Carbon-silicon nanofiber negative electrode material and preparation method thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a carbon-silicon nanofiber negative electrode material and a preparation method thereof. The method comprises the following steps: preparing modified SiO2 nanoparticles, preparing an electrospinning solution, and preparing the carbon-silicon nanofiber negative electrode material. The carbon-silicon nanofiber prepared by the method can be directly used as a self-supporting negative electrode material of a lithium battery, does not need a binder or a conductive agent, and has the performances of high battery specific capacity, high cycle stability and the like.

Description

Technical Field

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

[0002] The commercialization of lithium-ion batteries has greatly promoted the growth of the portable electronic products market. However, with the expansion of the use scope and application fields of lithium-ion batteries, the energy density and power density of the existing system can no longer meet the requirements of large-scale power storage. In addition, traditional lithium-ion batteries cannot take into account flexibility and electrochemical performance at the same time, which is manifested in low rate performance and short cycle life after flexibility. Electrodes are an important component of lithium-ion batteries, and the development of advanced flexible electrodes is one of the key issues. Traditional lithium-ion battery negative electrodes are mostly rigid materials. Typical negative electrode materials are active particles coated on copper foil. The active particles in this type of negative electrode material are easy to fall off the current collector copper foil, and binders, conductive agents, etc. need to be added during electrode preparation. In comparison, flexible self-supporting negative electrode materials for lithium-ion batteries have the advantages of light weight, good mechanical stability, no need for binders, and a relatively simple preparation process. They will play an increasingly important role in various fields in the future.

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

[0004] Although the electrochemical performance of the negative electrode can be effectively improved by combining silicon particles with carbon fibers, there are still many problems in the electrochemical reaction process of directly combining silicon nanoparticles with carbon fibers, such as poor cycle performance. For example, the invention patent CN 113097469 A discloses a Si / SiC / C nanofiber membrane, which is used as the negative electrode of a lithium-ion battery. After 200 cycles at the current density, only Based on this, it is urgent to develop more self-supporting negative electrode materials with high battery specific capacity and cycle stability. Summary of the invention

[0005] The purpose of the present invention is to provide a carbon silicon nanofiber negative electrode material and a preparation method thereof, which can be used as a self-supporting negative electrode material for lithium batteries to solve the problems of low specific capacity and poor cycle stability of existing batteries. In order to solve the above technical problems, the present invention provides the following technical solutions: A method for preparing a carbon-silicon nanofiber negative electrode material comprises the following steps: Step 1: Modification of SiO 2 Preparation of nanoparticles SiO 2 Nanoparticles, metal ionic liquid and organic solvent are added into the reactor, ultrasonically stirred, the organic solvent is removed by vacuum distillation, and then vacuum dried to obtain modified SiO 2 Nanoparticles; Step 2: Preparation of electrospinning solution Dissolve polyacrylonitrile in N , N - dimethylformamide, stir evenly; then add the modified SiO 2 The nanoparticles were subjected to magnetic stirring and ultrasonic treatment to obtain a uniform electrospinning solution; 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; the carbon silicon nanofiber mat is then 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: .

[0006] In some embodiments, the organic solvent in step 1 is selected from one or more of methanol, ethanol and isopropanol.

[0007] In some embodiments, the SiO 2 The mass ratio of the nanoparticles to the metal ion liquid is 1:(0.1-0.5); the temperature of the ultrasonic stirring in step 1 is 50-100° C. and the time is 1-5 hours.

[0008] In some embodiments, the polyacrylonitrile and modified SiO 2 The mass ratio of nanoparticles is 1:(1.0~2.0).

[0009] In some embodiments, the capacity of the injection pump in step 3 is 5-10 mL; 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 10-20 cm, and the spinning voltage is 15-20 kV.

[0010] In some embodiments, the method for preparing 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 h; after the reaction, ethyl acetate is added to the reaction mixture, and then centrifuged and purified 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, and then add SnCl 4 ·5H 2 O, 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 ion liquid; The reaction route is: , .

[0011] The present invention also protects the carbon silicon nanofiber negative electrode material prepared by the above method, and a lithium ion battery containing the carbon silicon nanofiber.

