Reversible Dual Anionic-Redox Reaction in Layered Chalcogenide Cathode Materials

Abstract

Utilizing the reversible sulfur redox reaction in layered chalcogenides opens new approaches for the development of new battery cathode materials with higher capacities for sodium-ion batteries. However, only limited number of studies on the nature of anionic redox chemistry in layered chalcogenides has been reported in the literature. We have designed and synthesized a series of layered chalcogenide cathode materials NaCrS1-xSex and investigated their sodium storage performances. Among them, NaCrSeS exhibits a unique charge/discharge feature with a quite small polarization of 0.15 V and more than 90% high coulombic efficiency. At the same time, a very high charge capacities of 115.5mAh g-1 (0.80 Na+/CrSSe) is achieved at a charging rate as high as 27.8 C. The charge compensation mechanisms and structural evolution of these cathode materials have been investigated using synchrotron based multi-model characterization techniques such as ex situ x-ray absorption spectroscopy, x-ray diffraction and x-ray pair distribution function analysis combined with DFT calculation. The results show that the charge compensation in NaCrSSe cathode is mainly through the dual anionic-redox reaction with the reversible formation of (S)n– and (Se)n– as well as (S/Se)2 m– species during the Na intercalation/deintercalation processes. These results will provide valuable information for developing new anion redox based cathode materials with high-capacity and fast kinetics. Acknowledgment: The work at Brookhaven National Laboratory was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technology Office of the U.S. Department of Energy through the Advanced Battery Materials Research (BMR) Program under contract DE-SC0012704. This research used resources at beamlines 7-BM (QAS) and 28-ID-2 (XPD) of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704.