JPH05174872A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To obtain a high voltage and a high energy intensity, and to prevent a deterioration of the battery performance even in an overdischarging, by forming a positive electrode with a lithium-including oxide as the main component, and a negative electrode with a carbonaceous material in which a lithium- including oxide is added and mixed as the main component. CONSTITUTION:This nonaqueous secondary battery is provided with a positive electrode 5 mainly of a lithium-including oxide, a negative electrode 6 mainly of a carbonaceous material to which a lithium-including oxide is added and mixed, and a nonaqueous electrolyte. The lithium-including oxide consists of LiCoO2, LiNiO2, LiFeO2, and LiMn2O4. In this case, a lithium-including oxide in which the Co, Ni, Fe, and Mn are replaced by other transition metals can be used to obtain the same effect. Consequently, a deterioration of the battery performance after an overdischarging can be prevented, and the over-discharge resisting property can be improved.

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.

[0002]

2. Description of the Related Art In recent years, portable electronic devices for consumer use,
With the progress of cordless technology, it has been demanded that the battery for the driving power source be small, lightweight and have high energy density. From this point of view, non-aqueous secondary batteries, especially lithium secondary batteries, are highly expected to be developed as batteries having high voltage and high energy density.

In the conventional lithium secondary battery, manganese dioxide, vanadium pentoxide, titanium disulfide, etc. are used as the positive electrode active material, lithium is used as the negative electrode, and an organic electrolytic solution is used as the electrolytic solution. However, in general, a secondary battery using lithium metal for the negative electrode has problems such as an internal short circuit due to dendrite-like lithium generated at the time of charging and a side reaction between the active material and the electrolytic solution, which is a major problem in forming a secondary battery. It was an obstacle. Further, no satisfactory one was found in the high rate charge / discharge characteristics and the overdischarge characteristics.

In recent years, the safety of lithium batteries has been pointed out severely, and ensuring safety is a problem in battery systems using lithium metal or lithium alloy for the negative electrode.

On the other hand, a new type of electrode active material utilizing the intercalation reaction of a layered compound has been attracting attention, and a graphite intercalation compound has been used as an electrode material for secondary batteries for a long time. In particular, ClO ₄ ^-, PF ₆ ^-,
A graphite layer compound incorporating anions such as BF ₄ ⁻ ions is used as the positive electrode.

On the other hand, graphite intercalation compounds incorporating cations such as Li ⁺ and Na ⁺ are considered as negative electrodes.
Especially carbon (graphite) that forms an intercalation compound with Li
Theoretically has a capacity of 372 mAh / g (C ₆ Li), and is therefore attracting attention as a negative electrode material for lithium secondary batteries, and its research and development has been actively conducted.

Further, since a carbon material is used for the negative electrode, the positive electrode active material has a higher voltage and Li
It has been proposed to use a compound containing LiCoO ₂ or LiMn ₂ O ₄ , and further a composite oxide in which some of Co and Mn are replaced with other elements.

A non-aqueous electrolyte secondary battery using a lithium-containing oxide such as LiCoO ₂ as a positive electrode and a carbon material capable of forming an intercalation compound with Li as a negative electrode has a high voltage close to 4 V and high energy. It is possible to obtain a secondary battery having a high density. However, when this battery system is over-discharged to 0 V, the original capacity is not restored even if the battery is charged again, and the cycle deterioration in the subsequent charge / discharge becomes significant.
This was traced to the positive and negative unipolar behavior during overdischarge, and both polarities at 0 V reached 2.5 with respect to the Li potential.
Although it is near V, the potentials of both electrodes change with the lapse of time thereafter, and are induced by the potential on the positive electrode side to reach 3V or more. Therefore, the current collector used for the negative electrode, such as copper, is dissolved and deposited on the surfaces of the separator and the positive electrode. Further, when the carbon material of the negative electrode is held at a potential of approximately 3 V or higher, the crystal structure is destroyed due to the influence of anion intercalation. Therefore, even if the battery is charged again, it becomes difficult to intercalate Li and the capacity deterioration becomes remarkable.

Generally, in a lithium secondary battery composed of a positive electrode made of a lithium-containing oxide such as LiCoO ₂ and a negative electrode made of a carbon material, the lithium source is limited to lithium contained in the positive electrode. At the time of discharging, especially at the time of over-discharging, Li does not exist in the negative electrode carbon material, so that the potential of the negative electrode is induced on the positive electrode side and reaches 3 V or more. Therefore, the potential of the negative electrode during overdischarge is 3V
In order to maintain the base electric potential below, Li was previously added to the negative electrode carbon material.
Attempts have been made to occlude. For example, a method of electrochemically intercalating Li, a method of chemically intercalating Li by a gas phase or solid phase reaction, and the like can be considered. However, in any of these methods, the burden on the process is large, and the carbon material in which Li is intercalated is extremely unstable, and its handling is difficult.

