Three-dimensional porous carbon-coated silicon powder composite material, preparation method thereof and application thereof in lithium ion batteries

Abstract

The application discloses a three-dimensional porous carbon-coated silicon powder composite material, a preparation method thereof and application of the material in lithium ion batteries, and belongs to the technical field of lithium ion battery materials. The material is obtained by annealing and calcining a carbon-coated silicon alloy powder and an oxidizing agent under a protective atmosphere, and then performing acid pickling and drying. The carbon-coated silicon alloy powder is obtained by mixing a silicon-magnesium alloy precursor, pitch and a mixing agent, and then performing compounding by using a closed mill, high-temperature carbonization under a protective atmosphere, and crushing. The silicon-magnesium alloy precursor is obtained by mixing silicon powder, magnesium powder and a heat-absorbing agent, and then performing sealing calcination under a protective atmosphere and water washing. The composite material can be used as a negative electrode material of a lithium ion battery, and is used in the fields of high-power and high-energy density such as energy storage power stations and new energy vehicles, and has high specific capacity, high initial efficiency and excellent long-period cyclic performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery negative electrode materials, and particularly relates to a three-dimensional porous carbon-coated silicon powder composite material and a design and preparation method thereof. In addition, the present application also relates to the three-dimensional porous carbon-coated silicon powder composite material and the preparation method thereof as a lithium ion battery negative electrode and related test results. BACKGROUND

[0002] Nowadays, the excessive consumption of fossil energy and the resulting increasing environmental pollution problem have triggered people's exploration of large-scale, environmentally friendly new energy. Lithium ion batteries are widely used in portable devices and power car power storage power sources due to their high energy density, chargeability and excellent cycle life, and have attracted much attention. However, with the increasing demand for the endurance performance of power cars, the existing commercial graphite material (the theoretical specific capacity is only 372 mAh g -1 ) has been increasingly unable to meet the needs of high energy density performance of lithium ion batteries, and therefore better new generation substitutes need to be developed.

[0003] Silicon-based materials have attracted more and more attention in recent years due to their high theoretical specific capacity (4200 mAh g -1 ), low working voltage (<0.5 V), natural abundance, low cost and environmental friendliness. However, silicon-based negative electrode materials also face many challenges in actual industrialization applications, such as the huge volume expansion (>300%) of silicon-based materials during charging and discharging, which leads to material pulverization and structure collapse of active materials during cycling, and seriously limits the application of silicon-based materials in lithium ion battery negative electrodes. Therefore, overcoming or inhibiting the volume expansion problem of silicon-based materials during cycling is the key to the practical application problem. At present, the common solution is to nanoize the silicon-based materials and combine the silicon materials with carbon to form silicon-carbon materials to achieve better cycle stability. Researchers analyzed the volume change of Si nanoparticles during charging and discharging by in-situ transmission electron microscopy and determined that the critical fracture size is ~150 nm, that is, when the particle size of silicon material is <150 nm, the volume expansion effect has become insignificant. In addition to the fact that carbon materials and silicon materials can be closely combined due to their similar chemical properties, the addition of carbon materials can improve the conductivity of silicon-based materials, improve the theoretical lithium storage performance, and also buffer the volume change of silicon materials during cycling.

[0004] For example, the Chinese invention patent application with the application publication number CN 108807892 A discloses a kind of silicon nanoparticles as core, NaCl as hard template and pore-forming agent, pitch as carbon source, through high-energy ball milling method, successful realization of coating and composite, subsequent high temperature carbonization, washing, obtain the final silicon-carbon nanosheet composite material. Although the volume expansion of the final product material is relieved, the cycle performance is improved: after 50 cycles at a current density of 300 mAg -1 However, due to the need for excessive carbon source for coating in the ball milling process to achieve better results, the actual active material is reduced, which finally results in low initial capacity of the battery. In addition, the ball milling process also increases the structural defects of the material itself, and the commonly used pitch material is a mixture composed of more than 5000 different molecular weight hydrocarbons and their non-metal derivatives, with complex composition and excessive heteroatoms. After carbonization, most of the heteroatoms remain in the carbon layer of the composite material, forming active sites. During the first charge and discharge process of the corresponding battery, many extra lithium ions are consumed, causing irreversible loss of lithium battery capacity, resulting in low first coulombic efficiency of the material prepared by the invention. Low first coulombic efficiency will cause a large amount of lithium metal to participate in the formation of SEI film in the form of "dead lithium", which cannot participate in subsequent cycles, causing serious waste of lithium resources. Since China's lithium resources are mainly imported, it is very important to improve the first coulombic efficiency of silicon-carbon materials in lithium ion batteries.

[0005] In addition, the commonly used nanosilicon is mainly obtained by using silane (SiH4) chemical vapor decomposition, metal silicide oxidation, metal thermal reduction, chemical etching and ball milling, etc. The process usually involves expensive precursors and complex equipment, experimental safety problems, and it is difficult to produce on a commercial scale, affecting its application and promotion in the field of lithium ion batteries.

[0006] Therefore, it is imperative to develop low-cost, scalable production, high first coulombic efficiency (ICE), and high reversible capacity silicon-carbon composite materials, which is the key to improving the energy density of power batteries. The invention is very important for the technical progress of the next generation of power batteries and will promote the healthy development of the new energy industry. SUMMARY

[0007] In order to overcome the performance problems of existing silicon-based materials such as low capacity, low first coulombic efficiency (ICE), and rapid capacity decay, as well as the production problems such as complicated synthesis steps, expensive raw materials, low production capacity, and difficulty in commercialization in actual production, the present invention aims to provide a three-dimensional porous carbon-coated silicon powder composite material with high safety, low cost, environmental friendliness, and commercial large-scale production potential, and a preparation method thereof.

[0008] Another object of the present application is to provide an application of the three-dimensional porous carbon-coated silicon powder composite material in lithium ion batteries.

[0009] The object of the present application is achieved by the following technical solutions:

[0010] The three-dimensional porous carbon-coated silicon powder composite material is obtained by annealing and calcining the carbon-coated silicon alloy powder with an oxidizing agent under a protective atmosphere, then removing magnesium, and then acid washing and drying.

[0011] To further achieve the object of the present application, preferably, the temperature of the internal mixing is 150-300 DEG C, the rotating speed is 40-100 r / min, and the internal mixing time is 10-120 min; the temperature of the high-temperature carbonization is 500-1000 DEG C, the time is 1-10 h, and the heating rate is 2-10 DEG C / min; the temperature of the annealing and calcining to remove magnesium is 650-900 DEG C, the time is 2-8 h, and the heating rate is 2-10 DEG C / min.

[0012] Preferably, the sealing calcination is to seal the silicon powder, the magnesium powder and the heat-absorbing agent in a stainless steel tube and calcine in a rotary furnace; the calcination temperature is 550-700 DEG C, the calcination time is 2-8 h, the heating rate is 3-10 DEG C / min, and the rotating speed of the rotary furnace is 50-200 r / min; the acid washing uses at least one of hydrochloric acid, acetic acid and hydrofluoric acid, the concentration of the acid washing substance is 2-8 mol / L, and the acid washing time is 15 min-10 h.

[0013] Preferably, the mass ratio of the silicon powder, the magnesium powder and the heat-absorbing agent is 1:1-1.77:2-8; and the mass ratio of the carbon-coated silicon alloy powder and the oxidizing agent is 1:1.5-3.5.

[0014] Preferably, the silicon powder is treated by a sand milling process or an airflow breaking process before use; the sand milling process is to mix micron-sized silicon powder and organic matter, sand mill, collect the silicon powder by rotary evaporation, and sieve; the mass ratio of the silicon powder and the organic matter is 1:1-6; the sand milling rotating speed is 500-3000 r / min, and the time is 10-180 min.

