Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2000-06-05
2002-09-10
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S306000, C429S310000, C429S311000, C429S313000, C429S317000, C429S219000, C429S220000, C429S223000, C429S224000, C429S231100, C429S231200, C429S231500, C429S231950, C252S062200
Reexamination Certificate
active
06447952
ABSTRACT:
BACKGROUND OF THE INVENTION
With the increasing popularity and demand for portable electronic devices for computing, communication, and entertainment, the need for batteries for use in such portable applications has also increased. There is a particular need for rechargeable, i.e., secondary batteries, in portable device applications. Batteries that are reliable, long-lasting, low-cost, and environmentally friendly, yet which possess both high energy and power densities are most desirable. There is a particular need for high energy density secondary batteries for use in portable military applications. Batteries that exhibit energy and power densities of up to about 110 Wh/kg and 40 W/kg, respectively, at an operating current density of about 20 mA/cm
2
are preferred for military applications.
In theory, alkali metal batteries, most importantly those where the alkali metal is lithium, utilizing an alkali metal anode, an alkali metal ion-conducting polymer electrolyte and an alkali metal-intercalating cathode, can provide secondary batteries for portable applications and meet the preferred performance characteristics for portable military applications. However, the application of polymer electrolytes in electrochemical cells, particularly in battery construction, has been restricted by inadequate ionic conductivity of the electrolyte. Most materials that have been examined possess values between 10
−9
to 10
−5
S/cm at room temperature. Target ionic conductivities to meet preferred performance characteristics under ambient conditions, are in the 10
−3
to 10
−2
S/cm range. The most widely studied material, poly(ethylene oxide) (PEO), incorporating lithium salts such as LiClO
4
and LiCF
3
SO
3
, demonstrated ionic conductivities well below the 10
−3
S/cm target at room temperature (Berthier, C. et al. (1983) Solid State Ionics 11:91; Shi, J. and Vincent, C. A. (1993) Solid State Ionics 60:11; Chang, W. and Xu, G. (1993) J. Chem. Phys. 99:2001; Torell, L. M. et al. (1993) Polym. Advan. Technol. 4:152).
Polymer blends and copolymers of various linear and cross-linked polymers have been examined as polymer electrolytes (Li, N. et al. (1992) J. Appl. Electrochem. 22:512; Prabhu, P. V. S. et al. (1993) J. Appl. Electrochem. 23:151; Takeoka, H. A. and Tsuchida, E. (1993) Polym. Advan. Technol. 4:53), including poly(vinyl acetate) (Greenbaum, S. G. et al. (1985) Solid State Ionics 18-19:326), poly(dimethyl siloxane) (PDMS) based matrices (Greenbaum, S. G. et al. (1986) J. Appl. Phys. 60:1342), propylene carbonate or ethyl carbonate (Abraham, K. M. and Alamgir, M. (1990) J. Electrochem. Soc. 137:1657; Alamgir, M. et al. (1991) in “Primary and Secondary Lithium Batteries,” K. M. Abraham and M. Solomon (eds.), Electrochem. Soc. Proc. Ser. PV91-3:131; Alamgir, M. and Abraham, K. M. (1993) J. Electrochem. Soc. 140:L96; Huq, R. et al. (1991) in “Primary and Secondary Lithium Batteries,” K. M. Abraham and M. Solomon (eds.), Electro-chem. Soc. Proc. Ser. PV—91-3:142; Huq, R. et al. (1992) Solid State Ionics 57:277; Huq, R. et al. (1992) Electrochim Acta 37:1681), poly(propylene oxide) (Greenbaum, G. et al. (1988) Brit. Polym. J. 20:195), and poly[bis(methoxyethoxy) ethoxy phosphazene] (MEEP) (Greenbaum, S. G. et al. (1991) Mat. Res. Soc. Symp. Proc. 210:237). Although some incremental ionic conductivity performance improvements were realized with these materials, ionic conductivities of 10
−3
S/cm at room temperature were not achieved.
