JP2855877B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery,
In particular, it relates to improvement of characteristics of a battery using a lithium composite oxide for a positive electrode.

[0002]

2. Description of the Related Art In recent years, portable devices and cordless electronic devices such as AV devices and personal computers have been rapidly developed, and secondary power sources having a small size, light weight and high energy density are used as power sources for driving these devices. Demand for batteries is high. In this respect, non-aqueous secondary batteries, especially lithium secondary batteries, are expected to have high voltage and high energy density.

[0003] As a positive electrode active material satisfying this demand, a layered compound capable of intercalating and deintercalating lithium, for example, LiCoO ₂ , Li
NiO ₂ (eg, US Pat. No. 4,302,518) or Li
Co _x Ni _1-x O ₂ (x ≦ 0.27) (JP-A-62-26)
No. 4560) and other composite oxides mainly composed of lithium and a transition metal (hereinafter referred to as lithium composite oxides). Using these active materials, a high-energy-density secondary having a voltage of 4 V class has been proposed. The practical development of batteries is underway.

[0004]

SUMMARY OF THE INVENTION Li _1-x CoO ₂ (0 ≦
x <1) (hereinafter referred to as LiCoO ₂ ) shows a potential of 4 V or more with respect to lithium, and a secondary battery having a high energy density can be realized when used as a positive electrode active material. However, on the contrary, since the potential is high, an organic solvent such as propylene carbonate or dimethoxyethane that forms an electrolytic solution is decomposed, thereby adversely affecting the charge / discharge characteristics of the battery and causing deterioration of the battery characteristics. Was. To solve such a problem, part of cobalt is replaced by nickel (Japanese Patent Application Laid-Open No. 63-299056).
), Iron (JP-A-63-212564), aluminum, tin, and indium (JP-A-62-90863) to synthesize a composite oxide, which is improved by modifying the positive electrode active material. It has been proposed that discharge characteristics can be obtained. However, a lithium composite oxide in which cobalt is partially substituted with such an element tends to have a low discharge voltage, which results in a reduction in the inherent characteristics of high voltage and high energy density. Further, such a lithium composite oxide, when stored at a high temperature in a charged state, has a LiCoO 2
_{As in 2} , the problem that the capacity is significantly reduced still remains.

An object of the present invention is to solve the above-mentioned problem, and an object of the present invention is to provide a secondary battery which maintains a high operating voltage and has excellent charge / discharge characteristics and storage characteristics.

[0006]

SUMMARY OF THE INVENTION In order to solve these problems, the present invention provides a high voltage, excellent charge / discharge characteristics and excellent storage characteristics by adding zirconium to LiCoO ₂ as a positive electrode active material. It has been found that a nonaqueous electrolyte secondary battery exhibiting characteristics can be obtained.

[0007]

When a battery using LiCoO ₂ as a positive electrode active material is stored at a high temperature in a charged state, the capacity and cycle characteristics of the battery after storage are extremely deteriorated. This is considered to be caused by decomposition of the electrolyte and destruction of the crystal structure. It is a very important point for a practical battery to suppress the decomposition reaction and crystal destruction of the electrolytic solution on LiCoO _{2 at} such a high potential.

[0008] The present invention is by adding a zirconium LiCoO _2, is stabilized by the surface of the LiCoO ₂ particles are covered with the composite oxide Li ₂ ZrO ₃ with zirconium oxide ZrO ₂ or lithium and zirconium, as a result This is because a positive electrode active material exhibiting excellent cycle characteristics and storage characteristics can be obtained without causing decomposition reaction or crystal destruction of the electrolytic solution even at a high potential. In addition, this effect can not be obtained simply by mixing zirconium or a zirconium compound with LiCoO ₂ after firing , but by mixing a lithium salt with a cobalt compound.
By adding zirconium and firing
It is obtained.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the drawings according to specific embodiments.

[0010] Zirconium oxide (ZrO ₂ ) is added to a mixture of Li ₂ CO ₃ and CoCO _{3 so} that the atomic ratio of Li to Co is 1 to 1, and 900 in air.
The material fired at 5 ° C. for 5 hours was used as a positive electrode active material. The addition ratio of zirconium oxide (ZrO ₂ ) is represented by mol% of zirconium with respect to the cobalt of the synthesized main active material LiCoO ₂ , and six kinds of studies were performed as shown in Table 1.

[0011]

[Table 1]

The positive electrode active material 100 synthesized as described above
Parts by weight, acetylene black 4 parts by weight, graphite 4
By weight, 7 parts by weight of a fluororesin binder was mixed to prepare a positive electrode mixture, and the mixture was suspended in an aqueous solution of carboxymethyl cellulose to form a paste. The paste was applied on both sides of an aluminum foil, dried and rolled to obtain an electrode plate.

The negative electrode is made of carbon material 100 obtained by firing coke.
10 parts by weight of a fluororesin binder was mixed with the parts by weight and suspended in an aqueous solution of carboxymethyl cellulose to form a paste. And apply this paste on both sides of the copper foil,
After drying, it was rolled to obtain an electrode plate.

