KR20040091895A - Anode active material for rechargeable lithium battery, producing method thereof and lithium secondary battery using the same - Google Patents

Abstract

PURPOSE: Provided is an anode active material for a lithium secondary battery, which shows high capacity and excellent cycle life characteristics. A method for preparing the same is also provided. CONSTITUTION: The anode active material for a lithium secondary battery comprises a coating layer in which any one element selected from the group consisting of O, F, S and Se is distributed in a concentration gradient different from that of other elements from the top surface of the coating layer. The coating layer has a thickness of 0.1-5 microns. The anode active material is prepared by the method comprising the step of: mixing an anode active material in a buffered solution with a pH of 0.1-5; and drying the resultant mixture.

Description

Anode active material for lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery manufactured using the same.

(Industrial use)

The present invention relates to a negative electrode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery produced using the same. More specifically, the present invention relates to a negative electrode active material for a lithium secondary battery having a high capacity and excellent cycle life characteristics, a method of manufacturing the same, and a lithium secondary battery manufactured using the same.

(Prior Art)

Lithium secondary batteries are manufactured by reversibly inserting and detaching lithium ions as a positive electrode and a negative electrode, and filling an organic or polymer electrolyte between the positive electrode and the negative electrode, and lithium ions are inserted / Electrical energy is generated by oxidation and reduction reactions when desorption.

As a cathode active material of a lithium secondary battery, a chalcogenide compound is used, and examples thereof include LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _1-x Co _x O ₂ (0 <x <1) Composite metal oxides, such as these, are used.

Lithium metal is used as the negative electrode active material, but when lithium metal is used, a battery short circuit occurs due to the formation of dendrite, which is a risk of explosion and is being replaced with a carbon-based material instead of lithium metal. The carbon-based active material used as a negative electrode active material of a lithium secondary battery includes crystalline carbon such as natural graphite and artificial graphite, and amorphous carbon such as soft carbon and hard carbon. The amorphous carbon has a large capacity, but has a problem in that irreversibility is large during charging and discharging. Natural graphite is typically used as the crystalline carbon, and has a theoretical limit capacity of 372 mAh / g, which is used as a negative electrode active material due to its high capacity, but has a serious life deterioration. On the other hand, such a natural graphite (graphite) or carbon-based active material has a theoretical capacity of only about 380 mAh / g, there is a problem that the current negative electrode can not be used in the development of a high capacity secondary battery in the future.

Therefore, currently active research is a negative electrode active material of the metal-based or intermetallic compounds (intermetallic compounds). In particular, Sn, Si, SnO ₂ system has the advantage that the capacity is more than twice the conventional cathode. However, the conventional SnO or SnO ₂ -based negative electrode active material has a disadvantage that the irreversible capacity not only occupies 65% or more of the total capacity, but also has very bad life characteristics. For example, SnO ₂ has an initial discharge capacity of 1450 mAh / g, but has a disadvantage in that the use efficiency is considerably lowered at an initial charge capacity of 650 mAh / g. There is a deterioration characteristic has a serious problem for use in a secondary battery. (Reference paper J. Electrochem. Soc. 144 (6) 1997 Page 2045., J. Electrochem. Soc. 144 (9) 1997 Page 2943.) To overcome this, complex oxides of the Sn ₂ BPO ₆ strain were studied. However, this also has the disadvantage that the initial capacity is sharply dropped.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a negative electrode active material for a lithium secondary battery having a high capacity.

Another object of the present invention is to provide a negative electrode active material for a lithium secondary battery having excellent cycle life characteristics.

Another object of the present invention is to provide a method for producing a negative electrode active material for a lithium secondary battery having high capacity and excellent cycle life characteristics.

1 is a result of an electron probe micro-analysis (EPMA) analysis of Example 3 and Example 4 according to the present invention.

In order to achieve the above object, the present invention provides a negative electrode active material for a lithium secondary battery comprising a coating layer in which an element selected from the group consisting of O, F, S and Se is distributed in different concentration gradients from the surface of the coating layer.

