KR102186834B1 - Manufacturing method of Nb2O5-Ge/GeO2 microcomposite for electrodes of secondary battery and electrode active material containing Nb2O5-Ge/GeO2 microcomposite prepared therefrom - Google Patents

Abstract

The present invention relates to a secondary battery manufacturing method of the electrode Nb ₂ O ₅ -Ge / GeO ₂ and micro-composites for the secondary cell electrode active materials including the Nb ₂ O ₅ -Ge / GeO ₂ micro composites fabricated by this, and more specifically For the secondary battery electrode Nb ₂ O ₅ -Ge/GeO ₂ micro, which has remarkably excellent long-term stability as well as high capacity and high output characteristics as it has a shape suitable for minimizing volume change due to lithium ion charging and discharging and a remarkably small specific surface area. It relates to a method for manufacturing a composite and an electrode active material for a secondary battery including the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared through the same.

Description

Manufacturing method of Nb2O5-Ge/GeO2 microcomposite for electrodes of secondary battery and electrode active material containing Nb2O5-Ge/GeO2 microcomposite prepared therefrom}

The present invention relates to a secondary battery manufacturing method of the electrode Nb ₂ O ₅ -Ge / GeO ₂ and micro-composites for the secondary cell electrode active materials including the Nb ₂ O ₅ -Ge / GeO ₂ micro composites fabricated by this, and more specifically For the secondary battery electrode Nb ₂ O ₅ -Ge/GeO ₂ micro, which has remarkably excellent long-term stability as well as high capacity and high output characteristics as it has a shape suitable for minimizing volume change due to lithium ion charging and discharging and a remarkably small specific surface area. It relates to a method for manufacturing a composite and an electrode active material for a secondary battery including the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared through the same.

Lithium ion-based energy storage devices can be typically divided into lithium secondary batteries and electrochemical capacitors (lithium ion-capacitors, supercapacitors). The two storage systems exhibit fundamentally different storage mechanisms, such as lithium ions being inserted into the electrode material or stored on the electrode active material surface. Since such a storage mechanism essentially depends on the electrode material, a high understanding and application of the reaction mechanism of each electrode material is required.

The representative negative active material used in lithium-ion batteries up to now is graphite, which has a relatively low theoretical capacity of 372 mAh·g ^-1 , and it is difficult to increase the energy density further due to the layered lithium insertion type reaction mechanism. To overcome these shortcomings, silicon (Li ₁₅ Si ₄ : 3580 mAh·g ^-1 ), tin (Li ₂₂ Sn ₄ : 990 mAh·g ^-1 ) and germanium (Li ₁₅ Ge ₄ : 1390 mAh·g ^-1) ), etc., lithium-alloy materials have been proposed. However, these materials exhibit a high capacity in the electrochemical lithium-alloy reaction, but cause mechanical deterioration accompanied by a change in the volume of the electrode material in the lithium insertion and extraction reaction, resulting in a reversible capacity reduction.

Meanwhile, in the case of lithium ion capacitors, metal oxide materials such as Li ₄ Ti ₅ O ₁₂ , TiO ₂ and Nb ₂ O ₅ have been extensively studied. These materials also have a low reversible capacity of ~200mAh·g ^-1 due to the layered lithium insertion type reaction mechanism of the electrode active material, but due to the unique lithium ion diffusion mechanism within their crystal structure, lithium ions are inserted between layers or inside the tunnel. Charge transfer is possible without phase change and high output characteristics are shown. However, internally, since they are oxide-based materials with low electron conductivity, complex surface treatment and carbon composites are required.

Some limited high-capacity lithium-alloy materials and lithium-ion capacitor materials have been studied to reduce capacity reduction due to structural instability and mechanical deterioration, and to conduct faster and larger amounts of electrons. However, the microstructure of the synthetic material is not elaborate to amplify the synergistic effect of the composite material, and the electrochemical properties are not satisfactory even to meet the current market demand.

In addition, in the case of the majority of composites, nanotechnology was used to induce rapid diffusion of lithium ions, and structural stabilization of the active material was sought through relatively small volume changes during lithium insertion and extraction. However, nano-sized materials show a low particle density when used as an electrode, which is a problem in cell design. In addition, since it has a high specific surface area, it causes repetitive generation of a solid electrolyte interface (SEI) during a continuous charge/discharge cycle, resulting in a decrease in reversible capacity.

Accordingly, there is a need for a lithium-ion storage material having a high-capacity and excellent output characteristics and lifetime characteristics and a manufacturing method thereof.

Korean Patent Publication No. 10-2007-0083384

The present invention has been devised in consideration of the above points, and has a shape suitable for minimizing volume change due to lithium ion charging and discharging, and a remarkably small specific surface area, so that the secondary battery has remarkably excellent long-term stability and high capacity and high output characteristics. An object of the present invention is to provide a method for preparing an electrode Nb ₂ O ₅ -Ge/GeO ₂ microcomposite.

In addition, the present invention has another object to provide an electrode active material for a secondary battery including the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite according to the present invention.

In the present invention, a niobium oxide precursor, a nonionic surfactant, and a first solvent are mixed to prepare a first solution, and a germanium oxide precursor and a capping agent are added to the first solution to prepare a second solution. The preparing step, wherein the second solution is thermally synthesized with a solvent at a predetermined temperature, and niobium oxide nanoparticles formed from the niobium oxide precursor and germanium oxide nanonets formed from the germanium oxide precursor are the niobium oxide The steps of forming a spherical niobium oxide-germanium oxide microcomposite having a three-dimensional network structure by interconnecting the nanoparticles, and heat treatment of the niobium oxide-germanium oxide microcomposite at a predetermined temperature to Nb ₂ O ₅ -Ge/ provides a method of producing a secondary battery electrode Nb ₂ O ₅ -Ge / GeO ₂ micro-composite comprising the steps of producing a GeO ₂ micro-composite material.

