Organic Small Molecules with Electrochemical-Active Phenolic Enolate Groups for Ready-to-Charge Organic Sodium-Ion Batteries

Organic materials have attracted much attention in sodium ion batteries (SIBs) because of their advantages such as being environmentally benign and having high designability. Capacities and cycle life of organic materials are the most important parameters in most research which has been paid much effort to obtain an impressive electrochemical performance on the material level, and the sodium-detachable ability of these materials to directly match with the sodium-free anode is neglected. In this work, one organic sodium salt (C6H2Na2O6) exhibits the unique ability (charging first in half cell) unlike other reported organic cathode materials (normally discharging first) for SIBs. The redox mechanism and structure change are investigated by in situ and ex situ tests to give a better understanding for C6H2Na2O6. Satisfying electrochemical performance (74% capacity retention after 600 cycles at 0.05 A g−1 and 63% capacity retention at 5 A g−1 when compared with capacity at 0.05 A g−1) is achieved by the C6H2Na2O6 electrode. In addition, matched with hard carbon, full cells are assembled successfully like other transition metal containing cathode materials because C6H2Na2O6 electrode can deliver its sodium ions to a sodium-free anode directly without any presodiation.