JPH06150928A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

(57) [Summary] [Object] To provide a non-aqueous electrolyte secondary battery having a high voltage and a high energy density, and having excellent charge-discharge cycle life characteristics and storage characteristics. [Structure] Li _(1-x) CoO ₂ (x is 0 ≦ x where the particle surface is covered with samarium (Sm) oxide or composite oxide
<1) or Li _(1-x) CoMO ₂ (where M is Co
Other than transition metals, x is 0 ≦ x <1), a negative electrode made of lithium, a lithium alloy or a carbon material capable of intercalating / deintercalating lithium, and a non-aqueous electrolyte. A non-aqueous electrolyte secondary battery composed of.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a non-aqueous electrolyte secondary battery, particularly a lithium composite oxide used for a positive electrode.

[0002]

2. Description of the Related Art In recent years, along with portable and cordless electronic devices such as AV devices and personal computers, there has been a strong demand for a high energy density secondary battery as a driving power source for these devices. Electrolyte secondary batteries are expected as high voltage and high energy density secondary batteries. A layered compound capable of intercalating / deintercalating lithium, such as LiCoO ₂ or LiN, as an active material used for the positive electrode of this battery.
io ₂ (US Pat. No. 4,302,518) and LiC
o _x Ni _(1-x) O ₂ (x ≦ 0.27) (JP-A-62-26)
4560) and the like, a composite oxide of lithium has been proposed.

Further, by using these lithium composite oxides as a positive electrode active material, development of a high energy density non-aqueous electrolyte secondary battery having an output voltage of 4 V class is under way.

[0004]

However, in the above non-aqueous electrolyte secondary battery, since the organic solvent such as propylene carbonate or dimethoxyethane used in the electrolyte is decomposed at a high voltage, the battery There has been a problem that charge / discharge characteristics are deteriorated.

In order to solve this problem, the complex oxide L
A technique of substituting a part of cobalt of iCoO ₂ with another metal element has been proposed. Specifically, a part of cobalt is replaced with nickel (Japanese Patent Laid-Open No. 63-299056), and with iron. (Japanese Patent Application Laid-Open No. 63-2111564) or substitution with aluminum, tin or indium (Japanese Patent Application Laid-Open No. 62-90863).

However, when a lithium composite oxide in which a part of cobalt is substituted by such a metal element is used as a positive electrode active material, the discharge voltage as a battery is lowered,
It has been difficult to realize a high voltage, high energy density secondary battery.

Further, a battery using a lithium composite oxide such as LiCoO ₂ as a positive electrode active material has a problem that the battery capacity is remarkably reduced when stored at a high temperature in a charged state.

It is considered that this is due to the decomposition reaction of the electrolytic solution solvent on the positive electrode active material and the crystal destruction of the positive electrode active material.

The present invention is intended to solve such problems, and in order to realize a non-aqueous electrolyte having a high voltage and a high energy density, and excellent charge / discharge cycle life characteristics and storage characteristics, It is intended to provide a non-aqueous electrolyte secondary battery using a positive electrode active material capable of preventing a decomposition reaction of an electrolytic solution solvent on a positive electrode active material under high voltage and crystal collapse during charge / discharge.

[0010]

In order to solve the above problems, the non-aqueous electrolyte secondary battery of the present invention is a lithium composite oxide Li in which the surface of the particles is covered with samarium oxide or composite oxide. _(1-x) CoO ₂ (x is 0 ≦ x <1) or Li _(1-x) CoMO ₂ (where M is a transition metal other than Co and x is 0 ≦ x <1) as an active material And a negative electrode made of a carbon material capable of intercalating / deintercalating lithium, a lithium alloy or lithium, and a non-aqueous electrolyte.

[0011]

Samarium on the particle surface of the working composite oxide of lithium is present as a complex oxide mainly samarium oxide or lithium and samarium,, LiCoO ₂ and Li
The surface of CoMO ₂ (where M is a transition metal other than Co) is coated.

By this coating, the direct reaction between the surface of the positive electrode active material particles and the electrolytic solution can be suppressed, and the decomposition reaction of the electrolytic solution solvent on the positive electrode active material can be prevented.

