JPH05242913A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To increase CO2 gas generation efficiency at the time of over-charge and enable overheat due to the over-charge to be early prevented. CONSTITUTION:In a nonaqueous electrolyte secondary battery where LixMO2 (M stands for at least one of transition metals, or more preferably at least one of Co and Ni, and X stands for a value expressed as 0.05<=X<=1.10.) is used as a positive electrode 2, and a current cutout means 8 operating according to a rise in battery internal pressure is fitted, the electrode active material LixMO2 is made to contain a ribbon or needle type of lithium carbonate.

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 having a lithium composite oxide as a positive electrode and a current interrupting means which operates in response to an increase in internal pressure of the battery.

[0002]

2. Description of the Related Art In recent years, advances in electronic technology have led to advances in the performance, miniaturization, and portability of electronic devices, and the demand for high energy density secondary batteries used in these electronic devices is increasing. Conventionally, nickel-cadmium batteries and lead batteries have been known as secondary batteries used in these electronic devices, but these batteries have a low discharge potential and a high energy density. It is still insufficient.

In recent years, non-aqueous materials such as lithium, lithium alloys, or carbon materials that can be doped or dedoped with lithium ions are used as the negative electrode, and lithium composite oxides such as lithium cobalt composite oxide are used as the positive electrode. Research and development of electrolyte secondary batteries are being conducted. This non-aqueous electrolyte secondary battery has a high battery voltage, a high energy density, little self-discharge, and excellent cycle characteristics.

By the way, generally, in the above non-aqueous electrolyte secondary battery, heat is generated at the time of overcharging, and further overheating may occur. Therefore, in order to prevent overheating during overcharge, for example, Li ₂ CO ₃ contained in the positive electrode material is used.
There has been proposed a method of activating a current interruption means mounted on a battery by utilizing the generation of CO ₂ gas due to the electrochemical decomposition reaction of.

For example, in a non-aqueous electrolyte secondary battery using LiCoO ₂ as a main positive electrode material, Li ₂ CO ₃ contained in the positive electrode material at the time of overcharging is expressed by the formula (1) below. It is chemically decomposed to generate CO ₂ gas.

[0006]

[Chemical 1]

When the pressure inside the battery rises due to the generation of such CO ₂ gas, the current interrupting means mounted on the battery operates and the charging is stopped. As a result, overheating due to the progress of overcharge can be prevented.

[0008]

However, as described above, the current cutoff means is provided, and Li ₂ CO ₃ is contained in the positive electrode.
In a non-aqueous electrolyte secondary battery containing,
The Li ₂ CO ₃ is present in the positive electrode material simply in an excessively contained state, and the CO ₂ gas generation efficiency as shown in the formula (1) is not always sufficient. Therefore, it takes time until the current interruption means is activated, and there is a risk of ignition due to progress of overcharge,
The solution is desired.

Therefore, an object of the present invention is to provide a highly safe non-aqueous electrolyte secondary battery in which overheating during overcharging is prevented at an early stage.

[0010]

The inventors of the present invention have conducted extensive studies to achieve the above-mentioned object, and as a result, the generation efficiency of CO ₂ gas by Li ₂ CO ₃ contained in the positive electrode is
Depending on the crystal structure of ₂ CO _3, by incorporating the Li ₂ CO ₃ in a state that the surface area is increased, found that it is possible to significantly improve the generation efficiency of the CO ₂ gas, the present invention It came to.

That is, the non-aqueous electrolyte secondary battery of the present invention is L
i _x MO ₂ (wherein M represents at least one kind of transition metal and 0.05 ≦ x ≦ 1.10) as a main component, a negative electrode capable of doping / dedoping lithium, A lithium electrolyte having a water electrolyte and a current interruption means that operates in response to an increase in battery internal pressure, wherein the positive electrode is ribbon-shaped or needle-shaped Li.
It is characterized by containing ₂ CO ₃ .

In the present invention, Li _x MO is used for the positive electrode.
₂ (wherein M represents at least one kind of transition metal, preferably Co or Ni, and x is 0.05 ≦ x ≦ 1.10). used. As such an active material, LiCoO 2
₂ , LiNiO ₂ , LiNi _y Co _(1-y) O ₂ (however,
The compound oxide represented by 0.05 ≦ x ≦ 1.10 and 0 <y <1) is included.

