A three-dimensional flower-shaped silicon@zinc selenide / cobalt selenide@carbon composite material, a preparation method thereof, a lithium ion battery silicon-based negative electrode and a battery

Abstract

The application provides a three-dimensional flower-shaped silicon@zinc selenide / cobalt selenide@carbon composite material and a preparation method thereof, a lithium ion battery silicon-based negative electrode and a battery. Compared with the prior art, the silicon particles are first prepared to grow in nanometer flower sheets, then the silicon particles are carbon-coated, and then the silicon particles are put into a tube furnace to be converted into the Si@ZnSe / CoSe@C composite material by using selenium powder. The flower-shaped structure can not only increase a large number of surface active sites but also effectively relieve the volume expansion of the silicon particles, so that the cycle stability of the battery is improved, and the battery obtains an extremely high specific capacity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of silicon negative electrode materials of lithium ion batteries, and particularly relates to a three-dimensional flower-like silicon@zinc selenide / cobalt selenide@carbon composite material, a preparation method thereof, a silicon-based negative electrode of a lithium ion battery, and a battery. BACKGROUND

[0002] In the high-speed developing contemporary society, due to the exhaustion of fossil fuels such as coal, oil, and natural gas, and the environmental problems caused by their combustion, clean energy such as solar energy, wind energy, water energy, nuclear energy, and new electric energy has been developed unprecedentedly. Lithium ion batteries have been widely concerned due to their long cycle life, high working voltage, high energy density, and green environmental protection. However, the traditional negative electrode material of lithium ion batteries, such as graphite, has a low theoretical capacity, which limits its development. Silicon has become one of the most promising negative electrode materials of lithium ion batteries due to its extremely high capacity. However, silicon is easy to powderize, has poor cycle stability, and has volume expansion, poor conductivity, and short cycle life during charging and discharging, which limits its commercial use.

[0003] A patent with publication number CN 105070894 A, published on November 18, 2015, discloses a porous silicon-based composite negative electrode material for lithium ion batteries, a preparation method, and an application. The negative electrode material has a capsule structure, the capsule core is amorphous porous silicon, and the capsule wall is conductive carbon material. The particle size of the amorphous porous silicon is 10-300 nm, the pore size of the amorphous porous silicon is 0.5-100 nm, and the thickness of the capsule wall is 0.5-10 μm. The preparation method of the porous silicon-based composite negative electrode material for lithium ion batteries provided by the patent is complex and is not suitable for industrial promotion. SUMMARY

[0004] The present application aims to provide a three-dimensional flower-like silicon@zinc selenide / cobalt selenide@carbon composite material and a preparation method thereof. Si@Zn(OH)2 / Co(OH)2 is prepared from low-cost raw materials, and then carbon is coated and calcined with selenium powder to obtain the composite material Si@ZnSe / CoSe@C. The product has a novel structure, high yield, and low cost. The preparation method is simple and suitable for industrial promotion.

[0005] The present application also aims to provide a silicon-based negative electrode of a lithium ion battery, which is prepared from the above-mentioned three-dimensional flower-like silicon@zinc selenide / cobalt selenide@carbon composite material. The cycle stability of the silicon-based material as an electrode material is improved, and technical problems such as easy volume expansion are solved.

[0006] The last purpose of the present application is to provide a battery, which is prepared from the above-mentioned silicon-based negative electrode of a lithium ion battery, and has high reversible capacity, high specific capacity, stable cycle performance, and robust rate performance.

[0007] The specific technical solutions of the present application are as follows:

[0008] A preparation method of a three-dimensional flower-shaped Si@ZnSe / CoSe@C composite material, comprising the following steps:

[0009] 1) dispersing a silicon material in a solvent to form a uniform solution, denoted as A solution; mixing a cobalt salt, a zinc salt and urea in water and stirring uniformly, denoted as B solution; mixing the A solution and the B solution uniformly, and then performing a water bath reaction to obtain a flower-shaped Si@Zn(OH)2 / Co(OH)2;

[0010] 2) dispersing the Si@Zn(OH)2 / Co(OH)2 obtained in step 1) in water, adding tris(hydroxymethyl)aminomethane, adjusting the pH to 8-9 with hydrochloric acid, and then adding dopamine hydrochloride and stirring to react;

[0011] 3) calcining the product of step 2) and selenium powder to obtain a three-dimensional flower-shaped Si@ZnSe / CoSe@C composite material.

[0012] In step 1), the silicon material is dispersed in a solvent, and the amount ratio of the silicon material to the solvent is 0.05-0.3 mol / L, preferably 0.1 mol / L;

[0013] In step 1), the silicon material is a silicon particle; the size of the silicon particle is 10-60 nm; preferably, the size is 30 nm;

[0014] In step 1), the solvent is anhydrous ethanol; silicon is very difficult to disperse, so the present application disperses the silicon uniformly in ethanol, which enables each silicon ball to grow in the petals uniformly; if the silicon is directly added, the silicon will not be dispersed uniformly, so the present application needs to first disperse the silicon material in a solvent to prepare the A solution.

