CN103456934B - A kind of used as negative electrode of Li-ion battery nano-TiO 2(B) preparation method and application of/carbon composite fibre - Google Patents

Abstract

The invention relates to a preparation method and application of nano TiO ₂ (B)/carbon composite fiber for lithium ion battery negative electrode. First, tetrabutyl titanate/polyvinylpyrrolidone precursor fibers were synthesized by electrospinning; then, the precursor fibers were dried and carbonized at 300-500°C under the protection of nitrogen or argon; finally, the The carbonized product is subjected to hydrothermal treatment to obtain the nano-TiO ₂ (B)/carbon composite fiber. The preparation method of the present invention has a simple process, realizes the compounding of titanium dioxide and carbon source in one step, does not need to introduce carbon source in subsequent experiments, ensures the purity of the product, saves raw materials, and has low production cost. The obtained nano-TiO ₂ (B)/carbon composite fiber is used as a negative electrode material for lithium-ion batteries, showing good cycle performance, especially at a fast charge and discharge rate, it can still maintain a high capacity, high cycle efficiency, and slow capacity decline. The introduction of Carbon increases the conductivity and reduces the resistance.

Description

Preparation method and application of nano-TiO2(B)/carbon composite fiber for negative electrode of lithium ion battery

technical field

The invention discloses a preparation method and application of nanometer TiO ₂ (B)/carbon composite fiber for negative electrodes of lithium ion batteries, belonging to the fields of electrochemistry and material chemistry.

Background technique

Titanium dioxide has become a research hotspot in the field of materials due to its broad application prospects in photocatalysis, photolysis of water, sensors, dye-sensitized solar cells, and lithium-ion batteries. Common titanium dioxide mainly includes four crystal phases: anatase phase, rutile phase, brookite phase and TiO ₂ (B) phase. Among all the crystalline phases, TiO ₂ (B) type titanium dioxide belongs to the monoclinic system, with the loosest structure, larger interlayer distance and lower density, which is conducive to the intercalation and removal of lithium ions. Applications in batteries have potentially superior properties.

To a large extent, the size, morphology and crystal growth direction of TiO ₂ (B) will affect its application in lithium-ion batteries. For example, the nanometer size and cross network can shorten the transmission distance of lithium ions and electrons, and the small size of TiO ₂ (B) can expand the contact area between the electrode and the electrolyte, reduce the current density, reduce the internal resistance of the battery, and improve battery performance. The one-dimensional TiO ₂ (B) nanostructure is conducive to the movement of electrons along the long axis, and lithium ions can also be quickly intercalated and removed along the short axis. Therefore, it is very important to control the size, morphology and growth direction of TiO ₂ (B), which can improve the charging and discharging performance of lithium-ion batteries.

As a typical one-dimensional nanostructure, the synthesis method of TiO ₂ (B) nanowires is mainly based on literature (AR Armstrong, G. Armstrong, J. Canales, PGBruce, Angew. Chem. Int. Ed. 2004, 43: 2286.) , that is: starting from titanium dioxide powder, sodium titanate nanowires are obtained by hydrothermal method in concentrated sodium hydroxide solution; after hydrogen ion exchange in a certain concentration of hydrochloric acid, the sodium titanate nanowires are converted into titanic acid nanowires; finally, the titanate nanowires are calcined and annealed to convert the titanate nanowires into TiO ₂ (B) nanowires. Chinese invention patent (publication number: CN102531050A) discloses a method for preparing TiO ₂ (B) nanowires and the use of the prepared TiO ₂ (B) nanowires. The nanowires of potassium titanate are obtained by hydrothermal or heating method, and the potassium titanate nanowires are converted into TiO ₂ (B) nanowires by secondary hydrothermal treatment. Lithium-ion batteries using TiO ₂ (B) nanowires as negative electrode materials can still maintain a large capacity under fast charge and discharge rates.

