JPH097596A - Negative electrode for nonaqueous electrolyte secondary battery and battery suing this negative electrode - Google Patents

Abstract

PURPOSE: To suppress forming a needle crystal in a negative electrode surface when charged/discharged with a large charge/discharge capacity per volume, by using a compound oxide represented by Lix CeO2 (0<=x<=1.0) as a negative electrode active material. CONSTITUTION: A battery comprises metal lithium 4 in contact bonding to inside a sealing plate 2, negative electrode 5, fine porous polypropylene-made separator 6, insulating gasket 7, etc. As a negative electrode active material, cerium chloride serves as a start substance, to be melted by adding thick hydrochloric acid to this substance, and to obtain nitrate in nitric acidic bath. After filtering, washing and drying deposited nitrate, selenium oxide, obtained by burning for four hours at 800 deg.C under circulating air, is used. A prescribed amount of compound, obtained by mixing 10 pts.wt. polyfluorovinylidene as a binder relating to 90 pts.wt. CeO2 , is formed on a collector 3, to be dried by reducing a pressure at 150 deg.C, thereafter to obtain the negative electrode. When carried a current in the metal lithium 4 in a discharge direction, lithium is melted also to store a lithium ion in the negative electrode 5, and to be charged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery and a high performance battery using the same, and more particularly to an improvement in capacity density per volume.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries are small and lightweight,
Moreover, since it has a high energy density, its expectations are increasing as the equipment becomes more portable and cordless. Conventionally, L has been used as a positive electrode active material for non-aqueous electrolyte secondary batteries.
Lithium-containing metal oxides such as i _x CoO ₂ and Li _x NiO ₂ have been proposed. On the other hand, as a negative electrode active material, metallic lithium, a lithium alloy, and a graphite material capable of inserting and extracting lithium ions have been proposed and partially put into practical use.

[0003]

However, in the conventional negative electrode using metallic lithium, metallic lithium is deposited as needle-like crystals on the surface of the negative electrode plate during charging, and the needle-like crystals pierce the separator. , In some cases, it may come into contact with the positive electrode to cause an internal short circuit. In order to solve this problem, a carbon material capable of occluding / releasing lithium has been studied for use in the negative electrode. In this case, carbon is theoretically C ₆ Li (6 carbon atoms to 6 Li atoms). The theoretical capacity is about 370 mAh / g, and the specific capacity of these carbon materials is small. Packing volume density per plate volume is approximately 480
Energy per volume staying around mAh / cc
It was difficult to increase efficiency.

The present invention solves such a problem and prevents metallic lithium from accumulating in the shape of needles on the surface of the negative electrode, and the filling capacity density per negative electrode volume when a graphite material is used. It is intended to provide a non-aqueous electrolyte secondary battery having a high energy density per volume by using a novel negative electrode active material that can be exceeded.

[0005]

The present invention has the general formula Li _x C.
Provided is a negative electrode for a non-aqueous electrolyte secondary battery using a composite oxide represented by eO ₂ (0 ≦ x ≦ 1.0) as an active material, and further, this negative electrode and an active material capable of inserting and extracting lithium. A high-performance non-aqueous electrolyte secondary battery is provided by constructing a battery including a positive electrode using a non-aqueous electrolyte solution in which a lithium salt is dissolved in an organic solvent, and solving the above problems. It is a thing.

[0006]

Function: Li _x CeO ₂ is monoclinic (space group P121 / c
1, lattice constant a ₀ is 5.824 angstrom (Å), b ₀ is 6.616 Å, c ₀ is 5.793 Å, β angle is 102.48 deg. ), In which movable lithium ions are housed in the interstitial position of the oxide unit composed of five-coordinate oxygen around the central Ce ion. The theoretical electric capacity obtained from the formula weight of this material is about 150 mAh / g assuming a one-electron reaction, but since the specific gravity is large, the apparent specific gravity when a negative electrode plate using this is made of a graphite material. Since it is as high as about 3.55 g / cc compared to 1.3 g / cc in the case where it is present, a large packing capacity density of the active material per volume of about 530 mAh / cc can be expected, and a high capacity of the negative electrode is possible. Becomes

Further, since the lithium ion storage / release reaction of Li _x CeO ₂ occurs at a potential nobler than the dissolution and deposition potential of metallic lithium, the deposition of lithium does not occur without passing through the potential for deposition of lithium.

Based on the above, Li _x Ce is used as the negative electrode active material.
By using O ₂ , it is possible to obtain a negative electrode with high volume efficiency in which lithium is not deposited on the surface of the negative electrode due to the charging reaction, and it is possible to provide a non-aqueous electrolyte secondary battery with high capacity and in which internal short circuit hardly occurs. Becomes

[0009]

EXAMPLE FIG. 1 shows a vertical sectional view of a battery for evaluating the characteristics of the negative electrode according to the present invention. In FIG. 1, 1 is a battery case made of a stainless steel plate resistant to organic electrolyte, 2 is a sealing plate made of the same material, and 3 is a current collector made of the same material.
It is spot welded to the inner surface of. Reference numeral 4 denotes metallic lithium, which is pressed inside the sealing plate 2. 5 is the negative electrode of the present invention, 6 is a microporous polypropylene separator, and 7 is a polypropylene insulating gasket. The battery for evaluation has a diameter of 20 mm and a total battery height of 1.6 mm.
It is. As the negative electrode active material, cerium chloride was used as a starting material, concentrated hydrochloric acid was added to and dissolved in the starting material, and then this was converted to a nitrate in a nitric acid acidic bath. Selenium oxide (CeO ₂ ) obtained by filtering, washing and drying the precipitated nitrate was used for 4 hours at 800 ° C. under air flow. Ce of negative electrode active material
A predetermined amount of a mixture obtained by mixing 10 parts by weight of polyvinylidene fluoride as a binder with 90 parts by weight of O ₂ was molded on the current collector 3 and dried under reduced pressure at 150 ° C.,
A battery was assembled using this as a negative electrode. The electrolytic solution was prepared by dissolving lithium perchlorate at a concentration of 1 mol / liter as a solute in an equal volume mixed solvent of ethylene carbonate and 1,3-dimethoxyethane. Lithium ions are electrochemically inserted into the negative electrode active material (CeO ₂ ) by assembling the battery and then charging the battery, so that the general formula Li _x CeO ₂ (0 ≦ x ≦ 1.
0).

