Silicon-based phase / metal phase compounded silicon-based composite material, and preparation method therefor and use thereof

Abstract

A silicon-based phase / metal phase compounded silicon-based composite material. A silicon-based phase is formed by assembling silicon-based nanocrystals, the outer surface of the silicon-based phase is coated with metal phases, and the metal phases are mutually connected to form a body-shaped network structure; the silicon-based phase comprises a single silicon phase or an Si-Ge composite phase; when the single silicon phase is selected as the silicon-based phase, the silicon-based nanocrystals are selected from silicon nanocrystals; when the Si-Ge composite phase is selected as the silicon-based phase, the silicon-based nanocrystals are selected from Si-Ge nanocrystals; and the melting point of the metal phases is lower than that of the silicon-based phase. A lithium-ion battery assembled by using the silicon-based composite material as a negative electrode has extremely good rate capability and cycling stability, and also has a high initial capacity and high initial efficiency.

Description

Silicon-based composite material composed of a silicon-based phase and a metal phase, and its preparation method and application

[0001] This application claims priority to the Chinese invention patent application filed with the State Intellectual Property Office of China on October 20, 2023, with application number 202311364342.7 and application name “A silicon-based composite material composed of a silicon-based phase and a metal phase, its preparation method and application”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of secondary batteries, and in particular to a silicon-based composite material composed of a silicon-based phase and a metal phase, a preparation method thereof, and an application in lithium-ion batteries. Background Art

[0003] Since the 21st century, with the rapid growth of economic development, the contradiction between energy and the environment has become increasingly acute. As a new generation of "green" secondary batteries, lithium-ion batteries have been widely used in various fields such as electric vehicles, small mobile home appliance power supplies, energy storage, and electronic products. High-performance electrode materials are the key to high-performance lithium-ion batteries. With the increasing demand for high energy density and high power density of lithium-ion batteries, the research and development of high-performance lithium-ion battery electrode materials is imminent. The negative electrode material is one of the key factors affecting the main performance indicators of lithium-ion batteries. At present, the graphite-based carbon negative electrode material used in commercial lithium-ion batteries can no longer meet the use requirements of high energy density and high power density of batteries, and there is an urgent need to further develop high-performance negative electrode materials.

[0004] Regarding new lithium-ion battery anode materials, the theoretical specific capacity of silicon (Si) anode materials (based on the room-temperature phase Li15Si4) is as high as 3579 mAh / g, nearly 10 times the theoretical capacity of commercial graphite anode materials (372 mAh / g). Furthermore, its abundance and low cost make it a highly promising next-generation high-capacity anode material. However, the following major problems still restrict its large-scale commercial application: First, during the process of lithium insertion and extraction, the silicon negative electrode material will undergo a huge volume change (about ~300%), which will lead to material pulverization, reduce the electrical contact between silicon particles, and cause the silicon material to peel off from the current collector, ultimately resulting in a significant reduction in cycle life; Second, the huge volume change of the silicon material during the cycle causes the solid electrolyte membrane (SEI membrane) generated by the reaction between the surface of the silicon particles and the electrolyte to continuously rupture. The fresh surface of the silicon material is continuously exposed to the electrolyte and a new SEI membrane is continuously formed, which not only consumes too much lithium ions in the electrolyte, but also has uneven thickness of the SEI membrane, which reduces the coulombic efficiency, cycle and rate performance of the battery; Third, elemental silicon is a semiconductor material with low electronic conductivity, which leads to sluggish electrode kinetics, reduced utilization of active materials, poor high current charge and discharge capabilities, and poor kinetic performance and high rate performance.

[0005] Currently, the commonly used methods for improving the electrochemical performance of silicon-based negative electrode materials are: (1) reducing the expansion stress of silicon-based materials during the lithium insertion process and improving the anti-pulverization ability of silicon materials by nano-scaling, adding lithium-deintercalation inert phases, and constructing porous structures; (2) improving the overall electronic conductivity of silicon-based negative electrodes by introducing high electronic conductivity phases, such as carbon coating and graphene; (3) improving the first coulombic efficiency of silicon-based negative electrode materials by artificially preforming a uniform and stable SEI film, reducing the irreversible loss of lithium during the cycle, and improving its cycle stability. However, for nano-silicon materials that can effectively reduce volume expansion during the cycle, their size is often required to be less than tens of nanometers, or even smaller than 10 nanometers.

[0006] However, due to the nano effect, nanomaterials are prone to agglomeration, and the negative electrode of nanomaterials also has the problem of low volume capacity density, and high volume specific capacity is particularly important for practical applications. In addition, the preparation methods of silicon-based materials with special structures such as nano-silicon-based materials and porous structures are usually complicated, and the coating process requirements of nanomaterial electrodes are also high. Compared with nanomaterials, from the current practical point of view, micron materials have the advantages of high tap density, high specific capacity and low preparation cost. However, due to the large particle size of micron materials, the lithium ion diffusion path is longer, which is not conducive to the transport of lithium ions. For porous materials, porous structures with low porosity cannot buffer the volume expansion of silicon-based negative electrode materials during the lithium insertion process, while porous structures with high porosity reduce the volume capacity of the electrode. Methods such as carbon coating to improve the electronic conductivity of silicon-based negative electrodes are still insufficient to maintain high conductivity of the electrode when the silicon-based negative electrode material is severely pulverized and peeled off from the current collector, and cannot effectively prevent the rapid decrease in capacity during the cycle. The preparation of artificial SEI film usually requires a more complicated process, high cost and low efficiency. In addition, for crystalline silicon-based materials, due to their <110> Lithium is more readily inserted in the {111} direction, leading to greater exfoliation and pulverization on the {111} plane. Amorphous silicon, on the other hand, experiences isotropic stress during lithium insertion due to its isotropic lithium insertion process. Therefore, compared to crystalline silicon, amorphous silicon exhibits greater resistance to pulverization during lithium insertion and better cycling performance. However, the theoretical lithium insertion capacity of amorphous silicon is somewhat lower than that of crystalline silicon.

[0007] Summary of the Invention

[0008] In response to the above-mentioned problems existing in the prior art, the present application discloses a silicon-based composite material composed of a silicon-based phase and a metal phase. The lithium-ion battery assembled using this composite material as the negative electrode has extremely excellent rate performance and cycle stability, and has both high initial capacity and high first efficiency.

[0009] The specific technical solutions are as follows:

[0010] A silicon-based composite material composed of a silicon-based phase and a metal phase, wherein the silicon-based phase is assembled from silicon-based nanocrystals, the outer surface of the silicon-based phase is coated with a metal phase, and the metal phases are interconnected to form a three-dimensional network structure;

[0011] The silicon-based phase includes a single silicon phase or a Si-Ge composite phase;

[0012] When the silicon-based phase is selected from a single silicon phase, the silicon-based nanocrystal particles are selected from silicon nanocrystal particles;

[0013] When the silicon-based phase is selected from a Si-Ge composite phase, the silicon-based nanocrystal particles are selected from Si-Ge nanocrystal particles;

[0014] The melting point of the metal phase is lower than the melting point of the silicon-based phase.

[0015] It has been characterized that when the silicon-based phase is selected from the Si-Ge composite phase, Si-Ge sometimes forms a solid solution, or a composite phase of the Si-Ge solid solution phase and the Ge phase; the Si-Ge nanoparticles actually include Si-Ge solid solution nanoparticles and Ge nanoparticles.

[0016] The silicon-based composite material disclosed in this application obtains a small volume expansion stress and strain during the lithium insertion process of the material through advanced structural component design, reduces pulverization, and reduces the formation of SEI film of silicon-based negative electrode materials during the cycle. Under the condition of improving the anti-pulverization of silicon-based materials, submicron and micron-scale silicon-based negative electrode materials are used to reduce the formation of SEI film, obtain a high tap density of the electrode material, and improve the volume capacity density of the silicon-based negative electrode and the corresponding lithium-ion battery. At the same time, through advanced structural component design, the electronic conductivity and lithium ion diffusion performance of the material are improved. Thereby, a silicon-based negative electrode material with high capacity, excellent cycle stability and rate performance and a low-cost and high-yield preparation method thereof are obtained to meet the requirements for commercial use in lithium-ion batteries.

[0017] In the silicon-based composite material, the size of the silicon-based nano-crystal particles is 2 to 200 nm; the size of the silicon-based phase is 10 to 1000 nm; and the size of the silicon-based composite material is 200 nm to 5 μm.

[0018] Preferably, the size of the silicon-based nanocrystals is 2 to 50 nm; the size of the silicon-based phase is 10 to 800 nm; and the size of the silicon-based composite material is 300 nm to 3 μm.

[0019] More preferably, the size of the silicon-based nanocrystals is 2 to 30 nm; the size of the silicon-based phase is 30 to 300 nm; and the size of the silicon-based composite material is 300 nm to 1.5 μm.

[0020] The melting point of the metal phase used in this application is limited. When the silicon-based phase is selected from a single silicon phase, the melting point of the metal phase is lower than the melting point of silicon.

