.
[0014] The preparation method of porous Si nanospheres in step 1) is as follows:
[0015] 1-1) Mix ethanol, deionized water and ammonia, stir, add tetraethyl silicate dropwise, continue stirring, let stand, centrifuge and wash the product, dry it to obtain SiO2;
[0016] 1-2) After mixing and grinding SiO2, Mg powder and NaCl, calcination is performed. After calcination, the mixture is soaked in HCl solution, washed alternately with HCl solution and deionized water, and then dried to obtain porous Si microspheres.
[0017] Further, in step 1-1), the volume ratio of ethanol, ammonia, tetraethyl silicate, and deionized water is 9:1.5:1:3 to 130:3.5:3:21; preferably, the volume ratio of ethanol, ammonia, tetraethyl silicate, and deionized water is 30:1.5:1:6; and the mass concentration of the ammonia is 25%.
[0018] In step 1-1), the stirring time is 30 min-60 min, the stirring time is 0.5-2 h, and the settling time is 5-10 h, preferably 1 h of stirring followed by 10 h of settling; all are carried out at room temperature.
[0019] The size of the SiO2 particles prepared in step 1-1) is 200–800 nm; preferably 200–500 nm.
[0020] In steps 1-2), the mass ratio of SiO2, Mg powder and NaCl is 1:1:10 to 1:1.2:30, and the preferred mass ratio is 1:1:20.
[0021] In steps 1-2), the calcination conditions are as follows: calcination is carried out in a hydrogen-argon mixed gas atmosphere at 600-750°C for 4-8 hours; preferably, the calcination conditions are 650°C for 6 hours; in the hydrogen-argon mixed gas, the hydrogen gas fraction is 5% and the argon gas fraction is 95%.
[0022] In steps 1-2), after calcination, the sample is soaked in HCl solution, and finally washed alternately with HCl solution and deionized water. The sample is then dried in an oven to obtain porous Si microspheres. The concentration of HCl solution is 3-5 M, and the soaking time is 3-10 h, preferably 3 M and 5 h.
[0023] The protective atmosphere mentioned in step 2) refers to a nitrogen atmosphere;
[0024] The calcination described in step 2) involves raising the temperature to 550±30℃ at a rate of 2℃ / min and calcining for 2±0.2h to obtain a three-dimensional porous Si@C nanosphere structure material.
[0025] The washing and drying described in step 2) refers to washing with water three times and then drying in a 60℃ oven for 12 hours.
[0026] In the preparation method of this invention, the silicon microspheres themselves are three-dimensional structures. After magnesium thermoelectric reduction: first, Mg vapor reacts with SiO2 to generate Si crystals and MgO solid, then they are soaked in hydrochloric acid and etched with HCl to remove MgO, finally forming a porous Si structure. Subsequently, lithium nitrate is added, and lithium nitrate is used as a template. The lithium nitrate template is easily soluble in water and washed away, forming pores on the surface of the carbon layer, thus forming a unique three-dimensional porous structure.
[0027] This invention synthesizes SiO2 microspheres using ethanol, deionized water, tetraethyl silicate, and ammonia. The SiO2 is then thermally reduced with magnesium powder to obtain porous Si, which is subsequently calcined in a tube furnace to transform it into a Si@C composite material with a three-dimensional porous structure. This porous structure not only increases the specific surface area but also effectively mitigates the volume expansion of silicon particles. Furthermore, the introduction of lithium nitrate allows a small amount of lithium ions to be adsorbed on the surface of the nanomaterial, acting as a lithium replenishment agent, thereby further improving the electrochemical performance of the battery.
[0028] The present invention provides a three-dimensional porous silicon@carbon nanosphere structure material with lithium nitrate as template and lithium supplementation agent. It is prepared by the above method, with a size of 200-500 nm, a porous Si core and a carbon layer as outer shell, and pores distributed in the core and outer shell. Lithium nitrate is used as template for pore formation.
