JPS63126157A - Lithium cell - Google Patents

Abstract

PURPOSE:To expand the effective reaction area of a negative electrode, and to improve the pulse closed-circuit voltage property, by furnishing a lithium alloy layer made by an electrochemical alloying at the side opposing to a separator of a lithium layer, and moreover, making the surface of the lithium layer contacting the lithium alloy layer in an uneven surface. CONSTITUTION:At the side opposing to a separator 3 of a lithium layer 2a of a negative electrode 2, a lithium alloy layer 2b made by an electrochemical alloying from lithium and a metal alloyable electrochemically, and moreover, the surface of the lithium layer 2a contacting the lithium alloy layer 2b is formed into an uneven surface. Therefore, the effective reaction area of the negative electrode 2 is expanded, the current density per unit area is reduced, the inner resistance is also reduced, and the pulse closed-circuit voltage property can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a lithium battery, and further relates to a'r: L
< relates to improvement of the negative electrode.

[Conventional technology]

In lithium batteries, metallic lithium is used for the negative electrode, but lithium is chemically very active, and although its high chemical activity gives it various features as a battery, on the other hand, it is highly active. For example, in secondary batteries, electrodeposited lithium is particularly active during charging and reacts with components in the electrolyte, causing various problems during battery use or storage. It has been reported that this causes the formation of a 3-layer film, which deteriorates the negative electrode and causes a decrease in charge-discharge cycle characteristics. Therefore, by alloying lithium with aluminum and utilizing the electrochemical alloying reaction between lithium and aluminum during charging, we minimize the amount of lithium remaining in the active electrodeposited state and prevent deterioration of the negative electrode. It has been proposed to improve charge-discharge cycle characteristics (e.g., U.S. Pat. No. 4,002,492).
No. Specification). However, when alloying lithium as described above, it is not necessary to pay as much consideration to the decrease in discharge capacity in secondary batteries as in primary batteries, and the improvement in charge-discharge cycle characteristics is more important than the decrease in discharge capacity due to alloying. This is based on the fact that lithium is more desirable, and alloying is performed until the lithium content is considerably low. For example, in JP-A-61-208749, the lithium content is 35
It is stated that favorable results can be obtained at atomic% of 58 to 58 atomic%.

Also, in secondary batteries, a thin plate of a metal that electrochemically alloys with lithium, such as aluminum, lead, zinc, tin, bismuth, indium, gallium, or magnesium, is placed on the side of the lithium plate facing the separator. , electrochemically alloys lithium with the above metals in the presence of an electrolyte, reduces the activity of the lithium surface, suppresses reaction with the electrolyte, and forms a passive film on the negative electrode surface. Research has been conducted on preventing the formation of , suppressing the increase in interfacial resistance of the negative electrode, and improving storage characteristics and closed circuit voltage characteristics, and a patent application has already been filed (Japanese Patent Application Laid-Open No. 74264/1983).

By the way, when this type of battery is applied to watches, electronic thermometers, etc., it is necessary to intermittently operate a step motor, turn on a light, sound an alarm, etc. Although a high heavy-load pulse closing voltage is required, the batteries proposed so far do not necessarily have sufficient performance to meet such requirements.

That is, the above-mentioned prior invention does not mention anything about the shape of the surface of the negative electrode on the side of the lithium plate facing the separator (the surface of the lithium plate facing the separator is formed into a flat shape; The metal plate to be alloyed with lithium is also formed in a flat shape.Therefore, although the pulsed circuit voltage characteristics are improved, this can only be achieved by alloying lithium with aluminum, etc. As the demands for improved battery performance from consumers are becoming more and more severe, it cannot be said that the pulse closing voltage characteristics alone are sufficiently satisfactory, and it is desirable to further improve the pulse closing voltage characteristics. .

[Problem that the invention seeks to solve]

The object of the present invention is to solve the problem that conventional lithium batteries had insufficient pulse closing voltage characteristics, and to provide a lithium battery with further improved pulse closing voltage characteristics.

[Means for solving problems]

The present invention provides a lithium alloy layer formed by electrochemical alloying of lithium and a metal that electrochemically alloys with the lithium on the side of the lithium layer of the negative electrode facing the separator, and a lithium alloy layer of the lithium layer. By making the surface in contact with the layer uneven, the effective reaction area of the negative electrode is increased, the current density per unit area is reduced, the internal resistance is reduced, and the pulsed circuit voltage characteristics are improved. It is.

That is, the lithium alloy layer formed by electrochemical alloying of lithium and a metal that electrochemically alloys with the lithium is pulverized, and this pulverized lithium alloy layer expands the reaction area. It also holds the electrolyte and contributes to improving the pulse closing voltage characteristics, but during the battery discharge reaction, lithium is thought to be ionized from the side of the lithium layer facing the separator via this lithium alloy layer. . Therefore, it is considered preferable that the lithium layer itself has a large surface area.

