JPH01239761A - Thin lithium battery - Google Patents

Abstract

PURPOSE:To increase the performance of a battery and to prevent the battery from short circuit by forming a negative electrode with two layers of lithium and a specified lithium alloy and using a nonwoven fabric having a specified pore size and METSUKE weight as a separator. CONSTITUTION:A negative electrode 2 of a thin lithium battery consists of two layers of a lithium layer 2a and a lithium alloy layer 2b. The lithium alloy layer 2b is prepared by electrochemically alloying lithium with a metal capable of electrochemically alloying with lithium such as aluminum. The activity of the lithium layer 2a is optimized, and storage life and closed circuit voltage are improved, but the fine powder of lithium alloy is generated. As a separator 3, nonwoven fabric made of polypropylene having a maximum pore size of 5mum or less and a METSUKE weight of 30-70g/cm<2> is used. The separator 3 efficiently retains an electrolyte, and retards the transfer of the fine powder of lithium alloy by entangling fibers. The short circuit of a battery is thereby prevented.

Description

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

[Conventional technology]

In lithium batteries, 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 too active. For example, in secondary batteries, electrodeposited lithium during charging is particularly active and reacts with components in the electrolyte, causing various problems during battery use or storage. generate,
It has been reported that it 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 (eg, US Pat. No. 4,002,492).

Furthermore, 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. Place it and
Lithium and the above metals are electrochemically alloyed in the presence of an electrolyte to reduce the activity of the lithium surface, suppress the reaction with the electrolyte, and prevent the formation of a passive film on the negative electrode surface. Therefore, it is recommended to immediately control the increase in the interfacial resistance of the negative electrode and improve the storage characteristics and closed circuit voltage characteristics (for example,
(Japanese Patent Application Laid-Open No. 61-74269).

However, when lithium and other metals are electrochemically alloyed in the presence of an electrolyte as described above, the alloy becomes a fine powder, which increases the reaction area of the negative electrode and retains the electrolyte. This is a factor that improves battery performance by increasing the pulse closing voltage, but on the other hand, there is a problem in that the finely powdered lithium alloy passes through the separator and reaches the positive electrode, causing a short circuit.

In particular, in thin lithium batteries that use manganese dioxide as the positive electrode active material, the porosity of the positive electrode is molded to be relatively small in order to increase the filling amount of the positive electrode active material and maintain appropriate strength even with a thin positive electrode. Ru.

For this reason, it is not possible to store sufficient electrolyte in the positive electrode, so a nonwoven fabric with a high electrolyte retention capacity, such as a polypropylene nonwoven fabric, is used for the separator.However, conventional nonwoven fabrics have poor electrolyte retention properties. However, the pore diameter was as large as approximately 40 μm, and no particular attention was paid to the pore diameter.
Therefore, when the lithium alloy layer is provided on the side facing the separator, the finely powdered lithium alloy passes through the separator and short circuits are very likely to occur.

[Problem to be solved by the invention]

As described above, the present invention provides that conventional thin lithium batteries
The purpose is to solve the problem that lithium alloy powder easily passes through the separator and cause internal short circuits, and to provide a thin lithium battery that does not have short circuits and has excellent battery performance. ] The present invention improves battery performance such as pulse-circuit voltage characteristics by providing a lithium alloy layer by electrochemical alloying on the side of the lithium layer of the negative electrode opposite to the separator. Below,
By using a non-woven fabric with a date type fi of 30 to 70 g/rd, it is possible to prevent the lithium alloy from passing through the separator due to the pulverization of the lithium alloy, thereby providing a thin lithium battery that does not cause short circuits and has excellent battery performance. be.

That is, when lithium is electrochemically alloyed with aluminum or the like in the presence of an electrolyte, the lithium alloy becomes fine powder. The degree of this pulverization varies depending on the type of metal to be alloyed, the alloying ratio of other metals to lithium, the temperature during alloying, etc., but the smallest particle is 0.4
If a conventionally used polypropylene nonwoven fabric or the like is used as a separator without paying any consideration to the separator used, the lithium alloy powder will pass through the separator and reach the positive electrode, causing an internal short circuit. Therefore, in the present invention, the separator has a pore diameter of 5 μm or less and a date mN of 30 to 70 g/r.
By using the nonwoven fabric of d, the lithium alloy powder is prevented from passing through the separator, and short circuits do not occur (
The present invention also provides a lithium battery with excellent battery performance.