[0015] The airflow breaking process has a crushing pressure of 0.2-1.2 Mpa, a gas flow rate of 1-10 m 3 / min, and a constant-speed feeding by frequency conversion, and the silicon powder is collected by a grading turbine.

[0016] Preferably, the organic matter is one or more of diethylene glycol dimethyl ether, diethylene glycol monomethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether and oleic acid.

[0017] Preferably, the silicon-magnesium alloy precursor is Mg2Si; the mass ratio of Mg2Si, pitch and mixing agent is 40-63:8-20:29-40.

[0018] The protective atmosphere is an argon atmosphere.

[0019] Preferably, the mixing agent is at least one of styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS) and styrene-ethylene-butylene-styrene block copolymer (SEBS); the oxidizing agent is at least one of Al2O3, Fe2O3, Fe3O4, FeO, NiO and CuO; and the endothermic agent is sodium chloride, potassium chloride or lithium chloride.

[0020] The preparation method of the three-dimensional porous carbon-coated silicon powder composite material comprises the following steps:

[0021] 1) After mixing silicon powder, magnesium powder and an endothermic agent, the mixture is sealed and calcined under a protective atmosphere, then washed with water to obtain a silicon-magnesium alloy precursor;

[0022] 2) After uniformly mixing the silicon-magnesium alloy precursor, pitch and mixing agent, the mixture is subjected to mixing in a banbury mixer to obtain a mixed intermediate;

[0023] 3) The mixed intermediate is transferred to a tube furnace, calcined at high temperature under a protective atmosphere, then crushed by a crusher after cooling to obtain carbon-coated silicon alloy powder;

[0024] 4) The carbon-coated silicon alloy powder is mixed with an oxidizing agent and annealed and calcined under a protective atmosphere to remove magnesium, thereby obtaining powder; the powder is pickled and dried to obtain a three-dimensional porous carbon-coated silicon powder composite material.

[0025] The three-dimensional porous carbon-coated silicon powder composite material is used for preparing a lithium ion battery negative electrode material; the three-dimensional porous carbon-coated silicon powder composite material, carbon black and CMC are mixed to prepare a slurry, which is coated on a copper foil to obtain a lithium ion battery negative electrode sheet; the mass ratio of the three-dimensional porous carbon-coated silicon powder composite material, carbon black and CMC is 5:3:2-8:1.

[0026] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0027] 1) Unlike existing high-energy ball milling carbon coating processes, which suffer from drawbacks such as long coating time, large product defects, and low instrument space utilization, this invention employs a kneading process for carbon coating. This kneading carbon coating process is simple, easy to operate, low-cost, and can quickly and massively coat organic carbon sources directly onto the surface of silicon-based materials. After high-temperature annealing, the organic carbon source forms carbon walls with a porous structure, and the effective bonding between the organic carbon source and the silicon core allows for a tight bond between the two.

[0028] 2) This invention introduces magnesium powder as a sacrificial agent. Utilizing the strong metallic properties of magnesium powder, it effectively protects the material during synthesis, preventing excessive oxidation of the silicon-based material, improving material purity, and facilitating higher reversible capacity in batteries. Simultaneously, the presence of magnesium powder effectively removes most heteroatoms from the pitch carbon source, reducing excess active sites and improving the material's initial coulombic efficiency. In particular, after oxidation to magnesium oxide by the magnesium remover, magnesium metal also acts as a pore-forming agent. Following a subsequent controlled acid etching process, a unique network silicon framework structure forms inside the material, along with abundant three-dimensional pores between the carbon walls. This unique structure, rich in pores both internally and externally, effectively mitigates the volume changes of silicon particles during lithiation and delithiation processes at multiple scales when the material is used as a lithium-ion battery anode material, improving the material's electrochemical stability. Therefore, this invention has the potential for large-scale commercial application.

[0029] 3) By constructing covalent bonds such as Si-OC, Si-O-Si, and Si-O between the silicon substrate and the porous carbon layer, this invention can not only shorten the ion and electron transfer time, but also prevent the active material from escaping from the carbon layer during long-term cycling, stabilize the overall structure of the active material, and enable it to fully exert its capacity advantage.

[0030] 4) The endothermic agent of this invention is sodium chloride, potassium chloride, or lithium chloride, which serves as both an endothermic agent and a dispersant for the silicon-magnesium alloy. This is another feature of this invention. The silicon source used in this invention is widely available and inexpensive large-size silicon powder. By combining two simple, effective, and mild processes, various micron-sized silicon powders were prepared. These powders were then modified with metals to obtain silicon-magnesium alloys of different sizes, subsequently yielding a silicon-carbon composite material with a unique three-dimensional porous network structure and high initial coulombic efficiency.

[0031] 5) The silicon particles used in this invention have a micron-scale size, exhibiting significant advantages in high initial efficiency and excellent electrochemical performance. After being prepared into a composite material, it is assembled into a battery for testing. At 0.2 Ag... -1The three-dimensional porous carbon-coated silicon micropowder composite material prepared from silicon sources with two different processing techniques exhibits a first-stage coulombic efficiency of >90% at 1Ag. -1 After 200 cycles at high current density, it consistently exhibits >1200mAh g⁻¹. -1 Reversible capacity; in 1Ag -1 After cycling 460 times at a current density, it still retains 1039mAh g. -1 The reversible capacity is evident. It is clear that the three-dimensional porous carbon-coated silicon micropowder composite material synthesized in this invention not only possesses good cycle performance but also high initial coulombic efficiency. This meets the requirements of existing lithium-ion batteries for high initial efficiency and high energy density in high-power applications such as new energy electric vehicles, and is expected to become the next generation of high-energy-density commercial lithium-ion battery anode material. Attached Figure Description

[0032] Figure 1 The image shows the XRD pattern of the precursor Mg2Si obtained in Example 1.

[0033] Figure 2 The images show the XRD patterns of the three-dimensional porous carbon-coated silicon micropowder composite material in Example 1 before and after acid washing.

[0034] Figure 3 This is a SEM image of a commercial silicon sphere from Example 1.

[0035] Figure 4 This is a SEM image of Mg2Si, the precursor of Example 1.

[0036] Figure 5 This is a SEM image of the 325-mesh raw silicon powder from Example 2.

[0037] Figure 6 This is a SEM image of the micron-sized silicon powder from Example 4.

[0038] Figure 7 This is a SEM image of the micron-sized silicon powder from Example 5.

[0039] Figure 8 This is a SEM image of the three-dimensional porous carbon-coated silicon micropowder composite material of Example 2.

[0040] Figure 9 This is a TEM image of the three-dimensional porous carbon-coated silicon micropowder composite material of Example 2.

[0041] Figure 10 The image shows the infrared spectrum of the porous carbon-coated silica powder composite material of Example 2.

[0042] Figure 11 The image shows the high-resolution XPS spectrum of Si 2p in the three-dimensional porous carbon-coated silicon micropowder composite material of Example 2.

[0043] Figure 12 XPS high resolution spectrum of C1s of the three-dimensional porous carbon-coated silicon powder composite material of Example 2.

