Active Sulfur-Host Material VS₄ with Surface Defect Engineering: Intercalation-Conversion Hybrid Cathode Boosting Electrochemical Performance of Li–S Batteries

Abstract

Transition-metal sulfides as late-model electrocatalysts usually remain inactive in lithium−sulfur (Li−S) batteries in spite of their advantages to accelerate the rapid conversion of lithium polysulfides (LiPSs). Herein, a series of cobalt-doped vanadium tetrasulfide/reduced graphene oxide (x%Co-VS 4 /rGO) composites with an ultrathin layered structure as an active sulfurhost material are prepared by a one-pot hydrothermal method. The well-designed two-dimensional ultrathin 3%Co-VS 4 /rGO with heteroatom architecture defects (defect of Co-doping and defect of S-vacancies) can significantly improve the adsorption ability on LiPSs, the electrocatalytic activity in the Li 2 S potentiostatic deposition, and the active sulfur reduction/oxidation conversion reactions and greatly boost the electrochemical performances of Li−S batteries. On the one hand, the ultrathin 3%Co-VS 4 /rGO possesses good conductivity inheriting from rGO which contributes to the capacity of internal redox reactions on lithiation from VS 4 . On the other hand, the hybrid architectures provide strong adsorption and excellent electrocatalytic ability on LiPSs, which benefit from the surface defects caused by heteroatom doping. The S@3%Co-VS 4 /rGO cathode displays a high specific capacity of 1332.6 mA h g −1 at 0.2 C and a low-capacity decay of only 0.05% per cycle over 1000 cycles at 3 C with a primary capacity of 633.1 mA h g −1 . Furthermore, when the sulfur loading (single-side coating) reaches 4.48 mg cm −2 , it still can deliver 756.2 mA h g −1 after the 100th cycle at 0.2 C with 89.5% capacity retention. In addition, the in situ X-ray diffraction test reveals that the sulfur conversion mechanism is the processes of α-S 8 → Li 2 S → β-S 8 (first cycle) and then β-S 8 ↔ Li 2 S during the subsequent cycles. The designing strategy with heteroatom doping and self-intercalation capacity adopted in this work would provide novel inspiration for fabricating advanced sulfur-host materials to achieve excellent electrochemical capability in Li−S batteries.

Understanding the Catalytic Kinetics of Polysulfide Redox Reactions on Transition Metal Compounds in Li–S Batteries

“…The doping of metal heteroatoms would disrupt the local lattice arrangement in TMCs, thereby producing more defects and active sites. 104 Recently, Zhang et al 105 prepared 2D ultrathin 3% Co-VS 4 /rGO as cathode materials for Li−S batteries, of which the electronic structure was modulated by Co-doping and S-vacancy defects (SVs). The excellent conductivity of rGO and the strong polysulfides adsorption/ catalysis of the hybrid structure greatly improved the electrochemical performance of the corresponding Li−S batteries.…”

“…The doping of metal heteroatoms would disrupt the local lattice arrangement in TMCs, thereby producing more defects and active sites . Recently, Zhang et al . prepared 2D ultrathin 3% Co-VS 4 /rGO as cathode materials for Li–S batteries, of which the electronic structure was modulated by Co-doping and S-vacancy defects (SVs).…”

“…(c) In situ XRD results of multiple cycles of the S@3%Co-VS 4 /rGO cathode. Reprinted with permission from ref . Copyright 2022 American Chemical Society.…”

Few-layered V2C MXene derived 3D V3S4nanocrystal functionalized carbon flakes boosting polysulfide adsorption and catalytic conversion towards Li–S batteries

“…20,21 Similarly, as another “family member” with the same oxidation state as that of vanadium (V 4+ ), the VS 4 crystal is a quasi-one-dimensional chain-like compound that is held together by vdW interactions as well, and the polar LPSs are mainly trapped between the V 4+ (S 2 2− ) 2 chains through stronger vdW forces. 22,23…”

“…20,21 Similarly, as another "family member" with the same oxidation state as that of vanadium (V 4+ ), the VS 4 crystal is a quasi-one-dimensional chain-like compound that is held together by vdW interactions as well, and the polar LPSs are mainly trapped between the V 4+ (S 2 2À ) 2 chains through stronger vdW forces. 22,23 Different from 2D layered VS 2 and one-dimensional linear VS 4 , V 3 S 4 , in the form of V 0.5 VS 2 , possesses a typical threedimensional (3D) NiAs-type crystal structure, where 0.5 V atoms are intercalated between VS 2 monolayers. 24,25 In this structure, the intercalated V atoms (V 3+ ) show a metallic conduction along the c-axis direction due to the strong interaction between V 3+ and V 4+ cations, which will hopefully facilitate the transmission of electrons along their c-axis direction.…”