KR101872639B1 - Preparing method of anode active materials for lithium secondary battery using polymer with snowflake shape - Google Patents

Abstract

The present invention relates to a method of preparing an anode active material for a lithium secondary battery using a polymer with snowflake shape. More specifically, the present invention provides a method of preparing an anode active material for a lithium secondary battery using a polymer with snowflake shape, the method comprising the steps of: dissolving a polymer into a solvent to prepare a mixed solution; mixing the mixed solution with a titanium salt compound and a lithium salt compound and making the mixed solution react with the titanium salt compound and the lithium salt compound to form a precipitate; filtering the precipitate and drying the filtered precipitate to obtain powder; and raising the temperature of the dried powder at an air atmosphere and heat-treating the temperature-raised powder to obtain a snowflake shaped lithium-titanium oxide (LTO). When the anode active material with snowflake shape prepared by the method according to the present invention is applied to an electrode, there is an effect that the anode active material can exhibit high electrochemical properties by inducing improvement of an electrode-electrolyte interfacial area and reducing interfacial resistance due to high specific surface area.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for preparing an anode active material for a lithium secondary battery using a polymer having a snow flake shape,

The present invention relates to a method of manufacturing an anode active material for a lithium secondary battery using a polymer having a snow flake shape applicable to applications requiring high output.

A lithium secondary battery is an energy storage device in which lithium moves from a cathode to an anode during a discharge process and lithium ions move from an anode to a cathode during charging to store electric energy in the battery.

Compared to other cells, the degree of self-discharge with a high energy density is small, and it is used in various projects.

Components of the lithium secondary battery can be divided into an anode, a cathode, an electrolyte, and a separator. In the early lithium secondary battery, lithium metal was used as an anode active material. However, lithium metal was replaced with a carbon-based material such as graphite due to repeated safety of charging and discharging.

The carbonaceous anode active material has a similar electrochemical reaction potential with the lithium ion and is widely used for the development of the anode active material since the crystal structure is not changed during the continuous insertion and desorption of lithium ions and the continuous charge discharge can be performed .

Carbon-based materials are widely used as an anode active material. However, when graphite is used, there is a problem that the cycle is rapidly lowered due to corrosion.

Therefore, in order to overcome the problem that the lifetime of the battery is shortened due to structural stability and side reactions during the reaction, it is urgent to research and develop an anode active material composed of a lithium titanium compound applicable to high power applications.

Korea Patent Publication No. 2015-0102662

An object of the present invention is to provide a method for manufacturing a negative electrode active material for a lithium secondary battery using a polymer having a snow flake shape having a high specific surface area and excellent electrochemical characteristics for application to a lithium secondary battery requiring high stability and high output.

According to an aspect of the present invention, there is provided a method for preparing a mixed solution, comprising: preparing a mixed solution by dissolving a polymer in a solvent; Adding a titanium salt compound and a lithium salt compound to the mixed solution, and then reacting to form a precipitate; Filtering the precipitate and drying to obtain a powder; And a step of heating the dried powder in an atmospheric environment and then subjecting the dried powder to heat treatment to obtain a snowflake-shaped lithium titanium compound (LTO). The method for manufacturing an anode active material for a lithium secondary battery using the Sn- .

When the anode active material having a Sno flake shape manufactured by the method of the present invention is applied to an electrode, it is possible to improve the electrode-electrolyte system area due to a high specific surface area and decrease the interfacial resistance, There is an effect.

1 is a graph showing SEM images (a and b) of a lithium-titanium compound (hereinafter referred to as 'S-LTO') having a Sno flake shape synthesized according to Example 1 and a lithium-titanium nanoparticle compound synthesized according to Comparative Example 1 (D, e) of the S-LTO sample and the XRD pattern (c, f) of the N-LTO sample;
2 is a graph showing a BET analysis result of the S-LTO sample synthesized according to Example 1 and the N-LTO synthesized according to Comparative Example 1;
3 is a graph showing a charge / discharge curve (a) at 160 mAh / g of the S-LTO sample synthesized according to Example 1 and a charge / discharge graph at 160 mAh / g of the N-LTO sample synthesized according to Comparative Example 1 b), the cycling performance (c) of the S-LTO sample synthesized according to Example 1 and the N-LTO synthesized according to Comparative Example 1, and the comparison with the S-LTO sample synthesized according to Example 1 A circulation performance (d) at a current density of 25600 mA / g at 80 mA / g of N-LTO synthesized according to Example 1; And
FIG. 4 is a graph showing the Nyquist polt (a) at 5 cycles of the S-LTO sample synthesized according to Example 1 and the N-LTO synthesized according to Comparative Example 1, S-LTO sample and the Nyquist plot (b) at 250 cycles of N-LTO synthesized according to Comparative Example 1. FIG.

