JPH01128371A - Nonaqueous electrolyte secondary cell - Google Patents

Abstract

PURPOSE:To suppress the generation of dendrite of lithium separated from the surface of a negative electrode plate and to prevent the inner short circuit by making the width of the negative electrode plate mainly of lithium larger than the width of a positive electrode plate mainly of LiMn2O4. CONSTITUTION:In a nonaqueous electrolyte lithium type secondary cell, the width of the negative electrode plate is made larger than that of the positive electrode plate, to suppress the generation of dendrite of lithium separated from the surface of the negative electrode plate by the repeated charge and discharge and to prevent the inner short circuit, resulting in an improvement of the charge and discharge performance. When such a composition in which the width of the negative electrode plate is made larger than that of the positive electrode plate is compared with the composition in which both widths are equal or the width of the negative electrode plate is smaller than that of the positive electrode plate, a fairly large difference can be observed in the cycle life numbers.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a non-aqueous electrolyte secondary battery, and particularly to an improvement in electrode structure.

[Summary of the invention]

The present invention provides a negative scratch plate mainly composed of lithium and a LiMn2O
In a non-aqueous electrolyte secondary battery using a positive electrode plate mainly composed of 4, by making the width of the negative electrode plate larger than the width of the positive electrode plate, the generation of dendrites of lithium desorbed from the surface of the negative electrode plate can be suppressed. The aim is to realize a nonaqueous electrolyte secondary battery that prevents internal short circuits and has excellent charge/discharge cycle characteristics.

[Conventional technology]

Lithium was used as the negative electrode active material, and a non-aqueous electrolyte was used as the electrolyte. So-called non-aqueous electrolyte batteries are known as batteries with low self-discharge and excellent storage stability, and are widely used as power sources for electronic wristwatches and various memory backup devices that require long-term use of 5 to 10 years. It is now possible to do so.

By the way, these conventionally used non-aqueous electrolyte batteries are usually primary batteries, but there are many demands for rechargeable non-aqueous electrolyte secondary batteries as a power source that can be used economically for long periods of time, and there are many demands from various fields. Research is underway. Among them, non-aqueous electrolyte secondary batteries that use lithium as the negative electrode active material are particularly
It is expected to be a secondary battery with high battery voltage and high energy density.

[Problem that the invention seeks to solve]

However, a non-aqueous electrolyte secondary battery using lithium as the negative electrode active material has not yet been put into practical use. One of the reasons for this is the short lifespan due to deterioration of the negative electrode plate. This is because lithium, which is a negative electrode active material, is desorbed from the surface of the negative electrode plate due to repeated charging and discharging, and the desorbed lithium grows in a dendrite shape and comes into contact with the positive electrode plate, resulting in a short circuit. This is the reason why it is not possible to obtain a long-life secondary battery.

Therefore, the present invention was proposed in view of the above-mentioned circumstances, and is a non-woven fabric that suppresses the generation of dendrites of lithium desorbed from the surface of the negative electrode plate, prevents internal short circuits, and provides excellent charge-discharge cycle characteristics. The purpose is to provide a water electrolyte secondary battery.

[Means for Solving the Problems] As a result of intensive research to solve the above-mentioned problems, the present inventors found that when the width of the negative electrode plate is the same as or less than the width of the positive electrode plate, Lithium that is desorbed from the surface of the negative electrode plate during discharge, especially lithium that is desorbed from the widthwise ends of the negative electrode plate, grows in a dendrite shape, and then crosses over the separator and contacts the positive electrode plate, causing a short circuit. We have obtained the following knowledge.

The present invention was completed based on this knowledge, and includes a negative electrode plate mainly composed of lithium and LiM nz O.
In a non-aqueous electrolyte secondary battery in which a positive electrode plate mainly composed of a and a positive electrode plate are laminated and wound through a separator and housed in a battery can, the width of the negative electrode plate is larger than the width of the positive electrode plate. It is characterized by this.

Here, it is particularly preferable that the width of the negative electrode plate be larger than the width of the positive electrode plate by 0.5 to 2.0 mm on one side.

For example, the width of the negative electrode plate is 0.5 m on one side relative to the width of the positive plate.
If it is less than m, the width of the negative electrode plate may become equal to or less than the width of the positive electrode plate due to winding misalignment when forming an electrode group, and there is a possibility that lithium dendrites will occur. On the other hand, if the width of the negative electrode plate is made larger by 2.0 mm or more on one side than the width of the positive electrode plate, the amount of lithium that does not affect charging and discharging increases and is wasted.

In the positive electrode plate of the non-aqueous electrolyte secondary battery according to the present invention, L i M n zoa, which is a positive electrode active material, is mainly used. For example, lithium carbonate and manganese dioxide are heated to about 400'C in air or an inert gas atmosphere such as nitrogen, or lithium iodide and manganese dioxide are reacted in a similar manner. It can be easily obtained by heating to about 300°C in an atmosphere to cause a reaction.

