KR102067512B1 - Synthesis of Anode Active Material and Lithium Rechargeable Battery Using the same - Google Patents

Abstract

The present invention relates to a method for manufacturing a high output lithium secondary battery by synthesis of a shape-controlled negative electrode active material, in the case of the negative electrode active material prepared by the manufacturing method according to the present invention by synthesizing the octahedron-shaped nanoparticles to the negative electrode active material of a lithium ion battery The application has an effect of improving the electrical conductivity of the lithium ion battery.

Description

Method of manufacturing a negative electrode active material and a lithium secondary battery comprising the same {Synthesis of Anode Active Material and Lithium Rechargeable Battery Using the same}

The present invention relates to a method for preparing a negative electrode active material and a lithium secondary battery including the negative electrode active material, and more particularly, to a negative electrode active material including a shape-controlled copper nanostructure and a lithium secondary battery including the same.

Lithium secondary battery is the largest part of the secondary battery market. It has high operating voltage and energy density, and is used in various fields such as portable electronic devices, electric vehicles, and energy storage systems (ESS). .

In general, a lithium secondary battery is prepared by using a material capable of intercalation and disintercalation of lithium ions as a cathode and an anode, and filling an organic electrolyte or a polymer electrolyte between a cathode and an anode, and the lithium ion is a cathode and an anode. Electrical energy is generated by oxidation and reduction reaction when inserted and detached at

Currently, carbonaceous materials are mainly used as an electrode active material constituting the negative electrode of a lithium secondary battery. In the case of graphite, the theoretical capacity is about 372 mAh / g, and the actual capacity of commercially available graphite is realized up to about 350 to 360 mAh / g. However, the capacity of the carbonaceous material such as graphite does not meet the lithium secondary battery that requires a high capacity negative electrode active material.

In order to satisfy these demands, there is an example of using an oxide or an alloy thereof with Cu, Ni, Ti, Sn, and the like, which have a higher charge / discharge capacity than carbonaceous materials and which can be electrochemically alloyed with lithium, as an anode active material. .

For example, Cu ₂ O as a negative electrode active material is lithiation / delithiation of lithium ions, and Cu nanocrystals formed during lithiation are dispersed in the LiO ₂ matrix and return to an oxide state during delithiation. The volume expansion of the electrode during such charging / discharging may result in decreasing the electrochemical performance in the lithium secondary battery.

In order to solve such a problem, a method of manufacturing a shape-controlled nanostructure is known. For example, Non-Patent Literature 1 below discloses polyvinylpi as a surfactant in producing a copper oxide nanostructure from a copper precursor. The shape of the nanostructures can be controlled according to the use of rolidone, and the electrochemical properties are changed according to the results.

By the way, when the shape-controlled nanostructure is used as an electrode active material, the electrochemical properties are improved depending on the shape, but there are limitations in meeting the trend of the fuel cell industry which continuously requires high capacity. .

Min-Cheol Kim, Si-Jin Kim, Sang-Beom Han, Da-Hee Kwak, Eui-Tak Hwang, Da-Mi Kim, Cyu-Ho Lee, Hui-Seon Choe and Kyung-Won Park, J. Mater . Chem. A. 2015.3.23003-23010.

The present invention is to provide an electrode active material having high capacity and improved electrical conductivity for high stability and high output of a lithium ion battery.

In addition, the present invention is to provide a lithium ion battery that satisfies high output and high stability.

In order to achieve the above object, the present invention comprises a first step of preparing a copper precursor aqueous solution; A second step of adding and stirring polyvinylpyrrolidone to the copper precursor aqueous solution; A third step of adding and reacting NaOH and an organic acid to the mixed solution of the second step; A fourth step of separating and recovering the reaction product from the reaction solution of the third step; A fifth step of drying the reaction product recovered from the fourth step; And a sixth step of heat-treating the drying result of the fifth step.

In the method of manufacturing a negative electrode active material according to a preferred embodiment, the polyvinylpyrrolidone may be used having a weight average molecular weight of 25,000 to 30,000.

In the method of manufacturing a negative electrode active material according to a preferred embodiment, the polyvinylpyrrolidone may be used in 1,700 to 3,000 parts by weight based on 100 parts by weight of the copper precursor.

