Lithium-nickel complex oxide, a process for preparing the same a

Details Lithium-nickel complex oxide, a process for preparing the same a Lithium-nickel complex oxide, a process for preparing the same a

1997-07-24

2000-04-04

Nuzzolillo, Maria

Chemistry of inorganic compounds

Oxygen or compound thereof

Metal containing

423600, 4292181, 429223, 4292316, 4292311, H01M 432, C01G 5304

Patent

active

060457716

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a novel lithium nickel complex oxide having a high charge and discharge capacity and excellent stability in retaining the capacity so that the degree of decrease in the capacity is small even with increasing the number of cycles, to a process for preparing the same, and to a positive electrode active material for a secondary battery.


BACKGROUND ART

As small size electronic appliances have become portable in recent years, there has been an increase in demand for a lithium secondary battery having a small size, a light weight and a high energy density to replace nickel/cadmium batteries.
As active materials for a positive electrode in such a lithium secondary battery, LiCoO.sub.2 and LiNiO.sub.2 are layered compounds capable of being intercalated and deintercalated with lithium. Of them, LiNiO.sub.2 is being investigated because of its higher electric capacity than LiCoO.sub.2.
Usually LiNiO.sub.2 is prepared by mixing a lithium component (LiOH, Li.sub.2 CO.sub.3, LiNO.sub.3 etc.) with a nickel component (hydroxide, carbonate etc.) in a powdery form and reacting the mixture by the so-called dry process, and hence required heating at an elevated temperature for a long time. Especially in the case of Ni, it is hard to convert a divalent ion into a trivalent ion and therefore heating at an elevated temperature for a long time was essential. Consequently, as the crystal growth proceeds, but some of the lithium is evaporated off and NiO as a by-product is formed, thereby lowering the purity.
To the contrary, the present inventors succeeded in preparing highly purified LiNiO.sub.2 having a high crystallization degree by forming a uniform precursor of Li and Ni components using a wet process and heating it for a short time as disclosed in Japanese Patent Application No. 6-80895 (Japanese Patent Kokai NO. 8-130013).
As to LiNiO.sub.2, however, when much of the Li was evaporated off (at the time of discharging), the structure tended to become unstable owing to the two-dimensional structure. Therefore the essential problem of a poor cycle property of a lithium secondary battery could not be completely overcome. Although the effect of improving the cycle characteristics was achieved to some extent by using the technique of the Japanese Patent Application No. 6-80895, the improvement was still insufficient for long term cycle characteristics of more than 100 cycles.
Under such circumstance, many attempts have been made to stabilize the structure by substituting a part of the nickel with another component (third component). For example, active materials of positive electrode represented by Li.sub.y Ni.sub.x Co.sub.1-x O.sub.2 (wherein x is 0<x.ltoreq.0.75 and y is y.ltoreq.1), where Co was doped in a solid solution into LiNiO.sub.2, and Li.sub.y Ni.sub.1-x Me.sub.x O.sub.2 (wherein Me represents any one of Ti, V, Mn and Fe, x is O<x.ltoreq.0.6 and y is 0.2<y.ltoreq.1.3), where Ti, V, Mn or Fe was doped as solid solution into LiNiO.sub.2 are disclosed in Japanese Patent Kokai Nos. 63-299056 and 5-283076 respectively.
However, the process by which the third component was doped in a solid solution was carried out by a dry process described above and hence it was difficult to homogeneously dope the third component in a solid solution. The process involved the increasing the amount of the third component, heating at an elevated temperature for a long time, and inevitably pulverizing several times. Consequently, Li was evaporated off and the by-product of NiO was formed, thereby lowering the purity and sufficient improvement in the cycle property could not be achieved, as with the LiNiO.sub.2 described above. Also, since the dry process required heating for a long time and pulverizing the product it was inefficient and uneconomical. Furthermore, since these dry processes take a long time for heating, it was impossible to adjust the crystal size to a desired level while keeping the crystallization degree and purity at high level.
Under these circumstances, attempts h

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Elements of X-Ray Diffraction by B.D. Cullity. Addison-Wesley Publishing Company, Inc., p. 178, 1978.

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