High-Potential Redox Shuttle for Use in Lithium-Ion Batteries

Redox shuttle additives can be used in lithium-ion cells to protect against overcharging and for cell balancing in multicell packs. Most previously reported redox shuttles have been either unstable as shuttles, resulting in a short duration of overcharge protection, or have redox potentials that make them suitable only for cells containing lower potential positive electrode materials, such as LiFePO4. A new molecule, 1,4-di-t-butyl-2,5-bis(2,2,2-trifluoroethoxy)benzene, is shown here to be a stable redox shuttle with a redox potential of 4.25 V and provides overcharge protection in full Li-ion cells, implying adequate reductive stability. Experiments using Li/LiCoO2 and Li/Li[Ni1/3Mn1/3Co1/3]O-2 cells show that this molecule can work with high-energy-density positive electrodes as well as in full cells containing LiFePO4 positive electrodes and Li, mesocarbon microbead, or Li4Ti5O12 negative electrodes. c 2009 The Electrochemical Society. [DOI: 10.1149/1.3077578] All rights reserved.