KR102021895B1 - 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 the electrode potential without increasing the cell resistance between the working electrode and the counter electrode, and a method of manufacturing the same, wherein the three-electrode coin according to the present invention The cell improves the evaluation characteristics of the three-electrode cell by simultaneously measuring not only the battery potential (potential difference between the operating and counter electrodes) but also the accurate electrode potential (working electrode and counter electrode) even under high current density battery operating conditions. It can be usefully used in secondary batteries such as batteries.

Description

Three-Electrode Coin Cell with Low Overpotential

The present invention relates to a three-electrode coin cell with improved overvoltage characteristics, and more particularly, to a three-electrode cell for measuring an operating potential difference of a secondary battery, wherein the three-electrode cell includes a working electrode, a counter electrode, and a reference electrode. Electrode group; A separator which prevents electrical contact between the electrode groups and is impregnated with an electrolyte capable of ion migration; And a coin-shaped housing in which components including the electrode group, the electrolyte, and the separator are sealed in a sealed state.

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

In general, a secondary battery has two electrodes (a cathode and an anode for convenience) and a working electrode and a counter electrode, and prevents physical contact between the two electrodes. It consists of an electrolyte (the liquid is impregnated with the membrane) that functions to allow the movement of ions between the separator and 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 the storage and emission of energy, and measuring the electrode potential constituting the secondary battery for checking the performance of the battery and evaluating the material of the battery. Done. The potential of an electrode is a relative value. In general, the potential value in a two-electrode cell using two electrodes indicates a difference between an operation and a counter electrode potential. The self-potential of the electrode changes when a current flows. In the case of a 2-electrode cell, the potential of the working electrode changes under the operating conditions under which the current flows, and the counter electrode potential also changes so that the potential of the actual working electrode can be precisely adjusted. You will have trouble measuring it. Accordingly, in order to accurately measure the voltage of the working electrode, electrochemical characteristics are generally measured by configuring a three-electrode cell having an additional reference electrode. 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. The current itself flows between the working electrode and the counter electrode, and almost no current flows to the reference electrode. The potential of the electrode itself is not changed. For more accurate potential measurements, the reference electrode needs to be positioned as close to the working electrode as possible to reduce the resistance without disturbing the flow of current between the working and counter electrodes. Types of trielectrode cells include beaker cell type, Swagelok type, and pouch type. However, most of these three electrode cells are not standardized, and thus the experimenter arbitrarily configures the cell. The cell resistance value changes significantly, which may cause a large amount of error in measuring and analyzing the electrode potential.

In the secondary battery field, coin type cells having dimensions such as 2032 and 2016 are commercially available and are widely used in research fields related to secondary battery design, characterization, and material development. Although the dimensions of the cell are fixed, there is a limit to increasing the size of the electrode, but it is easy to assemble and has a big advantage in evaluating electrode performance as a standardized cell. However, it is simple to configure, and it is a cell that can only evaluate a general two-electrode system.It has a limitation in measuring accurate electrode potential, and it is possible to measure a precise electrode potential and develop a coin-type three-electrode cell that is easy to assemble. This is necessary.

Accordingly, 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, in consideration of the problems of the prior art, and thus a battery having a high current density. The present invention has been completed by producing a three-electrode coin cell capable of simultaneously measuring not only battery potential (potential difference between operating and counter electrodes) but also accurate electrode potential (working electrode and counter electrodes) under operating conditions.

Korean Patent Registration No. 10-1739625 Japanese Patent Publication No. 2015-065096 Korean Patent Registration No. 10-1471966 Japanese Patent Publication No. 2010-231963

In the three-electrode cell for measuring the electrode potential of the conventional secondary battery, the gap between the working electrode and the counter electrode is widened to insert a reference electrode between the working electrode and the counter electrode, which causes the IR resistance of the cell to rise so that overvoltage characteristics are important. In the system, there is a problem that it is not easy to apply, or to increase the volume of the three-electrode cell to measure, which ultimately makes it difficult to accurately measure the actual potential of the secondary battery.

An object of the present invention, in consideration of the problems of the prior art, a three-electrode coin cell comprising a reference electrode capable of accurately measuring the electrode potential without increasing the cell resistance between the working electrode and the counter electrode and a method of manufacturing the same This allows the evaluation of three-electrode cells by simultaneously measuring not only the battery potential (potential difference between operating and counter electrode) but also the correct electrode potential (working electrode and counter electrode) even under high current density cell operating conditions. Properties can be improved.

