Porous carbon-silicon negative electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a porous carbon-silicon negative electrode material as well as a preparation method and application thereof. The method comprises the following steps: (1) adding an acidic substance into a dispersion liquid containing an MOFs material, and carrying out chemical etching to obtain a carbon precursor; (2) carrying out carbonization treatment on the carbon precursor to obtain a carbon coating layer; and (3) carrying out vapor deposition on the carbon coating layer by adopting SiH4 in a protective atmosphere to obtain the porous carbon-silicon negative electrode material. According to the method for preparing the porous carbon-silicon negative electrode material, on one hand, an enough transmission path can be provided for lithium ion diffusion, on the other hand, contact between the porous carbon-silicon negative electrode material and electrolyte is promoted, and excellent rate capability can be shown. In addition, the stable structure of the porous carbon-silicon negative electrode material enables the volume expansion of silicon and the stress generated thereby to be adjusted more effectively, so that the expansion of the electrode is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly relates to a porous carbon-silicon anode material, a preparation method thereof, and an application thereof. Background Art

[0002] Nowadays, the growing power demands of emerging portable electronic devices and electric vehicles have imposed higher energy and power requirements on the energy output of lithium-ion batteries (LIBs). Currently, the lithium storage capacity of graphite anodes has reached its limit (360 mAh g -1 ), which is very close to its theoretical capacity (372 mAh g -1 ), making it difficult to achieve further improvement. Therefore, high-capacity anodes have become a top priority in the development of lithium batteries.

[0003] Due to its ultra-high theoretical specific capacity (4200 mAh g -1 ), silicon anodes are becoming a highly competitive candidate material for high-energy anodes. However, the alloying reaction between Si and Li often causes a large volume expansion (exceeding 300%), which leads to the destruction of the anode structure and the continuous formation of a solid electrolyte interface (SEI) on the surface of Si particles. In addition, the electrical conductivity of silicon is very low (6.7×10 -4 S cm -1 , which is the intrinsic electronic conductivity). These factors greatly limit the practical application of silicon-based anodes.

[0004] MOF has a highly ordered porous structure, making it have a more flexible pore size adjustment ability than the commonly used carbon coating methods on the market, and its components have high tunability, enabling it to be customized for different scenarios and requirements. CN113571683A discloses a preparation method of a carbon-silicon anode material. This method is to first adsorb the precursor of ZIF-8 onto the surface of Si particles by the interaction between polyvinylpyrrolidone (PVP) and the precursor of ZIF-8, prepare ZIF-8 in a silicon dispersion to obtain Si@ZIF-8 with ZIF-8 coating silicon, and then carbonize the obtained Si@ZIF-8 / MXene composite of Si@ZIF-8 and MXene to prepare a carbon-silicon anode material, which has good electrochemical performance. However, in the preparation process of this prior art, the dispersion of Si is poor, it is difficult to form effective carbon coating, and it still has the defects of difficult to form a uniform and stable SEI during the cycling process and poor cycling performance. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problem of poor cycling performance of silicon-based anode materials existing in the prior art.

[0006] In order to achieve the above object, the first aspect of the present invention provides a method for preparing a porous carbon silicon negative electrode material, the method comprising:

[0007] (1) adding an acidic substance to a dispersion containing MOFs material for chemical etching to obtain a carbon precursor;

[0008] (2) carbonizing the carbon precursor to obtain a carbon coating layer;

[0009] (3) Under protective atmosphere, use SiH 4 vapor-depositing the carbon coating layer to obtain a porous carbon-silicon negative electrode material;

[0010] Wherein, in step (1), relative to 1g of the MOFs material, the addition rate of the acidic substance is 2-3mL / min;

[0011] In step (3), the SiH 4 The inflow rate is 20-40cm 3 / min, and the temperature of the vapor deposition is 400-600°C.

[0012] The second aspect of the present invention provides a porous carbon silicon negative electrode material prepared by the method described in the first aspect.

[0013] The third aspect of the present invention provides the use of the porous carbon silicon negative electrode material described in the second aspect in a lithium ion battery.

