CN101847712B - Method for depositing TiO2 on surface of multiwall carbon nano-tube for improving memory property of lithium ion - Google Patents

Abstract

The invention relates to a method for depositing TiO2 on the surface of a multiwall carbon nano-tube for improving the memory property of a lithium ion, which belongs to the technical field of the preparation technology of anode materials for lithium ion batteries. The method is characterized by comprising the following steps of: preparing a precursor by mixing oleic acid and tetrabutyl titanate in the weight ratio of 4 to 1, and then adding proper catalyst triethylamine into the precursor; weighting a certain amount of multiwall carbon nano-tubes (MWCNTs), adding the multiwall carbon nano-tubes into a mixed solvent of ethanol and toluene, then carrying out ultrasonic mixing on the obtained mixture and adding the mixture into the precursor; stirring and mixing the mixture, and moving the mixture to a Teflon high pressure reactor, and then putting the high pressure reactor in a baking oven at the temperature of 150 DEG C so as to make the mixture in the high pressure reactor react completely; washing reaction products by using the ethanol and the toluene, and then carrying out centrifugal separation on the reaction products so as to obtain an MWCNTs-TiO2 composite. The composite is easy to be dispersed in the toluene, and can be coated on a copper foil by the spin coating process so as to prepare the anode materials for thin film type lithium ion batteries.

Description

Method of depositing nano-TiO2 on the surface of multi-walled carbon nanotubes to improve lithium ion storage performance

technical field

The invention relates to a method for depositing nanometer _TiO2 on the surface of multi-walled carbon nanotubes to improve lithium ion storage performance, and belongs to the technical field of lithium ion battery negative electrode material preparation technology.

Background technique

In the process of exploring new lithium-ion battery anode materials, it was found that the charge and discharge capacity of carbon nanotubes can be more than double that of graphite lithium intercalation compounds, making the research of carbon nanotube lithium battery anode materials a hot spot. However, during the first charge and discharge process of carbon nanotubes, an irreversible SEI film (solid electrolyte interfacial film) is easily formed at the interface between the electrode and the electrolyte, resulting in very low initial Coulombic efficiency (<40%) and extremely poor cycle stability of carbon nanotubes. And other problems hinder its industrialization development.

MWCNT-TiO ₂ composite is a carbon-based heterojunction composite material that has been studied more in recent years. On the one hand, the study discusses the use of carbon nanotubes to assist the separation of photogenerated electron-hole pairs of nano-TiO2 to improve the photocatalytic activity of TiO2. efficiency; on the other hand, carbon nanotubes with good conductivity are used to modify nano-titanium dioxide to improve the lithium-ion storage performance of titanium dioxide. However, the effect of nano-titanium dioxide deposited on the surface of this composite on the Li-ion storage performance of carbon nanotubes has not been studied.

Contents of the invention

The object of the present invention is to provide a method for depositing nano- _TiO2 on the surface of multi-walled carbon nanotubes to improve lithium ion storage performance.

The present invention deposits nano _TiO on the surface of multi-walled carbon nanotubes The method for improving lithium ion storage performance is characterized in that it has the following process and steps:

a. Measure a certain volume of butyl titanate and oleic acid to prepare a titanium dioxide precursor; the volume ratio of butyl titanate to oleic acid is 1:4; heat the oleic acid to 55-65°C, and add titanium dioxide while stirring Acetate butyl ester, obtain bright brown precursor liquid; Cool to room temperature and set aside;

b. Take a certain amount of the above-mentioned precursor liquid, and add an appropriate amount of catalyst triethylamine during stirring; the amount of triethylamine added is 6-7% of the volume of the precursor liquid;

c. take a certain amount of multi-walled carbon nanotubes (MWCNTs) and join in the mixed solvent of a certain amount of ethanol and toluene; The volume ratio of ethanol and toluene in the mixed solvent is 1: 1.5～1: 3; The mixing ratio of carbon nanotubes (MWCNTs) and the mixed solvent is 2.5-4.0 mg/ml by mass volume ratio, that is, 2.5-4.0 mg of multi-walled carbon nanotubes (MWCNTs) are configured per 1 ml of mixed solvent; ultrasonic mixing 15-20 minutes;

d. Then add it to the above-mentioned precursor fluid with triethylamine added, and continue to stir for 2 to 3 hours to make the mixture uniform; then move the mixture to a Teflon high-pressure reactor and place it in an oven at 120-150°C, React for 12 to 15 hours; get a black mixture;

e. Centrifuge and settle the above-mentioned black mixture with a centrifuge at 10,000 rpm to obtain a black precipitate; then wash once with ethanol to remove excess oleic acid, and then wash 1 to 2 times with toluene to remove free Titanium dioxide nanoparticles; and then centrifuged to obtain MWCNTs-TiO ₂ composite.

The method of the invention is characterized in that: the MWCNTs-TiO ₂ composite is prepared through the self-assembly and in-situ growth of the TiO ₂ nanometer particles on the carbon nanotube. The deposition of _TiO2 on the surface of multi-walled carbon nanotubes can be used as a protective layer, which can effectively inhibit the irreversible solid electrolyte interfacial film (SEI film) on the electrode surface, thereby improving the lithium ion storage performance.

In the present invention, catalytic triethylamine is used to catalyze the aminolysis of the precursor to form nano-titanium dioxide.

The MWCNTs- _TiO2 composite prepared by the method of the invention is easily dispersed in toluene, and can be directly coated on copper foil by a solution operation method such as a spin coating process to prepare a negative electrode material for a thin film lithium ion battery.

Description of drawings

Fig. 1 is a transmission electron microscope (TEM) photograph of the MWCNTs-TiO ₂ composite prepared by the method of the present invention.

