Self-assembly of conformal polymer electrolyte film for lithium ion microbatteries

Abstract

I apply the theory of polar and apolar intermolecular interactions to predict the behavior of combinations of common battery materials, specifically the cathode substrate lithium cobalt oxide (LCO) and the polymer separator poly(ethylene oxide). These predictions were first tested qualitatively using hexane and PTFE, which have well-established surface energies, and then by measuring the contact angles of PEO on LCO in hexane and hexadecane, chosen for their immiscibility in PEO. For better comparison, these experiments were repeated using water instead of PEO, for a total of four systems tested. This data allowed an estimate for the experimental surface energy components of LCO to be derived, resulting in 18.3 ± 1 mJ/m2 for [gamma]LW, 0.22 ± 0.02 mJ/m2 for [gamma]+, and 5.8 ± 1.6 mJ/m2 for [gamma]-, compared to the previously reported values of 40.8 mJ/m2 for [gamma]LW, 0.0008 mJ/m2 for [gamma]+, and 0.21 mJ/m2 for [gamma]-. This variation is probably due to a variety of factors, including instrumental uncertainty in the contact angle measurement, a difference in contact angle measurement procedure, and inevitable contamination by water and other materials. Using this new data, self-assembling electrolyte-cathode systems are predicted, like LCO-polyacrylonitrile-chloroform.