A carbon-silicon nanofiber anode material and its preparation method

Abstract

The present invention belongs to the technical field of lithium-ion batteries, and specifically relates to a carbon-silicon nanofiber anode material and a preparation method thereof. The method includes the preparation of modified SiO2 nanoparticles, the preparation of an electrospinning solution, and the preparation of the carbon-silicon nanofiber anode material. The carbon-silicon nanofibers prepared by the present invention can be directly used as a self-supporting anode material for lithium batteries, without the need for binders and conductive agents, and have properties such as high specific capacity of the battery and high cycle stability.

Description

Technical Field

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

[0002] The commercialization of lithium-ion batteries has greatly promoted the growth of the portable electronic product market. However, with the expansion of the usage scope and application fields of lithium-ion batteries, the energy density and power density of the existing systems are difficult to meet the requirements of large-scale power storage. In addition, traditional lithium-ion batteries cannot simultaneously achieve flexibility and electrochemical performance, showing low rate performance and short cycle life after being made flexible. The electrode is an important part of a lithium-ion battery, and developing advanced flexible electrodes is one of the key issues. Most traditional lithium-ion battery anodes are rigid materials. A typical anode material is to coat active particles on a copper foil. In such anode materials, the active particles are prone to fall off from the current collector copper foil, and binders, conductive agents, etc. need to be added during electrode preparation. In contrast, lithium-ion battery flexible self-supporting anode materials have the advantages of light weight, good mechanical stability, and no need to use binders, etc., and the preparation process is relatively simple, and will play an increasingly important role in various fields in the future.

[0003] The anode material is one of the key components of a lithium-ion battery. During the charge and discharge process, it undergoes deintercalation / insertion of lithium reactions, which directly affects the battery performance. In recent years, the research on lithium-ion anode materials mainly includes: graphitized carbon materials, amorphous carbon materials, nitrides, silicon-based materials, tin-based materials, new alloys, nano-oxides, and other materials. Among them, the silicon-based material is the research system with the highest theoretical specific capacity among the anode materials under research, with a theoretical specific capacity as high as , and is considered an alternative product to carbon anode materials due to its low lithium insertion potential, low atomic mass, and high energy density. However, due to the severe volume expansion and contraction of silicon anodes during the lithium insertion / extraction cycle, the material structure is damaged and mechanically pulverized, resulting in poor cycle performance of the electrode. Carbon nanofibers (CNFs) are widely used in the research of lithium-ion batteries as a new type of carbon material. They have a high aspect ratio and can effectively improve the charge and discharge rate. However, when cycling for a long time at a high current density, the CNFs structure collapses severely, resulting in irreversible capacity loss and being difficult to be applied in high-power devices.

[0004] Although the electrochemical performance of the anode can be effectively improved by compounding silicon particles with carbon fibers, however, there are still many problems in the direct composite form of silicon nanoparticles and carbon fibers during the electrochemical reaction process, such as poor cycle performance. For example, the invention patent CN 113097469 A discloses a Si / SiC / C nanofiber membrane, which shows Only maintain after 200 cycles at the current density of the capacity. Based on this, it is urgent to develop more self-supporting anode materials with high specific capacity and cycling stability of the battery. SUMMARY OF THE INVENTION

[0005] The purpose of the present invention is to provide a carbon-silicon nanofiber anode material and a preparation method thereof, which can be used as a self-supporting anode material for lithium batteries to solve the problems of low specific capacity and poor cycling stability of the existing technology batteries. To solve the above technical problems, the present invention provides the following technical solutions:

[0006] A preparation method of a carbon-silicon nanofiber anode material, comprising the following steps:

[0007] Step 1: Preparation of modified SiO2 nanoparticles

[0008] Add SiO2 nanoparticles, metal ionic liquid and organic solvent into the reactor, stir ultrasonically, remove the organic solvent by reduced pressure distillation, and then dry in vacuum to obtain modified SiO2 nanoparticles;

