CN106784692A - Graphene array load lithium titanate/carbon/carbon nano tube composite array electrode material and its preparation method and application - Google Patents

Abstract

The invention discloses a graphene array-loaded lithium titanate/carbon nanotube composite array electrode material and its preparation method and application. The method comprises: using microwave plasma enhanced chemical vapor deposition technology to vertically grow graphene arrays on carbon cloth ; use atomic layer deposition technology to grow TiO ₂ on the resulting graphene array; dissolve lithium hydroxide in water to form solution A; place the vertical graphene-loaded titanium dioxide composite electrode material in solution A for hydrothermal reaction, and then Washing, drying and calcination; using chemical vapor deposition technology, using acetylene as a carbon source, in the atmosphere of hydrogen and argon, growing carbon nanotubes on graphene array-supported lithium titanate composite array electrodes to obtain graphene array-supported Lithium titanate/carbon nanotube composite array electrode material. When the electrode material is used as an anode material of a lithium ion battery, it has excellent high-rate performance and cycle stability.

Description

Graphene array supported lithium titanate/carbon nanotube composite array electrode material and its preparation preparation methods and applications

technical field

The invention relates to the technical field of lithium-ion battery electrode materials, in particular to a graphene array-supported lithium titanate/carbon nanotube composite array electrode material and a preparation method and application thereof.

Background technique

At present, with the continuous development of the economy, the continuous consumption of energy, and the increasingly prominent environmental problems, green energy has become a hot spot that people pay attention to. Because of its convenient storage and no pollution to the environment, electric energy is considered to be one of the ideal energy sources in the 21st century. As a storage device for electrical energy, lithium-ion batteries have the advantages of high energy density, long cycle life, and environmental friendliness, and have been commercialized on a large scale. In recent years, with the development of technology, the research of lithium-ion battery electrode materials has paid more and more attention to high-rate performance. However, the current commercial graphite anode cannot meet this requirement due to the low ion and electron transport efficiency. Therefore, there is an urgent need to develop a lithium-ion battery anode material with ultra-fast charge-discharge performance.

Among the anode materials for lithium-ion batteries, lithium titanate, as a zero-strain material, has excellent cycle stability and high rate performance, with a theoretical capacity of 175mAh g ^-1 . In addition, it has a charge and discharge platform of 1.55V, which can effectively avoid the formation of lithium dendrites and SEI film (solid electrolyte interface, solid electrolyte interface film), and improve safety performance. The lithium storage process of lithium titanate is completed through the phase transition between Li ₄ Ti ₅ O ₁₂ and Li ₇ Ti ₅ O ₁₂ , and the volume expansion rate is only 0.2%. Therefore, in the process of lithium delithiation and lithium intercalation, there is less capacity loss due to material cracking due to volume expansion, so it has better cycle stability. However, the low electronic conductivity limits its application under high current charging and discharging. Therefore, how to improve the electronic conductivity of lithium titanate is a key scientific problem to be solved urgently for its application as a negative electrode material for lithium ion batteries.

At present, compounding lithium titanate with other conductive materials and nanonizing it is an effective way to improve its electronic conductivity. Generally, the conductive material compounded with it is carbon material, such as graphene, carbon nanotube, activated carbon and so on. The carbon material provides a conductive framework for lithium titanate, which improves the electronic conductivity of the entire electrode, thereby improving high-rate performance.

Contents of the invention

The object of the present invention is to provide a graphene array-loaded lithium titanate/carbon nanotube composite array electrode material and its preparation method and application. When the electrode material is used as a lithium-ion battery negative electrode material, it has excellent high-rate performance and cycle stability.

