Silicon-carbon composite material, preparation method thereof, application thereof, and electrochemical device

Abstract

The present invention discloses a silicon-carbon composite material and its preparation method, application, and electrochemical device. The method comprises: (1) calcining a mixture of alkaline earth metal and silicon powder at 300-800°C for 2-8 hours under an inert atmosphere to prepare a metal silicon precursor; (2) subjecting the metal silicon precursor to a mixture of liquid aromatic halogenated hydrocarbons through a solvothermal reaction to obtain the silicon-carbon composite material; the mass ratio of the metal silicon precursor to the liquid aromatic halogenated hydrocarbon is 1:(1-20). The nano-silicon-carbon negative electrode material prepared by the present invention has a small silicon particle size and is uniformly coated with an elastic carbon layer network, which is beneficial for suppressing silicon expansion before and after the silicon negative electrode is charged and discharged, improving the material's conductivity, and increasing the material's cycle life.

Description

Technical Field

[0001] The present invention specifically relates to a silicon-carbon composite material, a preparation method thereof, an application thereof and an electrochemical device. Background Art

[0002] Silicon-based negative electrode materials have extremely high research value and application prospects in the field of lithium-ion batteries. Their theoretical specific capacity is as high as 4200mAh / g. Compared with traditional graphite negative electrodes, silicon-based negative electrodes can achieve higher endurance in lithium-ion batteries. However, in actual applications, due to the significant volume expansion of silicon-based negative electrodes during the charging and discharging process, this expansion will lead to pulverization of electrode materials, destruction of electrode structure, and repeated formation of solid electrolyte interface (SEI) films. These problems seriously affect the cycle performance of the battery. Therefore, the potential of silicon-based negative electrodes has not been fully utilized, and their usage ratio in batteries is often difficult to exceed 10%. In order to solve this problem, researchers mainly use nano-silicon technology to improve the performance of silicon negative electrodes.

[0003] Nanosilicon, due to its unique size effect, can, to a certain extent, alleviate the stress caused by volume expansion. Numerous studies have shown that by combining nanosilicon with carbon materials, the electrochemical properties of nanosilicon anode materials, such as conductivity and cyclability, can be improved. However, the preparation cost of nanosilicon-carbon anode materials is relatively high, relying on equipment such as sand mills, chemical vapor deposition equipment, or carbonization furnaces to separately perform silicon nano-sizing and carbon coating, making it difficult to meet the requirements of low-cost production applications. Summary of the Invention

[0004] The technical problem addressed by the present invention is to overcome the existing technical challenges of high preparation costs and poor electrochemical performance of nano-silicon-carbon composite materials. The present invention provides a silicon-carbon composite material, its preparation method, applications, and electrochemical devices. The silicon-carbon composite material prepared by the present invention exhibits excellent conductivity and cycle life; the preparation method is simple, low-cost, and can be produced on an industrial scale.

[0005] The present invention first uses alkaline earth metal and silicon powder to prepare a metallic silicon precursor, so that silicon atoms are uniformly dispersed in the alkaline earth metal; then the metallic silicon precursor is subjected to a solvent thermal reaction with liquid aromatic halogenated hydrocarbons. During the solvent thermal reaction, the alkaline earth metal in the metallic silicon precursor catalyzes the dehalogenation of the aromatic halogenated hydrocarbons. Simultaneously with the dehalogenation, planar and spatial polymerization of the benzene rings occurs to form amorphous carbon, and the silicon in the metallic silicon precursor further forms nano-silicon particles at a lower temperature, thereby forming a carbon-coated small-sized silicon nanomaterial, and the alkaline earth metal in the metallic silicon precursor will generate alkali metal salts with the halogen; the carbon material coated on the surface of the nano-silicon can uniformly disperse and fix the nano-silicon particles to prevent their agglomeration, inhibit the expansion of silicon during the charge and discharge process, and provide a three-dimensional conductive network, thereby improving rate performance and reducing capacity attenuation.

[0006] The present invention solves the above technical problems through the following technical solutions:

[0007] The present invention provides a method for preparing a silicon-carbon composite material, which comprises the following steps:

[0008] (1) Under an inert atmosphere, calcining a mixture of alkaline earth metal and silicon powder at 300-800° C. for 2-8 hours to prepare a metallic silicon precursor;

[0009] (2) subjecting the metallic silicon precursor and the mixture of liquid aromatic halogenated hydrocarbons to a solvent thermal reaction to obtain the silicon-carbon composite material; the mass ratio of the metallic silicon precursor to the liquid aromatic halogenated hydrocarbon is 1:(1-20).

