The demand for lithium secondary batteries to meet high power and high-energy system applications has resulted in substantial research and development activities to improve their safety, as well as performance. As the world becomes increasingly dependent on portable electronic devices, and looks toward increased use of electrochemical storage devices for vehicles, power distribution load leveling and the like, it is increasingly important that the safety of such devices be paramount, especially as these devices are being used in such environments as airliners and space vehicles. The effort to date has included research in flame-retardants, solid polymer electrolytes, and new electrolyte concepts with improved thermostability. Thus, the development of highly conductive electrolytes, free of any problems associated with volatile and combustible solvents, is of paramount importance. Polymer electrolytes have a number of advantages over the materials currently used in high-performance batteries. Compared to conventional batteries using heavy metals such as lead, nickel, and cadmium, the lithium-based polymer electrolyte batteries would be many times lighter. The proposed designs of these batteries would also allow them to be formed into various shapes besides the traditional cylindrical or rectangular shapes typical in regular batteries. (See, Gray, F. M. Solid Polymer Electrolytes; VCH Publishers: New York, 1991, at 1-4, 5-21). These advantages have fueled commercial interests and research interests into improving the conductive properties of polymer electrolytes. Poly(ethylene oxide) (PEO) has been known to dissolve alkali metal salts and exhibit conductivity since the early 1970's. (See, Fenton, D. E.; Parker, J. M.; Wright, P. V. Polymer 1973, 14, at 589). The properties of PEO have been studied extensively and are outlined in a number of review articles and texts. (See Gray supra; See also, Shriver, D. F.; Bruce, P. G. in Solid State Electrochemistry, P. G. Bruce, ed., Cambridge University Press: New York, 1995, at 95, 97-106). Of more recent interest has been a class of polymers with Si—O backbones known as polysiloxanes. (See, Mark, J. E.; Allcock, H. R.; West, R. Inorganic Polymers; Prentice Hall: N.J., 1992, at 3). The Si—O backbone of these polymers is highly flexible, yet retains its chemical and thermal integrity. Polysiloxanes also have low glass transition temperatures, Tg, and, when substituted with oligoethylene oxide groups, solvate lithium salts, making the polysiloxanes good candidates for potentially useful polymer electrolytes. (See, Hooper, R.; Lyons, L. J.; Mapes, M. K.; Schumacher, D.; Moline, D. A.; West, R. Macromolecules 2001, 34, 931. R. Hooper, L. J. Lyons, D. A. Moline, R. West, Silicon Chemistry 2002, 1, at 121; Lin, C.; Kao, H.; Wu, R.; Kuo, P. Macromolecules 2002, 35, at 3083; Zhou, G.; Khan, I. M.; Smid, J. Macromolecules 1993, 26, at 2202; Siska, D. P.; Shriver, D. F. Chem. Mater 2001, 13, at 4698; Zhu, Z.; Einset, A. G.; Yang, C.; Chen, W.; Wnek, G. E. Zhu, Z.; Einset, A. G.; Yang, C.; Chen, W.; Wnek, G. E. Macromolecules 1994, 27, at 4076; Zhu, Z.; Einset, A. G.; Yang, C.; Chen, W.; Wnek, G. E.; Fish, D; Khan, I. M.; Wu, E.; Smid, J. British Polymer Journal 1988, 20, at 286; Morales, E.; Acosta, J. L. Electrochimica Acta 1999, 45, at 1049.)
The present inventors synthesized the polysiloxane polymers of the present invention with the goal of creating low viscosity, low molecular weight samples to enhance ionic conductivity.
A primary objective of the present invention is to provide a high conductivity, safe liquid electrolyte for use in electrochemical storage devices, especially lithium secondary batteries, as well as super capacitors and hybrid devices.
Another objective is to provide a safe electrolyte that is easy and inexpensive to manufacture.
Yet another objective is to provide an electrolyte for medical and high energy applications.