KR100704277B1 - Active material for electrical device, method for preparing the same and lithium secondary battery comprising thereof - Google Patents

Abstract

The present invention relates to a novel composite oxide that can be used as an electrode active material of an electric device, and provides a Li ₃ CuFe ₃ O ₇ having a crystal structure of γ-LiFeO ₂ , and a method for producing the same. Provided is an active material for an electric element, and a lithium secondary battery containing the active material with improved capacity and lifespan characteristics.

Electrode active material, lithium secondary battery, active material, γ-LiFeO2, Li3CuFe3O7, large capacity

Description

ACTIVE MATERIAL FOR ELECTRICAL DEVICE, METHOD FOR PREPARING THE SAME AND LITHIUM SECONDARY BATTERY COMPRISING THEREOF

1 is an XRD pattern of Li ₃ CuFe ₃ O ₇ having a crystal structure of γ-LiFeO ₂ prepared by the high phase synthesis of the present invention.

2 is an XRD pattern of Li ₃ CuFe ₃ O ₇ having a crystal structure of γ-LiFeO ₂ prepared by the sol-gel method of the present invention.

3 is an XRD pattern of Li ₃ CuFe ₃ O ₇ .

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4 is a characteristic graph of C-rate (0.2C, 0.1C, 0.02) of the coin cell battery of Example 3.

5 is a graph measuring charge and discharge life of the coin cell battery of Example 3 with respect to C-rate (0.2C, 0.1C, 0.02).

6 is a graph comparing the electrochemical characteristics of the coin cell batteries prepared in Examples 3, 4, and 5 according to the composition of the respective electrode constituents for C-rate (0.2C, 0.1C, 0.02).

7 is a graph showing charge and discharge life characteristics of C-rate (0.1C) of the coin cell batteries prepared in Examples 3, 4, and 5.

The present invention relates to a novel material exhibiting electrochemical properties, and more particularly, to a novel composite oxide that can be used as an active material of a positive electrode or a negative electrode of a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same.

Recently, electronic devices such as portable telephones, video cameras, computers, etc. have been miniaturized as portable devices. In addition to this situation, the battery, the main power supply of these devices, is also becoming smaller. However, as these devices diversify, the power consumed is on the rise. Lithium or lithium ion secondary batteries are one of the batteries that satisfies these requirements because they have a higher energy density and show higher voltage and higher voltage than conventional Ni / Cd batteries or Ni / MH batteries. Lithium ion secondary batteries use a non-aqueous electrolyte solution and use a material capable of inserting and removing lithium as a positive electrode and a negative electrode, and are driven as a battery by separating these two electrodes in a electrolyte by a separator.

The most influential factor on the battery life characteristics is the electrochemical characteristics of the positive electrode and the negative electrode active material, and there have been many studies in the field of the negative electrode active material in recent years.                         

Currently, commercially available negative electrode active materials operate a system through lithium desorption and insertion reaction, but recently, a new type of reaction mechanism has emerged by chemical reaction (decomposition / combination) between lithium and active materials. As the material used for this reaction mechanism, MO (M = Co, Cu, Fe, Ni), Co ₃ O ₄ and the like are known.

However, the conventional active materials have a limitation in improving the capacity of the battery, and thus there is a problem in that the life characteristics of the battery are limited. Therefore, there is a further need for a study on a cathode or an anode active material for a lithium secondary battery that can significantly improve capacity compared with a conventional lithium secondary battery.

Disclosure of Invention It is an object of the present invention to provide a novel Li-Cu-Fe-based composite oxide exhibiting electrochemical properties and a method of manufacturing the same, in consideration of the problems of the prior art.

Another object of the present invention is to provide an active material for an electric device that can significantly improve the conventional capacity.

Still another object of the present invention is to provide a lithium secondary battery containing the active material with improved capacity and lifespan characteristics.

The present invention provides a crystalline composite oxide represented by the following formula (1) to achieve the above object.

