Highly compacted density porous silicon-carbon composite material, and preparation method and application thereof

Abstract

The application discloses high-compaction-density porous silicon-carbon composite material and a preparation method and application thereof, and the preparation method comprises the following steps: step 1, performing dealloying treatment on a micrometer silicon-based material to obtain a porous silicon framework; step 2, performing pore filling to fill a nano silicon material in the pores of the silicon-based material to obtain an intermediate product; and step 3, performing carbon coating to form a carbon coating layer on the surface of the intermediate product, and obtaining the composite material after sintering. In the three-dimensional porous silicon framework, the nano Si is filled, on one hand, the micrometer porous silicon framework can effectively relieve the volume expansion problem caused by the insertion and extraction of lithium ions (Li + ) in the charging and discharging process; on the other hand, the filling of the nano Si in the micrometer porous silicon framework can effectively improve the compaction density of the negative electrode material, thereby significantly improving the volume energy density.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery negative electrode material, in particular to a high-compaction-density porous silicon-carbon composite material and a preparation method and application thereof. BACKGROUND

[0002] With the popularity of pure electric vehicles and plug-in hybrid electric vehicles, new requirements are put forward for the development of lithium ion batteries. Among them, high capacity and long life are the core issues that attract much attention. Graphite-based negative electrode materials are commercialized due to their long life and high initial coulombic efficiency (ICE), but their theoretical capacity (372 mAh / g) is insufficient to meet the growing energy storage demand. Silicon (Si) has an ultra-high theoretical capacity (3579 mAh / g) and a suitable working voltage (~0.4 V), and is considered one of the most promising negative electrode materials for lithium ion batteries. However, Si-based negative electrode materials have the following problems: 1. During charging and discharging, the volume expansion of Si is as high as 300%, which causes the pulverization of the electrode material and leads to electrochemical failure, resulting in a sharp decrease in capacity and cycle life; 2. Since Si is a semiconductor in its natural state, each Si atom has four electrons in its outer shell that form stable chemical bonds with adjacent silicon atoms, and the electrical conductivity of Si material is poor.

[0003] The nanocrystallization of Si can effectively alleviate the pulverization and fragmentation problems caused by volume expansion, and improve the reaction kinetics and rate performance. However, the high specific surface area of nanomaterials has problems such as low compaction density, low ICE, and low volumetric energy density, and the high cost of nanomaterials also makes it difficult to popularize nano-Si. Micron-Si has the advantages of high compaction density, low surface area, and low cost. On this basis, the use of microstructure design to prepare a porous structure is beneficial to alleviate a series of problems such as the volume expansion of Si during lithium storage, and then carbon filling or carbon coating is performed to increase its electrical conductivity and stability. However, a large number of pores will also increase the specific surface area of the material and reduce the compaction density. Therefore, it is urgent to prepare a micron-sized porous silicon-carbon composite material with high cycle stability, high compaction density, and low cost.

[0004] CN107507972A discloses a preparation method of a silicon-carbon negative electrode material, which comprises: using silicon alloy powder as raw material, acid washing treatment, etching the remaining metals in the silicon alloy powder except silicon to obtain porous silicon; performing carbon coating treatment on the porous silicon to form a silicon-carbon precursor; and then performing carbonization treatment on the silicon-carbon precursor to obtain a silicon-carbon negative electrode material. However, the porous structure existing in the interior of the silicon-carbon negative electrode material causes the negative electrode material to have a low compaction density, which in turn leads to a decrease in volumetric energy density.

[0005] CN115548300A discloses a porous silicon-based composite material, which has a core-shell structure and comprises a silicon-based material as an inner core and a porous layer and a carbon coating layer successively coated on the outer surface of the inner core, wherein the porous layer is silicon or a mixture of silicon and metal, and the pores of the porous layer are filled with carbon material. However, the silicon-based composite material has problems such as increased side reactions due to high specific surface area, reduced ICE, and reduced volume energy density caused by low compaction density. Therefore, there is an urgent need for a porous silicon-carbon composite material with high compaction density. SUMMARY

[0006] The purpose of the present application is to overcome the problems of existing silicon-based alloys as negative electrode materials, low compaction density and high specific surface area (nano Si-based negative electrode), and electrode pulverization caused by large volume expansion during cycling, and to provide a preparation method of a high-compaction-density porous silicon-carbon composite material.

[0007] Another purpose of the present application is to provide a high-compaction-density porous silicon-carbon composite material prepared by the preparation method.

