CN104319377A - Ternary multilevel multi-dimensional structure composite material and preparation method thereof - Google Patents

Abstract

The invention discloses a ternary multi-level multi-dimensional structure composite material and a preparation method thereof. By utilizing its outstanding synergistic effect and unique multi-level multi-dimensional structure, it can exert excellent electrochemical comprehensive performance. The composite material is composed of TiO ₂ with low-dimensional nanostructure, secondary phase high specific capacity metal oxide and two-dimensional micron (xy plane direction) pristine graphene with high conductivity. The invention adopts the THF solution mixing method, takes reducing the total surface free energy of the solution system as the driving force, uniformly loads and tightly combines nanostructured _TiO2 and high specific capacity metal oxides on the exposed surface of the pristine graphene nanosheets. The ternary multi-level multi-dimensional structure composite material of the present invention effectively combines the outstanding functions of each component: the excellent cycle performance and outstanding safety of _TiO2 , the high specific capacity of the secondary phase metal oxide and the good performance of pristine graphene Electrical conductivity.

Description

Ternary multilevel multidimensional structure composite material and its preparation method

technical field

The invention belongs to the technical field of energy materials, and relates to a ternary multilevel multidimensional structure TiO ₂ -high specific capacity metal oxide-pristine graphene composite material and a preparation method thereof.

Background technique

The over-exploitation of fossil resources by humans has brought serious energy crisis and environmental pollution, which has triggered the vigorous development of electric vehicles, which requires the development of lithium-ion batteries to higher energy density and power density. However, graphite, the current commercial anode material for lithium-ion batteries, not only has a low specific capacity, but also has a low lithium intercalation potential that may easily cause serious safety problems, which is far from meeting the needs of the next generation of high-performance lithium-ion batteries. Therefore, the search for anode alternative materials with higher electrochemical performance has attracted extensive attention of researchers all over the world. the

Among the many anode alternative materials proposed by researchers, TiO ₂ with nanostructures (such as nanoparticles, nanorods, nanotubes, etc.) stands out due to its advantages, such as low cost, environmental friendliness, Li ⁺ diffusion path Short, especially the high structural stability brought about by the zero volume strain characteristic. In addition, its relatively high lithium intercalation potential (1.6-1.8Vvs.Li ⁺ /Li) can effectively avoid the decomposition of the electrolyte (its reduction potential is below 1V(vs.Li ⁺ /Li)) and the formation of lithium dendrites , making nanostructured TiO ₂ a highly safe anode material. However, despite the above-mentioned advantages, the practical application of nanostructured TiO ₂ is still limited by the following two defects: (1) the low theoretical specific capacity (~170mAh g ^-1 ) cannot even compete with graphite; (2) Lower electronic conductivity (~10 ^-12 S cm-1) leads to lower capacity at high rate discharge.

In order to make up for the defect of low capacity, people try to combine nanostructured TiO ₂ with secondary metal oxide materials with high specific capacity (750-1250mA h g ^-1 ), such as Fe ₂ O ₃ , Fe ₃ O ₄ , SnO ₂ , Co ₃ O ₄ or MnO ₂ etc. These binary heterostructures greatly increase the specific capacity while retaining the advantages of nano- _TiO2 . However, these oxide materials, like TiO ₂ , belong to wide-bandgap semiconductor materials or even insulators, and their inherent low conductivity leads to poor charge transport kinetics and rapid capacity decay. Low conductivity is also not conducive to eliminating the Joule heat generated on the electrodes, which brings certain safety hazards. Moreover, the nanoscale metal oxide increases the resistance due to the increase of the grain boundary, further deteriorating the cycle performance.

In general, the conductivity defect of active materials can be solved by introducing conductive agents, such as chemically modified graphene (Chemically Converted Grephene, CCG) or reduced-Grephene Oxide (r-GO). Using CCG as a matrix to support metal oxide nanoparticles can provide a fast electron transport channel for the electrode. Unfortunately, the oxidation-reduction process in the preparation of CCG needs to consume a large amount of toxic oxidants and reductants, causing inevitable damage to the environment. And in the process, the conductivity of CCG will also be weakened to a large extent. Therefore, compared with the high-quality pristine graphene (Pristine Graphene, PG) obtained directly from natural graphite by ultrasonic exfoliation, the conductivity of CCG is neither sufficient nor uniform. Moreover, the preparation conditions of pristine graphene are milder, more economical and environmentally friendly than CCG, so pristine graphene is more conducive to being used as a high-efficiency conductive agent for electrodes to ensure good reliability and reproducibility of active materials in terms of cycle and rate performance. . However, loading metal oxides on pristine graphene is a huge technical challenge. So far, few reports have been reported. The difficulty is that pristine graphene is chemically inert and lacks the oxygen-containing functional groups of CCG, so it is difficult to realize functionalization by hydrothermal synthesis or electrostatic interaction. Liu Yitao of Tsinghua University and others successfully realized the assembly of pristine graphene and metal or metal oxide nanoparticles by complexation. However, this method needs to introduce organic ligands and metal ions as cross-linking agents, which is not only cumbersome steps, complex process, but also high cost. the

After searching the existing technology, it is found that there is no relevant TiO ₂ - high specific capacity metal oxide (Fe ₂ O ₃ , Fe ₃ O ₄ , SnO ₂ , Co ₃ O ₄ or MnO ₂ , etc.) - pristine graphene at home and abroad. Public reports of composite materials, such as TiO ₂ -Fe ₃ O ₄ -Graphene (Lu Jin et al. Appl. Mater. Interfaces 2013, 5, 7330-7334), TiO ₂ -SnO ₂ -Graphene (Jiang Xin et al. al.New J.Chem.2013, 37, 3671-3678), G-TiO ₂ Co ₃ O ₄ NBs (Luo Yongsong et al.J.Mater.Chem.A2013, 1, 273-281) are all TiO ₂ and Combination of metal oxides with CCG, even TiO ₂ -Fe ₃ O ₄ -Graphene (Min Qianhao et al.Chem.Commun.2011, 47, 11709-11711; Lin Yue et al.Eur.J.Inorg.Chem.2012 , 4439-4444; Tian Miaomiao et al.Anal.Methods 2013, 5, 3984-3991; Liang Yulu et al.RSCAdv.2014, 4, 18132-18135), TiO ₂ -SnO ₂ -Graphene (Tang Yanping et al. Energy Environ.Sci.2013, 6, 2447-2451) is a composite of TiO ₂ and metal oxides with graphene oxide (Graphene Oxide, GO). The electrical conductivity of graphene oxide (GO) is extremely low, while the electrical conductivity of chemically modified graphene (CCG) is neither sufficient nor uniform compared to that of pristine graphene (PG).