[0029] This invention provides a lithium-ion battery anode, prepared using the aforementioned three-dimensional porous silicon@carbon nanosphere structure material as the active material. The specific preparation method is as follows:
[0030] A three-dimensional porous silicon@carbon nanosphere structure material is mixed with a conductive agent and a binder, then ground to obtain a slurry. This slurry is then stretched and coated onto a copper foil and dried to obtain a three-dimensional porous composite material, which is used as the negative electrode of a lithium-ion battery to produce a lithium-ion battery.
[0031] The mass ratio of the three-dimensional porous silicon@carbon nanosphere structure material to the conductive agent and binder is 7:2:1;
[0032] The conductive agent is conductive carbon black; the binder is polyvinylidene fluoride.
[0033] The film stretching process is carried out on copper foil, and the drying conditions are 60–80°C for 20–24 hours.
[0034] The film is stretched and coated on copper foil, dried at 60-80℃ for 20-24 hours, and cut into small discs to obtain a three-dimensional porous Si@C composite material, which can be used as a negative electrode for lithium-ion batteries.
[0035] This invention provides a lithium-ion battery, prepared using the aforementioned lithium-ion battery negative electrode. The specific method for assembling the battery is as follows:
[0036] A lithium-ion battery was assembled in a glove box using a lithium sheet as the counter electrode and a solvent consisting of ethylene carbonate (EC) and diethyl carbonate (DEC) in a 1:1 volume ratio, with LiPF6 as the solute.
[0037] The method for preparing a three-dimensional porous Si@C nanosphere structure material provided by this invention involves synthesizing SiO2 microspheres using ethanol, deionized water, and ammonia. The SiO2 microspheres are then thermally reduced with magnesium powder at 600–750°C to obtain porous Si. Finally, the Si@C composite material is calcined at 550±30°C, washed, and dried to obtain a three-dimensional porous Si@C composite material. Lithium nitrate is used as a template; its dissolution in water further forms a porous structure on the carbon layer surface. This allows the composite material to provide more active sites during charge and discharge. The porous structure effectively alleviates the volume expansion problem, and the residual lithium ions after cleaning act as a lithium replenishing agent, contributing to better battery stability during charge and discharge.
[0038] This invention synthesizes SiO2 microspheres by mixing low-cost ethanol, deionized water, tetraethyl silicate, and ammonia, significantly reducing experimental costs. The obtained SiO2 microspheres are then subjected to magnesium thermothermal reduction to porous silicon in the presence of magnesium powder and NaCl. NaCl is used as a heat sink to prevent the silicon nanoparticles from melting and agglomerating due to high temperatures, while maintaining the integrity of the porous structure. The porous silicon nanoparticles are coated with a thin carbon shell, forming a three-dimensional, omnidirectional conductive network with the internal porous structure, providing a rapid diffusion electron transport channel and thus promoting electrode reaction kinetics. Simultaneously, the external carbon shell protects the silicon nanoparticles, buffers the internal voids of the material, and alleviates Li-induced degradation. + The significant volume changes of materials during insertion / extraction ensure the integrity of the electrode structure and can greatly improve the cycle life of the battery.
[0039] During the charging and discharging process of Si@C batteries, severe silicon volume expansion and repeated damage and reconstruction of the SEI film lead to rapid capacity decay. Nanostructuring the composite material and rationally designing its spatial structure can effectively increase its specific surface area and active sites. Simultaneously, the addition of lithium nitrate can relatively reduce lithium ion loss from the active material, thereby mitigating battery capacity decay. In this invention, porous silicon particles are synthesized, a carbon layer is grown on their surface, and lithium nitrate is added externally. Lithium nitrate acts as both a reaction template and a supplement of lithium ions during the reaction process, effectively improving battery capacity and cycle life.