[0008] Another purpose of the present application is to provide an application of a high-compaction-density porous silicon-carbon composite material.

[0009] The technical solution adopted to achieve the purpose of the present application is as follows:

[0010] A preparation method of a high-compaction-density porous silicon-carbon composite material, comprising the following steps:

[0011] Step 1: subjecting a micron silicon-based material to dealloying treatment to obtain a porous silicon skeleton;

[0012] Step 2: performing pore filling to fill the pores of the silicon-based material with nano silicon material to obtain an intermediate product;

[0013] Step 3: performing carbon coating to form a carbon coating layer on the surface of the intermediate product, and sintering to obtain a composite material.

[0014] In the above technical solution, the micron silicon-based material in step 1 is one or more of aluminum silicon, magnesium silicon, or iron silicon, preferably, the average particle size D50 of the silicon-based material is 1-50 μm, preferably 1-10 μm, and preferably, the Si content in the silicon-based material is 12%-50%.

[0015] The dealloying treatment is selected from one or both of acid pickling etching treatment and alkali pickling etching treatment, preferably acid pickling etching treatment, and more preferably, the acid for the acid pickling etching treatment is selected from one or more of hydrochloric acid, sulfuric acid, and hydrofluoric acid, and most preferably hydrochloric acid.

[0016] In the above technical solution, the nano-silicon filling material in step 2 comprises nano-silicon, and the average particle size D50 of the nano-silicon is 1-100 nm, preferably 20-80 nm.

[0017] In the above technical solution, in step 2, the porous silicon framework, nano-silicon and dispersant are mixed, uniformly dispersed in the porous Si material by a spray drying method, and then heat-treated to obtain an intermediate product.

[0018] Preferably, the mixing weight ratio of the porous silicon framework to the nano-silicon is (8-2):1, preferably 3:1.

[0019] Preferably, the inlet temperature during the spray drying is 150-250℃, preferably 170℃.

[0020] Preferably, the heat treatment conditions include: a temperature of 750-1200℃, preferably 800-900℃; and a holding time of 1-10 h, preferably 3-5 h.

[0021] In the above technical solution, in step 3, the intermediate product and a carbon source are sequentially mixed, carbonized and heat-treated under the condition of an inert gas and an optional solvent.

[0022] Preferably, the weight ratio of the intermediate product to the carbon source is 10:(1-3).

[0023] Preferably, the carbon material is selected from one or more of pitch, phenolic resin, glucose, sucrose, dopamine, resorcinol and graphene.

[0024] Preferably, the carbonization process conditions include: a temperature of 750-1200℃, preferably 800-1000℃; and a holding time of 1-10 h, preferably 3-5 h.

[0025] In another aspect of the present application, a high-compaction-density porous silicon-carbon composite material is provided, which is prepared by the preparation method.

[0026] In another aspect of the present application, the high-compaction-density porous silicon-carbon composite material or the composite material prepared by the preparation method is applied in a lithium ion battery.

[0027] In another aspect of the present application, a negative electrode sheet is provided, which comprises the high-compaction-density porous silicon-carbon or the composite material prepared by the preparation method.

[0028] In another aspect of the present application, a lithium ion battery is provided, which comprises the negative electrode sheet.

[0029] In the technical scheme, the lithium ion battery has a reversible capacity greater than 1800 mAh / g.

[0030] And / or the lithium ion battery has a capacity retention rate of more than 70% after 100 cycles.

[0031] Compared with the prior art, the present application has the following beneficial effects:

[0032] The present application fills nano-Si in a three-dimensional porous silicon framework. On the one hand, the microporous silicon framework can effectively alleviate the volume expansion problem caused by the insertion and extraction of lithium ions (Li + ) during the charging and discharging process; on the other hand, the filling of nano-Si in the microporous Si framework can effectively improve the compaction density of the negative electrode material, thereby significantly improving the volumetric energy density. Nano-Si has a larger specific surface area and can provide more reaction sites, thus improving the rate performance of the material. At the same time, it can alleviate the volume expansion during lithium storage and improve the structural stability. The microporous silicon framework has a larger particle size, fewer interface reactions, and a higher compaction density compared to nano-Si. The porous micro-nano silicon-carbon composite material prepared by the present application can significantly improve the compaction density while maintaining good rate performance, structural stability, and long cycle performance.

