3-Hexylthiophene as a Stabilizing Additive for High Voltage Cathodes in Lithium-Ion Batteries

3-Hexylthiophene was incorporated into battery electrolyte as a life-extending additive. Upon oxidation, this monomer forms a conductive, conjugated polymer, resulting in significant increase in the cycle lifetimes of lithium half-cells containing high capacity Li 1.2 Ni 0.15 Co 0.1 Mn 0.55 O 2 and high voltage LiNi 0.5 Mn 1.5 O 4 cathodes. This additive significantly reduces the interfacial impedance growth observed in the cell without additive, which indicates an effective protection of the interface when using 3-hexythiophene. We also observed an improvement in safety when 3-hexylthiophene was incorporated. Electron microscopy images show the new polymer on the cathode surface, specifically poly(3-hexylthiophene) as supported by characterization of the cathode surface using vibrational spectroscopy (Raman and infrared) and mass spectrometry (MALDI).