A preparation method of a graphene array loaded lithium titanate/carbon nanotube composite array electrode material, comprising the following steps:

(1) Using microwave plasma enhanced chemical vapor deposition (MPECVD) technology to vertically grow graphene arrays on carbon cloth;

(2) using atomic layer deposition (ALD) technology to grow TiO ₂ on the graphene array obtained in step (1), to obtain a vertical graphene-loaded titanium dioxide composite electrode material;

(3) Lithium hydroxide is dissolved in water to form solution A;

(4) Place the vertical graphene-supported titania composite electrode material obtained in step (2) in solution A, carry out hydrothermal reaction, and then wash, dry and calcinate to obtain graphene (VG) array-supported lithium titanate (Li ₄ Ti ₅ O ₁₂ , LTO) composite array electrode, namely VG/LTO composite array electrode;

(5) Utilize chemical vapor deposition (CVD) technology, take acetylene as carbon source, under the atmosphere of hydrogen and argon, grow carbon nanotube on the graphene array supported lithium titanate composite array electrode of step (4) gained ( CNTs) to obtain a graphene array-loaded lithium titanate/carbon nanotube composite array electrode material, that is, a VG/LTO-CNTs composite array electrode material.

Following as preferred technical scheme of the present invention:

In step (1), utilize microwave plasma enhanced chemical vapor deposition (MPECVD) technology to vertically grow graphene array on carbon cloth, specific condition is: reaction atmosphere is methane and hydrogen, the flow of methane is 30-50sccm, the flow of hydrogen It is 40-60 sccm, and the reaction temperature and time are respectively 400-500° C. and 1-3 hours.

In step (2), use atomic layer deposition (ALD) technology to grow TiO ₂ on the graphene array obtained in step (1), the specific conditions are: Ti source is titanium tetrachloride, O source is water, and the reaction temperature is 200 -300°C.

In step (3), the concentration of lithium hydroxide in the solution A is 1-3 mol·L ^-1 .

In step (4), the hydrothermal reaction is carried out at 80-90° C. for 1-2 hours.

During calcination, the protective atmosphere is argon, the reaction temperature is 500-600° C., and the reaction time is 2-3 hours.

In step (5), the flow of acetylene is 2-10 sccm, the flow of hydrogen is 5-10 sccm, the flow of argon is 50-100 sccm, and the reaction temperature and time are 600-700° C. and 1-10 minutes respectively.

The graphene array loaded lithium titanate/carbon nanotube composite array electrode material includes carbon cloth, a graphene array vertically grown on the carbon cloth, and lithium titanate nanotubes coated on the graphene array. particles and carbon nanotubes interwoven and grown on the lithium titanate nanoparticles. Lithium titanate nanoparticles uniformly cover the vertical graphene arrays. Then, the carbon nanotubes are interwoven and grown on the lithium titanate nanoparticles to obtain a graphene array-supported lithium titanate/carbon nanotube composite electrode material, which is in the form of a sheet with a total thickness of 0.4-0.8 mm, more preferably 0.5 mm. ~0.65mm.

The lithium titanate/carbon nanotube composite electrode material supported by the graphene array is calculated by unit area, the loading capacity of the graphene array is 0.3-0.7 mg cm ^-2 , and the loading capacity of lithium titanate nanoparticles is 0.5-1.5 mg cm ^-2 , the loading capacity of carbon nanotubes is 0.3-0.7 mg cm ^-2 . Further preferably, the loading amount of the graphene array is 0.4-0.6 mg cm ^-2 , the loading amount of lithium titanate nanoparticles is 0.8-1.2 mg cm ^-2 , and the loading amount of carbon nanotubes is 0.4-0.6 mg cm ^-2 . More preferably, the loading capacity of the graphene array is 0.5 mg cm ^-2 , the loading capacity of lithium titanate nanoparticles is 1 mg cm ^-2 , and the loading capacity of carbon nanotubes is 0.5 mg cm ^-2 .

In the present invention, lithium titanate (Li ₄ Ti ₅ O ₁₂ , LTO) nanoparticles obtained by using vertical graphene (VG) as a conductive framework, atomic layer deposition combined with chemical lithium intercalation method are evenly covered on the vertical graphene, carbon nanometer tubes (CNTs) as the coated conductive network to construct the VG/LTO-CNTs core-shell array electrode material, resulting in ultra-long cycle life and excellent high-rate performance.

Graphene array loaded lithium titanate/carbon nanotube composite array electrode material is used as lithium ion battery electrode material, and the obtained VG/LTO-CNTs film is cut into small pieces as lithium ion battery electrode, that is, the counter electrode, and the battery is assembled. The separator is a microporous polypropylene membrane, the electrolyte uses 1mol L ^-1 LiPF ₆ as the solute, ethylene carbonate (EC) and dimethyl carbonate (DMC) with a volume ratio of 1:1 as the solvent, and the counter electrode is lithium The cells were assembled in an argon-filled glove box.