Contents of the invention

Aiming at the defects in specific capacity and electrical conductivity of nano-TiO ₂ , the present invention provides a ternary multi-level multi-dimensional structure TiO ₂ through the co-doping of sub-phase high specific capacity metal oxides and high-conductivity pristine graphene components - High specific capacity metal oxide-pristine graphene composite material and its preparation method, using its outstanding synergistic effect and unique multi-level multi-dimensional structure, to exert excellent comprehensive electrochemical performance.

The ternary multi-level multi-dimensional structure TiO ₂ -high specific capacity metal oxide-pristine graphene composite material of the present invention is characterized in that the composite material is composed of low-dimensional nanostructured TiO ₂ , secondary phase high specific capacity metal oxide and Two-dimensional micron (xy plane direction) high-conductivity pristine graphene is a ternary heterostructure composed of three components with a molar ratio of 2 to 5:1 to 4:3 to 5, effectively combining each component The outstanding functions of TiO ₂ are: excellent cycle performance and outstanding safety of TiO 2 , high specific capacity (750-1250mAh g ^-1 ) of secondary metal oxides and good electrical conductivity of pristine graphene.

In the present invention, the high specific capacity metal oxide is any one of high specific capacity metal oxides such as Fe ₂ O ₃ , Fe ₃ O ₄ , SnO ₂ , Co ₃ O ₄ or MnO ₂ .

In the present invention, the molar ratio of TiO ₂ , high specific capacity metal oxide and pristine graphene can be 3:3:4, 4:2:4, 4:3:3, 3:4:3, 5: 2:3, 4:1:5, 3:2:5, 2:3:5, the molar ratio is determined according to the actual electrochemical performance of the composite material.

The ternary multilevel multidimensional structure TiO ₂ -high specific capacity metal oxide-pristine graphene composite material of the present invention is characterized in that the nanostructured TiO ₂ and high specific capacity metal oxide are uniformly loaded and tightly combined on the pristine graphene The multi-level and multi-dimensional structure formed on the exposed surface of the nanosheets, in which the pristine graphene nanosheets have a micron-scale two-dimensional structure on the xy plane, TiO ₂ is a zero-dimensional nanoparticle, and the high specific capacity metal oxide is a one-dimensional nanometer Any one-dimensional nanostructures such as rods, nanowires, nanotubes, nanoneedles or nanobelts; or _TiO2 is any one-dimensional nanostructures such as one-dimensional nanorods, nanowires, nanotubes, nanoneedles or nanobelts , while the high specific capacity metal oxides are zero-dimensional nanoparticles. The ternary composite material formed in this way not only has a multi-dimensional structure with zero-dimensional, one-dimensional and two-dimensional coexistence, but also has a multi-level structure combining nanometers and micrometers. This kind of micro-nano multi-level structure not only increases the reactive area, but also provides a fast channel for charge transport. This ternary multi-level multi-dimensional composite structure can give full play to the structural properties of each component: (1) Nano-scale structure of zero/one-dimensional _TiO2 and high specific capacity metal oxide, which can shorten the transport of Li ⁺ and electrons (2) As a conductive agent, micron-sized two-dimensional pristine graphene nanosheets can form a three-dimensional network with TiO ₂ and high-capacity metal oxides to form a fast conductive three-dimensional network structure (3) _TiO2 , as a zero-structural strain material, can provide primary safety during charging and discharging; (4) As a matrix, pristine graphene nanosheets have good flexibility and elasticity, which can alleviate high Structural stress brought about by the Li ⁺ intercalation/extraction process in the specific capacity metal oxide, inhibiting the volume change of the composite and the pulverization of the electrode; (5) Zero/one-dimensional high specific capacity metal oxide and TiO on the surface of pristine graphene ₂ as a spacer can avoid the restacking of pristine graphene, further increase the interlayer spacing, and facilitate the intercalation/extraction of Li ⁺ .

The above-mentioned one-dimensional nanostructure may be any one-dimensional nanostructure such as nanorod, nanowire, nanotube, nanoneedle or nanoribbon. the

The preparation method of the above-mentioned ternary multi-level multi-dimensional structure TiO ₂ -high specific capacity metal oxide-pristine graphene composite material, its specific implementation steps are as follows:

(1) Ultrasonically exfoliate the natural graphite powder into pristine graphene in N-methyl-2-pyrrolidone (NMP), and transfer the pristine graphene to its poor solvent tetrahydrofuran (THF);

(2) Synthesize nanostructured TiO ₂ by hydrothermal reaction, hydrolysis reaction, etc., and transfer TiO ₂ to its good solvent tetrahydrofuran;

(3) Synthesize a Fe ₂ O ₃ , Fe ₃ O ₄ , SnO ₂ , Co ₃ O ₄ or MnO ₂ nanostructured metal oxide with high specific capacity by hydrothermal reaction, hydrolysis reaction, etc., and transfer it to its good solvent tetrahydrofuran middle;

(4) Mix the above three solutions in a certain proportion and stir for 6 to 12 hours. Under the driving force of reducing the free energy of the system, assemble into a ternary multi-level multi-dimensional structure TiO ₂ nanoparticles-high specific capacity metal oxide - Pristine graphene nanosheet composites.

