A hierarchical porous structure aluminum-doped polycrystalline silicon nanosheet carbon composite material and its preparation method and battery pack

Abstract

The present invention provides a hierarchical porous structure aluminum-doped polysilicon nanosheet carbon composite material and a preparation method and a battery pack, which belongs to the field of lithium ion battery negative electrode materials, and includes the following steps: taking aluminum powder, silicon source powder, and conductive carbon powder, adding an organic solvent, ball milling, and obtaining a liquid sample; drying the liquid sample to obtain a solid sample, grinding it, adding aluminum chloride powder and sodium chloride powder, and obtaining a mixed powder; loading the mixed powder into a hydrothermal reactor for reaction, drying, and obtaining powder A; adding HCl aqueous solution to powder A and stirring, centrifuging and drying to obtain powder B; adding HF ethanol solution to powder B and stirring, centrifuging and drying to obtain powder C; putting powder C into a tubular furnace, passing acetylene gas, and depositing to obtain a target material. The present invention can effectively improve the conductivity and structural stability of the composite material, can effectively alleviate the volume expansion effect of the material during the electrochemical cycle, and can significantly improve the electrochemical performance of the material.

Description

Technical Field

[0001] The invention relates to the field of lithium-ion batteries, and specifically discloses a hierarchical porous structure aluminum-doped polycrystalline silicon nanosheet carbon composite material, a preparation method thereof, and a battery pack. Background Art

[0002] The development of clean new energy has become a global concern. However, many renewable energy sources in nature, such as wind power, solar energy, tidal energy, etc., are intermittent. Therefore, energy storage systems, especially rechargeable secondary batteries, are seen as key to achieving dual carbon goals. Among these available batteries, lithium-ion batteries (LIBs) are widely used in electric vehicles and various portable electronic devices due to their high energy density and long cycle life. But the current technology of using low-capacity graphite as anode for commercial lithium-ion batteries is gradually unable to meet the rapidly developing market demand. Therefore, it is imperative to develop anode materials with high energy density, durability and long cycle life.

[0003] Silicon-based materials are considered to be one of the most attractive anode materials for next-generation lithium-ion batteries because of their ultra-high theoretical capacity (4200 mAh g -1 , 10 times that of graphite anode), low lithium insertion potential (<0.4 V vs Li / Li + ) and natural abundance. Unfortunately, bulk Si is + During the insertion process, a large volume expansion (>300%) will occur, which cannot withstand the excessive stress during the expansion process, resulting in particle breakage and crushing. At the same time, the inherent low conductivity of silicon will also reduce the transport rate of electrons and lithium ions during long-term cycling, resulting in unsatisfactory cycle stability.

[0004] Since the preparation of porous silicon materials by magnesium thermal reduction was reported in 2007, the preparation of silicon materials by reduction method has been widely studied. The high porosity and large specific surface area of ​​porous silicon can be used for Li + During the insertion process, the volume expansion of Si is reduced to provide storage space, shorten the diffusion path of electrons / ions, and provide more electrochemical reaction sites, thereby improving the storage capacity of lithium. However, the inherent conductivity of pure silicon is still low, and it still needs to be compounded with conductive materials such as metals, graphite and other carbon materials to further improve its conductivity and thus improve its electrochemical performance.

[0005] Chinese patent application CN116161665A (publication number) discloses a method for preparing a porous silicon / aluminum oxide / amorphous carbon composite material and its application in lithium-ion batteries. The preparation method has the following defects: ① Aluminum oxide is not conductive, which will hinder the conductivity of silicon-based materials. When it is actually used as a negative electrode material for lithium-ion batteries, it will reduce the overall energy density of lithium-ion batteries and hinder its application; ② The content of aluminum oxide is uncontrollable: CN116161665A uses hydrochloric acid to etch aluminum in aluminum-silicon alloy. The content of the remaining aluminum is uncontrollable, making it difficult to ensure consistent performance of silicon-based materials in different batches.

[0006] Chinese patent application CN116375035A (publication number) discloses a method for preparing a three-dimensional porous silicon-carbon composite material and the composite material thereof. The preparation method has the following defects: ① The materials synthesized by this method are of different sizes and have many fine impurities. Many side reactions will occur during actual application, reducing the capacity of the battery; ② The porous structure of the material synthesized by this method is not obvious. In actual application, the silicon-based material will undergo a huge volume expansion (>300%), resulting in powdering of the electrode and a decrease in electrochemical performance.

