JPH0210652A - Cylindrical lithium secondary battery - Google Patents

Abstract

PURPOSE:To increase safety and charge-discharge performance by bending the upper and lower ends of a separator in the winding axial direction by hot air heating, and by sticking electrolyte-resistant, insulating adhesive tapes onto the upper and lower surfaces of an electrode body to cover positive and negative plates. CONSTITUTION:The upper and lower ends, which protrude from an electrode body, of a separator 3 are heated by hot air to be bent along the upper and lower recesses and projections of the electrode body in the winding axial direction. Electrolyte-resistant, insulating adhesive tapes 6, 7 are sticked onto the upper and lower surfaces of the electrode body to uniformly cover the upper and lower surfaces of the electrode body. Dendrites hardly come off, and even if they come off, their floating in an electrolyte is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention has an electrode body formed of a negative electrode plate using metallic lithium as an active material and a positive electrode plate in a spiral shape with a separator interposed between the two electrodes. This relates to a cylindrical lithium secondary battery.

BACKGROUND OF THE INVENTION Organic electrolyte lithium batteries generally have high energy density, excellent long-term reliability, and a wide operating temperature range.

In recent years, development of so-called lithium secondary batteries, which are rechargeable while taking advantage of these advantages, has become active. −
Inside the membrane, a negative electrode with metallic lithium as the main active material and various intercalation compounds such as titanium disulfide (TLS2) are used as positive electrode active materials, and perchlorine is used in an organic solvent such as propylene carbonate. An organic electrolyte in which lithium oxide or the like is dissolved is used.

However, due to the short life of the negative electrode's charge/discharge cycle, it has not yet been put into practical use. Lithium as a negative electrode active material has some difficult problems, such as deformation during charging and discharging cycles and forming dendrites, which form internal short-circuit bridges. In particular, dendrites are concentrated in areas with high current density and have the property of growing perpendicularly from the lithium negative electrode surface.As the charge/discharge cycle progresses, the surface becomes more uneven due to dendrites, and eventually It will fall off. Lithium dendrites that have fallen off from the negative electrode in this way float in the electrolyte, so there is a risk that they may come into contact with the battery case or leads that are in electrical contact with the positive electrode. This causes a so-called internal short circuit, and the battery's function is lost.

Further, even if the dendrites do not fall off, there is a high risk that their growth will progress and cause an internal short circuit.

In order to improve these drawbacks of negative electrodes, from the perspective of cycle life, methods such as adding additives to the electrolyte to suppress the formation of dendrites or using alloys with lithium have been investigated. Improvements in reliability, especially from the perspective of battery safety, are lagging behind.

That is, when dendrites are generated, it is important not to allow them to float in the electrolyte. To this end, it is necessary to optimize the structure of the separator so that it is highly reliable and does not reduce the energy density as much as possible. However, the conventional separator construction method for this type of electrode body is
There are the following two cases, and as shown in FIGS. 3 and 4, which are cross-sectional views of the structure of each electrode body, the structure method of the existing lithium-secondary battery is adopted as is.

The first method, as shown in Fig. 3, consists of filling a core material such as expanded metal or net with a mixture containing titanium disulfide as an active material and drying the positive electrode plate 1, and activating metallic lithium. A strip separator 3 is placed between the negative electrode plate 2 and the material.
This is a method in which the entire structure is formed into a spiral shape by intervening.

In the second method, as shown in FIG. 4, the positive and negative electrode plates 1 and 2 are each covered with a separator 3, and the whole is configured in a spiral shape.

Problems to be Solved by the Invention In such a conventional configuration, first of all, in the case of the first method, since the upper and lower parts of the separator 3 are open, there is an extremely high risk of causing an internal short circuit due to floating dendrites or bridging. It's large.