The above-mentioned composite oxide is obtained by using, for example, a carbonate of lithium, cobalt, or nickel as a starting material, and mixing these carbonates in accordance with the composition, and then in an oxygen-existing atmosphere at 600.degree.
It is obtained by firing in the temperature range of 1000 ° C.
Further, the starting material is not limited to carbonate, and can be similarly synthesized from hydroxide or oxide.

In the present invention, this positive electrode contains ribbon-shaped or needle-shaped Li ₂ CO ₃ . As a result, the generation efficiency of CO ₂ gas generated during overcharging becomes extremely good, and overheating during overcharging can be stopped early.

The ribbon-shaped or needle-shaped Li ₂ Co ₃ is
Lattice constant a = 8.359Å, b = 4.9767Å, c =
6.194Å, β = 114 ° 43 'monoclinic system (m
It is a material having an onoclinic) crystal structure.
Further, this Li ₂ CO ₃ is a ribbon-shaped crystal having a very long length and a very thin thickness, and the crystal orientation in the longitudinal direction is perpendicular to the (−102) plane.
(However, in the method of expressing the crystal orientation using the Miller index, when the surfaces intersect on the negative side of the basic vector, a negative symbol is added above the number in principle, but here, for convenience,
A negative sign was added before the number. The same applies hereinafter. )

Therefore, such Li ₂ CO ₃ is a substance having a very large surface area and poor conductivity, but its thickness is very thin, so that electric conduction is facilitated.
For this reason, the CO ₂ gas generation efficiency at the time of overcharge is high, and the CO ₂ gas generation amount at the same overcharge amount is large, so that the current interruption means can be activated at an early point. Therefore, it is possible to stop charging before overheating due to overcharging.

Ribbon-shaped or needle-shaped Li ₂ CO is added to the positive electrode.
_{As a} means for incorporating ₃ , for example, a method of leaving Li ₂ CO ₃ at the time of synthesizing the positive electrode active material can be considered, but it is not limited to this. The amount of Li ₂ CO ₃ introduced is preferably 0.5 to 15% by weight in the positive electrode active material.

On the other hand, in the present invention, for example, a carbon material is used for the negative electrode. The carbon material may be any one that can be doped or dedoped with lithium, such as pyrolytic carbons,
Cokes (pitch coke, needle coke, petroleum coke, etc.), graphites, glassy carbons, organic polymer compound fired products (phenolic resin, furan resin, etc. fired at an appropriate temperature to carbonize), carbon fibers , Activated carbon and the like. Alternatively, in addition to carbon materials, metallic lithium, lithium alloys (for example, lithium-aluminum alloys), and polymers such as polyacetylene and polypyrrole can also be used.

As the electrolytic solution, for example, an electrolytic solution in which a lithium salt is used as an electrolyte and this is dissolved in an organic solvent is used. Here, the organic solvent is not particularly limited, but propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, γ-butyl lactone,
Tetrahydrofuran, 2-methyltetrahydrofuran,
1,3-dioxolane, sulfolane, acetonitrile,
A single solvent such as diethyl carbonate or dipropyl carbonate or a mixed solvent of two or more kinds can be used.

As the electrolyte, LiClO ₄ , LiAs
F ₆ , LiPF ₆ , FiBF ₄ , LiB (C
₆ H ₅ ) ₄ , LiCl, LiBr, CH ₃ SO ₃ Li,
CF ₃ SO ₃ Li or the like can be used. As the current interrupting means, any current interrupting means usually provided in this type of battery can be adopted, and any device can be used as long as it can interrupt the current in accordance with the internal pressure of the battery.

[0021]

By using a ribbon-shaped or needle-shaped lithium composite oxide containing Li ₂ CO ₃ for the positive electrode, the CO ₂ gas generation efficiency at the time of overcharging becomes high, and the overcharging is stopped early. It is possible to prevent overheating. The reason for this is considered as follows.

That is, Li ₂ CO contained in the positive electrode
₃ is electrochemically decomposed during overcharge to generate CO ₂ gas. As a result, when the critical pressure is reached, the current interruption means attached to the battery is activated, the charging current is interrupted, and overheating of the battery due to overcharging can be prevented.

