Structure-design and theoretical-calculation for ultrasmall Co₃O₄ anchored into ionic liquid modified graphene as anode of flexible lithium-ion batteries

Cobalt oxide (Co₃O₄) is currently suitable in energy storage applications because of its high capacity based on the conversion reaction mechanism. However, unmodified Co₃O₄ suffers from distinctly inferior rate capability and poor cycling stability. On the basis of the aforementioned considerations and density functional theory (DFT) simulations, the three-dimensional hierarchical porous structure (HPS) ultrasmall Co₃O₄ anchored into ionic liquid (IL) modified graphene oxide (GO) has been successfully prepared (ultrasmall/Co₃O₄-GA-IL). The ultrasmall/Co₃O₄-GA-IL consists of Co₃O₄ co-assembled with IL modified GO to generate the HPS which can facilitate ion transfer channels through reduction of the electron and ion transportation path and transmission impedance. In addition, N-doping graphene can enhance the inherent electrical conductivity of Co₃O₄, which is proved by the DFT calculations. By virtue of the novel superstructure, the ultrasmall/Co₃O₄-GA-IL electrode demonstrates a high reversible capacity of 1,304 mAh·g⁻¹, an enhanced high-rate capability (715 mAh·g⁻¹ at 5 C), and a capacity retention of 98.4% even after 500 cycles at 5 C rate, which corresponds to 0.0003% capacity loss per cycle. Pouch cells based on the cathode are further fabricated and demonstrate excellent mechanical and electrochemical properties under bent and folded state, highlighting the practical application of our deliberately designed electrode in wearable electronics.