[0014] Through the above technical solution, the present invention has at least the following advantages:

[0015] The method for preparing a porous carbon-silicon negative electrode material provided by the present invention designs the structure of a silicon-based negative electrode, and adopts MOF materials to provide a variety of pore structures for silicon nanoparticles. The prepared porous carbon-silicon negative electrode material has a three-dimensional porous structure. Therefore, this method can screen out the optimal structure and effectively regulate the volume expansion of silicon.

[0016] The porous carbon silicon negative electrode material provided by the present invention can provide sufficient transmission paths for lithium ion diffusion on the one hand, and promote its contact with the electrolyte on the other hand, and can show excellent rate capability. In addition, the stable structure of the carbon skeleton makes the volume expansion of silicon and the stress generated thereby more effectively regulated, thereby reducing the expansion of the electrode.

[0017] The method for preparing porous carbon silicon negative electrode material provided by the present invention has more flexible pore size adjustment capability than the common carbon coating means on the market. The vapor deposition process forms silicon single substance on the surface of the carbon coating layer. The silicon single substance is mostly nano-sized and can also inhibit volume expansion to a certain extent, further improving the cycle performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a flow chart of the preparation method of the porous carbon-silicon anode material provided by the present invention. Specific Embodiments

[0019] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values and individual point values of each range, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0020] In the present invention, Chemical Vapor Deposition (CVD) is a technique for depositing solid thin films on the surface of a substrate through chemical reactions. Its basic principle is to introduce gaseous precursors into the reaction chamber, where chemical reactions occur under conditions such as high temperature or plasma, generating solid products and depositing them on the substrate.

[0021] As described above, the first aspect of the present invention provides a method for preparing a porous carbon-silicon anode material, the method comprising:

[0022] (1) Adding an acidic substance to a dispersion containing MOFs material for chemical etching to obtain a carbon precursor;

[0023] (2) Carbonizing the carbon precursor to obtain a carbon coating layer;

[0024] (3) Under a protective atmosphere, using SiH 4 to perform chemical vapor deposition on the carbon coating layer to obtain a porous carbon-silicon anode material;

[0025] Wherein, in step (1), relative to 1 g of the MOFs material, the addition rate of the acidic substance is 2 - 3 mL / min;

[0026] In step (3), the flow rate of the introduced SiH 4 is 20 - 40 cm 3 / min, and the temperature of the chemical vapor deposition is 400 - 600 °C.

[0027] Preferably, in step (1), the weight ratio of the acidic substance to the MOFs material is 2 - 3:1.

[0028] Preferably, in step (1), the acidic substance is provided in the form of an acidic substance solution, and the mass concentration of the acidic substance in the acidic substance solution is 0.02 - 0.03 g / mL.

[0029] Preferably, in step (2), the carbonization treatment is carried out under a protective atmosphere selected from argon or nitrogen.

[0030] Preferably, in step (2), the conditions of the carbonization treatment include: the heating rate is 2-6 °C / min, the final heating temperature is 800-1000 °C, and the heat preservation time is 1-4 h.

[0031] According to a preferred specific embodiment, in step (1), the product obtained by the chemical etching is washed and dried in sequence.

[0032] Preferably, in step (3), the protective atmosphere is selected from argon or nitrogen.

[0033] Preferably, in step (3), the heat preservation time of the chemical vapor deposition is 3-5 h.

[0034] Preferably, in step (3), the conditions of the chemical vapor deposition are controlled such that the weight content of Si in the porous carbon-silicon anode material is 40-60 wt%.

[0035] Preferably, in step (1), the average particle diameter of the MOFs material is 0.05-1.5 μm.

[0036] Preferably, in step (1), the MOFs material is ZIF-8.

[0037] Preferably, in step (1), the ZIF-8 is prepared by a method comprising the following steps:

[0038] A solution containing a zinc salt is added to a solution containing 2-methylimidazole for a mixing reaction to obtain the ZIF-8; relative to 1 g of the 2-methylimidazole solution, the addition rate of the zinc salt solution is 1-2 mL / min.

[0039] Preferably, the zinc salt is an acetate of zinc ions and / or a nitrate of zinc ions, preferably zinc acetate dihydrate and / or zinc nitrate hexahydrate.

[0040] Preferably, the molar ratio of the amount of the zinc salt to the 2-methylimidazole is 0.5-1.7:1.

[0041] According to a preferred specific embodiment, the solution containing the zinc salt includes a zinc salt and an alcohol solvent, optionally further including a surfactant; the solution containing 2-methylimidazole includes 2-methylimidazole and an alcohol solvent.

