JP2018170112A - Electrode fabrication method - Google Patents

Abstract

【Task】
To provide a method for bringing a metal or alloy electrode into close contact with a solid electrolyte by a simple operation.
[Solution]
When the electrode material is thermally fused on the solid electrolyte, ultrasonic waves are simultaneously irradiated. As a result, a metal or alloy-based electrode having high adhesion can be produced on the solid electrolyte. In an electrochemical cell constructed using the electrode-solid electrolyte structure produced in this manner, the internal resistance at the electrode-solid electrolyte interface is small, and good electrochemical characteristics are obtained.
[Selection] Figure 3

Description

  The present invention relates to an electrode for an electrochemical cell such as a battery using a solid electrolyte.

Batteries are becoming increasingly important as power sources for mobile devices, automobiles and aircraft, and for storing power generated by renewable energy.
In recent years, research on solid electrolytes has been promoted for various applications, such as electrolytes for all-solid-state batteries excellent in safety, and as electrolyte layers provided on the positive electrode side or the negative electrode side in batteries using liquid electrolytes. ing. In addition, metal-based and alloy-based electrodes such as Li are expected to have a larger capacity than conventional electrodes, and are being developed as promising electrodes even when using solid electrolytes. Yes.
In a battery using a solid electrolyte, when a metal or alloy electrode is used, it is important to construct a solid electrolyte / electrode interface. As a conventional technique for constructing such an interface, techniques such as pressure bonding, vapor deposition, deposition, thermal fusion, and interface modification are used (crimping and vapor deposition: Non-Patent Document 1, thermal fusion and interface modification: Non-patent. Reference 2).

Electrochem. Commun., 22, 177 (2012) Nature Mater. (2016) doi: 10.1038 / nmat4821 Phys.Chme.Chem.Phys., 14, 10008 (2012) J. Mater. Sci., 48, 5846 (2013)

When an electrode is pressure-bonded to a molded solid electrolyte, there is a risk that the solid electrolyte will break. Moreover, it is difficult to apply a uniform pressure to the bonding surface, and it is difficult to produce a uniform interface. In addition, this method cannot be used for materials having poor adhesion. On the other hand, vapor deposition and deposition methods are suitable for producing highly adhesive interfaces, but vacuum conditions are required, and the deposition rate is slow and the area that can be deposited is limited. It takes. Also, these methods are often used in the interface modification method, which increases the number of work steps. In heat fusion, there are materials that are difficult to fuse, and it is difficult to create an interface with high adhesion (Non-Patent Documents 2 to 4).
An object of the present invention is to provide a technique for bringing an electrode into close contact with a solid electrolyte by a simple operation without the disadvantages of these conventional techniques.

  As a result of intensive research for the above purpose, the inventors of the present invention have a metal or alloy having high adhesion on the solid electrolyte by simultaneously irradiating ultrasonic waves when the electrode material is thermally fused on the solid electrolyte. In an electrochemical cell constructed using the electrode-solid electrolyte structure, the internal resistance of the electrode-solid electrolyte interface is small, and good electrochemical characteristics are obtained. It was.

Specifically, the present inventors have found that, as the solid _{electrolyte, Li 1 + x Al y Ge} 2-y (PO 4) 3 ( hereinafter referred to as LAGP), _{and, Al doped-Li 7 La 3} Zr 2 O 12 (Hereinafter referred to as LLZ), and using an ultrasonic soldering iron (FIG. 1), Li metal is thermally melted and fused to the solid electrolyte while applying ultrasonic waves. By forming an electrode, a uniform Li / solid electrolyte interface with high adhesion is formed (Fig. 3). As a result, Li / solid electrolyte compared to ordinary heat fusion, in which Li metal is simply heated and melted. The interface resistance can be remarkably reduced (Figs. 4 and 5), and the symmetric cell Li / LLZ / Li fabricated in this way can stably dissolve and precipitate Li for a long period of time. It was found that this can be done (FIG. 6).
The present invention has been made based on these findings by the present inventors.