In particular, when X-ray diffraction was performed using FeKα rays, the half-width of the diffraction peak at a diffraction angle of 46.1° was 1.1°.
If LiMnzOa having a particle diameter of ˜2.1” is used as a positive electrode active material, better charge/discharge characteristics can be obtained.

Note that a conductive agent, a binder, a dispersant, and the like are added to the above-mentioned positive electrode active material as necessary, and the material is processed into a positive electrode plate.

On the other hand, for the negative electrode plate, metal lithium such as lithium foil, lithium alloy (for example, LiAjl!, LiPb, etc.) is used.

LiSn, LiB1. LiCd, etc.), metal lithium, lithium alloys with trace amounts of additional elements, etc. can be used.

Further, as the electrolytic solution, a non-aqueous electrolytic solution in which a lithium salt is used as an electrolyte and dissolved in an organic solvent (non-aqueous solvent) is used.

Here, the organic solvent is not particularly limited, but for example, propylene carbonate, ethylene carbonate, 1,2-jethoxyethane, 1,2-jethoxyethane, T-butyrolactone, 2-methyl-γ-butyrolactone, tetrahydrofuran, -Methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3
- Solvents such as dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, and propionitrile may be used alone or in combination of two or more.

Any conventionally known electrolyte can be used,
L i Cl0a , L 1AsFa , L i PF
6, L i BFa , L i B (C6H5)4
,L i Cf,LiBr, ,CHsSOsL i,C
It is possible to use one kind or a mixture of two or more kinds, such as FsSOzL.

[Effect]

The nonaqueous electrolyte secondary battery according to the present invention, which is composed of a negative electrode plate mainly composed of lithium and a positive electrode plate mainly composed of LtMnzOa, has improved charging and discharging performance by making the width of the negative electrode plate larger than the width of the positive electrode plate. By repeating this, the generation of dendrites of lithium desorbed from the surface of the negative electrode plate is suppressed, and internal short circuits are prevented. Therefore, charge/discharge cycle characteristics are improved.

[Example] Hereinafter, a specific example of the present invention will be described with reference to the drawings.
It is suitable for a cylindrical (so-called jelly roll type) non-aqueous electrolyte secondary battery in which a positive electrode plate mainly composed of O4 is laminated and wound through a separator and housed in a battery can.

To create the above-mentioned non-aqueous electrolyte secondary battery, first, 86.9 g of commercially available manganese dioxide was added to 18.5 g of manganese dioxide as a positive electrode active material.
g of lithium carbonate was added and thoroughly mixed in a mortar. Next, this mixture was calcined on an alumina boat at a temperature of 450°C in air for 1 hour to obtain l, '1Mn20.
n was synthesized.

Next, 82.8 parts by weight of the obtained LiMnzOa, 12 parts by weight of graphite as a conductive agent, 5.2 parts by weight of polyvinylidene fluoride as a binder, 1 part by weight of polyvinylidene fluoride as a binder, 1 part by weight of N-methyl-2-pyrrolidone as a dispersant were mixed, and a positive electrode was prepared. Created a paste.

Next, this positive electrode paste was uniformly applied to both sides of an aluminum current collector with a thickness of 0.03 mm, and this was roller pressed to form a positive electrode sheet with a thickness of 0.14 m+, and a width of 32 mm+.
A positive electrode plate (1) was prepared by cutting the positive electrode plate (1) into pieces having a length of 400 mm and ultrasonically welding an aluminum lead (8) to one end.

On the other hand, the negative electrode active material has a thickness of 0.046 mm and a length of 4
00 mm of lithium foil was placed with the above positive electrode plate width W I (32 m
+w) on each side: 2+n+, 1 mm,
The width W of the lithium foil is increased by 0.5mff1! After cutting into 36 mm, 34 mm, and 33 mm, nickel leads were crimped to the ends to create negative electrode plates (2).

Next, the above positive electrode plate (1) and this negative electrode plate (2) are rolled up and laminated through a polypropylene separator (3), and insulating plates (4) are arranged on both end faces. It was stored in a nickel-plated iron box (5). here,
The negative electrode plate (2) comes into contact with the inner peripheral surface of the iron can (5), and the iron can (5) corresponds to a negative electrode mill.

Next, a mixed electrolyte of propylene carbonate and 1,2-dimethoxyethane in which LiPFa was dissolved at a ratio of 1 mol/2 was impregnated into the steel shell (5), and nickel plating was also applied via the gasket (6). The lid body is made of iron (
7). A lead (8) connected to the winding plate (1) is welded to the inner surface of the lid (7), and the lid (7) serves as a winding can for the battery.

Through the above steps, cylindrical nonaqueous electrolyte secondary batteries A, B, and C each having an outer diameter of 13.8 mm and a height of 42 mm were assembled. The width of the lithium foil in Battery A is 36 mm, the width of the lithium foil in Battery B is 34 mm, and the width of the lithium foil in Battery C is 33 mm.

A thickness of 0.14 mm and a width of 3
Create a positive electrode plate (1) with a thickness of 2 mm and a length of 400I, then create a positive electrode plate (1) with a thickness of 0.046 mm and a length of 400 mm.
A negative electrode plate (2) having a width of 321III1, which is the same as the width of the sample, was prepared, and a cylindrical non-aqueous electrolyte secondary battery was assembled in the same manner as in the example.