[0042] Preferably, the alcohol solvent is selected from at least one of methanol, ethanol, and isopropanol; the surfactant is selected from polyvinylpyrrolidone and / or cetyltrimethylammonium bromide.

[0043] The method for preparing ZIF-8 according to the present invention may further include post-treatment means known in the art such as washing and drying. Exemplarily, the material obtained from the mixed reaction is rinsed with methanol or deionized water and then dried to obtain the ZIF-8. The present invention will not elaborate herein, and those skilled in the art should not construe it as a limitation to the present invention.

[0044] Preferably, the conditions for the mixed reaction include: a rotation speed of 200 - 500 rpm, a temperature of 25 - 35 °C, and a time of 5 - 15 min.

[0045] It should be noted that the time for the chemical etching and the mixed reaction described in the present invention both include the addition time.

[0046] Preferably, in step (1), the conditions for the chemical etching include: a rotation speed of 200 - 500 rpm, a temperature of 25 - 35 °C, and a time of 150 - 200 min.

[0047] Preferably, in step (1), the acidic substance is selected from at least one of tannic acid, hydrochloric acid, and sulfuric acid.

[0048] According to a preferred specific embodiment, in step (3), the method further includes: before performing step (3), preheating the carbon coating layer first.

[0049] The method for preparing the porous carbon-silicon negative electrode material according to the present invention may further include post-treatment means known in the art such as washing and drying. Exemplarily, the material obtained from the chemical etching is rinsed with methanol or deionized water and then dried to obtain the carbon precursor. The present invention will not elaborate herein, and those skilled in the art should not construe it as a limitation to the present invention.

[0050] According to a particularly preferred specific embodiment, the present invention provides a flowchart of the preparation method of the above-mentioned porous carbon-silicon negative electrode material, and the preparation method includes: Figure 1 in which provides the preparation method flowchart of the above-mentioned porous carbon-silicon negative electrode material, and the preparation method includes:

[0051] (1) Adding a solution containing a zinc salt to a solution containing 2-methylimidazole for a mixed reaction to obtain the ZIF-8; relative to 1 g of the 2-methylimidazole solution, the addition rate of the zinc salt solution is 1 - 2 mL / min;

[0052] (2) Adding an acidic substance to the dispersion containing the ZIF-8 for chemical etching to obtain a carbon precursor;

[0053] (3) Carbonizing the carbon precursor to obtain a carbon coating layer;

[0054] (4) Under a protective atmosphere, using SiH4 Perform chemical vapor deposition on the carbon coating layer to obtain a porous carbon-silicon anode material.

[0055] As described above, the second aspect of the present invention provides a porous carbon-silicon anode material prepared by the method described in the first aspect.

[0056] As described above, the third aspect of the present invention provides the application of the porous carbon-silicon anode material described in the second aspect in a lithium-ion battery.

[0057] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, the raw materials and reagents used are all commercially available products.

[0058] SiH 4 : Purchased from Hubei Newred Electronic Gas Co., Ltd.

[0059] The following preparation examples are used to illustrate the preparation method of the MOFs material of the present invention.

[0060] Preparation Example 1-1

[0061] Dissolve 0.352 g of zinc acetate dihydrate and 0.6 g of polyvinylpyrrolidone (PVP) in 40 mL of methanol, and ultrasonically stir for 30 min to completely dissolve to obtain Solution A;

[0062] Dissolve 0.526 g of dimethylimidazole in 40 mL of methanol to obtain Solution B;

[0063] At 25 °C, slowly add Solution A to Solution B, stir at 400 rpm for 10 min, then age at room temperature for 24 h, remove the supernatant, centrifuge the solid at the bottom of the beaker, wash it 3 times with methanol and 3 times with deionized water, and dry it in a blast dryer at 80 °C to obtain ZIF-8 with an average particle diameter of 1.5 μm, denoted as C-1;

[0064] Among them, the addition rate of Solution A is 1 mL / min relative to 1 g of the 2-methylimidazole solution.

