JP3291750B2 - Non-aqueous electrolyte secondary battery and method of manufacturing the same - Google Patents

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 and a method for producing the same.

[0002]

2. Description of the Related Art A non-aqueous electrolyte secondary battery using lithium or a lithium compound as a negative electrode is expected to have a high voltage and a high energy density, and many studies have been conducted for practical use.

Heretofore, V ₂ O ₅ , Cr ₂ O ₅ , MnO ₂ , TiS ₂ , and the like have been used as the positive electrode active material of this nonaqueous electrolyte secondary battery.
Although these positive electrode active materials have a potential of about 3 V or less with respect to Li, recently, LiMn ₂ O ₄ , LiCoO _2, LiNiO _{2, and the} like have a potential of 4 V or more with respect to Li. Since it shows a potential, it has attracted attention as a positive electrode active material for high energy density. These high-potential positive electrode active materials release Li upon charging,
Li is occluded by discharging.

On the other hand, as the negative electrode active material, foil-like metal Li alone has been widely studied from the beginning. However, there has been a problem that an internal short circuit occurs due to contact with the positive electrode. As means for solving such a problem, Al alone, which can suppress dendritic growth of Li and occlude and release Li by charging and discharging,
Studies have been made on the use of metal plates or metal powders such as alloys and wood alloys, carbon materials or metal oxides and sulfides as the negative electrode active material.

In recent years, LiMn ₂ O ₄ , Li, which is a positive electrode active material that releases Li by the above-described charging and occludes Li by discharging and has a high potential of 4 V or more with respect to Li
Developed high-energy-density lithium secondary batteries with high voltage and excellent safety by combining CoO ₂ or LiNiO ₂ with a carbon material that is a negative electrode active material that occludes Li by charging and releases Li by discharging Is being done.

When a battery is constructed using a negative electrode active material such as a carbon material and a lithium composite oxide such as LiMn ₂ O ₄ , LiCoO ₂ or LiNiO ₂ as a positive electrode active material,
Lithium released from the positive electrode active material in the first charge,
It is occluded by the negative electrode active material, and in a subsequent discharge, this reverse reaction occurs, and lithium ions are released from the negative electrode active material and occluded by the positive electrode active material. Therefore, the only lithium ions involved in the battery reaction are those initially present in the positive electrode, and the amount of the lithium ions determines the battery capacity.

[0007]

In such a conventional negative electrode active material, gas is generated due to decomposition of the electrolytic solution on the negative electrode in the first charge, and is taken into the negative electrode active material in the first charge. In addition, since there are lithium ions not involved in the subsequent battery reaction, a large charge / discharge capacity difference occurs in the first charge / discharge. As described above, the amount of lithium ions that can be reversibly moved in the battery decreases, and the capacity of the battery decreases.

Therefore, it is conceivable that a lithium metal foil having a charge / discharge capacity difference is previously set on the electrode. However, when a battery having a spiral structure is usually assumed, lithium having a charge / discharge capacity difference is formed on the electrode as a lithium metal foil. For uniform installation, the thickness is several μm depending on the weight of the negative electrode, which is extremely difficult to work. If a tens of μm lithium metal foil is partially installed,
There is a possibility that it takes a long time for the lithium to participate in charge and discharge, or the lithium may remain as metallic lithium, which poses a problem in safety.

An object of the present invention is to solve the above problems and to provide a high-capacity and safe non-aqueous electrolyte secondary battery.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a carbon material which absorbs lithium by charging and releases lithium by discharging, as a negative electrode, a lithium composite oxide as a positive electrode, and a lithium salt. And a non-aqueous electrolyte secondary battery comprising: a lithium battery having a charge / discharge capacity difference, which is previously deposited on the positive electrode as lithium powder.

[0011]

According to the present invention, lithium can be uniformly dispersed on the electrode by the above-described structure. After lithium is injected, a local battery is formed on the electrode, and the lithium is uniformly absorbed in the electrode so that the lithium battery has a high capacity and is safe. Thus, a non-aqueous electrolyte secondary battery having high performance can be obtained.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

(Example 1) A battery was manufactured according to the following procedure.

LiMn ₂ O _{4 as} a positive electrode active material is Li ₂ C
O ₃ and Mn ₃ O ₄ are mixed in a weight ratio of 3: 4, and 900 ° C.
And synthesized by heating. LiCoO ₂ is obtained by mixing Li ₂ CO ₃ and CoCO ₃ at a weight ratio of 1: 2,
It was synthesized by heating at 00 ° C. Furthermore, these were pulverized and classified to 100 mesh or less to obtain a positive electrode active material.

