A silicon-carbon composite anode material, its preparation method and application

Abstract

This invention belongs to the technical field of lithium-ion battery anode materials, specifically relating to a silicon-carbon composite anode material, its preparation method, and its application. The silicon-carbon composite anode material is composed of the following raw materials in weight percentages: 39-67 wt% porous carbon, 40-60 wt% nano-silicon composite, and 1-3 wt% conductive binder. The preparation method of the nano-silicon composite includes: mixing Ti, V, Zr, Al, and graphite powders to obtain a multi-element MAX powder, then etching it with HF to form a layered multi-element MXene, and finally depositing nano-silicon on its surface. The silicon-carbon composite anode material prepared by this invention exhibits small volume expansion and low electrochemical impedance during lithium-ion deposition, and can adsorb lithium ions, demonstrating excellent cycle performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery negative electrode materials, and particularly relates to a silicon-carbon composite negative electrode material and a preparation method and application thereof. BACKGROUND

[0002] Energy storage field has put forward strict requirements on the performance of lithium ion batteries, especially in terms of energy density, cycle life and safety, and major breakthroughs are urgently needed. However, the performance of traditional graphite negative electrode materials has gradually approached the limit due to the limitation of the theoretical specific capacity (372 mAh / g) and the problem of lithium ion dendrite growth during fast charging. Under this background, the development of a new generation of high-capacity, long-life and safe negative electrode materials has become the focus of industry technology research.

[0003] Silicon material has become the core choice for breaking through the energy density bottleneck due to its advantages of a theoretical specific capacity of up to 4200 mAh / g and a low working voltage (0.4 V). However, silicon will expand by 300% in volume during charging and discharging, which will cause problems such as material pulverization. In view of this problem, silicon-carbon composite technology has emerged. This technology uniformly disperses nano-silicon particles in a carbon matrix, uses the mechanical strength and elastic buffer of carbon material to reduce the expansion rate and prolong the cycle life, and has become an important development direction of a new generation of high-energy-density lithium ion battery negative electrode materials. However, the silicon-carbon composite material still has problems such as large volume expansion, poor cycle efficiency and insufficient cycle stability in the application of battery negative electrode.

[0004] Therefore, there is an urgent need for a silicon-carbon composite negative electrode material with small expansion volume and excellent cycle performance. SUMMARY

[0005] The first purpose of the application is to provide a silicon-carbon composite negative electrode material, which has small volume expansion degree, low electrochemical impedance and can adsorb lithium ions during lithium ion deposition.

[0006] The second purpose of the application is to provide a preparation method of the above-mentioned silicon-carbon composite negative electrode material.

[0007] The third purpose of the application is to provide the application of the above-mentioned silicon-carbon composite negative electrode material in lithium ion batteries.

[0008] In order to achieve the above-mentioned purposes, the technical scheme adopted by the application is as follows:

[0009] A silicon-carbon composite negative electrode material, which is composed of the following raw materials in weight percentage: 39-67 wt% porous carbon, 40-60 wt% nano-silicon composite and 1-3 wt% conductive binder.

[0010] The preparation method of the nanosilicon composite comprises the following steps:

[0011] (1) Ti, V, Zr, Al and graphite powder are mixed and ball milled, then sintered under inert gas atmosphere, ground and sieved after cooling to room temperature to obtain multi-element MAX powder;

[0012] (2) The multi-element MAX powder is added into HF solution and stirred to react, after the reaction, the reaction solution is added into isopropanol and ultrasonically treated, and then washed, dried to obtain layered multi-element MXene;

[0013] (3) The layered multi-element MXene is mixed with graphene by ball milling to obtain a mixture, then silane is introduced into the mixture under inert gas atmosphere at 400-500 ℃ to perform chemical vapor deposition to obtain the nanosilicon composite.

[0014] Further, in step (1), the molar ratio of Ti, V, Zr, Al and graphite powder is 2:2:2:3:3; the sintering temperature is 1400-1500 ℃, and the time is 1-2 h.

[0015] Further, in step (2), the mass fraction of the HF solution is 40%-50%; the mass ratio of the multi-element MAX powder to the HF solution is 1:(5-15).

