JPS6174264A - Lithium cell - Google Patents

Abstract

PURPOSE:To improve a strage property and a closed circuit voltage property by arranging a thin foil of a metal with which alloy lithium electrochemically at the face where la negative lithium pole is opposited to its positive pole. CONSTITUTION:A thin foil 3b of a metal with which alloy lithium such as aluminum, lead, zinc, bithmuth, gallium and magnesium is arranged to a plane 3a of a negative lithium pole opposited to is positive pole 6. Thereby, it enables to lower the reaction with electrolytic liquid reducing the degree of activation without a large loss of its discharging capacity and restaining the increase in the interfacial resistance of the negative pole 3 based on the reaction of the electrolytic liquid and lithium and it enables also to obtain a lithium cell which is superior in a strage property and a closed circuit voltage property.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to lithium batteries.

[Conventional technology]

In lithium batteries, foil-shaped lithium gold mud is used for the negative electrode, but since lithium is highly active, there are problems such as deterioration of charge/discharge characteristics in secondary batteries. It has been proposed (U.S. Pat. No. 4,002,492) to alloy lithium with aluminum to lower the activity of lithium and improve charge/discharge characteristics. This is based on the fact that there is no need to pay any consideration to a decrease in discharge capacity, and improvement in charge-discharge characteristics is more desirable than a decrease in discharge capacity due to alloying. Therefore, alloying is carried out until the lithium content is considerably low, about 63 to 92% in atomic percent.

However, in negative electrodes, loss of discharge capacity is a major drawback in battery characteristics, and therefore, at present, almost no research has been conducted on reducing the activity of lithium in negative electrodes.

(Problem to be solved by the invention) However, even in negative batteries, the activity of lithium is too strong, so lithium reacts with the precipitate electrolyte during storage.
A lithium organic film that does not participate in battery reactions forms on the lithium surface, increasing the interfacial resistance of the lithium negative electrode.
In particular, there is a problem in that battery performance such as closed circuit voltage characteristics deteriorates.

[Means for solving problems]

The present invention was made to solve the above-mentioned problems, and the surface of the negative lithium electrode facing the positive electrode contains aluminum, lead, zinc, tin, bismuth, indium, gallium, etc.
By placing a thin foil of a metal that electrochemically alloys with lithium, such as MagFusium, it is possible to reduce the activity of the lithium and reduce its reactivity with the electrolyte without incurring significant loss of discharge capacity. The present invention provides a lithium battery with excellent storage characteristics and closed circuit voltage characteristics by suppressing an increase in the interfacial resistance of the negative electrode due to the reaction between the electrolyte and lithium.

In other words, if a thin foil of a metal that electrochemically alloys with lithium is placed on the surface of the negative lithium electrode facing the positive electrode, an electrochemical alloying reaction between lithium and the metal will occur in the electrolyte. As the process progresses, a thin layer of lithium alloy is formed on the lithium surface, and this lithium alloy is less reactive than lithium, so the reaction with the electrolyte is suppressed.
The formation of an organic film of lithium due to the reaction with the electrolyte reduces the interfacial resistance of the negative electrode and improves the storage characteristics and closed circuit voltage characteristics.

The metal foil that electrochemically alloys with lithium is 1μ
It can be very thin, from about 1.5 m thick, and it only needs to be 1/200 or more thicker than the lithium used for the negative electrode (usually foil-shaped lithium). Even if the metal foil to be alloyed is thick, there is no problem in reducing the interfacial resistance, but in a secondary battery, the discharge capacity will be increased by the amount of metal added, so it is not necessary to make it thick. The ratio of the metal foil electrochemically alloyed with lithium to the thickness of the lithium foil is preferably 10/200 or less of the thickness of the lithium foil, and the ratio of the thickness of the metal foil electrochemically alloyed with lithium to the thickness of the lithium foil is calculated as atomic percent. This corresponds to 0.1 to 6% of the metal that is electrochemically alloyed.

〔Example〕

Next, the present invention will be explained in more detail by giving Examples.

“Example 1 An aluminum foil with a thickness of 5 μm and a diameter of 14 mm was layered on a lithium foil with a thickness of 0.23+ am and a diameter of 14 m II+, and the aluminum foil side was placed on the side facing the positive electrode to serve as a negative electrode, and titanium disulfide was used as the positive electrode. Using a molding mixture as an active material, the volume ratio of i!electrolyte 4-methyl-1,3-nookyfuran, 1,2-dimethyneethane, and hexamethylphosphoramide was 60: 34.8: 5゜2.
A button-shaped battery having the configuration shown in FIG. 1 was prepared using an incubating electrolyte solution prepared by dissolving 1 mol/11 g of 1iPF6 in a mixed solvent.

In Fig. 1, 1 is a pole can made of stainless steel and nickel plated on the surface, 2 is a negative electrode current collector made of stainless steel mesh, 3 is a negative electrode, and this negative 1fi3 is a lithium foil 3a. and a thin metal foil 3 that electrochemically alloys with the lithium, disposed on its surface facing the positive electrode.
As mentioned above, in this embodiment, aluminum is used as the metal that electrochemically alloys with lithium. This aluminum is electrochemically alloyed with lithium due to the presence of the electrolyte, forming a lithium-aluminum alloy. 4 is a separator made of a microporous polypropylene film, 5 is an electrolyte absorber made of polypropylene nonwoven fabric, 6 is a positive electrode made of a molding mixture containing titanium disulfide as the positive electrode active material, and 7 is a positive electrode made of a stainless steel mesh. Current collector 8 is a positive electrode can made of stainless steel with a nickel-plated surface, and 9 is an annular gasket made of polypropylene.