That is, this application provides the following invention.
<1> A method for producing an electrode / solid electrolyte structure by thermally fusing an electrode material on a solid electrolyte and forming a metal or alloy-based electrode on the solid electrolyte, the electrode material being formed on the solid electrolyte A method characterized by applying ultrasonic waves when heat-sealing.
<2> A method for producing an electrochemical cell by producing an electrode / solid electrolyte structure by the method of <1> and combining the obtained electrode / solid electrolyte structure with other components.
<3> The method according to <2>, wherein the electrochemical cell is a battery.
<4> The method according to <2>, wherein the electrochemical cell is an all solid state battery.
<5> The method according to <2>, wherein the electrochemical cell is a metal-air battery.

In the method employed in the present invention for applying ultrasonic waves during thermal fusion (hereinafter referred to as ultrasonic-assisted thermal fusion method), an electrode / solid electrolyte interface with high adhesion can be formed in a very short time of several seconds. It is possible to form.
In addition, according to the present invention, an electrode / solid electrolyte interface with high adhesion is formed, and the resistance of the interface is reduced, whereby the resistance of the entire electrochemical cell configured using the interface can be reduced. Thus, the rate characteristics can be improved.
Further, the electrode / solid electrolyte interface formed by the present invention is electrochemically stable, and by using this, a battery having stable charge / discharge characteristics for a long time can be obtained.

A photograph of an ultrasonic soldering iron used in the present invention. Photographs of Li metal fused on LLZ pellets by (a) heat fusion using a hot plate and (b) ultrasonic-assisted heat fusion using an ultrasonic soldering iron. Scanning electron microscope of a fracture surface of Li / LLZ fused by (a) a thermal fusion method using a hot plate, and (b) an ultrasonic-assisted thermal fusion method using an ultrasonic soldering iron ( SEM) Photo. (A) Au / LAGP / Au, (b) Li / LAGP / Au fused by a thermal fusion method using a hot plate, and (c) Ultrasonic-assisted thermal fusion using an ultrasonic soldering iron Impedance plot of Li / LAGP / Au fused by the method. The value at the right end of the arc means the total resistance. Impedance plots of Li / LLZ / Li fused by (a) a thermal fusion method using a hot plate and (b) an ultrasonic-assisted thermal fusion method using an ultrasonic soldering iron. The results of constant current polarization measurement of Li / LLZ / Li fused by (a) thermal fusion method using a hot plate and (b) ultrasonic-assisted thermal fusion method using an ultrasonic soldering iron. FIG. A current of 0.1 mA / cm ² is applied every 30 minutes with the direction reversed. Optical photograph when Li metal is bonded on a slide glass by ultrasonic-assisted heat fusion method at each temperature and each ultrasonic output (ultrasonic frequency is fixed at 60 kHz). Optical photograph when Li metal is bonded onto a slide glass under the conditions of ultrasonic output of 240 ° C and 5W.

Examples of the solid electrolyte used in the present invention include a lithium-containing phosphate compound having a NASICON type structure such as the above-described Li _{1 + x} Al _y Ge _2-y (PO ₄ ) ₃ (LAGP), and the above-described Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ) and other garnet-type compounds, lithium phosphate doped with nitrogen and LiPON (LiPO _4-x N _x ) and similar compounds, Li _3x La _{2 / 3-x} TiO Compounds having a perovskite structure such as ₃ ; oxide solid electrolytes such as Li ₄ SiO ₄ ; and lithium ion conductors such as sulfide solid electrolytes such as lithium phosphorus sulfide; sodium-containing phosphoric acid having a NASICON structure Compound, β-alumina such as Na ₂ O-11Al ₂ O ₃ and sodium ion conductors such as sulfide-based solid electrolytes such as sodium phosphorous sulfide, and not only lithium ions and sodium ions, but also Mg Other cations and oxide ions Also anion conductor, the present invention is applicable.

  Examples of the metal or alloy-based electrode used in the present invention include electrodes made of Li, Na, Al, K, Sn, Pb, In, Li—In alloy, Li—Sn alloy, Li—Al alloy and the like.

