KR100471983B1 - Electrode for lithium battery - Google Patents

Abstract

The present invention relates to an electrode for a lithium battery, the electrode comprising a current collector; A porous conductive layer formed on the current collector; And an active material layer formed on the porous conductive layer.

The electrode of the present invention can provide a battery having excellent high rate charge / discharge characteristics and lifetime characteristics, and can also reduce battery internal resistance.

Description

Electrode for lithium battery {ELECTRODE FOR LITHIUM BATTERY}

[Industrial use]

The present invention relates to a lithium battery electrode, and more particularly to a lithium battery electrode that can provide a battery exhibiting improved high rate charge and discharge characteristics and life characteristics.

[Prior art]

With the development of portable electronic devices, there is an increasing demand for light and high capacity batteries.

Secondary batteries that satisfy these requirements include lithium ion batteries or lithium sulfur batteries, depending on the type of active material. Lithium ion batteries use transition metal oxides as positive electrode active materials, and lithium sulfur batteries use sulfur-based materials.

These lithium batteries are actively studied as power sources of portable electronic devices due to their high capacity, nature-friendly, and abundant raw materials, compared to other batteries, but still exhibit optimal performance, for example, high rate charge / discharge characteristics, and lifetime characteristics. Development is not happening.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a lithium battery electrode exhibiting excellent high rate charge and discharge characteristics and life characteristics.

Another object of the present invention is to provide an electrode for a lithium battery that can reduce the internal resistance of the battery.

In order to achieve the above object, the present invention is a current collector; Two or more active material layers formed on the current collector; And a porous conductive layer formed between the active material layers.

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

The electrode for lithium batteries of this invention contains a current collector and the active material layer formed on this current collector. More preferably, as illustrated in FIG. 1, the current collector 1, at least two active material layers 3 formed on the current collector, and a porous conducting layer 5 formed between the active material layers. It includes.

The porous conductive layer may include any material capable of forming a conductive network, and includes, for example, a material selected from the group consisting of crystalline carbon, amorphous carbon, and metal. The crystalline carbon includes artificial graphite or natural graphite, and the amorphous carbon includes carbon black, carbon fiber or carbon powder. The metal includes those selected from the group consisting of Al, Cu, Ni, Fe, Mn, Co, and Mo.

The porous conductive layer preferably has a thickness of 0.5 to 20㎛. When the thickness of the porous conductive layer is thinner than 0.5 μm, there is a problem in improving electrode performance. When the thickness of the porous conductive layer is thicker than 20 μm, there is a problem in that battery capacity is improved due to a thicker electrode plate.

The porosity of the porous conductive layer may be sufficient to smoothly move lithium ions, and there is no particular limitation, but it is preferably 5% to 70%.

Since the porous conductive layer plays a role of supporting the electrode structure, the active material layer can be well supported even during high charge / discharge during charging and discharging even when the active material layer has two layers to increase the capacity. In addition, since the conductive layer having the conductive network superior to the active material layer is formed in the center, the internal resistance decreases due to the effect of increasing the movement path of the battery which is transmitted and received by the movement of ions.

As the current collector, the electrode of the present invention may be used as a positive electrode or a negative electrode of a lithium-sulfur battery, or a positive electrode or a negative electrode of a lithium ion battery. The materials of construction vary. When the electrode of the present invention is used as a positive electrode of a lithium-sulfur battery, a conductive material such as stainless steel, copper, titanium, aluminum, or carbon-coated aluminum may be used. In general, the use of a carbon-coated aluminum substrate is most preferable because it has excellent adhesion to the active material, low contact resistance, and prevents corrosion due to polysulfide of aluminum, compared with the non-carbon coated coating. All.

In addition, when the electrode of the present invention is used as a positive electrode of a lithium ion battery, a current collector may generally use aluminum, and when used as a negative electrode, copper may be used.

In the electrode of the present invention, the active material layer includes an active material capable of an electrochemically reversible oxidation / reduction reaction. The electrode of the present invention may be used as a positive electrode or a negative electrode of a lithium-sulfur battery, or a positive electrode or a negative electrode of a lithium ion battery. The active material included in the active material layer varies depending on which battery is used and used as a positive electrode or a negative electrode.

