JPH09232002A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the destruction of an electrode following a charging/ discharging cycle, to improve high capacity, long time reliability, and battery capacity, by constituting a battery of a positive electrode composed of a metallic oxide containing Li and Ni, a negative electrode composed of iron oxide doping/ dedoping the Li and a nonaqueous electrolyte. SOLUTION: Slurry; wherein a positive electrode mixture, obtained by mixing (a metallic oxide containing the Li and Ni in a formula LiNix M(1-x) O2 (0.5<=x<=0.95, M: transition metals and/or Al), a conductive agent, and a binding agent), is dispersed in a solvent; is dried and powdered, and then compressedly formed together with a carrier to obtain a positive electrode 1. The positive electrode 1 is put into an aluminum clad can 3, and thereon a separator 4 is placed to inject a nonaqueous electrolyte. Then, a negative electrode 2; composed of iron oxide for doping/dedoping the Li, the conductive agent, and the binding agent; is placed onto the separator 4 to be sealed by an insulating gasket 5 and an anode cup 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion secondary battery used as a power source for portable electronic equipment.

[0002]

2. Description of the Related Art Due to recent remarkable progress in electronic technology, electronic devices have been reduced in size, weight and performance, and secondary batteries having high energy density are required for these electronic devices. Conventionally, nickel-cadmium batteries and lead batteries have been used as secondary batteries used in these electronic devices. However, these batteries are insufficient in terms of obtaining batteries having a high energy density.

Under such circumstances, research and development of a non-aqueous electrolyte secondary battery using lithium or a lithium alloy for the negative electrode and a lithium complex oxide such as a lithium cobalt complex oxide for the positive electrode are being conducted. . This lithium secondary battery is
It has high energy density, little self-discharge, and light weight. However, since the lithium secondary battery is accompanied by dissolution and deposition of metallic lithium during charging and discharging, lithium deposited on the negative electrode during charging may grow into dendrite-like crystals and reach the positive electrode, that is, an internal short circuit may occur. Further, this probability tends to increase with the progress of charge / discharge cycles, which is not preferable from the viewpoint of safety and reliability, which is a major obstacle to practical use.

As a battery system that overcomes the problems of such a lithium secondary battery having metal lithium as a negative electrode,
There is a lithium-ion secondary battery. This battery is a so-called rocking chair type battery system in which lithium ions move back and forth between the positive electrode and the negative electrode. Since lithium ions can be stored in the negative electrode material, metallic lithium is not deposited. Therefore, good charge / discharge cycle characteristics and safety are exhibited. In addition, this lithium-ion secondary battery is also excellent in rapid charge / discharge characteristics and low-temperature characteristics, as compared with lithium secondary batteries.

[0005]

Currently available lithium-ion batteries include those using lithium cobalt oxide for the positive electrode and a carbon material for the negative electrode, which are operated at 4V level. Indicates the voltage. However, as a portable power source, it is expected that the driving voltage of electronic devices will decrease due to the progress of electronic technology in the future, and along with this, it is more likely than the current lithium ion secondary batteries such as 3V class and 2V class. There is a demand for a battery system having a low operating voltage.

Various usable materials have been reported as the negative electrode material of the battery system, but iron oxides are attracting attention because they are particularly abundant as resources. In Japanese Patent Laid-Open No. 3-11070, a lithium ion using iron oxide as a negative electrode material and LiCoO ₂ (lithium / cobalt oxide) or LiMn ₂ O ₄ (lithium / manganese oxide) as a positive electrode material. Secondary batteries have been proposed.

However, in a battery using iron oxide for the negative electrode and lithium cobalt oxide for the positive electrode, 4.2 V
The discharge capacity at constant voltage current is as large as 135 mAh / g,
Although a relatively large battery capacity was obtained, the electrodes were destroyed as the cycle progressed, and a sufficient cycle life was not obtained. In secondary batteries that use lithium-cobalt oxide for the positive electrode and iron oxide for the negative electrode, the iron oxide expands during charging and contracts during discharging, while the lithium-cobalt oxide for the positive electrode also expands during charging. Since it greatly expands and contracts during discharge, the positive electrode and the negative electrode collide with each other during charging, and the electrode breaks down as the cycle progresses.

