JP3166880B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode containing lithium and lithium ions as active materials, and a non-aqueous electrolyte. The present invention is to improve the safety in abnormal use and the like by improving the battery structure of the cylindrical lithium secondary battery having good heat dissipation.

[0002]

2. Description of the Related Art Electronic devices have become smaller, lighter and more portable.
There is a demand for the development of a high energy density battery as the power source. As a battery that meets such demands, development of a battery using an electrode that emits and absorbs lithium metal, a lithium alloy with aluminum or the like, or a lithium ion such as carbon as a negative electrode (in this specification, The negative electrode using lithium or lithium ion as an active material is referred to as a lithium negative electrode, and a chargeable / dischargeable battery using the lithium negative electrode is referred to as a lithium secondary battery).

However, as reported in a battery using manganese dioxide as a positive electrode active material, when a lithium secondary battery is heated in an oven, spontaneous heat generation occurs due to a chemical reaction between a lithium anode and an electrolytic solution. Battery may ignite due to thermal runaway condition (Extended Abstracts o
f Electrochemical Society Fall Meeting, Seattle, Wa
shington, p-85, 1990). Although the above report is an example in which the battery temperature rises due to oven heating, in a battery, it is expected that the battery temperature will rise even in an external short circuit, an internal short circuit, reverse charging, overcharging, etc. Ensuring safety is extremely important in commercializing a lithium secondary battery.

It is considered that spontaneous heat generation in a lithium secondary battery is mainly caused by a reaction between a lithium anode and an electrolytic solution. Therefore, in order to improve the safety of the battery, it is difficult to react with lithium. An electrolyte may be used. From these viewpoints, an electrolyte using sulfolane or the like as an electrolyte solvent has been proposed (Proceedings of the 59th Annual Meeting of the Electrochemical Society of Japan, p-238). Since the reaction product between the lithium anode and the electrolyte also has an effect (Lithium Batteri)
es, Edited by J.S. P. Gabano, A
CademicPress, New York, p-1
95 (1988)), and negative effects such as deterioration of the charge / discharge cycle characteristics are obtained.

[0005]

On the other hand, thermal runaway of a battery is considered to be a phenomenon in which heat is accumulated inside the battery due to the imbalance between heat generation inside the battery and heat diffusion from the battery. It is thought that by designing a battery structure that excels in heat dissipation as much as possible, it is possible to improve the safety of the battery. A lithium primary battery using thionyl chloride has been studied for a battery structure with excellent heat dissipation (J. Power Sources, 18 , 109 (1986)). Is not suitable as a structure.

[0006]

In order to solve the above-mentioned problems, a nonaqueous electrolyte secondary battery according to the present invention comprises a strip-shaped positive electrode, a strip-shaped negative electrode using lithium or lithium ion as an active material, and a strip-shaped negative electrode. In a cylindrical lithium nonaqueous electrolyte secondary battery having a spiral electrode structure using a separator and a nonaqueous electrolyte, a metal foil longer than the positive and negative electrode active materials is used.
A negative electrode substrate is provided, and the negative electrode is disposed at one end of the negative electrode substrate.
Wherein a three-layer structure portion on either side of arranging the anode active material
The structure without the negative electrode active material is left,
A negative electrode is placed on the positive electrode via the separator
It is housed in a battery can as a spiral electrode, and the
A portion of the negative electrode where the negative electrode active material is not attached
And a structure that directly contacts the battery can .

In the present invention, attention is paid to the fact that the spontaneous heat generation of the battery during the reaction in the battery is mainly caused by the reaction between the lithium anode and the electrolyte, and a metal foil having high thermal conductivity is used for the substrate of the lithium anode. It is characterized by a structure in which heat generated inside the battery is efficiently diffused to the outside by directly contacting the substrate with the negative electrode case.