However, as a semiconductor material, TiO ₂ (B) has a low electronic conductivity (~10Ω ^-1 cm ^-1 ), so lithium-ion batteries using pure TiO ₂ (B) as the negative electrode material suffer from serious energy loss inside the battery . One of the solutions is to combine materials with excellent electrical conductivity, such as carbon materials, with TiO ₂ (B) to increase the electron import and export rates. In order to realize the compounding of carbon materials and TiO ₂ (B), the Chinese invention patent (Patent No. ZL200710050748.2) provides a preparation method of carbon-coated TiO ₂ core-shell composite nanopowder. It uses long-chain organic matter as a carbon source, and TiO ₂ /C nanometer powder is obtained after heat treatment of TiO ₂ powder at a certain temperature under vacuum condition. In addition to the role of carbon materials in protecting the internal TiO ₂ powder, the formed core-shell TiO ₂ /C composite powder is easier to adjust its properties and functions.

Electrospinning is an excellent method for preparing one-dimensional nanostructured materials. It has been extensively studied, the process is simple, and it can realize the controllable structure of material components. The invention adopts the electrospinning method to firstly prepare tetrabutyl titanate (TBT)/polyvinylpyrrolidone (PVP) precursor fibers, and then undergo heat treatment to obtain TiO ₂ (B)/C composite fibers. In the preparation of materials, there is no need to introduce carbon sources, but at the same time as electrospinning to prepare nanofibers, the composite of titanium dioxide and carbon sources is realized in one step, and only one crystal transformation process of heat treatment is experienced in the preparation process. Therefore, the invention not only simplifies the preparation process of the composite material, improves the purity of the product, but also saves the carbon source. The obtained TiO ₂ (B)/C composite material has high specific capacity and high cycle stability, and is a lithium ion battery negative electrode material with good performance. This preparation method has not yet been reported in literature and patents.

Contents of the invention

The purpose of the present invention is to provide a preparation method of TiO ₂ (B)/carbon composite fiber for negative electrode of lithium ion battery. Firstly, tetrabutyl titanate (TBT)/polyvinylpyrrolidone (PVP) precursor is prepared by electrospinning The fibers are then subjected to high-temperature carbonization and hydrothermal treatment to synthesize TiO ₂ (B)/C composite fibers. The resulting product is a composite fiber composed of two components, TiO ₂ (B) and carbon (C), which can realize the close composite of TiO ₂ (B) and carbon materials, and the obtained composite material has high specific capacity and cycle stability sex. The specific technical scheme is as follows:

A method for preparing nano-TiO ₂ (B)/carbon composite fibers for negative electrodes of lithium-ion batteries. First, electrospinning is used to synthesize tetrabutyl titanate (TBT)/polyvinylpyrrolidone (PVP) precursor fibers; then, the After the precursor fiber is dried, it is carbonized at 300-500°C (optimally 500°C) for 3-6 hours under the protection of nitrogen or argon; finally, the carbonized product is subjected to hydrothermal treatment to obtain the nano-TiO ₂ ( B)/carbon composite fiber;

The method for synthesizing TBT/PVP precursor fiber by electrospinning is as follows: under the condition of magnetic stirring, 0.8-1.2g (optimum 1.0g) tetrabutyl titanate, 0.3-0.5g (optimum 0.3g) polyethylene Pyrrolidone (PVP), dissolved in a mixture of 4-7 mL (optimally 7 mL) of ethanol, 1-3 mL (optimally 2 mL) of acetic acid, and 0.5-2 mL (optimally 1.8 mL) of N,N-dimethylformamide (DMF) In the solution, mix and stir evenly; take the aforementioned uniformly stirred solution and electrospin at a voltage of 9-12kV (optimally 12kV) to obtain the tetrabutyl titanate/polyvinylpyrrolidone precursor fiber;

The method of hydrothermal treatment is as follows: dissolve the carbonized product in 8-11 mol/L (optimum 9 mol/L) sodium hydroxide solution to obtain a suspension, and heat it in a closed hydrothermal kettle at 180-210°C ( Optimally 200°C) for 12-24 hours, wash the precipitated product with dilute acid and deionized water until the pH of the washing solution is neutral, and dry it under the protection of nitrogen or argon at 400-500°C (optimum 500 ℃) for 3-6 hours to obtain the nano-TiO ₂ (B)/carbon composite fiber.