Although manganese is richer in resources than cobalt, a battery using lithium manganese oxide for the positive electrode has a discharge capacity of 120 at a constant voltage of 4.2V.
As small as mAh / g, it is not satisfactory in terms of battery capacity.

The present invention has been made in view of the above-mentioned problems, and suppresses the destruction of the electrodes due to the progress of charging / discharging cycles, realizes a long cycle life, and increases the capacity of the battery. An object of the present invention is to provide a highly safe non-aqueous electrolyte secondary battery having long-term reliability and high battery capacity.

[0010]

A non-aqueous electrolyte secondary battery according to the present invention comprises a positive electrode made of a metal oxide containing at least lithium and nickel, and a negative electrode made of an iron oxide doped with lithium and dedoped. , A non-aqueous electrolyte solution.

In the non-aqueous electrolyte secondary battery according to the present invention, the crystal lattice of the iron oxide used for the negative electrode expands during charging,
In contrast to contraction during discharge, the crystal lattice of the lithium-nickel-based oxide used for the positive electrode contracts during charge and expands during discharge, so that expansion and contraction of the crystal lattices of each other is relaxed. Further, the total volume of the positive electrode and the negative electrode during charge / discharge does not change so much. As a result, the destruction of the electrode due to the progress of the charging / discharging cycle is suppressed, and a long cycle life can be realized.

Further, the lithium-nickel oxide is
Since the capacity per unit weight is larger than that of lithium / cobalt oxide or lithium / manganese oxide, the capacity of the battery can be increased. Further, nickel is rich in resources as compared with cobalt, and thus has a great industrial value.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A non-aqueous electrolyte secondary battery according to the present invention comprises a positive electrode made of a lithium-nickel metal oxide containing lithium and at least Ni, and an iron oxide for doping and dedoping lithium. It consists of a negative electrode made of a material and a non-aqueous electrolyte.

The positive electrode made of the above-mentioned lithium-nickel oxide is LiNi _x M _(1-x) O ₂ (0.5≤x≤0.9 _).
When represented by 5), M is preferably at least one selected from transition metals and Al. As the transition metal, Co, Mn, Fe, Ti and V are more preferable.

In LiNi _x M _(1-x) O ₂ , 0.95
When ≦ x ≦ 1 (including LiNiO ₂ ), it is desirable to regulate the charging voltage to 4.1 V on the basis of the lithium reference electrode. This is LiN in the potential range of 4.1V to 4.2V.
This is because the crystal structure of iO ₂ changes and the charge capacity thereof is significantly attenuated when the charge / discharge cycle is repeated.

Further, as the iron oxide as the negative electrode material,
FeO, Fe ₂ O ₃ and Fe ₃ O ₄ are typical. Further, as its crystal system, α-Fe ₂ O ₃ , γ-Fe ₂ O ₃ , η-
Fe ₂ O ₃ exists, and various crystal forms can be obtained depending on the adjusting method, the starting material, and the like. Among them, α-Fe ₂ O ₃ is
In the composition formula of Li _x Fe ₂ O ₃ , lithium of 0 ≦ x ≦ 6 can be doped and dedoped, and a large capacity can be expected.

As the non-aqueous electrolyte, an electrolyte in which a lithium salt is used as an electrolyte and this is dissolved in an organic solvent is used.
Here, the organic solvent is not particularly limited, but for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-dicarbonate. Ethoxyethane, γ-butyrolactone, tetrahydrofuran,
A single solvent or a mixed solvent of two or more kinds of 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile and the like can be used. As the electrolyte, one or more kinds of electrolytes can be mixed and used as long as they are used in this type of battery, and LiPF ₆ is preferable, but L
iClO ₄ , LiAsF ₆ , LiBF ₄ , LiB (C
₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiC
l, LiBr, etc. can also be used.

