Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Patent
1998-11-12
2000-09-05
Nuzzolillo, Maria
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
42923195, H01M 1024
Patent
active
061140651
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a secondary cell having a non-aqueous electrolyte, particularly a positive electrode thereof.
BACKGROUND ART
Recently, development of portable and cordless types of such electronic apparatuses as AV equipment and personal computers has made rapid progress, and a secondary cell of small size, light weight and providing a high energy density is highly demanded as a driving power supply for such apparatus. Particularly, a secondary lithium cell with a negative electrode of metallic lithium used as an active material is highly expected to be a cell capable of providing a high voltage and a high energy density. However, because of insufficiency in safety and reliability, such lithium cell has not been practically applied for the present.
It is considered that the safety is reduced because the negative electrode of metallic lithium is changed to a dendritic shape by repetitive charging and discharging, leading to possible internal short circuiting and heat generating reaction between the electrolyte and lithium of the dendritic shape.
In order to solve the problem, a secondary lithium ion cell with a negative electrode of carbon material that is capable of reversibly intercalating and deintercalating lithium and a positive electrode of such oxide of a transition metal containing lithium as LiCoO.sub.2, LiNiO.sub.2 and LiMn.sub.2 O.sub.4 has been suggested.
In such secondary lithium ion cell, since lithium is intercalated into the carbon material of negative electrode during charging, precipitation of lithium is theoretically never caused on the negative electrode plate, it is advantageous in that internal short circuiting of the cell is restricted, and the cell is superior in safety and reliability.
Even in the case of such secondary lithium ion cell with a negative pole of carbon material that is capable of reversibly intercalating and deintercalating lithium, however, lithium is deposited on the negative electrode plate gradually as charging and discharging are repetitively conducted, and it has been a problem that the cell is reduced in safety and reliability in the final stage of its cycle life.
Hence, it is an object of the invention to solve the problem, and provide a cell superior in charging and discharging cycle life characteristics, safety and reliability by preventing precipitation of lithium on a negative electrode plate in the final stage of cycle life.
SUMMARY OF THE INVENTION
A secondary cell according to the invention comprises a positive electrode having an active material and a conductive element, a negative electrode and an electrolyte in contact with the positive and negative electrodes, wherein the conductive element contains Ketjenblack. Ketjenblack is a kind of carbonblack powder, produced by Ketjenblack International, Inc. Ketjenblack is a carbon black having a hollow shell structure with graphite crystals accumulated outside thereof, a DBP oil absorption of about 200 ml/100 g a surface area of about 500 m.sup.2 /g nitrogen adsorption method, and porosity about 35% or more.
It is particularly desirable that the content of the Ketjenblack is within a range of about 0.3 parts by weight to about 1.2 parts by weight with respect to 100 parts by weight of the active material.
Another secondary cell according to the invention comprises a positive electrode having an active material and a conductive element, a negative electrode and an electrolyte in contact with the positive and negative electrodes, wherein the conductive element contains Ketjenblack and flake graphite.
It is particularly desirable that the content of the Ketjenblack is within a range of about 0.2 parts by weight to about 1.0 part by weight with respect to 100 parts by weight of the active material, and a value of [3X+(3/8)Y] is within a range of about 1.0 to about 3.5 where X is the content of the Ketjenblack expressed by units of part by weight, and Y is the content of the flake graphite expressed by units of part by weight with respect to 100 parts by weight of the acti
REFERENCES:
patent: 5133842 (1992-07-01), Taylor et al.
patent: 5759714 (1998-06-01), Matsufuji et al.
patent: 5789114 (1998-08-01), Adachi et al.
patent: 5856043 (1999-01-01), Ohsaki et al.
Japanese language search report for Int'l Appln No. PCT/JP98/00752 dated Jun. 16, 1998.
Copy of Form PCT/ISA/210.
Inoue Kaoru
Kitagawa Masaki
Koshina Hizuru
Oura Takafumi
Matsushita Electric - Industrial Co., Ltd.
Nuzzolillo Maria
Wills Monique
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