In the present invention, the tetrahydrofuran (THF) described in step (1) is a poor solvent for pristine graphene, and there is a mismatched Hansen solubility parameter between pristine graphene and THF in THF, thereby having a strong tendency to re-stack, Therefore, THF cannot reduce the huge surface free energy of pristine graphene. the

In the present invention, the tetrahydrofuran (THF) described in steps (2) and (3) is a good solvent for TiO ₂ and metal oxides with high specific capacity, and these metal oxides can exist stably in THF.

In the present invention, the driving force described in step (4) is to reduce the total free energy of the solution system. Pristine graphene has a huge surface free energy in THF, and once the more stable nanostructured _TiO2 and high specific capacity metal oxides are introduced into THF, they tend to reside in pristine graphene under the van der Waals interaction. On the exposed surface of graphene nanosheets to reduce the total surface free energy of the solution system, the pristine graphene 2D nanosheets in THF were stabilized, resulting in the successful assembly of ternary hierarchical multidimensional _TiO2 -high specific capacity metals Oxide-pristine graphene composites.

In the present invention, the natural graphite powder is directly exfoliated into pristine graphene by ultrasonic in N-methyl-2-pyrrolidone (NMP); then pristine graphene is transferred to its poor solvent-tetrahydrofuran (THF), and pristine graphite is Alkenes have a strong tendency to restack due to the mismatched Hansen solubility parameters between solvents. This step is critical for the subsequent successful hierarchical cooperative assembly, because THF cannot reduce the huge surface free energy of insoluble 2D nanosheets. . Thus more stable nanostructured _TiO2 and high specific capacity metal oxides, once introduced into THF, tend to reside on the bare surfaces of pristine graphene nanosheets due to the van der Waals interaction, reducing the solution The total surface free energy of the system, which stabilizes the 2D nanolayer in THF. This self-assembly method has the advantages of mildness and low cost compared with the method of preparing metal oxide-pristine graphene composites by complexation because no foreign cross-linking agent is introduced.

Description of drawings

Fig. 1 is the X-ray diffraction pattern of ternary multilevel multidimensional structure TiO ₂ -high specific capacity metal oxide (Fe ₃ O ₄ )-pristine graphene (PG) composite material in embodiment 1;

Fig. 2 is the transmission electron microscope image of the ternary multi-level multi-dimensional structure TiO ₂ -high specific capacity metal oxide (Fe ₃ O ₄ )-pristine graphene (PG) composite material in Example 1;

3 is a high-resolution transmission electron microscope image of the ternary multi-level multi-dimensional structure TiO ₂ -high specific capacity metal oxide (Fe ₃ O ₄ )-pristine graphene (PG) composite material in Example 1;

Figure 4 is the cycle performance curve of the ternary multi-level multi-dimensional structure TiO ₂ - high specific capacity metal oxide (Fe ₃ O ₄ ) - pristine graphene (PG) composite material in Example 1 at a current density of 0.5A g ^-1 picture.

Detailed ways

The technical solution of the present invention will be further described below in conjunction with the accompanying drawings, but it is not limited to this. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered by the technical solution of the present invention. in the scope of protection. the

Example 1

Aiming at the defects of low specific capacity and low electrical conductivity of nano-TiO ₂ , through the co-doping of secondary phase high specific capacity metal oxide Fe ₃ O ₄ (927mA h g ^-1 ) and pristine graphene components with high electrical conductivity, this implementation The example provides a ternary multi-level multi-dimensional structure TiO ₂ nanorod-Fe ₃ O ₄ nano-particles-pristine graphene nanosheet composite material, using its outstanding synergistic effect and unique multi-level multi-dimensional structure, it exerts excellent electrical properties Comprehensive chemical properties.

The ternary multilevel multidimensional structure _TiO2 nanorod- _Fe3O4 nanoparticle- _pristine graphene nanosheet composite material provided by this embodiment is composed of _three components: _TiO2 , _Fe3O4 and high conductivity pristine graphene The ternary heterostructure formed with a molar ratio of 4:2:4 can be prepared as follows:

(1) The natural graphite powder was added to N-methyl-2-pyrrolidone (NMP) with an initial concentration of 10 mg mL ^-1 , and then ultrasonicated at 70W for 4 hours. The resulting suspension was centrifuged at 2000 rpm for 30 minutes, then the supernatant was collected and vacuum filtered. The filtered solid powder was added into THF and ultrasonicated to obtain a black pristine graphene dispersion solution.

(2) 3 mmol Fe(acac) ₃ , 30 mL oleylamine and 30 mL octadecene were mixed, heated to 280° C. for 1 hour under the protection of nitrogen atmosphere, and then naturally cooled to room temperature. The precipitated product was washed 2-3 times with ethanol, and vacuum-dried at 40° C. for 12 hours to obtain Fe ₃ O ₄ nanoparticles. The above dried Fe ₃ O ₄ nanoparticles were dissolved in THF to obtain a 1 mg/mL brown Fe ₃ O ₄ solution.

(3) Add 5mmol tetrabutyl titanate, 25mmol oleylamine, 25mmol oleic acid and 100mL ethanol to a 35mL polytetrafluoroethylene cup and stir for 10 minutes, then put the polytetrafluoroethylene cup into a 130mL polytetrafluoroethylene Vinyl liner, and add 20mL (96Vol%) ethanol solution to the liner. The stainless steel reaction kettle was kept at 180°C for 18 hours. After natural cooling, the product was collected and washed with ethanol for 2 to 3 times, and dried in vacuum at 40 °C for 12 hours to obtain _TiO2 nanorods. Dissolve the above dried _TiO2 nanorods in THF to obtain a milky white solution at 1 mg/mL.

