Preparation method of metal-coated nano silicon material for lithium ion battery

Abstract

The invention relates to the technical field of lithium ion battery negative electrode materials, and particularly discloses a preparation method of a metal-coated nano silicon material for a lithium ion battery. The preparation method comprises the following steps: mixing silicon powder with metal A, changing Si into an alloy phase with metal M and A into an alloy phase with metal Na through cathode potential polarization in a molten salt medium containing MX and NaX, dissolving out the metal M and Na through anodic oxidation, and simultaneously generating the metal-coated nano silicon material in which the liquid metal A coats the surface of silicon. The method is environment-friendly, the process is simple, the cost is relatively low, and the prepared metal-coated nano silicon material has relatively high capacity, good multiplying power and cycling stability when being applied to a lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of anode materials for lithium-ion batteries, and particularly to a preparation method of a metal-coated nano-silicon material for lithium-ion batteries. Background Art

[0002] The theoretical capacity of silicon is as high as 4200 mAh g -1 , which is 10 times that of current commercial graphite electrodes, and is considered to be one of the most promising anode materials for next-generation lithium-ion batteries. However, silicon has a serious volume expansion problem as an anode for lithium-ion batteries, which affects the electrochemical performance of lithium-ion batteries and seriously hinders the application of silicon in lithium-ion batteries.

[0003] Currently, the strategies to alleviate the volume expansion effect of silicon are as follows: First, reduce the size of silicon to prepare nano-silicon, design 0D nano-silicon spheres, 1D nano-silicon rods, 2D nano-silicon sheets, etc. to change the morphology of silicon to reduce the size of silicon in one or multiple dimensions, and then composite silicon with buffer materials, including designing structures such as coating, doping, and mixing to alleviate the volume expansion of silicon. Among them, composite with antimony, tin, or bismuth can contribute part of the capacity on the one hand, and is also expected to change the interface properties of silicon. When these methods generally prepare nano-silicon, there are high costs in solid-solid composite and it is difficult to form a complete coating structure.

[0004] Micro-silicon is widely sourced and inexpensive. After mixing industrial micro-silicon with some low-melting-point metals, above the melting points of these metals, molten salt electrolysis is combined to generate liquid metal and nano-silicon and complete the liquid-solid coating to transform into a metal-coated nano-silicon material, which is expected to prepare high-performance silicon-based anode materials for lithium-ion batteries at low cost. Summary of the Invention

[0005] Aiming at the deficiencies in the prior art, the present invention provides a new and efficient preparation method of a metal-coated nano-silicon material, which can effectively alleviate the volume expansion problem of silicon during charge and discharge.

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

[0007] A preparation method of a metal-coated silicon nano-material for lithium-ion batteries, the specific steps are as follows:

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

[0009] (2) Using the mixture obtained in (1) as the working electrode, a single metal M, alloy, or graphite as the counter electrode, perform cathodic polarization in a molten salt medium containing metal halide MX and a halide of Na, where the cathodic polarization voltage is less than the voltage for forming the MSi alloy: Under an inert atmosphere, at a temperature of 300°C to 800°C, first generate an alloy phase of silicon with metal M and metal A with Na through cathodic polarization, and then dissolve out metal M and Na through anodic polarization to form a metal A-coated nano-silicon composite material, where the anodic polarization voltage is greater than the voltage for dissolving out Na from the alloy phase of metal A and 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 micro-silicon powder.

[0013] Preferably, in (1), after mixing the silicon powder with metal A, (a) directly use it as the working electrode; or (b) fix it in a mesh or basket made of solid conductive metal as the working electrode; or (c) composite it on solid conductive metal as the electrode, more preferably: fix it on a molybdenum rod current collector with a molybdenum mesh to make the working electrode.

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

[0015] Preferably, in (2), control the cathodic polarization potential to be 0.01 - 0.1V relative to the molten salt decomposition potential, and control the cathodic polarization time to be 1 - 50h; control the anodic polarization potential to be 0.8 - 1.5V relative to the molten salt decomposition potential, and control the anodic polarization time to be 1 - 50h.