[0033] In addition, carbon coating can not only effectively improve the conductivity of silicon-based materials, but also alleviate the volume expansion of silicon particles during the charging and discharging process. The carbon coating layer can prevent direct contact between silicon and electrolyte, thereby reducing side reactions such as solid electrolyte interface film (SEI) accumulation and improving electrochemical stability. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The figure shows the characterization diagram of the composite prepared in Example 2, wherein, Figure 1 (a) is the SEM image of the Al 80 Si 20 raw silicon-based alloy powder, Figure 1 (b) is the SEM image of the microporous silicon framework obtained in step 1, Figure 1 (c) is the SEM image of the microporous silicon filled with 50 nm Si obtained in step 2, Figure 1 (d) is the SEM image of the carbon-coated intermediate product in step 3.

[0035] Figure 2 The figure shows the SEM cross-sectional image of the negative electrode sheet, wherein, Figure 2 (a) is the cross-sectional image of the negative electrode sheet prepared by the porous silicon framework obtained by Al 80 Si 20 de-alloying treatment, Figure 2(b) is a cross-sectional view of the anode electrode sheet prepared from the high-compactness porous silicon-carbon composite material obtained in Example 2.

[0036] Figure 3 Fig. 4 shows the XRD characterization diagram of the corresponding composite obtained in each step of Example 2.

[0037] Figure 4 Fig. 5 shows the comparison diagram of the electrochemical performance of the product obtained in Example 2, wherein, Figure 4 (a) is the Al 80 Si 20 Fig. 6 shows the comparison diagram of the cycle performance of the silicon-carbon composite prepared by dealloying treatment and preparation, Figure 4 (b) is the comparison diagram of the rate performance of the two. DETAILED DESCRIPTION

[0038] The application will be further described in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and not to limit the application.

[0039] A high-compactness porous silicon-carbon composite material is prepared by the following steps:

[0040] Step 1, preparing a three-dimensional porous silicon skeleton;

[0041] The micron-sized silicon-based alloy powder is placed in a container for dealloying treatment to obtain a three-dimensional porous silicon skeleton. The micron-sized silicon-based material is one or more of aluminum-silicon, magnesium-silicon or iron-silicon, preferably, the average particle size D50 of the silicon-based material is 1-50 μm, preferably 1-10 μm, and preferably the Si content in the silicon-based material is 12%-50%; the etching liquid can be selected as one or both of acid washing or alkali washing, the acid washing can be selected as one or more of hydrochloric acid, sulfuric acid, hydrofluoric acid, preferably hydrochloric acid etching, the concentration of hydrochloric acid is selected as 1 mol / L-4 mol / L, and the alkali washing can be selected as one or more of potassium hydroxide and sodium hydroxide.

[0042] Step 2, filling nano-Si particles into the micron-sized porous silicon;

[0043] The nano-Si particles are mixed with a dispersant at a mass ratio of (8-2):1, then uniformly dispersed, and then the porous silicon is added and uniformly dispersed, and then the nano-Si is uniformly dispersed in the porous silicon material by a spray drying method, and then an intermediate product is obtained by heat treatment; wherein the average size D50 of the nano-Si is 1-100 nm; the inlet temperature of the spray drying is 150°C-200°C, and the feeding speed is 1 mL / min-10 mL / min. The heat treatment conditions include: the temperature is 750-1200°C; and the holding time is 1-10 h.

[0044] Step 3, the intermediate product is carbon-coated to obtain a silicon-carbon composite material precursor;

[0045] The intermediate product is mixed with a selected carbon source and stirred uniformly, and then dried and solidified to obtain a silicon-carbon composite material precursor. The silicon-carbon composite material precursor is subjected to high-temperature sintering to obtain the three-dimensional porous silicon-carbon composite material. The high-temperature sintering has a heating rate of 1-10°C / min, a holding temperature of 700-1200°C, and a holding time of 1-10h.

[0046] The dispersing agent used for filling the nano-Si into the microporous silicon is one or more of sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, polyvinyl pyrrolidone, trimethoxysilane acrylate, and 3-aminopropyl trimethoxysilane. The organic carbon source used for carbon coating is one or more of sucrose, glucose, citric acid, phenolic resin, epoxy resin, pitch, polyvinyl alcohol, polypyrrole, polypyrrolidone, polyaniline, polyacrylonitrile, polydopamine, and lignin.

[0047] Example 1

[0048] A high-compactness porous silicon-carbon composite material is prepared by the following method:

[0049] Step 1, Al 80 Si 20 is added into HCl (2 mol / L), and after acid washing at 40°C for 24h, the mixture is subjected to suction filtration and drying to obtain a microporous Si skeleton.

