PEDOT Encapsulated FeOF Nanorod Cathodes for High Energy Lithium-Ion Batteries.

Conversion-reaction cathodes can potentially double the energy density of current Li-ion batteries. However, the poor cycling stability, low energy efficiency, and low power density of conversion-reaction cathodes limit their applications for Li-ion batteries. Herein, we report a revolutionary advance in a conversion-reaction cathode by developing a core-shell FeOF@PEDOT nanorods, in which partial substitution of fluorine with oxygen in FeF3 substantially enhance the reaction kinetics and reduce the potential hysteresis, while conformal nanolayer PEDOT coating provides a roubst fast electronic connection and prevents the side reactions. The FeOF@PEDOT nanorods deliver a capacity of 560 mA h g(-1) at 10 mA g(-1) with an energy density of >1100 W h kg(-1), which is more than two times higher than the theoretical energy density of LiCoO2. The FeOF@PEDOT nanorods can maintain a capacity of ~430 mA h g(-1) at 50 mA g(-1) (840 W h kg(-1)) for over 150 cycles with capacity decay rate of only 0.04% per cycle, which is 2 orders of magnitude lower than the capacity decay rate ever reported among all conversion-reaction cathodes. Detailed characterizations were conducted to identify the structure and mechanism responsible for these significant improvements that could translate into a Li-ion cell with a 2× increase in energy density.