[0016] More preferably, in (2), control the cathodic polarization potential to be 0.1V relative to the molten salt decomposition potential, and control the cathodic polarization time to be 400min; control the anodic polarization potential to be 1.2V relative to the molten salt decomposition potential, and control the anodic polarization time to be 180min.

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

[0018] Preferably, in (1), the mixing method of the silicon powder with metal A or its compound is: (a) physical mixing; or (b) mixing in a chemical or electroplating manner, where the selected metal A exists in the molten salt in the form of a compound, and then deposit A on the silicon surface chemically or electrochemically to obtain a mixture of silicon and A.

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

[0020] 1. In the preparation method of the present invention, the raw material silicon powder has a wide source, is inexpensive and of good quality, and can be industrial micron silicon powder, silicon cutting powder or photovoltaic recycled silicon powder.

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

[0022] 3. The material prepared in the present invention has a structure in which the metal is uniformly coated on the surface of the nano-silicon, which can effectively alleviate the volume expansion problem of silicon during charge and discharge, prevent the structural damage of silicon, and significantly improve the electrochemical performance of the battery, especially the cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 XRD pattern of the antimony-coated nano-silicon material prepared in Example 1 of the present invention;

[0024] Figure 2 TEM mapping diagram of the antimony-coated nano-silicon material prepared in Example 1 of the present invention;

[0025] Figure 3 TEM mapping diagram of the antimony-coated nano-silicon material prepared in Example 10 of the present invention;

[0026] Figure 4 Cycle performance diagram of the antimony-coated nano-silicon material prepared in Example 1 of the present invention used as the anode material of a lithium-ion battery;

[0027] Figure 5 XRD patterns of micron silicon (mSi) and electrolytic product nano-silicon (nSi);

[0028] Figure 6 TEM image of the electrolytic product nano-silicon;

[0029] Figure 7 Cyclic voltammetry curves of micron silicon and metallic antimony in MgCl 2 -based molten salt. DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described below are only used to explain the related invention, rather than limiting the present invention. Additionally, it should be noted that for the convenience of description, only the parts related to the invention are shown in the drawings.

[0031] In the following examples, the median particle size of the micron silicon powder used is 3 - 5 microns, and the particle size of the nano-silicon is about 50 nm.

[0032] Comparative Example 1

[0033] Prepare a porous specimen with a porosity of about 70% from 1 g of industrial micron-sized silicon powder: Fix the specimen on a molybdenum rod current collector with a molybdenum mesh to make a working electrode. The molten salt medium is a mixed molten salt of MgCl 2 , NaCl, and KCl. Select metallic magnesium as the counter electrode, argon as the protective gas, and the polarization temperature is 500 °C. First, apply a cell voltage of 0.1 V and hold for 400 min for cathodic polarization, and then apply a cell voltage of 1.0 V and hold for 180 min for anodic polarization. After the entire reaction is completed, take out the working electrode after it cools to room temperature. First, clean it with 0.1 M HCl, then wash it with deionized water, and then perform vacuum drying to obtain the porous nanosilicon material.

[0034] Characterize the prepared porous nanosilicon material by XRD, TEM mapping, etc. The obtained results are shown in Figure 5 and Figure 6 respectively. It can be seen from the test results that the material is a pure silicon phase, and the particle size is about 20 nm. After assembling it into a lithium-ion battery and testing, its capacity is 2913 mAh / g, and the capacity retention rate after 100 cycles is 84%.

[0035] Example 1 A preparation method of a metal-coated nanosilicon material for a lithium-ion battery, the steps are as follows:

[0036] Mix 1 g of industrial micron-sized silicon powder and 0.8 g of metallic antimony powder evenly, press into a tablet and then perform polarization: Fix the mixture specimen on a molybdenum rod current collector with a molybdenum mesh to make a working electrode. The molten salt medium is a mixed molten salt of MgCl 2 , NaCl, and KCl. Select metallic magnesium as the counter electrode, argon as the protective gas, and the polarization temperature is 500 °C. First, apply a cell voltage of 0.1 V and hold for 400 min for cathodic polarization, and then apply a cell voltage of 1.2 V and hold for 180 min for anodic polarization. After the entire reaction is completed, take out the working electrode after it cools to room temperature. First, clean it with 0.1 M HCl, then wash it with deionized water, and then perform vacuum drying to obtain the antimony-coated nanosilicon material.