[0044] Figure 13 The first three circle charge-discharge specific capacity curve of the three-dimensional porous carbon-coated silicon powder composite material of Example 2 at 25℃, 0.2Ag -1 The first three circle charge-discharge specific capacity curve of the three-dimensional porous carbon-coated silicon powder composite material of Example 2 at 25℃, 0.2Ag

[0045] Figure 14 The long cycle performance graph of the three-dimensional porous carbon-coated silicon powder composite material of Example 2 at 25℃, 1Ag -1 The long cycle performance graph of the three-dimensional porous carbon-coated silicon powder composite material of Example 2 at 25℃, 1Ag DETAILED DESCRIPTION

[0046] The application will be further described below in conjunction with examples, comparative examples and the accompanying drawings, but the embodiments of the application are not limited thereto. It should be noted that if the following processes are not specifically described in detail, they can be implemented or understood by those skilled in the art according to the prior art. If the reagents or instruments used are not marked with the manufacturer, they are considered to be conventional products that can be purchased on the market.

[0047] When the internal mixer is mixing, the mixing material is added from the hopper, first brought into the gap between the two rotors by the pressure of the upper jackscrew and the friction force, then separated into two parts by the protrusions of the lower jackscrew, and then passed through the gap between the rotor surface and the front wall of the mixing chamber along with the rotation of the rotors. After being subjected to strong mechanical shearing and tearing in the gap, the material reaches the upper part of the mixing chamber. During the mixing process in the internal mixer, the material is subjected to strong mechanical stress and thermal oxidation and melting, and finally achieves the dual effects of dispersion and coating. It is worth noting that if too much powder is added to the material, the molten melt cannot be well coated on the powder, and the dispersion effect cannot be achieved.

[0048] Example 1

[0049] A preparation method of a three-dimensional porous carbon-coated silicon powder composite material, comprising the following steps:

[0050] (1) 13.53 g of commercial 2-5 μm silicon balls, 13.53 g of magnesium powder and 27 g of NaCl were mixed uniformly in a mixer, and then packaged in a stainless steel tube in an argon atmosphere in a glove box. The temperature was raised to 550℃ at a rate of 5℃ / min in a rotary furnace under an argon atmosphere, and the rotary furnace was rotated at a speed of 50 r / min. After the reaction was completed, the heat absorber NaCl was washed away, and a precursor raw material Mg2Si was obtained. The single magnesium silicide crystal still maintained the overall spherical structure, with a size of about 5 μm, and there were protrusions on the surface, and a flaky flower-like structure appeared on the surface.

[0051] (2) Take 10 g of the Mg2Si collected above, 1.3 g of pitch, and 4.58 g of SBS (the mass ratio of Mg2Si: pitch: SBS is 63:8:29), mix them uniformly, then transfer the mixture to a banbury mixer for mixing, the mixing temperature is controlled at 200℃, the rotation speed is 50 r / min, and the mixing time is 60 min; after the mixing, the sample is collected and transferred to a tube furnace for carbonization: under the argon atmosphere, the temperature is raised to 350℃ at a rate of 2℃ / min, then the temperature is kept for 1 h, then the temperature is raised to 720℃ at a rate of 8℃ / min, and the temperature is kept for 6 h; after the carbonization, a black block-shaped intermediate product is collected.

[0052] (3) The black block-shaped intermediate product is crushed by a crusher to obtain a powder sample; then the powder sample and Al2O3 pellets (about 5 mm) are weighed according to the mass ratio of 1:2, mixed uniformly, then transferred to a tube furnace, and heated to 720℃ at a rate of 6℃ / min under the argon atmosphere, and kept for 6 h to obtain a black-green powder; under the condition of argon gas being introduced, 2 mol / L hydrochloric acid solution is added dropwise to the black-green powder in a three-necked flask, and stirred for 6 h to remove the byproduct MgO; after washing, suction filtration and drying, a preliminary silicon-carbon composite material is obtained; the silicon-carbon composite material is added to a 5 mol / L hydrofluoric acid solution, stirred for 20 min, washed, and dried at 80℃ to obtain a three-dimensional porous carbon-coated silicon powder composite material.

[0053] 0.14 g of the three-dimensional porous carbon-coated silicon powder composite material, 0.03 g of CMC binder, and 0.03 g of carbon black are weighed, mixed and ground, then transferred to a small glass bottle, 2.5 mL of deionized water is added, and the mixture is stirred magnetically for 1 h; the material is coated on a copper foil (diameter of 14 mm), dried, and pressed into an electrode; a lithium metal sheet is used as a counter electrode to assemble a CR 2016 type button cell in a glove box.

[0054] Figure 1 The XRD spectrum of the precursor Mg2Si obtained by mixing the silicon balls used in Example 1 of the present application with magnesium powder and then sintering is consistent with the standard card of Mg2Si (JCPDS No. 350773), indicating that the material has high purity during the whole process.

[0055] Figure 2 The XRD patterns of the products before and after acid washing of the intermediate product in Example 1 of the present application can be seen that before acid washing, the phase composition of the intermediate product is mainly MgO and Si, which corresponds to the standard cards MgO-JCPDS No. 50946 and Si-JCPDS No. 271402; after acid washing, the XRD pattern of the final product three-dimensional porous carbon-coated silicon powder composite material can be seen that the material retains the characteristics of high purity.

[0056] Figure 3 SEM image of the silicon spheres in Example 1 of the present application. From the scanning electron microscope image, it can be seen that the particle size of the commercial silicon spheres in Example 1 is 2-5 μm.

[0057] Figure 4 SEM image of the precursor Mg2Si after firing in Example 1 of the present application. From the scanning electron microscope, it can be seen that the intermediate product Mg2Si after firing retains the overall spherical morphology, and the surface retains the flaky flower-like structure left after the NaCl acting as a heat sink is washed away.

[0058] Figure 8 SEM image of the three-dimensional porous carbon-coated silicon micro-powder composite material obtained in Example 1 of the present application at different scales. From the SEM at low magnification, it can be seen that the size of the three-dimensional porous carbon-coated silicon micro-powder composite material is overall micron grade, and the SEM at high magnification can see that the monodisperse three-dimensional porous carbon-coated silicon micro-powder composite material particles present a three-dimensional porous cage, and the surface can see the obvious carbon coating layer, which uniformly and fully wraps the surface of the silicon material.

[0059] Figure 9 TEM image of the three-dimensional porous carbon-coated silicon micro-powder composite material obtained in Example 1 of the present application at different scales. From the TEM at low magnification, it can be seen that the carbon coating layer is uniformly distributed on the surface of the silicon-based material, and there are large and abundant pore structures in the interior of the silicon-based material, which may be due to the Mg2Si precursor reacting with Al2O3 at high temperature to form MgO; the MgO is uniformly present in the interior of the silicon-based material, and after acid washing with hydrochloric acid, abundant large pores are left. The large and abundant pore structures are beneficial to providing sufficient buffer space for the silicon-based material, greatly relieving the volume expansion phenomenon of the silicon-carbon material in the charging and discharging process. At the same time, due to the removal of MgO in the interior of the material, a unique silicon skeleton network structure is formed, which can also be clearly verified by the internal details exposed by the surface part of the material in the above SEM image. In addition, from the TEM at high magnification, it can be seen that there are many small pore structures on the carbon shell on the surface of the silicon-carbon material, which is beneficial to providing abundant lithium ion diffusion and migration paths and electron transmission paths, accelerating the penetration process of the electrolyte, and making the electrolyte fully and uniformly infiltrate into the interior of the material.

[0060] Figure 10 FTIR spectrum of the three-dimensional porous carbon-coated silicon micro-powder composite material and the preparation method thereof obtained in Example 1 of the present application. In the FTIR spectrum, 1639, 1628, 1214, 1078, 760, 463 cm -1The characteristic peaks of the nearby position can be attributed to C-C, C=C, Si-O-C, Si-O-Si, Si-C and Si-O respectively. The results of FTIR show that the existence of such chemical bond bridges not only accelerates the rapid transmission of charges, but also improves the electrochemical activity and speeds up the transmission of electrons / ions.

