KR20190061297A - Three-Electrode Coin Cell with Low Overpotential - Google Patents

Abstract

The present invention relates to a three-electrode coin cell comprising a reference electrode capable of accurately measuring electrode potential without increasing the cell resistance between a working electrode and a counter electrode, and to a method for manufacturing the same. The three-electrode coin cell according to the present invention enhances the evaluation properties of the three-electrode cell by simultaneously measuring the battery potential (potential difference between the working electrode and the counter electrode) and accurate electrode potential (the working electrode and the counter electrode) even under high current density battery operating condition, thereby being usefully used in secondary batteries such as lithium ion batteries.

Description

Electrode Coin Cell with Low Overpotential < RTI ID = 0.0 >

The present invention relates to a three-electrode coin cell having improved overvoltage characteristics, and more particularly, to a three-electrode cell for measuring a working potential difference of a secondary battery, the three-electrode cell including a working electrode, a counter electrode, Electrode group; A separation membrane impregnated with an electrolytic solution capable of ion-transferring to prevent electrical contact between the electrode groups; And a coin-shaped housing in which the electrode assembly, the electrolyte, and the separator are enclosed in a sealed state.

Recently, researches on secondary batteries such as lithium ion batteries have been actively conducted for efficient use of energy, and various efforts have been made to use them as energy sources for electric vehicles and electric power storage as well as small-sized mobile electronic devices.

Generally, a secondary cell has two electrodes, a working electrode and a counter electrode (also referred to as a cathode and an anode for convenience) and a pair of electrodes that prevent physical contact between the two electrodes The separator consists of an electrolyte (which is impregnated in the separator in the case of liquid) which functions to allow movement of ions between the two electrodes (which prevents the movement of electrons). A current flows between the working electrode and the counter electrode and a voltage difference is generated thereby enabling energy storage and discharge. In order to confirm the performance of the battery and evaluate the constituent materials of the battery, the electrode potential of the secondary battery is measured . The potential of the electrode is a relative value. In general, a potential value in a two-electrode cell using two electrodes represents the difference between the operation and the counter electrode potential. In the case of a two-electrode cell, the potential of the working electrode is also changed under the operating condition under which current flows, and the potential of the working electrode is also changed, It is difficult to measure it. Therefore, in order to accurately measure the voltage of the working electrode, a three-electrode cell having a reference electrode is generally constructed to measure electrochemical characteristics. In the three-electrode cell, the reference electrode is used as a reference of the potential when measuring the relative value of the electrode potential in the detection system. Since the current itself flows between the working electrode and the counter electrode and almost no current flows through the reference electrode, The potential of the electrode itself does not change. For more precise potential measurement, the reference electrode needs to be located as close as possible to the working electrode to reduce the resistance, without interfering with the flow of current between the working electrode and the counter electrode. The three electrode cell types include a beaker cell type, a Swagelok type cell type, and a pouch type cell type. However, most of these three-electrode cells are not standardized, The cell resistance value is greatly changed, which may cause a large error in measuring and analyzing the electrode potential.

In the field of secondary batteries, coin type cells having dimensions such as 2032 and 2016 are commercially available and are widely used in research fields related to secondary cell design, characterization and material development. Although the dimensions of the cell are fixed, there is a limit to increase the size of the electrode. However, it has a great advantage in evaluating the electrode performance as a standardized cell that is easy to assemble. However, it is possible to evaluate the electrode potential accurately by using simple two-electrode system evaluation. Therefore, it is possible to measure the electrode potential accurately and to develop a technology for a coin-type three-electrode cell which is easy to assemble. .

Therefore, in consideration of the problems of the prior art, the present invention includes a reference electrode capable of accurately measuring the electrode potential, without increasing the cell resistance between the working electrode and the counter electrode, Electrode coin cell capable of simultaneously measuring the electrode potential (working electrode and counter electrode) as well as the cell potential (potential difference between the working electrode and the charging electrode) under the operating conditions.

Korean Patent Registration No. 10-1739625 Japanese Patent Application Laid-Open No. 2015-065096 Korean Patent Registration No. 10-1471966 Japanese Patent Application Laid-Open No. 2010-231963

Conventionally, a three-electrode cell for measuring the electrode potential of a secondary battery has a gap between a working electrode and a charging electrode in order to insert a reference electrode between the working electrode and the charging electrode, thereby increasing the IR resistance of the cell, There is a problem in that it is not applicable to the system or it is necessary to measure by increasing the volume of the three electrode cell, which ultimately makes it difficult to accurately measure the actual potential of the secondary battery.