[0037] Characterize the prepared antimony-coated nanosilicon material by XRD, TEM mapping, etc. The obtained results are shown in Figure 1 and Figure 2 respectively. It can be seen from the test results that the material is a pure silicon phase and antimony phase, and antimony is evenly coated on the surface of the nanosilicon. The particle size is about 100 nm. After assembling it into a lithium-ion battery and testing, its capacity is 1616 mAh / g, and the capacity retention rate after 100 cycles is 97%, showing excellent cycle stability.

[0038] As Figure 7As shown, in Examples 1 to 14 of the present invention, during the alloying process, cathodic polarization is carried out at a cell voltage of 0.1 V. At this time, the potential is less than the potential corresponding to c3, which can ensure the formation of Mg 2 Si intermediate phase material, thereby realizing the alloying of sodium and antimony. After the alloying is completed, an anodic polarization is applied at a cell voltage of 1.2 V. At this time, the potential is greater than the potential corresponding to a2, which can ensure the 3 removal of Na in Na

[0039] Example 2 A method for preparing a metal-coated nano-silicon material for a lithium-ion battery, the steps are as follows:

[0040] Mix 1 g of industrial micron silicon powder and 0.1 g of metal antimony powder evenly, press into tablets and then polarize: fix the mixture test piece on a molybdenum rod current collector with a molybdenum mesh as the working electrode, and the molten salt medium is MgCl 2 A mixed molten salt of, NaCl and KCl, the counter electrode is made of metallic magnesium, the protective gas is argon, the working temperature is 500 °C, first apply a cell voltage of 0.1 V and keep it for 400 min for cathodic polarization, and then apply a cell voltage of 1.2 V and keep it for 180 min for anodic polarization. After the reaction is completed, take out the working electrode. After cooling to room temperature, first wash it with 0.1 M HCl, then wash it with deionized water, and then perform vacuum drying to obtain the antimony-coated nano-silicon material.

[0041] The prepared antimony-coated nano-silicon material was characterized by XRD, TEM mapping, etc. The results showed that the coating of this material was uneven. Assembled into a lithium-ion battery, its capacity was relatively high, about 2180 mAh / g, but its capacity retention rate after 100 cycles was only 77%.

[0042] Example 3 A method for preparing a metal-coated nano-silicon material for a lithium-ion battery, the steps are as follows:

[0043] Mix 1 g of industrial micron silicon powder and 0.3 g of metal antimony powder evenly, press into tablets and then polarize: fix it on a molybdenum rod current collector with a molybdenum mesh as the working electrode, and the molten salt medium is MgCl 2 A mixed molten salt of, NaCl and KCl, the counter electrode is made of metallic magnesium, the protective gas is argon, the polarization temperature is 500 °C, first apply a cell voltage of 0.1 V and keep it for 400 min for cathodic polarization, and then apply a cell voltage of 1.2 V and keep it for 180 min for anodic polarization. After the reaction is completed, take out the working electrode. After cooling to room temperature, first wash it with 0.1 M HCl, then wash it with deionized water, and then perform vacuum drying to obtain the antimony-coated nano-silicon material.

[0044] The prepared antimony-coated nanosilicon materials were characterized by XRD, TEM mapping, etc. The results showed that only part of the antimony was coated on the surface of the nanosilicon. When assembled into a lithium-ion battery, its capacity was about 1349 mAh / g, and the capacity retention rate after 100 cycles was 76%.