[0015] In step 1), the mass ratio of the cobalt salt, the zinc salt and urea is 2.5:1.3:1.3-6.54:3.6:3.6;

[0016] In step 1), in the B solution, the concentration of the cobalt salt in deionized water is 0.8-1.5 mol·L -1 , preferably 1.1 mol·L -1 ;

[0017] In step 1), the cobalt salt is cobalt nitrate hexahydrate;

[0018] In step 1), the concentration of the zinc salt in deionized water is 0.3-0.8 mol·L -1 , preferably 0.56 mol·L -1 ;

[0019] In step 1), the zinc salt is zinc nitrate hexahydrate;

[0020] In step 1), the concentration of urea in deionized water is 2.0–4.0 mol·L⁻¹. -1 The preferred concentration is 2.8 mol·L⁻¹. -1 ;

[0021] In step 1), the volume ratio of the solvent to deionized water is 32:15;

[0022] In step 1), the water bath reaction conditions are 60-100°C for 30 minutes to 2 hours; preferably, 90°C for 1 hour.

[0023] In step 1), after the reaction is completed, the product is centrifuged, washed, and dried to obtain flower-shaped Si@Zn(OH)2 / Co(OH)2.

[0024] In step 2), the mass ratio of Si@Zn(OH)2 / Co(OH)2, tris(hydroxymethyl)aminomethane, and dopamine hydrochloride is 1:3:0.175 to 1:6:0.3; preferably 1:3:0.175; the pH is adjusted to 8 to 9 with hydrochloric acid, preferably 8.5.

[0025] In step 2), the ratio of Si@Zn(OH)2 / Co(OH)2 to deionized water is 0.003-0.005 g / mL; preferably 0.004 g / mL.

[0026] The stirring reaction described in step 2) is carried out at room temperature for 20-30 hours, preferably 24 hours.

[0027] In step 2), after the reaction is complete, the product is collected by centrifugation, washing, and drying.

[0028] Step 2) Prepare Si@Co(OH)2 / Zn(OH)2@PDA;

[0029] In step 3), the mass ratio of the product from step 2) to selenium powder is 1:3 to 1:8; preferably 1:5; the calcination conditions are 500 to 700°C for 1 to 4 hours, preferably 560°C for 2 hours; the calcination atmosphere is hydrogen-argon gas, which, as a reducing gas, is 5% hydrogen and 95% argon by volume.

[0030] This invention grows silicon particles within nanofloral structures, which are then coated with carbon and subsequently placed in a tube furnace to transform them into a Si@ZnSe / CoSe@C composite material using selenium powder. The flower-like structure not only increases the number of surface active sites but also effectively mitigates the volume expansion of silicon particles, thereby improving battery cycle stability. Because the previously synthesized Zn(OH)₂ / Co(OH)₂ has a flower-like structure, directly adding silicon particles during the synthesis process allows silicon microspheres to participate in the synthesis of nanomaterials, ensuring their proper growth within the nanofloral structures, ultimately forming a flower-like material containing silicon microspheres. The flower-like structure helps mitigate silicon volume expansion and possesses a large specific surface area, providing more reactive sites and enabling the battery to achieve extremely high specific capacity.

[0031] In this invention, silicon, due to its small volume and uniform distribution within the nanosheet-assembled flowers, along with its large specific surface area and high surface activity, allows silicon particles to grow within the flower's sheets. The flower-like structure is composed of sheets because the self-assembly process of the nanosheets into flower-like structures is relatively simple and easy to control. The process of nanosheet self-assembly into flower-like structures involves the interaction of physical and chemical forces, including van der Waals forces, hydrogen bonds, and electrostatic interactions. These forces enable the nanosheets to spontaneously aggregate, forming stable flower-like structures. Furthermore, the high surface energy of the nanosheets means they have a strong tendency to aggregate to reduce surface energy, which is also a driving force for the self-assembly of sheets into flowers. Because the product of this invention has a three-dimensional flower-like structure, it is a three-dimensional structure.

[0032] This invention provides a three-dimensional flower-like silicon@zinc selenide / cobalt selenide@carbon composite material, prepared using the above-described method. The morphology is as follows: the three-dimensional flower-like silicon@zinc selenide / cobalt selenide@carbon composite material has a size between 10-15 μm, with Si particles growing within ZnSe / CoSe petals, and the outermost layer being a carbon layer; the particle size of the Si particles is 30±5 nm, and the thickness of the nanosheets is 100±20 nm. The synthesized material has a flower-like structure composed of intersecting sheets. The interlaced 'petals' generate a large number of irregular and layered pores, with large openings and gradient channels within the particles, thus constituting a unique porous structure.

