KR100440931B1 - Lithuim vanadium oxide doped with Cu, method for manufacturing thereof and lithium secondary battery usin the same - Google Patents

Abstract

The present invention relates to lithium vanadium oxide (Li _{1 + x} Cu _y V ₃ O ₈ ) doped with copper of Formula 1, a method of manufacturing the same, and a lithium secondary battery employing the same.

Li _{1 + x} Cu _y V ₃ O ₈

Wherein x is 0 to 0.3,

y is 0.1-0.3.

The present invention provides a lithium vanadium oxide in which copper is incorporated using a solid-state reaction as a cathode material, and a lithium secondary battery employing a cathode material according to the present invention has a high capacity and a fast charge / discharge rate. This has the advantage of low production cost.

Description

Lithium vanadium oxide incorporating copper, a method of manufacturing the same, and a lithium secondary battery employing the same {Lithuim vanadium oxide doped with Cu, method for manufacturing applications and lithium secondary battery usin the same}

The present invention relates to a lithium vanadium oxide (Li _{1 + x} Cu _y V ₃ O ₈ ) in which copper is mixed, a method of manufacturing the same, and a lithium secondary battery employing the same. The present invention relates to a lithium vanadium oxide added with copper obtained through a high temperature solid-state reaction, a method for producing the same, and a lithium secondary battery employing the same.

With the rapid development of the information society, the spread of portable information terminal devices such as notebook computers and mobile phones is expanding rapidly. The development of secondary batteries as a power source of such portable information devices and pollution-free electric vehicles has been in the spotlight recently, and for this purpose, development of high-performance secondary batteries having high density energy is essential. Lithium secondary batteries have attracted much attention recently because they have advantages such as lighter, larger theoretical capacity, higher operating voltage, and longer shelf life than conventional secondary batteries.

At present, the theoretical capacity of the carbon-based electrode used as an anode of a lithium secondary battery is 372 Ah / kg, but most metal oxides used as a cathode have a capacity of 200 Ah / kg or less. That is, the main performance limiting factor of the lithium secondary battery can be seen that the cathode material. Typical cathode material of LiCoO _2, LiNiO ₂ has been the center metal is a study for a new kind of metal oxide is conducted in the protection of economic and environment because it represents a rare metal is toxic and is now lithium vanadium oxide also currently used ( LiV ₃ O ₅ ) is actively researched on the electrode material added with various additives.

U.S. Patent No. 6004697 discloses an electrode material in which fluorine is added to lithium vanadium oxide, but an initial discharge capacity value of about 220 mAh has a problem in that the increase in capacity is not so large compared with conventional lithium vanadium oxide electrode materials. have.

On the other hand, the manufacturing method of lithium vanadium oxide is a solid-state reaction (solid-state reaction), hydrothermal reaction (hydrothermal reaction), low temperature synthesis method and the like.

Korean Patent Application No. 98-048459 discloses a method for producing a double oxide film containing lithium and vanadium by using a hydrothermal reaction, but lithium vanadium oxide obtained through the hydrothermal reaction is charged due to the problem of amorphous. It has a disadvantage in that the discharge life is short, and there is a problem in that water molecules are contained in the product due to the nature of the synthesis method, and the reaction process is complicated and the manufacturing cost is high compared to the solid phase reaction.

Accordingly, the first technical problem of the present invention is to add a third material to the conventional lithium vanadium oxide to provide a cathode material which is superior in performance to the conventional cathode material.

A second technical problem of the present invention is to provide a method of manufacturing an electrode material which is simpler and has improved performance than a conventional method of manufacturing lithium vanadium oxide.

A third technical problem of the present invention is to provide a lithium secondary battery employing the cathode material.

Figure 1 shows the results of the X-ray diffraction measurement (x-ray diffraction) to observe the structural change of the lithium vanadium oxide with the incorporation of copper.

2 shows a charge and discharge curve of a lithium secondary battery employing LiV ₃ O ₅ and Li _{1 + x} Cu _y V ₃ O ₈ (y = 0.2) according to the present invention as a cathode material.

Figure 3 shows the life characteristics according to the charge and discharge of a lithium secondary battery employing Li _{1 + x} Cu _y V ₃ O ₈ (y = 0.2) according to the present invention as a cathode material.