After the assembled lithium-ion battery is placed for 12 hours, a constant current charge-discharge test is performed. The charge-discharge voltage is 2.5V to 1.0V. The capacity, rate characteristics and charge-discharge cycle performance of the negative electrode of the lithium-ion battery are measured in an environment of 25±1°C.

Compared with prior art, the present invention has following advantage:

(1) The present invention uses atomic layer deposition technology combined with hydrothermal lithiation to prepare lithium titanate, which ensures that lithium titanate is evenly covered on the substrate, and is not easy to agglomerate during the formation process, and the scale is controllable, thereby ensuring stable electrode performance .

(2) The prepared VG/LTO-CNTs has a flexible core-shell array sandwich structure. The vertical graphene at the bottom provides a conductive framework, and the carbon nanotubes provide an interwoven conductive network at the top, thus providing a good environment for electron transport. Expressway.

(3) The prepared VG/LTO-CNTs composite material, vertical graphene as a conductive framework has a certain mechanical strength, and a certain gap between the graphene sheets is conducive to the ion exchange between the electrode and the electrolyte. In addition, the large specific surface area of graphene sheets can provide more active sites, and the extremely thin thickness is conducive to the rapid transport of electron ions, thereby improving the electrochemical performance of the entire electrode.

(4) The prepared VG/LTO-CNTs are prepared as negative electrodes for lithium-ion batteries, which are self-supporting thin-film electrodes, which can be used as electrodes by direct shearing, eliminating the cumbersome steps of slurry preparation.

(5) The sandwich core-shell array structure VG/LTO-CNTs lithium-ion battery anode material prepared by the present invention has flexible support, ultra-high rate performance (100C still has 75% theoretical capacity) and ultra-long cycle stability (10000 times After cycling, there are still 89.5% of the initial capacity), and the constructed composite material has excellent high-rate performance and ultra-long cycle life as an anode material for lithium-ion batteries, and has excellent application prospects in the field of rapid charge and discharge.

Description of drawings

Fig. 1 is the schematic diagram of the process of the graphene array prepared in embodiment 1 supporting lithium titanate/carbon nanotube composite array electrode material, wherein, among Fig. 1 (a) is the vertical graphene (VG) that grows on the carbon cloth, (b) is the VG/LTO array structure, (c) is the VG/LTO-CNTs array structure;

Fig. 2 (a), (b) is the physical photo of the graphene array loaded lithium titanate/carbon nanotube composite array electrode material prepared in embodiment 1;

Fig. 3 is the XRD spectrum of the graphene array supported lithium titanate/carbon nanotube composite array electrode material prepared in embodiment 1;

Fig. 4 is the different magnification SEM figure of the VG/LTO array prepared in embodiment 1, wherein, among Fig. 4 (a) is the high magnification SEM figure, (b) is the low magnification SEM figure;

Fig. 5 is an SEM image of different magnifications of the VG/LTO-CNTs array prepared in Example 1, wherein (a) in Fig. 5 is a high magnification SEM image, and (b) is a low magnification SEM image.

FIG. 6 shows the battery rate performance of the graphene array-supported lithium titanate/carbon nanotube composite array electrode material prepared in Example 1. FIG.

7 is the battery cycle performance of the graphene array-loaded lithium titanate/carbon nanotube composite array electrode material prepared in Example 1.

detailed description

The present invention is further specifically described below by way of examples, but the present invention is not limited to the following examples.

Example 1

(1) Vertical graphene (VG) arrays were grown on carbon cloth by microwave plasma enhanced chemical vapor deposition (MPECVD). The carbon was arranged in a tube furnace, and 30 sccm of methane and 40 sccm of hydrogen were introduced to react at a temperature of 400° C. for 1 hour.

(2) TiO ₂ is grown on the vertical graphene obtained in step (1) by atomic layer deposition (ALD), the source of Ti and the source of O are titanium tetrachloride and water respectively, and the reaction temperature is 200°C.

(3) Dissolve 2.9372g of lithium hydroxide in 70mL of water to form solution A, the concentration of lithium hydroxide in solution A is 1molL ^-1 .