[0050] Step 2, 200mg of nano-Si (20nm) and 200mg of polyvinyl pyrrolidone (PVP) are dissolved in 50ml of deionized water, and the mixture is uniformly dispersed in an ultrasonic oscillator for 1h. Then, 600mg of the microporous Si skeleton is added, and the mixture is continuously oscillated in the ultrasonic oscillator for 1h, and then stirred in a magnetic stirrer at 40°C for 3h. The uniformly mixed mixture is subjected to spray drying, in which the inlet air temperature is 170°C, the outlet air temperature is 110°C, and the feeding speed is 5ml / min. After the end of the process, the collected material is an intermediate product of nano-spheres filled in the microporous silicon.

[0051] Step 3, 30mg of phenolic resin is dissolved in 40ml of alcohol, and the intermediate product obtained in Step 2 is added. The mixture is stirred for 3h, soaked for 3h, and solidified at 100°C for 24h to obtain a silicon-carbon precursor. The silicon-carbon precursor is placed in a tube furnace, inert gas is introduced, the temperature is raised to 850°C at a rate of 5°C / min and held for 3h, and then naturally cooled to room temperature to obtain a high-compactness porous silicon-carbon composite material.

[0052] Example 2

[0053] A high-compactness porous silicon-carbon composite material is prepared by the following method:

[0054] Step 1, Al 80 Si 20 (average particle size D50 of 7 μm) was added into HCl (2 mol / L), after acid washing at 40℃ for 24 h, suction filtration and drying, micron porous Si skeleton was obtained, the XRD pattern of which is shown in Figure 3 .

[0055] Step 2, 200 mg of nano-Si (50 nm) and 200 mg of polyvinylpyrrolidone (PVP) were dissolved in 50 ml of deionized water, and the mixture was uniformly dispersed in an ultrasonic oscillator for 1 h. Then, 600 mg of micron porous Si skeleton was added, and the mixture was continuously oscillated in the ultrasonic oscillator for 1 h, and then stirred on a magnetic stirrer at 40℃ for 3 h. The uniformly mixed mixture was subjected to spray drying, in which the inlet temperature was 170℃, the outlet temperature was 110℃, and the feeding speed was 5 ml / min. After the end of the process, the collected material was an intermediate product of micron porous silicon filled with nanospheres.

[0056] Step 3, 30 mg of phenolic resin was dissolved in 40 ml of alcohol, and the intermediate product obtained in step 2 was added. The mixture was stirred for 3 h, soaked for 3 h, and cured at 100℃ for 24 h to obtain a silicon-carbon precursor. The silicon-carbon precursor was placed in a tube furnace, and inert gas was introduced. The temperature was raised to 850℃ at a rate of 5℃ / min and maintained for 3 h, and then naturally cooled to room temperature to obtain a high-density porous silicon-carbon composite material. The XRD patterns of the products of each step are shown in Figure 3 .

[0057] The SEM images of the materials in the preparation process are shown in Figure 1 (a)- Figure 1 (d), and the high-density porous silicon-carbon composite material comprises a three-dimensional porous skeleton, a filling layer and a coating layer. The three-dimensional porous skeleton is a three-dimensional porous silicon skeleton, the filling layer is a nano-Si particle uniformly dispersed in the porous silicon skeleton, and the coating layer is a carbon coating layer.

[0058] Example 3:

[0059] The high-density porous silicon-based composite material in this example is different from that of example 1 in that:

[0060] The materials Al 80 Si 20 selected in step 1 of example 1 were changed to Al 60 Si 40 (same size as example 1), to obtain micron porous Si skeleton with different porosities and pore sizes.

[0061] Example 4:

[0062] The high-density porous silicon-based composite material in this example is different from that of example 1 in that:

[0063] The material Al selected in step 1 is changed to Al 80 Si 20 The material Al selected in step 1 is changed to Al 60 Si 40 ( the same size as example 1 ), to obtain a microporous Si skeleton with different porosity and pore size. And the mass ratio of microporous Si skeleton in step 2: dispersant: nano Si is changed from 6: 2: 2 to 8: 1: 1.

[0064] Comparative example 1:

[0065] The preparation method provided in example 1 is adopted, and the difference is that:

[0066] Only step 1 of preparing a micrometer three-dimensional porous skeleton is performed.

