JP3378756B2 - Lithium battery - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium battery, and more particularly to a lithium battery using a positive electrode in which a positive electrode current collector is provided with a positive electrode material layer made of a composite oxide of lithium and cobalt or nickel. This is intended to improve the cycle characteristics by suppressing the decrease of the discharge capacity when the discharge is repeated.

[0002]

2. Description of the Related Art In recent years, as one of new type batteries with high output and high energy density, a high electromotive force lithium battery utilizing oxidation and reduction of lithium using a non-aqueous electrolyte solution using an organic solvent has been used. Came to be.

Here, in such a lithium battery, various kinds of materials have been conventionally used as the positive electrode material in the positive electrode, but there is a problem that the discharge capacity is not sufficient.

Therefore, in recent years, in order to improve the discharge capacity of a lithium battery, Japanese Patent Laid-Open No. 1-2943 has been proposed.
As disclosed in Japanese Patent Laid-Open No. 64, a material using a composite oxide of lithium, cobalt and nickel as a positive electrode material in a positive electrode has been developed.

However, in the case of the lithium battery using the composite oxide of lithium, cobalt and nickel as the positive electrode material as described above, when charging and discharging are repeated, the positive electrode material and the above non-aqueous electrolyte solution in the lithium battery are used. However, there is a problem that the discharge capacity gradually decreases and the cycle characteristics deteriorate.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems in a lithium battery using a composite oxide of lithium, cobalt and nickel as a positive electrode material in a positive electrode.

That is, according to the present invention, in the lithium battery using the composite oxide of lithium, cobalt, and nickel as the positive electrode material in the positive electrode as described above, even when charging and discharging are repeatedly performed, It is an object of the present invention to obtain a lithium battery having excellent cycle characteristics, in which the positive electrode material rarely reacts with a non-aqueous electrolyte solution or the like to gradually reduce the discharge capacity.

[0008]

In order to solve the above problems, in the lithium battery of the present invention, Li _X Co _1-Y Ni _Y O _Z (0 <X ≦
1.3, 0 ≦ Y ≦ 1, 1.8 ≦ Z ≦ 2.2) In a lithium battery using a positive electrode provided with a positive electrode material layer, the positive electrode collector has the positive electrode. A plurality of material layers are laminated so that the atomic ratio of Co in the positive electrode material layer apart from the positive electrode current collector is higher than the atomic ratio of Co in the positive electrode material layer close to the positive electrode current collector. I did it.

Here, as in the lithium battery according to the present invention, the above-mentioned Li _X Co is used as the positive electrode current collector in the positive electrode.
_A plurality of layers of _1-Y Ni _Y O _Z positive electrode material are laminated, and the atomic ratio of Co in the layer of the positive electrode material at a position distant from the positive electrode current collector is set to the positive electrode material at a position close to the positive electrode current collector. If it is higher than the atomic ratio of Co in the layer of the above, the ratio of lithium in the layer of the positive electrode material separated from the positive electrode current collector having the large atomic ratio of Co becomes higher at the same potential, and the nonaqueous electrolyte solution It is considered that the catalytic activity for the decomposition of the like becomes low. It is considered that this suppresses the reaction at the interface between the positive electrode material and the non-aqueous electrolyte solution, reduces the decrease in discharge capacity due to charge and discharge, and improves the cycle characteristics of this lithium battery.

Here, if the atomic ratio of Co in the layer of the positive electrode material at a position distant from the positive electrode current collector increases as described above, the decrease in discharge capacity due to charge and discharge can be suppressed, and in particular, As shown in Item 2, the composition of the positive electrode material in the layer of the positive electrode material farthest from the positive electrode current collector is Li _X Co _{1 -Y} Ni _Y O _Z (0 <X ≦ 1.3, 0 ≦
When Y ≦ 0.2, 1.8 ≦ Z ≦ 2.2) is used, the decrease in discharge capacity due to charge / discharge is further suppressed, and the cycle characteristics are further improved.

When the positive electrode material layer having a high Co atom ratio is provided on the surface farthest from the positive electrode current collector as described above, if the thickness of the positive electrode material layer on this surface is thin, non-aqueous Since the reaction at the interface with the electrolytic solution or the like may not be sufficiently suppressed, the thickness of the layer of the positive electrode material on this surface is preferably 5 μm or more.

