Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2001-12-21
2004-06-22
Kalafut, Stephen J. (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C252S182100
Reexamination Certificate
active
06753112
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a positive electrode active material and non-aqueous secondary battery using the same capable of increasing a molding density (packing density) of the active material in a positive electrode, and capable of improving discharging rate characteristic of the battery by lowering an impedance of the electrode.
2. Description of the Related Art
In recent years, developments of a relatively safe negative electrode material and a non-aqueous electrolyte having an increased decomposition voltage have been advanced, so that various non-aqueous secondary batteries having a high operating voltage have been practically used in many technical fields. In particular, a secondary battery using a lithium ion has excellent characteristics such as a high discharge voltage, light weight, and a high energy density or the like, so that the demand of the secondary battery has been rapidly increased as power sources of equipments and devices such as portable telephone (cellular phone), notebook-sized personal computer, camera-integrated video recorder, and as dispersed-type power sources, power sources of EV (electrical vehicle) and HEV (hybrid electrical vehicle), and a large-scaled battery.
The lithium ion secondary battery of this type comprises: a positive electrode containing the active material and a negative electrode containing carbon, that are capable of reversibly deintercalating/intercalating lithium ion; and a non-aqueous electrolyte which is prepared by dissolving lithium salt into non-aqueous solvent.
As the positive electrode active material for the above lithium ion secondary battery, for example, lithium-cobalt composite oxides such as LiCoO
2
, lithium-nickel composite oxides such as LiNiO
2
, lithium-manganese composite oxides such as LiMn
2
O
4
and other metal oxides have been generally used.
As the positive electrode for the above secondary battery, there has been generally used a positive electrode formed in such a manner that a mixture of positive electrode material consisting of Li-containing transition metal composite oxide, conductive material and binder is coated onto an Al plate as a collector, then the coated mixture is dried and followed by press-compacting the dried material.
In order to increase a charging/discharging capacity per unit volume of the above secondary battery, it is required to increase a finished density (final density) of a positive electrode material layer containing the above active material, filler, binder or the like. Therefore, for the purpose of increasing the density of the active material layer, there has been adopted a method comprising steps of: forming a positive electrode active material layer (positive electrode film); and thereafter, conducting a press-rolling operation for densifying the positive electrode film thereby to increase the density thereof.
Even if the conventional positive electrode active materials were press-densified by the press-rolling operation, the pressed material could attain a density to some extent, however, the resulting density was still insufficient indeed. That is, even if the pressing pressure is increased so as to obtain a high density for the positive electrode active material layer, a high density cannot be obtained no longer when the pressing pressure exceeds predetermined pressure level, so that there has been raised a problem that a sufficient charging/discharging capacity for the secondary battery cannot be obtained.
Further, although only a surface portion of the active material layer can be highly densified, a portion apart from the surface and close to the collector cannot obtain a sufficiently high density. At any rate, there has been raised a problem that a charging/discharging capacity and discharging rate characteristic of the secondary battery become insufficient.
Furthermore, there has been also proposed a secondary battery using a positive electrode formed in accordance with alkoxide method in which a thin film-shaped (layer-shaped) oxide layer is formed on the surface of the positive electrode active material. However, in the active material having such thin film, migration and movement of lithium ion are obstructed, so that there is posed a problem of disadvantageously lowering the battery characteristics.
On the other hand, a notebook-sized personal computer, a personal digital assistant (PDA), a cellular phone or the like have been rapidly come into wide use in recent years, and a realization of a mobile computing system is remarkably progressed. To cope with the situation, multi-functioned portable electronic devices or the like have been required to be operated for a long time. Therefore, with respect to the secondary battery to be used as the power sources for various equipments including the portable electronic devices, a technical demand for realizing compact size and a high capacity for the batteries has been raised.
SUMMARY OF THE INVENTION
The present invention had been achieved to solve the aforementioned problems and an object of the present invention is to provide a positive electrode active material and a non-aqueous secondary battery capable of increasing molding density (packing density) of the active material in a positive electrode, and capable of improving discharging rate characteristic of the battery by lowering an impedance of the electrode.
In order to achieve the aforementioned object, the inventors of this invention had prepared positive electrode active materials by adhering particles as various adhered substances onto active materials having various compositions, and the inventors had comparatively reviewed the influences of kind, adhering amount, grain size of the particles on the densifying property of the active materials.
As a result, the inventors had obtained the following knowledge. Namely, when fine oxide particles or carbon particles were adhered onto the surface of the active material body thereby to prepare a positive electrode active material, the packing characteristic of the active material could be significantly improved.
More concretely to say, the following findings were obtained. When particles of oxide of specified elements such as Bi, Sb, Al, Sn or the like were adhered to the surface of the active material body thereby to prepare the positive electrode active material, friction force among the active materials was greatly reduced thereby to increase a flowability of the active material, so that a positive electrode film having a higher density than that of the conventional one could be obtained through a rolling operation under a high pressure. As a result, there could be obtained a secondary battery excellent in charging/discharging characteristic and capacity.
In addition, when carbon particles such as general carbon black, electrically conductive carbon black, acetylene black or the like were adhered to the surface of the active material body consisting of Li-containing transition metal composite oxide thereby to prepare the positive electrode active material, electrical conductivity among the positive electrode active materials was greatly improved, so that it became possible to reduce an amount of filler which had been used in the conventional positive electrode active material layer (film) for the purpose of increasing the electrical conductivity, and thus also making it possible to increase density of the positive electrode active material layer and to improve the discharging capacity.
Furthermore, in also a case where the carbon particles were adhered to the surface of the active material, friction force among the active materials was greatly reduced thereby to increase the flowability of the active material, so that a positive electrode film having a higher density than that of the conventional one could be obtained through a rolling operation under a high pressure. As a result, there could be obtained a secondary battery excellent in charging/discharging characteristic and capacity.
In addition, the following finding was also obtained. Namely, when
Amemiya Kazuki
Endou Shouta
Ooya Yasumasa
Sakai Ryo
Shirakawa Yasuhiro
Foley & Lardner LLP
Kalafut Stephen J.
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