JP3886974B2 - Microelectrode for electrochemical measurement and manufacturing method thereof - Google Patents

Description

The present invention relates to a microelectrode for electrochemical measurement used for evaluation of physical properties, electrochemical characteristics and the like of a battery material in a nonaqueous solvent and a method for producing the same.

Currently, as the advanced information society has developed and mobile information terminals have spread rapidly,
The importance of lighter and higher output high performance secondary batteries as portable power sources is increasing. In particular, lithium ion secondary batteries are expected to be applied to electric vehicles and power storage,
There is an urgent need for higher performance. In the research and development of these high-performance batteries, it is essential to evaluate the physical and electrochemical characteristics of newly developed battery materials.

Conventionally, evaluation of electrochemical characteristics of a battery active material for a lithium ion secondary battery has been performed by kneading a battery active material powder, a conductive additive (such as carbon black), and an organic binder (such as polyvinylidene fluoride) to form a current collector. It has been carried out by sheet-like composite electrodes crimped to metal foil and actual battery trial manufacture. The evaluation with the composite electrode is very important because it is an evaluation in a state where it is incorporated in an actual commercially available battery. However, in the composite electrode, empirical factors at the time of electrode production have a great influence on the electrochemical response, and the electrochemical response varies greatly depending on the mixing ratio of the conductive assistant, the thickness of the electrode, and the like. In addition, there has been a problem that it takes a very long time to evaluate the actual battery prototype. In any of the evaluation methods, it is difficult to accurately know the electrochemical characteristics of the active material itself, and the evaluation was performed by a method that is not the best as a material selection method in the initial stage.

On the other hand, an evaluation method in which the microelectrode method is applied to the analysis of solid electrochemical reaction has been developed. For example, Patent Document 1 discloses a diameter of 50 μm for measuring powder containing a non-aqueous electrolyte.
Discloses a microelectrode in which a thin metal wire is insulated. It is disclosed that the insulating material is glass or fluororesin, and “a thin metal wire is inserted into a glass capillary and sealed with an organic adhesive”.

However, in this case, it is difficult for an organic adhesive having a relatively high viscosity to uniformly penetrate between the fine metal wire and the glass capillary, and there is an organic adhesive particularly on the surface of the fine metal wire contacting the inner wall of the glass capillary. Voids may occur. When such a microelectrode is left for a long time, the gas (air / organic solvent) in the gap is released to the outside of the microelectrode while causing a crack between the glass capillary and the fine metal wire. When this microelectrode is immersed in an electrolytic solution and operated as an electrode, the electrolytic solution comes into contact with the fine metal wire through the crack, Li and the fine metal wire in the electrolytic solution undergo an alloying reaction, and the fine metal wire deteriorates. As a result, problems such as an increase in the background current occur due to insufficient electrical insulation, and highly accurate measurement is very difficult.
JP2003-234256

When a conventional microelectrode is used as an electrode for an electrochemical reaction, a fine metal wire is deteriorated, so that highly accurate measurement is very difficult.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide an electrochemical measurement microelectrode and a method for manufacturing the same, in which a fine metal wire is unlikely to deteriorate and high-precision measurement is possible.

In order to achieve the above object, an electrochemical measurement microelectrode according to claim 1 is formed on a metal thin wire having both ends and one end being an external output terminal of an electric signal, and the other end surface of the metal thin wire. A first fluororesin layer exposing a part of the end; a glass tube circumscribing the first fluororesin layer; and a second solidified after dipping between the glass tube and the first fluororesin layer. A microelectrode for electrochemical measurement, comprising a fluororesin layer.

The electrochemical measurement microelectrode according to claim 2 is the microelectrode for electrochemical measurements according to claim 1, wherein the thin metal wire is one or two or more alloys selected from the group consisting of stainless steel, Ni, Fe, Cu, Mo, and W. It is characterized by things.

According to a third aspect of the present invention, there is provided a method for producing a microelectrode for electrochemical measurement, wherein the first end is exposed so that a part of the other end of the fine metal wire is exposed with respect to the fine metal wire having both ends and one end being an external output terminal for an electrical signal. A step of forming a fluororesin layer, a step of forming a glass tube circumscribing the first fluororesin layer, and a second fluororesin that is solidified after being immersed between the glass tube and the first fluororesin layer. And a step of forming a layer.

The method for producing a microelectrode for electrochemical measurement according to claim 4 is the method according to claim 3, wherein the thin metal wire is one or more selected from the group consisting of stainless steel, Ni, Fe, Cu, Mo, and W. It is characterized by being an alloy.