When the positive electrode current collector is provided with the positive electrode material layer as described above, a known conductive agent is added to the positive electrode current collector, and when a carbon material is used as the conductive agent, the In order to efficiently occlude and release lithium, it is preferable to use graphite having an interplanar spacing (d ₀₀₂ ) in the lattice plane (002) of 3.37Å or less.

In the lithium battery of the present invention, as the positive electrode current collector used for the positive electrode, a positive electrode current collector made of a commonly used known material can be used. As shown, when this positive electrode current collector composed of a material containing aluminum is used, this positive electrode current collector is stable even at a high potential, and the cycle characteristics are further improved.

On the other hand, in the lithium battery of the present invention, the negative electrode material used for the negative electrode may be a known negative electrode active material which has been conventionally used,
For example, in addition to metallic lithium and lithium alloys, carbon materials such as graphite, coke, and an organic material calcined material that can store and release lithium ions can be used.

As the non-aqueous electrolyte used in the lithium battery of the present invention, a known non-aqueous electrolytic solution or solid electrolyte can be used.

Here, in the above-mentioned non-aqueous electrolyte, a known solvent generally used can be used, for example, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, Sulfolane, dimethylsulfolane, 3-methyl-1,3-oxazolidine-2-
ON, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate,
A combination of one or more organic solvents such as ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate and ethyl acetate. It is possible to use, and it is particularly preferable to use a cyclic carbonic acid ester and a chain carbonic acid ester in combination.

As the solid electrolyte, those generally used in the past can be used. For example, polyethylene oxide, polypropylene oxide, cross-linked polyethylene glycol diacrylate, cross-linked polypropylene glycol diacrylate, polyethylene glycol methyl ether. A polymer electrolyte such as a cross-linked acrylate or a cross-linked polypropylene glycol methyl ether acrylate can be used.

As the solute to be added to the above-mentioned non-aqueous electrolytic solution or solid electrolyte, known solutes can be used. For example, lithium trifluoromethanesulfonate L
iCF ₃ SO ₃ , Lithium hexafluorophosphate LiP
Lithium compounds such as F ₆ , lithium perchlorate LiClO ₄ , lithium tetrafluoroborate LiBF ₄ , and trifluoromethanesulfonic acid imide lithium LiN (CF ₃ SO ₂ ) ₂ can be used.

[0019]

EXAMPLES Hereinafter, the lithium battery of the present invention will be specifically described with reference to examples, and in the lithium battery of this example, a decrease in discharge capacity when charging and discharging are repeated is suppressed, It is clarified that the cycle characteristics are improved by giving a comparative example. The lithium battery according to the present invention is not limited to the ones shown in the following examples, and can be implemented by appropriately changing it without departing from the scope of the invention.

(Examples 1 to 10) These Examples 1 to 1
0, a positive electrode, a negative electrode and a non-aqueous electrolyte prepared as described below were used, and the diameter as shown in FIG.
A flat coin-type lithium battery having a thickness of 4.0 mm and a thickness of 3.0 mm was produced.

[Preparation of Positive Electrode] To prepare a positive electrode, LiOH, Co (OH) ₂ and Ni (OH) ₂ were mixed in a predetermined molar ratio, and then mixed.
After firing at 50 ° C. for 20 hours, as shown in Table 1 below, L
Various positive electrode materials in which i, Co, and Ni had the respective predetermined molar ratios were produced, and these positive electrode materials were crushed in an Ishikawa-type Raikai mortar.

Then, with respect to the powder of each positive electrode material pulverized in this way, graphite having a lattice spacing (d ₀₀₂ ) of 3.35Å in the lattice plane (002) as a conductive agent, and polyvinylidene fluoride as a binder. Of N-methyl-2-pyrrolidone solution, and the positive electrode material described above, graphite as a conductive agent, and polyvinylidene fluoride as a binder are mixed with each other.
Each positive electrode mixture having a weight ratio of 0: 6: 4 was prepared.

In these examples, two positive electrode mixtures prepared as described above are used, and two positive electrode mixtures are applied on each positive electrode current collector made of aluminum foil having a thickness of 30 μm. Then, after drying, they were pressure-molded at a pressure of ² t / cm ^{2 into} a disk shape having a diameter of 20 mm, and further heat-treated at 100 ° C. for 2 hours, and as shown in FIG. A first positive electrode layer 1a and a second positive electrode layer 1b each containing the positive electrode material shown in Table 1 are stacked on each other with a thickness shown in the same table, and the second positive electrode layer 1b is separated from the positive electrode current collector 5. Each of the positive electrodes 1 was manufactured in which the atomic ratio of Co in the positive electrode material was higher than the atomic ratio of Co in the positive electrode material of the first positive electrode layer 1a close to the positive electrode current collector 5.