By the way, as shown in FIG.
The nickel-based oxide (Li _x NiO ₂ ) contracts when lithium is undoped (charged) and expands when doped (discharged), and lithium-cobalt oxide (Li _x CoO ₂ ) dedoped lithium on the contrary. It expands when it is charged and contracts when it is discharged. On the other hand, as shown in FIG.
The iron oxide (Li _x Fe ₂ O ₃ ) that is the negative electrode contracts when dedoped (discharged) and expands when doped (charged).

Therefore, when lithium cobalt oxide is used as the positive electrode, the same phenomenon as expansion and contraction of the crystal lattice for the iron oxide, which is the negative electrode, is exhibited, and the electrode is destroyed as the charge / discharge cycle progresses. Easy to proceed. On the other hand, when a lithium-nickel oxide is used as the positive electrode, it exhibits the opposite phenomenon to the expansion and contraction of the crystal lattice of the iron oxide, which is the negative electrode. The electrode does not break with the progress of, and as a result, a long cycle life becomes possible.

The lithium-nickel oxide can be doped / undoped in the range of 0.4 ≦ x ≦ 1 in the composition of Li _x CoO ₂ while the lithium-cobalt oxide can be doped with Li _x NiO. _In the composition of ₂ , lithium can be doped and dedoped in the range of 0 ≦ x ≦ 1. for that reason,
When a lithium-nickel oxide is used as the positive electrode material, the charging capacity at constant voltage charging of 4.2 V is 150 to 220.
It is as large as mAh / g, and it is possible to obtain a larger battery capacity than when using lithium cobalt oxide.

Further, nickel is rich in resources as compared with cobalt, and therefore has a great industrial value.

[0022]

The preferred embodiments of the non-aqueous electrolyte secondary battery according to the present invention will be described below with reference to the drawings. Needless to say, the present invention is not limited to this embodiment.

Example 1 A coin type lithium ion secondary battery produced in this example is shown in FIG. First, the positive electrode 1 of this battery was manufactured as follows. 1 mol of lithium hydroxide and 1 mol of nickel nitrate are mixed and baked in air at 800 ° C. for 6 hours to obtain LiN.
iO ₂ was synthesized. The obtained LiNiO ₂ was pulverized to a particle size of 5 μm, and 91 parts by weight of this was used as a positive electrode active material, 6 parts by weight of graphite was used as a conductive agent, and 3 parts by weight of polyvinylidene fluoride was used as a binder to prepare a positive electrode mixture. This was dispersed in N-methylpyrrolidone as a solvent to form a slurry (paste). Then, after drying and crushing this positive electrode mixture slurry, it is compression molded with an aluminum mesh,
A positive electrode 1 was produced.

The negative electrode 2 was produced as follows. α-F
eO (OH) (III) was calcined in air at 600 ° C. for 3 hours to obtain α-Fe ₂ O ₃ . The obtained α-Fe ₂ O ₃ was pulverized to a particle size of 1 μm, and mixed with 88 parts by weight of a negative electrode active material, 9 parts by weight of nickel powder as a conductive agent, and 3 parts by weight of polyvinylidene fluoride as a binder. This was used as a negative electrode mixture, and this was dispersed in a solvent, N-methylpyrrolidone, to form a slurry (paste form). Then, this negative electrode mixture slurry was dried, pulverized, and then compression-molded together with a stainless mesh to prepare a negative electrode 2.

Next, as shown in FIG. 3, the positive electrode 1 was placed in an aluminum clad can 3, and a separator 4 of a polypropylene porous film was placed thereon and an electrolytic solution was injected. The electrolyte is
1 mol of LiPF ₆ as an electrolyte in an equal volume mixed solvent of ethylene carbonate and diethylene carbonate.
What was melt | dissolved in the ratio of / l was used. Subsequently, the negative electrode 2 was put on the separator 4 and sealed with the insulating gasket 5 and the anode cup 6. This was caulked to maintain the airtightness in the battery, and a coin-type battery (Example 1) was produced.

Example 2 A coin-type battery (Example 2) was prepared in the same manner as in Example 1 except that LiNi _0.7 Co _0.2 Al _0.1 O ₂ was used as the positive electrode active material.

