KR102219161B1 - Anode actine material conprising polydopamine coating layer for secondary battery and method for preparing the same - Google Patents

Abstract

The present invention relates to a secondary battery negative electrode active material comprising: a graphene oxide (PGO) including a graphene oxide (GO), and a polydopamine coating layer including a polydopamine layer coated on the surface of the graphene oxide (GO); and TNO (TiNb_2O_7) microparticles attached to the surface of the graphene oxide (PGO) including a polydopamine coating layer. According to the present invention, in a secondary battery negative electrode active material, a tight electron conduction pathway can be formed, as TNO (TiNb_2O_7) particles produced by a solvothermal synthesis process are attached to a polydopamine-coated graphene oxide surface by using hydrophilicity and adhesiveness of polydopamine and the TNO (TiNb_2O_7) particles are precisely and uniformly attached to a graphene oxide surface. Accordingly, a secondary battery to which the secondary battery negative electrode of the present invention is introduced has an effect of improving output characteristics and lifespan characteristics.

Description

Anode active material for secondary battery including polydopamine coating layer and its manufacturing method {ANODE ACTINE MATERIAL CONPRISING POLYDOPAMINE COATING LAYER FOR SECONDARY BATTERY AND METHOD FOR PREPARING THE SAME}

The present invention relates to a negative electrode active material for a secondary battery and a method for manufacturing the same, and more particularly, to prepare a negative electrode active material by compounding graphene oxide surface-treated with a polydopamine coating layer to provide a uniform and intimate electrical conduction path. The present invention relates to a negative electrode active material for a secondary battery and a method of manufacturing the same to have high output characteristics and lifetime characteristics when applied to.

Various studies to increase the energy density and stability of lithium-ion batteries have been continuously conducted, and in the case of commercialized graphite in research on anode materials, low capacity and rate characteristics are pointed out as limitations. In addition, the safety of lithium-ion batteries such as deterioration of lifespan characteristics due to irreversible loss of lithium due to the formation of a solid-electrolyte interphase (SEI) layer and generation of lithium dendrites due to electrodeposition on the anode surface. As interest increases, new interlayered cathode oxide materials that can be solved together are being studied. _{Li 4} Ti ₅ O _{12, which} has been attracting much attention recently, is a cathode material that has been discussed as an excellent solution to surface deterioration due to SEI formation due to its high lifespan, output characteristics, and high discharge voltage (1.55 V vs. Li ^{+ /Li).} However, the low theoretical capacity (175 mAh g ^-1 ) has been a major limiting factor in commercialization as a negative electrode material for lithium ion batteries.

_{TiNb 2} O ₇ (TNO) has been considered as an excellent alternative material to overcome the problem of low theoretical capacity as well as the advantages of the same intercalated oxide material. TNO, which was first reported as a lithium-ion battery anode material in 2011 by Professor Goodenough's research team, is Li ₄ Ti ₄ O ₁₂ (175 mAh g ^-1 ), TiO ₂ (335 mAh g ^-1 ). It has 388 mAh g ^-1 ) and discharge voltage (1.65 V), which is from the redox couple of ^{Ti 4 +} /Ti ^{3 +} and Nb ^{5 +} /Nb ^{4 +} Nb ^{4 +} /Nb ^{3 + capable of 5 electron conduction.} However ^{, by increasing the band gap of the titanium-based oxide having an electronic structure of 3d 0,} the electron diffusion behavior is deteriorated and the Li ion conduction is severely limited, which is a high-speed charge in relation to the rate characteristics of the TNO material. /In case of discharging, it causes severe capacity reduction.

Therefore, in order to solve this problem, many improvement measures such as carbon composite, nano-structuring, and hetero-element substitution for TNO materials have been considered. As 2D graphene materials have high electrical conductivity with high surface area, there have been attempts to improve the problem of low electron/ionic conductivity of the negative electrode by compounding it with the negative active material. For example, Ashish's team reported a TNO/graphene hybrid material, which showed a capacity retention rate of 80% at 16 C-rate and a discharge capacity of ^{~230 mAh g -1 at 0.1 C.} In addition, the Li research team synthesized the TNO/graphene complex using a freeze-drying method, and showed a capacity of ^{180 mAh g -1 in a high-speed charge/discharge evaluation of 100 C-rate.}

However, it is difficult to uniformly disperse TNO and graphene in the complex with graphene material. It is difficult to provide an effective conducting matrix because there is no reliable driving force for contact with the TNO particles. To solve this, cetyltrimethylammonium bromide (CTAB) surfactant was introduced. By forming a positive charge on the surface of TNO with a CTAB solution, a relatively negatively charged graphene oxide (GO) was brought into contact with an electrostatic attraction to synthesize TNO wrapped in GO.

Korean Patent Registration No. 10-1999616

An object of the present invention is to solve the problems of the prior art, using the hydrophilicity and adhesion of polydopamine, TNO (TiNb ₂ O ₇ ) particles produced by a solvent heat synthesis process are coated with polydopamine By attaching to the graphene oxide surface, TNO (TiNb ₂ O ₇ ) particles are densely and uniformly attached to the graphene oxide surface to form an electron conducting matrix to provide an anode active material for secondary batteries that improves rate characteristics and lifetime characteristics. Have.