  In the ultrasonic-assisted heat fusion method used in the present invention, it is preferable to apply ultrasonic waves having a frequency of about 10 to 60 kHz at an output of about 2 to 10 W for about 1 to 3 seconds. The deposition temperature is preferably about 60 to 750 ° C. depending on the melting point of each metal or alloy. In the embodiment of the present invention, an ultrasonic soldering iron is used as a means for realizing such ultrasonic-assisted heat fusion, but the present invention is not limited to this, and the ultrasonic waves can be applied. Any means can be used as long as it is a means capable of realizing the heat fusion.

The electrode / solid electrolyte structure produced according to the present invention can be used in various electrochemical cells such as a primary battery, a secondary battery, a capacitor, and an electrochemical measurement cell by appropriately combining with other components. it can.
Examples of the battery produced by the present invention include an all solid state battery such as a lithium ion battery composed of a Li negative electrode / lithium ion conductive solid electrolyte structure and a positive electrode such as Li _1-x FePO ₄ , And a metal-air battery such as a Li-air battery comprising a negative electrode / lithium ion conductive solid electrolyte structure and an air electrode such as porous carbon.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not restrict | limited to a following example.

Example 1. Li _{1 + x} Al _y Ge _2-y (PO ₄ ) ₃ (LAGP) is used as the solid electrolyte for the adhesion of Li metal to LAGP , the usual heat fusion method, and ultrasonic-assisted heat fusion according to the present invention. By the method, a Li metal electrode was formed on the solid electrolyte. Each fusion was performed in the following procedure in a glove box filled with Ar gas.
(1) Ordinary heat fusion method (fusion by hot plate)
A Cu mesh on which a Φ10 mm Li metal was attached was placed on a hot plate heated to 230 ° C., and a LAGP pellet in which an Au electrode was sputtered on one side was placed thereon with the Au electrode facing upward. The LAGP pellet was pushed with tweezers and held for about 3 minutes to confirm that the Li metal was melted, and then removed from the hot plate and cooled.
(2) Ultrasonic-assisted heat fusion method Ultrasonic soldering iron (Figure 1) (Manufacturer name: Kuroda Techno Co., product number: Sunbonder USM-560, ultrasonic oscillation frequency) : 60 kHz ± 5 kHz, ultrasonic oscillation output: 1 to 12 W, heater temperature setting: 200 to 500 ° C.).
Masking of Φ10mm was performed on the LAGP pellet with masking tape. The heater was set at 240 ° C., Li metal was placed on the heated iron tip, contacted with the LAGP pellet, and then 60 kHz, 5 W ultrasonic waves were applied for about 1 second for adhesion.

Example 2 Li -doped metal to LLZ As the solid electrolyte, Al doped-Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ) is used, and by the usual heat fusion method and the ultrasonic-assisted heat fusion method according to the present invention, Li metal electrode was formed on the solid electrolyte. Each fusion was performed in the following procedure in a glove box filled with Ar gas. The doping of Al in the LLZ is performed to stabilize the garnet structure of the LLZ.
(1) Ordinary heat fusion method (fusion by hot plate)
LLZ pellets were placed on a hot plate heated to 230 ° C, and a Φ10mm disc-shaped Li metal was placed on top of it, and was pushed from above with tweezers. After holding for about 3 minutes and confirming that the Li metal was melted, it was removed from the hot plate and cooled. Similarly, Li metal was fused on the reverse side to produce a Li / LLZ / Li cell.
(2) Ultrasonic-assisted heat fusion method As a means for performing ultrasonic-assisted heat fusion, an ultrasonic soldering iron (FIG. 1) was used.
Masking of Φ10mm was performed on the LLZ pellets with masking tape. The heater was set to 240 ° C., Li metal was placed on the heated iron tip, contacted with the LLZ pellet, and then 60 kHz, 5 W ultrasonic waves were applied for about 1 second for adhesion. Similarly, Li metal was fused on the reverse side to produce a Li / LLZ / Li cell.
FIG. 2 shows a photograph when Li is fused on LLZ by hot plate (a) or by ultrasonic-assisted thermal fusion (b).
LLZ is known as a solid electrolyte that does not easily react with Li metal (Non-patent Document 3 and Non-patent Document 4). Although both seem to be fused at first glance in FIG. 2, they are fused with a hot plate. The case can be easily removed. On the other hand, when it was fused using the ultrasonic-assisted heat fusion method, it was not easily peeled off. This is presumably because the surface of the solid electrolyte is activated by the ultrasonic wave and the reaction between Li / solid electrolyte is promoted.
FIG. 3 shows an electron micrograph of the Li / LLZ fracture surface. When fused by a hot plate (a), many voids are observed at the Li / LLZ interface. On the other hand, it can be seen that a uniform interface with high adhesion can be constructed in the case of (b) fusion using the ultrasonic-assisted heat fusion method.

