JP3003431B2 - 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 an improvement of a lithium composite oxide used for a nonaqueous electrolyte secondary battery, particularly for a positive electrode.

[0002]

2. Description of the Related Art In recent years, as electronic devices such as AV devices and personal computers have become portable and cordless, there has been a strong demand for secondary batteries having a high energy density as power sources for driving these devices. Electrolyte secondary batteries are expected to be high voltage, high energy density secondary batteries. Layered compound capable of intercalating / deintercalating lithium as an active material used for the positive electrode of this battery, for example, LiCoO ₂ , LiN
iO ₂ (US Pat. No. 4,302,518) and LiC
_{o x Ni (1-x)} O 2 (x ≦ 0.27) ( JP 62-26
No. 4560) has been proposed.

By using these lithium composite oxides as a positive electrode active material, development of a non-aqueous electrolyte secondary battery having a high energy density and an output voltage of 4 V class has been advanced.

[0004]

However, in the above-mentioned non-aqueous electrolyte secondary battery, the organic solvent such as propylene carbonate and dimethoxyethane used in the electrolyte is decomposed under a high voltage. There has been a problem that the charge / discharge characteristics deteriorate.

In order to solve this problem, a composite oxide L
A technique has been proposed in which part of cobalt of iCoO ₂ is replaced with another metal element. Specifically, a part of cobalt is replaced with nickel (Japanese Patent Application Laid-Open No. 63-299056) and replaced with iron. (Japanese Unexamined Patent Publication No. Sho 63-211564), or substitution with aluminum, tin and indium (Japanese Unexamined Patent Publication No. Sho 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 made it difficult to realize a high voltage, high energy density secondary battery.

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

This is considered to be caused by the decomposition reaction of the electrolyte solution solvent on the positive electrode active material and the crystal destruction of the positive electrode active material.

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

[0010]

In order to solve the above-mentioned problems, a nonaqueous electrolyte secondary battery of the present invention comprises a lithium composite oxide Li whose particles are 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 , A negative electrode made of lithium, a lithium alloy or a carbon material capable of intercalating / deintercalating lithium, and a non-aqueous electrolyte.

[0011]

The samarium on the surface of the lithium composite oxide particles is mainly present as samarium oxide or a composite oxide of lithium and samarium. LiCoO ₂ or LiCoO ₂
It covers the surface of CoMO ₂ (where M is a transition metal other than Co).

By this coating, a direct reaction between the surface of the positive electrode active material particles and the electrolytic solution can be suppressed, and a 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 composite oxide of lithium as a positive electrode active material of the nonaqueous electrolyte secondary battery of the present invention was produced as follows.

Lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) are mixed at an atomic ratio of 1: 1 and samarium oxide (Sm ₂ O ₃ ) is mixed with Co in cobalt carbonate. (Table 1).

[0017]

[Table 1]

Next, these mixtures are fired in air at 900 ° C. for 5 hours to obtain six types of positive electrode active materials A to A.
F was obtained.

Next, 100 parts by weight of the thus obtained positive electrode active material, 4 parts by weight of acetylene black, and 7 parts by weight of a fluororesin binder were mixed to form a positive electrode mixture. Into a paste.

This paste is applied to both sides of the aluminum foil,
After drying, rolling was performed to obtain positive plates A to F.

Further, the negative electrode plate was manufactured as follows.
10 parts by weight of a fluororesin binder was mixed with 100 parts by weight of the carbon material obtained by calcining the coke, 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. Using these positive electrode plate, negative electrode plate, polypropylene separator, and non-aqueous electrolyte, a sealed non-aqueous electrolyte secondary battery as shown in FIG.

Here, the non-aqueous electrolyte used was a solution prepared by dissolving lithium perchlorate at a ratio of 1 mol / l in an equal volume mixed solvent of propylene carbonate and ethylene carbonate.

In FIG. 1, a positive electrode plate and a negative electrode plate are spirally wound with a separator interposed therebetween to form an electrode group 1, and this positive electrode group 1 is formed in a battery case 2 made of a stainless steel sheet having resistance to organic electrolytic solution. It is stored in.

