KR100359054B1 - Metal oxide electrodes modified by conductive slurries and lithium secondary batteries - Google Patents

Abstract

The present invention includes a conductive material and a binder coated on the base layer, the conductive layer having a positive electrode active material and a conventional lithium secondary battery positive electrode containing a conductive material and / or a binder as a base layer, the weight ratio of 10 to 100 times It provides a lithium secondary battery positive electrode, a manufacturing method and a lithium secondary battery comprising the same.

The manufacturing method of the present invention includes a cathode active material, a conductive material and / or a binder, and coats, dries, and rolls a conductive slurry on which a component of the conductive material is reinforced on a cathode for a lithium secondary battery coated, dried, and rolled on a current collector. And a second method of coating a mixture comprising a cathode active material, a conductive material and / or a binder on a current collector, coating a conductive slurry reinforced with a conductive material component thereon, and then drying and rolling. .

The potential distribution and interfacial characteristics of the electrode were improved by the positive electrode of the present invention, which was surface treated with a conductive slurry, thereby greatly improving the capacity, high rate charge / discharge characteristics, and lifetime characteristics of the lithium secondary battery. Therefore, the lithium secondary battery including the positive electrode of the present invention surface-treated with a conductive slurry may be applied to various industrial fields such as various small electronic devices, communication devices, and power supplies for electric vehicles.

Description

Metal oxide anode surface-treated with conductive slurry, manufacturing method and lithium secondary battery using the same {METAL OXIDE ELECTRODES MODIFIED BY CONDUCTIVE SLURRIES AND LITHIUM SECONDARY BATTERIES}

The present invention is a lithium secondary battery positive electrode comprising a positive electrode active material, a conductive material and / or a binder, characterized in that the positive electrode further comprises a conductive layer to a positive electrode for a lithium secondary battery, a manufacturing method and a lithium secondary battery using the same It is about.

The positive electrode for a lithium secondary battery is generally composed of a positive electrode active material capable of inserting lithium, a conductive material added to impart conductivity, and a binder for fixing them to a current collector (eg, aluminum). Among them, a metal oxide is usually used as a cathode active material for a lithium secondary battery, and since it is poor in electrical conductivity due to its material properties, it is challenging for smooth electron supply between the packed cathode active materials and between the current collector and the surface of the active material. Ash is required and its role is very important (D. Linden, Handbook of Batteries, McGRAW-HILL INC., New York (1995)). However, in order to increase the amount of the conductive material added, the amount of the binder must be increased as well, and thus, optimization of the amount of the conductive material and the binder added is necessary. For example, when the mixed state of the positive electrode active material, the conductive material, and the binder is nonuniform, nonuniformity of electrode performance occurs, resulting in deterioration of battery performance and problems in reliability. The binder prevents the detachment of the positive electrode active material and increases the bonding force between the positive electrode active materials. However, when the binder is added more than necessary, the battery performance decreases due to the decrease of the positive electrode active material used for the electrode and the increase of internal resistance. Therefore, there is a limit in increasing the battery performance only by increasing the amount of the conductive material.

The literature on the effect of conductive materials on the performance of lithium secondary batteries includes literatures on the characteristics of conductive materials in LiCoO ₂ electrodes (Electrochemical Journal, Vol. 2, No. 2, 1999) and positive and negative electrodes for lithium ion batteries. Reports on the characteristics of conductive materials in Korea (2nd Battery Technology Symposium, pp. 79-88, Korean Institute of Industrial Chemistry (1998)). 20 wt%.

An object of the present invention is to improve the performance of a lithium secondary battery by changing the surface characteristics of the positive electrode. Specifically, in a lithium secondary battery positive electrode comprising a positive electrode active material, a conductive material and / or a binder, it is to obtain excellent battery characteristics by further coating a conductive layer on the positive electrode.

Still another object of the present invention is to provide a method of manufacturing a cathode for a lithium secondary battery, further coated with a conductive layer. One example of the manufacturing method of the present invention includes a cathode active material, a conductive material and / or a binder, and coated and dried a conductive slurry reinforced with a conductive material component on the positive electrode for a lithium secondary battery coated, dried and rolled on a current collector And rolling. Another manufacturing method consists of coating a mixture comprising a cathode active material and a conductive material and / or a binder on a current collector, coating a conductive slurry reinforced with a conductive material component thereon, followed by drying and rolling.

Another object of the present invention is to provide a lithium secondary battery having a positive electrode further coated with a conductive layer as part of the battery.