Specifically, a negative electrode substrate 2 as shown in FIG.
A negative electrode having a three-layer structure in which lithium (negative electrode active material) 6 is disposed on both sides of the negative electrode is used. Here, the reason why the substrate 2 is used for the lithium anode is that lithium metal or lithium alloy cannot be said to have good thermal conductivity, and that when the lithium anode is missing by repeating the charge / discharge cycle, the heat conduction becomes poor. This is because the portion becomes extremely small.

As shown in FIGS. 2 and 3, a three-layered negative electrode having lithium 6 on both sides of a negative electrode substrate 2 is stacked with a positive electrode having a positive electrode active material 5 disposed on a positive electrode substrate 4 with a separator 3 interposed therebetween. The spiral shape is combined and stored in the battery can 1. The negative electrode substrate 2 having no negative electrode active material is located at the outermost periphery of the spiral-shaped cylindrical battery, and the negative electrode substrate 2 has a structure in which the negative electrode substrate 2 is in direct contact with the battery can 1. Heat can be efficiently dissipated to the outside. Further, if the outermost negative electrode substrate 2 is provided with a negative electrode active material, it is not preferable from the viewpoint of a decrease in thermal stability due to an increase in the number of heat sources and an increase in cost. The outermost negative electrode substrate is preferably wound at least two more turns from the final end of the separator 3 in the outer circumferential direction. This is for improving heat dissipation to the outside.

A structure similar to the negative electrode structure used in the present invention is as follows.
As already known in Japanese Patent Application Laid-Open No. 2-51875,
In FIGS. 2 and 3 of -51875, the final end in the outer peripheral direction of the negative electrode and the final end in the outer peripheral direction of the positive electrode are close to each other. On the other hand, the present invention is characterized in that the negative electrode substrate is wound at least two more times around the final end of the positive electrode. The structural features of the present invention are as follows.

In Japanese Patent Application Laid-Open No. 2-51875, the purpose was to prevent a reduction in the charge / discharge cycle life due to the lack of the negative electrode, so that a sufficient effect could be expected only by electrically connecting the negative electrode lead to the battery can. However, since the purpose of this study is to efficiently dissipate the heat generated inside the battery to the outside, it is not sufficient to connect only the negative electrode lead to the battery can. Therefore, not only the negative electrode lead but also the entire negative electrode substrate needs to be in contact with the battery can. However, in this case, when inserting the spiral electrode into the battery can,
Since there is a risk of contact between the positive electrode and the battery can due to the curling of the negative electrode or the like, it is necessary to extraly wind the negative electrode substrate to cover and protect the entire spiral electrode.

The material of the electrode substrate is not particularly limited as long as it does not react with lithium to form an alloy and has good thermal conductivity. For example, a foil made of copper, nickel, stainless steel mesh or the like and having a thickness of about 10 micrometers is desirable.

[0013]

In the cylindrical battery using the spiral electrode having the above structure, even if the battery temperature rises due to some abnormal use, heat can be efficiently dissipated, so that safety can be improved. .

[0014]

Embodiments of the present invention will be described below in detail.

[0015]

EXAMPLE 1 and P ₂ O ₅ to 5 mol% added amorphous V ₂ O ₅ positive electrode active material was, width 42mm to the substrate, using a band-shaped copper foil having a thickness of 10 [mu] m, the same as the substrate on both sides 60 μm in width
A thick lithium metal electrode is used as a negative electrode, the positive electrode and the negative electrode are electrically insulated with a polyethylene separator having an average pore diameter of 0.15 μm and a thickness of 50 μm, and a mixed solvent-based electrolyte of propylene carbonate and ethylene carbonate is used as an electrolyte. Battery A used (a negative electrode substrate was brought into contact with a battery can), and
The positive electrode, the separator, and the electrolytic solution are the same as those of A, but the battery B having a structure in which the negative electrode is made of lithium metal having a thickness of 130 μm and the outermost periphery of the battery is wrapped by the separator is put into a constant temperature bath at room temperature to -7 ° C. Figure 4 shows the temperature change at the center of the battery when
Shown in As is clear from the figure, the temperature transmission is accelerated by bringing the negative electrode substrate into direct contact with the battery can.

