KR20060021252A - Anode active material for secondary battery coated with zirconia and manufacturing method thereof, and secondary battery using same - Google Patents

Abstract

The present invention provides a lithium cobalt-based positive electrode active material for a secondary battery having a surface of particles of a lithium cobalt-based active material coated with zirconia or an alloy containing zirconia or zirconia oxide, and a secondary battery using the same.

Preferably, the surface of the particles of the lithium cobalt-based active material is coated with zirconia or an alloy containing zirconia or zirconia oxide by 0.2% by weight to 2% by weight.

In addition, the present invention is a method for producing a positive electrode active material for a secondary battery, the step of diluting zirconium oxide with isopropyl alcohol to inhibit the reaction with water, the amount of zirconia coated in the resulting solution, 0.2 to 2% by weight Adjust the amount of LiCoO ₂ so that it is added, and then stir it, adding 3-glycidoxyproryltrimethoxysilane as an adhesion promoter during stirring, and stirring Provided is a method for producing a lithium cobalt-based positive electrode active material for a secondary battery comprising the step of evaporating the solvent by heating after completion, and performing a heat treatment after the solvent is evaporated.

Description

Positive electrode active material for secondary battery coated with zirconia and its manufacturing method, and secondary battery using same {POSITIVE ELECTRODE ACTIVE MATERIAL COATED WITH ZIRCONIA, METHOD FOR MANUFACTURING THE SAME, AND SECONDARY CELL USING THIS}

1 is a graph showing the specific resistance characteristics according to Examples 1 to 4 and Comparative Example 1 of the present invention.

2 is a graph showing the cycle life characteristics according to Examples 5 to 8 and Comparative Example 2 of the present invention.

3 is a graph showing initial discharge capacity characteristics during high rate charge and discharge according to Examples 9 to 12 and Comparative Example 3 of the present invention.

4 is a graph showing the high temperature life characteristics according to Examples 13 to 16 and Comparative Example 4 of the present invention.

The present invention relates to a positive electrode active material of a secondary battery, and more particularly, to a positive electrode active material for a secondary battery, a method for manufacturing the same, and a secondary battery using the same, having improved characteristics by coating a surface of the positive electrode active material.

In general, a schematic structure of a lithium-based secondary battery is composed of a positive electrode active material applied to a positive electrode current collector (Ni), a negative electrode active material applied to a negative electrode current collector (Cu), an electrolyte and a separator.

Lithium metal was initially used as a negative electrode active material. However, a secondary battery using lithium metal as a negative electrode active material has a significant decrease in capacity as charging and discharging continues, and lithium ions are precipitated to form a dendrite to destroy the separator, thereby shortening the life of the battery. The point was pointed out as a problem. In order to solve this problem, a lithium alloy was used, but the above problems caused when using lithium metal were not greatly improved.

Therefore, in recent years, carbon materials are used as negative electrode active materials by using the principle that the electric energy values stored and released during the process of intercalating and deintercalating Li ions in the electrolyte into the carbon material are different. Doing.

Lithium metal or lithium transition metal oxide (LiCoO ₂ ), LiNiO ₂ , LiMn ₂ , LiNiO ₂ , LiMn ₂ O _4, etc. are used as the positive electrode active material, and an organic electrolyte or a solid polymer electrolyte is used as the electrolyte. Furnace uses a polyethylene-based porous polymer.

Since determining the battery capacity of the lithium battery is substantially a positive electrode active material, the positive electrode active material related technology in the lithium battery technology field occupies a very important position. In particular, the LiCoO ₂ (lithium cobalt-based) active material of the positive electrode active material has a large discharge capacity and excellent charge and discharge characteristics.

However, lithium cobalt-based positive electrode active material is likely to collapse the layer structure of LiCoO ₂ as the insertion and desorption of Li ions are repeated. That is, the layer structure of LiCoO ₂ is a shape in which Li ions are supported by pillars between layers of CoO ₂ , but when Li ions are released during charging, the layer structure is in an unstable state where deformation is easy. If the layer structure is deformed after the Li ions are released, Li ions cannot be inserted into the modified structure. Therefore, as the charge and discharge are repeated, the discharge capacity of the lithium battery decreases, and the cycle characteristics deteriorate.