Hereinafter, a method for manufacturing a negative electrode active material for a lithium secondary battery using a polymer having a snow flake shape according to the present invention will be described in detail.

The inventors of the present invention have been studying the synthesis of a lithium titanium compound for a high output lithium secondary battery while synthesizing a polymer acting as a surfactant to form a micelle on a solvent to improve the specific surface area as compared with a nanoparticulate lithium titanium compound The lithium titanium compound can be synthesized, and the lithium-titanium compound thus synthesized can induce the improvement of the area of the electrode-electrolyte system and can exhibit high electrochemical characteristics by reducing the interfacial resistance.

The present invention relates to a method for preparing a mixed solution, comprising: preparing a mixed solution by dissolving a polymer in a solvent; Adding a titanium salt compound and a lithium salt compound to the mixed solution, and then reacting to form a precipitate; Filtering the precipitate and drying to obtain a powder; And a step of heating the dried powder in an atmospheric environment and then subjecting the dried powder to heat treatment to obtain a snowflake-shaped lithium titanium compound (LTO). The method for manufacturing an anode active material for a lithium secondary battery using the Sn- .

The polymer may be any one of pluronic F-68 or pluronic F-127, but is not limited thereto.

The solvent may be any one of n-butanol and tert-butanol, but is not limited thereto.

The step of preparing the mixed solution may include, but is not limited to, adding the polymer to a solvent and stirring the mixture at 40 to 60 ° C for 2 to 4 hours to prepare a mixed solution.

The titanium salt compound may be any one selected from the group consisting of titanium isopropoxide, titanium ethoxide, and titanium butoxide, but is not limited thereto.

The lithium salt compound may be any one selected from the group consisting of lithium acetate, lithium nitrate, lithium sulphate, and lithium chloride (LiCl), but is not limited thereto.

The step of forming the precipitate may include mixing a titanium salt compound and a lithium salt compound in a molar ratio of 5: (4 to 6) to the mixed solution, and then reacting to form a precipitate, but the present invention is not limited thereto.

The step of forming the precipitate may include mixing a titanium salt compound and a lithium salt compound into the mixed solution and then reacting the mixture at 150 to 210 ° C for 18 to 30 hours to form a precipitate, but the present invention is not limited thereto.

The step of obtaining the powder may include filtering the precipitate and drying the powder at 40 to 60 ° C for 36 to 60 hours to obtain a powder, but the present invention is not limited thereto.

In the step of obtaining the snowflake-shaped lithium titanium compound (LTO), the dried powder is heated to 650 to 750 ° C at a heating rate of 3 to 6 ° C / min in an atmospheric environment, and then heat-treated for 8 to 12 hours But is not limited to, obtaining a lithium titanium compound (LTO) in the shape of a snowflake.

The snowflake-shaped lithium titanium compound (LTO) may have an average diameter of 200 to 300 nm, but is not limited thereto.

Hereinafter, a method for producing a negative electrode active material for a lithium secondary battery using a polymer having a snow flake shape according to the present invention will be described in more detail with reference to the following examples. However, the present invention is not limited by these examples.

Example 1 Synthesis of lithium titanium compound (hereinafter referred to as 'S-LTO') having a snow flake shape

A lithium titanium compound (hereinafter referred to as 'S-LTO') having a snow flake shape was synthesized by a hydrothermal synthesis method using an autoclave.

First, 2 g of pluronic F-127 (Sigma Aldrich, pluronic F-127) was added to 72 ml of tert-butanol and the mixture was stirred at 50 ° C for 3 hours (Paste mixer, A homogeneous mixed solution was prepared.

Thereafter, 7.729 g of titanium butoxide (Sigma Aldrich, 97%) and 1.381 g of lithium acetate (Sigma Aldrich, 99.95%) as a lithium salt were used as a titanium salt (molar ratio: Ti : Li = 5: 4.4) was added to the mixed solution, and the mixed solution was reacted at 180 캜 for 24 hours using an autoclave reactor.

