Abstract
Lithium–sulfur batteries have attracted attention due to their six-fold specific energy compared with conventional lithium-ion batteries. Dissolution of lithium polysulfides, volume expansion of sulfur and uncontrollable deposition of lithium sulfide are three of the main challenges for this technology. State-of-the-art sulfur cathodes based on metal-oxide nanostructures can suppress the shuttle-effect and enable controlled lithium sulfide deposition. However, a clear mechanistic understanding and corresponding selection criteria for the oxides are still lacking. Herein, various nonconductive metal-oxide nanoparticle-decorated carbon flakes are synthesized via a facile biotemplating method. The cathodes based on magnesium oxide, cerium oxide and lanthanum oxide show enhanced cycling performance. Adsorption experiments and theoretical calculations reveal that polysulfide capture by the oxides is via monolayered chemisorption. Moreover, we show that better surface diffusion leads to higher deposition efficiency of sulfide species on electrodes. Hence, oxide selection is proposed to balance optimization between sulfide-adsorption and diffusion on the oxides.
Highlights
Lithium–sulfur batteries have attracted attention due to their six-fold specific energy compared with conventional lithium-ion batteries
To reveal the role of metal oxides in Li–S batteries, five kinds of pure metal oxidenanoparticles were prepared by a generic Pechini sol–gel method13. 1,3-dioxolane (DOL) and dimethoxyethane (DME) are commonly used solvent in the Li–S battery electrolyte[4]
The colour of the solution containing Al2O3 and CeO2 is lighter than the others, indicating better adsorption of these two metal oxide nanoparticles
Summary
Lithium–sulfur batteries have attracted attention due to their six-fold specific energy compared with conventional lithium-ion batteries. There have been significant developments for designing state-of-the-art Li–S batteries in the past two decades, the practical application is still hindered by many material challenges, including dissolution of intermediate lithium polysulfides (Li2Sx, x43) in the electrolyte[28], large volumetric expansion (80%) of sulfur upon lithiation[6], and poor electronic/ ionic conductivity of sulfur and lithium sulfide (Li2S) Our recent work showed that indium tin oxide decorated carbon nanofibres can enhance the redox kinetics of Li2Sx, realize the controllable deposition of Li2S and improve the electrochemical performance of Li–S batteries[4]. The above background research has motivated us to hypothesize that surface diffusion of Li2Sx species on solid substrates can play an important role in Li–S battery electrochemical performance. The competition between the adsorption and diffusion of the Li2Sx adsorbates on solid substrates can be very important, yet has been overlooked for Li–S batteries
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