The upper part of the battery case 2 is sealed by a sealing plate 3 provided with a safety valve. A positive electrode lead 4 is drawn out from the positive electrode and is electrically connected to the sealing plate 3. A 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 disposed between the battery case 2 and the sealing plate 3, and an insulating ring 7 is disposed on the upper and lower surfaces of the electrode plate group 1.

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

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

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

Further, the capacity retention rate of the battery after the charge storage test at high temperature [(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), the capacity greatly decreased due to charge and discharge, and after 300 cycles, the capacity became half of the initial capacity.

On the other hand, in the batteries BF containing samarium, as the amount of samarium increased, the initial capacity of the battery decreased somewhat, but the decrease in capacity due to the charge / discharge cycle was significantly suppressed. .

In the batteries C to F containing 1 to 5 mol% of samarium with respect to cobalt in the lithium composite oxide, the battery capacity must be maintained at 80% or more of the initial capacity even after 300 cycles. Was completed.

However, in the battery F containing 8 mol% of samarium with respect to cobalt, LiCoO by samarium is used.
_Since the surface coverage of No. ₂ became too large, the reaction of the active material was extremely suppressed, so that the capacity of the battery was considerably reduced from the beginning.

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%, while the samarium was 1 mol% based on cobalt. In the batteries C to F containing 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 storage at high temperature was hardly changed.

From these results, the addition amount of samarium is preferably 5 mol% or less based on cobalt.

In this embodiment, L is used as the positive electrode active material.
iCoO ₂ was used, but in addition, L in which a part of Co was replaced with any of transition metals Ni, Fe, and Mn.
The same effect was obtained with the composite oxide of i.

In this embodiment, lithium carbonate (Li ₂ CO ₃ ), which is a carbonate of lithium and cobalt, and cobalt carbonate (CoC) were used as starting materials in the synthesis of the positive electrode active material.
O ₃ ) was used, but other than these, oxides of lithium and cobalt, or hydroxides and acetates thereof may also be used.

In this embodiment, a carbon material capable of intercalating / deintercalating lithium as an active material is used as a negative electrode constituting material. It may be a metal or a lithium alloy.

Further, as the electrolytic solution, a solution in which lithium perchlorate is dissolved in an equal volume mixed solvent of propylene carbonate and ethylene carbonate is used, but a solution in which a lithium salt is dissolved as a solute in another organic solvent may be used.

[0043]

As described above, in the non-aqueous electrolyte of the present invention, Li _(1-x) CoO ₂ (x is 0 ≦ x ₎ whose surface is covered with an oxide or a composite 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 lithium composite oxide is formed on the positive electrode active material under a high voltage. In this case, the decomposition reaction of the electrolyte solution and the collapse of the crystal of the positive electrode active material can be prevented, and the charge / discharge cycle life characteristics and the storage characteristics of the battery can be improved.

[Brief description of the 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 discharge capacity.

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

[Description of Signs] 1 Electrode group 2 Battery case 3 Sealing plate 4 Positive electrode lead 5 Negative electrode lead 6 Insulation packing 7 Insulation ring

Continuation of the front page (56) References JP-A-4-319259 (JP, A) JP-A-4-274164 (JP, A) Tsukamoto et al., “Lithium using lithium-cobalt composite oxide as positive electrode active material” Rechargeable Batteries, "Proceedings of the 31st Battery Symposium, pp. 125-126, November 1990 (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01M 4/02-4 / 04 H01M 4/52-4/58 H01M 10/40

Claims (5)

(57) [Claims] 1. A lithium composite oxide Li _(1-x) Co whose particles are covered with a samarium oxide or 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 electrolyte Non-aqueous electrolyte secondary battery. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the amount of samarium (Sm) added is 5% or less in molar ratio with respect to Co in the lithium composite oxide. 3. A lithium composite oxide Li.sub. _(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 made of <1); a negative electrode made of 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.
4. 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 amount of samarium (Sm) added is 5% or less in molar ratio with respect to Co in the lithium composite oxide.