JPS63175348A - Lithium cell - Google Patents

Abstract

PURPOSE:To prevent a short from occurring, by installing a lithium alloy layer in the side opposed to a separator of the lithium layer of a negative electrode, and combining a micro-porous resin film of the specified hole diameter as the separator together with a nonwoven fabric of the specified porosity. CONSTITUTION:As metals to be electrochemically alloyed with lithium, those of aluminum, tin, zinc, lead, bismuth, silicon, antimony, magnesium, gallium, germanium, etc., are used. As a separator 2, a micro-porous resin film of less than 0.3mum in hole diameter and a nonwoven fabric of 70-90 capacity% in porosity are combined together and used. And, the micro-porous resin film small in hole diameter and high in stopping power of movement in lithium alloy powder is set up at the side of a negative electrode 2, preventing this lithium alloy powder from being passed through, while the nonwoven fabric high in holding capacity of an electrolyte is set up at the side of a positive electrode 4, respectively.

Description

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

[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 also highly 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. It has been reported that the negative electrode is generated and the negative electrode is deteriorated, resulting in 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). However, the alloying of lithium as described above
In secondary batteries, it is not necessary to pay as much consideration to a decrease in discharge capacity as in primary batteries, and it is argued that it is more desirable to improve charge-discharge cycle characteristics than to reduce discharge capacity due to alloying. The degree of alloying is also carried out until the lithium content is considerably low. For example, in JP-A No. 61-208749, the lithium content is 35
It is stated that preferable results can be obtained at atomic % to 58 atomic %.

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, research has been conducted on suppressing the increase in the 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).

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 also increases the reaction area of the negative electrode and displaces the electrolyte. This is a factor that improves battery performance by increasing the pulse closing voltage, but on the other hand, the powdered lithium alloy passes through the separator and reaches the positive electrode, causing a short circuit.

In particular, in 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. It is not possible to store enough electrolyte in the positive electrode, so nonwoven fabrics with high electrolyte holding capacity, such as polypropylene nonwoven fabric, are used for the separator, but conventionally used nonwoven fabrics have pores of about 40μ
If the lithium alloy layer is provided on the side facing the separator, the finely powdered lithium alloy will pass through the separator and cause a short circuit.

[Problem that the invention seeks to solve]

The purpose of this invention is to solve the problem of the lithium alloy powder of the conventional lithium battery passing through the separator and causing an internal short circuit, and to provide a lithium battery that is free from short circuits and has excellent battery performance. shall be.

[Means for solving problems]

The present invention improves battery performance such as pulsed circuit voltage characteristics by providing a lithium alloy layer by electrochemical alloying on the side facing the separator of the lithium layer of the negative electrode, and the pore diameter of the separator is 0.3 μm or less. A microporous resin film and a nonwoven fabric having a porosity of 70 to 90% by volume are used in combination, and the microporous resin film is placed on the side facing the negative electrode, and the nonwoven fabric is placed on the side facing the positive electrode. By doing so, it was possible to prevent the lithium alloy layer from passing through the separator due to the pulverization, and to ensure sufficient electrolyte at the positive and negative electrode interfaces, thereby providing a lithium battery with no short circuits and excellent battery performance. It is something.

That is, when lithium is electrochemically alloyed with aluminum or the like in the presence of an electrolyte, the lithium alloy is powdered. The degree of this powdering varies depending on the alloying ratio of other metals to lithium, the type of metal to be alloyed, the temperature during alloying, etc., but the smallest particle is 0.4 μm.
If conventionally used polypropylene nonwoven fabric 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. In the invention, a microporous resin film with a pore diameter of 0.3 μm or less and a porosity of 7 is used as a separator.
A microporous resin film that uses a combination of 0 to 90% by volume nonwoven fabric and has a small pore size and a high ability to inhibit the movement of lithium alloy powder as described above is placed on the negative electrode side to prevent the lithium alloy powder from passing through. , a nonwoven fabric with high electrolyte retention capacity is placed on the positive electrode side to ensure sufficient electrolyte at the interface between the positive and negative electrodes, thereby providing a lithium battery that is free from short circuits and has excellent battery performance. be.

In the present invention, examples of the microporous resin film used for the separator include microporous polypropylene film, microporous polyethylene film, and microporous nylon film. In particular, a microporous polypropylene film commercially available under the trade name "Duraguard" is preferably used. In the above-mentioned microporous polypropylene film, the micropores are not perfectly circular but have directionality, and the length in the long axis direction (long axis) and the short axis direction (length in the short axis direction) are different. However, if the micropores have directionality, even if the length in the major axis direction (major axis) is 0.3μ
Even if it is larger than steel, the length in the minor axis direction (minor axis) is 0.
If the diameter is 3 μm or less, the fine pores of the separator can be reduced by stacking two or more microporous resin films with such directional micropores so that the directions of the micropores are perpendicular to each other. Since the pore diameter can be substantially reduced to 0.3 μm or less, this case is also within the scope of the present invention.

