Biomimetic Synthesis of Polydopamine Coated ZnFe₂O₄ Composites as Anode Materials for Lithium-Ion Batteries

Metal oxides as anode materials for lithium storage suffer from poor cycling stability due to their conversion mechanisms. Here, we report an efficient biomimetic method to fabricate a conformal coating of conductive polymer on ZnFe₂O₄ nanoparticles, which shows outstanding electrochemical performance as anode material for lithium storage. Polydopamine (PDA) film, a bionic ionic permeable film, was successfully coated on the surfaces of ZnFe₂O₄ particles by the self-polymerization of dopamine in the presence of an alkaline buffer solution. The thickness of PDA coating layer was tunable by controlling the reaction time, and the obtained ZnFe₂O₄/PDA sample with 8 nm coating layer exhibited an outstanding electrochemical performance in terms of cycling stability and rate capability. ZnFe₂O₄/PDA composites delivered an initial discharge capacity of 2079 mAh g^-1 at 1 A g^-1 and showed a minimum capacity decay after 150 cycles. Importantly, the coating layer improved the rate capability of composites compared to that of its counterpart, the bare ZnFe₂O₄ particle materials. The outstanding electrochemical performance was because of the buffering and protective effects of the PDA coating layer, which could be a general protection strategy for electrode materials in lithium-ion batteries.