[0023] Here, the only Li ₂ CO ₃ is simply contained excessively in the positive electrode, the reaction area of the Li ₂ CO ₃ is small, is possible to efficiently perform electrochemical decomposition reaction Li ₂ CO ₃ Can not.

On the other hand, in the present invention, the positive electrode is made of long and thin ribbon-like or needle-like Li ₂ C having a very thin thickness.
By forming O ₃ , the surface area of the Li ₂ CO ₃ becomes very large, and the Li ₂ CO ₃ is in an energetically unstable state, so that decomposition during overcharge easily occurs. Also, L
Since i ₂ CO ₃ originally has a relatively large specific resistance ρ, its electrical conductivity is poor. However, as represented by the following equation (2), the electrical resistance R has a small value as a whole even if the specific resistance ρ is large, if the conduction distance l is short and the conduction area S is large.

[0025]

[Equation 1]

Therefore, in the ribbon-shaped or needle-shaped Li ₂ CO ₃ crystal as described above, considering the case where a current flows in the direction perpendicular to the longitudinal direction, the electric resistance R becomes small due to the shape. Is expected. From these facts, the CO ₂ gas generation efficiency at the time of overcharging becomes good, and the CO ₂ gas generation amount at the same overcharge amount increases, so that it becomes possible to prevent overheating due to overcharge early. It seems to be.

[0027]

EXAMPLES Preferred examples of the present invention will be described below based on experimental results. First, the structure of the non-aqueous electrolyte secondary battery produced in each of the examples described below is shown in FIG. As shown in FIG. 1, this non-aqueous electrolyte secondary battery includes a negative electrode 1 formed by coating a negative electrode current collector 9 with a negative electrode active material, and a positive electrode current collector 1.
0 is coated with a positive electrode 2 having a positive electrode active material applied thereto via a separator 3, and an insulating plate 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 1 or the positive electrode 2 via a negative electrode lead 11 and a positive electrode lead 12, respectively. , And is configured to function as a negative electrode or a positive electrode of a battery.

In the non-aqueous electrolyte secondary battery of this embodiment, the positive electrode lead 12 is welded and attached to the thin plate 8 for current interruption, and the battery lid 7 is attached via the thin plate 8 for current interruption.
Is electrically connected to. In a battery having such a configuration, when the pressure inside the battery rises,
As shown in FIG. 3, the current interruption thin plate 8 is pushed up and deformed. Then, the positive electrode lead 12 is connected to the thin plate 8 for interrupting current.
The current is cut off by cutting with the welded part left.

Example In this example, acicular Li ₂ Co ₃ was used as the main positive electrode active material.
₂ is an example of a non-aqueous electrolyte secondary battery using LiCoO ₂ containing Si. First, Li ₂ CO ₃ and CoCO ₃ are used as raw materials, and these Li ₂ CO ₃ and CoCO ₃ are mixed with Li ₂ C.
After mixing so that O ₃ : CoCO ₃ = 1.1: 2 (molar ratio), the positive electrode active material was synthesized by firing in a firing furnace at a temperature of 900 ° C.

FIG. 3 is a transmission electron micrograph of the positive electrode active material thus obtained, and FIG. 4 shows it. As shown in FIGS. 3 and 4, Li ₂ having a ribbon-like or needle-like shape on the surface of the LiCoO ₂ crystal 13
Co ₃ crystals 14 are present. The ribbon-shaped or needle-shaped Li ₂ Co ₃ crystal 14 has a lattice constant of a =
8.359Å, b = 4.9767Å, c = 6.194
Å, β = 114 ° 43 ', having monoclinic crystal structure, long length is about 10 μm, width is 1 μm
m or less, and the thickness was on the order of 10 ^-2 μm in the thin portion.

With respect to this Li ₂ Co ₃ crystal, X
As a result of the line diffraction measurement, as shown in FIG. 5, it was found that the longitudinal direction was the direction perpendicular to the (−102) plane.

Then, this positive electrode active material was crushed by an automatic mortar. Subsequently, 91% by weight of this positive electrode active material, 6% by weight of graphite as a conductive material, and 3% by weight of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture, and this was mixed with N-methyl-2-. It was dispersed in pyrrolidone to form a slurry. Then, this slurry is mixed with the positive electrode current collector 10
Was applied to both sides of the strip-shaped aluminum foil, which was then dried and compression-molded by a roll press machine to form a positive electrode 2.