[Formula 1]                     

Li ₃ CuFe ₃ O ₇

In addition, the present invention

a) lithium oxide, or lithium salt;

   Ii) copper oxide or copper salt; And

   Iii) iron oxide or iron salt

Mixing each of the equivalent ratios of Li ₃ CuFe ₃ O ₇ ; And

b) calcining the mixture

It provides a method for producing crystalline Li ₃ CuFe ₃ O ₇ comprising a.

In addition, the present invention

a) lithium oxide, or lithium salt;

   Ii) copper oxide or copper salt; And

   Iii) iron oxide or iron salt

Respectively dissolving in a solvent in an equivalent ratio of Li ₃ CuFe ₃ O ₇ to generate a sol;

b) adding a chelate agent to the sol to produce a gel;

c) removing the solvent to obtain a gel powder;

d) sintering the gel powder

It provides a method for producing crystalline Li ₃ CuFe ₃ O ₇ comprising a.

In another aspect, the present invention provides an active material for an electric device comprising crystalline Li ₃ CuFe ₃ O ₇ .

The present invention also provides a lithium secondary battery comprising crystalline Li ₃ CuFe ₃ O ₇ as the active material.

Hereinafter, the present invention will be described in detail.

The present inventors studied a method for improving the capacity of a lithium secondary battery, and when applying Li ₃ CuFe ₃ O ₇ having a crystal structure of γ-LiFeO ₂ to an electric device, the compound exhibited excellent electrochemical properties. In addition, when it is applied as an active material of a lithium secondary battery, it is confirmed that the lithium ion has a storage capacity, and especially when used as a negative electrode active material, the battery capacity is 3 to 4 times higher than that of a conventional carbon-based negative electrode active material. It was confirmed that the improvement, and based on this, the present invention was completed.

The present invention provides a Li ₃ CuFe ₃ O ₇ composite oxide having a crystal structure of γ-LiFeO ₂ as a novel material exhibiting electrochemical properties, and a method for manufacturing the same, comprising an active material for an electric device containing the composite oxide, and It is to provide a lithium secondary battery containing an active material and improved capacity and life characteristics.

Li ₃ CuFe ₃ O ₇ of the present invention has a crystal structure of γ-LiFeO ₂ . Conventionally known γ-LiFeO ₂ has weak electrochemical properties, but the newly synthesized crystalline Li ₃ CuFe ₃ O ₇ of the present invention has the same X-ray diffraction (XRD) pattern and tetragonal (tetragonal) pattern as γ-LiFeO ₂ . While maintaining the crystal structure, it exhibits electrochemical characteristics such as storing electrochemical elements such as lithium ions. In fact, it can be seen that the XRD pattern of Li ₃ CuFe ₃ O ₇ of the present invention is the same as compared with the XRD pattern of γ-LiFeO ₂ . Their XRD patterns are shown in FIGS. 1, 2, and 3.

The composite oxide of crystalline Li ₃ CuFe ₃ O ₇ of the present invention is a new oxide having a very large capacity. Like other oxides known in the art, the initial irreversibility is very large. Therefore, when applying them to the battery, in order to improve the life characteristics and the electrochemical characteristics, by adjusting the morphology of the composite oxide, select the appropriate electrolyte, conductive agent and binder, and adjust the particle size, lithium 2 It is preferable to apply it as an active material of electric elements, such as a tea battery.

Li ₃ CuFe ₃ O ₇ containing the crystal structure of γ-LiFeO ₂ of the present invention exhibits electrochemically specific physical properties. In the case of a lithium secondary battery, both a positive electrode active material and a negative electrode active material can be used. It accepts lithium towards the electrode at 0.5 to 1.0 V, the capacity in this process is 1000 to 1500 mAh / g, and again the voltage traveling to the opposite pole is between 1.0 and 2.0 V. In other words, it is a composite oxide capable of performing both decomposition and reassembly reaction by the movement of lithium. It also has charge and discharge characteristics.

