KR101738228B1 - Titanium-niobium mesoporous oxide and manufacturing mehtod thereof - Google Patents

Abstract

The present invention relates to a process for producing a mesoporous composite comprising a titanium oxide-niobium oxide-silica oxide; And removing the silica oxide. The present invention also relates to a method for producing a mesoporous titanium-niobium oxide composite.
The composite according to the present invention consists of a crystalline titanium-nidium oxide having a substantially aligned mesopore.

Description

TECHNICAL FIELD [0001] The present invention relates to a titanium-niobium mesoporous oxide and a method for producing the same. BACKGROUND ART [0002] TITANIUM-NIOBIUM MESOPOROUS OXIDE AND MANUFACTURING MEHTOD THEREOF [0003]

More particularly, the present invention relates to a titanium-niobium oxide for an electrode of a secondary battery having a mesoporous structure and a method of manufacturing the same.

Titanium-based electrode materials, such as TiO2 or LiTi5O12, have been proposed as potential candidates for replacing carbon-based cathodes in lithium-based batteries (LiBs). Although graphite carbon is the most widely used material commercially, there are fundamental problems such as irreversible loss of capacity during solid-electrolyte interfacial (SEI) formation and low Li + insertion potential of graphite (0.2 V vs Li / Li +).

On the other hand, Ti-based electrodes enable reversible insertion / extraction of lithium cations within a safe voltage range (> 1 V) using Ti4 + / Ti3 + as a redox couple (1.5 V vs Li / Li +). This reaction does not form a SEI layer and ensures faster Li + ion charging and longer cycle life compared to carbon based electrodes.

Due to these advantages, methods have been attempted over the past decade in a variety of ways, such as nano-EH, complex structure, phase control, surface modification, and doping. However, despite the improvement in stability, there are drawbacks such as a low lithium charge capacity (< 200 mAh g-1) and loss of energy density.

Titanium-niobium oxide is known as an alternative electrode due to its high lithium charge capacity and wide lithium charge potential (1.7 to 1.0 V). In particular, this material has the capacity of 387.6 mA h g-1 because five Li ions can be inserted in the unit TiNb2O7, and it exceeds the Ti or Nb-based oxide (TiO2, Nb2O5, etc.) in terms of capacity.

Since titanium-niobium oxide forms crystals at a temperature of 900 ° C or higher, relatively large nanostructures (100-200 nm) are formed, leading to destruction of nanostructures and rate capability. Thus, there is a continuing need for a method of forming nanostructures of small size nanocrystals that provide a connected void structure to achieve high speed characteristics and capacity of the TiNb2O7 cathode.

A problem to be solved by the present invention is to provide a titanium-niobium oxide made of nanocrystals of small size.

Another object of the present invention is to provide a method for producing a titanium-niobium oxide having a small size of nanocrystals.

Another object of the present invention is to provide a titanium-niobium oxide having a nanoporous structure, which is made of nanocrystals of small size.

Another object of the present invention is to provide an electrode for a lithium battery using titanium-niobium oxide having a nanoporous structure, which is made of nanocrystals of small size.

Another object of the present invention is to provide a secondary battery using a titanium-niobium oxide having a nanoporous structure, which is made of nanocrystals of small size.

Another problem to be solved by the present invention is to provide a nanostructured electrode which remains composed of small nanocrystals even after high temperature treatment.

In order to solve the above problems, the present invention provides a method for producing a mesoporous composite comprising: preparing a mesoporous composite comprising titanium oxide-niobium oxide-silica oxide; And removing the silica oxide. The present invention also provides a method for producing a mesoporous titanium-niobium oxide composite.

In the present invention, the mesoporous composite comprising the titanium oxide-niobium oxide-silica oxide may be prepared by preparing a titanium oxide-niobium oxide composite; Assembling an evaporation inducer by mixing a block copolymer comprising a block having a relatively high affinity to the oxide complex, a silica precursor, the oxide complex and a silica oxide precursor, and a solvent; And a firing step of firing the self-assembled assembly at a high temperature to remove the block copolymer to form regular mesoporous pores.

In the present invention, the titanium oxide-niobium oxide complex in the preparation step may be produced by hydrolysis and / or condensation of a titanium oxide precursor, for example, a titanium alkoxide compound and a mixture of a niobium oxide precursor and a niobium alkoxide compound, Can be prepared by reacting.

The reaction of the alkoxide mixture is carried out under strong acidic conditions so that the alkoxide compounds can be prevented from being agglomerated severely or separated into macrophages due to differences in growth rate and interaction when the mixture is hydrolyzed and / desirable.