[0040] Compared with existing technologies, this invention has the following advantages: the Si@C nanomaterials prepared by the magnesothermic reduction method and the template method can well maintain the three-dimensional porous spherical structure, providing a large specific surface area and more active sites, and the porous structure can effectively suppress the volume expansion of silicon; the prepared Si@C nanocomposite materials are chemically stable, not easily oxidized in air, and easy to store; Li +Significant differences in silicon volume before and after insertion / extraction lead to a rapid decrease in capacity, while the carbon matrix shortens the electron / ion pathway and alleviates the strain caused by volume changes; lithium nitrate, as a template and lithium replenisher, can effectively improve the electrochemical performance of the battery. Attached Figure Description
[0041] Figure 1 SEM image of the SiO2 nanospheres prepared in Example 1;
[0042] Figure 2 SEM image of the porous Si microspheres prepared in Example 1;
[0043] Figure 3 TEM image of the porous Si microspheres prepared in Example 1;
[0044] Figure 4 SEM image of the three-dimensional porous Si@C nanospheres prepared in Example 1;
[0045] Figure 5 TEM image of the three-dimensional porous Si@C nanospheres prepared in Example 1;
[0046] Figure 6 XRD pattern of the three-dimensional porous Si@C nanospheres prepared in Example 1;
[0047] Figure 7 SEM image of the SiO2 nanospheres prepared in Example 2;
[0048] Figure 8 SEM image of the three-dimensional porous Si@C nanospheres prepared in Example 2;
[0049] Figure 9 SEM image of the three-dimensional porous Si@C nanospheres prepared in Example 3;
[0050] Figure 10 TEM image of the porous Si microspheres prepared in Example 4;
[0051] Figure 11 SEM image of the three-dimensional porous Si@C nanospheres prepared in Example 4;
[0052] Figure 12 SEM image of the three-dimensional porous Si@C nanospheres prepared in Example 5;
[0053] Figure 13 SEM image of the three-dimensional porous Si@C nanospheres prepared in Example 7;
[0054] Figure 14 TEM image of the three-dimensional porous Si@C nanospheres prepared in Example 8;
[0055] Figure 15 TEM image of the three-dimensional porous Si@C nanospheres prepared in Example 9;
[0056] Figure 16 TEM image of the three-dimensional porous Si@C-0.6 nanospheres prepared in Example 10;
[0057] Figure 17 The three-dimensional porous Si@C nanomaterial prepared in Example 1 was used as a negative electrode in a lithium-ion battery at 0.1 Ag. -1 Charge-discharge curves at current density;
[0058] Figure 18 The three-dimensional porous Si@C nanomaterial prepared in Example 1 was used as a negative electrode in a lithium-ion battery at 0.1 Ag. -1 Cyclic performance at current density;
[0059] Figure 19 The three-dimensional porous Si@C nanomaterial prepared in Example 1 was used as a negative electrode in a lithium-ion battery at 0.5 Ag. -1 Charge-discharge curves at current density;
[0060] Figure 20 The three-dimensional porous Si@C nanomaterial prepared in Example 1 was used as a negative electrode in a lithium-ion battery at 0.5 Ag. -1 Cyclic performance at current density;
[0061] Figure 21 The three-dimensional porous Si@C nanomaterial prepared in Example 1 was used as a negative electrode for lithium-ion batteries in the range of 0.1–0.5 A g. -1 Rate performance at current density;
[0062] Figure 22 The three-dimensional porous Si@C nanomaterial prepared in Example 2 was used as a negative electrode in a lithium-ion battery at 0.1 Ag. -1 Cyclic performance at current density;
[0063] Figure 23 The three-dimensional porous Si@C nanomaterial prepared in Example 3 was used as a negative electrode in a lithium-ion battery at 0.1 Ag. -1 Cyclic performance at current density;
[0064] Figure 24 The three-dimensional porous Si@C nanomaterial prepared in Example 4 was used as a negative electrode in a lithium-ion battery at 0.1 Ag. -1 Cyclic performance at current density;
[0065] Figure 25The three-dimensional porous Si@C nanomaterial prepared in Example 5 was used as a negative electrode in a lithium-ion battery at 0.1 Ag. -1 Cyclic performance at current density;
[0066] Figure 26 The three-dimensional core-shell structured Si@C nanomaterials prepared in Example 6 were used as a negative electrode in a lithium-ion battery at 0.1 Ag. -1 Cyclic performance at current density;
[0067] Figure 27 In Example 7, Si particles purchased from Aladdin were used as the negative electrode for a lithium-ion battery at a concentration of 0.1 A g. -1 Cyclic performance at current density;
[0068] Figure 28 The three-dimensional core-shell structured Si@C / Li2CO3 nanomaterial prepared in Example 8 was used as a lithium-ion battery anode at 0.1 A g. -1 Cyclic performance at current density;
[0069] Figure 29 The three-dimensional core-shell structured Si@C / LiCl nanomaterial prepared in Example 9 was used as a lithium-ion battery anode at 0.1 A g. -1 Cyclic performance at current density;
[0070] Figure 30 The three-dimensional core-shell structured Si@C-0.6 nanomaterial prepared in Example 10 was used as a lithium-ion battery anode at 0.1 A g. -1 Cyclic performance at current density. Detailed Implementation
[0071] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0072] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.