Therefore, it is necessary to install insulating plates above and below the electrode body. However, when insulating plates are pressed onto the top and bottom of the electrode body,
The separators protruding from the top and bottom of the electrode body are bent unevenly. Furthermore, since the insulating plate is pushed up by the repulsive action of the bent separator, the adhesion of the insulating plate to the electrode body is uneven and insufficient, making it difficult to prevent internal short circuits due to dendrites. Furthermore, if the insulating plate is pressed more firmly to improve the adhesion between the electrode body and the insulating plate, the electrode plate may fall off, which not only reduces battery performance but also makes it impossible to prevent internal short circuits. Ta.

Further, in the case of the second method, wrinkles occur in the separator at the shaded area A in FIG. 5 when the separator is wound spirally. This increases the outer diameter of the electrode body, making it difficult to insert it into the case. Therefore, the electrode plate size must be made thinner or shorter to cope with the problem, resulting in a problem of lowering the discharge capacity.

Furthermore, since it is difficult for the electrolytic solution to penetrate uniformly into the wrinkled portions, there is also the problem of increased variation in charge/discharge characteristics.

The present invention solves these problems and aims to improve safety and charge/discharge characteristics.

Means for Solving the Problems In order to solve these problems, the present invention heats both upper and lower ends of the electrode body constructed by the first method to shrink the separator protruding from the electrode body in the direction of the winding core. The electrode body is bent, and electrolyte-resistant adhesive tape is applied to the upper and lower surfaces of the electrode body to cover the positive and negative electrode plates.

In addition, attempts were made to attach a non-adhesive insulating plate instead of the above-mentioned adhesive tape, but the electrode body and the insulating plate tend to misalign, and the adhesion is uneven, so internal short circuits due to dendrites may occur as in the conventional method. There was something that happened.

Operation With the above configuration, the upper and lower parts of the electrode body can be uniformly coated, so dendrites are difficult to fall off, and even if dendrites do fall off, they are prevented from floating in the electrolyte. Become.

Embodiment FIG. 1 is a sectional view of a cylindrical lithium secondary battery according to an embodiment of the present invention, which will be described in detail below.

In FIG. 1, the positive electrode plate 1 is chromium sesquioxide (Cr2o
A positive electrode mixture containing 6) as a living substance is filled into a core material made of expanded titanium metal and dried. 4 is a positive electrode lead plate made of the same material as the core material and spot welded to the core material. The negative electrode plate 2 is made of metal lithium, and a negative electrode current collector 5 is crimped to the negative side surface thereof.

The separator 3 is made by cutting a nonwoven fabric or a microporous membrane sheet made of polypropylene, polyethylene, or a copolymer of propylene and ethylene into a strip wider than the positive and negative electrodes 1 and 2. In this example, a microporous membrane sheet made of polypropylene was used.

Next, a separator 3 is interposed between these positive and negative electrodes 1 and 2, and the whole is spirally wound to form an electrode body. Then, while rotating the electrode body, hot air is blown from slightly obliquely upward in the direction of the winding core of the electrode body to the separators protruding from the upper and lower end surfaces of the electrode body, that is, the upper and lower parts of the positive and negative electrodes 1 and 2, thereby blowing the protruding portions of the separators. The electrode body is covered by bending while contracting in the direction of the winding core. Incidentally, the heating temperature is determined by pasting separator tapes 6.7 to the upper and lower parts of the electrode body, respectively, to complete the construction of the electrode body.

Next, after forming a step in the upper part of the case 8, an electrolytic solution (in this example, an electrolytic solution in which lithium perchlorate was dissolved as a solute in a mixed solvent of propylene carbonate 1,2-dimethoxyethane was used). ).

When injecting liquid, operate under reduced pressure to achieve a uniform impregnated state in a short time. After installing the sealing plate 9, the case 8
The battery assembly is completed by caulking and sealing the open end. Table 1 summarizes the number of voltage failures due to internal short circuits and the maximum, minimum, and average values of discharge capacity at the 60th cycle during a charge/discharge test of 100 products of the present invention and conventional products. The test conditions in this case were repeated charging and discharging at a constant current of 60 mA at 20° C. to a depth of 600 mAh, which is about so% of the filling capacity of the positive electrode.