As described above in detail, according to the present invention, it is possible to provide a microelectrode for electrochemical measurement and a method for manufacturing the same, in which a fine metal wire is hardly deteriorated and high-precision measurement is possible.

When evaluating the electrochemical characteristics of battery materials in a non-aqueous solvent, especially when performing measurements while maintaining a voltage near 0 V for a long period of time, the microelectrode is a back-up of the electrolyte. To suppress the rise in ground current,
(1) Except for the electrode tip, it must be covered with an insulator and completely sealed.

Furthermore, in order to avoid an increase in the background current caused by alloying with Li of a fine metal wire, which is a material of the microelectrode, and soaking up of the electrolyte due to micronization,
(2) The microelectrode must be fabricated using a material that is difficult to alloy with Li.

Since a metal material that does not alloy with Li is oxidized when heated by a burner, it cannot be thermally welded to glass.

Therefore, in the present invention, a microelectrode satisfying the conditions (1) and (2) was produced by the following procedure. The production procedure is simply shown in FIG. First, the fine metal wire 1 is dip coated with the fluororesin solution 2 in advance. Immerse the fine metal wire 1 in the fluororesin solution 2 and dip coat it.
Thereafter, the procedure of drying in air at 100 ° C. for about 5 minutes is repeated 5 to 20 times, more preferably 10 to 15 times. In this way, the thin metal wire 1 on which the first fluororesin layer 3 is formed is 1
After being dried in air at 00 ° C. for about 1 hour, it is inserted into the glass capillary 4. Thereafter, the tip of the glass capillary 4 in which the fine metal wire 1 is inserted is cut to leave about 1 mm to the fine metal wire 1, and the tip of the glass capillary 4 in which the fine metal wire 1 is inserted is further immersed in the fluororesin solution 2. By repeating the procedure of dip coating and then drying in air at 100 ° C. for about 5 minutes 5 to 20 times, more preferably 10 to 15 times, the space between the metal wire 1 and the glass capillary 4 and the first A second fluororesin layer 5 is formed on the surface of the fluororesin layer 3 and the surface of the glass capillary 4. Thereafter, it is vacuum dried at 200 ° C. for 12 hours. Finally, the tip of the glass capillary 4 of the microelectrode is polished with a micro grinder, and the fine metal wire 1 is exposed at the tip.

The metal fine 1 used in the present invention is a metal that is difficult to alloy with Li, such as stainless steel, Ni,
One or two or more alloys selected from the group consisting of Fe, Cu, Mo, and W are 0V to 3V.
vs. Li / Li ⁺ is preferable in that it is electrochemically inactive in the potential region. When evaluating the electrochemical characteristics of the carbon material for a non-aqueous electrolyte secondary battery negative electrode, it is more preferable to use stainless steel because the background current is the smallest.

The diameter of the fine metal wire is preferably 5 μm or more and 50 μm or less, and more preferably 10 μm or more and 30 μm from the viewpoint of miniaturization of the electrode, electrode strength, and elasticity. The reason is that the balance between the particle size of the battery material to be evaluated and the diameter of the microelectrode is in a range that is most easily measured.

Hereinafter, the present invention will be described in detail by way of examples.
Example 1
A stainless steel (SUS304) fine wire having a diameter of 20 μm was selected as a metal fine wire that is a material of the microelectrode, and a microelectrode was produced by the following procedure according to FIG. First, the SUS304 wire 1 is dip coated with the fluororesin solution 2. This fluororesin coating is repeated 10 times. The SUS304 wire 1 thus coated with the fluororesin is inserted into the glass capillary 4. After this, SU
By coating the tip of the glass capillary 4 into which the S304 wire 1 is inserted with the fluororesin solution 2, the space between the SUS304 wire 1 and the glass glass capillary 4 is eliminated. This fluororesin coating of the glass capillary 4 is repeated 10 times.

Thereafter, the microelectrode is vacuum-dried at 200 ° C. for 12 hours. Finally, the tip of the glass capillary 4 is polished with a micro grinder to expose the SUS304 wire 1 at the tip. FIG. 2 shows a schematic diagram of the tip of the stainless steel microelectrode thus produced. Stainless steel is exposed only in the cross section, and the periphery thereof is insulated by three layers of the first fluororesin layer 3, the glass capillary 4, and the second fluororesin layer 5, which are naturally not laminated in this order). I understand.

That is, the second fluororesin layer 5 exists on the outer periphery of the glass capillary 4 and also exists in a gap or a crack between the first fluororesin layer 3 and the glass capillary 4. In some cases, SUS304
There are also gaps and cracks between the line 1 and the first fluororesin layer 3. The second fluororesin layer 5 is
Except for a predetermined tip portion where the SUS304 wire 1 is exposed by being present in a gap or crack between the first fluororesin layer 3 and the glass capillary 4 or a gap or crack between the SUS304 wire 1 and the first fluororesin layer 3. There is no need to worry about contact with air or liquid.