[0016] Further, in step (3), the mass ratio of the layered multi-element MXene to graphene is 1:(1-4); the mass ratio of the silane to the mixture is 1:(0.5-2).

[0017] Further, the preparation method of the conductive adhesive comprises the following steps:

[0018] (a) Nanometer zinc alumina oxide and silane coupling agent are added into a mixed solution of ethanol and water, and reacted under heating condition, then the solid is collected by centrifugation, washed, dried to obtain modified nanometer zinc alumina oxide;

[0019] (b) The modified nanometer zinc alumina oxide is dispersed into methyl methacrylate, and an aqueous solution of polysorbate 20 is added and stirred uniformly to obtain a pre-emulsion;

[0020] (c) Ammonium persulfate is added into the pre-emulsion and reacted under heating, and then treated to obtain the conductive adhesive.

[0021] Further, in step (a), the mass ratio of the nanometer zinc alumina oxide, the silane coupling agent, ethanol and water is 20:(1-2):(190-200):(5-10); the silane coupling agent is γ-methacryloyloxypropyltrimethoxysilane; the heating temperature is 55-65 ℃; and the reaction time is 1-2 h.

[0022] Further, in step (b), the mass ratio of the modified nano-zinc aluminum oxide, methyl methacrylate, and polysorbate 20 is 1:(20~30):(0.5~1).

[0023] Further, in step (c), the mass ratio of the pre-emulsion to ammonium persulfate is 100:(0.2~0.5); the heating reaction temperature is 75~85 °C, and the time is 2~4 h.

[0024] The preparation method of the above-mentioned silicon-carbon composite anode material includes the following steps: adding porous carbon, nano-silicon composite and conductive binder into ethanol according to the weight percentage, ball milling and mixing evenly, and then vacuum drying to obtain the silicon-carbon composite anode material.

[0025] The above-mentioned silicon-carbon composite anode material is used in the preparation of lithium-ion batteries.

[0026] The beneficial technical effects of this invention are as follows:

[0027] 1. The main components of the silicon-carbon composite anode material of the present invention are porous carbon and nano-silicon composites. By inserting MXene into the interlayer of graphene to form a continuous conductive network, the resistance between π-π stacked layers is reduced, and abundant lithium-ion adsorption sites are provided, thereby improving the overall conductivity of graphene. At the same time, ball milling is used to combine the transition metal carbide framework of MXene with the sp² hybrid carbon network of graphene to form a mechanically interlocked structure, and nano-silicon is deposited between the MXene / graphene composites, thereby suppressing volume expansion during charging and discharging and improving the structural stability of the material.

[0028] 2. In addition, this invention adjusts the M site element of traditional MXenes to a multi-element transition metal (Ti, V, Zr) to obtain a multi-element MXene. The differences in atomic radius and electronic orbital of different metals complement each other, optimizing the electronic band structure of the material. Furthermore, the multi-metal active sites and surface functional groups synergistically enhance the adsorption of lithium ions, reduce charge transport resistance, and improve the conductivity and charge storage capacity of MXenes, which helps to achieve high-capacity stable cycling.

[0029] 3. This invention uses zinc oxide aluminum nanoparticles to modify polyacrylate binders, which not only improves the bonding between silicon and carbon and buffers the volume expansion of silicon, but also enhances its conductivity and reduces the interfacial resistance. No additional conductive agent is needed, which helps to enable the negative electrode material to have a higher capacity.

[0030] 4. This invention provides a method for preparing silicon-carbon composite anode materials. This method is efficient, simple to operate, and easy to scale up for mass production. Attached Figure Description

[0031] Figure 1 This is a SEM image of the nano-silicon composite prepared in Example 1 of the present invention. Detailed Implementation

[0032] The following is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention. Specific conditions not specified in the embodiments are performed according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, all reagents or instruments used are conventional products obtained through commercial channels.

[0033] (I) Implementation Examples

[0034] Example 1

[0035] Example 1 provides a silicon-carbon composite anode material, which is composed of the following raw materials in weight percentage: 48 wt% porous carbon, 50 wt% nano-silicon composite and 2 wt% conductive binder.

