Carbon nanofiber@platinum by a coaxial electrospinning and their improved electrochemical performance as a Li−O2 battery cathode

Abstract

Non-woven mats constructed from carbon nanofibers with metal (Pt, Co, or Pd) nanoparticles on their surfaces (CNF@metal) were fabricated by coaxial electrospinning for use in non-aqueous lithium‒oxygen (Li‒O2) battery (LOB) cathodes. Through coaxial electrospinning, the metal nanoparticles were evenly distributed on the CNF surfaces, and the samples were directly applied as LOB cathodes. Although the Co and Pd nanoparticles did not promote the desired Li‒O2 reactions, the CNF@Pt exhibited much improved electrochemical performance with highly reversible Li‒O2 operations. Therefore, the Li‒O2 cell using the CNF@Pt cathode exhibited significantly enhanced specific capacity, rate capability, energy efficiency, and cycle stability compared to the other samples. The observed formation of Li2O2 film, rather than toroidal particles, on the CNF@Pt after an early stage of discharge may be attributed to greatly reduced overpotentials both on discharge and charge, as well as a considerably prolonged cycle life (163 cycles) with a limiting capacity of 1000 mAh/gc at a current density of 500 mA/gc. In particular, in-situ differential electrochemical mass spectrometry studies revealed that the cycles of the Pt-catalyzed Li‒O2 cell were mainly based on the reversible formation/decomposition of Li2O2, as evidenced by high O2 evolution and negligible CO2 evolution, even after long-term cycles.