[0009] Step 2: Preparation of electrospinning solution

[0010] Dissolve polyacrylonitrile in N , N -dimethylformamide, stir evenly; then add the modified SiO2 nanoparticles obtained in Step 1, and obtain a uniform electrospinning solution through magnetic stirring and ultrasonic treatment;

[0011] Step 3: Preparation of carbon-silicon nanofiber anode material

[0012] Inhale the electrospinning solution obtained in Step 2 into an injection pump for coaxial electrospinning to obtain a carbon-silicon nanofiber mat; then put the carbon-silicon nanofiber mat into a muffle furnace, heat it to 200-250 °C at a rate of 2-5 °C / min in an air atmosphere, keep it warm for 1-5 h and then cool it to room temperature to obtain a pre-oxidized nanofiber mat; finally, put the above pre-oxidized nanofiber mat into a tubular furnace, heat it to 800-1000 °C at a rate of 3-8 °C / min in a nitrogen atmosphere, keep it warm for 1-5 h and then cool it to room temperature to obtain the carbon-silicon nanofiber anode material;

[0013] The structure of the metal ionic liquid described in Step 1 is: .

[0014] In some embodiments, the organic solvent described in Step 1 is selected from one or more of methanol, ethanol and isopropanol.

[0015] In some embodiments, the mass ratio of the SiO2 nanoparticles described in step 1 to the metal ionic liquid is 1:(0.1~0.5); the temperature of the ultrasonic stirring described in step 1 is 50~100 °C, and the time is 1~5 h.

[0016] In some embodiments, the mass ratio of the polyacrylonitrile described in step 2 to the modified SiO2 nanoparticles is 1:(1.0~2.0).

[0017] In some embodiments, the capacity of the syringe pump described in step 3 is 5~10 mL; the liquid supply rate of the syringe pump is 0.5~0.1 mL / h, the rotation speed of the receiver is set to 100~500 r / min, the receiving distance is 10~20 cm, and the spinning voltage is 15~20 kV.

[0018] In some embodiments, the preparation method of the metal ionic liquid described in step 1 includes the following steps:

[0019] Step 1: Add pyridine, 1,4-dichlorobutane and acetonitrile into the reactor, heat up to 50~80 °C and stir for reaction for 12~24 h; after the reaction is completed, add ethyl acetate to the reaction mixture, and then centrifugally purify to obtain a light yellow liquid. Vacuum dry the light yellow liquid to obtain the intermediate compound Di-[EtPy] / 2Cl;

[0020] Step 2: Add the intermediate compound Di-[EtPy] / 2Cl prepared in step 1 into the reactor, then add SnCl4·5H2O, heat up to 60~90 °C and stir for reaction for 5~12 h; after the reaction is completed, vacuum dry the reaction mixture to obtain the metal ionic liquid;

[0021] The reaction route is:

[0022] ,

[0023] .

[0024] The present invention also protects the carbon-silicon nanofiber anode material prepared by the above method, and the lithium ion battery containing the above carbon-silicon nanofibers.

[0025] The present invention has achieved the following beneficial effects:

[0026] 1) The carbon-silicon nanofibers prepared by the present invention can be directly used as the self-supporting anode material of the lithium battery, without the need for a binder and a conductive agent, and have properties such as high battery specific capacity and high cycle stability;

[0027] 2) The anion Cl of the metal ionic liquid of the present invention -Interact with the Si-OH of SiO2 nanoparticles to change the interface between the nanoparticles and the electrospinning solution, improving the dispersion ability of SiO2 nanoparticles in the electrospinning solution. The introduction of ionic liquid can increase the surface area of the carbon nanofiber anode material, which is beneficial to enhancing the wettability of the electrolyte for the anode material, reducing the lithium ion transport distance and increasing the electron transport speed, alleviating the stress concentration caused by the volume expansion of the anode material, and improving the cycle stability of the anode material;

[0028] 3) The incorporation of N and Sn in the metal ionic liquid can increase the conductivity and lithium storage active sites of the anode material, enhancing the electrochemical performance of the anode material. Specific implementation manners

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the tables in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] The present invention does not limit the sources of the raw materials used. Unless otherwise specified, the raw materials used in the present invention are all ordinary commercially available products in the technical field.

