Dual functional effect of oxygen vacancies and depolarity shield embedded NiCo2O4 cathode in lithium sulfur battery

Abstract

Lithium–sulfur (Li–S) batteries are considered as promising candidates for next-generation energy-storage devices. However, their reaction reversibility is impacted by severe capacity fading caused by the lithium polysulfides (LiPSs) shuttle effect and consequent loss of active materials in the cathode. Typically, light-weight and nonpolar carbon materials are used as hosts of sulfur but face several issues such as short lifetime, low activity and capacity, which limit the cycling stability and volumetric energy density. Herein, fluorine-doped NiCo2O4 nanofibers with oxygen vacancies are explored as a high-performance host in Li–S batteries. By regulating the ratio of the fluoride ion, the formation of a cathode electrolyte interface (CEI) layer is suppressed during the charge/discharge cycles. Accordingly, the nanofiber electrode exhibits lower polarization and faster reaction kinetics than fluorine-doped NiCo2O4 without oxygen vacancies or NiCo2O4 with a CEI layer. The optimized fluorine-doped NiCo2O4 electrode with oxygen vacancies delivers 628 mAh g−1 at 0.3 C and a low fading rate of 0.052% per cycle over 1300 cycles at 1 C. The present strategy provides insights in the development of host materials that is based on regulating the formation of the CEI layer and the adsorption and conversion of LiPSs.