According to an embodiment of the present invention, the first solvent may include a polar protic solvent and a polar aprotic solvent.

In addition, the first solvent may be a mixture of a polar protic solvent and a polar aprotic solvent in a volume ratio of 3:7 to 5:5.

In addition, the niobium element in the niobium oxide precursor and the germanium element in the germanium oxide precursor may be included in a molar ratio of 1:0.1 to 1:0.8.

In addition, the solvent thermal synthesis may be performed at a temperature of 180 ~ 240 ℃.

In addition, the niobium oxide-germanium oxide microcomposite may be heat-treated at a temperature of 550 to 900°C in an Ar gas atmosphere.

In addition, the first solution may further contain an acidic agent, and the pH of the first solution may be 0 to 3.

In addition, in the present invention, a first nanonet formed by a plurality of Nb ₂ O ₅ nanoparticles and a plurality of Ge/GeO ₂ nanoparticles each having a particle diameter smaller than that of the Nb ₂ O ₅ nanoparticles are outside the first nanonet. And a secondary battery electrode, which is a spherical cluster having a three-dimensional network structure, including a second nanonet formed in an empty space inside, for a secondary battery including a plurality of Nb ₂ O ₅ -Ge/GeO ₂ microcomposites Provide an electrode active material.

According to an embodiment of the present invention, the Nb ₂ O ₅ nanoparticles may have an average particle diameter of 10 to 100 nm.

In addition, the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite may have an average particle diameter of 1 to 6 μm.

The bulk of the average particle diameter within a predetermined range a number having an average particle size of the _{Nb 2 O 5 -Ge / GeO Nb} 2 that the grain size exceeds ₂ 9㎛ in micro composite O ₅ -Ge / GeO ₂ micro-complex is a micro complex It may be less than 5% of the total volume of them.

In addition, the BET specific surface area of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite may be 15 m ² /g or less.

In addition, the present invention provides a secondary battery electrode comprising the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite according to the present invention.

In the present invention, the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite has a shape suitable for minimizing volume change due to lithium ion charging and discharging, and a remarkably low specific surface area, so that long-term stability is remarkably excellent, and at the same time, it has high capacity and high output characteristics. It can be widely used in electrodes for secondary batteries.

1 is a schematic diagram of an Nb ₂ O ₅ -Ge/GeO ₂ microcomposite according to an embodiment of the present invention.
2A is a SEM image of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1. FIG.
2B is a SEM image of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1. FIG.
2C is a SEM image of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Comparative Example 1.
2D is a SEM image of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Comparative Example 1.
2E is a SEM image of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Comparative Example 1.
2F is a SEM image of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 2.
2G is a SEM image of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 2.
2H is a SEM image of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Comparative Example 2.
2I is a SEM image of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Comparative Example 2.
3A is an image showing a cross-sectional TEM image of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1 and an EDS analysis result for the cross-section, and FIGS. 3a (a) and 3a (b) are cross-sectional TEM 3a(c) is an EDS analysis result image for a cross section, FIG. 3a(d) is an EDS analysis result image for an Nb element in a cross section, and FIG. 3a(e) is an EDS analysis result image for a Ge element in a cross section. , Figure 3a(f) is an EDS analysis result image for the O element of the cross section.
3B is an image showing a cross-sectional TEM image of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 2 and an EDS analysis result for the cross-section, and FIGS. 3b(a) and 3b(b) are cross-sectional TEM 3b(c) is an EDS analysis result image for a cross-section, FIG. 3b(d) is an EDS analysis result image for an Nb element in a cross-section, and FIG. 3b(e) is an EDS analysis result image for an element O in a cross-section. , Figure 3b(f) is an EDS analysis result image for the Ge element of the cross section.
3C is an image showing a TEM image and an EDS analysis result for a cross section of a portion of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Comparative Example 2, and FIG. 3c(a) is a cross-sectional TEM image, 3c (b) is a high-angle annular dark-field (HAADF) TEM image, FIG. 3c(c) is an EDS analysis result image for a cross section, and FIG. 3c(d) is an EDS analysis result image for an Nb element in a cross-section, FIG. 3c(e) is an EDS analysis result image for element O in a cross section, and FIG. 3c(f) is an EDS analysis result image for Ge element in a cross section.
4A is a high magnification TEM image of a cross section of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1. FIG.
4B is a fast Fourier transform (FFT) pattern image for region b shown in FIG. 4A.
4C is a fast Fourier transform (FFT) pattern image for region c shown in FIG. 4A.
4D is a fast Fourier transform (FFT) pattern image for a region d shown in FIG. 4A.
FIG. 4E is a fast Fourier transform (FFT) pattern image for region e shown in FIG. 4A.
5 is a graph showing the results of small-angle X-ray scattering (SAXS) analysis of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1. FIG.
6 is a graph showing the BET specific surface area measurement results of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1.
7 is a graph showing the XRD analysis results of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1. FIG.
8A is a charge/discharge curve of a coin cell including a secondary battery electrode according to an embodiment of the present invention.
8B is a graph showing a result of measuring capacity according to the number of cycles of a coin cell including a secondary battery electrode according to an embodiment of the present invention.
8C is a graph showing a result of measuring a change in current through a cyclic voltage scanning method for a coin cell including a secondary battery electrode according to an embodiment of the present invention.
8D is a graph measuring an increase in current amount for each scan voltage for a coin cell including a secondary battery electrode according to an embodiment of the present invention.
9A is a graph showing the results of particle size distribution analysis of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1. FIG.
9B is a graph showing the particle size distribution analysis results of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Comparative Example 1. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art can easily implement the present invention. The present invention may be implemented in various different forms and is not limited to the embodiments described herein.

