A method for preparing a metal-coated nanosilicon material for lithium-ion batteries

Abstract

The application relates to the technical field of lithium ion battery negative electrode materials, and particularly discloses a preparation method of metal-coated nanometer silicon material for lithium ion batteries. After silicon powder is mixed with metal A, the Si is changed into an alloy phase of the Si and metal M and the A is changed into an alloy phase of the A and metal Na by cathode potential polarization in a molten salt medium containing MX and NaX, and then the metal M and Na are dissolved out by anode oxidation, and the metal-coated nanometer silicon material with liquid metal A coated on the surface of the silicon is generated. The method is environment-friendly, simple in process, low in cost, and the prepared metal-coated nanometer silicon material has high capacity, good rate and cycle stability when applied to lithium ion batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, specifically to a method for preparing metal-coated nano-silicon materials for lithium-ion batteries. Background Technology

[0002] Silicon has a theoretical capacity of up to 4200mAh g. -1 Silicon has a volume expansion rate 10 times that of currently available commercial graphite electrodes, making it one of the most promising anode materials for next-generation lithium-ion batteries. However, silicon as an anode material in lithium-ion batteries suffers from severe volume expansion, affecting the electrochemical performance of lithium-ion batteries and seriously hindering its application.

[0003] Currently, strategies to mitigate the volume expansion effect of silicon include: firstly, reducing the size of silicon to prepare nano-silicon, designing 0D nano-silicon spheres, 1D nano-silicon rods, 2D nano-silicon wafers, etc., to change the morphology of silicon and reduce its size in one or more dimensions; then, combining silicon with buffer materials, including designing structures such as coating, doping, and mixing, to alleviate the volume expansion of silicon. Combining with antimony, tin, or bismuth can contribute to the capacity and also potentially alter the interfacial properties of silicon. However, these methods generally involve preparing nano-silicon in solid-solid composites, which is costly and difficult to form a complete coating structure.

[0004] Micron-sized silicon is widely available and inexpensive. By mixing industrial micron-sized silicon with some low-melting-point metals, and then combining this mixture with molten salt electrolysis above the melting point of these metals to generate liquid metal and nano-silicon, liquid-solid coating is completed to transform it into metal-coated nano-silicon material. This method is expected to produce high-performance silicon-based lithium-ion battery anode materials at low cost. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a novel and efficient method for preparing metal-coated nano-silicon materials, which can effectively alleviate the volume expansion problem of silicon during charging and discharging.

[0006] The technical solution provided by the present invention to achieve the above objectives is as follows:

[0007] A method for preparing metal-coated silicon nanomaterials for lithium-ion batteries, the specific steps of which are as follows:

[0008] (1) Mix silicon powder with metal A or a compound of metal A evenly to obtain a mixture;

[0009] (2) Using the mixture obtained in (1) as the working electrode, and metal M element or alloy or graphite as the counter electrode, cathodic polarization is carried out in a molten salt medium containing metal halide MX and Na halide. The cathodic polarization voltage is less than the voltage for forming the MSi alloy. Under an inert atmosphere, at a temperature of 300℃~800℃, silicon and metal M and metal A and Na are first formed into an alloy phase by cathodic polarization, and then metal M and Na are dissolved by anodic polarization to generate metal A coated nano-silicon composite material. The anodic polarization voltage is greater than the voltage at which the alloy phase of metal A and Na dissolves Na.

[0010] The metal A is antimony, tin or bismuth, and its compound is a sulfide or oxide;

[0011] The metal M is one or more of Mg, Ca, Ba, and Li.

[0012] Preferably, the silicon powder is at least one of industrial micron-sized silicon powders.

[0013] Preferably, in step (1), the silicon powder is mixed with metal A and then (a) directly used as a working electrode; or (b) fixed in a mesh or basket made of solid conductive metal as a working electrode; or (c) composited on solid conductive metal as an electrode. More preferably, it is fixed on a molybdenum rod current collector with a molybdenum mesh as a working electrode.

[0014] Preferably, X is one or more of F, Cl, and Br.

[0015] Preferably, in step (2), the cathode polarization potential is controlled to be 0.01 to 0.1 V relative to the molten salt decomposition potential, and the cathode polarization time is controlled to be 1 to 50 h; the anode polarization potential is controlled to be 0.8 to 1.5 V relative to the molten salt decomposition potential, and the anode polarization time is controlled to be 1 to 50 h.