Another object of the present invention is to secure the world competitiveness of the electrochemical capacitor industry by introducing such a negative electrode into a secondary battery, particularly a lithium ion battery, and applying it to an energy storage device included in various electronic and electrical products. .

According to an aspect of the present invention,

Graphene oxide (PGO) including graphene oxide (GO), and a polydopamine coating layer including a polydopamine layer coated on the surface of the graphene oxide (GO); And

A negative electrode active material for a secondary battery comprising; _{TNO (TiNb 2} O ₇ ) microparticles attached to the surface of graphene oxide (PGO) including the polydopamine coating layer is provided.

Graphene oxide (PGO) including the polydopamine coating layer may be a sheet (sheet) type.

The negative active material for a secondary battery may include a monoclinic crystal.

In the negative active material for a secondary battery, a peak located at ^{1220 to 1230 cm -1 according to CN binding may be detected during Fourier transform infrared (FT-IR) analysis.}

In the negative active material for secondary batteries, 400 eV peak, 286 eV peak, 532 eV peak, and 200 to 600 eV peak may be detected upon X-ray photoelectron spectroscopy (XPS) analysis.

The negative active material for secondary batteries may include a (-303) crystal plane.

The TNO microparticles may be microcres secondary particles formed by assembling a plurality of nano-sized primary particles.

The average particle diameter of the TNO microparticles may be 500 to 600 nm.

In the graphene oxide (PGO) including the polydopamine coating layer, polydopamine may be in an amount of 8 to 15 wt%.

The negative electrode active material for a secondary battery may include graphene oxide (PGO) including TNO microparticles and a polydopamine coating layer in a weight ratio of 10:2 to 10:6.

In the negative active material for secondary batteries, the TNO microparticles may surround 80 to 90% of the surface area of the graphene oxide (PGO) including the polydopamine coating layer.

According to another aspect of the invention,

_{(a) preparing TNO (TiNb 2} O ₇ ) microparticles according to solvent heat (solvothermal) synthesis;

(b) preparing polydopamine-coated graphene oxide (PGO) by coating polydopamine on the surface of graphene oxide (GO) according to an ultrasonic process; And

(c) adding the polydopamine-coated graphene oxide (PGO) to a solvent in which the TNO microparticles are dispersed, and attaching the TNO microparticles to the surface of the polydopamine-coated graphene oxide (PGO); There is provided a method of manufacturing a negative active material for a secondary battery including.

Step (a),

(a-1) preparing a mixture by mixing titanium alkoxide, niobium halogenide, and acid in a solvent;

(a-2) preparing a TNO precursor by performing solvothermal synthesis by heating the mixture;

(a-3) washing the TNO precursor; And

(a-4) drying and heat treating the washed TNO precursor to prepare TNO microparticles; may include.

In step (a-2), the solvothermal synthesis may be performed by heating to 180 to 220°C.

Step (b),

(b-1) preparing a buffer solution containing graphene oxide by adding graphene oxide (GO) to the buffer solution and performing ultrasonic treatment;

(b-2) preparing polydopamine-coated graphene oxide (PGO) by adding dopamine hydrochloride to the buffer solution containing graphene oxide and further performing ultrasonic treatment; And

(b-3) washing and drying the graphene oxide coated with the polydopamine; may include.

Step (c),

(c-1) adding the TNO microparticles synthesized in step (a) to distilled water and ultrasonically dispersing it to prepare a TNO dispersion;

(c-2) preparing a PGO dispersion by ultrasonically dispersing the graphene oxide (PGO) coated with the polydopamine synthesized in step (b) in distilled water;

(c-3) preparing a mixed dispersion by dropwise adding the PGO dispersion to the TNO dispersion; And

(c-4) stirring the mixed dispersion for 20 to 40 minutes to allow the TNO microparticles to adhere to the PGO sheet; may include.

According to another aspect of the present invention,

It provides a secondary battery including the negative electrode active material for the secondary battery.

The secondary battery may be a lithium ion battery.

According to another aspect of the present invention,

Any one device selected from a portable electronic device including the secondary battery, a mobile unit, a power device, and an energy storage device is provided.

The negative electrode active material for secondary batteries of the present invention uses the hydrophilicity and adhesive properties of polydopamine to attach TNO (TiNb ₂ O ₇ ) particles prepared by a solvent heat synthesis process to the polydopamine-coated graphene oxide surface. As a result, TNO (TiNb ₂ O ₇ ) particles are densely and uniformly attached to the graphene oxide surface, thereby forming a close electron conduction path. Accordingly, the secondary battery into which the anode active material for a secondary battery of the present invention is introduced has an effect of improving output characteristics and life characteristics.