The application of the nano-TiO _{2 (B)/carbon composite fiber obtained by the preparation method, the nano-TiO 2 (} B)/carbon composite fiber is used as the working electrode of lithium ion battery, and the lithium sheet is the auxiliary and reference electrode, and Electrolyte (for example, the volume ratio of 1MLiPF ₆ /DMC to EC is 1:1), assembled into a sleeve model battery, charged and discharged at a current density of 50mA/g, and the initial discharge capacity is 353-364mAh/g.

The advantages of this preparation method are: 1. Electrospinning to prepare one-dimensional nanostructured fibers, the component structure is controllable, the technology is mature, and the process is simple, which provides solid technical support for the controllable preparation of TBT/PVP precursor fibers; 2. 1. While preparing the TBT/PVP precursor fiber by electrospinning, the composite of titanium dioxide and carbon source is realized in one step, and no carbon source is needed in subsequent experiments. The preparation process is simplified, the purity of the product is guaranteed, and raw materials are saved; 3. The TiO ₂ (B)/C composite fiber obtained by this method has a one-dimensional structure and short b-axis and c-axis (Figure 1); 4. The raw material is easy to obtain, the preparation method is simple, and the production cost is low.

The nano TiO ₂ (B)/carbon composite fiber that this preparation method obtains is used in the advantage of lithium-ion battery negative electrode material and is: 1, because composite fiber has good one-dimensional structure, less particle size, high specific surface area, and Short b-axis and c-axis and other characteristics, showing good cycle performance, especially in the fast charge and discharge rate can still maintain a high capacity, such as the first discharge capacity can even reach 364mAh/g, for lithium-ion battery negative electrode , is the best effect among all titanium-oxygen systems at present; 2. High cycle efficiency and slow capacity decline; 3. The introduction of carbon increases the conductivity and reduces the resistance.

Description of drawings

Fig. 1 is the TEM photo of the product TiO ₂ (B)TiO ₂ /C composite fiber I of embodiment 1;

Fig. 2 is the charge-discharge curve of the product TiO ₂ (B)TiO ₂ /C composite fiber I of embodiment 1;

Fig. 3 is a cycle stability graph of the TiO ₂ (B)TiO ₂ /C composite fiber I produced in Example 1.

detailed description

The following are examples of the present invention, providing detailed implementation and specific operation process, the purpose of which is only to better understand the content of the present invention. The scope of protection of the invention is therefore not restricted by the examples given.

Example 1 Preparation of TiO ₂ (B)/C Composite Fiber I

Under the condition of magnetic stirring, 0.8g of tetrabutyl titanate and 0.4g of PVP were dissolved in a mixed solution of 6mL of ethanol, 2mL of acetic acid and 1mL of N,N-dimethylformamide, mixed and stirred evenly. Take 10mL of the solution with a syringe, the front of the spinneret is a copper mesh collection device, the voltage is 10kV, and the flow rate is 1.0mL/h. After spinning, the TBT/PVP precursor fiber was obtained, the fiber membrane was carefully removed, and vacuum dried at 60°C. Then, under the protection of nitrogen, the temperature was raised to 300° C. for calcination at a rate of 2° C./min, and the temperature was kept for 120 minutes.

Dissolve 0.35 g of the calcined sample in 10M NaOH solution to obtain a suspension. React in a closed 50mL hydrothermal kettle at 200°C for 24 hours. After stopping the reaction, wash the precipitated product with 0.1M hydrochloric acid and deionized water until the pH of the washing solution is neutral. Then, the temperature was raised to 500°C at a rate of 2°C/min and held for 300 minutes for further carbonization. TiO ₂ (B)/C composite fiber I was obtained. The TEM photo of the product is shown in Figure 1.

The test conditions of the electrode material are: charging and discharging at a current density of 50mA/g, and a temperature of 25°C; since it is sealed, pressure and humidity will not affect it. The test results are shown in Figure 2, which shows that the initial discharge capacity of the material is 364mAh/g, and the charge capacity after 100 cycles is 268mAh/g, with excellent cycle performance (as shown in Figure 3).