[0045] Example 4

[0046] 1 g of industrial micron-sized silicon powder was mixed evenly with 0.5 g of metallic antimony powder, pressed into a tablet, and then polarized: it was fixed on a molybdenum rod current collector with a molybdenum mesh as the working electrode. The molten salt medium was a mixed molten salt of MgCl 2 , NaCl and KCl. The counter electrode was made of metallic magnesium, the protective gas was argon, and the polarization temperature was 500 °C. First, a cell voltage of 0.1 V was applied and maintained for 400 min for cathodic polarization, and then a cell voltage of 1.2 V was applied and maintained for 180 min for anodic polarization. After the reaction ended, the working electrode was taken out. After cooling to room temperature, it was first washed with 0.1 M HCl, then washed with deionized water, and then dried in vacuum to obtain the antimony-coated nanosilicon materials.

[0047] The prepared antimony-coated nanosilicon materials were characterized by XRD, SEM, TEM mapping, etc. It was found that a phase separation structure appeared in the product at this time, and the coating effect was not good. When assembled into a lithium-ion battery, its capacity was 826 mAh / g, and the capacity retention rate after 100 cycles was 69%.

[0048] Example 5

[0049] 1 g of industrial micron-sized silicon powder was mixed evenly with 1 g of metallic antimony powder, pressed into a tablet, and then polarized: it was fixed on a molybdenum rod current collector with a molybdenum mesh as the working electrode. The molten salt medium was a mixed molten salt of MgCl 2 , NaCl and KCl. The counter electrode was made of metallic magnesium, the protective gas was argon, and the polarization temperature was 500 °C. First, a cell voltage of 0.1 V was applied and maintained for 400 min for cathodic polarization, and then a cell voltage of 1.2 V was applied and maintained for 180 min for anodic polarization. After the reaction ended, the working electrode was taken out. After cooling to room temperature, it was first washed with 0.1 M HCl, then washed with deionized water, and then dried in vacuum to obtain the antimony-coated nanosilicon materials.

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

[0051] Comparing Examples 1-5, considering the capacity and cycling performance comprehensively, the optimal weight ratio of industrial micron silicon powder to added antimony metal is 1:0.8. If the content of antimony is too low, the coating will be uneven, and not all of the antimony can be evenly coated on the surface of the nanosilicon. If the content of antimony is too high, antimony particle agglomeration will occur, which is not conducive to the formation of the coating structure.

[0052] Example 6

[0053] Mix 1 g of silicon cutting powder (purity 93%, in decimillimeter scale) with 0.8 g of antimony metal powder evenly, press into tablets and then polarize: fix it on a molybdenum rod current collector with a molybdenum mesh as the working electrode. The molten salt medium is a mixed molten salt of MgCl 2 , NaCl and KCl. The counter electrode is made of a magnesium-tin alloy, the protective gas is argon, the polarization temperature is 500 °C. First, apply a cell voltage of 0.1 V and hold for 400 min for cathodic polarization, then apply a cell voltage of 1.2 V and hold for 180 min for anodic polarization. After the reaction is completed, take out the working electrode. After cooling to room temperature, first wash it with 0.1 M HCl, then wash it with deionized water, and then perform vacuum drying to obtain the antimony-coated nanosilicon material.

[0054] Characterize the prepared antimony-coated nanosilicon material by XRD, TEM mapping, etc. The results show that antimony is evenly coated on the surface of the nanosilicon. Assemble it into a lithium-ion battery, its capacity is about 1919 mAh / g, and the capacity retention rate after 100 cycles is 85%, showing excellent cycling performance.

[0055] Example 7

[0056] Mix 1 g of industrial micron silicon powder with 0.8 g of tin metal powder evenly, press into tablets and then polarize: fix it on a molybdenum rod current collector with a molybdenum mesh as the working electrode. The molten salt medium is a mixed molten salt of MgCl 2 , NaCl and KCl. The counter electrode is made of metal magnesium, the protective gas is argon, the polarization temperature is 500 °C. First, apply a cell voltage of 0.3 V and hold for 400 min for cathodic polarization, then apply a cell voltage of 1.2 V and hold for 180 min for anodic polarization. After the reaction is completed, take out the working electrode. After cooling to room temperature, first wash it with 0.1 M HCl, then wash it with deionized water, and then perform vacuum drying to obtain the tin-coated nanosilicon material.