1 is a flowchart sequentially showing a method of manufacturing an anode active material for a secondary battery according to the present invention.
FIG. 2 is an X-ray diffraction (XRD) structure analysis result of Experimental Example 1. FIG.
3 is a result of Fourier transform infrared (FT-IR) spectroscopic analysis of Experimental Example 2.
4 is a thermogravimetric analysis (TGA) result for quantitative analysis of polydopamine coated on GO of Experimental Example 3.
5 is a thermogravimetric analysis (TGA) result for measuring the weight ratio of TNO and PGO of Experimental Example 4.
6 is an FE-SEM image for analyzing a difference in shape of a complex according to the presence or absence of polydopamine in Experimental Example 5.
7 is an analysis result according to X-ray photoelectron spectroscopy (XPS) of Experimental Example 6.
8 is a transmission electron microscope (TEM) analysis result of Experimental Example 7.
9 is a result of charging and discharging evaluation in Experimental Example 8.
10 is a result of evaluation of charge and discharge cycles in Experimental Example 9.
11 is a result of evaluation of rate characteristics in Experimental Example 10.

Hereinafter, various aspects and various embodiments of the present invention will be described in more detail.

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 may easily implement the present invention.

However, the following description is not intended to limit the present invention to a specific embodiment, and in describing the present invention, when it is determined that a detailed description of a related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted. .

The terms used herein are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, actions, elements, or combinations thereof described in the specification, but one or more other features or It is to be understood that the possibility of the presence or addition of numbers, steps, actions, elements, or combinations thereof is not preliminarily excluded.

Hereinafter, an anode active material for a secondary battery of the present invention will be described.

The negative electrode active material for a secondary battery of the present invention includes graphene oxide (PGO) including a polydopamine coating layer including graphene oxide (GO), and a polydopamine layer coated on the surface of the graphene oxide (GO); _{And TNO (TiNb 2} O ₇ ) microparticles attached to the surface of graphene oxide (PGO) including the polydopamine coating layer.

Graphene oxide (PGO) including the polydopamine coating layer is characterized in that the sheet (sheet) type.

The negative electrode active material for a secondary battery is characterized in that it contains a monoclinic crystal (monoclinic crystal).

In the negative active material for secondary batteries, a peak located at ^{1220 to 1230 cm -1} according to CN binding is detected during Fourier transform infrared (FT-IR) analysis.

The anode active material for secondary batteries is 400 eV peak of N 1s, 286 eV peak of C 1s, O 1s 532 eV peak, and 200 of Nb3d, Nb3p, Ti2p, Ti3s, Ti2s, O1s when analyzed by X-ray photoelectron spectroscopy (XPS) It is characterized by a ~600 eV peak.

The negative active material for secondary batteries may include a (-303) crystal plane.

The TNO microparticles may be micro-sized secondary particles formed by assembling a plurality of nano-sized primary particles.

The TNO microparticles may be spherical particles having an average particle diameter of 500 to 600 nm.

In this way, if TNO nanoparticles are used instead of TNO microparticles as in the past, there is a concern that aggregation between TNO nanoparticles may occur, making it difficult to achieve uniform and dense adhesion to the surface of graphene oxide coated with polydopamine. .

In graphene oxide (PGO) including the polydopamine coating layer, polydopamine may be included in an amount of 8 to 15 wt%, more preferably 10 to 13 wt%, and even more preferably 11 to 12 wt%. . If the polydopamine is contained in an amount of less than 8wt%, it is difficult to impart sufficient adhesion between graphene oxide and TNO microparticles, and if it exceeds 15wt%, the electrical conductivity of graphene oxide (GO) may decrease.

In the negative active material for secondary batteries, it is preferable that the TNO microparticles surround 80 to 90% of the surface area of the graphene oxide (PGO) including the polydopamine coating layer. If the surface area is surrounded by less than 80%, the density of TNO microparticles on the surface of PGO is too low, making it difficult to achieve effective electron transfer between TNO particles.If the surface area is surrounded by more than 90%, the density of TNO microparticles on the surface of PGO It is too high to provide an effective electron transport path to the TNO particles.

Graphene oxide (PGO) comprising the TNO microparticles and the polydopamine coating layer is preferably in a weight ratio of 10:2 to 10:6, more preferably 10:3 to 10:5, even more preferably 10 It may be included in a weight ratio of :4 to 10:4.5. If the content of TNO microparticles is higher than 10:2 in the weight ratio, the density of TNO microparticles on the surface of PGO may be too high to provide an effective electron transport path to the TNO particles, and the content of TNO microparticles is higher than 10:6. If this is low, the ratio of the active material reacting with the lithium ions of the negative electrode is lowered, and thus energy density may be lowered.

The negative active material for secondary batteries may contain graphene oxide in an amount of 25 to 30 wt% based on the total weight. If the graphene oxide content is less than 25wt%, it is difficult to provide an effective electron transport path between TNO microparticles, and if it exceeds 30wt%, the TNO microparticles and adhesion to the TNO microparticles are poor because the content of the TNO microparticles and polydopamine is not appropriate. Since the content of the TNO microparticles is insufficient, the energy density of the negative electrode may be lowered.

Graphene oxide having a surface functionalized by the abundant functional groups (-OH catechol group) of the polydopamine has high adhesion to the inorganic surface, so it can have TNO microparticles uniformly and densely attached to the surface. have. In contrast, conventionally, however, TNO particles are inevitably distributed due to a decrease in adhesion due to adhesion of TNO particles to the surface of graphene oxide without polydopamine coating.