(4) The above three components were mixed at a molar ratio of TiO ₂ :Fe ₃ O ₄ :PG=4:2:4, and stirred for 10 hours. During the stirring process, the organically modified Fe ₃ O ₄ nanoparticles and TiO ₂ nanorods would spontaneously assemble on the exposed surface of the pristine graphene, resulting in a ternary hierarchical multidimensional structure of TiO ₂ nanorods-Fe ₃ O ₄ nanorods Particle-pristine graphene nanosheet composites.

The ternary multilevel multidimensional structure TiO ₂ nanorods-Fe ₃ O ₄ nanoparticles-pristine graphene composite material in this example can effectively combine the outstanding functions of each component: excellent cycle performance and outstanding safety of TiO ₂ properties, high specific capacity (927mA h g ^-1 ) of Fe ₃ O ₄ , low cost and good electrical conductivity of pristine graphene, thus exhibiting excellent comprehensive electrochemical performance. Its structural features are: TiO ₂ nanorods and Fe ₃ O ₄ nanoparticles are uniformly loaded and tightly combined on the exposed surface of the pristine graphene nanosheets to form a multi-level multidimensional structure, in which the pristine graphene nanosheets on the xy plane are Micron-scale two-dimensional structure, TiO ₂ is one-dimensional nanorods, and Fe ₃ O ₄ is zero-dimensional nanoparticles. The ternary composite material formed in this way not only has a multi-dimensional structure with zero-dimensional, one-dimensional and two-dimensional coexistence, but also has nano , Micron combined multi-level structure. This ternary multi-level multi-dimensional composite structure can give full play to the structural characteristics of each component: (1) The nanoscale structure of low-dimensional TiO ₂ and Fe ₃ O ₄ can shorten the transmission path of Li ⁺ and electrons, and improve the recombination High rate performance of the material; (2) micron-scale two-dimensional pristine graphene nanosheets as a conductive agent can form a three-dimensional network with TiO ₂ and Fe ₃ O ₄ to build a fast conductive three-dimensional network structure electrode; (3) TiO ₂ As a zero-structural-strain material, it can provide the primary safety during charging and discharging; (4) As a matrix, pristine graphene nanosheets have good flexibility and elasticity, which can relieve Fe ₃ O ₄ in Li ⁺ The structural stress brought by the intercalation/extraction process can inhibit the volume change of the composite material and the pulverization of the electrode; (5) the zero-dimensional Fe ₃ O ₄ and one-dimensional TiO ₂ on the surface of pristine graphene can be used as spacers to avoid pristine graphite The re-stacking of alkenes further increases the interlayer spacing, which is beneficial to the intercalation/extraction of Li ⁺ .

Example 2

The difference between this embodiment and Example 1 is: Step (3): 35 grams of oleic acid was added to a 50 ml three-necked bottle connected with a reflux cooler, and dried at 120° C. for 1 hour under vigorous stirring, Cool to 80-100°C in the stream. Then 1 mmol of titanium tetraisopropoxide was added to oleic acid and stirred for 5 minutes to make the solution change from white to pale yellow. Dissolve 10mmol hydroxylated tetrabutylammonium in 2mL water, suck it into the syringe, and then quickly inject it into the mixed solution, keep the solution at 80-100°C, and stir for 8 hours under mild water reflux conditions, then stop heating, Water was removed under vacuum to give a clear solution. 20 mL of ethanol was added to the above solution to obtain a precipitate, which was washed with ethanol twice after centrifugation and vacuum dried at 40 °C for 12 h to obtain _TiO2 nanorods. The above dried TiO _{nanoparticles} were dissolved in THF to obtain a milky white solution at 1 mg/mL. Step (4): The molar ratio of the three components is TiO ₂ :Fe ₃ O ₄ :PG=3:3:4.

Example 3

Aiming at the defects of low specific capacity and low electrical conductivity of nano-TiO ₂ , through the co-doping of secondary phase high specific capacity metal oxide Co ₃ O ₄ (891mA h g ^-1 ) and pristine graphene components with high electrical conductivity, this implementation The example provides a ternary multi-level multi-dimensional structure TiO ₂ nanoparticles-Co ₃ O ₄ nanoribbons-pristine graphene nanosheet composite material, using its outstanding synergistic effect and unique multi-level multi-dimensional structure, it exerts excellent electrical Comprehensive chemical properties.

_The ternary multilevel multidimensional structure _TiO2 nanoparticle- _Co3O4 nanoribbon-pristine graphene nanosheet composite material in this embodiment is composed of _three components: _TiO2 , _Co3O4 and high conductivity pristine graphene The ternary heterostructure formed with a molar ratio of 3:3:4 can be prepared as follows:

(1) The natural graphite powder was added to N-methyl-2-pyrrolidone (NMP) with an initial concentration of 10 mg mL ^-1 , and then ultrasonicated at 70W for 4 hours. The resulting suspension was centrifuged at 2000 rpm for 30 minutes, then the supernatant was collected and vacuum filtered. The filtered solid powder was added into THF and ultrasonicated to obtain a black pristine graphene dispersion solution.

(2) 0.1 g of Co(NO ₃ ) ₂ ·6H ₂ O, 0.5 g of CO(NH ₂ ) ₂ and 0.37 g of NH ₄ F were added to 40 mL of deionized water, and stirred at room temperature for 10 minutes. Then transferred to a 50mL stainless steel reaction kettle, reacted at 120°C for 4 hours, and cooled naturally to room temperature. The product was washed 3 times with ethanol, and dried under vacuum at 40 °C for 12 hours to obtain Co ₃ O ₄ nanobelts. The above dried Co ₃ O ₄ nanobelts were dissolved in THF to obtain a 1 mg/mL Co ₃ O ₄ solution.