The brown precipitates obtained through the reaction were filtered out and dried in an oven at 50 ° C for 48 hours to obtain a dried powder.

The obtained brown powders were heated to 700 ° C. at a rate of 5 ° C./min in an air atmosphere for crystallization and then subjected to heat treatment for 10 hours to obtain a Sn-flake-shaped lithium titanium compound having an average diameter of 200 to 300 nm S-LTO) was synthesized.

Comparative Example 1 Synthesis of nanoparticulate lithium titanium compound (hereinafter referred to as 'N-LTO')

A lithium titanium compound (N-LTO) in nanoparticle form was synthesized under the same conditions as in Example 1, except that Pluronic F-127 was not used.

<Experimental Example 1> Scanning electron microscopic analysis

(SEM) analysis was performed using a scanning electron microscope (SEM) to examine the morphology of the sample synthesized with the variables of Pluronic F-127. And an SEM image is shown in Fig.

Specifically, as a result of observing images observed at a low magnification of the S-LTO sample synthesized using Pluronic F-127 as a surfactant (see FIG. 1 (a)), a diameter of 200 to 300 nm It was confirmed that the particles having a circular shape having

Further, the S-LTO synthesized according to Example 1 of the present invention was observed at a high magnification (see Fig. 1 (b)), and the spherical particles formed a shape similar to snowflake I could confirm.

The above results can be considered as the influence of micelles formed in solvent-derived butanol in the presence of pluronic F-127 as a surfactant during the synthesis of S-LTO.

On the other hand, SEM images (see FIGS. 1D and 1E) of the N-LTO sample synthesized according to Comparative Example 1 were observed. As a result, It can be seen that the nanoparticles are aggregated and this is due to the fact that the use of pluronic F-127 is not used.

Experimental Example 2 X-ray diffraction analysis

XRD patterns were analyzed using X-ray diffraction (XRD) and Rigaku X-ray diffractometer in order to examine the crystallinity of S-LTO and N-LTO samples. 1 (c) and 1 (f).

In particular, both the S-LTO sample and the N-LTO sample can be confirmed to have high crystallinity through the heat treatment at 700 ° C. and Li ₄ Ti ₅ O ₁₂ (JCPDS No. ₂ ) with a face centered cubic spinel. 49-.0207).

In particular, the peak of the N-LTO sample synthesized according to Comparative Example 1 was observed to have a higher intensity relative to the peak of the S-LTO sample synthesized according to Example 1, which is a SEM image (Fig. 1 (d) and (See Fig. 1 (e)) can be considered to be due to aggregation of the nanoparticles.

<Experimental Example 3> Specific surface area analysis

A Brunauer-Emmett-Teller analysis (hereafter, "BET analysis", Micromeritics ASAP 2020) was performed for the quantitative specific surface area analysis of S-LTO and N-LTO samples.

Specifically, the S-LTO sample synthesized according to Example 1 showed a value of 102.59 m ² / g, and the N-LTO sample synthesized according to Comparative Example 1 had a value of 10.17 m ² / g, The specific surface area of the S-LTO sample was measured to be about 10 times higher (see Fig. 2).

As a result, the S-LTO sample and the N-LTO sample synthesized according to Example 1 and Comparative Example 1 were confirmed to be samples having crystallinity.

In particular, the S-LTO sample synthesized according to Example 1 was identified as a Sno flake-like sample having a specific surface area about 10 times higher than that of the N-LTO sample synthesized according to Comparative Example 1 as intended.

The results are shown in Table 1. The results are shown in Table 1. The results are shown in Table 1 and Table 2, respectively. As a result, the structure of the S-LTO sample synthesized according to Example 1 and the N-LTO It can be expected that there is a difference in specific surface area due to the structural difference of the structure of the sample, and the BET analysis can be considered to support the above structural analysis.

<Experimental Example 4> Electrochemical analysis

1. Electrochemical analysis method

For electrochemical analysis of the S-LTO and N-LTO samples synthesized according to Example 1 and Comparative Example 1, the slurry was analyzed by S-LTO sample synthesized according to Example 1 and Comparative Example 1, respectively, 10 wt% of N-LTO sample, 10 wt% of Ketjen black as a conductive material, and 10 wt% of polyvinylidene fluoride (PVDF) as a binder. N-methyl-pyrrolidone (hereinafter referred to as 'NMP') was added to adjust the viscosity.

