JPH0536439A - Nonaqueous electrolytic secondary battery - Google Patents

Abstract

PURPOSE:To prevent a sudden exothermic and comparatively sudden breakage of a battery by overcharge and provide a highly safe nonaqueous electrolytic secondary battery. CONSTITUTION:In a nonaqueous electrolytic secondary battery having a positive electrode 2 consisting of a lithium composite oxide, a negative electrode 1 capable of doping and dedoping lithium, a nonaqueous electrolyte and a current interrupting means 8, alkyl benzenes are added to the nonaqueous electrolyte.

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, and more particularly to an improved explosion-proof sealed non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art In recent years, advances in electronic technology have led to advances in performance, miniaturization, and portability of electronic devices, and the demand for secondary batteries of high energy density used in these electronic devices is increasing. Conventionally, secondary batteries used in these electronic devices include nickel-cadmium batteries and lead batteries, but these batteries are still insufficient in terms of obtaining batteries with low discharge potential and high energy density. is there. Recently, non-aqueous materials such as lithium, lithium alloys or carbonaceous materials, which can be doped and dedoped with lithium ions, are used as the negative electrode, and lithium composite oxides such as lithium cobalt composite oxide are used for the positive electrode. Research and development of electrolyte secondary batteries are being conducted. This battery has a high battery voltage, a high energy density, little self-discharge, and excellent cycle characteristics.

By the way, in general, when a battery has a sealed structure, if the internal pressure of the battery rises for some reason, the battery suddenly breaks, the battery loses its function, or peripheral devices are damaged. It may happen. In particular, when a non-aqueous electrolyte secondary battery as described above is created in a sealed structure, if for some reason an electric current of a predetermined amount or more flows during charging and the battery becomes overcharged, the battery voltage increases and The liquid or the like decomposes to generate gas, and the internal pressure of the battery rises. Furthermore, if this overcharged state continues, an abnormal reaction such as rapid decomposition of the electrolyte or active material may occur, and the battery temperature may rise rapidly.

As a countermeasure against such a problem, an explosion-proof sealed battery has been proposed. This explosion-proof sealed battery includes a current interrupting device that operates in response to an increase in battery internal pressure. A battery provided with this current interrupting device is, for example, an overcharged state, gas generation and filling due to chemical change inside the battery, and when the internal pressure of the battery begins to rise due to the filling of the gas, the current interrupting device causes the current interrupting device to rise. It activates and cuts off the charging current. Therefore, the abnormal reaction inside the battery can be stopped to prevent the battery temperature from rising rapidly and the battery internal pressure from rising.

However, in the structure of this explosion-proof sealed battery, a substance capable of doping and undoping lithium ions such as lithium, a lithium alloy or a carbon material is used as the negative electrode, and the lithium cobalt composite is used as the positive electrode. When a non-aqueous electrolyte secondary battery is made using a lithium composite oxide such as an oxide and placed in an overcharged state, there are some that show a damage state such as heat generation with a rapid temperature rise or relatively rapid damage. ..

[0006]

The inventors of the present invention have investigated the cause of the exothermic reaction accompanied by a rapid temperature rise of the battery and the relatively rapid breakage in the explosion-proof sealed battery when the battery is overcharged. It has been found that the damage to the battery is triggered by the temperature increase due to the exothermic reaction that is still occurring even after the current interrupting device is activated and the charging current is interrupted. Therefore, the present invention has been proposed in view of such conventional circumstances, and it is an object of the present invention to provide a non-aqueous electrolyte secondary battery capable of preventing temperature rise and damage after the operation of the current interrupting device. To aim.

[0007]

The inventors of the present invention have conducted various studies in order to achieve the above-mentioned object, and as a result, by adding alkylbenzenes to the electrolytic solution, charging by the operation of the current interruption device has been performed. It was found that the temperature rise after current interruption can be suppressed.

