Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2001-11-09
2004-03-30
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S231700, C429S329000
Reexamination Certificate
active
06713214
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a positive electrode active material that can be used in a secondary battery such as a lithium secondary battery, and to a secondary battery using the same, and to a lithium secondary battery using graphite fluoride as a positive electrode active material.
2. Related Art
Along with the wide spread use and development of portable equipment in recent years, a demand for a battery with a high energy density, which is a power supply, has been further piled up. Since a lithium secondary battery can be expected to be a high energy density, various systems thereof have been studied.
While, in connection with a negative electrode, lithium metal, lithium alloys, carbon materials and metal oxide materials have been studied, the carbon materials are at present in the actual use because of the excellent reversibility and abundant resources thereof regardless of the least capacity thereof among the above kinds.
While, in connection with a positive electrode, oxides, halides, chalcogenides and the like are promising candidates, transition metal oxides such as MnO
2
, V
2
O
5
and LiCoO
2
are now put into practical use. The transition metal oxides include a heavy metal and are problematic for its expensiveness and other reasons.
As other positive electrode active materials for a secondary battery, elemental sulfur, sulfur compounds and conductive polymers are named. However, since elemental sulfur and sulfur compounds include sulfur, there are problems such as nasty smell and others, making the materials incompatible with a work place environment. In a conductive polymer, since carriers to transport an electric charge during charge/discharge are not lithium ions but anions, a battery capacity is governed by an anion concentration in an electrolyte and the conductive polymer has a fatal problem in point of increase in the battery capacity.
As a positive electrode active material for a lithium primary battery, graphite fluoride is used. Graphite fluoride is formed by C-F bonds and, therefore, an electrode reaction thereof is to reduce a C-F bond with Li, thereby producing LiF and C. Since the reaction product is LiF having almost no solubility in an electrolyte, a charge reaction is hard to occur and there is difficulty in using graphite fluoride as an electrode for a secondary battery.
As described above, a positive electrode active material, including no heavy metal, and with environmental compatibility, has been desired as a positive electrode active material for a lithium secondary battery.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide a novel positive electrode active material for a secondary battery that can solve the above problem and a secondary battery using the same.
It is a second object of the present invention to provide a lithium secondary battery, using graphite fluoride as a positive electrode active material, and having a high capacity and excellence in cycle performance.
A positive electrode active material for a secondary battery according to a first aspect of the present invention is constituted of an organic material including a carbon atom, having a conjugate electron cloud, and coupled with an electron attractive group.
When the electron attractive group is in coupling with a carbon having a conjugate electron cloud, an electron density in the conjugate electron cloud decreases, causing a state of the conjugate electron cloud to be similar to a state assuming as if an electron in the conjugate electron cloud is withdrawn: an oxidized state is produced in the broad sense. If the conjugate electron cloud is put into an oxidized state, a doping potential of an Li (lithium) ion shifts to the noble side (positive side), as compared with that of the ion having the conjugate electron cloud in an ordinary neutral state. Accordingly, charge/discharge at a higher potential is enabled; thus, the organic material can be used as a positive electrode active material.
In discharge, doping of an Li ion and injection of an electron into the conjugate electron cloud occur, while in charge, dedoping of an Li ion and withdrawal of an electron from the conjugate electron cloud occur. Since the reactions are reversible, charge/discharge at a high potential is enabled.
As an active material according to the first aspect of the present invention, an organic material having an aromatic ring at least part of which is substituted by an electron attractive group is named. One example of such an organic material is an aromatic condensed polycyclic hydrocarbon at least part of which is substituted by an electron attractive group. The hydrocarbon is a compound obtained by substituting part of hydrogen atoms of a polycyclic hydrocarbon having aromatic rings condensed together such as anthracene, pyrene, naphthalene or the like with an electron attractive group.
Furthermore, as another example, a polymer of an aromatic compound such as benzene with an electron attractive group or electron attractive groups substituting part of hydrogen atoms thereof is named. As such a benzene polymer, a polymer expressed by the following general formula can be named:
where X, Y, Z and T are hydrogen, fluorine, or C
n
F
2n+1
providing that n is an integer of 0 or more, at least one of X, Y, Z and T is fluorine or C
n
F
2n+1
, and m is an integer of 0 or more.
To be concrete, for example, a polymer of fluorobenzene, a polymer of trifluoromethylbenzene or the like is named.
As polymers of fluorobenzene, polymers of the following specific fluorobenzenes are named: monofluorobenzene, paradifluorobenzene, orthodifluorobenzene, metadifluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, 1,3,5-trifluorobenzene, 1,2,3,4-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene and 1,2,4,5-tetrafluorobenzene and others.
Furthermore, as polymers of trifluoromethylbenzene, polymers of the following specific trifluoromethylbenzenes are named: &agr;&agr;&agr;-trifluorotoluene, paraditrifluoromethylbenzene, orthoditrifluoromethylbenzene, 1,2,3-tristrifluoromethylbenzene, 1,2,4-tristrifluoromethylbenzene, 1,3,5-tristrifluoromethylbenzene, 1,2,3,4-tetratrifluoromethylbenzene, 1,2,3,5-tetratrifluoromethylbenzene and 1,2,4,5-tetratrifluoromethylbenzene and others.
As an electron attractive group, as described above, fluorine or a fluoroalkyl group is named. The fluoroalkyl group is a group expressed by C
n
F
2n+1
, wherein n is a natural number, and to be specific, trifluoromethyl group is named as described above.
A positive electrode active material for a secondary battery according to a second aspect of the present invention is characterized by constituting of a material obtained by baking a fluorocarbon polymer in an inert atmosphere at a temperature in the range of from a decomposition start temperature to 1000° C. As fluorocarbon polymers, polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyfluoroethylenepropylene, a copolymer of vinylidene fluoride and hexafluoropropylene, and others are named.
A positive electrode active material for a secondary battery according to a third aspect of the present invention is characterized by constituting of a material obtained by baking graphite fluoride in an inert atmosphere at a temperature in the range of from a decomposition start temperature to 1000° C. A heat treatment temperature of graphite fluoride is preferably on the order of the range of 400 to 550° C.
A secondary battery according to a fourth aspect of the present invention is characterized by including a positive electrode containing a positive electrode active material according to any of the first to third aspect of the present invention, a negative electrode and a nonaqueous electrolyte.
In a secondary battery according to the fourth aspect of the present invention, the negative electrode preferably contains an active material absorbing and releasing alkali metal or alkali earth metal.
In the present invention, it is preferable that the alkali metal is lithium and the s
Fujimoto Masahisa
Fujitani Shin
Koga Hideyuki
Kalafut Stephen
Kubovcik & Kubovcik
Sanyo Electric Co,. Ltd.
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