Fig. 2 is the X-ray diffraction analysis (XRD) pattern of (a) original MWCNTs, (b) TiO ₂ nanoparticles, (c) MWCNTs-TiO ₂ composite in the present invention.

Figure 3 is the specific capacity-voltage curves of (a) original carbon nanotubes and (b) MWCNTs-TiO ₂ composites.

Fig. 4 is a curve diagram of the coulombic efficiency of the MWCNTs-TiO ₂ composite obtained by the method of the present invention.

Detailed ways

Specific embodiments of the present invention are described below.

Example 1

The steps of this embodiment are as follows:

(1) Take oleic acid and heat it to about 60°C, add butyl titanate during stirring to obtain a bright brown precursor (volume ratio of oleic acid and butyl titanate is 4:1), cool to room temperature for later use.

(2) Take 3mL of the precursor and add 0.2ml of triethylamine while stirring.

(3) Weigh 20mg of MWCNTS and add it to the mixture of 2ml ethanol and 5ml toluene, ultrasonically add it for 15min and mix it with the precursor; after stirring for 2h, move it to a teflon autoclave (the volume of the reactor is 30mL), and place it in a 150 ℃ in an electric oven, keep the constant temperature for 15h to fully react.

(4) Wash the obtained product once with ethanol to remove excess oleic acid, then wash with toluene 1-2 times to remove free titanium dioxide nanoparticles, and obtain MWCNTs-TiO2 composites after centrifugation. The sample can be stably dispersed in toluene.

Detection and test of the product obtained in the present embodiment

(1), transmission electron microscope (TEM) detection

The detection results of MWCNTs- _TiO2 composites are shown in Fig. 1.

(2), X-ray diffractometer (XRD) analysis and detection

Referring to Fig. 2, in Fig. 2, a is the original carbon nanotube XRD diffraction pattern, b is the pure anatase nano-titanium dioxide diffraction pattern, c is the MWCNTs-TiO ₂ composite diffraction pattern, it contains the diffraction pattern of titanium dioxide and Diffraction peaks containing carbon nanotubes. (Although the 101 peak of titanium dioxide overlaps with the carbon nanotube (002) peak in the figure, the (101) peak of the carbon nanotube appears in the composite and shows that there are carbon nanotubes in the composite.)

(3), measurement of lithium ion storage performance (cyclic voltammetry)

Production of negative electrode:

The preparation method of lithium-ion anode material in this experiment is as follows: drop MWCNTs-TiO ₂ toluene solution on a copper sheet with a diameter of 14mm to throw the film, anneal at 200°C for 1min, repeat twice, the quality of the active material is the difference in the quality of the copper sheet before and after film throwing , which is 0.0006g in this example, is tested as the negative electrode;

As a comparison, a control test was performed on the storage characteristics of the original carbon nanotubes, and the specific method was: a mixture of carbon nanotubes and PTFE (20%) in a mass ratio of 4:1 was pressed into a tablet as the negative electrode of the battery.

See Figures 3 and 4.

In Figure 3, (a) and (b) are the specific capacity-voltage curves of the original carbon nanotubes and the composite samples obtained in the example for the first 20 cycles, and their lithium ion storage performance is compared in the potential range of 0.005 to 2.5. It can be seen from (a) that the initial discharge capacity of pristine carbon nanotubes is ~750 mAh/g, while the charge capacity is ~175 mAh/g, and the first Coulombic efficiency is only ~23%; it can be seen from (b) : While the first discharge of the prepared composite sample is ~320 mAh/g, the charging capacity is still ~298 mAh/g, and the first Coulombic efficiency reaches 93%. This shows that the reversible capacity of the composite of carbon nanotubes and titanium dioxide is significantly improved compared with carbon nanotubes, that is, the Coulombic efficiency is significantly improved.

In Fig. 4, the coulombic efficiency curve of the 20th to 100th cycle of the composite sample is stable between 95% and 97%, indicating that the composite sample has superior charge-discharge cycle performance.

Claims (1)

1. a kind of deposition nano _TiO on the surface of multi-walled carbon nanotubes The method that improves lithium ion storage performance is characterized in that having following technological process and step: a. Measure a certain volume of butyl titanate and oleic acid to prepare a titanium dioxide precursor; the volume ratio of butyl titanate to oleic acid is 1:4; heat the oleic acid to 55-65°C, and add titanium dioxide while stirring Acetate butyl ester, obtain bright brown precursor liquid; Cool to room temperature and set aside; b. Take a certain amount of the above-mentioned precursor liquid, and add an appropriate amount of catalyst triethylamine during stirring; the amount of triethylamine added is 6-7% of the volume of the precursor liquid; c. Take a certain amount of multi-walled carbon nanotubes, i.e. MWCNTs, and add them to a certain amount of mixed solvent of ethanol and toluene; the volume ratio of ethanol and toluene in the mixed solvent is 1: 1.5 to 1: 3; The mixing ratio of the walled carbon nanotubes and the mixed solvent is 2.5-4.0 mg/ml by mass volume ratio, that is, 2.5-4.0 mg of multi-walled carbon nanotubes are prepared per 1 ml of the mixed solvent; ultrasonically mixed for 15-20 minutes; d. Then add it to the above-mentioned precursor fluid with triethylamine added, and continue to stir for 2 to 3 hours to make the mixture uniform; then move the mixture to a Teflon high-pressure reactor and place it in an oven at 120-150°C, React for 12 to 15 hours; get a black mixture; e. Centrifuge and settle the above-mentioned black mixture with a centrifuge at 10,000 rpm to obtain a black precipitate; then wash once with ethanol to remove excess oleic acid, and then wash 1 to 2 times with toluene to remove free Titanium dioxide nanoparticles; and then centrifuged to obtain MWCNTs-TiO ₂ composite.

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