JPH04319260A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To give a non-aqueous electrolyte secondary battery having high capacity, good cycle properties, and good high temperature storage properties by making the cathode active material better quality. CONSTITUTION:LiCoO2 or a composite oxide, which is the compound of which cobalt is partly substituted with a transition metal, to which zirconium is added is used as a cathode active mass powder. Consequently, cycle properties and high temperature storage properties of a secondary battery are remarkably improved.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to non-aqueous electrolyte secondary batteries,
In particular, it relates to improving the characteristics of batteries using lithium composite oxides as positive electrodes.

0002

[Prior Art] In recent years, electronic devices such as AV devices and personal computers have rapidly become portable and cordless. Demand for batteries is high. In this respect, non-aqueous secondary batteries, especially lithium secondary batteries, have high expectations as batteries with particularly high voltage and high energy density.

[0003] Layered compounds capable of intercalating and deintercalating lithium, such as LiCoO2, Li
NiO2 (e.g. U.S. Pat. No. 4,302,518) and Li
CoxNi1-xO2 (x≦0.27) (Unexamined Japanese Patent Publication No. 1986-
Composite oxides mainly composed of lithium and transition metals (hereinafter referred to as lithium composite oxides) such as No. 264560) have been proposed, and high energy density secondary The specific development of the battery is progressing.

0004

[Problem to be solved by the invention] Li1-xCoO2 (
0≦x<1) (hereinafter referred to as LiCoO2) exhibits a potential of 4 V or more with respect to lithium, and when used as a positive electrode active material, a secondary battery with high energy density can be realized. However, on the other hand, because of its high potential, it decomposes organic solvents such as propylene carbonate and dimethoxyethane that form the electrolyte, which adversely affects the charge and discharge characteristics of the battery and causes deterioration of battery characteristics. Ta. To solve this problem, some of the cobalt is replaced with nickel (Japanese Patent Application Laid-Open No. 63-299056), iron (Japanese Patent Application Laid-Open No. 63-211564), aluminum, tin, and indium (Japanese Patent Application Laid-Open No. 62-90863). It has been proposed that excellent charge-discharge characteristics can be obtained by synthesizing composite oxides and modifying the positive electrode active material. However, a lithium composite oxide in which a portion of cobalt is replaced with such an element tends to have a low discharge voltage, resulting in a reduction in the original characteristics of high voltage and high energy density. In addition, when such lithium composite oxide is stored at high temperature in a charged state, LiCoO2
Similarly, there still remains the problem of a significant reduction in capacity.

[0005] The present invention solves these problems by maintaining a high operating voltage and providing excellent charge/discharge characteristics.
The purpose is to provide a secondary battery with storage characteristics.

[0006]

[Means for Solving the Problems] In order to solve these problems, the present invention generates high voltage by adding lanthanum to LiCoO2, which is a positive electrode active material, and has excellent charge/discharge characteristics and storage characteristics. It has been discovered that a non-aqueous electrolyte secondary battery can be obtained.

[0007]

[Operation] When a battery using LiCoO2 as a positive electrode active material is stored in a charged state at a high temperature, the capacity and cycle characteristics of the battery after storage are extremely deteriorated. This is thought to be caused by decomposition of the electrolyte and destruction of the crystal structure. Suppressing the decomposition reaction and crystal destruction of the electrolyte on LiCoO2 at such a high potential is a very important point for a practical battery.

In the present invention, by adding lanthanum to LiCoO2, the surface of the LiCoO2 particles becomes lanthanum oxide (La2O3), a composite oxide of lithium and lanthanum (
It is stabilized by being covered with LiLaO2) or a composite oxide of lanthanum and cobalt (LaCoO3), and as a result, it does not cause electrolyte decomposition reactions or crystal destruction even at high potentials, and has excellent cycle and storage characteristics. This is because the positive electrode active material shown in FIG. Further, this effect cannot be obtained simply by mixing zirconium or a zirconium compound with LiCoO2.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below with reference to the drawings and specific examples.

[0010] Li2CO3 and CoCO3 are Li and Co
Zirconium oxide (ZrO2) was added to the mixture with an atomic ratio of 1:1, and the mixture was heated to 90% in air.
The material that was fired at 0° C. for 5 hours was used as a positive electrode active material. The addition ratio of zirconium oxide (ZrO2) is the mol% of zirconium to cobalt of the synthesized main active material LiCoO2.
As shown in Table 1, six types of studies were conducted.

[0011]

[Table 1]

[0012] Positive electrode active material 100 synthesized in this way
Parts by weight, 4 parts by weight of acetylene black, 4 parts by weight of graphite
parts by weight and 7 parts by weight of a fluororesin binder were mixed to prepare a positive electrode mixture, which was suspended in an aqueous carboxymethyl cellulose solution to form a paste. This paste was applied to both sides of aluminum foil, dried, and then rolled to form an electrode plate.

[0013] The negative electrode is a carbon material 100 made of fired coke.
10 parts by weight of a fluororesin binder was mixed with each part by weight, and the mixture was suspended in an aqueous carboxymethyl cellulose solution to form a paste. Then apply this paste to both sides of the copper foil,
After drying, it was rolled into an electrode plate.

