Abstract
In recent years, researchers have been exploring the so-called "Li-rich anion redox" cathode chemistry, wherein electrons stored on oxide anions are reversibly utilized during redox reaction along with conventional transition metal redox.(1)The combined redox of both anion and cation causes significantly higher energy storage capability from these Li-rich cathode materials.(2) However, these anionic redox reactions in transition metal oxide-based cathodes attained by extracting excess lithium ions have resulted in stability issues due to weak metal – oxygen ligand covalency.(3) Here, we present an alternative approach of introducing improved metal – ligand covalency by less electronegative chalcogen sulfur ligands in the cathode structural framework where the metal d band penetration into ligand p band thereby utilizing mixed anionic and cationic redox chemistry.(4) Through this design strategy, we report a new layered cathode material based on Li2SnS3 Li-ion conducting phase and their lithiation/delithiation properties were evaluated through in depth electrochemical analysis. Further, the electron energy loss spectroscopy (EELS) and X-ray absorption near-edge structure (XANES) analysis are used to identify the charge contributors at the metal and ligand sites during electrochemical Li+extraction. The detailed high-resolution transmission electron microscopy (HR-TEM) and high annular dark field-scanning transmission electron microscopy (HAADF-STEM) investigation revealed the structural transformations such as surface amorphization, pore formation during electrochemical cycling. Findings from this research will inspire Ni and Co free chalcogen cathode design and various functional materials in the pursuit of next generation cathode materials.
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