In addition, Li ₃ CuFe ₃ O ₇ containing the crystal structure of γ-LiFeO ₂ of the present invention, when used as a negative electrode active material of a lithium secondary battery, a capacity improvement of 3 to 4 times that of a conventional graphite-based negative electrode active material, The service life characteristic of is also excellent. Therefore, the conventional graphite-based negative electrode active material may be completely replaced or partially replaced. The same effect can also be obtained with the positive electrode active material.

When Li ₃ CuFe ₃ O ₇ containing the crystal structure of γ-LiFeO ₂ of the present invention is applied as a negative electrode active material in a lithium secondary battery, the opposite electrode may be applied with a transition metal oxide or lithium capable of absorbing and releasing lithium ions. In particular, the active material preferably contains Li. Representative active materials comprising Li are most oxides containing Li. Examples include LiMO ₂ (here, M is Co, Ni, Fe, Cr, V, Ti, or Sc), LiMaMbO ₂ (here, Ma is Co, Ni, Fe, Cr, V, Ti, Sc, or Co, Mb is Co, Ni, Fe, Ci, V, Ti, Sc, or Co), LiM ₂ O ₄ (where M is Co, Ni, Fe, Cr, V, Ti, or Sc), Li _x MaO _y (where x, and y are real numbers from 0 to 10, and Ma is Co, Ni, Fe, Cr, V, Ti, or Sc), Li _x MaMbO _y (where x, and y are 0 to 10, Ma is Co, Ni, Fe, Cr, V, Ti, or Sc, Mb is Co, Ni, Fe, Cr, V, Ti, or Sc).

When Li ₃ CuFe ₃ O ₇ containing the crystal structure of γ-LiFeO ₂ of the present invention is applied as a positive electrode active material in a lithium secondary battery, the active material of the counter electrode is preferably a graphite active material.

Li ₃ CuFe ₃ O ₇ containing the crystal structure of γ-LiFeO ₂ of the present invention can be prepared by various methods, and among them, solid phase synthesis and sol-gel method are preferable.

The solid phase synthesis is a raw material of lithium, copper and iron components forming Li ₃ CuFe ₃ O ₇ , and the oxides or salts thereof are mixed at the equivalent ratio of Li ₃ CuFe ₃ O ₇ to be finally obtained, and then fired at high temperature. It is. If the equivalent ratio is selected within the upper and lower limits of 10 equivalent% in each equivalent, there is no difficulty in manufacturing. The firing is preferably carried out in an air atmosphere for 2 to 48 hours at a temperature of 300 to 1200 ℃, more preferably 5 to 24 hours at a temperature of 600 to 1000 ℃.

The sol-gel method is a lithium, copper, a raw material of the iron component constituting the Li ₃ CuFe ₃ O _7, the oxides thereof, or a brush by putting dissolving the salt in each and finally, as the equivalent ratio of trying to Li ₃ CuFe ₃ O ₇ obtain solvent The gel is obtained by adding, chelating agent and aging the pH to neutral (pH 4-10, preferably 6-8). The solvent used can be removed and heated to obtain a powder. The resulting powder is sintered to obtain the final Li ₃ CuFe ₃ O ₇ . If the equivalent ratio is selected within the upper and lower limits of 10 equivalent% in each equivalent, there is no difficulty in manufacturing. The solvent may be a variety of solvents, preferably a polar solvent such as water or alcohol. Chelating agents, such as citric acid, which can be easily burned and volatilized at low temperature sintering, are preferred for obtaining high purity end products. The aging can be easily formed a gel by maintaining 1 to 12 hours at a temperature of 70 to 80 ℃. The sintering is preferably carried out in an air atmosphere for 1 to 48 hours at a temperature of 400 to 1000 ℃.

