Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2001-04-24
2003-11-11
Ruthkosky, Mark (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S231950
Reexamination Certificate
active
06645671
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a lithium secondary battery used as a power source for memory retention in electronic equipment, a power source for driving portable electronic equipment, or the like, to an anode for a lithium secondary battery, and to a method for manufacturing the anode.
BACKGROUND ART
In recent years, lithium batteries which have lithium salts as electrolytic components have attracted attention since such batteries give a high energy density at a high voltage (3 to 4V), and such batteries have been developed to the extent that they can be used in practical applications. In order to make personal computers, word processors, portable telephones and the like yet more portable, it will be necessary in the future to make lithium batteries into the form of rechargeable secondary batteries and to further improve cycle characteristics (charging efficiency, cycle life, etc.).
A lithium secondary battery has a cathode capable of charging and discharging lithium ions, an anode comprising a material which may be doped and de-doped with lithium ions, lithium metal or the like, and an electrolyte that allows migration of lithium ions. A nonaqueous electrolytic solution in which a lithium salt is dissolved in an organic solvent is generally used as the electrolyte.
However, with lithium metal batteries that use metallic lithium or a lithium alloy as an anode active substance, the electrolytic solution has a tendency to decompose due to reaction between the organic solvent in the electrolytic solution and the anode active substance. There is thus a problem that good cycle characteristics cannot be obtained with lithium metal batteries that use an electrolytic solution containing an organic solvent.
The invention disclosed in JP-A-10-261435 attempts to solve this problem. The invention in this document attempts to suppress the reaction between the organic solvent and the anode active substance by adding an imide compound to the electrolytic solution. This method certainly gives good results with ‘coin-shaped’ batteries. However, with cylindrical batteries it is difficult to put in a large quantity of the electrolytic solution, meaning that it is difficult to put in a large quantity of the imide compound. With the method disclosed in the above-mentioned publication, it is thus difficult to sufficiently suppress the reaction between the organic solvent and the anode active substance in the case of a cylindrical lithium metal battery.
One of the problems with lithium secondary batteries is thus that good cycle characteristics cannot be obtained for a variety of different battery forms.
An object of the present invention is to solve this problem.
DISCLOSURE OF THE INVENTION
The present invention provides, as a first aspect, a lithium secondary battery that comprises a cathode capable of charging and discharging lithium ions, an anode containing a material which can be doped and de-doped with lithium ions, lithium metal, or a lithium alloy, and an electrolyte that allows migration of lithium ions, wherein the aforementioned anode also contains an imide compound.
Imide compounds have a strong ability to coordinate with metal ions. It is thought that in an electrolyte containing an organic solvent and lithium ions, the imide compound coordinates with the lithium ions more quickly and more strongly than the organic solvent coordinates with the lithium ions, so that the imide compound exists in the form of coordination complex with the lithium ions. It can thus be envisaged that, even if an electrolyte containing an organic solvent is used, reaction between the organic solvent and the anode (the anode active substance) is suppressed due to the presence of the imide compound(s) in the lithium secondary battery of the present invention. Consequently, reaction between the organic solvent and the anode active substance can be adequately avoided and the cycle characteristics of the lithium secondary battery improved, regardless of whether the lithium secondary battery has a coin-shaped form or a cylindrical form.
Lithium secondary batteries can broadly be categorized into lithium metal secondary batteries and lithium ion secondary batteries. The technical ideas of the present invention can be applied to either type of lithium secondary battery.
In the lithium metal secondary battery of the present invention, the cathode is, for example, composed of a mixture comprising a cathode active substance that is capable of occluding and releasing lithium ions, a conductant agent that has the function of supplementing the conductivity of the cathode, and abinder for binding the cathode active substance and the conductant agent together.
The above-mentioned cathode active substance is, for example, a macromolecular conductive material, a metal oxide, a metal sulfide, an inorganic conductive material, or the like.
Examples of the above-mentioned macromolecular conductive material include polyaniline, polyacetylene, poly-p-phenylene, polybenzene, polypyridine, polythiophene, polyfuran, polypyrrole, polyanthracene and polynaphthalene, along with derivatives of these macromolecular compounds.
Examples of the above-mentioned metal oxide include manganese dioxide, vanadium pentoxide, molybdenum trioxide, chromium trioxide and cupric oxide.
Examples of the above-mentioned metal sulfide include molybdenum disulfide, titanium disulfide and iron disulfide.
Examples of the above-mentioned inorganic conductive material include fluorocarbons.
The above-mentioned conductant agent is, for example, acetylene black, graphite, carbon, or the like.
The above-mentioned binder is, for example, Teflon resin, an ethylene-propylene-diene terpolymer, or the like.
The anode used in the lithium metal secondary battery of the present invention comprises, for example, an anode active substance and an imide compound.
The above-mentioned anode active substance is, for example, metallic lithium or a lithium alloy. In the anode, the anode active substance is in the form, for example, of foil or a plate.
An example of the above-mentioned lithium alloy is an alloy of metallic lithium and at least one metal selected from the group consisting of metals such as aluminum, magnesium, indium, mercury, zinc, cadmium, lead, bismuth, tin and antimony.
Specific examples of the above-mentioned lithium alloy include a lithium-aluminum alloy, a lithium-tin alloy and a lithium-lead alloy.
Examples of the above-mentioned imide compound are compounds represented by undermentioned general formula (1).
Here, Z is an optionally substituted —(CH
2
)
n
— (where n is an integer from 2 to 7), 1,2-cyclohexylene, or 1,2-phenylene. X is a hydrogen atom, or an optionally substituted alkyl group, aralkylcarbonyl group, alkylcarbonyl group, alkoxycarbonyl group, aralkyloxycarbonyl group, or imidyloxycarbonyl group.
‘—(CH
2
)
n
— (where n is an integer from 2 to 7)’ in the definition of Z includes alkylene radicals such as ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene and heptamethylene. n is preferably 2 or 3.
Possible substituents in the definition of Z include lower alkyl groups, lower alkoxy group, and residues that can form a cyclic imide with the atoms that make up Z.
In view of the above, Z is preferably ethylene, trimethylene, 1,2-cyclohexylene, 1,2-cyclopentylene or 1,2-phenylene, and out of these most preferably ethylene or 1,2-phenylene.
The alkyl group in the definition of X may be either a straight chain alkyl group or a branched alkyl group, and preferably contains 1 to 20 carbon atoms, more preferably 1 to 6 carbon atoms.
Examples of the above-mentioned straight chain alkyl group include methyl, ethyl, propyl, butyl, pentyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl and icosyl.
Examples of the above-mentioned branched alkyl group include isopropyl, methylpropyl, methylbutyl, methylpentyl, methylheptyl, methyloctyl, methylnonyl, methyldecyl, methylundecyl, methyldodecyl, methyltridecyl, methyltetradecyl, methylpentadecyl, met
Horiuchi Hiroshi
Tsutsumi Masami
Yamamoto Tamotsu
Armstrong Westerman & Hattori, LLP
Ruthkosky Mark
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