[0016] More preferably, in step (2), the cathode polarization potential is controlled to be 0.1V relative to the molten salt decomposition potential, and the cathode polarization time is controlled to be 400min; the anode polarization potential is controlled to be 1.2V relative to the molten salt decomposition potential, and the anode polarization time is controlled to be 180min.

[0017] Preferably, the mass ratio of silicon powder to metal A is 1:0.6-0.9, more preferably 1:0.8.

[0018] Preferably, in step (1), the silicon powder is mixed with metal A or its compound in the following ways: (a) physical mixing; or (b) chemical or electrochemical plating, wherein the selected metal A exists in the form of a compound in the molten salt, and then a mixture of silicon and A is obtained by chemical or electrochemical plating A on the silicon surface.

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0020] 1. The raw material silicon powder used in the preparation method of the present invention is widely available, inexpensive and of good quality, and can be industrial micron silicon powder, silicon cutting powder or photovoltaic recycled silicon powder.

[0021] 2. In this invention, the coating metal is in a liquid state at the molten salt working temperature, which can ensure that the metal is effectively coated on the nano-silicon surface.

[0022] 3. The material structure prepared in this invention is a uniform metal coating on the surface of nano-silicon, which can effectively alleviate the volume expansion problem of silicon during charging and discharging, prevent the structural damage of silicon, and significantly improve the electrochemical performance of the battery, especially the cycle performance. Attached Figure Description

[0023] Figure 1 The image shows the XRD pattern of the antimony-coated silicon nanomaterial prepared in Example 1 of this invention.

[0024] Figure 2 This is a transmission electron microscope (TEM) mapping image of the antimony-coated silicon nanomaterial prepared in Example 1 of the present invention.

[0025] Figure 3 This is a transmission electron microscope (TEM) mapping image of the antimony-coated silicon nanomaterial prepared in Example 10 of the present invention.

[0026] Figure 4 The cycling performance diagram of the antimony-coated nano-silicon material prepared in Example 1 of this invention as a negative electrode material for lithium-ion batteries is shown.

[0027] Figure 5 XRD patterns of micron-sized silicon (mSi) and nano-sized silicon (nSi) from electrolysis products;

[0028] Figure 6 TEM image of nano-silicon, a product of electrolysis;

[0029] Figure 7 Cyclic voltammetry curves of micron-sized silicon and metallic antimony in MgCl2-based molten salt. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described below are merely illustrative of the invention and not intended to limit its scope. Furthermore, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0031] The micron-sized silicon powder used in the following examples has a medium particle size of 3 to 5 micrometers, and the nano-sized silicon powder has a particle size of about 50 nm.

[0032] Comparative Example 1

[0033] One gram of industrial micron-sized silicon powder was used to prepare a porous sample with a porosity of approximately 70%. The sample was fixed to a molybdenum rod current collector using a molybdenum mesh as the working electrode. The molten salt medium was a mixed molten salt of MgCl2, NaCl, and KCl. Magnesium metal was used as the counter electrode. Argon was used as the protective gas, and the polarization temperature was 500℃. First, a cell voltage of 0.1V was applied and maintained for 400 minutes for cathodic polarization, then a cell voltage of 1.0V was applied and maintained for 180 minutes for anodic polarization. After the entire reaction was completed, the working electrode was cooled to room temperature and removed. It was first cleaned with 0.1M HCl, then washed with deionized water, and finally vacuum dried to obtain the porous nano-silicon material.

[0034] The prepared porous silicon nanomaterials were characterized by XRD and TEM mapping, and the results are as follows: Figure 5 and Figure 6 As shown in the image. Test results indicate that the material is a pure silicon phase with a particle size of approximately 20 nm. After being assembled into a lithium-ion battery, its capacity was measured at 2913 mAh / g, with a capacity retention of 84% over 100 cycles.

[0035] Example 1: A method for preparing metal-coated nano-silicon materials for lithium-ion batteries, comprising the following steps:

[0036] 1g of industrial micron-sized silicon powder and 0.8g of antimony powder were mixed evenly, pressed into a tablet, and then polarized. A molybdenum mesh was used to fix the mixture onto a molybdenum rod current collector as the working electrode. The molten salt medium was a mixed molten salt of MgCl2, NaCl, and KCl. Magnesium metal was used as the counter electrode. Argon was used as the protective gas. The polarization temperature was 500℃. First, a cell voltage of 0.1V was applied and maintained for 400min for cathodic polarization, then a cell voltage of 1.2V was applied and maintained for 180min for anodic polarization. After the entire reaction was completed, the working electrode was cooled to room temperature and removed. It was first cleaned with 0.1M HCl, then washed with deionized water, and finally vacuum dried to obtain antimony-coated nano-silicon material.