When the electrode of the present invention is used as a positive electrode of a lithium-sulfur battery, the active material includes inorganic sulfur (S ₈ ) or a sulfur-based compound. This sulfur-based compound may be selected from the group consisting of Li ₂ S _n (n ≧ 1), organic sulfur compounds and carbon-sulfur polymers ((C ₂ S _x ) _n : x = 2.5 to 50, n ≥ 2) Can be. In this case, the active material layer includes a conductive material and a binder. In this case, the conductive material may include at least one electrically conductive conductive material and at least one ion conductive conductive material for allowing electrons to move smoothly in the positive electrode active material. The electrically conductive conductive material is not particularly limited, but conductive materials such as carbon (eg, Super-P), carbon black, or conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole may be used alone or in combination. The ion conductive conductive material may be polyethylene oxide, a copolymer of polyhexafluoropropylene and polyvinylidene fluoride, polyvinyl pyrrolidone, or the like. The binder includes poly (vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, alkylated polyethylene oxide, crosslinked polyethylene oxide, polyvinyl ether, poly (methyl methacrylate), polyvinylidene Copolymers of fluoride, polyhexafluoropropylene and polyvinylidene fluoride (trade name: Kynar), poly (ethyl acrylate), polytetrafluoroethylene, polyvinylchloride, polyacrylonitrile, polyvinylpyridine, polystyrene , Copolymers of polystyrene and butadiene (SBR) Derivatives, blends, copolymers and the like thereof may be used.

When the electrode of the present invention is used in a lithium ion battery, both an anode and a cathode may be used. In this case, the active material capable of the electrochemically reversible oxidation / reduction reaction may be a reversible intercalation / deintercalation of lithium ions. Use possible materials. The reversible intercalation / deintercalation material of the lithium ions may be a positive electrode active material of a lithium metal oxide or a lithium-containing chalcogenide compound or a negative electrode active material of a carbon material.

The lithium metal oxide or the lithium-containing chalcogenide compound is a material capable of reversible intercalation / deintercalation of lithium ions, and means a retired intercalation compound.

The lithium intercalation compound has any one of a monoclinic, hexagonal or cubic structure as a basic structure.

As the lithium intercalation compound used in the present invention, all existing lithium compounds (lithium metal oxides and lithium-containing chalcogenide compounds) may be used, and preferred examples thereof include the following compounds.

[Formula 1]

Li _x Mn _1-y M _y A ₂

[Formula 2]

Li _x Mn _1-y M _y O _2-z X _z

[Formula 3]

Li _x Mn ₂ O _4-z X _z

[Formula 4]

Li _x Mn _2-y M _y A ₄

[Formula 5]

Li _x Co _1-y M _y A ₂

[Formula 6]

Li _x Co _1-y M _y O _2-z X _z

[Formula 7]

Li _x Ni _1-y M _y A ₂

[Formula 8]

Li _x Ni _1-y M _y O _2-z X _z

[Formula 9]

Li _x Ni _1-y Co _y O _2-z X _z

[Formula 10]

Li _x Ni _1-yz Co _y M _z A _α

[Formula 11]

Li _x Ni _1-yz Co _y M _z O _2-α X _α

[Formula 12]

Li _x Ni _1-yz Mn _y M _z A _α

[Formula 13]

Li _x Ni _1-yz Mn _y M _z O _2-α X _α

Wherein 0.90 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.5, 0 ≦ α ≦ 2, and M is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V or rare earth At least one element selected from the group consisting of elements, A is an element selected from the group consisting of O, F, S and P, and X is F, S or P.)

As the carbonaceous material, both amorphous carbon, crystalline carbon, or a mixture thereof may be used. Examples of the amorphous carbon include soft carbon (low temperature calcined carbon) or hard carbon (hard carbon calcined carbon), and crystalline carbon includes plate-like, spherical or fibrous natural graphite or artificial graphite.