1 illustrates an anode of the present invention,

2 illustrates a process of surface treating a metal oxide anode material in accordance with the present invention,

Figure 3 is a graph comparing the electrode capacity and the life test results of the lithium secondary battery prepared in Comparative Example 1 and a lithium secondary battery having a surface-treated metal oxide according to the present invention,

Figure 4 is a graph comparing the high rate discharge characteristics of the lithium secondary battery prepared in Comparative Example 1 and a lithium secondary battery having a surface-treated metal oxide according to the present invention.

The present invention relates to a cathode for a lithium secondary battery comprising a base layer comprising a cathode active material, a conductive material and / or a binder, and a conductive layer coated on the base layer. That is, a typical lithium secondary battery positive electrode is composed of only a base layer containing a positive electrode active material and a conductive material and / or a binder, the lithium secondary battery positive electrode of the present invention is characterized in that it further comprises a conductive layer on the base layer do. In the present specification, the base layer refers to a conventional lithium secondary battery positive electrode containing a positive electrode active material, a conductive material and / or a binder, the conductive layer contains a conductive material and a binder as an essential component, optionally a positive electrode The layer may contain an active material and contains a conductive material in a weight ratio of 10 to 100 times the binder.

A typical lithium secondary battery includes a positive electrode having a positive electrode active material coated on both surfaces of an Al current collector, an electrolyte layer, and a negative electrode having a negative electrode active material coated on both surfaces of a Cu current collector. In addition, the positive electrode generally includes a conductive material and / or a binder in addition to the positive electrode active material. However, such a positive electrode has not had sufficient battery capacity as described above, and there has been a problem that the charge and discharge cycle characteristics are low. As shown in FIG. 1, the positive electrode 1 of the present invention is a base layer 101 which is formed of a conventional positive electrode having a positive electrode active material and a conductive material and / or a binder coated on both surfaces of a current collector 103. The conductive layer 102 is further coated on the 101. As can be seen from the embodiment, by further introducing the conductive layer 102, the battery capacity was increased and the cycle characteristics were improved.

As described above, the conductive layer of the present invention contains a conductive material and a binder as essential components, and may optionally contain a positive electrode active material, and contains a conductive material in a weight ratio of 10 to 100 times the binder, and the thickness thereof is It is preferable that they are 1 micrometer-100 micrometers.

The conductive material used for the base layer or the conductive layer is not particularly limited and may be a mixture of metal, carbon material, conductive metal oxide, and the like. Examples of the metal used as the conductive material include aluminum, tin, bismuth, silicon, antimony, nickel, copper, titanium, vanadium, chromium, manganese, iron, cobalt, zinc, molybdenum, tungsten, silver, gold, lanthanum, and ru Tenium, platinum, iridium, and the like, and alloys thereof may also be used. Examples of the conductive carbon material include graphite, coke, hard carbon, acetylene black (AB), carbon black, activated carbon or mixtures thereof. Examples of the metal oxide having excellent conductivity include CrOx, CoOx, CuOx, NiOx, SnOx, AgOx, LaOx, InOx, RuOx, PtOx, IrOx and mixed oxides or superconducting metal oxides thereof.

The positive electrode active material used in the base layer or the conductive layer is not particularly limited as long as it is a metal oxide used in a conventional lithium secondary battery, and examples thereof include LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNiCoO ₂ , V ₆ O ₁₃ , and V _2. O ₅ or a mixture thereof.

Examples of the binder used in the base layer or the conductive layer include, but are not limited to, PVdF, PTFE, EPDM, or mixtures thereof.

In the method for producing a cathode for a lithium secondary battery of the present invention, a mixture of a cathode active material and a conductive material and / or a binder is coated on a current collector by coating, drying, and rolling to form a base layer, and a conductive material component on the base layer. The first method of coating the reinforced conductive slurry by coating, drying and rolling, and coating the mixture of the positive electrode active material, the conductive material and / or the binder on the current collector, and then the conductive slurry reinforced with the conductive material component thereon Is coated, dried and rolled to form a base layer and a conductive layer. 2 is a process diagram schematically illustrating the two manufacturing methods.

Lithium battery positive electrode of the present invention having a conductive layer further has improved electrical conductivity due to coating of a porous metal oxide layer, a metal layer, or a carbon layer having excellent conductivity on the surface of the metal oxide electrode, resulting in a constant current and potential distribution. Since the phosphorus overcharge reaction is suppressed, the utilization rate and cycle life of the electrode are increased, and the porous film has the advantage of improving the high rate charge / discharge characteristics without lowering the lithium transfer rate, and particularly, the effect is great for large batteries. In addition, by making the current and potential distribution of the positive electrode constant, there is an advantage of increasing the lifetime by suppressing dendrite deposition of a lithium metal battery using lithium metal. The metal oxide electrode according to the present invention is a positive electrode of a lithium ion battery using a separator such as polypropylene (PP) and polyethylene (PE), a lithium polymer battery using a polymer electrolyte, and an all-solid-state lithium secondary battery using a solid electrolyte. There is an advantage to use.