[0033] Silicon particles suffer from problems such as easy expansion, poor cycle stability, and weak conductivity, which severely limit their development potential. To solve this problem, the inventors discovered through extensive experimental research that Si can be embedded in porous materials to accommodate its volume expansion through the voids in the porous framework. In this method, three-dimensional porous nanostructures also achieve rapid ion transport by increasing the surface area in contact with the electrolyte. Therefore, this invention combines ZnSe / CoSe with silicon particles. ZnSe and CoSe are important members of transition metal selenides, possessing good conductivity and high theoretical capacity, and are considered excellent anode materials for lithium-ion batteries. Thus, bimetallic selenides have become the preferred material. Assembling and combining them with silicon gives the composite material excellent conductivity. It not only buffers the volume expansion of silicon but also, due to its high ductility, improves the dispersion of silicon, significantly increasing the cycle life of silicon.

[0034] While composite materials of selenium, cobalt, and zinc offer the aforementioned advantages, they also present several challenges. For example, significant volume expansion during charging and discharging can lead to electrode material breakage and fragmentation, loss of connection to the current collector, and rapid capacity decay. Additionally, silicon volume expansion is a concern. Therefore, this invention employs material porosity to maximize the specific surface area and minimize the loss of active material, thereby mitigating capacity decay. Furthermore, silicon is an extremely stable material, exhibiting no compositional change during high-temperature selenization. Based on these factors, the composite material synthesized in this invention possesses the advantage of porosity. In designing the experiments, this invention utilizes metal selenides with a flower-like structure, allowing silicon to grow within the petals. This not only maintains the advantage of a large specific surface area for nanomaterials but also mitigates the volume expansion of silicon particles.

[0035] The present invention provides a silicon-based negative electrode for lithium-ion batteries, which is prepared using the above-mentioned three-dimensional flower-shaped silicon@zinc selenide / cobalt selenide@carbon composite material.

[0036] This invention provides a lithium-ion battery prepared using the aforementioned silicon-based anode material. Specifically, a three-dimensional flower-shaped silicon@zinc selenide / cobalt selenide@carbon composite material is used as the active material. This material is mixed uniformly with conductive carbon black and PVDF at a mass ratio of 7:2:1. NMP is then added dropwise, and the mixture is magnetically stirred for 6-8 hours to uniformly disperse the NMP. The uniformly mixed slurry is then coated onto copper foil using a coater and placed in a vacuum drying oven at 60-80°C. After drying for 12-24 hours, the foil is pressed into sheets using a sheet press and then cut into small circular electrode sheets using a sheet cutter. The electrode sheets are then assembled into button batteries in a glove box filled with high-purity argon gas and where the water and oxygen levels are ≤0.01ppm. The electrolyte is a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 2:6:2, with LiPF6 as the solute. The lithium sheet has a purity of Li≥99.99% and a thickness of 0.5mm. After rolling, it is cut to the size of the electrode sheet.

[0037] After adding 1 drop of electrolyte to the positive electrode shell of the battery, place the electrode plate, then add 1 drop of electrolyte and place the separator. After adding 2 drops of electrolyte to the separator, place the lithium sheet as the counter electrode, then place two pieces of nickel foam, add 1 drop of electrolyte, cover with the negative electrode shell, press and seal the battery with a hydraulic press, and let it stand for 6 to 12 hours.

[0038] Battery mechanism of this invention:

[0039] The cyclic voltammetry curves for the Si@ZnSe / CoSe@C anode are shown below. Figure 25 During the first cathode scan, three reduction peaks were observed at 1.70, 1.31, and 0.73 V. The weak peak at 1.70 V can be attributed to Li. + Initial insertion in the Si@ZnSe / CoSe@C electrode; the peak at 1.31V is likely due to Li + Intercalation in Co forms LixZn(Co)Se, which then forms a solid electrolyte interphase (SEI) film on the anode surface. Simultaneously, the other cathode peak at 0.73 V may be due to the interaction between LixZn(Co)Se and Li... +The accompanying transformation reactions between these phases lead to the formation of Co, Zn, and Li₂Se. The cathode peak at 0.21 V is associated with the reduction of Si to LixSi alloy. In the second cycle, the reduction peak shifts to 1.41 V and a broad peak at 0.91 V; this shift in peak position is likely due to irreversible side reactions and activation processes caused by the initial lithium insertion during the first cycle. Two high-resolution anodic peaks at 0.35 V and 0.52 V correspond to the transformation of LixSi alloy to amorphous Si. The oxidation peak at 1.36 V can be attributed to the multi-step dealloying reaction of the LixZn alloy phase and the oxidation of LiZn to ZnSe, while the oxidation peak at 2.09 V can be attributed to the reversible selenization of Co to CoSe (Co + Li₂Se / LixCoSe / CoSe). Correspondingly, several small peaks in the 0.01–0.7 V potential range during the anodic scan are attributed to the reverse reaction between metallic Co, Zn, and Li₂Se, forming LixZn(Co)Se. Subsequent scans showed unchanged CV curves, indicating that the Si@ZnSe / CoSe@C conversion process is highly reversible and stable. The reaction formula for Si@ZnSe / CoSe@C is as follows:

[0040] reduction peak

[0041] CoSe+xLi + →LixCoSe(1.31V)

[0042] LixZn(Co)Se+Li + →Co + Zn + Li₂Se (0.73V)

[0043] Si+Li + →LixSi(0.35V, 0.52V)

[0044] Oxidation peak

[0045] Co+Li2Se→LixCoSe→CoSe(2.09V)

[0046] LixZn→xLi + +Zn(1.36V)

[0047] Co+Zn+Li2Se→LixZn(Co)Se(0.01-0.7V)

[0048] LixSi→Si+Li + (0.21V).