[0061] Figure 11 The high-resolution photoelectron spectrum of element Si 2p of the three-dimensional porous carbon-coated silicon powder composite material and the preparation method thereof obtained in this example 1. The four peaks at 103.65, 103.10, 102.15 and 101.32 eV correspond to Si 4 + 3+ + Si-O-C and Si -1 chemical bonds respectively, proving that the silicon-based material and the carbon coating layer are closely combined together; the two peaks at 100.06 and 99.46 eV are respectively attributed to the Si 2p1 / 2 and Si 2p3 / 2 binding energy positions of Si(0), proving the existence of elemental silicon.

[0062] Figure 12 The high-resolution photoelectron spectrum of element C 1s of the three-dimensional porous carbon-coated silicon powder composite material and the preparation method thereof obtained in this example 1, proving the existence of C-C, C-O and C-Si bonds.

[0063] The above shows that the active material (silicon) and the carbon coating layer in this example are bonded through Si-C and Si-O-C bonds, and effective combination between the two is successfully achieved.

[0064] Figure 13 The first three circle charge-discharge curve diagram of the three-dimensional porous carbon-coated silicon powder composite material obtained in this example 1 at 25℃, 0.2Ag -1 current density. From the figure, it can be seen that after the sample of example 1 is assembled into a half battery, the first circle discharge specific capacity is 2317mAh g -1 , the charge specific capacity is 2094mAh g -1 , and the first coulombic efficiency is 90.38%.

[0065] Figure 14 The long cycle diagram of the three-dimensional porous carbon-coated silicon powder composite material obtained in this example 1 at 25℃, 1Ag -1 current density. After 460 cycles at a current density of 1Ag -1 , the discharge specific capacity is 1039mAh g -1 .

[0066] Example 2

[0067] A preparation method of a three-dimensional porous carbon-coated silicon powder composite material, comprising the following steps:

[0068] (1) 100 g of commercial silicon powder of 325 mesh was weighed and dispersed in a sand mill tank containing 600 mL of diethylene glycol dimethyl ether solvent and 20 mL of oleic acid, and was sand-milled at a speed of 500 r / min for 20 min; after spin evaporation collection, micron silicon powder was obtained; subsequent vibration screening was performed using 2000 and 2500 mesh screens respectively to obtain screened silicon particle powder; the size of the single silicon particle was 5-6.5 μm.

[0069] (2) 13.53 g of the screened silicon powder, 20.30 g of magnesium powder and 81.18 g of KCl were weighed and uniformly mixed in a mixer; under an argon atmosphere in a glove box, the mixture was packaged in a stainless steel tube; under an argon atmosphere in a tube furnace, the temperature was raised to 700 ℃ at a rate of 5 ℃ / min, and the temperature was maintained for 2 h; the whole process was static; after the reaction was completed, the heat absorber KCl was washed away to obtain a precursor raw material Mg2Si.

[0070] (3) 10 g of the collected Mg2Si, 1.6 g of pitch and 5 g of SBS (the mass ratio of Mg2Si: pitch: SBS was 60:10:30) were mixed uniformly, and then the mixture was transferred to a banbury mixer for banburying; the banburying temperature was controlled at 230 ℃, the rotating speed was 60 r / min, and the banburying time was 25 min; after the banburyed sample was collected, it was transferred to a tube furnace for carbonization; under an argon atmosphere, the temperature was raised to 350 ℃ at a rate of 3 ℃ / min, and the temperature was maintained for 1 h; then the temperature was continuously raised to 1000 ℃ at a rate of 8 ℃ / min, and the temperature was maintained for 1 h; after the calcination was completed, a black block-shaped intermediate product was collected.

[0071] (4) The black block-shaped intermediate product was preliminarily crushed by a crusher to obtain a powder sample; then the powder sample and Fe3O4 small balls (about 5 mm) were weighed according to a mass ratio of 1:1.5, uniformly mixed, and then transferred to a tube furnace under an argon atmosphere; the temperature was raised to 650 ℃ at a rate of 2 ℃ / min, and the temperature was maintained for 8 h; a black-green powder was collected; under the condition of argon gas being introduced, 3 mol / L hydrochloric acid solution was added dropwise to the black-green powder in a three-necked flask, and stirring was performed for 5 h to remove the byproduct MgO; after washing, suction filtration and drying, a preliminary silicon-carbon composite material was obtained; the preliminary silicon-carbon composite material was added to a 4 mol / L hydrofluoric acid solution, stirred for 35 min, washed, and dried at 80 ℃ to obtain a three-dimensional porous carbon-coated silicon powder composite material.

[0072] The CR 2016 type button cell was processed in the same manner as in Example 1.

[0073] Figure 5 The SEM image of the 325 mesh silicon powder described in Example 2 can be seen from the scanning electron microscope image: the size of the single silicon powder particle is about 40 μm.

[0074] Example 3

[0075] A preparation method of a three-dimensional porous carbon-coated silicon powder composite material, comprising the following steps:

[0076] (1) 100 g of commercial silicon powder of 325 mesh was weighed and dispersed in a sand mill tank containing 400 mL of diethylene glycol monomethyl ether solvent, and sand milling was performed at a speed of 1000 r / min for 60 min. After spin evaporation collection, micron-sized silicon powder was obtained. Subsequently, 6250 and 8000 mesh sieves were used for vibration sieving, respectively, to obtain sieved silicon particle powder. The size of the individual silicon particles was 1.3-2 μm.

[0077] (2) 13.53 g of the above sieved nano-silicon powder, 23.95 g of magnesium powder, and 108.24 g of LiCl were weighed and mixed uniformly in a mixer. The mixture was packaged in a stainless steel tube under an argon atmosphere in a glove box. The temperature was raised to 650°C at a rate of 5°C / min in a rotary furnace under an argon atmosphere, and the rotary furnace was rotated at a speed of 100 r / min. After the reaction was completed, the heat absorber LiCl was washed away to obtain the precursor material Mg2Si.

[0078] (3) 10 g of the above collected Mg2Si, 2.7 g of pitch, and 4.55 g of SIS (Mg2Si: pitch: SBS mass ratio of 55:15:25) were mixed uniformly, and then the mixture was transferred to a banbury mixer for banburying. The banburying temperature was controlled at 280°C, and the rotation speed was 70 r / min. The banburying time was 80 min. After the banburying was completed, the sample was collected and transferred to a tube furnace for carbonization. The temperature was raised to 350°C at a rate of 7°C / min under an argon atmosphere, and then the temperature was raised to 850°C at a rate of 9°C / min. After 1 h of holding at 350°C and 3 h of holding at 850°C, the calcination was completed. The black block-shaped intermediate product was collected.

[0079] (4) The black block-shaped intermediate product obtained by calcination was preliminarily crushed by a crusher to obtain a powder sample. Then, the powder sample and CuO pellets (-5 mm) were weighed according to a mass ratio of 1:3.5, mixed uniformly, and then transferred to a tube furnace under an argon atmosphere. The temperature was raised to 850°C at a rate of 8°C / min, and the temperature was held for 3 h. A black-green powder was collected. In a three-necked flask, 5 mol / L hydrochloric acid solution was added dropwise to the black-green powder under the condition of argon gas being introduced. After stirring for 12 h, the byproduct MgO was removed. After washing, suction filtration, and drying, a preliminary silicon-carbon composite material was obtained. The preliminary silicon-carbon composite material was added to 1 mol / L hydrofluoric acid solution, stirred for 50 min, washed, and dried at 80°C to obtain a three-dimensional porous carbon-coated silicon powder composite material.