In the method of manufacturing a negative electrode active material according to a preferred embodiment, the sixth step may be performed by a method of heat treatment at 200 to 400 ℃, in a more preferred embodiment the sixth step to 180 to 220 ℃ 1 in an air atmosphere The secondary heat treatment may be carried out by a second heat treatment at 280 to 400 ℃ under a nitrogen atmosphere.

In a method of manufacturing a negative active material according to a preferred embodiment, the copper precursor is copper sulfate (CuSO ₄ ), cuprous chloride (CuCl), cupric chloride (CuCl ₂ ), copper nitrate (Cu (NO ₃ ) ₂ ) Any one selected from the group consisting of, copper acetate (CH ₃ COOCu), copper carbonate (CuCO ₃ ), copper cyanide (Cu (CN) ₂ ), copper iodide (CuI), and combinations thereof.

In a preferred embodiment, the first to third steps may be performed at 28 to 32 ℃.

In the method of preparing a negative electrode active material according to a preferred embodiment, the third step is a method of adding NaOH to the mixed solution of the second step and reacting for 0.5 to 1 hour, and adding an organic acid to it for 3 to 4 hours The reducing agent may be used in 2 to 2.2 molar ratios based on 1 mole of the copper precursor, and the organic acid may be used in 0.5 to 0.7 molar ratios based on 1 mole of the copper precursor.

In a method of manufacturing a negative active material according to a preferred embodiment, the organic acid is ascorbic acid (Escorbic acid), erythorbic acid (Erythorbic acid), glucuronolactone (Glucuronolactone), triformin (Triformin, 2,3-diformyloxypropyl formate ) And a combination thereof.

In a preferred embodiment, the fifth step may be performed by drying at 48 to 52 ° C. for 23 to 25 hours.

The present invention also provides a negative electrode active material which is prepared by the manufacturing method according to the above-described example and comprises an octahedral Cu ₂ O nanostructure and carbon.

Here, the carbon may be derived from polyvinylpyrrolidone.

The present invention also provides an electrode comprising the negative electrode active material prepared by the above-described example.

The present invention also provides a lithium ion battery comprising such an electrode.

The method for preparing a negative electrode active material according to the present invention makes it possible to easily control the shape of the Cu ₂ O nanostructure into an octahedral shape exhibiting excellent electrochemical properties, and to use polyvinylpyrrolidone as a carbon source, which contributes to such shape control. This is useful in that way.

Nanostructures prepared in this way are useful as electrode materials having high capacity and improved electrical conductivity, and lithium ion batteries containing them have high industrial value in that they can meet high stability and high output.

1 is an XRD analysis of each negative electrode active material obtained from Example 1 (PVP 0.12) to Example 2 (PVP 0.16).
2 to 3 are SEM analysis results of the negative electrode active material obtained from Example 1 (PVP 0.12) to Example 2 (PVP 0.16), respectively.
4 is a cyclic voltammetry graph of two samples (a) Example 1 (PVP 0.12) and (b) Example 2 (PVP 0.16) measured at a scanning rate of 0.2, 0.5, 1.0 mV / s.
5 shows (a) cycling performance at 200 mA / g, (b) cycling performance at 500 mA / g, (c) 200, of two samples of Example 1 (PVP 0.12), Example 2 (PVP 0.16) High-rate performance at 500, 1000, 2000, 3000 and 200 mA / g.

Hereinafter, the present invention will be described in more detail.

Method for producing a negative electrode active material according to an embodiment of the present invention, the first step of preparing a copper precursor aqueous solution; A second step of adding and stirring polyvinylpyrrolidone to the copper precursor aqueous solution; A third step of adding and reacting NaOH and an organic acid to the mixed solution of the second step; A fourth step of separating and recovering the reaction product from the reaction solution of the third step; A fifth step of drying the reaction product recovered from the fourth step; And a sixth step of heat treating the drying result of the fifth step.