Since the above-mentioned battery for evaluation is constructed to evaluate the charge / discharge performance of the negative electrode according to the present invention, when a current is passed in the discharging direction of the metallic lithium 4, the lithium is dissolved and the negative electrode of the present invention is dissolved. Lithium ions are stored in the battery 5 and charged. Further, when a current is passed in the discharging direction of the negative electrode 5 of the present invention, lithium ions are released and lithium is electrodeposited on the surface of the metallic lithium 4. This battery is constructed in a state of a large excess of metallic lithium 4 in terms of electric capacity, and the characteristics of the evaluation battery can be evaluated substantially as the characteristics of the negative electrode 5 of the present invention. 1.0 mA / cm at room temperature (20 ° C) for these evaluation batteries
² , the charge and discharge test was performed in the voltage range of 2.0V to 0V, and the discharge capacity and the cycle characteristics were examined. FIG.
In addition, an evaluation battery using the negative electrode of the present invention and a negative electrode prepared by the same compounding ratio and manufacturing method as the negative electrode of the present invention using a graphite material (carbon material heat-treated at 2900 ° C.) as a negative electrode active material as a comparative example. The discharge capacity, that is, the change in the negative electrode discharge capacity, with respect to the number of charge / discharge cycles of the evaluation battery was shown. As can be seen from FIG. 2, assuming that the discharge capacity when the conventional graphite material is used as the negative electrode active material is 100, a discharge capacity about 10% higher is obtained when the composite oxide of the present invention is used,
In the subsequent cycle test as well, it was found that the deterioration rate was similar to that of the conventional product, and that the characteristics with higher capacity than the conventional product were maintained.

Further, when the content of lithium in the negative electrode was examined, it was found that the Li _x CeO _{2 had} an X value of about 1.0 when charged to 0 V (a potential equal to the potential of the metal lithium electrode). However, even when discharged to 2 V (with respect to the potential of the metal lithium electrode), the X value does not return to 0, and about 0.2 lithium remains in the negative electrode active material. Remaining of lithium in the negative electrode during this initial charge / discharge cycle also occurs when graphite is used. Therefore, although the capacity is slightly deteriorated from the next cycle, the X value is about 0.2 to 0.3 to 1.0.
It is possible to obtain a discharge capacity equivalent to that of the conventional graphite material, which is larger than that of a conventional graphite material. Therefore,
When the amount of lithium that moves by occlusion / release when the composite oxide of the present invention is used as a negative electrode is expressed by an X value, 0 ≦ x
It is specified by ≦ 1.0. In addition, acicular lithium was not observed on the surface of the negative electrode after charging the battery using this composite oxide.

Li _x CeO _{2 of the} present invention (0≤x≤1.0)
When the negative electrode using the active material as the active material is charged and discharged at 0.2 mA / cm ² , the flat portion of the charging potential is about 0.5 V and the flat portion of the discharging potential is about 0.7 V with respect to the potential of metallic lithium. Indicates a value. Therefore, for example, this negative electrode and LiCoO ₂ (1.
When a positive electrode having O ≧ x ≧ 0) as an active material is combined, a non-aqueous electrolyte secondary battery having an average discharge voltage of about 3.5 V can be formed.

The negative electrode active material in the present invention is Li
_In addition to _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x
It can be widely applied to so-called rocking chair type non-aqueous electrolyte secondary batteries that use a positive electrode active material capable of inserting and extracting lithium such as Mn ₂ O ₄ , and is extremely effective in improving the performance of these batteries. is there.

[0014]

As described above, according to the present invention, the general formula Li _x C
By using the composite oxide represented by eO ₂ (0 ≦ x ≦ 1.0) as the negative electrode active material, the charge / discharge capacity per volume is large, and the acicular crystals on the surface of the negative electrode accompanying the charge / discharge reaction are formed. Provided is a negative electrode for a non-aqueous electrolyte secondary battery capable of suppressing formation, and by using this negative electrode, it is possible to provide a high-performance battery having a large capacity, excellent charge / discharge characteristics, and less likely to cause an internal short circuit. .

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a battery for evaluating a negative electrode.

FIG. 2 is a diagram showing charge-discharge cycle characteristics of a negative electrode.

[Explanation of symbols]

 1 Battery Case 2 Sealing Plate 3 Current Collector 4 Metal Lithium 5 Negative Electrode 6 Separator 7 Gasket

Claims (2)

[Claims] 1. An active material of the general formula Li _x CeO ₂ (0 ≦
A negative electrode for a non-aqueous electrolyte secondary battery, characterized by using a composite oxide represented by x ≦ 1.0). 2. A positive electrode using an active material capable of occluding and releasing lithium, and a general formula Li _x CeO ₂ (0 ≦ x ≦
A non-aqueous electrolyte secondary battery comprising a negative electrode using the composite oxide represented by 1.0) and a non-aqueous electrolyte in which a lithium salt is dissolved in an organic solvent.