The negative electrode active material uniformly and densely attaches TNO microparticles to the polydopamine-coated graphene oxide surface to provide an effective electron transfer path to the TNO particles to form an electron conducting matrix, thereby forming an electron conducting matrix, so that such a negative electrode active material is used as a lithium secondary battery. When applied to, the reduction in capacity due to resistance factors caused by continuous charging and discharging can be minimized by improving electrical conductivity.

1 is a flowchart sequentially showing a method of manufacturing an anode active material for a secondary battery according to the present invention. Hereinafter, a method of manufacturing a negative active material for a secondary battery according to the present invention will be described with reference to FIG. 1.

first, Solvent heat ( solvothermal ) According to the synthesis TNO ( TiNb ₂ O ₇ ) To prepare a micro powder (step a).

Specifically, this step is preferably performed in the following order.

A mixture was prepared by mixing titanium alkoxide, niobium halogenide, and acid in a polar solvent (step a).

The solvent is water, ethanol, methanol, aceton, DMAc (N,N-dimethylene acetamide), NMP (N-Methyl-2-pyrrolidone), DMSO (dimethyl sulfoxide), DMF (N ,N-dimethylformamide), etc., but the scope of the present invention is not limited thereto.

The titanium alkoxide is titanium ethoxide, titanium propoxide, titanium isopropoxide, titanium n-butoxide, titanium tert-butoxide. tert-butoxide), and the like, and more preferably titanium n-butoxide.

The niobium halogenide is preferably niobium chloride, niobium bromide, niobium iodide, or the like, and more preferably niobium chloride.

The acid is preferably acetic acid, boric acid, phosphoric acid, perchloric acid, hydrochloric acid, nitric acid, sulfuric acid, and the like, more preferably acetic acid.

Thereafter, by heating the mixture, solvent heat synthesis is performed to prepare a TNO precursor (step a-2).

The solvothermal synthesis is preferably carried out by heating to 180 to 220 °C, more preferably 190 to 210 °C, even more preferably can be heated to 195 to 205 °C.

The heating is preferably performed for 15 to 30 hours, more preferably 20 to 28 hours, and even more preferably may be performed for 22 to 26 hours.

Next, the TNO precursor is washed (step a-3).

The TNO precursor may be washed with water, methanol, ethanol, propanol, butanol, or the like.

Thereafter, the washed TNO precursor is dried and heat-treated to prepare TNO microparticles (step a-4).

The drying is preferably carried out at 50 to 70 ℃ for 10 to 15 hours.

In addition, the heat treatment is preferably performed at 700 to 1000°C for 1 to 8 hours, and is preferably performed in air.

Next, according to the ultrasonic process Graphene oxide On the surface Polydopamine By coating Polydopamine Coated Graphene oxide To prepare (step b).

It is preferable that this step is specifically performed in the following order.

First, graphene oxide (GO) is added to the buffer solution and subjected to ultrasonic treatment to prepare a buffer solution containing graphene oxide (step b-1).

The ultrasonic treatment may be performed for 20 to 40 minutes, more preferably 25 to 35 minutes.

The graphene oxide is preferably added to the buffer solution in an amount of 0.05 to 0.2% (w/v), more preferably 0.07 to 0.15% (w/v), even more preferably 0.08 to 0.12% (w /v) Can be used.

Next, dopamine hydrochloride is added to the buffer solution containing graphene oxide, and ultrasonic treatment is further performed to prepare graphene oxide (PGO) coated with polydopamine (step b-2).

The ultrasonic treatment may be performed for 20 to 40 minutes, more preferably 25 to 35 minutes.

The dopamine hydrochloride is preferably added to the buffer solution in an amount of 0.01 to 1% (w/v), more preferably 0.02 to 0.08% (w/v), even more preferably 0.05 to 0.06% (w /v) Can be used.

After, above TNO In a solvent in which microparticles are dispersed, the above Polydopamine By adding coated graphene oxide, Polydopamine Coated Graphene oxide On the surface TNO Attach the microparticles (step c).

It is preferable that this step is specifically performed in the following order.

First, the TNO microparticles synthesized in step (a) are added to distilled water and ultrasonically dispersed to prepare a TNO dispersion (step c-1).

Meanwhile, a PGO dispersion is prepared by ultrasonically dispersing graphene oxide (PGO) coated with polydopamine synthesized in step (b) in distilled water (step c-2).

Steps c-1 and c-2 need not be performed sequentially.

Next, the PGO dispersion is added dropwise to the TNO dispersion to prepare a mixed dispersion (step c-3).

At this time, it is preferable to prepare a mixed dispersion by dropwise adding the PGO dispersion to the TNO dispersion liquid by drop per second.

The TNO microparticles and PGO used in this step are preferably mixed in a weight ratio of 10:2 to 10:6, more preferably 10:3 to 10:5, even more preferably 10:4 to 10 It can be mixed in a weight ratio of :4.5.

