Rationalizing the impact of oxygen vacancy on polysulfide conversion kinetics for highly efficient lithium-sulfur batteries

Abstract

The “shuttle effect” of lithium polysulfides (LiPSs) is a huge challenge for practical use of high-energy-density lithium-sulfur (Li-S) batteries, and one of the main reasons is the sluggish kinetics of sulfur conversion. Metal oxides are able to expedite the sulfur electrochemistry, and the structural defects enhance the adsorption-conversion ability of metal oxides for polysulfides. However, a significant research gap still remains regarding the relationship between the oxygen vacancy concentration and the adsorptive-catalytic performance of metal oxides. Herein, we establish a correlation between oxygen vacancy concentration and adsorptive-catalytic properties by using tungsten oxide (WOx) as model catalysts. It is revealed that high-concentration oxygen vacancy is beneficial for enhancing the binding between tungsten oxide and LiPSs, reducing the energy barrier of Li2S decomposition, and promoting polysulfide conversion kinetics. Consequently, the Li-S batteries using the tungsten oxide with high-concentration oxygen vacancies deliver high initial discharge capacity of 1169 mA h g−1 at 0.2 C and 865 mA h g−1 at 2 C, low attenuation rate of 0.064% per cycle over 1100 cycles at 2 C. With a high sulfur area loading of 5.34 mg cm−2, the Li-S batteries still exhibit high initial gravimetric capacity of 982 mA h g−1 at 0.1 C and areal capacity of 5.92 mA h cm−2. This work promotes the feasibility of defect engineering on metal oxides as an effective mean to enhance the practicality of Li-S batteries.