4 shows charge and discharge curves of a lithium secondary battery employing a cathode material according to Example 2 and Comparative Examples 1-2 of the present invention.

<Description of the symbols for the main parts of the drawings>

(a) Example 2

(b) Comparative Example 1

(c) Comparative Example 2

In order to achieve the first technical problem, the present invention provides a lithium vanadium oxide having a structure of formula (1).

[Formula 1]

Li _{1 + x} Cu _y V ₃ O ₈

Wherein x is 0 to 0.3,

y is 0.1-0.3.

According to one embodiment of the present invention, in the lithium vanadium oxide, y is preferably 0.2.

In addition, the lithium vanadium oxide may further include DMcT (2,5-dimercapto-1,3,4-thiadiazole).

According to another embodiment of the present invention, the amount of DMcT added is preferably 0.1 to 0.4 relative to lithium. If it is less than 0.1 there is a disadvantage that doping effect does not appear and when it exceeds 0.4 is not preferable because the secondary phase is present.

The present invention is a mixture of lithium carbonate (Li ₂ CO ₃ ), vanadium oxide (V ₂ O ₅ ) and copper oxide (CuO) to achieve the second technical problem, and then heating at 600 ~ 800 ℃;

Cooling the material to room temperature;

It provides a method for producing a lithium vanadium oxide, characterized in that it comprises the step of preparing the material obtained in the above powder and then drying.

According to another embodiment of the present invention, the mixing ratio of lithium carbonate and vanadium oxide is 1: 3 based on the molar ratio of Li and V, and the mixing ratio of copper oxide is preferably 0.1 to 0.3 with respect to Li. . When the mixing ratio of copper oxide is less than 0.1, there is a disadvantage in that the additive effect does not appear, and when it exceeds 0.3, the secondary phase is not preferable.

The manufacturing method according to the present invention may further include DMcT in a mixture of the lithium carbonate, vanadium oxide and copper oxide.

According to a preferred embodiment of the present invention, the mixing ratio of the DMcT is preferably 0.1 to 0.4 with respect to lithium. If it is less than 0.1 there is a disadvantage that doping effect does not appear and when it exceeds 0.4 is not preferable because the secondary phase is present.

In order to achieve the third technical problem, the present invention provides a lithium secondary battery characterized by employing the cathode material obtained above.

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

The cathode material for a lithium secondary battery according to the present invention has a high capacity and excellent charge and discharge life compared to vanadium oxide in which copper is not mixed by adding a small amount of copper oxide during synthesis of lithium vanadium oxide so that copper is incorporated into lithium vanadium oxide during a high temperature solid phase reaction. Its characteristics are that it can be represented.

In the method for producing lithium vanadium oxide according to the present invention, the step of heating after mixing lithium carbonate, vanadium oxide and copper oxide is preferably 1 to 2 hours.

The copper-containing compound according to the present invention causes a decrease in the internal resistance without changing the crystal structure, thereby reducing the IR drop, thereby realizing a high capacity.

The lithium vanadium oxide incorporating copper according to the present invention may further include DMcT (2,5-dimercapto-1,3,4-thiadiazole). DMcT, an organic sulfur-based material, can be changed from monomers to polymers according to redox reactions, and thus has been studied as a cathode material for lithium secondary batteries. According to the present invention, an organic / inorganic composite using DMcT as an organic material and copper as an inorganic material has the following effects. First, the DMcT used has an effect of increasing the number of reactions with the electron, and copper serves to reduce the resistance of the composite, thereby increasing the battery capacity. Second, when the DMcT is inserted into the layered structure, the interlayer distance of the mixed copper is increased to increase the diffusion coefficient of lithium ions, and as a result, the rate-performing property of the cathode material may be improved.

Hereinafter, the present invention will be described in more detail with reference to the following Examples and Experimental Examples, but the present invention is not limited thereto.

<Example 1>

Li ₂ CO ₃ and V ₂ O ₅ were mixed at a molar ratio of Li: V = 1: 1, and copper oxide (CuO) was mixed at a ratio of 0.1 mole with respect to the Li element. Next, dry mixing in a mortar and pestle, and then heated to 700 ℃ using an electric furnace and maintained for 1 hour, and then cooled to room temperature. In order to make the synthesized powder into a powder using a Freezer Mill to prepare a powder and then dried in an oven at 120 ℃ for ₁ day to obtain a Li _{1 + x} Cu _y V ₃ O ₈ powder.