Hereinafter, a method of manufacturing the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite for a secondary battery electrode according to the present invention will be described.

First, a niobium oxide precursor, a surfactant, and a first solvent are mixed to prepare a first solution. Preferably, the niobium oxide precursor and the surfactant are each independently added to and mixed with the first solvent, followed by stirring continuously.

The niobium oxide precursor may be a hydrate containing a niobium element, preferably C ₄ H ₄ NNbO _9· xH ₂ O and/or NbCl ₄ . However, C ₄ H ₄ NNbO _9· xH ₂ O may be more preferable to form a spherical niobium oxide-germanium oxide microcomposite having a three-dimensional network structure in a step described later. For example, the niobium oxide precursor may be included in a concentration of 2.7 to 8.4 mmol based on 100 ml of the solvent in the first solution. If the niobium oxide precursor exceeds 8.4 mmol, it may be difficult to form nanonets between the niobium oxide nanoparticles, and as a result, Nb ₂ O ₅ -Ge/GeO having a spherical three-dimensional network structure. ₂ Microcomposites can be difficult to implement. In addition, if it is contained in less than 2.7 mmol, it may be difficult for niobium oxide to form nanonets, and even if the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite is formed, the Nb ₂ O ₅ -oxide nanoparticles are in the form of particles rather than a network structure. It may be difficult to form a microcomposite of a desired structure, such as being separated or present in a cluster.

The surfactant may be used without limitation as long as it is a nonionic surfactant commonly used in the art, and for example, it may be F-127. In addition, the nonionic surfactant may have a different shape of the micelle colloid formed according to the polarity of the first solvent. The nonionic surfactant may be added in an amount of 10 to 30% by weight of the total weight of the niobium oxide precursor and the germanium oxide precursor contained in the second solution to be described later. If the content of the non-ionic surfactant exceeds 30% by weight, the carbon content increases during thermal decomposition, and thus, a thick carbon layer is formed between primary particles such as niobium oxide nanoparticles and germanium oxide nanoparticles and on the surface. The formation of nanonet structures can be difficult. In addition, if the content of the nonionic surfactant is less than 10% by weight, the size of each primary particle is not controlled and becomes large, resulting in less binding between particles, thereby obtaining a microcomposite having a desired spherical shape and a network structure. It can be difficult to do.

The first solvent may include a polar protic solvent and a polar aprotic solvent. By simultaneously including the polar protic solvent and the polar aprotic solvent, it may be suitable for forming a spherical niobium oxide-germanium oxide microcomposite having a three-dimensional network structure in a step described below.

The polar protic solvent may include at least one selected from methanol, ethanol and isopropyl alcohol, preferably ethanol. The polar aprotic solvent may include at least one selected from dimethylformamide, tetrahydrofuran and acetonitrile, preferably dimethylformamide. Even more preferably, the first solvent may be a mixture of a polar protic solvent and a polar aprotic solvent in a volume ratio of 3:7 to 5:5, and when mixed in the volume ratio, the three-dimensional It may be suitable for forming a spherical niobium oxide-germanium oxide microcomposite having a network structure.

In addition, the first solution may further contain an acidic agent, and the pH of the first solution may be 0 to 3. The powder may be selected without limitation, as long as it is a powder commonly used in the art, and preferably HCl. When the pH of the first solution is 0 to 3, the crystallinity of the Nb ₂ O ₅ particles in the finally prepared Nb ₂ O ₅ -Ge/GeO ₂ microcomposite is improved, preferably an orthorhombic crystal structure. structure), the content of Nb ₂ O ₅ particles can be further increased.

Next, a second solution is prepared by adding a germanium oxide precursor and a capping agent to the first solution. Preferably, the capping agent may be added in a dissolved state in a solvent capable of dissolving the capping agent, and the germanium oxide precursor may also be added in a form dissolved in a solvent capable of dissolving the germanium oxide precursor. I can. In addition, after preparing the second solution, it may be continuously stirred.

The germanium oxide precursor may be converted into a germanium oxide nanoseed by decomposing ethanol in the second solution. In addition, the niobium oxide precursor may be converted into a niobium oxide nano seed in the second solution. The germanium oxide nanoseeds and niobium oxide nanoseeds may be grown into germanium oxide nanoparticles and niobium oxide nanoparticles, respectively, in the thermal solvent synthesis step described below.

