JPS61214359A - Thin lithium battery - Google Patents

Abstract

PURPOSE:To make the thickness of a unit cell thin by forming a negative electrode by evapolating ammonium from ammonium solution of lithium on a negative current collecting plate. CONSTITUTION:A negative electrode 9 is formed by evapolating ammonium from ammonium solution 5 of lithium on a negative current collecting plate 1. Lithium easily and uniformly dissolves in liquid ammonium, and the ammonium solution of lithium forms flat surface on the plate. By evapolation of ammonium, a uniform lithium film having smooth surface is formed on the negative current collecting plate 1. Since the thickness of the lithium film depends on the concentration of lithium dissolved, the thickness of the negative electrode 9 can be controlled. Therefore, a thin battery having a thickness of 1mm or less, preferably 0.5mm or less can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thin lithium battery using lithium or a lithium alloy as a negative electrode.

[Conventional technology]

Generally, lithium batteries use TiS2, MoB2 as the positive electrode.
A molded body containing a positive electrode active material such as ,v,,ol3, VSe5, VSe2, vs2, a binder such as Teflon powder, and an electron conduction aid if necessary, lithium or a lithium alloy as a negative electrode, and lithium as an electrolyte. Each uses a salt dissolved in a non-aqueous solvent,
Various shapes are known depending on the purpose, such as a cylinder shape, a button shape, a coin shape, and a card shape.

The negative electrode in such a lithium battery is generally made of foil-shaped lithium punched out to the required size and pressed onto a wire mesh made of stainless steel, or pellets made of lithium alloy powder molded with a mold. In order to improve the electrical conductivity of the negative electrode current collector plate, it is usually hammered into close contact with the current collector plate (unspecified literature).

[Problem that the invention seeks to solve]

However, in recent years, the miniaturization of various electronic devices,
As lithium batteries become lighter and thinner, there is a demand for ultra-thin lithium batteries with a total thickness of 0.5 #ff or less. When batteries become ultra-thin like this, the negative electrodes that go with them also become thinner, so when using the lithium foil mentioned above, it is necessary to use it alone without using a wire mesh, but since lithium is soft, In this case, there is a problem in that the peripheral edges are likely to bend during punching or handling, and good flatness cannot be obtained. In addition, in the case of the above-mentioned alloy powder pellets, when the pellets become thin, it becomes difficult to mold them, and the strength of the molded product is extremely low, making it difficult to obtain satisfactory properties. Furthermore, when the foils and pellets mentioned above become thin, there is the problem that pounding cannot be used to make them adhere tightly to the negative electrode current collector plate.From these points of view, conventionally, the thickness of the negative electrode is about 0.1fl, and the thickness of the negative electrode is about 0.1fl, and the thickness of the negative electrode is about 0.1fl. Total thickness: 1. OH level was the practical limit for thinning.

On the other hand, a method of vapor depositing lithium may be considered as a means of forming a negative electrode with a thickness of 0.1 ff or less, but this method is expensive and has problems in terms of productivity.

Therefore, the present invention solves the above problems and allows the total thickness of a unit cell to be reduced to 1. Off, preferably 0.5ff
The purpose of the present invention is to provide a lithium battery that is thin, has high performance, and is advantageous in terms of cost and productivity.

[Means for solving problems]

In the process of intensive research for the above purpose, the inventors noticed that lithium dissolves easily in liquid ammonia, and by volatilizing ammonia from a lithium ammonia solution, they could produce lithium with a very thin and uniform thickness and a smooth surface. The present inventors have discovered that a film can be formed, and that by forming this film on a negative electrode current collector plate, a negative electrode with excellent adhesion and suitable for use in thin batteries can be easily obtained at low cost, and this invention has been accomplished.

That is, the present invention has a negative electrode made of lithium or a lithium alloy formed by volatilizing the ammonia component from a lithium ammonia solution present on a negative electrode current collector plate, and the total thickness of a single battery is 1. Off, preferably 0.5
The present invention relates to a thin lithium battery that is less than or equal to fi.