The non-aqueous electrolyte secondary battery of the present invention was proposed on the basis of such findings, and Li _x MO ₂
(However, M represents one or more kinds of transition metals, and 0.05 ≦ x
≦ 1.10. ) As a main component, a negative electrode capable of being doped or dedoped with lithium, a non-aqueous electrolyte solution, and a current interruption means that operates in response to an increase in internal pressure of the battery, respectively. It is characterized in that the water solvent is obtained by adding alkylbenzenes to a mixed solvent in which at least one of chain carbonic acid esters, esters and cyclic carbonic acid esters and propylene carbonate are mixed. In the present invention, as the solvent constituting the electrolytic solution, for example, R ¹ OCOOR ² (R ¹ , R ² = CH
₃ , C ₂ H ₅ , C ₃ H ₇ ) chain carbonates, R ³ COOR ⁴ (R ³ , R ⁴ = CH ₃ , C ₂ H ₅ ,
C ₃ H ₇ , C ₄ H ₉ ) ester and compound 1
A mixed solvent prepared by mixing at least one selected from cyclic carbonates represented by and propylene carbonate can be used.

[0009]

[Chemical 1]

From the viewpoint of battery characteristics, it is preferable to use a mixed solvent having the following composition as the mixed solvent. Propylene carbonate: Diethyl carbonate = 60: 40-
20:80 Propylene carbonate: Dipropyl carbonate = 60: 40-
20:80 Propylene carbonate: Esters such as butyl acetate = 6
0: 40-20: 80 Propylene carbonate: Ethylene carbonate = 75: 25-
35:65 The structural formulas of propylene carbonate, diethyl carbonate, dipropyl carbonate, butyl acetate, and ethylene carbonate are shown in Chemical formulas 2 to 6, respectively.

[0011]

[Chemical 2]

[0012]

[Chemical 3]

[0013]

[Chemical 4]

[0014]

[Chemical 5]

[0015]

[Chemical 6]

In the present invention, in order to reduce the occurrence rate of battery damage due to overcharge, alkylbenzenes represented by the general formula 7 are added.

[Chemical 7]

The amount of these alkylbenzenes added is preferably 0.1% by volume or more in order to sufficiently suppress damage to the battery due to overcharge. On the other hand, regarding the upper limit,
It is possible to reach the compatibility limit at which a homogeneous phase can be formed with the selected mixed solvent, but if it exceeds 10% by volume, the internal pressure of the battery will increase rapidly when continuous charging is performed at a high temperature of about 60 ° C. The breaker operates, which causes a practical problem such as shortening the battery life. Therefore, in consideration of such a point, the addition amount of alkylbenzenes is 0.1
It is desirable that the content is -10% by volume.

Further, as the electrolyte of the non-aqueous electrolyte,
It is not particularly limited, and for example, LiClO ₄ ,
LiAsF ₆ , LiPF ₆ , LiBF _4, etc. can be used,
Of these, it is particularly preferable to use LiPF ₆ .

The positive electrode contains Li _X MO ₂ (where M represents at least one transition metal, preferably at least one of Co and Ni, and 0.05 ≦ X ≦ 1.10.). Active material is used. As such an active material, L
iCoO ₂ , LiNiO ₂ , Li _x Ni _y Co _(1-y) O
₂ (provided that 0.05 ≦ x ≦ 1.10 and 0 <y <1). The composite oxide is obtained by using, for example, a carbonate of lithium, cobalt, or nickel as a starting material, mixing these carbonates according to the composition, and firing the mixture in an oxygen-present atmosphere at a temperature range of 600 ° C to 1000 ° C. .. Further, the starting material is not limited to carbonate, and it can be similarly synthesized from hydroxide or oxide.

On the other hand, as the negative electrode, lithium is doped,
Any material that can be dedoped can be used, including pyrolytic carbons, cokes (pitch cokes, needle cokes, petroleum cokes, etc.), graphites, glassy carbons, organic polymer compound fired products (phenolic resins, furan resins, etc.) Of carbon dioxide obtained by firing at a suitable temperature), carbon fiber, activated carbon or the like, or metal lithium, a lithium alloy (for example, a lithium-aluminum alloy), or a polymer such as polyacetylene or polypyrrole.

In the non-aqueous electrolyte secondary battery of the present invention,
It is necessary to provide a current interruption device, but as this current interruption device, any current interruption device normally provided in this type of battery can be adopted, and the current interruption device is interrupted according to the internal pressure of the battery. Anything is possible as long as it can.