(3) 0.2 mL of tetrabutyl titanate and 25 mL of isopropanol were mixed and stirred for 30 minutes, then 1 mL of deionized water was added dropwise and stirred for 30 minutes. Then the above mixed solution was transferred to a 50mL polytetrafluoroethylene-lined stainless steel autoclave, reacted at 180°C for 6 hours, cooled to room temperature naturally, washed the product 3 times with ethanol, and dried in vacuum at 40°C for 12 hours to obtain _TiO2 nanoparticles. The above dried TiO _{nanoparticles} were dissolved in THF to obtain a milky white solution at 1 mg/mL.

(4) The above three components were mixed in a molar ratio of TiO ₂ :Co ₃ O ₄ :PG=3:3:4, and stirred for 10 hours. During the stirring process, the organically modified Co ₃ O ₄ nanoribbons and TiO ₂ nanoparticles will spontaneously assemble on the exposed surface of the pristine graphene, resulting in a ternary multi-level multidimensional structure of TiO ₂ nanoparticles- _{Co 3} O ₄ nano Ribbon-pristine graphene nanosheet composites.

The ternary multilevel multidimensional structure _{TiO2nanoparticle} - _{Co3O4nanobelt} -pristine graphene nanosheet composite material of this embodiment has outstanding functions that can effectively combine each component: _{TiO2Excellent} cycle _performance and Outstanding safety, high specific capacity of Co ₃ O ₄ (891mA h g ^-1 ) and good electrical conductivity of pristine graphene show excellent comprehensive electrochemical performance. Its structural features are: TiO ₂ nanoparticles and Co ₃ O ₄ nanobelts are uniformly loaded and tightly combined on the exposed surface of the pristine graphene nanosheets to form a multi-level multidimensional structure, in which the pristine graphene nanosheets are micron-sized on the xy plane Two-dimensional structure, TiO ₂ is a zero-dimensional nanoparticle, and Co ₃ O ₄ is a one-dimensional nanoribbon. The ternary composite material formed in this way not only has a multi-dimensional structure with zero-dimensional, one-dimensional and two-dimensional coexistence, but also has nano, Micron-combined hierarchical structure. This ternary multi-level multi-dimensional composite structure can give full play to the structural characteristics of each component: (1) The nanoscale structure of low-dimensional TiO ₂ and Co ₃ O ₄ can shorten the transport path of Li ⁺ and electrons, and improve the recombination High rate performance of the material; (2) Micron-sized two-dimensional pristine graphene nanosheets as a conductive agent can form a three-dimensional network with TiO ₂ and Co ₃ O ₄ to build a fast conductive three-dimensional network structure electrode; (3) TiO ₂ As a zero-structural-strain material, it can provide the primary safety during charging and discharging; (4) As a matrix, pristine graphene nanosheets have good flexibility and elasticity, which can relieve Co ₃ O ₄ in Li ⁺ Structural stress brought by the intercalation/extraction process suppresses the volume change of the composite material and the pulverization of the electrode; (5) the zero-dimensional TiO ₂ and one-dimensional Co ₃ O ₄ on the surface of pristine graphene are used as spacers to avoid pristine graphite The re-stacking of alkenes further increases the interlayer spacing, which is beneficial to the intercalation/extraction of Li ⁺ .

Example 4

Aiming at the defects of low specific capacity and low electrical conductivity of nano TiO ₂ , through the co-doping of secondary phase high specific capacity metal oxide SnO ₂ (782mA h g ^-1 ) and pristine graphene components with high electrical conductivity, this embodiment provides A ternary multi-level multi-dimensional structure TiO ₂ nanorod-SnO ₂ nanoparticle-pristine graphene nanosheet composite material is developed, and its outstanding synergistic effect and unique multi-level multi-dimensional structure are used to exert excellent comprehensive electrochemical performance.

The ternary multilevel multidimensional structure _TiO2 nanorod- _SnO2 nanoparticle-pristine graphene nanosheet composite material in the present embodiment is by _TiO2 , _SnO2 and three kinds of components of high conductivity pristine graphene with 4:2 : The ternary heterostructure formed by the molar ratio of 4, its preparation method is as follows:

(1) The natural graphite powder was added to N-methyl-2-pyrrolidone (NMP) with an initial concentration of 10 mg mL ^-1 , and then ultrasonicated at 70W for 4 hours. The resulting suspension was centrifuged at 2000 rpm for 30 minutes, then the supernatant was collected and vacuum filtered. The filtered solid powder was added into THF and ultrasonicated to obtain a black pristine graphene dispersion solution.

(2) Dissolve 0.3g of Sn(Cl) ₄ ·5H ₂ O in 25mL of deionized water and sonicate for 10 minutes at a power of 240 watts, then transfer to a reaction kettle, react at 180°C for 8 hours, and wash the product with ethanol 3 times, naturally cooled to room temperature, and dried in vacuum at 40 °C for 12 hours to obtain SnO ₂ nanoparticles. Dissolve the above dried SnO _{nanoparticles} in THF to obtain a 1 mg/mL SnO _solution .

(3) Add 5mmol tetrabutyl titanate, 25mmol oleylamine, 25mmol oleic acid and 100mL ethanol to a 35mL polytetrafluoroethylene cup and stir for 10 minutes, then put the polytetrafluoroethylene cup into a 130mL polytetrafluoroethylene Vinyl liner, and add 20mL (96Vol%) ethanol solution to the liner. The stainless steel reaction kettle was kept at 180°C for 18 hours. After natural cooling, the product was collected and washed with ethanol for 2 to 3 times, and dried in vacuum at 40 °C for 12 hours to obtain _TiO2 nanorods. Dissolve the above dried _TiO2 nanorods in THF to obtain a milky white solution at 1 mg/mL.