SUMMARY OF THE INVENTION An object of the present invention is to provide a three-electrode coin cell including a reference electrode capable of accurately measuring the electrode potential without increasing the cell resistance between the working electrode and the counter electrode, (Operation electrode and counter electrode) as well as cell potential (potential difference between operation and counter electrode) as well as accurate electrode potential (working electrode and counter electrode) under battery operating conditions of high current density, The characteristics can be improved.

In order to achieve the above object,

The present invention

A three electrode cell for measuring a working potential difference of a secondary battery,

An electrode group including a working electrode, a counter electrode, and a reference electrode;

A separation membrane impregnated with an electrolytic solution capable of ion-transferring to prevent electrical contact between the electrode groups; And

And a coin-shaped housing in which a structure including the electrode group, the electrolyte, and the separator is embedded in a sealed state.

In addition,

1) an electrode group including a working electrode, a counter electrode, and a reference electrode; A separation membrane comprising a first separation membrane and a second separation membrane impregnated with an electrolyte; A gasket formed on upper and lower portions of a gap portion into which a reference electrode is inserted; And a housing having an upper case and a lower case in a coin shape and having receiving grooves, respectively; And

2) Lower case; Counter electrode; A first separation membrane; Gas Cat; A second separation membrane; Working electrode; And the upper case are stacked in this order, and the reference electrode is inserted into the gasket void portion, and the components are housed in the coin-shaped housing in a sealed state.

In addition,

Electrode coin cell according to the present invention, or a three-electrode coin cell manufactured by the manufacturing method.

The present invention is a technique for manufacturing a three-electrode coin cell including a reference electrode capable of accurately measuring the electrode potential, without increasing the cell resistance between the working electrode and the counter electrode, The evaluation characteristic of the three electrode cell can be improved by simultaneously measuring the accurate electrode potential (working electrode and counter electrode) as well as the cell potential (potential difference between the operation and the charging electrode).

1 is a view showing a configuration of a three-electrode coin cell according to the present invention.
FIG. 2 is a graph showing the results of charging curves of current density (0.5 and 6 C) of the lithium ion batteries manufactured in Examples 1 and 2 and Comparative Examples 1, 2, 3 and 4. FIG.
3 is a graph showing electrode capacities and charging time results in a constant voltage-constant current region when the lithium ion batteries prepared in Examples 1 and 2 and Comparative Examples 1, 2, 3 and 4 are charged.
4 is a graph showing the results of charge density curve and current density of the three-electrode coin cell manufactured in Example 1. FIG.

Hereinafter, the present invention will be described in detail.

A three electrode cell for measuring a working potential difference of a secondary battery, wherein the three electrode cell comprises an electrode group including a working electrode, a counter electrode and a reference electrode; A separation membrane impregnated with an electrolytic solution capable of ionic movement and preventing electrical contact between the electrode groups; And a coin-shaped housing in which the structure is embedded in a sealed state.

In the case of the working electrode and the counter electrode, in general, the electrode material is coated on the current collector to electrically and electrically connect the coin cell to the outer casing and the spacer. There is no big problem if it is physically adhered well and can be assembled into a coin cell.

In the case of the reference electrode, a metal foil having a small thickness is used as the current collector, and the current collector portion contacting the working electrode and the separating film is coated with a material used as a reference electrode. It is preferable to make a tip shape.

It is preferable that a portion of the current collector of the reference electrode which contacts the coin cell case is coated with an insulating layer for preventing a cell short circuit. As the current collector, Al, Ni, Cu, Ti, etc. can be used as a reference electrode and a metal material having no side reaction, and a carbon-based current collector having excellent conductivity can also be used if the self-sustaining type is possible. The insulating layer is preferably coated with a PTFE material. However, if the insulating layer can be electrically insulated and can be thinly coated and adhered, the material itself is not limited.

If the area of the reference electrode is large, the movement of the current between the working electrode and the counter electrode is prevented and the cell overvoltage can be increased. Therefore, if it is necessary to minimize the area of the reference electrode that is in contact with the working electrode, It is preferable to have a size of 5% or less and more preferably have a size of 1 to 5% of the working electrode area. The thickness of the current collector of the reference electrode inserted between the working electrode and the counter electrode is preferably within 100 占 퐉 because the IR of the cell becomes larger as the thickness of the reference electrode increases. The thickness of the current collector and the insulating layer is preferably 400 m or less. When the thickness is thicker, sealing becomes difficult during cell sealing and contamination due to electrolyte leakage and external air inflow may occur. In addition, The possibility may increase.

