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 Li1.2Ni0.15Co0.1Mn0.55O₂ and high voltage LiNi0.5Mn1.5O4 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).