To 100 g of the positive electrode active material, 10 g of carbon powder as a conductive agent and 5 g of polyvinylidene fluoride as a binder were added, and the paste was formed using dimethylformamide, applied to a titanium core material, and dried and rolled. Is immersed in a hexane solution in which lithium powder having an average particle diameter of 100 μm is dispersed, dried and rolled, and when a local battery is composed of a positive electrode after injecting an electrolyte, LiMn ₂ O ₄ becomes Li _1.15 M
A positive electrode in which lithium was attached to n ₂ O ₄ so that LiCoO ₂ became Li _1.15 CoO ₂ was obtained.

As a negative electrode, graphite 10 as a negative electrode active material is used.
10 g of polyfukka vinylidene as a binder to 0 g
g was added to form a paste using dimethylformamide, which was applied to a nickel core and dried to obtain a paste.

FIG. 1 shows a sectional view of the battery used in this embodiment. The electrode body has a band-shaped porous polypropylene separator 3 wider than both electrode plates between a positive electrode plate 1 having a positive electrode lead 4 and a negative electrode plate 2 having a negative electrode lead 5 of the same material as the core material attached by spot welding. And the whole is spirally wound. Further, insulating plates 6 and 7 made of polypropylene are arranged on the upper and lower sides of the electrode body, respectively, and inserted into the battery case 8 to form a step on the upper portion of the battery case 8. /

[0018]

[Outside 1]

A propylene carbonate solution in which lithium perchlorate is dissolved is injected and sealed with a sealing plate 9 to obtain a battery.

In the above procedure, L is used as the positive electrode active material.
Battery (A) using iMn ₂ O ₄ , LiCo as positive electrode active material
A battery (B) using O ₂ was produced.

As comparative examples, a battery (C) using LiMn ₂ O ₄ as a positive electrode active material having no lithium adhered on the positive electrode and a battery (D) using LiCoO ₂ as a positive electrode active material were prepared.

The batteries thus prepared were allowed to stand for 3 days after preparation, and were charged and discharged at a charge / discharge current of 0.5 mA / cm ² . However, the voltage range was 4.3 to 3.0 V for the battery using LiMn ₂ O ₄ as the positive electrode active material, and 4.1 to 3.0 V for the battery using LiCoO ₂ . (Table 1) summarizes the results.

[0023]

[Table 1]

The comparative battery (C) to which no lithium powder was attached had a charge capacity in the first cycle of 410 mAh, a discharge capacity of 328 mAh, and a difference in capacity between charge and discharge of 82 mAh. Lithium having a charge / discharge capacity difference of 82 mAh generated in the first cycle is occluded in graphite, which is a negative electrode active material, and does not participate in subsequent charge / discharge reactions. Therefore, the battery capacity after the second cycle is 326
mAh. As described above, when graphite is used for the negative electrode, the battery capacity is reduced by about 20%. L as positive electrode active material
Also in the case of using iCoO ₂ (D), the charge capacity in the first cycle was 462 mAh, whereas the discharge capacity was 369 mAh, and the difference between the charge and discharge capacities was 93 mA.
h. Like the battery (C), the battery capacity decreases.

On the other hand, in the battery (A) which is one of the present embodiments, lithium having a charge / discharge capacity difference generated in the first cycle in the battery (C) is previously deposited on the positive electrode as lithium powder. . Actually, the charge capacity in the first cycle of the battery (A) is 489 mAh, and the discharge capacity is 405 m
Ah. In this case, lithium powder having a charge / discharge capacity difference was previously attached to graphite, and lithium was occluded in the positive electrode during standing for 3 days.
The discharge capacity comparable to the charge capacity in the first cycle of the comparative example battery (C) was obtained. In addition, the charge / discharge capacity difference was substantially eliminated at the fifth cycle. As described above, the reduction in the capacity of the battery caused by the carbon material having the initial charge / discharge capacity difference is eliminated, and a high-capacity battery is obtained. In the same manner as for the battery (B), a discharge capacity almost equal to the charge capacity in the first cycle of the comparative battery (D) was obtained from the first cycle, and a high-capacity battery was obtained.

Although the charge / discharge capacity difference varies depending on the type of carbon material used, before assembling as a battery as in this embodiment, the charge / discharge capacity difference of the carbon material is estimated in advance, and excess lithium in the carbon material is added. By storing ozone, a battery having a large capacity can be obtained.

Example 2 Next, the particle size of the lithium metal powder was examined. Five types of lithium metal powder having an average particle size of 50, 100, 150, 200, and 300 μm were examined.