[0067] Comparative example 2:

[0068] The preparation method provided in example 1 is adopted, and the difference is that:

[0069] Only step 1 of preparing a micrometer three-dimensional porous skeleton is performed, and the Al 80 Si 20 The material Al selected in step 1 is changed to Al 60 Si 40 .

[0070] Comparative example 3:

[0071] The micrometer Si balls (average particle size D50 is 7 μm) are not subjected to etching, filling and coating treatment.

[0072] Comparative example 4:

[0073] The nano Si balls (average particle size D50 is 50 nm) are not subjected to etching, filling and coating treatment.

[0074] Each example of the present application is tested by the following test method:

[0075] By using the high-compactness-density porous silicon-carbon composite material of the present application, each comparative example which is not subjected to etching, filling and carbon coating is compared, that is, each parameter of the porous silicon skeleton and the nano Si filled therein is compared, and the electrochemical performance is compared, so that the advantage of the cycle performance retention rate of the present patent is more prominent. By adjusting the doping ratio and the particle size of the filled nano Si in each step, silicon balls with different filling densities are prepared, so that negative electrode sheets with different compactness densities are prepared, and the purpose of optimizing the material performance is achieved.

[0076] To further verify the electrochemical properties of the porous silicon-based composite material provided in this application, such as cycle performance and rate performance, the specific structure of the negative electrode prepared from the porous silicon-based composite material obtained in the above examples is as follows: The negative electrode material, conductive agent carbon black (Super P), and polyacrylic acid (PAA) are mixed in a mass ratio of 6:2:2 in pure water, homogenized, and the solid content is controlled at 45%. The mixture is then coated onto a copper foil current collector, vacuum dried, and the negative electrode sheet is obtained. A cross-sectional view of the negative electrode sheet is shown below. Figure 2 As shown. Figure 2 (a) shows a cross-sectional view of the negative electrode sheet prepared with a porous silicon framework. Calculations show that the compaction density is 0.75 g / cm³. 3 ; Figure 2 (b) A cross-sectional view of the negative electrode sheet prepared after the intermediate product is coated with carbon (i.e., the high-density porous silicon-carbon composite material obtained in Example 2), with a compaction density of 1.28 g / cm³. 3 Compared to porous silicon frameworks, the compaction density is significantly improved, and through Figure 4 Significant improvements in cycle and rate performance were observed. The electrolyte used consisted of 10% fluoroethylene carbonate (FEC) additive added to a 1M LiPF6 / EC:DEC (1:1 vol%) electrolyte. Battery assembly was performed in a glove box filled with high-purity argon. Required materials included 2025 type positive and negative electrode shells, electrode sheets, a Celgard 2400 separator, 1mm diameter and 1mm thick lithium metal sheets, 18mm diameter stainless steel gaskets, 18mm diameter stainless steel springs, and the electrolyte. The instrument used in this patent was a Neware BTS4008, with a test voltage range of 0.01-1.5V. The current density for the first three cycles was 0.2A / g, and subsequent cycles were 0.5A / g, simultaneously testing the cycle and rate performance of the materials.

[0077] The test results are as follows Figure 4 (a) and Figure 4 (b) shows the cycle performance and rate performance of lithium-ion batteries based on the final product of Example 2 and the porous silicon-based composite material obtained in Comparative Example 1.

[0078] Table 1 Performance of each embodiment and comparative example

[0079]

[0080] As shown in Table 1, the porous silicon-carbon composite material prepared by the method described in this application, by changing the preparation conditions, such as the size of the filled nano-Si and the doping ratio, significantly improved the compaction density of the anode material, thereby increasing the volumetric energy density and significantly improving the cycle performance. Example 2 is made from Al 80 Si 20The etched three-dimensional porous micron-sized Si framework filled with 50 nm nano-sized Si particles achieved a compaction density of 1.28 g / cm³. 3 Compared to Comparative Example 1 without nano-silicon filling (0.75 g / cm³), the compaction density is significantly higher. 3 In Example 2, the compaction density was significantly improved. Simultaneously, the reversible capacity increased from 1004.63 mAh / g in Comparative Example 1 to 2113.25 mAh / g in Example 2, and the capacity retention rate after 100 cycles reached 96%, far exceeding the 34.3% of Comparative Example 1. The variable between Example 2 and Example 1 was the change in the size of the filled nano-Si during self-assembly. As shown in the table, nano-Si with different particle sizes all exhibited higher compaction densities than Comparative Example 1, and the cycling stability was improved to varying degrees. The porous silicon framework used in Examples 3 and 4 was made of Al... 60 Si 40 Etching preparation, due to the silicon content compared to Al 80 Si 20 As the concentration of nano-Si particles increases, the porosity of the silicon framework after etching decreases, preventing the nano-Si particles from effectively entering the porous silicon voids. Therefore, the dispersion ratio of the porous silicon framework to the nano-Si particles is used as a variable for comparison. In Example 3, the high proportion of nano-Si particles resulted in a relatively high compaction density after carbon coating, reaching 1.32 g / cm³. 3 Both were higher than those of the unfilled Comparative Example 2. Furthermore, after 100 cycles, the capacity retention rates of both were 93% and 95%, respectively, significantly higher than the 41% of Comparative Example 2.