FIG. 1 is a longitudinal sectional view of a cylindrical battery used in this embodiment. The battery was constructed such that a lead was attached to each of the positive and negative electrodes, spirally wound through a polypropylene separator, and housed in a battery case. As the electrolytic solution, 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 was used, and the sealed battery was used as a test battery.

In FIG. 1, reference numeral 1 denotes a battery case made of a stainless steel sheet having resistance to organic electrolyte, 2 denotes a sealing plate provided with a safety valve, and 3 denotes an insulating packing. Reference numeral 4 denotes an electrode plate group, in which a positive electrode and a negative electrode are spirally wound via a separator and housed in a case. Then, a positive electrode lead 5 is pulled out from the positive electrode and connected to the sealing plate 2,
A negative electrode lead 6 is drawn from the negative electrode and connected to the bottom of the battery case 1. Reference numeral 7 denotes an insulating ring provided on the upper and lower portions of the electrode plate group 4, respectively.

These test batteries were charged and discharged at a current of 100 mA.
h, a constant current charge / discharge test was performed under the conditions of a charge end voltage of 4.1 V and a discharge end voltage of 3.0 V. In addition, charge and discharge
After repeating the cycle, the battery is charged at 60 ° C. and 20 ° C.
Day storage test (hereinafter referred to as high temperature charge storage)
The capacity retention of the battery after storage was determined.

FIG. 2 shows the relationship between the number of charge / discharge cycles and the discharge capacity of the batteries A to F at this time. In addition, LiCoO ₂
Of Zirconium to Battery and Batteries A to F Corresponding to It
FIG. 3 shows the relationship between the battery capacity retention rate (capacity after storage / capacity before storage) after the high-temperature charge storage test.

FIG. 2 shows that the battery A to which no zirconium is added has a large initial discharge capacity, but has a large capacity decrease due to charge / discharge, and becomes 50% of the initial capacity at 300 cycles. On the other hand, in the batteries B to F to which zirconium is added, the capacity decreases as the addition amount increases. In D to F, the initial capacity is 8 even at the time of 300 cycles.
Maintain 0% or more.

Further, from FIG. 3, by adding zirconium, the capacity retention rate of the battery after high-temperature storage is remarkably improved, and the battery A without added zirconium is 52%, while the battery D with 5% added. Showed 88% or more.
Further, even when the amount of zirconium added was increased, the capacity retention did not change much. Battery F containing 10% zirconium has good cycle characteristics and storage characteristics,
Since the surface coverage of iCoO ₂ increases, the discharge capacity becomes relatively small. For this reason, the addition amount of zirconium is suitably about 5%.

A part of the cobalt of LiCoO ₂ is replaced with nickel (JP-A-63-299056) and iron (JP-A-63-2990).
11564 No.), aluminum, tin, when substituted with indium (JP _{62-90863), LiM y Co 1-} y O 2 to form cobalt and solid solution (0 ≦ y ≦ 1: M
Is a composite oxide represented by Ni, Fe, Al, etc.), so that an effect such as zirconium for stabilizing the surface cannot be obtained.

Further, these composite oxides in which a part of cobalt is replaced by a transition metal have a disadvantage that the average voltage is reduced, but when zirconium is added, such a voltage drop is not recognized. Therefore, zirconium can be said to be the optimal additive.

Although Li ₂ CO ₃ and CoCO ₃ are used as starting materials in the synthesis of the positive electrode in this embodiment, they may be oxides, hydroxides and acetates of lithium and cobalt, respectively. . Although zirconium oxide is used for zirconium to be added, other zirconium compounds may be used. In addition, although LiCoO ₂ was used as the positive electrode active material, the same effect can be obtained with a compound in which a part of cobalt in the compound is replaced with a transition metal. Further, although a carbonaceous material was used as the negative electrode, it may be a lithium metal or a lithium alloy. Further, as the electrolytic solution, 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 was used. However, an electrolytic solution obtained by dissolving a lithium salt in another solvent was used. But the same is true.

[0023]

As is apparent from the above description, according to the present invention, by adding an appropriate amount of zirconium to LiCoO ₂ as a positive electrode active material, a non-aqueous electrolyte having excellent charge-discharge cycle characteristics and high-temperature storage characteristics can be obtained. A liquid secondary battery can be obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a cylindrical battery according to an embodiment of the present invention.

FIG. 2 is a charge / discharge cycle characteristic diagram of the battery at 20 ° C.

FIG. 3 is a diagram showing the relationship between the amount of zirconium added and the capacity retention rate after high-temperature storage of the battery corresponding thereto.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Insulation packing 4 Electrode group 5 Positive electrode lead 6 Negative electrode lead 7 Insulation ring

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01M 4/58 H01M 4/02 H01M 10/40

Claims (2)

(57) [Claims] 1. Li _1-x containing zirconium (Zr)
A positive electrode composed of CoO ₂ (0 ≦ x <1) or a substance obtained by substituting a part of cobalt thereof with another transition metal; a negative electrode composed of lithium, lithium alloy or carbonaceous material;
A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the zirconium is added in a molar ratio of 1 to 10% with respect to the cobalt.