[0021] When the silicon-based phase is selected from a Si-Ge composite phase, the melting point of the metal phase should be lower than the melting point of the Si-Ge composite phase.

[0022] Experiments have found that when the melting point of the metal phase used is higher than that of the silicon-based phase, such as when the metal used is Cr, the Cr phase or the conductive network containing Cr cannot be formed on the outer surface of the silicon-based phase, and thus cannot play a role in improving the electrochemical performance of the silicon negative electrode material.

[0023] Preferably, the metal in the metal phase is selected from one or more of Sn, In, Al, Pb, Zn, Sb, Bi, Se, and Ag.

[0024] More preferably, the metal has a temperature difference ΔT of ≥ 500° C. between the melting point of the metal phase and the melting point of the silicon-based phase.

[0025] Further experiments found that when the temperature difference between the melting point of the metal phase and the melting point of the silicon-based phase is less than 500°C, the network structure cannot be fully formed, and its conductive network structure and coating of Si particles are weakened, thereby improving the electrochemical properties of Si-based materials.

[0026] More preferably, the metal is selected from Sn and / or In, and most preferably is metallic Sn.

[0027] Preferably, the silicon-based phase is selected from a Si-Ge composite phase. Experiments have shown that when Ge is added, the size of the prepared silicon-based nanocrystals is smaller, the carrier concentration of the composite material is greatly improved, the size of the assembled silicon-based phase is also smaller, and the composite material finally prepared has better electrochemical properties overall, especially better cycle stability at high current density.

[0028] The present application also discloses a method for preparing the silicon-based composite material composed of a silicon-based phase and a metal phase, comprising the following steps:

[0029] Step 1: uniformly mixing the silicon-based raw material and the metal raw material, and performing suspension induction melting under an argon atmosphere to obtain a silicon-based composite material ingot;

[0030] The silicon-based raw material is selected from Si, or a mixture of Si and Ge;

[0031] The metal raw material is selected from one or more of Sn, In, Al, Pb, Zn, Sb, Bi, Se, and Ag;

[0032] Step 2: The silicon-based composite material ingot is crushed into powder and placed in a vacuum rotary quenching furnace for suspension melting under an argon atmosphere. The obtained melt is transferred through a nozzle carrying an argon flow and spray-casted on a high-speed rotating copper roller. After cooling, the quenched product is collected to obtain a rapid quenching product;

[0033] Step 3: sand-milling the rapid quenching product to obtain the silicon-based composite material composed of the silicon-based phase and the metal phase.

[0034] The preparation methods disclosed in this application include suspension melting, rapid quenching and sand milling, which are all mature industrial preparation methods with good controllability of preparation process parameters, low cost, high yield, and are suitable for commercial production. By optimizing the metal phase raw materials and their addition amount, and by adding Ge to the silicon material, combined with regulating the rapid quenching process and parameters to achieve the effect of regulating the Si-based phase properties (including the regulation of the Si-based phase particle size and the size of the silicon-based nanocrystals that constitute the Si-based phase), the present application provides silicon-based composite materials with different silicon-based phase particle sizes and nanocrystal sizes in the silicon-based phase and metal composites.

[0035] In step 1: the molar ratio of the silicon-based raw material to the metal raw material is 1: (0.01-0.3);

[0036] When the silicon-based raw material is selected from a mixture of Si and Ge, the molar ratio of Si to Ge is 1:(0.01-0.5).

[0037] Preferably, the molar ratio of the silicon-based raw material to the metal raw material is 1:(0.03-0.11); more preferably 1:(0.03-0.08), and even more preferably 1:0.05.

[0038] Experiments have found that by regulating the molar ratio of silicon-based raw materials to metal raw materials, the particle size of silicon-based nanocrystals and silicon-based phases can be regulated, and the carrier mobility and exchange current density of the composite material can be regulated; and as the molar ratio of the above-mentioned silicon-based raw materials to metal raw materials is continuously optimized, the prepared composite material has better electrochemical properties.

[0039] Preferably, the silicon-based raw material is selected from a mixture of Si and Ge;

[0040] More preferably, the molar ratio of Si to Ge is 1:(0.03-0.12); further preferably, it is 1:(0.03-0.08), and even more preferably, it is 1:(0.05-0.06).

[0041] Experiments have found that by regulating the molar ratio of Si to Ge, the particle size of silicon-based nanocrystals and silicon-based phases can be controlled, and the carrier mobility and exchange current density of the composite material can be controlled; and with the continuous optimization of the above-mentioned molar ratio of Si to Ge, the prepared composite material has better electrochemical properties.

[0042] In step 2: the pressure of the argon gas flow is 0.4 to 4.0 atmospheres;

[0043] The rotation speed of the copper roller is 10-100 m / s;

[0044] The spray casting distance is 0.5 to 2.5 m.

[0045] Experiments have shown that the particle size of silicon-based nanocrystals and silicon-based phases in silicon-based composite materials can also be controlled by regulating the pressure of the argon gas flow during spraying and the rotational speed of the copper roller.

[0046] Preferably, the pressure of the argon gas flow is 1.5 to 3.0 atmospheres;

[0047] The rotational linear speed of the copper roller is 25-60 m / s.

[0048] Further preferably, the pressure of the argon gas flow is 1.7 to 2.5 atmospheres;

[0049] The rotation linear speed of the copper roller is 30-40 m / s.

[0050] The present application also discloses the use of the silicon-based composite material composed of a silicon-based phase and a metal phase in the preparation of lithium-ion batteries.

[0051] Specifically, the silicon-based composite material is used as the negative electrode, and the positive electrode can adopt conventional lithium-ion battery positive electrode materials, such as LiFePO4, LiCoO2, ternary materials, etc., and the separator and electrolyte conventionally used in commercial lithium-ion batteries are used to assemble a lithium-ion battery.

[0052] Compared with the prior art, this application has the following advantages:

[0053] 1. In the silicon-based composite material disclosed in the present application, the size of the silicon particles constituting the silicon-based phase is mainly in the range of tens of nanometers to submicron scales, and the silicon-based phase is composed of smaller nanocrystals with a size of mainly several nanometers to tens of nanometers or a small amount of amorphous. During the lithium insertion process of the composite material, a large number of silicon-based nanocrystals with different arrangement directions actually form isotropic stress and strain. The silicon particles constituting the silicon-based phase have high strain resistance, thereby greatly improving the anti-pulverization ability of the silicon-based composite material, thereby effectively improving the cycle performance of the composite material. In addition, the bulk network structure metal phase coated between the silicon particles constituting the silicon-based phase, in addition to having high electronic conductivity, greatly improves the overall electronic conductivity of the silicon-based composite material, and also buffers the volume expansion of the silicon particles constituting the silicon-based phase to a certain extent. The anti-pulverization ability of the composite material is further improved, and the cycle stability of the composite material is further improved. The small size of the silicon-based phase also greatly shortens the diffusion distance of lithium ions, which is beneficial to the improvement of the kinetic properties of the silicon-based negative electrode material and obtains excellent rate performance.

[0054] 2. The silicon-based composite material disclosed in this application, under the condition of using Sn and In as the composite phase, Sn and In themselves are reversible lithium intercalation materials, and their theoretical lithium intercalation capacities are 994 mAh / g and 700 mAh / g, respectively. In the silicon-based composite material of this application, it can not only serve as a conductive network, but also act as an active material. In addition to contributing to capacity, its network structure in the composite material is also conducive to the migration of lithium ions in the silicon-based phase. This further ensures the high capacity and excellent rate performance of the composite material.

[0055] 3. In the composite material disclosed in this application, Ge is introduced into the Si-based phase. Ge itself is also a lithium-intercalating material. 22 In terms of Ge5, its lithium insertion capacity is about 1623 mAh / g. Although it is lower than that of Si, the electronic conductivity of Ge is about 4 orders of magnitude higher than that of Si, and the hole mobility is more than 4 times that of Si, which is conducive to the rapid transmission of lithium ions. Its introduction is conducive to improving the kinetic performance of silicon-based composite materials as negative electrode materials, thereby improving the rate performance. After Ge and Si form a solid solution, the interplanar spacing of Si becomes larger, which is conducive to the insertion and extraction of lithium ions, which is also conducive to the transmission of lithium ions in Si. However, the volume expansion of Ge during the lithium insertion process is also as high as about 200%. However, in the composite material of the present application, since the Si-Ge phase formed is in the range of tens to hundreds of nanometers, and further, the Si-Ge phase is composed of nanocrystals with a scale of several to tens of nanometers, the stress-strain capacity of the Si-Ge phase to resist volume expansion during the lithium insertion process is greatly improved, effectively improving the volume expansion problem that also exists in Ge during the lithium insertion process. The composite material has a greatly improved ability to resist pulverization during the cycle. Combined with its high carrier mobility and excellent lithium ion transport capacity, the composite negative electrode material composed of the Si-Ge phase and the metal phase has excellent cycle stability, especially high-rate cycle performance. And because of the high specific gravity of Ge, the composite material has a large tap density, which is conducive to improving the volume density of the electrode and battery.