[0057] Characterize the prepared tin-coated nanosilicon material by XRD, TEM mapping, etc. The results show that the tin coating layer on the surface of the nanosilicon is relatively uniform. Assemble it into a lithium-ion battery, its capacity is about 2105 mAh / g, and the capacity retention rate after 100 cycles is 61%.

[0058] Example 8

[0059] Mix 1 g of industrial micron silicon powder with 0.8 g of metallic bismuth powder evenly, press into tablets and then polarize: Fix it on a molybdenum rod current collector with a molybdenum mesh to make a working electrode. The molten salt medium is a mixed molten salt of MgCl 2 , NaCl and KCl. Select metallic magnesium as the counter electrode, argon as the protective gas, and the working temperature is 500 °C. First, apply a cell voltage of 0.1 V and hold for 400 min for cathodic polarization, and then apply a cell voltage of 1.2 V and hold for 180 min for anodic polarization. After the reaction is completed, take out the working electrode. After cooling to room temperature, first wash it with 0.1 M HCl, then wash it with deionized water, and then perform vacuum drying to obtain the metallic bismuth-coated nano-silicon material.

[0060] Characterize the prepared bismuth-coated nano-silicon material by XRD, TEM mapping, etc. The results show that metallic bismuth can be evenly coated on the surface of nano-silicon. Assembled into a lithium-ion battery, it has excellent cycling performance.

[0061] Example 9

[0062] Mix 1 g of industrial micron silicon powder with 1.12 g of antimony sulfide powder evenly, press into tablets and then polarize: Fix it on a molybdenum rod current collector with a molybdenum mesh to make a working electrode. The molten salt medium is a mixed molten salt of MgCl 2 , NaCl and KCl. Select metallic magnesium as the counter electrode, argon as the protective gas, and the working temperature is 500 °C. First, apply a cell voltage of 0.1 V and hold for 400 min for cathodic polarization, and then apply a cell voltage of 1.2 V and hold for 180 min for anodic polarization. After the reaction is completed, take out the working electrode. After cooling to room temperature, first wash it with 0.1 M HCl, then wash it with deionized water, and then perform vacuum drying to obtain the metallic antimony-coated nano-silicon material.

[0063] Characterize the prepared antimony-coated nano-silicon material by XRD, TEM mapping, etc. The results show that after electrochemical reduction, antimony can be well coated on the surface of the formed nano-silicon. Assembled into a lithium-ion battery, it has excellent cycling performance, with a capacity of about 1850 mAh / g and a capacity retention rate of 82.4% after 100 cycles.

[0064] Example 10

[0065] Mix 1 g of nano-silicon powder (average particle size is 50 nm, the same below) with 1.12 g of antimony sulfide evenly, press into tablets and then polarize: Fix the test piece on a molybdenum rod current collector with a molybdenum mesh to make a working electrode. The molten salt medium is a mixed molten salt of MgCl 2A mixed molten salt of NaCl and KCl was used. The counter electrode was made of metallic magnesium, and the protective gas was argon. A cell voltage of 1.0 V was applied at 500 °C for 120 min for cathodic polarization. After the reaction, the working electrode was taken out. After cooling to room temperature, it was first washed with 0.1 M HCl, then washed with deionized water, and then dried under vacuum to obtain the antimony-coated nanosilicon material.

[0066] The prepared antimony-coated nanosilicon material was characterized by XRD, TEM mapping, etc. The results are shown in Figure 3 , Figure 3 indicating that direct electrochemical reduction of antimony coating using nanosilicon as the raw material results in an uneven coating layer, and only part of the antimony is coated on the surface of the nanosilicon. When assembled into a lithium-ion battery, its capacity is only 1085 mAh / g, and the capacity retention rate after 100 cycles is 76.4%.