When used as a positive electrode and a negative electrode of a lithium ion battery, the binder included in the active material layer may be any binder generally used in a lithium ion battery such as polyvinylidene fluoride and polyvinyl chloride. When used as a positive electrode, the active material layer also contains a conductive material. As such a conductive material, a conductive material such as carbon or carbon black may be used.

In the lithium battery electrode of the present invention having the above-described configuration, first, the electrode active material composition is applied to a current collector to form an active material layer. Since the active material layer forming process is well known in the art, a detailed description thereof will be omitted herein, which may be widely understood by those skilled in the art.

The electrode active material composition includes an active material, a binder, and a solvent, and optionally a conductive material. As the solvent, any active material, a binder, and optionally a solvent capable of dispersing the conductive material may be used, and may be appropriately selected according to the type of the active material, the binder, and in some cases, the conductive material. Since it is well known in the detailed description thereof will be omitted.

A conductive material composition is coated on the active material layer to form a porous conductive layer.

Subsequently, an active material layer is formed again on the porous conductive layer using an electrode active material composition.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only one preferred embodiment of the present invention and the present invention is not limited to the following examples.

(Example 1)

60 wt% of inorganic sulfur (S ₈ ), 20 wt% of carbon conductive material, and 20 wt% of polyethylene oxide binder were mixed to prepare a cathode active material composition for a lithium-sulfur battery.

The positive electrode active material composition was applied to an aluminum current collector to form a positive electrode active material layer on the current collector. Subsequently, 70% by weight of carbon fiber and 30% of polyethylene oxide were mixed in an acetonitrile solvent to prepare a carbon fiber slurry composition, and then coated on the cathode active material layer to form a porous conductive layer.

Subsequently, the cathode active material composition was applied to the porous conductive layer again to form a cathode active material layer on the porous conductive layer. As a result, a positive electrode for a lithium-sulfur battery was produced.

The negative electrode used a lithium foil having a thickness of 100um.

(Example 2)

Except for using the positive electrode active material slurry prepared by dissolving 94% by weight of LiCoO ₂ positive electrode active material, 3% by weight of polyvinylpyrrolidone binder, and 3% by weight of carbon conductive agent in N-methylpyrrolidone solvent. In the same manner, a positive electrode for a lithium ion battery was manufactured. As the negative electrode, 96% by weight of the artificial graphite negative electrode active material and 4% by weight of the polyvinylidene fluoride binder were mixed in an N-methylpyrrolidone solvent to prepare a negative electrode active material slurry for a lithium ion battery. The negative electrode active material slurry was applied to a copper foil current collector and dried to form a negative electrode active material layer on the current collector.

(Example 3)

A cathode plate using a cathode active material slurry prepared by dissolving 94% by weight of LiCoO ₂ cathode active material, 3% by weight of polyvinylpyrrolidone binder, and 3% by weight of carbon conductive agent in N-methylpyrrolidone solvent was prepared.

As the negative electrode, 96% by weight of the artificial graphite negative electrode active material and 4% by weight of the polyvinylidene fluoride binder were mixed in an N-methylpyrrolidone solvent to prepare a negative electrode active material slurry for a lithium ion battery. The negative electrode active material slurry was applied to a copper foil current collector and dried to form a negative electrode active material layer on the current collector. Subsequently, 70% by weight of carbon fiber and 30% of polyethylene oxide were mixed in an acetonitrile solvent to prepare a carbon fiber slurry composition, and then coated on the cathode active material layer to form a porous conductive layer.

Subsequently, the negative electrode active material composition was applied to the porous conductive layer again to form a negative electrode active material layer on the porous conductive layer. As a result, a negative electrode for a lithium-ion battery was produced.

(Comparative Example 1)

60 wt% of inorganic sulfur (S ₈ ), 20 wt% of carbon conductive material, and 20 wt% of polyethylene oxide binder were mixed to prepare a cathode active material composition for a lithium-sulfur battery.

Subsequently, the cathode active material composition was applied to an aluminum current collector to prepare a cathode for a lithium-sulfur battery.

The negative electrode is the same as in Example 1.

(Comparative Example 2)

The positive electrode active material composition was applied to an aluminum current collector twice, and thus, the same procedure as in Comparative Example 1 was performed except that two positive electrode active material layers were formed.