In the second solution, the niobium element in the niobium oxide precursor and the germanium element in the germanium oxide precursor may include precursors having a molar ratio of 1:0.1 to 1:0.8. When the germanium element is less than 0.1 mol based on 1 mol of the niobium element, the germanium oxide nanonets in the niobium oxide-germanium oxide microcomposite formed in the solvent thermal synthesis step described later are not formed in the desired shape and/or ratio. It may not be possible, and accordingly, the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite finally prepared may be difficult to express high capacity and long-term stability. In addition, if the germanium element exceeds 0.8 mol, in Nb ₂ O ₅ is not included for the purpose of the content of the level of Nb ₂ O ₅ -Ge / GeO ₂ micro-composite is finally prepared in the basis of 1 mol of the niobium I can. In addition, the cluster shape may not be manufactured in an irregular shape other than a spherical shape, and the internal structure may not be formed as a whole, such as a 3D network not formed or partially formed. As a result, when used as an electrode material, there is a concern that long-term stability may be remarkably deteriorated as it may cause collapse of the internal structure and sustained generation of SEI.

The capping agent prevents the agglomeration of niobium oxide nanoparticles and germanium oxide nanoparticles grown in the solvent thermal synthesis step to be described later, and allows each to grow into nanoparticles of a desired level, and finally It can play a role of controlling the particle size and shape of the formed niobium oxide-germanium oxide microcomposite. Specifically, in the case of the microcomposite of FIGS. 2A and 2B implemented using a capping agent, it can be seen that the size of the microcomposite is spherical and the size of each microcomposite is very uniform. On the other hand, it can be seen that the microcomposite of FIGS. 2C to 2E implemented without a capping agent has reduced particle size and uniformity, and includes those that are not formed in an intact spherical shape. The capping agent may be selected without limitation as long as it is a material capable of capping microparticles in the art, and may be preferably polyvinylpyrrolidone (PVP). The capping agent may be included in an amount of 5 to 10% by weight based on the total weight of the niobium oxide precursor and the germanium oxide precursor in the second solution, through which a three-dimensional network structure and a niobium oxide/germanium oxide nanoparticle size are desired. It may be more suitable to implement at the level of

The germanium oxide precursor may be a halide containing a germanium element, preferably GeCl ₄ . The germanium oxide precursor is preferably added to satisfy the molar ratio described above in consideration of the content of the niobium oxide precursor in the first solution. The solvent capable of dissolving the germanium oxide precursor may be tetrahydrofuran, for example, but may vary depending on the material selected as the capping agent.

Next, the second solution is subjected to solvent heat synthesis at a predetermined temperature to form a niobium oxide-germanium oxide microcomposite, which is a spherical cluster having a three-dimensional network structure. In the niobium oxide-germanium oxide microcomposite, the niobium oxide exists in nano-sized granular form, and a plurality of granular nanoparticles may form the first nanonet. In addition, the germanium oxide exists in nano-sized granular form, and a plurality of granular nanoparticles may form the second nanonet. In this case, the second nanonet may be formed by positioning germanium oxide nanoparticles in empty spaces outside and inside the first nanonet. Accordingly, the first nanonet and the second nanonet are entangled with each other to implement a spherical cluster, and the cluster has a three-dimensional network structure, and preferably, the three-dimensional network structure can be formed in the entire cluster.

The niobium oxide-germanium oxide microcomposite is the niobium oxide The nanonets of the nanoparticles and the nanonets of the germanium oxide nanoparticles are entangled with each other, so that they may be crystallized at a temperature lower than the independent crystallization temperatures of the niobium oxide and the germanium oxide in the heat treatment step described later.

The solvent thermal synthesis may be performed for 12 to 48 hours at a temperature of 180 to 240°C.

When the temperature condition of the solvent thermal synthesis is less than 180°C and/or the execution time is less than 12 hours, it may be difficult for the niobium oxide nanoparticles and/or the germanium oxide nanoparticles to have a desired crystal structure. In addition, if the temperature condition exceeds 240°C and/or the execution time exceeds 48 hours, it may be difficult for the niobium oxide nanoparticles and/or the germanium oxide nanoparticles to form a nanonet structure.

After solvent thermosynthesis, it may be washed several times with ethanol and/or water to remove the surfactant from the obtained suspension, and centrifuged to obtain a precipitate in the washed suspension. The obtained precipitate may be dried, for example, vacuum-dried to obtain a precipitate, that is, the niobium oxide-germanium oxide microcomposite.

Next, the niobium oxide-germanium oxide microcomposite is heat-treated at a predetermined temperature to prepare a Nb ₂ O ₅ -Ge/GeO ₂ microcomposite.

Through the heat treatment, a surfactant and/or a capping agent remaining in the niobium oxide-germanium oxide microcomposite may be removed.

The heat treatment may be performed at a temperature of 550 to 900° C. in order to realize a preferable crystal structure of Nb ₂ O ₅ , for example, an orthorhombic crystal structure, and at the same time to reduce Ge and oxidize GeO ₂ , more preferably It may be performed at 550 ~ 700 ℃. If performed at a temperature of less than 550°C, it may be difficult for Nb ₂ O ₅ to implement an orthorhombic crystal structure, and thus, the desired level of electrochemical properties may not be expressed. In addition, if it is carried out at a temperature exceeding 900°C, it may be difficult to achieve a stable second nanonet structure or melt and vaporize Ge when it exceeds, and as a result, it is difficult to form a Nb ₂ O ₅ -Ge/GeO ₂ microcomposite Even if the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite is formed, it may be difficult to have a desired three-dimensional network structure. The heat treatment may be heated to a desired temperature at a rate of 5 to 15° C./min, and preferably may be performed for 1 to 5 hours in an inert gas atmosphere, for example an argon gas atmosphere. If heat treatment in the atmospheric atmosphere or if the heat treatment time is not satisfied, it may be difficult to implement a Nb ₂ O ₅ -Ge/GeO ₂ microcomposite having a desired size, and it may be difficult to obtain niobium oxide nanoparticles having an orthorhombic crystal structure. Meanwhile, in the finally implemented microcomposite, the crystal structure of GeO ₂ may be a hexagonal structure.

