JP3035677B2 - Secondary battery with safety element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel secondary battery excellent in safety.

[0002]

2. Description of the Related Art In recent years, various non-aqueous secondary batteries have been proposed as small and lightweight secondary batteries replacing conventional acid-lead batteries and nickel / cadmium batteries. Above all, for example, JP-A-62-90,863, JP-A-63-121,
No. 260, Japanese Unexamined Patent Publication No. 3-49, 155, etc., a new secondary battery system using a composite metal oxide containing Li and Co as main components for the positive electrode and a carbonaceous material for the negative electrode attracts attention. Have been. Conventionally, as such a non-aqueous secondary battery, a metal L is used as a negative electrode active material.
i or Li alloy was used. A secondary battery using such a metal Li or the like as the negative electrode is satisfactory from the viewpoints of small size and light weight, but has problems in performance such as cycleability and storage characteristics based on dendrite deposition, and also has a problem of a separator due to dendrite deposition. Life problem that an internal short circuit is caused by breaking through the metal,
i had serious obstacles to practical use, such as safety problems based on the active chemical reactivity of i. On the other hand, a new battery system using a carbonaceous material as the negative electrode active material has excellent cycleability and storage characteristics without causing such dendrite precipitation, and has an active chemical reaction such as metallic Li. Since it does not have the property, it has a feature that the safety is very excellent.

In particular, when combined with a composite metal oxide containing Li and Co as main components as a positive electrode active material, it is expected that a high-voltage, high-capacity battery can be obtained.

[0004]

By the way, such L
A secondary battery using a composite metal oxide containing i and Co as main components as a positive electrode active material and a carbonaceous material as a negative electrode active material,
It has many aspects of battery characteristics such as high voltage, high capacity, and high output, and is also excellent in safety. For example, even during a short circuit, the metal L using the above-described metal Li for the negative electrode
No phenomena such as explosion or fire as seen in the secondary battery are caused. Further, safety has been confirmed in a wide range even when charging at an appropriate voltage or higher, that is, at the time of overcharging.

However, when a case where voltage control fails under a large current condition of a certain current value or more, that is, a 0.5 hour rate (2C) and a 0.1 hour rate (10C), it is also assumed that a burst occurs. Inevitable.

In particular, in recent years, rapid charging, that is, charging in a short time such as 10 minutes or 15 minutes has been desired, and securing safety against overcharging under such conditions is practically solved. It is a big task to be done.

[0007]

Means and Action for Solving the Problems The present inventors have
As a result of a detailed study of the overcharge phenomenon under such a large current condition, it was found that heat is always generated in the process of rupture, and a PTC element having an operating temperature in a specific temperature range matches well with this temperature rise. It has been found that the rupture due to overcharging can be prevented in advance by operating.

The secondary battery of the present invention has been completed on the basis of this finding, and comprises a composite metal oxide containing Li and Co as main components as a positive electrode active material and a carbonaceous material as a negative electrode active material. A secondary battery having an operating temperature of 140 ° C.
In the following, a PTC element having a sensitive temperature coefficient in a range of -10 to -130 is mounted.

The composite metal oxide containing Li and Co as main components in the present invention is a compound having a layered structure and capable of electrochemically intercalating and deintercalating Li ions. Is contained in the metal component in an amount of 50% by weight or more. Although not particularly limited, an example of such a composite metal oxide is described in, for example, JP-A-55-1.
LiCoO ₂ disclosed in JP-A-36,131 and the general formula Li disclosed in JP-A-62-90,863.
_x Co _y N _z O ₂ (where N represents at least one selected from the group consisting of Al, In, and Sn, and x, y, and z are respectively 0.05 ≦ x ≦ 1.10, 0.85 ≦ y ≦ 1.00,
Represents the number 0.001 ≦ z ≦ 0.10. ) And Li _x Ni _y C disclosed in JP-A-3-49,155.
o _(1-y) O ₂ (however, 0 <x ≦ 1, 0 ≦ y <0.50)
And the like.

In order to obtain such a compound, a compound such as lithium hydroxide, lithium oxide, lithium carbonate, lithium nitrate or the like is used.
It can be easily obtained by a calcination reaction of the i compound, a cobalt compound such as cobalt oxide, cobalt hydroxide, cobalt carbonate, cobalt nitrate and, if necessary, another metal compound.