(4) The above three components were mixed in a molar ratio of TiO ₂ :SnO ₂ :PG=4:2:4, and stirred for 10 hours. During the stirring process, organically modified _SnO2 nanoparticles and _TiO2 nanorods would spontaneously assemble on the exposed surface of pristine graphene, resulting in a ternary multi-level multidimensional structure _TiO2 nanorods- _SnO2 nanoparticles-pristine graphite ene nanosheet composites.

The ternary multilevel multidimensional structure _TiO2 nanorod- _SnO2 nanoparticle-pristine graphene composite material of this embodiment can effectively combine the outstanding functions of each component: excellent cycle performance and outstanding safety of _TiO2 , The high specific capacity of SnO ₂ (782mA h g ^-1 ) and the good conductivity of pristine graphene show excellent comprehensive electrochemical performance. Its structural features are: TiO ₂ nanorods and SnO ₂ nanoparticles are uniformly loaded and tightly combined on the exposed surface of the pristine graphene nanosheets to form a multi-level multidimensional structure, in which the pristine graphene nanosheets are micron-scale two-dimensional on the xy plane structure, TiO ₂ is a one-dimensional nanorod, and SnO ₂ is a zero-dimensional nanoparticle. The ternary composite material formed in this way not only has a multi-dimensional structure with zero-dimensional, one-dimensional and two-dimensional coexistence, but also has a combination of nanometer and micrometer. multilevel structure. This ternary multi-level multi-dimensional composite structure can give full play to the structural properties of each component: (1) The nanoscale structure of low-dimensional _SnO2 and _TiO2 can shorten the transmission path of Li ⁺ and electrons, and improve the High rate performance; (2) Micron-scale two-dimensional pristine graphene nanosheets as a conductive agent can form a three-dimensional network with TiO ₂ and SnO ₂ to build a fast conductive three-dimensional network structure electrode; (3) TiO ₂ as a Zero structural strain material, which can provide the primary safety during charge and discharge; (4) pristine graphene nanosheets, as a matrix, have good flexibility and elasticity, which can ease the Li ⁺ intercalation/extraction process in _SnO2 . (5) The zero-dimensional SnO ₂ and one-dimensional TiO ₂ on the surface of pristine graphene as spacers can avoid the re-stacking of pristine graphene and further increase the interlayer spacing, which is favorable for intercalation/extraction of Li ⁺ .

Example 5

For the defects of nano-TiO ₂ low specific capacity and low electrical conductivity, through the co-doping of secondary phase high specific capacity metal oxide MnO ₂ (1233mA h g ^-1 ) and high conductivity pristine graphene components, this embodiment provides A ternary multi-level multi-dimensional structure TiO ₂ nanoparticle-MnO ₂ nanowire-pristine graphene nanosheet composite material is developed, which exhibits excellent comprehensive electrochemical performance by utilizing its outstanding synergistic effect and unique multi-level multi-dimensional structure.

The ternary multilevel multi-dimensional structure _TiO2 nanoparticle- _MnO2 nanowire-pristine graphene nanosheet composite material in the present embodiment is by _TiO2 , _MnO2 and three kinds of components of high conductivity pristine graphene with 3:2 : The ternary heterostructure formed by the molar ratio of 5, its preparation method is as follows:

(1) The natural graphite powder was added to N-methyl-2-pyrrolidone (NMP) with an initial concentration of 10 mg mL ^-1 , and then ultrasonicated at 70W for 4 hours. The resulting suspension was centrifuged at 2000 rpm for 30 minutes, then the supernatant was collected and vacuum filtered. The filtered solid powder was added into THF and ultrasonicated to obtain a black pristine graphene dispersion solution.

(2) Add 0.008mol MnSO ₄ ·H ₂ O and 0.008mol (NH ₄ ) ₂ S ₂ O ₈ into 50mL deionized water and stir for 10 minutes, then transfer the above mixed solution to 50mL Teflon liner In a stainless steel autoclave, reacted at 120 °C for 6 hours, cooled naturally to room temperature, washed the black solid product with ethanol three times, and dried in vacuum at 40 °C for 12 hours to obtain _MnO2 nanowires. The above dried _MnO2 nanowires were dissolved in THF to obtain a 1 mg/mL black _MnO2 solution.

(3) 0.2 mL of tetrabutyl titanate and 25 mL of isopropanol were mixed and stirred for 30 minutes, then 1 mL of deionized water was added dropwise and stirred for 30 minutes. Then the above mixed solution was transferred to a 50mL polytetrafluoroethylene-lined stainless steel autoclave, reacted at 180°C for 6 hours, cooled to room temperature naturally, washed the product 3 times with ethanol, and dried in vacuum at 40°C for 12 hours to obtain _TiO2 nanoparticles. The above dried TiO _{nanoparticles} were dissolved in THF to obtain a milky white solution at 1 mg/mL.

(4) The above three components were mixed in a molar ratio of TiO ₂ :MnO ₂ :PG=3:2:5, and stirred for 10 hours. During the stirring process, organically modified _MnO2 nanowires and _TiO2 nanoparticles will spontaneously assemble on the exposed surface of pristine graphene, resulting in a ternary multi-level multidimensional structure _TiO2 nanoparticles- _MnO2 nanowires-pristine graphite ene nanosheet composites.