[0007] Therefore, it is of great significance to develop a hierarchical porous structure aluminum-doped polycrystalline silicon nanosheet carbon composite material. Summary of the invention

[0008] In order to solve the technical problems existing in the existing silicon-carbon negative electrode materials for lithium-ion batteries, the first purpose of the present invention is to provide a hierarchical porous aluminum-doped polycrystalline silicon / carbon composite material, which uses the ductility of metallic aluminum to act as a "glue" to tightly combine the conductive carbon material and nano-silicon dioxide and the reducing agent aluminum, shorten the path of the molten salt reduction reaction, and increase the rate of the molten salt reduction reaction. At the same time, the structure of the reduction product silicon is changed to form a silicon / carbon composite material with a porous structure, aiming to improve the electrochemical performance of the negative electrode material of lithium-ion batteries.

[0009] The technical solution of the present invention is achieved as follows: A method for preparing a hierarchical porous aluminum-doped polysilicon nanosheet / carbon composite material comprises the following steps:

[0010] 1) Take aluminum powder, silicon source powder, and conductive carbon powder, add organic solvent, and ball mill to obtain a liquid sample; dry the liquid sample to obtain a solid sample;

[0011] 2) Grinding the solid sample in step 1), adding aluminum chloride powder and sodium chloride powder, and mixing them evenly in a mortar to obtain a mixed powder;

[0012] 3) The mixed powder obtained in step 2) is placed in a hydrothermal reactor for reaction, and then dried to obtain solid powder A;

[0013] 4) placing the solid powder A obtained in step 3) into a container, adding HCl aqueous solution and stirring, centrifuging and washing, and then drying to obtain solid powder B;

[0014] 5) Put the solid powder B obtained in step 4) into a container, add HF ethanol solution (HF: hydrofluoric acid, ethanol as solvent), stir, centrifuge, wash and dry to obtain solid powder C;

[0015] 6) The solid powder C of step 5) is placed in a porcelain boat, placed in a tube furnace, and acetylene gas is introduced to deposit to obtain a hierarchical porous structure aluminum-doped polycrystalline silicon nanosheet / carbon composite material.

[0016] Preferably, in step 1), the mass ratio of the aluminum powder to the silicon source powder and the conductive carbon powder is 1-2:1:0.2-0.5.

[0017] Preferably, in step 1), the ratio of the total mass of the aluminum powder, the silicon source powder and the conductive carbon powder to the volume of the organic solvent is 1 g: 10-20 mL.

[0018] Preferably, in step 1), the conductive carbon powder is one or more of graphite, graphene, and carbon nanotubes; and the silicon source powder is nano-silicon dioxide powder.

[0019] Preferably, in step 1), the organic solvent is isopropanol.

[0020] Preferably, in step 1), the ball milling time is 4-12 hours, the ball milling speed is 200-400 rpm; and the drying temperature is 80-100°C.

[0021] Preferably, in step 2), the mass ratio of the aluminum chloride powder to the sodium chloride powder is 4-6:0.8-1.0, and the mass ratio of the aluminum chloride powder to the silicon source powder is 4-6:0.4-0.6.

[0022] Preferably, in step 3), the reaction temperature is 250-300° C., and the reaction time is 10-12 h.

[0023] Preferably, in step 4), the concentration of the HCl aqueous solution is 2-6 mol / L; and the stirring time is 24-48 h.

[0024] Preferably, in step 5), the concentration of the HF ethanol solution is 4% to 6%wt; and the stirring time is 3 to 10 min.

[0025] Preferably, in step 6), the deposition temperature is 700-850° C., and the deposition time is 1 h-2 h, preferably the deposition temperature is 800° C., and the deposition time is 2 h.

[0026] Preferably, the aluminum chloride powder is anhydrous aluminum chloride powder.

[0027] A hierarchical porous structure aluminum-doped polycrystalline silicon nanosheet / carbon composite material is prepared by any preparation method described in the present invention.

[0028] A battery pack includes a plurality of batteries, an insulating plate, a heat sink and a protective circuit board. The batteries are lithium-ion batteries, and the raw materials of the negative electrodes of the lithium-ion batteries include the hierarchical porous structure aluminum-doped polycrystalline silicon nanosheet / carbon composite material described in the present invention.

