Synthesis of a class of oxocarbons (C4O4, C5O5) and the application as high-capacity cathode materials for lithium-ion batteries

Oxocarbons (C_nO_n, n=3, 4, 5, 6, …) are a series of compounds that are only composed of carbonyl groups. The highly electrophilic carbon atoms in C_nO_n make their poor stability toward H₂O, and thus the synthesis of C_nO_n is very challenging. Here an oxidation-dehydration method is developed to successfully synthesize C₄O₄ and C₅O₅. The combination of nuclear magnetic resonance (¹³C NMR, ¹H NMR), mass spectra, and infrared spectra unambiguously proves the exact chemical structure of C₄O₄ and C₅O₅. When used as a cathode material in lithium-ion batteries (LIBs), C₅O₅ could deliver a high discharge capacity of 698 mAh g^-1 (corresponding to an energy density of 1,256 Wh kg^-1_C5O5). Furthermore, ex-situ infrared spectra and density functional theory (DFT) calculations demonstrate that the carbonyl groups are redox active sites during discharge and charge processes. This work paves the way to achieve the synthesis and battery application of oxocarbons.