Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Patent
1993-02-19
1995-03-28
Willis, Jr., Prince
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
429194, H01H 402
Patent
active
054015987
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an electrode for a secondary battery having high capacity and excellent charging and discharging characteristics. Further, it relates to a negative electrode for a secondary battery, having, as an active substance, an alkali metal, preferably lithium metal.
2. Discussion of the Background
As an electrode for a lithium secondary battery, a conductive polymer such as polyacetylene, etc. has been proposed. However, a conductive polymer is insufficient in its doping amount of Li ions, i.e. its electrode capacity and stable charging and discharging characteristics. Also, an attempt has been made to use metallic lithium as a negative electrode of a lithium secondary battery, but in this case, the charging and discharging cycle characteristics are extremely bad.
That is, during the discharging of the battery, lithium moves as lithium ions from a negative electrode into an electrolyte. During charging, these lithium ions are again electrodeposited as metallic lithium onto the negative electrode body. When this charging and discharging cycle is repeated, the metallic lithium electrodeposited becomes dendrite-shaped. Since this dendrite-shaped metallic lithium is a very active substance, it decomposes the electrolyte, thereby causing the deterioration of the charging and discharging cycle characteristics of the battery. Further, with continued growth this dendrite-shaped metallic lithium product finally reaches a positive electrode body by penetrating through a separator, causing a short-circuit. In other words, with such a system the charging and discharging life cycle is short.
In order to avoid such problems, a negative electrode in which lithium or an alkali metal composed mainly of lithium as an active substance has been attempted which is carried on a carbonaceous material prepared by sintering an organic compound. However, by using such a negative the electrode body, the charging and discharging cycle characteristics of the negative electrode could be dramatically improved, but, on the other hand, the electrode capacity of this negative electrode was not satisfactory.
OBJECTS OF THE INVENTION
An object of the present invention is, under the state of the art as described above, to provide a negative electrode for a secondary battery having large electrode capacity and excellent charging and discharging cycle characteristics.
SUMMARY OF THE INVENTION
The present inventors have found that an electrode having an alkali metal which is an active substance carried on a carrier comprising a carbonaceous material described below is extremely effective for accomplishing the above object.
That is, the electrode for secondary battery of the present invention comprises an alkali metal which is an active substance carried on a carrier composed mainly of a carbonaceous material satisfying the following requirements (1) and (2), and having a multi-phasic structure comprising a nucleus and a surface layer involving the nucleus,
(1) a true density of 1.80 g/cm.sup.3 or more, and
(2) in the Raman spectrum analysis using an argon ion laser beam with a wavelength of 5145 .ANG., it has a peak P.sub.A in the region of 1580 to 1620 cm.sup.-1 and a peak P.sub.B in the region of 1350 to 1370 cm.sup.-1, and the ratio of intensity I.sub.B of P.sub.B to intensity I.sub.A of P.sub.A as mentioned above, R=I.sub.B /I.sub.A, is 0.4 or more.
The carbonaceous material to be used in the present invention has these characteristics of true density and Raman spectrum irrespective of its shape, such as granular, fibrous, etc.
This carbonaceous material has a multi-phasic structure comprises at least two phases: a carbonaceous material forming a surface layer and a carbonaceous material forming a nucleus involved thereby. The fine structure of this carbonaceous material forming a surface layer contributes to the Raman spectrum described above. On the other hand, the true density is an average value of the densities of the carbonaceous materials in the multi-phasic
REFERENCES:
patent: 5028500 (1991-07-01), Fong et al.
patent: 5153082 (1992-10-01), Ogino et al.
Hayashi Manabu
Miyabayashi Mitsutaka
Mitsubishi Petrochemical Co. Ltd.
Nuzzolillo M.
Willis Jr. Prince
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