[0080] The CR 2016 type button cell battery process was the same as that of Example 1.

[0081] Example 4

[0082] A method for preparing a three-dimensional porous carbon-coated silicon powder composite material, comprising the following steps:

[0083] (1) 100 g of commercial silicon powder of 325 mesh was weighed and dispersed in a sand mill tank containing 500 mL of diethylene glycol diethyl ether solvent and 30 mL of oleic acid, and sand milling was performed at a speed of 800 r / min for 30 min. After spin evaporation collection, micron-sized silicon powder was obtained. Subsequently, 2500 and 5000 mesh sieves were used for vibration sieving, respectively, to obtain sieved silicon particle powder: the size of the individual silicon particles was 2.6-5 μm.

[0084] (2) 13.53 g of the above sieved silicon powder, 23.95 g of magnesium powder, and 67.65 g of NaCl were weighed and mixed uniformly in a mixer, and then encapsulated in a stainless steel tube under an argon atmosphere in a glove box. The tube furnace was heated to 600 ℃ at a heating rate of 5 ℃ / min under an argon atmosphere, and the rotation speed of the rotary furnace was 150 r / min. After the reaction was completed, the heat absorber NaCl was washed away, and the precursor raw material Mg2Si was obtained.

[0085] (3) 10 g of the above collected Mg2Si, 5 g of pitch, and 10 g of SEBS (the mass ratio of Mg2Si: pitch: SBS was 40:20:40) were mixed uniformly, and then transferred to an internal mixer for internal mixing. The internal mixing temperature was controlled at 300 ℃, and the rotation speed was 100 r / min. The internal mixing time was 10 min. After the internal mixing was completed, the sample was collected and transferred to a tube furnace for carbonization. The temperature was increased to 350 ℃ at a rate of 2 ℃ / min under an argon atmosphere, and then the temperature was kept at 350 ℃ for 1 h. Subsequently, the temperature was increased to 900 ℃ at a rate of 6 ℃ / min, and then the temperature was kept at 900 ℃ for 3 h. After the calcination was completed, a black block-shaped intermediate product was obtained.

[0086] (4) The black block-shaped intermediate product was preliminarily crushed by a crusher to obtain a powder sample. Then, the powder sample and FeO pellets (-5 mm) were weighed according to a mass ratio of 1:3, mixed uniformly, and then transferred to a tube furnace. The temperature was increased to 800 ℃ at a rate of 5 ℃ / min under an argon atmosphere, and then the temperature was kept at 800 ℃ for 4 h. A black-green powder was obtained. In a three-necked flask, 6 mol / L hydrochloric acid solution was added dropwise to the black-green powder under the condition of argon gas being introduced. The stirring time was 4 h, and the byproduct MgO was removed. After washing, suction filtration, and drying, a preliminary silicon-carbon composite material was obtained. The preliminary silicon-carbon composite material was added to a 3 mol / L hydrofluoric acid solution, stirred for 40 min, washed, and dried at 80 ℃ to obtain a three-dimensional porous carbon-coated silicon powder composite material.

[0087] The CR 2016 button cell battery process was the same as that of Example 1.

[0088] Figure 6The SEM image of the silicon powder after the treatment described in Embodiment 4 shows that the size of the single silicon powder particle is between 2.6 and 5 μm.

[0089] Embodiment 5

[0090] A preparation method of a three-dimensional porous carbon-coated silicon powder composite material, comprising the following steps:

[0091] (1) 10 kg of commercial silicon powder of 325 mesh is weighed and loaded into an air flow crusher, the compressed air is 0.80 MPa, the gas flow rate is controlled to be 6 m 3 / min, and the whole process is fed at a constant speed by frequency conversion; the air flow crushed silicon particle powder is collected by a grading turbine, and the size of the single silicon particle is about 5 μm.

[0092] (2) 13.53 g of the above air flow crushed silicon powder, 23.95 g of magnesium powder, and 41.59 g of NaCl are weighed, mixed uniformly in a mixer, and packaged in a stainless steel tube in an argon atmosphere in a glove box, heated to 700 DEG C at a heating rate of 5 DEG C / min in a tube furnace under an argon atmosphere, and kept for 4 h, and the reaction is static. After the reaction is completed, the endothermic agent NaCl is washed away to obtain a precursor raw material Mg2Si.

[0093] (3) 10 g of the above collected Mg2Si, 2.5 g of pitch, and 4.16 g of SBS (the mass ratio of Mg2Si: pitch: SBS is 60: 15: 25) are mixed uniformly, and then the mixture is transferred to a banbury mixer for banburying, the banburying temperature is controlled at 190 DEG C, the rotating speed is 80 r / min, and the banburying time is 50 min; after the banburying is completed, the sample is collected and transferred to a tube furnace for carbonization: under an argon atmosphere, the temperature is increased to 350 DEG C at a rate of 6 DEG C / min, kept for 1 h, then increased to 800 DEG C at a rate of 8 DEG C / min, and kept for 4 h. After calcination is completed, a black block-shaped intermediate product is collected.

[0094] (4) The black block-shaped intermediate product is preliminarily crushed by a crusher to obtain a powder sample; then the powder sample and Al2O3 pellets (-5 mm) are weighed according to a mass ratio of 1:2, mixed uniformly, and then heated to 900 DEG C at a rate of 5 DEG C / min in a tube furnace under an argon atmosphere, and kept for 2 h to obtain a black green powder; under the condition of argon gas being introduced, 8 mol / L hydrochloric acid solution is added dropwise to the black green powder in a three-necked flask, stirred for 10 h, and the byproduct MgO is removed; after washing, suction filtration and drying, a preliminary silicon-carbon composite material is obtained; the preliminary silicon-carbon composite material is added into 5 mol / L hydrofluoric acid solution, stirred for 30 min, washed, and dried at 80 DEG C to obtain a three-dimensional porous carbon-coated silicon powder composite material.

[0095] The CR2016 type button cell is the same as Embodiment 1.

[0096] Figure 7 The SEM image of the nanometer silicon described in Embodiment 5 can be seen from the scanning electron microscope image: the particle size of the single nanometer silicon powder is about 5 μm.

[0097] Embodiment 6

[0098] A preparation method of a three-dimensional porous carbon-coated silicon powder composite material, comprising the following steps:

[0099] (1) 10 kg of commercial silicon powder of 325 mesh is weighed and loaded into an air flow crusher, the compressed air is 0.20 MPa, the gas flow rate is controlled to be 10 m 3 / min, and the whole process is uniformly fed at a variable frequency; the air flow crushed silicon particle powder is collected by a grading turbine, and the size of the single silicon particle is about 6 μm.

[0100] (2) 13.53 g of the above air flow crushed silicon powder, 23.95 g of magnesium powder and 60 g of NaCl are weighed, uniformly mixed in a mixer, and packaged in a stainless steel tube in an argon atmosphere glove box, heated to 700 DEG C at a heating rate of 5 DEG C / min in a rotary furnace in an argon atmosphere, and the rotary furnace rotates at 200 r / min. After the reaction is completed, the heat absorber NaCl is washed away to obtain the precursor raw material Mg2Si.

[0101] (3) 10 g of the above collected Mg2Si, 1.3 g of pitch and 4.58 g of SBS (the mass ratio of Mg2Si: pitch: SBS is 63:8:29) are taken, uniformly mixed, and then transferred to a banbury mixer for banburying, the banburying temperature is controlled at 210 DEG C, the rotating speed is 90 r / min, and the banburying time is 20 min; after the banburying is completed, the sample is collected and transferred to a tube furnace for carbonization: under an argon atmosphere, the temperature is increased to 350 DEG C at a rate of 4 DEG C / min, and then the temperature is increased to 650 DEG C at a rate of 10 DEG C / min, and the temperature is kept for 8 h. After the calcination is completed, the black blocky intermediate product is collected.