In particular, when the lithium battery is charged at a high voltage, the leakage of Li is greater than that at the low voltage, so that the layer structure is more likely to collapse. Therefore, it is difficult to repeat charge and discharge under a high voltage.

In addition, as the Li ions are released from LiCoO ₂ during charging, the cobalt (Co) ions are changed from trivalent to tetravalent, and the cobalt ions are changed to a state that is likely to cause side reactions with the electrolyte. That is, as charge and discharge are repeated, cobalt ions are dissolved in the electrolyte, and as a result, the structure of LiCoO ₂ is collapsed.

In addition, a lithium battery using a lithium cobalt-based positive electrode active material has a problem in that battery life sharply decreases, particularly at high temperatures.

In order to solve these problems, in order to prevent the crystal lattice collapse of LiCoO ₂ during high-rate charging and discharging, a non-aqueous secondary battery using lithium cobalt acid containing a zirconium compound as a cathode active material in the manufacturing step of lithium cobalt is proposed. There is a bar.

For example, a non-aqueous secondary battery using a positive electrode active material in which zirconium having a molar ratio of 1 to 10% of cobalt is added to lithium cobalt or a composite oxide in which a part of cobalt is substituted with a transition metal among these compounds has been proposed.

However, although the lithium cobalt-based composite oxide added with zirconium atoms slightly improved the cycle characteristics, this improved the cycle characteristics at the expense of the discharge capacity, which inevitably causes the discharge capacity to decrease.

In addition, attempts have been made to improve cycle characteristics by improving the electrical conductivity of lithium cobalt-based metal oxides, but this method cannot prevent the structural collapse of lithium cobalt-based metal oxides themselves. In addition, in order to mix the conductive material, a separate binder must be added so that the conductive material and the metal oxide are well bonded, and as a result, the amount of the active material is relatively reduced, and also due to the nonuniformity of the mixed state of the active material, the conductive material and the binder material. It caused a new problem that the reliability of the battery is lowered.

Accordingly, the present invention provides a lithium cobalt-based cathode active material, a method of manufacturing the same, and a secondary battery using the same as a cathode active material of a lithium secondary battery, the crystal structure of which does not collapse even after repeated charging and discharging. For the purpose of

Another object of the present invention is to provide a lithium cobalt-based positive electrode active material, a method of manufacturing the same, and a secondary battery using the same, having improved thermal conductivity and good life characteristics even at high temperatures.

Still another object of the present invention is to provide a lithium cobalt-based positive electrode active material, a method of manufacturing the same, and a secondary battery using the same, having improved electrical conductivity, reducing the terminal voltage at the end of discharge, and having excellent rate characteristics.

In order to achieve the above object, the present invention provides a lithium cobalt-based positive electrode active material for a secondary battery, and a secondary battery using the same, the surface of the particles of the lithium cobalt-based active material is coated with zirconia or an alloy containing zirconia or zirconia oxide.

Preferably, the surface of the particles of the lithium cobalt-based active material is coated with zirconia or an alloy containing zirconia or zirconia oxide by 0.2% by weight to 2% by weight.

More preferably, zirconia or an alloy containing zirconia or zirconia oxide is coated on the particle surface of the lithium cobalt-based active material by 0.5% by weight.

In addition, the present invention is a method for producing a positive electrode active material for a secondary battery, the step of diluting zirconium oxide with isopropyl alcohol to inhibit the reaction with water, the amount of zirconia coated in the resulting solution, 0.2 to 2% by weight Adjusting the amount of LiCoO ₂ to be added, followed by stirring, and adding 3-glycidoxyproryltrimethoxysilane as an adhesion promoter during stirring, stirring After the completion of the heating to provide a method for producing a lithium cobalt-based positive electrode active material for a secondary battery comprising the step of evaporating the solvent, and the heat treatment after the solvent is evaporated.