In the case of the separator, the separator may include a first separator interposed between the working electrode and the counter electrode, and a second separator interposed between the reference electrode and the working electrode. In the case of the first separation membrane, there is no restriction on the separation membrane area if the electrolyzer is impregnated and the working electrode and the counter electrode are not in physical contact with each other. However, in the case of the second separation membrane, It is desirable to minimize the area while preventing physical contact between the working electrode and the reference electrode and to have a size of 5% or less of the working electrode area because the cell overvoltage can be increased.

As the cell sealing is performed, a void portion should be formed in the upper and lower portions of the gaskets so that the reference electrode can be inserted. If the reference electrode is inserted without the gap, there is a problem that the reference electrode is cut off at the coin cell bonding surface during assembly of the coin cell, so that the reference electrode can not operate. When the size of the air gap is increased, it is difficult to seal the coin cell after assembling the cell, so that electrolyte leakage and contamination due to external air inflow may occur.

The active material of the working electrode (anode) can be used as long as it is commonly used in a lithium battery. For _{example, LiCoO 2, LiMnO 2, LiMn} 2 O 4, LiNi 1 - x Mn x O2 (0 <x <1), LiNi 1 -x- y Co x Mn y O 2 (0 <x <0.5, 0 <y <0.5), lithium transition metal oxide of LiFePO ₄ , TiS ₂ , FeS ₂ , transition metal sulfide, and the like.

The positive electrode (negative electrode) active material can be used as long as it is commonly used in a lithium battery. For example, at least one selected from the group consisting of a lithium metal, a metal capable of alloying with lithium, a metal oxide, and a carbon-based material. For example, examples of the metal capable of being alloyed with lithium include Si, Sn, Al, Ge, Pb and Bi. Examples of the metal oxide include lithium titanium oxide, SnO ₂ , SiO _x to be. The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof.

The reference electrode material is not limited to an electrode material that can maintain a constant voltage. For example, LiFePO ₄ and Li ₄ Ti ₅ O ₁₂ having flat voltage characteristics can be utilized even if they can maintain a constant electrode voltage such as a lithium metal and a lithium alloy metal or exhibit an intercalation reaction.

The non-aqueous electrolyte acts as a medium through which lithium ions can move, and an organic solvent that does not contain water can be used. Examples of the electrolyte solution include propylene carbonate, ethylene carbonate, fluoroethylene carbonate, diethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, But are not limited to, butyrolactone, dioxolane, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetamide, dimethylsulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, Dimethyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, dipropyl carbonate, dibutyl carbonate, diethylene glycol, dimethyl ether, dimethyldiglycol, dimethyltriglycol , tetraethylene glycol dimethyl or in a solvent such as a mixture thereof LiPF _6, LiBF _{4 , LiSbF 6, LiAsF 6, LiClO} 4, LiCF 3 SO 3, Li (CF 3 SO 2) 2 N, LiC 4 F 9 SO 3, LiSbF 6, LiAlO 4, LiAlCl 4, LiN (C x F 2x + 1 SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (where x and y are natural numbers), LiCl, LiI, or a mixture thereof.

The electrolyte may be impregnated into a porous separator. The separator may be any of those conventionally used in lithium batteries. Particularly, it is preferable that the electrolytic solution has a low resistance against the ion movement of the electrolyte and an excellent electrolytic solution impregnation ability. For example, selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be nonwoven fabric or woven fabric. Specifically, a windable separator such as polyethylene, polypropylene or the like, or a separator excellent in the ability to impregnate the organic electrolyte is used.

The three-electrode cell is not limited to a lithium secondary battery, and may be a secondary battery which can be manufactured in the form of a coin cell using Na, Ca, K, Zn, or the like as a battery operating medium and using an organic electrolyte, an aqueous electrolyte, Super capacitors, and the like.

The present invention also provides a method of manufacturing a three-electrode coin cell according to the present invention.

Specifically, the manufacturing method includes: 1) an electrode group including a working electrode, a counter electrode, and a reference electrode; A separation membrane comprising a first separation membrane and a second separation membrane impregnated with an electrolyte; A gasket formed on upper and lower portions of a gap portion into which a reference electrode is inserted; And a housing having an upper case and a lower case in a coin shape and having receiving grooves, respectively; And 2) a lower case; Counter electrode; A first separation membrane; Gas Cat; A second separation membrane; Working electrode; And the upper case, and inserting the reference electrode into the gasket void portion to enclose the components in a sealed state in the coin-shaped housing.