[0102] (4) The black blocky intermediate product is preliminarily crushed by a crusher to obtain a powder sample; then the powder sample and NiO small balls (-5 mm) are weighed according to a mass ratio of 1:2.5, uniformly mixed, and then transferred to a tube furnace under an argon atmosphere, and heated to 750 DEG C at a rate of 8 DEG C / min, and kept for 5 h to obtain a black green powder; under the condition of argon gas being introduced, 2 mol / L hydrochloric acid solution is added dropwise into the black green powder in a three-necked flask, stirred for 8 h, and the byproduct MgO is removed; after washing, suction filtration and drying, a preliminary silicon-carbon composite material is obtained; the preliminary silicon-carbon composite material is added into 2 mol / L hydrofluoric acid solution, stirred for 30 min, washed, and dried at 80 DEG C to obtain a three-dimensional porous carbon-coated silicon powder composite material.

[0103] CR 2016 type button cell process is the same as example 1.

[0104] Example 7

[0105] A preparation method of a three-dimensional porous carbon-coated silicon powder composite material, comprising the following steps:

[0106] (1) 10 kg of commercial silicon powder of 325 mesh was weighed and loaded into an air flow crusher, the compressed air was 1.2 MPa, the gas flow rate was controlled at 2 m 3 / min, and the whole process was fed at a constant speed by frequency conversion; the air flow crushed silicon particle powder was collected by a grading turbine, and the size of the single silicon particle was about 3 μm.

[0107] (2) 13.53 g of the above air flow crushed silicon powder, 23.95 g of magnesium powder, and 60 g of NaCl were weighed, mixed uniformly in a mixer, and packaged in a stainless steel tube under an argon atmosphere in a glove box, and then heated to 700℃ at a heating rate of 5℃ / min under an argon atmosphere in a tube furnace, and kept for 4 h, and the reaction was carried out statically. After the reaction was completed, the endothermic agent NaCl was washed away to obtain the precursor raw material Mg2Si.

[0108] (3) 10 g of the above collected Mg2Si, 1.3 g of pitch, and 4.58 g of SBS (Mg2Si: pitch: SBS mass ratio 63:8:29) were mixed uniformly, and then the mixture was transferred to a banbury mixer for banburying, the banburying temperature was controlled at 190℃, the rotating speed was 95 r / min, and the banburying time was 70 min; after the banburying was completed, the sample was collected and transferred to a tube furnace for carbonization: under an argon atmosphere, the temperature was increased to 350℃ at a rate of 5℃ / min, kept for 1 h, then increased to 800℃ at a rate of 5℃ / min, and kept for 4 h. After calcination was completed, a black block-shaped intermediate product was collected.

[0109] (4) The black block-shaped intermediate product was preliminarily crushed by a crusher to obtain a powder sample; then the powder sample and Fe3O4 small balls (-5 mm) were weighed according to a mass ratio of 1:3.5, mixed uniformly, and then heated to 800℃ at a rate of 5℃ / min under an argon atmosphere in a tube furnace, and kept for 4 h to obtain a black-green powder; under the condition of argon gas being introduced, 5 mol / L hydrochloric acid solution was added dropwise into the black-green powder in a three-necked flask, stirred for 7 h, and the byproduct MgO was removed; after washing, suction filtration and drying, a preliminary silicon-carbon composite material was obtained; the preliminary silicon-carbon composite material was added into a 2 mol / L hydrofluoric acid solution, stirred for 45 min, washed, and dried at 80℃ to obtain a three-dimensional porous carbon-coated silicon powder composite material.

[0110] CR 2016 type button cell process is the same as example 1.

[0111] Comparative example:

[0112] Comparative Example 1

[0113] A preparation method of a carbon-coated silicon micro-powder composite material, comprising the following steps:

[0114] (1) 10 g of commercially purchased 2-5 μm silicon balls, 7 g of pitch, and 10 g of SBS (the mass ratio of Si: pitch: SBS is 37:26:37) were weighed, uniformly mixed, and then transferred to a banbury mixer for banburying. The banburying temperature was controlled at 150°C, the rotation speed was 40 r / min, and the banburying time was 120 min to obtain a preliminary sample after banburying.

[0115] (2) The banburyed sample collected above was transferred to a tube furnace for carbonization: under an argon atmosphere, the temperature was raised to 350°C at a rate of 2°C / min, and after 1 h of holding, the temperature was continuously raised to 500°C at a rate of 10°C / min, and held for 10 h. After calcination, a black block-shaped intermediate product was collected, which was then crushed by a crusher to obtain a black-green powder.

[0116] (3) The obtained black-green powder was added to a 5 mol / L hydrofluoric acid solution, stirred for 20 min, washed, and dried at 80°C to obtain a carbon-coated silicon micro-powder composite material.

[0117] The CR 2016 type button cell was processed in the same way as in Example 1.

[0118] Comparative Example 2

[0119] A three-dimensional porous silicon-carbon composite material prepared by a ball milling method, comprising the following steps:

[0120] (1) 100 g of commercial silicon powder with a mesh size of 325 was weighed and dispersed in a sand mill tank containing 100 mL of diethylene glycol diethyl ether solvent and 20 mL of oleic acid. The sand milling was performed at a speed of 3000 r / min for 180 min. After rotary evaporation, micron-sized silicon powder was collected. Subsequently, the silicon powder was sieved using 1250 and 2000 mesh sieves, respectively, to obtain sieved silicon particle powder. The size of the individual silicon particles was 6.5-10 μm.

[0121] (2) 13.53 g of the sieved silicon powder above, 23.95 g of magnesium powder, and 60 g of NaCl were weighed and uniformly mixed in a mixer. The mixture was sealed in a stainless steel tube under an argon atmosphere in a glove box. The tube furnace was heated to 700°C at a rate of 5°C / min under an argon atmosphere, and the reaction was carried out statically for 4 h. After the reaction, the endothermic agent NaCl was washed away to obtain a precursor material Mg2Si.

[0122] (3) Take 10 g of the Mg2Si collected above, 2.6 g of pitch, and 10 mL of oleic acid, mix them evenly, and then transfer the mixture to a ball mill tank. Add zirconium balls at a mass ratio of 1:5, and mill at a speed of 350 r / min for 12 h. After the milling is completed, collect the sample and transfer it to a tube furnace for carbonization: under an argon atmosphere, heat it to 350°C at a rate of 5°C / min, keep it at this temperature for 1 h, continue to heat it to 700°C at a rate of 5°C / min, and keep it at this temperature for 8 h. After the calcination is completed, collect the black block-shaped intermediate product.

[0123] (4) The black block-shaped intermediate product obtained is preliminarily crushed with a crusher to obtain a powder sample. Then, the powder sample and Fe2O3 pellets (about 5 mm) are weighed at a mass ratio of 1:1.5, mixed evenly, and then heated to 700°C at a rate of 5°C / min under an argon atmosphere in a tube furnace, and kept at this temperature for 8 h to obtain black-green powder. In a three-necked flask, 3 mol / L hydrochloric acid solution is added dropwise to the black-green powder under the condition of argon gas being introduced, and stirred for 7 h to remove the byproduct MgO. After washing, suction filtration, and drying, a preliminary silicon-carbon composite material is obtained. The preliminary silicon-carbon composite material is added to a 2 mol / L hydrofluoric acid solution, stirred for 35 min, washed, and dried at 80°C to obtain a three-dimensional porous carbon-coated silicon powder composite material and a preparation method thereof.