[0056] 4. When the silicon-based composite material disclosed in this application is compounded with other metals besides aluminum, the tap density of the composite material is much higher than that of the silicon material due to the large atomic number and high density of the other metals. As a negative electrode material for lithium-ion batteries, the volume capacity density of the corresponding lithium-ion battery is greatly improved, which is very important for the practical application of lithium-ion batteries.

[0057] 5. If the silicon-based composite material disclosed in this application uses a non-lithium-deintercalating active metal, the metal coating of the silicon-based phase can further reduce the interfacial reaction between the Si-based phase and the electrolyte, further improving the first coulombic efficiency of the material.

[0058] 6. The suspension melting, rapid quenching and sand milling methods used in the preparation of the silicon-based composite material disclosed in this application are all industrial preparation methods. The preparation methods are mature, have good process controllability, low cost, high yield, are environmentally friendly, and are suitable for large-scale production.

[0059] 7. When the silicon-based composite material disclosed in the present application is used as the negative electrode material of a lithium-ion battery, the particle size of the quenched product is refined by sand milling, and the sand milling process is highly efficient and takes a short time. The particle size of the obtained composite material ranges from several hundred nanometers to 2 to 3 microns. Compared with nanomaterials with particle sizes of several nanometers to tens of nanometers, its specific surface area is small, the tap density of the material is large, and the electrode preparation operation is simple. In addition, due to the small specific surface area of ​​the material, the interfacial reaction between it and the electrolyte is small, and the first coulombic efficiency of the material is high. In addition, due to the coating of the Si-based phase by the metal material, the contact between the silicon-based composite material and the electrolyte interface is further reduced, and the formation of the SEI film is reduced, which is conducive to improving the coulombic efficiency of the silicon-based composite material as a negative electrode material during the cycle.

[0060] 8. The present application obtains a silicon-based composite material composed of a silicon-based phase having nanocrystalline grains or containing a small amount of amorphous components and a metal phase by optimizing the selection of raw materials and the preparation process conditions. The metal does not form an alloy phase or solid solution phase with the Si or Si-Ge phase. Since the melting point of the selected metal is lower than the melting point of the Si material, or when the Si-Ge phase is used as the silicon-based phase, the melting point of the selected metal is lower than the melting point of the Si-Ge phase, during the rapid quenching process, the Si phase or Si-Ge phase solidifies rapidly first, and the low-melting-point metal phase solidifies after the Si phase or Si-Ge phase solidifies, solidifying in the gaps between the Si phase or Si-Ge phase particles, coating the surface of the silicon-based phase, and connecting with each other to form a network structure. Due to the good electrical conductivity of the metal, this interconnected metal network structure significantly improves the electronic conductivity of the silicon-based composite material. By regulating and optimizing the content of the metal phase, its electronic conductivity can reach a value several orders of magnitude greater than that of Si-based materials, and high carrier mobility and high exchange current density can be obtained, thereby effectively improving the comprehensive electrochemical performance of silicon-based composite materials as negative electrode materials for lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] FIG1 is a metallographic photograph of the ingot prepared in step 1 of Example 1;

[0062] Figure 2 is a SEM morphology image (a) and a BSE morphology image (b) of the quenched product prepared in step 2 of Example 1;

[0063] FIG3 is an XRD pattern (a) of the silicon-based composite materials prepared in Examples 1 to 3, respectively, and an SEM morphology image (b) of the silicon-based composite material prepared in Example 1;

[0064] FIG4 is an SEM morphology image (a), a BSE morphology image (b) of the quenched product prepared in step 2 of Example 2, and an SEM morphology image (c) of the finally prepared silicon-based composite material;

[0065] FIG5 is a BSE morphology of the quenched product prepared in step 2 of Example 3;

[0066] FIG6 shows the cycle performance curves of lithium-ion batteries assembled with the silicon-based negative electrode materials prepared in Examples 1 to 3 at a current density of 300 mAh / g (a), 1500 mAh / g (b), and 15,000 mAh / g (c), as well as the capacity curves at different current densities (mAh / g) (d);

[0067] FIG7 is a SEM morphology image (a) and a TEM morphology image (b) of the silicon-based composite material finally prepared in Example 4;

[0068] FIG8 is a TEM morphology of the silicon-based negative electrode material prepared in Example 5;

[0069] FIG9 is a SEM morphology image (a) of the quenched product prepared in step 2 of Example 6 and a TEM morphology image (b) of the finally prepared silicon-based composite material;

[0070] FIG10 is a SEM morphology image (a) and a TEM morphology image (b) of the silicon-based composite material finally prepared in Example 7;

[0071] FIG11 is an XRD pattern of the silicon-based composite materials prepared in Examples 4 to 7, respectively;

[0072] FIG12 shows the cycle performance curves of lithium-ion batteries assembled with silicon-based composite materials prepared in Examples 4 to 7 at a current density of 300 mAh / g (a), 1500 mAh / g (b), and 15,000 mAh / g (c), as well as the capacity curves at different current densities (mAh / g) (d);

[0073] FIG13 is an XRD pattern of the silicon-based composite material prepared in Example 9;

[0074] FIG14 shows the cycle performance curves of the lithium-ion battery assembled in Example 9 at a current density of 300 mAh / g (a), 1500 mAh / g (b), and 15,000 mAh / g (c), as well as the capacity curve (d) at different current densities (mAh / g);

[0075] FIG15 is an SEM image of the quenched products prepared in step 2 of Example 11(a) and Example 13(b), respectively;

[0076] FIG16 is an XRD pattern (a) of the silicon-based composite materials prepared in Examples 10 to 13, and an enlarged view of the diffraction peak of the (422) crystal plane of Si (b);

[0077] FIG17 is an SEM morphology image (a) and a TEM morphology image (b) of the silicon-based composite material prepared in Example 11, and a TEM morphology image (c) of the silicon-based composite material prepared in Example 13;

[0078] FIG18 shows the cycle performance curves of the batteries assembled in Examples 10 to 13 at a current density of 300 mAh / g (a), 1500 mAh / g (b), and 15,000 mAh / g (c), as well as the capacity curves at different current densities (mAh / g) (d);

[0079] FIG19 is an SEM morphology of the final products prepared in Comparative Example 1(a) and Comparative Example 2(b), respectively;

[0080] Figure 20 shows the cycle performance curves of the batteries assembled in Comparative Examples 1 and 2 at a current density of 300 mAh / g (a), 1500 mAh / g (b), and 15,000 mAh / g (c), as well as the capacity curves at different current densities (mAh / g) (d);

[0081] FIG21 is an XRD pattern of the silicon-based composite material prepared in Comparative Example 3;

[0082] FIG22 is a BSE morphology of the silicon-based composite material prepared in Comparative Example 3;

[0083] FIG23 is an EDS spectrum of the silicon-based composite material prepared in Comparative Example 3;

[0084] FIG24 is a cycle performance curve of the battery assembled in Comparative Example 3 at a current density of 300 mAh / g. DETAILED DESCRIPTION

[0085] The specific implementation method of the present application is further described below with reference to examples. It should be noted that the specific implementation method described here is only for illustrating and explaining the present application and is not intended to limit the scope of protection of the present application.

[0086] Example 1

[0087] Step 1: 100 grams of silicon (Si) ingots (mass purity greater than 99.9%, the same below) and indium (In) powder (greater than 99.9 wt%) were weighed at a molar ratio of 95:5 and placed in a graphite crucible for suspension induction melting under argon protection. The melting power was 15 kW and the melting time was 5 minutes. Upon completion of the melting, an ingot was obtained.

[0088] Step 2: After mechanically crushing the ingot, the powder sample was placed in a quartz tube. This tube was then placed in a vacuum rotary quenching furnace. The furnace chamber was first evacuated, and then argon gas was introduced to a pressure of 0.5 atmospheres for suspension melting. The melting process lasted for 5 minutes. Once the melt was completely melted, it was spray-casted onto a high-speed rotating copper roller through a nozzle with an argon flow at 2.5 atmospheres for rapid cooling. The roller rotated at a linear speed of 40 meters per second and the spraying distance was 2 meters. After cooling, the resulting rapid quenching product was collected and recorded as a Si / 5 at% In (at%, atomic percentage) composite material.

[0089] Step 3: Grind the quenched product using a sand mill. Use anhydrous ethanol as the grinding medium, zirconium oxide grinding beads, and grind at a speed of 1500 rpm for 25 minutes. After drying, the Si-In composite material is obtained.

[0090] FIG1 is a metallographic photograph of the ingot prepared in step 1 of this embodiment. The product consists of a coarse Si phase (dendritic phase in the figure) with a size of 200 to 1000 μm and an In phase between the Si phases.