Comparison ■Also, using the same method as in the previous example, a thickness of 0.14 mm and a width of 3
Create a positive electrode plate (1) with 2 openings and a length of 400mm, then create a positive electrode plate (1) with a thickness of 0.046mm and a length of 4QOmm.
A negative electrode plate (2) having a width of 30 mm, which is smaller than the width of , was created, and a cylindrical non-aqueous electrolyte secondary battery E was assembled in the same manner as in the example below.

After discharging these batteries A, B, C, D, and H to a final voltage of 2.0 ■ with a constant current of 250 mA,
A cycle life test was carried out by charging at a final voltage of 3.9■ at 60 mA for 8 hours, with a rest period of 24 hours from charging to discharging, and using this as one cycle. The end of the cycle life in this cycle life test was defined as the time when the capacity decreased to 50% of the initial capacity. The results are shown in Table 1. Further, FIG. 2 shows the number of cycle life and discharge capacity for each battery A, B, C, D, and E. In addition, the second
In the figure, the A line corresponds to the battery A, the B line to the battery B, the C line to the battery C, the D line to the battery, and the E line to the battery.

As can be seen from Table 1 and FIG.
, B, and C all have a long cycle life of 125 times or more, and the discharge capacity remains constant at approximately 400 mAt1 from 1 cycle to 125 cycles, indicating excellent cycle life characteristics. It turned out that there was. On the other hand, battery E, in which the width of the negative electrode plate (2) is the same as or smaller than the width of the positive electrode plate (1), has a short cycle life of 84 and 54 cycles, respectively, and has a short discharge life. The capacity also decreases from the first cycle and continues to decrease until the final cycle, and at the final cycle, the discharge capacity shows a low value of about 230 mAH.

When we disassembled and inspected these short-life batteries, we found that the negative electrode plate (2) was damaged at both widthwise ends of the negative electrode plate (2).
It was observed that lithium desorbed from the surface was generated and grown in the form of dendrites, and that the lithium dendrites climbed over the separator and came into contact with the positive electrode plate (1), causing an internal short circuit. On the other hand, in batteries A, B, and C in which the width of the negative electrode plate (2) is larger than the width of the positive electrode plate (1), the width of the negative electrode plate (2) is larger than the width of the positive electrode plate (1). In other words, the lithium on the negative electrode plate (2), which is not facing the positive electrode plate, is not used for charging and discharging, and remains as unreacted lithium on the surface of the negative electrode plate (2), and no lithium dendrite formation is observed. Ta.

It is not clear why lithium dendrites occur when the width of the negative electrode plate (2) is the same as or less than the width of the positive electrode plate (1), but the width of the negative electrode plate (2) is the same as or less than the width of the positive electrode plate (1).
It is clear from the above that by making the width larger than 1), the generation of lithium dendrites is suppressed, internal short circuits are prevented, and the recycling life characteristics of the battery are improved.

In addition, it was found that the generation of lithium dendrites was suppressed by setting the width of the negative electrode plate (2) larger than the width of the positive electrode plate. As can be seen from FIG. 2, when the width of the positive electrode plate (1) is set to 0.5 mm or more on one side, both the number of cycle life and the discharge capacity characteristics have good values. On the other hand, battery B, in which the width of the negative electrode plate (2) is 11 larger on one side than the width of the positive electrode plate (1), is larger than battery A, in which the width of the negative electrode plate (2) is larger on one side by 2, C1 than the width of the positive electrode plate (1). The discharge capacity characteristics are slightly superior. For this reason, the negative electrode plate (2)
The upper limit of the width is 2.0 m on one side relative to the width of the positive electrode plate (1).
It is preferable that it is below m.

〔Effect of the invention〕

As is clear from the above description, in the non-aqueous electrolyte secondary battery of the present invention, a negative electrode plate mainly composed of lithium and a
Since a positive electrode plate mainly composed of MnzOa is used, and the width of the negative electrode plate is made larger than the width of the positive electrode plate, it is possible to suppress the generation of dendrites of lithium desorbed from the surface of the negative electrode plate, and to prevent internal short circuits. It can be prevented. Therefore, a secondary battery having excellent charge/discharge cycle characteristics can be obtained, and its industrial value is great.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway side view showing the configuration of a cylindrical non-aqueous electrolyte secondary battery, and FIG. 2 shows the relationship between the number of cycles and discharge capacity in a non-aqueous electrolyte secondary battery with such a configuration. It is a characteristic diagram. 1... Positive electrode plate 2... Negative electrode plate 3... Separator

Claims (1)

[Scope of Claims] A non-aqueous electrolyte secondary battery in which a negative electrode plate mainly composed of lithium and a positive electrode plate mainly composed of LiMn_2O_4 are laminated and wound through a separator and housed in a battery can, A non-aqueous electrolyte secondary battery characterized in that the width of the plate is larger than the width of the positive electrode plate.