[0010] In the present invention, the inert atmosphere may be any conventional gas in the art, and generally refers to a gas that does not react with the reactants, such as nitrogen, argon or helium.

[0011] In the present invention, the alkaline earth metal may be one or more of Mg, Ca, Sr and Ba, preferably Ca and / or Mg.

[0012] In the present invention, the size of the silicon powder may be 10 nm-2 μm.

[0013] In the present invention, the molar ratio of the alkaline earth metal to the silicon powder may be 4:(1.5-8), preferably 4:(1.5-2), for example, 4:1.8, 4:1.85, 4:1.9, 4:1.95 or 4:2.

[0014] In some embodiments, the alkaline earth metals are Mg and Ca, and the molar ratio of Mg to Ca may be (1-4):1, preferably (2-4):1, for example 3:1.

[0015] In some embodiments, the alkaline earth metals are Mg and Ca, and the molar ratio of Mg:Ca:silicon powder can be (1-4):1:(1.5-2), for example, 3:1:1.8, 3:1:1.9, or 3:1:2. By adjusting the composition and ratio of the alkaline earth metal and silicon, the chemical reactivity can be controlled.

[0016] In the present invention, the calcination is generally carried out in a tube furnace.

[0017] In the present invention, the rate of heating to the calcination temperature may be 2-5°C / min.

[0018] In the present invention, the calcination temperature is preferably 400-600°C, for example 500°C.

[0019] In the present invention, the calcination time is preferably 3-6 hours, such as 4 hours or 5 hours.

[0020] In the present invention, the chemical formula of the metal silicon precursor can be Ca 4-x Mg x Si2, where 0≤x≤4, for example, x is 0.5, 1, 2 or 4.

[0021] In the present invention, the liquid aromatic halogenated hydrocarbon generally refers to an aromatic hydrocarbon molecule in which one or more hydrogen atoms are replaced by halogen atoms. The halogen in the liquid aromatic halogenated hydrocarbon may be one or more of F, Cl, Br and I, such as Cl. The number of halogen atoms in the liquid aromatic halogenated hydrocarbon may be 1-6, such as 1, 2 or 3. The liquid aromatic halogenated hydrocarbon may be a liquid side chain halogenated aromatic hydrocarbon and / or a liquid aromatic ring halogenated aromatic hydrocarbon. The halogen in the liquid side chain halogenated aromatic hydrocarbon is preferably a halogenated aromatic hydrocarbon connected to the α position of the side chain, such as benzyl chloride. The liquid aromatic ring halogenated aromatic hydrocarbon may be one or more of chlorobenzene, 2,6-dichlorotoluene, 1,2-dichlorobenzene and p-chlorotoluene.

[0022] In the present invention, the mass ratio of the metallic silicon precursor to the liquid aromatic halogenated hydrocarbon is, for example, 1:1, 1:2, 1:3, 1:5 or 1:10, preferably 1:(8-15).

[0023] In the present invention, the solvothermal reaction generally refers to a synthesis method in which the original mixture reacts in a closed system using an organic solvent or a non-aqueous solvent at a certain temperature and autogenous pressure of the solution. The solvothermal reaction is generally carried out in a reactor.

[0024] In the present invention, the rate of heating to the temperature of the solvothermal reaction may be 1-5°C / min.

[0025] In the present invention, the temperature of the solvothermal reaction generally does not exceed the boiling point of the liquid aromatic halogenated hydrocarbon, and is preferably 80-160°C, such as 85°C, 100°C, 120°C or 150°C, more preferably 100-160°C.

[0026] In some embodiments, when the liquid aromatic halogenated hydrocarbon is chlorobenzene, the temperature of the solvothermal reaction is preferably 80-120°C, such as 85°C or 120°C, more preferably 100-120°C.

[0027] In some embodiments, when the liquid aromatic halogenated hydrocarbon is 2,6-dichlorotoluene, the temperature of the solvothermal reaction is preferably 100-160°C, such as 120°C or 150°C, more preferably 100-130°C.

[0028] In some embodiments, when the liquid aromatic halogenated hydrocarbon is benzyl chloride, the temperature of the solvothermal reaction is preferably 100-160°C, such as 120°C or 150°C, more preferably 100-130°C.

[0029] In the present invention, the solvent thermal reaction time may be 3-18 h, such as 5 h, 6 h, 8 h or 10 h, preferably 8-12 h.

[0030] In the present invention, according to conventional techniques in the art, washing and drying are generally required after the solvent thermal reaction is completed. The solvent used in the washing process can be one or more of DMF, DMSO and NMP, such as DMF.

[0031] The present invention also provides a silicon-carbon composite material prepared by the above-mentioned preparation method.