[0036] The preparation method of the nano-silicon composite includes the following steps:

[0037] (1) Ti, V, Zr, Al and graphite powders were mixed in a molar ratio of 2:2:2:3:3, ball-milled until uniform, sintered at 1450 °C for 1.5 h in an argon atmosphere, cooled to room temperature, ground and sieved to obtain multi-element MAX powder;

[0038] (2) Add the multi-component MAX powder to a 45% HF solution at a mass ratio of 1:10. After stirring and reacting for 36 h, separate the solid and wash it. Add the washed solid product to isopropanol and ultrasonically exfoliate it at 0 °C for 30 min. Then, separate, wash and dry it to obtain layered multi-component MXene.

[0039] (3) Layered multi-component MXene and graphene were ball-milled and mixed at a mass ratio of 1:3 to obtain a mixture; then, silane was introduced into the mixture at a mass ratio of 1:1.2 to obtain a nano-silicon composite by plasma chemical vapor deposition for 15 min at 450 °C in an inert gas atmosphere.

[0040] The method for preparing the conductive adhesive includes the following steps:

[0041] (a) Nano-sized aluminum zinc oxide, γ-methacryloxypropyltrimethoxysilane, ethanol and water were mixed at a mass ratio of 20:2:195:8 and stirred at 60 °C for 2 h. After the reaction was completed, the mixture was centrifuged, the precipitate was collected, washed successively with ethanol and water, and dried to obtain modified aluminum zinc oxide nano-sized zinc oxide;

[0042] (b) Modified nano-zinc aluminum oxide, methyl methacrylate, polysorbate 20 and water were mixed and stirred in a mass ratio of 1:25:0.8:70 and ultrasonically treated under ice bath conditions to obtain a pre-emulsion;

[0043] (c) Add ammonium persulfate to the pre-emulsion at a mass ratio of 100:0.3, then heat to 80 °C and react for 3 h. After the reaction is completed, cool, filter and dry to obtain the conductive binder.

[0044] This embodiment also provides a method for preparing the above-mentioned silicon-carbon composite anode material. The specific steps are as follows: porous carbon, nano-silicon composite and conductive binder are added to ethanol according to the weight percentage, and the mixture is ball-milled and vacuum dried to obtain the final product.

[0045] The nano-silicon composite prepared in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 .

[0046] Example 2

[0047] Example 2 provides a silicon-carbon composite anode material, which is composed of the following raw materials by weight percentage: 39 wt% porous carbon, 60 wt% nano-silicon composite and 1 wt% conductive binder.

[0048] The preparation method of the nano-silicon composite includes the following steps:

[0049] (1) Ti, V, Zr, Al and graphite powders were mixed in a molar ratio of 2:2:2:3:3, ball-milled until uniform, sintered at 1400 °C for 1 h in an argon atmosphere, cooled, ground and sieved to obtain multi-element MAX powder;

[0050] (2) Add the multi-component MAX powder to a 40% HF solution at a mass ratio of 1:5. After stirring and reacting for 24 hours, separate the solid and wash it. Place the washed solid product in isopropanol and ultrasonically peel it for 20 minutes at 0 °C. Then, separate, wash and dry it to obtain layered multi-component MXene.

[0051] (3) Layered multi-component MXene and graphene were ball-milled and mixed at a mass ratio of 1:1 to obtain a mixture. Then, silane was introduced into the mixture at a mass ratio of 1:0.5 to silane and in an inert gas atmosphere at 400 °C for plasma chemical vapor deposition for 10 min to obtain a nano-silicon composite.

[0052] The method for preparing the conductive adhesive includes the following steps:

[0053] (a) Nano-sized aluminum zinc oxide, γ-methacryloxypropyltrimethoxysilane, ethanol and water were mixed at a mass ratio of 20:1:190:5 and stirred at 55 °C for 1 h. After the reaction was completed, the mixture was centrifuged, the precipitate was collected, and the precipitate was washed with ethanol and water in sequence and then dried to obtain modified aluminum zinc oxide nano-sized zinc oxide.