Dielectric properties and ionic conductivities of lithium triflate complexes of polysiloxanes (average molecular weight 4500-5000) having certain cyclic carbonate side chains have also been examined (Z. Zhu et al. (1994) Macromolecules 27:4076-4079). These derivatized polysiloxanes were reported to be very viscous and to exhibit maximum lithium ion conductivities of 1-2×10
−4
S/cm.
Desirable features in technically useful polymer electrolytes include: i) high ionic conductivity at or close to ambient temperatures; ii) ionic transport numbers of unity or near unity for the cation of interest; iii) the ability to maintain mechanical integrity and dimensional stability within a cell subjected to electrochemical cycling; iv) environmental stability; v) the ability to maintain stable interfacial regions between electrodes; and vi) safety. There remains a significant need in the art for polymer electrolytes conductivity and mechanical properties suitable for battery applications and particularly for use as interelectrode spacers in such batteries.
SUMMARY OF THE INVENTION
This invention provides alkali ion-conducting polymer electrolytes having high ionic conductivity and improved elastomeric properties compared to currently available materials. These polymer electrolytes are useful, for example, in high energy density secondary batteries for portable electronic devices.
The polymer electrolytes of this invention consist of polymer matrices complexed with alkali metal salts. The ability of polymers, most notably polyethers, to chelate alkali metal cations is used to achieve ionic conduction within these materials. The electrolyte is formed by solubilizing an alkali metal salt in a polymer matrix which facilitates ionic dissociation and enhanced ion mobilities. The polymer electrolytes of most interest are those incorporating lithium ion salts and which exhibit high lithium ion conductivity at or below ambient temperatures. The cross-linked siloxane polymer electrolytes of this invention also possess favorable elastomeric properties for use as thin and flexible interelectrode layers for construction of battery cells and batteries.
Provided herein is an alkali ion-conducting polymer electrolyte comprising a cyclic carbonate-containing polysiloxane preferably treated with a modification agent capable of crosslinking the siloxane or extending the chain length of the siloxane, and having an alkali metal ion-containing material solubilized therein. Preferably the alkali metal ion is lithium.
The alkali ion-conducting polymer electrolytes of this invention comprise a polysiloxane derivatized with cyclic carbonate groups and preferably treated with crosslinking agents and/or polymer chain extenders (modification agents). The carbonate groups facilitate ionic dissociation and treatment with crosslinking/chain extension agents is believed to provide desirable elastomeric properties. Polymer electrolytes are prepared by treatment of a cyclic carbonate-containing polysiloxane with a crosslinking agent or a polymer chain extension agent (modification agent) in the presence of an alkali metal ion salt, preferably a lithium salt. This strategy exploits the concept that carbonate oxygens, within a single phase carbonate-siloxane polymer matrix, facilitates extensive ionic dissociation of introduced alkali metal salts, and that furthermore elastomeric behavior of the matrix under ambient temperature conditions leads to enhanced mobility of lithium ions. Polymer electrolytes having these properties permit small interelectrode distances to be achieved within portable secondary lithium batteries.
Preferred polymer electrolytes of this invention exhibit alkali metal ion conductivities in the range of 10
−4
to 10
−2
S/cm or higher. Preferred polymer electrolytes having these properties that are useful for applications in batteries exhibit glass transition temperatures that are lower than ambient temperature. In particular, the use of ionically conducting polymeric electrolytes facilitates the fabrication of thin-layer, flexible battery designs provided that the polymer can maintain a reliable interelectrode spacing without electronic shorting. This ability facilitates achieving low internal resistance and thereby improving electrochemical performance in terms of delivered energy density and discharge performance.
More specifically, polymer electrolytes of this invention are prepared by crosslinking or chain extension (modification) of internally derivatized polysiloxanes (I) or end dervatized polysiloxanes (II)
Adamic Kresimir
Sammells Anthony F.
Spiegel Ella F.
Eltron Research, Inc.
Greenlee Winner and Sullivan P.C.
Weiner Laura
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