[0029] The beneficial effects of the present invention are:

[0030] 1) The present invention uses nanographite sheets, acetylene-derived carbon and silicon sheets with polycrystalline, two-dimensional nanosheets and disordered stacked micrometer-level structures as raw materials; the graphite nanosheets are interspersed in the two-dimensional nanosheet stacking structure, the acetylene-derived carbon is coated on the surface of the nanographite sheets and the two-dimensional silicon nanosheets, the two-dimensional nanosilicon sheets have a polycrystalline structure, and are rich in lattice defects, and aluminum atoms are doped in the silicon lattice. The present invention utilizes the two-dimensional sheet characteristics and aluminum atom doping characteristics of silicon sheets, combined with the conductive properties of the nanographite sheets interspersed therein and the acetylene-derived carbon coated on the surface, which can effectively improve the conductivity and structural stability of the composite material, can effectively alleviate the volume expansion effect of the material during the electrochemical cycle, improve the electron / ion transmission rate, and can significantly improve the electrochemical performance of the material.

[0031] 2) The product of the present invention has a uniform hierarchical porous morphology, which solves the problem that silicon materials expand greatly in volume and are easy to pulverize during the cycle, leading to battery failure.

[0032] 3) The product of the present invention has aluminum-doped silicon material, and the migration rate of aluminum-doped lithium ions in silicon further improves the performance of lithium battery silicon-based negative electrode.

[0033] 4) The product of the present invention has polycrystalline silicon and silicon material with multiple lattice defects, and the polycrystalline silicon and lattice defects are helpful to improve the lithium ion transmission performance.

[0034] 5) The present invention has low cost: it uses cheap and readily available raw materials, thus reducing production costs.

[0035] 6) The present invention uses aluminum as "glue" through simple ball milling, and after low-temperature molten salt reduction, obtains a silicon / carbon composite material with controllable morphology and hierarchical porous structure. This method can be widely used in ball milling systems of various silicon sources and conductive carbon materials. And the study found that the obtained aluminum-doped silicon material has a certain degree of adaptability and can remain stable after long-term cycling of lithium-ion batteries. This can further guide the rational design of high-performance alloy-type silicon-based materials, which can be used as negative electrode materials for lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0037] Figure 1 is a SEM image of the aluminum / silicon dioxide / graphite composite prepared in step (1) of Example 1;

[0038] Figure 2 This is a micron-scale SEM image of the hierarchical porous structure produced by the secondary stacking of silicon nanosheets and graphite nanosheets prepared in Example 1;

[0039] Figure 3 This is a partially enlarged SEM image of the silicon nanosheet porous structure of the silicon-carbon composite material prepared in Example 1;

[0040] Figure 4 TEM and EDX images of the aluminum-doped silicon in the silicon-carbon composite material prepared in Example 1;

[0041] Figure 5 TEM image of silicon having a polycrystalline structure in the silicon-carbon composite material prepared in Example 1;

[0042] Figure 6 TEM image showing that silicon in the silicon-carbon composite material prepared in Example 1 has multiple lattice defects;

[0043] Figure 7 This is a micron-scale SEM image of the hierarchical porous structure produced by the secondary stacking of silicon nanosheets and graphite nanosheets prepared in Example 2;

[0044] Figure 8 This is a micrometer-scale SEM image of the hierarchical porous structure produced by the secondary stacking of silicon nanosheets and graphene prepared in Example 3;

[0045] Fig. 9 The cycle performance diagram of the silicon-carbon composite material prepared in Example 1 as the negative electrode active material of lithium-ion battery in half-cell (200 mA g -1 );

[0046] Fig.10 The voltage capacity diagram of the silicon-carbon composite material prepared in Example 1 as the negative electrode active material of a lithium-ion battery in a half-cell (200 mA g -1 );

[0047] Fig.11 This is a rate performance diagram of the silicon-carbon composite material prepared in Example 1 as a negative electrode active material for a lithium-ion battery in a half-cell;

[0048] Fig.12The cycle performance diagram of the silicon-carbon composite material prepared in Example 1 as the negative electrode active material of a lithium-ion battery in a full battery with lithium iron phosphate as the positive electrode (200 mA g -1 );

[0049] Fig.13 The rate performance diagram of the silicon-carbon composite material prepared in Example 1 as the negative electrode active material of a lithium-ion battery in a full battery with lithium iron phosphate as the positive electrode (200 mA g -1 ). DETAILED DESCRIPTION

[0050] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0051] The mechanism of action of the present invention is as follows: using ductile aluminum powder as glue, silicon dioxide and graphite are tightly combined during the ball milling process, providing a porous framework structure for molten salt reduction, and providing a conductive agent for the molten salt reduction reaction, thereby improving the reaction kinetics and shortening the reaction distance. In addition, the introduction of disordered heteroatoms and the reducing agent aluminum powder can directly provide aluminum atoms doped in the silicon lattice to complete the atomic doping work and enhance the lithium conductivity. The hierarchical porous structure is prepared, and the compact secondary stacking structure of nano-silicon and nano-graphite sheets can be widely used in composite systems of various silicon sources and conductive carbon materials.