[0016]

EXAMPLE 2 Amorphous V ₂ O ₅ to which P ₂ O ₅ was added in an amount of 5 mol% was used as a positive electrode active material, and a 42 mm wide, 10 μm thick strip-shaped copper foil was used for the substrate. 60 μm in width
A thick lithium metal electrode is used as a negative electrode, the positive electrode and the negative electrode are electrically insulated with a polyethylene separator having an average pore diameter of 0.15 μm and a thickness of 50 μm, and a mixed solvent-based electrolyte of propylene carbonate and ethylene carbonate is used as an electrolyte. Battery A used (a negative electrode substrate was brought into contact with a battery can), and
The positive electrode, the separator, and the electrolytic solution are the same as A, but after charging and discharging the battery B having a structure in which the negative electrode is made of lithium metal having a thickness of 130 μm and the outermost periphery of the battery is wrapped by the separator at 60 mA, 25 times, Conduct a short-circuit test via a 40 mΩ resistor and a UL-standard heating test for lithium primary batteries (heat from room temperature to 165 ° C at 5 ° C / min and maintain at 165 ° C for 10 minutes) to compare the presence or absence of ignition did. The results are shown in FIG. In the short circuit test, neither battery A nor B ignited. However, in the heating test, the battery of B ignited, while the battery of A did not ignite (FIG. 5).
It can be seen that the effect is large regarding the safety of the battery.

[0017]

[0018]

As described above, a negative electrode having a three-layer structure in which a metal foil is used as a substrate and a negative electrode active material is disposed on both sides of the substrate is used. In a battery that is wound extra than the circumference, the heat generated inside the battery is efficiently dissipated to the outside of the battery, so that the safety of the battery can be improved, and its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a negative electrode structure of a nonaqueous electrolyte secondary battery of the present invention.

FIG. 2 is a lateral cross-sectional view of the non-aqueous electrolyte secondary battery of the present invention.

FIG. 3 is a longitudinal sectional view of the nonaqueous electrolyte secondary battery of the present invention.

FIG. 4 is a diagram showing a change in temperature at the center of the battery when the battery is put into a -7 ° C. constant temperature bath based on the sound quality of the battery shown in Example 1.

FIG. 5 is a diagram showing a result of a heating test of the battery shown in Example 2.

[Explanation of symbols]

 Reference Signs List 1 battery can 2 negative electrode substrate 3 separator 4 positive electrode substrate 5 positive electrode active material 6 lithium (negative electrode active material)

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shigeo Sugihara 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Masahiro Ichimura 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-2-51875 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40

Claims (2)

(57) [Claims] 1. A cylindrical lithium non-aqueous electrolyte having a spiral electrode structure, comprising a strip-shaped positive electrode, a strip-shaped negative electrode using lithium or lithium ions as an active material, a strip-shaped separator, and a non-aqueous electrolyte. In the next battery, a metal foil longer than the positive electrode and the negative electrode active material is used as a negative electrode substrate, and the negative electrode is
Serial does not have one end than the negative electrode active material was placed a three-layer structure portion on both sides of the negative electrode substrate and of said negative electrode active material portion
And the negative electrode is interposed through the separator.
Superposed on the positive electrode and stored in a battery can as a spiral electrode
The outermost periphery of the spiral electrode has the negative electrode active of the negative electrode.
The part without substance is located and directly connected to the battery can.
A non-aqueous electrolyte secondary battery having a structure that can be touched . 2. The non-aqueous electrolyte secondary battery according to claim 1,
The portion of the negative electrode without the negative electrode active material ,
The positive electrode and the separator, even more final end of the outer circumference of the spiral electrode, a nonaqueous electrolyte secondary battery, characterized by winding extra least two turns or more.