The following are examples and comparative examples in which a porous metal oxide, a metal or carbon-coated metal oxide electrode and a lithium secondary battery having excellent conductivity and performance tests were performed using the manufacturing method of the present invention. It will be clearly understood.

Example

Example 1

The LiMn ₂ O ₄ positive electrode has a composition of 5.7 g of LiMn ₂ O ₄ , AB 0.6 g, and 0.4 g of polyvinylidene difluoride (hereinafter “PVdF”) in an appropriate amount of N-methyl-2-pyrrolidone (hereinafter “NMP”). And mixed with acetone and then cast on an aluminum thin plate when the proper viscosity was obtained, dried, and rolled. After mixing the composition of LiCoO ₂ 5.0g, AB 1.3g, 0.4g PVdF in an appropriate amount of NMP and acetone, when a suitable viscosity was obtained, cast to a thickness of 10 ㎛ on the anode, dried and rolled to increase the conductive material A metal oxide electrode coated with an oxide slurry was obtained. The carbon cathode is Gr. 6 g, 0.3 g of AB, and 0.4 g of PVdF were mixed with an appropriate amount of NMP and acetone, and then cast on a copper foil, dried, and rolled when a suitable viscosity was obtained. The lithium secondary battery is manufactured by stacking a metal oxide cathode, a PP separator, and a carbon anode coated with a metal oxide slurry having an increased conductive material, and injecting an ethylene carbonate: diethyl carbonate (EC: DEC) solution in which 1M LiPF ₆ is dissolved. It was.

Comparative Example 1

The LiMn ₂ O ₄ positive electrode was obtained by mixing LiMn ₂ O ₄ 5.7 g, AB 0.6 g, and PVdF 0.4 g in an appropriate amount of NMP and acetone, then casting on a thin aluminum sheet, drying, and rolling after a suitable viscosity was obtained. The carbon cathode is Gr. 6 g, 0.3 g of AB, and 0.4 g of PVdF were mixed with an appropriate amount of NMP and acetone, and then cast on a copper foil, dried, and rolled when a suitable viscosity was obtained. The lithium secondary battery was prepared by stacking a LiMn ₂ O ₄ positive electrode, a PP separator, and a carbon negative electrode, and injecting an EC-DEC solution in which 1M LiPF ₆ was dissolved.

Example 2

The composition of 5.7 g of LiMn ₂ O ₄ , 0.6 g of AB, and 0.4 g of PVdF was mixed with an appropriate amount of NMP and acetone, and then cast on an aluminum sheet, dried, and rolled to obtain a base layer when a suitable viscosity was obtained. The composition of AB 6g and PVdF 0.4g was mixed with an appropriate amount of NMP and acetone, and when a suitable viscosity was obtained, cast to a thickness of 5 μm on the electrode, dried, and rolled to obtain a metal oxide electrode having a conductive material laminated thereon. The carbon cathode is Gr. 6 g, 0.3 g of AB, and 0.4 g of PVdF were mixed with an appropriate amount of NMP and acetone, and then cast on a copper foil, dried, and rolled when a suitable viscosity was obtained. The lithium secondary battery was prepared by stacking an AB-coated metal oxide cathode, a PP separator, and a carbon anode, and injecting an EC: DEC solution in which 1M LiPF ₆ was dissolved.

Example 3

The composition of 5.7 g of LiMn ₂ O ₄ , 0.6 g of AB, and 0.4 g of PVdF was mixed with an appropriate amount of NMP and acetone, and then cast on an aluminum sheet, dried, and rolled to obtain a base layer when a suitable viscosity was obtained. 10 g of Cu and 0.4 g of PVdF were mixed with an appropriate amount of NMP and acetone, and when a suitable viscosity was obtained, a metal oxide electrode coated with a conductive material was obtained by casting, drying, and rolling a thickness of 5 μm on the electrode. The carbon cathode is Gr. 6 g, 0.3 g of AB, and 0.4 g of PVdF were mixed with an appropriate amount of NMP and acetone, and then cast on a copper foil, dried, and rolled when a suitable viscosity was obtained. The lithium secondary battery was manufactured by stacking a metal oxide cathode, a PP separator, and a carbon anode coated with Cu, and injecting an EC: DEC solution in which 1M LiPF ₆ was dissolved.