(4) Place the vertical graphene-supported titania composite electrode material obtained in step (2) in solution A, perform a hydrothermal reaction at 80°C for 1 hour, then wash and dry, and finally in an argon protective atmosphere, at 500°C Calcined for 2 hours to obtain a VG/LTO composite array structure;

(5) Using chemical vapor deposition (CVD) technology, the Li ₄ Ti ₅ O ₁₂ /VG composite array obtained in step (4) is placed in a tube furnace, and 2sccm of acetylene, 5sccm of hydrogen and 50sccm of argon are introduced. Carbon nanotubes were grown by reacting at 600°C for 1 minute, and finally a graphene array-supported lithium titanate/carbon nanotube composite array electrode, namely VG/LTO-CNTs, was obtained.

(6) slice and dry the VG/LTO-CNTs composite material obtained in step (5) as an electrode material, the diaphragm is a microporous polypropylene film, and the electrolyte is 1mol L ^-1 LiPF ₆ as the solute, and the volume ratio is 1:1 Ethylene carbonate (EC) and dimethyl carbonate (DMC) were used as solvents, and the counter electrode was a lithium sheet. The battery was assembled in a glove box filled with argon.

The preparation process of graphene array-loaded lithium titanate/carbon nanotube composite array electrode material by combining chemical vapor deposition, atomic layer deposition and hydrothermal method is shown in Figure 1, where (a) in Figure 1 is the growth Vertical graphene (VG) on carbon cloth, (b) is the VG/LTO array structure, (c) is the VG/LTO-CNTs array structure. The physical pictures of this electrode are shown in Figure 2(a) and (b), and it can be seen from the figures that the VG/LTO-CNTs composite electrode prepared in Example 1 has the characteristics of flexibility and self-support, and the thickness is 0.57mm.

Fig. 3 is the XRD spectrum of the VG/LTO-CNTs composite material prepared in Example 1. It can be seen from Figure 3 that the VG/LTO-CNTs composite material prepared in Example 1 has the characteristic peaks of lithium titanate (JCPDS 49-0207) and graphene (JCPDS 65-6212). Figure 4 is the SEM image of the VG/LTO core-shell array. Lithium titanate particles with a diameter of about 10-20 nm are evenly covered on the vertical graphene, with a thickness of about 30-40 nm. Fig. 5 is a SEM image of the VG/LTO-CNTs composite material after growing carbon nanotubes, and the carbon nanotubes are interwoven and covered on the VG/LTO nanosheets to form a network structure. In the VG/LTO-CNTs composite electrode, the loading of vertical graphene is 0.5mg cm ^-2 , the loading of lithium titanate layer is 1mg cm ^-2 , and the loading of carbon nanotubes is 0.5mg cm ^-2 .

The assembled lithium-ion battery was subjected to a constant current charge and discharge test, and the charge and discharge voltage range was 2.5V to 1.0V. Figure 6 is the ratio diagram of lithium-ion batteries. It can be seen from the figure that the capacities of lithium-ion batteries are 171mA hg ^-1 , 151mA hg ^-1 , and 150mA hg -1 at current densities of 1C, 10C, 20C, 50C and 100C, respectively ^{. 1} , 146mA hg ^-1 and 131mAh g ^-1 , showing excellent rate performance. From the cycle performance diagram in Figure 7, it can be seen that the lithium-ion battery still has a capacity retention rate of 89.5% after 10,000 cycles at a high current density of 20C, and the Coulombic efficiency is maintained above 99%, showing ultra-high cycle stability. With super long cycle life.

Example 2

(1) Vertical graphene arrays were grown on carbon cloth by microwave plasma enhanced chemical vapor deposition (MPECVD). The carbon was arranged in a tube furnace, and 40 sccm of methane and 50 sccm of hydrogen were introduced to react at a temperature of 450° C. for 2 hours.

(2) TiO ₂ is grown on the vertical graphene obtained in step (1) by atomic layer deposition (ALD), the source of Ti and the source of O are titanium tetrachloride and water respectively, and the reaction temperature is 250°C.

(3) Dissolve 5.8744g of lithium hydroxide in 70mL of water to form solution A, the concentration of lithium hydroxide in solution A is 2molL ^-1 .