[0091] Figure 2 shows the scanning electron microscope (SEM) morphology (a) and backscattered scanning electron microscope (BSE, backscattered electron) morphology (b) of the Si / 5at%In composite material prepared in step 2 of this embodiment. Observing (a) in Figure 2, the surface is not dense, which may be due to the low melting point of In and a small amount of volatilization during the rapid quenching process. Observing (b) in Figure 2, the dark phase is the Si phase and the light phase is the In phase. The particle size of the Si phase in the composite material is mainly 30 to 80 nm. The Si phase is surrounded by the In phase, and the In phases are interconnected between the Si phases to form a network structure. The In network structure with high electronic conductivity greatly improves the electronic conductivity of the Si / In composite material.

[0092] It should be noted that due to the high volatility of In, which can damage the instrument, the crystallization of the Si phase particles in the In-containing composite material cannot be further observed using a transmission electron microscope (TEM). Therefore, the size of the nanocrystals in the Si phase particles cannot be determined. However, because the Si phase particles are only 30 to 80 nm in size, the grain size of the constituent particles is smaller than the particle size. In the following examples, the grain size of the Si nanocrystals in the In-containing composite material cannot be characterized. Referring to the grain size of other examples, the Si phase in the In-containing composite material should be composed of nanocrystals of similar size, all smaller than the size of a single Si phase particle.

[0093] Figure 3 (a) shows the X-ray diffraction (XRD) pattern of the silicon-based composite material finally prepared in this example. XRD analysis revealed that the composite material contained only Si (JCPDS27-1402) and In (JCPDS04-0673) phases, with no other phases detected, indicating that Si and In did not form an alloy phase during the preparation process. Figure 3 (b) shows the SEM morphology of the silicon-based composite material finally prepared in this example. The composite material's particle size primarily ranged from 300 nm to 1 μm, with a small amount of particles ranging from 1 to 2 μm. The composite material's particle morphology exhibited typical mechanical crushing morphology.

[0094] The tap density of the silicon-based composite material prepared in this example was tested (using a 5 ml graduated cylinder, a vibration frequency of 250 times / min, an amplitude of 3 cm, and 3000 vibrations), and its tap density was 0.81 g / ml, which was much higher than 0.65 g / ml of the product prepared in Comparative Example 1 and 0.66 g / ml of the product prepared in Comparative Example 2.

[0095] The conductivity test of the silicon-based composite material prepared in this embodiment was carried out using a four-probe tester, and its electronic conductivity was as high as 27.3 Siemens / cm, which is nearly 6 orders of magnitude higher than the electronic conductivity of the silicon-based materials prepared in Comparative Examples 1 and 2. The carrier mobility of the silicon-based composite material prepared in this embodiment was tested using the Hall effect test, which was 1208 square centimeters / (volt-second), which was approximately 1000 times and 600 times higher than the carrier mobility of the silicon-based materials prepared in Comparative Examples 1 and 2, respectively. In addition, the exchange current density of the silicon-based composite material prepared in this embodiment was tested using a symmetrical cell linear potential scanning method to be 3.9 mA / square centimeter, which was more than 3 orders of magnitude higher than the products of Comparative Examples 1 and 2. High electronic conductivity, carrier mobility and exchange current density are extremely beneficial and effective for improving the utilization rate of silicon-based active materials and improving their cycle performance and rate performance.

[0096] Example 2

[0097] The preparation process is basically the same as that of Example 1, except that in step 1, silicon blocks and powdered indium are weighed at a molar ratio of 90:10 to obtain a total of 100 grams of sample.

[0098] The X-ray diffraction (XRD) pattern of the silicon-based composite material finally prepared in this example is also shown in Figure 3 (a). XRD detection shows that the composite material also contains only Si and In phases, and no other phases are detected. Si and In do not form an alloy phase.

[0099] Figure 4 shows the SEM morphology (a), BSE morphology (b), and SEM morphology (c) of the quenched product (denoted as Si / 10at%In composite material) prepared in step 2 of this example. Observing Figure 4 (a), the surface porosity of the quenched product is greater than that of Example 1. Observing Figure 4 (b), the positional state of the Si phase and the metallic In phase is similar to that of Example 1, but the particle size of the Si phase is mainly 30 to 100 nm, slightly larger than that of Example 1. Observing Figure 4 (c), the particle size of the silicon-based composite material is basically between 300 nm and 1 μm, with a small amount of particles sized between 1 and 2 μm. The particle morphology of the composite material is typical of mechanical crushing.

[0100] After testing, the tap density of the silicon-based composite material prepared in this embodiment is 0.79 g / ml, the electronic conductivity is as high as 714.3 Siemens / cm, the carrier mobility and exchange current density are 566.5 square centimeters / (V·s) and 1.701 mA / square centimeter, respectively.

[0101] Example 3

[0102] The preparation process is basically the same as that of Example 2, except that in step 2:

[0103] After suspension smelting, when the melt is completely melted, it is sprayed onto a high-speed rotating copper roller through a nozzle with an argon flow of 1.5 atmospheres for rapid cooling. The linear speed of the copper roller is 25 meters per second and the spraying distance is 2 meters.

[0104] Figure 5 shows the BSE morphology of the quenched product prepared in step 2 of this example. Observation reveals that the positional distribution of the Si and metallic In phases is similar to that in Example 1, but the Si particles are primarily 100 to 300 nm in size, significantly larger than those in the quenched products prepared in Examples 1 and 2, respectively. This is primarily due to the reduced linear velocity of the copper roller and the reduced argon flow in the nozzle.

[0105] After testing, the tap density of the silicon-based composite material prepared in this embodiment is 0.78 g / ml, the electronic conductivity is 701 Siemens / cm, the carrier mobility and exchange current density are 171 square centimeters / (V·s) and 0.65 mA / square centimeter, respectively.

[0106] Performance Testing

[0107] The Si / In composite materials prepared in Examples 1 to 3 were used to prepare negative electrode sheets, and batteries were assembled to test the electrochemical performance of the batteries and electrodes. The process was as follows:

[0108] When preparing the negative electrode of a lithium-ion battery, the undried sand-milled product (Si / In composite material) in step 3 is directly mixed with the conductive agent acetylene black (the amount of the conductive agent added is 20% by weight of the Si / In composite material), and then sand-milled for 5 minutes at a sand mill speed of 500 rpm. After mixing evenly, the mixed slurry is dried and directly used as the negative electrode material.

[0109] The negative electrode material and aqueous sodium alginate binder were mixed uniformly in a mass ratio of 83:17, with a concentration of 3 wt%. The mixed slurry was applied to a copper current collector, dried in an oven, and compacted under a pressure of 12 MPa for 30 seconds to form an electrode sheet. The electrode sheet was then punched into 10 mm diameter discs and assembled into CR2025 button cells using a lithium sheet as the counter electrode to test the electrochemical performance of the electrodes. The cells were assembled in an argon-filled glove box. A Celgard-2400 separator, specifically designed for lithium-ion batteries, was used as the separator. A 1 mol / L electrolyte solution was prepared using LiPF6 as the solute and a 1:1:1 ratio of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) as the solvent. 10 wt% of fluoroethylene carbonate (FEC) was added as an additive. The specific capacity, cycle performance (the cycle performance tests at current densities of 1500 mAh / g and 15,000 mAh / g were first activated three times at current densities of 150 and 300 mAh / g, respectively) and rate performance of the electrode were carried out on an electrochemical tester using a constant current test method. The voltage window was 0.01 to 1.5 V.

[0110] Figure 6 shows the cycle performance curves of lithium-ion batteries assembled with the silicon-based negative electrode materials prepared in Examples 1 to 3 at a current density of 300 mAh / g (a), 1500 mAh / g (b), and 15,000 mAh / g (c), as well as the capacity curves at different current densities (mAh / g) (d).

[0111] As shown in the figure, the battery assembled in Example 1 has an initial reversible capacity of 3660 mAh / g at a current density of 300 mAh / g, an initial coulombic efficiency of 80.4%, and a capacity retention of 3063 mAh / g after 100 cycles, with a capacity retention rate of 83.7%. The initial reversible capacity at a current density of 1500 mAh / g is 2609 mAh / g, and after 500 cycles, the capacity retention is 1686 mAh / g, with a capacity retention rate of 64.6%. The initial reversible capacity at a current density of 15,000 mAh / g is 1467 mAh / g, and after 800 cycles, the capacity retention is 432 mAh / g, with a capacity retention rate of 29.4%. Its specific capacity at different current densities of 150, 300, 750, 1500, 3000, 7500, 15000, 30000, 45000 and 75000 mAh / g are 3852, 3472, 3142, 2794, 2295, 1863, 1304, 855, 523 and 357 mAh / g respectively.

[0112] The battery assembled in Example 2 had an initial reversible capacity of 3253 mAh / g at a current density of 300 mAh / g, an initial coulombic efficiency of 79.6%, and a capacity retention of 2432 mAh / g after 100 cycles, with a capacity retention rate of 74.8%. At a current density of 1500 mAh / g, the initial reversible capacity was 2529 mAh / g, and after 500 cycles, the capacity retention was 1374 mAh / g. When cycling at a current density of 15,000 mAh / g, the initial reversible capacity was 1332 mAh / g, and after 500 cycles, the capacity retention was 269 mAh / g. At current densities of 150, 300, 750, 1500, 3000, 7500, 15000, 30000, 45000 and 75000 mAh / g, the specific capacities are 3335, 3101, 2681, 2349, 1955, 1580, 1090, 693, 324 and 211 mAh / g, respectively, achieving excellent comprehensive electrochemical performance.