The ternary multilevel multidimensional structure _TiO2 nanoparticle- _MnO2 nanowires-pristine graphene nanosheet composite material of the present invention can effectively combine the outstanding functions of each component: excellent cycle performance and outstanding safety of _TiO2 , the high specific capacity of MnO ₂ (1233mA h g ^-1 ) and the low cost and good electrical conductivity of pristine graphene, thus exhibiting excellent comprehensive electrochemical performance. Its structural features are: TiO ₂ nanoparticles and MnO ₂ nanowires are uniformly loaded and tightly combined on the exposed surface of the pristine graphene nanosheets to form a multi-level multidimensional structure, in which the pristine graphene nanosheets are micron-scale two-dimensional on the xy plane TiO ₂ is a zero-dimensional nanoparticle, and MnO ₂ is a one-dimensional nanowire. The ternary composite material formed in this way not only has a multi-dimensional structure with zero-dimensional, one-dimensional and two-dimensional coexistence, but also has a combination of nanometer and micrometer. multilevel structure. This ternary multi-level multi-dimensional composite structure can give full play to the structural characteristics of each component: (1) The nanoscale structure of low-dimensional TiO ₂ and MnO ₂ can shorten the transport path of Li ⁺ and electrons, and improve the High rate performance; (2) Micron-scale two-dimensional pristine graphene nanosheets as a conductive agent can form a three-dimensional network with TiO ₂ and MnO ₂ to build a fast conductive three-dimensional network structure electrode; (3) TiO ₂ as a Zero structural strain material, which can provide the primary safety during charge and discharge; (4) As a matrix, pristine graphene nanosheets have good flexibility and elasticity, which can alleviate the Li ⁺ intercalation/extraction process in _MnO2 . (5) The zero-dimensional TiO ₂ and one-dimensional MnO ₂ on the surface of pristine graphene are used as spacers, which can avoid the re-stacking of pristine graphene and further increase the interlayer spacing, which is favorable for intercalation/extraction of Li ⁺ .

Example 6

Aiming at the defects of low specific capacity and low electrical conductivity of nano-TiO ₂ , through the co-doping of secondary phase high specific capacity metal oxide Fe ₂ O ₃ (1007mA h g ^-1 ) and pristine graphene components with high electrical conductivity, this implementation The example provides a ternary multi-level multi-dimensional structure TiO ₂ nanoparticle-Fe ₂ O ₃ nanotube-pristine graphene nanosheet composite material, using its outstanding synergistic effect and unique multi-level multi-dimensional structure, it exerts excellent electrical Comprehensive chemical properties.

The ternary multilevel multidimensional structure TiO ₂ nanoparticle- _{Fe 2} O ₃ nanotube-pristine graphene nanosheet composite material in this example is composed of three components: TiO ₂ , Fe ₂ O ₃ and high conductivity pristine graphene. The ternary heterostructure formed with a molar ratio of 4:2:4 can be prepared as follows:

(1) The natural graphite powder was added to N-methyl-2-pyrrolidone (NMP) with an initial concentration of 10 mg mL ^-1 , and then ultrasonicated at 70W for 4 hours. The resulting suspension was centrifuged at 2000 rpm for 30 minutes, then the supernatant was collected and vacuum filtered. The filtered solid powder was added into THF and ultrasonicated to obtain a black pristine graphene dispersion solution.

(2) Mix 3.2 mL of 0.5 mol/L FeCl ₃ solution and 2.88 mL of 0.02 mol/L NH ₄ H ₂ PO ₄ solution under vigorous stirring, then add deionized water to a total volume of 80 mL and Stir for 30 minutes. Then the above mixed solution was transferred to a 100mL polytetrafluoroethylene-lined stainless steel autoclave, reacted at 220°C for 16 hours, cooled to room temperature naturally, washed the solid product three times with ethanol and deionized water, and heated at 80°C Vacuum dried for 6 hours to obtain Fe ₂ O ₃ nanotubes. The above dried Fe ₂ O ₃ nanotubes were dissolved in THF to obtain a 1 mg/mL Fe ₂ O ₃ solution.

(3) 0.2 mL of tetrabutyl titanate and 25 mL of isopropanol were mixed and stirred for 30 minutes, then 1 mL of deionized water was added dropwise and stirred for 30 minutes. Then the above mixed solution was transferred to a 50mL polytetrafluoroethylene-lined stainless steel autoclave, reacted at 180°C for 6 hours, cooled to room temperature naturally, washed the product 3 times with ethanol, and dried in vacuum at 40°C for 12 hours to obtain _TiO2 nanoparticles. The above dried TiO _{nanoparticles} were dissolved in THF to obtain a milky white solution at 1 mg/mL.

(4) The above three components were mixed at a molar ratio of TiO ₂ :Fe ₂ O ₃ :PG=4:2:4, and stirred for 10 hours. During the stirring process, the organically modified Fe ₂ O ₃ nanotubes and TiO ₂ nanoparticles will spontaneously assemble on the exposed surface of pristine graphene, resulting in a ternary multi-level multidimensional structure of TiO ₂ nanoparticles-Fe ₂ O ₃ nano Tube-pristine graphene nanosheet composites.

The ternary multilevel multidimensional structure TiO ₂ nanoparticles- _{Fe 2} O ₃ nanotubes-pristine graphene nanosheet composite material in this example can effectively combine the outstanding functions of each component: TiO ₂ excellent cycle performance and outstanding Safety, high specific capacity of Fe ₂ O ₃ (1007mA h g ^-1 ) and low cost and good electrical conductivity of pristine graphene, thus showing excellent comprehensive electrochemical performance. Its structural features are: TiO ₂ nanoparticles and Fe ₂ O ₃ nanotubes are uniformly loaded and tightly combined on the exposed surface of the pristine graphene nanosheets to form a multi-level multidimensional structure, in which the pristine graphene nanosheets on the xy plane are Micron-scale two-dimensional structure, TiO ₂ is zero-dimensional nanoparticles, and Fe ₂ O ₃ is one-dimensional nanotubes. The ternary composite material formed in this way not only has a multi-dimensional structure with zero-dimensional, one-dimensional and two-dimensional coexistence, but also has A multilevel structure combining nanometers and micrometers. This ternary multi-level multi-dimensional composite structure can give full play to the structural characteristics of each component: (1) The nanoscale structure of low-dimensional TiO ₂ and Fe ₂ O ₃ can shorten the transmission path of Li ⁺ and electrons, and improve the composite structure. High rate performance of the material; (2) Micron-sized two-dimensional pristine graphene nanosheets as a conductive agent can form a three-dimensional network with TiO ₂ and Fe ₂ O ₃ to build a fast conductive three-dimensional network structure electrode; (3) TiO ₂ As a zero-structural strain material, it can provide the primary safety during charge and discharge; (4) As a matrix, pristine graphene nanosheets have good flexibility and elasticity, which can relieve Li in Fe ₂ O ₃ ⁺ The structural stress brought by the intercalation/extraction process can inhibit the volume change of the composite material and the pulverization of the electrode; (5) the zero-dimensional TiO ₂ and one-dimensional Fe ₂ O ₃ on the surface of pristine graphene can be used as spacers to avoid pristine graphite The re-stacking of alkenes further increases the interlayer spacing, which is beneficial to the intercalation/extraction of Li ⁺ .