[0073] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.
[0074] Example 1
[0075] A method for preparing a three-dimensional porous silicon@carbon nanosphere structured material using lithium nitrate as a template and lithium supplementer includes the following steps:
[0076] 1) Preparation of SiO2 microspheres
[0077] 40 mL of ethanol, 8 mL of deionized water, and 2 mL of 25% ammonia solution were mixed and magnetically stirred for 30 min. Then, 1.6 mL of tetraethyl orthosilicate was added dropwise, and stirring continued for 1 h. After standing for 10 h, the sample was collected, centrifuged, washed, and dried in a 60℃ oven. The SEM image is shown below. Figure 1 As shown in the figure, it can be seen that it is a micro-nanosphere with a size of 200-500 nm.
[0078] 2) Preparation of porous Si microspheres
[0079] The synthesized SiO2 microspheres were subjected to thermal reduction with magnesium powder, specifically 0.1 g SiO2, 0.1 g Mg powder, and 2.0 g NaCl. After mixing and grinding for 10 min, the mixture was placed in a hydrogen-argon mixed gas atmosphere (5% hydrogen, 95% argon) and calcined at 650 °C for 6 h at a heating rate of 5 °C / min. After calcination, the sample was soaked in 3 M HCl solution for 5 h, and then washed three times alternately with HCl solution and deionized water. The sample was then dried in a 60 °C oven to obtain porous Si microspheres. The SEM image is shown below. Figure 2 As shown, the TEM image is as follows Figure 3 As shown in the figure, it has a porous structure with a size of 200-500 nm.
[0080] 3) Preparation of porous Si@C
[0081] 0.1 g of the prepared porous silicon microspheres were dispersed in 50 mL of deionized water and sonicated for 10 min. Under magnetic stirring, 1.21 g of tris(hydroxymethyl)aminomethane was added to the solution. The pH was then adjusted to 8.5 with 12 mol / L hydrochloric acid solution, followed by the addition of 60 mg of dopamine hydrochloride and finally 0.2 g of lithium nitrate. The reaction was carried out at room temperature for 24 h. The composite material was collected and washed with deionized water and ethanol, then dried in a 60 °C oven. The dried nanomaterials were calcined at 550 °C for 2 h under a nitrogen atmosphere after a heating rate of 2 °C / min. Finally, the nanomaterials were washed three times with deionized water and dried in a 60 °C oven for 12 h to obtain porous Si@C. The SEM image is shown below. Figure 4 As shown in the image, it can be seen that it is a clustered spherical structure. TEM image as follows. Figure 5 As shown.
[0082] The XRD pattern of the Si@C composite material obtained in this embodiment is as follows: Figure 6 As shown, the obtained product is Si@C.
