WO2013183848A1

WO2013183848A1 - Electrode for lithium secondary battery, method for manufacturing same, and lithium secondary battery

Info

Publication number: WO2013183848A1
Application number: PCT/KR2013/000793
Authority: WO
Inventors: 윤우영; 이준규
Original assignee: 고려대학교 산학협력단
Priority date: 2012-06-04
Filing date: 2013-01-31
Publication date: 2013-12-12
Also published as: KR20130136131A

Abstract

An electrode for a lithium secondary battery comprises an active material body and a diamond-like carbon (DLC) layer covering the active material body, wherein the active material body includes silicon nanopowders, a carbon-based conductive material, and a binder. The DLC layer can suppress the volumetric expansion of the active material body. The DLC layer can suppress a reaction between the active material body and an electrolyte. Therefore, when the electrode including the DLC layer is applied to the lithium secondary battery, the lithium secondary battery can have stable cycle properties.

Description

Electrode for Lithium Secondary Battery, Formation Method thereof and Lithium Secondary Battery

The present invention relates to an electrode for a lithium secondary battery, a method for forming the electrode for a lithium secondary battery, and a lithium secondary battery, and more particularly, a lithium secondary battery electrode for forming a secondary battery capable of charging and discharging, a method for forming the electrode, and a lithium secondary battery. It relates to a battery.

Lithium secondary battery is a type of secondary battery that is charged and discharged by insertion and desorption of lithium ions in the battery. During charging, lithium ions move from cathode to cathode toward anode. It is inserted into the active material of, on the contrary, during discharge, lithium ions inserted into the negative electrode move toward the positive electrode and are inserted into the active material of the positive electrode. Such lithium secondary batteries have high energy density, large electromotive force, and high capacity, and thus are widely used as power sources for mobile phones and laptops.

The lithium secondary battery is usually composed of a negative electrode, a positive electrode, a separator and an electrolyte. The negative electrode and the positive electrode include a negative electrode active material and a positive electrode active material capable of inserting and detaching lithium ions as described above. A separator prevents physical cell contact between the positive and negative electrodes. Instead, the movement of ions through the separator is free. The electrolyte serves as a path through which ions can move freely between the anode and the cathode.

Meanwhile, carbon for constituting the negative electrode may be used. The carbon material is widely used as a negative electrode material of a lithium ion battery due to its low volume change, excellent reversibility, and relatively low price when intercalating / deintercalating lithium. Carbon materials used as such a cathode material include graphite, coke, fiber, pitch, meso carbon, and the like. However, the graphite has a theoretical limit (372 mAh g ⁻¹ ) in the charge capacity per unit mass. Therefore, there has been a demand for development of a new negative electrode material capable of greatly improving operating characteristics such as energy density, reversible capacity, and initial charging efficiency of a lithium ion battery.

Recently, the development of electrodes using silicon has been attracting attention in an attempt to solve the above problems. Silicon has a lot of interest in the field of lithium ion batteries because it has a theoretical capacity per unit mass (approximately 4,200 mAh g ^-1 ) which is more than 10 times higher than the charge capacity of graphite electrodes or other various oxide and nitride material electrodes. It is a material.

However, when silicon is applied to a lithium ion battery electrode, a large volume change of 400% or more occurs due to the insertion / desorption of lithium, which leads to many limitations in the application to the actual anode material. This is because mechanical stress generated in the silicon crystal lattice due to the volume change causes breakage and crushing of the silicon electrode, thereby lowering the stability and capacity of the lithium ion battery.

One object of the present invention is to provide an electrode for a lithium secondary battery having an improved capacity and lifetime.

Another object of the present invention is to provide a method for forming the electrode for a lithium secondary battery.

Still another object of the present invention is to provide a lithium secondary battery including an electrode for a lithium secondary battery having a capacity and a lifetime.

An electrode for a rechargeable lithium battery according to an embodiment of the present invention includes an active material body made of silicon nano powder, a carbon-based conductive material and a binder, and a diamond like carbon (DLC) layer covering a surface of the active material. The carbon-based conductive material may include at least one of carbon black, ketjen black, acetylene black, and carbon super P. In addition, the binder may include carboxy methyl cellulose (CMC).

In the method of forming an electrode for a lithium secondary battery according to an embodiment of the present invention, after forming an active material body made of silicon nano powder, a carbon-based conductive material and a binder, a diamond like carbon; DLC) layer is coated. The diamond like carbon (DLC) layer may be formed through a plasma enhanced chemical vapor deposition (PECVD) process.

Lithium secondary battery according to an embodiment of the present invention, a positive electrode including a positive electrode active material, disposed to face the positive electrode, and covers the surface of the negative electrode active material body and the surface of the active material made of silicon nano powder, a carbon-based conductive material and a binder A cathode including a diamond like carbon (DLC) layer and interposed between the anode and the cathode and includes an electrolyte layer.