[0113] The electrochemical performance of the battery assembled in Example 3 is significantly lower than that in Examples 1 and 2.

[0114] Comparing the performance data of Examples 1 and 2, it can be found that increasing the In content increases the electronic conductivity of the composite material, which is beneficial to improving the electrochemical performance of the composite negative electrode material. However, the excessive introduction of In hinders carrier transport, resulting in a decrease in carrier mobility. Furthermore, the increased particle size of the Si phase is also detrimental to the electrochemical performance of the material.

[0115] By comparing the performance data of Example 2 and Example 3, it can be found that the electrochemical performance of the battery assembled in Example 3 is lower than that of Example 2, mainly because the Si phase particles formed in Example 3 are larger in size, and its carrier mobility and exchange current density are also lower than those in Example 2.

[0116] Example 4

[0117] Step 1: 100 grams of silicon (Si) ingots (purity greater than 99.9%) and tin (Sn) particles (purity greater than 99.9%) were weighed at a molar ratio of 97:3 and placed in a graphite crucible for suspension induction melting under argon protection. The melting power was 15 kW and the melting time was 5 minutes. Upon completion of the melting, an ingot was obtained.

[0118] Step 2: After mechanically crushing the ingot, the powder sample was placed in a quartz tube. This tube was then placed in a vacuum rotary quenching furnace. The furnace chamber was first evacuated, then argon was introduced to a pressure of 0.6 atmospheres for suspension melting. The melting process lasted for 5 minutes. Once the melt was completely melted, it was sprayed onto a high-speed rotating copper roller through a nozzle flowing argon at 1.7 atmospheres for rapid cooling. The roller rotated at a linear speed of 30 meters per second and the spraying distance was 2 meters. After cooling, the resulting rapid quenching product was collected and designated as the Si / 3 at% Sn composite.

[0119] Step 3: Grind the quenched product using a sand mill. Use anhydrous ethanol as the grinding medium, zirconium oxide grinding beads, and grind at a speed of 1200 rpm for 30 minutes. After drying, the Si-Sn composite material is obtained.

[0120] Figure 7 shows the SEM morphology (a) and TEM morphology (b) of the silicon-based composite material finally prepared in this embodiment. In Figure 7 (a), the particle size of the silicon-based composite material is between 300nm and 1μm, and a small part is slightly larger than 1μm. In the silicon-based composite material, the size of the Si phase particles is relatively uniform, ranging from 200 to 300nm. In Figure 7 (b), the white dotted line is within the Si nanocrystals. It can be seen that the Si phase particles are assembled from Si nanocrystals, and the size of the Si nanocrystals is 20 to 30nm. No Sn phase was observed in TEM, mainly because the amount of Sn is small and the melting point is low. Under the action of the high-energy electron beam during TEM observation, the Sn is basically melted and evaporated.

[0121] The test results show that the tap density of the silicon-based composite material prepared in this embodiment is 0.98 g / ml and the electronic conductivity is 8.3×10 -3 Siemens / cm, the carrier mobility and exchange current density are 378 square centimeters / (volt-second) and 43.6 mA / square centimeter, respectively.

[0122] Example 5

[0123] The preparation process is basically the same as that of Example 1, except that in step 1, silicon blocks and tin particles are used as raw materials, and a total of 100 grams of sample is weighed at a molar ratio of 95:5.

[0124] SEM analysis revealed that the particle size of the silicon-based composite material prepared in this example primarily ranged from 400 nm to 1 μm, with a small portion ranging from 1 to 2 μm, comparable to that of Example 4. The composite material exhibited a typical mechanically crushed morphology. The Si phase particles in the silicon-based composite material were also relatively uniform, ranging from 60 to 150 nm.

[0125] Figure 8 shows the TEM morphology of the silicon-based composite material prepared in this example. The Si phase particles are composed of Si nanocrystals with a size of 5 to 10 nm, or they may contain a small amount of amorphous particles. No Sn phase was observed in the TEM. Compared to Example 4, the size of the Si nanocrystals in the final product prepared in this example was significantly reduced. This is likely due to the increased linear speed of the copper roller and the increased pressure of the argon gas flow in the nozzle transporting the melt, which further refined the size of the nanocrystals in the Si phase particles.

[0126] Testing showed that the silicon-based composite material prepared in this example had a tap density of 1.00 g / ml. This high tap density is beneficial for improving the volumetric capacity density of electrodes and batteries. The electronic conductivity was 0.249 siemens / cm, and the carrier mobility and exchange current density reached 9850 cm² / (V·s) and 85.3 mA / cm², respectively.

[0127] Example 6

[0128] The preparation process is basically the same as that of Example 1, except that in step 1, silicon blocks and tin particles are used as raw materials, and a total of 100 grams of sample is weighed at a molar ratio of 93:7.

[0129] Figure 9 shows the SEM morphology (a) of the quenched product (Si / 7at% Sn composite material) prepared in step 2 of this embodiment and the TEM morphology (b) of the final silicon-based composite material. In Figure 9 (a), the dark phase is the Si phase, and the light phase with a network structure is the Sn phase. It can be seen that the particles of the Si phase are uniform in size, mainly ranging from 80 to 200 nm. Figure 9 (b) shows that the Si phase particles are composed of a large number of Si nanocrystals with a size of 6 to 15 nm, or contain a small amount of amorphous silicon. The particle size of the silicon-based composite material prepared in this embodiment is mainly between 400 nm and 1 μm, with a small portion ranging from 1 to 2 μm.

[0130] After testing, the silicon-based composite material prepared in this embodiment has a tap density of 1.06 g / ml, an electronic conductivity of 1.3 Siemens / cm, a carrier mobility of 4870 cm2 / (V·s) and an exchange current density of 66.5 mA / cm2, respectively.

[0131] Example 7

[0132] Step 1: 100 grams of silicon (Si) ingots (purity greater than 99.9%) and tin (Sn) particles (purity greater than 99.9%) were weighed in a 90:10 molar ratio and placed in a graphite crucible for suspension induction melting under argon protection. The melting power was 15 kW for 5 minutes. Upon completion of the melting, an ingot was obtained.

[0133] Step 2: After mechanically crushing the ingot, the powder sample was placed in a quartz tube. This tube was then placed in a vacuum rotary quenching furnace. The furnace chamber was first evacuated, then argon was introduced to a pressure of 0.4 atmospheres for suspension melting. The melting process lasted for 5 minutes. Once the melt was completely melted, it was sprayed onto a high-speed rotating copper roller through a nozzle flowing argon at 1.5 atmospheres for rapid cooling. The roller rotated at a linear speed of 30 meters per second and the spraying distance was 1 meter. After cooling, the resulting rapid quenching product was collected and designated as the Si / 10 at% Sn composite.

[0134] Step 3: Grind the quenched product using a sand mill. Use anhydrous ethanol as the grinding medium, zirconium oxide grinding beads, and grind at a speed of 1000 rpm for 50 minutes. After drying, the Si-Sn composite material is obtained.

[0135] Figure 10 shows the SEM (a) and TEM (b) images of the silicon-based composite material prepared in this example. As shown in Figure 10 (a), the composite material's particle size ranges from 400 nm to 1.5 μm, with a small portion ranging from 1 to 2 μm. The Si phase particles are larger, ranging from 200 to 300 nm.

[0136] As can be seen from Figure 10(b), the size of the Si nanoparticles in the Si phase particles is between 10 and 18 nm. Compared to Example 5, the increase in the Si nanoparticles in the Si phase particles is mainly due to the reduction in the linear velocity of the copper roller and the reduction in the argon gas flow pressure in the nozzle. In addition, the increase in Sn content also leads to the increase in the Si nanoparticles in the Si phase particles. This may be because the increase in Sn content releases more heat during the solidification process of the Sn phase, leading to the growth of the Si nanoparticles.

[0137] After testing, the tap density of the silicon-based composite material prepared in this embodiment is 1.21 g / ml, the electronic conductivity is 41.1 Siemens / cm, the carrier mobility and exchange current density are 521 square centimeters / (V·s) and 35.8 mA / square centimeter, respectively.

[0138] FIG11 shows the XRD patterns of the silicon-based composite materials prepared in Examples 4 to 7. It is found that the different silicon-based composite materials prepared in each example contain only Si (JCPDS 27-1402) and Sn (JCPDS-04-0673) phases.

[0139] Performance Testing

[0140] The silicon-based composite materials prepared in Examples 4 to 7 were assembled into lithium-ion batteries using exactly the same means as in Example 1. FIG12 shows the cycle performance curves of the assembled lithium-ion batteries at a current density of 300 mAh / g (a), 1500 mAh / g (b), and 15,000 mAh / g (c), as well as the capacity curves at different current densities (mAh / g) (d).