[0037] The prepared antimony-coated silicon nanomaterials were characterized by XRD and TEM mapping, and the results are as follows: Figure 1 and Figure 2 As shown in the figure, the test results indicate that the material consists of pure silicon and antimony phases, with antimony uniformly coated on the surface of the nano-silicon, and the particle size is approximately 100 nm. After being assembled into a lithium-ion battery, the battery exhibited a capacity of 1616 mAh / g and a capacity retention rate of 97% over 100 cycles, demonstrating excellent cycle stability.

[0038] like Figure 7As shown in Examples 1-14 of the present invention, cathodic polarization is performed at a cell voltage of 0.1V during the alloying process. At this voltage, the potential is less than the potential corresponding to c3, ensuring the formation of the Mg2Si intermediate phase, thereby achieving the alloying of sodium and antimony. After alloying is completed, anodic polarization is performed at a cell voltage of 1.2V. At this voltage, the potential is greater than the potential corresponding to a2, ensuring the removal of Na from Na3Sb, thereby achieving dealloying. This process removes sodium from the alloy, forming the final antimony-coated nano-silicon material.

[0039] Example 2: A method for preparing metal-coated nano-silicon materials for lithium-ion batteries, comprising the following steps:

[0040] 1g of industrial micron-sized silicon powder and 0.1g of antimony powder were mixed evenly, pressed into a tablet, and then polarized. A molybdenum mesh was used to fix the mixture onto a molybdenum rod current collector as the working electrode. The molten salt medium was a mixture of MgCl2, NaCl, and KCl. Magnesium metal was used as the counter electrode. Argon was used as the protective gas, and the working temperature was 500℃. First, a 0.1V cell voltage was applied and maintained for 400min for cathodic polarization, then a 1.2V cell voltage was applied and maintained for 180min for anodic polarization. After the reaction was complete, the working electrode was removed and cooled to room temperature. It was then cleaned with 0.1M HCl, washed with deionized water, and finally vacuum dried to obtain the antimony-coated nano-silicon material.

[0041] The prepared antimony-coated silicon nanomaterials were characterized by XRD and TEM mapping. The results showed that the coating of the material was uneven. When assembled into a lithium-ion battery, the capacity was high, about 2180 mAh / g, but the capacity retention rate was only 77% per 100 cycles.

[0042] Example 3: A method for preparing metal-coated nano-silicon materials for lithium-ion batteries, comprising the following steps:

[0043] 1g of industrial micron-sized silicon powder and 0.3g of antimony powder were mixed evenly, pressed into a sheet, and then polarized. A molybdenum mesh was fixed on a molybdenum rod current collector to serve as the working electrode. The molten salt medium was a mixed molten salt of MgCl2, NaCl, and KCl. Magnesium metal was used as the counter electrode. Argon was used as the protective gas. The polarization temperature was 500℃. First, a cell voltage of 0.1V was applied and maintained for 400min for cathodic polarization, then a cell voltage of 1.2V was applied and maintained for 180min for anodic polarization. After the reaction was complete, the working electrode was removed and cooled to room temperature. It was then cleaned with 0.1M HCl, washed with deionized water, and finally vacuum dried to obtain the antimony-coated nano-silicon material.

[0044] The prepared antimony-coated silicon nanomaterials were characterized by XRD and TEM mapping, showing that only a portion of the antimony was coated on the surface of the silicon nanomaterials. When assembled into a lithium-ion battery, the capacity was approximately 1349 mAh / g, with a capacity retention of 76% over 100 cycles.

[0045] Example 4

[0046] 1g of industrial micron-sized silicon powder and 0.5g of antimony powder were mixed evenly, pressed into a sheet, and then polarized. A molybdenum mesh was fixed on a molybdenum rod current collector to serve as the working electrode. The molten salt medium was a mixed molten salt of MgCl2, NaCl, and KCl. Magnesium metal was used as the counter electrode. Argon was used as the protective gas. The polarization temperature was 500℃. First, a cell voltage of 0.1V was applied and held for 400min for cathodic polarization, then a cell voltage of 1.2V was applied and held for 180min for anodic polarization. After the reaction was complete, the working electrode was removed and cooled to room temperature. It was then cleaned with 0.1M HCl, washed with deionized water, and finally vacuum dried to obtain the antimony-coated nano-silicon material.