[0052] Example 1

[0053] A method for preparing a hierarchical porous aluminum-doped polysilicon nanosheet / carbon composite material comprises the following steps:

[0054] (1) Weigh 0.8 g aluminum powder, 0.5 g nano-silicon dioxide, and 0.1 g graphite into a ball mill, add 20 mL isopropanol, and ball mill at 300 rpm for 12 h to obtain a liquid sample, which is then dried in an oven at 80 °C to obtain a solid powder, namely, an aluminum powder / silicon dioxide powder / graphite powder composite.

[0055] (2) After grinding the solid sample in step (1), add 5 g of anhydrous aluminum chloride powder and 0.9 g of sodium chloride powder, and mix them evenly in a mortar to obtain a mixed powder;

[0056] (3) The mixed powder of step (2) is placed in a hydrothermal reactor for reaction for 10 to 12 hours at a reaction temperature of 250 to 300° C. After the reaction, the mixed powder is dried to obtain solid powder A;

[0057] (4) Put the solid powder A obtained in step (3) into a beaker, add 3M HCl aqueous solution and stir for 24 hours, then centrifuge, wash and dry to obtain solid powder B;

[0058] (5) Put the solid powder B obtained in step (4) into a beaker, add 5% wt HF ethanol solution and stir for 4 min, centrifuge and wash, and then put into an oven for drying;

[0059] (6) The solid powder C obtained in step (5) is placed in a porcelain boat, acetylene gas is introduced, and the mixture is deposited at 800° C. for 1 h to obtain a hierarchical porous structure aluminum-doped polycrystalline silicon nanosheet / carbon composite material (abbreviated as: silicon / carbon composite material).

[0060] The SEM image of the aluminum powder / silicon dioxide powder / graphite powder composite prepared in step (1) of Example 1 is as follows: Figure 1 As shown, it can be seen that the silica / graphite / aluminum powder is evenly distributed.

[0061] The SEM image of the silicon / carbon composite material prepared in Example 1 is as follows Figure 2 As shown, the porous structure of the silicon-carbon composite material can be seen, with graphene sheets stacked in the middle of the hierarchical porous silicon skeleton.

[0062] The SEM image of the silicon / carbon composite material prepared in Example 1 is as follows Figure 3 As shown, it can be seen that the silicon-carbon composite material has a hierarchical porous structure.

[0063] HRTEM of aluminum-doped silicon in the silicon / carbon composite material prepared in Example 1 is as follows Figure 4 As shown, with aluminum doping, HETEM images are Figure 4 shown.

[0064] The silicon / carbon composite material prepared in Example 1 has polycrystalline silicon TEM as shown in FIG. Figure 5 shown.

[0065] The silicon TEM of the silicon / carbon composite material with multiple lattice defects prepared in Example 1 is as follows Figure 6 shown.

[0066] Example 2

[0067] The present invention provides a method for preparing a hierarchical porous aluminum-doped polycrystalline silicon nanosheet / carbon composite material, which is basically the same as Example 1, except that: in step (1), the mass of graphite added is 0.2 g, and the SEM image of the sample is as follows: Figure 7 As shown in the figure, it can be seen that it still has a porous structure, indicating that this method can be applied to the preparation of porous silicon-carbon composite materials after composite ball milling with graphite of different masses.

[0068] Example 3

[0069] The present invention provides a method for preparing a hierarchical porous aluminum-doped polycrystalline silicon nanosheet / carbon composite material, which is basically the same as Example 1, except that: in step (1), the added conductive material is replaced by graphene instead of graphite, and the sample SEM image is as follows: Figure 8 As shown in the figure, it can be seen that it still has a porous structure, indicating that this method can be applied to the preparation of porous silicon-carbon composite materials after composite ball milling with different conductive materials.