Note that the smaller the pore diameter of the separator is, the better it is from the viewpoint of preventing short circuits, but if the pore diameter is small, the internal resistance of the battery may become thicker, so the maximum pore diameter should be 0.3
It is preferable to use a microporous resin film of 0.03 μm or more within the range of μm or less.

On the other hand, examples of nonwoven fabric include polypropylene nonwoven fabric,
Polyethylene nonwoven fabric, nylon nonwoven fabric, polyester nonwoven fabric, etc. are used. In the present invention, a nonwoven fabric with a porosity of 70 to 90% by volume is used, but if the porosity is less than 70% by volume, the electrolyte retention capacity will decrease and the discharge reaction will be inhibited. If the porosity exceeds 90% by volume, the material will not be able to hold the necessary electrolytic solution, and if the porosity exceeds 90% by volume, the strength will become weak, and it will break and be unable to fulfill its role as an electrolyte-retaining material.

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 great effect of improving the pulse closed circuit voltage characteristics and are preferably used in the present invention.

The formation of the lithium alloy layer is usually done by placing a lithium plate in the negative electrode can and a metal that electrochemically alloys with lithium, such as an aluminum plate (hereinafter, aluminum will be explained as a representative example for simplicity). Insert the board, assemble the battery,
It is formed by electrochemically alloying lithium and aluminum near the aluminum plate of a lithium plate in the presence of an electrolyte in a battery.

The thickness of the lithium alloy layer can be thin, and it is difficult to accurately measure the thickness because it is finely powdered, but if it is about 5 μm or more, there is a possibility that lithium may react with moisture or impurities in the electrolyte during storage. Furthermore, by increasing the 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 is possible to exhibit the effect of improving battery performance such as pulse 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, the electrical capacity of the negative electrode probably decreases. is 0.5 to 10 atomic% (ato++i
c%), particularly 1 to 7 atom%, more preferably 2 to 4 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 the electrolyte, for example, 1.2
- A single or mixed solvent of two or more organic solvents such as dimethoxyethane, 1,2-jethoxyethane, ethylene carbonate, propylene carbonate, T-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, etc. For example, LiCl0
a, LiPF6, LiAsF6, Li5bF, ,L
One prepared by dissolving one or more electrolytes such as iBFn and LiB(CiHs)4 can be used. In addition, as a positive electrode active material,
For example, manganese dioxide can be used.

〔Example〕

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

Example 1 A lithium plate with a diameter of 16+wm and a thickness of 0.2mm and an aluminum plate with a diameter of 16ffim and a thickness of 0.005IN+m were stacked and inserted into a negative electrode can, and manganese dioxide (MnO□) was used as an active material in the positive electrode. A molding mixture is used, and the electrolyte contains lithium perchlorate (
Using an organic electrolyte in which 1 mol/l of LiC10,) is dissolved, the separator is made of microporous polypropylene with a thickness of 25 μm and a large number of directional micropores with a major axis of 0.4 μm and a minor axis of 0.04 μm. A lithium battery with a diameter of 20.0+ sm and a height of 1.61 cm was fabricated using two films stacked one on top of the other so that the long directions of the pores were perpendicular to each other, as shown in FIG.

In Fig. 1, 1 is a negative electrode can made of stainless steel and plated with nickel on the surface, 2 is a negative electrode made of a lithium layer 2a and a lithium alloy layer 2b, and 3 is a negative electrode made of a microporous resin film 3a and a nonwoven fabric 3b. A separator consisting of

In this embodiment, the lithium alloy layer 2b of the negative electrode 2 is placed inside the negative electrode can 1 as described above, with a diameter of 16 m+w and a thickness of 0.5 m.
2mm lithium plate, diameter 16mm, thickness 0.005mm
Insert the aluminum plates in a stacked manner to assemble the battery, and electrochemically alloy the lithium and aluminum near the aluminum plate of the lithium plate in the presence of an electrolyte in the battery. The lithium alloy layer 2b is arranged on the separator 3 side. 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 2 corresponds to 3 atomic %.

Although the microporous resin film 3a constituting the separator 3 is shown as being composed of one layer in FIG. 1, it actually has a major axis of 0.4 μm and a minor axis as shown in FIG. Two microporous polypropylene films 3a+ each having a large number of directional micropores 3az of 0.04 μm.
The nonwoven fabric 3b is a polypropylene nonwoven fabric with a porosity of 84% by volume, a maximum pore diameter of 40 μl, and a thickness of 350 μl.

The microporous resin film 3a is placed on the side facing the negative electrode 2, and the nonwoven fabric 3b is placed on the positive electrode 4 side. The positive electrode 4 is made by pressure-molding a mixed powder consisting of 100 parts by weight of manganese dioxide, 10 parts by weight of phosphorous graphite, and 1 part by weight of polytetrafluoroethylene, and has a diameter of 16 PRm and a thickness of 0.6 m.
A stainless steel mesh is placed on one side as a current collector 5 on the positive electrode side during pressure molding.