[Preparation of Negative Electrode] In preparing the negative electrode, a rolled plate of lithium-aluminum alloy was punched into a circle to prepare a disc-shaped negative electrode of lithium aluminum alloy.

[Preparation of Non-Aqueous Electrolyte] In preparing the non-aqueous electrolyte, a mixed solvent prepared by mixing propylene carbonate (PC) and dimethyl carbonate (DMC) in a volume ratio of 1: 1 was used. Lithium perchlorate LiClO ₄ was dissolved in a mixed solvent at a ratio of 1 mol / l to prepare a non-aqueous electrolytic solution.

[Production of Battery] When producing a battery, as shown in FIG. 1, the positive electrode current collector 5 is manufactured as described above.
Using each of the positive electrodes 1 produced above, the above negative electrode 2 was attached to the negative electrode current collector 6, and the above-mentioned non-aqueous solution was added to the separator 3 composed of a polypropylene microporous film (Hoechst Celanese Co., Ltd .: Celgard). The separator 3 is impregnated with the electrolytic solution, the separator 3 is provided between each of the positive electrode 1 and the negative electrode 2, and these are housed in the battery case 4 formed of the positive electrode can 4a and the negative electrode can 4b. The positive electrode 1 is connected to the positive electrode can 4a through the negative electrode 2 while the negative electrode 2 is connected through the negative electrode current collector 6.
Is connected to the negative electrode can 4b, and the positive electrode can 4a and the negative electrode can 4b are connected.
And lithium were electrically insulated by the insulating packing 7, and each lithium battery was produced.

Comparative Examples 1 to 4 In these Comparative Examples 1 to 4, as in the case of Examples 1 to 10 described above, Li
While preparing each positive electrode mixture using various positive electrode materials in which Co and Ni have a predetermined molar ratio, in each of these comparative examples, as shown in FIG. 1 containing the positive electrode materials shown in Table 1 below.
Each positive electrode 1 was produced by providing one positive electrode layer, and other lithium batteries were produced in the same manner as in Examples 1 to 10 above.

(Comparative Examples 5 and 6) Also in these Comparative Examples 5 and 6, as in the above Examples 1 to 10, Li
Each positive electrode mixture was prepared by using various positive electrode materials in which Co and Ni had a predetermined molar ratio, and as shown in FIG. First positive electrode layer 1a and second positive electrode layer 1 containing the positive electrode material shown
Each of the positive electrodes 1 was manufactured by stacking b with the thickness shown in the same table.

Here, in Comparative Examples 5 and 6, as shown in Table 1 below, contrary to the cases of Examples 1 to 10 described above, the second electrode separated from the positive electrode current collector 5 was used. Positive electrode layer 1
The atomic ratio of Co in the positive electrode material of b is the positive electrode current collector 5
Each lithium battery was produced in the same manner as in Examples 1 to 10 above except that the atomic ratio of Co in the positive electrode material of the first positive electrode layer 1a was close to.

For each of the lithium batteries of Examples 1 to 10 and Comparative Examples 1 to 6 described above, the charging current was 1
After charging to a cut-off voltage of 4.3 V at mA, discharge to a cut-off voltage of 2.0 V at a discharge current of 3 mA, and such charging / discharging is repeated as 100 cycles. The initial discharge capacity was measured, the capacity deterioration rate of each lithium battery after 100 cycles was determined, and the results are also shown in Table 1 below.

[0031]

[Table 1]

As is clear from this result, the second positive electrode separated from the positive electrode current collector 5 as compared with the atomic ratio of Co in the positive electrode material of the first positive electrode layer 1 a provided on the positive electrode current collector 5. Each of the lithium batteries of Examples 1 to 10 using the positive electrode 1 in which the atomic ratio of Co in the positive electrode material of the layer 1b was high was compared with only one positive electrode material layer provided on the positive electrode current collector 5. The positive electrode material of the first positive electrode layer 1a in which the atomic ratio of Co in the positive electrode material of each of the lithium batteries of Examples 1 to 4 and the second positive electrode layer 1b separated from the positive electrode current collector 5 is close to the positive electrode current collector 5 Comparative Example 5, in which the atomic ratio of Co in the inside was less than
The capacity deterioration rate after 100 cycles was remarkably reduced as compared with each lithium battery of No. 6.

