Three-dimensional nitrogen-doped hollow carbon fiber with a micro-scale diameter as a binder-free oxygen electrode for Li-O₂ batteries

A nitrogen-doped hollow carbon fiber was prepared using polydopamine and electrospun polystyrene fibers as a sacrificial template for the oxygen electrode of Li-O₂ batteries. Owing to the fiber structure, a binder is not needed to fabricate the electrode, which eliminates the possibility of side reactions associated with a binder. It was demonstrated that the hollow tubular structure with a large inner diameter is highly effective for accommodating a substantial amount of discharge products without hindering the mass transfer of reactants, even under the fully discharged condition. The reversibility and rate capability were improved by optimizing the length of the fiber. The nitrogen-doped carbon reduced the overall overpotential between the oxygen reduction and oxygen evolution reactions. Therefore, the nitrogen-doped hollow carbon fiber can be used to obtain a highly effective oxygen electrode for Li-O₂ batteries.