[0065] Preparation Example 1-2

[0066] Dissolve 0.810 g of zinc nitrate hexahydrate in 40 mL of methanol, and ultrasonically stir for 30 min to completely dissolve to obtain Solution A;

[0067] Dissolve 0.526 g of dimethylimidazole in 40 mL of methanol to obtain Solution B;

[0068] At 25 °C, slowly add Solution A to Solution B, stir at 400 rpm for 10 min, then age at room temperature for 24 h, remove the supernatant, centrifuge the solid at the bottom of the beaker, wash it 3 times with deionized water, and dry it at 80 °C to obtain ZIF-8 with an average particle diameter of 0.5 μm, denoted as C-2;

[0069] Among them, the addition rate of solution A is 1 mL / min relative to 1 g of the 2-methylimidazole solution.

[0070] Preparation Examples 1-3

[0071] Dissolve 0.810 g of zinc nitrate hexahydrate and 0.3 g of polyvinylpyrrolidone (PVP) in 40 mL of methanol, and ultrasonicate for 30 min to completely dissolve it to obtain solution A;

[0072] Dissolve 0.526 g of dimethylimidazole in 40 mL of methanol to obtain solution B;

[0073] At 25°C, slowly add solution A to solution B, stir at 400 rpm for 10 min, then age at room temperature for 24 h, remove the supernatant, centrifuge the solid at the bottom of the beaker, wash it 3 times with deionized water, and dry it at 80°C to obtain ZIF-8 with an average particle diameter of 0.05 μm, denoted as C-3;

[0074] Among them, the addition rate of solution A is 1 mL / min relative to 1 g of the 2-methylimidazole solution.

[0075] Preparation Examples 1-4

[0076] According to a method similar to that of Preparation Example 1-1, except that the addition rate of solution A is 3 mL / min relative to 1 g of the 2-methylimidazole solution;

[0077] The rest are the same, and ZIF-8 with an average particle diameter of 2.5 μm is obtained, denoted as C-4.

[0078] The following examples are used to illustrate the preparation method of the porous carbon-silicon anode material of the present invention

[0079] Example 1

[0080] (1) Dissolve 1.25 g of tannic acid (C 76 H 52 O 46 ) in 50 mL of deionized water, ultrasonicate for 60 min to completely dissolve it to obtain a transparent brown tannic acid solution;

[0081] Prepare a 0.01 g / mL dispersion of the MOFs material with water as the solvent to obtain a dispersion containing the MOFs material;

[0082] At 25°C, slowly add the prepared tannic acid solution to the dispersion containing the MOFs material for chemical etching, continuously stir at 400 rpm for 180 min, and the color gradually changes from white to ivory and finally to beige;

[0083] Centrifuge the etched solution, wash it three times with deionized water first, then wash it three times with methanol and deionized water respectively, and finally dry it in a blast dryer at 80 °C to obtain the carbon precursor;

[0084] (2) Under argon, heat the carbon precursor after the above etching treatment to 900 °C at a heating rate of 5 °C / min and hold for 2 h for carbonization treatment to obtain a carbon coating layer;

[0085] (3) Under argon, first heat 0.2 g of the carbon coating layer to 500 °C, and then inject SiH 4 gas for chemical vapor deposition on the carbon coating layer (holding time is 3 h) to obtain a porous carbon-silicon negative electrode material;

[0086] For the specific materials and reaction conditions of this example, please refer to Table 1.

[0087] The remaining examples are prepared using the same preparation method as Example 1. The difference is that the specific materials and reaction conditions are different, as specifically shown in Table 1.

[0088] Table 1

[0089]

[0090] Note: The addition rate of the acidic substance is measured relative to 1 g of the MOFs material.

[0091] Example 4

[0092] According to a method similar to Example 1, the difference is that in step (2), the carbonization treatment conditions are: the heating rate is 10 °C / min, the final heating temperature is 700 °C, and the holding time is 2 h;

[0093] The rest are the same to obtain a porous carbon-silicon negative electrode material.

[0094] Example 5

[0095] According to a method similar to Example 1, the difference is that in step (3), the chemical vapor deposition conditions are controlled so that the weight content of Si in the porous carbon-silicon negative electrode material is 70 wt%.

[0096] The rest are the same to obtain a porous carbon-silicon negative electrode material.

[0097] Example 6

[0098] According to a method similar to Example 1, the difference is that in step (1), C-4 of equal weight is used to replace C-1;

[0099] The rest are the same to obtain a porous carbon-silicon negative electrode material.