[0047] The prepared antimony-coated silicon nanomaterials were characterized by XRD, SEM, and TEM mapping. The results showed that the product exhibited a phase-separated structure, indicating poor coating performance. When assembled into a lithium-ion battery, the battery achieved a capacity of 826 mAh / g and a capacity retention of 69% over 100 cycles.

[0048] Example 5

[0049] 1g of industrial micron-sized silicon powder and 1g of antimony powder were mixed evenly, pressed into a tablet, and then polarized. A molybdenum mesh was fixed on a molybdenum rod current collector to serve as the working electrode. The molten salt medium was a mixed molten salt of MgCl2, NaCl, and KCl. Magnesium metal was used as the counter electrode. Argon was used as the protective gas. The polarization temperature was 500℃. First, a cell voltage of 0.1V was applied and maintained for 400min for cathodic polarization, then a cell voltage of 1.2V was applied and maintained for 180min for anodic polarization. After the reaction was complete, the working electrode was removed and cooled to room temperature. It was then cleaned with 0.1M HCl, washed with deionized water, and finally vacuum dried to obtain the antimony-coated nano-silicon material.

[0050] The prepared antimony-coated silicon nanomaterials were characterized by XRD and TEM mapping. The results showed that the surface coating degree was poor. When assembled into a lithium-ion battery, the capacity retention rate was almost 100% after 100 cycles, but the capacity was poor, only 458 mAh / g.

[0051] Comparing Examples 1-5, it is evident that, considering both capacity and cycle performance, the optimal weight ratio of industrial micron-sized silicon powder to metallic antimony is 1:0.8. Insufficient antimony content results in uneven coating, preventing the antimony from being fully and uniformly coated on the nano-silicon surface. Conversely, excessive antimony content leads to antimony particle agglomeration, hindering the formation of a coating structure.

[0052] Example 6

[0053] 1g of silicon cutting powder (93% purity, micrometer-level) was mixed evenly with 0.8g of antimony powder, pressed into a sheet, and then polarized. A molybdenum mesh was fixed on a molybdenum rod current collector to serve as the working electrode. The molten salt medium was a mixed molten salt of MgCl2, NaCl, and KCl. A magnesium-tin alloy was used as the counter electrode. Argon was used as the protective gas. The polarization temperature was 500℃. First, a 0.1V cell voltage was applied and held for 400min for cathodic polarization, then a 1.2V cell voltage was applied and held for 180min for anodic polarization. After the reaction was complete, the working electrode was removed and cooled to room temperature. It was then cleaned with 0.1M HCl, washed with deionized water, and finally vacuum dried to obtain antimony-coated silicon nanomaterials.

[0054] The prepared antimony-coated silicon nanomaterials were characterized by XRD and TEM mapping. The results showed that antimony was uniformly coated on the surface of the silicon nanomaterials. When assembled into a lithium-ion battery, the capacity was about 1919 mAh / g and the capacity retention rate was 85% after 100 cycles, which showed excellent cycling performance.

[0055] Example 7

[0056] 1g of industrial micron-sized silicon powder and 0.8g of metallic tin powder were mixed evenly, pressed into a sheet, and then polarized. A molybdenum mesh was used to fix the sheet onto a molybdenum rod current collector as the working electrode. The molten salt medium was a mixed molten salt of MgCl2, NaCl, and KCl. Magnesium metal was used as the counter electrode. Argon was used as the protective gas. The polarization temperature was 500℃. First, a cell voltage of 0.3V was applied and maintained for 400min for cathodic polarization, then a cell voltage of 1.2V was applied and maintained for 180min for anodic polarization. After the reaction was complete, the working electrode was removed and cooled to room temperature. It was then cleaned with 0.1M HCl, washed with deionized water, and finally vacuum dried to obtain the tin-coated nano-silicon material.

[0057] The prepared tin-coated silicon nanomaterials were characterized by XRD and TEM mapping. The results showed that the tin coating layer on the surface of the silicon nanomaterials was relatively uniform. When assembled into a lithium-ion battery, the capacity was about 2105 mAh / g and the capacity retention rate was 61% over 100 cycles.