Example 4

The LiMn ₂ O ₄ anode was mixed with a composition of 5.7 g of LiMn ₂ O ₄ , 0.6 g of AB, and 0.4 g of PVdF in an appropriate amount of NMP and acetone, and then cast on an aluminum sheet when a suitable viscosity was obtained, and RuOx 10 g and PVdF 0.4 g were mixed. After mixing with an appropriate amount of NMP and acetone, when a suitable viscosity was obtained, it was cast on a thickness of 10 µm on the electrode, dried, and rolled. The carbon cathode is Gr. 6 g, 0.3 g of AB, and 0.4 g of PVdF were mixed with an appropriate amount of NMP and acetone, and then cast on a copper foil, dried, and rolled when a suitable viscosity was obtained. The lithium secondary battery was manufactured by stacking a metal oxide cathode, a PP separator, and a carbon anode coated with RuOx, and injecting an EC: DEC solution in which 1M LiPF ₆ was dissolved.

Example 5

Discharge capacities were measured according to the number of charge and discharge cycles using the lithium secondary batteries prepared in Examples 1-4 and Comparative Example 1, and the results are shown in FIG. 3. As can be seen in FIG. 3, the cycle life is improved by the anode having the conductive layer.

Example 6

The high-rate discharge characteristics were measured using the lithium secondary battery prepared in Example 2 and the lithium secondary battery prepared in Comparative Example 1, and the results are shown in FIG. 4 (However, FIG. 4A shows lithium manufactured in Example 2). It is a graph measuring the high rate discharge characteristics of the secondary battery, Figure 4b is a graph measuring the high rate discharge characteristics of the lithium secondary battery manufactured in Comparative Example 1). As can be seen in Figures 4a and 4b, the lithium secondary battery prepared in Example 2 was superior to the high rate discharge characteristics than the lithium secondary battery prepared in Comparative Example 1. This proves that the high rate discharge characteristic is improved by the anode having the conductive layer.

As described above, the potential distribution and the interfacial characteristics of the electrode were improved by coating the conductive layer on the normal anode, thereby greatly improving the capacity, high rate charge and discharge characteristics, and the life characteristics of the lithium secondary battery. Therefore, the lithium secondary battery including the positive electrode of the present invention surface-treated with a conductive slurry can be applied to various industrial fields, such as for various small electronic devices, communication devices and power supplies of electric vehicles, localization, import replacement and export of various devices May have augmentation effect.

Claims (10)

A conventional lithium secondary battery positive electrode containing a positive electrode active material and a conductive material and / or a binder as a base layer, comprising a conductive material and a binder, coated on the base layer, the weight ratio of the conductive material and the binder is 10-100: 1. A lithium secondary battery positive electrode containing a phosphorus conductive layer. The positive electrode for a lithium secondary battery according to claim 1, wherein the conductive layer has a thickness of 1 µm to 100 µm. The conductive material used for the conductive layer is aluminum, tin, bismuth, silicon, antimony, nickel, copper, titanium, vanadium, chromium, manganese, iron, cobalt, zinc, molybdenum, tungsten, silver, gold , Lanthanum, ruthenium, platinum, iridium or an alloy thereof. The cathode for a lithium secondary battery according to claim 1, wherein the conductive material used for the conductive layer is graphite, coke, hard carbon, acetylene black, carbon black, activated carbon, or a mixture thereof. The lithium secondary battery according to claim 1, wherein the conductive material used for the conductive layer is CrOx, CoOx, CuOx, NiOx, SnOx, AgOx, LaOx, InOx, RuOx, PtOx, IrOx, mixed oxides thereof, or superconducting metal oxides. Battery positive electrode. The cathode for a lithium secondary battery according to any one of claims 1 to 5, wherein the conductive layer further comprises a cathode active material. The cathode for a lithium secondary battery according to claim 6, wherein the cathode active material is LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNiCoO ₂ , V ₆ O ₁₃ , V ₂ O _5, or a mixture thereof. The method of claim 1 comprising coating a cathode active material and a mixture of a conductive material and / or a binder on a current collector by coating, drying, and rolling, and coating, drying, and rolling a conductive slurry on which the conductive material component is reinforced thereon. Method of manufacturing a positive electrode for a lithium secondary battery according to. delete A lithium secondary battery comprising the positive electrode for a lithium secondary battery of claim 1.