The present invention also (a) mixing step of mixing the negative electrode active material into a buffer solution of pH 0.1 to 5; And (b) a drying step of drying the mixed mixture; It provides a method for producing a negative electrode active material for a lithium secondary battery comprising a coating layer in which the element selected from the group consisting of O, F, S and Se comprising a different concentration gradient from the surface of the coating layer.

The present invention also relates to a compound comprising a reversible intercalation / deintercalation compound of lithium (lithiated intercalation compound) and a material capable of reversibly reacting with lithium to form a lithium-containing compound. A positive electrode including a selected positive electrode active material; An anode including an anode active material for a lithium secondary battery including a coating layer in which elements selected from the group consisting of O, F, S, and Se are distributed in different concentration gradients from the surface of the coating layer; And a nonaqueous electrolyte impregnated in the positive electrode, the negative electrode, and the separator. It provides a lithium secondary battery comprising a.

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

The inventors of the present invention while studying a negative active material for a lithium secondary battery having excellent cycle life characteristics, the coating layer is selected so that the element selected from the group consisting of O, F, S and Se in the negative electrode active material is distributed in a different concentration gradient from the surface of the coating layer As a result of the formed experiment, it was confirmed that a negative active material for a lithium secondary battery having a high capacity and excellent cycle life characteristics could be manufactured, and based on this, the present invention was completed.

The negative electrode active material for a lithium secondary battery of the present invention includes a coating layer in which elements selected from the group consisting of O, F, S, and Se are distributed in different concentration gradients from the surface of the coating layer. When the material selected from the group consisting of O, F, S and Se is oxidized together with the cation of the negative electrode active material and coated with different concentration gradients on the surface of the negative electrode active material, the lithium secondary battery has excellent capacity characteristics and lifespan. A negative electrode active material can be obtained.

The thickness of the coating layer is preferably 0.1 to 5 micron. If the thickness of the coating layer is less than 0.1 micron is not preferable because the effect of coating the negative electrode active material is not preferable, if the thickness of the coating layer exceeds 5 micron, it is not preferable because the capacity and life characteristics of the negative electrode active material worsens.

The manufacturing method of the negative electrode active material for a lithium secondary battery of the present invention will be described in detail as follows.

First, the negative electrode active material is added to a buffer solution of pH 0.1 to 5 and mixed ((a) mixing step).

Sn, SnO ₂ , Si, Mg and the like can be used as the negative electrode active material. The buffer solution is preferably H ₃ PO ₄ . The mixing step is preferably carried out for 1 to 12 minutes. If the mixing time is less than 1 minute, the effect of the coating is insignificant and not preferable. If the mixing time is more than 12 minutes, all of the negative electrode active material is oxidized to lower capacity and lifespan.

Second, the mixture mixed in the mixing step is dried. ((b) drying step)

The drying step is carried out to remove moisture. The drying step is preferably carried out at 100 to 600 ℃. If the temperature of the drying step is less than 100 ℃ is not preferable because the moisture is not sufficiently removed, if it exceeds 300 ℃ is oxidized to the inside of the negative electrode active material is not preferable because the capacity and life characteristics are lowered.

The lithium secondary battery according to the present invention is a compound capable of reversible intercalation / deintercalation of lithium (lithiated intercalation compound), and a material capable of reversibly reacting with lithium to form a lithium-containing compound. A positive electrode comprising a positive electrode active material selected from the group consisting of; An anode including an anode active material for a lithium secondary battery including a coating layer in which elements selected from the group consisting of O, F, S, and Se are distributed in different concentration gradients from the surface of the coating layer; And a nonaqueous electrolyte impregnated in the positive electrode, the negative electrode, and the separator. It includes. The lithium secondary battery of the present invention including a negative active material for a lithium secondary battery including a coating layer in which an element selected from the group consisting of O, F, S, and Se is distributed at different concentration gradients from the surface of the coating layer has a cycle life characteristic. great.

