Molecularly reinforced polymers and self assembled nanocomposites for secondary lithium batteries

A series of soluble poly(p-phenylene)s (PPP) substituted with short poly(ethylene oxide) (PEO) side chains were synthesized. Characterization data for these polymers indicate that they take on hairy rod-like structures. As the side chain increases in length, the characteristics of these materials evolve from those of PPP to resembling those of PEO at long side chains. When the weight fraction of the tethered chains exceeds 80%, the thermal transitions of the polymers and the resulting ionic conductivities nearly match those of polyethylene oxide. Solid polymer electrolytes based on oligo(ethylene oxide)-substituted PPP and lithium perchlorate exhibit conductivities ranging from 10-6 to 5 x 10-4 S/cm at 30°C, with the conductivity dependent on the length of the ethylene oxide chain attached to each ring. When the ethylene oxide chain is short, the solubility of LiClO4 is low, leading to undissolved salt and low conductivities. Lengthening the ethylene oxide chains increases the solubility of LiClO4 and chain mobility, causing a more than two order of magnitude increase in the room temperature conductivity.; The properties of composites based on modified silica nanoparticles in poly(ethylene oxide) (PEO) is also reported. Silica bound lithium sulfonimide salts were prepared through the synthesis of triethoxysilane, N-pentane trifluoromethane sulfonimide, subsequent attachment to the surface and formation of the lithium salt. The experimental results of PEO/modified silica composites revealed that an optimum conductivity was attained at a weight loading of 30 wt%. These composites exhibit ionic conductivities that are weakly dependent on temperature and are on the order of 10-6 S/cm at 30°C. The lithium ion transport numbers were determined to be 0.86 +/- 0.03.