First, a reaction for preparing a negative electrode active material including the Cu ₂ O nanostructure of the present invention is carried out through a series of reduction reactions using a copper precursor, and the copper precursor is a compound capable of forming copper ions under an aqueous solution. For example, copper sulfate (CuSO ₄ ), cuprous chloride (CuCl), cupric chloride (CuCl ₂ ), copper nitrate (Cu (NO ₃ ) ₂ ), copper acetate (CH ₃ COOCu), It may be any one selected from the group consisting of copper carbonate (CuCO ₃ ), copper cyanide (Cu (CN) ₂ ), copper iodide (CuI), and combinations thereof. In a specific example of the present invention, it may be preferable to use cupric chloride hydrate (CuCl ₂ · 2H ₂ O) among these copper precursors.

The copper precursor aqueous solution is prepared using the copper precursor (first step), and then polyvinylpyrrolidone is added thereto and stirred to prepare a mixed solution (second step).

In the second step, the addition of polyvinylpyrrolidone serves to control the particle size and shape of the nanostructure by functioning as a surfactant in reducing the copper ions through subsequent reduction reaction to form Cu ₂ O nanostructures. can do.

Although the stirring time of the first step is not particularly limited, it is preferably 30 minutes to 1 hour, and the stirring time of the second step may also be preferably 30 minutes to 1 hour.

Next, the third step is a step of reacting by adding NaOH and an organic acid to the mixed solution containing a copper precursor aqueous solution and polyvinylpyrrolidone and stirred.

Specifically, the third step is performed by adding NaOH to the mixed solution of the second step and reacting for 0.5 to 1 hour, adding an organic acid thereto and reacting for 3 to 4 hours.

NaOH reacts with copper ions in the mixed solution to form a copper hydroxide.

NaOH may be added in a ratio of 2 to 2.2 moles based on 1 mole of the copper precursor in consideration of the reaction ratio.

On the other hand, the organic acid serves to produce copper oxide through the reaction with the copper hydroxide obtained through the reaction with NaOH, specific examples are ascorbic acid, erythorbic acid, glucuro Nor may be selected from the group consisting of glucuronolactone, triformin (2,3-diformyloxypropyl formate), and a combination thereof, preferably ascorbic acid.

In consideration of the reaction ratio, the organic acid may be preferably used in a molar ratio of 0.5 to 0.7 based on 1 mole of the copper precursor.

In the present invention, the first to third steps described above are all performed in an aqueous solution environment, and the temperature condition is performed at 28 to 32 ° C. to form an octahedral structure of Cu ₂ O nanostructures intended in the present invention. It may be advantageous in that respect.

In the reaction solution that passed through the third step, the octahedral structure Cu ₂ O nanostructures are included as a reaction product, and polyvinylpyrrolidone may be obtained in the form of surrounding the surface of the nanostructures.

This is followed by the step of separating and recovering the reaction product from the reaction solution of the third step (fourth step), wherein the method of separation and recovery is a method of separating and recovering the reaction product present in the solution. Application is possible, and the reaction product may be recovered by centrifugation and filtering with water.

Next, the reaction product thus recovered is dried. At this time, the drying is a process for obtaining a powdery reaction product. When the reaction product is dried at 48 to 52 ° C. for 23 to 25 hours, a sufficiently powdery reaction product can be obtained.

Meanwhile, the polyvinylpyrrolidone in the negative electrode active material manufacturing method of the present invention plays a role as a surfactant for controlling the shape in the production of Cu ₂ O nanostructures, which also ultimately remain in the Cu ₂ O nanostructures In order to act as a carbon source, in terms of these two functional aspects, the weight average molecular weight may be 25,000 to 30,000.

The polyvinylpyrrolidone may be preferably used in an amount of 1,700 to 3,000 parts by weight based on 100 parts by weight of the copper precursor. As the amount of polyvinylpyrrolidone increases, the size of the Cu ₂ O nanostructure becomes smaller. As a result, the desired octahedral structure may be collapsed, and ultimately, there may be a problem of lowering stability as the negative electrode active material. If the amount is too small, there may be a problem that the effect of improving the electrical conductivity by remaining as carbon may be insignificant. In consideration of this point, the amount of polyvinylpyrrolidone used is 1,700 to 3,000 parts by weight, more preferably 1,750 to 2,400 parts by weight based on 100 parts by weight of the copper precursor.

On the other hand, in order to apply the polyvinylpyrrolidone in consideration of the two functions described above, the heat treatment (sixth step) is finally performed on the dried material that has passed through the fifth step. The organic component in the ralidone can be removed as much as possible and the carbon component can be mainly retained.