Hereinafter, preferred examples and comparative examples of the present invention are described.

However, the following examples are only preferred embodiments of the present invention and the present invention is not limited to the following examples.

(Example 1)

Sn metal powder was immersed in a buffer solution of pH 3 for 1 minute and then filtered to remove the filtrate and dried in an oven at 150 ℃ for 5 hours. The average particle size of the Sn metal powder was 10 micron. 0.3 g of polyvinylidene fluoride (PVDF, KF1100, Nippon Kureha Chemical) binder, 0.3 g of Super P carbon black and 2.4 g of this dried powder were dissolved in N-methylpyrrolidone (NMP) solution. After mixing in a copper foil (Cu foil) was coated to prepare a pole plate. Using this electrode plate, a 2016-type coin cell was manufactured using Li metal as an anode, and then charged and discharged 10 times between 2.5 and 0 V. As the current density, 0.3 mA / cm ² was used. The electrolyte solution is a mixed solution of ethylene carbonate (EC), diethylene carbonate (DEC) and ethyl-methyl carbonate (EMC) in which 1.03 M LiPF ₆ is dissolved (3/3/4 volume ratio). ) Was used.

(Example 2)

A coin cell was obtained in the same manner as in Example 1, except that the Sn metal powder was immersed in a buffer solution of pH 3 for 3 minutes.

(Example 3)

A coin cell was obtained in the same manner as in Example 1, except that the Sn metal powder was immersed in a buffer solution of pH 3 for 6 minutes.

(Example 4)

A coin cell was obtained in the same manner as in Example 1 except that the Sn metal powder was immersed in a buffer solution of pH 3 for 12 minutes.

(Example 5)

50 g of SnO powder was added to 20 g of a H ₃ PO ₄ solution at pH 2, and mixed for 3 minutes to prepare a negative electrode active material slurry without filtration. The slurry was dried in an oven at 100 ° C. for 1 hour and then calcined at 500 ° C. for 10 minutes.

(Comparative Example 1)

2.4 g of Sn metal powder, 0.3 g of polyvinylidene fluoride (PVDF, KF1100, Kureha Chemical, Japan), and 0.3 g of Super P carbon black were added to a solution of N-methylpyrrolidone (NMP). After mixing, a copper foil (Cu foil) was coated to prepare an electrode plate. Using this electrode plate, a 2016-type coin cell was manufactured using Li metal as an anode, and then charged and discharged 10 times between 2.5 and 0 V. As the current density, 0.3 mA / cm ² was used. Electrolyte solution is a mixed solution of ethylene carbonate (EC), diethylene carbonate (DEC) and ethyl-methyl carbonate (EMC) in which 1.03 M LiPF ₆ is dissolved (3/3/4) Volume ratio).

(Comparative Example 2)

A cell was prepared in the same manner as in Comparative Example 1 except that Sn ₂ BPO ₆ powder was used.

The cycle life of the batteries prepared by the method of Examples 1, 2, 3, 4, 5 and Comparative Examples 1, 2 and 10 between 2.5 and 0 V was evaluated for cycle life, and initial charge and discharge. Doses and doses after 10 rounds were measured and the results are shown in Table 1.

Initial discharge capacity (mAh / g) Initial Charge Capacity (mAh / g) Charge capacity after 10 times (mAh / g) Example 1 830 570 100 Example 2 900 600 200 Example 3 1300 640 450 Example 4 1450 750 600 Example 5 1450 730 560 Comparative Example 1 800 550 50 Comparative Example 2 1000 600 200

As shown in Table 1, the cycle life after 10 times showed that the lithium ion batteries of Examples 1, 2, 3, 4 and 5 were superior to the lithium ion batteries of Comparative Examples 1 and 2, respectively. In the lithium ion batteries of Examples 1 and 2, it can be seen that the life characteristics of the lithium ion batteries of Comparative Example 1 increased by about 50% or more and 20% or more, respectively.

The negative electrode active materials prepared by the methods of Examples 1,2,3,4,5 and Comparative Examples 1,2 were analyzed using Auger Electron Spectroscopy.