[0141] After testing, the battery assembled in Example 4 had an initial reversible capacity of 4001 mAh / g at a current density of 300 mAh / g, an initial coulombic efficiency of 81.3%, and a capacity retention of 3337 mAh / g after 100 cycles, with a capacity retention rate of 83.4%. At a current density of 1500 mAh / g, the initial reversible capacity was 2441 mAh / g, and after 500 cycles, the capacity retained was 1879 mAh / g, with a capacity retention rate of 77.0%. At a current density of 15,000 mAh / g, the initial reversible capacity was 1766 mAh / g, and after 1500 cycles, the capacity retained was 950 mAh / g. At current densities of 150, 300, 750, 1500, 3000, 7500, 15000, 30000, 45000, and 75000 mAh / g, the specific capacities were 4329, 3989, 3448, 2710, 2228, 2007, 1697, 1426, 1180, and 563 mAh / g, respectively. This indicates that the silicon-based composite material prepared in this example has excellent electrochemical properties.

[0142] The battery assembled in Example 5 had an initial reversible capacity of 4028 mAh / g at a current density of 300 mAh / g, an initial coulombic efficiency of 82.5%, and a capacity retention of 3578 mAh / g after 100 cycles, with a capacity retention rate of 88.8%. At a current density of 1500 mAh / g, the initial reversible capacity was 2501 mAh / g, and after 500 cycles, the capacity retention was 2059 mAh / g, with a capacity retention rate of 82.3%. At a current density of 15,000 mAh / g, the initial reversible capacity was 2440 mAh / g, and after 1500 cycles, the capacity retention was 1142 mAh / g, with a capacity retention rate of 47%. The specific capacities at current densities of 150, 300, 750, 1500, 3000, 7500, 15000, 30000, 45000 and 75000 mAh / g are 4224, 4002, 3695, 3459, 3156, 2892, 2431, 2072, 1689 and 1254 mAh / g, respectively, demonstrating excellent electrochemical performance.

[0143] The battery assembled in Example 6 had an initial reversible capacity of 3811 mAh / g at a current density of 300 mAh / g, an initial coulombic efficiency of 81.4%, and a capacity retention of 3173 mAh / g after 100 cycles, with a capacity retention rate of 83.2%. At a current density of 1500 mAh / g, the initial reversible capacity was 2521 mAh / g, and after 500 cycles, the capacity retention was 2021 mAh / g, with a capacity retention rate of 80.2%. At a current density of 15,000 mAh / g, the initial reversible capacity was 2187 mAh / g, and after 1500 cycles, the capacity retention was 995 mAh / g, with a capacity retention rate of 45.5%. The composite material exhibits excellent comprehensive electrochemical performance at current densities of 150, 300, 750, 1500, 3000, 7500, 15000, 30000, 45000, and 75000 mAh / g, with specific capacities of 4010, 3876, 3662, 3412, 3039, 2763, 2280, 1882, 1502, and 930 mAh / g, respectively.

[0144] The electrochemical performance of the assembled battery of Example 7 is generally worse than that of Examples 4-6.

[0145] Example 8

[0146] The preparation process is basically the same as that of Example 1, except that in step 1, silicon blocks and silver (Ag) particles with a purity greater than 99.9% are used as raw materials, and a total of 100 grams of sample is weighed at a molar ratio of 95:5.

[0147] The test results show that the electronic conductivity of the composite material finally prepared in this embodiment is 4.3×10-2 Siemens / cm is more than five times lower than that of the silicon-based composite material with the same Sn mole fraction (Example 5). However, the conductivity of the Ag element is almost an order of magnitude higher than that of the Sn element. This is probably because, although Ag has a lower melting point than Si, its melting point of 961°C is approximately 453°C lower than that of Si. Compared with Sn (melting point of 232°C, 1182°C lower than that of Si), the temperature difference with Si is significantly smaller.

[0148] This may cause some Ag to solidify almost simultaneously with Si during the rapid quenching and solidification process, forming a particle distribution with the Si phase, failing to fully form a network structure and exert its conductive network structure and coating of Si particles, thereby weakening the effect of improving the electrochemical properties of Si-based materials.

[0149] Example 9

[0150] The preparation process is basically the same as that of Example 5, with the only difference being that in step 1, Si blocks, Sn particles and In powder are used as raw materials, and a total of 100 g of sample is weighed at a molar ratio of 92:5:3.

[0151] According to morphological characterization, the particle size of the silicon-based composite material prepared in this embodiment is 300 nm to 1 μm, and the particle size of the Si phase is 80 to 150 nm.

[0152] FIG13 is an XRD pattern of the silicon-based composite material prepared in this embodiment. After testing, the silicon-based composite material contains Si, In 0.2 Sn 0.8 (JCPDS48-1547) and In3Sn(JCPDS07-0345) phases. Although Sn reacts with In to form a compound, its melting point is lower than that of Sn. Therefore, during the rapid cooling process of the strip, In 0.2 Sn 0.8 The In3Sn phase solidifies later than Si and exists between Si particles after cooling.

[0153] According to tests, the tap density of the silicon-based composite material prepared in this embodiment is 0.91 g / ml, the electronic conductivity is 108 Siemens / cm, the carrier mobility and exchange current density are 1010 square centimeters / (V·s) and 5.922 mA / square centimeter, respectively.

[0154] Performance Testing

[0155] The silicon-based composite material prepared in Example 9 was assembled into a lithium-ion battery using exactly the same means as in Example 1. FIG14 shows the cycle performance curves of the assembled battery at a current density of 300 mAh / g (a), 1500 mAh / g (b), and 15,000 mAh / g (c), as well as the capacity curves at different current densities (mAh / g) (d).

[0156] Testing revealed that the battery assembled in Example 9 had an initial reversible capacity of 3395 mAh / g at a current density of 300 mAh / g, an initial coulombic efficiency of 81.7%, and a capacity retention of 2910 mAh / g after 100 cycles, with a capacity retention rate of 85.7%. At a current density of 1500 mAh / g, the initial reversible capacity was 2489 mAh / g, and after 500 cycles, the capacity retention was 1983 mAh / g, with a capacity retention rate of 79.7%. At a current density of 15,000 mAh / g, the initial reversible capacity was 1399 mAh / g, and after 1500 cycles, the capacity retention was 632 mAh / g. At current densities of 150, 300, 750, 1500, 3000, 7500, 15000, 30000, 45000, and 75000 mAh / g, the specific capacities were 3581, 3374, 3033, 2714, 2288, 1851, 1296, 902, 375, and 120 mAh / g, respectively. The composite negative electrode material of this embodiment exhibits excellent electrochemical performance.

[0157] Example 10

[0158] The preparation process is basically the same as that of Example 1, except that in step 1, silicon blocks, powdered germanium (Ge, purity not less than 99.9%) and tin particles are used as raw materials, and a total of 100 grams of sample is weighed at a molar ratio of 92:3:5.

[0159] Example 11

[0160] The preparation process is basically the same as that of Example 1, except that in step 1, silicon blocks, powdered germanium (Ge, purity not less than 99.9%) and tin particles are used as raw materials, and a total of 100 grams of sample is weighed at a molar ratio of 90:5:5.

[0161] Example 12

[0162] The preparation process is basically the same as that of Example 1, except that in step 1, silicon blocks, powdered germanium (Ge, purity not less than 99.9%) and tin particles are used as raw materials, and a total of 100 grams of sample is weighed at a molar ratio of 88:7:5.

[0163] Example 13

[0164] The preparation process is basically the same as that of Example 1, except that in step 1, silicon blocks, powdered germanium (Ge, purity not less than 99.9%) and tin particles are used as raw materials, and a total of 100 grams of sample is weighed at a molar ratio of 85:10:5.

[0165] Figure 15 shows the SEM morphologies of the quenched products prepared in step 2 of Example 11(a) and Example 13(b), respectively. As can be seen, after quenching, the surfaces of the products are relatively uniform and dense, with no apparent grain coarsening or grain boundary precipitation. The particle size of the Si-Ge composite phase in the quenched products is 60-120 nm in Example 11 and 100-200 nm in Example 13.

[0166] Figure 16 shows the XRD patterns of the final products prepared in Examples 10-13. XRD analysis shows that the products are primarily composed of Si, Sn, and a small amount of Ge (JCPDS04-0545). Because the Ge diffraction peak is very close to the main Si peak, it is easily obscured by the Si phase at low Ge content. At Ge additions of 7 and 10 mol%, a faint Ge diffraction peak is visible at 27.5°. Although Si and Ge form an infinite solid solution in thermodynamic equilibrium, the rapid cooling rate during quenching, the difference in melting points between Ge and Si, and the increased Ge content may cause a large difference between the Si-Ge liquidus and solidus, preventing Ge from dissolving with Si in time. Consequently, a small amount of elemental Ge precipitates. However, at lower Ge content, Ge dissolves relatively readily. XRD analysis shows that, in this example, the Si diffraction peak shifts to smaller angles with increasing Ge addition in the composite material, indicating that some Ge forms a solid solution with Si. The magnified image of the Si (422) diffraction peak in Figure 16 clearly shows a leftward shift in the peak position, indicating an increase in interplanar spacing. Furthermore, the greater the amount of Ge added, the greater the peak shift, indicating greater Ge solid solution. After the Si-Ge solid solution forms, the lattice constant of Si increases due to the Ge solid solution, facilitating the deintercalation and insertion of lithium ions, thereby improving its kinetic properties.