In the present invention, a nonwoven fabric with a pore size of 5 μm or less and a basis weight of 30 to 70 g/nf is used as a separator.
It may be difficult to understand that a nonwoven fabric with pores larger than the particle size of lithium alloy powder can prevent lithium alloy powder from passing through, but nonwoven fabric is made by intertwining fibers. Since the pores are not straight but curved, the distance through which the lithium alloy powder passes is long compared to the thickness, and due to the movement prevention effect due to the entanglement of these non-directional fibers, as shown in the examples below. As such, the passage of lithium alloy powder can be sufficiently prevented.

In the present invention, suitable nonwoven fabrics include, for example, polypropylene nonwoven fabrics, polyethylene nonwoven fabrics, nylon nonwoven fabrics, polyester nonwoven fabrics, and the like. This is because they are resistant to organic solvents.

In the present invention, the upper limit of the pore diameter of the nonwoven fabric used is 5 μm as described above, but on the other hand, the smaller the pore diameter of the nonwoven fabric is, the more preferable it is from the viewpoint of preventing lithium alloy powder from passing through. However, as the pore size decreases, the porosity decreases accordingly, and there is a risk that the electrolyte retention capacity of the separator will decrease. Therefore, it is preferable to use a material with a pore size of 5 μm or less and a maximum pore size of 1 μm or more. .

In addition, not only the surface of the separator that is in contact with the lithium alloy powder, but also the depth direction, that is, the thickness of the separator,
If it is too thin, the electrolyte retention capacity will decrease, making it impossible to fully demonstrate battery performance, and the ability to prevent lithium alloy powder from passing through will also decrease. Therefore, in the present invention, the density in the thickness direction, that is, the basis weight is 30~70g/rr
r nonwoven fabric is used. This means that the basis weight of the nonwoven fabric is 30
g/r+? If the amount is less, as is clear from the above, the battery performance will not be fully demonstrated due to the low electrolyte retention capacity, and there is a risk that the lithium alloy powder will pass through the separator and cause a short circuit. This is because when the date weight is larger than 708/rrf, the distance between the positive electrode and the negative electrode becomes longer due to the increase in the thickness of the separator lake, resulting in an increase in internal resistance.

Examples of metals that electrochemically alloy with lithium used to form the lithium alloy layer include aluminum, tin, zinc, lead, bismuth, silicon, antimony,
Examples include magnesium, indium, gallium, and germanium. In particular, aluminum, tin, zinc, lead, bismuth, silicon, antimony, magnesium, etc. have a great effect on 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 pressing a lithium plate onto a negative electrode current collector, and applying a metal such as an aluminum plate (hereinafter, aluminum is representatively used) to be electrochemically alloyed with lithium, such as an aluminum plate, onto the lithium plate. (explained using an example), the plates are stacked and crimped together, the battery is assembled, and the presence of an electrolyte in the battery. Formed by alloying.

The thickness of the lithium alloy layer can be thin, and accurate measurement is difficult because it is finely powdered, but if it is about 5 μm or more, it will prevent the reaction of lithium with moisture and impurities in the electrolyte during storage. Furthermore, the increase in the reaction area of the negative electrode due to the pulverization of the lithium alloy and the electrolyte retaining effect of the lithium alloy powder can have the effect of improving battery performance such as pulsed closed circuit voltage characteristics. On the other hand, a thicker lithium alloy layer is advantageous in terms of improving pulse-circuit voltage characteristics, etc., but since the amount of alloying elements such as aluminum that make up the lithium alloy increases and the electrical capacity of the negative electrode decreases, The alloying element is 0.5 to 10 atomic% (aLomic%) of the entire page, that is, the total amount of alloying elements such as lithium and aluminum.
, especially preferably from 1 to 7 atom %.

As the electrolytic solution and the positive electrode active material, those commonly used in this type of battery can be used as they are.