In the negative electrode active material of Example 1, oxygen was detected from the surface of the powder to 0.2 micron, whereas oxygen was not detected thereafter, indicating that SnO ₂ was present on the surface. Electron probe micro-analysis (EPMA) analysis of the negative electrode active material of Example 2 found that oxygen was present from the surface to the inside of 0.7 micron.

1 shows the EPMA results of Examples 3 and 4.

As can be seen in Figure 1, the negative electrode active material of Example 3 was found to exist in the oxygen from the surface to the inner 1.4 micron, that is, the presence of SnO ₂ from the surface to 1.4 micron. In the case of the negative electrode active material of Example 4, it was found that oxygen existed from the powder surface to the inner 4 micron. That is, it was found that SnO ₂ exists from the surface to 4 micron. As the time for immersing the negative electrode active material in the buffer increases, oxygen exists deeper from the surface to the inside, and as shown in Table 1 above, the oxygen present deeper from the surface to the inside, the initial capacity and after 10 times It can be found that the capacity of is improved. In the case of the negative electrode active material of Example 5, it was found that P ₂ O ₅ was formed on the surface, a SnO ₂ layer was formed therein, and SnO remained in the core portion.

As a result of the charge / discharge test of the lithium battery manufactured by the method of Comparative Example 1, the initial charge capacity was 550 mAh / g, and after 10 times, the capacity was 50 mAh / g. In addition, in the case of the lithium battery of Comparative Example 2, the initial charge capacity was 600 mAh / g, and after 10 times, the capacity was 200 mAh / g. That is, the surface of the negative electrode active material is coated with a material obtained by oxidizing a different concentration gradient of oxygen, it can be seen that it is excellent in terms of capacity characteristics and life.

The lithium secondary battery containing the negative electrode active material for lithium secondary batteries of the present invention has high capacity and excellent cycle life characteristics.

Claims (8)

An anode active material for a lithium secondary battery comprising a coating layer in which elements selected from the group consisting of O, F, S, and Se are distributed in different concentration gradients from the surface of the coating layer. The method of claim 1, wherein the thickness of the coating layer, A negative active material for a lithium secondary battery, characterized in that 0.1 to 5 micron. (a) a mixing step of mixing the negative active material into a buffer solution of pH 0.1 to 5; And, (b) a drying step of drying the mixed mixture; An element selected from the group consisting of O, F, S and Se comprising a method for producing a negative electrode active material for a lithium secondary battery comprising a coating layer is distributed in a different concentration gradient from the surface of the coating layer. The method of claim 3, wherein the buffer solution, Method for producing a negative electrode active material for a lithium secondary battery, characterized in that H ₃ PO ₄ . The method of claim 3, wherein the drying step, Method for producing a negative electrode active material for a lithium secondary battery, characterized in that carried out at 100 to 600 ℃. The method of claim 3, wherein the mixing step, Method for producing a negative electrode active material for a lithium secondary battery, characterized in that performed for 1 to 12 minutes. A positive electrode active material selected from the group consisting of a compound capable of reversible intercalation / deintercalation of lithium (lithiated intercalation compound) and a material capable of reversibly reacting with lithium to form a lithium-containing compound Anode comprising a; An anode including an anode active material for a lithium secondary battery including a coating layer in which elements selected from the group consisting of O, F, S, and Se are distributed in different concentration gradients from the surface of the coating layer; And A non-aqueous electrolyte impregnated in the positive electrode, the negative electrode, and the separator; Lithium secondary battery comprising a. A positive electrode active material selected from the group consisting of a compound capable of reversible intercalation / deintercalation of lithium (lithiated intercalation compound) and a material capable of reversibly reacting with lithium to form a lithium-containing compound Anode comprising a; A negative electrode comprising a negative electrode active material prepared according to any one of claims 3 to 6; And A non-aqueous electrolyte impregnated in the positive electrode, the negative electrode, and the separator; Lithium secondary battery comprising a.