[0058] Example 8

[0059] 1g of industrial micron-sized silicon powder and 0.8g of metallic bismuth powder were mixed evenly, pressed into a tablet, and then polarized. A molybdenum mesh was fixed on a molybdenum rod current collector to serve as the working electrode. The molten salt medium was a mixed molten salt of MgCl2, NaCl, and KCl. Magnesium metal was used as the counter electrode. Argon was used as the protective gas, and the operating temperature was 500℃. First, a cell voltage of 0.1V was applied and maintained for 400min for cathodic polarization, then a cell voltage of 1.2V was applied and maintained for 180min for anodic polarization. After the reaction was complete, the working electrode was removed and cooled to room temperature. It was then cleaned with 0.1M HCl, washed with deionized water, and finally vacuum dried to obtain the metallic bismuth-coated nano-silicon material.

[0060] The prepared bismuth-coated silicon nanomaterials were characterized by XRD and TEM mapping. The results showed that metallic bismuth could be uniformly coated on the surface of silicon nanomaterials and assembled into lithium-ion batteries with excellent cycle performance.

[0061] Example 9

[0062] 1g of industrial micron-sized silicon powder and 1.12g of antimony sulfide powder were mixed evenly, pressed into a tablet, and then polarized. The tablet was fixed to a molybdenum rod current collector using a molybdenum mesh as the working electrode. The molten salt medium was a mixed molten salt of MgCl2, NaCl, and KCl. Magnesium metal was used as the counter electrode. Argon was used as the protective gas, and the operating temperature was 500℃. First, a cell voltage of 0.1V was applied and maintained for 400min for cathodic polarization, then a cell voltage of 1.2V was applied and maintained for 180min for anodic polarization. After the reaction was complete, the working electrode was removed and cooled to room temperature. It was then cleaned with 0.1M HCl, washed with deionized water, and finally vacuum dried to obtain antimony-coated nano-silicon material.

[0063] The prepared antimony-coated silicon nanomaterials were characterized by XRD and TEM mapping. The results showed that antimony could be well coated on the surface of the formed silicon nanomaterials after electrochemical reduction. When assembled into a lithium-ion battery, it had excellent cycle performance with a capacity of about 1850 mAh / g and a capacity retention of 82.4% over 100 cycles.

[0064] Example 10

[0065] 1g of nano-silicon powder (average particle size 50nm, the same below) was mixed evenly with 1.12g of antimony sulfide, pressed into a tablet, and then polarized. The tablet was fixed on a molybdenum rod current collector using a molybdenum mesh as the working electrode. The molten salt medium was a mixed molten salt of MgCl2, NaCl, and KCl. Magnesium metal was used as the counter electrode, and argon was used as the protective gas. A cell voltage of 1.0V was applied at 500℃ and maintained for 120min for cathodic polarization. After the reaction was completed, the working electrode was removed and cooled to room temperature. It was first cleaned with 0.1M HCl, then washed with deionized water, and then vacuum dried to obtain the antimony-coated nano-silicon material.

[0066] The prepared antimony-coated silicon nanomaterials were characterized by XRD and TEM mapping, and the results are shown in the figure. Figure 3 , Figure 3 This indicates that when antimony is directly electrochemically reduced and coated using nano-silicon as a raw material, the coating layer is uneven, with only a portion of the antimony coating on the surface of the nano-silicon. When assembled into a lithium-ion battery, its capacity is only 1085 mAh / g, with a capacity retention of 76.4% over 100 cycles.

[0067] Example 11

[0068] 1g of nano-silicon powder (average particle size 50nm) was mixed evenly with 0.8g of metallic antimony powder, pressed into a sheet, and then polarized. A molybdenum mesh was used to fix the sheet onto a molybdenum rod current collector as the working electrode. The molten salt medium was a mixed molten salt of MgCl2, NaCl, and KCl. Magnesium metal was used as the counter electrode. Argon was used as the protective gas, and the operating temperature was 400℃. First, a 0.1V cell voltage was applied and held for 400min for cathodic polarization, then a 1.2V cell voltage was applied and held for 180min for anodic polarization. After polarization, the working electrode was removed and allowed to cool to room temperature. It was then cleaned with 0.1M HCl, washed with deionized water, and finally vacuum dried to obtain the antimony-coated nano-silicon material.