FIG. 1 shows a longitudinal cross-sectional view of the cylindrical battery used in this example. The battery was constructed by attaching leads to each of the positive and negative electrodes, winding them in a spiral shape through a polypropylene separator, and storing them in a battery case. The electrolyte was prepared by dissolving lithium perchlorate at a ratio of 1 mol/l in an equal volume mixed solvent of propylene carbonate and ethylene carbonate, and the test battery was sealed.

In FIG. 1, numeral 1 indicates a battery case made of a stainless steel plate resistant to organic electrolytes, 2 a sealing plate provided with a safety valve, and 3 an insulating packing. Reference numeral 4 denotes a group of electrode plates, in which a positive electrode and a negative electrode are spirally wound through a separator and housed in a case. 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 out from the negative electrode and connected to the bottom of the battery case 1. Insulating rings 7 are provided at 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.
A constant current charge/discharge test was conducted under conditions of a charge end voltage of 4.1 V and a discharge end voltage of 3.0 V. Also, charge/discharge 10
After repeating the cycle, the battery was heated to 60°C and 20°C in the charged state.
A storage test (hereinafter referred to as high-temperature charging storage) was conducted for 1 day.
The capacity retention rate of the battery after storage was determined.

FIG. 2 shows the relationship between the number of charge/discharge cycles and the discharge capacity of batteries A to F at this time. Also, LiCoO2
The amount of zirconium added to the battery and the corresponding batteries A to F
FIG. 3 shows the relationship between the battery capacity retention rate (capacity after storage/capacity before storage) after the high temperature charging storage test.

From FIG. 2, although battery A to which no zirconium is added has a large initial discharge capacity, the capacity decreases significantly with charging and discharging, reaching 50% of the initial capacity at the 300th cycle. On the other hand, in batteries B to F with zirconium added, the capacity decreases as the amount added increases, but the capacity decrease due to charge/discharge cycles is significantly alleviated compared to battery A, and batteries with zirconium added of 5 mol% or more In D to F, the initial capacity is 8 even after 300 cycles.
It remains above 0%.

Furthermore, as shown in FIG. 3, by adding zirconium, the capacity retention rate of the battery after high-temperature storage is significantly improved, and while battery A with no zirconium added has a capacity retention rate of 52%, battery D with 5% zirconium added has a capacity retention rate of 52%. It showed more than 88%. Furthermore, even when the amount of zirconium added was increased, the capacity retention rate did not change much. Battery F with 10% zirconium added has good cycle characteristics and storage characteristics, but L
Since the surface coverage of iCoO2 increases, the discharge capacity becomes relatively small. Therefore, the appropriate amount of zirconium added is about 5%.

Part of the cobalt in LiCoO2 is replaced with nickel (Japanese Patent Application Laid-open No. 63-299056) and iron (Japanese Patent Application Laid-open No. 63-299056).
11564), aluminum, tin, and indium (JP-A-62-90863), it forms a solid solution with cobalt and LiMyCo1-yO2 (0≦y≦1
:M is a composite oxide represented by Ni, Fe, Al, etc.), so it cannot have the effect of stabilizing the surface like zirconium.

[0021] Furthermore, these composite oxides in which a part of cobalt was replaced with a transition metal had a drawback that the average voltage was small, but such a voltage drop was not observed in the case of adding zirconium. Therefore, zirconium can be said to be the optimal additive.

[0022] In this example, Li2CO3 and CoCO3 were used as starting materials for the synthesis of the positive electrode, but oxides, hydroxides, acetates, etc. of lithium and cobalt, respectively, may also be used. Although zirconium oxide was used as the zirconium to be added, other zirconium compounds may be used. Furthermore, although LiCoO2 was used as the positive electrode active material, a similar effect can also be observed with a compound in which part of the cobalt in the compound is replaced with a transition metal. Furthermore, although a carbonaceous material was used as the negative electrode, it may also be lithium metal or a lithium alloy. Furthermore, the electrolytic solution used was one in which lithium perchlorate was dissolved at a ratio of 1 mol/l in an equal volume mixed solvent of propylene carbonate and ethylene carbonate, but an electrolytic solution in which lithium salt was dissolved in another solvent was used. But it's the same.

[0023]

Effects of the Invention As is clear from the above explanation, according to the present invention, by adding an appropriate amount of zirconium to LiCoO2, which is a positive electrode active material, a non-aqueous electrolyte with excellent charge-discharge cycle characteristics and high-temperature storage characteristics can be obtained. A secondary battery can be obtained.

[Brief explanation of the drawing]

FIG. 1: A longitudinal cross-sectional view of a cylindrical battery in an embodiment of the present invention.

[Figure 2] Charging and discharging cycle characteristics diagram of the same battery at 20°C

[Figure 3] Relationship diagram between the amount of zirconium added and the corresponding capacity storage rate of batteries after high-temperature storage

[Explanation of symbols]

1 Battery case 2 Sealing plate 3 Insulating packing 4 Plate group 5 Positive electrode lead 6 Negative electrode lead 7 Insulation ring

Claims (2)

[Claims] Claim 1: Li1- added with zirconium (Zr)
A positive electrode made of xCoO2 (0≦x<1) or one in which a part of the cobalt is replaced with another transition metal, and a negative electrode made of lithium, a lithium alloy, or a carbonaceous material,
A non-aqueous electrolyte secondary battery consisting of a non-aqueous electrolyte. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the molar ratio of the zirconium to the cobalt is 1 to 10%.