In the case of the reference electrode, a metal foil having a small thickness is used as the current collector, and the current collector portion contacting the working electrode and the separating film is coated with a material used as a reference electrode. It is preferable to make a tip shape.

It is preferable that a portion of the current collector of the reference electrode which contacts the coin cell case is coated with an insulating layer for preventing a cell short circuit. As the current collector, Al, Ni, Cu, Ti, etc. can be used as a reference electrode and a metal material having no side reaction, and a carbon-based current collector having excellent conductivity can also be used if the self-sustaining type is possible. The insulating layer is preferably coated with a PTFE material. However, if the insulating layer can be electrically insulated and can be thinly coated and adhered, the material itself is not limited.

If the area of the reference electrode is large, the movement of the current between the working electrode and the counter electrode is prevented and the cell overvoltage can be increased. Therefore, if it is necessary to minimize the area of the reference electrode that is in contact with the working electrode, It is preferable to have a size of 5% or less and more preferably have a size of 1 to 5% of the working electrode area. The thickness of the current collector of the reference electrode inserted between the working electrode and the counter electrode is preferably within 100 占 퐉 because the IR of the cell becomes larger as the thickness of the reference electrode increases. It is preferable that the current collector and the insulating layer have a thickness of 400 占 퐉 or less. The thicker the thickness, the more difficult it is to seal during the cell sealing, and the electrolyte leakage and contamination due to external air inflow may occur. Can be increased.

The present invention also provides a secondary battery including the three-electrode coin cell according to the present invention.

The secondary battery is preferably a lithium ion battery.

A preferred embodiment of the present invention is as follows. The following embodiments are illustrative of the technical features of the present invention, and the present invention is not limited to these embodiments.

Example  One

LiNi ₀ used as the cathode active material of the lithium ion battery as working electrode _{. 6} Co _{0 . 2} Mn _{0 . 2} O ₂ was weighed and mixed with N-methyl pyrrolidine (NMP) solution at a weight ratio of super-P (conductive material) and PVdF (binder) in a weight ratio of 94: 3: 3, and the slurry was placed on an aluminum foil And blade coating was performed to produce an electrode plate. After sufficiently drying in a vacuum oven at 120 ° C, the solvent such as NMP was volatilized and the electrode density was increased through a roll press. A positive electrode plate having a diameter of 12 mm was prepared for coin cell assembly. Lithium foil (200 μm thick) punched out with a diameter of 16 mm was used as the counter electrode (cathode) and 1 M LiPF ₆ in EC / EMC (30:70 vol%) as the organic liquid electrolyte. A polypropylene-based commercial separation membrane (25 μm) was used for the first separation membrane and the second separation membrane. In case of the first separation membrane, the size was 18 mm to cover the working electrode and the counter electrode. In the case of the second separation membrane, the size and shape were adjusted according to the tip of the reference electrode. A Cu foil (20 μm thick) was used as a reference electrode current collector, and a portion contacting the coin cell was prepared by attaching an insulator for insulation. A lithium foil (100 μm) used as a reference electrode material was attached to both sides of the collector tip, and the reference electrode material was applied to the working electrode area Of the total volume. 1, for assembly of a three-electrode coin cell, grooves were prepared on the upper and lower sides of the gasket so that the reference electrode could be inserted into the gasket portion of the coin cell, and the working electrode, the counter electrode, The first and second separation membranes were laminated as shown in Fig. 1 to prepare a three-electrode coin cell.

Example 2

A three-electrode coin cell was prepared in the same manner as in Example 1, except that the sizes of the reference electrode and the second separator contacting the working electrode were adjusted to 5% of the working electrode area.

Comparative Example  One

A three-electrode coin cell was fabricated in the same manner as in Example 1, except that the second separator and the reference electrode were not added and the groove of the gasket was not formed.

Comparative Example  2

A three-electrode coin cell was fabricated in the same manner as in Example 1, except that the second separation membrane was applied in the same size as the first separation membrane, no reference electrode was added, and no grooves were formed in the gasket.

Comparative Example  3

A three electrode coin cell was prepared in the same manner as in Example 1 except that the size of the reference electrode and the second separator contacting the working electrode was adjusted to 30% of the working electrode area.

Comparative Example  4

Electrode coin cell was prepared in the same manner as in Example 1 except that the sizes of the reference electrode and the second separator contacting the working electrode were adjusted to 50% of the working electrode area.