<Example 2>

A lithium vanadium oxide was obtained in the same manner as in Example 1, except that the copper oxide was mixed at a ratio of 0.2 mol to the Li element.

<Example 3>

A lithium vanadium oxide was obtained in the same manner as in Example 1, except that the copper oxide was mixed at a ratio of 0.3 mol to the Li element.

<Example 4>

Li ₂ CO ₃ and V ₂ O ₅ were mixed at a molar ratio of Li: V = 1: 1, and copper oxide (CuO) was mixed at a ratio of 0.1 mole with respect to the Li element. Next, dry mixing in a mortar and pestle, and then heated to 700 ℃ using an electric furnace and maintained for 1 hour, and then cooled to room temperature. In order to make the synthesized powder into a powder using a Freezer Mill to prepare a powder and then dried in an oven at 120 ℃ for ₁ day to obtain a Li _{1 + x} Cu _y V ₃ O ₈ powder. DMcT was dissolved in acetone to maintain a molar ratio of 0.1 to 0.4 relative to lithium, and then the powder obtained above was dispersed. Thus, the slurry mixed with DMcT was dried for 4 hours at 120 ℃ was used as a cathode material.

Comparative Example 1

As described below, LiV ₃ O ₈ was prepared using hydrothermal reaction. LiOH and V ₂ O ₅ powder were dissolved in water at a molar fraction of 2: 3, and then stirred while heating to about 50 ° C. to obtain a reddish brown LiV ₃ O ₈ . The reddish brown precipitate obtained above was filtered off, washed with water and then dried under vacuum at room temperature, and dried at 200 ° C. for 6 hours. The dried LiV ₃ O ₈ precipitate mass was pulverized and used as a cathode powder.

Comparative Example 2

As described below, LiV ₃ O ₈ was prepared using a low temperature synthesis method. After mixing Li ₂ CO ₃ and NH ₄ VO ₃ in an aqueous solution at a molar ratio of 1: 3 (Li: V), the precipitate formed was reacted for 10 hours in an electric furnace at 300 ° C.

Comparative Example 3

A lithium vanadium oxide was obtained in the same manner as in Example 1, except that the copper oxide was mixed at a ratio of 1 mol with respect to the Li element.

<Test Example 1>

X-ray diffraction (X-ray diffraction) was measured to investigate the crystal structure change of Li _{1 + x} V ₃ O _{8 with} or without copper in the cathode materials of Examples 1-3 and Comparative Example 1. The results are shown in FIG. As a result, no significant change was observed in the structure of Li _{1 + x} V ₃ O ₈ even if copper was mixed.

Experimental Example 1

In order to observe the characteristics of the lithium secondary battery as a cathode material, a 2-electrode system as shown in FIG. 2 was manufactured and tested in a glove box under an argon gas atmosphere. The anode was cut and used lithium metal (99.9%, Aldrich), the cathode was acetylene black as the active material and the conductive material obtained in Example 2 and Comparative Example 1, PTFE (polytetrafluoroethylene) as a binder After mixing the pressure was added to prepare an electrode. As the electrolyte, 1M LiPF ₆ / EC: DEC (weight ratio 1: 1) [Merck, Battery grade] was used. The charging and discharging measurement conditions were tested at various current densities in the voltage range of about 2-3.5 V and the characteristics thereof are shown in FIG. 3.

As shown in FIG. 3, the vanadium oxide (Li _{1 + x} V ₃ O ₈ ) of Comparative Example 1 exhibited a capacity of about 220 mAh / g at a current density of 0.5 mA / cm ² , while Example 2 of the present invention In case of using a cathode material containing copper, an increase of about 12% was observed at 247 mAh / g. In order to examine the charge and discharge life characteristics of the material, the change in charge and discharge capacity was observed under constant current conditions, and the results are shown in FIG. 4. In order to be used as an electrode material of a lithium secondary battery, a change in capacity should be small according to charging and discharging. As shown in FIG. 4, vanadium oxide containing copper has a constant capacity according to charging and discharging, and thus it is suitable as a cathode material of a lithium secondary battery. Could know.