Preferably in the polyvinylpyrrolidone by carbonizing the money to be preferred in view to maximize the improvement of the electrical conductivity that remains on the nanostructure surface with only only crystalline carbon, but due to this heat-treated Cu ₂ O nano-through heat treatment Preferably, the sixth step may be preferably performed by heat treatment at 200 to 400 ° C., since it should not inhibit the original purpose of controlling the shape of the structure to an octahedral.

Although the first heat treatment at low temperature conditions under nitrogen atmosphere is experimentally simple, it is not possible to maintain the octahedral nanostructure shape through this, preferably first heat treatment at 180 to 220 ° C. under an air atmosphere, It may be preferably carried out by a second heat treatment at 280 to 400 ℃ under a nitrogen atmosphere.

Through such a series of manufacturing methods, an octahedral Cu ₂ O nanostructure and a negative electrode active material including carbon are obtained, wherein the carbon is derived from polyvinylpyrrolidone.

In the description of the present invention, 'carbon' may be defined to include not only elements other than carbon in the molecular chain or even include trace amounts of non-carbon elements to the extent that they are substantially interpreted as crystalline carbon forms. have.

According to the manufacturing method of the present invention, the carbon defined as above may exist in a modified form on the surface of the octahedral Cu ₂ O nanostructure, or may simply exist in a dispersed form.

The obtained negative electrode active material is a nanostructure whose particle size (average particle diameter) is 225 to 260 nm.

The cathode active material thus obtained, a bar which can determine the affect the improvement of the electrical conductivity of the cathode active material only control of the amount of polyvinylpyrrolidone in the method of manufacturing the same, which is the polyvinylpyrrolidone-derived carbon Cu ₂ It can be inferred to improve the electrical conductivity by acting as a carbon source on the O nanostructure.

Such a negative electrode active material obtained according to the present invention may be prepared as an electrode according to a conventional method, for example, a conductive material such as Ketjenblack and a conductive polymer may be mixed as a binder to be prepared as an electrode, but is not limited thereto. .

Such an electrode is particularly useful as a negative electrode of a lithium ion battery, and a lithium ion battery including such a negative electrode can satisfy high stability and high output.

Hereinafter, 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>

Put 0.6820 g so that the 0.01 M CuCl _{2 ·} 2H ₂ O was stirred at 30 ℃ for 30 minutes in H ₂ O 400 ㎖.

Then, 12 g of polyvinylpyrrolidone (Mw = 29,000; 'PVP') was added thereto, stirred at 30 ° C. for 30 minutes, and 40 ml of 2M NaOH was added thereto, followed by 30 minutes at 30 ° C. Was stirred.

And 40 ml of ascorbic acid (0.6 M) was added, followed by stirring at 30 ° C. for 3 hours.

Then, centrifugation was performed at 8000 rpm for 15 minutes and filtered with H ₂ O.

After drying for 24 hours in an oven (temperature 50 ℃), heat treatment for 2 hours at 200 ℃ in air, and then heat treatment for 3 hours at 300 ℃ under a nitrogen atmosphere to synthesize a negative electrode active material.

<Example 2>

Put 0.6820 g so that the 0.01 M CuCl ₂ · 2H ₂ O was stirred at 30 ℃ for 30 minutes in H ₂ O 400 ㎖.

Then, 16 g of polyvinylpyrrolidone (Mw = 29,000; hereinafter 'PVP') was added thereto, stirred at 30 ° C. for 30 minutes, and 40 ml of 2M NaOH was added thereto, followed by 30 minutes at 30 ° C. Was stirred.

And 40 ml of ascorbic acid (0.6 M) was added, followed by stirring at 30 ° C. for 3 hours.

Then, centrifugation was performed at 8000 rpm for 15 minutes and filtered with H ₂ O.

After drying for 24 hours in an oven (temperature 50 ℃), heat treatment at 200 ℃ in air for 2 hours, and then heat treatment at 300 ℃ under nitrogen atmosphere for 3 hours to synthesize a negative electrode active material.

Experimental Example 1

For each negative electrode active material obtained in Examples 1 to 2, the structural characteristics were analyzed by X-ray diffraction analysis (XRD).