[0032] The present invention also provides an application of the aforementioned silicon-carbon composite material in a lithium-ion battery.

[0033] The present invention also provides an electrochemical device, which comprises the silicon-carbon composite material as described above.

[0034] In the present invention, the electrochemical device may be conventional in the art, such as a lithium-ion battery.

[0035] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0036] The reagents and raw materials used in the present invention are commercially available.

[0037] The positive progress effect of the present invention is:

[0038] The silicon-carbon composite material prepared by the present invention can prepare a highly dispersed nano-silicon negative electrode material uniformly coated with carbon by in-situ catalytic dehalogenation at a relatively low temperature by adjusting the reaction activity of the metallic silicon precursor. The carbon layer can inhibit silicon expansion and agglomeration, greatly improving the cycle life and rate performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The XRD pattern of the silicon-carbon composite material prepared in Example 1;

[0040] Figure 2 This is a TEM image of the silicon-carbon composite material prepared in Example 1. DETAILED DESCRIPTION

[0041] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0042] The silicon powder used in the following examples and comparative examples was purchased from Aladdin, with a purity of 99.9% and a particle size of about 1 μm.

[0043] Example 1

[0044] (1) Magnesium powder, calcium powder and silicon powder were mixed evenly in a molar ratio of 3:1:1.8 and placed in a crucible. The mixture was placed in a tube furnace and heated to 500°C at a heating rate of 5°C / min in a nitrogen atmosphere. The mixture was kept for 4 hours and then naturally cooled to room temperature to obtain a metal silicon precursor.

[0045] (2) The metallic silicon precursor and chlorobenzene (AR) were mixed in a mass ratio of 1:10, heated to 120°C in a reactor at a heating rate of 3°C / min, kept warm for 10 h, cooled to room temperature, washed three times with DMF, and dried to obtain a nano-silicon-carbon composite material.

[0046] Example 2

[0047] Compared with Example 1, except that the molar ratio of metal magnesium powder, metal calcium powder and silicon powder in step (1) is adjusted to 3:1:1.9, the other parameters and conditions are the same as those in Example 1.

[0048] Example 3

[0049] Compared with Example 1, except that the molar ratio of metal magnesium powder, metal calcium powder and silicon powder in step (1) is adjusted to 3:1:2, the other parameters and conditions are the same as those in Example 1.

[0050] Example 4

[0051] Compared with Example 1, except that the molar ratio of metal magnesium powder, metal calcium powder and silicon powder in step (1) is adjusted to 0:4:1.8, the other parameters and conditions are the same as those in Example 1.

[0052] Example 5

[0053] Compared with Example 1, except that the mass ratio of the metallic silicon precursor to chlorobenzene in step (2) is adjusted to 1:5, the other parameters and conditions are the same as those in Example 1.

[0054] Example 6

[0055] Compared with Example 1, except that the temperature of the solvent thermal reaction in step (2) is adjusted to 85°C, the other parameters and conditions are the same as those in Example 1.

[0056] Example 7

[0057] Compared with Example 1, except that the holding time of the solvent thermal reaction in step (2) was adjusted to 5 h, the other parameters and conditions were the same as those in Example 1.

[0058] Example 8

[0059] Compared with Example 1, except that chlorobenzene in step (2) is replaced by 2,6-dichlorotoluene, the other parameters and conditions are the same as those in Example 1.

[0060] Example 9

[0061] Compared with Example 1, except that chlorobenzene in step (2) was replaced by 2,6-dichlorotoluene and the reaction temperature was adjusted to 150° C., the other parameters and conditions were the same as those in Example 1.

[0062] Example 10

[0063] Compared with Example 1, except that chlorobenzene in step (2) is replaced by benzyl chloride, the other parameters and conditions are the same as those in Example 1.

[0064] Example 11

[0065] Compared with Example 1, except that chlorobenzene in step (2) was replaced by benzyl chloride and the reaction temperature was adjusted to 150° C., the other parameters and conditions were the same as those in Example 1.

[0066] Comparative Example 1

[0067] 300nm silicon powder (the purchased silicon powder was crushed to D using ethanol medium sand mill 50 is 300nm).

[0068] Comparative Example 2

[0069] The nano-silicon powder in Comparative Example 1 was mixed with chlorobenzene (AR) at a mass ratio of 0.11:1, heated to 120°C at a heating rate of 3°C / min in a reactor, kept warm for 10 hours, cooled to room temperature, washed three times with DMF, and dried.