[0069] The prepared antimony-coated silicon nanomaterials were characterized by XRD and TEM mapping. The results compared with those of Example 10 showed that antimony can be well coated on the surface of silicon nanomaterials after alloying / dealloying. However, the silicon nanomaterials will undergo partial sintering, resulting in larger particles. When assembled into a lithium-ion battery, the capacity is about 1446 mAh / g and the capacity retention rate is 78% over 100 cycles.

[0070] Example 12

[0071] 1g of industrial micron-sized silicon powder and 0.96g of antimony oxide powder were mixed evenly, pressed into a tablet, and then polarized. The tablet was fixed to a molybdenum rod current collector using a molybdenum mesh as the working electrode. The molten salt medium was a mixed molten salt of MgCl2, NaCl, and KCl. Magnesium metal was used as the counter electrode. Argon was used as the protective gas, and the operating temperature was 500℃. First, a cell voltage of 0.1V was applied and held for 400min for cathodic polarization, then a cell voltage of 1.2V was applied and held for 180min for anodic polarization. After polarization, the working electrode was removed and allowed to cool to room temperature. It was then cleaned with 0.1M HCl, washed with deionized water, and finally vacuum dried to obtain the antimony-coated nano-silicon material.

[0072] The prepared antimony-coated silicon nanomaterials were characterized by XRD and TEM mapping, and assembled into a lithium-ion battery. The battery exhibited good cycle performance with a capacity of approximately 1588 mAh / g and a capacity retention rate of 86% over 100 cycles.

[0073] Example 13

[0074] 1g of industrial micron-sized silicon powder and 0.8g of metallic antimony powder were mixed evenly, pressed into a sheet, and then polarized. A molybdenum mesh was fixed on a molybdenum rod current collector to serve as the working electrode. The molten salt medium was a mixed molten salt of CaCl2, NaCl, and KCl. A graphite rod was used as the counter electrode. Argon was used as the protective gas. Cathode polarization was performed at 700℃ with a cell voltage of 0.2V for 400 minutes, followed by anodic polarization with a cell voltage of 1.1V for 180 minutes. After polarization, the working electrode was removed and allowed to cool to room temperature. It was then cleaned with 0.1M HCl, washed with deionized water, and finally vacuum dried to obtain the antimony-coated nano-silicon material.

[0075] The prepared antimony-coated silicon nanomaterials were characterized by XRD and TEM mapping, and assembled into lithium-ion batteries. The batteries exhibited excellent capacity and cycle performance, with a capacity of approximately 1638 mAh / g and a capacity retention rate of 88% over 100 cycles.

[0076] Example 14

[0077] Five grams of industrial micron-sized silicon powder were used to fabricate an electrode, which was then electrochemically plated in a potassium antimony tartrate plating solution to obtain a mixture of micron-sized silicon and antimony (with an antimony content of 44% by mass). This mixture was then pressed into a sheet and fixed onto a molybdenum rod current collector using a molybdenum mesh to serve as the working electrode. The molten salt medium was a mixed molten salt of MgCl2, NaCl, and KCl. Magnesium metal was used as the counter electrode, and argon was used as the protective gas. Cathodic polarization was performed at 500°C by first applying a tank voltage of 0.1V for 400 minutes, followed by anodic polarization by applying a tank voltage of 1.2V for 180 minutes. After polarization, the working electrode was removed and allowed to cool to room temperature. It was then cleaned with 0.1M HCl, washed with deionized water, and finally vacuum dried to obtain antimony-coated nano-silicon material.

[0078] The prepared antimony-coated silicon nanomaterials were characterized by XRD and TEM mapping. The results showed that, similar to Example 1, the antimony formed by electrochemical plating could be uniformly coated on the surface of silicon nanomaterials after alloying / dealloying and assembled into lithium-ion batteries with good cycle performance. The capacity was about 1611 mAh / g and the capacity retention rate was 84% ​​over 100 cycles.

[0079] The capacities given above are all initial discharge capacities.

[0080] The assembly and testing steps of the lithium battery in the above embodiments are as follows:

[0081] The antimony-coated silicon nanomaterial prepared in the examples was used as the negative electrode active material, acetylene black as the conductive agent, and polyacrylic acid PAA as the binder. They were mixed according to the mass ratio of silicon-antimony composite material: acetylene black: PAA = 6:2:2, with deionized water as the dispersant, and uniformly mixed to obtain a slurry. The slurry was then uniformly coated on the current collector copper foil, vacuum dried at 60°C for 12 hours, and then cut into small round pieces with a diameter of 12 mm.