The lithium secondary battery electrode according to the present invention includes a diamond like carbon (DLC) covering the surface of the active material body. Here, the DLC layer has a relatively good chemical stability. In addition, the DLC layer has a relatively high Young's Modulus value. Therefore, the DLC layer can suppress the volume expansion of the active material body. In addition, when the electrode including the DLC layer is applied to a secondary battery, a reaction between the electrode and the electrolyte may be suppressed. Thus, when the electrode including the die layer is applied to a lithium secondary battery, the lithium secondary battery may have stable cycle characteristics.

FIG. 1 is an electron micrograph comparing before (a) and after coating (b) of an active material body by using a DL layer.

Figure 2 is a graph showing the charge capacity according to the charge and discharge cycle for the electrode before coating the active material body and the electrode after the coating using the die layer.

3 is an electron micrograph showing the surface after 15 cycles of the electrode (a) before coating the active material body and the electrode (b) after coating using the DLC layer.

4 and 5 are graphs of X-ray photoelectron spectroscopy analysis of the surface after 15 cycles of the electrode before coating the active material body and the electrode after coating using the DLC layer.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. As the inventive concept allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed form, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. In the accompanying drawings, the size and amount of the objects are shown to be enlarged or reduced than actual for clarity of the invention.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "include" are intended to indicate that there is a feature, step, function, component, or combination thereof described on the specification, and other features, steps, functions, components Or it does not exclude in advance the possibility of the presence or addition of them in combination.

On the other hand, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

Electrode for Lithium Secondary Battery

An electrode for a lithium secondary battery according to an embodiment of the present invention includes an active material body and a DLC layer.

The active material body is composed of silicon nano powder, a carbon-based conductive material and a binder. The silicon nano powder has a powder form having a nano size. The carbon-based conductive material may include at least one of carbon black, ketjen black, acetylene black, and carbon super P (manufactured by MMM). As the carbon-based conductive material is included in the active material, electrical conductivity of the active material may be improved. The binder interconnects the silicon nano powder and the carbon-based conductive material. Examples of the binder include carboxy methyl cellulose.

When an electrode having an active material body including the silicon nano powder is applied to a lithium secondary battery, the lithium secondary battery may theoretically have a charging capacity of about 4,200 mAh g ⁻¹ per unit mass.

The diamond like carbon (DLC) covers the surface of the active material body. The DLC layer has a relatively good chemical stability. In addition, the DLC layer has a relatively high Young's Modulus value.

Therefore, the DLC layer can suppress the volume expansion of the active material body. In addition, when applied to a secondary battery including an electrode including the dielc layer, the electrode may be suppressed from reacting with the electrolyte. Therefore, when the electrode including the die layer is applied to a lithium secondary battery, the lithium secondary battery may have a stable cycle characteristics.

Formation Method of Electrode for Lithium Secondary Battery

In the method for forming an electrode for a lithium secondary battery according to an embodiment of the present invention, an active material body formed of silicon nano powder, a carbon-based conductive material and a binder is formed. The silicon nano powder, the carbon-based conductive material and the binder may be controlled by a weight ratio of 4: 4: 2, for example. Here, the binder is mixed with de-ionized water or N-methylpyrrolidone (NMP). Subsequently, the active material body may be formed by further mixing the silicon nano powder and the carbon-based conductive material.

Subsequently, a diamond like carbon (DLC) layer is coated on the surface of the active material. In this case, the DLC layer may be formed through a plasma enhanced chemical vapor deposition (PECVD) process.

In the plasma enhanced chemical vapor deposition process, after placing the active material body in the chamber, a reaction gas is supplied into the chamber and ionized in a plasma state to generate reactive radicals and ions. The reaction gas may be supplied at a pressure of 1 to 100 Pa. In order to form the plasma, a radio frequency power source can be used. The radio frequency power source may use a frequency of 13.56 MHz. In addition, the radio frequency power may range from 10 to 1,000 watts. On the other hand, examples of the reaction gas include methane (CH ₄ ), acetylene (C ₂ H ₂ ).

Lithium secondary battery

Lithium secondary battery according to an embodiment of the present invention includes a positive electrode, a negative electrode and an electrolyte layer.

The positive electrode includes a positive electrode active material capable of inserting and detaching lithium ions. Such a cathode active material may be a lithium-containing transition metal oxide (lithiated cathode) used in a battery reaction such as LiCoO 2, LiMnO 2, LiNiO 2, LiCrO 2, LiMn 2 O 4. In addition, the positive electrode active material included in the positive electrode part 120 is environmentally friendly, does not use a rare metal such as cobalt (Co), and instead contains iron having abundant reserves, thus the raw material is very inexpensive, and also has a large battery capacity. It can be Lithium Iron Phosphate (LiFePO4) with contributing advantages.