[0022]

In the non-aqueous electrolyte secondary battery, when alkylbenzenes are added to the non-aqueous solvent obtained by mixing propylene carbonate with at least one of chain carbonic acid ester, ester, and cyclic carbonic acid ether, the current cutoff device is activated. The exothermic reaction that continues to occur is suppressed. Although the reason for this is not clear, it has been found from experiments that a large amount of carbon monoxide is detected in the gas analysis inside the battery when the alkylbenzenes are added to the battery in which the current is cut off by overcharging. This means that the alkylbenzenes were electrochemically decomposed due to the increased battery voltage due to overcharge, and the methane generated as a result of this decomposition was oxidized by the oxygen liberated from the positive electrode to become carbon monoxide. Suggests. Therefore, since this reaction suppresses the increase in oxygen concentration inside the battery, it is presumed that this exothermic reaction involving active oxygen is suppressed.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

Structure of Battery Produced FIG. 1 shows the structure of the battery produced in each Example described later. As shown in FIG. 1, this non-aqueous electrolyte secondary battery includes a negative electrode 1 in which a negative electrode current collector 9 is coated with a negative electrode active material, and a positive electrode in which a positive electrode current collector 10 is coated with a positive electrode active material. 2 and 2 are wound via a separator 3, and the insulator 4 is placed on the upper and lower sides of the wound body and housed in a battery can 5. A battery lid 7 is attached to the battery can 5 by caulking through a sealing gasket 6, and is electrically connected to the negative electrode or the positive electrode 2 through a negative electrode lead 11 and a positive electrode lead 12, respectively, and a negative electrode or a positive electrode of the battery. Is configured to function as. Further, in the battery of this embodiment, the positive electrode lead 12 is welded and attached to the thin plate 8 for current interruption, and electrical connection with the battery lid 7 is achieved through this thin plate for current interruption.

In the battery having such a structure, when the internal pressure of the battery rises, the current interruption thin plate 8 is pushed up and deformed as shown in FIG. Then, the positive electrode lead 12 is cut, leaving the portion welded to the thin plate 8 for current interruption, and the current is interrupted.

Example 1 First, the negative electrode 1 was prepared as follows. For the negative electrode active material,
Petroleum pitch is used as a starting material, 10 to 20% of a functional group containing oxygen is introduced into this (so-called oxygen cross-linking), and then fired in an inert gas stream at 1000 ° C. A graphite carbon material was used. As a result of X-ray analysis measurement of this material, the spacing between (002) planes was 3.76 Å and the true specific gravity was 1.58 g / cm ³ . The carbon material thus obtained was pulverized into a carbon material powder having an average particle size of 10 μm, and the carbon material powder
Parts by weight, polyvinylidene fluoride as a binder (PVD
F) 10 parts by weight of the mixture was mixed to prepare a negative electrode mixture, which was dispersed in N-methyl-2-pyrrolidone to form a slurry. Next, this slurry is uniformly applied to both sides of a strip-shaped copper foil having a thickness of 10 μm, which is the negative electrode current collector 9, and after drying,
A negative electrode 1 was prepared by compression molding with a roll press.

Next, the positive electrode 2 was produced as follows. As the positive electrode active material (LiCoO ₂ ), lithium carbonate and cobalt carbonate were mixed at a ratio of 0.5 mol to 1 mol, and the mixture was mixed in air at 900
It was obtained by firing at ℃ for 5 hours. LiCoO obtained in this way
₂ 85.5 parts by weight, 6 parts by weight of graphite as a conductive agent, 3 parts by weight of polyvinylidene fluoride as a binder, were mixed in a ratio of lithium carbonate 5.5 parts by weight as the battery internal pressure increasing agent during overcharge A positive electrode agent was prepared and dispersed in N-methyl-2-pyrrolidone to form a slurry. next,
This slurry was uniformly applied to both sides of a 20 μm-thick strip-shaped aluminum foil as the positive electrode current collector 10, dried and then compression-molded with a roll press machine to form a positive electrode 2.

This strip-shaped positive electrode 2, negative electrode 1, and 25 μm
The separator 3 made of the microporous polypropylene film was sequentially laminated and then wound in a spiral shape many times to form a wound body. Next, the insulating plate 4 was inserted into the bottom of the nickel-plated iron battery can 5 and the wound body was housed. Then, in order to collect current from the negative electrode, one end of a negative electrode lead 11 made of nickel was pressure-bonded to the negative electrode 1, and the other end was welded to the battery can 5. Further, one end of a positive electrode lead 12 made of aluminum is attached to the positive electrode 2 in order to collect the current of the positive electrode, and the other end is welded to a current interrupting thin plate 8 which interrupts the current according to the internal pressure of the battery. It was electrically connected to the battery lid 7 via 8.