[0070] Example 4

[0071] The hierarchical porous structure aluminum-doped polycrystalline silicon nanosheets / carbon composite material prepared in Example 1 was assembled into a lithium-ion battery as a negative electrode active material.

[0072] The cycling performance of the material in a half-cell (200 mAh / g) is shown in Fig. 9 As shown, it can be seen that the silicon-carbon composite material has excellent capacity retention.

[0073] The charge and discharge curve of the material in a half-cell (200 mAh / g) is shown in Fig.10 As shown, it can be seen that the silicon-carbon composite material has excellent Coulomb efficiency.

[0074] The rate performance of this material in a half-cell is shown in the figure Fig.11 As shown, it can be seen that the silicon-carbon composite material has excellent Coulomb efficiency.

[0075] Example 5

[0076] This embodiment provides a lithium-ion battery. The negative electrode material of the lithium-ion battery is the hierarchical porous structure aluminum-doped polycrystalline silicon nanosheet / carbon composite material prepared in Example 1, and the positive electrode is lithium iron phosphate. The full battery cycle performance diagram (200 mAg -1 )like Fig.12 As shown, its excellent cycle performance can be seen; its full battery rate performance is shown in Fig.13 As shown, its excellent rate performance can be seen.

[0077] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any ordinary technician in the industry can smoothly implement the present invention as shown in the drawings and described above. However, any equivalent changes, modifications and evolutions made by technicians familiar with the profession without departing from the scope of the technical solution of the present invention using the technical content disclosed above are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a hierarchical porous aluminum-doped polycrystalline silicon nanosheet / carbon composite material, characterized in that: The following steps are involved: 1) Take aluminum powder, silicon source powder and conductive carbon powder, add organic solvent, ball mill for 4-12 hours at a ball milling speed of 200-400rpm to obtain a liquid sample; dry the liquid sample to obtain a solid sample; the mass ratio of the aluminum powder to the silicon source powder and the conductive carbon powder is 1-2:1:0.2-0.5; the ratio of the total mass of the aluminum powder, silicon source powder and conductive carbon powder to the volume of the organic solvent is 1g:10-20mL; the conductive carbon powder is one or more of graphite, graphene and carbon nanotubes; the silicon source powder is nano-silicon dioxide powder; the organic solvent is isopropanol; 2) Grinding the solid sample in step 1), adding aluminum chloride powder and sodium chloride powder, and mixing them evenly in a mortar to obtain a mixed powder; The mass ratio of the aluminum chloride powder and the sodium chloride powder to the silicon source powder is 4-6:0.8-1.0:0.4-0.6; 3) The mixed powder of step 2) is placed in a hydrothermal reactor for reaction, and then dried to obtain solid powder A; the reaction temperature is 250-300° C., and the reaction time is 10-12 h; 4) putting the solid powder A obtained in step 3) into a container, adding 3-6 mol / L HCl aqueous solution, stirring, centrifuging, washing and drying to obtain solid powder B; 5) placing the solid powder B obtained in step 4) into a container, adding 4% to 6%wt HF ethanol solution, stirring, centrifuging, washing, and drying to obtain solid powder C; 6) The solid powder C of step 5) is placed in a porcelain boat, placed in a tube furnace, acetylene gas is introduced, and deposited at 700-850° C. for 1 h-2 h to obtain a hierarchical porous structure aluminum-doped polycrystalline silicon nanosheet / carbon composite material.

2. The method for preparing a hierarchical porous aluminum-doped polysilicon nanosheet / carbon composite material according to claim 1, characterized in that: In step 1), the drying temperature is 80-100°C.

3. The method for preparing a hierarchical porous aluminum-doped polysilicon nanosheet / carbon composite material according to claim 1, characterized in that: In step 4), the stirring time is 24 to 48 hours.

4. The method for preparing a hierarchical porous aluminum-doped polysilicon nanosheet / carbon composite material according to claim 1, characterized in that: In step 5), the stirring time is 3 to 10 minutes.

5. A hierarchical porous structure aluminum-doped polycrystalline silicon nanosheet / carbon composite material, characterized in that: Prepared by the preparation method described in claim 1.

6. A battery pack, comprising a plurality of batteries, an insulating plate, a heat sink and a protective circuit board, characterized in that: The battery is a lithium-ion battery, and the raw material of the negative electrode of the lithium-ion battery includes the hierarchical porous structure aluminum-doped polycrystalline silicon nanosheet / carbon composite material according to claim 5.

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