Boosting Polysulfide Redox Kinetics by Temperature-Induced Metal-Insulator Transition Effect of Tungsten-Doped Vanadium Dioxide for High-Temperature Lithium-Sulfur Batteries

The practical application of Li-S batteries is still severely restricted by poor cyclic performance caused by the intrinsic polysulfides shuttle effect, which is even more severe under the high-temperature condition owing to the inevitable increase of polysulfides' solubility and diffusion rate. Herein, tungsten-doped vanadium dioxide (W-VO2) micro-flowers are employed with first-order metal-insulator phase transition (MIT) property as a robust and multifunctional modification layer to hamper the shuttle effect and simultaneously improve the thermotolerance of the common separator. Tungsten doping significantly reduces the transition temperature from 68 to 35 degrees C of vanadium dioxide, which renders the W-VO2 easier to turn from the insulating monoclinic phase into the metallic rutile phase. The systematic experiments and theoretical analysis demonstrate that the temperature-induced in-suit MIT property endows the W-VO2 catalyst with strong chemisorption against polysulfides, low energy barrier for liquid-to-solid conversion, and outstanding diffusion kinetics of Li-ion under high temperatures. Benefiting from these advantages, the Li-S batteries with W-VO2 modified separator exhibit significantly improved rate and long-term cyclic performance under 50 degrees C. Remarkably, even at an elevated temperature (80 degrees C), they still exhibit superior electrochemical performance. This work opens a rewarding avenue to use phase-changing materials for high-temperature Li-S batteries. Adjustable catalytic activity is an important property for the practical electrocatalysts at high temperature condition. Doping modulates the metal-insulator transition temperature, promotes the tight anchoring of polysulfides on the W-VO2 catalyst, as well as reduces the overpotential of the sulfur reduction reaction (SRR) and sulfur evolution reaction (SER), fundamentally accelerating the conversion of LiPSs between the liquid and solid phases, and thus suppressing the shuttle effect.image