Next, an electrode active material for a secondary battery according to the present invention including a plurality of microcomposites manufactured through the above-described manufacturing method will be described. The electrode active material for a secondary battery of the present invention includes a plurality of spherical Nb ₂ O ₅ -Ge/GeO ₂ microcomposites for secondary battery electrodes as shown in FIG. 1.

The spherical Nb ₂ O ₅ -Ge/GeO ₂ microcomposite for secondary battery electrodes has a _first nanonet formed by a plurality of Nb ₂ O ₅ nanoparticles and a plurality of individual particle diameters smaller than the particle diameter of Nb ₂ O ₅ nanoparticles. As a cluster implemented including a second nanonet formed by being located in an empty space outside and inside the first nanonet of Ge/GeO ₂ nanoparticles, the cluster is spherical and has a three-dimensional network structure.

The Nb ₂ O ₅ -Ge/GeO ₂ microcomposite has the advantage of excellent charge transfer on the nanoparticle surface by forming the first nanonet of Nb ₂ O ₅ nanoparticles, and Ge/GeO ₂ nanoparticles having high capacity characteristics The particles are located outside the first nanonet and in empty spaces inside the first nanonet to form the second nanonet, thereby remarkably improving the particle density and improving the electronic conductivity inside the microcomposite. In addition, the first nanonet and the second nanonet are entangled with each other to form a cluster of a spherical three-dimensional network structure, so that the first nanonet of Nb ₂ O ₅ nanoparticles with relatively low volume change rate during lithium ion charging and discharging has high capacity and It is possible to buffer the volume expansion of Ge/GeO ₂ nanoparticles having high output characteristics, thereby reducing the reversible capacity of the electrode and preventing or minimizing damage to the electrode.

The Nb ₂ O ₅ -Ge/GeO ₂ microcomposite may have an average particle diameter of 1 to 6 μm. If the average particle diameter of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite exceeds 6 μm, it may be difficult to control the electrode thickness, and the possibility of collapse of the network structure of the cluster due to inflexibility to the internal stress action of the electrode is remarkable. There is a risk of increase. In addition, if the average particle diameter is less than 1㎛, the particle density is low, and there may be a lot of by-products on the surface of the particles, which may cause side reactions, and the specific surface area is relatively large, making it difficult to use as an electrode material and the coating process is not easy. There is no concern. In addition, as more lithium is required to form the SEI, there is a concern that the battery efficiency is significantly reduced.

More preferably the volume of the average particle diameter within a predetermined range a number having an average particle size of the _{Nb 2 O 5 -Ge / GeO Nb} 2 O to a particle size in excess of ₂ microseconds 9㎛ complex ₅ -Ge / GeO ₂ micro-complexes It may contain up to 5% of the total volume of microcomposites. In this case, due to the microcomposite having a uniform particle diameter, the solid electrolyte interface (SEI) initially formed is stable, may not be easily broken, and may be continuously generated and not thickened. In addition, it may be advantageous in expressing stable life characteristics and fast rate characteristics during a long cycle by affecting the diffusion and electron transfer speed of lithium ions. If the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite with a particle diameter exceeding 9㎛ exceeds 5% of the total number of microcomposites, the uniformity of the particle size is significantly lowered, and the SEI continues due to the large particle diameter microcomposite. It may be difficult to achieve the desired effect, such as being produced and reducing life over long cycles.

Nb ₂ O ₅ nanoparticles to form a first nano-nets in the Nb ₂ O ₅ -Ge / GeO ₂ micro-composite is the average particle diameter of 10 ~ 100 ㎚, more preferably, may have an average particle diameter of 25 ~ 55㎚ .

When the average particle diameter of the Nb ₂ O ₅ nanoparticles is 10 to 100 nm, a shape suitable for minimizing the volume change due to charge and discharge of lithium ions of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite and a significantly low specific surface area It can have remarkably excellent long-term stability and excellent high capacity and high output characteristics.

In addition, the average particle size of the Ge / GeO ₂ nanoparticles may be less than the average diameter of the Nb ₂ O ₅ nano-particles, so that Ge / GeO ₂ nanoparticles first nano formed of the Nb ₂ O ₅ nanoparticles It is located in an empty space outside and inside the net, so it may be easy to form the second nanonet. For example, the average particle diameter of the Ge/GeO ₂ nanoparticles may be 2 to 50 nm, but is not limited thereto, and may be determined according to the size of a space between nanonets formed of niobium oxide nanoparticles.

The BET specific surface area of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite may be 15 m ² /g or less, more preferably 5 to 10 m ² /g.

When the BET specific surface area of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite exceeds 15 m ² /g, a solid electrolyte interface is continuously generated during a continuous charge/discharge cycle, so that the reversible capacity can be significantly reduced, Since the particle density of the microcomposite is not as high as the desired level of the present invention, a problem may occur during cell design. When the BET specific surface area of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite is 5 to 10 m ² /g, stability may be even more excellent even in a continuous charge/discharge cycle.

Meanwhile, the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite according to the present invention can be used as a secondary battery electrode. The Nb ₂ O ₅ -Ge/GeO ₂ microcomposite may be prepared as a secondary battery electrode through a method of manufacturing a secondary battery electrode commonly used in the art as an electrode active material, and as an example, mixed with activated carbon and a binder. Then, it may be coated on a metal thin film to form a secondary battery electrode, but is not limited thereto.