[0012] The present invention has achieved the following beneficial effects: 1) The carbon silicon nanofibers prepared by the present invention can be directly used as self-supporting negative electrode materials for lithium batteries, without the need for binders and conductive agents, and have the properties of high battery specific capacity, high cycle stability, etc.; 2) Anion Cl of the metal ionic liquid of the present invention - With SiO 2 The Si-OH interaction of nanoparticles changes the interface between the particles and the electrospinning solution, improving the SiO 2 The dispersion ability of nanoparticles in the electrospinning solution. The introduction of ionic liquid can increase the surface area of ​​carbon nanofibers of negative electrode materials, which is beneficial to enhance the wettability of electrolyte to negative electrode materials, reduce the transmission distance of lithium ions and increase the transmission speed of electrons, alleviate the stress concentration caused by the volume expansion of negative electrode materials, and improve the cycle stability of negative electrode materials; 3) The incorporation of N and Sn into metal ion liquids can improve the conductivity and lithium storage active sites of the negative electrode materials and enhance the electrochemical properties of the negative electrode materials. DETAILED DESCRIPTION

[0013] The following will be combined with the tables in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0014] 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 common commercial products in the technical field.

[0015] Preparation Example 1 Metal ionic liquid Di-[EtPy] / [2SnCl 5 Synthesis of , .

[0016] Step 1: Pyridine (0.21 mol), 1,4-dichlorobutane (0.1 mol) and acetonitrile (100 mL) were added to the reactor, and the temperature was raised to 60 °C and stirred for 24 h. After the reaction, ethyl acetate (200 mL) was added to the reaction mixture to remove unreacted impurities, and then centrifuged to purify to obtain a light yellow liquid, which was placed in a vacuum oven at 70 °C for 12 h to obtain the intermediate compound Di-[EtPy] / 2Cl with a yield of 75.8%.

[0017] 1 H NMR (400 MHz, D 2 O- d 6 ) δ 8.83 (d, 4H, Py), 8.54 (d, 2H, Py), 8.05 (d,4H, Py), 4.67 (t, 4H, NCH 2 -), 2.12 (dt, 4H, -CH 2 -).

[0018] Step 2: Add the intermediate compound Di-[EtPy] / 2Cl (0.1 mol) prepared in step 1 into the reactor, and then quickly add SnCl 4 ·5H 2O (0.2 mol), heated to 70 °C and stirred for 12 h. After the reaction, the reaction mixture was vacuum dried at 80 °C for 12 h to obtain the metal ionic liquid Di-[EtPy] / [2SnCl 5 ], with a yield of 96.7%.

[0019] Example 1 Preparation of carbon silicon nanofiber negative electrode material Step 1: Modification of SiO 2 Preparation of nanoparticles SiO 2 Nanoparticles (diameter 50 nm, 50.0 g), metal ionic liquid Di-[EtPy] / [2SnCl 5 ] (10.0 g) and anhydrous ethanol (150 mL) were added into a three-necked flask, ultrasonically stirred in a constant temperature water bath at 70 °C for 3 h, then poured out and dried in a vacuum drying oven at 90 °C for 12 h to obtain modified SiO 2 Nanoparticles, sealed for later use.

[0020] Step 2: Preparation of electrospinning solution Polyacrylonitrile (PAN, Mw = 450000, 10.0 g) was dissolved in N , N -dimethylformamide (100 mL) and stirred magnetically at room temperature for 5 h. Then the modified SiO 2 Nanoparticles (15.0 g) were magnetically stirred for 10 h and ultrasonically treated for 2 h to prepare a uniform electrospinning solution.

[0021] Step 3: Preparation of carbon silicon nanofiber negative electrode material The electrospinning solution was sucked into a 5 mL syringe pump for coaxial electrospinning. The syringe pump supply rate was 0.8 mL / h, the receiver speed was set to 300 r / min, the receiving distance was 15 cm, and the spinning voltage was 18 kV. After 6 h of electrospinning, the carbon silicon nanofiber mat was peeled off from the receiver. The carbon silicon nanofiber mat was placed in a muffle furnace, heated to 225°C at a rate of 2°C / min in an air atmosphere, and kept at 225°C for 2.0 h, cooled to room temperature and taken out. The pre-oxidized nanofiber mat was then placed in a tubular furnace, heated to 850°C at a rate of 6°C / min in a nitrogen atmosphere, and kept at 850°C for 2.0 h. After cooling to room temperature, a carbon silicon nanofiber negative electrode material was obtained.

[0022] Example 2 Preparation of carbon silicon nanofiber negative electrode material Step 1: Modification of SiO 2 Preparation of nanoparticles SiO2 Nanoparticles (diameter 50 nm, 50.0 g), metal ionic liquid Di-[EtPy] / [2SnCl 5 ] (5.0 g) and anhydrous ethanol (100 mL) were added into a three-necked flask, ultrasonically stirred in a 60°C constant temperature water bath for 2 h, then poured out and dried in a 90°C vacuum drying oven for 12 h to obtain modified SiO 2 Nanoparticles, sealed for later use.