The ternary multilevel multidimensional structure _TiO2 -high specific capacity metal oxide-pristine graphene composite material described in the above examples is assembled into a button battery, and the material ratio in the button battery is composite material: acetylene black: PVDF=70: 20:10, using Clgard2300 diaphragm, the counter electrode is a metal embedded sheet, the electrolyte is composed of LiPF ₆ , ethylene carbonate and diethyl carbonate (the concentration of LiPF ₆ in the electrolyte is 1mol/L, ethylene carbonate and diethyl carbonate The volume ratio of fat is 1:1), and assembled into a 2025-type button battery in a glove box filled with hydrogen, and the charging and discharging voltage range is 2.5-1.0V.

Figure 1 is the X-ray diffraction pattern of the TiO ₂ -Fe ₃ O ₄ -PG composite material, and the results show that the composite material is a composite of TiO ₂ , Fe ₃ O ₄ and PG without other impurity phases; Figure 2 is the TiO ₂ - The transmission electron microscope image of the Fe ₃ O ₄ -PG composite material, it can be seen that the larger TiO ₂ nanorods and smaller Fe ₃ O ₄ nanoparticles are uniformly loaded on the pristine graphene nanosheets with a planar size of micron; 3 is the high-resolution transmission electron microscope image of the TiO ₂ -Fe ₃ O ₄ -PG composite material, and the results show that the interplanar spacings of TiO ₂ (101), Fe ₃ O ₄ (311), and PG (002) are 0350-0.354nm, respectively , 0.255nm, 0.35nm, consistent with the literature; Figure 4 is the cycle performance curve of the TiO ₂ -Fe ₃ O ₄ -PG composite material at a current density of 0.5A g ^-1 , it can be seen that the electrode is equivalent to 1C It shows good electrochemical performance at a high rate, and the discharge specific capacity is still higher than 500mAh g ^-1 after 100 cycles.

Claims (8)

1. A ternary multilevel multidimensional structure TiO ₂ —high specific capacity metal oxide —pristine graphene composite material, characterized in that said composite material is made of TiO ₂ , secondary phase high specific capacity metal oxide and high electrical conductivity A ternary heterostructure composed of pristine graphene, wherein the molar ratio of TiO ₂ , high specific capacity metal oxide and pristine graphene is 2-5:1-4:3-5. 2. ternary multilevel multidimensional structure _TiO2 -high specific capacity metal oxide-pristine graphene composite material according to claim 1, is characterized in that described ternary heterostructure is nanostructured _TiO2 and high specific capacity Capacitive metal oxides are uniformly loaded and tightly combined on the exposed surface of pristine graphene nanosheets to form a multi-level and multi-dimensional structure. 3. The ternary multilevel multidimensional structure _TiO2 -high specific capacity metal oxide-pristine graphene composite material according to claim 2, characterized in that the pristine graphene nanosheets are micron-scale two-dimensional on the xy plane Structure, TiO ₂ is a zero-dimensional nanoparticle, and the high specific capacity metal oxide is a one-dimensional nanostructure. 4. The ternary multilevel multidimensional structure _TiO2 -high specific capacity metal oxide-pristine graphene composite material according to claim 2, characterized in that the pristine graphene nanosheets are micron-scale two-dimensional on the xy plane Structure, TiO ₂ is a one-dimensional nanostructure, and the high specific capacity metal oxide is a zero-dimensional nanoparticle. 5. ternary multilevel multidimensional structure TiO according to claim 1 ₂ -high specific capacity metal oxide-pristine graphene composite material, is characterized in that described TiO ₂ , high specific capacity metal oxide and simple graphene The molar ratio is 3:3:4, 4:2:4, 4:3:3, 3:4:3, 5:2:3, 4:1:5, 3:2:5 or 2:3:5 . 6. according to claim 1, 2, 3, 4 or 5 described ternary multi-level multi-dimensional structure TiO ₂ - high specific capacity metal oxide - pristine graphene composite material, it is characterized in that described high specific capacity metal oxide It is Fe ₂ O ₃ , Fe ₃ O ₄ , SnO ₂ , Co ₃ O ₄ or MnO ₂ . 7. according to claim 3 or 4 described ternary multi-level multi-dimensional structure TiO ₂ -high specific capacity metal oxide-pristine graphene composite material, it is characterized in that described one-dimensional nanostructure is nanorod, nanowire, nanometer tubes, nanoneedles or nanobelts. 8. A preparation method of the ternary multi-level multi-dimensional structure _TiO2 -high specific capacity metal oxide-pristine graphene composite material according to any one of claims 1-7, characterized in that the steps of the preparation method are as follows : (1) join simple graphene in tetrahydrofuran, obtain black simple graphene dispersion solution; (2) _TiO2 is added in tetrahydrofuran to obtain milky white solution; (3) Adding high specific capacity metal oxides into tetrahydrofuran to obtain a metal oxide solution; (4) The above three solutions are mixed and stirred for 6-12 hours, and assembled into a ternary multi-level multi-dimensional structure TiO ₂ nanoparticle-high specific capacity metal oxide-pristine graphene nanosheet composite material.