Table 1 and FIG. 6 show the relationship between the cumulative number of voltage defects caused by internal short circuits and the number of charge/discharge cycles between the products of the present invention and the conventional products.

Although it varies depending on the material, in this example it is 140 to 18
It was carried out at 0°C. Further, in order to improve the adhesion of the bent portion of the separator, a flat plate may be pressed against the separator appropriately. Further, insulating adhesive tapes 6 and 7 made of polypropylene, polyethylene, etc. are pasted on the upper and lower parts of the electrode body, respectively, to complete the construction of the electrode body.

Next, after forming a step on the upper part of the case 8, an electrolytic solution (in this example, lithium perchlorate is dissolved as a solute in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane) is used. inject). When injecting liquid, operate under reduced pressure to achieve a uniform impregnated state in a short time. After attaching the sealing plate 9, the open end of the case 8 is caulked to complete the assembly of the battery.

Table 1 summarizes the number of voltage failures due to internal short circuits and the maximum, minimum, and average values of the discharge capacity at the 5Q cycle during the charge/discharge test for the products of the present invention and 100 conventional products. The test conditions in this case are EiO at 20°C.
eo, which is approximately 80% of the filling capacity of the positive electrode at a constant current of mA.
Charging and discharging were repeated at a depth of omAh.

FIG. 6 shows the relationship between the cumulative number of voltage defects caused by internal short circuits and the number of charge/discharge cycles between the products of the present invention and the conventional products.

FIG. 7 shows an example of the discharge characteristics after 200 cycles when the product of the present invention and the conventional product were subjected to a charge/discharge test under the same conditions as described above.

As is clear from these results, the present invention eliminates the wrinkles of the separator that occur when the electrode plate is previously covered with a bag-like separator to form a spiral electrode body. It does not become difficult to insert into the case due to the large diameter. Furthermore, the penetration of the electrolytic solution is uniform, and variations in charging and discharging characteristics can be reduced. Furthermore, by heating the upper and lower end surfaces of the seven pallets that protrude above and below the electrode body, the upper and lower end surfaces of the seven pallets that protrude above and below the electrode body are heated with hot air, allowing them to conform well to the irregularities on the top and bottom of the electrode body, and at the same time bending in the direction of the winding core. By pasting the adhesive tape on the upper and lower surfaces of the electrode body, the upper and lower parts of the electrode body can be uniformly coated, making it difficult for dendrites to fall off, and even if dendrites do fall off, they will not float in the electrolyte. It can be seen that it is excellent in terms of preventing internal short circuits related to safety and charging and discharging characteristics.

Effects of the Invention As described above, according to the present invention, it is possible to provide a battery that is free from internal short circuits and deterioration and variation in charge/discharge characteristics caused by the occurrence of dendrites in the negative electrode lithium.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a cylindrical lithium secondary battery according to an embodiment of the present invention, FIG. 2 is a cross-sectional view showing the configuration of a spiral electrode body according to an embodiment of the present invention, and FIGS. 3 and 4 5 is a cross-sectional view showing the configuration of a conventional spiral electrode body, and FIG.
FIG. 6 is a diagram showing the relationship between the number of charge/discharge cycles and the cumulative number of voltage failures, and FIG. 7 is a diagram showing the discharge characteristics at the 200th cycle in the charge/discharge test. 1...Positive electrode, 2...Negative electrode, 3...
...Separator, 6.7...Tape. Name of agent: Patent attorney Toshio Nakao and one other person

Claims (1)

[Claims] It has an electrode body consisting of a positive electrode and a negative electrode, with a band-shaped separator wider than the two electrode plates interposed between them, and the whole spirally wound. A cylindrical lithium secondary battery whose end faces are bent in the direction of the winding core by heating with hot air, and electrolyte-resistant insulating adhesive tapes are attached to the upper and lower surfaces of the electrode body to cover the positive and negative electrode plates.