[0100] Comparative Example 1

[0101] According to a method similar to that of Example 1, except that in step (1), the addition rate of tannic acid is 5 mL / min relative to 1 g of the MOFs material;

[0102] The rest are the same, and a porous carbon-silicon negative electrode material is obtained.

[0103] Comparative Example 2

[0104] According to a method similar to that of Example 1, except that in step (1) and step (3), the flow rate of SiH 4 being introduced is 45 cm 3 / min, and the temperature of chemical vapor deposition is 450 °C;

[0105] The rest are the same, and a porous carbon-silicon negative electrode material is obtained.

[0106] Application Example

[0107] The porous carbon-silicon negative electrode materials (active substances) prepared in the examples were respectively weighed with SWCNT (carbon nanotubes), SP (conductive carbon black), and binder according to a mass ratio of 94:1:1:4, water was added as a solvent, and after stirring evenly, it was coated on a copper foil, and then vacuum dried and pressed into tablets. In a glove box under an argon atmosphere, a complete and smooth electrode plate with no burrs on the edge and a flat lithium plate with no black spots and no concave points were selected to assemble a button cell. The order of assembling the button cell is as follows: positive electrode shell + electrode plate + 80 μL of electrolyte + separator + 80 μL of electrolyte + gasket + spring piece + negative electrode shell. The half-cell test voltage is 0.001 V - 2.0 V.

[0108] A full cell was prepared by matching with a lithium iron phosphate positive electrode, and the full cell test voltage was 2.5 - 3.65 V. At 25 °C, 1C rate charge and discharge cycles were carried out to test its cycling performance.

[0109] The lithium storage performance of the full cell was tested, that is, its cycling performance (capacity retention rate at 25 °C) was tested, and the test results are shown in Table 2.

[0110] Table 2

[0111]

[0112]

[0113] It can be seen from the above results that the technical solution provided by the present invention can effectively alleviate the volume expansion of silicon and greatly improve the cycling performance of the porous carbon-silicon negative electrode material.

[0114] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing a porous carbon-silicon negative electrode material, characterized in that: The method includes: (1) adding an acidic substance to a dispersion containing a MOFs material for chemical etching to obtain a carbon precursor; (2) carbonizing the carbon precursor to obtain a carbon coating layer; (3) Under a protective atmosphere, the carbon coating layer is vapor deposited using SiH4 to obtain a porous carbon silicon negative electrode material; Wherein, in step (1), relative to 1g of the MOFs material, the addition rate of the acidic substance is 2-3mL / min; In step (3), the SiH4 inlet flow rate is 20-40cm 3 / min, and the temperature of the vapor deposition is 400-600°C.

2. The method according to claim 1, wherein: In step (2), the carbonization treatment conditions include: a heating rate of 2-6°C / min, a heating end point temperature of 800-1000°C, and a holding time of 1-4h.

3. The method according to claim 1 or 2, wherein: In step (3), the protective atmosphere is selected from argon or nitrogen; And / or, the vapor deposition insulation time is 3-5h.

4. The method according to any one of claims 1 to 3, wherein: In step (3), the conditions of the vapor deposition are controlled so that the weight content of Si in the porous carbon silicon negative electrode material is 40-60wt%.

5. The method according to any one of claims 1 to 4, wherein: In step (1), the average particle diameter of the MOFs material is 0.05-1.5 μm.

6. The method according to any one of claims 1 to 5, wherein: In step (1), the MOFs material is ZIF-8.

7. The method according to claim 6, wherein: In step (1), the ZIF-8 is prepared by a method comprising the following steps: A solution containing zinc salt is added to a solution containing 2-methylimidazole for a mixed reaction to obtain the ZIF-8; the addition rate of the zinc salt solution is 1-2 mL / min relative to 1 g of the 2-methylimidazole solution.

8. The method according to any one of claims 1 to 7, wherein: In step (1), the weight ratio of the acidic substance to the MOFs material is 2-3:1; And / or, the acidic substance is selected from at least one of tannic acid, hydrochloric acid and sulfuric acid.

9. A porous carbon silicon negative electrode material prepared by the method according to any one of claims 1 to 8.

10. Use of the porous carbon silicon negative electrode material according to claim 9 in lithium ion batteries.

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