Origin of Phase Engineering CoTe₂ Alloy Toward Kinetics-Reinforced and Dendrite-Free Lithium-Sulfur Batteries.

Abstract

Slow electrochemistry kinetics and dendrite growth are major obstacles for lithium-sulfur (Li-S) batteries. The investigations over the polymorph effect require more endeavors to further access the related catalyst design principles. Herein, the systematic evaluation of CoTe₂ alloy with two polymorphs regarding sulfur reduction reaction (SRR) and lithium plating/stripping is reported. As disclosed by theoretical calculations and electrochemical measurements, the orthorhombic (o-) and hexagonal (h-) CoTe₂ make a substantial difference. The reactivity origin of the CoTe₂ polymorphs is explored. The higher position of d-band centers for the Co atoms on the o-CoTe₂ leads to a higher displacement of the antibonding state; the lower antibonding state occupancy, the more effective the interaction with the sulfide moieties and lithium. Hence, o-CoTe₂ annihilates h-CoTe₂ and exhibits better catalysis and more uniform lithium deposition, consolidated by excellent performance of full cell made of o-CoTe₂ . It keeps stable charging/discharging for 800 cycles at 0.5 C with only 0.055% capacity decay per cycle and even achieves an areal capacity of 6.5 mAh cm^-2 at lean electrolyte and high sulfur loading of 6.4 mg cm^-2 . This work establishes the mechanistic perspective about the catalysts in Li-S batteries and provides new insight into the unified solution.