In the practice of the invention, it is preferred that the alkoxide mixture maintains acidity and 35 to 37% of HCl is used for binding with the block copolymer. For example, 35% HCl ([H2O] / [ ) x] > 2) can be added to a mixture of titanium alkoxide and niobium alkoxide in a 1: 2 molar ratio. Strongly acidic conditions accelerate the hydrolysis of the metal alkoxide while preventing the inorganic condensation, allowing them to be uniformly mixed at the nanoscale, and a small hydrophilic body that can be mixed with the hydrophilic block of the block copolymer Ti, Nb sol) can be formed.

The titanium oxide-niobium oxide sol complex preferably has a smaller size than that of the PEO block combined with the hydrophilic body so as to prevent separation from the block copolymer. For example, the PEO block having a size of 7.5 nm And can have a diameter of 2 to 4 nm.

In the step of assembling the block copolymer, the block copolymer is used as a structural derivative to form a porous nanostructure, and is also used as a pore-forming agent which is removed in a high-temperature firing process to form pores. The block copolymer may be an amphiphilic block copolymer composed of a hydrophilic block and a hydrophobic block, and the two blocks incompatible with each other are not mixed with each other, resulting in the separation of the microphase to form various nanostructures.

The hydrophilic oxides and / or precursors are each selectively bonded to hydrophilic blocks having high affinity. Herein, it is understood that the "bonding" includes not only chemical bonding but also mixing, mixing, absorption, and agglomeration due to similar affinity. In addition, the hydrophilicity and the hydrophobicity can be understood as relative affinity for water.

In the practice of the present invention, the block copolymer is preferably an amphiphilic diblock copolymer comprising a hydrophobic block and a hydrophilic block. In a preferred embodiment of the present invention, the block copolymer may be poly (ethylene oxide-b-methyl methacrylate), poly (isoprene-b-ethylene oxide) Polystyrene block copolymer (PEO-b-PS). The PEO-b-PS block copolymer may be prepared by known atomic transfer radical polymerization.

In the present invention, the silica oxide precursor may be a compound capable of forming a silica oxide in a subsequent firing step. For example, tetraethyl orthosilicate (TEOS) may be used.

In the practice of the present invention, the nano-sized metal hydrophilic bodies are positively charged in the HCl acidic water, and when mixed with the PEO-b-PS / THF solution, the metal (Ti and Nb) Under the condition, it binds to the PEO block via Cl ^- ion and hydrogen bond. During the self-assembly process by evaporation of the solvent, the strongly separated PEO-b-PS forms a meso structure in which the PS block columns are regularly arranged in the PEO matrix.

In the sintering process of the present invention, columns of the PS block are removed to form oxide complexes in which hexagonal mesopores are regularly arranged. The silica oxide precursor is converted to a silica oxide, such as SiO ₂ , in the firing process, providing thermal and mechanical stability in a given process. The firing can be performed at a temperature of 700 ° C or higher, preferably 800 ° C or higher so that the block copolymers can be removed, more preferably at a temperature of 900 ° C or higher so that titanium and niobium can be crystallized.

In the present invention, the composite prepared by calcining at a high temperature of 900 ° C. or higher forms a nanostructure in which SiO 2 nanoparticles are distributed in the TNO crystal, and the block copolymer is removed to form a mesoporous structure.

In the practice of the present invention, the m-TNO-SiO2 produced by the calcination may have a pore size of between 10 and 50 nm, preferably between 20 and 45 nm, most preferably between 30 and 40 nm, May preferably be 10 to 20 nm, and most preferably 15 nm.

In the present invention, in order to increase the surface area and to remove the amorphous SiO 2 portion to form pores having a size of several nanometers, it is necessary to remove the oxide of silica to enable easy permeation of the electrolyte / .

In the present invention, in the step of removing SiO 2, the synthesized titanium-niobium oxide-silica composite is put into 1 molar sodium hydroxide (NaOH) solution, stirred for 5 hours or longer, and washed with water and ethanol. In this process, SiO2 is dissolved and dissolved by NaOH solution.

In one aspect, the present invention provides an oxide composite having mesopores, wherein amorphous SiO2 nanoparticles are dispersed in a Ti-Ni-Oxide crystal.

In the present invention, the content of the silica oxide in the mesoporous nanostructure (m-TNO-SiO2) composed of the TNO crystal and the SiO2 nanoparticles is 1 to 30% by weight, preferably 5 to 20% by weight, 15% by weight, and the remainder may be a TNO complex. For example, the m-TNO-SiO2 composite may have an atomic ratio of Nb: Ti: Si of 2: 1: 1. The nanostructure can be used as an electrode material, and it can be used as a high-performance electrode material by increasing the surface area by removing SiO2 and increasing the ion permeability.