[Structure and operation of the invention]

In the thin lithium battery of the present invention, as described above, the negative electrode is formed by volatilizing the ammonia component from the ammonia solution of lithium present on the negative electrode plate. In other words, lithium is easily dissolved in liquid ammonia and is forced to be uniformly dissolved in the solution, and the liquid level before the ammonia component is volatilized naturally becomes an ideal flat surface, so the ammonia component is By volatilization, a lithium film having an extremely uniform thickness and excellent surface smoothness is formed on the negative electrode current collector plate. Since the thickness of the lithium coating is determined by the amount of ammonia solution used and the concentration of lithium dissolved therein, this thickness can be adjusted over a wide range, and the total thickness is 1. It is possible to form a negative electrode with a thickness of OH or less, preferably 0.5 iff or less, which is suitable for thin batteries.

To form such a negative electrode, when the negative electrode is made of lithium alone, first, as shown in FIG. After forming a recess 8 and placing a lithium piece 4 on this recess 3, either ``liquid ammonia is injected to dissolve the lithium piece 4, or an ammonia solution in which lithium has been dissolved in advance is injected into the recess 3. As a result, an ammonia solution layer 5 containing lithium as shown in FIG. 1 is formed. Next, when the ammonia component of this solution layer S is evaporated and diffused by raising the temperature, a lithium coating layer 6 having a uniform thickness and a very smooth surface is formed as shown in FIG. 1(C).

In the above example, the spacer 2 is used as a means for forming the recess 8, but for example, as shown in FIG. By using the plate 7, the spacer 2 may be omitted.

On the other hand, when the negative electrode is made of an alloy with aluminum or the like, a thin coating layer 8 of aluminum or the like is previously formed on the recess 3 by vacuum deposition or plating, as shown in FIG. A lithium coating layer 6 may be formed on the lithium oxide film 8 by the same means as described above, that is, by evaporating and evaporating the ammonia component from an ammonia solution in which lithium is dissolved, as shown in ) in FIG. In this case, the negative electrode before battery assembly is made up of two layers: a coating layer 8 made of aluminum or the like and a lithium coating layer 6, but after the electrolyte is injected and assembled, an alloy naturally forms within the battery due to the action of the electrolyte. The result is a negative electrode made of a uniform lithium alloy with a very smooth surface inherited from the original lithium coating layer 6. A negative electrode made of such an alloy has battery characteristics such as a reduced possibility of reacting with the electrolyte during long-term storage and improved reversibility as a negative electrode for secondary batteries compared to lithium alone. It has great advantages.

In addition, since liquid ammonia has a boiling point of 134°C,
Needless to say, when dissolving lithium as described above and when handling it as a solution, it should be cooled to below the above-mentioned boiling point, usually to about -40'C. In order to volatilize and remove the ammonia component from the solution, there is no need to perform special heating, and cooling can be gradually stopped and vacuuming can be performed as necessary.

The thickness of the thus formed negative electrode made of lithium metal mr4Pz can be arbitrarily set by selecting the amount of ammonia solution used and the lithium concentration, but the total thickness is 1. A thin layer of less than 100 μm, especially less than 70 μm is desirable for thin batteries of less than 0.0 m, preferably less than 0.95 nm. When the negative electrode is made of a lithium alloy, the thickness ratio between the lithium coating layer and the other metal layer such as aluminum is preferably about i:o, about a to 1.2.

On the other hand, the amount of lithium dissolved in liquid ammonia is preferably about 2 to 10.7 parts by weight per 100 parts by weight of liquid ammonia.

Note that the negative electrode formed using a lithium ammonia solution is characterized by an extremely smooth surface and extremely high activity. In other words, conventional lithium foil usually has a film of oxide, hydroxide, carbonate, etc. formed on its surface, which acts as a resistance layer, whereas in the negative electrode of this invention, the ammonia component evaporates and transpires. Since the surface that appears is an active lithium metal surface without the above-mentioned film, combined with high surface smoothness, battery performance such as discharge capacity during charging and discharging of the battery and cycle characteristics as a secondary battery is improved. .