[0010]

The problem of the non-aqueous electrolyte secondary battery using the conventional positive electrode made of a lithium-containing oxide and the negative electrode made of a carbon material is that when the battery is over-discharged, it is charged again. Is that the original capacity is not restored and the battery characteristics are deteriorated.

The present invention solves this conventional problem, and easily provides a non-aqueous electrolyte secondary battery which has a high voltage and a high energy density and does not cause deterioration of the battery characteristics even if it is over-discharged. This is the purpose.

[0012]

In order to solve the above-mentioned problems, the present invention provides a positive electrode mainly composed of a lithium-containing oxide and a negative electrode mainly composed of a carbonaceous material to which a lithium-containing oxide is added and mixed. , A non-aqueous electrolyte secondary battery including a non-aqueous electrolyte.

[0013]

Since the present invention has the above-mentioned structure, the potential of the negative electrode during over-discharging can be maintained at a base potential of 3 V or less.
Therefore, side reactions such as dissolution of the current collector of the negative electrode and destruction of the crystal structure of the carbon material can be prevented, the original state can be restored by recharging, and no deterioration in battery characteristics can be seen. In addition, since lithium-containing oxide, particularly lithium-containing oxide similar to or different from that of the positive electrode, is added to and mixed with the carbon material instead of occluding Li in the negative electrode material in advance, there is no inconvenience in the electrode manufacturing process. It is stable in the atmosphere and easy to handle. In this respect, the method of handling lithium itself is quite different in the process.

The negative electrode carbon material used in the present invention is preferably a graphitizable material and a relatively graphitized material in order to reversibly and easily intercalate / deintercalate Li. If it shows, a high temperature calcined body of coke can be mentioned. Further, carbon fibers such as vapor grown carbon fibers and mesophase pitch carbon fibers can also be used.

On the other hand, as the lithium-containing oxide to be added to the positive electrode and the negative electrode, for example, LiCoO ₂ can be easily prepared by using a carbonate or oxide of lithium or cobalt as a raw material and mixing and firing them according to the target composition. Obtainable. Of course, similar synthesis can be performed when other raw materials are used. Usually, the firing temperature is 650 ° C to 12
It is set between 00 ° C. Other lithium-containing oxides can also be synthesized by the method according to the above.

[0016]

EXAMPLES The present invention will be described in detail below with reference to examples.
FIG. 1 shows a vertical sectional view of a cylindrical battery used in one embodiment of the present invention. In the figure, 1 is a battery case formed by processing a stainless steel plate resistant to organic electrolyte, 2 is a sealing plate provided with a safety valve, and 3 is an insulating packing. Reference numeral 4 denotes an electrode plate group, in which the positive electrode and the negative electrode are spirally wound a plurality of times with a separator interposed therebetween and are housed in the case 1. Then, the 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 on the upper and lower portions of the electrode plate group 4, respectively. The positive and negative electrode plates, the electrolytic solution and the like will be described in detail below.

For the positive electrode, LiCoO ₂ was prepared by mixing Li ₂ CO ₃ and CO ₃ O ₄ and firing at 900 ° C. for 10 hours.
100 parts by weight of powder of acetylene black, 3 parts by weight of
4 parts by weight of graphite and 7 parts by weight of a fluororesin-based binder were mixed and suspended in a carboxymethylcellulose aqueous solution to form a paste. This paste is applied to both sides of 0.03 mm thick aluminum foil, dried and rolled to a thickness of 0.18 m.
m, width 40 mm, length 260 mm.

The negative electrode was the same as that used for the positive electrode in 100 parts by weight of petroleum coke heat-treated at 2800 ° C.
5 parts by weight of a fluororesin-based binder was mixed with a mixture of 5 parts by weight of iCoO ₂ , and the mixture was suspended in an aqueous carboxymethyl cellulose solution to form a paste. This paste is applied to both sides of a 0.02 mm thick copper foil, dried and rolled to a thickness of 0.19 mm, a width of 40 mm and a length of 280 mm.
It was used as an electrode plate.