Experimental Example 2

In order to measure the charge and discharge characteristics of the cathode material according to Example 5 of the present invention, the current density was 0.2 mA / cm 2, and the charge and discharge voltage range was 2 to 3.2 V, except that the charge and discharge were carried out under the same conditions as in Experimental Example 1. The measurement was made. The initial discharge capacity is very high as compared with 358 mAh / g as Li _{1 + x} V ₃ O ₈ The initial discharge capacity 223 mAh / g and the initial discharge capacity of 247 mAh / g of Li _{1 + x} Cu _y V ₃ O ₈ in the And it was found.

Experimental Example 3

The charge and discharge characteristics of the cathode material obtained in Example 2 and Comparative Example 1-2 were measured. When charging and discharging at a current density of 0.1 mA / cm ² or less in a voltage range of 1 to 3.5 V, 3 mol of lithium ions corresponding to the theoretical capacity are inserted into the lithium vanadium oxide. However, these experimental conditions are much different from the actual operating conditions of the battery, so in this experiment, a constant current experiment was conducted at a current density of 0.2 mA / cm ² in the voltage range of 2 to 3.2 V to investigate the characteristics of the cathode material. The first charge and discharge curve is shown in FIG. 5. The initial discharge capacity of the cathode material according to Example 2 is about 247 mAh / g and the initial discharge capacity of the cathode material according to Comparative Examples 1 and 2 is 182 mAh / g and 125 mAh / g, respectively, by mixing the solid phase It was found that the cathode material obtained through the reaction showed the largest capacity. Using the discharge capacity obtained above, the number of lithium molar intercalated and the cathode utilization compared to the theoretical capacity are shown in Table 1 below.

Theoretical Capacity of Li _{1 + x} V ₃ O ₈ Initial discharge capacity Li (Mall) Cathode utilization (%) Example 2 280 mAh / g 247 mAh / g 2.39 79.6 Comparative Example 1 182 mAh / g 1.96 65.0 Comparative Example 2 125 mAh / g 1.34 44.6

As can be seen from the above results, the lithium vanadium oxide incorporating copper according to the present invention has a capacity in comparison with the capacity (110-200 mAh / g) of the transition metal oxide currently used as a cathode material of a lithium secondary battery. It can be seen that it is very excellent.

The lithium vanadium oxide incorporating copper through the present invention is easy to manufacture, unlike many existing methods, and can develop electrode material materials for lithium secondary batteries at low cost. The lithium secondary battery employing the cathode material according to the present invention exhibits higher capacity than conventional lithium vanadium oxide and has a small capacity reduction even at high current density. In addition, the charging and discharging speed is fast, has a stable life, and has the advantage of low production cost.

Claims (9)

Lithium vanadium oxide having the structure of formula (1). Li _{1 + x} Cu _y V ₃ O ₈ (1) Wherein x is 0 to 0.3, y is 0.1-0.3. The lithium vanadium oxide of claim 1 wherein y is 0.2. The organic / inorganic composite of claim 1 or 2, further comprising DMcT (2,5-dimercapto-1,3,4-thiadiazole). The organic / inorganic composite according to claim 3, wherein the amount of DMcT added is 0.1 to 0.4 with respect to lithium. Mixing lithium carbonate, vanadium oxide (V ₂ O ₅ ) and copper oxide (CuO), and then heating at 600 to 800 ° C .; Cooling the material to room temperature; Method for producing a lithium vanadium oxide, characterized in that it comprises the step of preparing the material obtained in the above powder and then drying. The lithium vanadium oxide according to claim 5, wherein the mixing ratio of the lithium carbonate and the vanadium oxide is 1: 3 based on the molar ratio of Li and V, and the mixing ratio of the copper oxide is 0.1 to 0.3 moles with respect to Li. Manufacturing method. 6. The method of claim 5, further comprising DMcT in the mixture of lithium carbonate, vanadium oxide and copper oxide. The method for producing lithium vanadium oxide according to claim 7, wherein the mixing ratio of DMcT is 0.1 to 0.4 with respect to lithium. The lithium secondary battery which employ | adopted the cathode material in any one of Claims 1-4.