In the present invention as described above, since the zirconia is coated on the surface of the lithium cobalt-based oxide, the cobalt element is not replaced by the zirconia element, and thus the lithium cobalt-based oxide crystal is coated with the coating film ( Since it is protected by external force), the collapse of the layered structure due to desorption of lithium ions generated during charging can be suppressed.

In addition, according to the present invention, since the zirconia is coated on the surface of the lithium cobalt-based oxide, the electrolyte solution is prevented from reacting with the cobalt, thereby preventing the cobalt from dissolving in the electrolyte solution and the collapse of the crystal structure.

In addition, according to the present invention, since zirconia having good thermal conductivity is coated on the surface of the lithium cobalt-based oxide, heat generated from the anode can be easily released to the outside, thereby exhibiting good life characteristics even at high temperatures.

In addition, according to the present invention, since the zirconia having good electrical conductivity is coated on the surface of the lithium cobalt oxide, the internal resistance of the anode is reduced, so that the drop in discharge voltage at the end of discharge is suppressed, the rate characteristic is improved, and under high voltage It is possible to obtain a lithium cobalt-based cathode active material which does not deteriorate cycle characteristics even after repeated charging and discharging.

Hereinafter, first, the manufacturing process of the positive electrode active material according to the present invention will be described, and the results of Examples and Comparative Examples using the prepared positive electrode active material will be considered with reference to the drawings.

The process of forming the zirconia film on the surface of the lithium cobalt oxide according to the present invention is as follows.

First, zirconium oxide is diluted with isopropyl alcohol to suppress the reaction with water.

Next, LiCoO ₂ is added to this solution and stirred for 3 hours. At this time, by adjusting the amount of LiCoO ₂ is added, the amount of the coated zirconia is 0.2 to 2% by weight (wt%).

While stirring, 3-glycidoxyproryltrimethoxysilane is added as an adhesion promoter.

Next, the solvent is evaporated by heating at 100 ° C. for 12 hours.

Subsequently, heat treatment at 400 to 700 ° C. produces a lithium cobalt oxide coated with a zirconia layer having a thickness of 1 to 100 nm.

The positive electrode was formed using the positive electrode active material produced through the above process, and the battery characteristics such as cycle characteristics and discharge capacity were investigated.

(Example 1)

After zirconia coated 0.2 wt% (wt%) of LiCoO ₂ and conductive material Super-P together with PVdF used as a binder in an appropriate amount of NMP, when appropriate viscosity was obtained, it was cast on aluminum sheet and dried , And rolled to make an electrode.

At this time, the amount of the zirconia coated LiCoO ₂ and the conductive material was 96%, 2% by weight, respectively. The specific resistance was measured by the electrode manufactured as described above, and the result is shown in FIG. 1.

(Example 2)

LiCoO ₂ coated with 0.5% by weight of zirconia and Super-P, a conductive material, were mixed with PVdF used as a binder in an appropriate amount of NMP. When a suitable viscosity was obtained, it was cast on an aluminum sheet, dried, and rolled to form an electrode. Made.

At this time, the amount of the zirconia coated LiCoO ₂ and the conductive material was 96%, 2% by weight, respectively. The specific resistance was measured by the electrode manufactured as described above, and the result is shown in FIG. 1.

(Example 3)

LiCoO ₂ coated with 1% by weight of zirconia and Super-P, a conductive material, were mixed with PVdF used as a binder in an appropriate amount of NMP. When a suitable viscosity was obtained, it was cast on an aluminum sheet, dried, and rolled to form an electrode. Made.

At this time, the amount of the zirconia coated LiCoO ₂ and the conductive material was 96%, 2% by weight, respectively. The specific resistance was measured by the electrode manufactured as described above, and the result is shown in FIG. 1.

(Example 4)

LiCoO ₂ coated with 2% by weight of zirconia and Super-P conductive material were mixed with PVdF used as a binder in an appropriate amount of NMP. When a suitable viscosity was obtained, it was cast on an aluminum sheet, dried, and rolled to form an electrode. Made.

At this time, the amount of the zirconia coated LiCoO ₂ and the conductive material was 96%, 2% by weight, respectively. The specific resistance was measured by the electrode manufactured as described above, and the result is shown in FIG. 1.