On the other hand, as the negative electrode active material, petroleum pitch was used as a starting material, and a functional group containing oxygen was added to 10 to 20
% Introduction (so-called oxygen crosslinking), then 10 in an inert gas
A non-graphite carbon material having properties close to those of the glassy carbon obtained by firing at 00 ° C. was used. As a result of X-ray diffraction measurement of this non-graphite carbon material, the interplanar spacing of the (002) plane was 3.76Å and the true specific gravity was 1.58.

90% by weight of this carbon material and 10% by weight of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture, which was dispersed in N-methyl-2-pyrrolidone to form a slurry. And Subsequently, this slurry was applied on both sides of a strip-shaped copper foil which is a negative electrode current collector, dried and then compression-molded with a roller press machine to prepare a negative electrode 1.

Then, the strip-shaped positive electrode 2, negative electrode 1, and separator 3 made of a microporous polypropylene film having a thickness of 25 μm are sequentially laminated and then wound in a spiral shape many times to form a wound body. .. Then, insert the insulating plate 4 into the bottom of the nickel-plated iron battery can 5,
The wound body was stored. 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 was attached to the positive electrode 2 in order to collect current from the positive electrode, and the other end was welded to a battery lid 7 having a current interruption thin film 8 for interrupting current according to the internal pressure of the battery.

An electrolytic solution obtained by dissolving 1 mol of LiPF _{6 in a} mixed solvent of 50% by volume of propylene carbonate and 50% by volume of diethyl carbonate was poured into the battery can 5. Then, the battery can 5 was caulked through the insulating sealing gasket 6 coated with asphalt to fix the battery lid 7 and to manufacture a cylindrical battery having a diameter of 14 mm and a height of 50 mm.

Comparative Example Here, for comparison, a non-aqueous electrolyte secondary battery was manufactured using LiCoO ₂ containing only excess Li ₂ Co ₃ on the surface as a positive electrode active material. First, Li ₂ CO ₃ and CoCO ₃ were mixed so that Li ₂ CO ₃ : CoCO ₃ = 1: 2 (molar ratio), and then the temperature was set to 900 ° C. in a firing furnace.
A positive electrode active material was synthesized by firing at 5 hours.

Then, this positive electrode active material was crushed by an automatic mortar. Then, a predetermined amount of Li ₂ C was added to the positive electrode active material.
After adding O ₃ and mixing, it was baked in air at 750 ° C. for 5 hours.

When the amount of Li ₂ CO ₃ in this positive electrode active material was quantified, it was 3.6% by weight (5% in molar ratio).
Then, this positive electrode active material was crushed using an automatic mortar, and the positive electrode active material 91% by weight, graphite 6% by weight as a conductive material, and polyvinylidene fluoride 3% by weight as a binder were mixed to produce a positive electrode. A cylindrical battery was prepared in the same manner as in the above-described example except for the above.

Each of the non-aqueous electrolyte secondary batteries obtained in the above Examples and Comparative Examples was subjected to constant current charging under the conditions of a temperature of 25 ° C. and a current of 3.7 A to be in an overcharged state, and each non-aqueous electrolyte secondary battery was charged. The time until the current interruption device in the next battery was activated (the current interruption thin plate 8 was pushed up and deformed and a part of the positive electrode lead 12 was cut) was measured. In addition, the measurement is performed twice,
The average value was calculated. The results are shown in Table 1.

[0042]

[Table 1]

As shown in Table 1, a ribbon-shaped Li was formed on the positive electrode.
It has been found that when ₂ CO ₃ is contained, the current breaker operates early to prevent overheating due to overcharging. This is because the surface area of Li ₂ CO ₃ is very large, so that decomposition easily occurs during overcharge, and the electrical resistance decreases due to its shape, so the efficiency of generating CO ₂ gas during overcharge is high. It is thought that it became good.

[0044]

As is clear from the above description, in the present invention, the lithium composite oxide containing Li ₂ CO ₃ having a long and very thin shape and a large surface area is used for the positive electrode. Therefore, the CO ₂ gas generation efficiency at the time of overcharging becomes good, and the overcharging can be stopped early. Therefore, overheating during overcharging is prevented, and safety is improved.