Then, in the battery can 5, LiPF ₆ 1 was added in a mixed solvent of 50% by volume of propylene carbonate, 49.97% by volume of diethyl carbonate and 0.03% by volume of ethylbenzene.
An electrolyte solution in which moles were dissolved was injected. Then, the battery can 5 is inserted through the insulating sealing gasket 6 coated with asphalt.
By crimping, the battery lid 7 is fixed, and the diameter is 20 mm,
Cylindrical non-aqueous electrolyte battery with a height of 50 mm (Example battery 1)
It was created.

Examples 2 to 16 Cylindrical non-aqueous electrolytes were used in the same manner as in Example 1 except that as the non-aqueous electrolytes, the ones having the compositions shown in Table 1 and the alkylbenzenes shown in Table 2 were added. Battery (Example battery 2)
-Example battery 16) was created.

Comparative Examples 1 to 3 Cylindrical non-aqueous electrolyte secondary batteries (Comparative Example Battery 1 to Comparative Example Battery) as in Example 1 except that the composition shown in Table 1 was used as the non-aqueous electrolytic solution. 3) was created.

[0032]

[Table 1]

Two batteries each are prepared as described above.
The occurrence rate of damaged products of the battery was investigated, in which 0 batteries were overcharged at a current of 3.7 A and heat generation accompanied by a rapid temperature rise and relatively rapid damage occurred. The results are shown in Table 2.

[0034]

[Table 2]

The structural formulas of the added alkylbenzenes are shown in Chemical formulas 8 to 13.

[0036]

[Chemical 8]

[0037]

[Chemical 9]

[0038]

[Chemical 10]

[0039]

[Chemical 11]

[0040]

[Chemical formula 12]

[0041]

[Chemical 13]

As shown in Table 2, in Comparative battery 1 to Comparative battery 3, the occurrence rate of battery damage due to overcharge is 100%, whereas the non-aqueous solvent contains alkylbenzenes. In each of Example batteries 1 to 16, the occurrence rate of damaged products was low, and in particular, in Example batteries 3 to 16 in which alkylbenzenes were added in an amount of 0.1% by volume or more, the battery damage was completely caused. You can see that it is prevented. Therefore, from this, it was shown that adding alkylbenzenes to the non-aqueous solvent is effective in suppressing damage to the battery due to overcharge. At this time, a battery was made using a non-aqueous solvent containing 10% by volume of methylbenzenes. However, when the battery was continuously charged at a high temperature such as 60 ° C, the internal pressure of the battery increased rapidly. As a result, the current breaker operates, and a sufficient life cannot be obtained. From this, it was found that the addition amount of methylbenzenes added to the non-aqueous solvent is preferably 0.1 to 10% by volume.

Further, since the battery loss damage effect by the alkylbenzenes is obtained to the same extent in all of the example batteries 1 to 12, any alkylbenzenes having a predetermined carbon number can be used. Even if it exists, it is shown that the same effect is exhibited, and even if the type and composition of the chain carbonic acid ester, ester, and cyclic carbonic acid ester constituting the non-aqueous solvent are changed, the same effect is obtained. It was shown to be obtained.

[0044]

As is apparent from the above description, in the non-aqueous electrolyte secondary battery of the present invention, since alkylbenzenes are added to the non-aqueous solvent, rapid heat generation of the battery due to overcharge and Relatively rapid damage can be prevented. Therefore, a non-aqueous electrolyte secondary battery having high energy density, excellent cycle characteristics, and high safety can be provided, and its industrial and commercial value is great.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a configuration example of a non-aqueous electrolyte secondary battery.

FIG. 2 is a schematic cross-sectional view showing an operating state of a current interruption means.

[Explanation of symbols]

 1 ... Negative electrode 2 ... Positive electrode 3 ... Separator 8 ... Current blocking thin plate

Claims (1)

Claim: What is claimed is: 1. A positive electrode mainly comprising Li _x MO ₂ (wherein M represents one or more kinds of transition metals, and 0.05 ≦ x ≦ 1.10), and lithium. A non-aqueous electrolyte, a non-aqueous electrolyte solution, and a current interrupting means that operates in response to an increase in battery internal pressure. The non-aqueous solvent of the non-aqueous electrolyte solution is a chain carbonate ester. A non-aqueous electrolyte secondary battery, characterized in that it is obtained by adding alkylbenzenes to a mixed solvent in which at least one of esters and cyclic carbonates is mixed with propylene carbonate.