The cathode is disposed to face the anode. The negative electrode includes a negative electrode active material composed of silicon nano powder, a carbon-based conductive material and a binder, and a diamond like carbon (DLC) layer covering a surface of the active material.

The active material body is composed of silicon nano powder, a carbon-based conductive material and a binder. The silicon nano powder has a powder form having a nano size. The carbon-based conductive material may include at least one of carbon black, ketjen black, acetylene black, and carbon super P (manufactured by MMM). As the carbon-based conductive material is included in the active material, electrical conductivity of the active material may be improved. The binder interconnects the silicon nano powder and the carbon-based conductive material. Examples of the binder include PVDF carboxy methyl cellulose.

The electrolyte layer is interposed between the positive electrode and the negative electrode. The electrolyte layer includes an electrolyte solution. Examples of the electrolyte may be a non-aqueous organic solvent, which may include a lithium salt. As said non-aqueous organic solvent, cyclic or acyclic carbonate, an aliphatic carboxylic acid ester, etc. can use what is single or 2 or more types are mixed.

Evaluation of the electrode for lithium secondary batteries

An active material was prepared by using silicon nano powder and carbon-based conductors such as denka black and CMC (carboxy methyl cellulose) binder in a mass ratio of 2: 2 to 1. Through the plasma enhanced chemical vapor deposition (PECVD) process on the active material body, acetylene (C2H2) gas was supplied at 100 ° C. for 5 minutes to form a DL layer.

Referring to FIG. 1, it can be seen that a DLC layer is formed on an upper surface of the active material body.

Referring to FIG. 2, in the case of the electrode not coated with the active material body using the DLC layer, it can be seen that the charge capacity rapidly decreases after 10 cycles. On the other hand, in the case of the electrode coated with the active material body using the DLC layer it can be seen that the charge capacity is maintained stably after 100 cycles.

FIG. 3 is an electron micrograph showing a surface after 15 cycles of the electrode (a) and the electrode (b) coated with the DLC layer before coating the active material body using the DLC layer.

Referring to FIG. 3, a crack occurs on the surface of the electrode (a) before the active material body is coated using the dielc layer as the active material body is expanded in volume, whereas the electrode (b) coated with the dielc layer is cracked. You can see that this does not occur. Therefore, it can be seen that the DLC layer suppresses the volume expansion of the active material body.

4 and 5 are graphs analyzed by X-ray photoelectron spectroscopy on the surface after 15 cycles of the electrode before coating the active material body and the electrode after coating using the die layer.

Referring to FIGS. 4 and 5, after 15 cycles of charging and discharging, the reaction product was confirmed on the surface of the electrode. In the case of the uncoated electrode (see FIG. 4), the fluorine component of the electrolyte was coated with a dielc layer (FIG. 4). It can be confirmed that it is contained in a large amount compared to). Therefore, the DLC layer may improve the chemical stability of the active material.

The lithium secondary battery electrode according to the present invention includes a diamond like carbon (DLC) covering the surface of the active material body. Here, the DLC layer has a relatively good chemical stability. In addition, the DLC layer has a relatively high Young's Modulus value. Therefore, the DLC layer can suppress the volume expansion of the active material body. In addition, when the electrode including the die layer is applied to a secondary battery, a reaction between the electrode and the electrolyte may be suppressed. Thus, when the electrode including the die layer is applied to a lithium secondary battery, the lithium secondary battery may have stable cycle characteristics.

Claims

An active material body made of silicon nano powder, a carbon-based conductive material, and a binder; And

An electrode for a lithium secondary battery comprising a diamond like carbon (DLC) layer covering the surface of the active material.
The electrode of claim 1, wherein the carbon-based conductive material comprises one selected from the group consisting of carbon black, ketjen black, acetylene black, and carbon super P.
The electrode of claim 1, wherein the binder comprises carboxy methyl cellulose (CMC).
Forming an active material body made of silicon nano powder, a carbon-based conductive material, and a binder; And

A method of manufacturing an electrode for a lithium secondary battery comprising coating a diamond like carbon (DLC) layer on a surface of the active material.
The method of claim 4, wherein the coating of the diamond like carbon (DLC) layer is performed through a plasma enhanced chemical vapor deposition (PECVD) process. Manufacturing method.
A positive electrode including a positive electrode active material;

A negative electrode disposed to face the positive electrode and including a negative electrode active material body including silicon nano powder, a carbon-based conductive material and a binder, and a diamond like carbon (DLC) layer covering a surface of the active material; And

A lithium secondary battery interposed between the positive electrode and the negative electrode and comprising an electrolyte layer.