Lamellar multi-arch microstructure of Co3O4/N-CNTs-CNF composites as anodes for high-performance flexible lithium-ion batteries

Co3O4 is considered as one of the most promising candidates in lithium-ion batteries (LIBs) anodes due to its low-cost, abundant availability, and high theoretical capacity. However, problems of heavy aggregation, and volume change of Co3O4 hinder its practical applicability. Based on above challenges, we successfully designed and prepared an electrode by adding carbon nanotubes (CNTs) and carbon nanofiber (CNF) via directional freeze-drying. The as-prepared Co3O4/N-CNTs-CNF anode exhibits three-dimensional (3D) network structure to alleviate the volume expansion of Co3O4 and short the electron/ion transport paths. CNTs form a continuous conductive network that provides electron migration paths and prevents agglomeration of Co3O4, while CNF enhances the mechanical strength granting better flexibility. Density functional theory (DFT) calculations reveal that the N-CNTs/Co3O4 interface resulted in an electric field of the heterointerface, which facilitated charge transport. Moreover, the heterointerface possesses good electronic conductivity since more electronic states across the Fermi level. Based on these advantages, Co3O4/N-CNTs-CNF anode demonstrates an initial discharge capacity of 1176 mAh g−1 at a current density of 0.2C, high discharge specific capacity of 545 mAh g−1 at a current density of 5C, only 17.5% capacity loss over 824 cycles at 5C rate. Owing to its good electrochemical performance and flexibility, such design has great potential for applications of portable electronics.