[0167] Figure 17 shows the SEM morphology (a) and TEM morphology (b) of the silicon-based composite material prepared in Example 11, as well as the TEM morphology (c) of the silicon-based composite material prepared in Example 13. It can be seen that the Si-Ge composite phase is composed of Si-Ge solid solution nanocrystals and a small amount of Ge nanocrystals. In the silicon-based composite material prepared in Example 11, the grain size of the Si-Ge solid solution nanocrystals and Ge in the Si-Ge composite phase is 3-5 nm. In contrast, in the silicon-based composite material prepared in Example 13, the grain size of the Si-Ge solid solution nanocrystals and Ge in the Si-Ge composite phase is 5-10 nm. The relatively low Ge content in the silicon-based composite material facilitates the reduction of the nanocrystal size in the Si-Ge composite phase. It is worth noting that due to its very low melting point, Sn melts under irradiation with a high-energy electron beam, forming the obvious droplets in Figure (b), making it difficult to directly observe in the TEM. Furthermore, the segregation of the Si-Ge solid solution phase causes localized Ge segregation at the microscopic level, forming a small amount of Ge nanocrystals. Although Ge does not fully dissolve in Si, which does not fully play its role in increasing the Si interplanar spacing and thus promoting the insertion and extraction of lithium ions, its relatively high electronic conductivity and ion diffusion capacity compared to Si still provide beneficial effects on the electrochemical properties of Si.

[0168] Tests show that the tap density of the silicon-based composite materials prepared in Examples 10 to 13 ranges from 0.87 to 0.9 g / ml, with the greater the amount of Ge added, the higher the tap density. A high tap density is beneficial for improving the volumetric capacity density of electrodes and batteries.

[0169] According to tests, the electronic conductivity of each silicon-based composite material prepared in Examples 10 to 13 is 2.5 to 3.9 Siemens / cm, which is nearly 5 orders of magnitude higher than that of the products prepared in Comparative Examples 1 and 2.

[0170] The carrier mobility and exchange current density of the silicon-based composite materials prepared in Examples 10 to 13 are 6970, 18900, 14300, and 8680 square centimeters / (volt-second) and 60.53, 79.43, 65.46, and 45.71 milliamperes / square centimeter, respectively, which are significantly higher than the corresponding values ​​of Comparative Examples 1 and 2, and are beneficial to improving the comprehensive electrochemical properties of the composite materials.

[0171] Performance Testing

[0172] The silicon-based composite materials prepared in Examples 10 to 13 were assembled into lithium-ion batteries using exactly the same means as in Example 1. FIG18 shows the cycle performance curves of the assembled batteries at a current density of 300 mAh / g (a), 1500 mAh / g (b), and 15,000 mAh / g (c), as well as the capacity curves at different current densities (mAh / g).

[0173] As shown in the figure, the Si-Ge / 5at% Sn composite material with a Ge addition of 5at% (Example 11) has the best comprehensive electrochemical performance. At a current density of 300 mAh / g, its initial reversible capacity is 3953 mAh / g, its initial coulombic efficiency is 81.4%, and its capacity after 100 cycles is 3343 mAh / g, with a capacity retention rate of 84.5%. At a current density of 1500 mAh / g, its initial discharge capacity is 3222 mAh / g, and its capacity after 500 cycles is 2244 mAh / g, with a capacity retention rate of 69.6%. At a current density of 15000 mAh / g, its initial discharge capacity is 1692 mAh / g, and after 1500 cycles, it maintains a capacity of 1145 mAh / g, with a capacity retention rate of 67.7%. In terms of capacity retention alone, the silicon-based composite material prepared with a Si:Ge:Sn molar ratio of 88:7:5 (Example 12) retained a capacity of 980 mAh / g after 1500 cycles, with a capacity retention rate of 72.6%, which is higher than all previous examples. However, its capacity is slightly lower than that of the silicon-based composite material prepared in Example 11.

[0174] The silicon-based composite material prepared in Example 11 has a reversible specific capacity of 4167, 3982, 3697, 3358, 2863, 2556, 2238, 2009, 1706 and 1225 mAh / g at current densities of 150, 300, 750, 1500, 3000, 7500, 15000, 30000, 45000 and 75000 mAh / g, respectively. The introduction of Ge significantly improves the electronic conductivity and lithium ion mobility of the composite material. The carrier mobility of the silicon-based composite material prepared in Example 11 is as high as 18900 square centimeters / (volt-second), which plays an important role in the excellent cycle performance of the material of this embodiment, especially the cycle performance at high rate.

[0175] Comparative Example 1

[0176] The preparation process is basically the same as that of Example 1, except that in step 1, only 100 g of silicon block is used as the raw material sample and is placed in a graphite crucible.

[0177] Comparative Example 2

[0178] The preparation process is basically the same as that of Comparative Example 1, except that the rapid quenching step in step 2 is not performed, that is, the ingot is directly crushed and then sand-milled.

[0179] Figure 19 shows the SEM morphologies of the final products prepared in Comparative Example 1(a) and Comparative Example 2(b), respectively. In Figure 19(a), the particle size of the product ranges from several hundred nm to 1 μm, with a small portion being 1 to 2 μm; in Figure 19(b), the particle size of the product ranges from submicron to micron order, with a small portion being 1 to 2 μm.

[0180] XRD analysis showed that the products prepared in Comparative Example 1 and Comparative Example 2 contained only Si phase. The diffraction peak intensity of Si in Comparative Example 2 was higher than that in Comparative Example 1, which was because the rapid quenching process reduced the crystallinity of the material.

[0181] The test results show that the tap density of the product prepared in Comparative Example 1 is 0.66 g / ml and the electronic conductivity is 9.3×10 -5 Siemens / cm, the carrier mobility and exchange current density are 2.1 square centimeters / (volt·second) and 3.3×10 -3 mA / cm².

[0182] The tap density of the product prepared in Comparative Example 2 was 0.65 g / ml and the electronic conductivity was 6.7×10 -5 Siemens / cm, the carrier mobility and exchange current density are 1.24 square cm / (V·s) and 8.2×10 -4 mA / cm².

[0183] Performance Testing

[0184] The products prepared in Comparative Examples 1 to 2 were assembled into lithium-ion batteries using exactly the same means as in Example 1. Figure 20 shows the cycle performance curves of the assembled batteries at a current density of 300 mAh / g (a), 1500 mAh / g (b), and 15,000 mAh / g (c), as well as the capacity curves at different current densities (mAh / g) (d).

[0185] After testing, the battery assembled in Comparative Example 1 had an initial reversible capacity of 3631 mAh / g at a current density of 300 mAh / g, an initial coulombic efficiency of 77.9%, and a capacity retention of 986 mAh / g after 100 cycles, with a capacity retention rate of 27.2%. At a current density of 1500 mAh / g, the initial reversible capacity was 2454 mAh / g, and after 500 cycles, the capacity retained 330 mAh / g, with a capacity retention rate of 13.4%. At a current density of 15,000 mAh / g, the initial reversible capacity was 646 mAh / g, and after 800 cycles, the capacity retained 61 mAh / g. At current densities of 150, 300, 750, 1500, 3000, 7500, 15000, 30000, 45000, and 75000 mAh / g, the specific capacities were 3906, 2671, 1930, 1457, 971, 503, 185, 42, 21, and 15 mAh / g, respectively. In the late stage of high-current discharge, the negative electrode material obtained in this comparative example completely lost its electrochemical activity.

[0186] The battery assembled in Comparative Example 2 had an initial reversible capacity of 3765 mAh / g at a current density of 300 mAh / g, an initial coulombic efficiency of 80.0%, and a capacity retention of 109 mAh / g after 100 cycles, with a capacity retention rate of 2.9%. At a current density of 1500 mAh / g, the initial reversible capacity was 2631 mAh / g, and after 500 cycles, the capacity retention was 47 mAh / g, with a capacity retention rate of 1.8%. At a current density of 15,000 mAh / g, the initial reversible capacity was 458 mAh / g, and after 800 cycles, the capacity retention was 45 mAh / g. At current densities of 150, 300, 750, 1500, 3000, 7500, 15000, 30000, 45000, and 75000 mAh / g, the specific capacities were 3613, 2483, 1694, 1123, 668, 243, 85, 34, 14, and 9 mAh / g, respectively. The electrochemical performance of the negative electrode material obtained in this comparative example was significantly lower than that of comparative example 1, and it quickly lost its electrochemical activity as the cycle progressed.