The binder may be used without limitation as long as it is a material commonly used as a binder for an active material in the art, but may be polyacrylic acid as an example.

The Nb ₂ O ₅ -Ge/GeO ₂ microcomposite according to the present invention has an internal structure that forms a network in which each of the two nano-sized materials is interconnected, so that lithium storage that forms a complex reaction mechanism with lithium When used as a material, high capacity can be expressed through a lithium-alloy type reactive material, and high power characteristics can be obtained through a lithium-inserted pseudocapacitor reaction material. Furthermore, as it has a particle size of an appropriate size, non-alloy-type reactants around the periphery during a continuous cycle have a buffering effect, reduce the volume change during the insertion and extraction of lithium, slow physical deterioration, and improve the internal electronic conductivity through a network structure. Therefore, it is advantageous to obtain stable and long-term life characteristics without carbon compounding or surface coating.

(Example 1)

Ammonium niobate (V) oxalate hydrate: C ₄ H ₄ NNb ₉ in a solvent mixed with dimethylformamide (DMF) and ethyl alcohol (EtOH) in a volume ratio of 6:4 xH ₂ O, Sigma-Aldrich) is 10 mmol based on 180 ml of the mixed solvent, and Pluronic F-127, a nonionic surfactant, is based on the total weight of ammonium niobium oxalate hydrate and GeCl _{4 to} be added when preparing the second solution. After adding 28% by weight, the mixture was stirred for 30 minutes to prepare a first solution. Thereafter, a 2M hydrochloric acid (HCl) solution was added to lower the pH of the solution to 3 or less.

Meanwhile, GeCl ₄ and polyvinylpyrrolidone (PVP) as a capping agent are added to tetrohydrofuran, but the capping agent is the total total weight of the ammonium niobium oxalate hydrate and the GeCl ₄ input amount in the first solution. 10% by weight was added, and the prepared mixed solution was added to the first solution to prepare a second solution. At this time, GeCl ₄ was added so as to have a molar ratio of 0.3, based on the _{C 4 H 4 NNbO 9 · xH} 2 O 1 mol.

The second solution was put into an autoclave and reacted at 200° C. for 24 hours. The obtained suspension was washed with ethanol and demineralized water and then vacuum-dried at a temperature of 60° C. to obtain a niobium oxide-germanium oxide microcomposite.

The obtained niobium oxide-germanium oxide microcomposite was heat-treated for 2 hours in an argon atmosphere and an electric furnace at 600°C to prepare a spherical Nb ₂ O ₅ -Ge/GeO ₂ microcomposite having a three-dimensional network structure.

(Example 2)

In the same manner as in Example 1, C ₄ H ₄ NNbO _9· xH ₂ O and GeCl ₄ were added in a molar ratio of 1:0.6.

(Comparative Example 1)

In the same manner as in Example 1, except that PVP was not added when preparing the second solution, an Nb ₂ O ₅ -Ge/GeO ₂ microcomposite was prepared.

(Comparative Example 2)

In the same manner as in Example 1, C ₄ H ₄ NNbO ₉ x _· H ₂ O and GeCl ₄ were added in a molar ratio of 1:1.

(Production Example 1)

The Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1, activated carbon (Super P), and polyacrylic acid were mixed in a weight ratio of 7:1.5:1.5, and then 28 weights in demineralized water % To prepare a composition for preparing a negative electrode. This composition was coated on a copper thin film (thickness: 10 µm) and vacuum-dried at 80°C. After drying, a negative electrode was prepared by compressing with a roll presser at a compression rate of 30%.

A coin cell was manufactured using the prepared negative electrode, a lithium thin film, a separator, and an electrolyte. The coin cell used a 2032 standard, a porous polypropylene membrane was used as a separator, and the total weight was mixed in ethyl carbonate and diethyl carbonate solvents in a volume ratio of 3:7 in which 1M lithium salt (LiPF ₆ ) was dispersed. An electrolytic solution to which fluoroethylene carbonate was added in an amount of 10% by weight was used.

(Experimental Example 1)

SEM analysis was performed on the microcomposites prepared in Examples and Comparative Examples.

2A and 2B are SEM images of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1. 2A and 2B, it can be seen that the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1 has a spherical shape and an average particle diameter of about 3 μm.

2C to 2E are SEM images of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Comparative Example 1. Referring to FIG. 2C, it can be seen that the microcomposite of Comparative Example 1 has a less uniform particle size than that of Example 1, and the average particle diameter is about 7.2 μm, which is larger than that of Example 1.

2F and 2G are SEM images of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 2. 2F and 2G, the microcomposite has a spherical shape, but it can be seen that the surface of the microcomposite is uneven compared to Example 1. In addition, the average particle diameter of the microcomposite was about 3 μm.

2H and 2I are SEM images of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Comparative Example 2. 2H and 2I, it can be seen that the microcomposite did not have a spherical shape and nanoparticles were irregularly grown.

(Experimental Example 2)

The microcomposites prepared in Example 1, Example 2 and Comparative Example 2 were subjected to TEM and EDS analysis.

3A(a) and 3A(b) are cross-sectional TEM images of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1. Referring to FIGS. 3A(a) and 3A(b), it can be seen that a three-dimensional network structure is also formed inside the microcomposite.