Li ₃ CuFe ₃ O ₇ containing the crystal structure of γ-LiFeO ₂ of the present invention can be applied not only as an active material of a lithium secondary battery, but also in consideration of the intrinsic electrochemical properties of a super capacitor, It can be applied as an active material of various electric devices such as ultra capacitors, secondary batteries, primary batteries, fuel cells, various sensors, electrolysis devices, electrochemical reactors, and the like.

The present invention will be described in more detail with reference to the following examples. However, an Example is for illustrating this invention and is not limited only to these.

EXAMPLE

Example 1

(Preparation of crystalline Li ₃ CuFe ₃ O ₇ by solid phase synthesis)

Lithium oxide powder as a lithium source, copper oxide powder as a copper source, and iron oxide powder as an iron source were respectively mixed in an equivalence ratio of Li ₃ CuFe ₃ O ₇ , and then heated at 900 ° C. in an electric furnace under an air atmosphere. Firing for a time to obtain a Li ₃ CuFe ₃ O ₇ powder.

XRD diffraction analysis of the powder prepared above is shown in FIG. 1. The XRD pattern (reference pattern; reference) of γ-LiFeO ₂ is shown in FIG. 3.

It can be seen that the prepared crystalline Li ₃ CuFe ₃ O ₇ is the same as the XRD pattern of γ-LiFeO ₂ .

Example 2

(Preparation of crystalline Li ₃ CuFe ₃ O ₇ by sol gel method)

Lithium hydroxide (LiOH) as a lithium source, copper nitrate (Cu (NO ₃ ) ₂ · 6H ₂ O) as a copper source, ferric nitrate (Fe (NO ₃ ) ₃ · 9H ₂ O) Was dissolved in water in an equivalence ratio of Li ₃ CuFe ₃ O ₇ , respectively, and then dissolved in an appropriate amount of citric acid as a chelating agent. After all the material was completely dissolved, the pH of the solution was adjusted to 7 by adding ammonia. The solvent was dried while stirring the solution at a temperature of 70 ° C. to produce a gel.

The resulting gel was heated to a temperature of 60 to 220 deg. C (using 130 deg. C) to decompose and remove citric acid to obtain a powder. Again it was heat-treated to a temperature of 300 ℃ to remove impurities completely.

The resulting powder was calcined in an electric furnace at 600 ° C. under an air atmosphere for 5 hours to obtain Li ₃ CuFe ₃ O ₇ powder.

XRD analysis of the prepared powder is shown in FIG. 2. It can be seen that the prepared crystalline Li ₃ CuFe ₃ O ₇ is the same as the XRD pattern of γ-LiFeO ₂ compared to FIG. 3.

Example 3

(Manufacture of lithium secondary battery)                     

Li ₃ CuFe ₃ O ₇ having a crystal structure of γ-LiFeO ₂ prepared in Example 1, a conductive material (carbon-based KS-6), and a polyvinylidene dichloride (PVDF) binder were mixed with an organic solvent to form a negative electrode. A slurry for the electrode was prepared. The mixing ratio of the negative electrode active material: conductive material: binder at this time was 40: 53: 7 by weight. After applying the slurry on a copper foil (Cu foil), it was dried and roll press (roll press) to a predetermined thickness to prepare a negative electrode.

A positive electrode was formed using lithium foil (Li-fole) as an electrode for supplying lithium ions, and a coin cell was manufactured by plywood with the negative electrode. This battery used a mixed solution having a volume mixing ratio of 1: 1 of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) containing 1 M LiPF ₆ as an electrolyte.

Example 4

A coin cell was manufactured in the same manner as in Example 3, except that the mixing ratio of the negative electrode active material: conductive material: binder was changed to the weight ratio of 60: 33: 7.

Example 5

A coin cell was manufactured in the same manner as in Example 3, except that the mixing ratio of the negative electrode active material: conductive material: binder was changed to the weight ratio of 80: 13: 7.

Charge and discharge characteristics of the coin cell battery prepared in Example 3 were measured, and the results are shown in FIG. 4.

