Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1997-06-27
2001-10-16
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S231800
Reexamination Certificate
active
06303249
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a carbonaceous material suitable as an electrode material for a non-aqueous solvent-type secondary battery, and a process for production thereof. The present invention also relates to an electrode structure comprising such a carbonaceous electrode material, and a non-aqueous solvent-type secondary battery having such an electrode structure.
Non-aqueous solvent-type lithium secondary batteries having a negative electrode comprising a carbonaceous material have been proposed as a type of high energy-density secondary batteries (Japanese Laid-Open Patent Application (JP-A) 57-208079, JP-A 62-90863, JP-A 62-122066, JP-A 2-66856, etc.). When such a secondary battery is charged, lithium in a positive electrode comprising a chalcogenide, such as LiCoO
2
, is introduced into negative electrode carbon (i.e., dopes the carbon) electrochemically. The carbon thus doped with lithium functions as a lithium electrode, from which the lithium is released (i.e., de-doped) during discharge to return to the positive electrode. Thus, a secondary battery capable of repetitive charge-discharge is formed.
As carbonaceous materials capable of providing non-aqueous solvent-type lithium secondary batteries, there is the so-called “non-graphitizable carbon” obtained by calcining phenolic resin or furan resin, the “graphitizable carbon” obtained by carbonizing pitch or tar; and activated carbon having a large specific surface area on the order of 900-2000 m
2
/g.
There has also been proposed a process for producing a carbonaceous material for providing high-performance secondary batteries comprising treating plant fiber of, e.g., coconut shell with hydrochloric acid, etc., for removal of an inorganic substance contained therein and then carbonizing the treated plant fiber at 900-1500° C. under a reduced pressure of at most 10 kPa (European Laid-Open Patent Application (EP-A) 0700105.
However, the above-mentioned known carbonaceous materials are accompanied with a problem that a large amount of active substance, such as lithium, remains in the carbon (i.e., the carbon shows a large non-dedoping capacity) during the dedoping step, so that the active substance is wasted uselessly, and also a problem that the dedoping capacity per se determining the battery performance (discharge capacity) is relatively small.
SUMMARY OF THE INVENTION
As a result of study by our research and development group, it has already been found that a carbonaceous material obtained by carbonizing an organic material of plant origin characterized by the presence of vessel, sieve tube, plant fiber, etc., can be doped with a large quantity of active substance, and is therefore promising as a carbonaceous electrode material, and a patent application (European Patent Appln. No. 95305897.1, later laid open as EP-A 0767505) was filed based on the finding. However the carbonaceous material is liable to exhibit a relatively large non-dedoping capacity which is the amount of active substance, such as lithium, that is not completely de-doped from but remains within the carbonaceous material during a discharge step, and a reduction of the non-dedoping capacity has been earnestly desired.
Accordingly, a principal object of the present invention is to provide a carbonaceous material useful as a carbonaceous electrode material for providing high-performance secondary batteries exhibiting large capacities for doping and de-doping of an active substance, such as lithium, and also exhibiting a reduced non-dedoping capacity, i.e., a reduced amount of active substance remaining within the carbonaceous material without de-doping.
Further objects of the present invention are to provide a process for producing such a carbonaceous material, an electrode structure composed from such a carbonaceous material, and a high-performance secondary battery including such an electrode structure.
In the course of our study for obtaining high-performance carbonaceous electrode materials more suitably used for non-aqueous solvent-type secondary batteries from organic materials of plant origin, it has been found that not all the ash content (inorganic substance) contained in such an organic material adversely affect the resultant carbonaceous material obtained therefrom but the potassium element contained in the organic material adversely affects the resultant carbonaceous material. It has been further found that a carbonaceous material obtained by removing the potassium from an organic material of plant origin and then carbonizing the organic material under appropriate conditions provides an excellent carbonaceous electrode material having well-balanced performances including a small non-dedoping capacity and a large dedoping capacity in combination, and the resultant carbonaceous material has a large pore volume suitable for doping with a cell active substance not found in conventional carbonaceous electrode materials.
Incidentally, the above-mentioned EP-A 0700105 discloses an example of production of a carbonaceous electrode material through de-ashing of a carbon precursor of plant origin and carbonization of the de-ashed carbon precursor (Example 5). It has been found however that such an ordinary de-ashing treatment is not effective enough to reduce the potassium content, and the resultant carbonaceous material cannot exhibit a sufficiently reduced non-dedoping capacity (see Comparative Example 7 described hereinafter).
According to the present invention, there is provided a carbonaceous electrode material (first carbonaceous material) for a non-aqueous solvent-type secondary battery, having porus with a pore volume of at least 0.55 ml/g and a pore diameter of at most 5 &mgr;m as measured by mercury injection method, a potassium content of at most 0.5 wt. % as measured by fluorescent X-ray analysis, and a specific surface area of at most 100 m
2
/g as measured by nitrogen adsorption BET method.
According to another aspect of the present invention, there is provided a carbonaceous electrode material (second carbonaceous material) for a non-aqueous solvent-type secondary battery, obtained by carbonizing an organic material of plant origin, and having a potassium content of at most 0.5 wt. % as measured by fluorescent X-ray analysis, and a specific surface area of at most 100 m
2
/g as measured by nitrogen adsorption BET method.
It is preferred that both the first carbonaceous material and the second carbonaceous material of the present invention have a hydrogen-to-carbon atomic ratio H/C of below 0.1 as measured by elementary analysis, and an average (002)-plane spacing of at least 0.365 nm as measured by X-ray diffraction method.
According to the present invention, there is further provided a process for producing a carbonaceous electrode material for a non-aqueous solvent-type secondary battery, comprising: carbonizing a carbon precursor of plant origin having a potassium content of at most 0.5 wt. % as measured by fluorescent X-ray analysis, in contact with a stream of an inert gas optionally containing a halogen gas at a temperature of 700-1500° C.
According to the present invention, there is also provided an electrode structure for a non-aqueous solvent-type secondary battery, comprising: an electroconductive substrate and a composite electrode layer disposed on at least one surface of the electroconductive substrate; the composite electrode layer comprising the above-mentioned first or second carbonaceous material in a particulate form, and a binder.
According to the present invention, there is further provided a non-aqueous solvent-type secondary battery, comprising a positive electrode, a negative electrode, and a separator and a non-aqueous electrolytic solution disposed between the positive and negative electrodes; wherein at least one of the positive and negative electrodes comprises an electrode structure as described above.
The carbonaceous material according to the present invention is practically so-called non-graphitizable carbon capable of storing a large amount of active substanc
Masuko Jiro
Shibata Fumio
Sonobe Naohiro
Chaney Carol
Kureha Kogaku Kogyo Kabushiki Kaisha
Wenderoth , Lind & Ponack, L.L.P.
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