As shown in FIG. 1, it was confirmed that the peaks of the samples of the negative electrode active materials (PVP 0.12 and PVP 0.16) obtained in Examples 1 and 2 were identical to the reference peaks of Cu ₂ O (JCPDS 77-0199). Through this, Cu ₂ O was synthesized from Examples 1 and 2, and it was confirmed that the (111) plane was superior to the (200) plane.

In addition, the results of analysis using a scanning microscope (SEM) are shown in Fig. 2 (Example 1, hereinafter referred to as PVP 0.12) and Fig. 3 (Example 2, hereinafter referred to as PVP 0.16). Through this, it can be seen that both samples were obtained as nanostructures having an octahedral shape, and the particle size (average particle diameter) of each sample was measured at about 252 to 230 nm.

Experimental Example 2 Electrochemical Characteristic Analysis

1. Electrochemical Analysis Method

Slurry for the electrochemical analysis of each negative electrode active material obtained from Examples 1 to 2 is 10 wt% of the resultant of Examples 1 to 2 synthesized as the active material, Ketjen as the conductive material based on 100% by weight of the total slurry composition Prepared by stirring 10% by weight of black (Ketjen black) and 10% by weight of polyvinylidene fluoride (hereinafter referred to as 'PVDF') as a binder, the remaining amount of N-methylpyrrolidone (N -methyl-pyrrolidone (hereinafter referred to as 'NMP') was prepared.

The stirred slurry was cast to 2 mil on a copper foil (Cu foil), which is a current collector for cell assembly, and dried in a 110 ° C. oven for 24 hours to remove moisture.

Thereafter, roll pressing was performed to increase the adhesion between the current collector and the active material, and roll pressing was performed at 80% of the electrode thickness, and cut into a size of 1.32 cm ² for a 2032 coin cell. The water removal process was performed by drying for 12 hours in a vacuum oven at ℃.

Coin cell assembly was assembled using lithium metal (FMC Corporation, lithium metal) as a counter electrode in a glove box (<5 ppm, H ₂ O and O ₂ ) filled with argon (Ar).

At this time, a porous membrane made of polyethylene was used to separate the positive electrode and the negative electrode, and as the electrolyte, ethylene carbonate and diethyl carbonate were mixed in a volume ratio of 1: 1. An electrolyte in which 1.1 M lithium phosphate (LiPF ₆ ) (TechonoSemichem) was dissolved was used.

The assembled cell was subjected to a charge / discharge test using a multi-channel battery tester (WBCS300L, Wonatech Co., multichannel battery tester), and the test condition was between charge and discharge in the range of 0 to 3.0 V (vs. Li / Li +). The process was carried out at 25 ℃ with a break of 30 minutes.

The cyclic voltammetry of the samples was carried out at voltage rates of 0.2, 0.5, and 1.0 mV / s, and the charge and discharge evaluation method was performed for 200 cycles at current densities of 200 and 500 mA / g to confirm basic sample stability. It was. In order to evaluate high-rate performance, charging and discharging were performed for 10 cycles at various current densities (200 to 3000 mA / g) to measure high-rate performance.

2. Analysis Results

4 is 0.2, 0.5, the (a) measured with a scanning rate of 1.0 mV / s PVP 0.12, ( b) PVP 0.16 to cyclic voltammetry graph of two samples, both through which the sample Cu ₂ in all the scanning speed O The reaction peaks of were confirmed, and the peaks were about 2.6 V, 1.5 V, and 0.7 V, respectively. At this time, when the voltage shift according to the scanning speed at about 0.7V when Cu ₂ O reacts with lithium ions under the scanning speed conditions of 0.5 mV / s and 1.0 mV / s, it is 370, 80 mV. The smaller the voltage shift, the better the diffusion of lithium ions. From these results, it was confirmed that the PVP 0.16 sample rapidly reacted with lithium ions even at a high scanning speed. It can be inferred that the diffusion is excellent due to improved conductivity through carbon of PVP.