[0067] Example 11

[0068] 1 g of nanosilicon powder (average particle size of 50 nm) was mixed evenly with 0.8 g of metallic antimony powder, and after pressing into a tablet, polarization was carried out: it was fixed on a molybdenum rod current collector with a molybdenum mesh as the working electrode. The molten salt medium was MgCl 2 , a mixed molten salt of NaCl and KCl. The counter electrode was made of metallic magnesium, the protective gas was argon, and the working temperature was 400 °C. First, a cell voltage of 0.1 V was applied and maintained for 400 min for cathodic polarization, and then a cell voltage of 1.2 V was applied and maintained for 180 min for anodic polarization. After the polarization, the working electrode was taken out. After cooling to room temperature, it was first washed with 0.1 M HCl, then washed with deionized water, and then dried under vacuum to obtain the antimony-coated nanosilicon material.

[0069] The prepared antimony-coated nanosilicon material was characterized by XRD, TEM mapping, etc. The results after comparison with Example 10 showed that: after alloying / dealloying, antimony can be well coated on the surface of the nanosilicon, but partial sintering of the nanosilicon occurred, resulting in larger particles. When assembled into a lithium-ion battery, its capacity was about 1446 mAh / g, and the capacity retention rate after 100 cycles was 78%.

[0070] Example 12

[0071] 1 g of industrial micron-sized silicon powder was mixed evenly with 0.96 g of antimony oxide powder, and after pressing into a tablet, polarization was carried out: it was fixed on a molybdenum rod current collector with a molybdenum mesh as the working electrode. The molten salt medium was MgCl 2A mixed molten salt of NaCl and KCl is used. The counter electrode is made of metallic magnesium, the protective gas is argon, and the working temperature is 500 °C. First, a cell voltage of 0.1 V is applied and maintained for 400 min for cathodic polarization, and then a cell voltage of 1.2 V is applied and maintained for 180 min for anodic polarization. After the polarization is completed, the working electrode is taken out. After cooling to room temperature, it is first washed with 0.1 M HCl and then with deionized water, and then vacuum dried to obtain the metal antimony-coated nanosilicon material.

[0072] The prepared antimony-coated nanosilicon material is characterized by XRD, TEM mapping, etc. and assembled into a lithium-ion battery, which has good cycling performance. Its capacity is about 1588 mAh / g, and the capacity retention rate after 100 cycles is 86%.

[0073] Example 13

[0074] 1 g of industrial micron silicon powder and 0.8 g of metallic antimony powder are mixed evenly and pressed into a tablet for polarization: It is fixed on a molybdenum rod current collector with a molybdenum mesh as the working electrode. The molten salt medium is CaCl 2 A mixed molten salt of NaCl and KCl. The counter electrode is a graphite rod, the protective gas is argon, the cell voltage is 0.2 V at 700 °C, and the holding time is 400 min for cathodic polarization, and then a cell voltage of 1.1 V is applied and the holding time is 180 min for anodic polarization. After the polarization is completed, the working electrode is taken out. After cooling to room temperature, it is first washed with 0.1 M HCl and then with deionized water, and then vacuum dried to obtain the antimony-coated nanosilicon material.

[0075] The prepared antimony-coated nanosilicon material is characterized by XRD, TEM mapping, etc. and assembled into a lithium-ion battery, which has excellent capacity and cycling performance. Its capacity is about 1638 mAh / g, and the capacity retention rate after 100 cycles is 88%.

[0076] Example 14

[0077] 5 g of industrial micron silicon powder is made into an electrode and put into a potassium antimonyl tartrate plating solution to obtain a mixture of micron silicon and antimony (the mass content of antimony is 44%) by electroplating. After pressing the mixture into a tablet, it is fixed on a molybdenum rod current collector with a molybdenum mesh as the working electrode. The molten salt medium is MgCl 2 A mixed molten salt of NaCl and KCl. The counter electrode is made of metallic magnesium, the protective gas is argon, the cell voltage is 0.1 V at 500 °C, and the holding time is 400 min for cathodic polarization, and then a cell voltage of 1.2 V is applied and the holding time is 180 min for anodic polarization. After the polarization is completed, the working electrode is taken out. After cooling to room temperature, it is first washed with 0.1 M HCl and then with deionized water, and then vacuum dried to obtain the metal antimony-coated nanosilicon material.