[0082] Using the aforementioned small disc as the positive electrode, a lithium metal sheet as the negative electrode, a polypropylene membrane as the separator, and lithium hexafluorophosphate (LiPF6) dissolved in a 1:1 volume ratio mixture of ethylene carbonate (EC) and diethyl carbonate (FEC), with 10% fluoroethylene carbonate (FEC) added, and the concentration of LiPF6 being 1M, the lithium-ion button cell was then assembled in a glove box.

[0083] Electrochemical performance tests were conducted on coin cells prepared using the antimony-coated silicon nanomaterial prepared in Example 1 as the active material, according to the above method. Cyclic performance tests were performed at a voltage range of 0.01-1.5V and a current density of 1A / g, yielding the following results. Figure 4 The results are shown.

[0084] Depend on Figure 4 It can be seen that the antimony-coated silicon nanomaterial of the present invention has high discharge capacity and good cycle performance. The first charge-discharge specific capacity of the antimony-coated silicon nanomaterial obtained in Example 1 was 1221 mAh g. -1 The sum is 1616mAh g -1 The coulomb efficiency in the first week was 75.6%. After 100 cycles, it still maintained a capacity of 1186 mAh g. -1 The specific capacity retention rate was 97% in the first week. This indicates that antimony-coated nano-silicon materials, when used as a negative electrode material in lithium-ion batteries, can effectively alleviate the volume expansion problem of silicon, greatly improving the capacity and cycle stability of lithium-ion batteries. The main reason is that the antimony coating can selectively decompose the electrolyte additive fluoroethylene carbonate (FEC) to form a favorable LiF-dominated solid electrolyte interface (SEI), which is much more stable than the SEI formed without antimony and can prevent the consumption of electrolyte and active materials.

[0085] The above description is merely a preferred embodiment of the present invention, and should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing metal-coated silicon nanomaterials for lithium-ion batteries, comprising the following specific steps: (1) Mix silicon powder with metal A or a compound of metal A until homogeneous to obtain a mixture; (2) Using the mixture obtained in (1) as the working electrode, and metal M element or alloy or graphite as the counter electrode, cathodic polarization is carried out in a molten salt medium containing metal halide MX and Na halide. The cathodic polarization voltage is less than the voltage for forming the MSi alloy: Under an inert atmosphere, at a temperature of 300℃~800℃, silicon and metal M and metal A and Na are first formed into an alloy phase by cathodic polarization, and then metal M and Na are dissolved by anodic polarization to generate metal A coated nano-silicon composite material. The anodic polarization voltage is greater than the voltage at which the alloy phase of metal A and Na dissolves Na. The metal A is antimony, tin or bismuth, and its compound is a sulfide or oxide; The metal M is one or more of Mg, Ca, Ba, and Li; The mass ratio of silicon powder to metal A or its compound is 1:0.6-0.

9.

2. The preparation method according to claim 1, characterized in that, The polarization temperature in step (2) is 500℃.

3. The preparation method according to claim 1, characterized in that, The silicon powder is industrial micron silicon powder or nano silicon powder.

4. The preparation method according to claim 1, characterized in that, In (1), the silicon powder is mixed with metal A and (a) directly used as a working electrode; or (b) fixed in a mesh or basket made of solid conductive metal as a working electrode; or (c) composited on solid conductive metal as an electrode.

5. The preparation method according to claim 1, characterized in that, X is one or more of F, Cl, and Br.

6. The preparation method according to claim 1, characterized in that, In step (2), the cathode polarization potential is controlled to be 0.01 to 0.1 V relative to the molten salt decomposition potential, and the cathode polarization time is controlled to be 1 to 50 h; the anode polarization potential is controlled to be 0.8 to 1.5 V relative to the molten salt decomposition potential, and the anode polarization time is controlled to be 1 to 50 h.

7. The preparation method according to claim 6, characterized in that, In (1), the silicon powder is mixed with metal A or its compound in the following ways: (a) physical mixing; or (b) chemical or electrochemical plating, wherein the selected metal A exists in the form of a compound in the molten salt, and then a mixture of silicon and A is obtained by chemical or electrochemical plating A on the silicon surface.

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