Electrochemically engineered single Li-ion conducting solid polymer electrolyte on titania nanotubes for microbatteries

Single Li-ion conducting p-sulfonated poly(allyl phenyl ether) (SPAPE) is electrochemically synthesized directly on TiO2 nanotubes in the range of −1.5 to −1.8 V vs. Ag/AgCl. The electrochemical deposition conditions are studied by cyclic voltammetry and chronoamperometry; the polymer formation can be followed by electrochemical impedance spectroscopy. The polymer structure is analyzed by NMR and FTIR spectroscopies, showing the formation of linear aliphatic chains with methyl-oxy-benzene sulfonate side groups. SEM observations of the polymer morphology show that a thin (∼300 nm) and continuous layer is obtained depending on the electrochemical synthesis conditions. The combination of a mobile aliphatic backbone, ether groups with reduced cation affinity and immobile anions grafted on the side chains allows obtaining a single lithium-ion conducting polymer. Half-cell battery tests against Li metal show an excellent cycling performance with high areal capacity (up to 110 μAh cm−2) and very good retention especially at large C-rates, studied up to 12 C.