Operando study of Fe ₃ O ₄ anodes by electrochemical atomic force microscopy

Present study provided visual evidence of solid electrolyte interphase (SEI) layer formation on Fe ₃ O ₄ anode during charge and discharge using in situ electrochemical atomic force microscopy. AFM images show that SEI layer formed on Fe ₃ O ₄ electrode from fluoroethylene carbonate (FEC)-based electrolyte was more stable and compact than that formed from ethylene carbonate (EC)-based electrolyte. In addition, presence of surface cracks on the electrodes indicated poor formation of an intact SEI layer. This observation was more apparent in the EC-based electrolyte. Lack of an intact SEI layer resulted in decomposition of electrolytes which were reflected by presence of large air bubbles and dendrites on the electrode during CV. Although FEC-based electrolyte improved the performance of Fe ₃ O ₄ anodes in lithium ion batteries, its protective effects were far from perfect. To accelerate the application of Fe ₃ O ₄ or other metal oxide anodes in lithium ion batteries, better electrolytes and sophisticated carbon coating techniques are needed.