Positive electrode active material LiNi _0.7 Co _0.2 Al _0.1
O ₂ is obtained by mixing 1 mol of lithium hydroxide, 0.7 mol of nickel nitrate, 0.2 mol of cobalt (III) oxide and 0.1 mol of aluminum hydroxide, and calcining in air at 750 ° C. for 5 hours. It was This was ground to a particle size of 5 μm.

Comparative Example 1 A coin type battery (Comparative Example 1) was prepared in the same manner as in Example 1 except that LiCoO ₂ was used as the positive electrode active material.

LiCoO _{2 as the} positive electrode active material was obtained by mixing 0.5 mol of lithium carbonate and 1 mol of cobalt (III) oxide and firing the mixture in air at 900 ° C. for 5 hours. This was ground to a particle size of 5 μm.

Comparative Example 2 A coin type battery (Comparative Example 2) was prepared in the same manner as in Example 1 except that LiMn ₂ O ₄ was used as the positive electrode active material.

LiMn ₂ O _{4 as the} positive electrode active material was obtained by mixing 0.5 mol of lithium carbonate and 1 mol of manganese dioxide and firing the mixture in air at 850 ° C. for 3 hours. This has a particle size of 3 μm
Crushed.

Example 1, Example 2, Comparative Example 1, Comparative Example 2
A cycle test was performed for each of the batteries. In the cycle test, constant-current constant-voltage charging with a maximum charging voltage of 3.7 V and a charging current of 2 mA was performed for 60 hours. In addition, in Example 1, charging was performed at a maximum charging voltage of 3.6V.
After this initial charging, the battery was disassembled and the potential with respect to the lithium reference electrode was measured. Table 1 shows the results.

[0033]

[Table 1]

Similarly, Example 1, Example 2, Comparative Example 1,
A cycle test was performed on each of the batteries of Comparative Example 2. In the cycle test, constant-current constant-voltage charging with a maximum charging voltage of 3.7 V and a charging current of 2 mA was performed for 60 hours, and discharging was performed with a constant current of 1 mA to a final voltage of 0.5V. In addition, in Example 1, charging was performed at a maximum charging voltage of 3.6V. The discharge curve at the beginning of the cycle at that time is shown in FIG.

In the battery of Example 1 using LiNiO ₂ as the positive electrode active material, as shown in Table 1, the positive electrode potential after initial charging was 4.2 V, and the positive electrode active material per unit weight at this time was Had a charging capacity of 240 mAh / g. In the subsequent discharge, as shown in FIG. 4, the largest battery capacity of 100 mAh was obtained.

The positive electrode active material is LiNi _0.7 Co _0.2 A
In the battery of Example 2 using 1 _0.1 O ₂ , the positive electrode potential after initial charging was 4.2 V, and the charging capacity per unit weight of the positive electrode active material at this time was 200 mAh / g.
In the subsequent discharge, a large battery capacity of 90 mAh was obtained.

On the other hand, in the battery of Comparative Example 1, the positive electrode active material was L
iCoO ₂ is used, but the positive electrode potential after initial charging is 4.
Since it was 2 V, and the charging capacity per unit weight of the positive electrode active material at this time was as small as 145 mAh / g, the initial battery capacity obtained was as small as 78 mAh.

In the battery of Comparative Example 2, the positive electrode active material was L
Although iMn ₂ O ₄ is used, the positive electrode potential after the initial charge is 4.
The voltage was 2 V, and the charging capacity per unit weight of the positive electrode active material was 120 mAh / g, which was even smaller. Therefore, the initial battery capacity obtained was 62 mAh, which was the smallest.

Next, changes in the battery capacity with respect to the number of cycles when charging / discharging was performed up to 50 cycles under the charging / discharging conditions were examined. The result is shown in FIG.

