Nonaqueous electrolyte solution secondary battery using...

Details Nonaqueous electrolyte solution secondary battery using... Nonaqueous electrolyte solution secondary battery using...

2001-02-26

2004-01-27

Chaney, Carol (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Electrode

C429S209000, C429S218100, C429S223000, C429S304000

Reexamination Certificate

active

06682850

ABSTRACT:

BACKGROUND OF THE INVENTION
(i) Field of the Invention
The present invention relates to a nonaqueous electrolyte solution secondary battery. More particularly, the present invention relates to a lithium secondary battery or a lithium ion secondary battery, and to a nonaqueous electrolyte solution secondary battery having a high capacity and improved charge and discharge properties, especially improved cycle life duration and capacity retention properties/self-discharge properties.
(ii) Description of the Related Art
Lithium manganate is a material which is very expectable as one positive electrode material for a lithium ion secondary battery. This material system has been reported as a research subject of a magnetic behavior in 1950's (Journal of American Chemical Society, Vol. 78, pp. 3255-3260). Since M. M. Thackeray et al. reported that Lithium manganate could electrochemically absorbs/releases Li ions in Material Research Bulletin, Vol. 18, pp. 461-472 in 1983, it has been investigated as a positive electrode material for a lithium secondary battery (e.g., Journal of Electrochemical Society, Vol. 136, No. 11, pp. 3169-3174 or Journal of Electrochemical Society, Vol. 1138, No. 10, pp. 2859-2864).
This lithium manganate has a spinel structure represented by the chemical formula LiMn
2
O
4
, and functions as a 4V class positive electrode material with respect to a composition of &lgr;-MnO
2
. Since lithium manganate of the spinel structure has a three-dimensional host structure which is different from a layer structure of, e.g., LiCoO
2
, most of its theoretical capacity can be used, and hence it is expected to be excellent in cycle properties.
However, in practice, the lithium secondary battery in which lithium manganate is used as the positive electrode cannot avoid capacity deterioration that the capacity is gradually lowered by repeating charge and discharge, and there remains such a serious problem in practical use of lithium manganate.
Various methods have been investigated in order to improve the cycle properties of an organic electrolyte solution secondary battery in which lithium manganate is used for the positive electrode. For example, there are characteristic improvement by enhancing reactivity at the time of synthesization (disclosed in, e.g., Japanese Patent Applications Laid-Open Nos. 67464/1991, 119656/1991, 127453/1991, 245106/1995 and 73833/1995), characteristic improvement by controlling a particle diameter (disclosed in, e.g., Japanese Patent Applications Laid-Open Nos. 198028/1992, 28307/1993, 295724/1994 and 97216/1995), and characteristic improvement by removing impurities (disclosed in, e.g., Japanese Patent Applications Laid-Open No. 21063/1993), but none of them can achieve the satisfactory improvement in cycle properties.
Besides the above applications, Japanese Patent Applications Laid-Open No. 270268/1990 discloses an attempt that a composition ratio of Li is set to be sufficiently excessive with respect to a stoichiometry ratio to improve the cycle properties. The synthetic techniques of composite oxides having the similar excessive Li composition are also disclosed in, e.g., Japanese Patent Applications Laid-Open Nos. 123769/1992, 147573/1992, 205744/1993 and 282798/1995. Improvement in the cycle properties by these techniques can be apparently confirmed by experiments.
Furthermore, with the intention of obtaining an effect similar to the case of using the Li excessive composition, there is also disclosed, in Japanese Patent Applications Laid-Open Nos. 338320/1994 and 262984/1995 and the like, a technique of using a positive electrode active material prepared by mixing an Mn spinel material LiMn
2
O
4
with an Li—Mn composite oxide Li
2
Mn
2
O
4
, LiMnO
2
, Li
2
MnO
3
or the like which is richer in Li than the above spinel material.
When Li is excessively added or mixed with the other Li-rich compound, the cycle properties are improved, but on the other hand, a charge and discharge capacity value and a charge and discharge energy value decrease, so that there is a problem that both of the high energy density and the long cycle life duration cannot be achieved. On the contrary, Japanese Patent Applications Laid-Open No. 275276/1994 aims at the high energy density, improvement in high-rate charge and discharge properties (an electric current at the time of charge and discharge is large with respect to a capacity), and the perfectibility of reaction to enlarge a specific surface area, but on the contrary, the long cycle life duration is hard to be achieved.
On the other hand, there have also been conducted investigations for improvement in the properties by adding another element to a compound having three components of Li, Mn and O. For example, they include techniques of adding Co, Ni, Fe, Cr, Al or the like, and doping with such an element (which are disclosed in Japanese Patent Applications Laid-Open Nos. 141954/1992, 160758/1992, 169076/1992, 237970/1992, 282560/1992, 289662/1992, 28991/1993 and 14572/1995). The addition of these metal elements involves the reduction in the charge and discharge capacity, and more ingenuities are necessary for satisfaction as the total performance.
In the investigation of the techniques of adding another element, the addition of boron is expected, because it permits the achievement of improvement in other properties, e.g., cycle properties or self-discharge properties without substantially reducing the charge and discharge capacity. For example, Japanese Patent Applications Laid-Open Nos. 253560/1990, 297058/1991 and 115515/1997 disclose such a technique. In any of these applications, manganese dioxide or an Li—Mn composite oxide is solid-mixed with a boron compound (e.g., boric acid) or immersed into an aqueous solution of a boron compound and then subjected to a heat treatment to synthesize a composite oxide of lithium, manganese and boron. Since the complex particle powder of the boron compound and the manganese oxide has a reduced surface activity, it is expected that the reaction with the electrolyte solution is suppressed and the capacity holding properties are improved.
However, the mere addition of boron causes disadvantages such as the reduction in grain growth or tap density, and hence, it cannot directly lead to the realization of the high capacity as a battery. Further, the reduction in the capacity in an effective potential range when combined with a carbon negative electrode is observed depending on synthetic conditions, or the suppression of the reaction with the electrolyte solution is insufficient sometimes. Therefore, the addition of boron is not always effective for improvement in the capacity retention properties.
Various approaches have been made for improving the cycle properties of lithium manganate as described above. For realizing the cycle properties comparable to a Co system which is currently a mainstream, especially the cycle properties during use at a high temperature, more investigations are required since a deterioration mechanism is promoted in the high-temperature use environment. In particular, on considering the future spread of application fields such as a notebook computer and an electric vehicle, the assurance of the cycle properties at a high temperature becomes more important.
As described above, lithium manganate LiMn
2
O
4
is a composite oxide which is largely expected as an alternative material for the positive electrode active material LiCoO
2
which is currently a mainstream, but the conventional battery using LiMn
2
O
4
have two problems, i.e., (1) difficulty in realizing both of the high energy density (high charge and discharge capacity) and the high cycle life duration, and (2) reduction in the retained capacity due to self-discharge.
Technical drawbacks in battery production and compatibility with the electrolyte solution are pointed out as causes of these problems, but the following can be considered when paying attention to the positive electrode material itself or the influence due to the positive electrode material.
As causes for preventing the rea

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