Evaluation Example 1: Measurement of charging performance by current density for comparison of overvoltage characteristics

The constant current-constant voltage charging evaluation of the lithium ion batteries fabricated through Examples 1 and 2 and Comparative Examples 1, 2, 3 and 4 was carried out by comparing current density. The overvoltage characteristic can be characterized by the higher current density. Constant current charging up to 4.3 V for low current (0.5 C) and high current (6 C) - Constant voltage within 10% , And the charging curve of each cell is shown in FIG.

The similar charging performance was observed at 0.5 C low current except for Comparative Example 4 and the overvoltage characteristic of Comparative Example 4 was found to be lowest even at 6 C high current condition. It was found that the overvoltage characteristics were lowered in Comparative Example 2 and Comparative Example 3, Comparative Example 1, and Examples 1 and 2 under the 6C current condition. It can be seen that Examples 1 and 2 exhibit an overvoltage characteristic substantially similar to Comparative Example 1 which is a two-electrode cell except for the initial stage of charging.

In order to quantitatively confirm the overvoltage characteristic, the charge curve of FIG. 2 was analyzed by dividing it by the capacity and the charge time (in minutes) in the constant current and constant voltage regions and is shown in FIG.

The better the overvoltage characteristic, the greater the capacity and charge time under constant current conditions, and the capacity and charge time under constant voltage conditions are reduced. Compared with Comparative Example 1, which is a two-electrode cell at 0.5 C low current, similar characteristics were obtained in Examples 1 and 2, and the same results were obtained even under 6 C high current conditions. In Comparative Examples 2, 3 and 4, overvoltage characteristics were lowered at low current and high current compared to Comparative Example 1 and Embodiments 1 and 2, which were caused by the reference electrode and the second separator added to constitute the three electrodes This is because the flow of current between the electrode and the counter electrode is disturbed. Particularly, as the thickness and area of the reference electrode and the second separation membrane become larger, the overvoltage characteristic deteriorates. When the size of the reference electrode and the second separation membrane is less than 5% of the reference electrode as in the first and second embodiments, It was found that a three electrode cell could be constructed with similar overvoltage characteristics.

FIG. 4 is a graph showing a charging behavior of the three electrode cell fabricated through Example 1 according to the current density. In the two-electrode cell of Comparative Example 1, only the voltage value between the working electrode and the counter electrode can be measured. On the other hand, as shown in FIG. 4, in the three-electrode cell of Example 1, the voltage value between the working electrode and the counter electrode Color line) as well as the voltage value of the working electrode and the counter electrode (as compared with the reference electrode).

Claims (9)

A three electrode cell for measuring a working potential difference of a secondary battery,
An electrode group including a working electrode, a counter electrode, and a reference electrode;
A separation membrane impregnated with an electrolytic solution capable of ion-transferring to prevent electrical contact between the electrode groups; And
And a coin-shaped housing in which the electrode assembly, the electrolytic solution, and the separator are formed in a sealed state.
The method according to claim 1,
The reference electrode uses a metal foil as a current collector and the current collector portion contacting the working electrode and the separating film is coated with a material used as a reference electrode. Electrode coin cell according to claim 1,
The method according to claim 1,
Wherein the size of the reference electrode contacting the working electrode is 1 to 5% of the working electrode area.
The method according to claim 1,
Wherein the separator comprises a first separator interposed between the working electrode and the counter electrode, and a second separator interposed between the reference electrode and the working electrode.
The method according to claim 1,
Wherein a gap is formed in the upper and lower portions of the gasket so that the reference electrode can be inserted while the cell is sealed.
1) an electrode group including a working electrode, a counter electrode, and a reference electrode; A separation membrane comprising a first separation membrane and a second separation membrane impregnated with an electrolyte; A gasket formed on upper and lower portions of a gap portion into which a reference electrode is inserted; And a housing having an upper case and a lower case in a coin shape and having receiving grooves, respectively; And
2) Lower case; Counter electrode; A first separation membrane; Gas Cat; A second separation membrane; Working electrode; And the upper case, and inserting a reference electrode into the gasket void portion to enclose the components in a sealed state in the coin-shaped housing.
The method according to claim 6,
The reference electrode uses a metal foil as a current collector and the current collector portion contacting the working electrode and the separating film is coated with a material used as a reference electrode. Electrode coin cell according to claim 1,
The method according to claim 6,
Wherein the size of the reference electrode contacting the working electrode is 1 to 5% of the working electrode area.
A secondary battery comprising a three-electrode coin cell according to any one of claims 1 to 5.

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