The agitated slurry was cast to 2 mils on a current collector Cu foil for cell assembly and dried in a 110 ° C oven for 12 hours to remove moisture.

Thereafter, roll pressing was performed at 80% of the prepared electrode thickness in order to increase the adhesion between the current collector and the active material, and cut to a size of 1.32 cm ² for a 2032 coin cell. Deg.] C for 12 hours in a vacuum oven.

The coin cell assembly was assembled with lithium metal (FMC Corporation, lithium metal) as a counter electrode in argon (Ar) filled grove boxes (<5 ppm, H ₂ O and O ₂ ).

A porous polyethylene separator (Wellcos) was used to separate the positive and negative electrodes, and ethylene carbonate (EC) and di-methyl carbonate (DMC) were mixed at a ratio of 1: 1 (LiPF ₆ ) (TechonoSemichem) was dissolved in a mixed solvent at a volume ratio of 1: 1.

The assembled cells were charged and discharged using a multichannel battery tester (WBCS300L, Wonatech Co., multichannel battery tester). The test conditions were between 1.0 to 3.0 V (vs. Li / Li +) Lt; RTI ID = 0.0 &gt; 25 C. &lt; / RTI &gt;

The S-LTO sample and the N-LTO sample synthesized according to Example 1 and Comparative Example 1 were subjected to charge / discharge evaluation at a current density of 160 mA / g, which is a comparatively low current value, for 250 cycles, The cycle characteristics were evaluated according to the high current density by performing 1000 cycles at a current density of 12800 mA / g, which is an additional high current value.

In order to evaluate the high-rate performance, high-rate characteristics were measured by charging / discharging at various current densities (80 to 25600 mA / g) for 10 cycles each.

2. Analysis results

Figures 3 (a) and 3 (b) show various cycles of the charge / discharge graph of the synthesized sample, which was carried out for 250 cycles at a current density of 160 mA / g at a voltage of 1 to 3 V.

Specifically, both the S-LTO sample and the N-LTO sample synthesized according to Example 1 and Comparative Example 1 exhibit a flat curve indicating the insertion process of LTO and lithium ion at about 1.55 V in the discharge graph , And the flatness curve can be observed in the charging graph in the vicinity of about 1.6 V, which is the theoretical desorption voltage of LTO and lithium ion.

FIG. 3 (c) shows the capacity of each cycle observed during 250 cycles of the charge / discharge cycle.

Specifically, the discharge capacity retention of the S-LTO sample and the N-LTO sample synthesized according to Example 1 and Comparative Example 1 was 94.9% (S-LTO) and 93.6% (N-LTO) And it can be seen that this value does not make a large difference, which is due to the intrinsic high stability of the LTO material.

However, when comparing the average capacities, the S-LTO sample synthesized according to Example 1 showed an average capacity of 160.25 mAh / g, and the N-LTO sample synthesized according to Comparative Example 1 had a capacity of 147.73 mAh / g And the S-LTO sample synthesized according to Example 1 exhibited a relatively high capacity.

In addition, in order to confirm the advantages of the high specific surface area of the S-LTO sample synthesized according to Example 1, the results of the rate-dependence characteristic of observing the change in capacitance as the current density of charge and discharge gradually increases is shown in Fig. 3 d).

Specifically, as the charge and discharge cycles were progressed for 10 cycles with increasing current density from 0.46 C-rate (80 mA / g) to 524 C-rate (25600 mA / g), the relatively high C- -rate (12800 mA / g), the capacity difference between the S-LTO sample and the N-LTO sample synthesized according to Example 1 and Comparative Example 1 occurred.

The S-LTO sample synthesized according to Example 1 was found to have a density of 93.33 mA / g, which was synthesized according to Comparative Example 1, and the average capacity was calculated at a current density of 524 C-rate (25600 mA / The N-LTO sample had an average capacity of 48.84 mA / g and the average capacity of the S-LTO sample synthesized according to Example 1 was 52% higher than that of the N-LTO sample synthesized according to Comparative Example 1.

In general, a sample having a high specific surface area can induce an improvement in the electrolyte-interface reaction, and the interface resistance can also be reduced.

In addition, when the N-LTO sample synthesized according to Comparative Example 1 having a relatively large particle size was charged and discharged at a high current density at a high current density, it was difficult to completely insert and desorb lithium ions into the entire particle within a short time , And electrons also have difficulty in charge / discharge reaction because the distance from the center to the outermost part of the particle becomes longer.