(4) Place the vertical graphene-loaded titania composite electrode material obtained in step (2) in solution A, perform a hydrothermal reaction at 85°C for 1.5 hours, then wash and dry, and finally in an argon protective atmosphere, at 550°C Calcined for 2.5 hours to obtain a VG/LTO composite array structure;

(5) Using chemical vapor deposition (CVD) technology, the Li ₄ Ti ₅ O ₁₂ /VG composite array obtained in step (4) is placed in a tube furnace, and 5 sccm of acetylene, 7 sccm of hydrogen and 80 sccm of argon are introduced, and the The carbon nanotubes were grown by reacting at 650°C for 5 minutes, and finally the graphene array-supported lithium titanate/carbon nanotube composite array electrode, that is, VG/LTO-CNTs, was obtained.

(6) slice and dry the VG/LTO-CNTs composite material obtained in step (5) as an electrode material, the diaphragm is a microporous polypropylene film, and the electrolyte is 1mol L ^-1 LiPF ₆ as the solute, and the volume ratio is 1:1 Ethylene carbonate (EC) and dimethyl carbonate (DMC) were used as solvents, and the counter electrode was a lithium sheet. The battery was assembled in a glove box filled with argon.

The assembled lithium-ion battery was subjected to a constant current charge and discharge test, and the charge and discharge voltage range was 2.5V to 1.0V. Lithium-ion batteries have capacities of 171mA hg ^-1 , 150mA hg ^-1 , 149mA hg ^-1 , 145mA hg ^-1 and 129mA hg ^-1 at current densities of 1C, 10C, 20C, 50C and 100C, respectively, showing excellent rate performance. The lithium-ion battery still has a capacity retention rate of 88% after 10,000 cycles at a high current density of 20C, and the Coulombic efficiency remains above 99%, showing ultra-high cycle stability and ultra-long cycle life.

Example 3

(1) Vertical graphene arrays were grown on carbon cloth by microwave plasma enhanced chemical vapor deposition (MPECVD). The carbon was placed in a tube furnace, 50 sccm of methane and 60 sccm of hydrogen were introduced, and the reaction was carried out at a temperature of 500° C. for 3 hours.

(2) TiO ₂ is grown on the vertical graphene obtained in step (1) by atomic layer deposition (ALD), the source of Ti and the source of O are titanium tetrachloride and water respectively, and the reaction temperature is 300°C.

(3) Dissolve 8.8116g of lithium hydroxide in 70mL of water to form solution A, the concentration of lithium hydroxide in solution A is 3molL ^-1 .

(4) Place the vertical graphene-supported titania composite electrode material obtained in step (2) in solution A, react with hydrothermal reaction at 90°C for 2 hours, then wash and dry, and finally in an argon protective atmosphere, at 600°C Calcined for 3 hours to obtain a VG/LTO composite array structure;

(5) Using chemical vapor deposition (CVD) technology, the Li ₄ Ti ₅ O ₁₂ /VG composite array obtained in step (4) is placed in a tube furnace, and 10 sccm of acetylene, 10 sccm of hydrogen and 100 sccm of argon are introduced, and the The reaction at 700°C for 10 minutes grows carbon nanotubes, and finally a graphene array-supported lithium titanate/carbon nanotube composite array electrode, that is, VG/LTO-CNTs, is obtained.

(6) slice and dry the VG/LTO-CNTs composite material obtained in step (5) as an electrode material, the diaphragm is a microporous polypropylene film, and the electrolyte is 1mol L ^-1 LiPF ₆ as the solute, and the volume ratio is 1:1 Ethylene carbonate (EC) and dimethyl carbonate (DMC) were used as solvents, and the counter electrode was a lithium sheet. The battery was assembled in a glove box filled with argon.

The assembled lithium-ion battery was subjected to a constant current charge and discharge test, and the charge and discharge voltage range was 2.5V to 1.0V. Figure 6 is the ratio diagram of lithium-ion batteries. It can be seen from the figure that the capacities of lithium-ion batteries are 170mA hg ^-1 , 149mA hg ^-1 , and 145mA hg -1 at current densities of 1C, 10C, 20C, 50C and 100C, respectively ^{. 1} , 140mA hg ^-1 and 123mA hg ^-1 , showing excellent rate performance. From the cycle performance diagram in Figure 7, it can be seen that the lithium-ion battery still has a capacity retention rate of 86% after 10,000 cycles at a high current density of 20C, and the Coulombic efficiency is maintained above 99%, showing ultra-high cycle stability. With super long cycle life.