[0049] This invention provides a method for preparing a three-dimensional flower-like silicon@zinc selenide / cobalt selenide@carbon composite material. Using cobalt salts, zinc salts, and urea as raw materials and deionized water as a solvent, silicon particles are reacted in a water bath to synthesize Si@Zn(OH)2 / Co(OH)2. Ethanol is used as the solvent for silicon, serving to better disperse and dissolve the silicon particles. Deionized water is used as the solvent for cobalt salts, zinc salts, and urea, with water playing a role in dissolution and dispersion. This invention uses selenium powder as a selenizing agent, calcining and selenizing to generate a special three-dimensional flower-like Si@ZnSe / CoSe@C composite material. Its special structural material provides more active sites during charge and discharge, solving the volume expansion problem and giving the battery better stability. Furthermore, this nanomaterial has advantages such as safety, environmental friendliness, and low cost.

[0050] Compared with the prior art, the present invention has the following advantages: (1) The Si@ZnSe / CoSe@C composite material prepared is novel for use in lithium-ion batteries and is the first application of this combination; (2) The prepared composite material can maintain the three-dimensional flower structure well, provide a large specific surface area, and effectively suppress the volume expansion of silicon; (3) The prepared composite material has stable performance, is not easily deformed in air, and is easy to store; (4) The prepared composite material, when used as a negative electrode material for lithium-ion batteries, has a large specific capacity and good cycle performance; (5) The carbon matrix shortens the electron / ion path and reduces the strain of volume change. The Si@ZnSe / CoSe@C composite material prepared in this invention has a specific capacity of 1Ag. -1 After 650 cycles at the current density, the display showed 298.13 mAh g. -1 The high reversible capacity, high specific capacity, stable cycle performance, and robust rate performance indicate that Si@ZnSe / CoSe@C is an excellent and promising lithium-ion anode material. Attached Figure Description

[0051] Figure 1 SEM image of the precursor Si@Zn(OH)2 / Co(OH)2 prepared in Example 1;

[0052] Figure 2 SEM image of Si@ZnSe / CoSe@C prepared in Example 1;

[0053] Figure 3 The image shows a TEM image of the three-dimensional flower-like structure Si@ZnSe / CoSe@C prepared in Example 1.

[0054] Figure 4 The image shows the XRD pattern of the three-dimensional flower-like Si@ZnSe / CoSe@C material prepared in Example 1.

[0055] Figure 5XRD pattern of the precursor Si@Zn(OH)2 / Co(OH)2 prepared in Example 1;

[0056] Figure 6 SEM image of Si@Zn(OH)2 / Co(OH)2 prepared in Example 2;

[0057] Figure 7 SEM image of Si@ZnSe / CoSe@C prepared in Example 2;

[0058] Figure 8 TEM image of the three-dimensional flower-like Si@ZnSe / CoSe@C material prepared in Example 2;

[0059] Figure 9 SEM image of the three-dimensional flower-like Si@ZnSe / CoSe@C material prepared in Example 3;

[0060] Figure 10 SEM image of the three-dimensional flower-like Si@ZnSe / CoSe@C material prepared in Example 4;

[0061] Figure 11 TEM image of the three-dimensional flower-like Si@ZnSe / CoSe@C material prepared in Example 4;

[0062] Figure 12 SEM image of the three-dimensional flower-like Si@ZnSe / CoSe@C material prepared in Example 5;

[0063] Figure 13 TEM image of the three-dimensional flower-like Si@ZnSe / CoSe@C material prepared in Example 5;

[0064] Figure 14 The three-dimensional flower-like Si@ZnSe / CoSe@C material prepared in Example 1 was used as a negative electrode material for lithium-ion batteries in 0.5 Ag. -1 Test graph of charge-discharge curves at current density;

[0065] Figure 15 The three-dimensional flower-like Si@ZnSe / CoSe@C material prepared in Example 1 was used as a negative electrode material for lithium-ion batteries in 0.5 Ag. -1 Cyclic performance test graph at current density;

[0066] Figure 16 The three-dimensional flower-like Si@ZnSe / CoSe@C material prepared in Example 1 was used as a negative electrode material for lithium-ion batteries at 1.0 Ag. -1 Cyclic performance test graph at current density;

[0067] Figure 17The cycle performance test diagram of the three-dimensional flower-like Si@ZnSe / CoSe@C material prepared in Example 1 as a negative electrode material for lithium-ion batteries at different current densities;

[0068] Figure 18 This is a specific surface area diagram of the composite material synthesized in Example 1;