Example 2 A lithium foil with a thickness of 0.23 mm and a diameter of 14IIIn was used as the negative electrode, and a lithium foil with a thickness of 10 μm was placed on the surface facing the positive electrode. A battery similar to that of Example 1 was prepared except that 14 mm thick lead foil was used.

Example 3 A lithium foil with a thickness of 0.23+vm and a diameter of 14+v+ was used as the negative electrode, and a lithium foil with a thickness of 7[deg.
A battery was produced in the same manner as in Fall 1, except that a sub-10 boiler with a diameter of 14 μm and an i diameter of 14] was used.

Example 4 Negative electrode has a thickness of 0231M11. Lithium foil of 1 + 4 + n11 and the surface facing the positive electrode) I 10 μm
, Example 1 except that tin foils with a diameter of 141 were used in layers.
A battery similar to that was fabricated.

Example 5 A lithium foil with a thickness of 0.23 mm and a diameter of 141 was placed on the negative 1t, and a lithium foil with a thickness of lOIJm and a straight line was placed on the surface facing the positive electrode.
A battery was produced in the same manner as in Example 1, except that winter 141 bismuth foil was used in layers.

Example 6 Negative electrode thickness: 0, 23+nm, straight i-line 14III11
Nori tium foil with a thickness of 10 mm on the surface facing the positive electrode.
A battery similar to Example I was produced except that indium foils having a diameter of 14 wm and a diameter of 14 wm were used.

Example 7 A lithium foil with a thickness of 0, 23+a+a, and a diameter of 141 was used as the i-electrode, and a lithium foil with a thickness of 5μ and a diameter of 1 was used on the surface facing the positive electrode.
A battery was prepared in the same manner as in Example 1 except that 4 pieces of gallium foil were used.

Example 8 A battery similar to that of Example 1 was used, except that a lithium foil with a thickness of 0.23 mm and a diameter of 14III11 was used as the negative electrode, and a lithium foil with a thickness of 5 μm and a diameter of 14 mm was stacked on the surface facing the positive electrode. Manufactured 6 Comparative Example 1 A battery similar to Example 1 was manufactured except that a lithium foil with a thickness of 0.23 mm and a diameter of 14 mm was used as the negative electrode.

20°C of the batteries of Examples 1 to 8 and the battery of Comparative Example 1
The open circuit voltage, closed circuit voltage and impedance were measured. In addition, the open circuit voltage, closed circuit voltage, and 120 Hz impedance of the battery were measured after storage at 60° C. for 60 days. The results are shown in Table 1.

Also, what about the batteries and ratios of Examples 1 and 2? 2. When the battery of Example 1 was stored at 60°C, the open circuit voltage change, closed circuit voltage change, and impedance change at 120 Hz due to storage were investigated. The open circuit voltage change is shown in Figure 2, and the closed circuit voltage change is shown in Figure 3. Figure 4 shows the impedance change.

As shown in Table 1, the batteries of Examples 1 to 8 of the present invention were:
Conventional 1! 120 compared to the battery of Comparative Example 1, which is an i-cell.
The Hz impedance (impedance including the interfacial resistance of the negative electrode) was low, and the closed circuit voltage characteristics were excellent. Moreover, as shown in Table 1 and FIGS. 3 and 4, the batteries of Examples 1 to 8 of the present invention had little increase in impedance and little decrease in closed circuit voltage due to high temperature storage.

〔Effect of the invention〕

As explained above, according to the present invention, at least one type of lithium selected from the group consisting of aluminum, lead, zinc, tin, bismuth, indium, gallium, and magnonium is added to the surface of the negative lithium electrode facing the positive electrode. By placing a thin foil of metal that alloys electrochemically,
Storage characteristics and closed circuit voltage characteristics have been improved.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing one embodiment of the lithium battery of the present invention, and Figure 2 is a comparison with the batteries of Examples 1 and 2 of the present invention.
Figure 3 shows the change in open circuit voltage due to storage of the fl+ 1 battery, and Figure 3 shows the change in closed circuit voltage due to storage of the batteries of Examples 1 and 2 of the present invention and the battery of Comparative Example 1. FIG. 4 is a diagram showing 120 Hz impedance changes during storage of the batteries of Examples 1 and 2 of the present invention and the battery of Comparative Example 1. 3... Negative electrode, 3a... Lithium foil, 3b.
... Thin foil of metal that electrochemically alloys with lithium, 4... Separator, 6... Positive electrode 3--
Tribute 3a--・S+Nmhui 11/ 3b--・Riz-i-shi 5tt Fii Otsusho 9ri 4...- in Peeta Figure 3 4T Bakunichi (Separate)

Claims (2)

[Claims] (1) In a lithium battery using lithium as a negative electrode active material, at least one type of lithium selected from the group consisting of aluminum, lead, zinc, tin, bismuth, indium, gallium, and magnesium is placed on the surface facing the lithium positive electrode. A lithium battery characterized by an arrangement of thin foils of metal that are electrochemically alloyed with. (2) The lithium battery according to claim 1, wherein the thickness of the metal foil that electrochemically alloys with lithium is 1/200 to 10/200 of the thickness of lithium.