[0078] The prepared antimony-coated nanosilicon materials were characterized by XRD, TEM mapping, etc. The results showed that, similar to Example 1, the antimony formed by electroplating could be uniformly coated on the surface of nanosilicon after alloying / dealloying. When assembled into a lithium-ion battery, it had good cycling performance, with a capacity of about 1611 mAh / g and a capacity retention rate of 84% after 100 cycles.

[0079] The capacities given above are all the first discharge capacities.

[0080] The steps for assembling the lithium battery and the detection in the above examples are as follows:

[0081] Taking the antimony-coated nanosilicon material prepared in the example 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. Using deionized water as the dispersant, they were uniformly mixed to obtain a slurry. Then the slurry was 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 above small round pieces as the positive electrode, a lithium metal sheet as the negative electrode, a polypropylene membrane as the separator, and the electrolyte was lithium hexafluorophosphate (LiPF 6 ) dissolved in a mixed solution of ethylene carbonate (EC) and diethyl carbonate (FEC) with a volume ratio of 1:1, and 10% fluoroethylene carbonate (FEC) was added. The concentration of LiPF 6 was 1 M. Then it was assembled into a lithium-ion button half-cell in a glove box.

[0083] The electrochemical performance of the button battery prepared by the above method using the antimony-coated nanosilicon material prepared in Example 1 as the active material was tested. In the voltage range of 0.01 - 1.5 V and at a current density of 1 A / g, the cycling performance test was carried out, and the Figure 4 shown results were obtained.

[0084] From Figure 4 it can be seen that the antimony-coated nanosilicon material of the present invention has a high discharge capacity and good cycling performance. The initial charge and discharge specific capacities of the antimony-coated nanosilicon material obtained in Example 1 were 1221 mAh g -1 and 1616 mAh g -1 respectively, and the Coulomb efficiency in the first week was 75.6%. After 100 cycles, it could still maintain 1186 mAh g -1The specific capacity has a retention rate of 97% in the first week. This indicates that when the antimony-coated nanosilicon material is used as the anode material of a lithium-ion battery, it can effectively alleviate the volume expansion problem of silicon and greatly improve the capacity and cycling stability of the lithium-ion battery. 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 the electrolyte and the active material.

[0085] The above are the preferred embodiments of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and changes can be made, and these improvements and changes are also regarded as the protection scope of the present invention.

Claims

1. A method for preparing metal-coated silicon nanomaterials for lithium-ion batteries, the specific steps are as follows: (1) mixing silicon powder and metal A or a compound of metal A uniformly to obtain a mixture; (2) The mixture obtained in (1) is used as a working electrode, and a metal M single substance or alloy or graphite is used as a counter electrode, and cathodic polarization is performed in a molten salt medium containing a metal halide MX and a halide of Na, wherein the cathodic polarization voltage is less than the voltage for forming an MSi alloy: in an inert atmosphere, at a temperature of 300°C to 800°C, firstly, an alloy phase is formed between silicon and metal M and between metal A and Na by cathodic polarization, and then metal M and Na are dissolved by anodic polarization to form a metal A-coated nano-silicon composite material, wherein the anodic polarization voltage is greater than the voltage for dissolving Na from the alloy phase of metal A and 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.

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

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 the above (1), the silicon powder is mixed with the metal A and (a) is directly used as a working electrode; or (b) is fixed in a net or basket made of a solid conductive metal as a working electrode; or (c) is composited on a solid conductive metal as an electrode.

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

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

7. The preparation method according to claim 1, characterized in that: The mass ratio of silicon powder to metal A or its compound is 1:0.6-0.

9.

8. The preparation method according to claim 7, characterized in that: In the above (1), the silicon powder and the metal A or its compound are mixed in the following ways: (a) physically mixed; or (b) mixed by chemical or electrochemical plating, wherein the selected metal A exists in the molten salt in the form of a compound, and then A is chemically or electrochemically plated on the silicon surface to obtain a mixture of silicon and A.

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