In the final prepared negative electrode active material for secondary batteries, TNO microparticles surround 80 to 90% of the total surface area of the PGO sheet.

In addition, the TNO microparticles attached to PGO in the final prepared negative electrode active material for secondary batteries have an average particle diameter of 500 to 600 nm and are characterized in that they are spherical secondary particles composed of nano-sized primary particles.

The negative electrode active material for a secondary battery prepared as described above is characterized in that it is a negative electrode active material for a lithium ion battery.

The present invention provides a method of manufacturing a secondary battery including the method of manufacturing the negative active material for a secondary battery.

The secondary battery may be a lithium ion battery.

The present invention provides any one device selected from a portable electronic device, a mobile unit, a power device, and an energy storage device including the secondary battery.

In particular, although not explicitly described in the following examples, in the method for preparing a negative electrode active material for a secondary battery according to the present invention, in step (a), solvents, titanium alkoxides, niobium halogenides and types of acids, solvent heat synthesis The temperature and time, the heat treatment temperature and time of the TNO microparticles, in step (b), the ultrasonic treatment time in steps (b-1) and (b-2), the amount of graphene oxide added to the buffer solution, and graphene oxide A negative electrode active material for a secondary battery was prepared while changing the dopamine hydrochloride input amount to the containing buffer solution, step (c), the dropwise addition rate of the PGO dispersion to the TNO dispersion, and the ratio of the amount of TNO microparticles and PGO used.

The performance was confirmed by performing an electrochemical property test on the negative active material for a lithium secondary battery thus prepared. As a result, unlike other conditions and other numerical ranges, only when all of the following conditions were satisfied, the rate characteristics and life characteristics of the lithium secondary battery were measured to be remarkably high. Such manufacturing conditions are as follows.

In step (a), the solvent is an aqueous ethanol solution or anhydrous ethanol, titanium butoxide, niobium chloride, and acetic acid, and the solvent heat synthesis is performed at 180 to 220°C for 15 to 30 hours, and the TNO microparticles are dried from 700 to Heat treatment at 1000° C. for 1 to 8 hours, in step (b), ultrasonic treatment of steps (b-1) and (b-2) is 20 to 40 minutes, and the amount of graphene oxide added to the buffer solution is 0.05 to 0.2% (w / v), dopamine hydrochloride input to the buffer solution containing graphene oxide is 0.01 to 1% (w / v), in step (c), the dropping rate of the PGO dispersion to the TNO dispersion is one per second Drop by drop, TNO microparticles and PGO are used in a weight ratio of 10:2 to 10:6.

Hereinafter, an embodiment according to the present invention will be described in detail.

[ Example ]

Example One: TNO Particle attached Polydopamine coating Graphene oxide (TNO@PGO) synthesis

(1) Pristine TNO synthesis

Titanium(?)butoxide (Ti(OBu) ₄ , Sigma-Aldrich, 97%) 0.36 g, Niobium(Ⅴ)chloride (NbCl ₅ , Sigma-Aldrich, 99%) 0.55 g and acetic acid 1.32 ml in 100 mL of anhydrous ethanol After mixing for 1 hour, the solution was transferred to a Teflon-lined autoclave, and a solvent heat reaction (heating 5°C/min, 200°C, maintained for 24 hours) was carried out. After the synthesis is complete, the TNO precursor is washed 6 times, 3 times each, using ethanol and distilled water through centrifugation (4000rpm, 13 min). After drying the obtained TNO precursor powder in a vacuum oven at 60° C. for 12 hours or more, post-treatment (heating 5° C./min, 850° C., air atmosphere, maintaining for 4 hours) is performed to synthesize pristine TNO.

(2) PGO synthesis

Add 0.1 g of GO to 100 ml of Tris-buffer solution (10 mM, pH 8.5) and perform the ultrasonic process for 30 minutes, and then add 0.05 g of Dopamine hydrochloride (2-(3,4-Dihydroxyphenyl)ethylamine hydrochloride)(Sigma-Aldrich). Put in and proceed to the ultrasonic process for 30 minutes again. Thereafter, the polydopamine-coated graphene oxide (PGO) is recovered through a vacuum filter. The washing solvent is washed three times with ethanol and distilled water alternately, and dried in a vacuum oven at 60°C for recovery.

(3) TNO@PGO synthesis

After dispersing 0.175 g of Pristine TNO in 25 ml of distilled water, at the same time, 0.075 g of PGO was added to 25 ml of distilled water, followed by ultrasonication for 30 minutes to disperse. At the end of the ultrasonic process, PGO is dropped into the TNO dispersion using a burette. At this time, the rate at which PGO falls is slowly dropped at the rate of one drop per second. Thereafter, after stirring the dispersion for 30 minutes, the PGO powder (TNO@PGO) to which the TNO particles recovered by the vacuum filter are uniformly attached is recovered and dried in a vacuum oven at 60°C.

Comparative example One: Pristine TNO synthesis

Pristine TNO was synthesized in the same manner as in Example 1 (1) Pristine TNO synthesis.

Comparative example 2: TNO@GO synthesis

TNO@GO was synthesized in the same manner as in Example 1, except that GO was not coated with polydopamine and complexed with TNO.