Next, the structure of the thin battery according to the present invention will be explained based on FIG. 4. In the figure, 1 is a rectangular flat negative electrode current collector plate made of stainless steel as described above, 2 is a rectangular annular spacer made of ceramic or the like as described above, and 9 is a rectangular annular spacer made of ammonia solution of lithium as described above. A negative electrode made of lithium or a lithium alloy formed by evaporation and diffusion, 10 a rectangular flat positive electrode current collector plate made of stainless steel similar to the negative electrode current collector plate 1, 11 a positive electrode containing a positive electrode active material, 12 a negative electrode 9 and the positive electrode 11; a luciferator 13 made of a microporous polypropylene film, etc.
are both sides of the spacer 2 and the bipolar collector electrode 1. A sealing material layer seals between the inner surface of the periphery of the lO. Note that an electrolyte containing a lithium salt and a non-aqueous solvent that dissolves the lithium salt is added to the battery.

Here, the positive electrode 11 is generally T'182, MO
A molded body containing positive electrode active materials such as 82, V2O5, V2O38, vse2, and vs2, a binder such as Teflon powder, and, if necessary, an electron conduction aid such as carbonyl nickel or carbon powder, is used, but the above-mentioned binder Instead, a viscous kneaded product prepared by kneading an electrolyte gelled with a polymeric material or the like may be used, and this may be applied onto the positive electrode current collector plate 10.

Various adhesives can be used for the sealing material layer 13, and although general paint solution type adhesives can also be used, molded sheets and molded sheets that are easy to handle and can avoid mixing with the electrolyte are also suitable. The use of heat-sealable materials is recommended. Such thermofusible materials include, for example, hot melt adhesives and hermetically sealable ceramics.

Furthermore, as the electrolyte, a liquid in which a lithium salt is dissolved in a non-aqueous solvent is generally used, but a gelling agent or the like may be added to this liquid to make it viscous. That is, there is an advantage that the latter viscous electrolyte can be added by coating means. Note that as the lithium salt and non-aqueous solvent, various substances conventionally known for use in lithium batteries can be used. For example, a typical example of the lithium salt is LiBφ4.
(φ means phenyl group), rjPF6, LiC
Examples of the nonaqueous solvent include F3SO3 and IjASF6, and examples of the nonaqueous solvent include propylene carbonate, γ-butyrolactone, dimethoxyethane, and dioxolane. Moreover, polymethacrylic acid alkyl ester and the like are preferably used as the gelling agent.

The thin lithium battery of the present invention constructed as described above can have a negative electrode that is extremely thin and has an extremely smooth surface, whether it is made of lithium alone or a lithium alloy. It is useful as a thin battery with a total thickness of 0.5 nm or less, which corresponds to a type or flexible type.

In the configuration example shown in FIG. 4, the bipolar current collector plates 1 and 10 have a flat plate shape, but the spacer may be omitted by making one or both of them plate-shaped as shown in FIG. .

〔Effect of the invention〕

In the thin lithium battery according to the present invention, since the negative electrode is made of lithium or a lithium alloy formed by volatilizing the ammonia component from a lithium ammonia solution present on the negative electrode current collector plate, the total battery thickness is 1. Although it is a thin battery, preferably 0.5n or less, the corresponding thin negative electrode has a uniform thickness and a very smooth surface, and has good adhesion to the negative electrode current collector plate. It has excellent performance in that it has a high discharge capacity and a long cycle life as a secondary battery. Moreover, the thickness of the negative electrode can be easily adjusted over a wide range depending on the total battery thickness, application, required characteristics, etc. Further, the battery of the present invention does not require a highly variable method such as pounding to form the negative electrode, and a constant quality product can be obtained under certain conditions, resulting in excellent productivity.

〔Example〕

Examples of the present invention will be specifically described below in comparison with comparative examples. Note that in the following, parts mean parts by weight.

Example 1 A rectangular annular ceramic spacer with a width of 2 cm and a thickness of 0.4 tm was hot-melted on a stainless steel negative electrode current collector plate with a square size of 15 fl on each side and a thickness of 0.05 m as shown in Fig. 1. After heat-sealing with an adhesive, a 5.4~ lithium piece was placed in the center, the whole was cooled to -40°C, and 50 cm of liquid ammonia (-40'C) was dropped. When this state was left for 10 minutes, the lithium pieces were completely dissolved, and a solution surface was spread over the entire surface surrounded by the spacers of the negative electrode current collector plate. Next, the degree of cooling was gradually loosened to raise the temperature to room temperature, and vacuum was applied to completely volatilize the ammonia component, resulting in the formation of a lithium coating layer with a thickness of about 100 μm and an extremely smooth surface.

