Nanoporosity of Carbon-Sulfur Nanocomposites toward the Lithium-Sulfur Battery Electrochemistry

Progress on critical cell fabrication parameters and designs for advanced lithium-sulfur batteries

Since 1990, commercial lithium-ion batteries have made significant strides, approaching their theoretical performance limits, albeit with escalating costs. To address these challenges, attention has shifted toward lithium-sulfur batteries, which offer higher theoretical energy densities and cost-effectiveness. However, lithium-sulfur cells face challenges such as active-material loss, excessive electrolyte usage, and rapid degradation of lithium-metal anodes. To overcome these issues, research has focused on optimizing cell configurations and fabrication parameters while exploring novel electrolytes and electrode materials. This feature article delves into the intrinsic material challenges and extrinsic engineering issues in current lithium-sulfur research and explores the development of advanced lithium-sulfur cells with crucial progress on high-loading sulfur cathodes, lean-electrolyte cells, and solid-state electrolytes. Moreover, it outlines the fundamental principles, structures, performances, and developmental trajectories indicated in research articles published after 2020, highlighting future research directions aimed at resolving key challenges for the practical application of lithium-sulfur cells.

High Entropy Oxide (CrMnFeNiMg)3 O4 with Large Compositional Space Shows Long-Term Stability as Cathode in Lithium-Sulfur Batteries

The repeated formation and irreversible diffusion of liquid-state lithium polysulfides (LiPSs) are the primary challenges in the development of high-energy-density lithium-sulfur battery (LSB). An effective strategy to alleviate the resulting polysulfide loss is critical for the stability of LSBs. In this regard, high entropy oxides (HEOs) appear as a promising additive for the adsorption and conversion of LiPSs owing to the diverse active sites, offering unparalleled synergistic effects. Herein, we have developed a (CrMnFeNiMg)₃ O₄ HEO as a functional polysulfide trapper in LSB cathode. The adsorption of LiPSs by the metal species (i. e., Cr, Mn, Fe, Ni, and Mg) in the HEO takes place through two different paths and leads to enhanced electrochemical stability. We demonstrate that the optimal sulfur cathode with the (CrMnFeNiMg)₃ O₄ HEO attains a high peak and reversible discharge capacities of 857 mAh g^-1 and 552 mAh g^-1 , respectively, at a cycling rate of C/10, a long cycle life of 300 cycles, and a high rate performance at the cycling rates from C/10 to C/2.

Water Kefir Grains-Microbial Biomass Source for Carbonaceous Materials Used as Sulfur-Host Cathode in Li-S Batteries

Nowadays, the use of biomass to produce cathode materials for lithium-sulfur (Li-S) batteries is an excellent alternative due to its numerous advantages. Generally, biomass-derived materials are abundant, and their production processes are environmentally friendly, inexpensive, safe, and easily scalable. Herein, a novel biomass-derived material was used as the cathode material in Li-S batteries. The synthesis of the new carbonaceous materials by simple carbonization and washing of water kefir grains, i.e., a mixed culture of micro-organisms, is reported. The carbonaceous materials were characterized morphologically, texturally and chemically by using scanning electron microscopy, N₂ adsorption-desorption, thermogravimetric analysis, X-ray diffraction, and both Raman and X-ray photoelectron spectroscopy. After sulfur infiltration using the melt diffusion method, a high sulfur content of ~70% was achieved. Results demonstrated that the cell fitted with a cathode prepared following a washing step with distilled water after carbonization of the water kefir grains only, i.e., not subjected to any chemical activation, achieved good electrochemical performance at 0.1 C. The cell reached capacity values of 1019 and 500 mAh g^-1 sulfur for the first cycle and after 200 cycles, respectively, at a high mass loading of 2.5 mg_S cm^-2. Finally, a mass loading study was carried out.

Structural and Surfacial Modification of Carbon Nanofoam as an Interlayer for Electrochemically Stable Lithium-Sulfur Cells

Electrochemical lithium-sulfur batteries engage the attention of researchers due to their high-capacity sulfur cathodes, which meet the increasing energy-density needs of next-generation energy-storage systems. We present here the design, modification, and investigation of a carbon nanofoam as the interlayer in a lithium-sulfur cell to enable its high-loading sulfur cathode to attain high electrochemical utilization, efficiency, and stability. The carbon-nanofoam interlayer features a porous and tortuous carbon network that accelerates the charge transfer while decelerating the polysulfide diffusion. The improved cell demonstrates a high electrochemical utilization of over 80% and an enhanced stability of 200 cycles. With such a high-performance cell configuration, we investigate how the battery chemistry is affected by an additional polysulfide-trapping MoS2 layer and an additional electron-transferring graphene layer on the interlayer. Our results confirm that the cell-configuration modification brings major benefits to the development of a high-loading sulfur cathode for excellent electrochemical performances. We further demonstrate a high-loading cathode with the carbon-nanofoam interlayer, which attains a high sulfur loading of 8 mg cm-2, an excellent areal capacity of 8.7 mAh cm-2, and a superior energy density of 18.7 mWh cm-2 at a low electrolyte-to-sulfur ratio of 10 µL mg-1.