Each of these composite oxides has a high voltage and a high capacity, which are excellent characteristics not found in other active materials, as a positive electrode active material. In particular, the general formula Li _x Co _y
N _z O ₂ (where N represents at least one selected from the group consisting of Al, In and Sn, and x, y and z are each 0.05
≦ x ≦ 1.10, 0.85 ≦ y ≦ 1.00, 0.001
≤z≤0.10. ) Is a composite oxide which is particularly excellent in characteristics such as cycleability and is preferably used in the present invention.

Further, the carbonaceous material referred to in the present invention is not particularly limited.
JP-A-35-881, high surface area carbon materials, baked carbides such as phenolic resins described in JP-A-58-209,864, and JP-A 61-111,907. Examples include a calcined carbide of a condensed polycyclic hydrocarbon compound. Among them, the BET specific surface area A (m ² / g) disclosed in JP-A-62-90,863 is 0.1.
Crystal thickness Lc in X-ray diffraction in the range of <A <100
(Å) and the value of true density ρ (g / cm ³ ) satisfy the following condition 1.7.
Carbonaceous materials in the range satisfying 0 <ρ <2.18 and 10 <Lc <120ρ-189 have high capacity and excellent cycle characteristics, and are particularly preferably used in the present invention.

The basic components for assembling the non-aqueous secondary battery of the present invention include an electrode using the active material of the present invention, a separator, and a non-aqueous electrolyte. Examples of the separator include, but are not particularly limited to, woven fabric, nonwoven fabric, glass woven fabric, and synthetic resin microporous membrane.
In the case of using a thin film and a large area electrode, for example, see
The microporous synthetic resin membrane disclosed in JP-A-59072, particularly a polyolefin-based microporous membrane, is preferred in terms of thickness, strength, and membrane resistance.

The electrolyte of the non-aqueous electrolyte is not particularly limited. For example, LiClO ₄ , LiBF ₄ , L
iAsF ₆ , CF ₃ SO ₃ Li, LiPF ₆ , LiI,
LiAlCl ₄ , NaClO ₄ , NaBF ₄ , NaI,
^{_{(N-Bu) 4 N +}} ClO 4, (n-Bu) 4 N + BF 4
, KPF _{6 and the} like. Further, as the organic solvent of the electrolytic solution used, for example, ethers, ketones, lactones, nitriles, amines, amides, sulfur compounds, chlorinated hydrocarbons, esters, carbonates,
Nitro compounds, phosphate compounds, sulfolane compounds and the like can be used, and among them, ethers, ketones, nitriles, chlorinated hydrocarbons,
Carbonates and sulfolane compounds are preferred. More preferred are cyclic carbonates.

Representative examples of these are tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, anisole, monoglyme, acetonitrile, propionitrile, 4-methyl-2-pentanone, butyronitrile, valeronitrile, benzonitrile, , 2-
Dichloroethane, γ-butyrolactone, dimethoxyethane, methylformate, propylene carbonate, ethylene carbonate, vinylene carbonate, dimethylformamide, dimethylsulfoxide, dimethylthioformamide, sulfolane, 3-methyl-sulfolane, trimethyl phosphate, triethyl phosphate and these ethyl salts Examples thereof include a mixed solvent, but are not necessarily limited thereto.

If necessary, a battery is formed by using components such as a current collector, a terminal, and an insulating plate. In addition, the structure of the battery is not particularly limited, but a positive electrode, a negative electrode, and, if necessary, a paper type battery having a single or multiple layers of separators, a laminated type battery, or a positive electrode, a negative electrode, For example, a form of a cylindrical battery or the like in which a separator is wound in a roll shape is given as an example.

Various types of PTC elements such as BaTiO ₃ ceramics are conventionally known, but the PTC element defined in the present invention has PTC characteristics (a characteristic in which the resistance increases as the temperature rises). An overcurrent and overheat protection element made of a conductive polymer. For example, Polyswitch (registered trademark) from Raychem Corporation
There are commercially available polyswitches under the trade name of various types of protection elements. This element has a function of responding to both temperature and current and automatically interrupting the current by increasing the element resistance automatically when a certain upper limit is exceeded. It is already known to mount such a PTC element on a battery.
For example, when the battery is mounted on a lithium primary battery, for example, when the battery is short-circuited via an external circuit, the PTC element operates to cut off the current, thereby ensuring the safety of the battery.