This film layer is used as a negative electrode and has a thickness of 25 μm as a separator.
A microporous polypropylene film (product name: Duraguard, manufactured by Polyplastics) was used as an electrolyte in LiBφ.
A viscous body consisting of 11.2 parts of the dimethoxyethane adduct of No. 4 (LiBφ4; molar ratio of dimethoxyethane 1:3), 23.8 parts of propylene carbonate, and 5.2 parts of polymethyl methacrylate was used as a positive electrode, and 527 parts of Ti and the above were used. A viscous kneaded product with 3 parts of viscous material was applied to a positive electrode current collector plate similar to the negative electrode current collector plate to a thickness of 100 μm, and the total thickness was approximately 0.5 μm with the structure shown in FIG. 4. A ff1ll thin lithium battery was manufactured.

Example 2 Instead of dissolving lithium pieces on the positive electrode current collector plate, 11.8 parts of lithium was added to 100 parts of liquid ammonia at -40°C in advance.
A thin lithium battery in which the negative electrode consists of a lithium coating layer approximately 100 μm thick was prepared by dropping a solution of 53 μm in which 53 μm was dissolved onto a negative electrode current collector plate to which a spacer similar to that in Example 1 was fixed. was created.

Example 3 After forming an aluminum coating layer with a thickness of 930 μm by vacuum evaporation on the surface of a negative electrode current collector plate to which a spacer similar to that in Example 1 was fixed, a lithium coating layer was formed in the same manner as in Example 2, Hereinafter, in the same manner as in Example 1, the negative electrode was
A thin lithium battery made of a lithium alloy of m was fabricated.

Comparative Example A lithium foil with a thickness of 100 μm was cut into a square with 10 mm on each side, and this was placed on a negative electrode current collector plate to which a spacer similar to that in Example 1 was fixed, and the sheet was crimped from above with a push rod made of vinylidene chloride. Using this as a negative electrode, a thin lithium battery was produced in the same manner as in Example 1.

Regarding the batteries obtained in the above examples and comparative examples,
The cycle characteristics were investigated at a charging end voltage of 2.7 V, a discharging end voltage of 1.5 V, and a charging/discharging current of 100 μA. The results are shown in FIG. Note that the curve A1 in the figure corresponds to Example 1, A2
shows the characteristics of the batteries of Example 2, A3 of Example 3, and B of Comparative Example.

As is clear from FIG. 5, a battery (
It can be seen that Examples 1 and 2) are significantly superior in discharge capacity and cycle life during charging and discharging, compared to a battery (comparative example) having a negative electrode formed from lithium foil. It is also seen that the cycle characteristics of the battery (Example 3) having a lithium alloy negative electrode in which a lithium film layer was formed using the above ammonia solution on a pre-formed aluminum layer further improved in cycle characteristics.

Note that in the above Examples and Comparative Examples, the thickness of the negative electrode was set to about 100 μm for performance comparison, but needless to say, in the present invention, an infinitely thin negative electrode can be formed. On the other hand, when using lithium foil, the negative electrode thickness is approximately 1
The limit is approximately 00 μm.

[Brief explanation of the drawing]

Figures 1 (4) to (C) are longitudinal cross-sectional views showing in order of steps an example of forming a negative electrode made of lithium alone in a thin lithium battery according to the present invention, and Figure 2 shows another embodiment of the negative electrode current collector plate in the same battery. 3(4) and (B) are longitudinal sectional views showing an example of forming a negative electrode made of a lithium alloy in the order of steps, and FIG. The plan view and FIG. 5 are charge/discharge cycle characteristic diagrams of batteries obtained in Examples and Comparative Examples of the present invention. DESCRIPTION OF SYMBOLS 1... Negative electrode current collector plate, 5... Lithium ammonia solution, 7... Negative electrode current collector plate, 9... Negative electrode. Patent applicant Hitachi Maxell Ltd. Figure 3 Figure 4 9; Figure 5 Dimensions 2 sheets

Claims (1)

[Claims] (1) A thin lithium battery having a negative electrode made of lithium or a lithium alloy formed by volatilizing the ammonia component from a lithium ammonia solution present on a negative electrode current collector plate.