On the other hand, in the case of the S-LTO sample synthesized according to Example 1, since the insertion-desorption distance of the lithium ion is relatively short due to the thin particle shape of about 10 nm which is in the shape of snow flake, The lithium ion can be diffused relatively easily throughout.

These results are related to the low interfacial resistance of the S-LTO sample synthesized according to Example 1 according to the structural characteristics of the lithium titanium compound as described in the previous charge and discharge results, and in order to analyze the quantitative interfacial resistance, 1 and Comparative Example 1, and the S-LTO sample and the N-LTO sample synthesized according to Comparative Example 1 were measured.

4 is a Nyquist plot obtained through impedance analysis. The S-LTO sample and the N-LTO sample synthesized according to Example 1 and Comparative Example 1 were subjected to 5 cycles at a current density of 160 mA / g, And 250 cycles.

Specifically, the S-LTO sample synthesized according to Example 1 showed 19.69 ohms and 13.84 ohms at 5 cycles and 250 cycles, respectively, and the N-LTO samples synthesized according to Comparative Example 1 were 32.22 ohms, And 23.72 ohm.

In all cycles, the interfacial resistance (Rct) of the S-LTO sample synthesized according to Example 1 was measured lower than that of N-LTO synthesized according to Comparative Example 1.

The above results indicate that the interfacial resistance is lowered due to the structural characteristic of the S-LTO sample synthesized according to Example 1 which is the cause of the preceding charge / discharge result. Consequently, the S-LTO sample SnO flakes The shape leads to the improvement of the area of the electrode-electrolyte system due to the high specific surface area, and it can be said that it exhibits high electrochemical characteristics by reducing the interface resistance.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It is to be understood that various modifications and changes may be made without departing from the scope of the appended claims.

Claims (11)

Preparing a mixed solution by dissolving the polymer in a solvent;
Mixing the titanium salt compound and the lithium salt compound in the mixed solution at a molar ratio of 5: (4 to 6) and reacting at 150 to 210 ° C for 18 to 30 hours to form a precipitate;
Filtering the precipitate and drying to obtain a powder; And
Heating the dried powder in an atmospheric environment and then performing heat treatment to obtain a snowflake-shaped lithium titanium compound (LTO);
Wherein the negative active material for a lithium secondary battery is formed by using a polymer having a snow flake shape. The method according to claim 1,
The polymer may be,
A method for preparing an anode active material for a lithium secondary battery, comprising using a polymer having a snow flake shape, wherein the polymer is any one of pluronic F-68 and pluronic F-127. The method according to claim 1,
The solvent may be,
wherein the anode active material is any one selected from the group consisting of n-butanol and tert-butanol. The method according to claim 1,
The step of preparing the mixed solution includes:
A method for preparing a negative active material for a lithium secondary battery, the method comprising: adding a polymer to a solvent and dissolving the mixture at 40 to 60 ° C for 2 to 4 hours to prepare a mixed solution. The method according to claim 1,
The titanium salt compound,
The anode for a lithium secondary battery according to any one of claims 1 to 3, wherein the anode is made of a material selected from the group consisting of titanium isopropoxide, titanium ethoxide and titanium butoxide. A method for manufacturing an active material. The method according to claim 1,
The lithium salt compound,
The lithium secondary battery according to any one of the preceding claims, wherein the lithium secondary battery is any one selected from the group consisting of lithium acetate, lithium nitrate, lithium sulphate, and lithium chloride (LiCl) A method for manufacturing a negative electrode active material for a battery. delete delete The method according to claim 1,
The step of obtaining the powder may include:
Wherein the precipitate is filtered and dried at 40 to 60 ° C for 36 to 60 hours to obtain a powder. The method for producing a negative active material for a lithium secondary battery according to claim 1, The method according to claim 1,
The step of obtaining the snowflake-shaped lithium titanium compound (LTO)
The dried powder is heated in an atmospheric environment at a temperature rising rate of 3 to 6 ° C / min to 650 to 750 ° C and then heat-treated for 8 to 12 hours to obtain a snowflake-shaped lithium titanium compound (LTO) A method for manufacturing a negative electrode active material for a lithium secondary battery using a polymer having a snow flake shape. The method according to claim 1,
The snowflake-shaped lithium titanium compound (LTO)
Wherein the anode active material has an average diameter of 200 to 300 nm.

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