[0187] Comparative Example 3

[0188] The preparation process is basically the same as that of Example 6, with the only difference being that in step 1, silicon blocks with a purity greater than 99.9% and powdered chromium (Cr, melting point 1907°C) are used as raw materials, and a total of 100 g of sample is weighed at a molar ratio of 93:7.

[0189] The electronic conductivity of the silicon-based composite material prepared in this comparative example was tested to be 0.25 Siemens / cm, which is significantly lower than that of other examples of the present application with the same molar fraction of Si added.

[0190] The silicon-based composite material finally prepared in this comparative example was subjected to XRD analysis. As shown in FIG21 , a CrSi2 phase (JCPDS35-0781) was formed in the final product, and the rest was Si phase.

[0191] The quenched product prepared in step 2 was observed and analyzed using backscattered scanning electron microscopy and energy dispersive spectroscopy (EDS). In the BSE morphology image in Figure 22, the light-colored particle phase is the CrSi2 phase, and the dark-colored matrix phase is the Si phase. CrSi2 precipitates in the Si matrix in granular form, with the CrSi2 particles ranging in size from 200 to 500 nm. As shown in the EDS spectrum in Figure 23, both the melting point of Cr (1907°C) and the melting point of the formed CrSi2 phase (slightly above 1500°C, as determined from the Cr-Si phase diagram) are higher than the melting point of Si. Therefore, during the quenching process, the CrSi2 phase solidifies first, and the later-solidified Si phase exists between the CrSi2 particles, preventing the formation of a conductive network of Cr or CrSi2.

[0192] Performance Testing

[0193] Using the same methods as in Example 1, the silicon-based composite material prepared in Comparative Example 3 was assembled into a lithium-ion battery. Figure 24 shows the cycling performance curve of the assembled battery at a current density of 300 mAh / g. Testing shows that the capacity of the battery assembled in this comparative example rapidly decays during cycling. This indicates that isolated CrSi2 does not improve the cycling performance of the composite material.

[0194] The above description is only a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. The above application uses specific examples to illustrate the present application, which is only used to help understand the present application and is not intended to limit the present application. Those skilled in the art of the present application can also make several simple deductions, deformations, substitutions or combinations based on the concept of the present application. These deductions, deformations, substitutions or combinations also fall within the scope of the claims of the present application.

Claims

1. A silicon-based composite material composed of a silicon-based phase and a metal phase, characterized in that: The silicon-based phase is assembled from silicon-based nanocrystals, the outer surface of the silicon-based phase is coated with a metal phase, and the metal phases are interconnected to form a body-shaped network structure; The silicon-based phase includes a single silicon phase or a Si-Ge composite phase; When the silicon-based phase is selected from a single silicon phase, the silicon-based nanocrystal particles are selected from silicon nanocrystal particles; When the silicon-based phase is selected from a Si-Ge composite phase, the silicon-based nanocrystal particles are selected from Si-Ge nanocrystal particles; The melting point of the metal phase is lower than the melting point of the silicon-based phase.

2. The silicon-based composite material of a silicon-based phase and a metal phase according to claim 1, characterized in that: The size of the silicon-based nanocrystal particles is 2 to 200 nm; The size of the silicon-based phase is 10 to 1000 nm; The size of the silicon-based composite material is 200nm-5μm.

3. The silicon-based composite material of a silicon-based phase and a metal phase according to claim 1, characterized in that: The metal in the metal phase is selected from one or more of Sn, In, Al, Pb, Zn, Sb, Bi, Se, and Ag.

4. The silicon-based composite material of a silicon-based phase and a metal phase according to claim 1, characterized in that: The metal in the metal phase is selected from Sn and / or In.

5. The silicon-based composite material of a silicon-based phase and a metal phase according to claim 1, characterized in that: The metal in the metal phase is selected from Sn.

6. The silicon-based composite material of a silicon-based phase and a metal phase according to claim 1, characterized in that: The temperature difference ΔT between the melting point of the silicon-based phase and the melting point of the metal phase is ≥500°C.

7. The silicon-based composite material of a silicon-based phase and a metal phase according to claim 1, characterized in that: The size of the silicon-based nanocrystal particles is 2 to 50 nm; The size of the silicon-based phase is 10 to 800 nm; The size of the silicon-based composite material is 300nm-3μm.

8. The silicon-based composite material of a silicon-based phase and a metal phase according to claim 1, characterized in that: The size of the silicon-based nanocrystal particles is 2 to 30 nm; The size of the silicon-based phase is 30 to 300 nm; The size of the silicon-based composite material is 300nm-1.5μm.

9. A method for preparing a silicon-based composite material of a silicon-based phase and a metal phase as claimed in any one of claims 1 to 8, characterized in that: The steps include: Step 1: Evenly mix the silicon-based raw material and the metal raw material, and perform suspension induction melting in an argon atmosphere to obtain a silicon-based composite material ingot; The silicon-based raw material is selected from Si, or a mixture of Si and Ge; Step 2: crushing the silicon-based composite material ingot into powder and placing it in a vacuum rotary quenching furnace for suspension smelting under an argon atmosphere, transmitting the obtained melt through a nozzle carrying an argon gas flow, and spray-casting it on a high-speed rotating copper roller, and collecting it after cooling to obtain a rapid quenching product; Step 3: sand-milling the rapid quenching product to obtain the silicon-based composite material composed of the silicon-based phase and the metal phase.

10. The method for preparing a silicon-based composite material of a silicon-based phase and a metal phase according to claim 9, characterized in that: The metal raw material is selected from one or more of Sn, In, Al, Pb, Zn, Sb, Bi, Se, and Ag.

11. The method for preparing a silicon-based composite material of a silicon-based phase and a metal phase according to claim 9 or 10, characterized in that: In step 1: The molar ratio of the silicon-based raw material to the metal raw material is 1:(0.01-0.3); When the silicon-based raw material is selected from a mixture of Si and Ge, the molar ratio of Si to Ge is 1:(0.01-0.5).

12. The method for preparing a silicon-based composite material of a silicon-based phase and a metal phase according to claim 9 or 10, characterized in that: In step 1: The molar ratio of the silicon-based raw material to the metal raw material is 1:(0.03-0.11).

13. The method for preparing a silicon-based composite material of a silicon-based phase and a metal phase according to claim 9 or 10, characterized in that: In step 1: The molar ratio of the silicon-based raw material to the metal raw material is 1:(0.03-0.08).

14. The method for preparing a silicon-based composite material of a silicon-based phase and a metal phase according to claim 9 or 10, characterized in that: In step 1: The molar ratio of the silicon-based raw material to the metal raw material is 1:0.

05.

15. The method for preparing a silicon-based composite material of a silicon-based phase and a metal phase according to claim 9, characterized in that: In step 1: When the silicon-based raw material is selected from a mixture of Si and Ge, the molar ratio of Si to Ge is 1:(0.03-0.12).

16. The method for preparing a silicon-based composite material of a silicon-based phase and a metal phase according to claim 9, characterized in that: In step 1: When the silicon-based raw material is selected from a mixture of Si and Ge, the molar ratio of Si to Ge is 1:(0.03-0.08).

17. The method for preparing a silicon-based composite material of a silicon-based phase and a metal phase according to claim 9, characterized in that: In step 1: When the silicon-based raw material is selected from a mixture of Si and Ge, the molar ratio of Si to Ge is 1:(0.05-0.06).

18. The method for preparing a silicon-based composite material of a silicon-based phase and a metal phase according to claim 9, characterized in that: In step 2: The pressure of the argon gas flow is 0.4 to 4.0 atmospheres; The rotation linear speed of the copper roller is 10-100 m / s.

19. The method for preparing a silicon-based composite material of a silicon-based phase and a metal phase according to claim 9 or 18, characterized in that: In step 2: the distance of the spray casting is 0.5 to 2.5 m.

20. The method for preparing a silicon-based composite material of a silicon-based phase and a metal phase according to claim 9, characterized in that: In step 2: The pressure of the argon gas flow is 1.5 to 3.0 atmospheres; The rotational linear speed of the copper roller is 25-60 m / s.

21. The method for preparing a silicon-based composite material of a silicon-based phase and a metal phase according to claim 9, characterized in that: In step 2: The pressure of the argon gas flow is 1.7 to 2.5 atmospheres; The rotational linear speed of the copper roller is 30-40 m / s.

22. Use of the silicon-based composite material of a silicon-based phase and a metal phase as claimed in any one of claims 1 to 8 in preparing a negative electrode for a lithium-ion battery.

23. Use of the silicon-based composite material of a silicon-based phase and a metal phase as claimed in any one of claims 1 to 8 in the preparation of a lithium-ion battery.

24. A lithium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and an electrolyte; the active material of the negative electrode comprises the silicon-based composite material of a silicon-based phase and a metal phase as claimed in any one of claims 1 to 8.

25. The lithium ion battery according to claim 22, characterized in that The positive electrode is LiFePO4, LiCoO2 or a ternary material.

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