A graphene array loaded lithium titanate/carbon nanotube composite array in Examples 1 to 3 is assembled into a lithium ion battery as a lithium ion electrode material, and its maximum discharge capacity at different current densities is shown in Table 1:

Table 1

Claims (10)

1. a kind of graphene array loads the preparation method of lithium titanate/carbon/carbon nano tube composite array electrode material, it is characterised in that Comprise the following steps：

(1) microwave plasma enhanced chemical vapour deposition technique vertical-growth graphene array on carbon cloth is utilized；

(2) TiO is grown in the graphene array obtained by step (1) using technique for atomic layer deposition₂, obtain vertical Graphene and bear Carrying of titanium dioxide combination electrode material；

(3) lithium hydroxide is dissolved in water, forms solution A；

(4) the vertical graphene-supported titanium dioxide combination electrode material obtained by step (2) is placed in solution A, carries out hydro-thermal Reaction, is washed, drying and calcination afterwards, obtains graphene array load lithium titanate composite array electrode；

(5) chemical vapour deposition technique is utilized, with acetylene as carbon source, under the atmosphere of hydrogen and argon gas, obtained by step (4) CNT is grown on graphene array load lithium titanate composite array electrode, graphene array load lithium titanate/carbon is obtained and is received Mitron composite array electrode material.

2. graphene array according to claim 1 loads the preparation of lithium titanate/carbon/carbon nano tube composite array electrode material Method, it is characterised in that in step (1), vertically given birth on carbon cloth using microwave plasma enhanced chemical vapour deposition technique Graphene array long, actual conditions is：Reaction atmosphere is methane and hydrogen, and the flow of methane is 30-50sccm, the flow of hydrogen It is 40-60sccm, reaction temperature and time are respectively 400-500 DEG C and 1-3 hour.

3. graphene array according to claim 1 loads the preparation of lithium titanate/carbon/carbon nano tube composite array electrode material Method, it is characterised in that in step (2), is grown using technique for atomic layer deposition in the graphene array obtained by step (1) TiO₂, actual conditions is：Ti sources are titanium tetrachloride, and O sources are water, and reaction temperature is 200-300 DEG C.

4. graphene array according to claim 1 loads the preparation of lithium titanate/carbon/carbon nano tube composite array electrode material Method, it is characterised in that in step (3), lithium hydroxide concentration is 1-3molL in described solution A^-1。

5. graphene array according to claim 1 loads the preparation of lithium titanate/carbon/carbon nano tube composite array electrode material Method, it is characterised in that in step (4), is carried out hydro-thermal reaction 1-2 hours at 80-90 DEG C.

6. graphene array according to claim 1 loads the preparation of lithium titanate/carbon/carbon nano tube composite array electrode material Method, it is characterised in that in step (4), protective atmosphere is argon gas during calcining, and reaction temperature is 500-600 DEG C, and the reaction time is 2-3 hours.

7. graphene array according to claim 1 loads the preparation of lithium titanate/carbon/carbon nano tube composite array electrode material Method, it is characterised in that in step (5), the flow of acetylene is 2-10sccm, and hydrogen is 5-10sccm, and the flow of argon gas is 50- 100sccm, reaction temperature is respectively 600-700 DEG C and 1-10 minute with the time.

8. the graphene array load lithium titanate/carbon/carbon nano tube that prepared by the preparation method according to any one of claim 1~7 Composite array electrode material.

9. graphene array according to claim 8 loads lithium titanate/carbon/carbon nano tube composite array electrode material, its feature It is, including graphene array on the carbon cloth of carbon cloth, vertical-growth, the lithium titanate that is coated in the graphene array Nano particle and the CNT being grown in being interweaved on the lithium titanate nano particle.

10. graphene array load lithium titanate/carbon/carbon nano tube composite array electrode material according to claim 8 or claim 9 exists As the application of lithium ion battery electrode material.