[0023] Step 2: Preparation of electrospinning solution Polyacrylonitrile (PAN, Mw = 450000, 10.0 g) was dissolved in N , N -dimethylformamide (100 mL) and stirred magnetically at room temperature for 5 h. Then the modified SiO 2 Nanoparticles (10.0 g) were magnetically stirred for 12 h and ultrasonically treated for 1 h to prepare a uniform electrospinning solution.

[0024] Step 3: Preparation of carbon silicon nanofiber negative electrode material The electrospinning solution was sucked into a 5 mL syringe pump for coaxial electrospinning. The syringe pump supply rate was 1.0 mL / h, the receiver speed was set to 200 r / min, the receiving distance was 13 cm, and the spinning voltage was 20 kV. After 5 h of electrospinning, the carbon silicon nanofiber mat was peeled off from the receiver. The carbon silicon nanofiber mat was placed in a muffle furnace, heated to 250°C at a rate of 1°C / min in an air atmosphere, and kept at 250°C for 1.5 hours, cooled to room temperature and taken out. The pre-oxidized nanofiber mat was then placed in a tubular furnace, heated to 800°C at a rate of 5°C / min in a nitrogen atmosphere, and kept at 800°C for 2.0 hours. After cooling to room temperature, a carbon silicon nanofiber negative electrode material was obtained.

[0025] Comparative Example 1 Based on Example 1, modified SiO 2 Nanoparticles replaced with unmodified SiO 2 Nanoparticles, other operations and conditions are the same as in Example 1.

[0026] Comparative Example 2 Based on Example 1, the metal ionic liquid Di-[EtPy] / [2SnCl 5 ] Replaced by Di-[EtPy] / 2Cl , other operations and conditions are the same as in Example 1.

[0027] Performance Testing The battery specific capacity and cycle performance of the carbon silicon nanofiber negative electrode materials prepared in Example 1-2 and Comparative Example 1-2 were tested, and the test method was as follows: The carbon silicon nanofiber negative electrode material prepared by the present invention has good bending performance and can be restored to its original state after bending, showing that the electrode has certain flexibility and bendability. It can be directly used as a self-supporting negative electrode material, that is, after preparation, it can be sliced ​​using a slicer and can be directly used for the assembly of a half-cell after being fully dried under vacuum, without the need for a binder or a conductive agent.

[0028] The CR2016 button cell was assembled for testing. All the assembly was done in a glove box protected by pure argon. First, the thin lithium foil was placed in the positive electrode shell, and then the separator (Celgard2400) and carbon silicon nanofiber negative electrode material were placed in the battery, and then the appropriate electrolyte was added and packaged. The electrolyte was 1 mol / L LiPF 6 / EC-DMC (1:1). The specific capacity and cycle performance of the battery were tested using a blue battery tester (CHI660E) from Shanghai Huachen Company. The current density used in the test was 0.1A / g. The results are shown in Table 1.

[0029] Table 1 Battery performance test results: , It can be seen from Table 1 that the carbon silicon nanofibers prepared by the present invention as a self-supporting negative electrode material have excellent battery specific capacity and cycle stability.

[0030] It can be seen from Example 1 and Comparative Examples 1-2 that the present invention uses metal ion liquid For SiO 2 The modification of nanoparticles greatly improves the battery specific capacity and cycle stability. The main reasons may be: 1) The anion Cl of the metal ion liquid - With SiO 2 The Si-OH interaction of nanoparticles changes the interface between the particles and the electrospinning solution, improving the SiO 2 The dispersibility of nanoparticles in the electrospinning solution. The introduction of ionic liquid increases the surface area of ​​carbon nanofibers of negative electrode materials, which is beneficial to enhance the wettability of electrolytes to negative electrode materials, reduce the transmission distance of lithium ions and increase the transmission speed of electrons, alleviate the stress concentration caused by the volume expansion of negative electrode materials, and improve the cycle stability of negative electrode materials; 2) The incorporation of N and Sn in metal ionic liquids can improve the conductivity and lithium storage active sites of negative electrode materials and enhance the electrochemical performance of negative electrode materials.

[0031] The above embodiments are merely examples for clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the 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: .

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 mass ratio of polyacrylonitrile to modified SiO2 nanoparticles in step 2 is 1:(1.0~2.0).

5. 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.

6. 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: ， 。 7. A carbon silicon nanofiber negative electrode material prepared by the preparation method according to any one of claims 1-6.

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

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