In addition, the coin cell battery prepared in Example 3 was characterized for the C-rate (0.2C, 0.1C, 0.02) and the results are shown in FIG. At this time, 1C was analyzed in the same manner at 700 mAh / g. Looking at the results, the active material of the present invention is a material having a high resistance, the greater the C-rate, the lower the electrochemical properties.

In addition, the charge and discharge life of the coin cell battery prepared in Example 3 for C-rate (0.2C, 0.1C, 0.02) was measured and the results are shown in FIG. 5.

In addition, the coin cell batteries prepared in Examples 3, 4, and 5 were analyzed for C-rate (0.2C, 0.1C, 0.02) and compared with electrochemical characteristics according to the composition of each electrode constituent material. 6 is shown. The results showed that the electrochemical properties improved as the amount of the conductive material increased.

In addition, the charge and discharge life of the coin cell battery prepared in Examples 3, 4, and 5 for C-rate (0.1C) was measured and compared with the life characteristics according to the composition of each electrode constituent material, and are shown in FIG. 7. It was.

Li ₃ CuFe ₃ O ₇ having a crystal structure of γ-LiFeO ₂ of the present invention exhibits electrochemical properties and can be used as a positive electrode or a negative electrode active material of an electric device. In particular, when used as a negative electrode active material of a lithium secondary battery, Exhibits a capacity of 3 to 4 times that of the graphite-based negative electrode active material, and is excellent in life characteristics.

Claims (15)

Crystalline composite oxide represented by the following formula (1): [Formula 1] Li ₃ CuFe ₃ O ₇ The method of claim 1, A crystalline composite oxide, wherein the crystalline composite oxide contains a crystal structure of γ-LiFeO ₂ . a) lithium oxide, or lithium salt;    Ii) copper oxide or copper salt; And    Iii) iron oxide or iron salt Mixing each of the equivalent ratios of Li ₃ CuFe ₃ O ₇ ; And b) calcining the mixture Method for producing a crystalline Li ₃ CuFe ₃ O ₇ comprising a. The method of claim 3, wherein Firing step b) is a method for producing crystalline Li ₃ CuFe ₃ O ₇ is carried out in an air atmosphere for 2 to 48 hours at a temperature of 300 to 1200 ℃. a) lithium oxide, or lithium salt;    Ii) copper oxide or copper salt; And    Iii) iron oxide or iron salt Respectively dissolving in a solvent in an equivalent ratio of Li ₃ CuFe ₃ O ₇ to generate a sol; b) adding a chelate agent to the sol to produce a gel; c) removing the solvent to obtain a gel powder; d) sintering the gel powder Method for producing a crystalline Li ₃ CuFe ₃ O ₇ comprising a. The method of claim 5, Method for producing crystalline Li ₃ CuFe ₃ O ₇ wherein the solvent of step a) is a polar solvent. The method of claim 5, Method for producing crystalline Li ₃ CuFe ₃ O ₇ wherein the chelating agent of step b) is citric acid. The method of claim 5, The sintering of step d) is a method for producing crystalline Li ₃ CuFe ₃ O ₇ is carried out in an air atmosphere for 1 to 48 hours at a temperature of 400 to 1000 ℃. An active material for an electric device comprising a crystalline Li ₃ CuFe ₃ O ₇ composite oxide. The method of claim 9, An active material for an electric device, wherein the active material is a negative electrode active material. The method of claim 9, An active material for an electric device, wherein the active material is a cathode active material. A lithium secondary battery comprising a crystalline Li ₃ CuFe ₃ O ₇ composite oxide as an active material. The method of claim 12, A lithium secondary battery, wherein the active material is a negative electrode active material. The method of claim 12, A lithium secondary battery, wherein the active material is a positive electrode active material. The method of claim 12, A lithium secondary battery, wherein said crystalline Li ₃ CuFe ₃ O ₇ composite oxide contains a crystal structure of γ-LiFeO ₂ .

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