To give a specific example of an electrolytic solution, for example, 1°2-
Dimethoxyethane, 1,2-jethoxyethane, ethylene carbonate, propylene carbonate, T-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, etc. alone or in a mixture of two or more organic solvents. , for example LLCIO
,, LiPFi, LiAsF4, LiBFn, L +
Those prepared by dissolving one or more types of electrolytes such as B(C*Hs)a can be used. Further, as the positive electrode active material, for example, manganese dioxide, iron sulfide, copper oxide, titanium disulfide, etc. can be used.

〔Example〕

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

Example 1 A lithium plate of [7 mm, width 251, thickness O, 1 mm] was pressed onto a negative current collector plate, and further 71 I of stitches were placed on the lithium plate.
I11, width 25m+, I! Aluminum plates of Jsa0 and 005■ are overlapped and crimped together, a molding mixture containing manganese dioxide as an active material is used for the positive and negative parts, and propylene carbonate and lithium perchlorate (L) are used for the electrolytic solution.
Using an organic electrolyte in which 1 wol/n of iCIO=) was dissolved, the separator had a maximum pore diameter of 3 μm and a fabric weight type of 130 g.
/rd polypropylene non-woven fabric, the structure is as shown in Figure 1, and the outer diameter is 16.5 mm long and 34.5 mm wide.
A thin lithium battery with a gamma thickness of 0.5 mm and 0.5 cm was fabricated.

In Figure 1, ■ is a negative current collector plate with a thickness of 0.03 mm.
It is made of nickel plate, and its planar shape is 117 mm.
It is formed into a rectangle with a length of 16m+w and a width of 34IIIffi. 2 is lithium! ! 2a and a lithium alloy [2b], and 3 is a separator made of nonwoven fabric.

In this example, the lithium alloy layer 2b of the negative electrode 2 is formed by pressing the lithium plate onto one surface of the negative current collector plate 1 as described above, and then superimposing the aluminum plate on the lithium plate. The lithium alloy is formed by crimping and assembling the battery, and electrochemically alloying the lithium and aluminum near the aluminum plate of the lithium plate in the presence of an electrolyte within the battery.
2b is arranged on the separator 3 side. 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 2 corresponds to 6 at %. In this way, the negative electrode 2 has the lithium alloy layer 2b formed on the side facing the separator 3, but during discharge, lithium in the lithium 12a is eluted into the electrolytic solution as lithium ions through the lithium alloy 112b. However, lithium acts as a negative electrode active material. As described above, the nonwoven fabric constituting the separator 3 is a polypropylene nonwoven fabric with a maximum pore diameter of 3 μm and a basis weight of 130 g/rrf.

4 is a positive electrode, and this positive electrode 4 is made by pressure-molding a mixture powder consisting of 100 parts by weight of manganese dioxide, 1 part by weight of phosphorous graphite 1O, and 1 part by weight of polytetrafluoroethylene, and has a length of 7 mm, a width of 25 a + Im, and a thickness. 0.21, and a stainless steel mesh is placed on one side as the positive electrode current collector 5 during pressure molding. 6 is positive! This is an i-electronic plate, which is formed into a shallow container shape using a stainless steel plate with a thickness of 0.0511111, and its peripheral edge 6a
is formed in the shape of a flat brim, its width is 21111 mm, the width of the central recess is 0.3 n+m, and the planar shape is a rectangle with a length of 16.5 mm and a width of 34.5 m+w. Reference numeral 7 denotes a true-melt adhesive, which adheres the peripheral edge 1a of the negative current collector plate l and the flat flange-shaped peripheral edge 6a of the positive electrode current collector plate 6. ．． board l
While insulating the two, the gap between the two is sealed.

Example 2 The maximum pore diameter of the nonwoven fabric constituting the separator lake 3 was 5 μm.
A type 1 lithium battery having a fabric weight ffl M of 70 g/o (having the same structure as in Example 1 except for using a polypropylene nonwoven fabric) was prepared.

Comparative Example 1 The maximum pore diameter of the nonwoven fabric constituting the separator 3 was 40u.
A thin lithium battery having the same structure as in Example 1 was produced except that a polypropylene nonwoven fabric with a fabric weight of 1100 g/rrf was used.

Comparative Example 2 As a nonwoven fabric constituting the separator 3, the maximum pore diameter lOμ
A thin lithium battery was fabricated with the same structure as in Example 1 except that a polypropylene nonwoven fabric with a fabric weight of 150 g/rrr was used.