When comparing the lithium batteries of Examples 1 to 10, the second positive electrode layer 1b separated from the positive electrode current collector 5 was used.
The lithium batteries of Examples 1 to 3 and 5 to 9 in which the atomic ratio of Co in the positive electrode material was 0.8 mol or more were used for the second positive electrode layer 1b separated from the positive electrode current collector 5. The cycle characteristics were further improved as compared with the lithium battery of Example 4 in which the atomic ratio of Co in the positive electrode material was 0.5 mol.

In addition, Example 3 using the same positive electrode material
When comparing the lithium batteries 7 to 10, when the thickness of the second positive electrode layer 1b is 5 μm or more, the capacity deterioration rate after 100 cycles has the same low value, while the second positive electrode layer 1b has the same value. The initial discharge capacity gradually decreased as the thickness of the layer 1b increased. Therefore, it is preferable to set the thickness of the second positive electrode layer to about 5 to 50 μm.

(Examples 11 to 14) These examples 11
Nos. 15 to 15 are similar to those in the above-described first embodiment.
LiCo _0.8 Ni _0.2 O is used as the positive electrode material in the positive electrode layer 1a.
₂ is used as the positive electrode material in the second positive electrode layer 1b.
CoO ₂ was used, and the thickness of the first positive electrode layer 1a was 80 μm and the thickness of the second positive electrode layer 1b was 20 μm.

On the other hand, as shown in Table 2, in Example 11, the positive electrode current collector 5 on which the first and second positive electrode layers 1a and 1b are laminated is made of SUS instead of the aluminum foil. The positive electrode current collector 5 thus prepared is used,
Further, in Example 12, in producing the positive electrode mixture, the above-mentioned d ₀₀₂ was 3.38 instead of graphite as the conductive agent.
Å coke was used, and in Example 13, ethylene carbonate (EC) and 1,2-dimethoxyethane (DME) were used as the solvent in the above nonaqueous electrolytic solution.
The mixed solvent in which and were mixed at a volume ratio of 1: 1 was prepared as in Example 1.
In 4, a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 1: 1 was used, and other than that, each lithium battery was manufactured in the same manner as in Example 1 above. did.

Also for each of the lithium batteries of Examples 11 to 14, the initial discharge capacity and the capacity deterioration rate after 100 cycles were determined in the same manner as described above, and the results are shown in Table 2.

[0038]

[Table 2]

As a result, the capacity deterioration rate after 100 cycles was higher in Example 1 using the aluminum foil as the positive electrode current collector in the positive electrode than in Example 11 in which the positive electrode current collector was made of SUS. In addition, the capacity deterioration rate after 100 cycles was lower in Example 1 than in the case where coke was used as the conductive agent in the positive electrode.

Regarding the solvent in the non-aqueous electrolytic solution, the above-mentioned Example 1 and Example? As shown in Fig. 2, when a mixture of propylene carbonate and dimethyl carbonate or a mixed solvent of ethylene carbonate and dimethyl carbonate is used, the capacity deterioration rate after 100 cycles is ethylene carbonate and 1,2-
The capacity deterioration rate after 100 cycles was lower than that of a mixed solvent in which dimethoxyethane was mixed and a mixed solvent in which propylene carbonate and dimethyl carbonate were mixed.

(Examples 15 to 16) These examples 1
In Examples 5 and 16, the cases of Examples 1 to 10 above,
Each lithium battery was produced in the same manner as in Examples 1 to 10 except that only the positive electrode was changed.

Here, in Example 15, in producing the positive electrode 1, as shown in FIG. 3, the first positive electrode layer 1a and the second positive electrode layer 1a were formed on the positive electrode current collector 5 made of aluminum foil. 1b and the third positive electrode layer 1c are laminated, and as shown in Table 3 below, LiCo _0.2 Ni _0.8 O ₂ is used as the positive electrode material in the first positive electrode layer 1a and the thickness thereof is set to 60 μm. LiCo _0.8 Ni _0.2 O ₂ was used as the positive electrode material in the layer 1b, the thickness thereof was set to 20 μm, and LiC was used as the positive electrode material in the third positive electrode layer 1c.
oO ₂ was used and its thickness was 20 μm.