[0124] The CR 2016 button cell battery has the same process as that of Example 1.

[0125] Comparative Example 3

[0126] A three-dimensional porous silicon-carbon composite material prepared by a solvent-rotary evaporation method includes the following steps:

[0127] (1) 100 g of commercial silicon powder with a mesh size of 325 is weighed and dispersed in a sand mill tank containing 300 mL of diethylene glycol diethyl ether solvent and 20 mL of oleic acid, and is sand-milled at a speed of 1500 r / min for 120 min. After rotary evaporation and collection, micron-sized silicon powder is obtained. Subsequently, 10000-mesh sieving is performed to obtain sieved silicon particle powder, and the size of a single silicon particle is about 1 μm.

[0128] (2) 13.53 g of the sieved silicon powder, 23.95 g of magnesium powder, and 60 g of NaCl are weighed, mixed evenly in a mixer, and then sealed in a stainless steel tube in a glove box under an argon atmosphere. The tube is heated to 650°C at a rate of 5°C / min in a tube furnace under an argon atmosphere, and kept at this temperature for 6 h to perform a reaction in a static state. After the reaction is completed, the heat absorber NaCl is washed away to obtain a precursor raw material Mg2Si.

[0129] (3) Take 10 g of the Mg2Si collected above, 200 mL of anhydrous ethanol, and ultrasonically disperse for 2 h to obtain a suspension A; take 3 g of pitch and 100 mL of tetrahydrofuran, and ultrasonically stir to dissolve for 2 h to obtain a solution B. After mixing the suspension A and the solution B, ultrasonic for 1 h, stir for 2 h, then transfer to a rotary evaporation flask for rotary evaporation, and dry. After rotary evaporation, the sample is transferred to a tube furnace for carbonization: under an argon atmosphere, 5 ℃ / min to 350 ℃, keep for 1 h, then continue to 5 ℃ / min to 800 ℃, keep for 4 h. After calcination, a black block-shaped intermediate product is collected.

[0130] (4) The black block-shaped intermediate product obtained is preliminarily crushed by a crusher to obtain a powder sample; then the powder sample and Al2O3 pellets (~ 5 mm) are weighed according to a mass ratio of 1:3.5, mixed uniformly, and then heated to 800 ℃ at a rate of 5 ℃ / min under an argon atmosphere in a tube furnace, and a black-green powder is collected; in a three-necked flask, under the condition of argon gas being introduced, 2 mol / L hydrochloric acid solution is added dropwise into the black-green powder, and stirred for 12 h to remove the byproduct MgO; after washing, suction filtration and drying, a preliminary silicon-carbon composite material is obtained; the preliminary silicon-carbon composite material is added into 4 mol / L hydrofluoric acid solution, stirred for 25 min, washed, and dried at 80 ℃ to obtain a three-dimensional porous carbon-coated silicon powder composite material.

[0131] The CR 2016 button cell battery process is the same as that of Example 1.

[0132] Comparative Example 4

[0133] A preparation method of a three-dimensional porous carbon-coated silicon powder composite material, comprising the following steps:

[0134] (1) Take 10 g of commercial silicon-aluminum alloy powder (the content of silicon is 20%, and the size of the alloy powder is 2 microns), 1.3 g of pitch, and 4.58 g of SBS (the mass ratio of the silicon-aluminum alloy powder: pitch: SBS is 63:8:29), mix uniformly, then transfer the mixture to a banbury mixer for banburying, the banburying temperature is controlled at 190 ℃, the rotating speed is 40 r / min, and the banburying time is 55 min; after the banburying, the sample is collected and transferred to a tube furnace for carbonization: under an argon atmosphere, 5 ℃ / min to 350 ℃, keep for 1 h, then continue to 5 ℃ / min to 780 ℃, keep for 6 h. After calcination, a black block-shaped intermediate product is collected.

[0135] (2) the obtained black blocky intermediate product is preliminarily crushed by a crusher to obtain a powder sample; under the condition of argon gas being introduced, a 6 mol / L hydrochloric acid solution is added dropwise into the black green powder, heating and stirring for 20 h, and the metal Al and the byproduct Al2O3 are removed; after washing, suction filtration and drying, a preliminary silicon-carbon composite material is obtained; the preliminary silicon-carbon composite material is added into a 3 mol / L hydrofluoric acid solution, stirred for 40 min, washed, and dried at 80 DEG C to obtain a three-dimensional porous carbon-coated silicon powder composite material.

[0136] The CR 2016 type button cell process is the same as that of example 1.

[0137] Performance test:

[0138] The material prepared in the above examples is fully analyzed in terms of particle size, morphology and composition by using X-ray diffraction technology (XRD), X-ray photoelectron spectroscopy technology (XPS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermal gravimetric analyzer (TG).

[0139] The application mainly uses sanding process and air flow breaking process to treat the silicon source, combines with the carbon coating process of the dense mixing process, and efficiently and quickly prepares the three-dimensional porous carbon-coated silicon powder composite material with rich three-dimensional porous structure, which is used as a negative electrode material of a lithium ion battery. After the batteries prepared in the above examples and comparative examples are placed for 12 h, the battery tester (Shenzhen Xinwei) and BTS 7.6.0 software are used to test the long cycle performance of the batteries under the condition that the temperature is 25 DEG C constant and the current density is 0.2-1 Ag -1 The preparation characteristics and electrochemical performance of the sample of the example and the sample of the comparative example are shown in Table 1 and Table 2.

[0140] The application mainly uses the silicon powder treated by different processes as a raw material, bitumen as an effective carbon source, SBS as a mixing agent, adopts the carbon coating process of dense mixing, and finally obtains the three-dimensional porous carbon-coated silicon powder composite material after annealing, calcination, carbonization and oxidation magnesium removal and acid washing. The silicon-carbon material modified by the magnesium element in the silicon-magnesium alloy precursor can effectively improve the micro defects in the material, eliminate the excess active sites, and improve the first coulomb efficiency.

[0141] Table 1 test results of the silicon-carbon composite material prepared in examples 1-7 at 25 DEG C

[0142]

[0143] According to the test results in Table 1, the three-dimensional porous carbon-coated silicon powder composite material has obvious high initial efficiency and excellent electrochemical performance advantages: Example 1 uses commercial silicon balls of 2-5 micron silicon balls as raw materials to prepare a three-dimensional porous carbon-coated silicon powder composite material, 1Ag -1 The reversible capacity is 1039 mAh g -1 after 460 cycles at a current density, and the initial coulombic efficiency is 90.61%; Examples 2-4 are subjected to a sanding process and a second classification by a screen, and a three-dimensional porous carbon-coated silicon powder composite material is prepared using 1.3-6 micron silicon powder as a raw material, and the initial coulombic efficiency is 91-93%; Examples 5-7 use an air flow crushing process, and a three-dimensional porous carbon-coated silicon powder composite material is prepared using 3-6 micron silicon powder as a raw material, and the initial coulombic efficiency is 90-92%. It can also be seen that the three-dimensional porous carbon-coated silicon powder composite material prepared using micron silicon powder has a reversible capacity of more than 1200 mAh g -1 after 200 cycles at a current density of 1Ag -1 The above may be due to the construction of the multi-level pore structure, which promotes ion migration and provides sufficient expansion space.