[ Experimental example ]

Experimental example 1: X-ray diffraction (X- ray diffraction , XRD ) Structure analysis

In order to examine the crystal structures of the TNO@PGO of Example 1 and the Pristine TNO powder samples of Comparative Example 1, XRD patterns of each sample were obtained in a 2-theta angle range of 10 to 60, and the results are shown in FIG. 2.

Accordingly, the pristine TNO of Comparative Example 1 and TNO@PGO of Example 1 were the same, and the diffraction peaks of TNO having a monoclinic structure were clearly observed with high intensity. Therefore, it was shown that TNO well maintains high crystallinity even after the complexing process with PGO. However, the diffraction peak for GO was not clearly revealed due to the high crystallinity of the TNO phase.

Experimental example 2: Fourier transform infrared ( FT - IR ) Spectroscopic analysis

In order to synthesize the GO complex in contact with the TNO powder particles effectively, in the present invention, polydopamine was applied for the GO surface coating, and FT-IR analysis was performed to confirm this, and the results are shown in FIG. 3. According to this, in the obtained spectrum of GO, a peak of ^{1379 cm -1} corresponding to OH deformation vibration, a peak corresponding to C=O stretching vibration at ^{1625 cm -1} , and CO (alkoxy) stretching vibration of ^{1042 cm -1} Peaks are found and these are all peaks for GO. The spectrum of the PGO addition to appear are other peaks, for example, that the functional group occurs on the surface of the GO by the amino group with a reducing reaction caused by the poly dopamine is CN stretching vibration peaks related to the CN group 1222 cm ^{- It} can be confirmed as 1. On the other hand, the aforementioned CO peak decreases after polydopamine coating, which contains oxygen due to the partial reduction effect that occurs during polydopamine coating, as a 2014 study by Hu research group at Shanghai Jiao Tong University. It appears that some of the functional groups have been removed, and it can be explained that the size of the -OH stretching vibration peak at ^{~3350 cm -1 decreases.}

Experimental example 3: GO Coated on Polydopamine For quantitative analysis Thermal weight analysis( Thermogravimetric analysis , TGA )

For quantitative analysis of polydopamine coated on GO, TGA curves from room temperature to 600°C were obtained for GO and PGO in an atmospheric atmosphere, and the results are shown in FIG. 4. According to this, there are three sections in which weight reduction occurs in both samples. In the first 30~200℃ section, evaporation of water adsorbed on the GO surface occurs, and in the second 200~300℃ section, pyrolysis of functional groups occurs. In the case of partially reduced PGO, which has relatively reduced surface functional groups by polydopamine coating, the second section becomes smaller, and then pyrolysis of GO occurs in the section above 300℃ where the third weight loss occurs. The weight loss at is 56.07% and 67.33%. Therefore, when comparing the final remaining weight, the difference in weight loss between the two samples, 11.25%, is the amount of polydopamine coated on PGO.

Experimental example 4: TNO Wow PGO For measuring the weight ratio of Thermal weight analysis( TGA )

In order to find out the weight ratio of TNO and PGO after the complexing process of Example 1, a TGA curve was obtained in a temperature range of 800°C at room temperature, and the results are shown in FIG. According to this, in the case of pristine TNO, when it is considered that there is almost no weight loss up to 800℃, as discussed above, in the case of TNO@PGO where the pyrolysis of GO occurs, PGO is 27.0 wt% of the total sample weight, which is the amount in which the weight decreases to ~400℃. It can be seen that it contains.

Experimental example 5: Polydopamine For analysis of the difference in shape of the complex with or without FE - SEM

In order to observe the effect of the polydopamine coating on the shape of the complex, that is, the difference in the shape of the complex depending on the presence or absence of polydopamine, each powder sample was observed using FE-SEM, and the results are shown in FIG. 6. Here, (a) is an FE-SEM image of the TNO@GO complex of Comparative Example 2, and (b) is an image of the TNO@PGO complex of Example 1.

According to this, in (a), in the case of the TNO@GO composite using the polydopamine-coated GO of Comparative Example 2, the spherical TNO particles did not adhere well and the GO surface was observed a lot, and the TNO particles and GO were non-uniform. You can see that it exists in one distribution. On the other hand, in (b) in the case of TNO@PGO of Example 1, it can be seen that TNO and PGO are uniformly distributed, and in particular, TNO particles are attached along the GO surface. This is because TNO has a high contact between TNO and PGO through the ultrasonic process through the adhesiveness of PDA. In this process, polydopamine has hydrophilicity and adhesive properties to obtain uniform dispersion and contact of the composite in the ultrasonic process. can see.

Experimental example 6: X-ray photoelectron spectroscopy ( XPS ) According to the analysis

To find out the surface composition of the samples, XPS analysis was performed and the results are shown in FIG. 7. According to this, the XPS full scan spectrum clearly shows peaks for each element appearing on the surface of each sample. In the spectrum of GO, distinct C1s (286 eV) and O1s (532 eV) peaks appear, and in the case of PGO, N1s (400 eV) peaks appear. In the case of pristine TNO, peaks of Nb3d, Nb3p, Ti2p, Ti3s, Ti2s, and O1s corresponding to the composition of _{TiNb 2} O _{7 appear between 200 and 600 eV in the spectrum.} In the case of TNO@PGO, all the peaks mentioned above appear well, and in particular, the N1s peak contained in PGO is well observed.