[0081] Comparative Example 3 consists of unprocessed micron-sized Si spheres (average particle size D50 of 7 μm). As shown in the table, their compacted density reaches 1.22 g / cm³. 3 However, the assembled battery exhibited extremely poor cycle stability, with a capacity retention of only 23% after 100 cycles. In contrast, Comparative Example 4, composed of unprocessed nano-Si spheres (average particle size D50 of 50 nm), had a compaction density of only 0.53 g / cm³. 3 However, it exhibits good cycle stability, with a capacity retention rate of 58% after 100 cycles. In summary, this patented method, utilizing a three-dimensional porous silicon framework for in-situ self-assembly and carbon coating followed by compaction, achieves a compaction density of 1.28 g / cm³. 3 After 100 cycles, the capacity retention rate is as high as 96%, and the cycle performance is improved while the compaction density is greatly increased.

[0082] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-compact-density porous silicon-carbon composite material, characterized by, It comprises the following steps: Step 1: subjecting a micron silicon-based material to dealloying treatment to obtain a porous silicon skeleton; Step 2: subjecting to pore filling to form a nano-silicon material in the pores of the silicon-based material to obtain an intermediate product; Step 3: subjecting to carbon coating to form a carbon coating layer on the surface of the intermediate product, and sintering to obtain a composite material.

2. The production method according to claim 1, wherein The micron silicon-based material in step 1 is one or more of aluminum silicon, magnesium silicon or iron silicon, the average particle size D50 of the silicon-based material is 1-50 μm, and the Si content in the silicon-based material is 12%-50%. The dealloying treatment is selected from one or both of acid pickling etching treatment and alkali pickling etching treatment, wherein the acid for the acid pickling etching treatment is selected from one or more of hydrochloric acid, sulfuric acid and hydrofluoric acid.

3. The production method according to claim 1, wherein The nano-silicon filling material in step 2 comprises nano-silicon, and the average particle size D50 of the nano-silicon is 1-100 nm.

4. The production method according to claim 1, wherein In step 2, the porous silicon skeleton, nano-silicon and dispersant are mixed, uniformly dispersed in the porous Si material by spray drying, and then heat treated to obtain an intermediate product. The mixing weight ratio of the porous silicon skeleton to the nano-silicon is (8-2):1, the inlet temperature during spray drying is 150-250℃, and the heat treatment conditions include a temperature of 750-1200℃ and a holding time of 1-10 h.

5. The production method according to claim 1, wherein In step 3, the intermediate product and carbon material are sequentially mixed, carbonized and heat treated under inert gas and solvent conditions; wherein the weight ratio of the intermediate product to the carbon material is 10:(1-3); the carbon material is selected from one or more of pitch, phenolic resin, glucose, sucrose, dopamine, resorcinol and graphene; and the carbonization process conditions include a temperature of 750-1200℃ and a holding time of 1-10 h.

6. A high compacted density porous silicon-carbon composite material, characterized by, The composite material is prepared by the preparation method of any one of claims 1-5.

7. Use of the high-density porous silicon-carbon composite material of claim 6 or the composite material prepared by the preparation method of any one of claims 1-5 in a lithium ion battery.

8. A negative electrode sheet characterized by comprising: The negative electrode sheet comprises the high-density porous silicon-carbon composite material of claim 6 or the composite material prepared by the preparation method of any one of claims 1-5.

9. A lithium-ion battery, characterized by The lithium ion battery comprises the negative electrode sheet of claim 8.

10. The lithium-ion battery of claim 9, wherein, The lithium ion battery has a reversible capacity greater than 1800 mAh / g. And / or the lithium ion battery has a capacity retention rate of greater than 70% after 100 cycles.

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