(Comparative Example 1)

Zirconia-coated LiCoO ₂ and the conductive material Super-P were mixed with PVdF used as a binder in an appropriate amount of NMP, and then, when an appropriate viscosity was obtained, they were cast on an aluminum sheet, dried, and rolled to make an electrode.

At this time, the amount of LiCoO ₂ and the conductive material not coated with zirconia were 96% and 2% by weight, respectively. The specific resistance was measured by the electrode manufactured as described above, and the result is shown in FIG. 1.

Referring to the results of Examples 1 to 4 and Comparative Example 1 with reference to Figure 1, when the zirconia according to the present invention using lithium cobalt-based metal oxide coated by 0.2% to 2% by weight, The resistivity was much lower than that without the coating.

However, in the case of coating 0.5% by weight or more of zirconia, even if the weight% of zirconia was increased more than, the difference in specific resistance did not occur significantly.

From the above, it can be seen that when the lithium cobalt-based metal oxide is coated with zirconia having excellent electrical conductivity according to the present invention, the internal resistance of the active material can be greatly reduced.

(Example 5)

LiCoO ₂ coated with 0.2% by weight of zirconia and Super-P, a conductive material, were mixed with PVdF used as a binder in an appropriate amount of NMP. When a suitable viscosity was obtained, it was cast on an aluminum sheet, dried, and rolled to form an electrode. Made.

At this time, the amount of the zirconia coated LiCoO ₂ and the conductive material was 96%, 2% by weight, respectively. A lithium metal plate was used as a negative electrode as a counter electrode, and a PO (Poly Olefine) separator was used as a separator, and an EC: EMC solution in which 1M LiPF6 was dissolved was sufficiently wetted in the separator as an electrolyte. Then, the charge and discharge rate was set to C / 5, and the electrode capacity and cycle life based on the LiCoO ₂ electrode were examined, and the results are shown in FIG. 2.

(Example 6)

LiCoO ₂ coated with 0.5% by weight of zirconia and Super-P, a conductive material, were mixed with PVdF used as a binder in an appropriate amount of NMP. When a suitable viscosity was obtained, it was cast on an aluminum sheet, dried, and rolled to form an electrode. Made.

At this time, the amount of the zirconia coated LiCoO ₂ and the conductive material was 96%, 2% by weight, respectively. A lithium metal plate was used as a negative electrode as a counter electrode, and a PO (Poly Olefine) separator was used as a separator, and an EC: EMC solution in which 1M LiPF6 was dissolved was sufficiently wetted in the separator as an electrolyte. Then, the charge and discharge rate was set to C / 5, and the electrode capacity and cycle life based on the LiCoO ₂ electrode were examined, and the results are shown in FIG. 2.

(Example 7)

LiCoO ₂ coated with 1% by weight of zirconia and Super-P, a conductive material, were mixed with PVdF used as a binder in an appropriate amount of NMP. When a suitable viscosity was obtained, it was cast on an aluminum sheet, dried, and rolled to form an electrode. Made.

At this time, the amount of the zirconia coated LiCoO ₂ and the conductive material was 96%, 2% by weight, respectively. A lithium metal plate was used as a negative electrode as a counter electrode, and a PO (Poly Olefine) separator was used as a separator, and an EC: EMC solution in which 1M LiPF6 was dissolved was sufficiently wetted in the separator as an electrolyte. Then, the charge and discharge rate was set to C / 5, and the electrode capacity and cycle life based on the LiCoO ₂ electrode were examined, and the results are shown in FIG. 2.

(Example 8)

LiCoO ₂ coated with 2% by weight of zirconia and Super-P, a conductive material, were mixed with PVdF used as a binder in an appropriate amount of NMP. When a suitable viscosity was obtained, it was cast on an aluminum sheet, dried, and rolled. An electrode was made.