[0083] Example 2 (as a comparison)
[0084] A method for preparing a three-dimensional porous silicon@carbon nanosphere structured material using lithium nitrate as a template and lithium supplementer includes the following steps:
[0085] 1) Preparation of SiO2 microspheres
[0086] Mix 40 mL of ethanol, 8 mL of deionized water, and 2 mL of 25% ammonia solution. Stir magnetically for 30 min, then add 1.6 mL of tetraethyl orthosilicate dropwise and continue stirring for 2 h. Let stand for 15 h, collect the sample, centrifuge, wash, and dry in a 60℃ oven. The SEM image is shown below. Figure 7 As shown in the figure, it can be seen that it is a micro-nanosphere with a size of 400-800 nm.
[0087] 2) The preparation of porous Si is the same as in Example 1;
[0088] 3) The preparation of porous Si@C is the same as in Example 1.
[0089] Its SEM image is as follows Figure 8 As shown in the figure, it can be seen that they are uniformly sized nanospheres with a size of 400-800 nm.
[0090] Figure 7 It can be seen that during the synthesis of SiO2 microspheres in Example 2, as the reaction time increased, the size of the SiO2 growth also increased and the microspheres were uniformly and densely packed together.
[0091] Example 3 (as a comparison)
[0092] A method for preparing a three-dimensional porous silicon@carbon nanosphere structured material using lithium nitrate as a template and lithium supplementer includes the following steps:
[0093] 1) The preparation of the precursor is the same as in Example 1;
[0094] 2) Preparation of porous Si microspheres:
[0095] The synthesized SiO2 microspheres were subjected to thermal reduction with magnesium powder, specifically 0.1 g of SiO2, 0.08 g of Mg powder, and 2.0 g of NaCl. After mixing and grinding for 10 min, the mixture was placed in a hydrogen-argon mixed gas atmosphere and calcined at 600 °C for 8 h at a heating rate of 5 °C / min. After calcination, the sample was soaked in 3 M HCl solution for 5 h, and finally washed three times alternately with HCl solution and deionized water. The sample was then dried in a 60 °C oven to obtain porous Si microspheres.
[0096] 3) The preparation of porous Si@C is the same as in Example 1.
[0097] Its SEM image is as follows Figure 9 As shown in the figure, it can be seen that it has a uniform nanosphere structure.
[0098] During the magnesian reduction process, when the proportion of magnesium powder decreases, excess SiO2 cannot be completely reduced to Si particles. The final product, Si@C, will have a large amount of white powdery SiO2 on its surface, and MgO will also be generated. When treated with hydrochloric acid, the excess SiO2 will not react, resulting in porous Si and SiO2 as the final products. This leads to rapid battery performance degradation and poor cycle stability.
[0099] Example 4 (as a comparison)
[0100] A method for preparing a three-dimensional porous silicon@carbon nanosphere structured material using lithium nitrate as a template and lithium supplementer includes the following steps:
[0101] 1) The preparation of the precursor is the same as in Example 1;
[0102] 2) Preparation of porous Si microspheres:
[0103] The synthesized SiO2 microspheres were subjected to thermal reduction with magnesium powder. Specifically, 0.1 g of SiO2, 0.1 g of Mg powder, and 2.0 g of NaCl were mixed and ground for 10 min, then calcined in a hydrogen-argon mixed gas atmosphere at a heating rate of 5 °C / min to 650 °C for 6 h. After calcination, the sample was soaked in 1 M HCl solution for 5 h, and finally washed three times alternately with HCl solution and deionized water. The sample was then dried in a 60 °C oven to obtain porous Si microspheres. TEM images are shown below. Figure 10 As shown in the figure, it can be seen that it is a porous micro-nanosphere with a size of 200-500 nm. After reducing the concentration of HCl solution, the porous structure on the surface of the nanosphere is not obvious through TEM image, which makes it easier for volume expansion to occur during charging and discharging.
[0104] 3) The preparation of porous Si@C is the same as in Example 1.
[0105] Its SEM image is as follows Figure 11 As shown in the figure, it can be seen that it is a nanosphere structure with uniform size.