The present inventors have studied in detail the overcharge process of a secondary battery using the above-described composite metal oxide containing Li and Co as main components as a positive electrode active material and a carbonaceous material as a negative electrode active material. The following facts became clear.

[0019] Heat must be generated before rupture during overcharge.

[0020] The temperature rise of the battery due to this heat generation should be proportional to the overcharge current.

[0021] The battery can temperature at the time of rupture is correlated with the overcharge current, and the larger the overcharge current, the lower the measured battery can temperature at the time of rupture. (This is presumed to be due to the fact that a temperature distribution occurs due to the high rate of temperature rise and a value lower than the actual temperature inside the battery can is detected.) From the above facts, the secondary battery of the present invention is considered. It has been found that it is not effective to mount a thermal fuse that is sensitive only to temperature as a means for ensuring safety during overcharging.

Also, if a current fuse sensitive to only the current is mounted, the sensitive current accuracy is poor, and it is impossible to distinguish between the normal current and the overcharge current, and it is not an effective means. There was found.

Therefore, the behavior of the secondary battery of the present invention at the time of overcharging is significantly different from the behavior of other batteries, which is based on the combination of the active materials of the positive and negative electrodes used in the secondary battery of the present invention. Seems to behave. Therefore, in order to ensure the safety at the time of overcharging of the secondary battery of the present invention, the secondary battery is sensitive to both temperature and current, and its sensitive temperature coefficient is a negative value. It is necessary to have. Here, the sensitive temperature coefficient is a parameter that is measured by a measuring method described later and indicates the current dependency of the sensitive temperature. Also, the operating temperature in the present invention, when the current value is zero,
In other words, it refers to the temperature at which the resistance value reaches 1,000 times the room temperature at the temperature alone.

Based on the above facts, the present inventors have found that a PTC element having specific characteristics is particularly effective against overcharging.

The operating temperature of the PTC element used in the present invention is 1
It must be below 40 ° C. Preferably it is in the range of 75 ° C. or more and 140 ° C. or less. If the temperature exceeds 140 ° C., even if the PTC element operates at that temperature, heat generation continues and leads to rupture.

The sensitive temperature coefficient must be in the range of -10 to -130. It is preferably in the range of -15 to -100, and more preferably in the range of -25 to -80.

If the temperature coefficient of sensitivity is less than -10, the protection against overcharging in a region where the current value is large is not perfect, and a case may occur in which the battery ruptures. On the other hand, if it exceeds -130, the current value that can be conducted in a practical area, that is, near room temperature, becomes small, making it practically unusable.

The method of mounting the PTC element of the present invention on a battery is not particularly limited, and examples thereof include a method of mounting it in a battery can, a method of mounting it on a battery can lid, and a method of mounting it on a battery can wall. However, it is preferable to mount the battery at a location where the temperature of the battery can be detected more accurately.

By mounting a PTC element having the characteristics in the above range, safety against overcharging is secured in all current ranges.

[0030]

The present invention will be described in more detail with reference to the following examples.

Measurement of Operating Temperature and Sensitive Temperature Coefficient A PTC element is connected to a constant current DC power supply, and a constant current (A)
While the power is on, the temperature is raised in the oven. The temperature (° C.) at the time when the resistance value of the PTC element becomes 1,000 times that at room temperature is measured. Change the current value and repeat the same operation to measure a total of 5 points.

The current value is plotted on the horizontal axis and the temperature is plotted on the vertical axis at five points. The slope of this straight line is defined as a sensitive temperature coefficient. The temperature when the current value is zero is defined as the operating temperature.

Reference Example 1 Li, C having a composition of Li _1.03 Co _0.92 Sn _0.02 O ₂
o After 100 parts by weight of the composite oxide, 2.5 parts by weight of graphite and 2.5 parts by weight of acetylene black are mixed, 2 parts by weight of fluororubber is mixed with 60 parts by weight of a 1: 1 (weight ratio) mixed solvent of ethyl acetate / ethyl cellosolve. The liquids dissolved in the portions were mixed to obtain a slurry-like coating liquid.