Example 2 Preparation of TiO ₂ (B)/C Composite Fiber II

Under magnetic stirring conditions, 0.8 g of tetrabutyl titanate and 0.4 g of PVP were dissolved in a mixed solution of 5 mL of ethanol, 2 mL of acetic acid and 1 mL of N,N-dimethylformamide. Mix and stir well. Take 10mL of the solution with a syringe, the front of the spinneret is a copper mesh collection device, the voltage is 11kV, and the flow rate is 1.0mL/h. After spinning, the TBT/PVP precursor fiber was obtained, the fiber membrane was carefully removed, and vacuum dried at 60°C. Then, under the protection of nitrogen, the temperature was raised to 500° C. for calcination at a rate of 2° C./min, and the temperature was kept for 120 minutes.

Dissolve 0.4 g of the calcined sample in 10M NaOH solution to obtain a suspension, react in a closed 50mL hydrothermal kettle at 180°C for 24 hours, stop the reaction, and wash the precipitated product with 0.1M hydrochloric acid and deionized water Wash until the pH of the washing liquid is neutral. After drying, under the protection of nitrogen, raise the temperature to 400°C at a rate of 2°C/min, keep it warm for 300min, and further carbonize to obtain TiO ₂ (B)/C composite fiber II.

The test conditions of the electrode material are as described in Example 1, charging and discharging at a current density of 50 mA/g. The test results show that the initial charging capacity of the material is 353mAh/g, and the charging capacity after 100 cycles is 260mAh/g, showing excellent cycle performance.

Claims (5)

1. a kind of preparation method of nanometer TiO ₂ (B)/carbon composite fiber for negative electrode of lithium ion battery, it is characterized in that, at first, adopt electrospinning synthetic tetrabutyl titanate/polyvinylpyrrolidone precursor fiber; Then, will After the precursor fiber is dried, it is carbonized at 300-500°C for 3-6 hours under the protection of nitrogen or argon; finally, the carbonized product is subjected to hydrothermal treatment to obtain the nano-TiO ₂ (B)/carbon composite fiber; The method for synthesizing tetrabutyl titanate/polyvinylpyrrolidone precursor fibers by electrospinning is as follows: under the condition of magnetic stirring, dissolve 0.8-1.2g tetrabutyl titanate and 0.3-0.5g polyvinylpyrrolidone in 4- In a mixed solution of 7mL ethanol, 1-3mL acetic acid and 0.5-2mL N, N-dimethylformamide, mix and stir evenly; take the mixed and stirred solution and electrospin at a voltage of 9-12kV to obtain the tetrabutyl titanate Ester/polyvinylpyrrolidone precursor fibers; The method of hydrothermal treatment is as follows: dissolve the carbonized product in 8-11mol/L sodium hydroxide solution to obtain a suspension, react in a closed hydrothermal kettle at 180-210°C for 12-24h, and dissolve the obtained The precipitated product is washed with dilute acid and deionized water until the pH of the washing solution is neutral, and after drying, it is calcined at 400-500°C for 3-6 hours under the protection of nitrogen or argon to obtain the nano-TiO ₂ (B)/carbon Composite fibers. 2. The preparation method according to claim 1, characterized in that, the tetrabutyl titanate is 1.0 g, and the polyvinylpyrrolidone is 0.3 g. 3. The preparation method according to claim 1, characterized in that, the electrospinning voltage is 12kV. 4. The preparation method according to claim 1, characterized in that, the temperature of the hydrothermal kettle is 200°C. 5. according to the application of the nano-TiO ₂ (B)/carbon composite fiber that the arbitrary described preparation method of claim 1 to 4 obtains, it is characterized in that, use described nano-TiO ₂ (B)/carbon composite fiber as lithium ion The working electrode of the battery, the lithium sheet is the auxiliary and reference electrode, and the electrolyte is assembled into a sleeve model battery, charged and discharged at a current density of 50mA/g, the first discharge capacity is 353-364mAh/g, and the charge capacity after 100 cycles is 268mAh/g.