6 is a positive electrode can made of stainless steel with a nickel-plated surface, and 7 is an annular gasket made of polypropylene. This battery uses propylene carbonate and 1,2-dimethoxyethane as an electrolyte at a capacity ratio of 2:
Add 1 mol/l of lithium perchlorate to the mixed solvent mixed in 1.
A dissolved organic electrolyte is injected.

Example 2 A microporous resin film 3a constituting the separator 3 has a thickness of 25 μm and has a pore diameter of 0.3 μm and a circular micropore shape.
m microporous polypropylene film (however, 1
A lithium battery was produced having the same structure as in Example 1, except that a polypropylene nonwoven fabric with a porosity of 75% by volume, a maximum pore diameter of 20 μm, and a thickness of 350 μm was used as the nonwoven fabric 3b.

Comparative Example 1 As a separator, the porosity was 84% by volume and the maximum pore diameter was 40 μm.
1. Using only polypropylene non-woven fabric with a thickness of 350μ,
A lithium battery having the same structure as in Example 1 was produced except that a microporous polypropylene film was not used.

Comparative Example 2 As a separator, two microporous polypropylene films each having a large number of micropores with a major diameter of 0.4 μm and a minor diameter of 0.04 μm were used, stacked so that the directions of the micropores were perpendicular to each other, and no polypropylene nonwoven fabric was used. A lithium battery having the same structure as in Example 1 except for the above was produced.

Comparative Example 3 The nonwoven fabric 3b constituting the separator 3 had a porosity of 60
A lithium battery was produced having the same structure as in Example 1, except that a polypropylene nonwoven fabric having a maximum pore diameter of 15 μm in volume % and a thickness of 350 μl was used.

The batteries of Examples 1 and 2 and the batteries of Comparative Examples 1 and 3 were
Fig. 3 shows the discharge characteristics when continuously discharging at 5°C and 215Ω.

As shown in FIG. 3, the batteries of Examples 1 and 2 were
Compared to batteries No. 3 to 3, it exhibited stable discharge characteristics and a longer discharge duration.

On the other hand, in the battery of Comparative Example 1 in which only polypropylene nonwoven fabric was used as a separator, an internal short circuit occurred due to the passage of the lithium alloy powder, a sudden voltage drop occurred at the beginning of discharge, and the discharge duration was very short. In addition, although the battery of Comparative Example 2, which used only a microporous polypropylene film as a separator, was able to prevent internal short circuits due to the passage of lithium alloy powder, the separator's ability to retain electrolyte was small, so the discharge duration was is Example 1
The battery life was significantly shorter than that of the battery No.2. In the battery of Comparative Example 3, the porosity of the nonwoven fabric is small, so the electrolyte holding capacity is small, and as a result, the discharge duration is the same as that of Example 1.
It was shorter than the second battery.

In addition, both of the batteries of Examples 1 and 2 had the above-mentioned discharge 270
After an hour (80% depth of discharge) at 20°C, 15Ω, 7.
The pulse closing voltage of 8m5ec was more than 2.7v,
In a battery as shown in FIG. 4 in which the negative electrode 2 is composed of only a lithium plate with a diameter of 16 nm+m and a thickness of 0.2+ am, the separator 3 is made of a polypropylene nonwoven fabric with a porosity of 84% by volume, a maximum pore diameter of 40 μm, and a thickness of 350 μm. However, under the same conditions as the batteries of Examples 1 and 2 above, the pulse closed circuit voltage was 2.
．． 5V1. , it didn't work.

[Effects 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 separator has a pore diameter of 0.3.
By using a combination of a microporous resin film of micrometers or less and a nonwoven fabric with a porosity of 70 to 90% by volume, and placing the microporous resin film on the negative electrode side and the nonwoven fabric on the positive electrode side, short circuits can be prevented. We were able to provide a lithium battery with excellent battery performance.

[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 main part schematically showing an example of a microporous resin film used as a component of a separator in the battery of the present invention. FIG. FIG. 3 is a diagram showing the discharge characteristics of the batteries of Examples 1 and 2 and the batteries of Comparative Examples 1 and 3. FIG. 4 is a sectional view showing an example of a conventional lithium battery. 2... Negative electrode, 2a... Lithium layer, 2b...
lithium alloy layer, 3... separator, 3a...
Microporous resin film, 3b... Nonwoven fabric, 4...
Positive pole 3rd leap lane 4

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. , using a combination of a microporous resin film with a pore diameter of 0.3 μm or less and a nonwoven fabric with a porosity of 70 to 90% by volume as a separator,
A lithium battery characterized in that the microporous resin film is disposed on a side facing the negative electrode, and the nonwoven fabric is disposed on the side facing the positive electrode. (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.