Leads are attached to each of the positive and negative plates, and the thickness is 0.025 mm, the width is 46 mm, and the length is 700 mm.
It was wound in a spiral shape through the polypropylene separator of No. 1 and was housed in a battery case having a diameter of 13.8 mm and a height of 50 mm to obtain a battery of an example of the present invention. As the electrolytic solution, a solution prepared by dissolving lithium perchlorate in a mixed solvent of equal volume of propylene carbonate and ethylene carbonate at a rate of 1 mol / liter was used.

The over-discharge characteristics were evaluated by the following test method. First, a battery was constructed and a constant current charge / discharge of 100 mA at 20 ° C. was repeated 50 cycles. The end-of-charge voltage is 4.1
V and the final voltage of discharge were set to 3.0V. Then, the battery was placed in a discharged state and further subjected to constant resistance discharge of 1 kΩ, and the battery was allowed to stand for another 2 weeks in a state where the battery voltage was 0V. Then, the constant current charge / discharge of 100 mA was repeated again for 50 cycles.
Here, the capacity recovery and cycle characteristics were compared before and after over-discharge. The battery after over-discharging was disassembled, and the electrode plate, separator, etc. were observed and analyzed.

On the other hand, as a conventional example for comparison with the examples of the present invention, the petroleum coke used in the examples of the present invention was used for the negative electrode, and a lithium-containing oxide was not added at all to obtain a negative electrode plate. Other than that, the battery was constructed exactly as in the example of the present invention, and the battery of the conventional example was obtained.

FIG. 2 shows a comparison of cycle characteristics before and after over-discharging of the batteries of the example of the present invention and the conventional example. With the battery of the conventional example, the capacity recovers only 50% after over discharge,
Subsequent cycle characteristics also deteriorate significantly. However, in the batteries of the examples of the present invention, the capacity after overdischarge was 95
It can be seen that the cycle recovers up to%, and the cycle deterioration thereafter is extremely small.

Further, when the battery after over-discharging was disassembled and analyzed, in the battery of the conventional example, copper as the negative electrode current collector was dissolved and deposited on the surfaces of the separator and the positive electrode plate. On the other hand, no noticeable change was observed in the batteries of Examples of the present invention, and copper was not detected in the separator and the positive electrode plate.

In the examples of the present invention, LiCoO ₂ was added to the negative electrode, but LiNiO ₂ , LiFeO ₂ , LiMn ₂ were added.
Similar effects were obtained when O ₄ was added.

In the embodiment of the present invention, the positive electrode is made of LiCo.
O ₂ was used, but the above-mentioned other lithium-containing oxides or C
Similar effects are obtained when a lithium-containing oxide in which a part of o, Ni, Fe, Mn, etc. is replaced with another transition metal is used, and further, when the oxide added to the positive electrode active material and the oxide added to the negative electrode are different. Was obtained.

[0026]

As is apparent from the above description of the embodiments of the present invention, the non-aqueous electrolyte secondary battery of the present invention in which a lithium-containing oxide similar to or different from the positive electrode is added to and mixed with the negative electrode carbon material is By maintaining the negative electrode potential during over-discharging at a base potential, it is possible to prevent the deterioration of characteristics after over-discharging and to improve the over-discharge resistance.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a comparison of cycle characteristics between a cylindrical battery according to one embodiment of the present invention and a cylindrical battery according to a conventional example.

[Explanation of symbols]

 1 Battery Case 2 Sealing Plate 3 Insulation Packing 4 Electrode Plate Group 5 Positive Electrode Lead 6 Negative Electrode Lead 7 Insulation Ring

Claims (4)

[Claims] 1. A positive electrode containing a lithium-containing oxide as a main component,
A non-aqueous electrolyte secondary battery comprising a negative electrode mainly composed of a carbonaceous material mixed with a lithium-containing oxide, and an electrolyte mainly composed of an organic electrolyte. 2. LiCoO ₂ , LiNiO ₂ , LiFeO
_2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode is composed mainly of one or more lithium-containing oxides selected from the group consisting of ₂ and LiMn ₂ O ₄ . 3. LiCoO ₂ , LiNiO ₂ , LiFeO
_{3. The} positive electrode mainly composed of one or more lithium-containing oxides selected from the group consisting of substituting a part of each of ₂ and LiMn ₂ O ₄ with another transition metal. Non-aqueous electrolyte secondary battery. 4. LiCoO ₂ , LiNiO ₂ , LiFeO
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the negative electrode is composed mainly of a carbonaceous material mixed with a lithium-containing oxide selected from the group consisting of ₂ and LiMn ₂ O ₄ .