[0106] Example 5 (as a comparison)
[0107] A method for preparing a three-dimensional porous silicon@carbon nanosphere structured material using lithium nitrate as a template and lithium supplementer includes the following steps:
[0108] 1) The preparation of the precursor is the same as in Example 1;
[0109] 2) The preparation of porous Si microspheres is the same as in Example 1;
[0110] 3) Preparation of porous Si@C
[0111] 0.1 g of the porous silicon microspheres prepared in step 2) were dispersed in 50 mL of deionized water and sonicated for 10 min. Under magnetic stirring, 1.8 g of tris(hydroxymethyl)aminomethane was added to the solution. The pH was then adjusted to 8.5 with hydrochloric acid solution, followed by the addition of 90 mg of dopamine hydrochloride and finally 0.2 g of lithium nitrate. The reaction was carried out at room temperature for 24 h. The composite material was collected and washed with deionized water and ethanol, then dried in a 60 °C oven. The dried nanomaterials were calcined at 550 °C at a heating rate of 2 °C / min under a nitrogen atmosphere for 2 h. Finally, the nanomaterials were washed three times with deionized water and dried in a 60 °C oven for 12 h to obtain porous Si@C. The SEM image is shown below. Figure 12 As shown in the figure, it can be seen that it is a spherical structure with a thick carbon layer that is clustered together, with a size of 200-500 nm.
[0112] Example 6 (as a comparison)
[0113] A method for preparing porous Si@C includes the following steps:
[0114] 1) The preparation of the precursor is the same as in Example 1;
[0115] 2) The preparation of porous Si microspheres is the same as in Example 1;
[0116] 3) Preparation of porous Si@C
[0117] 0.1 g of the porous silica microspheres prepared in step 2) were dispersed in 50 mL of deionized water and sonicated for 10 min. Under magnetic stirring, 1.21 g of tris(hydroxymethyl)aminomethane was added to the solution. The pH was then adjusted to 8.5 with hydrochloric acid solution, and 60 mg of dopamine hydrochloride was added. The reaction was carried out at room temperature for 24 h. The composite material was collected and washed with deionized water and ethanol, and then dried in a 60 °C oven. The dried nanomaterials were calcined at 550 °C for 2 h under a nitrogen atmosphere at a heating rate of 2 °C / min to finally obtain porous Si@C.
[0118] Example 7 (as a comparison)
[0119] A method for preparing silicon@carbon using lithium nitrate as a template and lithium supplementer includes the following steps:
[0120] 0.1 g of Si microspheres purchased from Aladdin were dispersed in 50 mL of deionized water and sonicated for 10 min. Under magnetic stirring, 1.21 g of tris(hydroxymethyl)aminomethane was added to the solution. The pH was then adjusted to 8.5 with hydrochloric acid solution, followed by the addition of 60 mg of dopamine hydrochloride, and finally 0.2 g of lithium nitrate. The reaction was allowed to proceed for 24 h. The composite material was collected and washed multiple times with deionized water and ethanol. The sample was then dried in a 60 °C oven. The dried nanomaterials were calcined at a temperature of 2 °C / min to 550 °C under a nitrogen atmosphere for 2 h, and finally washed with water and dried to obtain Si@C. The SEM image is shown below. Figure 13 As shown in the figure, it can be seen that it is a clustered spherical structure.
[0121] Example 8 (as a comparison)
[0122] A method for preparing three-dimensional porous silicon@carbon using lithium carbonate as a template and lithium supplementer includes the following steps:
[0123] 1) The preparation of the precursor is the same as in Example 1;
[0124] 2) The preparation of porous Si microspheres is the same as in Example 1;
[0125] 3) Preparation of porous Si@C / Li2CO3:
[0126] 0.1 g of the porous silica microspheres prepared in step 2) were dispersed in 50 mL of deionized water and sonicated for 10 min. Under magnetic stirring, 1.21 g of tris(hydroxymethyl)aminomethane was added to the solution. The pH was then adjusted to 8.5 with hydrochloric acid solution, followed by the addition of 60 mg of dopamine hydrochloride, and finally 0.2 g of lithium carbonate. The reaction was allowed to proceed for 24 h. The composite material was collected and washed multiple times with deionized water and ethanol. The sample was then dried in a 60 °C oven. The dried nanomaterials were calcined at 550 °C under a nitrogen atmosphere for 2 h at a heating rate of 2 °C / min. After washing with water and drying, porous Si@C / Li₂CO₃ was obtained. Its TEM image is shown below. Figure 14 As shown, the carbon layer on the surface of the silicon particles is not obvious.