[0070] Effect embodiment

[0071] (1) Morphology characterization and XRD testing

[0072] Figure 1 The XRD pattern of the silicon-carbon composite material prepared in Example 1; Figure 2 TEM image of the silicon-carbon composite material prepared in Example 1. Figure 2 It can be seen that in the prepared silicon-carbon composite material, the silicon particles are small in size and have not undergone obvious agglomeration, and a layer of amorphous carbon is coated on the surface of the nano-silicon particles.

[0073] (2) Electrochemical performance test

[0074] The silicon-carbon composite materials prepared in Examples 1-11 and the materials prepared in Comparative Examples 1-2 were subjected to half-cell tests. The test method is as follows: the above-mentioned materials to be tested are uniformly mixed with the binder CMC (sodium carboxymethyl cellulose) and the conductive carbon black in a mass ratio of 85:5:10, adjusted into a slurry, coated on a copper foil with a coating thickness of 100 microns, and dried at 90°C in a vacuum for 12 hours to prepare a lithium battery negative electrode sheet. The simulated battery was assembled in an argon-filled glove box, using a 1 mol / L LiPF6 electrolyte (the solvent is EC, EMC and DMC, EC:EMC:DMC=1:1:1 (volume ratio), a polypropylene microporous membrane as a diaphragm, and a metal lithium sheet as a counter electrode. The electrochemical performance test was carried out on a Land CT2001A battery tester at a temperature of 20°C and a charge and discharge voltage range of 0.01 to 1.5V (1C=250mAh g -1 ). The test results are shown in Table 1.

[0075] Table 1

[0076]

[0077] The above experimental results show that the silicon-carbon composite material prepared by the present invention has excellent specific capacity and cycle life. According to Comparative Examples 1 and 2, when only silicon powder is used or silicon powder is directly reacted with chlorobenzene in a solvothermal reaction, the initial charge specific capacity and energy retention after 500 cycles are both poor, especially the cycle capacity retention rate is low.

[0078] Although specific embodiments of the present invention have been described above, those skilled in the art will appreciate that these are merely illustrative and that the scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, and such changes and modifications are intended to fall within the scope of the present invention.

Claims

1. A method for preparing a silicon-carbon composite material, characterized in that: The following steps are involved: (1) Under an inert atmosphere, a mixture of alkaline earth metal and silicon powder is calcined at 300-800°C for 2-8 hours to prepare a metallic silicon precursor; (2) subjecting the metallic silicon precursor and the mixture of liquid aromatic halogenated hydrocarbon to a solvent thermal reaction to obtain the silicon-carbon composite material; the mass ratio of the metallic silicon precursor to the liquid aromatic halogenated hydrocarbon is 1:(1-20).

2. The method for preparing the silicon-carbon composite material according to claim 1, wherein The alkaline earth metal is one or more of Mg, Ca, Sr and Ba; And / or, the size of the silicon powder is 10 nm-2 μm; and / or, the molar ratio of the alkaline earth metal to the silicon powder is 4:(1.5-8); And / or, when the alkaline earth metals are Mg and Ca, the molar ratio of Mg:Ca:silicon powder is (1-4):1:(1.5-2).

3. The method for preparing the silicon-carbon composite material according to claim 2, wherein: The alkaline earth metal is Ca and / or Mg.

4. The method for preparing the silicon-carbon composite material according to claim 2, wherein: The molar ratio of the alkaline earth metal to the silicon powder is 4:(1.5-2).

5. The method for preparing the silicon-carbon composite material according to claim 4, wherein: The molar ratio of the alkaline earth metal to the silicon powder is 4:1.8, 4:1.85, 4:1.9, 4:1.95 or 4:

2.

6. The method for preparing the silicon-carbon composite material according to claim 2, wherein: When the alkaline earth metals are Mg and Ca, the molar ratio of Mg:Ca:silicon powder is 3:1:1.8, 3:1:1.9 or 3:1:

2.

7. The method for preparing the silicon-carbon composite material according to claim 1, wherein: The calcination temperature is 400-600°C; And / or, the calcination time is 3-6 hours.

8. The method for preparing the silicon-carbon composite material according to claim 7, wherein: The calcination temperature is 500°C; And / or, the calcination time is 4 hours or 5 hours.

9. The method for preparing the silicon-carbon composite material according to claim 1, wherein: The chemical formula of the metal silicon precursor is Ca 4-x Mg x Si2, where 0≤x≤4; And / or, the mass ratio of the metallic silicon precursor to the liquid aromatic halogenated hydrocarbon is 1:1, 1:2, 1:3, 1:5 or 1:

10.

10. The method for preparing the silicon-carbon composite material according to claim 9, wherein: The chemical formula of the metal silicon precursor is Ca 4-x Mg x Si2, wherein x is 0.5, 1, 2 or 4.