Experimental example 7: Transmission electron microscope ( TEM ) analysis

In order to examine the change in the crystal structure of the material in each synthesis step, TEM images, HR-TEM images, and EDS element mapping images were obtained for two powder samples of pristine TNO and TNO@PGO, and are shown in FIG. 8. According to this, TNO is made of spherical secondary particles, like the TEM image of pristine TNO in (a), and the crystal plane in the (-303) direction is well observed in the HR-TEM image, and in the EDS element mapping image, the TNO It can be observed that elements of Nb, Ti, and O are uniformly distributed throughout the particles. In the TEM image of TNO@PGO in (b), the shape of the GO sheet form together with the spherical TNO particles is well observed, and the (-303) crystal plane of TNO is well observed in the HR-TEM image. In the EDS mapping image, element C contained in GO is well observed along with the distribution of elements of Nb, Ti, and O constituting the spherical particles.

Experimental example 8: Charge and discharge evaluation

For the electrochemical evaluation of the electrodes prepared from each sample, a lithium half-cell was assembled, and ^{a C-rate of 0.1 C (1 C = 387.6 mA g -1} ) was 1.0 to 3.0 V (vs. Li ^{+ ).} The charge/discharge curve of the initial cycle was obtained in the voltage range of /Li) and is shown in FIG. 9.

According to this, the pristine TNO of (a) had a charge/discharge capacity of 251.7/269.0 mAh g ^-1 , respectively, and showed a Coulombic efficiency (CE) of 93.57%. The voltage plateau in the 1.65 V region corresponds to the electrochemical reaction associated with the solid-solution reaction expressing the capacity of TNO. In the case of (b), TNO@PGO ^{showed a charge/discharge capacity of 270.0/286.8 mAh g -1} , respectively, and showed 94.14% CE. This is higher reversible capacity than pristine TNO and it seems that a high capacity can be obtained through the formation of a tight and uniform complex with GO having high electrical conductivity. To obtain the electrochemical process of each electrode, a dQ/dV plot was obtained. In the case of pristine TNO in (c), two strong peaks were seen, at 1.66 V (charging process) and 1.68 V (discharging process), respectively. A peak appears, which corresponds to the change in the ionic oxidation number of ^{Nb 5 +} /Nb ^{4 +.} And the small peaks appearing at 1.7 V (discharging process) and 2.1 V (charging process) ^{correspond to Ti 4+} /Ti ³⁺ redox couples. TNO@PGO in (d) also shows peaks related to each redox reaction at the same position as pristine TNO, and it can be seen that TNO reversibly reacts well with lithium even after the complexing process.

Experimental example 9: Charge and discharge Cycle evaluation

The lifespan characteristics of the TNO@PGO complex and pristine TNO electrodes at 1 C-rate after 300 charge/discharge cycles are shown in FIG. 10. According to this, as a result, it can be seen that TNO@PGO has better life characteristics than pristine TNO. After 300 cycle charge/discharge evaluation at 1 C, TNO@PGO has a reversible capacity of 162.1 mAh g ^-1 in the 300th cycle. It showed a lower capacity reduction than pristine TNO, which was only 108.5 mAh g ^-1 , and maintained a high CE of 99.8% even after repeated charging/discharging. This is because TNO particles and PGO are uniformly and closely distributed within the complex to provide an effective electron transport path to TNO, so the decrease in capacity due to resistance factors caused by continuous charging/discharging was well prevented by increasing the electrical conductivity. see.

Experimental example 10: Rate characteristics evaluation

In order to evaluate the output characteristics of each electrode, rate characteristics were evaluated at each current density (1 C, 2 C, 5 C, 10 C, 20 C, 50 C), and the results are shown in FIG. 11. ^{According to this, for Pristine TNO, the charging capacity of 212, 189.7, 147.4, 111.4, 59.28, 9.043 mAh g -1} at 1 C, 2 C, 5 C, 10 C, 20 C and 50 C respectively, and the last 1 C cycle Recovered to 200.6 mAh g ^-1. On the other hand, in contrast, TNO@PGO showed higher charging capacity than pristine TNO of 246.8, 240.4, 214.1, 183.1, 122.6 44.97 mAh g ^{-1 , and 249.2 mAh g -1} again in the last 1 C cycle. It can be seen that the high dose is well recovered after activation. This can confirm the excellent rate characteristics of TNO@PGO. This means that PGO effectively complements the low electrical conductivity of pristine TNO, reducing the electrical resistance when charging/discharging the electrode and greatly enhancing the output characteristics.