3a(c) to 3a(f) are images showing EDS analysis results for the cross section of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1. 3A(c) to 3A(f), Nb ₂ O ₅ nanoparticles detected as Nb elements form nanonets, and Ge/GeO detected as Ge elements between the outer and inner voids of the nanonets. _{2 It} can be seen that the nanonets of nanoparticles are entangled and filled.

3b(a) and 3b(b) are cross-sectional TEM images of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 2. Referring to FIGS. 3B(a) and 3B(b), it can be seen that a three-dimensional network structure is also formed inside the microcomposite. 3b(c) to 3b(f) are images showing EDS analysis results for the cross section of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 2. 3b(c) to 3b(f), Nb ₂ O ₅ nanoparticles detected as Nb elements form a nanonet, and Ge/GeO detected as a Ge element between the outer and inner voids of the nanonet. _{2 It} can be seen that the nanonets of nanoparticles are entangled and filled.

More specifically, inside of the first embodiment of a smaller diameter than Nb ₂ O ₅ obtained in the Nb ₂ O ₅ were obtained were, so to stick together a number of Nb ₂ O ₅ was observed in larger Nb ₂ O ₅ mass. In addition, it was observed that the reduced Ge is densely present on the small Nb ₂ O ₅ surface. In terms of the network structure, there was no significant difference between Example 1 and Example 2, but it was observed that the shapes of the particles constituting the network were different. On the other hand, it was confirmed that the uneven shape on the surface was due to the strong reduction of Ge and the tendency of the crystal structure of Nb ₂ O ₅ to exist as a monoclinic crystal phase. On the other hand, than the microcomposite of Example 2, the lifespan characteristics may be better than the microcomposite according to Example 1 in a long cycle of 1000 cycles or more.

3c(a) and 3c(b) are TEM images of a portion of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Comparative Example 2. Referring to FIGS. 3C(a) and 3C(b), it can be seen that a three-dimensional network structure is not formed in the microcomposite.

3c(c) to 3c(f) are images showing EDS analysis results for the cross section of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Comparative Example 2. 3c(c) to 3c(f), Nb ₂ O ₅ nanoparticles detected as Nb elements partially form nanonets, and Ge/GeO ₂ nanoparticles detected as Ge elements are also partially It can be seen that only nanonets are formed, and the rest of the nanonets unite and exist.

4A is a high magnification TEM image of a cross section of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1. FIG. Referring to Figure 4a, and inside the micro-composite material is Nb ₂ O ₅ nanoparticle confirmed that existing in the primary particles, the Nb ₂ O ₅ is GeO ₂ nano net consisting of GeO ₂ nanoparticles between nanoparticles filled You can confirm that there is. 4B to 4E are fast Fourier transform (FFT) pattern images for each region indicated in FIG. 4A.

(Experimental Example 3)

SAXS (small-angle X-ray scattering) analysis was performed on the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1, and the results are shown in FIG. 5.

Referring to FIG. 5, d-spacing of 48.3 nm was calculated from the q value of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1, and it was confirmed that the material has high crystallinity.

(Experimental Example 4)

The BET specific surface area of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1 was measured, and the results are shown in FIG. 6.

6, the BET specific surface area of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1 was calculated as 7.2 m ² /g.

(Experimental Example 5)

XRD analysis was performed on the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1, and the results are shown in FIG. 7. Referring to FIG. 7, rather than monoclinic Nb ₂ O ₅ (H-Nb ₂ O ₅ ), orthorhombic Nb ₂ O ₅ (T-Nb ₂ O ₅ ) peaks are mainly observed, which is the same polymorph of Nb ₂ It is known that lithium ions move and store the fastest among O ₅ . In addition, some reduced germanium (Ge) was identified along with germanium oxide (GeO ₂ ).

(Experimental Example 6)

A negative half cell experiment was performed using the coin cell prepared in Preparation Example 1. 8A to 8D are graphs showing capacity, life, and rate characteristics of electrodes obtained through a half cell experiment.

8A is a charge/discharge curve obtained through a constant current test method in a potential range of 0.001-3.0 V with a current density of 0.1 A·g ⁻¹ . A reversible capacity of about 600 mAh·g ^-1 , which is an initial efficiency of 66.5%, was expressed. It has a significantly higher capacity than the currently commercialized graphite-based anode material. In addition, it was confirmed that the initial reversible capacity was maintained without a large decrease in capacity at various current densities (0.1, 0.5, 1.0 A·g ⁻¹ ) for 100 cycles as shown in FIG. 8B. Although the internal structure of the electrode active material is stable and the main material forming the network structure is oxide (Nb ₂ O ₅ -GeO ₂ ), it exhibited high electronic conductivity and lithium ion mobility without carbon coating or complexing.

8C shows the change in current for various voltage changes through the cyclic voltage scanning method. Referring to FIG. 8C, it can be seen that sequential oxidation/reduction reactions of active materials of Nb ₂ O ₅ -Ge/GeO ₂ forming a network structure and insertion and extraction of lithium occurred at each peak.

Since the rate characteristics of each material can be known through the increase in the amount of current by scanning voltage in FIG. 8D using the following calculation equation 1, the reaction mechanism of lithium ions (charge transfer and diffusion of ions on the surface) You can check the variable b.

[Calculation 1]

I= av ^b

In Equation 1, I is a current, v is a voltage, a is a pre-factor, and b is a variable depending on the reaction mechanism with lithium.

In Table 1 below, the b value calculated through Formula 1 is described.