[0144] As can be seen from Example 1 in Table 1 and Comparative Example 1 in Table 2, the silicon-carbon composite material obtained by introducing magnesium powder to modify the precursor has an ultra-high initial coulombic efficiency of >90%, which is a major breakthrough. According to the results of the current literature research, ordinary silicon materials are almost difficult to break through the threshold of 88% in the initial coulombic efficiency. It may be due to the perfect coating effect of the carbon coating process and the effective protection of the magnesium element in the precursor to the silicon-based material at each stage, which inhibits the excessive oxidation of the silicon material while removing the heteroatoms in the pitch-based carbon. At the same time, the formation of a large number of three-dimensional pore structures in the material is beneficial to alleviate the volume expansion effect of the silicon-carbon material during the charging and discharging process, which can be reflected in the capacity retention after a certain number of cycles.

[0145] From the comparative examples 2-3 in table 2, it can be seen that: under the condition of the same silicon-magnesium alloy modification and asphalt as carbon source, the silicon-carbon composite material obtained by using different carbon coating processes is obviously superior to the ball milling process and the solvent-rotary evaporation process in terms of the initial efficiency and the capacity retention after a certain number of cycles, which indicates that the three-dimensional porous carbon-coated silicon powder composite material prepared by the internal mixing process has less defects, good coating effect and is more conducive to the performance of the silicon-carbon material. It is emphasized that the internal mixing process is applied to carbon coating for the first time. From the comparative example 4 in table 2, it can be seen that after the sacrificial agent and the pore-forming agent are changed to metal Al, the first coulombic efficiency is improved compared with other comparative examples, but it is still significantly lower than the breakthrough of more than 90% of the embodiment of the present application. It is possible that Mg is more active than Al, which can more effectively reduce the generation of material defects and remove impurities in the carbon source.

[0146] Table 2: Test results of the silicon-carbon composite materials prepared in comparative examples 1-4 at 25 DEG C

[0147]

[0148]

[0149] From the above examples and comparative examples, it can be seen that the present application has the following characteristics:

[0150] The present application uses the internal mixing process as the main process for carbon coating, which quickly and effectively coats the organic carbon source asphalt on the surface of the silicon-based material, and forms a porous carbon shell at a high temperature in the subsequent process. At the same time, the active metal magnesium powder is used as a sacrificial agent and a pore-forming agent to participate in the synthesis of the precursor, supplemented by high-temperature annealing and calcination to improve the internal micro defects and eliminate the active sites. At the same time, the raw materials required by the process are widely available and low in cost; the magnesium and silicon are made into a silicon-magnesium alloy to avoid the direct participation of the active metal in the subsequent process, thereby improving the overall safety; the raw materials and chemical reagents involved in the process are common chemicals, which have the characteristics of environmental friendliness; in summary, the present application has the potential for commercial large-scale production.

[0151] The three-dimensional porous carbon-coated silicon powder composite material in the present application has a porous cage shape, and is a three-dimensional material with multiple scales and multiple chemical bonds coexisting in nano-pores and micro-macropores. The external carbon shell has a rich distribution of nano-pores, the silicon core and the carbon shell have a micro-macroporous structure after MgO pickling, and a unique silicon skeleton network is formed inside; there are also various types of chemical bonds tightly linked between the silicon core and the carbon shell, which is a multi-bond three-dimensional material.

[0152] The three-dimensional porous carbon-coated silicon powder composite material can be applied to the negative electrode material of lithium ion batteries in the field of new energy vehicles, energy storage power stations and other high-power fields, and has large specific capacity and excellent long-cycle performance.

[0153] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above embodiments, and any changes, modifications, substitutions, combinations, simplifications, etc. made without departing from the spirit and principles of the present application should be equivalent replacement manners and should be included in the protection scope of the present application.

Claims

1. A method for preparing a three-dimensional porous carbon-coated silicon fine powder composite material, characterized by It comprises the following steps: 1) mixing silicon powder, magnesium powder and heat-absorbing agent, then sealing and calcining under a protective atmosphere, and washing with water to obtain a silicon-magnesium alloy precursor; the heat-absorbing agent is sodium chloride, potassium chloride or lithium chloride; 2) uniformly mixing the silicon-magnesium alloy precursor, pitch and mixing agent, then performing mixing in a banbury mixer to obtain a mixed intermediate; the silicon-magnesium alloy precursor is Mg2Si; the mass ratio of Mg2Si, pitch and mixing agent is 40-63:8-20:29-40; the mixing agent is at least one of styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer and styrene-ethylene-butylene-styrene block copolymer; 3) transferring the mixed intermediate to a tube furnace, calcining at high temperature under a protective atmosphere, then crushing by a crusher after cooling to obtain carbon-coated silicon alloy powder; 4) mixing the carbon-coated silicon alloy powder with an oxidizing agent, annealing and calcining under a protective atmosphere to remove magnesium, then obtaining powder; acid washing and drying the powder to obtain a three-dimensional porous carbon-coated silicon powder composite material; the mass ratio of the carbon-coated silicon alloy powder and the oxidizing agent is 1:1.5-3.5; the oxidizing agent is at least one of Al2O3, Fe2O3, Fe3O4, FeO, NiO and CuO.

2. The method of claim 1, wherein the method is characterized by: The temperature of the mixing is 150-300℃, the rotating speed is 40-100r / min, and the mixing time is 10-120min; the calcining temperature is 500-1000℃, the time is 1-10h, and the heating rate is 2-10℃ / min; the annealing and calcining temperature for removing magnesium is 650-900℃, the time is 2-8h, and the heating rate is 2-10℃ / min.

3. The method of claim 1, wherein the method is characterized by: The sealing calcining is to seal the silicon powder, magnesium powder and heat-absorbing agent in a stainless steel tube, and calcining in a rotary furnace; the calcining temperature is 550-700℃, the calcining time is 2-8h, the heating rate is 3-10℃ / min, and the rotating speed of the rotary furnace is 50-200r / min; the acid washing uses at least one of hydrochloric acid, acetic acid and hydrofluoric acid as the acid washing substance, the concentration of the acid washing substance is 2-8mol / L, and the acid washing time is 15min-10h.

4. The method of claim 3, wherein the method is characterized by: The mass ratio of the silicon powder, magnesium powder and heat-absorbing agent is 1:1-1.77:2-8.

5. The method of claim 4, wherein the method further comprises: The silicon powder is treated by a sand milling process or an air flow crushing process before use; the sand milling process is to mix micron-sized silicon powder with an organic substance, sand milling, collecting the silicon powder by rotary evaporation, and sieving; the mass ratio of the silicon powder and the organic substance is 1:1-6; the sand milling rotating speed is 500-3000r / min, and the time is 10-180min; The crushing pressure of the gas flow breaking process is 0.2-1.2 Mpa, the gas flow rate is controlled to be 1-10 m 3 / min; the whole process is fed at a constant speed by frequency conversion, and the silicon powder is collected by a grading turbine.

6. The method of claim 5, wherein the method further comprises: The organic substance is one or more of diethylene glycol dimethyl ether, diethylene glycol monomethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether and oleic acid.

7. The method of claim 1, wherein the method is characterized by: The protective atmosphere in steps 1), 3) and 4) is all argon atmosphere.

8. A three-dimensional porous carbon-coated silicon fine powder composite, characterized by comprising: It is prepared by the preparation method in any one of claims 1-7.

9. Use of the three-dimensional porous carbon-coated silicon powder composite material of claim 8 in the preparation of a lithium ion battery negative electrode material, wherein the three-dimensional porous carbon-coated silicon powder composite material, carbon black and CMC are mixed to form a slurry, which is coated on a copper foil to obtain a lithium ion battery negative electrode sheet; and the mass ratio of the three-dimensional porous carbon-coated silicon powder composite material, carbon black and CMC is 5:3:2 to 8:1:1.

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