FIG. 3 shows the results of measuring the background current of this stainless steel microelectrode in a 1M LiClO ₄ / EC + PC solution by cyclic voltammetry (CV, sweep rate: 10 mV / s). It can be confirmed that almost no current flows (less than 1 nA) in the potential region of ⁰ V to 3 V vs. Li / Li ⁺ . Therefore, it was confirmed that the stainless steel microelectrode itself hardly operated in this potential region and operated stably. Furthermore, it was kept at 0 V for 120 hours with respect to Li. Table 1 shows changes in the current value obtained at that time.
Shown in Even after 120 hours, the current value did not increase, and it was confirmed that the electrode was stable.
(Example 2 to Example 6)
A microelectrode was prepared in the same manner as in Example 1 except that a metal wire other than a stainless steel (SUS304) wire having a diameter of 20 μm was selected as the metal wire used as the material of the microelectrode. As in Example 1, it was maintained at 0 V for 120 hours with respect to Li. Table 1 shows the time variation of the current value obtained at that time.
(Comparative Example 1)
In the microelectrode manufacturing process, a microelectrode was produced in the same manner as in Example 1 except that the metal thin wire was not insulated with a fluororesin coat before inserting the glass capillary. In the same manner as in Example 1, it was maintained at 0 V for 120 hours with respect to Li. Table 1 shows the time variation of the current value obtained at that time.
(Comparative Example 2)
In the manufacturing process of the microelectrode, a microelectrode was produced in the same manner as in Example 1 except that the insulation of the thin metal wire with a glass capillary was not performed. Was maintained at 0 V for 120 hours. Table 1 shows the time variation of the current value obtained at that time.
(Comparative Example 3)
In the microelectrode manufacturing process, a microelectrode was produced in the same manner as in Example 1 except that the insulation with the fluororesin coat after inserting the glass capillary of the fine metal wire previously coated with the fluororesin was not performed. The electrode was held at 0 V with respect to Li for 120 hours as in Example 1. Table 1 shows the time variation of the current value obtained at that time.

As shown in Table 1 above, in the microelectrode for electrochemical measurement in a non-aqueous solvent, a metal fine wire as a microelectrode material is coated with an insulating layer in the order of fluororesin, glass and fluororesin, and fluororesin, glass, fluororesin It has been found that it is possible to form an electrically insulating layer with higher insulation by forming an electrically insulating layer having a three-layer structure of resin.

Although not mentioned in the above embodiment, the metal thin wire described in Embodiment 1 is made of a metal that is difficult to alloy with Li, such as Fe, W, or stainless steel, Ni, Fe, Cu, Mo, and W. The same effect as in Example 1 can be expected even if the other structure is the same as that in Example 1 in place of two or more kinds of alloys selected from the group.

The process order explanatory drawing of the preparation procedure of the microelectrode of the best form for implementing this invention. The schematic diagram of the microelectrode front-end | tip part of the best form for implementing a book. The cyclic voltammogram in the nonaqueous solvent of the microelectrode which is an example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Metal fine wire 2 ... Fluorine resin solution 3 ... 1st fluorine resin layer 4 ... Glass capillary 5 ... 2nd fluorine resin layer

Claims (4)

A metal thin wire having both ends and one end being an external output terminal of an electric signal, a first fluororesin layer formed on the other end surface of the metal thin wire and exposing a part of the other end, and the first fluorine A microelectrode for electrochemical measurement, comprising: a glass tube circumscribing a resin layer; and a second fluororesin layer that is solidified after being immersed between the glass tube and the first fluororesin layer. 2. The microelectrode for electrochemical measurements according to claim 1, wherein the thin metal wire is one or more alloys selected from the group consisting of stainless steel, Ni, Fe, Cu, Mo, and W. 3. Forming a first fluororesin layer so that a part of the other end of the fine metal wire is exposed with respect to the fine metal wire having both ends and one end being an external output terminal of an electrical signal; An electrochemical process comprising: forming a glass tube circumscribing the resin layer; and forming a second fluororesin layer that is solidified after being immersed between the glass tube and the first fluororesin layer. A method for producing a microelectrode for measurement. 4. The microelectrode for electrochemical measurements according to claim 3, wherein the thin metal wire is one or more alloys selected from the group consisting of stainless steel, Ni, Fe, Cu, Mo, and W. Production method.

Images