In the present invention, a polydopamine coating method was introduced to GO. GO, which has a surface functionalized by the abundant functional groups of polydopamine (-OH catechol group), has high adhesion to inorganic surfaces during synthesis, so that a uniform TNO/GO complex was effectively formed by a simple ultrasonic process. The obtained TNO/PGO complex showed a homogeneous complex shape in which micro-sized TNO particles were densely attached along the GO surface, unlike the non-uniform distribution of each of the GO and the active material when using conventional GO. This has had a profound effect on improving rate characteristics and long life characteristics by forming an electron conduction matrix that provides an easy electron conduction path by connecting each TNO particle well electrically.

In the above, embodiments of the present invention have been described, but those of ordinary skill in the art will add, change, delete or add components within the scope not departing from the spirit of the present invention described in the claims. Various modifications and changes can be made to the present invention by means of the like, and this will also be said to be included within the scope of the present invention.

Claims (19)

Graphene oxide (PGO) including graphene oxide (GO), and a polydopamine coating layer including a polydopamine layer coated on the surface of the graphene oxide (GO); And
_{Including; TNO (TiNb 2} O ₇ ) microparticles attached to the surface of graphene oxide (PGO) including the polydopamine coating layer,
Graphene oxide (PGO) including the polydopamine coating layer is a negative active material for a secondary battery, characterized in that the sheet (sheet) type. delete The method of claim 1,
The negative electrode active material for a secondary battery, characterized in that it comprises a monoclinic crystal (monoclinic crystal). The method of claim 1,
The anode active material for a secondary battery, characterized in that the peak located at ^{1220 to 1230 cm -1} according to CN binding is detected when Fourier transform infrared (FT-IR) analysis. The method of claim 1,
The anode active material for secondary batteries is an anode active material for secondary batteries, characterized in that 400 eV peak, 286 eV peak, 532 eV peak, and 200 to 600 eV peak are detected upon X-ray photoelectron spectroscopy (XPS) analysis. The method of claim 1,
The negative electrode active material for a secondary battery, characterized in that it comprises a (-303) crystal plane. The method of claim 1,
The TNO microparticles are micro-sized secondary particles formed by assembling a plurality of nano-sized primary particles. delete The method of claim 1,
In the graphene oxide (PGO) including the polydopamine coating layer, polydopamine is an anode active material for a secondary battery, characterized in that the content of 8 to 15wt%. The method of claim 1,
The negative electrode active material for a secondary battery is a negative active material for a secondary battery, characterized in that the graphene oxide (PGO) including the TNO microparticles and the polydopamine coating layer is included in a weight ratio of 10:2 to 10:6. The method of claim 1,
The negative active material for a secondary battery is a negative active material for a secondary battery, characterized in that the TNO microparticles surround 80 to 90% of a surface area of graphene oxide (PGO) including the polydopamine coating layer. _{(a) preparing TNO (TiNb 2} O ₇ ) microparticles according to solvent heat (solvothermal) synthesis;
(b) preparing polydopamine-coated graphene oxide (PGO) by coating polydopamine on the surface of graphene oxide (GO) according to an ultrasonic process; And
(c) adding the polydopamine-coated graphene oxide (PGO) to a solvent in which the TNO microparticles are dispersed, and attaching the TNO microparticles to the surface of the polydopamine-coated graphene oxide (PGO); Method for producing a negative active material for secondary battery comprising. The method of claim 12,
Step (a),
(a-1) preparing a mixture by mixing titanium alkoxide, niobium halogenide, and acid in a solvent;
(a-2) preparing a TNO precursor by performing solvothermal synthesis by heating the mixture;
(a-3) washing the TNO precursor; And
(a-4) drying and heat treatment of the washed TNO precursor to prepare TNO microparticles; a method for producing a negative electrode active material for a secondary battery comprising a. The method of claim 13,
In step (a-2), the solvent heat synthesis is performed by heating at 180 to 220°C. The method of claim 12,
Step (b),
(b-1) preparing a buffer solution containing graphene oxide by adding graphene oxide (GO) to the buffer solution and performing ultrasonic treatment;
(b-2) preparing polydopamine-coated graphene oxide (PGO) by adding dopamine hydrochloride to the buffer solution containing graphene oxide and further performing ultrasonic treatment; And
(b-3) washing and drying the graphene oxide coated with the polydopamine; method for producing a negative active material for a secondary battery comprising: The method of claim 12,
Step (c),
(c-1) adding the TNO microparticles synthesized in step (a) to distilled water and ultrasonically dispersing it to prepare a TNO dispersion;
(c-2) preparing a PGO dispersion by ultrasonically dispersing the graphene oxide (PGO) coated with the polydopamine synthesized in step (b) in distilled water;
(c-3) preparing a mixed dispersion by dropwise adding the PGO dispersion to the TNO dispersion; And
(c-4) stirring the mixed dispersion for 20 to 40 minutes so that the TNO microparticles adhere to the PGO sheet; a method for producing a negative electrode active material for a secondary battery comprising: A secondary battery comprising a negative active material for a secondary battery comprising any one selected from claims 1, 3 to 7, and 9 to 11. The method of claim 17,
The secondary battery, characterized in that the lithium ion battery. Any one device selected from a portable electronic device, a mobile unit, a power device, and an energy storage device including the secondary battery of claim 17.

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