Cobalt-doped mesoporous carbon nanofibres as free-standing cathodes for lithium-oxygen batteries

Herein, we present binder-free O-2 electrodes of mesoporous carbon nanofibres and Co nanoparticles (Co-doped CNF). Such electrodes are synthesized using electrospinning techniques coupled with subsequent thermal treatments. The fibre-based mats behave as free-standing electrodes due to the presence of 3D cross-linked web structures, and thus additional metal mesh or gas diffusion layer supports are not required. The absence of polymeric binders in the cathode avoids side reactions due to binder instability during cell cycling. The Co-doped CNFs are characterized by field emission scanning electron microscopy, inductively coupled plasma atomic emission spectroscopy, X-ray diffraction and Raman analysis. CNFs are decorated by homogeneously distributed Co (0) nanoparticles, with sizes in the range of 10-50 nm and Co content lower than 10 wt%. N-2 adsorption-desorption measurements show that the specific surface area of the CNFs is greatly affected by incorporation of the metal nanoparticles. The introduction of Co nanoparticles enhances the degree of graphitization of the CNFs, which is beneficial to CNF conductivity. Measured BET surface areas of Co-doped CNFs are in the range of 40-300 m(2) g(- 1), depending on Co content. Results show that the Li-O-2 cell comprising the Co-doped CNF free-standing cathodes can deliver specific capacities of 3700 mA h g(- 1) based on the total mass of the electrodes and good cycling performance is achieved at the curtailed capacity of 100 mA h g(- 1). The good performance of the Co-doped CNFs may be attributed to the mesoporous structure of CNFs which could facilitate the deposition of solid products during discharge and decrease the mass transport resistance. Different morphologies of the Li2O2 crystals obtained during discharge with Co-doped CNF cathodes support the hypothesis that the presence of Co may induce alterations by forming easily decomposable Li2O2.