[0127] Example 9 (as a comparison)
[0128] A method for preparing three-dimensional porous silicon@carbon using lithium chloride as a template and lithium supplementer includes the following steps:
[0129] 1) The preparation of the precursor is the same as in Example 1;
[0130] 2) The preparation of porous Si microspheres is the same as in Example 1;
[0131] 3) Preparation of porous Si@C / LiCl
[0132] 0.1 g of the porous silica microspheres prepared in step 2) were dispersed in 50 mL of deionized water and sonicated for 10 min. Under magnetic stirring, 1.21 g of tris(hydroxymethyl)aminomethane was added to the solution. The pH was then adjusted to 8.5 with hydrochloric acid solution, followed by the addition of 60 mg of dopamine hydrochloride, and finally 0.2 g of lithium chloride. The reaction was allowed to proceed for 24 h. The composite material was collected and washed multiple times with deionized water and ethanol. The sample was then dried in a 60 °C oven. The dried nanomaterials were calcined at 550 °C under a nitrogen atmosphere for 2 h at a heating rate of 2 °C / min. After washing with water and drying, porous Si@C / LiCl was obtained. Its TEM image is shown below. Figure 15 As shown, the surface carbon layer is not obvious.
[0133] Example 10 (as a comparison)
[0134] 1) The preparation of the precursor is the same as in Example 1;
[0135] 2) The preparation of porous Si microspheres is the same as in Example 1;
[0136] 3) Preparation of porous Si@C-0.6
[0137] 0.1 g of the porous silicon microspheres prepared in step 2) were dispersed in 50 mL of deionized water and sonicated for 10 min. Under magnetic stirring, 1.21 g of tris(hydroxymethyl)aminomethane was added to the solution. The pH was then adjusted to 8.5 with hydrochloric acid solution, followed by the addition of 60 mg of dopamine hydrochloride, and finally 2 g of lithium nitrate. The reaction was allowed to proceed for 24 h. The composite material was collected and washed multiple times with deionized water and ethanol. The sample was then dried in a 60 °C oven. After drying, it was calcined at 550 °C under a nitrogen atmosphere for 2 h at a heating rate of 2 °C / min. Finally, it was washed with water and dried to obtain porous Si@C-0.6. Its TEM image is shown below. Figure 16 As shown, the carbon layer on the surface of silicon particles is thinner after increasing the lithium nitrate concentration.
[0138] Example 11
[0139] A lithium-ion battery anode is prepared using a three-dimensional porous silicon@carbon nanosphere structure material with lithium nitrate as a template and lithium replenishing agent as the active material. The specific preparation method is as follows:
[0140] The three-dimensional porous Si@C composite material obtained in Example 1 was used as an active material and mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 7:2:1. After grinding, a slurry was obtained, which was then stretched and coated on copper foil. The mixture was dried at 80°C for 20 hours to obtain a three-dimensional porous composite material. The composite material was then cut into small discs to obtain a three-dimensional porous Si@C composite material, which was used as the negative electrode of a lithium-ion battery.
[0141] A lithium-ion battery was assembled in a glove box using lithium foil as the counter electrode and LiPF6 with a volume ratio of ethylene carbonate (EC) and diethyl carbonate (DEC) of 1:1 as the electrolyte.
