Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1998-05-29
2001-08-28
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S236000, C429S245000, C429S231100, C429S231800, C429S330000, C429S300000, C429S304000
Reexamination Certificate
active
06280878
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electrode structure having a current collector of a lithium secondary battery, electric double-layer capacitor or the like, and a lithium secondary battery and electric double-layer capacitor using the electrode.
2. Background Art
Secondary batteries for use in notebook size personal computers, video cameras and the like are required to have a high energy density and a satisfactory charge/discharge cycle life. The secondary batteries which have been used heretofore include lead acid batteries, nickel-cadmium batteries, and nickel-hydrogen batteries. Lithium secondary batteries were proposed and have been used in practice as a secondary battery having a higher energy density.
In the prior art, liquids are used as the electrolyte of such secondary batteries. If the electrolyte is made solid, it is attractive as batteries of the next generation type because solid electrolytes can prevent liquid leakage and enables sheet structuring. In particular, if lithium ion secondary batteries which now enjoy rapid widespread use in notebook size personal computers and the like can be structured into a sheet form or multilayer compact size, they are expected to find a wider range of application.
In order that such solid electrolytes be used, it is proposed to construct them as ceramic materials, polymeric materials or composite materials. Among others, gel electrolytes which are plasticized using a polymeric electrolyte and an electrolytic solution are considered promising in the development of electrolytes because they have both the high conductivity of liquids and the plasticity of polymers.
An example of utilizing a gel electrolyte in a battery is already disclosed in U.S. Pat. No. 3,985,574. This patent includes examples in which a polyacetal which has been gelled by incorporating therein a supporting electrolyte such as ammonium perchlorate and a solvent such as propylene carbonate is used as a separator or positive electrode. A battery is constructed using lithium as the negative electrode. The positive electrode is prepared by bonding a honeycomb grid to a metal such as silver under heat and pressure and applying the gel thereto. Further, U.S. Pat. No. 5,296,318 discloses a practical system.
Specifically, U.S. Pat. No. 5,296,318 discloses that a copolymer of poly(vinylidene fluoride) with hexafluoropropylene is used as polymeric matrices of a positive electrode, negative electrode and separator of a lithium intercalation battery. The key feature of this disclosure is the use of the specific copolymer. The reason why characteristics can be improved is believed to be that since not only a binder alone is added to the electrode, but a gel electrolyte composition is also mixed during formation of the electrode, the electrode well matches with the electrolyte so that the internal resistance can be reduced. That is, unlike the solution system, an electrode composition inherent to the gel electrolyte system (referred to as gel electrode composition, hereinafter) is constructed.
Further, U.S. Pat. No. 5,470,357 discloses an electrode structure wherein a metal grid of aluminum or copper is used as the current collector. The method of making electrodes involves forming a film of a gel electrode composition and then bonding a metal grid thereto by the application of heat and pressure. The electrode composition cannot be applied to the grid during formation of the electrode because when a practical slurry is used, it cannot be fully held by the grid. Also, the results of our study showed that the use of a copolymer of poly(vinylidene fluoride) with hexafluoropropylene as the gel electrolyte was impractical because adhesion between the electrode and the collector metal was weak. Accordingly, it is believed that the manufacturing process described in Examples of U.S. Pat. No. 5,470,357 is used in practice. More particularly, it is necessary to previously coat the collector with a paint in which a conductive aid is mixed with a polymeric matrix component in a gel electrolyte, a paste in which a conductive material is added to a hot-melt paint as shown in the above-referred patent, or a conductive paint for use in electrolytic capacitors. Usually, the electrode (film+collector) is prepared by bonding the thus obtained grid to the gel electrode composition film under heat and pressure. It is thus apparent that a special step is necessary during formation of the electrode, leading to a reduced mass productivity and an increased cost.
SUMMARY OF THE INVENTION
An object of the invention is to provide an electrode capable of increasing the retaining force of a gel electrolyte component to a collector for enabling direct coating of the gel electrolyte component to the collector and thus featuring improved mass productivity and a reduced cost; and to provide a lithium secondary battery and an electric double-layer capacitor using the electrode.
The above object is achieved by the following construction.
(1) An electrode comprising a porous metal member in sheet form having a three-dimensional skeleton structure and a solid polymer electrolyte.
(2) The electrode of (1) wherein said solid polymer electrolyte comprises a gelled polymer matrix containing an electrolytic solution.
(3) The electrode of (1) wherein said porous metal member has a porosity of 80 to 98% and a mean maximum pore diameter of 100 to 800 &mgr;m.
(4) A lithium secondary battery comprising the electrode of (1).
(5) An electric double-layer capacitor comprising the electrode of (1).
FUNCTION
With the above-described problems borne in mind, we made investigations on the electrode which is easier to manufacture. We have found that the desired electrode can be obtained by tailoring the electrode structure using a porous metal member having a three-dimensional skeleton structure. That is, a porous metal member having a three-dimensional skeleton structure is used as the collector instead of the grid, thereby increasing the retaining force of a gel electrolyte component to the collector for enabling direct coating or printing of the gel electrolyte component to the collector. Further, as will be described later, since the porous metal member having a three-dimensional skeleton structure is contained within the electrode, the internal resistance of the electrode is reduced and rated properties are improved. This advantage is attributable to the porous metal member having a three-dimensional skeleton structure as used herein, and becomes more prominent when a gel electrolyte favored by the invention is used.
It is already disclosed in JP-A 315768/1992 to apply to the collector a porous metal member having a three-dimensional skeleton structure. In this patent, the porous metal member is used in a nickel-oxygen battery for the purpose of preventing the active material from separating from the collector surface. As opposed to this, in the present invention, the porous metal member having a three-dimensional skeleton structure plays not only the role of holding the active material, but also the role of holding the gelled electrolyte.
When the gelled solid polymer electrolyte favored by the invention is used, mere contact of the active material with the collector surface is not important, but the co-presence of three phases which are the collector, the gelled solid polymer electrolyte and the active material is important. Herein, the active material must be in contact with the collector, with a conductive aid interposed therebetween. In the case of a solution system, a three-phase coexisting region is generally formed even when the active material is not in contact with the collector because the solution fully penetrates internally. Therefore, a three-phase interface is formed even when it is not positively intended to form such an interface, and direct coating to a foil is possible. However, in the even where the solid electrolyte is used, if the active material is in direct contact with the collector surface, the formation of a three-phase interface becomes diffi
Kakinuma Akira
Kurihara Masato
Maruyama Satoshi
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
TDK Corporation
Weiner Laura
LandOfFree
Electrode and lithium secondary battery using this electrode does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrode and lithium secondary battery using this electrode, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrode and lithium secondary battery using this electrode will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2457055