Using a coating machine having a doctor blade coater head, the above coating liquid was applied to both surfaces of an Al foil having a width of 600 mm and a thickness of 15 μm. Coating thickness after both-side coating is 290μ
Met.

A solution obtained by dissolving 100 parts by weight of a needle coke pulverized product and 5 parts by weight of a fluororubber in 90 parts by weight of a 1: 1 (weight ratio) mixed solvent of ethyl acetate / ethyl cellosolve is mixed to obtain a slurry coating liquid. Was.

Using a coating machine having a doctor blade coater head, the above coating solution was applied to both surfaces of a Cu foil having a width of 600 mm and a thickness of 10 μm. The coating thickness after both-side coating is 350μ
Met.

After pressing the two types of coated products with a calender roll, both of them were slit to a width of 41 mm using a slitter. A Li _1.03 Co _0.92 Sn _0.02 O ₂ coated product is used as a positive electrode, a needle coke coated product is used as a negative electrode, and a polyethylene microporous membrane (Hypore 4030) is used as a separator.
U Asahi Kasei Corporation) and an outer diameter of 14.9 mm with a winding machine
In the form of a coil. The outer diameter of this wound coil is 16 mm.
After being put into a battery can, a mixture of propylene carbonate / ethylene carbonate / γ-butyrolactone in a ratio of 1: 1: 2 (weight ratio) in which LiBF ₄ was dissolved at a concentration of 1 M was impregnated as an electrolyte, and then sealed. Height 5 shown in FIG.
A 0 mm A-size battery can was prototyped.

REFERENCE EXAMPLE 2 Using the battery of Reference Example 1, overcharge tests were performed at various current values without voltage limitation. The temperature of the side wall of the battery can immediately before the rupture was measured. The results are shown in FIG.

FIG. 2 shows that in order to prevent the battery from bursting in a large current range, it is necessary to interrupt the current at a lower temperature as the overcharge current increases.

Example 1 The PTC element Po was attached to the lid of the A-size battery of Reference Example 1.
lyswitch (registered trademark) polyswitch (PSR-
21820), and 3A,
An overcharge test was performed with unlimited voltage. When the voltage reached 5.2 V, the PTC element was activated and did not burst. The temperature of the battery can when the PTC element was activated was 83 ° C.
Met.

FIG. 3 shows measured data of the operating temperature and the responsive temperature coefficient of the PTC element used in this embodiment.

FIG. 3 shows that the operating temperature (at 0 A) of the PTC element used in this embodiment is 130 ° C. and the sensitive temperature coefficient is -40.0.

Examples 2 to 6 and Comparative Examples 1 to 4 The same operation as in Example 1 was carried out except that the PTC elements having various operating temperatures and the responsive temperature coefficients shown in Table 1 and other protection elements were used. An overcharge test was performed at 2A to 6A.

Table 1 also shows the results.

[0045]

[Table 1] Comparative Example 5 The same operation as in Example 1 was performed except that the PTC element having an operating temperature of 115 ° C. and a sensitive temperature coefficient of −135 was used, but normal charging at a normal current of 1 A was impossible. Was.

[0046]

As is clear from the above description, L
In a secondary battery using i, Co composite oxide as a positive electrode active material and a carbonaceous material as a negative electrode active material, selecting a PTC element having a specific range of characteristics and mounting it on the battery allows all currents to be increased. Safety against overcharging in the range can be ensured.

[Brief description of the drawings]

FIG. 1 is a half sectional view of a battery according to the present invention.

FIG. 2 is a graph showing a relationship between a current value at the time of overcharge and a battery can temperature immediately before rupture in Reference Example 2.

FIG. 3 is a graph showing a relationship between a temperature and a flowing current when the resistance of the PTC element changes in the first embodiment.

[Explanation of symbols]

 Reference Signs List 1 positive electrode 2 separator 3 negative electrode 4 insulating plate 5 negative electrode lead 6 positive electrode lead 7 gasket 8 PTC element

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 10/40 H01M 2/34

Claims (1)

(57) [Claims] 1. A secondary battery in which a composite metal oxide mainly composed of Li and Co is used as a positive electrode active material and a carbonaceous material is used as a negative electrode active material, wherein the secondary battery has an operating temperature of 140 ° C. or lower. And a PTC element having a temperature coefficient of sensitivity in a range of -10 to -130.