At this time, the amount of the zirconia coated LiCoO ₂ and the conductive material was 96%, 2% by weight, respectively. A lithium metal plate was used as a negative electrode as a counter electrode, and a PO (Poly Olefine) separator was used as a separator, and an EC: EMC solution in which 1M LiPF6 was dissolved was sufficiently wetted in the separator as an electrolyte. Then, the charge and discharge rate was set to C / 5, and the electrode capacity and cycle life based on the LiCoO ₂ electrode were examined, and the results are shown in FIG. 2.

(Comparative Example 2)

The zirconia-coated LiCoO ₂ and the conductive material Super-P were mixed with PVdF used as a binder in an appropriate amount of NMP, and then, when an appropriate viscosity was obtained, cast on an aluminum sheet, dried it, and rolled to make an electrode.

At this time, the amount of LiCoO ₂ and the conductive material not coated with zirconia were 96% and 2% by weight, respectively. A lithium metal plate was used as a negative electrode as a counter electrode, and a PO (Poly Olefine) separator was used as a separator, and an EC: EMC solution in which 1M LiPF6 was dissolved was sufficiently wetted in the separator as an electrolyte. Then, the charge and discharge rate was set to C / 5, and the electrode capacity and cycle life based on the LiCoO ₂ electrode were examined, and the results are shown in FIG. 2.

Referring to the results of Examples 5 to 8 and Comparative Example 2 with reference to Figure 2, according to the present invention, the case of using a lithium cobalt-based metal oxide coated with 0.2% to 2% by weight of zirconia as zirconia It can be seen that the cycle properties are much better than the uncoated case.

When the coating was not coated, the discharge capacity was reduced by 20% as the number of charge and discharge cycles exceeded 30 times, and rapidly decreased to 40% or less at around 50 times. In contrast, in the case of using lithium cobalt-based oxide coated with zirconia by 0.2% by weight to 2% by weight according to the present invention, even when the number of charge and discharge cycles reached 50 times, a phenomenon in which the discharge capacity was greatly reduced did not occur. In particular, when the zirconia was coated by 0.5% by weight, there was almost no decrease in the discharge capacity.

This is because even if charge and discharge are repeated in the lithium cobalt-based positive electrode active material, structural collapse due to desorption of Li ions by the zirconia coating film is suppressed, thereby deteriorating cycle characteristics of the positive electrode.

In addition, the zirconia coating film prevents side reactions between the electrolyte solution and the cobalt element, thereby preventing the cobalt element from dissolving in the electrolyte solution and disintegrating the structure of the positive electrode active material as charge and discharge are repeated. In addition, since the positive electrode active material is coated with zirconia having excellent electrical conductivity, the internal resistance of the active material is reduced, thereby improving cycle characteristics.

(Example 9)

LiCoO ₂ coated with 0.2% by weight of zirconia and Super-P, a conductive material, were mixed with PVdF used as a binder in an appropriate amount of NMP. When a suitable viscosity was obtained, it was cast on an aluminum sheet, dried, and rolled to form an electrode. Made.

At this time, the amount of the zirconia coated LiCoO ₂ and the conductive material was 96%, 2% by weight, respectively. A lithium metal plate was used as a negative electrode as a counter electrode, and a PO (Poly Olefine) separator was used as a separator, and an EC: EMC solution in which 1M LiPF6 was dissolved was sufficiently wetted in the separator as an electrolyte. Thereafter, the charge and discharge rates were set to C / 5, 1C, and 2C, and the electrode capacities based on the LiCoO ₂ electrodes were examined, and the results are shown in FIG. 3.

(Example 10)

LiCoO ₂ coated with 0.5% by weight of zirconia and Super-P, a conductive material, were mixed with PVdF used as a binder in an appropriate amount of NMP. When a suitable viscosity was obtained, it was cast on an aluminum sheet, dried, and rolled to form an electrode. Made.

At this time, the amount of the zirconia coated LiCoO ₂ and the conductive material was 96%, 2% by weight, respectively. A lithium metal plate was used as a negative electrode as a counter electrode, and a PO (Poly Olefine) separator was used as a separator, and an EC: EMC solution in which 1M LiPF6 was dissolved was sufficiently wetted in the separator as an electrolyte. Thereafter, the charge and discharge rates were set to C / 5, 1C, and 2C, and the electrode capacities based on the LiCoO ₂ electrodes were examined, and the results are shown in FIG. 3.