Reaction mechanism Li-Nb ₂ O ₅ Li-GeO ₂ Li-Ge Peak position C1 A3 C2 A2 C3 A1 1.2~2.2V 2.0V 0.3~0.8V ~1.2V 0.3V ~0.6V b value 0.92 0.91 0.85 0.82 0.87 0.96

(Experimental Example 9)

Particle size distribution analysis of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1 and Comparative Example 1 was performed, and the results are shown in FIGS. 9A, 9B and Table 2 below. In Table 2, %Tile means the cumulative volume% in the particle size distribution.

Example 1 Comparative Example 1 %Tile Size(um) %Tile Size(um) 10.00 1.555 10.00 3.24 20.00 1.86 20.00 3.93 30.00 2.17 30.00 4.56 40.00 2.45 40.00 5.22 50.00 2.70 50.00 5.95 60.00 2.93 60.00 6.78 70.00 3.19 70.00 7.79 80.00 3.71 80.00 9.2 90.00 4.96 90.00 11.7 95.00 6.00 95.00 15.2

9A and Table 2, the average particle diameter of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Example 1 was measured to be about 3 μm, and the number of microcomposites having a particle diameter exceeding 9 μm was total It can be seen that it is less than 5% of the number of composites.

9B and Table 2, the average particle diameter of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite prepared in Comparative Example 1 was measured to be about 7.2 μm, and in Comparative Example 1, the particle size distribution was wider than in Example 1. It can be seen that the number of microcomposites having a particle diameter exceeding 9 μm is 20% or more of the total number of composites.

Through this particle size distribution result, the electrode manufactured through the microcomposite of Comparative Example 1 is expected to continuously generate SEI due to the microcomposite having a large particle diameter, and the lifespan is expected to decrease compared to Example 1 during a long cycle.

Although an embodiment of the present invention has been described above, the spirit of the present invention is not limited to the embodiment presented in the present specification, and those skilled in the art who understand the spirit of the present invention can add components within the scope of the same idea. It will be possible to easily propose other embodiments by changing, deleting, adding, etc., but it will be said that this is also within the scope of the present invention.

Claims (13)

Preparing a first solution by mixing a niobium oxide precursor, a nonionic surfactant, and a first solvent including a polar protic solvent and a polar aprotic solvent;
Preparing a second solution by adding a germanium oxide precursor and a capping agent to the first solution;
Forming a niobium oxide-germanium oxide microcomposite, which is a spherical cluster having a three-dimensional network structure, by solvent-heating the second solution at a predetermined temperature; And
Heat-treating the niobium oxide-germanium oxide microcomposite at a predetermined temperature to prepare an Nb ₂ O ₅ -Ge/GeO ₂ microcomposite;
A method of manufacturing a secondary battery electrode comprising a Nb ₂ O ₅ -Ge/GeO ₂ microcomposite. delete The method of claim 1,
The first solvent is a method for producing a Nb ₂ O ₅ -Ge/GeO ₂ microcomposite for a secondary battery electrode in which a polar protic solvent and a polar aprotic solvent are mixed in a volume ratio of 3:7 to 5:5. The method of claim 1,
Nb ₂ O ₅ -Ge/GeO for secondary battery electrodes, characterized in that the niobium element in the niobium oxide precursor and the germanium element in the germanium oxide precursor are included in the second solvent in a molar ratio of 1:0.1 to 1:0.8 ₂ Method for producing microcomposite. The method of claim 1,
The solvent thermal synthesis is a method of manufacturing a Nb ₂ O ₅ -Ge/GeO ₂ microcomposite for a secondary battery electrode, characterized in that performed at a temperature of 180 ~ 240 ℃. The method of claim 1,
The niobium oxide-germanium oxide microcomposite is a method of manufacturing a Nb ₂ O ₅ -Ge/GeO ₂ microcomposite for a secondary battery electrode, characterized in that heat treatment at a temperature of 550 to 900° C. in an Ar gas atmosphere. The method of claim 1,
The first solution further includes an acidic agent, and the first solution has a pH of 0 to 3, wherein the method of manufacturing a Nb ₂ O ₅ -Ge/GeO ₂ microcomposite for a secondary battery electrode. The first nanonet formed by a plurality of Nb ₂ O ₅ nanoparticles and a plurality of Ge/GeO ₂ nanoparticles whose individual particle diameter is smaller than the particle diameter of the Nb ₂ O ₅ nanoparticles are located outside and inside the first nanonet. An electrode active material for a secondary battery comprising a plurality of Nb ₂ O ₅ -Ge/GeO ₂ microcomposite for secondary battery electrodes, which is a spherical cluster having a three-dimensional network structure including a second nanonet formed by positioning. The method of claim 8,
The Nb ₂ O ₅ nanoparticles are electrode active materials for secondary batteries, characterized in that having an average particle diameter of 10 ~ 100 nm. The method of claim 8,
The plurality of Nb ₂ O ₅ -Ge/GeO ₂ microcomposites have an average particle diameter of 1 to 6 μm. The method of claim 10,
By volume of the average particle diameter within a predetermined range a number having an average particle size of the _{Nb 2 O 5 -Ge / GeO Nb} 2 O to a particle size in excess of ₂ microseconds 9㎛ complex ₅ -Ge / GeO ₂ micro-composite is full of micro-complexes An electrode active material for a secondary battery, characterized in that less than 5% by volume. The method of claim 8,
An electrode active material for a secondary battery, characterized in that the BET specific surface area of the Nb ₂ O ₅ -Ge/GeO ₂ microcomposite is 15 m ² /g or less. An electrode for a secondary battery comprising the electrode active material according to claim 8.

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