Therefore, by using such a lithium composite oxide as the positive electrode active material, the decomposition reaction of the electrolyte solvent can be suppressed, and the charge / discharge cycle life characteristics and storage characteristics can be improved.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

A lithium composite oxide, which is a positive electrode active material of the non-aqueous electrolyte secondary battery of the present invention, was produced as follows.

Lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) were mixed at an atomic ratio of 1: 1 and samarium oxide (Sm ₂ O ₃ ) was added to Co in cobalt carbonate. (Table 1).

[0017]

[Table 1]

Next, these mixtures were fired in air at 900 ° C. for 5 hours to obtain six kinds of positive electrode active materials A to
I got F.

Next, 100 parts by weight of the positive electrode active material thus obtained, 4 parts by weight of acetylene black and 7 parts by weight of a fluororesin binder were mixed to prepare a positive electrode mixture, which was used as an aqueous solution of carboxymethyl cellulose. To form a paste.

Apply this paste on both sides of aluminum foil,
After drying, it was rolled into positive electrode plates A to F.

The negative electrode plate was manufactured as follows.
100 parts by weight of the carbon material obtained by baking the coke was mixed with 10 parts by weight of a fluororesin-based binder, and the mixture was suspended in an aqueous solution of carboxymethyl cellulose to form a paste.

This paste was applied to both sides of a copper foil, dried and rolled to obtain a negative electrode plate. The positive electrode plate, the negative electrode plate, the polypropylene separator, and the nonaqueous electrolytic solution were used to construct a sealed nonaqueous electrolytic solution secondary battery as shown in FIG.

Here, the non-aqueous electrolytic solution used was one dissolved in an equal volume mixed solvent of propylene carbonate and ethylene carbonate at a rate of 1 mol / l lithium perchlorate.

In FIG. 1, a positive electrode plate and a negative electrode plate are spirally wound via a separator to form an electrode plate group 1, and this positive electrode group 1 is inside a battery case 2 made of an organic electrolyte resistant stainless steel plate. It is stored in.

The upper part of the battery case 2 is sealed with a sealing plate 3 having a safety valve. Further, the positive electrode lead 4 is drawn out from the positive electrode and is electrically connected to the sealing plate 3, and the negative electrode lead 5 is drawn out from the negative electrode and is electrically connected to the battery case 2.

Further, an insulating packing 6 is arranged between the battery case 2 and the sealing plate 3, and an insulating ring 7 is arranged on the upper and lower surfaces of the electrode plate group 1.

Next, using these batteries, a charge / discharge cycle life test and a high temperature charge storage test were conducted.

In the constant current charge / discharge cycle life test, charging was performed at a current of 100 mA up to a voltage of 4.1 V, and discharging was performed at a current of 1
A final voltage of 3.0 V was applied at 00 mA to complete one cycle.

The high temperature charge storage test was carried out by repeating the above charge / discharge cycle 10 times and then storing the battery in a charged state at 60 ° C. for 20 days.

FIG. 2 shows the relationship between the number of charge / discharge cycles and the discharge capacity in the charge / discharge cycle life test of the batteries A to F.

The capacity retention rate of the battery after the high temperature charge storage test [(capacity after storage / capacity before storage) × 1]
00] is shown in FIG.

As can be seen from FIG. 3, samarium (S
In the battery A containing no m) at all, the capacity was greatly decreased with charge and discharge, and became half of the initial capacity after 300 cycles.

On the other hand, in the batteries B to F containing samarium, as the amount of samarium increased, the initial capacity of the battery decreased to some extent, but the decrease in capacity with charge / discharge cycles was significantly suppressed. .

In the batteries C to F containing samarium in an amount of 1 to 5 mol% with respect to cobalt in the lithium composite oxide, the battery capacity should be maintained as high as 80% or more of the initial capacity even after 300 cycles. I was able to.

However, in the battery F containing 8 mol% of samarium with respect to cobalt, LiCoO formed by samarium was used.
_Since the surface coverage of No. ₂ became too large, the reaction of the active material was extremely suppressed, and the capacity of the battery was considerably lowered from the initial stage.