(Example 11)

LiCoO ₂ coated with 1% by weight of zirconia and Super-P, a conductive material, were mixed with PVdF used as a binder in an appropriate amount of NMP. When a suitable viscosity was obtained, it was cast on an aluminum sheet, dried, and rolled. An electrode was made.

At this time, the amount of the zirconia coated LiCoO ₂ and the conductive material was 96%, 2% by weight, respectively. A lithium metal plate was used as a negative electrode as a counter electrode, and a PO (Poly Olefine) separator was used as a separator, and an EC: EMC solution in which 1M LiPF6 was dissolved was sufficiently wetted in the separator as an electrolyte. Thereafter, the charge and discharge rates were set to C / 5, 1C, and 2C, and the electrode capacities based on the LiCoO ₂ electrodes were examined, and the results are shown in FIG. 3.

(Example 12)

LiCoO ₂ coated with 2% by weight of zirconia and Super-P conductive material were mixed with PVdF used as a binder in an appropriate amount of NMP. When a suitable viscosity was obtained, it was cast on an aluminum sheet, dried, and rolled to form an electrode. Made.

At this time, the amount of the zirconia coated LiCoO ₂ and the conductive material was 96%, 2% by weight, respectively. A lithium metal plate was used as a negative electrode as a counter electrode, and a PO (Poly Olefine) separator was used as a separator, and an EC: EMC solution in which 1M LiPF6 was dissolved was sufficiently wetted in the separator as an electrolyte. Thereafter, the charge and discharge rates were set to C / 5, 1C, and 2C, and the electrode capacities based on the LiCoO ₂ electrodes were examined, and the results are shown in FIG. 3.

Examples 9 to 12 are distinguished from Examples 5 to 8 in that initial electrode capacities were measured while changing charge and discharge rates.

(Comparative Example 3)

Zirconia-coated LiCoO ₂ and the conductive material Super-P were mixed with PVdF used as a binder in an appropriate amount of NMP, and then, when an appropriate viscosity was obtained, they were cast on an aluminum sheet, dried, and rolled to make an electrode.

At this time, the amount of LiCoO ₂ and the conductive material not coated with zirconia were 96% and 2% by weight, respectively. A lithium metal plate was used as a negative electrode as a counter electrode, and a PO (Poly Olefine) separator was used as a separator, and an EC: EMC solution in which 1M LiPF6 was dissolved was sufficiently wetted in the separator as an electrolyte. Thereafter, the charge and discharge rates were set to C / 5, 1C, and 2C, and the electrode capacities based on the LiCoO ₂ electrodes were examined, and the results are shown in FIG. 3.

Comparative Example 3 is distinguished from Comparative Example 2 in that the initial electrode capacity was measured while changing the charge / discharge rate.

Referring to Figure 3, considering the results of Examples 9 to 12 and Comparative Example 3, the initial electrode capacity at low charge and discharge rate (C / 5) is 0.2 to 2% by weight of zirconia according to the present invention There is no difference between when coated by% and uncoated.

However, the higher the charge / discharge rate, the larger the difference between the initial electrode capacity values when the zirconia is coated by 0.2 wt% to 2 wt% and when it is not coated. In other words, when the zirconia is not coated, the initial electrode capacity decreases significantly as the charge / discharge rate increases. However, when the zirconia is coated, the initial electrode capacity is maintained even at high rate charge and discharge. have. In particular, when the zirconia was coated by 0.5% by weight, there was almost no decrease in the initial electrode capacitance value.

This is because a large amount of Li ions are desorbed during high rate charge and discharge, thereby increasing the possibility of structural breakdown, and when not coated with zirconia, the initial electrode capacity value decreases as the charge and discharge rate increases, but when coated with zirconia according to the present invention. This is because the coating film acts as an external force, and even when Li ions escape, the collapse of the layered structure from which Li ions escapes is suppressed.