In order to achieve the above object,

The present invention

A three electrode cell for measuring the operation potential difference of the secondary battery, the three electrode cell

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

A separator which prevents electrical contact between the electrode groups and is impregnated with an electrolyte capable of ion migration; And

It provides a three-electrode coin cell comprising a; housing in the form of a coin in which the components including the electrode group, the electrolyte and the separator is embedded in a sealed state.

In addition, the present invention

1) an electrode group including a working electrode, a counter electrode and a reference electrode; A separator consisting of a first separator and a second separator impregnated with an electrolyte; A gas kat formed in the upper and lower portions of the gap into which the reference electrode is inserted; And a housing having a coin shape and an upper case and a lower case in which receiving grooves are formed. And

2) bottom case; Counter electrode; A first separator; Gascat; A second separator; Working electrode; And stacking in order of the upper case and inserting the reference electrode into the gasket gap so that the components are sealed in a coin-shaped housing and embedded therein.

In addition, the present invention

It provides a secondary battery comprising a three-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 comprising a reference electrode capable of accurately measuring the electrode potential without increasing the cell resistance between the working electrode and the counter electrode, and thus the battery operating conditions of high current density Under these conditions, the evaluation characteristics of the three-electrode cell can be improved by simultaneously measuring not only the battery potential (potential difference between the operation and counter electrodes) but also the accurate electrode potential (working electrode and counter electrodes).

1 is a view showing a three-electrode coin cell configuration according to the present invention.
Figure 2 is a graph showing the charging curve results for each of the current density (0.5 and 6 C) of the lithium ion batteries prepared in Examples 1 and 2, and Comparative Examples 1, 2, 3 and 4.
3 is a graph showing the electrode capacity and the charging time results in the constant voltage-constant current region during charging of the lithium ion batteries prepared in Examples 1 and 2 and Comparative Examples 1, 2, 3, and 4. FIG.
Figure 4 is a graph showing the results of the charging curve for each current density and electrode of the three-electrode coin cell prepared in Example 1.

Hereinafter, the present invention will be described in detail.

The present invention is a three-electrode cell for measuring the operating potential difference of the secondary battery, the three-electrode cell comprising an electrode group including a working electrode, a counter electrode and a reference electrode; A separator which prevents electrical contact between the electrode groups and is impregnated with an electrolyte capable of ion migration; It provides a three-electrode coin cell comprising a; and a housing in the form of a coin in which the component is embedded in a sealed state.

The three-electrode cell is composed of an electrode group consisting of a working electrode, a counter electrode, and a reference electrode. In the case of the working electrode and the counter electrode, an electrode material is generally coated on a current collector to electrically and externally cover an outer material and a spacer of a coin cell. Physically adhered well, if the form can be assembled into a coin cell is not a big problem.

In the case of the reference electrode, a thin metal foil is used as the current collector, and a portion of the current collector contacting the working electrode with the separator therebetween is coated with a material used as the reference electrode, and the size of the working electrode is reduced. In order to produce a tip shape is preferable.

The portion of the current collector of the reference electrode, which is in contact with the coin cell case, is preferably coated with an insulating layer for preventing a cell short circuit. As the current collector, Al, Ni, Cu, Ti, or the like may be used as a metal material having no side reaction with the material used as the reference electrode. A carbon-based current collector having excellent conductivity may be used if a self-supporting form is possible. In general, the insulating layer is preferably coated with a PTFE material, but in addition, if electrically insulating and thin coating and attachment are possible, the material itself is not limited.

If the area of the reference electrode is large, the movement of current between the working electrode and the counter electrode can be disturbed, and the cell overvoltage can be increased. Therefore, if it is necessary to minimize the area of the reference electrode that matches the working electrode, It is preferred to have a size of 5% or less and more preferably 1 to 5% of the working electrode area. The current collector thickness of the reference electrode inserted between the working electrode and the counter electrode is preferably 100 μm or less, because the thicker the thickness, the greater the IR of the cell, and thus the overvoltage performance is degraded. The thickness of the current collector and the insulating layer is preferably within 400 μm, and the thicker the thickness, the more difficult the sealing is when the cell is sealed, which may cause electrolyte leakage and contamination due to inflow of external air. The chances are high.