[0054] (b) Modified nano-aluminum zinc oxide, methyl methacrylate, polysorbate 20 and water were mixed in a mass ratio of 1:20:0.5:60, stirred and ultrasonically treated under ice bath conditions to obtain a pre-emulsion;

[0055] (c) Add ammonium persulfate to the pre-emulsion at a mass ratio of 100:0.2, then heat to 75 °C and react for 2 h. After the reaction is completed, cool, filter and dry to obtain the conductive binder.

[0056] This embodiment also provides a method for preparing the above-mentioned silicon-carbon composite anode material. The specific steps are as follows: porous carbon, nano-silicon composite and conductive binder are added to ethanol according to the weight percentage, and the mixture is ball-milled and vacuum dried to obtain the final product.

[0057] Example 3

[0058] Example 3 provides a silicon-carbon composite anode material, which is composed of the following raw materials in weight percentage: 67 wt% porous carbon, 60 wt% nano-silicon composite and 3 wt% conductive binder.

[0059] The preparation method of the nano-silicon composite includes the following steps:

[0060] (1) Ti, V, Zr, Al and graphite powders were mixed in a molar ratio of 2:2:2:3:3, ball-milled until uniform, sintered at 1500 °C for 2 h in an argon atmosphere, cooled, ground and sieved to obtain multi-element MAX powder;

[0061] (2) Mix the multi-element MAX powder with 50% HF solution at a mass ratio of 1:15 and soak it. After stirring and reacting for 48 h, separate the solid and wash it. Add the washed solid product to isopropanol and ultrasonically peel it at 0 °C for 30 min. Then, separate, wash and dry it to obtain layered multi-element MXene.

[0062] (3) Layered multi-component MXene and graphene were ball-milled and mixed at a mass ratio of 1:4 to obtain a mixture; then, silane was introduced into the mixture at a mass ratio of 1:2 to silane and in an inert gas atmosphere at 500°C for plasma chemical vapor deposition for 20 min to obtain nano-silicon composite.

[0063] The method for preparing the conductive adhesive includes the following steps:

[0064] (a) Nano-sized aluminum zinc oxide, γ-methacryloxypropyltrimethoxysilane, ethanol and water were mixed at a mass ratio of 20:2:200:10 and stirred at 65 °C for 2 h. After the reaction was completed, the mixture was centrifuged, the precipitate was collected, and the precipitate was washed with ethanol and water in sequence and then dried to obtain modified aluminum zinc oxide nano-sized zinc oxide.

[0065] (b) Modified nano-zinc aluminum oxide, methyl methacrylate, polysorbate 20 and water were mixed in a mass ratio of 1:30:1:80, stirred and ultrasonically treated under ice bath conditions to obtain a pre-emulsion;

[0066] (c) Add ammonium persulfate to the pre-emulsion at a mass ratio of 100:0.5, then heat to 85 °C and react for 4 h. After the reaction is completed, cool, filter and dry to obtain the conductive binder.

[0067] This embodiment also provides a method for preparing the above-mentioned silicon-carbon composite anode material, the specific steps of which are: adding porous carbon, nano-silicon composite and conductive binder into ethanol according to the weight percentage, ball milling and vacuum drying to obtain the material.

[0068] (ii) Comparative Example

[0069] Comparative Example 1

[0070] Comparative Example 1 is basically the same as Example 1, except that the graphene in step (3) of Example 1 is omitted. That is, step (3) of Comparative Example 1 is to directly introduce silane into the layered multi-element MXene for vapor phase chemical deposition.

[0071] Comparative Example 2

[0072] Comparative Example 2 is basically the same as Example 1, except that the layered multi-component MXene in steps (1), (2) and (3) of Example 1 is omitted. In other words, Comparative Example 2 directly introduces silane into graphene for vapor phase chemical deposition.

[0073] Comparative Example 3

[0074] Comparative Example 3 is basically the same as Example 1, except that steps (1) and (2) in Example 1 are omitted, and the layered multi-element MXene in step (3) is replaced with Ti2C MXene. That is, Comparative Example 3 introduces silane into Ti2C MXene for vapor phase chemical deposition.