5 shows (a) cycling performance at 200 mA / g, (b) cycling performance at 500 mA / g, (c) 200, 500, 1000, 2000, 3000, 200 mA of two samples of PVP 0.12, PVP 0.16 With high-rate performance at / g, as can be seen from FIG. 5 (a), the cycling performance at 200 mA / g has retention values of 56% and 143% after 200 cycles, respectively. As can be seen from FIG. 5 (b), the cycling performance at 500 mA / g was measured to have 49% and 89% retention values after 200 cycles, respectively. In both current density conditions of 200 and 500 mA / g, it was confirmed that the stability of the PVP 0.16 sample was better.

Therefore, when combining these results, it was confirmed that there is a difference in stability according to the content of PVP, and when comparing the two samples, it was confirmed that the long-term stability of the PVP 0.16 sample with a higher PVP content is better.

On the other hand, Figure 5 (c) is a result of high-rate performance at 200, 500, 1000, 2000, 3000, 200 mA / g of two samples of PVP 0.12, PVP 0.16, two samples at 200, 500 mA / g current density Although the performance is similar, the higher the current density, the higher the current density of 1000, 2000, 3000 mA / g of the PVP 0.12 sample capacity was found to drop rapidly. It was confirmed that the high-rate performance of the PVP 0.16 sample was better, which means that the higher the PVP content, the higher the carbon content, and the higher the conductivity.

As mentioned above, although this invention was demonstrated by the limited embodiment and drawing, this invention is not limited by this, The person of ordinary skill in the art to which this invention belongs, Of course, various modifications and variations are possible within the scope of equivalents of the claims to be described.

Claims (15)

A first step of preparing an aqueous copper precursor solution;
A second step of adding and stirring polyvinylpyrrolidone to the copper precursor aqueous solution;
A third step of adding and reacting NaOH and an organic acid to the mixed solution of the second step;
A fourth step of separating and recovering the reaction product from the reaction solution of the third step;
A fifth step of drying the reaction product recovered from the fourth step; And
A sixth step of heat-treating the drying result of the fifth step,
The polyvinylpyrrolidone has a weight average molecular weight of 25,000 to 30,000, characterized in that 2,350 parts by weight based on 100 parts by weight of the copper precursor,
The sixth step is carried out by a first heat treatment at 180 to 220 ℃ under an air atmosphere, and a second heat treatment at 280 to 400 ℃ under a nitrogen atmosphere,
Method for producing a negative electrode active material. delete delete delete delete The method according to claim 1,
The copper precursor is copper sulfate (CuSO ₄ ), cuprous chloride (CuCl), cupric chloride (CuCl ₂ ), copper nitrate (Cu (NO ₃ ) ₂ ), copper acetate (CH ₃ COOCu), copper carbonate (CuCO ₃ ), copper cyanide (Cu (CN) ₂ ), copper iodide (CuI) and any one selected from the group consisting of a combination thereof,
Method for producing a negative electrode active material. The method according to claim 1,
The first to third steps are characterized in that carried out at 28 to 32 ℃,
Method for producing a negative electrode active material. The method according to claim 1,
The third step is performed by adding NaOH to the mixed solution of the second step and reacting for 0.5 to 1 hour, adding an organic acid thereto and reacting for 3 to 4 hours,
NaOH is used in 2 to 2.2 molar ratio based on 1 mole of copper precursor, organic acid is characterized in that it is used in 0.5 to 0.7 molar ratio based on 1 mole of copper precursor,
Method for producing a negative electrode active material. The method according to claim 1 or 8,
The organic acid is any one selected from the group consisting of ascorbic acid (Esthorbic acid), erythorbic acid (Erythorbic acid), glucuronolactone (Glucuronolactone), triformin (Triformin, 2,3-diformyloxypropyl formate) and combinations thereof Characterized in that,
Method for producing a negative electrode active material. The method according to claim 1,
The fifth step is characterized in that carried out by a method for drying for 23 to 25 hours at 48 to 52 ℃,
Method for producing a negative electrode active material. It is prepared by the manufacturing method of claim 1,
Including octahedral Cu ₂ O nanostructures and carbon,
Negative electrode active material. 12. The method of claim 11 wherein the carbon is derived from polyvinylpyrrolidone,
Negative electrode active material. An electrode comprising a negative electrode active material prepared by the manufacturing method of claim 1. An electrode comprising the negative electrode active material of claim 11. A lithium ion battery comprising the electrode of claim 13 or 14.

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