JPS6342819B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lithium negative electrode for use in lithium batteries.

Batteries using lithium as a negative electrode active material are being researched as small-sized batteries with high energy density, but secondaryization has become a major problem.

Many compounds are being considered as cathode active materials that can be secondaryized. For example, batteries using titanium, zirconium, hafnium, niobium, tantalum, and vanadium sulfide, selenide, and telluride (US Patent No. 4089052) (see the specification of the patent), etc. have been disclosed.

However, compared to such research on positive electrode active materials for secondary batteries, research on the charging and discharging characteristics of Li electrodes is not sufficient, and in order to realize Li secondary batteries,
A method for producing Li electrodes with good charge-discharge characteristics such as charge-discharge efficiency and cycle life has become a serious issue.

In an attempt to improve the charging and discharging characteristics of Li electrodes,
There have been attempts to use Li treated with gases such as O ₂ and CO ₂ for the negative electrode [J.Electrochm.Soc., Vol. 125, pp. 1371-1377] and attempts to use an alloy of Li and Al for the negative electrode [J. .Electrochem.Soc., Vol.127, pp. 2100-2104
[Page] etc. have been carried out, but they are not necessarily sufficient, and there is a demand for the production of Li negative electrodes with even better characteristics.

Lithium is also pressure-bonded to metal plates such as aluminum (Japanese Patent Application No. 1973-
No. 80058), but its properties are insufficient as a negative electrode for secondary batteries.

The present invention was made in view of the current situation, and its purpose is to provide a lithium negative electrode with excellent discharge and charge characteristics.

To summarize the present invention, the negative electrode active material is lithium, the positive electrode active material is a material that performs a reversible electrochemical reaction with lithium ions, and the electrolyte material is chemically stable with respect to the positive electrode active material and lithium. A negative electrode used in a lithium secondary battery, which is a material in which lithium ions move to perform an electrochemical reaction with a positive electrode active material, has microporous aluminum, and the microporous aluminum is
The microporous aluminum has pores with a specific surface area of 1400 m ² /m ³ or more, and lithium is attached to the microporous aluminum, and the contact area with the microporous aluminum is alloyed with lithium. .

When using a lithium negative electrode with a smooth surface such as a lithium metal plate or lithium flake, when the discharging or charging current increases, local reactions are accelerated and holes may form in the lithium negative electrode.
During charging, phenomena such as dendrite-like lithium precipitating and falling off the negative electrode occur. This is a cause of decreasing the charging and discharging efficiency of Li electrodes. Therefore, the above-mentioned drawbacks can be overcome by increasing the reaction surface area of the lithium negative electrode and supporting lithium on a material that has pores that facilitate the deposition of lithium metal and has good conductivity. From this point of view, it is effective to use microporous aluminum supporting lithium as the negative electrode.

In this case, if the pores in the aluminum are too large, lithium will not be supported properly, so as shown in Examples below, microporous aluminum with a specific surface area of pores of 1400 m ² /m ³ or more is used. Furthermore, as mentioned above, attempts have been made to use an alloy (flat plate) of Li and Al, but it is better to use the microporous aluminum according to the present invention that supports Li. Desorption and dendrite formation can be prevented, resulting in much better properties.

The effects of the present invention will be explained below using Examples. The microporous aluminum used has a specific surface area of pores of 1400 to 2500 m ² /m ³ (number of pores 17 to 26 meshes).
and 13,000 to 17,000 m ² /m ³ (85 to 130 meshes), and the thickness of each is 1 mm.

The methods for supporting lithium on these microporous aluminum are (1) electrochemically depositing lithium in a solution containing Li ⁺ ions, and (2) electrochemically depositing lithium in molten salt. ,(3)
A method of immersing microporous aluminum in a molten liquid of lithium metal, (4) A method of stacking and pressing lithium metal and microporous aluminum, (5) A method of stacking and pressing lithium metal powder with microporous aluminum, (6)
Various methods can be considered, such as a method of precipitating lithium on microporous aluminum with n-butyllithium, and a method of (7) vapor deposition of lithium on microporous aluminum, but in any case, in microporous aluminum, The method is not limited in the present invention as long as a lithium-aluminum alloy is formed in a part of the portion where lithium is attached to aluminum and lithium is supported. That is, it works effectively as a lithium negative electrode. In the examples below, lithium is electrochemically deposited on microporous aluminum in INLiClO ₄ /propylene carbonate and used as the negative electrode. The method is just an example and is not limiting in any way.