Therefore, in the present invention, the surface of the lithium layer in contact with the lithium alloy layer is made uneven to increase the surface area of the lithium layer itself, thereby improving the pulse circuit voltage characteristics due to the formation of the lithium alloy layer described above. This increase in the effective reaction area due to the increase in the surface area of the lithium layer itself significantly improved the pulsed circuit voltage characteristics.

In order to make the surface of the lithium layer in contact with the lithium alloy layer uneven, the lithium plate should be electrochemically coated with lithium such as an aluminum plate before punching the lithium plate into the desired shape during battery assembly. metal to be alloyed with (
In the following, for the sake of simplicity, aluminum plates are used as a representative example) are stacked together, and a pressing jig with an uneven pressing surface is pressed from the aluminum plate onto the laminated plate of the lithium plate and the aluminum plate. It is preferable to perform this so that the aluminum plate and the surface of the lithium plate in contact with the aluminum plate are made uneven. By doing this, in addition to improving the pulse closing voltage mentioned above, the lithium plate and the aluminum plate are fixed to each other by the adhesive force of lithium, so that when the lithium plate and the aluminum plate are bonded to each other, or when they are inserted into the negative electrode can, There is no peeling or misalignment between the lithium plate and the aluminum plate, and the contact area is wider than when the lithium plate and aluminum plate are in contact with each other on a flat surface, so alloying is promoted and the aging time for alloying is shortened. This also improves productivity in battery manufacturing.

In the present invention, metals that are electrochemically alloyed with lithium and used to form the lithium alloy layer include, for example, aluminum, tin, zinc, lead, bismuth, silicon, antimony, magnesium, indium, gallium, germanium, etc. can be given. Especially aluminum,
Tin, zinc, lead, bismuth, silicon, antimony, magnesium, etc. have a strong effect of improving the pulse closed circuit voltage characteristics and are preferably used in the present invention.

The formation of a lithium alloy layer is usually done by adding a lithium plate and a metal plate such as an aluminum plate (hereinafter, aluminum will be used as a representative example for simplicity) to form a negative electrode can. is inserted, the battery is assembled, and the lithium and aluminum near the aluminum plate of the lithium plate are electrochemically alloyed in the presence of an electrolyte within the battery.

Then, when inserting the lithium plate into the negative electrode can as described above, the lithium plate and the aluminum plate are overlapped in advance as described above, and in that state, the lithium plate is roughened from the aluminum plate side so that the surface of the lithium plate becomes an uneven surface. It is preferable to leave it there.

By making the surface of the lithium plate uneven as described above, the surface of the lithium layer will remain uneven even after the aluminum and the lithium in its vicinity are electrochemically alloyed in the presence of an electrolyte. It will be done.

The thickness of the lithium alloy layer needs to be very thin, and accurate measurement is difficult because it is finely powdered, but if it is about 5 μm or more, it is possible to prevent the lithium from interfering with water and impurities in the electrolyte during storage. The reaction can be suppressed, and due to the increased reaction area of the negative electrode due to the pulverization of the lithium alloy and the electrolyte retention effect of the lithium alloy fine powder, it can be effective in improving battery performance such as pulsed closed circuit voltage characteristics. . On the other hand, if the lithium alloy layer becomes thicker, it is advantageous in terms of improving the pulse closing voltage characteristics, etc., but the amount of alloying elements such as aluminum that make up the lithium alloy increases, and the electrical capacity of the negative electrode probably decreases. The alloying element accounts for 0.5 to 10 atomic% (atom
ic%), particularly from 1 to 7 atom%, more preferably from 2 to 4 atom%.

As the electrolyte and the positive electrode active material, those commonly used in this type of battery can be used without any special restrictions. Specific examples of electrolytes include 1,2-dimethoxyethane, 1,2-jethoxyethane, ethylene carbonate, propylene carbonate,
For example, LiClO
, LiPF6, LiAsF6, LiSbF6, LiBF
4. Those prepared by dissolving one or more electrolytes such as LiB (C6Hs) 4 can be used. Further, as the positive electrode active material, for example, manganese dioxide, iron sulfide, copper oxide, a mixture of iron sulfide and copper oxide, titanium disulfide, etc. can be used.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 A lithium plate with a thickness of 0.72+uw and an aluminum plate with a thickness of 0.01 mm were stacked together, and the lithium plate and aluminum plate were pressed together using a pressing jig with a checkered pattern of irregularities formed on the pressing surface. After pressing the base plate from the aluminum plate side and forming irregularities in a checkered pattern on the surface of the lithium plate in contact with the aluminum plate, a disk shape with a diameter of 6.2 mm is punched out, and the negative electrode can is inserted from the lithium plate side. inserted into. In addition,
The area of each recess of the pressing jig is 0.2-. Further, the area of each convex portion is also 0.2-. The positive electrode contains iron disulfide (
A molding mixture containing a mixture of F e S2 ) and cupric oxide (Cub) as an active material was used, and the electrolyte had a volume ratio of propylene carbonate and 1,2-dimethoxyethane of 2:1.
A lithium battery with a diameter of 9.51 mm and a height of 2.05 mm was prepared using an organic electrolyte containing 1 mol/l/8 of lithium perchlorate (LiCIO4) dissolved in a mixed solvent of was created.