11. The method for preparing the silicon-carbon composite material according to claim 9, wherein: The mass ratio of the metal silicon precursor to the liquid aromatic halogenated hydrocarbon is 1:(8-15).

12. The method for preparing the silicon-carbon composite material according to claim 1, wherein: The halogen in the liquid aromatic halogenated hydrocarbon is one or more of F, Cl, Br and I; and / or, the number of halogen atoms in the liquid aromatic halogenated hydrocarbon is 1-6; And / or, the liquid aromatic halogenated hydrocarbon is a liquid side-chain halogenated aromatic hydrocarbon and / or a liquid aromatic ring halogenated aromatic hydrocarbon.

13. The method for preparing the silicon-carbon composite material according to claim 12, wherein: The halogen in the liquid aromatic halogenated hydrocarbon is Cl; And / or, the number of halogen atoms in the liquid aromatic halogenated hydrocarbon is 1, 2 or 3.

14. The method for preparing the silicon-carbon composite material according to claim 12, wherein: The liquid side chain halogenated aromatic hydrocarbon is a halogenated aromatic hydrocarbon connected to the α position of the side chain; And / or, the liquid aromatic halogenated aromatic hydrocarbon is one or more of chlorobenzene, 2,6-dichlorotoluene, 1,2-dichlorobenzene and p-chlorotoluene.

15. The method for preparing the silicon-carbon composite material according to claim 14, wherein: The liquid side-chain halogenated aromatic hydrocarbon is benzyl chloride.

16. The method for preparing the silicon-carbon composite material according to claim 1, wherein: The temperature of the solvent thermal reaction does not exceed the boiling point of the liquid aromatic halogenated hydrocarbon; And / or, the solvent thermal reaction time is 3-18 hours.

17. The method for preparing the silicon-carbon composite material according to claim 16, wherein: The temperature of the solvent thermal reaction is 80-160°C; And / or, the solvent thermal reaction time is 5 h, 6 h, 8 h or 10 h.

18. The method for preparing the silicon-carbon composite material according to claim 17, wherein: The temperature of the solvent thermal reaction is 85°C, 100°C, 120°C or 150°C.

19. The method for preparing the silicon-carbon composite material according to claim 16, wherein: The solvent thermal reaction time is 8-12h.

20. The method for preparing the silicon-carbon composite material according to claim 16, wherein: When the liquid aromatic halogenated hydrocarbon is chlorobenzene, the temperature of the solvent thermal reaction is 80-120°C.

21. The method for preparing the silicon-carbon composite material according to claim 20, characterized in that: When the liquid aromatic halogenated hydrocarbon is chlorobenzene, the temperature of the solvent thermal reaction is 85°C or 120°C.

22. The method for preparing the silicon-carbon composite material according to claim 20, wherein: When the liquid aromatic halogenated hydrocarbon is chlorobenzene, the temperature of the solvent thermal reaction is 100-120°C.

23. The method for preparing the silicon-carbon composite material according to claim 16, wherein: When the liquid aromatic halogenated hydrocarbon is 2,6-dichlorotoluene, the temperature of the solvent thermal reaction is 100-160°C.

24. The method for preparing the silicon-carbon composite material according to claim 23, wherein: When the liquid aromatic halogenated hydrocarbon is 2,6-dichlorotoluene, the temperature of the solvent thermal reaction is 120°C or 150°C.

25. The method for preparing the silicon-carbon composite material according to claim 23, wherein: When the liquid aromatic halogenated hydrocarbon is 2,6-dichlorotoluene, the temperature of the solvent thermal reaction is 100-130°C.

26. The method for preparing the silicon-carbon composite material according to claim 16, wherein: When the liquid aromatic halogenated hydrocarbon is benzyl chloride, the temperature of the solvent thermal reaction is 100-160°C.

27. The method for preparing the silicon-carbon composite material according to claim 26, wherein: When the liquid aromatic halogenated hydrocarbon is benzyl chloride, the temperature of the solvent thermal reaction is 120°C or 150°C.

28. The method for preparing the silicon-carbon composite material according to claim 26, wherein: When the liquid aromatic halogenated hydrocarbon is benzyl chloride, the temperature of the solvent thermal reaction is 100-130°C.

29. A silicon-carbon composite material, characterized in that The silicon-carbon composite material is prepared according to the preparation method of any one of claims 1 to 28.

30. Use of the silicon-carbon composite material according to claim 29 in a lithium-ion battery.

31. An electrochemical device, characterized in that It includes a positive electrode, a negative electrode, an electrolyte and a separator, and the negative electrode includes the silicon-carbon composite material as claimed in claim 29.

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