[0075] Comparative Example 4

[0076] Comparative Example 4 is basically the same as Example 1, except that the conductive adhesive in Example 1 is replaced with a polyacrylate adhesive.

[0077] Comparative Example 5

[0078] Comparative Example 5 is basically the same as Example 1, except that the conductive adhesive in Example 1 is replaced with a mixture of polyacrylate and aluminum zinc oxide.

[0079] (III) Experimental Examples

[0080] Battery manufacturing and electrochemical performance testing:

[0081] To test the performance of the silicon-carbon composite materials obtained in Examples 1-3 and Comparative Examples 1-5 of the present invention, each silicon-carbon composite material was used as a negative electrode material to fabricate batteries. The specific fabrication process is as follows:

[0082] Negative electrode sheets were prepared using the silicon-carbon composite negative electrode materials obtained in Examples 1-3 and Comparative Examples 1-5, respectively. Button batteries were assembled in a glove box using a 2032 coin cell casing. The positive electrode casing was placed on a horizontal worktable, and the negative electrode sheet, Celgard 2500 separator, lithium sheet, steel sheet, and spring sheet were placed in sequence (separator diameter > negative electrode sheet > positive electrode sheet). 15 μL of electrolyte (1M LiPF6 solvent EC:DEC (1:1v / v) + 5% FEC) was dropped onto the surface of the electrode sheet and separator using a pipette. The negative electrode casing was then covered, and finally, the coin cell was sealed with a coin cell sealing machine at 10 MPa for 5 seconds. After sealing, the cells were allowed to stand for 2 hours to ensure that the electrolyte was fully impregnated. Finally, the coin cells were removed from the glove box for electrochemical performance testing.

[0083] Electrochemical performance testing: The assembled battery was tested using a Blue Electric test cabinet. The charge and discharge regime was as follows: stand for 7 hours; discharge to 5mV at 0.1C, then charge to 1.5V at 0.1C; stand for 1 minute; cycle 10 times at 0.1C, then perform charge and discharge cycle test at 1.0C. The electrochemical test results are shown in Table 1.

[0084] Electrode volume expansion rate: After 100 charge-discharge cycles at 1.0 C, the button cell was removed and disassembled, and the negative electrode was taken out. The negative electrode was dried and cleaned at room temperature, and its thickness was measured with a micrometer. The thickness was then compared with the initial electrode thickness to calculate the electrode volume expansion rate.

[0085] Table 1 Electrochemical performance test results

[0086]

[0087] As shown in Table 1, the silicon-carbon composite anode materials prepared in Examples 1-3 of this invention, when applied to lithium-ion batteries, can significantly improve the battery capacity and cycle stability. After 100 cycles, the capacity retention rate is above 95%, and the electrode expansion rate is in the range of 22%-24%. Compared with Example 1, Comparative Examples 1-3 changed the preparation process of the nano-silicon composite. In Comparative Example 4, the zinc oxide aluminum nanoparticle-modified polyacrylate binder was replaced with a common polyacrylate binder, and in Comparative Example 5, a mixture of polyacrylate and zinc oxide aluminum was used. The battery capacity and cycle stability of Comparative Examples 1-5 decreased, while the electrode expansion rate increased. Detailed analysis reveals that the silicon-carbon composite anode material of this invention reduces the resistance between π-π stacked layers and provides abundant lithium-ion adsorption sites by inserting MXene into the interlayer of graphene to form a continuous conductive network, thereby improving the overall conductivity of graphene. At the same time, ball milling allows the transition metal carbide framework of MXene to combine with the sp² hybrid carbon network of graphene to form a mechanically interlocked structure, and nano-silicon is deposited between the MXene / graphene composite, thereby suppressing volume expansion during charging and discharging and improving the structural stability of the material. Furthermore, this invention adjusts the M-site element of traditional MXenes to a multi-element transition metal (Ti, V, Zr) to obtain a multi-element MXene. The differences in atomic radii and electronic orbitals of different metals complement each other, optimizing the electronic band structure of the material. Moreover, the multi-metal active sites and surface functional groups synergistically enhance the adsorption of lithium ions, reduce charge transport resistance, and improve the conductivity and charge storage capacity of MXenes, which helps to achieve high-capacity stable cycling. In addition, this invention uses zinc oxide aluminum nanoparticles to modify the polyacrylate binder, which not only improves the binding between silicon and carbon and buffers the volume expansion of silicon, but also improves its conductivity and reduces the interfacial resistance. No additional conductive agent is needed, which helps to enable the anode material to have a higher capacity.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. The basic principles and main features of the present invention have been described above with specific implementation schemes. Based on the present invention, some modifications or substitutions can be made, but these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of protection claimed by the present invention.

