Non-crystalline oligopyrene as a cathode material with a high-voltage plateau for sodium ion batteries

Oligopyrene (OPr, 3-4 pyrene units) is chemically synthesized and used as a high-voltage organic cathode for sodium ion batteries (SIBs). OPr shows anion-dominant transport behaviors during redoxswitching in NaCIO4 electrolytes, indicating that, when implemented in SIBs, OPr can reversibly incorporate/release perchlorate anions for charge-balance. A composite film, in which OPr maintains a crystalline phase with a layered structure, shows a sloping charge discharge (C-D) curve (discharge capacity = 42.5 mAh g(-1) and average voltage = 2.9 V vs. Na/Na+ at 20 mA g(-1)), implying a large overpotential due to slow CIO4- diffusion through the crystalline phase. In contrast, a composite film containing amorphous OPr exhibits substantially reduced overpotential with a plateau potential at 3.5 V during discharge. An initial reversible capacity of 121.0 mAh g(-1), which is close to one-electron transfer per pyrene unit, is decreased to 95.8 mAh g(-1) during the first 10 C-D cycles, but is subsequently stabilized with a decreasing rate of 0.30 mAh g(-1) per C-D cycle. The energy density of amorphous OPr (423 Wh kg(-1) for the 1st discharge) is so large that it exceeds those of most inorganic-based cathode materials that have been reported thus far. (c) 2013 Elsevier B.V. All rights reserved.