3D ant-nest network of Α-Fe₂O₃ on stainless steel for all-in-one anode for Li-ion battery

Ant-nest nanostructured α-Fe₂O₃ films with a thickness of 10 μm are anodically grown on stainless steel without any binder, and the resulting material functioned as a current collector in the negative electrode of Li-ion batteries. Phase of Fe₂O₃ in the structure is the key factor determining the battery performance for a high capacity and cyclability. For example, single anodization allows Fe to be dissolved faster than other components such as Cr, resulting in a high Cr ratio in the stainless steel, which deteriorates the retention of the battery capacity during cycling. On the other hand, the Fe–Cr–Ni ratio is not significantly changed if a proper pretreatment for activation, which is able to dissolve all components with a similar dissolution rate in the subsequent anodization step, is performed. The anodic ant-nest nanostructures play a vital role in not only the pathway of Li ions but also releasing the stress of volume expansion during Li insertion/extraction. The optimized electrode delivers a high reversible capacity of 737 μAh cm⁻² (737 mAh cm⁻³ or 1157 mAh g⁻¹) at a current density of 650 μA cm⁻² (1 C-rate) and sustains up to 500 cycles with only 0.13% capacity fading per cycle.