[0069] Figure 19 The pure silicon particle material of Example 6 was used as the negative electrode material for a lithium-ion battery in 0.1 Ag. -1 Cyclic performance test graph at current density;

[0070] Figure 20 The ZnSe material synthesized in Example 7 was used as a negative electrode material for lithium-ion batteries in 0.5 Ag. -1 Cyclic performance test graph at current density;

[0071] Figure 21 The ZnSe material synthesized in Example 7 was used as a negative electrode material for lithium-ion batteries at a concentration of 1.0 Ag. -1 Cyclic performance test graph at current density;

[0072] Figure 22 The CoSe material synthesized in Example 8 was used as a negative electrode material for lithium-ion batteries in 0.5 Ag. -1 Cyclic performance test graph at current density;

[0073] Figure 23 The CoSe material synthesized in Example 8 was used as a negative electrode material for lithium-ion batteries at a concentration of 1.0 Ag. -1 Cyclic performance test graph at current density;

[0074] Figure 24 XRD pattern of the comparative material prepared in Example 9;

[0075] Figure 25 CV diagram of the three-dimensional flower-like Si@ZnSe / CoSe@C material prepared in Example 1 as a negative electrode material for lithium-ion batteries;

[0076] Figure 26 Raman spectroscopy of the three-dimensional flower-like Si@ZnSe / CoSe@C material prepared in Example 1. Detailed Implementation

[0077] 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.

[0078] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0079] 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.

[0080] Example 1

[0081] A method for preparing a three-dimensional flower-like Si@ZnSe / CoSe@C composite material includes the following steps:

[0082] 1) Preparation of precursor Si@Zn(OH)2 / Co(OH)2:

[0083] 0.1 g of 30 nm silicon powder was ultrasonically dispersed in a 50 mL beaker containing 32 mL of anhydrous ethanol to form a homogeneous solution, denoted as solution A. 4.9 g of Co(NO3)2·6H2O, 2.5 g of Zn(NO3)2·6H2O, and 2.5 g of urea were weighed and added to a 100 mL beaker containing 15 mL of deionized water. The mixture was stirred to form a homogeneous solution, denoted as solution B. Solution A was poured into solution B and magnetically stirred for 10 min to ensure thorough mixing. The mixture was then transferred to a water bath and reacted at 90 °C for 1 h. After natural cooling to room temperature, the product was washed four times with deionized water and twice with ethanol, and then vacuum dried at 60 °C for 12 h. The precursor Si@Zn(OH)2 / Co(OH)2 precipitate was collected. Its SEM image is shown below. Figure 1 As shown in the figure, it can be seen that it is a micro-nano flower with a diameter of 10-15 μm.

[0084] 2) Preparation of Si@ZnSe / CoSe@C:

[0085] 0.2 g of Si@Zn(OH)2 / Co(OH)2 obtained in step 1) was dispersed in 50 mL of deionized water. 0.611 g of tris(hydroxymethyl)aminomethane was added to the solution. After sonication for 10 min, the pH was adjusted to 8.5 with 36% hydrochloric acid. 35 mg of dopamine hydrochloride was added and the mixture was stirred at room temperature for 24 hours. After the reaction was completed, the product was obtained by centrifugation, washing and drying.

[0086] 3) The obtained product was then mixed with selenium powder at a mass ratio of 1:5 and placed in two separate ceramic boats. The mixture was calcined in a hydrogen-argon flowing atmosphere at a heating rate of 2℃ / min, reaching a calcination temperature of 560℃ for 2 hours. The calcination atmosphere consisted of 5% hydrogen and 95% argon by volume. The final product, Si@ZnSe / CoSe@C, was obtained, and its SEM image is shown below. Figure 2 As shown in the image, it has a flower-like structure. TEM image as follows. Figure 3 As shown, Si particles are borne within the petals. The petals are composed of ZnSe / CoSe, with an outermost layer of carbon.

[0087] The XRD pattern of the Si@ZnSe / CoSe@C composite material obtained in this embodiment is as follows: Figure 4 As shown, Figure 26 The presence of carbon can be verified by the D and G bands in the Raman spectroscopy, confirming that the obtained product is Si@ZnSe / CoSe@C. The XRD pattern of the Si@Zn(OH)2 / Co(OH)2 precursor material obtained in this embodiment is shown below. Figure 5 As shown.

[0088] A lithium-ion battery is prepared as follows: The three-dimensional flower-shaped Si@ZnSe / CoSe@C composite material obtained in Example 1 is used as the active material. It is mixed uniformly with conductive carbon black and PVDF in a 7:2:1 ratio. NMP is then added dropwise, and the mixture is magnetically stirred for 8 hours to uniformly disperse the active material. The uniformly mixed slurry is coated onto copper foil using a coater and placed in a vacuum drying oven at 60°C for 24 hours. After drying, it is pressed into sheets using a sheet press and then cut into small circular electrode sheets using a sheet cutter. The electrode sheets are assembled into button cells in a glove box filled with high-purity argon gas and where the water and oxygen values ​​are ≤0.01ppm. The electrolyte is a solvent consisting of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 2:6:2, containing 1M LiPF6. The lithium sheet has a purity of Li≥99.99%, a thickness of 0.5mm, and is rolled and then cut to the size of the electrode sheet.