The separator may include a first separator inserted between the working electrode and the counter electrode and a second separator inserted between the reference electrode and the working electrode. In the case of the first separator, if the working electrode and the counter electrode have an area where physical contact does not occur while the electrolyte is impregnated, there is no restriction in the separator area. Since the cell overvoltage can be increased, it is necessary to minimize the area while preventing physical contact between the working electrode and the reference electrode, and preferably have a size of 5% or less of the working electrode area.

As the cell seals, a gap must be made in the top and bottom of the gasket to allow the reference electrode to be inserted. When the reference electrode is inserted without the gap, a problem arises in that the reference electrode is cut off at the coin cell bonding surface when the coin cell is assembled, and thus the reference electrode cannot operate. If the pore size increases, coin cell sealing is difficult after cell assembly, and contamination due to leakage of electrolyte and inflow of external air may occur.

The active material of the working electrode (anode) may be used without limitation as long as it is commonly used in lithium batteries. 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), LiFePO ₄ , TiS ₂ , lithium transition metal oxides of FeS ₂ , transition metal sulfides, and the like.

The counter electrode (cathode) active material may be used without limitation as long as it is commonly used in lithium batteries. For example, it may include one or more selected from the group consisting of lithium metal, a metal alloyable with lithium, a metal oxide, and a carbon-based material. For example, the metal alloyable with lithium may include Si, Sn, Al, Ge, Pb, Bi, and the like, and the metal oxide may be lithium titanium oxide, SnO ₂ , SiO _x (0 <x <2), or the like. to be. The carbonaceous material may be crystalline carbon, amorphous carbon or a mixture thereof.

The reference electrode material is not limited in kind as long as it is an electrode material capable of maintaining a constant voltage. For example, it is possible to maintain a constant electrode voltage, such as lithium metal and lithium alloy metal, even if the intercalation reaction, LiFePO ₄ and Li ₄ Ti ₅ O ₁₂ having a flat voltage characteristics can be utilized.

The non-aqueous electrolyte may serve as a medium in which lithium ions may move and may use an organic solvent that does not contain water. Examples of the electrolyte include propylene carbonate, ethylene carbonate, fluoroethylene carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ- Butyrolactone, dioxolane, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetamide, dimethylsulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene , Nitrobenzene, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, dipropyl carbonate, dibutyl carbonate, diethylene glycol, dimethyl ether, dimethyl diglycol, dimethyl triglycol , Solvents such as dimethyl tetraglycol or mixtures 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 water), lithium salts such as LiCl, LiI or a mixture thereof may be dissolved and used.

The electrolyte may be used by being impregnated in a porous separator. As the separator, any one commonly used in a lithium battery may be used. In particular, it is desirable to have low resistance to ion migration of the electrolyte and excellent electrolyte impregnation ability. For example, it is selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in a nonwoven or woven form. Specifically, a rollable separator such as polyethylene or polypropylene, or a separator having excellent organic electrolyte solution impregnation ability is used.

The three-electrode cell is not limited to a lithium secondary battery, a secondary battery that can be manufactured in the form of a coin cell using Na, Ca, K, Zn, etc. as a battery operating medium, using an organic electrolyte, an aqueous electrolyte, a solid electrolyte, and the like; It can be used for all applications such as supercapacitor field.

In addition, the present invention 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 separator consisting of a first separator and a second separator impregnated with an electrolyte; A gas kat formed in the upper and lower portions of the gap into which the reference electrode is inserted; And a housing having a coin shape and an upper case and a lower case in which receiving grooves are formed. And, 2) lower case; Counter electrode; A first separator; Gascat; A second separator; Working electrode; And stacking the upper case in order, and inserting the reference electrode into the gasket gap to embed the components in a sealed state in a coin-shaped housing.

In the case of the reference electrode, a thin metal foil is used as the current collector, and a portion of the current collector contacting the working electrode with the separator therebetween is coated with a material used as the reference electrode, and the size of the working electrode is reduced. In order to produce a tip shape is preferable.

The portion of the current collector of the reference electrode, which is in contact with the coin cell case, is preferably coated with an insulating layer for preventing a cell short circuit. As the current collector, Al, Ni, Cu, Ti, or the like may be used as a metal material having no side reaction with the material used as the reference electrode. A carbon-based current collector having excellent conductivity may be used if a self-supporting form is possible. In general, the insulating layer is preferably coated with a PTFE material, but in addition, if electrically insulating and thin coating and attachment are possible, the material itself is not limited.