In another aspect, the present invention provides a titanium-nidium oxide composite having a well-ordered mesopore.

In the present invention, the oxide complex is a crystalline Nb ₂ O ₇ structure consisting of small nanocrystals, preferably 1 to 20 nm, more preferably nanocrystals having an average diameter of 10 to 20 nm, It may have a nanopore formed by etching silica particles.

In another aspect, the present invention provides an electrode comprising a crystalline nanoporous titanium-niobium oxide complex having a well-aligned vertical mesopore.

In another aspect, the present invention provides a secondary cell comprising an electrode comprising a crystalline nanoporous titanium-niobium oxide complex having a well-aligned vertical mesophore.

The present invention provides a titanium-niobium oxide consisting of nanocrystals of small size. The titanium-niobium oxide provides a lithium-niobium oxide having a mesoporous nanostructure, thereby providing a stable and electrode-efficient electrode.

1 is a schematic diagram of a synthesis method of (a) a one-step synthesis method using a block copolymer, (b) an aligned mesoporous TiNb2O7 (m-TNO), and also shows a TNO crystal structure along the b-axis.
Figure 2 is an electron microscope image. (A, b) TEM image, (a) TNO and (b) m-TNO-SiO2. (c, d, e, f) EELS mapping image, (d) Nb, (e) Ti, and (f) Si. (g, h) SEM image, (g) m-TNO-SiO2, (h) m-TNO silica after etching.
Figure 3 shows (a) N2 physically adsorbed isotherms and (b) BJH pore size distribution curves, m-TNO-SiO2 and m-TNO. (c) SAXS pattern TNO (black line), m-TNO-SiO2 (red line), and m-TNO (blue line)
Figure 4 shows (a) constant current charge / discharge curves (initial 3 cycles) m-TNO and bulk-TNO electrodes at 0.1 C rate conditions (= 38.7 mA g ^-1 ). (b) Cycle and rate performance plots, and (c) Various current densities of m-TNO and bulk-TNO electrodes, capacity retention rates obtained in the range of 0.1 to 50 C-rate (d) In order to investigate the capacity maintenance and the function of the rate of ovoid-based electrodes (electrospun-TiNb2O7,18 Ti2Nb10O29,19 mesoporous Li4Ti5O12-carbon, 12 mesoporous TiO2-graphene, 47 carbon-coated Li4Ti5O12,11 Cr-doped Li4Ti5O12,48 mesoporous TiO2 and TiO2 nanodisk45).
Figure 5 shows the cycle performance (a) m-TNO / Li and m-TNO-C / Li cells, 10 C rate and (b) m-TNO / LiFePO4 cell (0.2 Cm- _TNO x 5, C x 100, 5 C x 500, 10 C x 1600 cycles, 1.0 to 2.55 V). Capacity is calculated based on m-TNO mass.

Hereinafter, the present invention will be described in detail by way of examples.

m- TNO Synthesis of

4.5 mmol of titanium isopopoxide and 9 mmol of niobium ethoxide are mixed. Add 2 ml of HCl solution (35 wt% in H2O) slowly to the mixed solution to make a clear solution. 1 ml of the transparent solution is added to 4 ml of THF solution containing 0.3 g of PEO-b-PS dissolved therein, followed by stirring. Then, 0.2 g of tetraethyl orthosilicate is added and stirred for 2 hours. It is then poured onto a petri dish placed on a 40 degree hot-plate and allowed to dry for 12 hours. The dried material is subjected to an annealing process in an oven at 100 ° C. for 12 hours, followed by a heat treatment at 900 ° C. for 2 hours in an oxygen atmosphere furnace (temperature rising rate: 1 ° C./min). After the heat treatment, add 1 M NaOH solution to remove silica, stir for 5 hours or longer, and wash with water and ethanol. For carbon coating, 0.2 g of TiNb2O7 material is added to Tris-buffer (pH 8.5) solution containing 0.15 g of dopamine hydrochloride and stirred for 20 hours. After stirring, obtain powder using centrifugation and wash with water. Finally, the carbonization process is performed through heat treatment in a nitrogen atmosphere at 700 ° C.

m- TNO  Structure analysis

Aligned mesoporous structures of the TNO samples were confirmed by microscopy. As shown in FIG. 2, TEM images show very well aligned hexagonal mesopores. This structure was maintained after the heat treatment at 900 ° C (expressed as m-TNO-SIO2). The EELS image of m-TNO-SIO2 showed that all metal species were uniformly present within the wall (Figs. 2c-f), and this distribution shows that the mesoporous wall was composed of TNO crystals and SiO2 particles ).