[0089] The specific method for assembling the battery is as follows: After adding 1 drop of electrolyte to the positive electrode shell, place the electrode plate, then add 1 drop of electrolyte and place the separator, add 2 drops of electrolyte to the separator and place the lithium sheet as the counter electrode, then place two pieces of nickel foam, add 1 drop of electrolyte, cover with the negative electrode shell, press and seal the battery with a hydraulic press, and let it stand for 12 hours.

[0090] Then in 0.5Ag -1 1Ag -1 The cycle performance and charge / discharge performance of the coin cell were tested under the given current, and the results are as follows: Figure 14 , Figure 15 ,Figure 16 As shown: Figure 14 Three-dimensional flower-like Si@ZnSe / CoSe@C material was used as a negative electrode material for lithium-ion batteries at 0.5 Ag. -1 Test graph of charge-discharge curves at current density; Figure 15 The Si@ZnSe / CoSe@C material was used as a negative electrode material for lithium-ion batteries in 0.5Ag. -1 Cyclic performance test graph at current density, at 0.5Ag -1 After 300 cycles at the current density, the specific capacity is 501.18 mAh g. -1 . Figure 16 Si@ZnSe / CoSe@C materials as anode materials for lithium-ion batteries in 1Ag -1 Cyclic performance test graph at current density, at 1Ag -1 After 650 cycles at the current density, the specific capacity is 298.13 mAh g. -1 Furthermore, the Coulomb efficiency is 99.66%. Figure 17 The three-dimensional flower-like structure Si@ prepared in Example 1

[0091] Rate performance test results of ZnSe / CoSe@C material as a negative electrode material for lithium-ion batteries at 0.1, 0.2, 0.3, 0.4, and 0.5 Ag. -1 The specific capacities at different current densities were 1308.26, 1083.16, 906.82, 744.64, and 691.12 mAh g. -1 . Figure 18 The specific surface area of ​​the Si@ZnSe / CoSe@C materials prepared in Example 1, the ZnSe materials prepared in Example 7, and the CoSe materials prepared in Example 8 was measured. Before the BET test, the samples were degassed in a vacuum at 120°C for 12 h to remove adsorbed water from the surface. Then, the physical adsorption isotherms (adsorption-desorption branch) were recorded using a specific surface area analyzer (ASAP Micromeritics Tristar 2460). The results are as follows: Figure 18 The specific surface area of ​​the Si@ZnSe / CoSe@C shown is 56.93 m². 2 g -1 Higher than ZnSe(38.20m) 2 g -1 The specific surface area of ​​CoSe (4.26 m²) and CoSe 2 g -1 The large specific surface area and abundant porous structure can reduce diffusion paths and increase active sites. Further evidence demonstrates the excellent performance of the synthesized Si@ZnSe / CoSe@C composite material. It provides shuttle channels for lithium-ion transfer, thereby increasing lithium-ion storage capacity.

[0092] Example 2 (as a comparison)

[0093] A method for preparing a three-dimensional flower-like Si@ZnSe / CoSe@C composite material includes the following steps:

[0094] 1) Preparation of precursor Si@Zn(OH)2 / Co(OH)2:

[0095] 0.1g of 30nm silicon powder was ultrasonically dispersed in a 50mL beaker containing 32mL of anhydrous ethanol to form a homogeneous solution, denoted as solution A. 4.9g of Co(NO3)2·6H2O, 2.5g of Zn(NO3)2·6H2O, and 2.5g of urea were weighed and added to a 100mL beaker containing 15mL of deionized water. The mixture was vigorously stirred to form a homogeneous solution, denoted as solution B. Solution A was poured into solution B and magnetically stirred for 10 minutes to ensure thorough mixing. The mixture was then transferred to a water bath and incubated at 90℃. Reaction 3h After naturally cooling to room temperature, the product was washed four times with deionized water by centrifugation, twice with ethanol, and then vacuum dried at 60℃ for 12 h. The precursor Si@Zn(OH)2 / Co(OH)2 precipitate was collected. Its SEM image is shown below. Figure 6 As shown, the composite material structure is not complete.

[0096] 2) Preparation of Si@ZnSe / CoSe@C:

[0097] The 0.2 g Si@Zn(OH)2 / Co(OH)2 obtained in step 1) was dispersed in 50 mL of deionized water. 0.611 g tris(hydroxymethyl)aminomethane was added to the solution. After sonication for 10 min, the pH was adjusted to 8.5 with hydrochloric acid. 35 mg dopamine hydrochloride was added and the mixture was stirred at room temperature for 24 hours. After the reaction was completed, the product was obtained by centrifugation, washing and drying.