Further, as can be seen from FIG. 3, in the battery A containing no samarium, the capacity retention of the battery after high temperature storage was 52%, whereas in the battery A containing 1 mol% of samarium to cobalt. In the batteries C to F containing the above, the capacity retention rate was improved to 85% or more.

However, even if samarium was further added, the capacity retention rate of the battery after high temperature storage remained almost unchanged.

From these results, the amount of samarium added is preferably 5 mol% or less with respect to cobalt.

In this example, L was used as the positive electrode active material.
iCoO ₂ was used, but in addition to this, L was obtained by substituting a part of Co with any one of transition metals Ni, Fe, and Mn.
Similar effects were obtained even with the complex oxide of i.

Further, in this example, lithium carbonate (Li ₂ CO ₃ ) which is a carbonate of lithium and cobalt and cobalt carbonate (CoC) were used as starting materials for synthesizing the positive electrode active material.
Although O ₃ ) is used, other oxides of lithium and cobalt, or hydroxides or acetates thereof may be used.

Further, in this embodiment, a carbon material capable of intercalating / deintercalating lithium as an active material was used as a negative electrode constituent material, but in addition to this, lithium which is itself an active material is used. It may be a metal or a lithium alloy.

Further, as the electrolytic solution, a solution obtained by dissolving lithium perchlorate in a mixed solvent of equal volume of propylene carbonate and ethylene carbonate was used, but a solution obtained by dissolving a lithium salt as a solute in another organic solvent may be used.

[0043]

As described above, in the non-aqueous electrolytic solution of the present invention, the surface of Li _(1-x) CoO ₂ (x is 0 ≦ x is covered with an oxide or complex oxide of samarium (Sm). <1),
Alternatively, since a lithium composite oxide composed of Li _(1-x) CoMO ₂ (where M is a transition metal other than Co and x is 0 ≦ x <1) is used for the positive electrode, the positive electrode active material on the positive electrode active material under high voltage is used. It is possible to prevent the decomposition reaction of the electrolytic solution and the crystal collapse of the positive electrode active material in the above, and it is possible to improve the charge / discharge cycle life characteristics and the storage characteristics of the battery.

[Brief description of drawings]

FIG. 1 is a diagram showing a non-aqueous electrolyte secondary battery of the present invention.

FIG. 2 is a diagram showing the relationship between the number of charge / discharge cycles and the discharge capacity.

FIG. 3 is a diagram showing the relationship between the amount of samarium added and the battery capacity retention rate after a high temperature storage test.

[Explanation of symbols]

 1 electrode plate group 2 battery case 3 sealing plate 4 positive electrode lead 5 negative electrode lead 6 insulating packing 7 insulating ring

Claims (5)

[Claims] 1. A lithium composite oxide Li _(1-x) Co whose surface is covered with a samarium oxide or a composite oxide.
A positive electrode composed of O ₂ (x is 0 ≦ x <1), a negative electrode composed of lithium, a lithium alloy or a carbon material capable of intercalating / deintercalating lithium, and a non-aqueous electrolytic solution. Non-aqueous electrolyte secondary battery. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the added amount of Sm is 5% or less in terms of molar ratio with respect to Co in the lithium composite oxide. 3. A lithium composite oxide Li _(1-x) Co whose particles are covered with a samarium oxide or a composite oxide.
MO ₂ (where M is a transition metal other than Co, x is 0 ≦ x
A non-aqueous electrolyte secondary battery comprising a positive electrode comprising <1), a negative electrode comprising lithium, a lithium alloy or a carbon material capable of intercalating / deintercalating lithium, and a non-aqueous electrolyte. 4. A transition metal other than Co is Ni, Mn, Fe.
The non-aqueous electrolyte secondary battery according to claim 3, which is any one of the group consisting of: 5. The non-aqueous electrolyte secondary battery according to claim 3, wherein the added amount of Sm is 5% or less in terms of molar ratio with respect to Co in the lithium composite oxide.