(Example 13)

LiCoO ₂ coated with 0.2% by weight of zirconia and Super-P, a conductive material, were mixed with PVdF used as a binder in an appropriate amount of NMP. When a suitable viscosity was obtained, it was cast on an aluminum sheet, dried, and rolled to form an electrode. Made.

At this time, the amount of the zirconia coated LiCoO ₂ and the conductive material was 96%, 2% by weight, respectively. A lithium metal plate was used as a negative electrode as a counter electrode, and a PO (Poly Olefine) separator was used as a separator, and an EC: EMC solution in which 1M LiPF6 was dissolved was sufficiently wetted in the separator as an electrolyte. In addition, after leaving the electrode plate at 90 ° C. for 4 hours, the electrode discharge capacity based on the LiCoO ₂ electrode was investigated with the charge / discharge rate as C / 5, and the results are shown in FIG. 4.

(Example 14)

LiCoO ₂ coated with 0.5% by weight of zirconia and Super-P, a conductive material, were mixed with PVdF used as a binder in an appropriate amount of NMP. When a suitable viscosity was obtained, it was cast on an aluminum sheet, dried, and rolled to form an electrode. Made.

At this time, the amount of the zirconia coated LiCoO ₂ and the conductive material was 96%, 2% by weight, respectively. A lithium metal plate was used as a negative electrode as a counter electrode, and a PO (Poly Olefine) separator was used as a separator, and an EC: EMC solution in which 1M LiPF6 was dissolved was sufficiently wetted in the separator as an electrolyte. In addition, after leaving the electrode plate at 90 ° C. for 4 hours, the electrode discharge capacity based on the LiCoO ₂ electrode was investigated with the charge / discharge rate as C / 5, and the results are shown in FIG. 4.

(Example 15)

LiCoO ₂ coated with 1% by weight of zirconia and Super-P, a conductive material, were mixed with PVdF used as a binder in an appropriate amount of NMP. When a suitable viscosity was obtained, it was cast on an aluminum sheet, dried, and rolled to form an electrode. Made.

At this time, the amount of the zirconia coated LiCoO ₂ and the conductive material was 96%, 2% by weight, respectively. A lithium metal plate was used as a negative electrode as a counter electrode, and a PO (Poly Olefine) separator was used as a separator, and an EC: EMC solution in which 1M LiPF6 was dissolved was sufficiently wetted in the separator as an electrolyte. In addition, after the electrode plate was left at 90 ° C. for 4 hours, the electrode discharge capacity based on the LiCoO ₂ electrode was investigated with the charge / discharge rate as C / 5, and the result is shown in FIG. 4.

(Example 16)

LiCoO ₂ coated with 2% by weight of zirconia and Super-P conductive material were mixed with PVdF used as a binder in an appropriate amount of NMP. When a suitable viscosity was obtained, it was cast on an aluminum sheet, dried, and rolled to form an electrode. Made.

At this time, the amount of the zirconia coated LiCoO ₂ and the conductive material was 96%, 2% by weight, respectively. A lithium metal plate was used as a negative electrode as a counter electrode, and a PO (Poly Olefine) separator was used as a separator, and an EC: EMC solution in which 1M LiPF6 was dissolved was sufficiently wetted in the separator as an electrolyte. In addition, after leaving the electrode plate at 90 ° C. for 4 hours, the electrode discharge capacity based on the LiCoO ₂ electrode was investigated with the charge / discharge rate as C / 5, and the results are shown in FIG. 4.

Examples 13 to 16 are distinguished from the previous examples in that the discharge capacity was measured after leaving the electrode plate at a high temperature (90 ° C.) for a predetermined time.

(Comparative Example 4)

Zirconia-coated LiCoO ₂ and the conductive material Super-P were mixed with PVdF used as a binder in an appropriate amount of NMP, and then, when an appropriate viscosity was obtained, cast on an aluminum sheet, dried it, and rolled to make an electrode.