Comparative Example 3 The maximum pore diameter of the nonwoven fabric constituting the separator 3 was 3 μm.
A thin lithium battery having the same structure as in Example 1 was produced except that a polypropylene nonwoven fabric having a basis weight of 10 g/rd was used.

The batteries of Examples 1 and 2 and the batteries of Comparative Examples 1 and 3 were
Vibration frequency 10-55Hz, total amplitude 1.5mm, according to electronic component vibration test method A specified in IS C5025.
Table 1 shows the results of examining the occurrence of short circuits after vibration for 6 hours. The number of batteries tested was 1,000 for each battery.

Table 1 As shown in Table 1, the batteries of Examples 1 and 2 had no short circuits at all even after the vibration test, but the battery of Comparative Example 1, in which the conventionally used polypropylene nonwoven fabric was used for the separator, failed to pass the test. Short circuits occurred in 280 of the 1,000 batteries provided. In addition, in the battery of Comparative Example 2, in which the pore diameter of the separator is relatively small, the number of short-circuited batteries is lower than that of the battery of Comparative Example 1, which corresponds to the conventional product, but still, 50 of the 1,000 batteries subjected to the test were short-circuited. A short circuit occurred. In the battery of Comparative Example 3, where the maximum pore diameter of the separator was as small as 3 μm, the number of short-circuited batteries was further reduced, but because the basis weight was small, the 1,0
A short circuit occurred in 25 of the 00 batteries.

Next, Table 2 shows the results of measuring the internal resistance of the batteries of Examples 1 and 2 above and the battery of Comparative Example 4, which was fabricated using a polypropylene nonwoven fabric with a large basis weight as a separator for comparison.

Table 2 As shown in Table 2, the batteries of Examples 1 and 2 have an internal resistance of 30 to 35 Ω, which is within the usable range, but a comparative example using a polypropylene nonwoven fabric with a large basis weight as a separator The battery No. 4 had an internal resistance of 80Ω, which was too high for a practical battery, making it difficult to use for boat fishing.

In addition, both of the batteries of Examples 1 and 2 were heated at 20°C115
-10゛C1 after discharging to 80% depth of discharge at Ω
5, the pulse closing voltage of 7.8m5ec was 2.8V or more, but the negative electrode was 7mm long, 25+u+ wide, and 0.5mm thick.
In a battery composed only of 1 m+w lithium plates, the pulse closing voltage under the same conditions was 2.5 VL.

〔Effect of the invention〕

As explained above, in the present invention, a lithium alloy layer formed by electrochemical alloying is provided on the side facing the separator of the lithium layer of the negative electrode, and the pore size of the separator is 5 μm.
In the following, by using a nonwoven fabric having a basis weight of 30 to 70 g/rd, it was possible to provide a thin lithium battery that does not cause short circuits and has excellent battery performance.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a thin lithium battery according to the present invention. DESCRIPTION OF SYMBOLS 1... Negative electrode current collector plate, 1a... Peripheral part, 2...
Negative electrode, 28... Lithium layer, 2b... Lithium alloy layer, 3... Separator, 4... Kingship, 6.
... Positive current collector plate, 6a... Peripheral part, 7... Hot melt adhesive parking pupami

Claims (2)

[Claims] (1) A battery element including a negative electrode 2 containing lithium as an active material, a positive electrode 4, and a separator 3 interposed between the two electrodes is arranged between the negative electrode current collector plate 1 and the positive electrode current collector plate 6, and the battery element is arranged between the negative electrode current collector plate 1 and the positive electrode current collector plate 6. Board 1,
In the thin lithium battery having a structure in which the flat peripheral edges 1a and 6a of the lithium layer 2a are adhesively sealed, the negative electrode 2 has lithium on the side of the lithium layer 2a facing the separator 3, and the lithium is electrochemically bonded to the lithium layer 2a. A lithium alloy layer 2b is provided by electrochemical alloying with the metal to be alloyed, and the separator 3 has a maximum pore diameter of 5 μm or less and a basis weight of 30 to 70.
A thin lithium battery characterized by using a non-woven fabric of g/m^2. (2) The thin lithium battery according to claim 1, wherein 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. .