[0098] 3) The obtained product was then mixed with selenium powder at a mass ratio of 1:5 and placed in two separate ceramic boats. The mixture was calcined in a hydrogen-argon flowing atmosphere at a heating rate of 2℃ / min, reaching a calcination temperature of 560℃ for 2 hours. The calcination atmosphere consisted of 5% hydrogen and 95% argon by volume. The final product, Si@ZnSe / CoSe@C, was obtained, and its SEM image is shown below. Figure 7 As shown in the image, the composite material has poor morphology and does not form flowers. TEM image is shown below. Figure 8 As shown.

[0099] Figure 6As can be seen, the reaction time for synthesizing Si@Zn(OH)2 / Co(OH)2 in Example 2 was 3 hours, which was too long and resulted in poor morphology. Therefore, the preferred reaction time in this invention is 1 hour at 90°C.

[0100] Example 3 (as a comparison)

[0101] A method for preparing a three-dimensional flower-like Si@ZnSe / CoSe@C composite material includes the following steps:

[0102] 1) The preparation of the precursor is the same as in Example 1;

[0103] 2) Preparation of Si@ZnSe / CoSe@C:

[0104] The obtained 0.2 g Si@Zn(OH)2 / Co(OH)2 was dispersed in 50 mL of deionized water. 1.6g Tris(hydroxymethyl)aminomethane was added to the solution, and after sonication for 10 minutes, the pH was adjusted to 8.5 with hydrochloric acid. 85 mg Dopamine hydrochloride was stirred at room temperature for 24 hours. After the reaction was completed, the product was obtained by centrifugation, washing, and drying.

[0105] 3) Subsequently, the obtained product was mixed with selenium powder at a mass ratio of 1:5 and placed in two separate ceramic boats. The mixture was then calcined in a hydrogen-argon atmosphere at a heating rate of 2℃ / min until the calcination temperature reached 560℃. The calcination time was 2 hours. The calcination atmosphere consisted of 5% hydrogen and 95% argon by volume, ultimately yielding the product Si@.

[0106] ZnSe / CoSe@C, its SEM image is as follows Figure 9 As shown in the figure, it has a spherical structure.

[0107] from Figure 9 As can be seen, increasing the amount of reagent added during carbon coating resulted in a thicker carbon coating, thus disrupting the flower-like morphology. Therefore, the composite material synthesized according to Example 1 showed the best results.

[0108] Example 4 (as a comparison)

[0109] A method for preparing a three-dimensional flower-like Si@ZnSe / CoSe@C composite material includes the following steps:

[0110] 1) The preparation of the precursor is the same as in Example 1;

[0111] 2) Disperse the obtained 0.2g Si@Zn(OH)2 / Co(OH)2 in 50mL of deionized water, add 0.611g tris(hydroxymethyl)aminomethane to the solution, sonicate for 10min, adjust the pH to 8.5 with hydrochloric acid, add 35mg dopamine hydrochloride, stir at room temperature for 24 hours, and after the reaction is completed, obtain the product by centrifugation, washing and drying.

[0112] 3) The obtained product is then mixed with selenium powder according to the mass ratio. 1:10 The samples were placed in two separate ceramic boats and calcined in a flowing hydrogen-argon atmosphere. The heating rate was 2℃ / min, reaching a calcination temperature of 560℃, and the calcination time was 2 hours. The calcination atmosphere consisted of 5% hydrogen and 95% argon by volume. The final product, Si@ZnSe / CoSe@C, was obtained, and its SEM image is shown below. Figure 10 As shown in the image, it has a flower-like structure. The TEM image is as follows. Figure 11 As shown, no flake-like flower-like structure was formed. This further highlights that Example 1, with a mass ratio of 1:5, is the optimal embodiment.

[0113] Example 5 (as a comparison)

[0114] A method for preparing a three-dimensional flower-like Si@ZnSe / CoSe@C composite material includes the following steps:

[0115] 1) The preparation of the precursor is the same as in Example 1;

[0116] 2) Disperse the obtained 0.2g Si@Zn(OH)2 / Co(OH)2 in 50mL of deionized water, add 0.611g tris(hydroxymethyl)aminomethane to the solution, sonicate for 10min, adjust the pH to 8.5 with hydrochloric acid, add 35mg dopamine hydrochloride, stir at room temperature for 24 hours, and after the reaction is completed, obtain the product by centrifugation, washing and drying.

[0117] 3) The obtained product was then mixed with selenium powder at a mass ratio of 1:5 and placed in two separate ceramic boats. The mixture was calcined in a flowing hydrogen-argon atmosphere at a heating rate of 2℃ / min until the calcination temperature was reached. 800℃ The calcination time was 2 hours, and the calcination atmosphere was hydrogen and argon gas, with a volume fraction of 5% hydrogen and 95% argon. The final product was still Si@ZnSe / CoSe@C, and its SEM image is shown below. Figure 12 As shown, the TEM image is as follows Figure 13 As shown.

[0118] After increasing the calcination temperature, although the XRD of the composite material was basically the same as that of Example 1, the flower-like structure collapsed.