At this time, the amount of LiCoO ₂ and the conductive material not coated with zirconia were 96% and 2% by weight, respectively. A lithium metal plate was used as a negative electrode as a counter electrode, and a PO (Poly Olefine) separator was used as a separator, and an EC: EMC solution in which 1M LiPF6 was dissolved was sufficiently wetted in the separator as an electrolyte. In addition, after leaving the electrode plate at 90 ° C. for 4 hours, the electrode discharge capacity based on the LiCoO ₂ electrode was investigated with the charge / discharge rate as C / 5, and the results are shown in FIG. 4.

The comparative example 4 is distinguished from the comparative example by the point which measured discharge capacity after leaving a pole plate at high temperature (90 degreeC) for predetermined time.

Referring to FIG. 4, considering the results of Examples 13 to 16 and Comparative Example 4, when the zirconia is not coated, the voltage change is very large with respect to the change in the discharge capacity at a high temperature, whereas the positive electrode active material is zirconia. In the case of coating by 0.2% by weight to 2% by weight, it can be seen that the change in voltage is small according to the change in discharge capacity at high temperature. In particular, when the zirconia was coated by 0.5% by weight, the change in voltage was the smallest.

This is because the zirconia film having excellent thermal conductivity helps heat dissipation of the positive electrode, and prevents the positive electrode active material from deteriorating battery characteristics such as life characteristics at high temperatures.

The foregoing has described the present invention with reference to the examples, and the present invention is not limited to the above-described examples, and the rights of the present invention are determined according to the appended claims. In addition, various modifications of the present invention can be carried out by those skilled in the art, but it is obvious that all belong to the scope of the present invention.

As discussed above, when using a lithium cobalt-based electrode coated with 0.2% by weight to 2% by weight of zirconia according to the present invention, lithium cobalt-based oxide crystals are protected by a coating film (external force), It is possible to suppress the collapse of the layered structure upon desorption (when charging).

In addition, according to the present invention, since the zirconia is coated by 0.2 wt% to 2 wt% on the surface of the lithium cobalt oxide, the electrolyte is prevented from reacting with the cobalt, thereby preventing the cobalt from dissolving in the electrolyte and causing the crystal structure to collapse. do.

In addition, according to the present invention, since the zirconia having good thermal conductivity is coated by 0.2 wt% to 2 wt% on the surface of the lithium cobalt oxide, the heat generated from the anode is easily released to the outside, thereby showing good life characteristics even at high temperatures.

In addition, according to the present invention, since the zirconia having good electrical conductivity is coated by 0.2 wt% to 2 wt% on the surface of the lithium cobalt oxide, the internal resistance of the anode is reduced, so that the drop in the discharge voltage at the end of discharge is suppressed. It is possible to obtain a lithium cobalt-based positive active material in which the characteristics are also improved and the cycle characteristics are not deteriorated even after repeated charging and discharging under high voltage.

Claims (5)

In the lithium cobalt-based active material for secondary batteries, Zirconia or an alloy containing zirconia or zirconia oxide is coated on the surface of the particles of the lithium cobalt-based active material, lithium cobalt-based positive electrode active material for secondary batteries. The method of claim 1, The lithium cobalt-based positive electrode active material for secondary batteries, characterized in that the zirconia or the alloy containing zirconia or zirconia oxide is coated by 0.2% by weight to 2% by weight on the surface of the particles of the lithium cobalt-based active material. The method of claim 2, The lithium cobalt-based positive electrode active material for secondary batteries, characterized in that the zirconia or the alloy containing zirconia or zirconia oxide is coated by 0.5% by weight on the particle surface of the lithium cobalt-based active material. The secondary battery using the positive electrode active material in any one of Claims 1-3. In the method for producing a positive electrode active material for a secondary battery, Diluting zirconium oxide with isopropyl alcohol to inhibit the reaction with moisture; Adding to the solution produced in the above step by adjusting the amount of LiCoO ₂ so that the amount of the coated zirconia is 0.2 to 2% by weight; While stirring, adding 3-glycidoxyproryltrimethoxysilane as an adhesion promoter; After stirring is complete, heating to evaporate the solvent; And After the solvent is evaporated, the method for producing a lithium cobalt-based positive electrode active material for a secondary battery comprising the step of performing a heat treatment.

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