The m-TNO-SiO2 samples were cut with a SISM Faratom XL at a thickness of 100 nm. Because nanometer sized TNO crystals and amorphous SiO2 are well dispersed inside the nanowall, all metal species appear overlapping in the mapping image. The results of the SEM show a hexagonal 2D mesoporous structure (Fig. 2g), no collapse of the structure or formation of agglomerated particles was observed, indicating that the TNO nanocrystals were in a limited space determined by PEO-b- It shows that it is developed. The pore size and wall thickness of m-TNO-SiO2 were observed at 35 nm and 10 nm, respectively. Considering that SiO2 is not an active material in LIBs, the existing SiO2 (~ 15% by weight) should be removed before it can be used as an anode. Although less regular 2-D hexagonal arrangements were obtained after SiO2 etching, structures interconnected with nanometer sized TNO nanoparticles in the porous matrix were well preserved. This process is useful because it increases the surface area and creates new nanometer sized pores from the removal of the amorphous SiO2 portion, which allows high electrode / electrolyte interfacial area and easy electrolyte permeation. The EDX spectrum before and after etching is shown in Fig. The atomic ratio of Nb: Ti: Si was 2: 1: 1 in m-TNO-SiO2. The negligible amount of Si shows that most of the silica remains on the nanowire in oxide form and the silica is completely removed by the etching process.

Figure 3A shows a nitrogen adsorption graph of m-TNO-SiO2 and m-TNO. Both samples show a typical form of IV-adsorption and desorption curves with sharp capillary condensation steps at 0.9 to 0.95 P / Po, indicating uniform and large voids. After removal of silica, it showed a BET surface area of m-TNOsms 74㎡g ^-1, 0.37㎤g ^- exhibited a void volume of ^1, which BET surface area and ratio of 0.20 ㎤g 37㎡g ^{-1 -} a pore volume of ¹ Is increased compared to m-TNO-SiO2. The pore size of m-TNO-SiO2 measured by BJH was 33 nm, which is consistent with the microscopic results of Figure 3b. The pore size distribution of m-TNO is the result of the removal of SiO2 particles showing a 40 nm peak with some nano-sized pores. These structural analyzes are also supported by the SAXS pattern of the TNO sample shown in Figure 3c. Some scattering peaks of TNO and mm-TNO-SiO2 indicate a very regular hexagonal mesoporous structure over a wide range. The value of d100 changed from 37.2 to 34.9 after heat treatment and is due to heat shrinkage. The SAXS pattern of m-TNO shows that the 2-D hexagonal aligned mesoporous structure is retained even after the SiO2 removal process.

The powder XRD pattern, as shown in Figure 3d, is a monoclinic TiNb2O7 (space

group: C2 / m, JCPDS #: 77-1374). The TNO crystals developed from the limited wall shows a broad peak despite the calcination at 900 ° C. The average particle size is 15 nm, and small nanocrystals facilitate fast lithium insertion / extraction, enabling high performance.

TNO synthesized by firing of PEO-b-PS block copolymer and TE and Nb sol without TEOS shows sharp peak and crystal size of 49 nm (named as nano-TNO). These results show that block copolymers and silica sources play an important role in the development of nanoscale TNO particles. The structural analysis shows that successful synthesis of orderp menopore structures with large pores (~ 40 nm) consisting of small TNO nanocrystals (~ 15 nm) was achieved. The structure obtained is an ideal structure for rapid diffusion of Li ions and electrons.

Electrochemical performance

The electrochemical performance of m-TNO as LIB was confirmed by a series of constant current charge and discharge tests (Fig. 4). 4A shows the lithiation and delithiation curves of m-TNO / Li and bulk-TNO / Li cells at a charge rate of 0.1 C (= 38.7 mA g. 1) at a potential range of 1.0 to 3.0 V Show. This voltage range protects the electrodes from the formation of SEI.

