Heterostructure FeO nanorods@imine-based covalent organic framework for long cycling and high-rate lithium storage.

FeO as an anode for lithium-ion batteries has attracted intense attention because of its high theoretical capacity, natural abundance, and good safety. However, the inferior cycling stability, low-rate performance, and limited composite varieties hinder the application of FeO-based materials. In this work, an FeO@COF-LZU1 (FO@LZU1) anode was prepared an imine-based covalent organic framework (COF-LZU1) covering on the exterior surface of FeO after rational optimization. With its unique heterostructure, the COF-LZU1 layer not only effectively alleviated the volume expansion during cycling but also improved the charge-transfer capability because of the π-conjugated system. Moreover, the organic functional group (CN, benzene ring) for COF-LZU1 provided more redox-active sites for Li storage. Under the contributions of both FeO nanorods and COF-LZU1, the FO@LZU1 exhibited an ultrahigh initial capacity and long-term cycling performance with initial discharge capacities of 2143 and 2171 mA h g after 300 cycles under 0.1 A g, and rate performance of 1310 and 501 mA h g at 0.3 and 3 A g, respectively. In addition, a high retention capacity of 1185 mA h g was achieved at 1 A g after 500 cycles. Furthermore, a full-cell with the FO@LZU1 anode and LiCoO cathode exhibited superior cycling and rate performance, which still maintained a reversible capacity of 260 mA h g after 200 cycles even at a current density of 1 A g. The proposed strategy offers a new perspective for exploring the high-rate capability and designability of FeO-based electrode materials.