Therefore, according to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having high energy density, excellent cycle characteristics, and high safety. In addition, the industrial and commercial value of this non-aqueous electrolyte secondary battery seems to be very large.

[Brief description of drawings]

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

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

FIG. 3 is an electron micrograph showing a crystal structure of Li ₂ Co ₃ contained in LiCoO ₂ .

FIG. 4 is a schematic diagram showing a crystal structure of Li ₂ Co ₃ contained in LiCoO ₂ .

FIG. 5 is a schematic diagram for explaining the crystal orientation of Li ₂ Co ₃ contained in LiCoO ₂ .

[Explanation of symbols]

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

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] June 2, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

[0008]

[Problems to be Solved by the Invention] However, in recent years,
In addition, the rapid charging of batteries is progressing, and higher charging
Safety in the fashion is becoming more demanding. Above
Current interruption devices are added, and lithium carbonate is added to the positive electrode
Batteries with the above configuration can withstand overcharging with conventional charging currents.
Was secured, but with a higher charging current
When overcharged, the
Damage due to relatively rapid breakage due to rising heat
Some had a condition.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

Ribbon-shaped or needle-shaped Li ₂ CO is added to the positive electrode.
_{As a} means for incorporating ₃ , for example , a method of leaving Li ₂ CO ₃ at the time of synthesizing the positive electrode active material can be considered, but the method is not limited to this. The amount of Li ₂ CO ₃ introduced is
It is preferably 0.5 to 15% by weight in the positive electrode active material.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0030

[Correction method] Change

[Correction content]

Example In this example, acicular Li ₂ CO ₃ was used as the main positive electrode active material.
It is an example of a non-aqueous electrolyte secondary battery using LiCoO ₂ containing. First, Li ₂ CO ₃ and CoCO ₃ are used as raw materials, and these LiCoO ₂ and CoCO ₃ are mixed with Li ₂ C.
After mixing so that O ₃ : CoCO ₃ = 1.2: 2 (molar ratio), the positive electrode active material was synthesized by firing at a temperature of 900 ° C. in a firing furnace.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0031

[Correction method] Change

[Correction content]

FIG. 3 is a transmission electron micrograph of the positive electrode active material thus obtained, and FIG. 4 shows it. As shown in FIGS. 3 and 4, Li ₂ having a ribbon-like or needle-like shape on the surface of the LiCoO ₂ crystal 13
Crystals of CO ₃ 14 are present. The ribbon-shaped or needle-shaped crystals of Li ₂ CO ₃ both have a lattice constant of a =
8.359Å, b = 4.9767Å, c = 6.194
Å, β = 114 ° 43 ′, having monoclinic crystal structure, long length is about 10 μm, width is 1 μm
It was below, and the thickness was on the order of 10 ⁻² μm in the thin portion.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Name of item to be corrected] 0032

[Correction method] Change

[Correction content]

In addition, the Li ₂ CO ₃ crystal is electrically charged.
As a result of the analysis by the sagittal diffraction, as shown in FIG.
It was found that the longitudinal direction was the direction perpendicular to the (-102) plane.

[Procedure correction 6]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

FIG. 3 is an electron micrograph showing a crystal structure of Li ₂ CO ₃ contained in LiCoO ₂ .

[Procedure Amendment 7]

[Document name to be amended] Statement

[Name of item to be corrected] Fig. 4

[Correction method] Change

[Correction content]

FIG. 4 is a schematic diagram showing a crystal structure of Li ₂ CO ₃ contained in LiCoO ₂ .

[Procedure Amendment 8]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 5

[Correction method] Change

[Correction content]

FIG. 5 is a schematic diagram for explaining a crystal orientation of Li ₂ CO ₃ contained in LiCoO ₂ .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji World 7-6-35 Kita-Shinagawa, Shinagawa-ku, Tokyo, Sony Corporation 1-1 Sony Energy Tech Koriyama Factory

Claims (1)

[Claims] 1. A positive electrode mainly composed of Li _x MO ₂ (wherein M represents at least one kind of transition metal and 0.05 ≦ x ≦ 1.10) and lithium is doped / dedoped. The obtained negative electrode, a non-aqueous electrolyte, and a current interruption means that operates in response to a rise in the internal pressure of the battery, wherein the positive electrode contains ribbon-shaped or needle-shaped Li ₂ CO _3. Secondary battery.