[0031] Preparation Example 1 Synthesis of metal ionic liquid Di-[EtPy] / [2SnCl5]

[0032] ,

[0033] .

[0034] Step 1: Add pyridine (0.21 mol), 1,4-dichlorobutane (0.1 mol) and acetonitrile (100 mL) into a reactor, heat up to 60 °C and stir for reaction for 24 h. After the reaction is completed, add ethyl acetate (200 mL) to the reaction mixture to remove unreacted impurities, and then centrifuge and purify to obtain a light yellow liquid. Place the light yellow liquid in a vacuum oven at 70 °C and dry for 12 h to obtain the intermediate compound Di-[EtPy] / 2Cl, with a yield of 75.8%.

[0035] 1 H NMR (400 MHz, D2O- d 6) δ 8.83 (d, 4H, Py), 8.54(d, 2H, Py), 8.05 (d,4H, Py), 4.67 (t, 4H, NCH2-), 2.12 (dt, 4H, -CH2-).

[0036] Step 2: Add the intermediate compound Di-[EtPy] / 2Cl (0.1 mol) prepared in Step 1 into a reactor, then quickly add SnCl4·5H2O (0.2 mol), and raise the temperature to 70 °C and stir for reaction for 12 h. After the reaction is completed, vacuum-dry the reaction mixture at 80 °C for 12 h to obtain the metal ionic liquid Di-[EtPy] / [2SnCl5] with a yield of 96.7%.

[0037] Example 1 Preparation of Carbon-Silicon Nanofiber Anode Material

[0038] Step 1: Preparation of Modified SiO2 Nanoparticles

[0039] Add SiO2 nanoparticles (diameter 50 nm, 50.0 g), the metal ionic liquid Di-[EtPy] / [2SnCl5] obtained in Preparation Example 1 (10.0 g), and absolute ethanol (150 mL) into a three-necked flask, ultrasonically stir in a constant temperature water bath at 70 °C for 3 h, then take out and dry in a vacuum drying oven at 90 °C for 12 h to obtain modified SiO2 nanoparticles, which are sealed for use.

[0040] Step 2: Preparation of Electrospinning Solution

[0041] Dissolve polyacrylonitrile (PAN, Mw = 450000, 10.0 g) in N , N N,N-dimethylformamide (100 mL), and magnetically stir at room temperature for 5 h. Then add the above-mentioned modified SiO2 nanoparticles (15.0 g), magnetically stir for 10 h, and ultrasonically treat for 2 h to prepare a uniform electrospinning solution.

[0042] Step 3: Preparation of Carbon-Silicon Nanofiber Anode Material

[0043] Inhale the electrospinning solution into a 5 mL syringe pump for coaxial electrospinning. The liquid supply rate of the syringe pump is 0.8 mL / h, the rotation speed of the receiver is set to 300 r / min, the receiving distance is 15 cm, and the electrospinning voltage is 18 kV; after electrospinning for 6 h, peel off the carbon-silicon nanofiber mat from the receiver;

[0044] Take the above carbon-silicon nanofiber mat and put it into a muffle furnace, heat it to 225 °C at a rate of 2 °C / min in an air atmosphere, and keep it at 225 °C for 2.0 h, then cool it to room temperature and take it out. Then put the above pre-oxidized nanofiber mat into a tube furnace, heat it to 850 °C at a rate of 6 °C / min in a nitrogen atmosphere, and keep it at 850 °C for 2.0 h. Cool it to room temperature to obtain the carbon-silicon nanofiber anode material.

[0045] Example 2 Preparation of Carbon-Silicon Nanofiber Anode Material

[0046] Step 1: Preparation of Modified SiO2 Nanoparticles

[0047] Add SiO2 nanoparticles (diameter 50 nm, 50.0 g), the metal ionic liquid Di-[EtPy] / [2SnCl5] obtained in Preparation Example 1 (5.0 g), and absolute ethanol (100 mL) into a three-necked flask. Ultrasonically stir in a constant temperature water bath at 60 °C for 2 h, then take out and dry in a vacuum drying oven at 90 °C for 12 h to obtain modified SiO2 nanoparticles, and seal for later use.