In FIG. 1, reference numeral 1 denotes a negative electrode can made of stainless steel and having its outer surface plated with nickel. 2 is a type of fish, and this negative electrode 2 is composed of a lithium layer 2a and a lithium alloy layer 2b. and aluminum are electrochemically alloyed in the presence of an electrolyte in a battery, and this lithium alloy lft2b is placed on the side facing the separator 3. The lithium layer 2a is composed of a portion of the lithium plate that is not alloyed with aluminum, and the amount of aluminum in the negative electrode corresponds to 2 atomic %. The surface of the lithium layer 2a that is in contact with the lithium alloy 1if2b is uneven, and the convex portions 2
a1 and the recessed portion 2a2 are formed in a checkered pattern. Further, the surface of the lithium alloy Fi2b facing the separator 3 is uneven along the unevenness of the lithium ff12a.

The separator 3 is made of a microporous polypropylene film, and 4 is a positive electrode. A mixture having a composition of 2 parts by weight of polytetrafluoroethylene was filled into a mold in which an annular pedestal 5 made of stainless steel was arranged, and the mixture was press-molded. 6 is a positive electrode can made of stainless steel with a nickel coating on its outer surface, and 7 is an annular gasket made of polypropylene.

Comparative Example 1 A lithium battery having the same configuration as Example 1 was produced, except that the negative electrode was constructed by inserting a lithium plate and an aluminum plate whose surfaces were not roughened into the battery. In this battery, unlike the battery of Example 1, as shown in FIG. 2, the surface of the lithium layer 2a that is in contact with the lithium alloy layer 2b is planar, and the surface of the lithium alloy layer 2b that is opposite to the separator 3. The surface of is also planar.

The results of measuring the internal resistance of the battery of Example 1 and the battery of Comparative Example 1 at 25°C and 1 kllz AC, and the results of measuring the pulsed closed circuit voltage of the above batteries at 10°C, Ω load on 2, and 7.3 m5ec. are shown in Table 1.

Fifty batteries were tested for each type of battery, and Table 1 shows the measured values in the range from the minimum value to the maximum value.

Table 1 As shown in Table 1, the battery of Example 1 had lower internal resistance and higher pulsed closed circuit voltage than the battery of Comparative Example 1. This is because in the present invention, the surface of the lithium layer of the negative electrode in contact with the lithium alloy layer is made uneven to increase the surface area, so the effective reaction area of the negative electrode is widened, and the current density per unit area is reduced. This is thought to be due to the fact that the internal resistance has become smaller.

Regarding the time required for alloying, X-ray diffraction analysis (i'1) confirmed that the battery of Example 1 was almost completely alloyed within 24 hours from battery assembly, but the battery of Comparative Example 1 Even after 48 hours had passed since the battery was assembled, about 6% of the aluminum remained unalloyed.

〔Effect of the invention〕

As explained above, in the present invention, a lithium alloy layer is provided by electrochemical alloying on the side of the lithium layer facing the separator, and the surface of the lithium layer on the side in contact with the lithium alloy layer is made uneven. We were able to expand the effective reaction area of the negative electrode and improve the pulse closing voltage characteristics.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a lithium battery according to the present invention, and FIG. 2 is a sectional view of a lithium battery having a different configuration from that of the present invention. 2... Negative electrode, 2a... Lithium layer, 2a1...
・Convex part, 2a2... Concave part, 2b... Lithium alloy layer, 3... Separator, 4... Positive electrode mark t-Samurai

Claims (2)

[Claims] (1) In a lithium battery using lithium as a negative electrode active material, a lithium alloy layer is provided on the side of the lithium layer facing the separator by electrochemical alloying of lithium and a metal that electrochemically alloys with the lithium. , and the surface of the lithium layer in contact with the lithium alloy layer is an uneven surface. (2) Claims characterized in that the metal electrochemically alloyed with lithium is at least one selected from the group consisting of aluminum, tin, zinc, lead, bismuth, silicon, antimony, and magnesium. The lithium battery according to item 1.