If the area of the reference electrode is large, the movement of current between the working electrode and the counter electrode can be disturbed, and the cell overvoltage can be increased. Therefore, if it is necessary to minimize the area of the reference electrode that matches the working electrode, It is preferred to have a size of 5% or less and more preferably 1 to 5% of the working electrode area. The current collector thickness of the reference electrode inserted between the working electrode and the counter electrode is preferably 100 μm or less, because the thicker the thickness, the greater the IR of the cell, and thus the overvoltage performance is degraded. The thickness of the current collector and the insulating layer is preferably within 400 μm. The thicker the thickness of the current collector and the insulating layer, the more difficult it is to seal during cell sealing, which may cause electrolyte leakage and contamination due to inflow of external air. This can be high.

In addition, the present invention provides a secondary battery including the three-electrode coin cell according to the present invention.

It is preferable that the secondary battery is a lithium ion battery.

Preferred embodiments of the present invention are as follows. The following examples are merely illustrative of the technical features of the present invention, the present invention is not limited to these embodiments.

Example  One

LiNi ₀ used as a positive electrode active material of a lithium ion battery as a working electrode _{. 6} Co _{0 . 2} Mn _{0 . 2} O ₂ is weighed 94: 3: 3 by weight of super-P (conductor), PVdF (binder), dissolved in NMP (N-methyl pyrrolidinine) solution, and then the slurry is applied over Al foil. The electrode plate was produced by blade coating. After drying sufficiently in a vacuum oven at 120 ° C. to evaporate a solvent such as NMP, the electrode density was increased through a roll press, and a cathode electrode plate having a diameter of 12 mm was punched out to prepare a coin cell. As the counter electrode (cathode), a lithium foil (200 μm thick) punched out with a diameter of 16 mm was used, and 1 M LiPF ₆ in EC / EMC (30:70 vol%) was used for the organic liquid electrolyte. As the first separator and the second separator, a polypropylene-based commercial separator (25 μm) was used. The first separator was manufactured in an 18 mm size to cover the working electrode and the counter electrode, and the second separator was adjusted in size and shape according to the reference electrode tip. 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. The reference electrode current collector portion, which is in contact with the working electrode and the second separator, is manufactured in the form of a tip. Lithium foil (100 μm), which is used as the reference electrode material, is attached to both sides of the current collector tip, and the reference electrode material is applied to the working electrode area. 2% of the size was adjusted. As shown in FIG. 1, for assembling a three-electrode coin cell, grooves were prepared in the upper and lower sides of the gasket so that the reference electrode was inserted into the gasket portion of the coin cell, and the working electrode, the counter electrode, the reference electrode, and the electrolyte were impregnated. The prepared first and second separators were stacked as shown in FIG. 1 to prepare a three-electrode coin cell.

Example 2

A three-electrode coin cell was manufactured 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 5% of the working electrode area.

Comparative example  One

A three-electrode coin cell was manufactured 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 made.

Comparative example  2

A three-electrode coin cell was manufactured in the same manner as in Example 1, except that the second separator was applied to the same size as the first separator, the reference electrode was not added, and the groove of the gasket was not made.

Comparative example  3

A three-electrode coin cell was manufactured 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 area of the working electrode.

Comparative example  4

A three-electrode coin cell was manufactured in the same manner as in Example 1 except that the size of the reference electrode and the second separator in contact with the working electrode was 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 produced through Examples 1 and 2 and Comparative Examples 1, 2, 3, and 4 was performed by comparing the current density. The overvoltage characteristics are characterized by the higher current density, so for low current (0.5 C) and high current (6 C), it is 27 ℃ under constant voltage condition within 10% of constant current charge-constant current value up to 4.3 V voltage. Charge evaluation was performed at, and the charge curve of each cell is shown in FIG. 2.

0.5C low current showed similar charging performance except for Comparative Example 4, and it was confirmed that the overvoltage characteristic of Comparative Example 4 was the worst in 6C high current condition. Under 6C current conditions, it was found that the overvoltage characteristics were lowered in comparison with Comparative Example 2 and Comparative Example 3, Comparative Example 1, and Examples 1 and 2, respectively. Example 1 and Example 2 exhibited almost the same overvoltage characteristics as those of Comparative Example 1, which was a two-electrode cell except for the initial charge.