The high-speed performance of the m-TNO electrode is shown in Figure 4b. At a rate of 0.1 to 50 C, the electrode exhibited a stable Li + insertion / extraction capacity. The reversible capacity of the m-TNO electrode decreased from 289 to 215. The capacity values at 10 C were certainly better than those of Li4Ti5O12 and anatase TiO2 (175 and 168 mAh g.1). Also, at 20 C, the reversible capacity value of 162 mA hg ^-1 is much greater than the value obtained in previous studies (~ 63 mA hg ^-1 at 20 C). At 50 C (= 19.35 A g ^-1 ), the m-TNO electrode showed a reversible capacity of 116 mAh g ^{- 1} . In addition, the m-TNO electrode showed stable cycle performance at different charge rates. When the current density was fixed at 2 C, the reversible capacity was maintained without loss of capacity. In all comparisons, the capacitance value of the m-TNO electrode exceeds that of the bulk-TNO electrode.

In bipolar applications, the long-term stability of any electrode is very important, so cycle testing was done to evaluate the reversibility of the m-TNO electrode. The test was performed after 10 cycles of charging and discharging. As shown in FIG. 5A, the capacity of the m-TNO / Li cell slightly increased and reached 208 mA hg ^-1 after only a few cycles at a rate of 10 C. The m-TNO / Li cell showed a capacity of 100 mAhg ^-1 , corresponding to an initial 48% after 2000 cycles. The monoclinic phase of the m-TNO electrode did not change during cycle 10c.

The cycle performance of m-TNO can be further improved through the surface modification process. Typically, the carbon layer improves the surface stability of the material and the electrical contact of the particles with the electrical conductivity. The application of the coating carbon layer consisted of coating with polydodamine and carbonization at 700 ° C (m-TNO-C). The added carbon content was 10% by weight and, as expected, the cycle stability was rapidly increased by the carbon coating process. The m-TNO-C electrode showed a maximum capacity of 235 mA hg ^{- 1} at 10 C (208 mA hg ^{-1 for} m-TNO), and 191 mA hg ^-1 after 2000 cycles, maintaining 81%.

Claims (19)

Preparing a mesoporous composite comprising titanium oxide-niobium oxide-silica oxide; And
And removing the silica oxide. &Lt; RTI ID = 0.0 &gt; 21. &lt; / RTI &gt; The method of claim 1, wherein the step of preparing the mesoporous composite comprising the titanium oxide-niobium oxide-silica oxide comprises
A titanium oxide-niobium oxide complex;
An assembling step of assembling the evaporation inducer by mixing a block copolymer including a block having a relatively high affinity for the oxide complex and the silica oxide precursor and a solvent; And
The self-assembled assembly is fired at a high temperature to remove block copolymers to form regular mesoporous pores
&Lt; / RTI &gt; wherein the method comprises the steps of: preparing a mesoporous titanium-niobium oxide composite. The titanium oxide-niobium oxide composite according to claim 2, wherein the titanium oxide-niobium oxide composite is prepared by hydrolysis, condensation reaction, or a combination thereof of a precursor mixture composed of a titanium alkoxide compound and a niobium alkoxide compound, - Method for preparing niobium oxide complexes. 4. The method of claim 3, wherein the reaction of the precursor mixture comprising the alkoxide compound is carried out under strong acid conditions. 5. The method of claim 4, wherein the reaction of the precursor mixture comprising the alkoxide compound is performed using HCl. 3. The method of claim 2, wherein the titanium oxide-niobium oxide composite is a hydrophilic sol. 3. The method of claim 2, wherein the block copolymer is an amphiphilic block copolymer consisting of a hydrophilic block-b-hydrophobic block. 8. The method of claim 7, wherein the amphiphilic block copolymer is a PEO-b-PS block copolymer. The method for producing a meso mesoporous titanium-niobium oxide composite according to claim 2, wherein the block copolymer is removed by calcining at 900 ° C or higher. 2. The method of claim 1, wherein the silica oxide is removed by elution. 2. The method of claim 1, wherein the mesoporous void is a vertical mesopore having a diameter between 10 and 50 nm. TiO2-niobium oxide crystals and amorphous SiO2 silica nanoparticles and having regularly ordered mesopores. 13. The oxide composite according to claim 12, wherein the content of the silica nanoparticles is 1 to 30% by weight. A composite for an electrode comprising crystalline titanium-niobium oxide having regularly arranged mesopores and having nanopores on the wall surface of the mesopore. 15. The electrode composite according to claim 14, wherein the mesopore has a diameter of 10 to 50 nm. delete 15. The electrode composite according to claim 14, wherein the titanium-niobium crystal has a diameter of 1 to 20 nm. An electrode for a lithium battery comprising a crystalline titanium-niobium oxide having regularly arranged mesopores and nanopores on the wall surface of the mesopores. The electrode for a lithium battery according to claim 18, wherein the electrode is coated with carbon.

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