(Comparative Example 3)

A positive electrode active material slurry was prepared by dissolving 94% by weight of LiCoO ₂ positive electrode active material, 3% by weight of polyvinylpyrrolidone binder, and 3% by weight of carbon conductive agent in an N-methylpyrrolidone solvent. The cathode active material slurry was applied to an aluminum foil current collector to prepare a cathode for a lithium ion battery.

As the negative electrode, 96% by weight of the artificial graphite negative electrode active material and 4% by weight of the polyvinylidene fluoride binder were mixed in an N-methylpyrrolidone solvent to prepare a negative electrode active material slurry for a lithium ion battery. The negative electrode active material slurry was applied to a copper foil current collector and dried to form a negative electrode active material layer.

Winding the positive electrode, the negative electrode and the separator with the prepared electrode plates to prepare a pouch battery of the square type to evaluate the battery characteristics and the results are shown in Table 1 below. In Table 1 below, the 0.5C and 2.0C discharge capacities are values for 0.2C discharge capacities, and the discharge capacities after 300 charge / discharge cycles are values for the first cycle.

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Battery mode Li-S Li-ion Li-ion Li-S Li-S Li-ion Design capacity 2mAh / cm ² 3 mAh / cm ² 3 mAh / cm ² 2mAh / cm ² 3 mAh / cm ² 3 mAh / cm ² Porous conductive layer location anode anode cathode none none none 0.5C discharge capacity 100% 100% 100% 85% 90% 100% 2.0C discharge capacity 70% 95% 97% 30% 40% 90% Discharge capacity after 300 charge and discharge cycles 55% 95% 95% 25% 30% 90%

As shown in Table 1, when comparing Example 1 and Comparative Examples 1 and 2, which is a lithium-sulfur battery, the battery of Example 1 has an excellent discharge capacity of 0.5C, 2.0C compared to Comparative Examples 1 and 2, In particular, it can be seen that the high rate (2.0C) capacity characteristics are excellent, and the cycle characteristics are also very excellent compared to Comparative Examples 1 and 2. In addition, comparing Examples 2 and 3 and Comparative Example 3, which are lithium-ion batteries, shows that the batteries of Examples 2 and 3 are superior in high rate characteristics (2.0 C discharge capacity) and cycle characteristics, as compared with Comparative Example 3. have.

The electrode of the present invention can provide a battery having excellent high rate charge / discharge characteristics and lifetime characteristics, and can also reduce battery internal resistance.

1 is a cross-sectional view schematically showing an electrode for a lithium battery of the present invention.

Claims (10)

Current collectors; Two or more active material layers formed on the current collector; And Porous conductive layer formed between the active material layer Lithium battery electrode comprising a. The electrode of claim 1, wherein the porous conductive layer is selected from the group consisting of crystalline carbon, amorphous carbon, and metal. The electrode of claim 2, wherein the metal is selected from the group consisting of Al, Cu, Ni, Fe, Mn, Co, and Mo. The electrode of claim 1, wherein the porous conductive layer has a thickness of 0.5 to 10 μm. The electrode of claim 1, wherein the active material in the active material layer is a material capable of an electrochemically reversible oxidation / reduction reaction. The electrode of claim 5, wherein the electrochemically reversible oxidation / reduction reaction material is an elemental sulfur or a sulfur compound. The method of claim 6, wherein the sulfur compound is a group consisting of Li ₂ S _n (n ≥ 1), an organic sulfur compound and a carbon-sulfur polymer ((C ₂ S _x ) _n : x = 2.5 to 50, n ≥ 2) The electrode for lithium batteries selected from. The electrode of claim 5, wherein the electrochemically reversible oxidation / reduction reaction material is a reversible intercalation / deintercalation material of lithium ions. The lithium battery of claim 8, wherein the reversible intercalation / deintercalation material of the lithium ion is at least one material selected from the group consisting of lithium metal oxides, lithium-containing chalcogenide compounds, and carbonaceous materials. electrode. The lithium battery electrode according to claim 1, wherein the electrode is used in a battery selected from the group consisting of lithium ion batteries and lithium-sulfur batteries.