In the battery of Example 1 having the largest capacity, as shown in FIG. 5, when the charging / discharging cycle was carried out at the maximum charging voltage of 3.7 V, the capacity of the battery increased as the cycle progressed due to deterioration of the positive electrode active material. The drop was severe. However, good cycle characteristics were obtained with the battery of Example 1 which was subjected to charge / discharge cycles at a maximum charge voltage of 3.6V. As shown in Table 1 and FIG. 4, in the battery of Example 1 which was subjected to the charging / discharging cycle with the maximum charging voltage of 3.6V, the positive electrode potential after the initial charging was 4.1V, and the positive electrode potential of 4.2V.
The charging capacity per unit weight of the positive electrode active material is 215 mAh / g, and the battery capacity is slightly smaller than 90 mAh, but deterioration of the positive electrode active material is suppressed by lowering the charging voltage, and a long cycle life is obtained. Was given.

Further, LiNi _0.7 Co _0.2 A was used as the positive electrode active material.
Also in the battery of Example 2 using _0.1 O ₂ , L was added to the positive electrode.
A battery capacity and a long cycle life almost equal to those of the battery of Example 1 using iNiO ₂ were obtained.

On the other hand, in the battery of Comparative Example 1 in which LiCoO ₂ was used as the positive electrode active material, the battery capacity greatly decreased with the progress of cycles, and the long-term reliability of the battery performance was lacking.

Further, in the battery of Comparative Example 2 using LiMn ₂ O ₄ as the positive electrode active material, compared with the batteries using lithium-nickel oxide as the positive electrode active material of Examples 1 and 2, the cycle was longer. The life was short, and sufficient battery capacity was not obtained as described above.

As is clear from the above results, in the lithium ion secondary battery using iron oxide in the negative electrode, the battery using lithium cobalt oxide in the positive electrode is damaged by the charge / discharge cycle. The cycle life was short. Further, the battery using lithium-manganese oxide for the positive electrode could not obtain a sufficient battery capacity. From this, lithium / cobalt oxide and lithium / manganese oxide are not suitable as the positive electrode active material of the lithium ion secondary battery using the iron oxide as the negative electrode active material.

On the other hand, battery using the lithium nickel based oxide in the positive electrode _{(LiNi x M (1-x} ) O 2) , since the electrode breakage due to the progress of charge-discharge cycles can be suppressed to obtain a long cycle life In addition, since the lithium-nickel oxide has a large discharge capacity per unit weight of the active material, a large battery capacity can be obtained.

When LiNiO ₂ is used as the lithium-nickel oxide in the positive electrode, a long cycle life can be obtained by limiting the charging voltage to 4.1 V based on the lithium reference electrode.

[0047]

As is apparent from the above description, in the non-aqueous electrolyte secondary battery of the present invention, it is possible to suppress the destruction of the electrodes associated with the progress of the charging / discharging cycle and realize a long cycle life. It is possible to obtain a highly safe non-aqueous electrolyte secondary battery having high capacity, long-term reliability and high battery capacity.

Further, the present invention is useful and practical in a battery system using iron oxide for the negative electrode, and has great industrial value.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a volume change rate of crystal lattices of lithium-nickel oxide and lithium-cobalt oxide doped with lithium.

FIG. 2 is a characteristic diagram showing a volume change rate of a crystal lattice of a lithium-doped iron oxide.

FIG. 3 is a schematic vertical sectional view of a coin type lithium ion secondary battery to which the present invention is applied.

FIG. 4 is a characteristic diagram showing a relationship between battery capacity and potential.

FIG. 5 is a characteristic diagram showing the relationship between the number of cycles and the capacity ratio.

[Explanation of symbols]

1 positive electrode, 2 negative electrode, 3 aluminum clad can, 4 separator, 5 insulating gasket, 6 anode cup

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masayuki Nagamine Inventor Masayuki Nagamine 1 Shimosugishita, Takakura, Hiwada Town, Koriyama City, Fukushima Prefecture -1 Sony Energy Tech Inc.

Claims (2)

[Claims] 1. A nonaqueous electrolytic solution comprising a positive electrode made of a metal oxide containing at least lithium and nickel, a negative electrode made of an iron oxide doped with lithium and dedoped, and a nonaqueous electrolytic solution. Secondary battery. 2. The metal oxide is LiNi _x M _(1-x) O
₂ (0.5 ≦ x ≦ 0.95, M is at least one selected from transition metals and Al), The non-aqueous electrolyte secondary battery according to claim 1.