Example 3 Impedance measurement Li / LAGP / Au and Li / LLZ / Li cells prepared by the thermal fusion method and ultrasonic-assisted thermal fusion method described in Examples 1 and 2 were put into a plastic film and a sealed bottle, respectively, in a glove box. The package was sealed, removed from the glove box, and impedance was measured in a thermostatic chamber heated to 30 ° C. The AC voltage was 10mV and the frequency range was 100mHz to 1MHz.
Figure 4 shows Au / LAGP / Au with Au electrodes sputtered on both sides of LAGP, Li / LAGP / Au with Li fused by hot plate, and Li / LAGP / with Li fused by ultrasonic assisted fusion method. An impedance plot of Au is shown. The value at the right end of the arc in the impedance plot means the resistance of the entire cell.
In Au / LAGP / Au (a), the resistance of the LAGP solid electrolyte itself was observed, and a resistance of about 930 ohms was observed. In Li / LAGP / Au, resistance at the Li / LAGP interface was added to this, and when it was fused with a hot plate (b), the resistance was about 4300 ohms. On the other hand, in the case of (c) fused by the ultrasonic-assisted heat fusion method, the resistance is about 1250 ohms, and it can be seen that the resistance at the Li / LAGP interface could be remarkably reduced.
FIG. 5 shows an impedance plot of Li / LLZ / Li fused by (a) by a hot plate or by (b) ultrasonic-assisted heat fusion.
As with LAGP, it can be seen that the resistance of the Li / LLZ interface could be significantly reduced by using the ultrasonic-assisted thermal fusion method.

Example 4 Constant-current polarization measurement Li / LLZ / Li cells prepared by the thermal fusion method and ultrasonic-assisted thermal fusion method described in Example 2 were enclosed in a plastic film and a sealed bottle in a glove box, respectively, The constant current polarization was measured in a thermostatic chamber heated to 30 ° C. The measurement was performed by applying a current of 0.1 mA / cm ² with the direction reversed every 30 minutes and observing the change in voltage for 100 hours.
FIG. 6 shows the results obtained in each Li / LLZ / Li cell.
When fused using a hot plate (a), the voltage dropped rapidly immediately after the start of measurement. This is thought to be because Li was concentrated and partly deposited, causing a short circuit. On the other hand, in the case of fusion using the ultrasonic-assisted heat fusion method (b), such behavior is not observed, and even if the current reversal is repeated 100 times or more, the constant fluctuation width is maintained. The voltage could be observed.

Example 5 FIG.
The Li metal was ultrasonically assisted and heat-sealed on the slide glass by changing the heat melting temperature and the applied ultrasonic power. The ultrasonic frequency was fixed at 60 kHz. The result is shown in FIG.
From FIG. 7, it can be seen that when the temperature and the ultrasonic power are low, Li metal is difficult to fuse, can be adhered well from about 220 ° C, 1W, and can be sufficiently adhered at about 240 ° C, 5W.
As shown in FIG. 8, under the conditions of 240 ° C. and 5 W, it is possible to form a complicated shape such as letters by spreading Li metal on the slide glass.

Claims (5)

  A method for producing an electrode / solid electrolyte structure by thermally fusing an electrode material on a solid electrolyte and forming a metal or alloy-based electrode on the solid electrolyte. The electrode material is thermally fused on the solid electrolyte. A method characterized by applying ultrasonic waves when wearing.   A method for producing an electrochemical cell by producing an electrode / solid electrolyte structure by the method according to claim 1 and combining the obtained electrode / solid electrolyte structure with other components.   The method according to claim 2, wherein the electrochemical cell is a battery.   The method according to claim 2, wherein the electrochemical cell is an all-solid battery.   The method according to claim 2, wherein the electrochemical cell is a metal-air battery.

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