[0048] Step 2: Preparation of Electrospinning Solution

[0049] Dissolve polyacrylonitrile (PAN, Mw = 450000, 10.0 g) in N , N N,N-dimethylformamide (100 mL), and magnetically stir at room temperature for 5 h. Then add the above-mentioned modified SiO2 nanoparticles (10.0 g), magnetically stir for 12 h, and ultrasonically treat for 1 h to prepare a uniform electrospinning solution.

[0050] Step 3: Preparation of Carbon-Silicon Nanofiber Anode Material

[0051] Inhale the electrospinning solution into a 5 mL syringe pump for coaxial electrospinning. The liquid supply rate of the syringe pump is 1.0 mL / h, the rotation speed of the receiver is set to 200 r / min, the receiving distance is 13 cm, and the electrospinning voltage is 20 kV; after electrospinning for 5 h, peel off the carbon-silicon nanofiber mat from the receiver;

[0052] Put the above-mentioned carbon-silicon nanofiber mat into a muffle furnace, heat it to 250 °C at a rate of 1 °C / min in an air atmosphere, and keep it at 250 °C for 1.5 h, then cool to room temperature and take out. Then put the above-mentioned pre-oxidized nanofiber mat into a tube furnace, heat it to 800 °C at a rate of 5 °C / min in a nitrogen atmosphere, and keep it at 800 °C for 2.0 h. Cool to room temperature to obtain the carbon-silicon nanofiber anode material.

[0053] Comparative Example 1

[0054] On the basis of Example 1, replace the modified SiO2 nanoparticles with unmodified SiO2 nanoparticles, and the other operations and conditions are the same as in Example 1.

[0055] Comparative Example 2

[0056] On the basis of Example 1, replace the metal ionic liquid Di-[EtPy] / [2SnCl5] with Di-[EtPy] / 2Cl For other operations and conditions, they are the same as those in Example 1.

[0057] Performance Test

[0058] The specific capacity and cycling performance of the carbon-silicon nanofiber anode materials prepared in Examples 1-2 and Comparative Examples 1-2 were tested. The test method is as follows:

[0059] The carbon-silicon nanofiber anode material prepared in the present invention has good bending performance and can return to its original state after being bent, demonstrating that the electrode has a certain degree of flexibility and bendability. It can be directly used as a self-supporting anode material, that is, after being prepared, it is sliced by a slicing machine and can be directly used for the assembly of a half-cell after being fully dried under vacuum, without the need for a binder and a conductive agent.

[0060] The CR2016 button battery was assembled for testing. The assembly was carried out entirely in a glove box under pure argon protection. First, the electrode thin lithium foil was placed in the positive electrode case, then the separator (Celgard 2400) and the carbon-silicon nanofiber anode material were placed in the battery, and after adding an appropriate electrolyte, it was sealed. The electrolyte was 1 mol / L LiPF6 / EC-DMC (1:1). The specific capacity and cycling performance of the battery were tested using a blue electrochemical workstation (CHI660E) from Shanghai Chenhua Co., Ltd., and the current density used for the test was 0.1 A / g. The results are shown in Table 1.

[0061] Table 1 Test results of battery performance:

[0062] ,

[0063] As can be seen from Table 1, the carbon-silicon nanofibers prepared in the present invention as self-supporting anode materials have excellent specific capacity and cycling stability of the battery.

