Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
1998-07-30
2001-04-03
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S303000, C429S188000, C429S310000, C429S311000, C429S317000, C429S251000, C525S403000
Reexamination Certificate
active
06210838
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a substrate for an ion conductor, and an ion conductor. The substrate when combined with the salt can be applied to solid conductors for batteries.
2. Description of the Prior Art
There has been expectation that ion conductive polymers can be applied to the field of electrochemistry, for example, to all solid state lithium secondary batteries, etc., because ion conductive polymers are readily processed into thin films, light-weight, and flexible. It is known that polyethylene oxide complexes of alkali metal salts are useful materials to make batteries, because the complexes exhibit ion conduction. Accordingly, systems have been investigated in which alkali metal salts which exhibit good dissociation are dissolved in polymers having polyether chains. Motion of the polyether chains promotes cation conductivity. However, polyethylene oxide exhibits high crystallinity, and low ion conductivity at room temperature. Consequently, in order to improve the mobility of the polymer-chain segments responsible for promoting ion conductivity, comb-shaped polymers have been developed. In the comb-shaped polymers, polymethyl methacrylate, polysiloxane, or polyphosphasene constitutes the main chain, and oligo ether chains are introduced into the main chain to constitute side chains. In particular, in order to reduce the temperature dependence of ionic conductivity, other systems have attracted engineer's attention in which oligoether side chains are introduced into polyether main chains in a dendritic fashion.
In the complexes of ether based polymers and alkali metal salts, however, not only the cations but also the anions are likely to move. When an electrode blocking with respect to anions is used, the anions accumulate at the interface with the electrode and the dc ionic conductivity decreases as time elapses. Therefore, single ion conductors, in which only cations move, are better than other ion conductors in terms of the application of ion conductors to batteries. In order to obtain single cation conduction, it is necessary to fix the anions to the polymer chains. In this case, ion pairing between the cations and fixed anions hinders the motion of the cations, thereby reducing the mobility of the cations. As a result, the ion conductivity decreases sharply in systems where anions, such as carboxylate or sulphonate groups, are introduced into the polymer chains.
It is possible to think of the following counter-measures in order to reduce the influences of the ion pairing: introduction of electron-withdrawing groups into polymer chains to reduce the electron density on the anions; introduction of bulky groups into the polymer chains to sterically hinder the approach of the cations towards the anions; and reduction of the distance between the fixed anions in order to reduce the activation energy required for cation movement.
Several ideas have been proposed to reduce the influence of ion pairing, because the presence of fixed anions reduces the cation mobility as described above. For example, Japanese Unexamined Patent Publication (KOKAI) No. 8-339,827 discloses the introduction of electrophilic groups into polymer chains to attract the electrons at the center of the anions, thereby lowering the electron density at the center of the anions. Accordingly, the electrons are less easily removed from the anions which are thus inhibited from being oxidized. However, the proposal fails to produce a single ion conductor, because the anions are not fixed therein.
In the literature, D. Benrabah, S. Sylla, F. Alloin, J. M. Sanchez, M. Armand, Electrochim. Acta., 40, 2259 (1995) report a system in which lithium sulfonate is fixed to a polymer. The lithium sulfonate is substituted with a fluoroalkyl group, and works as an electron-withdrawing group.
However, these conventional proposals are based on fixing anions onto the polymers. In other words, the resulting polymers have a structure in which the anions are fixed onto the polymers during the synthesis. It is necessary to carry out difficult reactions in order to synthesize the polymers in which the anions fixed therein.
SUMMARY OF THE INVENTION
The present invention has been developed in view of the aforementioned circumstances. It is therefore the object of the present invention to provide a substrate for an ion conductor, and an ion conductor which shows enhanced single ion conduction at room temperature.
A substrate for an ion conductor according to the present invention comprises:
a polymer or molecule capable of sustaining ion conduction; and
a boroxine ring bonded to the above mentioned polymer or molecule capable of sustaining ion conduction, and which captures anions resulting from a dissolved salt.
An ion conductor according to the present invention comprises:
the aforementioned present ion conductor substrate; and
a salt combined with the substrate.
The present ion conductor is a combination of the present ion conductor substrate and a salt. The boroxine ring structure is present in the molecules or polymers of the ion conductor. Boron atoms in the boroxine ring are electron pair acceptors and the boroxine ring accordingly strongly interacts with the anions (i.e., acts as an anion trap). Thus, when the salt is dissolved in the present ion conductor substrate, the resulting anions are captured by the boroxine ring. Thus, in the present ion conductor, the proportion of charge transported by the cations is greatly enhanced. As a result, high cation transport numbers can be obtained for these ion conductors.
REFERENCES:
patent: 0 856 901 (1998-08-01), None
patent: 8-45794 (1996-02-01), None
patent: 8-339827 (1996-12-01), None
patent: WO 97/16862 (1997-05-01), None
D. Benrabah et al., “Perflurorsulfonate-Polymer Based Single Ion Conductors,”Electrochimica Acta, vol. 40, pp. 2259-2264, (1995).
George L. O'Connor et al., “The Boric Acid Dehydration of Alcohols,” vol. 77, pp. 1578-1581, Mar. 20, 1955.
M.F. Lappert, “Cyclic Organic Boron Compounds. Part II.1Chemical Properties of n-Butyl Metaborate,” pp. 3256-3259 (1958).
E.W. Abel et al., “The Trialkylsilyl Esters of Boron,” pp. 690-693 (1959).
Arthur Finch et al., “Boron Ring Compounds. A New Series,” vol. 26, pp. 3250-3253 (Sep. 1961).
N. Venkatasubramanian et al., “Synthesis and characterization of spinnable sol-gel derived polyborates,”Journal of Non-Crystalline Solids130 (1991) pp. 144-156, North Holland.
Bruce Wade et al., “Synthesis of Fiber Forming Polyborates,”Polym. Mat. Sci-Eng., vol. 64 (1991), pp. 377-378.
Bruce Wade et al., “Boron Nitride Fibers From Polyborates,” Poly. Prepr. (1991), 32(3), pp. 554-555.
N. Venkatasubramanian et al., “Synthesis and Characterization of Spinnable Sol-Gel Derived Polyborates,”Polym. Mater. Sci. &Eng., vol. 62 (1990) pp. 614-619.
S.S. Zhang et al., “A Novel Electrolyte Solvent for Rechargeable Lithium and Lithium-Ion Batteries”,J. Electrochem. Soc., vol. 143, No. 12, Dec. 1996, pp. 4047-4053.
Eliana Quartarone et al., “Sol-Gel Synthesis, Thermal Characterization and Conductivity of New Glass-Polymer Solid Electrolytes,”Journal of Thermal Analysis, vol. 47 (1996) pp. 235-245.
D. Benrabah et al., “Perfluorosulfonate-Polyether Based Single Ion Conductors,” Electrochimica Acta, vol. 40, No. 13-14 (1995) pp. 2259-2264.
Mehta, M.A. et al, “Chemistry Letters” vol. 9, Jul. 31, 1997, pp 915-916, XPOO2085988, Japan.
Fujinami Tatsuo
Mehta Mary Anne
Burns Doane , Swecker, Mathis LLP
Weiner Laura
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