Further, in Example 16, when manufacturing the positive electrode 1, as shown in FIG. 4, the first positive electrode layer 1a and the second positive electrode layer 1a were formed on the positive electrode current collector 5 made of aluminum foil.
The positive electrode layer 1b, the third positive electrode layer 1c, and the fourth positive electrode layer 1d were laminated, and as shown in Table 3 below, LiCo _0.2 Ni _0.8 O ₂ was used as the positive electrode material in the first positive electrode layer 1a, and The thickness is 40 μm, LiCo _0.5 Ni _0.5 O ₂ is used as the positive electrode material in the second positive electrode layer 1b, the thickness is 20 μm, and LiCo _0.8 Ni _0.2 O ₂ is used as the positive electrode material in the third positive electrode layer 1c. 20 μm, the positive electrode material in the fourth positive electrode layer 1d has L
iCoO ₂ was used and its thickness was 20 μm.

Then, for each of the lithium batteries of Examples 15 and 16, the initial discharge capacity and the capacity deterioration rate after 100 cycles were determined in the same manner as described above, and the results are shown in Table 3 below. It was

[0045]

[Table 3]

As a result, as shown in Examples 15 and 16, two or more positive electrode layers were laminated on the positive electrode current collector 5,
When the atomic ratio of Co contained in the positive electrode material in the positive electrode layer is increased as the distance from the positive electrode current collector 5 increases, the capacity deterioration rate after 100 cycles is the same as in each of the above Examples. A low lithium battery was obtained.

[0047]

As described above in detail, in the lithium battery of the present invention, the positive electrode current collector in the positive electrode is formed by laminating a plurality of layers made of the above-mentioned positive electrode material of Li _X Co _{1 -Y} Ni _Y O _Z. At this time, the atomic ratio of Co in the layer of the positive electrode material at a position distant from the positive electrode current collector is Co in the layer of the positive electrode material at a position close to the positive electrode current collector.
Therefore, the reaction between the positive electrode material in the layer separated from the positive electrode current collector and the non-aqueous electrolyte is suppressed, and the decrease in discharge capacity due to charge and discharge is reduced, and the cycle characteristics are improved. An excellent lithium battery has come to be obtained.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the internal structure of each lithium battery in Examples and Comparative Examples of the present invention.

FIG. 2 is a schematic cross-sectional view showing a state in which two positive electrode layers are laminated on a positive electrode current collector in Examples 1 to 14 and Comparative Examples 5 and 6 of the present invention.

FIG. 3 is a schematic cross-sectional view showing a state in which one positive electrode material layer is provided on a positive electrode current collector in Comparative Examples 1 to 4.

FIG. 4 is a schematic cross-sectional view showing a state in which three positive electrode layers are stacked on the positive electrode current collector in Example 15 of the present invention.

FIG. 5 is a schematic cross-sectional view showing a state in which four positive electrode layers are stacked on a positive electrode current collector in Example 16 of the present invention.

[Explanation of symbols]

1 positive electrode 1a First positive electrode layer 1b Second positive electrode layer 1c Third positive electrode layer 1d Fourth positive electrode layer

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Koji Nishio 2-5-5 Keihan Hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Hiroshi Watanabe 2-5-5 Keihan-hondori, Moriguchi-shi, Osaka No. 5 within Sanyo Electric Co., Ltd. (56) Reference JP-A-8-222219 (JP, A) JP-A-8-171935 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4/00-4/04 H01M 4/36-4/62 H01M 10/40

Claims (3)

(57) [Claims] 1. A positive electrode current collector comprising Li _X Co _1-Y Ni _Y O _Z
(0 <X ≦ 1.3, 0 ≦ Y ≦ 1, 1.8 ≦ Z ≦ 2.2)
In a lithium battery using a positive electrode provided with a layer of a positive electrode material, a plurality of layers of the above positive electrode material are laminated on the above positive electrode current collector, and a layer of the positive electrode material close to the positive electrode current collector is formed. The lithium battery is characterized in that the atomic ratio of Co in the layer of the positive electrode material separated from the positive electrode current collector is higher than the atomic ratio of Co in. 2. The lithium battery according to claim 1, wherein the composition of the positive electrode material in the layer of the positive electrode material farthest from the positive electrode current collector is Li _X Co _{1 -Y} Ni _Y O _Z (0 <X ≦ 1.
3, 0≤Y≤0.2, 1.8≤Z≤2.2). 3. The lithium battery according to claim 1 or 2, wherein the positive electrode current collector in the positive electrode is made of a material containing aluminum.