Example 1 Lithium was applied as a counter electrode in INLiClO ₄ /propylene carbonate at a constant current of 1 mA/cm ² for 16 to 20 hours to a microelectrode with an average specific surface area of vacancies of 1400 m ² /m ³ (average number of vacancies 17 meshes). Electrodeposited on porous aluminum (aluminum/lithium molar ratio is approximately 1/1)
1) Using a battery with an effective reaction surface area of 1 cm ² , a battery was assembled using a Pt electrode as a working electrode and Li as a reference electrode, and Li was deposited on the Pt electrode to measure the charge/discharge characteristics of the Li electrode. The electrolyte contains INLiClO ₄
was dissolved in propylene carbonate.

First, the measurement was performed using a constant current of 1 mA/cm ² for 1 minute.
After depositing Li on the Pt electrode and charging it, a cycle test was performed in which the Li deposited on the Pt electrode was discharged as Li ⁺ ions at a constant current of 1 mA/cm ² . The charge/discharge efficiency is
The potential change of the Pt electrode is determined, and the Li deposited on the Pt electrode is determined.
The amount of electricity required to discharge Li ⁺ ions and
It was calculated from the ratio to the amount of electricity required to deposit Li on Pt.

Figure 1 is a diagram showing the relationship between the charge ^/ discharge efficiency and the ^number of cycles of Li electrodes. This is the case when aluminum supporting Li is used, and b is a reference example in which a Li thin piece (thickness
This figure shows the charge/discharge characteristics of Li electrodes when using 0.5 mm). As can be seen from Figure 1, the charge-discharge characteristics of the Li electrode are significantly improved by using microporous aluminum with an average specific surface area of pores of 1400 m ² /m ³ supporting lithium as the lithium negative electrode. are doing.

Example 2 As a lithium negative electrode, the specific surface area of pores is average
The charge-discharge characteristics of a lithium negative electrode were measured in the same manner as in Example 1, except that 15000 m ² /m ³ (average 100 mesh) of microporous aluminum supporting lithium was used.

FIG. 3 is a diagram showing the relationship between the charging/discharging efficiency and the number of cycles of Li electrodes, and a in the diagram indicates the relationship between the charge and discharge efficiency ^of Li electrodes and the ^number of cycles. This is the case when using a material carrying
b shows the charge/discharge characteristics when a thin lithium flake (thickness: 0.5 mm) was used as a lithium negative electrode in a reference example. As can be seen from Figure 2, the charge-discharge characteristics of the Li electrode are improved by using microporous aluminum with an average specific surface area of pores of 15,000 m ² /m ³ supporting lithium as the lithium negative electrode. There is.

Example 3 A battery was produced in the same manner as in Example 1, and the charge/discharge efficiency was measured. FIG. 3 shows the relationship between charge/discharge efficiency and lithium/aluminum molar ratio when lithium is supported on microporous aluminum. In FIG. 3, the charge/discharge efficiency is shown as an average value for 1 to 10 cycles. It can be seen that particularly good properties are exhibited when the Li/Al molar ratio is 0.3 or more.

As is clear from the above explanation, according to the present invention, by using microporous aluminum with a specific surface area of pores of 1400 m ² /m ³ or more to support lithium, lithium with excellent charge and discharge characteristics can be produced. A negative electrode for secondary batteries can be realized.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams showing the relationship between the charging and discharging efficiency of the lithium electrode and the number of cycles in an example of the present invention, and Figure 3 is a diagram showing the relationship between the charging and discharging efficiency and the molar ratio of lithium and aluminum. It is a diagram.

Claims (1)

[Claims] 1 has microporous aluminum, the microporous aluminum has pores with a specific surface area of 1400 m ² /m ³ or more, the microporous aluminum has lithium attached, and the contact portion with the microporous aluminum A lithium negative electrode for a secondary battery, characterized in that it is alloyed with lithium.