The battery was manufactured in the same manner as in Example 1 except that the average particle size of the lithium metal powder was different.

The batteries thus fabricated were left for 3 days after fabrication, and were charged and discharged at a charge / discharge current of 0.5 mA / cm ² . However, the voltage range was 4.3 to 3.0 V for the battery using LiMn ₂ O ₄ as the positive electrode active material, and 4.1 to 3.0 V for the battery using LiCoO ₂ . Table 2 summarizes the results of the discharge capacity at the fifth cycle.

[0030]

[Table 2]

As shown in (Table 2), when the average particle size in the range of 50 to 300 μm studied in the present example, LiM
In each of the positive electrodes of n ₂ O ₄ and LiCoO _2, the discharge capacity was increased as compared with the comparative example in which lithium powder was not adhered on the positive electrode shown in Example 1. Above all, 100 ~
The range of 150 μm is most preferable because the discharge capacity is large.
It was recognized that the discharge capacity tended to decrease when the thickness was 50 μm or more or 100 μm or less. Although the cause is unknown, if the particle size becomes too fine, the surface area increases, and the oxide layer on the surface increases.On the contrary, if the particle size becomes too large, the standing time after preparation is short, and the electrode It is conceivable that the moldability is not good.

[0032]

[0033]

[0034]

[0035]

[0036]

[0037]

[0038]

[0039]

[0040]

[0041]

[0042]

[0043]

[0044]

[0045]

[0046]

[0047]

[0048]

In the above embodiments, LiMn ₂ O ₄ and LiCoO ₂ were used as the positive electrode active materials. However, LiNi which releases lithium by charging and stores lithium by discharging is used.
_{O 2 r-LiV 2 O 5} LiFeO there are also the effects by using a lithium composite oxide such as _2.

Further, in the examples, 1 mol / mol
The results obtained in the case of using a propylene carbonate solution in which lithium perchlorate (1) was dissolved were used. In addition to the electrolytic solution, lithium perchlorate, lithium hexafluorophosphate and trifluoromethanesulfonic acid were used as solutes. Lithium, lithium borofluoride, carbonates such as propylene carbonate and ethylene carbonate as solvents,
Similar results were obtained with electrolytes using esters such as gamma-butyl lactone and methyl acetate. In addition, although the embodiment has been described with reference to a cylindrical battery, it goes without saying that a coin-shaped or square-shaped battery is also effective.

[0051]

As is apparent from the above description, according to the present invention, the lithium powder having a difference in charge / discharge capacity is uniformly deposited on the electrodes in advance, so that the capacity is large and the lithium ions are uniformly absorbed during charging. Thus, a non-aqueous electrolyte secondary battery with high capacity and high safety can be provided.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a nonaqueous electrolyte secondary battery according to one embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the amount of Li in the active material of the positive electrode active material LixMn ₂ , X, and the open circuit potential.

FIG. 3 is a graph showing the relationship between the amount of Li in the active material of the positive electrode active material LixMn ₂ , X, and the open circuit potential.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Positive electrode lead plate 5 Negative electrode lead plate 6 Upper insulating plate 7 Lower insulating plate 8 Battery case 9 Sealing plate

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Yasuhiko Mito 1006 Kadoma, Kazuma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Yoshinori Toyoguchi 1006 Kadoma, Kazuma, Kadoma, Osaka Matsushita Electric Industrial Co., Ltd. In-company (56) References JP-A-4-39859 (JP, A) JP-A-5-67468 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 4/02-4/04 H01M 4/58

Claims (4)

(57) [Claims] 1. A positive electrode using, as an active material, a lithium composite oxide that releases lithium on charging and stores lithium on discharging, and a carbon material on an active material that stores lithium on charging and releases lithium on discharging. A non-aqueous electrolyte secondary battery comprising: the used negative electrode; and a non-aqueous electrolyte solution containing a lithium salt, wherein lithium powder is previously attached to the positive electrode. 2. A mixture of lithium composite oxide as a positive electrode active material, a conductive material and a binder and a solvent, applying the mixture material, the positive electrode is made by drying, immersed in lithium powder dispersion bath 2. The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein lithium powder is adhered. 3. The lithium composite oxide is LiMn ₂ O ₄ ,
At least is one claim selected from LiCoO ₂
2. The non-aqueous electrolyte secondary battery according to 1. 4. The lithium composite oxide is LiMn ₂ O ₄ ,
At least is one claim selected from LiCoO ₂
3. The method for producing a non-aqueous electrolyte secondary battery according to item 2.