[0119] Example 6 (as a comparison)

[0120] 30nm Pure silicon particle loaded battery (The silicon particles are the same as those used in Example 1, and the battery assembly process is the same as that of the materials used in Example 1.) The battery was assembled using the same method described above, and tested using the same methods and parameters. Figure 19 It can be seen that pure silicon particles at 0.1Ag -1 At the current density, its cycling performance is worse and its degradation is faster compared to the composite material of Example 1.

[0121] Example 7 (as a comparison)

[0122] The procedure was carried out according to Example 1, except during the preparation process. Without adding silicon particles and cobalt nitrate hexahydrate, ZnSe nanomaterials were synthesized separately and assembled into batteries using the same method described above. Tests were conducted using the same methods and parameters. Figure 20 , Figure 21 It can be observed that it is at 0.5 and 1 Ag -1 Under certain conditions, the specific capacity is low and the cycle performance is poor.

[0123] Example 8 (as a comparison)

[0124] The procedure was carried out according to Example 1, except that no [further details were provided in the preparation process]. With adding silicon particles and zinc nitrate hexahydrate, Individually synthesized CoSe nanomaterials were assembled into batteries using the same method described above, and tested using the same methods and parameters. Figure 22 , Figure 23 It can be observed that it is at 0.5 and 1 Ag -1 Under certain conditions, the specific capacity is low and the cycle performance is poor.

[0125] Example 9 (as a comparison)

[0126] Following the same preparation method as in Example 1, Just replace the silicon particles with Fe304 pellets, Fe304 pellets are commercially available Product of The particle size is 20nm, from Figure 24 The XRD pattern shows that Fe3O4@ZnSe / CoSe@C cannot be synthesized, further verifying the stability of silicon particles. Even during selenization, the composition of silicon particles remains unchanged, demonstrating the superiority and uniqueness of the composite material synthesized in this invention.

[0127] The data underlined above do not meet the requirements of this invention.

[0128] 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 flower-like silicon@zinc selenide / cobalt selenide@carbon composite material, characterized in that, The preparation method comprises the following steps: 1) dispersing a silicon material in a solvent to form a uniform solution, denoted as solution A; mixing a cobalt salt, a zinc salt and urea in water and stirring uniformly, denoted as solution B; mixing solution A and solution B uniformly, and then performing a water bath reaction to obtain a flower-shaped Si@Zn(OH)2 / Co(OH)2; 2) dispersing the Si@Zn(OH)2 / Co(OH)2 obtained in step 1) in water, adding tris(hydroxymethyl)aminomethane, adjusting the pH to 8-9 with hydrochloric acid, and then adding dopamine hydrochloride and stirring to react; 3) calcining the product of step 2) and selenium powder to obtain a three-dimensional flower-shaped Si@ZnSe / CoSe@C composite material.

2. The production method according to claim 1, characterized by, In step 1), the amount ratio of the silicon material to the solvent is 0.05-0.3 mol / L; the solvent is anhydrous ethanol.

3. The production method according to claim 1, characterized by, In step 1), the mass ratio of the cobalt salt, the zinc salt and urea is 2.5:1.3:1.3-6.54:3.6:3.

6.

4. The production method according to claim 1 or 3, characterized by, In step 1), the volume ratio of the solvent to deionized water is 32:

15.

5. The preparation method according to claim 1, characterized in that, In step 1), the water bath reaction conditions are 60-100℃ for 30 minutes-2 hours.

6. The method of claim 1, wherein, In step 2), the mass ratio of Si@Zn(OH)2 / Co(OH)2, tris(hydroxymethyl)aminomethane and dopamine hydrochloride is 1:3:0.175-1:6:0.

3.

7. The preparation method according to claim 1, characterized in that, In step 3), the mass ratio of the product of step 2) to selenium powder is 1:3-1:8; the calcination conditions are 500-700℃ for 1-4 hours, the calcination atmosphere is hydrogen-argon gas, and the hydrogen-argon gas is 5% hydrogen and 95% argon by volume.

8. The three-dimensional flower-like silicon@zinc selenide / cobalt selenide@carbon composite material prepared by the preparation method of any one of claims 1-7, characterized in that, The three-dimensional flower-shaped silicon@zinc selenide / cobalt selenide@carbon composite material has a size of 10-15 um, the Si particles are grown in the ZnSe / CoSe petals, the outermost layer is a carbon layer, the particle size of the Si particles is 30±5 nm, and the thickness of the nanosheet is 100±20 nm.

9. A silicon-based anode for a lithium-ion battery, characterized in that, The three-dimensional flower-shaped silicon@zinc selenide / cobalt selenide@carbon composite material is prepared by using the three-dimensional flower-shaped silicon@zinc selenide / cobalt selenide@carbon composite material of claim 8.

10. A lithium-ion battery, characterized by, The lithium ion battery silicon-based negative electrode is prepared by using the lithium ion battery silicon-based negative electrode of claim 9.

Images