In order to quantitatively identify the overvoltage characteristic, the charging curve of FIG. 2 was analyzed by dividing the capacity and the charging time (in minutes) in the constant current and constant voltage regions, which are shown in FIG. 3.

The better the overvoltage characteristic, the longer the capacity and charging time under constant current conditions, and the lower the capacity and charging time under constant voltage conditions. Compared with Comparative Example 1, which is a two-electrode cell at 0.5 C low current, Examples 1 and 2 showed similar characteristics, and the same results were obtained even at 6 C high current. In Comparative Examples 2, 3 and 4, the overvoltage characteristics were lowered at low current and high current compared to Comparative Examples 1, 1 and 2, which were operated due to the reference electrode and the second separator added to configure the three electrodes. This is because the flow of current between the electrode and the counter electrode is disturbed. In particular, as the thickness and area of the reference electrode and the second separator increase, the overvoltage characteristics deteriorate. When the size of the reference electrode and the second separator is 5% or less of the reference electrode as in Examples 1 and 2, It was found that the three-electrode cell can be configured with similar overvoltage characteristics.

4 is a result showing the charging behavior according to the current density of the three-electrode cell produced in Example 1. In the two-electrode cell as in Comparative Example 1, only the voltage value between the working electrode and the counter electrode can be measured, whereas in the three-electrode cell of Example 1, as shown in FIG. 4, the voltage value between the working electrode and the counter electrode (black In addition to the color line), it was confirmed that the voltage values (relative to the reference electrode) of the working electrode and the counter electrode can be successfully measured simultaneously.

Claims (9)

A three electrode cell for measuring the operation potential difference of the secondary battery, the three electrode cell
An electrode group including a working electrode, a counter electrode, and a reference electrode;
A separator which prevents electrical contact between the electrode groups and is impregnated with an electrolyte capable of ion movement, wherein the separator is a first separator inserted between a working electrode and a counter electrode, and a second separator inserted between a reference electrode and a working electrode. Separation membrane, characterized in that consisting of a membrane;
A gasket formed in the upper and lower portions of the gap into which the reference electrode can be inserted; And
And a housing formed of an upper case and a lower case each having a coin shape and receiving grooves formed therein.
here
Lower case; Counter electrode; A first separator; Gascat; A second separator; Working electrode; And top case is stacked in order,
The reference electrode is inserted into the gasket gap.
Characterized in that the components including the electrode group, the electrolyte and the separator is embedded in a sealed state consisting of the upper case and the lower case of the coin type,
Trielectrode coin cell.
The method of claim 1,
The reference electrode uses a metal foil as a current collector, and a portion of the current collector which is in contact with the working electrode and the separator therebetween is coated with a material used as a reference electrode, and a portion that is in contact with the coin cell case prevents a cell short circuit. Three-electrode coin cell characterized in that the insulating layer for coating.
Claim 3 has been abandoned upon payment of a set-up fee. The method of claim 1,
The size of the reference electrode in contact with the working electrode is a three-electrode coin cell, characterized in that 1 to 5% of the area of the working electrode.
delete delete 1) an electrode group including a working electrode, a counter electrode and a reference electrode; A separator consisting of a first separator and a second separator impregnated with an electrolyte; A gas kat formed in the upper and lower portions of the gap into which the reference electrode is inserted; And a housing having a coin shape and an upper case and a lower case in which receiving grooves are formed. And
2) bottom case; Counter electrode; A first separator; Gascat; A second separator; Working electrode; And stacking in the upper case order and inserting the reference electrode into the gasket gap to embed components in a sealed state in a coin-shaped housing.
The method of claim 6,
The reference electrode uses a metal foil as a current collector, and a portion of the current collector which is in contact with the working electrode and the separator therebetween is coated with a material used as a reference electrode, and a portion that is in contact with the coin cell case prevents a cell short circuit. Method for producing a three-electrode coin cell characterized by coating an insulating layer for.
Claim 8 has been abandoned upon payment of a set-up fee. The method of claim 6,
The size of the reference electrode in contact with the working electrode is a manufacturing method of a three-electrode coin cell, characterized in that used in 1 to 5% of the area of the working electrode.
Secondary battery comprising a three-electrode coin cell according to claim 1.

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