[0142] The assembled lithium-ion batteries were tested for charge-discharge performance using a Newway battery tester. Cycle stability test results at different current densities are as follows: Figures 17-21 As shown, 0.1A g -1 After 100 cycles at the current density, the battery discharge specific capacity is 507 mAh g. -1 The average charge / discharge efficiency remains above 99%; 0.5A g -1 After 100 cycles at the current density, the battery discharge specific capacity is 105 mAh g. -1 The coulombic efficiency remains around 100%. This is true when the current density ranges from 0.1 to 0.5 Ag. -1 Back to 0.1A g -1 At that time, the battery's discharge specific capacity was still 673 mAh g. -1 This indicates that it has good reversibility.
[0143] The negative electrode was prepared using the same method with the raw materials prepared in Examples 2-10, and the battery performance was tested. Figures 22-30 The graphs show the cycle performance of lithium-ion batteries using the composite materials prepared in Examples 2 through 10 as the negative electrode. (0.1 A g) -1 At different current densities, the lithium-ion batteries assembled from the composite materials synthesized in different embodiments exhibited discharge specific capacities of 247, 138, 164, 321, 400, 122, 300, 170, and 160 mAh g, respectively, after 50 cycles. -1 The performance of the battery is far lower than that of the battery prepared in Example 1, and only by using lithium nitrate can the high battery performance of the present invention be achieved.
[0144] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.
Claims
1. A method for preparing a three-dimensional porous silicon@carbon nanosphere structure material using lithium nitrate as a template and lithium supplementer, characterized in that, The preparation method includes the following steps: 1) Under magnetic stirring, porous Si nanospheres and tris(hydroxymethyl)aminomethane were dispersed in water, and the pH was adjusted with hydrochloric acid solution. Dopamine hydrochloride was added, and finally lithium nitrate was added to react. 2) The product from step 1) was calcined in a protective atmosphere, washed and dried to obtain a three-dimensional porous Si@C nanosphere structure material; The prepared three-dimensional porous silicon@carbon nanosphere structure material has a size of 200-500 nm, with a porous Si core and a carbon layer as the outer shell, and the pore size is distributed in the core and the outer shell.
2. The preparation method according to claim 1, characterized in that, In step 1), the ratio of porous Si nanospheres to water is 0.001–0.004 g / mL; the ratio of tris(hydroxymethyl)aminomethane to water is 0.15–0.25 mol / L; the ratio of dopamine hydrochloride to water is 0.005–0.007 mol / L; and the pH of the hydrochloric acid solution is adjusted to 8–9.
3. The preparation method according to claim 1, characterized in that, In step 1), the ratio of lithium nitrate to water is 0.05 to 0.07 mol / L.
4. The preparation method according to claim 1, characterized in that, In step 1), the reaction refers to a reaction time of 20-30 hours.
5. The preparation method according to claim 1, characterized in that, The preparation method of porous Si nanospheres in step 1) is as follows: 1-1) Mix ethanol, deionized water and ammonia, stir, add tetraethyl silicate dropwise, continue stirring, let stand, centrifuge and wash the product, dry it to obtain SiO2; 1-2) After mixing and grinding SiO2, Mg powder and NaCl, calcination is performed. After calcination, the mixture is soaked in HCl solution, washed alternately with HCl solution and deionized water, and then dried to obtain porous Si microspheres.
6. The preparation method according to claim 5, characterized in that, In step 1-1), the volume ratio of ethanol, ammonia, tetraethyl silicate and deionized water is 9:1.5:1:3 to 130:3.5:3:
21.
7. The preparation method according to claim 5 or 6, characterized in that, In steps 1-2), the mass ratio of SiO2, Mg powder and NaCl is 1:1:10 to 1:1.2:
30.
8. A three-dimensional porous silicon@carbon nanosphere structure material prepared by the preparation method according to any one of claims 1-7, using lithium nitrate as a template and lithium supplementing agent.
9. A lithium-ion battery negative electrode, characterized in that, It is prepared using the three-dimensional porous silicon@carbon nanosphere structure material as described in claim 8 as the active material.
10. A lithium-ion battery, characterized in that, It is prepared using the lithium-ion battery anode described in claim 9.