Claims

1. A silicon-carbon composite negative electrode material, characterized by, The silicon-carbon composite negative electrode material is composed of the following raw materials in weight percentage: 39-67 wt% porous carbon, 40-60 wt% nano-silicon composite and 1-3 wt% conductive binder; The preparation method of the nano-silicon composite comprises the following steps: (1) mixing Ti, V, Zr, Al and graphite powder, ball milling, then sintering under inert gas atmosphere, grinding and sieving after cooling to room temperature, to obtain multi-element MAX powder; (2) adding the multi-element MAX powder into HF solution for stirring reaction, then adding the reaction liquid into isopropyl alcohol for ultrasonic treatment, and cleaning and drying to obtain layered multi-element MXene; (3) ball milling the layered multi-element MXene and graphene to obtain a mixture, then introducing silane into the mixture for chemical vapor deposition under inert gas atmosphere at 400-500 ℃, to obtain the nano-silicon composite.

2. The silicon-carbon composite negative electrode material according to claim 1, characterized in that In step (1), the molar ratio of the Ti, V, Zr, Al and graphite powder is 2:2:2:3:3; the sintering temperature is 1400-1500 ℃, and the time is 1-2 h. 3.The silicon-carbon composite negative electrode material of claim 1, wherein, In step (2), the mass fraction of the HF solution is 40-50%; the mass ratio of the multi-element MAX powder to the HF solution is 1:(5-15). 4.The silicon-carbon composite negative electrode material of claim 1, wherein, In step (3), the mass ratio of the layered multi-element MXene to the graphene is 1:(1-4); the mass ratio of the silane to the mixture is 1:(0.5-2).

5. The silicon-carbon composite negative electrode material according to claim 1, characterized in that, The preparation method of the conductive binder comprises the following steps: (a) adding nano-aluminum zinc oxide and silane coupling agent into a mixed solution of ethanol and water, reacting under heating condition, centrifuging and collecting solid, and cleaning and drying to obtain modified nano-aluminum zinc oxide; (b) dispersing the modified nano-aluminum zinc oxide into methyl methacrylate, adding aqueous solution of polysorbate 20 and stirring uniformly to obtain a pre-emulsion; (c) adding ammonium persulfate into the pre-emulsion, heating and reacting to obtain the conductive binder.

6. The silicon-carbon composite negative electrode material according to claim 5, characterized in that In step (a), the mass ratio of the nano-aluminum zinc oxide, silane coupling agent, ethanol and water is 20:(1-2):(190-200):(5-10); the silane coupling agent is γ-methacryloyloxypropyltrimethoxysilane; the heating temperature is 55-65 ℃; and the reaction time is 1-2 h.

7. The silicon-carbon composite negative electrode material according to claim 5, characterized in that In step (b), the mass ratio of the modified nano-aluminum zinc oxide, methyl methacrylate and polysorbate 20 is 1:(20-30):(0.5-1). 8.The silicon-carbon composite negative electrode material of claim 5, wherein, In step (c), the mass ratio of the pre-emulsion to ammonium persulfate is 100:(0.2-0.5); the heating reaction temperature is 75-85 ℃, and the time is 2-4 h.

9. The method for preparing the silicon-carbon composite negative electrode material according to any one of claims 1-8, characterized in that, comprises the following steps: adding porous carbon, nano-silicon composite and conductive binder into ethanol according to the weight percentage, ball milling and mixing uniformly, and vacuum drying to obtain a carbon-silicon composite negative electrode material.

10. Application of the silicon-carbon composite negative electrode material according to any one of claims 1-8 in preparing lithium ion batteries.

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