Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1995-08-23
1997-07-01
Bell, Bruce F.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
429 40, 429218, 252502, 423445R, 423460, C25B 1112
Patent
active
056434260
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates to an anode material used in a non-aqueous electrolyte secondary battery and for doping or undoping lithium, and a method of manufacturing such an anode material.
2. Background Art
With miniaturization of electronic equipments, realization of high energy density of battery has been required. To meet with such requirement, various non-aqueous electrolyte batteries like so called lithium battery have been proposed.
However, e.g., in batteries using lithium metal as anode, particularly in the case where such batteries are caused to be secondary battery, there are following drawbacks. Namely,
(1) 5 to 10 hours are ordinarily required for charging, resulting in the fact that quick charge characteristic is poor.
(2) Cycle life-time is short
These drawbacks all result from lithium metal itself, and are considered to be caused by change of lithium form, formation of lithium in dendrite form and/or irreversible change of lithium, etc. produced by repetition of charge/discharge operations.
In view of the above, as one technique for solving these problems, a method using carbonaceous material as anode is proposed. This method utilizes the fact that lithium carbon interlayer compound can be electrochemically formed wise ease. For example, when charge operation is carried out within a non-aqueous electrolyte in the state where carbon is used as an anode and compound including lithium is used as a cathode, lithium in the cathode is electrochemically doped between layers of anode carbon. The carbon into which lithium is doped in this way functions as lithium electrode, and lithium in the anode is undoped from between carbon layers followed by discharge and is returned into the cathode.
We have demonstrated in the Japanese Patent Application Laid Open No. 252053/1991 publication that, as such carbonaceous material, non-graphitizable carbon material having spacing d.sub.002 of (002) plane of 3.70 angsttoms or more, true density less than 1.70 g/cm.sup.3, and no exothermic peak at 700.degree. C. or more in the Differential Thermal Analysis (DTA) in air is excellent in quantity of lithium doped/undoped (hereinafter simply referred to as lithium dope/undope quantity depending upon circumstances).
Meanwhile, in the above-described non-aqueous electrolyte secondary battery using carbonaceous material, current capacity (mAh/g) per unit weight of the anode is determined by quantity of lithium doped of carbonaceous material. Accordingly, it is desirable that lithium dope quantity is as great as possible as the carbonaceous material (Theoretically, ratio of single Li atom to six carbon atoms is upper limit). When viewed from the above, while employment of the above-described carbonaceous material results in a great quantity of lithium being doped as compared to the conventional carbonaceous material, it cannot be said that even such carbonaceous material is sufficient.
DISCLOSURE OF THE INVENTION
An object of this invention is to provide an anode material which has great quantity of lithium doped and is capable of sufficient current capacity, and a method of manufacturing such an anode material.
In order to attain the above-described object, as the result of the fact that the inventors of this invention repeatedly conducted studies for a long time, they have obtained findings that, in non-graphitizable carbon material, ratio by weight of carbon in stacking structure Ps, stacking index SI, and average number of carbon layers n.sub.ave in stacking structure are restricted so that ratio (percentage) of the portion forming the stacked layer structure is caused to be small, and the half width at half maximum HW of peak in the vicinity of 1340 cm.sup.-1 of Raman spectrum is restricted, whereby an anode material having extremely large capacity can be obtained. Further, they have found out that such carbonaceous material is produced by baking (firing) carbon precursor under an atmosphere such that volatile component produced in carbonization is removed to the outside of the reaction
REFERENCES:
patent: 4544469 (1985-10-01), Boxall et al.
patent: 5306415 (1994-04-01), Cornec et al.
patent: 5344726 (1994-09-01), Tanaka et al.
patent: 5451477 (1995-09-01), Omaru et al.
International Search Report; Synthetic Metals, 18, (1987) pp. 587-542 No month available.
Azuma Hideto
Gonno Yoshihisa
Imoto Hiroshi
Nagamine Masayuki
Nishi Yoshio
Bell Bruce F.
Kananen Ronald P.
Sony Corporation
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