[0064] From Examples 1 and Comparative Examples 1-2, it can be seen that the present invention uses metal ionic liquids to modify SiO2 nanoparticles, which greatly improves the specific capacity and cycling stability of the battery. The main reasons may be as follows: 1) The anion Cl - of the metal ionic liquid interacts with the Si-OH of the SiO2 nanoparticles, thereby changing the interface between the particles and the electrospinning solution and improving the dispersion ability of the SiO2 nanoparticles in the electrospinning solution. The introduction of the ionic liquid increases the surface area of the carbon nanofiber anode material, which is beneficial to enhancing the wettability of the electrolyte to the anode material, reducing the lithium ion transport distance and increasing the electron transport speed, alleviating the stress concentration caused by the volume expansion of the anode material, and improving the cycling stability of the anode material; 2) The incorporation of N and Sn in the metal ionic liquid can increase the conductivity and lithium storage active sites of the anode material, enhancing the electrochemical performance of the anode material.

[0065] The above embodiments are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or alterations can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. Thus, the obvious changes or alterations derived therefrom still fall within the protection scope of the present invention.

Claims

1. A method for preparing a carbon-silicon nanofiber negative electrode material, comprising the following steps: Step 1: Preparation of modified SiO2 nanoparticles Adding SiO2 nanoparticles, metal ion liquid and organic solvent into a reactor, stirring with ultrasound, removing the organic solvent by vacuum distillation, and then vacuum drying to obtain modified SiO2 nanoparticles; Step 2: Preparation of electrospinning solution Dissolve polyacrylonitrile in N , N - dimethylformamide, stirring evenly; then adding the modified SiO2 nanoparticles obtained in step 1, and obtaining a uniform electrospinning solution through magnetic stirring and ultrasonic treatment; Step 3: Preparation of carbon silicon nanofiber negative electrode material The electrospinning solution obtained in step 2 is sucked into a syringe pump for coaxial electrospinning to obtain a carbon silicon nanofiber mat; then the carbon silicon nanofiber mat is placed in a muffle furnace, heated to 200-250°C at a rate of 2-5°C / min in an air atmosphere, kept warm for 1-5 hours, and then cooled to room temperature to obtain a pre-oxidized nanofiber mat; finally, the pre-oxidized nanofiber mat is placed in a tubular furnace, heated to 800-1000°C at a rate of 3-8°C / min in a nitrogen atmosphere, kept warm for 1-5 hours, and then cooled to room temperature to obtain a carbon silicon nanofiber negative electrode material; The structure of the metal ion liquid in step 1 is: ; The mass ratio of polyacrylonitrile to modified SiO2 nanoparticles in step 2 is 1:(1.0~2.0).

2. The preparation method according to claim 1, characterized in that: The organic solvent in step 1 is selected from one or more of methanol, ethanol and isopropanol.

3. The preparation method according to claim 1, characterized in that: The mass ratio of the SiO2 nanoparticles to the metal ion liquid in step 1 is 1:(0.1-0.5); the temperature of the ultrasonic stirring in step 1 is 50-100°C and the time is 1-5h.

4. The preparation method according to claim 1, characterized in that: The capacity of the injection pump in step 3 is 5~10mL; the liquid supply rate of the injection pump is 0.5~0.1 mL / h, the speed of the receiver is set to 100~500 r / min, the receiving distance is 10~20cm, and the spinning voltage is 15~20 kV.

5. The preparation method according to claim 1, characterized in that: The preparation method of the metal ionic liquid in step 1 comprises the following steps: Step 1: Pyridine, 1,4-dichlorobutane and acetonitrile are added to a reactor, and the temperature is raised to 50-80 °C and stirred for reaction for 12-24 hours; after the reaction, ethyl acetate is added to the reaction mixture, and then centrifuged to purify to obtain a light yellow liquid, and the light yellow liquid is vacuum dried to obtain the intermediate compound Di-[EtPy] / 2Cl; Step 2: Add the intermediate compound Di-[EtPy] / 2Cl prepared in step 1 into the reactor, then add SnCl4·5H2O, raise the temperature to 60-90°C and stir to react for 5-12h; after the reaction, vacuum dry the reaction mixture to obtain a metal ionic liquid; The reaction route is: ， 。 6. A carbon-silicon nanofiber negative electrode material prepared by the preparation method according to any one of claims 1-5.

7. A lithium ion battery comprising the carbon silicon nanofiber negative electrode material according to claim 6.

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